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Morphological Control of Mesoporosity and Nanoparticles within Co3O4–CuO Electrospun Nanofibers: Quantum Confinement and Visible Light Photocatalysis Performance

Pradhan, Amaresh C, Uyar, Tamer
ACS applied materials & interfaces 2017 v.9 no.41 pp. 35757-35774
Raman spectroscopy, absorption, cobalt, cupric oxide, dielectric spectroscopy, equations, mixing, nanofibers, nanoparticles, oxygen, phenolic compounds, photocatalysis, photoluminescence, polyethylene glycol, polyvinylpyrrolidone, porous media, reflectance spectroscopy, transmission electron microscopy, ultraviolet-visible spectroscopy
The one-dimensional (1D) mesoporous and interconnected nanoparticles (NPs) enriched composite Co₃O₄–CuO nanofibers (NFs) in the ratio Co:Cu = 1/4 (Co₃O₄–CuO NFs) composite have been synthesized by electrospinning and calcination of mixed polymeric template. Not merely the mesoporous composite Co₃O₄–CuO NFs but also single mesoporous Co₃O₄ NFs and CuO NFs have been produced for comparison. The choice of mixed polymer templates such as polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG) for electrospinning is responsible for the formation of 1D mesoporous NFs. The HR-TEM result showed evolution of interconnected nanoparticles (NPs) and creation of mesoporosity in all electrospun NFs. The quantum confinement is due to NPs within NFs and has been proved by the surface-enhanced Raman scattering (SERS) study and the UV–vis–NRI diffuse reflectance spectra (DRS). The high intense photoluminescence (PL) spectra showing blue shift of all NFs also confirmed the quantum confinement phenomena. The lowering of PL spectrum after mixing of CuO in Co₃O₄ nanofibers framework (Co₃O₄–CuO NFs) proved CuO as an efficient visible light response low cost cocatalyst/charge separator. The red shifting of the band gap in composite Co₃O₄–CuO NFs is due to the internal charge transfer between Co²⁺ to Co³⁺ and Cu²⁺, proved by UV–vis absorption spectroscopy. Creation of oxygen vacancies by mixing of CuO and Co₃O₄ also prevents the electron–hole recombination and enhances the photocatalytic activity in composite Co₃O₄–CuO NFs. The photocurrent density, Mott–Schottky (MS), and electrochemical impedance spectroscopy (EIS) studies of all NFs favor the high photocatalytic performance. The mesoporous composite Co₃O₄–CuO NFs exhibits high photocatalytic activity toward phenolic compounds degradation as compared to the other two NFs (Co₃O₄ NFs and CuO NFs). The kinetic study of phenolic compounds followed first order rate equation. The high photocatalytic activity of composite Co₃O₄–CuO NFs is attributed to the formation of mesoporosity and interconnected NPs within NFs framework, quantum confinement, extended light absorption property, internal charge transfer, and effective photogenerated charge separations.