Construction Of Sodium Alginate-based Macroscopic Material And Adsorption Of Dimethyl Phthalate In Water

Phthalic acid esters（PAEs）are hydrophobic organic compounds that are used primarily as polymer additives to improve plasticity in plastics.Dimethyl phthalate（DMP）is one of the most common PAEs,which is mainly linked to the plastic matrix by hydrogen bonds or van der Waals forces and can easily leach into the water environment.Therefore,it is important to find out how to effectively remove DMP from water.The preparation of porous carbon materials for DMP adsorption in water has the advantages of simplicity,high efficiency and low cost.However,most of the porous carbon materials studied so far are in powder or granular structure,and the adsorption process is difficult to be completely separated from water,which will not only cause waste of resources,but even cause secondary pollution.Therefore,it is urgent to realize the macroscopic porous carbon materials by a simple method.（1）Sodium alginate-based macro materials were prepared by one-step pyrolysis using sodium alginate as the carbon precursor and K₂CO₃ as the activator.The best morphology and adsorption capacity of the fabricated macroscopic material（C800-2）were obtained when the mass ratio of K₂CO₃ to sodium alginate was 2:1 and the tube furnace temperature was at 800℃.The adsorption of DMP by C800-2 was more consistent with the proposed secondary kinetic model and Langmuir isothermal model,and DMP was mainly adsorbed on the surface of C800-2 as a monolayer cover.The isothermally fitted saturation adsorption capacity at 313 K was614.98 mg/g.Thermodynamic studies revealed that the adsorption of DMP on C800-2 was a spontaneous heat absorption process dominated by physical adsorption.The anti-disturbance experiments and regeneration experiments showed that C800-2 had good stability and regeneration performance.（2）To further improve the adsorption properties of the macroscopic materials,ammonium polyphosphate was introduced as a nitrogen-phosphorus dopant for the preparation of N/P co-doped sodium alginate-based macroscopic materials by one-step pyrolysis.The N/P co-doped sodium alginate-based macroscopic materials（C/N/P-0.3）synthesized at 800°C with the mass ratio of K₂CO₃:sodium alginate:ammonium polyphosphate of 1:1:0.3 had the best macroscopic morphology and adsorption properties.The adsorption experiments showed that the saturation adsorption capacity of C/N/P-0.3 for DMP reached 771.10 mg/g at 313 K,which was 25.39%higher compared to C800-2.The adsorption of C/N/P-0.3 for DMP was more consistent with the proposed secondary kinetic model,and the applicability of the Freundlich isotherm model indicated that C/N/P-0.3 has a heterogeneous surface.The adsorption process was a spontaneous heat absorption process based on physical adsorption,and C/N/P-0.3 also had excellent stability and regeneration performance.（3）To further investigate the properties of sodium alginate-based macroscopic materials,the materials were characterized by SEM,BET,XPS and FTIR to reveal the mechanism of its adsorption effect on DMP.SEM analysis showed that the addition of activator K₂CO₃ enriched the pore structure of the carbon materials,the doping of ammonium polyphosphate was more favorable to the generation of defects and active sites during the activation process,and the acid washing process further increased.The specific surface area and total pore volume of C/N/P-0.3 were 1.30 and 1.34 times higher than those of C800-2,respectively.The presence of mesopores played an important role in enhancing the adsorption capacity of the carbon material,and the addition of low-dose ammonium polyphosphate was beneficial to the formation of multi-level pore structures.The successful incorporation of N/P elements not only created more active sites for DMP adsorption and synergistically improved the adsorption performance of carbon-based materials,but also enhanced the mechanical properties and thermal stability of macroscopic materials.Potential adsorption mechanisms of DMP on macroscopic materials were attributed to micropore filling,π-πEDA interactions,hydrophobic interactions and hydrogen bonding interactions.This study provides a new idea for the preparation of porous carbon macroscopic materials and opens the way for further research and practical application of DMP adsorption on porous carbon.