Innovative synthesis of black zeolites-based kaolin and their adsorption behavior in the removal of methylene blue from water

Abstract

An innovative method for preparation of carbon-coated zeolites (black zeolites) has been developed. The method involves dehydration of sucrose on kaolin surfaces followed by hydrothermal treatment. Raw and dealuminated kaolins were used to prepare black zeolites (CZ1 and CZ2, respectively). Characteristics of the black zeolites were influenced by the criteria of the used kaolin. Analyses indicate the formation of Na-A and Na-P zeolites in CZ1. However, Na-A, Na-X, and Na-P zeolites were found in CZ2. Surface areas and pore volume values of CZ2 are lower than the corresponding bare zeolite (Z2). Meanwhile, these values remain approximately the same in case of CZ1 when compared with the corresponding bare zeolite (Z1). Carbon is probably trapped in the wide pores of CZ2 during the preparation process. Contrarily, carbon mainly coats the external surface of CZ1. The adsorption capacities of CZ1 and CZ2 using methylene blue (MB) were determined to be 48.33 and 57.64 mg/g, respectively. The higher estimated value of CZ2 is attributed to its higher surface area. Moreover, the adsorption capacities of black zeolites were much higher than the corresponding uncoated zeolites and the unsupported carbon. These indicate that the supported carbon on zeolites possesses higher exposed surfaces to MB.