Enhanced Interfacial Electron Transfer by Asymmetric Cu-Ov-In Sites on In2O3 for Efficient Peroxymonosulfate Activation

Enhancing the peroxymonosulfate (PMS) activation efficiency to generate more radicals is vital to promote the Fenton-like reaction activity, however, how to promote the PMS adsorption and accelerate the interfacial electron transfer to boost its activation kinetics remains a great challenge. Herein, we prepared Cu-doped defect-rich In₂O₃ (Cu-In₂O₃/O_v) catalysts containing asymmetric Cu−O_v−In sites for PMS activation in water purification. The intrinsic catalytic activity is that the side-on adsorption configuration of the O−O bond (Cu−O−O−In) at the Cu-O_v-In sites significantly stretches the O−O bond length. Meanwhile, the Cu-O_v-In sites increase the electron density near the Fermi energy level, promoting more and faster electron transfer to the O−O bond for generating more SO₄⋅⁻ and ⋅OH. The degradation rate constant of tetracycline achieved by Cu-In₂O₃/O_v is 31.8 times faster than In₂O₃/O_v, and it shows the possibility of membrane reactor for practical wastewater treatment.     

INFLUENCE OF ELECTRON-WITHDRAWING SUBSTITUENTS IN THE OXAPHOSPHOLE RING ON THE AXIAL CONFORMATIONAL TRANSMISSION IN Pv COMPOUNDS

Abstract

A MNDO and 300-MHz ¹H NMR study of some trigonal-bipyramidal (TBP) five-coördinated phosphorus (P^v) compounds is reported. It is shown by the MNDO calculations that, in the oxaphosphole P^v TBP compounds 5a-c, the electron distribution in the axial bonds of the TBP is affected by the electronegativity of the substituent at C₄ of the oxaphosphole ring. With increasing electronegativity of the substituent at C₄, the electron density on the axial exocyclic oxygen atom O₁ decreases whereas the electron density on the axial endocyclic atom O₁ increases. This is supported by a ¹H NMR conformational analysis of the C₁[sbnd]C₂ bond of the oxaphosphole P^v TBP compounds 6–11. The gauche(-) rotamer fraction (O¹ and O¹ trans situated) of these compounds, which is correlated to the electron density on O₁, is reduced to 30% as compared to the absolute axial g^?rotamer fraction (59%) of the dioxaphosphole P^v TBP compound 13, most likely because of the presence of the carbonyl group at C₄ of the oxaphosphole ring. So, both the ¹H NMR and MNDO study show that electron withdrawing substituents on the oxaphosphole ring of P^v TBP compounds reverse the electron transfer in the axial P[sbnd]O bonds of the TBP (as compared to dioxaphosphole compounds), from exocyclic O₁ towards endocyclic O₁.     

Tunneling dynamics of internal rotation in the nitric acid molecule

The Hamiltonian of internal rotation about theC ₂ axis in the HNO₃ molecule and its H/D-, O¹⁸/O¹⁶-, and N¹⁵/N¹⁴-isotopomers was reconstructed using the results of quantumchemical calculations. The Fermi resonance between the torsional (2v₉) and ONO bending (v₅) vibrations is a characteristic feature of the molecule. Tunneling splittings in the ground and excited states were calculated using the perturbative instanton approach. Abnormally large changes in the splittings upon isotope substitution of heavy atoms are predicted. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2052–2060, November, 1999.     

Understanding the Roles of Oxygen Vacancies in Hematite‐Based Photoelectrochemical Processes

Oxygen vacancy (V_O) engineering is an effective method to tune the photoelectrochemical (PEC) performance, but the influence of V_O on photoelectrodes is not well understood. Using hematite as a prototype, we herein report that V_O functions in a more complicated way in PEC process than previously reported. Through a comprehensive analysis of the key charge transfer and surface reaction steps in PEC processes on a hematite photoanode, we clarify that V_O can facilitate surface electrocatalytic processes while leading to severe interfacial recombination at the semiconductor/electrolyte (S‐E) interface, in addition to the well‐reported improvements in bulk conductivity. The improved bulk conductivity and surface catalysis are beneficial for bulk charge transfer and surface charge consumption while interfacial charge transfer deteriorates because of recombination through V_O‐induced trap states at the S‐E interface.     

A Plasma‐Triggered O−S Bond and P−N Junction Near the Surface of a SnS2 Nanosheet Array to Enable Efficient Solar Water Oxidation

A photoelectrochemical (PEC) cell can split water into hydrogen and oxygen with the assistance of solar illumination. However, its application is still limited by excessive bulk carrier recombination and sluggish surface oxygen evolution reaction (OER) kinetics. Taking SnS₂ as an example, a promising layered optoelectronic semiconductor, Ar plasma treatment strategy was used to introduce a SnS/SnS₂ P?N heterojunction and O?S bond near the surface of a SnS₂ nanosheet array, simultaneously increasing the separation efficiency of photogenerated electron–hole pairs in the bulk and lowering the OER overpotential at the surface. The onset potential of the plasma‐treated SnS₂ nanosheet array shifts negatively to 0.16 V, and the photocurrent density at 1.23 V vs. RHE boosts to 2.15 mA cm^?2, which is 7 times that of pristine SnS₂. This work demonstrates a facile plasma treatment strategy to modulate the energy band structure and surface chemical states for improved PEC performance.     

Long‐Lived Charge Carriers in Mn‐Doped CdS Quantum Dots for Photoelectrochemical Cytosensing

Photoelectrochemical (PEC) biosensing with semiconductor quantum dots (QDs) has received great attention because it integrates the advantages of both photo‐excitation and electrochemical detection. During the photon‐to‐electricity conversion in PEC processes, electron–hole (charge) separation competes with electron–hole recombination, and the net effect essentially determines the performance of PEC biosensors. Herein, we propose a new approach for slowing down electron–hole recombination to increase charge separation efficiency for PEC biosensor development. Through doping with Mn²⁺, a pair of d bands (⁴T₁ and ⁶A₁) is inserted between the conduction and valence bands of CdS QDs, which alters the electron–hole separation and recombination dynamics, allowing the generation of long‐lived charge carriers with ms‐scale lifetime that decay about 10⁴–10⁵‐fold more slowly than in the case of undoped QDs. Photocurrent tests indicated that Mn²⁺ doping resulted in an approximately 80 % increase in photocurrent generation compared with undoped CdS QDs. For application, the Mn‐doped CdS QDs were coated on the surface of a glassy carbon electrode and functionalized with a cell surface carbohydrate‐specific ligand (3‐aminophenylboronic acid). In this way, a sensitive cytosensor for K562 leukemia cells was constructed. Moreover, the sugar‐specific binding property of 3‐aminophenylboronic acid allowed the electrode to serve as a switch for the capture and release of cells. This has been further explored with a view to developing a reusable PEC cytosensing platform.     

A Photoelectrochemical Biosensor Fabricated using Hierarchically Structured Gold Nanoparticle and MoS2 on Tannic Acid Templated Mesoporous TiO2

In a tannic acid assisted synthesis of mesoporous TiO₂, tannic acid was used as a cost effective and non‐toxic template for pore formation. Meanwhile, a gold nanoparticles (Au NPs) deposited TiO₂ nanocomposite was coated on an indium tin oxide electrode for the fabrication of a photoelectrochemical (PEC) biosensing system. Upon the formation of anatase structure, the electrode was coated with MoS₂ for effective visible light absorption. The mesoporous structure led to an enhanced surface area by improving Au NPs and glucose oxidase adsorption. Incorporation of Au NPs led to an enhanced photonic efficiency due to the generation of Schottky barriers. The obtained nanocomposite was used for the light‐driven, real‐time, and selective PEC glucose sensing. Under visible light irradiation, the enzyme immobilized electrodes yielded significant photocurrent improvement owing to the releasing electron donor H₂O₂. The obtained PEC biosensor demonstrated acceptable reproducibility and stability with a sensitivity of 4.42 μA mM^?1 cm^?2 and a low detection limit of 1.2 μM glucose. Also, the linear measurement range was found to be 0.004–1.75 mM glucose. The results indicated that the proposed production method of mesoporous TiO₂ will pave the way for a green chemistry based porous material production, along with the extension of the implementation of semiconductors in PEC biosensing systems.     

Combined analysis of microwave and infrared spectra of methyl iodide: rotational and l-type doubling constants of the v5, v3+v6 and v2 states

The rotational constant B and the l-type doubling constant q were determined for the v₅, v₃+v₆ and v₂, states of CH₂I from the microwave transition frequencies, in combination with the infrared data previously reported. Since these vibrational states were coupled through the Fermi resonance and the xy-type E-E and A₁-E Coriolis resonances, the analysis was made by setting up and solving the complete form of the secular determinants of the energy matrices. The rotational and l-type doubling constants were determined as B₅, = 0.250 173 cm^?1, B₃₆ = 0.247 600 cm^?1, B₂ = 0.249 369 cm^?1, q₅ = ?0.000 027 cm^?1 and q₃₆ = ?0.000 179 cm^?1, which are unperturbed by Fermi and Coriolis interactions. Other band constants for v₅ and v₃+v₆ were also refined in accordance with the new values of B₅ and B₃₆. The present study indicated that the combined analysis of microwave and infrared spectral data was useful for the precise determination of vibration-rotation, levels in the perturbed system.     

Identifying the O2 diffusion and reduction mechanisms on CeO2 electrolyte in solid oxide fuel cells: A DFT + U study

The interactions and reduction mechanisms of O₂ molecule on the fully oxidized and reduced CeO₂ surface were studied using periodic density functional theory calculations implementing on‐site Coulomb interactions (DFT + U) consideration. The adsorbed O₂ species on the oxidized CeO₂ surface were characterized by physisorption. Their adsorption energies and vibrational frequencies are within ?0.05 to 0.02 eV and 1530–1552 cm^?1, respectively. For the reduced CeO₂ surface, the adsorption of O₂ on Ce⁴⁺, one‐electron defects (Ce³⁺ on the CeO₂ surface) and two‐electron defects (neutral oxygen vacancy) can alter geometrical parameters and results in the formation of surface physisorbed O₂, O₂^a? (0 < a < 1), superoxide (O₂^?), and peroxide (O₂^2?) species. Their corresponding adsorption energies are ?0.01 to ?0.09, ?0.20 to ?0.37, ?1.34 and ?1.86 eV, respectively. The predicted vibrational frequencies of the peroxide, superoxide, O₂^a? (0 < a < 1) and physisorbed species are 897, 1234, 1323–1389, and 1462–1545 cm^?1, respectively, which are in good agreement with experimental data. Potential energy profiles for the O₂ reduction on the oxidized and reduced CeO₂ (111) surface were constructed using the nudged elastic band method. Our calculations show that the reduced surface is energetically more favorable than the unreduced surface for oxygen reduction. In addition, we have studied the oxygen ion diffusion process on the surface and in bulk ceria. The small barrier for the oxygen ion diffusion through the subsurface and bulk implies that ceria‐based oxides are high ionic conductivity at relatively low temperatures which can be suitable for IT‐SOFC electrolyte materials. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009     

Experimental study and thermodynamic analysis on the selective oxidation of DP1180 dual-phase steel

The selective oxidation process of dual-phase 1180 steel was investigated in this study. Annealing was carried out in Cr/Cr₂O₃ Rhines pack at 820°C for 60, 120, and 240 s, under the oxygen partial pressures of 10⁻²³, 10⁻²⁵, and 10⁻²⁹ atm, respectively. Field emission scanning electron microscopy (FE-SEM), electron backscattered diffraction (EBSD), and X-ray photoelectron spectroscopy (XPS) were used to analyze the experimental results. The oxides involved SiO₂, MnO, MnSiO₃, Mn₂SiO₄, and MnCr₂O₄. The amount of oxides augmented along with the increasing oxygen partial pressure. The Fe–Mn–Cr–Si–C–O₂ oxidation diagram was calculated by thermodynamic software and was used to explain the selective oxidation process of dual-phase 1180 steel. Experimental results combined with the thermodynamic computations well.     

DFT+U Analysis on Stability of Low-Index Facets in Hexagonal LaCoO3 Perovskite:Effect of Co3+ Spin States

By the first-principles calculations,most studies indicated that the (11102)-CoO₂ termination of LaCoO₃ cannot be stabilized,which disagrees with the experimental observation.Besides the crystal structure,we found that the spin states of Co³⁺ ions could affect surface stability,which previously were not well considered.By examining the different states of Co³⁺ ions in hexagonal-phase LaCoO₃,including low spin,intermediate spin,and high spin states,the surface grand potentials of these facets are calculated and compared.The results show that the spin states of Co³⁺ ions have an important influence on stability of the LaCoO₃ facets.Different from the previous results,the stability diagrams demonstrate that the (11102)-CoO₂ termination can stably exist under O-rich condition,which can get an agreement with the experimental ones.Furthermore,the surface oxygen vacancy formation energies (E_Ov) of stable facets are computed in different spin states.The E_Ov of these possible exposed terminations strongly depend on the spin state of Co³⁺ ions:in particular,the E_Ov of the HS states is lower than that of other spin states.This indicates that one can tune the properties of LaCoO₃ by directly tuning the spin states of Co³⁺ ions.     

Optical energy storage properties of Sr<Subscript>2</Subscript>MgSi<Subscript>2</Subscript>O<Subscript>7</Subscript>:Eu<Superscript>2+</Superscript>,R<Superscript>3+</Superscript> persistent luminescence materials

The details of the mechanism of persistent luminescence were probed by investigating the trap level structure of Sr₂MgSi₂O₇:Eu²⁺,R³⁺ materials (R: Y, La-Lu, excluding Pm and Eu) with thermoluminescence (TL) measurements and Density Functional Theory (DFT) calculations. The TL results indicated that the shallowest traps for each Sr₂MgSi₂O₇:Eu²⁺,R³⁺ material above room temperature were always ca. 0.7 eV corresponding to a strong TL maximum at ca. 90 °C. This main trap energy was only slightly modified by the different co-dopants, which, in contrast, had a significant effect on the depths of the deeper traps. The combined results of the trap level energies obtained from the experimental data and DFT calculations suggest that the main trap responsible for the persistent luminescence of the Sr₂MgSi₂O₇:Eu²⁺,R³⁺ materials is created by charge compensation lattice defects, identified tentatively as oxygen vacancies, induced by the R³⁺ co-dopants.     

Cavity ring‐down study of BrO radicals: Kinetics of the Br + O3 reaction and rate of relaxation of vibrationally excited BrO by collisions with N2 and O2

Cavity ring‐down (CRD) techniques were used to study the kinetics of the reaction of Br atoms with ozone in 1–205 Torr of either N₂ or O₂, diluent at 298 K. By monitoring the rate of formation of BrO radicals, a value of k(Br + O₃) = (1.2 ± 0.1) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ was established that was independent of the nature and pressure of diluent gas. The rate of relaxation of vibrationally excited BrO radicals by collisions with N₂ and O₂ was measured; k(BrO(v) + O₂ → BrO(v − 1) + O₂) = (5.7 ± 0.3) × 10⁻¹³ and k(BrO(v) + N₂ → BrO(v − 1) + N₂) = (1.5 ± 0.2) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹. The increased efficiency of O₂ compared with N₂ as a relaxing agent for vibrationally excited BrO radicals is ascribed to the formation of a transient BrO–O₂ complex. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 125–130, 2000     

Anodized Iron Oxide Nanostructures on Different Carbon Steels for Photoelectrochemical Water Splitting

In this study, two different nanostructural iron oxide films were prepared on two kinds of carbon steels (CS) with different contents of impurities via anodization in a mixture of aqueous ammonium fluoride solution and ethylene glycol, respectively, and apply to photoelectrochemical (PEC) water splitting. After annealing, iron oxide nanotubes (NTs) was coated on surface of lower purity CS and iron oxide nanoporous (NPs) was coated on surface of higher purity CS via scanning electron microscope. X‐ray diffraction pattern shows both of samples contain a major phase of α‐Fe₂O₃ and a slight phase of Fe₃O₄. Compared with NPs, NTs behaves better absorbance ability in visible spectra range via UV‐visible absorbance spectra. From PEC response, the iron oxide NTs showed higher water splitting performance (0.10 mA/cm² at 0.4 V vs. Ag/AgCl) than NPs (0.04 mA/cm² at 0.4 V vs. Ag/AgCl) due to better absorbance, higher car‐ rier concentration and low charge transfer resistance.     

介孔α-Fe2O3表面配合反应平衡常数测定

采用十二胺为模板剂、氨水做沉淀剂成功制备了介孔α-Fe₂O₃, 通过粉末X射线衍射(XRD)、透射电镜(TEM)、N₂吸附/脱附技术对样品晶相、形貌和比表面积进行了表征. 根据介孔α-Fe₂O₃悬浮液的酸碱滴定数据, 使用FITEQL软件, 采用双电层恒电容模型计算得出了介孔α-Fe₂O₃的表面酸碱反应平衡常数. 在此基础上研究了Cu^2＋, Pb^2＋, Zn^2＋在介孔氧化铁表面的吸附行为, 使用WinSGW软件模拟得出了相应的表面配合反应平衡常数并讨论了其吸附机理.     

Probing the Catalytic Activity of Reduced Graphene Oxide Decorated with Au Nanoparticles Triggered by Visible Light

Hybrid materials in which reduced graphene oxide (rGO) is decorated with Au nanoparticles (rGO–Au NPs) were obtained by the in situ reduction of GO and AuCl₄^?_(aq) by ascorbic acid. On laser excitation, rGO could be oxidized as a result of the surface plasmon resonance (SPR) excitation in the Au NPs, which generates activated O₂ through the transfer of SPR‐excited hot electrons to O₂ molecules adsorbed from air. The SPR‐mediated catalytic oxidation of p‐aminothiophenol (PATP) to p,p′‐dimercaptoazobenzene (DMAB) was then employed as a model reaction to probe the effect of rGO as a support for Au NPs on their SPR‐mediated catalytic activities. The increased conversion of PATP to DMAB relative to individual Au NPs indicated that charge‐transfer processes from rGO to Au took place and contributed to improved SPR‐mediated activity. Since the transfer of electrons from Au to adsorbed O₂ molecules is the crucial step for PATP oxidation, in addition to the SPR‐excited hot electrons of Au NPs, the transfer of electrons from rGO to Au contributed to increasing the electron density of Au above the Fermi level and thus the Au‐to‐O₂ charge‐transfer process.     

NiFe2O4@SiO2@Cu3(BTC)2 nanocomposite as a magnetic metal–organic framework

A new magnetic metal–organic framework (MOF), namely, NiFe₂O₄@SiO₂@Cu₃(BTC)₂, was synthesized via an in situ method using Fe(NO₃)₃, Ni(NO₃)₂, CuN₂O₆, TEOS, (3-aminopropyl)triethoxysilane, and benzene-1,3,5-tricarboxylic acid. Three different samples were fabricated according to a formula; xNiFe₂O₄@(100 − x)SiO₂@Cu₃(BTC)₂, where x = 10, 30, and 50. The integration of the intrinsic characteristic of Cu₃(BTC)₂ as an MOF with strong magnetic properties of NiFe₂O₄ could lead to an exquisite material with specific behaviors. X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET), diffuse reflectance spectroscopy (DRS), photoluminescence (PL), vibrating sample magnetometer (VSM), transmission electron microscopy (TEM), and simulated thermal analyzer (STA) were utilized to characterize the mentioned samples. Results approved that the synthesized compounds were composed of SiO₂ and Cu-MOF and NiFe₂O₄ crystalline phases with rod-like morphology. The similarity between the morphology of the synthesized samples and Cu-MOF approved that an appropriate fabrication method has been selected. This fact led to observe mesoporous composites with 38–90 m² g⁻¹ specific surface area. PL spectroscopy confirmed the near bandgap emission, ligand-to-metal charge transfer, and metal-to-ligand charge transfer. Although all the samples had magnetic hysteresis, the highest magnetization was seen in the 50NiFe₂O₄@SiO₂@Cu₃(BTC)₂ sample. This composite compound with a magnetization value of 2 emu g⁻¹ at 8000 Oe and a specific surface area of 90 m² g⁻¹ could be classified as a magnetic MOF (MMOF). STA results suggested that 400°C is the highest operating temperature for this compound.     

Chemisorbed Oxygen Species over the (110) Face of SnO2

The electronic states of chemisorbed oxygen species on the (110) face of SnO₂ and their variations caused by heat treatments and/or O₂ exposure have been investigated. The reactivities of the chemisorbed oxygen species for methane oxidations were also examined.Four different chemisorbed oxygen species (O₂ ^2-, O_2-, O^-, O_b) were observed, in addition to the lattice oxygen (O^2-), on the surface of the stabilized (110) surface of SnO₂ after O₂ exposure. The O_b species was assumed to be the bridging oxygen at the topmost layer of the SnO₂ (110) surface having no neighboring oxygen vacancies. The electronic state of O_b was converted to O^- upon CH₄ exposure at 473 K by coupling with newly produced vacancies at the bridging site of the SnO₂ (110) surface.     

Theoretical study of the low‐lying electronic states of the molecular ion KRb+

The potential energy curves of the molecular ion KRb⁺ have been investigated for the 60 lowest molecular states of symmetry ²Σ⁺, ²Π, ²Δ, and Ω = 1/2, 3/2, and 5/2. Using an ab initio method, the calculation has been done in a one active electron approach based on nonempirical pseudopotentials with core valence effects taken into account through parameterized l‐dependent polarization potentials. Using the canonicals functions approach a rovibrational study is done by calculating the eigenvalues E_v, the rotational constants B_v, the centrifugal distortion constants D_v (up to 135 vibrational levels), and the spectroscopic constants ω_e and B_e for the five electronic states (1)²Σ⁺, (3)²Σ⁺, (1)²Π, (1)Ω = 1/2, and (1)Ω = 3/2. No comparison of these values with other results is yet possible because they are given here for the first time. Extensive tables of energy values of E_v, B_v, and D_v are displayed at http://hplasim2.univ‐lyon1.fr/allouche . © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

Doublet instability and the molecular structure of AlO2

The possible C_s, C_2v, and C_∞v structures of AlO₂ corresponding to the two lowest electronic states which dissociate into the neutral Al(²P) and O₂(³Σ_g^?) fragments have been investigated at the ab initio self-consistent field (SCF) and CI levels using nonempirical pseudopotentials. The most stable structure corresponds to a C_2v symmetry in the ²A₂ electronic state. However, this structure presents the three-center three-electron Hartree-Fock instability and CASSCF calculations were necessary to unequivocally characterize it as true minimum. Moreover, only another stable structure, of C_2v geometry, was found to be a minimum, corresponding to a low-lying excited state of ²A₁ symmetry. The optimized C_∞v structures were not minima on the corresponding potential energy surfaces and no evidence of any stable C_s structure was found. Calculating values are compared with the different experimental data obtained from the reaction of Al and O₂ in frozen gas inert matrices.