Based On Functionalized Graphene For Enrichment And Detection Of Mercury Species In Water And Rice

Mercury and its compounds are hazardous heavy metal pollutants in water and food,which can be accumulated into the body and have harmful effects on human health.The pollution of mercury in the water and rice had been received increasing attention in recent years.The toxicity of mercury is highly dependent on its chemical form.Organic mercury compounds are known to be more toxic than inorganic mercury.Methylmercury(MMHg)is the most dangerous form.However,any mercury speciation can be converted into the most dangerous MMHg by biogeochemical transformation,especially in the aquatic environment.So,the detection of total mercury cannot reveal its toxicity and bioavailability.Mercury speciation analysis is significant for food safety,human health and relevant toxicology studies.Because of low concentration and complex matrices,the development of mercury speciation analysis method has been one of hot issues.In this study,two novel functional graphene nano-materials were prepared independently and used as efficient adsorbents for mercury species.We developed two new methods for the determination of mercury species.The methodology validation,real water and rice samples analysis were carried out.The adsorption mechanisms of the novel adsorbents are explained in the paper.The main research results are as follows:1.The G-SH was prepared by substitution of the epoxy and hydroxyl groups with mercapto on the bulk and edge of the GO: firstly,the GO suspension was treated with hydrobromic acids,which generate nucleophilic substitution on hydroxyl and addition reactions on epoxide groups;the simultaneous high-temperature treatment caused dehydration and partial dehydrobromination;subsequently,thiourea containing a nucleophilic sulfur center reacted with the bromine moieties,producing isothiouronium salts;finally,the hydrolysis by base treatment resulted in the G-SH.The prepared G-SH were characterized by transmission electron microscopy(TEM),Fourier transform infrared spectra(FT-IR),X-ray photoelectron spectroscopy(XPS),and so on.Due to high dispersity of the G-SH,a stable and uniform solution like colloidal solution could be formed,which could immediately aggregate with the addition of electrolyte solution,such as NaCl,similarly to that conventional CPE method.In this work,a novel cloud point extraction-like method(CPEL)based on the G-SH for speciation of mercury by HPLC-ICP-MS was developed.The effects of the experimental parameters,including pH,adsorbent amounts,extraction time,NaCl concentration,eluenttype and its concentration and the coexisting ions,were investigated.Under the optimal conditions,the enrichment factors of IHg and MMHg were 78 and77,respectively;the detection limits(3?)of IHg and MMHg were 3.8 and 1.3 ng·L-1,respectively.The proposed CPEL-HPLC-ICP-MS method was successfully applied into the analysis of mercury species in water and rice samples.2.The magnetic reduced graphene oxide composite(rGO-Fe3O4)was prepared via the solvothermal reaction of graphene oxide(GO)and iron(III)acetylacetonate(Fe(acac)3)in ethylenediamine(EDA)and water under high temperature and high pressure.In this process,the chemical reduction of GO and the deposition of Fe3O4 nanoparticles are combined with one single step;the bonding of the rGO-Fe3O4 stem formed covalent interactions between NH2 groups of EDA and Fe3O4 nanoparticles.Therefore,the obtained rGO-Fe3O4 had high stability and its size distribution.The coverage density of Fe3O4 nanoparticles can be controlled by varying the initial mass ratio of GO and Fe(acac)3.As an efficient mercury chelating agent,dithizone can be grafted on the rGO with high exposed area by the ?-?stacking mechanism.Characterizations of the D@rGO-Fe3O4 were carried out by transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS),vibrating sample magnetometer(VSM),and so on.A novel MSPE-HPLC-ICP-MS method was developed for detection trace mercury species,based on the superparamagnetic D@rGOFe3O4 as adsorbent.Some experiment parameters were optimized,including the preparation technique of adsorbents,solution pH,adsorption time,elution types,and desorption time and coexisting ions.Under the optimal conditions,the proposed MSPE-HPLC-ICP-MS was investigated by methodology validation and the analysis of real water and rice samples.The enrichment factors of IHg and MMHg were 400 and 380,respectively.The detection limits(3?)were 0.48 and 0.17 ng·L-1for IHg and MMHg.Compared with the previously reported method,the developed method based on the D@rGO-Fe3O4 as adsorbents had simple pretreatment and high sensitivity.