A novel photocatalyst AgBr/ZnO/RGO with high visible light photocatalytic activity

A novel ternary photocatalyst AgBr/ZnO/RGO, where AgBr/ZnO is supported on reduced graphene oxide, is synthesized via a facile hydrothermal–impregnation method. The resultant composite presents a lamellar structure with AgBr nanoparticles homogeneously dispersing on the surface. The photocatalytic experiment for methyl orange dye degradation under visible light irradiation shows that ternary composite AgBr/ZnO/RGO has an activity 12.8 times and 2.3 times higher than binary photocatalysts ZnO/RGO and AgBr/ZnO respectively. More importantly, the ternary composite also demonstrates a good photostability. Metallic Ag is produced during the photocatalytic process, which may serve as the electron transfer mediator in the vectorial Z-scheme transfer of photogenerated charge carriers at the interface of AgBr/ZnO/RGO. The effective separation of photogenerated electrons and holes was proposed to be responsible for the enhancement of visible light photoactivity.     

AgBr纳米粒子的制备及其光催化性能的研究

通过简单的沉淀法,加入适量浓度的表面活性剂十六烷基三甲基溴化铵（CTAB）制备纳米AgBr粒子。利用XRD、SEM表征手段证明了所制得的纳米粒子纯度高、粒径小、尺寸分布窄、稳定性好。通过UV-Vis表征可以知道,沉淀法制备的纳米粒子吸收波长范围可至可见光区域。在以紫外光及自然光（太阳光）为光源的条件下,经过60min的光催化降解反应,甲基橙（MO）的降解率可达到96％以上。与纳米二氧化钛粒子和纳米氧化锌粒子光催化性能相比,纳米溴化银不仅催化效率更高,而且在自然光照的条件下仍然可以保持很好的光催化性能。     

A g-C3N4/PANI S-scheme heterojunction with face-to-face structure to improve the anticorrosion property on Q235 steel and enhanced mechanism study

In photocatalytic anticorrosion perspective, the migration rate of excited electrons from surface layers to substrate steels restricted the performance of g-C₃N₄ due to the high resistance between interface of g-C₃N₄ layers and adhesive layers. Herein, an S-scheme g-C₃N₄/polyaniline (PANI) heterojunction with face-to-face structure was established by a secondary calcining method. The as-prepared heterojunctions were applied to protect Q235 carbon steel, and the results showed that the anticorrosion performance of S-scheme g-C₃N₄/PANI heterojunction is much higher than that of g-C₃N₄ and PANI coating layers according to salt spray test. Photocurrent intensity indicated that the optimum amounts of g-C₃N₄ and PANI were 0.06 and 0.09 mL/cm², which are benefit for the transport of excited electrons due to the optimum thickness of coating layers. Furthermore, the S-scheme g-C₃N₄/PANI heterojunction can promote the separation rate of charge carriers and suppress the recombination rate at the same time, which are inferred from photocurrent intensity, electrochemical impedance spectra, super-depth-of-field microscope, and photoluminescence investigation. In the last, the enhanced anticorrosion performance of S-scheme g-C₃N₄/PANI heterojunction with face-to-face structure was deduced according to mentioned characterization.     

锡酸铅纳米粒子的制备及其光催化性能

以有机碱四甲基氢氧化铵［N（CH₃）₄OH］为矿化剂,采用水热合成法制备锡酸铅（PbSnO₃）纳米粒子。通过X射线衍射（XRD）、热重-差式扫描量热分析（TG-DSC）和红外光谱分析（IR）等手段对产物的形成过程和结构进行表征,并研究了其对亚甲基蓝溶液的光催化降解性能。结果表明：由于采用有机碱四甲基氢氧化铵作为矿化剂,可以在较低的温度和较短的时间内制备出纯的立方相锡酸铅纳米粒子,其反应温度可降至120 ℃,反应时间可缩短至5 min;前躯体溶液pH是合成纯锡酸铅纳米粒子的关键,其值应在13以上。锡酸铅纳米粒子对亚甲基蓝溶液有良好的光催化降解效果,当催化剂用量为60 mg/L、反应时间为100 min时,亚甲基蓝的降解率可达88.5%。     

S-scheme g-C3N4/TiO2/CFs heterojunction composites with multi-dimensional through-holes and enhanced visible-light photocatalytic activity

A novel multi-dimensional through-holes structure of g-C₃N₄ with adjustable pore size was prepared by controlling the mass ratio of oxamide (OA, structure guiding agent) to urea during one-step calcination process, and a break-rearrangement mechanism was explored. Then, a series of porous g-C₃N₄/TiO₂ (CT) composites with uniformly deposited TiO₂ nanoparticles were prepared based on the multi-dimensional framework by a facile hydrothermal method. The results show that a new S-scheme heterojunction with multi-dimensional through-channel structure was obtained, which is particularly desired for enhancing the visible-light utilization, reducing the carrier recombination rate and enhancing redox capacity. The CT composite obtained at hydrothermal treatment time of 2 h has a specific surface area of 180.15 m² g^-1, which shows high degradation capability (99.99%) for tetracycline hydrochloride (TC·HCl) under 350 W Xe lamp irradiation for 90 min. In addition, CT nanostructures was in-situ growth on carbon fiber (CFs), the degradation rate constant is 0.1566 min^-1, and 90% of the degradation efficiency can be maintained even after 5 consecutive cycles. It is expected to provide an effective reference for solving the problems of recovery difficulty and low reuse rate of powder photocatalytic materials.     

Dual Z-scheme heterojunction g-C3N4/Ag3PO4/AgBr photocatalyst with enhanced visible-light photocatalytic activity

Recently, there has been a significant interest in developing high-performance photocatalysts for removing organic pollutants from water environment. Herein, a ternary graphitic C₃N₄ (g-C₃N₄)/Ag₃PO₄/AgBr composite photocatalyst is synthesized using an in-situ precipitation-anion-exchange process and characterized by several spectroscopic and microscopic techniques. During the photocatalytic reaction, X-ray photoelectron spectroscopy clearly illustrated the formation of metallic Ag on the g-C₃N₄/Ag₃PO₄/AgBr composite surface. The ternary composite photocatalyst demonstrated an increased photoactivity under visible light (>420 nm), achieving a complete decolorization of methyl orange (MO) in 5 min. The ternary g-C₃N₄/Ag₃PO₄/AgBr hybrid was also applied to the 2-chlorophenol degradation under visible light, further confirming its excellent photocatalytic activity. In addition, quenching experiments revealed that holes (h⁺) and O₂^?– were the major attack species in the decolorization of MO. The enhanced photoactivity of g-C₃N₄/Ag₃PO₄/AgBr results from the efficient transfer/separation of photoinduced charges with the dual Z-scheme pathway and the charge recombination sites on the formed Ag particles.     

Dy2BaCuO5/Ba4DyCu3O9.09 S-scheme heterojunction nanocomposite with enhanced photocatalytic and antibacterial activities

Semiconductor heterogeneous photocatalysis has been received much attention from the scientific and researchers in the last decade. The combination of two semiconductors with various energy diagram can dramatically enhance the lifetime and separation of the charge carriers, restrain photogenerated electron-hole recombination, and considerably enhance photocatalytic performance as compared with other single or binary components. In this regard, we introduced the Dy₂BaCuO₅/Ba₄DyCu₃O_9.09 nanocomposites as active photocatalysts below UV radiation. Dy₂BaCuO₅/Ba₄DyCu₃O_9.09 nanocomposites were prepared by a simple hydrothermal method and applied as a catalyst to treat water containing organic pollutions and microorganisms. Dy₂BaCuO₅/Ba₄DyCu₃O_9.09 nanocomposites degraded Methyl Orange (MO) about 87.0% after 120 min. In addition, these nanocomposites show antimicrobial activity against Gram-positive species, including a pathogenic strain of Enterococcus faecalis, and Staphylococcus aureus, and a Gram-negative species, including Klebsiella pneumonia and Escherichia coli.     

Recyclable 0D/2D ZnFe2O4/Bi5FeTi3O15 S-scheme heterojunction with bismuth decoration for enhanced visible-light-driven tetracycline photodegradation

Practical application of photocatalysis is often challenged by some intrinsic issues such as recombination of photogenerated charge carriers, stability and separation, etc. Herein, bismuth decorated 0D/2D ZnFe₂O₄/Bi₅FeTi₃O₁₅ (Bi/ZF/BFT) step-scheme (S-scheme) heterojunction was fabricated by an in-situ method. Due to the advantages of structure and composition, the Bi/ZF/BFT with the desired proportion (Bi/ZF/BFT-35) exhibits favorable photocatalytic performance towards tetracycline (TC) degradation. Compared with the pure ZF, the nanohybrid shows superior stability after 5 times cycle tests. Moreover, Bi/ZF/BFT-35 is convenient to be separated from the reaction system due to its magnetic nature. As identified by ESR measurement, ?O₂^? and ?OH radicals were involved in the photodegradation of TC, which supports that the S-scheme is successfully prepared. Also, the Bi/ZF/BFT-35 shows great ability of chemical oxygen demand (COD) removal in the practical wastewater as well. Importantly, antibacterial activity against E. coli test indicates that photodegraded TC has lower biotoxicity. The present work demonstrates that cocatalyst Bi modified ZF/BFT S-scheme can not only significantly improve its stability with good recyclability from the reaction system, but also inhibits the recombination of charge carriers, giving insight on the strategy of fabricating a promising photocatalyst for practical wastewater treatment.     

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.     

An S-scheme heterojunction of Bi2WO6/AgIO3 nanocomposites that enhances photocatalytic degradation of Rhodamine B and antifouling properties

Bi₂WO₆/AgIO₃ (BWO/AIO) nanosheet composites were constructed by a two-step hydrothermal method. The structure, morphology and photoelectrochemical properties of the composites were characterized by X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectra (UV-DRS), transmission electron microscopy (TEM), impedance, X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The constructed photocatalyst composites exhibited the best photocatalytic performance at a molar ratio of BWO/AIO-0.8. In addition, there was complete degradation of RhB by the BWO/AIO-0.8 in 180 min under illumination, and the bactericidal rates were 99.10%, 97.32% and 96.3% for P. aeruginosa, S. aureus and E. coli, respectively, in 60 min. Based on the energy band structure of the semiconductor and radical trapping experiments, the S-scheme heterojunction was associated with the enhanced photocatalytic properties.     

Dielectric,thermal and mechanical properties of hybrid PMMA/RGO/Fe2O3 nanocomposites fabricated by in-situ polymerization

Currently, the organic-inorganic hybrid materials have gained tremendous importance due to their unique applications in different technological fields. In this connection, the chemical synthesis of poly(methyl methacrylate) (PMMA) and its binary and ternary nanocomposites by in-situ bulk polymerization with various percentages of reduced graphene oxide (RGO) and hematite nanoparticles (Fe₂O₃ NPs) is presented. Dielectric properties of binary and ternary nanocomposites are investigated in the frequency range of 25 Hz-1 MHz for each composition. Ternary nanocomposite of PMMA with RGO:Fe₂O₃ NPs (2:2 wt%) exhibits a substantial enhancement of the dielectric constant up to ≈308 and suppressed dielectric loss of 0.12 at 25 Hz. Appearance of three types of interfaces in ternary PMMA nanocomposites accounts for the superior dielectric properties due to the accumulation of greater number of charges at the interfaces as compared to the binary nanocomposites with only one interface. The same optimized ternary PMMA nanocomposite shows a remarkable improvement in the thermal conductivity (2.04 W/mK), which is attributed to the formation of efficient thermal conducting pathways contributed by the synergic reduction in thermal resistance of both RGO and Fe₂O₃ NPs (2:2 wt%) relative to the binary nanocomposites PMMA/2 wt% RGO (1.04 W/mK) and PMMA/2 wt% Fe₂O₃ (0.98 W/mK). Thus, ternary nanocomposites prove to be the excellent candidates for thermal management applications. Furthermore, a comparison of the mechanical strength and thermal stability for all the binary and ternary nanocomposites is presented. In the last section, respective precursors and optimized binary and ternary nanocomposites are characterized by XRD, FTIR and SEM which reveal the strong interaction of respective nanofillers into PMMA matrix.     

Electrodeposition of flexible stainless steel mesh supported ZnO nanorod arrays with enhanced photocatalytic performance

Large scale well oriented ZnO nanorod arrays (ZNRAs) were electrodeposited on flexible stainless steel mesh (SSM) substrate pre-treated by Al doped ZnO (AZO) seed layers. The effects of substrate pre-treatment conditions such as Al doping and spin coating times of the colloid on the morphology characteristics and photocatalytic properties of as-prepared ZNRAs were systematically studied. The results showed that by introducing Al into ZnO colloid solution, well aligned ZNRAs with relatively higher specific surface area (higher growth density and smaller rod diameter) could be obtained on the premodified SSM substrate. In addition, increasing spin coating times of AZO colloid solution would decrease the average diameter of ZNRAs. Under the optimum preparing conditions, the formed flexible SSM supported ZNRAs exihibited enhanced photocatalytic performance of 93.42% and remarkable photocatalytic stability under the UV-lamp for degradation of Rhodamine B.     

Synthesis of a Fe3O4-rGO-ZnO-catalyzed photo-Fenton system with enhanced photocatalytic performance

In this work, we designed a magnetically-separable Fe₃O₄-rGO-ZnO ternary catalyst, ZnO anchored on the surface of reduced graphene oxide (rGO)-wrapped Fe₃O₄ magnetic nanoparticles, where rGO, as an effective interlayer, can enhance the synergistic effect between ZnO and Fe₃O₄. The effects of three operational parameters, namely irradiation time, hydrogen peroxide dosage, and the catalyst dosage, on the photo-Fenton degradation of methylene blue and methyl orange were investigated. The results showed that the Fe₃O₄-rGO-ZnO had great potential for the destruction of organic compounds from wastewater using the Fenton chemical oxidation method at neutral pH. Repeatability of the photocatalytic activity after 5 cycles showed only a tiny drop in the catalytic efficiency.     

Novel CdIn2S4 nano-octahedra/TiO2 hollow hybrid heterostructure: In-situ synthesis,synergistic effect and enhanced dual-functional photocatalytic activities

The development of highly efficient and multifunctional composite photocatalysts for both energy conversion and environmental governance has obtained great concerns. Here, a novel CdIn₂S₄/TiO₂ (CIS/THS) hollow composite photocatalyst was firstly designed and synthesized via a facile in-situ growth process, where the CdIn₂S₄ nano-octahedra densely attached on the surface of TiO₂ hollow spheres to form the unique hybrid heterostructure. The as-synthesized CIS/THS heterojunctions exhibit much superior photocatalytic activities for hydrogen evolution and Methyl Orange (MO) decomposition in comparison to pure CdIn₂S₄ and TiO₂ hollow spheres. The experimental results display that the CIS/THS-3 sample with the 30 wt% of TiO₂ presents the optimal photocatalytic H₂ production efficiency and its generation rate is 3.38 and 2.56 times as high as those of pure TiO₂ and CdIn₂S₄. Besides, the as-synthesized CIS/THS-3 hybrid also possesses the best MO photodegradation performance and its rate constant is 11.43 and 8.34 times higher than those of pure TiO₂ and CdIn₂S₄. The enhanced photocatalytic activities can be assigned to the synergistic effect, optimized light-harvesting capacity and the formation of hybrid heterostructure for boosting interfacial charge transfer and separation. Furthermore, based on the trapping experiments and ESR analysis, the possible type-Ⅱ interface charge transport mechanism was also proposed. Our study may provide the direct guidance for constructing other hollow TiO₂-based composite photocatalysts with superior photocatalytic water splitting and degradation performances.     

Construction of CoS/CeO2 heterostructure nanocages with enhanced photocatalytic performance under visible light

Exploring non-noble metal photocatalysts with high activity and stability is always fascinating. Herein, the hollow CoS nanocages deriven from ZIF-67 have been reported for the first time to combine with CeO₂ NPs grown in situ for photocatalytic degradation of stubborn pollutants. The unique CoS nanocages not only provide rich active sites but also enhance light capture. CeO₂ NPs loaded on the surface accelerate the separation of photocharges and extend the lifetime of photogenerated carriers. The optimized photocatalysts show outstanding activity and stability for the photodegradation of tetracycline and phenol under visible light, and the corresponding photodegradation efficiency is 96.5% and 90.5% at 60 minutes. The novel multi-stage nanocage structure simultaneously realizes extended light absorption and improved photocharges transfer efficiency. This work provides an exclusive perspective to design high-efficiency photocatalysts with hollow structures for environmental restoration.     

氮掺杂对SrTiO3光催化性能的影响

以尿素为氮源,利用溶胶-凝胶法制备了掺氮的N-SrTiO₃光催化剂。采用XRD、SEM和UV-Vis对N-SrTiO₃的物相、形貌和吸光性能进行表征,以高压汞灯为光源,通过甲基橙脱色率考察催化剂活性。结果表明,氮元素的掺杂增强了SrTiO₃在可见光区的吸收强度,当制备过程pH=3～4、n(N)∶n(Sr)=6∶1和焙烧温度800 ℃时,甲基橙溶液降解率达72.69%,未掺杂样品降解率为28.55%。     

Bi@Bi4Ti3O12/TiO2 films on glass with photocatalytic and self-cleaning performance

A stable and translucent Bi@Bi₄Ti₃O₁₂/TiO₂ film was fabricated on conventional glass substrates for the first time. The film exhibited a good photocatalytic performance and efficient self-cleaning capability against organic dyes under full spectral irradiation and visible light irradiation. Bi₄Ti₃O₁₂/TiO₂ film was first prepared on a glass substrate with colloidal silica as a high temperature binder, followed by implantation of nanoscale Bi in it by an in-situ partially reduction of Bi₄Ti₃O₁₂ to generate Bi@Bi₄Ti₃O₁₂/TiO₂ films. The improved photocatalytic ability is probably attributed to the surface plasmon resonance of Bi atom as well as the enhanced electron transfer efficiency and synergistic effect of Bi₄Ti₃O₁₂ and TiO₂. According to trapping experiments, hydroxyl radicals (OH) were active species in the photocatalytic degradation of dyes under full spectral light irradiation and possible photocatalytic mechanism was proposed. The film prepared in this work may well have potential practical applications in many aspects, such as cleansing treatments for high building external decorative panels and also systematic characterization of the film suggests that the in-situ reduction is an effective and simple way to produce nanoscale Bi@Bi₄Ti₃O₁₂.     

CuGaO2/TiO2 heterostructure nanosheets: Synthesis,enhanced photocatalytic performance,and underlying mechanism

Effective separation and fast transport of photogenerated carriers are vital links determining the photocatalytic performance. Heterostructure constructed by two complementary semiconductors is a feasible strategy to achieve this goal. By one-pot hydrothermal method, 0D-TiO₂ nanoparticles are loaded onto 2D-CuGaO₂ nanosheets, forming a mixed dimension, closely combined heterostructure. The photocurrent density of CuGaO₂/TiO₂ heterostructure is ∼16.6 μA/cm², which is 1.24 times higher than that of pristine CuGaO₂ nanosheets (∼13.4 μA/cm²) and 15 times higher than that of TiO₂ (∼1.1 μA/cm²). In the tetracycline hydrochloride degradation experiment, the degradation efficiency of tetracycline hydrochloride by CuGaO₂/TiO₂ heterostructure reached 99% within 90 min, which was 1.2 times the degradation efficiency of CuGaO₂ nanoparticles (82%) and 20.2 times the degradation rate of TiO₂ (4.9%). A series of experimental characterizations combined with density functional theory calculations revealed that it is the built-in electric field in the CuGaO₂/TiO₂ interface region that drives the photogenerated electron–hole pairs to travel in the opposite direction, thus inhibiting their recombination. Furthermore, the energy band offset of the CuGaO₂/TiO₂ interface makes it easier for the photogenerated holes and electrons to gather onto the valence band of the CuGaO₂ nanosheets and the conduction band of the TiO₂ nanoparticles, respectively. Therefore, appropriate interface lattice matching, suitable configuration of band gap and band edge positions, and strong opposite drive of interface electric field enable CuGaO₂/TiO₂ heterostructure to achieve wide spectral response and effective separation of photogenerated electron–hole pairs at the same time.