Strategy,Method And Application Of Highly Sensitive Electrochemical Sensing Of Phenolic Contaminants

Phenolic organic compounds are the main pollutants in the chemical,petroleum and steel metallurgy industry.Due to their high toxicity,wide distribution,refractory and bioaccumulation,phenolic pollutants not only damage the ecosystem and cause environmental pollution,but also seriously threaten human health,even trace level of phenolic contaminants can cause irreparable damage to human body.Therefore,it is necessary to establish sensitive,rapid and simple methods for the detection of phenolic pollutants.The electrochemical sensor has its own advantages in simple operation,portable instrument,fast analysis process and high sensitivity,which make it the most promising method for real-time online monitoring of environmental pollutants.Sensing interface is the key of electrochemical sensor,for its performance largely determines the sensitivity,selectivity,and usability of the fabricated sensing platform.In this paper,three different kinds of electrochemical sensing interfaces,namely ball-mill-exfoliated graphene,ball-mill-exfoliated graphene/MOFs composite and gold nanoparticles,were constructed.The structure-activity relationship between the structural morphology of different materials and their electrochemical sensing activity was explored,the mechanism of improved electrochemical sensing performance was further studied.Using phenolic pollutants as the analytes,three highly sensitive electrochemical sensing platforms were constructed and applied for actual sample determination successfully.The main works of this paper are as follows:?1?A simple wet ball-milling method for exfoliating pristine graphite to graphene nanosheets?GS?is proposed.The surfactant of cetyltrimethyl ammonium bromide is utilized to greatly improve the exfoliation efficiency of graphene nanosheets.Variation of the ball-milling time is an efficient way to control the size and thickness of graphene nanosheets,as well as the level of edge defects.With an increase of ball-milling time,superior electrochemical reactivity is imparted owing to enlarged active area and increased catalytic ability.The obtained graphene nanosheets are sensitive for electrochemical oxidation of phenols?e.g.hydroquinone,p-chlorophenol and p-nitrophenol?,and thus qualified for the simultaneous sensing of phenols.The detection limits of simultaneous monitoring of hydroquinone,p-chlorophenol and p-nitrophenol are as low as17?g L^-1,24?g L^-1,and 0.42 mg L^-1,respectively.?2?Based on the GS from the previous chapter,a highly sensitive electrochemical sensing system is developed via in situ integration of Cu-based metal-organic frameworks?Cu-BTC?and high-conductivity ball-mill-exfoliated graphene?Cu-BTC@GS?by a simple method.The as-synthesized Cu-BTC@GS hybrids display remarkably enhanced electrochemical activity due to the synergistic effect resulting from the integration.Compared to pristine GS,the introduction of Cu-BTC nanoparticles leads to significant improvement in the surface area and porosity,as revealed by the nitrogen adsorption-desorption analysis.In addition,the oxidation behavior of nicotinamide adenine dinucleotide?NADH?studied using the rotating ring disk electrode further reveals a superior electron-transfer rate constant for the composite,indicating higher catalytic ability.Moreover,double potential step chronocoulometry of phenolic pollutants?bisphenol A and p-chlorophenol?reveals that the prepared composite possesses greatly-enhanced adsorption properties,resulting in much higher response signals and detection sensitivities.Benefiting from the superior reactivity,a highly sensitive electrochemical sensing platform is successfully fabricated,the detect limits of bisphenol A and p-chlorophenol are 1.2?g L^-1 and 1.9?g L^-1.It was used in the analysis of receipt and wastewater samples,and the results were highly consistent with those obtained by high-performance liquid chromatography.?3?In situ and antomatic modification of sensitive materials on the substrate is important for the construction of on-line monitoring electrochemical sensing.Thus,gold nanoparticles?AuNPs?were in situ deposited on the surface of glassy carbon electrode by cyclic voltammetry method to construct a sensing interface,and functionalized by different groups of 2-mercaptobenzothiazole?MBT?.Tetrabromobisphenol A?TBBPA?,a widely used brominated flame retardant in electronic products,was used as a probe molecule.The effect of cyclic voltammetric scanning potential range on the morphology of AuNPs and the sensitization effect of TBBPA were investigated.On this basis,the oxidation activity of TBBPA on the surface of AuNPs in the presence of MBT,6-nitro-2-mercaptobenzothiazole?NMBT?and 6-ethoxy-2-mercaptobenzothiazole?EMBT?was further studied.It was found that the substituent group at the C-6 position of the MBT molecule has a remarkable influence on the oxidation activity of TBBPA.In the presence of electron-donating group substituented MBT?EMBT?,the accumulation ability of TBBPA on the surface of AuNPs is significantly increased,resulting in higher oxidation signal and detection sensitivity.In the presence of electron-withdrawing group substituented MBT?NMBT?,the enrichment ability of TBBPA is instead reduced,resulting in a weak oxidation signal.Based on the synergistic signal amplification strategy of AuNPs and EMBT,a highly sensitive electrochemical sensing platform for TBBPA was constructed with a detection limit of 7.2 ng L^-1.The sensing system was used for the determination of e-waste and wastewater samples,and the results were consistent with the values that obtained by high-performance liquid chromatography.