X-ray Photoelectron Spectroscopy Investigation Research Articles

Study of stereochemical crystallization of racemic mixtures of [5] and [7]thiaheterohelicene molecules on Ag(111) surface by scanning tunneling microscopy and Raman scattering spectroscopy

The crystallization of a racemic mixture of [5] and [7]thiaheterohelicene molecules into two-dimensional highly ordered molecular domains on a Ag(111) surface was investigated by scanning tunneling microscopy (STM) at 80 K. We observed that the crystallization of both thiaheterohelicene molecules on a Ag(111) surface was strongly affected by stereospecific interactions resulting from different numbers of aromatic rings incorporated into the helical skeletons of molecules. [5]Thiaheterohelicene molecules crystallized predominant into a few racemate polymorphic molecular domains, allowing us to obtain high-resolution STM images with the unambiguous identification of the absolute handedness of enantiomeric species. In contrast, the stereochemical chiral interactions among [7]thiaheterohelicene molecules led to the formation of one type of racemate molecular domain consisting of self-assembled zigzagged twin rows. X-ray photoelectron spectroscopy investigation strongly suggests weak interaction between thiaheterohelicene molecules and Ag(111) surface and lack of formation the S-Ag chemical bond. Surface-enhanced Raman spectroscopy combined with theoretical calculation based on a density functional theory was applied to the chemical verification of molecules adsorbed on a plasmonic silver surface for future tip-enhanced Raman spectroscopy.

Facile preparation of novel magnetic mesoporous Fe[sbnd]Mn binary oxides from Mn encapsulated carboxymethyl cellulose-Fe(III) hydrogel for antimony removal from water

Effective removal of Sb(III) and Sb(V) has long been an urgent task for protecting human health and environment. In this study, novel magnetic mesoporous FeMn binary oxides (MMFMs) were fabricated via calcinating the Mn encapsulated carboxymethyl cellulose-Fe(III) hydrogel, and the structure of MMFMs were closely related to the Fe:Mn ratio. Owing to the mesoporous structure together with synergistic effect of FeMn binary component, the MMFMs exhibited excellent mass transfer and adsorption ability to Sb(III) and Sb(V). MMFM3 achieved a maximum Sb(III) and Sb(V) adsorption capacity of 281.5 and 204.6 mg/g, respectively. Co-existing anions of Cl−, NO3− and SO42− exhibited marginal influence on the adsorption for both Sb(III) and Sb(V), except the PO43− for Sb(III) and SiO32− or PO43− for Sb(V). X-ray photoelectron spectroscopic investigation revealed that high valence Mn(IV) was mainly responsible for the oxidation transformation of the highly toxic Sb(III) into less toxic Sb(V), while the FeOx content played major role for the adsorption of Sb(V). The generated inner-sphere FeOSb complex between Fe-OH groups and Sb(III/V) dominantly contributed to the removal of Sb(III/V). Overall, mesoporous structure, magnetic separation ability, excellent adsorption performance together with exceptional regeneration properties demonstrated the great potential of MMFMs for Sb(III/V) remediation.

Time-resolved x-ray diffraction and photoelectron spectroscopy investigation of the reactive molecular beam epitaxy of Fe3O4 ultrathin films

We present time-resolved high energy x-ray diffraction (tr-HEXRD), time-resolved hard x-ray photoelectron spectroscopy (tr-HAXPES) and time-resolved grazing incidence small angle x-ray scattering (tr-GISAXS) data of the reactive molecular beam epitaxy (RMBE) of $\mathrm{Fe_3O_4}$ ultrathin films on various substrates. Reciprocal space maps are recorded during the deposition of $\mathrm{Fe_3O_4}$ on $\mathrm{SrTiO_3(001)}$, MgO(001) and NiO/MgO(001) in order to observe the temporal evolution of Bragg reflections sensitive to the octahedral and tetrahedral sublattices of the inverse spinel structure of $\mathrm{Fe_3O_4}$. A time delay between the appearance of rock salt and spinel-exclusive reflections reveals that first, the iron oxide film grows with $\mathrm{Fe_{1-\delta}O}$ rock salt structure with exclusive occupation of octahedral lattice sites. When this film is 1.1$\,$nm thick, the further growth of the iron oxide film proceeds in the inverse spinel structure, with both octahedral and tetrahedral lattice sites being occupied. In addition, iron oxide on $\mathrm{SrTiO_3(001)}$ initially grows with none of these structures. Here, the formation of the rock salt structure starts when the film is 1.5$\,$nm thick. This is confirmed by tr-HAXPES data obtained during growth of iron oxide on $\mathrm{SrTiO_3(001)}$, which demonstrate an excess of $\mathrm{Fe^{2+}}$ cations in growing films thinner than 3.2$\,$nm. This rock salt phase only appears during growth and vanishes after the supply of the Fe molecular beam is stopped. Thus, it can be concluded the rock salt structure of the interlayer is a property of the dynamic growth process. The tr-GISAXS data link these structural results to an island growth mode of the first 2-3$\,$nm on both MgO(001) and $\mathrm{SrTiO_3(001)}$ substrates.

Exploration of photocatalytic performance of TiO2, 5% Ni/TiO2, and 5% Fe/TiO2 for degradation of eosine blue dye: Comparative study

In the present investigation, the TiO2, 5 % Fe/TiO2, and 5 % Ni/TiO2 were successfully synthesized by the co-precipitation (CPT) method. The synthesized undoped and doped TiO2 nanomaterials were employed for photocatalytic degradation of eosine blue dye in the aqueous heterogeneous suspension. X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), High resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET) analyses were performed to investigate the crystallinity, surface morphology, elemental composition, crystal lattice, chemical state of the elements, and surface area of the fabricated photocatalysts, respectively. XRD indicated that TiO2 nanoparticles are formed in the anatase phase. HR-TEM pictures clearly showed that synthesized material as a tetragonal anatase crystal lattice. The BET analysis revealed that 5 % Fe/TiO2 material has an enhanced surface area of 80.98 m2/g. The oxidation states of Fe3+ and Ni2+ were confirmed based on XPS investigation. The experimental parameters like nanocatalyst dosage, pH of the solution, initial concentration of dye, light intensity, and contact time were studied. The photocatalysis results revealed that dye removal in acidic pH was greater than in neutral and alkaline pH. Photocatalyst efficiency of dye degradation was found to be increased with the increase in nanocatalyst dose, light intensity, and contact time. The photo induced degradation (96.45 %) of eosine blue dye is more efficient at a minimum dose of 5 % Fe/TiO2 nanocatalyst (0.8 g/L) at the optimum conditions of pH 7.0, and contact time 110 min.

Deciphering the adsorption potential of a functionalized green hydrogel nanocomposite for aspartame from aqueous phase

Herein, a functionalized green hydrogel nanocomposite based on carboxymethylated gum tragacanth and nanobentonite (GTBCH) was designed via free-radical polymerization approach for the elimination of Aspartame (AS) from wastewater. The GTBCH fabrication was validated by Fourier Transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX) techniques. Central composite design (CCD) was efficaciously applied to determine the quadratic polynomial approach for predicting the adsorption capacity (qe) of AS. The optimum sequestration conditions were dosage (0.8 g L‒1), agitation time (35 min) initial AS concentration (60 mg L−1), pH (6) and temperature (308 K). The CCD results revealed that dosage of GTBCH and initial concentration have greater impact on qe followed by pH, time, and temperature. The significant adsorption capacity (392.04 mg g−1), calculated from Langmuir model, could be attributed to the stronger interactions prevalent between AS and GTBCH. Diffusion investigations depicted the uptake of AS via surface adsorption, liquid film and intraparticle diffusion, respectively. Ionic strength and real water have minor effect on the adsorption capacity demonstrating electrostatic interaction has least impact in adsorption process. The pHzpc, FTIR and XPS investigations revealed hydrogen bonding, n-π and van der Waals interactions as the principal removal mechanisms. Robust design, high adsorption capacity, eco-friendly facets along with excellent reusability indicated the GTBCH as a competent adsorbent for AS decontamination from wastewater.

Aminopropylimidazole as an Advantageous Coating in the Synthesis of Functionalized Magnetite Nanoparticles.

Implementing new methods to prepare magnetite nanoparticles with a covered or uncovered surface has been, and still is, a significant challenge. In this work, we describe a very clear and effortless way for the preparation of magnetite nanoparticles using two types of bases, namely: 1-(3-aminopropyl)imidazole and sodium hydroxide. Fourier transform infrared spectroscopy (FTIR) served as a tool for the structural investigation of the as-prepared magnetite nanoparticles. The morphology of the samples was investigated using Transmission Electron Microscopy (TEM). Comprehensive high-resolution X-ray photoelectron spectroscopy investigations (XPS) were applied as an effective tool for analyzing the composition of the various types of magnetic nanoparticles. Further polymer linkage was accomplished with poly(benzofuran-co-arylacetic acid) on the amino-functionalized surface of aminopropylimidazole-containing magnetic nanoparticles. The findings are promising for biomedicine, catalysis, and nanotechnology applications.

Optically sensitive isolated silver nano-dots development by broad ion implantation on nitrogen ion-induced pre-patterned silicon nano-templates

We report broad ion beam-induced isolated silver nano-dot formation on the pre-patterned silicon nitride nano template. The nano templates are developed and optimized on Si (100) surfaces using N2+ ion bombardment at different incidence angles and fluences. Atomic Force Microscopy shows that the well-defined pyramidal structures can be formed by 14 keV, N2 ion bombardment at incidence angle 70° with ion fluence 2 × 1018 ions/cm2. Optical sensitive, implanted Ag nano-dots are placed at selective sites of the patterns by exploiting the geometrical structure of the pattern and local ion implantation angle. Surface chemical analysis by X-ray photoelectron spectroscopy and cross-sectional investigation by transmission electron microscopy (TEM) confirms the presence of isolated Ag dots arrays at the specific sites of the nano-pyramidal template structures. The presence of isolated Ag dots on the silicon/silicon nitride surface shows a significant enhancement of the Raman signal, which further rises by the increase of Ag ion fluence. A change of light reflectance from the substrate surface is also observed due to the presence of Ag dots. The growth mechanism of the pyramidal structure by grazing incidence ion bombardment and the approach of isolated Ag dot formation by the self-masking process as well as optical responses are described.

Re-examination of the Aqueous Stability of Atomic Layer Deposited (ALD) Amorphous Alumina (Al2O3) Thin Films and the Use of a Postdeposition Air Plasma Anneal to Enhance Stability.

Amorphous aluminum oxide (alumina) thin films are of interest as inert chemical barriers for various applications. However, the existing literature on the aqueous stability of atomic layer deposited (ALD) amorphous alumina thin films remains incomplete and, in some cases, inconsistent. Because these films have a metastable amorphous structure─which is likely partially hydrated in the as-deposited state─hydration and degradation behavior likely deviate from what is expected for the equilibrium, crystalline Al2O3 phase. Deposition conditions and the aqueous solution composition (ion content) appear to influence the reactivity and stability of amorphous ALD alumina films, but a full understanding of why these alumina films hydrate, solvate, and/or dissolve in near-neutral pH = 7 conditions, for which crystalline Al2O3 is expected to be stable, remains unsolved. In this work, we conduct an extensive X-ray photoelectron spectroscopy investigation of the surface chemistry as a function of water immersion time to reveal the formation of oxyhydroxide (AlOOH), hydroxide (Al(OH)3), and possible carbonate species. We further show that brief postdeposition exposures of these ALD alumina films to an air plasma anneal can significantly enhance the film's stability in near-neutral pH aqueous conditions. The simplicity and effectiveness of this plasma treatment may provide a new alternative to thermal annealing and capping treatments typically used to promote aqueous stability of low-temperature ALD metal oxide barrier layers.

Corrosion Behavior of Chromium Coated Zy-4 Cladding under CANDU Primary Circuit Conditions

The manuscript is focused on corrosion behavior of a Cr coating under CANada Deuterium Uranium(CANDU) primary circuit conditions. The Cr coating is obtained via the thermionic vacuum arc procedure on Zircaloy -4 cladding. The surface coating characterization was performed using metallographic analysis and scanning electron microscopy (SEM) with an energy dispersive spectra detector (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) investigations. The thickness of the Cr coating determined from SEM images is around 500 nm layers After the autoclaving period, the thickness of the samples increased in time slowly. The kinetic of oxidation established a logarithmic oxidation law. The corrosion tests for various autoclaving periods of time include electrochemical impedance spectroscopy (EIS) and potentiodynamic tests, permitting computing porosity and efficiency of protection. All surface investigations sustain electrochemical results and promote the Cr coating on Zircaloy-4 alloy autoclaved for 3024 h as the best corrosion resistance based on decrease in corrosion current density values simultaneously with the increase of the time spent in autoclave. A slow increase of Vickers micro hardness was observed as a function of the autoclaved period as well. The value reached for 3024 h being 219 Kgf/mm2 compared with 210 Kgf/mm2 value before autoclaving.

Altering magnetic and optical features of rare earth orthoferrite LuFeO3 ceramics via substitution of Ir into Fe sites

LuFeO3 and LuFe1-xIrxO3 ceramics with x ​= ​0.05 and 0.10 have been obtained by solid-state reaction process. Scanning electron microscope (SEM) analyses have revealed the existence of both particle agglomeration and porosity of nature of the studied samples. The X-ray photoelectron spectroscopy (XPS) investigations have revealed that while Lu has 3+, Fe has mix valence states, 2+ and 3+. On the other hand, the Ir dopant has metallic and 4+ valence states in the study samples. The Raman investigations unveiled i) the Raman peak intensity reduces with Ir doping until ∼600 ​cm−1, ii) the peaks appearing between 200 ​cm−1 and 600 ​cm−1 wavenumbers shift toward the smaller values. Magnetic measurements, conducted by vibrating sample magnetometer (VSM), have shown the spin re-orientation (SR) transition temperature around 47 ​K for all the investigated samples. Furthermore, it is noticed the 5 ​mol % Ir doped sample has higher magnetization than other samples owing to existence of magnetic impurities such as Lu3Fe5O12. M ​− ​H loops have unveiled that Ir doping advances both Hc and Mr values compared to the undoped LFO sample. This increase in both Hc and Mr values could be due to 1) the variation of the canted angels of Fe3+ moments, 2) the advancement of energy of magnetocrystalline anisotropy, and 3) formation of secondary phases such as Lu3Fe5O12 and Fe3O4. Furthermore, the optical band gap examinations have revealed that the band gap of LFO reduces from 2.19 ​eV to 2.

Matching the Cellulose/Silica Films Surface Properties for Design of Biomaterials That Modulate Extracellular Matrix.

The surface properties of composite films are important to know for many applications from the industrial domain to the medical domain. The physical and chemical characteristics of film/membrane surfaces are totally different from those of the bulk due to the surface segregation of the low surface energy components. Thus, the surfaces of cellulose acetate/silica composite films are analyzed in order to obtain information on the morphology, topography and wettability through atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and contact angle investigations. The studied composite films present different surface properties depending on the tetraethyl orthosilicate (TEOS) content from the casting solutions. Up to a content of 1.5 wt.% TEOS, the surface roughness and hydrophobicity increase, after which there is a decrease in these parameters. This behavior suggests that up to a critical amount of TEOS, the results are influenced by the morphology and topographical features, after which a major role seems to be played by surface chemistry—increasing the oxygenation surfaces. The morphological and chemical details and also the hydrophobicity/hydrophilicity characteristics are discussed in the attempt to design biological surfaces with optimal wettability properties and possibility of application in tissue engineering.

The fabrication and characterization of half-Heusler YPdBi thin films

The electrical, optical, and magnetic properties of half-Heusler compounds make them novel interesting materials being studied by many groups worldwide. The synthesis of YPdBi, a member of half-Heusler compounds, thin films have been achieved at different deposition temperatures such as 360 °C and 470 °C by employing magnetron co-sputtering technique. X-ray diffraction (XRD) examinations have revealed that the film deposited at 360 °C has a slightly larger lattice parameter, 6.82 Å, than the film fabricated at 470 °C, having 6.73 Å. The induced strain of the films has been 2.1% and 0.7% for the films deposited at 360 °C and 470 °C, respectively. X-ray photoelectron spectroscopy (XPS) investigations have revealed the obtained films have the stoichiometry close to the 1:1:1 ratio. Scanning electron microscopy (SEM) studies have shown that surface topography varies dramatically as the deposition temperature advances. Furthermore, high-resolution scanning transmission electron microscopy (STEM) has shown that layer-plus-island growth known as the Stranski–Krastanov (SK) growth mode, taking place due to minimization of strain energy, leads to the island formation from a specific film thickness on. It has been shown that while the resistance of the sample grown at 470 °C changes abruptly at 2.45 K, which indicates the onset of superconductivity, the sample deposited at 360 °C does not show this effect. The absence of the onset of superconductivity in this latter case might be associated with the lattice strain and intensive scattering in this sample.

Multifunctional feature of double perovskite strontium iron vanadate for storage device

In this report, we have investigated the structure, vibration, optical, dielectric, transport and magnetic features of the double perovskite Sr2FeVO6. The structural investigation of the sample is done by incorporating X-ray diffraction (XRD) and scanning electron microscopic (SEM) technique at room temperature. The structural investigation suggests the formation of a single phase polycrystalline sample having monoclinic symmetry. The chemical composition and valence of the involved elements are investigated by incorporating the X-ray photoelectron spectroscopic (XPS) technique. The dual oxidation state of Fe is revealed through the XPS investigation. The vibrational property of the sample is analyzed through both Raman and FTIR spectroscopic methods. The various modes of vibrations such as symmetric, anti-symmetric and bending modes are illustrated through Raman and FTIR techniques. Analysis of optical spectrum and energy bandgap of the sample is done by UV–Visible spectroscopic technique. The bandgap (Eg = 2.88 eV) of the material is found suitable for photocatalytic activities. The dielectric spectrum of the sample is analyzed by investigating the variation of dielectric parameters, that is εr and tanδ, w.r.t frequency-temperature. The dielectric spectrum is found consistent with Maxwell-Wagner model. The electrical and transport activities in the material are investigated by analyzing the spectra of impedance, modulus and AC conductivity at varying frequencies and temperatures. The relaxation feature of the material is illustrated through impedance and modulus spectroscopic techniques whereas the significant contribution of hopping conduction mechanism is depicted through AC conductivity spectra. Finally, the ferromagnetic property of the material at room temperature is clarified through the hysteresis curve.

Raman and X-ray photoelectron spectroscopic investigation of solution processed Alq3/ZnO hybrid thin films

In this study, we characterize the solution processed tris-(8-hydroxyquinoline)aluminum(Alq3)/ZnO hybrid thin films using Raman and X-ray photoelectron spectroscopic (XPS) techniques. Raman studies reveal the sol–gel derived spin-coated ZnO thin film has hexagonal wurtzite structure. The incorporation of Alq3 molecules in the hybrid film results in the formation of bonding onto the surface of highly crystalline ZnO nanoparticles. The XPS confirms the incorporation of Alq3 in the hybrid thin films and corroborates that the Alq3 molecules may be adsorbed onto the surface of ZnO nanoparticles (chemisorption), showing the existence of chemical interaction between Alq3 and ZnO in the hybrid films. These studies support that the chemisorbed Alq3 molecules onto the ZnO nanoparticles may facilitate the charge transfer (non-radiative) between Alq3 and ZnO in the hybrid thin films which will be useful to enhance the optical and electrical properties for the optoelectronic device applications.

Ultrafine PdRu Nanoparticles Immobilized in Metal–Organic Frameworks for Efficient Fluorophenol Hydrodefluorination under Mild Aqueous Conditions

Ultrafine PdRu Nanoparticles Immobilized in Metal–Organic Frameworks for Efficient Fluorophenol Hydrodefluorination under Mild Aqueous Conditions

Hard/soft effects of multivalence co-dopants in correlation with their location in PZT ceramics

Piezoelectric hard/soft effects of multivalence co-dopants (Sb and Mn) in correlation with their location in the lattice, were investigated in PZT ceramics, prepared by conventional ceramic technology, with the following compositions: Pb0.98Sr0.02 ((Ti0.49Zr0.51)1-0.015-xMn0.015Sbx)O3 with x = 0, 0.005, 0.01, 0.02, 0.03, where antimony was initially assumed to substitute for Ti/Zr ions. The antimony valence state was found to be +3 in all samples by X-ray Photoelectron Spectroscopy investigations. The Electron Paramagnetic Resonance spectra evidenced a steep enhancement of the Mn2+ concentration upon increasing antimony doping level, explained by a charge compensation mechanism, between the Sb3+ ions substituting Pb2+ at the A-sites and the Mn2+ ions, localized at the B-sites. The incorporation of Sb3+ at the A-site of the PZT lattice is also supported by the variation of the lattice parameters, determined by X-ray Diffraction, with the increasing Sb concentration. The investigation of the dielectric, electromechanical and ferroelectric properties evidenced a hard piezoelectric behavior, mainly attributed to the presence of large sized Mn2+ ions, localized at B-sites. Our results prove that the piezoelectric hard/soft response is decisively influenced by the interplay between multiple valence states and locations of the co-dopants, on one hand, and the charge compensation mechanisms, on the other hand. This provides indirect information about the location of some co-dopants which can substitute for both cationic sites in the PZT based ceramics.

Boosting Efficient Ammonia Synthesis over Atomically Dispersed Co-Based Catalyst via the Modulation of Geometric and Electronic Structures

Boosting Efficient Ammonia Synthesis over Atomically Dispersed Co-Based Catalyst via the Modulation of Geometric and Electronic Structures

Iodine local environment in high pressure borosilicate glasses: An X-ray photoelectron spectroscopy and X-ray absorption spectroscopy investigation

• Iodine is dissolved as iodide (I − ) in high pressure borosilicate glasses. • Both alkali and alkaline-earth cations act as a charge compensator to I − species. • The absence of iodate (I 5+ ) suggests that there is a complex interplay between I − species and oxygen species within the glass structure. The 129 I radioactive isotope is a by-product of nuclear plants activity. Owing to its strong volatility, there is currently no ideal protocol to immobilize 129 I in nuclear waste borosilicate glasses. Recently, we have proposed the use of high-pressure syntheses to dissolve iodine in various glass compositions; however, I speciation and dissolution mechanism could not be determined. We have adopted an approach combining X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS) methods to determine I speciation and molecular environment in glasses containing from 0.5 to 2.5 mol.% I. The XPS spectra reveal that I is mostly dissolved as iodide (>85% I − ) with a small proportion of elemental iodine (<15% I 0 ) and the absence of iodate species (I 5+ ). For borosilicate glasses, the XAS results and subsequent spectrum simulations suggested that Na and Ca are involved in the I − vicinity with averaged derived coordination number (CN) of 3.6 and 2.0 and bond length to the nearest neighbour (r X-I ) 2.98 and 2.85 Å, respectively. These results suggest that the coexistence of both I − and I 5+ species is not requested for electric neutrality but instead, we explain the I speciation by the possible interplay with oxygen species from the borosilicate matrix. In addition, the results imply that the borosilicate network is affected by the I dissolution.

Study of the electronic structure of Ce0.95Fe0.05O2-δ thin film using X-ray photoelectron spectroscopy

In the present work, the effect of the oxygen partial pressure (OPP) has been studied on the electronic structure of the Ce0.95Fe0.05O2-δ thin film (TF) through Raman spectroscopy, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The varying OPP, from 200 mTorr to 1 mTorr, was observed to vary the oxidation conditions during TF deposition. The oxygen valency was estimated to be reduced along with the generation of oxygen vacancies as determined via Raman analysis. The AFM analysis revealed the lowered values of the roughness parameters which indicated that reduction in OPP is associated with the smoothness of the film surface. The film surface was found to be reduced, as characterized by XPS investigation, as a result of the change in valency of Ce from +4 to +3 due to reduced OPP. The concentration of Ce3+ state was estimated to increase from 19.5% to 33% with reducing OPP. This evidently supports the formation of oxygen vacancies since the reduction of the valence state of Ce is known to be accompanied by the generation of oxygen vacancies. The O1 s spectra confirmed the oxygen non-stoichiometry as a function of OPP, whereas, Fe 2p suggested the mixed-valence state of Fe (Fe2+/Fe3+) in Ce0.95Fe0.05O2-δ (TF). To put in brief, the variation in OPP affects the chemical composition of the material by modifying its electronic structure via controlling the exchange interactions in the core structure of the compound.

Effects of Surface Heterogeneity of α-Quartz and α-Cristobalite on Adsorption of Crystal Violet

Silica minerals are a kind of important minerals and widespread on the earth’s surface. They play an irreplaceable role in the whole geochemistry and environment processes. The diversity in the crystal structure of SiO2 polymorphs might lead to the heterogeneity in their surface microstructures and properties. As two common SiO2 polymorph minerals in soil and sediments, α-quartz and α-cristobalite have been studied for the effects of their surface heterogeneity on adsorption behaviors toward crystal violet (CV) by batch adsorption experiments in different specific surface areas (SSAs) and at different pH values and temperatures, as well as by X-ray photoelectron spectroscopy (XPS) investigation. Owing to the larger surface site density, the saturated adsorption amount of α-quartz was larger than that of α-cristobalite. It was also indicated by the larger slope of adsorption lines as a function of SSA. The adsorption capacity of both increased with increasing pH and temperature. In the thermodynamic study, the negative ΔG indicated that the adsorption of CV on the surface was spontaneous and the positive ΔH suggested that the reaction was endothermic. The well-fitted Langmuir adsorption isotherms suggested that the CV adsorption was monolayer adsorption. The adsorption interaction force was mainly involved in electrostatic attraction force between the negatively charged surface reactive sites and positively charged N atoms in the dimethylamino groups of CV. The XPS spectra of N 1s showed that the stoichiometric ratio of Nlow/Nhigh changed from lower than 2:1 to about 2:1 as the adsorption changed from the unsaturated to saturated state. The change reflected that the spatial arrangement of adsorbed CV monomer on the mineral surface could be readjusted by lifting the average tilt angle between the average plane of the CV monomer and the sample surface during the adsorption process. Surface heterogeneity of α-quartz and α-cristobalite controlled the different distributions and postures of adsorbed CV monomers on the surface. The CV monomers adsorbed on α-quartz presented a larger average tilt angle because of its larger surface reactive site density, while α-cristobalite did conversely.