Photocatalytic
hydrogen production from water is considered to
be a potentially cost-efficient method to produce hydrogen fuel with
little impact on the environment. Nevertheless, hydrogen production
efficiencies via photocatalysis remain to be low. Here, a photocatalyst
system composed of 1 wt % Pt/TiO2 and dye-sensitized Pt/TiO2 particulates encapsulated by an ionic liquid is proposed.
In particular, the enhancement of photocatalytic hydrogen production
over 1 wt % Pt/TiO2 particulates sensitized with N719 dye
(di-tetrabutylammonium cis-bis(isothiocyanato)bis(2,2′-bipyridyl-4,4′-dicarboxylato)
ruthenium(II)) and coated by a thin layer of ionic liquid [BMIM][BF4] (1-butyl-3-methylimidazolium tetrafluoroborate) has been
investigated. The Pt was loaded onto the TiO2 surface by
incipient wetness impregnation, while the dye and ionic liquid were
loaded by solvent evaporation using ethanol and acetone, respectively.
The photocatalytic tests were performed in a semibatch glass reactor
under visible light irradiation provided by a solar simulator; the
hydrogen production rates over Pt/TiO2, dye-sensitized
Pt/TiO2, ionic liquid-coated Pt/TiO2, and ionic
liquid-coated Pt/TiO2 after dye sensitization were compared.
The hydrogen production rate was ∼21 μmol/h·gcat on Pt/TiO2, and it increased to ∼27 μmol/h·gcat with dye sensitization, while the [BMIM][BF4] coating alone improved hydrogen production three times (∼60
μmol/h·gcat). Coating the dye-sensitized particulates
with an ionic liquid resulted in another 17% increase in hydrogen
production (∼70 μmol/h·gcat). Scanning
electron microscopy–energy dispersive X-ray analysis (SEM–EDAX),
contrast transmission electron microscopy (CTEM), X-ray diffraction
(XRD), Fourier transform infrared (FTIR) spectroscopy, UV–vis
characterization of the photocatalysts and electrochemical analysis
of the respective photoelectrodes were also performed. The ionic liquid
coating increased the performance of Pt/TiO2 by providing
better charge transfer between the photocatalyst and the aqueous reaction
medium while simultaneously preventing the recombination of photogenerated
electron–hole pairs. The improved performance of the dye-sensitized
photocatalyst upon the ionic liquid coating indicated that the ionic
liquid stabilized the dye on the photocatalyst surface while simultaneously
enhancing the charge transfer between the dye and TiO2.