Functional nanoporous carbons from hydrothermally treated biomass for environmental purification

Hydrothermal carbonization (HTC) was utilized as a pretreatment method to convert high oxygen content lignocellulosic biomass, otherwise invaluable renewable material, to a more condensed functional material for higher value applications. Hazelnut shells (HS), an abundant agricultural biomass, were pre-carbonized to hydrophilic and thermochemically more stable hydrochar (HH) under hydrothermal conditions. Successive calcination of HH under inert atmosphere yielded a hydrophobic nanoarchitectured carbon material with a 250 m2 g−1 specific surface area (HH-T) while the same procedure in the presence of a porogen yielded a highly porous hydrophilic carbon material with a specific surface area of 1700 m2 g−1 (HH-KT). The batch-equilibrium and batch-kinetic methylene blue dye (MB) adsorption experiments, in aqueous solutions revealed that the HH-KT exhibits adsorption rates and capacities higher than biomass-derived activated carbons obtained by traditional routes. Monolayer adsorption capacity and pseudo-second order kinetic rate constant, as high as 524 mg g−1 and 0.052 g mg−1 min−1 were recorded for HH-KT, respectively. HH-KT, with its honeycomb-like structure dominated by micropores and mesopores, high pore volume, and appropriate surface functionality to anchor basic dyes, proves ideal for adsorption of polar organic pollutants from aqueous solutions. Materials produced by the presented sustainable approach, which eliminates the fossil fuel based precursors by mimicking the nature’s way of coal making, can also be utilized in drug delivery, catalysis and energy storage applications.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Biomass was self-functionalized by hydrothermal pretreatment without additional chemicals. ► Porosity was enhanced by carbonization of hydrochar in the presence of a porogen. ► Hydrophilic, nanoporous and high capacity adsorbents were utilized in water purification.