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Ubiquitous carbon nanomaterials have great potential for emerging technologies, but they also pose a threat to human health at the end of their lifecycle, especially when they are introduced into waste or ground waters. Graphene field-effect transistors (GFET) and real time in situ confocal Raman microscopy (CRM) were employed to detect a submonolayer of carbon quantum dots (CQDs) in water. An effective GFET channel was formed on exfoliated and chemical vapor deposited (CVD) graphene. The adsorption of CQDs was monitored by measuring conductance changes in GFETs. The graphene channel was functionalized with (3-aminopropyl) triethoxysilane (APTES), which allowed for easy observation of a shift in the charge neutrality point (CNP) when the graphene channel was exposed to CQDs. The affinity of the CQD's carboxyl terminal groups to the aminofunctionalized channel enabled a highly sensitive CQD detection based on changes in the GFET conductivity. The adsorption of the CQDs induced a positive shift of the CNP with a limit of detection at concentrations of 239 ppm and 62 ppm for the exfoliated and CVD graphene, respectively. A supporting study of graphene functionalization and CQD adsorption was performed by real time in situ CRM, ellipsometry, and ex situ X-ray photoelectron spectroscopy. [ABSTRACT FROM AUTHOR]

Few-layer MoS 2 films stay at the forefront of current research of two-dimensional materials. At present, continuous MoS 2 films are prepared by chemical vapor deposition (CVD) techniques. Herein, we present a cost-effective fabrication of the large-area spatially uniform films of few-layer MoS 2 flakes using a modified Langmuir-Schaefer technique. The compression of the liquid-phase exfoliated MoS 2 flakes on the water subphase was used to form a continuous layer, which was subsequently transferred onto a submerged substrate by removing the subphase. After vacuum annealing, the electrical sheet resistance dropped to a level of 10 kΩ/sq, being highly competitive with that of CVD-deposited MoS 2 nanosheet films. In addition, a consistent fabrication protocol of the large-area conductive MoS 2 films was established. The morphology and electrical properties predetermine these films to advanced detecting, sensing, and catalytic applications. A large number of experimental techniques were used to characterize the exfoliated few-layer MoS 2 flakes and to elucidate the formation of the few-layer MoS 2 Langmuir film.