Crystallization at Nanodroplet Interfaces in Emulsion Systems: A Soft-Template Strategy for Preparing Porous and Hollow Nanoparticles

Abstract

A heterophase method to prepare hollow and/or porous crystalline nanoparticles of metal oxides at room temperature is presented, taking cerium(IV) oxide and γ-iron(III) oxide (i.e., maghemite) as representative cases. The crystallization begins at the oil-water interface in aqueous nanodroplets of the precursor in inverse (water-in-oil) miniemulsion systems, and it may continue toward the inner part of the droplets. A poly(styrene-b-acrylic acid) block copolymer is used as a structuring agent because the ability of the carboxylic groups to bind metal ions improves the inorganic shell formation. A precipitating base is added from the continuous phase, generating hydroxide species at the interface that begin the crystallization. We analyze the effects of the synthetic parameters in terms of colloidal stability and morphology of the resulting materials. In the case of maghemite samples, the prepared dispersions of hollow particles present a distinct magnetofluidic behavior.

Zinc‐Doped Nickel Oxide Hollow Microspheres – Preparation Hydrothermal Synthesis and Electrochemical Properties

“…Besides, the relatively low output was another problem in practical application. In template‐free methods, hydrothermal method, is simplicity of operator and high output, resulting in low cost and practical value. However, the controllability and the uniformity of the hollow microspheres morphology were relatively poor with hydrothermal method in previous works.…”

“…Hollow microspheres structure would offer a buffer space for metal oxides to fit the change of the volume in the charge–discharge processes, which also could lead to the improvement of the electrical conductivity. The preparation methods of hollow microspheres have attracted much attention, including the template method (such as hard templates and soft templates) and template‐free method, (such as hydrothermal method and self‐assembly method). Among numerous preparation methods, hydrothermal method, has many advantages such as simplicity of operator, low cost, and high output.…”

Controllable Architecture of Mesoporous Double-Nanoshell SiO2/TiO2 Hollow Tube Based on Layer by Layer Method

“…Hollow-structured mesoporous materials with unique features of high surface area, high permeability, low density, confined inner cavity, and optical properties have been of great interest and received much research, which makes them a promising application in drug delivery systems [1][2][3], chemical and catalysts [4][5][6][7][8][9][10], biological sensors [11][12][13][14][15][16][17], and solar cells [18][19][20]. For example, the inner cavity of the hollow structure is very essential for drug delivery by offering a large volume transportation for DNA, drugs, and cosmetics [21,22]. In addition, the inner-and outer-shell surface provides more active sites; when contacting with reactant molecules, the hollow-structured materials would display high sensor and catalytic activities [23][24][25][26].…”

Confined Crystallization of Pigment Red 146 in Emulsion Droplets and Its Mechanism

“…The emulsion droplets can be considered as nanoreactors and confine the spaces where crystallization occurs, thereby controlling the size and shape of materials [12]. This method has been used for preparing highly specific surface area catalysts [13,14] and hollow spheres of metals and oxides [15,16,17]. Emulsions typically include macroemulsions, miniemulsions, and microemulsions, which are distinguished by sizes of emulsion droplets.…”