Recebido em 25/2/12; aceito em 27/7/12; publicado na web em 27/11/12 SYNTHESIS AND CHARACTERIZATION OF POLY (ACRYLAMIDE-CO-ACRYLATE) AND KAOLIN HYDROGEL COMPOSITES: EFFECT OF THE CONSTITUTION OF DIFFERENT KAOLINS FROM NORTHEASTERN BRAZIL. Superabsorbent hydrogels based on poly (acrylamide-co-acrylate) and different kaolins, were prepared by free-radical aqueous copolymerization. FTIR and WAXS techniques were employed for characterization of a series of hydrogels, obtained by varying the percentage of clay, crosslinking and constitution of kaolin. The water absorbency at equilibrium (W eq ) decreased with increasing clay content and the amount of crosslinking agent. Superabsorbent hydrogel (W eq > 1084 g H 2 O/g gel) was obtained as 10 wt% of white kaolin and 0.05 mol% of crosslinking agent were used. The hydrogel proved sensitive to pH variation and the presence of salts.

The synthesis of porous materials has attracted interest for decades due to their applications in catalysis and gas adsorption. 7 + (where x equals the molar amount of lanthanum), followed by calcination, may cause variation in the acidic properties. The analyzes showed that increasing the amount of La on oligomer results in a higher acidity shown in the spectrum a characteristic band in the region of 1445 and 1545cm -1 to Lewis and Brönsted respectively, predominantly of the last one. The Mössbauer spectroscopy results showed a relationship between increased symmetry of the octahedral site of iron (Fe 3+ ) and increased lanthanum doping, and consequently a sharp increase in acidity.

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ResumoA viabilidade da utilização de importantes argilas tais como os caulins em processos de adsorção, pode ocorrer mediante a modificação química através de intercalação em suas estruturas filitosas. Amostras de caulin da região do nordeste do Brasil, um branco e outro cinza de uma porção da região borborema-seridó no estado da Paraíba foram intercalados com dimetilsulfóxido, ácido oxálico e ácido cítrico. Na caracterização das amostras naturais e modificadas foram utilizadas técnicas de difração de raios X, análise térmica e espectrometria de absorção na região do infravermelho. Palavras-chave: caulim, intercalação, dimetil sulfóxido, ácido oxálico, ácido cítrico. Abstract The feasibility of using major clays such as kaolin in the adsorption processes, can occur through chemical modification by intercalation in their structures phyllite. Samples of kaolin in the region of northeast