H₂S gas adsorption study using copper impregnated on KOH activated carbon from coffee residue for indoor air purification

Hydrogen sulfide (H2S) can negatively affect human health in confined spaces at even very low concentration due to its strong toxicity. In this work, coffee residue was used to prepare the activated carbon, then was further developed into a copper-impregnated activated carbon filter (Cu/AC) for H2S adsorption. The carbonization temperature has a great influence on the texture characteristics of activated carbon. The optimal activated carbon (BET: 1422 m2/g, Vtotal: 0.655 cm3/g) was achieved at 450 °C carbonization and at 750 °C KOH-activation. Copper catalyst greatly altered the surface properties of activated carbon by producing a lot of functional groups. The Cu/AC filter showed good H2S adsorption performance (max adsorption capacity: 132.22 mg/g) as it can completely remove H2S with an initial concentration of 400 ppm in a 0.1 m3 chamber within 10 min. The adsorption capacity depended not only on BET surface area, but also on the metal catalyst (copper). In addition, functional groups produced by copper-impregnation also enhanced the adsorption performance and the rate of adsorption, especially oxygen-containing functional groups (eg. O-H and C-O). The isotherm studies showed that the adsorption of H2S on the Cu/AC filter obeyed the Langmuir model, while the adsorption kinetics followed the pseudo-first-order and pseudo-second-order models. The adsorption mechanism is governed by initial film diffusion and subsequent intraparticle diffusion. Furthermore, the Cu/AC filter had excellent regeneration and reusability (still maintained >95% remove efficiency after 5 cycles). Finally, the current study suggested that coffee residue is good activated carbon precursor and can be used as an excellent adsorbent for H2S in confined spaces.