X-ray Photoelectron Spectroscopy Investigation Research Articles

Insights into the interactions between cellulose and hemicellulose during pyrolysis for optimizing the properties of biochar as a potential energy vector

Cellulose and hemicellulose, the main components of biomass, undergo noticeable interactions during biomass pyrolysis. In this study, biochar was produced by the co-pyrolysis of cellulose and hemicellulose. Three co-pyrolysis parameters, namely, pyrolysis temperature (400–800 °C), residence time (5–30 min), and percentage of cellulose (0–100 %), were investigated to optimize the properties of biochar, including the application of response surface methodology in the experimental study. The analysis revealed that co-pyrolysis interactions could improve the biochar yield by up to 41.37 % (567.74 °C, 19.52 min, 50 % cellulose percentage). The co-pyrolysis interactions specifically enhanced the fixed carbon content, elemental carbon content, and higher heating value of the biochar, with the most significant enhancements being 0.87 %, 3.60 %, and 3.85 %, respectively, while simultaneously decreasing the volatile content, [H]/[C] ratio, and [O]/[C] ratio of the biochar, with the most significant reductions of −9.30 %, −10.81 %, and −26.71 %. Based on the observed decrease in the intensity ratio of the D-band and G-band of biochar in the Raman spectra, greater co-pyrolysis interactions increased the graphitization degree of the biochar. The analysis of X-ray photoelectron spectroscopy (XPS) investigations revealed that the interactions enhanced the contents of the C-C, C-O/C-O-C, aromatic, and OH functionalities while reducing the number of COO-, COOH, and CO functional groups. The results of this work indicate that the co-pyrolysis interaction between cellulose and hemicellulose contributes to optimizing the properties of biochar as a potential energy vector.

Thiourea based fluorescent chemosensor for selective detection of mercury ions in real samples and live cells imaging

A novel fluorescent sensor L having a thiourea moiety was devised and characterized by using FTIR, 1H NMR, 13C NMR and ESI-MS spectrometry. The receptor L effectively detects Hg2+ using a binding site-signalling approach in which the thiourea moiety serves as the binding unit and the phenol group serves as the signalling unit. Noticeable changes in the UV–Vis and emission spectra of L have been observed when reacts with Hg2+, as well as a visible color change in DMSO/H2O (10:90, v/v) solution. The X-ray photoelectron spectroscopy (XPS) investigation was performed to analyze the involvement of functional groups in the mercury complexation. The SEM analysis was also utilized to investigate the morphology of L. The limit of detection and association constant were calculated to be 0.60 µM and 1.63 × 104 M−1, respectively. L has been effectively utilized for the recognition of Hg2+ in soil samples, serum sample and live cells.

XPS post-mortem analysis of plasma-facing units extracted from WEST after the C3 (2018) and C4 (2019) campaigns

Four monoblocks coming from one ITER-like plasma-facing unit from the Q3B sector of the lower divertor, named as monoblock (MB)3, MB9, MB20, and MB30, were exposed to the deuterium and helium plasma mixture during the C3 (2018) and C4 (2019) campaigns of the Tungsten Environment in Steady-state Tokamak (WEST), followed by a detailed ex-situ X-ray photoelectron spectroscopy investigation. The surface and in-depth chemistry of the tungsten monoblocks indicated the formation of a re-deposited mixture in the deposition-dominated area of the divertor, thicker than 218 and 172 nm for MB3 and MB9, respectively. The redeposition layer was dominated by a mixture of boron carbides accompanied by tungsten carbides in MB3, while in MB9, the redeposition layer was dominated by tungsten borides. The remaining two monoblocks, MB20 and MB30, were collected from the erosion region and showed similar chemical behavior with a blended mixture of oxidized and metallic tungsten followed by boron carbides within a 50 nm depth range. Boron fixation in the layers is an expected consequence of the boronizations used during the operation, but the chemical status of redeposited elements was characterized for the first time in this work.

Enhanced optoelectronic properties of spray deposited antimony-doped tin oxide thin films

Antimony-doped tin oxide (Sb:SnO2) thin films with varying Sb concentrations were deposited using the spray pyrolysis technique. A comprehensive analysis of the films' elemental, structural, and optoelectronic properties is presented. All films possess a polycrystalline single-phase nature and have a tetragonal rutile structure. As Sb concentration increases, the unit cell shrinks continuously, suggesting proper substitution of Sn4+ by Sb5+. This substitution causes a continuous increase in the concentration of charge carriers and a reduction in electron mobility. X-ray photoelectron spectroscopy investigations revealed the presence of asymmetric Sn 3d core-level peaks distinguished by peak splitting, which increases with increasing carrier concentration. Utilizing the plasmon absorption model, an effective mass value of (0.51 ± 0.07)me for the conduction electron at the fermi level is obtained. With increasing Sb concentration, the optical energy gap increases gradually from 3.84 eV for undoped SnO2 to 4.35 eV for 5.0 at. % Sb. After considering the Urbach tailing phenomenon as well as the Moss–Burstein effect, this increase was attributed to the increase in Moss–Burstein energy due to increased charge carrier concentration. Our study revealed that the film doped with 2.0 at. % Sb has the best optoelectronic properties, with a figure of merit of 4.18 (Ω/cm2)−1.

Enhanced Peroxidase-like Activity of Ruthenium-Modified Single-Atom-Thick A Layers in MAX Phases for Biomedical Applications.

Nanozymes have demonstrated significant potential as promising alternatives to natural enzymes in biomedical applications. However, their lower catalytic activity compared to that of natural enzymes has limited their practical utility. Addressing this challenge necessitates the development of innovative enzymatic systems capable of achieving specific activity levels of natural enzymes. In this study, we focus on enhancing the catalytic performance of nanozymes by introducing Ru atoms into the single-atom-thick A layer of the V2SnC MAX phase, resulting in the formation of V2(Sn0.8Ru0.2)C with Ru single-atom sites. The V2(Sn0.8Ru0.2)C MAX phase demonstrated an exceptional peroxidase-like specific activity of up to 1792.6 U mg-1, surpassing the specific activity of a previously reported horseradish peroxidase (HRP). Through X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) investigations, it has been revealed that both the V2C atom layers and single-atom-thick Sn readily accept a negative charge from Ru, leading to a reduction of the energy barrier for H2O2 adsorption. This discovery has enabled the successful application of V2(Sn0.8Ru0.2)C in the development of a lateral flow immunoassay for heart failure biomarkers, achieving a detection sensitivity of 4 pg mL-1. Additionally, V2(Sn0.8Ru0.2)C demonstrated exceptional broad-spectrum antibacterial efficacy. This study lays the groundwork for the precise design of MAX phase-based nanozymes with high specific activity, offering a viable alternative to natural enzymes for various applications.

Ligand-free Ni-Cu bimetallic nanocatalyst: Laser synthesis, characterization and its high performance for borohydride assisted catalytic reduction of 4-nitrophenol

In the present work, nickel and copper bimetallic nanoparticles with three different concentration ratios of 70:30, 50:50, and 30:70 were synthesized by laser ablation of Ni and Cu in deionized water. The suitability of Ni-Cu bimetallics as nanocatalysts was investigated in the catalytic reduction of pollutant 4-nitrophenol. The nanocatalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible (UV–Vis) spectroscopy. The morphology using SEM and TEM indicated that Cu had an elongated or flake-like structure, whereas Ni had a quasi-spherical structure. XPS investigation has been performed to study the elemental composition and chemical states near-surface regions of the generated Ni-Cu bimetallic nanoparticles. XRD and XPS confirm high oxidation of Cu to CuO with approximately no residual Cu metal. However, the XRD patterns did not show complete Ni oxidation to NiO, confirming the presence of a Ni dopant part in the Ni-Cu samples. The behavior of the photoelectron peaks in the XPS spectra suggested that the Ni-Cu nanocomposites exhibited surface charge transfer. Pulsed laser ablation developed ligand-free Ni-Cu nanoparticles, which affected the structure and catalytic properties. The nanocatalyst for 50:50 of Ni and Cu had the highest rate constant, corresponding to the shortest time required to achieve 100 % conversion/reduction of the pollutant dye. The apparent synergistic effect between Ni and Cu is clearly dictated by the amount of Cu embedded in the nanocomposites, with this becoming a key factor in lowering the band gap energy values. Overall, the surface charge transfer rate can enhance the catalytic performance by tuning the Ni and Cu concentrations.

Graphitic carbon nitride functionalized with NiO nanoaggregates: An X-ray photoelectron spectroscopy investigation

The design and synthesis of low-cost oxygen evolution reaction (OER) photoelectrocatalysts endowed with high activity and durability is of utmost importance for sustainable energy generation via solar-assisted water splitting. In this regard, and in the framework of our recent activities, we have focused on the electrophoretic deposition of graphitic carbon nitride (gCN) specimens containing dispersed NiO nanoaggregates on carbon cloth substrates. In the present study, the attention is devoted to the x-ray photoelectron spectroscopy characterization of a representative gCN–NiO specimen. In particular, we provide an analysis of C 1s, N 1s, O 1s, and Ni 2p regions, discussing in detail the main spectral features. The obtained results, that provide evidence for a direct electronic interplay between the single material components, may serve as a useful comparison for additional research on analogous materials for energy and environmental applications.

Atomic insights into the interaction mechanism underpinning carbonate ion adsorption in smithsonite flotation

In industrial practice, smithsonite flotation separation and purification are nearly invariably conducted in highly alkaline environments. According to latest studies, sodium carbonate is a cheap, sustainable, stable, and safe substitute pH modifier that additionally assists with deep extraction recovery of smithsonite. In this work, the influence of carbonate as a pH modifier on smithsonite flotation behavior was comprehensively explored through flotation experiments, contact angle tests, X-ray photoelectron spectroscopy (XPS) investigations, and density functional theory (DFT) calculations. In comparison to sodium hydroxide, smithsonite exhibits far better floatability and hydrophobicity in the carbonate system, as demonstrated by the results of micro-flotation and contact angle experiments. XPS demonstrates that the underlying reason of the distinct pH modifications of smithsonite floatability in the carbonate system is the creation of different zinc-containing compounds, with the highly reactive CO32- forming a Zn5(CO3)2(OH)6 complex with Zn atoms at pH 10.5. Comprehensive DFT calculations further demonstrated that the hybridization reactions between Zn 2 s, O 2 s, and O 2p orbitals and the formation of stable Zn-O covalent bonds between OH- and Zn atoms shielded the preferential adsorption of oleate (OL-) on the smithsonite surface. Uniquely, the ionic bonding generated by carbonate is distinguished by the formation of a low-bonding-capacity Zn-O chemical bond, causing it susceptible to breaking during adsorption competition and allowing OL- to adsorb preferentially on Zn sites.

Investigating Co and Fe Single-Atom (SA) Decorated NS-Doped Reduced Graphene Oxide (Co SA/NS-rGO, Fe SA/NS-rGO) Catalysts for NOx - to NH3 Pulsed Electroreduction

Electrochemical NH3 production has attracted much attention due to its potential to compensate for and supplement the Haber-Bosch process that produces hundreds of billions of kg of NH3 annually.1 One of the proposed electrochemical pathways to produce NH3 is the N2 reduction reaction. However, this reaction suffers from a high bond dissociation energy of 945 kJ mol−1, low NH3 Faradaic efficiency (F.E.) at high overpotentials, and NH3 quantification problems, limiting the extent of its applications.2,3 On the other hand, other N-containing species, NO3 - and NO2 -, that are commonly found in sewages and agricultural water, hold great potential for electrochemical NH3 production owing to their high NH3 yield rate and F.E. as well as building a self-sustaining NH3 production cycle working tandem with denitrification processes.1,4 In this study, we investigated Co and Fe single-atom (SA) decorated NS-doped reduced graphene oxide (Co SA/NS-rGO and Fe SA/NS-rGO) catalysts for nitrate reduction reaction (NO3RR) and nitrite reduction reaction (NO2RR). Both materials have defect-rich properties owing to preserving the nature of doped graphene materials even after the metal incorporation. The presence of the layered structure of graphene and homogenous distribution of Fe and Co SAs in the doped graphene basal plane is shown through High-Resolution Scanning Transmission Electron Microscopy (HR-STEM) measurements. In addition to the Co and Fe SAs on the NS-rGO planes, SEM and X-ray Photoelectron Spectroscopy (XPS) investigations demonstrated that CoS and FeS could be simultaneously formed.We performed NO3RR and NO2RR experiments in 0.1 M KOH + 0.1 M KNO3 and 0.1 M KOH + 0.1 M KNO2 electrolytes with constant Ar purging in a glass H-Cell with a Nafion proton exchange membrane. We obtained NH3 with 65% F.E. at -0.4 V and a maximum of 2 mol s-1 molM -1 yield rate using Co SA/NS-rGO catalyst while with 60% F.E. at -0.5 V and 2.3 mol s-1 molM -1 yield rate using Fe SA/NS-rGO catalyst for NO3RR. Furthermore, the ∼10% NO2 - F.E. that is obtained for NO3RR experiments at -0.3 V and a significant increase in NH3 F.E. after -0.3 V for NO2RR indicates that NO3 - to NO2 - reduction takes place at this potential and our catalysts follow a two-step electron transfer mechanism. Moreover, linear sweep voltammetry (LSV) measurements indicated an onset potential of -0.4 V and -0.5 V for Co SA/NS-rGO and Fe SA/NS-rGO, respectively, for the NO3RR which are in excellent agreement with NO3RR F.E. results. We demonstrate that after prereduction at high negative potentials and with optimizations in experimental conditions, one can obtain >80% NH3 F.E. for NO3RR.To further increase the NH3 yield, three different pulsed electroreduction studies such as applying a potential at (1) the open circuit potential (OCP), (2) NO2 - reduction potential, (3) Co2+ or Fe2+ red-ox potentials and NH3 reduction potentials for 1-5 s intervals were performed. On Co SA/NS-rGO, an increased NH3 F.E. of ∼100% at -0.4 V was obtained under pulsed conditions. Also, by modulating NO3 - to NO2 - conversion to more negative potentials by pulsed electroreduction, significantly higher NH3 F.E. values were obtained for both catalysts. The higher NH3 F.E. and lower overpotential of Co SA/NS-rGO compared to Fe SA/NS-rGO could be attributed to the CoS formation that is more stable than FeS.

An electrochemical flow cell for operando XPS and NEXAFS investigation of solid–liquid interfaces

Suitable reaction cells are critical for operando near ambient pressure (NAP) soft x-ray photoelectron spectroscopy (XPS) and near-edge x-ray absorption fine structure (NEXAFS) studies. They enable tracking the chemical state and structural properties of catalytically active materials under realistic reaction conditions, and thus allow a better understanding of charge transfer at the liquid–solid interface, activation of reactant molecules, and surface intermediate species. In order to facilitate such studies, we have developed a top-side illuminated operando spectro-electrochemical flow cell for synchrotron-based NAP-XPS/-NEXAFS studies. Our modular design uses a non-metal (PEEK) body, and replaceable membranes which can be either of x-ray transparent silicon nitride (SiN x ) or of water permeable polymer membrane materials (e.g. NafionTM). The design allows rapid sample exchange and simultaneous measurements of total electron yield, Auger electron yield and fluorescence-yield. The developed system is highly modular and can be used in the laboratory or directly at the beamline for operando XPS/ x-ray absorption spectroscopy investigations of surfaces and interfaces. We present examples to demonstrate the capabilities of the flow cell. These include an operando NEXAFS study of the Cu-redox chemistry using a SiN x /Ti-Au/Cu working electrode assembly (WEA) and a NAP-XPS/-NEXAFS study of water adsorption on a NafionTM polymer membrane based WEA (NafionTM/C/IrO x catalyst). More importantly, the spectro-electrochemical flow cell is available for user community of B07 beamlines at Diamond Light Source.

Silver Decoration of Vertically Aligned MoS2-MoOx Nanosheets: A Comprehensive XPS Investigation.

This study investigates the simultaneous decoration of vertically aligned molybdenum disulfide nanostructure (VA-MoS2) with Ag nanoparticles (NPs) and nitrogen functionalization. Nitrogen functionalization was achieved through physical vapor deposition (PVD) DC-magnetron sputtering using nitrogen as a reactive gas, aiming to induce p-type behavior in MoS2. The utilization of reactive sputtering resulted in the growth of three-dimensional silver structures on the surface of MoS2, promoting the formation of silver nanoparticles. A comprehensive characterization was conducted to assess surface modifications and analyze chemical and structural changes. X-ray photoelectron spectroscopy (XPS) showed the presence of silver on the MoS2 surface. Scanning electron microscopy (SEM) confirmed successful decoration with silver nanoparticles, showing that deposition time affects the size and distribution of the silver on the MoS2 surface.

A comprehensive XPS investigation of the effect of aqueous corrosion on the surface of glass-zirconolite composite material (Fe–Al–BG–CaZrTi2O7)

Extensive X-ray photoelectron spectroscopy (XPS) analyses of iron–aluminum borosilicate glass (Fe–Al–BG), zirconolite (CaZrTi2O7), and Fe–Al–BG–CaZrTi2O7 composite material have demonstrated that a hydrated layer has been formed on the surface of these materials after exposure to water. The surface chemistry of Fe–Al–BG–CaZrTi2O7 composite material as a potential nuclear wasteform candidate was observed to change in a similar fashion to the borosilicate glass as a current wasteform material after these materials are exposed to water. The XPS measurements suggest that the aqueous corrosion of the Fe–Al–BG–CaZrTi2O7 composite material is a result of ion exchange, hydrolysis, and redox reactions of metal–oxygen bonds with water at the surface of the Fe–Al–BG–CaZrTi2O7 composite material. Moreover, the XPS results proved that the composition and chemical environment of the precipitated layer on the surface of the Fe–Al–BG–CaZrTi2O7 composite material after exposure to water remained unchanged between 270 and 365 days of exposure to water. The stability of the surface layer during this time frame could potentially protect the surface of the Fe–Al–BG–CaZrTi2O7 composite material from further corrosion.

Two-step process for the fabrication of direct FLG\\MoS2 heterostructures

MoS2 has proven its efficacy in flexible electronics, transistor devices, and various biological and chemical applications. However, it is still challenging to achieve large-area MoS2 monolayers with desired material quality and electrical properties to fulfill the requirement for practical applications. Moreover, the main strategy for the preparation of a 2D heterostructure it is based on the sequential stacking of the layered materials using wet or dry transfer methods which introduces many defects. This paper presents an economically viable and straightforward two-step methodology to obtain MoS2 thin films, encompassing magnetron sputtering deposition of Mo and subsequent annealing in a sulfur-rich environment. This approach successfully yielded MoS2 thin films on Si\\SiO2 substrates. Additionally, heterostructures consisting of few layer graphene (FLG) and MoS2 were directly obtained using the same method. The utilization of grazing incidence X-ray diffraction verified the formation of the hexagonal MoS2 phase, a finding further confirmed by Raman spectroscopy. X-ray photoelectron spectroscopy (XPS) investigations revealed the successful sulfurization process, with surface-bound oxides forming only subsequent to air exposure. Comprehensive assessment involving X-ray reflectivity, atomic force microscopy and XPS collectively inferred the fabrication of thin films comprised of a small number of MoS2 layers covering the entire substrate. Electrical assessments exhibited an electrical hysteresis, demonstrating its potential for memristor applications. Overall, this study outlines a cost-effective fabrication method for producing nanoscale MoS2 thin films with excellent properties, avoiding the use of toxic gases such as H2S. These findings contribute to the potential development of cutting-edge applications.

Cerium doping modulates the surface electronic structure of IrOx/TiN to promote the stability of acid oxygen evolution

The stability of supported Ir-based catalysts in acid oxygen evolution reaction (OER) remains a pressing challenge, which hinders the commercial viability of proton exchange membrane water electrolysis (PEMWE) technology. Herein, we propose a cerium doping strategy to enhance the stability of supported Ir-based catalyst toward OER. The Ce-doped supported catalysts, designated as Ce-IrOx/TiN, were synthesized using an organic colloidal method. Transmission Electron Microscopy (TEM) analysis reveals highly dispersed IrOx nanoparticles averaging 1.5 nm on the TiN support. X-ray Photoelectron Spectroscopy (XPS) investigations further elucidate that Ce doping effectively stabilizes the Ir species predominantly in states below 4+, crucial for modulating the surface electronic structure and thereby improving both the activity and stability of the catalysts. Electrochemical characterization highlights the superior performance of the optimized catalyst, 6 %-Ce-IrOx/TiN, with an impressively low overpotential of 242 mV at 10 mA cm−2 and a Tafel slope of 57.5 mV dec−1, showcasing its significance in facilitating OER. Moreover, its mass activity surpasses that of commercial IrO2 by 5.1 times at 1.7 V. Prolonged constant current testing further demonstrates the exceptional stability of the catalyst, affirming the critical role of Ce doping as a pivotal strategy for enhancing the stability of supported Ir-based catalysts and advancing the prospects for robust OER performance in PEMWE systems.

XPS Investigation of Magnetization Reduction Behavior and Kinetics of Oolitic Hematite in Gas-Based Roasting

Magnetization reduction roasting is an important method for the utilization of oolitic magnetite. In this study, the magnetization reduction behavior and kinetics of oolitic hematite in gas-based roasting were systematically investigated by X-ray photoelectron spectroscopy (XPS). The results revealed that under optimal roasting conditions of 650 °C, a roasting time of 60 min, and a CO concentration of 30%, the magnetization reduction rate of the roasted product reached 44.34%. Furthermore, the weak magnetic separation concentrate presented a TFe of 58.09% and a concentrate iron recovery of 94.3%. The results of the XPS spectrum indicated that the peak area ratio (Fe2+/Fe3+) gradually increased with an increase in roasting temperature, roasting time, and CO concentration, while over-reduction occurred when the roasting temperature exceeded 750 °C. The investigation of magnetization roasting kinetics for varying particle sizes demonstrated that the magnetization reduction process is controlled by chemical reaction, with a corresponding activation energy range of 42.96 kJ/mol to 63.29 kJ/mol, indicating the particle size has little effect on the magnetization reduction of oolitic hematite.

A comparative analysis of corrosion assessment techniques for steel in reinforced concrete exposed to brine water environments

Abstract Corrosion assessment of steel-reinforced concrete specimens submerged in synthetic brine water with various chloride concentrations for 1–16 weeks was performed. Mass loss measurements combined with electrochemical techniques – half-cell potential, linear polarization (LP), and electrochemical impedance spectroscopy (EIS) – were employed. The results obtained from all corrosion assessments – on-site testing (half-cell potential measurements), laboratory scale (LP and EIS measurements), and destructive testing (mass loss or immersion measurements) – exhibited remarkable consistency, complementarity, and mutual supportiveness. Corrosion rate (CR) values from mass loss were close to those obtained from LP and EIS. The corrosion resistance decreased with increasing chloride concentration and immersion time, as indicated by the highest CR, Ca2+, and Fe2+ concentrations, and the lowest half-cell potential and polarization resistance. X-ray photoelectron spectroscopy investigation on the corroded steel surface revealed Fe(III) oxides and hydroxides and Fe(III) (FeCl3), corresponding to the reduction in polarization resistance in the LP and EIS results.

Enhanced Adsorption of Methyl Orange from Aqueous Phase Using Chitosan-Palmer Amaranth Biochar Composite Microspheres.

To develop valuable applications for the invasive weed Palmer amaranth, we utilized it as a novel biochar source and explored its potential for methyl orange adsorption through the synthesis of chitosan-encapsulated Palmer amaranth biochar composite microspheres. Firstly, the prepared microspheres were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy and were demonstrated to have a surface area of 19.6 m2/g, a total pore volume of 0.0664 cm3/g and an average pore diameter of 10.6 nm. Then, the influences of pH, dosage and salt type and concentration on the adsorption efficiency were systematically investigated alongside the adsorption kinetics, isotherms, and thermodynamics. The results reveal that the highest adsorption capacity of methyl orange was obtained at pH 4.0. The adsorption process was well fitted by a pseudo-second-order kinetic model and the Langmuir isotherm model, and was spontaneous and endothermic. Through the Langmuir model, the maximal adsorption capacities of methyl orange were calculated as 495.0, 537.1 and 554.3 mg/g at 25.0, 35.0 and 45.0 °C, respectively. Subsequently, the adsorption mechanisms were elucidated by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy investigations. It is indicated that electrostatic interactions, hydrogen bonding, π-π interactions and hydrophobic interactions between methyl orange and the composite microspheres were pivotal for the adsorption process. Finally, the regeneration studies demonstrated that after five adsorption-desorption cycles, the microspheres still maintained 93.6% of their initial adsorption capacity for methyl orange. This work not only presents a promising method for mitigating methyl orange pollution but also offers a sustainable approach to managing Palmer amaranth invasion.

Interface defect formation for atomic layer deposition of SnO2 on metal halide perovskites

With the rapidly advancing perovskite solar cell (PSC) technology, dedicated interface engineering is critical for improving device stability. Atomic layer deposition (ALD) grown metal oxide films have drawn immense attention for the fabrication of stable PSC. Despite the advantages of ALD, the deposition of metal oxides directly on bare perovskite has so far not been achieved without damaging the perovskite layer underneath. In addition, the changes to the physicochemical and electronic properties at the perovskite interface upon exposure to the ALD precursors can alter the material and hence device functionality. Herein, we report on a synchrotron-based hard X-ray photoelectron spectroscopy (HAXPES) investigation of the interface between metal halide perovskite (MHP) absorber and ALD-SnO2 electron transport layer. We find clear evidence for the formation of new chemical species (nitrogen compound, lead dihalides) and an upward band bending in the MHP and downward band bending in the SnO2 towards the MHP/ALD-SnO2 interface. The upward bending at the interface forms an electron barrier layer of ∼400 meV, which is detrimental to the PSC performance. In addition, we assess the effectiveness of introducing a thin interlayer of the organic electron transport material Phenyl-C61-butyric acid methyl ester (PCBM) between MHP and ALD-SnO2 to mitigate the effects of ALD deposition.

Preparation and Characterization of Porous Carbon Material from Banana Pseudo-Stem

In this work, pseudo-stem of a banana plant was used as a sustainable and affordable source to prepare porous carbon materials (PCM) on a large scale. After fine treatment, the material was annealed at 500, 600, and 700 °C using a tube furnace under nitrogen flow. The prepared materials were characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). FT-IR spectra show that the broad peak at the range of 1110-1160 cm-1 comes from the superimposed peaks of C-N for a single or more than one functional group which debunks the possibility of generating nitrogen-doped carbon. TEM and SEM analyses confirmed the porous structure of PCM with the pores connected to one, and a spongy structure was observed in the prepared carbon material. XRD analysis revealed that the carbon materials are crystalline. XPS investigation provided information regarding the dimension of which elements are present in the valence states and constituent elements, depicting the presence of a dominant graphitic C1speak at approximately 284 eV, along with a distinct O1s peak at around 532 eV. Additionally, a relatively weaker N1s peak (approximately 400 eV) was observed. Dhaka Univ. J. Sci. 72(1): 63-70, 2024 (January)

Structural Parameters and Behavior in Simulated Body Fluid of High Entropy Alloy Thin Films.

The structure, composition and corrosion properties of thin films synthesized using the Pulsed Laser Deposition (PLD) technique starting from a three high entropy alloy (HEA) AlCoCrFeNix produced by vacuum arc remelting (VAR) method were investigated. The depositions were performed at room temperature on Si and mirror-like polished Ti substrates either under residual vacuum (low 10-7 mbar, films denoted HEA2, HEA6, and HEA10, which were grown from targets with Ni concentration molar ratio, x, equal to 0.4, 1.2, and 2.0, respectively) or under N2 (10-4 mbar, films denoted HEN2, HEN6, and HEN10 for the same Ni concentration molar ratios). The deposited films' structures, investigated using Grazing Incidence X-ray Diffraction, showed the presence of face-centered cubic and body-centered cubic phases, while their surface morphology, investigated using scanning electron microscopy, exhibited a smooth surface with micrometer size droplets. The mass density and thickness were obtained from simulations of acquired X-ray reflectivity curves. The films' elemental composition, estimated using the energy dispersion X-ray spectroscopy, was quite close to that of the targets used. X-ray Photoelectron Spectroscopy investigation showed that films deposited under a N2 atmosphere contained several percentages of N atoms in metallic nitride compounds. The electrochemical behavior of films under simulated body fluid (SBF) conditions was investigated by Open Circuit Potential (OCP) and Electrochemical Impedance Spectroscopy measurements. The measured OCP values increased over time, implying that a passive layer was formed on the surface of the films. It was observed that all films started to passivate in SBF solution, with the HEN6 film exhibiting the highest increase. The highest repassivation potential was exhibited by the same film, implying that it had the highest stability range of all analyzed films. Impedance measurements indicated high corrosion resistance values for HEA2, HEA6, and HEN6 samples. Much lower resistances were found for HEN10 and HEN2. Overall, HEN6 films exhibited the best corrosion behavior among the investigated films. It was noticed that for 24 h of immersion in SBF solution, this film was also a physical barrier to the corrosion process, not only a chemical one.