OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 3 2025 Conclusions This work reports the effective synthesis of ZnO nanoparticles doped with nanographite material (NGM) for high-performance capacitive humidity sensing. UV–Vis spectroscopy verified a strong absorption peak at 367 nm, confirming the semiconductor nature and optical suitability of the ZnO structure. Structural (XRD) and morphological (SEM) analyses showed enhanced crystallinity and surface texture, while NGM doping significantly improved adsorption kinetics and charge transport. Among the different doping levels that were tested, the 4% NGM-doped ZnO sensor had the best sensitivity-speed balance with a fast response time of 4.0 s and recovery time of 6.2 s. While doping levels of 5% and above provided higher capacitance sensitivity, the response speed was reduced, possibly due to agglomeration and lower active surface area. The sensors also exhibited very good repeatability, negligible hysteresis, and robust performance over a broad frequency and humidity range (10–95% RH, 10 kHz–1 MHz). References 1. Saqib M., Ali Khan S., Mutee Ur Rehman H.M., Yang Y., Kim S., Rehman M.M., Young Kim W. Highperformance humidity sensor based on the graphene flower/zinc oxide composite. Nanomaterials, 2021, vol. 11 (1), p. 242. DOI: 10.3390/nano11010242. 2. Yang H., Ye Q., Zeng R., Zhang J., Yue L., Xu M., Qiu Z.-J., Wu D. Stable and fast-response capacitive humidity sensors based on a ZnO nanopowder/PVP-RGO multilayer. Sensors, 2017, vol. 17 (10), p. 2415. DOI: 10.3390/ s17102415. 3. Ullah Z., Mustafa G.M., Raza A., Khalil A., Awadh Bahajjaj A.A., Batool R., Sonil N.I., Ali I., Nazar M.F. Facile assembly of flexible humidity sensors based on nanostructured graphite/zinc oxide-coated cellulose fibrous frameworks for human healthcare. RSCAdvances, 2024, vol. 14 (50), pp. 37570–37579. DOI: 10.1039/D4RA05761A. 4. Sun Y., Gao X., Shiwei A., Fang H., Lu M., Yao D., Lu C. Hydrophobic multifunctional flexible sensors with a rapid humidity response for long-term respiratory monitoring. ACS Sustainable Chemistry & Engineering, 2023, vol. 11 (6), pp. 2375–2386. DOI: 10.1021/acssuschemeng.2c06162. 5. Ding S., Yin T., Zhang S., Yang D., Zhou H., Guo S., Li Q., Wang Y., Yang Y., Peng B., Yang R., Jiang Z. Fast-speed, highly sensitive, flexible humidity sensors based on a printable composite of carbon nanotubes and hydrophilic polymers. Langmuir, 2023, vol. 39 (4), pp. 1474–1481. DOI: 10.1021/acs.langmuir.2c02827. 6. Wu K., Miao X., Zhao H., Liu S., Fei T., Zhang T. Selective encapsulation of ionic liquids in UiO-66NH2 nanopores for enhanced humidity sensing. ACS Applied Nano Materials, 2023, vol. 6 (10), pp. 9050–9058. DOI: 10.1021/acsanm.3c01727. 7. Lei D., Zhang Q., Liu N., Su T., Wang L., Ren Z., Zhang Z., Su J., Gao Y. Self-powered graphene oxide humidity sensor based on potentiometric humidity transduction mechanism. Advanced Functional Materials, 2022, vol. 32 (10), p. 2107330. DOI: 10.1002/adfm.202107330. 8. Adib M.R., Lee Y., Kondalkar V.V., Kim S., Lee K. A highly sensitive and stable rGO: MoS2-based chemiresistive humidity sensor directly insertable to transformer insulating oil analyzed by customized electronic sensor interface. ACS Sensors, 2021, vol. 6 (3), pp. 1012–1021. DOI: 10.1021/acssensors.0c02219. 9. Yu W., Chen D., Li J., Zhang Z. TiO2-SnS2 nanoheterostructures for high-performance humidity sensor. Crystals, 2023, vol. 13 (3), p. 482. DOI: 10.3390/cryst13030482. 10. Baig M.F.W., Hasany S.F., Shirazi M.F. Green synthesis of nano graphite materials from lemon and orange peel: A sustainable approach for carbon-based materials. Engineering Proceedings, 2023, vol. 46 (1), p. 42. DOI: 10.3390/engproc2023046042. 11. Dare E., Adanu‐Ogbole B., Oladoyinbo F., Makinde F., Uzosike A.O. Synthesis and characterization of silver–zinc oxide nanocomposites for humidity sensing. Nano Select, 2023, vol. 4 (4), pp. 255–262. DOI: 10.1002/ nano.202200106. 12. MahjoubM.A., Monier G., Robert-Goumet C., Réveret F., Echabaane M., Chaudanson D., Petit M., Bideux L., Gruzza B. Synthesis and study of stable and size-controlled ZnO–SiO2 quantum dots: Application as a humidity sensor. The Journal of Physical Chemistry C, 2016, vol. 120 (21), pp. 11652–11662. DOI: 10.1021/acs.jpcc.6b00135. 13. Qian L., Fang C., Gui Y., Tian K., Guo H., Guo D., Guo X., Liu P. Heterojunctions of ZnO-nanorod-decorated WO3 nanosheets coated with ZIF-71 for humidity-independent NO2 sensing. ACS Applied Nano Materials, 2023, vol. 6 (14), pp. 13216–13226. DOI: 10.1021/acsanm.3c01955.
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