Effect of Micropore Topology on the Structure and Properties of Zeolite Polymer Replicas

Abstract

Zeolites were used as templates to prepare microporous polymer replicas. Phenolformaldehyde polymers were synthesized and cured within the channel networks of zeolites Y, β, and L. Dissolution of the aluminosilicate framework in aqueous HF yields an organic replica that contains <2% aluminosilicate. The zeolite template exerts important topological effects on the structure and physical properties of the replica. Using zeolites Y and β, which have three-dimensionally interconnected channel structures, the microporosity of the template is reflected in the replica polymer. Pore size distributions are consistent with the predominance of 5-6 Å walls in the parent zeolite. In contrast, complete collapse of the replica, to a give nonporous material, occurs upon removal of the zeolite L template, since the latter has a one-dimensional channel structure. TEM and SEM micrographs also show evidence of collapse in the latter case. Pyrolysis of the zeolite-resin composites at 900 °C, and subsequent etching, produces very high surface area, electronically conducting replicas. Under these conditions the zeolite Y replica has markedly lower conductivity than those obtained from β and L, which have straight channels.

Mesoporous carbons prepared by nano-casting with meso- or non-porous silica nanoparticles

“…After carbonisation and silica dissolution these bands attributed to the impregnated sucrose molecules are strongly decreased, which indicates the nearly complete decomposition of the organic material. On the other hand, bands at around 1384 and 1596 cm -1 , which would indicate the formation of graphite like structures 30,31 cannot be observed in the M Aerosil matrix.…”

Preparação de carbonos porosos por moldagem sequencial

“…As zeólitas com estruturas tridimensionais são adequadas como molde, enquanto aquelas com estruturas unidimensionais não o são. Johson e colaboradores 35 prepararam resinas fenol/formaldeído em zeólitas Y, β e L e, em seguida, pirolizaram esse material, obtendo peneiras moleculares de carbono. A pirólise do compósito zeólita/resina e a subsequente dissolução produziu réplicas com alta área superficial específica e estruturas porosas diferentes.…”

“…A peneira molecular de carbono produzida utilizando zeólitas tridimensionais apresentou área superficial específica mais alta que o molde original e aquela obtida com a zeólita L mostrou um valor aproximadamente igual à metade daquele da zeólita (Tabela 1). 35 As técnicas empregadas na etapa de impregnação influenciam na regularidade estrutural e nas características químicas do carbono poroso formado. O método de deposição química de vapor leva à formação de carbonos que herdam a regularidade estrutural dos moldes zeolitícos, mas o grau da transferência de regularidade depende fortemente do tipo de zeólita.…”

Why are carbon molecular sieves interesting?

“…25 Figure 10 shows the results of such procedures, using the phenol/formaldehyde resin (phen/form) in zeolites Y, beta and L while Table 1, shows the porosity characteristics for the zeolites and the resulting carbon materials.…”