Hydrothermal char, produced by heating of carbohydrate rich solids in the presence of liquid water, has shown remarkably high affinity for heavy metals, despite possessing only modest surface areas (&lt;10 m2 g-1). The un-expected adsorption performance of hydrothermal char motivates an investigation of the relationship between the chemical properties of the hydrothermal char and the char’s uptake of heavy metal cations. First, we developed a new method to interpret Raman spectra of hydrothermal char to describe the material as small clusters of polycyclic aromatic hydrocarbons and fused furanic compounds and which bears alkyl chains and oxygen functional groups. In collaboration with Prof. Klaus Schmidt-Rohr and his research group at Brandeis University as well as with partners at Cabot Corp., we have compared characterization results from the Raman method to those obtained from magic-angle spinning NMR. Next, we have used glucose solutions as a model feed to study the effects of carbonization time on hydrothermal char composition; finding that chemical diversity of the material increases to a maximum at 8 hours, followed by a gradual increase in material uniformity to produce a more highly aromatic/furanic substance with fewer alkyl side chains and oxygen functional groups. Complementary analysis was performed using infra-red spectroscopy, to confirm the presence of oxygen functional groups, and gas sorption, to quantify N2 accessible surface area. Finally, we used copper as a model heavy metal cation to investigate the relationship between char composition and metal uptake. Here, we find that increasing carbonization time leads to increased copper uptake, potentially a consequence of the increasingly aromatic content of the char. Adsorption onto two activated carbons – chosen to represent a wide range of surface chemistry - was used as a control. As expected, we find that the adsorption capacity per unit surface area is nearly 100-fold greater for the hydrothermal chars compared to activated carbon controls, regardless of the surface composition of the control materials. This work provides a basis for developing synthesis-structure-property relationships that can guide design of char adsorbents in a wide range of applications.

Removal of heavy metals from drinking water using hydrothermal char

253rd National Meeting (2017)

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