Xiaolong Cai

The use of photocatalytic CO₂ reduction as a green technology has attracted the attention of scholars. Nevertheless, the lower visible-light utilisation and photocatalytic efficiency of catalysts remain a challenge. In this work, Bi_xO_yBr_z photocatalysts were synthesised using a hydrothermal method by adjusting the molar ratio of Bi(NO₃)₃·5H₂O and C₁₉H₄₂BrN (Bi:Br ratio) and the pH value of the precursor solution. The obtained samples were characterised, and the CO₂ reduction performance was tested. The results showed that the phase composition for most of the samples was Bi₄O₅Br₂, and BiOBr or Bi₅O₇Br was also confirmed in a small number of samples. Owing to the effects of pH and the Bi:Br ratio on the reaction process, BiOBr→Bi₄O₅Br₂→Bi₅O₇Br transformation occurred. Acidic conditions are conducive to the formation of BiOBr. In alkaline environments, bismuth-rich Bi₄O₅Br₂ or even Bi₅O₇Br easily forms. Bi₄O₅Br₂ has self-assembled microsphere and irregular polyhedron morphologies. The polyhedron Bi₄O₅Br₂ results in CO and CH₄ yields of 10.34 μmol·g⁻¹·h⁻¹ and 1.86 μmol·g⁻¹·h⁻¹ in CO₂ reduction, respectively. Although the microsphere Bi₄O₅Br₂ has a maximum light absorption wavelength of 438 nm, the polyhedron Bi₄O₅Br₂ has the best photocatalytic CO₂ reduction performance and CO selectivity. This work describes the controllable preparation of Bi₄O₅Br₂ at various pH values and Bi:Br ratios and the optimisation of its photocatalytic performance.

In this article, COD, volatile phenol and ammonia nitrogen concentrations of the wastewater from semicarbon are reported as 38,000; 6,400 and 5,700 mg/L, respectively. According to the field test, when the pH of the wastewater is 9, the field test temperature is 20 °C, the adsorption time is 30 min and the optimal dosing ratio of nitrogen-doped gasification slag (HX-NGS) to the wastewater is 1:4, HX-NGS has the best removal effect on COD, volatile phenol and ammonia nitrogen in the wastewater from the semicarbon. The removal rates of COD, volatile phenol and ammonia nitrogen are 94, 91 and 85%, respectively, and the concentrations of the remaining COD, volatile phenol and ammonia nitrogen are 2,280, 576 and 855 mg/L, respectively, after regeneration, the material HX-NGS has a good effect on the treatment of the wastewater from the semicarbon. The reuse rate of the adsorption material is at least eight times. The adsorption effect of the material HX-NGS conforms to the mechanism law of dynamics and thermodynamics.

BiOI loaded flower-like CeO 2 (BiOI/CeO 2 ) p-n heterojunction was synthesized via a simple two-step chemical route. The phase structure and chemical states of the heterojunction were analyzed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The transmission electron microscopic (TEM) and the scanning electron microscope (SEM) reveal the close contact between BiOI and CeO 2 . The formation of the p-n heterojunction is verified by the Mott-Schottky curves. The p-type BiOI with narrow band-gap when loaded on CeO 2 can not only improve the separation of photogenerated electron-hole pairs but also facilitate the absorption of visible light. The photo-oxidative removal efficiency of 9%BiOI/CeO 2 for NO reaches 45.49% and remains highly stable with efficiency of 40.40% after the five cycles. Trapping experiments and ESR measurements were conducted to explore the contribution of charge carriers and the reactive oxygen species during for the photocatalytic NO removal. This work highlights that constructing such p-n heterojunction by loading BiOI on CeO 2 microstructures can significantly enhance the photocatalytic NO removal.