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Synthesis,property And Application Of Novel Water-soluble Fluorescent Carbon Dots

Posted on:2018-05-31Degree:MasterType:Thesis
Country:ChinaCandidate:Y Z FanFull Text:PDF
GTID:2321330536473106Subject:Analytical Chemistry
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Carbon dots(CDs),as novel fluorescent nanomaterials,have attracted tremendous attention in detection due to their favorable performances.The CDs possess various merits including outstanding optical properties,robust chemical inertness,and good biocompatibility.In addition,it is essential to develop simple and eco-friendly precursors and preparation methods to promote the practical use of CDs.For these reasons,we carried out a series of studies on the preparation,property,and application in detection of novel fluorescent CDs.Based on the goal of practical application,the effects of carbon sources and preparation process on the performances of CDs were studied.The formation mechanism,morphology and structure,surface state,stability,and optical properties were characterized with various techniques.The relations between the physical and chemical characteristics of CDs and their optical properties were explored.Then the CDs were used to picric acid,dissolved ammonia detection and pH sensing.The main research contents are as follows: Part 1: A facile one-pot synthesis of water-soluble carbon dots for picric acid sensing from malonic acid and urea.In this work,novel water-soluble and blue fluorescent CDs were synthesized using one-pot hydrothermal method with malonic acid and urea.In order to obtain optimal fluorescence properties of CDs,some synthesis reaction conditions were optimized.The size,morphology,functional groups,and optical properties of CDs were characterized by high resolution transmission electron microscope(HRTEM),Fourier transform infrared(FTIR)spectrum,ultraviolet visible(UV-vis)absorption and fluorescence spectra.The CDs possessed good monodispersed property with mean diameter of 2.5 nm.And the abundant hydroxyl(-OH),carboxyl(-COOH),and amino groups(-NH2)on the surface of CDs improved the stability and hydrophilicity of CDs in an aqueous system.As for optical properties,the CDs held good absorption and emission property,excitation wavelength-dependent photoluminescence(PL)properties,and quantum yield of 12.6%.Moreover,the CDs showed good stability and anti-photobleaching ability.Interestingly,the fluorescence of CDs could be selectively quenched by picric acid(PA)within 10 s.Based on this phenomenon,a label-free fluorescence assay was proposed for specific determination of PA.The fluorescence intensity of probe showed a linear response to PA in the concentration range of 0.1 to 26.5 μM with a low detection limit of 51 nM(S/N = 3).Finally,the resultant fluorescent probe was successfully applied to the detection of PA in real water samples Part 2: One-pot hydrothermal synthesis of fluorescent carbon dots for pH sensing with onion as precursor.Based on the purpose of “green chemistry”,we used onion juice as precursor to one-pot hydrothermal synthesize fluorescent CDs.The HRTEM image showed that the CDs appeared as spherical particles with good monodispersity,and had an average size of 3.43 ± 0.39 nm with a lattice parameter of 0.18 nm.The FTIR and Nuclear magnetic resonance(NMR)spectroscopy revealed that there were plenty of functional groups such as-COOH,-OH and N-containing groups on the surface of the CDs.The UV-vis and fluorescence spectra exhibited that CDs possessed good absorption and emission property,and emitted blue fluorescence.Furthermore,the excellent salt tolerance,heat resistance,and photostability of CDs guaranteed their widespread availability under harsh and sophisticated conditions.The fluorescence intensity of CDs could be sensitively changed by different pH values,so a fluorescent method was proposed for sensing pH.The fluorescence intensity of CDs had a good linear relationship with the pH values over a wide range from 5.02 to 11.20,and the yellow color of solution changed from shallow to deep.Finally,the resultant fluorescent sensor was successfully applied to detecting pH in real water samples.Part 3: pH-sensitive fluorescent carbon dots for dissolved ammonia detection with onion as precursor.Due to the deprotonation of carboxyl groups-modified CDs by OH-which was generated from hydrolysis reaction of ammonium hydroxide,the fluorescence intensity of CDs could be sensitively changed by dissolved ammonia with different concentration.Based on this phenomenon,a fluorescence method was established for specific determination of dissolved ammonia.The analytical results showed the sensitivity for sensing dissolved ammonia by the presented method with a wide linear range of 0.1-50 mM and a detection limit of 34 μM.Finally,the resultant fluorescent sensor was successfully applied to detect dissolved ammonia in real water samples.
Keywords/Search Tags:carbon dots, fluorescence quenching, picric acid, pH sensing, dissolved ammonia
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