Cellulose nanocrystals and fibers isolated form bioresources or residues are being used as functional additives in many applications during the past decades, recently these nanocrystals and fibers in its native form or modified form has been used as functional component in water purification processes.1,2 The current study explores the equlibrum adsorption time and adsorption capacitiy of three heavy metal ions: Ag+, Cu2+; Fe3+. Cellulose nanocrystals (CNCs) with different surface functionalities were used as adsorbant mateials. All the nano materials have nano-scale diameters from 10 – 20 nm (measured by AFM) and high specific surface area. Zeta sizer studies showed very negatively charged surface for all the nanocrystals at neutral pH conditions.The adsorptions of silver, copper and iron ions onto the differents CNCs were evaluated using ICP-OES (inductively coupled plasma- optical emission spectrometry) and EDS (energy dispersive spectroscopy). The nature and amount of surface groups are found to significantly impact the functionality of cellulose nanocrystals and the adsorption efficiency. It was hypothised that the electrostatic interactions between the negatively charged nanocrystals and positively charged metal ions drives the adsoprtion process. Theoretical modelling was used to gain insight into the mechanism of adsorption.Acknowledgment: Financial support from European Commission under EU FP7, NMP4-SL-2012-280519, NanoSelect is gratefully acknowledged. Johnny Grahn is acknowledged for the help with EDS measurements. University of Maribor is acknowledged for supplied functionalised cellulose nanocrystals.Reference:1. Ma, H.; Hsiao, K. B.; Chu, B. Nanofibrous Microfiltration Membrane Based on Cellulose Nanowhiskers. Biomacromolecules 2012, 13, 180−186.2. Lui P;Sehaqui H, Tingaut P, Wischer A, Oksman K, Mathew AP, Cellulose and chitin nanomaterials for capturing silver ions (Ag+) from water via surface adsorption. Cellulose, doi : 10.1007/s10570-013-0139-5.