Study On The Preparation Of Pistia Stratiotes Biochars And Its Sorption Removal Of Diethyl Phthalate In Water

As an emerging pollutant,Phthalic acid ester（PAEs）,have generally existed in the environment,especially in the water environment,and have attracted much attention because of their teratogenicity,carcinogenicity and mutagenicity and they can easily enter into the human body through the food chain.Therefore,the removal of PAEs in the environment has become a research hotspot.sorption is widely used to remove pollutants due to its simple,efficient and environmentally friendly method.Biochar is a carbon-rich product generated by thermal cracking of biomass under the oxygen-limited conditions.It has the characteristics of porosity,large specific surface area,and rich functional groups.It has been widely used in various fields,especially showing good application prospects in terms of the sorption and fixation of various pollutants.However,the performance of biochar depends on the choice of biomass feedstock.Pistia stratiotes,as an invasive plant,has severely endangered the ecological environment due to their insane reproductivity.However,as a kind of biomass,high-value utilization is in line with the concept of sustainable development.In this study,Pistia stratiotes was selected as the raw material for the preparation of biochar,porous biochar and magnetic porous biochar through thermal cracking at the different temperatures,the co-carbonization of KOH and different precursors,and the co-precipitation of Fe²⁺/Fe³⁺while investigating their sorption properties and mechanism of diethyl phthalate（DEP）widely exists in aquatic environments and was used as the model PAEs.This provides a new solution for the two major environmental problems in water:the flooding of Pistia stratiotes and the pollution of organic matter,and also provides a new idea for the resource utilization of invasive plants.The main findings are as follows:（1）Pistia stratiotes was directly pyrolyzed at 400,500,600 and 700℃into nitrogen-doped Pistia stratiotes biochars without adding nitrogen-containing reagents.Characterization of nitrogen-doped Pistia stratiotes biochars by SEM,elemental analysis,XPS,Raman spectroscopy and FTIR tests,the characterization results show that the specific surface area and pore volume of nitrogen-doped Pistia stratiotes biochars were significantly increased(2.2 m² g^-1 to 126.72 m² g^-1 and 0.011cm³ g^-1 to 0.042 cm³ g^-1)with the increase of pyrolysis temperature,providing more sorption sites for pollutants.Meanwhile,nitrogen-doped Pistia stratiotes biochars have high nitrogen content（2.02%–2.66%）,abundant surface functional groups,hydrophobicity,and graphene structure.Furthermore,nitrogen-doped Pistia stratiotes biochars have high ash content（24.7%～34.1%）.The sorption capacity of nitrogen-doped Pistia stratiotes biochars for DEP is very high,especially the NB700 produced by pyrolysis at 700°C,the sorption performance for DEP is as high as 161.7 mg g^-1,which is better than many reported sorption agent.According to the sorption kinetics and isotherm results,the Pseudo-second-order model and the Freundlich model fit the experimental data well,indicating that the sorption of DEP by nitrogen-doped Pistia stratiotes biochars is a multiple sorption process,intraparticle diffusion and Dubinin-Radushkevich models suggest that porous packing and partitioning dominate the process of DEP sorption onto nitrogen-doped Pistia stratiotes biochars,hydrogen bonding,Lewis acid-base interaction,functional group interaction,cationic-πinteractions andπ-πstacking interactions as possible rate-limiting steps for chemisorption.This study converts invasive plant biomass into biochar for efficient environmental remediation,provideing a new method for the resource utilization of invasive plants.（2）Optimizing the pore structure helps to improve the sorption performance of biochar to DEP.Three kinds of porous Pistia stratiotes biochars（RPB,HPB,and BPB）were prepared by co-carbonizing Pistia stratiotes-derived precursors（biomass,hydrochar and biochar）with KOH,and use them to sorb DEP from aqueous solutions.RPB,HPB and BPB were found to have high specific surface area and pore volume by N₂-sorption/desorption,SEM,elemental analysis and Raman spectroscopy characterization,the characterization results show that RPB,HPB and BPB have high specific surface area and pore volume,as well as high hydrophobicity and graphene structure,which can improve the ability of biochar to adsorb DEP,especially the porous biochar prepared by the hydrochar as precursor,showing a better performance in terms of specific surface area(2284.4 m²g^-1),pore volume(0.683 cm³ g^-1),hydrophobicity and oxygen-containing surface functional groups,and representing the highest sorption capacity of 813 mg g^-1(DEP The equilibrium concentration is25 mg L^-1).After 4 cycles of recycling(the initial concentration of DEP is 20 mg L^-1),the sorption removal rate of DEP is still as high as 95.34%.Sorption kinetics and isotherm experiments show that the pore filling and partitioning dominate the sorption capacity,while mass transfer,hydrogen bonding,andπ-πstacking limit the sorption rate.This study helps to propose a feasible method for the efficient utilization of invasive plants and provides new insights into the selection of precursors for the preparation of porous biochars.（3）In order to realize the rapid recycling and utilization of biochar,based on the porous Pistia stratiotes biochars as the background material,the magnetic porous biochar was rapidly prepared by co-precipitate with Fe²⁺/Fe³⁺mixed salt.EDX,XRD,FTIR,XPS and hysteresis loops indicated that Fe₃O₄ was successfully loaded on the biochar.With the increase of Fe²⁺/Fe³⁺mixed salt content,the specific surface area of the magnetic porous Pistia stratiotes biochars gradually decreased,especially MB0.5,its specific surface area decreased significantly(718.01 m² g^-1),but much higher than other magnetic sorption,which provides more sorption sites for the sorption of DEP.The Pseudo-second-order model can better fit the sorption kinetics,indicating that chemisorption is the rate-limiting step.The Sips model can better fit the sorption isotherm process,indicating that the sorption process is multiple and energy non-uniform,conforming to the Freundlich model at the low concentration stage,and then following the Langmuir process as the DEP concentration increases.Using magnet canquickly recover the magnetic porous biochar.After 4 cycles of recycling,it is found that the magnetic porous biochar has magnetic properties and DEP sorption stability(the sorption capacity of MB0.5,MB1,MB2 and MB4 respectively were 261.95,324.45,351.69 and 356.89 mg g^-1,the initial concentration of DEP was 15 mg L^-1).This research realizes the rapid recovery and reuse of synthetic materials and reduces waste of resources.It is expected to be applied to practical sewage treatment and is worthy of promotion.