Enhancing Charge Transfer in Photocatalytic Hydrogen Production over Dye-Sensitized Pt/TiO₂ by Ionic Liquid Coating

Abstract

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.

NIR-Driven Photocatalytic Hydrogen Production by Silane- and Tertiary Amine-Bound Plasmonic Gold Nanoprisms

“…The development of robust photocatalysts for efficient harvesting of broadband solar radiation, particularly near-infrared wavelengths, is essential for the solar-to-fuel technology. − Most commonly used semiconductor-based photocatalysts operate in the UV and visible wavelengths. − two-dimensional (2D)-nanomaterial-based photocatalysts enhance the charge transfer kinetics and surface activity due to high surface-to-volume ratios, and the light harvesting can be extended; however, it requires a complex preparation process. − Organic molecules provide the wavelength flexibility, but they also suffer from acute photobleaching. ,− Plasmonic nanoparticles have recently emerged as potential photocatalysts for visible as well as near-infrared (NIR) wavelengths due to their tunable plasmon resonance wavelengths across the visible and NIR spectral range. − The surface plasmon resonance (SPR) of a plasmonic nanostructure is sensitive toward its size, shape, and the surrounding dielectric environment. , The SPR band of isotropic nanostructures such as gold nanospheres (AuNSs) can be tuned in the range of 500–580 nm, while that of anisotropic nanostructures such as nanorods and nanoprisms is tunable over the entire visible–NIR wavelength ranges, providing an opportunity to harvest photons from the entire visible–NIR region. ,, The photoexcitation of the surface plasmons creates energetic charge carriers, commonly known as hot carriers. These charge carriers can initiate and enhance a chemical reaction on the surface of these nanoparticles. − However, the incident photon-to-chemical conversio...…”

Ionic liquid gel microspheres as an emerging platform for constructing liquid compartment microreactors

“…It means that the BiOBr@ILG-microspheres can effectively reduce the recombination opportunity of the photogenerated electron–hole pairs, which is mainly attributed to the wider band gap of the BiOBr/BiF 3 heterostructure and efficient charge transfer on the semiconductor surface assisted by ILs. 65 In addition, from the surface photovoltage spectra results (Fig. S12†), we further know that the photogenerated charges produced by the BiOBr@ILG-microspheres have a longer lifetime.…”

“…S17†), which should be due to the fact that ILs can provide a highly efficient charge transfer catalytic microenvironment. 65,66 Meanwhile, the formed BiOBr/BiF 3 heterostructure is also conducive to the photocatalytic redox reaction. 58…”

“…S17 †), which should be due to the fact that ILs can provide a highly efficient charge transfer catalytic microenvironment. 65,66 Meanwhile, the formed BiOBr/BiF 3 heterostructure is also conducive to the photocatalytic redox reaction. 58 Therefore, the excellent catalytic performance of the BiOBr@ILG-microspheres is attributed to the effective enrich- ment of the substrates by the ILG-microspheres near the catalytic active centers of BiOBr@ILG-microspheres, the efficient charge transfer microenvironment provided by ILs in the ILGmicrospheres for the catalytic reaction and the formation of the BiOBr/BiF 3 heterostructure.…”

Recent Advances in Ionic Liquids and Ionic Liquid-Functionalized Graphene: Catalytic Application and Environmental Remediation

“…At present, TiO 2 is widely used as a photocatalyst for water decomposition. Pt is loaded onto the surface of TiO 2 , and dyes and ILs are loaded with ethanol and acetone as solvents to improve the catalytic performance of Pt/TiO 2 for hydrogen production [ 19 ]. Supported IL catalysis (SILC) was applied to a hydrogenation reaction [ 20 ], which reduced the amount of IL phase and made the fixed-bed technology possible.…”