The addition of biochar to soil in grasslands and cultivated areas has emerged as a promising way of mitigating global warming. Porous carbon, such as biochar and activated carbon, has been widely used as an adsorbent for gaseous and liquid phases. In recent years, there has also been a growing interest in investigating the adsorption activity of biochar. This review summarizes kinetic models to evaluate the adsorption performance by measuring the amount adsorbed as a function of time. Key kinetic models such as pseudo-first order, pseudo-second order, Elovich, and intraparticle diffusion are presented, and their uses reported in the literature are stated. Using these models, we have investigated phosphate adsorption on a Ca-loaded rice husk biochar prepared by carbonizing rice husk immersed in a CaCl₂ solution at 1000 °C and discuss the results.

Carbon aerogels are promising materials for the electrodes in electric double-layer capacitors, catalyst supports, and adsorbents because they are monolithic and have a high mesoporosity, high electric conductivity, and excellent chemical stability. The most representative carbon aerogels are obtained by carbonizing resorcinol-formaldehyde (RF) aerogels derived from the sol-gel reaction of RF aqueous solutions and supercritical drying with carbon dioxide. Since these aerogels are neither fusible nor soluble, the macroscopic shape of the carbon aerogels can be controlled only during the sol-gel reaction. The reaction, which requires long-term heating, should be conducted in a closed container to suppress the evaporation of water. Large blocks of RF wet gels can be easily recovered from closed containers, which is why most prior work has been on carbon aerogels with a blocky shape. When attempting to obtain carbon aerogels in the form of spheres, fibers, or films, special techniques are required. In the first half of this review, we summarize previous reports on RF-based carbon aerogels in the form of spheres, hollow-fibers, and films, and in the latter half, we describe recent studies on organic and carbon aerogel films derived from polyimides.

The aim of this thesis is to gain the novel findings about carbon-based cathodes using anion insertion and deinsertion reaction. Firstly, we conducted operando X-ray diffraction (XRD) and operando Raman spectroscopy measurements in aqueous electrolytes to compare the differences in graphite intercalation compounds (GICs) formation behavior and anion residual behavior for several anions with different structures. Secondly, we focused on developing a carbon cathode in which fluoride ions are inserted and deinserted by using the secondary battery reaction of Li-graphite fluoride batteries. We analyzed the cathode before and after charging and discharging, using XRD, Raman, and X-ray photoelectron spectroscopy (XPS) to analyze the reaction mechanism.