Tri-metallic ZIF mediated synthesis of defect rich N-doped Co3O4/ZnO/NiO S-scheme heterostructure for detection and photocatalytic degradation of persistent organic pollutants

Abstract

Heteroatom doping, heterojunction formation and defect engineering are some of the commonly utilized strategies to enhance the opto-electronic properties of transition metal oxides. Hence, it's imperative to design such a synthetic approach, which allows unifying these strategies and thereby constructing robust and multifunctional materials. To this end, a bi-functional N-doped Co₃O₄/ZnO/NiO S-scheme heterostructure was constructed by calcination of the tri-metallic zeolitic imidazolate framework (Co/Zn/Ni-ZIF). High temperature calcination (600 °C) of tri-metallic ZIF not only induced oxygen vacancies in the semiconductor lattice, but also created homogeneously mixed metal oxides. XPS studies confirmed the formation of nitrogen substitution defects and zinc broken bonds in the heterostructure. UV-vis DRS studies were employed to probe deeper into the opto-electronic properties of the materials. The prepared heterostructure exhibited enhanced photocatalytic degradation of doxorubicin (90%) and chlorpyrifos (80.5%) within 120 min of visible light illumination (without the aid of co-oxidants). Furthermore, a proposed mechanistic pathway of photocatalytic degradation via generation of reactive oxygen species has been discussed in detail. Besides photocatalysis, the fluorescence properties of this bi-functional nanomaterial were also exploited for selective fluorescence sensing of doxorubicin, Cr⁶⁺ and chlorpyrifos. The proposed sensor exhibited extremely low detection limit with values of 0.60 μM (doxorubicin), 5.01 μM (Cr⁶⁺) and 15.4 μM (chlorpyrifos). Real sample analysis further confirmed the viability of the proposed sensor.