تأثير التطعيم بأوكسيد النحاس في خصائص جسيمات أوكسيد الزنك النانوية وتطبيقاتها في استشعار الغازات

Effect of CuO Doping on the Properties of ZnO Nanoparticles and their Applications in Gas Sensing

Abstract
In this work, the sol-gel method was successfully employed to form nanocrystals of zinc oxide (ZnO) and copper oxide (CuO), followed by doping ZnO with varying weight percentages of (0.25, 0.5, 0.75 wt% CuO). The dip-coating technique was used to fabricate the thin films. Several characterization techniques were applied to study the effect of copper oxide content on the properties of the ZnO nanoparticles. All samples exhibited a hexagonal wurtzite structure, as revealed by X-ray diffraction (XRD) patterns, indicating the incorporation of copper ions into the ZnO nanocrystalline lattice. Morphological analysis using a Field Emission Scanning Electron Microscope (FESEM) showed that the CuO-doped samples consisted of a mixture of spherical nanoparticles of varying sizes. In addition, optical properties were examined.
The optical measurements showed that the prepared films had a direct band gap, and the energy gap decreased as doping increased. The band gap of pure ZnO was found to be 3.1 eV, while for the 0.25% doped sample it was 2.9 eV, for the 0.50% sample it was 2.7 eV, and for the 0.75% sample it was 2.5 eV.
Subsequently, the electrical properties were then measured using the Hall effect. It was found that the outward diffusion of CuO atoms from the ZnO lattice with increasing CuO addition results in a steady increase in resistivity at 0.25% and 0.50% of the film resistance. A significant decrease in resistivity is observed at 0.75%. Therefore, it can be concluded that as the doping of copper oxide (CuO) increases, the electrical conductivity decreases. At 0.25%, we also observe a decrease at 0.50%, and then the conductivity of the 0.75% doped sample begins to increase slightly.
Moreover, this study provides an overview of the most commonly used thin-film fabrication techniques for gas sensors, as well as the effects of CuO doping, nanoparticle size, and operating temperature on the sensing properties of these films. Gas sensing mechanisms and detection techniques were also discussed in detail. ZnO is known for its high sensitivity within a temperature range of( 150°C–200 °C- 250 °C). Pure ZnO showed a strong response to hydrogen sulfide (H₂S), while doping with CuO nanoparticles played a crucial role in enhancing its sensitivity to both hydrogen sulfide and nitrogen dioxide (NO₂). The sensitivity of all samples to these two gases was measured using a gas sensing system.
All samples were tested, and the optimal operating temperature was found to be 150 °C. The sample doped with 0.75% CuO achieved the highest sensitivity to hydrogen sulfide, with a value of 241.81%, a fast response time of 12.6 seconds, and a recovery time of 76.5 seconds. For nitrogen dioxide, the 0.75% CuO-doped sample also showed the highest sensitivity, reaching 194%, with a response time of 44.1 seconds and a recovery time of 110.7 seconds.