Reductive transformation of 2,4-dichlorophenoxyacetic acid by nanoscale and microscale Fe3O4 particles.

Reductive transformation of 2,4-dichlorophenoxyacetic acid (2,4-D) by nanoscale and microscale Fe(3)O(4) was investigated and compared. Disappearance of the parent species and formation of reaction intermediates and products were kinetically analyzed. Results suggest that the transformation of 2,4-D followed a primary pathway of its complete reduction to phenol and a secondary pathway of sequential reductive hydrogenolysis to 2,4-dichlorophenol (2,4-DCP), chlorophenol (2-CP, 4-CP) and phenol. About 65% of 2,4-D with initial concentration of 50 micro M was transformed within 48 h in the presence of 300 mg L(-1) nanoscale Fe(3)O(4), and the reaction rates increased with increasing dosage of nanoscale Fe(3)O(4). The decomposition of 2,4-D proceeded rapidly at optimum pH 3.0. Chloride was identified as a reduction product for 2,4-D in the magnetite-water system. Reductive transformation of 2,4-D by microscale Fe(3)O(4) was slower than that by nanoscale Fe(3)O(4). The reactions apparently followed pseudo-first-order kinetics with respect to the 2,4-D transformation. The degradation rate of 2,4-D decreased with the increase of initial 2,4-D concentration. In addition, anions had a significant adverse impact on the degradation efficiency of 2,4-D.