Hierarchically hydrothermal synthesis

Huang Y, Cai H, Feng D, Gu D, Deng Y, Tu B, Wang H, Webley PA, Zhao D (2008) One-step hydrothermal synthesis of ordered mesostructured carbonaceous monoliths with hierarchical porosities. Chem Commun 23 2641-2643... 

Sun, S., Wang, W., Xu, H., Zhou, L., Shang, M., and Zhang, L. (2008) BisFeTi30i5 hierarchical microflowers hydrothermal synthesis, growth mechanism, and associated visible-light-... 

Recently, with the developed technique, the hydrothermal synthesis has been established as an efficient way to fabricate multifunctional materials with different morphologies. Thanks to the advantages of hydrothermal synthesis, various kinds of micro-Znanofibers with versatile secondary hierarchical structures can be obtained easily. Chang designed a facile and effective strategy that combines electrospinning method with hydrothermal process to prepare firecracker-shaped ZnO/polyimide (PI) hybrid nanofibers (Fig. 18.14) [54], Firstly, PI nanofibers were prepared. In this case, the polyamic acid (PAA) solution produced from pyromellitic dianhydride... 

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. ... 

Ordered mesoporous carbons, prepared by nanocasting, have also been used successfully as templates for the synthesis of hierarchical zeolites [159, 160). This is the case of CMK-3, an ordered mesoporous carbon attained by nanoreplication of pure silica SBA-15. The hierarchical zeolites obtained by employing CMK-3 as a template mainly present supermicropores or small mesopores with a size around 2 nm. The textural properties of the hierarchical zeohtes can be tuned by changing the type of CMK-3 carbon used. A modification of this method consists of directly impregnating the composite SBA-15-carbon or MCM-41-carbon with TPAOH and leaving the mixture crystallizing hydrothermally under steam. After calcination, a mesoporous ZSM-5 is formed with mesopore sizes around 3.5 and... 

Wide range of mild synthesis conditions The spontaneous self-formation pro-cediu-e can take place under a wide range of synthesis conditions. Hierarchically porous materials can be synthesized by this simple method in pure water or aqueous acidic or alkaline solution, in the presence or absence of a siu actant or a cosolvent, and with or without hydrothermal treatment... 

In comparison with the materials synthesized in the presence of surfactants, the surface area of the hierarchically porous zirconium oxides obtained via the self-formation phenomenon is relatively lower. Furthermore, the synthesis temperature can affect the crystallinity of the final product [124,139]. Upon increase of the hydrothermal treatment temperature to 130 °C (generally reported to be 60-80 °C), thermally stable meso-macroporous zirconias with a nanocrystalline framework were prepared by using a mixture of amphiphilic block copolymer P123 and poly(ethylene oxide) surfactant Brij 56. 

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