A process for producing a cellulose based sorbent material for the removal of water soluble contaminants from water and other aqueous solutions comprising reacting one or more biomass based cellulose containing raw materials with dilute phosphoric acid where the reaction mixture containing said cellulose containing materials is heated to a reaction temperature and after completion of the reaction time, separation of the dilute phosphoric acid solution from the remaining insoluble raw material, neutralization of the solution by means of a suitable neutralizing agent resulting in precipitation of the modified cellulose, and then separating, washing and removing excess water from the resultant precipitate.