Preparation Of MgO-modified Biochar By Ball Milling For Applications In Adsorption And Catalysis

In recent years,the problem of environmental pollution caused by the improper disposal of a large number of agricultural wastes in the agricultural production process has become a difficult problem in the field of environmental governance.How to effectively deal with a large amount of agricultural waste and realize its resource utilization and energy utilization has become an important research direction in the environmental field.Straw,as the main agricultural waste,can be converted into biochar under certain conditions.However,the application of biochar is limited by its low active sites,and modification is an effective method to improve the performance of biochar in all aspects.The current modification method is mainly based on the impregnation method,which requires a large amount of solvent treatment and takes a long time.As an efficient,widely adaptable and environmentally friendly method,ball milling has been widely used in the preparation and synthesis of new materials.The application of ball milling in the field of bio-carbon modification has become an important research direction in recent years.In this paper,using rice straw as carbon source and magnesium acetate tetrahydrate（Mg（CH₃COO）₂·4H₂O）as modifier,MgO-modified biochar was prepared by solvent-free ball milling method,and its adsorption and catalytic properties were studied.Among them,the adsorption of phosphate in the aqueous phase was selected to study the adsorption performance,and the catalytic isomerization of glucose to fructose was selected to study the catalytic performance,which provided new ideas for biochar in the field of adsorption and catalysis.The research contents and main conclusions are as follows:（1）In this paper,the common agricultural waste rice straw was used as the carbon source,magnesium acetate tetrahydrate as the modifier,and the MgO-modified biochar was prepared by solvent-free ball milling method.MgO-modified biochars of magnesium acetate tetrahydrate and rice straw were prepared under different weight ratios,different ball milling times and different pyrolysis temperatures,respectively.The prepared different MgO-modified biochar materials were characterized by SEM,BET,XRD and XPS to study the influence of synthesis conditions on the morphology and chemical structure of biochar.The results showed that the ball milling treatment not only enabled the successful loading of MgO into the biochar but also significantly increased the specific surface area of the carbon material.（2）The MgO-modified biochar prepared above was applied to adsorb phosphate in the aqueous phase to study the adsorption performance.The MgO-modified biochar（2MgO/BC-450-0.5）was prepared when the weight ratio of magnesium acetate tetrahydrate and rice straw was 2:1,the calcination temperature was 450 ℃,and the ball milling time was 30 min.The most excellent phosphate adsorption effect,the adsorption capacity can reach up to 202.10 mg/g.The adsorption process of phosphate by 2MgO/BC-450-0.5 is in line with the pseudo-second-order kinetic model（R²>0.999）and the Langmuir model（R²>0.974）,respectively,indicating that the adsorption process of phosphate by this material mainly occurs in the monolayer on the surface of the adsorbent.Adsorption,in which chemical adsorption is dominant,thermodynamic experiments show that the adsorption process is a spontaneous（ΔG⁰<0）endothermic reaction（ΔH⁰>0）;at the same time,2MgO/BC-450-0.5 also has strong acid and alkali resistance（The adsorption effect is the best when pH=5）,strong anti-ion interference ability(HCO₃^->SO₄^2->NO₃^->Cl^-)and good recyclability.In addition,according to the characterization and analysis results,it can be concluded that the adsorption process of phosphate by 2MgO/BC-450-0.5 is mainly chemical process of protonation process,electrostatic attraction process and precipitation process.Overall,the low-cost,efficient,and recyclable 2MgO/BC-450-0.5 is a promising phosphorus adsorbent.The preparation of MgO-modified biochar by solvent-free ball milling has the advantages of simple preparation process,excellent adsorption performance and good reusability,which provides new ideas for the preparation of new modified adsorbents and their applications.（3）The MgO-modified biochar prepared above was applied to catalyze the isomerization of glucose to fructose to study the catalytic performance,and the fructose was rapidly produced by microwave assistance,and the highest fructose yield could reach35.54%（much higher than the average in this field Level）.MgO-modified biochar（0.5MgO/BC-450-0.5）when the weight ratio of magnesium acetate tetrahydrate and rice straw was 1:2,the calcination temperature was 450℃,the ball milling time was 30 min,and the reaction time was 120 min.,showing the best catalytic effect.Subsequently,systematic catalytic experiments were carried out on the modified material.The experimental results showed that even if a small amount of MgO was added,the catalytic effect was still significant.Therefore,the following experiments were carried out with the weight ratio of magnesium acetate tetrahydrate and rice straw as 2:1;The catalytic effect of 0.5MgO/BC-450-0.5 increases with the increase of reaction temperature,and it is worth noting that the catalytic effect is still significant at 80 ℃.In the optimization experiment,the fructose yield showed an upward trend with the addition of 0.5MgO/BC-450-0.5,and0.5MgO/BC-450-0.5 had a strong ability to tolerate high concentrations of glucose;The catalytic effect of 0.5MgO/BC-450-0.5 showed a trend of first increasing and then decreasing with the increase of ball milling time;0.5MgO/BC-450-0.5 had good recyclability,and was reused three times without obvious deactivation.It provides new ideas for the preparation of new modified catalysts and their applications.In this study,MgO-modified biochar was prepared by a solvent-free ball milling method and applied to adsorb phosphate in the aqueous phase and catalyze the isomerization of glucose to fructose,respectively.All showed excellent results.It provides a new method for biochar modification with green environmental protection and simple operation,and provides a new idea for the application of biochar modified materials.