Photocatalytic degradation of bisphenol A in the presence of C-doped ZnO: Effect of operational parameters and photodegradation mechanism

Novel furfural-complexed approach to synthesizing carbon-Doped ZnO with breakthrough photocatalytic efficacy

INTRODUCTION

The efficiency of zinc oxide (ZnO) nanoparticles for environmental decontamination is limited by their reliance on ultraviolet (UV) light and rapid charge carrier recombination. Carbon doping has been proposed to address these challenges by potentially enhancing visible light absorption and charge separation.

OBJECTIVES

This study aims to introduce a novel, single-step synthesis method for carbon-doped ZnO (C-Z) nanoparticles, leveraging the decomposition of zinc nitrate hexahydrate and furfural under a nitrogen atmosphere to improve photocatalytic activity under visible light.

METHODS

A series of C-Z variants (C-Z-1 to C-Z-5) and an undoped sample (ZnO-0) were synthesized. The influence of furfural on the synthesis process and doping mechanism was analyzed by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and UV-visible diffuse reflectance spectroscopy (DRS).

RESULTS

XPS confirmed the integration of carbon within the ZnO matrix, and XRD indicated increased lattice dimensions owing to doping. DRS revealed bandgap narrowing, suggesting enhanced charge separation. Among the variants, C-Z-3 significantly outperformed the others, showing a 12-fold increase in the photocatalytic degradation rate of Rhodamine B compared to undoped ZnO.

CONCLUSION

The developed single-step synthesis method for C-Z nanoparticles represents a major advancement in materials engineering for ecological applications. The enhanced photocatalytic activity under visible light, as demonstrated by C-Z-3, underscores the potential of these nanoparticles for environmental decontamination.

Fabrication of a highly efficient CuO/ZnCo2O4/CNTs ternary composite for photocatalytic degradation of hazardous pollutants

In the current study, CuO, ZnCo2O4, CuO/ZnCo2O4, and CuO/ZnCo2O4/CNTs photocatalysts were prepared to remove crystal violet (CV) and colorless pollutants (diclofenac sodium and phenol) from wastewater. Herein, sol-gel and co-precipitation methods were used to synthesize CuO and ZnCo2O4, respectively. The sonication method was used to synthesize CuO/ZnCo2O4 and a CNTs-based composite (CuO/ZnCo2O4/CNTs). From the UV-Vis spectra of CuO, ZnCo2O4, CuO/ZnCo2O4, and CuO/ZnCo2O4/CNTs, the optical band gap value was calculated to be 2.11, 2.18, 1.71 and 1.63 eV respectively. The photocatalytic results revealed that CuO/ZnCo2O4/CNTs exhibited higher degradation of 87.7% against CV dye, 82% against diclofenac sodium, and 72% against phenol as compared to other prepared photocatalysts. The OH˙ radical is identified as the active species in the photocatalytic process over CuO/ZnCo2O4/CNTs. The impact of several parameters, such as pH, concentration, and catalyst dosage, has also been investigated. The better activity of the CNTs-based composite was due to the synergic effect of both CuO/ZnCo2O4 nanocomposite and carbon nanotubes. Therefore, the synthesized CuO/ZnCo2O4/CNTs photocatalyst has the potential to degrade organic wastewater effluents effectively.

Vibrational, optical, and photocatalytic properties of ZnO/layered carbon nanocomposite synthesized by ball milling

ZnO/layered carbon nanocomposites with varied sizes of ZnO nanoparticles (NPs) were synthesized by mechanical milling of mixture of ZnO NPs and carbon NPs. The NP size of ZnO was controlled with average particle sizes about 19.33, 21.87, 24.21, and 27.89 nm by varying the concentrations of carbon NPs viz 0, 2, 5, and 10 weight percent, respectively, in the mixture. Presence of carbon with ZnO in the form of composite also resulted in the enhanced shift of the band gap of ZnO due to the optical transitions in the impurity states or presence of carbon as compared to the ZnO size change alone. Additionally, the enhancement of absorbance in the visible region with an increase in carbon content was observed. Such an increase in absorbance can enhance the photocatalytic activity of ZnO NPs. Raman bands for ZnO NPs also were found to shift faster in the presence of layered carbon. The quenching of visible photoluminescence emission of ZnO NPs with an increase in concentration of carbon NPs in the composite indicated the phenomenon associated with transfer of electrons from ZnO to layered carbon helping the separation of photo-generated electrons and holes in ZnO and can lead to enhancement of the photocatalytic activity of ZnO NPs. In the photocatalytic studies, it was observed that the degradation of methylene blue (MB) dye was significantly enhanced by the increase of content of layered carbon in the nanocomposite. The sample containing 10% carbon showed the highest adsorption in dark conditions which was up to 60% of the starting strength and this was further enhanced to 88% in the presence of UV radiation. Enhanced adsorption of MB dye and the effective separation of electron-hole pairs due to charge transfer were believed to be the main causes behind such kind of improvement in the photocatalytic effects.

Tungsten-based nanocatalysts with different structures for visible light responsive photocatalytic degradation of bisphenol A

Environmental pollution, such as water contamination, is a critical issue that must be absolutely addressed. Here, three different morphologies of tungsten-based photocatalysts (WO3 nanorods, WO3/WS2 nanobricks, WO3/WS2 nanorods) are made using a simple hydrothermal method by changing the solvents (H2O, DMF, aqueous HCl solution). The as-prepared nanocatalysts have excellent thermal stability, large porosity, and high hydrophilicity. The results show all materials have good photocatalytic activity in aqueous media, with WO3/WS2 nanorods (NRs) having the best activity in the photodegradation of bisphenol A (BPA) under visible-light irradiation. This may originate from increased migration of charge carriers and effective prevention of electron‒hole recombination in WO3/WS2 NRs, whereby this photocatalyst is able to generate more reactive •OH and •O2- species, leading to greater photocatalytic activity. About 99.6% of BPA is photodegraded within 60 min when using 1.5 g/L WO3/WS2 NRs and 5.0 mg/L BPA at pH 7.0. Additionally, the optimal conditions (pH, catalyst dosage, initial BPA concentration) for WO3/WS2 NRs are also elaborately investigated. These rod-like heterostructures are expressed as potential catalysts with excellent photostability, efficient reusability, and highly active effectivity in different types of water. In particular, the removal efficiency of BPA by WO3/WS2 NRs reduces by only 1.5% after five recycling runs and even reaches 89.1% in contaminated lake water. This study provides promising insights for the nearly complete removal of BPA from wastewater or different water resources, which is advantageous to various applications in environmental remediation.

Photocatalytic activity enhancement of nanostructured metal-oxides photocatalyst: a review

Nanostructured metal oxide semiconductors have emerged as promising nanoscale photocatalysts due to their excellent photosensitivity, chemical stability, non-toxicity, and biocompatibility. Enhancing the photocatalytic activity of metal oxide is critical in improving their efficiency in radical ion production upon optical exposure for various applications. Therefore, this review paper provides an in-depth analysis of the photocatalytic activity of nanostructured metal oxides, including the photocatalytic mechanism, factors affecting the photocatalytic efficiency, and approaches taken to boost the photocatalytic performance through structure or material modifications. This paper also highlights an overview of the recent applications and discusses the recent advancement of ZnO-based nanocomposite as a promising photocatalytic material for environmental remediation, energy conversion, and biomedical applications.

Differential photodegradation processes of adsorbed polychlorinated biphenyls on biochar colloids with various pyrolysis temperatures

Despite the crucial role of photodegradation in the environmental transformation of organic pollutants, the photodegradation process of organic pollutants irreversibly absorbed on biochar colloids (BCCs) remains poorly understood. This study investigated the photodegradation processes and mechanisms of 2,4,4'-trichlorobiphenyl (PCB28) adsorbed on BCCs released from bulk biochars derived from bamboo chips at pyrolysis temperatures of 300, 500, and 700 °C. Results show that BCCs-adsorbed PCB28 could be degraded under simulated solar illumination (95-105 mW·cm-2) but at decreased photodegradation rates compared to the dissolved PCB28. The inhibition effect of BCCs on the PCB28 photodegradation increased with increasing pyrolysis temperature. After adsorptive binding to BCCs, the half-life of PCB28 (0.1 mg/L) was prolonged from 2.65 h for the dissolved PCB28 alone in deionized water to 7.48, 40.67, and 81.82 h in the presence of BCC300, BCC500, and BCC700 (5.0 mg/L), respectively. Mechanistically, the photodegradation of adsorbed pollutants was regulated by the photogenerated free radicals and surface functional groups of the low-temperature BCCs, as well as the defects and direct electron transfer capabilities of the high-temperature BCCs; PCB28 adsorbed on the low-temperature BCCs accepted electrons from persistent free radicals under light illumination, which led to PCB28 dechlorination, followed by ring-opening oxidation through hydroxyl radical attack, ultimately resulting in progressive mineralization; singlet oxygen caused preferential ring opening of adsorbed PCB28 on the high-temperature BCCs, preceding dechlorination. The photodegradation of BCCs-adsorbed PCB28 remained significant though more or less being inhibited under the effects of water pH, ionic strength, dissolved organic matters (humic acid and fulvic acid), and in natural water samples. These findings contribute to a better understanding of the structural properties of BCCs that impact phototransformation processes of adsorbed pollutants and facilitate an accurate assessment of the environmental risk associated with biochar application.

Nanocomposite from tannery sludge-derived biochar and Zinc oxide nanoparticles for photocatalytic degradation of Bisphenol A toward dual environmental benefits

The growing concern over the presence of pollutants like Bisphenol A (BPA) in water sources has led to the growth of novel treatment technologies for its removal. This research work investigates the development of a novel biochar-metal oxide nanocomposite derived from tannery sludge and Zinc oxide (ZnO) nanoparticles for the photodegradation of BPA. The biochar was obtained by pyrolysis process, followed by impregnation of ZnO nanoparticles using a hydrothermal technique. The critical properties of as-prepared nanocomposite were evaluated by FT-IR, BET surface area, XRD, FE-SEM, HR-TEM, XPS, PL, EPR, and Raman Spectroscopy. In addition, the photocatalytic activity of nanocomposites was evaluated by measuring the degradation of BPA in visible light irradiation. The outcomes revealed that ZnO-loaded chemically activated biochar exhibited higher photocatalytic activity for the degradation of BPA than the pristine and non-chemically activated biochar. At pH 5, 0.2 g/L of photocatalyst dosage, 20 ppm of initial pollutant concentration, and 150 min of contact time, the maximum degradation efficiency of BPA was observed as 94.50 %. Also, nanocomposites showed good stability and reusability, with only a slight decrease in photocatalytic activity after multiple cycles of use. More importantly, the degradation mechanisms of BPA using as-prepared nanocomposites were analyzed in detail, indicating that the observed photocatalytic activity could be attributed to the synergistic effect between the biochar and ZnO, which provided a large surface area for the adsorption of BPA and promoted the generation of reactive oxygen species for its degradation. Overall, this study highlighted the potential of using nanocomposites from tannery sludge-derived biochar and ZnO nanoparticles for the degradation of BPA from polluted water sources using a photocatalytic process toward the dual environmental benefits.

MWCNTs Decorated with TiO2 as Highly Performing Filler in the Preparation of Nanocomposite Membranes for Scalable Photocatalytic Degradation of Bisphenol A in Water

Bisphenol A (BPA), an endocrine-disrupting compound with estrogenic behavior, is of great concern within the scientific community due to its high production levels and increasing concentration in various surface aquifers. While several materials exhibit excellent capacity for the photocatalytic degradation of BPA, their powdered nature and poor chemical stability render them unsuitable for practical application in large-scale water decontamination. In this study, a new class of nanocomposite membranes based on sulfonated polyethersulfone (sPES) and multiwalled carbon nanotubes decorated with TiO2 nanoparticles (MWCNTs-TiO2) were investigated as efficient and scalable photocatalysts for the photodegradation of BPA in aqueous solutions. The MWCNTs-TiO2 hybrid material was prepared through a facile and inexpensive hydrothermal method and extensively characterized by XRD, Raman, FTIR, BET, and TGA. Meanwhile, nanocomposite membranes at different filler loadings were prepared by a simple casting procedure. Swelling tests and PFG NMR analyses provided insights into the impact of filler introduction on membrane hydrophilicity and water molecular dynamics, whereas the effectiveness of the various photocatalysts in BPA removal was monitored using HPLC. Among the different MWCNTs-TiO2 content nanocomposites, the one at 10 wt% loading (sP-MT10) showed the best photoactivity. Under UV irradiation at 254 nm and 365 nm for 240 min, photocatalytic oxidation of 5 mg/L bisphenol A by sP-MT10 resulted in 91% and 82% degradation, respectively. Both the effect of BPA concentration and the membrane regenerability were evaluated, revealing that the sP-MT10 maintained its maximum BPA removal capability over more than 10 cycles. Our findings indicate that sP-MT nanocomposite membranes are versatile, scalable, efficient, and highly reusable photocatalysts for the degradation of BPA, as well as potentially for other endocrine disruptors.

In situ doping lignin-derived carbon quantum dots on magnetic hydrotalcite for enhanced degradation of Congo Red over a wide pH range and simultaneous removal of heavy metal ions

A new N, S-CQDs@Fe₃O₄@HTC composite was prepared by loading N, S carbon quantum dots (N, S-CQDs) derived from lignin on magnetic hydrotalcite (HTC) via an in-situ growth method. The characterization results showed that the catalyst had a mesoporous structure. These pores facilitate the diffusion and mass transfer of pollutant molecules inside the catalyst, allowing them to approach the active site smoothly. The catalyst performed well in the UV degradation of Congo red (CR) over a wide pH range (3-11), with efficiencies over 95.43 % in all cases. Even at a high NaCl content (100 g/L), the catalyst showed extraordinary CR degradation (99.30 %). ESR analysis and free radical quenching experiments demonstrated that OH and O₂^- were the main active species governing CR degradation. Besides, the composite had outstanding removal efficiency for Cu²⁺ (99.90 %) and Cd²⁺ (85.08 %) simultaneously due to the electrostatic attraction between the HTC and metal ions. Moreover, the N, S-CQDs@Fe₃O₄@HTC had excellent stability and recyclability during five cycles, making it free of secondary contamination. This work provides a new environment-friendly catalyst for the simultaneous removal of multiple pollutants and a waste-to-waste strategy for the value-added utilization of lignin.

Using a promising biomass-based biochar in photocatalytic degradation: highly impressive performance of RHB/SnO2/Fe3O4 for elimination of AO7

The release of industrial dyes into the environment has recently increased, resulting in harmful effects on people and ecosystems. In recent years, the use of adsorbents in photocatalytic nanocomposites has attracted significant interest due to their low cost, efficiency, and eco-friendly physical and chemical characteristics. Herein, Acid Orange 7 (AO7) removal was investigated by photocatalytic degradation using Rice Rusk Biochar (RHB), Tin (IV) Oxide (SnO₂), and Iron Oxide (Fe₃O₄) as heterogeneous nanocomposite. After the preparation of RHB, the nanocomposite was synthesized and characterized using Field Emission Scanning Electron Microscope (FESEM), X-ray Powder Diffraction (XRD), Brunauer-Emmett-Teller (BET), and Fourier-Transform Infrared Spectroscopy (FT-IR). To optimize the elimination of AO7 by the One-Factor-At-a-Time (OFAT) method, effective parameters including mixing ratio (RHB:SnO₂:Fe₃O₄), dye concentration, solution pH, and nanocomposite dose were studied. The results showed that the removal efficiency of AO7 after 120 min under the optimal mixing ratio of 1:1.5:0.6, dye concentration of 75 mg/l, solution pH of 4, and nanocomposite dose of 0.7 g/l was 92.37%. Moreover, Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) removal rates were obtained at 82.22 and 72.22%, respectively. The Average Oxidation State (AOS) and Carbon Oxidation State (COS) of the AO7 solution were increased after the process, indicating biodegradability improvement. Various scavenger effects were studied under optimal conditions, and the results revealed that O₂^- and H⁺ reactive species play a crucial role in the photocatalytic degradation of AO7. The reusability and stability of nanocomposite were tested in several consecutive experiments, and the degradation efficiency was reduced from 92 to 79% after five consecutive cycles. It is expected that this research contributes significantly to the utilization of agricultural waste in photocatalytic nanocomposites for the degradation of environmental pollutants.

Photocatalytic degradation of bisphenol-A (BPA) over titanium dioxide, and determination of its by-products by HF-LPME/GC-MS

In this work, analytical strategies were developed based on the technique of hollow fiber liquid-phase microextraction and chromatographic methods (LC-UV and GC/MS). These methods allowed the identification of the main Bisphenol-A by-products applying heterogeneous photocatalysis in water samples. BPA degradation in this study was in the order of 90%, and the conditions used in the HF-LPME were optimized through 2³ factorial design (6 cm fiber length, stirring speed of 750 rpm, and an extraction time of 30 min). Using a HF-LPME/GC-MS analytical strategy, it was possible to identify six by-products of BPA photodegradation, two of which have not been reported in the literature so far. This knowledge was quite important since the degradation can lead to the formation of more toxic and persistent by-products than the BPA. With the Toxtree software, three degradation products were found to be persistent to the environment, in addition to BPA; however, in 360 minutes of reaction, chromatographic peaks of the precursors were not identified, suggesting that there may have been a total degradation of these compounds. The results showed a great application potential of a miniaturized extraction technique to extract and pre-concentrate the degradation products of emerging contaminants.

Chlorophyll sensitized and salicylic acid functionalized TiO2 nanoparticles as a stable and efficient catalyst for the photocatalytic degradation of ciprofloxacin with visible light

Developing efficient and stable visible light active photocatalyst has significant environmental applications. Though dye sensitization of TiO₂ nanoparticles with natural chlorophyll pigments can potentially impart visible light activity, their long-term stability is a major concern. We investigated the functionalization of TiO₂ with salicylic acid, and subsequent sensitization with chlorophylls to improve the catalyst stability for the photocatalytic degradation of Ciprofloxacin (CPX) under visible light. A significant improvement in the degradation efficiency and catalyst stability was observed for five reuse cycles. Further, an optimum CPX degradation of ∼75% was achieved with 0.75 g L^-1 catalyst dosage of 0.1 chl/0.1 SA-TiO₂, initial pH of 6, and 10 ppm of initial CPX for a visible light exposure of 2 h. The degradation followed the pseudo-second-order kinetics. In addition, the ciprofloxacin degradation was reduced in the wastewater matrix system due to the presence of other scavenging species such as chlorides, sulphates, and alkalinity. Significant reduction in the toxicity of degradation compounds after the photocatalytic degradation was observed in comparison to parent CPX. Further, the degradation pathway and plausible mechanism of degradation of CPX were also proposed.

Current progress in treatment technologies for plastic waste (bisphenol A) in aquatic environment: Occurrence, toxicity and remediation mechanisms

Bisphenol-A (BPA) is a type of endocrine disrupting compound (EDC) that is being widely used in the production of polycarbonate and epoxy resins. In the last few years, human exposure to BPA has been extensively high due to the continuous increment in the Annual Growth Rate (AGR) of the BPA global market. The presence and transportation of BPA in the environment could cause serious damage to aquatic life and human health. This paper reviewed the literature on the exposure and toxicity mechanisms of BPA and advanced analytical techniques for the detection of BPA in the environment and human beings. The study indicated that BPA can cause damaging effects on numerous tissues and organs, including the reproductive system, metabolic dysfunction, respiratory system, immune system and central nervous system. On the basis of reported studies on animals, it appears that the exposure of BPA can be carcinogenic and responsible for causing a variety of cancers like ovarian cancer, uterine cancer, prostate cancer, testicular cancer, and liver cancer. This review paper focused mainly on the current progress in BPA removal technologies within last ten years (2012-2022). This paper presents a comprehensive overview of individual removal technologies, including adsorption, photocatalysis/photodegradation, ozonation/advance oxidation, photo-fenton, membranes/nanofilters, and biodegradation, along with removal mechanisms. The extensive literature study shows that each technology has its own removal mechanism and their respective limitations in BPA treatment. In adsorption and membrane separation process, most of BPA has been treated by electrostatic interaction, hydrogen boning and π-π interations mechanism. Whereas in the degradation mechanism, O* and OH* species have played a major role in BPA removal. Some factors could alter the removal potential and efficiency of BPA removal. This review paper will provide a useful guide in providing directions for future investigation to address the problem of BPA-containing wastewater treatment.

Photocatalytic Treatment of Emerging Contaminants with Ag-Modified Titania—Is There a Risk Arising from the Degradation Products?

Bisphenol A, bisphenol S, and fluconazole are environmental contaminants widely found in surface waters because of their extensive usage and low biodegradability. Therefore, other methods are often considered for the removal of these compounds. The present study aims at their photodegradation with the use of UV light and three different catalysts, ZnO, TiO2, and Ag-TiO2. The results obtained show that photocatalytic removal of these compounds is also problematic and the use of catalysts, such as ZnO and TiO2, at increasing concentrations mostly leads to lower degradation of the tested compounds. The modification of TiO2 with silver increases the degradation of both bisphenols up to 100%, which was achieved in 60 min by bisphenol A and in as little as 10 min by bisphenol S. Nevertheless, the degradation of fluconazole remained at the same level, not exceeding 70% in 60 min, i.e., still much lower than expected. In addition, the degradation products of bisphenols show the hydroxylation and destruction of their phenolic rings, while no degradation products were found during the test with fluconazole. Although the potentially genotoxic bisphenol A degradation product was found, the acute toxicity of the formed compounds differs little in comparison to the parent bisphenols.

Endocrine disrupting chemicals in the environment: Environmental sources, biological effects, remediation techniques, and perspective

Endocrine disrupting chemicals (EDCs) have been identified as emerging contaminants, which poses a great threat to human health and ecosystem. Pesticides, polycyclic aromatic hydrocarbons, dioxins, brominated flame retardants, steroid hormones and alkylphenols are representative of this type of contaminant, which are closely related to daily life. Unfortunately, many wastewater treatment plants (WWTPs) do not treat EDCs as targets in the normal treatment process, resulting in EDCs entering the environment. Few studies have systematically reviewed the related content of EDCs in terms of occurrence, harm and remediation. For this reason, in this article, the sources and exposure routes of common EDCs are systematically described. The existence of EDCs in the environment is mainly related to human activities (Wastewater discharges and industrial activities). The common hazards of these EDCs are clarified based on available toxicological data. At the same time, the mechanism and effect of some mainstream EDCs remediation technologies (such as adsorption, advanced oxidation, membrane bioreactor, constructed wetland, etc.) are separately mentioned. Moreover, our perspectives are provided for further research of EDCs.

Visible light responsive Cu-N/TiO2 nanoparticles for the photocatalytic degradation of bisphenol A

Visible light active co-doped Cu-N/TiO₂ photocatalyst was synthesized by the sol-gel method. The synthesized catalysts were characterized by X-ray diffraction (XRD), field-emission transmission electron microscope (FE-TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and UV-visible diffuse reflectance spectrophotometry (UV-vis DRS). The co-doping with Cu-N reduced the bandgap (∼2.83 eV) and extended the optical absorption range of TiO₂ catalysts to the visible region. The incorporation of Cu and N on TiO₂ lattice results in sub-conduction and valence band formation, which enhanced the photoactivity and electron-hole generation rate. The visible light activity of Cu-N/TiO₂ was evaluated via photocatalytic degradation of bisphenol A (BPA) under blue LED illumination. The maximum BPA degradation of 42.7% was observed at 0.5 g L^-1 catalyst dosage, initial pH of BPA solution = 8.2, and initial BPA concentration of 10 ppm. Further, a possible mechanism of photocatalytic degradation of BPA was also established.

Hydrothermally Grown ZnO Nanostructures for Water Purification via Photocatalysis

Semiconductor-based photocatalysis is a well-known and efficient process for achieving water depollution with very limited rejects in the environment. Zinc oxide (ZnO), as a wide-bandgap metallic oxide, is an excellent photocatalyst, able to mineralize a large scale of organic pollutants in water, under UV irradiation, that can be enlarged to visible range by doping nontoxic elements such as Ag and Fe. With high surface/volume ratio, the ZnO nanostructures have been shown to be prominent photocatalyst candidates with enhanced photocatalytic efficiency, owing to their being low-cost, non-toxic, and able to be produced with easy and controllable synthesis. Thus, ZnO nanostructures-based photocatalysis can be considered as an eco-friendly and sustainable process. This paper presents the photocatalytic activity of ZnO nanostructures (NSs) grown on different substrates. The photocatalysis has been carried out both under classic mode and microfluidic mode. All tests show the notable photocatalytic efficiency of ZnO NSs with remarkable results obtained from a ZnO-NSs-integrated microfluidic reactor, which exhibited an important enhancement of photocatalytic activity by drastically reducing the photodegradation time. UV-visible spectrometry and high-performance liquid chromatography, coupled with mass spectrometry (HPLC-MS), are simultaneously used to follow real-time information, revealing both the photodegradation efficiency and the degradation mechanism of the organic dye methylene blue.

ZnO-CdO nanocomposites incorporated with graphene oxide nanosheets for efficient photocatalytic degradation of bisphenol A, thymol blue and ciprofloxacin

The widespread existence of different organic contaminants mostly phenolic compounds, organic dyes and antibiotics in water bodies initiated by the various industrial wastes that raised great scientific concern and public awareness as well recently owing to their prospective capability to spread these contaminants resistant gene and pose hazard to human. In the present study, a series of nanostructured ZnO-CdO incorporated with reduced graphene oxide (ZCG nanocomposites) were successfully synthesized by a simple refluxing method and characterized by using the X-ray diffraction (XRD), Raman spectroscopy, FT-IR spectroscopy, photoluminescence spectroscopy, field emission-scanning microscope (FE-SEM) and UV-visible diffused reflectance spectroscopy (DRS) for the photocatalytic degradation of bisphenol A (BPA), thymol blue (ThB) and ciprofloxacin (CFn) with illumination of UV light. The maximum degradation and mineralization of BPA, ThB and CFn was achieved around 98.5%, 98.38% and 99.28% over the ZCG-5 nanocomposite photocatalyst after UV light irradiation for 180 min, 120 min and 75 min, respectively. The superior photocatalytic activity of ZCG-5 ascribed to enhance adsorption capacity, effective separation of charge carriers consequential for the production of more ROS after incorporation of RGO nanosheets with ZnO-CdO in photocatalyst. The conceivable photocatalytic degradation mechanism of BPA, ThB and CFn was elucidated through ROS identification and the assessment of photocatalyst stability by reusability, EEO (kwh/m³order) and UV light dose (mJ/cm²) were evaluated. The plausible photocatalytic degradation pathways were proposed for the degradation of BPA, ThB and CFn via GC-MS analysis. The present work investigates the efficient removal of BPA, ThB and CFn using ZCG nanocomposites as photocatalyst.

Structure and Photocatalytic Activity of Copper and Carbon-Doped Metallic Zn Phase-Rich ZnO Oxide Films

ZnO is one of the most important industrial metal oxide semiconductors. However, in order to fully realise its potential, the electronic structure of ZnO has to be modified to better fit the needs of specific fields. Recent studies demonstrated that reactive magnetron sputtering under Zn-rich conditions promotes the formation of intrinsic ZnO defects and allows the deposition of metallic Zn phase-rich ZnO films. In photocatalytic efficiency tests these films were superior to traditional ZnO oxide, therefore, the purposeful formation of intrinsic ZnO defects, namely Zn interstitials and oxygen vacancies, can be considered as advantageous self-doping. Considering that such self-doped ZnO remains a semiconductor, the natural question is if it is possible to further improve its properties by adding extrinsic dopants. Accordingly, in the current study, the metallic Zn phase-rich ZnO oxide film formation process (reactive magnetron sputtering) was supplemented by simultaneous sputtering of copper or carbon. Effects of the selected dopants on the structure of self-doped ZnO were investigated by X-ray diffractometer, scanning electron microscope, X-ray photoelectron spectroscope and photoluminescence techniques. Meanwhile, its effect on photocatalytic activity was estimated by visible light activated bleaching of Methylene Blue. It was observed that both dopants modify the microstructure of the films, but only carbon has a positive effect on photocatalytic efficiency.

Visible light-assisted degradation of 4-nitrophenol and methylene blue using low energy carbon ion-implanted ZnO nanorod arrays: Effect on mechanistic insights and stability

The present investigation demonstrates an enhancement of the visible photocatalytic activities by C ion implantation in ZnO nanorod arrays (NRAs). Vertically aligned ZnO NRAs were prepared by seed layer assisted solution-phase growth and implanted with 70 keV carbon ions at various fluencies: 1E15, 5E15, 1E16, and 3E16 ions/cm². X-ray diffraction and FESEM results revealed the crystalline 1D ZnO NRAs having a length of ∼3 μm with a diameter in the range of 150-200 nm. C implantation induces the absorption towards the visible region and a substantial decrease in the optical bandgap energy from 3.2 eV to 2.43 eV. The photocatalytic activities (PC) of C ion-implanted ZnO NRAs were investigated through the degradation of 4-Nitrophenol (4-NP) and methylene blue dye (MB) under ambient visible light irradiation. The degradation efficiency of C ion-implanted ZnO NRAs increases compared to the pristine ZnO NRAs from 60.12% to 93.7% and 48.6 to 97.5% for MB and 4-NP, respectively. The synergistic effects of low energy carbon ion-induced bulk and surface interface electronic states facilitate a narrow band of visible light absorption and efficient charge separation to increase the visible-light-driven photocatalytic performance of ZnO NRAs.

Biodegradation and photo-Fenton degradation of bisphenol A, bisphenol S and fluconazole in water

Bisphenol A, bisphenol S, and fluconazole are ubiquitous environmental pollutants and their removal from water is of utmost importance. As the biodegradation of these compounds is usually not enough effective, often other degradation methods are required. The study presents the difference between biodegradation and photo-Fenton degradation with a much higher efficiency obtained in the latter process. Levels of biodegradation and chemical degradation were assessed based on high-performance liquid chromatography determination. Optimization of the photo-Fenton removal of bisphenol A, bisphenol S, and fluconazole resulted in about 100 % primary degradation of both bisphenols during 10-20 min and almost 90 % primary degradation of fluconazole within an hour. Degradation products formed in the process were identified using liquid chromatography with mass spectrometry and showed central scission of bisphenol S with the formation of phenol and sulfuric acid while for bisphenol A and fluconazole the oxidation resulted in much smaller structural changes.

Predicting the trend and utility of different photocatalysts for degradation of pharmaceutically active compounds: A special emphasis on photocatalytic materials, modifications, and performance comparison

The rapid rise in the healthcare sector has led to an increase in pharmaceutically active compounds (PhACs) in different aqueous bodies. The toxicity of the PhACs and their ability to persist after conventional treatment processes have escalated research in the field of photocatalytic treatment. Although different photocatalysts have been successful in degrading PhACs, their inherent drawbacks have severely limited their application on a large scale. A substantial amount of research has been aimed at overcoming the high cost of the photocatalytic material, low quantum yield, the formation of toxic end products, etc. Hence, to further research in this field, researchers must have a fair idea of the current trends in the application of different photocatalysts. In this article, the trends in the use of various photocatalysts for the removal of different PhACs have been circumscribed. The performance of different groups of photocatalysts to degrade PhACs from synthetic and real wastewater has been addressed. The drawbacks and advantages of these materials have been compared, and their future in the field of PhACs removal has been predicted using S-curve analysis. Zinc and titanium-based photocatalysts were efficient under UV irradiation, while bismuth and graphene-based materials exhibited exemplary performance in visible light. However, iron-based compounds were found to have the most promising future, which may be because of their magnetic properties, easy availability, low bandgap, etc. Different modification techniques, such as morphology modification, doping, heterojunction formation, etc., have also been discussed. This study may help researchers to clarify the current research status in the field of photocatalytic treatment of PhACs and provide valuable information for future research.

Metal organic framework-derived C-doped ZnO/TiO2 nanocomposite catalysts for enhanced photodegradation of Rhodamine B

A series of C-doped ZnO/TiO₂ composites with various molar ratios of ZnO to TiO₂ were synthesized by one-step controllable pyrolysis of Zn/Ti bimetallic metal-organic frameworks (Zn/Ti-MOF). The Zn/Ti-MOF was prepared using a facile microwave hydrothermal method. Electron microscopic analysis proved that the composites presented regularity cubic morphology with an edge length of about 1 μm and the C atoms were successfully doped into ZnO/TiO₂ composites. X-ray photoelectron spectroscopy (XPS) measurement results confirmed the C-doping in the ZnO/TiO_2. Comparative experimental studies showed that 2% ZnO/TiO₂ composites prepared with the calcination temperature of 600℃ displayed the best photocatalytic degradation efficiency (94%) of RhB under the simulated sunlight irradiation. Cyclical experiment indicated the high stability and reusability of 2% ZnO/TiO₂ composites. Electron spin resonance (ESR) and trapping experiments illustrated that the produced O₂^- served as the main active species for the efficient RhB removal. This work provides an efficient way for preparing C-doped bimetal oxides composites, which would have an important application prospect in the photocatalytic degradation of organic pollutants in environmental water.

W-Doped ZnO Photocatalyst for the Degradation of Glyphosate in Aqueous Solution

In this paper, the photocatalytic degradation of glyphosate by zinc oxide (ZnO) photocatalysts doped with tungsten (W) was investigated under solar simulated light. The photocatalysts were successfully synthesized through a simple precipitation method and subsequently characterized by different techniques: Raman spectroscopy, UV–Vis, N2 adsorption at −196 °C, X-ray diffraction, and SEM analysis. In particular, all the prepared catalysts were characterized by a crystallite size of about 28 nm and a hexagonal wurtzite structure. After the W doping, the bandgap energy decreased from 3.22 of pure ZnO to 3.19 for doped ZnO. This allowed us to obtain good results in terms of glyphosate degradation and simultaneous mineralization under solar simulated lamps, making the process environmentally friendly and with almost zero energy costs. In particular, the best photocatalytic performance was obtained with 100 W-ZnO (prepared with 1.5 mol% of W). With this catalyst, after 180 min of exposure to solar simulated light, the glyphosate degradation and mineralization was equal to 74% and 30%, respectively. Furthermore, it has been shown that the best catalyst dosage was equal to 1.5 g/L. The study on the influence of pH evidenced that the best photocatalytic performances are obtained at spontaneous (neutral) pH conditions. Finally, to determine the main reactive species in the glyphosate oxidation, the effects of different radical scavengers were tested. The results evidenced that the glyphosate oxidation mechanism seems to be related mainly to the O2•− generated under simulated solar light irradiation, but also in minor part to h+.

Facile synthesis of Ag2O/ZnO/rGO heterojunction with enhanced photocatalytic activity under simulated solar light: Kinetics and mechanism

Ag₂O/ZnO/rGO heterojunction photocatalysts were synthesized via a rapid microwave hydrothermal method for photocatalytic degradation of bisphenol A (BPA) under simulated solar light. Ag doping efficiently decreased the bandgap of ZnO, and loading on rGO inhibited the recombination of photoinduced electron-hole pairs. The highest BPA removal rate (80%) was achieved with an Ag doping ratio of 5% and a GO loading ratio of 3 wt%. The enhanced photocatalytic performance was attributed to the narrower bandgap and the improved separation efficiency of electron-hole pairs. Moreover, the recycling experiments proved that Ag₂O/ZnO/rGO possessed excellent photostability. Hole (h⁺) and •OH played crucial roles in the photocatalytic system. The degradation pathway of BPA including hydroxylation and the cleavage of covalent bonds was proposed. The toxicity assessment of intermediates elucidated that most of intermediates were less toxic than BPA. The as-prepared Ag₂O/ZnO/rGO exhibited outstanding photostability and pH adaptability, having great potential to be applied to the degradation of emerging organic pollutants in wastewater.

Facile Synthesis of Porous ZnO Nanoparticles Efficient for Photocatalytic Degradation of Biomass-Derived Bisphenol A Under Simulated Sunlight Irradiation

Bisphenol A (BPA) produced from biomass is a typical endocrine disrupting compound that is carcinogenic and genotoxic and can be accumulated in water due to its extensive use and difficult degradation. In this study, the porous ZnO photocatalyst with core-shell structure and large surface area was successfully developed for the efficient photocatalytic degradation of BPA. The various effects of calcination temperatures, BPA concentrations, ZnO dosages, pH and inorganic ions on the degradation performance were systemically studied. The results showed that 99% degradation of BPA was achieved in 1 h using the porous ZnO calcined at 550°C under the conditions of 30 mg/L BPA, 1 g/L ZnO, and pH of 6.5. Besides, the inhibition effects of anions for the photocatalytic removal of BPA decreased in the order of H2PO 4 - >HCO 3 - >SO 4 2 - > Cl-, while the cations K+, Ca2+, and Na+ had little effect on the photocatalytic degradation of BPA. The results of scavenging experiments showed that h+, ·O 2 - , and e- played the key role in the photocatalytic degradation process. Finally, the main pathways of BPA degradation were proposed based on ten intermediates found in the degradation process. This work may provide a good guideline to degrade various endocrine disrupting compounds in wastewater treatment.

Polyaniline-Coated TiO2 Nanorods for Photocatalytic Degradation of Bisphenol A in Water

Polyaniline (PANI)-wrapped TiO₂ nanorods (PANI/TiO₂), obtained through the oxidative polymerization of aniline at the surface of hydrothermally presynthesized TiO₂ nanorods, were evaluated as photocatalysts for the degradation of Bisphenol A (BPA). Fourier-transform infrared spectroscopy analysis revealed the successful incorporation of PANI into TiO₂ by the appearance of peaks at 1577 and 1502 cm^-1 that are due to the C=C and C-N stretch of the benzenoid or quinoid ring in PANI. Brunauer-Emmett-Teller analysis revealed that PANI/TiO₂ had almost double the surface area of TiO₂ (44.8999 m²/g vs 28.2179 m²/g). Transmission electron microscopy (TEM) analysis showed that TiO₂ nanorods with different diameters were synthesized. The TEM analysis showed that a thin layer of PANI wrapped the TiO₂ nanorods. X-ray photon spectroscopy survey scan of the PANI/TiO₂ nanocomposite revealed the presence of C, O, Ti, and N. Photocatalytic activity evaluation under UV radiation through the effect of key parameters, including pH, contact time, dosage, and initial concentration of BPA, was carried out in batch studies. Within 80 min, 99.7% of 5 ppm BPA was attained using the 0.2 g/L PANI/TiO₂ photocatalyst at pH 10. The quantum yield (QY) of these photocatalysts was evaluated to be 9.86 × 10^-5 molecules/photon and 2.82 × 10^-5 molecules/photon for PANI/TiO₂ and TiO₂, respectively. PANI/TiO₂ showed better performance than as-synthesized TiO₂ with a rate constant of 4.46 × 10^-2 min^-1 compared to 2.18 × 10^-2 min^-1. The rate of degradation of PANI/TiO₂ was also superior to that of TiO₂ (150 mmol/g/h vs 74.89 mmol/g/h). Nitrate ions increased the rate of degradation of BPA, while humic acid consistently inhibited the degradation of BPA. LC-MS analysis identified degradation products with m/z 213.1, 135.1, and 93.1. The PANI/TiO₂ nanocomposite was reused up to five cycles with a removal of at least 80% in the fifth cycle. LC-MS results revealed three possible BPA degradation intermediates. LC-MS analysis identified degradation products which included protonated BPA, [C₁₄H₁₃O₂ ⁺], and [C₉H₁₁O⁺]. The PANI/TiO₂ nanocomposite demonstrated superior photocatalytic activity with respect to improved QY and figure of merit and lower energy consumption.

Application of Hierarchical Nanostructured WO3 and Fe2O3 Composites for Photodegradation of Surfactants in Water Samples

This study describes the utilization of hierarchical photoactive surface films for the decomposition of surfactants in water samples (with different pH). Photoactive films, containing tungsten (VI) oxide and iron (III) oxide (hematite), were deposited in a systematic and controlled manner using a layer-by-layer method. Physicochemical properties of the photoactive materials were developed and characterized using XRD analysis, Raman spectroscopy, water contact angle, voltammetry, and microscopic (SEM) techniques. The resulting multilayer films showed attractive performances in the photodegradation of the anionic surfactant sodium dodecyl sulfate (SDS) and the nonionic surfactant (1,1,3,3-tetramethylbutyl)phenyl-polyethylene glycol (Triton™ X-144) under solar light irradiation. The efficiency of the surfactants’ photodegradation was evaluated with a “test” based on a method, which is extremely sensitive to surfactants’ interference, with trace analysis of Pb using anodic stripping voltammetry on mercury electrodes (recovery study). The usefulness of hierarchical photoactive systems in the photodegradation of both surfactants is demonstrated in the presence and absence of the applied bias voltage. The maximum decomposition times were 2–3 h and 30 min, respectively. Furthermore, a properly designed layer system may be proposed, matching the pH of the water sample (depending on the treatment on the sampling side).

Degradation of 1,2-dichloroethane by photocatalysis using immobilized PAni-TiO2 nano-photocatalyst

1,2-Dichloroethane is one of the most hazardous environmental pollutants in wastewaters. It is mainly used to produce vinyl chloride monomer, the major precursor for PVC production. It is determined to be a probable human carcinogen and has been listed as a priority pollutant by the United States Environmental Protection Agency. Due to high chemical stability and low biodegradability of 1,2-dichloroethane, heterogeneous photocatalysis was used for degradation of this chlorinated hydrocarbon. PAni-TiO₂ nanocomposite was synthesized by in situ deposition oxidative polymerization method and immobilized on glass beads by a modified dip coating and heat attachment method. The characteristics of synthesized PAni-TiO₂ nanoparticles were confirmed using the results of morphology tests including Fourier-transform infrared spectra, X-ray diffraction patterns, particle size analysis, UV-Visible spectrophotometer, scanning electron microscope, and energy-dispersive X-ray spectroscopy. The performance of photocatalytic degradation of 1,2-dichloroethane using synthesized PAni-TiO₂ nanocomposite in a designed and constructed pilot scale packed bed recirculating photocatalytic reactor under xenon light irradiation was investigated. The response surface methodology based on the central composite design was used to evaluate and optimize the effect of 1,2-dichloroethane concentration, residence time, pH, and coating mass as independent variables on the photocatalytic degradation of 1,2-dichloroethane as the response function. Results showed that actual and predicted results were well fitted with R² of 0.9870, adjusted R² of 0.9718, and predicted R² of 0.9422. The optimum conditions for 1,2-dichloroethane photocatalytic degradation were the 1,2-dichloroethane concentration of 250 mg/L, the residence time of 240 min, pH of 5, and coating mass of 0.5 mg/cm², which resulted in 88.84% photocatalytic degradation. Kinetic of the photocatalytic degradation at optimal condition follows the Langmuir-Hinshelwood first-order reaction with k = 0.0095 min^-1 with R² = 0.9455. Complete photocatalytic degradation of 1,2-DCE was achieved after 360 min.

Photocatalytic degradation of phenazopyridine contaminant in soil with direct solar light

Photocatalytic degradation of waste pharmaceutics, with solar radiation, is described here as a feasible method to purify pre-contaminated soils. Phenazopyridine has been used as a model soil contaminant. Two different nano-size powders have been first examined as catalysts, namely commercial TiO₂ (anatase) and commercial ZnO. As the ZnO showed higher catalytic efficiency, the study was then focused on it. The commercial ZnO powder was then compared with lab-prepared ZnO powder, and the latter shows relatively higher efficiency. The ZnO was used in two different ways. In one way, dry ZnO catalyst powder was spread onto the soil, while in the other way the ZnO was sprayed onto the soil surface by a wet spray method. The spray technique shows slightly higher efficiency, in addition to being easier to apply at future large scale. Depending on conditions and type of photocatalyst used, up to 90% contaminant removal can be achieved in 30 min. In case of photocatalysis experiments, the reacted contaminant molecules undergo complete degradation with no detectable side reaction organic products. Possible evaporation or escape of organic contaminant, or other possibly resulting organics, is ruled out by a series of control experiments. Photodegradation process takes place only at the catalytic sites on the soil surface, where contaminant molecules that diffuse from the soil bulk are completely degraded. Other useful organisms inside the soil are not affected as they are kept away from catalyst sites. A plausible mechanism is proposed for the degradation process.