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The hybrid structure of nanoparticles (NPs) with nanosheets has the advantage of both anisotropic properties of NPs and large specific surface areas of nanosheets, which is desirable for many technological applications. In this study, MgCrO spinel NPs decorated on highly porous MgO nanosheets forming MgO/MgCr O( x) nanocomposites were synthesized by a one pot coprecipitation method followed by a heat treatment process of the solvated wet gel of MgCr-LDH with polar solvent N, N-dimethylformamide (DMF) at 400 °C. This novel synthetic methodology generates materials consisting of porous metal oxides nanosheets adhered with spinel phase NPs due to the slow generation of gases such as HO, CO, and NH under moderate temperature during the heat treatment process. The synergistic effect of much wider band gap MgO nanosheets and narrow band gap MgCrO NPs added increased stability due to the stronger bonding coordination of MgCrO NPs with MgO nanosheets. The obtained MgO/MgCr O( x) nanocomposites possess large specific surface areas, highly porous structure, and excellent interface between MgCrO NPs and MgO nanosheets, which proved from N sorption isotherm, TEM, HR-TEM study. With metallic ratio of MgCr3:1, MgO/MgCrO(MgCr3:1) nanocomposites exhibit highest H evolution rate of 840 μmolg2h, which was 2 times higher than that of pure MgCrO(420 μmolg2h). The LSV measurement study of MgO/MgCrO (MgCr3:1) nanocomposite shows an enhancement of light current density of 0.22 μA/cm at potential bias of -1.1 V. The Mott-Schottky analysis suggested the band edge positions of the n-type constituents and formation of n-n type heterojunctions in MgO/MgCrO (MgCr3:1) nanocomposite, which facilitates the flow of charge carriers. The EIS and Bode phase plot of MgO/MgCrO (MgCr3:1) nanocomposite signifies the lower interfacial charge transfer resistance and higher lifetime of electrons (2.7 ms) for enhanced H production. Lastly, the enhanced photocatalytic H production activity and long-term stability of MgO/MgCrO(MgCr3:1) could be attributed to maximum specific surface area, porous structure, close intimacy contact angle between two cubic phases of MgCrO NPs and MgO nanosheets, abundant oxygen vacancies sites, reduced charge transfer resistance and suitable band edge potential to drive the thermodynamic energy for H production. This work highlighted an effective strategy for the synthesis of cost-effective 2D porous heterojunctions nanocomposite photocatalyst for promising applications in the field of clean H production utilizing abundant solar energy.

The one-dimensional (1D) mesoporous and interconnected nanoparticles (NPs) enriched composite CoO-CuO nanofibers (NFs) in the ratio Co:Cu = 1/4 (CoO-CuO NFs) composite have been synthesized by electrospinning and calcination of mixed polymeric template. Not merely the mesoporous composite CoO-CuO NFs but also single mesoporous CoO 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 CoO nanofibers framework (CoO-CuO NFs) proved CuO as an efficient visible light response low cost cocatalyst/charge separator. The red shifting of the band gap in composite CoO-CuO NFs is due to the internal charge transfer between Co to Co and Cu, proved by UV-vis absorption spectroscopy. Creation of oxygen vacancies by mixing of CuO and CoO also prevents the electron-hole recombination and enhances the photocatalytic activity in composite CoO-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 CoO-CuO NFs exhibits high photocatalytic activity toward phenolic compounds degradation as compared to the other two NFs (CoO NFs and CuO NFs). The kinetic study of phenolic compounds followed first order rate equation. The high photocatalytic activity of composite CoO-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.

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