Fabrication of ternary p-n heterostructures AgCl/Ag2O/NaTaO3 photocatalysts: Enhanced charge separation and photocatalytic properties under visible light irradiation

Ternary p-n heterostructures photocatalysts of AgCl/Ag₂O/NaTaO₃ were synthesized via a simple method and the crystal structure characterized by X-ray diffraction (XRD). The morphology of the photocatalysts were characterized by scanning electron microscopy and transmission electron microscopy. The composition of the photocatalysts was studied by X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscope. The photocatalytic activity of the AgCl/Ag₂O/NaTaO₃ photocatalysts was evaluated using the degradation of Rhodamine B. The AgCl/Ag₂O/NaTaO₃ photocatalysts showed higher visible light activity than the pure NaTaO₃ and Ag₂O/NaTaO₃ photocatalysts. Additionally, the photocatalytic mechanism was that the rapidly separation of photoinduced electrons and holes resulted the enhancement of photocatalytic activity.     

Preparation, characterization and photocatalytic activity of N-doped NaTaO3 nanocubes

The N-doped NaTaO₃ catalysts with cubic morphology had been successfully synthesized by one-step hydrothermal method, using Ta₂O₅ and NH₃·H₂O as the raw materials for the first time. The as-prepared samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and UV-vis diffuse reflectance spectra. The results showed that the synthesis parameters such as reaction temperature and reaction time played important roles in the formation of N-doped NaTaO₃ nanocubes. As observed by SEM images, when the reaction time reached 12 h, most of the products exhibited the square morphology with the size of 200-500 nm, which can be easily removed by filtration after photocatalytic reaction. The photocatalytic activity of N-doped NaTaO₃ was tested by Methylene Blue degradation process under ultraviolet and visible light irradiation, respectively. The results showed that both under the ultraviolet and visible light irradiation, N-doped NaTaO₃ displayed much higher photocatalytic activity than that of pure NaTaO₃. In addition, NaTaO_3-xN_x composites exhibited excellent stability in the visible-light photocatalytic process.     

Environmental remediation of aqueous nitrate solutions by photocatalytic reduction using Pd/NaTaO3 nanoparticles

NaTaO₃ nanoparticles were prepared by an ultrasonic method, and Pd was deposited onto the surface of NaTaO₃ via photoassisted deposition. The resulting samples were characterised by X-ray diffraction, ultraviolet and visible spectroscopy, photoluminescence emission spectroscopy, transmission electron microscopy, extended X-ray absorption fine structure analysis, and surface area measurements. The catalytic performance of the samples in the photoreduction of nitrate under visible light was determined. The UV–vis analysis indicated that a red shift occurred after Pd was loaded onto NaTaO₃. The maximum reduction efficiency was 100%, which was obtained using 0.6 wt% Pd/NaTaO₃ after a reaction time of 50 min.     

Visible light-induced photocatalytic activity of delafossite AgMO2 (M = Al, Ga, In) prepared via a hydrothermal method

Delafossite-structured oxides AgMO₂ (M = Al, Ga, In) were successfully synthesized using fluoro(ethylene-propylene) (FEP) pouch via a facile hydrothermal method. The obtained samples were characterized by X-ray diffraction (XRD), BET surface area measurement, UV–vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the as-prepared samples was evaluated by the degradation of rhodamine B (RhB) and methyl orange (MO) under visible light irradiation. All three samples showed photocatalytic activity for RhB and MO degradation under visible light irradiations and their photocatalytic activity followed the order of AgInO₂ > AgGaO₂ > AgAlO₂. The relative high photocatalytic activity of AgInO₂ can be attributed to its high quantity of the surface hydroxyl groups. The photocatalytic mechanism of AgInO₂ was proposed and its stability was also investigated.     

Nanosized Au Particles as an Efficient Cocatalyst for Photocatalytic Overall Water Splitting

The effect of the photodeposition of gold particles onto several photocatalysts on the photocatalytic activities was studied. The photocatalytic activities of K₄Nb₆O₁₇, Sr₂Nb₂O₇, KTaO₃ NaTaO₃, and NaTaO₃ doped with La for water splitting were improved when gold particles were deposited. The latter were nanoparticles, consistent with their surface plasmon absorption. The nanosized gold particle functioned as an efficient cocatalyst for photocatalytic water splitting by assisting H₂ evolution.     

Synthesis of a CoTiO3/BiOBr heterojunction composite with enhanced photocatalytic performance

A novel heterojunction CoTiO₃/BiOBr nanocomposite with enhanced photocatalytic performance was synthesized by a precipitation-deposition method. The samples were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV–vis spectrophotometry. Moreover, the photocatalytic activities were evaluated by decomposing the dye molecule Rhodamine B under visible light irradiation. The results showed that high photocatalytic performance can be achieved on the heterojunction photocatalysts, with the 0.15CoTiO₃/0.85BiOBr composite displaying the highest activity. The results of the study concluded that it was the introduction of CoTiO₃ into the catalyst that mainly enhanced the activity of the photocatalyst by promoting the separation of the electron-hole group on the interface between BiOBr and CoTiO₃.     

One-pot synthesis of CdS sensitized TiO2 decorated reduced graphene oxide nanosheets for the hydrolysis of ammonia-borane and the effective removal of organic pollutant from water

A hybrid material of reduced graphene oxide (RGO) sheets decorated with CdS-TiO₂ NPs was prepared through a facile one-pot hydrothermal method. The assembly of CdS-TiO₂ nanoparticles (NPs) on RGO sheets was in-situ produced. As-synthesized nanocomposites were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy disperse X-ray spectrum (EDS), fourier transform infrared spectroscopy (FTIR), and photoluminescence spectroscopy (PL). The obtained nanocomposites exhibited a good photocatalytic activity for the visible-light-induced decomposition of methylene blue (MB) dye and hydrolysis of ammonia borane. The results showed that by incorporation of CdS and TiO₂ NPs on graphene oxide sheets the photocatalytic efficiency was enhanced. The significant enhancement in the photocatalytic activity of CdS-TiO₂/RGO nanocomposites under visible light irradiation can be ascribed to the effect of CdS by acting as electron traps in TiO₂ band gap. Reduced graphene oxide worked as the adsorbent, electron acceptor and a photo-sensitizer to efficiently enhance the dye photo decomposition. Such nanocomposite photocatalyst might find potential application in a wide range of fields, including hydrogen energy generation, air purification, and wastewater treatment.     

Direct hydrolysis synthesis of BiOI flowerlike hierarchical structures and it's photocatalytic activity under simulated sunlight irradiation

BiOI flowerlike hierarchical structure was synthesized via direct hydrolysis from BiI₃ and characterized by powder X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) spectra, and transmission electron microscopy (TEM). As-synthesized BiOI showed higher photocatalytic activity in aqueous RhB photodegradation system than P25 TiO₂ under simulated sunlight irradiation. The trapping experiments of active species and electron spin resonance (ESR) experiment during the photocatalytic reaction showed that the photocatalytic degradation of organic pollutants in BiOI system proceeds through direct hole transfer and O₂⁻ rather than OH.     

Photocatalytic degradation of bisphenol A and dye by graphene-oxide/Ag3PO4 composite under visible light irradiation

A facile, one-step synthesis of graphene-oxide (GO)/Ag₃PO₄ was prepared. The as-prepared samples were characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS) and fourier transformed infrared (FT-IR) spectroscopy. The SEM image indicated that Ag₃PO₄ particles were mainly distributed on the surface of GO sheets uniformly. DRS analysis revealed that the samples had good visible light response. The photocatalytic activity of the composites was evaluated by the degradation of Rhodamine B (RhB) and Bisphenol A (BPA). The results indicated that the photocatalytic performance of GO/Ag₃PO₄ was greatly enhanced after introduction of GO. The photocatalytic degradation efficiency of colorless chemical pollutants (BPA) over GO/Ag₃PO₄ was higher than that of Ag₃PO₄, and the possible degradation path was proposed by liquid chromatography mass spectrometry (LC-MS) analysis. Moreover, the photocatalytic stability was discussed by XRD and FT-IR spectroscopy analysis. Based on the experimental results, a possible visible-light photocatalytic degradation mechanism was also discussed.     

Conduction properties of Ti-doped NaTaO3 at intermediate temperature

In this work, the ionic conductivity and charge carriers of acceptor-doped sodium tantalate (NaTaO₃) with perovskite structure were investigated at intermediate temperatures. The Ta-site of NaTaO₃ was doped with up to 20% titanium (Ti) with the conventional solid-state reaction method. After calcination at 900°C, samples nominally doped with 5, 10% Ti show X-ray diffraction (XRD) pattern of orthorhombic NaTaO₃ only, while peaks of Na₂Ti₃O₇ can be observed in those doped with 15, 20% Ti. The conductivity of undoped, 5% Ti and 10% Ti-doped NaTaO₃ at 300°C–700°C was measured with electrochemical impedance spectroscopy (EIS) under dry and wet O₂ atmospheres. Ti-doped NaTaO₃ samples have higher conductivity in the wet atmosphere than in the dry atmosphere, reaching 3 × 10⁻⁴ S/cm at 700°C (10% Ti-doped NaTaO₃), which confirms the hydration and proton conduction in Ti-doped NaTaO₃. Through the investigation on the dependence of conductivity on oxygen partial pressure, hole conduction in an oxidizing atmosphere, and electron conduction in reducing atmosphere can be verified. Na⁺ conduction was proven to be negligible with direct current polarization.     

Facile Preparation of LaFeO<Subscript>3</Subscript>/rGO Nanocomposites with Enhanced Visible Light Photocatalytic Activity

The present work demonstrates a facile route for preparing LaFeO₃/rGO nanocomposites comprising of metal oxide nanoparticles and graphene. Structural, morphology, optical and photocatalytic studies of the samples were characterized using powder X-ray diffraction (XRD), FT-IR, Raman, high resolution scanning electron microscopy (HRSEM), high resolution transmission electron microscope (HRTEM), atomic force microscopy (AFM), thermogravimetry (TGA), X-ray photoelectron spectroscopy, UV–visible and photocatalytic. LaFeO₃/rGO nanocomposites believed as an effective photocatalyst for the degradation of methyl orange (MO) dye under visible light irradiation. The inclusion of carbon enhances the light absorption of LaFeO₃, resulting in the enhanced photocatalytic activity of the nanocomposite. The degradation of MO dye under visible light source was completely achieved using LaFeO₃/rGO as a catalyst.     

Effect of carbon doping on WO3/TiO2 coupled oxide and its photocatalytic activity on diclofenac degradation

The improved photocatalyst carbon-doped WO₃/TiO₂ mixed oxide was synthesized in this study using the sol–gel method. The catalyst was thoroughly characterized by X-ray diffraction (XRD), diffuse reflectance UV–vis spectroscopy, N₂ adsorption desorption analysis, scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM/EDX), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The photocatalytic efficiency of the prepared materials was evaluated with respect to the degradation of sodium diclofenac (DCF) in a batch reactor irradiated under simulated solar light. The progress of the degradation process of the drug was evaluated by high-performance liquid chromatography (HPLC), whereas mineralization was monitored by total organic carbon analysis (TOC) and ion chromatography (IC). The results of the photocatalytic evaluation indicated that the modified catalyst with tungsten and carbon (TWC) exhibited higher photocatalytic activity than TiO₂ (T) and WO₃/TiO₂ (TW) in the degradation and mineralization of diclofenac (TWC>TW>T). Complete degradation of diclofenac occurred at 250 kJ m⁻² of accumulated energy, whereas 82.4% mineralization at 400 kJ m⁻² was achieved using the photocatalytic system WO₃/TiO₂-C. The improvement in the photocatalytic activity was attributed to the synergistic effect between carbon and WO₃ incorporated into the TiO₂ structure.     

Fabrication of CdS and CuWO4 modified TiO2 nanoparticles and its photocatalytic activity under visible light irradiation

CdS and CuWO₄ modified TiO₂ nanoparticles (CdS–CuWO₄-TiO₂) were prepared by the chemical impregnation method. The as-prepared nanoparticles were characterized using UV–visible-diffuse reflectance spectroscopy (UV–vis-DRS), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and B.E.T. surface area analysis techniques. The photocatalytic activity was evaluated based on the degradation of a dye (eosin-Y) and inactivation of a bacterium (Pseudomonas aeruginosa). The results revealed that CdS–CuWO₄-TiO₂ showed high photocatalytic activity over CdS-TiO₂, CuWO₄-TiO₂ and TiO₂. Moreover the reusability and stability of the photocatalyst for the degradation of eosin-Y was also studied.     

Ultrasound-assisted synthesis of high-efficiency Ag3PO4/CeO2 heterojunction photocatalyst

The Ag₃PO₄/CeO₂ heterojunction photocatalyst prepared by an ultrasound-assisted method exhibits an enhanced photocatalytic activity compared to pure Ag₃PO₄, CeO₂, and Ag₃PO₄/CeO₂ obtained without ultrasound action. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and ultraviolet–visible absorption spectroscopy (UV–vis), and the effects of ultrasound on the physicochemical properties and photocatalytic activity of Ag₃PO₄/CeO₂ are discussed. Results show that the ultrasound-assisted synthesis method significantly improves the photocatalytic ability. The mechanism about the improvement was discussed in details.     

Synthesis and photocatalytic activity of BiFeO3 and Bi/BiFeO3 cubic microcrystals

BiFeO₃ and Bi/BiFeO₃ cubic microcrystals were synthesized in this work. The phase, microstructure, optical and photo electrochemical properties, as well as the photocatalytic activities in photocatalytic hydrogen generation were investigated. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results demonstrate the successful synthesis of BiFeO₃ and Bi/BiFeO₃. The scanning electron microscope (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray (EDX) results give the evidence of cubic morphology and the deposition of metal Bi on the surface of BiFeO₃. The absorption spectra show that Bi/BiFeO₃ has longer absorption edge and stronger absorption capability to visible light. The photocurrent curves, emission spectra, and electrochemical impedance spectroscopy (EIS) spectra demonstrate that Bi/BiFeO₃ has higher efficiency of electron-hole separation and charge transfer, as well as longer lifetime of the charge carriers. These benefit to the enhancement of activity in photocatalytic hydrogen generation.     

Synthesis of perovskite KMgF3 with microemulsion for photocatalytic removal of various pollutants under visible light

The perovskite-type fluoride KMgF₃ photocatalysts were prepared by microemulsion and sol–gel methods. The as-prepared catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV–vis diffuse reflectance spectra (UV–vis DRS). Photocatalytic activity of the samples was evaluated in the degradation of rhodanmine B, methyl orange, phenol, and chlorophenol under visible light irradiation. Results demonstrated that photocatalytic activities of KMgF₃ synthesized by microemulsion method were superior to those of sol–gel method. It is considered that the excellent photocatalytic activities of KMgF₃ have a close relation to the crystal defects of fluorine vacancies.     

Surface doping of TiO2 powders via a gas–melt reaction using thermal plasma as an excitation source

Surface doping is an effective method to engineer and functionalize powder materials without modulating the internal crystal structure. This study proposed a facile technique for surface doping via a gas–melt reaction using thermal plasma as an excitation source. Doping molten titania (TiO₂) particles with La was preliminarily explored owing to the broad photocatalytic applications of TiO₂. Scanning electron microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy, transmission electron microscope, diffuse reflectance spectroscopy, photoluminescence spectroscopy and Fourier transform infrared spectroscopy were adopted to characterize the morphology, phase composite, chemical state, fine structure, and optical property of the doped TiO₂ powder, respectively. Results indicated that molten TiO₂ doped with La solidified into spherical particles under the effect of surface tension. No modification of the internal crystal structure was indicated in the XRD patterns, except that the diffraction peak of rutile TiO₂ (110) shifted to low angles after surface doping with La. The obtained TiO₂ powder exhibited sensitivity to sunlight and near-infrared light, and a La/Ti atomic ratio of 19.4% was achieved. The diffusivity D_i of La in molten TiO₂ ranged from 10⁻⁸ m²/s to 10⁻⁷ m²/s, as determined from the gas–melt reaction.     

Preparation of g-C3N4/MoS2 Composite Material and Its Visible Light Catalytic Performance

The g-C₃N₄ nanosheet was prepared by calcination method, the MoS₂ nanosheet was prepared by hydrothermal method. The g-C₃N₄/MoS₂ composites were prepared by ultrasonic composite in anhydrous ethanol. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet–visible spectroscopy, and photoluminescence techniques were used to characterize the materials. The photocatalytic degradation of Rhodamine B (Rh B) by g-C₃N₄/MoS₂ composites with different mass ratios was investigated under visible light. The results show that a small amount of MoS₂ combined with g-C₃N₄ can significantly improve photocatalytic activity. The g-C₃N₄/MoS₂ composite with a mass ratio of 1:8 has the highest photocatalytic activity, and the degradation rate of Rh B increases from 50 to 99.6%. The main reason is that MoS₂ and g-C₃N₄ have a matching band structure. The separation rate of photogenerated electron–hole pairs is enhanced. So the g-C₃N₄/MoS₂ composite can improve the photocatalytic activity. Through the active material capture experiment, it is found that the main active material in the photocatalytic reaction process is holes, followed by superoxide radicals.

     

Property Characterization and Photocatalytic Activity Evaluation of BiGdO3 Nanoparticles under Visible Light Irradiation

BiGdO₃ nanoparticles were prepared by a solid-state reaction method and applied in photocatalytic degradation of dyes in this study. BiGdO₃ was characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, Brunauer-Emmett-Teller, UV-Vis diffuse reflectance spectroscopy and transmission electron microscopy. The results showed that BiGdO₃ crystallized well with the fluorite-type structure, a face-centered cubic crystal system and a space group Fm3m 225. The lattice parameter of BiGdO₃ was 5.465 angstrom. The band gap of BiGdO₃ was estimated to be 2.25 eV. BiGdO₃ showed a strong optical absorption during the visible light region. Moreover, the photocatalytic activity of BiGdO₃ was evaluated by photocatalytic degradation of direct dyes in aqueous solution under visible light irradiation. BiGdO₃ demonstrated excellent photocatalytic activity in degrading Direct Orange 26 (DO-26) or Direct Red 23 (DR-23) under visible light irradiation. The photocatalytic degradation of DO-26 or DR-23 followed the first-order reaction kinetics, and the first-order rate constant was 0.0046 or 0.0023 min⁻¹ with BiGdO₃ as catalyst. The degradation intermediates of DO-26 were observed and the possible photocatalytic degradation pathway of DO-26 under visible light irradiation was provided. The effect of various operational parameters on the photocatalytic activity and the stability of BiGdO₃ particles were also discussed in detail. BiGdO₃/(visible light) photocatalysis system was confirmed to be suitable for textile industry wastewater treatment.     

Multi-walled carbon nanotubes modified Bi2S3 microspheres for enhanced photocatalytic decomposition efficiency

A series of multi-walled carbon nanotubes (MWCNTs)-loaded Bi₂S₃ nanomaterials composites (MWCNTs/Bi₂S₃) were prepared by hydrothermal method. The crystallization, morphology and other properties of the obtained MWCNTs/Bi₂S₃ composites were completely characterized by powder X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier transformed infrared spectroscopy (FT-IR), Thermal gravimetric analysis and differential thermal analysis (DTA-TG), N₂ adsorption-desorption isotherm, and UV–vis diffuse reflectance spectroscopy (DRS). In this work, the photocatalytic activity of the as-prepared materials was evaluated for methylene blue (MB) degradation under visible light irradiation. Comparing with others work, the composites showed excellent photocatalytic performance and maintained a good stability during the constant cycling experiment. Finally, a possible photocatalytic reaction mechanism on the MWCNTs/Bi₂S₃ composites was proposed.