In this work, we report on the microwave-assisted hydrothermal synthesis of Sn 2+ -doped ZnWO 4 nanocrystals with controlled particle sizes and lattice structures for tunable optical and photocatalytic properties. The samples were carefully characterized by X-ray diffraction, transmission electron microscopy, inductive coupled plasma optical emission spectroscopy, UV−vis diffuse reflectance spectroscopy, and Barrett−Emmett−Teller technique. The effects of Sn 2+ doping in ZnWO 4 lattice on the crystal structure, electronic structure, and photodegradation of methylene orange dye solution were investigated both experimentally and theoretically. It is found that part of the Sn 2+ ions were homogeneously incorporated in the ZnWO 4 host lattice, leading to a monotonous lattice expansion, and part of Sn 2+ ions were expelled at surface sites for decreased crystallinity and particle size reduction. By Sn 2+ doping, ZnWO 4 nanocrystals showed a significant XPS binding energy shift of Zn 2p, W 4f, and O 1s, which is attributed to the combination of electronegativity between Sn 2+ and Zn 2+ , lattice variation, and particle size reduction. Meanwhile, the BET surface areas were also greatly enlarged from 40.1 to ∼110 m 2 ·g −1 . Contrary to the theoretical predictions of the quantum size effect, Sn 2+ -doped ZnWO 4 nanocrystals showed an abnormal band gap narrowing, which can be well-defined as a consequence of bulk and surface doping effects as well as lattice variations. With well-controlled particle size, crystallinity, and electronic structure via Sn 2+ doping, the photocatalytic performance of Sn 2+ -doped ZnWO 4 nanocrystals was optimized at Sn 2+ doping level of 0.451. ■ INTRODUCTIONSemiconductor nanomaterials have distinct properties that promise new inventions and new materials for widespread technological applications and economic impacts. 1 It is a wellestablished fact that the physical properties of nanocrystals are strongly influenced by particle size, chemical composition, and surface chemistry. 2 Till now, vigorous efforts have been dedicated to tailoring the fundamental properties of semiconductors as a function of particle size, chemical composition as well as surface chemistry, including structural and electronic properties of ZnS nanoclusters, 3 photocatalytic performance of TiO 2 -based photocatalyts, 4 magnetic properties of EuS nanoparticles, 5 and so on. From the viewpoint of solid-state physics, the reduction of particle sizes and variation of chemical compositions often predict variations in lattice parameters and surface structures, which can have consequences on the electronic structures and properties. 6 Therefore, the ability to manipulate the size, shape, composition, crystal structure, and surface properties of nanocrystals is essential for uncovering the nature of structure-related physical properties.Metal tungstate is a very important family of inorganic materials that has high potential applications in various fields, such as photoluminescence, microwave applications, optical fibers, and sc...

Catalytic base-free oxidation of biomass-derived glycerol represents a promising approach for the value-added utilization of glycerol. However, the commonly used Pt/carbon nanotubes (Pt/CNT) catalysts suffer from the severe deactivation, because of the strong adsorption of glyceric acid (GLYA), resulting in the serious Pt-surface poisoning and their consequent poor activity with low selectivity toward GLYA. Here, we demonstrate that integrating CeO2 with Pt/CNT could effectively alleviate the catalyst deactivation, delivering high activity and selectivity to produce GLYA. The valence band analysis and kinetic experiments suggest that the Pt-CeO2/CNT ternary interface would weaken the GLYA adsorption on Pt and lower the energy barrier for glycerol oxidation. Moreover, via the generated OH* from H2O dissociation, CeO2 can promote the oxidation of primary hydroxyl groups of glycerol, leading to a high selectivity of GLYA.

Conversion of CO 2 into valuable chemical feedstocks through artificial photosynthesis is an effective strategy to alleviate energy and environmental issues. Herein, we have developed a novel perovskite-based catalyst via in situ growing CsPbBr 3 quantum dots (QDs) on the affinal 2D CsPb 2 Br 5 nanosheets for CO 2 photoconversion. CsPbBr 3 QDs were generated by peeling off layers from their cubic counterpart; meanwhile, CsPb 2 Br 5 nanosheets were formed by heaping up the peeled layers. The resultant dual-phase composite exhibited outstanding activity and selectivity for photocatalytic conversion of gaseous CO 2 with a CO generation rate of 197.11 μmol g −1 h −1 under 300 W Xe lamp irradiation, which is 2.5 and 1.1 times higher than that of pure CsPb 2 Br 5 or CsPbBr 3 . Importantly, the fabricated dual-phase material presented extremely high stability and was able to maintain an unchangeable CO 2 conversion rate under wet air in the consecutive 10 h of recycling test. Furthermore, attributing to the in situ assembling strategy, the close contact allowed photo-generated electrons in CsPbBr 3 QDs to transfer rapidly to CsPb 2 Br 5 , and the affluent active sites in such an architecture enabled achieving enhanced CO 2 photoconversion activity. The present work provides an attractive approach for in situ constructing a consubstantial perovskite-based composite photocatalyst to ensure great stability and excellent activity for artificial photocatalytic CO 2 conversion.

The present work explores a solid state route to synthesis of trivalent ions (Eu 3+ , La 3+ , etc.) doped NaTaO 3 with controlled nonstoichiometric chemistry and lattice parameters with an aim to exploring electronic structure and photocatalytic performance. All samples were fully characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic absorption spectrophotometry, UV− vis diffuse reflectance spectroscopy, and photoluminescence measurement. By employing Eu 3+ as a model trivalent ion doped in NaTaO 3 lattice, the effects of siteselective doping and nonstoichiometric chemistry on the lattice parameters, band gap structure, photocatalytic activity toward methylene blue solution, and photocatalytic hydrogen evolution were systematically investigated. A nonstoichiometric Na/Ta molar ratio led to site-selective occupation of Eu 3+ ions which was changed from sole substitution to dual substitutions. Meanwhile, the nonstoichiometric Na/Ta molar ratio and site-selective occupation of Eu 3+ resulted in a monotonous lattice expansion and local symmetry distortion. Lattice variation, doping effects, and its relevant defect chemistry had a great impact on the ν 3 mode vibration of the O−Ta bond, which became asymmetric and shifted toward higher wavenumbers. Moreover, contrary to theoretical predictions, Eu 3+ -doped NaTaO 3 nanocrystals showed an abnormal narrowing of the band gap energies and weak visible light absorption with variation of Na/Ta molar ratios, which is thought to be related to doping effects, defect chemistry, and variation of lattice parameters. With well-defined lattice structure and defect centers and electronic structure via nonstoichiometric control and trivalent ions doping, the photocatalytic activity of trivalent ions-doped NaTaO 3 can be well regulated and optimized.

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