Mansour Mohamed

Despite being relatively new to 2D nanoworld, TiO₂ nanosheets (TiO₂NS) are rapidly gaining prominence as highly effective materials for chemical sensor, photocatalysis and electrochemical energy storage. In this study, the potential of density functional theory employ to thoroughly investigate how defects and dopants influence the physical properties of TiO₂ nanosheets (TiO₂NS). Our research aims to reveal the fascinating interactions that occur between both pristine and defective lepidocrocite-type TiO₂ nanosheets when exposed to acetone molecules. Furthermore, we are eager to explore the compelling concept of quantum capacitance in the defected and doped nanosheets, opening new avenues for innovation in material science. The TiO₂NS having an energy band gap of 3.48 eV, exhibits new impurity state near the Fermi level on incorporation of oxygen or titanium vacancy (O_V or Ti_V). These states in the O_V(1)/Ti_V(3)- TiO₂NS play an important role in holding acetone molecules with adsorption energies (E_ads) of −2.37 eV/–1.83 eV. Various electronic analyses, including Mulliken population, inter-frontier orbital, and electron difference density (EDD) plots, all point to an apparent dispersion of electronic charge from acetone to the O_V(1)/Ti_V(3)-TiO₂NS. Contrary to these findings the pristine and O_V(2)-TiO₂ nanosheets weakly hold the acetone molecule. Engineering the surface morphology of TiO₂NS either by creating O_V/Ti_V defect or N/Sc/V doping results in robust quantum capacitance appearing in the electrolytic range of −1.00 V to 1.00 V. Titanium deficient TiO₂NS has wide spread large C_Q spectra with C_Qmax and Q_max of 1198 μF cm⁻² and 512 μC cm⁻²; respectively. The O_V(1)/O_V(2)- TiO₂NS shows low intense C_Q peaks in negative voltage region. Doping with N, Sc, and V has a profound impact on the quantum capacitance of TiO₂NS. In particular, Sc doping introduces remarkable C_Q spectra in the positive region. This demonstrates that defected and doped TiO₂NS holds great promise for applications in acetone sensing and energy storage devices.

Two-dimensional (2D) nanomaterials with enhanced quantum capacitance have been in high demand over the past few years due to super capacitors application. A number of 2D nanosheet, including MoS₂, arsenene, antimonene, and germanene, have also been explored for the same reason. The present investigation aims to explore modified germanene such as monovacant germanene/divacant germanene(MVG/DVG) and their derivatives, such as Ns substituted MVG/DVG and transition metal incorporated MVG. It is observed that 1N-MVG/3N-MVG shows the characteristics of a p-type semiconductor, while 3N-MVG/4N-DVG is considered as semiconductor. A robust binding of under-coordinated Ge to transition metals (TMs) at MVG surfaces suggests such functionalization can be accomplished. Except Ti and Co other studied TMs-MVG show metallic nature. Furthermore, it is revealed that there is an asymmetric C_Q dispersion in 1N-MVG, 2N-MVG, 3N-MVG, and 4N-DVG, as opposed to the pristine germanene/MVG/DVG. Additionally, it is predicted that TMs such as Ti, V, Cr, Mn, Fe and Co incorporated MVG can provide high quantum capacitance (C_Q). Enormous amount of C_Q is noticed for 3N-MVG with maximum of 726 μF cm⁻² in the positive biased region. Among TM-MVG, V-MVG and Mn-MVG are well suited to serve as anodes for asymmetric super capacitors due to their C_Q peak of 978 μF cm⁻² and 1180 μF cm⁻², respectively, in negative bias region.