Study On The One-Pot Synthesis Of MFe₂O₄ Functionalized Magnetic Biochars By The Sol-Gel/Pyrolysis Method And Their Adsorption Performance

Agroforestry solid waste can cause the eutrophication of water bodies,pathogenic pollution and the greenhouse effect.Nevertheless,converting the agroforestry solid waste into functional adsorbent materials has the effect of"treating waste with waste",which is conducive to the joint development of sustainable agriculture and the environment.The sol-gel process is a traditional wet chemical method that uses inorganic or metal-alcohol salts as precursors to produce a wide range of functional materials through hydrolytic condensation and gelation processes.In this study,a combination of the sol-gel method and pyrolytic carbonization was used to prepare low-cost,high-performance and easily separable biochar composites for the adsorption of diclofenac sodium（DCF）and phosphorus（IP）in water.The main studies and results are as follows:（1）A sol-gel/pyrolysis process was used to prepare MnFe₂O₄@SBC from sawdust biomass,which simultaneously enabled the loading of MnFe₂O₄nanoparticles and carbonization of the sawdust biomass.In comparison to sawdust biochar（SBC）without MnFe₂O₄-loading,MnFe₂O₄@SBC exhibits a well-developed honeycomb pore structure,abundant functional groups,and ease of separation.By comparing the adsorption effeciency,it was found that MnFe₂O₄@SBC consistently outperformed SBC and commercial activated carbon in the adsorption of DCF.Both pseudo-first-order and pseudo-second-order kinetic models could well describe the adsorption of DCF by MnFe₂O₄@SBC,revealing that the adsorption mechanism involved both physical and chemical adsorption,including hydrogen bonding,surface complexation,n-π/π-πEDA,hydrophobic and pore filling effects.The maximum adsorption capacity was obtained to be 352.17 mg/g for MnFe₂O₄@SBC by the Sips model.Furthermore,the prepared MnFe₂O₄@SBC exhibited satisfactory adsorption performance in water bodies containing commonly interfering ions,as well as in actual water samples.The"one-pot"sol-gel/pyrolysis method was simpler than the impregnation/pyrolysis and co-precipitation/pyrolysis methods,which can also achieve the uniform loading of nanoparticles on the biochar skeleton,and thus could be a promising means of biochar preparation.（2）Three magnetic biochar materials（Mg Fe₂O₄@PSBC,Mg Fe₂O₄@SSBC and Mg Fe₂O₄@PPBC）were prepared by the"one-pot"sol-gel/pyrolysis method using peanut shells,soybean straw and grapefruit peel as raw materials.In spite of the fact that the specific surface areas of the three carbon materials were similar,there were significant differences in the pore structure,the nanoparticle morphology,and the surface functional groups of the materials.According to the experiments investigating the effect of p H,all three showed the most effectively removal of IP at a p H of 3.0.Interfering ions such as SO₄^2-,CO₃^2-and HCO₃^-inhibited phosphate removal,with CO₃^2-exhibiting the strongest inhibitory effect.Based on the Sips model,the maximum adsorption capacities were predicted to be 41.97 mg/g,38.56 mg/g and 46.42 mg/g for Mg Fe₂O₄@PSBC,Mg Fe₂O₄@SSBC and Mg Fe₂O₄@PPBC,respectively.The thermodynamic study showed that the adsorption of IP on the three biochars was an endothermic absorption process,while the internal diffusion model and kinetic model fitting results indicated that boundary-layer diffusion,interparticle diffusion and chemisorption together dominated the entire adsorption process.The analysis of mechanism further revealed that IP adsorption was dominated by internal sphere complexation,electrostatic attraction,hydrogen bonding and pore filling.