Chemical bonding and facet modulating of p-n heterojunction enable vectorial charge transfer for enhanced photocatalysis

Enhancing peroxymonosulfate activation via silver nanoparticle-decorated bismuth oxybromide/silver sulfide S-scheme heterojunction with surface plasmon resonance for tetracycline degradation: Mechanisms and pathways

Catalysts with S-scheme semiconductor junctions offers an enhanced redox capacity. Herein, BiOBr/Ag/Ag2S composites with a three-dimensional structure were prepared by hydrothermal reaction. The growth of Ag2S nanoparticles on the surface of BiOBr nanoflowers was successfully achieved, leading to strong light absorption and surface plasmon resonance (SPR) effect, together with improved rates of light-induced carriers. In the presence of peroxymonosulfate (PMS), the BiOBr/Ag/Ag2S composite removed 90.1 % of tetracycline (TC), outperforming BiOBr or Ag/Ag2S, owing to its superior redox capability and reduced carrier recombination efficiency. Additionally, BiOBr/Ag/Ag2S demonstrated excellent recovery performance and stability. Liquid chromatography-mass spectrometry (LC-MS) was employed to investigate the possible intermediate products and reaction pathways. The reaction mechanism of the S-scheme semiconductor heterojunction was further elucidated through density functional theory (DFT) calculations. In conclusion, the research provides a novel approach to activate PMS using an S-scheme semiconductor heterojunction with high redox capacity for practical use in wastewater treatment.

Interfacial Bi-S chemical bond-coupled sulfur vacancy in Bi4NbO8Cl@ZnIn2S4-x S-scheme heterojunction for superior photocatalytic hydrogen generation

Strategies such as reducing charge transfer resistance and enhancing transmission driving force are considered effective in achieving higher photocatalytic performance. In this study, Bi4NbO8Cl@ZnIn2S4-x S-scheme heterojunction photocatalyst with atomic-level interface Bi-S chemical bond connection was successfully constructed through in-situ growth of ZnIn2S4-x nanosheets containing sulfur vacancies (Sv) on Bi4NbO8Cl microplates. Firstly, the S-scheme charge transfer mode effectively spatially separated photogenerated carriers while retaining their reactivity to the maximum extent. Secondly, the interfacial Bi-S bond served as a "bridge" to lessen the interface resistance and provide a high-speed channel for the transmission of photogenerated carriers. Lastly, Sv effectively expanded the Fermi level (Ef) difference between the two semiconductors in the heterojunction, so as to enlarge the built-in electric field (IEF) at the interface and reinforce the driving force for charge transfer. Owing to the synergistic effects of these advantages, the Bi4NbO8Cl@ZnIn2S4-x composite exhibited an average hydrogen production rate of up to 8.7 mmol g-1 h-1 under visible light, which was 4.0 and 14.5 times that of ZnIn2S4-x and Bi4NbO8Cl samples, respectively. This work presents a novel approach for designing interfacial chemically bonded S-scheme heterojunction photocatalysts with high catalytic activity.

Enhanced visible light responsive piezoelectric photocatalysis based on Bi2S3 coated BaTiO3 nanorods heterostructures

Although the presence of the built-in electric field will solve the problem of carrier complexation in photocatalytic systems to some extent. However, free carriers will quickly shield the stabilized electric field and lose its effect. Therefore, how to introduce the dynamic piezoelectric field into the photocatalytic system has become an imminent problem. Herein, we developed an overcoated, visible light responsive, piezoelectric-assisted photocatalytic system by depositing Bi2S3 photocatalysts with a narrow-band system onto the surface of highly piezo-responsive BaTiO3 nanorods (BTO NRs). The heterojunction structure, bound by Bi-O chemical bonding, enhances carrier transport efficiency under the influence of the piezoelectric field. In the degradation experiments, the first-order rate constant for the degradation of chlortetracycline hydrochloride (CTC) in the BTO NRs/Bi2S3 system with the optimal complex ratio was 0.0276 min-1, which was 3.1 and 7.8 times higher than that of BTO NRs and Bi2S3, respectively. Additionally, we deduced the degradation pathways of CTC through a combination of Density functional theory (DFT) calculations and Liquid Chromatograph Mass Spectrometer (LC-MS), evaluating the toxicity of the intermediates. This complex system, featuring a highly photo-responsive semiconductor as a photo-acceptor deposited on a piezoelectric semiconductor surface providing a dynamic built-in electric field, enhances carrier separation efficiency under optimal light energy utilization conditions. These findings present novel and effective strategies for addressing two primary challenges in photocatalytic systems: low spectral utilization and significant photogenerated carrier complexation.

Interfacial Engineering of a Z-Scheme Bi2O2S/NiTiO3 Heterojunction Photoanode for the Degradation of Sulfamethoxazole in Water

To develop a semiconductor interface with enhanced spatial separation of carriers under visible light irradiation for the photoelectrochemical (PEC) oxidation process, we explored the fabrication of a Bi2O2S/NiTiO3 heterojunction photoanode for the removal of sulfamethoxazole in water. The Bi2O2S/NiTiO3 photoanode was synthesized via an in situ hydrothermal process, and it exhibited better light absorption and charge separation, as well as a reduced rate of recombination of photoexcited charge species compared to pristine Bi2O2S and NiTiO3. The improved photoelectrocatalytic performance was attributed to the synergistic interaction between Bi2O2S and NiTiO3 and the presence of an S-O bond at the heterojunction interface, thus resulting in Z-scheme heterojunction formation. Various characterization methods such as XPS, UV-DRS, electrochemical impedance spectroscopy, photoluminescence, FESEM, TEM, and photocurrent response measurements were explored to explain the optical and electrochemical properties of the semiconductor heterojunction. The PEC degradation process was optimized, demonstrating a degradation efficiency removal of 80% for 5 mg/L sulfamethoxazole in water, with a TOC removal of 45.5%. A Z-scheme heterojunction formation mechanism was proposed to explain the enhanced photoelectrocatalytic activity of the photoanode. This work generally contributes to the development of efficient and sustainable photoanodes for environmental remediation.

Enhanced piezocatalytic and piezo-photocatalytic dye degradation via S-scheme mechanism with photodeposited nickel oxide nanoparticles on PbBiO2Br nanosheets

The fabrication of an S-scheme heterojunction demonstrates as an efficient strategy for achieving efficient charge separation and enhancing catalytic activity of piezocatalysts. In this study, a new S-scheme heterojunction was fabricated on the PbBiO2Br surface through the photo-deposition of NiO nanoparticles. It was then employed in the piezoelectric catalytic degradation of Rhodamine B (RhB). The results demonstrate that the NiO/PbBiO2Br composite exhibits efficient performance in piezocatalytic RhB degradation. The optimal sample is the NiO/PbBiO2Br synthesized after 2 h of irradiation, achieving a RhB degradation rate of 3.11 h-1, which is 12.4 times higher than that of pure PbBiO2Br. Simultaneous exposure to visible light and ultrasound further increases in the RhB degradation rate, reaching 4.60 h-1, highlighting the synergistic effect of light and piezoelectricity in the NiO/PbBiO2Br composite. A comprehensive exploration of the charge migration mechanism at the NiO/PbBiO2Br heterojunction was undertaken through electrochemical analyses, theoretical calculations, and in-situ X-ray photoelectron spectroscopy analysis. The outcomes reveal that p-type semiconductor NiO and n-type semiconductor PbBiO2Br possess matching band structures, establishing an S-scheme heterojunction structure at their interface. Under the combined effects of band bending, interface electric fields, and Coulomb attraction, electrons and holes migrate and accumulate on the conduction band of PbBiO2Br and valence band of NiO, respectively, thereby achieving effective spatial separation of charge carriers. The catalyst's synergistic photo-piezoelectric catalysis effect can be ascribed to its role in promoting the generation and separation of charge carriers under both light irradiation and the piezoelectric field. The results of this investigation offer valuable insights into the development and production of catalytic materials that exhibit outstanding performance through the synergy of piezocatalysis and photocatalysis.

Construction of a Bi2S3/Bi0.5Na0.5TiO3 Composite Catalyst with S Vacancies for Efficient Piezo-Photocatalytic Hydrogen Production

Photocatalytic hydrogen production with low environmental and economic costs is expected to be a powerful means to alleviate energy and environmental problems. However, how to inhibit the rapid recombination of photogenerated carriers is a challenge that photocatalytic hydrogen production has to face. In this study, the coupling of the piezoelectric effect and vacancy engineering into the photocatalytic reaction process synergistically promoted carrier separation, thereby promoting the improvement of hydrogen production performance. Specifically, the novel dual piezoelectric Bi2S3/Bi0.5Na0.5TiO3 (BS-12/BNT) piezo-photocatalyst rich in S vacancies was synthesized by an impregnation method. The hydrogen generation rate of 5% BS-12/BNT under the combined impact of light and ultrasound was up to 1019.39 μmol/g/h, which is 9.5 times higher than that of pure BNT. Various characterization analyses have confirmed that the piezoelectric-photocatalytic activity of BS/BNT composite materials is significantly improved, mainly due to the introduction of S vacancies and piezoelectric fields, which enhance the absorption of sunlight, reduce interface resistance, and so raise the photogenerated carriers' separation efficiency. In addition, the stability of BS/BNT is significantly better than that of the previously synthesized catalysts. Finally, according to the results of XPS, UV-vis, and ESR, the active groups and possible electron transfer paths generated during the piezoelectric-photocatalytic hydrogen production process were studied. This work presents a new approach to promote hydrogen production performance through the synergistic effect of the piezoelectric effect and S vacancies.

One-step in-situ construction engineering of ZnO-Zn2SnO4 heterojunction for deeply photocatalytic oxidation of nitric oxide

The generation of hazardous intermediates during the process of photocatalytic nitric oxide (NO) oxidation presents a tough issue. Herein, a one-step microwave strategy was employed to introduce oxygen vacancies (OVs) into zinc oxide-zinc stannate (ZnO-Zn2SnO4) heterojunction, resulting in an improvement in the photocatalytic efficiency for NO removal. The construction ZnO-Zn2SnO4 heterojunction with the OVs (ZSO-3) owns a significant contribution towards highly efficient electron transfer efficiency (99.7%), which renders ZSO-3 to exert a deep oxidation of NO-to-nitrate (NO3-) rather than NO-to-nitrite (NO2-) or NO-to-nitrogen dioxide (NO2). Based on the solid supports of experimental and simulated calculations, it can be found that OVs play an irreplaceable role in activating small molecules such as NO and O2. Moreover, the enhanced adsorption capacity of small molecules, which guarantees the high yield of active radical due to the formation of S-scheme heterojunction. This work illuminates a novel viewpoint on one-step in-situ route to prepare Zn2SnO4-based heterojunction photocatalyst with deep oxidation ability of NO-to-NO3-.