Insights into the Mechanism of the Bi/BiVO4 Composites for Improved Photocatalytic Activity

Facile Hydrothermal Synthesis of BiVO4/MWCNTs Nanocomposites and Their Influences on the Biofilm Formation of Multidrug Resistance Streptococcus mutans and Proteus mirabilis

This study utilized a simple hydrothermal technique to prepare pure BiVO4 and tightly bound BiVO4/multiwalled carbon nanotubes (MWCNTs) nanocomposite materials. The surfactant was employed to control the growth, size, and assembly of BiVO4 and the nanocomposite. Various techniques including X-ray diffraction (XRD), Ultraviolet-visible (UV-vis), photoluminescence (PL), Raman, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) were utilized to analyze and characterize BiVO4 and the BiVO4/MWCNTs nanocomposite. Through XRD analysis, it was found that the carbon nanotubes were effectively embedded within the lattice of BiVO4 without generating any separate impurity phase and had no influence on the BiVO4 monoclinic structure. TEM images confirmed the presence of MWCNTs within BiVO4. Furthermore, adding MWCNTs in the BiVO4/MWCNTs nanocomposite resulted in an effective charge transfer transition and improved carrier separation, as evidenced by PL analysis. The introduction of MWCNTs also led to a significant reduction in the optical band gap due to quantum effects. Finally, the antibacterial activity of pure BiVO4 and the BiVO4/MWCNTs nanocomposite was assessed by exposing Proteus mirabilis and Streptococcus mutans to these materials. Biofilm inhibition and antibiofilm activity were measured using a crystal violet assay and a FilmTracer LIVE/DEAD Biofilm Viability Kit. The results demonstrated that pure BiVO4 and BiVO4/MWCNTs effectively inhibited biofilm formation. In conclusion, both pure BiVO4 and BiVO4/MWCNTs are promising materials for inhibiting the bacterial biofilm during bacterial infections.

A novel n-p heterojunction Bi2S3/ZnCo2O4 photocatalyst for boosting visible-light-driven photocatalytic performance toward indigo carmine

An innovative p-n heterojunction Bi₂S₃/ZnCo₂O₄ composite was first fabricated via a two-step co-precipitation and hydrothermal method. By controlling the weight amount of Na₂S and Bi(NO₃)₃ precursor, different heterogeneous xBi₂S₃/ZnCo₂O₄ were synthesized (x = 0, 2, 6, 12, and 20). The p-n heterojunction Bi₂S₃/ZnCo₂O₄ was characterized by structural, optical, and photochemical properties and the photocatalyst decoloration of indigo carmine. Mott-Schottky plots proved a heterojunction formed between n-Bi₂S₃ and p-ZnCo₂O₄. Furthermore, the investigation of the photocurrent response indicated that the Bi₂S₃/ZnCo₂O₄ composite displayed an enhanced response, which was respectively 4.6 and 7.3 times (4.76 μA cm^-2) greater than that of the pure Bi₂S₃ (1.02 μA cm^-2) and ZnCo₂O₄ (0.65 μA cm^-2). Especially the optimized p-n Bi₂S₃/ZnCo₂O₄ heterojunction with 12 wt% Bi₂S₃ showed the highest photocatalyst efficacy of 92.1% at 40 mg L^-1 solutions, a loading of 1.0 g L^-1, and a pH of 6 within 90 min of visible light illumination. These studies prove that p-n Bi₂S₃/ZnCo₂O₄ heterojunction photocatalysts can greatly boost their photocatalytic performance because the inner electric field enhances the process of separating photogenerated electron-hole pairs. Furthermore, this composite catalyst showed good stability and recyclability for environmental remediation.

Unravelling ciprofloxacin removal in a nitrifying moving bed biofilm reactor: Biodegradation mechanisms and pathways

Although moving bed biofilm reactors (MBBRs) have shown excellent antibiotic removal potentials, the information on underlying mechanisms is yet limited. This work assessed the removal of ciprofloxacin in an enriched nitrifying MBBR by clarifying the contribution of adsorption and microbial-induced biodegradation. Results demonstrated the considerable biomass adsorption (55%) in first 30 min. Limiting nitrite oxidizing bacteria growth or inhibiting nitrification would lead to lower adsorption capacities. The highest ciprofloxacin biodegradation rate constant was 0.082 L g SS^-1 h^-1 in the presence of ammonium, owing to ammonia oxidizing bacteria (AOB)-induced cometabolism, while heterotrophs played an insignificant role (∼9%) in ciprofloxacin biodegradation. The developed model also suggested the importance of AOB-induced cometabolism and metabolism over heterotrophs-induced biodegradation by analyzing the respective biodegradation coefficients. Cometabolic biodegradation pathways of ciprofloxacin mainly involved the piperazine ring cleavage, probably alleviating antimicrobial activities. It implies the feasibility of nitrifying biofilm systems towards efficient antibiotic removal from wastewater.

Boosted photocatalytic performance of OVs-rich BiVO4 hollow microsphere self-assembled with the assistance of SDBS

In this study, monoclinic phase bismuth vanadate (BiOV₄) photocatalyst with unique hollow microsphere morphology was successfully prepared by a hydrothermal method in the existence of sodium dodecyl benzene sulfonate (SDBS). The prepared photocatalysts were characterized by X-ray diffraction (XRD), scanning electron (SEM) and X-ray photoelectron spectrometer (XPS) and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). Experimental results show that SDBS definitely changes the microstructure of BiVO₄, which is allocated to the template role of SDBS in the preparation process. Moreover, the hydrothermal treatment time is also of crucial importance in affecting the structure and morphology of the photocatalysts, and the optimal hydrothermal treatment time for the formation of hollow microsphere is 24 h. Furthermore, the feasible growth mechanism for hollow microsphere was elaborated. Enriched oxygen vacancies (OVs) are introduced into BiOV₄ prepared with SDBS, largely elevating the separation efficiency of photo-generated charges. Under visible light irradiation, the photocatalytic activities of BiOV₄ for destruction of rhodamine (RhB) were evaluated. The photocatalytic degradation rate constant of RhB on the 3SBVO is 2.23 times of that on the blank BiOV₄ as the mass ratio of SDBS/BiOV₄ is 3 %. Photocatalytic degradation mechanism of BiVO₄ toward detoxification of organic pollutants was presented.

Electrospun Porous Nanofibers: Pore−Forming Mechanisms and Applications for Photocatalytic Degradation of Organic Pollutants in Wastewater

Electrospun porous nanofibers have large specific surface areas and abundant active centers, which can effectively improve the properties of nanofibers. In the field of photocatalysis, electrospun porous nanofibers can increase the contact area of loaded photocatalytic particles with light, shorten the electron transfer path, and improve photocatalytic activity. In this paper, the main pore−forming mechanisms of electrospun porous nanofiber are summarized as breath figures, phase separation (vapor−induced phase separation, non−solvent−induced phase separation, and thermally induced phase separation) and post−processing (selective removal). Then, the application of electrospun porous nanofiber loading photocatalytic particles in the degradation of pollutants (such as organic, inorganic, and bacteria) in water is introduced, and its future development prospected. Although porous structures are beneficial in improving the photocatalytic performance of nanofibers, they reduce their mechanical properties. Therefore, strategies for improving the mechanical properties of electrospun porous nanofibers are also briefly discussed.

Enhanced photocatalytic efficiency by direct photoexcited electron transfer from pollutants adsorbed on the surface valence band of BiOBr modified with graphitized C

Herein, a novel BiOBr photocatalyst with partial surface modification by graphitized C (BiOBr-C_g) was synthesized through a hydrothermal method with hydrothermal carbonation carbon (HTCC) as a slow-releasing carbon source and characterized by experimental and theoretical methods. BiOBr-C_g exhibited excellent visible-light photocatalytic performance toward various refractory pollutants, such as bisphenol A, ibuprofen, ciprofloxacin, 2,4-dichlorophenoxyacetic acid, and diphenhydramine. The characterization results demonstrate that a strong molecular orbital interaction occurs between graphitized C and BiOBr, resulting in the formation of a new surface valence band on graphitized C. This not only promotes the oxidation of pollutants by surface holes but also reduces the recombination of carriers during the bulk phase transfer process, thereby increasing the number of photogenerated carriers. Intriguingly, the analytical results for degradation intermediates and other characterization techniques demonstrate that the pollutants adsorbed on the graphitized C of BiOBr-C_g can be directly excited through light irradiation and react along the organic radical degradation pathway in addition to pollutant degradation by holes and HO₂^•/O₂^•-.