Regeneration of novel visible-light-driven Ag/Ag3PO4@C3N4 hybrid materials and their high photocatalytic stability

Novel visible-light-driven Ag₃PO₄@C₃N₄PO₄ loaded with metal Ag were synthesised via an anion-exchange precipitation method and regenerated by H₂O₂ and NaNH₃HPO₄. The obtained Ag/Ag₃PO₄@C₃N₄ and regenerated Ag/Ag₃PO₄@C₃N₄ were characterised by XRD, XPS, SEM and UV–vis. The XRD and UV–vis results revealed that the crystal structure and light adsorption property of Ag/Ag₃PO₄@C₃N₄ were similar to that of regenerated Ag/Ag₃PO₄@C₃N₄. The XPS result showed that the metallic Ag⁰ deposited on the surface of Ag/Ag₃PO₄@C₃N₄ and regenerated Ag/Ag₃PO₄@C₃N₄. The Ag/Ag₃PO₄@C₃N₄ hybrids displayed remarkable photocatalytic activity and stability after regeneration. Compared with pure Ag₃PO₄ or C₃N₄, the Ag/Ag₃PO₄@C₃N₄ and regenerated Ag/Ag₃PO₄@C₃N₄ enhancement in the photodegradation rate towards methyl orange is observed over under visible light irradiation. The enhanced photocatalytic performance was attributed to the synergistic effect between Ag₃PO₄ and C₃N₄ and a small amount of Ag⁰ which suppresses the charge recombination during photocatalytic process. This work could provide new insights into the fabrication of high stability visible photocatalysts and facilitate their practical application in environment issues.     

Investigation of the antibacterial and photocatalytic properties of the zeolitic nanosized AgBr/TiO2 composites

Zeolite-based Ag/AgBr and Ag/AgBr/TiO₂ photocatalysts were prepared by sol–gel and deposition methods and were characterized. Their photocatalytic activities were evaluated by inactivation of Escherichia (E.) coli and the photodegradation of Acid Blue 92 and potassium permanganate. The composites containing Ag/AgBr showed the antibacterial activity in the dark by releasing Ag⁺ ions into the medium. The results for inactivation of E. coli indicated that Ag/AgBr/TiO₂ modified photocatalyst had better antibacterial activity than Ag/AgBr/zeolite, while zeolite and TiO₂/zeolite did not show any antibacterial activity under visible light and dark conditions. Photodecolarization rate was affected differently in the presence of H₂O₂ depending upon the illumination source. Under visible light the photodecolorization rate is decreased while with UV light it is increased initially and then decreased by increasing hydrogen peroxide concentration. A mechanism for KMnO₄ photodegradation is proposed. The effects of catalyst concentration, initial dye concentration and temperature were also studied.     

Construction of Built‐In Electric Field within Silver Phosphate Photocatalyst for Enhanced Removal of Recalcitrant Organic Pollutants

Semiconductor photocatalysis technology has aroused great interest in photocatalytic degradation, but it suffers from the drawbacks of fast electron‐hole recombination and unsatisfactory degradation efficiency. Herein, a novel photocatalyst Ag₃PO₄@NC with excellent photocatalytic activity is successfully prepared, characterized, and evaluated for the efficient removal of organic pollutants. After visible light irradiation for 5, 8, and 12 min, the photocatalytic degradation efficiency of norfloxacin, diclofenac, and phenol on the composite catalyst reaches 100%, and the apparent rate constant of which is 19.2, 48.7, and 23.2 times than that of the pure Ag₃PO₄, respectively. The density functional theory calculation results indicate that there is a built‐in electric field from N‐doped carbon (NC) to Ag₃PO₄ at the interface of the composite catalyst. Driven by the electric field, the photogenerated electrons of Ag₃PO₄ can be readily transferred to the NC, leading to the efficient separation of photogenerated carriers and the significant improvement of the catalytic performance. The results of radical trapping experiments and electron spin resonance analysis show that photogenerated holes and O₂^? play an important role in the photodegradation process. This work provides a universal strategy of construction built‐in electric field through coupling with NC to improve the photocatalytic performance of photocatalysts.     

Ag3PO4/BiPO4 p–n heterojunction nanocomposite prepared in room-temperature ionic liquid medium with improved photocatalytic activity

A visible-light-active Ag₃PO₄/BiPO₄ nanocomposite with a p–n heterojunction structure was fabricated via a co-precipitation hydrothermal process using 2-hydroxylethylammonium formate (RTIL) as a room-temperature ionic liquid. The resulting catalysts were characterized by various techniques. The photocatalytic activity of the photocatalysts was evaluated by the photodegradation of phthalocyanine Reactive Blue 21 (RB21) under both visible and UV light irradiations. The results reveal that the heterojunction composite prepared in RTIL noticeably exhibited an improvement in both efficiency and rate of RB21 photodegradation in comparison with pure Ag₃PO₄ and BiPO₄. The enhanced photocatalytic activity of Ag₃PO₄/BiPO₄ heterostructure prepared in RTIL is mainly ascribed to the internal electric field built at the heterojunction interface and efficient charge separation and transfer across the p–n junction. RTIL can also assist in decreasing the crystalline size, orderly distributing the particles, preventing the collapse of pore structures, and losing of composite surface area.     

Development of novel Ag modified BiOF squares/g-C3N4 composite for photocatalytic applications

A novel Ag modified BiOF/g-C₃N₄ (Ag-BiOF/g-C₃N₄) organic–inorganic hybrid photocatalysts have been synthesized by a facile solvothermal route. The photocatalyst was characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis diffuse reflection spectroscopy (UV-DRS) and X-ray photoelectron spectroscopy (XPS). The photocatalytic studies reveals that the as-prepared Ag-BiOF/g-C₃N₄ photocatalyst exhibited significantly enhanced photocatalytic activity than the pure BiOF and BiOF/g-C₃N₄ photocatalysts toward degrading methylene blue (MB) under visible light irradiation. The heterostructured combination of Ag, g-C₃N₄ and BiOF micro squares provides synergistic photocatalytic performance through an efficient electron transport mechanism.     

Enhanced photocatalytic decolorization of methyl orange by gallium-doped α-Fe2O3

Gallium (Ga)-doped hematite (α-Fe₂O₃) with different molar ratios of Ga/Fe (1%, 2%, 3% and 4%) was prepared by a facile parallel flow co-precipitation method. The photocatalysts prepared were characterized by the Brunauer–Emmett–Teller method, X-ray diffraction, UV/vis diffuse reflectance spectroscopy, and scanning electron microscope. The photo-generated charges separation efficiency of different photocatalysts was investigated using benzoquinone as scavenger. The formation rate of OH radicals produced during the photocatalytic reaction process was studied by a terephthalic acid photoluminescence probing technique. Doping Ga³⁺ into α-Fe₂O₃ increases the specific surface area and the separation efficiency of photo-induced charges. The catalytic activity of the photocatalysts for decolorization of methyl orange aqueous solution was investigated. The results show that α-Fe₂O₃ doped with 3% Ga possesses the best photocatalytic activity. The underlying mechanism is suggested.     

Highly efficient photocatalytic treatment of mixed dyes wastewater via visible-light-driven AgI–Ag3PO4/MWCNTs

A high-performance photocatalyst of AgI–Ag₃PO₄/multi-walled carbon nanotubes (MWCNTs) was fabricated by chemical precipitation method using KI, K₂HPO₄ and AgNO₃ in the presence of MWCNTs. Its structure and physical properties were characterized by means of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscope (TEM), X-ray diffraction (XRD), UV–vis absorption spectra, X-ray photo-electron spectroscopy (XPS), photoluminescence spectra (PL) and photocurrent techniques. SEM, TEM and EDS analyses verified that AgI–Ag₃PO₄ is successfully loaded on MWCNTs. AgI–Ag₃PO₄/MWCNTs possess the absorption edge of red shift and small band gap energy, and could absorb more photons in the visible region. PL and photocurrent analyses illustrated that AgI–Ag₃PO₄/MWCNTs have the lowest emission peak intensity and the highest photoelectric current, compared with Ag₃PO₄, AgI and AgI–Ag₃PO₄. By using the photocatalytic degradation of mixed dyes wastewater of Orange II and ponceau 4R as a model reaction, the photocatalytic efficiencies of Ag₃PO₄, AgI, AgI–Ag₃PO₄ and AgI–Ag₃PO₄/MWCNTs were evaluated. The reaction results showed that AgI–Ag₃PO₄/MWCNTs have strong photocatalytic activity and excellent chemical stability in repeated and long-term applications. Therefore, the prepared AgI–Ag₃PO₄/MWCNTs could act as a high-performance catalyst for the photocatalytic degradation of mixed dyes wastewater and also suggested the promising applications.     

Synthesis of micro-nano Ag3PO4/ZnFe2O4 with different organic additives and its enhanced photocatalytic activity under visible light irradiation

Several novel micro-nano Ag₃PO₄/ZnFe₂O₄ with excellent magnetic separation property and photocatalytic performance were successfully synthesized using different organic additives for the first time. In the composite, Ag₃PO₄ with flower-like, quadrangular prism and flake structures were obtained when the organic additive is hexadecyl trimethyl ammonium bromide (CTAB), sodium diethyldithiocarbamate (DDTC), or DL-malic acid (DLMA), respectively, while the ZnFe₂O₄ showed uniform spherical structure. From the results of the photocatalytic activity analysis, the Ag₃PO₄/ZnFe₂O₄ gained with the organic additive of DDTC showed the highest photocatalytic capability for 2, 4-dichlorophenol (2, 4-DCP) degradation under visible light irradiation compared with those of CTAB and DLMA as the additives. Moreover, the composition of the composite seriously influences the photocatalytic activity, and when the mass ratio of Ag₃PO₄ and ZnFe₂O₄ in the Ag₃PO₄/ZnFe₂O₄ (DITCH) is 9:1, the apparent photo degradation rate constant of 2, 4-DC is 0.0155 min⁻¹, which is 5.74 times of ZnFe₂O₄ (0.0027 min⁻¹) and 1.89 times of Ag₃PO₄ (0.0082 min⁻¹). Finally, the photocatalytic mechanism of Ag₃PO₄/ZnFe₂O₄ was discussed based on the heterojunction energy-band theory and Z-Scheme theory in detail.     

Enhanced photo-induced charge separation and solar-driven photocatalytic activity of g-C3N4 decorated by SO42−

SO₄²⁻ decorated g-C₃N₄ with enhanced photocatalytic performance was prepared by a facile pore impregnating method using (NH₄)₂S₂O₈ solution. The photocatalysts were characterized by the Brunauer–Emmett–Teller (BET) method, X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis diffuse reflectance spectroscopy (DRS), transmission electron microscopy (TEM), Fourier-transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS) and surface photovoltage (SPV) spectroscopy, respectively. The separation efficiency of photo-generated charge was investigated using benzoquinone as scavenger. The results demonstrate that sulfating of g-C₃N₄ increases the adsorption of rhodamine B on g-C₃N₄, the hydroxyl content and the separation efficiency of photo-generated charge. The photocatalytic activity of SO₄²⁻/g-C₃N₄ for decolorization of rhodamine B and methyl orange (MO) aqueous solution was evaluated. The result shows that loading of 6.0 wt% SO₄²⁻ results in the best photocatalytic activity under simulated solar irradiation and SO₄²⁻ play an important role in boosting the photocatalytic activity.     

g-C3N4/Ag3PO4 composites with synergistic effect for increased photocatalytic activity under the visible light irradiation

The g-C₃N₄ was synthesized by a hydrothermal method and the g-C₃N₄/Ag₃PO₄ composites were prepared by a ordinary precipitation method. Microstructures, morphologies and optical properties of the as-prepared samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), UV–vis diffuse reflectance spectroscopy (DRS), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The results showed that the Ag₃PO₄ nanoparticles were dispersed on the surface of the flake-like g-C₃N₄, and the heterojunction was formed on the interface. The g-C₃N₄/Ag₃PO₄ (2 wt%) photocatalyst presented the highest photocatalytic activity for organic dye methylene blue (MB) degradation, and its photocurrent intensity was approximately 2 times than that of the pure Ag₃PO₄. The g-C₃N₄/Ag₃PO₄ (2 wt%) photocatalyst also exhibited photocatalytic performance in the decomposition of colorless antibiotic ciprofloxacin (CIP). The capture experiment confirmed that holes acted as the main active species during the photocatalytic reaction.     

Facile regeneration and photocatalytic activity of CuO-modified silver bromide photocatalyst

CuO-modified silver bromide (AgBr/CuO) crystal was successful synthesized by a facile method at room temperature. The physical and chemical properties of AgBr/CuO crystals were carefully detected through X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (DRS), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and Electron spin resonance (ESR) techniques. The photocatalytic activity and stability of AgBr/CuO hybrid were evaluated by photocatalytic degradation of methyl orange (MO) under visible light irradiation. The AgBr/CuO sample exhibited high photocatalytic activity, degrading 92% MO after irradiation for 40 min, which was 3.8 times higher than that of pure AgBr. Both the experimental scavenging results and characterization results revealed that O₂⁻ acts as the main active specie. Based on above, the high photocatalytic performance is mainly attributed to the abundant of oxygen vacancies, and which further generate lots of superoxide radicals. Moreover, the method by using bromide water to rejuvenate AgBr/CuO could well maintain the photocatalytic activity and stability without any environment pollution.     

Efficient charge separation of Ag2CO3/ZnO composites prepared by a facile precipitation approach and its dependence on loading content of Ag2CO3

To further improve the separation of photo-induced charge carriers, Ag₂CO₃ was employed to couple with ZnO. In this paper, Ag₂CO₃ was facilely deposited on the surface of ZnO through a precipitation method. The effects of loading content of Ag₂CO₃ on the charge separation of Ag₂CO₃/ZnO composites and their photocatalytic performance were studied by the means of surface photovoltage spectroscopy (SPS). Coupling of ZnO with Ag₂CO₃ can greatly accelerate the charge separation under the simulated solar light irradiation, supported by the SPS results. The enhancement of charge separation rate and photocatalytic activities of Ag₂CO₃/ZnO composites notably depends on the loading content of Ag₂CO₃. With the optimal theoretical Ag/Zn molar ratio of 3/100, the composite exhibits the highest charge separation rate and photocatalytic activity under the simulated solar light illumination. To better comprehend the improved separation of the photo-induced charge carriers, a Z-scheme charge separation mechanism was proposed.     

Influence of annealing temperature on visible-light photocatalytic activities of Ag3PO4 particulates synthesized using CH3COOAg as a precursor

Ag3PO4 microparticles (MPs) were prepared through a facile chemical precipitation route and using silver acetate (AgAc) as metal salt. The effect of annealing temperature (Ta) and time (τa) on the actual photocatalytic (PC) activity of Ag3PO4 MPs is investigated. The optimal annealing parameters are Ta of 400 °C and τa of 90 min. The enhanced PC activity by annealing at 400 °C is ascribed to the increase of electron mobility. Besides, an Ag3PO4 photoelectrode was fabricated through a drop-coating deposition route, which demonstrates a photocurrent density of 80 μA/cm2 and acceptable stability. The n-type conduction behavior of Ag3PO4 is verified by a Mott-Schottky (M-S) plot.     

Synthesis and photocatalytic performance of Ag3PO4/AgCl hybrids

Ag3POa/AgC1 hybrids have been synthesized via a facile ion-exchange method. The hybrids exhibit an enhanced photocatalytie activity for degradation of rhodamine B （RhB） than the single Ag-3PO_4 or AgCl under a visible light irradiation. Such a behavior might be attributed to the increased number of high active sites and suitable energy band structure. The possible mechanism is also discussed.     

Effective Prevention of Charge Trapping in Graphitic Carbon Nitride with Nanosized Red Phosphorus Modification for Superior Photo(electro)catalysis

The high occurrence of trapped unreactive charges due to chemical defects seriously affects the performance of g‐C₃N₄ in photocatalytic applications. This problem can be overcome by introducing ultrasmall red phosphorus (red P) crystals on g‐C₃N₄ sheets. The elemental red P atoms reduce the number of defects in the g‐C₃N₄ structure by forming new chemical bonds for much more effective charge separation. The product shows significantly enhanced photocatalytic activity toward hydrogen production. To the best of our knowledge, the hydrogen evolution rate obtained on this hybrid should be the highest among all P‐containing g‐C₃N₄ photocatalysts reported so far. The trapping and detrapping processes in this red P/g‐C₃N₄ system are thoroughly revealed by using time‐resolved transient absorption spectroscopy.     

Ultrasonic-assisted preparation of novel ternary ZnO/AgI/Ag2CrO4 nanocomposites as visible-light-driven photocatalysts with excellent activity

This work reports ultrasonic-assisted preparation of novel ternary ZnO/AgI/Ag₂CrO₄ nanocomposites as excellent visible-light-driven photocatalysts. The ZnO/AgI/Ag₂CrO₄ nanocomposite with 20% of Ag₂CrO₄ has the superior activity in degradation of rhodamine B. Activity of this nanocomposite is nearly 167, 6.5, and 45-fold higher than those of the ZnO, ZnO/AgI, and ZnO/Ag₂CrO₄ samples, respectively. The ternary nanocomposite also showed enhanced activity relative to its counterparts for degradation of methylene blue and methyl orange as two dye pollutants under visible-light irradiation. The UV–vis DRS and PL spectra confirmed that the excellent photocatalytic activities are due to more visible-light absorption ability and efficiently separation of the charge carriers. Based on the effects of different scavengers, it was found that superoxide ions are the primary reactive species to cause the degradation reaction. Furthermore, the highly enhanced activity of the ternary nanocomposite was described using a proposed mechanism.     

Fabrication of tin-doped zinc oxide by parallel flow co-precipitation with enhanced photocatalytic performance

Sn-doped ZnO photocatalysts with different molar ratios of Sn/Zn (1%, 2% and 3%) were prepared by a parallel flow precipitation. The photocatalysts fabricated were characterized by BET surface area, X-ray diffraction, scanning electron microscope, UV/Vis diffuse reflectance spectroscopy and surface photovoltage spectroscopy, respectively. The results showed that doping ZnO with Sn increased BET surface area of ZnO. The XRD patterns of Sn-doped ZnO photocatalysts calcined at 573 K showed only the characteristic peaks of wurtzite-type. Doping ZnO with Sn changed the morphology of ZnO, the morphology changed from irregular lump and particle to irregular honeycomb. The photoinduced charge separation rate of 1% Sn doped-ZnO was higher than that of ZnO, while 2% and 3% Sn doped-ZnO had lower photovoltage than that of ZnO. The photocatalytic activity of Sn-doped ZnO photocatalysts for decolorization of methyl orange solution was evaluated, of all photocatalysts prepared, Sn-doped ZnO with 1% Sn exhibited the best photocatalytic activity and the underlying reason was discussed.     

Ag3VO4/ZnO nanocomposites with an n–n heterojunction as novel visible-light-driven photocatalysts with highly enhanced activity

The present work demonstrates the preparation of Ag₃VO₄/ZnO nanocomposites with an n–n heterojunction, as novel visible-light-driven photocatalysts, with different mole fractions of silver vanadate. The preparation method is facile one-pot, large-scale, and low-temperature and does not require any post preparation treatments. The microstructure, morphology, purity, and electronic properties of the as-prepared samples were studied using X-ray diffraction, scanning electron microscopy, energy dispersive analysis of X-rays, UV–vis diffuse reflectance spectroscopy, Fourier transform-infrared spectroscopy, and photoluminescence techniques. Photocatalytic activity of the nanocomposites was examined by degradation of rhodamine B under visible-light irradiation. It was found that mole fraction of silver vanadate has a considerable influence on the photocatalytic activity. The nanocomposite with 0.218 mol fraction of Ag₃VO₄ exhibited the superior activity relative to the other compositions. Compared with the pure ZnO and Ag₃VO₄, the nanocomposite exhibited 10.5 and 1.6-fold enhancement, respectively, in the degradation rate constant. In addition, influence of the refluxing time, calcination temperature, and scavengers of reactive species on the degradation activity was investigated in detail and the results were discussed. Moreover, the nanocomposite was found to be a reusable photocatalyst.     

Improved photocatalytic activity of dysprosium-doped Bi2O3 prepared by sol–gel method

Bi₂O₃ and dysprosium-doped Bi₂O₃ photocatalysts with different molar ratio of Dy/Bi (1/100, 2/100, 3/100 and 4/100) were prepared by a sol–gel method. The photocatalysts prepared were characterized by Brunauer–Emmett–Teller (BET) method, X-ray diffraction (XRD), UV/vis diffuse reflectance, X-ray photoelectron spectroscopic techniques and surface photovoltage spectroscopy, respectively. The results show that dysprosium-doped Bi₂O₃ with 3/100 Dy prepared has the highest BET surface area, pore volume, the smallest pore size. XRD spectra of dysprosium-doped Bi₂O₃ catalysts calcined at 773 K are composed of monoclinic and tetragonal phase. Doping Dy into Bi₂O₃ increases the BET surface area and decreases the crystal size and the band gap of doped Bi₂O₃ photocatalysts, induces binding energy value of Bi 4f_7/2-shift and promotes the photoinduced charge separation rate. Of all of the photocatalysts prepared among the experimented compositions, dysprosium-doped Bi₂O₃ with 3/100 Dy possesses the best photocatalytic activity and the underlying reason was discussed.     

Photocatalyst Interface Engineering: Spatially Confined Growth of ZnFe2O4 within Graphene Networks as Excellent Visible‐Light‐Driven Photocatalysts

High‐performance photocatalysts should have highly crystallized nanocrystals (NCs) with small sizes, high separation efficiency of photogenerated electron–hole pairs, fast transport and consumption of photon‐excited electrons from the surface of catalyst, high adsorption of organic pollutant, and suitable band gap for maximally utilizing sunlight energy. However, the design and synthesis of these versatile structures still remain a big challenge. Here, we report a novel strategy for the synthesis of ultrasmall and highly crystallized graphene–ZnFe₂O₄ photocatalyst through interface engineering by using interconnected graphene network as barrier for spatially confined growth of ZnFe₂O₄, as transport channels for photon‐excited electron from the surface of catalyst, as well as the electron reservoir for suppressing the recombination of photogenerated electron–hole pairs. As a result, about 20 nm ZnFe₂O₄ NCs with highly crystallized (311) plane confined in the graphene network exhibit an excellent visible‐light‐driven photocatalytic activity with an ultrafast degradation rate of 1.924 × 10^?7 mol g^?1 s^?1 for methylene blue, much higher than those of previously reported photocatalysts such as spinel‐based photocatalysts (20 times), TiO₂‐based photocatalysts (4 times), and other photocatalysts (4 times). Our strategy can be further extended to fabricate other catalysts and electrode materials for supercapacitors and Li‐ion batteries.