Carbon Nitride Nanosheets:Preparation,Surface Functionalization And Application In Drug Delivery

Biocompatibility,drug compatibility of carbon nitride nanosheets（CNNS）and their stability in physiological media are of great significance to expand the biomedical applications.In this thesis,the colloidal stability of charged CNNS was adequately studied in theoretical level and surface-engineered C3N4 complexes also were synthesized.Based on this,drug delivery applications of CNNS were further investigated.Main issues in this thesis can be summarized as follows:1.Three representative pathways were used to prepare the ultrathinCNNS from bulk C3N4,and which show a lateral dimension of¹00 nm and a height distribution ranging from 1.5 to 6 nm.Average size of nanosheets can be controlled by adjusting the ultrasound time.It was found that the redispersibility of CNNS powders in water can be improved by adding freeze-drying protectant during the freeze drying process.We also found the CNNS prepared via a H₂SO₄ exfoliation route showed clear mesoporous structure.2.The relationship between ion and colloidal stability of CNNS was fully investigated,and a theory of charge-driven layer-by-layer self-assembly was put forward to study the flocculation phenomenon occurred when CNNS met ions or some small molecules with charge.3.Exfoliation route,pH and surface modification all can be used to control the surface charge of CNNS.And it changed from positive to negative by decoration of BSA,on the contrary,it changed from negative to positive by modification of PEI.4.It was found that surface functionalization by means of BSA or PEI could improve the colloidal stability of CNNS in various environments and achieved the charge inversion.In addition,the interaction forces between CNNS and BSA included hydrophobic force,hydrogen bond and electrostatic force,and PEI could interact with CNNS by electrostatic attraction.5.CNNS possess an ultrahigh drug-loading capacity of 300%for the delivery of Sal B with aromatic structure.In contrast to TSIIA,TSIIA/HP-β-CD can avoid the situation that hydrophobic drugs would crystallise when encountered with hydrophilic carrier and achieve loading of TSIIA successfully.This innovative strategy can provide suggestions for other two-dimensional nano-carriers to load hydrophobic drugs.In addition,sustained drug-release pattern can be achieved from CNNS.6.TSIIA nanocrystal was prepared by an antisolvent precipitation method augmented by sonication,and CNNS were used as stabilizers in drug nanosuspensions.The results showed that BSA-engineered CNNS could partly improve the stability of drug nanocrystals.7.CNNS were shown to feature amphiphilic behavior at liquid-liquid interface and solid-liquid interface.They could be used as solid emulsifiers to form Pickering emulsion,and improve the dispersion performance of hydrophobic TSIIA in aqueous phase.In addition,the preparation of CNNS coated paraffin microspheres indicated that the morphological transformation from 2D to 3D was achieved.