Removal of p-nitrophenol (PNP) in aqueous solution by the micron-scale iron–copper (Fe/Cu) bimetallic particles

In this study, in order to further investigate the degradation capacity and mechanism of Fe/Cu bimetallic system, the prepared Fe/Cu bimetallic particles with different theoretical copper mass loadings (0.05, 0.11, 0.24, 0.41, 0.62, 0.89, 1.26 and 1.81 g Cu/g Fe) were characterized by SEM, EDS, XRD and laser particle size analyzer. Also, the effect of theoretical Cu mass loading and five key operating parameters on the PNP removal efficiency was investigated thoroughly. Furthermore, the mineralization process of PNP was studied by using COD, TOC, UV–vis spectra, FTIR spectra and GC/MS. The results show that a large number of fine Cu particles were produced from the excessive theoretical Cu mass loading, and they facilitated the catalytic reactivity of the Fe/Cu bimetallic particles at Cu loading <0.89 g Cu/g Fe. Additionally, the heterogeneous Cu layer is also favor for the catalytic reactivity of the Fe/Cu bimetallic particles, while the uniform and dense Cu layer can decrease its reactivity severely. The degradation rates of PNP by the Fe/Cu particles with different theoretical Cu mass loadings are all in accordance with the pseudo-first-order kinetics model, and the optimal operating parameters were obtained by the batch experiments. In addition, both the indirect reduction by atomic hydrogen and the direct reduction on the catalytic activity sites play a leading role on the pollutants removal. Finally, the degradation pathway of PNP was proposed according to the detected intermediates by GC/MS. Collectively, these results suggest that the Fe/Cu bimetallic system should be proposed as a cost-effective pretreatment process for the toxic and refractory PNP wastewater.