In Situ Fabrication of Ag/Ag3PO4/Graphene Triple Heterostructure Visible-Light Photocatalyst through Graphene-Assisted Reduction Strategy

Graphene oxide-incorporated silver-based photocatalysts for enhanced degradation of organic toxins: a review

Environmental contamination and scarcity of energy have been deepening over the last few decades. Heterogeneous photocatalysis plays a prominent role in environmental remediation. The failure of earlier metal oxide systems like pure TiO₂ and ZnO as stable visible-light photocatalysts demanded more stable catalysts with high photodegradation efficiency. Silver-based semiconductor materials gained popularity as visible-light-responsive photocatalysts with a narrow bandgap. But their large-scale usage in natural water bodies for organic contaminant removal is minimal. The factors like self-photocorrosion and their slight solubility in water have prevented the commercial use. Various efforts have been made to improve their photocatalytic activity. This review focuses on those studies in which silver-based semiconductor materials are integrated with carbonaceous graphene oxide (GO) and reduced graphene oxide (RGO). The decoration of Ag-based semiconductor components on graphene oxide having high-surface area results in binary composites with enhanced visible-light photocatalytic activity and stability. It is found that the introduction of new efficient materials further increases the effectiveness of the system. So binary and ternary composites of GO and Ag-based materials are reviewed in this paper.

Enhanced photocatalytic activity of a visible-light-driven ternary WO3/Ag/Ag3PO4 heterojunction: a discussion on electron transfer mechanisms

WO₃/Ag₃PO₄ with different weight ratios were prepared by ultrasonic assisted two-step deposition method. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence spectroscopy (PL) and transmission electron microscopy (TEM). The photocatalytic activities of all samples were evaluated by the degradation of rhodamine B (RhB) under visible light irradiation. WA-60 shows the highest photocatalytic activity in the WA-x series composite, while the photocatalytic activity of WAA-60 is the best among all samples. The free radical trapping experiments show that photogenerated holes (h⁺) are the main active species. The Ag nanoparticles produced by the decomposition of Ag₃PO₄ are located at the interface of Ag₃PO₄/WO₃, which promotes the separation efficiency of photogenerated electrons and holes. To further explain the photocatalytic mechanism, electrochemical and physical tests are introduced to explore the flow of electrons inside the catalyst.

WO₃/Ag₃PO₄ with different weight ratios were prepared by ultrasonic assisted two-step deposition method.

3D Bombax-structured carbon nanotube sponge coupling with Ag3PO4 for tetracycline degradation under ultrasound and visible light irradiation

A novel photocatalytic carbon nanotube sponge with three-dimensional Bombax-structure was fabricated by a facile chemical vapor deposition followed by in situ ion-exchange approach. The as-prepared sponge achieved both high-efficiency adsorption and photocatalysis towards antibiotics, which can remove up to 90% of tetracycline within an hour. The morphology and mechanism of the photocatalytic CNT sponge were explored by multiple measures. Results show the functional groups and high specific surface area of CNT sponge play vital roles in preparing this Bombax-structured Ag₃PO₄/CNT sponge, the band gap of which can be tuned by varying the ration between Ag₃PO₄ and CNT. The photodegradation experiments of tetracycline with the assistance of ultrasound irradiation were performed, Ag₃PO₄/CNT sponge exhibits preferable photocatalytic activity, which can be attributed to both the enhancement of specific surface area of Ag₃PO₄ and the cavitation effect on CNT surface. The efficiency contributed by ultrasound could account for more than half of the degradation efficiency when the ultrasound power was 100 W. The improvement in transfer efficiency and the delay in charge recombination of Ag₃PO₄/CNT sponge were further verified by Electrochemical impedance spectra (EIS) and Photoluminescence tests (PL). Reactive free-radical species were detected by the Electron Spin Resonance (ESR). The intermediates and possible pathway were analyzed by gas chromatography-mass spectrometer (GC-MS) technique.

In-Situ Construction of 2D/2D ZnIn2S4/BiOCl Heterostructure with Enhanced Photocatalytic Activity for N2 Fixation and Phenol Degradation

Photocatalytic nitrogen fixation and pollutants degradation at ambient temperature and pressure as a clean and efficient means represents a sustainable direction. In this paper, novel two-dimensional (2D) ZnIn2S4/2D BiOCl (ZIS/BOC) nanosheets heterostructures were successfully synthesized by in-situ solvothermal techniques. XPS and TEM results showed the formation of heterostructure. The photocatalytic properties of these materials were further studied by degradating phenol and nitrogen fixation under visible light irradiation. In particular, heterostructure obtained with a mass ratio of 0.5 wt % of ZnIn2S4 had a good application prospect and can achieve 77.4% phenol degradation rate within 6 h and a rate of ammonium production of 14.6 µmol∙gcat−1·h−1. The reaction rate of 0.5 wt % ZIS/BOC heterostructure exhibited 8.6 and 2.6 times relative to BiOCl for the degradation of phenol and nitrogen fixation, respectively. The enhanced photocatalytic activity was attributed to the collaboration of low recombination rate of photo-generated carriers and enhanced visible light absorption. Based on capture experiments and electron spin resonance (ESR) techniques, the main active species that may appear in photocatalytic systems were explored, and the corresponding photocatalytic mechanism was also proposed appropriately. This strategy will open up new ideas for the design and manufacture of more energy-efficient materials with high photocatalytic activity.

Plasmon-assisted demolition of antibiotic using sono-photoreduction decoration of Ag on 2D C3N4 nanophotocatalyst enhanced with acid-treated clinoptilolite

In this study, the plasmon silver/bulk graphitic carbon nitride-clinoptilolite (denoted as: Ag/BCN-CLT) nanophotocatalysts synthesized using sono-photoreduction dispersion of Ag over C₃N₄ nanophotocatalyst with various contents of acid-treated clinoptilolite (10, 20, 40 wt%) that was employed in the tetracycline degradation, as the model antibiotic pollutant, using simulated solar-light radiation. X-ray diffraction, field emission scanning electron microscopy, Energy-dispersive X-ray spectroscopy-Dot mapping, Brunauer-Emmett-Teller and Barrett-Joyner-Halenda, particle size distribution, and Ultraviolet-Visible diffuse reflectance spectroscopy analyses results showed a high quality of synthesis of nanophotocatalysts and good dispersion of particles on the surface of nanophotocatalyst. Using photodegradation results, the Ag/BCN-CLT(10) sample with 10 wt% of clinoptilolite showed a better tetracycline degradation efficiency (87.23%), which is a result of a high surface area of nanophotocatalyst due to the exerting sonication in synthesis procedure. Also, using Ag nanoparticles as a noble metal and creation of surface plasmon resonance effect, the edge of light absorption was shifted to the visible light region, which was proven by UV-Vis DRS results. Furthermore, the using of both Ag and acid-treated clinoptilolite had an efficient influence on decreasing band gap energy position. At last, the effect of different operational parameters and the reusable property of the photocatalyst have experimented. Finally, the suggested mechanisms of the tetracycline degradation reactions were drawn and were analyzed accurately.

New Magnetically Recyclable Reduced Graphene Oxide rGO/MFe2 O4 (M= Ca, Mg)/Ag3 PO4 Nanocomposites With Remarkably Enhanced Visible-light Photocatalytic Activity and Stability

New magnetically separable CaFe₂ O₄ /Ag₃ PO₄ , MgFe₂ O₄ /Ag₃ PO₄ , rGO/CaFe₂ O₄ /Ag₃ PO₄ and rGO/MgFe₂ O₄ /Ag₃ PO₄ photocatalysts were synthesized by the hydrothermal and ion-exchange deposition method. These four types of photocatalyst were used for degradation of Methylene blue (MB), Methyl orange (MO) and 4-chlorophenol (4-CP) in aqueous solution under visible-light illumination. The optimized photocatalyst, i.e. rGO/CaFe₂ O₄ /Ag₃ PO₄ with a mass ratio of (1:3:9) composite not only shows the highest photocatalytic performance for the degradation of MB, MO and 4-CP under visible light irradiation among the other synthesized photocatalysts but also exhibits high reusability and stability for at least five cycles. It was found that the impressive separation of electron-hole pairs as well as presence of rGO sheets which act as a high speed charge transfer were responsible for increasing photocatalytic activity over the optimized photocatalyst under visible-light irradiation. A possible mechanism for the increased photocatalytic activity of the rGO/CaFe₂ O₄ /Ag₃ PO₄ with a mass ratio of (1:3:9) composite was discussed in detail.

Growth study of hierarchical Ag3PO4/LaCO3OH heterostructures and their efficient photocatalytic activity for RhB degradation

We demonstrate a simple, cost effective co-precipitation method to synthesize APO/LCO heterostructures and investigate the effect of a mixed solvent system (H₂O:THF) on the growth of microstructures.

Minuscule weight percent of graphene oxide and reduced graphene oxide modified Ag3PO4: new insight into improved photocatalytic activity

Improved photocatalytic activity of controllably reduced and minuscule weight percent graphene oxide modified Ag₃PO₄ composite.

The roles of conjugations of graphene and Ag in Ag3PO4-based photocatalysts for degradation of sulfamethoxazole

Three different photocatalysts, namely silver phosphate (Ag₃PO₄; AGP), Ag₃PO₄-graphene (AGP–G) and Ag/Ag₃PO₄–graphene (AAGP–G), were fabricated by a chemical precipitation approach. The mechanism of AAGP–G to degrade SMX was explained in detail.

Low-temperature NOx(x = 1, 2) removal with ˙OH radicals from catalytic ozonation over a RGO–CeO2nanocomposite: the highly promotional effect of oxygen vacancies

CeO₂grown on a reduced graphene oxide nanocomposite (RGO–CeO₂) was successfully synthesized by a facile alkaline hydrothermal method with the addition of ethylene glycol.

Silver nanoparticles modified reduced graphene oxide wrapped Ag3PO4/TiO2 visible-light-active photocatalysts with superior performance

Rational design of a novel Ag₃PO₄/TiO₂/Ag-rGO photocatalyst with both electron and hole pathways for charge separation.

A new application of high-efficient silver salts-based photocatalyst under natural indoor weak light for wastewater cleaning

As a high-quantum-efficiency photocatalyst, the serious photo-corrosion of silver phosphate (Ag3PO4), limits the practical applications in water purification and challenges us. Herein, Ag3PO4 is found to have a high stability under natural indoor weak light irradiation, suggesting that we can employ it by adopting a new application strategy. In our studies, rhodamine B (RhB, cationic dye), methyl orange (MO, anionic dye) and RhB-MO mixture aqueous solutions are used as the probing reaction for the degradation of organic wastewater. It is found that RhB, MO and RhB-MO can be completely degraded after 28 h under natural indoor weak light irradiation, indicating that multi-component organic contaminants can be efficiently degraded by Ag3PO4 under natural indoor weak light irradiation. The density of natural indoor weak light is measured to be 72cd, which is merely one-thousandth of 300 W xenon lamp (68.2 × 10(3)cd). Most importantly, Ag3PO4 shows a high stability under natural indoor weak light irradiation, demonstrated by the formation of fairly rare Ag. Furthermore, we also investigate the influence of inorganic ions on organic dyes degradation. It shows that the Cl(-) and Cr(6+) ions with high concentrations in wastewater have significantly decreased the degradation rate. From the viewpoint of energy saving and stability, this study shows us that we can utilize the Ag-containing photocatalysts under natural indoor weak light, which could be extended to indoor air cleaning process.

Silver phosphate/graphitic carbon nitride as an efficient photocatalytic tandem system for oxygen evolution

Herein, we show the facile synthesis of an efficient silver phosphate/graphitic carbon nitride (Ag3 PO4 /g-C3 N4 ) photocatalyst for oxygen production and pollutant degradation by using electrostatically driven assembly and ion-exchange processes. The composite materials demonstrate a sheet-like C3 N4 structure, decorated with different Ag3 PO4 particles sizes. Detailed analysis of the reactions mechanism by electron-spin resonance and radical-capture agents strongly imply the formation of an in situ Z-scheme by the evolution of small silver nanoparticles in the interface of the materials under illumination. The Ag nanoparticles improve charge separation within the composite material by acting as a storage and recombination center for electrons and holes from Ag3 PO4 and C3 N4 , respectively. In addition, the photostability of Ag3 PO4 is enhanced relative to that of the bulk materials, which results in a stabilized heterojunction. We believe that this work provides new insight into the operation mechanism of composite photocatalysts for water splitting and opens the possibility for advanced photocatalysis based on the higher oxidation power of Ag3 PO4 .

Thin carbon layer coated Ti(3+)-TiO2 nanocrystallites for visible-light driven photocatalysis

Black TiO2 containing Ti(3+) attracts enormous attention due to its excellent visible-light driven photocatalytic activity. Herein, an in situ thermal decomposition approach to synthesize uniform thin carbon coated Ti(3+)-TiO2 nanocrystals is presented. During the oleic acid-assisted solvothermal process, the crystal size and morphology of TiO2 were controlled through oleic acid with carboxylic acid groups. Then the residual small quantities of oleic acid anchored on TiO2 were used as a carbon source, which could be in situ pyrolyzed into a carbon layer on TiO2 at high temperature and under an inert atmosphere. Meanwhile, Ti(4+) species were partly reduced into Ti(3+) states/oxygen vacancies on the surface of TiO2 due to the carbothermal reduction reaction for the carbon-encapsulated Ti(3+)-TiO2 structure. A series of characterizations indicated that the 20-25 nm TiO2 nanocrystals obtained were wrapped evenly by 1-2 nm carbon layers, which had an important effect on the energy band structure change of TiO2. The presence of the carbon layer also improves the Ti(3+) stability and the conduction behavior of the composites. The Ti(3+) states/oxygen vacancies created on the surface of TiO2 were responsible for the remarkable photogenerated charge separation and extended visible-light absorption range. Furthermore, Ti(3+) states/oxygen vacancies and the carbon layer together could enhance the adsorption ability of O2 so as to promote the photogenerated electrons captured by the adsorbed O2, leading to a great increase in the charge separation. As a result, the composites exhibit high photocatalytic performance for organic pollutants under visible light irradiation. This simple and new method may pave the way to practical applications for efficient photocatalytic degradation under visible light.

Advanced nanoarchitectures of silver/silver compound composites for photochemical reactions

Silver/silver compound (SSC) composites have received much attention as a type of potential materials in photochemical reactions due to their high efficiency, facile syntheses and availability of raw materials. This article reviews the state-of-the-art progress on the advanced nanoarchitectures of SSC composites. We begin with a survey on the general synthetic strategies for SSC composites, and then step into relatively detailed methods for size and morphology tunable two-component and more delicate multi-component SSC nanostructures. In addition, the electronic structure-related mechanisms of such materials and the recent studies on their stability are summarized. This review also highlights some perspectives on challenges related to the SSC composites and the possible research in the future.

Recent progress in highly efficient Ag-based visible-light photocatalysts

This review summarizes the recent progress in Ag-compound-based semiconductor photocatalysts, which will provide insights for future photocatalytic designs.