Synthesis And Performance Of Carbon Dots

Carbon dots,a type of environmental friendly nanomaterials,have attracted widespread attention and been applied into biomedical,photoelectric and other fields in recent years due to its low toxicity,stable chemical properties,low cost,simple preparation methods as well as excellent optical properties.This thesis aims to explore the physical and chemical properties,fluorescence mechanism and practical application of carbon dots through synthesizing typical carbon dot materials?carbonized polymer dots?CPDs?and graphene quantum dots?GQDs??.The critical views of innovation in this thesis are as follows:Pioneered the red self-quenching-resistant solid-state fluorescent CPDs and synthesized fluorescent powder with full-color emission by adjusting the ratio of CPDs to solid matrix;Synthesized n-type GQDs loaded SnO₂ nanotubes by single-spinneret electrospinning and prepared the gas sensor based on GQDs-SnO₂ nanotubes which exhibit high sensitivity and good selectivity to ethanol.To be more specific,there are two aspects in details in the following parts.In chapter II,utilizing maleic acid and ethylenediamine as starting materials,we prepared the fluorescent CPDs,which exhibit strong red solid state fluorescence without any other additional solid matrices,while having a large production yield??89%?and a considerable quantum yield of 8.50%through a microwave-assisted method.When dispersed in water or solid matrices in gradient concentrations,they can exhibit yellow,green,and blue fluorescence under UV light.We analyzed the chemical structure of these CPDs,investigated the fluorescence mechanism of the CPDs powder as well as solutions with different concentrations through utilizing time-resolved emission spectra,and obtained fluorescent powder with tunable full-color solid state fluorescence.These fluorescent powders with different emissions can be used in various forms to satisfy the requirements of different important applications.For example,they can be utilized as the phosphor in LED application to obtain full-color emission LEDs and white LEDs.Additionally,we successfully fabricate fluorescent inks and polymer films with full-color emission.In chapter III,we prepared a novel n-type GQDs through acid-cutting method and successfully fabricated GQDs loaded SnO₂ nanotubes by single-spinneret electrospinning process.The gas sensor based on GQDs-SnO₂ nanotubes exhibit high sensitivity and good selectivity to ethanol.The loading concentration of GQDs to 0.4wt%showed the maximum ethanol response?S=80.0?at 325?C.The gas sensing mechanism of GQDs-SnO₂ based sensor was also investigated.In detail,the formation of n-n hetero-junction between SnO₂ nanoparticles and GQDs with different work function is responsible for the enhanced ethanol response in 0.4 wt%GQDs-SnO₂ nanotubes.In summary,this thesis starts from the preparation of CPDs that can resist self-quenching and has a concentration-dependent fluorescence,analyses their fluorescence mechanism and applies them into light-emitting diodes,fluorescent inks,and polymer films.Then we synthesized a kind of n-type property GQDs through acid-cutting method and fabricated a serious of GQDs loaded SnO₂ nanotubes,improving the sensitivity and selectivity of one-dimensional semiconductor oxides to ethanol gas.This thesis combines practical application with theoretical exploration,providing an instructive idea for the application of carbon dots materials.