Preparation and CO₂ adsorption properties of tannin modified phenolic based carbon cryogels

Based on the large number of reactive hydroxyl of green and low cost of tannin, its hold the similar mechanism as phenol and resorcinol reacted with formaldehyde. On the basis of carbon cryogels from traditional phenolic resin (phenol-urea-formaldehyde), a new type of carbon cryogels for efficient CO₂ capture were successfully prepared by tannin modification. The surface chemistry and pore structure of carbon aerogel were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and nitrogen adsorption and desorption analysis. The adsorption capacity, selectivity and adsorption heat of carbon cryogel were studied by carbon dioxide adsorption and desorption analysis. The results show that the new and efficient phenolic carbon cryogel can be prepared by using green and renewable biomass raw material tannin to partially replace the traditional phenol or resorcinol, which can not only significantly reduce the product cost, but also significantly improve the carbon dioxide adsorption performance. When the addition amount of tannin (15 g) is 50wt% of that of phenol, the sample has the maximum specific surface area (1376.31 m²·g⁻¹) and micropore volume (0.55 cm³·g⁻¹), which is a potential gas adsorption material. The corresponding CO₂ adsorption capacity is as high as 5.36 mmol·g⁻¹, and the selective adsorption and adsorption heat are 16.84 and 34.49 kJ·mol⁻¹, respectively. The properties of phenolic carbon aerogels are significantly better than those of unmodified phenolic carbon aerogels, and also better than most of the traditional carbon aerogels. This is mainly attributed to its high specific surface area, micropore volume, suitable pore size distribution and good 3D network structure.