Constructing Z-scheme 1D/2D heterojunction of ZnIn2S4 nanosheets decorated WO3 nanorods to enhance Cr(VI) photocatalytic reduction and rhodamine B degradation

Self-assembly of snowflake-like Cu2S with ultrathin ZnIn2S4 nanosheets to form S-scheme heterojunctions for photocatalytic hydrogen production

Step-scheme (S-scheme) heterojunction has attracted much attention in the design of heterostructures for photocatalysts. In this study, we successfully utilized the principle of electrostatic self-assembly to load ultrathin ZnIn2S4 nanosheets onto snowflake-like Cu2S using a simple grinding method, and synthesized Cu2S/ZnIn2S4 S-scheme heterojunctions according to the different work functions (Φ). At the optimal Cu2S loading ratio (5 wt%), the hydrogen yield of the Cu2S/ZnIn2S4 composites reaches 5.58 mmol·h-1·g-1, which is 5.12 times higher than that of pure ZnIn2S4 (1.09 mmol·h-1·g-1). The apparent quantum efficiency (AQE) of the Cu2S/ZnIn2S4 composites reaches 5.8 % (λ = 370 nm), which is an improvement compared to pure ZnIn2S4 (2.7 %). The AQE of pure ZnIn2S4 is 0.4 %, while the AQE of Cu2S/ZnIn2S4 composites is enhanced to 1.0 % at λ = 456 nm. The heterojunction interface of Cu2S and ZnIn2S4 builds a built-in electric field (IEF), which greatly reduces the recombination rate of photogenerated electrons and holes, retains highly reduced photoelectrons in the conduction band (CB) of ZnIn2S4. The snowflake structure of Cu2S effectively increases the active sites and specific surface area, and improves the light absorption. This work opens a new avenue for designing photocatalysts, synergizing energy development and protecting the environment.

Enhanced visible light driven photodegradation of rifampicin and Cr(VI) reduction activity of ultra-thin ZnO nanosheets/CuCo2S4QDs: A mechanistic insights, degradation pathway and toxicity assessment

In this study, we focused on fabrication of porous ultra-thin ZnO nanosheet (PUNs)/CuCo2S4 quantum dots (CCS QDs) for visible light-driven photodegradation of rifampicin (RIF) and Cr(VI) reduction. The morphology, structural, optical and textural properties of fabricated photocatalyst were critically analyzed with different analytical and spectroscopic techniques. An exceptionally high RIF degradation (99.97%) and maximum hexavalent Cr(VI) reduction (96.17%) under visible light was achieved at 10 wt% CCS QDs loaded ZnO, which is 213% and 517% greater than bare ZnO PUNs. This enhancement attributed to the improved visible light absorption, interfacial synergistic effect, and high surface-rich active sites. Extremely high generation of ●OH attributed to the spin-orbit coupling in ZnO PUNs@CCS QDs and the existence of oxygen vacancies. Besides, the ZnOPUNs@CCS QDs, forming Z-scheme heterojunctions, enhanced the separation of photogenerated charge carriers. We investigated the influencing factors such as pH, inorganic ions, catalyst dosage and drug dosage on the degradation process. More impressively, a stable performance of ZnO PUNs@CCS QDs obtained even after six consecutive degradation (85.9%) and Cr(VI) reduction (67.7%) cycles. Furthermore, the toxicity of intermediates produced during the photodegradation process were assessed using ECOSAR program. This work provides a new strategy for ZnO-based photocatalysis as a promising candidate for the treatment of various contaminants present in water bodies.

WO3/MIL-125 (Ti) composite material for enhancing the reduction of Cr(vi) under visible light

In wastewater containing heavy metals, Cr(vi) is a potentially toxic metal, mainly derived from production and processing processes such as textile printing, dyeing, ore mining, battery applications, metal cleaning and electroplating. WO3 is widely used in photocatalytic degradation and reduction, and its utilization rate of visible light is high. However, the rapid recombination of photogenerated electron-hole pairs of WO3 limits its use. In this work, the composite material (WxMy) of WO3 and MIL-125 (Ti) was prepared by the ball milling method, and the catalyst was used to photocatalytically reduce Cr(vi). After using W90M10 as a photocatalyst for 50 min, the reduction rate of Cr(vi) can reach 99.2%, and the reduction rate is 2.3 times that of WO3. After 5 cycles of use, the reduction rate can still reach 91.3%. It is mainly due to the formation of a II-type heterojunction between WO3 and MIL-125 (Ti), which promotes the separation of photogenerated electron-hole pairs, thus improving the efficiency of photocatalytic reduction of Cr(vi).

Synthesis of highly efficient novel two-step spatial 2D photocatalyst material WS2/ZnIn2S4 for degradation/reduction of various toxic pollutants

In this article, we report the synthesis, characterization of novel biofriendly 2D/2D heterostructure WS2/ZnIn2S4 material in which 2D WS2 nanosheets are uniformly distributed spatially onto the spherically arranged 2D leaves of ZnIn2S4. We then studied the in-depth photocatalytic degradation activity of this novel nanocomposite and its pristine component materials on cationic dye: malachite green, anionic dye: congo red and reduction of heavy metal: chromium(VI) and the degradation efficiency of composite material was also tested on rhodamine-B, methylene blue, methyl orange dyes and acetaminophen/paracetamol drug. Form factor, structure factor and shape factor analysis has been carried out using X-ray diffractometry (XRD). Bond vibrations, functional groups and phonon vibration mode analysis has been done based on Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy. Morphological and compositional analysis has been done using field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDAX) and X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HR-TEM). Surface area and pore size/distribution was characterized using Brunauer-Emmett-Teller (BET) method and Barrett-Joyner-Halenda Model. Degradation pathways and intermediate products are proposed using the high-performance liquid chromatography (HPLC). Photocatalytic activity of the nanocomposite WS2/ZnIn2S4 is compared with pristine ZnIn2S4 and pristine WS2, which shows more than 50% enhancement in both efficiency and rate of degradation/reduction for all the pollutants. A scavenger study was carried out to get insight of primary and secondary reactive oxygen species (ROS) taking part in degradation. Exciton lifetime, surface charge and stability, and flat band positions were studied based on time-correlated single photon counting (TCSPC) also known as time-resolved photoluminescence (TRPL), zeta potential, and Mott-Schottky respectively. Rate kinetics study was performed to analyze the physical and chemical behaviour of the nanocomposite with pollutants in consideration. Results show ∼100%, ∼90%, and ∼95% degradation efficiency by the heterostructure for malachite green (MG), congo red (CR), and reduction of heavy metal chromium (Cr(VI)) respectively within 5 min, which is a huge improvement as compared to pristine WS2 and pristine ZnIn2S4, both of which show the efficiencies of only ∼25% to∼75% in all the cases.

Roles of CeO2 in preparing Ce-doped CdIn2S4 with boosted photocatalytic degradation performance for methyl orange and tetracycline hydrochloride

Element doping is considered as a feasible strategy to develop efficient photocatalysts. In this study, a Ce-doped CdIn2S4 photocatalyst was prepared through a modified coprecipitation method. During the synthesis of Ce-doped CdIn2S4, the CeO2 nanorods were gradually reduced by the decomposition products of thioacetamide (TAA), and mainly existed as Ce(III) in the supernatant. This resulted in a large increase in the specific surface area of the as-obtained products, providing more exposed active sites for the reactant. Additionally, a trace amount of Ce was doped into the lattice of the CdIn2S4, resulting in a significant effect on the band structure. By tracing the roles of CeO2 during the synthesis process, a possible reaction mechanism was proposed. Benefiting from the synergistic advantages of the structural and compositional features, the optimal sample showed enhanced photocatalytic activities for the degradation of methyl orange (94.6% within 25 min) and tetracycline hydrochloride (85.6% within 120 min). The degradation rates were 13.3 times and 2.7 times higher than that of pristine CdIn2S4. This work may provide a strategy for designing metal element doped photocatalysts with good activity for pollutant removal.