Sergio H. Domingues

pKa determination of graphene-like materials: Validating chemical functionalization.

We report a novel pKa determination for different graphene-like samples: graphene oxide (GO), reduced GO (rGO), graphene nanoribbons (GNR), oxidized GNR (GONR), thiol- and imidazole-functionalized GO (GOSH and GOIMZ, respectively) and thiol-functionalized GONR (GONRSH). Using the specialized computational program BEST7 for treating titration curves, pKas for different functional groups were discriminated (confirmed by infrared spectra) and their composition quantified. Overall, three equilibria were distinguished, two relative to carboxylic acids exhibiting different acidic degrees (pKa1∼4.0 and pKa2∼6.0) and one relative to alcohols (pKa4∼10.0). Upon functionalization on carboxylate sites, thiol (pKa(GOSH/GONRSH)=6.7) and imidazole (pKa(GOIMZ)=6.6) moieties were discerned, followed by a decrease of their carboxylate percentage (compared to the precursors), thus allowing determining the degree of functionalization (48% and 36% of thiol content for GOSH and GONRSH respectively, and 29% of imidazole for GOIMZ). The proposed method is innovative and simpler when compared to the traditional tools usually employed to quantify chemical functionalization.

Supports matter: unraveling the role of charge transfer in the plasmonic catalytic activity of silver nanoparticles

The immobilization of plasmonic nanoparticles onto supports with suitable electronic properties represents an intuitive strategy for the modulation of nanoscale charge-transfer processes and thus the optimization of plasmonic catalytic performances. Here, we report the investigation of the effect of two kinds of bi-dimensional (2D) supports, i.e., partially reduced graphene oxide (prGO) and ultrathin titanate nanosheets (TixO2), on the plasmonic catalytic performances of Ag nanoparticles (NPs). As prGO and TixO2 act as electron donor and acceptor materials, respectively, when combined with plasmonic nanoparticles under 633 nm excitation, their similar 2D morphologies enabled us to systematically probe and compare how charge transfer to and from Ag NPs affected their plasmonic catalytic activities. By employing the SPR-mediated oxidation of p-aminothiophenol (PATP) to p,p′-dimercaptoazobenzene (DMAB) as a model reaction, we found that the performances of the hybrids were superior relative to unsupported Ag NPs and that the PATP oxidation mechanism and conversion were dependent on the nature of the support. We also prepared the tri-component hybrid comprised of Ag NPs, prGO and TixO2 nanosheets (Ag/TixO2/prGO), which displayed a similar performance to Ag/prGO. In this material, a mechanism based on the cooperative effect of the supports was proposed, in which charge transfer from prGO to Ag NPs is intensified by the presence of TixO2 nanosheets. We believe that our results expand the understanding on the electronic behavior of complex plasmonic systems, which can allow the rational design of nanoparticle systems with improved performances towards plasmonically triggered or enhanced transformations.

Air stable black phosphorous in polyaniline-based nanocomposite

The greatest challenge regarding black phosphorus (BP) comes as a result of its fast degradation when exposed to ambient conditions, which has overshadowed its applications. Herein, we report a simple and efficient route towards overcoming BP deterioration by preparing a nanocomposite with the conducting polymer polyaniline (PANI). The liquid/liquid interfacial method was employed to produce transparent, freestanding and transferable thin film of BP covered by PANI, with high stability under ambient atmosphere, up to 60 days. Otherwise, the uncapped exfoliated neat BP degraded in solely 3 days under the same conditions. Characterization data show that PANI covers efficiently the BP flakes, indicating favorable interactions between the components. The results presented here can be considered a breakthrough for employing BP as thin film in different technological applications, considering the properties of BP itself or taking advantage of synergistically combining the properties of both components.

Theoretical Design and Experimental Realization of Quasi‐Single Electron Enhancement in Plasmonic Catalysis

By a combination of theoretical and experimental design, we probed the effect of a quasi-single electron on the surface plasmon resonance (SPR)-mediated catalytic activities of Ag nanoparticles. Specifically, we started by theoretically investigating how the E-field distribution around the surface of a Ag nanosphere was influenced by static electric field induced by one, two, or three extra fixed electrons embedded in graphene oxide (GO) next to the Ag nanosphere. We found that the presence of the extra electron(s) changed the E-field distributions and led to higher electric field intensities. Then, we experimentally observed that a quasi-single electron trapped at the interface between GO and Ag NPs in Ag NPs supported on graphene oxide (GO-Ag NPs) led to higher catalytic activities as compared to Ag and GO-Ag NPs without electrons trapped at the interface, representing the first observation of catalytic enhancement promoted by a quasi-single electron.

Graphene oxide and reduced graphene oxide as saturable absorbers onto D-shaped fibers for sub 200-fs EDFL mode-locking

We present high mode-locking performances from an erbium-doped fiber laser (EDFL) by using graphene oxide (GO) and reduced graphene oxide (r-GO) as saturable absorbers (SA) deposited onto the polished surface of a D-shaped optical fiber. The samples were prepared with different concentrations and its characterization was performed by using an optical microscope, a Raman spectrometer, nonlinear saturable absorption measurements, polarization setup, and laser mode-locking analysis. As a 1550-nm polarizer, the best GO (r-GO) samples exhibited higher polarization extinction ratio (PER) of 7.94 (7.65) dB, corresponding to 84 (83) %, both showing similar graphene TE absorption behavior. In a managed-intracavity dispersion laser, broadest bandwidths of 27.2 and 24.1 nm and the corresponding shortest pulse duration of 190 fs could be generated when incorporating the SA with high modulation depth (above 20%), being so far the best mode-locking results ever reported in the literature for GO and r-GO SA onto D-shaped optical fibers in EDFL.

Sub-300fs mode-locked erbium doped fiber laser using graphene oxide and reduced graphene oxide onto D-shaped optical fibers

We present the ultrashort pulse generation of sub-300 fs from a mode-locked Erbium doped fiber laser by using spin-coated graphene oxide and reduced graphene oxide saturable absorbers deposited onto polished surface of D-shaped optical fibers.