Construction Of Functionalized Graphene Electrochemical Sensors To Detect Organic Pollutants In Water Environment

Electrochemical sensors have been extensively applied to food detection,biomedical analysis and environmental monitoring due to their characteristics of easy miniaturization,low cost,high sensitivity and rapid response.Common phenolic and nitrobenzene organic pollutants in water environment,such as 4-nitrophenol（4-NP）,4-methoxy-phenol（4-MP）and 4-nitrochlorobenzene（4-CNB）,have great harm to the environment and human health,and accurate detection of such pollutants is a prerequisite for efficient treatment.Modification of bare electrode is generally considered as a feasible means to improve the electrocatalytic performance,because the detection effect of organic substance in water environment is not good by directly using bare electrode to construct sensor.Graphene has attracted much attention in the research of electrochemical sensor modification materials due to its unique structure and excellent electrochemical performance.Graphene has been combined with transition metal compounds to obtain modified electrodes,which have been then used to construct sensors for accurate detection of the three organic pollutants in the water environment.Meanwhile,the performance of the electrochemical sensor has been evaluated from the perspectives of detection linear range,detection limit and selectivity.The main research contents are as follows.（1）The nickel selenide/reduced graphene oxide/indium tin oxide modified electrode（Ni₃Se₄/rGO/ITO）is prepared by electrodeposition method.The electrochemical behavior of 4-NP on Ni₃Se₄/rGO/ITO electrode is studied by cyclic voltammetry and differential pulse voltammetry,and the factors affecting the determination of 4-NP such as deposition time of Ni₃Se₄,type of buffer solution and pH are investigated.The results show that the electrochemical sensor constructed with Ni₃Se₄/rGO/ITO as the working electrode can achieve the selective determination of 4-NP.Under optimized conditions,the detection linear range of the sensor for 4-NP is 0.05～200μM,and the detection limit is 17.1 n M（S/N=3）.At the same time,the water environment samples are tested by standard addition method,the obtained average recoveries are 98.6～104.6%and the relative standard deviations（RSD,n=5）are less than 5.0%.（2）The reduced graphene oxide combined with pyridine diketopyrrolopyrrole（PDPP）composite is prepared by hydrothermal method,and manganese dioxide（MnO₂）nanomaterial is modified on the surface of the composite utilizing hydrothermal method again.The prepared composite is modified on the glassy carbon electrode（GCE）to obtain MnO₂/rGO-PDPP/GCE electrode.The electrochemical catalytic performance of MnO₂/rGO-PDPP/GCE electrode on 4-MP is investigated by cyclic voltammetry and differential pulse voltammetry,and the conditions affecting the determination of 4-MP are investigated.The results suggest that the electrochemical sensor constructed with MnO₂/rGO-PDPP/GCE as the working electrode exhibits excellent electrocatalysis and selectivity for 4-MP.Under optimized conditions,the peak current of 4-MP is linearly correlated with the concentration in the range of 0.10～300μM,and the detection limit is15.0 n M（S/N=3）.Meanwhile,the electrode is used for the detection of 4-MP in water environment samples by standard addition method,the obtained average recoveries are 99.5～104.2%and RSD（n=5）are less than 5.0%.（3）Manganese selenide（MnSe₂）modified rGO-PDPP composite is prepared by a two-step hydrothermal method,and then modified on GCE to obtain MnSe₂/rGO-PDPP/GCE electrode.The electrochemical behavior of 4-nitrochlorobenzene（4-CNB）on MnSe₂/rGO-PDPP/GCE is investigated by cyclic voltammetry and differential pulse voltammetry and the determination conditions are optimized.The results show that the electrochemical sensor constructed with MnSe₂/rGO-PDPP/GCE as working electrode can be used for the selective detection of 4-CNB.Under optimal conditions,the linear range of the sensor for 4-CNB detection is 0.01～300μM,and the detection limit was 4.8 n M（S/N=3）.At the same time,the standard addition method is used to detect 4-CNB in water environment samples,the obtained average recoveries are 98.6～110.7%and RSD（n=5）are less than 5.0%.,which verified the practicability of the sensor for the determination of4-CNB.In conclusion,three modified electrodes,Ni₃Se₄/rGO/ITO,MnO₂/rGO-PDPP/GCE and MnSe₂/rGO-PDPP/GCE are prepared.And the electrochemical sensors based on these three modified electrodes are used to detect organic pollutants 4-NP,4-MP and 4-CNB in water environment,respectively.It suggests that three electrochemical sensors can selectively detect target analytes,and show good stability,which has certain application value.