Study On Adsorption And Combined Toxic Effects Of Arsenic In Water By Functionalized Iron-based Metal-organic Frameworks

Inorganic arsenic（As）exists widely in nature,and chronic exposure can increase the risk of various cancers.How to reduce arsenic exposure and toxicity has become an important issue of long-term concern in the environmental field.MOFs are ordered porous crystal materials composed of metal ions/clusters and organic ligands.The interaction between MOFs and inorganic arsenic not only affects the migration and transformation of arsenic in the environment,but also affects its toxicity.MOFs have excellent adsorption and removal properties for various pollutants,and amino functionalization can further improve the adsorption capacity of some MOFs.However,whether this modification affects the adsorption of inorganic arsenic in water by iron-based MOFs and the mechanism of its effect are still unclear.In addition,whether the adsorption capacity can regulate the toxicity of arsenic remains to be explored.Therefore,in this paper,MIL-101（Fe）and NH₂-MIL-101（Fe）are used as iron-based MOFs models,and the mechanism of adsorption,removal and toxicity of functionalized iron-based MOFs on inorganic arsenic is mainly discussed through the following two aspects of work:（1）By comparing the adsorption properties of MIL-101（Fe）and NH₂-MIL-101（Fe）on arsenite As（III）and arsenate As（V）in water,the mechanism of improving the adsorption capacity of iron-based MOFs by amino functionalization was investigated.（2）The mechanism of the effect of iron-based MOFs on arsenic toxicity was elucidated by the cytotoxicity test and the change of arsenic content and morphology in cells.The main research results are as follows:（1）Enhanced adsorption of inorganic arsenic in water by amino functionalized MIL-101（Fe）and its mechanismOctahedral MIL-101（Fe）and NH₂-MIL-101（Fe）were obtained by using two organic ligands of terephthalic acid and 2-amino-terephthalic acid with metal ion Fe³⁺under solvethermal conditions.The adsorption experiments showed that the adsorption capacity of NH₂-MIL-101（Fe）for As（V）and As（III）was 147.7 mg/g and 153.4 mg/g,respectively,which was significantly higher than that of MIL-101（Fe）（82.8 mg/g and 131.2 mg/g,respectively）.The results showed that amino functionalization improved the adsorption capacity of MIL-101（Fe）for two inorganic arsenic in water.Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy showed that the adsorption mechanism of arsenic by Fe-O-As bond was mainly formed through complexation.Compared with MIL-101（Fe）,amino functionalization increased the Fe content,Fe³⁺/Fe²⁺ratio,specific surface area and pore volume of NH₂-MIL-101（Fe）,so the adsorption capacity for arsenic was significantly improved.In addition,NH₂-MIL-101（Fe）showed good adsorption performance for As（V）in a wide p H range（4-9）（>70%）.NH₂-MIL-101（Fe）also has high anti-interference ability and reusability.In spike experiments with incurred river samples,95%of arsenic was removed,reducing the arsenic concentration below the WHO safety threshold（10μg/L）.（2）Study on the combined toxicity of iron-based MOFs and arsenicUsing human hepatocellular carcinoma cells（Hep G2）as test cells,the changes of cell activity,arsenic morphological content and reactive oxygen species（ROS）levels were investigated under single and combined exposure of two kinds of iron-based MOFs and As（V）.The results showed that the higher the concentration of MOF,the weaker the binding strength with arsenic,and the smaller the bioaccumulation of arsenic at the cellular level.MOF blocks the intracellular conversion of As（V）to As（III）.In cell activity tests,MIL-101（Fe）and NH₂-MIL-101（Fe）showed weak toxicity to Hep G2 cells at high concentrations（25g/L）（108.5±19.4%and 100.3±14.5%,respectively）.Hep G2 cell viability decreased to 40.4±13.4%after exposure to As（V）alone.The cell viability of MOFs and As exposed group was significantly higher than that of As exposed group alone,indicating that MOFs could inhibit the cytotoxicity of As（Ⅴ）.The results of ROS test showed that arsenic could induce the increase of total ROS,superoxide anion（·O₂^-）and hydroxyl radical（·OH）levels,but the introduction of MOF could inhibit the arsenic induced ROS levels.The combined toxicity study confirmed that these two iron-based MOFs can promote the biological absorption of As（V）,inhibit the reduction of As（V）,reduce the oxidative stress induced by arsenic,and reduce the toxicity of arsenic to cells.These results provide a scientific basis for in-depth understanding of the ecological and environmental risks of arsenic and MOFs,help to screen suitable MOFs for reducing arsenic exposure and arsenic toxicity,and also provide theoretical support for the engineering and safe use of MOFs in sewage treatment and agriculture.