Enhanced photocatalytic performance of SnS2 under visible light irradiation: strategies and future perspectives

Tin(II) sulfide (SnS2) has emerged as a promising candidate for visible light photocatalytic materials. As a member of the transition metal dichalcogenides (TMDs) family, SnS2 features a band gap of approximately 2.20 eV and a layered structure, rendering it suitable for visible light activation with a high specific surface area. However, the application of SnS2 as a visible light photocatalyst still requires improvement, particularly in addressing the high recombination of electrons and holes, as well as the poor selectivity inherent in its perfect crystal structure. Therefore, ongoing research focuses on strategies to enhance the photocatalytic performance of SnS2. In this comprehensive review, we analyze recent advances and promising strategies for improving the photocatalytic performance of SnS2. Various successful approaches have been reported, including controlling the reactive facets of SnS2, inducing defects in the crystal structure, manipulating morphologies, depositing noble metals, and forming heterostructures. We provide a detailed understanding of these phenomena and the preparation techniques involved, as well as future considerations for exploring new science in SnS2 photocatalysis and optimizing performance.

Saiz P, Reizabal A, Wuttke S, Celaya-Azcoaga L, Valverde A, Fernández de Luis R. A State-of-the-Art of Metal-Organic Frameworks for Chromium Photoreduction vs. Photocatalytic Water Remediation

Hexavalent chromium (Cr(VI)) is a highly mobile cancerogenic and teratogenic heavy metal ion. Among the varied technologies applied today to address chromium water pollution, photocatalysis offers a rapid reduction of Cr(VI) to the less toxic Cr(III). In contrast to classic photocatalysts, Metal-Organic frameworks (MOFs) are porous semiconductors that can couple the Cr(VI) to Cr(III) photoreduction to the chromium species immobilization. In this minireview, we wish to discuss and analyze the state-of-the-art of MOFs for Cr(VI) detoxification and contextualizing it to the most recent advances and strategies of MOFs for photocatalysis purposes. The minireview has been structured in three sections: (i) a detailed discussion of the specific experimental techniques employed to characterize MOF photocatalysts, (ii) a description and identification of the key characteristics of MOFs for Cr(VI) photoreduction, and (iii) an outlook and perspective section in order to identify future trends.

Process enhancing strategies for the reduction of Cr(VI) to Cr(III) via photocatalytic pathway

This discourse aimed at providing insight into the strategies that can be adopted to boost the process of photoreduction of Cr(VI) to Cr(III). Cr(VI) is amongst the highly detestable pollutants; thus, its removal or reduction to an innocuous and more tolerable Cr(III) has been the focus. The high promise of photocatalysis hinged on the sustainability, low cost, simplicity, and zero sludge generation. Consequently, the present dissertation provided a comprehensive review of the process enhancement procedures that have been reported for the photoreduction of Cr(VI) to Cr(III). Premised on the findings from experimental studies on Cr(VI) reductions, the factors that enhanced the process were identified, dilated, and interrogated. While the salient reaction conditions for the process optimization include the degree of ionization of reacting medium, available photogenerated electrons, reactor ambience, type of semiconductors, surface area of semiconductor, hole scavengers, quantum efficiency, and competing reactions, the relevant process variables are photocatalyst dosage, initial Cr(VI) concentration, interfering ion, and organic load. In addition, the practicability of photoreduction of Cr(VI) to Cr(III) was explored according to the potential for photocatalyst recovery, reactivation, and reuse reaction conditions and the process variables.

Enhanced As(III) transformation and removal with biochar/SnS2/phosphotungstic acid composites: Synergic effect of overcoming the electronic inertness of biochar and W2O3(AsO4)2 (As(V)-POMs) coprecipitation

The activation of carbon atoms in biochar is an important approach for realizing the reuse of discarded woody biomass resources. In this work, a strategy for the construction of carbon-based catalysts was proposed with Magnoliaceae root biomass as a carbon source, doped by SnS₂ and further decorated with heteropoly acid. The introduction of SnS₂ can activate the carbon atom and destroy the electronic inertness of the disordered biochar with 002 planes. In addition, the synergy between the Keggin unit of phosphotungstic acid and biochar/SnS₂ can suppress recombination of e^--h⁺ carriers. The adsorption and photocatalysis experiments results showed that the efficiency of removing As(III) by biochar/SnS₂/phosphotungstic acid (biochar/SnS₂/PTA) systems was 1.5 times that of biochar/SnS₂ systems, and the concentration of total arsenic in the biochar/SnS₂/PTA composite system gradually decreased during the photocatalysis process. The formation of As-POMs can simultaneously realize As(III) photooxidation and As(V) coprecipitation. The phase transfer of arsenic by As-POMs could significantly increase the As adsorption capacity. Specifically, the composites achieved the conversion of S atoms at the interface of biochar into SO₄^•- radicals to enhance the As(III) photooxidation performance.

Facile strategy for the fabrication of noble metal/ZnS composites with enhanced photocatalytic activities

The introduction of noble metal nanoparticles to photocatalysts can effectively improve the separation efficiency of the photogenerated electron–holes. Therefore, noble metal/ZnS composites were synthesized using a low-temperature solid-phase chemical method with sodium borohydride as the reducing agent. The characterization results showed that the noble metal/ZnS composites have been successfully obtained and that the noble metals were distributed on the surface of ZnS. The catalytic results suggested that the composites exhibited improved activity after introduction of noble metals, which can be attributed to the rapid migration of carriers and the enhancement of the light absorption, mainly owing to the tight combination between the ZnS and noble metals and the plasmon resonance effect of the noble metals. The catalytic mechanism was explored by using photoluminescence spectroscopy, photocurrent spectra, valence band X-ray photoelectron spectroscopy (XPS-VB) spectra and capture agent experiments, and a possible mechanism was proposed. This work provides a new strategy for the high-volume synthesis of noble metal-based composite photocatalysts, which could be helpful for sustainable development.

The introduction of noble metal nanoparticles to photocatalysts can effectively improve the separation efficiency of the photogenerated electron–holes.

A heterojunction photocatalyst constructed by the modification of 2D-CeO2 on 2D-MoS2 nanosheets with enhanced degrading activity

A new 2D/2D heterojunction of MoS₂/CeO₂ is successfully prepared by a facile hydrothermal method.

Facile synthesis of a novel WO3/Ag2MoO4 particles-on-plate staggered type II heterojunction with improved visible-light photocatalytic activity in removing environmental pollutants

A novel WO3/Ag2MoO4 heterojunction has been synthesized through a facile precipitation method with Ag2MoO4 particles firmly deposited on the surface of WO3 nanoplates, forming "particles-on-plate" type II heterojunction structures. This heterojunction exhibited improved photocatalytic activities for the degradation of rhodamine B (RhB), 4 chlorophenol (4-CP) and tetracycline hydrochloride (TC) under visible-light irradiation compared to pure Ag2MoO4 and WO3. In addition, the heterojunction with 10 wt% Ag2MoO4 displays the best photocatalytic performance, which was about 2 times better than that of pure WO3 or Ag2MoO4. The TC photodegradation rate reaches up to 91% within 90 min visible light irradiation. Furthermore, the photocatalytic efficiency of the Ag2MoO4/WO3 heterojunction is 1.3 times higher than that of the mixture of the two individual photocatalysts. This remarkable enhanced photocatalytic performance results from the staggered bandgap between Ag2MoO4 and WO3, which can suppress the recombination of electron-hole pairs efficiently. Moreover, based on the radical trapping experiment, the superoxide radical anions (·OH) and photogenerated holes (h+) are the crucial active oxidizing species.