Tuning electron transfer by crystal facet engineering of BiVO4 for boosting visible-light driven photocatalytic reduction of bromate

Controlled crystal facet of tungsten trioxide photoanode to improve on-demand hydrogen peroxide production for in-situ tetracycline degradation

Advanced oxidation processes utilizing hydrogen peroxide (H2O2) are widely employed for the treatment of organic pollutions. However, the conventional anthraquinone method for H2O2 synthesis is unsuitable for this application owing to its hazardous and costly nature. Alternative approaches involve a photoelectrochemical method. Herein, tungsten trioxide (WO3) photoanode has been used for the conversion of H2O into H2O2 through oxidation reaction from a PEC system, simultaneously utilizing in-situ generated hydroxyl (OH•) radicals for tetracycline degradation. By manipulating the ratio of crystal facets between (020) and (200) of the WO3 photoanode, a significant improvement in H2O2 production has been achieved by increasing the proportion of (020) facet. The production rate of WO3 photoanode enriched with the (020) facet is approximately 1.9 times higher than that enriched with (200) facet. This enhanced H2O2 production performance can be attributed to the improved formation of OH• radicals and the accelerated desorption of H2O2 on the (020) facet. Simultaneously, the in-situ generated OH• radicals are applied for tetracycline degradation. Under illumination of sunlight stimulator for 180 min, the optimal photoanode achieves a degradation rate of 86.7% for tetracycline. Furthermore, the resulting chemicals have been analyzed, revealing that C8H10O and C7H8O were formed as the primary products. Notably, these products exhibit significantly lower toxicity compared to tetracycline. This study presents a promising approach for the rational design of WO3 based photoanodes for oxidation reaction, including not only H2O2 production but also the efficient degradation of organic pollutants.

Sulfur tuning oxygen vacancy of Ba2Bi1.4Ta0.6O6 for boosted photocatalytic tetracycline hydrochloride degradation and hydrogen evolution

Photocatalysis, such as solar-driven photodegradation and energy conversion, has attracted great attention, given that it provides a promising solution for alleviating the energy shortage and environmental contamination issues. However, the insufficient light absorption and charge separation/transport efficiency restrict the solar conversion efficiency. It has been proved that oxygen vacancies (O_v) can improve the photocatalytic activity by enhancing the light absorption. But in this study, we show that oxygen vacancies hinder the charge separation/transfer in Ba₂Bi_1.4Ta_0.6O₆. The incorporation of S further pushes the light absorption edge up to 1170 nm. Therefore, the S/O_v-Ba₂Bi_1.4Ta_0.6O₆ sample can absorb not only the full range of visible light but also part of near-infrared light. More importantly, it mitigates the drawback of oxygen vacancies, improving the charge separation/transport by 1.65 times. As a result, The S/O_v-Ba₂Bi_1.4Ta_0.6O₆ nanowires manifest 4.41 times and over 100 times higher photocatalytic activity for tetracycline hydrochloride degradation and hydrogen production, respectively.

An optimization strategy for photo-Fenton-like catalysts: Based on crystal plane engineering of BiVO4 and electron transfer properties of 0D CQDs

Herein, we report a novel Cu₂(OH)₃ F/CQDs-BiVO₄ composite photo-Fenton-like system, which used BiVO₄ and Cu₂(OH)₃F as electron donor and acceptor, respectively, and achieved efficient electron transfer between them through the electron bridging effect of Carbon quantum dots (CQDs). The material exhibited excellent ciprofloxacin (CIP) removal efficiency in the photo-Fenton-like coupled system. Cu₂(OH)₃ F/CQDs-BiVO₄ had an incredibly fast response rate, eliminating 98.1% of CIP from the solution in just 1 h, according to the reaction kinetics. Exploratory tests proved that the catalyst kept up a sufficient level of activity across a wide pH range of 3-11 and in the presence of various anions. The activity, morphology, and crystal structure of the samples did not appreciably alter after five recycles. Finally, a possible reaction mechanism was also proposed based on the band structure, position and reaction species.

Degradation mechanism of ammonia nitrogen synergistic with bromate under UV or UV/TiO2

Bromate (BrO₃^-) and ammonia nitrogen (NH₄⁺) are both typical environmental pollutants: BrO₃^- has been categorized as one of the Group 2B carcinogen by IARC; an excess of NH₄⁺ might result in the eutrophication of water. The existence of NH₄⁺ could inhibit the transformation of bromide (Br^-) to bromate (BrO₃^-). However, the interaction of NH₄⁺ and BrO₃^- during the removal process is not clear. This study intends to disclose the mutual relationships of ammonia nitrogen and bromate ions under UV irradiation or UV/TiO₂ conditions. Without UV irradiation, BrO₃^- and NH₄⁺ were both stable even under the presentation of each other. Under UV irradiation or UV/TiO₂ conditions, BrO₃^- and NH₄⁺ promoted the degradation of each other, showing the synergistic degradation mechanism. In the neutral environment, both of BrO₃^- and NH₄⁺ could be transformed effectively. Furthermore, NH₄⁺ accelerated the transformation of BrO₃^- to Br^- at the reaction beginning and the existence of BrO₃^- is beneficial for the transformation of NH₄⁺ to N₂.

New insights into the efficient charge transfer by construction of adjustable dominant facet of BiOI/CdS heterojunction for antibiotics degradation and chromium Cr(VI) reduction under visible-light irradiation

The narrow light-response range and high electron/hole recombination rate greatly restrict the widespread use of photocatalytic technology. The integration of exposing dominant facet of semiconductor and Z-scheme heterostructures designing is expected to break those barriers. Herein，In this work, hydrothermal and ultrasonic stirring methods were used to selectively exposed the (001) and (110) facet of BiOI to construct the BiOI/CdS heterostructures. The obtained BiOI(001)/CdS material shown the maximum degradation for tetracycline-based antibiotics (Oxytetracycline, Tetracycline and Doxycycline), and excellent reduction of hexavalent chromium. Combining the electron spin resonance and scavenger experiments, the superior photocatalytic capacity was attributed to the generation of superoxide and hydroxyl radicals. DFT calculation results shown BiOI(001)/CdS performed high binding energy and adsorption energy for hexavalent chromium, and the different work function between BiOI(001) and CdS confirmed the building of internal electric field, thereby increased the charge separation. Finally, the Gaussian 09 and HPLC-MS program investigated the attack sites of free radicals and degradation pathways in the degradation of antibiotics. This study not only provides a potential photocatalyst, also gives an in-depth understanding of the photocatalytic properties of heterojunctions constructed by different exposed crystal facets.

Persulfate assisted photocatalytic degradation of tetracycline by bismuth titanate under visible light irradiation

Tetracycline is a commonly used broad-spectrum antibiotic to prevent and cure the bacterial infections. However, the incompletely metabolic tetracycline molecules by organisms discharged into aquatic environment increase the ecological toxicity....

F- regulate the preparation of polyhedral BiVO4 enclosed by High-Index facet and enhance its photocatalytic activity

The selective exposure of high-index facets at the surface of nanocrystals is an important and challenging research topic. Herein, polyhedral bismuth vanadate (BiVO₄) crystals predominantly surrounded by {2 1 3} and {1 2 1} high-index facets were fabricated through the engineering of high-index surfaces by fluorinion (F^-) mediated hydrothermal process. The as-prepared BiVO₄-0.2F (the feeding amount of NaF was 0.2 g) catalyst exhibited high apparent quantum efficiency of 17.7% under 420 nm light irradiation and 9.3 fold enhancement of O₂ evolution relative to its low-index counterparts. Moreover, the growth of high-index facets results in significant enhancement of hydroxyl radical (•OH) production, photocatalytic degradation of Rhodamine B (RhB) and photoelectrochemical (PEC) properties by the BiVO₄ polyhedron, relative to its low-index counterparts. The enhanced photoreactivity is the result of the synergistic effect of F^- on the surface of the BiVO₄ crystals and exposed high-index facets. For one thing, F^- on the surface of the BiVO₄ facilitate the separation and transport of photo-induced charge carriers. For another, the exposed high-index facets on polyhedral BiVO₄ provided much more reactive sites for photocatalytic reactions. Hopefully, this F^- mediated method will be a useful guideline for designing and synthesizing novel high-index faceted micro-/nanostructures for overcoming the practical energy and environment problems.