Preparation Of Modified Straw Biochar And Its Performance In Removing Microplastics From Water

Straw is a kind of renewable biomass resource that can be used to produce biochar through pyrolysis.Biochars are known for their large specific surface area,rich surface functional groups,and low cost,making them effective for treating water pollutants.Microplastics（MPs）are a new type of water pollutant that poses a significant threat to aquatic organisms and human health due to their biological toxicity and ability to adsorb heavy metals,antibiotics,persistent organic pollutants.The application of biochar to water treatment promotes the resource utilization of straw.In this study,we prepared a series of biochar from different types of straw by pyrolysis,and investigated the effects of pyrolysis temperature on the physicochemical properties of biochar.Furthermore,we studied the performance of hexadecyl trimethyl ammonium bromide（CTAB）modified magnetic biochar for removing microplastics from water,and clarified the mechanism of removing microplastics from water.The main results of this study are summarized as follows:1.A series of biochar were prepared at pyrolysis temperatures of 350,500,650,and 800°C,including rape stalks（YCJG）,corn stalks（YMJG）,and reed stalks（LWJG）et al.The biomass carbonization process can be divided into three stages:dehydration,pyrolysis,and slow carbonization.As the pyrolysis temperature increased,the yield and surface oxygen-containing functional groups of biochar decreased,while ash content,p H,and electrical conductivity increased.The surface areas of biochar were mainly affected by the type of feedstock and pyrolysis temperature.The specific surface area,total pore volume,and pore size of biochar prepared from the same feedstock were positively correlated with the pyrolysis temperature.Among the biochar samples prepared,the rape stalks biochar（YCJG-800）prepared at 800°C had the largest specific surface area（616.6 m²/g）.2.CTAB modified magnetic biochar（CMB）was prepared from YCJG-800.the removal efficiency of polystyrene（PS）and carboxylate-modified polystyrene（CPS）by CMB was 95.2%and 91.2%,respectively.The efficiency of CMB in removing microplastics was influenced by several factors,including the CMB dosage,the concentration of microplastics,the p H value of the solution,and the concentration and type of interfering ions.The removal efficiency of microplastics increased with the CMB dosage,while first increased and then decreased with the increase of microplastics concentration and the p H value of the solution.K⁺,Mg²⁺and Ca²⁺exerted little effect on the removal of PS.In contrast,the CPS removal efficiencies were decreased in the presence of K⁺,Mg²⁺and Ca²⁺.The inhibitory effects of H₂PO₄^-on removal efficiencies of PS and CPS were stronger than Cl^-,HCO₃^-and SO₄^2-.Moreover,when used to remove PS/CPS from lake water,the removal efficiency of both PS and CPS remained higher than 90%after 5 cycles of recycling.3.Acid washing treatment could effectively remove impurities from the surface of biochar,increase the specific surface area,and facilitate the loading of Fe₃O₄ and CTAB.Fe₃O₄ nanoparticles were uniformly dispersed on the surface of biochar,enabling CMB to possess magnetic separation properties with a saturation magnetization of 5.00 emu/g.CTAB modification enhanced the hydrophobicity of magnetic biochar,and then improved the interaction between CMB and PS/CPS.The microplastics were destabilized by CMB,and then aggregated and floated to the surface of the solution.Therefore,PS and CPS were removed by CMB from water mainly through aggregation instead of adsorption.