Chitosan capped noble metal doped CeO₂ nanomaterial: Synthesis, and their enhanced catalytic activities

Chitosan (Ch) capped Ch-CeO₂, Ch-CeO₂/Ag, Ch-CeO₂/Pd and Ch-CeO₂/Ag/Pd nanomaterials were fabricated using seedless and metal displacement plating method. The Ce⁴⁺ ions first formed complex with Ch through amino and hydroxyl groups and then reduced in presence of NaOH and molecular oxygen at higher temperature. Ch-Ag⁺ and Ch-Pd²⁺ complexes adsorbed on the surface of Ch-CeO₂ and reduced under potential deposition. Ninhydrin reaction test was conducted to confirm the presence of chitosan on the surface of NMs. The catalytic efficiency was increases markedly with incorporating noble metal into Ch-CeO₂ NMs. Ch-CeO₂/Ag/Pd exhibits higher catalytic performance towards hydrogen generation due to the narrow band gap (2.65 eV) and smaller work function of CeO₂ (ϕ = 2.8 eV) than that of Ag⁰(ϕ =4.6 eV) and Pd⁰ (ϕ = 5.2 eV). Hydrogen generation rates increases with temperature and activation energies were found to be 63.2, 60.3, 56.2 and 53.0 kJ/mol for Ch-CeO₂, Ch-CeO₂/Ag, Ch-CeO₂/Pd, and Ch-CeO₂/Ag/Pd, respectively. CeO₂/Ag/Pd shows better catalytic efficiency due to the strong interaction between Ag/Pd metal and active support CeO₂. The photocatalytic rates drastically inhibited with scavengers, demonstrate that the reactive radical oxygen species (HO and O₂^-), holes (h⁺) and electrons (e^-) played major role in the NaBH₄ hydrolysis.