One-Step Synthesis of Water-Soluble Quantum Dots from Ag2S and AgInS2 QDs

Water-soluble quantum dots (QDs) have attracted much attention because of their excellent optical stability and biocompatibility. Here we report a simple, easy to operate, safe, and nontoxic method to synthesize water-soluble Ag2S QDs and AgInS2 (AIS) QDs. By addition of l-cysteine to the Ag+ and In3+ precursor solution, the water-soluble Ag2S and AIS QDs can be synthesized through the hydrothermal method. With increased reaction temperatures and times, Ag2S QDs were converted to AIS QDs. The colors were adjusted from green light to red light under UV light. The absorption spectra were red-shifted as a whole with increasing time and temperature. The fluorescence peaks at 80 and 90 °C did not change with time (greater or equal to 2 h), but the fluorescence peaks at 100 °C had a relatively large change from 470 to 650 nm. The band gaps of Ag2S QDs had a large change from 2.2 to 0.9 eV due to crystallinity, and the band gap of the AIS QDs was about 0.9 eV. The photocatalytic H2 production performance was studied. The results indicated that the Ag2S QDs obtained by reaction at 90 °C for 4 h exhibited the greatest amount of H2 production (1240 μmol·g–1·h–1). Finally, the reaction process was also investigated.