Generalized One-Pot Synthesis, Characterization, and Photocatalytic Activity of Hierarchical BiOX (X = Cl, Br, I) Nanoplate Microspheres

Abstract

A general one-pot solvothermal process was explored to prepare BiOX (X = Cl, Br, I) powders by employing ethylene glycol as the solvent. The as-prepared BiOX powders were characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, UV−vis diffuse reflectance spectroscopy, and nitrogen sorption. The resulting BiOX samples were phase-pure and of hierarchical microspheres consisting of nanoplates. The band gaps of the as-prepared powders were estimated to about 3.22, 2.64, and 1.77 eV for BiOCl, BiOBr, and BiOI, respectively. On the basis of characterization results, we proposed a possible process for the growth of hierarchical BiOX nanoplate microspheres. Moreover, we evaluated their photocatalytic activities on the degradation of methyl orange and compared them with TiO2 (Degussa, P25) under UV−vis light irradiation and C-doped TiO2 under visible light (λ > 420 nm) irradiation, respectively. It was found that all the BiOX samples were photocatalytically active and BiOI exhibited excellent activity under both UV−vis and visible light irradiation. The resulting hierarchical BiOX nanoplate microspheres are very promising photocatalysts for degrading organic pollutants and other applications.

Photocatalytic properties of hierarchical BiOXs obtained via an ethanol-assisted solvothermal process

“…7a), indicating that the BiOBr is an excellent visible − light-response photocatalyst, as reported earlier. Again, no degradation of SA is observed in the BiOI system under either visible-light and UV irradiation, which is different from the results in previous reports (Chang et al, 2010;Qin et al, 2013;Zhang et al, 2008b), where it was reported that BiOI had the highest activity among BiOXs. Considering the narrow band gap and strong visible light absorption of BiOI, its inactivity in photocatalytic degradation is somewhat striking in our study.…”

“…Qin and their coworkers (Qin et al, 2013) found that 2-methoxyethanol could help BiOCl and BiOBr construct into even hierarchical architectures, while the same type of BiOI could not be obtained under otherwise identical reaction conditions unless ethylene glycol was substituted for 2-methoxyethanol. Ethylene glycol was always used in the formation of hierarchical microspheres (Zhang et al, 2008b(Zhang et al, , 2011, and glycols tended to help obtain more compact, dense and larger catalyst particles compared with those synthesized with ethanol. In order to determine the effect of solvent, we also synthesized BiOBr-EG using ethylene glycol instead of ethanol under otherwise identical conditions, and BiOBr-H 2 O with a hydrothermal method according to previous work of our laboratory (Wang et al, 2012).…”

“…EG was believed to function as a soft template, directing the growth of BiOBr nanoparticles into nanoplates, and then into sphere-like superstructures due to its special chemical and physical properties. The hydrogen bonds between hydroxyl groups of EG could interact in long chains, which might be the reason why compact sphere-like BiOBr formed (Zhang et al, 2008b). Ethanol only has one hydroxyl group in its structure, so that hydrogen bonds between ethanol molecules will be far less prevalent than in EG, thus more loose BiOBr could be obtained.…”

“…Since the most famous wide-band-gap (3.2 eV) photocatalyst TiO 2 cannot utilize sun light efficiently, BiOX semiconductors have attracted much attention as a class of promising photocatalysts due to their special structural and optical properties, with band gaps of approximately 3.2, 2.6 and 1.7 eV for BiOCl, BiOBr and BiOI powders (Chang et al, 2010;Qin et al, 2013;Zhang et al, 2008b), respectively, and can be excited by UV and/or visible light.…”

“…However, using Bi 2 O 3 and halogen acid as raw materials, also in aqueous solution, BiOBr has been observed to be the most active one in the photodegradation of RhB under UV-visible irradiation and in splitting water under UV irradiation, BiOCl has been observed to photodegrade isopropanol under visible light more efficiently than BiOBr and BiOI . Using the ionic liquid 1-hexyl-3-methylimidazolium halide ([C 16 Mim]X) or KX as a halogen source and Bi(NO 3 ) 3 ·5H 2 O as a bismuth source, three-dimensional BiOXs were prepared with the solvothermal method in 2-methoxyethanol or ethylene glycol (Qin et al, 2013;Zhang et al, 2008b). In this family of catalysts, BiOI was the most active one under visible light irradiation due to its small band gap of 1.76 eV.…”