RESUMO
The lateral size of graphene nanosheets plays a critical role in the properties and microstructure of 3D graphene as well as their application as supports of electrocatalysts for CO2 reduction reactions (CRRs). Here, graphene oxide (GO) nanosheets with different lateral sizes (1.5, 5, and 14 µm) were utilized as building blocks for 3D graphene aerogel (GA) to research the size effects of GO on the CRR performances of 3D Au/GA catalysts. It was found that GO-L (14 µm) led to the formation of GA with large pores and a low surface area and that GO-S (1.5 µm) induced the formation of GA with a thicker wall and isolated pores, which were not conducive to the mass transfer of CO2 or its interaction with catalysts. Au/GA constructed with a suitable-sized GO (5 µm) exhibited a hierarchical porous network and the highest surface area and conductivity. As a result, Au/GA-M exhibited the highest Faradaic efficiency (FE) of CO (FECO = 81%) and CO/H2 ratio at -0.82 V (vs. a Reversible Hydrogen Electrode (RHE)). This study indicates that for 3D GA-supported catalysts, there is a balance between the improvement of conductivity, the adsorption capacity of CO2, and the inhibition of the hydrogen evolution reaction (HER) during the CRR, which is related to the lateral size of GO.
RESUMO
Cooperative effects of a series of equimolar binary zwitterionic-ionic surfactant mixtures on the interfacial water structure at the air-water interfaces have been studied by sum frequency generation vibrational spectroscopy (SFG-VS). For zwitterionic surfactant palmityl sulfobetaine (SNC16), anionic surfactant sodium hexadecyl sulfate (SHS), and cationic surfactant cetyltrimethylammonium bromide (CTAB) with the same length of alkyl chain, significantly enhanced ordering of interfacial water molecules was observed for the zwitterionic-anionic surfactant mixtures SNC16-SHS, indicating that SNC16 interacts more strongly with SHS than with CTAB because of the strong headgroup-headgroup electrostatic attraction for SNC16-SHS. Meanwhile, the SFG amplitude ratio of methyl and methylene symmetric stretching modes was used to verify the stronger interaction between SNC16 and SHS. The conformational order indicator increased from 0.64 for SNC16 to 7.17 for SNC16-SHS but only 0.94 for SNC16-CTAB. In addition, another anionic surfactant sodium dodecyl sulfate (SDS) was introduced to study the influence of chain-chain interaction. Decreased SFG amplitude of interfacial water molecules for SNC16-SDS was observed. Therefore, both the headgroup-headgroup electrostatic interaction and chain-chain van der Waals attractive interaction of the surfactants play an important role in enhancing the ordering of interfacial water molecules. The results provided experimental and theoretical bases for practical applications of the surfactants.
RESUMO
Both the localized resonance and excitation of spoof surface plasmon polaritons are observed in the terahertz transmission spectra of periodic subwavelength hole arrays. Analyzing with the coupled oscillator model, we find that the terahertz transmission is actually facilitated by three successive processes: the incident terahertz field first initiates the localized oscillation around each hole, and then the spoof surface plasmon polaritons are excited by the localized resonance, and finally the two resonances couple and contribute to the transmission. Tailoring the localized resonance by hole size, the coupling strength between spoof surface plasmon polaritons and localized resonances is quantitatively extracted. The hole size dependent transmittance and the coupling mechanism are further confirmed by fitting the measured spectra to a modified multi-order Fano model.
RESUMO
Surface-enhanced electromagnetic response in the resonant regions of split-ring resonators offers a sensitive way to probe the surface dipoles formed by alkanethiol molecules with a terahertz wave by a differential transmission (DT) interrogation method. The DT signal mainly comes from the interaction between alkanethiols and metamaterials by electron transfer and/or the variation of the dielectric constant. The Lorentz model is used to demonstrate the principle of DT interrogation theoretically, which suggests the variation of both frequency and damping of resonance can be captured cooperatively. This method has been employed to experimentally demonstrate the sensing feasibility for the chain length dependence of the alkanethiol molecules. Numerical simulations confirm that the enhancement is large at the gap and corner regions of this kind of metamaterials.
RESUMO
Specific biorecognition is essential for many biological processes, for which highly sensitive and label-free biosensors are strongly demanded. The recently developed metamaterials are a potential choice for biosensing due to their exotic properties. In the current work, a label-free and specific sensor for streptavidin-agarose (SA) was fabricated based on terahertz metamaterial functionlized by octadecanthiols and biotins. Both low and high frequency resonant modes from the metamaterials are found applicable for the detection of SA, and a redshift up to 6.76 GHz for the high frequency mode was measured in the undiluted commercial solution. The low frequency mode is attributed to inductor-capacitor (LC) oscillation, while the high frequency mode originates from the plasmonic dipole oscillator, both of which are highly sensitive to the micro-environment change. Adsorption of SA of different concentrations causes different redshifts, and the replacement of high refractive-index substrate with low refractive-index substrate can efficiently promote the sensitivity, well agreeing with the numerical simulation. Moreover, for a particular biomolecule, the sensitivity can be further improved by optimizing the metamaterial design. This method might be very helpful for desirable biorecognition in biology, medicine, and drug industry.
