Molecular adsorption films play a crucial role in friction reduction and wear inhibition. Despite extensive studies, the molecular behavior of these films under actual lubrication conditions has not yet been fully elucidated. This limitation arises from the fact that molecular adsorption films typically consist of only a single or a few molecular layers, requiring analytical methods with extremely high sensitivity as well as the capability for in situ measurements under sliding conditions. Such requirements are met by only a limited number of techniques. Among them, sum frequency generation (SFG) spectroscopy is particularly powerful, as it enables the acquisition of vibrational information of interfacial molecules with high sensitivity, and it allows for the analysis of molecular orientation. This review outlines recent advances in the in-situ observation of friction interfaces using SFG spectroscopy. It also presents the latest findings that enhance our understanding of interfacial molecular behavior and elucidate boundary lubrication mechanisms.

Optical waves originating from electromagnetic radiation and plasmonic waves generated in metallic nanostructures create unique force fields for manipulating matter at the nanoscale. This review describes the fundamental mechanisms of optical trapping, focusing on optical forces and thermophoresis, and summarizes trapping principles based on both optical and plasmonic waves. It then discusses how the high-efficiency trapping of nanoparticles is enabled by plasmonic optical tweezers, and how intriguing phenomena such as phase separation and droplet formation are driven by the interplay between optical forces and photothermal effects. The integration of trapping techniques with microspectroscopic methods is introduced to demonstrate the potential of single-particle spectroscopic analysis, enabling sensitive evaluation of physicochemical properties and chemical sensing within optical trapping fields. In addition, recent developments in non-plasmonic trapping using titanium nano-wrinkle structures are presented, demonstrating an emerging approach that leverages modest field enhancement and material-specific optical responses. Finally, future prospects are discussed for optical trapping technologies based on the synergistic action of optical and plasmonic waves, emphasizing how wave-driven manipulation strategies will advance analytical chemistry. These developments are expected to expand the analytical capabilities of optical tweezers, enabling new modes of nanoscale control and spectroscopic interrogation that could significantly impact the study of nanomaterials, soft matter, and biochemical systems.

Enhancing the efficiency of photoenergy conversion critically depends on controlling the wavelength of photoabsorption and improving the efficiency of photocarrier generation. This review provides an overview of recent advances in wavelength-tuning technologies using metallic nanoparticles and nanostructures, with a focus on our recent efforts. Precise control of particle size and shape enables optimization of localized surface plasmon resonance (LSPR), allowing broad-spectrum photoabsorption. Furthermore, combining LSPR with photo-harvesting effects from nanoparticle arrays or composite structures can significantly enhance energy conversion performance. In addition, plasmon-induced charge separation (PICS) offers a pathway not only to enhanced photoabsorption but also to dramatic improvements in carrier generation efficiency. This review summarizes the current status and future perspectives of nanoplasmonics applications centered on wavelength tuning and PICS, providing guidance for the development of next-generation high-efficiency photonic devices.

This review presents a systematic study on the development and functional design of plasmonic nanoparticle–photofunctional material composites based on analytical chemistry approaches. By integrating spectroscopic and electrochemical techniques, nanoscale control over the structure and interfaces of plasmonic nanoparticles was achieved, enabling quantitative analysis of light–matter interactions. Material design guidelines were established to maximize the optical antenna effect derived from localized surface plasmon resonance (LSPR) of metal nanoparticles. Based on these principles, highly sensitive optical sensing systems responsive to weak light stimuli were successfully developed, demonstrating effective signal amplification through plasmonic enhancement. In addition, plasmon-induced charge separation (PICS) at interfaces between plasmonic nanoparticles and p-type semiconductors was investigated as a novel photoresponse mechanism distinct from conventional semiconductor band-gap excitation. Systematic photoelectrochemical and spectroscopic analyses clarified the interfacial charge separation behavior and demonstrated the applicability of this mechanism to optical sensing. The concepts were further extended to hydrogen-evolving photocatalytic systems. Combined spectroscopic and electrochemical measurements provided mechanistic insights into interfacial charge transfer and reaction processes, revealing the functional roles of plasmonic nanoparticles in enhancing photocatalytic performance. Overall, the studies presented here propose new analytical and measurement strategies for efficient harvesting and conversion of weak light energy, contributing to the advancement of photofunctional materials research across environmental sensing, spectroscopic analysis, and photoenergy conversion.

The ultrasonic-induced reduction of Au(III) in the Au(III) unary aqueous solutions and in the Au(III)/TiO₂ binary aqueous suspensions was kinetically investigated. UV–vis spectral analyses reveal that Au(III) decay in the acidic binary suspensions (pH 2) during ultrasonication (430 kHz, 100 W) deviates from simple first-order kinetics and instead proceeds through two competitive pathways: (i) solution-phase reduction via radical species generated by cavitation-driven water homolysis, and (ii) surface-mediated reduction via electron transfer from TiO₂ activated by localized heating and/or sonoluminescence. A kinetic framework incorporating the Langmuir adsorption model clarifies that the relative contribution of each pathway depends on pH, resulting in markedly different overall reduction rates. These findings provide quantitative evidence that ultrasonic-induced reduction in heterogeneous systems proceeds through concurrent radical and semiconductor-mediated pathways, offering new mechanistic insight into the synergistic interplay between sonochemistry and semiconductor surface redox processes.

The phosphorus (P) concentration in Australian iron ore is predicted to increase in the future. To effectively utilize high-P Australian ores by introducing a new dephosphorization process into the existing operational process, it is necessary to analyze the chemical structure of phosphorus adsorbed goethite in iron ore, which has not been reported before. In this study, we analyzed the chemical structure of phosphorus adsorbed goethite (P-adsorbed α-(Fe,Al)OOH), in which part of the iron (Fe) in goethite is substituted with aluminum (Al), using infrared spectroscopy (IR) and quantum chemical calculations. The results showed that the chemical structure of P-adsorbed α-(Fe,Al)OOH in iron ore can be explained by monodentate (Fe,Al)PO₂(OH)₂ and (Fe,Al)PO₃OH, in addition to the monodentate FePO₂(OH)₂ and FePO₃OH reported in our previous paper. Furthermore, the binding energy of P-adsorbed α-(Fe,Al)OOH is smaller than that of P-adsorbed α-FeOOH with the same chemical structure, suggesting that P desorption from P-adsorbed α-(Fe,Al)OOH is easier. One possible reason for the smaller binding energy of P-adsorbed α-(Fe,Al)OOH is that the adsorption force of phosphate ions onto goethite may have weakened due to the substitution of Al. If the chemical structures of P-adsorbed α-FeOOH and P-adsorbed α-(Fe,Al)OOH present in Australian high-P ores can be identified by IR and quantum chemical calculations, it may be possible to optimize the dephosphorization process based on chemical structure and select ores that are useful for operation. Obtaining this information is expected to expand the use of high-P Australian ores that have not been utilized until now.

Elemental composition and distribution information derived from pigments and materials are essential for the conservation, restoration, and understanding of production techniques of pictorial materials, including ukiyo-e prints and other cultural heritage objects. However, because such materials are valuable and often fragile, analytical methods applied to them are generally required to be non-destructive. X-ray fluorescence (XRF) analysis is a non-destructive and non-contact technique that enables the acquisition of elemental information without sample preparation. In particular, micro–X-ray fluorescence (M-XRF) analysis is effective for pigment analysis in pictorial materials because it allows two-dimensional elemental imaging. In this study, elemental imaging of an ukiyo-e print depicted on the cover of a k_odan book supplement of the Yamato Shimbun was performed using M-XRF. In addition, to improve the clarity of elemental distribution maps, measurements were conducted under controlled conditions on the rear side of the sample. Furthermore, depth-selective elemental imaging of individual pages was attempted using confocal micro–X-ray fluorescence (CM-XRF) analysis. This approach enabled non-destructive acquisition of elemental distribution information from both the cover and underlying layers. The results obtained in this study suggest that the proposed methods are applicable not only to ukiyo-e materials but also to a wide range of pictorial and booklet-type cultural heritage objects for non-destructive elemental imaging.

A comparative study on trace element bulk analysis in glass was carried out, mainly focusing on Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). Approximately 20 institutions participated and more than 40 analytical results, including those from Laser Ablation Inductively Coupled Plasma Optical Emission Spectrometry (LA-ICP-OES), were reported. The test sample was alkali-free glass, and the target elements for measurement were three elements such as Ba, Sr, and Ti, which were homogeneously contained at different concentration levels. The study examined the correlation between measurement parameters and analytical results, as well as comparisons with quantitative values obtained by wet chemical analysis. For many measurement parameters, no correlation with the analytical values was confirmed, but a correlation was observed for some parameters. Additionally, a comparison of analytical results with and without the use of an internal standardization showed that applying the internal standardization tended to reduce the repeatability of analytical results for each institution, although the distribution of the results between institutions became larger. When compared with the quantitative values from wet chemical analysis, the median of the analytical results obtained without the internal standardization was slightly lower, whereas the median of the results obtained with the internal standardization showed consistency with the values obtained by wet chemical analysis. From these results, it was confirmed that the internal standardization was useful for LA-ICP-MS and LA-ICP-OES in quantitative analysis, even though it should be applied appropriately.

Simultaneous and depth-specific measurements of five anions, iodate (IO₃⁻), bromide (Br⁻), nitrite (NO₂⁻), nitrate (NO₃⁻), and iodide (I⁻) were performed at three sampling sites in Hiroshima Bay, Seto Inland Sea, using ion chromatography with ultraviolet detection (IC-UV). 1-Aminoundecyl group chemically bonded silica columns (AUS) with high anion-exchange capacities were used as separation columns. Seawater samples were filtered and then measured without dilution. Depth-specific IC (ion chromatographic) measurements of high concentrations of bromine (Br⁻), an indicator of seawater salinity, allowed us to understand the mixing of seawater and river water. Also, depth-specific IC measurements of trace amounts of inorganic iodine (IO₃⁻, I⁻) and nutrient nitrogen (NO₂⁻, NO₃⁻) were useful for understanding the dynamics of inland seawater without interference by seawater salinity. Furthermore, a good correlation was obtained between IC data by AUS and those by n-dodecylammonium coated ODS columns.