Synthesis,Structures And Applications Of Metal Ions-doped Carbon Dots Based On Gluconate Salts

Carbon dots?CDs?,as a new type of carbon-based fluorescent nanomaterials,possess the advantages of simple preparation,tunable emission,high photostability,good biocompatibility and ease of surface modification,showing great application potential in the fields of display,sensing,catalysis,biomedicine and optoelectronic devices.Since the first report of CDs synthesis,there have been plenty of works on regulating its structure and properties,aiming at improving the photoluminescent quantum yield?PLQY?of CDs,broadening the PL spectral coverage and developing its special applications.Among them,heteroatom?mainly nitrogen?doping is widely utilized and considered as the most effective method,which can adjust the charge distribution of carbon atoms,resulting in changes of the optical and electronic properties of CDs.Except for non-metallic elements,the metal ions-doping strategy is expected to give CDs specific properties and applications due to the active electronic layer structure and special functions of metal elements.Different from the previously reported CDs/metal-based composite hybrid materials,in which metal is the main component,while CDs usually only serve as an additive to improve the performance of metal semiconductors,and the problems of complicated preparation process and high cost still exist.In contrast,the metal ions-doped CDs are mostly composed of carbon dots doped with low content of metal,thus retaining the advantages of facile synthesis and low toxicity of CDs.However,as an emerging research area,there are few metal ions-doped CDs related works and the reported methods are not universal,lacking of customized capabilities and applications of CDs derived from the metal dopants.In this paper,for the first time,a series of metal ions-doped CDs were systematically designed and synthesized based on a novel system of raw materials based on metal gluconate salts.Moreover,the introduction of different metals could endow CDs new functions in detection,osteogensis and electrocatalysis.In the second chapter,zinc gluconate was used as the sole raw material,which could serve as both carbonaceous precursor and metal source.In-situ doping of zinc ions was achieved by one-step pyrolysis to synthesize zinc ion-doped carbon dots?Z-CDs?.It was found that the charge repulsion of the zinc carboxylate groups prevented the aggregation of CDs during the carbonization process,and at the same time,zinc ions could act as passivation agents of CDs surface defects,thus significantly improving the PL intensity of CDs.Then,disodium ethylenediamine tetraacetate?EDTA?,a strong chelating agent of metal ions,was introduced to remove Zn²⁺from the surface of Z-CDs,leading to fluorescence quenching,and the quenched PL could be recovered by adding Zn²⁺to re-passivate Z-CDs.Based on the mechanism of zinc ions passivation enhancing fluorescencen,a reversible"Off-on"fluorescent probe for the detection of EDTA/Zn²⁺was constructed with high sensitivity and selectivity,which was further applied in tap water environment and in vitro cell level sensing.In the third chapter,based on the biological functions of magnesium ions that affect the proliferation and differentiation of osteoblasts cells,magnesium ions-doped carbon dots?Mg-CDs?were designed and synthesized using magnesium gluconate as precursor through a one-step hydrothermal method,and its application in bone promotion was first reporeted.The Mg-CDs showed very low cytotoxicity to mouse embryo osteoblast precursor cells?MC3T3-E1?,and it could promote osteoblastic differentiation by improving osteogenesis enzyme activity and up-regulating related mRNA expression.The control experimental results presented that Mg-CDs had stronger osteogensis effect than magnesium gluconate within a shorter period of time.This was due to the efficient cells uptake of CDs,which provided an excellent Mg²⁺nanocarrier.Moreover,the fluorescence nature made Mg-CDs have the dual function of cell labeling.In order to extend the retention time of CDs in vivo,CDs and gelatin/hydroxyapatite scaffold composite material was fabricated,which showed good bone regeneration effect in the animal experiments of rat skull defect model.In the fourth chapter,the active transition metals containing cobalt gluconate and ferrous gluconate salts were selected to synthesize cobalt,iron ions co-doped carbon dots?CoFe-CDs?to enhance the intrinsic electrochemical activity of CDs.For the first time,the active metal ions-doped CDs could be directly applied as electrocatalytic oxygen evolution reaction?OER?catalysts.The CoFe-CDs had the lowest overpotential among the reported individual CDs-based OER electrocatalysts,and even comparable with the complex CDs/metal-based composites.Comparative experiments showed that the electrocatalytic activity of the dual metal-doped carbon dots was much higher than that of the non-metal and single-metal doped CDs.The active centers and synergistic effects were revealed through detailed characterization and theoretical simulation.Moreover,using the reducing capability from the hydroxyl groups of glucose molecule,ruthenium ion(Ru³⁺)was introduced into the above system,and two types of electrocatalysts with different functions were innovatively synthesized within one-pot hydrothermal reactor.The carbon-loaded Co,Fe co-doped ruthenium nanoparticles networks?CoFeRu@C?exhibited superior electrocatalytic hydrogen evolution reaction?HER?acitivity with the lowest overpotential record among all the HER electrocatalysts.Based on CoFe-CDs/CoFeRu@C system,the application of electrocatalytic overall water splitting was initially explored in alkaline media with excellent performance and stability.In summary,systematic study of metal ions-doped CDs was carried out in this thesis,and a universal method for designing and synthesizing a series of metal ions-doped CDs from metal gluconate salts was established,the novel properties and functions of which were carefully investigated.The as-prepared metal ions-doped CDs enriched the constituent members of CDs family,and provided empirical strategies for the preparations or applications of other metal ions-doped CDs in the future.