Surface and interfaces play key roles in heterogeneous catalysis, electrochemistry and photo(electro)chemistry. Tip-enhanced Raman spectroscopy (TERS) combines plasmon-enhanced Raman spectroscopy ...with scanning probe microscopy to simultaneously provide a chemical fingerprint and morphological information for the sample at the nanometer spatial resolution. It is an ideal tool for achieving an in-depth understanding of the surface and interfacial processes, so that the relationship between structure and chemical performance can be established. We begin with the background of surfaces and interfaces and TERS, followed by a detailed discussion on some issues in experimental TERS, including tip preparation and TERS instrument configuration. We then focus on the progress of TERS for studying the surfaces and interfaces under different conditions, from ambient, to UHV, solid-liquid and electrochemical environments, followed by a brief introduction to the current understanding of the unprecedented high spatial resolution and surface selection rules. We conclude by discussing the future challenges for TERS practical applications in surfaces and interfaces.
TERS offers the high spatial resolution to establish structure-function correlation for surfaces and interfaces.
Abstract
Defects can induce drastic changes of the electronic properties of two-dimensional transition metal dichalcogenides and influence their applications. It is still a great challenge to ...characterize small defects and correlate their structures with properties. Here, we show that tip-enhanced Raman spectroscopy (TERS) can obtain distinctly different Raman features of edge defects in atomically thin MoS
2
, which allows us to probe their unique electronic properties and identify defect types (e.g., armchair and zigzag edges) in ambient. We observed an edge-induced Raman peak (396 cm
−1
) activated by the double resonance Raman scattering (DRRS) process and revealed electron–phonon interaction in edges. We further visualize the edge-induced band bending region by using this DRRS peak and electronic transition region using the electron density-sensitive Raman peak at 406 cm
−1
. The power of TERS demonstrated in MoS
2
can also be extended to other 2D materials, which may guide the defect engineering for desired properties.
Tip‐enhanced Raman spectroscopy can provide molecular fingerprint information with ultrahigh spatial resolution, but the tip will be easily contaminated, thus leading to artifacts. It also remains a ...great challenge to establish tip‐enhanced fluorescence because of the quenching resulting from the proximity of the metal tip. Herein, we report shell‐isolated tip‐enhanced Raman and fluorescence spectroscopies by employing ultrathin shell‐isolated tips fabricated by atomic layer deposition. Such shell‐isolated tips not only show outstanding electromagnetic field enhancement in TERS but also exclude interference by contaminants, thus greatly promoting applications in solution. Tip‐enhanced fluorescence has also been achieved using these shell‐isolated tips, with enhancement factors of up to 1.7×103, consistent with theoretical simulations. Furthermore, tip‐enhanced Raman and fluorescence signals are acquired simultaneously, and their relative intensities can be manipulated by changing the shell thickness. This work opens a new avenue for ultrahigh resolution surface analysis using plasmon‐enhanced spectroscopies.
Combined tip‐enhanced Raman and fluorescence spectroscopy using shell‐isolate tips is presented. With this method, clear and strong Raman and fluorescence signals can be obtained, and their relative intensities can be tuned by changing the shell thickness.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Excellent electroconductivity, fire resistance, and mechanical properties are several important indexes for electromagnetic shielding sealing materials. In this work, a novel functionalized graphene ...decorated with a nickel-Schiff base (rGO-Salen-Ni) was first synthesized
via
a chemical modification process, and applied in enhancing the mechanical properties, electroconductivity, and fire resistance of a thermoplastic polyurethane elastomer (TPU). The experimental result illustrated that the rGO-Salen-Ni significantly improved the above vital properties of TPU. First, the tensile strength, elongation at break, and storage modulus of the TPU containing only 1.5 wt% rGO-Salen-Ni (TPU/rGO-Salen-Ni1.5) were respectively increased by 1.50 times, 1.58 times, and 2.17 times; second, the electrical conductivity of the TPU/rGO-Salen-Ni1.5 was increased by 5 orders of magnitude in comparison with that of a pure TPU, up to 7.3 × 10
−5
S m
−1
; finally, the TPU/rGO-Salen-Ni1.5 displayed excellent flame retardancy; for instance, the peak of heat release rate, total heat release, and total smoke production were respectively decreased by 43%, 22%, and 28% compared with the corresponding values of pure TPU. The analysis of the enhancement in mechanical properties and electroconductivity of TPU/rGO-Salen-Ni revealed that the uniform dispersion of rGO-Salen-Ni, resulting from the incorporation of the nickel-Schiff base into the GO, was the leading reason for their improvements. The study on the flame-retardant mechanism demonstrated that a more continuous and compact protective layer related to the nickel-Schiff base played the key role in the excellent fire resistance of TPU/rGO-Salen-Ni. The rGO-Salen-Ni shows great potential for application in electromagnetic shielding sealing materials.
Excellent electroconductivity, fire resistance, and mechanical properties are several important indexes for electromagnetic shielding sealing materials.
Due to more extreme weather events and accelerating sea-level rise, coastal sand dunes are subjected to more frequent storm wave inundation and surge impacts, which contribute to widespread coastal ...erosion problems. In this study, two novel bio-mediated methods, microbial-induced carbonate precipitation (MICP) and enzymatic-induced carbonate precipitation (EICP), were investigated and compared for their effectiveness in mitigating sand dune erosion under wave attack. Small-scale laboratory model tests were performed on MICP-treated, EICP-treated, and untreated sand dunes at dune slope angles and two wave intensities for up to 2 h. The cross-shore profile was captured continuously during the course of the erosion test. The erosion volume above the still water level (SWL) and landward retreat distance at the SWL were calculated based on the captured bed profiles. The results show that both EICP and MICP could substantially reduce sand dune erosion at mild-to-moderate wave and dune slope conditions. However, the effectiveness of MICP treatment deteriorated at steeper dune slopes with longer period of wave attack. Under the most adverse condition (i.e., steepest dune slope, biggest wave, and longest period of wave attack), neither EICP nor MICP could effectively mitigate erosion. Fundamentally, the variable effectiveness of MICP and EICP treatment for sand dune erosion control was attributed to the spatial distribution pattern of formed calcite precipitation, which was determined by the way how EICP and MICP were applied. The calcite precipitation was relatively uniform in EICP-treated sand dunes. In MICP-treated ones, however, substantial calcite precipitation concentrated in the shallow surface layer as confirmed by the surface penetration test and SEM observation.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Abstract
Surface plasmons (SPs) of metals enable the tight focusing and strong absorption of light to realize an efficient utilization of photons at nanoscale. In particular, the SP-generated hot ...carriers have emerged as a promising way to efficiently drive photochemical and photoelectric processes under moderate conditions. In situ measuring of the transport process and spatial distribution of hot carriers in real space is crucial to efficiently capture the hot carriers. Here, we use electrochemical tip-enhanced Raman spectroscopy (EC-TERS) to in situ monitor an SP-driven decarboxylation and resolve the spatial distribution of hot carriers with a nanometer spatial resolution. The transport distance of about 20 nm for the reactive hot carriers is obtained from the TERS imaging result. The hot carriers with a higher energy have a shorter transport distance. These conclusions can be guides for the design and arrangement of reactants and devices to efficiently make use of plasmonic hot carriers.
In the past work, few study considers an effect of nanoparticle as a synergistic flame retardant on the interfacial interaction between flame retardants and polymer matrix, as well as further ...influence on the flame retardancy and mechanical properties of flame-retarding polymers. In this work, the electrostatic action was used to prepare a novel ammonium polyphosphate@layered double hydroxide (APP@LDH) in which the LDH nanoparticles accumulated at the surface of APP to achieve the highly-efficient synergistic action of LDH in thermoplastic polyurethane/APP (TPU/APP) and reduce the deterioration of APP to mechanical properties of TPU. Scanning electron microscope, etc., demonstrated that the APP@LDH was prepared successfully. Combustion tests results showed that the APP@LDH had much higher flame-retarding efficiency than the APP/LDH which was prepared through a simple physical blending process. Only 1.0 wt% LDH made the TPU pass the V-0 rating with no dripping in the UL-94 test and a limiting oxygen index (LOI) of 29.2% in the case of 7.0 wt% APP@LDH. However, the TPU/APP/LDH with 1.0 wt% LDH did not pass the V-0 rating, and a dripping behavior also existed at 7.0 wt% APP/LDH. In cone calorimeter test, the heat release and smoke production of TPU/APP@LDH were also lower than the corresponding values of TPU/APP/LDH under equal amount of LDH. The analysis of flame-retardant mechanism proved that an enhanced condensed action induced by the interfacial LDH dominated the better flame retardance of APP@LDH system than that of APP/LDH system. Another important aspect is that the mechanical properties of APP@LDH system showed remarkable improvements in comparison with those of APP/LDH system. The tensile strength of TPU with 7.0 wt% APP@LDH was 32.5% higher than that of TPU with 7.0 wt% APP/LDH under equal 1.0 wt% LDH. Meanwhile, the elongation at break for the former was maintained at 863.0%, almost equal to that of TPU. This work illustrates that the interfacial accumulation of LDH may enhance its synergistic flame-retarding efficiency and meanwhile achieve the mechanical enhancement for TPU/APP.
•Electrostatic action induced ammonium polyphosphate@layered double hydroxide.•Highly-efficient synergistic flame retardance and mechanical enhancement for TPU.•Mechanisms for the improved flame retardance and mechanical properties.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
For a long time in the practice of geotechnical engineering, soil has been viewed as an inert material, comprising only inorganic phases. However, microorganisms including bacteria, archaea and ...eukaryotes are ubiquitous in soil and have the capacity and capability to alter bio‐geochemical processes in the local soil environment. The cumulative changes could consequently modify the physical, mechanical, conductive and chemical properties of the bulk soil matrix. In recent years, the topic of bio‐mediated geotechnics has gained momentum in the scientific literature. It involves the manipulation of various bio‐geochemical soil processes to improve soil engineering performance. In particular, the process of microbial‐induced calcium carbonate precipitation (MICP) has received the most attention for its superior performance for soil improvement. The present work aims to shape a comprehensive understanding of recent developments in bio‐mediated geotechnics, with a focus on MICP. Referring to around one hundred studies published over the past five years, this review focuses on popular and alternative MICP processes, innovative raw materials and additives for MICP, emerging tools and testing methodologies for characterizing MICP at multi‐scale, and applications in emerging and/or unconventional geotechnical fields.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Phytic acid mainly exists in seeds, roots and stems of plants, which has a potential value in flame-retarding polymers due to the high content of phosphorus. In this work, a novel bio-based phytic ...acid salt PHYPI was prepared through a salt formation reaction between phytic acid and piperazine. The structure of the bio-based PHYPI was verified using 1H NMR spectrascoppy. When PHYPI was used to fabricate flame-retardant polypropylene (PP), it showed high efficiency in combustion tests. The limiting oxygen index (LOI) value for PP containing 18.0 wt% PHYPI is 25.0%, showing a 38.9% increase compared to 18.0% for PP containing no additive. Moreover, it passed the UL-94 V-0 rating in the vertical burning test, superior to the no rating for pure PP. Obviously, the flame-retarding efficiency of PHYPI is higher than that of typical traditional intumescent flame retardant containing ammonium polyphosphate or pentaerythritol. Cone calorimeter test revealed that the heat release and smoke production of PP were efficiently restrained by the presence of PHYPI. The peak of heat release rate (PHRR), total heat release (THR), and the peak of smoke release rate (PSPR) for PP containing 20 wt% PHYPI were decreased by 65.6%, 13.5%, and 32.8%, respectively, compared to the same values for PP alone. Fourier transform infrared spectroscopy (FTIR) was used to investigate the changes which accompanied the thermal degradation of the polymer containing PHYPI. Changes in the infrared spectra for the polymer undergoing degradation indicate that structures containing C=C and P-N-C were formed as a consequence of the presence of PHYPI. These transformations enhanced char formation to provide condensed phase protective action. At the same time, non-combustion volatile gases such as water and carbon dioxide may be released to dilute the fuel load in the gas phase. All evidences illustrate that PHYPI is an effective flame retardant for PP.
•A novel bio-based flame retardant named PHYPI from phytic acid.•High flame-retarding efficiency of PHYPI for polypropylene.•Flame-retardant mechanism of polypropylene/PHYPI.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In an effort to overcome issues encountered in additive flame retardants for rigid polyurethane foams (RPUFs), a novel reactive flame-retardant triol (TDHTPP) based on a triazine and phosphate ...structure was designed and synthesized. This triol was chemically incorporated in the main chains of RPUFs as a chain-extender to prepare inherently flame-retardant RPUFs. TDHTPP showed good solubility in the polyols (polyol 4110 and PEG 400) of RPUF, making it convenient for industrial fabrication, such as in spay foaming. Excellent compatibility of TDHTPP with the polymer matrix endowed flame-retardant RPUFs (FR-RPUFs) much higher compressive strength than that of the neat RPUF, and a low thermal conductivity of ∼0.03 W/(m·K). Notably, with only 5 wt% of TDHTPP incorporated, the resultant RPUF displayed a UL-94 V-0 rating and more importantly, exhibited a great persistent flame retardancy during thermal accelerated aging tests at 140 °C for 96 h. Further characterization revealed that TDHTPP possessed both vapor-phase and condensed-phase flame-retardant behaviors, in which, vapor-phase action was dominant. This work provides a facile route to synthesize RPUFs with persistent flame retardancy, excellent thermal insulation and mechanical properties.
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•A novel reactive retardant THDTPP was designed to prepare inherently flame-retardant RPUFs.•Great compatibility of TDHTPP with matrix endows FR-RPUFs with excellent thermal insulating and mechanical properties.•The persistent flame retardancy of these foams was confirmed by thermal aging tests.•These foams with excellent properties show a promising prospect in the field of building thermal insulation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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