OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 3 2025 Ta b l e 2 Comparison of recent nano humidity sensors No. Sensor Material Sensitivity (pF/%RH or %) Response Time (s) Recovery Time (s) Reference Key Observation 1 Gram Carbon Quantum Dots (C-1, C-2) 178.6–254.86 13.3 / 7.3 14.1 / 4.7 [33] – High sensitivity; – Slow recovery 2 PAA-MWCNT (1:4 ratio) 930 Ом (resistance change) 680 380 [34] – Excessively high response/recovery time 3 GO-modified PEDOT 4.97 % at 97 % RH 31 72 [35] – Poor dynamic response 4 MWCNT in NMP 6.41 36 32 [36] – Moderate performance 5 SnO₂–RGO 146.53 102 “several seconds” [37] – Slow at high RH 6 GO 37,800 % 10.5 41 [38] – Very high sensitivity; – Long recovery 7 Fe–GO 5.18 31 11 [39] – Low sensitivity at low RH 8 GO –9.5 пФ/% RH 5 – [40] – Good speed; – Limited range 9 GO/WS₂ Composite Not specified 11.3 12.4 [41] – Stable performance 25–95% RH 10 CNT@CPM (Chitosan-PAMAM Not specified <20 <20 [42] – Fast; – No sensitivity data 11 5% ZnO–NGM (this work) 53.9 4.2 6.6 this work – Best balance; – High sensitivity; – Fast response 12 2% ZnO–NGM (this work) 38.7 4.5 6.9 this work – Slightly lower sensitivity; – Still fast Electrical characterization demonstrated that NGM doping significantly enhanced sensor performance. Among the samples, the ZnO sensor doped with 2% NGM exhibited the most favorable dynamic response, with a response time of 4.5 seconds and a recovery time of 6.9 seconds. This improvement is attributed to enhanced charge transport properties and a greater number of available adsorption sites. However, at higher doping concentrations (above 5%), although sensitivity increased, the response and recovery times became longer. This behavior is likely due to agglomeration effects, which reduce the effective surface area and hinder rapid adsorption-desorption kinetics. A comparison with previously reported humidity sensors highlights the advantages of ZnO-NGM nanocomposites. While many conventional sensors suffer from slow response and poor recovery, the optimized doping concentration in this study achieved a desirable balance between sensitivity and speed. These enhancements suggest that NGM-doped ZnO sensors are promising candidates for real-time humidity monitoring across various domains, including industrial process control, environmental sensing, and biomedical diagnostics. Future work should focus on further optimizing the doping concentration to enhance performance without compromising long-term stability. Additionally, exploring alternative film deposition techniques and integrating the sensor onto flexible substrates could enable the development of wearable or portable humidity sensors for next-generation smart systems.
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