# Analysis of Technologies for Carbon Dioxide Capture from the Air
## 2 DAC Technologies
### Adsorption
#### 2.2.2 Chemisorbents
[36], considering a polystyrene sorbent functionalized with a primary amine. The analysis was developed in real conditions, such as low partial pressure, low temperature (similar to temperatures in Finland, 273 K and 263 K) and presence of humidity. The results showed that the highest CO\({}_{2}\) uptake (1.06 molCO\({}_{2}\)/kg) was achieved at 263 K with humidity. A few works about class III amine-functionalized sorbents have been published, as shown in Table 4[103; 104; 105; 106]. Among these, [PERSON] et al. [104] studied, for the first time, a poly(l-lysine) brush-mesoporous silica hybrid to capture CO\({}_{2}\) from the air, under dry conditions at ambient temperature. Comparing the results with other functionalized amine sorbents, they found that the investigated sorbent had a CO\({}_{2}\) capture capacity of 0.6 molCO\({}_{2}\)/kg, higher than that of PEI-SBA-15 (0.32 molCO\({}_{2}\)/kg) and dimethylamine (DMA)-SBA-15 (0.19 molCO\({}_{2}\)/kg), with a slightly higher amine loading. The sorbent was robust during short regeneration tests. Good performances have been reported in the work of [PERSON] et al. [103], considering hyperbranched aminosilica (HAS) sorbents, for a simulated humidified air with 400 ppm of CO\({}_{2}\). The authors found that, by increasing the amine loading from 2.3 mmolN/g to 9.9 mmolN/g, the CO\({}_{2}\) adsorption capacity increased from 0.16 molCO\({}_{2}\)/kg to 1.78 molCO\({}_{2}\)/kg. CO\({}_{2}\) was captured reversibly without a significant degradation of performances in short, multi-cyclic operations. Functionalized polysilsesquioxane-based hybrid silica materials were studied by [PERSON] et al. [105], showing an adsorption capacity of 1.68 molCO\({}_{2}\)/kg. Moreover, the authors found a good recycling capability without efficiency losses after 50 cycles of adsorption/desorption in ambient air. Other sorbents have been proposed and investigated for class III. Diethylenediamine (DETA) supported on CB-N-g-PCMS-OH\({}^{-}\) was obtained from the polymerization of nitrene and showed a CO\({}_{2}\) uptake of 0.14 molCO\({}_{2}\)/kg with 95% relative humidity [18]. Faster absorption and desorption rates were obtained using a CB-g-xPCMS-OH\({}^{-}\) support (8.6 \(\times\) 10\({}^{-3}\) m\({}^{-1}\)), although the CO\({}_{2}\) adsorption capacity was the same [18]. These two previous supports were in carbon black functionalized with atom transfer radical polymerization (ATRP) initiators. Inverse templating is another method used to prepare highly porous polymeric structures [18]. PS-CC and colloidal crystals were functionalized by DETA with a CO\({}_{2}\) uptake of 0.57 molCO\({}_{2}\)/kg and 0.36 molCO\({}_{2}\)/kg, respectively. High internal phase emulsion (HIPE)-based materials have also been investigated, achieving an adsorption capacity of 0.5 molCO\({}_{2}\)/kg and 0.72 molCO\({}_{2}\)/kg [18]. An alternative sorbent of class III has been proposed by [PERSON] and [PERSON] [106]. The material was based on the polymerization of Z-protected L-lysine N-carboxyanhydride on an aminopropyl-functionalized SBA-15 support. This approach resulted in polymer brushes tethered to the oxide surface within the mesoporous silica network, yielding a hybrid aminosilica rich in primary amine groups.