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

Abstract 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.