Subsequent UV Irradiation Research Articles

Fouling of WO 3 nanoparticle-incorporated PSf membranes in ultrafiltration of landfill leachate and dairy a combined wastewaters: An investigation using model

Abstract As fouling has always been a major drawback of membrane technology, qualitative and quantitative understanding of membrane fouling mechanisms therefore becomes vital in order to help push membrane separation technologies forward. In this study, firstly, self-cleaning Polysulfone (PSf) membranes were synthesized by incorporation of WO3 nanoparticles (0–2 wt%) and subsequent UV irradiation for efficient ultrafiltration (UF) of landfill leachate and dairy wastewater. The membrane surface properties were characterized by scanning electron microscopy (SEM) and contact angle analysis. It was found that UV-irradiated membranes exhibited higher percent COD removals due to the hydrophilicity and photocatalytic properties of nano-WO3. Subsequently, in order to analyze the fouling behavior of the membranes, a set of experimental data from cross-flow ultrafiltration of municipal landfill leachate and industrial dairy wastewater at 25 °C was obtained. A new model of membrane fouling was proposed based on a resistance in series concept and was fitted well with all experimental data sets. Almost all relative errors of prediction provided by the proposed model were less than 2.5%. In addition, it was revealed that this newly-developed model exhibited smooth transition between the common successive two-step pore blockage-cake filtration phenomena and thus eliminates the need to use separate equations for different mechanisms.

Live Templates of a Supramolecular Block Copolymer for the Synthesis of Ordered Nanostructured TiO2 Films via Guest Exchange.

In this work, we introduce a facile method based on host-guest chemistry to synthesize a range of nanostructured TiO2 materials using supramolecular templates of a dendron-jacketed block copolymer (DJBCP). The DJBCP is composed of amphiphilic dendrons (4'-(3,4,5-tridodecyloxybenzoyloxy)benzoic acid, TDB) selectively incorporated into a P4VP block of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) via hydrogen bonding. The PS-b-P4VP host acts as a structure-directing template, while the guest molecules (TDB) assist the self-assembly nanostructures and zone-axis alignment, resulting in the nanostructured template of vertically oriented cylinders formed via successive phase transformations from Im3̅m to R3̅m to P6mm upon thermal annealing in the doctor-blade-cast film. The guest molecules subsequently direct the titania precursors into the P4VP domains of the templates via supramolecular guest exchange during immersion of the film in a designated precursor solution containing a P4VP-selective solvent. The subsequent UV irradiation step leads to the formation of PS-b-P4VP/TiO2 hybrids. Finally, removal of the host template by calcination leaves behind mesoporous channels and makes sacrifices to be a carbon source for carbon-doping TiO2 materials. Various TiO2 nanoarchitectures, namely, vertical and wiggly micrometer-length channels, inverse opals, fingerprint-like channels, heterogeneous multilayers, and nanotubes, have been fabricated by highly tunable DJBCP nanostructures.

Surface modification of polyamide thin film composite membrane by coating of titanium dioxide nanoparticles

Abstract In this paper, the coating of TiO 2 nanoparticles onto the surface of a polyamide thin film composite nanofiltration membrane has been studied. Changes in the properties and separation performance of the modified membranes were systematically characterized. The experimental results indicated that the membrane surface hydrophilicity was significantly improved by the presence of the coated TiO 2 nanoparticles with subsequent UV irradiation. The separation performance of the UV-irradiated TiO 2 -coated membranes was improved with a great enhancement of flux and a very high retention for removal of residual dye in an aqueous feed solution. The antifouling property of the UV-irradiated TiO 2 -coated membranes was enhanced with higher maintained flux ratios and lower irreversible fouling factors compared with an uncoated membrane.

Creation of functional polydiacetylene images on paper using inkjet printing technology

We feature the recent developments of patterning of functional polydiacetylene (PDA) on a paper substrate that can be fully integrated with conventional inkjet printing techniques. The use of the paper substrate facilitates the fabrication of flexible, lightweight, and disposable devices. The PDA systems loaded on paper display their uniquely optical properties. In general, diacetylene ink solutions are inkjet-printed on paper and the subsequent UV-irradiation induces photopolymerization of self-assembled DA molecules, leading to the blue phase PDAcoated paper film. The typical blue-to-red transition of the PDA paper film undergoes when it is exposed to a variety of external stimuli. We introduce three types of ink formulation protocols to prepare the PDA precursor solutions that are compatible with inkjet-printing. We also represent the PDA printed paper system and their practical applications, such as counterfeit-proof ink, electrothermochromic paper display, and human sweat pore mapping.

Multivalence Charge Transfer in Doped and Codoped Photocatalytic TiO2.

The present work reports data for the mineralogical and chemical properties of anatase thin films individually doped or codoped with chromium and vanadium, fabricated by sol-gel spin coating on glass substrates and annealing at 450 °C for 2 h. X-ray photoelectron spectroscopy data indicated the presence of Ti(4+), Ti(3+), Cr(3+), and possibly Cr(4+) in the Cr-doped thin films; Ti(4+), Ti(3+), V(3+), V(4+), and possibly V(5+) in the V-doped thin films; and Ti(4+), Ti(3+), Cr(3+), Cr(4+), V(3+), V(4+), and possibly V(5+) in the codoped thin films. While the thermodynamically stable valences Ti(4+), Cr(3+), and V(5+) would be expected to have formed, the presence of the nonequilibrium valences Ti(3+), Cr(4+), V(3+), and V(4+) is considered to have resulted from intervalence charge transfer for the Cr-doped and V-doped systems but from multivalence charge transfer (MVCT) for the codoped system. The latter phenomenon, which is introduced as a new conceptual term, describes the nature of the mutual exchange of electrons during valence changes of both dopant (Cr, V) and matrix (Ti) ions during annealing. In the present case, MVCT appears to be a transient metastable condition that acts during annealing, but subsequent UV irradiation can alter its effects.

Synthesis and application of photo-active carboxymethyl cellulose derivatives

In this work, the polysaccharide carboxymethyl cellulose (CMC) was first activated via periodate oxidation then modified by insertion of photo-active cinnamic acid hydrazide moieties to finally produce the photo-crosslinkable CMC-CM with various extents of functionalizations. The chemical structures of the manufactured polymeric materials were entirely investigated utilizing FTIR, 1H, 13C NMR, and UV–vis spectra. Upon irradiation in UV light, the progress and kinetics of the cross-linking were detected using UV–vis spectra. Moreover, the crystallinity changes before and after chemical modification and subsequent UV irradiation were examined by XRD spectra. Also, the obtained hydrogels with various cross-linking densities were freeze dried to visualize the morphological changes using SEM. In addition, the rheological experiments indicated the improvement of the hydrogel mechanical properties by increasing both UV irradiation time and degree of cinnamate functionalization. The obtained hydrogel exhibited good swelling, gelation and biodegradation properties, which indicate a promising potential in different biomedical applications.

Enhancement of encaged electron concentration by Sr(2+) doping and improvement of Gd(3+) emission through controlling encaged anions in conductive C12A7 phosphors.

Conductive C12A7:0.1%Gd(3+),y%Sr(2+) powders with different Sr(2+) doping concentrations have been prepared in a H2 atmosphere by a solid state method in combination with subsequent UV-irradiation. The encaged electron concentration could be modulated through tuning Sr(2+) doping and its maximum value reaches 2.3 × 10(19) cm(-3). This is attributed to the competition between enhanced uptake and the release of the encaged anions during their formation and diffusion processes and the suppression of encaged electrons generation due to the increased encaged OH(-) anions and the decreased encaged O(2-) anions. Although there exists encaged electrons and different encaged anions (O(2-), H(-) and OH(-)) in C12A7 conductive powders prepared through the hydrogen route, a dominant local environment around Gd(3+) could be observed using electron spin resonance (ESR) detection. It can be ascribed to the stronger coupling of the encaged OH(-) to the framework of C12A7 than those of the encaged electrons, O(2-) and H(-) anions. In addition, emission of Gd(3+) ions is enhanced under UV or low voltage electron beam excitation and a new local environment around Gd(3+) ions appears through the thermal annealing in air because of the decrease of the encaged OH(-) anions and the increase of the encaged O(2-) anions. Our results suggested that Sr(2+) doping in combination with thermal annealing in air is an effective strategy for increasing the conductive performance and enhancing the emission of rare earth ions doped into C12A7 conductive phosphors for low-voltage field emission displays (FEDs).

Fabrication and characterization of UV‐crosslinkable thermoresponsive composite fibers with magnetic properties

ABSTRACTCrosslinking magnetic thermoresponsive composite (MTC) fiber mats were fabricated by electrospinning process and followed by UV curing. Thermoresponsive poly‐(N‐isopropylacrylamide) (PNIPAAm) and magnetic Fe3O4 were firstly synthesized by redox‐initiated polymerization and co‐precipitation, respectively. A crosslinking agent (dipentaerythritol hexylacrylate) and photoinitiator for providing crosslinking ability were then mixed with PNIPAAm and Fe3O4 in ethanol as the electrospinning solution. After electrospinning and subsequent UV irradiation, the MTC fiber mats were thus obtained. Thermoresponsivity of the MTC fibers was measured by both DSC and swelling test. MTC fiber mat exhibited better water‐absorption capability and thermoresponsivity than corresponding film. Morphological analysis was observed by SEM and TEM, and the magnetic property was measured by SQUID. The thermoresponsive magnetic behavior of MTC fiber mat in water was observed under various temperatures and magnetic fields. Vitamin B12 used as a model drug was loaded in the MTC fiber mats and the drug‐release behavior was then studied. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 2152–2162

Strengthened graphene oxide/diazoresin multilayer composites from layer-by-layer assembly and cross-linking

Abstract The layer-by-layer assembly of graphene oxide and diazoresin is carried out via the electrostatic and hydrogen bond interactions on planar substrates and colloidal templates. The successful planar and spherical growth of multilayer could be investigated by UV–vis spectrophotometry and scanning electron microscopy, respectively. Subsequent UV irradiation or heating would convert the ionic bonds and hydrogen bonds to covalent bands, which significantly improves the stability of the multilayer composite against solvent etching. For the cross-linked core–shell composites, the template cores could be removed by dissolution and hollow microspheres are obtained.

Effects of silver ion exchange and subsequent treatments on the UV–VIS spectra of silicate glasses. I. Undoped, CeO2-doped, and (CeO2 + Sb2O3)-codoped photo-thermo-refractive matrix glasses

The effects of the silver ion exchange and of subsequent UV irradiation and/or heat treatment on the optical density spectra of photo-thermo-refractive matrix glass samples both virgin and doped with cerium and/or antimony oxides were investigated. The incorporation of silver by ion exchange for ~15min at 310°C was found to cause, for all glasses except those with CeO2 content around 0.1mol% or more, a shift of the UV limit of strong absorption to the greater wavelengths by ~70–100nm due to the occurrence of Ag+-related absorption. Complicated changes caused by the UV irradiation and/or heat treatment of ion-exchanged samples in the location of their UV limit of strong absorption and in the absorption throughout the 330–550nm region were analyzed and shown to be greatly influenced by (i) the kind of dopant(s), (ii) chances for shifting the redox and other equilibria involving the dopants at temperatures of particular treatment processes, and (iii) NaBr presence in the glass batch composition. The effect of NaBr addition was explained tentatively in terms of formation, after the heat treatment, of AgBr clusters or nanocrystals.

Self-Assembled Benzophenone Bis-urea Macrocycles Facilitate Selective Oxidations by Singlet Oxygen

This manuscript investigates how incorporation of benzophenone, a well-known triplet sensitizer, within a bis-urea macrocycle, which self-assembles into a columnar host, influences its photophysical properties and affects the reactivity of bound guest molecules. We further report the generation of a remarkably stable organic radical. As expected, UV irradiation of the host suspended in oxygenated solvents efficiently generates singlet oxygen similar to the parent benzophenone. In addition, this host can bind guests such as 2-methyl-2-butene and cumene to form stable solid host-guest complexes. Subsequent UV irradiation of these complexes facilitated the selective oxidation of 2-methyl-2-butene into the allylic alcohol, 3-methyl-2-buten-1-ol, at 90% selectivity as well as the selective reaction of cumene to the tertiary alcohol, α,α'-dimethyl benzyl alcohol, at 63% selectivity. However, these products usually arise through radical pathways and are not observed in the presence of benzophenone in solution. In contrast, typical reactions with benzophenone result in the formation of the reactive singlet oxygen that reacts with alkenes to form endoperoxides, diooxetanes, or hydroperoxides, which are not observed in our system. Our results suggest that the confinement, the formation of a stable radical species, and the singlet oxygen photoproduction are responsible for the selective oxidation processes. A greater understanding of the mechanism of this selective oxidation could lead to development of greener oxidants.

Chemistry of NOx on TiO2 Surfaces Studied by Ambient Pressure XPS: Products, Effect of UV Irradiation, Water, and Coadsorbed K(.).

Self-cleaning surfaces containing TiO2 nanoparticles have been postulated to efficiently remove NOx from the atmosphere. However, UV irradiation of NOx adsorbed on TiO2 also was shown to form harmful gas-phase byproducts such as HONO and N2O that may limit their depolluting potential. Ambient pressure XPS was used to study surface and gas-phase species formed during adsorption of NO2 on TiO2 and subsequent UV irradiation at λ = 365 nm. It is shown here that NO3(-), adsorbed on TiO2 as a byproduct of NO2 disproportionation, was quantitatively converted to surface NO2 and other reduced nitrogenated species under UV irradiation in the absence of moisture. When water vapor was present, a faster NO3(-) conversion occurred, leading to a net loss of surface-bound nitrogenated species. Strongly adsorbed NO3(-) in the vicinity of coadsorbed K(+) cations was stable under UV light, leading to an efficient capture of nitrogenated compounds.

In situ photochemical generation of silver and gold nanoparticles on chitosan

Silver and gold nanoparticles (NPs) were generated via a mild wet-chemistry process in aqueous chitosan solutions. Gold and silver NPs were created in situ in presence of chitosan through the addition of the corresponding salt solution under a subsequent UV irradiation. Gold and silver NPs were also created by using a sequence of gold and then silver and vice versa. The amine function existing in the chain monomer operates as the anchoring centre of the metal NP, enabling thus a selective generation of the metal NPs through their nucleation followed by their growth. Ensuing hybrid systems were characterized by UV/vis spectroscopy, X-ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscopy (TEM) and Grazing Incident X-ray Diffraction (GIXRD). The NPs average sizes ranges from 10 to 40nm for gold and 20 to 100nm for silver. XPS studies on NPs generation through a sequence of gold followed by silver solutions suggest that gold cores enveloped by silver shells with some discontinuities exist.

Photoreactive oligoethylene glycol polymers – versatile compounds for surface modification by thin hydrogel films

Solid surfaces are modified using photo-crosslinkable copolymers based on oligo(ethylene glycol) methacrylate (OEGMA) bearing 2-(4-benzoylphenoxy)ethyl methacrylate (BPEM) as a photosensitive crosslinking unit. Thin films of about 100 nm are formed by spin-coating these a priori highly biocompatible copolymers onto silicon substrates. Subsequent UV-irradiation assures immobilization and crosslinking of the hydrogel films. Their stability is controlled by the number of crosslinker units per chain and the molar mass of the copolymers. The swelling of the hydrogel layers, as investigated by ellipsometry, can be tuned by the crosslinker content in the copolymer. If films are built from the ternary copolymers of OEGMA, BPEM and 2-(2-methoxyethoxy) ethyl methacrylate (MEO2MA), the hydrogel films exhibit a swelling/deswelling transition of the lower critical solution temperature (LCST) type. The observed thermally induced hydrogel collapse is fully reversible and the onset temperature of the transition can be tuned at will by the copolymer composition. Different from analogously prepared thermo-responsive hydrogel films of photocrosslinked poly(N-isopropylacrylamide), the swelling–deswelling transition occurs more gradually, but shows no hysteresis.

Cationic merocyanine dyes by photomodulation of [4-(naphthopyran-3-yl)phenyl]methines

Abstract A series of mono-, bis- and tris-4-(naphthopyran-3-yl)phenyl substituted methanols were efficiently synthesised using a 4-(naphthopyran-3-yl)phenyllithium intermediate. The resulting substituted methanols displayed good photochromism leading to the reversible generation of red–orange photomerocyanines. Acidic dehydration of the methanols gave intensely coloured cations which, upon subsequent UV irradiation, reversibly generated cationic photomerocyanines with long wavelength absorption maxima at ca. 640 nm.

Ethanol and UV-assisted instantaneous bonding of PMMA assemblies and tuning in bonding reversibility

Here, we introduce an instantaneous and robust strategy for bonding poly(methylmethacrylate) (PMMA) substrates via ethanol treatment combined with subsequent UV irradiation under ambient conditions, and examine the bonding reversibility by varying the percentage of the ethanolic solution manufactured. Organic solvent such as ethanol can activate the surface of PMMA without sacrificing the optical property of the PMMA substrate, and a subsequent exposure to UV recrosslinks the diffused monomers of acrylate functionalities to realize permanent bonding of two PMMA substrates under mild and ambient experimental conditions, which minimizes the deformation of channel profiles. To achieve robust sealing, two PMMA substrates were immediately placed in direct contact with each other after the treatment with ethanolic solution, and were irradiated under UV. Permanent sealing was realized in less than 1min. Various bonding analyses were conducted by performing tensile strength measurement, high-throughput leakage test, burst test, and peel test. The highest bonding strength was determined to be approximately 6.17MPa when 90% ethanolic solution was employed, and the bonding was sufficiently robust to endure intense introduction of liquid whose per-minute injection volume was almost 1200-fold higher than the total internal volume of the microchannel adopted. We also investigated the potential in the manipulation of bonding reversibility, and the critical percentage of ethanolic solution to realize irreversible bonding for PMMA assemblies based on the proposed strategy was determined to be just over 50%.

Effect of precursor solution dark incubation on gold nanorods morphology

Gold nanorods were synthesized in an aqueous solution of hexadecyltrimethylammonium bromide via a combination of chemical reduction and UV photoirradiation. Gold ligand complexes, present in the stock solution, are initially reduced, by ascorbic acid as mild reducing agent. The gold ions nucleation and colloid growth proceeds then by subsequent UV irradiation of the so-obtained precursor solution. We present a systematic study of the effect of incubation of the precursor solution on the dispersion state and aspect ratio of the produced nanorods. Incubation of the precursor solution allows the synthesis of higher aspect ratio nanorods with narrower size distribution compared to those obtained without incubation. We propose a mechanism for the gold nanorods formation including two stages, a nucleation and a diffusive growth. This allows us to explain the synthesis improvement as a consequence of the increase in the size of the gold ligand complexes aggregates, leading to a decrease of the nanorods growth rate.

Benzene adsorption and protonation in perfluorosulfonic membrane

Benzene adsorption in a perfluorosulfonic membrane was performed through deep dehydration of the latter over the phosphoric anhydride. The subsequent UV irradiation is accompanied by a gradual transition of the benzene π-complexes in the protonated form C6H7+ that allows us to consider the perfluorosulfonic membrane as a solid superacids. The photoexcitation on the absorption band of adsorbed carbonium ion causes its fluorescence in the region of 450–600 nm.

Infrared Matrix Isolation Study of the Thermal and Photochemical Reactions of Ozone with Dimethylcadmium

The matrix isolation technique has been combined with infrared spectroscopy and theoretical calculations to explore the reaction of (CH(3))(2)Cd with O(3) over a range of time scales and upon irradiation. During twin jet deposition, multiple novel product species were observed along with several stable "late" products. Following annealing of these matrices to 35 K, absorptions due to two novel product species increased in intensity. In addition, new bands appeared, indicating the formation of an additional product. Subsequent UV irradiation destroyed several of the initial products and produced a new photoproduct. On the basis of (18)O and (16,18)O spectroscopic data and theoretical calculations, the novel intermediates H(3)COCdCH(3), H(3)CCdCH(2)OH, H(3)COCdOOCH(3), and H(3)CCdCHO were identified. Merged jet deposition led to a number of stable "late" products, including H(2)CO, CH(3)OH, and C(2)H(6), identifications that were confirmed by (18)O substitution. Mechanistic inferences for this reaction are discussed.

Responsive Macroscopic Materials From Self‐Assembled Cross‐Linked SiO2‐PNIPAAm Core/Shell Structures

AbstractA way to obtain macroscopic responsive materials from silicon‐oxide polymer core/shell microstructures is presented. The microparticles are composed of a 60 nm SiO2‐core with a random copolymer corona of the temperature responsive poly‐N‐isopropylacrylamide (PNIPAAm) and the UV‐cross‐linkable 2‐(dimethyl maleinimido)‐N‐ethyl‐acrylamide. The particles shrink upon heating and form a stable gel in both water and tetrahydrofuran (THF) at 3–5 wt% particle content. Cross‐linking the aqueous gel results in shrinkage when the temperature is increased above the lower critical solution temperature and it regains its original size upon cooling. By freeze drying with subsequent UV irradiation, thin stable layers are prepared. Stable fibers are produced by extruding a THF gel into water and subsequent UV irradiation, harnessing the cononsolvency effect of PNIPAAm in water/THF mixtures. The temperature responsiveness translates to the macroscopic materials as both films and fibers show the same collapsing behavior as the microcore/shell particle. The collapse and re‐swelling of the materials is related to the expelling and re‐uptake of water, which is used to incorporate gold nanoparticles into the materials by a simple heating/cooling cycle. This allows for future applications, as various functional particles (antibacterial, fluorescence, catalysis, etc.) can easily be incorporated in these systems.