Highly Robust Hybrid Photocatalyst for Carbon Dioxide Reduction: Tuning and Optimization of Catalytic Activities of Dye/TiO₂/Re(I) Organic–Inorganic Ternary Systems

Abstract

Herein we report a detailed investigation of a highly robust hybrid system (sensitizer/TiO2/catalyst) for the visible-light reduction of CO2 to CO; the system comprises 5'-(4-[bis(4-methoxymethylphenyl)amino]phenyl-2,2'-dithiophen-5-yl)cyanoacrylic acid as the sensitizer and (4,4'-bis(methylphosphonic acid)-2,2'-bipyridine)Re(I)(CO)3Cl as the catalyst, both of which have been anchored on three different types of TiO2 particles (s-TiO2, h-TiO2, d-TiO2). It was found that remarkable enhancements in the CO2 conversion activity of the hybrid photocatalytic system can be achieved by addition of water or such other additives as Li(+), Na(+), and TEOA. The photocatalytic CO2 reduction efficiency was enhanced by approximately 300% upon addition of 3% (v/v) H2O, giving a turnover number of ≥570 for 30 h. A series of Mott-Schottky (MS) analyses on nanoparticle TiO2 films demonstrated that the flat-band potential (V(fb)) of TiO2 in dry DMF is substantially negative but positively shifts to considerable degrees in the presence of water or Li(+), indicating that the enhancement effects of the additives on the catalytic activity should mainly arise from optimal alignment of the TiO2 V(fb) with respect to the excited-state oxidation potential of the sensitizer and the reduction potential of the catalyst in our ternary system. The present results confirm that the TiO2 semiconductor in our heterogeneous hybrid system is an essential component that can effectively work as an electron reservoir and as an electron transporting mediator to play essential roles in the persistent photocatalysis activity of the hybrid system in the selective reduction of CO2 to CO.

Solar H2 evolution in water with modified diketopyrrolopyrrole dyes immobilised on molecular Co and Ni catalyst–TiO2 hybrids

“…8,27–30 Only few studies are available with organic chromophores under DSP conditions and even less with commonly used aqueous electron donors, such as triethanolamine (TEOA) or ascorbic acid (AA), or with a molecular catalyst in a semi-heterogeneous photocatalytic scheme. 11,31–34 …”

The Pros and Cons of Polydopamine-Sensitized Titanium Oxide for the Photoreduction of CO2

“…Limited by its wide bandgap (e.g., 3.2 eV for anatase), however, TiO 2 can only absorb UV light of the solar spectrum which is only~4% of the total solar energy. Various methods, including impurity doping, surface sensitization, oxygen vacancies, and the localized surface plasmon resonance (SPR) effect have been developed to improve the light-harvesting ability of TiO 2 under visible light which accounts for 45% of energy in the solar spectrum [12][13][14][15][16][17][18][19][20]. Among them,…”

Continuous Synthesis of Ag/TiO2 Nanoparticles with Enhanced Photocatalytic Activity by Pulsed Laser Ablation

“…On the other hand, limited by its wide band gap (∼3.2 eV), TiO 2 can only take effect in the UV region of the solar spectrum (∼5% of the solar energy), while the energy absorption in the range of visible light containing about 45% of the solar energy [8] cannot be captured. In order to extend the spectral range of the TiO 2 response, various methods have been proposed, such as coupling with metals or narrow band gap semiconductors, doping, and surface sensitization by organic dyes [9][10][11]. However, there are some unavoidable defects in these methods.…”