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  • 1. Ai, Yuejie
    et al.
    Li, Xin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ji, Yongfei
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Song, Wei-Guo
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Hydrophobicity and Hydrophilicity Balance Determines Shape Selectivity of Suzuki Coupling Reactions Inside Pd@meso-SiO2 Nanoreactor2016In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, no 19, p. 10244-10251Article in journal (Refereed)
    Abstract [en]

    Molecular sorting and catalysis directed by shape selectivity have been extensively applied in porous extended frameworks for a low-carbon, predictable, renewable component of modern industry. A comprehensive understanding of the underlying recognition mechanism toward different shapes is unfortunately still missing, owing to the lack of structural and dynamic information under operating conditions. We demonstrate here that such difficulties can be overcome by state-of-the-art molecular dynamics simulations which provide atomistic details that are not accessible experimentally, as exemplified by our interpretation for the experimentally observed aggregation induced shape selectivity for Suzuki C-C coupling reaction catalyzed by Pd particles in mesoporous silica. It is found that both aggregation ability and aggregating pattern of the reactants play the decisive role in controlling the shape selectivity, which are in turn determined by the balance between the hydrophobicity and hydrophilicity of the reactants, or in other words, by the balance between the noncovalent hydrogen bonding interaction and van der Waals forces. A general rule that allows prediction of the shape selectivity of a reactant has been proposed and verified against experiments. We show that molecular modeling is a powerful tool for rational design of new mesoporous systems and for the control of catalytic reactions that are important for the petrochemical industry.

  • 2.
    Cao, Xinrui
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ji, Yongfei
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Hu, Wei
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Department of Chemical Physics, University of Science and Technology of ChinaHefei, China.
    Duan, Sai
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Department of Chemical Physics, University of Science and Technology of ChinaHefei, China .
    Feasible Catalytic Strategy for Writing Conductive Nanoribbons on a Single-Layer Graphene Fluoride2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 39, p. 22643-22648Article in journal (Refereed)
    Abstract [en]

    An accessible method for local reduction of graphene fluoride catalyzed by the Pt-coated nanotip with the assistance of a mixture of hydrogen and ethylene atmosphere is proposed and fully explored theoretically. Detailed mechanisms and roles of hydrogen and ethylene molecules in the cyclic reduction is discussed based on extensive first-principles calculations. It is demonstrated that the proposed cyclic reduction strategy is energetically favorable. This new strategy can be effectively applied in scanning probe lithography to fabricate electronic circuits at the nanoscale on graphene fluoride under mild conditions.

  • 3.
    Cao, Xinrui
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ji, Yongfei
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. University of Science and Technology of China, China.
    Dehydrogenation of Propane to Propylene by a Pd/Cu Single-Atom Catalyst: Insight from First-Principles Calculations2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 2, p. 1016-1023Article in journal (Refereed)
    Abstract [en]

    The catalytic properties of the single-Pd-doped Cu55 nanoparticle toward propane dehydrogenation have been systemically investigated by first-principles calculations, and the possible reaction mechanisms and effects of the single and multiple Pd doping on the catalytic activity have been discussed. Calculations reveal that the low-energy catalytic conversion of propane to propylene by the Pd/Cu single-atom catalyst comprises the initial crucial C–H bond breaking at either the methyl or methylene group, the facile diffusion of detached H atoms on the Cu surface, and the subsequent C–H bond dissociation activation of the adsorbed propyl species. The single-Pd-doped Cu55 nanoparticle shows remarkable activity toward C–H bond activation, and the presence of relatively inactive Cu surface is beneficial for the coupling and desorption of detached H atoms and can reduce side reactions such as deep dehydrogenation and C–C bond breaking. The single-Pd-doped Cu55 cluster bears good balance between the maximum use of the noble metal and the activity, and it may serve as a promising single-atom catalyst toward selective dehydrogenation of propane.

  • 4. Chen, Zhe
    et al.
    Lu, Jinfeng
    Ai, Yuejie
    Ji, Yongfei
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Adschiri, Tadafumi
    Wan, Lijun
    Ruthenium/Graphene-like Layered Carbon Composite as an Efficient Hydrogen Evolution Reaction Electrocatalyst2016In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 8, no 51, p. 35132-35137Article in journal (Refereed)
    Abstract [en]

    Efficient water splitting through electrocatalysis has been studied extensively in modern energy devices, while the development of catalysts with activity and stability comparable to those of Pt is still a great challenge. In this work, we successfully developed a facile route to synthesize graphene-like layered carbon (GLC) from a layered silicate template. The obtained GLC has layered structure similar to that of the template and can be used as support to load ultrasmall Ru nanoparticles on it in supercritical water. The specific structure and surface properties of GLC enable Ru nanoparticles to disperse highly uniformly on it even at a large loading amount (62 wt %). When the novel Ru/GLC was used as catalyst on a glass carbon electrode for hydrogen evolution reaction (HER) in a 0.5 M H2SO4 solution, it exhibits an extremely low onset potential of only 3 mV and a small Tafel slope of 46 mV/decade. The outstanding performance proved that Ru/GLC is highly active catalyst for HER, comparable with transition-metal dichalcogenides or selenides. As the price of ruthenium is much lower than platinum, our study shows that Ru/GLC might be a promising candidate as an HER catalyst in future energy applications.

  • 5. Ding, Xin
    et al.
    Gao, Yan
    Fan, Ting
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ji, Yongfei
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Zhang, Linlin
    Yu, Ze
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry. Dalian University of Technology (DUT), China.
    Silicon Compound Decorated Photoanode for Performance Enhanced Visible Light Driven Water Splitting2016In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 215, p. 682-688Article in journal (Refereed)
    Abstract [en]

    An efficient dye (1) sensitized photoelectrochemical cell (DS-PEC) has been assembled with a silicon compound (3-chloropropyl) trimethoxy-silane (Si-Cl) decorated working electrode (WE) TiO2(1 + 2). The introduction of this Si-Cl molecule on photoanode leads to better performances on efficiency than untreated ones for light driven water splitting. The firm Si-O layer formed on TiO2 increased the resistance of the TiO2/catalyst interface which is assumed to decrease charge recombination from TiO2 to the oxidized catalyst 2. The work presented here provides an effective method to improve the performances of DS-PECs.

  • 6.
    Duan, Sai
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ji, Yong-Fei
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Fang, Ping-Ping
    Chen, Yan-Xia
    Xu, Xin
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Tian, Zhong-Qun
    Density functional theory study on the adsorption and decomposition of the formic acid catalyzed by highly active mushroom-like Au@Pd@Pt tri-metallic nanoparticles2013In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, no 13, p. 4625-4633Article in journal (Refereed)
    Abstract [en]

    Local structures and adsorption energies of a formic acid molecule and its decomposed intermediates (H, O, OH, CO, HCOO, and COOH) on highly electrocatalytically active mushroom-like Au-core@Pd-shell@Pt-cluster nanoparticles with two atomic layers of the Pd shell and stoichiometric Pt coverage of around half-monolayer (Au@2 ML Pd@0.5 ML Pt) have been investigated by first principles calculations. The adsorption sites at the center (far away from the Pt cluster) and the edge (close to the Pt cluster) are considered and compared. Significant repulsive interaction between the edge sites and CO is observed. The calculated potential energy surfaces demonstrate that, with respect to the center sites, the CO2 pathway is considerably promoted in the edge area. Our results reveal that the unique edge structure of the Pt cluster is responsible for the experimentally observed high electrocatalytic activity of the Au@Pd@Pt nanoparticles toward formic acid oxidation. Such microscopic understanding should be useful for the design of new electrochemical catalysts.

  • 7.
    Duan, Sai
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. University of Science and Technology of China, China.
    Tian, Guangjun
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ji, Yongfei
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Shao, Jiushu
    Dong, Zhenchao
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. University of Science and Technology of China, China.
    Theoretical Modeling of Plasmon-Enhanced Raman Images of a Single Molecule with Subnanometer Resolution2015In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 137, no 30, p. 9515-9518Article in journal (Refereed)
    Abstract [en]

    Under local plasmonic excitation, Raman images of single molecules can now surprisingly reach subnanometer resolution. However, its physical origin has not been fully understood. Here we report a quantum-mechanical description of the interaction between a molecule and a highly confined plasmonic field. We show that When the spatial distribution of the plasmonic field is comparable to the size of the molecule, the optical transition matrix of the molecule becomes dependent on the position and distribution of the plasmonic field, resulting in a spatially resolved high-resolution Raman image of the molecule. The resonant Raman image reflects the electronic transition density of the molecule. In combination with first-principles calculations, the simulated Raman linage of a porphyrin derivative adsorbed on a silver surface nicely reproduces its experimental counterpart. The present theory provides the basic framework for describing linear and nonlinear responses of molecules under highly confined plasmonic fields.

  • 8.
    Ji, Yongfei
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Theoretical Studies on the Molecular Mechanisms of Photo-Catalytic Reactions on TiO2 Surfaces2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Photocatalysis is a promising technology that can effectively convert the solar energyinto sustainable green energy. However, theoretical studies on the molecular mechanisms of photocatalytic reactions are rare. This thesis is devoted to investigate several typical photocatalytic reactions on the surfaces of the most popular photocatalysis TiO2 with density functional theory. We start our study with the characterization of both the free and trapped hole on the surface generated by the light. The oxidation of physisorbed H2O molecule by the hole trapped at bridge oxygen on rutile TiO2(110) surface has been studied. The hole is found to transferto the molecule via the anti-bonding orbital as a result of the hybridization between the hole orbital and the HOMO of the molecule. The energy and symmetry mismatching between the trapped hole orbital and the HOMO of the molecule explains why the trapped hole cannot directly transfer to the chemisorbed H2O molecule. On the other hand, we have found that the chemisorbed H2O moleculecan be more efficiently oxidized by the free hole with a lower barrier and higher reaction energy compared to the oxidation by the trapped hole. In this reaction, the free hole is transferred to the chemisorbed H2O after the dissociation. This is different from the oxidation of chemisorbed H2O on anatase TiO2(101) surface by free hole, in which the hole is transferred concertedly with the dissociation of themolecule.

        In order to understand the hole scavenger ability of organic molecules, the oxidation of three small organic molecules (CH3OH, HCOOH and HCOH) onanatase TiO2(101) surface has been systematically investigated. The concerted hole and proton transfer is found for all these molecules. The calculations suggestthat both kinetic and thermodynamic effects need to be considered to correctly describe the hole transfer process. The order of hole scavenging power is found tofollow: HCOH > HCOOH > CH3OH > H2O, which agrees well with experiments.

        Photo-selective catalytic reduction of the NO by NH3 and the photooxidationof CO by O2 are closely related to the environment application. Both reactionsinvolve the formation and/or breaking of non R–H bonds. The mechanism for the photoreduction of NO proposed by experiment has been verified by our calculations.The role of the hole is to oxidize the adsorbed NH3 into ·NH2 radical, which canform a NH2NO complex with a gaseous NO molecule easily. The photooxidation of CO by O2 is the first multi-step photoreaction we ever studied. By combining thepotential energy surfaces at the ground and excited state we have found that thehole and electron both take part in the reaction. A molecular mechanism which is in consistent with various experiments is proposed.

        These studies show that density functional theory is a powerful tool for studying the photocatalytic reaction. Apparently, more work needs to be done in orderto improve the performance of the existing materials and to design new ones thatcan take advantage of the solar light more efficiently

  • 9.
    Ji, Yongfei
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    First-Principles Study on the Mechanism of Photoselective Catalytic Reduction of NO by NH3 on Anatase TiO2(101) Surface2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 12, p. 6359-6364Article in journal (Refereed)
    Abstract [en]

    A promising method for NO abatement is photoselective reduction with a proper semiconductor, such as TiO2. Here we report a systematic theoretical study on NO abatement through an adsorbed NH3 molecule on the anatase TiO2(101) surface. The reaction mechanism proposed by experiments has been verified. The key process, namely, the oxidation of the adsorbed NH3 molecule by photogenerated hole, has been investigated by two different methods: one is to use the triplet state to mimic the real excited state and the other is to inject a hole to the slab by the adsorption of center dot OH radical. Both methods give almost the same result, and the oxidation of the NH3 molecule is found to be a concerted proton coupled charge transfer process. The center dot NH2 radical, resulting from the oxidation of NH3, can be attacked by a NO molecule from the gas phase to form a NH2NO complex spontaneously. The decomposition of this complex to N-2 and H2O is the rate limiting step of the overall reaction. This multistep decomposition process consists of the following sequences: the H atom transfers to the O atom in the molecule first to form HNNOH that further decomposes to N-2 and OH groups, and the latter group recombines to produce the H2O molecule.

  • 10.
    Ji, Yongfei
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    New Mechanism for Photocatalytic Reduction of CO2 on the Anatase TiO2(101) Surface: The Essential Role of Oxygen Vacancy2016In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 138, no 49, p. 15896-15902Article in journal (Refereed)
    Abstract [en]

    Photocatalytic reduction of CO2 into organic molecules is a very complicated and important reaction. Two possible pathways, the fast-hydrogenation (FH) path and the fast-deoxygenation (FdO) path, have been proposed on the most popular photocatalyst TiO2. We have carried out first-principles calculations to investigate both pathways on the perfect and defective anatase TiO2(101) surfaces to provide comprehensive understanding of the reaction mechanism. For the FH path, it is found that oxygen vacancy on defective surface can greatly lower the barrier of the deoxygenation processes, which makes it a more active site than the surface Ti. For the FdO path, our calculation suggests that it can not proceed on the perfect surface, nor can it proceed on the defective surface due to their unfavorable energetics. Based on the fact that the FH path can proceed both at the surface Ti site and the oxygen vacancy site, we have proposed a simple mechanism that is compatible with various experiments. It can properly rationalize the selectivity of the reaction and greatly simplify the picture of the reaction. The important role played by oxygen vacancy in the new mechanism is highlighted and a strategy for design of more efficient photocatalysts is proposed accordingly.

  • 11.
    Ji, Yongfei
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Univ Sci & Technol China.
    Structure-dependent photocatalytic decomposition of formic acid on the anatase TiO2(101) surface and strategies to increase its reaction rate2016In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 306, p. 208-212Article in journal (Refereed)
    Abstract [en]

    Formic acid is a typical molecule that is involved in a lot important solar energy conversion processes. We perform first-principles calculations on the molecular mechanism of its photocatalytic decomposition reaction (PCD) on the anatase TiO2(101) surface. We find that the reaction barrier is sensitively dependent on the adsorption structure of the molecule. The one-step PCD of the monodentate formic acid has a lower barrier than that of bidentate formate. Coadsorbed water molecules can transform the formate from a bidentate to a monodentate configuration which greatly lower its decomposition barrier. Water molecule can also induce the spontaneous dissociation of the formic acid molecule. The monodentate dissociated formic acid is stabilized by the hydrogen bonds which will slightly enhance the barrier for its photodecomposition. However, the reaction rate can be further enhanced if the hydrogens are removed (for example, by oxygen molecules). Therefore, using coadsorbate and deliberately introducing and removing hydrogen bonds can be two strategies to tailor the photoreaction rate of the molecules.

  • 12.
    Ji, Yongfei
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. University of Science and Technology of China, Anhui, China.
    Theoretical Study on the Mechanism of Photoreduction of CO2 to CH4 on the Anatase TiO2(101) Surface2016In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 6, no 3, p. 2018-2025Article in journal (Refereed)
    Abstract [en]

    Artificial photosynthesis of CO, has recently attracted intense attention as a potential solution for the energy crisis and global warming. However, the molecular mechanism of the reaction is quite complicated and is far from understood. We performed a first-principles calculation on the thermodynamically feasible formaldehyde pathway: CO2 -> HCOOH -> H2CO -> CH3OH -> CH4. The interconversion of the Cl molecules has been systematically investigated. We find that a two-electron process has a lower barrier than a one-electron process for the photoreduction of all of the molecules under investigation except for methanol. On the basis of the full potential energy surface for photoreduction of CO, to methane, the rate-limiting step is found to be the photoreduction of formic acid to formaldehyde, which contains the elementary step that has the largest kinetic barrier. It will be more efficient if CO instead of formic acid is the precursor of formaldehyde. Then the rate-limiting step becomes the photoreduction of CO, to CO. However, the barriers for the photoreduction of the organic molecules are all higher than the barriers for their photodecomposition reaction, which suggests that all of the Cl organic molecules are more easily oxidized than reduced. Thus, charge separation is crucial for improving the efficiency and selectivity of the reaction. The intertwining of photoreduction and photooxidation reactions might be one of the major reasons for the complexity and low efficiency of the reaction. On the basis of the calculations, a new mechanism for the reaction is proposed.

  • 13.
    Ji, Yongfei
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Wang, B.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    First principles study of O2 adsorption on reduced rutile TiO2-(110) surface under UV illumination and its role on CO oxidation2013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 2, p. 956-961Article in journal (Refereed)
    Abstract [en]

    Oxidation of CO by O2 on the reduced rutile TiO2(110) surface under UV illumination has been explored by first-principles simulations. It is found that, at the ground state, the O2 molecule prefers to be adsorbed at the oxygen vacancy horizontally; whereas under photo excitation, it can capture a hole as it transforms itself into a near-perpendicular geometry. Such a photoexcited O2 can be effectively connected to the CO molecule to form a O-O-CO complex, which can then convert to CO2 by overcoming a small barrier. This mechanism can be applied to both low and high O2 coverage and is consistent with the off-normal desorption behavior of the CO2 observed in recent experiments.

  • 14.
    Ji, Yongfei
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Wang, Bing
    University of Science and Technology of China, China.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. University of Science and Technology of China, China.
    A Comparative Theoretical Study of Proton-Coupled Hole Transfer for H2O and Small Organic Molecules (CH3OH, HCOOH, H2CO) on the Anatase TiO2(101) Surface2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 37, p. 21457-21462Article in journal (Refereed)
    Abstract [en]

    The high oxidation power of the photogenerated hole in TiO2 has made it useful in many applications. It is of fundamental importance to understand how the hole transfers from the catalysis to adsorbates. We have performed a comparative study on the mechanism for the first proton-coupled hole transfer process in water, methanol, formic acid, and formaldehyde on the anatase TiO2(101) surface. Our results show that this process for all the molecules is concerted rather than sequential. Both the kinetic and thermodynamic effects need to be taken into account. The hole scavenging power for the four molecules under investigation is found to follow the order formaldehyde > formic acid > methanol > water, which agrees well with various experiments.

  • 15.
    Ji, Yongfei
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Wang, Bing
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    GGA plus U Study on the Mechanism of Photodecomposition of Water Adsorbed on Rutile TiO2(110) Surface: Free vs Trapped Hole2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 2, p. 1027-1034Article in journal (Refereed)
    Abstract [en]

    The initial step of O-2 evolution reaction on a TiO2 surface is a long-standing puzzle. A recent scanning tunneling microscopy experiment showed that the H2O molecule adsorbed on rutile TiO2(110) surface could decompose under ultraviolet illumination (Tan, S. J.; et al. J. Am. Chem. Soc., 2012, 134, 9978). The underlying reaction mechanism is now examined by our GGA+U study, in which the oxidation of the H2O molecule by both free and trapped holes has been carefully investigated. It is found that the transfer of the hole trapped at the bridge oxygen to the molecule is hindered by the mismatch between the energy and spatial symmetry of the trapped hole orbital and the highest occupied molecule orbital of H2O. The entire oxidation reaction has a high energy barrier and is barely exothermic. In contrast, the oxidation of the molecule by the free hole is energetically more favorable. The free hole is transferred to the H2O molecule via the in-plane oxygen atom when the molecule stays in the transient dissociation state. This mechanism may also be applicable to the photooxidation of other R OH type molecules adsorbed on the rutile TiO2(110) surface.

  • 16.
    Ji, Yongfei
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Wang, Bing
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Location of Trapped Hole on Rutile-TiO2(110) Surface and Its Role in Water Oxidation2012In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 14, p. 7863-7866Article in journal (Refereed)
    Abstract [en]

    The trapped hole and its nature on rutile TiO2(110) surface has been fully examined by first-principles GGA+U method with U(p) ranged from 3.0 to 7.0 eV. The bridge oxygen is found to be the most stable hole trapping site, and it is of a p-type orbital perpendicular to the bridge oxygen row. How the hole reacts with a H2O molecule above the surface is investigated with constrained minimization method. The highest occupied molecular orbital of approaching H2O is found to hybridize with the hole orbital and to form bonding and antibonding orbitals. An electron is seen to be transferred from H2O to the bridge oxygen mediated by the formed bonding state. The electron transfer is accompanied by H2O dissociation concertedly, which results in a hydroxyl radical adsorbed on the surface sharing the hole orbital with an in-plane oxygen atom. The reaction pathway is also estimated.

  • 17.
    Lian, Ke-Yan
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ji, Yong-Fei
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Li, Xiao-Fei
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Jin, Ming-Xing
    Ding, Da-Jun
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Big Bandgap in Highly Reduced Graphene Oxides2013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 12, p. 6049-6054Article in journal (Refereed)
    Abstract [en]

    It is generally believed that the bandgap of the graphene oxide is proportional to the concentration of the oxygen atoms and a highly reduced graphene oxide (rGO) without vacancy defects should be gapless. We show here from first principles calculations that the bandgap can be effectively opened even in low oxidation level with the absorption of oxygen atoms either symmetrically or asymmetrically. The properly arranged absorption can induce a bandgap up to 1.19 eV for a C/O ratio of 16/1 in a symmetric system and a bandgap up to 1.58 eV for a C/O ratio of 32/3 in an asymmetric system, at generalized gradient approximation (GGA) level. The hybridization between the in-plane p(xy) orbitals of oxygen atoms and the out-of-plane p(z) frontier orbital of graphene is responsible for the opening of the bandgap. This finding sheds new light on the bandgap engineering of graphene.

  • 18.
    Yongfei, Ji
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Proton Coupled Hole Transfer for H2O and small organic molecules (CH3OH, HCOOH and HCOH) on AnataseTiO2(101) SurfaceManuscript (preprint) (Other academic)
  • 19. Yu, Shujun
    et al.
    Wang, Xiangxue
    Ai, Yuejie
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. North China Electric Power University, China.
    Liang, Yu
    Ji, Yongfei
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Li, Jiaxing
    Hayat, Tasawar
    Alsaedi, Ahmed
    Wang, Xiangke
    Spectroscopic and theoretical studies on the counterion effect of Cu(II) ion and graphene oxide interaction with titanium dioxide2016In: ENVIRONMENTAL SCIENCE-NANO, ISSN 2051-8153, Vol. 3, no 6, p. 1361-1368Article in journal (Refereed)
    Abstract [en]

    With the widespread use of graphene oxide (GO), it is inevitable that part of GO is released into the environment and co-exist with heavy metal ions as contaminants and is likely to be co-adsorbed on minerals and oxides. This study, for the first time, demonstrates the individual and mutual removal mechanism of GO and Cu(II) on titanium dioxide (TiO2) by batch experiments, spectroscopic analysis and density functional theory (DFT) computations. Electrostatic interaction and hydrogen bonding are the dominant modes of GO sorption onto TiO2, and the interaction of Cu(II) with TiO2 is mainly dominated by inner-sphere surface complexation. The presence of Cu(II) enhances GO coagulation on TiO2 and vice versa. The experimental results are further verified by DFT sorption energy (Es) calculations in the order (TiO2-GO)-Cu > TiO2-GO for GO interaction and (TiO2-GO)-Cu > TiO2-Cu for Cu(II) interaction. The mutual interaction is favorable for the simultaneous removal of GO and heavy metal ions by surface complexation between Cu(II) and oxygen-containing functional groups. These findings might facilitate better understanding of the co-removal behavior of carbon nanomaterials and heavy metal ions on oxides, which is crucial to decreasing the environmental toxicity of pollutants in the natural environment.

  • 20. Yu, Shujun
    et al.
    Wang, Xiangxue
    Yao, Wen
    Wang, Jian
    Ji, Yongfei
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ai, Yuejie
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Alsaedi, Ahmed
    Hayat, Tasawar
    Wang, Xiangke
    Macroscopic, Spectroscopic, and Theoretical Investigation for the Interaction of Phenol and Naphthol on Reduced Graphene Oxide2017In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 51, no 6, p. 3278-3286Article in journal (Refereed)
    Abstract [en]

    Interaction of phenol and naphthol with reduced graphene oxide (rGO), and their competitive behavior on rGO were examined by batch experiments, spectroscopic analysis and theoretical calculations. The batch sorption showed that the removal percentage of phenol or naphthol on rGO in bisolute systems was significantly lower than those of phenol or naphthol in single-solute systems. However, the overall sorption capacity of rGO in bisolute system was higher than single-solute system, indicating that the rGO was a very suitable material for the simultaneous elimination of organic pollutants from aqueous solutions. The interaction mechanism was mainly pi-pi interactions and hydrogen bonds, which was evidenced by FTIR, Raman and theoretical calculation. FTIR and Raman showed that a blue shift of C=C and -OH stretching modes and the enhanced intensity ratios of I-D/I-G after phenols sorption. The theoretical calculation indicated that the total hydrogen bond numbers, diffusion constant and solvent accessible surface area of naphthol were higher than those of phenol, indicating higher sorption affinity of rGO for naphthol as compared to phenol. These findings were valuable for elucidating the interaction mechanisms between phenols and graphene-based materials, and provided an essential start in simultaneous removal of organics from wastewater.

  • 21. Zou, Yidong
    et al.
    Liu, Yang
    Wang, Xiangxue
    Sheng, Guodong
    Wang, Suhua
    Ai, Yuejie
    Ji, Yongfei
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Liu, Yunhai
    Hayat, Tasawar
    Wang, Xiangke
    Glycerol-Modified Binary Layered Double Hydroxide Nanocomposites for Uranium Immobilization via Extended X-ray Absorption Fine Structure Technique and Density Functional Theory Calculation2017In: ACS SUSTAINABLE CHEMISTRY & ENGINEERING, ISSN 2168-0485, Vol. 5, no 4, p. 3583-3595Article in journal (Refereed)
    Abstract [en]

    Novel, efficient, glycerol-modified nanoscale layered double hydroxides (rods Ca/Al LDH-Gl and flocculent Ni/Al LDH-Gl) were successfully synthesized by a simple one-step hydrothermal synthesis route and showed excellent adsorption capacities for U(VI) from aqueous solutions under various environmental conditions. The advanced spectroscopy analysis confirmed the existence of abundant oxygen-containing functional groups (e.g., C-O, O-C=O, and C=O) on the surfaces of Ca/AI LDH-Gl and Ni/Al LDH-Gl, which could provide enough free active sites for the binding of U(VI). The maximum adsorption capacities of Macro-application (Environment U(VI) calculated from the Sips model were 266.5 mg.g(-1) for Ca/Al LDH-Gl and 142.3 mg.g(-1) for Ni/Al LDH-Gl at 298.15 K, and the higher adsorption capacity of Ca/Al LDH-Gl might be due to more functional groups and abundant high-activity "Ca-O" groups. Macroscopic experiments proved that the interaction of U(VI) on Ca/Al LDH-Gl and Ni/Al LDH-Gl was due to surface complexation and electrostatic interactions. The extended Xray absorption fine structure analysis confirmed that U(IV) did not transformation to U(VI) on solid particles, and stable inner sphere complexes were not formed by reduction interaction but by chemical adsorption. The density functional theory (DFT) calculations further evidenced that the higher adsorption energies (i.e., E-ad = 4.00 eV for Ca/AI LDH-Gl-UO22+ and E-ad = 2.43 eV for Ca/Al LDH-Gl-UO2CO3) were mainly attributed to stronger hydrogen bonds and electrostatic interactions. The superior immobilization performance of Ca/AI LDH-Gl supports a potential strategy for decontamination of UO22+ from wastewater, and it may provide new insights for the efficient removal of radionuclides in environmental pollution cleanup.

  • 22. Zou, Yidong
    et al.
    Wang, Xiangxue
    Ai, Yuejie
    Liu, Yunhai
    Ji, Yongfei
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Wang, Hongqing
    Hayat, Tasawar
    Alsaedi, Ahmed
    Hu, Wenping
    Wang, Xiangke
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    beta-Cyclodextrin modified graphitic carbon nitride for the removal of pollutants from aqueous solution: experimental and theoretical calculation study2016In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 4, no 37, p. 14170-14179Article in journal (Refereed)
    Abstract [en]

    A novel beta-cyclodextrin modified, multifunctional, layer-by-layer graphitic carbon nitride (g-C3N4/beta-CD) was successfully synthesized and applied as an effective adsorbent for the removal of methyl orange (MO) and Pb(II) from aqueous solutions under various environmental conditions (e.g., solution pH, solid content, contact time and temperature). The kinetic results indicated that the adsorption was dominated by chemisorption, and the higher adsorption capacity of g-C3N4/beta-CD was attributed to it having more oxygen-containing functional groups than g-C3N4. The Langmuir, Freundlich and Sips models were applied to simulate the adsorption isotherms of MO and Pb(II), and the results demonstrated that the adsorption of MO was attributed to multilayer adsorption, while the coverage adsorption of Pb(II) on the g-C3N4/beta-CD was monolayer adsorption. The thermodynamic parameters showed that the adsorption of both MO and Pb(II) was spontaneous and endothermic. The DFT calculations further evidenced the surface complexation and electrostatic interaction of Pb(II) on the g-C3N4 and g-C3N4/beta-CD, whereas, the interaction of MO with g-C3N4 and g-C3N4/beta-CD was mainly attributed to hydrogen bonds and strong pi-pi interactions. The results demonstrated that g-C3N4/beta-CD is a promising material for the efficient removal of organic and inorganic pollutants in environmental pollution remediation.

  • 23. Zou, Yidong
    et al.
    Wang, Xiangxue
    Ai, Yuejie
    Liu, Yunhai
    Li, Jiaxing
    Ji, Yongfei
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Wang, Xiangke
    Coagulation Behavior of Graphene Oxide on Nanocrystallined Mg/AI Layered Double Hydroxides: Batch Experimental and Theoretical Calculation Study2016In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 50, no 7, p. 3658-3667Article in journal (Refereed)
    Abstract [en]

    Graphene oxide (GO) has attracted considerable attention because of its remarkable enhanced adsorption and multifunctional properties. However, the toxic properties of GO nanosheets released into the environment could lead to the instability of biological system. In aqueous phase, GO may interact with fine mineral particles, such as chloridion intercalated nanocrystallined Mg/Al layered double hydroxides (LDH-Cl) and nanocrystallined Mg/Al LDHs (LDH CO3), which are considered as coagulant molecules for the coagulation and removal of GO from aqueous solutions. Herein the coagulation of GO on LDHs were studied as a function of solution pH, ionic strength, contact time, temperature and coagulant concentration. The presence of LDH Cl and LDH-CO3 improved the coagulation of GO in solution efficiently, which was mainly attributed to the surface oxygen-containing functional groups of LDH Cl and LDH-CO3 occupying the binding sites of GO. The coagulation of GO by LDH-CI and LDH-CO3 was strongly dependent on pH and ionic strength. Results of coagulation of GO on LDHs was energetically favored by electrostatic interactions and hydrogen bonds, which was further evidenced by FTIR and XPS analysis. By integrating the experimental results, it was clear that LDH Cl could be potentially used as a cost-effective coagulant for the elimination of GO from aqueous solutions, which could efficiently decrease the potential toxicity of GO in the natural environment.

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