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Cyamelurate anions obtained from the hydrolysis of polymeric graphitic carbon nitride were used for the preparation of a water-stable and crystalline coordination polymer based on nickel(II)–cyamelurate. The polymer was prepared and applied as a catalyst for the reduction of 4-nitrophenol to 4-aminophenol in the presence of borohydride under ambient conditions. The catalyst was prepared by a simple and environmentally friendly method in an aqueous medium, and it was completely characterized by a variety of techniques, including FTIR, UV–Vis, XRD, TGA, TEM, and STEM. The obtained catalyst was able to catalyze the reaction of 4-nitrophenol to 4-aminophenol with a good kinetic constant. In addition, the catalyst proved to be significantly robust, maintaining a conversion rate greater than 80% after five minutes of reaction for eight consecutive catalytic cycles. In addition, the catalytic activity of the coordination polymer was much higher than that observed for a homogeneous catalyst based on aqueous Ni2+ ions, suggesting the importance of the structure of the coordination sphere formed by the cyamelurate anions. The results presented here can contribute to the application of other coordination polymers anchored with cyamelurate-like ligands and derivatives, as well as to new catalyst designs based on this coordination site formed by oxygen and nitrogen donor atoms. [ABSTRACT FROM AUTHOR]

Carbon dots (CDs) have emerged in the last few years as new carbon nanostructures due to their excellent optical and physicochemical properties and thus promising applications in different areas. In this work, we describe the preparation of different CDs obtained from distinct bottom-up methods and also using different low molar mass precursors in order to study advantages and disadvantages of each experimental method used. Different techniques were performed to characterize the nanoparticles, such as Transmission electron microscopy, Potentiometric titration, Fourier transform infrared, Fluorescence and Ultraviolet-visible spectroscopy. The CDs obtained using conventional hydrothermal carbonization showed the highest values of quantum yield (QY), whereas the nanoparticles obtained by the heating reflux reaction method exhibited the lowest QY values mainly due to incomplete polymerization and/or carbonization reactions of the material. In addition, a study to evaluate the use of the CDs as nanoprobes for metallic ions showed that one of the samples exhibited high selective and sensitive response toward Fe3+, with a detection limit of 0.89 µM. Furthermore, the nanoparticles used as sensors were obtained with an environmentally friendly strategy, and the CD-based photoluminescence method is simple, has a short response time and present low-cost. [ABSTRACT FROM AUTHOR]

The current study demonstrates that cellulose nanocrystals (CNCs) that are assembled in different arrangements can be thermally decomposed under controlled conditions to produce different carbon nanostructures. The results from FTIR, Raman, TGA, SEM, TEM and potentiometric titration indicated that thermal decomposition in the 300–1000 °C range produced carbons containing surface oxygen groups with different morphologies. The obtained results suggest that the obtained carbon structures are defined by the CNC precursor arrangement; i.e., CNCs organized as filaments produce carbon fibers, CNCs sheets result in carbon films and CNCs agglomerated as spheres will produce carbon spheres. Furthermore, the thermal decomposition of CNCs also produced water-soluble 4–8 nm carbon dots (CDs), exhibiting photoluminescence emission as a function of the excitation energy that covered the blue-to-green visible light region. [ABSTRACT FROM AUTHOR]