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

Takayuki Yamagishi,Kaoru Nishikiori,Shigeru Yamauchi,Yasuji Kurimoto

doi:10.1186/s10086-019-1805-5

Takayuki Yamagishi, Kaoru Nishikiori + Show 2 more

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https://doi.org/10.1186/s10086-019-1805-5

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Abstract

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.

Highlights

The nuclear power plant accident caused by the Great East Japan Earthquake (2011) has raised several important and serious issues and led to many countries considering shutting down of their nuclear power plants
The holding time (HT) at the carbonization temperature (CT) is appended to the sample name; for example, oak charcoal (OC) carbonized at 500 °C for 2.0 h is referred to as OC500-2
The change in Cs+-adsorption ability with CT can be expected to provide insights into the functional groups and nanostructures of OC, the optimum temperature may fluctuate with carbonization conditions

Summary

Introduction

The nuclear power plant accident caused by the Great East Japan Earthquake (2011) has raised several important and serious issues and led to many countries considering shutting down of their nuclear power plants. Cs-134 and Cs-137 are the most troublesome radioisotopes with respect to decontamination and have been the most difficult to remove from contaminated areas in Fukushima Prefecture This situation would recur as a result of future adsorptive [1,2,3,4] other than ours [5,6,7,8,9,10] despite 8 years passing from the Fukushima accident, because the Cs+-adsorption ability of ordinary biochar is inferior to that of inorganic adsorptives. These studies suggested that the content of acidic functional groups, such as hydroxy (OH) or carboxy groups, included in the charcoal is a governing factor determining the ability to adsorb Cs+

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