Preparation of nitrogen-doped biocarbon from sewage sludge and pine sawdust for superior hydrogen sulfide removal: Experimental and DFT studies.

Hydrogen sulfide (HS) is a major air pollutant posing a serious threat to both the environment and public health. In this study, a novel nitrogen-rich biocarbon that effectively removes HS was produced from a mixture of sewage sludge and pine sawdust using melamine as nitrogen source. Compared with pristine biocarbons, nitrogen (N)-doped biocarbons possessed an adjustable porosity, e.g., higher specific surface area of 786-1547 m/g, richer nitrogen content of 9.02-10.22%, and larger pore volume of 0.31-0.88 cm/g. In particular, when HS flow rate was 100 mL/min at 25 °C under dry conditions, a higher HS adsorption capacity (376.7 mg/g) was observed on nitrogen-rich biocarbon pyrolyzed at 800 °C (BC800N) due to the larger surface area (1547 m/g), higher pore volume (0.88 cm/g), and richer nitrogen content (10.22%). The presence of CO in the gas reduced HS adsorption; however, this was partially overcome by the presence of water vapor. After ten consecutive adsorption/desorption cycles, BC800N retained 96.7% of its adsorption capacity. Scanning electron microscopy, X-ray diffraction analysis, and quasi-in-situ X-ray photoelectron spectroscopy were employed to identify the transformed composites of HS on the biocarbons. The higher nitrogen content resulting from melamine doping mainly increased the pyridinium N-6 and pyrrole N-5 levels, which serve as nitrogen-containing active sites for HS adsorption. Density functional theory analysis confirmed that the N-6 atoms affected the adsorption of HS molecules significantly and play an important role in gas adsorption. This innovative biocarbon material has the potential to facilitate optimized adsorption of HS and assist in effectively mitigating the environmental impact thereof.