Highly Selective Photoreduction of CO2 with Suppressing H2 Evolution by Plasmonic Au/CdSe–Cu2O Hierarchical Nanostructures under Visible Light

Here, the photocatalytic CO₂ reduction reaction (CO₂RR) with the selectivity of carbon products up to 100% is realized by completely suppressing the H₂ evolution reaction under visible light (λ > 420 nm) irradiation. To target this, plasmonic Au/CdSe dumbbell nanorods enhance light harvesting and produce a plasmon‐enhanced charge‐rich environment; peripheral Cu₂O provides rich active sites for CO₂ reduction and suppresses the hydrogen generation to improve the selectivity of carbon products. The middle CdSe serves as a bridge to transfer the photocharges. Based on synthesizing these Au/CdSe–Cu₂O hierarchical nanostructures (HNSs), efficient photoinduced electron/hole (e^?/h⁺) separation and 100% of CO selectivity can be realized. Also, the 2e^?/2H⁺ products of CO can be further enhanced and hydrogenated to effectively complete 8e^?/8H⁺ reduction of CO₂ to methane (CH₄), where a sufficient CO concentration and the proton provided by H₂O reduction are indispensable. Under the optimum condition, the Au/CdSe–Cu₂O HNSs display high photocatalytic activity and stability, where the stable gas generation rates are 254 and 123 µmol g^?1 h^?1 for CO and CH₄ over a 60 h period.     

Preparation, characterization and photocatalytic performances of materials based on CS2-modified titanate nanotubes

CS₂-modified titanate nanotubes (CS₂/TiO₂-NTs) are fabricated by reaction of CS₂ and Ti-O^?Na⁺ species on titanate nanotubes. Pb²⁺ ions are coated on the modified nanotubes by ion exchange (Pb/CS₂/TiO₂-NTs). The products are characterized by means of nitrogen adsorption-desorption isotherms at 77 K (BET method), transmission electron microscopy (TEM), X-ray photoelectron spectrometry (XPS), X-ray diffraction (XRD), atomic absorption spectrometry (AAS), and diffuse reflectance spectroscopy (DRS). The photocatalytic performances of the products are evaluated by monitoring their catalytic activities for degradation of methyl orange under UV light irradiation. The effects of calcination temperature and atmosphere on the photocatalytic performance are investigated. The results reveal that the photocatalytic activities of CS₂/TiO₂-NTs and Pb/CS₂/TiO₂-NTs are far higher than that of primary nanotubes, and the optimum calcination temperature is 500 °C under N₂ atmosphere. It is also discovered that physically adsorbed Pb²⁺ ions affect the photocatalytic activity of Pb/CS₂/TiO₂-NTs obviously. The photocatalytic activity of washed Pb/CS₂/TiO₂-NTs is higher than that of the unwashed one under the same thermal treatment and reaction conditions.     

Morphology and photoluminescence properties of KSm(MoO4)2 microcrystals by a molten salt method

Octahedron-like KSm(MoO₄)₂ microcrystals with monoclinic scheelite-type structure were successfully synthesized via a molten salt method using KCl as the reaction medium. The as-prepared products were characterized by X-ray powder diffractometer, scanning electron microscope, and photoluminescence spectrometer. The results show that the reaction parameters including calcining temperature, reaction time, and salt content play important roles on the morphologies and sizes of the final products. The possible growth process of the octahedron-like microcrystals was proposed based on the time-dependent shape evolution, which contained an oriented aggregation and Ostwald ripening process. Room temperature photoluminescence spectra of KSm(MoO₄)₂ microcrystals reveal the characteristic orange–red emission peaks at 565, 600 and 646 nm via ⁴G_5/2 → ⁶H_5/2, ⁴G_5/2 → ⁶H_7/2 and ⁴G_5/2 → ⁶H_9/2 electronic transitions of Sm³⁺ ions, respectively. These imply that the KSm(MoO₄)₂ microcrystals have potential application in the field of luminescence materials. The possible reasons for the difference in the relative intensities of photoluminescence are also discussed.     

Spontaneous Decay of Highly-Charged Fullerene Ions C60Z+ and C58z+

Abstract

Using isotope-resolved, two sector field mass spectrometric techniques we have identified and investigated quantitatively the energetics and kinetics (in particular the kinetic energy release, KER) of the spontaneous decay reactions C_60–2m ^z+ → C_60-2m-p(z-1)+ ₊ C_p ⁺ with m = 0 or 1, z ranging from 3 to 6 and p = 2 and 4. The obtained KER results are not compatible with the properties expected for a single-step fissioning reaction as described by the liquid drop model. Therefore the present data had to be interpreted by a different fragmentation mechanism. This novel reaction sequence, termed auto charge transfer (ACT) reaction, is initiated by the statistically driven neutral C₂ (or C₄₎ evaporation followed by an electron transfer process from the receding C₂ (or C₄) fragment to the remaining highly-charged fullerene ion thereby leading finally to the two charged reaction products observed in the exit channel of the decay reaction. Moreover, in the case that a C₂ ⁺ loss from C₆₀z+ is occurring in the first field-free region we have been able to demonstrate that it is possible to observe in the second field-free region a subsequent C₂ evaporation from the C₅₈(z-1)⁺ fragment ion.     

Spectroscopic investigations of Cu2+ in Li2O-Na2O-B2O3-Bi2O3 glasses

Pure and copper doped glasses with composition,x Li ₂ O-(40-x)Na ₂ O-50B ₂ O ₃-10Bi ₂ O ₃,have been prepared over the range 0 ≤ x ≤ 40. The electron paramagnetic resonance (EPR) spectra of Cu²⁺ ions of these glasses have been recorded in the X-band at room temperature. Spin Hamiltonian parameters have been calculated. The molecular bonding coefficients, α² and β², have been calculated by recording the optical absorption spectra in the wavelength range 200–1200 nm. It has been observed that the site symmetry around Cu²⁺ ions is tetragonally distorted octahedral. The density and glass transition temperature variation with alkali content shows non-linear behaviour. The IR studies show that the glassy system contains BO₃ and BO₄ units in the disordered manner.     

Preparation of SiC ultrafine particles from SiH2Cl2 and C2H4 gas mixtures by a CO2 laser

Preparation of SiC ultrafine particles from SiH₂Cl₂-C₂H₄ mixtures by a CO₂ laser was investigated. The powders with specific surface area in the 8–150 m² g^–1 range were obtained by irradiating SiH₂Cl₂-C₂H₄ gas mixtures with a CO₂ laser at atmospheric pressure. X-ray diffraction of the products showed that silicon, SiC and free carbon were produced and the composition of the powders depended on the C₂H₄/SiH₂Cl₂ ratio. The reaction flame temperature changed from less than 1273 K to more than 3073 K with the laser power density and C₂H₄/SiH₂Cl₂ ratio. When SiH₂Cl₂ was irradiated with the CO₂ laser, the reaction temperature was less than 1273 K and silicon particles were formed. When the SiH₂Cl₂-C₂H₄ mixture was irradiated with a CO₂ laser, the reaction temperature was low (<1273 K) at low power density and low C₂H₄/SiH₂Cl₂ ratio, but it increased rapidly to around 3000 K at high laser power density and high C₂H₄/SiH₂Cl₂ ratio (>0.3). SiC was formed at both high and low reaction flame temperatures. It was considered that the rapid increase in the reaction flame temperature was caused by the initiation of exothermic reactions and the increase in laser absorption which was caused mainly by carbon particle formation. Hysteresis was observed between the reaction flame temperature and the power density of the laser beam. It was found that SiH₂Cl₂ underwent a disproportionation reaction on irradiation with the CO₂ laser, and silicon and SiC particles were formed through the various products of the disproportionation reaction. In particular, at low reaction flame temperature, the reactive species, such as SiH₄ and SiH₃Cl, produced by the disproportionation of SiH₂Cl₂ were considered to play an important role in the formation of silicon and SiC particles.     

Study on the synthesis and ion-exchange properties of layered titanate Na2Ti3O7 powders with different sizes

Layered titanate Na₂Ti₃O₇ powders with varying sizes were prepared by solid-state reaction of Na₂CO₃ and TiO₂ with different average particle sizes. The structures of the titanates and the products which had undergone H⁺ and Ag⁺ exchange were investigated by XRD, TEM and BET analysis. The influence of the particle size of starting material TiO₂ on the reaction rate, the particle size and ion-exchange property of the resulting products was studied. It is found that nanometer sized TiO₂ facilitates the solid-state reaction and leads to the formation of ultrafine titanate. The H⁺-exchange property is improved by decreasing the particle size of Na₂Ti₃O₇ and the small sized layered titanate can be exfoliated easily by AgNO₃ solution.     

Optical absorption and electron spin resonance studies of Cu2+ in Li2O-Na2O-B2O3-As2O3 glasses

The local structure around Cu²⁺ ion has been examined by means of electron spin resonance and optical absorption measurements in xLi₂O-(40-x)Na₂O-50B₂O₃-10As₂O₃ glasses. The site symmetry around Cu²⁺ ions is tetragonally distorted octahedral. The ground state of Cu²⁺ isd _x ²−y ².The glass exhibited broad absorption band near infrared region and small absorption band around 548 nm, which was assigned to the ²B_1g →²E_g transition.     

Interfacial reactions in Nb/NbSi2 and Nb/NbSi2-B systems

For the use of Nb-based alloys at high temperatures, a high oxidation resistant coating such as NbSi₂ coating is required. In the present study, to clarify the physico-chemical compatibility between Nb and NbSi₂, the extent of the interfacial reaction and the reaction products were studied at temperatures ranging from 1573 to 1773 K. Growth of the reaction layer formed in the interfacial reactions was caused by the preferential diffusion of Si toward to the Nb side, leading to the formation of a Nb₅Si₃ layer. The growth followed a parabolic rate law, and the growth rate constant was expressed by k_p (m² s⁻¹) = 7.98 × 10⁻¹⁰ exp(−131.84 kJ mol⁻¹/RT). In addition, behavior of boron in the Nb/NbSi₂ interfacial reaction was clarified.     

Oxygen Reduction Reaction Promotes Li+ Desorption from Cathode Surface in Li‐O2 Batteries

Li‐O₂ batteries are claimed to be one of the future energy storage technologies. Great number of scientific and technological challenges should be solved first to transform Li‐O₂ battery from a promise to real practical devices. Proposed mechanisms for oxygen reduction assume a reservoir of solved Li⁺ ions in the electrolyte. However, the role that adsorbed Li⁺ on the electrode surface might have on the overall oxygen reduction reaction (ORR) has not deserved much attention. Adsorbed Li⁺ consumption is monitored here using impedance measurements from extended electrochemical double layer capacitance, which depends on the carbon matrix surface area. The presence of O₂ drastically reduces the amount of adsorbed Li⁺, signaling the kinetic competition between Li⁺ surface adsorption and its consumption, only for potentials corresponding to the oxygen reduction reaction. Noticeably double layer capacitance remains unaltered after cycling. This fact suggests that the ORR products (Li₂O₂ and Li₂CO₃) are not covering the internal electrode surface, but deposited on the outer electrode‐contact interface, hindering thereby the subsequent reaction. Current results show new insights into the discharge mechanism of Li‐O₂ batteries and reveal the evidence of Li⁺ desorption from the C surface when the ORR starts.     

Oxidation of Fe–Si alloys in CO2–H2O atmospheres

Abstract

Iron and model alloys containing 1, 2, and 3wt% Si were reacted with dry and wet CO₂ gases at 800°C. All oxidised in dry CO₂ according to approximately linear kinetics. Additions of H₂O accelerated the reaction until steady-state parabolic kinetics were achieved. However, the effect of H₂O was small in the steady-state reaction stage of Fe – 3Si. Alloy reaction products were a duplex scale consisting of an outer FeO+Fe₃O₄ layer and an inner FeO+Fe₂SiO₄ layer, plus an internal oxidation zone, in all gases. In Fe – 1Si, amorphous SiO₂ precipitates in the internal oxidation zone grew with rod-like morphologies in all gases. However, internal amorphous SiO₂ precipitates grown in Fe – 2Si and Fe – 3Si formed network patterns. Internal penetration rates were initially rapid in Fe – 1Si, but slowed considerably at longer times. In Fe – 3Si, the internal oxidation zone grew wider in the first 20 h of reaction, and then remained constant in dry gas. In the wet gases this zone subsequently diminished, and disappeared after 50 h reaction.     

Preparation of ultrafine layered tetratitanate powders using nanoscale TiO<Subscript>2</Subscript> as reactant and their intercalation property

Ultrafine layered potassium tetratitanate K₂Ti₄O₉ powders were prepared by solid-state reaction using nanometer sized TiO₂ as the reactant. The structures of the titanates and the products which had undergone H⁺ exchange and intercalated by propylamine and [Al₁₃O₄(OH)₂₄(H₂O)₁₂]^{7 +} (Al₁₃^{7 +}) were investigated by XRD, TEM, TG and BET analysis. Compared with the larger-sized products prepared by using micrometer sized TiO₂, the ultrafine K₂Ti₄O₉ takes in more intercalating molecules, which leads to the expanding of the interlayer distance of the resulting products. The final Al₂O₃ pillared ultrafine tetratitanate exhibits higher BET surface area (212.8 cm g^{− 1}) and narrow pore-size distribution.     

IR-stimulated second harmonic generation in Sb2Te2 Se-BaF2-PbCl2 glasses

Abstract

Theoretically predicted and experimentally observed infraredinduced second-harmonic generation of glasses in the mid-infrared spectral region can be described by fifth-order nonlinear optical susceptibility. The effect is observed in the mid-IR region when the value of the electronic energy gap is comparable to the energies of actual phonons participating in the anharmonic (non-centrosymmetric) electron-phonon interactions. As subjects for investigation, chalcohalide Sb₂Te₂Se-BaF₂-PbCl₂ glasses were chosen. They are transparent, over a spectral range of 1.1–10.9 μm. The second-harmonic generation (SHG) output signal within the 1.5–4.8 μm spectral range has significant spectral dependence. Correlation of the SHG spectral maxima positions with spectral positions of anharmonic phonon frequencies confirms that the fifth-order steady-state process occurs due to cascading processes and IR-induced charge density non-centrosymmetry. A maximum value of the SHG is achieved at a pump-probe delay time of 18–36 ps, which is typical for anharmonic electron-phonon interactions. As temperature rises, the values of the photoinduced SHG signal susceptibility increases up to 3 × 10^?39 m⁴/V⁴. The SHG signal reaches a saturation point for the IR-pump power densities of about 0.8 GW/cm², which corresponds to the output SHG intensities of about 6 × 10^?4 with respect to fundamental one. The values of the diagonal fifth-order tensor component χ^(2ω) _xxxxx are at least one order of magnitude larger than the off-diagonal tensor components.     

CeO2 induced dispersive distribution of TiB2 particles in in situ TiB2/Al composite

Abstract

The roles of CeO₂ additive during preparation of in situ TiB₂/Al composite, alleviating particle settlement in composite melt and significantly improving particle dispersion in final microstructure, are studied in this paper. It is evidenced that the CeO₂ additive reacts with Al melts to release Ce solute into the melts, and the released surface active Ce is absorbed in the Al/TiB₂ interfaces without any other reaction products. First principles calculations show that the interfacial energy of Al/TiB₂ interfaces is reduced owing to the presence of Ce in Al/TiB₂ interfacial area. Therefore, the wettability of molten Al on TiB₂ surface is increased and the dispersion of TiB₂ particles in Al matrix is eventually improved.     

Synthesis and Spectroscopic Studies of Endohedral Metallofullerenes Tb@C2N

Abstract

Endohedral metallofullerenes Tb@C_2n were synthesized and extracted with high-yield by K-H carbon-are evaporation and an effective pyridine extraction technique at high-temperature high-pressure. Laser-desorption-ionization time-of-flight (LD-TOF) mass spectrometry, X-ray photoelectron spectroscopy (XPS), solid-state fluorescent emission spectroscopy and gas phase derivation reaction with the self-chemical ionization mass spectrometric ion system of vinyl acetate were employed for studying the electronic structures, fluorescent properties and gas phase reactivities of metallofullerenes Tb@C_2n. The experimental results suggest that endohedral metallofullerenes Tb@C_2n would have the approximate structures of Tb³⁺@C_2n ³⁺ similar to other metallofullerenes, good fluorescent emission properties and active reactivities in gas phase ion-molecular reactions.     

Reaction mechanism of the hydrothermally treated CaO-SiO2-Al2O3 and CaO-SiO2-Al2O3-CaSO4 systems

Mixtures of CaO, amorphous SiO₂ and kaolinite in the presence or absence of SO ₄ ^2– ions (added as CaSO₄·2H₂O) were treated in suspension under hydrothermal conditions at temperatures of 80–200 °C. Kaolinite was added to replace 3 and 10% of the total weight of the dry mix with the overall CaO/SiO₂ mole ratio being 0.83. The hydration products were investigated by XRD, IR spectroscopy and DTA techniques in order to elucidate their phase compositions. The results indicate that the presence of SO ₄ ^2– ions leads to a marked increase in the reaction rate at all temperatures investigated. In the C-S-A system, the detected hydration products are calcium silicate hydrate which is then transformed into 1.13 nm aluminium-substituted tobermorite and -C₂SH by increasing the autoclaving temperature. In the C-S-A-C¯s system the hydrated products are calcium silicate hydrate, ettringite and monosulpho-alumirtate. On increasing the hydrothermal temperature they decompose, recrystallize and 1.13 nm aluminium-substituted tobermorite, -C₂SH and anhydrite II are formed. In both systems the excess Al₂O₃ appeared as a hydrogarnet phase, C₃ASH₄.Cement Notations used are C CaO - S SiO₂ - A Al₂O₃ - H H₂O - CH Ca(OH)₂ - C¯s CaSO₄     

A Mathematical Model of Radiolysis of Water Sorbed on PuO2

A mathematical model of radiolysis of water sorbed on PuO₂ was developed. The model is basedon the postulate that the kinetic characteristics of formation of the initial products in -radiolysis of sorbedwater (H₂, O₂, H₂O, e^- _{e q}, OH) depend on its content. To explain experimental data showing that the steady-state amounts of H₂ are practically equal to the initial amount of sorbed water, the reaction betweenPuO₂ and H₂O₂ yielding H₂O and superstoichiometric plutonium dioxide was postulated. The minimum value of the rate constant of this reaction was found (2 ×10^{- 3} mol^{- 1} s^{- 1}). The proposed mathematical model adequately describes the experimental data on formation of hydrogen and oxygen released from water in contact with PuO₂ at its prolonged storage.     

Chemical synthesis and characterization of hydrous tin oxide (SnO<Subscript><Emphasis Type="Bold">2</Emphasis></Subscript>:H<Subscript><Emphasis Type="Bold">2</Emphasis></Subscript>O) thin films

In the present investigation, we report chemical synthesis of hydrous tin oxide (SnO ₂ :H ₂ O) thin films by successive ionic layer adsorption and reaction (SILAR) method at room temperature ( \thicksim \thicksim 300 K). The films are characterized for their structural and surface morphological properties. The formation of nanocrystalline SnO ₂ with porous and agglomerated particle morphology is revealed from X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies, respectively. The Fourier transform infrared spectroscopy (FTIR) study confirmed the formation of Sn–O phase and hydrous nature of the deposited film. Static water contact angle studies showed the hydrophilic nature of SnO ₂ :H ₂ O thin film. Electrical resistivity showed the semiconducting behaviour with room temperature electrical resistivity of 10 ⁵  W\boldsymbol\Omega cm. The electrochemical properties studied in 0·5 M Na ₂ SO ₄ electrolyte showed a specific capacitance of 25 F g ^− 1 at 5 mVs ^− 1 scan rate.     

Influence of matrix alloying elements on reactive synthesis of 2124 aluminium alloy metal matrix composites

Abstract

In situ TiB₂ particle reinforced Al alloys are produced by reactive synthesis from elemental and prealloyed powders. The influence of 2124 alloying elements on the reactive synthesis is evaluated with a comparison of elemental AI, elemental AI-Cu mixture, and 2124 Al prealloyed powders as matrix materials. Experimental investigations by differential scanning calorimetry and dilatometry showed that the presence of Cu leads to an increase in the reaction rate during the formation of intermediate reaction products in comparison with the elemental Al matrix. X-ray diffraction of the reaction products showed a more complete conversion of the intermediate Al₃ Ti as a result of Cu addition. The Cu has no influence on the TiB₂ particle size, but the TiB₂ morphology changed from pure hexagonal to a more rounded morphology.