The material CNC-MNP was synthesized in situ with a co-precipitation method based on the work of Hassan and coworkers . Briefly, 20 mL of the CNC suspension was thoroughly mixed in 100 mL of MiliQ water (18.2 MOhm) until fully dispersed. A separate 10 mL aqueous solution containing 1.0 mmol of FeCl2 and two equivalents of FeCl3 was prepared and was slowly injected into the stirred CNC suspension under argon. The mixture was heated to 70 ℃ for one hour before magnetite nanoparticles were co-precipitated using 1:10 diluted NH3OH(aq). The product was washed many times using DI water until the wash reached a pH of 7. Excess water was removed by centrifuge at 500 rpm, higher frequencies can lead to phase separation between the nanoparticles and CNC. The compositions of the CNC and CNC-MNP particles obtained were examined by XPS, and the attachment of the MNP onto CNC was verified using TEM (Section 1 in Supporting Information).