Preparation Of Au_nano/Fe-MOF Composite And Its Application For The Detection Of Arsenic（Ⅲ） In Water

Arsenic and its compounds threaten the environment and human health due to their toxicity.In recent years,the steady increase of As（Ⅲ） concentration in the ecosystem partly associated with anthropic activities.Therefore,It is essential to achieve a fast and sensitive measurement of trace As（Ⅲ） in the environmental field in the aqueous environment.Compared with other methods,electrochemical analysis stands out for its rapidity,low cost and portability,ideal for field analysis.With the development of nanomaterials,electrochemical sensing has made breakthrough progress.Due to their high porosity,large specific surface area and variable pore sizes,MOFs are often considered as the promising materials for surface modification of the electrodes.However,most MOFs have poor electrical conductivity which limits the direct application as the electrode materials.Gold nanoparticles(Au_nano),are one of the most popular conductive materials due to their high electrical conductivity and easy combination with many materials.The nanocomposites(Au_nano/MOF)designed by combining gold nanoparticles(Au_nano) with MOFs have a wide range of applications in electrochemical sensing.However,the current methods for the preparation of Aunano/MOF composites are complicated,the material morphology is not controllable,and the framework structure of MOFs is greatly affected.In this paper,Au_nano/Fe-MOF composites were designed and synthesized.The morphological structure of the Au_nano/Fe-MOF composites was investigated by different characterization techniques.The Au_nano/Fe-MOF modified electrode was prepared by drop coating method as an electrochemical sensor for the detection of trace As（Ⅲ） in water.The main research results are as follows:The amino-functionalized Fe（Ⅲ）-based terephthalate metal-organic framework materials（NH₂-MIL-101（Fe）,named as Fe-MOF）was prepared,and used as a carrier in an ethanol-water solution to enrich AuCl₄^-within Fe-MOF materials using the high specific surface area of MOFs and the electrostatic adsorption between its amino groups and AuCl₄^-,AuCl₄^- was later reduced by reducing agent.We researched the influences of the reducing agent type on the Au_nano/Fe-MOF composites’structure and morphology.Scanning electron microscopy（SEM） and Energy dispersive spectroscopy（EDS） equipped with SEM detection showed that the composites synthesized with sodium borohydride as the reducing agent(Au_nano/Fe-MOF（NaBH₄）) were more uniform in gold content than those obtained with ascorbic acid and sodium citrate as the reducing agents (Au_nano/Fe-MOF（AA）and Au_nano/Fe-MOF（AR）).nanoparticles with higher loading and uniform distribution.The Au_nano/Fe-MOF prepared by sodium borohydride reduction were characterized using other characterization techniques（transmission electron microscopy（TEM）,nitrogen adsorption/desorption curve（BET）,Fourier infrared spectroscopy（FT-IR）,X-ray diffractometry（XRD） and X-ray photoelectron spectroscopy（XPS））.The results showed that AuCl₄^-was successfully reduced to Au_nano.Au_nano/Fe-MOF modified electrodes were prepared by drop coating method and their electrochemical properties were investigated.Electrochemical impedance spectroscopy（EIS） showed a significant reduction in the charge transfer resistance of the Au_nano/Fe-MOF after loading of gold nanoparticles.Cyclic voltammetric curves demonstrate that the gold nanoparticles have been successfully decorated on the Fe-MOF.The response signals of each modified electrode to As（Ⅲ）were investigated using square wave anodic solvation voltammetry（SWASV）.It was confirmed that the Au_nano/Fe-MOF composites prepared by sodium borohydride were the most responsive to As（Ⅲ）.The important experimental parameters that affect the determination of As（Ⅲ）,including the modification amount of Au_nano/Fe-MOF,the pH value of buffer solution,deposition time and potential,are further optimized to achieve the maximum sensitivity of the Au_nano/Fe-MOF/GCE for As（Ⅲ）determination.In summary,the experimental conditions of the modifying amount of Au_nano/Fe-MOF,solution pH,deposition potential and time were applied as 8μL（mass of active material attached to unit electrode area 0.11 mg/cm²）,5.0,-0.9 V,240 s,respectively in the following square wave anodic solvation voltammetry tests.Under the optimized conditions,the Au_nano/Fe-MOF/GCE-based sensor exhibited excellent electrochemical performance,wider linearity（0.02～2ppb and 2～30 ppb）,higher sensitivity(66.61μA·cm^-2·ppb^-1),lower quantitative concentration（0.02 ppb）and limit of detection（0.0085 ppb）,in acetate buffer solution（pH=5.0）.The test procedure has good selectivity from metal ions such as Mg（Ⅱ）,Fe（Ⅲ）and heavy metal ions such as Pb（Ⅱ）,Cu（Ⅱ）,Cd（Ⅱ）and Hg（Ⅱ）.The processed sensor has good stability and reproducibility for the detection of As（Ⅲ）and can reliably analyses As（Ⅲ）in real samples.Excellent results of spiked recovery of As（Ⅲ）detection in actual water samples.This Au_nano/Fe-MOF/GCE electrochemical sensor has great potential for As（Ⅲ）monitoring in the real environmental sample.