Novel Self-Assembled MgO Nanosheet and Its Precursors

Bottom-up Synthesis of Nanosheets at Various Interfaces

Nanostructured materials with high aspect ratios have been widely studied for their unique properties. In particular, nanosheets have safety, dispersibility, and nanosized effects, and nanosheets with exceptionally small thicknesses exhibit unique properties. For non-exfoliable materials, the bottom-up nanosheet growth using various interfaces as templates have been investigated. This review article presents the synthesis of nanosheets at the interfaces and layered structure; it explains the features of each interface type, its advantages, and its uniqueness. The interfaces work as templates for nanosheet synthesis. We can easily use the liquid-liquid and gas-liquid interfaces as the templates; however, the thickness of nanosheets usually becomes thick because it allows materials to grow in thickness. The solid-gas and solid-liquid interfaces can prevent nanosheets from growing in thickness. However, the removal of template solids is required after the synthesis. The layered structures of various materials provide two-dimensional reaction fields between the layers. These methods have high versatility, and the nanosheets synthesized by these methods are thin. Finally, this review examines the key challenges and opportunities associated with scalable nanosheet synthesis methods for industrial production.

Template synthesis of ordered mesoporous MgO with superior adsorption for Pb(II) and Cd(II)

Ordered mesoporous MgO was synthesized via template method by using magnesium nitrate as a precursor and amphiphilic triblock copolymer Pluronic F127 as a template. The products were characterized by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM), and the Brunauer-Emmett-Teller (BET) method was used to calculate the specific surface areas. The effects of aging time, relative humidity, and magnesium nitrate content on the morphology and textural properties of the products were studied. When the aging time was 36 h and the relative humidity was 40%, the ordered mesoporous MgO with uniform pore sizes (3.2 nm), high specific surface areas (517.2 m²/g), and high pore volumes (0.42 cm³/g) were obtained. Furthermore, the adsorption properties of ordered mesoporous MgO as adsorbent for removal of Pb(II) and Cd(II) ions were studied. The adsorption kinetics and isotherm data agreed well with pseudo-second-order model and Langmuir model, indicating that the adsorption of heavy metal ions on the ordered mesoporous MgO was mainly chemical and homogeneous adsorption. The maximum adsorption capacities for Pb(II) and Cd(II) ions were up to 3073.5 mg/g and 1485.1 mg/g, respectively.

Approaches to synthesize MgO nanostructures for diverse applications

Magnesium oxide remained interesting from long time for several important phenomena like; defect induced magnetism, spin electron reflectivity, broad laser emission etc. Moreover, nanostructures of this material exhibited suitability for different kinds of applications ranging from wastewater treatment to spintronics depending upon their shape and size. In this way, researchers had grown nanostructures in the form of nanoparticles, thin films, nanotubes, nanowalls, nanobelts. Though nanoparticles and thin films are well known form of nanostructures and wide variety of synthesis approaches are available, however, limited methodology for other nanostructures are available. In order to grow these nanostructures in an optimized way an understanding of these methods is essential. Thus, this review article depicts an overview of various approaches for design of different kinds of nanostructures.

Synthesis of magnesium carbonate hydrate from natural talc

Various morphologies of magnesium carbonate hydrate had been synthesized without using any organic additives by carefully adjusting the reaction temperature and time during the talc carbonation process. At lower temperatures, magnesium carbonate hydrate was prone to display needle-like morphology. With the further increase of the carbonation temperature, the sheet-like crystallites became the preferred morphology, and at higher aging temperatures, these crystallites tended to assemble into layer-like structures with diverse morphologies, such as rose-like particles and nest-like structure. The reaction time had no effect on the crystal morphology, but it affected the particle size and situation of the crystal growth. X-Ray diffraction results showed that these various morphologies were closely related to their crystal structure and compositions. The needle-like magnesium carbonate hydrate had a formula of MgCO3·3H2O, whereas with the morphological transformation from needle-like to sheet-like, rose-like, and nest-like structure, their corresponding compositions also changed from MgCO3·3H2O to 4MgCO3·Mg(OH)2·8H2O, 4MgCO3·Mg(OH)2·5H2O, and 4MgCO3·Mg(OH)2·4H2O.

Hierarchical magnetic petal-like Fe3O4-ZnO@g-C3N4 for removal of sulfamethoxazole, suppression of photocorrosion, by-products identification and toxicity assessment

Herein, a petal-like photocatalyst, Fe₃O₄-ZnO@g-C₃N₄ (FZG) with different g-C₃N₄ to ZnO ratios was synthesized with hierarchical structure. The FZG1 photocatalyst, having the weight ratio of 1:1 for the initial urea and Fe₃O₄-ZnO (Fe-ZnO), presented the highest sulfamethoxazole (SMX) degradation rate of 0.0351 (min^-1), which was 2.6 times higher than that of pristine ZnO. Besides the facile separation, the performance of photocatalyst was improved due to the function of iron oxide as an electron acceptor that reduced the electron/hole recombination rate. The coating of g-C₃N₄ on the Fe-ZnO surface not only acted as a protective layer for ZnO against photocorrosion, but it also enhanced the photocatalytic activity of the catalyst for SMX degradation through the heterojunction mechanism. By using the FZG1 photocatalyst, 95% SMX removal was obtained after 90 min reaction, while 47% COD and 30% TOC removal were achieved after 60 min treatment under a low energy-consuming UV lamp (10 W). Moreover, a substantial reduction in the solution toxicity was shown after the treatment, as compared with the SMX solution before treatment. The LC-HR-MS/MS analysis results showed that the concentration of most detected by-products produced after 90 min reaction by FZG1 was considerably lower than those obtained using other synthesized photocatalysts. By performing radical scavenging experiments, OH^° radical was found to be the major reactive species. The FZG1 photocatalyst also displayed excellent reusability in five cycles and the leaching of zinc and iron ions was reduced by 54% and ∼100%, respectively, after coating Fe-ZnO with g-C₃N₄.

Nanosheet Formation by an Anionic Surfactant-like Peptide and Modulation of Self-Assembly through Ionic Complexation

The surfactant-like peptide (Ala)₆-(Asp) (A₆D) is shown to self-assemble into ultrathin (3 nm thick) nanosheets in aqueous solution above a critical aggregation concentration. A combination of circular dichroism and FTIR spectroscopy and X-ray diffraction shows that the nanosheets comprise interdigitated bilayers of the peptide with β-sheet conformation. The self-assembly can be modulated by addition of hexamethylenediamine which is expected to interact with the anionic C terminus (and C-terminal D residue) of the peptide. Multiple ordered nanostructures can be accessed depending on the amount of added diamine. Nanosheet and bicontinuous network structures were observed using cryogenic-TEM and small-angle X-ray scattering. Addition of hexamethylenediamine at a sufficiently large molar ratio leads to disruption of the ordered nanostructure and the formation of a solution of A₆D-diamine molecular complexes with highly charged end groups. The multiple acid-functionalized nanostructures that are accessible in this system are expected to have many applications in the fabrication of new nanomaterials.

Room temperature stable CO x -free H2 production from methanol with magnesium oxide nanophotocatalysts

Methanol, which contains 12.6 weight percent hydrogen, is a good hydrogen storage medium because it is a liquid at room temperature. However, by releasing the hydrogen, undesirable CO and/or CO₂ byproducts are formed during catalytic fuel reforming. We show that alkaline earth metal oxides, in our case MgO nanocrystals, exhibit stable photocatalytic activity for CO/CO₂-free H₂ production from liquid methanol at room temperature. The performance of MgO nanocrystals toward methanol dehydrogenation increases with time and approaches ~320 μmol g^-1 hour^-1 after a 2-day photocatalytic reaction. The CO _x -free H₂ production is attributed to methanol photodecomposition to formaldehyde, photocatalyzed by surface electronic states of unique monodispersed, porous MgO nanocrystals, which were synthesized with a novel facile colloidal chemical strategy. An oxygen plasma treatment allows for the removal of organic surfactants, producing MgO nanocrystals that are well dispersible in methanol.

Shape evolution of parallelogrammic magnesium oxalate controlled by phosphate species

The shape evolution of magnesium oxalate dihydrate to parallelogrammic micro-particles is closely related to the amount of Na₅P₃O₁₀ participating in the self-assembly of the layer-like parallelogram.

Synthesis of porous hierarchical MgO and its superb adsorption properties

The porous hierarchical MgO with superb adsorption properties has been synthesized by a facile and scaled-up method. The X-ray powder diffraction, electron microscopy, Fourier transformed infrared, and N2 adsorption-desorption were carried out to study the microstructure of the as-synthesized precursor and product. It has been demonstrated that the as-prepared MgO has a porous hierarchical structure and a high specific surface area (148 m(2) g(-1)). And the MgO sample exhibited super adsorption properties, with maximum adsorption capacity of 2409 mg g(-1) for Congo red, which is the highest reported value. Moreover, the adsorption process of Congo red on porous hierarchical MgO was systematically investigated, which was found to obey the pseudo-second-order rate equation and Langmuir adsorption model.

Self-assembled 3D ZnO porous structures with exposed reactive {0001} facets and their enhanced gas sensitivity

Complex three-dimensional structures comprised of porous ZnO plates were synthesized in a controlled fashion by hydrothermal methods. Through subtle changes to reaction conditions, the ZnO structures could be self-assembled from 20 nm thick nanosheets into grass-like and flower-like structures which led to the exposure of high proportions of ZnO {0001} crystal facets for both these materials. The measured surface area of the flower-like and the grass, or platelet-like ZnO samples were 72.8 and 52.4 m²·g⁻¹, respectively. Gas sensing results demonstrated that the porous, flower-like ZnO structures exhibited enhanced sensing performance towards NO₂ gas compared with either grass-like ZnO or commercially sourced ZnO nanoparticle samples. The porous, flower-like ZnO structures provided a high surface area which enhanced the ZnO gas sensor response. X-ray photoelectron spectroscopy characterization revealed that flower-like ZnO samples possessed a higher percentage of oxygen vacancies than the other ZnO sample-types, which also contributed to their excellent gas sensing performance.

CHEMICAL DESIGN OF COMPLEX NANOSTRUCTURED METAL OXIDES IN SOLUTION

Nanostructured materials with controlled architectures are desirable for many applications, among which, metal oxides are especially important in optics, electronics, biology, catalysis, and energy conversions. Various chemical routes have been widely investigated for the synthesis of nanostructured metal oxide particles and films. More recently, deliberately designed chemical strategies have been used to produce particles and films composed of more complex crystal structures. In this paper, we discuss some recent progresses in the design of complex nanostructures through chemical routes, emphasize particularly on metal oxides. We first review some basic concepts involved in the fabrication of complex nanostructures, including crystal nucleation and growth, shape controlling and ripening process. We then describe more recent work on the use of different methods to synthesize a wide range of complex nanostructures, including hierarchical structures, heterostructures, as well as oriented nanowires and nanotubes. Such purposely built materials are designed, and engineered to match the physical, chemical, and structural requirements of their applications.