The University of Belgrade’s Institute for Multidisciplinary Research invented an urban photo-bioreactor. Liquid 3 cleans the air and serves as a bench in the Belgrade city centre.
It's a tank filled with microalgae, a solar panel on the top generates electricity for USB charging ports for citizens and a pump that pumps air into the tank where the algae process the CO² and produce Oxygen.
https://balkangreenenergynews.com/liquid-tree-to-combat-air-pollution-in-belgrade/
Cost per year of maintenance versus equivalent tree.
Might make sense in a space colony. But only barely.
The article says it: it's not meant to replace trees.
But it could be an option for places where a tree cannot be planted. If cities want to build street infrastructure, for example a shelter at a bus stop, then a microalgae CO2 filter and solar power could be integrated. Or tanks like this could be integrated into other architecture like in house walls.