In-situ synthesis of TiO2/La2O2CO3/rGO composite under acidic/basic treatment with La3+/Ti3+ as mediators for boosting photocatalytic H2 evolution

Abstract

Graphene-bridged, carbonate-coordinated and lanthanum modified TiO2 nanocomposite (La/Ti3+/TiO2/La2O2CO3/rGO) was established using sol-gel assisted modified hydrothermal method followed by acidic/basic heat treatment. The synergistic effect of La/La2O2CO3 in rGO bridged Ti+3/TiO2 nanocomposite was investigated for dynamic H2 production from ethylene glycerol-water mixture in a slurry phase continuous flow photoreactor system. La-TiO2/rGO showed H2 evolution rate of 462 μmol/h which was about 1.24, 1.51 and 5.13 folds higher compared to La/TiO2, rGO/TiO2 and pure TiO2 samples, respectively. Furthermore, when La-TiO2/rGO nanocomposite was treated under H2/CO2 atmosphere, a great potential in photocatalytic H2 production with a rate of 583 μmol/h was obtained, which was ~1.02, 1.17 and 1.26 times higher than using H2, CO2 and N2 atmospheres, respectively. This significantly enhanced productivity was due to formation of La2O2CO3, increased absorptive properties of TiO2 and changes in elemental level like Ti3+ state, which improves light absorption properties and producing more electrons with their hindered recombination rate by rGO. Specifically, existence of La2O2CO3 could facilitate the basicity of catalyst and contributes in the decomposition of ethylene glycol for H2 evolution. Next, apparent quantum yield of La-TiO2/rGO calcined in CO2/H2 composite was 1.3 folds higher than using La-TiO2/rGO composite. Moreover, the stability comparison reveals that CO2/H2 treated sample showed stability in cyclic runs due to better interactions of its components and formation of interface species like Ti3+ and La2O2CO3. Therefore, fabrication of composite under well-controlled atmospheric heat treatment could be promising to develop graphene supported metal oxides with their unique structures towards visible light enhanced photocatalytic H2 production applications.