Multifunctional nanocomposites combine multiple optical and physical phenomena to perform new functions. An article published in the journal Optical Materials discussed the synthesis of copper (Cu)-aluminum (Al) codoped zinc oxide (ZnO) nanocomposites and their corresponding photosensing and photocatalytic activities.
Study: Synthesis of multifunctional Cu and Al codoped ZnO nanoparticles towards photosensor and photocatalytic applications. Image Credit: Rendix Alextian/Shutterstock.com
While X-ray diffraction (XRD) studies have revealed the crystal structure and effect of Al and Cu dopants in ZnO lattice, field emission scanning electron microscopy (FESEM) helped examine the surface morphology of the prepared codoped ZnO nanocomposites. Additionally, Fourier transform infrared (FTIR) spectroscopy and energy-dispersive X-ray spectroscopy (EDX) confirmed the doping of Cu and Al on ZnO nanocomposites.
Photoluminescence (PL) studies showed low PL intensity for Cu–Al codoped ZnO nanocomposites. Moreover, the photosensing properties, including responsivity (R), detectivity (D*), and external quantum efficiency (EQE) of the Cu-Al codoped ZnO nanocomposites along with their photocatalytic degradation capacity for methylene blue (MB) dye, were analyzed for the prepared ZnO nanocomposites.
ZnO Nanocomposites Towards Photosensing and Photodegradation
Nanotechnology can help address water pollution caused by chemical dyes. For example, metal oxide-based nanoparticles, including ZnO, tin oxide (SnO2), and titanium oxide (TiO2), are applied to remove chemical dyes through photodetection and photodegradation.
Multifunctional materials with combined multiple optical and physical phenomena perform functionalities, including ultraviolet (UV) photodetection, photodegradation, and photocatalysis. ZnO is a non-toxic, environmentally friendly, cost-effective, and multifunctional semiconducting metal oxide, showing significant physical and chemical properties, including a wide bandgap.
ZnO is preferred in UV photosensing, photodegradation of chemical dyes, and decomposing organic pollutants. Doping ZnO nanocomposites with other elements, including copper (Cu), nickel (Ni), aluminum (Al), cobalt (Co), gallium (Ga), tin (Sn), iron (Fe), cadmium (Cd), and silver (Ag) improves optical, electrical, and chemical properties by modifying the crystal lattice in terms of vacancy sites, interstitials, and substitutional sites without changing the structure.
Al-doped ZnO nanocomposites are inexpensive materials that are naturally abundant with enhanced photocatalytic performance and significant physical properties such as good conductivity and stability. Previous studies mentioned that incorporating Al into the ZnO matrix improved adsorption and desorption of oxygen on the sample surface and generated more electron-hole pairs, increasing the free charge carriers, making it a significant material for photosensor applications.
Cu-Al Codoped ZnO Nanoparticles for Photosensing and Photocatalytic Applications
Cu-doped ZnO nanocomposites have been shown to have high ionization and reduced ZnO lattice formation energy. Moreover, these ZnO nanocomposites also showed narrowing and widening of optical bandgap based on the Cu concentration and annealing temperatures. Additionally, incorporating the Cu nanowire enhanced the photosensing behavior of ZnO nanocomposites.
Similarly, incorporating Al into the ZnO matrix showed photocatalytic activity on methyl orange (MO) dye. In addition, Al doping on ZnO nanoparticles was reported to increase the visible light the adsorption of methyl orange (MO) dye on the nanoparticle’s surface.
In the present work, the Cu–Al codoped ZnO nanocomposites were prepared via a simple wet chemical method and tested for their photosensing activity over UV light irradiation and photocatalytic activity on organic dyes.
The results revealed that the R, D*, and EQE of the Cu-Al codoped ZnO nanocomposites, were 6.96 x 10-2 amperes per watt, 5.30 x 109 Jones, and 16.2%, respectively.
The studies conducted to understand the mechanism of photocatalytic degradation revealed that, under UV light irradiation, the catalyst generated electron-hole pairs. The holes generated in the Cu element of Cu–Al codoped ZnO nanocomposites interacted with water molecules and produced hydroxyl free radicals.
On the other hand, the Al element of Cu–Al codoped ZnO nanocomposites prevented the recombination of photo-induced electron-hole pairs and produced oxygen free radicals. The generated hydroxyl and oxygen free radicals in Cu and Al with adsorbed on MB dye molecule resulted in its degradation. Thus, the constructed Cu–Al codoped ZnO nanocomposites were demonstrated as potential photocatalysts for dye degradation.
Conclusion
The Cu-Al codoped ZnO nanocomposites were synthesized via the simple wet chemical method. XRD studies revealed that incorporating Cu and Al decreased the grain size of the ZnO nanocomposites and enhanced the photodegradation behavior.
Moreover, FESEM measurements confirmed the higher particle size of Cu–Al codoped ZnO nanocomposites with a uniform structure and improved photocatalytic activity. The PL spectra of Cu–Al codoped ZnO nanocomposites revealed the least PL emission intensity due to photo-induced interaction between electron-hole pairs, favorable for photodegradation.
The presence of dopant elements in ZnO nanocomposites was confirmed by the FTIR and EDX spectral studies. Diffuse reflectance spectroscopy (DRS) revealed a low optical band gap energy in Cu-Al codoped ZnO nanocomposites.
The photosensing properties, including R, D*, and EQE of the codoped ZnO nanocomposites, were determined to be 6.96 x 10-2 amperes per watt, 5.30 x 109 Jones, and 16.2%, respectively. Thus, the results proved the efficiency of the Cu–Al codoped ZnO nanocomposites as photocatalysts for dye degradation.
Reference
Ganesh, V. (2022). Synthesis of Multifunctional Cu and Al Codoped ZnO Nanoparticles Towards Photosensor and Photocatalytic Applications. Optical Materials. https://www.sciencedirect.com/science/article/pii/S0925346722008680
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