A novel particle electrode fabricated by graphite-assisted alum sludge for effective diuron degradation in wide pH ranges

The removal of diuron in electrochemical advanced oxidation process is typically limited by the solution pH. In this study, graphite powder (GP) was successfully doped in alum sludge (AS) by a sol–gel and embedding method and then calcined at 700 ℃ to prepare a novel particle electrode (GP/AS). The results showed that the GP/AS system can effectively degrade more than 82 % of diuron over a wide pH range (3–11) within 40 min. This was attributed to the surface-bonded free radicals and 1O2 generated in the GP/AS system resisting the influence of pH on diuron degradation. The generated graphite structure and electron hole accumulation of GP/AS, which greatly promoted the formation of active species, were systematically characterized using scanning electron microscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. In addition, five pathways of diuron degradation were proposed, with similar steps being the main targets attacked by reactive oxygen species, including the aromatic ring, amide group, and methyl group. The dominant step was methyl group hydroxylation. The findings of this study provide an efficient and sustainable method for the application of reused waste mineral materials in water remediation.