Dye-sensitized H2 evolution from water facilitated by photoinduced electron transfer between molecules on the inside and the outside of a carbon nanotube

Abstract

Dye-encapsulated single-walled carbon nanotubes (dye@SWCNTs) were physically modified to fabricate a water-dispersible dye@SWCNT/dendrimer hybrid. A photocatalytic H2 evolution reaction that uses this dye@SWCNT hybrid as a particulate photocatalyst was conducted in the presence of an electron-relay molecule [methyl viologen (MV2+)], a co-catalyst [PVP–Pt; poly(vinylpyrrolidone)], and a sacrificial donor [1-benzyl-1,4-dihydronicotinamide]. Photoinduced electron transfer occurs between the encapsulated dye molecule inside the SWCNT and the MV2+ ion outside the SWCNT. This is followed by the relay of the electron to the co-catalyst, which reduces H+ to generate H2. The external quantum yield of the H2 evolution reached a maximum of 8.5% under irradiation with light at 510 nm. Notably, the photoinduced electron transfer between the molecules on the inside and the outside of the SWCNT proceeded smoothly despite the possibility of energy migration from the encapsulated dye to the SWCNT or the possibility of charge recombination.

Organic Functionalized Carbon Nanostructures for Solar Energy Conversion

“…Once again, functionalization played a relevant role in a system based on different non-covalent interactions between a SWCNT and two molecules, inside and outside the tube. The same team very recently reported an evolution of this system, in which the nanopeapods were rendered dispersible in water through non-covalent exohedral functionalization with solubilizing dendrimers [ 138 ].…”

Organic Functionalized Carbon Nanostructures for Solar Energy Conversion

“…Once again, functionalization plays a relevant role, in a system based on different non-covalent interactions between a SWCNT and two molecules, inside and outside the tube. The same team reported very recently an evolution of this system, where the nanopeapods was rendered dispersible in water through non-covalent exohedral functionalization with solubilizing dendrimers [123].…”

Enhanced Photocatalytic Hydrogen Evolution by Star-Shaped Viologen-Sensitized TiO2 Nanoparticles

“…Inspired by this idea, photocatalytic H 2 evolution has been considered an ideal and feasible technology as a green process for solar-driven water splitting. − H 2 can be generated from the photocatalytic decomposition of water by using appropriate catalysts that absorb the light in the available region of the solar spectrum, and this energy is generated by conversion into photogenerated charges to drive surface redox reactions. , Since TiO 2 as a semiconductor photocatalyst was implemented in 1972 for water-splitting, it has been extensively studied due to its low cost, nontoxicity, high photostability, and great redox capacity. − However, the wide band gap ( E g = 3.2 eV) and the high recombination rate of TiO 2 limit its further applications. , To overcome these obstacles, many studies have been conducted, including atomic doping, − metal deposition, − semiconductor incorporation, − photosensitization, etc. , The photosensitization has been known as an effective way to extend the photoresponse of inorganic semiconductors to the visible-light region . Efficient photosensitizers have been reported to date, for instance, a Ru­(bpy) 3 2+ metal complex, squarylium dyes, quaterthiophene, thienopyrazine-triarylamine, perylene-quinoxaline, multi-carbazole, and xanthene dyes for hydrogen evolution systems. − The reduction of photosensitizers of the methyl viologen with suitable electron donors and subsequent hydrogen production was achieved with the aid of noble metal cocatalysts. , Kotani et al systematically investigated photocatalytic H 2 evolution using platinum clusters functionalized with methyl viologen-alkanethiol (MVA 2+ ) and a simple electron-donor dyad. The amount of H 2 evolution of the MVA 2+ –Pt C system was estimated to be 2.4 μmol h –1 in the presence of a NADPH sacrificial agent .…”