A method for chemically functionalizing a cellulosic material using a diazo compound, and the functionalized cellulosic materials obtained by the method. The cellulosic materials may be functionalized with a functional groups selected from hydrophobic agents, catalyzing agents, sensing agent, diagnostic agents, printing agents chelating agents, ligands, antioxidants, antimicrobial agents, or drugs. Also, the uses of functionalized cellulosic materials obtained by the method in a variety of applications.