Uptake and degradation of Orange II by zinc aluminum layered double oxides

In this work ZnAl-layered double oxide composites (LDO) were developed to remove organic dyes in wastewater by adsorption and photocatalysis. Various LDO composites were synthesized by adjusting synthetic parameters including the molar ratio of Zn to Al, and calcination temperature. LDO adsorption and photocatalytic properties for decomposition of organic dyes were also investigated. Orange II sodium salt (OrgII), an azo dye and water contaminant, was chosen as the model to investigate the properties of LDOs compared with commercial ZnO, TiO2 (P25) and ZnO−LDH. The adsorption and photocatalytic performance results showed that LDO composites significantly enhanced adsorption–photocatalytic performance for OrgII degradation. LDO at the Zn/Al molar ratio of 2 (2)LDO has the best adsorption capacity (800.8 mg/g of OrgII for (2)LDO), and improved photocatalytic activity (74.3% of OrgII decomposition for (2)LDO). It is believed that the better adsorption properties of LDO are due to the adsorption and intercalation of dyes in the interlayer during LDO’s rehydration process. ZnO/ZnAl-rehydrated layered double hydroxide composites (ZnO−rLDH) after rehydration of LDOs in aqueous solution was also obtained. After restoration in water, the structure and morphology of ZnO−rLDHs were characterized by XRD, FTIR, SEM/TEM, N2 adsorption/desorption and UV–vis-DRS. Finally, the relations between the structural features of the ZnO−rLDH composites and the adsorption properties and photocatalytic activity of LDO was studied.

LDO is synthesized via calcination of the ZnO−LDH precursor. LDO exerts a strong adsorption and intercalation of anionic dyes during its rehydration process in OrgII solution which is due to the structure memory effect of LDH. After adsorption, OrgII can be further removed by photocatalysis under the UV irradiation.Figure optionsDownload high-quality image (105 K)Download as PowerPoint slide