Optical Properties Of Composites Research Articles

Efficient removal of U(VI) from aqueous solution by CNN/UiO-66 under simulated sunlight irradiation: the synergy of adsorption and photocatalysis.

The reduction of soluble U(VI) to insoluble and less toxic U(IV) by photocatalysis is an effective method to control uranium contamination. The graphitic carbon nitride nanosheet (CNN)/UiO-66 composites (CNNU) were prepared by thermal polymerization and solvothermal methods for the removal of U(VI). The morphology, crystal structure and optical properties of composites were analyzed by SEM, XRD, BET, UV-DRS, PL and EIS. The results showed the introduction of UiO-66 increased the specific surface of CNN from 9.07 m2/g to 46.24 m2/g, and effectively suppressed the recombination of photogenerated electrons and holes and improved the photocatalytic activity. The U(VI) removal capacity by adsorption and photocatalysis of CNNU was reached 779.47mg/g, which significantly higher than that of adsorption (478.38mg/g). The adsorption process was found to conform to the pseudo-second-order kinetic model and the Langmuir isothermal model. Meanwhile, U(VI) adsorbed on the CNNU was reduced to U(IV) via e- and ·O2- generated in the photocatalytic process. Therefore, this outstanding performance of CNNU in U(VI) removal is attributed to the synergistic effect of adsorption and photocatalytic reduction.

Synthesis of two-dimensional CeO2-δ-GQD composites and their structural and optical properties

The present study reports on the synthesis of two-dimensional (2D) ceria and graphene quantum dots (CeO2-δ-GQD) composites and their functional properties. Composites were prepared by a simple liquid phase deposition (LPD) method followed by a thermal treatment in air at 250 and 400 °C. The structural and optical properties of composites were investigated by X-ray diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM), High-Resolution Transmission Electron Microscopy (HR-TEM), Raman spectroscopy, Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), UV-Vis and photoluminescence (PL). The composites consist of crystalline CeO2-δ regions of about 1.8–2.9 nm in size, coexisting with highly disordered GQDs areas. The CeO2-δ-GQD composites experience gradual dehydration and oxidation of carbon processes during thermal treatment, influencing the CeO2 crystal size, Ce3+/Ce4+ ratio, and O vacancies presence. These effects allow for the control of some of the composite functional properties. Specifically, the CeO2-GQD250 composites exhibit a low recombination rate of charge carriers due to the synergistic interaction between the components and low presence of Ce3+. In contrast, the CeO2-GQD400 composites show a high Eg of 3.8 eV (Eg ∼3.2 eV for CeO2NPs) associated with a CeO2 quantum size effect and extremely low fraction of GQDs.

17 - Mechanical and optical properties of composites containing calcium orthophosphate particles

17 - Mechanical and optical properties of composites containing calcium orthophosphate particles

Effect of Glass Filler Geometry on the Mechanical and Optical Properties of Highly Transparent Polymer Composite.

In this work, we studied the influence of the geometry and degree of filling of glass dispersed particles on the optical and mechanical properties of flexible high-transmission composites, based on thermoplastic polyurethane. Glass spheres, glass flake and milling glass fiber were used as fillers. Studies of mechanical properties have shown that the introduction of any filler leads to a decrease in tensile strength and an increase in the elastic modulus of the composite material, however, with the introduction of glass flakes and milling glass fiber, a significant increase in the yield strength of the material is observed. The optical properties of composites with glass spheres decrease exponentially with an increase in the volume fraction of the filler. With an increase in the concentration of glass flakes and milling glass fiber to 10 vol.%, a sharp decrease in transmission is observed. With a further increase in concentration, the orientation of the filler along the film occurs, due to which the transmission in the visible range increases to values close to those of a pure polymer.

A Facile Approach to the Hydrothermal Synthesis of Silica Nanoparticle/Carbon Nanostructure Luminescent Composites.

Luminescent carbon nanostructures (CNSs) have been intensively researched, but there is still no consensus on a fundamental understanding of their structure and properties that limits their potential applications. In this study, we developed a facile approach to the synthesis of luminescent composite SiO2 nanoparticles/CNSs by the targeted formation of a molecular fluorophore, as the significant luminescent component of CNSs, on the surface of a silica matrix during a one-stage hydrothermal synthesis. Silica nanoparticles were synthesized by reverse microemulsion and used as a matrix for luminescent composites. The as-prepared silica nanoparticles had a functional surface, a spherical shape, and a narrow size distribution of about 29 nm. One-stage hydrothermal treatment of citric acid and modified silica nanoparticles made it possible to directly form the luminescent composite. The optical properties of composites could be easily controlled by changing the hydrothermal reaction time and temperature. Thus, we successfully synthesized luminescent composites with an emission maximum of 450 nm, a quantum yield (QY) of 65 ± 4%, and an average size of ~26 nm. The synthesis of fluorophore doped composite, in contrast to CNSs, makes it possible to control the shape, size, and surface functionality of particles and allows for avoiding difficult and time-consuming fractionation steps.

Self-sensing fluorescence polymer composites for chemical degradation protection and monitoring

The development of epoxy-based composites with the combination of protective and self-sensing capabilities continues to be a challenge in particular with respect to chemical and UV degradation. A promising approach is to fabricate these composites with phosphors particles, which provide the needed self-sensing characteristics. In this context, Y3Al5O12:Ce3+ (YAG:Ce) particles at different concentrations have been introduced into an epoxy polymer matrix, further placed in a laminate structure. The system was then exposed to specific degradation environments, including sulfuric acid and ultraviolet (UV) irradiation. The effects of these exposure treatments on the structural, mechanical, and optical properties of composites were investigated. A correlation between the variation of the physical-chemical parameters of the samples and the presence of YAG:Ce particles was observed, which demonstrate the self-sensing capabilities of the system. It is also demonstrated that fiberglass reinforced epoxy layered structures act as a good protective coating in sulfuric acid solution, while these layers degrade under UV irradiation. These findings provide a suitable platform for the development of coatings allowing to protect, detect and monitor corrosion in pipes and tanks under different industrial conditions.

Applicability of Exposure Reciprocity Law for Fast Polymerization of Restorative Composites Containing Various Photoinitiating Systems.

The exposure reciprocity law (ERL) has been used to calculate the optimal irradiation time of dental composites. This study examined the applicability of ERL for fast polymerization of restorative composites containing various photoinitiating systems using a high-power multi-peak light-emitting diode (LED) lamp. Three commercial composites differing in photoinitiating systems were tested: Filtek Ultimate Universal Restorative (FU) with a camphorquinone-amine (CQ-A) photoinitiating system, Tetric EvoCeram (TEC) with CQ-A and (2,4,6-trimethylbenzoyl)phosphine oxide (TPO), and Estelite Σ Quick (ESQ) with CQ and a radical amplified photopolymerization (RAP) initiator. Specimens 2-mm thick were polymerized using a high-power multipeak LED lamp (Valo) at 3 pairs of radiant exposures (referred to as low, moderate, and high) ranging from 15.8-26.7 J/cm2. They were achieved by different combinations of irradiation time (5-20 seconds) and irradiance (1300-2980 mW/cm2) as determined with a calibrated spectrometer. Knoop microhardness was measured 1, 24, and 168 hours after polymerization on specimen top (irradiated) and bottom surfaces to characterize the degree of polymerization. The results were statistically analyzed using a three-way analysis of variance and Tukey's post hoc tests, α = 0.05. Microhardness increased with radiant exposure and except for ESQ, top-surface microhardness was significantly higher than that on bottom surfaces. Combinations of high irradiance and short irradiation time significantly increased the top-surface microhardness of TEC at low and moderate radiant exposures, and the bottom-surface microhardness of FU at a low radiant exposure. In contrast, the microhardness of ESQ on both surfaces at high radiant exposure increased significantly when low irradiance and long irradiation time were used. With all tested composites, bottom-surface microhardness obtained at low radiant exposure was below 80% of the maximum top-surface microhardness, indicating insufficient polymerization. Combinations of irradiance and irradiation time had a significant effect on microhardness, which was affected by photoinitiators and the optical properties of composites as well as spectral characteristics of the polymerization lamp. Therefore, ERL cannot be universally applied for the calculation of optimal composite irradiation time. Despite high irradiance, fast polymerization led to insufficient bottom-surface microhardness, suggesting the necessity to also characterize the degree of polymerization on the bottom surfaces of composite increments when assessing the validity of ERL.

Dielectric Properties of MWNTs/HDPE Composites in Terahertz Region Studied with Reverse Effective Medium Approach

Optical properties of composites MWNTs/HDPE were explored by terahertz time-domain spectroscopy (THz-TDS). It was found that with the increasing of frequency from 0.4 to 2 THz the absorption coefficient increases gradually whereas the refractive index decreases. Furthermore, composites with thick MWNTs possesses larger absorption coefficient and index of refraction compared to that with the thin MWNTs at the same concentration. The dielectric properties of the MWNTs were extracted with reverse effective medium approach (REMA) from that of the composites. The results of the absorption coefficient and refractive index for MWNTs calculated from different concentrations coincides well with each other. The extracted results were then analyzed with the Drude model combined with a localized Lorentz absorption.

Dielectric Properties of MWNTs/HDPE Composites in Terahertz Region Studied with Reverse Effective Medium Approach

Optical properties of composites MWNTs/HDPE were explored by terahertz time-domain spectroscopy (THz-TDS). It was found that with the increasing of frequency from 0.4 to 2 THz the absorption coefficient increases gradually whereas the refractive index decreases. Furthermore, composites with thick MWNTs possesses larger absorption coefficient and index of refraction compared to that with the thin MWNTs at the same concentration. The dielectric properties of the MWNTs were extracted with reverse effective medium approach (REMA) from that of the composites. The results of the absorption coefficient and refractive index for MWNTs calculated from different concentrations coincides well with each other. The extracted results were then analyzed with the Drude model combined with a localized Lorentz absorption.

Comparative Study of Polymer Nanoparticles on the Basis of Caprolactone–Polyvinyl Alcohol Mixtures with an Encapsulated Antitumor Preparation by Atomic Force Microscopy, X-Ray Diffraction, and Dynamic Light Scattering

The morphology, structure, and optical properties of composites with biodegradable polymeric particles, which are based on poly-e-caprolactone–polyvinyl alcohol (stabilizer) mixtures and contain 5-Fluorouracil (an antitumor preparation), have been studied by atomic-force and optical microscopy, X-ray diffraction, and dynamic and static light scattering. Studies have shown that the morphology of synthesized composites sustains appreciable transformations depending on their stabilizer content. No crystalline reflections corresponding to 5-Fluorouracil have been revealed, thus arguing for a high dispersity of this preparation in the polymeric matrix of caprolactone. The correlations between the structural and morphological parameters, composition, stabilizer concentration and the efficiency of the encapsulation of 5-Fluorouracil by the composites have been established.

Method for Calculating the Optical Properties of Composites Based on a Transparent Matrix with Residual Porosity and Metal Nanoparticles

A method is proposed for calculating the optical characteristics of composites based on a transparent matrix with residual porosity and metal nanoparticles by solving the transport equation for monochromatic radiation employing a spherical harmonic method and Fresnel boundary conditions. The method is tested by modeling the transport of monochromatic radiation at four wavelengths of practical importance in cyclotrimethylenetrinitramine–aluminum nanoparticle composites with a Rayleigh distribution of pores with respect to radius. It is shown that in the case of small-radius pores the reflectivity increases as the mass fraction of nanoparticles is increased. In the case of pores with large radii, a kink corresponding to complete filling of the pores appears on the dependence of the transmission on the nanoparticle mass fraction. The application of these results to inverse problems in the spectroscopy of lightscattering system is discussed.

Optical properties of the glass composites with nano dimensional films dependence on the sol disperse phase characteristics studies

It has been proved that the characteristics of sols affect the optical properties of composites with the glass surface and nanofilms. Film thickness and composite transmission are proportionally on the volume fraction of the sol disperse phase. The laser ablation threshold energy density under the irradiation of a nanosecond laser radiation pulse increases with increasing the packing density of the dispersed phase in the layer. And the ablation threshold energy density under the laser radiation microseconds pulse increases with increasing particles size of the dispersed phase and decreases with the increasing volume fraction of the dispersed phase and the particle packing density.

Changes of Color and Fluorescence of Resin Composites Immersed in Beer.

The aim of this study was to evaluate changes of color and fluorescence of resin based composite exposed to beer. 84 samples (13 mm in diameter and 1.5 mm thick) of microhybrid composite Gradia DirectTM extra bleach white were immersed in 5 different beers (dark and light) or distilled water. Color and fluorescence were measured prior and after 1-, 7-, and 14-day immersion by Spectrophotometer Thermo Evolution 600 and Fluorolog-3-221 spectrofluorometer. Resin based composites changed color after immersion in beers of different types. Beers with higher optical absorption induced greater color changes. The fluorescence intensity of composites was decreased after immersion in beer, but the shape of fluorescence spectra was not changed. 14-day immersion in Bernard dark beer caused the greatest changes in optical properties of composite: ΔE*=9.0 and 57.6% reduced fluorescence. Dark and light beers changed optical properties of resin based composite. The color change come exclusively from the change of chroma. To fully meet esthetic criteria when using dental materials in restoration it is crucial to match optical properties of teeth and dental restoration at the moment of placement, but also to keep the match over the time. Considering that staining in beer causes changes in color and fluorescence of composites and that discoloration is a frequent reason for replacement of composite restorations, the data and conclusions on discoloration of dental restorations caused by beer consumption should aid dental professionals when reaching for high esthetics of modern dentistry.(J Esthet Restor Dent 28:330-338, 2016).

How the diffusion of sodium from a glass substrate affects the optical properties of composites

How the diffusion of sodium from a glass substrate affects the optical properties of composites

Enhancing absorption in coated semiconductor nanowire/nanorod core–shell arrays using active host matrices

In the present work, we investigated theoretically and experimentally the interaction of radiation field phenomena interacting with arrays of nanowire/nanorod core–shell embedded in active host matrices. The optical properties of composites are explored including the case when the absorption of propagating wave by dissipative component is completely compensated by amplification in active (lasing) medium. On the basis of more elaborated modeling approach and extended effective medium theory, the effective polarizability and the refractive index of electromagnetic mode dispersion of the core–shell nanowire arrays are derived. ZnS(shell)-coated by sulphidation process on ZnO(shell) nanorod arrays grown on (100) silicon substrate by chemical bath deposition (CBD) has been used for theoretical comparison. Compared with the bare ZnO nanorods, ZnS-coated core/shell nanorods exhibit a strongly reduced ultraviolet (UV) emission and a dramatically enhanced deep level (DL) emission. Obviously, the UV and DL emission peaks are attributed to the emissions of ZnO nanorods within ZnO/ZnS core/shell nanorods. The reduction of UV emission after ZnS coating seems to agree with the charge separation mechanism of type-II band alignment that holes transfer from the core to shell, which would quench the UV emission to a certain extent. Our theoretical calculations and numerical simulation demonstrate that the use of active host (amplifying) medium to compensate absorption at metallic inclusions. Moreover the core–shell nanorod/nanowire arrays create the opportunity for broad band absorption and light harvesting applications.

Structural, Optical and Photocatalytic Properties of Co-Tio2 Prepared by Sol-Gel Technique

In the present work, the Co/TiO2 nanocomposite was prepared by sol-gel method. The structural and optical properties of nanocomposite were studied using, X-ray diffraction (XRD) and diffuse reflectance UV-VIS spectrometry. The XRD spectra revealed its tetrahedral anatase structure. The grain size and optical properties of composite are also reported. Syntesied Co/TiO2photocatalyst showed excellent activity for the photodegradation of Methyl orange whether under visible and ultraviolet light irradiation.

Synthesis Of C/ZnO/CdS Nanocomposite With Enhanced Visible Light Photocatalytic Activity

C/ZnO/CdS nanocomposite was synthesized using microemulsion method. Thermal stability of precursor was studied with TG and DTA techniques. Structural and optical properties of composite were studied using various characterization techniques like X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), energy dispersive x-ray spectroscopy (EDX), transmission electron microscopy (TEM) and UV-visible absorption spectroscopy and photoluminescence spectroscopy. XRD study indicates that ZnO and CdS are having wurtzite and cubic phase in the composite sample. SEM and TEM study indicates formation of CdS nanospheres on ZnO nanorods. C doping and CdS coupling are responsible for red shift and shifting of absorption edge of ZnO from UV to visible region. C/ZnO/CdS nanocomposite exhibits better visible light photocatalytic activity for degradation of methylene blue (MB). Stability of photocatalyst was studied using recovered photocatalyst up to third cycle and it was found that photocatalyst prepared in the present work is stable and reusable. Copyright © 2016 VBRI Press.

Local Interfacial Structure Influences Charge Localization in Titania Composites: Beyond the Band Alignment Paradigm

The phase junction of nanocomposite materials is key to enhanced performance but is largely ignored in recent theoretical examinations of photocatalytic interactions in titania-based composites. Computational advances now allow more precise modeling of the electronic and optical properties of composites, and focusing on mixed-phase TiO2 as a model, we use density functional theory (DFT) to interrogate the essential structural feature, namely, the rutile–anatase interface, and its relationship to photogenerated charge localization, bulk band alignments, and defect formation. The interfacial region is disordered and distinct from rutile and anatase and contains low coordinated Ti sites and oxygen vacancies, both drivers of charge localization. The relaxations of the interface upon formation of excited electrons and holes determine the final location of charges which cannot always be predicted from bulk band alignments. A detailed understanding of the interfacial phase junction lays the foundation for direct...

Photocatalytic activity performance of novel cross-linked PEBAX copolymer nanocomposite on azo dye degradation

The results of investigations on advanced oxidation process (AOP) regarding a new embedded heterogeneous photocatalyst on poly ether block amides/polyvinyl alcohol/titanium dioxide/multiwalled carbon nanotube (PEBAX/PVA/TiO2/MWCNT) composite are presented. Scanning electron microscopy (SEM), atomic force microscopy (AFM), thermogravimetry analysis (TGA), UV–Vis-NIR diffuse reflectance spectroscopy, Fourier-transform infrared spectrometry (FT-IR), and chemical oxygen demand analysis (COD) were applied to characterize the effect of functionalization, structure, surface morphology, and optical properties of composites and mineralization of pollutants. The present work confirmed the role of MWCNT as a factor which not only activated the catalyst with visible light but also raised the adsorption of species by increasing the active surface area. The oxalic acid (OA) treated composite with bath casting method showed high potential for the mineralization of pollutant. Heterogeneous advanced oxidation process carried out for 240min utilizing composite films resulted in complete loss of Remazol Black Brilliant (RBB) under UV irradiation. The OA treated composite with bath casting method was the most active composite film. Removal of RBB proceeded corresponding to Langmuir–Hinshelwood and zero order kinetics.

Synthesis and characterization of g-C3N4/BiFeO3 composites with an enhanced visible light photocatalytic activity

The novel visible light-induced g-C3N4/BiFeO3 composites were successfully synthesized by introducing BiFeO3 into polymeric g-C3N4. The structures and optical properties of composites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), field-emission transmission electron microscope (TEM), UV–vis diffuse reflection spectroscopy (DRS), respectively. For the degradation of Rhodamine B (RhB), the g-C3N4/BiFeO3 composites exhibited significantly higher visible light photocatalytic activity than that of a single semiconductor. The optimal percentage of doped g-C3N4 was 50%. Both photooxidation and photoreduction processes follow first order kinetics. In addition, the stability of the prepared photocatalyst in the photocatalytic process was also investigated. The enhanced photocatalytic performance could be due to the high separation efficiency of the photogenerated electron–holes pairs. The possible photocatalytic mechanism of g-C3N4/BiFeO3 was proposed to guide the further improvement of their photocatalytic activity.