Dye recovery with photoresponsive citric acid-modified BiOCOOH smart material: Simple synthesis, adsorption-desorption properties, and mechanisms

Photo-induced adsorption-desorption behavior of methylene blue on CA-BMO under visible light irradiation

In this work, the modification of Bi2MoO6 with critic acid (CA-BMO) to achieve enhanced adsorption of methylene blue (MB) solution in dark and desorption under visible light irradiation was reported. The as-prepared materials were synthesized by a hydrothermal method and characterized via SEM, FT-IR, XRD, and XPS techniques. Only 16.5% of 10 mg L-1 MB was removed within 10 min by using 0.5 g L-1 Bi2MoO6, while 92.9% removal of MB could be achieved by using 0.5 g L-1 CA-BMO, which enhanced the adsorption removal by a factor of 4.6. The adsorption capacity for MB was 18.9 mg g-1. Desorption efficiency of MB was only observed in CA-BMO system, and it depends on the wavelength of the light source, pH, and the presence of metal ions. Characterization results suggested that carboxyl groups, which were modified onto the surface of Bi2MoO6, could serve as adsorption sites for MB, and the connections were damaged under light, thus leading to the desorption of MB from the surface of the CA-BMO. This study provides a novel reagent-free desorption strategy for dye recovery without secondary pollution, which facilitates the development and application of Bi-based adsorbent for dye-containing wastewater treatment.

Bismuth oxyformate microspheres assembled by ultrathin nanosheets as an efficient negative material for aqueous alkali battery

A negative electrode with high capacity and rate capability is essential to match the capacity of a positive electrode and maximize the overall charge storage performance of an aqueous alkali battery (AAB). Due to the 3-electron redox reactions within a wide negative potential range, bismuth (Bi)-based compounds are recognized as efficient negative electrode materials. Herein, hierarchically structured bismuth oxyformate (BiOCOOH) assembled by ultrathin nanosheets was prepared by a solvothermal reaction for application as negative material for AAB. Given the efficient ion diffusion channels and sufficient exposure of the inner surface area, as well as the pronounced 3-electron redox activity of Bi species, the BiOCOOH electrode offered a high specific capacity (C_s, 229 ± 4 mAh g^-1 at 1 A g^-1) and superior rate capability (198 ± 6 mAh g^-1 at 10 A g^-1) within 0 ∼ -1 V. When pairing with the Ni₃S₂-MoS₂ battery electrode, the AAB delivered a high energy density (E_cell, 217 mWh cm^-2 at a power density (P_cell) of 661 mW cm^-2), showing the potential of such a novel BiOCOOH negative material in battery-type charge storage.

Construction of Z scheme S-g-C3N4/Bi5O7I photocatalysts for enhanced photocatalytic removal of Hg0 and carrier separation

Photocatalysis has demonstrated the potential to solve challenges in various practical application fields such as energy and environmental science due to its environmental friendliness. However, the photocatalytic activity is mainly affected by the weak absorption of visible light and the low separation efficiency of photogenerated carriers. Herein, an S-doped g-C₃N₄/Bi₅O₇I heterojunction was designed by the calcination method. It was found that S doping not only reduces the band gap of g-C₃N₄, which raises the optical absorption boundary of g-C₃N₄ from 465 nm to 550 nm. At the same time, the introduction of S elements leads to new doping energy levels, which can act as photogenerated electron trapping centers and thus inhibit the complexation of photogenerated carriers. Second, the construction of the heterojunction greatly facilitates the transport of carriers and the separation of electrons and holes driven by the built-in electric field. Finally, the abundant oxygen vacancies in the system result in defective energy levels that not only promote the activation of molecular oxygen, but also act as photogenerated electron traps, which further boost the separation of electron-hole pairs. Benefiting from the optimized performance, the photocatalytic reaction rates of S-doped g-C₃N₄/Bi₅O₇I are 5.2 and 2.1 times higher than those of g-C₃N₄ and Bi₅O₇I, respectively. This work provides a viable idea for the potential development of non-metal doping combined with heterojunction photocatalytic systems.

Citric acid modified ultrasmall copper peroxide nanozyme for in situ remediation of environmental sulfonylurea herbicide contamination

Herbicide residues in the environment threaten high-quality agriculture and human health. Consequently, in situ remediation of herbicide contamination is vital. We synthesized a novel self-catalyzed nanozyme, ultrasmall (2-3 nm) copper peroxide nanodots modified by citric acid (CP@CA) for this purpose, which can break down into H₂O₂ and Cu²⁺ in water or soil. Ubiquitous glutathione reduces Cu²⁺ into Cu⁺, which promotes the decomposition of H₂O₂ into •OH through a Fenton-like reaction under mild acid conditions created by the presence of citric acid. The generated •OH efficiently degrade nicosulfuron in water and soil, and the maximum degradation efficiency could be achieved at 97.58% in water at 56 min. The possible degradation mechanisms of nicosulfuron were proposed through the 25 intermediates detected. The overall ecotoxicity of the nicosulfuron system was significantly reduced after CP@CA treatment. Furthermore, CP@CA had little impact on active components of soil bacterial community. Moreover, CP@CA nanozyme could effectively remove seven other sulfonylurea herbicides from the water. In this paper, a high-efficiency method for herbicide degradation was proposed, which provides a new reference for the in situ remediation of herbicide pollution.