Fabrication of mesoporous biochar/silicate nanocomposites via full-component sustainable utilization of oil shale semi-coke waste for efficient removal of pollutants

Oil shale semi-coke (OSSC) waste composed of multi-minerals and organic matters, it is still a challenge to realize the full-component sustainable utilization, especially high content of inert quartz and organic matters. In this study, OSSC was one-pot hydrothermally converted into the mesoporous biochar/silicate nanocomposite in the presence of silicate and magnesium ion for the efficient removal of organic pollutants from aqueous solution. The phase transformation, structural evolution and pore structure properties of the nanocomposites were studied by X-ray diffraction, magic-angle spinning solid-state nuclear magnetic resonance, high-resolution transmission electron microscope and Brunauer Emmett Teller method. The results indicated that the hydrothermal induction realized the conversion of multi-minerals to analcime and amorphous magnesium silicate with the increase in the Si/Mg molar ratio from 3:1 to 1:3, while the organic matters was carbonized accompanied with the increase in the number of oxygen-containing functional groups. As the Si/Mg molar ratio was 1:1, the obtained nanocomposites exhibited high specific surface area of 399.12 m2/g and maximum adsorption capacity toward methylene blue and tetracycline of 227.02 mg/g and 188.22 mg/g due to the electrostatic attraction, coordination reaction and hydrogen bond. Furthermore, the KOH-assisted carbonization technique was developed to regenerate the spent nanocomposites loaded with organic pollutants for sustainable adsorption Pb2+ with an adsorption capacity of 234.84 mg/g due to the surface complexation and precipitation. It is expected to realize the full-component sustainable utilization of oil shale semi-coke for the removal of organic pollutants and heavy metal ions.