Nanosilica polyamidoamine dendrimers for enhanced direct air CO ₂ capture

Exploring efficient systems to recover CO₂ from the atmosphere could be a way to address the global carbon emissions issue. Herein, we report the synthesis of nanosilica (NS) functionalized with polyamidoamine (PAMAM) dendrimers (NS-PAMAM) as efficient adsorbents for CO₂ capture under simulated direct air capture (DAC) (400 ppm CO₂ in helium at 30 °C) and indoor air (≥400 ppm, 50 ± 3% RH at 30 °C) conditions. The results inferred that the 1^st (NS-G1.0), 2^nd (NS-G2.0), 3^rd (NS-G3.0), and 4^th (NS-G4.0) generations of the NS-PAMAM dendrimers exhibited excellent performance for CO₂ capture. Compared to the other generations, NS-G3.0 demonstrated superior CO₂ adsorption capacities of 0.50 mmol g^-1 under simulated dry CO₂ conditions (400 ppm in He), 1.02 mmol g^-1 under indoor air (dry) CO₂ conditions (≥400 ppm, 26 ± 3% RH), and 1.54 mmol g^-1 under indoor air (humid) CO₂ conditions (≥400 ppm, 50 ± 3% RH). The study included the evaluation of CO₂ adsorption-desorption performance of the NS-PAMAM dendrimers under varying structural and chemical parameters, kinetics, regeneration at low temperature (80 °C), as well as CO₂ adsorption under humid conditions. Additionally, NS-G3.0 displayed a substantially superior performance with stable CO₂ capture displayed during ten short temperature swing adsorption (TSA) cycles, making it a promising candidate for CO₂ capture from ambient air. Finally, we demonstrated the recovery and reutilization of the captured CO₂ for both the synthesis of formate via carbonate hydrogenation and for the production of calcium carbonate pellets.