Preparation Of Sawdust Activated Carbon By H₃PO₄ Hydrothermal Pretreatment And Dye Adsorption Study

As the depletion of energy and the deterioration of the environment,biomass resources with wide sources,low prices and renewable resources are increasingly favored.The use of biomass as a raw material for the preparation of activated carbon and adsorption of pollutants has become a research focus of scholars at domestic and overseas.The sapphire sawdust is chosen as raw material,the hydrothermal treatment is used during the process of preparing hydrothermal carbon.And then using activated carbon to prepare activated carbon.With the specific surface area as the optimization target,the influence of preparation conditions on the performance of activated carbon is investigated by single factor experiment.The feasibility of the process is verified through the experiments.On the basis of the above experiments,high-porosity activated carbon is prepared by hydrothermal pretreatment of phosphoric acid.The phosphoric acid solution and the sawdust mixture are put into a reaction vessel and activated by hydrothermal treatment at 200 °C.The specific surface area and pore volume are used as the optimization indexes.The influence of the preparation process on the performance of activated carbon is investigated by single factor experiments.The analysis of the mesoporous development of activated carbon shows that changing the acid ratio of the phosphoric acid pretreatment process and the subsequent activation temperature can significantly control the mesoporosity of the prepared activated carbon.The mesoporosity of the prepared sample reaches 96.6%,which indicate that the optimized process can prepare high mesoporosity activated carbon.The results of methylene blue adsorption on the prepared mesoporous activated carbon show that the Redlich-Peterson isotherm adsorption model fits to the experimental data best,which indicate that the adsorption of methylene blue by activated carbon is single-layer adsorption,and the maximum adsorption amount is 631.82 mg/g.Kinetic studies show that the adsorption of methylene blue by activated carbon is mainly chemical adsorption.The magnetic activated carbon which is easy to recover is prepared by chemical coprecipitation method using optimized mesoporous activated carbon as raw material.The BET results show that the prepared magnetic mesoporous activated carbon has a high specific surface area and a rich mesoporous structure.XRD and SEM results show that the magnetite is uniformly dispersed on the surface of the activated carbon with nano-sized particles(<200 nm).The adsorption isotherm indicates that the adsorption of MB by magnetic activated carbon was monolayer adsorption,and the maximum single layer adsorption is 429.47 mg/g.The adsorption behavior is dominated by chemisorption and is mainly affected by the valency adsorption force generated by the shared electrons between the MB and the adsorbent.Thermodynamic analysis shows that the adsorption process is spontaneous and endothermic.The prepared magnetic mesoporous activated carbon not only has excellent adsorption performance,but also has convenient recycling ability.Through the research on the preparation of high specific surface area and high mesoporous activated carbon by hydrothermal treatment of phosphoric acid and the study of adsorption behavior,the new ideas for the resource utilization of agricultural and forestry waste are expected to be provided in China.