Preparation And Application Of Porous Carbon Materials Using Metal Lignin Complex As Precursors

Under the current general trend of social progress and rapid economic development,environmental damage and resource shortages also follow.Therefore,the high-value development and utilization of renewable and abundant biomass resources in the field of environmental restoration have attracted extensive attention of researchers.As a kind of abundant and renewable low-cost biopolymer with high carbon content and high aromaticity,lignin is considered to be an ideal carbon precursor.In addition,lignin also exhibits excellent flexibility and designability as a carbon precursor due to the abundant active functional groups such as phenolic hydroxyl groups,alcoholic hydroxyl groups and carboxyl groups.In this study,metal lignin complex obtained by compounding metal salts with poplar sulfate lignin were used as carbon precursors to prepare lignin porous carbon-based function materials with high absorbability and catalytic activity,which were applied to the treatment of polluted wastewater.This realizes the high-value utilization of industrial lignin,which also has great significance to the green and sustainable development of the economy.（1）Lignin was isolated from the black liquor by forming lignin-Zn complex by directly adding Zn Cl₂ solution into the black liquor,and the obtained lignin-Zn complex was used as a precursor to prepare activated carbon though an activator-free carbonization process.Compared with the traditional process of preparing activated carbon by acid precipitation and impregnation,it not only simplifies the process,but also avoids a large amount of acid consumption.After Zn Cl₂ complexation（0.5 mmol/m L Zn Cl₂,0.6 m L/m L black liquor）,over85%of lignin in black liquor was isolated accompanied with an over 70%of COD reduction and a neutral p H for the treated black liquor.The zinc ions were distributed evenly in the lignin-Zn complex and that contributed to the well-proportioned development of porous structure during carbonization process.Therefore,the activated carbon carbonized from lignin-Zn complex exhibited a substantial increase in both specific surface area and adsorption capacity compared to that from acid-precipitated lignin pre-impregnated in Zn Cl₂solution.Moreover,the as-prepared activated carbon presented maximum equilibrium adsorption capacities of 1047 mg/g and 264 mg/g for cationic methylene blue and anionic methyl orange,respectively,which were superior to most reported activated carbon adsorbents.Consequently,this work has developed a simplified and efficient method for producing activated carbon from black liquor using lignin-Zn as the precursor,which has offered a promising route for the value-oriented treatment of black liquor.（2）The nitrogen-doped carbon-supported Palladium zinc alloy（Pd/Zn@NC）catalysts were prepared by"one-pot synthesis"using lignin-Pd Zn complex as the precursor through simple mixing of poplar wood sulfate lignin with Zn Cl₂ and Pd Cl₂ solution,and used for the catalytic reduction of hexavalent chromium.The dispersion and particle size of alloy nanoparticles can be regulated effectively by varying the weight ratio of melamine to lignin and the molar mass ratio of Pd and Zn salts.When the weight ratio of melamine to lignin reached 10:1 and the molar mass ratio of Pd and Zn salts was 1:29,the highly-dispersed and small-sized Pd Zn NPs immobilized N-doped carbon catalyst(Pd/Zn₂₉@N₁₀C)was synthesized.It has good catalytic activity for Cr（VI）in the presence of FA reductant,which outperformed that of single Zn metal counterparts(Zn@N₁₀C)and commercial palladium carbon（Pd/C）with the same Pd loading,and also has a great advantage over the nitrogen free catalyst(Pd/Zn₂₉@C).The catalytic performance largely depended on the synergistic effect of Pd Zn nanoalloy and NC support.In addition,the Pd/Zn₂₉@N₁₀C catalyst also exhibited excellent cycling stability.Overall,this work has provided a simplified and feasible method for the preparation of highly active alloy catalysts,and has offered a new and efficient way to develop lignin-functionalized catalyst materials.