In the present study, we report synthesis of new cellulose-based functional adsorbent for the adsorption of Hg2+ ions from their aqueous solutions. The nanocellulose spheres or the spherical nanocellulose (SNC) was synthesized via acid hydrolysis which was followed with lipase catalyzed esterification using 3-mercaptopropionic acid. The thiolated-SNC was well characterized and it was found to be rapid, efficient and selective absorbent for Hg2+ ions with similar to 98.6% removal within 20 min from a 100 ppm solution. Contrary to this, the SNCs does not show adsorption under these conditions. The adsorbent can be regenerated and its reusability was studied up to nine cycles with cumulative adsorption capacity of 404.95 mg/g. The maximum % removal achieved was 88% from tap water and 78% in the presence of some common competing ions, thus exhibiting the specificity of the adsorbent for Hg2+ ions. Regeneration studies were carried out by using 0.1N HCl, HNO3, NaCl, NaNO3 and CH3COONa and among these 0.1N HCl returned the best results. This study thus embodies multiple aspects of environmental sustainability right from the utilization of the most abundant biopolymer to develop a smart material for use to correct the environmental imbalances.