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Log in with Gmail. In this paper, we design a general strategy to fabricate nanoscale cavity in functional materials. Zn OH 2 octahedron template is taken as a case study, as shown in Fig. Zn OH 2 octahedra with controllable diameters were first prepared in low temperature aqueous solution. A series of ZnO-based heterostructures and octahedral hollow structures were then fabricated by using Zn OH 2 octahedra as promising sacrificial template.
Taking advantage of the inherent properties of this hard template, two strategies were applied to construct hollow structures. ZnS and Ag 2 S hollow octahedra were obtained via chemical conversion. SiO 2 and CeO 2 hollow octahedra were synthesized through a controlled deposition. The scheme for constructing hollow octahedron by using Zn OH 2 as template.
A core removal results in various nanoscale sulfide cavities. Therefore, Zn OH 2 octahedra can be used as a promising hard template for synthesizing nonspherical hollow structures and ZnO-based heterostructures.
In order to control the diameter of the template, the reaction parameter was slightly adjusted. The solution was aged under room temperature water bath for 2 days. The mixture was stirred under room temperature for 30 min. Subsequently, 10 mL 0. All the white precipitation was collected by centrifugation and washed thoroughly with distilled water and absolute ethanol several times.
Finally, the as-prepared products were centrifuged, washed with distilled water and absolute ethanol several times.
The suspension was stirred for 30 min under room temperature to obtain black products, and then the pH value of the solutions was adjusted to 2 by several drops of diluted HNO 3.
Another 20 min was allowed to obtain Ag 2 S hollow octahedron. The as-formed suspension was placed into ultrasonic irradiation and 0. The mixture was subsequently stirred at room temperature for 3 h, the final white product was collected by centrifugation and washed with water and absolute ethanol for several times. Then, 2 mL double-distilled water containing 0. The solution was stirred for 30 min to form a homogenous suspension.
Subsequently, 5 mmol urea was added into the suspension and stirred for another 30 min to dissolve the urea completely. Finally, the heterostructure was washed with 0. The accelerating voltage was set at 40 KV with a mA flux. The magnified image Fig. The crystals are well defined with smooth surface, which can be confirmed by the corresponding TEM image shown in Fig.
The XRD patterns in Fig. The weight loss ratio is about These hydroxyl groups exhibit good combining ability toward the positive charged metal cations, which can lead to the enrichment of the metal cations on the surface of the template.
Though many researches have been done to tailor the shape and size of the materials to enrich their properties, controllable fabrication still remains a big challenge in material science. The average diameter of Zn OH 2 octahedra can be readily tuned in a large range by altering the reaction parameters. To our knowledge, this is the first time to study the size control over Zn OH 2 crystal and fabricate hollow structures by using Zn OH 2 octahedron as sacrificing template.
By using these templates, a series of hollow structured materials with controllable sizes can be fabricated. Two strategies were applied to fabricate different octahedral hollow structures by using Zn OH 2 as templates.
Transition metal sulfides were prepared through a facile chemical conversion. Zn OH 2 templates were directly immersed into 0. From the inset of Fig. The hole can serve as the entrance for sensitive materials such as medicine molecules or proteins. The corresponding TEM image is depicted in Fig. The interior of the products is completely hollowed and the shell is comprised of numerous nanoparticles.
The whole conversion process was recorded by XRD patterns Fig. Due to the strong coordination ability of NH 3 , the core-removing duration can be dramatically reduced. Moreover, the good volatility and solubility of ammonia make it easier to be evacuated from the final product.
PL measurements were performed for optical characterization of the hollow ZnS shell powder. The sample is photoexcited at nm. As shown in Fig. The strong-defect-related signal implies that ZnS nanoshells contain more defects. During chemical conversion, the driven force for the chemical conversion is attributed to the gap between the solubility of Zn OH 2 and ZnS.
Based on this point, the method can be also utilized to fabricate other transition metal sulfides via a similar chemical conversion [ 32 , 33 ]. The XRD pattern Fig. PL spectrum in Fig. Therefore, it is reasonable to deduce that, after appropriate modification to this method, hollow octahedra of more thermodynamically stable transition metal sulfide e. A controlled chemical deposition was also utilized to coat a layer of silica onto Zn OH 2 template. The coating technique has been detailedly described in recent work [ 34 ].
Based on the coordination ability of the hydroxyl groups, the mineralization of the cations can occur on the template to form a layer of SiO 2 without additional surface modification.
After treated with diluted HCl, SiO 2 hollow structure was generated. The magnified SEM image Fig. Moreover, there are broken parts on the hollow particles which may serve as the intake entrance for drug delivery or DNA storage.
The thickness of the shell is measured to be about 30 nm. Figure 7c displays a TEM image of the products. The silica hollow structures are octahedral in shape and the thin shell can well support the hollow structure. ZnO and SiO 2 nanomaterials have been of interest for construction of many gas- and biosensing devices because of their biocompatibility, high chemical stability, and low cost. Detailed work is being carried out to tailor the thickness and the porosity of the silica shell for the potential applications in drug delivery and controlled release.
In addition, taking advantage of the function groups located on the template surface, a similar route in an ethanol—water system could also be utilized to synthesize other inorganic hollow compounds [ 35 ]. For example, CeO 2 hollow octahedra were also synthesized through a similar method Fig.
SEM image in Fig. XRD pattern in Fig. Under the stimulation of nm laser, the PL spectrum of the CeO 2 shells has a strong emission band with the center at about nm Fig. It is believed that these CeO 2 shells may have find potential applications in displays, sensors, and photosensitive devices.
A general template route has been designed to chemically engineering nanoscale cavities, which provides a simple scheme for the fabrication of highly crystalline hollow nanostructures with tailorable size.
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