Hierarchically porous diatomite-activated carbon composite for TMA and NH₃ removal in confined spaces

Indoor air pollution is becoming more prominent, which requires an urgent need to develop cost-effective adsorption materials. In this work, a novel and bimodal composite of diatomite (Dt) and activated carbon (AC) was developed. Then copper was impregnated on the surface of the diatomite-activated carbon composite (Cu/Dt-AC) for the adsorption of indoor air pollutants (Trimethylamine (TMA) and NH₃). The Dt-AC composites contained the inherent characteristics of Dt and AC, showing the bimodal and hierarchically porous structures. The mass ratio of Dt-AC can significantly affect BET (Brunauer Emmet and Teller) surface area and pore size of the Dt-AC composite. Cu-loading can generate many surface functional groups (especially oxygen-containing functional groups –OH, –C–O, O–Si–O, SiO–H), thereby greatly improving the adsorption efficiency. The optimum copper proportion on TMA adsorption performance was 22 wt.% regardless of the ratios of Dt-AC whereas the best NH₃ adsorption performance was obtained with a ratio of 1:3 and 22 wt.% of copper. The maximum adsorption capacities of TMA and NH₃ were 185.59 and 37.48 mg/g, respectively. The adsorption process of TMA and NH₃ well followed the Langmuir isotherm and pseudo-second-order kinetics models. Furthermore, both the intraparticle diffusion and film diffusion models jointly controlled the adsorption mechanism of TMA and NH₃ on the Cu/Dt-AC filter. The spent Cu/Dt-AC filter can be regenerated, and its adsorption efficiency remained above 90% for TMA and above 80% for NH₃ over five cycles.