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.     

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.     

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.     

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.     

Significant improvement of photocatalytic activity of porous graphitic-carbon nitride/bismuth oxybromide microspheres synthesized in an ionic liquid by microwave-assisted processing

Graphitic-carbon nitride/bismuth oxybromide (g-C₃N₄/BiOBr) porous microspheres have been successfully synthesized by a one-pot ethylene glycol (EG) assisted microwave process in the presence of 1-hexadecyl-3-methylimidazolium bromine ([C₁₆mim]Br). The as-prepared samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and UV–vis diffuse reflectance spectroscopy (DRS). During the reaction process, the ionic liquid acts not only as solvent and Br source but also as a template for fabrication of g-C₃N₄/BiOBr porous microspheres. In addition, the photocatalytic activity of the g-C₃N₄/BiOBr is evaluated by degrading Rhodamine B (RhB) and ciprofloxacin (CIP) under visible-light irradiation. It is found that 12.75 wt% g-C₃N₄/BiOBr microspheres exhibit higher photocatalytic activity than that of the as-prepared BiOBr. A possible photocatalytic mechanism based on the relative band positions of g-C₃N₄/BiOBr has been proposed.     

Preparation and characterization of BiFeO3@Ce-doped TiO2 core-shell structured nanocomposites

BiFeO₃@TiO₂–Ce composite nanoparticles with a BiFeO₃ core and a Ce-doped TiO₂ shell structure were fabricated via a sol–gel method. The nanoparticles were characterized by scanning electron microscopy with energy dispersive spectroscopy, X-ray diffraction, transmission electron microscopy and UV–vis diffuse reflectance spectroscopy. The results reveal that core-shell structured BiFeO₃@TiO₂–Ce nanoparticles show a significant redshift in the UV–vis absorption spectra in comparison with both Ce-TiO₂ and BiFeO₃@TiO₂ nanoparticles. The photocatalytic activities of the samples were tested in the degradation of methyl orange in aqueous solutions under visible light and UV light irradiations. The core-shell structured BiFeO₃@TiO₂–Ce sample exhibits higher photocatalytic activity, which is attributed to the synergistic effects of BiFeO₃ and cerium.     

Enhanced photodegradation of Rhodamine B under visible light by N-K2Ti4O9/MIL-101 composite

N-K₂Ti₄O₉/MIL-101 composites were successfully synthesized by a facile hydrothermal method, and were characterized by powder X-ray diffraction, UV–vis diffuse reflectance spectroscopy, the valence band X-ray photoelectron spectroscopy, field emission transmission electron microscopy, photoluminescence emission spectra, N₂ adsorption–desorption and thermogravimetric analysis. Photocatalytic activities of N-K₂Ti₄O₉, MIL-101 and the composites were investigated by the degradation of Rhodamine B (RhB) under visible light irradiation. The results show that the composites exhibit higher photocatalytic activity as compared with the pure materials. The synergistically enhanced photocatalytic activity of the composites is due to big adsorption capacity of MIL-101 and high separation efficiency of photogenerated electron-hole pairs through interfaces between N-K₂Ti₄O₉ and MIL-101.     

Near-Field Drives Long-Lived Shallow Trapping of Polymeric C3N4 for Efficient Photocatalytic Hydrogen Evolution

Undesired photoelectronic dormancy through active species decay is adverse to photoactivity enhancement. An insufficient extrinsic driving force leads to ultrafast deep charge trapping and photoactive species depopulation in carbon nitride (g-C₃N₄). Excitation of shallow trapping in g-C₃N₄ with long-lived excited states opens up the possibility of pursuing high-efficiency photocatalysis. Herein, a near-field-assisted model is constructed consisting of an In₂O₃-cube/g-C₃N₄ heterojunction associated with ultrafast photodynamic coupling. This In₂O₃-cube-induced near-field assistance system provides catalytic “hot areas”, efficiently enhances the lifetimes of excited states and shallow trapping in g-C₃N₄ and this favors an increased active species density. Optical simulations combined with time-resolved transient absorption spectroscopy shows there is a built-in charge transfer and the active species lifetimes are longer in the In₂O₃-cube/g-C₃N₄ hybrid. Besides these properties, the estimated overpotential and interfacial kinetics of the In₂O₃-cube/g-C₃N₄ hybrid co-promotes the liquid phase reaction and also helps in boosting the photocatalytic performance. The photocatalytic results exhibit a tremendous improvement (34-fold) for visible-light-driven hydrogen production. Near-field-assisted long-lived active species and the influences of trap states is a novel finding for enhancing (g-C₃N₄)-based photocatalytic performance.     

Microwave hydrothermal synthesis of BiFeO3: Impact of different surfactants on the morphology and photocatalytic properties

Pure-phase BiFeO₃ catalysts with different morphologies were synthesized by microwave hydrothermal treatment at 200 °C with and without surfactant. The as-prepared catalysts were characterized by X-ray diffraction, scanning electron microscopy, and diffuse reflectance spectroscopy. Their photocatalytic properties were also explored. Ball-like (no surfactant), flower-like (EDTA), and honeycomb-like (polyvinylpyrrolidone) BiFeO₃ catalysts were obtained. Surfactant addition decreased the bandgap of BiFeO₃ catalysts. The specific surface area for ball-like, flower-like, and honeycomb-like BiFeO₃ catalysts was 7.48, 3.48, and 12.38 m²/g, and the rate of rhodamine B degradation under UV light was 49%, 61%, and 87%, respectively, at 4 h.     

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.     

Modulation of Charge Trapping by Island-like Single-Atom Cobalt Catalyst for Enhanced Photo-Fenton-Like reaction

Composites-based photocatalysis relies on the interfacial electron transfer between the metallic cocatalyst and photosensitizer (the semiconductor) to realize spatial separation of charge carriers. Herein, an ingenious heterojunction between Co-CN single atom catalysts (SACs) and g-C₃N₄ is constructed for heterogeneous photo-Fenton-like reactions. Driven by built-in electric field across the heterojunctions, the separation and migration of the photogenerated charge carriers is promoted, leading to the fast electron transfer from the g-C₃N₄ to the Co-CN SACs. Theoretical calculations and transient absorption spectroscopy reveal the modulated charge transfer and trapping in the SA-Co-CN/g-C₃N₄ heterostructure, resulting in the remarkably enhanced generation of reactive oxygen species via peroxymonosulfate activation under light irradiation. This ingenious SA-Co-CN/g-C₃N₄/PMS/vis system is efficient for the oxidation of various antibiotics with high removal efficiency (>98%), a wide operating pH range (pH 3–11) and excellent stability in long-term operation. This study provides a new tactic for rational design of SACs-based heterojunctions to bridge photocatalysis and heterogeneous catalysis, attaining superior photoredox activity via interfacial coupling.     

Dual Functions of CO2 Molecular Activation and 4f Levels as Electron Transport Bridge in Dysprosium Single Atom Composite Photocatalysts with Enhanced Visible-Light Photoactivities

The effect of rare earth (RE) single atoms on photocatalytic activity is very complex due to its special electronic configuration, which leads to few reports on the RE single atoms. Here, Dy³⁺ single atom composite photocatalysts are successfully constructed based on both the special role of Dy³⁺ and the special advantages of CdS/g-C₃N₄ heterojunction in the field of photocatalysis. The results show that an efficient way of electron transfer is provided to promote charge separation, and the dual functions of CO₂ molecular activation of rare-earth single atom and 4f levels as electron transport bridge are fully exploited. It is exciting that under visible-light irradiation, the catalytic performance of CdS:Dy³⁺/g-C₃N₄ is ≈ 6.9 times higher than that of pure g-C₃N₄. The catalytic performance of CdS:Dy³⁺ and CdS:Dy³⁺/g-C₃N₄ are ≈ 7 and ≈ 13.7 times higher than those of pure CdS, respectively. Besides, not all RE ions are suitable for charge transfer bridges, which is not only related to the 4f levels of RE ions but also related to the bandgap structure of CdS and g-C₃N₄. The pattern of combining single-atom catalysis and heterojunction opens up new methods for enhancing photocatalytic activity.     

Highly Visible Light Activity of Nitrogen Doped TiO<Subscript>2</Subscript> Prepared by Sol–Gel Approach

A simple approach was explored to prepare N-doped anatase TiO₂ nanoparticles (N-TiO₂ NPs) from titanium chloride (TiCl₄) and ammonia (NH₃) via sol–gel method. The effects of important process parameters such as calcination temperatures, NH₃/TiCl₄ molar ratio (R _N) on crystallite size, structure, phase transformation, and photocatalytic activity of titanium dioxide (TiO₂) were thoroughly investigated. The as-prepared samples were characterized by ultraviolet–visible spectroscopy, x-ray diffraction, transmission electron microscopy, energy dispersive x-ray spectroscopy, and x-ray photoelectron spectroscopy. The photocatalytic activity of the samples was evaluated upon the degradation of methylene blue aqueous solution under visible-light irradiation. The results demonstrated that both calcination temperatures and NH₃/TiCl₄ molar ratios had significant impacts on the formation of crystallite nanostructures, physicochemical, as well as catalytic properties of the obtained TiO₂. Under the studied conditions, calcination temperature of 600°C and NH₃/TiCl₄ molar ratio of 4.2 produced N-TiO₂ with the best crystallinity and photocatalytic activity. The high visible light activity of the N-TiO₂ nanomaterials was ascribed to the interstitial nitrogen atoms within TiO₂ lattice units. These findings could provide a practical pathway capable of large-scale production of a visible light-active N-TiO₂ photocatalyst.     

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.     

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.     

Visible light assisted photocatalytic activity of TiO2–metal vanadate (M=Sr,Ag and Cd) nanocomposites

TiO₂–metal vanadate nanocomposites (TiO₂–MV) were synthesized by the precipitation method and successfully characterized using UV–visible diffuse reflectance spectroscopy (UV–vis-DRS), powder X-ray diffraction (XRD), photoluminescence (PL) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX) techniques. The photocatalytic activity of TiO₂–MV was investigated for the degradation of fast green (FG) dye under visible light irradiation. The photocatalytic activity of TiO₂–silver vanadate [TiO₂–Ag₃VO₄] was found to be much higher than that of TiO₂–cadmium vanadate [TiO₂–CdV₂O₆], TiO₂–strontium vanadate [TiO₂–Sr₃(VO₄)₂] and TiO₂. The effect of operational parameters such as pH, photocatalyst concentration and initial dye concentration on the photodegradation of FG was examined in detail. The mineralization of FG was confirmed by chemical oxygen demand (COD) and total organic carbon (TOC) measurements. Moreover, TiO₂–Ag₃VO₄ was found to be a reusable photocatalyst.     

Visible light active TiO2–ZnO composite films by cerium and fluorine codoping for photocatalytic decontamination

The visible light active Ce/F codoped TiO₂–ZnO composite films with a bad gap of 1.82 eV were successfully prepared though a simple sol–gel method. Experimental results indicated that the composite films showed excellent photocatalytic performance towards photocatalytic oxidation of organic pollutants including formaldehyde, acid naphthol red (ANR) and methyl green (MG). The catalysts were characterized by photoluminescence (PL) spectra, UV–vis diffraction reflectance absorption spectra (DRS), X-ray diffraction (XRD), differential thermal analysis-thermogravimetry (DTA-TG), field emission scanning electron microscopy (FE-SEM) equipped with energy-dispersive spectroscopy (EDS), and N₂ adsorption/desorption isotherms. The DRS and PL spectra results showed that multi-modification not only induced strong visible light absorption but also reduced the recombination rate of electron–hole pairs. The DTA-TG and XRD results indicated that the crystal type of the TiO₂-based catalyst was mostly stabilized in anatase. The FE-SEM and BET surface area results revealed that the nanocrystalline Ce/F codoped TiO₂–ZnO composite samples with the larger specific surface area were composed of smaller nanoparticles compared to pure TiO₂. The mechanism of the enhanced photocatalytic activity was discussed in this study.     

A unique and facile preparation of lanthanum ferrite nanoparticles in emulsion nanoreactors: Morphology,structure, and efficient photocatalysis

Lanthanum ferrite nanoparticles (LaFeO₃ NPs) with light absorption properties in the visible region were successfully synthesized in CTAB (cetyltrimethyl ammonium bromide) emulsion nanoreactors at room temperature. The morphology, size, structure, elemental composition, and optical properties of these particles were characterized by field emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), X-ray fluorescence (XRF), and ultraviolet–visible absorption (UV–Vis) spectroscopy. Through this method, highly crystalline and well-dispersed perovskite LaFeO₃ NPs with a phase-pure were successfully obtained. The band gap energy (E_g) of the LaFeO₃ NPs was calculated by UV-Vis spectroscopy at the wavelength of about 517 nm and is observed to have a value of 2.43 eV. The photocatalytic activities of LaFeO₃ NPs were evaluated by the degradation of toluidine blue O (TBO, used as a probe) dye under visible light irradiation, which exhibits a high photocatalytic TBO dye degradation activity as compared to the commercial P-25 titania powder. This phenomenon is due to smaller band gap energy and changing from bulk to nanostructure. The higher photocatalytic activity is also related to the photo absorption.     

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.