Visible LED Research Articles

Reactive Ceramic Membrane for Efficient Micropollutant Purification with High Flux by LED Visible-Light Photocatalysis: Device Level Attempts

Micropollutants (MPs) are widely occurring in surface water all over the world with extremely low concentrations, and their treatment requires high energy consumption and efficiency. In this study, a large-sized planar photocatalytic reactive ceramic membrane (PRCM) was prepared using the facile dip-coating method with nitrogen-doped TiO2 (N-TiO2-CM) for the purification of tetracycline hydrochloride (TC) as a model MP. The N-TiO2 nanoparticles and the as-prepared N-TiO2-CM were characterized by SEM/EDS, TEM, XPS, UV–Vis DRS, and FT-IR. A fixed bed reactor integrated N-TiO2-CM, and visible LED light was fabricated for the new PRCM water treatment system for the removal of TC with a comprehensive consideration of the degradation rate and permeate flux. The SEM/EDS results indicated that the N-TiO2 was uniformly and tightly loaded onto the flat CM, and the pure water flux could reach over 2000 L/(m2 × h) under a trans-membrane pressure (TMP) of −92 kPa. The fixed bed PRCM water treatment system is extremely suited for MP purification, and the removal efficiency of TC was as high as 92% with 270 min even though its initial concentration was as low as 20 mg/L. The degradation rate and permeate flux of N-TiO2-CM was 2.57 and 2.30 times as high as that of the CM, indicating its good self-cleaning characteristics. The quenching experiments illustrated that the reactive radicals involved in the PRCM process, •OH and •O2−, were responsible for TC degradation. This research also provides a utilization proposal for a scale-up N-TiO2-CM system for water and wastewater treatment.

Photodegradation and oxidizing action of peroxotitanium complex film

Photodegradation and accompanying oxidizing action of peroxotitanium complex (PTC) film were investigated, which made from PTC aqueous solution containing 61.3 mol % peroxo groups (O-O) to total Ti. The apparent activation energy (Ea) of the PTC degradation was revealed to be 132 kJ·mol−1 (λ = 905 nm), according to Arrhenius plot of the degradation rate constant of PTC aqueous solution with microwave hydrothermal treatment at 100–180 °C. The PTC films were slowly decomposed by light irradiation of UV lamp, visible light LED or light bulb, and simultaneously oxidatively decomposed methylene blue dissolved in water. The oxidation reaction occurred even under the light of long wavelength around 900 nm closed to the Ea. Furthermore, the utilization efficiency of active oxygen generated by the photodegradation to the oxidation reaction of acetaldehyde gas was estimated to be 66 and 80 % under UV light (2.00 mW·cm−2) and LED visible light (1.50 mW·cm−2), respectively.

UiO-66 MOF-Derived Ru@ZrO2 Catalysts for Photo-Thermal CO2 Hydrogenation

The use of metal–organic frameworks (MOFs) as templates or precursors in the manufacture of heterogeneous catalysts is highly attractive due to the transfer of MOFs’ inherent porosity and homogeneous metallic distribution to the derived structure. Herein, we report on the preparation of MOF-derived Ru@ZrO2 catalysts by controlled thermal treatment of zirconium-based MOF UiO-66 with ruthenium moieties. Ru3+ (3 or 10 mol%) precursor was added to UiO-66 synthesis and, subsequently, the as-synthesized hybrid structure was calcined in flowing air at different temperatures (400–600 °C) to obtain ZrO2-derived oxides doped with highly dispersed Ru metallic clusters. The materials were tested for the catalytic photo-thermal conversion of CO2 to CH4. Methanation experiments were conducted in a continuous flow (feed flow rate of 5 sccm and 1:4 CO2 to H2 molar ratio) reactor at temperatures from 80 to 300 °C. Ru0.10@ZrO2 catalyst calcined at 600 °C was able to hydrogenate CO2 to CH4 with production rates up to 65 mmolCH4·gcat.–1·h–1, CH4 yield of 80% and nearly 100% selectivity at 300 °C. The effect of the illumination was investigated with this catalyst using a high-power visible LED. A CO2 conversion enhancement from 18% to 38% was measured when 24 sun of visible LED radiation was applied, mainly due to the increase in the temperature as a result of the efficient absorption of the radiation received. MOF-derived Ru@ZrO2 catalysts have resulted to be noticeably active materials for the photo-thermal hydrogenation of CO2 for the purpose of the production of carbon-neutral methane. A remarkable effect of the ZrO2 crystalline phase on the CH4 selectivity has been found, with monoclinic zirconia being much more selective to CH4 than its cubic allotrope.

Quantitative Evaluation of Municipal Wastewater Disinfection by 280 nm UVC LED

UV-LED irradiation has attracted attention in water and wastewater disinfection applications. However, no studies have quantitatively investigated the impact of light intensity on the UV dosage for the same magnitude of disinfection. This study presents a powerful 280 nm UV-LED photoreactor with adjustable light intensity to disinfect municipal wastewater contaminated with E. coli, SARS-CoV-2 genetic materials and others. The disinfection performance of the 280 nm LED was also compared with 405 nm visible light LEDs, in terms of inactivating E. coli and total coliforms, as well as reducing cATP activities. The results showed that the UV dose needed per log reduction of E. coli and total coliforms, as well as cATP, could be decreased by increasing the light intensity within the investigated range (0–9640 µW/cm2). Higher energy consumption is needed for microbial disinfection using the 405 nm LED when compared to 280 nm LED. The signal of SARS-CoV-2 genetic material in wastewater and the SARS-CoV-2 spike protein in pure water decreased upon 280 nm UV irradiation.

Comparative study of the photocatalytic degradation of tetracycline under visible light irradiation using Bi24O31Br11-anchored carbonaceous and silicates catalyst support

Abstract This study compared two hydrothermally synthesized heterojunctions composites, Bi24O31Br10 – carbonaceous (activated carbon from zinc chloride [ACZ], phosphoric acid [ACH], carbonized material [CM]), and Bi24O31Br10 – silicates (SBA-15 and MCM-41), with nanosheets structure. The photocatalytic degradation of tetracycline (TC) was used to evaluate the synergistic influence of the catalyst supports for the corresponding heterojunction composites. The X-Ray diffractometry (XRD), Fourier transform infrared spectroscopy and scanning electron microscopy (SEM) confirmed the synthesis of the Bi24O31Br10 (BOB) – composites. After 120 min of visible LED light photocatalytic reactions, the degradation trend in removal efficiency of TC was BOB-ACZ > BOB > ACH > BOB-CM > BOB-MCM-41 > BOB-SBA-15 > BOB. The study reveals that Bi24O31Br11 – carbonaceous composite exhibits much better degradation efficiency than Bi24O31Br11 – silicates. Crucially, the synergistic surface interaction of ACZ with BOB, and the efficient separation of photogenerated charge carriers, from the SEM, XRD analysis, and photocurrent response, confirmed the photocatalytic enhancement of the heterojunction formation of the BOB-ACZ composite. This study further provides convincing insights on the superiority of carbonaceous nanomaterial to silica materials as efficient catalyst support in catalytic applications.

A photoperiod including visible spectrum LEDs increased sulforaphane in fresh-cut broccoli

The objective was to elucidate if a photoperiod including fluorescent light (14 h) and visible spectrum LEDs (10 h), during night periods, can increase the phytochemical content in fresh-cut broccoli while not affecting other quality attributes. Monochromatic LEDs used were Cool White -CW-, Blue -B-, Green -G-, Red -R-, and Far-Red -FR-, while darkness was used as control. Changes in weight losses, colour, epiphytic microorganisms, and main bioactive compounds (glucosinolates and isothiocyanates) were assessed during 16 days at 5 ºC. Illumination with G and R lights accelerated yellowing of florets after 14 days. Higher weight losses were registered for LEDs treatments regarding darkness while no changes were observed for microbial development among treatments. All studied photoperiods including LEDs enhanced the sulforaphane content regarding darkness, especially after 7 days, reporting CW, B, and FR treatments increases over 40%. However, the glucosinolate content and myrosinase activity were not stimulated by LEDs. In conclusion, a supplementation with CW, B, or FR LEDs during night periods at retail sale seems a strategy to enhance the sulforaphane accumulation in Brassicaceae. Probably, higher and / or other stresses can be applied to increase / activate the synthesis and accumulation of more secondary metabolites.

Enhanced photocatalytic degradation of organic contaminants in water by highly tunable surface microlenses

Photocatalysis is one of the dominant technologies used to enhance the efficiency of water decontamination with light-based treatments. However, the effectiveness of photocatalysts is usually limited by the irradiation conditions and the properties of the water matrix. In this work, we have demonstrated the capability of surface microlenses (MLs) as a clean technology for more efficient photocatalytic water decontamination. Random or ordered surface MLs were fabricated from simple polymerization of nanodroplets produced in a solvent exchange process. Both random microlenses (MLR) and microlenses array (MLA) could enhance the photocatalytic degradation efficiency (η) of four representative organic pollutants, including methyl orange (MO), norfloxacin (NFX), sulfadiazine (SFD), sulfamethoxazole (SMX), spiked in ultra-pure water, synthetic natural water, or real river water. By controlling the conditions of light treatment, η could be enhanced by up to 402%. The effectiveness of surface MLs was validated under both visible LED light and simulated solar light and for two photocatalysts zinc oxide (ZnO) and titanium dioxide (TiO2). By reducing the concentration of the photocatalysts from 100 to 5 mg/L and the intensity of irradiation intensity from 1 Sun to 0.3 Sun, our findings suggest that the enhancement factor by MLs was higher at lower catalyst concentration, or at lower light intensity. Based on optical simulations and experimental results, we demonstrated that surface MLs optimize the light distribution and promote the formation of active species, which results in the enhancement of η. The use of MLs may serve as a novel strategy to improve the photocatalytic degradation of micropollutants, especially in places where the available light source is weak, such as indoors or in cloudy regions.Synopsis: MLs-enhanced photocatalysis degradation of organic contaminants in different water matrices.

Abatement of 1,2,4-Trichlorobencene by Wet Peroxide Oxidation Catalysed by Goethite and Enhanced by Visible LED Light at Neutral pH

Abatement of 1,2,4-Trichlorobencene by Wet Peroxide Oxidation Catalysed by Goethite and Enhanced by Visible LED Light at Neutral pH

Single-Step Synthesis of Graphitic Carbon Nitride Nanomaterials by Directly Calcining the Mixture of Urea and Thiourea: Application for Rhodamine B (RhB) Dye Degradation

Recently, polymeric graphitic carbon nitride (g-C3N4) has been explored as a potential catalytic material for the removal of organic pollutants in wastewater. In this work, graphitic carbon nitride (g-C3N4) photocatalysts were synthesized using mixtures of low-cost, environment-friendly urea and thiourea as precursors by varying calcination temperatures ranging from 500 to 650 °C for 3 h in an air medium. Different analytical methods were used to characterize prepared g-C3N4 samples. The effects of different calcination temperatures on the structural, morphological, optical, and physiochemical properties of g-C3N4 photocatalysts were investigated. The results showed that rhodamine B (RhB) dye removal efficiency of g-C3N4 prepared at a calcination temperature of 600 °C exhibited 94.83% within 180 min visible LED light irradiation. Photocatalytic activity of g-C3N4 was enhanced by calcination at higher temperatures, possibly by increasing crystallinity that ameliorated the separation of photoinduced charge carriers. Thus, controlling the type of precursors and calcination temperatures has a great impact on the photocatalytic performance of g-C3N4 towards the photodegradation of RhB dye. This investigation provides useful information about the synthesis of novel polymeric g-C3N4 photocatalysts using a mixture of two different environmentally benign precursors at high calcination temperatures for the photodegradation of organic pollutants.

Multicolor Light-Induced Immune Activation via Polymer Photocaged Cytokines.

Cytokines act as potent, extracellular signals of the human immune system and can elicit striking treatment responses in patients with autoimmune disease, tissue damage, and cancer. Yet, despite their therapeutic potential, recombinant cytokine-mediated immune responses remain difficult to control as their administration is often systemic, whereas their intended sites of action are localized. To address the challenge of spatially and temporally constraining cytokine signals, we recently devised a strategy whereby recombinant cytokines are reversibly inactivated via chemical modification with photo-labile polymers that respond to visible LED light. Extending this approach to enable both in vivo and multicolor immune activation, here we describe a strategy whereby cytokines appended with heptamethine cyanine-polyethylene glycol are selectively re-activated ex vivo using tissue-penetrating near-infrared (NIR) light. We show that NIR LED light illumination of caged, pro-inflammatory cytokines restores cognate receptor signaling and potentiates the activity of T cell-engager cancer immunotherapies ex vivo. Using combinations of visible- and NIR-responsive cytokines, we further demonstrate multiwavelength optical control of T cell cytolysis ex vivo, as well as the ability to perform Boolean logic using multicolored light and orthogonally photocaged cytokine pairs as inputs and T cell activity as outputs. Together, this work demonstrates a novel approach to control extracellular immune cell signals using light, a strategy that in the future may improve our understanding of and ability to treat cancer and other diseases.

Visible Blue LED Mediated Aqueous Photochlorination of PVC to CPVC: A Shrinking Core Kinetic Model and Experimental Study

The visible blue LED mediated aqueous suspension photochlorination of polyvinyl chloride (PVC) to chlorinated polyvinyl chloride (CPVC) is described. A shrinking core model (SCM) of the photochlorination process is proposed by considering diffusional resistances of chlorine gas at various steps involved in the photochlorination of PVC particles. Diffusion of Cl2 through the outer product layer contributes major resistance to the overall reaction, and this is the rate-controlling step. The proposed SCM model estimated values are in close agreement with the experimental data.

Dual asymmetric centrifugation as a new tool to prepare TiO2/S-g-C3N4 heterojunctions with high photocatalytic performance

This work reports the use of dual asymmetric centrifugation (DAC) for the synthesis of TiO2/S-doped carbon nitride (TiO2/S-g-C3N4) heterojunctions and their performance on rhodamine B (RhB) photodegradation. The optimal TiO2/S-g-C3N4 ratio was determined to be 1.0/0.1 w/w and the XRD, UV-VIS, XPS and FT-IR data confirm the formation of the heterojunction. The TEM analysis indicated TiO2 nanoparticles dispersed on the surface and/or within the interlayer space of the carbonaceous material. TiO2/S-g-C3N4 (1.0/0.1) heterojunction was able to photodegrade 98.9% of RhB in 60 min under a visible LED light, with photocatalytic performance similar or superior to other similar heterojunctions reported in the literature. Radical trapping experiments and VB-XPS spectra indicated that TiO2/S-g-C3N4 (1.0/0.1) acted via the Z-scheme mechanism.

The Effect of Visible Light on the Postharvest Life of Tomatoes (Solanum lycopersicum L.)

Tomatoes (Solanum lycopersicum L.) are widely cultivated and consumed, but ripening should be carried out in controlled storage conditions to extend their shelf life and avoid economic losses. The aim of this study was to investigate the effects of visible artificial light on the ripening and quality of fresh market tomatoes stored at a low temperature and high humidity. The postharvest performance with respect to the ripening of organically grown tomatoes in the Toscano cultivar, with a long storage life, was studied in the presence and the absence of visible LED light. The maturation kinetics of the tomatoes was modeled using the Power Law equation. Results showed that tomatoes stored in the presence of light exhibited an increased respiration rate and a faster preclimacteric phase. Lycopene content, total soluble solids, and maturity index increased in the presence of light. Hence, light increased the postharvest ripening of tomatoes, affecting their shelf life.

G-C3N4 supported Ag/AgCl@MIL-88A MOF based triple composites for highly efficient diuron photodegradation under visible LED light irradiation

In this work, a series of g-C3N4 supported Ag/AgCl doped MIL-88A composites were synthesized and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), UV–vis diffuse reflectance spectroscopy (UV–vis DRS), and photoluminescence spectroscopy (PL). The photocatalytic performances of as-prepared composites were examined by the photodegradation of diuron (DRN), which is used as an herbicide in agriculture. The composites exhibit exceptional visible-light photocatalytic activities for photodegradation of DRN with complete degradation within 60 min in the absence of oxidants. However, in the presence of H2O2 or persulfate, complete degradation of DRN was achieved in 15 min and 30 min, respectively. The photocatalyst also gave very high conversions in water containing dissolved inorganic salts and natural organic matter (NOM). The Ag/AgCl@MIL-88A/g-C3N4 composite retained excellent photocatalytic properties after repeated use. Radical trapping experiments revealed that the most important reactive species in the photodegradation were O2−• and h+. Role of active radicals were discussed via proposed degradation mechanism for the degradation of DRN in the presence of MIL-88A/g-C3N4 and Ag/AgCl@MIL-88A/g-C3N4.

Effect of postharvest visible spectrum LED lighting on quality and bioactive compounds of tomatoes during shelf life

The objective was to evaluate the effect of visible spectrum LED lighting during shelf-life on physicochemical quality and the main bioactive compounds of Kumato® cherry tomatoes. Tomatoes were stored 13 days at 5 °C under white (W), blue (B), blue + red (B + R), green + red (G + R), and green + far-red (G + FR) LED lights. Darkness (D) was used as control. Tomatoes under illumination showed higher weight losses and firmness decreases (30–35%). No chilling injury was observed. B + R lighting increased the carotenoid content by ∼27%, while G + R and G + FR reported an increase ∼30% in phenolics. B and B + R showed the highest increase in the phytochemical biosynthesis (lycopene and naringenin, as main carotenoid and flavonoid found) compared to D and W. Conclusively, illumination with B + R or B during shelf-life is recommended to enhance the main bioactive compounds. G + R and G + FR, also reported to be good elicitors of the phenolics and carotenoids biosynthesis.

Nano cocatalyst–catalytic system for boosting photothermal–photocatalytic water treatment enabled by visible LEDs

Cocatalyst–catalytic system is rationally proposed in photothermal–photocatalytic water treatment.

New functionalized thioxanthone derivatives as type I photoinitiators for polymerization under UV-Vis LEDs

Thioxanthone derivatives, well known as type II photoinitiators, can perform as type I photoinitiators to efficiently induce polymerization under visible LEDs, owing to the advantages of photodecarboxylation reaction and photolysis of oxime-esters.

Bactericidal Effect of 405-nm LED Light against <i>Aggregatibacter Actinomycetemcomitans</i> Is Due Primarily to Disruption of Respiratory Chain Terminal Members Cytochrome <i>bd</i> Oxidase and Quinol Peroxidase

Irradiation with 405-nm visible violet LED light without additional photosensitizers decreased the viability of the aggressive periodontopathic bacterium Aggregatibacter actinomycetemcomitans. The number of CFU/mL decreased linearly on a logarithm chart versus irradiation time, with a 1-log reduction time of 1.32 min. The antimicrobial photodynamic effect of 405-nm LED light involved inhibition of the activity of membrane-bound cytochrome bd, a terminal quinone: oxygen oxidoreductase, and quinol peroxidase, a terminal quinone:H2O2 oxidoreductase. The 405-nm LED irradiation reduced minus oxidized difference spectrum showed that the 640-nm peak (α-peak of heme d) completely disappeared, and the height of the 556-nm (α-peak of hemes b and c) and Soret band (425 nm; γ-peak of hemes b, c, and d) was reduced to approximately half of the peak heights of non-irradiated controls. Survival of bacteria-injected silkworm larvae was also examined. Fifth-instar silkworm larvae were almost completely killed by approximately 40 h after bacterial injection, but almost all silkworm larvae irradiated with 405-nm LED light (20 mW/cm2 for 5 min, energy density: 6 J/cm2) survived, similar to controls not injected with bacteria, indicating that 405-nm LED light killed the injected bacteria. The bactericidal effect of 405-nm blue-light on A. actinomycetemcomitans is primarily due to disruption of cytochrome bd oxidase and quinol peroxidase of the respiratory chain.

TiO2/Bi2O3/PANI nanocomposite materials for enhanced photocatalytic decontamination of organic pollutants

• TiO 2 /Bi 2 O 3 /PANI nanocomposites were synthesized. • Materials characterized for structural, morphological and optical characteristics. • Nanocomposites employed for RhB and Triclopyr photocatalytic degradation. • Close contact between TiO 2 , Bi 2 O 3 and PANI promotes interfacial charge transfer. • holes are the prominent ROS for the degradation of RhB; holes and O 2 ∙ - for TC. In this present work, TiO 2 /Bi 2 O 3 /PANI nanocomposites were synthesized and employed as photocatalyst for the degradation of organic pollutants i.e. Rhodamine B dye and Triclopyr pesticides. TiO 2 /Bi 2 O 3 /PANI nanocomposites were characterized with the help of various advanced instrumentation techniques including X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), photoluminescence (PL), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analysis. The absorption in the visible wavelength region (λ > 400 nm) increased with increasing PANI amount accompanied by π → π ∗ transition. The close contact between TiO 2 , Bi 2 O 3 and PANI promotes the interfacial charge transfer and significantly improved photocatalytic performance under the irradiation of visible LEDs. Among the prepared nanocomposites, the sample containing 5 wt. % PANI of TiO 2 /Bi 2 O 3 (TB(15)) was found to be most efficient photocatalyst and stable even after four cyclic runs for the degradation of organic pollutants. TB(15)/PANI(5) exhibited the lowest PL intensity, indicating the minimum reunion in the photoproduced electron-hole pairs, which was favorable to improve the efficiency of the photocatalyst for the removal of organic pollutants. The photodegradation rate of RhB and TC using TB(15)/PANI(5) photocatalyst reached to 99.6 % in 50 minutes and 76.1 % in 120 minutes under the visible LEDs irradiation respectively. Kinetics analysis of photocatalytic reaction obeys the pseudo first-order kinetic model with respect to concentration of organic pollutants with a regression coefficient value in the range of 0.941-0.999. The trapping experiments confirmed that holes are prominent species for the degradation of RhB, and holes and superoxide anion radical for photocatalytic degradation of TC. Finally, the mechanism of photocatalytic degradation using TiO 2 /Bi 2 O 3 /PANI nanocomposite was also proposed.

Simultaneous Wireless Transmission Based on Visible LED of On-Off-Keying and Discrete Multitone Signal Using Sparse Compressive Sampling and Derivative-Subtractive Sampling

Simultaneous Wireless Transmission Based on Visible LED of On-Off-Keying and Discrete Multitone Signal Using Sparse Compressive Sampling and Derivative-Subtractive Sampling