Preperation And Assembly Of Carbon Nitride Nanoribbons For Sensing Applications

As a novel organic semiconductor,graphitic carbon nitride?CN?has received enormous attention in recent years.It has been widely used ranging from photocatalysis,photoelectric conversion to biosensor due to its excellent properties such as visible light response,chemical stability and low cost.Owning to its polymer nature,the molecular structure of carbon nitride can be easily tuned by doping and nanostructure regulation,thus optimizing the electronic band structure,improving the separation efficiency of photogenerated carriers and changing the interfacial properties.However,the research of carbon nitride is mainly focused on photocatalysis based on its semiconductor properties,meanwhile the research of other unique properties for carbon nitride are still in infancy,especially for sensing applications.The purpose of this dissertation is to explore the structure-activity relationship by regulating the nanostructure and interfacial properties of one-dimensional carbon nitride,then to develop new applications in selective adsorption/desorption,humidity and metal ion sensing.The main contents and innovations are summarized as follows:1.The C-N bond linking heptazine ring in CN skeleton is fragile under alkaline conditions,thus highly dispersible CN nanoribbons?CNNRs?with abundant amino and hydroxyl functional groups on the edge were prepared by hydrolyzing bulk CN in a NaOH solution.Due to the interfacial modification,the as-obtained CNNRs dispersion could reversibly transform into a 3D hydrogel network by bubbling CO₂ or N₂.Further taking advantage of the collaborative electrostatic and?-?interactions between hydrolyzed CNNRs and target molecules,as illustrated,a highly selective dye uptake and release were realized.Compared to the most widespread absorbent materials such as active carbon and graphene and previously reported supramolecular gel,the proposed CN hydrogel network not only exhibited competitive absorbing capacity?402 mg/g of MB?but also overcame the typical deficiencies of poor selectivity and high energy consuming regeneration.This work not only would provide a strategy for the assembly of bulk CN and expand the intriguing properties of 2D layered CN into 3D network but also open an avenue for developing a low-cost smart assembly with high performance for potential applications in selective extraction for sensing and environmental fields.2.A CN nanoribbons-based humidity sensor via anisotropic deformations was fabricated and used for breathing detection.The few layers characteristics and well-balanced affinity for water molecules between hydrophilic edge and hydrophobic framework of CNNRs made the anisotropic deformation rapid and reversible.After coupling to carbon nanotubes via a strong?-?interaction into a network,such delicate deformation could be converted into an easy-measurable resistance change.The CNNRs-based humidity sensor exhibited an ultrafast response?ca.50 ms?,high reproducibility and selectivity,and linearity almost in the full humidity range.As an example,it was successfully applied to real-time respiratory monitoring with a higher sensitivity even under a simpler setup,compared with traditional clinic pulmonary function testing.3.Based on the coordination interaction between carbon nitride nanoribbons and silver ions,a new visual detection method for silver ions has been developed.It was found that a new fluorescence peak was appeared at 530 nm when the hydrolyzed carbon nitride nanoribbons were combined with silver ions,and the original emission peak of carbon nitride at 420 nm was quenched.For comparison,carbon nitride nanosheets was prepared,and the results show that the emission of carbon nitride was quenched without new peak formed.The mechanism of this phenomenon may be attributed to the coordination of silver ions with the edge groups,thus introducing new energy levels below the conduction band of carbon nitride.Compared with the traditional metal ion detection method based on fluorescence quenching mechanism,this strategy has high selectivity which can effectively avoid the occurrence of false positives.