Mesoporous carbon materials mesopore size control

Ma, X. M., L. H. Gan, M. X. Liu et al. 2014. Mesoporous size controllable carbon microspheres and their electrochemical performances for supercapacitor electrodes. Journal of Materials Chemistry A 2 8407-8415. 

Recent reports describe the use of various porous carbon materials for protein adsorption. For example, Hyeon and coworkers summarized the recent development of porous carbon materials in their review [163], where the successful use of mesoporous carbons as adsorbents for bulky pollutants, as electrodes for supercapacitors and fuel cells, and as hosts for protein immobilization are described. Gogotsi and coworkers synthesized novel mesoporous carbon materials using ternary MAX-phase carbides that can be optimized for efficient adsorption of large inflammatory proteins [164]. The synthesized carbons possess tunable pore size with a large volume of slit-shaped mesopores. They demonstrated that not only micropores (0.4—2 nm) but also mesopores (2-50 nm) can be tuned in a controlled way by extraction of metals from carbides, providing a mechanism for the optimization of adsorption systems for selective adsorption of a large variety of biomolecules. Furthermore, Vinu and coworkers have successfully developed the synthesis of... 

Textural mesoporosity is a feature that is quite frequently found in materials consisting of particles with sizes on the nanometer scale. For such materials, the voids in between the particles form a quasi-pore system. The dimensions of the voids are in the nanometer range. However, the particles themselves are typically dense bodies without an intrinsic porosity. This type of material is quite frequently found in catalysis, e.g., oxidic catalyst supports, but will not be dealt with in the present chapter. Here, we will learn that some materials possess a structural porosity with pore sizes in the mesopore range (2 to 50 nm). The pore sizes of these materials are tunable and the pore size distribution of a given material is typically uniform and very narrow. The dimensions of the pores and the easy control of their pore sizes make these materials very promising candidates for catalytic applications. The present chapter will describe these rather novel classes of mesoporous silica and carbon materials, and discuss their structural and catalytic properties. 

Ordered mesoporous materials, due to their periodic and size-controllable pore channels and high surface areas, have been regarded as a nano-reactor to construct novel ordered and well dispersed nanostructured composites with controlled size and size distribution.[303] A number of studies have reported on the encapsulation of guest materials, such as metal oxides,[304] semiconductors, metal sulfides,[305] carbon, metals,[306] and polymers into mesoporous silica hosts. 

Ordered mesoporous carbons (OMCs) are new carbon materials that were developed over the last ten years. Their mesopores have a defined width with a very narrow pore size distribution. This sets them aside from older nanoporous carbons, such as activated carbons or activated carbon fibers. The last two classes of carbons are produced from various carbon-containing materials by carbonization followed by partial oxidation (activation). To a certain degree, the pore structure of these materials can be controlled by the carbonization and activation conditions. However, it is not possible to produce purely mesoporous activated carbons or activated carbon fibers. Furthermore, these materials generally exhibit a broad pore size distribution [1, 2]. 

The morphology of ordered mesostructured carbons is another important factor with respect to their practical applications. Various macroscopic morphologies are required, for example, films (in sensor, separation and optical applications), uniformly sized spheres (in chromatography) or transparent monoliths. Using suitable synthesis strategies, it is possible to control the external shape of the templated mesoporous carbon materials to generate powders, films and membranes, spheres, hollow spheres, rods, fibres, nanowires, nanotubes and monoliths. 

Contrary to colloidal silica templating where the pore size is determined by the diameter of the silica colloids used, the pore widths of the hard-templated OMCs depend on the pore wall thickness of the selected OMS template. The mesopore width of SBA-15 will then influence the wall thickness of the resulting CMK-3 carbon. Hence, control over tlie mesopore size in OMS hard-templated carbons is possible by tailoring the adsorption and structural properties of the starting template (Figure 12.10). Small variations in the expected pore widths and pore wall thicknesses of the final OMCs result from shrinkage of the carbonaceous materials inside the silica template... 

The carbon materials used in this study were obtained from MAST Carbon Ltd. and are phenolic resin derived activated carbons, NOVACARB [4]. The voids between the primary microporous particles result in a controlled mesopore size. In this way combined micro- and mesoporous materials are obtained. The different letter in the sample name of the carbon samples refers to a different percentage bum-off or a different precursor is used in preparation. The niunber in the sample name refers to the temperature (K) at which the samples have been thermally treated after bum-off. 

Recently, attention has been paid to porous carbon materials, owing to their large surface area, large pore volume, chemical inertness, and electrical conducting properties. Porous carbon materials with controlled architecture, morphology, and relatively narrow pore size distribution are usually prepared by a templating (hard or soft) method followed by carbonization processes. The main synthetic way to produce ordered mesoporous carbons relies on the use of ordered mesoporous silica with interconnected pore structures as a hard template. This synthetic route (see Fig. 16.6 for the hard template route) requires (1) preparation of... 

HMC is a very interesting porous carbon material with unique hierarchical macro/mesoporous spherical morphology. HMCs with various core sizes and/or shell thicknesses can be fabricated through the independent control of the core sizes and/or shell thicknesses of the SCMS silica templates [28,62,63], while the micro- and mesoporosity of the HMCs can be controlled to some extent by the source type and amount of carbon precursor incorporated into the SCMS silica template. HMC with different core shapes (non-spherical) have been synthesised through nanocasting techniques [61,64], A key factor for the s)mthesis of HMCs with diverse shapes and sizes lies in the fabrication of SCMS silica replica templates. 

Optimization of the pore size distribution is important for the control of both the equilibria and the dynamics of physisorption (see Ruthven, 1984 Do et al., 1993). Most activated carbons are highly microporous, but for some purposes it is desirable to extend the range of pore size into the mesopore or macropore range - or even eliminate the microporosity. Progress in this direction has been made by the use of special pre-treatment procedures and the careful control of the conditions of carbonization and activation. In this connection, physisorption measurements have an important role to play in characterizing the material at various stages of manufacture. 

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