A comprehensive study on activated carbon prepared from spent shiitake substrate via pyrolysis with ZnCl2

Activated carbon was produced from spent shiitake substrate (SSS) via ZnCl2 activation. The product was studied by scanning electron microscopy (SEM), N2-adsorption, Fourier transform infrared spectroscopy and X-ray diffraction (XRD), and its adsorptive behavior was quantified using methylene blue. The pyrolysis of SSS with ZnCl2 was investigated by thermogravimetric analysis, XRD, SEM and energy dispersive X-ray spectrometry. Pyrolysis kinetic was analyzed via Coats–Redfern method. Experimental results demonstrated that the product had surface area of 1,743 m2 g−1 and total pore volume of 0.930 cm3 g−1. The adsorption equilibrium data followed Langmuir isotherm model with a monolayer adsorption capacity of 408.16 mg g−1, and pseudo-second-order kinetic model better described the adsorption kinetic. The adsorption mechanism was well described by the intraparticle diffusion model. SSS can transform into a plastic phase during activation, and zinc oxide chloride hydrate (Zn2OCl2·2H2O) was formed above 260 °C. The diffusion of the ZnCl2 gas generated from the decomposition of Zn2OCl2·2H2O around 500 °C was responsible for the porosity development. ZnO was the main zinc-containing matter in the carbon at high pyrolysis temperatures. With the addition of ZnCl2, the activation energy of the pyrolysis of the lignocellulose structure in SSS was reduced to 12.27 kJ mol−1.