Visible-Light Photocatalytic Degradation Efficiency of Tetracycline and Rhodamine B Using a Double Z-Scheme Heterojunction Catalyst of UiO-66-NH2/BiOCl/Bi2S3

BiOCl is a promising photocatalyst, but due to its weak visible light absorption capacity and low photogenerated electron-hole pair separation rate, its practical application is limited to a certain extent. In this study, a novel double Z-scheme heterojunction UiO-66-NH2/BiOCl/Bi2S3 catalyst was constructed to broaden the visible light response range and promote high photogenerated hole-electron separation of BiOCl. Its photocatalytic performance is evaluated by dissociating tetracycline (TC) and rhodamine B (RhB) in visible light. The optimal proportion of UiO-66-NH2/BiOCl/Bi2S3 hybrids exhibits the best degradation efficiency of visible light illumination (∼93% in 120 min for TC and ∼98% in 60 min for RhB). The synergistic effect of a large visible light response range and the Z-scheme charge transfer mechanism ensure the excellent visible photocatalytic activity of UiO-66-NH2/BiOCl/Bi2S3. It is proven that h+ and •O2- are the main active substances in the photocatalysis process by active substance capture experiments and electron spin resonance tests. The intermediates and degradation processes are analyzed by high-performance liquid chromatography-mass spectrometry. This study proves that the new UiO-66-NH2/BiOCl/Bi2S3 photocatalyst has great application potential in the field of water pollution degradation and will provide a new idea for the optimization of BiOCl.

Comparative study of synthesis methods and pH-dependent adsorption of methylene blue dye on UiO-66 and NH2-UiO-66

Metal-organic frameworks (MOFs) are highly promising adsorbents with notable properties such as elevated adsorption capacities and versatile surface design capabilities. This study introduces two distinct synthesis methods, one lasting 1 h and the other 24 h, for UiO-66 and NH2-UiO-66. While both methods yield structures with comparable crystallinity and morphology, the adsorption performance of the cationic methylene blue dye varies at different pH levels. Despite the 24 h synthesis time being optimal for maximum adsorption in both MOFs, the relative difference in NH2-UiO-66 adsorption percentage at different times suggests reduced dependency on synthesis time for this property. Notably, NH2-UiO-66 exhibits consistent and effective performance across three pH levels, warranting further investigation into its adsorption kinetics and isotherm. The achievement of high adsorption efficiency coupled with a significantly reduced synthesis time underscores the importance of developing simplified synthetic methods, essential for enhancing the practical applicability of MOFs in diverse applications.

Construction of ZnIn2S4/MOF-525 heterojunction system to enhance photocatalytic degradation of tetracycline

Zirconium-based porphyrin metal organic frameworks (Zr-PMOFs) had attracted attention in the field of photocatalysis in recent years. However, the recombination of photogenerated carriers of monomer PMOF limits its performance of photocatalytic organic pollutants degradation. Metal sulfide has a suitable visible band gap, which can form a heterojunction with MOF materials to enhance the photocatalytic efficiency of MOF. Therefore, a typical metal sulfide semiconductor ZnIn₂S₄ (ZIS) was introduced into a Zr-MOF (MOF-525) by solvothermal method to prepare a series of ZIS/MOF-525 (ZIS/MOF-525-1, ZIS/MOF-525-2, ZIS/MOF-525-3 and ZIS/MOF-525-4) composite photocatalysts in this work. The results of characterization analysis, optical analysis and electrochemical analysis showed that the interface of ZIS/MOF-525 formed a typical type-II heterojunction, which accelerated the electron transport rate and effectively inhibited the recombination of photogenerated e^- and h⁺ in MOF-525. The optimal removal efficiency of tetracycline (TC) by ZIS/MOF-525-3 (the mass of MOF-525 is 30 mg) reached 93.8% under 60 min visible light illumination, which was greater than that of pure MOF-525 (37.2%) and ZnIn₂S₄ (70.0%), and it still maintained good stability after five cycles reusing experiment. This work provides feasible insight for the preparation of novel and efficient PMOF-based photocatalysts in the future.

Efficient ofloxacin degradation via photo-Fenton process over eco-friendly MIL-88A(Fe): Performance, degradation pathways, intermediate library establishment and toxicity evaluation

The high-throughput production of the eco-friendly MIL-88A(Fe) was achieved under mild reaction conditions with normal pressure and temperature. The as-prepared MIL-88A(Fe) exhibited efficient photo-Fenton catalytic ofloxacin (OFL) degradation upon visible light irradiation with good stability and reusability. The OFL (20.0 mg/L) was completely degraded within 50 min under visible light with the aid of MIL-88A(Fe) (0.25 g/L) and H₂O₂ (1.0 mL/L) in aqueous solution (pH = 7.0). The hydroxyl radicals (·OH) are the main active species during the photo-Fenton oxidation process. Meanwhile, the degradation intermediates and the corresponding degradation pathways were identified and proposed with the aid of both ultra-high performance liquid chromatography tandem quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF-MS) and density functional theory (DFT) calculations. Finally, the degradation product library was firstly established to identify intermediate transformation products (TPs) with their variation of concentration, and their corresponding toxicologic activities were assessed via Toxtree and T.E.S.T software as well. Finally, the MIL-88A is efficient and stable with four cycles' catalysis operations, demonstrating good potential for water treatment.

Operando Converting BiOCl into Bi2O2(CO3)xCly for Efficient Electrocatalytic Reduction of Carbon Dioxide to Formate

Bismuth-based materials (e.g., metallic, oxides and subcarbonate) are emerged as promising electrocatalysts for converting CO2 to formate. However, Bio-based electrocatalysts possess high overpotentials, while bismuth oxides and subcarbonate encounter stability issues. This work is designated to exemplify that the operando synthesis can be an effective means to enhance the stability of electrocatalysts under operando CO2RR conditions. A synthetic approach is developed to electrochemically convert BiOCl into Cl-containing subcarbonate (Bi2O2(CO3)xCly) under operando CO2RR conditions. The systematic operando spectroscopic studies depict that BiOCl is converted to Bi2O2(CO3)xCly via a cathodic potential-promoted anion-exchange process. The operando synthesized Bi2O2(CO3)xCly can tolerate - 1.0 V versus RHE, while for the wet-chemistry synthesized pure Bi2O2CO3, the formation of metallic Bio occurs at - 0.6 V versus RHE. At - 0.8 V versus RHE, Bi2O2(CO3)xCly can readily attain a FEHCOO- of 97.9%, much higher than that of the pure Bi2O2CO3 (81.3%). DFT calculations indicate that differing from the pure Bi2O2CO3-catalyzed CO2RR, where formate is formed via a *OCHO intermediate step that requires a high energy input energy of 2.69 eV to proceed, the formation of HCOO- over Bi2O2(CO3)xCly has proceeded via a *COOH intermediate step that only requires low energy input of 2.56 eV.

Highly efficient heterogeneous photo-Fenton BiOCl/MIL-100(Fe) nanoscaled hybrid catalysts prepared by green one-step coprecipitation for degradation of organic contaminants

An excellent heterojunction structure is vital for the improvement of photocatalytic performance. In this study, BiOCl/MIL-100(Fe) hybrid composites were prepared via a one-pot coprecipitation method for the first time. The prepared materials were characterized and then used as a photo-Fenton catalyst for the removal of organic pollutants in wastewater. The BiOCl/MIL-100(Fe) hybrid exhibited better photo-Fenton activity than MIL-100(Fe) and BiOCl for RhB degradation; in particular, the hybrid with 50% Bi molar concentration showed the highest efficiency. The excellent performance can be ascribed to the presence of coordinatively unsaturated iron centers, abundant Lewis acid sites, fast H₂O₂ activation, and efficient carrier separation on BiOCl nanosheets due to the high charge carrier mobility of the nanosheets. The photo-Fenton mechanism was studied, and the results indicated that ˙OH and h⁺ were the main active species for organic pollutant degradation. The coprecipitation-based hybridization approach presented in this paper opens up an avenue for the sustainable fabrication of photo-Fenton catalysts with abundant coordinatively unsaturated metal centers and efficient electron–hole separation capacity.

An excellent heterojunction structure is vital for the improvement of photocatalytic performance.

Controlling the Structural Robustness of Zirconium-Based Metal Organic Frameworks for Efficient Adsorption on Tetracycline Antibiotics

Tetracyclines (TCs) are the most widely used antibiotics for the prevention and treatment of livestock diseases, but they are toxic to humans and have frequently been detected in water bodies. In this study, the physical and chemical properties of the zirconium-based metal organic framework (MOF) UiO-66 and its NH2-functionalized congener UiO-66-NH2 were investigated along with batch TC adsorption tests to determine the effect of functionalization on TC removal. TC removal was highest at pH 3 and decreased with increasing pH. Pseudo-1st and pseudo-2nd-order kinetic models were used to study the adsorption equilibrium times, and Langmuir isotherm model was found to be more suitable than Freundlich model. The maximum uptake for UiO-66 and UIO-66-NH2 was measured to be 93.6 and 76.5 mg/g, respectively. Unexpectedly, the TC adsorption capacity of UiO-66-NH2 was observed to be lower than that of UiO-66. Density functional theory calculations revealed that the pore structures are irrelevant to TC adsorption, and that the –NH2 functional group could weaken the structural robustness of UiO-66-NH2, causing a reduction in TC adsorption capacity. Accordingly, robust MOFs with zirconium-based metal clusters can be effectively applied for the treatment of antibiotics such as TC in water.

Magnetic BiFeO3 decorated UiO-66 as a p–n heterojunction photocatalyst for simultaneous degradation of a binary mixture of anionic and cationic dyes

Magnetic UiO-66/BiFeO₃ composite for simultaneous photodegradation of a binary mixture of anionic and cationic dyes.

The synthesis of a BiOClxBr1−x nanostructure photocatalyst with high surface area for the enhanced visible-light photocatalytic reduction of Cr(vi)

The photocatalytic reduction of poisonous Cr(vi) to environmentally friendly Cr(iii) driven by visible-light is highly foreseen. The construction of heterojunctions is a promising and solid strategy to tune the photocatalytic performance of BiOCl in the visible region. Herein, for the first time, we report Cr(vi) reduction by a BiOCl_0.8Br_0.2 composite produced via a facile in situ synthetic process at room temperature while making use of PVP (MW = 10 000). In this study, a series of BiOCl_xBr_1−x nanocomposites with different concentrations of chlorine and bromine have been prepared. The results show that BiOCl_0.8Br_0.2 has crystalline lattice, a large surface area (147 m² g⁻¹), a microporous structure (0.377 cm³ g⁻¹), and very high chemical stability. It is revealed that the BiOCl_0.8Br_0.2 composite is much more active than those synthesized using different molar concentrations of chlorine and bromine. The DRS analysis and high photocurrent suggested that BiOCl_0.8Br_0.2 possessed absorption properties under visible light, which is beneficial for the efficient generation and separation of electron–hole pairs. In addition, we evaluated the photocatalytic activity of BiOCl_0.8Br_0.2 on the reduction of Cr(vi) under visible light irradiation and found that the obtained composite material exhibited a higher photocatalytic activity than single BiOCl or BiOBr without any decline in the activity after five cycles and is the best performing photocatalyst among those tested.

Cr(vi) reduction is performed by BiOCl_0.8Br_0.2 composite produced via a facile in situ synthetic process at room temperature while making use of PVP (M_w = 10 000).

Flower-like BiOBr/UiO-66-NH2 nanosphere with improved photocatalytic property for norfloxacin removal

Metal-organic frameworks (MOFs) have attracted widespread concerns in the photocatalysis research. However, MOFs-based photocatalyts for antibiotics treatment are still very limited. There are also few reports on selecting MOFs as supports to regulate the morphology of Bismuthoxyhalides. In this study, BiOBr/UiO-66-NH₂ composites with three-dimensional structure of flower-like nanosphere were fabricated via a facile synthetic route. Various characterizations, such as XRD, SEM and XPS, proved the successful synthesis of composite and revealed that BiOBr nanoplates grow on the surfaces of the UiO-66-NH₂ with an intimate interaction. A typical fluoroquinolones antibiotics, norfloxacin (NOR) was selected to estimate the photocatalytic efficiency of the BiOBr/UiO-66-NH₂ complex. A series of the composites all exhibited higher NOR removal performance than the pure components and mechanically mixed sample under simulated sunlight. Among them, the composite with UiO-66-NH₂ content of 20 w% (BUN-20), had good structural stability and the best performance on the removal of NOR. The removal efficiency of NOR (10 mg/L) over BUN-20 (0.3 g/L) was 93.60% within 180 min irradiation. Three factors during the fabricating process, such as increased surface active sites, improved photoadsorption capacity and lower recombination probability of electron-hole pair might be accountable for the meliorative photocatalytic performance. Ultimately, a plausible photocatalytic mechanism was also proposed.