N,S-co-doped carbon dots (N,S-CDs) were synthesized via a single-step solvothermal process by using sodium lignosulfonate and p-phenylenediamine as carbon/nitrogen/sulfur sources. The N,S-CDs have an average diameter of 2.02 ± 1 nm and display green fluorescence, with excitation/emission peak wavelengths at 380/540 nm for optimal fluorescence. Fluorescence is excitation wavelength-dependent and stable in aqueous salt solutions. The fluorescence of the N,S-CDs is selectively quenched by Fe(III) and Ag(I) ions. These ions can be quantified by fluorometry with a limit of detection of 1.7 μM for Fe(III) ions and 11.6 μM for Ag(I) ions. The N,S-CDs also undergo solvatochromism in that emission is green in water solution but blue in polar organic solvents such as ethanol or N,N-dimethylformamide. The color of fluorescence gradually shifts from green to blue when continuously increasing the fraction of organic solvent in water.
N,S-co-doped carbon dots (N,S-CDs) are synthesized by using sodium lignosulfonate and p-phenylenediamine as C/N/S sources. The N,S-CDs can sensitively detect Fe(III) and Ag(I) ions based on fluorometry, and can be used as a solvatochromic probe.
Carboxylative cyclization of propargylic alcohols with CO2 is significant in synthetic chemistry, but harsh conditions are often needed according to reported results. Herein, a new stable nitro-functionalized metal–organic framework (MOF) of {[Co3(L)2(bpy)4(H2O)2]·DMF·H2O·bpy}n (1) was fabricated through the solvothermal reaction, which exhibited excellent stability in acid and basic solutions. Owing to the porous structure, unsaturated metal sites, and uncoordinated 4,4′-bpy ligands, 1 can serve as an excellent platform for catalytic applications. Hence, Ag(I) ions were incorporated in 1 through a postsynthetic method, and the as-synthesized Ag-1 catalyst with low metal loading (0.64 mol %) displayed excellent catalytic performance in the chemical fixation of CO2 with alkynols under room temperature and atmospheric pressure. The results of 1H NMR analyses further confirmed that Ag-1 can efficiently activate hydroxyl groups and promote the reaction. Moreover, the turnover frequency (TOF) of the Ag-1 catalyst can reach 262 h–1 in a short period of time, which is a high TOF value among the state-of-the-art MOF-based catalysts for catalyzing cycloaddition of CO2 with propargylic alcohols.
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