Polyethylene glycol (PEG)-modified Ag/Ag2O/Ag3PO4/Bi2WO6 photocatalyst film with enhanced efficiency and stability under solar light

Photocatalytic degradation of multiple-organic-pollutant under visible light by graphene oxide modified composite: degradation pathway, DFT calculation and mechanism

Wastewater containing antibiotics, organic dyes, and waterborne bacteria is a severe threat to human health and the environment. Amoxicillin has a slow metabolism rate in humans. Methylene blue is mutagenic and carcinogenic. In addition, Salmonella causes serious diarrhea. In this study, an effective 2D/2D photocatalyst with excellent elimination of these pollutants was fabricated by combining graphene oxide (GO), Bi2WO6, BiPO4 and Ag species. GO was applied at varying loading contents (0.8, 1.6, 2.4, 3.2 wt%) to improve the properties of the photocatalyst toward the removal of representative pollutants. The chemical structures, morphology, light absorption and charge mobility were investigated by different GO loading samples. The results indicated that when the wt% of GO was 2.4%, the photocatalyst showed excellent photocatalytic properties and removal rates for typical pollutants. Amoxicillin and methylene blue were mineralized into CO2, H2O, and small molecules, while Salmonella was disinfected with excellent photocatalytic efficiency. Furthermore, the possible photodecomposition pathways of amoxicillin and methylene blue were proposed by DFT calculations and intermediates identified by LCMS. The mechanism of the photocatalytic process was investigated by radical trapping experiments, ESR spectroscopy, and Motty-Schottky plots. The free radicals could be produced constantly during the photocatalytic process, leading to mineralization of amoxicillin and methylene blue, and disinfection of Salmonella. In this work, a new perspective on GO modified Bi2WO6 with different loading contents and the degradation pathways of antibiotics and dyes was proposed.

Highly Efficient Photo-Fenton Ag/Fe2O3/BiOI Z-Scheme Heterojunction for the Promoted Degradation of Tetracycline

Novel Ag/Fe₂O₃/BiOI Z-scheme heterostructures are first fabricated through a facile hydrothermal method. The composition and properties of as-synthesized Ag/Fe₂O₃/BiOI nanocomposites are characterized by powder X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, UV-Vis diffuse reflectance spectra, etc. The Ag/Fe₂O₃/BiOI systems exhibit remarkable degradation performance for tetracycline (TC). In particular, the composite (Ag/Fe₂O₃/BiOI-2) shows the highest efficiency when the contents of Ag and α-Fe₂O₃ are 2 wt% and 15%, respectively. The effects of operating parameters, including the solution pH, H₂O₂ concentration, TC concentration, and catalyst concentration, on the degradation efficiency are investigated. The photo-Fenton mechanism is studied, and the results indicated that •O^2- is the main active specie for TC degradation. The enhanced performance of Ag/Fe₂O₃/BiOI heterostructures may be ascribed to the synergic effect between photocatalysis and the Fenton reaction. The formation of Ag/Fe₂O₃/BiOI heterojunction is beneficial to the transfer and separation of charge carriers. The photo-generated electrons accelerate the Fe²⁺/Fe³⁺ cycle and create the reductive reaction of H₂O₂. This research reveals that the Ag/Fe₂O₃/BiOI composite possesses great potential in wastewater treatment.

Characterization and investigation of biological properties of silver nanoparticle-doped hydroxyapatite-based surfaces on zirconium

The infections leading to failed implants can be controlled mainly by metal and metal oxide-based nanoparticles. In this work, the randomly distributed AgNPs-doped onto hydroxyapatite-based surfaces were produced on zirconium by micro arc oxidation (MAO) and electrochemical deposition processes. The surfaces were characterized by XRD, SEM, EDX mapping and EDX area and contact angle goniometer. AgNPs-doped MAO surfaces, which is beneficial for bone tissue growth exhibited hydrophilic behaviors. The bioactivity of the AgNPs-doped MAO surfaces is improved compared to bare Zr substrate under SBF conditions. Importantly, the AgNPs-doped MAO surfaces exhibited antimicrobial activity for E. coli and S. aureus compared to control samples.

Advanced photocatalytic sterilization for recalcitrant Enterococcus sp. contaminated water by newly developed Z-scheme Bi2WO6 based composites under solar light

Pathogenic contamination is one of the major causes of clean water shortage, which poses great risk to human health. Herein, g-C₃N₄ (CN) was firstly introduced to Ag/Ag₂O/BiPO₄/Bi₂WO₆ (Ag/P/BWO) to construct a novel Z-scheme composite CN-Ag/P/BWO for disinfecting Enterococcus sp. contaminated water. CN-Ag/P/BWO showed excellent disinfection performance toward recalcitrant Enterococcus sp. under simulated solar light irradiation, achieving complete inactivation of 1.5 × 10⁷ cfu mL^-1 of bacterial cells only within 60 min, which was mainly attributed to the improved light absorption ability, charge carries separation/transfer efficiency and surface wettability. Additionally, the disinfection mechanism of CN-Ag/P/BWO toward Enterococcus sp. was systematically investigated. Photogenerated active species h⁺, ·OH and ·O₂^- worked together and played crucial roles in photocatalytic inactivation. The antioxidant system enabled Enterococcus sp. self-protection ability at the beginning of disinfection through secreting more antioxidant enzymes. However, with accumulation of active species, bacterial cell membrane and energy system were damaged, which further led to leakage of intracellular components and decomposition of bacteria. Besides, CN-Ag/P/BWO exhibited high practicability for different environmental factors and also performed well for real lake water disinfection. The high stability further confirmed its practicability for water disinfection. This work not only systematically revealed the disinfection mechanism toward Enterococcus sp., but also provided an efficient method for water disinfection.

Visible light active graphene oxide modified Ag/Ag2O/BiPO4/Bi2WO6 for photocatalytic removal of organic pollutants and bacteria in wastewater

Wastewater problems caused by antibiotics and bacteria contamination have become the primary environmental concern due to their harm to terrestrial organisms and health risk. To obtain the efficient removal approach of antibiotics and bacteria, visible driven advanced oxidation process by photocatalyst for the efficient removal and reducing waterborne disease was demonstrated in this study. 2D/2D GO-Ag/P/BWO heterostructure photocatalyst (GO: graphene oxide, Ag: Ag, Ag₂O; P: BiPO₄; BWO: Bi₂WO₆) were synthesized for effectively purification of antibiotics and bacteria contaminated wastewater. GO added in synthesis of BWO (1st-hydrothermal) and induced of Ag dopants (2nd-hydrothermal) of GO-Ag/P/BWO were fabricated separately and marked as GO_(I)-Ag/P/BWO and GO_(II)-Ag/P/BWO, characterized by different tests (FT-IR, XRD, Raman, XPS, SEM, TEM, TG, UV-VIS, PL, photocurrent density, and EIS). To testify the visible light driven photocatalytic activity of the fabricated photocatalysts, Rhodamine B (Rh B) and amoxicillin (AMX) was chosen as model emerging organic contaminants and antibiotics, respectively. While gram-negative strain Escherichia coli (E. coli) was selected as model waterborne bacteria. The results showed that GO_(II)-Ag/P/BWO photocatalyst was synthesized successfully, and possessed high crystallinity, low generated electron-hole recombination rate, and high photocurrent density. The system can produce energetic active species (h⁺, O₂^- and OH), exhibiting a superior performance towards removal of Rh B, AMX and E. coli under visible light irradiation. Comparing to other reported GO modified Bi based photocatalyst, GO_(II)-Ag/P/BWO had stronger photocatalytic performance in degradation of Rh B, AMX and E. coli, which indicated its high prospects for practical application in environmental wastewater treatment.

Solar-Driven Photocatalytic Films: Synthesis Approaches, Factors Affecting Environmental Activity, and Characterization Features

Solar-powered photocatalysis has come a long way since its humble beginnings in the 1990s, producing more than a thousand research papers per year over the past decade. In this review, immobilized photocatalysts operating under sunlight are highlighted. First, a literature review of solar-driven films is presented, along with some fundamental operational differences in relation to reactions involving suspended nanoparticles. Common strategies for achieving sunlight activity from films are then described, including doping, surface grafting, semiconductor coupling, and defect engineering. Synthetic routes to fabricate photocatalytically active films are briefly reviewed, followed by the important factors that determine solar photocatalysis efficiency, such as film thickness and structure. Finally, some important and specific characterization methods for films are described. This review shows that there are two main challenges in the study of photocatalytic materials in the form of (thin) films. First, the production of stable and efficient solar-driven films is still a challenge that requires an integrated approach from synthesis to characterization. The second is the difficulty in properly characterizing films. In any case, the research community needs to address these, as solar-driven photocatalytic films represent a viable option for sustainable air and water purification.

Sustainable and efficient reduction of pollutants by immobilized PEG-P/Ag/Ag2O/Ag3PO4/TiO2 photocatalyst for purification of saline wastewater

In this study, we have reported an efficient and stable degradation of pollutants at salinity condition using newly developed solar-light-driven silicone-TiO₂ based photocatalytic immobilized system. The interfacial layer of Silicone-PEG-P/Ag/Ag₂O/Ag₃PO₄/TiO₂ (S-PEG/PAgT) photocatalyst exhibited higher surface roughness, hydrophobicity, better light absorption, and narrow band gap than S-TiO₂. The Rh B degradation by S-PEG/PAgT (91.2%) was 1.71 folds higher than S-TiO₂ (53.5%) under simulated solar light irradiation. The reduction rate was significantly higher in S-PEG/PAgT (0.0792 min^-1) than S-TiO₂ (0.0229 min^-1). The S-PEG/PAgT demonstrated high TOC removal (>80%), high repeatability (10 cycles) and excellent activity after 30 days of incubation in aqueous NaCl. The mechanism analysis revealed the synergistic effect of surface morphology with irregular chamfered edges and photoinduced reactive species (O₂^-) with successive formation of free chlorine radicals (Cl) contributed to the removal of pollutants in saline wastewater. Therefore, considering the above advantages of high efficiency and effective elimination of organics illustrates the potential of newly developed S-PEG/PAgT immobilized system in long-term practical treatment real seawater and ballast water.

Photocatalytic membrane reactors for produced water treatment and reuse: Fundamentals, affecting factors, rational design, and evaluation metrics

Treatment and reuse of produced water (PW), the largest wastewater stream generated during oil and gas production, provides a promising option to address the increasing clean water demands. High-performance treatment technologies are needed to efficiently remove the organic and inorganic contaminants in PW for fit-for-purpose applications. Photocatalytic membrane reactor (PMR) is an emerging green technology for removal of organic pollutants, photoreduction of heavy metals, photo-inactivation of bacteria, and resource recovery. This study critically reviewed the mechanisms of photocatalysis and membrane processes in PMR, factors affecting PMR performance, rational design, and evaluation metrics for PW treatment. Specifically, PW characteristics, photocatalysts properties, membranes applied, and operating conditions are of utmost importance for rational design and reliable operation of PMR. PW pretreatment to remove oil and grease, colloidal and suspended solids is necessary to reduce membrane fouling and ensure optimal PMR performance. The metrics to evaluate PMR performance were developed including light utilization, exergetic efficiency, water recovery, product water improvement, lifetime of the photocatalyst, and costs. This review also presented the research gaps and outlook for future research.

Peroxymonosulfate Activation by Bi2WO6/BiOCl Heterojunction Nanocomposites under Visible Light for Bisphenol A Degradation

The combination of peroxymonosulfate (PMS) activation and photocatalysis has proven to be effective for organic contaminants treatment. However, the construction of an efficient catalytic material is an important challenge. Herein, novel Bi₂WO₆/BiOCl heterojunction nanocomposites were successfully designed and fabricated using a facile and effective strategy for bisphenol A (BPA) photodegradation with PMS activation. The well-designed heterojunction with improvement of the contact area and interface microstructure was obtained through in situ growth of the Bi₂WO₆ on the surface of BiOCl. The Bi₂WO₆/BiOCl nanocomposites exhibit excellent catalytic performance in PMS activation for BPA degradation under visible light irradiation. A possible photocatalytic reaction mechanism was systematically revealed. The excellent catalytic performance is mainly attributed to the strong interaction between Bi₂WO₆ and BiOCl, resulting in an enhanced photoabsorption and a more efficient interfacial charge separation and transfer. This paper provides a novel strategy to design efficient catalytic materials for organic contaminants remediation with PMS activation.

Preparation and characterization of silver orthophosphate photocatalytic coating on glass substrate

The photocatalytic activity of silver orthophosphate Ag3PO4 has been studied and shown to have a high photo-oxidation capability. However, there is few reported example of a simple method to prepare Ag3PO4 coatings on various substrates. In this study a novel and simple method to immobilize Ag3PO4 on the surface of glass substrates has been developed. A silver phosphate paste based on a polyelectrolyte solution was applied to a smooth glass surface. The resulting dried material was calcined to obtain a coating that remained on the glass substrate. The coating layer was characterized by X-ray diffraction and energy dispersive X-ray spectrometry, and the optical band gap of the material was determined. The results indicated that an Ag3PO4 coating responsive to visible light was successfully prepared. The coating, under visible light irradiation, has the ability to decompose methylene blue. Although the coating contained some elemental silver, this did not adversely affect the optical band gap or the photocatalytic ability.

Copper oxide/graphitic carbon nitride composite for bisphenol a degradation by boosted peroxymonosulfate activation: Mechanism of Cu-O covalency governs

Surface structure can govern heterogeneous catalysis, resulting in its critical role in nonradical reactions. Here, we explored whether Cu-O covalency plays a critical role in controlling the inherent properties of copper oxide/graphitic carbon nitride (CuO-CN). Experiments and theoretical calculations show that, in contrast to the traditional concept of low-valent metal control activity, surface modification enlarges Cu-O covalency, and high-valent copper species at the surface easily bind peroxymonosulfate (PMS, (HSO₅^-)) anions. Therefore, optimized CuO-CN corresponds to a 14.8-fold higher kinetic reaction rate (0.10392 min^-1) for PMS activation and pollutant degradation over those of unoptimized CuO-CN. Based on two-dimensional Fourier transform infrared correlation spectroscopy (2D-FT-IR-COS), Cu-O was determined to be the main active site. Cu-O is more active than other groups and acts before other groups. Benefiting from this electron transfer mechanism, CuO-CN shows good environmental tolerance (pH, anions, humic acid and actual water bodies such as tap water and groundwater). The established empirical kinetic model shows a strong linear correlation with the experimental kinetic reaction rate (> 0.94). CuO-CN/PMS can degrade organic pollutants efficiently for up to 30 days in a filter reactor. This work provides an understanding of the key role of the surface electronic structure in the nonradical activation of PMS and may provide support for improving the design of PMS catalysts.

Enhanced solar-driven photocatalytic performance of a ternary composite of SnO2 quantum dots//AgVO3 nanoribbons//g-C3N4 nanosheets (0D/1D/2D) structures for hydrogen production and dye degradation

Herein, we report the synthesis of between SnO₂ QDs /AgVO₃ nanoribbons/g-C₃N₄ nanosheets of ternary photocatalytic systems for the production of H₂ through light irradiation. The SnO₂/AgVO₃/g-C₃N₄ photocatalyst was successfully produced by using the hydrothermal process. The structural characterizations of the samples revealed the successful formation of ternary heterostructures where SnO₂, AgVO₃ and g-C₃N₄ (quantum dots/nanoribbons/nanosheets) 0D/1D/2D structures make a good interface with each other. The fabricated heterostructures of AgVO₃/g-C₃N₄ and SnO₂/AgVO₃/g-C₃N₄ photocatalytic structures performed enriched photocatalytic performance for H₂ production over that of the pristine g-C₃N₄, AgVO₃ and SnO₂ photocatalysts. The AgVO₃/g-C₃N₄ and SnO₂ /AgVO₃/g-C₃N₄ of photocatalysts were found to produce H₂ of around 17,000 μmol g^-1 and 77,000 μmol g^-1, respectively, which is much 4.5 times greater than that of AgVO₃/g-C₃N₄ photocatalyst. Moreover, the photodegradation behaviours of prepared catalysts were studied with the dye (rhodamine B, RhB) under light irradiation. The ternary composite SnO₂/AgVO₃/g-C₃N₄ performed photodegradation of RhB in 50 min. The higher photocatalytic activity for the ternary photocatalysts is predominantly due to the effective charge separation at the perfect interface formation amid SnO₂ and AgVO₃/g-C₃N₄.

Efficient photocatalytic degradation of volatile organic compounds over carbon quantum dots decorated Bi2WO6 under visible light

A series of CQDs/Bi₂WO₆ (CBW) hybrid materials with different loading amounts of carbon quantum dots (CQDs) were prepared via a facile in situ hydrothermal method. As determined by multiple techniques including XRD, TEM, UV-vis, PL, TPR, and XPS, the CBW possessed expanded visible light response interval, decreased recombination rate of the photogenerated electron hole, and enhanced oxidation ability as compared with the pristine Bi₂WO₆. In addition, with different loading amounts of CQDs, the optical and electronic properties of the corresponding CBW were different. These CBW materials performed superior activities to the pristine Bi₂WO₆ in the photodegradation of VOCs under visible light, among which the CBW-2 demonstrated the best activity of almost complete degradation within only 120 min. Moreover, the CBW-2 exhibited high stability and reusability after five cycles.

Plasmonic quaternary heteronanostructures (HNSs) for improved solar light utilization, spatial charge separation, and stability in photocatalytic hydrogen production

Recently, the frenetic development of stable quaternary material with a wide range of solar energy absorption and separation of charge carrier has emerged as a favorable material for the solar-to-hydrogen conversion. In this work, quaternary CuS-AgVO₃/Ag-TNR heteronanostructures (HNSs) synthesized by an ultra-sonication method for stabilized solar light photocatalytic hydrogen production in glycerol-water mixture. Among the prepared photocatalysts, the 1 wt% CuS-AgVO₃/Ag-TNR HNS produced the highest H₂ activity (756 µmol/g), approximately 84 times greater than the TNR due to higher charge separation, excellent conductivity, plasmonic resonance effect, and electron-storing capacity. Interestingly, the accelerated charge transfer pathway through the Schottky junction between the AgVO₃ and Ag to the conduction band of the TNR and thereafter to the electron acceptor of CuS for the reduction of H⁺ ions to H₂. Additionally, a possible photocatalytic mechanism of CuS-AgVO₃/Ag-TNR HNS for improved H₂ production was proposed based on the results obtained by various characterization techniques. Therefore, present research work explores the new insights to design high-performance CuS-AgVO₃/Ag-TNR HNS material for the conversion of clean renewable H₂ energy for the futuristic transport applications.

Bandgap-tuned ultra-small SnO2-nanoparticle-decorated 2D-Bi2WO6 nanoplates for visible-light-driven photocatalytic applications

With the rapid rate of industrialization, the emission of effluents represents a serious threat to aquatic living organisms and the environment. Semiconductor-mediated photocatalysis has been highlighted as the most attractive technology for the elimination of pollutants. In this connection, bandgap-tuned ultra-small SnO₂-nanoparticle-decorated 2D-Bi₂WO₆ nanoplates were prepared via the hydrothermal method. The tuning of the bandgap was altered by the thermal annealing procedure. Moreover, we investigated the influence of different bandgaps of SnO₂ on the anchoring of the 2D-Bi₂WO₆ nanoplates and studied their photocatalytic activity through the degradation of Rhodamine B under visible light irradiation. The ultra-small SnO₂ nanoparticles were highly anchored on the surface of the 2D-Bi₂WO₆ plates, which resulted in more photon harvesting, improved charge separation, the transfer of photoinduced charge carriers, and the alteration of band positions towards the visible region of light. Furthermore, the anchored SnO₂ nanoparticles improved the performance of the photocatalytic activity of 2D-Bi₂WO₆ nanoplates by more than 2.7 times.

Construction of cerium oxide nanoparticles immobilized on the surface of zinc vanadate nanoflowers for accelerated photocatalytic degradation of tetracycline under visible light irradiation

Construction of Z-scheme heterojunction has been deemed to be an effective and promising approach to boost the photocatalytic activity on account of accelerating the separation efficiency of the photogenerated carriers and maintaining the strong redox ability. Herein, an attractive CeO₂/Zn₃V₂O₈ Z-scheme heterojunction photocatalyst was rationally constructed by zero-dimensional (0D) CeO₂ nanoparticles immobilized on the surface of three-dimensional (3D) Zn₃V₂O₈ nanoflowers using a simple mixing method, and applied to the photocatalytic degradation of tetracycline (TC) under visible light irradiation. As expected, it was observed that the prepared CeO₂/Zn₃V₂O₈ hybrid illustrated significantly boosted the photocatalytic activity for the elimination of TC compared to pure Zn₃V₂O₈. More importantly, the optimized CeO₂(40 wt%)/Zn₃V₂O₈ hybrid owned the largest elimination rate of TC with 1.13 × 10^-2 min^-1, which was around 8.1 and 3.8 times as high as single CeO₂ (0.14 × 10^-2 min^-1) and Zn₃V₂O₈ (0.30 × 10^-2 min^-1), respectively. The appreciable performance improvement was mainly ascribed to the formation of Z-scheme heterojunction between CeO₂ and Zn₃V₂O₈, facilitating the transfer rate of photogenerated carriers and remaining the high reducibility of photoexcited electrons in CeO₂ and strong oxidizability of photoinduced holes in Zn₃V₂O₈. Active species capture experiments and electron spin resonance spectra showed that superoxide radicals and holes were the main active species for TC degradation. Besides, the possible degradation pathways of TC were speculated by identifying degradation intermediates, and the reasonable degradation mechanism including migration and transport behaviors of charge carriers and generation processes of reactive species were revealed in depth. This investigation enriches Zn₃V₂O₈-based Z-scheme heterojunction photocatalytic system and offers a new inspiration for the construction and fabrication of high-efficiency Z-scheme heterojunction photocatalysts to remove the antibiotics from wastewater.

Characteristics of hydrogen production by photocatalytic water splitting using liquid phase plasma over Ag-doped TiO2 photocatalysts

Hydrogen production from water was investigated by applying liquid plasma (LPP) to photocatalytic splitting of water. The optical properties of LPP due to water emission were also evaluated. The correlation between the optical properties of plasma and the formation of active species in water was investigated with the photocatalytic activity of hydrogen production. TiO₂ was also doped with Ag to evaluate the effect of enhancing photocatalytic activity. The photocatalytic activity was evaluated by the rate of hydrogen production, and the effect of hydrogen formation was also investigated by injecting methanol as an additive. As a result of examining the luminescence properties of LPP, it showed high luminescence in the 309 nm UV region and the 656 nm visible region. The hydrogen doping rate was increased in the Ag-doped TiO₂ photocatalyst. Ag-doped TiO₂ has wider light absorption into the visible region and narrower band gap. Due to these properties, the rate of hydrogen generation is superior to TiO₂ photocatalysts. The photochemical reaction with LPP and photocatalyst in aqueous solution with CH₃OH showed a significant increase in hydrogen production rate. The increase in hydrogen production by injection of additives is because the optical properties of generating OH radicals are improved and CH₃OH is decomposed to act as an electron donor to improve hydrogen production.