| Coconut shell is a renewable biomass resource, which is widely used as a raw material for preparation of activated carbon. The resulting activated carbon has significant advantages such as highly-developed micropores, excellent adsorption performance, high strength, easy recovery, economy and durability. Therefore it is widely used for adsorption purification treatment of drinking water, wine, beverage, and industrial wastewater. Coconut shell contains abundant lignin, cellulose and pentosan, which bring about abundant oxygen-containing groups and unique carbon structure to coconut shell biochar. The study of structure, properties and applications of coconut shell biochar is a broad, developing area of research in the field of biomass chemical engineering. This thesis attempts to expand the application of coconut shell nanocarbon (CSC) in electrocatalytic and photocatalytic reactions.The prepared CSC powder has a nanosheet structure consisting of a typical disordered sp2 hybridized carbon network. It contains abundant oxygen-containing groups and a large amount of nanopores with pore size below 4 nm. The Brunauer-Emmett-Teller (BET) specific surface area of CSC is as high as above 2500 m2 g-1. The CSC powder was used to prepare carbon paste electrode for the cathodic reduction of lumazine (2,4(1h,3h)-pteridinedione or 2,4-dihydroxypteridine) and the evolution of hydrogen from acidic water. Without adsorption effect on lumazine, the CSC can not improve the cathodic and anodic Faradic currents of lumazine, but can greatly enhance the background current during the potential scan. The CSC paste electrode shows strong electrocatalytic effect on the hydrogen evolution reaction, with a much larger exchange current density as well as a much smaller charge transfer resistance than on the common graphite paste electrode. It can be deduced that the CSC surface with abundant oxygen-containing groups and nanopores does not favour the adsorption and reduction reaction of the electronegative groups of lumazine, but can catalyze the reduction reaction of positively charged hydronium ions with a small size. These results provide reference for selection of reactants that are possibly suitable for the CSC-based catalysts.The CSC nanosheets were used as support for loading CdS quantum dots (QDs) and Pt nanoparticles to form a Pt/CdS/CSC catalyst for the visible-light-driven photocatalytic hydrogen production from water. The hydrogen production rate on Pt/CdS/CSC can reach as high as 1679.5μmol h-1,which is much higher than the hydrogen production rate on Pt/CdS (636.2 μmol h-1). The CdS/Pt/CSC exhibits the highest quantum efficiency (39.4%) at a wavelength of 460 nm, with a good stability. The outstanding photocatalytic performance after introduction of CSC is associated with the electron-hole separation (in the CdS QDs) that is greatly improved by the fast electron transfer across the CdS/CSC interface. The accelerated electron transfer could result from the capture of photoinduced electrons by the surface charge traps such as the large amount of oxygen-containing groups and nanopores present on the CSC surface.The findings from this thesis will further expand the application of coconut shell carbon, and provide useful clues for designing efficient biochar-based catalysts for electrolysis and visible-light-driven photocatalysis. |
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