Herein, polymeric cryogels containing poly(N-isopropylacrylamide) were synthesized by cryo-polymerization at subzero temperature. The synthesized cryogels were loaded with silver and palladium nanoparticles by the chemical reduction method at room temperature using the reducing agent NaBH4. Moreover, for comparison with cryogels, pure poly(N-isopropylacrylamide) hydrogel and its silver hybrid were also prepared by the conventional method at room temperature. The chemical structure and functional group analysis of the pure cryogels was confirmed by Fourier transform infrared spectroscopy. The synthesis of hybrid cryogels was confirmed by the X-ray diffraction technique and energy dispersive X-ray. The pore size and surface morphology of the pure cryogels, their respective hybrid cryogels and of conventional hydrogels were studied by using the scanning electron microscopy technique. The hybrid cryogels were successfully used as a catalyst for the degradation of methyl orange dye. The degradation performance of the hybrid cryogels was much better than its counterpart hybrid hydrogel for methyl orange dye. The effect of temperature and amount of catalyst on catalytic performance was studied by UV-visible spectroscopy. The reduction follows pseudo-first-order reaction kinetics. In addition, the antibacterial activities of these cryogels were evaluated against Gram-positive bacteria (Staphylococcus aureus, ATCC: 2593) and Gram-negative bacteria (Escherichia coli, ATCC: 25922). Both hybrid cryogels have shown much better antibacterial activity for these two strains of bacteria compared to pure cryogels. The results indicate that these cryogels are potential candidates for water purification systems as well as biomedical applications.

Wastewater treatment is indispensable as wastewater can lead to adverse health effects and deteriorate the quality of life on earth. Photocatalysis is a facile methodology to address this issue. In this study, nanocomposites (NCs) of manganese oxide (Mn3O4) and nickel oxide (NiO) were synthesized in different weight ratios via the solid-state reaction route. Structural properties, optical properties, surface morphology, and functional group analysis of the synthesized nanomaterials were conducted using X-ray diffraction (XRD), UV– Vis spectroscopy, scanning electron microscopy (SEM) along with energy-dispersive X-ray (EDX) analysis, and Fourier-transform infrared (FTIR) spectroscopy, respectively. The bandgap of the nanocomposite decreases significantly from 2.35 eV for the Mn3O4 NPs to 1.65 eV for the Mn3O4/NiO nanocomposite (NC). Moreover, adsorption studies followed by the photocatalytic performance of the Mn3O4/NiO NCs were evaluated to determine the removal of methylene blue (MB) dye from wastewater. The photocatalytic performance of the nanocomposite enhances as the ratio of Mn3O4 in the composite increases from one weight percentage to three weight percentage. The photocatalytic degradation efficiency was calculated to be 95%. The results show that the synthesized NCs could play an important role in photocatalytic wastewater purification and environmental remediation.

Wastewater from the textile industry is chronic and hazardous for the human body due to the presence of a variety of organic dyes; therefore, its complete treatment requires efficient, simple, and low cost technology. For this purpose, we grew ZnO microstructures in the presence of psyllium husk, and the role of psyllium husk was to modify the surface of the ZnO microstructures, create defects in the semiconducting crystal structures, and to alter the morphology of the nanostructured material. The growth process involved a hydrothermal method followed by calcination in air. Additionally, the psyllium husk, after thermal combustion, added a certain value of carbon into the ZnO nanomaterial, consequently enhancing the photocatalytic activity towards the degradation of methylene blue. We also investigated the effect of varying doses of photocatalyst on the photocatalytic properties towards the photodegradation of methylene blue in aqueous solution under the illumination of ultraviolet light. The structure and morphology of the prepared ZnO microstructures were explored by scanning electron microscopy (SEM) and powder X-ray diffraction (XRD) techniques. The degradation of methylene blue was monitored under the irradiation of ultraviolet light and in the dark. Also, the degradation of methylene blue was measured with and without photocatalyst. The photodegradation of methylene blue is highly increased using the ZnO sample prepared with psyllium husk. The photodegradation efficiency is found to be approximately 99.35% for this sample. The outperforming functionality of psyllium-husk-assisted ZnO sample is attributed to large surface area of carbon material from the psyllium husk and the synergetic effect between the incorporated carbon and ZnO itself. Based on the performance of the hybrid material, it is safe to say that psyllium husk has high potential for use where surface roughness, morphology alteration, and defects in the crystal structure are vital for the enhancing the functionality of a nanostructured material. The observed performance of ZnO in the presence of psyllium husk provides evidence for the fabrication of a low cost and efficient photocatalyst for the wastewater treatment problems.

The cyclisation of citronellal to isopulegol is a significant intermediate stage in the production of menthols. In this research work, the effects of acid treatment on montmorillonite clay have been investigated and used in citronellal cyclisation reactions. Furthermore, the effects of acid treatment and hetero-poly acid impregnation have been determined on the textural and catalytic properties of montmorillonite clay. The designed catalysts were characterized by XRD, N2 sorption, and NH3- TPD techniques. Acid treatment of montmorillonite resulted in the enhancement of surface area and pore volume. The catalytic activity and selectivity parameters were lessened due to the severe leaching of Al ions from tetrahedral crystalline structures (e.g., weakened structure and loss of acidity). Among all prepared materials, the heteropoly acid supported HCl treated montmorillonite catalyst was observed as a more active, stable, and selective catalyst that showed the highest catalytic performance in citronellal cyclisation under optimized process parameters. The catalytic activity and selectivity were enhanced with rising mesoporosity and acidity parameters due to HCl acid treatment and HPA impregnation.