Malodors adsorption behavior of metal cation incorporated hydroxyapatite

Abstract Several kinds of hydroxyapatites (HAp) prepared by modification of Ca 2+ -HAp with transition metal (Fe 2+ , Fe 3+ , Co 2+ , Ni 2+ , Cu 2+ and Zn 2+ ) or aluminum (Al 3+ ) ions were evaluated via a gas bag-detection tube method whether they could be used as novel deodorant materials. The samples treated with divalent cation (Fe 2+ , Co 2+ , Ni 2+ , Cu 2+ and Zn 2+ ) retained hydroxyapatite structure as well as Ca 2+ -HAp, whereas those treated with trivalent cation (Al 3+ and Fe 3+ ) showed lower crystallinity than Ca 2+ -HAp. 5–8 wt% cation of the samples was introduced by modification with divalent metal cations, whereas about 40 wt% cation of the samples was introduced with relatively larger surface area and higher content of adsorbed water for trivalent cations. For NH 3 gas, modification of Ca 2+ -HAp with a divalent metal cation enhanced its adsorption ability, and that with a trivalent metal cation resulted in considerable improvement of the ability. On the other hand, modification of Ca 2+ -HAp with Cu 2+ ion gave it remarkable H 2 S gas adsorption ability in comparison to that with other metal cations. However, adsorption ability for H 2 S of some polycrystalline powders including Cu 2+ was not higher than that of Cu 2+ -modified HAp. The effect of the incorporated cation on adsorption ability for NH 3 molecules may be based not only on a simple Lewis acid-base reaction but also on specific surface area and adsorbed water content, and the effect for H 2 S molecules based on the specific local electron density around the cation present on/in the material.