Nature of water-biochar interface interactions

A poplar biochar obtained by an industrial gasification process was saturated with water and analyzed usingfast field cycling (FFC) NMR relaxometry in a temperature range between 299 and 353 K. Results revealed thatthe longitudinal relaxation rate increased with the increment of the temperature. This behavior was consistentwith that already observed for paramagnetic inorganic porous media for which two different relaxation mechanismscan be accounted for: outer- and inner-sphere mechanisms. The former is due to water diffusing from theclosest approach distance to infinity, whereas the second is due to water interacting by nonconventionalH-bonds to the porous surface of the solid material. In particular, the inner-sphere relaxation appeared to bepredominant in the water-saturated biochar used in the present study. This study represents a fundamental firststep for the full comprehension of the role played by biochar in the draining properties of biochar-amendedsoils.