Rice straw-derived highly mesoporous carbon-zinc oxide nanocomposites as high performance photocatalytic adsorbents for toxic dyes

Abstract Highly mesoporous carbon-zinc oxide nanocomposites were synthesized from rice straw through a simple pyrolysis method. These carbon-zinc oxide nanocomposites were ideal for adsorption and degradation of toxic dyes from wastewater. Synthetic methodology utilized a 1-step zinc chloride activation process that eliminated the need for acid washing, yielding a graphitic material with specific surface area of 942.7 m2 g−1 and 99% mesoporosity. X-ray diffraction and X-ray photoelectron spectroscopy patterns indicated the existence of zinc oxide and turbostratic graphite. Transmission electron microscopy images revealed zinc oxide particles sizes ranging between 20 and 100 nm. Surprisingly, graphene-like-sheets were also observed within the nanocomposite structure. Adsorption capacities for methylene blue and congo red were 399 mg g−1 and 410 mg g−1 respectively. By retaining zinc oxide in the carbon structure, catalytic degradation of dyes was possible in the presence of ultraviolet radiation. The synergistic effect of adsorption and photocatalytic degradation increased the maximum dye removal of methylene blue to 614 mg g−1, while congo red removal was exceptionally high at 2628 mg g−1.