One-Pot Synthesis of Ru-Doped ZnO Oxides for Photodegradation of 4-Chlorophenol

Manríquez, Maria E.; Noreña, Luis Enrique; Wang, Jin An; Chen, Lifang; Salmones, Jose; González-García, Julio; Reza, Carmen; Tzompantzi, Francisco; Hernández Cortez, José G.; Ye, Liqun; Xie, Haiquan

doi:https://doi.org/10.1155/2018/7605306

International Journal of Photoenergy

On this page

Abstract Introduction Experimental Results and Discussion Conclusions Data Availability Conflicts of Interest Acknowledgments References Copyright Related Articles

Research Article | Open Access

Volume 2018 | Article ID 7605306 | https://doi.org/10.1155/2018/7605306

One-Pot Synthesis of Ru-Doped ZnO Oxides for Photodegradation of 4-Chlorophenol

Maria E. Manríquez,¹Luis Enrique Noreña,²Jin An Wang,¹Lifang Chen,¹Jose Salmones,¹Julio González-García,¹Carmen Reza,¹Francisco Tzompantzi,³José G. Hernández Cortez,⁴Liqun Ye,⁵and Haiquan Xie⁵

Academic Editor: Ilya I. Tumkin

Received17 Feb 2018

Revised20 Jun 2018

Accepted19 Jul 2018

Published29 Oct 2018

Abstract

The photocatalytic degradation of 4-chlorophenol in water using Ru-doped ZnO mixed oxides (0, 0.5, 1, and 3 wt% RuO₂) synthesized by the one-pot homogeneous coprecipitation method is reported. ZnO with wurtzite structure was present in the mixed oxide as corroborated by Raman spectroscopy and X-ray diffraction analysis. All the samples showed nanorod morphological features. The presence of Ru⁶⁺/Ru⁴⁺ couples on ZnO modified the band gap of the mixed oxides and led to a shift of the band gap energy from 3.20 eV to 3.07 eV. Ru addition increased the surface area and significantly promoted the formation of active surface oxygen species such as hydroradicals evidenced by the fluorescence spectroscopy measurement. In the photodegradation of 4-chlorophenol solution under UV irradiation, a notable increase in photoactivity was obtained as the amount of RuO₂ in the mixed oxides increased to 3 wt%. The charge transfer between Ru⁶⁺/Ru⁴⁺ couples and ZnO nanoparticles together with the formation of free radical oxidant species effectively inhibits electron-hole recombination rate, thus favoring the photodegradation of 4-chlorophenol.

1. Introduction

Although most water effluents are effectively treated by traditional biological and/or physicochemical methods, the presence of chlorinated compounds represents an increasing problem, since these compounds, for example, chlorinated phenol derivatives, are often mutagenic or carcinogenic. 4-Chlorophenol is one of the most dangerous substances as far as toxicity is concerned. Therefore, it is highly necessary to develop more effective processes for the destruction of such contaminants. Actually, the expanding demand for efficient and economical techniques for wastewater treatment is the origin of a wide spectrum of investigations and technological innovation [1–5]. Some new technologies such as the advanced oxidation process (AOP) have been applied for the elimination of organic compounds in water systems. In AOPs, the oxidation of organic compounds by the very reactive free radicals takes place on the surface of heterogeneous catalysts which has been proven to be of interest due to the efficient degradation of recalcitrant organic compounds in water [6–8].

Developed in the 1970s, photocatalytic oxidation has attracted considerable attention, and in recent years, numerous studies have been carried out on the applications of photocatalytic oxidation in the presence of a semiconductor oxide [9–13]. As a good candidate of photocatalyst, ZnO has a band gap energy () of 3.37 eV, which corresponds to light absorption in the UV region [14]; this value indicates that its photocatalytic properties are almost comparable with TiO₂. Li et al. reported that the total photodegradation of chlorophenol and dichlorobenzene can be realized by using ZnO nanoparticles [15]. On the other hand, RuO₂ has been studied as a photocatalyst showing strong oxidation properties [16]. The catalytic role in the N₂O decomposition over the Ru-doped FAU zeolite was also investigated [17]. Zhuiykova et al. reported that the electrocatalytic activity of ZnO-RuO₂ catalysts appears to be governed by the redox behavior of the active surface sites [18].

In the present work, we report the one-pot homogeneous coprecipitation method for the synthesis of a set of Ru-doped ZnO oxides with different Ru contents (0.5, 1, and 3 wt% of RuO₂). These catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron, and UV-Vis spectroscopic techniques. The textural properties including the surface area and pore volume were determined by the N₂ adsorption-desorption isotherms method. The crystalline structure of the samples was refined by the Rietveld refinement method, and the surface chemical composition was analyzed by the electron dispersive spectroscopic (EDS) technique. The formation of the surface ^•OH radicals was monitored by using fluorescence emission spectroscopy. The photocatalytic performance of the RuO_x-ZnO catalysts with various RuO₂ contents for the degradation of 4-chlorophenol was investigated, and the surface photoreaction mechanism was discussed.

2. Experimental

2.1. Sample Preparation

The RuO_x-ZnO semiconductors were synthesized by the one-pot homogeneous coprecipitation method as follows: appropriate amounts of Zn(CH₃COO)₂ (Baker, 99.99%) and RuCl₃·3H₂O (Aldrich, 99.9%) solutions were mixed at a pH of ~8.5 adjusted with an ammonia solution. The amount of RuCl₃·3H₂O was calculated in order to obtain final solids with 0, 0.5, 1.0, and 3.0 wt% of RuO₂. Afterwards, the mixture containing both metallic precursors was heated at 80°C under constant stirring for 2 h. The resultant precipitate was collected by filtration and washed with deionized water until a neutral pH in the effluent was reached, and finally, the wet solid was dried at 100°C in air for 6 h and calcined at 400°C in a muffle furnace for 12 h. These solids will be hereinafter referred to as wt% RuO₂-ZnO, where , 0.5, 1, and 3.

2.2. Characterization

X-ray diffraction (XRD) patterns of the RuO₂-ZnO solids were obtained by an Empyrean multipurpose research X-ray diffractometer (PANalytical) with a Cu-Kα radiation (1.5418 Å) source. Diffraction intensity was measured between 4° and 70° with a 2θ step of 0.02°. The crystalline structures of the catalysts were refined using the Rietveld method. The JAVA-based software named Materials Analysis Using Diffraction (MAUD) was employed for refining each XRD pattern [19]. The atomic fraction coordinates for ZnO are reported in Table 1.

The textural properties of the samples were obtained by nitrogen adsorption-desorption isotherms at −196°C in a Quantachrome Autosorb-1C instrument. The surface area was calculated by the Brunauer–Emmett–Teller (BET) equation. All samples were degassed at 300°C for 6 h before N₂ adsorption.

Raman spectra were recorded at room temperature on previously calcined samples using an ISA Labram micro-Raman apparatus. The excitation line of a He-Ne laser was 632 nm. To avoid thermal effects, the laser power on the samples was kept at ~1 nW.

X-ray photoelectron spectroscopy (XPS) was used to analyze the surface metal oxidation state of the samples. The XPS spectra were acquired with a THERMO Scientific K-Alpha spectrometer, equipped with a hemispherical electron analyzer and Al Kα X-ray source (1486.6 eV).

Scanning electron microscopy analysis (SEM) was carried out on a Quanta 3D FEG microscope. The microscope has detectors for surface chemical analysis by X-ray energy dispersive spectroscopy (EDS).

The band gap energy () of the catalysts was measured using a Cary 100 spectrophotometer with an integration sphere, and MgO was used as 100% reflectance patron. The band gap energy values were determined using the Kubelka-Munk function by the method.

Fluorescence emission spectra of 2-hydroxyterephthalic acid were measured on a SCINCO fluorescence spectrometer FS-2. The ^•OH radicals generated by the semiconductor material in the absence of 4-chlorophenol were measured with the following procedure: terephthalic acid (TA) (5 × 10–4 M) was dissolved in a water/NaOH solution (2 × 10⁻³ M). Then 200 mg of the photocatalysts was added and the suspension was stirred for 60 min under dark conditions. Afterwards, it was irradiated by a UV light Pen-Ray lamp with a wavelength of 254 nm (0 = 4.4 mW cm⁻²), during 60 min, and aliquots were taken each 5 min. The fluorescence emission spectra of the irradiated solution were analyzed by PL (excited at 320 nm).

2.3. Photocatalytic Activity

The photocatalytic degradation of 4-chlorophenol in water was performed at room temperature (~25°C) using a solution of 4-chlorophenol in water (80 ppm) employing a Pyrex reactor (500 mL). 200 mg of the catalyst with particle size 60–80 meshes was used for the photodegradation reaction. The mixture was under stirring and bubbling with air (1 mL/s) generated by a magnetic stirring and electric pump at room temperature (approximately 30°C). The mixture prepared was exposed to UV radiation for 6 h. The irradiation source was a UV Pen-Ray lamp ( nm and intensity = 4400 μW/cm²), protected with a quartz tube whose outer and inner diameters were 0.5 and 0.35 in nm, respectively. The 4-chlorophenol photooxidation reaction procedure was monitored via following the variation of the characteristic absorption band at 221 nm using the UV-Vis spectrophotometer (Varian Cary 100 UV-Vis). The 4-chlorophenol concentration was monitored by taking aliquots of 3 mL every 15 min of reaction. The aliquots were filtered with a 0.45 μm nylon filter to eliminate any suspended solids.

3. Results and Discussion

3.1. Crystalline Structure and Rietveld Refinements

The XRD patterns of the samples calcined at 400°C are shown in Figure 1. All the diffraction peaks can be indexed to the hexagonal Wurtzite structure of ZnO (JCPDS card 36-1451) [20, 21]. XRD peaks corresponding to RuO₂ and changes in the crystalline structure of ZnO are not observed; thus, it can be assumed that the ruthenium oxide like RuO₂ is not detectable since its quantity is very small; perhaps, it is dispersed uniformly on the surface of ZnO with a crystallite size smaller than 4 nm.

The crystalline structures of the solids were refined with the Rietveld refinement technique. A plot of the Rietveld refinement for the 3 wt% RuO₂-ZnO catalyst is shown in Figure 2. The crystallite size, lattice cell parameters, and are reported in Table 2. The crystallite sizes determined by Scherrer’s equation and obtained by the Rietveld refinement were 60.6, 75.9, 69.5, and 61.8 nm for the 0RuO₂-ZnO, 0.5RuO₂-ZnO, 1RuO₂-ZnO, and 3RuO₂-ZnO samples, respectively. It seems that Ru addition led to a slightly greater ZnO crystallite size, even if this effect becomes weak for the higher Ru content sample. Ru doping probably promotes the formation of surface hydroxyls which may gain linkage degree with the hydroxide units during the synthesis, leading to a slight enlargement of the crystallite size. The lattice cell parameters of ZnO with a hexagonal wurtzite structure varied: from 3.2903 to 3.4098 Å and from 5.2219 to 5.4039 Å, depending on the Ru content.

3.2. Raman Spectroscopy

The Raman spectra of the samples were obtained in the wavelength interval 300–550 cm⁻¹, and they are shown in Figure 3(a). The Raman bands at 330, 380, and 437 cm⁻¹ are assigned to ZnO with a wurtzite (hexagonal) structure belonging to the P63mc space group. The dominant and sharp peak at 332 cm⁻¹ is due to the second-order Raman spectrum, and the peak labeled as at 437 cm⁻¹ is known as the Raman active phonon mode, which is a characteristic of the Wurtzite hexagonal phase of ZnO.

(a)

(b)

In Figure 3(b), the Raman modes of , , and at 528, 646, and 716 cm⁻¹, respectively, are shown, corresponding to RuO₂ in 1RuO₂-ZnO and 3RuO₂-ZnO samples. The intensity of Raman peaks increases with the increasing of the RuO₂ content [22, 23]. Although Ru oxides were not detectable by XRD analysis, Ru-O bonds are clearly present in the surface of the catalysts. Therefore, the Raman spectroscopy is more sensitive for identifying the surface Ru-O bonds.

3.3. XPS Characterization

The chemical oxidation states of Ru and Zn in the Ru-doped ZnO samples were analyzed by the XPS technique. The Ru 3d core levels in the XPS spectra of all samples are presented in Figure 4. By deconvoluting with software (XPS PEAK 4.1), two doublets in XPS spectra were determined: the peaks at 280.9 and 285.0 eV are assigned to Ru 3d 5/2 and Ru 3d 3/2, respectively, indicating that Ru is in the oxidation state Ru⁴⁺ (RuO₂) [24]. The other two small peaks at 282.5 and 286.3 eV correspond to Ru⁶⁺ (ReO₃). The intensity of these peaks increases with increasing content of RuO₂.

(a)

(b)

(c)

The XPS spectra of Zn 2p core levels are shown in Figure 5, and they exhibited two symmetric peaks centered at 1022.0 and 1044.7 eV, which are attributed to Zn 2p 3/2 and Zn 2p 1/2, respectively, indicating the Zn²⁺ oxidation state [25].

Figure 6 shows the asymmetric O1s spectra on the surface of 0RuO₂-ZnO, 0.5RuO₂-ZnO, 1RuO₂-ZnO, and 3RuO₂-ZnO samples. For the pure ZnO sample, the O1s signal was deconvoluted into two peaks at 530.6 eV and 532.6 eV, corresponding to the lattice O²⁻ in the Zn-O bond and surface oxygen in hydroxyls (OH) [26]. For the other three Ru-doped samples, four peaks at approximately 529.0, 530.3, 530.6, and 532.6 eV were observed. These are assigned to lattice oxygen in RuO₂ (529.0 eV, Ru⁴⁺-O) and RuO₃ (530.3 eV, Ru⁶⁺-O), lattice oxygen in ZnO (530.6 eV, Zn-O), and surface oxygen in the hydroxyl group (532.6 eV, O-H) in the RuO₂ and ZnO solids, respectively [27]. The XPS analyses confirm that different kinds of oxygen species exist on the surface of the RuO₂-ZnO solids and Ru ions have two oxidation states: Ru⁴⁺ (major) and Ru⁶⁺ (minor).

(a)

(b)

(c)

(d)

The surface atomic concentrations were obtained from the XPS quantitative analysis and are reported in Table 3. The surface Ru/Zn atomic ratio increases from 0.081 to 0.093 and 0.207 as the RuO₂ nominal content increases from 0.5 wt% to 1 and 3 wt%. The O/(Zn + Ru) atomic ratio varies from 1.12 for 0.5RuZnO to 1.40 for 1RuZnO and 2.84 for 3RuZnO. Therefore, the surface oxygen concentration clearly gains as the Ru content increases. Ru doping led to oxygen species rich in the surface of the RuO₂-ZnO solids.

3.4. SEM Observation and EDS Analysis

Figure 7 shows the SEM images and the selective EDS spectra for ZnO and RuO₂-ZnO solids. For the pure ZnO, nanorods with uniform size were obtained (Figure 7(a)). These nanorods did not present a preferential alignment but had a random distribution. The length of the rods varied from 300 to 500 nm. In the sample with 0.5 wt% of RuO₂ (Figure 7(c)), the morphology is slightly modified as the nanorods become thinner and shorter. When the RuO₂ content increases to 1 wt% (Figure 7(e)), the length of nanorods ranges between 100 and 500 nm in length. Finally, with a greater amount of RuO₂ (Figure 7(g)), the morphology was more homogeneous and the nanorods had a length of approximately 100 nm. So doping with a proper amount of Ru may lead to the formation of short and homogeneous ZnO nanorods.

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(h)

The surface elemental composition analysis of each sample was performed by the EDS technique. Signals belonging to Zn, Ru, C, and O elements are observed (see Figures 7(b), 7(d), 7(f), and 7(h)). Figure 7(b) only shows the signals of Zn and O with carbon traces. Carbon was probably formed from the acetate precursor used in the ZnO synthesis. Figures 7(d), 7(f), and 7(h) show the chemical composition of the xRuO₂-ZnO. A small peak for Ru appears which increases in intensity as the content of RuO₂ increases. It is also noted that as the RuO₂ content increases, the peak corresponding to oxygen increases in agreement with the results of XPS analysis. The increment of the surface oxygen content is important as the oxygen species usually take part in the oxidation reactions.

3.5. Textural Properties

The textural properties of the RuO₂-ZnO samples are reported in Table 4. The surface area of the samples with different RuO₂ loadings varies in the range of 11~38 m²/g. When the RuO₂ content is greater, the specific surface area is bigger. The 3 wt% RuO₂-ZnO sample shows the biggest specific surface area, three times greater than that obtained for pure ZnO. According to the above results, we can assume that the variations on the BET surface area are due to the changes of the structure resulted from the modification of RuO₂ doping.

3.6. Band-Gap Energy Measurement

Figure 8 shows the plots of the Kubelka-Munk function () against the absorbed light energy (). The optical band gap energies () of each sample can be estimated by extrapolating the slope to cut the abscissa axis [28–30]. The presence of RuO₂ (0.5, 1, and 3 wt %) produces to a red-shift of the absorption band towards the visible region. The band gap energy for pure ZnO was approximately 3.20 eV, which is close to report in the literature [31, 32]. Several previous investigations suggest that the visible emission is due to the surface defects and oxygen vacancies in the crystalline structure of the ZnO nanomaterials [33, 34]. These RuO₂-ZnO catalysts show a continuous absorption in the visible range and the absorption is stronger when the RuO₂ content is greater. The estimated band gap energies decrease from 3.20 eV for pure ZnO to 3.07 eV for 3 wt% RuO₂-ZnO. The data obtained from Figure 8 are reported in Table 4.

3.7. Photocatalytic Activity Test

To investigate the photocatalytic activity, the RuO₂-ZnO samples were evaluated in the photocatalytic degradation of 4-chlorophenol in aqueous solution. Figure 9 illustrates a set of UV-Vis absorption spectra of 4-chlorophenol molecule at different intervals of reaction time for the 3 wt% RuO₂-ZnO catalyst. The maximum absorption bands of 4-chlorophenol appear at 221 and 277 nm under UV irradiation. These absorption bands gradually decrease in intensity within 150 min, indicating that 4-chlorophenol was photodegradated.

The influence of the content of RuO₂ on the photodegradation efficiency (noted as C/C₀) of 4-chlorophenol is presented in Figure 10. The Ru-doped ZnO catalysts exhibit an increased photocatalytic activity compared to pure ZnO. After 225 min of reaction time, the photodegradation efficiency of 4-chlorophenol pollutant is about 46%, 61%, 70%, and 92% for 0RuO₂-ZnO, 0.5RuO₂-ZnO, 1RuO₂-ZnO, and 3RuO₂-ZnO, respectively.

3.8. Determination of ^•OH Radical Generation and Reaction Mechanism

In order to understand the mechanism of the photodegradation of 4-chlorophenol, it is important to obtain information about the formation of free radicals, especially the formation of ^•OH radicals, which have a high oxidative power and great capacity for degradation of organic contaminants in an aqueous medium. The ^•OH radicals can be monitored by the fluorescence spectrum resulting from the formation of 2-hydroxy terephthalic acid by the ^•OH radicals reacting with terephthalic acid when the solid was irradiated with ultraviolet light [35, 36]. The most active catalyst 3 wt%RuO₂ was measured by comparison with TiO₂-P25 in the absence of 4-chlorophenol. The photolysis performance was also obtained in the absence of any catalyst.

Figure 11(a) shows the fluorescence spectra obtained with the 3RuO₂-ZnO and TiO₂ P25 catalysts. The peak at 454 nm indicated the amount of produced 2-hydroxy terephthalic acid or the amount of ^•OH radicals produced. The peak intensity clearly increases as a function of irradiation time. Both 3RuO₂-ZnO and TiO₂ P25 show almost the linear relationship between the band intensity and the irradiation time, but 3RuO₂-ZnO exhibits a greater concentration of ^•OH radicals on the surface in comparison with TiO₂ P25 during the irradiation procedure. Without the catalyst, the photolysis produces a rather low concentration of hydroxyl terephthalic acid, indicating the low concentration of ^•OH radicals.

(a)

(b)

The reaction mechanism considered for heterogeneous photocatalysis usually consists of two steps: the fast adsorption of the reactants on the photocatalyst surface, followed by the slow surface reaction of the adsorbed reactants with photo-generated radicals (e.g., O₂⁻, ^•OH) to generate the photooxidized active species. In the presence of dissolved oxygen in aqueous solution and the surface hydroxyl radicals in the solid catalysts, oxygen species may exist in several forms such as O₂, ^•OH, , and O₂⁻, depending on the adsorption capability of the structure and temperature. The formation of surface oxygen species in the RuO₂-ZnO catalysts can be explained by the following reactions on the surface of the catalysts:

The surface of RuO₂-ZnO solids presents a high degree of surface hydroxylation. For instance, the catalyst with 3 wt%RuO₂ presents a high concentration of surface hydroxyl species as evidenced by the XPS spectra in Figure 6 and by the fluorescence spectroscopy in Figure 11, and therefore, it shows the highest concentration of surface active oxygen species and thus the best photoactivity. All catalysts with RuO₂ exhibit higher reaction rates than the pure ZnO. Perhaps, there is a synergistic interaction between RuO₂ and ZnO that favors the improvement of photocatalytic activity. It is assumed that a heterojunction structure was created in the interface of the ZnO and RuO₂ nanoparticles. Ru doping strongly affects the surface properties of semiconductors by generating a “barrier” in the ZnO which acts as an electron trap of the Ru metal in contact with the ZnO semiconductor surface. The electrons in the Ru conduction band (CB) transferred to the ZnO CB under the force of the electronic field of the heterojunction structure [37]. Thus, the surface of the ZnO was more negative and favors the formation of more hydroradicals. Therefore, Ru doping promotes the active surface oxygen formation via electron transfer. All these may inhibit the recombination rate of the electron-holes and benefit the photodegradation of 4-chlorophenol. A proposed reaction mechanism is illustrated in Scheme 1.

4. Conclusions

This work showed that Ru doping for ZnO reduced the band gap energy of ZnO solid, generated more surface active oxygen species such as hydroxyls, O₂²⁻, and O₂⁻, and increased the surface area by modification of the crystalline structure and morphological features. In the photodegradation of 4-chlorophenol solution, the RuO_x-ZnO catalysts could effectively photodegrade the 4-chlorophenol contaminant with a much faster reaction rate than the pure ZnO. This can be explained by rich active oxygen species and high concentration of free radicals on the surface of the Ru-doped catalyst that may inhibit the electron-hole recombination rate and promotes the Ru⁶⁺/Ru⁴⁺ ox-red cycles due to the electron transfer from the RuO_x (RuO₃ and RuO₂) nanoparticles to the Zn-O bond. These results show that the one-pot homogeneous coprecipitation synthesis reported herein is a simple but very effective method for obtaining RuO₂-ZnO nanocatalysts with high photocatalyic activity in the photodegradation of 4-chlorophenol.

Data Availability

The data used to support the findings of this study are available from the corresponding author upon request.

Conflicts of Interest

The authors declare herein that this article currently has no conflict of interests.

Acknowledgments

The authors are thankful to the financial support from projects SIP-20180199 and SIP-20181280 and the technical support from Centro de Nanociencias y Micro y Nanotecnologías del Instituto Politécnico Nacioonal. Jin An Wang thanks the Universidad Autónoma Metropolitana-Azcapotzalco for supporting his sabbatical year.

References

Y. Li, J. Niu, and L. Yin, “Photocatalytic degradation kinetics and mechanism of pentachlorophenol based on superoxide radicals,” Journal of Environmental Sciences, vol. 23, no. 11, pp. 1911–1918, 2011.
View at: Publisher Site | Google Scholar
J. Saien and S. Khezrianjoo, “Degradation of the fungicide carbendazim in aqueous solutions with UV/TiO₂ process: optimization, kinetics and toxicity studies,” Journal of Hazardous Materials, vol. 157, no. 2-3, pp. 269–276, 2008.
View at: Publisher Site | Google Scholar
B. Krishnakumar and M. Swaminathan, “Influence of operational parameters on photocatalytic degradation of a genotoxic azo dye Acid Violet 7 in aqueous ZnO suspensions,” Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, vol. 81, no. 1, pp. 739–744, 2011.
View at: Publisher Site | Google Scholar
K. Vasanth Kumar, K. Porkodi, and A. Selvaganapathi, “Constrain in solving Langmuir–Hinshelwood kinetic expression for the photocatalytic degradation of Auramine O aqueous solutions by ZnO catalyst,” Dyes and Pigments, vol. 75, no. 1, pp. 246–249, 2007.
View at: Publisher Site | Google Scholar
B. Ohtani, “Preparing articles on photocatalysis—beyond the illusions misconceptions and speculation,” Chemistry Letters, vol. 37, no. 3, pp. 216–229, 2008.
View at: Publisher Site | Google Scholar
N. Daneshvar, A. Aleboyeh, and A. R. Khataee, “The evaluation of electrical energy per order (EEo) for photooxidative decolorization of four textile dye solutions by the kinetic model,” Chemosphere, vol. 59, no. 6, pp. 761–767, 2005.
View at: Publisher Site | Google Scholar
M. Sleiman, D. Vildozo, C. Ferronato, and R. F. P. M. Moreira, “Photocatalytic degradation of azo dye Metanil Yellow: optimization and kinetic modeling using a chemometric approach,” Applied Catalysis B: Environmental, vol. 77, no. 1-2, pp. 1–11, 2007.
View at: Publisher Site | Google Scholar
Y. Dongju, Z. Lizhong, Z. Xiufeng, C. Han, and Z. Qian, “Iron-glutamate-silicotungstate ternary complex as highly active heterogeneous Fenton-like catalyst for 4-chlorophenol degradation,” Chinese Journal of Catalysis, vol. 36, no. 12, pp. 2203–2210, 2015.
View at: Publisher Site | Google Scholar
S. Valizadeh, M. H. Rasoulifard, and M. S. S. Dorraji, “Modified Fe₃O₄- hydroxyapatite nanocomposites as heterogeneous catalysts in three UV, Vis and Fenton like degradation systems,” Applied Surface Science, vol. 319, pp. 358–366, 2014.
View at: Publisher Site | Google Scholar
Z. J. Huang, P. X. Wu, B. N. Gong, Y. H. Lu, N. W. Zhu, and Z. X. Hu, “Preservation of Fe complexes into layered double hydroxides improves the efficiency and the chemical stability of Fe complexes used as heterogeneous photo-Fenton catalysts,” Applied Surface Science, vol. 286, pp. 371–378, 2013.
View at: Publisher Site | Google Scholar
Y. Huang, D. K. Sarkar, and X. Chen, “Superhydrophobic nanostructured ZnO thin films on aluminum alloy substrates by electrophoretic deposition process,” Applied Surface Science, vol. 327, pp. 327–334, 2015.
View at: Publisher Site | Google Scholar
S. Parra, J. Olivero, and C. Pulgarin, “Relationships between physicochemical properties and photoreactivity of four biorecalcitrant phenylurea herbicides in aqueous TiO₂ suspension,” Applied Catalysis B: Environmental, vol. 36, no. 1, pp. 75–85, 2002.
View at: Publisher Site | Google Scholar
T. Sauer, G. Cesconeto Neto, H. J. José, and R. F. P. M. Moreira, “Kinetics of photocatalytic degradation of reactive dyes in a TiO₂ slurry reactor,” Journal of Photochemistry and Photobiology A: Chemistry, vol. 149, no. 1-3, pp. 147–154, 2002.
View at: Publisher Site | Google Scholar
H. D. Mansilla, J. Villaseñor, G. Maturana, J. Baeza, J. Freer, and N. Durán, “Homogeneous and heterogeneous advanced oxidation of a bleaching effluent from the pulp and paper industry,” Water Science and Technology, vol. 35, no. 4, pp. 273–278, 1997.
View at: Publisher Site | Google Scholar
X. Li, J. W. Cubbage, and W. S. Jenks, “Photocatalytic degradation of 4-chlorophenol. 2. The 4-chlorocatechol pathway,” The Journal of Organic Chemistry, vol. 64, no. 23, pp. 8525–8536, 1999.
View at: Publisher Site | Google Scholar
L. Manĉiĉ, S. G. Sipka, V. M. Djinoviĉ, Z. Marinkoviĉ, T. Sabo, and O. Miloseviĉ, “Fine nanophased ZnO:Ru and ZnO:Pt powder synthesis through aerosols,” Materials Science Forum, vol. 494, pp. 149–154, 2005.
View at: Publisher Site | Google Scholar
D. Chen and A. K. Ray, “Photocatalytic kinetics of phenol and its derivatives over UV irradiated TiO₂,” Applied Catalysis B: Environmental, vol. 23, no. 2-3, pp. 143–157, 1999.
View at: Publisher Site | Google Scholar
S. Zhuiykova, E. Katsa, V. Plashnitsab, and N. Miurac, “Toward selective electrochemical “E-tongue”: potentiometric DO sensor based on sub-micron ZnO–RuO₂ sensing electrode,” Electrochimica Acta, vol. 56, no. 15, pp. 5435–5442, 2011.
View at: Publisher Site | Google Scholar
L. Lutterotti, “MAUD version 2.55,” May 2015, http://www.maud.radiographema.com.
View at: Google Scholar
L. Yuan-Chang, M. Y. Tsaib, H. Chiem-Lum, H. Chia-Yen, and C. S. Hwang, “Structural and optical properties of electrodeposited ZnO thin films on conductive RuO₂ oxides,” Journal of Alloys and Compounds, vol. 509, no. 8, pp. 3559–3565, 2011.
View at: Publisher Site | Google Scholar
S. Zhuiykov and E. Kats, “Electrochemical DO sensor based on sub-micron ZnO-doped RuO₂ sensing electrode: Influence of sintering temperature on sensing performance,” Sensors and Actuators B: Chemical, vol. 187, pp. 12–19, 2013.
View at: Publisher Site | Google Scholar
T. C. Damen, S. P. Porto, and B. Tell, “Raman effect in zinc oxide,” Physical Review, vol. 142, no. 2, pp. 570–574, 1966.
View at: Publisher Site | Google Scholar
C. K. Xu, G. D. Xu, Y. K. Liu, and G. H. Wang, “A simple and novel route for the preparation of ZnO nanorods,” Solid State Communications, vol. 122, no. 3-4, pp. 175–179, 2002.
View at: Publisher Site | Google Scholar
M. T. Uddin, Y. Nicolas, C. Olivier et al., “Preparation of RuO₂/TiO₂ mesoporous heterostructures and rationalization of their enhanced photocatalytic properties by band alignment investigations,” The Journal of Physical Chemistry C, vol. 117, no. 42, pp. 22098–22110, 2013.
View at: Publisher Site | Google Scholar
R. Al-Gaashania, S. Radimana, A. R. Dauda, N. Tabetc, and Y. Al-Dourid, “XPS and optical studies of different morphologies of ZnO nanostructures prepared by microwave methods,” Ceramics International, vol. 39, no. 3, pp. 2283–2292, 2013.
View at: Publisher Site | Google Scholar
K. Kotsis and S. Volker, “Ab initio calculations of the O1s XPS spectra of ZnO and Zn oxo compounds,” Physical Chemistry Chemical Physics, vol. 8, no. 13, pp. 1490–1498, 2006.
View at: Publisher Site | Google Scholar
K. S. Kim and N. Winograd, “X-ray photoelectron spectroscopic studies of ruthenium-oxygen surfaces,” Journal of Catalysis, vol. 35, no. 1, pp. 66–72, 1974.
View at: Publisher Site | Google Scholar
K. Vanheusden, C. H. Seager, W. L. Warren, D. R. Tallant, and J. A. Voigt, “Correlation between photoluminescence and oxygen vacancies in ZnO phosphors,” Applied Physics Letters, vol. 68, no. 3, pp. 403–405, 1996.
View at: Publisher Site | Google Scholar
H. J. Egelhaaf and D. Oelkrug, “Luminescence and nonradiative deactivation of excited states involving oxygen defect centers in polycrystalline ZnO,” Journal of Crystal Growth, vol. 161, no. 1-4, pp. 190–194, 1996.
View at: Publisher Site | Google Scholar
S. A. Studenikin and M. Cocivera, “Time-resolved luminescence and photoconductivity of polycrystalline ZnO films,” Journal of Applied Physics, vol. 91, no. 8, pp. 5060–5065, 2002.
View at: Publisher Site | Google Scholar
S. B. Zhang, S. H. Wei, and A. Zunger, “Intrinsic n-type versus p-type doping asymmetry and the defect physics of ZnO,” Physical Review B, vol. 63, no. 7, article 075205, 2001.
View at: Publisher Site | Google Scholar
Z. Wang, S. C. Su, M. Younas, F. C. C. Ling, W. Anwand, and A. Wagner, “The Zn-vacancy related green luminescence and donor–acceptor pair emission in ZnO grown by pulsed laser deposition,” RSC Advances, vol. 5, no. 17, pp. 12530–12535, 2015.
View at: Publisher Site | Google Scholar
F. D. Auret, S. A. Goodman, M. J. Legodi, W. E. Meyer, and D. C. Look, “Electrical characterization of vapor-phase-grown single-crystal ZnO,” Applied Physics Letters, vol. 80, no. 8, pp. 1340–1342, 2002.
View at: Publisher Site | Google Scholar
K. Ozoemena, N. Kuznetsova, and T. Nyokong, “Comparative photosensitised transformation of polychlorophenols with different sulphonated metallophthalocyanine complexes in aqueous medium,” Journal of Molecular Catalysis A: Chemical, vol. 176, no. 1-2, pp. 29–40, 2001.
View at: Publisher Site | Google Scholar
G. Mendoza-Damián, F. Tzompantzi, A. Mantilla, R. Pérez-Hernández, and A. Hernández-Gordillo, “Improved photocatalytic activity of SnO₂–ZnAl LDH prepared by one step Sn⁴⁺ incorporation,” Applied Clay Science, vol. 121-122, pp. 127–136, 2016.
View at: Publisher Site | Google Scholar
N. Milan-Segovia, Y. Wang, F. S. Cannon, R. C. Voigt, C. James, and J. C. Furness, “Comparison of hydroxyl radical generation for various advanced oxidation combinations as applied to foundries,” Ozone-Science & Engineering, vol. 29, no. 6, pp. 461–471, 2007.
View at: Publisher Site | Google Scholar
M. Tamez Uddin, Y. Nicolas, C. Olivier et al., “Improved photocatalytic activity in RuO₂–ZnO nanoparticulate heterostructures due to inhomogeneous space charge effects,” Physical Chemistry Chemical Physics, vol. 17, no. 7, pp. 5090–5102, 2015.
View at: Publisher Site | Google Scholar

Copyright

Copyright © 2018 Maria E. Manríquez 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.

PDF Download Citation

Download other formats

Order printed copies

Views

2319

Downloads

1026

Citations

International Journal of Photoenergy

One-Pot Synthesis of Ru-Doped ZnO Oxides for Photodegradation of 4-Chlorophenol

Abstract

1. Introduction

2. Experimental

2.1. Sample Preparation

2.2. Characterization

2.3. Photocatalytic Activity

3. Results and Discussion

3.1. Crystalline Structure and Rietveld Refinements

3.2. Raman Spectroscopy

3.3. XPS Characterization

3.4. SEM Observation and EDS Analysis

3.5. Textural Properties

3.6. Band-Gap Energy Measurement

3.7. Photocatalytic Activity Test

3.8. Determination of •OH Radical Generation and Reaction Mechanism

4. Conclusions

Data Availability

Conflicts of Interest

Acknowledgments

References

Copyright

3.8. Determination of ^•OH Radical Generation and Reaction Mechanism