Problem definition and objectives: Technological and industrial advancements have driven an increased demand for energy. Many conventional energy sources have contributed to rising atmospheric carbon dioxide levels, posing significant risks to the environment and human health. Surface adsorption using solid adsorbents is a promising method for mitigating CO2 emissions. Cellulose-based adsorbents have gained prominence recently due to their biodegradability and abundance. In this study, hairy nanocrystalline cellulose, a material used in diverse applications over the past decade, and nanocrystalline cellulose were synthesized via oxidation and acid hydrolysis, respectively. Then, the CO2 adsorption capacities of these materials were compared.
Methodology: A specific amount of alpha-cellulose, sodium metaperiodate, and sodium chloride were added to 300 mL of distilled water. The mixture was stirred using a magnetic stirrer for several hours until the reaction was complete. To quench the reaction, 3 mL of ethylene glycol was added. The resulting suspension was then washed using a vacuum pump. For hairy nanocrystalline cellulose synthesis, the obtained cellulose dialdehyde was added to 100 mL of distilled water and mixed at 80 °C until completely dissolved. The solution was centrifuged, and the supernatant was removed and weighed. Propanol was then added to the supernatant at a ratio of 1.7:1 (propanol: supernatant weight). Following a second centrifugation, the final material was obtained.
Results: The results of Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) analysis confirmed the synthesis of nanocrystalline cellulose and hairy nanocrystalline cellulose. According to the results of the adsorption capacity analysis, at 25 ° C, with an increase in carbon dioxide concentration from 10% to 90%, the adsorption rate of hairy nanocrystalline cellulose was increased from 2.12 mg/g to 7.63 mg/g on average. In other words, at 25 ° C, it increased by approximately 3.6 times. In contrast, the adsorption capacity of nanocrystalline cellulose did not increase significantly with increasing carbon dioxide concentration from 10% to 90%. Its average adsorption capacity at 25°C increased from 0.69 mg/g to 1.11 mg/g, meaning that the adsorption capacity for nanocrystalline cellulose at 25°C increased by about 61%. The main reason for increase in adsorption capacity with increasing carbon dioxide concentration is the increase in the number of carbon dioxide molecules per unit volume, followed by an increase in collisions. Also, with the temperature increasing from 25 to 50°C due to the physical nature of carbon dioxide adsorption, the amount of carbon dioxide adsorption by both adsorbents decreased. For example, the adsorption rate of hairy nanocrystalline cellulose at a concentration of 90% carbon dioxide decreased from 7.63 mg/g to 4.78 mg/g. The results of the study showed that hairy nanocrystalline cellulose, due to the presence of aldehyde groups and amorphous regions, had a higher adsorption rate than nanocrystalline cellulose. At a temperature of 25 ° C and a concentration of 90% carbon dioxide, the adsorption capacity of hairy nanocrystalline cellulose and nanocrystalline cellulose was 7.63 mg/g and 11.1 mg/g, respectively; which means, the adsorption capacity of hairy nanocrystalline cellulose was about 7 times higher than that of nanocrystalline cellulose under similar conditions.
Conclusion: In general, with increasing carbon dioxide concentration and decreasing temperature, the adsorption capacity of both adsorbents increased, because increasing carbon dioxide concentration increased the amount of contact between carbon dioxide molecules and the adsorbent surface, and also, considering the possibility that the adsorption is of a physical type, decreasing temperature increased the adsorption capacity. So, the maximum adsorption capacity at a temperature of 25° C and a concentration of 90% carbon dioxide was related to hairy nanocrystalline cellulose and was equal to 7.63 mg/g.