Construction of Hierarchical Hollow Co9S8/ZnIn2S4 Tubular Heterostructures for Highly Efficient Solar Energy Conversion and Environmental Remediation

Visible‐light‐responsive hierarchical Co₉S₈/ZnIn₂S₄ tubular heterostructures are fabricated by growing 2D ZnIn₂S₄ nanosheets on 1D hollow Co₉S₈ nanotubes. This design combines two photoresponsive sulfide semiconductors in a stable heterojunction with a hierarchical hollow tubular structure, improving visible‐light absorption, yielding a large surface area, exposing sufficient catalytically active sites, and promoting the separation and migration of photogenerated charges. The hierarchical nanotubes exhibit excellent photocatalytic H₂ evolution and Cr^VI reduction efficiency. Under visible‐light illumination, the optimized Co₉S₈/ZnIn₂S₄ heterostructure provides a remarkable H₂ generation rate of 9039 μmol h^?1 g^?1 without the use of any co‐catalysts and Cr^VI is completely reduced in 45 min. The Co₉S₈/ZnIn₂S₄ heterostructure is stable after multiple photocatalytic cycles.     

Fabrication of ternary dual Z-Scheme AgI/ZnIn2S4/BiVO4 heterojunction photocatalyst with enhanced photocatalytic degradation of tetracycline under visible light

In this study, a novel ternary AgI/ZnIn₂S₄/BiVO₄(AZB) composite photocatalyst was successfully prepared by hydrothermal method and in-situ precipitation method. The as-synthesized samples were characterized by XRD, SEM, TEM, XPS and so on, and the photocatalytic activity was evaluated through photocatalytic degradation of tetracycline (TC) under visible light irradiation. When the molar ratio of Bi to Ag was 1:1, the degradation rate of TC can reach 91.44 % within 150 min. The AZB heterojunction demonstrated outstanding efficiency with the apparent reaction rate constants of 0.02118 min^?1 for TC removal, was 4.68, 3.27 and 3.27 times higher than that of pure BiVO₄, AgI and ZnIn₂S₄. Based on active species trapping experiments and ESR analysis, a dual Z-Scheme pathways among BiVO₄, AgI and ZnIn₂S₄ for effective separation of photogenerated charges was recommended. This work provided a promising insight for the design of ternary dual Z-scheme heterojunction with multilevel electron transfer to present greater photo-absorption, charge separation, and photodegradation for environmental decontamination.     

A Z‐Scheme Strategy that Utilizes ZnIn2S4 and Hierarchical VS2 Microflowers with Improved Charge‐Carrier Dynamics for Superior Photoelectrochemical Water Oxidation

One of the major limiting factors for efficient photoelectrochemical water oxidation is the fast recombination kinetics of photogenerated charge carriers. Herein, we propose a model system that utilizes ZnIn₂S₄ and hierarchical VS₂ microflowers for efficient charge separation through a Z‐scheme pathway, without the need for an electron mediator. An impressive 18‐fold increase in photocurrent was observed for ZnIn₂S₄–VS₂ compared to ZnIn₂S₄ alone. The charge‐transfer dynamics in the composite were found to follow a Z‐scheme pathway, which resulted in decreased charge recombination and greater accumulation of the surface charge. Furthermore, slow kinetics of the surface reaction in the ZnIn₂S₄–VS₂ composite correlated to an increased surface‐charge capacitance. This feature of the composite material facilitated partial storage of the photogenerated charge carriers (e^?/h⁺) under illumination and dark‐current conditions, thus storing and utilizing solar energy more efficiently.     

Light-Driven Syngas Production over Defective ZnIn2S4 Nanosheets

Photocatalytic syngas (CO and H₂) production with CO₂ as gas source not only ameliorates greenhouse effect, but also produces valuable chemical feedstocks. However, traditional photocatalytic systems require noble metal or suffers from low yield. Here, we demonstrate that S vacancies ZnIn₂S₄ (V_S-ZnIn₂S₄) nanosheets are an ideal photocatalyst to drive CO₂ reduction into syngas. It is found that building S vacancies can endow ZnIn₂S₄ with stronger photoabsorption, efficient electron–hole separation, and larger CO₂ adsorption, finally promoting both hydrogen evolution reaction (HER) and CO₂ reduction reaction (CO₂RR). The syngas yield of CO and H₂ is therefore significantly increased. In contrast to pristine ZnIn₂S₄, the syngas yield over V_S-ZnIn₂S₄ can be improved by roughly ≈4.73 times and the CO/H₂ ratio is modified from 1:4.18 to 1:1. Total amount of syngas after 12 h photocatalysis is as high as 63.20 mmol g⁻¹ without use of any noble metals, which is even higher than those of traditional noble metal-based catalysts in the reported literatures. This work demonstrates the critical role of S vacancies in mediating catalytic activity and selectivity, and highlights the attractive ability of defective ZnIn₂S₄ for light-driven syngas production.     

N- and S-doped ordered mesoporous carbon tubes with efficient S confinement for high-performance Li–S batteries

The insulating properties of S/Li₂S₂/Li₂S and the soluble Li₂S₄/Li₂S₆/Li₂S₈ obstruct the practical application of Li–S batteries. In this work, highly ordered N and S co-doped mesoporous carbon tubes (NSMCTBs) with high specific surface areas and large pore volume are employed to confine and improve the utilization efficiency of S species in Li–S batteries. The strong S_nLi₂?N interaction and S–S chemical bond between thiophenic S and Li₂S_n guarantee the exceptional electrochemical performance of as-prepared NSMCTBs/S cathode. A relatively high discharge capacity of 1315.2 mAh g^?1 is achieved for the first cycle at 0.5 C and maintained at 644.1 mAh g^?1 after 500 cycles. The NSMCTBs/S with high S content of up to 80%, it also delivers a discharge capacity of 1092.1 mAh g^?1 and considerable cycling performance. More importantly, the NSMCTBs/S can effectively suppress the self-discharge behavior of Li–S batteries.     

Enhanced Photoexcited Carrier Separation in Oxygen‐Doped ZnIn2S4 Nanosheets for Hydrogen Evolution

Limited by the relatively sluggish charge‐carrier separation in semiconductors, the photocatalytic performance is still far below what is expected. Herein, a model of ZnIn₂S₄ (ZIS) nanosheets with oxygen doping is put forward to obtain in‐depth understanding of the role that doping atoms play in photocatalysis. It shows enhanced photocatalytic activity compared with pristine ZIS. The electron dynamics analyzed by ultrafast transient absorption spectroscopy reveals that the average recovery lifetime of photoexcited electrons is increased by 1.53 times upon oxygen incorporation into the ZIS crystals, indicating enhanced separation of photoexcited carriers in oxygen‐doped ZIS nanosheets. As expected, the oxygen‐doped ZIS nanosheets show a remarkably improved photocatalytic activity with a hydrogen evolution rate of up to 2120 μmol h^?1 g^?1 under visible‐light irradiation, which is 4.5 times higher than that of the pristine ZIS nanosheets.     

The effect of calcination temperature on the texture of silica gel waste

In this work, the effect of temperature on the texture of silica gel waste is presented and water vapour adsorption in a different humidity is highlighted. It was found that silica gel waste is a mesoporous material with the parallel plates pores. Its specific surface area is equal to 4.61 m² g^?1, and the calculated total pore volume is equal to 9.01 × 10^?3 cm³ g^?1. The texture of silica gel waste changed during calcination in a 188–550 °C temperature interval: S_BET and ΣV_P increased to 11.32 m² g^?1 and 30.06 × 10^?3 cm³ g^?1, respectively. It was determined that the water vapour pressure influenced the mineralogical composition and the quantity of adsorbed water in the samples. The obtained results were confirmed by the differential scanning microcalorimetry, X-ray diffraction, BET and water vapour adsorption analysis data.

     

Enhanced Photocatalytic Hydrogen Evolution over Hierarchical Composites of ZnIn2S4 Nanosheets Grown on MoS2 Slices

A highly active hierarchical MoS₂/ZnIn₂S₄ composite catalyst was synthesized in situ by using a facile controlled‐growth approach through a solvothermal process. During the solvothermal reaction, 2D ultrathin curled ZnIn₂S₄ nanosheets grew on the surface of MoS₂ slices, which could help to form a more‐homogeneous mixture, effective interfacial contact, and strong interactions between the ZnIn₂S₄ nanosheets and the MoS₂ slices. The intimate contact between ZnIn₂S₄ and MoS₂ favored the formation of junctions between the two components, thereby improving the charge separation and prolonging the mean lifetime of the electron–hole pairs. Moreover, growing ZnIn₂S₄ nanosheets by visible‐light catalysis on MoS₂ slices afforded a higher number of available catalytically active sites. So, the photocatalytic hydrogen‐evolution performance of the hierarchical MoS₂/ZnIn₂S₄ composite was significantly enhanced, owing to a synergistic effect of these factors. This work could provide new insights into the fabrication of a highly efficient and low‐cost non‐noble‐metal co‐catalyst for visible‐light H₂ generation.     

Improved photocatalytic performance of anatase TiO2 synthesized through ethanol supercritical drying technique

Anatase titania (TiO₂) nanoparticles were synthesized via a self‐developed ethanol vapor‐thermal method at 240°C (T240) and 250°C (T250), i.e. at temperatures lower and higher, respectively, than the supercritical temperature (243.5°C, 7.0 MPa) of ethanol. Compared to T240, T250 exhibited a higher ratio of exposed (001) facets, oxygen vacancies, and concomitant TiO_x. The specific surface area of T250 was 119.0 m² g^?1, smaller than that of T240 (144.2 m² g^?1). During the degradation of methylene blue, T250 exhibited a high apparent rate constant (K_app) of 14.5 × 10^?2 min^?1, which was 6.3 times larger than that for T240. Furthermore, compared to T240, T250 exhibited better performance toward degradation of phenol. Results of electron spin resonance spectroscopy and photoluminescence indicated that the photogenerated electron–hole pairs possessed higher separation efficiency for T250 than for T240. In summary, the excellent photocatalytic performance of T250 originates from the higher ratios of exposed (001) facets, oxygen vacancies or TiO_x, C═O groups adsorbed at the surface of particles, and higher separation efficiency of photogenerated electron–hole pairs. By employing this self‐developed vapor‐thermal method, a variety of catalysts and their composites can be synthesized, which may exhibit novel morphological characteristics and properties as well as excellent photocatalytic performance.     

Rational design of ternary NiS/CQDs/ZnIn2S4 nanocomposites as efficient noble-metal-free photocatalyst for hydrogen evolution under visible light

The NiS/CQDs nanocomposite (CQDs represents carbon quantum dots), with a mass ratio of NiS/CQDs to be 1.19:1 based on the ICP result, was obtained via a facile hydrothermal method from a mixture of CQDs, Ni(OAc)₂ and Na₂S. The self-assembly of ZnIn₂S₄ microspheres on the surface of NiS/CQDs was realized under microwave conditions to obtain a ternary NiS/CQDs/ZnIn₂S₄ nanocomposite. The as-obtained NiS/CQDs/ZnIn₂S₄ nanocomposite was fully characterized, and its photocatalytic hydrogen evolution under visible light irradiation was investigated. The ternary NiS/CQDs/ZnIn₂S₄ nanocomposite showed superior photocatalytic activity for hydrogen evolution than ternary CQDs/NiS/ZnIn₂S₄, which was obtained by deposition of NiS in the preformed CQDs/ZnIn₂S₄. The superior photocatalytic performance of ternary NiS/CQDs/ZnIn₂S₄ is ascribed to the introduction of CQDs, which act as a bridge to promote the vectorial transfer of photo-generated electrons from ZnIn₂S₄ to NiS. This result suggests that the rational design and fabrication of ternary CQDs-based systems are important for the efficient photocatalytic hydrogen evolution. This study provides a strategy for developing highly efficient noble-metal-free photocatalysts for hydrogen evolution using CQDs as a bridge to promote the charge transfer in the nanocomposite.     

Preparation of Yolk‐Shell and Filled Co9S8 Microspheres and Comparison of their Electrochemical Properties

In this study, we report the first preparation of phase‐pure Co₉S₈ yolk–shell microspheres in a facile two‐step process and their improved electrochemical properties. Yolk–shell Co₃O₄ precursor microspheres are initially obtained by spray pyrolysis and are subsequently transformed into Co₉S₈ yolk–shell microspheres by simple sulfidation in the presence of thiourea as a sulfur source at 350 °C under a reducing atmosphere. For comparison, filled Co₉S₈ microspheres were also prepared using the same procedure but in the absence of sucrose during the spray pyrolysis. The prepared yolk–shell Co₉S₈ microspheres exhibited a Brunauer–Emmett–Teller (BET) specific surface area of 18 m² g^?1 with a mean pore size of 16 nm. The yolk–shell Co₉S₈ microspheres have initial discharge and charge capacities of 1008 and 767 mA h g^?1 at a current density of 1000 mA g^?1, respectively, while the filled Co₉S₈ microspheres have initial discharge and charge capacities of 838 and 638 mA h g^?1, respectively. After 100 cycles, the discharge capacities of the yolk–shell and filled microspheres are 634 and 434 mA h g^?1, respectively, and the corresponding capacity retentions after the first cycle are 82 % and 66 %.     

Construction of porous NiCo2S4@CeO2 microspheres composites for high-performance pseudocapacitor electrode by morphology reshaping

NiCo₂S₄ microspheres consisting of nanoparticles were synthesized by a simple hydrothermal process, and then NiCo₂S₄@CeO₂ microspheres consisting of nanosheets or nanoneedles-like structures were constructed by a morphology reshaping process for the first time. The introduction of CeO₂ changes the nanoparticle morphology of NiCo₂S₄, and forms incompact nanosheet and nanoneedle structures. The porous, incompact nanosheet or nanoneedle structures with enhanced specific surface areas not only accelerate the charge transfer but also facilitate the electrolyte diffusion and provide more active sites for the redox reactions. These merits endow outstanding electrochemical performances to NiCo₂S₄@CeO₂ microspheres when used as electrode materials for electrochemical pseudocapacitor. Especially, NiCo₂S₄@CeO₂ (6 wt%) microspheres consisted of nanosheets show a high specific capacitance of 1263.6 F g^?1 with a retention rate of 81.1% at 20 A g^?1 after 10,000 cycles. Nonetheless, pristine NiCo₂S₄ microspheres consisted of nanoparticles only show a high specific capacitance of 555.2 F g^?1 with a retention rate of 63.5% at the same conditions. The first-principles calculation shows that the strong interactions between the NiCo₂S₄ and CeO₂ are favorable for the stabilization of the composite, being responsible for its good cycling performance. The result shows that the NiCo₂S₄@CeO₂ microspheres are promising electrode materials for high-performance pseudocapacitor, and morphology reshaping and CeO₂ modification are efficient ways to construct high-performance pseudocapacitor.     

Insights into photoluminescence property and photocatalytic activity of cubic and rhombohedral ZnIn2S4

Cubic and rhombohedral ZnIn₂S₄ were synthesized by thermal sulfidation of Zn-In mixed oxide precursor in H₂S atmosphere at different temperatures. Cubic ZnIn₂S₄ was obtained when Zn-In mixed oxide precursor was sulfurized at 400 °C. With sulfidation temperature increasing from 400 to 800 °C, the crystal phase of ZnIn₂S₄ gradually turned from cubic to rhombohedral, which was demonstrated by different analysis techniques such as XRD, Raman, SEM, etc. UV-vis absorption spectra indicated that cubic ZnIn₂S₄ displayed better light absorption property than rhombohedral ZnIn₂S₄, with band gaps calculated to be 2.0 and 2.5 eV, respectively. However, under visible light irradiation, rhombohedral ZnIn₂S₄ photocatalyzed H₂ evolution from aqueous sodium sulfite/sulfide solution efficiently, whereas cubic ZnIn₂S₄ was not active for this reaction. The photoluminescence property revealed the different dynamics of photogenerated carriers, which made a predominant contribution to the increasing photocatalytic performances of ZnIn₂S₄ with crystal phase turning from cubic to rhombohedral.     

Novel synthesis of high-surface-area ordered mesoporous TiO2 with anatase framework for photocatalytic applications

Ordered mesoporous TiO₂ materials with an anatase frameworks have been synthesized by using a cationic surfactant cetyltrimethylammonium bromide (C₁₆TMABr) as a structure-directing agent and soluble peroxytitanates as Ti precursor through a self-assembly between the positive charged surfactant S⁺ and the negatively charged inorganic framework I^? (S⁺I^? type). The low-angle X-ray diffraction (XRD) pattern of the as-prepared mesoporous TiO₂ materials indicates a hexagonal mesostructure. XRD and transmission electron microscopy results and nitrogen adsorption–desorption isotherms measurements indicate that the calcined mesoporous TiO₂ possesses an anatase crystalline framework having a maximum pore size of 6.9 nm and a maximum Brunauer–Emmett–Teller specific surface area of 284 m² g^?1. This ordered mesoporous anatase TiO₂ also demonstrates a high photocatalytic activity for degradation of methylene blue under ultraviolet irradiation.     

Visible‐Light Photocatalytic Hydrogen Production Activity of ZnIn2S4 Microspheres Using Carbon Quantum Dots and Platinum as Dual Co‐catalysts

ZnIn₂S₄ microspheres (ZIS MSs) were for the first time decorated with carbon quantum dots (CQDs) and platinum nanoparticles (NPs) as dual co‐catalysts of for photocatalytic H₂ production. The ZIS MSs co‐loaded with CQDs and Pt exhibited a high photocatalytic H₂ production rate of 1032.2 μmol h^?1 g^?1 with an apparent quantum efficiency of 2.2 % (420 nm) in triethanolamine aqueous solution under visible‐light irradiation, which was much higher than the respective photocatalytic rates of pure ZIS, Pt loaded ZIS, and CQDs‐decorated ZIS. Such a great enhancement was attributed to the integrative effect of good crystallization, enhanced light absorption, high electrical conductivity of CQDs, and the vectorial electron transfer from ZIS to CQDs and Pt NPs (ZIS→CQDs→Pt).     

Au nanoparticles loaded on hollow BiOCl microstructures boosting CO2 photoreduction

The BiOCl (BOC) synthesized by the water bath heating method was treated with sodium borohydride (NaBH₄) to introduce oxygen vacancies (OVs). At the same time, Au nanoparticles were loaded to prepare a series of Au/BiOCl samples with different ratios. OVs and Au nanoparticles can promote the light absorption of host photocatalyst in the visible region. The calculated work function of BiOCl and Au can verify the existence of Ohmic contact between the interface of them, which is conducive to the separation of charge carriers. Through a series of photoelectric tests, it was verified experimentally that the separation of charge carriers is indeed enhanced. The high-energy hot electrons produced by Au under the surface plasmon resonance (SPR) effect can increase the counts of electrons to participate in the CO₂ reduction reaction. Especially for 1.0%-Au/BOC, the yields of CO can reach 43.16 µmol g^?1 h^?1, which is 6.6 times more than that of BOC. Therefore, loading precious metal on semiconductors is an effective strategy to promote the photocatalytic performance of CO₂ reduction reactions.     

Three‐in‐One Oxygen Vacancies: Whole Visible‐Spectrum Absorption,Efficient Charge Separation,and Surface Site Activation for Robust CO2 Photoreduction

A facile and controllable in situ reduction strategy is used to create surface oxygen vacancies (OVs) on Aurivillius‐phase Sr₂Bi₂Nb₂TiO₁₂ nanosheets, which were prepared by a mineralizer‐assisted soft‐chemical method. Introduction of OVs on the surface of Sr₂Bi₂Nb₂TiO₁₂ extends photoresponse to cover the whole visible region and also tremendously promotes separation of photoinduced charge carriers. Adsorption and activation of CO₂ molecules on the surface of the catalyst are greatly enhanced. In the gas‐solid reaction system without co‐catalysts or sacrificial agents, OVs‐abundant Sr₂Bi₂Nb₂TiO₁₂ nanosheets show outstanding CO₂ photoreduction activity, producing CO with a rate of 17.11 μmol g^?1 h^?1, about 58 times higher than that of the bulk counterpart, surpassing most previously reported state‐of‐the‐art photocatalysts. Our study provides a three‐in‐one integrated solution to advance the performance of photocatalysts for solar‐energy conversion and generation of renewable energy.     

Efficient Visible‐Light‐Driven CO2 Reduction Mediated by Defect‐Engineered BiOBr Atomic Layers

Solar CO₂ reduction efficiency is largely limited by poor photoabsorption, sluggish electron–hole separation, and a high CO₂ activation barrier. Defect engineering was employed to optimize these crucial processes. As a prototype, BiOBr atomic layers were fabricated and abundant oxygen vacancies were deliberately created on their surfaces. X‐ray absorption near‐edge structure and electron paramagnetic resonance spectra confirm the formation of oxygen vacancies. Theoretical calculations reveal the creation of new defect levels resulting from the oxygen vacancies, which extends the photoresponse into the visible‐light region. The charge delocalization around the oxygen vacancies contributes to CO₂ conversion into COOH* intermediate, which was confirmed by in situ Fourier‐transform infrared spectroscopy. Surface photovoltage spectra and time‐resolved fluorescence emission decay spectra indicate that the introduced oxygen vacancies promote the separation of carriers. As a result, the oxygen‐deficient BiOBr atomic layers achieve visible‐light‐driven CO₂ reduction with a CO formation rate of 87.4 μmol g^?1 h^?1, which was not only 20 and 24 times higher than that of BiOBr atomic layers and bulk BiOBr, respectively, but also outperformed most previously reported single photocatalysts under comparable conditions.     

Three‐in‐One Oxygen Vacancies: Whole Visible‐Spectrum Absorption,Efficient Charge Separation,and Surface Site Activation for Robust CO2 Photoreduction

A facile and controllable in situ reduction strategy is used to create surface oxygen vacancies (OVs) on Aurivillius‐phase Sr₂Bi₂Nb₂TiO₁₂ nanosheets, which were prepared by a mineralizer‐assisted soft‐chemical method. Introduction of OVs on the surface of Sr₂Bi₂Nb₂TiO₁₂ extends photoresponse to cover the whole visible region and also tremendously promotes separation of photoinduced charge carriers. Adsorption and activation of CO₂ molecules on the surface of the catalyst are greatly enhanced. In the gas‐solid reaction system without co‐catalysts or sacrificial agents, OVs‐abundant Sr₂Bi₂Nb₂TiO₁₂ nanosheets show outstanding CO₂ photoreduction activity, producing CO with a rate of 17.11 μmol g^?1 h^?1, about 58 times higher than that of the bulk counterpart, surpassing most previously reported state‐of‐the‐art photocatalysts. Our study provides a three‐in‐one integrated solution to advance the performance of photocatalysts for solar‐energy conversion and generation of renewable energy.     

Excited states of pyrene excimer observed by photodissociation spectroscopy in a supersonic jet

The absorption spectrum of jet-cooled pyrene excimer was measured using photodissociation spectroscopy. Broad absorption bands were observed in the near-IR and visible regions, which were assigned to the B_2u^? ← B_3g^? and B_2u⁺ ← B_3g^? transitions of the excimer, respectively. Excitation of these bands results in rapid dissociation of the excimer into monomer fragments, one of which is an electronically excited monomer in the S₂ state. The formation mechanism of the pyrene excimer from the vdW dimer is also discussed.