Template-free synthesis of carbon self-doped ZnO superstructures as efficient support for ultra fine Pd nanoparticles and their catalytic activity towards benzene oxidation

This work reports the template-free synthesis of diverse Carbon, self-doped Zinc oxide (C-doped ZnOSPs) superstructures through synergy between Cinnamomum camphora leaf extract and NaOH assisted by freeze-drying and annealing at desired temperatures. The high-activity and cost-effective porous supports with improved reducibility and charge transport act as catalyst support for ultra fine Pd NPs in the gas-phase selective remediation of the volatile organic compounds (VOCs) benzene. Uv-vis spectroscopy, XRD, XPS, SEM and TEM and photoluminescence studies, were used to characterize and verify the nature of the ZnOSPs. XPS analyses reveal that C-doping is introduced into the lattice of the as-produced ZnOSPs and the extent varied with leaf extract amount used. FTIR-analysis and simulation experiments showed flavones, polyphenols, and proteins were responsible for the formation of the ZnOSPs. Moreover, ultrafine Pd NPs sizes 1(-)3 nm can be anchored on the exterior surfaces of ZnOSPs to form diverse surface contact boundaries for enhanced low-temperature benzene oxidation. Pd/ZnOSP-3 catalyst with the least crystallite size 17.4 nm and largest surface contact boundary 3.2 nm presented the best performance. The superior activity of Pd/ZnOSPs over commercial Pd/ZnO-C is attributed to its carbon modification, the high porous framework; defects incorporation which causes smaller optical energy gap, improved reducibility, enhanced mechanical responses and high charge transport to promote the benzene oxidation reaction.