A novel electrocatalyst from TOCN/CGG hydrogel-supported Fe-rich sludge and its performance in treating azo dyes-contaminated water

Monolithic electrocatalysts are desired for the electro-Fenton oxidation system. We used a hydrogel consisting of TEMPO-oxidized cellulose nanofibers (TOCN) and cationic guar gum (CGG) to disperse and support Fe-rich sludge and finally obtained a Fe-doped biochar (denoted as C-Sludge@TOCN/CGG) after the freeze-drying and carbonization. This C-Sludge@TOCN/CGG exhibited a porous structure with evenly-distributed Fe due to the inherently three-dimensional porous structure of TOCN/CGG hydrogel and the abundant carbon content. Importantly, Fe and FeO existed in C-Sludge@TOCN/CGG due to the presence of TOCN and CGG during the pyrolysis. The electrochemical properties of C-Sludge@TOCN/CGG demonstrated its good electrocatalytic activity and stability with few side reactions. It had good performance in the electrocatalytic degradation of various azo dyes, attributed to the synergistic integration of TOCN/CGG-derived carbon matrix and carbonized Fe-rich sludge particles. Specifically, two transient radicals (i.e. ·OH and ·O