Photocatalytic Cr Research Articles

Amino-Functionalized Metal-Organic Framework-Mediated Cellulose Aerogels for Efficient Cr(VI) Reduction.

Industrialization activities have increased the discharge of wastewater that is polluted with hexavalent chromium (Cr(VI)), posing risks to ecosystems and humans. The photocatalytic reduction of Cr(VI) is viewed as a promising method for the removal of Cr(VI) species. However, developing photocatalysts with the desired catalytic activity, recyclability, and reusability remains a challenge. Herein, a composite aerogel was designed and fabricated with a Ti-based metal-organic framework (MIL-125-NH2) and carboxylated nanocellulose. MIL-125-NH2 presents a strong visible-light response, and the interactions between the amino groups of MIL-125-NH2 and the carboxyl groups of cellulose produce a strong interface affinity in the composites. The as-prepared aerogels exhibited a micro/macroporous structure. At an optimal MIL-125-NH2 loading of 55 wt%, the MC-5 sample showed a specific surface area of 582 m2·g-1. MC-5 achieved a photocatalytic Cr(VI) removal efficiency of 99.8%. Meanwhile, the aerogel-type photocatalysts demonstrated good stability and recycling ability, as MC-5 maintained a removal rate of 82% after 10 cycles. This work sheds light on the preparation of novel photocatalysts with three-dimensional structures for environmental remediation.

The PDINH decorated NH2-UiO-67 MOF for promoted photocatalytic Cr(VI) reduction: Performance, and mechanism

A series of composite materials comprising NH₂-UiO-67 metal-organic framework (MOF) and highly π-conjugated 3,4,9,10-perylenetetracarboxylic diimide (PDINH) was synthesized via a facile ball-milling process. These hetero-conjugated MOFs, denoted as PNU-67(X) with varying amounts of PDINH (X = 0.5 %, 1 %, 2 %, and 3 % wt), were evaluated for their photoreduction of Cr(VI) to Cr(III) under visible light irradiation. Systematic investigations revealed a direct correlation between increasing PDINH content and enhancing the conductivity of the MOFs. Additionally, the incorporation of PDINH motifs significantly improved CO₂ capture capability by increasing charge transfer, charge separation, and light absorption. To elucidate the impact of various factors on the photocatalytic performance of PNU-67(3) in Cr(VI) remediation, a comprehensive study was conducted. These factors included pH, initial Cr(VI) concentration, catalyst dosage, scavengers, and scavenger concentration. Notably, PNU-67(3) (5 mg/L) demonstrated 100 % photoreduction efficiency within 35 min, highlighting its potential application in catalyst loading and efficiency compared to other reported UiO-type MOFs. Furthermore, the composites exhibited exceptional stability and reproducibility throughout multiple experimental cycles. Overall, this research presents a promising avenue for constructing heterojunction photocatalysts by integrating MOFs and organic PDINH molecules, offering a viable solution for wastewater remediation.

Charge-Tunable Bismuth-Hydroxamate Metal–Organic Frameworks for Photocatalytic Cr(VI) Mitigation

Charge-Tunable Bismuth-Hydroxamate Metal–Organic Frameworks for Photocatalytic Cr(VI) Mitigation

Efficient photocatalytic CO2 and Cr(VI) reduction on carbon quantum dots/carbon nitride heterojunctions

Carbon quantum dots (CQDs), known for their exceptional optical properties, hold the potential to enhance light absorption, charges separation and transfer in semiconductor materials. However, using cheap medicinal materials as precursors in the field of photocatalysis to obtain CQDs has seldom concerned. In this study, we utilized biomass-derived CQDs from carbon-rich licorice powder to improve photocatalytic CO2 and Cr(VI) reduction in polymer carbon nitride (PCN). The CQDs/g-C3N4 heterojunctions were synthesized via a hydrothermal method, and the successful fabrication and integration of CQDs on g-C3N4 surfaces were confirmed through detailed characterization. The optimal sample with a licorice powder to PCN mass ratio of 0.05:1 ((50CQDs/CN) demonstrates a tripling in CO2 conversion efficiency under simulated sunlight compared to the reference PCN. Under visible light irradiation, the 50CQDs/CN also performs superior photocatalytic Cr (VI) removal efficiency, which is 2.48 times of that of the reference PCN. This significant boost is attributable to the successful construction of the CQDs/CN heterojunction and the abundance of functional groups on the CQDs surface, which provide more active sites, improve light absorption and increase charges migration rates. The stability of these new photocatalysts was confirmed through repeated photocatalytic cycles, indicating their potential for practical applications. Mechanistic studies reveal insights into the enhanced photocatalytic pathways and intermediate conversion processes. Our findings present a novel, efficient and sustainable route to fabricate g-C3N4-based photocatalysts, offering a promising strategy for further mitigate the greenhouse gas crisis and environmental pollution.

Defect engineering on metal-organic frameworks for enhanced photocatalytic reduction of Cr(VI)

Cr(VI) stands as a profoundly toxic chemical and photocatalysis technology has shown promising potential in photocatalytic reduction of Cr(VI) to Cr(III), where the reduced Cr(III) is less toxic and can be further precipitated in a wide pH range. Metal-organic frameworks (MOFs), as emerging class of porous coordination polymers, is expected to be ideal platform for photocatalysis. In this study, defect engineering on MOFs was applied to promote photoreduction of Cr(VI). The obtained oxygen vacancy-containing MIL-125-NH2 samples showed modified electron structure, adjusted surface and porous properties, and enriched active sites. Among these oxygen vacancy-containing MIL-125-NH2 samples, the 300-M (MIL-125-NH2 heated at 300 °C for 2 h under N2 atmosphere) displayed the most remarkable performance in terms of photocatalytic Cr(VI) reduction. The pronounced efficacy of 300-M is evident from the achieved removal rate of Cr (VI), reaching an impressive 98 % in just 20 mins (19.6 mgCr(VI) g−1cata min−1), in stark contrast to MIL-125-NH2, which exhibited a modest removal rate of 53 %. Remarkably, the k-value for 300-M is 5.1 times that of MIL-125-NH2, further underscoring the superior efficiency of 300-M. The photoreduction mechanism of 300-M was further substantiated through a battery of advanced characterization techniques including transient photocurrent, electrochemical impedance spectroscopy, fluorescence spectroscopy, the Mott-Schottky analysis, and electron spin resonance. Those results disclosed that oxygen vacancies and mesopores introduced via controlled heat treatment play a pivotal role in facilitating the photoreduction of Cr(VI) within the MIL-125-NH2 structure. More advanced characterizations for the structures of photocatalysts and the photocatalytic mechanisms including charge transfer path need further studied. The systematic exploration of temperature-dependent effects on material properties opens avenues for future research in designing efficient and versatile MOF-based photocatalysts for environmental remediation applications.

Precisely controlling structure defects of Quasi-MIL-125 for improving its catalytic performance

Quasi-Metal-Organic Frameworks (Quasi-MOFs) are a class of promising porous materials with unique structural defectives. It is of significant importance to probe into the systematic relationship between catalytic performance of Quasi-MOFs and porous structure, metal nodes and ligands. Herein, a solvent-assisted strategy was developed to finely fabricate Quasi-MIL-125 with various structure defects by varying reaction temperature, where the ligands were removed by controlled esterification to create hierarchical pore and the metal nodes were transformed into TixOy to enrich catalytic active sites. Meanwhile, a morphological transformation of Quasi-MIL-125 was observed from disk-shape to nanosheets during this process. As a result, Quasi-MIL-125–130 displayed high catalytic performance in photocatalytic Cr(VI) reduction due to the strong synergistic effect between exposed metal active sites and ligands. What is more, Pd/Quasi-MIL-125–130 exhibited significantly enhanced catalytic activity in styrene hydrogenation reaction owing to its enriched porous structure. More importantly, functional Quasi-MOF crystals with different structural defects could be gently fabricated and used to enhance target functions.

New insights into the mechanism for Fe coordination promoting photocatalytic reduction of Cr(VI) by graphitic carbon nitride: The boosted transformation of Cr(V) to Cr(III)

Fe coordination is effective to promote photocatalytic Cr(VI) reduction by graphitic carbon nitride (g-C3N4) from wastewater; however, the role of Fe coordination in the Cr intermediate transformation is still unknown. Herein, a Cr intermediate, Cr(V), is detected by electron paramagnetic resonance and its generation and consumption kinetics are constructed for studying the visible-light photocatalytic processes of g-C3N4 and Fe anchored g-C3N4. The inclusion of Fe increased the photocatalytic Cr(VI) removal from 26.8 % to 51.3–85.6 %. The results reveal that Fe coordination of trivalent state can greatly enhance photocatalytic Cr(VI) reduction performance mainly through promoting interfacial electron transfer from g-C3N4 to Cr(V). Compared with pure g-C3N4, increasing Fe(III)/Fe(II) ratio of coordinated Fe species results in 8–11 times of enhancement of photocatalytic Cr(VI) reduction performance, 1–2 times of enhancement of photocatalytic Cr(V) generation, and 8–9 times of enhancement of photocatalytic Cr(V) consumption. This suggests the rate-limiting step for Cr(VI) reduction by g-C3N4-based photocatalysts is the transformation process of Cr(V) to Cr(III) and also illustrates the important role of the coordinated Fe(III) species in the photocatalytic transformation of Cr intermediates. This study deepens the understanding of Fe-coordination-promoted photocatalytic Cr(VI) reduction process and sheds light on developing high-performance g-C3N4-based photocatalysts for Cr(VI) removal from wastewater.

Carboxylated cellulose-derived carbon mediated flower-like bismuth oxyhalides for efficient Cr(VI) reduction under visible light

Exquisitely tailoring the morphologies of photocatalysts could achieve high activities. In this study, the morphological transformation of bismuth oxyhalide (BiOX, X = Br, I and Cl) from disordered lamellae to regular flowers was facilely achieved via the use of carboxylated cellulose-derived carbon (CDC). The sphere-like structure and abundant surface functional groups of CDC induce the formation of such flower-like morphologies of BiOX/CDC, and this morphology results in a pronounced increase in surface area (e.g., the surface area of BiOBr increases from 3 to 106 m2 g−1) and porosity. Combined with the good light absorption and conductivity of CDC, the flower-like BiOX/CDC exhibited impressive photocatalytic activity under visible light. Regarding the probing Cr(VI) reduction reaction, the representative BiOBr/CDC is capable of reducing 98% of Cr(VI) within 30 min of visible-light illumination, which is markedly greater than those of pure BiOBr (6%) and CDC (16%). Likewise, BiOI/CDC and BiOCl/CDC also have decent photocatalytic Cr(VI) reduction capacities (89% for BiOI/CDC and 69% for BiOCl/CDC) under visible light in comparison with pristine BiOI (13%) and BiOCl (1.5%). This work furnishes a novel and facile approach to tune photocatalyst morphologies and sheds light on the great potential of biomass-derived carbon, which may enlighten the judicious design of photocatalysts with high efficiency.

Facile fabrication of heavily N-doped Zn0.67Cd0.33S nanocatalyst with congenital sulfur vacancies for efficient photocatalytic reduction of water and hexavalent chromium

Twinned zinc cadmium sulfide (ZnxCd1-xS) has been widely investigated for efficient Cr(VI) reduction and H2 production under light irradiation due to its inherent homojunctions. However, long-distance migration of charge carriers and relatively low conduction band level inevitably cause low photocatalytic reduction ability. Herein, we developed a DMF-involved one-step solvothermal strategy to introduce N heteroatoms into Zn0.67Cd0.33S crystals incorporated with dopant-induced S vacancies. The synergetic promotion of the elevated conduction band, coupled with the robust aggregation of interactants, effectively impeded the recombination behavior of charge carriers, leading to a notable increase in photocurrent density (∼2.4 times), electron density (∼2.8 times), and a higher photo-reducing potential. The optimal NZCS-10 demonstrated a superior photocatalytic Cr(VI) reduction efficiency of 99.32 % within 30 min, and rendered ca. 5.8- and 7.6-fold enhancement for H2 evolution rate under alkaline and acidic conditions, respectively. This study provided a universal strategy for gaining highly reductive transition metal sulfides with more active sites.

Construction of direct Z-scheme Co9S8/CdS with tubular heterostructure through the simultaneous immobilization and in-situ reduction strategy for enhanced photocatalytic Cr(VI) reduction under visible light

Tubular Co9S8/CdS heterostructures have been successfully synthesized by in-situ growing CdS onto Co9S8 nanotubes through a simultaneous immobilization and in-situ reduction strategy. It turned out that the so-obtained heterostructure with Co9S8/CdS molar ratio of 1/10 can display a broad light absorption edge and especially much enhanced capacity for photocatalytic reduction of Cr(VI) under visible light. The characterization analysis and experimental results suggested that an interfacial electrostatic field between Co9S8 and CdS elements in the heterostructure could be constructed due to their different Fermi levels, allowing for more quantities of highly reductive electrons to participate in the photocatalytic reaction. Therefore, the so-obtained Co9S8/CdS (1/10) heterostructures could achieve the photocatalytic reduction efficiency of 100% within 20 min, which was more than two and four times larger than that of pristine CdS and Co9S8, respectively. Moreover, the possible photocatalytic reaction mechanism for reducing Cr(VI) was investigated and found to follow the direct Z-scheme charge transfer pathway. This novel fabrication route for composite photocatalysts with tubular heterostructures could lead to the widespread implementations for the elimination of various harmful pollutants in the process of environmental governance.

Enhanced photocatalytic Cr(VI) degradation and real-time detection using dual-fluorescent quantum dot-infused polysulfone microspheres

Conventional methodologies for the detection and remediation of hexavalent chromium (Cr(VI)) are characterized by their complexity and financial burden, necessitating the pursuit of methodologies that are both efficacious and economical, with minimal environmental impact. Within this investigation, we report the fabrication of hollow polysulfone (PSF) microspheres, imbued with bifluorescent quantum dots and metal-organic frameworks, utilizing a Pickering emulsion paradigm to facilitate photolytic Cr(VI) degradation and consistent visual detection. Our results reveal that these engineered microspheres sustain an exceptional degradation efficiency exceeding 98 % for Cr(VI) over quintuple cycles, devoid of agitation, alongside pronounced fluorescence quenching indicative of a durable and recyclable sensing modality. The inherent low density and vacuous architecture of these spheres afford them buoyancy, augmenting their interaction with aqueous pollutants. Furthermore, the material exhibits a distinguished selectivity for Cr(VI), markedly eclipsing alternative metal ions in fluorescence suppression assays, validating its efficacy for heavy metal detection. The dual-functional attributes, coupled with their enduring stability and eco-friendly profile, position the CCUP microspheres at the forefront of water treatment innovation, potentially revolutionizing the real-time tracing of heavy metal pollutants.

Halogen-functionalized covalent organic frameworks for photocatalytic Cr(VI) reduction under visible light

Covalent organic frameworks (COFs) are a type of novel organic catalysts which show great potential in the treatment of environmental contaminations. Herein, we synthesized three isoreticular halogen-functionalized (F, Cl and Br) porphyrin COFs for visible-light (420 nm ≤ λ ≤ 780 nm) photocatalytic reduction of Cr(VI) to Cr(III). Halogen substituents with tunable electronegativity can regulate the band structure and modulate the charge carrier kinetics of COFs. In the absence of any sacrificial reagent, the isoreticular COFs exhibited good photocatalytic reduction activity of Cr(VI). Particularly, the TAPP-2F showed nearly 100 % conversion efficiency and the highest reaction rate constants (k) on account of the strong electronegativity of F substituent. Experimental results and theoretical calculations showed that the conduction band (CB) potentials of COFs became more negative and charge carrier separation increased with the enhancement of electronegativity (Br < Cl < F), which could provide sufficient driving force for the photoreduction of Cr(VI) to Cr(III). The halogen substituents strategy for regulating the electronic structure of COFs can provide opportunities for designing efficient photocatalysts for environmental remediation. Meanwhile, the mechanistic insights reported in this study help to understand the photocatalytic degradation pathways of heavy metals.

A novel S-scheme heterojunction of MnCo2O4/CeO2 photocatalysts for effective and fast removal of Cr(VI) ion under visible illumination

The Cr(VI) ions’ pollution is the most common in anthropogenic activities and drinking water sources. The photocatalytic reduction approach has been considered a promising process and highly desirable for decontamination of Cr(VI)- polluted water. In this contribution, a series of MnCo2O4/CeO2 nanocomposites were constructed for Cr(VI) photoreduction under visible light illumination. The physicochemical characterizations revealed that the 12 wt% MnCo2O4/CeO2 heterojunction photocatalyst exhibited the maximum visible light photocatalytic Cr(VI) reduction efficiency of 100 % within 45 min. Moreover, a photoreduction rate of ⁓7.071 mmol g−1min−1 was achieved at 12 wt% MnCo2O4/CeO2 photocatalyst which was 3.32 times higher than the sole CeO2 nanoparticles (NPs) (2.132 mmol g−1min−1). The heterojunction of MnCo2O4/CeO2 photocatalyst with outstanding photocatalytic ability was maintained after five runs, which verified its superior candidate for efficient and ultrafast removal of Cr(VI) ions. The superb photocatalytic reduction ability was attributed to uniform morphology with well-dispersed MnCo2O4 on the CeO2 NPs, and mesostructured characteristics. In addition, the enhanced photoreduction rate was credited to the construction of S-scheme heterojunction of MnCo2O4/CeO2, which could significantly be transferred and separate photoinduced charge carriers, thus minimizing the photocarrier recombination. This work illustrates the idea of fabricating S-scheme heterojunction nanocomposites and enhancing photocatalytic performance under visible illumination.

Low-temperature microwave-assisted synthesis of Bi2WO6/Bi2S3 heterojunction for photocatalytic reduction of Cr(VI) in industrial wastewater

Cr(VI) pollution has become a worldwide environmental issue due to its toxicity and non-biodegradability in wastewater. Herein, a Bi2S3/Bi2WO6 (BWS) Z-scheme heterojunction was successfully fabricated via a low-temperature in situ sulfurization process assisted by microwave irradiation and applied to the photocatalytic reduction of Cr(VI) in industrial electroplating wastewater. The effects of Bi2S3 loading, catalyst dosage, light source, and synthesis method on the catalytic performance of the heterojunctions were investigated. Remarkably, the optimized BWS-6 heterojunction achieved 100% Cr(VI) removal within 50 min under LED light irradiation and 30 min under sunlight irradiation, which greatly exceeded the pure Bi2S3 and Bi2WO6. In addition, BWS-6 exhibited high photostability, and it still sustained preferable photocatalytic Cr(VI) reduction activity under sunlight irradiation when the experiment was scaled up 20 times. The high photocatalytic activity of BWS photocatalysts can be ascribed to enlarged surface area, active centers, and intimate interfacial contact of Z-scheme heterojunction, which greatly improve visible-light harvesting, surface adsorption, and the transport efficiency of interfacial charge. Experimental and theoretical calculation results further evidenced a built-in electric field forming at the interface of the Z-scheme heterojunction and unveiled a possible photocatalytic reduction pathway. This work provides valuable information for large-scale applications in the removal of Cr(VI) from industrial wastewater by Z-scheme heterojunctions.

Spatial separation of photocarriers and selective adsorption on flower-like core-shell heterojunction of Cr(VI) imprinted polymer@BiOI for boosted photocatalytic Cr(VI) reduction

BackgroundConstructing heterojunction photocatalyst is a well-established strategy for enhancing photocatalytic Cr(VI) reduction due to the heightened separation and transfer of photocarriers. Whereas, aimless and random transfer of photocarriers and low photocarrier utilization rate deriving from the weak interface interaction between heterojunction and Cr(VI) are still limited the photocatalytic reduction performance of Cr(VI). MethodsHerein, a flower-like core-shell heterojunction photocatalyst was designed by wrapping a pyridine-based Cr(VI) imprinted polymer (PCIP) onto flower-like BiOI to achieve spatial separation of photocarriers and selective adsorption of Cr(VI), resulting in an outstanding photocatalytic reduction performance of Cr(VI). Significant findingsIn the core-shell heterojunction, photocarriers could be spatially separated, and then brought about high-efficient photocatalytic Cr(VI) reduction close to the selective adsorption sites of Cr(VI). After measurement, the optimal PCIP@BiOI core-shell heterojunction, polymerized for ≈30 min, exhibited a robust photocatalytic reduction performance of Cr(VI), without adding any free radical sacrifice agents. Within 1 h, the aqueous solution containing 100 mg/L of Cr(VI) could be completely removed, and the photocatalytic reduction rate constant of Cr(VI) was ≈20 times superior to BiOI. This study presents a methodology for designing core-shell heterojunction photocatalysts on the basis of inorganic/organic conjunction for environmental remediation of high concentrations of Cr(VI).

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.

Efficient photocatalytic reduction of Cr(VI) and degradation of tetracycline by Bi2Se3@ZnIn2S4 binary heterostructures enriched with sulfur vacancies: Mechanism and mineralization analysis

Constructing a sulfur-vacancy-enriched heterostructure offers advantages in enhancing photocatalytic performance due to the synergy between the vacancy’s electron-trapping and the internal electric field (IEF) features. In this study, a series of IEF-modulated type-I heterostructures containing sulfur vacancies-rich ZnIn2S4 (SV-ZIS) and Bi2Se3 (BSe) was rationally developed by hydrothermal and reduction methods. The optimized BSe@SV-ZIS catalyst shows an outstanding photocatalytic Cr(VI) reduction and tetracycline degradation rates, which are ∼ 2.1 and ∼ 1.5 times higher than that of pure SV-ZIS and BSe, respectively. Notably, the enhanced catalytic performance of binary samples could be linked to efficient absorption of the full spectrum of light, heterojunction formation and larger contact area to enhance the charge carriers movement at their interface and exceptional photo-stability. By assisting DRS, VB-XPS, and UPS analyses, details of the energy band position, charge carriers transport route, and preliminary photocatalytic mechanism were systematically explored. Furthermore, radical scavenging and electron paramagnetic resonance experiments were conducted to provide evidence of the participation of the reactive species during photocatalysis over BSe@SV-ZIS. Kinetic analysis revealed that the rate of photocatalytic process adheres to the Langmuir–Hinshelwood kinetic model. These results demonstrated that the heterostructuring approach holds significant potential as an effective avenue for developing photocatalysts that can harness both visible and NIR light, offering promising solutions to contemporary challenges in the realms of environmental decontamination and energy.

S-scheme towards interfacial charge transfer between POMs and MOFs for efficient visible-light photocatalytic Cr (VI) reduction

The establishment of heterojunctions was considered as an exceptional strategy to obtain high-efficiency charge separation and enhanced photocatalytic performance. Herein, a series of FePMo/MIL-53(Fe) (FeM-53) heterojunctions were successfully constructed through in-situ growth of FePMo onto MIL-53(Fe) surface and their photocatalytic capacity were examined by visible-light-induced Cr(VI) reduction. Interestingly, the as-fabricated composites offered various photocatalytic activities controllably relying on the mass ratio of FePMo to MIL-53(Fe). Particularly, the one with the 10% ratio displayed the highest Cr(VI) reduction rate (100%) within 75 min, which was respectively over 4 and 2 folds higher than pure FePMo and MIL-53(Fe). The boosted photoactivity might be ascribed to the establishment of S-scheme heterojunction with suitable band alignment between FePMo and MIL-53(Fe), which broadened the light absorption range and improved charge separation. Further mechanism investigations implied both •O2− and e− were the key reactive species for Cr(VI) removal. Besides, the composite preserved excellent stability after 4 consecutive tests, and performed well in the presence of organic dyes. Such a S-scheme heterojunction may promise for highly efficient environmental mitigation.

Leveraging the photocatalytic Cr (VI) reduction by an IRMOF-3@NH2-MIL-101 (Fe) heterostructure based on interfacial Lewis acid-base interaction

A strategy to enhance the photocatalytic performance of metal-organic framework (MOF) based systems for the efficient elimination of Cr(VI) ions from polluted water under visible light irradiation has been developed by constructing MOF@MOF heterojunctions. Specifically, IRMOF-3 was grown in situ around NH2-MIL-101(Fe) based on interfacial Lewis acid-base interaction using 2-aminoterephthalic acid (ATA) as a linker, resulting in the formation of a MOF@MOF heterojunction, designated as IRMOF-3@NH2-MIL-101(Fe). In comparison to individual MOFs, the IRMOF-3@NH2-MIL-101(Fe) heterojunction exhibited a significantly higher photocatalytic reduction efficiency for Cr(VI), achieving a reduction of 95.98% within 120 min under visible-light irradiation. This performance surpasses that of individual MOFs and most reported photocatalysts. Additionally, the mechanism underlying Cr(VI) reduction by IRMOF-3@NH2-MIL-101(Fe) was comprehensively elucidated by analyzing optoelectronic properties, energy band structure, and structural results. It is worth noting that this study represents the first documented instance of photocatalytic Cr(VI) reduction utilizing IRMOF-3 and its interaction with NH2-MIL-101(Fe). The MOF@MOF photocatalyst, leveraging the synergistic effects of its various components, holds great promise for efficiently removing harmful pollutants from water and finds significant potential applications in environmental remediation.

Preparation of core-shell structure Ag@TiO2 plasma photocatalysts and reduction of Cr(VI): Size dependent and LSPR effect

The poor light absorption and low carrier separation efficiency of Titanium dioxide (TiO2) limit its further application. The introduction of plasma metal Ag have the potential to solve these drawbacks owing to its plasma resonance effect. Thus core-shell structure Ag@TiO2 plasma photocatalysts was prepared by using facile reduction method in this work. More specifically, Ag@TiO2 composite catalysts with different Ag loading amounts were prepared in the presence of surfactant PVP. Ag@TiO2 demonstrates excellent light absorption performance and photoelectric separation efficiency compared with pure TiO2. As a result, it displays excellent performance of Cr(VI) reduction under visible light. The optimal composite catalysts Ag@TiO2–5P achieves exceptional visible-light-driven photocatalytic Cr(VI) reduction efficiency of 0.01416 min−1 that is 2.29 times greater than pure TiO2. To investigate the role of PVP, we also synthesized Ag@TiO2-5 without PVP. The experimental results show that although Ag@TiO2-5 Cr(VI) reduction performance is superior to pure TiO2, it significantly decreases compared with Ag@TiO2–5P. The results of TEM and optoelectronic testing show that agglomeration of Ag particles leads to a decrease in the photoelectric separation efficiency of Ag@TiO2-5. The smaller Ag particles provide more active sites and demonstrating a stronger overall local surface plasmon resonance (LSPR) effect. DMPO spin-trapping ESR spectra testing indicates that ∙O2− and ∙OH are the main reactive species. This research provides a potential strategy to prepare Ag-based plasma photocatalysts for environment protection.