Coconut coir-derived nanocellulose as an efficient adsorbent for removal of cationic dye safranin-O: a detailed mechanistic adsorption study.

Abstract

Coconut (Cocos nucifera) coir is an abundant agricultural waste prevalent worldwide. Utilization of this waste has been carried out in this study by obtaining nanocellulose (NC) fibres for wastewater remediation purposes. Nanocellulose was obtained from coconut coir using bleaching and acid-alkali treatments followed by ultrasonication and lyophilization. The structural, compositional, surface and thermal properties of the synthesized material were identified using transmission electron microscopy (TEM), scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FT-IR), N2 adsorption/desorption, differential thermal (DT) and derivative thermogravimetric (DTG) analyses. These analyses confirmed the synthesized NC with enhanced thermal stability and porosity which was further used for adsorption process. After synthesis, NC was used for the removal of cationic dye safranin-O from water under ambient conditions through batch adsorption studies. The batch adsorption studies revealed that at 10ppm of dye concentration, above 99% removal was achieved by 100mg dosage of NC within 4.5h at room temperature with qe (maximum adsorption capacity at equilibrium)value of around 83mgg-1. The corresponding adsorption process fitted well with Langmuir isotherm and pseudo-second order kinetics. Theprimary mode of adsorption from the thermodynamic studies was found to be chemisorption. The adsorption process was achieved through response surface methodology (RSM) study which revealed that at optimized conditions of temperature 35°C with a dose of 137.50mg and contact time of 180min, above 99% of dye (conc. 0.01mgmL-1) was removed. In addition, the adsorbent can be recycled up to six cycles without any significant loss of its adsorption capacity. The present comprehensive study revealed that a greener eco-friendly synthesis ofNC from waste material coconut coir was an effective nanoadsorbent for dye removal withhigh efficacy. This surely opens up opportunities to develop sustainable protocols for efficient environmental remediation.