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A facile green approach has been developed to control the growth regime in the aqueous synthesis of Cd_xZn_1-xTe semiconductor quantum dots (QDs) based on the electrochemistry method. The Low growth temperature and slow injection of Te precursor are used to prolong the diffusion controlled stage and thus suppress Ostwald ripening during the nanocrystal growth. The experimental results showed that a low concentration of Te precursor will definitely influence the growth procedure. The UV–visible absorption spectra, as well as transmission electron microscopy (TEM) shows the QDs a good monodispersity at any interval of the reaction procedure. The high-resolution transmission electron microscopy (HRTEM) images and powder X-ray diffraction (XRD) pattern suggested that the as-prepared QDs have high crystallinity and cubic structure. The size and composition-dependent fluorescent emission wavelength of the resultant Cd_xZn_1-xTe alloyed QDs can be tuned from 460 to 610 nm, and their photoluminescent quantum yield can reach up to 70%. Especially in the wavelength range of 510–578 nm, the overall PL QYs of the as-prepared Cd_xZn_1-xTe QDs were above 50%. The current work suggests that electrochemical method is an attractive approach to the synthesis of high-quality II-VI ternary alloyed semiconductor QDs at large-scale with a prominent cost advantage.

4-Mercaptovaleric acid (4MVA) and 3-mercaptovaleric acid (3MVA), two branched isomers of 5-mercaptovaleric acid (MVA), were designed and synthesized. They were used as capping agents in the aqueous synthesis of CdTe quantum dots (QDs) by a modified hydrothermal method with sodium tellurite as Te source. Compared with MVA-CdTe, either 4MVA-QDs or 3MVA-QDs exhibited higher fluorescent quantum yield (QY) and sharper absorption peak, which confirmed the superiority of using branched mercapto acids in the aqueous synthesis of QDs for improved optical properties. The fluorescence of QDs capped with 4MVA was higher than that of QDs capped with 4-mercaptobutyric acid (MBA) but lower than that of QDs capped with 3-mercaptobutyric acid (3MBA), which further confirmed the advantage of designing methyl side group rather than methylene group in the main chain for desired optical properties. However, the lower fluorescence, less sharp absorption peak and faster growth rate of 3MVA-QDs than that of 3MBA-QDs indicated adverse effect of side group on the aqueous synthesis of QDs if the size of side group is very bulky. Our results are helpful for selecting and designing appropriate capping agents for QDs with excellent properties.

Amine-promoted process has been applied in conventional preparation of quantum dots (QDs) for years. However, the required amine quantity was large in a typical promotion procedure. For example, large amine amount was demanded in the organic phase method for polarity and solubility adjustment. Meanwhile, it was also essential for aqueous synthesis to achieve competitive coordination ability. In order to impel the promotion more efficiently, 1,2-diaminoethane (DAE) was selected in this study to decrease amine dosage while accelerating reaction rate in aqueous synthesis. Based on its bidentate structure and high formation constant, the reaction time at high temperature was efficiently shortened. Additive species and quantities were varied for comparison under different conditions. At room temperature, QDs with limited DAE were successfully generated within 3 h while the hydrazine group failed even after 100 h' storage. The optical properties of the QDs obtained using DAE additive were better than the other groups. QDs with higher quantum yield (QY) were also obtained through adjusting total ion strength. More attractive result was found in QDs' structure. Since the reaction was efficiently shortened in our method, CdS impurity reported in conventional CdTe QDs synthesis was eliminated.

Bi₅O₇I microflowers were synthesized through a simple liquid coprecipitation under alkaline condition at 75^∘C in an open system without using autoclave or other complex equipment. The addition of NaBr was a key factor for controlling the morphology of Bi₅O₇I. The assembled Bi₅O₇I samples are constructed by elementary nanowires, which were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and UV-Vis diffuse reflection spectroscopy (UV-Vis DRS) methods. The photocatalytic performance of Bi₅O₇I samples on rhodamine B (RhB), methylene blue (MB) and ciprofloxacin (CIP) was evaluated under 350 W xenon lamp irradiation. On comparison with the blank Bi₅O₇I microflowers, Bi₅O₇I microflowers with NaBr addition exhibited better photocatalytic performance, and the photocatalytic activity enhanced with the increase of NaBr amount. The photocatalytic efficiency reached 81.1% in 150min for RhB, 42.5% in 210min for MB and 56.3% in 210min for CIP in the degradation system at $\mathrm{\text{pH}}=7$ without any assistant agent. Trapping experiments were performed to reveal the degradation mechanism of Bi₅O₇I samples. It was proposed that valid separation of photogenerated electrons and holes in Bi₅O₇I microflowers led to good catalytic properties.