提高多孔碳自掺杂ZnO纳米片组装花的可见光催化活性外文翻译资料

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Improved visible-light photocatalytic activity of porous carbon self-doped

ZnO nanosheet-assembled flowers

Shengwei Liu, Chuan Li, Jiaguo Yu and Quanjun Xiang

Received 11th June 2010, Accepted 4th January 2011

DOI: 10.1039/c0ce00295j

Hierarchical flower-like C-doped ZnO superstructures (ZnO flowers) assembled from porousnanosheets are obtained by pyrolysis of morphology-analogous Zn₅ (CO₃)₂(OH)₆ precursors. The prepared ZnO flowers are characterized by X-ray diffraction, thermogravimetic and differential scanning calorimeter analysis, scanning electron microscopy, transmission electron microscopy, N₂ sorption measurements, UV-vis diffuse reflectance spectra and X-ray photoelectron spectroscopy. Theproduction of OH radicals on the ZnO surface under visible-light irradiation is detected by a photoluminescence technique using terephthalic acid as a probe molecule. The visible-light photocatalytic activity is evaluated by photocatalytic decomposition of the dye RhB in aqueous solution. The hierarchical organization of nanosheets, the multimode voids between and within porous

nanosheets, together with annealing-induced in situ carbon self-doping within the ZnO lattice, account for the enhanced light-absorption capacity, extended light-response range and thus better photocatalytic activity of the ZnO flowers. Furthermore, first-principle density functional theory (DFT) calculation further confirms the C-doping induced red shift in the absorption edges of C-doped ZnO flowers.

Heterogeneous semiconductor photocatalysis is a promising solution for many environment-related issues. Among various oxide semiconductor photocatalysts, TiO₂ and ZnO are recognized as most excellent materials for photocatalytic processes. Besides TiO₂ , ZnO has been intensively studied due to their high photosensitivity, nontoxic nature, large bandgap and low cost. Moreover, the ZnO photocatalyst can be easily manipulated with

desirable microstructures, which are proved to be important factors affecting the photocatalytic activities.In this connection, controllable design of ZnO photocatalysts with various textures is the focus of the current research. Especially, bottom-up self-assembly of low-dimensional nanoscale building blocks,e.g. nanoparticles, nanorods, nanosheets, into desired high-levelthree-dimensional (3D) superstructures has attracted great attention. These 3D ZnO assemblies show superior collective properties as compared with various low-dimensional ZnO nanostructures. Among various approaches, wet chemical routes are most widely applied owing to the mild reaction conditions,and flexible adjustment of the experimental parameters. Specifically, polymer-mediated organic–inorganic interface cooperative self-construction (OICS) is proved as a versatile approach for constructing 3D superstructures from low-dimensional building blocks. For example, self-assembled hollow micro-hemispheres and microspheres have been constructed by nanorods, nanosheets etc. by simply selecting specific organic polymers and chemical reaction systems.

Alternatively, a novel indirect way to 3D ZnO superstructures has been recently developed by pyrolysis of the analogous Zn-containing precursors, such as Zn ₅ (OH) ₈ Cl ₂ , Zn 5(CO3)2 (OH) 6 ,etc., which are pre-designed by the above-mentioned polymer-mediated OICS strategy. For example, spherical ZnO superstructures have been fabricated based on morphology invariant conversion from the zinc hydroxide carbonate (Zn ₅ (CO₃ ) ₂ (OH)₆ ) counterparts by calcination. Recently, it has been disclosed that hierarchical organization of superstructures is advantageous for enhanced light absorption.In this regard,those hierarchical ZnO superstructures are promising alternative candidates for highly active photocatalysts. In addition, such ZnO superstructures are highly porous, especially, with many voids or pores existing within the constituent building blocks (i.e.nanosheets), which are helpful for light-harvesting and matter transfer. Moreover, it should be noted that the C-impurities are probably in situ self-doped into the ZnO lattice during the thermal decomposition of (Zn ₅ (CO₃ ) ₂ (OH)₆ ), in addition to the release of CO₂. Usually, most ZnO photocatalysts are only active under UV light (3–5% of the total sunlight), and it is highly desirable to develop ZnO photocatalysts with high activities under visible light. Here, the C-doping will extend optical absorption of ZnO to the visible-light region (400–700 nm), enabling the fabrication of visible-light responsive ZnO-based photocatalysts with hierarchically assembled superstructures.Therefore, the combined features of hierarchical structure and lattice C-doping within ZnO 3D superstructures prepared by this route endow them with great potential for visible-light associated photocatalytic applications, which is, however, less considered.In this study, poly(ethylene glycol) (PEG) is selected to assist the self-assembly of(Zn ₅ (CO₃ ) ₂ (OH)₆ )nanosheets into novel flower-like 3D superstructures. Such (Zn ₅ (CO₃ ) ₂ (OH)₆ )super-structures are then converted into morphology-invariant ZnO

counterparts with evolutional porous nanosheets. The hierar-chically organized textural features, lattice C-doping and collective optical properties are further characterized. Moreover,the photocatalytic activity is carefully evaluated by photo-catalytic decomposition of the dye RhB in aqueous solution under visible-light illumination.

2. Experimental and computational details

2.1 Sample preparation

All the chemicals were of reagent-grade and were used without furth

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