Water-soluble and reductive carbon quantum dots (CQDs) were fabricated by the hydrothermal carbonization of chitosan. Acting as a reducing agent and stabilizer, the as-prepared CQDs were further used to synthesize gold nanoparticles (AuNPs). This synthetic process was carried out in aqueous solution, which was absolutely “green”. Furthermore, the CQDs/AuNPs composite was used to detect iodine ions by the colorimetric method. A color change from pink to colorless was observed with the constant addition of I⁻ ions, accompanied by a decrease in the absorbance of the CQDs/AuNPs composite. According to the absorbance change, a favorable linear relationship was obtained between ΔA and I⁻ concentration in the range of 20–140 μM and 140–400 μM. The detection limit of iodide ions, depending on the 3δ/slope, was estimated to be 2.3 μM, indicating high sensitivity to the determination of iodide. More importantly, it also showed good selectivity toward I⁻ over other anion ions, and was used for the analysis of salt samples. Moreover, TEM results indicated that I⁻ ions induced the aggregation of CQDs/AuNPs, resulting in changes in color and absorbance.

Calcium alginate (CaAlg) is a kind of biodegradable and eco-friendly functional material, and CaAlg/reduced graphene oxide (rGO) composites are expected to be applied as new textile, heat-generating, and flame-retardant materials. In this paper, the CaAlg/rGO composites were prepared by a sol-gel method and their morphological and thermal properties were studied. The results showed that the introduction of rGO can efficiently improve the thermal stability of CaAlg. Further study showed that rGO increased the carbon formation rate by 4.1%, indicating that the thermal stability was improved by the promotion of carbon formation. Moreover, the weight loss rate of the composites was faster at 180–200 °C than that of CaAlg, after which the rate was less comparatively, suggesting the better thermal stability of the composite. This maybe because the high heat transfer efficiency of rGO allowed the material to reach the temperature of the thermal decomposition of the glycan molecule chain within a short time, and then promoted carbon formation. The thermal cracking mechanism of the composites is proposed based on the experimental data.

In the present work, silver nanoparticles (AgNPs) were prepared by a simple and green method using carrageenan as reducing and capping agent. The as-synthesized carrageenan-AgNPs was demonstrated as an effective duel colorimetric sensing for selective and sensitive recognition of Cu²⁺ and S²⁻, which could be used to detect these ions with naked eyes. In addition, the possible sensing mechanism was that Cu²⁺ ions caused serious aggregation of carrageenan-AgNPs, which led to the color change of carrageenan-AgNPs. AgNPs were etched by S²⁻ forming Ag₂S, which played an important role in the determination of S²⁻ ions. Furthermore, it has been successfully applied to the determination of Cu²⁺ and S²⁻ in tap water and lake water, showing its great potential for the analysis of environmental water samples.

Detection of mercury (Hg²⁺) and sulfide (S²⁻), universal and well-known toxic ions, is crucial in monitoring several diseases. How to design and fabricate the high-performance sensor for simultaneously and accurately detecting the Hg²⁺ and S²⁻ is critical. Herein, we proposed a novel and convenient strategy for optical detection of Hg²⁺ and S²⁻ by employing a carboxymethyl cellulose sodium/silver nanoparticle (CMS/AgNPs) colloidal solution, in which AgNPs were used as monitor for Hg²⁺ and S²⁻, and the CMS was utilized as both the stabilizer and the hydrophilic substrate for AgNPs. Well-identifiable peaks for Hg²⁺ and S^2– were obtained in water based on UV–VIS absorption spectra, the absorbance intensity and/or position of nano-silver vary with the addition of Hg²⁺ cation and S^2– anion, accompanying with color change. Impressively, the optimal AgNPs anchored CMS exhibited a high sensitivity and selectivity toward Hg²⁺ and S²⁻, the change in absorbance was linear with the concentration of Hg²⁺ (0–50 μM) and S²⁻ (15–70 μM), and the lowest limits of detection (LOD) were 1.8 × 10⁻⁸ M and 2.4 × 10⁻⁷ M, respectively. More importantly, owing to the superior properties in testing Hg²⁺ and S²⁻, the fabricated sensor was successfully applied for detection of target ions in lake and tap water samples. All these good results implied that the designed strategy and as-designed samples is promising in detecting cation (Hg²⁺) and anion (S²⁻) ions and open up new opportunities for selecting other kinds of ions.

With Cu²⁺ complexes as precursors, nano-cuprous oxide was prepared on a sodium alginate template excluded of Cl⁻ and based on which the calcium alginate/nano-cuprous oxide hybrid materials were prepared by a Ca²⁺ crosslinking and freeze-drying process. The thermal degradation and combustion behavior of the materials were studied by related characterization techniques using pure calcium alginate as a comparison. The results show that the weight loss rate, heat release rate, peak heat release rate, total heat release rate and specific extinction area of the hybrid materials were remarkably lower than pure calcium alginate, and the flame-retardant performance was significantly improved. The experimental data indicates that nano-cuprous oxide formed a dense protective layer of copper oxide, calcium carbonate and carbon by lowering the initial degradation temperature of the polysaccharide chain during thermal degradation and catalytically dehydrating to char in the combustion process, and thereby can isolate combustible gases, increase carbon residual rates, and notably reduce heat release and smoke evacuation.

The development of highly selective and highly sensitive nanometer colorimetric chemical sensors is an urgent requirement in the immediate detection of heavy metal ions. In this work, silver-nanoparticle (Ag NPs)-based chemosensors were prepared by a simple and green method, in which the silver nitrate, carboxymethyl cellulose sodium (CMS) and Polyvinylpyrrolidone (PVP), and glucose are used as the silver source, double stabilizer and green reductant, respectively. The obtained colloidal CMS/PVP-Ag NPs showed a high dispersibility and stability, and creating a high selectivity and sensitivity to detect Hg²⁺ and Fe³⁺ with remarkable and rapid color variation. Low limits of detection (LOD) of 7.1 nM (0–20 μM) and 15.2 nM (20–100 μM) for Hg²⁺ and 3.6 nM for Fe³⁺ were achieved. More importantly, the CMS/PVP-Ag NPs has a high sensitivity even in a complex system with multiple heavy ions, the result of the practical ability to detect Hg²⁺ and Fe³⁺ in tap water and seawater reached a rational range of 98.33~104.2% (Hg²⁺) and 98.85~104.80% (Fe³⁺), indicating the great potential of the as-prepared nanocomposites colorimetric chemosensor for practical applications.