Associative versus dissociative adsorption of water on Al(100)

The adsorption of water on Al (100) at 100 K has been studied using Fourier transform infrared-reflection absorption spectroscopy (FTIR-RAS), nuclear reaction analysis (NRA) and work function measurements (Δφ). All results are consistent with molecular adsorption, as no evidence was found for other possible dissociation products such as atomic O or D (H) at this temperature. By condensing alternating layers of D₂O and H₂O, it was found that a narrow feature in the _v(OD) (_v(OH)) region of the spectrum at 2720 cm⁻¹ (3700 cm⁻¹) is associated with non-hydrogen bonded OD (OH) groups in water molecules existing at the ice-vacuum interface. Surface hydroxyl groups resulting from dissociative adsorption exhibit a broader O-D stretch at 2760 cm⁻¹.     

Ultrasound assisted synthesis of highly active nanoflower-like CoMoS4 electrocatalyst for oxygen and hydrogen evolution reactions

Rapid technological development requires sustainable, pure, and clean energy systems, such as hydrogen energy. It is difficult to fabricate efficient, highly active, and inexpensive electrocatalysts for the overall water splitting reaction: the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The present research work deals with a simple hydrothermal synthesis route assisted with ultrasound that was used to fabricate a 3D nanoflower-like porous CoMoS₄ electrocatalyst. A symmetric electrolyzer cell was fabricated using a CoMoS₄ electrode as both the anode and cathode, with a cell voltage of 1.51 V, to obtain a current density of 10 mA/cm². Low overpotentials were observed for the CoMoS₄ electrode (250 mV for OER and 141 mV for HER) at a current density of 10 mA/cm².     

Raman spectroscopic study of the uranyl carbonate mineral zellerite

Raman and infrared spectra of the uranyl mineral zellerite, Ca[(UO₂)(CO₃)₂(H₂O)₂]·3H₂O, were measured and tentatively interpreted. U O bond in uranyl and O H···O hydrogen bonds were calculated from the vibrational spectra. The presence of structurally nonequivalent water molecules in the crystal structure of zellerite was inferred. A proposed chemical formula of zellerite is supported. Raman bands at 3514, 3375 and 2945 cm⁻¹and broad infrared bands at 3513, 3396 and 3326 cm⁻¹ are related to the ν OH stretching vibrations of hydrogen‐bonded water molecules. Observed wavenumbers of these vibrations prove that in fact hydrogen bonds participate in the crystal structure of zellerite. The presence of two bands at 1618 and 1681 cm⁻¹ proves structurally distinct and nonequivalent water molecules in the crystal structure of zellerite. Copyright © 2008 John Wiley & Sons, Ltd.     

Raman microscopy of haidingerite Ca(AsO3OH)·H2O and brassite Mg(AsO3OH)·4H2O

Raman spectroscopy has been used to study the arsenate minerals haidingerite Ca(AsO₃OH)·H₂O and brassite Mg(AsO₃OH)·4H₂O. Intense Raman bands in the haidingerite spectrum observed at 745 and 855 cm⁻¹ are assigned to the (AsO₃OH)²⁻ν₃ antisymmetric stretching and ν₁ symmetric stretching vibrational modes. For brassite, two similarly assigned intense bands are found at 809 and 862 cm⁻¹. The observation of multiple Raman bands in the (AsO₃OH)²⁻ stretching and bending regions suggests that the arsenate tetrahedrons in the crystal structures of both minerals studied are strongly distorted. Broad Raman bands observed at 2842 cm⁻¹ for haidingerite and 3035 cm⁻¹ for brassite indicate strong hydrogen bonding of water molecules in the structure of these minerals. OH···O hydrogen‐bond lengths were calculated from the Raman spectra based on empirical relations. Copyright © 2009 John Wiley & Sons, Ltd.     

The impact of ultrasonic parameters on the exfoliation of NiFe LDH nanosheets as electrocatalysts for the oxygen evolution reaction in alkaline media

The ultrasonic process has been examined to exfoliate layered materials and upgrade their properties for a variety of applications in different media. Our previous studies have shown that the ultra-sonication treatment in water without chemicals has a positive influence on the physical and electrochemical performance of layered materials and nanoparticles. In this work, we have probed the impact of ultrasonication on the physical properties and the oxygen evolution reaction (OER) of the NiFe LDH materials under various conditions, including suspension concentration (2.5–12.5 mg mL⁻¹), sonication times (3–20 min) and amplitudes (50–90%) in water, in particular, sonication times and amplitudes. We found that the concentration, amplitude and time play significant roles on the exfoliation of the NiFe LDH material. Firstly, the NiFe LDH nanosheets displayed the best OER performance under ultrasonic conditions with the concentration of 10 mg mL⁻¹ (50% amplitude and 15 min). Secondly, it was revealed that the exfoliation of the NiFe LDH nanosheets in a short time (<10 min) or a higher amplitudes (≥80%) has left a cutdown on the OER activity. Comprehensively, the optimum OER activity was displayed on the exfoliated NiFe LDH materials under ultrasonic condition of 60% (amplitude), 10 mg mL⁻¹ and 15 min. It demanded only 250 mV overpotentials to reach 10 mA cm⁻² in 1 M KOH, which was 100 mV less than the starting NiFe LDH material. It was revealed from the mechanism of sonochemistry and the OER reaction that, after exfoliation, the promoted OER performance is ascribed to the enriched Fe³⁺ at the active sites, easier oxidation of Ni²⁺ to Ni³⁺, and the strong electrical coupling of the Ni²⁺ and Fe³⁺ during the OER process. This work provides a green strategy to improve the intrinsic activity of layered materials.     

Two-dimensional condensation of water and alcohols on NaF

On the surface of NaF the adsorption isotherms of H₂O, D₂O, CH₃OH, C₃H₃OH and 1-C₃H₇OH as well as the infrared spectra of H₃O, D₂O, dilute HDO, CH₃OH and CH₃OD were measured. The adsorption temperatures of H₃O (253–308 K) were within the phase transition region where two phases of low and high density coexist, while those of CH₃OH, C₂H₅OH and 1-C₃H₃OH were yet within a super-critical region. The entropy of the 2D condensed H₂O on NaF was found to be 14.0 cal K^?1 mol^?1, which suggests that the condensed phase of water on NaF is liquid-like. The OD stretching band of dilute HDO in the 2D condensed water gives a maximum adsorption at ca. 2530 cm^?1 with a half width of ca. 150 cm^?1, being in good agreement with that in liquid water. Comparison of the integrated absorbance of the D₂O bending mode with that of the OD stretching mode suggests that the cluster size of the 2D condensed water on NaF decreases with increasing temperature. The 2D critical temperature and the occupied areas of these adsorbates enable us to conclude that the compatibility of the molecular size with the surface lattice is not important in the occurrence of the 2D condensation of the hydrogen-bonding molecules on NaF and that adsorbed molecules are randomly oriented on the surface to the extent similar to that in 3D liquid state.     

Raman‐induced Kerr effect spectroscopy of single‐wall carbon nanotubes aqueous suspensions in the range 0.1–10 and 100–250 cm−1

Here, we study a low (less than 0.1 µg/ml) concentration aqueous suspension of single‐wall carbon nanotubes (SWNTs) by Raman‐induced Kerr effect spectroscopy (RIKES) in the spectral bands 0.1–10 and 100–250 cm⁻¹. This method is capable of carrying out direct investigation of SWNT hydration layers. A comparison of RIKES spectra of SWNT aqueous suspension and that of milli‐Q water shows a considerable growth in the intensity of low wavenumber Raman modes. These modes in the 0.1–10 cm⁻¹ range are attributed to the rotational transitions of H₂O₂ and H₂O molecules. We explain the observed intensity increase as due to the production of hydrogen peroxide and the formation of a low‐density depletion layer on the water–nanotube interface. A few SWNT radial breathing modes (RBM)are observed (ω_RBM = 118.5, 164.7 and 233.5 cm⁻¹) in aqueous suspension, which allows us to estimate the SWNT diameters (∼2.0, 1.5, and 1 nm, respectively). Copyright © 2011 John Wiley & Sons, Ltd.     

Raman spectroscopy of hydrogen‐arsenate group (AsO3OH) in solid‐state compounds: copper mineral phase geminite Cu(AsO3OH)·H2O from different geological environments

The participation of hydrogen‐arsenate group (AsO₃OH)²⁻ in solid‐state compounds may serve as a model example for explaining and clarifying the behaviour of As and other elements during weathering processes in natural environment. The mineral geminite, a hydrated hydrogen‐arsenate mineral of ideal formula Cu(AsO₃OH)·H₂O, has been studied by Raman and infrared spectroscopies. Two samples of geminite of different origin were investigated and the spectra proved quite similar. In the Raman spectra of geminite, six bands are observed at 741, 812, 836, 851, 859 and 885 cm⁻¹ (Salsigne, France), and 743, 813, 843, 853, 871 and 885 cm⁻¹ (Jáchymov, Czech Republic). The band at 851/853 cm⁻¹ is assigned to the ν₁ (AsO₃OH)²⁻ symmetric stretching mode; the other bands are assigned to the ν₃ (AsO₃OH)²⁻ split triply degenerate antisymmetric stretching mode. Raman bands at 309, 333, 345 and 364/310, 333 and 345 cm⁻¹ are attributed to the ν₂ (AsO₃OH)²⁻ bending mode, and a set of higher wavenumber bands (in the range 400–500 cm⁻¹) is assigned to the ν₄ (AsO₃OH)²⁻ split triply degenerate bending mode. A very complex set of overlapping bands is observed in both the Raman and infrared spectra. Raman bands are observed at 2289, 2433, 2737, 2855, 3235, 3377, 3449 and 3521/2288, 2438, 2814, 3152, 3314, 3448 and 3521 cm⁻¹. Two Raman bands at 2289 and 2433/2288 and 2438 cm⁻¹ are ascribed to the strong hydrogen bonded water molecules. The Raman bands at 3235, 3305 and 3377/3152 and 3314 cm⁻¹ may be assigned to the ν OH stretching vibrations of water molecules. Two bands at 3449 and 3521/3448 and 3521 cm⁻¹ are assigned to the OH stretching vibrations of the (AsO₃OH)²⁻ units. The lengths of the O H···O hydrogen bonds vary in the range 2.60–2.94 Å (Raman) and 2.61–3.07 Å (infrared). Two Raman and infrared bands in the region of the bending vibrations of the water molecules prove that structurally non‐equivalent water molecules are present in the crystal structure of geminite. Copyright © 2009 John Wiley & Sons, Ltd.     

SERS investigation of interfacial water at a silver electrode in acetonitrile solutions

Surface-enhanced Raman scattering from a silver electrode in solution of 0.1 M LiClO₄ in acetonitrile has been analyzed as a function of applied potential. Three ν(O-H) bands associated with the interfacial water and two ν(O-H) bands associated with the OH⁻ ion species were observed depending on the electrode potential. The band at 3487 cm⁻¹ is favored at relatively positive potentials and assigned to H₂O molecules interacting with the electrode surface via the oxygen atoms. Another band at 3586 cm⁻¹ appears in a wider potential region and is assigned to the H₂O molecules with one or both of the hydrogen atoms facing the electrode surface. Additionally, evidence for the possible surface ion pair, Li⁺OH⁻, which is closely associated with H₂O molecules and the quasi-crystalline form of LiOH are also presented in this paper.     

Raman spectroscopic investigations of natural jennite from Maroldsweisach,Bavaria, Germany

A full‐range pattern (100–3700 cm⁻¹) analysis of natural jennite was performed for the first time by Raman spectroscopy, applying a polarized laser at a wavelength of 532 nm. A prominent structural feature of jennite is the preferred orientation of Si‐tetrahedron and Ca‐octahedron chains parallel [010]. The latter ones are additionally coupled to H₂O molecules and OH groups. This arrangement leads to a strong dependence on orientation for the intensity ratios of mainly three different regions in the Raman spectra: 180–210, 950–1050 and 3100–3650 cm⁻¹. These sections can be assigned to Ca–O lattice vibrations, Q² Si–tetrahedron stretching and O–H vibrations of H₂O molecules and Ca–OH structures, respectively. Copyright © 2015 John Wiley & Sons, Ltd.     

A Highly Effective,Stable Oxygen Evolution Catalyst Derived from Transition Metal Selenides and Phosphides

Recently, transition metal chalcogenides and phosphides have been increasingly reported as efficient and stable oxygen evolution reaction (OER) catalysts in alkaline medium, despite the fact that they are thermodynamically unstable under highly oxidative potentials. Here the active forms of these materials are elucidated by synthesizing a hybrid catalyst, which has a metal chalcogenide in the form of CoSe₂ and metal phosphide in the form of CoP—CoSe₂|CoP. Both CoSe₂ and CoP in the as‐prepared catalyst are completely transformed into their respective oxyhydroxides and hydroxides, which are, in fact, the true OER‐active species in alkaline medium and not the selenide and phosphide themselves. The derived oxides from the hybrid catalyst deliver an excellent OER activity by reaching a current density of 10 mA cm⁻² at a low overpotential of 240 mV (vs reversible hydrogen electrode (RHE)) and a Tafel slope of 46.6 mV dec⁻¹. The stability of the derived oxyhydroxide/hydroxide catalyst shows no appreciable deactivation during 120 h of continuous electrolysis, displaying an extraordinary operational stability.     

Computer study of acetylene and ethane adsorption by disperse water medium

Adsorption of acetylene and ethane molecules by water clusters has been investigated by the molecular dynamics method at T=233 K. With the help of determination of statistical weights the cluster systems are created. In the frequency range of 0?ω?1000 cm⁻¹ the integral absorption coefficient of IR-radiation increases after the adsorption of acetylene or ethane molecules by the ultra disperse water system. The dissipation power of IR-radiation by cluster systems increases if C₂H₂ molecules are adsorbed, and it reduces in the case of C₂H₆ molecules' adsorption.     

Raman spectroscopic study of the hydrogen‐arsenate mineral pharmacolite Ca(AsO3OH)·2H2O—implications for aquifer and sediment remediation

The removal of arsenate anions from aqueous media, sediments and wasted soils is of environmental significance. The reaction of gypsum with the arsenate anion results in pharmacolite mineral formation, together with related minerals. Raman and infrared (IR) spectroscopy have been used to study the mineral pharmacolite Ca(AsO₃OH)· 2H₂O. The mineral is characterised by an intense Raman band at 865 cm⁻¹ assigned to the ν₁ (AsO₃)²⁻ symmetric stretching mode. The equivalent IR band is found at 864 cm⁻¹. The low‐intensity Raman bands in the range from 844 to 886 cm⁻¹ provide evidence for ν₃ (AsO₃) antisymmetric stretching vibrations. A series of overlapping bands in the 300‐450 cm⁻¹ region are attributed to ν₂ and ν₄ (AsO₃) bending modes. Prominent Raman bands at around 3187 cm⁻¹ are assigned to the OH stretching vibrations of hydrogen‐bonded water molecules and the two sharp bands at 3425 and 3526 cm⁻¹ to the OH stretching vibrations of only weakly hydrogen‐bonded hydroxyls in (AsO₃OH)²⁻ units. Copyright © 2009 John Wiley & Sons, Ltd.     

Ultrathin Fe‐N‐C Nanosheets Coordinated Fe‐Doped CoNi Alloy Nanoparticles for Electrochemical Water Splitting

The development of highly active and cost‐effective catalyst materials toward electrochemical water splitting is of great importance for converting and storing the intermittent solar energy in the form of hydrogen. Herein, for the first time, an ultrathin Fe and N‐co‐doped carbon nanosheet encapsulated Fe‐doped CoNi alloy nanoparticle (FeCoNi@FeNC) composite is obtained and applied as a bifunctional catalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). This catalyst exhibits prominent catalytic performances for both HER and OER, which only requires overpotentials of 102 and 330 mV, respectively, to reach a current density of 10 mA cm^?2 in alkaline media. The high catalytic activity is intrinsically associated with the presence of Fe in both nanosheets and nanoparticles, which has triggered the occurrence of coordinative effects between Fe‐N‐C and FeCoNi that are beneficial for HER and OER, as revealed by electrochemical techniques. In an overall water splitting electrolyzer, FeCoNi@FeNC is employed as both the cathode and anode catalysts, achieving 12 mA cm^?2 at 1.63 V for a duration of more than 12 h.     

Thermo‐Raman spectroscopy of synthetic nesquehonite — implication for the geosequestration of greenhouse gases

Pure nesquehonite (MgCO₃·3H₂O)/Mg(HCO₃)(OH)·2H₂O was synthesised and characterised by a combination of thermo‐Raman spectroscopy and thermogravimetry with evolved gas analysis. Thermo‐Raman spectroscopy shows an intense band at 1098 cm⁻¹, which shifts to 1105 cm⁻¹ at 450 °C, assigned to the ν₁CO₃²⁻ symmetric stretching mode. Two bands at 1419 and 1509 cm⁻¹ assigned to the ν₃ antisymmetric stretching mode shift to 1434 and 1504 cm⁻¹ at 175 °C. Two new peaks at 1385 and 1405 cm⁻¹ observed at temperatures higher than 175 °C are assigned to the antisymmetric stretching modes of the (HCO₃)⁻ units. Throughout all the thermo‐Raman spectra, a band at 3550 cm⁻¹ is attributed to the stretching vibration of OH units. Raman bands at 3124, 3295 and 3423 cm⁻¹ are assigned to water stretching vibrations. The intensity of these bands is lost by 175 °C. The Raman spectra were in harmony with the thermal analysis data. This research has defined the thermal stability of one of the hydrous carbonates, namely nesquehonite. Thermo‐Raman spectroscopy enables the thermal stability of the mineral nesquehonite to be defined, and, further, the changes in the formula of nesquehonite with temperature change can be defined. Indeed, Raman spectroscopy enables the formula of nesquehonite to be better defined as Mg(OH)(HCO₃)·2H₂O. Copyright © 2008 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the uranyl mineral pseudojohannite Cu6.5[(UO2)4O4(SO4)2]2(OH)5·25H2O

Raman spectra of pseudojohannite were studied and related to the structure of the mineral. Observed bands were assigned to the stretching and bending vibrations of (UO₂)²⁺ and (SO₄)²⁻ units and of water molecules. The published formula of pseudojohannite is Cu_6.5(UO₂)₈[O₈](OH)₅[(SO₄)₄]·25H₂O. Raman bands at 805 and 810 cm⁻¹ are assigned to (UO₂)²⁺ stretching modes. The Raman bands at 1017 and 1100 cm⁻¹ are assigned to the (SO₄)²⁻ symmetric and antisymmetric stretching vibrations. The three Raman bands at 423, 465 and 496 cm⁻¹ are assigned to the (SO₄)²⁻ν₂ bending modes. The bands at 210 and 279 cm⁻¹ are assigned to the doubly degenerate ν₂ bending vibration of the (UO₂)²⁺ units. U O bond lengths in uranyl and O H···O hydrogen bond lengths were calculated from the Raman and infrared spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the antimonate mineral brandholzite Mg[Sb2(OH)12]·6H2O

Raman spectra of brandholzite Mg[Sb₂(OH)₁₂]·6H₂O were studied, complemented with infrared spectra, and related to the structure of the mineral. An intense Raman sharp band at 618 cm⁻¹ is attributed to the SbO symmetric stretching mode. The low‐intensity band at 730 cm⁻¹ is ascribed to the SbO antisymmetric stretching vibration. Low‐intensity Raman bands were found at 503, 526 and 578 cm⁻¹. Corresponding infrared bands were observed at 527, 600, 637, 693, 741 and 788 cm⁻¹. Four Raman bands observed at 1043, 1092, 1160 and 1189 cm⁻¹ and eight infrared bands at 963, 1027, 1055, 1075, 1108, 1128, 1156 and 1196 cm⁻¹ are assigned to δ SbOH deformation modes. A complex pattern resulting from the overlapping band of the water and hydroxyl units is observed. Raman bands are observed at 3240, 3383, 3466, 3483 and 3552 cm⁻¹; infrared bands at 3248, 3434 and 3565 cm⁻¹. The Raman bands at 3240 and 3383 cm⁻¹ and the infrared band at 3248 cm⁻¹ are assigned to water‐stretching vibrations. The two higher wavenumber Raman bands observed at 3466 and 3552 cm⁻¹ and two infrared bands at 3434 and 3565 cm⁻¹ are assigned to the stretching vibrations of the hydroxyl units. Observed Raman and infrared bands in the OH stretching region are associated with O‐H···O hydrogen bonds and their lengths 2.72, 2.79, 2.86, 2.88 and 3.0 Å (Raman) and 2.73, 2.83 and 3.07 Å (infrared). Copyright © 2009 John Wiley & Sons, Ltd.     

Rotational contours of electronic and electronic-vibrational bands of carbazole complexes with water cooled in a supersonic jet

The rotational contours of the bands corresponding to electronic and electronic-vibrational transitions of the fluorescence excitation spectrum of jet-cooled carbazole complexes with one, two, and three water molecules have been studied. For the carbazole-(H₂O)₁ complex, two bands with a spectral shift of 0.57 cm^?1 were recorded under exposure to radiation with a spectral width of 0.08 cm^?1 at the frequency of the purely electronic transition and some other electronic-vibrational transitions. This is caused by the tunnel effect. The intensities of the shifted low-frequency bands are threefold weaker than those of high-frequency bands due to different values of nuclear spin-statistical weights. In the carbazole-(H₂O)₂ and carbazole-(H₂O)₃ complexes, water molecules are combined into a chain by the hydrogen bond, and the two ends of the chain are hydrogen-bonded to the carbazole molecule. The principal axes I _A and I _B of the moments of inertia in carbazole-(H₂O)₃ have different orientation compared to the other complexes considered, and this leads to an increase in the intensity of the Q-branch.     

Natural halotrichites—an EDX and Raman spectroscopic study

Raman spectroscopy has been used to characterise four natural halotrichites: halotrichite FeSO₄.Al₂(SO₄)₃. 22H₂O, apjohnite MnSO₄.Al₂(SO₄)₃.22H₂O, pickingerite MgSO₄.Al₂(SO₄)₃.22H₂O and wupatkiite CoSO₄.Al₂(SO₄)₃.22H₂O. A comparison of the Raman spectra is made with the spectra of the equivalent synthetic pseudo‐alums. Energy dispersive X‐ray analysis (EDX) was used to determine the exact composition of the minerals. The Raman spectrum of apjohnite and halotrichite display intense symmetric bands at ∼985 cm⁻¹ assigned to the ν₁(SO₄)²⁻ symmetric stretching mode. For pickingerite and wupatkiite, an intense band at ∼995 cm⁻¹ is observed. A second band is observed for these minerals at 976 cm⁻¹ attributed to a water librational mode The series of bands for apjohnite at 1104, 1078 and 1054 cm⁻¹, for halotrichite at 1106, 1072 and 1049 cm⁻¹, for pickingerite at 1106, 1070 and 1049 cm⁻¹ and for wupatkiite at 1106, 1075 and 1049 cm⁻¹ are attributed to the ν₃(SO₄)²⁻ antisymmetric stretching modes of ν₃(B_g) SO₄. Raman bands at around 474, 460 and 423 cm⁻¹ are attributed to the ν₂(A_g) SO₄ mode. The band at 618 cm⁻¹ is assigned to the ν₄(B_g) SO₄ mode. The splitting of the ν₂, ν₃ and ν₄ modes is attributed to the reduction of symmetry of the SO₄ and it is proposed that the sulphate coordinates to water in the hydrated aluminium in bidentate chelation. Copyright © 2007 John Wiley & Sons, Ltd.