Photodegradation of Rhodamine B on Sulfur Doped ZnO/TiO2 Nanocomposite Photocatalyst under Visible-light Irradiation

Sulfur doped ZnO/TiO₂ nanocomposite photocatalysts were synthesized by a facile sol‐gel method. The structure and properties of catalysts were characterized by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), UV‐vis diffusive reflectance spectroscopy (DRS) and N₂ desorption‐adsorption isotherm. The XRD study showed that TiO₂ was anatase phase and there was no obvious difference in crystal composition of various S‐ZnO/TiO₂. The XPS study showed that the Zn element exists as ZnO and S atoms form SO^2?₄. The prepared samples had mesoporosity revealed by N₂ desorption‐adsorption isotherm result. The degradation of Rhodamine B dye under visible light irradiation was chosen as probe reaction to evaluate the photocatalytic activity of the ZnO/TiO₂ nanocomposite. The commercial TiO₂ photocatalyst (Degussa P25) was taken as standard photocatalyst to contrast the prepared different photocatalyst in current work. The improvement of the photocatalytic activity of S‐ZnO/TiO₂ composite photocatalyst can be attributed to the suitable energetic positions between ZnO and TiO₂, the acidity site caused by sulfur doping and the enlargement of the specific area. S‐3.0ZnO/TiO₂ exhibited the highest photocatalytic activity under visible light irradiation after Zn amount was optimized, which was 2.6 times higher than P25.     

Voltage‐Driven Photoluminescence Modulation of Liquid‐Crystalline Hybridized ZnO Nanoparticles

Liquid‐crystalline hybrid nanomaterials have been obtained by grafting mesogenic units around luminescent ZnO nanocrystals of 5 nm in diameter. Modifying the mesogenic density around the inorganic core allows the modulation of the liquid‐crystalline behavior and its miscibility in commercial liquid crystal (LC). The strong blue photoluminescence observed for the hybrids can be modulated by applying a voltage on a LC cell containing commercial LC and 10 wt % of hybrid.     

Influence of rapid thermal annealing on structure and interfacial characteristic of ZnO thin films

Highly C‐axis oriented ZnO thin film was manufactured by radio‐frequency magnetron sputtering technique on Si (111) substrate. The main objective was to study the influence of rapid thermal annealing (RTA) temperature on the structure and interfacial characteristic of ZnO thin films. X‐ray diffraction results showed that the ZnO thin films annealed at 600 °C by RTA technique had a perfect C‐axis preferred orientation compared to the other ZnO thin films, and the full width at half maximum of ZnO (002) rocking curve measurements indicted that the RTA‐annealed ZnO thin films possessed better crystal structure. Atom force microscopy displayed that the grain size of RTA‐annealed ZnO thin films was fine and uniform compared with the as‐deposited ZnO thin films, although the grains grew in RTA process and the root meant square roughness was smaller than that of as‐deposited films. High‐resolution transmission electron microscopy showed that there was an obvious amorphous layer between ZnO thin films and Si substrate, but the RTA‐annealed ZnO thin films exhibited larger and denser columnar structure and a preferred orientation with highly c axis perpendicular to the amorphous layer. Copyright © 2012 John Wiley & Sons, Ltd.     

Facile Fabrication of Porous ZnS and ZnO Films by Coaxial Electrospinning for Highly Efficient Photodegradation of Organic Dyes

Porous ZnS and ZnO nano‐crystal films were fabricated via a three‐step procedure. First, Zn(CH₃COO)₂/Silk Fibroin nanofiber mats were prepared by coaxial electrospinning. Second, Zn(CH₃COO)₂/Silk Fibroin mats were immersed in NaS solution to react with S²⁻ to obtain ZnS/Silk Fibroin nanofiber mats. Finally, ZnO porous films were prepared by calcination of ZnS/Silk Fibroin composite mat at 600°C in air atmosphere. When ZnS/Silk Fibroin mats were calcinated in nitrogen, ZnS/Carbon composite mats were obtained accordingly. The resulting porous films were fully characterized. The ZnO porous films were the aggregation of ZnO nano‐crystal with hexagonal wurtzite structure. The seize of ZnO was estimated in the range of 10–20 nm. Both of the ZnS and ZnO nano‐crystal films exhibited high photocatalytic activities for the photodegradation of Methylene blue and Rhodamine B. It was also found that ZnO porous films are better than ZnS/Carbon nanofiber mats. In addition, photocatalysis of a real wastewater sample from a printing and dyeing company was conducted. The ZnO porous films exhibited excellent performance to treat the real samples. Moreover, the porous ZnO nano‐crystal photocatalyst could easily be recycled without notable loss of catalysis ability.     

Chains,Necklaces and Weaving Chain‐link Grids from Self‐Assembly Reactions

Assembly of two ditopic units, a phenanthroline substituted by 4‐ethynyl pyridines at the 2‐and 9‐positions and a dimetallic paddlewheel, gives a linear chain polymer rather than a closed cyclic species, which would appear equally possible. The chain may be decorated by binding a copper‐containing macrocycle around the phenanthroline units to form a polypseudorotaxane. When two phenanthroline ligands are assembled in a first step around copper(I), the paddlewheel acceptor can link them in a second step to form a two‐dimensional interwoven grid that resembles the form of a chain‐link fence. Each copper(I) centre in this structure is chiral, and the crystal shows complete homochirality, implying selection during the assembly process.     

Optical and photocatalytic properties of single crystalline ZnO at the air-liquid interface by an aminolytic reaction

Crystalline flowerlike ZnO was synthesized by an aminolytic reaction at the air-liquid interface in an aqueous media at an alkaline pH. A thin visible film was formed at the air-liquid interface by self-assembly of flowerlike ZnO. Diffraction studies show rearrangement of the single crystalline units at the air-liquid interface leading to the formation of nanobelts. These nanobelts overlap systematically to form petals of the flowerlike structure; individual petals get curved with time. Each nanobelt is found to be single crystalline and can be indexed as the hexagonal ZnO phase. The organic product formed in the aminolytic reaction and dissolution-reprecipitation mechanism is the driving force for the formation of flowerlike ZnO at the air-liquid interface. A clear relationship between the surface, photocatalytic, and photoluminescent properties of ZnO is observed. The flowerlike structure exhibits a blue shift (3.56 eV) in the band emission as compared to bulk ZnO (3.37 eV). The photodegradation of methylene blue over the flowerlike ZnO catalyst formed at the air-liquid interface and in the sediments shows enhanced photocatalytic activity. The sub-bands formed due to surface defects facilitate separation of charge carriers increasing their lifetime, leading to enhanced photocatalytic activity of flowerlike ZnO.     

Twin liquid crystals and segmented thermotropic polyesters containing azobenzene—effect of spacer length on LC properties

We report systematic studies on a homologous series of twin liquid crystalline (LC) molecules based on phenyl and naphthyl azobenzene ( PnP and NpnNp ) as well as segmented copolyesters based on them. The twin series had the structure azobenzene–oligooxyethylene–azobenzene, where the ethyleneoxy length was varied from 2 to 6 units. The LC properties of the twin series depended on the chemical structure of the azochromophore and also the length of the central oligooxyethylene segment. The PnP series exhibited smectic LC properties for n > three oligooxyethylene units. Conversely, NpnNp series exhibited spherulitic phases only for the shortest member – Np2Np . One non‐LC short spacer twin ( P2P ) and one LC long spacer twin ( P6P ) were incorporated as part of a main chain polyester composed of fully aliphatic segments of sebacate and di or tetraethylene glycol (DEG/TEG) units by melt polycondensation. Non‐LC P2P formed LC polymers even at low (5 mol %) incorporation in DEG‐based copolymers, whereas the LC‐ P6P could do so only at 30 mol % incorporation. The LC properties of the twin molecules as well as copolymers were studied using differential scanning calorimetry, polarized light microscopy (PLM) along with variable temperature wide angle X‐ray diffraction. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Morphology‐Dependent Gas‐Sensing Properties of ZnO Nanostructures for Chlorophenol

The crystal‐plane effect of ZnO nanostructures on the toxic 2‐chlorophenol gas‐sensing properties was examined. Three kinds of single‐crystalline ZnO nanostructures including nanoawls, nanorods, and nanodisks were synthesized by using different capping agents via simple hydrothermal routes. Different crystal surfaces were expected for these ZnO nanostructures. The sensing tests results showed that ZnO nanodisks exhibited the greatest sensitivity for the detection of toxic 2‐chlorophenol. The results revealed that the sensitivity of these ZnO samples was heavily dependent on their exposed surfaces. The polar (0001) planes were most reactive and could be considered as the critical factor for the gas‐sensing performance. In addition, calculations using density functional theory were employed to simulate the gas‐sensing reaction involving surface reconstruction and charge transfer both of which result in the change of electronic conductance of ZnO.     

Evolution from lyotropic liquid crystal to helical fibrous organogel of an achiral fluorescent twin-tapered bi-1,3,4-oxadiazole derivative

We report an unprecedented hierarchical self‐assembly of an achiral twin‐tapered bi‐1,3,4‐oxadiazole derivative (2,2‐bis(3,4,5‐trioctanoxyphenyl)‐bi‐1,3,4‐oxadiazole, BOXD‐T8). This molecule can form a layer‐structured lyotropic liquid crystal and further forms a helical fibrous organogel in DMF at concentrations above 0.6 wt %. The self‐assembly process of BOXD‐T8 in DMF is accompanied by a change in its fluorescence. The pitches of the helical fibers are non‐uniform, and both left‐ and right‐handed helical fibers are observed in equal quantities. Intermolecular π–π interactions between aromatic segments have been demonstrated to be the driving force for aggregate formation. This helical structure of BOXD‐T8 is dependent on the solvent, concentration, and the layer‐structured intermediate liquid‐crystalline state.     

5‐Amino‐2,4,6‐tribromoisophthalic acid: the MAD triangle for experimental phasing

The title compound, C₈H₄Br₃NO₄, shows an extensive hydrogen‐bond network. In the crystal structure, molecules are linked into chains by COO—H...O bonds, and pairs of chains are connected by additional COO—H...O bonds. This chain bundle shows stacking interactions and weak N—H...O hydrogen bonds with adjacent chain bundles. The three Br atoms present in the molecule form an equilateral triangle. This can be easily identified in the heavy‐atom substructure when this compound is used as a heavy‐atom derivative for experimental phasing of macromolecules. The title compound crystallizes as a nonmerohedral twin.     

Investigation of an Unusual Crystal Habit of Hydrochlorothiazide Reveals Large Polar Enantiopure Domains and a Possible Crystal Nucleation Mechanism

The observation of an unusual crystal habit in the common diuretic drug hydrochlorothiazide (HCT), and identification of its subtle conformational chirality, has stimulated a detailed investigation of its crystalline forms. Enantiomeric conformers of HCT resolve into an unusual structure of conjoined enantiomorphic twin crystals comprising enantiopure domains of opposite chirality. The purity of the domains and the chiral molecular conformation are confirmed by spatially revolved synchrotron micro‐XRD experiments and neutron diffraction, respectively. Macroscopic inversion twin symmetry observed between the crystal wings suggests a pseudoracemic structure that is not a solid solution or a layered crystal structure, but an unusual structural variant of conglomerates and racemic twins. Computed interaction energies for molecular pairs in the racemic and enantiopure polymorphs of HCT, and the observation of large opposing unit‐cell dipole moments for the enantiopure domains in these twin crystals, suggest a plausible crystal nucleation mechanism for this unusual crystal habit.     

Flowerlike ZnO nanostructures via hexamethylenetetramine-assisted thermolysis of zinc-ethylenediamine complex

Flowerlike ZnO nanostructures (FZNs) have been deposited on Si substrate from aqueous solution by the hexamethylenetetramine (HMT)-assisted thermolysis of zinc-ethylenediamine (en) complex at low temperature (95 degrees C) and in a short time (60 min). Obtained FZNs exhibit well-defined flowerlike morphology, hexagonal wurtzite structure, and strong UV photoluminescence. The flower petals constructed by many well-aligned nanorods possess the typical tapering feature with tip sizes of 30-50 nm. Effects of en, zinc-en molar ratio, HMT, and reaction time were investigated. Results show that en is determinative to the formation of FZNs, and the partial capping of NH(3).(CH(2))(2).NH(3) molecules on the side surface of the ZnO crystal is responsible for the tapering feature of petals. HMT can step into the nucleation process of ZnO and inhibit the formation of nanorods on the substrate by preventing heterogeneous precipitation. Moreover, the formation of twin crystal ZnO nuclei at low precursor concentrations and their further evolution into spindle crystals with clear middle interfaces are also vitally important for the development of FZNs.     

不同形貌氧化锌的微波水热法制备及其光催化性能

采用微波水热法在乙二醇的辅助下,制备出一系列不同形貌的氧化锌(Zn O)纳米/微米颗粒。扫描电子显微镜测试结果表明,乙二醇的加入量对样品的形貌有着非常显著的影响,通过控制乙二醇的加入量,可以得到不规则片状、六方棱柱孪晶、梭子形和球形等形貌的Zn O纳米/微米颗粒。从微波反应器检测压力结果可以看出,乙二醇的加入量对反应体系的压力影响非常显著,这起到了调控纳米晶生长速度的效果进而得到不同形貌的样品。在此基础上,系统测试了样品在氙灯照射下光催化降解罗丹明B的能力,结果表明,乙二醇加入量大于12 m L时的球状样品光催化效率要远高于其他样品,在50 min内能完成对罗丹明B的降解。     

Twinning in 5‐fluorosalicylic acid: description of a new polymorph

The crystal structure of 5‐fluorosalicylic acid is known from the literature [Choudhury & Guru Row (2004). Acta Cryst. E 60 , o1595–o1597] as crystallizing in the monoclinic crystal system with space‐group setting P2₁/n and with one molecule in the asymmetric unit (polymorph I). We describe here a new polymorph which is again monoclinic but with different unit‐cell parameters (polymorph II). Polymorph II has two molecules in the asymmetric unit. Its structure was modelled as a twin, with a pseudo‐orthorhombic C‐centred twin cell.     

Enantiotropic phase transition and twinning in 2,2,3,3,4,4‐hexafluoropentane‐1,5‐diol

Four crystal structure determinations of 2,2,3,3,4,4‐hexafluoropentane‐1,5‐diol (HFPD), C₅H₆F₆O₂, were conducted on a single specimen by varying the temperature. Two polymorphs of HFPD were found to be enantiotropically related as phases (I) and (II), both in the space group P1. These structures contain closely related R₄⁴(20) sheets. A structure determination was completed on form (Ia) at 283 K. Form (Ia) was then supercooled below the phase transition temperature at 279 to 173 K to give form (Ib) for a second structure determination. Metastable form (Ib) was transformed by momentary warming and recooling to give form (II) for a third structure determination at 173 K. Form (II) transformed to form (Ic) upon warming to 283 K. Enantiotropic phase transitions between phases (I) and (II) were confirmed with X‐ray powder diffraction and differential scanning calorimetry. Form (Ia) was found as a twin by nonmerohedry by a reflection in (011). This twinning persists in all phases described. Additional twinning was found after the phase (I) to phase (II) transformation. These two additional twin components are related to the first pair by a 180° rotation about the (012) plane. This latter pair of twins persisted as the specimen was warmed back to form (Ic) at 283 K.     

Preparation of ZnO nanoparticle‐reinforced polyamide 6 composite by in situ‐coproduced method and their properties

Polyamide 6/ZnO nanocomposites (noted as PA6/ZnO) were prepared by an in situ co‐producing method, during which Zn₂(OH)₂CO₃ decomposed into nano‐ZnO in the process of the opening‐ring polymerization of caprolactam at high temperature. Transmission electron microscopy, X‐ray diffraction, thermogravimetric analysis, and differential scanning calorimetry were used to analyze the size and dispersive properties of nano‐ZnO, the crystallization and melting properties, the thermal properties, and crystal structure of PA6/ZnO composite, respectively. The results showed that the nano‐ZnO derived from Zn₂(OH)₂CO₃ via in situ polymerization of PA6‐ZnO was uniformly dispersed in PA6 matrix. However, the overall nano‐ZnO crystallization rate and crystal size in the PA6 matrix were hindered by the bulky PA6 molecular chains. The mechanical properties were evaluated using universal tensile and impact testing instruments. The results revealed that PA6/ZnO composite with 0.2% nano‐ZnO content possessed excellent tensile strength, enhanced by 75% in comparison with the pure PA6. The nano‐ZnO had little influence on the impact strength of PA6. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 165–170     

Twinned α‐LiRb2(CF3SO3)3

The investigated crystal of α‐LiRb₂(CF₃SO₃)₃ [lithium dirubidium tris­(tri­fluoro­methane­sulfonate)] was a twin, with the twin matrix given by (00/010/001). The structure consists of channel‐like patterns built up of lipophilic CF₃ groups pointing towards each other. The polar interstices are occupied by cations. One Rb atom is coordinated by O atoms in the form of a distorted square antiprism, while the coordination around the second Rb atom is best described as a distorted pentagonal plane, with one O atom and one F atom situated above and an additional F atom below this plane. The O atoms around the Li atom form a strongly distorted tetrahedron.     

Surface‐Functionalized Latex Particles as Controlling Agents for the Mineralization of Zinc Oxide in Aqueous Medium

Polystyrene latex particles modified at the surface with different hydrophilic functional groups were prepared by miniemulsion polymerization and used as controlling agents in the crystallization of zinc oxide from aqueous medium. The effects of the chemical nature of the surface functionalization and the latex concentration on the crystal growth, morphology, and crystalline structure of the resulting zinc oxide were analyzed. Micro‐ and submicrosized crystals with a broad variety of morphologies depending on the functionalization were obtained. Among the different latexes studied, the acrylic‐acid‐derived particles were shown to be a convenient system for further quantitative investigations. In this case, as the additive concentration increases, the length‐to‐width ratio (aspect ratio) of the crystals decreases systematically. Preferential adsorption of the latex particles onto the fast‐growing faces {001} of ZnO is assumed to follow a Langmuir‐type isotherm, and interaction of the adsorbed particles with the growth centers will reduce the growth rate in [001]. This leads to a quantitative relationship linking the aspect ratio to the latex concentration at constant diameter and surface chemistry of the latex. The dependence of the aspect ratio on charge density of the latex can also be modeled by an algorithm in which attractive forces between the latex particle and the ZnO surface are balanced against repulsive forces of an osmotic nature. The latter are associated with the confined volume between the crystal and latex particle surfaces.     

5‐Iodouracil: structure of a reflection twin

The crystal structure of 5‐iodouracil, C₄H₃IN₂O₂, has been determined in the noncentrosymmetric space group P2₁ on a nonmerohedrally twinned crystal. Both twin components are enantiomorphically pure, but the twin element is a mirror plane perpendicular to c*. The molecular structure is discussed and stacking faults in the two‐dimensional packing are proposed as a reason for the twinning.     

Ferrocene‐Substituted Naphthalenediimide with Broad Absorption and Electron‐Transport Properties in the Segregated‐Stack Structure

A new naphthalenediimide (NDI) molecule, where two ferrocene (Fc) units were directly attached to both imide nitrogens ( Fc‐NDI‐Fc ), was synthesized. The Fc units provide high crystallinity to Fc‐NDI‐Fc with good solubility to conventional organic solvents. The Fc units also work as electron‐donating substituents, in contrast to the electron‐deficient NDI unit, resulting in broad charge‐transfer absorption of Fc‐NDI‐Fc from the UV region to 1500 nm in the solid state. The crystal structure analysis revealed that Fc‐NDI‐Fc formed a segregated‐stack structure. The DFT calculation based on the crystal structure showed that the NDI π‐orbitals extended over two axes. The extended π‐network of the NDI units led to the electron‐transport properties of Fc‐NDI‐Fc , which was confirmed using a flash‐photolysis time‐resolved microwave conductivity technique.