Photocatalytic Reduction Of Cr Research Articles

New insight into the effects of p-benzoquinone on photocatalytic reduction of Cr(VI) over Fe-doped g-C3N4

It is of great significance to establish an effective method for removing Cr(VI) from wastewater. Herein, Fe-doped g-C3N4 (namely Fe-g–C3N4–2) was synthesized and then employed as photocatalyst to conduct the test of Cr(VI) reduction. Notably, the embedding of Fe ion in g-C3N4 can offer the Fe2+/Fe3+ redox couples, so reducing the interfacial resistance of charge transfer and suppressing the recombination of photogenerated electrons and holes. The impurity energy levels will form in g-C3N4 after the introduction of Fe ion, thereby boosting the light absorption capacity of catalyst. Thus, Fe-g–C3N4–2 showed good performance in photocatalytic Cr(VI) reduction, and the reduction efficiency of Cr(VI) can reach 39.9% within 40 min. Different with many previous studies, current work unexpectedly found that the addition of p-benzoquinone (BQ) can promote the Cr(VI) reduction, and the reduction efficiency of Cr(VI) over Fe-g–C3N4–2 was as high as 93.2% in the presence of BQ (1.5 mM). Further analyses showed that BQ can be reduced to hydroquinone (HQ) by photogenerated electrons, and UV light can also directly induce BQ to generate HQ by using H2O as the hydrogen donor. The HQ with reducing ability can accelerate the Cr(VI) reduction. In short, current work shared some novel insights into photocatalytic Cr(VI) reduction in the presence of BQ. Future research should consider possible reactions between photogenerated electrons and BQ. For the UV-induced photocatalysis, the suitability of BQ as the scavenger of O2•‒ must be given carefully consideration.

A readily synthesized ZnIn2S4/attapulgite as a high-performance photocatalyst for Cr(VI) reduction

Herein, a ZnIn2S4-decorated attapulgite photocatalyst (ZnIn2S4/ATP) was successfully synthesized by a facile oil bath heating method. It shows superior reduction efficiency for the removal of Cr(Ⅵ). The improved photocatalytic performance is primarily attributed to the intercalation effect of ZnIn2S4 and attapulgite (ATP), enhanced separation efficiency of photogenerated electron-hole pairs, and improved transport efficiency of photogenerated carriers. Moreover, insight into the photocatalytic mechanism demonstrates that •O2− and e− are the major active species in the photocatalytic reduction of Cr(VI) over ZnIn2S4/ATP. This work serves as a reference for integrating natural clay with semiconductors for photocatalytic wastewater treatment.

Photocatalytic reduction of Cr(VI) by AgIn5S8/ZnIn2S4 heterojunction under visible light: Experimental and density functional theory study

Ternary metal sulfides have excellent light absorption properties, but their high recombination rate of photo generated carriers limits their practical application. To address this problem, this work constructed a novel nanoflower−like AgIn5S8/ZnIn2S4 heterojunction and explored its removal performance for Cr(VI) in water. AgIn5S8 was prepared by the solvothermal method, whereas ZnIn2S4 and AgIn5S8/ZnIn2S4 heterojunction was synthesized via the hydrothermal method. The morphological characteristics of AgIn5S8/ZnIn2S4 heterojunction showed that the AgIn5S8 particles uniformly distributed on the surface of ZnIn2S4 with a flower like structure. The obtained 10% AgIn5S8/ZnIn2S4 exhibited a higher specific surface area (75.07 m2/g) than AgIn5S8 (20.91 m2/g) and ZnIn2S4 (58.30 m2/g), with the maximum Cr(VI) removal efficiency of 88.5% at an initial concentration of 20 mg/L. The photocatalytic reduction of Cr(VI) by AgIn5S8/ZnIn2S4 conformed to the pseudo-first-order kinetic model. The superoxide radicals (·O2−) and photogenerated electrons (e−) were identified as the major active substances for Cr(VI) photoreduction according to the electron paramagnetic resonance (EPR) and free radical trapping experiments. The Mott−Schottky analysis demonstrated that the band structures of AgIn5S8 and ZnIn2S4 were compatible. Density functional theory (DFT) calculations showed that AgIn5S8/ZnIn2S4 heterojunction enhanced the separation efficiency of photogenerated carriers through an internal electric field (IEF). These results demonstrate that type–II AgIn5S8/ZnIn2S4 heterojunctions have the potential for effective removal of Cr(VI) in wastewater under visible light irradiation.

Photocatalytic reduction of Cr(VI) and degradation of RhB by assembled novel In2S3/Zr-biquinoline framework heterojunction photocatalyst via xenon lamp

Dichromates and dyes have been widely used in industrial and agricultural production, but they are also responsible for the deterioration of water environments. Photochemical purification of them based on MOFs based photocatalysts has been proven to be feasible. And construction of MOFs based heterojunctions to polish the band states is an effective method for enhancing the separation of photogenerated electron-hole separation and carriers migration under low energy light. Herein, a Zr(IV)-biquinoline framework with bcu topology was synthesized to act as a matrix for depositing the in-situ generated In2S3 species, providing a novel In2S3/Zr-MOF heterojunction. Indeed, owing to the highly matched band structure of the two components, the new heterojunction exhibits optimized visible light utility, photogenerated electron-hole recombination inhibition ability and carriers migration kinetics. Ingeniously, the 10%-Zr-MOF exhibited excellent photocatalytic REDOX abilities against Cr(VI) ions and dye RhB, with the photocatalytic deoxidation efficiency towards Cr(VI) ions (96.7 %) has been confirmed to be 3.14 and 1.42 times that of pristine Zr-MOF (30.8 %) and sole In2S3 (68.2 %), respectively. Moreover, it also displayed a photocatalytic reduction kinetic rate of 0.031 min−1, which is 11.3 times and 2.69 times higher than that of fresh Zr-MOF (0.00274 min−1) and pure In2S3 (0.0115 min−1). And the photocatalytic reduction and degradation mechanisms of In2S3/Zr-MOF also have been deliberately proposed, according to the detailed experimental and instrumental characterization results. This contribution presents a feasible post-modification reinforcement strategy to assemble novel Zr-MOFs based photocatalytic platforms for the decontamination of Cr(VI) and dyes from water.

Construction of Fe3O4@ZIF-8@BiOX (X = Cl, Br, I) heterojunctions toward simultaneous removal of oxytetracycline and Cr(VI) by adsorption-photocatalysis

The magnetic Fe3O4@ZIF-8 with high adsorption properties and easy separation were embedded in BiOX (X = Cl, Br, I) to synthesize Fe3O4@ZIF-8@BiOX using a simple one-pot solvothermal strategy. The crystal structure, surface morphology, photoelectric properties, thermal stability and magnetic response of the three materials were compared and analyzed, and the effect on the removal of OTC and Cr(VI) from single and coexisting systems by adsorption-photocatalysis is discussed. The results show Fe3O4@ZIF-8@BiOI has the highest separation efficiency of photogenerated carriers upon photoexcitation and stronger light absorption capacity, and exhibits better adsorption-photocatalytic activity than the other two materials in the photocatalytic reduction of Cr(VI) (68 % and 65 % removal for single and coexisting systems) and degradation of OTC (86 % and 59 % removal for single and coexisting systems). It is noteworthy that in the coexistence of Cr(VI) and OTC, a slight decrease of removal occurred, which could be due to a competitive effect between two pollutants being greater than the synergistic effect. ∙O2- is the main active substances in the adsorption-photocatalysis process. Finally, this work demonstrates the excellent adsorption and photocatalytic ability of Fe3O4@ZIF-8@BiOI for the simultaneous removal of Cr(VI) and OTC, which has great potential for practical wastewater treatment.

Facile construction of multifunctional xNiCo2O4/BiVO4 heterojunction with accelerated charge transfer for efficient photocatalytic treatment of Cr (VI), MB and TC under visible light

The release of industrial effluents, comprising of organic dyes, antibiotics, and heavy metals poses substantial environmental and ecological threats. Among the different approaches, the utilization of heterogeneous photocatalysis based on semiconducting metal oxides is of paramount important to removal of organic ( MB dye and TC antibiotic) and inorganic pollutants ( Cr (VI) ) in wastewater. In this work, a new approach for creating type-II heterojunction photocatalysts named xNiCo2O4/BiVO4 or BNC is suggested. The as-prepared samples were thoroughly examined by means of several sophisticated analytical tools to investigate their physicochemical properties. These composites were utilized in the decomposition of MB dye, TC drug and the reduction of Cr (VI) under visible light irradiation. According to the findings, the creation of type-II heterojunction at BiVO4–NiCo2O4 interface greatly improved charge transportation while successfully preventing electron-hole recombination. Among the various composites studied, BNC-2 demonstrated an enhanced photocatalytic activity towards degradation of MB and TC, which were found to be 91 % over a period of 150 min and 95 % within only 60 min, respectively. Moreover, the photocatalytic reduction of Cr (VI) was accomplished 96 % within just 25 min. Additionally, it is discovered that BNC-2 displayed promising photostability and recyclability with a retention of >90 % after five consecutive cycles. The enhanced photocatalytic activity of BNC-2 is evidently attributed to the expedited separation and transfer of charges, as proven by photocurrent measurement, photoluminescence and electrochemical impedance spectroscopy analyses. Hence, the current amalgamation of NiCo2O4 and BiVO4 heterojunction composite has paved novel paths towards photocatalytic removal of organic as well as inorganic contaminants.

Photocatalytic reduction of Cr(vi) on a series of defective MnmIn2S3+m (m = 1–5, integer)

A series of defective MnmIn2S3+m microflowers were successfully synthesized via a facile hydrothermal method. The Mn4In2S7 exhibited the highest photocatalytic activity.

Organic Ionic Liquid Grafted Nano‐CeO2: A Highly Efficient Photocatalyst for Hydroxylation of Benzene and Reduction of Cr (VI)

AbstractAn ionic liquid, namely imidazolium sulfonic acid chloride (ISAC) has been electrostatically grafted over cerium oxide nanoparticles to produce a nanocomposite, nano‐CeO2‐IL. The as‐prepared composite was characterized by various analytical techniques such as XRD, FT‐IR, SEM, TEM, XPS, BET, UV‐DRS, PL, and TGA to confirm the grafting of ISAC over CeO2 NPs. The photocatalytic process is regarded as the method of choice for the elimination of air pollutants because of its great efficiency and relatively benign working conditions. According to UV‐DRS spectra, its optical gap is 2.07 eV, which is appropriate for the visible light spectrum. The composite was investigated as a visible‐light‐driven photocatalyst for hydroxylation of benzene to phenol and heavy metal Cr (VI) reduction. Moreover, the scavenger experiments confirmed the detection of ⋅OH radicals which played a crucial role in the photocatalytic experiments. Within 60 minutes, 98.5 % of benzene was converted to phenol with 82.7 % selectivity in addition to 93.63 % Cr (VI) reduction within 30 mins. The photocatalytic reduction of Cr(VI) to Cr(III) follows a first‐order model with a rate constant of 0.027 min−1. The remarkably high photocatalytic performance of the catalyst may be ascribed to the synergistic interaction between the nano‐CeO2 catalyst and ionic liquid.

Z-scheme heterojunction Bi2WO6/NH2-MIL-53(Fe) photocatalyst: Simultaneous efficient photo-Fenton degradation of SMX and photocatalytic reduction of Cr(VI)

The aim of this study was to develop a Z-scheme heterojunction Bi2WO6/NH2-MIL-53(Fe) photo-Fenton catalyst with enhanced electron-hole separation using an in situ growth method. Bi2WO6/NH2-MIL-53(Fe) promotes Fe(II)/Fe(III) cycling under visible light and trace H2O2 (5 μL) conditions, photo-Fenton degraded 82% of SMX within 60 min, 6.3 times that of pure Bi2WO6. It was also able to reduce Cr(VI) (20 mg/L) up to 97% efficiency under strong acidic conditions, which was 2.4 times that of Bi2WO6. In addition, Bi2WO6/NH2-MIL-53(Fe) has good stability and reusability, capable of degrading 75% of SMX and reducing 87% of Cr(VI) even after four cycles of testing. The mechanism of action of this catalyst was investigated by free radical trapping experiments, and the formation of Z-scheme heterojunction was demonstrated. In conclusion, Bi2WO6/NH2-MIL-53(Fe) is a promising photo-Fenton catalyst, which not only efficiently degrades antibiotics, but also exhibits excellent photocatalytic performance against Cr(VI) under strong acid conditions, providing a new idea for the treatment of complex pollutants.

Photocatalytic Reduction of Cr(VI) and Pb(II) with Biogenically Synthesized Copper Oxide Nanoparticles Using an Extract of the Myriophyllum spicatum Plant

The biogenic synthesis of copper oxide nanoparticles was explored using the Myriophyllum spicatum plant through a process involving co-precipitation and was utilized as an effective photocatalyst for the reduction of Cr(VI) and Pb(II) ions in an aqueous solution. The plant-mediated CuO nanoparticles were characterized using microscopic techniques (TEM and SEM), FT-IR, and XRD analyses. The amount of the reduced metal ions was determined by UV–visible and Atomic Absorption (AA) spectrophotometers. The analyses of the functional group present in the leaf extract revealed the type of bioactive molecules that were involved in the formation of copper oxide nanoparticles. The nanoparticles were used in the photo-enhanced reduction of hexavalent Cr and divalent Pb ions, and the impact of solution pH, initial metal concentrations, and photocatalyst dosage was investigated to establish the optimal performance of the CuO nanoparticles. Results revealed a direct association between the reduction of metal ions and catalyst dosage in both cases. A maximum percentage reduction of 89.2% and 79.1% was achieved for Cr(VI) and Pb(II), respectively, using 3 g of the CuO nanoparticles. This confirms that the CuO nanoparticles exhibited higher efficiency for Cr(VI) reduction as compared to Pb(II) reduction and indicates that CuO nanoparticles are a promising photocatalyst that is capable of reducing these metal ions into less toxic products.

Simple preparation of polyaniline/SiC composite as an efficient photocatalyst for the reduction of Cr(VI)

In order to enhance the photocatalytic activity of SiC, polyaniline (PANI) was utilized to modify it by constructing PANI/SiC heterojunction composite. PANI/SiC heterojunction composite was prepared via first mixing of SiC and PANI in solution and subsequent evaporation of the solvent. The photocatalytic performance of the as-prepared PANI/SiC composite in the reduction of Cr(VI) under xenon lamp irradiation was tested. The results indicated that combination with PANI can dramatically improve the photocatalytic activity of SiC. The as-prepared PANI/SiC composite not only had a photocatalytic activity 6.2 times as that of SiC, but also was more efficient than many recently reported photocatalysts in photocatalytic reduction of Cr(VI). Based on the adsorption and photoelectrochemical analysis results, it was deduced that the superior photocatalytic activity of PANI/SiC composite was attributed to its larger Cr(VI)-adsorbing capacity, higher light-absorbing ability, and more efficient separation and transfer of photogenerated electrons (h+) and holes (e–). Considering its simple preparation and excellent photocatalytic Cr(VI) reduction activity, the PANI/SiC photocatalyst is hopeful for practical application in Cr(VI) effluent treatment.

Multipath collaboration mechanisms involved in the photocatalytic reduction of Cr(VI) by FeC2O4/Bi2.15WO6

FeC2O4/Bi2.15WO6 (FeC2O4/BWO) composites were prepared, and the mechanism involved in the photocatalytic reduction of Cr(VI) by FeC2O4/BWO was investigated. When the doping amount of FeC2O4 was 10%, the obtained 10-FeC2O4/BWO composite exhibited the best Cr(VI) reduction activity with a rate constant of 0.1934 min−1, which was 33.3 times higher than that of BWO. The improved photocatalytic performance of 10-FeC2O4/BWO was ascribed to the efficient carrier separation, which was confirmed by the higher transient photocurrent and lower PL intensity than single BWO. Capture experiments further revealed that photogenerated electrons were the major species for reducing Cr(VI) by 10-FeC2O4/BWO. Dissolved Fe(II) (Fe(II)diss) released from the surface of FeC2O4 can reduce Cr(VI) to Cr(III) directly, along with the formation of Fe(III)diss. Meanwhile, the potential difference between BWO and FeC2O4 can form a built-in electric field. This field facilitates the movement of photogenerated electrons, leading to the conversion of Fe(III)diss to Fe(II)diss, could transform and drive the circulation of ‘Fe(II)diss-Fe(III)diss-Fe(II)diss’. Furthermore, the electrons transferred to the conduction band (CB) of BWO enhance the reduction of Cr(VI). The above multipath collaboration mechanism enhanced the reduction of Cr(VI) by 10-FeC2O4/BWO. Therefore, this study provides data basis and theoretical support for remove Cr(VI) and other pollutants.

Fabrication of AgI/Ce-2MI Z-scheme heterojunction for enhanced photoreduction of Cr(VI) under visible light irradiation

Proper design and successful synthesis of photocatalysts with efficient interfacial charge transfer, strong redox capabilities, and strong environmental applications are critical. Herein, a novel Z-scheme heterojunction AgI/Ce-2MI nanocomposite with redox-retaining properties was successfully prepared by a simple precipitation method. Compared with AgI and Ce-2MI, the efficiency of the optimized Z-scheme AgI/Ce-2MI composites in photocatalytic reduction of Cr(VI) in water within 75 min could exceed 90%. The reduction rate of AgI/Ce-2MI to Cr(VI) was 0.0277 min−1, which was 2.6 times and 6.8 times that of AgI and Ce-2MI, respectively. In addition, the cycle performance of AgI/Ce-2MI under different pH conditions was compared, and it was found that under the condition of pH= 2, its five-time catalytic activity stability showed good performance. Moreover, the enhancement process of reactive oxygen species •O2- and •OH were further verified by active radical capture experiment and ESR. Therefore, this study can provide a Z-scheme heterojunction nanocomposite photocatalytic process with environmental purification functions.

Synergy of Adsorption and Photocatalytic Reduction for Efficient Removal of Cr(VI) with Polyvinylidene Fluoride@Polyvinyl Alcohol-FeC2O4/Bi2.15WO6.

Although the photocatalytic reduction of Cr(VI) to Cr(III) by traditional powder photocatalysts is a promising method, the difficulty and poor recovery of photocatalysts from water hinder their wide practical applications. Herein, we present that FeC2O4/Bi2.15WO6 (FeC2O4/BWO) composites were tightly bonded to modified polyvinylidene fluoride (PVDF) membranes by chemical grafting with the aid of polyvinyl alcohol (PVA) to form photocatalytic composite membranes (PVDF@PVA-FeC2O4/BWO). The contact angle of PVDF@PVA-FeC2O4/BWO (0.06 wt % of FeC2O4/BWO) is 48.0°, which is much lower than that of the pure PVDF membrane (80.5°). Meanwhile, the permeate flux of 61.43 g m-2 h-1 and water flux of 250.60 L m-2 h-1 were observed for PVDF@PVA-FeC2O4/BWO composite membranes. The tensile strength of composite membranes reached 48.84 MPa, which was 9.8 times higher than that of PVDF membrane. It was found that the PVDF@PVA-FeC2O4/BWO membrane exhibited excellent photocatalytic Cr(VI) reduction performance under both simulated and real sunlight irradiation. The adsorption for Cr(VI) by PVDF@PVA-FeC2O4/BWO can reach 47.6% in the dark process within 30 min, and the removal percentage of Cr(VI) could reach 100% with a rate constant k value of 0.2651 min-1 after 10 min of light exposure, indicating a synergistic effect of adsorption and photoreduction for Cr(VI) removal by the composite membrane. The PVDF@PVA-FeC2O4/BWO membrane had good stability and reusability after seven consecutive cycles. Most importantly, the influences of foreign ions on Cr(VI) reduction were investigated to mimic real sewage, which revealed that no obvious adverse effects can be found with the presence of common foreign ions in sewage. The photocatalytic membrane material developed in this study provides a new idea for treating Cr(VI)-containing wastewater and has a more significant application prospect.

A bifunctional 3D inorganic–organic hybrid framework constructed by [β-Mo8O26]n4n- chains and [Cu(dap)2]2+ cations for efficient electrochemical sensing and photocatalytic reduction of Cr(VI)

Under hydrothermal conditions, a new 3D inorganic–organic hybrid polyoxometalate(POM), {[Cu(dap)2]2[β-Mo8O26]}·H2O (1, dap = 1,2-diaminopropane) was synthesized and characterized. Structural analysis displays that 1 represents an interesting 3D POM-based framework constructed from the 1D infinite inorganic chains [β-Mo8O26]n4n- and [Cu(dap)2]2+ cations. 1 exhibits good electrochemical performance and acts as electrochemical sensor for the detection of Cr(VI) with low limit of detection (LOD) of 0.291 µM, high sensitivity of 0.483 μA μM−1 and good anti-interference. The LOD of Cr(VI) for 1 is lower than the maximum content of Cr(VI) in groundwater required by the World Health Organization (WHO). Interestingly, 1 also displays excellent photocatalytic activity for Cr(VI) reduction. The reduction rate of Cr(VI) by 1 can reach 96% within 80 min under the original pH condition. Furthermore, the photocatalytic process obeys the pseudo-first-order reaction kinetic with the half-life of 16.35 min.

C-doped BiOCl/Bi2S3 heterojunction for highly efficient photoelectrochemical detection and photocatalytic reduction of Cr(VI)

Novel C-BiOCl/Bi2S3 composites are prepared by hydrothermal C doping in BiOCl and in-situ growth of Bi2S3 on C-BiOCl. Compared with BiOCl, C-BiOCl has a larger exposed surface area and can effectively absorb visible light. The construction of a heterojunction in C-BiOCl/Bi2S3 further promotes the separation and transfer of photogenerated carriers. With improved photoelectric properties, the optimized 5C-BiOCl/5Bi2S3 is applied as a dual-functional composite for photoelectrochemical (PEC) detection and photocatalytic (PC) reduction of Cr(VI). The 5C-BiOCl/5Bi2S3 shows a linear range of 0.02–80 μM for PEC cathodic detection of Cr(VI) with a detection limit of 0.01628 μM. Additionally, 99.5% of Cr(VI) can be removed via absorption and PC reduction by 5C-BiOCl/5Bi2S3, with the reduction rate constant (k) 336 times higher than that of BiOCl.

Effect of Ruthenium Modification of g-C3N4 in the Visible-Light-Driven Photocatalytic Reduction of Cr(VI)

Graphitic carbon nitride (g-C3N4) is a promising heterogeneous photocatalyst in the visible range. It can be used, among others, for reductive conversion of the toxic hexavalent chromium occurring in various wastewaters. Its photocatalytic efficiency, however, has to be improved, which can be realized by modification with different dopants or co-catalysts forming heterojunctions. In our work, ruthenium-modified g-C3N4 has been prepared by ultrasonic impregnation of the pristine g-C3N4, which was synthesized from thiourea. The morphology, microstructure, and optical properties of the photocatalysts were characterized by XRD, SEM, FT-IR, TEM, XPS, and DRS. Their compositions were analyzed by EDS and XPS measurements, indicating 0.5% and 1.4% Ru, due to the different penetrating depths. XPS study showed mainly +2 for the oxidation state of Ru. DRS analysis indicated a slight change in both the CB (from −1.14 to −1.22 eV) and the VB (from 1.49 to 1.56 eV) energies of Ru/g-C3N4, compared to those of g-C3N4. The photocatalytic Cr(VI) reduction efficacy increased from 50.1 to 96.8%. Low pH (=2) was preferred for the photocatalytic Cr(VI) reduction due to the favorable surface charge and E(Cr(VI)/Cr(III)) redox potential. Ru modification proved to be promising for improving the photocatalytic performance of g-C3N4.

Mannitol-assisted Fe-O clusters@ZIF-L for Cr(VI) photocatalytic reduction under neutral conditions inspired by Fe-based MOFs photocatalysts

Photocatalytic reduction of Cr(VI) in non-acidic circumstances has been an essential problem in the recent research of wastewater treatment. In this study, unique xFe-O@ZIF-L photocatalysts were synthesized with the assistance of mannitol. Fe-O clusters were in-situ encapsulated into the cavities of ZIF-L via this method. The morphology, optical response, electrochemical properties, and Cr(VI) degradability of as-synthesized photocatalysts were investigated. Several experiments demonstrated that the addition of Fe-O clusters considerably expanded the photo-response range while also enhanced photogenerated electron usage through the redox cycling of Fe sites. The micro-mesoporous structure in hybrid samples provides better conditions for mass transfer and exposure of reaction sites. Benefiting from the incorporation of Fe-O clusters, the hybrid material showed improved photocatalytic Cr(VI) reduction ability. After 90 min illumination, the optimum sample with a dosage of 0.5 mg/mL achieved an 86.6% degradation rate of 30 mg/L K2Cr2O7 solution even under neutral conditions. The reaction rate constant of the optimum sample (0.0210 min−1) can be up to 105 times that of the original ZIF-L (0.0002 min−1). This innovative hybrid xFe-O@ZIF-L photocatalysts offer a fresh strategy for the photocatalytic treatment of non-acidic Cr(VI)-containing wastewater.

Photocatalytic reduction of Cr(VI) using newly synthesized black phosphorus/ZnO nanocomposites

ABSTRACT Removal of high toxic Cr(VI) with solar plays an important role in improving water pollution, but is facing a dilemma of developing excellent photocatalysts with high conversion efficiency and low cost. Different from traditional nano-structuring, this work focuses on the interfacial hybridization by considering the intrinsic difference in bonding interaction. Herein, we intentionally make some layered black phosphorus (BP) sheets with Van der Waals interaction to bond with ZnO surfaces, in which some additional electron channels can be formed by this multilevel atomic hybridization to accelerate carrier transfer and separation. Compared to the pristine ZnO and BP nanosheets, the light absorption and carrier separation efficiency can be sharply enhanced by this particular electronic structure, which makes the Cr reduction performance enhanced about 7.1 times. Our findings suggest a new insight into accelerating Cr(VI) reduction by designing interfacial atom hybridization.

Comparative investigation on defect-engineered Bi2S3-xSex for boosting photocatalytic Cr(VI) reduction and in-situ H2O2 generation: Mechanistic and kinetic studies

Heterogeneous photocatalysis has been demonstrated as a highly effective approach in addressing the difficulties encountered by conventional technologies in environmental remediation. Herein, for the first time, a novel hierarchical photocatalyst of selenium-doped Bi2S3 (Bi2S3-xSex) was successfully synthesized through a one-spot hydrothermal route followed by a vacancy engineering process (V-Bi2S3-xSex). The photocatalytic reduction of Cr(VI) and in-situ generation of hydrogen peroxide (H2O2) under simulated solar-light irradiation were performed to evaluate the catalytic activity of the as-prepared samples. The catalytic activity of as-prepared samples was evaluated toward the photocatalytic reduction of Cr(VI) and in-situ generation of H2O2 under simulated solar-light irradiation. Notably, V-Bi2S3-xSex (V-BSSe-5, as optimum sample) exhibited a photo-reduction of Cr(VI) at a rate of 97.04% during 150 min, which was 1.53- and 1.39-fold higher than those of pure Bi2S3 and Bi2Se3, respectively. Interestingly, the V-Bi2S3-xSex photocatalyst not only harvested more incident light in the UV–vis and near-infrared (NIR) regions but also supplied many active sites, improving the promotion of photo-generated charge-carriers, inhibiting charge recombination, and thus enhancing the photocatalytic activity. In addition, V-BSSe-5 showed greater photocatalytic efficiency for H2O2 generation, which was 15.69, 10.07, and 1.79 times higher than those of Bi2S3, Bi2Se3, and BSSe-5, respectively. The charge-carrier migration pathway and possible photocatalytic mechanisms were systematically discussed by assisting the electron spin resonance and ultraviolet photoelectron spectroscopy analyses. The findings of this study demonstrate that doping and defect engineering strategies have the potential to be a significant advancement in the development of visible- and NIR-light responsiveness photocatalysts, thereby providing a solution to current environmental and energy challenges.