Low‐Cost Solvent‐Free Single‐Step Surface Modification of Coconut‐Shell Activated Carbon Using Ambient‐Air Atmospheric Pressure Plasma Jet

Atmospheric pressure non‐thermal plasma provides a solvent‐free route to tailor the surface chemistry of porous carbons while preserving their bulk structure. Here, we report a cost effective, air‐operated KINPen‐type plasma jet for the surface functionalization of coconut‐shell activated carbon (AC) and correlate plasma conditions with resulting materials changes using optical and material diagnostics. Optical emission spectroscopy (OES) was utilized to deduce the key plasma parameters such as electron temperature (∼0.42 eV), rotational temperature (∼1210 K), and electron number density (∼10 16 cm −3 ). X‐ray diffraction (XRD) suggests that the carbon structure is largely maintained after treatment, with no apparent evidence of bulk phase transformation. Raman spectroscopy indicates minor structural modification, consistent with plasma‐induced surface activation, while scanning electron microscopy (SEM) signifies enhanced surface roughness and apparent pore development. Energy‐dispersive X‐ray spectroscopy (EDX) indicates an increase in surface oxygen content, while Fourier‐transform infrared spectroscopy (FTIR) shows changes in absorption features within the measured spectral range that are consistent with plasma‐induced surface oxidation and modification. Plasma‐treated AC shows improved methylene blue removal compared with untreated AC, suggesting that the plasma‐induced surface modification can enhance adsorption performance for environmental remediation. The presented approach offers a scalable pathway for engineering porous carbon surfaces using ambient‐air plasma at atmospheric pressure.