Preparation Of Sodium Alginate-Based Porous Carbon For The Adsorption Of Bisphenol A In Water

Bisphenol A(BPA)is a typical endocrine interference compound,which has been widely used to make polycarbonate,polymer plastic,epoxy resin,and other plastics.Due to its low biodegradability,BPA has high chemical degradation capability even at low concentration,which causes destruction of endocrine system and brings toxicological risks to animals and humans.Therefore,adsorption and removal of BPA in water environment is very urgent.Adsorption method is widely used to remove phenols in water environment because of its simple operation,low cost and simple equipment.Porous carbon materials are considered as the most promising adsorbents because of their highly dense pore structure,large specific surface area,adjustable pore structure,abundant raw materials and easy access.Therefore,it is necessary to prepare porous carbon materials with excellent performance by adopting simple and convenient preparation methods and developing and utilizing high-quality renewable carbon sources.Sodium alginate is a kind of natural macromolecular organic matter extracted from Marine algae,which contains a large amount of fixed carbon.In this paper,it is a carbon source,which adopts different activation and modification methods to obtain sodium alginate based polyporous carbon with excellent adsorption performance through one-step pyrolysis.SEM,BET,XPS,FT-IR,XRD,TG and VSM were used to characterize and analyze the adsorption behavior of BPA in water.Specific research content and conclusions were as follows:(1)With sodium alginate as carbon source and K2CO3 as activator,we investigated the effects of pyrolysis temperature and mass ratio of sodium alginate to K2CO3 on adsorption performance,and the optimum experimental preparation conditions were determined at 800℃and 1:1 mass ratio of sodium alginate to K2CO3.The product(SAC-1)obtained under this condition was characterized and adsorbed.The results showed that SAC-1’s specific surface area was 1073.40 m2·g-1 and pore volume was 0.585 cm3·g-1,and its carbon and oxygen content reached 91.66%and 7.77%respectively.The adsorption process of SAC-1 for BPA was more in line with Langmiur isothermal model and pseudo-second-order kinetics.At 308 K,the saturated adsorption capacity(Q.)of SAC-1 reached 632.91 mg·g-1.Thermodynamic fitting showed that the adsorption process was spontaneous and endothermic.The regeneration experiment showed that the adsorption capacity was only reduced by 22.94%after five cycles of regeneration experiments.The efficient adsorption of BPA by SAC-1 was attributed to the physical adsorption of microporous packing.It showed that porous carbon materials with excellent properties can be prepared by a simple one-step method,and sodium alginate is a promising carbon precursor material with broad application prospects.(2)In order to further improve the adsorption performance of porous carbon,N-doped sodium alginate-based porous carbon materials were prepared by one-step method with melamine as N source on the basis of the previous experiment.The porous carbon SAC/N-0.2 prepared with the mass ratio of sodium alginate:K2CO3:melamine of 1:1:0.2 had the best adsorption performance for BPA by adjusting the N-doping ratio.The results illustrated that the content of N in SAC/N-0.2 is 2.24%,mainly pyridine-N and pyrrole-N,and its specific surface area(2017.98 m2·g-1)and pore volume(1.23cm3·g-1)were nearly double those of SAC/N-0,which indicated that in the pyrolysis process of melamine,not only N element was successfully doped into porous carbon,but also played an active role in pore formation.Langmiur isothermal model and pseudo-second-order kinetics were more suitable to express the adsorption behavior of SAC/N-0.2 for BPA.At 308K,its Qm reached 1180.02 mg·g-1,and the adsorption equilibrium can be reached in only 30 minutes.Thermodynamics hold that the adsorption process was a spontaneous endothermic process dominated by physical adsorption.SAC/N-0.2 still maintains stable and efficient adsorption of BPA in a wide pH range,under the interference of different metal ions and natural organic substances.The regeneration experiment showed that the adsorption capacity decreased by 31.74%after four cycles of desorption experiments,showing good regeneration performance.The main adsorption mechanism was pore filling,and the existence of pyridine-N and pyrrole-N enhanced the hydrogen bonding force between SAC/N0.2 and BPA.It can be seen that SAC/N-0.2 with fast adsorption kinetics,ultra-high adsorption capacity and good regeneration performance has great application value in sewage treatment.(3)In order to quickly realize solid-liquid separation and improve the recovery rate of porous carbon,magnetic N-doped sodium alginate-based porous carbon materials were successfully prepared by one-step method by introducing Fe(NO3)3·9H2O,based on the experimental conditions in the first two chapters.SAC/N/Fe-0.2,which had both high adsorption capacity and good magnetic separation effect,was selected for subsequent experiments by optimizing the addition ratio of Fe(NO3)3·9H2O.XRD,XPS and FT-IR results showed that Fe3O4 nanoparticles attached to the carbon surface during the pyrolysis of Fe(NO3)3·9H2O,which made the surface of SAC/N/Fe-0.2 uneven and increased its specific surface area(2240.65 m2·g-1)and pore volume(1.44 cm3·g-1).The results of hysteresis loop(VSM)proved that SAC/N/Fe-0.2 is a soft magnetic material with low coercivity and high permeability.The adsorption experiment results showed that the Qm of SAC/N/Fe-0.2 for BPA was as high as 1248.23 mg·g-1 at 308K.Langmiur isothermal model and pseudo-second-order kinetics can express the adsorption behavior more accurately.Thermodynamics showed that the adsorption process was mainly physical adsorption and spontaneous endothermic process.According to some interference factor experiments and regeneration experiments,SAC/N/Fe0.2 had good acid and alkali resistance,strong stability and good regeneration performance,while SAC/N/Fe-0.2 had magnetic separation function,which greatly improved the recovery efficiency.The main adsorption mechanism of SAC/N/Fe-0.2 for BPA was micropore filling,and there were some hydrogen bonds,π-πEDA interactions,Van der Waals forces,hydrophobic interactions and electrostatic interactions.In summary,SAC/N/Fe-0.2 is expected to be applied to practical wastewater treatment on a large scale due to its excellent adsorption performance.The research results provided a theoretical basis for the development and application of porous carbon materials.