Faculty of Engineering Sciences, Ghulam Ishaq Khan Institute of Engineering Sciences and Technology, Topi, 23640, KPK, Pakistan.
Department of Mechanical Technology, University of Technology Nowshera, Amangarh, 24100, KPK, Pakistan.
Nanotechnology. 2021 Apr 27;32(29). doi: 10.1088/1361-6528/abe670.
Graphene quantum dots (GQDs) were prepared using a single-step hydrothermal treatment of glucose (CHO) powder. X-ray diffraction patterns confirmed the random stacking or amorphous character of GQDs. Additionally, the UV-vis spectra confirmed the formation of GQDs with evident absorption peaks at 237 and 305 nm, which is attributed to-* and-* transitions correspondingly. The average size and surface roughness of graphene quantum dots were estimated by atomic force microscopy images and found to be 27.0 ± 1.0 and 2.3 nm, respectively. Afterwards, the effect of increasing relative humidity (RH) from 0%-95%, and frequency, was analyzed using the capacitive and resistive responses of synthesized GQDs. The capacitive output at 0.1 kHz revealed that initially capacitance remains constant (15.0 ± 1.0 pF) up to a humidity level ranging between 0%-50%. Likewise, capacitance also displayed stabilized behavior after frequency levels were increased i.e., 1.0 and 10 kHz, at a humidity ranging from 0%-55%. Moreover, capacitance showed a 115,455, 22,480 and 3,620% improvement from their stable values at each respective frequency level i.e., 0.1, 1.0 and 10 kHz. The capacitive sensitivity decreased to 84.20 and 96.83% at greater frequencies (1.0 and 10 kHz) in comparison to the sensitivity at 0.1 kHz facing similar variations in a humid environment. In contrast, resistance displayed an exponential decline by 99.9900, 99.9796 and 99.9925%, accordingly, when RH increases from 0 to 95% at 0.1, 1.0 and 10 kHz, respectively. However, with the rise in frequency level from 0.1 to 1.0 kHz, resistive sensitivity increased considerably to 69 and 158.5%, respectively, in two prominent humidity ranges i.e., 0 ≤ RH ≤ 25% and 25% ≤ RH ≤ 50%. A further increase in testing frequency to 10 kHz enhances the resistive sensitivity by 598.5 and 178.5% when compared with the lowest sensitivity values at two noticeable humidity levels, 0%-25% and 25%-50%. The response and recovery times of our specimen were better than most of previously fabricated GQDs and other carbon-derived nanomaterials, which makes the nano-GQDs of our study more suitable for RH sensor application.
采用一步水热法，以葡萄糖（CHO）粉末为原料制备了石墨烯量子点（GQDs）。X 射线衍射图谱证实了 GQDs 的随机堆积或无定形特征。此外，紫外-可见光谱证实了 GQDs 的形成，其在 237 和 305nm 处有明显的吸收峰，这归因于 -*和 -*跃迁。通过原子力显微镜图像估计了石墨烯量子点的平均尺寸和表面粗糙度，分别为 27.0 ± 1.0nm 和 2.3nm。随后，分析了相对湿度（RH）从 0%增加到 95%以及频率对合成 GQDs 电容和电阻响应的影响。在 0.1kHz 时的电容输出表明，在 0%至 50%的湿度范围内，电容最初保持恒定（15.0 ± 1.0pF）。同样，在频率水平增加至 1.0 和 10kHz 时，电容在 0%至 55%的湿度范围内也表现出稳定的行为。此外，在每个相应的频率水平（即 0.1、1.0 和 10kHz），电容分别从其稳定值提高了 115,455、22,480 和 3,620%。与在类似湿度环境下在 0.1kHz 时的灵敏度相比，在更高频率（1.0 和 10kHz）时，电容灵敏度降低到 84.20%和 96.83%。相比之下，电阻在 0.1、1.0 和 10kHz 时分别从 99.9900、99.9796 和 99.9925%的 RH 增加到 99.9900、99.9796 和 99.9925%。然而，随着频率从 0.1 增加到 1.0kHz，电阻灵敏度在两个显著的湿度范围内分别显著增加到 69%和 158.5%，即 0%≤RH≤25%和 25%≤RH≤50%。当与两个显著的湿度水平（0%-25%和 25%-50%）下的最低灵敏度值相比，将测试频率进一步提高到 10kHz 时，电阻灵敏度提高了 598.5%和 178.5%。我们样品的响应和恢复时间优于大多数以前制造的 GQDs 和其他碳衍生纳米材料，这使得我们研究中的纳米 GQDs 更适合用于 RH 传感器应用。
