Controllable Preparation And Heavy Metal Ions Detection Performance Of Sulfur-doped Carbon Nitride Nanotubes And Its Composites

Heavy metal ions(HMIs)are characterized by sudden occurrence,diversity of species,high toxicity,difficult treatment of low concentration and unable to degrade.The pollution caused by HMIs has aroused more and more attention.In particular,HMIs have excellent solubility,which can be enriched by organisms.They will flow into the human body through diet and other ways,causing a very serious threat to human health and life safety.Therefore,for HMIs pollution in the water environment,it is of great significance to develop new sensitive materials and sensors with high sensitivity and selectivity for ensuring the water environment and drinking water safety.Graphitic carbon nitride(GCN),as an organic semiconductor compound,has been widely used in the adsorption removal and detection of HMIs due to its large number of N atoms and-NH2 groups.However,the low utilization rate of active sites and poor conductivity of GCN limit its application in the field of HMIs electrochemical detection.In this paper,the strategies of heteroatom doping,nanostructure regulation and carbon materials modification were selected:(1)By controlling the content and type of heteroatoms,the sensitivity and selectivity of electrochemical detection of HMIs could be improved by the coordination and chelation between active sites and HMIs.(2)More active sites of GCN could be exposed through nanostructure regulation,which could improve the utilization rate of active sites and the permeation and diffusion performance of the HMIs solution.(3)Through the modification of conductive carbon material,the problem of poor conductivity of GCN was solved,and the electrochemical reactivity and electronic transport performance were improved.Through the synergistic action of the above strategies,highly sensitive and selective GCN-based sensitive materials for HMIs electrochemical detection were successfully constructed.The electrochemical detection performance of HMIs was studied and the electrochemical detection mechanism was discussed.The main research contents of this paper were as follows:(1)Sulfur-doped GCN tube bundles/graphene nanosheets(STB/Gs)with hierarchical pore structure were prepared by hydrogen bond supermolecular self-assembly,induced evaporation and electrostatic assembly methods using melamine(MEL)and trithiocyanuric acid(TCA)as raw materials.By adjusting the proportion of raw materials and the temperature,time and heating rate of thermal polymerization,the in-situ sulfur doping content and the microstructure of S-doped GCN were controlled.The electronic transport performance of STB/Gs composites was enhanced by adjusting the amount of Gs.Through the synergistic action of STB and Gs,the HMIs electrochemical detection performance of STB/Gs composites was optimized.The limit of detections(LODs)of Cd2+,Pb2+and Hg2+ by STB/Gs composites were 1.173,0.382 and 0.616 nM for simultaneous detection,and 2.304,0.785 and 1.158 nM for individual detection,respectively.(2)Sulfur and oxygen co-doped GCN short nanotubes/expanded graphite(SOT/EG)composites with hierarchical pore structure were prepared by vacuum-assisted intercalation and confined hydrogen bond supermolecular self-assembly methods using MEL and TCA as raw materials and dimethyl sulfoxide(DMSO)as solvent.The HMIs electrochemical detection performance of SOT/EG composites was optimized by selecting EG with different mesh numbers and adjusting the amount of EG.The sulfur doping content of SOT/EG composites was further increased due to the slowing effect of EG slit holes on raw material decomposition and the ex-situ doping effect of DMSO.The confined preparation of SOT not only had a higher degree of nanosize,exposing more active sites,but also constructed more mesoporous in EG slit holes,enhancing the permeation and diffusion performance of HMIs solution.Through the synergistic action of SOT and EG,the sensitivity of HMIs electrochemical detection was further improved,the LODs were reduced,and the selectivity of Hg2+was enhanced.The LODs of Pb2+ and Hg2+ by SOT/EG composites were 0.184 and 0.256 nM for simultaneous detection,and 0.217 and 0.286 nM for individual detection,respectively.(3)Sulfur and oxygen co-doped GCN nanotubes/carbon nanotubes(SOT/CNT)composites with hierarchical pore structure were prepared by amidation reaction and insitu hydrogen bond supermolecular self-assembly using MEL and TCA as raw materials and DMSO as solvent.The HMIs electrochemical detection performance of SOT/CNT composites was optimized by selecting CNTs of different tube diameters and adjusting the amount of CNTs.The amidation process of MEL and CNTs significantly increased the oxygen doping content of SOT/CNT composites,while TCA in-situ doping and DMSO ex-situ doping increased the sulfur doping content.The steric-hindrance effect of CNTs was used to interfere with the in-situ hydrogen bond supermolecular self-assembly of SOT,which significantly increased the porosity and specific surface area of SOT/CNT composites,exposed more active sites,and enhanced the permeation and diffusion performance of HMIs solution.Through the synergistic action of SOT and CNTs,the selectivity of Cd2+ was enhanced and the electrochemical detection performance of HMIs was improved.The LODs of Cd2+,Pb2+ and Hg2+ by SOT/CNT composites were 0.502,0.276 and 0.438 nM for simultaneous detection,and 0.798,0.437 and 0.667 nM for individual detection,respectively.