Surface Modification Of Reduced Graphene Oxide For Electrochemical Identification

Graphene,a hexagonal nanosheet material ordered and packed with sp² hybridized carbon atoms,is a novel type of carbon material.Because of the exceptional physical,chemical,and mechanical properties,it has been widely used in various scientific fields.Ionic liquids have become current research hotspots as environmentally-friendly functional materials and catalysts,and have excellent electrical conductivity.In this work,ionic liquids and functionalized graphenes were integrated to produce nanocomposites with both combining performances.Then,the electrochemical recognition of nitrite was employed to explore the active sites of methylimidazolium ions on carboxyl-functionalized graphene.Finally,ethylene glycol?EG?was used as a co-reducer and stabilizer,and a facile method was developed to synthesize a series of graphene composites with different loadings of gold nanoparticles for detecting acetaminophen.The main contents of this work include:1.Improving the traditional synthesis methods of graphene oxide,we control the initial amount of water added into the reaction system to prepare a different oxidation degree of graphene oxide GO-n(V_water:V_{sulfuric acid}=n:10 in reaction mixtures).The carboxyl-functionalized graphene oxide?GO-n-COOH?was prepared using bromoacetic acid as a modifier in strong alkaline media.Subsequently,1-ethyl-3-methylimidazolium hydroxide?[C₂mim]OH?was added to GO-n-COOH suspension and intensively stirred at room temperature,[C₂mim]⁺ions were successfully immobilized on GO-n-COOH to form a series of GO-n-COO[C₂mim].Finally,GO-n-COO[C₂mim]was reduced using glucose to obtain RGO-n-COO[C₂mim].The as-prepared GO-n-COO[C₂mim]was characterizd by Infrared spectroscopy,Raman spectroscopy,X-ray diffraction,and X-ray photoelectron spectroscopy,confirming the carboxyl group and[C₂mim]⁺ions to be immobilized on graphite.It was shown that the content of[C₂mim]⁺was the highest as n=2,and was about 24.34%.2.Based on the prepared RGO-n-COO[C₂mim]and RGO-n-COOH composites,we used them as electrochemical senser to identify NO₂^-.The experimetal results show that the electrochemical performance of RGO-n-COO[C₂mim]is very different with the added amount of water.When n is equal to 2,correspondingly,the RGO-3-COO[C₂mim]exhibits the best electrochemical performances with the detection potential of 0.82 V and the oxidation peak current density of 4.68 mA cm^-2.In addition,the study also shows that the RGO-n-COOH-modified electrode almost has no response to NO₂^-,whereas the RGO-n-COO[C₂mim]-modified electrode represents the sensitive response to NO₂^-.It is concluded that[C₂mim]⁺ions play the key role in the reaction process,and are the active site on the composites.Furthermore,we study the interactions of[C₂mim]⁺with NO₂^-using UV-vis absorption spectroscopy,which reveals that the strong coupling of[C₂mim]⁺with NO₂^-promotes RGO-n-COO[C₂mim]to respond sensitivly toward NO₂^-.Based the electrochemical measurments for different RGO-n-COO[C₂mim]composites,the relative active surface areas are almost same about 21,and the capacitance for single[C₂mim]⁺ion on the composites is also almost same about 1×10^-15?F.3.A simple and environmentally friendly synthesis method was developed using EG as a co-reducing agent of HAuCl₄ and GO to detect acetaminophen.By controlling the amount of gold precursor,the graphene composites with different loadings of gold nanoparticles were prepared for the detection of acetaminophen.The experimental results show that the as-prepared composites have high electrocatalytic activity.When the loading of gold is about 16.87%,the composite has highest electrocatalytic activity,and the number of both proton and transfer electron is determined to be 1 during the electrochemical reaction.Due to the synergistic effect of the gold nanoparticles and the graphene,the prepared nanocomposite conbines the excellent properties of the gold nanoparticle and the graphene,such as good conductivity,large surface area and high catalytic activity.Therefore,the nanocomposite is an ideal candidate to sense acetaminophen in solution with high sensitivity(686?A mM^-1),low detection limit?0.058?M?,and low detection potential?0.4 V?.