Remarkably efficient charge transfer through a double heterojunction mechanism by a CdS-SnS-SnS2/rGO composite with excellent photocatalytic performance under visible light

Green synthesis of 3D core-shell SnS2/SnS-Cd0.5Zn0.5S multi-heterojunction for efficient photocatalytic H2 evolution

Low charge carrier separation efficiency is one of the key factors restricting photocatalytic hydrogen evolution performance. It is an effective strategy to build heterojunctions to steer charge migration. Herein, a series of x-SnS2/SnS-Cd0.5Zn0.5S (x-SS-CZS) nanosphere composites with varying mass ratios of SnS2/SnS (SS) were prepared through in situ hydrothermal synthesis. Moreover, XRD, TEM, and XPS were used to characterize the 3D core-shell SS-CZS multi-heterojunction composite. The 5-SS-CZS heterojunction composite with 5 wt% content of SS exhibits a remarkable hydrogen evolution rate of 168.85 mmol g-1 h-1, which is 5.4 times higher than that of pristine twin CZS (31.08 mmol g-1 h-1) and 1.9 times higher than that of 5-SnS2-CZS (88.21 mmol g-1 h-1). Furthermore, the composite catalyst showed excellent photostability after four cycles of reactions under visible light illumination. The apparent quantum yield at λ = 420 nm could reach up to 24.78%. The excellent hydrogen evolution performance of 5-SS-CZS nanospheres is ascribed to the following factors: (1) a core-shell catalyst with broad spectral absorption improves light utilization efficiency, (2) hybrid material with large surface area provides more active sites and shows the highest H2 activity, (3) a multi-heterojunction composite extends the lifetime of photoinduced carriers and accelerates charge separation and migration, and (4) SS as a hole trapping agent enhances the photocatalytic stability performance. This work proposes a possible photocatalytic mechanism, while also providing a novel approach for the synthesis of highly active and stable photocatalysts.

Nitrogen vacancy-induced spin polarization of ultrathin zinc porphyrin nanosheets for efficient photocatalytic CO2 reduction

Metalloporphyrin compounds have excellent electron transfer and visible light absorption ability, demonstrating broad application prospects in the field of photocatalysis. In this work, the nitrogen vacancies (NVs) were successfully introduced into zinc porphyrin (ZnTCPP) ultrathin nanosheets through surface N2 plasma treatment, which is environmentally friendly and can react in low temperatures. Furthermore, the prepared nitrogen vacancies-zinc porphyrin (NVs-ZnTCPP) materials exhibited excellent photocatalytic CO2 reduction activity and selectivity, specifically, the CO production rate of ZnTCPP-1 (N2 plasma treatment, 1 min) achieved as high as 12.5 µmol g-1h-1, which is about 2.7 times greater than that of untreated ZnTCPP. Based on the experimental and density functional theory calculation (DFT) results, it is found that the promoted photocatalytic performance of NVs-ZnTCPP could be mainly attributed to nitrogen vacancy-induced spin polarization by reducing the reaction barriers and inhibiting the recombination of photoexcited carriers. This work provides a new perspective for the construction of vacancy-based metalloporphyrin, and further explores the intrinsic mechanism between the electron spin property and the performance of the photocatalyst.

Selectively Permeable FeOOH Amorphous Layer Coating CdS for Enhancing Photocatalytic Conversion of Benzyl Alcohol and Selectivity to Benzaldehyde

The development of new strategies to improve reaction efficiency and light utilization is one of the biggest challenges in photosynthetic chemistry. Dynamics control, particularly tuning the adsorption/desorption of reactants and products, is an ideal way to improve the conversion and selectivity in catalytic reactions, but it is rarely studied for photocatalytic organic synthesis. This study concerns the design of an amorphous FeOOH coating to decorate CdS photocatalyst to control the adsorption and desorption of reactants and products to improve reaction efficiency for the photocatalytic conversion of benzyl alcohol (BA) into benzaldehyde (BAD). The best conversion of the core-shell photocatalyst is 74.1 % in 2 h, together with >99.9 % selectivity to BAD, and the photocatalyst exhibits response above 600 nm, which is the longest active wavelength reported for the reaction. Further data illustrate that the amorphous FeOOH coating enables selective sorption of BA/BAD molecules by H-bonding interactions, which may result in the excellent performance. Construction of amorphous coating layers and understanding the selective permeability may provide a new strategy for the design of more efficient photocatalytic systems for organic synthesis.

Characterization and genomic analysis of an efficient dibutyl phthalate degrading bacterium Microbacterium sp. USTB-Y

A promising bacterial strain for biodegrading dibutyl phthalate (DBP) was successfully isolated from activated sludge and characterized as a potential novel Microbacterium sp. USTB-Y based on 16S rRNA sequence analysis and whole genome average nucleotide identity (ANI). Initial DBP of 50 mg/L could be completely biodegraded by USTB-Y both in mineral salt medium and in DBP artificially contaminated soil within 12 h at the optimal culture conditions of pH 7.5 and 30 ℃, which indicates that USTB-Y has a strong ability in DBP biodegradation. Phthalic acid (PA) was identified as the end-product of DBP biodegraded by USTB-Y using GC/MS. The draft genome of USTB-Y was sequenced by Illumina NovaSeq and 29 and 188 genes encoding for putative esterase/carboxylesterase and hydrolase/alpha/beta hydrolase were annotated based on NR (non redundant protein sequence database) analysis, respectively. Gene3781 and gene3780 from strain USTB-Y showed 100% identity with dpeH and mpeH from Microbacterium sp. PAE-1. But no phthalate catabolic gene (pht) cluster was found in the genome of strain USTB-Y. The results in the present study are valuable for obtaining a more holistic understanding on diverse genetic mechanisms of PAEs biodegrading Microbacterium sp. strains.

Predicting the trend and utility of different photocatalysts for degradation of pharmaceutically active compounds: A special emphasis on photocatalytic materials, modifications, and performance comparison

The rapid rise in the healthcare sector has led to an increase in pharmaceutically active compounds (PhACs) in different aqueous bodies. The toxicity of the PhACs and their ability to persist after conventional treatment processes have escalated research in the field of photocatalytic treatment. Although different photocatalysts have been successful in degrading PhACs, their inherent drawbacks have severely limited their application on a large scale. A substantial amount of research has been aimed at overcoming the high cost of the photocatalytic material, low quantum yield, the formation of toxic end products, etc. Hence, to further research in this field, researchers must have a fair idea of the current trends in the application of different photocatalysts. In this article, the trends in the use of various photocatalysts for the removal of different PhACs have been circumscribed. The performance of different groups of photocatalysts to degrade PhACs from synthetic and real wastewater has been addressed. The drawbacks and advantages of these materials have been compared, and their future in the field of PhACs removal has been predicted using S-curve analysis. Zinc and titanium-based photocatalysts were efficient under UV irradiation, while bismuth and graphene-based materials exhibited exemplary performance in visible light. However, iron-based compounds were found to have the most promising future, which may be because of their magnetic properties, easy availability, low bandgap, etc. Different modification techniques, such as morphology modification, doping, heterojunction formation, etc., have also been discussed. This study may help researchers to clarify the current research status in the field of photocatalytic treatment of PhACs and provide valuable information for future research.

One-step synthesis of reduced graphene oxide based ceric dioxide modified with cadmium sulfide (CeO2/CdS/RGO) heterojunction with enhanced sunlight-driven photocatalytic activity

Heterojunction photocatalyst with efficient photocatalytic performance can remarkably promote the separation of photogenerated charge carriers. Herein, a ternary photocatalyst, reduced graphene oxide (RGO) based CeO₂ modified with CdS (CeO₂/CdS/RGO), was synthesized by a simple one-step hydrothermal method as a bifunctional catalyst for both photodegradation and photoreduction. The ternary composite exhibited a 90.04% photodegradation efficiency to ciprofloxacin (CIP) under simulated sunlight irradiation for 2 h, much higher than CeO₂ (54%). Moreover, CeO₂/CdS/RGO showed broad applicability to the photodegradation of organic pollutants, including norfloxacin (NFX), tetracycline (TC), methylene blue (MB), rhodamine B (RhB), methyl violet (MV), methyl orange (MO) and reactive blue BES (RB). Besides, CeO₂/CdS/RGO exhibited a 100.00% photoreduction efficiency to Cr(VI) within 60 min. The improvement of the photocatalytic performance is ascribed to the modification of CeO₂ with CdS, which improves the separation efficiency of photogenerated carriers. Also, the modification with RGO inhibits the agglomeration of CeO₂, improves the adsorption capacity toward pollutants and provides another nanochannel to separate photogenerated electron-hole (e^--h⁺) pairs. Additionally, the photocatalytic mechanism of CeO₂/CdS/RGO is explored. It is expected that this work would provide a promising way to construct efficient and versatile RGO-based photocatalysts applied to environmental remediation.

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.

Microbial synthesis of Cu7S4/rGO nanocomposites with efficient photocatalytic activity for the degradation of methyl green

Cu₇S₄/reduced graphene oxide (rGO) photocatalysts are attracting increasing interest because of their low cost and environmental friendliness.

Preparation of Ag/TiO2 nanocomposites with controlled crystallization and properties as a multifunctional material for SERS and photocatalytic applications

Ag/TiO₂ nanocomposites with controlled crystallization and properties were prepared by a simple solvothermal method. By using the same raw materials with different ratio and reaction conditions, the morphologies and crystallization of nanocomposites can be tuned. The components of the products were analyzed by TEM and XRD methods respectively. The as-prepared Ag/TiO₂ nanocomposites were used as surface-enhanced Raman spectroscopy (SERS) substrate to be evolved for detection of environmental organic dyes pollutants (CV and RhB) with excellent recyclability. Furthermore, it also showed enhanced catalytic performance of nitrophenol compounds (4-NP). After that, the Ag/TiO₂ nanocomposites were also used as an active substrate and a superior catalyst for reduction of 4-NTP monitored by Raman spectroscopy.

The enhanced photocatalytic performance of SnS2@MoS2 QDs with highly-efficient charge transfer and visible light utilization for selective reduction of mythlen-blue

Molybdenum disulfide (MoS₂) has recently been considered as an effective material for potential photocatalytic applications; however, its photocatalytic activity was limited due to the low density of active sites. In this work, MoS₂ Quantum dots (QDs) were synthesized via the ultrasonication technique to construct heterostructure with SnS₂ nanosheets (SnS₂@MoS₂ QDs) and the prepared materials were tested for photocatalytic applications for Methylene blue (MB). Pristine SnS₂ and SnS₂@MoS₂ QDs nanocomposite were analyzed by XRD, TEM, PL, and Uv-Vis. Both SnS₂ and SnS₂@MoS₂ QDs exhibited a single trigonal phase with the P-3m1 space group. The TEM analysis confirmed the coupling between the pristine SnS₂ and SnS₂@MoS₂ QDs. The results of photocatalytic activity toward MB indicated that SnS₂@MoS₂ QDs material exhibits much superior photocatalytic performance compared to pristine SnS₂. The excellent photodegradation performance of SnS₂@MoS₂ QDs is due in the main to the formation of heterojunction between SnS₂ and MoS₂ QDs with narrow bandgap formation, which results in a facile carriers transfer and thus high photocatalytic efficiency. A representative mechanism of the photodegradation for SnS₂@MoS₂ QDs photocatalyst was proposed. Such an ultrasonic technique is capable of producing small metallic particle size that can be used to construct new heterostructures for water remediation applications.

The Influence of Photoactive Heterostructures on the Photocatalytic Removal of Dyes and Pharmaceutical Active Compounds: A Mini-Review

The diversification of pollutants type and concentration in wastewater has underlined the importance of finding new alternatives to traditional treatment methods. Advanced oxidation processes (AOPs), among others, are considered as promising candidate to efficiently remove organic pollutants such as dyes or pharmaceutical active compounds (PhACs). The present minireview resumes several recent achievements on the implementation and optimization of photoactive heterostructures used as photocatalysts for dyes and PhACs removal. The paper is focused on various methods of enhancing the heterostructure photocatalytic properties by optimizing parameters such as synthesis methods, composition, crystallinity, morphology, pollutant concentration and light irradiation.