Preparation Of Functional Fibers With Microwave Assisted Method And Its Adsorption Performance And Mechanism For Heavy Metal Ions

Currently,there are some technique issues in dealing with sudden heavy metal pollution incidents in water.In order to sovle this problem,it is of important significance to develop noval functional material for the rapid detection and removal of heavy metal ions in water.Traditional method for the preparation of functional materials is commonly regarded as conventional heating method,which has sophisticated preparation route,long preparation time and high energy consumption.Due to the fact that arsenic and mercury ions in environment received more attentions and they were chosen as target ions in our study.In this paper,microwave assisted method has been appliedforthepreparationofcellulose-basedfunctionalfibersand polyacrylonitrile-based functional fibers,and adsorption performances of these two functional materials for arsenic and mercury were systematically studied.Furthermore,the adsorption and detection mechanism for arsenic and mercury were investigated thoroughly,and the removal effect for mercury ions were explored and simulated with fixed bed adsorption process,which could provide technical support for effective dispose of heavy metal pollution in water.A mutil-amino modificated cellulose-based functional material was rapidly prepared under microwave assisted synthesis method by using cellulose fibers as the matrix material,epichlorohydrin as the etherifying agent and polyethyleneimine as the animation reagent.Both single factor and orthogonal experiment were applied for the optimization of microwave assisted preparation condition.The functional fibers were characterized by infrared spectroscopy,elemental anaylsis and scanning electron microscope,and the adsorption performances for arsenic were systematically investigated.Results indicated that the concentration of polyethyleneimine and reaction time were key factors for the preparation of adsorbents.The adsorption amount of cellulose-based functional fibers for arsenic were relative highly influenced by pH value of the solution,and the maximum adsorption amount for the uptake of As???and As???were found to be 81.35 mg/g and 53.03 mg/g,respectively.Regeneration of functional fibers loaded with arsenic was efficienctly done with HCl,by which the investigated adsorbent could be used reproductively for five times with no significant decrease in sorption capacity.The mercury adsorptive functional fibers were prepared with microwave assisted synthesis method by using polyacrylonitrile fiber as the matrix material and sodium sulphide as the modification reagent.Response surface methodology was applied to optimize the preparation condition,and as prepared functional fibers were characterized with infrared spectroscopy,elemental analysis,scanning electron microscope,mechanical strength analysis and x-ray diffraction method.Furthurmore,the adsorption performances of functional fiber material were tested.Results indiated that the adsorption amount and mechanical strength of functional fibers prepared with microwave assisted method were higher than those prepared through with conventional heating method.When pH=7 and the adsorbent dosage is 0.10 g/L,the functional fibers has the maximum adsorption capacity for mercury ions at 345.2 mg/g.In the presence of Pb²⁺,Cu²⁺,Zn²⁺and Ni²⁺in the solution,the functional fibers still show relatively high adsorption amount for Hg²⁺ions.The functional fibers were desorbed with 0.05 M HCl with the 65.1%desorption rate within 30 min.The recognition functional fibers for mecury were prepared under microwave assisted synthesis method by using polyacrylonitrile fiber as the matrix material and4-?2-pyridylazo?-resorcinol as the modification reagent.The orthogonal experiment was applied for the optimization of microwave assisted conditions and the as prepared functional fibers were characterized by infrared spectroscopy and X-ray photoelectron spectroscopy.Additionally,the adsorption performances of functional fiber material were tested.Results demonstrated that functional fibers prepared by microwave assisted method exhibited better recongnition performance than those prepared with conventional heating method.At pH 3.0,the functional fibers revealed selectively colorimetric effect in Hg²⁺solution,and the coexistence of other metal ions showed slightly influence for the detection of mecury ions.The color change of functional fibers in Hg²⁺solution was fast,and the distinct color change could be visualized with naked eyes in 5 s.The detection limit for Hg²⁺was found to be 10^-5mol/L.In addition,the colorimetic effect of functional fibers changed slightly in 10 successive reuse.The UV-vis spectra and x-ray photoelectron spectroscopy analysis results for mercury recongnition process indicated that after binding with Hg²⁺,the maximum adsorption peak of functional fibers was bathochromic shifted from 402 nm to 520 nm,and both nitrogen and oxygen ions within functional fibers were involved in the incorporation process for mecury ions.The adsorption process for arsenic with cellulose-based functional fibers was fitted with models and the results revealed that pseudo-second-order kinetic and Langmuir isotherm model provided good correlation for the adsorption process,and the adsorption of arsenic onto the functional fibers is believed to be monlayer chemisorption.XPS analysis results showed that protonation of amine within the functional fibers is the main mechanism for the adsorption process.The nagtive charged AsO4^3-and AsO3^3-ions were adsorbed onto the fibers through anion exchange effect.In addition,the adsorption process for mercury with polyacrylonitrile-based functional fibers was fitted with models and the results revealed that pseudo-second-order kinetic show the cloest fit to the adsorption data,which indicated that chemisorption is the controlling mechanism.The nonlinear resolution of Langmuir isotherm equation has been found to give better correlation which demonstrate monolayer adsorption is dominant.XPS analysis results confirmed that the adsorption of mercury was attributed to the chelation effect between sulfur and Hg²⁺ion.In order to simulate the dynamic adsorption process in practical application,the fixed bed adsorption techonology equipment was designed,and the influence parameters including initial concentration,bed depth and flow rate on the removal efficicency were investigated.Three different dynamic adsorption models were applied to fit the adsorption date.And the results revealed that both Thomas model and Yoon-Nelson model fitted well with dynamic adsorption amount and 50%breakthrough time in terms of three influential conditions.Furthurmore,BDST model could estimated the breakthrough time of the fixed bed when the intial concentration or inlet concentration changed.