Highly efficient visible-light driven AgBr/Ag3PO4 hybrid photocatalysts with enhanced photocatalytic activity

Highly efficient visible-light-driven AgBr/Ag₃PO₄ hybrid photocatalysts with different mole ratios of AgBr were prepared via an in-situ anion-exchange method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) technique. Under visible light irradiation (>420 nm), the AgBr/Ag₃PO₄ photocatalysts displayed the higher photocatalytic activity than pure Ag₃PO₄ and AgBr for the decolorization of acid orange 7 (AO 7). Among the hybrid photocatalysts, AgBr/Ag₃PO₄ with 60% of AgBr exhibited the highest photocatalytic activity for the decolorization of AO 7. X-ray photoelectron spectroscopy (XPS) results revealed that AgBr/Ag₃PO₄ readily transformed to be Ag@AgBr/Ag₃PO₄ system while the photocatalytic activity of AgBr/Ag₃PO₄ remained after 5 recycling runs. In addition, the quenching effects of different scavengers displayed that the reactive h⁺ and O₂^∙− play the major role in the AO 7 decolorization. The photocatalytic activity enhancement of AgBr/Ag₃PO₄ hybrids can be ascribed to the efficient separation of electron–hole pairs through a Z-scheme system composed of Ag₃PO₄, Ag and AgBr, in which Ag nanoparticles act as the charge separation center.     

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.     

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.     

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.     

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.     

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.     

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.     

Enhanced properties for visible-light-driven photocatalysis of Ag nanoparticle modified Bi2MoO6 nanoplates

The visible light driven Bi₂MoO₆ photocatalyst doped with different contents of Ag nanoparticles was successfully synthesized by a combination of hydrothermal and sonochemical methods. The as-synthesized samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning and transmission electron microscopy (SEM and TEM) and UV–visible spectroscopy to investigate crystalline structure, morphology, composition and photocatalytic properties. XRD patterns and TEM images of the samples revealed pure phase orthorhombic Bi₂MoO₆ nanoplates without any detection of Ag dopant due to its low concentration and very tiny particle size. TEM images showed that Ag nanoparticles with the size of 10–15 nm were dispersed randomly on the surface of Bi₂MoO₆. The XPS analysis of Ag/Bi₂MoO₆ nanocomposites revealed the presence of additional metallic Ag. Photocatalytic activities of the Ag/Bi₂MoO₆ nanocomposites were evaluated by determining the degradation of rhodamine B (RhB) under visible light radiation. In this research, the 10 wt% Ag/Bi₂MoO₆ nanocomposites showed the best photocatalytic activity. The results suggest that the dispersion of Ag nanoparticles on the surface of Bi₂MoO₆ significantly enhances its photocatalytic activity.     

Fabrication of Bi2MoO6 nanoplates hybridized with g-C3N4 nanosheets as highly efficient visible light responsive heterojunction photocatalysts for Rhodamine B degradation

The Bi₂MoO₆/g-C₃N₄ heterojunction photocatalysts have been successfully fabricated using a simple liquid chemisorptions and thermal post-treatment. These nanostructured Bi₂MoO₆/g-C₃N₄ composites were extensively characterized by X-ray diffraction(XRD), field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR),UV–vis diffuse reflectance spectra (UV–vis DRS) and Photoluminescence (PL). The photocatalytic results show that 20 wt% Bi₂MoO₆/g-C₃N₄ sample exhibits efficient visible light activity and excellent photo-stability. The kinetic constant of RhB degradation over 20 wt% Bi₂MoO₆/g-C₃N₄ is about 5 and 2.5 times higher than that over pure Bi₂MoO₆ and g-C₃N₄ nanosheets, respectively. The enhanced photocatalytic performance is attributed to the construction of heterogeneous interface to promote photo-induced charge carrier pairs separation.     

Dramatic Activity of C3N4/BiPO4 Photocatalyst with Core/Shell Structure Formed by Self‐Assembly

Core/shell structured C₃N₄/BiPO₄ photocatalyst is fabricated via a facile ultrasonic dispersion method. The thickness of the shell may be controlled by tuning the amount of C₃N₄ in the dispersion, which determines the enhanced level of photocatalytic activity. The optimum photocatalytic activity of C₃N₄/BiPO₄ at a weight ratio of 4% (C₃N₄/BiPO₄) under UV irradiation is almost 4.5 times as high as that of reference P25 (TiO₂) and 2.5 times of BiPO₄. More attractively, the dramatic visible light photocatalytic activity is generated due to the C₃N₄ loaded. The enhancement in performance is demonstrated to be the match of lattice and energy level between the C₃N₄ and BiPO₄. This match facilitates the separation and transfer of photogenerated electron–hole pairs at the heterojunction interfaces and may be important for other core/shell structured materials. In addition, this method is expected to be extended for other C₃N₄ loaded materials.     

Synthesis and characterization of g-C3N4/BiFeO3 composites with an enhanced visible light photocatalytic activity

The novel visible light-induced g-C₃N₄/BiFeO₃ composites were successfully synthesized by introducing BiFeO₃ into polymeric g-C₃N₄. The structures and optical properties of composites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), field-emission transmission electron microscope (TEM), UV–vis diffuse reflection spectroscopy (DRS), respectively. For the degradation of Rhodamine B (RhB), the g-C₃N₄/BiFeO₃ composites exhibited significantly higher visible light photocatalytic activity than that of a single semiconductor. The optimal percentage of doped g-C₃N₄ was 50%. Both photooxidation and photoreduction processes follow first order kinetics. In addition, the stability of the prepared photocatalyst in the photocatalytic process was also investigated. The enhanced photocatalytic performance could be due to the high separation efficiency of the photogenerated electron–holes pairs. The possible photocatalytic mechanism of g-C₃N₄/BiFeO₃ was proposed to guide the further improvement of their photocatalytic activity.     

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.     

Effect of morphology on the photocatalytic activity of g-C3N4 photocatalysts under visible-light irradiation

Graphite-like carbon nitride (g-C₃N₄) photocatalysts with different morphologies have been synthesized using melamine as a precursor using a template-free wet chemical method. The as-prepared g-C₃N₄ nanorods, g-C₃N₄ microcones and porous g-C₃N₄ quadruple prisms were characterized by XRD, FESEM, FT-IR and UV–vis absorption spectrophotometer. These nanostructured g-C₃N₄ photocatalysts show better photocatalytic activity than bulk g-C₃N₄ under visible light irradiation in view of degrading Rhodamine B (RhB). The porous g-C₃N₄ quadruple prisms show the highest photocatalytic efficiency. We deduce that the surface area of the catalysts and their adsorption ability of target molecules play important roles in improving the photocatalytic activity of the g-C₃N₄ photocatalysts.     

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.     

Enhanced visible-light-driven photocatalytic activity of B-doped BiVO4 synthesized using a corn stem template

Through a combination of template and sol-gel methods, B-doped Corn stem-BiVO₄ (CS-BiVO₄) photocatalysts were prepared using CS as a template. The synthesized materials were characterized by XPS, XRD, SEM, BET, and UV–vis DRS. The photocatalytic performances of the BiVO₄ samples were evaluated during the degradation of methyl orange under visible light irradiation. Compared to the undoped CS-BiVO₄ sample, the B-doped CS-BiVO₄ samples retained their monoclinic structure while exhibiting higher surface areas, greater V⁴⁺ densities and lower band gap energies. Among the prepared samples, 0.04B CS-BiVO₄ exhibited the best photocatalytic performance during the photodegradation of MO. The apparent difference in photocatalytic activity between 0.04B CS-BiVO₄ and 0.04B-BiVO₄ may be attributed to the cellular morphology from the CS and the higher specific surface areas.     

Template‐Free Preparation of Hollow Sb2S3 Microspheres as Supports for Ag Nanoparticles and Photocatalytic Properties of the Constructed Metal–Semiconductor Nanostructures

A simple and convenient Ostwald ripening route to the morphology‐ and phase‐controlled preparation of hollow Sb₂S₃ microspheres is developed. The hollow spheres are clusters of smaller microspheres if orange amorphous Sb₂S₃ colloid is used as the precursor, whereas, if starting from the yellow precursor, the products are regular hollow spheres. By selecting appropriate experimental conditions for ripening, the phase of the hollow Sb₂S₃ microspheres can be controlled. Amorphous and orthorhombic hollow spheres are prepared by ripening the colloidal precursors at ambient temperature and in an autoclave, respectively. The closed shell of hollow Sb₂S₃ spheres can be easily eroded by hydrochloric acid to form an open structure. By the in situ reduction of adsorbed Ag⁺ on the surface and interior of the hollow spheres, Ag nanoparticles are introduced into them, to form functional metal–semiconductor composites, the weight content of which is controlled by regulating the concentration of the Ag⁺ source and the adsorption time. The composite structures composed of Ag nanoparticles and hollow Sb₂S₃ spheres exhibit a remarkably enhanced absorption covering the UV and visible regions of the electromagnetic spectrum. A study of the photocatalytic properties of the composite structures demonstrates that exposure to both UV and visible light enables them to induce the rapid decomposition of 2‐chlorophenol. The degradation rate increases with a larger weight content of Ag in the composite structure.     

Visible light photocatalytic activity of reduced graphene oxide synergistically enhanced by successive inclusion of γ-Fe2O3, TiO2, and Ag nanoparticles

Novel magnetic nanocomposites are synthesized by loading reduced graphene oxide (r-GO) with three brands of nanoparticles consisting of titanium dioxide (TiO₂), gamma-iron(III) oxide (γ-Fe₂O₃), and silver (Ag) with varying amounts. The resulting Ag/TiO₂/γ-Fe₂O₃@r-GO demonstrates synergistically enhanced visible light photocatalytic activity, on degradation of wastewater׳s toxic crystal violet (CV). Specifically, it exhibits higher photoactivity than those of neat graphene oxide (GO), TiO₂@GO, γ-Fe₂O₃@GO, and TiO₂/γ-Fe₂O₃@GO, possibly because of effective separation of photogenerated carriers via strongly coupled Ag/γ-Fe₂O₃@r-GO cocatalyst and the enrichment of organic molecules on the graphene nanosheets. A higher photocatalytic efficiency is observed when 11.5 wt% Ag nanoparticles are incorporated in TiO₂/γ-Fe₂O₃@GO. After 3 successive cycles, the latter nanocomposite maintains 97% removal efficiency with excellent stability and easy recovery. Considering its facile preparation and high photocatalytic activity, it is hoped that this photocatalyst will find its application in various fields such as air purification and wastewater treatment. The structure and properties of Ag/TiO₂/γ-Fe₂O₃@r-GO are characterized by Fourier-transform infrared (FTIR), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), ultraviolet–visible spectrometry (UV–vis) and Raman spectroscopy techniques.     

Fabrication of heterojunction SnO2/BiVO4 composites having enhanced visible light photocatalystic activity

SnO₂/BiVO₄ heterojunction composite photocatalysts with various mole ratios have been prepared via a simple hydrothermal method. The structure, composition and optical properties of the SnO₂/BiVO₄ composites were determined by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) surface analysis, X-ray photoelectron spectroscopy (XPS) and UV–vis diffuse reflectance spectroscopy (UV–vis DRS). Photocatalytic activities of the composites were evaluated by studying the degradation of methylene blue (MB) solutions under simulated visible light irradiation (500 W halogen tungsten lamp). The 3:7 mol ratio SnO₂/BiVO₄ composite exhibited the highest photocatalytic performance, leading to 72% decompositon of MB within 120 min of irradiation.     

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.     

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.