Pseudo First-order Rate Constants Research Articles

Sodium thiosulfate modified graphitic carbon nitride for enhancing the photocatalytic production of aldehydes

The oxidation of alcohols to aldehydes is one of the most relevant reactions in organic chemistry. The currently implemented methods based on expensive noble metallic catalysts, toxic solvents, and high temperature and pressure conditions have released the seek for softer and cheaper alternatives such as photocatalysis. In this sense, graphitic carbon nitride has been modified with sodium thiosulfate as a source of S and Na+ incorporation in the structure, aimed at enhancing the photocatalytic performance on the photocatalytic oxidation of alcohols to aldehydes, cinnamaldehyde, benzaldehyde, and vanillin in aqueous solution. Three g-C3N4 samples synthesized from different precursors, i.e. melamine, thiourea, and urea, were treated with sodium thiosulfate. Urea led to the g-C3N4 with the highest mesoporosity (surface area, 69 m2 g−1) and photocatalytic activity. The modification with 5 % (wt.) of Na2S2O3 enhanced the pseudo-first order rate constant of cinnamyl alcohol oxidation from 0.265 h−1 (bare sample) to 0.792 h−1 (Na2S2O3-modified). The characterization of the material suggests a better charge separation of the photogenerated charges after S and Na+ incorporation in the structure, minimizing the recombination rate of photogenerated charges. The optimum photocatalyst, tested in aqueous solution, was most selective in the production of benzaldehyde (selectivity, >100 %) > cinnamaldehyde (>23 %) > vanillin (~5 %). The selectivity was considerably boosted under acetonitrile as the solvent medium, raising the 23 % recorded in water to 51 % in pure acetonitrile. The degradation mechanism suggests a strong influence of the photogenerated holes and the superoxide radical, the latter being more selective in the oxidation of the alcohol.

Photolytic decomposition of PFOS by electrospun nanofiber composites of Fe(III)/PVDF Under UV-C light

Per- and polyfluoro alkyl substances (PFAS) are emerging pollutants that have contaminated various water streams of the world. Besides polluting the environment, it is related to several human diseases, including cancer. Various methods have been proposed to remove PFAS from water streams including, photocatalytic or photolytic decomposition of PFAS which decomposes PFAS in a quasi-perpetual fashion and does not generate secondary pollution. In this work, perfluoroctane sulfonic acid (PFOS) is used as a model PFAS to study its photolytic decomposition by nanofiber composites (NFC) of Fe (III) and polyvinylidene fluoride (PVDF) under ultraviolet (UV)-C light. The nanofiber composite was fabricated using an electrospinning technique with PVDF and iron precursor on the conductive surface of indium tin oxide (ITO) coated polyethylene terephthalate (PET) film. The composite was characterized with SEM-EDX, AFM, XRD, and TGA. It was found that a significant amount, 70 % of aqueous PFOS solution is decomposed by the composites in the presence of traces of hydrogen peroxide and UV-C light. The kinetics of PFOS degradation was fit with pseudo-first order rate constant of 0.056 hr−1. It is proposed that PFOS binds with Fe(III) to form an unstable complex that is decomposed under UV-C light and Fe(III) is reduced Fe(II). Hydrogen peroxide provides the simultaneous benefits of further decomposing the PFOS complex and regenerating Fe(III). The overall results suggest that this nanofiber composite can be used for the photolytic decomposition of PFOS. It is also revealed that two composite mats showed the optimal performance and the increase in concentration of hydrogen peroxide increased the degradation of PFOS monotonically.

Porphyrin photosensitizers compatible with both aqueous and non-aqueous conditions: Acid dependent spectral, solubility and photocatalytic properties of meso-tetra(pyridyl)porphyrins

The aerobic photooxidation of 1,3-diphenylisobenzofuran (DPBF) as a specific singlet oxygen quencher was studied in the presence of meso-tetra(aryl)porphyrins (aryl = 2-pyridyl, 3-pyridyl and 4-pyridyl) and their diprotonated and hexaprotonated derivatives to investigate the influence of the position of pyridine nitrogen atom, solvent, core protonation (with HCl or dichloroacetic acid) and full protonation of the porphyrins on their photocatalytic activity and photooxidative stability. The pseudo-first order rate constants (kobs) for the oxidation of DPBF with singlet oxygen were determined to compare the relative activity of the photosensitizers. 1,4-benzoquinone as a scavenger of superoxide anion radical provided evidence for the absence of this species in these photocatalytic systems. The singlet oxygen quantum yields (φΔ) of the porphyrin photosensitizers were estimated by determining the initial rate constants for the oxidation of DPBF. H4T(2-Py)P(Cl)2 and H4T(2-Py)P(CHCl2COO)2 were the most efficient photosensitizers of the series of the meso-tetra(2-, 3- or 4-pyridyl)porphyrins and the protonated derivatives.

Oxidation of tryptophan by benzimidazolium dichromate

In order to determine a likely mechanism, tryptophan oxidation with benzimidazolium dichromate (BIDC) in an acid medium utilizing sulfuric acid has been investigated at 313 K. First order dependence is demonstrated by the calculated pseudo-first order rate constant, which is found to be independent of the oxidant’s initial concentration. Additionally, the reaction exhibits first order behavior for both sulfuric acid and tryptophan. The rate of reaction is unaffected by an increase in ionic strength and is lowered by a decrease in the medium’s dielectric constant. Since acrylonitrile is not polymerizing, there is no chance of a free radical mechanism. The two electron transfers involved in the mechanism are confirmed when the concentration of manganous sulphate increases because it slows down the rate of reaction. A suitable mechanism and rate law have been derived from the experimental observations. The oxidation reaction yields carbon dioxide, ammonia, and indole-3-acetaldehyde as its products.

Assessment of abiotic reduction rates of organic compounds by interpretable structural factors and experimental conditions in anoxic water environments

For organic contaminants in lake sediments, aquifers, and anaerobic bioreactors, their reduction is one of the primary transformation paths in these anoxic water environments. A simple model is introduced to predict pseudo-first order rate constants (kobs) for the abiotic reduction of organic compounds featuring diverse reducible functional groups. It utilizes the largest experimental dataset of –log kobs, encompassing 59 organic compounds (278 data points). Unlike available complex quantitative structure–activity relationship (QSAR) methods, the novel approach requires both experimental conditions and structural parameters. In comparison to one of the available general QSAR methods, the new model demonstrates favorable performance. The average absolute deviation (AAD), absolute maximum deviation (ADmax), average absolute relative deviation (AARD%), and R-squared (R2) values of the estimated outputs for 54/5 training/test data sets of the new model are 0.641/1.761, 1.761/1.417, 20.52/83.87, and 0.797/0.949, respectively. On the other hand, the available general comparative QSAR method shows the AAD: 1.311/2.301, ADmax: 3.795/3.732, AARD%: 641.0/821.2, and R2: 0.003/0.447. For the test set, AAD, AARD%, ADmax, and R2 values for the new/comparative models are 0.649/2.403, 62.20/190.5, 1.215/3.732 and 0.974/0.789, respectively. In summary, the new model offers a straightforward approach for the manual calculation of –log kobs, demonstrating excellent goodness-of-fit, reliability, precision, and accuracy.

Anthocyanins and phenolics content of Thai black soybean extracts and their prevention against myoglobin autoxidation

Anthocyanin and phenolics found in black soybean are known as active antioxidants and have been linked to a variety of health benefits. The purpose of this study was to determine total monomeric anthocyanins (TMA), total phenolics (TP), and the retardation ability of protein autoxidation of an ethanolic extract of black soybeans planted in Thailand. We investigated the optimal conditions for extraction conditions. The ultrasonic-assisted approach successfully extracted both TMA and TP using 85% v/v ethanol as the solvent. The 15-min extraction time and solvent-to-sample ratio of 20:1 (v/w), at 30°C resulted in the highest concentration of TMA at 3.232±0.04 mg cyanidine-3-Oglucoside equivalent per gram dry weight whereas the longer time and higher temperature resulted in significantly decreased TMA content (P<0.05). The maximum TP concentration of 119.42±0.42 mg gallic acid equivalent per gram dry weight was obtained by using a method identical to that used to extract TMA, except that of the longer time, increased solvent consumption and temperature. The preventive effect of black soybean extracts on oxymyoglobin (oxyMb) autoxidation was investigated. The pseudo first-order rate constant of oxyMb oxidation is decreased in the presence of the extracts in comparison to oxyMb alone. Additionally, oxyMb's half -life was increased from 0.57 to 1.46 hrs in the presence of TMA-rich extracts and from 0.57 to 2.51 hrs in the presence of the highest concentration of TP extracts when compared to cyanidine-3- O-glucoside and gallic acid, respectively. The study revealed that the black soybean extract could stabilize the bound oxygen in the oxyMb lead to slow down autoxidation of the protein consumption of foods or products derived from black soybeans may help to reduce cellular oxidative stress and the risk of developing various diseases as the study's findings indicate.

A new insight into the pseudo-first-order model: investigation of the adsorption mechanism of amoxicillin, diclofenac sodium, and methylene blue on various adsorbents based on the pseudo-first-order rate constant

In this study, a new approach has been proposed to determine the adsorption mechanism based on the pseudo-first-order rate constant (PFO). The mathematical expression of the PFO rate constant based on the Langmuir adsorption mechanism was obtained. This expression includes a new parameter called the contact surface area of the adsorbed molecule with the adsorbent. By analyzing the relationship between the PFO rate constant and the initial concentration of the adsorbate, this parameter can be calculated. The value of this parameter provides information about the orientation and adsorption mechanism of a molecule on the adsorbent surface. The proposed method was evaluated using the adsorption data of amoxicillin, diclofenac sodium, and methylene blue on various adsorbents; the results were in good agreement with experimental data.

Microwave-assisted hydrothermal synthesis of ZnO@ZrO2 nanohybrid for biomedical and photocatalytic applications

The present study was conducted to synthesize zinc oxide decorated on zirconium oxide (ZnO@ZrO2) nanohybrid synthesized through microwave-hydrothermal (MW-HT) method. Various analytical techniques were used to analyze the morphology, surface properties, constitution of hybrid, and elemental composition. Additionally, the anti-microbial activity of ZnO@ZrO2 nanohybrid was assessed against Gram-positive and Gram-negative pathogenic bacteria, hemolytic, anti-oxidant as well as anti-inflammatory assay. The hexagonal wurtzite phase of the ZnO was revealed by the XRD analysis. The experimental results reveal that the synergetic effect between the Zn and Zr active sites results an excellent biomedical activity. The ZnO@ZrO2 nanohybrid was successfully applied to the photocatalytic degradation of basic fuchsin (BF) dye within short period of time under visible light (VL) radiation. Moreover, the ZnO@ZrO2 nanohybrid exhibited an extraordinary performance for photocatalytic degradation of BF with a pseudo-first order rate constant (k) of ca. 0.1702 min−1, which was 2.5 and 1.8 fold compared to ZnO and ZrO2 photocatalysts. These results indicated that the ZnO@ZrO2 nanohybrid can be used as a potential biomaterial for bioengineering and photocatalytic applications.

Kinetics and mechanistic investigation of the substitution from dinuclear Pt(II) complexes bridged by N,N’-bis(2-pyridylcarboxamide)phenylenediamines

The rates of substitution of the chloride ligand in dinuclear complexes, [Pt2(N,N'-bis(2-pyridylcarboxamide)-1,3-phenylenediamine)Cl4] (1), [Pt2(N,N'-bis(2-pyridylcarboxamide)-1,4-phenylenediamine)Cl4] (2), [Pt2(N,N'-bis(3-isoquinolylcarboxamide)-1,3-phenylenediamine)Cl4] (3) and [Pt2(N,N'-bis(3-isoquinolylcarboxamide)-1,4-phenylenediamine)Cl4] (4), by three bio-relevant nucleophiles, thiourea (TU), N,N-dimethylthiourea (DMTU) and N,N,N’,N’-tetramethylthiourea (TMTU), were investigated. The mononuclear analogue [Pt(N-phenylpyridine-2-carboxamide)Cl2] (5) was included to compare the results. The kinetics of the reactions were studied under pseudo first-order conditions in a methanol solution (I = 0.1 M LiCl) as a function of concentration and temperature using the stopped-flow spectrophotometer. The observed pseudo first-order rate constants for the substitution reactions of all the complexes were calculated from two well-separated steps and obey the rate law k obs (1 st /2 nd ) = k 2 (1 st /2 nd )[Nu]. The reactivity of the complexes decreases in the order 2 > 1 > 4 > 3 > 5. The conformational symmetry of the complexes as controlled by the phenylenediamine bridges, steric hindrance due to the bridges as well as the σ-donor capacity of the coordinated groups around the metal centers influence the reactivity of the dinuclear complexes. The low enthalpy (ΔH #) and negative intrinsic entropy (ΔS #) values support an associative mechanism of substitution. The kinetic data are supported by DFT calculations.

TiO2-kaolinite composite photocatalyst for industrial organic waste decontamination

The industrially feasible TiO2-clay based photocatalysts are essential to overcome the practical barriers that are intrinsic to currently available clay-based photocatalysts. The present study demonstrates the fabrication of heterogeneous photocatalyst consisting of TiO2 and kaolinite (TKCP) that has shown improved catalytic activity and strength, ensuring industrial viable photocatalyst. TKCP is prepared via an economical method, employing mechanical compression and dehydroxylation, forming TiO2-clay hybrid matrix. Amount of clay primarily determines mechanical strength and photocatalytic efficiency of TKCP where TKCP with the lowest clay percentage results in a homogeneous matrix that consists of tiny TiO2 particles embedded clay sheet-like structure. The TiO2 particles embedded clay sheet-like structure is responsible for the high specific surface area and small pore size, increasing the active surface that is available for effective disintegration of organic contaminants. By increasing clay fraction in TKCP, a significant increase in surface defects can be observed due to large clay fragments and TiO2 agglomerates, which results in flexural strength and catalytic activity decrease. Methylene blue degradation on TKCP with the maximum TiO2 percentage results in the highest pseudo first-order rate constant of 0.58 h−1, exhibiting improved photocatalytic activity due to well-organized matrix and high specific surface area (82.79 m2 g−1). TKCP can be obtained in variable sizes and shapes that ensure dynamic wastewater treatment applications.

Insights into the electron transfer mechanisms of peroxydisulfate activation by modified metal-free acetylene black for degradation of sulfisoxazole

Herein, a modified metal-free acetylene black (MMF-AB) catalyst was synthesized by a simple solvothermal-calcination method and designed successfully to activate peroxodisulfate (PDS) for the degradation of sulfisoxazole (SIZ). Due to the doping of N, S and O metal-free elements, the modified catalyst showed excellent catalytic performance with 100% SIZ removal within 30 min. Pseudo first-order reaction rate constants (evaluating catalytic efficiencies and activity) of MMF-AB (kobs = 0.105 min−1) was 3 times higher than pure-AB (kobs = 0.029 min−1). Interestingly, it was demonstrated that the reaction system is based on the transfer of electrons from SIZ to PDS to realize an electron-transfer-based mechanism by the evidence of premixing, electron paramagnetic resonance (EPR) spectroscopy, salt-bridge experiments and electrochemical analyses. The introduction of recyclable filtration device solved the secondary pollution caused by the dispersion of the powdered catalyst in the treated water, which further proved the practicality and superiority of the MMF-AB catalyst.

Hydroxyl radical-driven transformations of bisphenol A and 2,4-dinitroanisole: Experimental and computational analysis.

This study used experimental and computational analysis to investigate the advanced oxidation of bisphenol A (BPA) and 2,4-dinitroanisole (DNAN). The pseudo first-order reaction rate constants depended on the molar peroxide ratio and were between 0.13 and 0.28 min-1 for BPA and between 0.018 and 0.032 min-1 for DNAN. The kinetic differences appear to be due in part to the energy requirements for oxidation, which depended on the reaction mechanism but were typically lower for BPA than they were for DNAN. Density functional theory (DFT) was used to develop transformation pathways that included experimentally-detected byproducts. The most energetically favored pathway for BPA oxidation begins with the formation of hydroxylated derivatives, while for DNAN, the most energetically favorable degradation pathway begins with the substitution of the methoxy group. Overall, these findings demonstrate the power of combining experimental and computational tools to reveal transformation mechanisms during water treatment. PRACTITIONER POINTS: Advanced oxidation transformations for two emerging water pollutants, bisphenol A and dinitroanisole, was investigated. The observed reaction kinetics depended on molar peroxide ratio in a manner that is in keeping with previous findings. Density functional theory-based analysis revealed reaction energy requirements and degradation pathways.

Self-catalyst degradation of amoxicillin in alkaline condition driven by superoxide radical

We studied the rate of amoxicillin (AMX) degradation in oxygen-contained (OCG) and oxygen-free (OFG) groups under alkaline conditions by comparing the molecular structure of AMX with penicillin (PG) and penicillin V potassium (PV) resulting from measuring the hydrolysis rate, performing quenching experiments, and analyzing the products of AMX. The pseudo first-order rate constants of AMX hydrolysis were 0.003 h−1 and 0.032 h−1 (pH = 9, 25 ℃) in OCG and OFG, respectively, with both dissolved oxygen and OH− radicals playing important roles in AMX hydrolysis in OCG. According to the quenching experiments, the signal intensity of O2− in OCG appeared after 3 h and increased consistently, which confirmed that the participation of dissolved oxygen in AMX degradation accelerates the reaction and O2− generate from the reaction between dissolved oxygen and the hydrolysis products of AMX. The phenol group was the key functional group involved in the O2− reaction when comparing the molecular structure differences between PG, PV, and AMX. In total, 30 degradation products of AMX were found by liquid-chromatography triple-quadrupole mass spectrometry. Five degradation pathways of AMX were suggested, which are similar to those of photodegradation. Among them, path 3, which involves phenol (phenol, p-carboxyphenol, etc.) reactions, contained reactions with both dissolved oxygen and OH−. Considering there were no extra reagents added to the reaction system, the degradation of AMX in OCG appeared to be a self-catalytic reaction.

Degradation of emerging per- and polyfluoroalkyl substances (PFAS) using an electrochemical plug flow reactor

In recent years, shorter-chain fluorinated compounds have been manufactured as alternatives to legacy per- and polyfluoroalkyl substances (PFAS) after a global ban on some long-chain PFAS. This study is the first to investigate the degradability of emerging PFAS by an electrochemical plug flow reactor (EPFR). Ten different emerging PFAS, representing classes of fluorotelomer alcohol, perfluoroalkyl ether carboxylate, polyfluoroalkyl ethersulfonic acids, perfluoroalkyl ether/polyether carboxylates, perfluoroether sulfonate, N-alkyl perfluoroalkylsulfonamido carboxylate, fluoroalkyl phosphonic acid, and perfluoro alkane sulfonamide were investigated. The process kinetics was performed. The degradation of parent compounds increased with increasing retention time (RT). At 45.2 min of RT, the degradation of parent compounds ranged between 68%−100% with a current density of 17.2 mA/cm2. A linear increase in pseudo-first order rate constants was observed for all PFAS with increasing current density from 5.7 to 28.7 mA/cm2 (R2 > 0.91). The effect of pH, natural organic matter, and bicarbonate on the degradation, defluorination, and fluorine mass balance are reported. Alkaline pH (11) caused a decrease in degradation for all PFAS. While the presence of natural organic matter (NOM) significantly decreased the degradation and defluorination processes, the presence of bicarbonate at all studied concentrations (25, 50, and 100 mg/L) did not affect the process efficiency. The defluorination reduced to 34% from 81% with 15 mg/L NOM. The unknown/undetected fluorine fraction also increased in the presence of 15 mg/L NOM indicating the formation of NOM-PFAS complexes. Additionally, C2-C8 perfluoro carboxylic acids (PFCAs), one perfluoro sulfonic acid (PFSA), two H-PFCAs, and 4:2 fluorotelomer sulfonate (FTS) were identified as degradation byproducts in suspect screening. The electrical energy per order for PFAS ranged between 1.8 and 19.4 kWh/m3. This study demonstrates that emerging types of PFAS can potentially be degraded using an EPFR with relatively low electrical energy requirements.

Photophysical study on DNA & BSA binding and cytotoxic behaviour of piperidine-Pt(II) complexes: Their kinetics & mechanism and molecular docking

For the development of Pt(II) based anticancer drug candidates, carrier ligand 2-(Piperidine-1-yl)ethylamine (PIEAM) was used as a bidentate chelator to synthesize dichloro complex [Pt(PIEAM)Cl2] C-1 and its diaqua [Pt(PIEAM)(OH2)2](X)2 (C-2). The diaqua complex C-2 was further used to synthesize thiol substituted Pt(II)-sulfur complexes with l-cysteine (LC) and N-acetyl-l-cysteine (NAC). The Pt(II) complexes were characterized by multi spectroscopic methods and thermal analysis. The role of electronic and steric factors of carrier ligand PIEAM on substitution reactions of C-2 with LC and NAC was studied in aqueous medium at pH 4.0 under pseudo first-order kinetics and rate constant, equilibrium constant and thermodynamic parameters were calculated. The DNA binding activity and binding mode were confirmed by gel electrophoresis and viscosity measurement. The binding activity of Pt(II) complexes with DNA and BSA was explored by absorption and fluorometric titration methods. In vitro MTT assay of Pt(II) complexes were tested on different cancer cell lines like; MCF 7, A549, HCT 116 and also on normal human embryonic kidney cell HEK 293. The cell cycle arrest of MCF 7 cell growth and also the oxidative stress level (ROS) after treating with Pt(II) complexes were analysed. The structural optimization for molecular docking of Pt(II) complexes at B3LYP functional level were performed to correlate the experimental findings. The antineoplastic activity and drug likeness behaviour of Pt(II) complexes were further supported by PASS prediction and in silico ADME analysis.

Effect of size on physicochemical, antibacterial, and catalytic properties of Neolamarckia cadamba (burflower-tree) synthesized silver/silver chloride nanoparticles.

Aqueous extract of Neolamarchia cadamba leaves were used in the synthesis of silver/silver chloride nanoparticles (Ag/AgCl NPs). Further they were separated based on their using step-wise centrifugation approach at 09,000, 12,000, and 15,000rpm. Thus obtained NPs were characterized for their physicochemical features. NPs showed maximum absorbance at 455nm, 415nm, and 402nm. All the NPs were found to be crystalline in nature with average crystallite size (nm) of 58.31, 23.43, and 09.56. Particle size distribution (nm) of NPs was observed to 435.43, 276.75, and 105.49, Surface charge (-mV) of NPs was observed to be 14.59, 23.90, and 32.17. Ag/AgCl NPs-rpm@15,000 showed antibacterial activity against Escherichia coli, coagulase-negative Staphylococci, and Staphylococcus aureus with zone of inhibition (mm) of 16.65, 13.69, and 14.02 at 50µg per well, respectively. Ag/AgCl NPs-rpm@15,000 showed excellent catalytic activity in degradation of methyl red, methylene blue, rhodamine-B, and methyl orange dyes in the presence of sodium borohydride under 4, 6, 5, and 4min with pseudo-first order rate constant (min-1) of 0.981 (96.4%), 0.666 (97.1%), 0.905 (98.1%), and 1.032 (96.6%), respectively. Furthermore, Ag/AgCl NPs-rpm@15,000 showed good catalytic efficiency even under different dye combinations. Total combination was degraded under 18min.

Graphene foam mediated FeS2/α-Fe2O3 composites for chloramphenicol photodegradation using persulfate activation under visible light irradiation

The creation of an effective treatment system is necessary due to the threats posed by chloramphenicol (CAP) antibiotic residue in water streams. Photocatalytic composites provide potential replacements for getting rid of such a dangerous pollutant. Here, a nanohybrid comprised of FeS2/α-Fe2O3 nanoparticles produced via deposition-precipitation is built with an oxygen-rich graphene foam (GF). X-ray diffraction (XRD), FT-IR spectroscopy, XPS, UV-diffuse reflectance examination, TEM microscopy, SEM-EDX, Porosimetery analysis, and Point of Zero Charge testing were used to evaluate the magnetic nanomaterials with various FeS2/α-Fe2O3@GF ratios, giving a thorough picture of their structure, band gap, morphology and surface chemical features. Under visible light, the material FeS2/α-Fe2O3@GF (1:4) quickly oxidizes CAP (k = 0.0159 min−1, 20 ppm, pH 8.6) within only 10 min. In the composite-activated persulfate (PPS) system, holes are acknowledged as acceptable reactive species after the SO4− and OH radicals. Increased pore volume, surface area, and dimension reduction in comparison to individual counterparts, together with improved visible light absorption capabilities in the visible region, were the main causes of the CAP photodegradation enhancement on FeS2/α-Fe2O3@GF. In comparison to FeS2/α-Fe2O3 alone, the ratio of Fe2+ was twice as high in the FeS2/α-Fe2O3@GF composite, which improves PPS activation for CAP degradation. Using LC-MS, the intermediates of CAP photocatalytic oxidation that adhere to a pseudo first-order rate constant were discovered, and potential degradation routes were suggested along with a toxicity evaluation.

Photolysis of chlorite by solar light: An overlooked mitigation pathway for chlorite and micropollutants

Chlorite (ClO2−) is an undesirable toxic byproduct commonly produced in the chlorine dioxide and ultraviolet/chlorine dioxide oxidation processes. Various methods have been developed to remove ClO2− but require additional chemicals or energy input. In this study, an overlooked mitigation pathway of ClO2− by solar light photolysis with a bonus for simultaneous removal of micropollutant co-present was reported. ClO2− could be efficiently decomposed to chloride (Cl−) and chlorate by simulated solar light (SSL) at water-relevant pHs with Cl− yield up to 65% at neutral pH. Multiple reactive species including hydroxyl radical (•OH), ozone (O3), chloride radical (Cl•), and chlorine oxide radical (ClO•) were generated in the SSL/ClO2− system with the steady-state concentrations following the order of O3 (≈ 0.8 μΜ) > ClO• (≈ 4.4 × 10−6 μΜ)> •OH (≈ 1.1 × 10−7 μΜ)> Cl• (≈ 6.8 × 10−8 μΜ) at neutral pH under investigated condition. Bezafibrate (BZF) as well as the selected six other micropollutants was efficiently degraded by the SSL/ClO2− system with pseudofirst-order rate constants ranging from 0.057 to 0.21 min−1 at pH 7.0, while most of them were negligibly degraded by SSL or ClO2− treatment alone. Kinetic modeling of BZF degradation by SSL/ClO2− at pHs 6.0 – 8.0 suggested that •OH contributed the most, followed by Cl•, O3, and ClO•. The presence of water background components (i.e., humic acid, bicarbonate, and chloride) exhibited negative effects on BZF degradation by the SSL/ClO2− system, mainly due to their competitive scavenging of reactive species therein. The mitigation of ClO2− and BZF under photolysis by natural solar light or in realistic waters was also confirmed. This study discovered an overlooked natural mitigation pathway for ClO2− and micropollutants, which has significant implications for understanding their fate in natural environments.

Abiotic reduction of nitrate to ammonium by iron (oxy)(hydr)oxides and its stable isotope (δ15N, δ18O) dynamics

In this study, the kinetics and stable isotopic fractionation of nitrate (NO3−) reduction in Fe(II)/Fe(III) homogeneous/heterogeneous systems were investigated at circumneutral pH (i.e., pH 6.5 to 7.5) and ambient temperature (24 °C). Of the suite of iron (oxy)(hydr)oxides examined, NO3− reduction by Fe(II) was only significant in the presence of layered double hydroxide green rust (GR) minerals. Comparison of type 1 and type 2 GRs demonstrated that type 1 (GR(Cl−)) had the fastest NO3− reducing ability, with an Fe(II)-normalized pseudo first-order kinetic rate constant of kobs (NO3−) = 16.2 × 101 M−1 d−1. Anion concentrations (SO42− or Cl−) and the ratio of [Fe(II)] to [Fe(III)] also influenced reduction kinetics. Ammonium (NH4+) was the predominant reaction end-product (>50%) with the remaining reduced N species concluded to be comprised of N2(g) as other intermediates (nitrite (NO2−), nitric oxide (NO) and nitrous oxide (N2O) were not detected during NO3− reduction. Apparent nitrogen (δ15N-NO3−) isotopic fractionation (15ε) for GR(Cl−) and GR(SO42−) were were calculated to be 12.9 (CI: 8.2, 16)‰ and 37.9 (CI: 34, 41)‰, respectively. Similarly, oxygen (δ18O-NO3−) isotopic fractionation (18ε) differed between GR(Cl−) and GR(SO42−): 4.53 (CI: 2.5, 5.8)‰ and 14.4 (CI: 12, 16)‰. However, the ratio of 18ε:15ε for both minerals could be fitted to a linear regression of slope 0.369 (CI: 0.361, 0.377). These findings reaffirm the importance of GR minerals to NO3− reduction, especially in iron-rich systems hosting dynamic redox oscillations, including hyporheic zones, estuarine sediments and groundwater aquifers. These results also demonstrate that N and O stable isotope kinetic fractionation analyses as well as the ratio of 18ε:15ε can provide a means to distinguish between this abiotic anoxic reaction from anaerobic bacterial NO3− reduction processes.

Quantitative structure-activity relationship for the photooxidation of aromatic micro-pollutants induced by graphene oxide in water

The photocatalytic degradation behavior of aromatic micro-pollutants (AMPs) exhibits complexity and uncertainty, which mainly depends on the properties of different substituents on benzene. And with similar catalytic reaction substrates, the reaction rate constant could reveal the influence of different characteristics of molecular structure in a specific system. Therefore, the photooxidation pseudo first-order kinetic rate constants (kobs) of 30 AMPs were experimentally determined in Photo-GO system. A quantitative structure-activity relationship (QSAR) model for predicting the photooxidation reaction of AMPs has been developed by stepwise multiple linear regression (MLR) method, based on the lg kobs and representative molecule descriptors (20 in total) including physicochemical, quantum chemical and electrostatic descriptors. Afterwards, Radj2, QLOO2, and Qext2 were calculated as 0.870, 0.841, and 0.732 respectively, which exhibited the excellent goodness-of-fit, robustness, and predictability of the QSAR model, indicating its great prediction ability for photooxidation behavior of AMPs. Meanwhile, during the photooxidation process of AMPs with GO, the model revealed that the one-electron oxidation potential (Eox), molecular dipole moment (μ), and number of hydrogen bond donors (#HD) were the most important molecular structural parameters, which showed that the single electron transfer pathway and adsorption were as the significant steps. Additionally, the Hammett correlation showed that photooxidation of AMPs in Photo-GO system is of typical electrophilic reactions, which demonstrated that the electron-donating substituents could promote the photooxidation of AMPs. The QSAR model was constructed and evaluated to perform the prediction of AMPs reaction kinetics, which provided a guidance for the study of the mechanism and selective oxidation of AOPs photooxidation system based on GO.