Removal And Fluorescence Determination Of Hexavalent Chromium In Environmental Water Samples

Chromium and its compounds are widely used in metallurgical industry,chemical industry,refractories,cast iron,automobile industry and so on.Although trivalent chromium is essential for the metabolism of blood glucose,hexavalent chromium?Cr????is a highly toxic substance that seriously harms human health and the ecological environment,and Cr???has been listed as a priority pollutant in China's water environment list.In addition,chromium is also a rare metal.Therefore,it is necessary to develop advanced removal and recovery tech nologies and detection methods for Cr???in environmental water samples.The main content of this paper includes two parts:removal of hexavalent chromium ions from environmental water samples and the fluorescence detection of hexavalent chromium ions in environmental water samples."Removal of hexavalent chromium ions from environmental water samples"mainly includes the following:?1?Introduce the research background and significance of this study,and introduce the current removal methods of Cr???from environmental samples and their respective advantages and disadvantages.?2?Graphene oxide?GO?was prepared by Hummer method using flake graphite as raw material.The GO surface loaded with a layer of nanoscale mesoporous silica?GO-MS?was prepared using tetraethyl silicate?TEOS?as silicon source,CTAB as pore-forming agent,sodium hydroxide?Na OH?as cat alyst.Finally,GO-MS was used as a carrier.The Cr???-imprinted layer?Cr???-IIP?was modified on the surface by surface imprinting technique.At the same time,a non-imprinted adsorbent?NIP?was prepared in the same manner.?3?The synthesized materials were characterized by FT-IR,SEM,TEM,TGA and specific surface area analysis.?4?The synthesized Cr???-IIP was used as an adsorbent,we investigated the effects of functional monomer,solution p H,adsorption time,adsorption temperature,and coexistent ions on the adsorption.Adsorption results showed that the optimum solution p H was 2,and the adsorption amount increased with the increase of temperature or initial concentration.The adsorption process conforms to the quasi-secondary adsorption kinetics model,and equilibrium can be reached in about 5minutes.The adsorption isotherm data follow the Freundlich model,and an adsorption capacity of 438 mg/g at an initial Cr???concentration of 500 mg/L.At the same time,the reusability of materials was studied.Finally,the prepared adsorption material was compared with other Cr???adsorption materials.Fluorescence detection of hexavalent chromium ions in environmental water samples mainly includes the following:?1?Introduce the research background and significance of this study,and introduce the current detection methods for Cr???in environmental samples.?2?Mn-doped Zn S quantum dots?Zn S:Mn?were prepared by co-precipitation method and a layer of silicon oxide?Zn S:Mn@Si O₂?was modified on the surface.Then,using Zn S:Mn@Si O₂ as carrier,TEOS as silicon source,CTAB as pore-forming agent and Na OH as catalyst to prepared quantum dot fluorescent sensors?QDs-IIP?by surface imprinting technique.The obtained QDs-IIP with high selectivity.In addition,the influence of the amount of Si O₂ modification in Zn S:Mn@Si O₂ on the detection performance was investigated.At the same time,the optical stability of QDs-IIP was studied.?3?Characterization of the synthesized sensor:FT-IR,X-ray diffraction?XRD?,SEM,TEM,specific surface area analysis.?4?The detection performances of QDs-IIP and QDs-NIP were studied.The experiments showed that the fluorescence intensity quenching and Cr???concentration showed good linearity in the Cr???concentration range of 0.02¹.0mg/L,the imprinting factor imprinting factor?IF?was 2.53,the limit of detection?3?/k?of the sensor for Cr???was 5.48?g/L.The water samples were analyzed with tap water and the feasibility of the analytical method was investigate d.The results showed that the recoveries were between 94.4%and 108.2%,and the relative standard deviations?RSDs?were all less than 5%,indicating that the method had better precision and accuracy.?5?The selectivity of QDs-IIP for Cr???was studied.The results showed that the Mo O₄^2-interfered greatly with the detection,Cl^-had little effect on the detection,and the IF of the imprinting sensor on each ion.The order of IF is Cr???>Mo O₄^2->PO₄^3->SO₄^2->Cr?III?>Cu²⁺>Cl^-.?6?The reproducibility of the sensor was examined.Experiments show that the fluorescence intensity of the material can be restored to more than 90%after each elution.The reexamined fluorescence quenching degree is equivalent,indicating that the sensor has excellent reversibility after five times elutions.