Waste Polyester Textiles-based Activated Carbons Prepared By Templated Method Of MgO And Their Adsorption Of Cr(?)

With the rapid development of China's textile industry,a large quantity of waste textiles produced during the activities and production process of human beings have put forward higher requirements for environmental carrying capacity.Among them,waste polyester textiles have caused serious threat to the ecological environment because of its large production,complex chemical composition and imperfect treatment and disposal system.At present,the resource utilization methods still have the disadvantages of complex processing technology,low recovery rate and high operating cost,etc.In recent years,scholars at home and abroad have carried out the research on the preparation of activated carbon from waste textiles by pyrolysis activation.However,some problems such as secondary pollution and corrosion equipment were found in the usage of traditional activators.Therefore,green and efficient MgO template method was employed to prepare high surface area activated carbons from waste polyester textiles in this study.The optimum process parameters and influence of different Mg-containing compounds on the pyrolysis behavior characteristics of waste polyester textiles were clarified through the research on screening of MgO precursors,optimization of preparation conditions and pore-forming mechanism.Meanwhile,the optimal activated carbon was applied to the adsorption of Cr???.The adsorption performance and mechanism were evaluated and investigated systematically,which can provide certain basic theory for the practical application.The main research contents and results are as follows:?1?Different Mg-containing compounds were employed as the precursors of MgO to prepare waste polyester textiles-based activated carbons.Various characterization methods were achieved to analyze the physicochemical characteristics of different samples.The results showed that the porosity in the carbon matrix was improved significantly due to the addition of Mg-containing compounds.The specific surface areas of samples prepared by MgCl₂?1173 m²/g?and MgCi?1336 m²/g?were much higher than that by MgO?450 m²/g?,and the pores sizes of which were micro-mesoporous,mesoporous,and macropores,respectively,due to the formation of MgO crystal with different sizes.Meanwhile,Mg-containing compounds could promote the formation of graphite-like structures and oxygen functional groups on the surface,which were conducive to improving the surface reactivity of samples.In addition,the adsorption kinetic experiment showed that the adsorption of Cr???on three activated carbons exhibited a fast adsorption and slow equilibrium process.The adsorption performance of AC-MgCl₂ was the best,and the adsorption process was in accordance with the pseudo-second order model.?2?MgO-template method of using MgCl₂ as the template precursor was employed,and the response surface methodology coupled with Box-Behnken design?BBD?was conducted to determine optimized preparation conditions of waste polyester textiles-based activated carbons.The differences between the optimal sample and the sample prepared by traditional CO₂ activation method were compared through various characterizations.The results displayed that when the mixing ratio,carbonization time,and temperature were 5:1,90 min and 900°C,respectively,the specific surface area of activated carbon reached the maximum?1364 m²/g?.The error between the actual value and the predicted value?1315 m²/g?was less than 4%,which indicated that the fitting effect was significant.The most significant influence on specific surface area was the carbonization temperature,which was mainly attributed to the full release of the volatile matters from waste polyester textiles in higher temperature,thus promoting the formation of porous structures.The optimal sample was obviously superior to the sample prepared by CO₂ activation on specific surface area,mesoporous ratio and total pore volume.In addition,more turbostratic structure and oxygen-containing functional groups were found in optimal sample.?3?Mesoporous activated carbons synthesized by pyrolysis of waste polyester textiles mixed with MgCl₂,and the influences of different preparation conditions on the physicochemical properties of activated carbons were investigated by various characterization methods.Furthermore,the effect of MgCl₂ on the full-cycle pyrolysis pathway of waste polyester textiles was systematically investigated to explore the pore-forming mechanism of activated carbon.The results exhibited that higher pyrolysis temperature and appropriate MgCl₂ dosage were beneficial to the increase of surface area and porosity,meanwhile it could also promote the formation of the graphite-like structure and enhance the surface reactivity of activated carbon.In addition,pore-forming mechanism mainly includes:MgCl₂ inhibited the formation of tars through decarboxylic and dehydrogenation reactions,thus being beneficial to the formation of open pores structure;MgCl₂ possessed the catalysis ability for cross-linking reaction of WPT due to its Lewis acidity,which was favourable to the formation of carbonaceous materials during pyrolysis process;As a templating agent,MgO particles formed by pyrolysis of MgCl₂ were capable of forming porous wall on activated carbons.?4?The optimal sample was applied to the adsorption of Cr???,and the effects of different initial conditions on the adsorption process were studied.The results demonstrated that the adsorption efficiency increased with the decrease of initial pH and ionic strength,and the adsorption efficiency was the best when the values of pH and ionic strength were 2 and 0.002 mol/L,respectively.Adsorption process was in accordance with the pseudo-second order model,and the adsorption rate increased with the increment of the initial concentration.The adsorption isotherm accorded with the Freundlich model,indicating that the adsorption process was mainly multi molecular layer adsorption.The saturated adsorption amount reached 166 mg/g under 35°C.According to adsorption thermodynamics,the adsorption process was spontaneous endothermic reaction,and the adsorption behavior of Cr???on the surface of activated carbon increased the randomness of the system.The adsorption mechanism mainly included electrostatic adsorption,reduction of surface functional groups and ion exchange reaction.