Controlling the Photocatalytic Activity and Benzylamine Photooxidation Selectivity of Bi2WO6 via Ion Substitution: Effects of Electronegativity.

Doping or ion substitution is often used as an effective strategy to improve photocatalytic activities of several semiconductors. Most frequently, the dopants provide extra states to increase light absorption, alter the electronic structure, or lower the carrier recombination. This work focuses on ion substitution in Bi2WO6, where the dopants modify band-edge potentials of the catalysts. Specifically, we investigate how the electronegativity (EN) of the dopant could be used to tune the band-edge potentials and how such changes influence the photocatalytic mechanism. Compared to Te that has a lower EN, I lowers the band-edge potentials. While substitutions with both ions enhance Rh B photodegradation and benzylamine photooxidation, the modified band potentials of I-doped Bi2WO6 influence the benzylamine photooxidation pathway, resulting in higher selectivity. Additionally, substitution of I7+ in the Bi2WO6 lattice improves the morphologies, decreases the band-gap energy, and reduces the carrier recombination. As a result, I-doped Bi2WO6 shows almost 3 times higher %conversion while maintaining 100% selectivity in the oxidative coupling of benzylamine. The findings here signify the importance of the choices of dopants on the photocatalytic reactions and would benefit the design of other related materials for such applications.

Facile molten salt synthesis of Cs-MnO2 hollow microflowers for supercapacitor applications.

A facile molten salt technique is an interesting preparation method as it enables mass production of materials. With the use of CsNO3 salt, Cs-intercalated MnO2 hollow microflowers are obtained in this work. δ-MnO2 with a layered structure, instead of other allotropes with smaller structural cavities, is formed and stabilized by large Cs+ ions. Formation of the hollow microflowers is explained based on the Ostwald ripening process. The salt to starting agent ratio has little effect on the crystal structure and morphologies of the products but does influence the crystallinity, the interlayer distance, and the intercalating Cs+ content. The capacity of Cs+ in the structure and the interlayer distance are maximized when the weight ratio of CsNO3 : MnSO4 is 7 : 1. Cs-MnO2 obtained from this optimum ratio has most suitable crystallinity and interlayer distance, and consequently shows a highest specific capacitance of 155 F g-1 with excellent cycling performance. The obtained specific capacitance is comparable to that of other alkaline-intercalated MnO2, suggesting that Cs-MnO2 could be another interesting candidate for supercapacitor electrodes.