Quasi-Isothermal Thermogravimetric Insight Into Energetic Heterogeneity of Ni-Modified Biocarbons

Quasi-isothermal thermogravimetric analysis (Q-TG) was used to characterize the structure and energy heterogeneity of water layers adsorbed on the surface of nickel-modified biocarbons. The investigated materials were obtained from biomass in the pyrolysis process carried out at temperatures of 500°C and 800°C, with the nickel contents of 5% and 10% by weight. The combination of Q-TG, low-temperature nitrogen adsorption, and FTIR, XRD, and XPS analyses enabled a comprehensive assessment of the effect of carbonization temperature and the presence of the metallic phase on porosity, surface chemistry, and water/biocarbon interactions. Biocarbons obtained at 500°C proved to possess a dominant microporosity and hydrophilic surface character, while carbonized materials at 800°C exhibit a micro-/mesoporous structure, greater ordering of graphene domains, and increased hydrophobicity. The analysis of the relationship between $\Delta G=f\left(C_{H_{2}O}\right)$ and dG/dM derivatives revealed the presence of strong adsorption centers at a low degree of hydration and a shift in the capillary condensation threshold towards larger numbers of water monolayers with the increasing pyrolysis temperature and nickel content. The obtained results confirm the applicability of the Q-TG method for the determination of energetic heterogeneity of biocarbons and indicate the possibility of controlling their hydrophilic/hydrophobic properties for environmental applications.