Hydroxyapatite decorated TiO2 as efficient photocatalyst for selective reduction of CO2 with H2O into CH4

Abstract Efficient catalysts with high selectivity in products are highly desirable for photocatalytic CO 2 reduction. In this work, hydroxyapatite (HAP) decorated TiO 2 (HAP/TiO 2 ) were successfully fabricated via in-situ deposition of Ca(OH) 2 on rutile TiO 2 followed by a facile hydrothermal reaction. Comparing with TiO 2 , HAP/TiO 2 exhibited significant enhancement ( ca. 40 times) toward photocatalytic CO 2 reduction in the presence of H 2 O with a >95% selectivity of CH 4 . The characterizations revealed HAP possessed Lewis basic sites (O 2− in -PO 4 3- groups) and Lewis acidic sites (Ca 2+ or OH − vacancies), where Lewis basic sites could enhance the adsorption/activation of CO 2 and Lewis acidic sites facilitated the adsorption/dissociation of H 2 O respectively, thus promoting the photocatalytic reduction and oxidation half-reactions of CO 2 and H 2 O over Pt/TiO 2 . The formation of much more stable intermediates over HAP/TiO 2 would be responsible for the high selectivity of CH 4 . Moreover, photoelectrochemical and electrochemical characterizations revealed HAP could also promote the charge separation of TiO 2 and the charge transfer between TiO 2 and adsorbed species. The findings demonstrate HAP has a great potential as efficient assistant for photocatalytic CO 2 reduction with H 2 O and will stimulate us to design novel semiconductor-based materials with tuned Lewis acidic and Lewis basic sites to achieve highly efficient photocatalysts.