Preparation of nitrogen-doped hierarchical porous carbon aerogels from agricultural wastes for efficient pollution adsorption

The development of green, economic and high-performance pollutant adsorption materials is an important way to meet severe environmental challenges. Herein, aerogel-like N-doped hierarchical porous carbon materials (NHCs) were prepared by rapid pyrolysis of corn straw and urea using KHCO3 as the activator. A series of characterizations including SEM, (HR)TEM, N2 absorption and desorption, FTIR, Raman, XPS, and elemental analysis were carried out to explore influences of activation temperature on the physicochemical properties of NHCs. It is found that NHC-800 prepared at 800 °C has a well-developed hierarchical pore structure, a high specific surface area (1871 m2/g) and a very low density (0.032 g/cm3). Influences of various parameters including activation temperature, urea and KHCO3 ratio, biomass type on the NHC adsorption performance were investigated. The material naming NHC-800 prepared from corn straw (corn straw: KHCO3: urea is 1:4:1) has the best methylene blue adsorption performance, with a maximum adsorption capacity of 1009.6 mg/g. Adsorption kinetics and thermodynamic analysis were carried out, and mechanism research was performed. It is found that urea not only provides pyridinic N chemisorbent sites, but also provides more activable sites for NHCs to generate more pore structures for physical adsorption. Performances on the adsorption of acid fuchsin, methyl orange, tetracycline, Cr6+, Cu2+ and actual wastewater were also studied, and it is found that NHC-800 can selectively and effectively remove organic pollutants while retaining metal ions.