Nitrogen-doped carbon quantum dots (N-CDs) have become a current focus of chemical research due to their superior photoluminescence (PL) properties and high fluorescence quantum yield (QY). In this paper, we reported a facile, simple and low-cost approach for the synthesis of highly fluorescent and stable N-CDs by hydrothermal treatment of maleic acid and ethylenediamine. The as-prepared N-CDs emitted strong blue fluorescence with an absolute QY of up to 45%, and exhibited pH-independent behavior in a wide pH range from 1 to 13 and good water solubility. In addition, the fluorescence of the N-CDs can be significantly quenched by p-nitrophenol (4-NP) through an electron-transfer-induced dynamic quenching mechanism, leading to 4-NP being sensed optically. The sensor presented a good linearity with 4-NP concentration in the range of 0.10–11 μg mL⁻¹. The detection limit of 22 ng mL⁻¹ 4-NP could be obtained, which is lower than the 60 ng mL⁻¹ limit allowed in drinking water by the U. S. Environmental Protection Agency. The sensor exhibited rapid recognition and distinguished selectivity to 4-NP over other structural analogues of phenols. Moreover, the sensing system was successfully applied for the determination of 4-NP in environmental water samples.

In this work, carbon dot-decorated graphite carbon nitride composites (CDs/g-C₃N₄) were synthesized and innovatively used as a SPME coating for the sensitive determination of chlorobenzenes (CBs) from water samples, coupled with gas chromatography–mass spectrometry. The CDs/g-C₃N₄ coating presented superior extraction performance in comparison to pristine g-C₃N₄, owing to the enhancement of active groups by CDs. The extraction capacities of as-prepared SPME coatings are higher than those of commercial coatings due to the functions of nitrogen-containing and oxygen-containing group binding, π–π stacking, and hydrophobic interactions. Under optimized conditions, the proposed method exhibits a wide linearity range (0.25–2500 ng L⁻¹), extremely low detection of limits (0.002–0.086 ng L⁻¹), and excellent precision, with relative standard deviations of 5.3–9.7% for a single fiber and 7.5–12.6% for five fibers. Finally, the proposed method was successfully applied for the analysis of CBs from real river water samples, with spiked recoveries ranging from 73.4 to 109.1%. This study developed a novel and efficient SPME coating material for extracting organic pollutants from environmental samples.

Two simple and sensitive methods for rapid determination of hydrazine in water are described, based on the inhibition effect of hydrazine on the reaction of oxyhalogen ion + halogen ion (X⁻) with rhodamine B in an acid medium. It is found that the linear range and the detection limit for the determination of hydrazine are 7.88–78.8 ng mL⁻¹ and 1.7 ng mL⁻¹, respectively, in the system of potassium chlorate in hydrochloric acid. They are 3.49–78.8 ng mL⁻¹ and 0.81 ng mL⁻¹, respectively, in the system of potassium bromate + potassium bromide in sulphuric acid solutions. Recoveries are in the range of 94–104%. A comparison was made for the analytical characteristics of different methods, and a possible reaction mechanism was proposed.