Effect of pH and aging temperature on the phosphorus removal properties of layered hydroxide synthesized from zinc acetate

Abstract

Zinc hydroxide acetate (ZHA) is a promising material for anion exchange applications because it has a layered structure with intercalating CH 3 COO − and H 2 O. ZHA can be synthesized through a direct precipitation method by adding sodium hydroxide solution to a Zn(OCOCH 3) 2 solution. In this study, ZHAs were synthesized under various conditions and tested as phosphorous removal agents. The ZHA precipitates were obtained at pH 6, 7, and 9. They were then aged at 25°C, 60°C, 90°C, and 120°C under hydrothermal conditions. At pH 6, nearly pure single-phase ZHAs were obtained regardless of the aging temperature. On the other hand, most of the ZHAs that were prepared at higher pH and aged at higher temperature were transformed to ZnO. For the phosphorous removal experiments, the single-phase ZHA precipitates removed approximately 99% of the phosphate ions in a 100 mg L −1 phosphorous solution, and the phosphorus removal efficiency decreased with increasing amounts of ZnO. Therefore, ZHAs that were prepared at lower pH and aged at lower temperatures contained little to no ZnO, thereby showing high phosphorous removal capabilities.

Effects of aging conditions on the morphologies of ZnO particles synthesized under hydrothermal conditions from layered zinc hydroxide as a precursor derivered from zinc acetate

“…The endothermic process at 60-90°C is associated with about 8% weight loss, and the process at 110-150°C is associated with approximately 10% weight loss. This combined weight loss of 17-18% is close to the theoretical weight loss (17.5%) ascribed to the release of six water molecules from the formula unit, and the two associated reactions can be described by reaction formulae (1) and (2) [18,20]:…”

“…The thermal decomposition of Zn(OCOCH 3 ) 2 occurs at over 147°C, but the processes involved after reaction (2) are not straightforward. The decomposition of Zn(OCOCH 3 ) 2 upon heating is sensitive to the humidity of the surrounding atmosphere [18,20]. In this study, the weight loss observed by TG between 147 and 200°C can be mainly assigned to the processes that form ZnO through reaction (3).…”

“…The pH of a 1 molL −1 Zn(OCOCH 3 ) 2 aqueous solution before aging was 6.22 and that of CH 3 COONa aqueous solution was 8.53. In the CH 3 COONa aqueous solution, therefore, more ZHA was dissolved and more ZnO generated due to the high pH [18]. Also, in Zn(OCOCH 3 ) 2 solutions of higher concentrations containing large amounts of Zn 2+ , ZHA is probably difficult to dissolve and to convert to ZnO.…”

“…MHS consists of positively charged brucite-like layers of metal hydroxides that require the presence of interlayer anions to maintain their overall charge neutrality. These interlayer anions can be Cl − , CO [18][19][20], etc. Besides being studied as an ion-exchange application in catalysis [18], layered zinc hydroxide is often studied as a precursor of ZnO.…”

“…These interlayer anions can be Cl − , CO [18][19][20], etc. Besides being studied as an ion-exchange application in catalysis [18], layered zinc hydroxide is often studied as a precursor of ZnO. Layered zinc hydroxides can provide ZnO powders through dissolution/reprecipitation processes under wet conditions [21].…”