Ultrafast responsive humidity sensor based on roasted gram derived carbon quantum dots: Experimental and theoretical study

Herein, we have reported the sustainable, cost-effective and rapid synthesis of gram derived carbon quantum dots (GCQD) employed as capacitive humidity sensor. Synthesis of GCQDs C-1 & C-2 at different carbonization temperature has been performed by pyrolysis method. Crystallinity of as prepared GCQDs were confirmed by XRD and TEM analysis revealing the average particle size 5.5 and 2 nm for C-1 & C-2 respectively. Optical properties of samples were further analysed by UV-vis and photoluminescence meter which gave the band gap as 3.82 and 4.20 eV. Compositional analysis of GCQDs were confirmed by using XPS. GCQDs were subjected to sensing test at frequency 20 - 2 MHz. The C-2 gave an enhanced sensing performance with an average sensitivitiy of 254.861 pF/%RH. Also, sensor showed rapid response and recovery times of 7.3 & 4.7 s respectively. Theoretical modelling has been performed to further look into the insight of interaction between functional group of GCQDs and water vapour molecules. Transient parameters such as charge density, HOMO-LUMO gap, electron clouds and H-bonds were calculated using B3LYP hybrid functional at 6-31 g diffused and polarised basis set. This study provides an insight chemistry of GCQDs with water toward an efficient humidity sensor development.

Automated summary

This study reports a sustainable, cost-effective, and rapid synthesis method for carbon quantum dots (GCQD) used as a capacitive humidity sensor. Results show that GCQDs synthesized at different carbonization temperatures exhibit different crystallinity and optical properties, with C-2 showing higher sensitivity and shorter response times in sensing tests. Theoretical modeling was performed to investigate the interaction between GCQDs and water molecules, providing insights for the development of efficient humidity sensors.