Mesoporous coupled ZnO/TiO2 photocatalyst nanocomposites for hydrogen generation

Abstract

The present work investigates mesoporous coupled ZnO-TiO2 based nanocomposites towards photocatalytic hydrogen generation. The effect of Zn2+ loadings was examined on the photocatalytic activities of the sol-gel derived ZnO-TiO2 nanocomposites employing a structure-directing template. ZnO-TiO2 nanocomposites were characterized by powder X-ray diffraction, transmission electron microscopy, UV-vis diffuse reflectance spectroscopy, nitrogen isotherm, Raman, and electrochemical impedance spectroscopy (EIS) methods. The photocatalytic H2 evolution of the ZnO-TiO2 suspensions was evaluated in an aqueous methanol medium under UV illumination. The Zn2+ concentrations utilized to prepare ZnO-TiO2 nanocomposites were found to have significant effect on the specific surface area, pore volume, and photocatalytic activity. The H2 evolution results obtained with ZnO-TiO2 nanocomposites were compared with H2 generation using commercial TiO2 P25 and individual ZnO nanoparticles. The photocatalytic activity of ZnO-TiO2 composite enhanced significantly as compared to P25 or ZnO nanoparticles. With respect to an increment in Zn2+ loading, the photocatalytic activity of the composite increased and reaching an optimal H2 production of 17.3 ml/g of catalyst for the ZnO-TiO2 composite containing 30 wt. % ZnO (30ZnO). The specific surface area of the samples increased from 19 (single ZnO) to 122 m2/g for ZnO-TiO2 composite containing 50 wt. % ZnO (50ZnO). With an appropriate Zn2+ presence in ZnO-TiO2 nanocomposites, the specific surface area, total pore volume, charge transfer, and photocatalytic activity were significantly improved. Particularly, the samples containing 30 and 50 wt. % (30ZnO and 50ZnO) showed higher photocatalytic activity towards hydrogen generation, which attributed to higher specific surface areas, larger pore volumes, and lower interface resistance as confirmed by adsorption-desorption isotherms and EIS measurements, respectively. Hence, ZnO-TiO2 composites with higher than 50 wt. % ZnO were found to be not favorable to attain reasonable photocatalytic activity toward hydrogen generation as specific surface area and pore volume were drastically decreased.

Highly crystalline anatase TiO2 nanocuboids as an efficient photocatalyst for hydrogen generation

“…15 However, the wide band gap of the anatase TiO 2 and the high recombination rate of photogenerated charge carriers have severely restricted the efficiency of TiO 2 . 16 Currently, several strategies such as metallic or nonmetallic ion doping 13,[16][17][18][19] noble metal deposition [20][21][22] and coupling with other semiconductors [23][24][25] are developed to extend its photoresponse to visible light or to improve the charge separation. Besides these methods, morphological modication is another adopted method.…”

Gel-combustion-synthesized ZnO nanoparticles for visible light-assisted photocatalytic hydrogen generation

“…Since the discovery of water splitting by Fujishima and Honda [26], metal oxide semiconductors (in hydrogen generation) have come a long way. Though much research has been devoted to TiO 2 [27,28], doped TiO 2 [29] and TiO 2 nanocomposites [30], very few reports are available for ZnO [31] to produce hydrogen photocatalytically. Wang and Yao [32] have used ZnO rod-CdS/reduced graphene oxide and Peng et al [33] have used Pt-loaded ZnO.…”

Cu2ZnSnS4/MoS2-Reduced Graphene Oxide Heterostructure: Nanoscale Interfacial Contact and Enhanced Photocatalytic Hydrogen Generation

“…Oxide semiconductors, which have been widely used as a light absorbing material, usually have a wide band gap due to the low lying valence band (VB) composed of oxygen orbitals89101112. This poses a limit on the useful absorption range for exciton generation and thus lowers the power conversion efficiency in many cases of oxides.…”