Search

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.

Herein, a highly sensitive electrochemical immunosensor was presented for the cardiac troponin I (cTnI) determination using a multifunctional covalent organic framework-based nanocomposite (HRP-Ab2-Au-COF) as the signal amplification probe. The spherical COF with a large surface area was synthesized in a short time by a simple solution-based method at room temperature. The good biocompatibility, low toxicity, and high stability in water of the COF guarantee its application in biosensing. Besides, its high porosity makes it an excellent carrier for loading abundant horseradish peroxidase (HRP). The modified gold nanoparticles on the surface of COF not only provide a load platform for secondary antibody (Ab2) but also improve the conductivity of COF. Under the synergistic effect of the hydrogen peroxide (H2O2) and HRP, hydroquinone (HQ) in the solution is catalytically oxidized to benzoquinone (BQ), which is then reduced on the electrode surface to generate the electrochemical signal. The designed probes not only show the specific recognition behavior of Ab2 to cTnI but also improve the sensitivity of the biosensing system due to the signal amplification caused by the excellent enzyme catalytic performance of HRP. Based on the H2O2-HRP-HQ signal amplification system, the biosensor for cTnI was fabricated and exhibited a linear response as a function of logarithmic cTnI concentration ranging from 5 pg/mL to 10 ng/mL, and the detection limit was 1.7 pg/mL. Moreover, the biosensor exhibited excellent recovery and reproducibility in the actual sample testing. This work provided a simple approach to determine cTnI quantitatively in practical samples and broadened the utilization scope of the COF-based nanocomposite in the electrochemical immunosensor.

This work develops a kinetic model that allow to predict the water toxicity and the main degradation products concentration of aqueous solutions containing 4-chlorophenol oxidised by UV/H2O2. The kinetic model was developed grouping degradation products of similar toxicological nature: aromatics (hydroquinone, benzoquinone, 4-chlorocatechol and catechol), aliphatics (succinic, fumaric, maleic and malonic acids) and mineralised compounds (oxalic, acetic and formic acids). The degradation of each group versus time was described as a mathematical function of the rate constant of a second-order reaction involving the hydroxyl radical, the quantum yield of lump, the concentration of the hydroxyl radicals and the intensity of the emitted UV radiation. The photolytic and kinetic parameters characterising each lump were adjusted by experimental assays. The kinetic, mass balance and toxicity equations were solved using the Berkeley Madonna numerical calculation tool. Results showed that 4-chlorophenol would be completely removed during the first hour of the reaction, operating with oxidant molar ratios higher than R=200 at pH6.0 and UV=24 W. Under these conditions, a decrease in the rate of total organic carbon (TOC) removal close to 50% from the initial value was observed. The solution colour, attributed to the presence of oxidation products as p-benzoquinone and hydroquinone, were oxidised to colourless species, that resulted in a decrease in the toxicity of the solutions (9.95 TU) and the aromaticity lost. The authors are grateful to the University of the Basque Country (UPV/EHU) for their financial support of this study through the PPGA20/33 project, and C. Ferreiro's predoctoral PIF grant (PIF16/367). Document

Background A simple and simultaneous electrochemical sensing platform was fabricated by electropolymerization of allura red on glassy carbon electrode (GCE) for the interference-free detection of dihydroxy benzene isomers. Methods The modified working electrode was characterized by electrochemical and field emission scanning electron microscopy methods. The modified electrode showed excellent electrocatalytic activity for the electrooxidation of catechol (CC) and hydroquinone (HQ) at physiological pH of 7.4 by cyclic voltammetric (CV) and differential pulse voltammetric (DPV) techniques. Results The effective split in the overlapped oxidation signal of CC and HQ was achieved in a binary mixture with peak to peak separation of 0.102 V and 0.103 V by CV and DPV techniques. The electrode kinetics was found to be adsorption-controlled. The oxidation potential directly depends on the pH of the buffer solution, and it witnessed the transfer of equal number of protons and electrons in the redox phenomenon. Conclusions The limit of detection (LOD) for CC and HQ was calculated to be 0.126 μM and 0.132 μM in the linear range of 0 to 80.0 μM and 0 to 110.0 μM, respectively, by ultra-sensitive DPV technique. The practical applicability of the proposed sensor was evaluated for tap water sample analysis, and good recovery rates were observed. Graphical abstract Electrocatalytic interaction of ALR/GCE with dihydroxy benzene isomers.

BACKGROUND: A biomimetic method was developed for the synthesis of silver nanoparticles (AgNPs). Synthetic chemical compounds were used according to the metabolites present in the fungal extracts for the synthesis of AgNPs. The main objective of this study was to find a simple and effective synthesis method without the presence of a living organism. METHODOLOGY: A central composite design combined with response surface methodology was used to optimize the necessary metabolite concentrations (flavin adenine dinucleotide (FAD), hydroquinone (HQ), and l‐cysteine (l‐cys)) for the synthesis of AgNPs. The design was assessed based on the size distribution and zeta potential of the nanoparticles. In addition, the antibacterial activity of the AgNPs against Escherichia coli, Staphylococcus aureus, Serratia marcescens and Salmonella enterica was tested. RESULTS: The results demonstrated that AgNO₃ (2 mmol L⁻¹), HQ (20 mmol L⁻¹), l‐cys (20 mmol L⁻¹) and FAD (50.5 nmol L⁻¹) at pH 8.4 were the optimal reaction parameters. The characterization allowed the determination of quasi‐spherical AgNPs with an average hydrodynamic size of 101 nm, a zeta potential of −24 mV and the presence of elemental silver (Ag⁰) in their composition. Fourier transform infrared spectroscopy showed silver and l‐cys interactions, supporting the role of l‐cys as a coating agent. The antibacterial activity showed that AgNPs displayed a minimum inhibitory concentration of 20–30 μg mL⁻¹ and a minimum bactericidal concentration of 30–40 μg mL⁻¹. CONCLUSIONS: This study demonstrates the feasibility of the reduction of Ag⁺ to Ag⁰ using synthetic metabolites, which mimic the reduction and synthesis of fungal biomass. Therefore, it represents a new biocompatible, eco‐friendly and fast method to produce AgNPs. © 2021 Society of Chemical Industry (SCI).

Catechol and Hydroquinone are considered to be main organic pollutants in water, and have a threat to human health and ecology security. It is imperative to establish a detection method of catechol...

The stability of metal-organic frameworks is a key factor in many applications in some fields that require working under harsh conditions. It is known that a large number of MOFs are vulnerable to humid air. It means that when they are exposed to water, a structural collapse of the crystal happens. In this work, Molecular Dynamics simulations using a reactive force field have been performed to study the stability of MOF-74 against the adsorption of catechol, resorcinol and hydroquinone in the presence of water. We reproduced the water instability of Zn-MOF-74 and we studied the resistance of the structure. Our simulations showed that the three isomers generate a volume change in the framework but the structural collapse does not happen. In contrast, for water-isomer mixtures, there is structural collapse. Not only do catechol, resorcinol and hydroquinone not behave as stabilizing agents but they do enhance the hydration effect on the structure.

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.

Excessive oxidation of sulfite can lead to low utilization efficiency and inhibit its application in the wet flue gas denitration process. Using organic absorbent can retard the sulfite oxidation r...

An advanced electroanalytical technique for the simultaneous assessment of environmental contaminant dihydroxybenzene isomers, catechol (CC), hydroquinone (HQ), and resorcinol (RC), has been investigated using palladium nanoparticles (PdNPs) incorporated onto a poly(1,5-diaminonaphthalene) (DAN) matrix over a glassy carbon electrode (GCE). Concurrently, these types of phenols can be assessed by the PdDAN/GCE modified electrode employing square wave voltammetry and cyclic voltammetry (CV) techniques under optimal conditions. This modified electrode has demonstrated linear responses for CC, HQ, and RC from 50.0 to 1000.0 mM; concomitantly, low detection limits of 0.22, 0.22, and 0.47 nM and low quantification limits of 0.740, 0.758, and 1.590 nM, have been, respectively, shown. Successfully, the simultaneous assessment of the three isomers in river stream water, tap water, and underground water has been implemented via the modified electrode under investigation. In comparison to reported studies, the PdDAN catalytic electrode has shown an effective sensitivity, leverage reproducibility, long-term stability, and excellent anti-interference capability for the determination of dihydroxybenzene isomers.

Continuous and rapid synthesis of UiO-67 under mild conditions has been achieved by electrochemical methods for the first time. In the reaction system, a zirconium sheet was utilized as electrodes and a metal source for the assembly of UiO-67. High-crystalline UiO-67 with a regular tetrahedral morphology of around 1 μm was obtained within 1.5 h under the optimized solvent composition, voltage, and temperature conditions. This electrochemical synthetic method of UiO-67 in our work overcomes the shortcomings of high temperature and pressure of a traditional solvothermal method, which proposes new ideas for the large-scale and rapid synthesis of UiO-67. The UiO-67 synthesized by an electrochemical method was prepared as a UiO-67-carbon paste electrode (CPE), which exhibited a linear response to hydroquinone (HQ) in the range of 5-300 μM with a detection limit of 3.6 × 10-9 M (S/N = 3), for the electrochemical detection of HQ. It was confirmed that UiO-67-CPE possessed excellent reusability and antiinterference ability for the detection of HQ, and its detection ability even did not change after standing for 3 months. We further tried to apply UiO-67-CPE to the practical determination of HQ in tap water and river water samples, and the results proved that the recovery rate is 97.9-104.7% in real samples.

A novel electrochemical sensor for sensitive and selective detection of hydroquinone (HQ) was developed using graphene/iridium(III) dimer complex composite modified glassy carbon electrode (graphen...

Metal-organic frameworks (MOFs) have limited applications in electrochemistry owing to their poor conductivity. Now, an electroactive MOF (E-MOF) is designed as a highly crystallized electrochemiluminescence (ECL) emitter in aqueous medium. The E-MOF contains mixed ligands of hydroquinone and phenanthroline as oxidative and reductive couples, respectively. E-MOFs demonstrate excellent performance with surface state model in both co-reactant and annihilation ECL in aqueous medium. Compared with the individual components, E-MOFs significantly improve the ECL emission due to the framework structure. The self-enhanced ECL emission with high stability is realized by the accumulation of MOF cation radicals via pre-reduction electrolysis. The self-enhanced mechanism is theoretically identified by DFT. The mixed-ligand E-MOFs provide a proof of concept using molecular crystalline materials as new ECL emitters for fundamental mechanism studies.

Purpose The purpose of this study to investigate acetaminophen (ACT) degradation efficiencies by using ozone/persulfate oxidation process in a batch reactor. In addition, the effects of various parameters on the ACT removal efficiency toward pathway inference of ACT degradation were investigated. Design/methodology/approach The experiments were in the 2 L glass vessels. Ozone gas with flow rate at 70 L.h−1 was produced by ozone generator. After the adjustment of the pH, various dosages of persulfate (1, 3, 5, 7 and 9 mmol.L−1) were then added to the 500 mL ACT-containing solution with 150 mg.L−1 of concentration. Afterward, ozone gas was diffused in glass vessels. The solution after reaction flowed into the storage tank for the detection. The investigated parameters included pH and the amount of ozone and persulfate addition. For comparison of the ACT degradation efficiency, ozone/persulfate, ozone and persulfate oxidation in reactor was carried out. The ACT concentration using a HPLC system equipped with 2998 PDA detector was determined at an absorbance of 242 nm. Findings ACT degradation percentage by using ozone or persulfate in the process were at 63.7% and 22.3%, respectively, whereas O3/persulfate oxidation process achieved degradation percentage at 91.4% in 30 min. Degradation efficiency of ACT was affected by different parameter like pH and addition of ozone or persulfate, and highest degradation obtained when pH and concentrations of persulfate and ozone was 10 and 3 mmol.L−1 and 60 mg.L−1, respectively. O3, OH• and SO4− were evidenced to be the radicals for degradation of ACT through direct and indirect oxidation. Gas chromatography–mass spectrometer analysis showed intermediates including N-(3,4-dihydroxyphenyl) formamide, hydroquinone, benzoic acid, 4-methylbenzene-1,2-diol, 4-aminophenol. Practical implications This study provided a simple and effective way for degradation of activated ACT as emerging contaminants from aqueous solution. This way was conducted to protect environment from one of the most important and abundant pharmaceutical and personal care product in aquatic environments. Originality/value There are two main innovations. One is that the novel process is performed successfully for pharmaceutical degradation. The other is that the optimized conditions are obtained. In addition, the effects of various parameters on the ACT removal efficiency toward pathway inference of ACT degradation were investigated.

BACKGROUND: Dihydroxybenzene (DHB) which is an important raw material and intermediate of the organic chemical industry can be prepared by hydroxylation of phenol, so it promotes the study of highly selective catalyst for hydroxylation of phenol. RESULTS: Two novel PNP ((Ph₂P)₂NPh) ligand‐substituted di‐iron complexes were synthesized under controllable reaction conditions via carbon monoxide (CO)/ligand substitution of the parent complex (μ‐budt)Fe₂(CO)₆ [budt = SCH(CH₃)CH₂CH₂)S]. The substituted complexes 1 and 2 were fully characterized by solution infrared spectroscopy, nuclear magnetoresonance spectroscopy, single crystal X‐ray diffraction, cyclic voltammetry and density functional theory calculations. Due to its favorable redox properties, Complex 1 was adopted first as an efficient catalyst for the hydroxylation of phenol to DHB (dihydroxybenzene) with hydrogen peroxide (H₂O₂) as oxidant and H₂O as solvent. Under the optimum reaction conditions, the conversion of phenol achieved 42.0%, the selectivity of DHB was ≤88.6% and the catechol:hydroquinone ratio (mol mol⁻¹) was 2.2. Furthermore, only trace amounts of benzoquinone, as a deeply oxidized product, was detected (yield c. 0.1%). CONCLUSION: Complex 1 could be a new type of catalyst for the hydroxylation of phenol to hydroquinone owing to the mild reaction conditions and excellent catalytic performance. In addition, a possible catalytic reaction mechanism was related to the special structure of Complex 1 which features an internal base of amine in PNP ligand.

The redox reaction mechanism of a poly(phenanthrene quinone)/graphene composite (PFQ/rGO) was investigated using operando attenuated total reflection infrared (ATR‐IR) spectroscopy during cycling of Li and Mg batteries. The reference phenanthrene quinone and the Li and Mg salts of the hydroquinone monomers were synthesized and their IR spectra were measured. Additionally, IR spectra were calculated using DFT. A comparison of all three spectra allowed us to accurately assign the C=O and C−O− vibration bands and confirm the redox mechanism of the quinone/Li salt of hydroquinone, with radical anion formation as the intermediate product. PFQ/rGO also showed exceptional performance in an Mg battery: A potential of 1.8 V versus Mg/Mg2+, maximum capacity of 186 mAh g−1 (335 Wh kg−1 of cathode material), and high capacity retention with only 8 % drop/100 cycles. Operando ATR‐IR spectroscopy was performed in a Mg/organic system, revealing an analogous redox mechanism to a Li/organic cell., Charging mechanism: A new poly(phenanthrene quinone) cathode material shows exceptional electrochemical performance in Li and Mg batteries. The redox reactions during charge/discharge were investigated using operando attenuated total reflectance IR spectroscopy. In both battery systems, the hydroquinone salt was reversibly oxidized back to the quinone functional group.

Funding Information: The authors acknowledge the use of the Circular Raw MatTERS Finland Infrastructure (RAMI) at Aalto University. The authors at RUB and Paderborn University thank the SFB‐TR‐87 project for financial support. M.W. thanks COST‐Action HERALD for funding his research stay at Aalto University. Publisher Copyright: © 2021 The Authors. Advanced Engineering Materials published by Wiley-VCH GmbH High-quality copper metal thin films are demanded for a number of advanced technologies. Herein, a facile ALD (atomic layer deposition) process for the fabrication of Cu metal films directly from two solid readily usable precursors, copper acetylacetonate as the source of copper and hydroquinone as the reductant is reported. This process yields highly crystalline, dense, specularly reflecting, and electrically conductive Cu films with an appreciably high growth rate of 1.8 Å/cycle at deposition temperatures as low as 160 to 240 °C.

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.

Herein, we have reported a novel composite of nitrogen doped reduced graphene oxide (N-rGO) and strontium zirconate (SrZrO3). This new composite (N-rGO/SrZrO3) was synthesized using the reflux method. The physicochemical properties of N-rGO/SrZrO3 were determined using different advanced techniques such XRD, FE-SEM, EDX, FTIR and BET. Furthermore, a glassy carbon electrode was modified with N-rGO/SrZrO3 (GCE-2). This modified electrode was employed for the sensing of HQ. The electrochemically active surface area (ECSA) of this modified electrode (GCE-2) was calculated by employing the Randles–Sevcik equation. Furthermore, GCE-2 exhibited a good detection limit (0.61 μM) including high selectivity towards HQ.

An electrochemical sensor using copper oxide nanodots (CuO nanodots–ITO) developed from a block copolymer template is demonstrated for sensitive and selective determination of dopamine (DA). The current signal of CuO nanodots–ITO was linear with the concentration of DA in the range between 0.12 and 56.87 μM (R = 0.9975) with a sensitivity of 326.91 μA mM–1 cm–2 and a detection limit of 0.03 μM. Furthermore, the anti-interference ability of the present sensor to possible interfering substances including ascorbic acid, uric acid, acetaminophen, epinephrine, hydrogen peroxide, phenol, catechol, hydroquinone, and some inorganic compounds has been investigated. Our work highlights the significance of using a bottom-up nanofabrication technique to create a robust and reliable dopamine sensor that has critical importance in neurological disorders.

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.

We have demonstrated a hydroquinone stitched β-ketoenamine COF acting as an efficient organic cathode in an aqueous rechargeable zinc ion battery., The two-dimensional structural features of covalent organic frameworks (COFs) can promote the electrochemical storage of cations like H+, Li+, and Na+ through both faradaic and non-faradaic processes. However, the electrochemical storage of cations like Zn2+ ion is still unexplored although it bears a promising divalent charge. Herein, for the first time, we have utilized hydroquinone linked β-ketoenamine COF acting as a Zn2+ anchor in an aqueous rechargeable zinc ion battery. The charge-storage mechanism comprises of an efficient reversible interlayer interaction of Zn2+ ions with the functional moieties in the adjacent layers of COF (–182.0 kcal mol–1). Notably, due to the well-defined nanopores and structural organization, a constructed full cell, displays a discharge capacity as high as 276 mA h g–1 at a current rate of 125 mA g–1.

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.

Electrochemical oxidation of some dihydroxybenzene derivatives in the presence of methyl-Meldrum's acid (MMA) and phenyl-Meldrum's acid (PMA) as nucleophiles were investigated both experimentally and theoretically. Using recorded E-pH diagrams of some catechol derivatives, Ep0 of the studied species were obtained. Also, ∆Gtot of the electrochemical oxidation of the catechols have been calculated using different computational methods. Then, by the use of Ep0 vs. ∆Gtot graphs, it was found that BP86/6-31G(d,p) is the best method and it was selected for other computational studies. Electrolysis of the catechols in the presence of MMA and PMA was performed, and the results indicate that the final products are produced via an EC mechanism. The electrochemical oxidation of hydroquinone species in the presence of the nucleophiles was studied too. It was found that unlike what was observed for catechols, the electrochemical oxidation of hydroquinones in the presence of MMA and PMA is ECE. Also, the mechanism of the electrochemical oxidation of hydroquinone in the presence of MMA changed to ECECE due to the changing condition of the electrolysis. Different electrochemical behaviors of the studied dihydroxybenzenes in the presence of the nucleophiles were analyzed by the computational study, and the results indicate that although the mechanisms are not the same, all of them proceed in the thermodynamically favored directions.

A conducting redox polymer based on PEDOT with hydroquinone and pyridine pendant groups is reported and characterized as a proton trap material. The proton trap functionality, where protons are tra...

It is needed to speed up the development of a sensitive detection platform for simultaneous determination of dihydroxybenzene isomers with harmful properties. Here, two isomorphic Metal–organic frameworks (MOFs) [Zn(Trz)(R-BDC)1/2] (FJU-40-R, R = H or NH2; Trz = 1,2,4-Triazole; H-BDC = terephthalic acid) were selected to derive two N-doping porous carbon (NPC) materials. Further, a strategy for constructing electrochemical sensors for simultaneous determination of hydroquinone (HQ) and catechol (CT) was proposed by the MOF-derived NPC modifying glass carbon electrode (GCE). It was found that HQ and CT had good responses on NPC-FJU-40-H/GCE, but had no obvious responses on NPC-FJU-40-NH2/GCE. NPC-FJU-40-H/GCE displayed excellent reproducibility, stability, and anti-interference. Under the optimal conditions, the linear ranges of HQ and CT on NPC-FJU-40-H/GCE were 1 ~ 70 µmol L−1 and 1 ~ 100 µmol L−1 with the detection limits of 0.18 µmol L−1 for HQ and 0.31 µmol L−1 for CT, respectively. Although the porous carbon (PC) derived from MOFs has been applied in electrochemical sensing, the effect of the ligand functional groups of isomorphic MOFs on the electrochemical properties of the derived PC materials is still lack of relevant research. Our research provided an idea that the electrocatalysis properties of MOF-derived porous carbon materials could be tuned by changing the functional groups in ligands of isomorphic MOFs in electrochemical sensing field. A feasible strategy was proposed by changing the ligands of the two isomorphic MOFs (FJU-40-H and FJU-40-NH2) to tune the electrocatalysis properties of MOF-derived N-doped porous carbon materials for the simultaneous determination of dihydroxybenzene isomer.

The monitoring of pollutants has received significant attention from researchers in recent years owing to their hazardous nature and their toxic effect on the environment. Among them, water pollution plays a major role and results in dominant diseases along with life-long health problems. Hydroquinone (HQ), the major metabolite of benzene, is an industrially used organic compound which causes symptoms associated with nervous related disorders, such as faintness, therefore the research community has been inspired to detect sources of this carcinogenic agent. In this work, cobalt–iron based zeolitic imidazolate framework microfibers (CoFe-ZIF-MFs) were used for the selective detection of HQ. Micro-structured CoFe-ZIF fibers were fabricated using the wet chemical and electrospinning method. The electrochemical response of the prepared composite revealed an excellent redox behavior towards HQ and does not suffer from interference resulting from other analytes. The proposed sensor exhibited a wide linear range of 1 μM–1 mM with a detection limit of 230 nM, resulting in a good stability of up to 88%, even after 250 cycles. The designed sensor showed an exquisite performance for real sample analysis which indicates the device mechanism is reliable for use in environmental monitoring, public health care, industrialized areas and waste water management systems.

In age-related macular degeneration (AMD), hydroquinone (HQ)-induced oxidative damage in retinal pigment epithelium (RPE) is believed to be an early event contributing to dysregulation of inflammatory cytokines and vascular endothelial growth factor (VEGF) homeostasis. However, the roles of antioxidant mechanisms, such as autophagy and the ubiquitin-proteasome system, in modulating HQ-induced oxidative damage in RPE is not well-understood. This study utilized an in-vitro AMD model involving the incubation of human RPE cells (ARPE-19) with HQ. In comparison to hydrogen peroxide (H2O2), HQ induced fewer reactive oxygen species (ROS) but more oxidative damage as characterized by protein carbonyl levels, mitochondrial dysfunction, and the loss of cell viability. HQ blocked the autophagy flux and increased proteasome activity, whereas H2O2 did the opposite. Moreover, the lysosomal membrane-stabilizing protein LAMP2 and cathepsin D levels declined with HQ exposure, suggesting loss of lysosomal membrane integrity and function. Accordingly, HQ induced lysosomal alkalization, thereby compromising the acidic pH needed for optimal lysosomal degradation. Pretreatment with MG132, a proteasome inhibitor and lysosomal stabilizer, upregulated LAMP2 and autophagy and prevented HQ-induced oxidative damage in wildtype RPE cells but not cells transfected with shRNA against ATG5. This study demonstrated that lysosomal dysfunction underlies autophagy defects and oxidative damage induced by HQ in human RPE cells and supports lysosomal stabilization with the proteasome inhibitor MG132 as a potential remedy for oxidative damage in RPE and AMD.

Introducing redox-active moieties into an ionic liquid (IL) structure is an exciting and attractive approach that has received increasing interest over recent years for a various range of energy applications. The so-called redox-active ionic liquids (RAILs) provide a highly versatile platform to potentially create multifunctional electroactive materials. Ionic liquids are molten salts consisting of ionic species, often having a melting point lower than 100 °C. Such liquids are obtained by combining a bulky asymmetric organic cation and a small anion. Here, we report on the synthesis of a novel RAIL, namely 1-butyl-3-methylimidazolium hydroquinone sulfonate ((BMIM)(HQS)). (BMIM)(HQS) was synthesized in a two-step procedure, starting by the quaternization of methylimidazole using butylchloride to produce 1-butyl-3-methylimidazolium chloride ((BMIM)(Cl)), and followed by the anion exchange reaction, where the chloride anion is exchanged with hydroquinone sulfonate. The resulting product was characterized by 1H NMR, 13C NMR, FT-IR spectroscopy, themogravimetric analysis, and differential scanning calorimetry, and shows a high stability up to 340 °C. Its electrochemical behavior was investigated using cyclic voltammetry at different temperatures and its viscosity analysis was also performed at variable temperatures. The electrochemical response of the presented RAIL was found to be temperature dependent and diffusion controlled. Overall, our results demonstrated that (BMIM)(mix of HQS and HSQ) is redox active and possesses high stability and low volatility, leading to the employment of this RAIL without any additional supporting electrolyte or additives.

The fast and selective determination of hydrogen peroxide (H2O2) is of importance not only because of strong interest in this widely applied analyte, but also because of the development of enzymatic biosensors for glucose or other metabolites where the sensor for H2O2 can be used as the transducer. Here, we report on an electrocatalytical amperometric sensor for the detection of H2O2. It is a sensor that consists of a gold electrode covered by a self-assembled monolayer (SAM) with immobilized p-benzoquinone. To provide highly stable immobilization of p-benzoquinone at the distance of effective electron tunneling, a new anchor compound—1,3-dimercaptopropan-2-ol—was synthesized and used for preparation of the SAM. Due to two thiol groups binding gold surface, this compound provides high stability of the SAM. The surface concentration of p-benzoquinone obtained from cyclic voltammetry is 2.5 ± 0.2 × 10−10 mol·cm−2. Cyclic voltammetry and chronoamperometry experiments proved that the immobilized benzoquinone exhibited high electrocatalytic activity towards the decomposition of H2O2. Depending on the used potential range, different sensing modes can be realized. For example, one can measure electrochemical response due to the oxidation of H2O2 at anodic potentials, or due to the reduction of oxygen formed during oxidative decomposition of H2O2. Also, amperometric response at fixed potential of +0.4 V vs. Ag/AgCl corresponding to the oxidation of benzoquinone to hydroquinone was studied. The sensor exhibited a linear response over a concentration range of 0.1–2 mM with a low detection limit of 4.24 µM. The reproducibility of three different electrodes prepared was examined at the H2O2 concentration range from 0.1 till 3 mM, which resulted in a relative standard deviation below 4.2%.

Quinone derivatives and their metal complexes are well-known molecules that participate in electron-transfer reactions relevant to diverse fields. However, the fundamental knowledge on the unique reactivity of redox-active quinone complexes is limited by the difficulty in their isolation. Herein, the synthesis of isolable mononuclear polypyridylruthenium(II) complexes containing both hydroquinone and quinone units is described. Three types of monodentate ligands are conveniently used to control the electronic states of the complexes. Both reduced (hydroquinone) and oxidised (quinone) forms are successfully isolated and characterised by spectroscopic and crystallographic analysis, allowing direct comparisons of their properties. The redox-rich and visible light-responsive nature of the ruthenium complexes enables to investigate the quinone/hydroquinone interconversion induced by electron transfer, photoirradiation and photoswitching based on ligand substitution reactions. These results demonstrate the occurrence of synergistic effects between metal complexes and redox-active organic compounds.

Development of a new pH sensor system, which is simple to prepare, sensitive, selective and workable with low volume, is demanding research in biomedical and environmental studies. In the literature, organic molecules like methylene blue, toluidine blue, hydroquinone, catechol, anthraquinone and polyaniline-based redox probes have been widely used for this purpose. In general, these redox probes have easily interfered with common biochemicals such as dopamine, ascorbic acid, NADH, H2O2, cysteine, hydrazine, and some transition metal ions, etc., and in turn to marked potential and current drifts (pH-false positive response). In this work, a highly redox-active, stable and interference-free redox polymer based on poly(4-chloroaniline) (PANI(4-Cl)) modified graphitized mesoporous carbon (GMC), designated as GMC@PANI(4-Cl), has been prepared using 4-chloroaniline as a monomer in pH 7 phosphate buffer solution. The new redox polymer system showed a distinct redox peak at Eo’= 0.15 V vs Ag/AgCl with a stable voltammetric response. Transmission electron microscope analysis of the redox polymer composite had shown adhesion of black polymeric solid due to polyaniline like the molecular system as a surface layer on the GMC material. The constructed calibration plot was linear in the pH window 2-11 with a slope and regression values − 58 mV pH−1 and 0.9997, respectively. The GMC@PANI(4-Cl) modified electrode showed a sensitive and selective pH monitoring without any interference from the common biochemicals as listed above. As a practical application, pH sensing of commercial pH solutions, undiluted urine and saliva samples were demonstrated. Also, a three-in-one screen-printed carbon modified GMC@PANI(4-Cl) was explored for pH monitoring of a bacterial (E.coli) growth, which showed a comparable response with the conventional pH electrode.

Photocatalytic H2O2 production is an innovative on-site H2O2 synthesis method to treat organic pollutants through Fenton-like reactions, avoiding the need and potential liability of H2O2 storage and transportation. Accurate quantification of H2O2 is crucial to explore the mechanism of photocatalytic H2O2 production and optimize reaction parameters. In this work, three common H2O2 quantification methods (i.e., titration with potassium permanganate (KMnO4), and colorimetry with ammonium metavanadate (NH4VO3) or N,N-diethylp-phenylenediamine-horseradish peroxidase (DPD-POD)) were compared and their susceptibility to interference by seven types of representative organics were considered. Interference mechanisms were explored based on the electron-donating (Egap) and electron-accepting (ELUMO) ability of the present organics. The accuracy of the KMnO4 titration method is greatly compromised by aromatic compounds even at 0.1 mM due to the increased KMnO4 consumption by direct oxidation. The presence of p-benzoquinone that directly reacts with NH4VO3 and DPD compromises these colorimetric methods, especially DPD-POD colorimetry at concentrations as low as 0.1 mM. The DPD-POD method should also be scrutinized in the presence of phenols due to significant disturbance by oxidation byproducts (e.g. hydroquinone inducing immediate color disappearance). A flowchart was generated to provide guidelines for selecting an appropriate H2O2 quantification method for different water matrices treated by Fenton-like reactions.

It is difficult to accurately determine the pKa and pKb of Bronsted-Lowry weak acids and weak bases in aprotic solvents. We found that in aprotic solvent, the conjugated base of weak acid can cause a new unambiguous anodic peak of hydroquinone, and the conjugated acid of weak base can cause a new cathodic peak of p-benzoquinone. The new peaks are due to the drastic change of pH near the electrode surface, and their potentials are dependent on the strength of conjugated acids and bases, but independent of the concentration of hydroquinone and quinone. Therefore, the conjugated acid-base dissociation constant can be measured by the new peak potential. Then the weak acid-base dissociation constant can be obtained by the difference between the autoprotolysis constant of the aprotic solvent and the conjugated acid-base dissociation constant. The experimental results are consistent with those in the literatures.

In this study, a novel three-electrode integrated electrochemical platform (TEIEP) has been designed and fabricated for the simultaneous detection of hydroquinone (HQ) and catechol (CC), in which nanoporous gold (NPG) served as the working electrode, and Pt particles and nanoporous Ag/AgCl served as the courter electrode and the reference electrode, respectively. Due to the remarkable catalytic activity of NPG, the TEIEP exhibits high selectivity and sensitivity towards HQ and CC determination with a distinct separation between the peaks for their coexistence. The oxidation peak current densities of HQ and CC were linear over the range of 0.2-100 μM with the detection limits of 0.083 μM (S/N = 3) for HQ and 0.119 μM (S/N = 3) for CC. Moreover, TEIEP has a satisfactory reproducibility and anti-interference ability, and can be used in real water sample analysis. This work undoubtedly provides a remarkable choice for catalytic materials and an integrated structure, and further a promising application prospect for developing novel sensors for on-site environmental monitoring.

As the dominant manganese oxide mineral phase in terrestrial and aquatic environments, birnessite plays an important role in many biogeochemical processes. The coexistence of birnessite with aqueous Mn2+ is commonly found in the subsurface environments undergoing Mn redox cycling. This study investigates the change in Mn average oxidation state (AOS) of birnessite after reaction with 0.1&ndash, 0.4 mM Mn2+ at pH 4.5&ndash, 6.5, under conditions in which phase transformation of birnessite by Mn2+ was not detectable. The amount of Mn2+ uptake by birnessite and the equilibrium concentration of Mn(III) proportionally increased with the initial concentration of Mn2+. The Mn AOS of birnessite particles became 3.87, 3.75, 3.64, and 3.53, respectively, after reaction with 0.1, 0.2, 0.3, and 0.4 mM Mn2+ at pH 5.5. Oxidation potentials (Eh) of birnessite with different AOS values were estimated using the equilibrium concentrations of hydroquinone oxidized by the birnessite samples, indicating that Eh was linearly proportional to AOS. The oxidation kinetics of bisphenol A (BPA), a model organic pollutant, by birnessite suggest that the logarithms of surface area-normalized pseudo-first-order initial rate constants (log kSA) for BPA degradation by birnessite were linearly correlated with the Eh or AOS values of birnessite with AOS greater than 3.64.

To better understand the oxidative reactivity of iron oxides in the fate of contaminants in acidic environments, we examined the reactivity of goethite in binary mixtures with Al2O3 by carrying out oxidation experiments of hydroquinone (HQ) in the presence of goethite and/or Al2O3 at pH 3. Kinetic results revealed inhibiting effects of 0.2–20 g/L of three different types of Al2O3 on the oxidative reactivity of goethite. Surprisingly, soluble Al ions of 0.18–18 mM had a negligible impact on the reactivity. It turned out that the Fe3+ dissolved from goethite partly contributed to the observed HQ oxidation and the Al2O3 adsorbed the Fe3+ to lead to the slower HQ oxidation. The observed pseudo-first-order rate constants in HQ oxidation had a strong linear correlation with Fe3+ concentration in various goethite and Al2O3 mixtures. Separate experiments confirmed the reactivity of Fe3+ toward HQ and the linear correlation between [Fe3+] and HQ oxidation reactivity. Finally, sedimentation experiments showed negli...

Control of the active sites/centers plays an important role in the design of novel electrode materials with unusual properties and achievement of sensors with high performance. In this study, three-dimensional (3D) freestanding multi-doped hollow carbon spheres (N-Co-Fe-HCS) with a layer thickness of 30 nm, which contained multiple active sites of the heteroatom N and transition metals (Co and Fe), were synthesized via a simple template method (with SiO2 as the template) and cost-efficient in situ self-polymerization, self-adsorption/reduction and carbonization strategies. Moreover, a series of hollow carbon sphere composites of the same family (N-HCS, N-Co-HCS and N-Fe-HCS) were prepared by this sensible process using the same method and precursors but different doping elements. These differences lead to different active sites/centers from hollow carbon spheres and improved electrocatalytic activities for dihydroxybenzene isomers. Furthermore, N-Co-Fe-HCS as an electrochemical sensor exhibited excellent simultaneous qualitative and quantitative determination performance for catechol (CC) and hydroquinone (HQ). The detection limit and the linear range were 75 nmol L-1 and 0.5-500 μmol L-1 for CC and 80 nmol L-1 and 0.5-1500 μmol L-1 for HQ, respectively. The interference from the components coexisting in river water on the detection of CC and HQ was not observed. These results indicate that high-performance electrochemical sensors can be constructed by in situ multi-element doping into electrode materials to achieve multi-active sites.

Hydroquinone (HQ) and catechol (CC) are two isomers, which often coexist and interfere with each other during their identification in samples. To measure HQ and CC, electrochemists must handle the problem of the partial overlap of their voltammetric peaks. If the concentration of disodium hydrogen phosphate is twice that of HQ, then the peak separation between HQ and CC exceeds 0.2 V which is large enough for the simultaneous determination of HQ and CC. As a result, we developed a method to measure HQ and CC with a bare glassy carbon electrode. Without modifying the working electrode surface, the method presented excellent stability, good reproducibility and satisfactory anti-interference performance. This approach was successfully applied for the determination of HQ and CC in a tap water sample.

The photoelectrochemical removal of phenol from aqueous solution under solar light with polyaniline-modified TiO2 electrodes has been investigated. Nanotubular TiO2 electrodes (NTs) have been obtained by anodization of Ti; the coating with polyaniline (PANI) has been obtained with a three-step approach: (i) functionalization of NTs by electroreduction of 4-nitrobenzendiazonium salt, (ii) electrochemical reduction of the nitro group to amine, (iii) galvanostatic electropolymerisation of aniline. The results of galvanostatic electrolyses under simulated solar light are presented, degradation of phenol with TiO2 was achieved and the trends of concentration with time follow a pseudo-first order kinetics. As a comparison, also unmodified NTs have been tested. The results depend on the initial concentration of reactant, with 300 mg dm−3 of phenol and applying a current density i = 0.18 mA cm−2, the reaction rate with NT-PANI was more than double of that obtained with NTs. Moreover, the presence of PANI increases the conductivity of the electrode, which in turn depolarizes the cell. Hydroquinone and oxalic acid have been detected as main intermediates, which are distributed depending on the experimental conditions and kind of electrodes: the relevant data have been modelled assuming an in-series reaction scheme and pseudo first order kinetics.

The electrochemical behavior of hydroquinone in unbuffered aqueous solution was investigated using cyclic voltammetry. Subsequent cathodic scan showed a new cathodic peak at the negative potential and another similar cathodic peak for catechol. The peak current increased with the increasing pH of the bulk solution and concentration of hydroquinone. We observed that only the new cathodic peak increased, whereas the other peaks remained constant with the addition of quinone to the test solution. This new cathodic peak was caused by the ultrafast diffusion of proton from the electrode surface to the bulk solution. The results can help us understand the unique characteristics of hydroquinone in unbuffered solution.