Abstract
The aim of this work is to demonstrate the effectiveness of the photocatalytic process in the Methyl Orange azo dye degradation and simultaneous H2 production by using ZnO doped with ruthenium. Ru-modified ZnO photocatalysts were prepared by precipitation method and were characterized by different techniques (XRF, Raman, XRD, N2 adsorption at −196 °C, and UV–vis DRS). The experiments were carried out in a pyrex cylindrical reactor equipped with a nitrogen distributor device and irradiated by four UV lamps with the main wavelength emission at 365 nm. Different Ru amounts (from 0.10 to 0.50 mol%) were tested in order to establish the optimal amount of the metal to be used for the ZnO doping. The photocatalytic activity was evaluated both in terms of Methyl Orange removal and hydrogen production. The experimental results showed that the best activity, both in terms of H2 production and Methyl Orange degradation, was obtained with the Ru-modified ZnO photocatalyst at 0.25 mol% Ru loading. In particular, after four hours of UV irradiation time, the discoloration and mineralization degree were equal to 83% and 78%, with a simultaneous hydrogen production of 1216 µmol L−1. This result demonstrates the ability of the photocatalytic process to valorize a dye present in wastewater, managing to obtain a hydrogen production comparable with the data present in the literature today in the presence of other sacrificial substances.
Highlights
Renewable energies represent the future of our planet
The results of this work demonstrate the effectiveness of the Ru-modified ZnO photocatalyst in the simultaneous degradation and valorization of organic contaminants, such as Methyl Orange azo dye, present in aqueous solutions
XRD and Raman analysis showed the presence of the characteristic ZnO signals, while from UV–vis diffuse reflectance spectroscopy (DRS) results it was evidenced that the doping of ZnO with Ru enhances the intensity of the light absorption in the UV region, but has no significant effect on the band gap value
Summary
Renewable energies represent the future of our planet. Scientific research has begun to pay close attention to the efficiency of industrial processes and the minimization of waste, especially in the energy sector. H2 could be a promising choice for a future energy resource because it is free of pollution, storable, and highly demanded by fuel cell industries. The introduction of “sacrificial agents”, such as ethanol, methanol, and glucose promotes the photocatalytic hydrogen production [2,3]. The addition of these organic compounds can improve the photocatalytic H2 production efficiency by consuming the photo-induced hole for better electron–hole separation. An interesting approach is to explore the possibility of producing an Catalysts 2019, 9, 964; doi:10.3390/catal9110964 www.mdpi.com/journal/catalysts
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