Cu-doped Bio(x) composites were prepared with and without citric acid. In the presence of citric acid, Bi-0 and Cu2+/Cu+ were confirmed to coexist in the composite (BiCu9/Bi-0) by X-ray diffraction and X-ray photoelectron spectroscopy. The catalyst showed high Fenton activity and stability for the degradation and mineralization of 2-chlorophenol in the pH range of 6-8. H2O2 was predominately converted into (OH)-O-center dot radicals in BiCu9/Bi-0 suspension, as assessed by the electron spin resonance technique. In the composite, Bi-0 inhibited the oxidation of H2O2 by CO+ into O-2 and (OH)-O-center dot by reducing Cu2+, enhancing the reaction of H2O2 with Cu+ to produce (OH)-O-center dot. Intermediate determination showed that 2-chlorophenol was decomposed mainly by (OH)-O-center dot radicals into hydroxylation products, subsequently decomposed into short-chain organic acids, and eventually decomposed into CO2 and H2O. (C) 2015 Elsevier B.V. All rights reserved.