Photodegradation Of 4-chlorophenol Research Articles

Fluidized bed reactor for 4-chlorophenol photodegradation via solar and visible radiation using ZnO/g-C3N4/carbon xerogel as a photocatalyst

This study investigates the feasibility of employing a fluidized bed reactor for the degradation of 4-chlorophenol (4CP), considering multiple operational parameters (type of radiation, fresh inlet flow rate and recycle flow rate). The selection of the ZnO/g-C3N4/carbon xerogel as photocatalyst, a choice motivated by the improved charge transfer and increased catalyst activity under visible radiation provided by the presence of carbon xerogel and g-C3N4, was previously determined through tests conducted in a jacketed batch reactor under visible radiation, in which the ternary material efficiency was compared to their constituting counterpart materials. The semiconductors constituting the unary, binary, and ternary materials were chosen based on considerations of availability, sustainability, and abundance in nature. The use of the proposed fluidized bed reactor brings advantages in scalability, distribution of irradiated light and overall costs when compared to commonly used batch reactors, whereas the investigation of the flow parameters involved in such process is of great importance to understand and optimize the efficiency of the pollutant degradation process. Regarding the ternary photocatalyst, X-ray diffractometry (XRD) revealed the presence of zinc oxide's hexagonal crystalline structure. Moreover, additional characterization using Raman spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive spectroscopy (EDS) confirmed the presence not only of ZnO but also of carbon xerogel and g-C3N4 in the composite. From the photodegradation experiments, it was determined that the optimal fresh inlet flow rate to achieve the best degradation, as well as the recycle flow rate for this purpose, were 0.07 and 25 L h−1, respectively. Mathematical simulations described that the model that best fits the system's behavior considers the specific reaction rate as dependent on the concentration of the catalyst in the medium.

Polar peripheral substituent-regulated organic/inorganic hybrid photocatalysts promoting the degradation of phenolic pollutants

Constructing surface hybrid inorganic semiconductor photocatalysts with π conjugated structure is considered as an efficient way to improve the photocatalytic performance. Herein, by using porphyrin as light harvester and electron donor, BiOI as electron acceptor and active center, novel inorganic/organic (porphyrin/BiOI) hybrid photocatalysts with improved performance were prepared using impregnation method in non-covalent way. To explore the effects of porphyrin peripheral substituents on the performance of hybrid photocatalysts, four porphyrin/BiOI hybrids with different polar groups (–COOH, –OH, –NH2, –NO2) on the porphyrin substituents were prepared and their performances in the photocatalytic degradation of four phenolic pollutants were evaluated. All porphyrin/BiOI hybrids showed greatly improved photocatalytic activities compared to BiOI, and TCPP/BiOI hybrid containing –COOH groups was the best one. Under visible light irradiation, TCPP/BiOI could realise 100% photodegradation of 4-chlorophenol (4-CP) within 60 min, whose apparent kinetic constant was about 9.4 times that of BiOI. Substantial experimental results and theoretical calculation suggest that the different photocatalytic performances of the porphyrin/BiOI hybrids containing different porphyrin peripheral groups (–NO2 < –NH2 < –OH <–COOH) are highly correlated with the orientation of the dipole moment and the polarity of porphyrin substituent. This work illustrates that fine-tuning of the sensitizer molecular structure is essential to improve the photocatalytic activity of organic molecule-sensitized semiconductors.

Promotion effect of Ga3+ in ZnAlGa-x mixed oxides obtained from their layered double hydroxides on the enhancement in the transient photocurrent response, the inhibition in the recombination rate of photogenerated (e−, h+) charges and the photocatalytic activity in the photodegradation of 4-chlorophenol

ZnAlGa-x (x = 0, 0.5, 0.8, 1.0, 2.0 and 3.0 mol % of Ga3+) mixed oxides (MOs) obtained by calcination of their corresponding layered double hydroxides (LDHs) were characterized and evaluated in the photodegradation of 4-chlorophenol in aqueous media (4-CP) using UV light irradiation. Structural studies by X-ray diffraction (XRD) of ZnAlGa-x MOs indicated that the incorporation of a small molar concentration of Ga3+ (0.5–0.8 mol %) within the ZnAl LDH structure changed the micro-crystalline structure to an amorphous structure. A small molar content of Ga3+ in the ZnAlGa3+ MOx promotes the formation of a high amount of structural oxygen vacancies as evidenced by Raman and EPR spectroscopy studies. Transient photocurrent response (TPC) and fluorescence spectroscopy experiments reveal that the incorporation of a small molar concentration of Ga3+ in the structure of ZnAl MO promotes the enhancement in the transient photocurrent response, the separation of photogenerated charges and the inhibition of the recombination rate of (e−, h+) pairs. Furthermore, ZnAlGa-x MOs with a small molar concentration of Ga3+ reduced their band gap energies below of 3.0 eV. ZnAl MO photodegradated 69.0 % of 4-CP after 4 h of reaction. However, the photoconversion % of 4-CP increased to 80–90 % at 3 h of reaction using ZnAlGa-x MOs with a small molar concentration of Ga3+. ZnAlGa-x with small Ga3+ concentration mineralized approximately 70–75 % of total disolved organic carbon at 3 h of reaction. The photocatalytic degradation reaction of 4-CP fitted well to a pseudo-first order kinetics of Langmuir-Hinshelwood-type. The kinetic parameters of ZnAlGa-x MOs confirmed that ZnAlGa-0.8 MO was the best photocatalyst to photodegradate 4-CP in aqueous media. The highest photocatalytic activity and efficacy of ZnAlGa-0.8 MO to mineralize 4-CP in aqueous medium may be due to its higher amount of oxygen vacancies contained in its structure promoting a better separation of charges and the inhibition of the recombination rate of photogenerated (e−, h+) charges.

Mesoporous bimetallic S-doped nanoparticles prepared via hydrothermal method for enhanced photodegradation of 4-chlorophenol

Magnesium oxides (MgO) have gained shown significant promise for a variety of applications, which can be modified by ions doping. In this study, bimetallic Ag-doped S–MgO nanoparticles were prepared by hydrothermal method and used for photocatalytic degradation of 4-chlorophenl (4-CP). EDX suggested the presence of no impurities, which mainly contained Mg, Ag, and S elements, suggesting that S and Ag were incorporated into the lattice of MgO as a result of successful doping. Estimated bandgap of Ag-doped S–MgO nanoparticles was 3.7 eV, lower than MgO (7.8 eV), but useful to improve optical characteristics and photocatalytic efficiency to degrade 4-CP up to a maximum of 99.60 ± 0.50%. The synergetic parameter during photocatalysis of 4-CP was 6.91, confirming the degradation of 4-CP. Quenching experiments proved the presence of hydroxyl radicals (•OH) and singlet dioxygen (1O2) that were critical in 4-CP degradation. The kinetics rate constant was increased by 24.8% from 0.086 ± 0.004 to 0.108 ± 0.005 min−1 by the addition of sulfate in the reaction medium. The work proposes a new synthetic method for preparing catalysts that are capable of producing in-situ •OH radicals and 1O2 to decompose the organic contaminants.

Promoting photocatalytic performance of TiO2 nanomaterials by structural and electronic modulation

Titanium dioxide (TiO2) possessing excellent visible light response and high separation efficiency of charges without sacrificing its redox ability predicts significant opportunities for an efficient solar energy conversion system. Herein, novel TiO2 nanomaterials with upward-shifted conduction bands and tunable crystal phases were prepared by a lysine doping method. Lysine-doped TiO2 (LDT) showed enhanced reduction potential, efficient charge separation, and improved visible-light absorption. As photocatalysts, LDTs exhibited boosting photocatalytic ability both in light-to-chemical conversion and in refractory pollutant degradation. They can convert visible light to chemical energy and store in nicotinamide adenine dinucleotide (NADH) independent of any electron mediator with a yield of ca. 90%, far beyond that of the undoped TiO2 (13%). As for the refractory pollutant removal, compared to the negligible effect over the undoped TiO2 and commercial titania P25, lysine doping in TiO2 performs as a reaction switch to enable the photodegradation of 4-chlorophenol (4-CP) to proceed. More than 80% of 4-CP was removed with a kinetic constant of 0.8801 h−1. This work presents a distinctive strategy to precisely control the structure of TiO2 nanomaterials and provides a fresh insight into the structural and electronic modulation to promote their photocatalytic performance.

Photodegradation of 2-chlorophenol over ZnO/KCC-1: Reaction optimization by response surface methodology

Removing 2-chlorophenol (2CP) from water is an imperative task due to its toxicity. Various methods have been introduced for 2CP removal, and photocatalytic degradation is one of the best alternative solutions due to its effectiveness and simple process. This study focused on the potential of ZnO/KCC-1 as an effective photocatalyst for 2CP elimination from aqueous solutions. ZnO/KCC-1 was prepared by impregnating a commercial ZnO precursor into the synthesized KCC-1. The Zn/KCC-1 was characterized using TEM, FESEM, XRD, FTIR, and PL. The TEM and FESEM analyses confirmed the catalyst’s fibrous structure with good ZnO dispersion. The XRD results demonstrated the amorphous silica structure with the presence of ZnO, while the FTIR analysis confirmed the formation of a strong Si-O-Zn bond. The PL analysis revealed a slower recombination rate of electrons and holes during the reaction, thus enhancing the degradation rate efficiently. The analysis via response surface methodology (RSM) over independent variables of initial concentration (X1), catalyst dosage (X2), and pH (X3) revealed that X2 was the most essential variable, while X1 was the least significant variable. The ideal parameter for 2CP degradation was achieved at X1 = 10 mg/L, X2 = 2 g/L, and X3 = 10 with photodegradation efficiency (Y) of 90.62 % (predicted) and 88.93 % (experimental). This research revealed that ZnO/KCC-1 had a great prospect for photocatalytic degradation of 2CP from an aqueous solution.

Cation doped approach for photodegradation of 4-chlorophenol by highly efficient solar active NiS photocatalyst: The case of Cu2+ doping

This study reports an efficient photodegradation of 4-chlorophenol using Cu2+ doped nickel sulfide (NiS) nanoparticles. Our study provides a facile method to synthesize Cu2+ doped NiS nanoparticles by partial polyol method and structurally validates the formation of single phased random-shaped particles. Cu2+ doping in NiS matrix results in a red shift of the absorption band edge, thus lowering the band gap from 3.62 to 2.98 eV and creating electron trapping centers that prevent electron-hole recombination. The presence of such electron trapping centers was attributed to oxygen vacancies which were justified from the appearance of g-signal in electron paramagnetic resonance analysis. Photodegradation study of 4-chlorophenol by Cu2+ doped NiS nanoparticles under ambient solar light showed significant improvement in degradation efficiency up to 90 % as compared to 19 % for undoped NiS nanoparticles. Furthermore, increased degradation efficiency was also backed by total organic carbon (TOC) analysis of the mineralization ability of Cu2+ doped NiS nanoparticles. Moreover, scavenging trapping analysis showed holes, ⋅OH and superoxide radicals as reactive oxidative species (ROS) primarily responsible for increased photodegradation efficiency. Thus, the synthesized Cu doped NiS nanoparticles proved to be an efficient catalyst, which could be used as a potential candidate for industrial photocatalytic applications under ambient solar light.

ZnS-doped TiO2 photocatalysts for 4-chlorophenol photodegradation in water

ZnS-doped TiO2 photocatalysts for 4-chlorophenol photodegradation in water

High photoactivity of ZrxOy-Bi2O2(CO3) composite materials prepared by one-step synthesis for efficient photodegradation of 4-chlorophenol in water

The ZrBi composite materials were prepared in a single step by the chemical co-precipitation method. Bi2O2(CO3) joined ZrxOy modifying the mole percentage from 5 to 11 mol %. ZrBi composites dried at 80 °C were characterized by: XRD, FTIR, DRS, SEM, N2 adsorption, HR-TEM, PL, XPS and EDS-SEM. Later they were evaluated in the photodegradation of 4-Chlorophenol under UV irradiation. The degradation and mineralization percentages were determined after 150 min of reaction by UV–vis spectroscopy and Total Organic Carbon (TOC), respectively. The composite containing 9 mol % of Bi2O2(CO3) (ZrBi-9) with a specific volume of 0.03 m3/kg in solution with specific catalyst density of 1*10−3 kg/L, showed the highest photoactivity with 96 % photodegradation, a higher value compared to that obtained with the reference material TiO2-P25 (72 %). Finally, a possible reaction mechanism was proposed based on recent studies, which allow to follow the formation of active species OH, O2− and h+. The formation of OH radicals was measured by fluorescence spectroscopy while the inhibition of O2− radicals as well as the scavenge of h+ were determined by UV–vis spectroscopy. The results showed that ZrBi composite materials do not promote OH radical formation. The scavenge of h+ showed a total loss of photoactivity and the inhibition of O2− in the reaction medium results in a partial decrease of photoactivity. The formation of heterojunctions, the presence of localized states and oxygen vacancies in the synthesized materials promise an excellent alternative for the rapid photodegradation of 4-Chlorophenol under UV radiation.

Fabrication of ZnAl-LDH mixed metal-oxide composites for photocatalytic degradation of 4-chlorophenol.

In this work, two different types of ZnAl-layered double hydroxide (LDH) mixed metal-oxide composites (CeO2 and SnO2) were synthesized and applied for the photodegradation of 4-chlorophenol (4-CP) in wastewater. The fabricated CeO2/ZnAl-LDH and SnO2/ZnAl-LDH were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, UV-visible diffuse reflectance spectroscopy (UV-vis DRS), and theoretical density functional theory (DFT) calculations, suggesting that the band gaps of the synthesized hybrid composites were much lower than those of traditional ZnAl-LDH. In addition, the photocatalytic activity for 4-CP degradation and reaction kinetics were investigated to evaluate the catalytic behavior of the prepared composites. The results indicated that the photocatalytic process in this case followed a pseudo-first-order kinetic model, and SnO2/ZnAl-LDH illustrated the optimum performance for 4-CP degradation with an efficiency of 95.2% due to its stability and recyclability. Additionally, the reaction mechanism of 4-CP photodegradation was studied over SnO2/ZnAl-LDH; it presented that 4-CP could be oxidized by hydroxyl radicals, holes, and superoxide radicals, where hydroxyl radicals were identified as the dominant active species during the degradation process. Finally, decomposition intermediates were measured to deduce the reaction pathway of 4-CP, and three tentative pathways were proposed and discussed.

Fabrication of three-dimensional hierarchical BiOBr/Bi2O4 p–n heterojunction with excellent visible light photodegradation performance for 4-chlorophenol

Construction of heterojunction and design of its architecture are effective strategies to improve the catalytic performance of photocatalyst. Herein, BiOBr/Bi2O4 p-n heterojunction was fabricated by a co-precipitation method, in which two-dimensional (2D) BiOBr nanosheets sheathed well on the surface of quasi-one-dimensional (1D) Bi2O4 submicrorods, forming a three-dimensional (3D) hierarchical structure. Such structural feature can not only enhance the utilization of incident photons through multi-reflection within the hierarchical structure but also raise the specific surface areas to supply more surface-active sites to participate in photocatalytic reaction. More importantly, BiOBr/Bi2O4 p-n junction could accelerate the interfacial electron-hole pairs transfer and separation via the built-in electric field, extending the lifetime of charge carriers. Thus, as-prepared BiOBr/Bi2O4 heterojunctions exhibit superior visible light catalytic activity for the photodegradation of 4-chlorophenol (4-CP). The catalytic activity of optimal junction is 2.03-fold as high as that of pristine Bi2O4. The trapping experiments demonstrate that hole (h+) and superoxide radical (•O2−) are the major active species during the catalytic photodegradation process of 4-CP. This work presents a unique tactic for the construction of high-performance Bi2O4-based heterojunction for the removal of organic pollutants.

Step-scheme BiVO4/WO3 heterojunction photocatalyst under visible LED light irradiation removing 4-chlorophenol in aqueous solutions

In the present study, photodegradation of 4-chlorophenol (4-CP) using a step-scheme BiVO4/WO3 heterostructure under visible LED light irradiation (Vis LED) from aqueous solutions was investigated. The photocatalyst was synthesized through the hydrothermal process and characterized physically and chemically via X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), energy-dispersive X-ray (EDX), and Brunnauer–Emmett–Teller (BET) techniques. The effects of the operational parameters i.e., solution pH, contact time, nanocomposite dosage, and initial 4-CP concentration were evaluated. Results indicated that BiVO4/WO3/Vis LED process has higher efficiency in 4-CP degradation than BiVO4/Vis LED, WO3/Vis LED, and BiVO4/WO3 systems. At BiVO4/WO3 concentration of 0.125 g/L, initial pH of 7, and initial 4-CP concentration of 25 mg/L, complete degradation of 4-CP (>97%) was achieved in reaction time of 60 min. The phenol, chlorobenzene, catechol, 4-chlorocatechol, 5-chloro-1,2,4-benzenetriol, hydroquinone, hydroxyhydroquinone, p-benzoquinone, o-benzoquinone, formic acid, acetic acid, and oxalic acid were identified as the major intermediates of 4-CP degradation. In optimal condition, 67.5% and 88.5% of TOC and COD removal rates were obtained in 120 min contact time, respectively. The degradation of 4-CP was pseudo-first-order kinetics. Through the use of tert-Butyl alcohol (TBA) and ethylenediamine tetraacetic acid (EDTA) as radical scavengers, hydroxyl radicals and holes were identified as the main active species in photocatalytic degradation. Also, a tentative pathway for 4-CP degradation using the Vis LED/BiVO4/WO3 process was proposed.

Efficient photodegradation of 4-chlorophenol under solar radiation using a new ZnO/ZnS/carbon xerogel composite as a photocatalyst

This paper explored the development of a new zinc oxide/zinc sulfide/carbon xerogel composite photocatalyst aiming at the efficient 4-chlorophenol photodegradation under solar light. X-ray diffractometry highlights that the crystalline structure of zinc sulfide depended on the presence of zinc oxide, changing from face-centered cubic in the pure ZnS to hexagonal (2 H) in the composite. Furthermore, the addition of carbon xerogel to the composite led to a reduction in the particle size and an increase in the specific surface area. Photocatalytic results show that the ternary composite (XC/ZnO-ZnS) displayed the best photocatalytic response for 4-chlorophenol degradation among the tested materials. Such photocatalytic improvement is probably related to the formation of heterojunctions between the semiconductors and the carbonaceous phase, as well as the enhanced morphological properties of the composite. The superiority of the XC/ZnO-ZnS was further corroborated in the chronoamperometry tests, as it presented the highest photocurrent generation.

Visible light driven exotic p (CuO) - n (TiO2) heterojunction for the photodegradation of 4-chlorophenol and antibacterial activity

The treatment of industrial waste and harmful bacteria is an important topic due to the release of toxins from the industrial pollutants that damage the water resources. These harmful sources frighten the life of every organism which was later developed as the carcinogenic and mutagenic agents. Therefore, the current study focuses on the breakdown or degradation of 4-chlorophenol and the antibacterial activity against Escherichia coli (E. coli). As a well-known catalyst, pure titanium-di-oxide (TiO2) had not shown the photocatalytic activity in the visible light region. Hence, band position of TiO2 need to be shifted to bring out the absorption in the visible light region. For this purpose, the n-type TiO2 nanocrystalline material's band gap got varied by adding different ratios of p-type CuO. The result had appeared in the formation of p (CuO) – n (TiO2) junction synthesized from sol-gel followed by chemical precipitation methods. The optical band gap value was determined by Kubelka-Munk (K-M) plot through UV–Vis diffusive reflectance spectroscopy (DRS). Further, the comprehensive mechanism and the results of photocatalytic and antibacterial activities were discussed in detail. These investigations are made for tuning the TiO2 catalyst towards improving or eliminating the existing various environmental damages.

Development of a new zinc oxide/tin oxide/carbon xerogel photocatalyst for visible light photodegradation of 4-chlorophenol

This paper reports the development of a new carbon xerogel/zinc oxide/tin oxide ternary photocatalyst and its application for the enhancement of photocatalytic response through the formation of heterojunctions composed of different phases. The results obtained from X-ray diffractometry showed that all the materials exhibited the hexagonal structure of zinc oxide. The application of infrared spectroscopy, energy dispersive spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses helped confirm the presence of tin oxide and carbon xerogel in the photocatalytic material developed in the study. All the materials evaluated in the study showed photocatalytic activity under both solar and visible radiations. Under visible light, the optimized ternary material displayed higher photoactivity for 4-chlorophenol degradation, with total degradation of 55% in 5 h. The results obtained from chronoamperometry tests showed that the ternary composite exhibited the highest photocurrent among the samples evaluated when the materials were subjected to solar radiation.

New insight into sequential of silica-zirconia precursors in stabilizing silica-doped tetragonal zirconia nanoparticles for enhanced photoactivity

Silica-doped tetragonal zirconia nanoparticles (SiO2-ZrO2) catalysts were synthesized with the addition of ZrO2 prior to SiO2 by the microwave-assisted method and compared with a different sequence of ZrO2 and SiO2 (ZrO2-SiO2). The catalysts were characterized by X-ray diffraction, nitrogen adsorption-desorption, transmission electron microscopy, Fourier-transform infrared, electron spin resonance, ultraviolet–visible diffuse reflectance spectroscopy and photoluminescence analyses. The catalyst phase was pure tetragonal ZrO2 (t-ZrO2) with nano in size (9–10 nm). The sequential of SiO2 and ZrO2 precursors significantly affected the catalyst framework and led to a different number of pore volume and defect sites, including oxygen vacancies (OV), metal defects site (MDS) and Si-O-Zr bonds, which altered their behaviour towards t-ZrO2 stabilization and applications. It was found that the synergistic effect between nanocrystals and the appropriate amount of defect sites influenced the stabilization of t-ZrO2. The catalytic activity towards photodegradation of 2-chlorophenol (2-CP) are in the following order: SiO2-ZrO2 (92%) > ZrO2-SiO2 (59%) > ZrO2 (50%) > SiO2 (20%). The highest photoactivity of SiO2-ZrO2 is due to the large pore volume, which offered good surface contact with light. Besides, the higher crystallinity, Si-O-Zr bonds, and OV and MDS also could contribute to the excellent performance in 2-CP degradation. The abovementioned properties provided good electron-hole pair mobility and electron trapping for enhanced photoactivity.

Facile synthesis of silver decorated reduced graphene oxide@zinc oxide as ternary nanocomposite: an efficient photocatalyst for the enhanced degradation of organic dye under UV–visible light

Ternary combination of metal and metal oxide with reduced graphene oxide could be a novel potential photocatalyst towards highly efficient degradation of organic dyes under solar radiation. Herein, the novel ternary nanocomposite of silver nanoparticles with reduced graphene oxide and zinc oxide nanorods (Ag-rGO@ZnONR) were synthesized via in situ homogeneous coating of silver nanoparticles (Ag NPs) onto pre-assembled thermally reduced graphene oxide (rGO) encapsulated ZnO nanorods (ZnONR). The nanocomposite showed excellent aptitude towards the photodegradation of 2-chlorophenol (2-CP) under solar light irradiation. The Ag-rGO@ZnONR nanocomposite showed excellent UV–visible light harvesting due to the engineered reduced bandgap, and the Schottky barrier at the metal–semiconductor interface is expected to promote charge separation as also revealed by the optical calculations. The production of superoxide anions $$^{ \cdot } {\text{O}}_{2}^{ - }$$ and hydroxyl radicals $$(^{ \cdot } {\text{OH}})$$ acting as substantial reducing and oxidizing agents and further π − π stacking interactions with the aromatic ring of 2-CP provided an ultimate foundation for its 100% degradation. The photocatalyst showed high reproducibility, and 94% efficiency was observed even after three cycles. XPS chemical state analysis of C1s, O1s, Zn2p, and Ag3d confirm the variation of C =C (sp2), C–O, O= C–OH, and localization of Ag nanoparticles with rGO by confiscating the oxygen-comprising functional moieties which may be the possible reason for the enhanced photodegradation.

Solar active Cu2+-ZnS Photocatalyst for efficient photodegradation of 4-chlorophenol: effective cation doping effect

Cu2+ doped ZnS nanoparticles (Cu/ZnS) were prepared through a modified chemical precipitation method. The nanoparticles were characterized using UV–vis, PL, XRD, XPS, N2 sorpometry and TEM techniques. The nanoparticles morphology was spherical in shape with a particle size of ∼11.8 nm and ∼13.4 nm for bare and Cu2+ doped ZnS, respectively. Upon doping Cu2+ (0–5 mol %) into ZnS, tuning of band gap from 3.93 to 2.72 eV along with a remarkable enhancement in surface area from 89.5–152.7 m2. g−1 were successfully achieved. Moreover, Cu2+ act as electron trapping centers, which hinder the recombination of the photogenerated electrons and holes as evidenced from the PL intensity behavior. The photocatalytic experiment by degrading 4-chlorophenol (4-CP) under natural solar radiation indicated that the photodegradation efficiency of Cu2+ doped ZnS nanoparticles increased to 91.2 % compared to 22 % for undoped ZnS nanoparticles. Total organic carbon (TOC) analysis was performed to assess the mineralization ability of the Cu2+ doped ZnS nanoparticles which gave 91.5 % TOC removal. For in-depth understanding of the reasons behind Cu2+ doped ZnS nanoparticles photoreactivity, the revealing of reactive oxidative species (ROS) was achieved through scavenging trapping experiments.

Development of Nb2O5-doped ZnO/Carbon xerogel photocatalyst for the photodegradation of 4-chlorophenol

This work evaluates the properties of a new Nb2O5-doped ZnO/carbon xerogel photocatalyst and its efficiency for the degradation of 4-chlorophenol under solar radiation. The development of this material is aimed at diminishing charge recombination during the photocatalytic process. The diffractograms obtained confirm the presence of the hexagonal zinc oxide structure in all samples, whereas the X-ray photoelectron spectroscopy confirms the presence of Nb2O5 on the structure of the ternary photocatalyst. The higher specific surface area of the Nb2O5-doped material, as well as the lower value of gap energy, can be ascribed to the presence of the newly incorporated metallic oxide into the structure of the materials, along with the carbon xerogel. The photocatalytic tests results show that the material with Nb2O5 in its composition exhibited superior efficiency in the degradation of 4-chlorophenol under simulated solar radiation, obtaining a much higher apparent reaction rate constant. Furthermore, the modification impacts the photocatalytic mechanism, which becomes greatly dependent on the hydroxyl radical.

Raw clay supported ZnO nanoparticles in photodegradation of 2-chlorophenol under direct solar radiations

Abstract Advanced oxidation process of the water organic contaminants is among the promising technologies for water purification. In this work, ZnO nanoparticles have been supported on natural clay particles. The prepared composite ZnO/Clay has been characterized by solid state electronic absorption spectra, X-ray diffraction and scanning electronic microscopy. It is used in photodegradation of aqueous 2-chlorophenole (2-CP) with direct solar radiation. As the catalyst surface charge and point of zero charge presumably influence adsorption uptake and photodegradation of the 2-CP molecules, these two properties have been studied here. For the composite, the optimal contaminant adsorption pH is 8.7, which is the optimal photodegradation value as well. The composite ZnO/Clay shows higher adsorption and photodegradation efficiency in 2-CP degradation compared to naked ZnO. This highlights the future practicality of using this composite catalyst under various natural conditions. Moreover, the ZnO/Clay can be easily recovered and reused for third cycle with no significant loss of efficiency. Complete mineralization of the 2-CP has been confirmed after enough time (2 h). This has been manifested by analysis for remaining organic materials inside the reaction mixture, using UV-visible spectra, high performance liquid chromatography and total organic carbon measurements.