Fabrication of Carbon-based Nanocomposites with Special Structure:Highly Sensitive Heavy Metal Ion Electrochemical Sensors

Author:Lu Zhi Wei

Supervisor:ye jian shan


Degree Year:2019





The contamination of heavy metal ions(HMIs)is severely threatening human health,particularly some ions such as Pb2+,Cd2+,Hg2+,As3+,and Cr6+are highly toxic even at the trace amount level.Therefore,new methods for the profiling of such species with rapidness,accuracy,sensitivity,and reliability are under high demands.Optical analysis is the well-established methods and shows promising applications,while they have the limitations in terms of expensive instruments,complicated operation,and difficulty in real-time monitoring.Electrochemical determinations have attracted great attention owing to their fast response,high sensitivity and possibility for in-situ measurements.With the rapid development of nanotechnology,electrochemical sensors based on carbon-related materials have been widely applied for assays of the HMIs.However,there are some critical questions to be resolved,such as their ability against interferences and poor selectivity especially in the samples with complicated background signals.In addition,the clear understanding of their sensing mechanism is also important for the improvement of their performance.Therefore,electrochemical sensors with better sensitivity and selectivity are always the key research focus.This thesis focused on the synthesis of new nanomaterials,development of new electrochemical sensors as well as the study of their sensing mechanisms.We explored the new methods to synthesize the hierarchical carbon-based materials and established the electrochemical sensors to determine the HMIs with high sensitivity and selectivity.The details are listed below:(1)We developed a new nitrate-assisted bubbling strategy to develop 3D honeycomb-like N-doped carbon nanosheet framework decorated with bismuth nanoparticles via the sol-gel process.Through tunable ratios of Bi(NO3)3 and PVP,their morphology can be well controlled.Their corresponding chemical compositions and physiochemical properties were well characterized and the growth mechanism was proposed.The newly-developed nanocomposites have the porous network structures and high surface/volume and high doping of N element.After their modification,the electrode showed good sensing ability towards Pb2+and Cd2+using square wave anodic stripping voltammetry(SWASV),and both of them have the linear ranges of 1-120μg·L-1,the limit of detection(LOD)of 0.02 and 0.03μg·L-1,respectively.(2)We developed a one-pot method to prepare dandelion-like Au nanoparticles encapsulated with polyaniline(PANI).This is a simple and green method,can be used for large-scale preparation.Their morphologies and compositions were well characterized by the SEM,TEM,XRD,and XPS.By combining the strong adsorption characteristics of PANI with the excellent catalytic properties of Au NPs allowed the Au@PANI to modify on the electrode surface to fabricate Au@PANI/GCE,and the corresponding electrochemical sensors presented the linear ranges of 0.02-0.27 and 0.08-2.7μM with the LOD of 0.003 and 0.008μM for Pb2+and Cu2+respectively.This sensor also exhibited excellent performance in real sample measurement.(3)We constructed the flexible IL/PLC/LEGE electrochemical sensors based on the high coordination interaction of L-cysteine with Pb2+and laser-induced etching graphene electrode as well as the good conductivity of ionic liquid(IL).The sensor illustrated good sensitivity and selectivity without any interferences from other HMIs.The sensing mechanism indicates that the massive presence of amine,carboxylic acid,and HS groups generated excessive binding sites for the accumulation of Pb2+,and their synergistic effects enabled the sensor with a linear range of 1-180μg·L-11 and LOD of 0.17μg·L-1.Moreover,the electrochemical behavior of the flexible sensor was evaluated under flat,convex,and concave bending stresses to simulate various deformations in practical applications,thus,the flexibility of this sensor provides an opportunity for the monitoring of HMIs through wearable devices.(4)Considering the demands for in-situ monitoring of heavy metal ions,and the easily peeling off of the sensing materials loaded on the electrode,we used UPD method to modify the disposable screen-printed carbon electrode via the Bi/AuNPs nanocomposites,the developed sensor showed high sensitivity towards Zn2+、Pb2+and Cu2+in pH 4.5 acetate buffer solution.Their selectivity,reproducibility,repeatability,and stability were well investigated,and the accurate measurement in lake water proves its practical applications.We envision that this study will show promising values for the emergent monitoring of HMIs in wild area as well as the online monitoring devices.