Synthesis of Na-A and/or Na-X zeolite/porous carbon composites from carbonized rice husk

Na-A and/or Na-X zeolite/porous carbon composites were prepared under hydrothermal conditions by NaOH dissolution of silica first from carbonized rice husk followed by addition of NaAlO2 and in situ crystallization of zeolites i.e., using a two-step process. When a one-step process was used, both Na-A and Na-X zeolites crystallized on the surface of carbon. Na-A or Na-X zeolite crystals were prepared on the porous carbonized rice husk at 90 °C for 2–6 h by changing the SiO2/Al2O3, H2O/Na2O and Na2O/SiO2 molar ratios of precursors in the two-step process. The surface area and NH4+-cation exchange capacity (CEC) of Na-A zeolite/porous carbon were found to be 171 m2/g and 506 meq/100 g, respectively, while those of Na-X zeolite/porous carbon composites were 676 m2/g and 317 meq/100 g, respectively. Na-A and Na-X zeolites are well-known microporous and hydrophilic materials while carbonized rice husk was found to be mesoporous (pores of ∼3.9 nm) and hydrophobic. These hybrid microporous–mesoporous and hydrophilic–hydrophobic composites are expected to be useful for decontamination of metal cations as well as organic contaminants simultaneously.