Abstract
Cu/Ti photocatalysts were prepared by the sol-gel process with different copper loadings (1.0, 2.5, and 5.0 wt.%) and then thermally treated at several calcination temperatures from 400 to 600 °C. The materials were characterized by X-ray diffraction (XRD), N2 physisorption, Scanning Electronic Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS), Ultraviolet-visible-Diffuse Reflection Spectroscopy, Ultraviolet-visible spectroscopy as a function of the temperature, (Temperature Programmed Reduction) TPR-chemisorption, XPS (X-ray Photoelectron Spectroscopy) and OH determination through DRIFTS (Diffuse reflectance infrared Fourier transform spectroscopy). The Cu/Ti photocatalysts were evaluated for the photocatalytic production of hydrogen using hydrazine as scavenging agent. Moreover, a detailed study of the Cu1+/Cu2+ ratio and the corresponding formation of copper oxide was carried out to understand the correlation between the copper species and the photocatalytic activity. Simultaneously, the OH groups on the TiO2 surface also show insights into the behavior of these materials during the photocatalytic reaction. Despite the low hydrazine concentration (20 mM), the 1.0 (wt.%) Cu/Ti 500 photocatalyst enhanced the hydrogen production three and two times more than photolysis and bare TiO2, respectively. The 1.0 Cu/Ti 500 photocatalyst displayed outstanding stability for at least three continuous cycles of 8 h each, preserving the hydrogen production. The novel ability shown in this work represents an alternative to reduce the hydrazine residues in wastewater to transform it into a hydrogen-producing energy source and must be extended to other reductive pollutants found in wastewater.
Highlights
The water-splitting reaction could be considered as an environmentally sustainable method for producing hydrogen
As the copper concentration increases, the presence of the brookite crystalline phase starts to appear with the well-known crystallographic plane (121) at 30.7◦ (JCPDS 29-1360)
The OH groups elucidated by FTIR spectroscopy generate the titanol groups that were responsible for oxidizing the hydrazine and reducing the H+ to H2
Summary
The water-splitting reaction could be considered as an environmentally sustainable method for producing hydrogen. TiO2 can be modified by doping with transition metals to improve the electron flow in redox reactions [13] Due to their low cost and remarkable properties, the use of copper species at very low concentrations has been proposed to dope the TiO2 in order to form oxygen vacancies on the surface, where the rest of the copper that is not present in the TiO2 lattice is capable of carrying out the formation of copper oxides. The photocatalytic production of hydrogen using copper-TiO2 nanomaterials and hydrazine at negligible concentrations as a sacrificial agent is proposed In this sense, hydrazine wastewater was used with the environmental and energy purpose of producing hydrogen
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