Abstract
Inspired from the μ-oxido CaMn4 cluster unit present in the photosystem-II of plant cells, various manganese-based materials, particularly calcium-manganese oxides, have been investigated by the researchers as a new class of catalysts. Herein, we report the synthesis of single source heterobimetallic complex {[CaMn(OAc)(TFA)3(THF)(H2O)2].3THF}n (where OAc = acetate, TFA = trifluoroacetate and THF = tetrahydrofuran) for the deposition of thin films of Ca2Mn3O8–CaO composite on fluorine doped tin oxide (FTO) coated glass substrates at deposition temperatures of 450–550 °C via the aerosol assisted chemical vapour deposition (AACVD) method. The complex was characterized by melting point, microanalysis, proton nuclear magnetic resonance (1H NMR), Fourier transformed infra-red (FT-IR) spectroscopy, thermogravimetry (TGA) and single crystal X-ray diffraction. The deposited thin films were analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, energy dispersive X-ray spectroscopy (EDX) and field emission scanning electron microscopy (FESEM) which confirmed the growth of Ca2Mn3O8–CaO composite with high purity and precise stoichiometry. The optical characterization gave direct band gap energies of 2.74, 2.68 and 2.77 eV for the Ca2Mn3O8–CaO thin films deposited at 450, 500 and 550 °C, respectively. Furthermore, photoelectrochemical studies revealed that the thin film deposited at 500 °C showed the photocurrent of 3.75 mA cm−2 at +0.8 V vs. SCE with 1.64% photo-conversion efficiency and 310 Ω Rct value, upon illumination with a 150 W (100 mW cm−2) halogen lamp. The improved photocatalytic activity of Ca2Mn3O8–CaO composite was due to the increased photo absorption ability, elevated surface area, and more efficient electron/hole transfer. In addition, this work provides an insight to design the growth of visible light active calcium-manganese based photocatalyst materials for solar energy utilization.
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