Preparation And Catalytic Performance Of Lignin-based Carbon Materials

Lignin,one of the important components of lignocellulose,is nature’s second most abundant biomass resource,although only 5%of it is utilized commercially for low-value purposes,as a low-grade fuel for thermal and electrical uses,or as a concrete addition（lignosulfonate）.Therefore,it is urgent to develop new ways to convert it into high-value chemicals.It is simple to produce significant amounts of sulfur-doped carbon materials from lignin sulfonate,which has abundant oxygen-containing functional groups and sulfur-containing groups.These materials are anticipated to have great potential in photocatalysis and electrocatalysis.The catalytic activity is enhanced further by the addition of heteroatoms and doping with transition metals.As a result,the thesis work uses lignin as its raw material and regulates the surface-interface structures by carbonization,doping,and the addition of transition metal,etc.Various carbon-based catalysts were prepared and used for the degradation of water pollution.Additionally,a novel method for high-value of lignin was developed.（1）Lignin-based carbon materials were prepared by direct carbonization of sodium lignosulfonate,and tetracycline was photocatalytically degraded under visible light irradiation.The catalyst’s surface structure and photocatalytic degradation activity were greatly impacted by adjusting the roasting temperature,carbonization time,and roasting atmosphere.Through comparison experiments,it was shown that the S-C-N₂-12 produced by roasting for 12 hours at300°C in a nitrogen atmosphere exhibited excellent photocatalytic performance,and the characterization results of XPS and FT-IR revealed that it contained sulfur-containing functional groups such as C-S-C,R-SO₃,R-SO-R,and R-SO₂-R,of which sulfone and sulfoxide were the main active sites.And the reaction path of tetracycline under visible light irradiation was explored through free radical capture experiments and ESR characterization and the experimental mechanism was revealed.The findings demonstrated that h⁺was the primary reactive free radical and that the reaction process also involved a synergistic interaction between·OH and·O₂^-.（2）In order to fabricate sulfur-doped lignin-based carbon materials,sodium lignosulfonate was employed as the raw material,Na₂SO₃ was then used as a sulfur source and activated agent.The degradation of pollutants in water under visible light was used to test the catalytic activity of SC catalyst,and SC-1.6-500 not only exhibited well photocatalytic performance but also increased substrate adsorption in comparison to carbon materials prepared without the addition of Na₂SO₃.The nature tests of the catalyst were characterized by nitrogen adsorption and desorption,photocurrent response,SEM,TEM and ESR.The results revealed that adding Na₂SO₃ significantly increased the catalyst’s specific surface area and photocatalytic activity.Tetracycline degradation and infrared spectroscopy were used to determine the main active species and radical capture experimentation was used to prospect the reaction mechanism.（3）The generation of·SO₄^-oxidized organic pollutants by transition metal-activated PMS has attracted a lot of interest due to its great efficiency.In this work,a series of manganese-nitrogen composite catalysts were prepared by adding nitrogen in order to increase the oxidation activity and decrease the metal leaching rate.A one-step carbonization process was used to synthesize the transition metal manganese nitrogen-doped carbon.The primary active metal sites were determined by altering a single factor in order to compare the roles of manganese and nitrogen in the reaction process.The experimental results revealed that manganese-nitrogen co-doping had the maximum catalytic activity.On this basis,by changing the ratio of urea and sodium lignosulfonate and the content of manganese salt,the optimal ratio was obtained,and 0.5%Mn-2:1-900 had the highest catalytic activity in the reaction of activated PMS to degrade bisphenol A,and the degradation efficiency of BPA more than 95%could be achieved in 8 min.The content of manganese before and after the reaction was determined by ICP,and the results showed that the content of manganese remained slightly changed after five cycles,showing that the catalyst had good stability.By using a radical capture experiment and ESR characterization to identify the active species of the reaction,singlet oxygen（¹O₂）with no radicals.