Aims:
cobalt doped TiO2 composites were synthesized with the aim to decrease the TiO2 band gap which results
in enhanced visible absorption and then loaded with 1 wt.% of platinum for promoting the formation of molecular hydrogen.
Background:
Controversial results of the cobalt-based compounds create doubts about the photocatalytic activity of the
cobalt doped TiO2 materials. Thus, cobalt doped TiO2 composites were synthesized, and the photocatalytic activity was
checked for the hydrogen generation.
Objective:
The objective of this study is the synthesis of photocatalysts that are highly active for the photocatalytic hydrogen
evolution.
Methods:
The TiO2 and Co-TiO2 photocatalysts were synthesized using two different methods that are reflux and
hydrothermal synthesis. Additionally, The Pt deposition on the prepared TiO2 and Co-TiO2 catalysts (1 wt.% Pt) was
performed by the photoplatinization method.
Result:
The results showed that the reduction of protons over bare TiO2 and Co-TiO2 materials is possible from the
thermodynamic point of view. The evolution of molecular hydrogen from aqueous methanol employing 1 wt.% platinum
loaded on 0.5 wt.% Co-TiO2 photocatalysts under simulated solar light irradiation was investigated. The platinized CoTiO2 composites along with the platinized TiO2 samples have shown high photocatalytic hydrogen evolution. Higher
hydrogen evolution rates were determined in the presence of all platinized materials, and a maximum of 317 μmol h-1 is
observed on a Pt/Co-TiO2 photocatalyst prepared by a hydrothermal method.
Conclusion:
EPR results confirmed that the defects observed in the sample prepared within the hydrothermal processing
were in the surface and have better crystallinity, while the defects detected on the samples prepared by reflux synthesis were
less crystalline. The nature of semiconductor materials was explored through the determination of the flatband potential
using the Mott–Schottky equation. The Mott−Schottky analysis of electrochemical impedance measurements showed that
all semiconductors were n-type semiconductors and that cobalt doping induces impurity level within the band gap of TiO2.
The experimental results of photocatalytic hydrogen generation from methanol-reforming showed that the Co- doping does not affect the photocatalytic activity of both Pt/Co-TiO2 catalysts. Despite that, the Pt/Co-TiO2-HT was the best
photocatalyst under simulated solar light and show a maximum hydrogen evolution rate of 317 ± 44 μmol h-1.
Other:
Based on the experimental results, a possible mechanism for the continuous photocatalytic activity of Pt/Co-TiO2
photocatalysts under simulated solar light is proposed.
Realizing high hydrogen evolution activity under visible light using narrow band gap organic photocatalysts