Preparation Of Modified Multi-walled Carbon Nanotubes And Their Adsorption Of Mn(Ⅱ) In Solution

In recent years,the problem of excessive heavy metal Mn(Ⅱ)in various water bodies poses a serious threat to the health of organisms and ecological environment,and the research work on its removal methods has been attracting much attention.Adsorption is one of the main treatment techniques for removing heavy metals from water bodies,and with the development of technology,nanomaterials are increasingly used as adsorbents in the adsorption of heavy metals.In this paper,multi-walled carbon nanotubes MWCNTs were selected as the substrate materials and prepared with multiple modifications for the purpose of improving the adsorption performance of the materials on Mn(Ⅱ)and the corrosion resistance under acidic conditions;then experiments on the adsorption performance of various modified materials on Mn(Ⅱ)were carried out;the adsorption mechanism of the multiple modified materials was investigated by combining the performance characterization results and thermodynamic and kinetic simulation calculations;finally,an artificial neural network model was developed to fit and predict the main adsorption experimental data in the study,thus ensuring the reliability of the research work.The main conclusions are as follows:(1)On the basis of two materials,AO-WMCNTs were prepared by mixed acid oxidation modification and FCHAP were prepared by fluorocarbon-doped modified hydroxyapatite,the oxidized carbon nanotube-loaded fluorocarbon hydroxyapatite(FCH/AO-MWCNTs)composites were prepared by in situ synthesis method.The instrumental characterization results showed that the FCHAP on the composites mainly grew at the ports and bends of AO-WMCNTs,and the two supported each other to form a richer pore structure;the dispersion and stability of FCH/AO-MWCNTs in aqueous solution were significantly better than those of AO-WMCNTs and FCHAP.(2)A comparative static adsorption experimental study of the performance of the matrix materials MWCNTs and the modified three materials-AO-WMCNTs,FCHAP,and FCH/AOMWCNTs in the adsorption of Mn(Ⅱ)in aqueous solution was conducted,and the results showed that the maximum adsorption amounts of the four types of materials were 0.585 mg/g,5.77 mg/g,250.0 mg/g and 317.5 mg/g;the adsorption of Mn(Ⅱ)by FCH/AO-MWCNTs reached equilibrium after 8 h.The contact time,initial concentration and temperature in the system all had effects on the removal of Mn(Ⅱ),among which the p H value had a greater effect on the removal effect.(3)The adsorption kinetic and thermodynamic models were established based on the adsorption experimental data,and the simulation results showed that the fitted adsorption kinetic data of each modified material were in accordance with the quasi-secondary kinetic model,which indicated that the adsorption of Mn(Ⅱ)by the modified materials were mainly controlled by the chemisorption process.The fitting results of the thermodynamic model showed that the Langmuir model fitted better with the isothermal adsorption experimental data,and the adsorption reaction proceeded spontaneously,and the increase of temperature was not favorable to the adsorption reaction.The adsorption process mainly includes ion exchange,surface complexation,precipitation dissolution and physical adsorption.(4)The experimental data of Mn(Ⅱ)adsorption process of each material(MWCNTs,AOMWCNTs,and FCH/AO-MWCNTs)were modeled and predicted by building a neural network model,PSO-BP model.Through training,testing,validation and combined calculation of each model,the fitted correlation coefficients of each model with the original experimental data were higher than 0.95,and the average absolute percentage errors were lower than 10 %,which further confirmed the reliability of the experimental work and provided a new research idea for the quantitative study of adsorption experiments and online control of process operation.