Photocatalytic hydrogen evolution over cyanine-sensitized Ag/TiO2

Sensitization of TiO₂ by dyes such as cyanine and their derivatives is used as a technique to improve potency for the production of hydrogen gas as an alternative green fuel. These dyes shift the spectrum of TiO₂ from the UV region to the visible region, enabling it to harvest as much sunlight as possible. Herein, four different derivatives of cyanine (labelled C1, C2, C3, and C4) were prepared and doped in Ag/TiO₂via the impregnation method. The properties of the prepared photocatalysts were studied by XRD, SEM-EDS, FTIR, and UV-visible spectroscopy. The sensitized photocatalysts exhibited a similar morphology, nanoscale particle size, and good absorbance in the visible region. The rate constant for the photocatalytic activity of Ag/TiO₂ showed a great enhancement for hydrogen evolution after sensitization from 0.088 to 0.33 μmol min⁻¹. Doping of the C2 derivative in Ag/TiO₂ promoted the photocatalytic and sonophotocatalytic rates of H₂ production by 7.5 and 9 times, respectively. Also, the amount of photocatalyst had a significant effect on the photocatalytic activity of the sensitized Ag/TiO₂, where 0.14 g was the optimum dose, giving the maximum yield at both the initial rate and 300 min. One of the important factors causing the efficiency to reach high levels is the inhibition of photogenerated electron/hole recombination. This was achieved by adding a small quantity of methanol, which increased the rate by 9 times. The stability of the prepared photocatalysts was tested, which gave good results even after their 5th use. All the results confirmed that the sensitization of metal oxides is a promising solution in industry to produce clean energy (H₂) in high quantities over highly stable photocatalysts.

Comparison between photo- and sonophotocatalytic hydrogen production.

Synergetic effects of Cu/TiO2 sensitized with different cyanine dyes on hydrogen evolution

The production of hydrogen as an alternative fuel is a major challenge for developed countries. To achieve this, photocatalysis is a promising method, which depends mainly on a renewable energy source, namely, the sun. Many derivatives of cyanine-sensitized Cu/TiO₂ were prepared and characterized by XRD, SEM-EDS, TEM, BET surface area and UV-vis spectrophotometry and their photocatalytic activity was studied. The study of hydrogen production over the sensitized photocatalysts confirmed the significant role of the dyes in the enhancement of hydrogen production. Dye molecules harness light radiation to produce strong oxidizing species, such as hydroxyl radicals, which in turn form hydrogen molecules. Combining sonolysis with photocatalysis processes proved that ultrasound waves inhibit the agglomeration of particles and maintain their surface area. This synergetic process increased the efficiency of hydrogen production by 7 times using photocatalysis only.