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Oxidation of sulfite and competitive absorption existed in Na2SO3 solution for simultaneous removal of NOx and SO2, inhibited the long-term high-efficiency when used for practical applications. A matching strategy was developed to solve these problems. Antioxidants combination was used to retard the oxidation of antioxidant and enhance inhibition of S(IV) (tetravalent sulfur) oxidation. Hydroquinone (HQ) and sodium thiosulfate (ST) showed a positive synergistic effect on inhibition of S(IV) oxidation. When SO2 concentration was 500 and 2000 ppmV, the addition of 0.1 wt.% HQ and 1 wt.% ST decreased the percentage of S(IV) oxidized by oxygen by over 30% and 40%, respectively. Alkali (Na2CO3) alleviated the competitive absorption between NOx and SO2. Moreover, Na2CO3 exhibited an enhancement effect on the absorption of NOx and SO2 when coupled with anti-oxidants. While the increase of oxygen pressure accelerated the oxidation of S(IV), the anti-oxidants can retard the oxidation. The measurement of pH suggested the removal efficiency of NOx highly depended on SO32⁻ concentration rather than pH. The further investigation of the mechanism suggested the match effect was related to the interaction between ST and the intermediate product of HQ. The match strategy holds a potential for application of SO32⁻ to denitration.

Here, nickel cobalt oxide micro-flowers (NCO-F) have been prepared by the hydrothermal method for their application as electrode material in supercapacitors. The electrochemical performance of the prepared material has been studied in three different aqueous electrolytes (1 M Na2SO4, 1 M KOH, and 1 M Na2SO4 with hydroquinone (Hq) and benzoquinone (Bq) as redox additives). The NCO-F shows maximum specific capacitance in 1 M KOH (470 Fg−1) followed by 1 M Na2SO4 with Hq and Bq additives (173 Fg−1) and 1 M Na2SO4 (101 Fg−1) at the scan rate of 5 mVs−1. However, the higher value of energy density and power density is obtained in 1 M Na2SO4 (35.80 Whkg−1 at 424 Wkg−1). This is because of the higher potential window possessed by NCO-F in 1 M Na2SO4. The results illustrate that the role of the potential window is important which in turn is governed by the type of electrolyte.

Trichoderma harzianum S7113 as an efficient fungal isolate for laccase production was identified using the 18S rRNA sequencing. T. harzianum S7113 attained its maximal laccase production level on the 14th day of static incubation at 28 °C and pH 5.0 using the inoculum size of 5 discs (14 mm), according to the one factor per time (OFT) method. The most appropriate carbon, organic and inorganic nitrogen sources to promote maximal laccase synthesis were glucose (15 g/L), beef extract (5 g/L), and ammonium chloride (4 g/L), respectively. Results of Response Surface Methodology (RSM) revealed that glucose, meat extract, and ammonium chloride concentrations of 17.54, 7.17, and 4.36 g/L respectively, at a pH value of 6.74 are the favorite conditions for high titer production. The ANOVA analysis highlighted an excellent match between the actual experimental results and the model predicted laccase production levels. The biodegradation of hydroquinone (HQ) by T. harzianum S7113 laccase was most efficient in the pH range of 5.0 to 6.5. The increase in laccase concentration led to a significant increase in the HQ conversion to get a biodegradation rate of 92 ± 2.6% with a laccase concentration of 0.75 U/mL after 3 h of reaction.

Environmental remediation via semiconductor (SC) photocatalysis has attracted great attention over the past three decades. However, prospect for large scale application is still under debate, basically due to the bottleneck of fast charge recombination and/or slow surface reaction. Herein we report a universal solution of speeding up organic degradation simply via co-deposited Pt and nickel phosphate (NiP). Several representative SCs have been examined, including TiO2 (anatase, rutile, and brookite) under a 320 nm light, and Bi-based SC (BiVO4, Bi2WO6, and Bi2MoO6) under a 420 nm light. In all cases, the rates of phenol degradation in aqueous solution always varied not only in the order of NiP/Pt/SC > Pt/SC > NiP/SC > SC, but also NiP/Pt/SC > (Pt/SC + NiP/SC + SC). Meanwhile, hydroquinone and benzoquinone were produced as the main intermediates, but their concentration was much lower than that of phenol decreased, especially for NiP-containing sample. The solid was characterized with several techniques, including photoluminescence and (photo)electrochemical measurement. It is proposed that Pt and NiP act as co-catalysts for O2 reduction and phenol oxidation, respectively. Such electron and hole transfer promote each other, additionally improving the efficiency of charge separation, and further increasing the rates of surface reactions. This work highlights the necessity of a versatile co-catalyst in SC photocatalysis.

In this work, we proposed a facile chemical etching/pyrolysis strategy to prepare multi-heteroatoms doped yolk-shell porous carbon by using common ZIF-8 as the precursor and phytic acid as the etching agent. The as-prepared porous carbon was composed by N-doped carbon frame core (N-CF) and N, P-codoped carbon frame shell (N, P-CF) with unique hierarchically porous structure. Besides, the yolk-shell hierarchically porous carbon (N-CF@N, P-CF) exhibited large specific surface and pore volume, promoted electrochemical active area and electron transfer kinetics. Compared with pure ZIF-8 derived N-CF, the as-synthesized N-CF@N, P-CF displayed enhanced electrochemical activity toward the oxidation of various target analytes, including organic pollutants (hydroquinone and catechol), active pharmaceutical molecule (acetaminophen), and small biological molecules (dopamine and uric acid). As a result, a versatile electrochemical sensing platform was successfully developed for the sensing of hydroquinone, catechol, acetaminophen, dopamine and uric acid with high sensitivity and selectivity. Besides, the detection limits were evaluated as 15.4 nM, 18.8 nM, 16.2 nM, 22.2 nM and 24.5 nM, respectively, which were competitive with many other electrode materials. This work helps to prosper the type of carbon-based nanostructure, and provides an advanced electrode material with great application potential for electrochemical sensors design.

Bisphenol A (BPA) is a chemical found in polycarbonate plastics and epoxy resins which is biologically harmful and toxicologically relevant at low doses. Electrochemical sensors offer rapid and accurate detection of bisphenols but suffer from electrode fouling. Boron-doped diamond is known for its exceptional capability to resist chemical fouling due to the weak molecular adsorption of s p 3 carbon. In this work, we use nanodiamond to overcome electrode fouling and detect BPA with a low detection limit at 5 nM. Further, we demonstrate the use of nanocarbon-modified electrodes for BPA detection. One-time use nanocarbon electrodes detect BPA through direct oxidation of BPA in a sensitive and reproducible fashion. For continuous monitoring of BPA, we introduce a new approach based on the detection of the by-product of BPA oxidation, hydroquinone (HQ), which acts as a proxy for BPA quantitation without the need of electrode replacement. These findings aim to tackle the challenges of increasing concern of BPA food and water contamination, as an alternative to the more costly and time consuming central laboratory tests.

Organic pollutants in electroplating wastewater can be removed by photodegradation, however the effect mechanism of heavy metal ions on photocatalytic activity still remains unknown. Herein, we firstly reported the self-assembly synthesis of titanium dioxide/reduced graphene oxide (TiO2/rGO) composites for phenol-4-sulfonic acid (PSA) removal, and investigated the effects of Cu2+ ions on photocatalytic efficiency. During the self-assemble process, rGO nanosheets were connected together to form network macropores, and simultaneously induced the deposition of hierarchically nanostructured TiO2 microspheres. The synergetic effects of TiO2 microspheres and rGO nanosheets improved the photocatalytic activity by enhancing light adsorption ability, stabilizing electron-hole separation and decreasing band gap energy. The Cu2+ ions in wastewater showed positive and negative effects on PSA photodegradation. In the photocatalytic reaction, the electron-induced reduction reaction of Cu(II) into Cu(0) or Cu(I) took place, which inhibited electron-hole recombination and thus enhanced photocatalytic activity. However, the high chemical stability of PSA-Cu(II) complex compounds held back PSA photodegradation. The appropriate concentrations of Cu2+ ions at around 25 mg/L accelerated PSA photodegradation over TiO2/rGO composites. The PSA degradation into CO2 and H2O was performed by using hydroquinone, benzoquinone and maleic acid as degradation intermediates. Hence, TiO2/rGO composites are novel multifunctional photocatalysts to purify electroplating wastewater.

Hybrid composites of phosphomolybdic acid@UiO-66 (PMo12@UiO-66) and Co-substituted phosphomolybdic acid@UiO-66 (PMo11Co@UiO-66) were synthesized using the direct solvothermal method. A variety of characterization results demonstrated that phosphomolybdic acid (PMo12) or Co-substituted phosphomolybdate acid (PMo11Co) clusters are uniformly dispersed in the cages of Zr-based metal-organic UiO-66 frameworks. The catalytic properties of these hybrid composites were investigated by applying the epoxidation of olefins with tert-butyl hydroperoxide as the oxidant. Compared to PMo12@UiO-66, PMo11Co@UiO-66 showed a much higher catalytic activity and was simply recovered by filtration and reused for at least ten runs without significant loss of catalytic activity. Particularly, PMo11Co@UiO-66 can efficiently convert cyclic olefins like limonenes to epoxides, and its selectivity to 1,2-limonene oxide reached 91% in the presence of a radical inhibitor such as hydroquinone. The excellent catalytic activity and stability of the hybrid composite PMo11Co@UiO-66 are mainly attributed to the uniform distribution of highly active PMo11Co units within the smaller cages of UiO-66, to the suitable surface polarity of the hybrid composite for facilitating the access of reagents and solvent, and to the strong interface-interactions between the polyoxometalate and the UiO-66 framework.

Polymethacrylic acid (PMAA) and modified Polymethacrylic acid functionalized with catechol (PMAA/CAT), hydroquinone (PMAA/HQ) and catechol-hydroquinone (PMAA/CAT-HQ) were synthesized by oxidative decarboxylation method using ammonium persulphate as an oxidant and characterized using UV–Visible spectroscopy, FT-IR, XRD, TGA and SEM studies. The percentage of substitution was found to be 81%, 84% and 87% respectively for PMAA/CAT, PMAA/HQ and PMAA/CAT-HQ. The anticorrosion behavior of the synthesized polymers on pure aluminium in 0.7 M HCl was studied by potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS) and weight loss (WL) methods. As the concentration of the inhibitor increases, the anticorrosion activities increases and reaches the optimum, on further increase in the inhibitor concentration, the anticorrosion activity decreased and remained constant that determines the optimum inhibition efficiency. The increase in the anticorrosion activities at the optimum inhibitor concentration of 300 ppm is found to be in the order: PMAA

The storage of biodiesels is a major concern for its long term performance. The present work reports the kinematic viscosity and density of Jatropha biodiesel (JBD) and Pongamia biodiesel (PBD) when exposed to sunlight and ultraviolet (UV) irradiation for up to thirty days and ten hours respectively. Along with the exposure towards radiations, different antioxidants viz. Butylatedhydroxyanisole (BHA), Butylatedhydroxytoluene (BHT), Tert-butyl hydroquinone (TBHQ) were also added to the biodiesel samples to observe their impact along with varying storage ambiance. The study aimed to establish a concrete approach towards the stability of biodiesels when exposed to the diverse ambiance.

The oxidation of dopamine (DA) on a boron-doped diamond (BDD) electrode was investigated using in situ attenuated total reflection infrared spectroscopy (ATR-IR) and infrared reflection absorption spectroscopy (IRAS). Voltammogram showed multiple anodic/cathodic peaks for the oxidation/reduction of DA and its oxidized derivatives on the BDD electrode. The oxidation/reduction species on the surface and in solution were assigned using ATR-IR and IRAS, respectively. The anodic oxidation of DA promoted polymerization, and the polymerized DA (PDA) was continuously deposited on BDD without being reduced by potential cycles, which resulted in the irreversible behavior of the voltammogram. A decrease in the oxidation current of DA by potential cycles was due to the deposition of PDA. Some intermediate quinone species, such as dopaminequinone and dopaminechrome, were reversibly reduced to hydroquinone.

(-)-Epigallocatechin-3-O-gallate (EGCG), the most abundant polyphenolic compound in catechins, exerts excellent physiological effects including antioxidant. However, with its high hydrophilicity and poor lipophilicity, the application of EGCG in oil products is limited. In this study, EGCG acetylated derivatives were prepared by transesterification of EGCG with vinyl ester in acetonitrile/isopropanol (1:1 v/v). Lipase Lipozyme RM IM was found to be the optimum catalyst at concentration of 12 U/g EGCG, with a molar ratio of 1:5 of EGCG to vinyl acetate as the substrates. And 83.2% conversion was obtained after 10 h reaction at 50 °C. Based on the ping-pong model, the kinetic equation was constructed to determine the reaction kinetic parameters. The analysis of the initial rate and progress curve indicated that the transesterification of EGCG and vinyl acetate was kinetically regulated. Two major acetylated derivatives were identified as 5″-O-acetyl-EGCG and 3″, 5″-di-O-acetyl-EGCG by LC-MS/MS and NMR. Their enhanced lipophilicity was confirmed by transmittance test and octanol–water partition coefficient. The antioxidant activity of di-acetylated EGCG was superior to mono-acetylated EGCG and EGCG, but slightly lower than tert-butyl hydroquinone (TBHQ) as determined by peroxide values (POV) and Rancimat test. Acetylated EGCG might be used as a potent antioxidant for controlling oxidation of oil.

As synthesized AgBr nanoparticles (NPs) and g-C3N4 nanosheets were synthesized and coupled to obtain the AgBr-g-C3N4 catalyst, It showed a boosted activity in the photodegradation of methyl orange (MO) in aqueous solution (1.6 and 1.3 times greater than just the AgBr and g-C3N4 NPs in the initial degradation experiments without any optimization, respectively). The composite was characterized by X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR), cyclic voltammetry (CV), etc. The modified carbon paste electrode by the composite showed a significant increase in peak current, confirming a significant increase in charge transfer between the semiconductors of the coupled system. The bandgap energies of the samples were estimated by both DRS and CV methods. The composite with an AgBr:g-C3N4 mole ratio of 2:1 showed the best photocatalytic activity. The initial pH of the MO solution was changed from 6.5 to 5.5 during the photodegradation process. Experimental design by RSM was used for the study of the interaction effects between the influencing variables. The conditions of the optimized run were: pH: 3.5, Catalyst dosage: 0.9 g/L, Time: 83 min, CMO: 3.2 ppm, while those of the central point were: pH: 6.1, Catalyst dosage: 0.99 g/L, Time: 82.50 min, CMO: 2.9 ppm. Various degradation intermediates such as benzene, phenol, catechol, hydroquinone, aniline, dimethylamine, benzoquinone, p-amino phenol, ethendiol, ethylene glycol, oxalic acid, maleic acid, 1-propenoic acid, sulfate, etc. were detected by GC-Mass. Further attacking of hydroxyl and superoxide radicals can easily mineralize these intermediates to water, carbon dioxide, and other inorganic species.

Carbonaceous nanostructures stand out as an excellent electrode material to enhance the electrocatalytic, electroconductivity, and long-term stability of the electrochemical sensor in recent years. This review article focus on the important advancement in developing carbonaceous nanomaterials-based electrochemical sensors for simultaneous electrochemical sensing (binary and ternary mixtures) of environmental contaminants dihydroxybenzene isomers. The fabrication of electrochemical sensors such as graphene/carbon nanotubes hybrid composite, graphene/ carbon nanotubes supported nanomaterials, mesoporous carbon, carbon nanofiber, carbon nano-fragment and biochar modified electrode was presented coupled with suitable applications. This review discussed the selective reports on the application of dihydroxybenzene sensors during the period from 2015 to 2020.

A novel additive system comprising bis-(sodium sulfopropyl)-disulfide, polyethylene glycol and hydroquinone (HQ) was developed and investigated to achieve high rate copper electrodeposition at high temperature. HQ, as the key additive compound in this system, refines the Cu grain, makes the coating surface bright and smooth at high current density. The underlying mechanism of the additive-assisted electroplating was investigated through electrochemical, morphological characterizations and molecular dynamics simulation. Nanocubical copper particles were found through chronoamperometry tests, which explains the fine crystalline Cu grains and the bright coating surface. Additionally, the formation of the nanocubical copper particles is caused by the different adsorption energies of HQ on (311), (111) and (220) crystal faces and further leads to a strong suppression on the (220) orient crystal faces. Moreover, the electroplating results of through-holes illustrate the feasibility of this additive system in practical applications.

Herein, we report the synthesis and analysis of fern shaped La2O3 nanostructures as potential scaffolds for efficient hydroquinone chemical sensing application. A facile, low-cost hydrothermal method was applied for the synthesis of 3D fern shaped La2O3 nanostructures. Several techniques were employed to characterize the synthesized La2O3 nanostructures. XRD analysis confirmed the hexagonal phase for the La2O3 nanostructures with an average crystallite size of 35.18 nm. FESEM and TEM analysis established the 3D fern shaped structures for La2O3 nanostructures with dendritic arms of different lengths alongside triangular-ovate outlines. Purity, composition and vibrational features were confirmed by EDS, FTIR and Raman spectroscopic studies. The fabricated 3D fern shaped La2O3 nanostructures modified glassy carbon electrode (GCE) showed remarkable electron mediating properties towards hydroquinone even at very low analyte concentrations. The linear dynamic range (LDR), experimental limit of detection (LOD) and sensitivity for 3D fern shaped La2O3 nanostructures modified GCE in phosphate buffer solution (PBS) were found to be 0.0781–0.625 mM, 0.0781 mM and 463.3 μA mM−1cm−2, respectively. Finally, a mechanism was also proposed for the electrochemical sensing of the hydroquinone. The presented work thus, confirms that the 3D fern shaped La2O3 nanostructures may be the future potential candidates for fabricating efficient and reproducible electrochemical sensors.

We have designed a versatile reusable cooperative catalyst oxidation system, consisting of palladium nanoparticles and laccase with unprecedented reactivity. This biohybrid catalyst was synthesized by the stepwise immobilization of laccase as an enzyme and Pd as a nanometallic component into the same cavity of siliceous mesocellular foams (MCF). MCF and nanobiohybrid catalyst were characterized by BET, SAXS, SEM, EDX elemental mapping, ICP-OES, TEM, TGA, FT-IR, and XPS techniques and the stepwise immobilization of laccase enzyme and Pd onto MCF was evaluated through several compelling electrochemical studies. The present catalytic system exhibits high activity toward (i) aerobic oxidation of alcohols to the corresponding carbonyl compounds, (ii) aerobic oxidation of cyclohexanol and cyclohexanone to phenol and (iii) aerobic dehydrogenation of important N-heteocyclic compounds (tetrahydro quinazolines, quinazolonones, pyrazolines and 1,4-diydropyridines) in the presence of catalytic amount of hydroquinone (HQ) as mediator in phosphate buffer (0.1 M, pH 4.5, 4 mL)/THF (4%, 1 mL) as solvent under mild conditions. The immobilization of both oxygen-activating catalyst (laccase) and oxidizing catalyst (Pd) onto the same support makes the present catalyst system superior to other currently available heterogeneous palladium based catalytic aerobic oxidation systems.

A kinetic model derived from a simplified reaction sequence is proposed for the photo-Fenton degradation of Paracetamol (PCT), employing an annular photoreactor. The kinetic model explicitly included the effects of radiation absorption on pollutant degradation kinetics through the evaluation of the Local Volumetric Rate of Photon Absorption (LVRPA). Irradiated experiments achieved an average PCT conversion of 99.3% at 5 min of reaction, and a maximum of 69% of mineralization. Conversely, non-irradiated experiments reached an average PCT conversion of 86.6% at 5 min of reaction, and a maximum of 35% of mineralization. Kinetic parameters (, ,M-1s-1) were estimated employing a nonlinear, multi-parameter regression method, and the validated kinetic model was used to predict temporal variations of the concentrations of HP, PCT, and the main reaction intermediates: hydroquinone (HQ) and 1,4-benzoquinone (BQ). The root mean square error (RMSE) values obtained for HP, PCT, HP, HQ and BQ were 1.16¿×¿10-2, 7.13¿×¿10-1, 3.53¿×¿10-3, 3.05¿×¿10-3 mM, respectively, showing a good agreement between experimental and predicted data. Moreover, the kinetic model was validated with a new set of experimental tests, confirming its predictive capacity. Beyond the degree of mineralization attained, additional cytotoxicity tests proved that the photo-Fenton process is effective in generating a non-toxic effluent under the operating variables investigated.

A facile strategy to modify the surface of K2SiF6:Mn4+ (KSFM) with commercially available hydrophilic hydroquinone (HQ) has been developed and waterproof stability (moisture resistance) of the KSFM has been significantly improved. It has been demonstrated that there are strong interactions between KSFM and HQ on the interface due to the hydrogen bonds of fluorine in KSFM with hydrogen in HQ. The relative luminous intensity of HQ-modified KSFM (denoted as KSFM-HQ) remained 99.7% of its initial value after immersion in water for 336 h, remarkable higher than that of KSFM which remained only 38.0%. It is proposed that the high water resistance of KSFM-HQ is achieved via two possible mechanisms: in situ decomposition of dark brown manganese (owing to the hydrolysis of [MnF6]2−) on the KSFM crystal surface and consequently the formation of a more protective Mn4+-free layer. The process effectively combines the advantages of transparent organic materials (herein HQ) before immersion in water and durable moisture resistance of inorganic materials (herein K2SiF6) on surface after immersion in water. The importance of HQ loading on moisture-sensitive fluoride phosphors has been further confirmed by using HQ-treated K2GeF6:Mn4+ (KGFM) as an additional example. This strategy provides a one-of-a-kind way to the development of water-resistant Mn4+-doped fluoride phosphors with high luminous stability for potential applications in water-borne fluorescent anti-counterfeiting ink and even warm WLEDs operating in high humidity. © 2023

A series of ternary Cu(0)/Cu(II)@g-C3N4/MCM-41 composites have been fabricated by varying the different weight percentage of Cu (2, 4, 6 and 8) with the help of wetness impregnation and thermal condensation methods. The different characterization techniques were adopted to evaluate the morphological studies of as prepared composites provides a better support to distribute g-C3N4 on its surface. Again copper was impregnated onto the surface of g-C3N4/MCM-41 surface as co-catalyst. With increase in copper content, it reduces from Cu(II) to Cu(0) without using a reducing agent. The presence of g-C3N4 helps to shift the Fermi level of CuO towards more negative values due to accumulation of photogenerated electrons on the surface of Cu nanoparticle. Due to the surface plasmon resonance effect of Cu(0), more polarized light was absorbed by the composite and also favours charge separation by creating a Schottky barrier at the junction. The 4 wt% Cu loaded over g-C3N4/MCM-41 exhibits highest percentage of phenol oxidation (97%) under visible light irradiation with different byproduct like benzoquinone (BQ), hydroquinone (HQ) and catechol (CT) with selectivity of 92%, 3% and 2% respectively. The enhancement in catalytic activity has been explained on the basis of synergism between g-C3N4 and Cu(II) and the SPR effect of Cu(0) which also acts as a co-catalyst present on the surface.

The carbon paste electrode was modified with poly (benzydamine) by cyclic voltammetric technique (CV) and its electrocatalytic activity towards the oxidation of catechol (CC) and hydroquinone (HQ) was studied. The detailed investigation on the various parameters influencing the activity was also carried out. From the obtained result, it was concluded that the process was adsorption - controlled and the involvement of same number of electron and proton. The simulations resolution of CC and HQ along with excellent selectivity and sensitivity were also exhibited by the studied MCPE. The detection limits 5.79 and 3.78 μM were found for CC and HQ respectively.

In this study, cobalt-iron selenides embedded in porous carbon nanofibers (CoFe2Se4/PCF), derived from Prussian blue analogues, was prepared as a novel phenolic sensor. The obtained CoFe2Se4/PCF nanocomposites show three-dimensional (3D) networks nanostructures that can supply a desirable conductive network to accelerate electron transfer and avoid the aggregation of CoFe2Se4 nanoparticles. Electrochemical detection of hydroquinone (HQ), catechol (CC) and resorcinol (RS), at CoFe2Se4/PCF modified glassy carbon electrode (GCE) were researched. The results show the obtained 3D CoFe2Se4/PCF/GCE exhibits excellent electrochemical properties towards the simultaneous testing trace of HQ, CC and RS. The obtained electrode provides wide linear ranges of 0.5–200, 0.5–190 and 5–350 μM and low detection limit of 0.13, 0.15 and 1.36 μM for HQ, CC and RS, respectively. The as-prepared phenolic sensor displays satisfied selectivity and long-term storage stability. In addition, the constructed sensor can be used to determine HQ, CC and RS in actual samples.

This work investigated the application of partial least-squares regression of complex numbers on multivariate data obtained by electrochemical impedance spectroscopy (EIS). The use of complex numbers–PLS was evaluated in the individual determination of two well-known redox probes: ferrocyanide and hydroquinone. The predictive ability of complex numbers–PLS was evaluated for EIS spectra obtained at different applied potentials and perturbation amplitudes, and was also compared to that obtained with PLS applied to EIS data presented as real numbers - only the real or imaginary part of the complex impedance, or the absolute impedance or the phase angle. It is shown that complex numbers–PLS is more efficient (better prediction models) when more complex electrochemical systems (hydroquinone) are probed. Excellent predictions were obtained for the determination of hydroquinone and catechol in the direct analysis of spiked tap water samples with EIS and complex numbers–PLS. Fil: Rodrigues, Dayvison Ribeiro. Universidade Estadual da Paraiba; Brasil Fil: Olivieri, Alejandro Cesar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; Argentina Fil: Fragoso, Wallace Duarte. Universidade Estadual da Paraiba; Brasil Fil: Lemos, Sherlan Guimarães. Universidade Estadual da Paraiba; Brasil

Most commonly employed anodes for photoelectrochemical degradation of organic contaminants in water are too thick, resulting in a low degradation efficiency due to the excessive electron-hole recombination. Multilayer-type TiO 2 /Au/TiO 2 nanocomposites have been prepared as photoanode thin films by pulsed laser deposition (PLD). The films were composed of six TiO 2 and five Au alternate layers, with total thickness of about 212 nm, aimed to optimize the absorption of photons and minimize the recombination. The influence of gold on the optical, structural, and chemical properties of the semiconductor nanocomposites was investigated. The band gap determined from Tauc model was 3.22 eV, close to that obtained by spectroscopic ellipsometry and lower than that of the TiO 2 film, revealing an enhancement of visible light absorption. The catalytic performance of PLD films was evaluated by using them as anodes in electro-oxidation (EO) and photoanodes in photoelectrocatalysis (PEC) to degrade 39-157 mg L ⁻¹ paracetamol in sulfate medium. The drug removal was very slow in EO, due to the low ability to form [rad] OH on the anode surface, which was significantly enhanced upon UVA irradiation in PEC. The presence of Cl ⁻ allowed a faster degradation by produced active chlorine. Finally, a hybrid process involving PEC + photoelectro-Fenton (PEF) with an air-diffusion cathode yielded total paracetamol decay in 4-5 min at an anodic potential of +4.0 V because of the efficient [rad] OH generation from Fenton's and photo-Fenton reactions. Hydroquinone, p-benzoquinone and hydroxylated products were detected during EO and PEC. The generation of active chlorine was confirmed by identifying a chlorinated derivative, N-(4-chloro-2-hydroxyphenyl)acetamide, in PEC + PEF treatment.

An electrochemical sensor was successfully fabricated by coupled ammoniated modification with PBS activation on glassy carbon electrodes (CA-GCE) and characterized by electrochemical impedance spectra. The CA-GCE showed outstanding electrochemical performance, and was applied to simultaneous detection of resorcinol (RC), catechol (CC) and hydroquinone (HQ), which could be ascribed to new active sites by the introduction of amino and oxygen-containing groups and H-bonds formed between hydroxyl groups of RC, CC, and HQ with amine, hydroxyl and carboxyl groups of CA-GCE. The reaction kinetics of RC, CC, and HQ and their reaction on CA-GCE were studied. Experimental results showed that the electrochemical reaction was adsorption controlled. Under the optimal conditions, the linear detection ranges for RC, CC, and HQ were 5–200 μM, 10–300 μM, and 1–300 μM, respectively, with their detection limits of 0.47, 0.23 and 0.46 μM, respectively. Interference and repeatability was further investigated. This strategy opened a new horizon for qualitative and quantitative detection of dihydroxy benzene.

A novel microfluidic paper-based analytical device (μPAD) was developed with benzoquinone (BQ)-mediated E. coli respiration method to measure the biotoxicities of pollutants. Functional units including sample injection, fluid-cell separation, all-carbon electrode-enabled electrochemical detection, were integrated on a piece of chromatography paper. The three-electrode, working electrode, counter electrode and reference electrode, were simultaneously screen-printed on the μPAD with conductive carbon ink. The satisfying electrochemical performance of the paper-based carbon three-electrode was confirmed by cyclic voltammetry detecting K3 [Fe(CN)6]. The process of cell toxication was considered that toxicants inhibited cell respiration and diminished the electrons on E. coli respiratory chain. It was quantitatively reflected by measuring oxidation current of hydroquinone (HQ) as a reduced state of the redox mediator BQ after the incubation of cells with pollutants. The current detection time, BQ concentration and E. coli incubation time were carefully optimized to establish the systematic optimized operations of BQ-mediated E. coli respiration method. Using the fabricated μPAD the half inhibitory concentration (IC50) were Cu2+ solution 13.5 μg mL−1, Cu2+-soil 21.4 mg kg−1, penicillin sodium-soil 85.1 mg kg−1, and IC30 of Pb2+ solution was 60.0 μg mL−1. Detection of pesticide residues in vegetable juices were accomplished in a similar way. The proposed method is fascinating on three points; 1) The generality in the biotoxicity detection depends on toxicants inducing cellular respiratory inhibition; 2) The portability and affordability make it convenient for practical applications, because of replacing incubators and centrifuges; 3) There is potential applicability in less-developed areas due to its simple operation and low-cost.

In this study, a well-dispersed Pd nanoparticle (NP)-supported RGO/Mn3O4 (G/M/Pd) composite was synthesized by a clean synthetic route, where galvanic replacement reaction simply occurred between Mn3O4 and a palladium salt, thereby avoiding the use of harsh reducing and capping agents. The G/M/Pd composite served as a robust catalyst for the catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) with H2O2 in an aqueous solution. Oxidation was completed in only 4 min, with a turnover frequency (TOF) of 3613 h−1; this TOF is one hundred times those of previously reported Pd- and Ag-based catalysts. The superior performance was related to the electronic inductive effect between Mn3O4 and Pd NPs, which was verified by density functional theory calculations. Trapping experiments revealed that the oxidation of HQ was considerably related to the ·OH radicals generated from the decomposition of H2O2. In addition, the influencing factors were further investigated, including catalyst and HQ concentrations, solution pH, solvents, and various inorganic and organic interferences. Moreover, the G/M/Pd catalyst exhibits diverse applications for the catalytic oxidation of HQ derivatives with high TOFs.

A simple and efficient electrochemical sensing platform for simultaneous detection of hydroquinone (HQ), catechol (CC) and resorcinol (RC) based on in-situ prepared sodium hydroxide (NaOH) nanorods was reported for the first time. Sodium hydroxide (NaOH) nanorods on glassy carbon electrode (GCE) was synthesized via one electrochemical deposition step in NaOH solution using constant current. The affecting factors including content of NaOH solution, deposition current and deposition time were investigated. The obtained electrodes were also examined by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The electrochemical behaviour analysis and dynamic study indicated that the three dihydroxybenzene isomers can be catalytically oxidized and discriminated simultaneously on the proposed electrode. Using square wave voltammetry (SWV), the ultrasensitive and simultaneous detection of HQ, CC and RC was realized with wide linear range from 0.03 to 1500 μM and low detection limit of 0.01, 0.01, 0.09 μM, respectively. The detection of them in real water samples was also successfully performed and good recovery was obtained.

A hypercrosslinked resin, named St-DVB-Al, was prepared by optimizing the conditions of the Friedel–Crafts reaction. The nitro and amine groups were further introduced into the skeleton to prepare the composite functional resins St-DVB-nitro and St-DVB-amine. The adsorption capacity of the modified resins for phenolic compounds reached to 412.9 mg/g, which were 16.4–47.7% higher than the commercial resin H103 with similar physical structure. For the p-nitrophenol and p-hydroxybenzoic acid, the adsorption capacity trends were St-DVB-amine > St-DVB-Al > St-DVB-nitro, but for the hydroquinone was St-DVB-nitro > St-DVB-amine > St-DVB-Al. The reason St-DVB-nitro exhibited efficient adsorption for hydroquinone was that the electron-acceptor group enhanced the synergistic conjugation with the electron-donating compound. The introduction of the electron-donor group in St-DVB-amine enhanced the synergistic conjugation with electron-acceptor compounds as well as the hydrogen bonding and acid-base interaction, thus exhibiting highly efficient adsorption for p-nitrophenol and p-hydroxybenzoic acid. The DFT model was used to calculate the ΔE values of St-DVB-nitro, St-DVB-amine and St-DVB-Al with three adsorbates, and the results were consistent with the adsorption trends. Relationship between adsorption capacity and adsorption behavior was clarified by a quantitative perspective.

A dual redox-active (proton-conductive) electrolyte composed of the mixture of two different soluble redox species is considered here for application in hybrid (battery-type) energy storage devices operating like high-power supercapacitor-type systems with an enhanced specific energy. The Keggin-type polyoxometalate (phosphotungstic acid), undergoing fast (electrochemically reversible) one-electron redox processes has been selected to support the negative electrode. In order to develop the potential difference in the cell, the hydroquinone, capable of oxidation/reduction according to the fast two-electron mechanism has been adopted and its electroactivity was predominantly confined to the positive electrode. It enabled us to design a hybrid charge storage cell with the operating voltage of 0.8 V and the specific energy of 20 Wh kg−1 (per total mass of both electrodes). In the constant power discharge mode, 13 Wh kg−1 of the energy has been preserved at the power of 1 kW kg−1 during discharging down to ½ of the maximum voltage which is consistent with the fast charging/discharging dynamics of the proposed hybrid system. A mixed hierarchical micro-porous (predominantly mesoporous) carbon of high (>2 cm3g-1) total pore volume and the BET surface area approaching 1000 m2 g−1 has been selected as the electrode material permitting electrical double layer charging, supporting electroactivity of redox species and unimpeded mass transport. Also, the normalization of electrical parameters against the total mass of electrodes and electrolyte resulted in a ca. five-fold increase of discharge capacity and specific energy in comparison to the performance of a simple electrical double-layer capacitor.

The photocatalytic performance of a thermally exfoliated carbon nitride material was investigated in aqueous solution and employing visible-light emitting diodes (LEDs) as radiation source (λmax = 417 nm). The operating conditions were studied using phenol as model compound. The increase on the surface area of the catalyst with the exfoliation treatment promotes faster degradation and mineralization rates and an easier reduction of O2 into H2O2. The H2O2 production takes place only in the presence of both phenol and dissolved oxygen. The study was followed by assessing the photocatalytic degradation of ten organic compounds (individually or in a mixture) commonly found in agro-industrial wastewaters (phenol, catechol, resorcinol, hydroquinone, benzoic acid, 4-hydroxybenzoic acid, protocatechuic acid, gallic acid, 4-methoxyphenol and tyrosol). These compounds were selected to study the position, order and nature of substitution on the aromatic ring as well as the possible influence of the pKa. Generally, more reactive compounds yield higher amounts of H2O2 formed, whereas the pKa does not affect photocatalysis owing to the amphoteric properties of the catalyst. Thus, the successful oxidation of the organic compounds achieved in situ generation of H2O2 with relatively high productivities using a metal-free carbon nitride material stable in consecutive runs.

The multi-walled carbon nanotubes decorated with Co3O4 nanoparticles (Co3O4/MWCNTs) were successfully prepared by the hydrothermal method. A facile and practical electrochemical sensor based on Co3O4/MWCNTs was established for simultaneous detection of hydroquinone (HQ) and catechol (CC) by differential pulse voltammetry (DPV). The defined and separated oxidation peaks of a mixture of HQ and CC were obtained at pH 8.0, owing to the catalytic stability of Co3O4 in alkaline conditions as well as the high conductivity and excellent adsorption of MWCNTs. The proposed sensor exhibited the wide linear range from 10 to 800 μM (HQ) and 10–700 μM (CC), as well as the low detection limit of 5.6 μM (HQ) and 8.5 μM (CC). Meaningfully, in local seawater sample testing, the explored sensing platform achieved an excellent recovery for the simultaneous detection of CC (97.5–104.2%) and HQ (96.4–109.1%). According to the investigation, this is the first successful application of HQ and CC in direct seawater detection. This work demonstrated the Co3O4/MWCNTs nanocomposite was a promising material for electro-catalysis and electro-analyst in the marine environment.

Background: Skin lightening products containing dangerous levels of chemicals pose a serious health concern for consumers. However, to date, the extent of these products in Europe has not been extensively studied. The aim of this study was to determine whether harmful skin lightening products are available for sale in Europe and what violations exist regarding their composition., Materials and methods: We queried the Rapex database, which is the Rapid Alert System for dangerous non-food products among 31 European countries, to identify skin lightening cosmetics reported between 2005 and 2018, and presented a detailed summary of these notifications., Results: In the years 2005-2018, of all violations regarding cosmetics, 26.3% concerned skin lightening products. In the database, 266 reports on skin lightening products were identified. Most of the notifications came from Germany (17.29%), France (17.29%), Portugal (15.41%), and the United Kingdom (11.65%). The majority of the registered products originated from non-European countries, mainly the Cote d'Ivoire (29.70%). The major reason for the violation was the content of hydroquinone, mercury, or clobetasol propionate., Conclusions: Hazardous skin lightening products that are not in line with European cosmetics legislation are available on the European market. Most of the products are imported. The main risk associated with these products is the content of hydroquinone, mercury, and clobetasol propionate. It is important to bear in mind that this study focuses on the Rapex system and other sources of information may exist. Based on our findings, a more comprehensive evaluation by international authorities is justified.

The activities of heterogeneous Fenton and Photo-Fenton processes using pyrite (FeS2) prepared via a solvethermal method were evaluated by oxidation of p-nitrophenol (PNP). PNP could be completely ultrarapidly oxidized by Pyrite-Photo-Fenton (Pyrite-PF) system within 4 min, versus 10 min in Pyrite-Fenton (Pyrite-F) system. The excellent oxidation performance obtained by Pyrite-PF might be due to accelerated circulation between ferrous ions and ferric ions under visible light illumination, which improved generation of reactive oxygen species (ROS). X-ray diffraction (XRD), scanning electron microscope (SEM), high resolution transmission electron microscopy (HRTEM), electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) were applied to ascertain the morphology and crystal structure of fresh-pyrite as well as used-pyrite. According to these results, the synthesized pyrite particles performed eminent stability, and used-pyrite could even generated more ROS including hydroxyl radicals ( OH) and superoxide radicals ( O2−). EPR testing and quenching experiments also confirmed the generations of OH, O2− and holes (h+) during oxidation processes of PNP in both Pyrite-F and Pyrite-PF systems. The reaction pathway was proposed based on the detected intermediate products including 4-nitrocatechol, 4-nitropyrogallol, hydroquinone, benzoquinone, 1,2,4-trihydroxybenzene and 2,4-dinitrophenol. The mechanisms of PNP degradation in Pyrite-F and Pyrite-PF systems have also been studied by DFT calculations. Pyrite (111) should be responsible for the generations of free OH and surface OH.

This study focuses on post-sulfonated polysulfone membranes for potential applications in desalination by reverse osmosis or electrodialysis. A series of controlled molecular weight (5000 and 10,000 g/mol) polysulfones containing hydroquinone and their high molecular weight linear counterparts were synthesized using post-sulfonation of pre-formed polymers under mild conditions. The sulfonic acid groups were substituted on only the hydroquinone units. Amine terminated oligomers were crosslinked with a tetrafunctional epoxy molecule under suitable conditions to form membranes whereas the linear high molecular weight polymers were cast directly to form films with chain entanglements. Fixed charge concentrations of the membranes based on linear copolymers increased from 3.94 to 5.14 meq/mL when the ion exchange capacity was decreased from 1.30 to 0.88 meq/g. The fixed charge concentration of the networks cast from the 5000 g/mol oligomers increased from 4.04 to 6.23 meq/mL with a decrease in the ion exchange capacity from 1.51 to 0.90 meq/g.

Sensitive, selective, and reproducible monitoring of multiple phenols simultaneously needs an electrochemical interface with a large surface area and a big amount of active sites. Herein, expanded graphite (EG) as the supporter is decorated with the sensing material of carbon-coated palladium oxide (PdO@C) nanoparticles. After its characterization using transmission electron microscopy, X-ray photoelectron spectroscopy, and electrochemical techniques, this composite based electrochemical interface has been utilized for the voltammetric sensing of tetrabromobisphenol A (TBBPA), hydroquinone (HQ), and catechol (CC). Compared with either EG or PdO@C based interfaces, this one delivers much enhanced redox currents for three phenols. Individual and simultaneous detection of TBBPA, HQ, and CC has been realized at nano-molar levels. The calculated detection limits are 1.3, 26, and 17 nM for TBBPA, HQ, and CC, respectively. Such an interface thus owns great prospect in constructing a universal platform for individual and simultaneous detection of multiple phenols in different samples.

Extensive attention has been paid to rationally control the artificial nanoenzyme activities via suitable strategies to prepare various nanoscale functional materials. Herein, FeCo co-doped carbon sphere (FeCo@C) with intrinsic oxidase-like and peroxidase-like activity has been obtained from the carbonization of FeCo-ZIF. The unique dual-enzyme catalytic property of FeCo@C can be simply regulated and utilized for bifunctional colorimetric platforms. At pH 3.6 and catalytic reaction time of 6 min, the FeCo@C possesses strong oxidase-like activity which can catalytically oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) owing to the production of O2·− with the participation of O2 to result in typical color change of the system. Hydroquinone (HQ) as a reducing agent can induce the color fading, and therefore, a novel colorimetric biosensing platform for HQ was constructed with the linear range of 1–30 μM and detection limit of 0.8 μM. However, with the pH of 4.4 and catalytic reaction time of 3 min, the oxidase-like activity of FeCo@C was obviously weakened, and the peroxidase-like activity of FeCo@C is still high. Hence, a facile analytical method was developed to detect H2O2 based on the peroxidase-like activity of FeCo@C with the linear range of 1–240 μM and detection limit of 1 μM. Moreover, the FeCo@C has high stability and strong magnetism with the activity being kept well after several cycles of recycling, which shows great prospect in biosensing and catalysis areas.

We report the synthesis, characterization, electrochemical sensing and catalytic capability of the bimetallic heterojunction Al2O3/ZnO micro flowers (AZ MFs). In order to prepare this bifunctional material, the facile hydrothermal process was adopted. The material was thoroughly characterized for the crystal structure and morphology with Powder XRD, XPS and FE-SEM. The investigation of electrochemical sensing was done using hydroquinone (HQ) and the chemical catalysis was using rhodamine B (RhB) with our bimetallic Al2O3/ZnO micro flowers as these are harmful industrial pollutants. The process parameters like the influence of scan rate and pH was efficiently optimized for the electrochemical detection of HQ and kinetics for the time dependent catalytic degradation of RhB dye. The linear relationship between the peak current and the concentration of HQ was found to be in the range of 0.125–20.25 μM with an impressive detection limit of 11.2 nM. In the chemical catalytic degradation of the RhB dye, our bimetallic material thrived well during the reaction and degraded the material in 10 min. The performance of bimetallic Al2O3/ZnO micro flowers towards HQ detection and RhB degradation shows good stability, reproducibility and it can be efficiently utilized to treat the environmental pollutants.

A sensitive sandwich-type electrochemical immunosensor based on dual amplification strategy was constructed. The dual amplification strategy has been used secondary antibody(Ab2)-horseradish peroxidase(HRP)-Au@Ag nanoparticles (Au@Ag NPs) for carcinoembryonic antigen(CEA) detection. Ab2-HRP-Au@Ag NPs as dual amplification markers triggered the disproportionation of H2O2, which could facilitate the catalytic oxidation of hydroquinone to quinone(BQ). In addition, due to their large surface area and excellent conductivity, nitrogen-doped graphene were used as a platform to firmly assemble primary antibody (Ab1). Above mentioned generated amout of BQ are corresponding to trace CEA, resulting in the highly electrochemical reduction signal. Under the optimal conditions, the linear range of CEA concentration was 0.0001–100 ng mL−1, and the limit of detection (LOD) could be as low as 0.05 pg mL−1. Importantly, the immunosensor also showed acceptable stability, reproducibility and selectivity.

The detection of albumin in urine is of great significance for the early diagnosis and treatment of diseases. Herein, a molecularly imprinted electrochemical biosensor was designed for the detection of human serum albumin (HSA) in urine based on dual-signal strategy. The gold electrode (GE) was orderly modified by Au nanoparticles (AuNPs), polythionine-methylene blue (PTH-MB) and molecularly imprinted polymers (MIPs). The MIPs were synthesized through electro-polymerization, which utilized HSA as the template, and employed o-phenylenediamine (o-PD) and hydroquinone (HQ) as the functional monomers. The biosensor showed dual-signals at 0.20 V and −0.22 V corresponding to Fe(CN)63−/4− and PTH-MB, respectively. When HSA was captured on the MIPs, the dual-signal simultaneously decreased. Both of the current signals of the substrate probe PTH-MB (ΔIsubstrate) and the solution probe [Fe(CN)6]3-/4-(ΔIprobe) were converted before and after the incubation of target HSA. The sum of the signal conversions ΔID (ΔIsubstrate+ΔIprobe) was utilized to quantify the target amount. Under the optimal conditions, the proposed biosensor exhibited a linear regression equation in the concentration range from 1.0×10-10 to 1.0×10-4 g L-1, with a low detection limit of 3.0×10-11 g L-1 (S/N=3). Furthermore, the prepared biosensor was employed for the determination of albumin in urine with satisfied selectivity and reproducibility.

A highly sensitive electrochemical method was performed for simultaneous detection of hydroquinone (HQ) and catechol (CT) using poly(3,4-ethylenedioxythiophene)/reduced graphene oxide/manganese dioxide (PEDOT/rGO)/MnO2) composite. The PEDOT/rGO/MnO2 composite was prepared in two steps via cyclic voltammetry (CV). The composite was characterized using field emission scanning electron microscope (FESEM), Fourier transform infrared spectrometer (FTIR), X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), CV and electrochemical impedance spectroscopy (EIS). The PEDOT/rGO/MnO2 composite showed excellent electrochemical catalytic activity towards the oxidation of HQ and CT by displaying well-separated oxidation peaks and high oxidation peak currents of HQ and CT. The composite showed linear responses from 0.5 to 150 μM for HQ and 0.25–150 μM for CT. The sensor exhibited excellent sensitivity with the detection limits of 0.05 and 0.07 μM for HQ and CT, respectively. In addition, PEDOT/rGO/MnO2 composite showed excellent reproducibility, repeatability and stability. The PEDOT/rGO sensor was successfully studied in the real sample of lake water and tap water with high recoveries.

Pentachlorophenol (PCP) caused water quality problems owe to its past widespread application and stability, harmful to human health. Photocatalysis, which was mainly involved in the reactive oxygen species (ROS) reaction, has large potential as water treatment process. However, the roles of ROS on the degradation process of PCP are not yet clearly defined. The main objectives of this work were to investigate the roles of ROS involved in the whole degradation of PCP and main toxic intermediates and elucidate the degradation mechanisms. Tetrachloro-1,4-benzo/hydroquinone (TCBQ/TCHQ), trichlorohydroxy-1,4-benzoquinone (OH-TrCBQ) and 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (OH-DCBQ) were identified as main intermediates. The roles of generated ROS including OH, O2- and H2O2 were systematically explored for the degradation of PCP and its main intermediates using radical quenchers. The results showed that, OH played the dominant role for the degradation of PCP, O2- played more contributing roles for the degradation of TCBQ, H2O2 exhibited major contribution for the degradation of OH-TrCBQ and OH-DCBQ. These results offered us an insight into the degradation mechanism of PCP involved with ROS. It can also serve as the basis for controlling and blocking the generation of highly toxic substances through regulating the ROS generation during the PCP degradation.