Effect of ultrasound on the structural characteristics and oxidative stability of walnut oil oleogel coated with soy protein isolate-phosphatidylserine.

In this study, the three-dimensional network system formed by rice bran wax (RBW) was used as the internal structure, and the external structure formed by soybean protein isolate (SPI) and phosphatidylserine (PS) was added on the basis of the internal structure to prepare walnut oil oleogel (SPI-PS-WOG). Ultrasonic treatment was applied to the mixed solution to make SPI-PS-WOG, on the basis, the effects of ultrasonic treatment on SPI-PS-WOG were investigated. The results showed that both ß and ß' crystalline forms were present in all SPI-PS-WOG samples. When the ultrasonic power was 450 W, the first weight loss peak in the thermogravimetric (TGA) curve appeared at 326 °C, which was shifted to the right compared to the peak that occurred when the ultrasonic power was 0 W, indicating that the thermal stability of the SPI-PS-WOG was improved by the ultrasonic treatment. Moreover, when the ultrasonic power was 450 W, the oil holding capacity (OHC) reached 95.3 %, which was the best compared with other groups. Both confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) showed that the ultrasonic treatment of appropriate power succeeded in making the SPI-PS-WOG samples more evenly dispersed in the internal structure and denser in the external structure. In terms of oxidative stability, it was found that the peroxide value of SPI-PS-WOG remained at 9.8 mmol/kg oil for 50 days under 450 W ultrasonic power treatment, which was significantly improved compared with liquid walnut oil (WO). These results provide a new idea for the preparation of oleogels, and also lay a theoretical foundation for the application of ultrasonic treatment in oleogels.

Rapid photodegradation of terrestrial soil dissolved organic matter (DOM) with abundant humic-like substances under simulated ultraviolet radiation.

Solar ultraviolet (UV) radiation exhibits a significant degradation for dissolved organic matter (DOM) in natural water ecosystems. However, research on photodegradation process of terrestrial components (e.g., humic-like substances) of DOM are limited due to drastic water dilution and rapid degradation. Here, photochemical degradation of terrestrial soil DOM with abundant humic-like substances from different land use were investigated by utilizing spectral technologies. Simulated UV radiation caused obvious losses on concentration, component structures, and fluorescence characteristic of soil DOM samples. The correlations between absorption specific parameters (a280, SUVA254, and SR) and dissolved organic carbon (DOC) were especially pronounced (p < 0.05), which could be used as valid indicators to determine changes in DOM composition and molecular size during photobleaching process. The decreases of DOM fluorescence intensity were corresponded to first-order kinetic and half-life reactions. The greatest reduction on fluorescence intensity (31.56-81.97%) belonged to peak C (i.e., humic-like substances). Overall, DOM from forest and grass soil ecosystems was more easily photochemical degraded than anthropogenic soil DOM. Enhancive contribution of fresh DOM formed by photodegradation increased autochthonous characteristic and bioavailable nutrition by increasing biological index (BIX) values and ammonia nitrogen (NH4+-N) concentration. The slight microbial decomposition effects on DOM happened in unsterilized dark condition. Our findings provided insights for understanding the rapid photodegradation processes of composition and structure of terrestrial DOM. Graphical abstract.

Novel cadmium oxide-graphene nanocomposite grown on mesoporous silica for simultaneous photocatalytic H2-evolution.

Novel Cadmium Oxide-Graphene Nanocomposite Grown on Mesoporous Silica have been successfully prepared using a self-assembly method under the catering of cetyltrimethylammonium bromide (CTAB) as the surfactant template at ambient conditions. The structural and optical properties of the obtained nanocomposites were investigated by many different techniques. The results of photocatalytic measurements revealed that almost 100% of MB organic dye was removed with the presence of SiO2/CdO-graphene composite under visible light irradiation. Moreover, the initial pH also plays an important role in the photodegradation processes. On the other hand, this work opens a way to enhance the photocatalytic activity of gallic acid at ambient conditions without any further different oxidation processes. From the evolutionary aspect, SiO2/CdO-graphene composite revealed better H2 generation than that of binary photocatalyst (CdO-graphene nanocomposite). The results of characterization and photodegradation suggest that SiO2/CdO-graphene material constitutes a new photocatalyst for the degradation of organic contaminants, as well as the development of an efficient hetero-system for hydrogen production.

The composition difference of macrophyte litter-derived dissolved organic matter by photodegradation and biodegradation: Role of reactive oxygen species on refractory component.

The overgrowth of macrophytes has become serious due to increasing eutrophication in shallow lakes. The primary degradation processes of macrophytes litter, including photodegradation and biodegradation, induce considerable patchiness in the concentration and bioavailability of dissolved organic matter (DOM). In this study we investigated the composition evolution of DOM derived from emergent aquatic plant litter, Phragmites australis, in microbial degradation, photodegradation, and the combination of bio- and photo-degradation. Results revealed that the effects of photo- and biodegradation on the composition difference of macrophyte litter-derived DOM during short- and long-term degradation phase were different. Although large changes in DOM were observed after five days of incubation, the abundance and chemical composition were similar in the three treatments. However, more concentration of DOM was produced by combined photo- and biodegradation at the long-term degradation phase, and the composition of DOM showed less lignin-like formulae, as well as less condensed aromatic and aromatic compounds when compared to sole treatments. More reactive oxygen species (ROS) were found under the combined treatments, thus the contents of refractory components (condensed aromatic- and aromatic compound groups) were reduced. This study provide deeper insight into the fate of DOM and relevant biogeochemical processes in eutrophic lakes.

Physical Properties of Monoglycerides Oleogels Modified by Concentration, Cooling Rate, and High-Intensity Ultrasound.

The aim of this study was to investigate the effects of monoglycerides (MG) concentration (3, 4.5, and 6 wt%), cooling rate (0.1 and 10 °C/min), and high-intensity ultrasound (HIU) application on physical properties of oleogels from MG and high oleic sunflower oil. Microstructure, melting profile, elasticity (G'), and solid fat content (SFC) were measured immediately after preparation of samples (t = 0) and after 24 hr of storage at 25 °C. Samples' textural properties (hardness, adhesiveness, and cohesiveness) and oil binding capacity (OBC) were evaluated after 24 hr at 25 °C. In general, samples became less elastic over time. Slow cooling rate resulted in lower G' after 24 hr compared to the ones obtained using 10 °C/min. Network OBC was improved by increasing MG concentration and cooling rate, and by applying HIU. After storage, oleogel melting enthalpy increased with MG concentration. In general, this behavior was not correlated with an increase in SFC. An improvement in the network structure was generally reached with the increase in cooling rate, according to texture and rheology results, for both sonicated and nonsonicated conditions. At the highest MG concentration, HIU application was more efficient at increasing OBC and hardness of the network at 0.1 °C/min. Microscopy images showed that the oleogels microstructure was changed as a consequence of HIU application and cooling rate, evidencing smaller crystals both in sonicated and faster cooled samples. Obtained results demonstrate that cooling rate, MG concentration, and HIU can be used satisfactorily to tailor physical properties of MG oleogels. PRACTICAL APPLICATION: Oleogels have been studied in the last years as semisolid fat replacers in food products. Cooling rate is an important processing parameter in the oleogel preparation because it affects their final physical properties, while high-intensity ultrasound (HIU) is a relatively novel technique to tailor lipid properties. This study is focused on the application of a slow/fast cooling rate in combination with/without HIU treatment at different monoglycerides and high oleic sunflower oil mixtures as a successful strategy to obtain oleogels with different physical properties and with potential applications in the food industry, such as fat substitutes in bakery.

Photocatalytic treatment of organic pollutants in a synthetic wastewater using UV light and combinations of TiO2, H2O2 and Fe(III).

In this study, the photocatalytic treatment of an organic wastewater with/without phenolic compounds by means of ultraviolet irradiation, titanium dioxide and hydrogen peroxide was examined in an annular photoreactor. Specifically, the effect of initial total carbon concentration, catalyst loading and H2O2 amount on the removal of total carbon was first examined in the case of a synthetic organic wastewater. The influence of partial carbon substitution by phenol, 2-chlorophenol, 2,4-discholophenol, trichlorophenol, and 4-nitrophenol on total carbon removal and target compounds' conversion was studied keeping constant the initial organic carbon load. It was shown that the process applied was effective in treating the wastewater for initial total carbon 32 mg L-1, 0.5 g L-1 TiO2, and 66.6 mg L-1 H2O2. Applying UV/TiO2 and UV/H2O2, 58% and 53% total carbon removals were achieved, respectively, but combining TiO2 and H2O2 did not result in a better performance in the case of the synthetic wastewater without any phenolic compounds. In contrast, when a phenolic compound was added, the addition of H2O2 was beneficial, eliminating the differences observed from one phenolic compound to another. The total carbon removals observed were lower than the corresponding final conversions of the target phenolic compounds. Finally, the electric energy per order values were calculated and found to range in 52-248 kWh/m3/order, being dependent from the process applied and the phenolic compound present in the wastewater.

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.

Efficient and Long-Lived Room-Temperature Organic Phosphorescence: Theoretical Descriptors for Molecular Designs.

Room-temperature phosphorescence (RTP) with long afterglow from pure organic materials has attracted great attention for its potential applications in biological imaging, digital encryption, optoelectronic devices, and so on. Organic materials have been long considered to be nonphosphorescent owing to their weak molecular spin-orbit coupling and high sensitivity to temperature. However, recently, some purely organic compounds have demonstrated highly efficient RTP with long afterglow upon aggregation, while others fail. Namely, it remains a challenge to expound on the underlying mechanisms. In this study, we present the molecular descriptors to characterize the phosphorescence efficiency and lifetime. For a prototypical RTP system consisting of a carbonyl group and π-conjugated segments, the excited states can be regarded as an admixture of n → π* (with portion α) and π → π* (portion ß). Starting from the phosphorescent process and El-Sayed rule, we deduced that (i) the intersystem crossing (ISC) rate of S1 → T n is mostly governed by the modification of the product of α and ß and (ii) the ISC rate of T1 → S0 is determined by the ß value of T1. Thus, the descriptors (γ = α × ß, ß) can be employed to describe the RTP character of organic molecules. From hybrid quantum mechanics and molecular mechanics (QM/MM) calculations, we illustrated the relationships among the descriptors (γ, ß), phosphorescence efficiency and lifetime, and spin-orbit coupling constants. We stressed that the large γ and ß values are favorable for the strong and long-lived RTP in organic materials. Experiments have reported confirmations of these molecular design rules.

Photocatalytic degradation of organic pollutants in wastewater with g-C3N4/sulfite system under visible light irradiation.

To develop low cost and high efficient sulfate radical (SO4-) based advanced oxidation processes (AOPs) for rapid remediation of contaminated waters is of great interest. In this study, a green and novel SO4- based AOPs, in situ visible light activation of sulfite by graphitic carbon nitride (g-C3N4), for the degradation of organic pollutants is reported. The g-C3N4+HSO3- + Vis system could achieve remarkably enhanced degradation of organic pollutants such as organic dyes and phenol in aqueous solution. The excellent reusability of the metal free catalyst was also observed during ten successive cycles. The efficiency of the system was dependent on the reaction conditions, which first increased and then decreased with the increase of HSO3- concentration and initial solution pH. The addition of HCO3- stimulated the pollutant degradation, but other water matrix components such as Cl- and humic acid showed nearly no influence on the reaction. The mechanism investigations suggested that sulfite is oxidized in the system to sulfite radicals, which then react with dioxygen and superoxide radicals to form SO5- radicals and HSO5- respectively. SO5- radicals can be also reduced by sulfite or photoelectron to HSO5-. SO4- radicals were then produced from HSO5- reduction by photoelectron, and contributed to dye degradation in the system together with superoxide radicals. This study provides a novel new approach for efficient degradation of organic degradation via sulfite activation.

Petroleomic analysis of the treatment of naphthenic organics in oil sands process-affected water with buoyant photocatalysts.

The persistence of toxicity associated with the soluble naphthenic organic compounds (NOCs) of oil sands process-affected water (OSPW) implies that a treatment solution may be necessary to enable safe return of this water to the environment. Due to recent advances in high-resolution mass spectrometry (HRMS), the majority of the toxicity of OSPW is currently understood to derive from a subset of toxic classes, comprising only a minority of the total NOCs. Herein, oxidative treatment of OSPW with buoyant photocatalysts was evaluated under a petroleomics paradigm: chemical changes across acid-, base- and neutral-extractable organic fractions were tracked throughout the treatment with both positive and negative ion mode electrospray ionization (ESI) Orbitrap MS. Elimination of detected OS+ and NO+ classes of concern in the earliest stages of the treatment, along with preferential degradation of high carbon-numbered O2- acids, suggest that photocatalysis may detoxify OSPW with higher efficiency than previously thought. Application of petroleomic level analysis offers unprecedented insights into the treatment of petroleum impacted water, allowing reaction trends to be followed across multiple fractions and thousands of compounds simultaneously.

Trade-offs in ecosystem impacts from nanomaterial versus organic chemical ultraviolet filters in sunscreens.

Both nanoparticulate (nZnO and nTiO2) and organic chemical ultraviolet (UV) filters are active ingredients in sunscreen and protect against skin cancer, but limited research exists on the environmental effects of sunscreen release into aquatic systems. To examine the trade-offs of incorporating nanoparticles (NPs) into sunscreens over the past two decades, we targeted endpoints sensitive to the potential risks of different UV filters: solar reactive oxygen production in water and disruption of zebrafish embryo development. First, we developed methodology to extract nanoparticles from sunscreens with organic solvents. Zebrafish embryos exposed to parts-per-million NPs used in sunscreens displayed limited toxicological effects; nZnO particles appeared to be slightly more toxic than nTiO2 at the highest concentrations. In contrast, seven organic UV filters did not affect zebrafish embryogenesis at or near aqueous solubility. Second, to simulate potent photo-initiated reactions upon release into water, we examined methylene blue (MB) degradation under UV light. nTiO2 from sunscreen caused 10 times faster MB loss than nZnO and approached the photocatalytic degradation rate of a commercial nTiO2 photocatalysts (P25). Organic UV filters did not cause measurable MB degradation. Finally, we estimated that between 1 and 10 ppm of sunscreen NPs in surface waters could produce similar steady state hydroxyl radical concentrations as naturally occurring fluvic acids under sunlight irradiation. Incorporation of NPs into sunscreen may increase environmental concentrations of reactive oxygen, albeit to a limited extent, which can influence transformation of dissolved substances and potentially affect ecosystem processes.

Kinetic study on photostability of retinyl palmitate entrapped in policosanol oleogels.

Photostability of all-trans retinyl palmitate (RP) (100% bioactivity) was studied in policosanol oleogels (PCOs) (7-12% w/w policosanol in soybean oil) after UVA irradiation. RP was incorporated into PCOs at levels of 0.04%, 0.1% and 1% (w/w). PCOs efficiently protected RP from UVA-mediated degradation. Over 75% RP-activity remained in PCOs after 4 days of UVA irradiation, while 12% RP-activity remained in soybean oil. HPLC analysis showed that cis-RP was formed in liquid soybean oil after 2 days of UVA irradiation while it was absent in PCOs matrices. PCOs blocked the energy absorption from UVA and further dampened the UVA-mediated ionic photodissociation and free radical reaction due to matrix immobilization. For all samples, RP photodegradation followed a 2nd order reaction. From the reaction kinetics, it would be possible to predict the RP photodegradation rate in PCO matrices. PCOs were shown to be a promising matrix to protect RP from photodegradation.

Bimetallic Au-Pd nanoparticles on 2D supported graphitic carbon nitride and reduced graphene oxide sheets: A comparative photocatalytic degradation study of organic pollutants in water.

Novel and sustainable bimetallic nanoparticles of Au-Pd on 2D graphitic carbon nitride (g-C3N4) and reduced graphene oxide (rGO) sheets was designed adopting an eco-friendly chemical route to obtain Au-Pd/g-C3N4 and Au-Pd/rGO, respectively. Elimination of hazardous pollutants, particularly phenol from water is urgent for environment remediation due to its significant carcinogenicity. Considering this aspect, the Au-Pd/g-C3N4 and Au-Pd/rGO nanocomposites are used as photocatalyst towards degradation of toxic phenol, 2-chlorophenol (2-CP) and 2-nitrophenol (2-NP) under natural sunlight and UV light irradiation. Au-Pd/g-C3N4 nanocomposite exhibited higher activity then Au/g-C3N4, Pd/g-C3N4 and Au-Pd/rGO nanocomposites with more than 95% degradation in 180 min under sunlight. The obtained degradation efficiency of our materials is better than many other reported photocatalysts. Incorporation of nitrogen atoms in the carbon skeleton of g-C3N4 provides much better properties to Au-Pd/g-C3N4 nanocomposite than carbon based Au-Pd/rGO leading to its higher degradation efficiency. Due to the presence of these nitrogen atoms and some defects, g-C3N4 possesses appealing electrical, chemical and functional properties. Photoluminescence results further revealed the efficient charge separation and delayed recombination of photo-induced electron-hole pairs in the Au-Pd/g-C3N4 nanocomposite. Generation of reactive oxygen species during photocatalysis is well explained through photoluminescence study and the sustainability of these photocatalyst was ascertained through reusability study up to eight and five consecutive cycles for Au-Pd/g-C3N4 and Au-Pd/rGO nanocomposites, respectively without substantial loss in its activity. Characterization of the photocatalysts after reaction signified the stability of the nanocomposites and added advantage to our developed photocatalytic system.

Facile Photoinduced Generation of Hydroxyl Radical on a Nitrocellulose Membrane Surface and its Application in the Degradation of Organic Pollutants.

A simple, clean, and efficient method has been developed for generating hydroxyl radicals on a nitrocellulose membrane (NCM) under light of wavelengths greater than 280 nm. Hydroxyl radicals formed on the NCM surface, diffusing into the bulk solution under irradiation. Radical generation was shown to be dependent on the nature of the NCM and light, and independent of the properties of the bulk solution. The quantum yield for hydroxyl radicals from the NCM was 1.72×10-4 , which is approximately 2.46 times that from TiO2 . This hydroxyl radical generation method was preliminarily applied in the photodegradation of organic pollutants, in which electrostatic interactions between the pollutant molecules and the NCM surface were found to play a key role. Further applications of this hydroxyl radical generation method should be assessed.

Modulation of the Singlet Oxygen Generation from the Double Strand DNA-SYBR Green I Complex Mediated by T-Melamine-T Mismatch for Visual Detection of Melamine.

Singlet oxygen (1O2), generated via photosensitization, has been proved to oxidize chromogenic substrates with neither H2O2 oxidation nor enzyme (horseradish peroxidase, HRP) catalysis. Of the various methods for modulation of the 1O2 generation, DNA-controlled photosensitization received great attention. Therefore, integration of the formation/deformation DNA structures with DNA-controlled photosensitization will be extremely appealing in visual biosensor developments. Here, the stable melamine-thymine complex was explored in combination with DNA-controlled photosensitization for visual detection of melamine. A T-rich single stand DNA was utilized as the recognition unit. Upon the formation of the T-M-T complex, double stand DNA was formed, which was ready for the binding of SYBR Green I and activated the photosensitization. Subsequent oxidation of TMB allowed visual detection of melamine in dairy products, with spike-recoveries ranging from 94% to 106%.

A review of quantitative structure-property relationships for the fate of ionizable organic chemicals in water matrices and identification of knowledge gaps.

Many organic chemicals are ionizable by nature. After use and release into the environment, various fate processes determine their concentrations, and hence exposure to aquatic organisms. In the absence of suitable data, such fate processes can be estimated using Quantitative Structure-Property Relationships (QSPRs). In this review we compiled available QSPRs from the open literature and assessed their applicability towards ionizable organic chemicals. Using quantitative and qualitative criteria we selected the 'best' QSPRs for sorption, (a)biotic degradation, and bioconcentration. The results indicate that many suitable QSPRs exist, but some critical knowledge gaps remain. Specifically, future focus should be directed towards the development of QSPR models for biodegradation in wastewater and sediment systems, direct photolysis and reaction with singlet oxygen, as well as additional reactive intermediates. Adequate QSPRs for bioconcentration in fish exist, but more accurate assessments can be achieved using pharmacologically based toxicokinetic (PBTK) models. No adequate QSPRs exist for bioconcentration in non-fish species. Due to the high variability of chemical and biological species as well as environmental conditions in QSPR datasets, accurate predictions for specific systems and inter-dataset conversions are problematic, for which standardization is needed. For all QSPR endpoints, additional data requirements involve supplementing the current chemical space covered and accurately characterizing the test systems used.

Complete and Partial Photo-oxidation of Dissolved Organic Matter Draining Permafrost Soils.

Photochemical degradation of dissolved organic matter (DOM) to carbon dioxide (CO2) and partially oxidized compounds is an important component of the carbon cycle in the Arctic. Thawing permafrost soils will change the chemical composition of DOM exported to arctic surface waters, but the molecular controls on DOM photodegradation remain poorly understood, making it difficult to predict how inputs of thawing permafrost DOM may alter its photodegradation. To address this knowledge gap, we quantified the susceptibility of DOM draining the shallow organic mat and the deeper permafrost layer of arctic soils to complete and partial photo-oxidation and investigated changes in the chemical composition of each DOM source following sunlight exposure. Permafrost and organic mat DOM had similar lability to photomineralization despite substantial differences in initial chemical composition. Concurrent losses of carboxyl moieties and shifts in chemical composition during photodegradation indicated that photodecarboxylation could account for 40-90% of DOM photomineralized to CO2. Permafrost DOM had a higher susceptibility to partial photo-oxidation compared to organic mat DOM, potentially due to a lower abundance of phenolic moieties with antioxidant properties. These results suggest that photodegradation will likely continue to be an important control on DOM fate in arctic freshwaters as the climate warms and permafrost soils thaw.

Gated Materials for On-Command Release of Guest Molecules.

Multidisciplinary research at the forefront of the field of hybrid materials has paved the way to the development of endless examples of smart devices. One appealing concept in this fertile field is related to the design of gated materials. These are constructed for finely tuning the delivery of chemical or biochemical species from voids of porous supports to a solution in response to predefined stimuli. Such gated materials are composed mainly of two subunits: (i) a porous inorganic support in which a cargo is loaded and (ii) certain molecular or supramolecular entities, generally grafted onto the external surface, which can control mass transport from pores. On the basis of this concept, a large number of imaginative examples have been developed. This review intends to be a comprehensive analysis of papers published until 2014 on hybrid mesoporous gated materials. The molecules used as gates, the opening mechanisms, and controlled release behavior are detailed. We hope this review will not only help researchers who work in this field but also may open the minds of related ones to develop new advances in this fertile research area.

Time Resolved Spectroscopic Studies on a Novel Synthesized Photo-Switchable Organic Dyad and Its Nanocomposite Form in Order to Develop Light Energy Conversion Devices.

UV-vis absorption, steady state and time resolved spectroscopic investigations in pico and nanosecond time domain were made in the different environments on a novel synthesized dyad, 3-(2-methoxynaphthalen-1-yl)-1-(4-methoxyphenyl)prop-2-en-1-one (MNTMA) in its pristine form and when combined with gold (Au) nanoparticles i.e., in its nanocomposite structure. Both steady state and time resolved measurements coupled with the DFT calculations performed by using Gaussian 03 suit of software operated in the linux operating system show that though the dyad exhibits mainly the folded conformation in the ground state but on photoexcitation the nanocomposite form of dyad prefers to be in elongated structure in the excited state indicating its photoswitchable nature. Due to the predominancy of elongated isomeric form of the dyad in the excited state in presence of Au Nps, it appears that the dyad MNTMA may behave as a good light energy converter specially in its nanocomposite form. As larger charge separation rate (kcs ~ 4 x 10(8) s-1) is found relative to the rate associated with the energy wasting charge recombination processes (kcR ~ 3 x 10(5) s-1) in the nanocomposite form of the dyad, it demonstrates the suitability of constructing the efficient light energy conversion devices with Au-dyad hybrid nanomaterials.

Insight into photocatalytic degradation of dissolved organic matter in UVA/TiO2 systems revealed by fluorescence EEM-PARAFAC.

Photocatalytic degradation of dissolved organic matter (DOM) using TiO2 as a catalyst and UVA as a light source was examined under various experimental settings with different TiO2 doses, solution pH, and the light intensities. The changes in UV absorbance and fluorescence with the irradiation time followed a pseudo-first order model much better than those of dissolved organic carbon. In general, the degradation rates were increased by higher TiO2 doses and light intensities. However, the exact photocatalytic responses of DOM to the irradiation were affected by many other factors such as aggregation of TiO2, light scattering, hydroxyl radicals produced, and DOM sorption on TiO2. Fluorescence excitation-emission matrix (EEM) coupled with parallel factor analysis (PARAFAC) revealed that the DOM changes in fluorescence could be described by the combinations of four dissimilar components including one protein-like, two humic-like, and one terrestrial humic-like components, each of which followed well the pseudo-first order model. The photocatalytic degradation rates were higher for protein-like versus humic-like component, whereas the opposite order was displayed for the degradation rates in the absence of TiO2, suggesting different dominant mechanisms operating between the systems with and without TiO2. Our results based on EEM-PARAFAC provided new insights into the underlying mechanisms associated with the photocatalytic degradation of DOM as well as the potential environmental impact of the treated water. This study demonstrated a successful application of EEM-PARAFAC for photocatalytic systems via directly comparing the kinetic rates of the individual DOM components with different compositions.