Photocatalytic Conversion of Organic Pollutants in Air: Quantum Yields Using a Silver/Nitrogen/TiO2 Mesoporous Semiconductor under Visible Light

This research studies the photocatalytic conversion of methanol (25–90 µmol/L range) as a volatile organic compound (VOC) surrogate into CO2, using a N/Ag/TiO2 photocatalyst under visible light irradiation in a Photo-CREC Air unit. The N/Ag/TiO2 mesh supported photocatalyst is prepared via the solvothermal method. While the bare-TiO2 is inactive under visible light, the N/Ag/TiO2 2 wt.% loaded stainless-steel woven mesh displays 35% quantum yields, with 80% absorbed photons and 60% methanol conversion in a 110 min irradiation period. Results obtained are assigned to silver surface plasmon resonance, silver and nitrogen species synergistic impacts on band gap, and their influence on particle agglomerate size and semiconductor acidity. The determined quantum yields under visible light in a Photo-CREC Air unit, are the highest reported in the technical literature, that these authors are aware of, with this opening unique opportunity for the use of visible light for the purification of air from VOC contaminants.

Ultraviolet irradiation-responsive dynamic ultralong organic phosphorescence in polymeric systems

Room temperature phosphorescence (RTP) has drawn extensive attention in recent years. Efficient stimulus-responsive phosphorescent organic materials are attractive, but are extremely rare because of unclear design principles and intrinsically spin-forbidden intersystem crossing. Herein, we present a feasible and facile strategy to achieve ultraviolet irradiation-responsive ultralong RTP (IRRTP) of some simple organic phosphors by doping into amorphous poly(vinyl alcohol) matrix. In addition to the observed green and yellow afterglow emission with distinct irradiation-enhanced phosphorescence, the phosphorescence lifetime can be tuned by varying the irradiation period of 254 nm light. Significantly, the dynamic phosphorescence lifetime could be increased 14.3 folds from 58.03 ms to 828.81 ms in one of the obtained hybrid films after irradiation for 45 min under ambient conditions. As such, the application in polychromatic screen printing and multilevel information encryption is demonstrated. The extraordinary IRRTP in the amorphous state endows these systems with a highly promising potential for smart flexible luminescent materials and sensors with dynamically controlled phosphorescence.

Contrasting responses of DOM leachates to photodegradation observed in plant species collected along an estuarine salinity gradient

A series of abiotic processes affected by salinity changes involve light-mediated reactions and different degradation pathways of organic compounds, including altered photo-oxidation, photo-degradation, and photolysis of organic matter (OM). Sunlight is known to degrade, oxidize, or mineralize dissolved organic matter (DOM) in waterways, creating large changes in compositional structure of DOM near the water surface and ultimately in the mixed layer. DOM derived from various vegetation types has differing levels of susceptibility to photolytic degradation depending on initial chemical composition and in what matrix degradation takes place (e.g., salinity). The effect of sunlight and salinity on degradation of leached DOM derived from three dominant vegetative species, Avicennia germinans, Juncus romerianus, and Taxodium distichum, along a riverine continuum in northeast Florida was determined. Leachates from these three sources in a deionized or seawater matrix were irradiated in a continuous flow-through photolytic system over the course of 20 h. Avicennia germinans and Juncus roemerinaus DOM readily degraded as indicated by decreases in absorbance across all wavelengths during the irradiation period, while Taxodium distichum DOM was found to increase in absorbance across all wavelengths in the freshwater matrix, but not in seawater. PARAFAC analysis indicated differences in photochemical components and % change of absorbance and fluorescence over time indicate the importance and variability of individual contributions to the DOM pool across an estuarine continuum. This work characterizes the photochemical properties of three individual DOM sources, exhibits the need for further research on this topic, and explores the salinity effect on photo-degradation of DOM from unique plant-derived DOM.

Exploring the Applicability of Robot-Assisted UV Disinfection in Radiology

The importance of infection control procedures in hospital radiology departments has become increasingly apparent in recent months as the impact of COVID-19 has spread across the world. Existing disinfectant procedures that rely on the manual application of chemical-based disinfectants are time consuming, resource intensive and prone to high degrees of human error. Alternative non-touch disinfection methods, such as Ultraviolet Germicidal Irradiation (UVGI), have the potential to overcome many of the limitations of existing approaches while significantly improving workflow and equipment utilization. The aim of this research was to investigate the germicidal effectiveness and the practical feasibility of using a robotic UVGI device for disinfecting surfaces in a radiology setting. We present the design of a robotic UVGI platform that can be deployed alongside human workers and can operate autonomously within cramped rooms, thereby addressing two important requirements necessary for integrating the technology within radiology settings. In one hospital, we conducted experiments in a CT and X-ray room. In a second hospital, we investigated the germicidal performance of the robot when deployed to disinfect a CT room in <15 minutes, a period which is estimated to be 2–4 times faster than current practice for disinfecting rooms after infectious (or potentially infectious) patients. Findings from both test sites show that UVGI successfully inactivated all of measurable microbial load on 22 out of 24 surfaces. On the remaining two surfaces, UVGI reduced the microbial load by 84 and 95%, respectively. The study also exposes some of the challenges of manually disinfecting radiology suites, revealing high concentrations of microbial load in hard-to-reach places. Our findings provide compelling evidence that UVGI can effectively inactivate microbes on commonly touched surfaces in radiology suites, even if they were only exposed to relatively short bursts of irradiation. Despite the short irradiation period, we demonstrated the ability to inactivate microbes with more complex cell structures and requiring higher UV inactivation energies than SARS-CoV-2, thus indicating high likelihood of effectiveness against coronavirus.

Silicon twisted cone structure produced by optical vortex pulse with structure evaluation by radiation hydrodynamic simulation

We demonstrate a radiation hydrodynamic simulation of optical vortex pulse-ablated microcone structures on silicon (Si) substrates. Doughnut-shaped craters were formed by single pulse irradiation on the Si substrate, and a twisted cone structure with a height of 3.5 µm was created at the center of the irradiation spot by the circularly polarized optical vortex pulse. A two-dimensional (2-D) radiation hydrodynamic simulation reproduced the cone structure well with a height of 3 µm. The central part of the incident laser power was lowered from the initial profile due to plasma shielding over the laser pulse duration for an inverted double-well laser profile. The acute tip shape of the silicon surface can survive over the laser irradiation period.

Microwave-assisted conversion of palm kernel shell biomass waste to photoluminescent carbon dots

In the present work, palm kernel shell (PKS) biomass waste has been used as a low-cost and easily available precursor to prepare carbon dots (CDs) via microwave irradiation method. The impacts of the reacting medium: water and diethylene glycol (DEG), and irradiation period, as well as the presence of chitosan on the CDs properties, have been investigated. The synthesized CDs were characterized by several physical and optical analyses. The performance of the CDs in terms of bacteria cell imaging and copper (II) ions sensing and removal were also explored. All the CDs possessed a size of 6–7 nm in diameter and the presence of hydroxyl and alkene functional groups indicated the successful transformation of PKS into CDs with carbon core consisting of C = C elementary unit. The highest quantum yield (44.0%) obtained was from the CDs synthesised with DEG as the reacting medium at irradiation period of 1 min. It was postulated that the high boiling point of DEG resulted in a complete carbonisation of PKS into CDs. Subsequently, the absorbance intensity and photoluminescence intensity were also much higher compared to other precursor formulation. All the CDs fluoresced in the bacteria culture, and fluorescence quenching occurred in the presence of heavy metal ions. These showed the potential of CDs synthesised from PKS could be used for cellular imaging and detection as well as removal of heavy metal ions.

PHOTOCATALYST: A PROMISING SMART MATERIAL IN DEGRADATION OF DYE USING RESPONSE SURFACE METHODOLOGY (RSM

One of the environmental issues is water Pollution causing serious health related problem not only to human but also seriously affect aquatic life. Dyes are among the pollutants that pollute our water bodies. In the olden days so many methods were applied for the purification of water but recently photocatalysis shown a promising technique where the pollutants (dyes) were degraded to give clean water and carbon dioxide to be liberated as the end product. The specific surface area of the photocatalyst 243.80 m2g-1 and the PZC was found to be 8.10. Only 0.9% of the dye (MG) decolorized in the presence of light (photolysis) while 25% of the MG was adsorbs in the dark with 30 minutes of contact. The ANOVA showed an F-value of 1114.81 which suggests that the model is significant. All model terms i.e. MG initial concentration, photocatalyst dose, irradiation period and pH are all significant with Prob>” values <0.05. The predicted R-squared that has a value 0.995 was in perfect agreement reasonably with Adj R-squared that reached up to 99.8%. Adequate precision more than 4.00 by this model indicates desirable and adequate signal. The influence of MG initial concentration in removing the MG color was higher when compared to other parameters involved and this was indicated by the F-values.

Examination of Photocatalyzed Chlorophenols for Sequential Photocatalytic-Biological Treatment Optimization

Given the known adverse effect of chlorophenols for the aquatic environments which they can reach, the development of efficient methods both technically and economically to remove them has gained increasing attention over time. The combination of photocatalytic oxidation with biological treatment can lead to high removal efficiencies of chlorophenols, while reducing the costs associated with the need to treat large volumes of aqueous solutions. Therefore, the present paper had as its main objective the identification of the minimum photocatalytic oxidation period during which the aqueous solutions of 4-chlorophenol and 2,4-dichlorophenol can be considered as readily biodegradable. Thus, the results of photocatalytic oxidation and biodegradability tests showed that, regardless of the concentration of chlorophenol and its type, the working solutions become readily biodegradable after up to 120 min of irradiation in ultraviolet light. At this irradiation time, the maximum organic content of the aqueous solution is less than 40%, and the biochemical oxygen demand and chemical oxygen demand (BOD/COD) ratio is much higher than 0.4. The maximum specific heterotrophic growth rate of activated sludge has an average value of 4.221 d−1 for 4-chlorophenol, and 3.126 d−1 for 2,4-dichlorophenol. This irradiation period represents at most half of the total irradiation period necessary for the complete mineralization of the working solutions. The results obtained were correlated with the intermediates identified during the photocatalytic oxidation. It seems that, working solutions initially containing 4-chlorophenol can more easily form readily biodegradable intermediates.

Photochemical investigation of aromatic hydrocarbons of Balakhani crude oil as petroleum luminophores

In this paper, the photochemical conversion process of aromatic hydrocarbons in Balakhani oil well (BO) as a case study was investigated. To study the composition of BO, first, it has been separated into the first, second, third, and fourth groups of aromatics using chromatography absorption column. It has been established that the composition of the separated groups is mainly composed of mono-, tri-, and tetracyclic aromatic hydrocarbons. It has been shown that the optical densities of the absorption bands corresponding to bi-, tri-, and polycyclic aromatic hydrocarbons decrease with increasing the photo-irradiation period, hence their maximum absorption band undergoes the hypsochromatic shift, which is characteristic for electron donor substances. It has been determined that the photochemical conversion process in the sample oil (BO) occurs with radical-chain and molecular mechanisms. As a result of the photochemical conversion process of arene-type aromatic hydrocarbons, the first difference during the photooxidation of endoperoxides, hydroxynones, quinones, and phenes is the formation of cyclic peroxides and quinones.

A comparative study of the E. faecalis antibiofilm efficacy of photoactivated curcumin, chlorophyll and riboflavin

Background: Photosensitisers play a vital role for reactive oxygen species (ROS) production in diode laser 405 nm therapy. Curcumin, chlorophyll and riboflavin have been used and viewed in several studies as effective photosensitisers for the elimination of Enterococcus faecalis (E. faecalis), a persistent microorganism that may cause endodontic failure. While each has given valuable and promising results as an alternative endodontic irrigant, no study has compared the efficacy of these three natural dyes. Purpose: To prove that the photosensitiser curcumin in diode laser 405 nm therapy is more effective for E. faecalis biofilm degradation than chlorophyll and riboflavin, and that a duration of irradiation of 90 seconds is more effective than 60 seconds. Methods: The biofilm monospecies E. faecalis was divided into two microplates with 96-well according to the irradiation periods: 60 seconds (Group 1) and 90 seconds (Group 2). Each group contained one control (without a photosensitiser) and three treatments were carried out by adding the photosensitisers curcumin, chlorophyll and riboflavin, where each treatment contained eleven samples. After irradiation for 60 seconds and 90 seconds, a crystal violet assay was carried out for each group. Results: The one-way ANOVA test showed a significant difference between groups based on the irradiation period. Tukey’s test showed each treatment in each group also showed a significant difference (p<0.05) with curcumin as the best substance to cause biofilm degradation in both groups. The duration of the irradiation showed that the longer the biofilm was illuminated, the lower the absorbance value or optical density (OD). Conclusion: Curcumin irradiated for 90 seconds gives better biofilm degradation on E. faecalis due to its natural properties and molecular structure, highlighting its efficacy in photodynamic therapy