In this paper, functionalization of multiwall carbon nanotubes (MWCNTs) using phosphoric acid (H3 PO4 ) was attempted. Based on the One Factor at a Time (OFAT) analysis, 8 M of H3 PO4, 8 h of reflux time and 80 °C were identi-fied as an ideal condition for the acid oxidation process. Successful functionaliza-tion of MWCNTs using H3 PO4 was revealed from Fourier Transform Infrared Spectroscopy (FTIR) peaks and Scanning Electron Microscope (SEM) images. The resulting f-MWCNTs were immobilized with cellulase via adsorption. The optimum temperature for free cellulase was at 50 °C and for immobilized cel-lulase was at 60 °C. The optimum pH was at 5 for both free and immobilized cellulase. Higher thermal stability was achieved with immobilized cellulase in which 39% activity still was retained at 80 °C compared to free cellulase. Reus-ability study of immobilized cellulase depicted 28% of remaining activity after 5th cycle of analysis using model substrate (filter paper Whatman No. 1). These results suggest that H3 PO4 which is a mild acid is a promising substitution for functionalization of MWCNTs.
