The previous item (about generating Carbon nanotubes etc after “burning” off just the hydrogen from methane using CO2 as the oxidant) raises a point that soot is mostly just unburned carbon and repurposing it as such may ultimately be a good approach to CO2 removal – which challenges the ideal of always demanding complete combustion.
And the same issue of Scientific American where that came up (though just in the paid promo section from Qatar) also includes a real article (by Wade Rouche in the edited ‘Ventures’ section ) which raises some concerns that have often troubled me about bio-degradable plastics (which always end up back in the air as CO2 rather than underground or on the seabed in a form which may eventually get geologically reformed into petroleum). Perhaps coincidentally(?), the first of the ’emerging technologies’ touted in that issue is the use of bio-sourced materials for the production of bio-degradable plastics – but without any acknowledgement that using those materials to produce non-degradable products would be even better.