Kuang Hsuan Yang

Enhancements in intensity and stability of surface-enhanced Raman scattering on optimally electrochemically roughened silver substrates

In this work, different conditions for electrochemically roughening silver substrates were investigated to obtain the best surface-enhanced Raman scattering (SERS) performance. Experimental results indicate that Ag electrodes can be cycled in deoxygenated aqueous solutions containing 0.1 N HCl from −0.3 to +0.2 V vs.Ag/AgCl at 25 mV s−1 for five scans to obtain the strongest SERS effects. Using this substrate, the SERS intensity of adsorbed Rhodamine 6G (R6G) can be increased 9-fold, compared with that of R6G adsorbed on an Ag substrate prepared using the general literature methods. Moreover, the SERS enhancement capabilities of the newly developed Ag substrate seriously decays at 200 °C, compared to 125 °C for the generally roughened Ag substrates. The reduction of the SERS intensity upon aging is also lessened for this newly developed substrate. Further investigations revealed that surface morphology and the Cl content on the roughened Ag substrates have significant influence on the corresponding SERS performances.

Temperature effect of electrochemically roughened gold substrates on polymerization electrocatalysis of polypyrrole

In this work, electrochemical methods were used to prepare complexes with Au and Cl species on bulk Au substrates. Then the electrochemically roughened Au substrates were further heat-treated at different temperatures. The effect of temperatures used in heat treatments between 25 and 100 degrees C on electrocatalytical polymerization of polypyrrole (PPy) formed on the prepared gold substrates was first investigated. The result indicates that the optimally electrocatalytical capability of the heat-treated Au substrate for PPy polymerization is at 75 degrees C. Moreover, the autopolymerized PPy on the roughened Au substrate treated at 75 degrees C demonstrates the highest oxidation level and oxidation degree of 0.32 and 0.50, respectively. Primary results indicate that complexes with positively charged Au act as oxidants, and perchlorate and chloride ions act as dopants for the oxidation-polymerization of PPy.

Simple strategy to improve surface-enhanced Raman scattering based on electrochemically prepared roughened silver substrates.

We develop an easy and effective pathway to improve surface-enhanced Raman scattering (SERS) effects of probe molecules of Rhodamine 6G (R6G) adsorbed on electrochemically prepared roughened Ag substrates. In general SERS studies, SERS-active metal substrates are first prepared. Then probe molecules are adsorbed on them to evaluate the relative SERS effects. In this study, we employ electrochemical oxidation-reduction cycle (ORC) treatments in 0.1 M KCl solutions containing probe molecules of 2 x 10(-5) M R6G to prepare R6G-adsorbed SERS-active Ag substrates for one step. Encouragingly, based on this strategy, the SERS intensity of adsorbed R6G can be increased by 1 order of magnitude, as compared with that of R6G adsorbed on a roughened Ag substrate beforehand, which was generally shown in the literature. Moreover, this improved SERS effect based on this strategy is also effective for 2 x 10(-9) M probe molecules, which is at a level of single molecule detection based on Ag colloids. It is also effective for probe molecules of ClO(4)(-) with low Raman cross section and for other electrochemically prepared SERS-active substrates of Au. Further analyses indicate that the increase in SERS activity in this new method is most likely due to the incorporation of more chloride ions into the substrate.

Strategy to improve stability of surface-enhanced raman scattering-active Ag substrates

Surface-enhanced Raman scattering (SERS)-active Ag substrates were popularly employed for evaluating the structural situation of analytes because SERS-active Ag substrates can demonstrate more significant SERS effects than Au and Cu substrates. However, the stability of SERS-active Ag substrates is an issue of concern in their application. In this work, SERS-active modified Ag substrates were simply prepared in 0.1 N HCl solutions containing Al2O3 nanoparticles by electrochemical methods. Experimental results indicate that the Al2O3-modified Ag substrate can significantly improve its thermal stability by raising the operation temperature of the Ag substrate by over 100 °C. Moreover, the aging of SERS enhancement capabilities in an atmosphere of 50% relative humidity (RH) and 20% (v/v) O2 at 30 °C is markedly depressed based on this Al2O3-modified Ag substrate.

Size-controllable synthesis of surface-enhanced Raman scattering-active gold nanoparticles coated on TiO2

As shown in the literature, gold nanoparticles (NPs) were popularly used in the fields of catalyst and surface-enhanced Raman scattering (SERS). In this work, size-controllable Au NPs coated on TiO(2) are synthesized by adjusting the pH of solutions based on sonoelectrochemical methods. The size-controlled Au NPs on TiO(2), ranging from 2 to 80 nm in diameter, can be obtained by varying the pH of solutions from 3 to 7 and placing the sample for 3 h before sonoelectrochemical reductions. The optimal particle sizes of Au NPs on TiO(2) to obtain the strongest SERS effects under an irradiation of 785 nm for probe molecules of adsorbed Rhodamine 6G (R6G) and deposited polypyrrole (PPy) are all ca. 60 nm.

Quantitative evaluation on activated property-tunable bulk liquid water with reduced hydrogen bonds using deconvoluted raman spectroscopy

Interesting properties of water with distinguishable hydrogen-bonding structure on interfacial phase or in confined environment have drawn wide attentions. However, these unique properties of water are only found within the interfacial phase and confined environment, thus, their applications are limited. In addition, quantitative evaluation on these unique properties associating with the enhancement of waters physical and chemical activities represents a notable challenge. Here we report a practicable production of free-standing liquid water at room temperature with weak hydrogen-bonded structure naming Au nanoparticles (NPs)-treated (AuNT) water via treating by plasmon-induced hot electron transfer occurred on resonantly illuminated gold NPs (AuNPs). Compared to well-known untreated bulk water (deionized water), the prepared AuNT water exhibits many distinct activities in generally physical and chemical reactions, such as high solubilities to NaCl and O2. Also, reducing interaction energy within water molecules provides lower overpotential and higher efficiency in electrolytic hydrogen production. In addition, these enhanced catalytic activities of AuNT water are tunable by mixing with deionized water. Also, most of these tunable activities are linearly proportional to its degree of nonhydrogen-bonded structure (DNHBS), which is derived from the O-H stretching in deconvoluted Raman spectrum.

Surface-enhanced Raman scattering-active silver nanostructures with two domains.

Generally, a controllable and reproduced surface roughness for surface-enhanced Raman scattering (SERS) studies can be generated through control of the electrochemical oxidation-reduction cycles (ORC) procedure. In this work, we propose a new sonoelectrochemical approach to prepare SERS-active substrates with two domain-Ag nanostructures. The method is based on a strategy of deposition-dissolution cycles (DDCs) by using a cathodic overpotential and an anodic overpotential from open circuit potential (OCP) in turn under sonication. The prepared SERS-active substrate demonstrates large Raman scattering enhancement for adsorbed Rhodamine 6G (R6G) with an enhancement factor of 2.3×10(8) and a limit of detection of 2×10(-13)M. The improved SERS performances can be successfully explained from the viewpoints of electromagnetic (EM) and chemical (CHEM) enhancements.

Enhancements in conductivity and Raman spectroscopy of polypyrrole electropolymerized on electrochemically roughened Au substrates

In this study, gold substrates were first roughened by a triangular-wave oxidation-reduction cycle (ORC) in an aqueous solution containing 0.1 N HCl, and then polypyrrole (PPy) films were electrochemically deposited on the roughened gold substrates. In ORC treatment, Au- and Cl-containing complexes with nanostructure were formed on the surface of gold. The nanocomplexes show a catalytic electroxidation pathway for the polymerization of PPy. The characteristics of PPy deposited on this roughened Au are distinct from those of PPy deposited on the polished Au without further ORC treatment. They include the demonstration of the surface-enhanced Raman scattering effect, a higher conductivity and an increase in oxidation level of the prepared PPy.

New pathway to prepare gold nanoparticles and their applications in catalysis and surface-enhanced Raman scattering

As shown in the literature, additional energies are necessary for the reduction of positively charged noble metal ions to prepare metal nanoparticles (NPs). In this work, we report a new green pathway to prepare Au NPs in neutral 0.1M NaCl aqueous solutions from bulk Au substrates without addition of any stabilizer and reductant just via aid of natural chitosan (Ch) at room temperature. Au- and Ch-containing complexes in aqueous solution were electrochemically prepared. The role of Ch is just an intermediate to perform electron transfer with Au NPs. The stability of these prepared Au NPs is well maintained by Au NPs themselves with slightly positively charged Au remained on the surface of Au NPs. The particle size of prepared spherical Au (111) NPs is ca. 15 nm in diameter. Moreover, increasing the pH of preparation solutions can be contributive to preparing concentrated Au NPs in solutions. The prepared Au NPs are surface-enhanced Raman scattering (SERS)-active for probe molecules of Rhodamine 6G. They also demonstrate significantly catalytic activity for decomposition of acetaldehyde in rice wine.

Triggering comprehensive enhancement in oxygen evolution reaction by using newly created solvent

Theoretical calculations indicate that the properties of confined liquid water, or liquid water at surfaces, are dramatically different from those of liquid bulk water. Here we present an experimentally innovative strategy on comprehensively efficient oxygen evolution reaction (OER) utilizing plasmon-induced activated water, creating from hot electron decay at resonantly illuminated Au nanoparticles (NPs). Compared to conventional deionized (DI) water, the created water owns intrinsically reduced hydrogen-bonded structure and a higher chemical potential. The created water takes an advantage in OER because the corresponding activation energy can be effectively reduced by itself. Compared to DI water-based solutions, the OER efficiencies at Pt electrodes increased by 69.3%, 21.1% and 14.5% in created water-based acidic, neutral and alkaline electrolyte solutions, respectively. The created water was also effective for OERs in photoelectrochemically catalytic and in inert systems. In addition, the efficiency of OER increased by 47.5% in created water-based alkaline electrolyte solution prepared in situ on a roughened Au electrode. These results suggest that the created water has emerged as an innovative activator in comprehensively effective OERs.