Controllable Synthesis And Electrochemical Sensing Properties Of Carbon-based Micro/nano Composite Materials

With the improvement of people's living standards,the problem of public health has attracted more and more attention.Therefore,it is of vital importance to exploit a realiable and feasible means to accuratly determine environmental pollutants and biological organic small molecules from the viewpoint of environmental monitoring and human health.As far as we know,a series of analytical techniques,such as spectrophotometry,chromatography,atomic/molecular absorption spectrometry,spectrofluorimetry,chemiluminescence,Raman spectrometry,inductively coupled plasma optical emission spectrometry,inductively coupled plasma mass spectroscopy and high-performance liquid chromatography,have been established for the determination of environmental pollutants and biological organic small molecules.Notwithstanding these advances,most of them usually require expensive equipments,tedious treatment procedures,and high cost,greatly hindering their practical applications.In contrast,electrochemical technique has received increasing attention because of its fascinating features such as simple handling,fast response,superior sensitivity,low limit of detection(LOD),and excellent selectivity.Hence,the detection of environmental pollutants and biological organic small molecules based on electrochemical methods has attracted wide attention.Electrode materials play a vital role in the construction of electrochemical sensors.As reported,metal oxides and bimetal-layered double hydroxides have been tremendously explored as electrode materials due to excellent catalytic activity,strong resistance to oxidization and cost-effectiveness as well as extensive avaiablility.Nevertheless,the corresponding poor electrical conductivity greatly impedes their application in electrochemical sensing.To address the issue,an effective strategy is to integrate rationally these metal oxides or bimetal-layered double hydroxides with carbon materials,which can not only increase the resulting electrical conductivity and stability,but also inhibit the aggregation of active materials during the electrochemical reaction.It is highly expected that these carbon-based micro/nano composite materials can be utilized as electrochemical sensors with superior sensing.In summary,four different carbon-based materials,such as the MgFe-layered double hydroxide/graphene,?-Fe2O3 nanorod arrays/carbon foam,NiFe-layered double hydroxide nanosheet arrays/carbon cloth and Co3O4@NiFe-layered double hydroxide nanowire arrays/carbon cloth have been successfully fabricated.Furthermore,the electrochemical sensors based on the above composites for dection of nitrite,heavy metal ions,dopamine and uric acid are proposed.The main results aregiven as follows:1.Heavy metal contamination has been proven to pose the severe threats to the whole ecosystems and human health even at trace levels.Hence,it is of great significance to develop an ultrasensitive and reliable technique to determine the levels of heavy metal ions.In this work,hierarchical MgFe-layered double hydroxide(MgFe-LDH)microspheres have been successfully immobilized on the surface of graphene nanosheets through a facile one-pot hydrothermal method.Benefiting from the synergistic effects associated with high specific surface area,strong affinity of hierarchical MgFe-LDH architecture to heavy metal ions,fast electron transfer kinetics and good electrical conductivity of graphene,the resulting composites(denoted as MgFe-LDH/graphene)are explored as an electrochemical sensor for simultaneous detection of Cd(II)and Pb(II)in aqueous medium.As a consequence,MgFe-LDH/graphene modified electrode exhibits low detection limit of 5.9 nM for Cd(II)and 2.7 nM for Pb(II),which is dramatically lower than the respective threshold values of 3 ppb(27 nM)and 10 ppb(48 nM)in drinking water permitted by the WHO.Significantly,the electrochemical sensing system has a specific recognition capability toward Cd(II)and Pb(II)in the presence of a 50-fold higher concentration of other common species.Meaningfully,the proposed electrochemical sensor shows excellent reproducibility in repetitive measurements as well as feasibility in real water analysis,as illustrated by the satisfactory recovery in tap and lake water.2.Long-term accumulation and overdose of nitrite ions have been proven to pose a great threat to the ecological environment and public health.It is highly desirable to construct a novel architecture electrode for the accurate quantification of nitrite in a simple and inexpensive manner.Herein,a simple and cost-effective strategy is developed for the construction of three-dimensional(3D)a-Fe2O3 nanorod arrays(NAs)/carbon foam(CF)architecture,in which CF is initially obtained from direct carbonization of commercially available melamine foam and then a-Fe2O3 NAs are grown in-situ on the underlying CF skeleton via simple hydrothermal treatment and secondary pyrolysis.In the unique 3D architecture,?-Fe2O3 NAs provide abundant active sites for electrocatalytic reaction;in the meantime,CF featurs a large amount of interconnected channels to facilitate fast mass diffusion and electron transfers besides good electrical conductivity.Benefiting from theses collective effects,the unique 3D architecture is innovatively exploited as a binder-free electrode for the determination of nitrite.As expected,the as-fabricated ?-Fe2O3 NAs/CF sensor exhibits enhanced electrochemical performance towards the oxidation of nitrite in terms of higher catalytic peak current and reduced oxidation potential as compared with the binder-containing counterparts.Importantly,the as-fabricated sensor demonstrats excellent detection towards nitrite with a fast response time of approximately 3 s,a wide linear range from 0.5 ?M to 1000 ?M,a high sensitivity of 116.8 ?A· mM-1·cm-2 and a low detection limit of 0.12(?M,which is dramatically lower than the maximum allowable level of nitrites(65 ?M)in drinking water set by the World Health Organization(WHO).It is noteworthy that the current electrochemical sensor has a specific recognition capability towards nitrite anions,hardly interfered by the coexisting species in natural waters.Additionally,the proposed sensor can still maintain excellent reproducibility and stability after 30 days of storage in ambient conditions,supported by the neglect decrease in electrocatalytic activity.Furthermore,the ?-Fe2O3 NAs/CF electrode also shows perspective applications in the determination of nitrite in real samples,as illustrated by satisfactory recoveries in tap water and lake water.3.In order to acquire more stable electrochemical sensing performance,in this work,we select the commercialized carbon cloth as the substrate for the in-situ growth of active materials inspired by ?-Fe2O3 NAs/CF electrochemical sensor toward nitrite sensing in the first chapter.As a consequence,three dimensional(3D)NiFe-layered double hydroxide nanosheet arrays(NiFe-LDH NSAs)have been successfully fabricated on a carbon cloth(CC)substrate via a facile one-pot hydrothermal route.By integrating the collective merits of macroporous CC and NiFe-LDH NSAs such as superior electrical conductivity,striking synergistic effect between dual active components,enlarged electrochemically active surface area,unique 3D hierarchical porous network characteristics,as well as fast charge transport and ion diffusion,the proposed NiFe-LDH NSAs/CC architectures can be directly served as a free-standing electrode toward the detection of nitrite.As a consequence,the resulting NiFe-LDH NSAs/CC electrode demonstrates superior electrocatalytic activity for the oxidation of nitrite,accompanied by fast response time(approximately 3 s),high sensitivity(803.6 ?A·mM-1·cm-2)and low detection limit(0.02 ?M).Meanwhile,the electrochemical sensor possesses timeless stability,good reproducibility and strong anti-interference capacity.Significantly,the developed sensing system has been further utilized to determine the nitrite level in tap and lake water with the acceptable recoveries,suggesting its feasibility in practical application.These findings show that the obtained NiFe-LDH NSAs/CC electrode holds great prospect in highly sensitive and specific detection of nitrite.4.Dopamine(DA)and uric acid(UA)are considered as crucial molecules for physiological processes associated with human metabolism.Hence,it is of great significance to develop a realiable and sensitive electrochemical senor for the accurate determination of DA and UA.In this work,a three-dimensional(3D)Co3O4@NiFe-layered double hydroxide nanowire arrays/carbon cloth composite(Co3O4@NiFe-LDH NWAs/CC)have been successfully fabricated via a facile and eco-friendly strategy.Subsequently,the as-prepared materials are systematically characterized by various analytical techniques to investigate the structure-,morphology-and composition-dependent properties.Benefiting from the collective merits of macroporous CC and Co3O4@NiFe-LDH NWAs such as prominent synergistic effect between dual active materials,good mechanical stability and superior electrical conductivity of CC,the proposed Co3O4@NiFe-LDH NWAs/CC architectures can be directly served as a free-standing electrode for simultaneous detection of DA and UA.As a consequence,the proposed Co3O4@NiFe-LDH NWAs/CC electrode demonstrates excellent electrocatalytic activity for the oxidation of DA and UA,accompanied by low detection limit of 0.45 ?M for DA and 0.38 ?AM for UA.Meanwhile,the proposed electrochemical sensor possesses long-term stability and good reproducibility.