Preparation of magnetically retrievable flower-like AgBr/BiOBr/NiFe2O4 direct Z-scheme heterojunction photocatalyst with enhanced visible-light photoactivity

Efficient Catalytic Degradation of Methyl Orange by Various ZnO-Doped Lignin-Based Carbons

Herein, a series of ZnO-doped lignin-based carbons (LC/ZnO) were successfully prepared from different types of lignin and used for methyl orange (MO) photocatalytic degradation. The apparent morphology, internal structure, and photoelectric properties of prepared LC/ZnO composites and their effects on subsequent MO photocatalytic degradation were investigated by various characterization techniques. The results showed that the LC/ZnO composites that were prepared in this work mainly consisted of highly dispersed ZnO nanoparticles and lignin-based carbon nano-sheets, which were beneficial for subsequent photogenerated electrons and holes formation, dispersion, and migration. The MO could be significantly degraded with various ZnO-doped lignin-based carbons, especially over the LCSL/ZnO, and the maximum degradation rate was 96.9% within 30 min under the simulated 300w sunlight exposure. The experiments of free radical elimination showed that the photocatalytic degradation of MO over LC/ZnO were a result of the co-action of multiple free radicals, and h+ might play the predominant roles in MO degradation. In addition, the pH of the solution had little effect on MO degradation, and the MO could be effectively degraded even in an alkaline solution of pH = 12.0. The cycling experiments showed that the prepared LC/ZnO had a good stability for MO photodegradation, especially for LCSL/ZnO, even after 5 times recycling, and the degradation rate of MO only dropped from 97.0% to 93.0%. The research not only provided a fundamental theory for the efficient photocatalytic degradation of MO by LC/ZnO composites, but also offered a new insight into lignin valorization.

A magnetically reusable Ce-MOF/GO/Fe3O4 composite for effective photocatalytic degradation of chlortetracycline

Herein, we report a novel 1/GO/Fe3O4 photocatalyst, comprising Ce(BTB)(H2O) (MOF-1, H3BTB = 1,3,5-benzenetrisbenzoic acid), graphene oxide (GO), and iron oxide (Fe3O4) for photocatalytic degradation of chlortetracycline (CTC). This design enables the effective transfer of electrons from the MOF to GO, thereby reducing the photoelectron-hole recombination rate. Therefore, the optimized 1/GO/Fe3O4 photocatalyst with H2O2 shows the highest photocatalytic activity toward CTC. The kinetic constant is 5.4 times that in the system of MOF-1 and hydrogen peroxide, which usually acted as efficient electron acceptors to improve the photocatalytic performance of MOFs. More importantly, light absorption is extended from the ultraviolet to the visible region. Furthermore, 1/GO/Fe3O4 can be quickly recycled under an applied magnetic field and displays outstanding stability and reusability. According to the radical trapping experiments and electron paramagnetic resonance results, hydroxyl radicals, superoxide radicals, and holes all contribute to excellent photocatalytic activity. The possible catalytic mechanism of 1/GO/Fe3O4 is tentatively proposed. This work aims to explore the synergistic effect between metal-organic frameworks (MOFs) and GO, and provide a theoretical basis for MOF-based composites to remove antibiotic contaminants in the environment.

Rational Photodeposition of Cobalt Phosphate on Flower-like ZnIn2S4 for Efficient Photocatalytic Hydrogen Evolution

The high electrons and holes recombination rate of ZnIn2S4 significantly limits its photocatalytic performance. Herein, a simple in situ photodeposition strategy is adopted to introduce the cocatalyst cobalt phosphate (Co-Pi) on ZnIn2S4, aiming at facilitating the separation of electron-hole by promoting the transfer of photogenerated holes of ZnIn2S4. The study reveals that the composite catalyst has superior photocatalytic performance than blank ZnIn2S4. In particular, ZnIn2S4 loaded with 5% Co-Pi (ZnIn2S4/5%Co-Pi) has the best photocatalytic activity, and the H2 production rate reaches 3593 μmol·g-1·h-1, approximately double that of ZnIn2S4 alone. Subsequent characterization data demonstrate that the introduction of the cocatalyst Co-Pi facilitates the transfer of ZnIn2S4 holes, thus improving the efficiency of photogenerated carrier separation. This investigation focuses on the rational utilization of high-content and rich cocatalysts on earth to design low-cost and efficient composite catalysts to achieve sustainable photocatalytic hydrogen evolution.

Low temperature in situ fabrication of NiFe2O4/tetragonal-BiVO4/Bi2MoO6 ternary heterostructure: A conjugated step-scheme multijunction photocatalyst with synergistic charge migration for antibiotic photodegradation and H2 generation

Rational design of novel conjugated step-scheme (S-scheme) multijunction heterostructure with synergistic charge channelization, superior light harvesting efficiency and strong redox ability is a pioneering approach to mimic natural photosynthesis process. Herein, a mild cetyltrimethyl ammoniumbromide (CTAB) assisted one pot reflux synthesis route is designed for in situ integration of metal organic framework (MOF)-derived NiFe2O4 with tetragonal-BiVO4 (t-BiVO4) and γ-Bi2MoO6 to prepare NiFe2O4/t-BiVO4/Bi2MoO6 (NFO/BVO/BMO) ternary composites. Morphologically, fine dispersion of NiFe2O4 (NFO) quantum dots over γ-Bi2MoO6 (BMO) and t-BiVO4 (BVO) nanoplates yielded three types of microscopic heterojunctions among BMO-BVO, BVO-NFO and BMO-NFO phases. The ternary composites displayed important physicochemical attributes including high surface area, strong optical absorption, superior charge mobility and higher excited state lifetime which accounted for its improved photocatalytic activity towards ciprofloxacin degradation (>99% in 90 min) and H2 evolution (1.11 mmolh-1g-1, photon conversion efficiency 18.5%). Kinetics study revealed 12-55 fold higher ciprofloxacin photodegradation activity and 31-41 times higher H2 evolution rate for the ternary composite in comparison to the pure semiconductors. A conjugated S-scheme charge transfer mechanism has been deduced from comprehensive band position analysis and radical trapping study to explain the enhanced photocatalytic activity. This work for the first time demonstrated the rational construction of conjugated S-scheme heterostructures with potential application in water remediation and green H2 production.

Highly efficient flower-like ZnIn2S4/CoFe2O4 photocatalyst with p-n type heterojunction for enhanced hydrogen evolution under visible light irradiation

The construction of a p-n heterojunction structure is considered to be an effective method to improve the separation of electron-hole pairs in photocatalysts. A series of ZnIn₂S₄/CoFe₂O₄ (ZIS/CFO) photocatalysts with p-n heterojunctions were prepared via a method involving ultrasonication and calcination. The synthesized photocatalysts were tested and analyzed via various testing techniques, and their hydrogen evolution rates were evaluated. Compared with pure ZIS, ZIS/CFO with different mass ratios of CFO to ZIS showed improved photocatalytic hydrogen production performance, and the optimal photoactivity showed a nearly 12-fold increase, which can be attributed to the formation of p-n junctions and the formed internal electric field, accelerating the separation of electron-hole pairs and effectively improving the photocatalytic hydrogen evolution rate. The excellent stability of the ZIS/CFO composite was proven by three cycle experiments. In addition, the ZIS/CFO composite also possessed excellent magnetic properties to realize facial magnetic recoverability. This work paves the way for the design and preparation of magnetically recoverable p-n heterojunction photocatalysts.

A novel g-C3N4 nanosheet/Ag3PO4/α-Bi2O3 ternary dual Z-scheme heterojunction with increased light absorption and expanded specific surface area for efficient photocatalytic removal of TC

A novel ternary dual Z-scheme 2D g-C₃N₄ nanosheet/Ag₃PO₄/α-Bi₂O₃ (CNN/AP/BO) photocatalyst was successfully synthesized by an in situ deposition and hydrothermal-calcination method. The coupling of AP and BO remarkably enhanced the photocatalytic tetracycline (TC) degradation under visible light illumination, with an optimal removal efficiency of 91.6% (60 min), which can be attributed to the extended visible-light absorption and increased specific surface area owing to the interfacial intimate coupling with well-matched energy band positions between semiconductors. The improved photocatalytic activity resulted from the abundant free radicals by the order of ˙O₂^- > h⁺ > ˙OH based on the electron spin resonance (ESR) and quenching experiment results. In addition, the possible mechanism of TC degradation over the ternary dual Z-scheme heterojunction CNN/AP/BO was proposed.

Coconut Fiber Decorated with Bismuth Vanadate for Enhanced Photocatalytic Activity

Bismuth vanadate/coconut fiber (BiVO4/CF) composites were synthesized by coprecipitation and calcination methods. All catalysts used in this work were prepared by a simple coprecipitation method and fully characterized by means of XRD, SEM-EDS, PL, BET N2 adsorption, zeta potential, and UV-vis DRS. Degradation of indigo carmine (IC) under visible light irradiation was tracked by the UV-vis technique. It was documented that XRD patterns of BiVO4 and BiVO4/CF samples retained the monoclinic structure. From SEM, the CF sheets were visualized, covering the surface of BiVO4 particles. The specific surface area of the synthesized catalysts increased from 1.77 to 24.82 m2/g. The shift of absorption edge to a longer wavelength corresponded to a decrease in band gap energy from 2.3 to 2.2 eV. The photocatalytic degradation rate of the BiVO4/CF composite was five times higher than that of pristine BiVO4. Moreover, the photocatalyst can be separated and recycled with little change after the third times recycling. The improved activity of the composite resulted from the combination of the adsorption performance of the substrate CF and the photocatalytic activity of BiVO4. In addition, the position of the specific mechanism could occur via both the active species of superoxide radical and hydroxyl radical.

Bi nanosphere-decorated oxygen-vacancy BiOBr hollow microspheres with exposed (110) facets to enhance the photocatalytic performance for the degradation of azo dyes

A facile preparation strategy is proposed for a novel highly-active composite photocatalyst comprising Bi nanosphere-decorated oxygen-vacancy BiOBr hollow microspheres with exposed (110) facets for the efficient degradation of azo dyes.