Asparagine functionalized MWCNTs for adsorptive removal of hazardous cationic dyes: Exploring kinetics, isotherm and mechanism

In present work, a novel asparagine functionalized multiwalled carbon nanotube (Asp-CNT) was synthesized and characterized by SEM-EDX, and FTIR spectroscopy. Synthesized nanomaterial was used as an effective adsorbent for removal of hazardous cationic dyes like Malachite green (MG) and Methylene blue (MB) from water in single and binary system. The adsorption parameters like contact time (0-90 min), stirring speed (200-800 rpm), pH (29), adsorbent dosage (5-25 mg), initial dye concentration (10-350 mg L-1) and the temperature (25-55 degrees C) were optimized. The adsorption capacities obtained under optimum conditions were 637 mg g(-1) and 500 mg g(-1) for MG & MB respectively. The kinetic and equilibrium studies were performed using different models. The active investigation of kinetic and equilibrium studies demonstrated that the adsorption process followed pseudo second order and Langmuir model (R-2 > 0.99) for both dyes, which infers monolayer adsorption occurred via chemisorption. The simultaneous adsorption study of MG and MB in a binary system showed that MB has faster adsorption rate than MG which can be explained on the basis of structure of dyes. The high adsorption capacity of Asp-CNT for both dyes was explained with the help of adsorption mechanism and further confirmed by FTIR spectra of dyes saturated Asp-CNT. Desorption study of both dyes was conducted using various eluents. It was observed that the adsorbent could be easily regenerated by mixture of acid and ethanol and reused for 3 cycles without altering the adsorption efficiency. Hence, it is concluded from adsorption studies that the synthesized nanomaterial has a great potential to be used for large scale wastewater treatment.

Automated summary

The novel Asp-CNT synthesized in this study showed high adsorption capacity for MG and MB dyes, with maximum adsorption under optimized conditions. Kinetic and equilibrium studies indicated that the adsorption process followed pseudo second order and Langmuir model, demonstrating monolayer adsorption via chemisorption. The ability to easily regenerate the adsorbent and reuse it for multiple cycles makes it a promising candidate for large scale wastewater treatment.