Interfacial construction of SnS2/Zn0.2Cd0.8S nanopolyhedron heterojunctions for enhanced photocatalytic hydrogen evolution

ZnCdS, a metal chalcogenide solid solution, has attracted significant attention. However, two primary challenges hinder its widespread application in photocatalytic hydrogen evolution: the rapid recombination rate of photogenerated carriers and susceptibility to photo-oxidation in the aqueous environments. In this article, a facile hydrothermal route was employed for the first time to uniformly assemble SnS2 nanoparticles onto the surface of Zn0.2Cd0.8S (ZCS) nanopolyhedra. The intimate contact of two materials resulted in the formation of heterojunctions. By adjusting the content of SnS2, the hydrogen evolution reaction (HER) performance was optimized to reach up to 12170 μmol/gh, which is 1.9 times of the pristine ZCS. Notably, the photocatalyst demonstrated remarkable stability with an apparent quantum yield (AQY) of 15.5% at 420 nm. The enhanced photocatalytic performance can be attributed to the following factors: (i) The heterojunction composite, with larger surface area and more micropores, provides additional active sites and exhibits high photocatalytic activity; (ii) The internal electric field accelerates the separation of photogenerated carriers and reduces the recombination rate of electron-hole pairs; (iii) The photogenerated holes can be quickly transferred to the valence band of SnS2 and react with triethanolamine, thereby significantly reducing the photo-oxidation of ZCS. This work not only proposed a feasible route to improve the photocatalytic activity of ZCS, but also provided insights into the role of heterojunctions and the reaction mechanism.

Impact of Gd3+ doping on structural, electronic, magnetic, and photocatalytic properties of MnFe2O4 nanoferrites and application in dye-polluted wastewater remediation

The present work focuses on developing Gd-doped Mn spinel nanoferrites and their potential application in the photodegradation of water pollutants. The impact of Gd³⁺ ion substitution on structural, electronic, and magnetic characteristics of manganese ferrites has been studied. Nanocrystalline samples of MnGd_xFe_2-xO₄ (x = 0.0 to 0.10, in step size of 0.02) ferrites were prepared via sol-gel self-ignition route. The Rietveld, XPS, HRTEM, and SAED characterization methods confirmed the formation of phase pure ferrite nanoparticles (~ 8-22 nm) in the cubic spinel structure. The Gd³⁺ content in these nanoferrites responded to a systematic reduction in the size of nanocrystallites and an upsurge in the density of nanoferrites. The XPS study revealed fine assimilation of constituent elements in the fcc lattice and ruled out impurities in the nanoferrites. The Fe and the Gd ions were found to be in Fe³⁺ and Gd³⁺ states, respectively. While a major fraction of the Mn ions were found to be in the Mn²⁺ state, a small fraction of Mn⁴⁺ ions was observed on the surface of nanoparticles. The nanoferrites were found to exhibit a soft ferromagnetic state from 300 to 20 K limits. The highest saturation magnetization was observed for x = 0.02 (M_S = 66.6 emu/g at 20 K). The observed magnetic properties can be understood with the competing (Fe³⁺ and Mn²⁺)_A-O^2--[Fe³⁺, Mn²⁺, and Gd³⁺]_B superexchange interactions and magnetocrystalline anisotropy. Due to the small band gap energy of Gd-doped Mn ferrites than that of the pure Mn ferrite, they have demonstrated excellent photocatalytic activity for the degradation of methylene blue (MB) dye under visible light illumination. As much as 96.35% of the MB dye was found to get degraded in 70 min of light illumination over synthesized nanoparticles and the photodegradation reaction followed pseudo-first-order kinetics. The increased optical absorbance due to lower band gap, suppressed recombination rate of charge carriers, and enhanced charge mobility make them effective visible light active photocatalysts. This study revealed that the electronic, optical, and magnetic properties of MnFe₂O₄ nanoferrites could be easily tuned by varying the Gd³⁺ content and the prepared Gd-doped MnFe₂O₄ nanomaterials have boundless potential to be utilized in the future making promising active photocatalysts and degradation of harmful industrial dyes for enhanced protection in the fields of environment and health care.

Enhancement in photocatalytic water splitting using van der Waals heterostructure materials based on penta-layers

Recently, van der Waals heterostructures (vdWHs) have been used to improve the performance of 2D materials, enabling more applications. By using first-principles calculations, we have studied the electronic and optical properties of vdWHs composed of penta-siligraphene and other penta-layers (p-Si2C4/p-X; X = Si₂N₄, ZnO₂, Ge₂C₄ or SiGeC₄). The stability of the vdWHs is verified by computing their binding energy, vibrational phonon spectra and ab initio molecular dynamics simulations. By assessing the electronic properties, we have found that the p-Si2C4/p-ZnO2, p-Si2C4/p-Ge2C4 and p-Si2C4/p-SiGeC4 vdWHs are semiconductors with an indirect band gap characterized by type-I band alignment. Meanwhile, the p-Si2C4/p-Si2N4 vdWH is a quasi-direct band gap semiconductor characterized by type-II band alignment. Bader charge analysis and charge density of p-Si2C4/p-Si2N4 vdWHs showed that photogenerated electrons move from the p-Si2N4 monolayer to the p-Si2C4 monolayer limiting the recombination of photogenerated charges and improving the photocatalytic efficiency. Furthermore, the p-Si2C4/p-Si2N4 vdWH exhibits suitable band edge positions compared to isolated monolayers suggesting its potential applicability in photocatalytic water splitting. The calculated optical absorption revealed that the p-Si2N4 monolayer exhibits substantial optical absorption in the ultraviolet (UV) range, while the p-Si2C4 monolayer and the p-Si2C4/p-Si2N4 vdWH show outstanding optical absorption on the order of 10⁵ cm^-1 in the visible and UV ranges. More importantly, the p-Si2C4/p-Si2N4 vdWH can greatly improve the optical absorption in these regions, which leads to high-efficiency usage of solar energy. Our study provides a route to design new vdWHs based on pentagonal monolayers, as well as an efficient photocatalyst for photocatalytic water splitting and optical devices.

Millettia pinnata plant pod extract-mediated synthesis of Bi2O3 for degradation of water pollutants

In this study, plant extract obtained from pods of Millettia pinnata plant species was employed for nanosynthesis of Bi₂O₃. The as-synthesized semiconductor metal oxide nanoparticles were analyzed using various characterization tools such as X-ray diffraction (XRD), Scanning electron microscope (SEM), ultra violet-visible (UV-Vis), Fourier transform infrared (FTIR), Zeta potential, Raman, and X-ray photoelectron spectroscopy (XPS). The characterization results designate the formation of α and β forms of Bi₂O₃. FESEM images demonstrate rod and flake-like nanostructures ranging from 25 to 70 nm. The green synthesized nanomaterial was found efficient for reduction of 4-nitro phenol (4-NP) and 4-nitro aniline (4-NA). However, it showed better performance toward the reduction of 4-NA. Photocatalytic investigations demonstrated that the green synthesized nanophotocatalyst was capable in degrading Amido Black 10B (AB-10B) dye efficiently under visible light illumination. 98.83% degradation of AB-10B dye was achieved within 120 min of irradiation under optimum conditions of photocatalyst dose and dye concentration. Active species trapping experiments revealed prominent role of superoxide radicals (•O₂^-) while hydroxyl radicals (•OH) played considerable role in the AB-10B photocatalytic degradation process. Moreover, the photostability and reusability assessment study ascertained good performance of the catalyst after four runs of successive cycles.

Ultra-small molybdenum sulfide nanodot-coupled graphitic carbon nitride nanosheets: Trifunctional ammonium tetrathiomolybdate-assisted synthesis and high photocatalytic hydrogen evolution

The preparation of nanoscale molybdenum sulfide (MoS₂)-modified graphitic carbon nitride (g-C₃N₄) nanosheets usually contains complex and multiple-step operations, including the separate synthesis of nanoscale MoS₂ and g-C₃N₄ nanosheet, and their subsequent composite process. To effectively overcome the above drawbacks, herein, a facile one-step trifunctional ammonium tetrathiomolybdate ((NH₄)₂MoS₄)-assisted approach has been designed to produce ultra-small MoS_x nanodot-coupled g-C₃N₄ nanosheet photocatalyst, including the first addition of ammonium chloride (NH₄Cl) and (NH₄)₂MoS₄ into melamine precursors and their following one-step calcination. During high-temperature calcination, except for the promoting generation of the g-C₃N₄ nanosheets by produced ammonia (NH₃) and hydrogen sulfide (H₂S) gases, the above (NH₄)₂MoS₄ decomposition not only can efficiently clip the s-heptazine framework to produce more terminal amino groups and cyano groups, but also can produce ultra-small MoS_x nanodots on the resultant g-C₃N₄ nanosheet surface, resulting in the final production of ultra-small MoS_x nanodot-coupled g-C₃N₄ nanosheets. The resultant MoS_x nanodot-coupled g-C₃N₄ nanosheets evidently exhibit increased photocatalytic hydrogen (H₂)-generation rate, about 8-fold increase to the traditional MoS₂-modified g-C₃N₄ photocatalyst. The increased H₂-generation rate can be mainly attributed to the synergism of MoS_x nanodots and cyano group on the g-C₃N₄ nanosheet surface. The current facile technology could open the sights for the preparation of other high-efficiency photocatalysts.

Insights into the photocatalysis mechanism of the novel 2D/3D Z-Scheme g-C3N4/SnS2 heterojunction photocatalysts with excellent photocatalytic performances

A novel 2D/3D Z-scheme g-C₃N₄/SnS₂ photocatalyst was successfully fabricated via self-assembly forming 3D flower-like SnS₂ microspheres on the surface of the 2D g-C₃N₄ nanosheets. The photocatalytic performances of the samples were systematically explored through catalytic reduction of Cr⁶⁺ and oxidation of Bisphenol S (BPS) under the illumination of visible light, and the photocatalytic degradation pathway of BPS was also proposed based on the degradation products confirmed by GCMS. Among the as-prepared samples, 0.4-g-C₃N₄/SnS₂ exhibited the most efficient photocatalytic performances, and the apparent quantum efficiency (QE) for the removal of Cr⁶⁺ could achieve 30.3 %, which is 2.8 times higher than that of the SnS₂. The enhancing photocatalytic activities originated from the efficient interfacial charge migration and separation obtained in g-C₃N₄/SnS₂, which was firstly verified via the photoluminescence spectra, time-resolved photoluminescence spectra and photoelectrochemical characterizations. Importantly, the DFT calculated shows that the band distribution of the g-C₃N₄/SnS₂ sample is staggered near the forbidden, which can facilitate the efficient interfacial charge migration and separation as well as result in the improvement of the catalytic activity. Finally, we put forward a more reasonable Z-scheme charge transfer mechanism, it was verified by analysing the results of free radical scavenging tests, EPR experiments and theoretical calculations.

Interfaces of graphitic carbon nitride-based composite photocatalysts

This review concentrates on the interface issues of g-C₃N₄-based photocatalysts, including methods for constructing interfaces, techniques for identifying interfaces, and the types and roles of the as-developed interfaces.

TiO2 Nanosheet Arrays with Layered SnS2 and CoOx Nanoparticles for Efficient Photoelectrochemical Water Splitting

Converting solar energy into sustainable hydrogen fuel by photoelectrochemical (PEC) water splitting is a promising technology to solve increasingly serious global energy supply and environmental issues. However, the PEC performance based on TiO2 nanomaterials is hindered by the limited sunlight-harvesting ability and its high recombination rate of photogenerated charge carriers. In this work, layered SnS2 absorbers and CoOx nanoparticles decorated two-dimensional (2D) TiO2 nanosheet array photoelectrode have been rationally designed and successfully synthesized, which remarkably enhanced the PEC performance for water splitting. As the result, photoconversion efficiency of TiO2/SnS2/CoOx and TiO2/SnS2 hybrid photoanodes increases by 3.6 and 2.0 times under simulated sunlight illumination, compared with the bare TiO2 nanosheet arrays photoanode. Furthermore, the TiO2/SnS2/CoOx photoanode also presented higher PEC stability owing to CoOx catalyst served as efficient water oxidation catalyst as well as an effective protectant for preventing absorber photocorrosion.

Importance of Clean Surfaces on the Catalyst: SnS2 Nanorings for Environmental Remediation

The focus of the work is the synthesis of SnS₂ nanomaterials with (peg-SnS₂NF) and without (sf-SnS₂NR) the involvement of the organic template and the comparative study of their catalytic activities. The synthesis of these materials was achieved in a single-step procedure aided by hexamethyldisilazane (HMDS). These nanoparticles were subjected to X-ray diffraction, transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, and UV-vis spectroscopy analyses to investigate their structural, topographical, surface, and optical properties. The present work suggests that the surfactant-free SnS₂ nanoring (sf-SnS₂NR) catalyst has lower surface area compared to the poly(ethylene glycol)-stabilized SnS₂ nanoflower (peg-SnS₂NF) catalyst but shows high activity under visible light for the photoreduction of Cr(VI) and the photocatalytic degradation of organic dyes. The work exposed the importance of the clean surfaces on the catalyst and is expected to have a high impact on the photocatalytic activity of the SnS₂ nanomaterial. The study also endorses the utility of the HMDS-assisted synthetic method for the production of multifunctional semiconductor tin disulfide nanomaterials with multiple potential applications.

Two-dimensional SnS2 nanosheets exfoliated from an inorganic–organic hybrid with enhanced photocatalytic activity towards Cr(vi) reduction

Thin SnS₂ nanosheets with {001} facets dominating were obtained with the liquid-exfoliation method and exhibit largely improved photocatalytic activity for Cr(vi) reduction.

An amorphous MoSx modified g-C3N4 composite for efficient photocatalytic hydrogen evolution under visible light

In this work, an MoS_x/g-C₃N₄ composite photocatalyst was successfully fabricated by a sonochemical approach, where amorphous MoS_x was synthesized using a hydrothermal method with Na₂MoO₄·H₂O, H₄SiO₄(W₃O₉)₄ and CH₃CSNH₂ as precursors, and g-C₃N₄ nanosheets were produced using a two-step thermal polycondensation method. The hydrogen-evolution performance of the MoS_x/g-C₃N₄ composite was tested under visible light. The results show that the H₂-evolution rate of the MoS_x/g-C₃N₄ (7 wt%) photocatalyst reaches a maximum value of 1586 μmol g⁻¹ h⁻¹, which is about 70 times that of pure g-C₃N₄ nanosheets. The main reason is that amorphous MoS_x forms intimate heterojunctions with g-C₃N₄ nanosheets, and the introduction of MoS_x into g-C₃N₄ nanosheets not only enhances the ability to convert H⁺ into H₂, but also promotes the separation of photoinduced electron–hole pairs for the photocatalyst. BET analysis shows that the specific surface area and pore volume of g-C₃N₄ are decreased in the presence of MoS_x. XPS analysis manifests that MoS_x provides a number of active sites. Mott–Schottky plots show that the conduction band of MoS_x (−0.18 V vs. E_Ag/AgCl, pH = 7) is more negative than that of g-C₃N₄ nanosheets.

An MoS_x/g-C₃N₄ composite photocatalyst was successfully fabricated by a sonochemical approach, where amorphous MoS_x was synthesized using a hydrothermal method, and g-C₃N₄ nanosheets were produced using a two-step thermal polycondensation method.

Rationally designed MoS2/protonated g-C3N4 nanosheet composites as photocatalysts with an excellent synergistic effect toward photocatalytic degradation of organic pollutants

The positively charged ultrathin g-C₃N₄ nanosheets are prepared by ultrasonic-assisted exfoliation of the protonated g-C₃N₄. Compared with the protonated g-C₃N₄ and exfoliated g-C₃N₄, the positively charged ultrathin g-C₃N₄ has abundant functional groups as well as desired dispersibility in deionized water, thus it could serve as a basic building block for designing related heterojunction composites. To take a full advantage of these features, the positively charged ultrathin g-C₃N₄/MoS₂ composites are fabricated through a simple electrostatic adsorption and self-assembly process followed by a hydrothermal method. By loading an appropriate amount of MoS₂ on the ultrathin g-C₃N₄ nanosheets, the as-fabricated composites exhibit considerable improvement on the photocatalytic activities toward the degradation of typical organic pollutants (i.e., methyl orange and phenol) under visible light irradiation. The composite containing 2 wt% MoS₂ shows the highest efficiency of about 96.5% for the methyl orange degradation, which is about 3.5 times and 8 times compared to those of the positively charged ultrathin g-C₃N₄ and bulk g-C₃N₄, respectively. The superb photocatalytic performance benefits from the unique advantages, including richly available reaction sites, aligned energy levels between g-C₃N₄ and the MoS₂, and efficient electron transfer. This work opens new possibilities for the rational design and construction of the g-C₃N₄ based composites as highly efficient and stable visible-light driven photocatalysts for the degradation of organic pollutants.

Novel Ag2S quantum dot modified 3D flower-like SnS2 composites for photocatalytic and photoelectrochemical applications

Novel Ag₂S quantum dot modified 3D flower-like SnS₂ composites exhibit highly efficient photodegradation of MO and photocatalytic H₂ production.

Novel β-Ag2MoO4/g-C3N4 heterojunction catalysts with highly enhanced visible-light-driven photocatalytic activity

The kernel of photocatalysis research is the development of catalysts with remarkable photocatalytic activity.

C–S bond induced ultrafine SnS2 dot/porous g-C3N4 sheet 0D/2D heterojunction: synthesis and photocatalytic mechanism investigation

A C–S bond induced novel ultrafine SnS₂ dot/porous g-C₃N₄ sheet 0D/2D heterojunction for enhanced carrier separation and photocatalytic activities was developed.

Facile fabrication and enhanced visible-light photocatalytic activity of In2O3/Ag2CrO4 composites

The efficient charge transfer at the interfaces of In₂O₃/Ag₂CrO₄ composite due to the formation of Z-scheme system composed of In₂O₃, Ag and Ag₂CrO₄, which effectively improved the separation and transfer of photogenerated charge carriers.