Mesoporous pore-tuned

Zeolites form a class with tremendous variety. Besides the microporous solids described in the above, mesoporous materials have been synthesized. A breakthrough were the MCM-41 mesoporous zeolites with pores of typically 3 nm. Later, many related materials have been reported allowing fine-tuning of pore sizes. A recent example is the synthesis of materials with pores in the lOnm range with satisfactory uniformity and stability (Sun etai, 2001). 

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... 

SBA-15 samples with diameters from 5 to 10 nm have been prepared by tuning the temperature of the first step of the synthesis [5], MCM-41 has been prepared in the presence of hexadecyl trimethyl ammonium by using methylamine as pH-controlling agent [6], The pore size from N2 adsorption at 77 K has been evaluated by the Broekhoff and de Boer method, shown to correctly evaluate the pore size of ordered mesoporous silicas [7]. 

The last two examples have demonstrated in particular how subtle the effects can be and that much work is required to fine-tune the properties of a mesoporous material as a suitable host for active enzymes. Besides the stability of the enzyme itself, important factors include the pore size, the robustness of the host, and the distribution of functional groups within the material. 

Following similar principles of combining the aggregate-forming properties of bifunctional molecules with low cost and low toxicity, a mesoporous silica material with a three-dimensional worm-like pore system was reported. Triethanol amine (TEA) was used as the SDA and TEOS as the silica source in this mesoporous silica, TUD-1.[48] The formation mechanism is depicted in Figure 1.3(a). The properties of the material can be easily tuned by modifications in the synthesis procedure, for example, the pore size of the material was found to be proportional to... 

Catalysts and catalytic supports are often formulated from aluminas owing to their low cost, and their thermal, chemical and mechanical stability [27], To this end, nonionic surfactant templating with polyethylene oxide surfactants was used to synthesize mesoporous alumina [28], Partially ordered mesoporous materials with wormhole channels were obtained - this seems to be a characteristic of templating with nonionic surfactants. Cationic surfactants have recently been found to template mesoporous aluminum oxide with pore sizes that could be fine-tuned by varying the molar ratio of the reactants [29]. The material obtained was thermally stable to 900 °C and exhibited a narrow pore size distribution. 

The discovery of the family of model mesoporous adsorbents MCM-41 has resulted in intensive research in their synthesis and appfications, as well as in the refinement of existing adsorption models. These materials are gaining importance as a result of the reported presence of an ideal pore structure, the ease of tuning the pore diameter between 1.5 and 10 nm, and very high surface areas of the order of 1000 m /g. 

Establishing a mechanistic understanding is needed for better control of the synthesis process. A better understanding of the formation mechanism via combined characterization techniques and modeling may lead to a more rational approach for tuning the pore structure of mesoporous materials. 

Microporous silicas with pore size of 12.2 A were prepared by either S XT or S " pathways at room temperature using dodecyidimethylbenzylammonium chloride (DDBAC) surfactant. The pore size of the synthesized materials could be tuned from microporous to mesoporous range by the crystalline temperature or using mixed surfactants of DDBAC and cetyl-pyridinium chloride. The pore structure can transfer from disordered tubular array to ordered hexagonal phase by the increase of the molar ratio of CPCl to DDBAC. 

---