One-step synthesis of nitrogen-doped sludge carbon as a bifunctional material for the adsorption and catalytic oxidation of organic pollutants.

Nitrogen-doped carbon (NC) materials have been extensively investigated for their great potential applications in adsorption, catalysis, etc. Herein, we report a facile one-step pyrolysis process for NC synthesis using abundant bio-waste of excess sludge as carbon source and cheap precursor of urea as nitrogen source. The developed materials were evaluated for organic pollutants removal through adsorption and catalytic oxidation by peroxymonosulfate (PMS) activation. Experimental results demonstrated that nitrogen doping significantly affected the elemental composition and microstructure of NC, leading to improved adsorption capability as well as PMS activation activity for methylene blue (MB) removal. The adsorption capacity for MB reached 35.831 mg g-1 over NC-700 sample (NC prepared at 700 °C). In MB catalytic oxidation experiments, effects of sample calcination temperature, catalyst dosage, PMS loading, and co-existing ions were investigated. Under optimal reaction conditions, 98.70% of MB could be removed in 20 min. Through radical quenching and electron spin resonance (ESR) tests, it was confirmed that singlet oxygen (1O2) was the main reactive species for MB degradation. Additionally, NC-700 performed well in recycle studies without significant efficiency loss. Other typical organic pollutants including malachite green (MG), methyl orange (MO), bisphenol A (BPA), phenol (PE), and sulfamethoxazole (SMX) could also be removed using NC-700 as adsorbent and catalyst. These features manifest that excess sludge-derived NC could be a promising material for organic pollutants remediation.