Preparation, characterization and application of sorbent envelopes with Carica papaya seeds and Citrus grandis rind for cationic dyes removal

The sorption of cationic dyes was studied using sorbents derived from pulverized papaya seeds and pomelo rind. A convenient fixed sorbent envelope protocol with methods for quality check on the readiness of sorbent material for subsequent sorption was developed. Sorbents based on papaya seeds had higher affinity for methylene blue and brilliant green dyes than pomelo rind. Amongst Langmuir, Freundlich and Temkin isotherms, the sorption of both cationic dyes fitted the Langmuir isotherm best. The multi-step linearity behavior on the intra-particle diffusion model with a positive intercept indicated that intra-particle diffusion was not the sole sorption rate-determining factor. The utility of the envelope protocol as a convenient evaluation method for sorbent characteristics and effectiveness was also demonstrated. Magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy was explored and found to differentiate between the two fruit wastes and had the potential for elucidating sorbent–sorbate interactions.