Figure 4.

(a) general scheme of the carbon dioxide induced gelation; (b) as synthesized translucent monolithic alginate aerogel from 0.5 wt % sodium alginate solution (left panel), alginate aerogel after compression under a pressure of 10 kN/m² becomes flexible; (c) microtomography image of alginate–lignin aerogels produced by CO₂ induced gelation depressurized at 30 bar/min to introduce macropores. Part (a) is reprinted from Martins et al. [42], Copyright (2015), with permission from Elsevier; part (b) is reproduced from Gurikov et al. [39] with permission from the Royal Society of Chemistry; part (c) is reprinted from Quraishi et al. [43], Copyright (2015), with permission from Elsevier.