Low-power Visible Light Research Articles

Enhanced Gas-Phase pollutant removal using Pt nanoparticle-modified exfoliated carbon nitride photocatalysts under UV and visible light

Platinum nanoparticles (Pt NPs) have been prepared by the organometallic approach on the surface of exfoliated graphitic carbon nitride (exf-g-CN) with different metal loadings. Multi-technique characterisation shows a good dispersion of Pt NPs on the surface of exf-g-CN with a narrow size distribution between 1.7–2.2 nm and a BET area of about 120 m2/g. The Pt NPs are mainly composed of platinum metal with a minor contribution of oxidic surface species. The effect of UV-A and Vis light of different wavelengths on the photocatalytic performance is investigated. The as-prepared hybrid materials show excellent photocatalytic activity for the decontamination of air from volatile organic compounds (VOCs, in particular trichloroethylene, C2HCl3) under low power visible light irradiation. The conversion value reaches a maximum close to 85% at 405 nm Vis light for 0.5 wt% Pt loading. At this level of Pt content, electron and hole recombination rates are suppressed according to photoluminescence analysis. Photonic efficiencies of around 0.3% were achieved under Vis light. The optimised material shows high stability from 2,500 min of operation. XPS analysis suggests the crucial role of Pt/Pt2+ and chlorine species detected on used samples in the reaction rate and stability of the material.

Additive manufacturing of porous ceramic structures by indirect powder bed fusion with laser beam using a novel polyamide/alumina-based feedstock

Porous alumina structures were developed by indirect Powder Bed Fusion with Laser Beam (PBF-LB), employing a novel feedstock (composite granules) based on alumina (Al2O3), bio-renewable polyamide 612 (PA612), and micron-sized graphite (MG) using a commercial PBF-LB machine that operates with a low-power visible light diode laser. Regular and slightly rounded composite granules were prepared via the thermally induced phase separation (TIPS) process in dimethyl sulfoxide (DMSO) using 0.05 vol% of PA612, 40/60 vol% of Al2O3/PA612 and 6.25 wt% of MG, and then characterized via density measurements, Hausner's ratio, SEM-EDS, particle size distribution, Raman spectroscopy, DSC, and TGA. Experimental conditions to be used in the PBF-LB process were determined in order to obtain high-quality green porous structures with a controlled geometry. After the heating treatments, sintered components with good structural integrity, a high open porosity associated with interconnected pores in the struts, and a ceramic matrix with microsized-equiaxial grains were obtained. The evaluation of the mechanical properties was performed by diametral compression testing. In order to improve these properties, a vacuum infiltration process involving a low-concentration alumina-ethanol suspension was used on pre-sintered discs. As a consequence of the infiltration process, the discs showed improved mechanical properties after sintering without the porosity having been significantly affected.

Crystal violet degradation by visible light-driven AgNP/TiO2 hybrid photocatalyst tracked by SERRS spectroscopy

Dyes are important concerns regarding aquatic environmental contamination given their extensive industrial use and the occurrence of highly toxic and carcinogenic effects on the biota. In this work, photodegradation processes of the organic dye crystal violet (CV) by a hybrid plasmonic photocatalyst involving titanium dioxide (TiO2) and silver nanoparticles (AgNP), through irradiation with low-power visible light were studied, and the experiments were tracked by ultraviolet-visible absorption (UV–VIS) and surface-enhanced resonance Raman scattering (SERRS) spectroscopies. Enhanced photocatalytic activity was observed, reaching about 71, 80 and 87 % of CV removal with only 100 minutes of irradiation, depending on the Ag loading used. The high photocatalytic efficiency is further highlighted by the low energy consumption in the process, requiring only ca. 1.46 kW h L-1 in the best reaction condition. Quantum-mechanical calculations were used to the assignment of electronic spectra, as well as to the prediction of frontier molecular orbitals and atomic charges, aiming to propose mechanisms for radical attacks. Such results allow suggesting degradation processes involved mainly N-demethylation and bond breaking of central carbon. The presence of CV protonated species was also supported through Density Functional Theory (DFT) investigation. The integration of theoretical and experimental results allows proposing the formation of pararosaniline, phenol and benzophenone derivatives, which may have highest ecotoxicity than the original contaminant, outstanding the remarkable relevance of SERRS spectroscopy in monitoring such recalcitrant substances.

Enhanced photocatalytic activity of TiO2 anatase nanoparticles modified with malonic acid under reduced power visible light: Synthesis, characterization and degradation of tetracycline and chlorophenol

Charge transfer complexes (CTCs) between nano-TiO2 and chelating ligands are among the most promising alternatives for photocatalytic applications, such as environmental remediation. However, the development of CTCs based on nano-TiO2 modified with malonic acid (MoA) has not yet been investigated in detail.In this study, TiO2-MoA CTCs, synthesized via sol–gel route, were tested for tetracycline (antibiotic) and chlorophenol (pesticide) photocatalytic degradation with, and without, scavengers of reactive oxidizing species, under low-power visible light (26 W). The TiO2-MoA CTCs were thoroughly characterized. TGA-MS and FTIR analyses revealed malonic acid bonded to the TiO2 surface, while the PL and EPR analyses proved the generation of extrinsic oxygen vacancies due to calcination process of the xerogels.CTCs based on nano-TiO2 strongly bonded to malonic acid, and highly sensitive to visible light, have been synthesized by sol–gel method, followed by calcination at 270 °C in air. The as-prepared CTCs showed very high surface areas (between 180.9 and 323.9 m2.g−1), presence of F+ color centers in the calcined CTCs due to extrinsic oxygen vacancies and high photocatalytic activity, degrading approximately 100 % of the tetracycline after 6 h. In addition, it has been proved that the TiO2-MoA CTCs are efficient sources of •O2– radicals.The findings of this research can be generalized to the synthesis, via sol–gel, of other CTCs between TiO2 and bidentate ligands, such as dicarboxylic acids, and explored for air purification and hydrogen production.

Azo dye polyelectrolyte multilayer films reversibly re-soluble with visible light

Polymeric multilayer films were prepared using a layer-by-layer (LBL) technique on glass surfaces, by repeated and sequential dipping into dilute aqueous solutions of various combinations of water-soluble polyanions (polyacrylic acid (PAA)), polycations (polyallylamine hydrochloride (PAH) or chitosan (CS)), with bi-functional water-soluble cationic azo dyes bismark brown R bismarck brown red or bismark brown Y (BBY), or anionic azo dyes allura red (ALR) or amaranth (AMA), as ionic cross-linkers. The electrostatically-assembled ionically-paired films showed good long-term stability to dissolution, with no re-solubility in water. However, upon exposure to low power visible light under running water, the films photo-disassembled back to their water-soluble constituent components, via structural photo-isomerization of the azo ionic crosslinkers. The relative rate of the disassembly (RRD) of the films was established using UV-Vis spectroscopy, demonstrating that these assemblies can in principle represent fully recyclable, environmentally structurally degradable materials triggered by exposure to sunlight, with full recovery of starting components. A density functional theory treatment of the allura red azo dye rationalizes the geometrical isomerization mechanism of the photo-disassembly and provides insight into the energetics of the optically-induced structural changes that trigger the disassembly and recovery.

Rapid photocatalytic degradation of organic pollutants by Al3+ doped CuO powders under low power visible light and natural sunlight

The photocatalytic degradation of organic pollutants is a promising approach to deal with dye industry wastes released into water bodies. However rapid, inexpensive, and low power visible light photocatalytic degradation of water pollutants is challenging. This study tries to address these constraints by using inexpensive doped CuO Powders under low-power visible household LED light. Also, direct illumination of sunlight to achieve better photocatalytic degradation, reducing device and operational costs. Further, photocatalytic degradation is enhanced by doping of Al3+ in CuO. Under several optimized conditions, rapid and almost complete degradation of three different dyes, Methylene Blue (MB), Rhodamine B (RhB), and Methyl Orange (MO) were achieved within 6 min of light irradiation under household LED and within 30 min of direct irradiation of sunlight. Even after five times of repeated use of the catalyst, no significant decrease in the photocatalytic activity was observed indicating its stability and sustainability.

Visible-light-driven Au/PCN-224/Cu(II) modified fabric with enhanced photocatalytic antibacterial and degradation activity and mechanism insight

The development of novel photocatalytic platform for efficient water purification and sterilization is of utmost importance due to the significant threat of chronic diseases resulting from water pollution and bacterial contamination. Herein, a high-efficiency, easy-recyclable, and environment-friendly photocatalytic fabric was developed as a water disinfection and organic pollutant degradation platform. In which, microamounts of Au nanoparticles (2 wt%) and Cu(II) clusters (2.5 wt%) co-decorated porphyrinic MOF (Au/PCN-224/Cu(II)) coating was applied as photocatalytic surface, and flexible cotton fabric served as stable support. Au/PCN-224/Cu(II) composite photocatalyst was prepared via a facile photo-deposition procedure followed by impregnation method, and further immobilized onto polydopamine (PDA) pre-treated cotton fabric through catechol-amine reaction. The fabricated photocatalytic platform exhibited excellent ability to generate reactive oxygen species (ROS) by multiple routes under low-power visible light irradiation, and achieved efficient photodisinfection effects for causative organism including Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) without the obvious leakage of metal ions from the potocatalyst during the reaction. Additionally, the reaction rate constant for organic dye MB photodegradation achieved by Au/PCN-224/Cu(II)@Fabric was 3.73 times higher than that of PCN-224@Fabric, and the degradation intermediates analysis was also conducted. The band alignments of PCN-224, Au/PCN-224, Au/PCN-224/Cu(II) photocatalysts were determined, and the charge transfer mechanism within Au/PCN-224/Cu(II) photocatalyst was elucidated through the utilization of DRS, Mott − Schottky, ESR, EIS, and photocurrent analyses. It is suggested that the deposition of Au and doping of Cu(II) both with small amounts enhanced the light absorption capacity, and also improved the charge separation ability through the surface plasmon resonance (SPR) effect and interfacial electron transfer (IFCT) mechanism. Moreover, Au SPR and Cu doping exhibited a substantial enhancement in photothermal conversion effect, thereby synergistically reinforcing the sterilization performance. This work provides an approach for the development of effective photocatalytic platform based on porphyrinic MOFs combined with trace metal co-catalysts in the application of water disinfection and purification.

Three-in-One: Dye-Volatile Cocrystals Exhibiting Intensity-Dependent Photochromic, Photomechanical, and Photocarving Response.

Cocrystallization of a cis-azobenzene dye with volatile molecules, such as pyrazine and dioxane, leads to materials that exhibit at least three different light-intensity-dependent responses upon irradiation with low-power visible light. The halogen-bond-driven assembly of the dye cis-(p-iodoperfluorophenyl)azobenzene with volatile halogen bond acceptors produces cocrystals whose light-induced behavior varies significantly depending on the intensity of the light applied. Low-intensity (<1 mW·cm-2) light irradiation leads to a color change associated with low levels of cis → trans isomerization. Irradiation at higher intensities (150 mW·mm-2) produces photomechanical bending, caused by more extensive isomerization of the dye. At still higher irradiation intensities (2.25 W·mm-2) the cocrystals undergo cold photocarving; i.e., they can be cut and written on with micrometer precision using laser light without a major thermal effect. Real-time Raman spectroscopy shows that this novel photochemical behavior differs from what would be expected from thermal energy input alone. Overall, this work introduces a rational blueprint, based on supramolecular chemistry in the solid state, for new types of crystalline light-responsive materials, which not only respond to being exposed to light but also change their response based on the light intensity.

Synthetic molecular motor activates drug delivery from polymersomes.

The design of stimuli-responsive systems in nanomedicine arises from the challenges associated with the unsolved needs of current molecular drug delivery. Here, we present a delivery system with high spatiotemporal control and tunable release profiles. The design is based on the combination of an hydrophobic synthetic molecular rotary motor and a PDMS-b-PMOXA diblock copolymer to create a responsive self-assembled system. The successful incorporation and selective activation by low-power visible light (λ = 430 nm, 6.9 mW) allowed to trigger the delivery of a fluorescent dye with high efficiencies (up to 75%). Moreover, we proved the ability to turn on and off the responsive behavior on demand over sequential cycles. Low concentrations of photoresponsive units (down to 1 mol% of molecular motor) are shown to effectively promote release. Our system was also tested under relevant physiological conditions using a lung cancer cell line and the encapsulation of an Food and Drug Administration (FDA)-approved drug. Similar levels of cell viability are observed compared to the free given drug showing the potential of our platform to deliver functional drugs on request with high efficiency. This work provides an important step for the application of synthetic molecular machines in the next generation of smart delivery systems.

Engineering triple internal electric fields in Ag NWs@BaTiO3 composites for ultrasonic-visible-light driven antibacterial activity

Sono-photodynamic antibacterial therapy (SPDAT) is considered to be one of the most effective biomedical treatments, offering both practical flexibility and excellent performance. However, sono-photosensitizers with good biocompatibility, low cytotoxicity, and high antibacterial efficiency under harsh conditions are lacking nowadays. This paper presented attractive Ag NWs@BaTiO3 core–shell composites, which integrates three elements of piezoelectric effect, twin crystals, and heterojunction to engineer triple internal electric fields. Continuous co-disturbances induced by ultrasound and light disrupted the electrostatic balance and saturation effects of the triple internal electric field on composites, thereby regulating its own electrical properties and increasing its affinity and adhesion to bacterial cells through electrostatic attraction. Remarkably, the antibacterial efficiency of Ag NWs@BaTiO3 against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) reached 92.5% within 60 min and ∼ 100% within 30 min under low-power visible light irradiation and ultrasonic vibration, respectively. Moreover, the composites also exhibited good biocompatibility and low cytotoxicity. Intrinsically, the constructed triple internal electric fields could effectively extend the charges transfer pathway, accelerating the spatial separation of excited-charges pairs and thereby producing sufficient reactive oxygen species (ROSs) to boost the synergistic piezo-photocatalysis activity. Finally, we proposed a combined piezo-photocatalysis mechanism of energy band bending theory and screening charge effect under triple internal electric fields.

Durable photocatalytic membrane of PAN/TiO2/CNT for methylene blue removal through a cross-flow membrane reactor

ABSTRACT PAN/TiO2/CNT and PAN/TiO2/CNT-PVA composite nanofibrous membranes with photocatalytic activity were successfully synthesized using electrospinning. The effect of CNT concentration and PVA coating on the membrane surface toward the membrane performances was investigated. TiO2 anatase phase was exist on the respective membranes. SEM morphological investigation revealed the random orientation of the nanofibers with beads decorated in each strand. The PAN/TiO2/CNT composite nanofiber membrane exhibited high performance for the removal of cationic organic dye methylene blue (MB) in a cross-flow photocatalytic membrane reactor under low power visible light of LED lamp (14.5 W) and a constant pollutant flow rate of 0.21 L/min. The presence of TiO2/CNT photocatalyst was proven to prolong the lifetime of the photocatalytic membrane and retard membrane fouling to the maximum extent. PAN/TiO2/CNT membrane has displayed 100% MB rejection for the first 8 h of operation. Both, PAN/TiO2/CNT and PAN/TiO2/CNT-PVA maintained their membrane performances and did not show major flux decline even after five recycling uses. The incorporation of TiO2/CNTs on PAN nanofibers has resulted in a durable photocatalytic membrane for the effective removal of dye waste using a cross-flow membrane reactor.

Photocatalytic degradation of phenol under visible light using electrospun Ag/TiO2 as a 2D nano-powder: Optimizing calcination temperature and promoter content

• Electrospun Ag/TiO 2 nanofiber (2D nano powder) was tested for phenol degradation. • Calcination temperature of 450℃ is the best one with a Rutile fraction of 23.8%. • An optimum value of thr Ag promoter is 5% in these photocatalytic experiments. • Adding 5% Ag to the TiO 2 nanofiber decrease the band gap from 3.27 to 3.03 nm. • Nanofibers as 2D nano-powder can be separated easily because of micrometric length. Phenol is one of the toxic materials, and releasing it into the water can be quite irritating and harmful to the health of organisms and the environment. In this study, phenol degradation was investigated using Ag/TiO 2 electrospun nanofiber photocatalyst as a 2D nano-powder. Nanofibers have 2 dimensions in the range of nanometers but their length of them are in the range of micrometers. The micrometer size is an advantage for the separation of the photocatalyst from the suspension. Though, nanometer size is suitable for increasing the available surface for the light. The effect of silver content (0.5–15%) as a promoter and the calcination temperature (300–900 °C) was studied on the degradation of phenol over the synthesized nanofiber-based photocatalyst. Photocatalysts were characterized by various techniques including N 2 -physisorption, XRD, SEM, EDX, TEM, FTIR, TGA/DSC, TPO, and DRS. The results have indicated that 5% of Ag content on TiO 2 is the best promoter loading in these experiments. Furthermore, the calcination temperature of 450 °C is found to be the optimum value with an optimum rutile fraction of 23.8%. Maximum phenol degradation was 82.65% at pH = 7, catalyst dosage of 1.5 g/L, and phenol concentration of 5 ppm under a low power visible light (18 W).

Structure and functions of Aggregation-Induced Emission-Photosensitizers in anticancer and antimicrobial theranostics.

Photosensitizers with Aggregation-Induced Emission (AIE) can allow the efficient light-mediated generation of Reactive Oxygen Species (ROS) based on their complex molecular structure, while interacting with living cells. They achieve better tissue targeting and allow penetration of different wavelengths of Ultraviolet-Visible-Infrared irradiation. Not surprisingly, they are useful for fluorescence image-guided Photodynamic Therapy (PDT) against cancers of diverse origin. AIE-photosensitizers can also function as broad spectrum antimicrobials, capable of destroying the outer wall of microbes such as bacteria or fungi without the issues of drug resistance, and can also bind to viruses and deactivate them. Often, they exhibit poor solubility and cellular toxicity, which compromise their theranostic efficacy. This could be circumvented by using suitable nanomaterials for improved biological compatibility and cellular targeting. Such dual-function AIE-photosensitizers nanoparticles show unparalleled precision for image-guided detection of tumors as well as generation of ROS for targeted PDT in living systems, even while using low power visible light. In short, the development of AIE-photosensitizer nanoparticles could be a better solution for light-mediated destruction of unwanted eukaryotic cells and selective elimination of prokaryotic pathogens, although, there is a dearth of pre-clinical and clinical data in the literature.

Magnetic MgFe2O4/MIL-88A catalyst for photo-Fenton sulfamethoxazole decomposition under visible light

Series magnetic MgFe2O4/MIL-88A catalysts (MFxMy) were fabricated by a simple ball-milling method, which were applied to degrade sulfamethoxazole (SMX) antibiotic via photo-Fenton process under low power visible light. The influences of initial pH, H2O2 concentration, and co-existing inorganic anions on SMX degradation were explored. The results revealed that the optimal MgFe2O4/MIL-88A (MF140M60) demonstrated excellent photo-Fenton catalysis activity, in which ca. 99.8% of SMX could be degraded within 20.0 min. The outstanding catalytic activity of MgFe2O4/MIL-88A (MF140M60) can be ascribed to the effective transfer of charge carriers between MgFe2O4 and MIL-88A. As well, the optimal MgFe2O4/MIL-88A (MF140M60) catalyst possessed good stability and recyclability.

BUC-21 coated by NHPI-sensitized ST-01 for enhancing photocatalytic bisphenol A decomposition under low-power visible-light

BUC-21 coated by NHPI-sensitized ST-01 for enhancing photocatalytic bisphenol A decomposition under low-power visible-light

Cold photo-carving of halogen-bonded co-crystals of a dye and a volatile co-former using visible light.

The formation of co-crystals by the assembly of molecules with complementary molecular recognition functionalities is a popular strategy to design or improve a range of solid-state properties, including those relevant for pharmaceuticals, photo- or thermoresponsive materials and organic electronics. Here, we report halogen-bonded co-crystals of a fluorinated azobenzene derivative with a volatile component-either dioxane or pyrazine-that can be cut, carved or engraved with low-power visible light. This cold photo-carving process is enabled by the co-crystallization of a light-absorbing azo dye with a volatile component, which gives rise to materials that can be selectively disassembled with micrometre precision using low-power, non-burning laser irradiation or a commercial confocal microscope. The ability to shape co-crystals in three dimensions using laser powers of 0.5-20 mW-substantially lower than those used for metals, ceramics or polymers-is rationalized by photo-carving that targets the disruption of weak supramolecular interactions, rather than the covalent bonds or ionic structures targeted by conventional laser beam or focused ion beam machining processes.

Intermixed Time-Dependent Self-Focusing and Defocusing Nonlinearities in Polymer Solutions.

Low-power visible light can lead to spectacular nonlinear effects in soft-matter systems. The propagation of visible light through transparent solutions of certain polymers can experience either self-focusing or defocusing nonlinearity, depending on the solvent. We show how the self-focusing and defocusing responses can be captured by a nonlinear propagation model using local spatial and time-integrating responses. We realize a remarkable pattern formation in ternary solutions and model it assuming a linear combination of the self-focusing and defocusing nonlinearities in the constituent solvents. This versatile response of solutions to light irradiation may introduce a new approach for self-written waveguides and patterns.

TiO2-Acetylacetone as an Efficient Source of Superoxide Radicals under Reduced Power Visible Light: Photocatalytic Degradation of Chlorophenol and Tetracycline

Visible light-sensitive TiO2-based nanomaterials are widely investigated for photocatalytic applications under high power (≥300 W) UV and visible light. The formation of charge transfer complexes (CTCs) between bidentate ligands and nanocrystalline TiO2 promotes visible light absorption and constitutes a promising alternative for environmental remediation under reduced visible light power. However, the efficiency of photodegradation, the volatilization profile of bidentates, and the role of reactive oxidizing species (ROS) are not fully understood. In this study, thermogravimetric analyses coupled with mass spectroscopy (TGA-MS) were performed on TiO2-Acetylacetone (ACAC) CTC. TiO2-ACAC CTC calcined at 300 °C (TiO2-A300) was applied for the photocatalytic degradation of chlorophenol (4-CP) and tetracycline (TC) under low power visible light (26 W). Furthermore, the ROS scavengers isopropanol and benzoquinone were added for studying the photocatalytic role of •OH and •O2− radicals. The TGA-MS showed the release of ACAC fragments, such as ethyl ions and acetone, in the range between 150 °C and 265 °C, while between 300 °C and 450 °C only CO2 and H2O were released during oxidation of ACAC. The photocatalytic abatement of tetracycline (68.6%), performed by TiO2-A300, was ~two times higher than that observed for chlorophenol (31.3%) after 6 h, indicating a distinct participation of ROS in the degradation of these pollutants. The addition of the ROS scavenger revealed •O2− radicals as primarily responsible for the high efficiency of TiO2-ACAC CTC under reduced visible light. On the other hand, the •OH radicals are not efficiently generated in the CTC. Therefore, the development of heterostructures based on TiO2-ACAC CTC can increase the generation of ROS through coupling with semiconductors capable of generating •OH under visible light.

Switcheroo yields photoactivatable dyes

A simple new method generates fluorescent dyes of many colors that can be activated by visible light. The approach provides a new set of tools for visualizing how proteins and other molecules behave in living cells without damaging tissue (J. Am. Chem. Soc. 2019, DOI: 10.1021/jacs.9b06237). Most existing photoactivatable dyes are bulky, so they can’t label smaller molecules with good resolution. And they need to be activated with high-energy laser light, which damages DNA and mitochondria, causes proteins to cross-link, and can bleach the dyes’ fluorescence. Broadening the palette of dyes that can be triggered with low-power visible light would be a boon for biological imaging in living tissue. In the new study, Han Xiao of Rice University and his team used a thionating agent called Lawesson’s reagent to switch an oxygen atom in an ordinary, nonphotoactivatable fluorescent dye to sulfur, essentially suppressing the glow. Unleashing the fluorescence simply involves

Preliminary design and characterization of a low-cost and low-power visible light positioning system.

Designs and results for a low-power and economical fingerprint visible light positioning (VLP) system are discussed in this paper. A system using four white LEDs and one photodiode was deployed. The LEDs are independently controlled and modulated by individual transmitter circuits, removing the requirement for a large, expensive signal generator. The receiver circuit filters and converts the received signal to DC, allowing a simple microcontroller to save the received signal. We propose the creation of a fingerprint database by recording signal data, fitting a two-dimensional Gaussian distribution to the data, and then generating the fingerprint database for all positions in the evaluation system. System positioning accuracy of 13.44+/-0.36 mm was observed, corresponding to a relative error of 2.8% with respect to the system dimensions. This result presents an improvement on positioning accuracy for fingerprint positioning VLP systems, which build their own transmitters.