Imaging XPS Research Articles

Highly Efficient Dopamine Sensing with Carbon Nanotube Encapsulated Metal Chalcogenide Nanostructure

Carbon nanotube encapsulated nickel selenide composite nanostructures were used as a non-enzymatic electrochemical sensor for dopamine detection. These composite nanostructures were synthesized through a simple, one-step, and environmentally friendly chemical vapor deposition method, wherein the CNTs were formed in situ from pyrolysis of carbon-rich metallo-organic precursor. The composition and morphology of these NiSe2 filled hybrid nanostructures were confirmed by powder X-ray diffraction, Raman, XPS, and HRTEM images. Electrochemical tests demonstrated that the as-synthesized nanostructures exhibited outstanding electrocatalytic performance toward dopamine oxidation, with a high sensitivity of 19.62 μA μM−1 cm−2, low detection limit, broad linear range of (5 nM – 640 μM), and high selectivity. The synergistic effects of enhanced electrochemical activity of nickel selenide along with enhanced conductivity of carbon nanotubes leads to the high efficiency for these nanostructured composites. The high sensitivity and selectivity of this nano-structured composite could be exploited to develop simple, selective, and sensitive electrochemical sensor to detect and quantify dopamine in human tear samples with high reliability. This nanotube encapsulated sensor hence paves the way for new discoveries in the development of novel dopamine sensors with low cost and high stability than can be used for non-invasive dopamine detection in peripheral fluids.

Green synthesis of nanostructured 1T/2H-MoS2 hybrid phase with polyol solvents and microwave heating

Green synthesis approaches have attracted greatly of attention in recent years since they address the issues associated with sustainability than conventional synthesis methods. New research fields in green nanoscience are being developed as a result of the incorporation of green chemistry principles into nanoscience. In this paper, the successful microwave-assisted green synthesis of MoS2 nanoparticles in a single pot using polyol solvents such as ethylene glycol and glycerol is demonstrated. The coexistence of 1T and 2H phases in MoS2 nanomaterials was determined using advanced techniques such as XRD, Raman, XPS, and TEM images. The highest 1T proportion obtained was 84.5% when compared to the 2H phase. The reaction mechanism and the phase transition between 1T and 2H were described and illustrated. The role of polyol solvents in the practical synthesis of nano MoS2 under microwave heating is also evaluated and explained. Due to the ability of the metallic 1T phase to enhance electrical conductivity, it is believed that hybrid nanostructures exhibit superior electrochemical performance for energy storage and conversion applications.

Cycloaddition of natural epoxide and CO2 with the help of multi-nuclear phthalocyanine complexes attached to FPS as a nanosaramic

This study introduces a three-dimensional, densely packed amide polyphthalocyaninezinc, supported by fibrous phosphosilicate (FPS), for the first time (referred to as Complex@Zn-IL/FPS). The XPS and EDX images confirmed that the Complex@Zn-IL nanosaramic was evenly distributed on the FPS’s surface. The cycloaddition reaction from CO2 and natural epoxide using Complex@Zn-IL/FPS nanosaramic as catalysts was reported. Furthermore, the catalyst’s structural heterogeneity was examined using various methods, including SEM, FT-IR, XPS, TEM, and TGA. There was no evidence of zinc leaching into the fluid. In addition, hot filtration provided a comprehensive understanding of the catalyst’s heterogeneous nature. The catalyst’s practical and straightforward reusability was noted after the reaction was completed.

Aerobic Oxidative Desulfurization by Supported Polyoxometalate Ionic Liquid Hybrid Materials via Facile Ball Milling.

With the increasingly strict limitations on emission standards of vehicles, deep desulfurization in fuel is indispensable for social development worldwide. In this study, a series of hybrid materials based on SiO2-supported polyoxometalate ionic liquid were successfully prepared via a facile ball milling method and employed as catalysts in the aerobic oxidative desulfurization process. The composition and structure of prepared samples were studied by various techniques, including FT-IR, UV-vis DRS, wide-angle XRD, BET, XPS, and SEM images. The experimental results indicated that the synthesized polyoxometalate ionic liquids were successfully loaded on SiO2 with a highly uniform dispersion. The prepared catalyst (C16PMoV/10SiO2) exhibited good desulfurization activity on different sulfur compounds. Moreover, the oxidation product and active species in the ODS process were respectively investigated via GC-MS and ESR analysis, indicating that the catalyst can activate oxygen to superoxide radicals during the reaction to convert DBT to its corresponding sulfone in the fuel.

Functionality Modulation Toward Thianthrene-based Metal-Free Electrocatalysts for Water Splitting.

The development of metal-free bifunctional electrocatalysts for hydrogen and oxygen evolution reactions (HER and OER) is significant but rarely demonstrated. Porous organic polymers (POPs) with well-defined electroactive functionalities show superior performance in hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Precise control of the active sites' local environment requires careful modulation of linkers through the judicious selection of building units. Here, a systematic strategy is introduced for modulating functionality to design and synthesize a series of thianthrene-based bifunctional sp2 C═C bonded POPs with hollow spherical morphologies exhibiting superior electrocatalytic activity. This precise structural tuning allowed to gain insight into the effects of heteroatom incorporation, hydrophilicity, and variations in linker length on electrocatalytic activity. The most efficient bifunctional electrocatalyst THT-PyDAN achieves a current density of 10 mA cm─2 at an overpotential (η10) of ≈65 mV (in 0.5 m H2SO4) and ≈283 mV (in 1 m KOH) for HER and OER, respectively. THT-PyDAN exhibits superior activity to all previously reported metal-free bifunctional electrocatalysts in the literature. Furthermore, these investigations demonstrate that THT-PyDAN maintains its performance even after 36 h of chronoamperometry and 1000 CV cycling. Post-catalytic characterization using FT-IR, XPS, and microscopic imaging techniques underscores the long-term durability of THT-PyDAN.

Atomic-scale origin of the enantiospecific decomposition of tartaric acid on chiral copper surfaces.

The origin of the enantiospecific decomposition of L- and D-tartaric acid on chiral Cu surfaces is elucidated on a structure-spread domed Cu(110) crystal by spatially resolved XPS and atomic-scale STM imaging. Extensive enantiospecific surface restructuring leads to the formation of surfaces vicinal to Cu(14,17,2) which are responsible for the enantiospecificity.

Preparation and characterization of conductive blends of polyaniline with polyphenol red

Polymers are widely employed in biomedical applications, pharmaceutical product formulation, and drug delivery systems. Since every polymer has its own distinct properties, polymer blends will have novel chemical and physical properties. Functionally, the purpose of blending polymers is to improve, customize, or maximize material performance. In this study, polyaniline and polyphenol red polymer mixtures were prepared electrochemically and characterized with XPS imaging and SEM whether their distribution was homogeneous. The mixture of aniline and phenol red was deposited glassy carbon electrode (GCE) surface using the cyclic voltammetry technique in the potential range of -0.80 V to 2.00 V with 50 mV/s scan rate for 25 cycles. The phase separation of the two polymers was demonstrated by a combination of spectroscopic imaging and microscopy. For this purpose, the X-ray spot size and step number were set to 50μm. 1 x 1 mm2 area scan of the polymer mixtures was performed, and spectra were obtained at each pixel in an array of 20 x 20 pixels. Chemical imaging was obtained by applying Principal Component Analysis (PCA) to collected XPS survey spectra. For the morphological characterization, scanning electron microscopy (SEM) was employed, and images were obtained at magnifications of 5000 x. The results obtained in the mixtures prepared with 5%, 10% and 25% were better compared to the mixture prepared with 50% polyphenol red. Since the X-ray spot size is limited, the desired image resolution could not be obtained. It was shown that XPS imaging studies could also be used for examining the distribution of different and unknown polymer mixtures together with SEM.

Effects of dissolution by alkali treatment on anisotropic surface properties and flotation behavior of spodumene

The effect of dissolution pretreatment of spodumene using NaOH and Na2CO3 was investigated by micro-flotation test, contact angle measurement, XPS, ICP and AFM imaging. The results showed that NaOH treatment activated the spodumene flotation whilst Na2CO3 showed little depression effect. NaOH had more significant activating effect on the spodumene (001) surface than (110) surface. The surface dissolution was confirmed by AFM, showing that weak surface dissolution was observed in ultrapure water and Na2CO3 solution, while there was strong surface dissolution in NaOH solution. Some precipitates coated the surface at the very start in NaOH and Na2CO3 solution, and the precipitates redissolved rapidly in NaOH solution while redissolved very slowly in Na2CO3 solution. The ICP results verified the release of Si, Al and Li from spodumene surface. NaOH treatment gave larger relative contents of Al on spodumene surface than Na2CO3, and the relative contents of Al on the (001) surface increased to a greater extent than on the (110) surface, as revealed by XPS analysis. From the point of crystal structure, the dissolution made more dangling Al exposed on the (001) surface, making it more favor of NaOL adsorption.

Enhanced wear resistance of sustainable tire materials with plasma modified pyrolysis carbon black

In this study, pyrolysis carbon black (CBp) was pre-treated by the combination of air jet milling and Ar plasma technology to obtain the reinforcing filler, MP-CBp. The modification effect was verified by XPS, Raman spectroscopy and TEM images. The increment of introduced activation groups and the augmentation of surface area conferred MP-CBp an impressive reinforcement to natural rubber (NR) matrix. The excellent reinforcement of MP-CBp was attributed to the formation of strong filler network according to the mechanical properties. Besides, the tribological studies conducted under various load conditions revealed that the NR component filled with MP-CBp presented intensively improvement on the ground traction and the wear resistance. The addition of 60 phr MP-CBp intensified 20% dry traction, 33.3% wet traction and decreased 27.7% specific wear rate of NR vulcanizates. This strategy to modify CBp with cleanliness Ar plasma technique provides novel insights into not only the surface treatment of CBp, but also the manufacture of sustainable wear-resistant tire materials, which can tremendously promote the recycled utilization of waste tires.

Core shell heterojunction interface in green synthesized Sm3+ ions doped ZnO nano-particles to promote the charge separation for efficient photocatalytic applications

In this work, we report core-shell heterojunction of Sm3+ ions doped ZnO nanoparticles (NPs) by green synthesis technique and their photocatalytic activity for rapid degradation of methyl green dye molecules under UV light irradiation. High-resolution X-ray diffraction and high-resolution transmission electron microscope characterization techniques were employed to investigate structural and morphological studies. It is found that, the crystallite size of NPs is decreased with increasing Sm3+ ions concentration in NPs since Sm3+ ions are inhibiting the further growth of NPs. In addition, Sm3+: ZnO NPs catalyst shows irregular core shell heterojunction ensuing in the augmentation of a charge partition. Following that, the elemental compositional studies of Sm3+: ZnO NPs were estimated by energy dispersive spectroscopy. XPS imaging is also done in this work to get chemical mapping and the results suggested that the peaks are related to the Sm3+ ions in the ZnO lattice, which confirms the appropriate incorporation of Sm3+ into the ZnO. The optical energy band gap of NPs was estimated using diffuse reflectance spectroscopy. Excitation spectrum of Sm3+: ZnO NPs tinted the typical f-f transitions of Sm3+ ions. Photoluminescence emission shows the e− /h+ pair recombination rate reduced with increasing wt% of dopant Sm3+ ions in NPs. 10 wt% Sm3+: ZnO NPs showed the optimum photodegradation efficiency towards methyl green dye under the irradiation of UV light for 50 min. The dye degradation rate of Sm3+: ZnO NPs was 91% which is 26% higher than that of pristine ZnO NPs. Furthermore, the catalyst retains its original efficiency after fifth cycle.

In situ enzymatic generation of Au/Pt nanoparticles as an analytical photometric system: proof of concept determination of tyramine

In situ enzymatic generation of bimetallic nanoparticles, mainly Au/Pt, overcomes the drawbacks (continuous absorbance drift, modest LOQ, and long-time reaction) observed when AuNP alone are produced. In this study, Au/Pt nanoparticles have been characterized by EDS, XPS, and HRTEM images using the enzymatic determination of tyramine with tyramine oxidase (TAO) as a model. Under experimental conditions, the Au/Pt NPs show an absorption maximum at 580 nm which can be related to the concentration of tyramine in the range 1.0 × 10-6M to 2.5 × 10-4M with a RSD of 3.4% (n = 5, using 5 × 10-6M tyramine). The Au/Pt system enables low LOQ (1.0 × 10−6 M), high reduction of the absorbance drift, and a significant shortening of the reaction time (i.e., from 30 to 2 min for a [tyramine] = 1 × 10−4M); additionally, a better selectivity is also obtained. The method has been applied to tyramine determination in cured cheese and no significant differences were obtained compared to a reference method (HRP:TMB). The effect of Pt(II) seems to involve the previous reduction of Au(III) to Au(I) and NP generation from this oxidation state. Finally, a three-step (nucleation-growth-aggregation) kinetic model for the generation of NPs is proposed; this has enabled us to obtain a mathematical equation which explains the experimentally observed variation of the absorbance with time.Graphical abstract

Multimodal Radiobioconjugates of Magnetic Nanoparticles Labeled with 44Sc and 47Sc for Theranostic Application

This study was performed to synthesize multimodal radiopharmaceutical designed for the diagnosis and treatment of prostate cancer. To achieve this goal, superparamagnetic iron oxide (SPIO) nanoparticles were used as a platform for targeting molecule (PSMA-617) and for complexation of two scandium radionuclides, 44Sc for PET imaging and 47Sc for radionuclide therapy. TEM and XPS images showed that the Fe3O4 NPs have a uniform cubic shape and a size from 38 to 50 nm. The Fe3O4 core are surrounded by SiO2 and an organic layer. The saturation magnetization of the SPION core was 60 emu/g. However, coating the SPIONs with silica and polyglycerol reduces the magnetization significantly. The obtained bioconjugates were labeled with 44Sc and 47Sc, with a yield higher than 97%. The radiobioconjugate exhibited high affinity and cytotoxicity toward the human prostate cancer LNCaP (PSMA+) cell line, much higher than for PC-3 (PSMA-) cells. High cytotoxicity of the radiobioconjugate was confirmed by radiotoxicity studies on LNCaP 3D spheroids. In addition, the magnetic properties of the radiobioconjugate should allow for its use in guide drug delivery driven by magnetic field gradient.

Promotion of Au nanoparticles on carbon frameworks for alkali-free aerobic oxidation of benzyl alcohol

We synthesized a series of modified Co-ZIF-67 materials with tunable morphology to support fine Au nanoparticles for the alkali-free aerobic oxidation of benzyl alcohol. Structure promotion was performed using Stöber silica as a hard template, which was subsequently removed by NaOH etching before gold immobilization. The texture structure of Au/(Si)C was greatly improved with increasing surface area and volume. CoOx was simultaneously introduced into the carbon shell from the Co-ZIF-67 precursor, which consequently facilitated the specific Au-support interaction via bimetallic synergy. XRD, XPS, and TEM images demonstrated the redispersion of both Au and CoOx as well as the electronic delivery between metals. Analysis of the chemical and surface composition suggested a surface rich in Auδ+ with abundant lattice oxygen contributed by CoOx in the final Au/(Si)C, which improved the transformation rate of benzyl alcohol even in an alkali-free condition. Au/(Si)C with finely dispersed Au particles showed excellent catalytic performance in the alkali-free environment, with 89.3% benzyl conversion and 74.5% benzaldehyde yield under very mild conditions.

Real-Time Diagnostics of 2D Crystal Transformations by Pulsed Laser Deposition: Controlled Synthesis of Janus WSSe Monolayers and Alloys

Energetic processing methods such as hyperthermal implantation hold special promise to achieve the precision synthesis of metastable two-dimensional (2D) materials such as Janus monolayers; however, they require precise control. Here, we report a feedback approach to reveal and control the transformation pathways in materials synthesis by pulsed laser deposition (PLD) and apply it to investigate the transformation kinetics of monolayer WS2 crystals into Janus WSSe and WSe2 by implantation of Se clusters with different maximum kinetic energies (<42 eV/Se-atom) generated by laser ablation of a Se target. Real-time Raman spectroscopy and photoluminescence are used to assess the structure, composition, and optoelectronic quality of the monolayer crystal as it is implanted with well-controlled fluxes of selenium for different kinetic energies that are regulated with in situ ICCD imaging, ion probe, and spectroscopy diagnostics. First-principles calculations, XPS, and atomic-resolution HAADF STEM imaging are used to understand the intermediate alloy compositions and their vibrational modes to identify transformation pathways. The real-time kinetics measurements reveal highly selective top-layer conversion as WS2 transforms through WS2(1-x)Se2x alloys to WSe2 and provide the means to adjust processing conditions to achieve fractional and complete Janus WSSe monolayers as metastable transition states. The general approach demonstrates a real-time feedback method to achieve Janus layers or other metastable alloys of the desired composition, and a general means to adjust the structure and quality of materials grown by PLD, addressing priority research directions for precision synthesis with real-time adaptive control.

Fabrication, characterization and optical properties of Au-decorated Bi2Se3 nanoplatelets

Au-decorated Bi2Se3 nanoplatelet heterostructures are fabricated by a two-step process of thermal CVD at 600 °C and magnetron sputtering at room-temperature. The crystal structures and binding energies of rhombohedral Bi2Se3 and FCC Au are determined by XRD, HRTEM, XPS, and Raman spectroscopy. XPS and Raman spectroscopy reveal the interaction between Au and Bi2Se3 by shifting in the binding energies of Au–Au, Au–Se and Bi–Se bonds and the wavenumber of A1g2 and Eg2 modes. Au-decorated Bi2Se3 nanoplatelet heterostructures are observed using FESEM, and confirmed by XPS, Raman spectroscopy, and HRTEM imaging. Their optical band gap of the Au-decorated Bi2Se3 nanoplatelet heterostructures increases with Au thickness about 1.92-fold as much as that of pristine Bi2Se3 (0.39 eV), owing to the Burstein-Moss effect. The optical absorptance of the Au-decorated Bi2Se3 nanoplatelet heterostructures revealed increment with wavelength from 200 to 500 nm and decrement with increasing wavelength from 500 to 800 nm.

(Invited) DNA Kirigami with Tripod-C60 Scalpel

A tripod-C60 molecule was synthesized and attached onto a Au-coated AFM tip. Using the tripod skeleton of the molecule, tripod-C60 was immobilized onto the Au surface in a dispersed and stable manner, as observed by XPS and AFM imaging. Using an AFM tip functionalized with the tripod-C60, waffle-type DNA origami was scanned under visible light irradiation. Upon scanning, DNA damage was clearly observed by AFM imaging at the single molecule level. Control experiments in the absence of C60 (tripod only), in the dark, or in the presence of L-histidine or D2O confirmed that the observed DNA damage was induced by singlet oxygen (1O2) generated from C60 under photoirradiation.

Zeolitic Imidazolate Framework‑8 (ZIF-8) modified titanium alloy for controlled release of drugs for osteoporosis

The aim of this work was to prepare a biocompatible implant material that enables the release of drug for osteoporosis—risedronate. To achieve this goal, a titanium implant coated with a biocompatible Zeolitic Imidazolate Framework 8 (ZIF-8) layer was prepared that promotes osseointegration at the bone-implant interface. The modifications of the titanium alloy as well as sorption and desorption processes were confirmed using a variety of methods: SEM, EDS XPS, and FT-IR imaging (to determine surface modification, drug distribution, and risedronate sorption), and UV–Vis spectroscopy (to determine drug sorption and release profile). Both the ZIF-8 layer and the drug are evenly distributed on the surface of the titanium alloy. The obtained ZIF-8 layer did not contain impurities and zinc ions were strongly bounded by ZIF-8 layer. The ZIF-8 layer was stable during drug sorption. The drug was released in small doses for 16 h, which may help patients recover immediately after surgery. This is the first case of using ZIF-8 on the surface of the titanium alloy as carrier that releases the drug under the influence of body fluids directly at the site of the disease. It is an ideal material for implants designed for people suffering from osteoporosis.

Microporous carbon derived from cotton stalk crop-residue across diverse geographical locations as efficient and regenerable CO2 adsorbent with selectivity

Six porous carbons (PCs) were prepared via thermochemical methodology from cotton-stalk crop residue, collected from diverse geographical locations in India. Although similar in nature, the precursor collection sites majorly influenced the properties of the generated PCs, possibly due to variations in soil characteristics and fertilizer usage patterns. The microstructures were characterized by a series of analytical data, including FT-IR and Raman Spectra, XRD, TGA, SEM imaging, and in-depth XPS studies. Nitrogen sorption isotherms at 77 K of all PCs revealed well-defined microporosity and high specific surface area, varying from 1706 to 2438 m2/g under similar synthetic conditions. Further, gaseous CO2 adsorption studies showed that the PCs exhibited diverse uptake performances at 1 bar under varied temperatures. The maximum uptake capacity of 6.23 mmol/g (273 K), 3.85 mmol/g (298 K), and 3.28 mmol/g (313 K) defined superior values over contemporary adsorbents. A critical-point drying technique was employed further to enhance the CO2 uptake capacity of these carbons. Importantly, all the carbons revealed moderate to good CO2/N2 separation selectivity at low temperature (~25 at 273 K) that experienced a unique enhancement under elevated temperature, as calculated from ideal adsorbed solution theory. After vacuum regeneration, the activated carbons exhibited stable CO2 adsorption up to five cycles, validating their potential reusability for CO2 capture. Precisely, the cotton stalk crop residue-derived PCs represent one-of-a-kind low cost, eco-friendly, abundant, and scalable absorbents for regenerable CO2 capture with moderate heat of adsorption and selectivity values, with promises of practical usability.

XPS chemical state mapping in opto- and microelectronics

The strength of XPS imaging lies in its ability to (i) locate small patterns on sample surface, and (ii) inform, with micrometric lateral resolution, about the chemical environment of the elements detected at the surface. In this context, strontium-based perovskites appear to be well-adapted for such photoemission experiments thanks to their tunability and variability. These functional oxides have great potential for emerging optoand microelectronic applications, especially for transparent conductive oxide. Patterned heterostructure SrTiO3/SrVO3 was grown by pulsed laser deposition using a shadow mask. This stack was then analysed by XPS mapping in serial acquisition mode. Ti2p and V2p core level imaging clearly highlights the SrTiO3 and SrVO3 domains. The XPS mapping of the Sr3d core level will be extensively discussed: strontium being a common element to both oxides with a very similar chemical environment. Despite a lower contrast in Sr3d images, the two materials are discernible thanks to the topography. In addtion, the use of Sr3d FWHM image is a real asset to evidence the two phases. Finally, data processing by principal component analysis allows us to extract significant spectral information on the strontium atoms.

Vanadium oxide thin films with extremely narrow thermal hysteresis loop width were obtained by Ta doping for THz modulation applications

Based on the application potential of VO2 thin film in THz modulation field, only keeping its modulation amplitude is no longer applicable, and the film also needs to have lower phase transition temperature and narrower loop width, etc. In order to solve this problem, and since the high valence ion doping can reduce the phase transition temperature of VO2 films, the effect of Ta5+ doping on the phase transition performance of VO2 films is studied and analyzed in this paper. In this work, based on DC reactive magnetron sputtering technology, un-doped and Ta-doped VO2 films were prepared on high-resistance silicon substrate by two-step method. The microstructure of VO2 films before and after Ta doping was characterized by XPS, XRD and SEM images to assist the study and analysis of the influence of Ta5+ ions on the crystal phase structure of VO2. Finally, when the doping concentration of Ta5+ is 0.71%, the phase transition temperature (TC) of VO2 film decreases to 37.5 °C, the loop width (ΔH) narrows to 1.03 °C, and the optical modulation amplitude is maintained at 64.2%, which makes it more suitable for THz modulator.