Separated dual active sites for wide-visible-light driven o-chlorophenols mineralization with NiPc-modified nanosheet-Bi2O3 microsphere

Constructing separated dual active sites for selective dechlorination and activation of O2 to high-efficiency mineralize chlorinated pollutants is challenging in photocatalysis. Herein, we controllably engineer discrete active sites within Z-scheme heterojunctions (Niδ+Pc/BOv) by fabricating oxygen vacancies (OVs) on bismuth oxide (BO) through pre-treatment at 220 °C and partially reducing the central Ni2+ into Niδ+ in nickel phthalocyanine (NiPc) via post-treatment at 180 °C with H2 in turn. The optimized heterojunction exhibits remarkable photoactivity for o-chlorophenol (OCP) degradation, with 2- and 22-fold enhancement compared to P25-TiO2 under UV–visible light and BO under visible-light irradiation, respectively, and with high-efficiency mineralization and recyclability. The exceptional photoactivity can be attributed to three key factors based on the experimental and theoretical results: (i) enhanced charge separation resulting from the closely-integrated Z-scheme heterojunction with improved visible-light absorption and high two-molecule-layer NiPc dispersion due to OVs; (ii) promoted selective OCP adsorption on defective BO (BOv) by a dominating “Bi2–Cl” and assisted double-hydrogen-bonding interaction to synergistically induce preferential dechlorination via the desired direct hole attack, and (iii) strengthened O2 adsorption and activation by the valence-mixed Niδ+ species within Ni(I)–N2 and Ni(II)–N4 in-layer aggregates, serving as tandem reductive active sites. [Display omitted] •Niδ+Pc/BOv Z-scheme heterojunction with discrete active sites was controllably fabricated.•The optimized heterojunction displayed remarkable photoactivity for o-chlorophenol degradation and mineralization.•Oxygen vacancies on Bi2O3 nanosheet facilitate o-chlorophenol adsorption to induce a hole-attacking dechlorination.•An interesting o-chlorophenol adsorption with “Bi2–Cl” interaction and double hydrogen-bonding was confirmed.•Niδ+ species of Ni(I)–N2 and Ni(II)–N4 in-layer aggregates as tandem O2 active sites were verified.