Structural, textural and protein adsorption properties of kaolinite and surface modified kaolinite adsorbents

The structural, textural and protein adsorption properties of kaolinite from clay sedimentary deposits, metakaolinite obtained by thermal dehydroxylation of kaolinite, and the organic derivative prepared by reacting kaolinite with the silane coupling agent tert-butyldimethylchlorosilane, were studied. The retention capacities for the proteins α-lactalbumin (A-LA), bovine serum albumin (BSA) and β-lactoglobulin (B-LG) and the nature of the interactions responsible for protein binding were studied by adsorption experiments, performed at room temperature and pH 5.0. The protein adsorption capacity and the selectivity show a clear dependence on the chemical nature of the adsorbents surface and on the textural properties. Kaolinite behaves as a strong adsorbent for A-LA and BSA, and exhibits a very high affinity for B-LG. Metakaolinite shows good retention capacity for A-LA and B-LG, but does not retain significant amounts of BSA. The adsorption capacity of the organo–kaolinite hybrid considerably increases for BSA and A-LA. FTIR results indicate the absence of hydrogen bonding between the adsorbents surface and the polypeptides. The interactions responsible for protein binding are closely related to the hydrophilic or hydrophobic character of the adsorbent surface and the amino acid composition of the proteins, steric effects also should be considered for the adsorption patterns.