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Zhong Chen - One of the best experts on this subject based on the ideXlab platform.

  • enhanced visible light hydrogen production via a multiple heterojunction structure with defect engineered g c3n4 and two phase Anatase brookite tio2
    Journal of Catalysis, 2016
    Co-Authors: Qiuling Tay, Xinghui Wang, Xin Zhao, Jindui Hong, Qing Zhang, Zhong Chen
    Abstract:

    Abstract Polymeric g-C3N4 is a promising candidate for solar hydrogen production. However, its hydrogen production rate is low when used alone due to fast recombination of photogenerated electron–hole pairs. In this paper, we report much improved hydrogen production by coupling g-C3N4 with two-phase Anatase/brookite TiO2 nanoparticles to form multiple heterojunctions. Results have shown that under visible light illumination, photogenerated electrons transfer from g-C3N4 to TiO2. In addition, systematic comparison was carried out among different type of heterojunctions, viz., g-C3N4 coupled with a single phase of TiO2 (Anatase or brookite), dual-phase TiO2 (Anatase/brookite or Anatase/rutile), or a three-phase TiO2 (Anatase/brookite/rutile) mixture. g-C3N4 with two-phase Anatase/brookite TiO2 produces the largest amount of hydrogen under visible light illumination. The comparison reveals two important factors behind photocatalytic hydrogen generation: effective charge transfer and the conduction band potential position. The band edge positions of all the constituent phases of the heterojunction have to be more cathodic than the hydrogen reduction potential in order to realize the full benefit of effective charge separation.

  • enhanced photocatalytic hydrogen production with synergistic two phase Anatase brookite tio2 nanostructures
    Journal of Physical Chemistry C, 2013
    Co-Authors: Yuxin Tang, Zhelong Jiang, Zhong Chen
    Abstract:

    Highly crystalline pure brookite and two-phase Anatase/brookite TiO2 nanostructures were synthesized via a simple hydrothermal method with titanium sulfide as the precursors in sodium hydroxide solutions. The control of the phase composition has been demonstrated via solution concentration and reaction time, and the phase transformation mechanism has been elucidated. Photocatalytic activities of the as-synthesized two-phase Anatase/brookite TiO2, pure Anatase nanoparticles, and pure brookite nanoplates were appraised via photocatalytic hydrogen evolution in aqueous methanol solution. Results have shown that the photocatalytic activity is higher for the two-phase Anatase/brookite TiO2 and brookite nanoplates as compared to pure Anatase nanoparticles despite the lower surface areas of the two-phase Anatase/brookite TiO2 and brookite nanoplates. From the Mott–Schottky analysis, brookite phase is shown to have a more cathodic conduction band edge potential than Anatase phase, which leads to more energetically...

Xiuli Wang - One of the best experts on this subject based on the ideXlab platform.

  • time resolved photoluminescence of Anatase rutile tio2 phase junction revealing charge separation dynamics
    Chinese Journal of Catalysis, 2016
    Co-Authors: Xiuli Wang, Shuai Shen, Zhaochi Feng
    Abstract:

    Junctions are an important structure that allows charge separation in solar cells and photocatalysts. Here, we studied the charge transfer at an Anatase/rutile TiO 2 phase junction using time-resolved photoluminescence spectroscopy. Visible (~500 nm) and near-infrared (NIR, ~830 nm) emissions were monitored to give insight into the photoinduced charges of Anatase and rutile in the junction, respectively. New fast photoluminescence decay components appeared in the visible emission of rutile-phase dominated TiO 2 and in the NIR emission of many mixed phase TiO 2 samples. The fast decays confirmed that the charge separation occurred at the phase junction. The visible emission intensity from the mixed phase TiO 2 increased, revealing that charge transfer from rutile to Anatase was the main pathway. The charge separation slowed the microsecond time scale photoluminescence decay rate for charge carriers in both Anatase and rutile. However, the millisecond decay of the charge carriers in Anatase TiO 2 was accelerated, while there was almost no change in the charge carrier dynamics of rutile TiO 2 . Thus, charge separation at the Anatase/rutile phase junction caused an increase in the charge carrier concentration on a microsecond time scale, because of slower electron-hole recombination. The enhanced photocatalytic activity previously observed at Anatase/rutile phase junctions is likely caused by the improved charge carrier dynamics we report here. These findings may contribute to the development of improved photocatalytic materials.

  • where do photogenerated holes go in Anatase rutile tio2 a transient absorption spectroscopy study of charge transfer and lifetime
    Journal of Physical Chemistry A, 2016
    Co-Authors: Andreas Kafizas, Xiuli Wang, Stephanie R Pendlebury, Piers R F Barnes, Min Ling, Carlos Sotelovazquez, Raul Quesadacabrera, Ivan P Parkin, James R Durrant
    Abstract:

    Anatase:rutile TiO2 junctions are often shown to be more photocatalytically active than Anatase or rutile alone, but the underlying cause of this improvement is not fully understood. Herein, we employ transient absorption spectroscopy to study hole transfer across the Anatase:rutile heterojunction in films as a function of phase composition. By exploiting the different signatures in the photoinduced absorption of trapped charges in Anatase and rutile, we were able to separately track the yield and lifetime of holes in Anatase and rutile sites within phase composites. Photogenerated holes transfer from rutile to Anatase on submicrosecond time scales. This hole transfer can significantly increase the Anatase hole yield, with a 20:80 Anatase:rutile composite showing a 5-fold increase in Anatase holes observed from the microsecond. Hole transfer does not result in an increase in charge-carrier lifetime, where an intermediate recombination dynamic between that of pure Anatase (t1/2 ≈ 0.5 ms) and rutile (t1/2 ≈...

  • transient absorption spectroscopy of Anatase and rutile the impact of morphology and phase on photocatalytic activity
    Journal of Physical Chemistry C, 2015
    Co-Authors: Xiuli Wang, Andreas Kafizas, Ivan P Parkin, Savio J A Moniz, Philip James Thomas Reardon, Junwang Tang, James R Durrant
    Abstract:

    We employed transient absorption spectroscopy (TAS) to investigate the kinetic dependences of photocatalysis in Anatase and rutile TiO2 films of varying morphology. In mesoporous films, Anatase was ∼30 times more efficient than rutile in the photocatalytic degradation of an intelligent ink model system. Independent of phase, up to 100 lower levels of photocatalysis were found in dense films. Charge carrier lifetimes were probed by TAS on the microsecond to second time scale. For both rutile and Anatase, recombination was independent of morphology. Rutile exhibited up to 10 times slower recombination kinetics than Anatase. Efficient, irreversible hole scavenging by alcohols was present in mesoporous Anatase alone, resulting in the generation of long-lived electrons (τ ≈ 0.7 s) which, upon the addition of the dye reduction target resazurin, enabled efficient electron transfer (τ ≈ 3 ms). Hole scavenging by alcohols on mesoporous rutile was substantially less efficient and more reversible than Anatase, resul...

  • transfer of photoinduced electrons in Anatase rutile tio2 determined by time resolved mid infrared spectroscopy
    Journal of Physical Chemistry C, 2014
    Co-Authors: Shuai Shen, Xiuli Wang, Tao Chen, Zhaochi Feng
    Abstract:

    It has been a long-standing debate about the photogenerated charge transfer in Anatase–rutile mixed phase TiO2. In this work, we investigated this issue by studying Anatase, rutile, and Anatase–rutile mixed phase TiO2 with time-resolved mid-IR (MIR) spectroscopy (TR-MIR) in a vacuum or methanol vapor. Anatase TiO2 shows transient MIR absorption on microsecond time scale after 355 nm excitation, which is attributed to photoinduced electrons in the shallow states of Anatase. Conversely, there is no transient MIR absorption detected for rutile TiO2. For Anatase–rutile mixed phase TiO2, the initial MIR absorption intensity decreases relative to that calculated from its phase composition, indicating that electron transfer takes place in the Anatase–rutile phase junction of mixed phase TiO2. Our results suggest that the photogenerated electrons in the shallow states of Anatase transfer to rutile across the Anatase–rutile interface, but this does not exclude the possibility that the net electron transfer from ru...

Jillian F Banfield - One of the best experts on this subject based on the ideXlab platform.

  • kinetics of crystallization and crystal growth of nanocrystalline Anatase in nanometer sized amorphous titania
    Chemistry of Materials, 2002
    Co-Authors: Hengzhong Zhang, Jillian F Banfield
    Abstract:

    The kinetics of crystallization and crystal growth of nanocrystalline Anatase in amorphous titania (2.5−3 nm) samples in the temperature range 300−400 °C was studied by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). A kinetic model adopting the Smoluchowski coagulation formulation, combined with our phenomenologically derived model kernels, was used to quantitatively interpret the observed kinetic data. It was revealed that the transformation in the amorphous titania comprises four steps:  interface nucleation of Anatase on contact areas of amorphous particles, with an activation energy of 147 kJ/mol; crystal growth of Anatase by redistribution of atoms from either amorphous particles or smaller Anatase crystals onto nanocrystal surfaces, both with an activation energy of 78 kJ/mol; and oriented attachment of adjacent Anatase particles that are in appropriate orientations, which is less temperature dependent.

  • understanding polymorphic phase transformation behavior during growth of nanocrystalline aggregates insights from tio2
    Journal of Physical Chemistry B, 2000
    Co-Authors: Hengzhong Zhang, Jillian F Banfield
    Abstract:

    To understand the impact of particle size on phase stability and phase transformation during growth of nanocrystalline aggregates we conducted experiments using titania (TiO2) samples consisting of nanocrystalline Anatase (46.7 wt %, 5.1 nm) and brookite (53.3 wt %, 8.1 nm). Reactions were studied isochronally at reaction times of 2 h in the temperature range 598−1023 K and isothermally at 723, 853, and 973 K by X-ray diffraction (XRD). A numerical deconvolution method was developed to separate overlapping XRD peaks, and an analytical method for determining phase contents of Anatase, brookite, and rutile from XRD data was established. Results show that, in contrast to previous studies, Anatase in our samples transforms to brookite and/or rutile before brookite transforms to rutile. Thermodynamic and kinetic analyses further support this conclusion. For general titania samples, the transformation sequence among Anatase and brookite depends on the initial particle sizes of Anatase and brookite, since partic...

  • phase transformation of nanocrystalline Anatase to rutile via combined interface and surface nucleation
    Journal of Materials Research, 2000
    Co-Authors: Hengzhong Zhang, Jillian F Banfield
    Abstract:

    The kinetics of phase transformation of nanocrystalline Anatase samples was studied using x-ray diffraction at temperatures ranging from 600 to 1150 °C. Kinetic data were analyzed with an interface nucleation model and a newly proposed kinetic model for combined interface and surface nucleation. Results revealed that the activation energy of nucleation is size dependent. In Anatase samples with denser particle packing, rutile nucleates primarily at interfaces between contacting Anatase particles. In Anatase samples with less dense particle packing, rutile nucleates at both interfaces and free surfaces of Anatase particles. The predominant nucleation mode may change from interface nucleation at low temperatures to surface nucleation at intermediate temperatures and to bulk nucleation at very high temperatures. Alumina particles dispersed among the Anatase particles can effectively reduce the probability of interface nucleation at all temperatures.

  • formation of rutile nuclei at Anatase 112 twin interfaces and the phase transformation mechanism in nanocrystalline titania
    American Mineralogist, 1999
    Co-Authors: Lee R Penn, Jillian F Banfield
    Abstract:

    In nanocrystalline Anatase coarsened under hydrothermal conditions (250 C, P{sub sat}), the Anatase-to-rutile phase transformation is nucleated at Anatase {l_brace}112{r_brace} twin boundaries formed by oriented attachment. The Anatase twin boundary is constructed from structural elements common to rutile. Specifically, rutile nucleation involves displacement of only one half the titanium cations within the twin slab. Subsequent transformation of bulk Anatase involves rupture of 7 of the 24 Ti-O bonds per unit cell and cooperative displacement of Ti and O. As the transformation advances into the bulk material, adjacent slabs of Anatase octahedra are destabilized, resulting in rapid progression of the transformation of bulk Anatase to rutile. The implied chain reaction, scarcity of partly reacted crystals, absence of multiple twinned rutile, and the importance of nucleation at Anatase twins indicate a rate law based on slow nucleation and rapid growth. The displacements are comparable to those proposed previously for macroscopic Anatase at much higher temperatures, indicating the atomic mechanism is not modified by particle size or temperature, despite the rapid kinetics in finely crystalline aggregates. In addition to the formation of twins, clusters with rutile-like character may occur at some fraction of random Anatase-Anatase particle contacts. Such interfaces should result in decreasedmore » activation barriers for rutile nucleation and, thus, contribute significantly to the observed faster transformation rates in nanocrystalline compared to coarsely crystalline materials.« less

  • oriented attachment and growth twinning polytypism and formation of metastable phases insights from nanocrystalline tio2
    American Mineralogist, 1998
    Co-Authors: Lee R Penn, Jillian F Banfield
    Abstract:

    Atomic-resolution transmission electron micrographs show that nanocrystalline TiO2 coarsens by oriented attachment and growth under hydrothermal conditions. In addition to forming homogeneous single crystals, attachment at Anatase surfaces leads to twinning on {112} and intergrowths on (001) and {001}. Brookite, a polytype of Anatase, occurs at some {112} twin surfaces. Alternating two octahedra-wide structural slabs in brookite are shared with the two adjacent Anatase twin domains. Because {112} Anatase twin interfaces contain one unit cell of brookite, we propose that brookite may nucleate at twin planes and grow at the expense of Anatase. Alternatively, Anatase-brookite interfaces may form by oriented attachment of primary brookite and Anatase {112} crystallites. In this case, three unit cell-wide lamellae of brookite are interpreted as remnants of larger crystals that partly converted to Anatase by propagation of the Anatase-brookite interface. Which phase is stable is unclear over this particle size range, and products of random thermal fluctuations may be preserved by quenching. Regardless of reaction direction, polytypic interconversion of Anatase and brookite essentially involves displacement of Ti (by c/4 brookite) into adjacent octahedral sites in one of the pair of two octahedra-wide structural slabs. The results have broad relevance for nucleation and growth models as they suggest that twinning and polytypism in macroscopic crystals can originate at oriented interfaces between primary nanocrystalline particles early in their crystallization history.

James R Durrant - One of the best experts on this subject based on the ideXlab platform.

  • where do photogenerated holes go in Anatase rutile tio2 a transient absorption spectroscopy study of charge transfer and lifetime
    Journal of Physical Chemistry A, 2016
    Co-Authors: Andreas Kafizas, Xiuli Wang, Stephanie R Pendlebury, Piers R F Barnes, Min Ling, Carlos Sotelovazquez, Raul Quesadacabrera, Ivan P Parkin, James R Durrant
    Abstract:

    Anatase:rutile TiO2 junctions are often shown to be more photocatalytically active than Anatase or rutile alone, but the underlying cause of this improvement is not fully understood. Herein, we employ transient absorption spectroscopy to study hole transfer across the Anatase:rutile heterojunction in films as a function of phase composition. By exploiting the different signatures in the photoinduced absorption of trapped charges in Anatase and rutile, we were able to separately track the yield and lifetime of holes in Anatase and rutile sites within phase composites. Photogenerated holes transfer from rutile to Anatase on submicrosecond time scales. This hole transfer can significantly increase the Anatase hole yield, with a 20:80 Anatase:rutile composite showing a 5-fold increase in Anatase holes observed from the microsecond. Hole transfer does not result in an increase in charge-carrier lifetime, where an intermediate recombination dynamic between that of pure Anatase (t1/2 ≈ 0.5 ms) and rutile (t1/2 ≈...

  • transient absorption spectroscopy of Anatase and rutile the impact of morphology and phase on photocatalytic activity
    Journal of Physical Chemistry C, 2015
    Co-Authors: Xiuli Wang, Andreas Kafizas, Ivan P Parkin, Savio J A Moniz, Philip James Thomas Reardon, Junwang Tang, James R Durrant
    Abstract:

    We employed transient absorption spectroscopy (TAS) to investigate the kinetic dependences of photocatalysis in Anatase and rutile TiO2 films of varying morphology. In mesoporous films, Anatase was ∼30 times more efficient than rutile in the photocatalytic degradation of an intelligent ink model system. Independent of phase, up to 100 lower levels of photocatalysis were found in dense films. Charge carrier lifetimes were probed by TAS on the microsecond to second time scale. For both rutile and Anatase, recombination was independent of morphology. Rutile exhibited up to 10 times slower recombination kinetics than Anatase. Efficient, irreversible hole scavenging by alcohols was present in mesoporous Anatase alone, resulting in the generation of long-lived electrons (τ ≈ 0.7 s) which, upon the addition of the dye reduction target resazurin, enabled efficient electron transfer (τ ≈ 3 ms). Hole scavenging by alcohols on mesoporous rutile was substantially less efficient and more reversible than Anatase, resul...

Co Del Valle, Maria - One of the best experts on this subject based on the ideXlab platform.

  • Millora de la protecció UV de substrats tèxtils mitjançant l'aplicació, en l'extrusió, de nano i micropartícules
    Universitat Politècnica de Catalunya, 2017
    Co-Authors: Co Del Valle, Maria
    Abstract:

    In this thesis, we study the improvement of the UV protection of polyester textiles by introducing nano or microparticles of TiO2 in the polyester during the extrusion of the yarn. Initially, the influence of different dispersing agents on the good dispersion and mixing of TiO2 with PET is studied. The dispersing agents studied are a partially saponified ester wax of mountain acids (PSEMA), an ester of montanic acids with multifunctional alcohols (MAWMA), an amide wax based on N, N'-bisstearoyl ethylenediamine (AW) and an IQAP dispersant. By non-isothermal crystallization and birefringence microscopy, the good dispersion capacity of MAWMA is observed, so this dispersant is chosen for later study. Next, the importance of the crystalline form (rutile and Anatase), particle size (micro and nanometric) and the concentration (1, 2 and 3%) of titanium dioxide in mixtures with polyester in the presence of the dispersing agent chosen in the first part. Its behavior in nonisothermal crystallization by DSC and ultraviolet radiation (UPF, UV protection factor) is studied. The purpose is to know the concentration of optimum TiO2 particles and dispersant for subsequent generation of multifilament yarns with said particles. It is concluded that with 2% of particles, they are well dispersed. The PET wires are then obtained with TiO2 particle under the conditions selected above, a post-spin drawing is performed to provide the yarn with optimum textile properties, knitted fabrics are obtained from said yarns, and finally the fabrics are thermoset. It is studied the variation of the properties of the threads after each of the textile stages applied to know the influence not only of the processed but also of the contribution to this variation by the presence of TiO2 particles. The influence of particle inclusion on the yarn according to particle size (nano or micrometric) and crystalline form (rutile or Anatase) on mechanical properties, crystallinity (DSC) and ultraviolet protection (UPF) is studied. Finally, the microstructure of the tissues obtained by Differential Scanning Calorimetry (DSC) and the Ultraviolet Protection Factor (UPF) is characterized. A significant improvement of the UPF value of the particle tissues with respect to the UPF value of the original tissue is observed. The observed relationship, in order from highest to lowest protection, is the following: Rutile Micro> Rutile Nano ≈ Anatasa Micro> Anatasa Nano It is observed that substrates with rutile particles have higher ultraviolet protection than Anatase particles. As for the particle size, it is observed that the micro particles protect more than the nanometric ones.En aquesta tesi s'aprofundeix en l'estudi de la millora de la protecció UV que exerceixen els tèxtils de polièster mitjançant la introducció de nano o micro-partícules de TiO2 en el polièster durant l'extrusió del fil. Inicialment s'estudia la influència de diferents agents dispersants en la bona dispersió i mescla del TiO2 amb el PET. Els agents dispersants estudiats són una cera de èster parcialment saponificat d'àcids montànics (PSEMA), un èster d'àcids montànics amb alcohols multifuncionals (MAWMA), una cera de amida a base de N, N¿-bisstearoil etilendiamina (AW) i un dispersant IQAP. Mitjançant la cristal·lització no isotèrmica i la microscopia de birefringència s'observa la bona capacitat de dispersió de MAWMA, per la qual cosa aquest dispersant s'escull per a l'estudi posterior. Seguidament, s'estudia la importància de la forma cristal·lina (rútil i anatasa), de la mida de partícula (micro i nanométric) i de la concentració (1, 2 i 3%) del diòxid de titani en mescles amb polièster en presència de l'agent dispersant escollit en la primera part. S'estudia el seu comportament en la cristal·lització no isotèrmica mitjançant DSC i enfront de la radiació ultraviolada (UPF, factor de protecció UV). La finalitat és conèixer la concentració de partícules de TiO2 i de dispersant òptimes per a l'obtenció posterior de fils de multifilament amb aquestes partícules. Es conclou que amb un 2% de partícules, aquestes estan ben dispersades. A continuació, s'obtenen els fils PET amb partícula de TiO2 en les condicions seleccionades anteriorment, es realitza un estiratge post-filatura per proporcionar al fil propietats tèxtils òptimes, s'obtenen teixits de punt a partir d'aquests fils, i finalment es termofixen els teixits. S'estudia la variació de les propietats dels fils després de cadascuna de les etapes tèxtils aplicades per conèixer la influència no només del processament sinó també de l'aportació a aquesta variació per la presència de partícules de TiO2. S'estudia la influència de la inclusió de la partícula en el fil segons la mida de la partícula (nano o micrométric) i la forma cristal·lina (rútil o anatasa) en les propietats mecàniques, cristalinitat (DSC) i protecció Ultraviolada (UPF). Finalment, es caracteritza la microestructura dels teixits obtinguts mitjançant la Calorimetria Diferencial d'Escombratge (DSC), i el factor de Protecció Ultraviolada (UPF). S'observa una millora important del valor d'UPF dels teixits amb partícules respecte al valor de l'UPF del teixit original. La relació observada, en ordre de major a menor protecció, és la següent: Rútil Micro > Rútil Nano ¿ Anatasa Micro > Anatasa Nano S'observa que els substrats amb partícules rútil posseeixen major protecció ultraviolada que les partícules anatasa. Quant a la mida de partícula, s'observa que les partícules micro protegeixen més que les nanométriques.En esta tesis se profundiza en el estudio de la mejora de la protección UV que ejercen los textiles de poliéster mediante la introducción de nano o micropartículas de TiO2 en el poliéster durante la extrusión del hilo. Inicialmente se estudia la influencia de diferentes agentes dispersantes en la buena dispersión y mezcla del TiO2 con el PET. Los agentes dispersantes estudiados son una cera de éster parcialmente saponificado de ácidos montánicos (PSEMA), un éster de ácidos montánicos con alcoholes multifuncionales (MAWMA), una cera de amida a base de N, N’-bisstearoil etilendiamina (AW) y un dispersante IQAP. Mediante la cristalización no isotérmica y la microscopía de birrefringencia se observa la buena capacidad de dispersión de MAWMA, por lo que este dispersante se escoge para el estudio posterior. Seguidamente, se estudia la importancia de la forma cristalina (rutilo y anatasa), del tamaño de partícula (micro y nanométrico) y de la concentración (1, 2 y 3%) del dióxido de titanio en mezclas con poliéster en presencia del agente dispersante escogido en la primera parte. Se estudia su comportamiento en la cristalización no isotérmica mediante DSC y frente a la radiación ultravioleta (UPF, factor de protección UV). La finalidad es conocer la concentración de partículas de TiO2 y de dispersante óptimas para la obtención posterior de hilos de multifilamento con dichas partículas. Se concluye que con un 2% de partículas, estas están bien dispersadas. A continuación, se obtienen los hilos PET con partículas de TiO2 en las condiciones seleccionadas anteriormente, se realiza un estirado post-hilatura para proporcionar al hilo propiedades textiles óptimas, se obtienen tejidos de punto a partir de dichos hilos, y finalmente se termofijan los tejidos. Se estudia la variación de las propiedades de los hilos después de cada una de las etapas textiles aplicadas para conocer la influencia no sólo del procesado sino también del aporte a esta variación por la presencia de partículas de TiO2. Se estudia la influencia de la inclusión de la partícula en el hilo según el tamaño de la partícula (nano o micrométrico) y la forma cristalina (rutilo o anatasa) en las propiedades mecánicas, cristalinidad (DSC) y protección Ultravioleta (UPF). Finalmente, se caracteriza la microestructura de los tejidos obtenidos mediante la Calorimetría Diferencial de Barrido (DSC), y el factor de Protección Ultravioleta (UPF). Se observa una mejora importante del valor de UPF de los tejidos con partículas respecto al valor del UPF del tejido original. La relación observada, en orden de mayor a menor protección, es la siguiente: Rutilo Micro > Rutilo Nano ≈ Anatasa Micro > Anatasa Nano Se observa que los sustratos con partículas rutilo poseen mayor protección ultravioleta que las partículas anatasa. En cuanto al tamaño de partícula, se observa que las partículas micro protegen más que las nanométricas

  • Millora de la protecció UV de substrats tèxtils mitjançant l'aplicació, en l'extrusió, de nano i micropartícules
    Universitat Politècnica de Catalunya, 2017
    Co-Authors: Co Del Valle, Maria
    Abstract:

    In this thesis, we study the improvement of the UV protection of polyester textiles by introducing nano or microparticles of TiO2 in the polyester during the extrusion of the yarn. Initially, the influence of different dispersing agents on the good dispersion and mixing of TiO2 with PET is studied. The dispersing agents studied are a partially saponified ester wax of mountain acids (PSEMA), an ester of montanic acids with multifunctional alcohols (MAWMA), an amide wax based on N, N'-bisstearoyl ethylenediamine (AW) and an IQAP dispersant. By non-isothermal crystallization and birefringence microscopy, the good dispersion capacity of MAWMA is observed, so this dispersant is chosen for later study. Next, the importance of the crystalline form (rutile and Anatase), particle size (micro and nanometric) and the concentration (1, 2 and 3%) of titanium dioxide in mixtures with polyester in the presence of the dispersing agent chosen in the first part. Its behavior in nonisothermal crystallization by DSC and ultraviolet radiation (UPF, UV protection factor) is studied. The purpose is to know the concentration of optimum TiO2 particles and dispersant for subsequent generation of multifilament yarns with said particles. It is concluded that with 2% of particles, they are well dispersed. The PET wires are then obtained with TiO2 particle under the conditions selected above, a post-spin drawing is performed to provide the yarn with optimum textile properties, knitted fabrics are obtained from said yarns, and finally the fabrics are thermoset. It is studied the variation of the properties of the threads after each of the textile stages applied to know the influence not only of the processed but also of the contribution to this variation by the presence of TiO2 particles. The influence of particle inclusion on the yarn according to particle size (nano or micrometric) and crystalline form (rutile or Anatase) on mechanical properties, crystallinity (DSC) and ultraviolet protection (UPF) is studied. Finally, the microstructure of the tissues obtained by Differential Scanning Calorimetry (DSC) and the Ultraviolet Protection Factor (UPF) is characterized. A significant improvement of the UPF value of the particle tissues with respect to the UPF value of the original tissue is observed. The observed relationship, in order from highest to lowest protection, is the following: Rutile Micro> Rutile Nano ≈ Anatasa Micro> Anatasa Nano It is observed that substrates with rutile particles have higher ultraviolet protection than Anatase particles. As for the particle size, it is observed that the micro particles protect more than the nanometric ones.En aquesta tesi s'aprofundeix en l'estudi de la millora de la protecció UV que exerceixen els tèxtils de polièster mitjançant la introducció de nano o micro-partícules de TiO2 en el polièster durant l'extrusió del fil. Inicialment s'estudia la influència de diferents agents dispersants en la bona dispersió i mescla del TiO2 amb el PET. Els agents dispersants estudiats són una cera de èster parcialment saponificat d'àcids montànics (PSEMA), un èster d'àcids montànics amb alcohols multifuncionals (MAWMA), una cera de amida a base de N, N¿-bisstearoil etilendiamina (AW) i un dispersant IQAP. Mitjançant la cristal·lització no isotèrmica i la microscopia de birefringència s'observa la bona capacitat de dispersió de MAWMA, per la qual cosa aquest dispersant s'escull per a l'estudi posterior. Seguidament, s'estudia la importància de la forma cristal·lina (rútil i anatasa), de la mida de partícula (micro i nanométric) i de la concentració (1, 2 i 3%) del diòxid de titani en mescles amb polièster en presència de l'agent dispersant escollit en la primera part. S'estudia el seu comportament en la cristal·lització no isotèrmica mitjançant DSC i enfront de la radiació ultraviolada (UPF, factor de protecció UV). La finalitat és conèixer la concentració de partícules de TiO2 i de dispersant òptimes per a l'obtenció posterior de fils de multifilament amb aquestes partícules. Es conclou que amb un 2% de partícules, aquestes estan ben dispersades. A continuació, s'obtenen els fils PET amb partícula de TiO2 en les condicions seleccionades anteriorment, es realitza un estiratge post-filatura per proporcionar al fil propietats tèxtils òptimes, s'obtenen teixits de punt a partir d'aquests fils, i finalment es termofixen els teixits. S'estudia la variació de les propietats dels fils després de cadascuna de les etapes tèxtils aplicades per conèixer la influència no només del processament sinó també de l'aportació a aquesta variació per la presència de partícules de TiO2. S'estudia la influència de la inclusió de la partícula en el fil segons la mida de la partícula (nano o micrométric) i la forma cristal·lina (rútil o anatasa) en les propietats mecàniques, cristalinitat (DSC) i protecció Ultraviolada (UPF). Finalment, es caracteritza la microestructura dels teixits obtinguts mitjançant la Calorimetria Diferencial d'Escombratge (DSC), i el factor de Protecció Ultraviolada (UPF). S'observa una millora important del valor d'UPF dels teixits amb partícules respecte al valor de l'UPF del teixit original. La relació observada, en ordre de major a menor protecció, és la següent: Rútil Micro > Rútil Nano ¿ Anatasa Micro > Anatasa Nano S'observa que els substrats amb partícules rútil posseeixen major protecció ultraviolada que les partícules anatasa. Quant a la mida de partícula, s'observa que les partícules micro protegeixen més que les nanométriques.En esta tesis se profundiza en el estudio de la mejora de la protección UV que ejercen los textiles de poliéster mediante la introducción de nano o micropartículas de TiO2 en el poliéster durante la extrusión del hilo. Inicialmente se estudia la influencia de diferentes agentes dispersantes en la buena dispersión y mezcla del TiO2 con el PET. Los agentes dispersantes estudiados son una cera de éster parcialmente saponificado de ácidos montánicos (PSEMA), un éster de ácidos montánicos con alcoholes multifuncionales (MAWMA), una cera de amida a base de N, N’-bisstearoil etilendiamina (AW) y un dispersante IQAP. Mediante la cristalización no isotérmica y la microscopía de birrefringencia se observa la buena capacidad de dispersión de MAWMA, por lo que este dispersante se escoge para el estudio posterior. Seguidamente, se estudia la importancia de la forma cristalina (rutilo y anatasa), del tamaño de partícula (micro y nanométrico) y de la concentración (1, 2 y 3%) del dióxido de titanio en mezclas con poliéster en presencia del agente dispersante escogido en la primera parte. Se estudia su comportamiento en la cristalización no isotérmica mediante DSC y frente a la radiación ultravioleta (UPF, factor de protección UV). La finalidad es conocer la concentración de partículas de TiO2 y de dispersante óptimas para la obtención posterior de hilos de multifilamento con dichas partículas. Se concluye que con un 2% de partículas, estas están bien dispersadas. A continuación, se obtienen los hilos PET con partículas de TiO2 en las condiciones seleccionadas anteriormente, se realiza un estirado post-hilatura para proporcionar al hilo propiedades textiles óptimas, se obtienen tejidos de punto a partir de dichos hilos, y finalmente se termofijan los tejidos. Se estudia la variación de las propiedades de los hilos después de cada una de las etapas textiles aplicadas para conocer la influencia no sólo del procesado sino también del aporte a esta variación por la presencia de partículas de TiO2. Se estudia la influencia de la inclusión de la partícula en el hilo según el tamaño de la partícula (nano o micrométrico) y la forma cristalina (rutilo o anatasa) en las propiedades mecánicas, cristalinidad (DSC) y protección Ultravioleta (UPF). Finalmente, se caracteriza la microestructura de los tejidos obtenidos mediante la Calorimetría Diferencial de Barrido (DSC), y el factor de Protección Ultravioleta (UPF). Se observa una mejora importante del valor de UPF de los tejidos con partículas respecto al valor del UPF del tejido original. La relación observada, en orden de mayor a menor protección, es la siguiente: Rutilo Micro > Rutilo Nano ≈ Anatasa Micro > Anatasa Nano Se observa que los sustratos con partículas rutilo poseen mayor protección ultravioleta que las partículas anatasa. En cuanto al tamaño de partícula, se observa que las partículas micro protegen más que las nanométricas.Postprint (published version