ZnTi layered double hydroxides as photocatalysts for salicylic acid degradation under visible light irradiation

Abstract

A series of ZnTi layered double hydroxides (LDH) with different Zn/Ti ratios are prepared and used as catalysts for photodegradation of salicylic acid (SA) under visible light. The catalysts are characterized by X-Ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy, UV-vis diffuse reflectance spectroscopy, thermogravimetry, electron paramagnetic resonance and N2 adsorption-desorption. The results show that SA anions bind to the LDH surface and that an electron can be excited from the HOMO in the adsorbed molecules to the conduction band of the LDH under visible light illumination. This charge transfer further leads to an effective photodegradation and mineralization of SA with better conversion results than on P25 titania.Key factors influencing the charge-transfer process in LDH are the high surface area and the Ti/Zn ratio of the LDH materials. The combination of highly dispersed Zn 2+ and Ti 4+ cations in the brucite-like sheets of the LDH allows for a better charge separation, which also accounts for the high photocatalytic activity. The present results show that superoxide radicals play a role in the visible-light induced degradation of SA on LDH, while no  OH radicals are formed. In contrast to LDH, the light-induced degradation pathway of SA over P25 titania leads to the formation of CO2 -, a relatively stable anion that may hamper further conversion to CO2 and hence limit the photocatalytic performance. The introduction of an electron acceptor, such as peroxydisulfate, further improves the degradation and mineralization of SA over LDH, but care should be taken not to use an electron acceptor that can easily adsorb to the LDH surface, such as H2O2. ZnTi LDH are thus very promising alternatives to TiO2 for the photodegradation of colorless organic pollutants, such as SA, under visible light irradiation. Highlights-ZnTi layered double hydroxides (LDH) allow mineralization of salicylic acid under visible light -Visible light induces charge transfer from the adsorbed molecule to the semiconductor -The Ti/Zn ratio and specific surface area of ZnTi LDH influence the photoactivity -Photodegradation of SA involves different radical intermediates in LDH than in titania

Insights into thermally assisted photocatalytic overall water splitting over ZnTi-LDH in a gas–solid reaction system

“…The ZnTi-LDH sample at all temperatures displays a strong absorption band due to the ligand-to-metal charge transfer involving the octahedrally coordinated Zn and Ti atoms within the layered network. 36 With the increase of irradiation temperature from 30 °C to 250 °C, the absorption intensity of visible light and ultraviolet light for ZnTi-LDH is sharply enhanced and an obvious red-shift of the absorption band is observed. According to Fig.…”

Layered Double Hydroxide-Based Photocatalysts for the Removal of Emerging Contaminants: Progress in Past Ten Years

“…A ZnTi−LDH prepared with urea in the homogeneous co-precipitation method showed the superior removal of colorless salicylic acid (SA) under visible light irradiation, which was much higher than that of commercial P25. The Zn 2+ and Ti 4+ cations were highly dispersed on the brucite-like LDH sheets, effectively promoting charge separation and leading to excellent photocatalytic activity [65]. In addition, a ZnTi−LDH with a laminated architecture was deemed an effective and stable visible-light-induced photocatalyst [38,66].…”

Photodegradation of naproxen using CuZnAl-layered double hydroxides as photocatalysts

“…The results suggested that MCr NO 3 -LDHs (M = Cu, Ni) exhibit 20 times higher photocatalytic activity than P25 as well as excellent recycling ability. 8 Thus, the powerful photocatalytic performance made investigators realize the broad application prospects of LDHs in photocatalysis, such as dyes (rhodamine B, rhodamine 6G), 9 methylene blue degradation, 10,11 NO x gases (NO and NO 2 ) removal, 12 salicylic acid degradation, 13 CO 2 conversion, 14 and pesticide degradation. 15 However, there are few studies on the photocatalytic degradation of PPCPs by LDHs, including but not limited to NPX.…”