Recent advances in metal sulfides: from controlled fabrication to electrocatalytic, photocatalytic and photoelectrochemical water splitting and beyond

This review describes an in-depth overview and knowledge on the variety of synthetic strategies for forming metal sulfides and their potential use to achieve effective hydrogen generation and beyond.

Controlled growth of vertically aligned ultrathin In2S3 nanosheet arrays for photoelectrochemical water splitting

This paper reports a facile solvothermal method for the in situ growth of vertically aligned In₂S₃ nanosheet arrays (NSAs) on fluorine-doped tin oxide substrates. The as-synthesized two-dimensional graphene-like In₂S₃ nanosheets show an ultrathin thickness down to 3.7 nm consisting of the duodenary interplanar spacing of the (222) plane and a tunable bandgap varying from 2.32 to 2.58 eV. The film thickness and nanosheet density of the In₂S₃ NSAs can be adjusted by varying the reaction time and precursor concentration. The In₂S₃ NSAs with a higher film thickness exhibit relatively higher photocurrent due to their stronger light absorption as well as larger surface area for sufficient charge separation and redox reaction. The photoelectrochemical performance of the In₂S₃ photoanodes can be greatly enhanced by constructing an effective heterojunction with ZnO to promote the photocarrier separation. The In₂S₃/ZnO NSAs have demonstrated an optimal photocurrent density of 349.1 μA cm^-2 at 1.2 V vs. RHE and a maximum incident photon to current efficiency of 10.26% at 380 nm, which are 13.5 and 38 times higher than those of the pristine In₂S₃ counterparts, respectively.

Enhancing the stability of CsPbBr3 nanocrystals by sequential surface adsorption of S2− and metal ions

Enhancing the photostability of CsPbBr₃ NCs through sequential surface adsorption of S²⁻ and In³⁺.

Facile Synthesis of Indium Sulfide/Flexible Electrospun Carbon Nanofiber for Enhanced Photocatalytic Efficiency and Its Application

Heterojunction system has been proved as one of the best architectures for photocatalyst owing to extending specific surface area, expanding spectral response range, and increasing photoinduced charges generation, separation, and transmission, which can provide better light absorption range and higher reaction site. In this paper, Indium Sulfide/Flexible Electrospun Carbon Nanofiber (In₂S₃/CNF) heterogeneous systems were synthesized by a facile one-pot hydrothermal method. The results from characterizations of SEM, TEM, XRD, Raman, and UV-visible diffuse reflectance spectroscopy displayed that flower-like In₂S₃ was deposited on the hair-like CNF template, forming a one-dimensional nanofibrous network heterojunction photocatalyst. And the newly prepared In₂S₃/CNF photocatalysts exhibit greatly enhanced photocatalytic activity compared to pure In₂S₃. In addition, the formation mechanism of the one-dimensional heterojunction In₂S₃/CNF photocatalyst is discussed and a promising approach to degrade Rhodamine B (RB) in the photocatalytic process is processed.

Construction of CuO/In2S3/ZnO heterostructure arrays for enhanced photocatalytic efficiency

Novel one-dimensional (1D) heterostructure arrays composed of CuO nanowire cores, intermediate In₂S₃ nanostructures, and ZnO nanorod sheaths (i.e. CuO/In₂S₃/ZnO heterostructure arrays) have been successfully synthesized by a multi-step process. First, single-crystalline CuO nanowires were directly grown on flexible Cu mesh substrates using a one-step annealing process under ambient conditions. Second, In₂S₃ nanostructures and ZnO nanorods were sequentially grown on the CuO nanowires by a two-step hydrothermal method at low reaction temperature. The morphology, crystal structures, and optical properties of the CuO/In₂S₃/ZnO heterostructure arrays were studied by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, energy-dispersive spectroscopy, and photoluminescence spectroscopy. The resultant ternary CuO/In₂S₃/ZnO heterostructure arrays exhibit excellent photocatalytic activity in the photodegradation of rhodamine 6G (R6G) under 10 W UV light irradiation, which is much higher than that of single-component (CuO nanowire arrays) or two-component systems (CuO/In₂S₃ heterostructure arrays). Furthermore, the reusability test demonstrates that the CuO/In₂S₃/ZnO heterostructure arrays on the Cu mesh still maintain high photocatalytic activity in the degradation of three kinds of organic pollutants even after five cycles, without any significant decline. These findings provide an insight into the design and synthesis of new CuO-based composites to effectively improve their photocatalytic performance.

Biomolecule-mediated hydrothermal synthesis of polyoxoniobate-CdS nanohybrids with enhanced photocatalytic performance for hydrogen production and RhB degradation

Using a biomolecule of l-cystine as the sulfur source and coordinating agent, polyoxoniobate-CdS nanohybrids were successfully synthesized under mild hydrothermal conditions. The adsorption of ammonium group (-NH₂) in l-cystine molecular structure on the surface of CdS renders the amine-anchored CdS positively charged, which readily combines with the negatively charged polyoxoniobate clusters in terms of the electrostatic interaction. The as-obtained polyoxoniobate-CdS nanohybrids exhibit much superior activity for H₂ evolution and RhB degradation under visible light as compared to the unhybridized CdS and polyoxoniobate. After co-loading Nb₆ and NiS as cocatalyst, the H₂-evolution activity of the nanohybrids is further increased up to 39 times as high as that of naked CdS, which can be attributed to an enhanced electron-transfer by adopting polyoxoniobate as electron-acceptor to retard the electron-hole recombination. The work may open an avenue for the green synthesis of cost-effective POMs-CdS nanohybrid photocatalysts for solar energy applications.

Visible-light-driven photocatalytic properties of binary MoS2/ZnS heterostructured nanojunctions synthesized via one-step hydrothermal route

The MoS₂/ZnS binary heterojunctions obtained by a facile one-step hydrothermal route is competent to retrench the forbidden energy gap by creating sulfur vacancies. The tailoring of the lattice parameters of sulfides for interfacial charge transfer through the heterojunctions enhanced photocatalytic activity.

Ca(II) doped β-In2S3 hierarchical structures for photocatalytic hydrogen generation and organic dye degradation under visible light irradiation

Hierarchical structures assembled by two-dimensional (2D) nanosheets could inherit the characteristics of nanosheets and acquire additional advantages from the unique secondary architectures, which would have important influences on the photocatalytic properties of semiconductor nanomaterials. In this work, we successfully synthesized Ca(II) doped β-In₂S₃ hierarchical structures stacked by thin nanosheets by a simple solution chemical process. The effects of reaction temperature and Ca²⁺ concentration on the size and morphology of the products were systematically investigated. The photocatalytic applications of the β-In₂S₃ hierarchical structures were evaluated for hydrogen production and degradation of Rhodamine B (RhB) under visible light irradiation (λ>420nm). The β-In₂S₃ hierarchical structures showed promising activity towards photocatalytic hydrogen production (145.0μmolg^-1h^-1) and RhB solution (1×10^-5M) was completely degraded within 100min under visible light irradiation.

Strongly Coupled Ternary Hybrid Aerogels of N-deficient Porous Graphitic-C3N4 Nanosheets/N-Doped Graphene/NiFe-Layered Double Hydroxide for Solar-Driven Photoelectrochemical Water Oxidation

Developing photoanodes with efficient sunlight harvesting, excellent charge separation and transfer, and fast surface reaction kinetics remains a key challenge in photoelectrochemical water splitting devices. Here we report a new strongly coupled ternary hybrid aerogel that is designed and constructed by in situ assembly of N-deficient porous carbon nitride nanosheets and NiFe-layered double hydroxide into a 3D N-doped graphene framework architecture using a facile hydrothermal method. Such a 3D hierarchical structure combines several advantageous features, including effective light-trapping, multidimensional electron transport pathways, short charge transport time and distance, strong coupling effect, and improved surface reaction kinetics. Benefiting from the desirable nanostructure, the ternary hybrid aerogels exhibited remarkable photoelectrochemical performance for water oxidation. Results included a record-high photocurrent density that reached 162.3 μA cm(-2) at 1.4 V versus the reversible hydrogen electrode with a maximum incident photon-to-current efficiency of 2.5% at 350 nm under AM 1.5G irradiation, and remarkable photostability. The work represents a significant step toward the development of novel 3D aerogel-based photoanodes for solar water splitting.

Novel β-In2.77S4 nanosheet-assembled hierarchical microspheres: synthesis and high performance for photocatalytic reduction of Cr(vi)

A novel nanosheet-assembled hierarchical sulfur deficient β-In_2.77S₄ microsphere photocatalyst was prepared, and the β-In_2.77S₄ microsphere shown high visible light photocatalytic activity in the reduction of aqueous Cr(vi).

Ultralong In2S3 Nanotubes on Graphene Substrate with Enhanced Electrocatalytic Activity

Ultralong one-dimensional (1D) nanostructures including nanowires or nanotubes have been extensively studied because of their widespread applications in many fields. Although a lot of methods have been reported to prepare In2S3 nanotubes, approaching these nanotubes through one-pot solution synthesis is still extremely difficult, probably because of the intrinsic isotropic crystal growth characteristic of In2S3. In this article, we demonstrated a self-assembly approach for hydrothermal synthesis of In2S3 nanotubes/graphene composites, which contain ultralong (up to 10 μm) In2S3 nanotubes on graphene substrate. The influence of several important synthetic parameters on the final products has been systematically investigated. Importantly, the as-prepared In2S3 nanotubes/graphene composites can be easily cast on FTO to form a film, which can be used as a counter electrode. Our research indicates that the as-fabricated counter electrode exhibits excellent electrocatalytic activity toward the iodide species (I-/I3-) reduction reaction and very high energy conversion efficiency (8.01%) in dye-sensitized solar cells.

Preparation of AgInS₂ quantum dot/In₂S₃ co-sensitized photoelectrodes by a facile aqueous-phase synthesis route and their photovoltaic performance

In an aqueous-phase system, AgInS2 quantum dot (QD) sensitized TiO2 photoanodes were prepared in situ by the reaction of β-In2S3 nanocrystals and as-prepared TiO2/Ag2S-QD electrodes, followed by a covering process with a ZnS passivation layer. A facile successive ionic layer adsorption and reaction (SILAR) method was adopted to obtain TiO2/Ag2S-QD electrodes. β-In2S3 nanocrystals synthesized by the chemical bath deposition (CBD) process serve as the reactant of AgInS2 as well as a buffer layer between the interfaces of TiO2 and AgInS2-QDs. A polysulfide electrolyte and a Pt-coated FTO glass count electrode were used to test the photovoltaic performance of the constructed devices. The characteristics of the sensitized photoelectrodes were studied in more detail by electron microscopy, X-ray techniques, and optical and photoelectric performance measurements. AgInS2 is the main photo-sensitizer for TiO2/AgInS2-QD/In2S3 electrodes and excess In2S3 appears on the surface of the electrodes. Based on the optimal Ag2S SILAR cycle, the best photovoltaic performance of the prepared TiO2/AgInS2-QD/In2S3 electrode with the short-circuit photocurrent density (Jsc) of 7.87 mA cm(-2) and power conversion efficiency (η) of 0.70% under full one-sun illumination was achieved.

In₂S₃/carbon nanofibers/Au ternary synergetic system: hierarchical assembly and enhanced visible-light photocatalytic activity

In this paper, carbon nanofibers (CNFs) were successfully synthesized by electrospinning technique. Next, Au nanoparticles (NPs) were assembled on the electrospun CNFs through in situ reduction method. By using the obtained Au NPs modified CNFs (CNFs/Au) as hard template, the In2S3/CNFs/Au composites were synthesized through hydrothermal technique. The results showed that the super long one-dimensional (1D) CNFs (about 306 nm in average diameter) were well connected to form a nanofibrous network; and, the Au NPs with 18 nm in average diameter and In2S3 nanosheets with 5-10nm in thickness were uniformly grown onto the surface of CNFs. Photocatalytic studies revealed that the In2S3/CNFs/Au composites exhibited highest visible-light photocatalytic activities for the degradation of Rhodamine B (RB) compared with pure In2S3 and In2S3/CNFs. The enhanced photocatalytic activity might arise from the high separation efficiency of photogenerated electron-hole pairs based on the positive synergetic effect between In2S3, CNFs and Au components in this ternary photocatalytic system. Meanwhile, the In2S3/CNFs/Au composites with hierarchical structure possess a strong adsorption ability towards organic dyes, which also contributed to the enhancement of photocatalytic activity. Moreover, the In2S3/CNFs/Au composites could be recycled easily by sedimentation due to their nanofibrous network structure.

Facile solvothermal synthesis of 3D flowerlike β-In2S3 microspheres and their photocatalytic activity performance

Three-dimension (3D) flowerlike β-In₂S₃ microspheres have been successfully synthesized by a facile solvothermal method using thioacetamide (TAA, CH₃CSNH₂) as both a sulfur source and ligand of In³⁺ in the ethanol–water system.

One-dimensional hierarchical heterostructures of In₂S₃ nanosheets on electrospun TiO₂ nanofibers with enhanced visible photocatalytic activity

In₂S₃ nanosheets were assembled on electrospun TiO₂ nanofibers template by a hydrothermal technique. For the obtained one-dimensional In₂S₃/TiO₂ hierarchical heterostructures (1D In₂S₃/TiO₂ H-HSs), the density and size of the secondary In₂S₃ nanosheets could be controlled by adjusting the reactant concentrations for the preparation of In₂S₃ in the hydrothermal process. The 1D In₂S₃/TiO₂ H-HSs exhibited higher visible-light photocatalytic activity for the degradation of Methyl orange (MO) and the reduction of Cr(VI), as compared with the pure TiOv nanofibers and pure In₂S₃ nanosheets. The enhanced visible light photocatalytic activity might be attributed to the extended absorption in the visible light region from the narrow band-gap In₂S₃, the effective photogenerated electron-hole separation by the photosynergistic effects of the In₂S₃/TiO₂ H-HSs and quick electron-transfer in the 1D TiO₂ nanofibers. Meanwhile, the 1D In₂S₃/TiO₂ H-HSs could be recycled easily by sedimentation due to their nanofibrous nonwoven web structure. Moreover, the mechanisms of photodegradation of MO and photoreduction of Cr(VI) were proposed through systematical investigations. This work provided new insights into utilizing 1D In₂S₃/TiO₂ H-HSs as high efficiency visible-light-driven photocatalysts for environmental remediation and energy conversion.

Improving the visible light photoactivity of In2S3-graphene nanocomposite via a simple surface charge modification approach

We report an efficient and easily accessible self-assembly route to synthesize In2S3-GR nanocomposites via electrostatic interaction of positively charged In2S3 nanoparticles with negatively charged graphene oxide (GO) followed by a hydrothermal process for reduction of GO to graphene (GR). The as-synthesized In2S3-GR nanocomposites exhibit much higher visible light photocatalytic activity toward selective reduction of nitroaromatic compounds in water than bare In2S3 nanoparticles and In2S3-GR-H that is obtained from the simple "hard" integration of GR nanosheets with solid In2S3 nanoparticles without modification of surface charge. On the basis of the joint characterizations and structure-photoactivity correlation it is disclosed that the enhanced photocatalytic performance of In2S3-GR is mainly ascribed to the more efficient interfacial contact between In2S3 and the GR nanosheets than In2S3-GR-H, which would amplify the use of electron conductivity and mobility of GR to improve the lifetime and transfer of photogenerated charge carriers more efficiently and thus boost the photoactivity more effectively. This work highlights the significant effect of preparation methods on the photoactivity of GR-semiconductor nanocomposites. It is expected that such a simple electrostatic self-assembly strategy could aid to rationally fabricate more efficient GR-semiconductor nanocomposites with improved interfacial contact and photocatalytic performance toward various photocatalytic selective transformations.

Hierarchical assembly of ultrathin hexagonal SnS2 nanosheets onto electrospun TiO2 nanofibers: enhanced photocatalytic activity based on photoinduced interfacial charge transfer

Well-designed hierarchical nanostructures with one dimensional (1D) TiO(2) nanofibers (120-350 nm in diameter and several micrometers in length) and ultrathin hexagonal SnS(2) nanosheets (40-70 nm in lateral size and 4-8 nm in thickness) were successfully synthesized by combining the electrospinning technique (for TiO(2) nanofibers) and a hydrothermal growth method (for SnS(2) nanosheets). The single-crystalline SnS(2) nanosheets with a 2D layered structure were uniformly grown onto the electrospun TiO(2) nanofibers consisted of either anatase (A) phase or anatase-rutile (AR) mixed phase TiO(2) nanoparticles. The definite heterojunction interface between SnS(2) nanosheets and TiO(2) (A or R) nanoparticles were investigated by high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). Moreover, the as-prepared SnS(2)/TiO(2) hierarchical nanostructures as nanoheterojunction photocatalysts exhibited excellent UV and visible light photocatalytic activities for the degradation of organic dyes (rhodamine B and methyl orange) and phenols (4-nitrophenol), remarkably superior to the TiO(2) nanofibers and the SnS(2) nanosheets, mainly owing to the photoinduced interfacial charge transfer based on the photosynergistic effect of the SnS(2)/TiO(2) heterojunction. Significantly, the SnS(2)/TiO(2) (AR) hierarchical nanostructures as the tricomponent heterojunction system possessed stronger photocatalytic activity than the bicomponent heterojunction system of SnS(2)/TiO(2) (A) hierarchical nanostructures or TiO(2) (AR) nanofibers, which was discussed in terms of the three-way photosynergistic effect between SnS(2), TiO(2) (A) and TiO(2) (R) component in the SnS(2)/TiO(2) (AR) heterojunction resulting in the high separation efficiency of photoinduced electron-hole pairs, as evidenced by photoluminescence (PL) and surface photovoltage spectra (SPS).