Estrutura eletrônica, orientação molecular e organização em nanoescala de filmes finos de nanocompósitos de MoS2: uma abordagem espectroscópica

Abstract

In this work, we carried out the spectroscopic characterization of thin films of nanocomposites based on molybdenum disulfide (MoS2) with polyaniline (PANI) and with graphene oxide (GO), obtained through the liquid–liquid interfacial method. MoS2/PANI nanocomposites were synthesized in different aqueous phases, varying the type of acid (H2SO4 and HCl) and the pH (pH 0 and pH 1). X-ray photoelectron spectroscopy (XPS) revealed higher doping levels in the nanocomposites compared to pure PANI, as well as C–S bonds indicating strong interaction with MoS2. Reflection electron energy loss spectroscopy (REELS) showed a reduction in the energy gap, attributed to the elongation of the polymer chains, influenced by the acid type and by the presence of MoS2. MoS2/PANI nanocomposites were also analyzed after aging, and XPS indicated PANI deprotonation and an intensification of interactions with MoS2. Synchrotron infrared nanospectroscopy (SINS) proved particularly effective in identifying chemical variations at the nanometric scale, highlighting the influence of pH and dopant type on the structure and organization of the films. Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, performed at the nitrogen K-edge, suggested the coexistence of protonated and deprotonated units, indicating partial deprotonation of the polymer. The variation of the incidence angle of the beam showed that molecular organization depends on the synthesis and deposition conditions of the samples. MoS2 and GO nanocomposites were obtained through three interfacial routes: (i) one-pot, (ii) two-step, and (iii) layer-by-layer. Photoemission spectra revealed C–S bonds, indicating chemical interaction between MoS2 and GO. The SINS technique mapped chemical heterogeneities associated with the synthetic route. Films obtained by layer-by-layer deposition showed greater resemblance to pure MoS2 films, whereas those obtained via one-pot and two-step routes exhibited characteristics closer to GO. NEXAFS measurements at the sulfur L2,3-edge indicated a higher degree of structural organization of MoS2 in the nanocomposites compared to the isolated material. The results demonstrate that both the interaction between components and the synthesis route impact the structural and electronic properties of the films, underscoring the importance of synthetic control in the development of new materials.