Electron Spectroscopy Analysis Research Articles

CARBON MATERIALS FROM WASTE BIOMASS AS ANTI-BACTERIAL AIR FILTERS

Carbon materials from almond shells were developed for the adsorption of microorganisms from air. Samples were processed by means of a one-step process – high-temperature hydro-pyrolysis. Studies were carried out in a wide temperature range of 600-900 °C. As a result, carbonates with predominant micro- and mesopores were obtained. The samples were impregnated with zinc, silver, iron and copper 5% by weight. The obtained samples were characterized by XDR, BET, scanning electron spectroscopy and elemental analysis. The final products are distinguished by a moderate surface and the presence of nanosized metal particles. The antibacterial properties of the activated carbon composites were examined using standard methodology under dynamic contact conditions and Escherichia coli K12 as test microorganism. All tested composite materials exhibit strong antibacterial properties after 48 h of contact with microbial cells. Thus the application of these materials in filtering system will be possible solution for successful reduction of microbial cell number. It is assumed that a similar effect can be achieved in an air environment.

Engineering Conductivity and Performance in Electrorheological Fluids Using a Nanosilica Grafting Approach

Carbonization is considered an effective process for the preparation of carbon-rich solids for various applications. Raw carbonaceous particles however often possess high electrical conductivity, limiting their applicability in electrorheology. To address this drawback, the carbonaceous particles prepared from glucose through hydrothermal synthesis, followed by thermal carbonization in an inert atmosphere, were subsequently coated by compact and mesoporous nanosilica, giving rise to semiconducting particles. The successful coating was confirmed using transmission electron microscopy and spectroscopic analysis, and the composite particles were further used as a dispersed phase in electrorheological (ER) fluids of concentration 5 wt %. While an ER fluid based on pure carbonized particles caused a short circuit of the measuring device at the electric field of intensity 1 kV mm–1, the ER behavior of its analogue based on mesoporous silica-coated particles was successfully measured up to 3 kV mm–1, giving a high yield stress exceeding even the values estimated for ER fluids based on similar carbonaceous particles coated with a compact silica layer. Even though the conductivity decreased only about one order of magnitude after the coating process, the dielectric properties of the prepared ER fluid differed significantly, the relaxation process was shifted to lower frequencies, and most importantly, the dielectric relaxation strength increased, indicating an increased amount of interactions. The presence of mesoporous nanosilica further enhanced the sedimentation stability of the ER fluids when compared to its analogue with the compact silica coating, expanding the scope of practical applicability.

Effect of layer thickness on spatters oxidation of Hastelloy X alloy during powder bed fusion-laser beam processing

This study investigates the impact of powder layer thickness on spatter generation and oxidation behavior during the processing of Hastelloy X. In-situ monitoring using optical tomography reveals that thicker powder layers result in a higher number of hot spatters generated during laser-melt-powder interaction. Scanning electron microscopy and Auger electron spectroscopy analysis demonstrate the presence of different types of spatters that oxidize differently depending on their origin. X-ray photoelectron spectroscopy analysis further shows that the surface enrichment of oxide-forming elements such as Al, Ti, Cr, and Fe varies with the type of spatter particle. Additionally, depth profile analysis using X-ray photoelectron spectroscopy indicates that the average oxide layer thickness increases from ∼2.5 nm in virgin to ∼68 nm in spatters generated at 150 μm powder layer thickness. The findings suggest that powder layer thickness is a crucial factor in controlling spatter generation and oxidation behavior during powder bed fusion-laser beam processing.

Tuning the surface electronic structure of WS2 with Zn- and Cu-phthalocyanine for improved hydrogen evolution reaction: Experimental and DFT investigation

WS2 nanosheets have been successfully demonstrated to be promising materials for several important catalytic reactions including Hydrogen Evolution Reaction (HER) and Oxygen Reduction Reactions (ORR) either standalone or by functionalizing and as composites. Tungsten disulfide (WS2) is known to exist in two phases: 2H semiconducting and 1 T conducting. The 2H phase is commonly obtained by simple exfoliation of bulk WS2. Due to the semiconducting nature of the 2H phase, catalytic activity towards HER is very feeble compared to its 1 T counterpart. In this work, we have enhanced the activity of 2H WS2 nanosheets by interfacial modification through metal phthalocyanine (Pc) molecule (Cu-Pc and Zn-Pc) functionalization. We observe that the HER activity shows significant enhancement with the functionalization, with Zn-Pc showing better performance than the Cu-Pc. This functionalization creates an electronically coupled inorganic–organic heterostructure which shows improved response to HER. The WS2 functionalized nanosheets were studied in-depth with X-ray diffraction (XRD), X-ray photo electron spectroscopy (XPS) and High-Resolution Transmission Electron Microscopy (HRTEM) analyses. Electrochemical studies like linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) demonstrates that the heterostructures deliver enhanced charge transfer kinetics. The Zn-Pc functionalized nanosheets display an overpotential of 233 mV for attaining a current density of 10 mA.cm-2 and the overpotential decreased to 165 mV after cycling due to the surface reconstruction, when the stability was assessed with chronoamperometry. Density Functional Theory (DFT) studies reveal that the charge transfer due to the adsorption of Zn-Pc onto WS2 nanosheets is comparatively better than that of Cu-Pc. This work recounts that by simple metal phthalocyanine functionalization, charge transfer characteristics of WS2 can be markedly improved, thereby signifying the importance of interface modification in two-dimensional (2D) heterostructures.

Evidence for intrinsic defects and nanopores as hotspots in 2D PdSe2 dendrites for plasmon-free SERS substrate with a high enhancement factor

Surface-enhanced Raman spectroscopy (SERS), a very powerful tool for the identification of molecular species, has relied mostly on noble metal-based substrates to obtain a high enhancement factor. In this work, we demonstrate that self-driven intrinsic defects in 2D palladium di-selenide (PdSe2) dendrites grown at low temperature (280 °C) act as hotspots for high SERS enhancement. We grow 2D dendritic PdSe2 with ample intrinsic defects to exploit it for SERS application. X-ray electron spectroscopy (XPS) analysis reveals 9.3% outer layer and 4.7% interior Se vacancies. A detailed examination of atomic-scale defects revealed Se vacancy (VSe) coupled with Se–Pd–Se vacancy (VSe-Pd-Se) in monolayer PdSe2, and an array of line defects (Se vacancies) and nanopores in bilayer PdSe2 dendrites. Interestingly, our studies reveal that Se vacancy-rich PdSe2 gives rise to line defects that act like hotspots for SERS enhancement. Remarkably, the vacancy-rich dendritic PdSe2 shows a SERS enhancement factor >105 and can detect RhB at a concentration down to 10−8 M. We speculate that the topological line defects and the edge construction in PdSe2 dendrites act as metallic wire or edge, which is partly responsible for the high enhancement in the SERS signal. The high SERS sensitivity is explained on the basis of multiple charge transfer processes combined with the predicted metal-like behavior of the defected 2D PdSe2. Our conclusions are fully supported by the density functional theory calculation of the electronic density of states of the defective bilayer (2L) PdSe2, which remarkably exhibits metallic character. Being a defect-enabled SERS substrate, dendritic 2D PdSe2 fills the gap between conventional plasmonic SERS substrate and plasmon-free SERS substrate.

Chemical Conversion Treatment of AA5083 Aluminum Alloy and AISI 1045 Carbon Steel under Galvanically Coupled Condition in Na<sub>2</sub>MoO<sub>4</sub>: Effect of pH on Corrosion Resistance

To ascertain the effect of solution pH of Na2MoO4 chemical conversion treatment for aluminum/steel joints on corrosion resistance, AA5083 aluminum alloy and AISI 1045 carbon steel were immersed in 50 mM Na2MoO4 at pH ranges of 8–12 under galvanically coupled condition. Subsequently, in diluted synthetic seawater, the galvanic corrosion resistance of the AA5083 alloy connected to the AISI 1045 carbon steel was assessed. The number of localized corrosion damages was counted, and AA5083 treated at pH 11 was found to be the better corrosion resistance. The oxygen reduction current on bulk Al6(Fe, Mn) decreased with increasing solution pH of the conversion treatment. The Al6(Fe, Mn) particles on AA5083 were not preferential cathodes, and alkalization through oxygen reduction would not occur when the treatment was performed above pH 9. Auger electron spectroscopy analysis showed that Mo-accumulation, Fe-removal, and film thickening occurred on the particles of AA5083 treated at pH 11. These factors contributed to the suppression of the cathodic activity of the Al6(Fe, Mn) particles, resulting in the improved galvanic corrosion resistance of AA5083.

Rational Positioning of Metal Ions to Stabilize Open Tin Sites in Beta Zeolite for Catalytic Conversion of Sugars

AbstractVia hydrothermal synthesis of Sn‐Al gels, mild dealumination and ion exchange, a bimetallic Sn‐Ni‐Beta catalyst was prepared which can convert glucose to methyl lactate (MLA) and methyl vinyl glycolate (MVG) in methanol at yields of 71.2 % and 10.2 %, respectively. Results from solid‐state magic‐angle spinning nuclear magnetic resonance, X‐ray photoelectron spectroscopy, transmission electron microscopy, spectroscopic analysis, probe‐temperature‐programmed desorption, and density functional theory calculations conclusively reveal that the openness of the Sn sites, such as by the formation of [(SiO)3−Sn−OH] entities, is governed by an adjacent metal cation such as Ni2+, Co2+, and Mn2+. This relies on the low structure‐defective pore channel, provided by the current synthesis scheme, and the specific silica hydroxyl anchor point is associated with the incorporation of Sn for additional and precise metal ion localization. The presence of metal cations significantly improved the catalytic performance of Sn‐Ni‐Beta for glucose isomerization and conversion to MLA of sugar compared with Sn‐Beta.

Rational Positioning of Metal Ions to Stabilize Open Tin Sites in Beta Zeolite for Catalytic Conversion of Sugars.

Via hydrothermal synthesis of Sn-Al gels, mild dealumination and ion exchange, a bimetallic Sn-Ni-Beta catalyst was prepared which can convert glucose to methyl lactate (MLA) and methyl vinyl glycolate (MVG) in methanol at yields of 71.2% and 10.2%, respectively. Results from solid-state MAS NMR, XPS, TEM, spectroscopic analysis, probe-TPD, and DFT calculations conclusively reveal that the openness of the Sn sites, such as by the formation of [(SiO)3-Sn-OH] entities, is governed by an adjacent metal cation such as Ni2+, Co2+, and Mn2+. This relies on the low structure-defective pore channel, provided by the current synthesis scheme, and the specific silica hydroxyl anchor point is associated with the incorporation of Sn for additional and precise metal ion localization. The presence of metal cations significantly improved the catalytic performance of Sn-Ni-Beta for glucose isomerization and conversion to MLA of sugar compared with Sn-Beta.

Hyperbranched Polyester Polyfumaratomaleate Doped with Gd(III) and Dy(III) Ions: Synthesis, Structure and Properties.

For the first time, metal-polymer complexes have been synthesized using hyperbranched polyester polyfumaratomaleate as a matrix, the structure of which has been established by 1H NMR, IR, electron spectroscopy, and elemental analysis methods. The formation of complexes with Gd(III) and Dy(III) ions involving fumarate and maleate groups of the polyester was proved by IR and electron spectroscopy methods. It was established that the structure of the coordination units has the form of a square antiprism. The compositions and conditional logarithms of the stability constants of the complexes were determined. It was established that complexation with lanthanide ions promotes emission enhancement in the ligand.

Material removal analysis during MR polishing of complex gear teeth profiles

The geometric intricacy of tiny gears makes nano-finishing difficult. In the current study, the magnetorheological (MR) polishing process is used for the nano-finishing of intricate surfaces of tiny gear components uniformly. For polishing, the technique employs a dynamic fluid recognized as magnetorheological polishing fluid (MRPF), that has the ability to stiffen in the presence of a magnetic field. Base media, iron and abrasive particles are utilized to synthesize the MRPF. Permanent magnets produce the necessary magnetic field in the finishing zone. Finite element analysis (FEA) is utilized to model the iron and abrasive particles to understand better how they would react in the external magnetic field. FEA is utilized to analyze the magnetic flux density (MFD) distributions and the amount of magnetic force exerting on gear profiles through iron particles (IPs). It has been observed that the IPs present close to the active abrasives are primarily accountable for indenting active abrasives into the workpiece surfaces. In addition, the influence of particle dimension on the stiffness of iron particle chains in MRPF has been investigated. A mathematical model for material removal is developed by utilizing normal finishing force analysis on active abrasives. Lastly, the finishing surface characteristics of gear profiles are examined using an optical profilometer, field emission scanning electron microscope (FESEM) and spectroscopic analysis. Finally, 92.68% improvement in the surface finish is observed.

Intensified gas-phase hydrogenation of acetone to isopropanol catalyzed at metal-oxide interfacial sites

The gas-phase acetone hydrogenation to isopropanol is an environmentally benign process relevant to chemical, energy and medical fields, but the catalysts qualified at low temperature and pressure remain challenging. Herein, we show the intensified gas-phase hydrogenation of acetone to isopropanol at metal-oxide interface. The Pt/CeO2 catalyst with highly active and stable Pt-CeO2 interface delivers 92 % acetone conversion with 99 % isopropanol selectivity at 80 °C, weight hourly space velocity of 10 h−1, H2/acetone molar ratio of 2, and 0.1 MPa, and its catalytic performance is preserved during a single-running test of 200 h. A series of electron microscopic, thermal, and spectroscopic analyses testify that acetone could be efficiently adsorbed on oxygen vacancy at Pt-CeO2 interface. The H atoms dissociated by Pt spill over to the interface to hydrogenate the chemically-adsorbed acetone thereon to form isopropanol. Inspired by such observation, the Pt-CeO2 interface was extended to other metal-oxide interfaces (metal: Pt and Ni; oxide: CeO2, TiO2, ZrO2 and Fe3O4), all exhibiting excellent catalytic performance. For example, the Ni/CeO2 could offer 91 % acetone conversion and 99 % isopropanol selectivity, identical to that of Pt/CeO2 under the same conditions. This work particularly investigated the acetone adsorption at the metal-oxide interface, establishing the foundation for rational design of high cost performance catalysts for aldehydes/ketones hydrogenation and other reactions.

Investigation of Water-Washing Effect on Electrochemical Properties of Ni-Rich NCA Cathode Material for Lithium-Ion Batteries

This study was conducted to understand the effect of well-known water-washing process on Ni-rich LiNi0.885Co0.100Al0.015O2 (NCA) cathode material, which reduces the amount of residual lithium compounds in NCA to improve lithium-ion batteries (LIBs) characteristics. X-ray absorption fine structure (XAFS) analysis revealed that the oxidation state of the surface nickel in washed NCA particles was reduced. The fact was consistent with the increase in charge transfer resistance (Rct) measured by the electrochemical impedance spectroscopy (EIS) method. From X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) analyses, it was found that the residual lithium compounds were washed away not only from the surface of NCA particles but also from grain boundaries or voids in between primary particles of NCA, by water-washing process. Differential scanning calorimetry (DSC) measurements suggested that an increase in specific surface area of NCA particles by water-washing was attributed a rapid heat release from the charged cathode material during heating to. On the other hand, cross-sectional scanning electron microscope (SEM) images showed that the crack formation inside washed NCA particles were suppressed after charge/discharge cycling. As a result, the capacity retention of washed NCA electrode at 60 °C cycling was improved.

Effects of Amino Hyperbranched Polymer-Modified Carbon Nanotubes on the Crystallization Behavior of Poly (L-Lactic Acid) (PLLA).

Poly-L-lactic acid (PLLA) is an environmentally friendly and renewable polymer material with excellent prospects, but its low crystallization rate greatly limits its application. Through the amidation reaction between amino hyperbranched polymer (HBP N103) and carboxylated carbon nanotubes (CNTs), CNTs-N103 was obtained. The modification was confirmed by Fourier-transform infrared (FTIR) spectroscopy, X-ray electron spectroscopy (XPS) and thermogravimetric analysis (TGA). Using transmission electron microscopy (TEM), we observed the changes on the surface of modified CNTs. PLLA/CNT composites were prepared, and differential scanning calorimetry (DSC) was used to investigate the crystallization behavior of the composites. The results showed that the addition of CNTs could greatly improve the crystallization properties of PLLA; at the same concentration, the modified CNTs had better regulation ability in PLLA crystallization than the unmodified CNTs. Moreover, in the concentration range of 0.1–1%, with the increase in HBP concentration, the ability of CNTs-N103 to regulate the crystallization of PLLA increased as well. Wide-angle X-ray diffraction (WAXD) once again proved the improvement of the crystallization ability. The results of polarized optical microscopy (PLOM) showed that the number of nucleation points increased and the crystal became smaller.

Corrosion behavior of WC–Co coating by plasma transferred arc on EH40 steel in low-temperature

Abstract To investigate the corrosion behavior of WC–Co composite coating, plasma transferred arc (PTA) welding was applied to prepare WC–Co coating on hull steel EH40 for achieving good metallurgical bonding. The phases of coatings were mainly composed of WC particles, solid solution γ-Co, Fe3Ni2, SiO2 and Mo2C. After electrochemical test, it can be concluded that Co-based coating with 45% WC content has better corrosion resistance in low temperature marine environment for obtaining denser oxide film. Through X-ray photo electron spectroscopy (XPS) analysis, the main corrosion products of immersion were Co(OH)2 and Co3O4. These corrosion products aggregate to form a stable corrosion product film, which plays some protective role for the coating. Hard particle WC is also partially oxidized to WO3. The pitting hole of 60% WC is the most serious. Pitting corrosion is easy to occur at the interface defects.

Highly Efficient and Reusable Polymer Supported Palladium Catalyst for Copper Free Sonogashira Reaction in Water

AbstractDevelopment of a novel, greener and efficient heterogeneous catalytic system for copper free Sonogashira reaction in water is described. This novel catalyst can be easily prepared by a simple method through synthetic modification of nitrile group in Polyacrylonitrile (PAN) using monoethanolamine (MEA) followed by its complexation with palladium chloride (PdCl2). The resulting polymer Pd complex (mPAN‐Pd) was characterized by means of Fourier Transform Infrared Spectroscopy (FTIR), Energy‐Dispersive X‐ray Spectroscopy (EDAX), Inductively Coupled Mass Spectrometry (ICP‐MS) and X‐ray Photo Electron Spectroscopy (XPS) analyses. mPAN‐Pd was then explored as highly efficient heterogeneous catalyst for Sonogashira coupling reaction under copper and ligand free conditions in water affording the corresponding coupling products up to 97 % isolated yield. Moreover, the catalyst was recovered by simple filtration after the reaction and reused for next 5 cycles with excellent stability and activity. This is the first report on the use of ethanolamine modified PAN Pd (II) complex as an efficient heterogeneous catalyst for a coupling reaction.

Structural Heterogeneity Induced Li Dendrite Growth in Li0.33La0.56TiO3 Solid-State Electrolytes

Solid-state electrolytes (SSEs) are driving next-generation Li-ion batteries (LIBs) with higher energy density and improved safety compared with organic liquid electrolytes. However, the gradual Li dendrite growth during cycling is still a critical issue limiting the long-term service of SSEs, the mechanism of which remains largely unclear. Here, we investigate the Li dendrite growth-induced short circuiting of Li0.33La0.56TiO3 (LLTO) ceramic pellets through detailed electron microscopy and spectroscopy analysis. Under both electrochemical cycling and thermal chemical reaction between Li and LLTO, we find that the Li dendrites prefer to nucleate at the voids in the LLTO pellet, followed by vertical growth along the grain boundaries, and finally result in the buildup of internal stress and the cracking of LLTO. In addition, Li dendrite growth accompanies the decomposition of Li0.33La0.56TiO3 because of the reduction of Ti4+ to Ti3+, which inevitably alters the bulk diffusion of Li ions.

Polymer metal-organic clusters based on hyperbranched polyester polybenzoylthiocarbamate and Cu(II) and Co(II) ions

Polymer metal-organic framework (MOF) are a new class of hybrid porous materials that combine the advantages of both organic polymers and metal-organic frameworks. In this regard, a new ligand was synthesized - a hyperbranched polyester polybenzoylthiocarbamate, the structure of which was established by IR, 1H NMR, electron spectroscopy and elemental analysis. Complexing properties have been studied using the example of Cu(II) and Co(II) ions. The formation of metal-polymer clusters with metal ions with the participation of benzoylthiocarbamate groups of the polyester has been proved by IR, electron spectroscopy and electron microscopy. It was found that the structure of coordination sites is octahedral with tetragonal distortions. The compositions and conditional logarithms of the stability constants of the complexes were determined.

Modified photoactivated methylene blue-incorporated quartz particles for dentin disinfection: A scanning electron microscope and spectroscopic analysis.

The aim of this study was to synthesize methylene blue-incorporated quartz particles (MB@QP) and to investigate its anti-bactericidal properties. Methylene blue was incorporated inside QP and characterized for morphology and chemical structure using scanning electron microscope (SEM) and Fourier transformed infrared spectroscopy (FTIR). Specimens were randomly divided into experimental and control groups (n=9/groups). The dentin specimen infected with Enterococcus faecalis was treated using different treatment modalities: Control groups: treatment with 5.25% of sodium hypochlorite (NaOCl) for 60 s; MB: treatment with 1ml MB solution and incubated for 60 s; MB-PDT (photodynamic therapy): treatment with 1ml MB solution followed by irradiation using diode laser for 60 s; MB-QP-PDT: specimens treated with MB@QP and irradiated by the diode laser for 60s, and Er,Cr:YSGG laser alone. MB@PDT therapy showed the highest efficacy in reducing the survival rate of E.faecalis (0.49%) in comparison to control NaOCl (0.78%) and Er,Cr:YSGG laser treatment (2.17%). Encapsulating MB into QP followed by the PDT significantly improved the bactericidal capacity and significantly reduced the bacterial survival rate to 0.11% (p < .05) compared to other groups. The combination of MB incorporated into QP and PDT could be an alternative treatment modality to conventional disinfection method for eliminating bacteria from the tooth dentin. RESEARCH HIGHLIGHTS: Quartz particles are potent in delivering the photosensitizer. Photoactivated MB@QP has a higher efficacy in eliminating bacteria from tooth dentin.

Emerging Electrochemical Techniques for Probing Site Behavior in Single-Atom Electrocatalysts.

Single-atom catalysts (SACs) have aroused tremendous interest over the past decade, particularly in the community of energy and environment-related electrocatalysis. A rapidly growing number of recent publications have recognized it as a promising candidate with maximum atomic utilization, distinct activity, and selectivity in comparison to bulk catalysts and nanocatalysts. However, the complexity of localized coordination environments and the dispersion of isolated sites lead to significant difficulties when it comes to gaining insight into the intrinsic behavior of electrocatalytic reactions. Furthermore, the low metal loadings of most SACs make conventional ensemble measurements less likely to be accurate on the subnanoscale. Thus, it remains challenging to probe the activity and properties of individual atomic sites by available commercial instruments and analytical methods. In spite of this, continuing efforts have lately focused on the development of advanced measurement methodologies, which are very useful to the fundamental understanding of SACs. There have recently been a number of in situ/operando techniques applied to SACs, such as electron microscopy, spectroscopy, and other analysis methods, which support relevant functions to identify the active sites and reaction intermediates and to investigate the dynamic behavior of localized structures of the catalytic sites.This Account aims to present recent electrochemical probing techniques which can be used to identify single-atomic catalytic sites within solid supports. First, we describe the basic principles of molecular probe methods for the study and analysis of electrocatalytic site behavior. In particular, the in situ probing technique enabled by surface interrogation scanning electrochemical microscopy (SI-SECM) can measure the active site density and kinetic rate with high resolution. An alternative electrochemical probing technique is further demonstrated on the basis of single-entity electrochemistry, which allows the unique electrochemical imaging of the size and catalytic rate of single atoms, molecules, and clusters. The merits and limitations of different electrochemical techniques are then discussed, along with perspectives for future prospects. Apart from this, we further showcase the powerful capability of emerging electrochemical probing techniques for determining significant effects and properties of SACs for various electrocatalytic reactions, including oxygen reduction and evolution, hydrogen evolution, and nitrate reduction. Overall, electrochemical techniques with atomic resolution have greatly increased opportunities for observing, measuring, and understanding the surface and interface chemistry during energy conversion. In the future, it is anticipated that the development of electrochemical probing techniques will be advanced with innovative perspectives on the behavior and features of SACs. We hope that this Account can contribute in several ways to promoting the fundamental knowledge and technical progress of emerging electrochemical measurements for studying SACs.

Microstructural and Chemical Investigations of Presolar Silicates from Diverse Stellar Environments

Abstract We report the structural and chemical investigation of nine presolar silicate grains from the CH3/CBb3 chondrite Isheyevo and CR2 chondrite Northwest Africa (NWA) 801. Five of these grains belong to group 1, likely condensed in low- to intermediate-mass asymptotic giant branch (AGB) stars, super-AGB stars, or core-collapse supernovae, while the remaining four grains belong to group 4 and have a supernova origin. The advanced transmission electron microscopy and associated electron spectroscopy analyses show a diverse range of chemical and structural compositions for presolar silicates. Two GEMS (glass with embedded metal and sulfide)-like silicates, each from different groups, condensed under nonequilibrium conditions in stellar outflows. Two nonstoichiometric silicates from group 1 have dissimilar formation and alteration histories. An amorphous silicate from group 1 with olivine-like [(Mg,Fe)2SiO4] composition likely formed as a crystalline olivine that subsequently amorphized in the interstellar medium. An oldhamite (CaS) grain within a stoichiometric enstatite (MgSiO3) from group 1 probably formed by heterogeneous condensation in circumstellar outflows. Of the two crystalline grains from group 4, one is an antigorite [(Mg,Fe)3Si2O5(OH)4], while the other is a nontronite [Na,Fe2(Si,Al)4O10(OH)2.nH2O], both formed as a crystalline forsterite and later altered to have hydrated silicate composition. A group-4 silicate has a chemical composition similar to a low Ca-pyroxene [(Ca,Mg)(Si,Al)2O6]. Our data imply that presolar grains from different groups can have a similar range of grain-formation conditions.