Preparation,characterization and photocatalytic activity of Bi2O3–MgO composites

A series of Bi₂O₃–MgO composites were synthesized by solvent-thermal method. It was found that the Bi₂O₃–MgO composites perform much better than TiO₂ (P25), Bi₂O₃ and MgO in the photocatalytic degradation of rhodamine B (RhB) in the presence of HCl and under irradiation of visible light (λ > 400 nm). The effects of Bi/Mg molar ratio, crystallization temperature of Bi₂O₃–MgO and reaction conditions on photocatalytic activity were studied. The best performance was observed over the composite with Bi:Mg molar ratio equal to 2:1 that had been subject to crystallization at 120 °C for 20 h. In addition, the photocatalytic efficiency of the composite can be significantly enhanced by the presence of hydrochloric acid. The prepared samples were characterized by XRD and UV–vis DRS techniques. The relationships between the structure and photocatalytic performance of the as-prepared Bi₂O₃–MgO samples were also investigated.     

Preparation of Z-scheme Au-Ag2S/Bi2O3 composite by selective deposition method and its improved photocatalytic degradation and reduction activity

In this work, Z-scheme Ag₂S/Bi₂O₃ composites were fabricated through the precipitation of Ag₂S nanoplates on the surface of Bi₂O₃ microrods. Consequently, Au nanoparticles were selectively deposited on the Ag₂S nanoplates surface to obtain.Au-Ag₂S/Bi₂O₃ composites using near-infrared light photodeposition method. The characterization results indicate that the Ag₂S nanoplates were uniformly anchored on Bi₂O₃ surface, and Au nanoparticles were highly dispersed on the surface of Ag₂S nanoplate instead of Bi₂O₃. Acid orange 7 (AO7), Rhodamine B (RhB) and Cr(VI) were chosen as model reactant for the evaluation of photocatalytic degradation and reduction activity of the products under simulated sunlight irradiation. After the decoration of Ag₂S nanoplates, the photocatalytic activity of Ag₂S/Bi₂O₃ is much higher than that of bare Bi₂O₃, and the optimal catalytic efficiency is achieved by 12 %Ag₂S/Bi₂O₃ sample. More importantly, the photocatalytic activity of 12 %Ag₂S/Bi₂O₃ sample can be further enhanced by the selective decoration Au nanoparticles on the Ag₂S nanoplates. Among the ternary composites, 2Au-12 %Ag₂S/Bi₂O₃ sample with the Au content of 2% exhibits highest catalytic efficiency for 60 min (AO7: 96%; RhB: 56%; Cr(VI): 65%). The possible mechanism for the improvement of the photocatalytic activity of Bi₂O₃ by Ag₂S and Au decoration was proposed.     

Enhancement of Photocatalytic Activity of Bi2O3–BiOI Composite Nanosheets through Vacancy Engineering

Vacancy engineering is an effective strategy to enhance solar‐driven photocatalytic performance of semiconductors. It is highly desirable to improve the photocatalytic performance of composite nanomaterials by the introduction of vacancies, but the role of vacancies and the heterostructure in the photocatalytic process is elusive to the composite nanomaterials. Herein, the introduction of I vacancies can significantly enhance the photocatalytic activity of Bi₂O₃–BiOI composite nanosheets in a synergistic manner. The excellent photocatalytic performance of the Bi₂O₃–BiOI composites is attributed to the combination of Bi₂O₃ and BiOI and the existence of I vacancies in Bi₂O₃–BiOI composites. Specifically, density functional theory calculation shows that the existence of I vacancies would create a new electric states vacancy band below the conduction band of BiOI and thus can reduce the bandgap of BiOI nanosheets. This greatly facilitates the scavenging of the photogenerated electron on the surface of BiOI by Bi₂O₃, therefore, enhancing the overall photocatalytic activity of the composites. The enhanced photocatalytic efficiency is demonstrated by the degradation of tetracycline (TC), which reaches 96% after 180 min and by the high total organic carbon (TOC) removal (89% after 10 h visible light irradiation). This study provides a novel approach for the design of high‐performance composite catalysts.     

New Insight into Procedure of Interface Electron Transfer through Cascade System with Enhanced Photocatalytic Activity

Recombination of photogenerated electron–hole pairs is extremely limited in the practical application of photocatalysis toward solving the energy crisis and environmental pollution. A rational design of the cascade system (i.e., rGO/Bi₂WO₆/Au, and ternary composites) with highly efficient charge carrier separation is successfully constructed. As expected, the integrated system (rGO/Bi₂WO₆/Au) shows enhanced photocatalytic activity compared to bare Bi₂WO₆ and other binary composites, and it is proved in multiple electron transfer (MET) behavior, namely a cooperative electron transfer (ET) cascade effect. Simultaneously, UV–vis/scanning electrochemical microscopy is used to directly identify MET kinetic information through an in situ probe scanning technique, where the “fast” and “slow” heterogeneous ET rate constants (K_eff) of corresponding photocatalysts on the different interfaces are found, which further reveals that the MET behavior is the prime source for enhanced photocatalytic activity. This work not only offers a new insight to study catalytic performance during photocatalysis and electrocatalysis systems, but also opens up a new avenue to design highly efficient catalysts in photocatalytic CO₂ conversion to useful chemicals and photovoltaic devices.     

Novel CuO/Bi2WO6 heterojunction with enhanced visible light photoactivity

Novel CuO/Bi₂WO₆ composites with different CuO to Bi₂WO₆ weight ratios were synthesized via a facile two-step approach. The as-prepared CuO/Bi₂WO₆ composite photocatalyst was characterized by XRD, SEM, TEM, XPS, BET, UV–vis diffused reflectance, fluorescence spectrum and photocurrent measurements to investigate their physical, optical and photochemical properties. The photocatalytic activity of CuO/Bi₂WO₆ composites was evaluated by the photocatalytic degradation of RhB under simulated sunlight. The optimum photocatalytic activity of the CuO/Bi₂WO₆ composites for the degradation of RhB is almost 2 times higher than those of bare Bi₂WO₆ and CuO. The enhanced photocatalytic performance could be mainly attributed to the improved light response and effective separation of the photogenerated electrons and holes at the heterojunction interface of p-CuO and n-Bi₂WO₆.     

Fast preparation of Bi2GeO5 nanoflakes via a microwave-hydrothermal process and enhanced photocatalytic activity after loading with Ag nanoparticles

In this work, a facile and rapid microwave-assisted hydrothermal route has been developed to prepare Bi₂GeO₅ nanoflakes. Ag nanoparticles were subsequently deposited on the Bi₂GeO₅ nanoflakes by a photoreduction procedure. The phases and morphologies of the products were characterized by powder X-ray diffraction (XRD), X-ray photoelectron spectrum (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and UV–vis diffuse reflectance spectroscopy. Photocatalytic experiments indicate that such Ag/Bi₂GeO₅ nanocomposite possesses higher photocatalytic activity for RhB degradation under UV light irradiation in comparison to pure Bi₂GeO₅. The amount of Ag in the nanocomposite affects the catalytic activity, and 3 wt% Ag showed the highest photodegradation efficiency. Moreover, the catalyst remains active after four consecutive tests. The present study provides a new strategy to design composite materials with enhanced photocatalytic activity.     

Synthesis of porous Fe3O4/g-C3N4 nanospheres as highly efficient and recyclable photocatalysts

A facile approach for the preparation of Fe₃O₄/g-C₃N₄ nanospheres with good porous structure has been demonstrated by a hydrothermal method. The as-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet–visible light (UV–vis) absorbance spectra and X-ray photoelectron spectroscopy (XPS). The photocatalytic decomposition of methyl orange (MO) by the as-prepared samples was carried out under visible light irradiation. The reusability and magnetic properties were also investigated. The results revealed that the porous Fe₃O₄/g-C₃N₄ nanospheres showed considerable photocatalytic activity, and exhibited excellent reusability and magnetic properties with almost no change after five runs.     

Preparation of bismuth oxyiodides and oxides and their photooxidation characteristic under visible/UV light irradiation

Bismuth oxyiodides and oxides were prepared by a solution combination with thermal treatment method. The prepared samples were characterized by X-ray diffraction, thermogravimetry, scanning electron microscopy, transmission electron microscopy, and UV-vis diffuse reflectance spectra, and Brunauer-Emmett-Teller surface areas. The photooxidation activity of the samples was evaluated by photocatalytic decolorization of acid orange II under both visible light (λ > 420 nm) and UV light (λ = 365 nm) irradiation. Results show that a series of changes in the compounds take place during the course of calcination, described as: BiOI → Bi₅O₇I → α-Bi₂O₃. Under visible light irradiation, the photocatalytic activities follow the order: BiOI > Bi₅O₇I > Bi₅O₇I/Bi₂O₃ mixture > Bi₂O₃, which is mainly attributed to the different absorption ability to visible light due to the different band gap energy; the activities are in the order: BiOI < Bi₂O₃ < Bi₅O₇I/Bi₂O₃ mixture < Bi₅O₇I under UV light irradiation, which is mainly caused by the different oxidability.     

Preparation of grape-like Bi2O3/Ti photoanode and its visible light activity

Compact and grape-like bismuth oxide (Bi₂O₃) coated titania (Ti) anode was prepared by oxalic acid (H₂C₂O₄) etching, electrodeposition and calcination in order to explore its photoelectrocatalytic activities. The Bi₂O₃ coating was demonstrated to be full of pores, and a good combination between Bi₂O₃ layer and honeycomb-like Ti substrate was observed by scanning electron microscopy. The characteristic morphology of Bi₂O₃ coating indicated that the electrode is stable during degradation. The Bi₂O₃/Ti electrode was used in oxidative degradation of Acid Orange 7 by electrolysis, photocatalytic oxidation and photoelectrocatalytic oxidation processes. The pseudo-first order kinetics parameter (K_app) of photoelectrocatalytic process was 1.15 times of the sum of electrolysis and photocatalytic oxidation under visible light irradiation at 420 nm. The results indicated that the synergy of electrolysis and photocatalysis lead to an excellent photoelectrocatalytic property of the Bi₂O₃/Ti electrode.     

Synthesis of ZnOAl2O3 core-shell nanocomposite materials by fast and facile microwave irradiation method and investigation of their optical properties

Alumina (Al₂O₃) coated ZnO core-shell structures were synthesized by a novel, fast, and facile route utilizing microwave (MW) irradiation to control photocatalytic property of ZnO. The phase analysis and the core–shell structure development were corroborated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), X-ray fluorescence (XRF), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray (EDX) analysis and Fourier transform infrared spectroscopy (FT-IR). The XPS results affirmed that elements on the coated surface were Al and O. Zeta potential analysis predicted the presence of Al₂O₃ layer on ZnO due to almost similar zeta potential curve for pure Al₂O₃ and Al₂O₃ coated ZnO nanoparticles. There was no significant change in band gap energy of ZnO after amorphous Al₂O₃ coating as obtained from derived data of the reflectance spectra but gradual decreasing of reflectance in the visible range, measured by UV–vis spectroscopy, of the prepared core-shell nanoparticle may be due to the coating of amorphous Al₂O₃ on ZnO. The photocatalytic efficiency of ZnO was reduced after amorphous Al₂O₃ layer as confirmed by the photodegradation of methylene blue under UV irradiation.     

Ternary novel TiO2/MgBi2O6/Bi2O3 nanocomposites with n-n-p heterojunctions: Impressive visible-light-triggered photocatalytic degradation of tetracycline

A series of novel ternary TiO₂/MgBi₂O₆/Bi₂O₃ nanocomposites were synthesized by a facile hydrothermal method. The ternary nanocomposites were characterized by XRD, FESEM, HRTEM, EDX, PL, EIS, Photocurrent, UV–vis DRS, BET, XPS, Raman, and FT-IR analyses. The photocatalytic performance of TiO₂ for the degradation of tetracycline antibiotic after combining with MgBi₂O₆/Bi₂O₃ was significantly improved, which is 46.1 and 18.5 times higher than pristine TiO₂ and MgBi₂O₆/Bi₂O₃ photocatalysts, respectively. Furthermore, the ternary photocatalyst efficiently degraded MO, RhB, and MB dye pollutants, which is 22.5, 30.4, and 30.0 as high as TiO₂ and 11.2, 14.4, and 17.8 folds larger than MgBi₂O₆/Bi₂O₃ photocatalysts, respectively. The photoluminescence and electrochemical analyses confirmed promoted separation and facile transfer of the charges thanks to construction of n-n-p heterojunctions among n-TiO₂, n-MgBi₂O₆, and p-Bi₂O₃ components and more production of charge carriers due to integration of small band gap MgBi₂O₆ and Bi₂O₃ components with wide band gap TiO₂.     

Synthesis,characterisation, and effect of pH on degradation of dyes of copper-doped TiO2

Copper-doped TiO₂ nanoparticles were synthesised using an ultrasonic-assisted sol–gel method with various doping concentrations from 0 to 2.5 at.%. The samples were characterised by X-ray diffraction, UV–vis diffuse reflectance spectroscopy (UV–vis), transmission electron microscopy (TEM), Brunauer–Emmett–Teller surface area determination, and zeta potential. The presence of copper in TiO₂ crystal structure was revealed by UV–vis spectra, and the TEM analysis showed that particles are mainly spherical around the size range of 15–20 nm. In addition, doping copper into TiO₂ lattice caused a decrease in the surface area due to the aggregation of nanoparticles and a shift of isoelectric point towards lower pH when the dopant concentration increased. The photocatalytic reactivity of these materials was evaluated by the degradation of methylene blue and methyl orange under the UV light. The effect of the initial solution pH on the adsorption capacity and the photocatalytic behaviour of the Cu-doped TiO₂ in the decolourisation of these dyes were also studied.     

Construction of interface electric field by electrostatic self-assembly: enhancing the photocatalytic performance of 2D/2D Bi12O17Cl2/g-C3N4 nanosheets

Bi₁₂O₁₇Cl₂ is an ideal photocatalytic material with an appropriate band gap and visible light absorption. However, the performance of a single Bi₁₂O₁₇Cl₂ photocatalytic material is still limited by the low separation rate of photogenerated electrons and holes. In this paper, the 2D Bi₁₂O₁₇Cl₂ and 2D g-C₃N₄ materials were prepared, and fabricated 2D/2D Bi₁₂O₁₇Cl₂/g-C₃N₄ nanosheets by electrostatic self-assembly using the different surface electrical properties of the two materials. The formation of an electric interface field between Bi₁₂O₁₇Cl₂ and g-C₃N₄ nanosheets and the matched energy band structure of the two materials can effectively promote the separation of electrons and holes and reduce recombination to improve the photocatalytic performance of semiconductor materials. The Bi₁₂O₁₇Cl₂/g-C₃N₄ with appropriate composite ratio has good degradation activity of Rhodamine-B (RhB) organic pollutants. The composite material can degrade nearly 100% of 10 ppm RhB in the reaction time of 2 h under neutral conditions and completely degrade rhodamine B in 90 min under acidic conditions.

     

Anchoring Bi4O5I2 and AgI nanoparticles over g-C3N4 nanosheets: Impressive visible-light-induced photocatalysts in elimination of hazardous contaminates by a cascade mechanism

In this research, Bi₄O₅I₂ and AgI nanoparticles were anchored over g-C₃N₄ nanosheets (denoted as NGCN/Bi₄O₅I₂/AgI) to preparation highly impressive visible-light-driven samples. The synthesized nanocomposites were investigated by X-ray diffraction (XRD), Fourier transform-infrared (FT-IR), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), UV–vis diffuse reflectance spectroscopy (DRS), energy dispersive analysis of X-rays (EDX), electrochemical impedance spectroscopy (EIS), photocurrent density, Brunauer-Emmett-Teller (BET), and photoluminescence (PL) analyses. Among the ternary photocatalysts, the NGCN/Bi₄O₅I₂/AgI (20%) photocatalyst illustrated the highest photoactivity in degradation of rhodamine B (RhB), which was approximately 58.4, 15.2, and 12.8 times higher than the GCN, NGCN, and NGCN/Bi₄O₅I₂ (20%) samples, respectively. Furthermore, the O₂⁻ was discovered as the main species in the respective system by the quenching tests. Also, by studying the electrochemical properties, a cascade photocatalytic mechanism was suggested based on the energy bands to describe the enhanced charge carriers migration and separation, which caused impressive photocatalytic performances in degradations of four hazardous contaminants. This study highlights the rational anchoring of Bi₄O₅I₂ and AgI nanoparticles over NGCN to prepare highly efficient photocatalysts for wastewater remediation.     

Green gelatin-assisted: Synthesis of Co3O4NPs@rGO nanopowder for highly efficient magnetically separable methylene orange dye degradation

GO and Co(NO₃)₂ were respectively used as rGO and Co₃O₄ precursors for preparing magnetically separable Co₃O₄NPs attached Co₃O₄NPs@rGO nanocomposites by a straightforward sol–gel technique. To characterize the nanocomposite materials, FESEM, EDX, elemental mapping, XRD, FTIR, Raman spectroscopy, UV–vis, VSM and BET were employed. When exposed to UV rays, the nanocomposite showed extraordinary photocatalytic degradation of MO dye. According to the measurements of photocatalytic activity, the highly efficient photocatalytic efficiency of the nanocomposite could be attributed to preventing electron-hole recombination by highly effective electron transfer between rGO and semiconductor NPs. The nanocomposite succeeded in the efficient degradation of MO dye, even after five photocatalytic cycles.     

Synthesis of efficient composite photocatalysts from solid solution Bi3O4Cl0.5Br0.5 and Ag-AgI/AgCl for decomposition the oil field pollutants of phenol and acrylamide

Composite photocatalysts typically display enhanced photocatalytic performance. In this paper, the polycomplex Ag-AgI/AgCl/Bi₃O₄Cl_0.5Br_0.5 was prepared by a photo-reduction approach. The identity of the composite was confirmed by several characterization methods including, the structure of sample was confirmed by X-ray diffraction and high-resolution transmission electron microscopy, the morphology and element information of sample was investigated through scanning electron microscopy and SEM-mapping, the surface valence states of sample was confirmed by the X-ray photoelectron spectroscopy. Oilfield produced wastewater was chosen as the target in this study due to the toxicity and persistent nature of its components (pollutants such as, phenol and acrylamide). Ag-AgI/AgCl/Bi₃O₄Cl_0.5Br_0.5 exhibited superior photocatalytic activity than either Bi₃O₄Cl_0.5Br_0.5 or Ag-AgI/AgCl, after irradiation with visible and UV light for 5 h. Under visible irradiation 5 h, the Ag-AgI/AgCl/Bi₃O₄Cl_0.5Br_0.5 exhibited excellent photocatalytic activity for degradation phenol of 57.7%, which was about 4 times and 1.5 times higher than Bi₃O₄Cl_0.5Br_0.5 and Ag-AgI/AgCl, respectively. Additionally, the Ag-AgI/AgCl/Bi₃O₄Cl_0.5Br_0.5 displayed photodegradation rates of 41.0% for acrylamide after 5 h UV–visible light irradiation, which was approximately 3.1 times and 1.6 times when treated with Bi₃O₄Cl_0.5Br_0.5 and Ag-AgI/AgCl, respectively. The remarkable photocatalytic activity of AgI/AgCl/Bi₃O₄Cl_0.5Br_0.5 was further confirmed by the PL spectra, photocurrent response and electrochemical impedance. Furthermore, the stability and reusability were investigated by recycling experiments. In combination with the trapping experiments, the surface Plasmon resonance (SPR) of Ag-AgI/AgCl/Bi₃O₄Cl_0.5Br_0.5 reveals the catalyst has an ultra-fast charge-separation efficiency and possesses a high redox ability. In this this paper, a new approach for the synthesis of quaternary composites is described and these photocatalysts have been shown to efficiently degrade of oil field pollutants.     

Synthesis of carnation flower-like Bi2O2CO3 photocatalyst and its promising application for photoreduction of Cr(VI)

In this study, we have synthesized high-quality carnation flower-like Bi₂O₂CO₃ hierarchical architectures via a hydrothermal route. The as-synthesized Bi₂O₂CO₃ photocatalyst was systematically characterized and analyzed by various techniques. Its photocatalytic activity was investigated by simulated-sunlight driving photoreduction of Cr(VI), revealing that it exhibits excellent photocatalytic removal of Cr(VI). The effects of various factors (H₂SO₄, NaOH, Cr(VI) concentration, catalyst dosage) on the photoreduction efficiency and involved mechanism were systematically investigated and discussed. In addition, we have also systematically examined the effects of various parameters (H₂SO₄ concentration, 1,5-diphenylcarbazide (DPC) concentration, Cr(VI) concentration, reaction time t and reaction temperature T) on the absorbance of the Cr(VI) solution, with the aim of correctly determining the Cr(VI) concentration according to UV–vis absorption measurements using DPC as the chromogenic agent.     

Nest-like structures of Sr doped Bi2WO6: Synthesis and enhanced photocatalytic properties

A series of Sr-doped Bi₂WO₆ with three-dimensional (3D) nest-like structures were synthesized through simple hydrothermal route and characterized by XRD, FESEM, TEM, XPS, UV-vis DRS, etc. Morphology observation revealed that the as-synthesized Bi₂WO₆ were self-assembled three-dimensional (3D) nest-like structures, which were constructed from nanoplates. UV-vis diffuse reflectance spectra indicated that the samples had absorption in both UV and visible light areas. Their photocatalytic activities were evaluated by photodegradation of rhodamine B (RhB) under UV and visible light irradiation (λ > 420 nm). The photocatalytic properties were enhanced after Sr doping. Samples subsequently thermal treated at 500 °C showed higher photocatalytic activities. The reasons for the differences in the photocatalytic activities of these nest-like Bi₂WO₆ microstructures were further investigated.     

Synthesis of polyaniline-modified Fe3O4/SiO2/TiO2 composite microspheres and their photocatalytic application

Polyaniline-modified Fe₃O₄/SiO₂/TiO₂ composite microspheres have been successfully synthesized by sol–gel reactions on Fe₃O₄ microspheres followed by the chemical oxidative polymerization of aniline. The synthesized multilayer-structured composites were characterized by TEM, XRD, TGA, UV–vis diffuse reflectance spectra and magnetometer. The photocatalytic activity was evaluated by the photodegradation of methylene blue under visible light. The effect of polyaniline (PANI) amounts on the photocatalytic activity was investigated. The photocatalytic activity results show that the Fe₃O₄/SiO₂/TiO₂ composites with about 2.4 wt.%–4.1 wt.% PANI could show higher photocatalytic efficiency than that of Fe₃O₄/SiO₂/TiO₂. Furthermore, the PANI-Fe₃O₄/SiO₂/TiO₂ photocatalyst could be easily recovered using a magnet.     

Enhanced visible-light-induced photocatalytic disinfection of Escherichia coli by ternary Bi2WO6/TiO2/reduced graphene oxide composite materials: Insight into the underlying mechanism

Composites coupling different semiconductors have attracted increasing attention for photocatalytic application owing to low visible-light absorption capability and weak photocatalytic activity of the single-component system. In this study, Bi₂WO₆/TiO₂/rGO ternary composites, successfully synthesized by a facile hydrothermal method, were manifested as an outstanding visible-light-response photocatalyst for the disinfection towards E. coli. X-ray diffraction, Fourier-transform infrared, and X-ray photoelectron spectroscopy demonstrated that GO coupled in the composites was efficiently reduced to rGO during the hydrothermal process, which was greatly beneficial for enhancing light harvest, promoting charge separation, and improving photocatalytic disinfection activity. UV–vis diffuse reflectance spectra, photoluminescence and time-resolved photoluminescence, photocurrent measurements, and ultraviolet photoelectron spectroscopy clearly showed that Bi₂WO₆/TiO₂/rGO composites had narrower band gap energy and much better suppression capability of photoinduced electron-hole recombination in comparison to the pure Bi₂WO₆ and TiO₂, and Bi₂WO₆/TiO₂. The radical trapping results revealed that the photogenerated holes (h⁺) were the leading active species responsible for the effective inactivation of E. coli under visible-light irradiation. Hence, the underlying mechanism for the enhanced photocatalytic disinfection performance of Bi₂WO₆/TiO₂/rGO composites was proposed. This study provides new insight into the design and development of composite materials with enhanced photocatalytic activity, which can be an inspiring alternative for environmental application.