Tailored Nitrogen Sites on Biomass-Derived Activated Carbon for Enhanced Formaldehyde Detection at Room Temperature

This study introduces nitrogen atoms into biomass-derived activated carbon (AC) to enhance its sensitivity to formaldehyde vapor at room temperature. Nitrogen-doped activated carbon (N-AC) derived from coconut shells was successfully prepared by heat treatment with ammonia (NH3) at 800°C. The atomic ratio of nitrogen to carbon in N-AC was approximately 4.1 at.%. AC and N-AC were separately mixed with ethanol and then dropped onto a printed circuit board with Au/Cu electrodes, serving as the sensor substrate. The as-fabricated AC and N-AC sensors were exposed to formaldehyde concentrations ranging from 1 to 100 parts per million (ppm) at room temperature. N-AC sensor demonstrated a sensor response approximately 5- to 6-fold higher than that of the AC sensor. The enhancement of formaldehyde sensitivity is attributed to the increased surface area, porosity, and nitrogen doping of AC. The sensing mechanism can be explained by the charge transfer from formaldehyde molecules to the sensing materials. Nitrogen-doped sites play a crucial role in improving formaldehyde adsorption because of their high binding energy and significant charge transfer, resulting in an enhanced sensor response. This study proposes an effective method involving NH3 heat treatment for biomass-derived AC to improve the surface area, porosity, and nitrogen doping of AC to enhance the sensitivity of formaldehyde detection at room temperature.