Facile synthesis of AgI/BiOI-Bi2O3 multi-heterojunctions with high visible light activity for Cr(VI) reduction

Structure-phase transformation of bismuth oxide to BiOCl/Bi24O31Cl10 shoulder-by-shoulder heterojunctions for efficient photocatalytic removal of antibiotic

Developing heterojunction photocatalyst with well-matched interfaces and multiple charge transfer paths is vital to boost carrier separation efficiency for photocatalytic antibiotics removal, but still remains a great challenge. In present work, a new strategy of chloride anion intercalation in Bi2O3 via one-pot hydrothermal process is proposed. The as-prepared Ta-BiOCl/Bi24O31Cl10 (TBB) heterojunctions are featured with Ta-Bi24O31Cl10 and Ta-BiOCl lined shoulder-by-shouleder via semi-coherent interfaces. In this TBB heterojunctions, the well-matched semi-coherent interfaces and shoulder-by-shoulder structures provide fast electron transfer and multiple transfer paths, respectively, leading to enhanced visible light response and improved photogenerated charge separation. Meanwhile, a type-II heterojunction for photocharge separation has been obtained, in which photogenerated electrons are drove from the CB (conduction band) of Ta-Bi24O31Cl10 to the both of bilateral empty CB of Ta-BiOCl and gathered on the CB of Ta-BiOCl, while the photogenerated holes are left on the VB (valence band) of Ta-Bi24O31Cl10, effectively hindering the recombination of photogenerated electron-hole pairs. Furthermore, the separated electrons can effectively activate dissolved oxygen for the generation of reactive oxygen species (·O2-). Such TBB heterojunctions exhibit remarkably superior photocatalytic degradation activity for tetracycline hydrochloride (TCH) solution to Bi2O3, Ta-BiOCl and Ta-Bi24O31Cl10. This work not only proposes a Ta-BiOCl/Bi24O31Cl10 shoulder-by-shoulder micro-ribbon architectures with semi-coherent interfaces and successive type-II heterojunction for highly efficient photocatalytic activity, but offers a new insight into the design of highly efficient heterojunction through phase-structure synergistic transformation strategy.

Anisotropic Dual S-Scheme Heterojunctions Mimic Natural Photosynthetic System for Boosting Photoelectric Response

The design of heterojunctions that mimic natural photosynthetic systems holds great promise for enhancing photoelectric response. However, the limited interfacial space charge layer (SCL) often fails to provide sufficient driving force for the directional migration of inner charge carriers. Drawing inspiration from the electron transport chain (ETC) in natural photosynthesis system, we developed a novel anisotropic dual S-scheme heterojunction artificial photosynthetic system composed of Bi2O3-BiOBr-AgI for the first time, with Bi2O3 and AgI selectively distributed along the bicrystal facets of BiOBr. Compared to traditional semiconductors, the anisotropic carrier migration in BiOBr overcomes the recombination resulting from thermodynamic diffusion, thereby establishing a potential ETC for the directional migration of inner charge carriers. Importantly, this pioneering bioinspired design overcomes the limitations imposed by the limited distribution of SCL in heterojunctions, resulting in a remarkable 55-fold enhancement in photoelectric performance. Leveraging the etching of thiols on Ag-based materials, this dual S-scheme heterojunction is further employed in the construction of photoelectrochemical sensors for the detection of acetylcholinesterase and organophosphorus pesticides.

Growth of AgI semiconductors on tailored 3D porous Ti3C2 MXene/graphene oxide aerogel to develop sensitive and selective "signal-on" photoelectrochemical sensor for H2S determination

Long term exposure to hydrogen sulfide (H₂S) even in low concentration poses a serious threat to human health and the ecosystem, pointing to the significance for its effective supervision. In this study, we report a sensitive and selective "signal-on" photoelectrochemical (PEC) sensor for the determination of toxic H₂S in aqueous solution by in situ growth of AgI semiconductors on tailored three-dimensional (3D) porous Ti₃C₂ MXene/graphene oxide aerogel (MGA). Our research demonstrated that the resultant MGA with the starting feeding mass ratio of MXene and graphene oxide (GO) of 1:8 (MGA_1:8) possessed the most excellent PEC performance after the growth of AgI semiconductors than their monomers (Ti₃C₂ MXene and GO) and the MGAs with other starting feeding mass ratio. Such designed PEC sensor based on MGA_1:8/AgI heterojunction showed dramatically strengthened PEC responses with increasing concentrations of S^2-. Correspondingly, a wide linear range of 5 nM-200 μM, a low limit of detection of 1.54 nM (S/N = 3), and exclusively unique selectivity have been achieved. Our research illustrates that the PEC sensor designed with tailored MGA constitutes is an effective pathway to enhance the overall sensing performance, which will envision to boost more efforts for advanced 3D porous aerogel using in PEC sensors.

Exploring novel heterojunctions based on the cerium metal-organic framework family and CAU-1, as dissimilar structures, for the sake of photocatalytic activity enhancement

Ce-based metal-organic frameworks (Ce-MOFs) are excellent photocatalysts due to their high efficiency in charge transportation. The integration of this family with CAU-1 (CAU standing for Christian-Albrechts-University), as a MOF benefiting from its ultra-high surface area, can remarkably enhance the properties of the structure. This research includes four new heterojunctions, namely CAU-1/Ce-BDC-NH2, CAU-1/Ce-UiO-66, CAU-1/Ce-MOF-808, and CAU-1/Ce-BDC, prepared by an innovative method, and several characterization techniques were employed to study the structural features of the frameworks. Their high surface area and low bandgap energy seemed appropriate for catalytic applications. Therefore, CAU-1/Ce-BDC was chosen for the photocatalytic removal of Cr(vi), a dangerous heavy metal, from aqueous systems. According to the results, a 96% reduction of Cr(vi) to Cr(iii) within 75 min was observed, and the catalyst retained its stability after four runs of reactions under acidic conditions.

Bismuth impregnated biochar for efficient uranium removal from solution: Adsorption behavior and interfacial mechanism

In this work, Bi₂O₃ doped horse manure-derived biochar was obtained by carbonizing the H₂O₂-modified horse manure loaded with bismuth nitrate under nitrogen atmosphere at 500 °C. The results showed that there was a sharp response between the as-prepared bismuth impregnated biochar and uranium(VI) species in solution, which resulted in a short equilibrium time (<80 min), a fast adsorption rate (about 5.0 mg/(g·min)), a high removal efficiency (93.9%) and a large adsorption capacity (516.5 mg/g) (T = 298 K, pH = 4, C_i = 10 mg/L and m/V = 0.1 g/L). Besides, the removal behavior of the bismuth impregnated biochar for uranium(VI) did not depend on the interfering ions and ion strength, except Al³⁺, Ca²⁺, CO₃^2- and PO₄^3-. These results indicated that the modified biochar might possess the potential of remediating the actual uranium(VI)-containing wastewater. Moreover, the interaction mechanism between Bi₂O₃ doped biochar and uranium(VI) species was further explored. The results demonstrated that the enrichment of uranium(VI) on the surface of the as-prepared biochar was controlled by various factors, such as surface complexation, ion exchange, electrostatic attraction, precipitation and reduction, which facilitated the adsorption of uranium(VI) on the bismuth impregnated biochar.

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.

Construct interesting CuS/TiO2 architectures for effective removal of Cr(VI) in simulated wastewater via the strong synergistic adsorption and photocatalytic process

Most of the reduction processes for Cr (VI) removal tend to be available only at the acidic condition and the capable extent of pH is limited. Here, we developed a facile strategy for constructing CuS/TiO₂ architectures via a facile precipitation process. The as-prepared urchin-like CuS microspheres possessed hierarchical/large porous structure and unique electrical structure, which provided a strong ability to capture the Cr(VI) ions in water. Once CuS microspheres were combined with TiO₂ crystals (P25), a surprised high removal efficiency for Cr(VI) was obtained. With optimal molar ratio of CuS:TiO₂ (0.72:1), 4.4 and 1.3 times in Cr(VI) removal rate were obtained with respect to pure TiO₂ and CuS. The high removal efficiency was induced by the distinct synergistic role of strong adsorption and photocatalytic reduction originated from unique electrical structure in CuS/TiO₂ hetero-structure. Moreover, these novel CuS/TiO₂ architectures possess promising application for Cr⁶⁺ effluents remediation in a wide range of pH and with co-existing anions and cations.

Double Z-scheme FeVO4/Bi4O5Br2/BiOBr ternary heterojunction photocatalyst for simultaneous photocatalytic removal of hexavalent chromium and rhodamine B

HYPOTHESIS

Fabrication of the heterojunction photocatalyst with appropriate band potentials as a promising method of inhibiting electron-hole pair recombination leading to enhanced photocatalytic properties.

EXPERIMENTS

Herein, BiOBr, Bi₄O₅Br₂, and binary BiOBr/Bi₄O₅Br₂ composite were selectively synthesized by employing a one-step microwave irradiation method. Then, double Z-scheme FeVO₄/Bi₄O₅Br₂/BiOBr ternary composites with different weight percentages (%wt) of FeVO₄ were fabricated and their photocatalytic applications were studied. The photodegradation of organic compounds (rhodamine B (RhB), methylene blue (MB) and salicylic acid (SA)), along with the photoreduction of hexavalent chromium (Cr(VI)) were investigated.

FINDINGS

Comparing with the single and binary photocatalysts, and a commercial TiO₂, the 1 %wt-FeVO₄/Bi₄O₅Br₂/BiOBr photocatalyst demonstrated superior visible-light-driven photocatalytic performance. In a Cr(VI)/RhB combined system, Cr(VI) photoreduction was further improved and coexisting RhB molecules were simultaneously degraded. Removal of Cr(VI) and RhB were maximized by adjusting both pH values and catalyst dosages. Based on UV-vis diffuse reflectance spectroscopy, photoluminescence spectroscopy, electrochemical investigations, active-species trapping, nitrotetrazolium blue transformation, and silver photo-deposition experiments, a double Z-scheme charge transfer mechanism with an RhB-sensitized effect was proposed. This special mechanism has led to significant enhancement in charge segregation and migration, along with higher redox properties of the ternary composite, which were responsible for the excellent photocatalytic activity.

Solvent-mediated synthesis of BiOI with a tunable surface structure for effective visible light active photocatalytic removal of Cr(VI) from wastewater

The present study investigated the effect of various solvents on the tunable surface morphology and photocatalytic activity (PCA) of bismuth oxyiodide (BiOI), which could be used for the reduction of Cr(VI) under visible light irradiation (VLI). BiOI samples exhibiting different morphologies, i.e., two-dimensional square-like nanosheet and three-dimensional hierarchical flower-like morphology, were synthesized by a hydro/solvothermal process using different solvents, namely H₂O, MeOH, EtOH, and ethylene glycol (EG). The crystal structure, surface morphology, surface area, light-absorption capability, and recombination rate of the photogenerated charge carriers were examined by X-ray diffraction, scanning electron microscopy, Brunauer-Emmett-Teller analysis, UV-vis diffuse reflectance spectroscopy, photoluminescence, and transient photocurrent analyses, respectively. The BiOI sample fabricated in EG showed excellent photocatalytic efficiency (~99%) for the reduction of Cr(VI) after 90 min under VLI. The enhanced PCA demonstrated that the high surface area and well-structured surface characteristics of flower-like 3D BiOI microspheres played important roles in the photoreduction process. Moreover, a plausible mechanism for the reduction of Cr(VI) over the EG-BiOI photocatalyst was proposed. The results of the PCA evaluation and recycle test revealed that 3D EG-BiOI microspheres could serve as promising materials for the efficient removal of Cr(VI) from wastewater. Additionally, EG-BiOI could be utilized in other environmental remediation processes.

AgI/CuWO4 Z-scheme photocatalyst for the degradation of organic pollutants: Experimental and molecular dynamics studies

While the knowledge of the adsorption properties of components of a composite heterogeneous photocatalyst is critical to its applicability to a particular reaction, there has been little research in this direction. The present research is on the development of AgI/CuWO₄ nanocomposites that photocatalytically degraded ciprofloxacin and rhodamine B in an aqueous medium under visible light irradiation. The nanocomposites were prepared by a step-wise precipitation protocol. XPS analysis and active species trapping experiments demonstrated that the photocatalysis proceeded by a Z-scheme mechanism. Large scale aqueous medium molecular dynamics simulations showed that oxygen and CIP adsorb on the AgI part, while water interacts intensely with the CuWO₄ component. Information from experimental and molecular dynamics studies was combined to arrive at the photocatalysis mechanism.

Mesoporous Composite Networks of Linked MnFe2O4 and ZnFe2O4 Nanoparticles as Efficient Photocatalysts for the Reduction of Cr(VI)

Semiconductor photocatalysis has recently emerged as an effective and eco-friendly approach that could meet the stringent requirements for sustainable environmental remediation. To this end, the fabrication of novel photocatalysts with unique electrochemical properties and high catalytic efficiency is of utmost importance and requires adequate attention. In this work, dual component mesoporous frameworks of spinel ferrite ZnFe2O4 (ZFO) and MnFe2O4 (MFO) nanoparticles are reported as efficient photocatalysts for detoxification of hexavalent chromium (Cr(VI)) and organic pollutants. The as-prepared materials, which are synthesized via a polymer-templated aggregating self-assembly method, consist of a continuous network of linked nanoparticles (ca. 6–7 nm) and exhibit large surface area (up to 91 m2 g−1) arising from interstitial voids between the nanoparticles, according to electron microscopy and N2 physisorption measurements. By tuning the composition, MFO-ZFO composite catalyst containing 6 wt.% MFO attains excellent photocatalytic Cr(VI) reduction activity in the presence of phenol. In-depth studies with UV-visible absorption, electrochemical and photoelectrochemical measurements show that the performance enhancement of this catalyst predominantly arises from the suitable band edge positions of constituent nanoparticles that efficiently separates and transports the charge carriers through the interface of the ZFO/MFO junctions. Besides, the open pore structure and large surface area of these ensembled networks also boost the reaction kinetics. The remarkable activity and durability of the MFO-ZFO heterostructures implies the great possibility of implementing these new nanocomposite catalysts into a realistic Cr(VI) detoxification of contaminated wastewater.

Turning waste into treasure: Reuse of contaminant-laden adsorbents (Cr(vi)-Fe3O4/C) as anodes with high potassium-storage capacity

In this study, we try to find possible solutions to synchronously solving energy and environmental problems. In our design, orange peel is used as a carbon source to synthesize low-cost Fe₃O₄/C composites, which are employed as adsorbents to purify Cr(vi)-contaminated water. After that, these Cr(vi)-laden Fe₃O₄/C composites are used and tested as anodes in potassium-ion batteries. It is found that their K-storage capacity is more than 300 mAh g^-1 at a current density of 0.1 A g^-1, depending on the mass content of Fe₃O₄. The more Fe₃O₄ component in composite, the more adsorbed Cr(vi) species through chemisorption, and the larger K-storage capacity. The good electrical conductivity of cabon-based anodes endows them with superior rate performance. At current densities of 0.1, 0.5, 1 and 2 A g^-1, K-storage capacity amounts to 357.8, 316.3, 276.3 and 236.8 mAh g^-1, respectively. The reuse of contaminant-laden adsorbents as anodes will shed new light on the disposal of exhausted adsorbents after water treatment and development of anode materials for secondary batteries.

Enhanced bacterial disinfection by CuI–BiOI/rGO hydrogel under visible light irradiation

Compared with traditional layered graphene, graphene hydrogels have been used to construct highly efficient visible light-excited photocatalysts due to their particular three-dimensional network structure and efficient electron transport capacity. In this work, CuI–BiOI/rGO hydrogel with excellent photocatalytic antibacterial activity was prepared and its activity against Escherichia coli and Staphylococcus aureus was evaluated. The result indicates that CuI–BiOI/rGO hydrogel exhibits superior sterilization performance and higher stability than CuI–BiOI and BiOI/rGO, and could completely kill Escherichia coli and Staphylococcus aureus within 40 min. However, only a small amount of Escherichia coli and Staphylococcus aureus can be inactivated by CuI–BiOI and BiOI/rGO hydrogels. Graphene hydrogel plays a significant part in enhancing the disinfection activity of CuI–BiOI/rGO hydrogel. Furthermore, the synergistic effect between CuI of p-type semiconductors, as a hole transport layer, and graphene hydrogel greatly increases the separation and transfer efficiency of photogenerated electron holes excited by BiOI, and further improves the disinfection activity of CuI–BiOI/rGO hydrogel.

Compared with traditional layered graphene, graphene hydrogels have been used to construct highly efficient visible light-excited photocatalysts due to their particular three-dimensional network structure and efficient electron transport capacity.

Green and controllable synthesis of one-dimensional Bi2O3/BiOI heterojunction for highly efficient visible-light-driven photocatalytic reduction of Cr(VI)

BiOI nanosheets have been successfully deposited on the porous Bi₂O₃ nanorobs via a one-pot precipitation method. The physicochemical features of the as-prepared materials were characterized in detail by a series of techniques, and the results revealed that BiOI nanosheets were evenly distributed on the porous Bi₂O₃ nanorobs. Because of higher photogenerated electron-hole pairs separation efficiency and the larger specific surface area compared to the pristine Bi₂O₃ and BiOI, the 50%Bi₂O₃/BiOI composite exhibited significantly enhanced photocatalytic activity for Cr(VI) reduction under visible light irradiation, and the reduction rate constant was 0.02002 min^-1, which was about 27.4 and 2.6 times higher than that of pure Bi₂O₃ (0.00073 min^-1) and BiOI (0.00769 min^-1), respectively. Moreover, the 50%Bi₂O₃/BiOI composite also possessed the excellent photochemical stability and recyclability, thereby facilitating its wastewater treatment application.

ZnIn2S4 grown on nitrogen-doped hollow carbon spheres: An advanced catalyst for Cr(VI) reduction

Up to now, the environmental damage by heavy metal is getting worse and worse as the development of industry. Meanwhile, hexavalent chromium (Cr(VI)) in wastewater get special attention as its acute toxicity and potential carcinogencity. To solve this problem, we introduce a simple and efficient way to prepare a photocatalyst, ZnIn₂S₄ grown on nitrogen-doped hollow carbon spheres (ZIS-NHC), which is an effective catalyst that can used to reduce aqueous Cr(VI). This photocatalyst prepared by a three-step strategy. Benefiting from the excellent electrical conductivity and high specific surface area of the NHC which is superior to other carbon material and the favorable band gap of ZnIn₂S₄ makes ZIS-NHC has superior light-driven photocatalytic efficiency. The ZIS-NHC exhibits an excellent rate of degradation of aqueous Cr(VI) at a concentration of 50 mg/L within 50 min. Moreover, the ZIS-NHC retained excellent stability after five rounds of cycling experiments which was also discussed.

Direct Z-scheme FeVO4/BiOCl heterojunction as a highly efficient visible-light-driven photocatalyst for photocatalytic dye degradation and Cr(VI) reduction

In this work, potential applications of a direct Z-scheme FeVO₄/BiOCl heterojunction for photocatalytic degradation of organic dyes (methylene blue, MB and rhodamine B, RhB) and reduction of hexavalent chromium (Cr(VI)) ion under visible light irradiation were reported. Firstly, FeVO₄ and BiOCl were synthesized by using a microwave heating method. Then, the FeVO₄/BiOCl nanocomposites with different weight percentages of FeVO₄ (1, 3, 6.25, 12.5 and 25%wt) were fabricated by a method of modified wet impregnation. The photocatalytic degradation activities of the nanocomposites were investigated in parallel with pure BiOCl and FeVO₄. Among the as-prepared nanocomposites, the FeVO₄/BiOCl nanocomposite with 6.25%wt of FeVO₄ exhibited the highest photocatalytic dye degradation efficiency; 99.8% of RhB was degraded after being irradiated for 360 min, while 87.2% of MB was degraded. Similarly, this nanocomposite photocatalytically reduced 97.8% of Cr(VI) at a pH value of 3. The superior photocatalytic activity can be ascribed to the effective visible light absorption of the FeVO₄/BiOCl heterojunction and the suppression of the recombination process of photogenerated electron-hole pairs. Additionally, the improved charge migration and separation efficiencies between FeVO₄ and BiOCl through the direct Z-scheme charge transfer pathway are involved, as evidenced by the trapping experiments, and the UV-visible diffuse reflectance (UV-vis DRS), photoluminescence spectroscopy (PL) and electrochemical impedance spectroscopy analyses. Photocatalytic mechanisms of the direct Z-scheme FeVO₄/BiOCl heterojunction for the photodegradation of RhB and photoreduction of Cr(VI) have been proposed and discussed in greater detail.

Carbon Quantum Dots (CQDs) Decorated Bi2O3-x Hybrid Photocatalysts with Promising NIR-Light-Driven Photodegradation Activity for AO7

In this work, Bi2O3-x with surface oxygen vacancies was prepared through the NaBH4 reduction of Bi2O3. After that, carbon quantum dots (CQDs) were deposited onto the surface of the Bi2O3-x to obtain a series of the CQDs/Bi2O3-x composites. The HRTEM and XPS characterizations of the CQDs/Bi2O3-x composites suggest that the thickness of surface oxygen vacancies could be adjusted by changing the concentration of NaBH4 solution, and the intimate contact between CQDs and the Bi2O3-x is achieved. Acid orange 7 (AO7) was adopted as the target reactant for investigating the photocatalytic degradation activities of the CQDs/Bi2O3-x composites under simulated sunlight and NIR light irradiation. It is found that the photocatalytic activities of the samples are closely related to the concentration of NaBH4 and content of CQDs. The Bi2O3-x samples exhibit enhanced simulated-sunlight-driven photocatalytic activity compared with Bi2O3. Specifically, the optimal degradation efficiency of AO7 is achieved over the 3R-Bi2O3-x (concentration of NaBH4: 3 mmol/L), which is 1.38 times higher than the degradation AO7 efficiency over Bi2O3. After the decoration of the 3R-Bi2O3-x surface with CQDs, the simulated-sunlight-driven photocatalytic activity of the CQDs/Bi2O3-x composite could be further enhanced. Among the samples, the 15C/3R-Bi2O3-x sample reveals the highest photocatalytic activity, leading to an AO7 degradation percentage of ~97% after 60 min irradiation. Different from Bi2O3 and the 3R-Bi2O3-x, the 15C/3R-Bi2O3-x sample also exhibits near-infrared (NIR)-light-driven photocatalytic degradation activity. In addition, the intrinsic photocatalytic activity of CQDs/Bi2O3-x composite was further confirmed by the degradation of phenol under simulated sunlight and NIR light irradiation. The photocurrent response and electrochemical impedance spectroscopy (EIS) measurements confirm the efficient migration and separation of photogenerated charges in the CQDs/Bi2O3-x samples. The •OH and h+ are proved to be the main reactive species in the simulated sunlight and NIR light photocatalytic processes over the CQDs/Bi2O3-x composites. According to the above experiments, the photocatalytic degradation mechanisms of the CQDs/Bi2O3-x composites under simulated sunlight and NIR light illumination were proposed.

Synergistic Effect of Hydrochloric Acid and Phytic Acid Doping on Polyaniline-Coupled g-C3N4 Nanosheets for Photocatalytic Cr(VI) Reduction and Dye Degradation

In this study, graphitic carbon nitride (g-C₃N₄) nanosheets (CNns) were modified using polyaniline (PANI) codoped with an inorganic (hydrochloric acid, HCl) and an organic (phytic acid, PA) acid. Our results revealed that these samples exhibited extended visible-light absorption and a three-dimensional (3D) hierarchical structure with a large specific surface area. They also inhibited photoluminescence emission, reduced electrical resistance, and provided abundant free radicals, resulting in high photocatalytic performance. The PANI/g-C₃N₄ sample demonstrated outstanding photocatalytic activity of a Cr(VI) removal capacity of 4.76 mg·min^-1·g_c^-1, which is the best record for the reduction of a 100 ppm K₂Cr₂O₇ solution. Moreover, g-C₃N₄ coupled with PANI monotonically doped with HCl or PA did not demonstrate increased activity, suggesting that the codoping of HCl and PA plays a significant role in enhancing the performance. The improved photocatalytic activity of PANI/g-C₃N₄ can be attributed to the interchain and intrachain doping of PA and HCl over PANI, respectively, to create a 3D connected network and synergistically increase the electrical conductivity. Therefore, new insights into g-C₃N₄ coupled with PANI and codoped by HCl and PA may have excellent potential for the design of g-C₃N₄-based compounds for efficient photocatalytic reactions.

Constructing a new Z-scheme multi-heterojunction photocataslyts Ag-AgI/BiOI-Bi2O3 with enhanced photocatalytic activity

The series Ag-AgI/BiOI-Bi₂O₃ visible-light-driven photocataslyts were successfully synthesized by solvothermal method. The as-synthesized samples were systematically characterized by XRD, SEM, TEM, EDS, BET, XPS, FR-IR, UV-vis DRS, photoelectrochemical measurements and EPR. The formation mechanism of the new composite photocataslyts was investigated and the simulate formation process had been illustrated. The photocatalytic properties of the samples were evaluated by degradation of methyl orange under visible-light irradiation. The results shown that the 30% Ag-AgI/BiOI-Bi₂O₃ photocataslyts possessed the best photocatalytic activity and the kinetics reaction models were followed pseudo-first-order kinetics. The enhanced photocatalytic performance could be attributed to the effective separation and transfer of electron-hole pairs resulting by the deposing of Ag-AgI nanoparticles and Bi₂O₃. The photocatalytic mechanism was deduced by trapping experiments and EPR, and the results demonstrated that h⁺, OH, O₂^- radicals played different roles in the degradation. Furthermore, a new Z-scheme multi-heterojunction mechanism was proposed basing on the results of trapping experiments and EPR.

Synthesis of oxy-sulfide based nanocomposite catalyst for visible light-driven reduction of Cr(VI)

The oxy-sulfide based V₂O₅@(In,Ga)₂(O,S)₃ nanocomposite catalyst, at different weight percentages of V₂O₅, was successfully synthesized via a simplistic procedural route for the detoxification of hazardous Cr(VI). The two pure catalysts were intimately allied and used for visible light-driven reduction of hazardous Cr(VI). The nanocomposite catalysts were characterized to observe the effects of V₂O₅ on crystal phase, morphology, light absorption, catalytic activity, and electrical properties. Compared to all, 40% V₂O₅ loaded nanocomposite catalyst, designated as VOS-2, exhibited the best-reducing capability. It completely reduced toxic Cr(VI) at 2 min under visible light illumination. From the kinetics, it was found that the rate constant of the nanocomposite catalyst was improved by a factor of 3.6 compared to the host nanoflower catalyst. The plausible mechanism of charge transfer process across the interfacial region indicates the diminished recombination probability of photogenerated charge carriers. Therefore, the nanocomposite catalyst is promising for enhanced reduction of Cr(VI) in the Cr-based industrial activities, which is significantly relevant for environmental remediation.

Intercalation of Bi2O3/Bi2S3 nanoparticles into highly expanded MoS2 nanosheets for greatly enhanced gas sensing performance at room temperature

Synthesizing a gas sensor based on heterostructured nanomaterials (NMs) via a controllable morphology by a facile hydrothermal method is an area of frontier research. In the present work, we designed a facile strategy to synthesize a controllable morphology and composition for three component heterojunctions (MoS₂-Bi₂O₃-Bi₂S₃) NMs using different hydrothermal reaction times. The Bi₂S₃ easily form as an intermediate phase due to the strong interaction of the Bi₂O₃ with MoS₂ nanosheets (NSs). The as fabricated heterojunctions MB-5 NMs exhibited a sensitive response to NO_x gas (R_a/R_g = 10.7 at 50 ppm), with an ultra-fast response time of only 1 s (s) at room temperature (RT) in air. The detection limit was predicted to be as low as 50 ppb. This sensational behaviour of the sensor reveals the outstanding morphological structure and synergistic effect of the MoS₂ NSs with Bi₂O₃ nanoparticles (NPs), which was realized by the flow of electrons across MoS₂-Bi₂O₃-Bi₂S₃ interfaces through band energy alignment.

Facile preparation of Ti3+ self-doped TiO2 nanoparticles and their dramatic visible photocatalytic activity for the fast treatment of highly concentrated Cr(vi) effluent

An efficient visible photocatalyst which is suitable for the rapid removal of highly concentrated Cr(vi) for environmental therapy.

Photocatalytic reduction of Cr (VI) on nano-sized red phosphorus under visible light irradiation

Red phosphorus as a novel visible-light-responsive and metal-free photocatalyst has attracted extensive attention in the area of energy conversion and environmental remediation. Herein, nano-sized red phosphorus photocatalyst was synthesized via a hydrothermal and ultrasonic method and used for reduction of Cr (VI) for the first time. The as-prepared photocatalysts were characterized by XRD, UV-Vis-DRS, XPS, SEM, TEM and photoelectrochemical measurements. Compared to bulk red phosphorus, nano-sized red phosphorus exhibit a significantly enhanced photocatalytic activity for reduction of Cr (VI) due to the greatly reduced charge transfer resistance and enhanced adsorption capability of Cr (VI).

Review on nanoscale Bi-based photocatalysts

Nanoscale Bi-based photocatalysts are promising candidates for visible-light-driven photocatalytic environmental remediation and energy conversion. However, the performance of bulk bismuthal semiconductors is unsatisfactory. Increasing efforts have been focused on enhancing the performance of this photocatalyst family. Many studies have reported on component adjustment, morphology control, heterojunction construction, and surface modification. Herein, recent topics in these fields, including doping, changing stoichiometry, solid solutions, ultrathin nanosheets, hierarchical and hollow architectures, conventional heterojunctions, direct Z-scheme junctions, and surface modification of conductive materials and semiconductors, are reviewed. The progress in the enhancement mechanism involving light absorption, band structure tailoring, and separation and utilization of excited carriers, is also introduced. The challenges and tendencies in the studies of nanoscale Bi-based photocatalysts are discussed and summarized.

BiOX (X = Cl, Br, I) photocatalytic nanomaterials: Applications for fuels and environmental management

Energy and environmental issues are the major concerns in our contemporary "risk society". As a green technique, photocatalysis has been identified as a promising solution for above-mentioned problems. In recent decade, BiOX (X = Cl, Br, I) photocatalytic nanomaterials have sparked numerous interest as economical and efficient photocatalysts for energy conversion and environmental management. The distinctive physicochemical properties of BiOX nanomaterials, especially their energy band structures and levels as well as relaxed layered nanostructures, should be responsible for the visible-light-driven photocatalytic performance improvement, which could be utilized in dealing with the global energy and environmental challenges. In this review, recent advances for the enhancement of BiOX photocatalytic activity are detailedly summarized. Furthermore, the applications of BiOX photocatalysts in water splitting and refractory organic pollutants removal are highlighted to offer guidelines for better development in photocatalysis. Particularly, no relative reports in previous studies were documented in CO₂ reduction as well as heavy metals and air pollutants removal, thus this review presented as a considerable research value. Challenges in the construction of high-performance BiOX-based photocatalytic systems are also discussed. With the exponential growth of studies on BiOX photocatalytic nanomaterials, this review provides unique and comprehensive perspectives to design BiOX-based photocatalytic systems with superior visible light photocatalytic activity. The knowledge of both the merits and demerits of BiOX photocatalysts are updated and provided as a reference.