A new S-scheme heterojunction of 1D ZnGa2O4/ZnO nanofiber for efficient photocatalytic degradation of TC-HCl

Fabrication of 0D/1D S-scheme CoO-CuBi2O4 heterojunction for efficient photocatalytic degradation of tetracycline by activating peroxydisulfate and product risk assessment

The step-scheme (S-scheme) heterojunction has excellent redox capability, effectively degrading organic pollutants in wastewater. Combining S-scheme heterojunction with activated persulfate advanced oxidation process reasonably can further enhance the degradation of Emerging Contaminants. Herein, a novel zero-dimensional/one-dimensional (0D/1D) CoO-CuBi2O4 (CoO-CBO) photocatalyst with S-scheme heterojunction was designed by hydrothermal and solvothermal methods. The band structure and electron and hole transfer pathway of CoO-CBO were analyzed using the ex-situ and in-situ X-ray photoelectron spectroscopy (XPS), Ultraviolet and Visible Spectrophotometer (UV-Vis) and optical radiation Kelvin probe force microscope (KPFM), and the formation of S-scheme heterojunction was demonstrated. The photocatalytic activity of ·S-scheme CoO-CBO heterojunction was carried out by degrading tetracycline (TC) with activating potassium monopersulfate triple salt under visible light. Compared with pure CuBi2O4 and pure CoO, 30%CoO/CuBi2O4 catalyst exhibited the highest TC degradation performance after activating persulfate, degrading 89.5% of TC within 90 min. On the one hand, the S-scheme heterojunction formed between CoO and CBO had a high redox potential. On the other hand, the activation of persulfate by Co and Cu could accelerate redox cycles and facilitate the generation of active radicals such as SO4-, O2- and OH, promoting the separation of the photogenerated e- and h+ in the composite, enhancing the peroxydisulfate (PDS) activation performance and improving the degradation effect of TC. Then, a gradual decrease in the toxicity of the intermediates in the TC degradation process was detected by ECOCER. In all, this study provided an S-scheme CoO/CuBi2O4 heterojunction that can activate PDS to degrade TC efficiently, which provided a new idea for the study of novel pollutant degradation and environmental toxicology.

Ba3SnGa10-xInxO20 (0 ≤ x ≤ 2): site-selective doping, band structure engineering and photocatalytic overall water splitting

Developing new photocatalysts and deciphering the structure-property relationship are always the central topics in photocatalysis. In this study, a new photocatalyst Ba3SnGa10O20 containing two d10 metal cations was prepared by a high temperature solid state reaction, and its crystal structure was investigated by Rietveld refinements of monochromatic X-ray powder diffraction data for the first time. There are 2 Ba, 4 metal cations and 6 O independent atoms in a unit cell. Sn4+ and Ga3+ co-occupy the octahedral cavities named M1 and M2 sites, and the other two metal sites are fully occupied by Ga3+. Rational In3+-to-Ga3+ substitution was performed to reduce the potential of the conduction band minimum and enhance the light absorption ability, which was indeed confirmed using UV-vis diffuse reflectance spectra and Mott-Schottky plots for Ba3SnGa10-xInxO20 (0 ≤ x ≤ 2). Interestingly, In3+ exhibits site selective doping at M1 and M2 sites exclusively. With the light absorption ability enhanced, the photocatalytic overall water splitting activity was also improved, i.e. the photocatalytic H2 generation rate was 1.7(1) μmol h-1 for Ba3SnGa10O20, and the optimal catalyst Ba3SnGa8.5In1.5O20 loaded with 1.0 wt% Pd exhibited the H2 generation rate of 27.5(4) μmol h-1 and the apparent quantum yield at 254 nm was estimated to be 2.28% in pure water.

MOF-Derived In2O3 Microrod-Decorated MgIn2S4 Nanosheets: Z-Scheme Heterojunction for Efficient Photocatalytic Degradation of Tetracycline

The construction of Z-scheme heterostructures using matching band semiconductors is an effective strategy for producing highly efficient photocatalysts. In this study, MgIn2S4(MIS) was grown in situ on In2O3 microrods created with an In-based MOF material (In-MIL-68) as a template to successfully establish a unique MIS-In2O3 heterojunction with a well-matched Z-scheme interface charge transfer channel. Tetracycline (TC) as a typical antibiotic was chosen as the target pollutant to evaluate the photocatalytic activity. After 120 min of visible light irradiation, the MIS-In2O3-(10:1) material had the greatest photocatalytic degradation activity of tetracycline with 96.55%, which was 2.39 and 4.26 times that of MIS and In2O3, respectively. The improved photocatalytic activity is attributed to the in situ growth of MIS on In2O3, forming a Z-scheme heterojunction at the interface, which not only increases the specific surface area, exposes the abundant active site, and improves light utilization but also facilitates the migration and separation of photogenic carriers. The photocatalytic degradation products of TC were detected by liquid chromatography-mass spectrometry (LC-MS), and a preliminary degradation pathway was proposed. Radical capture experiments and ESR analysis confirmed that the main active species were holes (h+), superoxide radicals (•O2-), and superoxide and hydroxyl radicals (•OH). Finally, combined with band position analysis, this study proposes a direct Z-scheme heterojunction mechanism to improve the photocatalytic degradation of tetracycline in MIS under visible light.

Highly porous BiOBr@NU-1000 Z-scheme heterojunctions for synergistic efficient adsorption and photocatalytic degradation of tetracycline

Designing an effective photoactive heterojunction having dual benefits towards photoenergy conversion and pollutant adsorption is regarded as an affordable, green method for eliminating tetracycline (TC) from wastewater. In this regard, a series of BiOBr@NU-1000 (BNU-X, X = 1, 2 and 3) heterojunction photocatalysts are constructed. BNU-X preserves the original skeleton structure of the parent NU-1000, and its high porosity and specific surface area enable superior TC adsorption. At the same time, BNU-X is an effective Z-scheme photocatalyst that improves light trapping, promotes photoelectron-hole separation, and shows excellent photocatalytic degradation efficiency towards TC with the value of the photodegradation kinetic rate constant k being 2.2 and 24.8 times those of NU-1000 and BiOBr, respectively. The significant increase in the photocatalytic activity is ascribed to the construction of an efficient Z-scheme photocatalyst, which promotes the formation of superoxide radicals (˙O2-) and singlet oxygen (1O2) as the main oxidative species in the oxidation system. This research has the advantage of possibilities for the development of porous Z-scheme photocatalysts based on photoactive MOF materials and inorganic semiconductors for the self-purification and photodegradation of organic contaminants.

Mesoporous black TiO2 hollow shells with controlled cavity size for enhanced visible light photocatalysis

Black TiO2 formed by introducing lattice disorder into pristine TiO2 has a narrowed band gap and suppresses the recombination of charge carriers. This provides a potential strategy for visible light photocatalysis. However, the microstructural design of black TiO2 for a higher optimization of visible light is still in high demand. In this work, we proposed the preparation of black TiO2 hollow shells with controllable cavity diameters using silica spheres as templates for the cavities and the NaBH4 reduction method. The decreased cavity size resulted in a hollow shell with an enhanced visible-light absorption and improved photocatalytic performance. Moreover, we demonstrated that this cavity can be combined with gold nanoparticles (AuNPs) to form AuNPs@black TiO2 yolk-shells. The AuNPs provided additional visible light absorption and promoted the separation of photogenerated carriers in the yolk-shell structures. This further improved the photocatalysis, the degradation rate of Cr(VI) can reach 0.066 min-1. Our work evaluated the effect of the cavity size on the photocatalytic performance of hollow and yolk-shell structures and provided concepts for the further enhancement of visible-light photocatalysis.

Preparation of the self-accelerating photocatalytic self-cleaning carboxymethyl cellulose sodium-based hydrogel for removing cationic dyes

Hydrogels loaded with photocatalysts have shown great potential in effectively degrading dye wastewater. In this work, carboxymethyl cellulose sodium-based hydrogels loaded with nitrogen-doped graphene oxide-zinc oxide-zinc peroxide (NGO-ZnO-ZnO2) were synthesized using hydrothermal reaction and in-situ synthesis method. NGO acts as an electron mediator, suppressing the recombination of photoinduced electrons and holes. ZnO2 decomposes to generate hydrogen peroxide (H2O2), promoting a self-enhanced photocatalytic reaction. Carboxymethyl cellulose sodium (CMC) acts as a dispersant, improving the uniformity and stability of NGO-ZnO-ZnO2 within the hydrogel. The results demonstrate that NGO-ZnO-ZnO2 exhibits high photocatalytic degradation efficiency towards methyl orange (MO) (10 mg/L) and rhodamine B (RhB) (50 mg/L), with degradation rates of 99.99 % (200 min) and 99.26 % (160 min), respectively. The carboxymethyl cellulose sodium-based hydrogel achieves a photocatalytic degradation rate of 95.85 % (220 min) for RhB (10 mg/L). After 5 cycles of repeated photocatalytic tests, the degradation efficiency of the hydrogel towards RhB reaches 80.81 %. This work provides a low-cost and convenient method for constructing novel hydrogel carriers with high photocatalytic stability and efficiency.