Mesoporous $\gamma$-alumina was synthesized by the microwave-hydrothermal process with a shorter duration time at 150$^{\circ}$C/2 h followed by calcination at 550$^{\circ}$C/1 h. Ag nanoparticles (AgNPs) were impregnated into $\gamma$-alumina under a reducing atmosphere at 450$^{\circ}$C. The synthesized product was characterized by X-ray diffraction (XRD), thermogravimetric (TG)/differential thermal analysis (DTA), X-ray photoelectron spectroscopy (XPS), N$_2$ adsorption–desorption study, fieldemissionscanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The BET surface area values of $\gamma$-alumina and Ag-impregnated $\gamma$-alumina were found to be 258 and 230 m$^2$ g$^{−1}$, respectively. FESEM images showed the formation of grain-like particles of 50–70 nm in size with a flake-like microstructure. The XRD, XPS and TEM studies confirmed the presence of Ag in the synthesized product. Catalytic properties of the product for CO oxidation was studied with the $T_{50}$ (50% conversion) and $T_{100}$ (100% conversion) values of 118 and 135$^{\circ}$C, respectively; the enhancedvalues were compared with the literature reported values.

Mesoporous-nanostructured $\theta$-Al$_2$O$_3$ was synthesized by an autoclaving technique using different amidesi.e., formamide (F), dimethyl formamide (DMF) and diethyl formamide (DEF) at 150$^{\circ}$C/24 h followed by calcinationat 1000$^{\circ}$C. Crystallization and structural behaviour of the as-synthesized materials were characterized by X-raydiffraction and Fourier transform infrared spectroscopy. The porosity study was carried out by N2 adsorption–desorption(BET) technique. Microstructural features were measured by transmission electron microscopy (TEM). The amidebasedsolvents played a deliberate role in microstructural and textural features of $\theta$-Al$_2$O$_3$. The DMF-based solventshowed an enhanced surface area of 158 m$2^$ g$^{−1}$. The as-prepared $\theta$-Al$_2$O$_3$ rendered a nano-sheet, nano-rod and nano-flake like morphology for F, DMF and DEF derived products, respectively. From the UV–Vis spectroscopic measurement, the estimated band-gap of $\theta$-Al$_2$O$_3$ was found to be 5.16–5.40 eV. Photoluminescence investigation further revealed blue emission particularly for excitation at a wavelength of 252 nm. A DMF-derived sample rendered thelowest band gap due to its smaller crystallite size and higher surface area compared to that of F- and DEF-derivedsamples.