Facile Synthesis of Novel Redox-Mediator-free Direct Z-Scheme CaIn2S4 Marigold-Flower-like/TiO2 Photocatalysts with Superior Photocatalytic Efficiency

Construction of a novel S-scheme AgVO3/CaIn2S4 heterostructure for efficient photodegradation of tetracycline hydrochloride

Constructing an S-scheme system with highly active catalysts is a significant approach for improving the separation of photoinduced carriers to solve the related environmental aggravation. In this study, a well-designed S-scheme AgVO3/CaIn2S4 photocatalyst was synthesized for water purification by in situ growing CaIn2S4 nanocrystals on AgVO3 nanorod surfaces. The optimized AgVO3/CaIn2S4 heterostructure demonstrates an enhanced photocatalytic efficiency (94.1%) toward tetracycline hydrochloride (TCH) degradation compared with bare AgVO3 (42.6%) and CaIn2S4 (81.6%). The significant enhancement of photocatalytic activity is attributed to the S-scheme charge transfer mechanism in the AgVO3/CaIn2S4 heterostructure, which effectively directs photogenerated charge migration, boosts charge transfer, and preserves the high redox capacity of photoexcited electrons and holes on different active sites. This study is expected to offer insights into strategically designing and preparing S-scheme heterojunction photocatalysts to improve water purification.

A Review of Synthesis Methods, Modifications, and Mechanisms of ZnO/TiO2-Based Photocatalysts for Photodegradation of Contaminants

The environment being surrounded by accumulated durable waste organic compounds has become a critical crisis for human societies. Generally, organic effluents of industrial plants released into the water source and air are removed by some physical and chemical processes. Utilizing photocatalysts as cost-effective, accessible, thermally/mechanically stable, nontoxic, reusable, and powerful UV-absorber compounds creates a new gateway toward the removal of dissolved, suspended, and gaseous pollutants even in trace amounts. TiO2 and ZnO are two prevalent photocatalysts in the field of removing contaminants from wastewater and air. Structural modification of the photocatalysts with metals, nonmetals, metal ions, and other semiconductors reduces the band gap energy and agglomeration and increases the affinity toward organic compounds in the composite structures to expand their usability on an industrial scale. This increases the extent of light absorbance and improves the photocatalytic efficiency. Selecting a suitable synthesis method is necessary to prepare a target photocatalyst with distinct properties such as high specific surface area, numerous surface functional groups, and an appropriate crystalline phase. In this Review, significant parameters for the synthesis and modification of TiO2- and ZnO-based photocatalysts are discussed in detail. Several proposed mechanistic routes according to photocatalytic composite structures are provided. Some electrochemical analyses using charge carrier trapping agents and delayed recombination help to plot mechanistic routes according to the direction of photoexcited species (electron-hole pairs) and design more effective photocatalytic processes in terms of cost-effective photocatalysts, saving time and increasing productivity.

A 3D hierarchical TiO2/CaIn2S4/C3N4arrays photoanode with dual-heterojunction for enhanced photoelectrochemical performance

A novel 3D hierarchical TiO2/CaIn2S4/C3N4arrays with dual heterojunctions photoanode is constructed by stepwise deposition of CaIn2S4nanosheets and ultrathin C3N4onto the well-aligned TiO2nanorods arrays. Integrating the merit of the superior ability of CaIn2S4and C3N4to harvest visible light, dual type-Ⅱ heterojunction band structure and one-dimensional ordered nanostructures, the TiO2/CaIn2S4/C3N4photoanode exhibits simultaneous significant improvements in visible-light harvesting, charge separation and electron transfer capability. At 1.23 V (versus reversible hydrogen electrode) under AM 1.5 G irradiation, the TiO2/CaIn2S475/C3N4photoanode exhibits a photocurrent density of 4.5 mA cm-2, which is 5.2 and 51.1-fold higher than that of TiO2/CaIn2S475 and pristine TiO2photoanode, respectively. Moreover, the applied bias photo-to-current efficiency (ABPE) of the TiO2/CaIn2S475/C3N4photoanode reaches 3.5% at 0.36 V (versus reversible hydrogen electrode). These results are helpful for fabricating more efficient heterostructure photoelectrodes.

Modeling of adsorptive removal of azithromycin from aquatic media by CoFe2O4/NiO anchored microalgae-derived nitrogen-doped porous activated carbon adsorbent and colorimetric quantifying of azithromycin in pharmaceutical products

Herein, it was aimed to optimize the removal process of Azithromycin (Azi) from the aquatic environment via CoFe2O4/NiO nanoparticles anchored onto the microalgae-derived nitrogen-doped porous activated carbon (N-PAC), besides developing a colorimetric method for the swift monitoring of Azi in pharmaceutical products. In this study, the Spirulina platensis (Sp) was used as a biomass resource for fabricating CoFe2O4/NiO@N-PAC adsorbent. The pores of N-PAC mainly entail mesoporous structures with a mean pore diameter of 21.546 nm and total cavity volume (Vtotal) of 0.033578 cm3. g-1. The adsorption studies offered that 98.5% of Azi in aqueous media could remove by CoFe2O4/NiO@N-PAC. For the cyclic stability analysis, the adsorbent was separated magnetically and assessed at the end of five adsorption-desorption cycles with a negligible decrease in adsorption. The kinetic modeling revealed that the adsorption of Azi onto the CoFe2O4/NiO@N-PAC was well-fitted to the second-order reaction kinetics, and the highest adsorption capacity was found as 2000 mg. g-1 at 25 °C based on the Langmuir adsorption isotherm model at 0.8 g. L-1 adsorbent concentration. The Freundlich isotherm model had the best agreement with the experimental data. Thermodynamic modeling indicated the spontaneous and exothermic nature of the adsorption process. Moreover, the effects of pH, temperature, and operating time were also optimized in the colorimetric Azi detection. The blue ion-pair complexes between Azi and Coomassie Brilliant Blue G-250 (CBBG-250) reagent followed Beer's law at wavelengths of 640 nm in the concentration range of 1.0 μM to 1.0 mM with a 0.94 μM limit of detection (LOD). In addition, the selectivity of Azi determination was verified in presence of various species. Furthermore, the applicability of CBBG-250 dye for quantifying Azi was evaluated in Azi capsules as real samples, which revealed the acceptable recovery percentage (98.72-101.27%). This work paves the way for engineering advanced nanomaterials for the removal and monitoring of Azi and assures the sustainability of environmental protection and public health.

Boosting photocatalytic property of graphitic carbon nitride with metal complex fabrication for efficient degradation of organic pollutants

The development of efficient and stable photocatalysts for degradation of refractory pollutants using minimal amounts of metal remains a major challenge. Herein, we synthesize a novel catalyst by fabrication of manganese (III) acetylacetonate complex [Mn (acac)₃] over graphitic carbon nitride (GCN) denoted as 2-Mn/GCN by facile ultra-sonication method. The fabrication of the metal complex enables the migration of electrons from the conduction band of graphitic carbon nitride to Mn (acac)₃, and migration of holes from valence band of Mn (acac)₃ to GCN upon irradiation. Exploiting the improved surface properties, light absorption, and charge separation ensure generation of superoxide and hydroxyl radicals resulting in the rapid degradation of a variety of pollutants. The designed 2-Mn/GCN catalyst realized 99.59% rhodamine b (RhB) degradation in 55 min and 97.6% metronidazole (MTZ) degradation in 40 min with 0.7% Mn content. The influence of catalyst amount, different pH and presence of anions on the degradation kinetics was also explored to offer insights into photoactive material design.

CdTe QDs-sensitized TiO2 nanocomposite for magnetic-assisted photoelectrochemical immunoassay of SARS-CoV-2 nucleocapsid protein

A sensitive, reliable, and cost-effective detection for SARS-CoV-2 was urgently needed due to the rapid spread of COVID-19. Here, a "signal-on" magnetic-assisted PEC immunosensor was constructed for the quantitative detection of SARS-CoV-2 nucleocapsid (N) protein based on Z-scheme heterojunction. Fe₃O₄@SiO₂@Au was used to connect the capture antibody to act as a capture probe (Fe₃O₄@SiO₂@Au/Ab₁). It can extract target analytes selectively in complex samples and multiple electrode rinsing and assembly steps were avoided effectively. CdTe QDs sensitized TiO₂ coated on the surface of SiO₂ spheres to form Z-scheme heterojunction (SiO₂@TiO₂@CdTe QDs), which broadened the optical absorption range and inhibited the quick recombination of photogenerated electron/hole of the composite. With fascinating photoelectric conversion performance, SiO₂@TiO₂@CdTe QDs were utilized as a signal label, thus further realizing signal amplification. The migration mechanism of photogenerated electrons was further deduced by active material quenching experiment and electron spin resonance (ESR) measurement. The elaborated immunosensor can detect SARS-CoV-2 N protein in the linear range of 0.005-50 ng mL^-1 with a low detection limit of 1.8 pg mL^-1 (S/N = 3). The immunosensor displays extraordinary sensitivity, strong anti-interference, and high reproducibility in detecting SARS-CoV-2 N protein, which envisages its potential application in the clinical diagnosis of COVID-19.

Direct Z-scheme MgIn2S4/TiO2heterojunction for enhanced photocathodic protection of metals under visible light

To improve the photocathodic protection performance of traditional TiO₂photoanodes for metals, constructing a Z-scheme heterojunction is one of the most promising and creative strategies. Herein, we fabricated a novel Z-scheme MgIn₂S₄nanosheets/TiO₂nanotube nanocomposite through anodization and hydrothermal method. The optimized Z-scheme MgIn₂S₄/TiO₂nanocomposites exhibited stronger visible light absorption, higher separation efficiency of photoelectrons and photocathodic protection performances in comparison to pure TiO₂. The theoretical analysis and experimental results show that the Z-scheme heterojunction and oxygen vacancies jointly improved the separation efficiency of photogenerated electron-hole pairs and visible light absorption capacity, thereby improving the photoelectric conversion performance of the MgIn₂S₄/TiO₂nanocomposites. Furthermore, the influence of the precursor solution concentration on the photocathodic protection performances of the composites was investigated. As a result, when the concentration of magnesium source in the precursor solution was 0.06 mmol, the prepared MgIn₂S₄/TiO₂-0.06 displayed the best photocathodic protection performance. In addition, the hydroxyl radicals (·OH) generated in the electron spin resonance (ESR) experiment verified the Z-scheme heterojunction mechanism of the MgIn₂S₄/TiO₂composite, and also demonstrated the excellent redox performance of the composite. This work provides valuable reference for the construction of high-performance Z-scheme heterojunctions for photocathode protection of metals.

Immobilization of GOx Enzyme on SiO2-Coated Ni-Co Ferrite Nanocomposites as Magnetic Support and Their Antimicrobial and Photocatalytic Activities

The present study used a sol-gel auto-combustion approach to make silica (SiO2)-coated Ni-Co ferrite nanocomposites that would be used as a platform for enzyme immobilization. Using glutaraldehyde as a coupling agent, glucose oxidase (GOx) was covalently immobilized on this magnetic substrate. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM), and fourier transform infrared spectroscopy (FTIR) was used to determine the structural analysis and morphology of Ni-Co ferrite/SiO2 nanocomposites. FTIR spectra confirmed the binding of GOx to Ni-Co ferrite/SiO2 nanocomposites, with a loading efficiency of around 85%. At alkaline pH and higher temperature, the immobilized GOx enzyme exhibited increased catalytic activity. After 10 times of reuses, it still had 69% catalytic activity. Overall, the immobilized GOx displayed higher operational stability than the free enzyme under severe circumstances and was easily recovered by magnetic separation. With increased doping concentration of the nanocomposites, the photocatalytic activity was assessed using a degradation process in the presence of methylene blue dye under UV light irradiation, which revealed that the surface area of the nanocomposites with increased doping concentration played a significant role in improving photocatalytic activity. The antibacterial activity of Ni-Co ferrite/SiO2 nanocomposites was assessed using the agar well diffusion method against Escherichia coli, a gram-negative bacteria (ATCC 25922). Consequently, it was revealed that doping of Ni2+ and Co2+ in Fe2O4/SiO2 nanocomposites at varied concentrations improved their antibacterial properties.

Solid-State Synthesis of Direct Z-Scheme Cu2O/WO3 Nanocomposites with Enhanced Visible-Light Photocatalytic Performance

In this paper, we report the preparation of visible-light active direct Z-scheme Cu2O/WO3 nanocomposite photocatalyst by a solid-state reaction avoiding the otherwise inevitable formation of CuWO4 phase in wet syntheses. Structure, morphology, and thermal and optical properties of prepared WO3 nanoplatelets decorated by Cu2O were investigated by XRD, Raman spectroscopy, SEM/TEM, combined thermogravimetric (TG)/differential scanning calorimetry (DSC) analysis, and UV–VIS spectroscopy. The photocatalytic performance of the prepared samples under UV and visible light was studied through monitoring discoloration of methylene blue under illumination by selected wavelengths, allowing for the distinguishing between the contributions of the two semiconductive components. Experimental results showed that the decoration of WO3 nanoplates by Cu2O nanoparticles led to an improvement in photocatalytic performance, regardless of used LED (Light-Emitting Diode) wavelength, even at low concentrations. By using scavengers selectively blocking reactive species involved in the discoloration reaction, we determined that the Cu2O/WO3 nanocomposite exhibited the characteristics of direct Z-scheme-type photocatalyst.

A Direct Z-Scheme for the Photocatalytic Hydrogen Production from a Water Ethanol Mixture on CoTiO3/TiO2 Heterostructures

Photocatalytic H₂ evolution from ethanol dehydrogenation is a convenient strategy to store solar energy in a highly valuable fuel with potential zero net CO₂ balance. Herein, we report on the synthesis of CoTiO₃/TiO₂ composite catalysts with controlled amounts of highly distributed CoTiO₃ nanodomains for photocatalytic ethanol dehydrogenation. We demonstrate these materials to provide outstanding hydrogen evolution rates under UV and visible illumination. The origin of this enhanced activity is extensively analyzed. In contrast to previous assumptions, UV-vis absorption spectra and ultraviolet photoelectron spectroscopy (UPS) prove CoTiO₃/TiO₂ heterostructures to have a type II band alignment, with the conduction band minimum of CoTiO₃ below the H₂/H⁺ energy level. Additional steady-state photoluminescence (PL) spectra, time-resolved PL spectra (TRPLS), and electrochemical characterization prove such heterostructures to result in enlarged lifetimes of the photogenerated charge carriers. These experimental evidence point toward a direct Z-scheme as the mechanism enabling the high photocatalytic activity of CoTiO₃/TiO₂ composites toward ethanol dehydrogenation. In addition, we probe small changes of temperature to strongly modify the photocatalytic activity of the materials tested, which could be used to further promote performance in a solar thermophotocatalytic reactor.

Flower- and Grass-like Self-Assemblies of an Oleanane-Type Triterpenoid Erythrodiol: Application in the Removal of Toxic Dye from Water

Erythrodiol (3β-olean-12-ene-3, 28-diol) (C30H50O2) 1 is a nanosized oleanane-type fused 6-6-6-6-6 pentacyclic triterpeneoid extractable from the dried leaves of olive (Olea europia). One step reduction of oleanolic acid extracted from Lantana camara also yields the same compound. The triterpenoid has one secondary -OH group attached at C3 of the "A" ring and one primary -OH group at C28 present at the junction of the "D" and "E" rings. Here, we report the spontaneous self-assembly of erythrodiol in different neat organic liquids and aqueous-organic liquid mixtures. The nanosized dihydroxy triterpenoid having an oleanane-type lipophilic rigid skeleton self-assembled in liquids, yielding nanosized fibrils, microsized flowers, and grass-like architectures via formation of densely assembled fibrils and petals or 2D sheets. The microstructures of the self-assemblies have been characterized by different techniques like optical microscopy, electron microscopy, atomic force microscopy, FTIR, and wide angle X-ray diffraction studies. The porous self-assemblies having a large surface area obtained from 1 were capable of adsorbing toxic fluorophores like rhodamine-B, rhodamine-6G, methylene blue, and crystal violet (CV). Moreover, removal of the aforementioned toxic pigments has also been demonstrated from their aqueous solutions by using UV-visible spectrophotometry and epifluorescence microscopy.

Synthesis of Ph-Modified Graphitic Carbon Nitride for Degradation of Different Chromophoric Organic Pollutants in Aqueous Suspension under Visible Light

Recently, the preparation of visible-light-sensitive catalysts for the decomposition of organics has been of great interest. Herein, we report a single-step facile co-polymerization via the calcination process to produce a phenyl-modified-g-C₃N₄ semiconducting material. The product was characterized using standard analytical techniques. The UV/vis-DRS study indicates a shift of 23 nm toward higher wavelengths, whereas transmission electron microscopy analysis indicates the presence of phenyl group incorporation. The H¹ NMR of Ph-g-C₃N₄ showed a shift of aromatic proton toward down-field as compared with benzamide protons. The prepared products showed efficient performance for the removal of a dye and a drug derivative in water with light and air. The marked activity might be due to efficient light absorption and photoseparated (e^--h⁺) pair. The work embodied represents the construction of catalysts for the removal of organics in water with light.

Formation of hollow porous TiO2 nanospheres via the encapsulation of CO2 nanobubbles for high-performance adsorption and photocatalysis

Porous TiO2 structures have been of great interest in various photocatalytic applications over the past decade. However, the synthetic methods reported so far in the literature are complex and time consuming. This study presents a simple one-pot fabrication method of hollow porous TiO2 nanospheres using a sol-gel process involving CO2 generation in aqueous solution. The CO2 nanobubbles produced in the reaction act as a template for the crystal growth of TiO2 resulting in highly porous hollow nanospheres. The unique nanocrystal structure with a hollow nanosphere centre surrounded by an outer shell of prickle-like porous nanocrystals was observed. The prepared hollow porous TiO2 nanospheres exhibited excellent adsorption properties as demonstrated by the adsorption measurements and dynamic extraction of methylene blue in aqueous solution. Furthermore, the hollow porous TiO2 nanospheres hydrothermally treated at 180 °C exhibit 3.2 times higher photocatalytic performance in the decomposition of methylene blue than the commercial P25 TiO2. The idea of this work provides a new direction for facile green synthesis routes of various metal oxides with cavities, channels or crevices for various technological applications.

Direct Z-Scheme 2D/2D Photocatalyst Based on Ultrathin g-C3N4 and WO3 Nanosheets for Efficient Visible-Light-Driven H2 Generation

Ultrathin two-dimensional (2D) nanomaterials can not only boost the interfacial charge migration and separation but also provide abundant reactive sites for the photocatalytic H₂ generation. Herein, a kind of direct Z-scheme 2D/2D hybrid nanomaterial is fabricated by post-annealing atomically ultrathin Pt-loaded g-C₃N₄ nanosheets (Pt-CN NSs) with a thickness of ∼4.0 nm and hydrogen-treated WO₃ nanosheets (HWO NSs) with a thickness of ∼2.6 nm. The strong affinity existing between the two types of nanosheets with few-layer stacking results in the formation of atomically ultrathin 2D/2D hybrid nanomaterials (Pt-CN/HWO) with intimate interfacial contact in which the strong electronic interaction and efficient charge separation lead to a direct Z-scheme electron flowing from HWO NSs to CN NSs and then to the Pt cocatalyst for catalyzing the H₂ generation reaction. After optimizing the component ratio, the corresponding Pt-CN/HWO hybrid nanomaterial delivers a significantly boosted photocatalytic H₂ generation activity, up to 6.2 times as high as that of the Pt-CN/WO composite containing Pt-CN NSs and WO₃ nanoplates (WO NPs) without hydrogen treatment. This result reveals that the atomically ultrathin nanosheets in the 2D/2D hybrid nanomaterials can not only deliver strong electronic interaction to promote the Z-scheme mechanism for maintaining the high reduction ability of g-C₃N₄ and high oxidation ability of WO₃ but also alleviate the charge recombination, therefore resulting in the excellent photocatalytic H₂ generation performance.

Selected pharmaceuticals removal using algae derived porous carbon: experimental, modeling and DFT theoretical insights

Porous carbon from Laminaria digitata algae activated using NaOH (PCLD@NaOH) was prepared by a chemical activation approach and has been tested for the adsorption of ketoprofen and aspirin molecules. The prepared PCLD@NaOH was characterized using XPS, FTIR, Raman, N2-physisorption, SEM, acidic/basic character (Boehm), and pHPZC. The batch adsorption of ketoprofen and aspirin was investigated under different parameters. The adsorption kinetics on PCLD@NaOH were well described by the Avrami-fractional kinetic model and the equilibrium data by Liu isotherm model. The adsorption capacity of aspirin (970.88 mg g-1 at 25 °C) was higher than ketoprofen (443.45 mg g-1 at 25 °C). The thermodynamic values indicate that the adsorption of ketoprofen and aspirin is exothermic and spontaneous. These results were in good agreement with DFT calculation that shows that the aspirin molecule presents high reactivity, electrophilicity, and softness compared to the ketoprofen molecule. Finally, the response surface methodology was used to optimize the removal efficiency of ketoprofen and aspirin.

Antituberculosis drug isoniazid degraded by electro-Fenton and photoelectro-Fenton processes using a boron-doped diamond anode and a carbon-PTFE air-diffusion cathode

Solutions with 0.65 mM of the antituberculosis drug isoniazid (INH) in 0.050 M Na₂SO₄ at pH 3.0 were treated by electro-Fenton (EF) and UVA photoelectro-Fenton (PEF) processes using a cell with a BDD anode and a carbon-PTFE air-diffusion cathode. The influence of current density on degradation, mineralization rate, and current efficiency has been thoroughly evaluated in EF. The effect of the metallic catalyst (Fe²⁺ or Fe³⁺) and the formation of products like short-chain linear aliphatic carboxylic acids were assessed in PEF. Two consecutive pseudo-first-order kinetic regions were found using Fe²⁺ as catalyst. In the first region, at short time, the drug was rapidly oxidized by ^●OH, whereas in the second region, at longer time, a resulting Fe(III)-INH complex was much more slowly removed by oxidants. INH disappeared completely at 300 min by EF, attaining 88 and 94% mineralization at 66.6 and 100 mA cm^-2, respectively. Isonicotinamide and its hydroxylated derivative were identified as aromatic products of INH by GC-MS and oxalic, oxamic, and formic acids were quantified by ion-exclusion HPLC. The PEF treatment of a real wastewater polluted with the drug led to slower INH and TOC abatements because of the parallel destruction of its natural organic matter content.

Fabrication of nanostructured NiO/WO3with graphitic carbon nitride for visible light driven photocatalytic hydroxylation of benzene and metronidazole degradation

Fabrication of a novel NiO/WO₃nanohybrid modified graphitic carbon nitride nanosheets with enhanced photocatalytic activity towards photocatalytic hydroxylation of benzene and degradation of a pharmaceutical waste metronidazole.

Construction of direct Z-Scheme photocatalysts for overall water splitting using two-dimensional van der waals heterojunctions of metal dichalcogenides

The direct Z-scheme system constructed by two-dimensional (2D) materials is an efficient route for hydrogen production from photocatalytic water splitting. In the present work, the 2D van der Waals (vdW) heterojunctions of MoSe₂ /SnS₂ , MoSe₂ /SnSe₂ , MoSe₂ /CrS₂ , MoTe₂ /SnS₂ , MoTe₂ /SnSe₂ , and MoTe₂ /CrS₂ are proposed to be promising candidates for direct Z-scheme photocatalysts and verified by first principles calculations. Perpendicular electric field is induced in these 2D vdW heterojunctions, which enhances the efficiency of solar energy utilization. Replacing MoSe₂ with MoTe₂ not only facilitates the interlayer carrier migration, but also improves the optical absorption properties for these heterojunctions. Excitingly, the 2D vdW MoTe₂ /CrS₂ heterojunction is demonstrated, for the first time, to be 2D near-infrared-light driven photocatalyst for direct Z-scheme water splitting. © 2018 Wiley Periodicals, Inc.

Solar light harvesting with multinary metal chalcogenide nanocrystals

The paper reviews the state of the art in the synthesis of multinary (ternary, quaternary and more complex) metal chalcogenide nanocrystals (NCs) and their applications as a light absorbing or an auxiliary component of light-harvesting systems. This includes solid-state and liquid-junction solar cells and photocatalytic/photoelectrochemical systems designed for the conversion of solar light into the electric current or the accumulation of solar energy in the form of products of various chemical reactions. The review discusses general aspects of the light absorption and photophysical properties of multinary metal chalcogenide NCs, the modern state of the synthetic strategies applied to produce the multinary metal chalcogenide NCs and related nanoheterostructures, and recent achievements in the metal chalcogenide NC-based solar cells and the photocatalytic/photoelectrochemical systems. The review is concluded by an outlook with a critical discussion of the most promising ways and challenging aspects of further progress in the metal chalcogenide NC-based solar photovoltaics and photochemistry.

Facile Synthesis of Novel CaIn₂S₄/ZnIn₂S₄ Composites with Efficient Performance for Photocatalytic Reduction of Cr(VI) under Simulated Sunlight Irradiation

A series of novel and efficient heterostructured composites CaIn₂S₄/ZnIn₂S₄ have been synthesized using a facile hydrothermal method. XRD patterns indicate the as-prepared catalysts are two-phase composites of cubic phase CaIn₂S₄ and hexagonal phase ZnIn₂S₄. FESEM (field emission scanning electron microscope) images display that the synthesized composites are composed of flower-like microspheres with wide diameter distribution. UV–Vis diffuse reflectance spectra (DRS) show that the optical absorption edges of the CaIn₂S₄/ZnIn₂S₄ composites shift toward longer wavelengths with the increase of the CaIn₂S₄ component. The photocatalytic activities of the as-synthesized composites are investigated by using the aqueous-phase Cr(VI) reduction under simulated sunlight irradiation. This is the first report on the application of the CaIn₂S₄/ZnIn₂S₄ composites as stable and efficient photocatalysts for the Cr(VI) reduction. The fabricated CaIn₂S₄/ZnIn₂S₄ composites possess higher photocatalytic performance in comparison with pristine CaIn₂S₄ or ZnIn₂S₄. The CaIn₂S₄/ZnIn₂S₄ composite with a CaIn₂S₄ molar content of 30% exhibits the optimum photocatalytic activity. The primary reason for the significantly enhanced photoreduction activity is proved to be the substantially improved separation efficiency of photogenerated electrons/holes caused by forming the CaIn₂S₄/ZnIn₂S₄ heterostructured composites. The efficient charge separation can be evidenced by steady-state photoluminescence spectra (PLs) and transient photocurrent response. Based on the charge transfer between CaIn₂S₄ and ZnIn₂S₄, an enhancement mechanism of photocatalytic activity and stability for the Cr(VI) reduction is proposed.

Multiple carrier-transfer pathways in a flower-like In2S3/CdIn2S4/In2O3 ternary heterostructure for enhanced photocatalytic hydrogen production

A novel flower-like In2S3/CdIn2S4/In2O3 (ICS) ternary heterostructure (HS) is rationally constructed for the first time by a series of carefully designed procedures. In2O3 nanoflakes are the main constituent units which assemble into a flower-like skeleton structure, and CdIn2S4 nanoparticles are in situ generated on the surface of In2O3 nanoflakes through the transformation of CdS quantum dots (QDs) while In2S3 nanoparticles are in situ produced at the region between CdIn2S4 nanoparticles and In2O3 nanoflakes resulting from a synchronous sulfuration procedure. As expected, the rationally designed ICS ternary HSs display significantly enhanced photocatalytic H2 production, especially ICS5 (sulfurized for 5 h) with the highest H2 evolution rate of 20.04 μmol h-1 (10 mg catalyst is used for photocatalytic reaction), which is 26.7 times and 2.6 times higher than that of pure In2O3 (0.75 μmol h-1) and In2S3/In2O3 binary HS (7.88 μmol h-1), respectively. The enhanced photocatalytic activity can be attributed to the multiple interfaces formed in the ICS HSs, including the CdIn2S4-In2O3 interface, the In2S3-In2O3 interface, and the CdIn2S4-In2O3-In2S3 interface, which construct multiple pathways for the transfer of photogenerated charge carriers, effectively promoting the photocatalytic hydrogen production.

Constructing a novel strategy for controllable synthesis of corrosion resistant Ti3+ self-doped titanium-silicon materials with efficient hydrogen evolution activity from simulated seawater

Exploiting solar power for hydrogen production from seawater is a great challenge owing to the corrosive properties of seawater and inadequate visible-light conversion capabilities. Here we report an uncomplicated post-processing method to construct Ti³⁺ self-doped titanium-silicon material with corrosion resistance. This is a new experimental method to regulate the electrical, optical, and photocatalytic performances of titanium-containing photocatalysts in a controlled way. Moreover, we demonstrate that Ti-O-Si materials with different calcination temperatures can serve as a highly efficient and convenient catalyst for photogeneration of hydrogen from water and simulated seawater. Consequently, the optimized Ti-O-Si (400) sample exhibits impressive enhancement in the photocatalytic hydrogen evolution performance, by nearly 10.0 and 43.1 times compared with TiO₂ nanoparticles in water and simulated seawater. The Ti-O-Si (400) with substantial Ti³⁺ and oxygen vacancies exhibits an excellent photocatalytic H₂ production performance due to the improved separation and transmission of the photogenerated electron-hole, the extended visible light response, and corrosion resistance. Our work opens a new door to engineering the intrinsic properties of the titanium-containing materials.

Cu2O/TiO2 nanoparticles as visible light photocatalysts concerning C(sp2)–P bond formation

A novel and efficient method has been developed for the construction of an aromatic-phosphorus (Ar-P) bond under visible light irradiation using Cu₂O/TiO₂ nanoparticles as inexpensive and available photocatalysts.

Z-scheme CaIn2S4/Ag3PO4 nanocomposite with superior photocatalytic NO removal performance: fabrication, characterization and mechanistic study

A Z-scheme CaIn₂S₄/Ag₃PO₄ photocatalyst with superior photocatalytic NO removal performance was fabricated and characterized, and mechanistic analysis was also carried out.

Hydrothermal synthesis of In2O3 nanoparticles hybrid twins hexagonal disk ZnO heterostructures for enhanced photocatalytic activities and stability

In₂O₃ nanoparticles hybrid twins hexagonal disk (THD) ZnO with different ratios were fabricated by a hydrothermal method. The as-obtained ZnO/In₂O₃ composites are constituted by hexagonal disks ZnO with diameters of about 1 μm and In₂O₃ nanoparticles with sizes of about 20-50 nm. With the increase of In₂O₃ content in ZnO/In₂O₃ composites, the absorption band edges of samples shifted from UV to visible light region. Compared with pure ZnO, the ZnO/In₂O₃ composites show enhanced photocatalytic activities for degradation of methyl orange (MO) and 4-nitrophenol (4-NP) under solar light irradiation. Due to suitable alignment of their energy band-gap structure of the In₂O₃ and ZnO, the formation of type п heterostructure can enhance efficient separation of photo-generate electro-hole pairs and provides convenient carrier transfer paths.

Fabrication of Heterogeneous-Phase Solid-Solution Promoting Band Structure and Charge Separation for Enhancing Photocatalytic CO2 Reduction: A Case of ZnXCa1-XIn2S4

Photocatalytic CO₂ reduction into solar fuels illustrates huge charm for simultaneously settling energy and environmental issues. The photoreduction ability of a semiconductor is closely correlated to its conduction band (CB) position. A homogeneous-phase solid-solution with the same crystal system always has a monotonously changed CB position, and the high CB level has to be sacrificed to achieve a benign photoabsorption. Herein, we report the fabrication of heterogeneous-phase solid-solution Zn_XCa_1-XIn₂S₄ between trigonal ZnIn₂S₄ and cubic CaIn₂S₄. The Zn_XCa_1-XIn₂S₄ solid solutions with orderly tuned photoresponsive range from 540 to 640 nm present a more negative CB level and highly enhanced charge-separation efficiency. Profiting from these merits, all of these Zn_XCa_1-XIn₂S₄ solid solutions exhibit remarkably strengthened photocatalytic CO₂ reduction performance under visible light (λ > 420 nm) irradiation. Zn_0.4Ca_0.6In₂S₄, bearing the most negative CB position and highest charge-separation efficiency, casts the optimal photocatalytic CH₄ and CO evolution rates, which reach 16.7 and 6.8 times higher than that of ZnIn₂S₄ and 7.2 and 3.9 times higher than that of CaIn₂S₄, respectively. To verify the crucial role of the heterogeneous-phase solid solution in promoting the band structure and photocatalytic performance, another heterogeneous-phase solid-solution Zn_XCd_1-XIn₂S₄ has been synthesized. It also displays an upshifted CB level and promoted charge separation. This work may provide a new perspective into the development of an efficient visible-light driven photocatalyst for CO₂ reduction and other photoreduction reactions.

Anchoring Tailored Low-Index Faceted BiOBr Nanoplates onto TiO2 Nanorods to Enhance the Stability and Visible-Light-Driven Catalytic Activity

In this work, a fantastic one-dimensional (1D) BiOBr/TiO₂ nanorod (NR) heterojunction composite was rationally proposed and designed from the perspective of molecular and interface engineering. The fabricated intimately connected interfacial heterojunction between two-dimensional BiOBr nanoplates and 1D TiO₂ NRs acts as an interfacial nanochannel to promote efficient interfacial charge migration and separation of photogenerated electron-hole pairs. As a result, 1D BiOBr/TiO₂ NR heterojunctions exhibited outstanding visible-light photocatalytic activities and sustained cycling performance. Under visible-light irradiation for 120 min, the reduction efficiency of Cr(VI) over the TB-2 sample (molar ratio: n(Ti)/n(Bi) = 2:1) is as high as 95.4% without adding any scavengers. Furthermore, the sample also shows excellent photodegradation activity of RhB with a much higher apparent rate constant of 0.49 min^-1 and 88.5% total organic carbon removal ratio. Furthermore, the corresponding mechanism of enhanced photocatalytic activity is proposed according to comprehensively investigated results from photoluminescence spectroscopy, photoelectrochemical measurement analysis, and radical trapping experiments. This study provides an attractive avenue to design and fabricate highly efficient 1D NR heterojunction photocatalysts, which possessed a high application value in the field of environmental remediation, especially for wastewater purification.

Heterojunction Photocatalysts

Semiconductor-based photocatalysis attracts wide attention because of its ability to directly utilize solar energy for production of solar fuels, such as hydrogen and hydrocarbon fuels and for degradation of various pollutants. However, the efficiency of photocatalytic reactions remains low due to the fast electron-hole recombination and low light utilization. Therefore, enormous efforts have been undertaken to solve these problems. Particularly, properly engineered heterojunction photocatalysts are shown to be able to possess higher photocatalytic activity because of spatial separation of photogenerated electron-hole pairs. Here, the basic principles of various heterojunction photocatalysts are systematically discussed. Recent efforts toward the development of heterojunction photocatalysts for various photocatalytic applications are also presented and appraised. Finally, a brief summary and perspectives on the challenges and future directions in the area of heterojunction photocatalysts are also provided.