The citrate reduction method for the synthesis of gold nanoparticles (GNPs) has known advantages but usually provides the products with low nanoparticle concentration and limits its application. Herein, we report a facile method to synthesize GNPs from concentrated chloroauric acid (2.5 mM) via adding sodium hydroxide and controlling the temperature. It was found that adding a proper amount of sodium hydroxide can produce uniform concentrated GNPs with low size distribution; otherwise, the largely distributed nanoparticles or instable colloids were obtained. The low reaction temperature is helpful to control the nanoparticle formation rate, and uniform GNPs can be obtained in presence of optimized NaOH concentrations. The pH values of the obtained uniform GNPs were found to be very near to neutral, and the pH influence on the particle size distribution may reveal the different formation mechanism of GNPs at high or low pH condition. Moreover, this modified synthesis method can save more than 90% energy in the heating step. Such environmental-friendly synthesis method for gold nanoparticles may have a great potential in large-scale manufacturing for commercial and industrial demand.

A Bi₂MoO₆/Zn–Al LDH heterostructure exhibits significantly enhanced photodegradation efficiency for RhB relative to Bi₂MoO₆under visible light irradiation.

BiOBr lamellas were synthesized at different reaction pH values via a hydrothermal process. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance spectroscopy and N₂ sorption measurements were used to characterize the BiOBr samples. BiOBr samples have the same lamella structures and band gaps but different lamella sizes and thicknesses. Adjusting the pH of the reaction system tunes the BiOBr lamella thickness from 42 to 21 nm. The photodegradation efficiencies of the BiOBr lamellas for rhodamine B (RhB) and methylene blue (MB) in aqueous solution were examined. The degradation efficiency for RhB is much higher than that for MB. The decrease in BiOBr lamella thickness significantly enhances the photocatalytic activity for dye degradation, despite the decrease in exposed photoactive (001) facet percentage. Decreasing the lamella thickness from 42 to 21 nm yields a more than fourfold enhancement in photodegradation efficiency of BiOBr samples for RhB. The most important factor influencing the photocatalytic activity of the BiOBr samples is their lamella thickness, rather than the exposed (001) facet percentage. Thus, even for flaky semiconductors with high exposed photoactive facet contents, the influence of lamella thickness on photocatalytic activity should be preferentially considered.