In situ fabrication of Z-scheme C3N4/Ti3C2/CdS for efficient photocatalytic hydrogen peroxide production.

Photocatalysis is a potential technology to produce hydrogen peroxide with low energy consumption and no pollution. However, when using traditional photocatalysts it is hard to meet the requirements of wide visible light absorption, high carrier separation rate and sufficient active sites. Graphitic carbon nitride (g-C3N4) has great potential in the photocatalytic production of hydrogen peroxide, but its photocatalytic performance is limited by a high carrier recombination ratio. Here, we fabricated the Z-Scheme heterojunction of C3N4/Ti3C2/CdS in situ. The large specific surface area of C3N4 can provide plenty of reactive sites, and the absorption efficiency under visible light is improved with the addition of Ti3C2 and CdS. The better conductivity of Ti3C2 reduces the charge transfer resistance. With the increase of surface charge carriers, the width of the space charge region decreases and the photocurrent density increases significantly. Under visible light irradiation, the H2O2 yield of the ternary photocatalyst reaches 256 µM L-1 h-1, which is about 6 times that of pristine C3N4. After three cycles, the high photocatalytic efficiency can still be maintained. In this paper, the reaction mechanism of photocatalytic hydrogen peroxide production by the C3N4/Ti3C2/CdS composite material is proposed through an in-depth study of energy band theory, which provides a new reference for the design and preparation of high-performance materials for photocatalytic hydrogen peroxide production.

One-pot synthesis of 3D Au nanoparticle clusters with tunable size and their application.

In general, the preparation of Au nanoparticle clusters (NPCs) is more challenging than that of nanoparticles. The traditional multi-step method for preparing Au NPCs is time consuming and highly sensitive to the reaction conditions. Here, we report a simple and feasible method for the rapid preparation of Au NPCs (∼30 min), in which Au (III) is reduced to Au (0) by trisodium citrate, and assembled into NPCs in the presence of a trace amount of cysteine. The surface plasmon resonance peak of the Au NPCs is tunable and ranged from visible to near-IR regions by varying the content of cysteine added. The growth process of Au NPCs was monitored by dynamic light scattering, UV-vis absorption spectroscopy and transmission electron microscopy. Their elemental composition, chemical state and molecular structure of the sample surface were measured by x-ray photoelectron spectroscopy. The proposed synthesis mechanism has guiding significance for the preparation of other NPCs. Au NPCs used as surface-enhanced Raman spectroscopy substrate has a good enhancement effect because of its unique morphology.

Origins of Extreme Liquid Repellency on Structured, Flat, and Lubricated Hydrophobic Surfaces.

There are currently three main classes of liquid-repellent surfaces: micro- or nanostructured superhydrophobic surfaces, flat surfaces grafted with "liquidlike" polymer brushes, and lubricated surfaces. Despite recent progress, the mechanistic explanation for the differences in droplet behavior on such surfaces is still under debate. Here, we measure the dissipative force acting on a droplet moving on representatives of these surfaces at different velocities U=0.01-1 mm/s using a cantilever force sensor with submicronewton accuracy and correlate it to the contact line dynamics observed using optical interferometry at high spatial (micron) and temporal (<0.1 s) resolutions. We find that the dissipative force-due to very different physical mechanisms at the contact line-is independent of velocity on superhydrophobic surfaces but depends nonlinearly on velocity for flat and lubricated surfaces. The techniques and insights presented here will inform future work on liquid-repellent surfaces and enable their rational design.

In situ SERS monitoring of plasmonic nano-dopants during photopolymerization.

The motion of the plasmonic nano-dopant in photopolymers was monitored in situ and in real time using the surface-enhanced Raman scattering (SERS) technique. Here an Au@MBA@Ag (core-molecule-shell) nanoparticle colloid was synthesized to act as the nano-dopant and adsorbed 4-mercaptobenzoic acid (MBA) between the Au cells and Ag shells as the internal standard. The changes of the MBA signal closely reflect the motion of nanoparticles, since the MBA signal itself has time stability. Experimental data indicate that the optimized concentration of the nano-dopant can be obtained based on the peak intensity change of MBA at 1583 cm-1. This Letter provides a novel way for in situ monitoring of photophysicial and photochemical processes.

Morphology and Optical Properties of RF Sputtering Deposited Indium Nitride Layers Under Different N2/Ar Ratio.

InN thin films were prepared using reactive radio frequency sputtering on (111) Si substrates under different N2/Ar ratio. The surface morphology and optical properties of InN thin films were characterized by X-ray diffraction, atomic force microscopy, scanning electron microscope, energy dispersive spectrometer, and UV-visible-NIR spectrophotometer at room temperature. It was found that the growth rate and surface RMS roughness of InN layers all significantly decreased with the increasing of N2 content in the sputtering gas. All the InN films were wurtzite structure with the proportion of N2 increasing from 40% to 100% in the mixture gas. The highly c-axis orientation InN films could only be obtained in the composition ratios of N2 higher than 90%. The atomic percentage of N is much higher than that of In at high N2 content films, which mainly due to the chemical reaction on the surface of Si substrate. The apparent optical band gap energy is estimated at 1.83 eV. However, the InN absorption band tail is strongly influenced by the sputtering due to a change in the species of the plasma.

Stepwise Synthesis of Au@CdS-CdS Nanoflowers and Their Enhanced Photocatalytic Properties.

Fabrication of hybrid nanostructures with complex morphologies and high photocatalytic activity is a difficult challenge because these particles require extremely high preparation skills and are not always practical. Here, hierarchical flower-like Au@CdS-CdS nanoparticles (Au@CdS-CdS nanoflowers) have been synthesized using a stepwise method. The Au@CdS-CdS nanoflowers are consisted of Au core, CdS shell, and CdS nanorods. The UV-Vis absorption range of the Au@CdS-CdS nanoflowers reaches up to 850 nm which covers the whole visible range (400-760 nm). Photoinduced charge transfer property of Au@CdS-CdS nanoflowers was demonstrated using photoluminescence (PL) spectroscopy. Compared to CdS counterparts and Au@CdS counterparts, Au@CdS-CdS nanoflowers demonstrated the highest photocatalytic degradation rate under irradiation of λ = 400-780 nm and λ = 600-780 nm, respectively. Based on structure and morphology analyses, we have proposed a possible formation mechanism of the hybrid nanostructure which can be used to guide the design of other metal-semiconductor nanostructures with complex morphologies.

Polariton nanophotonics using phase-change materials.

Polaritons formed by the coupling of light and material excitations enable light-matter interactions at the nanoscale beyond what is currently possible with conventional optics. However, novel techniques are required to control the propagation of polaritons at the nanoscale and to implement the first practical devices. Here we report the experimental realization of polariton refractive and meta-optics in the mid-infrared by exploiting the properties of low-loss phonon polaritons in isotopically pure hexagonal boron nitride interacting with the surrounding dielectric environment comprising the low-loss phase change material Ge3Sb2Te6. We demonstrate rewritable waveguides, refractive optical elements such as lenses, prisms, and metalenses, which allow for polariton wavefront engineering and sub-wavelength focusing. This method will enable the realization of programmable miniaturized integrated optoelectronic devices and on-demand biosensors based on high quality phonon resonators.

Two-step phase shifting differential-recording digital holographic microscopy.

We present two-step phase-shifting differential-recording digital holographic microscopy (TPD-DH in microscopy) for phase imaging of microscopic transparent elements. Two CCDs are employed to record two interferograms at two different defocusing distances. The interferograms on the two CCD cameras are shifted for a phase retarder 0 and π via an all-optics phase shifting unit. A novel algorithm is proposed to reconstruct both amplitude and phase distributions of the object wave from the recorded interferograms. This method has the same spectrum bandwidth and measurement accuracy with those of conventional four-step phase-shifting interferometry (FS-PSI), whereas it reduces the measurement time by half.