Controllable plasmon-induced catalytic reaction by surface-enhanced and tip-enhanced Raman spectroscopy

Highly Reversible Molecular Photoswitches with Transition Metal Dichalcogenides Electrodes

The molecule-electrode coupling plays an essential role in photoresponsive devices with photochromic molecules, and the strong coupling between the molecule and the conventional electrodes leads to/ the quenching effect and limits the reversibility of molecular photoswitches. In this work, we developed a strategy of using transition metal dichalcogenides (TMDCs) electrodes to fabricate the thiol azobenzene (TAB) self-assembled monolayers (SAMs) junctions with the eutectic gallium-indium (EGaIn) technique. The current-voltage characteristics of the EGaIn/GaOx //TAB/TMDCs photoswitches showed an almost 100% reversible photoswitching behavior, which increased by ∼28% compared to EGaIn/GaOx //TAB/AuTS photoswitches. Density functional theory (DFT) calculations showed the coupling strength of the TAB-TMDCs electrode decreased by 42% compared to that of the TAB-AuTS electrode, giving rise to improved reversibility. our work demonstrated the feasibility of 2D TMDCs for fabricating SAMs-based photoswitches with unprecedentedly high reversibility.

In situ SERS monitoring of plasmon-driven catalytic reaction on gap-controlled Ag nanoparticle arrays under 785 nm irradiation

Plasmon-enhanced photocatalysis has attracted considerable attention due to its low energy consumption and high energy throughput. Surface-enhanced Raman scattering (SERS) is a highly sensitive and label-free nondestructive tool to investigate plasmon-driven photocatalytic reactions. Herein, we present a facile method to fabricate gap-controlled Ag nanoparticle (NP) arrays with uniform and high-density distribution of hot spots, which can be employed as both efficient plasmonic photocatalysts and stable SERS platforms. The plasmon-driven catalytic reaction of 4-nitrobenzenethiol (4NBT), which transforms it into p, p'-dimercaptoazobenzene (DMAB), is detected by using an in situ SERS technique at the excited wavelength of 785 nm. According to the temperature and laser power density dependent photocatalytic reaction rates observed on the Ag NP arrays, we quantitatively determined that the reductive coupling of 4NBT is more likely to occur as the gap decreases. The finite-difference time-domain (FDTD) simulation results demonstrate that the plasmonic hot spots are significantly enhanced with a decrease in gap, which in turn reduces activation energy. The gap-controlled Ag NP arrays are efficient for both promotion and detection of plasmon-driven catalytic reactions, and may pave a pathway for implementing efficient plasmonic photocatalytic platforms.

Investigate on plasma catalytic reaction of 4-nitrobenzenethiol on Ag@SiO2Core-Shell substrate via Surface-enhanced Raman scattering

Surface-enhanced Raman scattering (SERS) is a promising technique to investigate the plasmon-driven catalytic reaction, in which the Raman signal originates from the electromagnetic (EM)enhancement mechanism and the chemical enhancement (CE) mechanism. Here, we designed and synthesized a novel SERS substrate based on SiO₂ wrapped Ag nanoparticles (Ag@SiO₂ core-shell nanoparticles substrate, Ag@SiO₂ CSNS). Meanwhile, the SERS substrate based on Ag nanoparticles (Ag NS) also was prepared for comparison. Then, plasmon-driven catalytic reaction of 4-nitrobenzenethiol (4-NBT) to p,p'-dimercaptoazobenzene (DMAB) were systematically investigated on Ag and Ag@SiO₂, respectively. The result revealed that, the Fermi level of Ag@SiO₂ CSNS is lower than Ag NS, and the catalytic reaction greatly hindered by the Ag@SiO₂ CSNS under the same excitation laser wavelength. With the same condition excitation laser, Raman signal enhancement effects are different when applying Ag NS and Ag@SiO₂ CSNS, which could be attributed to that the inert SiO₂ shell eliminates CE mechanism of the Raman signal. These results provide a simple strategy to figure out the mechanism of the catalytic reaction based on Surface-enhanced Raman scattering.

Methods of Gold and Silver Nanoparticles Preparation

The versatile family of nanoparticles is considered to have a huge impact on the different fields of materials research, mostly nanoelectronics, catalytic chemistry and in study of cytocompatibility, targeted drug delivery and tissue engineering. Different approaches for nanoparticle preparation have been developed, not only based on "bottom up" and "top down" techniques, but also several procedures of effective nanoparticle modifications have been successfully used. This paper is focused on different techniques of nanoparticles' preparation, with primary focus on metal nanoparticles. Dispergation methods such as laser ablation and vacuum sputtering are introduced. Condensation methods such as reduction with sodium citrate, the Brust-Schiffrin method and approaches based on ultraviolet light or biosynthesis of silver and gold are also discussed. Basic properties of colloidal solutions are described. Also a historical overview of nanoparticles are briefly introduced together with short introduction to specific properties of nanoparticles and their solutions.