Peroxymonosulfate activation by Co3O4/SnO2 for efficient degradation of ofloxacin under visible light

Structural, Optical, Electrical and Photocatalytic Investigation of n-Type Zn2+-Doped α-Bi2O3 Nanoparticles for Optoelectronics Applications

Herein, n-type pure and Zn2+-doped monoclinic bismuth oxide nanoparticles were synthesized by the citrate sol-gel method. X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL) analysis, ultraviolet-visible (UV-vis) spectroscopy, and Hall effect measurements were used to study the effect of Zn2+ on the structural, optical, and electrical properties of nanoparticles. XRD revealed the monoclinic stable phase (α-Bi2O3) of all synthesized samples and the crystallite size of nanoparticles increased with increasing concentration of dopant. Optical analysis illustrated the red shift of absorption edge and blue shift of band gap with increasing concentration of dopant. Hall Effect measurements showed improved values (2.79 × 10-5 S cm-1 and 6.89 cm2/V·s) of conductivity and mobility, respectively, for Zn2+-doped α-Bi2O3 nanoparticles. The tuned optical band gap and improved electrical properties make Zn2+-doped α-Bi2O3 nanostructures promising candidates for optoelectronic devices. The degradation of methylene blue (MB, organic dye) in pure and zinc-doped α-Bi2O3 was investigated under solar irradiation. The optimum doping level of zinc (4.5% Zn2+-doped α-Bi2O3) reveals the attractive photocatalytic activity of α-Bi2O3 nanostructures due to electron trapping and detrapping for solar cells.

Advanced degradation of organic pollutants using sonophotocatalytic peroxymonosulfate activation with CoFe2O4/Cu- and Ce-doped SnO2 composites

The rampant upsurge of organic pollutants in aqueous media has become one of the major concerns nowadays. Finding non-specific catalysts that can target a wide range of organic pollutants is a key challenge. Eco-friendly oxidative radicals, such as promoted by peroxymonosulfate (PMS), are necessary for efficient water decontamination. We propose a multicomponent composite catalyst for activating PMS using a dual strategy of sonophotocatalysis. The composite integrates cobalt ferrite and Cu- or Ce-doped SnO2, with the at. % of doping metal and the mixture ratio carefully balanced. The top-performing architectures were able to decompose rhodamine B (20 ppm), a representative pollutant, in under 3 min and achieve over 70% mineralization in just 5 min. The synthesized nanocomposites demonstrated exceptional sonophotocatalytic performance, even when treating complex and diverse multipollutant solutions (80 ppm), achieving over 75% mineralization after 150 min. Considering their high stability and reusability, the proposed CoFe2O4/Cu- and Ce-doped SnO2 materials are among the state-of-the-art heterogeneous catalysts for mineralizing organic pollutants through PMS activation.

Recent advances of modification effect in Co3O4-based catalyst towards highly efficient photocatalysis

Tricobalt tetroxide (Co3O4) has been developed as a promising photocatalyst material for various applications. Several reports have been published on the self-modification of Co3O4 to achieve optimal photocatalytic performance. The pristine Co3O4 alone is inadequate for photocatalysis due to the rapid recombination process of photogenerated (PG) charge carriers. The modification of Co3O4 can be extended through the introduction of doping elements, incorporation of supporting materials, surface functionalization, metal loading, and combination with other photocatalysts. The addition of doping elements and support materials may enhance the photocatalysis process, although these modifications have a slight effect on decreasing the recombination process of PG charge carriers. On the other hand, combining Co3O4 with other semiconductors results in a different PG charge carrier mechanism, leading to a decrease in the recombination process and an increase in photocatalytic activity. Therefore, this work discusses recent modifications of Co3O4 and their effects on its photocatalytic performance. Additionally, the modification effects, such as enhanced surface area, generation of oxygen vacancies, tuning the band gap, and formation of heterojunctions, are reviewed to demonstrate the feasibility of separating PG charge carriers. Finally, the formation and mechanism of these modification effects are also reviewed based on theoretical and experimental approaches to validate their formation and the transfer process of charge carriers.

Construction of type-II scheme SnO@HfC photocatalyst for bisphenol A degradation via peroxymonosulfate activation; DFT and self-cleaning analysis

In this study, novel stannous oxide@hafnium carbide (SnO@HfC) nanocomposite was successfully manufactured by an appropriate hydrothermal scheme which was utilized for the photocatalytic degradation of BPA by stimulation of peroxymonosulfate (PMS) and self-cleaning application. Numerous methods were applied for the characterization of photocatalyst and demonstrated the successful preparation of SnO@HfC nanocomposite. The crystal structures, band structures and density of states for SnO and HfC were explored by DFT analysis. The amazing PMS stimulation performance of SnO@HfC nanocomposite originated from the establishment of a heterojunction, which led to the enhancement of the light response aptitude and the electron conduction competence of the composite. BPA was degraded by 0.75 g/L PMS and SnO@HfC at neutral pH during the period of 60 min. In order to identify active groups in the reaction procedure, quenching experiments and electron paramagnetic resonance (EPR) approaches were also used. In the subsequent active species scavenging assays, where sulfate radicals, hydroxyl radicals, holes, and superoxide radicals were engaged in the degradation of BPA. While, liquid phase mass spectrometry (LC-MS) was used to pinpoint the intermediate metabolites in the course of degradation. SnO@HfC/PMS/light system delivered excellent TOC removal efficiency and less ions leaching. The SnO@HfC nanocomposite proved good durability and reusability in continuous cycle tests along with excellent self-cleaning function on the glass substrate. The SnO@HfC nanocomposite performs admirably in terms of self-cleaning application. The SnO@HfC nanocomposite is expected to be used in the future for the treatment of wastewater that contains pharmaceuticals due to its superior stability and reusability after five consecutive cycles.

Drop-Dry Deposition of SnO2 Using a Complexing Agent and Fabrication of Heterojunctions with Co3O4

The drop-dry deposition (DDD) is a simple chemical technique of thin film deposition, which can be applied to metal oxides. The deposition solution is an aqueous solution including a metal salt and an alkali. However, some metal ions react spontaneously with water and precipitate. This work is the first attempt to use complexing agents in DDD to suppress the precipitation. SnO2 thin films are fabricated using DDD with Na2S2O3 as a complexing agent and via annealing in air. The results of the Auger electron spectroscopy measurement show that the O/Sn composition ratio of the annealed films approached two, indicating that the annealed films are SnO2. The photoelectrochemical measurement results show that the annealed films are n-type. Co3O4/SnO2 heterojunction is fabricated using p-type Co3O4 films which are also deposited via DDD. The heterojunction has rectification and photovoltaic properties. Thus, for the first time, a metal oxide thin film was successfully prepared via DDD using a complexing agent, and oxide thin film solar cells are successfully prepared using only DDD.

Effect of Higher Carrier Mobility of the Reduced Graphene Oxide-Zinc Telluride Nanocomposite on Efficient Charge Transfer Facility and the Photodecomposition of Rhodamine B

The synthesis of solar-light-responsive zinc telluride (ZnTe) nanoparticles and their composite with reduced graphene oxide (rGO-ZnTe) via a simple hydrothermal reaction is reported. The synthesized nanostructures were comprehensively characterized by a combination of X-ray diffraction and photoelectron spectroscopy, electron microscopy, UV-vis spectroscopy, photoluminescence spectroscopy and thermogravimetric analysis. The effects of graphene oxide on the crystallinity, microstructure, photo-excitation, light absorption, surface area and thermal stability of ZnTe were studied. The current-voltage (I-V) characteristics for both as-synthesized ZnTe and rGO-ZnTe composite-based Schottky devices were measured to estimate the charge transport parameters such as dc conductivity, photosensitivity, carrier's mobility and lifetime. The photocatalytic performance of both the materials in the degradation of an azo dye (Rhodamine B) was subsequently investigated using simulated solar light. The rGO-ZnTe composite exhibited a higher photocatalytic activity (66%) as compared to the as-synthesized ZnTe (23%), essentially due to the synergy between rGO sheets and ZnTe nanoparticles. The role of the carrier's mobility in the transportation of photo-induced charges (electrons and holes) through the complex network of the composite materials and thus facilitating the photo-degradation process is explained. In the end, the responsible reactive species for the decomposition of Rhodamine B was also interpreted.

Synthesis of TiC@C-anatase/rutile@polyvinyl alcohol/xylan: a powerful photocatalyst for degradation of organic pollutant under visible light

In this study, a composite bearing titanium carbide (TiC), titanium dioxide (TiO₂), polyvinyl alcohol and xylan (TiC@C-anatase/rutile@polyvinyl alcohol/xylan) was synthesized and applied as a photocatalyst for the degradation of bromophenol blue (BPB) solution through several steps. Nanostructure of TiC and TiO₂ in the anatase and rutile phases was obtained through heat treatment of TiC at different times and temperatures (TiC@AR) which led to a reduction in energy bandgap from UV to visible light, in addition to the enhancement of the surface activity. After TiC@AR polymerization by xylan and polyvinyl alcohol and obtaining TiC@AR/PX, the energy bandgap reduced to IR range (52% of the sunlight) while showing an enhancement in the surface activity. The photocatalytic activity of the compounds was tested by studying the decomposition of BPB solution under visible light. The result illustrated the ability of TiC and TiC@AR to decrease the concentration of BPB after 150 min by 35% and 37%, respectively, while this reduction was 72% for TiC@AR/PX. Considering the effective parameters, the energy bandgap and the surface layer played key roles in photocatalytic degradation.

Enhanced adsorption and catalytic degradation of antibiotics by porous 0D/3D Co3O4/g-C3N4 activated peroxymonosulfate: An experimental and mechanistic study

In this work, Co₃O₄/g-C₃N₄ catalyst with highly efficient adsorption and degradation of antibiotics was developed based on the combination of three-dimensional (3D) porous morphological controls of g-C₃N₄ and the loading of Co₃O₄ quantum dots (Co₃O₄ QDs). It was discovered that the catalyst can effectively activate peroxymonosulfate (PMS) through a non-photochemical path, and a high tetracycline elimination rate of 99.7% can be achieved within 18 min. The characterization and density functional theory calculation results demonstrated that the porous 3D structure can not only promote the substrate adsorption reaction but also provide large surface area and countless exposed active sites for catalytic reaction. The introduction of Co₃O₄ QDs lowered activation energy barrier and lead to high energy of PMS adsorption. More efficient charge migration between the catalyst and PMS further accelerated PMS activation. Thus, leading to the excellent catalytic performance. In addition, non-free radical mediated degradation mechanism of catalytic activity was also proposed. This work provides a scheme for designing novel and efficient PMS activators for the removal of abusive antibiotics from aqueous environments.

An excellent multifunctional photocatalyst cooperated by polyoxometalate-viologen framework for CEES oxidation, Cr(VI) reduction and dyes decolorization under different light regimes

Photocatalytic detoxification of highly toxic agents is a promising approach to protect ecological environment and human health, and the key problem lies in the development of novel efficient photocatalysts. Herein,...

Reduced graphene oxide–zinc sulfide (RGO–ZnS) nanocomposite: a new photocatalyst for oxidative cyclization of benzylamines to benzazoles under visible-light irradiation

A simple route for the preparation of a reduced graphene oxide–zinc sulfide (RGO–ZnS) nanocomposite via one-pot hydrothermal synthesis has been reported.