Construction Of Fluorescence-colorimetric Dual-mode Detection Of Wastewater Pollutants Based On Functionalized Carbon Dots

The technique of carbon-based nanomaterials have achieved important progress nowaday,which have been widely concerned by scientists because of their excellent physical and chemical properties,and have great application value and development space in the fields of material chemistry,biomedicine and environmental detection.Carbon dots（CDs）,as a kind of carbon-based fluorescent nanomaterials,inherit the advantages of carbon-based nanomaterials,but also have their charm.Compared with traditional fluorescent nanomaterials,CDs have been widely concerned by scientists in the detection of environmental pollutants due to their rich raw materials,low price,excellent optical properties,low cytotoxicity,easy functionalization,etc.To expand the application of CDs in the environmental field,research teams have done a lot of research on improving the luminescence performance and exploring the luminescence mechanism.Experimental results show that the doping of different heteroatoms can impart more groups to the surface of CDs,which will bring a wider application in environmental pollution control and remediation.At present,the sensing platform built based on CDs mainly uses a single fluorescence emission as the output signal for the detection of target pollutants.This sensing mode is susceptible to the influence of external environment and probe concentration and other conditions,and the dual-mode detection mode can greatly reduce the above interference factors and achieve high accuracy detection.Therefore,we prepared CDs with different functions by using different raw materials and designed a dual-mode fluorescence and colorimetric nanosensor with CDs for the detection and analysis of environmental pollutants（antibiotics and heavy metals）.The specific work is as follows:（1）The original CDs were prepared from sucrose,phosphoric acid,andethylenediamine,and then the reduced carbon dots co-doped with N,P,and B（r-CDs）was synthesized through a simple reduction pathway,and the functional groups of r-CDs were more reducible.Due to the specific binding between r-CDs surface functional groups and tetracycline（TC）,a fluorescent colorimetric dual-mode nanosensor for TC detection was designed using r-CDs as a detection platform.When TC was added into r-CDs solution,the fluorescence resonance energy transfer occurred between the two,and the fluorescence intensity of r-CDs was obviously quenched under ultraviolet lamp.The experimental results showed that the fluorescence quenching rate has an excellent linear relationship with the TC contants,and the detection limit is as low as 1.73 n M,realizing high-sensitivity detection.At the same time,due to the interaction between r-CDs and TC to form a specific complex,the mixed solution has obvious color changes（from colorless to red）.r-CDs can detect TC by visual observation,achieving high accuracy detection with a low detection limit.In addition,the anti-interference experiment and actual sample analysis were also carried out.TC was recovered from aquaculture wastewater,which had a good recovery effect compared with other fluorescence detection techniques.In this work,the dual-mode detection method was designed and successfully used for TC specific detection,which is expected to provide a new possibility for the study of real-time on-site TC detection in actual wastewater.（2）A new type of nanomaterial sensor called boron and nitrogen co-doped carbon dots（B,N-CDs）was designed with sucrose,boric acid,and melamine as raw materials.A series of characterization and analyses of its functional group composition elements and optical properties were performed.Due to the double combination of dynamic and static quenching of B,N-CDs and Mercury ion(Hg²⁺),B,N-CDs were used as fluorescence probes to detect Hg²⁺.At the same time,B,N-CDs catalyzed oxidation of 3,3’,5,5’-tetramethylbenzidine（TMB）to generate TMB cationic radicals by simulating the activity of peroxidase,resulting in the solution turning blue.Then cysteine was added to inhibit the emergence of TMB cationic radicals,resulting blue solution disappearing.The addition of Hg²⁺reopens the generation path of TMB cation radical,so as to construct an on-off-on colorimetric signal for detection.The dual-mode detection modes achieve high sensitivity and high accuracy detection of Hg²⁺with an extremely low detection limit.In addition,selective and actual sample analysis experiments were explored in the complex water environment,B,N-CDs fluorescence and colorimetric dual-mode detection of Hg²⁺has a good application prospect.Therefore,B,N-CDs dual-mode detection of Hg²⁺opens up a new way to solve the environmental monitoring and remediation of heavy metal ion pollution in the water environment.（3）The performance of the two functionalized CDs was compared with the detection methods reported in previous literatures,and the advantages and disadvantages of the two functionalized CDs were evaluated.The results showed that r-CDs fluorescence colorimetric detection TC had certain advantages,and B,N-CDs also had excellent performance in detecting Hg²⁺.According to the national water quality pollutant standards,and the waters where these two nanomaterials are applicable are analyzed.These two functional CDs have high sensitivity and accuracy for TC and Hg²⁺detection,and can realize field platform detection.r-CDs is mainly suitable for monitoring TC in aquaculture wastewater and agricultural wastewater,while B,N-CDs is suitable for Hg²⁺detection in electroplating plant wastewater and Xiangjiang river.