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Conversion of hydroquinone in a common direct methanol fuel cell (DMFC). The black line shows the UV
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... The results from UV-Vis shown in Figure S9 display how the two absorbance peaks centered at 210 and 270 nm that correspond to the phenol decreased at longer times of operation until it completely disappeared after 60 min. Simultaneously, during the degradation process, three additional peaks appeared according to the UV-Vis results (230-250 nm, 250-260 nm, and a very small 280-290 nm) which can be associated to a mixture of benzoquinone, hydroquinone, and catechol as intermediates of phenol degradation [66][67][68]. Additional results from GC/MS displayed in Figure S10 show that major intermediates include benzoquinone and hydroquinone. ...
The depletion of clean water resources and the consequent accumulation of contaminants in aquatic systems must be urgently addressed by means of innovative solutions. Electro-oxidation (EO) is considered a promising technology, prized for its versatility and eco-friendliness. However, the excessively high prices and the toxicity associated with some of the materials currently employed for EO impede its broader application. This study introduces cost-effective Ni-Mn binary oxide anodes prepared on Ni foam (NF) substrate. A scalable synthesis route that enables a 35-fold increase in the production of active material through a single optimization step has been devised. The synthesized binary oxide material underwent electrochemical characterization, and its effectiveness was assessed in an electrochemical flow-through cell, benchmarked against single Ni or Mn oxides and more conventional alternatives like boron-doped diamond (BDD) and dimensionally-stable anode (DSA). The novel binary oxide anode demonstrated exceptional performance, achieving complete removal of phenol at very low current density of 5 mA cm−2, along with an 80% of chemical oxygen demand (COD) decay within only 60 min. The NF/NiMnO3 anode outperformed the BDD and DSA when using comparable projected surface areas, owing to its high porosity and ability to produce hydroxyl radicals, as confirmed from the degradation profiles in the presence of radical scavengers. Furthermore, GC/MS analysis served to elucidate the degradation pathways of phenol.
... Thus, these peaks indicate that photooxidative structural changes of PTB7 involve the cleavage of the ether groups on the benzodithiophene during aging. The increase in absorption in the 300-400 nm region for the aged 80:20% PTB7:PCBM blend is supportive evidence for the formation of 1,4benzoquinone, which has an absorption profile near 300 nm 37 . Therefore, the 50:50% PTB7:PCBM blend exhibited enhanced photooxidative stability compared with the 80:20% PTB7:PCBM blend, similar to the trend observed in the UV-Vis spectra. ...
Previous studies have reported contradictory effects of small-molecule acceptors on the environmental stability of polymer:small-molecule blends, with one showing that a small-molecule acceptor stabilizes and another showing that it destabilizes the polymer donor. In this work, to investigate the origin of these contradictory results, the effects of the nanomorphologies of small-molecule acceptors on the environmental stability of polymer:small-molecule blends are demonstrated. Investigations on the environmental stabilities of polymer:fullerene blends of poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7):phenyl-C61-butyric acid methyl ester (PCBM) with contrasting nanomorphologies of PCBM reveal that dispersed PCBM in a mixed phase is the critical factor that causes triplet-mediated singlet oxygen generation and, hence, the severe photooxidation of PTB7, whereas an aggregated PCBM phase stabilizes PTB7 by reducing the formation of PTB7 triplet excitons. In addition, the photooxidation of PTB7 substantially degrades hole transport in the PTB7:PCBM blends by destroying the crystalline PTB7 phases within the films; this effect is strongly correlated with the efficiency losses of the PTB7:PCBM organic solar cells. These conclusions are also extended to polymer:nonfullerene blends of PTB7:ITIC and PTB7:Y6, thereby confirming the generality of this phenomenon for polymer:small-molecule organic solar cells.
... In order to confirm PAni degradation, after applying + 0.8 V vs. Ag/ AgCl, the solution in the positive SC was collected to be analyzed with UV-Vis spectrometry and compared with a reference solution (1 M NaCl). Fig. 5C shows the resulting absorbance spectra, which reveal the presence of an absorbance band at 250 nm ascribed to BQ for the SC [55]. The presence of BQ is a strong indication of the overoxidation of the electrode, which is the result from the irreversible oxidation of PAni under our working conditions (Scheme S2). ...
Capacitive deionization (CDI) is a technology used for water desalination and ion recovery based on the use of capacitive electrodes. Typically, the porous carbon electrodes used for CDI display limited ion storage capacity and selectivity due to the mechanism of ion storage in the electric double layer, but impressive improvements have been achieved using alternative, redox-based electrode materials, including conducting polymers like polyaniline (PAni). PAni is capable of capturing anions based on redox chemistry, but it degrades at anodic potentials typically used in CDI. In this work, we employed a multi-channel membrane CDI cell to map the stability window of a porous carbon electrode modified with PAni by controlling the anodic potential. We demonstrated for the first time that applying a potential as low as +0.35 V (vs. Ag/AgCl) yields a stable and high chloride removal capacity (65 mgCl/gAnode) with charge and coulombic efficiencies close to 100% for CDI. Furthermore, this is first work to explore the selectivity of the PAni-modified CDI electrodes towards chloride in binary solutions, evidencing that chloride is preferred regardless the valence of the competing anions. We believe that this work provides an important contribution for a larger figure, one in which CDI can be used for both high-performance water desalination, and efficient anion-selective removal and recovery.
... The test was performed under the condition described in Section 2.3, the only difference was the use of ammonium oxalate (C 2 H 8 N 2 O 4 ) with concentration of 0.57 g/L. The ammonium oxalate has been used by several authors as a hole scavenger [22][23][24][25][26][27][28][29][30]. The aliquots were taken every 30 min for 6 h and studied by UV-Vis spectroscopy and Total Organic Carbon (TOC). ...
... After the UV light irradiation, the absorption intensity increases as is also shown in Fig. 3S, this indicates the modification of phenol toward intermediate compounds, such as benzoquinone (B), catechol (C) and hydroquinone (H). The absorption bands for intermediates compounds can be observed at 247, 276 and 289 nm [26,27,60]. In this sense, the UV light promotes the intermediates formation but it is not capable to eliminate them. ...
The ZrSn composites materials were prepared in one pot by chemical co-precipitation method. SnO2 was incorporated to ZrxOy modifying the molar percentage from 1 to 5 mol%. The ZrSn composites were characterized by different techniques: XRD, FTIR, DRS, SEM, N2 physisorption and HR-TEM. The ZrSn composites were dried at 80 °C and thereafter were evaluated in the photodegradation of phenol under UV irradiation. The percentages of degradation and mineralization were determined after a reaction time of 150 min by UV–Vis spectroscopy and Total Organic Carbon analysis (TOC), respectively. The composite containing SnO2 in a 3 mol% showed the highest photoactivity with a 72% of photodegradation, a higher value compared with the obtained with TiO2-P25 (62%). Finally, a possible reaction mechanism was proposed based on certain studies, which allows to follow the formation of the active species •OH, •O2⁻ and h⁺. The formation of the •OH specie was measured by fluorescence spectroscopy whereas the inhibition of the species •O2⁻ and h⁺ was determined by UV–Vis spectroscopy. The results showed that the ZrSn composites not promotes the hydroxyl radical formation. In addition, the holes capture showed a full-loss of the photoactivity while the minimization of (•O2⁻) radicals in the reaction media results in a decrement of the photoactivity. The formation of heterojunctions and the presence of localized states in the synthesized composites offer an excellent alternative for a fast photodegradation of phenol.
... Compound 18 slowly oxidises to 19 ( Figure 2F) similar to the oxidation of 13 to 14. UV analysis of 19 is consistent with the quinone structure. [26] Late steps during the biosynthesis of terrein 1 ...
The mycotoxin terrein is derived from the C10‐precursor 6‐hydroxymellein (6‐HM) via an oxidative ring contraction. Although the corresponding biosynthetic gene cluster (BGC) has been identified, details of the enzymatic oxidative transformations are lacking. Combining heterologous expression and in vitro studies we show that the flavin‐dependent monooxygenase (FMO) TerC catalyzes the initial oxidative decarboxylation of 6‐HM. The reactive intermediate is further hydroxylated by the second FMO TerD to yield a highly oxygenated aromatic species, but further reconstitution of the pathway was hampered. A related BGC was identified in the marine‐derived Roussoella sp. DLM33 and confirmed by heterologous expression. These studies demonstrate that the biosynthetic pathways of terrein and related (polychlorinated) congeners diverge after oxidative decarboxylation of the lactone precursor that is catalyzed by a conserved FMO and further indicate that early dehydration of the side chain is an essential step.
... Quinones are used in numerous chemical systems, due to their good electron-transfer properties [53,54]. The simplest one, 1,4-benzoquinone is light sensitive and its photolysis has been studied since the beginning of the 20th century [55][56][57][58][59][60][61][62]. ...
In competition-based experiments, 1,4-benzoquinone (BQ) has been a frequently applied compound for determination of the role of O2⁻ radicals. In those studies, only the influence of BQ (as a competitive O2⁻ scavenger) on the degradation of a model compound (substrate) was investigated. Our goal was to develop a new, simple method monitoring a characteristic product of the reaction between the superoxide radical ion and BQ during heterogeneous photocatalysis. Interestingly, based on our results, if the concentration of BQ exceeds that of dissolved oxygen, it reacts with photogenerated electrons rather than with O2⁻ radicals. During this process, it is quantitatively reduced to 1,4-hydroquinone (H2Q), the degradation of which was found to be dependent of the presence of O2⁻ radicals. The photocatalytic transformation of both compounds (BQ, H2Q) was systematically investigated in anoxic and oxic atmosphere. Two new methods requiring only fluorescence measurements have been suggested: one for the determination of electrons with BQ (under anaerobic conditions) and another for the measurement of O2⁻ radicals with H2Q.
... The ratio of the peaks A276/A325 has been used to monitor the concentration of ionized phenolate groups. The peaks at 254 and 370 nm (at pH 10) are most likely related to the rearrangements of an ionized structure of TA to various conjugated quinone derivatives [26,27]. 1 H-NMR spectra of TA in PBS at 60 °C confirmed the decreased intensity of the peaks related to the hydroquinone form of TA and an increase in the intensity of the peak related to the quinone form. Similar chemical shifts are observed in TA equilibrated at pH 10 ( Figure S10). ...
... The ratio of the peaks A 276 /A 325 has been used to monitor the concentration of ionized phenolate groups. The peaks at 254 and 370 nm (at pH 10) are most likely related to the rearrangements of an ionized structure of TA to various conjugated quinone derivatives [26,27]. 1 H-NMR spectra of TA in PBS at 60 • C confirmed the decreased intensity of the peaks related to the hydroquinone form of TA and an increase in the intensity of the peak related to the quinone form. Similar chemical shifts are observed in TA equilibrated at pH 10 ( Figure S10). ...
Silver nanoparticles (AgNPs) may be synthesized by many different methods, with those based on the thermal reduction of silver salts by citric acid or citric acid/tannic acid being amongst the most commonly used. These methods, although widely used and technically simple, can produce particles in which the size, polydispersivity and morphology can vary greatly. In this work nearly mono-dispersed spherical AgNPs have been synthesized via a one-step reduction method by using sodium citrate and varying quantities of Tannic Acid (TA), which was thermally conditioned prior to use in the growth process. It was found that the final size can be further tailored by controlling the amount of TA and the thermal conditioning of the TA at 60 • C at different time points, which changes the size and polydispersivity of AgNPs. To better understand the origin of this effect, optical spectroscopic analysis and 1 H NMR of the TA following mild thermal conditioning of the solution have been done. Comparison of thermally conditioned TA and TA exposed to basic pH shows that similar chemical modifications occur and consequently produce similar effects on growth when used in the synthesis of AgNPs. It is proposed that thermal preconditioning of the TA introduces either chemical or structural changes, which decrease the final particle size under a given total silver content.
... However, the peak of Cdots was slightly red shifted after the interaction with p-benzoquinone. Previous studies demonstrated that the peaks at 222 nm and around 270 nm may be attributed to hydroquinone formed due to the acceptance of electrons donated by Cdots to benzoquinone [46][47][48][49][50]. Hence, this implies that an electron acceptor p-benzoquinone is being converted to hydroquinone upon interaction with Cdots by hydrogen-bond-donor-coupled electron transfer [51][52][53]. ...
Microwave mediated synthesis of catalytic fluorescent carbon dots (Cdots) has been reported using biodegradable starch as precursor. The as-synthesized Cdots were then characterized using various techniques such as fluorescence spectroscopy, fourier-transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and x-ray photoelectron spectroscopy (XPS) analysis. Interestingly, Cdots showed high catalytic activity in the photo-reduction of Ag+ to silver nanoparticles (Ag NPs). During the photo-reduction process, no additional surface passivating agents was needed to stabilize the Ag NPs. Further, TEM results indicated the formation of Cdot–Ag NP nanocomposite i.e. Ag NPs surrounded with Cdots, and the emission intensity of Cdots was significantly decreased whereas the lifetime of Cdots remained almost unaltered in the presence of Ag NPs following static quenching. Finally, combination therapy of Cdots and Ag NPs using Cdot–Ag NP nanocomposite was performed which indicated synergistic bactericidal activity against antibiotic resistant recombinant E. coli bacteria. The treatment elevated the reactive oxygen species (ROS) level as compared to its individual components. Additionally, the flow cytometer study demonstrated that combination therapy causing bacterial cell wall perforation that was possibly leading to synergistic
bactericidal activity against both Gram positive and Gram negative bacteria. The presence of Cdots on the surface of the Ag NPs due to their ground state complexation, possibly facilitated electrons towards Ag NPs which enhanced the ROS production in comparison to only Ag NPs.
... 35 Besides, an increase in the intensity is evidenced near 240 and 286 nm as the irradiation time passes, which could be associated with the formation of intermediate species such as benzoquinone and hydroquinone, respectively. 36,37 On the other hand, in the absence of photocatalyst (photolysis) a hyperchromic shift of the band located at 270 nm was observed wileyonlinelibrary.com/jctb in the UV spectrum (not shown), which is related to electronic modifications on the phenol molecule suggesting the generation of intermediates such as catechol and hydroquinones. 37,38 In this condition only 3.2% of phenol was degraded after 270 min of reaction. ...
BACKGROUND
Photocatalytic degradation is considered as an effective and eco‐friendly alternative for removal of persistent pollutants. The enhancement of the photocatalytic properties of conventional photocatalysts such as CeO2 can be realized by surface modification with metals or nonmetals, which allows a reduction in the recombination frequency of charge carriers. In this study, superficially phosphated CeO2 materials with various anion contents obtained using an impregnation method were evaluated in the photodegradation of phenol under UV irradiation.
RESULTS
The addition of phosphate anions promoted an increase in the surface area and a slight decrease in the crystallite size. The anchorage of the phosphate anions was via bidentate mode. An enhancement in the degradation of the pollutant was evidenced using the phosphated materials with respect to the results observed using unmodified CeO2. Also, an effect of the content of anions was evidenced, the optimal amount being equal to 1.0 wt%.
CONCLUSIONS
The surface modification of CeO2 with phosphate anions favors a control of the physical and chemical properties of the semiconductor and the effective separation of electron–hole pairs, which leads to an increase in the photocatalytic activity. © 2020 Society of Chemical Industry
... The UV-Vis absorption spectrum for AQDS and CD mixture prior and after the irradiation given below in Fig. 2 shows the formation of a new absorption line red shifted with respect to the AQDS absorption line. Such a redshift is typical for reduced quinones [18]. Assuming the intracomplex reaction between AQDS and CD which results in reduction of AQDS with formation of the AQDS-CD product (Scheme 1) and assuming that more than 90% of AQDS is The transient spectra of 3 AQDS in the presence of CD and the insets at different wavelengths corresponding to kinetics at longer times given below in Fig. 3 also show formation of a stable product which has spectrum similar to that given in Fig. 2 above, so we assume it pertains to the same AQDS-CD product. ...
The intracomplex reaction of anthraquinone-2,6-disulfonate (AQDS) in triplet excited state (3 AQDS) with beta-cyclodextrin (CD) and the reaction of 3 AQDS:CD complex with external quencher, N-Acetyl-l-Tyrosine (TyrO −), have been studied using laser flash photolysis, 1H NMR and 1H CIDNP. The two reactions were found to be competing with each other. The intracomplex hydrogen abstraction previously proposed for 3 AQDS:CD complex may represent a two-step process, where at first stage an electron is transferred from the-OH group of CD to 3 AQDS followed by a proton transfer and recombination of AQDS and CD radicals resulting in a stable AQDS-CD product. The rate constant of the intracomplex electron transfer from CD to 3 AQDS was found to be 6 ± 1 × 10 6 s −1 and the rate of subsequent proton transfer is 1 ± 0.1 × 10 6 s −1. The rate constant of electron transfer between TyrO − and 3 AQDS:CD complex (0.4 ± 0.1 × 10 9 M −1 s −1) drops approx. by half compared to that in the reaction between TyrO − and free 3 AQDS (0.8 ± 0.1 × 10 9 M −1 s −1).
