Low Intensity Visible Light Research Articles

Multiwavelength-Steerable Visible-Light-Driven Magnetic CoO-TiO2 Microswimmers.

While current light-driven microswimmers require high-intensity light, UV light, or toxic fuels to propel them, powering them with low-intensity UV-free visible light without fuels is essential to enable their potential high-impact applications. Therefore, in this study, a new material for light-driven microswimmers in the form of CoO is introduced. Janus CoO–TiO2 microswimmers powered with low-intensity, UV-free visible light inside water without using any toxic fuels like H2O2 is proposed. The microswimmers show propulsion under full spectrum of visible light with 17 times lower intensity than the mean solar intensity. They propel by breaking down water into oxygen and oxide radicals, which enables their potential applications for photocatalysis and drug delivery. The microswimmers are multiwavelength responsive, from the ultraviolet to the infrared region. The direction of swimming changes with the change in the illumination from the visible to UV light. In addition to being responsive, they are wavelength steerable and exhibit inherent magnetic properties enabling magnetic steering control of the CoO–TiO2 microswimmers. Thus, these microswimmers, which are propelled under low-intensity visible light, have direction-changing capability using light of different wavelengths, and have steering control capability by external magnetic fields, could be used in future potential applications, such as active and local cargo delivery, active photocatalysis, and hydrogen evolution.

Formation of an amorphous carbon nitride/titania composite for photocatalytic degradation of RR4 dye

A composite of amorphous carbon nitride and titanium dioxide (a-C3N4/TiO2) has been successfully synthesized using urea and P25-TiO2 under microwave irradiation. The characterizations suggested that the carbon nitride component of the a-C3N4/TiO2 composite prepared sample is the best described as amorphous like structure containing carbonyl and amine functionality. This amorphous carbon nitrite (a-C3N4) is coated on TiO2 surface with 2.5–3.9 nm of thin thickness layer detected by HRTEM. The low bandgap energy of a-C3N4 in a-C3N4/TiO2 induce this amorphous acted as electron injector. The a-C3N4/TiO2 provide a lower electron-hole recombination as compared with P25-TiO2 base PL intensity. The photocatalytic activities of a-C3N4/TiO2 and P25-TiO2 were compared for the photodegradation of the dye reactive red 4 (RR4) under low intensity visible light irradiation source (273 W m−2). The photocatalytic degradation of RR4 for a-C3N4/TiO2 was degrade completely within 60 min under visible light irradiation, approximately 5.3 times faster than P25-TiO2. This almost equivalent to their electron-hole recombination rate based on PL intensity. The hybridization of these two semiconductors have shown some improvement photocatalytic activity under visible light irradiation that influenced from the low bandgap energy of a-C3N4, which can act as an electron injector and electron hole recombination inhibitor.

Role of Photodynamic Therapy in Endodontics―A Review

The irrigants used commonly do not always eradicate the entire microbial flora in infected root canals. Thus in quest other strategies, such as photodynamic therapy (PDT) have been developed. The word photodynamic means the applications of the dynamics of photons of light on the biological molecules. German physician Friedreich Mayer performed the first study, which was first called as photo-radiation therapy with porphyrins (1913) in humans. Photoactivated disinfection is based primarly on the interaction of a photosensitive antibacterial agent and a light source which uses a nontoxic dye named photosensitizer (PS) and lowintensity visible light. In the presence of oxygen, these combine to produce some cytotoxic species. The PS molecules attach to the bacteria membrane. Irradiation with a specific wavelength of the light may result in the production of singlet oxygen, resulting in rupture of the microbial cell wall. There are several applications for PDT in dentistry.. Photodynamic therapy has also been used to disinfect caries dentin before the restoration, disinfecting oral tissues before or during surgical procedures, treating denture stomatitis, and treating oral candidiasis in immunocompromised patients. Photodynamic therapy can also be used in combination with mechanical instrumentation and chemical antimicrobial agents, such as sodium hypochlorite.

Photocatalytic indoor/outdoor air treatment and bacterial inactivation on CuxO/TiO2 prepared by HiPIMS on polyester cloth under low intensity visible light

In this study, photoactive CuxO/TiO2 coatings were prepared using magnetron sputtering operated at different powers and modes (Direct-current magnetron sputtering and High Power Impulse magnetron sputtering). Indoor/outdoor air pollutions (Volatile Organic Compounds, VOCs) degradation have been dramatically reduced on sputtered CuxO/TiO2 on polyester (PES) cloth under low intensity visible light. The Low intensity visible light was used to irradiate the sputtered photocatalysts, which degraded various VOC molecules concomitant with a bacterial inactivation ability. The VOC removal kinetics were studied in the dark and under visible light as a function of the deposition time and applied peak currents during the coating by HiPIMS. High concentrations of chloroform and butyraldehyde were shown to be degraded (90% and 85%, respectively) on CuxO/TiO2-PES fabrics under daylight irradiation. The repetitive reuse of the sputtered coatings was also investigated showing the long operational lifetime of the prepared fabrics. The deposition rates of Ti and Cu atoms and their atomic distribution along the sputtered film have been investigated by Transmission Electronic Microscopy (TEM). Redox catalysis was shown to happen within the VOC degradation time as detected by X-ray Photoelectron Spectroscopy (XPS). Deconvolution of the Cu2p3/2 peak in the CuxO/TiO2 on PES samples showed changes in the Cu2O and CuO within the VOCs degradation and the bacterial inactivation. The interfacial charge transfer (IFCT) between CuxO induced under light leading to VOCs oxidation path seemed to require a low photons energy and were able to oxidize the pollutants even at high concentrations. The mechanisms involving the VOCs degradation on CuxO/TiO2 catalysts are suggested in which the holes generated by Cu2O transfer to TiO2 in the TiO2(n)/CuxO(p) in the hetero-junction. This transfer is favored by the electrostatic interaction between both semiconductors. The photo-generated ROS, mainly ⦁OH-radicals were determined by fluorescence method. The possible contribution of the ⦁OH-radicals in the bacterial inactivation on the sputtered CuxO/TiO2 catalysts was discussed. DRS, TEM, contact angle (CA) and XPS were used to characterize the catalyst optical and structural properties.

Visible light-activated degradation of natural organic matter (NOM) using zinc-bismuth oxides-graphitic carbon nitride (ZBO-CN) photocatalyst: Mechanistic insights from EEM-PARAFAC

In this study, the complex degradation behavior of natural organic matter (NOM) was explored using photocatalytic oxidation systems with a novel catalyst based on a hybrid composite of zinc-bismuth oxides and g-C3N4 (ZBO-CN). The photooxidation system demonstrated the effective removal of NOM under low-intensity visible light irradiation, presenting removal rates of 53–74% and 65–88% on the basis of dissolved organic carbon (DOC) and the UV absorption coefficient (UV254), respectively, at 1.5 g/L of the catalyst. The NOM removal showed an increasing trend with a higher ZBO-CN dose. Comparative experiments with the hole and OH radical scavengers revealed that the direct oxidation occurring on the catalyst's surface might be the governing photocatalytic mechanism. Fluorescence excitation emission matrix-parallel factor analysis (EEM-PARAFAC) revealed the individual removal behavior of the different constituents in bulk NOM. Different tendencies towards preferential adsorption and subsequent oxidative removal were found among dissimilar fluorescent components within a bulk terrestrial NOM, following the order of terrestrial humic-like (C1) > humic-like (C2) > microbial humic-like (C3) components. The result suggests the dominant operation of π-π and/or hydrophobic interactions between the NOM and the catalyst. The discriminative removal behavior was more pronounced in visible light versus UV-activated systems, probably due to the incapability of visible light to excite è - h+ pairs of ZnO and the triplet state of NOM. The high photoactivity and structural stability of ZBO-CN under visible light implies its potential for an effective, low-cost and energy-saving treatment technology to selectively remove large sized humic-like substances from water.

Reversible photo-induced doping in WSe2 field effect transistors.

We report a reversible photo-induced doping effect in two-dimensional (2D) tungsten diselenide (WSe2) field effect transistors on hexagonal boron nitride (h-BN) substrates under low-intensity visible light illumination (∼10 nW μm-2). Our experimental results have shown that this reversible doping process is mainly attributed to two types of defects in h-BN substrates. Moreover, the photo-doped WSe2 transistors can be stable for more than one week in a dark environment and maintain the high on/off ratio (108) and carrier mobility, since there are no additional impurities involved during the photo-induced doping process to increase the columbic scattering in the conducting channel. These fundamental studies not only provide an accessible strategy to control the charge doping level and then to achieve a writing/erasing process in 2D transistors, but also shed light on the defect states and interfaces in 2D materials.

Designing visible-light-driven photocatalyst of Ag3PO4/CeO2 for enhanced photocatalytic activity under low light irradiation

In this study the preparation and the evaluation of Ag3PO4/CeO2 composites as visible-light-driven photocatalyst were reported. The composites, with different Ag3PO4:CeO2 molar ratio, were prepared via chemical precipitation and their photocatalytic performance were investigated by photodegradation of methyl orange solution (MO) under low intensity (23 W) visible light irradiation. Characterization analyses showed that the Ag3PO4 particles were irregular spherical-shaped and were well-distributed on the surface of CeO2. The photocatalytic activity of the composite was higher than that of Ag3PO4 and CeO2. The composite with 1:2.5 molar ratio exhibited the highest photocatalytic activity with degradation rate of 0.338 min−1 and 92% degradation efficiency. Besides, the composite can be used up to eight cycles without any regeneration process. Through radical scavenger experiments, the photogenerated holes (h+) and the $$ \cdot {\text{O}}_{2}^{ - }$$ radical were the active species for degradation of MO.

Light-stimulated actuators based on nickel hydroxide-oxyhydroxide.

Light-induced actuators that are self-contained and compact can be used as artificial muscles for microrobotics because their actuation can be induced wirelessly, which reduces the complexity of the device or system. Here, we report a material system, nickel hydroxide-oxyhydroxide, that could actuate because of a volume change stimulated by illumination of visible light of low intensities. The actuating material here exhibited a turbostratic crystal structure capable of intercalating water, and we show that the intercalated water can be rapidly and reversibly desorbed into the environment under visible light of low intensities, resulting in fast actuation driven wirelessly by light. By electroplating the actuating material on passive substrates, we have fabricated film actuators capable of undergoing reversible bending and curling with an intrinsic actuating stress of 5 to 65 megapascals at response rates in the order of tens to hundreds of degrees per second depending on the light intensity, which are comparable to mammalian skeletal muscles. By intentionally electroplating the nickel hydroxide-oxyhydroxide on selected areas of the substrate, a hinged actuator that can lift objects ~100 times the weight of the actuating material is achieved. Other demonstrations show the potential uses in robotic devices, including sunlight-induced actuation, a biomimicked "sensitive plant" with rapid leaf movement, and a light-powered walking bot.

Enhanced Negative Photoconductivity in InAs Nanowire Phototransistors Surface‐Modified with Molecular Monolayers

AbstractNegative photoconductivity (NPC) mechanisms are widely investigated for high‐performance InAs nanowire (NW) phototransistors, where these mechanisms are usually attributed to severe carrier scattering centers, light‐assisted hot electron trapping in the surface oxide, and/or defects induced photogating layer. However, further insights into their photodetecting mechanisms, as well as corresponding performance enhancement of these NW phototransistors, are still very limited. This work reports the NPC behavior in surface‐modified InAs NW phototransistors based on photoexcitation induced majority electron trapping in the bonded sulfur monolayer under optical illumination. In order to enhance hot electron trapping ability of the bonded sulfur layer, aromatic thiolate (ArS−)‐based molecular monolayer with strong electron‐withdrawing group is employed using simple wet chemistry for the surface modification of InAs NW phototransistors. The magnitude of the photoexcitation induced hot electron trapping is increased by the stronger electron‐withdrawing ability of the ArS−‐based molecular monolayer, enabling the hot electrons to be trapped and released more efficiently, resulting in NW phototransistors with good sensitivity, fast photoresponse, and long‐term stability to low intensity visible light. These results confirm the potential of InAs NW phototransistors surface‐passivated with molecular monolayers in the application and realization of high‐sensitive and long‐term stable room temperature nanoscale photodetectors.

Porous NH2-MIL-125 as an efficient nano-platform for drug delivery, imaging, and ROS therapy utilized Low-Intensity Visible light exposure system

Metal-organic frameworks are a novel class of organic-inorganic hybrid polymer with potential applications in bioimaging, drug delivery, and ROS therapy. NH2-MIL-125, which is a titanium-based metal organic framework with a large surface area of 1540m2/g, was synthesized using a hydrothermal method. The material was characterized by powder X-ray diffreaction (PXRD), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM), and N2 isotherm analyses. The size of the polymer was reduced to the nanoscale using a high-frequency sonication process. PEGylation was carried out to improve the stability and bioavailability of the NMOF. The as-synthesized nano-NH2-MIL-125/PEG (NMOF/PEG) exhibited good biocompatibility over the (Cancer) MCF-7 and (Normal) COS-7 cell line. The interaction of NMOF/PEG with the breast cancer cell line (MCF-7) was examined by BIO-TEM analysis and laser confocal imaging. 2′,7′–dichlorofluorescin diacetate (DCFDA) analysis confirmed that NMOF/PEG produced free radicals inside the cancer cell line (MCF-7) upon visible light irradiation. NMOF/PEG absorbed a large amount of DOX (20wt.% of DOX) and showed pH, and photosensitive release. This controlled drug delivery was attributed to the presence of NH2, Ti group in MOF and a hydroxyl group in PEG. This combination of chemo- and ROS-therapy showed excellent efficiency in killing cancer MCF-7 cells.

Fungicidal activity of copper-sputtered flexible surfaces under dark and actinic light against azole-resistant Candida albicans and Candida glabrata

Candida spp. are able to survive on hospital surfaces and causes healthcare-associated infections (HCAIs). Since surface cleaning and disinfecting interventions are not totally effective to eliminate Candida spp., new approaches should be devised. Copper (Cu) has widely recognized antifungal activity and the use of Cu-sputtered surfaces has recently been proposed to curb the spread of HCAIs. Moreover, the activity of Cu under the action of actinic light remains underexplored. We investigated the antifungal activity of Cu-sputtered polyester surfaces (Cu-PES) against azole-resistant Candida albicans and Candida glabrata under dark and low intensity visible light irradiation (4.65mW/cm2). The surface properties of Cu-PES photocatalysts were characterized by diffuse reflectance spectroscopy (DRS) and X-ray fluorescence (XRF). Under dark, Cu-PES showed a fungicidal activity (≥3log10CFU reduction of the initial inoculum) against both C. albicans DSY296 and C. glabrata DSY565 leading to a reduction of the starting inoculum of 3.1 and 3.0log10CFU, respectively, within 60min of exposure. Under low intensity visible light irradiation, Cu-PES exhibited an accelerated fungicidal activity against both strains with a reduction of 3.0 and 3.4log10CFU, respectively, within 30min of exposure. This effect was likely due to the semiconductor Cu2O/CuO charge separation. The decrease in cell viability of the two Candida strains under dark and light conditions correlated with the progressive loss of membrane integrity. These results indicate that Cu-PES represent a promising strategy for decreasing the colonization of surfaces by yeasts and that actinic light can improve its self-disinfecting activity.

Efficient photodegradation of chlorophenols by BiOBr/NaBiO3 heterojunctioned composites under visible light

Forming heterojunctioned composites is an effective way to develop visible-light-driven photocatalysts. A series of BiOBr/NaBiO3 composites were synthesized by surface transformation of NaBiO3 with hydrobromic acid. Commensurate planes of BiOBr and NaBiO3 enabled the formation of a closely bound interface. Composites with <20wt.% BiOBr exhibited excellent photocatalytic activity towards the degradation of chlorophenols under low intensity visible light (λ>400nm). The best photocatalyst was 9% BiOBr/NaBiO3 with a quantum yield of 0.365. No photocorrosion was observed after three cycles. Using radical scavengers and inert atmosphere, holes, superoxide and hydroxyl radicals were found to be involved in the photoactivity of the BiOBr/NaBiO3 composite. Hydroxylated and open-ring diacid molecules were identified as intermediates in the mineralization of 4-chlorophenol.

RAFT-mediated, visible light-initiated single unit monomer insertion and its application in the synthesis of sequence-defined polymers

In this communication, we report a catalyst-free methodology for single unit monomer insertion (SUMI) into reversible addition–fragmentation chain transfer (RAFT) agents initiated by low intensity visible light.

Effect of light and oxygen on repetitive bacterial inactivation on uniform, adhesive, robust and stable Cu-polyester surfaces

AbstractThis study reports new findings on the sputtered Cu-polyester (Cu-PES) bacterial inactivation under low intensity visible light (λ &gt;400 nm). Cu-PES samples sputtered for 160 s led to the complete inactivation of

Rhinophototherapy in persistent allergic rhinitis

Previous published results have revealed that Rhinolight® intranasal phototherapy is safe and effective in intermittent allergic rhinitis. The present objective was to assess whether phototherapy is also safe and effective in persistent allergic rhinitis. Thirty-four patients with persistent allergic rhinitis were randomized into two groups; twenty-five subjects completed the study. The Rhinolight® group was treated with a combination of UV-B, UV-A, and high-intensity visible light, while the placebo group received low-intensity visible white light intranasal phototherapy on a total of 13 occasions in 6weeks. The assessment was based on the diary of symptoms, nasal inspiratory peak flow, quantitative smell threshold, mucociliary transport function, and ICAM-1 expression of the epithelial cells. All nasal symptom scores and nasal inspiratory peak flow measurements improved significantly in the Rhinolight® group relative to the placebo group and this finding persisted after 4weeks of follow-up. The smell and mucociliary functions did not change significantly in either group. The number of ICAM-1 positive cells decreased non-significantly in the Rhinolight® group. No severe side-effects were reported during the treatment period. These results suggest that Rhinolight® treatment is safe and effective in persistent allergic rhinitis.

Organic Electronics: An El Dorado in the Quest of New Photocatalysts for Polymerization Reactions.

Photoinitiated polymerization has been the subject of continued research efforts due to the numerous applications in which this polymerization technique is involved (coatings, inks, adhesives, optoelectronic, laser imaging, stereolithography, nanotechnology, etc.). More recently, photopolymerization has received renewed interest due to the emergence of 3D-printing technologies. However, despite current academic and industrial interest in photopolymerization methodologies, a major limitation lies in the slow rates of photopolymerization. The development of new photoinitiating systems aimed at addressing this limitation is an active area of research. Photopolymerization occurs through the exposure of a curable formulation to light, generating radical and/or cationic species to initiate polymerization. At present, photopolymerization is facing numerous challenges related to safety, economic and ecological concerns. Furthermore, practical considerations such as the curing depth and the competition for light absorption between the chromophores and other species in the formulation are key parameters drastically affecting the photopolymerization process. To address these issues, photoinitiating systems operating under low intensity visible light irradiation, in the absence of solvents are highly sought after. In this context, the use of photoredox catalysis can be highly advantageous; that is, photoredox catalysts can provide high reactivities with low catalyst loading, permitting access to high performance photoinitiating systems. However, to act as efficient photoredox catalysts, specific criteria have to be fulfilled. A strong absorption over the visible range, an ability to easily oxidize or reduce as well as sufficient photochemical stability are basic prerequisites to make these molecules desirable candidates for photoredox catalysis. Considering the similarity of requirements between organic electronics and photopolymerization, numerous materials initially designed for applications in organic electronics have been revisited in the context of photopolymerization. Organic electronics is a branch of electronics and materials science focusing on the development of semiconductors devoted to three main research fields; organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs), and organic solar cells (OSCs). The contribution of organic electronics to the field of electronics is important as it paves the way toward cheaper, lighter, and more energy efficient devices. In the present context of photopolymerization, materials that were investigated as photocatalysts were indifferently organic semiconductors used for transistors, charge-transport materials, and light-emitting materials used in electroluminescent devices or conjugated polymers and small molecule dyes for solar cells. In this Account, we summarize our latest developments in elaborating on photocatalytic systems based on these new classes of compounds. Through an in-depth understanding of the parameters governing their reactivities and our efforts to incorporate these materials into photoinitiating systems, we provide new knowledge and a valuable insight for future prospects.

Highlights from Recent Cancer Literature

Highlights from Recent Cancer Literature

Light-Induced Mid-Infrared Emission of Liquid Carbon Tetrachloride and Benzene

Light-induced infrared emission spectroscopy (LIRES) is a novel technique that permits to receive high-quality spectra in the mid-infrared region. Low-intensity visible light connected to a highly sensitive FTIR spectrometer is more advantageous for studying any samples, including biological samples without any damage. This technique permits obtaining unique information on the molecule structure via vibrational excitation fundamental frequencies, overtones, and combination modes. It also enables a direct observation of vibrational radiation transitions in vibrationally excited molecules as well as the channels of vibration energy redistribution, which is not allowed with any other method. In this work, the LIRES is being tested as a technique for studying of vibrationally-excited molecules of carbon tetrachloride and benzene in the liquid phase. On the other hand, using transparent liquids, we had tried to understand some of the physical phenomena that can drive emission in mid-IR. The characteristics of the infrared emission of both liquid species produced by different wavelength radiation from various types of light systems (100 - watt Xe-lamp and Nd:YAG laser; lambda = 1064 nm (8 mW) and lambda = 532 nm (4 mW)) are presented. We demonstrated that the IR-signal, as well as spectral properties of carbon tetrachloride and benzene, was dependent on the wavelength and power of excitation beam. Results obtained with different light sources show that the visible light produces a nonlinear IR-emission signal in transparent liquids. We believe that the visible light is the source of the nonlinear response and is producing the vibration excitation as well as photostimulated transformations of the molecules possessing the high activity for the nonlinear response.

Enhanced photocatalytic activity of polyaniline through noncovalent functionalization with graphite oxide

Photocatalytic activities of polyaniline-graphite oxide (GO) hybrids are studied by considering the degradation of methylene blue (MB) under UV and visible illumination. Photocatalytic activity of the hybrid P1G2 (aniline to GO ratio 1:2) is significantly high (10 times) compared to pristine polyaniline under UV irradiation. The hybrid also shows 83% photodegradation of MB under low intensity visible light. The enhanced photocatalytic activity of the hybrid can be attributed to the synergetic effect between polyaniline and GO, which promoted the adsorption of the dye and migration efficiency of photogenerated electron–hole pair. A possible mechanism for the hybrid to act as a photocatalyst is proposed based on experimental evidence. The hybrids can be easily regenerated from the suspension and show fairly good cycling stability also. This is the first report on the visible light photodegradation of MB by polyaniline-GO hybrids.

Photochemistry and radical chemistry under low intensity visible light sources: application to photopolymerization reactions.

The search for radical initiators able to work under soft conditions is a great challenge, driven by the fact that the use of safe and cheap light sources is very attractive. In the present paper, a review of some recently reported photoinitiating systems for polymerization under soft conditions is provided. Different approaches based on multi-component systems (e.g., photoredox catalysis) or light harvesting photoinitiators are described and discussed. The chemical mechanisms associated with the production of free radicals usable as initiating species or mediators of cations are reported.