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This study utilizes density functional theory (DFT) with the Lanl2dz functional to investigate the effect of silver (Ag), gold (Au) and palladium (Pd) metal adsorption on the electronic properties of graphene oxide (GO). The studied structures, which are pristine GO, Ag-GO, Au-GO, and Pd-GO, are labeled as R (reference), X1, X2, and X3, respectively. The geometrical optimization indicates that Au forms a physical bond with a carbon atom on GO with a bond length 2.169 Å. While, the GO exhibited an energy band gap of approximately 2.39 eV, the subsequent adsorption of metals Ag, Au and Pd leads to a decrease in the band gap, with values of 2.07 eV for X1, 2.16 eV for X2, and 2.28 eV for X3. Further analysis reveals significant differences in the electronic properties of the various materials. Compared to the dipole moment of R (∼8.66 D), the dipole moment of X1-X3 ranged from 2.55 D to 6.11 D, which is lower than R. Our study reveals a modification in the charge distribution within the molecules upon metal adsorption. Interestingly, the open circuit voltage (V OC) exhibits a trend where X2 (1.72 eV) > R (1.16 eV) > X3 (0.95 eV) > X1 (0.54 eV). These findings highlight the crucial role of dopant selection in tuning the optoelectronic properties of GO. By carefully choosing dopants, we can optimize the optoelectronic properties of GO, making it suitable for various applications, including solar energy conversion. [Display omitted] [ABSTRACT FROM AUTHOR]

• Synthesis of high quality thermally reduced Graphene oxide coatings. • Excellent humidity sensing characteristics of the GO sheets. • An n- to p-type conductivity inversion was observed under humidity. • The conductivity inversion phenomenon is elucidated with basic characterization. Graphene oxide (GO) is regarded as one of the potential candidates for gas and humidity sensor applications owing to its excellent water adsorption capabilities. However, there is a lack of understanding the response of GO to humidity. Some authors believe the water adsorption leads to p-type response while other think it to be n-type. The present work demonstrates the mechanism of water adsorption and n- to p-type response inversion of GO to humidity. The GO suspension was synthesised by modified Hummers' method and then drop-casted onto the substrates having already patterned gold interdigital electrodes (IDE). The sensors can detect wide humidity range (5–95 %RH) with a low voltage 0.1 V leading to low power consumption <10−5 W. It is also found that rGO samples annealed at temperature below 150 °C show n-type (e.g. R air /R RH ~ 1.29 × 105 for rGO-40) while the samples annealed above this temperature demonstrate p-type humidity response (e.g. R RH /R air ~ 40 for rGO-150). The static test response time is 8 s, while recovery time is 13 s with excellent long-term stability and RH accuracy value (±4% RH). Further characterization are performed to elucidate the physio-chemical model of the sensing mechanism as well as n- to p-type conductivity inversion under humidity. [ABSTRACT FROM AUTHOR]