Graphene-based Composites Used For The Investigation On Electrochemical Sensors

On account of the high sensitivity,ease of operation,low cost,and rapid response,electrochemical sensors have become the most widely used analysis tools.As the core component of electrochemical sensors,working electrodes tend to decide the sensing performance of sensors.Therefore,it has always been the topic in the electrochemical fields that developing new electrode materials to improve the sensitivity,reproducibility and selectivity of sensors.Owing to large specific surface area,excellent electrical conductivity,high mechanical strength,and outstanding light transmission,graphene has shown great prospects in various research fields.In addition,graphene can serve as a kind of ideal matrix material,which provides opportunities for the research and development on graphene-based composites.Metal nanomaterials combine the qualities of metal materials and nanomaterials,exhibiting excellent electrical conductivity and electrocatalytic property.Incorporating graphene with metal nanomaterials can acquire a variety of graphene-metal nanocomposites with preeminent electrocatalytic performance.Hereby,it can be expected to improve the sensitivity of sensors by applying graphene-metal nanocomposites to electrochemical sensors.On the other hand,metal-organic frameworks(MOFs)have large specific surface area and controllable porous structures,showing the adsorption affinity to the specific molecules,as well as the size selectivity that was similar to molecular sieves.Taking advantage of this,combining MOFs with graphene can not only effectively improve the stability and conductivity of MOFs,but also obtain the highly selective and sensitive electrochemical sensors.In consequence,this paper aims to construct electrochemical sensors with excellent performance by preparing graphene-metal nanocomposites and graphene-MOFs composites.Making full use of their respective characteristics,we carried out the following work:1.A one-step strategy for the preparation of t-GR-Au composites was established based on the hydrothermal method,using a GO-HAuCl4 aqueous suspension as the precursor and H2SO4 as promoting agent.Subsequently,the t-GR-Au composites were directly used for constructing the dopamine electrochemical sensor.Due to combining the advantages of t-GR and Au nanoparticles,the t-GR-Au/GCE displayed higher electrochemical response to dopamine than that of the layer-stacking GR-Au.We have demonstrated the application of t-GR-Au composites in the amperometric determination of dopamine with good stability,wide linear range,and low detection limit.Furthermore,this method has been proven applicable in human urine and serum samples.2.A facile and cost-effective method was proposed for the fabrication of petal-like graphene-Ag composites(p-GR-Ag)with highly exposed active edge sites.The p-GR was prepared using a HCl assisted hydrothermal method,followed by Ag NPs decoration via modified silver mirror reaction.The p-GR-Ag composites possessed several features superior to traditional GR-Ag composites.Firstly,compared with the conventional GR-Ag composites,the p-GR-Ag composites was made of basal planes and highly reactive edge planes,which could expose more catalytical active edge sites for electrochemical and catalytic reactions.Secondly,the p-GR possessed large surface area and supplied more active sites as favorable nucleation sites for the highly crystalline Ag NPs deposition,enabling improved performance for electrochemical and catalytic activity.Finally,the p-GR-Ag composites with 3D open and porous structure could be used to make the surface readily accessible to liquid electrolyte and provided efficient channels for electron transport.These features presented a distinct opportunity to create a sensor for electrochemical detection of metronidazole,and the designed sensor demonstrated exceptional performance with enhanced metronidazole sensitivity,high stability,and excellent selectivity over interfering species.Furthermore,validation of the applicability of the prepared sensor was carried out by detecting metronidazole in human urine and local lake water samples.3.The rht-type Cu-based MOF-electrochemically reduced graphene oxide(Cu-TDPAT-n-ERGO)composites were successfully fabricated for the electrochemical determination of H2O2.Due to the synergistic effect of bifunctional Cu-TDPAT(high density of open metal sites and Lewis basic sites)and n-ERGO,the Cu-TDPAT-n-ERGO sensor exhibited the current amplification and electrocatalysis,and showed boosted electrocatalytic activity toward H2O2 reduction.In addition,the proposed sensor exhibited wide linear range,low detection limit,super stability,satisfying reproducibility,and excellent anti-interference ability,as well as the relatively simple preparation method.4.The ternary composite materials,ultrasmall metal nanoparticles encapsulated in the anionic metal-organic frameworks/electrochemically reduced graphene oxide(MNPs@Y-1,4-NDC-MOF/ERGO,where M = Ag,Cu)were prepared by a cationic exchange strategy and a subsequent electrochemical reduction process for the electrochemical determination of H2O2.The cationic exchange approach,affording well-dispersed MNPs with small and narrow size distribution,can effectively surmount the deficiencies of the conventional methods.Moreover,this strategy involved the preparation of an original design of the functional materials based on the hybridization of anionic MOF,MNPs,and ERGO that exhibited electrocatalysis and the molecular sieving effect.The proposed sensor showed superior electrocatalytic and sensing performances including extended linear range,comparatively low detection limit,high stability,excellent selectivity,and favorable practicability.In addition,instead of geometric parameters including particle size and electrochemical active area,the electrocatalytic activities of MNPs@Y-1,4-NDC-MOF/ERGO(M = Ag,Cu)toward H2O2 was primarily depended on the unique electronic properties of the MNPs.