Continuous UV Irradiation Research Articles

Green Synthesis of Multifunctional Carbon Nanodots and Their Applications as a Smart Nanothermometer and Cr(VI) Ions Sensor

In this work, water-soluble and blue-emitting carbon nanodots (CDs) were synthesized from apple peels for the first time via one-step hydrothermal method. The synthetic route is facile, green, economical and viable. The as-prepared CDs were characterized thoroughly by transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman, Fourier transform infrared (FT-IR), X-ray photoelectron (XPS), fluorescence and UV–Vis absorption spectroscopy in terms of their morphology, surface functional groups and optical properties. The results show that these CDs possessed ultrasmall size, good dispersivity, and high tolerance to pH, ionic strength and continuous UV irradiation. Significantly, the CDs had fast and reversible response towards temperature, and the accurate linear relationship between fluorescence intensity and temperature was used to design a novel nanothermometer in a broad temperature range from 5 to 65[Formula: see text]C facilely. In addition, the fluorescence intensity of CDs was observed to be quenched immediately by Cr(VI) ions based on the inner filter effect. A low-cost Cr(VI) ions sensor was proposed employing CDs as fluorescent probe, and it displayed a wide linear range from 0.5 to 200[Formula: see text][Formula: see text]M with a detection limit of 0.73[Formula: see text][Formula: see text]M. The practicability of the developed Cr(VI) sensor for real water sample assay was also validated with satisfactory recoveries.

Carbazole–Dibenzofuran Dyads as Metal‐Free Single‐Component White‐Color Photoemitters

AbstractWhite‐color light emitters from single organic molecule without heavy metals are valuable for practical applications in organic light‐emitting devices. In this study, carbazole (Cz)–dibenzofuran (DBF) donor–acceptor dyads are designed for white‐color light emitters. Originally, these molecules show photoluminescence (PL) in near ultraviolet region. However, upon successive ultraviolet (UV) irradiation, white‐color PL appears, comprising dual‐color phosphorescence from the amorphous and crystalline state of the dyad. A continuous UV irradiation makes the twisting angle between the Cz and DBF planes flatten through the triplet‐excited state, which proceeds crystallization. Thermal annealing and UV irradiation can switch the blue‐ and white‐color phosphorescences from the dyad. Furthermore, charge injection generates white‐color electroluminescence. The materials with PL color modulation ability by UV‐light irradiation and heating can be applicable as light‐ and thermo‐sensors.

A promising transparent and UV-shielding composite film prepared by aramid nanofibers and nanofibrillated cellulose

An aramid nanofibers (ANFs)-functionalized nanofibrillated cellulose (NFC) composite film is effectively fabricated by the incorporation of ANFs into nanocellulose matrix. The fabrication of the composite film imitates the traditional paper-making process after homogenous mixing. The as-prepared composite film shows excellent UV-shielding performance due to the incorporation of ANFs. Thus the effect of ANFs contents is evaluated in aspects of the surface morphology, physicochemical properties including crystallinity, chemical structure and photothermal stability of composite film. Results show that the composite film with 2 wt.% of ANFs has improved mechanical properties, surface wettability compared to pure NFC film, and presents excellent UV-shielding performance ranging up to 400 nm while still retaining its high transparency. Moreover, the composite film shows high photostability even after continuous UV irradiation (365 nm) for over 12 h. The findings in the present work indicate that the ANFs-functionalized NFC composite films are promising as UV-shielding and transparent materials.

Enhanced inactivation of E. coli by pulsed UV-LED irradiation during water disinfection

Pulsed ultraviolet (UV) irradiation has presented enhanced inactivation efficiency in water disinfection and food decontamination. As an emerging UV source, UV light-emitting diodes (UV-LEDs) are an attractive alternative for pulsed irradiation because they can be turned on and off with a high and adjustable frequency. In this study, disinfection efficiencies of pulsed and continuous UV-LED irradiation were compared for Escherichia coli (E. coli) inactivation in water using a high power 285 nm LED and low power 265 and 280 nm LEDs. Factors including various duty cycles, pulse frequencies and UV irradiances were evaluated. The log-inactivation of E. coli increased substantially as the duty cycle decreased from 100% to 5% at the same UV dose. For 265 and 280 nm LEDs, the log-inactivation enhancements of pulsed UV irradiation were similar. When a higher irradiance was applied, the energy efficiency enhancement of pulsed UV irradiation became more obvious. The log-inactivation of E. coli enhanced remarkably using high current pulsed irradiation of 280 nm LEDs. Compared to continuous UV irradiation, pulsed UV-LED irradiation is an attractive alternative for E. coli inactivation in water considering energy efficiency.

Selective detection of copper ion in complex real samples based on nitrogen-doped carbon quantum dots.

Highly selective nitrogen-doped carbon quantum dots (ND-CQDs) for copper ion (Cu2+) determination were synthesized by a solvent-free pyrolysis of citric acid and histidine. The resultant ND-CQDs display a stable bright blue fluorescence with a satisfactory product yield of 56% and quantum yield of 16%. The ND-CQDs not only show good photostability under continuous UV irradiation, but arealso dramatically stable against extreme ionic strengths. The solid powders of the ND-CQDs re-dispersed in water still maintain a strong blue fluorescence after storing at room temperature for 6months. The ND-CQDs can be employed to selectively detect Cu2+ in a wide linear range of 0.6-30μM. The detection limit is as low as 0.19μM. The ND-CQDs were applied for Cu2+ detection in environmental water samples, fruit juice samples, and urine sample. Satisfactory recoveries of 96-102% with relative standard deviations below 3% were obtained. The research provided a promising prospect for selective detection of Cu2+ in the complex matrix. Graphical abstract Schematic illustration of the preparation of the ND-CQDs and its detection mechanism to Cu2.

Continuous UV irradiation synthesis of ultra-small Au nanoparticles decorated Cu2O with enhanced photocatalytic activity

Abstract Noble metal nanoparticles (NPs) with controlled size and shape can be easily prepared by UV irradiation at room temperature. In this work, ultra-small Au NPs were successfully continuously synthesized via an UV irradiation approach, and the synthesis conditions of Au NPs with the size of 1.8 nm have been optimized to be an exposure time of 1.4 min, a HAuCl 4 precursor concentration of 0.8 mM and a pH value of 10.4. The growth dynamics of Au NPs was investigated under different exposing time of the electron beam in transmission electron microscopy (TEM), revealing the formation of NPs via the oriented attachment of individual nanoparticles. In addition, well dispersed ultra-small Au NPs decorated Cu 2O composites were obtained from this in-situ strategy and showed an enhanced photocatalytic activity compared with that of Au-free oxides and Au- Cu2O from direct replacement method.

Photoinduced Effects in the ZnO Luminescence Spectra

The effect of intense UV irradiation on the photoluminescence (PL) spectra of ZnO powders and nanocrystalline films obtained by atomic layer deposition (ALD) was investigated. At room temperature, the behavior of the spectra under continuous UV irradiation in multiple vacuum-atmosphere cycles was studied. The changes in the intensities of exciton radiation and radiation in the “green” band region, associated with the phenomena of oxygen photodesorption and photoadsorption, are discussed. In the temperature range of 5–300 K, the effect of strong UV irradiation on the near-edge luminescence spectrum of ZnO films was studied. The nature of a new line arising in the photoluminescence spectra of an irradiated film in the region of emission of bound excitons is discussed.

Fabrication of UV-absorbent cellulose-rosin based thermoplastic elastomer via “graft from” ATRP

Cellulose-rosin based thermoplastic elastomers with UV absorption properties were fabricated by a combination of rosin, poly(butyl acrylate) (PBA) and ethyl cellulose (EC) via “graft from” ATRP with the aid of EC-rosin macroinitiator (EC-g-(DA)-Br) prepared by a simple esterification reaction between EC, dehydroabietic acid (DA, one of rosin’s resin acids) and 2-bromoisobutylryl bromide. The introduction of rosin affords these elastomers with UV absorption property. And the glass transition temperature of these EC-rosin grafted copolymers could be tuned by changing the content of PBA. Moreover, the introduction of PBA to EC endowed EC-g-(DA)-g-PBA with a good film-forming property and excellent thermoplastic elastomer behavior. All of these EC-rosin grafted copolymers showed an excellent UV absorption performance, and maintained outstanding UV absorption capability after continuous UV-irradiation or being heated to 115 °C for 1 h. As a result, these EC-rosin grafted copolymers have a potential application in coating materials with UV absorption property.

Reducing the photo-bleaching effect of a new europium complex embedded in styrene butadiene copolymer

A highly luminescent europium complex obtained with two different ligands, succinimide (SI) and 2-thenoyltrifluoroacetone (TTA), was synthetized with different TTA concentrations. The photoluminescence (PL) emission from these materials corresponds to the characteristic inter-electronic energy level transitions of the Eu3+ ions. However, the excitation spectrum is strongly dependent on the presence of TTA, having an optimum response when 0.75 mmol of this compound is added to the EuL3(H2O)3 complex. The quantum yield obtained by these powders were around 72%±1.7% indicating an optimum sensitization of these complex. The EuL3TTA complex with the best PL properties was embedded in a styrene butadiene copolymer (SBC) film, produced by the drop casting method, obtaining similar PL behavior at different concentrations, the highest intensity was observed at 1.2% (w/v) of EuL3TTA complex and the quantum yield of these composite films was 60.5%±2%. These films were exposed to continuous UV irradiation and after 141 h no photo-bleaching effect was observed in contrast with the EuL3TTA complex that exhibited a noticeable photoluminescence intensity degradation at much shorter exposure times. Both the Eu-complexes and the composite films were characterized by FT-IR, XRD, SEM and fluorescence spectroscopy.

Фотоиндуцированные эффекты в спектрах люминесценции ZnO

AbstractThe effect of intense UV irradiation on the photoluminescence (PL) spectra of ZnO powders and nanocrystalline films obtained by atomic layer deposition (ALD) was investigated. At room temperature, the behavior of the spectra under continuous UV irradiation in multiple vacuum-atmosphere cycles was studied. The changes in the intensities of exciton radiation and radiation in the “green” band region, associated with the phenomena of oxygen photodesorption and photoadsorption, are discussed. In the temperature range of 5–300 K, the effect of strong UV irradiation on the near-edge luminescence spectrum of ZnO films was studied. The nature of a new line arising in the photoluminescence spectra of an irradiated film in the region of emission of bound excitons is discussed.

Ultrastable, cationic three-dimensional lead bromide frameworks that intrinsically emit broadband white-light.

Herein, we report the unusual broadband white-light emission as an intrinsic property from two cationic lead bromide frameworks. This is the first time that the metal halide materials adopting a purely inorganic positively-charged three-dimensional (3D) topology have been synthesized, thus affording highly distorted PbII centers. The single-component white-light emitters achieve an external quantum efficiency of up to 5.6% and a correlated color temperature of 5727 K, producing typical white-light close to that of fluorescent light sources. Unlike the air/moisture-sensitive 3D organolead halide perovskites, our cationic materials are chemically "inert" over a wide range of pH as well as aqueous boiling condition. Importantly, these long-sought ultrastable lead halide materials exhibit undiminished photoluminescence upon continuous UV-irradiation for 30 days under atmospheric condition (∼60% relative humidity, 1 bar). Our mechanistic studies indicate the broadband emission have contributions from the self-trapped excited states through electron-vibrational coupling in the highly deformable and anharmonic lattice, as demonstrated by variable-temperature photoluminescence/absorption spectra as well as X-ray crystallography studies. The chemical robustness and structural tunability of the 3D cationic bromoplumbates open new paths for the rational design of hybrid bulk emitters with high photostability.

Facile synthesis of TiO2–PC composites for enhanced photocatalytic abatement of multiple pollutant dye mixtures: a comprehensive study on the kinetics, mechanism, and effects of environmental factors

In the recent era, the inevitable emergence of versatile micropollutants in ground and surface water has become a serious concern for the long-term sustainability of the environment. Most of the recent studies, conducted to minimize water pollution, are mainly limited to either single or binary pollutant-based analyses. Hence, photocatalytic degradation of a multicomponent pollutant dye (four components) mixture was studied in the present work. Here, the economical TiO2–processed carbon (PC) nano-/microcomposite-mediated degradation of a pollutant dye mixture in aqueous solution under continuous UV irradiation was investigated and compared with bare TiO2 photocatalysis. The overall degradation kinetics, degradation mechanism and the impact of several environmental factors on photocatalytic decomposition of pollutant dye mixtures have also been identified and addressed. It is observed that the TiO2–PC composite-mediated photocatalysis has superior degradation performance over that with bare TiO2 treatment. Consequently, the degradation kinetics parameters have also shown significant improvements for cases of TiO2–PC composite-mediated photocatalysis, for which the degradation rate constant has shown an improvement up to 22%, mainly due to the synergistic effect of the TiO2–PC composites. However, the mineralization level is barely improved. It may be noted that the catalyst reusability test has also shown the superiority of TiO2–PC composites over bare TiO2. In addition, the environmental factors such as salt concentration, pH, temperature, mixing/stirring speed and catalyst dose have shown significant influences over the degradation efficiency of these photocatalysts. It is interesting to observe that the alkaline condition (pH > 9.0) favors the improved photocatalytic performance of TiO2–PC composite.

Ultraviolet-Durable Superhydrophobic Nanocomposite Thin Films Based on Cobalt Stearate-Coated TiO2 Nanoparticles Combined with Polymethylhydrosiloxane.

Ultraviolet (UV)-durable superhydrophobic nanocomposite thin films have been successfully fabricated on aluminum substrates by embedding cobalt stearate (CoSA)-coated TiO2 nanoparticles in a hydrophobic polymethylhydrosiloxane (PMHS) matrix (PMHS/TiO2@CoSA) using the sol–gel process. When compared to the sharp decrease of water contact angle (WCA) on the superhydrophobic PMHS/TiO2 thin films, the PMHS/TiO2@CoSA superhydrophobic thin films exhibited a nearly constant WCA of 160° under continuous UV irradiation for more than 1 month. The designed scheme of the TiO2@CoSA core–shell structure not only increased the hydrophobic properties of the TiO2 nanoparticle surface but also confined the photocatalytic efficiency of TiO2 nanoparticles. A plausible model has been suggested to explain the UV-durable mechanism of the superhydrophobic nanocomposite thin films based on PMHS/TiO2@CoSA. Furthermore, the elongated lifetime in the exposure of the solar light imparts this superhydrophobic nanocomposite thin film with potential practical applications where UV-resistant properties are emphasized including corrosion-resistant building walls, anti-icing airplanes, self-cleaning vehicles, and so forth.

Fluorescent Silicon Nanorods-Based Ratiometric Sensors for Long-Term and Real-Time Measurements of Intracellular pH in Live Cells.

Long-term and real-time investigation of the dynamic process of pHi changes is critically significant for understanding the related pathogenesis of diseases and the design of intracellular drug delivery systems. Herein, we present a one-step synthetic strategy to construct ratiometric pH sensors, which are made of europium (Eu)-doped one-dimensional silicon nanorods (Eu@SiNRs). The as-prepared Eu@SiNRs have distinct emission maxima peaks at 470 and 620 nm under 405 nm excitation. Of particular note, the fluorescence emission intensity at 470 nm decreases along with the increase of pH, while the one at 620 nm is nearly unaffected by pH changes, making Eu@SiNRs a feasible probe for pH sensing ratiometrically. Moreover, Eu@SiNRs are found to be responsive to a broad pH range (ca. 3-9), biocompatible (e.g., ∼100% of cell viability during 24 h treatment) and photostable (e.g., ∼10% loss of intensity after 40 min continuous UV irradiation). Taking advantages of these merits, we employ Eu@SiNRs for the visualization of the cytoplasmic alkalization process mediated by nigericin in living cells, for around 30 min without interruption, revealing important information for understanding the dynamic process of pHi fluctuations.

Intrinsic Broadband White‐Light Emission from Ultrastable, Cationic Lead Halide Layered Materials

AbstractWe report a family of cationic lead halide layered materials, formulated as [Pb2X2]2+[−O2C(CH)2CO2−] (X=F, Cl, Br), exhibiting pronounced broadband white‐light emission in bulk form. These well‐defined PbX‐based structures achieve an external quantum efficiency as high as 11.8 %, which is comparable to the highest reported value (ca.9 %) for broadband phosphors based on layered organolead halide perovskites. More importantly, our cationic materials are ultrastable lead halide materials, which overcome the air/moisture‐sensitivity problems of lead perovskites. In contrast to the perovskites and other bulk emitters, the white‐light emission intensity of our materials remains undiminished after continuous UV irradiation for 30 days under atmospheric conditions (ca.60 % relative humidity). Our mechanistic studies confirm that the broadband emission is ascribed to short‐range electron‐phonon coupling in the strongly deformable lattice and generated self‐trapped carriers.

Intrinsic Broadband White-Light Emission from Ultrastable, Cationic Lead Halide Layered Materials.

We report a family of cationic lead halide layered materials, formulated as [Pb2 X2 ]2+ [- O2 C(CH)2 CO2- ] (X=F, Cl, Br), exhibiting pronounced broadband white-light emission in bulk form. These well-defined PbX-based structures achieve an external quantum efficiency as high as 11.8 %, which is comparable to the highest reported value (ca.9 %) for broadband phosphors based on layered organolead halide perovskites. More importantly, our cationic materials are ultrastable lead halide materials, which overcome the air/moisture-sensitivity problems of lead perovskites. In contrast to the perovskites and other bulk emitters, the white-light emission intensity of our materials remains undiminished after continuous UV irradiation for 30 days under atmospheric conditions (ca.60 % relative humidity). Our mechanistic studies confirm that the broadband emission is ascribed to short-range electron-phonon coupling in the strongly deformable lattice and generated self-trapped carriers.

Photochemical Reactivity of 1,6-Methano[10]annulene.

1,6-Methano[10]annulene solutions in cyclohexane have been subjected to continuous and pulsed UV irradiation. Photolysis occurs in both cases, giving naphthalene as a minor and major product, respectively. The wavelength dependence of the reaction in solution indicates that the photochemical process occurs, exciting 1,6-methano[10]annulene in the second and third singlet electronic excited states. The reaction kinetics has been determined under pulsed irradiation. From the time dependence of concentrations, along with support of density functional theory calculations and early published data, two mechanisms are proposed for naphthalene production. Reaction steps such as direct migration of the bridging methylene of 1,6-methano[10]annulene to cyclohexane and 1,6-methano[10]annulene isomerization to benzotropilidene have been identified. The calculated energy diagrams relative to the ground and lowest excited states allow one to relate these steps to processes such as electrocyclic closure and sigmatropic shift. The norcaradienic form of 1,6-methano[10]annulene results in the critical species for methylene migration and the sigmatropic [1,5] shift. The present results and those arising from photolysis in the gas phase are good examples of the photochemical reactivity of 1,6-methano[10]annulene.

UV-assisted mechanoluminescence properties of SrAl2O4:(Eu,Dy) for impact sensing

SrAl2O4:(Eu,Dy) is one of the most promising mechanoluminescence materials that have potential applications in stress sensing, lighting, imaging and energy conversion. However, the ML intensity decays with the afterglow time of SrAl2O4:(Eu,Dy), which hampers its application in the real world. Here, the mechanoluminescence property of SrAl2O4:(Eu,Dy) was investigated by impact of a load. A method was proposed to overcome the drawback of the mechanoluminescence decay behavior associated with the afterglow time. During the measurement of mechanoluminescence, continuous UV irradiation on SrAl2O4:(Eu,Dy) can effectively realize steady-state mechanoluminescence that is independent of the afterglow time. The underlying mechanism is discussed in this paper.

Photoexfoliation of two-dimensional materials through continuous UV irradiation

This paper describes the preparation of fluorinated graphene nanosheets (FGNs) through photoexfoliation of fluorinated graphite (FG) in the liquid phase. We discovered that UV irradiation of FG dispersions in N-methyl-2-pyrolidone facilitated exfoliation to give FGNs. Transmission electron microscopy and atomic force microscopy revealed that the average thickness of the FGNs was approximately 3 nm; they were considerably thinner than the nanosheets prepared using a conventional sonication approach. Furthermore, when the FGNs were deposited uniformly onto substrates (through spin coating), they formed effective cathode interlayers for polymer solar cells (PSCs), the efficiency of which was 60% greater than that of PSCs containing FGNs prepared through ultrasonication.

Investigation into the potential chemical mechanism of the pro-oxidant activity of carotenoids with liposomes under UV-irradiation

This study focuses on the behavior of ?-carotene and lutein inside multilamellar liposomes under continuous UV-irradiation. The liposomes were obtained by the thin film method and carotenoids (Crts) were incorporated by mixing at various concentrations (0.005, 0.0075, 0.02, 0.07 and 0.5 mol %). Liposomes formation and the presence of Crts inside them were confirmed by SEM microscopy and FT-IR spectroscopy, respectively. The antioxidant/pro- -oxidant activity of Crts inside liposomes was determined by the thiobarbituric acid?malondialdehyde (TBA?MDA) test. The investigated Crts acted more or less unexpected (as pro-oxidants) inside the lipid bilayers, interacting with the UV-produced lipid radicals and simultaneously suffering under the UV-irradiation. Their pro-oxidant activity with liposomes and under UV-irradiation could be explained by the formation of unstable adducts in the reaction with peroxyl radicals, or by Crts-cation radicals formation via the electron transfer mechanism. Such tentatively unexpected behavior of carotenoids should be taken into consideration in further carotenoids-based UV-filters projections in cosmetic formulations for skin protection.