P-aminothiophenol Molecules Research Articles

Adsorbed p-Aminothiophenol Molecules on Platinum Nanoparticles Improve Electrocatalytic Hydrogen Evolution.

Electrocatalytic hydrogen evolution is an important approach to produce clean energy, and many electrocatalysts (e.g., platinum) are developed for hydrogen production. However, the electrocatalytic efficiency of commonly used metal catalysts needs to be improved to compensate their high cost. Herein, the electrocatalytic efficiency of platinum nanoparticles (PtNPs) in hydrogen evolution is largely improved via simple surface adsorption of sub-monolayer p-aminothiophenol (PATP) molecules. The overpotential goes down to 86.1mV, which is 50.2mV lower than that on naked PtNPs. This catalytic activity is even better than that of 20wt.% Pt/C, despite the much smaller active surface area of PATP-adsorbed PtNPs than Pt/C. It is theoretically and experimentally confirmed that the improved electrocatalytic activity in hydrogen evolution can be attributed to the change in electronic structure of PtNPs induced by surface adsorption of PATP molecules. More importantly, this strategy can also be used to improve the electrocatalytic activity of palladium, gold, and silver nanoparticles. Therefore, this work provides a simple, convenient, and versatile method for improving the electrocatalytic activity of metal nanocatalysts. This surface adsorption strategy may also be used for improving the efficiency of many other nanocatalysts in many reactions.

TiO2 Thickness-dependent charge transfer effect in p-aminothiophenol molecules chemisorbed on TiO2/Ni substrates

Semiconductors have been modulated in thickness to optimize their surface-enhanced Raman scattering (SERS) activity in noble metal/semiconductor SERS substrates. However, the charge transfer (CT) resonance mechanism caused by the change of the semiconductor thickness has not been fully clarified yet, due to the influence of the strong surface plasmon resonance (SPR) effect from the noble metals. Here, systems of p-aminothiophenol (PATP) molecules chemisorbed on TiO2/Ni nanopillar array films with precisely controlled TiO2 thicknesses (PATP/TiO2/Ni) were developed to systematically evaluate the TiO2 thickness-dependent CT mechanism on the premise of minimizing the SPR influence. Ultraviolet–visible, photoluminescence and X-ray photoelectron spectroscopy results demonstrated that four parts that ascribed to the SERS enhancement, photo-induced CT from Ni to TiO2, resonance excitation of TiO2, CT from TiO2 surface states to PATP molecules, and the molecular resonance of PATP molecules, are highly TiO2-thickness dependent. Hence the whole system exhibits a strong TiO2-thickness-dependent CT effect (at the two interfaces of Ni-TiO2 and TiO2-PATP) and SERS activity with a maximum SERS intensity at a TiO2 thickness of 40 nm. This work shall be valuable for future developing an optimal metal/semiconductor SERS substrates and obtaining an in-depth understanding of the semiconductor-thickness-dependent charge transfer mechanism for SERS applications.

In situ surface-enhanced Raman spectroscopy monitoring of molecular reorientation in plasmon-mediated chemical reactions

Understanding the molecular orientation is crucial for revealing the mechanism of chemical reactions. However, how to accurately monitor the molecular orientation remains a great challenge because of the motion of the molecules during the chemical reaction. Here, surface-enhanced Raman spectroscopy (SERS) was used to monitor the molecular reorientation from the plasmon-catalyzed conversion of p-aminothiophenol (PATP) to p,p'-dimercaptoazobenzene (DMAB). Spectral change due to molecular reorientation, which is often overlooked, is clearly extracted through the protonation of the PATP molecules to suppress the conversion of PATP to DMAB. Meanwhile, by monitoring the Raman features, the reaction process and molecular reorientation are simultaneously recorded, offering fresh insights on the long-standing puzzle that why the conversion to DMAB is suppressed with concentrated PATP: this is because the over-crowded PATP adsorbed on the substrate hampered its own space-taking reorientation (similar to the space-steric effect) which is a prerequisite for producing DMAB.

Plasmon-driven photocatalytic properties based on the surface of gold nanostar particles

Surface plasmon resonance (SPR) generated in gold nanoparticles can induce the conversion of p-Aminothiophenol (PATP) molecules into p,p’-dimercaptoazobenzene (DMAB) molecules by coupling reaction under the action of excitation light. Molecular detection of samples by surface enhanced Raman spectroscopy (SERS) techniques allows the study of their plasma-driven photocatalytic reaction processes. In this study, we used gold nanostars (GNS) as the substrate to study its catalytic performance and sensitivity. On this basis, catalytic substrates of gold nanospheres (GNPs) were prepared for comparison. The catalytic reactions of PATP molecules on each of the above two substrates were systematically investigated under 633 nm laser irradiation. The reduction process was subsequently observed by introducing NaBH4 solution. The results show that photocatalytic reactions can be achieved on both substrates under laser excitation at the same wavelength. However, the catalytic and reduction reaction rates on GNSs as a substrate are much faster than those of GNPs. This phenomenon may be due to the abundant nano-branched microstructures on the surface of GNSs, which will generate more and stronger local surface plasma hot spots under the irradiation of excitation light. In order to test the above hypothesis, the surface electromagnetic field distribution of two nanostructures was numerically simulated using the finite-difference time domain (FDTD) method. It is found that the star-like nanostructures not only have the same inter-particle hot spot system as the spherical nanostructures, but also have a large number of high-intensity single-particle hot spot systems arising from the abundance of branched nanostructures on their own surfaces. Compared with the spherical nanostructures, they are characterized by a dual hot spot system, which accelerates the photocatalytic reaction rate. The above experiments are of some reference significance for the in-depth study of multi-branched nanostructures and surface plasma distribution properties and their applications.

In Situ SERS Detection of Photocatalytic Degradation of Aminothiophenol on Carbon-Nanotubes/CoPt Hollow Nanoparticles Composite.

The phenol derivatives, as one kind of hormone, are analogous to endocrine disruptors with high carcinogenicity. The photocatalytic technology is an effective approach to mitigate environmental pollution by utilizing solar energy to degrade organic pollutants. In this work, CoPt hollow nanoparticles (NPs) attached to carbon nanotubes (CNTs) are employed to catalytically decompose the p-aminothiophenol (PATP) molecules under light irradiation, which is monitored by using surface-enhanced Raman scattering spectra. The effect of temperature on the catalytic efficacy of CoPt hollow NPs is investigated. Moreover, the use of CNTs coating on CoPt NPs is found to accelerate the photocatalytic degradation rate of PATP molecules, attributed to the enhanced plasmon-exciton coupling interaction of the CoPt/CNTs hybrid configuration.

Nano-scale image rendering via surface plasmon-driven reaction controlled by tip-enhanced Raman spectroscopy

Plasmon-driven selective oxidation reaction of p-aminothiophenol (PATP) to p,p′-dimercaptoazobenzene (DMAB) can be realized in a local electromagnetic field (hot spot) because of surface plasmon resonance (SPR). To a remarkable extent, the size and movement of the hot spot can be freely controlled, via tip-enhanced Raman scattering (TERS) spectroscopy. In a particular TERS system, the hot spot can move by following the TERS tip, and the PATP molecules located in the trajectory of the TERS tip, but not in other areas, can be transformed into DMAB molecules. Through this feature, we can realize artificially drawn DMAB molecular graphics on a flat surface equably covered by PATP molecules at the micronano scale using TERS. We analyzed the range and effect of the instant hot spot according to the results of simulation using the finite-difference time-domain (FDTD) method for the TERS system and surface-enhanced Raman scattering (SERS) mapping. The selectivity and controllability of catalysis in the TERS system provides a new technique for marking, with this work contributing to the field of nanotechnology by providing a new method to obtain nanoscale patterns.

In-situ monitoring reversible redox reaction and circulating detection of nitrite via an ultrasensitive magnetic Au@Ag SERS substrate

Surface plasmon-assisted catalytic reaction of p–aminothiophenol (P-ATP) to p-nitrothiophenol (P-NTP) on ultrasensitive magnetic Au@Ag nanoparticles (Fe3O4/Au@Ag NPs) has been observed by surface-enhanced Raman scattering (SERS). The as-prepared magnetic nanoparticles integrate magnetic and desired plasmonic on the same nanostructure, show great potential for simultaneous magnetic separation and SERS-based catalytic analysis. In acid media, high concentration of nitrite ion triggered the P-ATP molecules quickly transform into P-NTP on Fe3O4/Au@Ag NPs. These unique attributes enable in-situ SERS monitoring nitrite-triggered oxidation reactions of P-ATP to P-NTP and the subsequent NaBH4-drived reduction reactions of P-NTP to P-ATP on Fe3O4/Au@Ag could achieve under optimized condition. Moreover, this circulated reversible redox process could provide a circular and efficient approach to detection of nitrite ion. Considering this method without sample pretreatment and can circulate many times, indicating that it is a promising method in-situ fast detection nitrite ion.

Facile synthesis of silver nanoparticles/carbon dots for a charge transfer study and peroxidase-like catalytic monitoring by surface-enhanced Raman scattering

In this work, carbon dots (CDs) were combined with Ag nanoparticles (NPs) by a chemical reaction to form Ag NPs/CDs hybrid, which was then used as a novel surface-enhanced Raman scattering (SERS) substrate. During the synthetic process, carboxyl groups on the surface of Ag NPs were reacted with amino groups of CDs in an amidation reaction. The D and G bands of CDs in the Ag NPs/CDs hybrid could be easily detected by SERS. By employing p-aminothiophenol (PATP) molecules as SERS probes, the Ag NPs/CDs hybrid substrate could detect PATP in diluted solutions of concentration as low as 10−9M. The charge transfer (CT) effect on SERS spectra with different excitation wavelengths in the prepared Ag NPs/CDs hybrid and PATP system was also investigated. It was found that addition of CDs changes the degree of CT between Ag NPs and PATP molecules. Since the prepared Ag NPs/CDs hybrid also showed a peroxidase-like activity toward the oxidation of 3,3′,5,5′-tetramethylbenzidine using H2O2, which can provide the sensitive detection of H2O2 by SERS technique.

An Electrochemical Sensor based on p-aminothiophenol/Au Nanoparticle-Decorated HxTiS2 Nanosheets for Specific Detection of Picomolar Cu (II)

ABSTRACT An ultrasensitive electrochemical sensor for Cu 2+ detection was first developed based on p-aminothiophenol (PATP) anchored on the surface of Au nanoparticle-decorated hydrogen-incorporated TiS 2 nanosheets (PATP/Au-H x TiS 2 ). In the synthesis process, the plane edges of H x TiS 2 nanosheets offered Au nanoparticles with incubation sites for the heterogeneous nucleation and growth. On the other hand, Au nanoparticles were not only served as an excellent electrical catalyst to facilitate electron transfer and as a substrate for loading PATP molecules by Au-S valent bonds, but also could effectively avoid the aggregation of H x TiS 2 nanosheets. Due to the synergetic effects from Au-H x TiS 2 for signal amplification, the as-formed electrochemical sensor exhibited highly sensitive and selective assaying of Cu 2+ with a detection limit of 90 pM (3σ) and a linear range from 0.2 nM to 5 μM, under optimal conditions. Its specificity was ascribed to the strong coordination interaction between Cu 2+ and N atoms of imine moieties in PATP after electrochemical oxidation.

Laser-induced chemical transformation of PATP adsorbed on Ag nanoparticles by surface-enhanced Raman spectroscopy—A study of the effects from surface morphology of substrate and surface coverage of PATP

The laser induced transformation of p-aminothiophenol (PATP) to p,p′-dimercaptoazobenzene (DMAB) has attracted intensive interest recently, in which localized surface plasmon resonance (LSPR) assisted photocatalysis has been demonstrated to play an important role. In this paper, we systematically investigate the factors that influence the reaction for further understanding the mechanism using surface-enhanced Raman spectroscopy. The laser-induced formation of DMAB was found to depend on the surface coverage of PATP, the aggregation state of NPs, and the laser power. The disappearance of DMAB Raman signal at very low concentration of Ag NPs reveals that DMAB may only be formed between the neighboring NPs that can provide a suitable distance for the interaction between adsorbed PATP molecules.

Contribution of hydrogen bonding to charge-transfer induced surface-enhanced Raman scattering of an intermolecular system comprising p-aminothiophenol and benzoic acid

We investigated the influence of hydrogen bonds (H-bonds) on the intermolecular interactions of a system comprising p-aminothiophenol (PATP) and benzoic acid (BA) using surface-enhanced Raman scattering (SERS) for the first time. In this system, H-bonds form through intermolecular interactions between the -NH2 and -COOH groups and promote the charge-transfer (CT) transition from the Ag substrate to the adsorbed PATP molecules. Accordingly, the intensities of the non-totally symmetric vibrations (the b2-type bands) of PATP are influenced through the Herzberg-Teller contribution. This is clearly a BA concentration-dependent phenomenon. This behaviour can be attributed to an increase in the degree of conjugation of the system, which facilitates the CT process in the system with H-bonds. Furthermore, temperature-dependent SERS experiments and their two-dimensional (2D) correlation analysis confirmed that the formation of H-bonds facilitated the CT transition between the adsorbed molecules and substrate. The degree of CT was reduced by H-bond breakage that occurred with increasing temperature. An additional SERS experiment involving substituted BA molecules yielded similar conclusions.

Spontaneous Self-Assembly of Silver Nanoparticles into Lamellar Structured Silver Nanoleaves

Uniform lamellar silver nanoleaves (AgNLs) were spontaneously assembled from 4 nm silver nanoparticles (AgNPs) with p-aminothiophenol (PATP) as mediator under mild shaking at room temperature. The compositions of the AgNLs were verified to be ∼1 nm Ag25 nanoclusters and PATP molecules in quinonoid model. The underlying assembly mechanism was systematically investigated and a two-step reaction process was proposed. First, the 4 nm AgNPs were quickly etched to ∼1 nm Ag25 nanoclusters by PATP in the form of [Ag25(PATP)n]n+ (n<12), which were then further electrostatically or covalently interconnected by PATP to form the repeated unit cells of [Ag25(PATP)n-1](n-1)+-PATP-[Ag25(PATP)n-1](n-1)+ (abbreviated as Ag25-PATP-Ag25). Second, these Ag25-PATP-Ag25 complexes were employed as building blocks to construct lamellar AgNLs under the directions of the strong dipole-dipole interaction and the π-π stacking force between the neighboring benzene rings of PATP. Different reaction parameters including the types and concentrations of ligands, solvents, reaction temperature, ionic strength, and pH, etc., were carefully studied to confirm this mechanism. Finally, the preliminary investigations of the applications for AgNLs as "molecular junctions" and SERS properties were demonstrated. We expect that this convenient and simple method can be in principle extended to other systems, or even mixture system with different types of NPs, and will provide an important avenue for designing metamaterials and exploring their physicochemical properties.

A surface enhanced Raman spectroscopy study of aminothiophenol and aminothiophenol-C60 self-assembled monolayers: Evolution of Raman modes with experimental parameters

P-aminothiophenol (PATP) is a well-known molecule for the preparation of self-assembled monolayers on gold via its thiol functional group. After adsorption, it has been demonstrated that this molecule is anchored to gold through its thiol group, and standing nearly upright at the surface with the amino functional group on top. This molecule has been extensively studied by surface enhanced Raman spectroscopy but its exact SERS spectrum remains unclear. Here, we demonstrate that it can be strongly affected by at least two experimental parameters: laser power and layer density. Those features are discussed in terms of a dimerization of the PATP molecules. The free amino group affords the adsorption of other molecules such as C(60). In this case, a complex multilayer system is formed and the question of its precise characterisation remains a key point. In this article, we demonstrate that surface enhanced Raman spectroscopy combined with x ray photoelectron spectroscopy can bring very important information about the organization of such a self-assembled multilayer on gold. In our study, the strong evolution of Raman modes after C(60) adsorption suggests a change in the organization of aminothiophenol molecules during C(60) adsorption. These changes, also observed when the aminothiophenol layer is annealed in toluene, do not prevent the adsorption of C(60) molecules.

Controlled Synthesis of Gold Nanobelts and Nanocombs in Aqueous Mixed Surfactant Solutions

Well-defined gold nanobelts as well as unique gold nanocombs made of nanobelts were readily synthesized by the reduction of HAuCl4 with ascorbic acid in aqueous mixed solutions of the cationic surfactant cetyltrimethylammonium bromide (CTAB) and the anionic surfactant sodium dodecylsulfonate (SDSn). Single-crystalline gold nanobelts grown along the <110> and <211> directions were prepared in mixed CTAB-SDSn solutions at 4 and 27 degrees C, respectively. Furthermore, single-crystalline gold nanocombs consisting of a <110>-oriented stem nanobelt and numerous <211>-oriented nanobelts grown perpendicularly on one side of the stem were fabricated by a two-step process with temperature changing from 4 to 27 degrees C. It was proposed that the mixed cationic-anionic surfactants exerted a subtle control on the growth of gold nanocrystals in solution due to the cooperative effect of mixed surfactants. This synthetic strategy may open a new route for the mild fabrication and hierarchical assembly of metal nanobelts in solution. The obtained gold nanobelts showed good electrocatalytic activity toward the oxidation of methanol in alkaline solution; in particular, the electrode modified with the nanobelts obtained at 27 degrees C exhibited an electrocatalytic activity considerably higher than normal polycrystalline gold electrode. Moreover, the gold nanobelts were used as the surface-enhanced Raman scattering (SERS) substrate for detecting the enhanced Raman spectra of p-aminothiophenol (PATP) molecules, and the gold nanobelts obtained at 4 degrees C exhibited an unusual larger enhancement of the b2 modes relative to the a1 modes for the adsorbed PATP molecules.

Contribution of Charge‐Transfer Mechanisms to Surface‐Enhanced Raman Scattering with Near‐IR Excitation

Surface-enhanced Raman scattering under near-IR excitation is investigated for p-aminothiophenol (PATP) molecules that are either adsorbed on an electrochemically roughened silver electrode or embedded in an Au/PATP/Ag molecular junction assembled on an indium-doped tin oxide electrode. The contribution from chemical enhancement can be amplified relative to the contribution from electromagnetic enhancement, because the energy of the near-IR excitation is far from the surface plasmon resonance of the nanosized metal particles. The energy required for the charge-transfer process for the Au/PATP/Ag molecular junction is much lower than that of the PATP molecules adsorbed on the electrochemically roughened silver electrode. Coadsorption of chloride ions on the metal nanoparticles may result in an alteration of the local Fermi level of the metal nanoparticles, thus leading to better energy matching between the energy level of the interconnecting PATP molecules and the Fermi level of the metal nanoparticles.

Comparison of the Surface Properties of the Assembled Silver Nanoparticle Electrode and Roughened Silver Electrode

Surface properties of an assembled silver nanoparticle/ITO (AAgNP/ITO) electrode and an electrochemically roughened Ag electrode were studied by surface-enhanced Raman spectroscopy and electrochemical techniques. Methyl viologen (MV) and p-aminothiophenol (PATP) were used as the probing molecules. The electrochemical results show that MV can be strongly adsorbed on the surface of the roughened Ag electrode but not on the surface of the AAgNP/ITO electrode. The SERS spectra further indicate that the MV molecules are adsorbed with parallel orientation to the surface of the roughened Ag electrode. The fact that no SERS spectrum was observed on the AAgNP/ITO electrode may imply that there are no required active sites on the surface of the isolated Ag nanoparticle for the interaction between the ring plane of MV and Ag nanoparticle. On the other hand, the SERS spectra of PATP reveal that PATP molecules can be adsorbed on the surfaces of both electrodes, because of the perpendicular orientation of the adsorbed ...