Synthesis and characterization of carbon nanotube/copper oxide nanocomposite as an enhanced absorber for solar radiation

In this work, CNTs/CuO nanocomposite was synthesized by chemical deposition method using the alkaline tartrate bath. The CNTs underwent heat and chemical functionalization treatments before starting the deposition process. TEM investigations showed that the untreated CNTs are agglomerated, have long filaments with capped ending, uniform multi-walled graphitic layers of ∼20 nm diameter and 20 μm length. However; the functionalized CNTs were de-agglomerated under sonication and the CNTs long chains were shortened to small segments by breaking of the graphitic structure using the acid oxidizing mixture, besides a de-capping of the CNTs ends took place. The thermal analysis of the CNTs by TGA confirmed the thermal stability up to 600 °C. FESEM investigations showed that; the functionalized CNTs are coated by adhered nano layer composed of CuO and the EDAX analysis confirmed the chemical structure of the deposited cupric oxide. X-ray diffraction analysis confirmed the deposition of cupric oxide phase (CuO) on CNTs. However; a minor phase of cuprous oxide (Cu2O) was detected due to the reduction of the cupric oxide at the surfaces of the CNTs/CuO nanocomposite. For comparing the obtained results; CuO nanosized powder was also prepared by decomposition of copper nitrate trihydrate at 350 °C. The average crystallite size of CuO nanoparticles was estimated as 23–29 nm corresponding to the two main diffracted peaks, while for the CuO/CNTs nanocomposite was ∼9 nm. The optical absorbance and diffuse reflectance of the investigated CNTs, CuO nanoparticles and CuO/CNTs nanocomposites were studied in the UV-VIS-IR region. The absorption edges of both CuO nanoparticles as well as CuO/CNTs nanocomposite were calculated from Kubelka-Monk function of the diffuse reflectance that were found to be 1.48 and 1.53 eV, respectively. The shift of the band gap was discussed by the energy gap confinement effect of nano structured materials. The optical absorbance was increased in both short and long wavelengths for the CuO/CNTs nanocomposite than in the pure CNTs and CuO nanoparticles. Besides, the reflectance of the CuO/CNTs nanocomposite was observed to be smaller than that of both the CuO nanoparticles and CNTs, which gives a rise in utilization of this nanocomposite as solar selective coating than their individual forms.