Effects of hydrofluoric acid pre-deashing of rice husk on physicochemical properties and CO2 adsorption performance of nitrogen-enriched biochar

In order to enhance CO2 adsorption capacity of rice husk char, raw rice husk was pre-deashed by HF (hydrofluoric acid) and used as precursor for preparing nitrogen-enriched biochar with high temperature ammonia treatment in this work. The effects of rice husk pre-deashing on the physicochemical properties and CO2 adsorption performance of nitrogen-enriched biochar were investigated. The results show that the micropore surface area of the nitrogen-enriched biochar derived from pre-deashed rice husk (labeled as HF-N-Char) is 545.74 m2/g, more than that of the nitrogen-enriched biochar derived from raw rice husk (labeled as N-Char, and its micropore surface area is 303.10 m2/g). The nitrogen content of HF-N-Char is 2.53 wt%, much higher than that of N-Char (1.64 wt%). It indicates that the deashing treatment not only improves the pore structure of nitrogen-enriched biochar, but also enhances the introduction of nitrogen-containing functional groups. In addition, the CO2 adsorption capacity of HF-N-Char (77.9 mg/g at 30 °C and 18.1 mg/g at 120 °C) is larger than that of N-Char (59.5 mg/g at 30 °C and 15.1 mg/g at 120 °C). The results may be helpful for the development of novel cost-effective CO2 adsorbents.