Supawadee Namuangruk

Adsorption of ethylene, benzene, and ethylbenzene over faujasite zeolites investigated by the ONIOM method

The performance of the ONIOM (Our-own-N-layered Integrated molecular Orbital + molecular Mechanics) approach utilizing 10 combinations of two-layer ONIOM2 schemes has been tested for various sizes of faujasite clusters containing up to 84T tetrahedral atoms and the complexes they form with ethylene, benzene, and ethylbenzene molecules. Interaction energies of the adsorbates with a 3T bare quantum cluster are calculated to be −8.14, −7.48, and −7.76 kcal/mol at B3LYP/6-31G(d,p) level of theory, respectively. The long-range effects of the extended structure of zeolite were found to differentiate the stability of adsorption complexes that cannot be drawn from the typical 3T quantum cluster. The interaction energies of ethylene, benzene, and ethylbenzene molecules on the more realistic cluster, 84T, using ONIOM2(B3LYP/6-311++G(d,p):UFF) scheme are predicted to be −8.75, −15.17, and −21.08 kcal/mol, respectively, which compare well with the experimental estimates of −9.1, −15.3, and −19.6 kcal/mol, respectively. This finding clearly demonstrates that the interaction between adsorbate and acidic zeolites does not depend only on the Bronsted group center but also on the lattice framework surrounding the adsorption site. The results obtained in this study suggest that the ONIOM approach, when carefully calibrated, is a computationally efficient and accurate method for studying adsorption of aromatics on zeolites.

Manipulation of Amorphous‐to‐Crystalline Transformation: Towards the Construction of Covalent Organic Framework Hybrid Microspheres with NIR Photothermal Conversion Ability

An approach to transforming amorphous organic networks into crystalline covalent organic frameworks (COFs) with retention of the colloidal nanosize and uniform morphology is presented. Specifically, Fe3 O4 nanoclusters are encapsulated by a disordering polyimine network via the Schiff-base reaction. The formed imine bonds could be reconstructed under thermodynamic control to reform the polyimine networks into imine-linked COFs in situ. Such a core-shell microsphere exhibits the uniform size and spherical shape, controllable COF shell thickness, accessible surface modification, and improved solution dispersibility as well as maintenance of high surface area, periodic micropores, and superior magnetic responsiveness. Additionally, the photothermal conversion effect is demonstrated for the first time on the nanoCOF layers upon exposure to near infrared light, providing convincing evidence for potential use in phototherapy.

Carbazole-dendrimer-based donor-π-acceptor type organic dyes for dye-sensitized solar cells: effect of the size of the carbazole dendritic donor.

A series of novel D-π-A type organic dyes, namely, GnTA (n = 1-4), containing carbazole dendrons up to fourth generation as a donor, bithiophene as π-linkage, and cyanoacrylic acid as acceptor were synthesized and characterized for applications in dye-sensitized solar cells (DSSCs). The photophysical, thermal, electrochemical, and photovoltaic properties of the new dyes as dye sensitizers were investigated, and the effects of the carbazole dendritic donors on these properties were evaluated. Results demonstrated that increasing the size or generation of the carbazole dendritic donor of the dye molecules enhances their total light absorption abilities and unluckily reduces the amount of dye uptake per unit TiO2 area because of their high molecular volumes. The latter was found to have a strong effect on the power conversion efficiency of DSSCs. Importantly, electrochemical impedance spectroscopy (EIS) revealed that the size or generation of the donor had a significant influence on a charge-transfer resistance for electron recombination at the TiO2/electrolyte interface, causing a difference in open circuit voltage (Voc) of the solar cells. Among them, dye G1TA containing first generation dendron as a donor (having lowest molecular volume) exhibited the highest power conversion efficiency of 5.16% (Jsc = 9.89 mA cm(-2), Voc = 0.72 V, ff = 0.73) under simulated AM 1.5 irradiation (100 mW cm(-2)).

Novel Bis[5-(fluoren-2-yl)thiophen-2-yl]benzothiadiazole End-Capped with Carbazole Dendrons as Highly Efficient Solution-Processed Nondoped Red Emitters for Organic Light-Emitting Diodes

A series of novel red-emitting bis[5-(fluoren-2-yl)thiophen-2-yl]benzothiadiazole-cored dendrimers containing carbazole dendrons up to the third generation are synthesized. Their photophysical, thermal, electrochemical, and electroluminescent properties as nondoped solution-processed red light-emitters for OLEDs are investigated. By using carbazole dendrons as the end caps, we are able to reduce the crystallization and retain the high emissive ability of a planar fluorescent core in the solid state as well as improve the thermal stability of the material. These dendrimers show a bright-red fluorescence and can form morphologically stable amorphous thin films with glass-transition temperatures as high as 283 °C. Simple structured solution-processed OLEDs using these materials as hole-transporting nondoped emitters and BCP as the hole-blocking layer emit a stable red color around 622-645 nm, with high luminance efficiencies (up to 4.80 cd A(-1) at 1.2 mA cm(-2)) and CIE coordinates of (0.65, 0.33), which are close to the pure red color.

Theoretical investigation of novel carbazole-fluorene based D-π-A conjugated organic dyes as dye-sensitizer in dye-sensitized solar cells (DSCs).

The ground state structure and frontier molecular orbital of newly synthesized carbazole‐fluorene based D‐π‐A organic dyes, CFP1A, CFP2A, CFP1CA, and CFP2CA, were theoretically investigated using density functional theory (DFT) at B3LYP/6‐31G(d,p) level. These dye molecules have been constructed based on carbazole‐fluorene as the electron‐donating moiety while introducing benzene units as π‐spacer connected to different anchor groups, such as acrylic acid and cyanoacrylic acid, as acceptors. The electronic vertical excitation energies and absorption wavelength were carried out using time‐dependent DFT (TD‐DFT). Furthermore, the adsorptions of phenylacrylic acid and phenylcyanoacrylic acid on the TiO2 anatase (101) surface were carried out by means of quantum‐chemical periodic calculations employing periodic PBE functional with DNP basis set. The results promise that anchor dyes with strong withdrawing CN group have easier injected electron to the conduction band of semiconductor implying that CFP1CA and CFP2CA show better performance among four dyes. Additionally, the intramolecular charge transfers (ICT) from electron donor group to anchoring group of CFP1CA and CFP2CA have shown better performance. The calculated results provide the efficiency trend of our new dyes as CFP1CA ≈ CFP2CA > CFP1A ≈ CFP2A which are excellently agree with experimental observation.

Absorption and emission spectra of ultraviolet B blocking methoxy substituted cinnamates investigated using the symmetry-adapted cluster configuration interaction method

The absorption and emission spectra of ultraviolet B (UVB) blocking cinnamate derivatives with five different substituted positions were investigated using the symmetry-adapted cluster configuration interaction (SAC-CI) method. This series included cis- and trans-isomers of ortho-, meta-, and para-monomethoxy substituted compounds and 2,4,5-(ortho-, meta-, para-) and 2,4,6-(ortho-, para-) trimethoxy substituted compounds. The ground and excited state geometries were obtained at the B3LYP/6-311G(d) and CIS/D95(d) levels of theory. All the compounds were stable as cis- and trans-isomers in the planar structure in both the S(0) and S(1) states, except the 2,4,6-trimethoxy substituted compound. The SAC-CI/D95(d) calculations reproduced the recently observed absorption and emission spectra satisfactorily. Three low-lying excited states were found to be relevant for the absorption in the UV blocking energy region. The calculated oscillator strengths of the trans-isomers were larger than the respective cis-isomers, which is in good agreement with the experimental data. In the ortho- and meta-monomethoxy compounds, the most intense peak was assigned as the transition from next highest occupied molecular orbital (next HOMO) to lowest unoccupied molecular orbital (LUMO), whereas in the para-monomethoxy compound, it was assigned to the HOMO to LUMO transition. This feature was interpreted as being from the variation of the molecular orbitals (MOs) due to the different substituted positions, and was used to explain the behavior of the excited states of the trimethoxy compounds. The emission from the local minimum in the planar structure was calculated for the cis- and trans-isomers of the five compounds. The relaxation paths which lead to the nonradiative decay were also investigated briefly. Our SAC-CI calculations provide reliable results and a useful insight into the optical properties of these molecules, and therefore, provide a useful tool for developing UVB blocking compounds with regard to the tuning of the photoabsorption.

Morphology-dependent performance of Zr–CeVO4/TiO2 for selective catalytic reduction of NO with NH3

A novel Zr–CeVO4/TiO2 catalyst was developed for the selective catalytic reduction (SCR) of NO with NH3. Both TiO2 nanosheets (TiO2-NS) and nanoparticles (TiO2-NP) with different crystal facets were used as supports for the catalyst. It was found that the TiO2-NS-supported catalyst showed much better activity, stability and H2O/SO2 durability than the TiO2-NP-supported catalyst. In particular, the catalyst loading amount was much lower than those of previously reported vanadate-based SCR catalysts. The crystal structures and morphologies were analysed by X-ray diffraction (XRD), Raman spectroscopy and (high-resolution) transmission electron microscopy ((HR)TEM). The redox properties, surface active species and acid sites of the catalysts were investigated through hydrogen temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS), ammonia and nitrogen oxide temperature-programmed desorption (NH3-TPD and NOx-TPD) and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTs) experiments. The improved activity at lower temperature was due to the presence of more active oxygen species and Bronsted acid sites, as well as the formation of NO2 on the surface of the TiO2 nanosheets which have exposed (001) facets. The enhanced stability and H2O/SO2 durability of Zr–CeVO4/TiO2-NS was due to the limited formation of NH4NO3 and (NH4)2SO4/NH4HSO4. The excellent low operation temperature, low vanadium content and absence of WO3(MoO3) in this catalyst indicated that it has promising potential as a SCR catalyst for practical applications.

Sr–Mg Mixed Oxides as Biodiesel Production Catalysts

The Sr–Mg basic catalysts were developed for biodiesel production through transesterification of palm oil with methanol. The evidence for synergistic effects between active Sr and Mg species was clearly demonstrated by transesterification tests over a series of Sr–Mg catalysts with varied Sr‐to‐Mg molar ratios. The catalyst properties were characterised by means of temperature‐programmed desorption of CO2 (CO2‐TPD), N2 sorption, XRD, SEM and TEM experiments. The super strong basic site was formed in Sr–Mg catalysts through a partial solid state reaction induced by thermal treatment at 600 °C. The new basic site, together with the original basic site from SrO (average basic site density=757 μmol m−2), effectively catalysed a transesterification reaction at mild conditions. Biodiesel containing 96 % methyl esters was obtained at reaction conditions of 75 min, 60 °C, 0.1 MPa, 3 wt. % catalyst loading and a methanol‐to‐oil ratio of 6:1, and the catalyst exhibited good reusability. Improved surface areas and porosities were also achieved compared to the unsupported SrO. Density functional theory (DFT) calculations of methylpropanoate adsorption on SrO, MgO and Sr/MgO showed that the adsorption energies of all adsorbate–surface complexes corresponded well with the experimental catalytic activity, which increased in the order MgO

Bifunctional oligofluorene-cored carbazole dendrimers as solution-processed blue emitters and hole transporters for electroluminescent devices

A series of bifunctional oligofluorene-cored carbazole dendrimers (GnFm, n = 1–3, m = 2–3) containing carbazole dendrons up to the third generation as end-caps were synthesized and characterized as non-doped solution-processed blue-light emitters and hole transporters for organic light-emitting diodes (OLEDs). Their optical, thermal, electrochemical, and electroluminescence properties were investigated. They exhibited a strong deep-blue fluorescence with solution fluorescence quantum yields (ΦF) of around 0.91–0.99 and formed morphologically stable amorphous thin films with glass transition temperatures as high as 273 °C. As blue emitters, solution-processed OLEDs with structure of ITO/PEDOT:PSS/GnFm/BCP/LiF:Al displayed a deep-blue emission (λELem = 415 nm, CIE = 0.17, 0.11) with a maximum luminance efficiency as high as 3.79 cd A−1 and a low turn-on voltage of 4.2 V. As hole transporters, solution-processed OLEDs with structure of ITO/PEDOT:PSS/GnFm/Alq3/LiF:Al showed a bright green emission (λELem = 520 nm, CIE = 0.30, 0.54) with a maximum luminance efficiency as high as 5.63 cd A−1 and a low turn-on voltage of 2.4 V.

Metal–Porphyrin: A Potential Catalyst for Direct Decomposition of N2O by Theoretical Reaction Mechanism Investigation

The adsorption of nitrous oxide (N2O) on metal-porphyrins (metal: Ti, Cr, Fe, Co, Ni, Cu, or Zn) has been theoretically investigated using density functional theory with the M06L functional to explore their use as potential catalysts for the direct decomposition of N2O. Among these metal-porphyrins, Ti-porphyrin is the most active for N2O adsorption in the triplet ground state with the strongest adsorption energy (-13.32 kcal/mol). Ti-porphyrin was then assessed for the direct decomposition of N2O. For the overall reaction mechanism of three N2O molecules on Ti-porphyrin, two plausible catalytic cycles are proposed. Cycle 1 involves the consecutive decomposition of the first two N2O molecules, while cycle 2 is the decomposition of the third N2O molecule. For cycle 1, the activation energies of the first and second N2O decompositions are computed to be 3.77 and 49.99 kcal/mol, respectively. The activation energy for the third N2O decomposition in cycle 2 is 47.79 kcal/mol, which is slightly lower than that of the second activation energy of the first cycle. O2 molecules are released in cycles 1 and 2 as the products of the reaction, which requires endothermic energies of 102.96 and 3.63 kcal/mol, respectively. Therefore, the O2 desorption is mainly released in catalytic cycle 2 of a TiO3-porphyrin intermediate catalyst. In conclusion, regarding the O2 desorption step for the direct decomposition of N2O, the findings would be very useful to guide the search for potential N2O decomposition catalysts in new directions.