Synthesis of multifunctional porous carbon-silicon composites from coal gasification fine slag: Adsorption of methylene blue and microwave-induced biomass catalytic pyrolysis

Coal gasification fine slag (CGFS) is an important byproduct in the coal gasification process with a huge annual output in China and its efficient and green conversion is one of the key issues in the development of coal chemical technology. In this study, using CGFS as the raw material, a facile method was designed for the preparation of multifunctional porous carbon-silicon composites through one-step alkali fusion based on its carbon, silicon and metal elements composition. It was found that the reaction proceeded more adequately using KOH as the activator and the obtained material (T-K1) was mainly composed of micropores and mesopores. A great number of prismatic nepheline crystals were formed and embedded in the honeycomb porous carbon. The specific surface area of T-K1 reached 424.33 m2/g with a variety of active functional groups on the surface. The porous composite exhibited great potential as a multifunctional adsorbent and catalyst. Using T-K1 as an adsorbent, its equilibrium adsorption capacity on methylene blue (MB) reached 208.44 mg/g at 298 K. The adsorption process was consistent with the situation described by the pseudo-second-order kinetic and the Langmuir model, and the adsorption mechanism mainly originated from cation exchange, van der Waals forces, π-π interaction, hydrogen bond and electrostatic attraction. In addition, T-K1 can act as both a catalyst and a microwave absorber in the microwave pyrolysis of biomass. Taking pine sawdust as an example, H2 and CO in the gas product were enriched with high yields of 126.4 and 178.9 ml/g at 550 °C respectively, and the relative content of the phenolic in bio-oil increased to 53.6%. It is believed that this process can provide a useful alternative for the high-value-added transformation of solid waste containing carbon and silicon.