Unique water sensors based on carbon nanotube-cellulose composites

Electrically conductive films composed of carbon nanotubes (CNTs) and cellulose matrix were used as water sensors. They exhibited rapid response and high sensitivity, with a relative electrical resistance change of 5500-500% for cellulose-CNT composites with CNT loading from 2 to 10 wt%. This unique performance is well reproducible and high stable even on a long-term scale for 45 days. The sensitivity of cellulose-CNT composites was mainly caused by the hygroscopic swelling of the cellulose matrix, which was investigated by scanning electron microscope and wide-angle X-ray diffraction. The cellulose-CNT composites also showed a high selectivity for water-ethanol solutions with different fraction of water.