N-Doped carbon nanotubes encapsulated FeNi alloy in persulfate activation for nonradical Reaction: Confined metal redox

A heterophane FeNi alloy confined in N-doped carbon nanotubes (FeNi-NC) catalyst was fabricated via pyrolysis of a mixture of metal salts and N/C precursors under inert conditions. The as-synthesized FeNi-NC was functionalized as heterogeneous Fenton-like catalysts for elimination of aqueous organic contaminants via potassium peroxydisulfate (PDS) activation. The effects of carbonization temperatures and Ni/Fe atomic ratios on the structure of FeNi-NC and catalytic properties were investigated. Benefiting from the designed structure and highly exposed active sites, the FeNi-NC catalyst manifests excellent catalytic activities and durability, better than those of the corresponding monometallic catalysts. Electron paramagnetic resonance and radical quenching tests indicated that the typical nonradical-involved (i.e., mediated electron transfer and singlet oxygenation) catalytic process occurred during the PDS activation. The interaction between PDS and FeNi-NC could be boosted by inner FeNi redox process and thus accelerated the electron transfer between PDS and carbon layer due to confined effect, resulting in dramatically enhanced performance. The Fe species in the alloy can improve the charge transfer for the effective reduction of Ni3+ to Ni2+ and inhibit the generation of unwanted Ni component with a high oxidation state. This work offers new insights to non-precious-metal alloy catalysts toward highly efficient wastewater treatment.