One-pot synthesis of lightly doped Zn1−x Cu x O and Au–Zn1−x Cu x O with solar light photocatalytic activity in liquid phase

Abstract

We report on the facile and low-temperature one-pot chemical synthesis of lightly doped Zn Cu O and hybrid Au-Zn Cu O photocatalysts with low Cu molar content (0< x < 0.7%) using 1,3-propanediol polyol simultaneously as solvent, reducing and a stabilizing agent, without any final thermal treatment. The photocatalysts have been characterized by X-ray diffraction, N adsorption study, UV-vis diffuse reflectance spectroscopy, inductively coupled plasma optical emission spectroscopy, and transmission electron microscopy. The lightly doped hybrid Au-Zn Cu O photocatalysts consisted in faceted quasi-spherical large-size Au nanoparticle cores surrounded by closely packed small-size Zn Cu O nanoparticles. Taking the photocatalytic degradation of Diuron under solar light as liquid-phase test reaction, the lightly doped Au-Zn Cu O hybrid photocatalysts with optimized x = 0.09% Cu content showed strongly enhanced photocatalytic activity when compared to the bare ZnO counterpart. The observed 16-fold higher degradation rate constant resulted jointly from the light doping of ZnO with Cu to form Zn Cu O photocatalyst and further from the addition of gold nanoparticles allowing interfacial oxide-to-metal electron transfer within the hybrid Au-Zn Cu O photocatalyst.

Photoactive ZnO Materials for Solar Light Induced Cu_xO-ZnO Catalyst Preparation

“…In agreement with the previous works of Fkiri et al [14], the ZnO materials synthesized via the polyol method displayed a good crystallinity without any postsynthesis heat treatment, and exhibited the smallest average crystallite size at 7 nm and 11 nm, for an aging duration of 15 min and 60 min, respectively. The ZnO materials prepared via both precipitation routes had a larger mean crystallite size, as a result of the necessary calcination treatment at temperatures ranging from 300°C to 500°C, the use of carbonates as precipitating agent allowing to maintain a smaller mean crystallite size in the 10-20 nm range, while it strongly increased to 28-30 nm in the case of the carbamate agent.…”

“…It is worth noting that the carbamate-derived ZnO samples calcined at 400°C and 500°C displayed a lower surface area than their carbonate-derived counterparts, at 12 m 2 /g and 6 m 2 /g respectively, in agreement with a larger mean crystallite size. The synthesis method had no influence on the gand gap of the ZnO materials, graphically estimated at 3.2 eV via Tauc plot derived from UV-vis diffuse reflectance analysis, in agreement with the literature (not shown) [14,32]. Therefore, the ZnO materials will be activated by incident photons with wavelengths within the UV-A range, whether the photocatalytic tests are performed under solar light or pure UV-A light.…”

“…In the case of the polyol method, the XRD pattern shown in Figure 1a displayed the diffraction peaks corresponding to ZnO crystallized in the hexagonal wurtzite structure and attributed to the diffraction of the (100), (002), (101), (102), (110), and (103) planes for the most intense characteristic peaks (space group P63mc, JCPDS No. 00-036-1451) [5,[14][15][16]. As reported for the polyol synthesis, the ZnO material had a good crystallinity without any post-synthesis calcination treatment.…”

“…Figure 3a shows N2 adsorption-desorption isotherms of ZnO materials. The ZnO-P materials displayed type IV isotherms, corresponding to mainly mesoporous solids with a mainly H2-type hysteresis characteristic of interconnected mesopores with non-uniform shape or size [14]. For ZnO obtained by precipitation, the isotherms turned to be preferentially of type II with H3-type hysteresis, what suggested that the porosity mainly resulted from macropores (or large mesopores) and was characteristic of aggregates or agglomerates of nanoparticles forming slit shaped pores with non-uniform size and/or shape.…”

“…It has already been reported that the electron lifetime can be significantly higher and that the rate of recombination can be lower in ZnO in comparison to TiO2, making it an attractive material worth to investigate for photocatalytic applications [12]. Further, the photocatalytic activity of ZnO can be enhanced by designing ZnO supported metal nanoparticle photocatalysts, with promising results mainly in the case [13] of Au and Ag [14][15][16][17][18][19]. In such hybrid metal/ZnO nanostructure, the supported nanoparticles are proposed i) to act as a sink for photoinduced electrons, so that the metal/semi-conductor interface could promote effective charge separation with efficient interfacial charge transfer, or ii) to induce plasmonic effects either through the direct injection of hot (excited) electrons from the metal to the conduction band of ZnO thanks to intimate electrochemical contact between the plasmonic particle and the semiconductor, or through an near-field enhancement mechanism with overlap between the plasmon wavelength and the photocatalyst absorption.…”