Ternary alloyed AgCl(x)Br(1-x) nanocrystals: facile modulation of electronic structures toward advanced photocatalytic performance

Manipulating the electronic structure of semiconductor photocatalysts represents an ideal approach for the exploration and development of photocatalysis. However, it still remains a challenge in terms of silver halide photocatalysts. Herein, we report ternary alloyed AgClxBr1-x nanocrystals (NCs) synthesized by controlling the crystal growth process within a facile microemulsion system. The alloyed NCs crystallize in a homogeneous rock-salt crystal structure and possess tunable bandgaps from 2.5 to 3.0 eV obtained by varying the halogen mole ratios (Cl/Br). Their photocatalytic activities for dye degradation and CO2 reduction are found to depend strongly on the chemical compositions, and among them, the AgCl0.75Br0.25 sample exhibits the highest activity (about 2-4 times higher than AgCl and AgBr). Further theoretical calculations demonstrate that a decrease of the ratios of Cl/Br lowers the levels of the conduction band minimum and thereby narrows the bandgaps. Combining the theoretical and experimental results, the highest activity can be rationally ascribed to the optimum conduction band levels, which balances the overall effect of bandgap, electronic coupling and redox potential. This methodological exploration of engineering the bandgap of silver halide materials is a step forward toward the development of advanced photocatalysts and will shed light on devising various semiconductor photocatalytic systems.

Strongly visible-light responsive plasmonic shaped AgX:Ag (X = Cl, Br) nanoparticles for reduction of CO2 to methanol

Plasmonic shaped AgX:Ag (X = Cl, Br) nanoparticles have been synthesized by a facile and versatile glycerol-mediated solution route. The as-prepared AgX:Ag nanoparticles exhibit regular shapes, i.e., cube-tetrapod-like AgCl:Ag nanoparticles and AgBr:Ag nanoplates. Compared with the pristine AgX, AgX:Ag nanocomposites display stronger absorption in the visible region due to the surface plasmon resonance of silver nanoparticles. The calculation of bandgaps and band positions indicates the as-achieved AgX:Ag nanoparticles can be used as a class of potential photocatalyst for the reduction of CO(2). For example, reduction of CO(2) under visible light irradiation with the assistance of the anisotropic AgX:Ag nanoparticles yields as much as 100 μmol methanol in the products. Furthermore, the AgX:Ag nanoparticles can maintain its structure and activity after 3 runs of reactions. Therefore, the present route opens an avenue to acquire plasmonic photocatalysts for conversion of CO(2) into useful organic compounds.

Influence of solution composition and ultrasonic treatment on optical spectra of TiO2 aqueous suspensions

Investigation of TiO(2) aqueous suspensions has shown that their optical spectra can be unstable, with instability not related to precipitation or adherence of TiO(2) particles to the vessel walls. Increase of ionic strength of the suspension as well as neutralization of charged TiO(2) particles via pH adjustment accelerates the optical density drop. Vice versa, increasing the charge of TiO(2) particles via shifting pH in acidic or basic directions stabilizes the suspension's optical spectra, and ultrasonic treatment promotes optical density recovery. The observed behavior is attributed to alteration in the size of the suspension aggregates.