Novel strategies to develop efficient carbon/TiO2 photocatalysts for the total mineralization of VOCs in air flows: Improved synergism between phases by mobile N-, O- and S-functional groups

Abstract

New doped carbon/TiO2 composites were synthesized by sol–gel polycondensation of resorcinol with a heterocyclic aldehyde containing different heteroatoms (X= N, O and S), followed by impregnation with titanium(IV) isopropoxide and pyrolysis at 800 °C. Characterization techniques, such as physical adsorption of N2/CO2, EDX-mapping/SEM, XRD, XPS, ATR-FTIR and DRUV spectroscopy, were performed to determine the morphology, crystalline structure, physicochemical and optical properties of composites. The performance of composites in the photocatalytic oxidation of VOCs (ethylene) was evaluated in dynamic conditions. The influence of the material characteristics (heteroatom doping and TiO2 loading) and experimental conditions (irradiation source, presence of humidity) on the catalytic performance was analyzed. Heteroatom-doping, an increase in TiO2 loading and humidity exert negative effects on the adsorptive behavior of the composites. However, the photocatalytic activity of TiO2 phases substantially increases when being incorporated into the composites, especially on heteroatom-doped carbon supports, and also by the presence of humidity in the flow and higher TiO2 loadings. Doping the carbon support with heteroatoms enhances essentially the synergetic effect between carbon and TiO2 phases, as new Ti-O-X and Ti-X bonds are formed, reducing the crystallite size and rutile/anatase ratio, as well as the band gap from 3.0 eV for pure TiO2 to 1.9 eV for doped carbon/TiO2 composites, thus enhancing the catalytic performance. These effects become more evident with increasing the electronegativity of the dopant element (O > N > S), obtaining composites with unequal photocatalytic activity under Vis-radiation, allowing the selective ethylene oxidation to CO2 at room temperature in humid and dynamic conditions.