I think you should be a bit careful about the overall energetics of capturing CO2 using a chemical like NaOH or MEA. Where do you get the chemical from? Ultimately it has to be manufactured - and making NaOH is very energy intensive (I don't know about MEA but I suspect that it isn't that easy either). The principle is fine for experimental sized set-ups, but I don't see how it can scale up. The energetic cost of preparing your sequestrating chemical is too high.

Direct air capture may only make sense if all fossil fuel power plants are decarbonised. But still, it will be a rather expensive process due to very low concentration of CO2 in the air. The cost of CO2 capture using solvent-based technologies may reach 600-1000 €/tCO2. I got recently involved in a project (Balanced Energy Network) In which I evaluated feasibility of using solid sorbents (calcite, magnesite or dolomite) for direct air capture. The main critique of such process in the current literature is that it needs to be operated at a high temperature. However, when linked with SOFC, the cost of CO2 capture can be between 140-600 €/tCO2, depending on sorbents conversion. 

So how much of the energy produced by combustion process which yields the CO2 will have to be committed to sequestering it? And are you sure the process is sustainable in that it isn't producing anything except sequestered CO2 and isn't consuming anything that the process itself can't generate? I can't think of anything available on the scale required that could be used to sequester any significant amount of CO2 from the air.

The only process I can think of relies on cracking solar nitrogen fixation - you use that to generate ammonia and then form ammonium carbonate. But that's hard. Incidentally it might also help to increase the pH of the oceans.