Combustion-derived synthesis of nanostructured copper oxide (CuO) materials was synthesized by oxalic acid as a fuel, and copper nitrate as an oxidant. The combustion product showed mixed phases of CuO and Cu 2 O. The pure nanocrystalline CuO phase was obtained upon subsequent annealing of the combustion product at 700 °C for 3 h, whereas the planetary ball-milling of the combustion product at 300 rpm for 10 h yielded CuO phase with two weak peaks of Cu 2 O phase. The microstructural and optical properties of CuO nanomaterials were explored by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared (FT-IR), near infrared (NIR), and diffused reflectance spectroscopic (DRS) techniques. The annealed powder XRD pattern confirms that it crystallizes in a monoclinic C12/c1 (15) structure with lattice parameters: a = 0.4687( 4), b = 0.3419(3), c = 0.5128(4) nm, and β = 99° 39′ (4) with average crystalline size, D of 30.89 nm. The agglomeration of fine particles is seen for the ball-milled powder, while the annealed powder revealed different particle sizes in the range of 254 ~ 835 nm as evidenced from FESEM images. The NIR reflectance of (~ 45%) CuO powder (annealed) can be used as black pigments in color industries. The annealed CuO powder reveals narrow Raman peaks than ball-milled powder.

The wet chemical combustion synthesis and the effect of different (aniline, citric acid monohydrate, dextrose, glycine, hexamine, oleic acid, sucrose, and urea) fuels on the combustion products of CuO nanomaterials are reported for the first time as a comparative study. The pure nano-sized CuO phase combustion products were produced from hexamine, urea, and glycine as fuels, whereas fuel-like sucrose yielded nearly a single phase of the CuO combustion product. The quality of the combustion products revealed mixed phases of CuO and Cu2O for aniline, dextrose, citric acid monohydrate, and oleic acid as fuels. The pure combustion products crystallized in a monoclinic structure with a space group, C12/c1 (15). For the mixed phases of combustion products, weight gain (102.5%–109%) is noted >400 °C in the TG curves owing to the oxidation of the Cu2O phase into the CuO phase. The bandgap of the different CuO powder was in the range of 2.1–2.6 eV. From the NIR spectra, we conclude that the nanocrystallinty of the CuO phase plays a major role in the enhancement (∼35%) of NIR reflectance owing to the difference in the fuels used. The observed Raman modes confirm the characteristics of the CuO phase. Different morphologies are observed for the different CuO combustion products obtained from hexamine, urea, and glycine as fuels.

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