Solvothermal syntheses of Bi and Zn co-doped TiO2 with enhanced electron-hole separation and efficient photodegradation of gaseous toluene under visible-light

Highly Efficient Photocatalytic Degradation of Imidacloprid Based on Iron Metal-Organic Frameworks of Mesoporous NH2-MIL-88b/Graphite Carbon Nitride Nanocomposites by Visible Light Driven in Aqueous Media

Pesticides that protect crops from insects and other pests are some of the main causes of water pollution. Imidacloprid (IMC) is the most widely used insecticide in the world and should be removed from the environment. This work aims to prepare mesoporous nanocomposites to increase the photodegradation efficiency of IMC. To improve the surface properties and enhance the photocatalytic activity, mesoporous nanocomposites with different weight ratios of graphite carbon nitride (CN = 125, 250, and 500 mg) were prepared by the solvothermal method. Mesoporous NH2-MIL-88b(Fe)/graphite carbon nitride (CN = 250 mg, NH2-MCN-2) nanocomposites showed the best photocatalytic performance. To save the time and cost of the experiments, central composite design (CCD) and response surface methodology (RSM) were used and the results were obtained as the initial concentration of IMC (20 mg L-1), amount of photocatalyst (0.76 g L-1), pH = 5, and degradation time ∼46 min. The maximum photocatalytic degradation efficiency estimated by the model was obtained at 96.31%, which is very close to the actual value of 95.47%. The mesoporous NH2-MCN-2 nanocomposite showed excellent stability and suitable reusability with a maximum degradation of 84.5% after five cycles. Results obtained from kinetic studies indicated a rate constant value of 0.08 min-1, and isotherm models showed that equilibrium data are more consistent with the Langmuir model in photocatalytic degradation. Electrochemical experiments showed significant improvement in the electron transfer rate and photocatalytic activity of the mesoporous NH2-MCN-2 nanocomposite. Different trapping agents were used to investigate the effective active species in IMC photodegradation, and it was determined that the hole (h+) and OH radical (•OH) play the main role. The possible mechanism for IMC photocatalytic degradation was suggested by Mott-Schottky (M-S) electrochemical impedance.

Effect of bismuth doping on the crystal structure and photocatalytic activity of titanium oxide

The doping of TiO2 with metals and non-metals is considered one of the most significant approaches to improve its photocatalytic efficiency. In this study, the photodegradation of methyl orange (MO) was examined in relation to the impact of Bi-doping of TiO2. The doped TiO2 with various concentrations of metal was successfully synthesized by a one-step hydrothermal method and characterized using X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), and UV-vis spectroscopy. The XRD results revealed that the anatase phase, with an average crystallite size of 16.2 nm, was the main phase of TiO2. According to the anatase texture results, it was found that the doping of TiO2 increased the specific surface area for Bi2O3@TiO2 without a change in the crystal structure or the crystal phase of TiO2. Also, XPS analysis confirmed the formation of Ti4+ and Ti3+ as a result of doping with Bi. The activities of both pure TiO2 and Bi-doped TiO2 were tested to study their ability to decolorize MO dye in an aqueous solution. The photocatalytic degradation of MO over Bi2O3@TiO2 reached 98.21%, which was much higher than the 42% achieved by pure TiO2. Doping TiO2 with Bi increased its visible-light absorption as Bi-doping generated a new intermediate energy level below the CB edge of the TiO2 orbitals, causing a shift in the band gap from the UV to the visible region, thus enhancing its photocatalytic efficiency. In addition, the effects of the initial pH, initial pollutant concentration, and contact time were examined and discussed.

Photocatalytic degradation of four emerging antibiotic contaminants and toxicity assessment in wastewater: A comprehensive study

Excessive usage and unrestricted discharge of antibiotics in the environment lead to their accumulation in the ecosystem due to their highly stable and non-biodegradation nature. Photodegradation of four most consumed antibiotics such as amoxicillin, azithromycin, cefixime, and ciprofloxacin were studied using Cu2O-TiO2 nanotubes. Cytotoxicity evaluation of the native and transformed products was conducted on the RAW 264.7 cell lines. Photocatalyst loading (0.1-2.0 g/L), pH (5, 7 and 9), initial antibiotic load (50-1000 μg/mL) and cuprous oxide percentage (5, 10 and 20) were optimized for efficient photodegradation of antibiotics. Quenching experiments to evaluate the mechanism of photodegradation with hydroxyl and superoxide radicals were found the most reactive species of the selected antibiotics. Complete degradation of selected antibiotics was achieved in 90 min with 1.5 g/L of 10% Cu2O-TiO2 nanotubes with initial antibiotic concentration (100 μg/mL) at neutral pH of water matrix. The photocatalyst showed high chemical stability and reusability up to five consecutive cycles. Zeta potential studies confirms the high stability and activity of 10% C-TAC (Cuprous oxide doped Titanium dioxide nanotubes for Applied Catalysis) in the tested pH conditions. Photoluminescence and Electrochemical Impedance Spectroscopy data speculates that 10% C-TAC photocatalyst have efficient photoexcitation in the visible light for photodegradation of antibiotics samples. Inhibitory concentration (IC50) interpretation from the toxicity analysis of native antibiotics concluded that ciprofloxacin was the most toxic antibiotic among the selected antibiotics. Cytotoxicity percentage of transformed products showed r: -0.985, p: 0.01 (negative correlation) with the degradation percentage revealing the efficient degradation of selected antibiotics with no toxic by-products.

Crystal facet and Na-doping dual engineering ultrathin BiOCl nanosheets with efficient oxygen activation for enhanced photocatalytic performance

Photocatalytic oxidation (PCO) based on semiconductors offers a sustainable and promising way for environmental remediation. However, the photocatalytic performance currently suffers from weak light-harvesting ability, rapid charge combination and a lack of accessible reactive sites. Ultrathin two-dimensional (2D) materials are ideal candidates to overcome these problems and become hotpots in the research fields. Herein, we demonstrate an ultrathin (<4 nm thick) Na-doped BiOCl nanosheets with {001} facets (Na-BOC-001) fabricated via a facile bottom-up approach. Because of the synergistic effect of highly exposed active facets and optimal Na doping on the electronic and crystal structure, the Na-BOC-001 showed an upshifted conduction band (CB) with stronger reduction potential for O₂ activation, more defective surface for enhanced O₂ adsorption, as well as the highest visible-light driven charge separation and transfer ability. Compared with the bulk counterparts (BOC-010 and BOC-001), the largest amount of active species and the best photocatalytic performance for the tetracycline hydrochloride (TC) degradation were achieved for the Na-BOC-001 under visible-light irradiation, even though it had slightly weaker visible-light absorption ability. Moreover, the effect of the Na doping and crystal facet on the possible pathways for TC degradation was investigated. This work offers a feasible and economic strategy for the construction of highly efficient ultrathin 2D materials.

Volatile organic compounds (VOCs) removal by photocatalysts: A review

Amplified anthropogenic release of volatile organic compounds (VOCs) gets worse air quality and human health. Photocatalytic degradation of VOCs is the practical strategy due to its low cost, simplicity, high efficiency, and environmental sustainability. Different types of photocatalyst activated by UV and visible lights are applied for VOC degradation. This review tries to investigate the state-of-art of recently published papers on this subject with a focus on the high-efficiency photocatalyst. The novel photocatalysts are introduced and enhancing photocatalytic activity strategies such as the hybrid of two/three photocatalyst, impurity doping, and heterojunctions with narrow bandgap semiconductors have been explained. The procedures of visible light activation of the photocatalysts are discussed with attention to current problems and future challenges. In addition, effective operational parameters in the photocatalytic degradation of VOCs have been reviewed with their advantages and drawbacks. A series of strategies are developed for the efficient utilization of visible light photocatalysts and improving new materials or design structures to degrade produced toxic intermediates/by-products during photocatalytic degradation of VOCs. This review shows that there are significant challenges in the applications of photocatalysts in the selective removal of VOCs. Several approaches should be combined to produce synergistic effects, which may lead to much higher photocatalytic performance than individual strategies. Another challenge is to develop efficient photocatalysts to meet real problems on an industrial scale.

Acid Etching-Induced In Situ Growth of λ-MnO2 over CoMn Spinel for Low-Temperature Volatile Organic Compound Oxidation

Surface lattice oxygen is crucial to the degradation of volatile organic compounds (VOCs) over transition metal oxides according to the Mars-van Krevelen mechanism. Herein, λ-MnO₂ in situ grown on the surface of CoMn spinel was prepared by acid etching of corresponding spinel catalysts (CoMn-Hx-Ty) for VOC oxidation. Experimental and relevant theoretical exploration revealed that acid etching on the CoMn spinel surface could decrease the electron cloud density around the O atom and weaken the adjacent Mn-O bond due to the fracture of the surface Co-O bond, facilitating electron transfer and subsequently the activation of surface lattice oxygen. The obtained CoMn-H1-T1 exhibited an excellent catalytic performance with a 90% acetone conversion at 149 °C, which is 42 °C lower than that of CoMn spinel. Furthermore, the partially maintained spinel structure led to better stability than pure λ-MnO₂. In situ diffuse reflectance infrared Fourier transform spectroscopy confirmed a possible degradation pathway where adsorptive acetone converted into formate and acetate species and into CO₂, in which the consumption of acetate was identified as the rate-limiting step. This strategy can improve the catalytic performance of metal oxides by activating surface lattice oxygen, to broaden their application in VOC oxidation.

Defective Ultrafine MnOx Nanoparticles Confined within a Carbon Matrix for Low-Temperature Oxidation of Volatile Organic Compounds

The development of catalysts for volatile organic compound (VOC) treatment by catalytic oxidation is of great significance to improve the atmospheric environment. Size-effect and oxygen vacancy engineering are effective strategies for designing high-efficiency heterogeneous catalysts. Herein, we explored the in situ carbon-confinement-oxidation method to synthesize ultrafine MnO_x nanoparticles with adequately exposed defects. They exhibited an outstanding catalytic performance with a T₉₀ of 167 °C for acetone oxidation, which is 73 °C lower than that of bulk MnO_x (240 °C). This excellent catalytic activity was primarily ascribed to their high surface area, rich oxygen vacancies, abundant active oxygen species, and good reducibility at low temperatures. Importantly, the synthesized ultrafine MnO_x exhibited impressive stability in long-term, cycling and water-resistance tests. Moreover, the possible mechanism for acetone oxidation over MnO_x-NA was revealed. In this work, we not only prepared a promising material for removing VOCs but also provided a new strategy for the rational design of ultrafine nanoparticles with abundant defects.

MOF-Templated Preparation of Highly Dispersed Co/Al2O3 Composite as the Photothermal Catalyst with High Solar-to-Fuel Efficiency for CO2 Methanation

CH₄ production from CO₂ hydrogenation provides a clean approach to convert greenhouse gas CO₂ into chemical energy, but high energy consumption in this reaction still restrains its further application. Herein, we use a light-driven CO₂ methanation process instead of traditional thermocatalysis by an electrical heating mode, with the aim of greatly decreasing the energy consumption. Under UV-vis-IR light irradiation, the photothermal CO₂ methanation over highly dispersed Co nanoparticles supported on Al₂O₃ (Co/Al₂O₃) achieves impressive CH₄ production rates (as high as 6036 μmol g^-1 h^-1), good CH₄ selectivity (97.7%), and catalytic durability. The high light-harvesting property of the catalyst across the entire solar spectrum coupled with its strong adsorption capacity toward H₂, CO₂, CO, and abundant active sites are proposed to be responsible for the better photothermocatalytic performance of Co/Al₂O₃. Furthermore, a novel light-promotion effect is also revealed in CO₂ methanation, where UV-vis light irradiation induces oxygen vacancies and improves the proclivity toward adsorption of H₂, CO₂, and CO, finally resulting in a significant enhancement of the photothermocatalytic activity for CH₄ production. By concentrating the low-intensity light (120 mW/cm²) via a Fresnel lens, a photothermal CO₂ conversion efficiency of more than 50% with a good CH₄ selectivity (76%) is achieved on the optimal catalyst under a dynamic reaction system, which indicates the bright prospect of photothermal CO₂ methanation.

Delocalization Effect Promoted the Indoor Air Purification via Directly Unlocking the Ring-Opening Pathway of Toluene

The ring-opening process was generally considered as the rate-determining step for aromatic volatile organic compound photocatalytic degradation. A sophisticated and intensive degradation pathway is critical to the poor removal efficiency and low mineralization. In the present contribution, we successfully tailored and identified the ring-opening pathway of toluene elimination by electron delocalization in a borocarbonitride photocatalyst. By means of modulation of the dopant coordination configuration and electron geometry in the catalyst, the lone electrons of carbon transform into delocalized counterparts, sequentially elevating the interaction between the toluene molecules and photocatalyst. The aromatic ring of toluene can be attacked directly in the effect of electron delocalization without engendering additional intermediate species, significantly facilitating the removal and mineralization of toluene. This unprecedented route-control strategy alters the aromatic-ring-based reaction behavior from toluene to CO₂ and paves a way to purify the refractory pollutants from the top design.

Photocatalytic degradation of industrial acrylonitrile wastewater by F-S-Bi-TiO2 catalyst of ultrafine nanoparticles dispersed with SiO2 under natural sunlight

Highly active photocatalyst, having certain anti-ionic interfering function, of F, S and Bi doped TiO2/SiO2 was used for the first time to degrade the organic pollutants in acrylonitrile industrial wastewater under natural sunlight. The photocatalyst were prepared and characterized by UV-Vis, XRD, TEM, EDS, Nitrogen physical adsorption and XPS technique. UV-Vis analysis revealed addition of F, S and Bi into the lattice of TiO2 led to the expansion of TiO2 response in the visible region and hence the efficient separation of charge carrier. The photocatalytic potential of as prepared catalyst to degrade acrylonitrile wastewater under simulated and natural sunlight irradiation was investigated. The extent of degradation of acrylonitrile wastewater was evaluated by chemical oxygen demand (CODCr). CODCr in wastewater decreased from 88.36 to 7.20 mgL-1 via 14 h irradiation of simulated sunlight and achieved regulation discharge by 6 h under natural sunlight, illuminating our photocatalyst effectiveness for refractory industrial wastewater treatment. From TEM results, we found that SiO2 could disperse the photocatalyst with different component distributions between the surface and the bulk phase that should also be responsible for the light absorption and excellent photocatalytic performance. The XPS analysis confirmed the presence of surface hydroxyl group, oxygen vacancies.

Efficient photocatalytic degradation of acrylonitrile by Sulfur-Bismuth co-doped F-TiO2/SiO2 nanopowder

In this study, a simple sol-gel method was applied for preparing effectual photocatalyst of S-Bi co-doped F-TiO₂/SiO₂ (S-Bi-F-TiO₂/SiO₂) nanopowder. Optimal preparation conditions were obtained by optimizing the calcination temperature and the ratio of S and Bi. The synthesized powder was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectrometer (EDS), X-ray photoelectron spectroscopy (XPS), brunauer-emmett-teller (BET), UV-Visible diffuse-reflectance spectroscopy (UV-Vis DRS), photoluminescence spectroscopy (PL) and ammonia adsorption and temperature-programmed desorption (NH₃-TPD). The photocatalytic activity was evaluated by the degradation of acrylonitrile under simulated visible light irradiation. S-Bi-F-TiO₂/SiO₂ nanopowder possess excellent photocatalytic properties under visible light for the degradation of acrylonitrile, when the calcination temperature was 450 °C for 2 h and the ratio of S and Bi was 0.02: 0.007. The degradation efficiency of acrylonitrile reached to 81.9% within 6 min of visible light irradiation. Compared with F-TiO₂/SiO₂ sample, NH₃-TPD and PL results revealed the higher photocatalytic activity for S-Bi-F-TiO₂/SiO₂, which is mainly due to the increase strength and number of surface acid site with S doping. The co-doping with S & Bi improved the separation of electron-hole pairs and enhanced the photocatalytic oxidizing species. The UV-Vis DRS showed stronger absorption in S-Bi co-doped F-TiO₂/SiO₂ catalyst as compared to F-TiO₂/SiO₂ catalyst. XPS results demonstrated the presence of various surface species viz. oxygen vacancies, Ti³⁺, Ti⁴⁺, O^2- and OH group.

Assembling of Bi atoms on TiO2 nanorods boosts photoelectrochemical water splitting of semiconductors

Low photoconversion efficiency, high charge transfer resistance and fast recombination rate are the bottlenecks of semiconductor nanomaterials in photoelectrochemical (PEC) water splitting, where the introduction of an appropriate co-catalyst is an effective strategy to improve their performance. In the present study, we have purposely designed atomic-scale dispersed bismuth (Bi) assembled on titanium dioxide nanorods (TiO2), and demonstrated its effective role as a co-catalyst in enhancing the PEC water splitting performance of TiO2. As a result, functionalized Bi/TiO2 generates a high photocurrent intensity at 1.23 VRHE under simulated solar light irradiation, which is 4-fold higher than that of pristine TiO2, exhibiting a significantly improved PEC performance for water splitting. The strategy presented in this study opens a new window for the construction of non-precious metals dispersed at atomic scales as efficient co-catalysts for realizing sustainable solar energy-driven energy conversion and storage.

Oxygen vacancies enhanced photocatalytic activity towards VOCs oxidation over Pt deposited Bi2WO6 under visible light

A novel Pt assisted self-modified Bi₂WO₆ composites (Pt/Bi-BWO) with high oxygen vacancies concentration was successfully fabricated via a simple in-situ NaBH₄ reduction method in presence of H₂PtCl₆•6H₂O. The Pt/Bi-BWO performed excellent photocatalytic activity on the degradation of gaseous toluene under visible light illumination. The photocatalytic reaction rate of 0.15% Pt/Bi-BWO was 2.88 times higher than that of Bi₂WO₆. Over 90% gas phase toluene was removed by 0.15% Pt/Bi-BWO in one hour and over 80% of which was degraded into CO₂ and H₂O. The Pt/Bi-BWO also performed great stability confirmed by circulating runs test. The mechanism of the promotion was explored by electron paramagnetic resonance (EPR) and DFT calculations. The produced oxygen vacancies were below conduction band (CB) of Bi₂WO₆, leading to a narrowed band gap. Meantime, the generated oxygen vacancies could activate O₂ to enhance the production of reactive oxygen species (ROS), such as O₂^- and OH. In addition, the added Pt could act as electron trap to suppress the recombination of electrons-holes pairs. In a word, this work produced a novel simply made photocatalyst to remove volatile organic compounds.

Synchronously achieved surface Bi0 metallisation and incorporation of Bi3+/5+ ions into a W6+, N3− doped TiO2 lattice by the hydrothermal-reduction method: surface plasmonic resonance effect for efficient photocatalysis

Vectorial charge transfer mechanisms in a bicrystalline framework of Bi⁰ surface deposited Bi^3+/5+, W⁶⁺ and N³⁻ doped TiO₂ under solar light irradiation.

Performance of Bi2O3/TiO2 prepared by sol-gel on p-Cresol degradation under solar and visible light

Photocatalytic degradation of p-Cresol was evaluated using the mixed oxide Bi₂O₃/TiO₂ (containing 2 and 20% wt. Bi₂O₃ referred as TB2 and TB20) and was compared with bare TiO₂ under simulated solar radiation. Materials were prepared by the classic sol-gel method. All solids exhibited the anatase phase by X-ray diffraction (XRD) and Raman spectroscopy. The synthesized materials presented lower crystallite size and Eg value, and also higher surface area as Bi₂O₃ amount was increased. Bi content was quantified showing near to 70% of theoretical values in TB2 and TB20. Bi₂O₃ incorporation also was demonstrated by X-ray photoelectron spectroscopy (XPS). Characterization of mixed oxides suggests a homogeneous distribution of Bi₂O₃ on TiO₂ surface. Photocatalytic tests were carried out using a catalyst loading of 1 g L^-1 under simulated solar light and visible light. The incorporation of Bi₂O₃ in TiO₂ improved the photocatalytic properties of the synthesized materials obtaining better results with TB20 than the unmodified TiO₂ under both radiation sources.

Synergistically catalytic oxidation of toluene over Mn modified g-C3N4/ZSM-4 under vacuum UV irradiation

The process of vacuum ultraviolet (VUV)-assisted photocatalytic oxidation (PCO) has attracted great interest for volatile organic compounds (VOCs) degradation owing to its strong oxidation capability. However, the O₃ by-product from VUV irradiation causes secondary pollution and needs to be overcome. In this study, a multi-functional photocatalyst of Mn/g-C₃N₄/ZSM-4 was thus developed by a one-pot hydrothermal method, and then combined with VUV irradiation to eliminate O₃ byproduct as well as enhance toluene degradation via ozone-assisted catalytic oxidation (OZCO). Under VUV irradiation alone, 64% of toluene degradation was occurred but 51 ppm of O₃ was residual. In contrast, toluene degradation was enhanced to 96% over the Mn/g-C₃N₄/ZSM-4 while residual O₃ was decreased to 4 ppm. The enhanced performance was attributed to the synergistic PCO and OZCO, as the Mn modification can efficiently enhance the photocatalytic activity of g-C₃N₄ and trigger the catalytic ozonation simultaneously. The results of electron spin resonance (ESR) confirmed the generation of reactive species such as OH and O₂^- by VUV irradiation and then greatly enhanced after Mn/g-C₃N₄/ZSM-4 was added. Moreover, the possible mechanism of toluene degradation was also revealed through monitoring of reaction intermediate. Obviously, the process of Mn/g-C₃N₄/ZSM-4 cooperated well with VUV is promising for VOCs degradation.

Mesoporous nanoplate multi-directional assembled Bi2WO6 for high efficient photocatalytic oxidation of NO

Herein, a mesoporous nanoplate multi-directional assembled Bi₂WO₆ architecture was successfully prepared and applied for the photocatalytic removal of NOx pollutants at low concentrations under visible light and simulated solar light irradiation. Bi₂WO₆-180-C synthesized at a hydrothermal temperature of 180 °C with calcination exhibited an excellent conversion efficiency in the photocatalytic oxidation of gaseous NO. The crystallinity, morphology, specific surface area, pore environment, light absorption, and separation of photogenerated electrons and holes were investigated by various techniques; the excellent photocatalytic performance of Bi₂WO₆-180-C was attributed to its special hierarchical mesoporous structure with an appropriate pore size and interconnected porous network, which imparted good gas permeability and fast mass transfer of reaction intermediates and final products of NO oxidation. Furthermore, hierarchical mesoporous Bi₂WO₆ showed excellent photocatalytic durability and reusability.

Synthesis, crystallography, microstructure, crystal defects, and morphology of BixZn1−xO nanoparticles prepared by sol–gel technique

This study was allocated to synthesis Bi_xZn_1−xO (0.00 ≤ x ≤ 0.06) nanoparticles. In addition, to study the microstructural properties, crystal imperfections and the morphology for these samples.