Abstract
•HNO3 and ammonia modified sludge-based activated carbon (SAC) in turn.•Modification leads to beneficial effect on the porous structure and introduces nitrogen onto the SAC.•Ammonization temperature and time affected N-functional groups’ contents and types.
In this paper, sludge-based activated carbon (SAC) was treated by HNO3 and NH3 in turns. Under the conditions of ammonization temperature and residence time, the surface physico-chemical characteristics of modified SAC were characterized by SEM, BET, FTIR and XPS. The research results show that modification of SAC leads to beneficial effect on the porous structure, the maximum surface area and micro-pore volume reached to 273m2/g and 0.082cm3/g at 750°C, respectively. After ammonization, NCH3 and CN groups were detected on the surfaces of all the modified SACs. Moreover, XPS study indicated that the nitrogen content increased from 1.65% in origin sample to a larger content range of 2.93–4.69% at different treatment conditions and found that lower ammonization temperature and longer residence time will produce higher nitrogen content. The nitrogen introduced mainly in the forms of amines, pyridine nitrogen (N-6), pyrrole nitrogen (N-5), quaternary nitrogen (N-Q) and N-pyridine oxide (N-Ox). The sample of SAC-650-90 obtained the highest content of N-6 with the value of 1.46%. The highest content of N-5, N-Q and N-Ox which obtained in the sample of SAC-750-120 in the same time were 1.22%, 0.98% and 1.21%, respectively. Compared to the ratios of five kinds of nitrogenous substance, the highest ratios of N-Ox, N-5, N-Q and N-6 obtained among different samples were 27.11%, 29.09%, 33.14% and 31.11%, respectively. And they can transform from one type to another.