Novel macroporous silicas with ordered mesoporous wall structures (~15 nm in pore size) have been synthesized by finely balancing the emulsification of the oil phase with the self-assembly of the amphiphilic block copolymers. The nanocasting method was used to produce hierarchically ordered macro-mesoporous carbon materials. These porous materials have potential applications in catalysis, sorption, separation, etc.Keywords: Hierarchy; Macro-mesoporous; Silica; Carbon; Emulsion; Hydrophobic-hydrophilic balance
IntroductionSince the first report of self-assembled mesoporous silicas [1], great efforts have been made to construct inorganic hierarchical structures [2], especially materials with multimodal porosity [3], which is of great importance in the fields of controlled drug-delivery, catalysis, adsorption, and other energy-related applications. Various approaches have been invented for the fabrication of multimodal porous materials, which are well summarized in recent review papers [4,5]. Emulsion templating has been considered one of the most promising routes to produce macroporous materials with tunable pore sizes from 50 nm to a few micrometers [6]. The introduction of macroporosity into mesoporous materials by emulsion templating, however, was found to be far more difficult than expected [7]. For example, for the amphiphilic block copolymers involved emulsion systems [8], strong interactions between oil phase and amphiphilic block copolymers, especially when large amounts of oil (e.g., TMB) was used, often leads to the destruction of mesoscale ordering, forming a lamellar [9] or mesocellular foam (MCF) structures eventually [10]. On the other hand, systems with weaker oil-surfactant interactions are not easily emulsified. As a result, very large hollow spheres (a few micrometers in diameter) with mesoporous walls were obtained, in which high intrusion energy (high stir speed) was often involved [11]. In other works, vesicle structures [12], giant surfactant superstructures [13,14], even bubbles etc. have been used to assist in the construction of macro-mesoporous materials. Su et al. [14] have synthesized a set of hierarchically macro-mesoporous metal oxide in a single surfactant system, in which the templating of giant surfactant superstructures (from unreacted excess surfactant) is responsible for the formation of channel-like macropore systems. However, this approach does not work to prepare silica systems with similar porous structures [15]. To date, only hard template routes, such as colloidal crystals, have been successfully used in the construction of macro-mesoporous materials [4]. It remains a challenge to find a facile and efficient route to the fabrication of hierarchically ordered macro-mesostructures. Our previous studies show that different alkanes have different interactions with P123 amphiphilic block copolymer. By tuning the initial reaction temperatures and compositions of the synthetic mixture, control of inorganic-organic micelle arrangements may be achieved. As a result, mesopor...