Hierarchically synthesis strategies

In this chapter, we present an overview of the synthesis strategies based on the sol-gel process for the preparation of multimodal porous networks of hierarchically structured functional materials and a brief introduction to their applications is given at the end of the chapter. 

Synthesis Strategies for Hierarchically Structured Porous Materials... 

Another family of synthesis strategies uses small solid particles as additional templates to micellar templating to create hierarchical pore structures. These small solid particles as additional templates consist of colloidal crystals, biomaterials, macroporous polymers, salts, and ice crystals. This combination of surfactant and small solid particles offers an efficient way for the generation of ordered and interconnected mesoporous-macroporous architectures, small solid particles creating macropores and surfactant micelles creating mesopores. 

Tunable chemical composition Hierarchically porous materials with single or multiple chemical compositions can be prepared via this spontaneous selfformation procedure by using single or multiple alkoxide precursors. Pure oxide materials can be obtained by starting with just the alkoxide or alkylme-tal precursors in aqueous solutions, as opposed to other synthesis strategies where the resulting products are often contaminated by residual species. Furthermore, metal phosphates with hierarchically porous structures can also be prepared by this self-formation process. 

Therefore, hierarchically structured porous materials with novel structure have significantly stimulated the researchers to develop innovative synthesis strategies and therefore deserve more detailed studies, mainly devoted to the optimization, such as further modification of individual porosities and intricate morphologies with special functionalities, as well as surface functionalization, and scale-up of the synthesis methods. 

Wang H, Ma D, Huang Y, Zhang X (2012) General and controllable synthesis strategy of metal oxide/Ti02 hierarchical heterostructures with improved lithium-ion battery performance. Nat Sci Rep 2 701... 

The flowsheet synthesis of continuous chemical-like process can be performed following a systematic strategy known as the hierarchical approach. The procedure, initially proposed by Jim Douglas and coworkers in the decade 1980-90 [1, 2], describes the conceptual design process as a logical sequence of analysis and synthesis steps grouped in levels. Each level involves a flowsheet development mechanism based on design decisions. The result is not a unique solution but a collection of alternative flowsheets from which an evaluation procedure eliminates the less attractive ones. 

This entire strategy was applied to each of the four possible scaffold conformations. The top 50 components for each of the scaffold families were merged for each attachment point (i.e. Ri, R2, R3), and hierarchically clustered to maximize the diversity of the compounds chosen for library synthesis. In the end, the 10 best scoring compounds from unique clusters were chosen for each Ri, R2, R3 attachment point. Thus, our final library had the most diverse set of components that fitted our structural hypothesis. 

The strategy of this method is to utilize the inherent porosity of bulky substrates in the construction of hierarchical stractures by incorporating additional pore systems. Diatoms are unicellular algae whose walls are composed of silica with an internal pore diameter at submicron to micron scales. Zeolitization of diatoms, in which zeolite nanoparticles are dispersed on the surface of diatoms followed by a hydrothermal conversation of a portion of the diatom silicas into zeolites, resulted in the formation of a micro/mesoporous composite material. Similarly, wood has also been used as a substrate to prepare meso/macroporous composites and meso/macroporous zeolites. After the synthesis, wood is removed by calcination. ... 

Chemistry generally constitutes the first step in hierarchical process design. This relates to process synthesis, specifically the selection of reaction routes and separation agents (Chen et al., 2003). Anastas and Allen (2002) proposed a set of strategies based on the Green Chemistry principles discussed above, which include ... 

Heuristic methods were developed by well-experienced engineers and researchers. The first attempt to develop a systematic heuristic approach for the synthesis of multicomponent separation sequences was made by Siirola and Rudd. Common example is hierarchical heuristic approach.Heuristic rules are applied at five design levels to generate and evaluate the alternatives using economic criteria. The hierarchical heuristic method emphasizes the strategy of decomposition and screening. It allows for a quick location of flowsheet structures that are often near ... 

Hierarchical Approach is a methodological frame for the conceptual synthesis of process systems. The overall strategy is organised in a number of levels, each level being decomposed in a number of tasks. The approach presented below is organised in eight levels as follows (Douglas and Stephanopoulos, 1995) ... 

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