Bleaching Rate Research Articles

Antiswelling Photochromic Hydrogels for Underwater Optically Camouflageable Flexible Electronic Devices.

Optical camouflage offers an effective strategy for enhancing the survival chances of underwater flexible electronic devices akin to underwater organisms. Photochromism is one of the most effective methods to achieve optical camouflage. In this study, antiswelling hydrogels with photochromic properties were prepared using a two-step solvent replacement strategy and explored as underwater optically camouflaged flexible electronic devices. The hydrophobic network formed upon polymerization of hydroxyethyl methacrylate (HEMA) ensured that the hydrogels possessed outstanding antiswelling properties. Internetwork hydrogen bonding interactions allowed the hydrogels to exhibit tissue-adaptable mechanical properties and excellent self-bonding capabilities. The introduction of polyoxometalates further enhanced the hydrogels' mechanical and self-bonding properties while imparting photochromic capability. The hydrogels could be rapidly and reversibly colored under 365 nm UV irradiation. The bleaching rate of the colored hydrogels increased with temperature, bleaching within 12 h at 60 °C but maintaining the color for more than 5 days at room temperature. The self-bonding and photochromic properties enabled the hydrogels to be easily assembled into optically camouflaged underwater flexible electronic devices for underwater motion sensing and wireless information transmission. An optically camouflaged strain sensor was first assembled for underwater limb motion sensing. Additionally, an underwater optically camouflaged wireless information exchange device was assembled to enable wireless communication with a smartphone. This work provided an effective strategy for the optical camouflage of underwater flexible electronic devices, presenting opportunities for next-generation underwater hydrogel-based flexible devices.

High resolution luminescence and radiocarbon dating of Holocene Aeolian silt (loess) in west Greenland

Loess–palaeosol sequences serve as valuable archives of changes in climate and atmospheric mineral dust deposition. However, little work has been conducted on Holocene loess in the Arctic, despite the sensitivity of this region to climate changes. Aeolian silt/loess profiles in the ice-free region of western Greenland near Kangerlussuaq were sampled to develop a robust age framework using both luminescence and bulk organic matter radiocarbon dating. Radiocarbon ages generally show consistent age increases with depth but are likely offset to younger ages due to sediment mixing in the upper 10–20 cm of the profiles. Quartz OSL signals exhibit insensitivity, while low-temperature infrared stimulated luminescence performed at 50 °C (IR50) and the post-IR IRSL at 180 °C (pIRIR180) signals of polymineral fine grain revealed a consistent natural inherited dose of approximately 5 Gy for pIRIR180 and an unbleachable residual of around 2 Gy for IR50, with substantial fading rates in the latter. This led to a notable age overestimation when compared with bulk organic matter radiocarbon ages. To develop an appropriate dating approach, we evaluated the differential bleaching rates of feldspar IR50 and pIRIR180 signals, and corrected for modern inherited doses. Radiocarbon ages measured on the bulk organic carbon oxidised at 400 °C (LT 14C) increased very consistently with depth, allowing calculation of accumulation rates. The presence of the atmospheric radiocarbon bomb signal at depth indicated down-mixing of surface material into the profile, which caused negative (younger) age offsets. The offset-corrected radiocarbon-based age-depth model could be compared to the luminescence results.We show that a combination of LT 14C with polymineral pIRIR180 dating allows the development of age models for these deposits. This multi-chronological approach reveals that loess accumulation in the region was initiated around 4 ka, probably consisting of two main phases of loess accumulation at 4–3 ka and <1 ka. The initial phase matches the proposed onset of aeolian sand activity in the wider region, but post-dates local ice retreat by c. 3 kyr. The more recent phase of accumulation also matches the timing of increased sand accumulation in the region and likely coincides with Neoglacial to Little Ice Age ice advances, or even enhanced dust activity in the last decades.

Photostability and photodynamic antimicrobial profile of dye extracts from four (4) plants: prospects for eco-friendly low-cost food disinfection and topical biomedical applications.

In this study, photostability and photodynamic antimicrobial performance of dye extracts from Hibiscus sabdariffa (HS) calyces, Sorghum bicolor (SB) leaf sheaths, Lawsonia inermis (LI) leaves and Curcuma longa (CL) roots were investigated in Acetate-HCl (AH) Buffer (pH 4.6), Tris Base-HCl (TBH) Buffer (pH 8.6), distilled water (dH2O), and Phosphate Buffer Saline (PBS, pH 7.2) using Bacillus subtilis as model for gram positive bacteria, Escherichia coli as model for gram negative bacteria, phage MS2 as model for non-envelope viruses and phage phi6 as model for envelope viruses including SARS CoV-2 which is the causative agent of COVID-19. Our results showed that the photostability of the dye extracts is in the decreasing order of LI > CL > SB > HS. The dye extract-HS is photostable in dH2O but bleaches in buffers-AH, TBH and PBS. The rate of bleaching is higher in AH compared to in TBH and PBS. The bleaching and buffers affected the photodynamic and non-photodynamic antimicrobial activity of the dye extracts. The photodynamic antibacterial activity of the dye extracts is in the decreasing order of CL > HS > LI > SB while the non-photodynamic antibacterial activity is in the decreasing order of LI > CL > HS > SB. The non-photodynamic antiviral activity pattern observed is the same as that of non-photodynamic antibacterial activity observed. However, the photodynamic antiviral activity of the dye extracts is in the decreasing order of CL > LI > HS > SB. Given their performance, the dye extracts maybe mostly suitable for environmental applications including fresh produce and food disinfection, sanitation of hands and contact surfaces where water can serve as diluent for the extracts and the microenvironment is free of salts.

Quantify the Influence of Coral Reef Bleaching on Tourism in Small Island Developing States (SIDS)

As global climate change keeps deteriorating, adverse effects have emerged, including global warming, rising sea levels, and extreme weather. From diverse literature, we summarized that these effects have triggered irretrievable damage to coral reefs worldwide and indirectly influenced tourism in small island developing states (SIDS). Since the economy depends drastically on tourism, we propose the study to quantify the effect caused by coral bleaching, a by-product of global warming, on tourism in SIDS. We schedule to find the relationship between coral bleaching rate and tourism development in targeted areas via a panel data model and a regression model. We expect our result can contribute to part of the ministries' legislation in SIDS

Improving dispersibility of tungsten oxide particles with organic ligands for photochromic films

Tungsten trioxide (WO3) has been studied as a promising photochromic material due to its favorable properties such as low manufacturing cost, high thermal and photostabilities, and low toxicity. Nevertheless, its practical application has been hindered by a relatively slow bleaching rate compared to other photochromic materials. Furthermore, metal oxide particles such as tungsten oxide face challenges in dispersing within process solvents, leading to difficulties in solution-based film fabrication processes. In this study, we aimed to address this limitation by exploring novel approaches to enhance both the dispersibility of tungsten oxides in processing solvents and their photochromic properties. To achieve this, we synthesized tungsten oxide composites by introducing various organic ligands, including polyvinylpyrrolidone (PVP), oleylamine (OA), hexadecylamine (HDA), and cetyltrimethylammonium bromide (CTAB). Through a comparative analysis, we found that the introduction of organic ligands significantly improved the dispersibility of tungsten oxides in processing solvents, while also enhancing their photochromic properties, including bleaching rate. Notably, the PVP ligand demonstrated superior performance in enhancing the overall properties of tungsten oxide composites. Our findings provide insights into the optimization of tungsten oxide-based photochromic materials for practical applications, offering potential directions for improvement and proposals for enhancing their performance and broadening their utility in various fields.

XUV Absorption Spectroscopy and Photoconversion of a Tin-Oxo Cage Photoresist.

Extreme ultraviolet lithography has recently been introduced in high-volume production of integrated circuits for manufacturing the smallest features in high-end computer chips. Hybrid organic/inorganic materials are considered as the next generation of photoresists for this technology, but detailed knowledge about the response of such materials to the ionizing radiation used (13.5 nm, 92 eV) is still scarce. In the present work, we use broadband high-harmonic radiation in the energy range 22-70 eV for absorption spectroscopy and photobleaching (that is, the decrease of absorbance) of thin films of an n-butyltin oxo-cage, a representative of the class of metal-based EUV photoresist. The shape of the absorption spectrum in the range 22-92 eV matches well with the spectrum predicted using tabulated atomic cross sections. The photobleaching results are consistent with loss of the butyl side groups due to the breaking of Sn-C bonds following photoionization. Bleaching is strongest in the low-energy range (<40 eV), where the absorption is largely due to the carbon atoms in the organic groups. At higher energies (42-70 eV), absorption is dominated by the tin atoms, and since these remain in the film after photoconversion, the absorption change in this region is smaller. It is estimated that after prolonged irradiation (up to ∼3 J cm-2 in the range 22-40 eV) about 70% of the hydrocarbon groups are removed from the film. The rate of bleaching is high at the beginning of exposure, but it rapidly decreases with increasing conversion. We rationalize this using density functional theory calculations: the first Sn-C bonds are efficiently cleaved (quantum yield Φ ≈ 0.9), because the highest occupied molecular orbitals (HOMOs) (from which an electron is removed after photoionization) are located on Sn-C sigma bonds. In the photoproducts, the HOMO is localized on tin atoms that have lost their hydrocarbon group (formally reduced to the Sn(II) oxidation state), and holes formed on those tin atoms lead to less efficient cleavage reactions. Our results reveal the primary reaction steps following excitation with ionizing radiation of tin-oxo cages. Our methodology represents a systematic approach of studying and quantitatively assessing the performance of new photoresists and as such enables the development of future EUV photoresists.

Thermal bleaching in the northern South China Sea: impact of abnormal environment and climate on high-latitude coral reefs.

Extensive coral bleaching events can result in catastrophic degradation of coral reefs and reorganization of coral communities. In the present study, we analyzed the spatial differences in coral bleaching and possible reasons of large-scale coral bleaching, based on the results of a survey carried out in the northern South China Sea in 2020. In addition, we have continuously monitored the sea surface temperature (SST) of the northernmost Weizhou Island for more than six years. The living coral cover at Weizhou Island (W), Xuwen Nature Reserve (X), and Haihua Island (H) was relatively high at 24.6% ± 4.8%, 12.1% ± 3.8%, and 8.1% ± 2.6%, respectively, whereas their bleaching rates were 9.7% ± 2.6%, 9.7% ± 3.3%, and 6.9% ± 2.1%, respectively. Among them, the living coral cover of W was significantly different from those of X and H, whereas the bleaching rate was not significantly different among the three areas. In all three areas, the massive and encrusting corals predominate and exhibit relatively high bleaching rates, with Porites lutea and Bernardpora stutchburyi being the dominant species. In addition, the temperature monitoring results of Weizhou Island for six consecutive years showed that the critical SST of coral bleaching was 31.5 ℃. The monitoring results also showed that the average SST of Weizhou Island was 32.1 ℃, exceeding 32 ℃ in July 2020 for up to 533h. The longest continuous time when the SST exceeded 32 ℃ was 97h. These findings indicated that the coral bleaching event that occurred in the Beibu Gulf during 2020 was a large-scale and high-temperature transient event that presented a relatively homogeneous threat to the coral communities. We inferred that this sudden heat stress event was caused by the enclosed tidal current in the Beibu Gulf, which prevented the southern upwelling from reaching the north, as well as by the inability of the SST to decrease without rainfall caused by typhoon cyclones. Our findings suggested that abnormal heat waves can result in coral bleaching at high latitudes and even coral reef degradation. Furthermore, our study provides a new perspective for investigating the self-recovery and reorganization of coral communities following accumulated coral bleaching.

PH dependence of brown-carbon optical properties in cloud water

Abstract. Light-absorbing organic species present in aerosols, collectively called brown carbon (BrC), have important but highly uncertain effects on climate. Clouds likely represent a significant medium for secondary BrC production and for bleaching reactions, though the relative importance of the formation and loss processes in clouds is unknown at present. The acidity (or pH) of atmospheric particles and clouds affects the optical properties of BrC and bleaching rates. Given the wide variability of pH in the atmosphere (pH in particles and clouds ranges from −1 to 8), the optical properties of BrC and its bleaching behavior are expected to vary significantly, and the link between pH and BrC is yet another uncertainty in attempts to constrain its climate forcing effects. In this work, we characterize the pH dependence of BrC optical properties – including light absorption at 365 nm (Abs365), the mass absorption coefficient (MAC365), and the absorption Ångström exponent (AAE) – in bulk cloud water sampled from the summit of Whiteface Mountain, NY. In all samples (n=17), Abs365 and MAC365 increased linearly with increasing pH, highlighting the importance of reporting pH in studies of BrC in aqueous media. There was strong variability in the sensitivity of Abs365 to pH, with normalized slopes that ranged from 5.1 % to 17.2 % per pH unit. The normalized slope decreased strongly with increasing cloud water [K+], suggesting that the non-biomass-burning BrC has optical properties that are more sensitive to pH than BrC associated with biomass burning. AAE also showed a distinct pH dependence as it was relatively flat between pH 1.5–5 and then decreased significantly above pH 5. The cloud water composition was used to inform thermodynamic predictions of aerosol pH upwind and/or downwind of Whiteface Mountain and the subsequent changes in BrC optical properties. Overall, these results show that, in addition to secondary BrC production, photobleaching, and the altitudinal distribution, the climate forcing of BrC is quite strongly affected by its pH-dependent absorption.

Synthesis and Photochromic Properties of Diaryl [5]Helicene Derivatives.

Photoinduced tuning of aromaticity and correlative molecular properties has attracted enormous interest in recent years both for modulating photochromism properties and designing novel photochromic materials. Here, we report the synthesis and photochemical characterization of diaryl[5]helicene-based diarylethene molecular switches. 3,4-Bis(2,4-dimethyl-5-phenylthiophen-3-yl)dibenzo[c,g]phenanthrene derivative 1 a showed no photochromic reaction, whereas 3,4-bis(2-methyl-5-phenylthiophen-3-yl)dibenzo[c,g]phenanthrene derivative 2 a and 3,4-bis(5-methyl-2-phenylthiazol-4-yl)dibenzo[c,g]phenanthrene derivative 3 a exhibited reversible photochromism in different aprotic solvents with specific light irradiation. Meanwhile, the diarylethene compounds 2 a and 3 a underwent turn-off mode fluorescence photoswitching together with photoisomerization upon light irradiation. Remarkably, the photoinduced changes in the aromaticity of [5]helicene as a central ethene bridge along with the relative smaller activation energy and higher frequency factor facilitated the thermal bleaching rates of diarylethene switches 2 and 3 in solution. This research provides new insight for designing aromatic diarylethene photoswitches for reversible fluorescence switching, photoinduced changes in aromaticity and further fast thermal back reactions.

Turbidity buffers coral bleaching under extreme wind and rainfall conditions

Coral reefs in turbid waters have been hypothesized to be a refuge from climate change. These naturally occurring communities were brought into the spotlight because some of their species exhibited record levels of resistance to marine heatwaves (MHWs) by disturbance-tolerant corals. However, long-term monitoring data on the drivers of coral bleaching in these extreme reef habitats are scarce. Here, we describe the population structure and bleaching rates of a widespread and resilient coral (Siderastrea stellata). We examine the links between environmental factors, namely, rainfall, wind speed, turbidity, solar irradiance, sea surface temperature, MHWs, and coral bleaching status under the worst recorded drought cycle in the Tropical South Atlantic (2013–2015). We examined 2880 colonies, most of which (∼93%) fit in the size group of 2–10 cm, with a small number (∼1%) of larger and older colonies (>20 cm). The results indicated the absence of MHWs and normal sea surface temperature variations (between 26.6 °C and 29.3 °C), however, we detected an extreme rainfall deficit (30–40% less annual volume precipitation). In general, a high proportion (44–84%) of bleached colonies was found throughout the months when turbidity decreased. Siderastrea is the only reef-building coral that comprises this seascape with encrusting and low-relief colonies. During drought periods, cloudiness is reduced, turbidity and wind speed are reduced, and solar irradiance increase, driving coral bleaching in turbid reefs. However, episodic rainfall and higher wind speeds increase turbidity and decrease coral bleaching. Our hypothesis is that turbidity decreases during drought periods which increases bleaching risk to corals even without thermal stress. Our results suggest that turbidity may have related to wind and rainfall to provoke the coral bleaching phenomenon.

The Effect of Bleaching Agents on Color Change in Different Section Shapes in Beech And Fir Woods

Aim of study: It is an investigation of the effects of bleaching processes on the color change in the wood of tree species. Tree species Eastern Beech (Fagus Orientalis Lipsky.) and Eastern Black Sea Fir (Abies Nordmanniana subsp.) were used in the study. Sodium hydroxide-hydrogen peroxide, oxalic acid, peracetic acid diluted 1/3, peracetic acid diluted 1/6 were used as bleaching agents. Trial samples were prepared in accordance with standards and color change measurements were made.&#x0D; Area of study: Surface treatments on wooden materials&#x0D; Material and methods: In the study, two wood species and one varnish type were used; Color changes were tested by applying various bleaches to the wooden material by rubbing method.&#x0D; Main results: As a result of the study, differences were observed in all cross-section shapes in beech wood bleaching measurements with 1/6 diluted peracetic acid, and differences were observed in cross-section shapes in fir wood bleaching measurements. The best bleaching of fir wood was achieved with peracetic acid.&#x0D; Main results: As a result of the study, differences were observed in all cross-section shapes in the beech wood bleaching measurements with 1/6 diluted peracetic acid, and in the cross-section shapes in the fir tree bleaching measurements. The best bleaching of fir wood was achieved with peracetic acid.&#x0D; Highlights: The bleaching process allows the wooden material to easily acquire a homogeneous color. Since the cell arrangements are different in different cross-sectional shapes, the bleaching rates are different from each other. While there is not much difference in the color changes in the wood material when bleached with oxalic acid, the samples are bleached as a result of bleaching with sodium hydroxide-hydrogen peroxide and peracetic acid. Significant changes have occurred in color changes. The reason for this difference is due to the different degrees of corrosion of bleaching agents.

Differential bleaching of quartz and feldspar luminescence signals under high-turbidity conditions

Abstract. Sediment burial dating using optically stimulated luminescence (OSL) is a well-established tool in geochronology. An important but often inapplicable requirement for its successful use is that the OSL signal is sufficiently reset prior to deposition. However, subaqueous bleaching conditions during fluvial transport are vastly understudied; for example the effect of turbidity and sediment mixing on luminescence bleaching rates is only poorly established. The possibility that slow bleaching rates may dominate under certain transport conditions led to the concept that OSL could be used to derive sediment transport histories. The feasibility of this concept is still to be demonstrated, and experimental set-ups are still to be tested. Our contribution to this scientific challenge involves subaquatic bleaching experiments, in which we suspend saturated coastal sand of Miocene age in a circular flume and illuminate it for discrete time intervals with natural light. We record the in situ energy flux density received by the suspended grains in the UV-NIR frequency range by using a broadband spectrometer with a submersible probe. Our analysis includes pre-profiling of each sample following a polymineral multiple signal (PMS) protocol. Using the PMS, the quartz-dominated, blue-stimulated luminescence signal at 125 ∘C (BSL-125) decays slower than the K-feldspar-dominated, infrared-stimulated luminescence signal at 25 ∘C (IR-25) even under subaerial conditions. The BSL-125 from purified quartz shows the opposite behaviour, which renders the PMS unreliable in our case. We find a negative correlation between suspended-sediment concentration and bleaching rate for all the measured signals. For outdoor bleaching experiments we propose to relate the measured luminescence dose to the cumulative received irradiance rather than to the bleaching time. Increases in the sediment concentration lead to a stronger attenuation of the UV–blue compared to the red–NIR wavelength. This attenuation thereby follows an exponential decay that is controlled by the sediment concentration and a wavelength-dependent decay constant, λ. As such λ could potentially be used in numerical models of luminescence signal resetting in turbid suspensions.

Investigating the use of two-dimensional OSL laser scanning instruments and energy-dispersive x-ray spectroscopy for OSL exposure dating

Optically Stimulated Luminescence (OSL) depth profiles can be used to extrapolate rock surface exposure ages by understanding a sample's light attenuation and OSL bleaching behaviors. However, the current measuring procedure for producing depth profiles, by measuring the luminescence of millimeter slices from surface core samples, offers limited resolution data, limiting parameter extrapolative precision. The use of OSL laser scanning measuring protocols on transverse core slices has potential for improving the data resolution of OSL depth profiles from core samples. An 11-year exposed rock surface was parameterized for light attenuation and luminescence bleaching rates using depth profile data from four surface cores collected via wafer and scan measuring techniques, to show the potential of OSL laser scanning to improve depth profile dataset resolutions and parameter extrapolative precision. Additionally, non-quartz OSL anomalies were filtered from scan datasets to determine if non-quartz mineral filtering can further improve the resolution and parameterization of depth profile datasets. OSL scanning measures improved the resolution of depth profiles over wafer derived depth profiles for the measured samples, and in comparing absolute uncertainties of parameters, broadly improved parameter precision using maximum likelihood estimate fitting protocols. Non-test dose corrected spatially resolved data error bounds were generally larger than from wafer derived data. When compared to unfiltered spatially resolved depth profile data, OSL anomaly filtered scanned depth profiles improved error bounds of anomaly affected data, and improved parameter extrapolative precision with roughly a similar effect as using non-filtered scan data. The absolute uncertainty in parameterization was impacted by scatter prevalent from scan datasets, which is caused by low OSL sensitivity from samples, the potential recording of remnant OSL, the lack of regenerative dose normalization applied to the scan dataset, as well as other scanning instrument measuring limitations. Still, these influences can be mitigated with optimized instrumentation and scanning protocols.

Significantly Enhanced Self-Cleaning Capability in Anatase TiO2 for the Bleaching of Organic Dyes and Glazes

In this study, the Mg2+-doped anatase TiO2 phase was synthesized via the solvothermal method by changing the ratio of deionized water and absolute ethanol Vwater/Vethanol). This enhances the bleaching efficiency under visible light. The crystal structure, morphology, and photocatalytic properties of Mg-doped TiO2 were characterized by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, N2 adsorption-desorption, UV-Vis spectroscopy analysis, etc. Results showed that the photocatalytic activity of the Mg2+-doped TiO2 sample was effectively improved, and the morphology, specific surface area, and porosity of TiO2 could be controlled by Vwater/Vethanol. Compared with the Mg-undoped TiO2 sample, Mg-doped TiO2 samples have higher photocatalytic properties due to pure anatase phase formation. The Mg-doped TiO2 sample was synthesized at Vwater/Vethanol of 12.5:2.5, which has the highest bleaching rate of 99.5% for the rhodamine B dye during 80 min under visible light. Adding Mg2+-doped TiO2 into the phase-separated glaze is an essential factor for enhancing the self-cleaning capability. The glaze samples fired at 1180 °C achieved a water contact angle of 5.623° at room temperature and had high stain resistance (the blot floats as a whole after meeting the water).

Modeling of bleaching process of camellia oil using multiple surrogate models

The objective of this article is to study the effect of bleaching conditions on the quality of camellia oil. To achieve this goal, the relationship between bleaching conditions (e.g., heating temperature, stirring speed, stirring time, and adsorbent content) and quality indexes are established using four surrogate models. The performance of different surrogate models is then compared, and the best one is chosen to analyze the influence of process parameters on quality. Additionally, the global sensitive analysis (GSA) is conducted to determine the relative importance of the four process parameters on oil quality. The results show: the RSM yields the best modeling accuracy for bleaching rate (BR), while SVR performs best for peroxide value (PV); Activated clay is the most important factor affecting both BR and PV, followed by heating temperature, stirring time, and stirring speed; The BR of 96.33% and PV of 0.03 meq/kg are obtained under the optimum bleaching conditions (temperature of 80 °C, stirring time of 10 rmp, stirring speed of 60 rpm, and adsorbent content of 7 g/hg), which is validated by experiment under the same conditions.

Combined influences of sources and atmospheric bleaching on light absorption of water-soluble brown carbon aerosols

Light-absorbing Brown Carbon (BrC) aerosols partially offset the overall climate-cooling of aerosols. However, the evolution of BrC light-absorption during atmospheric transport is poorly constrained. Here, we utilize optical properties, ageing-diagnostic δ13C-BrC and transport time to deduce that the mass absorption cross-section (MACWS-BrC) is decreasing by ~50% during long-range oversea transport, resulting in a first-order bleaching rate of 0.24 day‒1 during the 3-day transit from continental East Asia to a south-east Yellow Sea receptor. A modern 14C signal points to a strong inverse correlation between BrC light-absorption and age of the source material. Combining this with results for South Asia reveals a striking agreement between these two major-emission regions of rapid photobleaching of BrC with a higher intrinsic absorptivity for BrC stemming from biomass burning. The consistency of bleaching parameters constrained independently for the outflows of both East and South Asia indicates that the weakening of BrC light absorption, thus primarily related to photochemical processes rather than sources, is likely a ubiquitous phenomenon.

Photocatalytic Bleaching of Fast Green in Presence of Zinc Oxide as Photocatalyst

Abstract: The photocatalytic bleaching of Fast Green on zinc oxide powder has been carried out in presence of light. The photocatalytic bleaching of dye was observed spectrophotometrically. The effect of variation of different parameters like concentration of Fast Green, pH, amount of zinc oxide, and light intensity on the rate of photocatalytic bleaching was observed. A tentative mechanism for the photocatalytic bleaching of Fast Green has been proposed.

Spirooxazine loading effects on the photochromism of polymer films

Spirooxazines are well-known photochromic dyes that, upon proper illumination, convert between uncolored/coloured forms. In order to take advantage of their photoswitchable properties, one strategy is represented by their encapsulation in transparent host matrices, like polymers, which may improve the performance of the material, thanks to a major protection from oxidative degradation, or induce a variation of the optical properties, since the photochromic systems are affected by the surrounding environment. The fine-tuning and the strict control of the photochromic behaviour of the polymeric films is extremely appealing for several purposes, going from optical switches to sensors and light harvesting devices.One of the most elegant ways to exploit the photochromic characteristic of these materials is the controlled switch of the colour and the colouring/bleaching rate of a single photochromic system, since this versatility can open the possibility to use the same material for different applications.Therefore, a study of the modulation of the colourability and the colouring/bleaching rates of two spirooxazines in different polymeric matrices is herein reported. The influence of the photochromic concentration and the chemical nature of the polymeric matrix on the photophysical behaviour of the proposed systems is investigated to achieve a photochromic/polymeric dual system with tailored properties.The optical characterization of increasing concentrations of photochromic compound in solution was essential for the design of colour-defined polymeric films, highlighting, indeed, a correlation between photochromic concentration and colour switching from blue to pink, effect assigned to formation of aggregate species.By the proper choice of photochromic concentration and polymeric matrix, solid films showing great photoconversion efficiency and different colours were achieved under irradiation, together with the possibility to modulate the bleaching rate from few seconds to tens of minutes. Furthermore, polymeric films with different colours before irradiation could be produced as well.The obtained results open the possibility of a multi-purpose use of a photochromic system by simply varying its concentration within the polymeric film. Moreover, interesting colouring effect can be obtained by changing the polymeric matrix, therefore further widening their applicability.

Semi-automated EPR system for direct monitoring the photocatalytic activity of TiO2 suspension using TEMPOL model compound.

The photocatalytic activity of TiO2 nanoparticles in aqueous solutions is commonly evaluated by monitoring the rate of methylene blue bleaching and phenols degradation, but both substrates suffer from many drawbacks, e.g., the high capacity of dark adsorption, self-degradation, and photosensitization. Besides, filtration is always required to separate the particulate photocatalyst before the analysis. Herein, we investigated the potential use of electron paramagnetic resonance(EPR) and 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPOL) to directly monitor the photocatalytic activity of TiO2 suspensions without the need for filtration. The results showed that TEMPOL aqueous solution is in the dark and under UV-A illumination, does not absorb UV-A and visible light, and has negligible dark adsorption. The influence of TEMPOL concentration, light intensity, and TiO2 loading on the photocatalytic deactivation rate has been investigated. The mechanisms of TEMPOL deactivation in the presence and absence of oxygen as well as in the presence of methanol •OH radicals' scavenger have been discussed. The photocatalytic deactivation products have been analyzed using EPR, 1H-NMR, and 13C-NMR spectroscopies. It is found that the deactivation of TEMPOL is initiated by •OH radicals and α-H abstraction from the 4-piperidine position followed by the formation of TEMPONE (4-oxo-2,2,6,6-tetramethylpiperidine-1-oxyl) and 4-oxo-2,2,6,6-tetramethylpiperidine). In the presence of methanol, the formed α-hydroxyl radicals (•CH2OH) attack the nitroxide side of TEMPOL and produce 4-hydroxy-tetramethylpiperidine. Same activity trends have been observed for the photocatalytic methanol oxidation and TEMPOL deactivation over different types of TiO2 photocatalysts evincing that the proposed method has a potential for direct monitoring of the activities of photocatalyst suspensions.

Coral Reef Bleaching under Climate Change: Prediction Modeling and Machine Learning

The coral reefs are important ecosystems to protect underwater life and coastal areas. It is also a natural attraction that attracts many tourists to eco-tourism under the sea. However, the impact of climate change has led to coral reef bleaching and elevated mortality rates. Thus, this paper modeled and predicted coral reef bleaching under climate change by using machine learning techniques to provide the data to support coral reefs protection. Supervised machine learning was used to predict the level of coral damage based on previous information, while unsupervised machine learning was applied to model the coral reef bleaching area and discovery knowledge of the relationship among bleaching factors. In supervised machine learning, three widely used algorithms were included: Naïve Bayes, support vector machine (SVM), and decision tree. The accuracy of classifying coral reef bleaching under climate change was compared between these three models. Unsupervised machine learning based on a clustering technique was used to group similar characteristics of coral reef bleaching. Then, the correlation between bleaching conditions and characteristics was examined. We used a 5-year dataset obtained from the Department of Marine and Coastal Resources, Thailand, during 2013–2018. The results showed that SVM was the most effective classification model with 88.85% accuracy, followed by decision tree and Naïve Bayes that achieved 80.25% and 71.34% accuracy, respectively. In unsupervised machine learning, coral reef characteristics were clustered into six groups, and we found that seawater pH and sea surface temperature correlated with coral reef bleaching.