Immobilization of Silver Nanoparticles on the Surface of Cellulose Nanofibers Using High-Pressure Wet-Type Jet Mill

Composite material immobilized silver nanoparticles (NPs) on the surface of cellulose nanofibers (CNF) was prepared using a high-pressure wet-type jet mill. A mixture containing both aqueous silver nitrate solution and CNF suspension were prepared as raw starting materials. The mixture was pulverized with a high-pressure wet-type jet mill at a pressure of 100 MPa or 200 MPa. An X-ray diffraction pattern of the obtained sample revealed not only cellulose type I crystallites, but also silver metal crystallites. According to observation by field-emission scanning electron microscopy, it was found that many silver NPs were immobilized on the surface of CNF. Note that almost the silver NPs were well dispersed on the surface of CNF. It was cleared that the silver NPs had spherical in shape with an average particle size of about 3 nm by the transmission electron microscope observation. The average size of silver NPs was slightly increased with increasing the number of jet milling, however, the change in discharge pressure of the high-pressure wet-type jet milling did not affect the size of silver NPs. The silver content in the composite materials increased with increasing both the number of jet milling and the discharge pressure. The silver particles were deposited with using the thermal energy caused by the jet milling, and then their grain growth was inhibited since the suspension was cooled immediately through the cooling tube. Therefore, it was assumed that silver NPs with a narrow size distribution could be immobilized on the surface of CNF.