4-nitrophenol Research Articles

The influence of pH on the liquid-phase transformation of phenolic compounds driven by nitrite photolysis: Implications for characteristics, products and cytotoxicity

The aqueous-phase conversion of phenolic compounds (PhCs) driven by nitrite photolysis has been recognized as a significant source of secondary brown carbon (BrC). However, the influence of pH on the conversion kinetics and product distribution of PhCs remains unclear. In this study, three representative PhCs with varying functional groups were selected to examine their aqueous-phase conversion kinetics in the presence of nitrite under different pH conditions and simulated sunlight conditions. The results indicate that as the pH increases, the decay rates of PhCs decrease, following first-order reaction kinetics. These varying decay rates also suggest that different substituents on the benzene ring significantly impact the reactivity of PhCs. The molecular composition of the products is pH-dependent, with 4-nitrocatechol (4NC) emerging as the primary reaction product. A range of conversion products were detected across different pH values: nitrification dominated at low pH, while hydroxylation products increased with rising pH, and polymerization products appeared prominently at high pH. Due to the electron-withdrawing effect of the nitro group on the benzene ring, fewer products formed from 4-nitrophenol were observed, and the visible absorption spectrum also showed a decreasing trend as the reaction progressed across various pH conditions. Toxicity assays on human non-small cell lung cancer cells (A549) revealed that the toxicity of the reaction products decreased with increasing pH. Correspondingly, the accumulation of reactive oxygen species (ROS) and apoptosis rates in cells also declined. This may be due to the fact that at lower pH levels, nitrophenols (NPs), which tend to promote ROS accumulation and cell death, dominate the product mix. This study provides valuable insights into the toxicological properties of secondary organic aerosols (SOA) formed from the photo-oxidation products of PhCs under different pH conditions. These findings contribute to a deeper understanding of the environmental and health impacts of SOA in atmospheric chemistry.

Construction of carbazole-conjugated dual-emission fluorescent covalent organic framework for distinguishing p-nitroaniline/p-nitrophenol and adsorbing nitroanilines/nitrophenols

Nitroanilines (NAs) and nitrophenols (NPs), crucial industrial raw materials, are extensively utilized across various sectors. However, the environmental pollution and health hazards stemming from their usage are significant, necessitating urgent monitoring and removal to address environmental and safety concerns. The challenge is further compounded by the presence of NAs/NPs isomers, making the selective analysis of specific isomers crucial. In response, a new post-modified fluorescent covalent organic framework (COF) termed COF@CB, exhibiting dual-emission fluorescence, was synthesized. This synthesis involved coupling a high-crystallinity fluorescent COF (COF-TTDB) with carbazole-9-ethanol (CB) via a “Williamson” reaction. COF@CB featured exceptional dual-emission fluorescence, a high specific surface area (919.4 m2·g−1), superior thermal stability, and abundant active sites. These attributes enabled COF@CB to function as a ratiometric fluorescence sensor capable of simultaneous detection and adsorption. The distinct number and arrangement of hydrogen bond sites in NAs/NPs isomers influenced the intramolecular charge transfer (ICT) effects on COF@CB, thereby enabling the COF@CB-ratiometric fluorescence sensor to distinguish and selectively detect p-NA/p-NP from isomers. Analysis of actual water samples further underscored the sensor's effectiveness in detecting p-NA/p-NP. Furthermore, the presence of multiple active sites on the COF@CB-ratiometric fluorescence sensor facilitated the adsorption of NAs/NPs, promoting the removal of them from actual samples.

Bio-inspired synthesis of Ag-g-C3N4 nanocomposites and their application for photocatalytic degradation of para-nitrophenol

Nanocomposites are promising in advanced materials for environmental applications due to their ability to boost functionality through synergistic effects. Graphitic carbon nitride (g-C3N4) is renowned for its exceptional characteristics in photocatalysis. This work examines the preparation of g-C3N4 from different precursors, and how the presence of silver nanoparticles (Ag NPs) and silver ions (Ag+) in g-C3N4 matrices improve their combined effect on photocatalytic activity, specifically in the degradation of para-nitrophenol (PNP), a persistent organic pollutant. From urea and melamine precursors for the preparation of g-C3N4, the latter provided a much higher yield. Using an easy synthesis approach, Ag NPs were evenly distributed in the g-C3N4 framework, whereas Ag+ ions were incorporated by an apparent physical procedure. A bio-inspired, environmentally friendly method was also applied to prepare Ag NPs. The nanocomposites showed improved light absorption and separation of charge carriers due to the synergistic interaction between g-C3N4 and Ag species. Using UV and Vis LED light sources, we investigated both pure g-C3N4 and Ag-g-C3N4 catalysts. For breaking down para-nitrophenol, the silver-modified catalysts performed significantly better than pure g-C3N4 in both UV and Vis. The study clarified the functions of Ag NPs and Ag+ ions in enhancing photocatalytic activity by examining their involvement in generating reactive oxygen species and degrading pollutants. This work highlights the capability of g-C3N4-based nanocomposites as effective photocatalysts for environmental remediation. It also explores the benefits of adding silver species to improve performance in degrading pollutants.

Mn-Fe Dual-Metal Assemblages on Carbon-Coated Al2O3 Spheres for Catalytic Ozonation Oxidation: Structure, Performance, and Reaction Mechanism.

Catalysts with high catalytic activity and low production cost are important for industrial application of heterogeneous catalytic ozonation (HCO). In this study, we designed a carbon-coated aluminum oxide carrier (C-Al2O3) and reinforced it with Mn-Fe bimetal assemblages to prepare a high-performance catalyst Mn-Fe/C-Al2O3. The results showed that the carbon embedding significantly improved the abundance of surface oxygen functional groups, conductivity, and adsorption capacity of γ-Al2O3, while preserving its exceptional mechanical strength as a carrier. The prepared Mn-Fe/C-Al2O3 catalyst exhibited satisfactory catalytic ozonation activity and stability in the degradation of p-nitrophenol (PNP). Electron paramagnetic resonance (EPR) and quenching experiments reveal that radical ( ⋅ OH and ⋅ O2 ⋅ ) and nonradical oxidation (1O2) dominated the PNP degradation process. Theoretical calculations corroborated that the anchored atomic Fe and Mn sites regulated the local electronic structure of the catalyst. This modulation effectively promoted the activation of O3 molecules, resulting in the generation of atomic oxygen species (AOS) and reactive oxygen species (ROS). The economic analysis on Mn-Fe/C-Al2O3 revealed that it was a cost-competitive catalyst for HCO. This study not only deepens the understanding on the reaction mechanism of HCO with transition metal/carbon composite catalysts, also provides a high-performance and cost-competitive ozone catalyst for prospective application.

Electrochemical detection of p-nitrophenol using glassy carbon electrode modified using high-entropy oxide nanoparticles

The electrochemical detection of p-nitrophenol (PNP) has gained significant attention due to its potential application in environmental monitoring and food safety. In this study, a novel electrochemical sensor based on a (CeGdHfPrZr)O2 (HEO) nanoparticle-modified glassy carbon electrode (GCE) has been developed for the detection of PNP. Hydrothermal synthesis was employed to prepare a single-phase HEO nanoparticle. Various characterization techniques were employed to investigate the prepared HEO nanoparticles. The GCE was modified with HEO nanoparticles to enhance its electrocatalytic activity for the detection of PNP. As a result, the oxidation peak current of PNP was greatly enhanced compared to unmodified GCE, indicating an improved electrode reaction kinetics. The sensor showed high sensitivity (0.1517 μA μM−1 cm−2) and selectivity towards PNP, with a detection limit as low as 0.321 μM. The developed electrochemical sensor exhibited excellent reproducibility and selectivity towards PNP over other interfering species. The reusability and stability of the sensor were also investigated. The modified GCE exhibited good long-term stability and could be reused for at least 50 cycles without significant loss of sensitivity.

Large-scale preparation of Na2CO3-modified attapulgite adsorbents for efficient removal of p-Nitrophenol in wastewater

Developing adsorbents with ultrahigh adsorption capacity for phenol-containing wastewater is crucial to solving the problem of water pollution. However, the adsorbents currently used still have the disadvantages of low adsorption capacity, slow adsorption kinetics and difficulty in large-scale preparation. Herein, a facile and environmentally friendly inorganic salt (Na2CO3)-assisted modification method is employed to produce a large-scale attapulgite (ATP)-based adsorbents with high adsorption efficiency for p-nitrophenol (PNP) in wastewater, and its adsorption performance and mechanism are investigated in detail. The results shown that Na2CO3-modified ATP (S-ATP-1.0) possesses excellent adsorption performance with the maximum adsorption capacity of 1467.52 mg g−1 for PNP, which is significantly better than most previously reported adsorbents with similar functions. More excitingly, S-ATP-1.0 can maintains remarkable recyclability and structural stability even after 5 cycles. Structural characterization and theoretical calculations reveal that the excellent adsorption performance of S-ATP-1.0 for PNP is mainly attributed to the strong interaction between PNP and Na+ on the ATP surface. This work provides a new strategy for the large-scale preparation of phenolic adsorbents with low-cost and ultra-high adsorption properties, which is expected to be practically applied in the removal of highly concentrated PNP wastewater and environmental remediation.

Adsorption of ortho-Nitrophenol from Aqueous Solution using Phosphated Biomass of Ailanthus excelsa: Kinetic and Equilibrium Studies

This study interprets phosphated biomass of Ailanthus excelsa (PBAE) as a eco-friendly, inexpensive and potential adsorbent for adsorption of ortho-nitrophenol (ONP) from aqueous solution by using batch adsorption method. The prepared biosorbent was characterized using a variety of techniques such as Brunauer Emmett Teller (BET), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscope (SEM). As a function of many process parameters including material dose, contact time, concentration, pH and temperature, batch studies were conducted. It was found that a pH of 6.0, a biosorbent dosage of 0.050 g and an initial phenol concentration of 25 mg/L and temperature 298 K were the best conditions for ONP removal. The maximum sorption was found to be 95.28%. Adsorption data was better fitted to the Langmuir, Freundlich, Temkin and Dubinin Radushkevich isotherms. It was demonstrated that the sorption rate follows the pseudo-second order kinetics and intraparticle diffusion theory and the biosorption process was spontaneous and exothermic in nature.

Metal‐Organic Framework (Cu@ZIF) for Photocatalytic Reduction of p‐Nitrophenol and its Toxicological Evaluation using Zebrafish (Danio Rerio)

AbstractGlobal food security depends on agricultural development, yet excessive fertilizer and pesticide usage is harmful to the environment. These substances have a role in human health problems, environmental changes, and erosion of the soil. Although p‐nitrophenol, an organic pollutant and other organophosphorous compounds are utilised in agriculture, their usage raises major health and environmental issues. These synthetic pesticides are quite effective at getting rid of pests, but they have also been linked to serious health problems for people and animals, degraded soil, and contaminated water. One typical persistent pollutant present in industrial wastewater is the organic pollutant, which is produced by organophosphorous compounds. The primary objective of this work is to use Cu@ZIF for photoreduction of p‐nitrophenol (PNP). A UV‐visible spectrophotometer test revealed that the deterioration peak after 60 mins. An analyzer for total organic carbon (TOC) was utilised to assess the PNP mineralization. The catalyst remained same and continued in the same behaviour even after four cycles. This study evaluated the acute toxicity of PNP on the development of early‐stage zebrafish, paying particular attention to the embryonic developmental deformities. The technique of photocatalytic decontamination is safe for the environment, financially practical, and technically achievable.

Trace Ru Incorporation Boosted Co2P Nanorods for Superior Water Electrolysis and Substrate-Paired Electrolysis Toward Value-Added Chemicals in Alkaline Medium.

Electro-valorization of biomass-derived chemicals has ensured sustainable production of value-added products, an effective approach for reducing carbon footprint, through renewable energy. Electrochemical oxidation and reduction reactions in aqueous media using H2O as a potential source for active hydrogenated and oxygenated species fulfill the purpose. In this study, Ru─Co2P nanorods are explored as a bifunctional electrocatalyst toward valorization of Organics at basic media. The in-situ electrogenerated Co3+ and Co4+ species act as active oxidants toward product selectivity. An overpotential of 68mV is found for hydrogen evolution reaction (1m NaOH) with Ru─Co2P. Further, used as cathode, Ru─Co2P effectively reduces furfuraldehyde to furfuryl alcohol and p-nitrophenol to p-aminophenol. Ru doping enables ease of formation of active species both for reduction and oxidation, faster charge transfer between catalyst to absorbates. Density Functional Theory calculation establishes Ru incorporation in Co2P surface results in enhanced adsorption of substrates. Ru doping modulates the electronic structure of Co2P which changes the density of states resulting in faster water dissociation and water splitting. To reach 10mAcm-2 current density only 1.6V is required for water electrolysis, whereas 1.4V is enough for substrate-paired electrolysis with simultaneous oxidation of benzyl alcohol and reduction of p-nitro phenol.

PH dependence of reactive oxygen species generation and pollutant degradation in Fe(II)/O2/tripolyphosphate system

It has been reported that tripolyphosphate (TPP) can effectively enhance the activation of O2 by Fe(II) to remove organic pollutants in the environment. However, the influence of solution pH on the generation and conversion of reactive oxygen species (ROS) and their degradation of pollutants in the Fe(II)/O2/TPP system needs further investigation. In this study, we demonstrated that O2•– and •OH were the main ROS responsible for degradation in the system at different pH conditions, and their formation rates were calculated using a steady-state model. Experiments combined with density functional theory (DFT) calculations showed that the p-nitrophenol (PNP) degradation pathway in the Fe(II)/O2/TPP system is regulated by solution pH. Specifically, at pH = 3, the existence of Fe(II) in the solution is dominated by [Fe(II)(HTPP)2]2−, which leads to a rapid conversion from O2 and HO2• to generate •OH, and PNP is primarily oxidatively degraded. However, at pH = 5/7, [Fe(II)(TPP)2]4− is taking the lead with which O2•– is accumulated in the solution due to the slow conversion to •OH in this condition, and the PNP is mainly reductively degraded. This study proposes a new strategy to achieve the targeted oxidative/reductive removal of different types of pollutants by simply varying the solution pH in the Fe(II)/O2/TPP system.

Associations between Neonicotinoid, Pyrethroid, and Organophosphate Insecticide Metabolites and Neurobehavioral Performance in Ecuadorian Adolescents.

Organophosphate and pyrethroid insecticides can affect children's neurodevelopment and increase inflammation. Limited evidence exists among adolescents and on whether inflammation may mediate pesticide-neurobehavior associations. We examined the associations between insecticide metabolite concentrations and neurobehavior among adolescents in Ecuadorian agricultural communities. We included 520 participants aged 11-17 years. We measured urinary insecticide metabolites (mass spectrometry) and neurobehavior (NEPSY-II). Associations were adjusted for socio-demographic and anthropometric characteristics. The associations of insecticide mixtures with neurobehavior were evaluated using PLS regression, and mediation by inflammatory biomarkers (TNF-α, IL-6, CRP, SAA, sICAM-1, sVCAM-1 and sCD-14) was conducted. Among organophosphates, para-nitrophenol (PNP) and 3,5,6-Trichloro-2-pyridinol (TCPy) were inversely associated with Social Perception (score difference per 50% increase [β 50% ] = -0.26 [95%CI: - 1.07, -0.20] and -0.10 [-0.22, 0.01], respectively). PNP and TCPy also had significant inverse associations with Attention/Inhibitory Control at concentrations >60 th percentile (β 50% = -0.26 [95%CI: -0.51, -0.01] and β 50% = -0.22 [95%CI: -0.43, -0.00], respectively). The pyrethroid, 3-phenoxybenzoic acid (3-PBA), was inversely associated with Language (β 50% = -0.13 [95%CI: -0.19, -0.01]) and had a negative quadratic association with Attention/Inhibitory Control. The neonicotinoid 5-Hydroxy imidacloprid (OHIM) was positively associated with Memory/Learning (β 50% = 0.20 [95%CI: 0.04, 0.37]). Mixtures of all insecticides were significantly negatively related to all domains, except for Memory/Learning, which was positively associated. No mediation by inflammatory markers on these associations was observed. Concurrent organophosphate, pyrethroid, and the mixtures of all metabolites were associated with lower performance in all domains except for Memory/Learning. Neonicotinoids were positively associated with Memory/Learning and Social Perception scores.

Bisulfite enhances p-nitrophenol degradation by zero-valent iron under oxic conditions: Combination of indirect reduction by superoxide radical and direct reduction

Advanced oxidation processes based on the combination of zero-valent iron (ZVI) and S(IV) have been extensively investigated for oxidative degradation of organic pollutants, but little attention has been paid to their reducing capacities in the presence of oxygen. This work found bisulfite (BS) could greatly enhance the degradation of p-nitrophenol (PNP) by ZVI under oxic conditions and PNP was only reduced to p-aminophenol without further degradation. A combination of indirect reduction by superoxide radical (O2•–) and direct reduction by ZVI was verified as the mechanism of PNP degradation. Highly oxidizing species, such as hydroxyl radical (HO•) and sulfate radical (SO4•−), were also produced in the ZVI/BS system under oxic conditions but did not contribute to pollutant degradation perhaps due to the rapid consumption by reducing substances like BS ions and the released Fe2+. BS concentration, ZVI dosage, initial solution pH and coexisting anions (CO32–, PO43– and Cl–) affected the degradation of PNP. ZVI lost the reactivity after used for three times because of the production of goethite and lepidocrocite covered on its surface. This study will provide a new insight into degradation of organic pollutants in ZVI/BS system under oxic conditions.

Boosting Fenton-like catalytic performance and environmental stability of nano zero-valent copper (nCu(0)) catalyst by inhibiting the formation of oxide layer: Catalytic performance and mechanistic study

Nano zero-valent copper (nCu(0)) as Fenton-like catalyst has shown great potential in the treatment of organic wastewater. However, nCu(0) is prone to be agglomerated and oxidated, causing to the reduction in catalytic ability. Herein, biochar supported highly dispersed nCu(0) (Cu/C) was synthesized by the carbonization method. And acid-modified strategy was proposed to inhibit the oxidation of nCu(0). Physicochemical properties of Cu/C catalysts modified by different acid (HCl, H2SO4 and HNO3) were analyzed by various characterizations. The results showed that only the introduction of HCl could obviously inhibit the formation of oxide layer on Cu(0), while HNO3 and H2SO4 couldn’t. Furthermore, the content of oxide layers decreased with the increase in HCl addition. Correspondingly, the catalytic performance enhanced gradually. Cu(0) was proved to be the active centers. And the presence of oxide layers was adverse to the catalytic reaction. When the adding amount of HCl reached to 1 mL, the Cu/C-HCl-1.0 catalyst showed the optimal catalytic performance. 97.1 % of p-nitrophenol (PNP) was degraded within 60 min. The reaction rate was 7.6 times that of unmodified Cu/C catalyst. Furthermore, Cu/C-HCl-1.0 catalyst possessed excellent environmental stability. After being directly exposed to air for 4 months, catalytic performance had no obvious decrease. In addition, the catalyst showed efficient degradation ability to phenols, dyes and antibiotics. And it was not sensitive to the initial pH of the organic solution (3.7 ∼ 11.2). OH was confirmed to be the main reactive species for the degradation of organic pollutants, which was formed by the decomposition of PMS by obtaining electrons from Cu(0). This work proposed a novel and efficient method to enhance the catalytic ability and environmental stability of Cu(0) by inhibiting the formation of oxide layer.

Kinetics of continuously catalyzed peroxymonosulfate in a fixed-bed reactor

Most studies have been conducted in batch reactors. Therefore, understanding the catalytic reaction kinetics and mass transfer in continuous catalytic reactors is essential for the design of heterogeneous catalysts and optimisation of catalytic degradation processes in heterogeneous systems. In this research, granular catalysts (Co-600/AlSi-0.25/AP) is used to investigate the kinetic constants and mass transfer resistance for the continuous catalytic decomposition of peroxymonosulfate (PMS) and degradation of p-nitrophenol (PNP) in a fixed bed reactor. The flow rate is 5 mL/min and reaction temperature is 30 °C, intrinsic kinetic constants of PMS decomposition and PNP degradation are 48 and 195 kg−1·min−1·L, respectively, which are 20–30 times of the apparent kinetic constants of PMS decomposition and PNP degradation in fixed bed reactors, respectively. The decomposition rates of PMS and PNP are controlled by mass transfer, and the reaction takes place in the diffusion-controlled regime. The mass transfer kinetic model based on the plug-flow model shows a good agreement between the calculated data and the experimental data. Which indicate that PMS decomposition and pollutant degradation in a fixed-bed reactor can be predicted by mass transfer kinetic modelling, guide the design of catalysts and the optimisation of heterogeneous catalytic reaction system in a fixed-bed reactor.

Non-radical activation of peracetic acid by Fe-Co sulfide modified activated carbon for the degradation of refractory organic matter

Recently, the non radical activation system had attracted much attention due to its strong anti-interference ability. In this study, a novel FeCo2S4/activated carbon (AC) catalyst was prepared and used to construct a non radical dominated degradation system. Due to the electron-donating groups (C-OH) of AC and the conversion of free radicals generated from the activation of PAA by iron (Fe) and cobalt (Co) ions, a large amount of singlet oxygen (1O2) were produced, making the activation system possessed excellent universality and applicability for the removal of organic pollutants. Within 5 min, about 89.87 % of tetracycline hydrochloride (TCH) was removed in FeCo2S4 /AC + PAA. After only 20 min of reaction, the TCH removal efficiency reached 94.12 %, accompany with the reaction rate reached 0.099 min−1. Other organic pollutants including ibuprofen (IBU), sulfamethoxazole (SMX), ciprofloxacin (CIP), p-nitrophenol (PNP) and atrazine (ATZ) were also efficiently removed within 20 min, with the removal efficiencies were 92.0 %, 91.5 %, 89.4 %, 88.3 %, and 84.5 %, respectively. When the solution pH changed from 5.01 to 9.48, FeCo2S4 /AC also showed excellent catalytic performances, with the TCH removal rates were maintained at over 85.18 %. Moreover, the removal rate of TCH still reached 90.23 % after 5 recycles. This study offered an efficient non-radical peracetic acid (PAA) activation system, which can be effectively used to degrade refractory organic pollutants from complex water environment.

Eco-conscious Silver nanoparticles through “flower extract” of Murraya paniculata (L) Jack for reduction of 4-nitro phenol

Green synthesis of metal nanoparticles using plant extracts has gained recognition. We report, the eco-friendly synthesis of Silver nanoparticles using the aqueous flower extract of Murraya paniculata (L) Jack (MP Silver NPs). Characterisation of the NPs was carried out using different spectroscopic and microscopic techniques. The findings confirmed the presence of Silver NPs via UV–vis spectroscopy, FTIR and XRD. SEM and TEM images indicated spherical structured MP Silver NPs, with an average size of 27.8 nm. Elemental analysis using XPS confirmed the presence of Ag in NPs. Biosynthesised silver NPs were explored for catalytical activity. The current work produces Silver NPs using a new green source with a wide range of applications.

Facile fabrication of NF-loaded Co3O4 monolithic catalyst and its application in the reduction of P-nitrophenol

In this work, a foam nickel-loaded Co3O4 nanosheet featuring an integral structure (NF@Co3O4) was successfully fabricated by a facile hydrothermal-calcination strategy. The catalytic performance of the NF@Co3O4 was evaluated using the reduction of P-nitrophenol (PNP) to P-aminophenol (PAP) under NaBH4 as a model reaction. A reduction rate of 94.44% for PNP was achieved under the following reaction parameters over 25 min at 25∘C: two slices of NF@Co3O4 monolithic catalysts (3 × 4 cm2), a PNP concentration of 15 mg L[Formula: see text] (500 mL), and a NaBH4 dosage of 15 mmol L[Formula: see text]. Moreover, NF@Co3O4 presented a stable performance in PNP reduction, maintaining a reductive conversion above 91% over sixteen consecutive runs. This study suggested that NF-loaded Co3O4 is a promising monolithic catalyst for the treatment of phenol-containing wastewater, owe to its superb catalytic performance and ease of recovery.

Green Synthesis of Clay/rGO Composite for Sensitive Detection of Para Nitrophenol in the Environment

AbstractNitrophenols (e. g., para nitrophenol), although they have beneficial properties, their residuals are injurious to the environment owing to their high lethal potential for many categories of nature (e. g. animals, humans, plants, etc.), which require their monitoring. In this paper, a new Clay/green reduced graphene oxide composite (Clay/rGO) was efficaciously synthesized and utilized as an excellent modifier for carbon paste electrode (CPE) for the electro‐analytical determination of paranitrophenol (PNØ). The electrochemical futures and reduction of PNØ at the surface of the as‐prepared Clay/rGO˧CPE have been executed using DPV differential pulse voltammetry (DPV), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The use of the EIS provided that the Clay/rGO˧CPE facilitate the electron exchange process. By using the DPV technique in phosphate buffer (PB) under biological pH (7) (PB_7) the prepared monitor exhibited an excellent linearity relationship in the concentration ranges from 1.0 to 1000.0 μM with a detection limit (DL=3×σ/P) of 0.16 μM and a quantification limit of (QL=10×σ/P) of 0.54 μM. The Clay/rGO˧CPE offered high selectivity and a satisfactory concert in the electroanalytical sensing of PNØ in wastewater sample.

Phosphate ligand-mediated production of reactive oxygen species during oxygenation of Fe(II)-phosphate complexes

Reactive oxygen species (ROS) production upon the oxygenation of reduced iron minerals is of critical importance to redox cycles of Fe and the fate of refractory organic contaminants. The environmental impact factors during this process, however, have been underappreciated. In this study, prominently enhanced production of hydroxyl radicals (•OH) was observed by oxygenation of Fe(II) with 5–50 mM phosphate. The results of spin trap electron spin resonance (ESR) experiment showed that Fe(II)-phosphate complexes facilitated the generation of •OH. The degradation experiment of p-nitrophenol (PNP) confirmed that •OH formation was dominated by a consecutive one-electron O2 reduction (90.2–96.9 %), and the quantification of PNP degradation products revealed that Fe(II)/phosphate molar ratios regulated the O2 activation pathways for O2•− or •OH production. The further experimental and theoretical investigation demonstrated that the coordination of phosphate with Fe(II) plays a dual role in ROS generation that facilitated O2•− formation by lowering the energy barrier for Fe(II) oxidation and altered the reaction pathway of •OH formation due to its occupation of sites for electron transfer. The present work highlights an important role of natural oxyanions in O2 activation by Fe(II) and raises the possibility of in situ degradation of contaminants in subsurface environment.

Rapid and efficient adsorption of p-nitrophenol over biomass-derived vertically aligned graphene nanosheets fabricated by hydrothermal/molten salt-assisted pyrolysis method

Vertical graphene (VG) is an emerging three-dimensional graphene with unique structure and properties, which is expected to possess outstanding adsorption performance. Nevertheless, the utilization of VG as an adsorbent has not been investigated, and its conventional preparation methods are complex and expensive. Herein, we utilize a facile hydrothermal/ molten K2CO3-assisted pyrolysis method for preparing VG from cost-effective and renewable fir bark. The optimized VG-1.0 achieved a high adsorption capacity (556 mg/g) for p-nitrophenol (PNP) within 10 min, far superior to commercial activated carbon (360 mg/g) and previously reported graphene-based materials. Its excellent performance can be ascribed to high specific surface area (1423 m2/g), open & vertical channels, rich oxygen-containing groups and high graphitization degree, providing sufficient adsorption sites and unhindered mass transfer pathways. VG-1.0 was easily regenerated by rinsing with NaOH solution and showed good reusability, maintaining > 80 % of its original adsorption capacity after 5 cycles of reuse. The adsorption isotherm and kinetic data of PNP over VG were fitted well with Freundlich/Temkin model and pseudo-second-order kinetic model, respectively. Various characterizations and density functional theory (DFT) simulations have confirmed that the adsorption of PNP on VG is a spontaneous and endothermic process, involving pore filling and surface adsorption such as hydrogen bonding and π-π interactions.