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This work focuses on the synthesis of undoped and doped lanthanum oxide nanoparticles (La 2 O 3 NPs) by a simple co-precipitation method for the catalytic reduction of 4-nitrophenol (4-NP) using NaBH 4 as a reducing agent. Their optical properties, morphologies, structure, chemical compositions and electronic properties were carefully characterized by XRD, FTIR, SEM, TEM, PL and UV–visible absorption spectroscopy. The SEM and TEM images showed various shape morphologies and sizes of the particles. The XRD pattern revealed a polycrystalline nature with the hexagonal structure of the La 2 O 3 NPs. The synthesized undoped and doped La 2 O 3 NPs were also employed as catalysts for the reduction of 4-nitrophenol, it shows that the doped (Sm 3+ , Gd 3+ and Hf 3+ ) La 2 O 3 NPs provided better catalytic activity than the undoped La 2 O 3 NPs. Moreover, Hf 3+ doped La 2 O 3 NPs exhibited an enhanced catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol in 90 min. The catalytic conversion was studied by UV–vis spectroscopy with high reduction rate (k = 2.048 min −1 ). The applications of the present study may utilize in the removal of toxic pollutants in a cleaning of environmental pollution as well as in industrial applications.

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Nano sized defect pyrochlore, KAl0.33W1.67O6 (KAW), is prepared through sol-gel method. Divalent tin-doped KAW is obtained at room temperature by ion exchange method using acidified SnCl2 and parent KAW. These materials are characterized by powder X-ray diffraction, thermogravimetric analysis (TGA), scanning electron microscopy-energy dispersive spectra (SEM-EDS), Raman Spectroscopy and X-ray photo electronic spectroscopy. The composition of tin-doped KAW is obtained from chemical analysis, SEM-EDS and TGA methods and written as Sn0.5Al0.33W1.67O6xH2O (x = 1.4-1.5) (SnAW). It crystallizes in cubic lattice with Fd3¯m space group. The band gap energies are found to be 2.82 and 2.21 eV for KAW and SnAW respectively. The observed reduction in the band gap with the introduction of Sn(2+) in defect pyrochlore lattice is due to mixing of 5s state of Sn(2+) with O 2p states leading to an upward shift in the valence band. The Raman spectra of these materials gave more bands than the number expected for defect pyrochlores due to substitutional disorder in 16c sites and displacive disorder of A ions. The photoactivity of SnAW is higher compared to KAW.

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