Enhancing Fluoride Adsorption And The Interfacial Effect On Aluminum-based Two-dimensional Material Containing Hydroxyl Group

Industrial wastewater containing fluoride not only threatens human beings’ lives,but also pollutes the ecology and environment.Because of the easy operation,low cost and strong affinity of fluorine,the treatment of fluoride-containing wastewater by aluminum-based(Al-based)adsorption materials has received high attention,and has been widely used in developing countries,especially in Asia,Africa and Latin America.The adsorption mechanism was extensively explored,such as electrostatic attraction and ligand exchange reaction,which provided theoretical and technical support for the structural design and performance strengthening of Al-based materials.It still remains some problems,such as a low adsorption performance and a high cost of modification,which restrict the adsorption technique promotion.Buliding an excellent adsoption performance is the key to the interaction of adsorbent and F-.In this paper,based on the systhesis of Al-based Layered Double Hydroxides(LDHs),a two-dimensional architecture material was prepared,with focusing on the metal ion and anionic doped interface characteristics,and exploring those changes in the interface properties(e.g.distribution of charge,hydroxyl groups density,chemical coordination environment,and the accepting electrons ability).The interface activity effects on different F-phase were investigated,and it was found that the hydrogen bond via F--Co-Al LDHs interaction is an effective method to improve F-adsorption,with realizing the quantitative analysis of F-adsorption behavior at interfacial media.How to enhance the interaction of F-and Al-based adsorbent interface was put forward preliminarily.Co-Al composition was synthesized to perform a high F-adsorption capacity.It provided theoretical and technical support for the Al-based materials design,preparation and application to achieve a high F-adsorption capacity.The main results are as follows:(1)The metal ion effects on among Al-based material structure,the electron distribution and coordination environment were investigated.What could improve F-adsorption performance by doping metal ion was analyzed,and it proved that doping metal ion method was able to change the chemical activity of Al-based adsorbent by DFT calculations.Cobalt is an effectively active component of LDHs to enhance the defluorination performance firstly,after electrostastics attraction and chemical activity calculations.we confirmed Co element not only acts as the electron acceptor from F-,but also plays a pivotal role in building a weaker-ligand environmental around Al3+ to promote the electron-attraction ability of Al atoms with π-donation on Co-OH bond,with strengthening the interaction of hydroxyl and F-via hydrogen bond;(2)We measure the releasing number of hydroxyl groups and Fadsorption number,and analyzed how both the releasing behavior of hydroxyl groups and F-adsorption process were affected by three factors:pH values and the species of anionic ligand.It was easily found that surface coordination effect led different defluorination mechanism.Therefore,we established the relationship between surface coordination effect and different defluorination performance.Particularly,increasing the accepting electron capacity of Al-OH structure is a promising strategy for the design and synthesis of defluorinated material.(3)We calculated and drew the E-pH mapping of F--H2O system at F-concentration of 0.3-1.0 mol·L-1.We also globally searched the F--H2O system cluster for different F-phase using artificial bee colony algorithm method,before optimized by DFT calculations.The appropriate hydration of F-and HF2-were 4,and the appropriate hydration of HF was 3.The interaction relationship and electron transferring between different F-phase and H2O were revealed.Based on DFT calculations and experimental evidences,we also studied how different F-phase was confined in the interlayer of LDHs,the order of strong interaction as following:HF>HF2>F-,with different interaction mechanism determining:the electrostastics attractions on HF by Co2Al-Cl mainly,and the hydrogen bond between F/HF2-and C02Al-Cl mainly.We also explain the role of H2O played when different F-phase confined in the interlayer of LDHs.(4)An effective and facile Co2Al-Cl-10 was systematically designed and synthesized for F-removal with the F-adsorption capacity reaching 122.54 mg·g-1,which is significantly higher than common Al-based LDHs.The adsorption mechanism and behavior were investigated using DFT calculations and characterizations.We also demonstatred Co2Al-Cl-10 was an environmentally friendly adsorbent in a wide pH range and a high F-concentration treatment.