Journal of Nanomaterials

Journal of Nanomaterials / 2017 / Article

Review Article | Open Access

Volume 2017 |Article ID 8510342 |

Ayesha Naveed Ul Haq, Akhtar Nadhman, Ikram Ullah, Ghulam Mustafa, Masoom Yasinzai, Imran Khan, "Synthesis Approaches of Zinc Oxide Nanoparticles: The Dilemma of Ecotoxicity", Journal of Nanomaterials, vol. 2017, Article ID 8510342, 14 pages, 2017.

Synthesis Approaches of Zinc Oxide Nanoparticles: The Dilemma of Ecotoxicity

Academic Editor: Mohamed Bououdina
Received19 Jan 2017
Accepted14 Mar 2017
Published18 Apr 2017


Human’s quest for innovation, finding solutions of problems, and upgrading the industrial yield with energy efficient and cost-effective materials has opened the avenues of nanotechnology. Among a variety of nanoparticles, zinc oxide nanoparticles (ZnO) have advantages because of the extraordinary physical and chemical properties. It is one of the cheap materials in cosmetic industry, nanofertilizers, and electrical devices and also a suitable agent for bioimaging and targeted drug and gene delivery and an excellent sensor for detecting ecological pollutants and environmental remediation. Despite inherent toxicity of nanoparticles, synthetic routes are making use of large amount of chemical and stringent reactions conditions that are contributing as environmental contaminants in the form of high energy consumption, heat generation, water consumption, and chemical waste. Further, it is also adding to the innate toxicity of nanoparticles (NPs) that is either entirely ignored or poorly investigated. The current review illustrates a comparison between pollutants and hazards spawned from chemical, physical, and biological methods used for the synthesis of ZnO. Further, the emphasis is on devising eco-friendly techniques for the synthesis of ZnO especially biological methods which are comparatively less hazardous and need to be optimized by controlling the reaction conditions in order to get desired yield and characteristics.

1. Introduction

Nanoparticles (NPs) have revolutionized all major industrial areas, from drug delivery to agriculture and food industry [1]. Chemical synthesis methods for NPs include emulsion solvent extraction method, double emulsion and evaporation method, salting out method, emulsion diffusion method, and solvent displacement/precipitation method. But, industrial scale production of NPs has familiarized a new kind of pollution into environment. It is highly desirable to reduce the loads of chemical pollution on environment by developing new and convenient methods to overcome the drawbacks of chemical methods, improve the yield, and reduce the cost [2].

Bulk zinc oxide is cost-effective and shows a variety of applications in industry including nanoparticle synthesis [3, 4]. ZnO nanoparticles are II–VI semiconductor with wide band gap energy, that is, 3.3 eV, and high excitation energy, that is, 60 eV. Thus, it can tolerate large electric fields, high temperature, and high power operations [5]. These properties make it highly applicable in solar cells, photo catalysis, and chemical sensors [612]. Moreover, it can also be made conductive by doping [13]. ZnO nanocrystals predominantly show wurtzite construction with lattice parameters  nm and  nm. ZnO in its simplest form shows tetrahedron geometry in which each ion is enclosed by four counter ions pointing towards corners of a tetrahedron (Table 1). This tetrahedron configuration is responsible for the piezoelectricity and pyroelectricity [14, 15]. Piezoelectricity of ZnO arises from its crystal structure and makes it applicable for acoustic wave resonators and acoustic-optic modulators. Also, because of its Centro symmetric structure, it is the highest tensor among all semiconductors and gives large electromechanical coupling [5].

Physical appearanceWhite, colorless, odorless solid
Crystalline structureWurtzite
Molecular Weight81.38 g/mol
Electron effective mass60
Melting Point1,975°C
Density5.47 g/cm2
Isoelectric point9.5–10
Space group-P63mc
Standard molar entropy43.9 J·K−1mol−1
Standard enthalpy of formation−348.0 kJ/mol

2. Importance of ZnO for Industries

Ultraviolet A and Ultraviolet B radiations from the sun can cause injury by free radical mechanism on skin cells. ZnO nanoparticles of size less than 200 nm have high efficiency in scattering light and induce cosmetically desired whitening to the skin. It has also been used in foot care, ointments, and over-the-counter topical products [1621]. Singh and Nanda performed a detailed comparative study between conventional zinc oxide and nanosized ZnO particles for their sun screen efficiency. Good texture, better spreadability, and enhanced in vitro sun protection factor (SPF) proved the advantageous role of nanoparticles in cosmetics [22]. Hypothesized hazards to human health due to these nanoparticles are still unexplored and it would be counterproductive to avoid them without any evidence.

Another astonishing property of ZnO is the green luminescence, related to the point defects, which makes it a useful agent for bioimaging. This can be further enhanced by doping with transition elements, for example, copper, cobalt, and nickel, for more desirable optical properties. Other application of ZnO includes gene delivery that is considered as an important milestone in therapeutics and has attained much attention of the researchers for the treatment of diseases like severe combined immune deficiency (ADA-SCID), chronic granulomatous disorder (CGD), hemophilia, genital blindness, lysosomal storage disease and muscular dystrophy, neurodegenerative diseases, viral infections (e.g., influenza, HIV, and hepatitis), heart disease, and diabetes. Quantum dots and tetrapod like structures of ZnO have been explored extensively for such applications [2325]. Such quantum dots are also playing a vital role as sensors. ZnO is a semiconductor and its properties can be altered by a number of ways that has made it an exciting candidate for the sensor exploration. Such sensors have indispensable role, that is, from detecting environmental pollutants to epidemic diseases outbreaks. A number of authors have reported ZnO based biosensors for sensing cholesterol, biochemistry of enzymes, and other biosensing applications [26, 27]. Kazemi and coauthors have synthesized ZnO by sol-gel and hydrothermal method and devised a home-built apparatus which responded best at its “working temperature” to sense ethanol. Adsorbed oxygen species trapped the electron creating a charge depleted layer supposed to be responsible for sensing properties of the created sensor [28]. In another study, Liu and coscientists reported a high performance ZnO based sensor for n-butanol sensing. Low temperature solvothermal method gave highly crystalline wurtzite NPs (spherical in shape with diameter of 8.4 ± 1.3 nm). The fabricated sample had the ability to sense n-butanol up to 500 ppm with a recovery time of 22 seconds. The designed sensor exhibited several advantages such as high and fast response, short recovery time, and good stability towards n-butanol gas [29].

Nowadays, ZnO has been widely investigated for plant protection products, fertilizers, soil improvement, water purification, and many other [3, 3033]. Antimicrobially active packaging is a new generation of nano-food packaging based on metal nanocomposites which are made by incorporating ZnO into polymer films [3438]. Espitia et al., has reviewed the utility of ZnO nanoparticles in food preservation and packaging industry when applied to biodegradable polymeric metrics. The NPs improved the quality of food and packaging mainly by three mechanisms, that is, release of antimicrobial ions, damaging the integrity of bacterial cell, and the formation of ROS by the effect of light radiation [39]. Elmer and White have reported the pesticidal properties of the ZnO. They sprayed synthesized ZnO on tomato and eggplant. It was noted that ZnO reduced disease estimate by 28% when compared to the control [40]. On the basis of thermodynamics, ZnO should dissolve faster and to a greater extent than bulk ZnO particles (equivalent spherical diameter > 100 nm). These novel solubility features of ZnO might be exploited to improve the efficiency of Zn fertilizers. Milani et al. found that urea and MAP granules coated with ZnO showed more thermodynamic dissolution may be due to pH difference; however kinetics of Zn dissolution remained unaffected [41].

3. Toxicity of ZnO in Mammalian Model

However, controversial results have been reported in the literature regarding toxicity of the ZnO in the living cells particularly in mammalian cells. Some of the reports have shown that ZnO are biocompatible and nontoxic [4244], while some studies have recently reported both in vivo and in vitro toxicity of the ZnO on mammalian cells [4548]. It can be elucidated from such studies that the toxicity of ZnO depends upon the concentration used. Vandebriel and Jong had reviewed the ZnO toxicity in mammalian model [48]. For more study, refer to reviews of [4951]. Further, such toxicity is important in other aspects, for example, for the treatment of cancerous, pathogenic, and leukemic T cells [5258]. Such nanoparticles are also important to overcome problems like drug resistance which is one of the major problem in the pharmaceutical industry [59]. This is because of the nonselectivity of ZnO.

4. Fabrication of ZnO Nanoparticles for Different Applications

A variety of synthetic techniques are used for the synthesis of ZnO. These techniques broadly can be divided into three types, that is, chemical, biological, and physical methods (Figures 1 and 2). Chemical synthesis can further be divided into liquid phase synthesis and gas phase synthesis. Liquid phase synthesis includes precipitation, coprecipitation method, colloidal methods, sol-gel processing, water–oil microemulsions method, hydrothermal synthesis, solvothermal, and sonochemical, and polyol method. And vapor phase fabrication includes pyrolysis and inert gas condensation methods.

4.1. Liquid Phase Synthesis

In a typical precipitation and coprecipitation method, a reducing agent (mostly inorganic alkalis) is allowed to react with the zinc salt. A resultant soluble or insoluble precipitate is produced that is afterwards washed and calcined at different temperatures to obtain the particular nanoparticles with desired morphology and characteristics. A range of nanoparticles and reaction conditions are used to control the size and shape of the ZnO by this method [60]. Colloidal methods rely on the simplest and well established chemistry since antiquity. However, in literature it was first reported by Faraday in 1857, who synthesized colloids of gold nanoparticles by the reduction of HAuCl4 with phosphorus. Sol-gel techniques rely on colloidal chemistry. Sols are referred to the colloidal solution consisting of solid particles suspended in liquid phase having a diameter of a few hundred nanometers. Gels are mostly formed by polycondensation or polyesterification methods followed by aging to achieve phase transformations and Ostwald ripening. The gels are dehydrated at temperature as high as 8000°C and finally densified at temperature greater than 8000°C to obtain metal oxide nanoparticles. An advantage of sol-gel methods is the insurance of highly pure and uniform structured ZnO [61]. Formation of thorn like ZnO in sol-gel method was reported by Khan and companions. The method was a little modified by mechanical stirring. Zinc acetate dihydrate [Zn(CH3COO)2·2H2O], sodium hydroxide (NaOH), and CTAB were used as precursors. Obtained nanoparticles were less than 50 nm which showed significant antimicrobial activity [61].

In solvothermal and hydrothermal processes, originators are dissolved in hot solvents (other than water) or water under moderate to high pressure (1–10,000 atm) and moderately high to high temperature (100–1000°C). These processes are used to synthesize a variety of zinc nanostructures such as thin films, bulk powders, spheres (3D), rods (2D), and wires (1D). Further, this method is also useful for the synthesis of metastable and thermodynamically stable ZnO via manipulation of the reaction conditions [62]. In a study, the solvothermal synthesis of single layer ZnO was reported by Rai et al. They aimed to investigate the effect of zinc salts on the morphology of NPs. Formation of NPs in a range of 100−150 nm and 20−25 nm length occurred, respectively, whereas NPs were 20−25 nm in diameter. The synthesized nanorods also showed more sensitivity towards NO2 [63].

4.2. Gas Phase Synthesis

One of the highly used techniques is spray pyrolysis method, in which aerosol droplets of the precursor zinc salt are produced via flame heating. The droplets are dispersed in the gas and their size is reduced by dehydration. The last steps involve the decomposition and sintering of the required material [64]. Another method is inert gas condensation methods that is subdivided into physical vapor deposition (without catalytic interaction) and chemical vapor deposition (with catalytic interaction). Principally, these methods comprise evaporation of zinc source inside a chamber by resistive heat. Different sources of heat such as electron or laser beams or radio frequencies are also used. From the heat chamber, the vapors are forced to migrate into cooler chamber having inert gas, from where they are collected for further consolidation. The major disadvantage of this method is the coalesces and agglomeration of ZnO nanoparticles. Another important method is the one-step levitational gas condensation method that was reported by Uhm and coworkers for ZnO. Apparatus consisted of 2.5 kW induction generator levitation and evaporation chamber and oxygen concentration control unit. Obtained nanoparticles showed very good morphology with diameter of 30 nm [65].

4.3. Physical Methods

Physical methods of ZnO nanoparticles synthesis include high energy ball milling, melt mixing, physical vapor deposition, laser ablation, sputter deposition, electric arc deposition, and ion implantation. In most physical/mechanical processes, the production rates of ZnO nanoparticles are very high and are mostly used for the industrial processes. High energy ball milling is a nonequilibrium process developed by Salah and coworkers in 1961. In this method powdered material placed inside a ball mill is subjected to high energy collision from balls [66]. Amirkhanlou and coscientists reported high energy ball milling processes as very efficient, cost-effective, and simple techniques for the preparation of ZnO nanostructures. They used 15 balls with diameter of 20 mm confined in a 500 ml bowl. XRD and field emission scanning electron microscopy (FESEM) showed ZnO nanopowder particles with crystallite size of 15 nm, particle size of about 60 nm, and lattice strain of 0.67%. Similar methodology was reported by Salah et al. and used such ZnO in antimicrobial activity [66]. Laser ablation technique utilizes a laser beam to remove particle from a solid or a liquid surface. Spherical ZnO with average diameter of 35 nm was reported by Ismail and companions. They used pulsed laser ablation in double distilled water [67]. At lower reflux, materials are heated by the energy absorbed through laser and evaporates, while, at higher refluxes, materials may convert into plasma. Other frequently and studied methods used are vapor solid liquid (VLS), physical vapor deposition (PVD), and chemical vapor deposition (CVD) [68]. Physical vapor deposition (PVD) methods are used to coat the surfaces by depositing the metals. Two types of techniques, namely, evaporation and sputtering, are used in PVD. Sputtering refers to the mechanism of particle escape from the surface by striking high energy particles. The ions for sputtering process are supplied from plasma [39].

4.4. Green Synthesis of Nanoparticles

Green routes are used for the synthesis of ZnO because of the least possible number of chemicals utilized that produces least amount of pollutants and are energy efficient as well as cost-effective. A number of natural moieties such as plants, fungi, algae, bacteria, and viruses are used to synthesize the ZnO (Figure 3).

4.4.1. Plant Mediated Synthesis

Plants and plant extracts as a machinery for metal nanoparticles synthesis are fascinating as they eliminate the need of using hazardous materials as well as the tedious process of culturing and downstream processing. However, plant extracts are more attractive because the methodology is much simpler and cost-effective [69, 70]. Nanoparticles synthesis driven by plant extracts is perhaps the most explored biological source. Plants have the ability to synthesize the nanoparticles both via in vivo and in vitro methods. The mechanism of synthesis of such nanoparticles by plants is their capability to uptake metals from the soil and water, hyperaccumulation, and further reduction to recoverable nanoparticles. Such techniques are extensively used in phytoremediation and phytomining. However, the focus is majorly on silver and gold nanoparticles on using plants. Literature is limited in the synthesis of ZnO by plant and plant extract based routes.

In vitro approaches make use of plant extracts to bioreduce a particular zinc salt (zinc nitrate, sulphate, chloride, and many other) and provide a control over size and shape of the nanoparticles. Basically, plants contain a number of primary and secondary metabolites, for example, tannins, terpenoids, saponins, starches, polypeptides, flavonoids, and phenolic, that act as an excellent reducing as well as capping agents. Mild solvents like water, ethanol, or methanol are used for the extraction of the plant metabolites, which are allowed to react with zinc salt solution under different conditions to obtain a maximum yield [7173].

4.4.2. Microorganisms Facilitated Synthesis of Nanoparticles

Microbes are considered as eco-friendly factories of nanoparticles synthesis. Interactions between metals and microbes have been exploited for various biological applications in the fields of bioremediation, biomineralization, bioleaching, and biocorrosion [74]. It is one of the most sustainable, eco-friendly techniques so far in spite of its few limitations. Both prokaryotes and eukaryotes are used for the synthesis of metal/metal oxide especially ZnO. Further, the synthesis may be intracellular or extracellular.

Fungi are decomposers as well as parasite in nature. In intracellular synthesis, fungal biomass is incubated for a particular time period in dark along with a zinc salt solution, while in extracellular synthesis fungal filtrates are treated with the precursor solution and synthesis is assessed [75]. A number of studies are available on using fungi as ZnO synthesizer. Jain et al. isolated 19 fungal cultures from rhizopheric soil. Among those cultures, Aspergillus aeneus isolate NJP12 showed highest potential for extracellular synthesis of ZnO under ambient conditions. The resultant nanoparticles were coated with protein which acted as a stabilizer [76]. In another study, fungal filtrate of Aspergillus niger was used by Jacob and coscientists for the production of the ZnO. The synthesized nanoparticles were spherical in shape with an average diameter of 39.4–114.6 nm [77]. Baskar and coworkers extracellularly prepared ZnO by Aspergillus terreus filtrate. The synthesized ZnO particles were spherical in shape with a size range of 54.8 to 82.6 nm [78].

However, a number of studies are also available on using bacteria as green synthesizer for ZnO; for example, bacterial strain Aeromonas hydrophila formed spherical and oval shaped nanoparticles with an average diameter of 57.72 nm [79]. Synthetic pathways of nanoparticles by microbes may involve basic combinations of cellular biochemistry, metal ions transportations in and out of the cells, microbial resistance towards toxic metal mechanism and activated metal-binding sites, intracellular metal ions accumulation, and metal oxide nucleation [80]. Lactobacillus sporogenes was reported to produce ZnO of diameter of 5–15 nm. The authors proposed the mechanism of synthesis that depends upon reduction of metals by oxidoreductases which were activated by the nutritional media contents and pH variations [81]. Actinomycetes, having properties of both prokaryotes (fungi) and bacteria, are also used for the synthesis of ZnO particles. Scientists are attempting to develop an eco-friendly and cost-effective method, for example, by using brown marine macroalgae Sargassum muticum aqueous extract. The resulting nanoparticles had diameter ranging from 30 to 57 nm and hexagonal wurtzite in structure [82].

4.4.3. Other Green Synthesis Methods

A number of other green means are used for the synthesis of ZnO. Jha and Prasad have reported the formation of ZnO by slaughtered goat waste (mainly intestine). Simple distillation method by methanol followed by boiling with zinc chloride salt was adopted. This resulted in agglomerates of nanoparticles as smaller as 3–11 nm. His work is an important contribution in getting rid of waste which subsequently may cause disease dispersal [83]. Researchers have also explored the ZnO synthetic capability of the peels obtained from different fruits and vegetables. Mishra and Sharma used fresh peels extract powder of Punica granatum. Distilled water was used to prepare the extract, which was mixed with zinc nitrate solution at 60–80°C under constant stirring. In another study, filtrate of Musa balbisiana peels and zinc nitrate dihydrate was used to obtain ZnO NPs by Tamuly and coworkers. Nanoflowers of less than 2 nm in diameter were obtained which were used as catalyst for the synthesis of chalcone derivatives [8488].

5. Environmental Implications of Physical, Chemical, and Green Synthesis

5.1. Capping Agents, Surfactants, and Stabilizers

Three major factors should be kept in view while devising an industrial scale synthesis of the nanoparticles. These factors are solvent choice, the use of an environmentally benign reducing agent, and the use of a nontoxic material for nanoparticle stabilization [95]. In chemical synthesis, capping agents and stabilizers are extensively used in order to control the size and to avoid agglomeration [96]. Owning to the wide application of the ZnO nanoparticles and their large production, potential of capping agents and stabilizers are investigated by many researchers. Despite inherent toxicity, organic and polymeric capping agents are majorly contributing in environmental pollution. Toxicity of the surface modified and unmodified ZnO on zebra fish were comprehensively studied by the Zhou and his colleagues. Their experiment showed a significant difference in toxicity level of surface modified and unmodified ZnO NPs [97]. Toxicity of some of the frequently used capping and stabilizing agents is mentioned in Table 2.

Capping agents/stabilizersInherent toxicityToxicity reported byReference of utility in ZnO NP synthesis

Triethyl amineReversible
ocular effects including corneal swelling and halo vision in humans
Oleic acidPromote apoptosis and necrosis, mitochondrial depolarization, lipid accumulation, and overexpression of C-MYC and P53[123][124]
ThioglycerolIrritant for skin, eye and inhalation; Hazardous in case of ingestion[127][128]
EDTACytotoxic and genotoxic[131]
Tetraethyl ammoniumbromideTremors, incoordination, flaccid prostration, and death from respiratory failure in animals[136][137]
Tetraethyl orthosilicateHighly damaging to eyes[140][141]
Polyethylene glycol (PEG)Immunogenic[144][11]
Polyethylene phthalate (PEP)Endocrine disruptor[146][147]
Ethylene glycolAdversely affects reproduction and development[150][11]
Polyvinyl alcohol (PVA)Toxic[156]
Polyvinyl pyrrolidine (PVP)Weight increase in lab mice[161][162]

5.2. Reducing Agents and pH

Most of the synthetic techniques for ZnO utilize a reducing agent to reduce a respective zinc salt and vigorous synthetic environment that involves either highly acidic or basic conditions. Precipitation/coprecipitation is the easiest and widely employed method for the ZnO synthesis. This method mainly employs sodium hydroxide (NaOH) as reducing agent, which is highly corrosive and degrades all kinds of protein. Dissolution of NaOH in water is exothermic and may cause heat burns or may ignite. On contact with metals it produces flammable hydrogen. In the synthesis of ZnO, excessive amounts of NaOH with higher molar concentrations are used to ensure the reaction completion. Upon filtration of reaction mixture, supernatant is discarded that might directly go to waste water and ultimately in water bodies. It not only may degrade the metallic parts of the sewage system but also alters the pH of water bodies causing hazards to aquatic flora and fauna.

Another highly used chemical for ZnO synthesis is hydrazine, which is a highly reactive alkali and reducing agent extensively used in industry and military. Strict protective instrument utilization is recommended while working with hydrazine. It may cause burns to skin and severely damages the respiratory track while overexposure may cause death. Due to its corrosive potential and its reactivity with oxidant, it is of great ecological concern. Metabolites of hydrazine have more ability to damage than the parent compound [98, 99]. Ethanol is known to be therapeutic in low to moderate dosage; however, high dosage or chronic exposures may lead to dehydration, central nervous system suppression, impaired sensory and motor function, slowed cognition, unconsciousness, and possible death [100102]. Ethylene glycol shares a number of characteristics. In earlier stage of metabolism, it is responsible for the metabolic acidosis of intoxication. In late stages, lactate may also accumulate, mainly due to formate inhibition of the respiratory chain. However, toxicity of ethylene glycol is complex and not fully understood yet [103]. High concentrations of 1,3 propandiol in lab rats have shown significant toxicity [81].

5.3. Sonication

Sonicators use ultrasonic or sound energy to agitate the particles in the mixture. Typical lab sonicators employ 20 kHz of ultrasonic frequency. The major hazards associated with the use of sonicator are the creation of hearing impairment and generation of aerosols [104]. Sonochemical synthesis of ZnO nanoparticles has been recently reported by many groups [105111]. Two types of aerosols are produced by the sonochemical method, namely, chemical aerosols produced by the reagents used in the method and aerosols of nanoparticles. Moreover, the aerosols produced by the chemicals often go unattended in the labs. Furthermore, there is no such report to understand the mechanism of NP aerosols. However, Taurozzi’s groups emphasized on the optimization and standardization of sonological parameters. They recommended the rational use of the sonicator and comprehending the unattended side effects [112].

5.4. Temperature

Anthropogenic accomplishments using high temperature processes are altering the overall heat balance of the earth; that is, it is increasing the entropy. The major disadvantage of the high temperature processes is the consumption of the energy. Majorly, heat evolving from high temperature processes may cause heat edema, heat rashes, heat cramps, heat exhaustion, heat syncope, and heat strokes [113]. A number of methods in synthesis of ZnO NP involve high temperatures, for example, hybrid electrochemical thermal method (60–700°C) [114], gas condensation method (595°C) [115], direct thermal decomposition method (600°C) [116], spray pyrolysis method (1200°C) [117], and high temperature mixing hydrothermal processes (160–200°C) [118], that might be lethal.

5.5. Toxicological Implications of Green Synthesis of ZnO

Instability of biologically synthesized nanoparticles is worth consideration. Physical instability of nanoparticles may alter their arrangement/confirmations due to different conditions like temperature pressure, light, medium, pH, and so on, which may lead to the creation of the different unwanted chemical moieties. Moreover, potential hazards of these chemical metabolites are very poorly investigated.

Inherent toxicity of ZnO nanoparticles is linked to dissolution and ROS generation. Dissolution is the leading phenomenon in chemical and biological instability of ZnO. Metal solubility and concentration gradient between particle surface and the bulk solution phase acts as a driving force. Dissolution of the ZnO nanoparticles may lead to the Zn2+ and Zn(OH)+ that are highly toxic [165]. However, it is possible to control the dissolution phenomenon by coating the nanoparticles, doping, surface area effect, additional factors such as size-dependent changes of the surface curvature, and roughness of the particles. Also, the crystalline nature of the nanoparticles may be changed by redox reaction taking place on the surface of NPs, which may occur at the same time or simultaneously. Electronic transfers taking place during these processes lead to the generation of the reactive oxygen species (ROS) and oxidative stress inducing toxicological injury [166]. Chemically synthesized NPs are considerably stable; still they pose both type of hazards, whereas green synthesized nanoparticles are relatively less stable. Thus, the problem of dissolution of ions and ROS augments which may act as potential threat to the surrounding environment.

6. Conclusion and Future Prospects

Referring to the varied and widespread use of ZnO in research and industry, it is inevitable to clearly understand the whole life cycle of the ZnO, from raw materials, synthesis, and applications because of lack of data. Further, these particles have altogether different properties from their parent bulk materials. Despite their proven utilities and benefits, still, there are apprehensions about their environmental impacts (Figure 4), as we are still copping with the outcomes of the industrial revolution, although, with a delay of almost fifty years, scientists are able to comprehend the environmental implications of the traditional pollutants created by anthropogenic activities. However, full understanding does not mean that we have successfully dealt with them. Nowadays, with the advancement of science and technology, we are entering in an era of nanomaterials that have rendered unlimited services due to their unique size and shape. Like industrial revolution, the environmental impacts and perils of these synthetic nanoparticles, pollutants emerging from their whole life cycle and potential hazards to biological systems (animals and plants), are least bothering. So far, the fate and distribution of ZnO pollution have been studied in mammalian models [167, 168]. However, the question of whether nanoparticles could have a negative/positive biological impact on exposed plants and other organisms is unclear as only few studies are published till date that have revealed variable and, in some cases, conflicting results. Also, there is a lack of regulations for the synthesis, manipulation, and disposal of engineered NPs and as a result these NPs in the environment are being accumulated. Nanoindustry has established itself as a viable substitute of traditional industrial processes. A large number of synthetic techniques have been used to get cheaper raw materials (ZnO NP) and to get maximum yield. Thus, that it may provide a milestone to the researchers to overcome the loop holes of the process.

Chemical synthesis as evident from the name relies on intensive consumption of the chemicals, which are exhausted to the environment as waste material contributing to anthropogenic waste. Techniques employed for the chemical synthesis have their own limitations and drawbacks which can be dealt with green synthesis (plants, microbes, and waste) of ZnO, which offers a relatively pollution free mechanism but optimization of reaction conditions to get higher yield, desired characteristics, and instability put a limitation on its use. It is unpredictable to gauge stability of biosynthesized ZnO which may otherwise cause serious damage to biological systems. Thus, there is a need to devise and optimize reaction mechanism and techniques for both chemical and green synthesis.

Further, most of the chemicals used in synthetic processes of ZnO are present in hazardous chemical list and maximum exhaustible limits in environment is well defined in most countries. However, we still need to define these limitations in case of nanopollutants exhausted from the nanoindustry. There is an utter requirement to perform environmental risk assessment in order to estimate the threat posed by ZnO. Also, simulation models should be developed to sketch an analogy between the increasing utility, amount of ZnO synthesized, and pollutants exhausted during these activities.

Conflicts of Interest

The authors declare no conflicts of interest.


  1. W. W. Adams and R. H. Baughman, “Richard E. Smalley (1943–2005),” Science, vol. 310, no. 5756, p. 1916, 2005. View at: Publisher Site | Google Scholar
  2. M. Nasrollahzadeh and S. Mohammad Sajadi, “Green synthesis of copper nanoparticles using Ginkgo biloba L. leaf extract and their catalytic activity for the Huisgen [3+2] cycloaddition of azides and alkynes at room temperature,” Journal of Colloid and Interface Science, vol. 457, pp. 141–147, 2015. View at: Publisher Site | Google Scholar
  3. S. Sabir, M. Arshad, and S. K. Chaudhari, “Zinc oxide nanoparticles for revolutionizing agriculture: synthesis and applications,” The Scientific World Journal, vol. 2014, Article ID 925494, 2014. View at: Publisher Site | Google Scholar
  4. X. Wang, Y. Ding, C. J. Summers, and Z. L. Wang, “Large-scale synthesis of six-nanometer-wide ZnO nanobelts,” The Journal of Physical Chemistry B, vol. 108, no. 26, pp. 8773–8777, 2004. View at: Publisher Site | Google Scholar
  5. O. Behera, Synthesis and Characterization of ZnO Nanoparticles of Various Sizes and Applications in Biological Systems, National Institute of Technology, Rourkela, India, 2008.
  6. X. Bai, L. Li, H. Liu, L. Tan, T. Liu, and X. Meng, “Solvothermal synthesis of ZnO nanoparticles and anti-infection application in vivo,” ACS Applied Materials and Interfaces, vol. 7, no. 2, pp. 1308–1317, 2015. View at: Publisher Site | Google Scholar
  7. Ü. Özgür, Y. I. Alivov, C. Liu et al., “A comprehensive review of ZnO materials and devices,” Journal of Applied Physics, vol. 98, no. 4, Article ID 041301, 2005. View at: Publisher Site | Google Scholar
  8. W. J. Jeong, S. K. Kim, and G. C. Park, “Preparation and characteristic of ZnO thin film with high and low resistivity for an application of solar cell,” Thin Solid Films, vol. 506-507, pp. 180–183, 2006. View at: Publisher Site | Google Scholar
  9. M. Moritz and M. Geszke-Moritz, “The newest achievements in synthesis, immobilization and practical applications of antibacterial nanoparticles,” Chemical Engineering Journal, vol. 228, pp. 596–613, 2013. View at: Publisher Site | Google Scholar
  10. K. Rekha, M. Nirmala, M. G. Nair, and A. Anukaliani, “Structural, optical, photocatalytic and antibacterial activity of zinc oxide and manganese doped zinc oxide nanoparticles,” Physica B: Condensed Matter, vol. 405, no. 15, pp. 3180–3185, 2010. View at: Publisher Site | Google Scholar
  11. S. Nair, A. Sasidharan, V. V. Divya Rani et al., “Role of size scale of ZnO nanoparticles and microparticles on toxicity toward bacteria and osteoblast cancer cells,” Journal of Materials Science: Materials in Medicine, vol. 20, no. 1, pp. S235–S241, 2009. View at: Publisher Site | Google Scholar
  12. A. A. Reinert, C. Payne, L. Wang, J. Ciston, Y. Zhu, and P. G. Khalifah, “Synthesis and characterization of visible light absorbing (GaN) 1-x(ZnO)x semiconductor nanorods,” Inorganic Chemistry, vol. 52, no. 15, pp. 8389–8398, 2013. View at: Publisher Site | Google Scholar
  13. B. Ludi and M. Niederberger, “Zinc oxide nanoparticles: chemical mechanisms and classical and non-classical crystallization,” Dalton Transactions, vol. 42, no. 35, pp. 12554–12568, 2013. View at: Publisher Site | Google Scholar
  14. D. Vanmaekelbergh and L. K. Van Vugt, “ZnO nanowire lasers,” Nanoscale, vol. 3, no. 7, pp. 2783–2800, 2011. View at: Publisher Site | Google Scholar
  15. Z. L. Wang, “Zinc oxide nanostructures: growth, properties and applications,” Journal of Physics Condensed Matter, vol. 16, no. 25, pp. R829–R858, 2004. View at: Publisher Site | Google Scholar
  16. M. J. Osmond and M. J. McCall, “Zinc oxide nanoparticles in modern sunscreens: an analysis of potential exposure and hazard,” Nanotoxicology, vol. 4, no. 1, pp. 15–41, 2010. View at: Publisher Site | Google Scholar
  17. M. E. Darvin, K. König, M. Kellner-Hoefer et al., “Safety assessment by multiphoton fluorescence/second harmonic generation/hyper-Rayleigh scattering tomography of ZnO nanoparticles used in cosmetic products,” Skin Pharmacology and Physiology, vol. 25, no. 4, pp. 219–226, 2012. View at: Publisher Site | Google Scholar
  18. M. E. Darvin, S. Haag, M. Meinke, L. Zastrow, W. Sterry, and J. Lademann, “Radical production by infrared A irradiation in human tissue,” Skin Pharmacology and Physiology, vol. 23, no. 1, pp. 40–46, 2010. View at: Publisher Site | Google Scholar
  19. M. E. Darvin, S. F. Haag, J. Lademann, L. Zastrow, W. Sterry, and M. C. Meinke, “Formation of free radicals in human skin during irradiation with infrared light,” Journal of Investigative Dermatology, vol. 130, no. 2, pp. 629–631, 2010. View at: Publisher Site | Google Scholar
  20. B. Baroli, “Penetration of nanoparticles and nanomaterials in the skin: fiction or reality?” Journal of Pharmaceutical Sciences, vol. 99, no. 1, pp. 21–50, 2010. View at: Publisher Site | Google Scholar
  21. P.-J. Lu, S.-C. Huang, Y.-P. Chen, L.-C. Chiueh, and D. Y.-C. Shih, “Analysis of titanium dioxide and zinc oxide nanoparticles in cosmetics,” Journal of Food and Drug Analysis, vol. 23, no. 3, pp. 587–594, 2015. View at: Publisher Site | Google Scholar
  22. P. Singh and A. Nanda, “Enhanced sun protection of nano-sized metal oxide particles over conventional metal oxide particles: an in vitro comparative study,” International Journal of Cosmetic Science, vol. 36, no. 3, pp. 273–283, 2014. View at: Publisher Site | Google Scholar
  23. Y. Zhang, T. R. Nayak, H. Hong, and W. Cai, “Biomedical applications of zinc oxide nanomaterials,” Current Molecular Medicine, vol. 13, no. 10, pp. 1633–1645, 2013. View at: Publisher Site | Google Scholar
  24. L. Nie, L. Gao, P. Feng et al., “Three-dimensional functionalized tetrapodlike ZnO nanostructures for plasmid DNA delivery,” Small, vol. 2, no. 5, pp. 621–625, 2006. View at: Publisher Site | Google Scholar
  25. L. Nie, L. Gao, X. Yan, and T. Wang, “Functionalized tetrapod-like ZnO nanostructures for plasmid DNA purification, polymerase chain reaction and delivery,” Nanotechnology, vol. 18, no. 1, Article ID 015101, 2007. View at: Publisher Site | Google Scholar
  26. A. Umar, M. M. Rahman, M. Vaseem, and Y.-B. Hahn, “Ultra-sensitive cholesterol biosensor based on low-temperature grown ZnO nanoparticles,” Electrochemistry Communications, vol. 11, no. 1, pp. 118–121, 2009. View at: Publisher Site | Google Scholar
  27. J. Liu, C. Guo, C. M. Li et al., “Carbon-decorated ZnO nanowire array: a novel platform for direct electrochemistry of enzymes and biosensing applications,” Electrochemistry Communications, vol. 11, no. 1, pp. 202–205, 2009. View at: Publisher Site | Google Scholar
  28. A. S. Kazemi, R. Afzalzadeh, and M. Abadyan, “ZnO nanoparticles as ethanol gas sensors and the effective parameters on their performance,” Journal of Materials Science and Technology, vol. 29, no. 5, pp. 393–400, 2013. View at: Publisher Site | Google Scholar
  29. X. Liu, N. Chen, X. Xing et al., “A high-performance n-butanol gas sensor based on ZnO nanoparticles synthesized by a low-temperature solvothermal route,” RSC Advances, vol. 5, no. 67, pp. 54372–54378, 2015. View at: Publisher Site | Google Scholar
  30. C. Parisi, M. Vigani, and E. Rodríguez-Cerezo, “Agricultural nanotechnologies: what are the current possibilities?” Nano Today, vol. 10, no. 2, pp. 124–127, 2015. View at: Publisher Site | Google Scholar
  31. P. Bedi and A. Kaur, “An overview on uses of zinc oxide nanoparticles,” World Journal of Pharmacy and Pharmaceutical Sciences, vol. 4, no. 12, pp. 1177–1196, 2015. View at: Google Scholar
  32. M. Taheri, H. A. Qarache, A. A. Qarache, and M. Yoosefi, “The effects of zinc-oxide nanoparticles on growth parameters of corn (SC704),” STEM Fellowship Journal, vol. 1, no. 2, pp. 17–20, 2015. View at: Publisher Site | Google Scholar
  33. L. R. Khot, S. Sankaran, J. M. Maja, R. Ehsani, and E. W. Schuster, “Applications of nanomaterials in agricultural production and crop protection: a review,” Crop Protection, vol. 35, pp. 64–70, 2012. View at: Publisher Site | Google Scholar
  34. Q. Chaudhry, M. Scotter, J. Blackburn et al., “Applications and implications of nanotechnologies for the food sector,” Food Additives and Contaminants. Part A, vol. 25, no. 3, pp. 241–258, 2008. View at: Publisher Site | Google Scholar
  35. A. Emamifar, “Applications of antimicrobial polymer nanocomposites in food packaging,” in Advances in Nanocomposite Technology, A. Hashim, Ed., chapter 13, InTech, Rijeka, Croatia, 2011. View at: Publisher Site | Google Scholar
  36. P. J. P. Espitia, N. D. F. F. Soares, J. S. dos Reis Coimbra, N. J. de Andrade, R. S. Cruz, and E. A. A. Medeiros, “Zinc oxide nanoparticles: synthesis, antimicrobial activity and food packaging applications,” Food and Bioprocess Technology, vol. 5, no. 5, pp. 1447–1464, 2012. View at: Publisher Site | Google Scholar
  37. X. H. Li, Y. G. Xing, W. L. Li, Y. H. Jiang, and Y. L. Ding, “Antibacterial and physical properties of poly(vinyl chloride)-based film coated with ZnO nanoparticles,” Food Science and Technology International, vol. 16, no. 3, pp. 225–232, 2010. View at: Publisher Site | Google Scholar
  38. F. S.-S. Chien, C.-R. Wang, Y.-L. Chan, H.-L. Lin, M.-H. Chen, and R.-J. Wu, “Fast-response ozone sensor with ZnO nanorods grown by chemical vapor deposition,” Sensors and Actuators, B: Chemical, vol. 144, no. 1, pp. 120–125, 2010. View at: Publisher Site | Google Scholar
  39. P. J. P. Espitia, N. D. F. F. Soares, J. S. D. R. Coimbra, N. J. de Andrade, R. S. Cruz, and E. A. A. Medeiros, “Zinc oxide nanoparticles: synthesis, antimicrobial activity and food packaging applications,” Food and Bioprocess Technology, vol. 5, no. 5, pp. 1447–1464, 2012. View at: Publisher Site | Google Scholar
  40. W. H. Elmer and J. C. White, “The use of metallic oxide nanoparticles to enhance growth of tomatoes and eggplants in disease infested soil or soilless medium,” Environmental Science: Nano, vol. 3, no. 5, pp. 1072–1079, 2016. View at: Publisher Site | Google Scholar
  41. N. Milani, M. J. McLaughlin, S. P. Stacey et al., “Dissolution kinetics of macronutrient fertilizers coated with manufactured zinc oxide nanoparticles,” Journal of Agricultural and Food Chemistry, vol. 60, no. 16, pp. 3991–3998, 2012. View at: Publisher Site | Google Scholar
  42. A. V. Zvyagin, X. Zhao, A. Gierden, W. Sanchez, J. A. Ross, and M. S. Roberts, “Imaging of zinc oxide nanoparticle penetration in human skin in vitro and in vivo,” Journal of Biomedical Optics, vol. 13, no. 6, Article ID 064031, 2008. View at: Publisher Site | Google Scholar
  43. A. V. Kachynski, A. N. Kuzmin, M. Nyk, I. Roy, and P. N. Prasad, “Zinc oxide nanocrystals for nonresonant nonlinear optical microscopy in biology and medicine,” The Journal of Physical Chemistry C, vol. 112, no. 29, pp. 10721–10724, 2008. View at: Publisher Site | Google Scholar
  44. K. Vanheusden, W. L. Warren, C. H. Seager, D. R. Tallant, J. A. Voigt, and B. E. Gnade, “Mechanisms behind green photoluminescence in ZnO phosphor powders,” Journal of Applied Physics, vol. 79, no. 10, pp. 7983–7990, 1996. View at: Publisher Site | Google Scholar
  45. L. Tian, B. Lin, L. Wu et al., “Neurotoxicity induced by zinc oxide nanoparticles: age-related differences and interaction,” Scientific Reports, vol. 5, Article ID 16117, 2015. View at: Publisher Site | Google Scholar
  46. E. E. Fröhlich and E. Fröhlich, “Cytotoxicity of nanoparticles contained in food on intestinal cells and the gut microbiota,” International Journal of Molecular Sciences, vol. 17, no. 4, article 509, 2016. View at: Publisher Site | Google Scholar
  47. W. Chen, Y. Cheng, N. Hsieh et al., “Physiologically based pharmacokinetic modeling of zinc oxide nanoparticles and zinc nitrate in mice,” International Journal of Nanomedicine, vol. 10, no. 1, pp. 6277–6292, 2015. View at: Publisher Site | Google Scholar
  48. R. J. Vandebriel and W. H. De Jong, “A review of mammalian toxicity of ZnO nanoparticles,” Nanotechnology, Science and Applications, vol. 5, no. 1, pp. 61–71, 2012. View at: Publisher Site | Google Scholar
  49. E. E. Connor, J. Mwamuka, A. Gole, C. J. Murphy, and M. D. Wyatt, “Gold nanoparticles are taken up by human cells but do not cause acute cytotoxicity,” Small, vol. 1, no. 3, pp. 325–327, 2005. View at: Publisher Site | Google Scholar
  50. O. Bondarenko, K. Juganson, A. Ivask, K. Kasemets, M. Mortimer, and A. Kahru, “Toxicity of Ag, CuO and ZnO nanoparticles to selected environmentally relevant test organisms and mammalian cells in vitro: a critical review,” Archives of Toxicology, vol. 87, no. 7, pp. 1181–1200, 2013. View at: Publisher Site | Google Scholar
  51. J. Liu, X. Feng, L. Wei, L. Chen, B. Song, and L. Shao, “The toxicology of ion-shedding zinc oxide nanoparticles,” Critical Reviews in Toxicology, vol. 46, no. 4, pp. 348–384, 2016. View at: Publisher Site | Google Scholar
  52. H. Wang, D. Wingett, M. H. Engelhard et al., “Fluorescent dye encapsulated ZnO particles with cell-specific toxicity for potential use in biomedical applications,” Journal of Materials Science: Materials in Medicine, vol. 20, no. 1, pp. 11–22, 2009. View at: Publisher Site | Google Scholar
  53. Q. Yuan, S. Hein, and R. D. K. Misra, “New generation of chitosan-encapsulated ZnO quantum dots loaded with drug: synthesis, characterization and in vitro drug delivery response,” Acta Biomaterialia, vol. 6, no. 7, pp. 2732–2739, 2010. View at: Publisher Site | Google Scholar
  54. J. W. Rasmussen, E. Martinez, P. Louka, and D. G. Wingett, “Zinc oxide nanoparticles for selective destruction of tumor cells and potential for drug delivery applications,” Expert Opinion on Drug Delivery, vol. 7, no. 9, pp. 1063–1077, 2010. View at: Publisher Site | Google Scholar
  55. M. Premanathan, K. Karthikeyan, K. Jeyasubramanian, and G. Manivannan, “Selective toxicity of ZnO nanoparticles toward Gram-positive bacteria and cancer cells by apoptosis through lipid peroxidation,” Nanomedicine: Nanotechnology, Biology, and Medicine, vol. 7, no. 2, pp. 184–192, 2011. View at: Publisher Site | Google Scholar
  56. F. Muhammad, M. Guo, W. Qi et al., “PH-triggered controlled drug release from mesoporous silica nanoparticles via intracelluar dissolution of ZnO nanolids,” Journal of the American Chemical Society, vol. 133, no. 23, pp. 8778–8781, 2011. View at: Publisher Site | Google Scholar
  57. D. Guo, C. Wu, H. Jiang, Q. Li, X. Wang, and B. Chen, “Synergistic cytotoxic effect of different sized ZnO nanoparticles and daunorubicin against leukemia cancer cells under UV irradiation,” Journal of Photochemistry and Photobiology B: Biology, vol. 93, no. 3, pp. 119–126, 2008. View at: Publisher Site | Google Scholar
  58. G. Lin, H. Zhang, and L. Huang, “Smart polymeric nanoparticles for cancer gene delivery,” Molecular Pharmaceutics, vol. 12, no. 2, pp. 314–321, 2015. View at: Publisher Site | Google Scholar
  59. J. Liu, X. Ma, S. Jin et al., “Zinc oxide nanoparticles as adjuvant to facilitate doxorubicin intracellular accumulation and visualize pH-responsive release for overcoming drug resistance,” Molecular Pharmaceutics, vol. 13, no. 5, pp. 1723–1730, 2016. View at: Publisher Site | Google Scholar
  60. N. V. Mantzaris, “Liquid-phase synthesis of nanoparticles: particle size distribution dynamics and control,” Chemical Engineering Science, vol. 60, no. 17, pp. 4749–4770, 2005. View at: Publisher Site | Google Scholar
  61. M. F. Khan, A. H. Ansari, M. Hameedullah et al., “Sol-gel synthesis of thorn-like ZnO nanoparticles endorsing mechanical stirring effect and their antimicrobial activities: potential role as nano-Antibiotics,” Scientific Reports, vol. 6, Article ID 27689, 2016. View at: Publisher Site | Google Scholar
  62. B. Gersten, “Solvothermal synthesis of nanoparticles,” Chemfiles, vol. 5, pp. 11–12, 2005. View at: Google Scholar
  63. P. Rai, W.-K. Kwak, and Y.-T. Yu, “Solvothermal synthesis of ZnO nanostructures and their morphology-dependent gas-sensing properties,” ACS Applied Materials and Interfaces, vol. 5, no. 8, pp. 3026–3032, 2013. View at: Publisher Site | Google Scholar
  64. F. Iskandar, “Nanoparticle processing for optical applications—a review,” Advanced Powder Technology, vol. 20, no. 4, pp. 283–292, 2009. View at: Publisher Site | Google Scholar
  65. Y. R. Uhm, B. S. Han, M. K. Lee, S. J. Hong, and C. K. Rhee, “Synthesis and characterization of nanoparticles of ZnO by levitational gas condensation,” Materials Science and Engineering A, vol. 448—451, pp. 813–816, 2007. View at: Publisher Site | Google Scholar
  66. N. Salah, S. S. Habib, Z. H. Khan et al., “High-energy ball milling technique for ZnO nanoparticles as antibacterial material,” International Journal of Nanomedicine, vol. 6, pp. 863–869, 2011. View at: Publisher Site | Google Scholar
  67. R. A. Ismail, A. K. Ali, M. M. Ismail, and K. I. Hassoon, “Preparation and characterization of colloidal ZnO nanoparticles using nanosecond laser ablation in water,” Applied Nanoscience, vol. 1, no. 1, pp. 45–49, 2011. View at: Publisher Site | Google Scholar
  68. O. Tigli and J. Juhala, “ZnO nanowire growth by physical vapor deposition,” in Proceedings of the 11th IEEE International Conference on Nanotechnology (NANO '11), pp. 608–611, Portland, Ore, USA, August 2011. View at: Publisher Site | Google Scholar
  69. Z.-U. Mashwani, M. A. Khan, T. Khan, and A. Nadhman, “Applications of plant terpenoids in the synthesis of colloidal silver nanoparticles,” Advances in Colloid and Interface Science, vol. 234, pp. 132–141, 2016. View at: Publisher Site | Google Scholar
  70. Z.-U.-R. Mashwani, T. Khan, M. A. Khan, and A. Nadhman, “Synthesis in plants and plant extracts of silver nanoparticles with potent antimicrobial properties: current status and future prospects,” Applied Microbiology and Biotechnology, vol. 99, no. 23, pp. 9923–9934, 2015. View at: Publisher Site | Google Scholar
  71. N. A. N. Mohamad, N. A. Arham, J. Jai, and A. Hadi, “Plant extract as reducing agent in synthesis of metallic nanoparticles: a review,” Advanced Materials Research, vol. 832, pp. 350–355, 2014. View at: Publisher Site | Google Scholar
  72. V. V. Makarov, A. J. Love, O. V. Sinitsyna et al., “‘Green’ nanotechnologies: synthesis of metal nanoparticles using plants,” Acta Naturae, vol. 6, no. 1, pp. 35–44, 2014. View at: Google Scholar
  73. A. G. Ingale and A. N. Chaudhari, “Biogenic synthesis of nanoparticles and potential applications: an eco-friendly approach,” Journal of Nanomedicine and Nanotechnology, vol. 4, no. 2, 2013. View at: Publisher Site | Google Scholar
  74. T. Klaus-Joerger, R. Joergere, E. Olsson, and C. Granqvist, “Bacteria as workers in the living factory: metal-accumulating bacteria and their potential for materials science,” Trends in Biotechnology, vol. 19, no. 1, pp. 15–20, 2001. View at: Publisher Site | Google Scholar
  75. A. Yadav, K. Kon, G. Kratosova, N. Duran, A. P. Ingle, and M. Rai, “Fungi as an efficient mycosystem for the synthesis of metal nanoparticles: progress and key aspects of research,” Biotechnology Letters, vol. 37, no. 11, pp. 2099–2120, 2015. View at: Publisher Site | Google Scholar
  76. N. Jain, A. Bhargava, J. C. Tarafdar, S. K. Singh, and J. Panwar, “A biomimetic approach towards synthesis of zinc oxide nanoparticles,” Applied Microbiology and Biotechnology, vol. 97, no. 2, pp. 859–869, 2013. View at: Publisher Site | Google Scholar
  77. S. Jacob, R. Bharathkumar, and G. Ashwathram, “Aspergillus niger mediated synthesis of ZnO nanoparticles and their antimicrobial and in vitro anticancerous activity,” World Journal of Pharmaceutical Sciences, vol. 3, no. 2, pp. 3044–3054, 2014. View at: Google Scholar
  78. G. Baskar, J. Chandhuru, K. S. Fahad, and A. Praveen, “Mycological synthesis, characterization and antifungal activity of zinc oxide nanoparticles,” Asian Journal of Pharmacy and Technology, vol. 3, no. 4, pp. 142–146, 2013. View at: Google Scholar
  79. C. Jayaseelan, A. A. Rahuman, A. V. Kirthi et al., “Novel microbial route to synthesize ZnO nanoparticles using Aeromonas hydrophila and their activity against pathogenic bacteria and fungi,” Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, vol. 90, pp. 78–84, 2012. View at: Publisher Site | Google Scholar
  80. M. Z. Hussein, W. H. W. N. Azmin, M. Mustafa, and A. H. Yahaya, “Bacillus cereus as a biotemplating agent for the synthesis of zinc oxide with raspberry- and plate-like structures,” Journal of Inorganic Biochemistry, vol. 103, no. 8, pp. 1145–1150, 2009. View at: Publisher Site | Google Scholar
  81. R. S. Scott, S. R. Frame, P. E. Ross, S. E. Loveless, and G. L. Kennedy, “Inhalation toxicity of 1,3-propanediol in the rat,” Inhalation Toxicology, vol. 17, no. 9, pp. 487–493, 2008. View at: Publisher Site | Google Scholar
  82. S. Azizi, M. B. Ahmad, F. Namvar, and R. Mohamad, “Green biosynthesis and characterization of zinc oxide nanoparticles using brown marine macroalga Sargassum muticum aqueous extract,” Materials Letters, vol. 116, pp. 275–277, 2014. View at: Publisher Site | Google Scholar
  83. A. K. Jha and K. Prasad, “Synthesis of ZnO nanoparticles from goat slaughter waste for environmental protection,” International Journal of Current Engineering and Technology, vol. 6, no. 1, pp. 147–151, 2016. View at: Publisher Site | Google Scholar
  84. R. Dobrucka and J. Długaszewska, “Biosynthesis and antibacterial activity of ZnO nanoparticles using Trifolium pratense flower extract,” Saudi Journal of Biological Sciences, vol. 23, no. 4, pp. 517–523, 2016. View at: Publisher Site | Google Scholar
  85. V. Mishra and R. Sharma, “Green synthesis of zinc oxide nanoparticles using fresh peels extract of Punica granatum and its antimicrobial activities,” International Journal of Pharma Research and Health Sciences, vol. 3, no. 3, pp. 694–699, 2015. View at: Google Scholar
  86. C. Tamuly, I. Saikia, M. Hazarika et al., “Bio-derived ZnO nanoflower: a highly efficient catalyst for the synthesis of chalcone derivatives,” RSC Advances, vol. 5, no. 12, pp. 8604–8608, 2015. View at: Publisher Site | Google Scholar
  87. B. Kumar, K. Smita, L. Cumbal, and A. Debut, “Green approach for fabrication and applications of zinc oxide nanoparticles,” Bioinorganic Chemistry and Applications, vol. 2014, Article ID 523869, 7 pages, 2014. View at: Publisher Site | Google Scholar
  88. F. Davar, A. Majedi, and A. Mirzaei, “Green synthesis of ZnO nanoparticles and its application in the degradation of some dyes,” Journal of the American Ceramic Society, vol. 98, no. 6, pp. 1739–1746, 2015. View at: Publisher Site | Google Scholar
  89. Z.-R. Tang, X. Yin, Y. Zhang, and Y.-J. Xu, “One-pot, high-yield synthesis of one-dimensional ZnO nanorods with well-defined morphology as a highly selective photocatalyst,” RSC Advances, vol. 3, no. 17, pp. 5956–5965, 2013. View at: Publisher Site | Google Scholar
  90. Z. L. Wang, “Splendid one-dimensional nanostructures of zinc oxide: a new nanomaterial family for nanotechnology,” ACS Nano, vol. 2, no. 10, pp. 1987–1992, 2008. View at: Publisher Site | Google Scholar
  91. Y. Lu, L. Wang, D. Wang, T. Xie, L. Chen, and Y. Lin, “A comparative study on plate-like and flower-like ZnO nanocrystals surface photovoltage property and photocatalytic activity,” Materials Chemistry and Physics, vol. 129, no. 1-2, pp. 281–287, 2011. View at: Publisher Site | Google Scholar
  92. J. Liu, Z.-Y. Hu, Y. Peng et al., “2D ZnO mesoporous single-crystal nanosheets with exposed {0001} polar facets for the depollution of cationic dye molecules by highly selective adsorption and photocatalytic decomposition,” Applied Catalysis B: Environmental, vol. 181, pp. 138–145, 2016. View at: Publisher Site | Google Scholar
  93. W. S. Chiu, P. S. Khiew, M. Cloke et al., “Photocatalytic study of two-dimensional ZnO nanopellets in the decomposition of methylene blue,” Chemical Engineering Journal, vol. 158, no. 2, pp. 345–352, 2010. View at: Publisher Site | Google Scholar
  94. Q. Xie, Z. Dai, J. Liang, L. Xu, W. Yu, and Y. Qian, “Synthesis of ZnO three-dimensional architectures and their optical properties,” Solid State Communications, vol. 136, no. 5, pp. 304–307, 2005. View at: Publisher Site | Google Scholar
  95. P. Raveendran, J. Fu, and S. L. Wallen, “Completely “green” synthesis and stabilization of metal nanoparticles,” Journal of the American Chemical Society, vol. 125, no. 46, pp. 13940–13941, 2003. View at: Publisher Site | Google Scholar
  96. E. E. L. Tanner, K. Tschulik, R. Tahany, K. Jurkschat, C. Batchelor-McAuley, and R. G. Compton, “Nanoparticle capping agent dynamics and electron transfer: polymer-gated oxidation of silver nanoparticles,” The Journal of Physical Chemistry C, vol. 119, no. 32, pp. 18808–18815, 2015. View at: Publisher Site | Google Scholar
  97. Z. Zhou, J. Son, B. Harper, Z. Zhou, and S. Harper, “Influence of surface chemical properties on the toxicity of engineered zinc oxide nanoparticles to embryonic zebrafish,” Beilstein Journal of Nanotechnology, vol. 6, no. 1, pp. 1568–1579, 2015. View at: Publisher Site | Google Scholar
  98. Y. Y. Liu, I. Schmeltz, and D. Hoffmann, “Chemical studies on tobacco smoke. Quantitative analysis of hydrazine in tobacco and cigarette smoke,” Analytical Chemistry, vol. 46, no. 7, pp. 885–889, 1974. View at: Publisher Site | Google Scholar
  99. G. Lunn, E. B. Sansone, and L. K. Keefer, “Notes. Reductive destruction of hydrazines as an approach to hazard control,” Environmental Science and Technology, vol. 17, no. 4, pp. 240–243, 1983. View at: Publisher Site | Google Scholar
  100. R. Rajendram and V. R. Preedy, “Effect of alcohol consumption on the gut,” Digestive Diseases, vol. 23, no. 3-4, pp. 214–221, 2006. View at: Publisher Site | Google Scholar
  101. R. B. Forney and R. N. Harger, “Toxicology of ethanol,” Annual Review of Pharmacology, vol. 9, no. 1, pp. 379–392, 1969. View at: Publisher Site | Google Scholar
  102. A. K. Mehta and M. K. Ticku, “Ethanol potentiation of GABAergic transmission in cultured spinal cord neurons involves gamma-aminobutyric acidA-gated chloride channels,” Journal of Pharmacology and Experimental Therapeutics, vol. 246, no. 2, pp. 558–564, 1988. View at: Google Scholar
  103. D. Jacobsen and K. E. McMartin, “Methanol and ethylene glycol poisonings,” Medical Toxicology, vol. 1, no. 5, pp. 309–334, 1986. View at: Publisher Site | Google Scholar
  104. Health, Safety and Environment, Occupational Safety Unit UoR. Environmental Health & Safety Occupational Safety Unit 2012.
  105. A. Khorsand Zak, W. H. A. Majid, H. Z. Wang, R. Yousefi, A. Moradi Golsheikh, and Z. F. Ren, “Sonochemical synthesis of hierarchical ZnO nanostructures,” Ultrasonics Sonochemistry, vol. 20, no. 1, pp. 395–400, 2013. View at: Publisher Site | Google Scholar
  106. H. Xu, B. W. Zeiger, and K. S. Suslick, “Sonochemical synthesis of nanomaterials,” Chemical Society Reviews, vol. 42, no. 7, pp. 2555–2567, 2013. View at: Publisher Site | Google Scholar
  107. H.-M. Xiong, D. G. Shchukin, H. Möhwald, Y. Xu, and Y.-Y. Xia, “Sonochemical synthesis of highly luminescent zinc oxide nanoparticles doped with magnesium(II),” Angewandte Chemie—International Edition, vol. 48, no. 15, pp. 2727–2731, 2009. View at: Publisher Site | Google Scholar
  108. A. E. Kandjani, M. F. Tabriz, and B. Pourabbas, “Sonochemical synthesis of ZnO nanoparticles: the effect of temperature and sonication power,” Materials Research Bulletin, vol. 43, no. 3, pp. 645–654, 2008. View at: Publisher Site | Google Scholar
  109. I. A. Siddiquey, T. Furusawa, M. Sato, N. M. Bahadur, M. Mahbubul Alam, and N. Suzuki, “Sonochemical synthesis, photocatalytic activity and optical properties of silica coated ZnO nanoparticles,” Ultrasonics Sonochemistry, vol. 19, no. 4, pp. 750–755, 2012. View at: Publisher Site | Google Scholar
  110. A. Askarinejad, M. A. Alavi, and A. Morsali, “Sonochemically assisted synthesis of ZnO nanoparticles: a novel direct method,” Iranian Journal of Chemistry and Chemical Engineering, vol. 30, no. 3, pp. 75–81, 2011. View at: Google Scholar
  111. C. Pholnak, C. Sirisathitkul, S. Danworaphong, and D. J. Harding, “Sonochemical synthesis of zinc oxide nanoparticles using an ultrasonic homogenizer,” Ferroelectrics, vol. 455, no. 1, pp. 15–20, 2013. View at: Publisher Site | Google Scholar
  112. J. S. Taurozzi, V. A. Hackley, and M. R. Wiesner, “Ultrasonic dispersion of nanoparticles for environmental, health and safety assessment–issues and recommendations,” Nanotoxicology, vol. 5, no. 4, pp. 711–729, 2011. View at: Publisher Site | Google Scholar
  113. J. E. Edinger, D. K. Brady, and J. C. Geyer, “Heat exchange and transport in the environment,” Tech. Rep. 14, Johns Hopkins University, Department of Geography and Environmental Engineering, Baltimore, Md, USA, 1974. View at: Google Scholar
  114. J. Soni and A. Koser, “Synthesis of ZnO nanoparticle using different concentration of capping agent,” International Journal of Technology Innovations and Research, vol. 16, pp. 1–7, 2015. View at: Google Scholar
  115. S. B. Rana, P. Singh, A. K. Sharma, A. W. Carbonari, and R. Dogra, “Synthesis and characterization of pure and doped ZnO nanoparticles,” Journal of Optoelectronics and Advanced Materials, vol. 12, no. 2, pp. 257–261, 2010. View at: Google Scholar
  116. Y. T. Prabhu, K. V. Rao, V. S. S. Kumar, and B. S. Kumari, “Synthesis of ZnO nanoparticles by a novel surfactant assisted amine combustion method,” Advances in Nanoparticles, vol. 2, no. 1, pp. 45–50, 2013. View at: Publisher Site | Google Scholar
  117. H. Chang and M.-H. Tsai, “Synthesis and characterization of ZnO nanoparticles having prism shape by a novel gas condensation process,” Reviews on Advanced Materials Science, vol. 18, no. 8, pp. 734–743, 2008. View at: Google Scholar
  118. J. Wen, Y. Hu, K. Zhu, Y. Li, and J. Song, “High-temperature-mixing hydrothermal synthesis of ZnO nanocrystals with wide growth window,” Current Applied Physics, vol. 14, no. 3, pp. 359–365, 2014. View at: Publisher Site | Google Scholar
  119. B. Åkesson, M. Bengtsson, and I. Florén, “Visual disturbances after industrial triethylamine exposure,” International Archives of Occupational and Environmental Health, vol. 57, no. 4, pp. 297–302, 1986. View at: Publisher Site | Google Scholar
  120. D. Ju, H. Xu, Z. Qiu, J. Guo, J. Zhang, and B. Cao, “Highly sensitive and selective triethylamine-sensing properties of nanosheets directly grown on ceramic tube by forming NiO/ZnO PN heterojunction,” Sensors and Actuators B: Chemical, vol. 200, pp. 288–296, 2014. View at: Publisher Site | Google Scholar
  121. M. El-Kemary, H. El-Shamy, and I. El-Mehasseb, “Photocatalytic degradation of ciprofloxacin drug in water using ZnO nanoparticles,” Journal of Luminescence, vol. 130, no. 12, pp. 2327–2331, 2010. View at: Publisher Site | Google Scholar
  122. M. Sato, H. Harada, S. Morito et al., “Preparation, characterization and properties of novel covalently surface-functionalized zinc oxide nanoparticles,” Applied Surface Science, vol. 256, no. 14, pp. 4497–4501, 2010. View at: Publisher Site | Google Scholar
  123. M. F. Cury-Boaventura, C. Pompéia, and R. Curi, “Comparative toxicity of oleic acid and linoleic acid on Raji cells,” Nutrition, vol. 21, no. 3, pp. 395–405, 2005. View at: Publisher Site | Google Scholar
  124. X. Tang, E. S. G. Choo, N. Li, J. Ding, and J. Xue, “One-pot synthesis of water-stable ZnO nanoparticles via a polyol hydrolysis route and their cell labeling applications,” Langmuir, vol. 25, no. 9, pp. 5271–5275, 2009. View at: Publisher Site | Google Scholar
  125. A. Mclaren, T. Valdes-Solis, G. Li, and S. C. Tsang, “Shape and size effects of ZnO nanocrystals on photocatalytic activity,” Journal of the American Chemical Society, vol. 131, no. 35, pp. 12540–12541, 2009. View at: Publisher Site | Google Scholar
  126. Y. Gong, T. Andelman, G. F. Neumark, S. O'Brien, and I. L. Kuskovsky, “Origin of defect-related green emission from ZnO nanoparticles: effect of surface modification,” Nanoscale Research Letters, vol. 2, no. 6, pp. 297–302, 2007. View at: Publisher Site | Google Scholar
  127. O. V. Singh, Bio-Nanoparticles: Biosynthesis and Sustainable Biotechnological Implications, John Wiley & Sons, 2015.
  128. R. K. Dutta, B. P. Nenavathu, M. K. Gangishetty, and A. V. R. Reddy, “Studies on antibacterial activity of ZnO nanoparticles by ROS induced lipid peroxidation,” Colloids and Surfaces B: Biointerfaces, vol. 94, pp. 143–150, 2012. View at: Publisher Site | Google Scholar
  129. R. Tripathi, A. Kumar, C. Bharti, and T. P. Sinha, “Dielectric relaxation of ZnO nanostructure synthesized by soft chemical method,” Current Applied Physics, vol. 10, no. 2, pp. 676–681, 2010. View at: Publisher Site | Google Scholar
  130. A. Aboulaich, L. Balan, J. Ghanbaja, G. Medjahdi, C. Merlin, and R. Schneider, “Aqueous route to biocompatible ZnSe:Mn/ZnO core/shell quantum dots using 1-thioglycerol as stabilizer,” Chemistry of Materials, vol. 23, no. 16, pp. 3706–3713, 2011. View at: Publisher Site | Google Scholar
  131. J. R. Hart, Ethylenediaminetetraacetic Acid and Related Chelating Agents, Ullmann's Encyclopedia of Industrial Chemistry, 2000.
  132. R. Lanigan and T. Yamarik, “Final report on the safety assessment of EDTA, calcium disodium EDTA, diammonium EDTA, dipotassium EDTA, disodium EDTA, TEA-EDTA, tetrasodium EDTA, tripotassium EDTA, trisodium EDTA, HEDTA, and trisodium HEDTA,” International Journal of Toxicology, vol. 21, no. 2, pp. 95–142, 2002. View at: Publisher Site | Google Scholar
  133. X. Zhao, X. Ren, C. Sun et al., “Morphology evolution at nano- to micro-scale,” Functional Materials Letters, vol. 1, no. 3, pp. 167–172, 2008. View at: Publisher Site | Google Scholar
  134. P. Chandrasekaran, G. Viruthagiri, and N. Srinivasan, “The effect of various capping agents on the surface modifications of sol–gel synthesised ZnO nanoparticles,” Journal of Alloys and Compounds, vol. 540, pp. 89–93, 2012. View at: Publisher Site | Google Scholar
  135. M. Ramani, S. Ponnusamy, C. Muthamizhchelvan, J. Cullen, S. Krishnamurthy, and E. Marsili, “Morphology-directed synthesis of ZnO nanostructures and their antibacterial activity,” Colloids and Surfaces B: Biointerfaces, vol. 105, pp. 24–30, 2013. View at: Publisher Site | Google Scholar
  136. A. J. P. Graham, “Toxic effects of tetraethylammonium bromide,” British Medical Journal, vol. 2, no. 4674, pp. 321–322, 1950. View at: Publisher Site | Google Scholar
  137. R.-O. Moussodia, L. Balan, and R. Schneider, “Synthesis and characterization of water-soluble ZnO quantum dots prepared through PEG-siloxane coating,” New Journal of Chemistry, vol. 32, no. 8, pp. 1388–1393, 2008. View at: Publisher Site | Google Scholar
  138. D. Verma, A. K. Kole, and P. Kumbhakar, “Red shift of the band-edge photoluminescence emission and effects of annealing and capping agent on structural and optical properties of ZnO nanoparticles,” Journal of Alloys and Compounds, vol. 625, pp. 122–130, 2015. View at: Publisher Site | Google Scholar
  139. S. Mallakpour and V. Behranvand, “Surface treatment of nano ZnO using 3,4,5,6-tetrabromo-N-(4-hydroxy-phenyl) -phthalamic acid as novel coupling agent for the preparation of poly(amide-imide)/ZnO nanocomposites,” Colloid and Polymer Science, vol. 292, no. 9, pp. 2275–2283, 2014. View at: Publisher Site | Google Scholar
  140. D. A. P. Bulla and N. I. Morimoto, “Deposition of thick TEOS PECVD silicon oxide layers for integrated optical waveguide applications,” Thin Solid Films, vol. 334, no. 1-2, pp. 60–64, 1998. View at: Publisher Site | Google Scholar
  141. L. Y. L. Wu, A. I. Y. Tok, F. Y. C. Boey, X. T. Zeng, and X. H. Zhang, “Chemical synthesis of ZnO nanocrystals,” IEEE Transactions on Nanotechnology, vol. 6, no. 5, pp. 497–503, 2007. View at: Publisher Site | Google Scholar
  142. J. Wang, T. Tsuzuki, L. Sun, and X. Wang, “Reverse microemulsion-mediated synthesis of SiO2-coated ZnO composite nanoparticles: multiple cores with tunable shell thickness,” ACS Applied Materials and Interfaces, vol. 2, no. 4, pp. 957–960, 2010. View at: Publisher Site | Google Scholar
  143. Z. Cao and Z. Zhang, “Deactivation of photocatalytically active ZnO nanoparticle and enhancement of its compatibility with organic compounds by surface-capping with organically modified silica,” Applied Surface Science, vol. 257, no. 9, pp. 4151–4158, 2011. View at: Publisher Site | Google Scholar
  144. H. J. Allen, C. A. Impellitteri, D. A. Macke et al., “Effects from filtration, capping agents, and presence/absence of food on the toxicity of silver nanoparticles to Daphnia magna,” Environmental Toxicology and Chemistry, vol. 29, no. 12, pp. 2742–2750, 2010. View at: Publisher Site | Google Scholar
  145. M. Sudha, S. Senthilkumar, R. Hariharan, A. Suganthi, and M. Rajarajan, “Synthesis, characterization and study of photocatalytic activity of surface modified ZnO nanoparticles by PEG capping,” Journal of Sol-Gel Science and Technology, vol. 65, no. 3, pp. 301–310, 2013. View at: Publisher Site | Google Scholar
  146. L. Sax, “Polyethylene terephthalate May yield endocrine disruptors,” Environmental Health Perspectives, vol. 118, no. 4, pp. 445–448, 2010. View at: Publisher Site | Google Scholar
  147. G. S. Thool, A. K. Singh, R. S. Singh, A. Gupta, and M. A. B. H. Susan, “Facile synthesis of flat crystal ZnO thin films by solution growth method: a micro-structural investigation,” Journal of Saudi Chemical Society, vol. 18, no. 5, pp. 712–721, 2014. View at: Publisher Site | Google Scholar
  148. D. Pradhan, Z. Su, S. Sindhwani, J. F. Honek, and K. T. Leung, “Electrochemical growth of ZnO nanobelt-like structures at 0°c: synthesis, characterization, and in-situ glucose oxidase embedment,” Journal of Physical Chemistry C, vol. 115, no. 37, pp. 18149–18156, 2011. View at: Publisher Site | Google Scholar
  149. T. Thirugnanam, “Effect of polymers (PEG and PVP) on sol-gel synthesis of microsized zinc oxide,” Journal of Nanomaterials, vol. 2013, Article ID 362175, 7 pages, 2013. View at: Publisher Site | Google Scholar
  150. National Toxicology Program, “NTP-CERHR monograph on the potential human reproductive and developmental effects of ethylene glycol,” NTP CERHR MON, no. 11, pp. 1–III36, 2004. View at: Google Scholar
  151. J. Sedlák, I. Kuřitka, M. Machovský, P. Šuly, P. Bažant, and T. Sedláček, “Zinc oxide nanoparticles with surface modified by degradation of capping polymers in situ during microwave synthesis,” Advanced Powder Technology, vol. 26, no. 4, pp. 1064–1071, 2015. View at: Publisher Site | Google Scholar
  152. R. Devaraj, K. Karthikeyan, and K. Jeyasubramanian, “Synthesis and properties of ZnO nanorods by modified Pechini process,” Applied Nanoscience, vol. 3, no. 1, pp. 37–40, 2013. View at: Publisher Site | Google Scholar
  153. K. Liu, J.-J. Zhang, F.-F. Cheng, T.-T. Zheng, C. Wang, and J.-J. Zhu, “Green and facile synthesis of highly biocompatible graphene nanosheets and its application for cellular imaging and drug delivery,” Journal of Materials Chemistry, vol. 21, no. 32, pp. 12034–12040, 2011. View at: Publisher Site | Google Scholar
  154. Y. Tamgadge, K. Patil, and R. Ganorkar, “Synthesis and characterization of gelatin capped Zno nanoparticles,” International Journal of Scientific Research, vol. 5, no. 1, article 7, 2016. View at: Google Scholar
  155. S. Shankar, X. Teng, G. Li, and J.-W. Rhim, “Preparation, characterization, and antimicrobial activity of gelatin/ZnO nanocomposite films,” Food Hydrocolloids, vol. 45, pp. 264–271, 2015. View at: Publisher Site | Google Scholar
  156. C. M. Kelly, C. C. DeMerlis, D. R. Schoneker, and J. F. Borzelleca, “Subchronic toxicity study in rats and genotoxicity tests with polyvinyl alcohol,” Food and Chemical Toxicology, vol. 41, no. 5, pp. 719–727, 2003. View at: Publisher Site | Google Scholar
  157. C. C. DeMerlis and D. R. Schoneker, “Review of the oral toxicity of polyvinyl alcohol (PVA),” Food and Chemical Toxicology, vol. 41, no. 3, pp. 319–326, 2003. View at: Publisher Site | Google Scholar
  158. T. K. Kundu, N. Karak, P. Barik, and S. Saha, “Optical properties of ZnO nanoparticles prepared by chemical method using poly (vinyl alcohol)(PVA) as capping agent,” International Journal of Soft Computing and Engineering, vol. 1, pp. 19–24, 2011. View at: Google Scholar
  159. D. Shao, H. Sun, M. Yu, J. Lian, and S. Sawyer, “Enhanced ultraviolet emission from poly(vinyl alcohol) ZnO nanoparticles using a SiO2-Au core/shell structure,” Nano Letters, vol. 12, no. 11, pp. 5840–5844, 2012. View at: Publisher Site | Google Scholar
  160. A. P. Nagvenkar, A. Deokar, I. Perelshtein, and A. Gedanken, “A one-step sonochemical synthesis of stable ZnO-PVA nanocolloid as a potential biocidal agent,” Journal of Materials Chemistry B, vol. 4, no. 12, pp. 2124–2132, 2016. View at: Publisher Site | Google Scholar
  161. Health UDo, H. Services, N. T. Program, and Reproduction CftEoRtH, NTP-CERHR Monograph on the Potential Human Reproductive and Developmental Effects of Ethylene Glycol, 04-4481, NIH Publication, 2004.
  162. S. Tachikawa, A. Noguchi, T. Tsuge, M. Hara, O. Odawara, and H. Wada, “Optical properties of ZnO nanoparticles capped with polymers,” Materials, vol. 4, no. 6, pp. 1132–1143, 2011. View at: Publisher Site | Google Scholar
  163. G. Bandekar, N. S. Rajurkar, I. S. Mulla, U. P. Mulik, D. P. Amalnerkar, and P. V. Adhyapak, “Synthesis, characterization and photocatalytic activity of PVP stabilized ZnO and modified ZnO nanostructures,” Applied Nanoscience, vol. 4, no. 2, pp. 199–208, 2014. View at: Publisher Site | Google Scholar
  164. M. L. Singla, M. M. Shafeeq, and M. Kumar, “Optical characterization of ZnO nanoparticles capped with various surfactants,” Journal of Luminescence, vol. 129, no. 5, pp. 434–438, 2009. View at: Publisher Site | Google Scholar
  165. X. Feng, Y. Yan, B. Wan et al., “Enhanced dissolution and transformation of ZnO nanoparticles: the role of inositol hexakisphosphate,” Environmental Science and Technology, vol. 50, no. 11, pp. 5651–5660, 2016. View at: Publisher Site | Google Scholar
  166. M. Auffan, J. Rose, M. R. Wiesner, and J.-Y. Bottero, “Chemical stability of metallic nanoparticles: a parameter controlling their potential cellular toxicity in vitro,” Environmental Pollution, vol. 157, no. 4, pp. 1127–1133, 2009. View at: Publisher Site | Google Scholar
  167. H. Kuang, P. Yang, L. Yang, Z. P. Aguilar, and H. Xu, “Size dependent effect of ZnO nanoparticles on endoplasmic reticulum stress signaling pathway in murine liver,” Journal of Hazardous Materials, vol. 317, pp. 119–126, 2016. View at: Publisher Site | Google Scholar
  168. C. Wang, X. Hu, Y. Gao, and Y. Ji, “ZnO nanoparticles treatment induces apoptosis by increasing intracellular ROS levels in LTEP-a-2 cells,” BioMed Research International, vol. 2015, Article ID 423287, 9 pages, 2015. View at: Publisher Site | Google Scholar

Copyright © 2017 Ayesha Naveed Ul Haq et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

More related articles

 PDF Download Citation Citation
 Download other formatsMore
 Order printed copiesOrder

Related articles

Article of the Year Award: Outstanding research contributions of 2020, as selected by our Chief Editors. Read the winning articles.