Structural characteristics of nanoparticles produced by hydrothermal pretreatment of cellulose and their applications for electrochemical hydrogen generation

Abstract Hydrothermal pretreatment (HTP) of microcrystalline cellulose (MCC) and wood sawdust in water at 200 °C and 250 °C and at pressures up to about 600 psi for different heating times (≤60 min) is shown to produce nanoparticles of about 210 nm diameter. For the shorter treatment times of 15 min, only partial conversion is observed. Investigations of the post-HTP solid products by scanning electron microscopy show that the original size of cellulose particles is reduced by a factor of about 50 to yield spherical nanoparticles of about 210 nm size. In X-ray diffraction studies, the characteristic Bragg peaks of the parent MCC and sawdust are not present in the post-HTP products with only a broad halo being observed, indicating that the crystallinity of cellulose has broken down under HTP. Electron spin resonance (ESR) spectroscopy shows the observation of free radicals in the post-HTP products whereas the parent MCC, sawdust and glucose are ESR inert. FTIR spectroscopy shows the breakdown of the bonds between glucose units of the cellulosic structure. As an application, the pre- and post-HTP cellulose and sawdust were tested for the electrochemical production of hydrogen. Whereas the pre-HTP samples were found to be inactive, the post-HTP cellulose treated at 250 °C for 60 min was nearly as active as carbon BP2000 (surface area = 1500 m 2 /g) for producing H 2 at energy efficient voltages. A comparative energy analysis for the electrochemical production of hydrogen using carbons and post-HTP cellulose vis-a-vis water electrolysis is also presented.