Adsorption and photocatalytic degradation of phenol and 2,4 dichlorophenoxiacetic acid by Mg-Zn-Al layered double hydroxides

Mg-Zn-Al layered double hydroxides (LDHs) with varying amounts of zinc were prepared by the coprecipitation method. Solids were analyzed by XRD and N-2 physisorption, confirming the formation of pure LDH phase; and the production of mixed oxides with high specific surface areas (182-276 m(2) g(-1)) after calcination. Band gap energy was also determined, presenting the expected decreasing tendency on increasing zinc amounts. These mixed oxides were tested both for the adsorption of 2,4 dichlorophenoxiacetic acid (2,4-D) and for the photocatalytic degradation of 2,4-D and phenol. Nearly total (97%) degradation of initial 1.45 mmol L-1 of 2,4-D, with 1 g calcined LDH per liter, was accomplished in 9 h, while phenol half-life was as short as 3.5 h, with the catalyst with lowest zinc amount (5 wt.%). Langmuir adsorption isotherms are presented. Solids were also characterized by XRD and MR analysis after photocatalytic and adsorption activity, to determine the presence of 2,4-D. The versatility of LDH decomposition products in the elimination of different contaminants by different mechanisms puts them forward as a viable alternative for environmental remediation. (C) 2009 Elsevier B.V. All rights reserved.