Research Article pubs.acs.org/journal/ascecg
Large-Scale Preparation, Chemical Exfoliation, and Structural Modification of Layered Zinc Hydroxide Nanocones: Transformation into Zinc Oxide Nanocones for Enhanced Photocatalytic Properties Dan Zhang,†,‡ Xiaohe Liu,*,†,‡ Hao Wan,‡ Ning Zhang,† Shuquan Liang,† Renzhi Ma,*,§ and Guanzhou Qiu*,‡ †
State Key Laboratory of Powder Metallurgy and School of Materials Science and Engineering, Central South University, Changsha, Hunan 410083, P.R. China ‡ School of Resources Processing and Bioengineering, Central South University, Changsha, Hunan 410083, P.R. China § International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan S Supporting Information *
ABSTRACT: A convenient and effective water-bath method is developed for the preparation of layered zinc hydroxide nanocones (NCs) intercalated with dodecyl sulfate (C12H25OSO3−, DS−) anions in large quantities. Furthermore, the morphology, size, and crystal structure of products could also be readily tuned by adjusting the experimental parameters. In particular, unilamellar zinc hydroxide nanosheets with a thickness of approximately 0.9 nm could be achieved by exfoliating the layered zinc hydroxide NCs in the formamide− water mixed solution. It is worth mentioning that layered zinc hydroxide NCs could be topologically converted to basic zinc sulfates (Zn4SO4(OH)6·5H2O, Osaka mine) and zinc oxide (ZnO) NCs through a calcination process at different temperatures. Benefitting from a special structure, narrow bandgap, and higher surface area, the photodegradation behavior of ZnO NCs for methylene blue (MB) solution is better than that of ZnO nanorods. KEYWORDS: Zinc hydroxide, Zinc oxide, Nanocone, Nanosheet, Photodegradation
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INTRODUCTION
by layer-by-layer (LBL) and Langmuir−Blodgett (LB) techniques to fabricate flexible nanodevices with exciting functionalities.24−28 Layered zinc hydroxide has a common formula of Zn(OH)2−xAn−x/n·mH2O or Zn1+x/2(OH)2An−x/n·mH2O, where the intercalated charge-balancing anions (An−) can compensate the deficiency of hydroxyls (OH−) on the host layers. Generally, the host layers consist of the tetrahedral and octahedral coordination of Zn(II) ions. In this structure, approximately one-fourth to one-sixth of the octahedral Zn(II) sites are not occupied in which a pair of tetrahedral Zn(II) sites are located above and below one octahedral vacancy, coordinating directly with guest anions (An−) in the interlayer gallery.29−31 On the other hand, layered zinc hydroxide can be converted into other related structures (such as ZnO) via a thermal decomposition method. As is known, ZnO, which is one kind of important semiconductor with a large band gap of 3−4.5 eV and a high exciton binding energy of 60−100
Layered metal hydroxides, a group of anionic inorganic materials composed of positively charged host layers and intercalated guest anions for charge balance, have attracted an increasing amount of attention in the past several decades because of their distinctive intercalation and anion-exchangeable characteristics.1−6 It is well-known that various layered materials possessing artificial or natural layer structures could form tubular and/or conical forms with hollow interiors by a rolling mechanism.7−10 However, most of layered metal hydroxides generally maintain lamellar or platelike morphologies.11−15 In recent years, we have made a significant breakthrough in the controlled fabrication of layered hydroxide NCs resulting from the rolling or curling up of lamellar structures by using microwave-assisted hydrothermal and/or oil-bath methods.16−19 In particular, the exfoliation of layered metal hydroxides can fabricate unilamellar nanosheets with homogeneous thickness (approximately
