The present work deals with the synthesis of cobalt oxide, and Fe²⁺- and Ni²⁺-doped cobalt oxide nanoparticles as a catalyst. The study is investigating the different factors in obtaining cobalt oxide, and Fe²⁺- and Ni²⁺-doped cobalt oxide nanoparticles. Photocatalytic degradation studies are carried out for water-soluble eosine blue (EB) dye using cobalt oxide, and Fe²⁺- and Ni²⁺-doped cobalt oxide nanoparticles in aqueous solution. Different parameters such as initial dye concentration, dose of catalyst, contact time and pH have been studied to optimize reaction conditions. It is observed that photocatalytic degradation is a more effective and faster mode of removing EB dye by cobalt oxide, and Fe²⁺- and Ni²⁺-doped cobalt oxide nanoparticles than work done before. The optimum conditions for the removal of the EB dye are initial concentration 40 mg/L, photocatalyst dose 0.8 g/L, and pH 7.5. The EDS technique gives the elemental composition of synthesised cobalt oxide, and Fe²⁺- and Ni²⁺-doped cobalt oxide nanoparticles. The TEM and XRD studies are carried for morphological feature characteristics of synthesized cobalt oxide, and Fe²⁺- and Ni²⁺-doped cobalt oxide nanoparticles. Pseudo-first-order kinetic has been investigated for both pure and doped cobalt oxide catalysts. Almost 95% dye degradation has been observed for doped cobalt oxide nanoparticles.

The inverse spinel nanocrystalline pure and doped nickel ferrite particles were synthesized by co-precipitation method. The thick films of both pure and doped nickel ferrite nanoparticles were prepared by coating the material on glass substrate via screen printing method. The XRD was used to confirm cubic, crystalline nickel ferrites. The scanning electron microscopy confirms nanosized, cubic nanoparticles of nickel ferrite, and their morphology was investigated. The energy-dispersive spectroscopy was used to comprise elemental composition for pure and doped ferrites. Transmission electron microscopy was attributed for investigation of surface morphology, crystal structure identification of nickel ferrites. The FT-IR was used to find the vibrational frequencies, symmetric, asymmetric stretching and bending modes of metal oxide linkage. The thick films of nickel ferrite were employed for sensing phenomenon of gases such as LPG, NO₂, CH₃-OH, C₂H₅-OH, NH₃ and petrol vapours. The pure nickel ferrite showed excellent results for ammonia and nitrogen dioxide gases up to 90.42 and 86.42, respectively. Manganese- and cobalt-doped ferrites were excellent for ammonia and petrol vapours. Modified nickel ferrite effect of dopants cobalt and manganese was investigated. Pure and doped ferrites showed excellent response and recovery for ammonia, NO₂, petrol vapours and LPG gases.

In the present work, we report an proficient, elegant, and rapid one-pot synthesis of variety of 3,4-dihydropyrimidine-2(1H)-one/thione derivatives from β-dicarbonyl compounds, urea/thiourea, and various aromatic aldehydes using nano-La₂O₃ catalyst under ultrasonic irradiation. This novel synthetic strategy benefits with excellent yields, short reaction time, benign reaction conditions, clean transformation, and purification of products by non-chromatographic strategies. In addition, the synthesized nano-material was also explored as an effective gas sensor for NO₂, LPG, methyl alcohol, and ammonia. The gas-sensing properties such as selectivity and sensitivity of selected gases along with response and recovery for nano-La₂O₃ sensor are reported in this paper. In this way, conferring nano-La₂O₃ is a multifunctional catalyst not only for organic synthesis but also for gas sensing. The synthesized La₂O₃ nano-material was characterized by Fourier transform IR, powder X-ray diffraction, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive spectroscopy, and Brunauer–Emmett–Teller isotherm. The formation of Biginelli adducts was confirmed by Fourier transform IR, ¹HNMR, ¹³CNMR, DEPT-135 (distortionless enhancement by polarization transfer spectra), and mass spectral techniques.