Muscetta, Marica (2021) Photocatalytic hydrogen production through photoreforming of organics using copper – based photocatalyst under visible light radiation. [Tesi di dottorato]

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Nowadays, 80% of global energy consumption is dependent on fossil fuels, leading different problems such as the decreasing of energy sources and the environmental problems (global warming, greenhouse effect, production of harmful gases, ozone layer depletion and acid rain). Hydrogen represents a potential alternative energy carrier due to its stability and zero emission of greenhouse gases, and many researches are directed toward the utilization of metal oxides semiconductors (such as TiO2 and ZnO) as photocatalysts to convert solar energy into hydrogen; in particular TiO2, due to its high chemical stability and photocatalytic activity in the UV range is the most widely used material; despite the great number of positive characteristics, TiO2 presents different problems such as high electron – hole recombination rate and poor absorption under the visible light, due to its wide band gap (about 3.2 eV). To overcome these drawbacks, several studies reported the utilization of TiO2 in association with other semiconductors such as ZnO and Cu2O; in particular much attention has attracted Cu2O: this is a non-toxic and abundant material, with a narrow band gap (about 2.1 eV); as p – type semiconductor, if combined with a n – type semiconductor, it is able to form a heterojunction photocatalyst, extending the light absorption in the visible range and reducing of electron-hole recombination rate. Several techniques have been used for Cu2O/TiO2 composite preparation and numerous disadvantages are still associated to each of them. In the present research, based on the outcomes of an extended literature analysis, a ball milling method to dryness has been chosen as alternative technique to prepare the photocatalysts, due to its simplicity and industrial applicability. The effect of milling time, rotation rate and Cu2O percentage on the photocatalytic hydrogen generation have been evaluated, obtaining the best performances (H2 generation about 60 μmol/h) with a milling time of 1 minute and a rotation rate of 200 rpm, when 1%wt of Cu2O is used in the composite in presence of methanol as scavenger. Moreover, the effect of the sacrificial agent used is evaluated adopting in the tests other species, and recognizing glycerol as the best candidate to produce hydrogen among the tested organics. Furthermore, the photocatalytic activity of the best prepared photocatalyst was evaluated at varying the pH and the temperature of the suspension, methanol concentration and catalyst load. In particular, a great positive effect was recorded at increasing the temperature of the system, showing a hydrogen productivity about 4.5 – fold higher than that obtained at the lowest temperature. Moreover, being the aim of the present work devoted to the development of a visible light active photocatalytic system, the possibility of using it by exploiting the solar light was evaluated, obtaining a hydrogen production about 5 – fold higher than that collected under simulated solar conditions. Finally, the development of a suitable mathematical model able to predict the hydrogen production in presence of the selected catalyst was also attempted.

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