Study On Wood-based Carbon Dots/Wood-structure Cerium Oxide Composites As A New Photocatalyst

Increasing environmental pollution and shortage of resources have promoted the research and development of semiconductor photocatalysts.The research on semiconductor photocatalysis has three main aspects.The first is the component system of catalyst,such as bismuth-based catalysts,titanium-based catalysts,etc.The second one is study on doping' or modification,as many experiments showed that doping,modifying,or loading another substance or element could adapt the band gap of the semiconductor and eventually improve the photocatalytic efficiency.For the same reason,various nanoparticles are often loaded on the surface or pores of catalysts.In those studies,nitrogenous or phosphorus groups are always introduced to catalysts.The third aspect maybe the synthetic processes and preparation method.Preparation method determines the structure and morphology of one particular catalyst,which play a decisive role on its photoelectric properties.This research contains three experimental parts.Cerium dioxide(CeO2)was chosen as the subject,which has received much attention in recent years,for its highest content in rare earth elements and the most extensive source.Secondly,carbon quantum dots(CQDs)prepared by wood flour as raw materials are used in this paper,as CQDs show an excelent optical property.The catalyst's preparation used wood templated method.This method is simple but can replicate natural organisms,and get the hierarchical structure that has evolved over billions of years.In this study,a new type of composed catalyst was prepared from wood-based carbon quantum dots and wood-structured cerium oxide.The properties of carbon quantum dots and wood-structured cerium oxide were studied respectively,and their photocatalytic degradation properties of methylene blue were tested.As follows are the main research findings:Nitrogen-doped carbon quantum dots were successfully synthesized by reacting wood flour with citric acid and ethylenediamine in a hydrothermal reactor at 200? for 6 hours.The average particle size of nitrogen-doped carbon quantum dots is 3.81nm,which is 10%smaller than that of undoped carbon quantum dots.The lattice spacing is 0.35nm,corresponding to the(002)crystal plane of the graphite structure,the surface contains a large number of amino and hydroxyl groups.Oxygen,nitrogen-containing functional groups such as,carboxyl.Carbon quantum dots can display blue-violet light when the concentration is low,and cyan when the concentration is high;the fluorescence emission is related to the concentration and the wavelength of the excitation light,which will redshift with the increase of the excitation wavelength;The quantum yield of nitrogen-doped carbon quantum dots is as high as 43.38%,surpassing most of the reported biomass-based carbon quantum dots,and the fluorescence lifetime is 14ns.Wood powder-based carbon quantum dots have good water solubility,can be directly used as fountain pen inks and stamp inks as anti-counterfeit fluorescent marks,and the patterns have good weather resistance and stability.After more than half a year of natural aging,they remain bright and fluorescent.This study compares the wood-structure cerium oxide with the cubic cerium oxide prepared by hydrothermal method.The results show that cerium oxide can completely replicate the multi-scale hierarchical pore structure of the wood template after the transformation process of the wood state.Compared with the traditional hydrothermal cerium oxide,the cerium oxide of the wood template method is fluffier and BET area increased.What's more,the average pore size of wood templeted CeO2 is 5.38nm;cerium oxide in the structure of the wood remains in a polycrystalline form,with the crystallinity reduced,and a higher electrons separation efficiency;The cerium oxide has higher electronic activity and higher active oxygen content,which reduces the electron-hole recombination.The wood-structure CeO2 has a band gap of 3.3eV and a maximum ultraviolet absorption wavelength at 335nm.The results of the methylene blue degradation test showed that the residual structure of the wood cerium oxide can greatly improve the efficiency and rate of catalysis.After all this,a composite material of carbon quantum dots and wood-templeted cerium oxide were studied.It was found that the doping of carbon quantum dots would not change the surface morphology and crystalline properties of the wood residual structure cerium oxide.Plugging some holes in cerium oxide,the specific surface area of the composite material decreased,as well as the pore volume.The average pore size increased.However,since the carbon dot itself also has a large amount of active oxygen,the active oxygen content of the composite material slightly increased.The maximum UV absorption of the composite is at 400nm,with a 2.5eV band gap,and the photocatalytic rate increased by about 40%.