Design Of Functionalized Layered Double(Hydr) Oxides And Their Performance On Sequestration And Advanced Oxidation Processes For Environmental Pollutants Elimination

Pollution control and remediation is always an important issue in human society.With the development of industrial and the improvement of people’s requirement to their lives,conventional technology for pollutants disposing encountered the bottleneck.For examples,the adsorbent for heavy metal do not have enough capacity,and cannot remove anion-cation combined heavy metal deeply;The free radical based AOPs has a low utilization rate of oxidants and may produce halogenated degradation byproducts.Therefore,it is necessary to seek innovative functionalized materials and technologies to deal with the increasingly serious pollution problems.Layered double hydroxides（LDHs）is a kind of inorganic nanomaterial with anionic exchangeability,surface acidity/alkalinity,regulable composition and size,optical activity,thermal stability,etc.Its unique two-dimensional layered structure and various physicochemical properties make it a promising material in adsorption,catalysis application.In this paper,a series of environmental functionalized LDHs are designed based on its various physicochemical properties to solve specific environmental problems.The main contents are as follows:（1）In order to solve the difficulty in the advanced treatment of anion-cation combined heavy metals,we employed the interlayer anion exchange capacity,surface group coordination ability and photocatalytic ability of LDHs and designed a calcined Mg Zn Fe-CO₃ LDH（CMZF）to deep remove combined arsenic and cadmium pollutants from water.After the treatment by CMZF,the concentration of arsenic and cadmium decreased to an ultra-low level of 4μg/L and3μg/L,respectively,from an initial concentration of 1mg/L when the solution p H is above 6,which can satisfy the drinking water provision.XRD,XPS and SEM/EDS results indicated that the removal mechanism of cadmium mainly include hydroxyl coordination and precipitation,and the removal mechanism of arsenic mainly include ion exchange and hydroxyl coordination.Besides,CMZF can achieve the photooxidation of trivalent arsenic to the less toxic pentavalent arsenic under light irradiation.The main interactions between arsenic and cadmium in the removal process are electrostatic attraction,shielding effect and ion bridge.（2）In order to solve the problem that the persulfate based AOPs dominated by free radicals may produce toxic byproducts,we employed the composition adjustability,（photo）catalytic ability of LDHs and designed a Cu Fe LDH.The functionalized catalyst Cu Fe LDO（CFO）is obtained by calcining the Cu Fe LDH at 450℃.CFO can utilize light-irradiation as a“photo-switch”to change the PDS non-radical/radical activation mechanism to degrade phenolic pollutants.Electrochemical tests and quantum chemistry calculations shows that Cu（II）site in CFO can polarize the peroxydisulfate（PDS）adsorbed on the surface under dark conditions,and thus initiating the electron transfer from pollutants to PDS.While under light irradiation,the excited photoelectrons in conduction band of CFO can eventually reduce the Fe（III）site to Fe（II）,Fe（II）sites will further lead to the one-electron reduction of PDS to form sulfate radicals and hydroxyl radicals to attack the pollutant.CFO can change the degradation mechanism and pathway to pollutants by the photo-switch and therefore can regulate the degradation efficiency and products.This technology is very useful as we could choose the rational pathway for pollutants degradation according to their properties on the basis of safety and efficiency.