| 1. |
- Ji, Yongfei, 1984-
(författare)
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Theoretical Studies on the Molecular Mechanisms of Photo-Catalytic Reactions on TiO2 Surfaces
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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
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| 2. |
- Liu, Juzhe, et al.
(författare)
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Ultrathin amorphous cobalt-vanadium hydr(oxy)oxide catalysts for the oxygen evolution reaction
- 2018
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Ingår i: Energy & Environmental Science. - : Royal Society of Chemistry. - 1754-5692 .- 1754-5706. ; 11:7, s. 1736-1741
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Tidskriftsartikel (refereegranskat)abstract
- Cost efficient and long-term stable catalysts are in great demand for the oxygen evolution reaction (OER), a key process involved in water splitting cells and metal-air batteries. Here, we demonstrate that the ultrathin amorphous cobalt-vanadium hydr(oxy)oxide we synthesized is a highly promising electrocatalytic material for the OER with a low overpotential of 0.250 V (even lower down to 0.215 V when supported on Au foam) at 10 mA cm(-2) and a long stable operation time (170 h) in alkaline media. In combination with in situ X-ray absorption spectral characterization and first-principles simulations, we reveal that the ultrathin, amorphous and alloyed structural characteristics have enabled its facile transformation to the desirable active phase, leading to a dramatically enhanced catalytic activity. Our finding highlights the remarkable advantages of the two-dimensional amorphous material and sheds new light on the design of high-performance electrocatalysts.
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| 3. |
- Yu, Shujun, et al.
(författare)
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Macroscopic, Spectroscopic, and Theoretical Investigation for the Interaction of Phenol and Naphthol on Reduced Graphene Oxide
- 2017
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 51:6, s. 3278-3286
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Zavaraki, A. Jamshidi, et al.
(författare)
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Low toxic Cu2GeS3/InP quantum dot sensitized infrared solar cells
- 2018
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Ingår i: Journal of Renewable and Sustainable Energy. - : American Institute of Physics (AIP). - 1941-7012. ; 10:4
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Tidskriftsartikel (refereegranskat)abstract
- Type-II Cu2GeS3/InP core/shell quantum dots (QDs) are designed using density functional theory and synthesized by a hot injection method in order to enhance the power conversion efficiency of quantum dot sensitized solar cells. The low toxicity and an absorption extending to the infrared region are key aspects of the importance of these QDs. The longer absorption achieved for type-II Cu2GeS3/InP QDs compared to single core Cu2GeS3 QDs is achieved by optimization of the band alignment. This leads to a more efficient carrier separation and a suppression of the electron-hole recombination. The results show that the efficiency and the electron injection rate constant increase by more than 5 and 2 times, respectively.
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| 5. |
- Zou, Yidong, et al.
(författare)
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Glycerol-Modified Binary Layered Double Hydroxide Nanocomposites for Uranium Immobilization via Extended X-ray Absorption Fine Structure Technique and Density Functional Theory Calculation
- 2017
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Ingår i: ACS Sustainable Chemistry and Engineering. - : AMER CHEMICAL SOC. - 2168-0485. ; 5:4, s. 3583-3595
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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