No abstract

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

Purpose The aim of the present study was to investigate structure alterations of a sandy-clay soil upon addition of different amounts of biochar (f bc ). Materials and methods All the f bc samples were analyzed by high energy moisture characteristic (HEMC) technique and 1 H nuclear magnetic resonance (NMR) relaxometry. HEMC was applied in order to evaluate aggregate stability of biocharamended soil samples. 1 H NMR relaxometry experiments were conducted for the evaluation of the pore distributions through the investigation of water dynamics of the same samples.Results and discussion The HEMC technique revealed improvement in aggregate stability through measurements of the amount of drainable pores and the stability ratio. The latter increased as the amount of biochar was raised up. The 1 H NMR relaxometry revealed a unimodal T 1 distribution for both the sole sandy-clay soil and the biochar. Conversely, a bimodal T 1 distribution was acquired for all the different f bc samples. Conclusions Improvement in aggregate stability was obtained as biochar was progressively added to the sandy-clay soil. A dual mechanism of water retention has been hypothesized. In particular, intra-aggregate porosity was indicated as the main responsible for molecular water diffusion when f bc comprised between 0 and 0.33. Conversely, inter-aggregate porosity resulted predominant, through swelling processes, when f bc overcame 0.33.

21The aim of this paper was to understand the water-surface interactions of two chars obtained by

Two commercial TiO2 samples, a 100% anatase\ud and a 100% rutile, were used for the fast field cycling NMR\ud experiments. The results showed a different behavior between\ud the different samples. In particular, water molecules were\ud unbonded to the solid surface for the rutile sample, whereas\ud they appeared to chemically interact with the surface through\ud H-bond formation with the anatase sample. The above\ud findings accord with the generally lower activity of rutile\ud with respect to anatase reported in literature for photocatalytic\ud oxidation reactions in water. The difficulty of water to interact\ud with rutile surface, indeed, could hinder the formation of OH\ud radicals, which are the most important oxidant species