Study On Preparation,Properties And DGT Application Of Adsorption Materials For Fluoride Anions In Water

With the development of urban industrialization and the destruction of ecological system,the global environmental problems have attracted the attention of human beings.Among them,water pollution is an urgent problem to be solved.Therefore,it is the research direction of many scholars to monitor and detect ions in water.the diffusive gradient in film（DGT）technology can effectively detect and monitor trace ions in many systems,such as water solution,soil and sediment.Most importantly,the binding phase is the key component used to detect the ions.The main work of this chapter is to prepare and develop new adsorption materials,then to explore their removal ability of fluoride anions in water.Furthermore,these adsorbents were applied to DGT technology as a combination of DGT to study the monitoring performance of trace fluoride anions in water.（1）Excessive fluoride anions in drinking water are toxic to the health of human beings.In this chapter,an effective adsorbent based on amino-functionalized polydivinylbenzene（PDVB）was synthesized through low cost processes,which included solvothermal preparation of porous PDVB and subsequent surface amino-functionalization.The obtained amino-functionalized porous PDVB（A-PDVB）has high surface area of 443 m²·g^-1and high adsorption capacity towards fluoride anions up to 41.6 mg·g^-1higher than that of original PDVB(105.9 mg·g^-1).Considering adsorbents’surface area,the adsorption capacity per unit surface area of A-PDVB is 0.24 mg·m^-2four times higher than that of PDVB(0.058 mg·m^-2).The enhanced adsorption performance of A-PDVB was due to amino groups electrostatic interaction coupled with hydrogen bond binding with fluoride anions.In addition,the amino-functionalized porous PDVB could be regenerated in high efficiency under alkaline conditions.This work not only exhibits the possibility of A-PDVB for application as an environment-friendly adsorbent for fluoride anions removal but also gives an insight into understanding mechanism of the fluoride anions adsorption onto amino-functionalized porous PDVB.（2）The precursor of Mg O was synthesized by solvothermal method,and the Mg O was obtained by calcining in vacuum tube furnace under air condition.The Mg O is a micro nano structure oxide.As the common oxides are easy to synthesize,low cost and high adsorption efficiency,so they are widely used in water pollution treatment.In this chapter,Mg O powder is hollow sphere.The structure is uniform and the morphology is regular.The Mg O gel made from Mg O powder was prepared by classical method.Then,Mg O gel was used to adsorb the fluoride anions in the water,in order to study the adsorption mechanism of fluoride anions.The effect of different p H on the adsorption of fluoride anions is also discussed.The results showed that at p H=4～8,the adsorption process quickly reached equilibrium.p H had no obvious effect on fluoride anions adsorption by Mg O gel.At p H=4,the adsorption capacity reached the maximum,indicating that Mg O gel can towards fluoride anions in this range.Then the Mg O gel was used as the binding phase of DGT to study the detection of trace fluoride anions in water.The results show that different p H and ionic strength have little effect on DGT.It can effectively detect the concentration of fluoride anions in water.The adsorption of fluoride anions by Mg O is mainly through the exchange of OH^-on the surface of the adsorbent and fluoride anions in the water.In the alkaline condition,the OH^-will compete for the adsorption site with the adsorbent,so the adsorption capacity is large in the acid condition.（3）New C（C1,C2,C3,C4）of amino group were obtained by low-temperature plasma modification under different conditions.Then,SEM and FTIR were used to investigate the morphology and structure of the material,and the best conditions of low temperature plasma modification were explored.Finally,biochar before and after modification was used for adsorption experiment.The results of kinetic experiments show that the adsorption of the material is closer to the pseudo-second-order model and belongs to chemical adsorption.However,C material is porous and has large specific surface area,which can also absorb fluoride anions.The whole adsorption process has both physical adsorption and chemical adsorption.However,the more obvious reason for the effect of amino modified biochar is not only the adsorption mechanism of the original biochar material,but also the electrostatic effect of amino and fluoride anions and the result of hydrogen bonding.