Azolla-derived hierarchical nanoporous carbons: From environmental concerns to industrial opportunities

Abstract Azolla biomass as a very fast growing fern was utilized to prepare hierarchically nanoporous activated carbons with high surface area and crystallinity. As-prepared activated carbons were characterized using powder X-ray diffraction (PXRD), Raman, Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS), N 2 sorption, scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HR-TEM). XRD and FTIR results confirmed that CaCO 3 which is naturally present in azolla biomass is responsible for crystallinity of the final materials and in collaboration with NaOH as activation agent led to high surface area nanoporous carbons. Activation process increased the specific surface area of the initial char from about 3 m 2  g −1 to 2680 m 2  g −1 . Large ordered atomic layers domains of carbon were observed in HR-TEM. CO 2 adsorption capacity was investigated for the azolla-derived carbons which proved the high room temperature capture ability of near 7.18 mmol g −1 at 1 bar and 12.5 mmol g −1 at 20 bar. More significantly, extraordinary capacity of methylene blue uptake by about 4448 mg g −1 has been observed in azolla-derived porous carbon which is the highest ever reported for water cleaning.