Publications by authors named "Zhong-Qun Tian"

189 Publications

Adsorption-Induced Active Vanadium Species Facilitate Excellent Performance in Low-Temperature Catalytic NO Abatement.

J Am Chem Soc 2021 Jul 30;143(27):10454-10461. Epub 2021 Jun 30.

Center for Excellence in Regional Atmospheric Environment and Key Laboratory of Urban Pollutant Conversion, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, Fujian 361021, People's Republic of China.

Vanadia-based catalysts have been widely used for catalyzing various reactions, including their long-standing application in the deNO process. It has been commonly considered that various vanadium species dispersed on supports with a large surface area act as the catalytically active sites. However, the role of crystalline VO in selective catalytic reduction of NO with NH (NH-SCR) remains unclear. In this study, a catalyst with low vanadia loading was synthesized, in which crystalline VO was deposited on a TiO support that had been pretreated at a high temperature. Surprisingly, the catalyst, which had a large amount of crystalline VO, showed excellent low-temperature NH-SCR activity. For the first time, crystalline VO on low-vanadium-loading catalysts was found to be transformed to polymeric vanadyl species by the adsorption of NH. The generated active polymeric vanadyl species played a crucial role in NH-SCR, leading to remarkably enhanced catalytic performance at low temperatures. This new finding provides a fundamental understanding of the metal oxide-catalyzed chemical reaction and has important implications for the development and commercial applications of NH-SCR catalysts.
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http://dx.doi.org/10.1021/jacs.1c05354DOI Listing
July 2021

Improving SERS Sensitivity toward Trace Sulfonamides: The Key Role of Trade-Off Interfacial Interactions among the Target Molecules, Anions, and Cations on the SERS Active Surface.

Anal Chem 2021 06 11;93(24):8603-8612. Epub 2021 Jun 11.

State Key Laboratory of Marine Environmental Science, Fujian Provincial Key Laboratory for Coastal Ecology and Environmental Studies, Center for Marine Environmental Chemistry & Toxicology, College of the Environment and Ecology, Xiamen University, Xiamen 361102, China.

In recent years, ensuring the rational use and effective control of antibiotics has been a major focus in the eco-environment, which requires an effective monitoring method. However, on-site rapid detection of antibiotics in water environments remains a challenging issue. In this study, surface-enhanced Raman spectroscopy (SERS) was used to systematically achieve selective, rapid, and highly sensitive detection of sulfonamides, based on their fingerprint characteristics. The results show that the trade-off between the competitive and coadsorption behaviors of target molecules and agglomerates (inorganic salts) on the surface of the SERS substrate determines whether the molecules can be detected with high sensitivity. Based on this, the qualitative differentiation and quantitative detection of three structurally similar antibiotics, sulfadiazine, sulfamerazine, and sulfamethazine, were achieved, with the lowest detectable concentration being 1 μg/L for sulfadiazine and 50 μg/L for sulfamerazine and sulfamethazine.
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http://dx.doi.org/10.1021/acs.analchem.1c01530DOI Listing
June 2021

Developing a Peak Extraction and Retention (PEER) Algorithm for Improving the Temporal Resolution of Raman Spectroscopy.

Anal Chem 2021 06 10;93(24):8408-8413. Epub 2021 Jun 10.

State Key Laboratory for Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, Fujian 361005, China.

In spectroscopic analysis, push-to-the-limit sensitivity is one of the important topics, particularly when facing the qualitative and quantitative analyses of the trace target. Normally, the effective recognition and extraction of weak signals are the first key steps, for which there has been considerable effort in developing various denoising algorithms for decades. Nevertheless, the lower the signal-to-noise ratio (SNR), the greater the deviation of the peak height and shape during the denoising process. Therefore, we propose a denoising algorithm along with peak extraction and retention (PEER). First, both the first and second derivatives of the Raman spectrum are used to determine Raman peaks with a high SNR whose peak information is kept away from the denoising process. Second, an optimized window smoothing algorithm is applied to the left part of the Raman spectrum, which is combined with the untreated Raman peaks to obtain the denoised Raman spectrum. The PEER algorithm is demonstrated with much better signal extraction and retention and successfully improves the temporal resolution of Raman imaging of a living cell by at least 1 order of magnitude higher than those by traditional algorithms.
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http://dx.doi.org/10.1021/acs.analchem.0c05391DOI Listing
June 2021

[email protected] Core-Shell Nanoparticles as a SERS Substrate for Volatile Organic Compound Gas Detection.

Anal Chem 2021 May 4;93(19):7188-7195. Epub 2021 May 4.

MOE Key Laboratory of Spectrochemical Analysis and Instrumentation, State Key Laboratory of Physical Chemistry of Solid Surfaces, iChEM, College of Chemistry and Chemical Engineering, College of Energy, College of Materials, Xiamen University, Xiamen 361005, China.

Surface-enhanced Raman spectroscopy (SERS) is a promising ultrasensitive analysis technology due to outstanding molecular fingerprint identification. However, the measured molecules generally need to be adsorbed on a SERS substrate, which makes it difficult to detect weakly adsorbed molecules, for example, the volatile organic compound (VOC) molecules. Herein, we developed a kind of a SERS detection method for weak adsorption molecules with [email protected] core-shell nanoparticles (NPs). The well-uniformed single- and multicore-shell NPs can be synthesized controllably, and the shell thickness of the ZIF-8 was able to be precisely controlled (from 3 to 50 nm) to adjust the distance and electromagnetic fields between metal nanoparticles. After analyzing the chemical and physical characterization, [email protected] core-shell NPs were employed to detect VOC gas by SERS. In contrast with multicore or thicker-shell nanoparticles, [email protected] with a shell thickness of 3 nm could efficiently probe various VOC gas molecules, such as toluene, ethylbenzene, and chlorobenzene. Besides, we were capable of observing the process of toluene gas adsorption and desorption using real-time SERS technology. As observed from the experimental results, this core-shell nanostructure has a promising prospect in diverse gas detection and is expected to be applied to the specific identification of intermediates in catalytic reactions.
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http://dx.doi.org/10.1021/acs.analchem.0c05432DOI Listing
May 2021

Revealing unconventional host-guest complexation at nanostructured interface by surface-enhanced Raman spectroscopy.

Light Sci Appl 2021 Apr 19;10(1):85. Epub 2021 Apr 19.

State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, China.

Interfacial host-guest complexation offers a versatile way to functionalize nanomaterials. However, the complicated interfacial environment and trace amounts of components present at the interface make the study of interfacial complexation very difficult. Herein, taking the advantages of near-single-molecule level sensitivity and molecular fingerprint of surface-enhanced Raman spectroscopy (SERS), we reveal that a cooperative effect between cucurbit[7]uril (CB[7]) and methyl viologen (MV2I) in aggregating Au NPs originates from the cooperative adsorption of halide counter anions I, MV, and CB[7] on Au NPs surface. Moreover, similar SERS peak shifts in the control experiments using CB[n]s but with smaller cavity sizes suggested the occurrence of the same guest complexations among CB[5], CB[6], and CB[7] with MV. Hence, an unconventional exclusive complexation model is proposed between CB[7] and MV on the surface of Au NPs, distinct from the well-known 1:1 inclusion complexation model in aqueous solutions. In summary, new insights into the fundamental understanding of host-guest interactions at nanostructured interfaces were obtained by SERS, which might be useful for applications related to host-guest chemistry in engineered nanomaterials.
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http://dx.doi.org/10.1038/s41377-021-00526-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8055983PMC
April 2021

Quantification of electron accumulation at grain boundaries in perovskite polycrystalline films by correlative infrared-spectroscopic nanoimaging and Kelvin probe force microscopy.

Light Sci Appl 2021 Apr 15;10(1):84. Epub 2021 Apr 15.

State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, China.

Organic-inorganic halide perovskites are emerging materials for photovoltaic applications with certified power conversion efficiencies (PCEs) over 25%. Generally, the microstructures of the perovskite materials are critical to the performances of PCEs. However, the role of the nanometer-sized grain boundaries (GBs) that universally existing in polycrystalline perovskite films could be benign or detrimental to solar cell performance, still remains controversial. Thus, nanometer-resolved quantification of charge carrier distribution to elucidate the role of GBs is highly desirable. Here, we employ correlative infrared-spectroscopic nanoimaging by the scattering-type scanning near-field optical microscopy with 20 nm spatial resolution and Kelvin probe force microscopy to quantify the density of electrons accumulated at the GBs in perovskite polycrystalline thin films. It is found that the electron accumulations are enhanced at the GBs and the electron density is increased from 6 × 10 cm in the dark to 8 × 10 cm under 10 min illumination with 532 nm light. Our results reveal that the electron accumulations are enhanced at the GBs especially under light illumination, featuring downward band bending toward the GBs, which would assist in electron-hole separation and thus be benign to the solar cell performance. Correlative infrared-spectroscopic nanoimaging by the scattering-type scanning near-field optical microscopy and Kelvin probe force microscopy quantitatively reveal the accumulated electrons at GBs in perovskite polycrystalline thin films.
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http://dx.doi.org/10.1038/s41377-021-00524-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8050298PMC
April 2021

Nonlinear valley phonon scattering under the strong coupling regime.

Nat Mater 2021 Apr 12. Epub 2021 Apr 12.

NSF Nanoscale Science and Engineering Center, University of California, Berkeley, CA, USA.

Research efforts of cavity quantum electrodynamics have focused on the manipulation of matter hybridized with photons under the strong coupling regime. This has led to striking discoveries including polariton condensation and single-photon nonlinearity, where the phonon scattering plays a critical role. However, resolving the phonon scattering remains challenging for its non-radiative complexity. Here we demonstrate nonlinear phonon scattering in monolayer MoS that is strongly coupled to a plasmonic cavity mode. By hybridizing excitons and cavity photons, the phonon scattering is equipped with valley degree of freedom and boosted with superlinear enhancement to a stimulated regime, as revealed by Raman spectroscopy and our theoretical model. The valley polarization is drastically enhanced and sustained throughout the stimulated regime, suggesting a coherent scattering process enabled by the strong coupling. Our findings clarify the feasibility of valley-cavity-based systems for lighting, imaging, optical information processing and manipulating quantum correlations in cavity quantum electrodynamics.
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http://dx.doi.org/10.1038/s41563-021-00972-xDOI Listing
April 2021

Plasmonic nanoreactors regulating selective oxidation by energetic electrons and nanoconfined thermal fields.

Sci Adv 2021 Mar 5;7(10). Epub 2021 Mar 5.

State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), Xiamen University, Xiamen 361005, China.

Optimizing product selectivity and conversion efficiency are primary goals in catalysis. However, efficiency and selectivity are often mutually antagonistic, so that high selectivity is accompanied by low efficiency and vice versa. Also, just increasing the temperature is very unlikely to change the reaction pathway. Here, by constructing hierarchical plasmonic nanoreactors, we show that nanoconfined thermal fields and energetic electrons, a combination of attributes that coexist almost uniquely in plasmonic nanostructures, can overcome the antagonism by regulating selectivity and promoting conversion rate concurrently. For propylene partial oxidation, they drive chemical reactions by not only regulating parallel reaction pathways to selectively produce acrolein but also reducing consecutive process to inhibit the overoxidation to CO, resulting in valuable products different from thermal catalysis. This suggests a strategy to rationally use plasmonic nanostructures to optimize chemical processes, thereby achieving high yield with high selectivity at lower temperature under visible light illumination.
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http://dx.doi.org/10.1126/sciadv.abf0962DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7935359PMC
March 2021

Probing Single-Atom Catalysts and Catalytic Reaction Processes by Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy.

Angew Chem Int Ed Engl 2021 Apr 17;60(17):9306-9310. Epub 2021 Mar 17.

College of Materials, State Key Laboratory of Physical Chemistry of Solid Surfaces,iChEM, College of Chemistry and Chemical Engineering, Fujian Key Laboratory of Advanced Materials, College of Energy, Xiamen University, Xiamen, 361005, China.

Developing advanced characterization techniques for single-atom catalysts (SACs) is of great significance to identify their structural and catalytic properties. Raman spectroscopy can provide molecular structure information, and thus, the technique is a promising tool for catalysis. However, its application in SACs remains a great challenge because of its low sensitivity. We develop a highly sensitive strategy that achieves the characterization of the structure of SACs and in situ monitoring of the catalytic reaction processes on them by shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) for the first time. Using the strategy, Pd SACs on different supports were identified by Raman spectroscopy and the nucleation process of Pd species from single atoms to nanoparticles was revealed. Moreover, the catalytic reaction processes of the hydrogenation of nitro compounds on Pd SACs were monitored in situ, and molecular insights were obtained to uncover the unique catalytic properties of SACs. This work provides a new spectroscopic tool for the in situ study of SACs, especially at solid-liquid interfaces.
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http://dx.doi.org/10.1002/anie.202100198DOI Listing
April 2021

In Situ Surface-Enhanced Raman Spectroscopy Characterization of Electrocatalysis with Different Nanostructures.

Annu Rev Phys Chem 2021 Apr 20;72:331-351. Epub 2021 Jan 20.

State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, iChEM, College of Energy, Xiamen University, Xiamen 361005, China; email:

As energy demands increase, electrocatalysis serves as a vital tool in energy conversion. Elucidating electrocatalytic mechanisms using in situ spectroscopic characterization techniques can provide experimental guidance for preparing high-efficiency electrocatalysts. Surface-enhanced Raman spectroscopy (SERS) can provide rich spectral information for ultratrace surface species and is extremely well suited to studying their activity. To improve the material and morphological universalities, researchers have employed different kinds of nanostructures that have played important roles in the development of SERS technologies. Different strategies, such as so-called borrowing enhancement from shell-isolated modes and shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS)-satellite structures, have been proposed to obtain highly effective Raman enhancement, and these methods make it possible to apply SERS to various electrocatalytic systems. Here, we discuss the development of SERS technology, focusing on its applications in different electrocatalytic reactions (such as oxygen reduction reactions) and at different nanostructure surfaces, and give a brief outlook on its development.
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http://dx.doi.org/10.1146/annurev-physchem-090519-034645DOI Listing
April 2021

Molecular Insight of the Critical Role of Ni in Pt-Based Nanocatalysts for Improving the Oxygen Reduction Reaction Probed Using an SERS Borrowing Strategy.

J Am Chem Soc 2021 Jan 15;143(3):1318-1322. Epub 2021 Jan 15.

College of Energy, State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, College of Materials, iChEM, Xiamen University, Xiamen 361005, China.

PtNi alloy catalysts have excellent catalytic activity and are considered some of the most promising electrocatalysts capable of replacing pure Pt for the oxygen reduction reaction (ORR). For PtNi alloys, Ni-doping can improve performance by changing the electronic and structural properties of the catalyst surface and its interaction with reaction intermediates. However, to date there is no direct spectral evidence detecting or identifying the effect of Ni on the ORR in PtNi alloy catalysts. Herein, we introduce a surface-enhanced Raman spectroscopic (SERS) "borrowing" strategy for investigating ORR processes catalyzed by [email protected] nanoparticles (NPs). The bond vibration of adsorbed peroxide intermediate species (*OOH) was obtained, and the effect of Ni on the interaction between surface Pt and *OOH was studied by varying the Ni content in the alloy. The frequency of the *OOH spectral band has an obvious red-shift with increasing Ni content. Combined with density functional theory (DFT) calculations, we show that Ni-doping can optimize *OOH surface binding on the Pt surface, achieving more efficient electron transfer, thus improving the ORR rate. Notably, these results evidence the SERS borrowing strategy as an effective technique for observations of catalytic processes.
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http://dx.doi.org/10.1021/jacs.0c12755DOI Listing
January 2021

Spectroscopic Verification of Adsorbed Hydroxy Intermediates in the Bifunctional Mechanism of the Hydrogen Oxidation Reaction.

Angew Chem Int Ed Engl 2021 Mar 29;60(11):5708-5711. Epub 2021 Jan 29.

State Key Laboratory of Physical Chemistry of Solid Surfaces,iChEM, College of Chemistry and Chemical Engineering, College of Energy, Xiamen University, Xiamen, 361005, China.

Elucidating hydrogen oxidation reaction (HOR) mechanisms in alkaline conditions is vital for understanding and improving the efficiency of anion-exchange-membrane fuel cells. However, uncertainty remains around the alkaline HOR mechanism owing to a lack of direct in situ evidence of intermediates. In this study, in situ electrochemical surface-enhanced Raman spectroscopy (SERS) and DFT were used to study HOR processes on PtNi alloy and Pt surfaces, respectively. Spectroscopic evidence indicates that adsorbed hydroxy species (OH ) were directly involved in HOR processes in alkaline conditions on the PtNi alloy surface. However, OH species were not observed on the Pt surface during the HOR. We show that Ni doping promoted hydroxy adsorption on the platinum-alloy catalytic surface, improving the HOR activity. DFT calculations also suggest that the free energy was decreased by hydroxy adsorption. Consequently, tuning OH adsorption by designing bifunctional catalysts is an efficient method for promoting HOR activity.
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http://dx.doi.org/10.1002/anie.202015571DOI Listing
March 2021

Plasmonic Hot Electron-Mediated Hydrodehalogenation Kinetics on Nanostructured Ag Electrodes.

J Am Chem Soc 2020 Oct 30;142(41):17489-17498. Epub 2020 Sep 30.

State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), Xiamen University, Xiamen 361005, China.

An attractive field of plasmon-mediated chemical reactions (PMCRs) is developing rapidly, but there is still incomplete understanding of how to control the kinetics of such a reaction related to hot carriers. Here, we chose 8-bromoadenine (8BrAd) as a probe molecule of hot electrons to investigate the influence of the electrode potential, laser wavelength, and power on the PMCR kinetics on silver nanoparticle-modified silver electrodes. Plasmonic hot electron-mediated cleavage of the C-Br bond in 8BrAd has been investigated by combining in situ electrochemical surface-enhanced Raman spectroscopy and density functional theory calculations. The experimental and theoretical results reveal that the energy position of plasmon relaxation-generated hot electrons can be modulated conveniently by applied potentials and laser light. This allows the proposal of a mechanism of modulating the matching energy of the hot electron of plasmon relaxation to promote the efficiency of PMCRs in electrochemical interfaces. Our work will be helpful to design surface plasmon resonance photoelectrochemical reactions on metal electrode surfaces of nanostructures with higher efficiency.
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http://dx.doi.org/10.1021/jacs.0c07027DOI Listing
October 2020

In Situ Raman Study of CO Electrooxidation on Pt(hkl) Single-Crystal Surfaces in Acidic Solution.

Angew Chem Int Ed Engl 2020 Dec 25;59(52):23554-23558. Epub 2020 Oct 25.

College of Energy, State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, College of Environment and Ecology, State key Laboratory of Marine Environmental Science, iChEM, Xiamen University, Xiamen, 361005, China.

The adsorption and electrooxidation of CO molecules at well-defined Pt(hkl) single-crystal electrode surfaces is a key step towards addressing catalyst poisoning mechanisms in fuel cells. Herein, we employed in situ electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) coupled with theoretical calculation to investigate CO electrooxidation on Pt(hkl) surfaces in acidic solution. We obtained the Raman signal of top- and bridge-site adsorbed CO* molecules on Pt(111) and Pt(100). In contrast, on Pt(110) surfaces only top-site adsorbed CO* was detected during the entire electrooxidation process. Direct spectroscopic evidence for OH* and COOH* species forming on Pt(100) and Pt(111) surfaces was afforded and confirmed subsequently via isotope substitution experiments and DFT calculations. In summary, the formation and adsorption of OH* and COOH* species plays a vital role in expediting the electrooxidation process, which relates with the pre-oxidation peak of CO electrooxidation. This work deepens knowledge of the CO electrooxidation process and provides new perspectives for the design of anti-poisoning and highly effective catalysts.
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http://dx.doi.org/10.1002/anie.202010431DOI Listing
December 2020

Polarization- and Wavelength-Dependent Shell-Isolated-Nanoparticle-Enhanced Sum-Frequency Generation with High Sensitivity.

Phys Rev Lett 2020 Jul;125(4):047401

State Key Laboratory of Physical Chemistry of Solid Surfaces, MOE Key Laboratory of Spectrochemical Analysis and Instrumentation, College of Chemistry and Chemical Engineering, College of Energy, Xiamen University, Xiamen 361005, China.

Sum-frequency generation (SFG) spectroscopy is a highly versatile tool for surface analysis. Improving the SFG intensity per molecule is important for observing low concentrations of surface species and intermediates in dynamic systems. Herein, Shell-Isolated-Nanoparticle-Enhanced SFG (SHINE-SFG) was used to probe a model substrate. The model substrate, p-mercaptobenzonitrile adsorbed on a Au film with SHINs deposited on top, provided an enhancement factor of up to 10^{5}. Through wavelength- and polarization-dependent SHINE-SFG spectroscopy, the majority of the signal enhancement was found to come from both plasmon enhanced emission and chemical enhancement mechanisms. A new enhancement regime, i.e., the nonlinear coupling of SHINE-SFG with difference frequency generation, was also identified. This novel mechanism provides insight into the enhancement of nonlinear coherent spectroscopies and a possible strategy for the rational design of enhancing substrates utilizing coupling processes.
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http://dx.doi.org/10.1103/PhysRevLett.125.047401DOI Listing
July 2020

Electroreduction Reaction Mechanism of Carbon Dioxide to C Products via Cu/Au Bimetallic Catalysis: A Theoretical Prediction.

J Phys Chem Lett 2020 Aug 3;11(16):6593-6599. Epub 2020 Aug 3.

State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.

Understanding the bimetallic interfacial effects on the catalytic CO reduction reaction (CORR) is an important and challenging issue. Herein, the geometric structure, electronic structure, and electrocatalytic property of Cu(submonolayer)/Au bimetallic interfaces are investigated by using density functional theory calculation. The results predict that the expansion of the Cu lattice can significantly modulate the CORR performance, the Cu(submonolayer)/Au interface has good surface activity promoting the reduction of CO to C compounds, and the final products of CORR on Cu/Au(111) and Cu/Au(100) surfaces are ethanol and a mixture of ethanol and ethylene, respectively. Furthermore, with regard to surface coverage and adsorption energy being two essential parameters for CORR, we demonstrate that the reaction of *CO and *CHO is the key process for obtaining the C products on the Cu/Au interface. This study offers a useful strategy for improving the surface activity and selectivity for CORR.
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http://dx.doi.org/10.1021/acs.jpclett.0c01970DOI Listing
August 2020

Observation of inhomogeneous plasmonic field distribution in a nanocavity.

Nat Nanotechnol 2020 11 10;15(11):922-926. Epub 2020 Aug 10.

College of Energy, State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, College of Chemistry and Chemical Engineering, College of Energy, College of Materials, Xiamen University, Xiamen, China.

The progress of plasmon-based technologies relies on an understanding of the properties of the enhanced electromagnetic fields generated by the coupling nanostrucutres. Plasmon-enhanced applications include advanced spectroscopies, optomechanics, optomagnetics and biosensing. However, precise determination of plasmon field intensity distribution within a nanogap remains challenging. Here, we demonstrate a molecular ruler made from a set of viologen-based, self-assembly monolayers with which we precisely measures field distribution within a plasmon nanocavity with ~2-Å spatial resolution. We observed an unusually large plasmon field intensity inhomogeneity that we attribute to the formation of a plasmonic comb in the nanocavity. As a consequence, we posit that the generally adopted continuous media approximation for molecular monolayers should be used carefully.
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http://dx.doi.org/10.1038/s41565-020-0753-yDOI Listing
November 2020

Direct Nanomachining on Semiconductor Wafer By Scanning Electrochemical Microscopy.

Angew Chem Int Ed Engl 2020 Nov 9;59(47):21129-21134. Epub 2020 Sep 9.

State Key Laboratory of Physical Chemistry of Solid Surfaces (PCOSS), Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), Engineering Research Center of Electrochemical Technologies of Ministry of Education, Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, China.

Scanning electrochemical microscopy (SECM) is one of the most important instrumental methods of modern electrochemistry due to its high spatial and temporal resolution. We introduced SECM into nanomachining by feeding the electrochemical modulations of the tip electrode back to the positioning system, and we demonstrated that SECM is a versatile nanomachining technique on semiconductor wafers using electrochemically induced chemical etching. The removal profile was correlated to the applied tip current when the tip was held stationary and when it was moving slowly (<20 μm s ), and it followed Faraday's law. Both regular and irregular nanopatterns were translated into a spatially distributed current by the homemade digitally controlled SECM instrument. The desired nanopatterns were "sculpted" directly on a semiconductor wafer by SECM direct-writing mode. The machining accuracy was controlled to the sub-micrometer and even nanometer scales. This advance is expected to play an important role in electrochemical nanomachining for 3D micro/nanostructures in the semiconductor industry.
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http://dx.doi.org/10.1002/anie.202008697DOI Listing
November 2020

Real-time detection of single-molecule reaction by plasmon-enhanced spectroscopy.

Sci Adv 2020 Jun 10;6(24):eaba6012. Epub 2020 Jun 10.

State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), College of Materials, College of Energy, Department of Physics, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.

Determining structural transformations of single molecules (SMs) is an important fundamental scientific endeavor. Optical spectroscopies are the dominant tools used to unravel the physical and chemical features of individual molecules and have substantially contributed to surface science and biotechnology. In particular, Raman spectroscopy can identify reaction intermediates and reveal underlying reaction mechanisms; however, SM Raman experiments are subject to intrinsically weak signal intensities and considerable signal attenuation within the spectral dispersion systems of the spectrometer. Here, to monitor the structural transformation of an SM on the millisecond time scale, a plasmonic nanocavity substrate has been used to enable Raman vibrational and fluorescence spectral signals to be simultaneously collected and correlated, which thus allows a detection of photo-induced bond cleavage between the xanthene and phenyl group of a single rhodamine B isothiocyanate molecule in real time. This technique provides a novel method for investigating light-matter interactions and chemical reactions at the SM level.
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http://dx.doi.org/10.1126/sciadv.aba6012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7286666PMC
June 2020

Probing Electric Field Distributions in the Double Layer of a Single-Crystal Electrode with Angstrom Spatial Resolution using Raman Spectroscopy.

J Am Chem Soc 2020 Jul 23;142(27):11698-11702. Epub 2020 Jun 23.

State Key Laboratory of Physical Chemistry of Solid Surfaces, iChEM, College of Chemistry and Chemical Engineering, College of Energy, Xiamen University, Xiamen 361005, China.

The electrical double layer (EDL) is the extremely important interfacial region involved in many electrochemical reactions, and it is the subject of significant study in electrochemistry and surface science. However, the direct measurement of interfacial electric fields in the EDL is challenging. In this work, both electrochemical resonant Raman spectroscopy and theoretical calculations were used to study electric field distributions in the EDL of an atomically flat single-crystal Au(111) electrode with self-assembled monolayer molecular films. This was achieved using a series of redox-active molecules containing the 4,4'-bipyridinium moiety as a Raman marker that were located at different precisely controlled distances away from the electrode surface. It was found that the electric field and the dipole moment of the probe molecule both directly affected its Raman signal intensity, which in turn could be used to map the electric field distribution at the interface. Also, by variation of the electrolyte anion concentration, the Raman intensity was found to decrease when the electric field strength increased. Moreover, the distance between adjacent Raman markers was ∼2.1 Å. Thus, angstrom-level spatial resolution in the mapping of electric field distributions at the electrode-electrolyte interface was realized. These results directly evidence the EDL structure, bridging the gap between the theoretical and experimental understandings of the interface.
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http://dx.doi.org/10.1021/jacs.0c05162DOI Listing
July 2020

Determining the Interfacial Refractive Index via Ultrasensitive Plasmonic Sensors.

J Am Chem Soc 2020 06 11;142(25):10905-10909. Epub 2020 Jun 11.

State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), Xiamen University, Xiamen 361005, China.

Plasmonic sensors are promising for ultrasensitive chemical and biological analysis. However, there are increasing experimental findings that cannot be well addressed by theoretical calculations, including the nonlinear dependence of the plasmonic peak wavelength on the refractive index (RI) and the ultrahigh sensitivity beyond the theoretical limit. The gap between experiments and theoretical calculations is that the bulk RI (BRI) used for calculation could be different from the interfacial RI (IRI) determining the electromagnetic response as a result of the interaction of molecules with the surface. But there is still no method to determine the IRI. Herein, we quantitatively determine the IRI by disentangling the surface RI (SRI) from the BRI. The obtained IRI can be directly applied in theoretical calculations to reliably reflect the experimental response and rigorously guide the design of plasmonic sensors. Moreover, it can be a fundamental dimensionless number to describe the light-matter interaction at the interface.
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http://dx.doi.org/10.1021/jacs.0c01907DOI Listing
June 2020

Enhancing Catalytic Activity and Selectivity by Plasmon-Induced Hot Carriers.

iScience 2020 May 27;23(5):101107. Epub 2020 Apr 27.

MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, The Key Lab of Low-carbon Chem & Energy Conservation of Guangdong Province, School of Chemistry, Sun Yat-Sen University, Guangzhou 510275, China. Electronic address:

Plasmon-assisted chemical transformation holds great potential for solar energy conversion. However, simultaneous enhancement of reactivity and selectivity is still challenging and the mechanism remains mysterious. Herein, we elucidate the localized surface plasmon resonance (LSPR)-induced principles underlying the enhanced activity (∼70%) and selectivity of photoelectrocatalytic redox of nitrobenzene (NB) on Au nanoparticles. Hot carriers selectively accelerate the conversion rate from NB to phenylhydroxylamine (PHA) by ∼14% but suppress the transformation rate from PHA to nitrosobenzene (NSB) by ∼13%. By adding an electron accepter, the as-observed suppression ratio is substantially enlarged up to 43%. Our experiments, supported by in situ surface-enhanced Raman spectroscopy and density functional theory simulations, reveal such particular hot-carrier-induced selectivity is conjointly contributed by the accelerated hot electron transfer and the corresponding residual hot holes. This work will help expand the applications of renewable sunlight in the directional production of value-added chemicals under mild conditions.
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http://dx.doi.org/10.1016/j.isci.2020.101107DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7225730PMC
May 2020

Revisiting the Atomistic Structures at the Interface of Au(111) Electrode-Sulfuric Acid Solution.

J Am Chem Soc 2020 May 11;142(20):9439-9446. Epub 2020 May 11.

State Key Laboratory of Physical Chemistry of Solid Surfaces (PCOSS), Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.

Knowledge of atomistic structures at solid/liquid interfaces is essential to elucidate interfacial processes in chemistry, physics, and materials sciences. The (√3 × √7) structure associated with a pair of sharp reversible current spikes in the cyclic voltammogram on a Au(111) electrode in sulfuric acid solution represents one of the most classical ordered structures at electrode/electrolyte interfaces. Although more than 10 adsorption configurations have been proposed in the past four decades, the atomistic structure remains ambiguous and is consequently an open problem in electrochemistry and surface science. Herein, by combining high-resolution electrochemical scanning tuning microscopy, electrochemical infrared and Raman spectroscopies, and, in particular, the newly developed quantitative computational method for electrochemical infrared and Raman spectra, we unambiguously reveal that the adstructure is Au(111)(√3 × √7)-(SO···w) with a sulfate anion (SO*) and two structured water molecules (w*) in a unit cell, and the crisscrossed [w···SO···w] and [w···w···] hydrogen-bonding network comprises the symmetric adstructure. We further elucidate that the electrostatic potential energy dictates the proton affinity of sulfate anions, leading to the potential-tuned structural transformations. Our work enlightens the structural details of the inner Helmholtz plane and thus advances our fundamental understanding of the processes at electrochemical interfaces.
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http://dx.doi.org/10.1021/jacs.0c02639DOI Listing
May 2020

Shell-Isolated Nanoparticle-Enhanced Luminescence of Metallic Nanoclusters.

Anal Chem 2020 05 28;92(10):7146-7153. Epub 2020 Apr 28.

College of Chemistry and Chemical Engineering, State Key Laboratory of Physical Chemistry of Solid Surfaces, iChEM, College of Energy, Department of Physics, Xiamen University, Xiamen 361005, China.

Metallic nanoclusters (NCs) have molecular-like structures and unique physical and chemical properties, making them an interesting new class of luminescent nanomaterials with various applications in chemical sensing, bioimaging, optoelectronics, light-emitting diodes (LEDs), etc. However, weak photoluminescence (PL) limits the practical applications of NCs. Herein, an effective and facile strategy of enhancing the PL of NCs was developed using Ag shell-isolated nanoparticle (Ag SHIN)-enhanced luminescence platforms with tuned SHINs shell thicknesses. 3D-FDTD theoretical calculations along with femtosecond transient absorption and fluorescence decay measurements were performed to elucidate the enhancement mechanisms. Maximum enhancements of up to 231-fold for the [AuAg(C≡CBu)] cluster and 126-fold for DNA-templated Ag NCs (DNA-Ag NCs) were achieved. We evidenced a novel and versatile method of achieving large PL enhancements with NCs with potential for practical biosensing applications for identifying target DNA in ultrasensitive surface analysis.
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http://dx.doi.org/10.1021/acs.analchem.0c00600DOI Listing
May 2020

Raman study of the photoinduced behavior of dye molecules on TiO() single crystal surfaces.

Chem Sci 2020 Apr 17;11(25):6431-6435. Epub 2020 Apr 17.

Department of Physics, State Key Laboratory of Physical Chemistry of Solid Surfaces, iChEM, College of Chemistry and Chemical Engineering, College of Energy, College of Materials, Xiamen University Xiamen 361005 China

In dye-sensitized solar cells (DSSCs), the TiO/dye interface significantly affects photovoltaic performance. However, the adsorption and photoinduced behavior of dye molecules on the TiO substrate remains unclear. Herein, shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) was used to study the adsorption and photoinduced behavior of dye (N719) molecules on different TiO() surfaces. On TiO(001) and TiO(110) surfaces, the SHINERS and mass spectrometry results indicate S[double bond, length as m-dash]C bond cleavage in the anchoring groups of adsorbed N719, whereas negligible bond cleavage occurs on the TiO(111) surface. Furthermore, DFT calculations show the stability of the S[double bond, length as m-dash]C anchoring group on three TiO() surfaces in the order TiO(001) < TiO(110) < TiO(111), which correlated well with the observed photocatalytic activities. This work reveals the photoactivity of different TiO() surface structures and can help with the rational design of DSSCs. Thus, this strategy can be applied to real-time probing of photoinduced processes on semiconductor single crystal surfaces.
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http://dx.doi.org/10.1039/d0sc00588fDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8159273PMC
April 2020

Microphotoelectrochemical Surface-Enhanced Raman Spectroscopy: Toward Bridging Hot-Electron Transfer with a Molecular Reaction.

J Am Chem Soc 2020 May 27;142(18):8483-8489. Epub 2020 Apr 27.

The State Key Laboratory of Physical Chemistry of Solid Surfaces, iChEM, Department of Chemistry, College of Chemistry & Chemical Engineering, Xiamen University, Xiamen 361005, China.

The rational design and applications of plasmon-mediated chemical reactions (PMCRs) are fundamentally determined by an understanding of photon-electron-molecule interactions. However, the current understanding of the PMCR of plasmon-decayed hot electron-mediated reactions remains implicit, since there has not been a single measurement of both hot-electron transfer and molecular transformation following photon excitation. Therefore, we invented a method called microphotoelectrochemical surface-enhanced Raman spectroscopy (μPEC-SERS) that uses an ultramicroelectrode (UME) whose dimensions match those of the focused laser spot. This system can simultaneously record the photocurrent (∼picoamps) of hot-electron transfer with a high signal-to-noise ratio and the SERS spectra of a molecular reaction in the same electrode area. The responses of the photocurrent and SERS spectra to laser illumination can correlate the surface reaction activated by hot electrons with the SERS spectral changes. A typical PMCR of -aminothiophenol (PATP) on a Ag UME was used to illustrate that the correlation of the photocurrent with the spectral changes is capable of revealing the reaction mechanism in terms of the formation of activated oxygenated species. The laser power-, laser wavelength-, and surface roughness-dependent photocurrents link the formation of activated oxygenated species to the hot-electron transfer. Further comparisons of the photocurrent with the conventional electrochemical current of the oxygen reduction reaction indicate that the activated oxygenated species are oxidative in transforming PATP to ,'-dimercaptoazobenzene, which is supported by a density functional theory (DFT) calculation. Therefore, μPEC-SERS could be a powerful tool for investigating PMCRs and other systems involving photon-electron-molecule interactions.
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http://dx.doi.org/10.1021/jacs.0c02523DOI Listing
May 2020

[email protected] Core-Shell Heterostructure as SERS Platform to Reveal the Hydrogen Evolution Active Sites of Single-Layer MoS.

J Am Chem Soc 2020 Apr 3;142(15):7161-7167. Epub 2020 Apr 3.

Department of Chemistry, City University of Hong Kong, Hong Kong, China.

Understanding the reaction mechanism for the catalytic process is essential to the rational design and synthesis of highly efficient catalysts. MoS has been reported to be an efficient catalyst toward the electrochemical hydrogen evolution reaction (HER), but it still lacks direct experimental evidence to reveal the mechanism for MoS-catalyzed electrochemical HER process at the atomic level. In this work, we develop a wet-chemical synthetic method to prepare the single-layer MoS-coated polyhedral Ag core-shell heterostructure ([email protected]) with tunable sizes as efficient catalysts for the electrochemical HER. The [email protected] core-shell heterostructures are used as ideal platforms for the real-time surface-enhanced Raman spectroscopy (SERS) study owing to the strong electromagnetic field generated in the plasmonic Ag core. The in situ SERS results provide solid Raman spectroscopic evidence proving the S-H bonding formation on the MoS surface during the HER process, suggesting that the S atom of MoS is the catalytic active site for the electrochemical HER. It paves the way on the design and synthesis of heterostructures for exploring their catalytic mechanism at atomic level based on the in situ SERS measurement.
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http://dx.doi.org/10.1021/jacs.0c01649DOI Listing
April 2020

Photosynergetic Electrochemical Synthesis of Graphene Oxide.

J Am Chem Soc 2020 Apr 30;142(14):6516-6520. Epub 2020 Mar 30.

State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, Engineering Research Center of Electrochemical Technologies of Ministry of Education, Department of Chemistry, College of Chemistry and Chemical Engineering; Department of Mechanical and Electrical Engineering, School of Aerospace Engineering; and Graphene Industry and Engineering Research Institute, Xiamen University, Xiamen 361005, China.

Here we propose a strategy of radical oxidation reaction for the high-efficiency production of graphene oxide (GO). GO plays important roles in the sustainable development of energy and the environment, taking advantages of oxygen-containing functional groups for good dispersibility and assembly. Compared with Hummers' method, electrochemical exfoliation of graphite is considered facile and green, although the oxidation is fairly low. To synthesize GO with better crystallinity and higher oxidation degree, we present a photosynergetic electrochemical method. By using oxalate anions as the intercalation ions and co-reactant, the interfacial concentration of hydroxyl radicals generated during electrochemical exfoliation was promoted, and the oxidation degree was comparable with that of GO prepared by Hummers' method. In addition, the crystallinity was improved with fewer layers and larger size. Moreover, the aniline coassembled GO membrane was selectively permeable to water molecules by the hydrogen-bond interaction, but it was impermeable to Na, K, and Mg, due to the electrostatic interactions. Thus, it has a prospective application to water desalination and purification. This work opens a novel approach to the direct functionalization of graphene during the electroexfoliation processes and to the subsequent assembly of the functionalized graphene.
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http://dx.doi.org/10.1021/jacs.0c02158DOI Listing
April 2020

In Situ Raman Monitoring and Manipulating of Interfacial Hydrogen Spillover by Precise Fabrication of Au/TiO /Pt Sandwich Structures.

Angew Chem Int Ed Engl 2020 Jun 15;59(26):10343-10347. Epub 2020 Apr 15.

State Key Laboratory of Physical Chemistry of Solid Surfaces,iChEM, College of Chemistry and Chemical Engineering, Fujian Key Laboratory of Advanced Materials, College of Materials, College of Energy, Xiamen University, Xiamen, 361005, China.

The spillover of hydrogen species and its role in tuning the activity and selectivity in catalytic hydrogenation have been investigated in situ using surface-enhanced Raman spectroscopy (SERS) with 10 nm spatial resolution through the precise fabrication of Au/TiO /Pt sandwich nanostructures. In situ SERS study reveals that hydrogen species can efficiently spillover at Pt-TiO -Au interfaces, and the ultimate spillover distance on TiO is about 50 nm. Combining kinetic isotope experiments and density functional theory calculations, it is found that the hydrogen spillover proceeds via the water-assisted cleavage and formation of surface hydrogen-oxygen bond. More importantly, the selectivity in the hydrogenation of the nitro or isocyanide group is manipulated by controlling the hydrogen spillover. This work provides molecular insights to deepen the understanding of hydrogen activation and boosts the design of active and selective catalysts for hydrogenation.
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http://dx.doi.org/10.1002/anie.202000426DOI Listing
June 2020

Unveiling the size effect of Pt-on-Au nanostructures on CO and methanol electrooxidation by in situ electrochemical SERS.

Nanoscale 2020 Mar 24;12(9):5341-5346. Epub 2020 Feb 24.

Ministry of Education Key Laboratory for Analytical Science of Food Safety and Biology, Fujian Provincial Key Laboratory of Analysis and Detection Technology for Food Safety, College of Chemistry, Fuzhou University, Fuzhou, Fujian 350108, China.

In situ monitoring of electrocatalytic processes at solid-liquid interfaces is essential for the fundamental understanding of reaction mechanisms, yet quite challenging. Herein, Pt-on-Au nanocatalysts with a Au-core Pt-satellite superstructure have been fabricated. In such Pt-on-Au nanocatalysts, the Au cores can greatly amplify the Raman signals of the species adsorbed on Pt, allowing the in situ surface-enhanced Raman spectroscopy (SERS) study of the electrocatalytic reactions on Pt. Using the combination of an electrochemical method and in situ SERS, size effects of Pt on the catalytic performance of the core-satellite nanocomposites towards CO and methanol electrooxidation are revealed. It is found that such Pt-on-Au nanocomposites show improved activity and long-term stability for the electrooxidation of CO and methanol with a decrease in the Pt size. This work demonstrates an effective strategy to achieve the in situ monitoring of electrocatalytic processes and to simultaneously boost their catalytic performance towards electrooxidation.
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http://dx.doi.org/10.1039/c9nr10304jDOI Listing
March 2020
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