Effects of a Nanoparticulate TiO₂ Modifier on the Visible-Light CO₂ Reduction Performance of a Metal-Complex/Semiconductor Hybrid Photocatalyst

Abstract

Graphitic carbon nitride nanosheets (NS-C 3 N 4 ) combined with a binuclear Ru(II)−Re(I) complex (RuRe) consisting of a photosensitizer and catalytic units are capable of selectively reducing CO 2 to CO under visible light (λ > 400 nm) using triethanolamine as an electron donor. In this system, the grafting of the nanoparticulate rutile TiO 2 on the NS-C 3 N 4 surface has previously been shown to enhance photocatalytic performance because of improved charge separation between the NS-C 3 N 4 and the TiO 2 and the reinforced adsorption of the RuRe. Here, a more detailed investigation of various polymorphic TiO 2 species loaded onto the NS-C 3 N 4 and the visible-light CO 2 reduction activity of the resultant photocatalysts was conducted. The experimental results showed that the RuRe/anatase-TiO 2 /NS-C 3 N 4 outperformed analogues with other TiO 2 polymorphs in terms of the CO generation rate, with a maximum catalytic turnover number of ∼100. Transient absorption and emission spectroscopy measurements were carried out to clarify the origin of the different CO evolution activities provided by different TiO 2 modifiers. The results revealed that the TiO 2 modifiers not only affected the charge separation ability but also controlled the efficiency of back electron transfer from the Ru-photosensitizer unit in the RuRe to the TiO 2 . The results also showed that, among the investigated TiO 2 polymorphs, anatase best facilitated the forward electron transfer from the NS-C 3 N 4 to the TiO 2 while suppressing the undesirable back electron transfer reaction.

Multi-functional photocatalytic systems for solar fuel production

“…[124][125][126][127][128][129][130][131] A Z-scheme conguration of a hybrid photoelectrochemical cell composed of a RuRe/CuGaO 2 photocathode and a CoO x / TaON photoanode has been constructed to perform CO 2 reduction by H 2 O without bias potential as shown in Scheme 16. 132,133 Two compartment cells that contain a CO 2 -saturated electrolyte solution were separated using a Naon membrane. 132 Visible light irradiation of the RuRe/CuGaO 2 photocathode and the CoO x /TaON photoanode in the wavelength region of l ex > 460 nm and l ex > 400 nm, respectively, resulted in formation of reduced products (CO and H 2 ) and O 2 (the four-electron oxidized product of water) in the cathode and anode cells, respectively.…”

Photocatalysis of CO2 Reduction by a Ru(II)–Ru(II) Supramolecular Catalyst Adsorbed on Al2O3

“…Hybrid systems consisting of supramolecular photocatalysts, , in which a metal-complex PS is bound to a catalyst (CAT) through an alkyl chain, and semiconducting materials have been developed for photocatalytic CO 2 reduction via the Z-scheme mechanism; that is, both the PS in the supramolecular photocatalyst and the semiconductor are excited in a stepwise manner to generate an electron and hole in the CAT and semiconductor, respectively, to impart both strong reduction and oxidation powers. − For example, a Ru­(II)–Ru­(II) supramolecular photocatalyst ( RuRu in Chart ) adsorbed on Ag-loaded tantalum oxynitride (TaON) particles selectively photocatalyzes CO 2 reduction using methanol ( E 0 ( • CH 2 OH,H + /CH 3 OH) = +0.47 V vs Ag/AgNO 3 ) as an electron donor, which cannot reduce the excited PS unit of RuRu owing to its low reduction power ( E 1/2 * ( Ru*Ru / Ru – Ru ) = +0.17 V), via the stepwise excitation of TaON and the PS unit . In recent years, photoelectrochemical systems consisting of an organic layer with Ru­(II) PS and Ru­(II) CAT units, which have a similar structure to that of RuRu , attached to a p-type semiconductor NiO electrode as a photocathode and an n-type semiconductor photoanode, such as CoO x -loaded TaON and BiVO 4 , have been developed for photocatalytic CO 2 reduction using water as an electron donor and visible light as the energy source. , In these systems, the formation of a connected structure of the PS and CAT units is important because rapid electron transfer is required from the reduced PS to CAT on the solid surface, where diffusional collision between the PS and CAT is not possible.…”

Highly Efficient Supramolecular Photocatalysts for CO2 Reduction with Eight Carbon–Carbon Bonds between a Ru(II) Photosensitizer and a Re(I) Catalyst Unit

“…Although many efficient molecular photocatalytic systems, including supramolecular photocatalysts, for CO 2 reduction have been reported, one controversial point for the future practical application of photocatalytic CO 2 reduction is the use of water as a reductant for CO 2 reduction. From this viewpoint, the hybridization of supramolecular and semiconductor photocatalysts with high water oxidation power is a prospective candidate. − In these systems, according to the artificial Z-scheme, both the PS units of the supramolecular photocatalysts and semiconductor photocatalysts are excited to induce electron transfer from the reductant to the CAT units. Moreover, the supramolecular photocatalysts have an advantage over the mixed system of mononuclear PS and CAT because systems using mononuclear PS and CAT molecules cannot ensure efficient electron transfer from PS to CAT owing to the random fixation of PS and CAT.…”