The present research work reports the facile and green synthesis of TiO2 nanoparticles from Phyllanthus niruri leaf extract using the coprecipitation method. The plant biomolecules were responsible for the nanoproduction and exhibited reduction and stabilization activity. The green synthesized TiO2 nanoparticles were analyzed in various characterization methods. The crystalline size (23 nm) and anatase phase of TiO2 nanoparticles were analyzed from X-ray diffraction study. The reduction and stabilization response functional group of TiO2 nanoparticles was studied from FTIR analysis. The optical properties of TiO2 nanoparticles were constructed from the UV-DRS technique, and their calculated bandgap is 3.16 eV. The spherical morphology and their existing materials were identified using FESEM with EDX. The catalytic activity of TiO2 nanoparticles was examined against methylene blue dye under ultraviolet and visible light irradiation. It was detected that ultraviolet irradiation showed higher photocatalytic activity than visible light irradiation. In addition, visible light irradiation provides the above 90 percentage degradation of methylene blue dye. Hence, TiO2 nanoparticles were proposed as a potential catalyst of photocatalytic dye degradation application and water remediation activities.

1. Introduction

Nanoscience is one of the most widely used and effective fields of research in scientific discovery. Nanotechnology has recently become a highly advanced technology with intra- and interstudy spanning chemistry, physics, biology, material science, and medicine. The production of nanometer-sized materials of various morphologies and sizes, as well as monodispersion, is an important field of research in nanoscience [1, 2]. Nanoparticles of varying sizes, shapes, and controlled disparity are synthesized by many researchers. Catalysis, optical, electric, and magnetic aspects; diagnostics; biological probes; and display devices are among the applications for metal nanoparticles [3]. The synthesis of metal and metal oxide nanoparticles is an existing field of material chemistry that has piqued interest due to applications in a wide range of fields, including air and water purification, medicine, antimicrobials, information technology, photocatalytic, antimicrobial, energy reservoirs, and biosensors [4]. Nanomaterial synthesis methods are divided into physical and chemical processes due to their enormous surface area. These procedures, however, are not ideal for medical and biological applications due to their environmental hazards. As a consequence, researchers are opting for a green synthesis method to synthesize nanomaterials although it is efficient, environmentally friendly, and cost effective [5, 6]. Green synthesis is an exciting material science approach [79]. Plants provide a better platform for nanoparticle manufacturing since they do not contain hazardous compounds and provide natural capping agents [10]. Numerous organic substances are widespread in nature extracts including amino acids, proteins, polysaccharides, alkaloids, flavonoids, and phenolic compounds [1113]. TiO2 has become extremely prevalent in a broad spectrum of applications [1424]. TiO2 is an excellent material for photocatalysis and biomaterial creation [25]. Titania’s biocompatibility makes it suitable for use in bone tissue engineering for bone regeneration and healing [26]. TiO2 is a powerful catalyst that may be used to remove a variety of contaminants from the environment and has been shown to clean water and surfaces [2634]. The Phyllanthus genus is one of the most prominent groupings of plants traded in India as a raw herbal medication [35]. The Phyllanthus genus, which belongs to the Euphorbiaceae family, contains over 1000 species that are found on tropical and subtropical continents like America, Africa, Australia, and Asia. The Phyllanthus genus is widely applicable in the human medical system [3539]. Phyllanthus niruri has been used in traditional medicine to treat lung and skin-related diseases. The presence of various biologically active substances serves an impeccable role in the reduction, capping, and stabilization processes. These plant compounds reduced the toxicity level during the production of nanophase materials. Moreover, the plant derivatives obtained various bioactive elements that can be used in antibacterial, antifungal, and diabetic-related applications [3947]. The bioreduction compounds of lignin, saponins, and flavonoids give the chemical-free zero-valent atom and provoke the stabilization process. In addition, these biocompounds increased microbial resistivity and are highly appreciable in liver-related diseases. The present work investigates the nanoproduction of TiO2 nanoparticles using Phyllanthus niruri leaf extract. The structural, optical, and morphological entities of the synthesized nanoparticles were investigated. In addition, the photocatalytic activity of the synthesized nanoparticles was observed from ultraviolet and visible light irradiation.

2. Experimental

2.1. Materials

The titanium tetra isopropoxide (TTIP) (Sigma-Aldrich, AR grade, percent) was used to synthesize the TiO2 nanoparticles. Fresh leaves of Phyllanthus niruri were collected from Tirunelveli, and their extract was used as a bioreductant. The methylene blue dye was purchased from HiMedia. There are no extra chemicals were used for the purification and synthesis process.

2.2. Green Synthesis of TiO2 NPs

The Phyllanthus niruri leaf extract and 0.1 M TTIP solutions were used in the green synthesis of TiO2 nanoparticles. 0.1 M TTIP solution was poured into 90 mL leaf extract under magnetic stirring. The stirring and biomolecules of the leaf extract have modified the color into white and produced precipitation. The white precipitation was centrifuged for 12000 rpm for 15 minutes two times. The obtained pellets were filtered with Whatman no. 1 filter paper and kept in an oven for 200°C at 3 hrs. Finally, the white TiO2 nanoparticles are characterized by various analyses. The formation of TiO2 is depicted in Scheme 1.

2.3. Characterization

The synthesized TiO2 nanoparticles were evaluated by structural, optical, and morphological analyses. The crystalline property of TiO2 nanoparticles was observed from the X-ray diffractometer (XRD) (PANalytical X-ray diffractometer, Cu-Kα, angle 10°–80° and 40 kV/15 mA). The optical property of TiO2 nanoparticles was captured from the UV Shimadzu 2700 UV-DRS spectrophotometer. The functional group and formed TiO2 nanoparticles were recorded from the FT-IR (PerkinElmer, 400–4000 cm–1, USA). The morphological entity was observed from scanning electron microscopy (HRSEM-SEM, Carl Zeiss, Germany) coupled with material identification energy-dispersive X-ray spectroscopy (EDX).

2.4. Photocatalytic Activity

The photocatalyst of TiO2 nanoparticles was performed against visible and UV light irradiation to determine the photocatalytic MB dye degradation. The light source is an important key factor to modify the rate of degradation to degrade the organic pollutants. The 10 ppm MB (100 mL) dye solution was inoculated with a 10 mg photocatalyst. After that, the combined solution was kept in dark condition to attain the adsorption-desorption equilibrium level. Finally, the mixed solution was placed in UV and visible light circumstances. The irradiated samples were withdrawn (5 mL) in a regular interval (30 minutes) to measure the degradation efficacy of TiO2 nanoparticles. The photocatalytic dye degradation efficacy was observed from the following equation: , where is the initial dye absorbance at , is the dye absorbance with light at , and is the time.

3. Results and Discussion

3.1. X-Ray Diffraction (XRD)

The X-ray diffraction pattern of the green synthesized TiO2 nanoparticles is shown in Figure 1. The structural, crystallite size and material phases were identified from X-ray diffraction. The obtained peaks are 25.27° (1 0 1), 37.86° (0 0 4), 48.23° (2 0 0), 54.31° (1 0 5), 55.09° (2 1 1), 62.62° (1 1 8), and 75.21° (2 1 5) compared with those of the standard JCPDS card no. 78-2486 [48, 49]. The anatase phase of TiO2 nanoparticles exhibits enhanced catalytic activity than the rutile and brookite phases. The photocatalyst TiO2 nanoparticle crystallite size was calculated from the Debye Scherrer formula, and their calculated value is 23 nm in (1 0 1) plane at a high-intensity peak. The lowest crystallite size demonstrates the large surface area and outstanding photocatalytic activity of the synthesized materials.

3.2. FTIR Analysis

The plant active functional groups of the TiO2 nanoparticles were analyzed by FTIR spectrum and displayed in Figure 2. The broad peak at 4000–3500 cm−1 specifically at 3420 cm−1 belongs to hydroxyl groups of O–H stretching vibration [50]. The band at 2923 cm−1 is attributed to C-H vibrations. The C-H vibrations are restricting the phase changes and promote the organic precipitation in synthesis time. Another prominent peak of TiO2 nanoparticles is located at 1627 cm−1, which can be ascribed to C=C which came from plant carbon molecules. The carbon molecules are associated with hydrogen and oxygen from the source materials. The carbon association produces the −C-O stretching and −C-H bending to the source precursors [5053]. These compounds come from the plant extract biomolecules which can control the growth of the particles and reduction/stabilization activity. The peak at 720 cm−1 is attributed to the Ti-O stretching bands. The stretching modes of Ti-O-Ti all are observed at 500–700 cm−1 [54]. The plant bioderivatives produce the nonvalent atoms through the flavonoids, saponins, and lignin. These plant derivatives are responsible for metal and oxygen bond formation. The formed metal and oxygen elements were stabilized from plant derivatives.

3.3. UV-DRS Analysis

The optical properties of the TiO2 nanoparticles were performed from the UV-DRS technique. The DRS spectrum is shown in Figure 3(a) which can indicate the optical reliability of the TiO2 nanoparticles in the UV region at 390 nm. The optical transformations and their defects were determined the bandgap of the materials. There is no adsorption edge involved in the visible region which can denote the highest photonic energy. The optical bandgap values are calculated from Tauc eqn. The calculated bandgap value shows the relationship between the incident photon energy of semiconductors and absorption coefficient: , where is the absorption coefficient, is the frequency, is the Bandgap, and is the 1/2 direct bandgap semiconductor. The obtained band gap is 3.16 eV. The wide bandgap of TiO2 nanoparticles exhibited the charge carrier formation and liberation in the photocatalytic activity [55, 56].

3.4. FESEM with EDX

Figure 4 shows the surface morphological and elemental analysis of green synthesized TiO2 nanoparticles. FESEM images represent the spherical morphology with even distribution on the surface. The formed spherical shape and their smaller size particles accelerate the free radical formation. The existing plant biomolecules occupied the surface which gives the agglomerations and large grain size particles. The existing plant molecules derived the irregular distribution of the TiO2 nanoparticles. The spherical shape is a more benefit able shape in catalytic activity than other shapes due to their large surface area [5760]. The EDX spectrum displays the Ti and O element existence over the surface. The remaining small peaks exhibit the plant molecules which was well explained in FTIR analysis. The elemental percentages were displayed in Figure 4(d). The Ti elements occupied the major places in synthesized TiO2 nanoparticles. The FE-SEM morphology images showed the spherical and semispherical shapes of the TiO2 nanoparticles. The spherical shape occupied the major area of the TiO2 nanoparticles which are attached to it shown as larger grain size particles due to their plant derivatives. The excessive plant compounds construct the layer over the TiO2 surface and merged the two particles. Therefore, it shows semispherical and spherical shapes. The distribution of the TiO2 nanoparticles was calculated from ImageJ software, and their values are displayed in Figure 5.

3.5. Photocatalytic Activity

The green synthesized TiO2 nanoparticles against methylene blue dye under different light sources are shown in Figures 6(a) and 6(b). The visible light irradiation slowly increased the degradation rate due to the reactive sites of the catalyst. Above 60 minutes of visible light irradiation exhibits the higher degradation because of their OH radicals which provokes the oxidation of the dye molecules [61, 62]. The plant biomolecules sustained the electron-hole pair recombination which derived strong oxidation and reduction of dye molecules over the catalyst. This process takes 60 minutes to 90 minutes with the migration of electrons and holes of the concern bands. The ultraviolet irradiation exhibits the vigorous degradation than visible light irradiation due to their OH radicals [1623]. The ultraviolet light provokes the electron mobilization and evoked the electron-hole pair which promotes better degradation efficiency. The 30-minute ultraviolet light irradiation of TiO2 nanoparticles exhibited above 80% degradation. The ultraviolet irradiation (98.2%) of TiO2 nanoparticles showed enhanced degradation efficiency than visible light irradiation (94.42%) (Figure 7(a)). The photocatalyst efficiency was calculated from the spectrum (Figure 7(b)) The degradation efficiency is dependent on a light source, catalyst dosage, pH, and dye concentration [63]. TiO2 nanoparticles are extensively used in photocatalytic activity due to their wide bandgap and e-h pair restriction property. The anatase TiO2 nanoparticles exhibited a wide bandgap (3.16 eV) and lower crystallite size and large surface area which was ensured by DRS, XRD, and FESEM analyses, respectively. The degradation rate of the catalyst was constructed from pseudo-first-order kinetics (Figure 7(c)). The kinetic equation is as follows: −, where is the light irradiated dye absorbance at time , is the initial dye absorbance at time , and is the activity time of degradation. The obtained pseudo-first-order kinetics delivered the ultraviolet irradiation potential which is more effective than visible light irradiation. The present work is compared with earlier published work of TiO2 nanoparticles. The comparison of TiO2 nanoparticle photocatalytic activity is tabulated in Table 1. The pure and doped TiO2 photocatalytic degradation work is reported. The degradation is based on the light source, size, dopants, and surface area. The table denotes the catalytic activity of TiO2 nanoparticles in various doping, light sources, and time. The visible light irradiation degradation is low compared to ultraviolet irradiation but the addition of metal compounds increased the catalytic efficiency. Free radicals production increased the oxidation ability of dye molecules. The radical formations are evoked in visible light irradiation [6467]. The present visible light irradiation catalytic activity produced the superoxides and radicals which exhibited a better photocatalytic dye degradation activity than previously reported works. Therefore, the present work focused on visible and ultraviolet light irradiation and demonstrates that biogenic TiO2 nanoparticles prove heightened degradation ability against the MB dye.

The photocatalyst mechanism of the TiO2 nanoparticles is shown in Figure 8. The mechanism of TiO2 nanoparticle-excited electrons traveled from the valence band to the conduction band during the illumination. The modified electrons and holes get a reduction and oxidation property. The generated charge carriers produce free radicals and superoxides. These compounds dissociated the dye molecules to noxious compounds [61, 62, 68, 69]. The UV light irradiation inhibits the e-h pair very strappingly and produces an enormous amount of free radicals than visible light irradiation. The detailed mechanism is as follows:

Based on the results, specify that the green synthesized TiO2 nanoparticles have upgraded catalytic activity and enhanced dye adsorption behavior in ultraviolet light irradiation. Hence, the green synthesized TiO2 nanoparticles detached the dye molecules from the aquatic surface and more powerful degradation in the ultraviolet region.

4. Conclusion

The current work reported the green production of nanoparticles from Phyllanthus niruri leaf extract. The plant extract using nanoparticles is an eco-friendly and noxious-free reduction to synthesize the nanophase materials. The photocatalyst of the TiO2 structural tetragonal pattern was confirmed by XRD, and their size 23 nm was calculated using the Debye Scherrer equation. The plant derivatives and their reduction/stabilization involved biomolecules, and their functional groups were identified from FTIR spectroscopy. The optical measurement and their wide bandgap values were evident by DRS analysis. The spherical surface and elemental investigation were obtained from FESEM with EDX. The photocatalyst of TiO2 nanoparticles was performed in ultraviolet and visible light irradiation against MB dye. The results exposed that ultraviolet irradiation of TiO2 nanoparticles exhibited better catalytic activity than visible light photocatalytic activity. Therefore, constructed on the results of the current study, we recommended that the green synthesized TiO2 nanoparticles are a more active and high possible catalyst in wastewater removal treatment.

Data Availability

All research data used to assist the findings of this work are included within the manuscript.

Conflicts of Interest

The authors have no conflict of interests.


The authors are grateful to the researchers supporting project no. (RSP-2021/326), King Saud University, Riyadh, Saudi Arabia.