The transition of tetragonal to monoclinic phase in BiVO4 coupled with peroxymonosulfate for photocatalytic degradation of tetracycline hydrochloride

At present, the mechanism difference between tetragonal BiVO4 (t-BiVO4) and monoclinic BiVO4 (m-BiVO4) coupled peroxymonosulfate (PMS) to realize photocatalysis is still unclear. In this study, m-BiVO4 and t-BiVO4 were obtained by adjusting the bismuth-vanadium ratio in the precursor solution (Bi:V = 3:1; 1:1; 1:2 and 1:3). The results of photocatalytic experiments showed that both t-BiVO4 and m-BiVO4 had certain activation effects on PMS, and the prepared monoclinic B1V2 has the strongest photocatalytic performance. Using 20 mg B1V2 to activate 4 mmol L-1 PMS in 30 min, the degradation rate of tetracycline hydrochloride (TCH) reached 92.8%. The free radical quenching experiment and EPR test showed that when m-BiVO4 coupled PMS degraded TCH, the contribution of active species was SO4•->•OH>•O2- > h+. Compared with m-BiVO4, the wide band gap of t-BiVO4 makes the photogenerated carrier recombination. When t-BiVO4 coupling PMS, the contribution of active species is •O2- > SO4•->•OH>h+. In addition, the intermediate products of TCH degradation were analyzed by LC-MS, and three possible degradation paths of TCH were proposed.

Electron Transfer Efficiency-Regulated Electrochemiluminescence for Rapid Crystallinity Analysis in Layered Materials

The electrochemiluminescence (ECL) signal is largely determined by the electron transfer efficiency. Therefore, in the nanomaterial-involved ECL system, the structure-related electron distribution could affect the electron transfer efficiency and further alter the ECL intensity. These features make the design of versatile ECL-based analytical techniques for probing the correlated structure possible. And it is generally accepted that the increased crystallinity of nanomaterials usually leads to a uniform electron distribution, which provides higher conductivity. Therefore, the crystallinity-improved conductivity could facilitate electron transfer, promote the electrochemical activity of support materials, and boost the efficiency of the ECL reaction. In this study, we have demonstrated that the ECL signal of the graphitic carbon nitride reporter was proportional to the crystallinity of layered double hydroxides (LDHs), which meets the supposition well. On the basis of this phenomenon, an ECL-based crystallinity analysis approach has been established using CdAl-LDHs as the model materials. The universality of this proposed technique was further validated by the rapid and accurate crystallinity determination of ZnAl-LDH samples with diverse crystallinities. This work not only contributes an alternative to the X-ray diffraction technique for the rapid screening of crystallinity in layered materials but also opens a new avenue for the design of ECL-based structure analysis techniques toward nanomaterials and even organic materials by involving electron transfer regulation correlation.

Crystallization Regulation Engineering in the Carbon Nitride Nanoflower for Strong and Stable Electrochemiluminescence

Cathode electrochemiluminescence (ECL) of C₃N₄ material has suffered from weak and unstable ECL emission for a long time, which greatly limits its practical application. Herein, a novel approach was developed to improve the ECL performance by regulating the crystallinity of the C₃N₄ nanoflower for the first time. The high-crystalline C₃N₄ nanoflower achieved a pretty strong ECL signal as well as excellent long-term stability compared to low-crystalline C₃N₄ when K₂S₂O₈ was used as a co-reactant. Through the investigation, it is found that the enhanced ECL signal is attributed to the simultaneous inhibition of K₂S₂O₈ catalytic reduction and enhancement of C₃N₄ reduction in the high-crystalline C₃N₄ nanoflower, which can provide more opportunities for SO₄^• - to react with electro-reduced C₃N₄^• -, and a new "activity passivation ECL mechanism" was proposed, while the improvement of the stability is mainly ascribed to the long-range ordered atomic arrangements caused by structure stability in the high-crystalline C₃N₄ nanoflower. As a benefit from the excellent ECL emission and stability of high-crystalline C₃N₄, the C₃N₄ nanoflower/K₂S₂O₈ system was employed as a Cu²⁺ detection sensing platform, which exhibited high sensitivity, excellent stability, and good selectivity with a wide linear range from 6 nM to 10 μM and a low detection limit of 1.8 nM.

Junction of ZnmIn2S3+m and bismuth vanadate as Z-scheme photocatalyst for enhanced hydrogen evolution activity: The role of interfacial interactions

A series of Zn_mIn₂S_3+m photocatalysts were synthesized to show tunable band gap energy with the variation of Zn/S atomic ratio. The junction of Zn_mIn₂S_3+m and BiVO₄ led to intimate interfacial contacts. Both experimental and theoretical results implied that electrons flowed from Zn_mIn₂S_3+m to BiVO₄ at the Zn_mIn₂S_3+m/BiVO₄ interface to form built-in electric field due to the variation of Fermi level, which promised Z scheme charge transfer feature for improving separation of charge carriers for enhanced photocatalytic performance. A higher degree of charge transfer process occurred for Zn₂In₂S₅/BiVO₄ heterostructure promised stronger built-in electric field, higher charge separation efficiency and improved photocatalytic activity in comparison to ZnIn₂S₄/BiVO₄ and Zn₃In₂S₆/BiVO₄ heterojunctions. The optimal hydrogen production rate of Zn₂In₂S₅/BiVO₄ photocatalyst is 8.42 mmol•g^-1•h^-1 with apparent quantum yield of 22.32 % at 435 nm, which is about 2.2 and 1.5 times higher than that of ZnIn₂S₄/BiVO₄ and Zn₃In₂S₆/BiVO₄, respectively.