Lignocellulose precursor regulated radical/non-radical pathways of diclofenac degradation in Fe/biochar activated percarbonate systems.

Percarbonate (SPC) an environmentally friendly peroxide has attracted increasing attention. Herein, two iron-carbon composites with distinct structures were synthesized regulated by the carbon precursors of cellulose and lignin, and the performance of SPC activation was compared using diclofenac (DCF) as the probe. The cellulose-derived Fe3C@Cel showed core-shell appearance and graphitic structure, demonstrating stronger ability of adsorption, retaining iron and electron transfer than the lignin-derived Fe0@Ln. The removal efficiency of DCF by both catalysts was comparable to that in corresponding processes activating peroxymonosulfate and H2O2. The complete degradation of 0.05 mM DCF could be achieved within 10 min. Compared with Fe0@Ln, Fe3C@Cel exhibited more significant advantages in adapting wide pH range and complex water compositions, reducing reagent dosage, and improving sustainability. The DCF removal rate in Fe3C@Cel/SPC could still maintain 84.0% after 5 cycles. The non-radical electron transfer mechanism contributed more significantly to DCF degradation in Fe3C@Cel/SPC, while •OH, O2•- and CO3•- were the dominant contributors in Fe0@Ln/SPC. The lattice oxygen and CO groups contributed to the ROS generation in Fe3C@Cel/SPC process, while the lattice oxygen and homogeneous activation by Fe2+ were the main routes of ROS generation in Fe0@Ln/SPC process. The identification of primary degradation intermediates revealed that fewer intermediates were identified in Fe3C@Cel/SPC, and the toxicity evaluation of the intermediates showed general decrease trends of bioconcentration factor, mutagenicity, developmental toxicity and biological toxicity. The intermediates identified in Fe3C@Cel/SPC showed lower developmental and biological toxicity. The results may provide insights in developing practical and environmentally friendly advanced water treatment technologies.