The novel 2D materials such as graphene and transition-metal dichalcogenides have already shown impressive volatile organic compound (VOC) gas monitoring performances as in sensitivity, limit of detection and response time. This thesis discusses the experimental-theoretical examination of optical, electronic and morphological properties of novel 2D materials and their utilization in VOC gas sensor field, by means of several characterization techniques and density functional theory (DFT). Aside from the basic familiarization with the experimental and theoretical methodology in Chapter 2, examination of the functionalization of exfoliated MoS2 using DDT (1-Dodecanethiol) in Chapter 3, which eventually led to a research paper. The DDT treatment is incorporated into the NMP (N-methyl pyrrolidone) exfoliation procedure, resulting in successful functionalization as confirmed by optical, morphological, and theoretical analysis. Raman spectroscopy showed the formation of graphitic species on MoS2 sheets, with decreased sulfur-vacant sites as the DDT ratio increased. STEM and AFM data confirmed the presence of graphitic quantum dots (GQDs) on MoS2 nanosheets, while PL intensities demonstrated significant improvements in photoluminescent properties. This study enhances our understanding of surface and edge chemistry in exfoliated MoS2 and expands the possibilities for broader applications of MoS2 and GQD particles. Moreover, the attention was drawn to the investigation of the contrasting responses of graphene gas sensors fabricated using different synthesis methods, in the submitted paper explained in Chapter 4. Exfoliated graphene sensors decrease in current when exposed to methanol, while CVD graphene sensors increase in current. The differences in edge site population and electrical properties contribute to these responses. The study provided theoretical and experimental findings for an understanding of the reasons behind the inverse sensor responses of CVD and exfoliated graphene on an atomic scale.