| Carbon quantum dots(CQDs, C-dots or CDs), a new class of zero dimensional semiconductor nanomaterials, which have attracted widespread attention as rising star in nanocarbon family in recent years because of low toxicity, cheaper, sample preparation technology, rich raw materials(coal, flour, crop stalks, pericarp and so on)and tunable fluorescence emissions, It also achieved environmental protection and greenization in the field of chemical sensing and photocatalysis. However, it have some disadvantages which carbon dots needing surface passivation and functionalization due to low fluorescence intensity and quantum yield. The complicated purification process lead to carbon dots is unstable.In addition, pure carbon dots did not efficiently use sunlight energy in photocatalytic processes. It significant to synthesize complex photocatalysts about carbon dots. we describe the recent progress in the field of CQDs, focusing on their synthetic methods, modification strategies, luminescent mechanism, and applications in catalysis and sensor issues.The major work includes the following aspects:1. Nitrogen-doped carbon quantum dots (N-CQDs) have been synthesized by one step with hydrothermal methods using garlic. The effects of the hydrothermal time, temperature, additive amount of garlic, the N-CQDs showed better fluorescence when added 6g garlic and hydrothermal time was 10 h in 120℃.The optical performance and structure characteristics of N-CQDs was further researched by TEM,AFM,XPS and FTIR. The uniform diameter of approximate 6 nm spherical particles, which have perfect water dispersion. It suggested that most of them consist of 1-5 graphene layers, and the N-CQDs are functionalized with hydroxyl, amino, carbonyl groups, and exhibited excellent water-solubility and high stability. The characteristic absorption peak of N-CQDs emerge at about 238nm and emit avisible strong bright blue light fluorescence with a high quantum yield (0.14). The formation mechanism of the N-CQDs was proposed. that is, nitrogen atoms finally arise in the form of six-circle annular(N-6, N-Q, N-X), whose chemical property is steady, and N-5(Pyrrolic-N)turn into N-H through "ring expanding" after high-temperature treatment.2. Nitrogen-doped carbon quantum dots(NCDs) was synthesized by one-step hydrothermal treatment with citric acid as carbon source, and ammonia as nitrogen source. The obtained NCDs exhibited excellent water-solubility and high stability. High-resolution TEM image showed that the diameter of particles was about 3 nm. Fourier transform infrared and X-ray photoelectron spectroscopy (XPS) spectra analysis demonstrated that the NCDs are functionalized with hydroxyl, amino, carbonyl, and carboxylic acid groups. It was further demonstrated that such NCDs can serve as effective fluorescent sensing platform for Hg2+ ions detection with sensitivity and selectivity. In a PBS butter solution(pH 7.0), the fluorescence quenching ratio (F/Fo) indicated linear responses with Hg2+ concentration ranging from 0.001 to 0.1μmol/L, with the detection limit of 2.1 nmol/L. It was successfully applied to determination of Hg2+ in samples.3. Fluorescent S,N co-doped carbon quantum dots (N,S-CQDs) were synthesized by hydrothermal treatment with citric acid as carbon source, and L-cysteine as N,S source. N,S-CQDs showed high quantum yield (0.81), excitation independent under excitation of 300-460nm. High-resolution TEM image showed that the diameter of particles was about 10nm. Fourier transform infrared and X-ray photoelectron spectroscopy (XPS) spectra analysis demonstrated that the N,S-CQDs are functionalized with hydroxyl, amino, carbonyl groups, and exhibited excellent water-solubility and high stability. It was further demonstrated that the obtained N,S-CQDs can serve as effective fluorescent sensing platform for Fe3+ions detection with sensitivity and selectivity. In a PBS butter solution(0.1 mol·L-1 pH 7.5), the fluorescence quenching ratio (F/Fo) indicated linear responses with Fe3+ concentration ranging 1-10 nmol·L-1 and 0.2-1μmol·L-1, with the detection limit of 0.4 nmol·L-1. It was successfully applied to determination of Fe3+ in samples.4. The water-souble carbon quantum dots(CQDs) were synthesized using the hydrothermal carbonization method with glucose as carbon source. Then a bit of CQDs was loaded on the BiOCl surface by a ultrasonic assisted hydrolysis, and the BiOCl/CQDs complex photocatalysts was goated. The structure and properties of BiOCl/CQDs photocatalysts was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier infrared spectrum(IR) and Fluorescence spectrophotometer. The photocatalytic activity was evaluated by photocatalytic degradation of Rhodamine B, and investigated different CQDs content of photocatalytic performance of the photocatalyst. The experiments demonstrated that the degradation rate was enhanced obviously compared with the single phase BiOCl, and the degradation rate reached to 93% in 40 minutes when the concentration of CQDs was 1.5 mg/mL. |
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