Urea/nitric acid co-impregnated pitch-based activated carbon fiber for the effective removal of formaldehyde

Urea/nitric acid co-impregnated pitch-based activated carbon fibers (ACFs) were examined as adsorbents for the removal of low-concentration formaldehyde gas from dry and humid atmospheres. Urea, which is a harmless and environmentally friendly primary amine, was selected as an effective reagent to capture formaldehyde and nitric acid was used to promote the oxidation of formaldehyde into formic acid, which inhibits the liberation of formaldehyde even under humid atmospheres. The optimized urea/nitric acid co-impregnated ACF showed a 110-fold (0.72 mg/g to 79.28 mg/g) improvement in its formaldehyde removal capability as compared to that of pristine ACF at 40% humidity. The formaldehyde removal mechanism is proposed based on careful analysis and quantification of the inlet and outlet gases. Further, the optimized sample facilitates complete removal of formaldehyde from ambient air at humidity of 11–88% and temperatures of 3–26.9 °C over 24 h, whereas only 81.5% formaldehyde removal is achieved with pristine ACF under the same conditions.