Highly efficient utilization of solar light with an excellent reduction capacity is achieved for plasmonic Fe@C nanostructures. By carbon layer coating, the optimized catalyst exhibits enhanced ...selectivity and stability applied to the solar‐driven reduction of CO2 into CO. The surface‐plasmon effect of iron particles is proposed to excite CO2 molecules, and thereby facilitates the final reaction activity.
A novel CO2 photoreduction method, CO2 conversion through methane reforming into syngas (DRM) was adopted as an efficient approach to not only reduce the environmental concentration of the greenhouse ...gas CO2 but also realize the net energy storage from solar energy to chemical energy. For the first time it is reported that gold, which was generally regarded to be inactive in improving the performance of a catalyst in DRM under thermal conditions, enhanced the catalytic performance of Rh/SBA‐15 in DRM under visible‐light irradiation (1.7 times, CO2 conversion increased from 2100 to 3600 μmol g−1 s−1). UV/Vis spectra and electromagnetic field simulation results revealed that the highly energetic electrons excited by local surface plasmon resonances of Au facilitated the polarization and activation of CO2 and CH4 with thermal assistance. This work provides a new route for CO2 photoreduction and offers a distinctive method to photocatalytically activate nonpolar molecules.
Storing solar energy: Gold enhances the catalytic performance of a Rh/SBA‐15 catalyst in the dry reforming process of methane under visible‐light irradiation (see picture). The highly energetic electrons excited by local surface plasmon resonances of gold facilitated the polarization and activation of carbon dioxide and methane under thermal conditions.
We fabricated large-area metallic (Al and Au) nanoantenna arrays on Si substrates using cost-effective colloidal lithography with different micrometer-sized polystyrene spheres. Variation of the ...sphere size leads to tunable plasmon resonances in the middle infrared (MIR) range. The enhanced near-fields allow us to detect the surface phonon polaritons in the natural SiO
thin layers. We demonstrated further tuning capability of the resonances by employing dry etching of the Si substrates with the nanoantennas acting as the etching masks. The effective refractive index of the nanoantenna surroundings is efficiently decreased giving rise to blueshifts of the resonances. In addition, partial removal of the Si substrates elevates the nanoantennas from the high-refractive-index substrates making more enhanced near-fields accessible for molecular sensing applications as demonstrated here with surface-enhanced infrared absorption (SEIRA) spectroscopy for a thin polymer film. We also directly compared the plasmonic enhancement from the Al and Au nanoantenna arrays.
Matured surface chemistry and excellent chemical stability have enabled gold to become the material‐of‐choice for plasmonic sensing in both visible and infrared wavelength range. Here, successful ...surface functionalization of metamaterials made from a low‐cost abundant plasmonic material, aluminum, with phosphonic acid and subsequent detection of the CO vibration mode via surface‐enhanced infrared absorption spectroscopy is demonstrated. The metamaterial consists of infrared perfect absorbers fabricated by colloidal lithography. Near perfect absorption is achieved at resonance wavelengths, which can be readily tuned by changing the diameters of the Al disk resonators, enabling excellent overlapping with the molecular vibration. Separately, the detection of a physically adsorbed protein layer on the Al metamaterial is also demonstrated. Surface functionalization with phosphonic acid provides various functional groups to the Al surfaces. Combined with tunable metamaterials, the work herein opens up great opportunities for Al‐based plasmonic nanostructures for biochemical sensing applications.
Infrared aluminum metamaterial perfect absorbers (MPAs) are fabricated using scalable and cost‐effective colloidal lithography and dry etching. The plasmon resonances can be readily tuned by the etching time of polystyrene spheres. Chemical surface functionalization of the MPAs is achieved using phosphonic acid making it possible to use Al for surface enhanced infrared absorption spectroscopy.
Vanadium dioxide (VO2), a well-known Mott insulator and a prominent thermochromic material, exhibits an intelligent optical response from the infrared-transparent state to the infrared-blocking state ...below and above its transition temperature, respectively. Despite there have been numerous studies on its synthesis, a few could readily obtain high quality VO2 thin films except on single crystal epitaxial substrates. Its lack of versatility to form onto various substrates while retaining the specific function also needs to be addressed. Here, we present a sputtering method using V2O5 target with in situ annealing to prepare high-quality VO2 thin films on Si and quartz substrates. The results show that pure monoclinic VO2 could be obtained in a narrow range of oxygen flow ratio (from 0 to 0.74%) in Ar/O2 working gas during sputter deposition. The structural evolution was verified by Raman spectroscopy. At the transition temperature, the remarkably large optical transmittance contrasts of ~74% and ~77% were obtained at the incident wavelength of 2.5 and 3 μm, respectively. The luminous transmittance values at room temperature and high temperature were 36.63 and 38.87%, respectively. The measured solar transmittance modulation efficiency (∆Tsol) was 5.87%, which is comparable to or even better than the reported values of VO2 films prepared using sputtering. We also demonstrated the spontaneous response of electrical performance with applying potential and varying temperature. Our results revealed the facile preparation of large area and high-performance thermochromic VO2 thin film on non-epitaxial substrates of Si and quartz which greatly augment its applications in solar-heat managements and optoelectronics.
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•VO2 films are prepared using sputter deposition from V2O5 with in situ annealing.•Sharp semiconductor-to-metal transition is revealed by Raman spectroscopy/mapping.•Remarkably high transmittance contrast of ~74% (λ = 2.5 μm) and ~77% (λ = 3 μm).•The prepared VO2 film provides a promising perspective for thermal management applications.
Photocatalytic reduction of carbon dioxide (CO2) is attractive for the production of valuable fuels and mitigating the influence of greenhouse gas emission. However, the extreme inertness of CO2 and ...the sluggish kinetics of photoexcited charge carrier transfer process greatly limit the conversion efficiency of CO2 photoreduction. Herein, we report that the plasmonic coupling effect of Pt and Au nanoparticles (NPs) profoundly enhances the efficiency of CO2 reduction through dry reforming of methane reaction assisted by light illumination, reducing activation energies for CO2 reduction ∼30% below thermal activation energies and achieving a reaction rate 2.4 times higher than that of the thermocatalytic reaction. UV–visible (vis) absorption spectra and wavelength-dependent performances show that not only UV but also visible light play important roles in promoting CO2 reduction due to effective localized surface plasmon resonance (LSPR) coupling between Pt and Au NPs. Finite-difference time-domain simulations and in situ diffuse reflectance infrared Fourier transform spectroscopy further reveal that effective coupling LSPR effect generates strong local electric fields and excites high concentration of hot electrons to activate the reactants and intermediate species, reduce the activation energies, and increase the reaction rate. This work provides a new pathway toward the efficient plasmon-enhanced chemical reactions via reducing the activation energies by utilizing solar energy.
We have developed moiré nanosphere lithography (M-NSL), which incorporates in-plane rotation between neighboring monolayers, to extend the patterning capability of conventional nanosphere ...lithography (NSL). NSL, which uses self-assembled layers of monodisperse micro/nanospheres as masks, is a low-cost, scalable nanofabrication technique and has been widely employed to fabricate various nanoparticle arrays. Combination with dry etching and/or angled deposition has greatly enriched the family of nanoparticles NSL can yield. In this work, we introduce a variant of this technique, which uses sequential stacking of polystyrene nanosphere monolayers to form a bilayer crystal instead of conventional spontaneous self-assembly. Sequential stacking leads to the formation of moiré patterns other than the usually observed thermodynamically stable configurations. Subsequent O2 plasma etching results in a variety of complex nanostructures. Using the etched moiré patterns as masks, we have fabricated complementary gold nanostructures and studied their optical properties. We believe this facile technique provides a strategy to fabricate complex nanostructures or metasurfaces.
Color-tunable resonant photoluminescence (PL) was attained from polystyrene microspheres doped with a single polymorphic fluorescent dye, boron-dipyrrin (BODIPY) 1. The color of the resonant PL ...depends on the assembling morphology of 1 in the microspheres, which can be selectively controlled from green to red by the initial concentration of 1 in the preparation process of the microspheres. Studies on intersphere PL propagation with multicoupled microspheres, prepared by micromanipulation technique, revealed that multistep photon transfer takes place through the microspheres, accompanying energy transfer cascade with stepwise PL color change. The intersphere energy transfer cascade is direction selective, where energy donor-to-acceptor down conversion direction is only allowed. Such cavity-mediated long-distance and multistep energy transfer will be advantageous for polymer photonics device application.
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