A visible-light-driven Z-scheme CdS/Bi12GeO20 heterostructure with enhanced photocatalytic degradation of various organics and the reduction of aqueous Cr(VI)

Development of a novel Z-scheme CoxNi1-xTiO3/CdS (x = 0.5) photocatalyst for the efficient degradation of organic pollutants via a visible-light-driven photocatalytic process

Herein, for the first time, we reported the synthesis of a novel Z-scheme CoxNi1-xTiO3/CdS (x = 0.5) heterojunction photocatalyst and the investigation of its visible-light-driven photocatalytic performance toward degradation of methylene blue (MB). The developed photocatalyst was structurally characterized by applying X-Ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET), differential reflectance spectroscopy (DRS), and photoluminescence (PL) techniques. The results indicated the formation of a highly porous structure with improved visible light adsorption capacity, favorable for the catalytic activity. At an optimum condition of 10 mg/L of MB and 300 mg/L of catalyst, the ternary photocatalyst demonstrated a MB removal efficiency of 99 % after 75 min of the treatment process. The radical trapping experiments unveiled that hydroxyl and superoxide radicals were two main reactive species formed under visible light, while the valance holes possessed an insignificant role. The synergetic impact of the CoxNi1-xTiO3 (x = 0.5) and CdS on the photodegradation of MB over the as-prepared CoxNi1-xTiO3/CdS (x = 0.5) photocatalyst through Z-scheme photocatalysis was indicated by the results of the mechanism studies. The percentage impact of the treatment time, MB concentration, the ratio of CoxNi1-xTiO3/CdS (x = 0.5), and the dosage of catalyst using analysis of the CCD modeling was obtained as 47.04, 16.67, 7.22 and 0.87 %, respectively. Furthermore, the as-synthesized photocatalyst possessed high recyclability and photostability with only a 3 % decline in activity after four repetitive cycles.

Interfacial effect between Ni2P/CdS for simultaneously heightening photocatalytic hydrogen production and lignocellulosic biomass photorefining

Photorefining of biomass is increasingly recognized as a pivotal technology for the simultaneous production of hydrogen and value-added chemicals. The intrinsic recalcitrance of lignocellulosic biomass puts high demands on the rational design of bifunctional photocatalyst. Herein, Ni2P/CdS with a strong interfacial effect in this work was designed to overcome lignocellulosic biomass photorefining. The strong interfacial effect between Ni2P and CdS not only improved the light absorbance, but also optimized the spatial redistribution of photogenerated electrons and holes. Therefore, Ni2P/CdS exhibited an unprecedented H2 evolution activity (ca. 199.7 mmol·h-1·g-1) in the presence of lactic acid as the traditional sacrificial agent. Considerable H2 generation was also achieved in the presence of lignin (ca. 322.8 μmol·h-1·g-1), cellulose (ca. 534.3 μmol·h-1·g-1) and hemicellulose (ca. 382.2 μmol·h-1·g-1) as the electron donor respectively. Theoretical calculation results indicated that establishing the interfacial effect between Ni2P and CdS optimized their work functions. This optimization fosters improved the redistribution between electrons and holes, as a result, photocatalytic hydrogen production from biomass solution was greatly enhanced. Significantly, Ni2P/CdS showed dual functionalities to produce H2 and value-added compounds from raw biomass directly. This present work demonstrates the potential of raw biomass photorefining through astutely designing photocatalysts.

Plant-based green fabrication of CuO-CdO-bentonite S-scheme heterojunction with enhanced photocatalytic performance for the degradation of levofloxacin

In this research, for the first time, CuO and CdO nanoparticles (NPs) were synthesized using Ferula persica and anchored on layered bentonite as a novel S-scheme nano-heterojunction (denoted as CuO-CdO-BT). Ferula persica acted as a naturally-sourced reducing agent and stabilizer for the synthesis of NPs. The performance of CuO-CdO-BT was evaluated for the degradation of levofloxacin from an aqueous solution under sunlight. The characterization results clarified that the bentonite as a support not only reduced the agglomeration of CuO and CdO NPs but also decreased the size of biosynthesized NPs, which increased the active surface of NPs and the photodegardation efficiency. The effect of operational reaction system variables was examined to optimize the photocatalytic capability of CuO-CdO-BT. Under optimum conditions (catalyst dosage = 0.4 g/L, LVF concentration = 10 mg/L and pH = 8), 96.11% of levofloxacin was degraded using CuO-CdO-BT after 30 min with degradation kinetic of 0.108 min-1, which was about 2.4 and 4.2 times higher than those of bare CuO and CdO NPs, respectively. The improvement of the photocatalytic degradation efficiency of CuO-CdO-BT compared to CuO and CdO NPs was due to preventing the recombination of charge carriers in the S-scheme system. The radical quenching experiments ascertained the generation of [Formula: see text]·OH, and [Formula: see text] species in the CuO-CdO-BT system, indicating that ·OH radicals have a more prominent role than [Formula: see text] and [Formula: see text] in the photocatalytic reaction. The six possible levofloxacin pathways of LVF degradation were suggested based on HPLC-MS analysis. Over 88.5% LVF was removed using CuO-CdO-BT after three catalyst reuse cycles, indicating a cost-effectiveness potential of the biosynthesized photocatalyst reusability. Almost complete mineralization of LVF was obtained by the CuO-CdO-BT photocatalyst after 180 min of reaction. Based on findings, the S-scheme mechanism of photo-generated electron-hole pairs transfer in the CuO-CdO-BT system was found. The unique structural features of the new generation of S-scheme heterojunction and green synthesis of NPs using plants provide promising photocatalysts to improve wastewater treatment.

Efficient photo-Fenton catalysis using magnetic iron nanoparticles decorated boron nitride quantum dots: theoretical and experimental investigations

To achieve the efficient removal of pharmaceutical wastes, novel photo-Fenton catalysts, iron-decorated boron nitride quantum dots (Fe@BNQDs) were prepared. Fe@BNQDs were characterized using XRD, SEM-EDX, FTIR, and UV-Vis spectrophotometry. The decoration of Fe on the surface of BNQDs enhanced the catalytic efficiency due to the photo-Fenton process. Photo-Fenton catalytic degradation of folic acid was investigated under UV and visible light. The influence of H₂O₂, catalyst dose, and temperature on the degradation yield of folic acid was investigated using Response Surface Methodology. Moreover, the efficiency of the photocatalysts and kinetics was investigated. Radical trapping experiments revealed that holes were the main dominant species in the photo-Fenton degradation mechanism and BNQDs played active roles because of their hole extraction ability. Additionally, active species such as e^- and O₂ ^-˙ have a medium effect. The computational simulation was utilized to provide insights into this fundamental process, and for this purpose, electronic and optical properties were calculated.

Silver-Loaded Carbon and Phosphorous Co-Doped Boron Nitride Quantum Dots (Ag@CP-BNQDs) for Efficient Organic Waste Removal: Theoretical and Experimental Investigations

In this paper, silver-loaded phosphorous and carbon co-doped boron nitride quantum dot (Ag@CP-BNQD) nanocomposites were synthesized using a co-precipitation method followed by a hydrothermal approach. The nanocomposites of Ag@CP-BNQDs were characterized by scanning electron microscopy, energy-dispersive spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and ultraviolet-visible spectrophotometry. The as-prepared Ag@CP-BNQDs were used for photocatalytic degradation of 10 common organic pollutants, including dyes, pharmaceuticals, and pesticides in aqueous solution under visible light irradiation. The high-performance photocatalysis of Ag@CP-BNQDs proved that Ag@CP-BNQDs is plasmonic and the n-p junction photocatalyst. Theoretical calculations were done to measure the crystals and electronic structures of Ag@CP-BNQDs. Theoretical results showed that loading of Ag behaves as plasmonic sensitizers and co-catalysts and provides extra bands, which make electron movement easier between valance and conduction bands. The mechanism of the charge separation enhancement was postulated. Our findings might deepen our understanding of how sensitizer surface modification works in photodegradation applications.

Emerging bismuth-based direct Z-scheme photocatalyst for the degradation of organic dye and antibiotic residues

Organic dye and antibiotic residues are some of the key substances that can contaminate the environment due to their wide usage in various industries and modern medicine. The degradation of these substances present in waterbodies is essential while contemplating human health. Photocatalysts (PSs) are promising materials that develop highly reactive species instantly by simple solar energy conversion for degrading the organic dye and antibiotic residues and converting them into nontoxic products. Among numerous semiconductors, the bismuth (Bi)-containing PS has received great attention due to its strong sunlight absorption, facile preparation, and high photostability. Owing to the technology advancement and demerits of the traditional methods, a Bi-containing direct Z-scheme PS has been developed for efficient photogenerated charge carrier separation and strong redox proficiency. In this review, a synthetic Bi-based Z-scheme heterojunction that mimics natural photosynthesis is described, and its design, fabrication methods, and applications are comprehensively reviewed. Specifically, the first section briefly explains the role of various semiconductors in the environmental applications and the importance of the Bi-based materials for constructing the Z-scheme photocatalytic systems. In the successive section, overview of Z-scheme PS are concisely discussed. The fourth and fifth sections extensively explain the degradation of the organic dyes and antibiotics utilizing the Bi-based direct Z-scheme heterojunction. Eventually, the conclusions and future perspectives of this emerging research field are addressed. Overall, this review is potentially useful for the researchers involved in the environmental remediation field as a collection of up-to-date research articles for the fabrication of the Bi-containing direct Z-scheme PS.

Reduced graphene oxide supported ZnO/CdS heterojunction enhances photocatalytic removal efficiency of hexavalent chromium from aqueous solution

The removal of toxic and harmful heavy metal contaminants from wastewater is of great importance for global environmental health. The development of efficient photocatalysts is attracting increasing interest with a current focus on material design for improved efficiency. Accordingly, this study aims to optimize the conformation of nanocomposite prepared from a CdS/ZnO heterojunction on reduced graphene oxide (RGO) for boosting the photocatalytic removal of heavy metal contaminants of aqueous systems. Under visible light, the candidate nanocomposites exhibited a range of photocatalytic activity in reducing hexavalent chromium [Cr(VI)] to trivalent chromium [Cr(III)] at room temperature. Among these different nanocomposites, the photocatalytic removal rate constant of Cr(VI) ranged as follows: ZnO/CdS_6:5/RGO₆ (0.106 min^-1) > ZnO/CdS_6:5 (0.0630 min^-1) > CdS (0.0335 min^-1) > ZnO (0.00121 min^-1). Moreover, after five cycles of use, the photocatalytic reduction rate of ZnO/CdS_6:5/RGO₆ was 93.2 %, which signifies its strong re-cycling performance. These results reveal the feasibility of using CdS/ZnO_6:5/RGO₆ to reduce heavy metal ions from wastewater and provide insights for efficiently removing heavy metal ions without additional chemical trapping agents in the photocatalytic process.

Incorporation of dumbbell-shaped and Y-shaped cross-linkers in adjustable pullulan/polydopamine hydrogels for selective adsorption of cationic dyes

Hydrogel adsorbents have attracted considerable attention due to their sludge minimization, good water permeability and renewable performance. Here, a promising strategy for the one-step preparation of pullulan/polydopamine hybird hydrogels (PPGels) was presented. Dumbbell-shaped cross-linker neopentyl glycol diglycidyl ether (NGDE, 2 arms) and Y-shaped cross-linker trimethylolpropane triglycidyl ether (TTE, 3 arms) were selected to study the relationship between cross-linker structure and hydrogel performances. The NGDE possessing less molecular repulsive force and higher reactivity demonstrated more effective cross-linking with the pullulan, which leaded to a decrease in pore size of the hydrogel. Meanwhile, the introduction of polydopamine significantly enhanced the adsorption ability and gave the resulting hybrid gel the specific selectivity toward cationic dyes (96 mg/g for crystal violet, 25.8 mg/g for methylene blue and barely not adsorption for azophloxine). Our data suggested that the electrostatic interaction played a vital role in the dye adsorption process, and the adsorption data could be explained by pseudo-second-order model and Langmuir isotherm model. Furthermore, the obtained PPGel could be easily separated after adsorption. This study describes the relationship between cross-linker structure and properties of pullulan/polydopamine hybrid gels, which provides a new strategy to create polysaccharide-based adsorbents for wastewater remediation.

Microwave-assisted synthesis of an RGO/CdS/TiO2 step-scheme with exposed TiO2 {001} facets and enhanced visible photocatalytic activity

Semiconductor-based heterojunction photocatalysts with a special active crystal surface act as an essential part in environmental remediation and renewable energy technologies. In this study, an RGO/CdS/TiO₂ step-scheme with high energy {001} TiO₂ facets was successfully fabricated via a microwave-assisted solvothermal method. The photocatalytic performance of as-prepared samples was assessed by degrading methylene blue under visible light irradiation. We found that the photocatalytic activity of the RGO/CdS/TiO₂ step-scheme heterojunction was related to the proportion of TiO₂. A ternary sample with a TiO₂ content of 10 wt% exhibited superior photocatalytic performance, and approximately 99.7% of methylene blue was degraded during 50 min of visible illumination which was much higher than the percentages found for TiO₂, CdS, RGO/TiO₂, and RGO/CdS. The greatly improved photocatalytic performance is due to the exposure of the reactive {001} surface of TiO₂ and the formation of a CdS/TiO₂ heterojunction step-scheme, which effectively inhibits the recombination of charge carriers at the heterogeneous interfaces. Moreover, the incorporation of graphene further enhances the visible light harvesting and serves as an electron transport channel for rapidly separating photogenerated carriers. Based on the PL, XPS, photoelectrochemical properties and the free radical capturing experiment results, a possible photodegradation mechanism was proposed.

The photocatalytic enhancement of RGO/CdS/TiO₂ is due to the high-energy {001} surface of TiO₂ and CdS forming a stepped heterojunction, which is dispersed on the surface of reduced graphene oxide.

Fabrication of metal-free PTET-T-COOH/g-C3N4 heterostructure for enhancing photocatalytic activity

In this research work, we successfully fabricated a range of PTET-T-COOH/g-C₃N₄ heterostructures via a simple method. The as-prepared PTET-T-COOH/g-C₃N₄ heterostructures show enhanced photocatalytic degradation activity as compared to pure g-C₃N₄. For the photocatalytic degradation of RhB, the optimal PTET-T-COOH/g-C₃N₄-1% heterostructure is nearly 3.83 times that of the pure g-C₃N₄. The enhancement of photocatalytic performance is ascribed to three aspects: one is the strong interaction between PTET-T-COOH and g-C₃N₄; the second is the larger surface area of the PTET-T-COOH/g-C₃N₄ heterostructure compared to that of pure g-C₃N₄; the third is the effectively improved transferability of photogenerated carriers. In addition, the whole photocatalytic reaction mechanism over the PTET-T-COOH/g-C₃N₄ heterostructure is provided. This work may offer a hopeful method to synthesize any other heterostructure with high stability and superior photocatalytic activity.

The metal-free PTET-T-COOH/g-C₃N₄ heterostructure exhibits a high degradation rate for RhB under visible light irradiation.

In-Situ Construction of 2D/2D ZnIn2S4/BiOCl Heterostructure with Enhanced Photocatalytic Activity for N2 Fixation and Phenol Degradation

Photocatalytic nitrogen fixation and pollutants degradation at ambient temperature and pressure as a clean and efficient means represents a sustainable direction. In this paper, novel two-dimensional (2D) ZnIn2S4/2D BiOCl (ZIS/BOC) nanosheets heterostructures were successfully synthesized by in-situ solvothermal techniques. XPS and TEM results showed the formation of heterostructure. The photocatalytic properties of these materials were further studied by degradating phenol and nitrogen fixation under visible light irradiation. In particular, heterostructure obtained with a mass ratio of 0.5 wt % of ZnIn2S4 had a good application prospect and can achieve 77.4% phenol degradation rate within 6 h and a rate of ammonium production of 14.6 µmol∙gcat−1·h−1. The reaction rate of 0.5 wt % ZIS/BOC heterostructure exhibited 8.6 and 2.6 times relative to BiOCl for the degradation of phenol and nitrogen fixation, respectively. The enhanced photocatalytic activity was attributed to the collaboration of low recombination rate of photo-generated carriers and enhanced visible light absorption. Based on capture experiments and electron spin resonance (ESR) techniques, the main active species that may appear in photocatalytic systems were explored, and the corresponding photocatalytic mechanism was also proposed appropriately. This strategy will open up new ideas for the design and manufacture of more energy-efficient materials with high photocatalytic activity.

2D In-Plane CuS/Bi2WO6 p-n Heterostructures with Promoted Visible-Light-Driven Photo-Fenton Degradation Performance

Photo-Fenton degradation of pollutants in wastewater is an ideal choice for large scale practical applications. Herein, two-dimensional (2D) in-plane CuS/Bi₂WO₆ p-n heterostructures have been successfully constructed by an in situ assembly strategy and characterized using XRD, XPS, SEM/TEM, EDX, UV-Vis-DRS, PL, TR-PL, ESR, and VB-XPS techniques. The XPS and the TEM results confirm the formation of CuS/Bi₂WO₆ heterostructures. The as-constructed CuS/Bi₂WO₆ showed excellent absorption in visible region and superior charge carrier separation efficiency due to the formation of a type-II heterojunctions. Under visible light irradiation, 0.1% CuS/Bi₂WO₆ heterostructure exhibited the best photo-Fenton-like catalytic performance. The degradation efficiency of Rhodamine B (RhB, 20 mg·L⁻¹) can reach nearly 100% within 25 min, the apparent rate constant (k_app/min⁻¹) is approximately 40.06 and 3.87 times higher than that of pure CuS and Bi₂WO₆, respectively. The degradation efficiency of tetracycline hydrochloride (TC-HCl, 40mg·L⁻¹) can reach 73% in 50 min by employing 0.1% CuS/Bi₂WO₆ heterostructure as a photo-Fenton-like catalyst. The promoted photo-Fenton catalytic activity of CuS/Bi₂WO₆ p-n heterostructures is partly ascribed to its low carriers recombination rate. Importantly, CuS in CuS/Bi₂WO₆ heterostructures is conducive to the formation of heterogeneous photo-Fenton catalytic system, in which Bi₂WO₆ provides a strong reaction site for CuS to avoid the loss of Cu²⁺ in Fenton reaction, resulting in its excellent stability and reusability. The possible photo-Fenton-like catalytic degradation mechanism of RhB and TC-HCl was also elucidated on the basis of energy band structure analysis and radical scavenger experiments. The present study provides strong evidence for CuS/Bi₂WO₆ heterostructures to be used as promising candidates for photo-Fenton treatment of organic pollutants.

The Roles of Nanomaterials in Conventional and Emerging Technologies for Heavy Metal Removal: A State-of-the-Art Review

Heavy metal (HM) pollution in waterways is a serious threat towards global water security, as high dosages of HM poisoning can significantly harm all living organisms. Researchers have developed promising methods to isolate, separate, or reduce these HMs from water bodies to overcome this. This includes techniques, such as adsorption, photocatalysis, and membrane removal. Nanomaterials play an integral role in all of these remediation techniques. Nanomaterials of different shapes have been atomically designed via various synthesis techniques, such as hydrothermal, wet chemical synthesis, and so on to develop unique nanomaterials with exceptional properties, including high surface area and porosity, modified surface charge, increment in active sites, enhanced photocatalytic efficiency, and improved HM removal selectivity. In this work, a comprehensive review on the role that nanomaterials play in removing HM from waterways. The unique characteristics of the nanomaterials, synthesis technique, and removal principles are presented. A detailed visualisation of HM removal performances and the mechanisms behind this improvement is also detailed. Finally, the future directions for the development of nanomaterials are highlighted.

Z-scheme inverse opal CN/BiOBr photocatalysts for highly efficient degradation of antibiotics

Optimizing the heterojunction structure of semiconductor photocatalysts is vital for utilizing their abilities in organic matter degradation.