Insight to the mechanism of tetracycline removal by ball-milled nanocomposite CeO2/Fe3O4/Biochar: Overlooked degradation behavior

A novel nanocomposite CeO2/Fe3O4/biochar (BC) was prepared using a straightforward, solvent-free mechanical ball milling method. Comparatively to the material prepared by chemical co-precipitation (77.14 %) and raw BC (33.64 %), CeO2/Fe3O4/BC prepared by ball milling achieved better tetracycline (TC) removal (94.35 %) under the optimal condition (TC concentration 10 mg center dot L-1, catalyst dose 0.5 g center dot L-1 and pH 9.01). Ball milling not only reduced the particle size, but also increased the surface area of composite, which was favorable to the adsorption of TC on CeO2/Fe3O4/BC. Meanwhile, the number of oxygen-containing functional groups in as-prepared nanocomposite increased after ball milling, which could serve as the bridge of electron transfer to enhance TC degradation. Dissolved oxygen (DO) was activated by CeO2/Fe3O4/BC to produce reactive oxygen species (ROS) for the TC degradation. X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) character-ization indicated that the enhanced oxygen activation should be attributed to the presence of Ce4+/Ce3+ and Fe3+/Fe2+ redox pairs and persistent free radicals (PFRs) in CeO2/Fe3O4/BC. Desorption experiments suggested that the adsorption and degradation induced by ball-milled CeO2/Fe3O4/BC were accounted for about 79.8 % and 20.2 % of total TC removal, respectively. This study revealed that the organic pollutants removal by BC-based nanocomposite is not alone contribution of the adsorption and the degradation behavior during this process should be concerned.

Automated summary

A novel nanocomposite CeO2/Fe3O4/biochar (BC) was prepared by ball milling method and exhibited superior performance in tetracycline (TC) removal compared to other materials. The ball milling process not only reduced particle size and increased surface area for enhanced TC adsorption, but also increased the number of oxygen-containing functional groups to enhance TC degradation. The enhanced oxygen activation was attributed to the redox pairs of Ce4+/Ce3+ and Fe3+/Fe2+ and the presence of persistent free radicals (PFRs) in the nanocomposite.