A tutorial mini-review on nanoporous carbons from biosourced building blocks: ordered hierarchical nanoarchitectures through benign methodologies

Ordered hierarchically porous carbons exhibiting micro- and mesopores are state-of-the-art porous structures with extraordinary performance in a range of applications (e.g., electrochemistry, catalysis, water treatment). Nevertheless, they are mostly prepared using petroleum-based chemicals, through resource- and energy-intensive, environmentally unfriendly processes. In this tutorial mini-review, we highlight major limitations in the methodologies, and showcase important achievements towards developing more sustainable synthetic strategies. Compared to multi-step hard-templating/nano-casting procedures, soft-templating techniques can provide more efficient, benign, and direct ways to produce these nanostructures. The original soft-templating method, using Pluronic® surfactants as structure-directing agents and phenolic resins as carbon precursors, has been substantially modified over the years in light of sustainability issues. The formaldehyde crosslinker has been replaced with more benign, less toxic alternatives (e.g., glyoxal), and catalyst-free crosslinking approaches have been developed. Furthermore, the use of biobased building-blocks for the carbon precursor, such as lignin, plant-derived polyphenols (e.g., tannins), and various saccharides (e.g., D-glucose, D-fructose), has also been explored. Novel techniques, such as the coordination-induced self-assembly, mechanosynthesis, and modified hydrothermal treatment strategies are amongst the greenest processes developed so far. We give some critical comments on ongoing research in this field and point towards interesting research directions.