Cesium-adsorption mechanisms of woody charcoal discussed on the basis of its functional groups and nanostructure

The present study examined the Cs + -adsorption behavior of Japanese oak ( Quercus serrata Thunb.) charcoal (OC) samples carbonized at 300, 500, and 700 °C to clarify the adsorption mechanisms from aqueous solution. Adsorption isotherms indicated that the Cs + -adsorption ability of OC depended strongly on carbonization temperature (CT) and suggested that the ability reached a maximum within the CT range from 300 to 700 °C. Infrared-photoacoustic (IR-PA) and Raman spectra of OC samples were obtained to investigate the functional groups and nanostructure in OC. Raman signals exhibited graphite precursor production even in OC synthesized at 300 °C. IR-PA spectral bands provided positive evidence that OC carbonized at 300 or 500 °C contained sufficient OH groups, and some of which were free from hydrogen bonding. Detecting free OH groups was the most important outcome in this study as it allowed exploration of the OC nanostructure. The experimental data indicated that the primary attraction to Cs + is due to the surface OH groups in OC, therefore offering an approach to synthesizing woody charcoal with a high Cs + -adsorption performance.