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Despite its considerable potential to address energy and environmental challenges, the practical application of photocatalysis is restricted by the limited efficiency of the photocatalysts. This research aims to improve the photocatalytic efficiency of Bi2MoO6 by adjusting the internal electric field within the crystal lattice via Te doping. Te-Bi2MoO6 nanosheets were prepared by a one-step hydrothermal method. Although the band gap energy and the long-range crystal structure are not affected upon doping, Te substitution provides several benefits to the performance of Bi2MoO6. First, the introduction of Te significantly reduces the thickness of the nanosheets, resulting in a larger surface area. Te states are also introduced into the conduction band, thereby increasing the carrier mobility. More importantly, the reduced cell parameters upon doping and the presence of Te in the lattice not only increase the potential difference between Bi–O and Mo-(Te)–O layers in the lattice but also create an asymmetric potential difference. As a result, an internal electric field is enlarged, leading to increased carrier separation. Consequently, 5.0 mol % Te-doped Bi2MoO6 could degrade 99.7% of Rhodamine B in 1 h under visible light, with 6.4 times higher rate constant than pristine Bi2MoO6. Additionally, the doped sample also exhibits about two times enhancement in benzylamine photooxidation (85% conversion vs 39% conversion) while maintaining excellent stability. Thus, this research highlights the efficacy of modulating the internal electric field through chemical modification as a viable strategy for enhancing the performance of photocatalysts. [ABSTRACT FROM AUTHOR]

This work focuses on the variation of solvents/additives as a key factor in hydrothermal and solvothermal syntheses of nanocrystal BiVO4 films. All synthesized films successfully formed the BiVO4 monoclinic phase, which was confirmed by XRD, XPS, XANES and EDS techniques. The physico-chemical characteristics of these solvents/additives have dramatic impacts on the crystal morphologies and surface crystal planes. Using ethanol and ethylene glycol gives plate-like BiVO4 with {121} as a dominant facet. On the other hand, preparations with low pH and higher polar solvents result in {010}-dominated nanocrystals. The effects of the three solvent molecules including water, methanol, and ethanol are investigated by computations. Interestingly, the adsorption energy of each solvent molecule on various facets is different, leading to diverse exposure of the lattice planes. Overall, the photoanodes with plate-like particles give better catalytic activities. These films have higher-index {121} exposed facets, more oxidative (110) plane and better charge transfer properties. The photoelectrochemical photocurrent switching effects are also observed with varied switching potentials, suggesting that the (110) and (040) planes are the controlling parameters. The obtained knowledge from this work may be useful for the fabrication of photoelectrodes with expanded fields of application. [ABSTRACT FROM AUTHOR]

Coating of photocatalytic nanomaterials on various surfaces enables interesting applications. This work demonstrates the ability of the aerosol-assisted chemical vapor deposition (AACVD) approach to prepare high-quality BiOCl nanostructure-based films and also to tune the nanostructure and photocatalytic properties of the films by varying the solvent and carrier gas. Solvents have a dramatic impact on the surface morphologies and crystallite size. X-ray diffraction (XRD) and grazing incidence X-ray diffraction (GIXRD) analyses indicate that BiOCl crystals displayed preferential growth in the (101) plane in most samples, while both the (101) and (102) planes were favored in films deposited using ethyl acetate and methanol. Surface energy and adsorption energy calculation reveal that the preferred growth depends on the interaction between the Bi atom and solvent molecules. X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDS) characterizations showed that all films did not contain any impurity elements but did contain some oxygen vacancies. The obtained nanostructured BiOCl films show good photocatalytic properties. The highest photocatalytic NOx removal efficiency is achieved in the film prepared using ethyl acetate and air, which we attribute to the large crystallite size and therefore high mobility of the carriers. Herein, we show that different crystal morphologies and sizes of BiOCl have strong impacts on the photocatalytic activity toward NO oxidation, and both factors can be effectively tuned in the AACVD process. Such knowledge may be useful for future research on coating materials for resolving environmental problems. [ABSTRACT FROM AUTHOR]

To gain deeper understanding on the relationships between crystal structure and electrochemical properties of manganese oxide electrodes for supercapacitors, acid-leached LiMn2 − xTixO4 were investigated. Based on both Reitveld refinement on X-ray diffraction patterns and X-ray absorption near edge structure, it is proposed that replacing some Mn with Ti not only enlarges the unit cells but also alters the crystal structure, specifically the occupancy of each element in the lattice. While the tetrahedral 8a position and octahedral 16c position are both vacant in leached MnO2, those in leached LiMn2 − xTixO4 with x > 0 are occupied by Ti and Mn, respectively. The differences in the unit cell dimension and the crystal structure affect the electrochemical behaviors of the compounds. Although the total specific capacitance generally decreases with Mn active species, trend in %Cins is opposite in samples with x = 0.25-0.75. Despite having some cations in the positions which should hinder the ion diffusion, the enlarged cavity size resulting from Ti substitution promotes the diffusion process and enhances the insertion capacitance in these samples. [ABSTRACT FROM AUTHOR]

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 Bi 2 WO 6 , 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 Bi 2 WO 6 influence the benzylamine photooxidation pathway, resulting in higher selectivity. Additionally, substitution of I 7+ in the Bi 2 WO 6 lattice improves the morphologies, decreases the band-gap energy, and reduces the carrier recombination. As a result, I-doped Bi 2 WO 6 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.

A facile molten salt technique is an interesting preparation method as it enables mass production of materials. With the use of CsNO 3 salt, Cs-intercalated MnO 2 hollow microflowers are obtained in this work. δ-MnO 2 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 CsNO 3  : MnSO 4 is 7 : 1. Cs-MnO 2 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 MnO 2 , suggesting that Cs-MnO 2 could be another interesting candidate for supercapacitor electrodes., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)