Preparation Of Wool Keratin-based Carbon Quantum Dots And Their Application In The Detection Of Heavy Metal Ions

With the industrial development and rapid process of urbanization,many factories such as electroplating,metal processing,pigment production,printing and dyeing bring about the emission of heavy metal ions such as chromium ions and iron ions.These heavy metal ions pollute rivers and lakes,not only causing direct harm to farmland and aquaculture,more seriously,through the enrichment of the food chain,heavy metal ions will enter the human body,causing serious health threats.Since heavy metal ions in water may cause irreversible damage to the environment and human body,their detection and treatment have become an urgent scientific problem to be solved.At present,the detection methods of heavy metal ions mainly based on atomic absorption spectrometry,atomic fluorescence spectrometry,inductively coupled plasma mass spectrometer,etc.These methods often require the use of large instruments,which are costly and inconvenient.In recent years,as a new type of heavy metal ion detection approach,the method by using the fluorescent detection reagents to indicate the presence of specific metal ions through visual fluorescence changes is attracting more and more attention.Carbon quantum dots(hereinafter referred to as "carbon dots")are a new type of fluorescent nanomaterials,which are green,non-toxic and bio-friendly compared with the traditional semiconductor quantum dots,and have promising application potentials in many fields such as bio-imaging,biosensing,chemical sensing and photocatalysis.The research on the synthesis and application of carbon dots is a research hotspot in recent years.In the existing research,organic acids,aldehydes,etc.are mostly used as carbon sources to synthesize carbon quantum dots,of which there are limitations in the environmental friendliness of precursor sources.In addition,the surface of carbon quantum dots often contains abundant functional groups,these functional groups affect the surface structure of carbon dots and thus affect the fluorescence properties,and are also reactive binding sites,which are easy to combine with metal ions,thereby carbon dots has high potential being used as a type of fluorescent detection reagent indicating the presence of metal ions,but the relevant mechanism is not yet clear.In this thesis,the process of preparing carbon quantum dots based on environmentally friendly and sustainable natural sources of raw materials was explored,for the purpose to provide new ideas for the greening of carbon dot preparation process.The variations of functional groups on the surface of carbon dots and their influence on their fluorescence properties were investigated,and the mechanism of their binding with metal ions were explored,the results are not only conducive to enrich the understanding of the regulation of carbon dots’ fluorescence properties,but also significant for the development of metal ion detection reagents based on carbon dot.The main contents of the thesis are as follows:(1)Wool keratin-based carbon quantum dots with good fluorescence properties were synthesized by a green and environmentally friendly hydrothermal method using wool keratin of natural origin as the carbon source.The effects of reaction temperature and reaction time on the fluorescence properties of the synthesized carbon dots were investigated,to find out the approach improving the fluorescence properties of the prepared carbon dots,the optimal reaction conditions for the hydrothermal preparation of carbon quantum dots from wool keratin were determined to be 200℃ and 10 h.By exploring the effect of reaction conditions.on the fluorescent properties of the synthesized carbon dots and examining the properties of hydrothermally synthesized carbon dots based on glutamic acid and cystine,the main components of the synthesized raw material,the reaction mechanism of hydrothermally synthesized carbon dots with high fluorescent properties based on wool keratin was further analyzed.(2)The surface functional groups and structural information of the prepared carbon quantum dots,and their light absorption and fluorescence emission ability were analyzed respectively by infrared spectroscopy,X-ray photoelectron spectroscopy,UV-vis spectroscopy and fluorescence spectroscopy,and the effect of adding different metal ions on their fluorescence was investigated.It was found that,chromium ions and iron ions could cause the quenching of their fluorescence.The theoretical mechanisms of the fluorescence quenching of the prepared carbon dots by Cr6+and Fe3+were revealed through a series of characterizations.The fluorescence detection ability of the prepared carbon dots for Cr6+ and Fe3+ was tested,respectively.Based on the experimental results,the application direction of the prepared carbon dots-the detection of Cr6+ in electroplating wastewater was designed.(3)In order to explore the performance and convenience of the prepared carbon quantum dots in sensing and detection,the prepared carbon quantum dots are loaded on a hydrogel composed of natural polysaccharide chitosan to obtain an environmental friendly fluorescent hydrogel.The prepared hydrogel has excellent fluorescence performance,and it has good adsorption ability for heavy metal ions because it has a three-dimensional porous network structure and contains abundant functional groups,which can realize the binding with metal ions,thus realizing both the detection function and the adsorption treatment of metal ions.To improve the convenience of carbon dot-hydrogel for the detection of heavy metal ions,we further prepared carbon dot/hydrogel composite film,which is easy to carry and can realize the rapid detection of specific metal ions.In summary,the carbon quantum dots prepared from wool keratin as the carbon source in this thesis have excellent fluorescence properties and show specific fluorescence quenching response to heavy metal ions such as chromium and iron,which have good application potential in realizing visible heavy metal detection in water bodies.Further,the fluorescent composite hydrogel was prepared by using the natural polysaccharide chitosan loaded with carbon dots,which combines the adsorption effect of the gel and the fluorescence property of the carbon dots,and can achieve the detection and treatment of heavy metal ions simultaneously.The research system in this paper was derived from natural source materials,which provides a new idea for developing green and efficient heavy metal detection methods and wastewater treatment systems.