A one‐step solvothermal method for the preparation of carbon dots with red fluorescence (R‐CDs) was put forward, in which sodium citrate and formamide were chosen as precursors, while formamide was adopted as the solvent. The fluorescence emission peak of the as‐prepared R‐CDs remained the same (600 nm) when the excitation wavelength increased from 490 nm to 560 nm, and the fluorescence quantum yield is 35.3%. Furthermore, the fluorescence intensity of the as‐prepared R‐CDs could be selectively quenched by copper ions, and the mechanism of Cu2+ quenching R‐CDs is the combination of static and dynamic quenching. As a result, the R‐CDs were applied for the construction of a fluorescent sensor without any modification for the quantitative and visual detection of copper ions, which is a typical contaminant in water. The limit of detection for the fluorescent sensor was as low as 5 nmol/L, and it can be used to fast and directly confirm whether the content of copper ions in drinking water meets the criteria of the United States Environmental Protection Agency and the World Health Organization.
Significant improvement in the fire resistance of polyethylene terephthalate (PET) while ensuring its mechanical properties is a tremendous challenge. A novel flame retardant (GO-HCCP, graphene oxide-hexachlorocyclotriphosphazene) was synthesized by nucleophilic substitution of the graphene oxide (GO) and hexachlorocyclotriphosphazene (HCCP) and then applied in PET by an in situ polymerization technique. The scanning electron microscope (SEM) showed a better dispersion of GO-HCCP than GO in the PET matrix. The char yield at 700 °C increased by 32.5% with the addition of GO-HCCP. Moreover, the peak heat release rate (pHRR), peak smoke produce rate (pSPR)and carbon monoxide production (COP)values significantly decreased by 26.0%, 16.7% and 37.5%, respectively, which indicates the outstanding fire and smoke suppression of GO-HCCP. In addition, the composites exhibited higher elastic modulus and tensile strength without compromising the toughness of PET matrix. These significantly reduced fire hazards properties are mainly attributed to the catalytic carbonation of HCCP and the barrier effect of GO. Thus, PET composites with good flame-retardant and mechanical properties were prepared, which provides a new strategy for further flame retardant PET preparation.
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