Abstract

Biomass thermochemical conversion-derived hydrochar has been increasingly recognized as a functional resource for environmental remediation, but knowledge about the effect of the carbonization conditions on the surface chemistry and binding behaviour of hydrochar is still limited. In this study, hydrochar from two different processing pathways, pressure reactor carbonization (P-RC) and microwave-assisted carbonization (M-RC), is compared to understand the mechanisms of contaminant interaction and the changes in structure that occur during the carbonization processing. P-RC was synthesized at the hydrothermal temperatures (180, 220, and 250 °C) for 2 and 5 h, while M-RC was synthesized at microwave irradiation for 30 min and 1 h. TGA, SEM–EDS, FTIR, and XRD were used for comprehensive characterization, which revealed systematic differences in functional group distribution, mineral phases, and microstructural development between the two carbonization methods and at different carbonization temperatures. The increase in P-RC temperature led to greater aromatic condensation, thermal stability, and mineral reorganization, while M-RC maintained a higher percentage of oxygenated functionality and a more heterogeneous surface morphology. Batch adsorption experiments indicated that the M-RC hydrochar had a faster adsorption rate, attributed to its greater number of reactive oxygenated functionalities, whereas the P-RC hydrochar produced at higher temperatures exhibited a more even distribution of adsorption sites and stronger mineral-assisted interactions. The kinetics and isotherm modeling also showed different interaction pathways: for M-RC, surface complexation on heterogeneous sites was favored, whereas for P-RC, a more monolayer-like adsorption was observed. These results collectively show how the method and temperature of carbonization affect reactivity and support the establishment of mechanistic relationships crucial to maximizing the utility of hydrochar as a functional material for environmental remediation.

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