Au Supported on Bovine-Bone-Derived Hydroxyapatite Catalyzes CO2 Photochemical Reduction toward Methanol

Abstract

In this work, gold-photo-catalyzed CO2 transformation was conducted and the effect of three variables with two levels was investigated: support (TiO2 and hydroxyapatite from bovine bone (BB)), Au content (5 and 10%) and activation wavelength (254 and 380–700 nm). Reactions were conducted in a stirred tank reactor by bubbling CO2 (9 × 10−3 dm3/min) in 0.1 dm3 of 0.5 M NaOH solution. The catalysts were synthesized using AuCl3, TiO2 and BB. Au nanoparticles were obtained by reduction with Hetheroteca inuloides, thus eliminating calcination and hydrogenation to reduce the gold species. By TEM, the particle size distribution was determined, and the synthesized nanoparticle sizes varied in the range of 9 to 19 nm, depending on the support and Au content. By UV–Vis spectroscopy, the energy band gaps of the prepared materials were 2.18 eV (10% Au/BB), 2.38 eV (5% Au/BB), 2.42 eV (BB), 3.39 eV (5% Au/TiO2), 3.41 eV (10% Au/TiO2) and 3.43 eV for pure TiO2. Methanol and formic and acetic acids were identified during the process. Selectivity toward methanol was found to be improved with the 10% Au/BB catalytic system.