Zinc-doped titanium oxynitride as a high-performance adsorbent for formaldehyde in air

The potential utility of titanium oxynitride doped with 5% zinc (ZnTON) has been investigated as an adsorbent for the treatment of gaseous formaldehyde (FA) using a fixed-bed adsorption system. The adsorption capacity of ZnTON, when estimated at 10%/100% breakthrough (BT) levels from a dry feed gas consisting of 10 Pa FA, was far superior to two reference materials (i.e., commercial P25-TiO₂ and activated carbon (AC)) by factors of 1.7/1.3 and 10/2.5, respectively. The adsorption capacity of ZnTON increased with the increase in the initial feeding concentration of FA (5-12.5 Pa), while decreasing with the rising temperature (25-100 ^oC). An increase in moisture level (0-100% relative humidity) also led to 5.4- and 2.5-fold reductions in adsorption capacity of ZnTON at 10% and 100% BT levels, respectively. Thermodynamically, the adsorption of FA onto ZnTON is an exothermic (ΔH^o = - 9.69 kJ.mol^-1) to be feasible in nature based on physisorption mechanism. Further, the adsorption of FA onto ZnTON was governed by surface interactions and monolayer surface coverage (Van der Waal's force/electrostatic attraction), as it obeyed the Langmuir isotherm and pseudo-second-order kinetic models. Regeneration tests indicated a positive effect of moisture on FA desorption and durability of ZnTON (i.e., over three adsorption-desorption cycles). This study offers valuable mechanistic insights into the synthesis of an advanced adsorbent for the efficient removal of hazardous volatile organic compounds under near-ambient conditions.