Hierarchical C/NiO-ZnO nanocomposite fibers with enhanced adsorption capacity for Congo red

Wastewater containing organic dyestuff has caused worldwide concern, hence, it is imperative to develop materials to remove organic dyes from wastewater. Herein, we report the synthesis of carbon fiber-based bimetallic oxide nanocomposite with high efficiency for the adsorptive removal of Congo red (CR), a typical anionic dye. Composite nanosheets of nickel(II) oxide (NiO) and zinc oxide (ZnO) were in situ grown over electrospun carbon fibers via one-step oil bath coprecipitation and subsequent calcination in air at 350 °C. The C/NiO-ZnO nanocomposite fibers exhibited fast adsorption rates towards CR at circumneutral pH, and maximal adsorption capacity according to the Langmuir model reached 613 mg g^-1, much higher than aggregated NiO-ZnO microspheres and the carbon fiber alone. The high adsorption capacity of the C/NiO-ZnO nanocomposite was attributed to its high specific surface area (222 m² g^-1), hierarchically porous structure with abundant mesopores and macropores, and the positive surface charge at circumneutral pH. Therefore, the flexible and easily recyclable C/NiO-ZnO nanocomposite fibers can become an alternative adsorbent for the treatment of anionic dye wastewater.