Absence Of UV Light Research Articles

Enhanced tetracycline degradation using UV/Fenton/titanium dioxide (TiO2) hybrid process

TiO2 was synthesized using neem leaf extract as soft bio template and Titanium (IV) isopropoxide (C12H28O4Ti) as a precursor. Morphological properties revealed well crystalline anatase phase of 19.8 nm size for the biotemplated TiO2 (B-TiO2) compared to 24.2 nm of the non-templated TiO2 (N-TiO2). TEM revealed a nano sheet-like structure for the B-TiO2 and it exhibited a larger SBET surface area (35.45 m2/g) and average pore diameter (5.74 nm) compared to the N-TiO2 (19.72 m2/g) and (2.028 nm) respectively. XPS results showed carbon peaks indicating small bio-carbon doping on the lattice of the TiO2, which can promote charge transfer upon light excitation during photocatalyst reactions. The results of the photoluminescence study indicate reduced PL intensity of the B-TiO2 which signifies the suppression of recombination of charge carriers or electron-hole pairs in the B-TiO2. The photocatalytic activity was assessed by the photodegradation of tetracycline (TC: 50 mg/L) under UV irradiation and the B-TiO2 was employed as a photocatalyst. In the absence of UV light, B-TiO2 catalyst slightly removed TC due to limited active species. However, the degradation of TC increases significantly due to the synergetic effect of the UV/Fenton/B-TiO2 hybrid system. Moreover, the biotemplate exposes the surface of the B-TiO2 which permits improved utilization of all surface-active sites. Quenching experiments were also performed via scavengers, results confirmed that hydroxyl radicals, superoxide radicals and electrons are the key reactive species in the TC degradation. The effects of influential parameters such as B-TiO2 dosage, TC concentration, pH, and Fe2+ to H2O2 molar ratio were also investigated, in addition, the catalyst is stable, as it achieved > 80 % TC degradation efficiency after five reuse cycles.

Photo-Controlled Reversible Uptake and Release of a Modified Sulfamethoxazole Antibiotic Drug from a Pillar[5]arene Cross-Linked Gelatin Hydrogel.

Pillararene cross-linked gelatin hydrogels were designed and synthesized to control the uptake and release of antibiotics using light. A suite of characterization techniques ranging from spectroscopy (FT-IR, 1H and 13C NMR, and MAS NMR), X-ray crystallographic analysis, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) was employed to investigate the physicochemical properties of hydrogels. The azobenzene-modified sulfamethoxazole (Azo-SMX) antibiotic was noncovalently incorporated into the hydrogel via supramolecular host-guest interactions to afford the A-hydrogel. While in its ground state, the Azo-SMX guest has a trans configuration structure and forms a thermodynamically stable inclusion complex with the pillar[5]arene motif in the hydrogel matrix. When the A-hydrogel was exposed to 365 nm UV light, Azo-SMX underwent a photoisomerization reaction. This changed the structure of Azo-SMX from trans to cis, and the material was released into the environment. The Azo-SMX released from the hydrogel was effective against both Gram-positive and Gram-negative bacteria. Importantly, the A-hydrogel exhibited a striking difference in antibacterial activity when applied to bacterial colonies in the presence and absence of UV light, highlighting the switchable antibacterial activity of A-hydrogel aided by light. In addition, all hydrogels containing pillar[5]arenes have demonstrated biocompatibility and effectiveness as scaffolds for biological and medical purposes.

Formulation and optimization of phytosomes of ethanolic extract of Viola tricolor flowers using design of experiment (DOE) to evaluate in vitro photoprotective potential as sunscreen cream

Viola tricolor L. has many uses in treatment of various skin disorders, which attributed to their antioxidant-flavonoid compounds. The aim of this study was evaluation of photoprotection, cytotoxicity and phototoxicity of the ethanolic extract of Viola tricolor flowers (EE-Viola). At concentration of 0.2 mg/mL of EE-Viola, the sun protection factor (SPF) value was 15.3 ± 0.7. By evaluation of the survival of mouse fibroblast cells (3T3) in the presence and absence of UV light using MTT-based colorimetric assay, the calculated IC50 was found to be 30.79 µg/mL and 34.89 µg/mL, respectively. The phytosomes of EE-Viola (Phy&EE-Viola) were then prepared using thin-layer hydration technique and optimized by experimental design method. The optimum particle size (487.6 nm) and encapsulation efficiency (95.2%) of the prepared phytosomes obtained when ratio of extract amount to lecithin amount (3 to 1), experiment temperature of 50 °C, and bath sonication were used. The optimum prepared phytosome was characterized by scanning electron microscopy, Fourier-transform infrared spectroscopy, and differential scanning calorimetry. In the next step, Phy&EE-Viola was formulated in a cream base and its photoprotective potential was evaluated. Finally, the Phy&EE-Viola cream was evaluated for its pH, spread-ability, occlusivity, in vitro SPF determination, release and stability studies. The SPF value of the cream containing 4% of Phy&EE-Viola was equal to 14.0 ± 0.7. The results clearly indicated that the cream formulations exhibited a good stability at applied temperatures and good release profile. Therefore, the obtained cream of Phy&EE-Viola might be introduced as candidate as for sun protection which merit further investigations.

Synergistic effect of adsorption and photo-catalysis on the removal of hazardous dyes using steam exploded banana fiber derived micro-cellulose

The utilization of banana fiber derived from micro-cellulose (MC) was exploited as a supporting material for advanced oxidation process (AOP) on the degradation of methylene blue and methyl violet dyes in the presence of H2O2-UV in aqueous medium for the first time using green chemistry protocols. Additionally, it was also effectively utilized for the adsorption of methylene blue dye using addition of H2O2 in the presence of sunlight. The MC powder was fabricated using an acid alkali process from the pseudo-stem of a banana tree. The as-fabricated MC powder was systematically characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectrometer (EDX), and zero point charge (pHzpc). The AOP assisted degradation of dye molecules was monitored by using calorimetric techniques as a function of dye concentration and pH in a batch reactor. In a short period of time, the maximum degradation efficiency of 98 % of methylene blue was achieved using MC powder assisted H2O2 under UV irradiation at a minimum irradiation time of 120 min at pH 7.0 using dosage of 0.2 g/L. However, in the absence of UV light, the degradation efficiency of MC powder assisted H2O2 was only about 5–10 % without UV light irradiation. The dye removal was studied as a function of various operational parameters such as pH (3–11), catalyst dose (0.2–0.6 g/L), and initial dye concentration (100–400 mg/L). In the presence of H2O2-sunlight and 0.2 g/L of dosage at pH 7.0 at a minimum contact time of 120 min, MC fiber showed maximum adsorption capacities of 98% and 85% for 100 mg/L and 400 mg/L of methylene blue concentrations. According to the obtained data, the adsorption of methylene blue dye on MC follows the Freundlich isotherm model (R2 = 0.9886) and pseudo-first-order kinetic model (R2 = 0.9596) due to the higher regression coefficients. This process of dye degradation and adsorption process is a novel one and environmentally benign for an effective removal of hazardous dyes.

Biosynthesis of Peptide Hydrogel-Titania Nanoparticle Composites with Antibacterial Properties.

The photoantibacterial properties of titania nanoparticles (TiO2NPs) are attracting much interest, but the separation of their suspension limits their application. In this study, the encapsulation of commercial TiO2NPs within self-assembling tripeptide hydrogels to form hgel-TiO2NP composites with significant photoantibacterial properties is reported. The Fmoc-Phe3 hydrogelator was synthesized via an enzymatic method. The resulting composite was characterized with DLS, ζ-potential, SAXS, FESEM-EDS and rheological measurements. Two different concentrations of TiO2NPs were used. The results showed that, by increasing the TiO2NP quantity from 5 to 10 mg, the value of the elastic modulus doubled, while the swelling ratio decreased from 63.6 to 45.5%. The antimicrobial efficacy of hgel-TiO2NPs was tested against a laboratory Staphylococcus aureus (S. aureus) strain and two methicillin-resistant S. aureus (MRSA) clinical isolates. Results highlighted a concentration-dependent superior antibacterial activity of hgel-TiO2NPs over TiO2NPs in the dark and after UV photoactivation. Notably, UV light exposure substantially increased the biocidal action of hgel-TiO2NPs compared to TiO2NPs. Surprisingly, in the absence of UV light, both composites significantly increased S. aureus growth relative to control groups. These findings support the role of hgel-TiO2NPs as promising biocidal agents in clinical and sanitation contexts. However, they also signal concerns about TiO2NP exposure influencing S. aureus virulence.

Complex Spectroscopy Studies of Nifedipine Photodegradation.

The aim of this work is to highlight the influence of UV light on the hydrolysis reaction of nifedipine (NIF) in the presence of alkaline solutions. In this context, the photodegradation of NIF in the absence of alkaline solutions caused (a) a change in the ratio between the absorbances of three bands in the UV-VIS spectra localized at 224-240 nm, 272-276 nm and 310-340 nm, assigned to the electronic transitions of -COOCH3 groups, -NO2 groups and a heterocycle with six atoms; (b) a red-shift of the photoluminescence (PL) band from 458 nm to 477 nm, simultaneous with an increase in its intensity; (c) a decrease in the ratio of the Raman line intensities, which peaked at 1224 cm-1 and 1649 cm-1, associated with the vibrational modes of -C-C-O in the ester group and C=C stretching; and (d) a decrease in the ratio between the absorbances of the IR bands, which peaked at 1493 cm-1 and 1223 cm-1, associated with the vibrational modes of the -NO2 group and C-N stretching. These changes were explained considering the NIF photodegradation reaction, which leads to the generation of the compound 4-(2-nitrosophenyl)-2.6-dimethyl-3.5-dimethoxy carbonyl pyridine. The interaction of NIF with NaOH in the absence of UV light was demonstrated to induce changes in the vibrational mode of the -C-C-O bond in the ester group. The photodegradation of NIF after its reaction with NaOH induces significant changes highlighted in its (a) UV-VIS spectra, by the shift of the absorption band at 238 nm; (b) PL spectra, by the supraunitary value of the ratio between the emission band intensities at 394-396 nm and 450 nm; (c) Raman spectra, by the change in the ratio between the intensities of the lines that peaked at 1224 cm-1 and 1649 cm-1 from 0.61 to 0.49; and (d) FTIR spectra, by the lowered absorbance of the IR band at 1493 cm-1 assigned to the vibrational mode of the -NO2 group as a result of the generation of the nitroso compound. These changes were explained considering the hydrolysis reaction products of NIF, as the nitroso compound is converted to a lactam-type compound. The photodegradation reaction rate constants of NIF and NIF after interaction with NaOH were also reported. The decrease in thermal stability of NIF samples after interaction with NaOH, as well as of NIF after exposure to UV light compared to NIF prior to exposure to UV light, was demonstrated by thermogravimetry, and the key fragments were confirmed by mass spectrometry.

Opto-electronic and electrochemical evaluations of particulate wo3 and sno2 in electrocodeposited Zn- tio2 nanocomposites coatings for sensor application

This study synthesized, characterized and determined the electronic and optical properties of Zn-TiO2, Zn-TiO2-WO3 and Zn-TiO2-SnO2 nano-composite coatings on low carbon steel. It has also determined the effect of these coatings on the corrosion of mild steel in saline environment. This was with a view to produce an active coating to providing alternative to hazardous chromium coating. Active multi functional nano crystalline coatings of the composites were electrolytically fabricated on low carbon steel from Zinc bath, with its Cation and nanoparticulates of TiO2, SnO2 and WO3 were uniformly codeposited in the Zn matrix. The nano-powders were characterized with Scanning Electron Microscope/Energy Dispersive Spectrometer (SEM/EDS) analyses for confirmation of the chemical compositions and purity. The electrocodeposition bath compositions were developed with 120 gram per litre of ZnCl2, 30 gram per litre of KCl along sides with the nanopowders. Other additives including cetylpridinum chloride, 2- Butyne 1,4diol were added as surfactants and Thiourea was added as stabilizer. The coated specimens were sectioned into parts, some of which were characterized with electrical meters and solar simulator to determine the electrical conductivity and solar response of the coated samples respectively. Samples were also subjected to corrosion experiment in 3.5% NaCl (saline) media to study their corrosion resistance properties in the test media through Potentiodynamic polarization method. The results, the electrical conductivity of the generated nano-composite coatings displayed a better electrical conductivity of 2.45E-01Ω-1m-1 which made it a better sensor material and outstanding corrosion resistance with corrosion rate at 0.10116 mm/year. The study concluded that both matrices with the Nano Particulate WO3 and SnO2 can be use as sensor materials but the WO3 matrix showed a better electrical conductivity both in the presence and absence of uv light and enhanced corrosion protection under light and dark conditions, thus a better sensor’s material.

Dual function Mg-doped binary metal ferrite: Photocatalytic degradation of trichlorophenol, bactericidal activity and molecular docking analysis

A new Mg-doped Zn0.5Ni0.5Fe2O4 (Mg–FZN) photocatalyst was synthesised using a simple co-precipitation-doping technique to develop a dual-function material with the ability to degrade hazardous and refractory pollutants and inactivate bacterial strains. The characterization results revealed that Mg-FZN is an n-type semiconductor with a conduction band of −0.413 eV, an average pore width of 2.32 nm, and a crystal size of 31.45 nm. The photocatalytic activity of Mg-FZN was assessed based on the degradation of 2,4,5-trichlorophenol and achieved 83.8% degradation efficiency under optimised conditions. The radical quenching results revealed that h+ significantly contributed to the photodegradation process while •OH, and •O2− played key roles. Additionally, within 60 min, 25 mg of Mg–FZN had bactericidal effects on the bacteria E. coli and S. aureus in both the presence and absence of UV light. Mg–FZN showed H-bonding, electrostatic, and metal-contact interactions with the amino acid residues of the bacterial protein with high binding scores (−4.711 kcal/mol and −5.872 kcal/mol), according to molecular docking.

Coral recruits are highly sensitive to heavy fuel oil exposure both in the presence and absence of UV light

Oil pollution remains a prominent local hazard to coral reefs, but the sensitivity of some coral life stages to oil exposure remains unstudied. Exposure to ultraviolet radiation (UVR), ubiquitous on coral reefs, may significantly increase oil toxicity towards these critical habitat-forming taxa. Here we present the first data on the sensitivity of two distinct post-settlement life stages of the model coral species Acropora millepora to a heavy fuel oil (HFO) water accommodated fraction (WAF) in the absence and presence of UVR. Assessment of lethal and sublethal endpoints indicates that both 1-week-old and 2-month-old recruits (1-wo and 2-mo) were negatively affected by chronic exposures to HFO (7 and 14 days, respectively). Relative growth (1-wo and 2-mo recruits) and survival (1-wo recruits) at end of exposure were the most sensitive endpoints in the absence of UVR, with no effect concentrations (NEC) of 34.3, 5.7 and 29.3 μg L-1 total aromatic hydrocarbons (TAH; ∑39 monocyclic- and polycyclic aromatic hydrocarbons), respectively. On average, UVR increased the negative effects by 10% for affected endpoints, and latent effects of exposure were evident for relative growth and symbiont uptake of recruits. Other sublethal endpoints, including maximum quantum yield and tissue colour score, were unaffected by chronic HFO exposure. A comparison of putative species-specific sensitivity constants for these ecologically relevant endpoints, indicates A. millepora recruits may be as sensitive as the most sensitive species currently included in oil toxicity databases. While the low intensity UVR only significantly increased the negative effects of the oil for one endpoint, the majority of endpoints showed trends towards increased toxicity in the presence of UVR. Therefore, the data presented here further support the standard incorporation of UVR in oil toxicity testing for tropical corals.

Statistical optimization of process conditions for pyrvinium pamoate elimination using UV/zeolite‐based nanostructures/H 2 O 2

Statistical optimization of process conditions for pyrvinium pamoate elimination using UV/zeolite‐based nanostructures/H ₂ O ₂

GAS PHASE OXIDATION OF FORMALDEHYDE BY TIO2/TIO2-V2O5/POLYPYRROLE ENERGY STORAGE PHOTOCATALYST

Photocatalytic oxidation of formaldehyde was performed through an electron storage photocatalyst named TiO2/TiO2-V2O5/PPy nanocomposites, consisting of TiO2 responsible for an electron generating source, TiO2-V2O5 functional as an electron storage substance, and PPy (polypyrrole) as an electron conducting substance between the formers. It was found that the TiO2/TiO2-V2O5/PPy nanocomposites showed both adsorption and photocatalytic activity for formaldehyde removal. Under UV irradiation, the catalytic activity of the TiO2/TiO2-V2O5/PPy catalyst was 57%, which was 0.1 and 0.4 times higher than that of TiO2 and TiO2/PPy catalysts, respectively. Moreover, the TiO2/TiO2-V2O5/PPy catalyst retained its function for at least 3 hours, after UV irradiation for 3.5 hours. The presence of TiO2-V2O5 was found to enhance the photocatalytic activity of the TiO2 catalyst, including the ability to function in the absence of UV light. This is due to the lower energy band gap of the TiO2/TiO2-V2O5/PPy, compared to that of TiO2; the TiO2-V2O5 also possesses energy storage ability. Further, the reaction rate of photocatalytic oxidation of formaldehyde by the electron storage photocatalyst was determined. The formaldehyde destruction rate is a function of formaldehyde concentration and can be formulated using a simplified Langmuir-Hinshelwood.

Plasma Vitamin D (25-Hydroxyvitamin D) Levels in Hispaniolan Amazon Parrots (Amazona ventralis) Housed Indoors Over Time.

Vitamin D is a hormone that can be ingested or synthesized in the body when skin is exposed to ultraviolet radiation (UV), typically from sunlight. In captivity, birds with no sunlight exposure may develop vitamin D deficiencies that may contribute to hypocalcemic conditions, even when fed a diet supplemented with vitamin D. An initial pilot study with Hispaniolan Amazon parrots (Amazona ventralis) conducted approximately 18 mo prior indicated there were significant differences in the 25-hydroxyvitamin D (vit D) plasma levels between the resident parrots (indoor-only housing) and a new group of historically outdoor-housed parrots (new parrots) 5 days after the arrival of the latter at our institution. The goals of this study were to determine if vit D, ionized calcium (Ca2+), and ionized magnesium (Mg2+) levels changed from baseline values (taken 18 mo prior) in the new birds as well as to compare those values to those of the resident birds over time. The treatment was a change in husbandry for the new parrots (no UV exposure and diet as provided for the resident parrots). To accomplish this, the authors compared vit D levels in the same two groups of birds that were fed the same vit D-fortified diet and given no access to natural or artificial UV light exposure for 18 mo. The resident parrots (N = 9) had been housed indoors for approximately 20 yr with no exposure to natural or supplemented UV light. The second group of birds (new parrots; N = 8) had been housed outdoors prior to the initiation of the pilot study in 2016 and were fed a similar-but not identical-diet prior to their arrival. Plasma samples were sent to the Michigan State University Diagnostic Center for Population and Animal Health for analysis. Test results demonstrated differences between the two groups of parrots, largely attributed to the decrease in vit D plasma levels in the new parrots over time to values equivalent to those measured in the resident birds. Differences were seen in plasma Ca2+, while no differences were demonstrated relative to Mg2+. We discuss these findings and suggest that plasma vit D levels decrease in the absence of UV light, even when animals are maintained on a vit D-fortified and balanced diet.

The effect of black carbon aging from NO2 oxidation of SO2 on its morphology, optical and hygroscopic properties

Atmospheric aging of black carbon (BC) leads to changes in its physiochemical properties, exerting complex effects on environment and climate. In this study, we have conducted laboratory chamber experiments to investigate the effects of BC aging on its morphology, hygroscopicity and optical properties by exposing monodisperse fresh BC particles to ambient ubiquitous species of nitrogen dioxide (NO2), sulfur dioxide (SO2) and ammonia (NH3) in absence of UV light. We show a rapid aging from highly fractal to compacted aggregates for the monodisperse BC particles with an initial diameter of 150 nm, with decline in the dynamic shape factor (χ) from about 1.8 to nearly 1. The effective density of the monodisperse BC particles increases from ∼0.54 to 1.50 g cm−3 accordingly. The aging process leads to that the light scattering, absorption, and single scattering albedo of the monodisperse BC particles are strongly enhanced by factors of 7.0, 1.8 and 3.0 respectively. By comparing with the BC aging from other mechanisms, we reveal a critical role of the composition of the coating materials on BC in determining its light absorption enhancement. Moreover, due to strong water uptake capacity of the aged BC particles, the light absorption enhancement (Eabs) could be 40–60% higher at humid atmosphere compared with dry conditions. This BC aging process from NO2 oxidation of SO2 may occur commonly in polluted regions and thus considerably alter its effects on regional air quality and climate.

Coupling Adsorption-Photocatalytic Degradation of Methylene Blue and Maxilon Red

The MB and MR removal process by two mechanisms of adsorption using rice straw (absence of UV light) and photodegradation on TiO2 surfaces was investigated. MB and MR removal efficiency were further intensified upon the sequential operation of adsorption followed by photocatalytic degradation over TiO2 under visible light irradiation. The TiO2 was used to remove methylene blue (MB) and Maxilon Red (MR) dye from aqueous media by continuous mode at 25 ± 2 °C, at pH 6.8 ± 0.2. Photo-illumination study revealed 75.81 and 65.51% MB and MR removal with the dose of 1 g/L TiO2 with an initial concentration of 5 mg/L within 120 min. This study can be deemed of potential applications for the removal of MB and MR dyes on an industrial level using the synergistic adsorption-photocatalytic oxidation approach. A probable photodegradation mechanism was proposed.

Group 6 photo-activable carbon monoxide-releasing molecules (PhotoCORMs) with 1’10-phenanthroline based ligand as potential anti-proliferative and anti-microbial agents

A new series of group 6 UV activable photoCORMs were synthesized by reacting the ligand (((1,10-phenanthroline-5-yl)imino)methyl)naphthalen-2-ol (1) with group 6 (Cr, Mo, and W) hexacarbonyl to form 2, 3, and 4, respectively. The structural elucidations of all compounds were conducted via IR, NMR, and CHN elemental analyses. The crystal structures of all the synthesized compounds were obtained and the half-life of the photoCORMs were determined by using the three-layered myoglobin solution assay. Results showed that the half-life of the compounds decreased down the group 6 in a concentration-dependent manner, with compound 2 displaying the shortest half-life (7.1 s) at 60 µM. In the absence of UV light, compounds 1 and 3 showed cytotoxicity and selectivity against human-derived colorectal adenocarcinoma HT-29 and carcinoma HCT 116, with ligand 1 being the most cytotoxic compound. Nonetheless, most compounds were inactive against bacteria and fungi when UV light is absent, while only 1 showed appreciable activity against B. cereus, B. subtilis, E. faecalis, and S. aureus. In the presence of UV light, the cytotoxicity and selectivity of photoCORMs 2, 3, and 4 were significantly elevated, with 2 and 4 demonstrating the most drastic improvement against HT-29 (from IC50 ≥ 100 to 26.03 and 38.03 µM, respectively). The growth inhibitory activity of 2, 3, and 4 were also considerably enhanced in the presence of UV illumination when tested against B. cereus, B. subtilis, S. aureus, E. coli, K. pneumoniae, and S. flexneri, with compound 2 demonstrating the biggest leap among the three photoCORMs.

Light-Powered Dissipative Assembly of Diazocine Coordination Cages

Stimuli-responsive coordination cages allow reversible control over guest binding and release, relevant for adaptive receptors, carriers, catalysts, and complex systems. Light serves as an advantageous stimulus, as it can be applied with precise spatial and temporal resolution without producing chemical waste products. We report the first Pd-mediated coordination cage based on ligands embedding a diazocine photoswitch. While the thermodynamically more stable cis-photoisomer sloppily assembles to a mixture of species with general formula [Pdncis-L2n], the less stable trans-isomer yields a defined [Pd2trans-L4] cage that reversibly converts back to the cis-system by irradiation at 530 nm or thermal relaxation. The [Pdncis-L2n] species do not bind a given guest; however, [Pd2trans-L4] is able to encapsulate a bis-sulfonate as long as it is kept assembled, requiring continuous irradiation at 385 nm. In the absence of UV light, thermal relaxation results in back-switching and guest release. Assembly and properties of the system were characterized by a combination of NMR, ion mobility ESI-MS, single-crystal X-ray diffraction, and UV–vis absorption studies.

Coral Recruits are Highly Sensitive to Heavy Fuel Oil Exposure Both in the Presence and Absence of Uv Light

Coral Recruits are Highly Sensitive to Heavy Fuel Oil Exposure Both in the Presence and Absence of Uv Light

Fast Photoswitchable Order-Disorder Transitions in Liquid-Crystalline Block Co-oligomers.

Optically driven ordering transitions are rarely observed in macromolecular systems, often because of kinetic limitations. Here, we report a series of block co-oligomers (BCOs) that rapidly order and disorder at room temperature in response to optical illumination, and the absence thereof. The system is a triblock where rigid azobenzene (Azo) mesogens are attached to each end of a flexible siloxane chain. UV-induced trans-to-cis Azo isomerization, and vice versa in the absence of UV light, drive disordering and ordering of lamellar superstructures and smectic mesophases, as manifested by liquefaction and solidification of the material, respectively. The impacts of chemical structure on BCO self-assembly and photoswitching kinetics are explored by in situ microscopy and X-ray measurements for different mesogen end groups (NO2 or CN), and different carbon chain lengths (0C or 12C) between the siloxane and the mesogen. The presence of the 12C spacer leads to hierarchical ordering with smectic layers of mesogens existing alongside larger length-scale lamellae, versus only smectic ordering without the spacer. These hierarchically ordered BCOs display highly persistent lamellar sheets that contrast with the tortuous, low-persistence "fingerprint"-type structures seen in conventional block copolymers. The reordering kinetics upon removal of UV illumination are extremely rapid (<5 s). This fast response is due to the electron-withdrawing NO2 and CN, which facilitate cis-to-trans isomerization via thermal relaxation at room temperature without additional stimuli. This work elucidates structure-property relationships in photoswitching BCOs and advances the possibility of developing systems in which ordered nanostructures can be easily optically written and erased.

Enhanced visible photocatalytic performance of un-doped TiO2 nanoparticles thin films through modifying the substrate surface roughness

Titanium oxide (TiO2) has been widely utilized for application in environmental pollution due to its unique properties. However, large bandgap (3.2 eV) and low surface area of bulk TiO2 are the main properties that limit its photocatalytic applications. In this work, a thin layer of TiO2 (<200 nm) nanoparticles (NPs) on mechanically roughened glass substrates is deposited by a simple sol-gel method followed by a dip-coating process along with fast heating and sintering. The effect of substrate surface roughness on the morphology, hydrophilicity, and optical properties which results in a more electron-hole generation and consequently improved photocatalytic activity was investigated by different characterization techniques. The TiO2 layer on the roughest substrate (RMS = 76.90 nm) showed the smallest average NP size (3 nm) with the highest surface roughness (RMS = 121.00 nm) and hydrophilicity (74.5%) as well as strong optical absorption. This sample photodegraded the pollutant with an efficiency of 85% at a rate of 0.0054 min−1 under the illumination of the vis-light emitting diode (LED)-based source (440 and 590 nm). Therefore, an enhanced photocatalytic activity accompanied by recyclability was achieved by modifying the substrate surface roughness and thermal treatment in the process of synthesis. Conclusively, intrinsic defects and grain boundaries appear which behave as active areas for charge transfer in the photocatalytic process under visible irradiation. This research may provide an insight into the fabrication of highly efficient photocatalysts based on commonly used wide band gap materials to work in the absence of UV light.

Testing Abiotic Reduction of NAD+ Directly Mediated by Iron/Sulfur Minerals.

Life emerged in a geochemical context, possibly in the midst of mineral substrates. However, it is not known to what extent minerals and dissolved inorganic ions could have facilitated the evolution of biochemical reactions. Herein, we have experimentally shown that iron sulfide minerals can act as electron transfer agents for the reduction of the ubiquitous biological protein cofactor nicotinamide adenine dinucleotide (NAD+) under anaerobic prebiotic conditions, observing the NAD+/NADH redox transition by using ultraviolet-visible spectroscopy and 1H nuclear magnetic resonance. This reaction was mediated with iron sulfide minerals, which were likely abundant on early Earth in seafloor and hydrothermal settings; and the NAD+/NADH redox reaction occurred in the absence of UV light, peptide ligand(s), or dissolved mediators. To better understand this reaction, thermodynamic modeling was also performed. The ability of an iron sulfide mineral to transfer electrons to a biochemical cofactor that is found in every living cell demonstrates how geologic materials could have played a direct role in the evolution of certain cofactor-driven metabolic pathways.