Hypothesis: ZSM-5 zeolite is an efficient adsorbent for several compounds. However, is a microporous material, and consequently, is little efficient for large dye molecules. In order to make ZSM-5 zeolite a mesoporous material with ability to adsorb dyes, the use of chitin (low-cost biopolymer) as template in the synthesis route can be an alternative.
Experiments: ZSM-5 zeolites were synthetized using a nucleating gel as structure-directing agent for the material formation, followed by the chitin insertion (or not), homogenization and hydrothermal treatment. The obtained zeolites (ZSM-5 and chitin/ZSM-5) from these different methods were characterized. The potential of ZSM-5 and chitin/ZSM-5 zeolites to adsorb crystal violet dye (CV) was evaluated in batch mode, considering the effects of adsorbent dosage and pH. Equilibrium, thermodynamic and kinetic studies were also performed.
Findings: The use of chitin in the synthesis route provided the following improvements on the ZSM-5 structure: (i) the mesopores volume increased from 0.027 (ZSM-5) to 0.142cm3g-1 (chitin/ZSM-5); (ii) the pore diameter increased from 1.97 (ZSM-5) to 22.49nm (chitin/ZSM-5); (iii) the porosity was increased and the crystallinity was decreased. For both, ZSM-5 and chitin/ZSM-5, the CV adsorption was favored with adsorbent dosage of 2.0gL-1 and pH of 7.5. The pseudo-second order model was suitable to represent the adsorption kinetics and, the Langmuir model was adequate to represent the equilibrium. The maximum adsorption capacity increased from 141.8 (ZSM-5) to 1217.3mgg-1 (chitin/ZSM-5). The adsorption was spontaneous, favorable and endothermic.
Keywords: Cationic dye; Chitin; Mesoporosity; Thermodynamic; Zeolite.
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