Values Of Rate Constants Research Articles

Unlocking the Catalytic Potential of Anionic Micelles: Insights into the Ce(IV)-Directed Phenylalanine Oxidation Kinetics in Asymmetric Hydrophobic Environments.

The oxidation kinetics of phenylalanine (Phe) by Ce(IV) have been examined in both the absence and presence of aqueous micellar media with asymmetric tails, specifically using sodium dodecyl sulfate (SDS) and sodium tetradecyl sulfate (STS) surfactants. The reaction progress was monitored by observing a decrease in absorbance using UV-vis spectroscopy. Interestingly, the kinetic profile revealed a consistent increase in the observed rate constant values as the concentration of the surfactant increased. The kinetic results have been analyzed by using numerous experimental studies, such as dynamic light scattering (DLS), zeta potential, 1H NMR analysis, FT-IR spectroscopy, conductometry, scanning electron microscopy (SEM), fluorometry, time-correlated single-photon counting (TCSPC), and transmission electron microscopy (TEM). Micellar aggregates maintain their spherical shape in the presence of the substrate, even at higher surfactant concentrations, as revealed by microstructural analysis. The substrate molecules are encapsulated to a greater extent in the inner micellar core of STS micelles on account of the more hydrophobic nature of STS surfactants. Therefore, in STS micellar media, fewer substrate molecules diffuse to the Stern layer compared to the SDS micellar medium, resulting in fewer molecules participating in the oxidative transformation reaction. As a result, the rate enhancement of oxidation kinetics is less pronounced in STS micelles than in SDS micelles. A plausible mechanism that aligns with the kinetic results has been highlighted, along with the interpretation of the Piszkiewicz model, to explain the observed catalytic effect of both micellar mediums.

Insights into Novel Doping Effect of Fe-Doped ZnS Nanostructures Derived from Oxystelma Esculentum: Kinetics-Based Photocatalysis, Nitrogen Fixation, and Antifungal Efficacy

Implementing greener approaches is a sustainable and eco-friendly methodology for nanocomposite synthesis. This work reports the sustainable fabrication of Fe-doped ZnS (Fe0.3Zn0.7S) nanocomposite and its broad-spectrum applications. The systematic characterization was carried out using several advanced analytical techniques. DLS, Zeta potential, SEM, XPS, and TEM performed morphological and size assessments of the engineered nanocomposite. Eventually, XRD provided valuable insights into the crystalline behavior of nanocomposite. The nanocomposites were then treated against the organic dye Safranin O, which displayed 93% degradation within an hour with the rate constant value of 0.0326 min−1. Parameters influencing the percentage degradation, such as temperature, pH, etc., were also discussed. Moreover, an LCMS test was also conducted to evaluate the presence of reactive intermediates. Safranin O’s degradation was confirmed by identifying intermediate products, such as compounds with m/z values of 335.84, 321.81, 306.79, 292.77, and 257.32, which were indicative of progressive dye breakdown. Finally, the photocatalytic enactment examination verified that the prepared nanocomposite’s nitrogen fixation rate (38.96 µmolg−1) was way greater (~4 times) than the pristine compound. In addition, prepared nanoparticles demonstrated a befitting ability to eliminate a wide range of threatening pathogenic fungi. The doping of Fe into ZnS further enhanced the inhibition against Fusarium oxysporum.

Photocatalytic Degradation of Methylene Blue by Engineering Tungstic Acid@ZIF‐67 Cocatalyst

AbstractThe zeolitic imidazolate frameworks have gained significant attention in various applications owing to their exceptional surface area, customizable porosity, and excellent thermal and chemical stability, making them a remarkable nanomaterial. The present study involved the utilization of ultrasonic‐assisted techniques to integrate tungstic acid into the zeolitic imidazolate framework (TA@ZIF‐67) with the aim of augmenting the photocatalytic activity. The as‐synthesized nanocomposite was characterized using X‐ray diffraction and scanning electron microscopic analysis to inspect the structural aspects and morphology. The reduction in particle size of TA@ZIF‐67 due to the incorporation of tungstic acid results in a higher surface area, leading to a significant improvement in the photocatalytic activity of ZIF‐67. The assessment of the photocatalytic performance of ZIF‐67 and TA@ZIF‐67 was conducted through the degradation of methylene blue (MB) under sunlight. The degradation efficiency of ZIF‐67 and TA@ZIF‐67 was observed to be 61% and 85%, respectively, of the MB solution following a 60 min irradiation period. The investigation of the kinetics study based on rate constant values revealed that the utilization of TA@ZIF‐67 presented a greater efficiency in the removal of MB from an aqueous solution. The results pave a new avenue toward the design of MOF‐based photocatalysts for water treatments.

Effect of grinding methods on slime dissociation characteristics and flotation kinetics of coking coal

Despite extensive research on the connection between coal flotation kinetics and particle size, little is known about the shape effect. To fill this gap, this study aims not only to explore dissociation characteristics and particle shape properties resulting from the grinding of coking coal in a planetary ball mill (PBM) and a vertical shaft impact crusher (VSIC) but also to investigate their effects on flotation kinetics. Moreover, for the first time in the literature, shape, kinetic rate constant, and bubble loading capacity (hydrophobicity) properties of coking coal products ground in two different mills were compared by shape characterization, flotation kinetics, and single bubble loading tests, respectively. The findings are: (1) Compared to PBM, VSIC produced rounder-shaped particles with a better communition selectivity, (2) Since PBM's flotation rate constant values (Km) were higher than VSIC's, the particles produced by the PBM exhibit a favorable aspect ratio for faster flotation.

Estimation of multicomponent reactions’ yields from networks of mechanistic steps

This work describes estimation of yields of complex, multicomponent reactions (MCRs) based on the modeled networks of mechanistic steps spanning both the main reaction pathway as well as immediate and downstream side reactions. Because experimental values of the kinetic rate constants for individual mechanistic transforms are extremely sparse, these constants are approximated here using Mayr’s nucleophilicity and electrophilicity parameters fine-tuned by correction terms grounded in linear free-energy relationships. With this formalism, the model trained on the mechanistic networks of only 20 – but mechanistically- and yield-diverse MCRs – transfers well to newly discovered MCRs that are based on markedly different mechanisms and types of individual mechanistic transforms. These results suggest that mechanistic-level approach to yield estimation may be a useful alternative to models that are derived from full-reaction data and lack information about yield-lowering side reactions.

Bioelectrochemical Characterization of a Molybdenum-Containing Aldehyde Dehydrogenase Variant Deleting Its Cytochrome C Subunit

Bioelectrocatalysis is a coupled system with enzymatic and electrode reactions. Some oxidoreductases can directly communicate with electrodes, which is called direct electron transfer (direct ET; DET)-type bioelectrocatalysis. The number of enzymes proceeding with DET-type reactions is still limited, and its mechanism is not fully elucidated. However, it is expected to be applied to electrochemical devices such as biosensors, biofuel cells, and bioreactors, owing to energy efficiency, biocompatibility, and design flexibility. In addition, this reaction is utilized for enzyme characterization based on kinetics and thermodynamics. In particular, a relationship between DET activity and the redox potential can be quickly and precisely characterized.We focused on aldehyde dehydrogenase (ALDH) from Gluconobacter oxydans, a membrane-bound protein catalyzing DET-type acetaldehyde oxidation. In previous studies, the three-dimensional structure of ALDH was elucidated using cryo-electron microscopy analysis (PDB: 8GY3). The structure is composed of the catalytic large subunit (L subunit), the small subunit (S subunit), and the cytochrome c subunit (C subunit). In vivo, electrons extracted from acetaldehyde are transferred to ubiquinone via the catalytic center (molybdenum cofactor; Moco) in the L subunit, two iron-sulfur clusters (FeSs) in the S subunit, and three hemes c in the C subunit, in this order. The ET associated with substrate oxidation through the C subunit is conserved in membrane-bound hemoproteins such as alcohol dehydrogenase, fructose dehydrogenase, and glucose dehydrogenase. These enzymes have similarities in high DET activities, and their variants truncating a C subunit, which are advantageous in ignoring interference of detergents and complexity of the multi-step ET through hemes c, have been characterized. However, such research has not been conducted for ALDH, and ALDH has the unique feature of having two cofactors in the S subunit. In this study, we attempted to quantitatively characterize the ALDH variant deleting the C subunit (ΔC_ALDH), focusing on pH dependence of kinetic and thermodynamic parameters.To construct an expression system of ΔC_ALDH, a plasmid containing genes of L and S subunits of ALDH was transformed into the knock-out strain in which genes of wild-type ALDH were disrupted. ΔC_ALDH was expressed in soluble fraction as expected and successfully purified. Cyclic voltammograms were recorded at ΔC_ALDH-modified multi-walled carbon nanotube-electrodes. The electrode showed clear DET activity, suggesting that the electrode-active site seems to be FeS which is located near the surface of the enzyme. In addition, we investigated the pH dependence of the DET activity and kinetically analyzed the voltammograms using a model in which distribution of enzyme orientation was considered. The kinetic analysis quantitatively estimated the formal potential of the electrode-active site (E°′E), the limiting catalytic current density (j cat), and the ratio of the maximum value of the standard rate constant of the heterogeneous ET to the catalytic constant in DET-type reaction (k°max/k c,DET). j cat exponentially increased from pH 2.5 to 5.5 and reached a plateau between pH 6.0 and 8.0, while E°′E changed by –48 mV pH–1 from pH 2.5 to 5.5 and became constant between pH 6.0 and 8.0. Since the formal potential of acetate/acetaldehyde redox couple (E°′S) changes by –89 mV pH–1, E°′E – E°′S increases as the condition becomes more basic. Then, we focused on a relationship between the potential difference and DET activity. The log (j cat / mA cm–2) vs. E°′E – E°′S plot showed a linear increasing region and a constant region independent of E°′E – E°′S, as shown in Figure 1. The former slope suggested that DET activity obeyed the ideal linear free energy relationship (LFER) without any specific interaction. In this region, k c,DET was controlled by the potential difference in the ET pathway. When E°′E – E°′S is sufficiently large, k c,DET seems to be limited by other factors such as entry of substrate into the catalytic site, a catalytic turnover in Moco, and the intramolecular ET.On the other hand, in the assay with ferricyanide as an alternative electron acceptor, the slope representing the ideal LFER was not observed. We assume that the potential difference between the enzyme and ferricyanide was insufficient, thus the catalytic constant in solution (k c,solution) was kinetically analyzed based on the ping-pong bi-bi mechanism considering changes in E°′E, E°′S, and the formal potential of ferricyanide/ferrocyanide. Using parameters obtained from the analysis for j cat and k c,solution, Γ E,eff, k°max, and k c,DET were separately evaluated with an assumption that Γ E,eff was independent of pH.In summary, we quantitively characterized the bioelectrochemical parameters of ΔC_ALDH and compared the properties between DET and ferricyanide reductase activities. This work will be beneficial for understanding ALDH, and comparing it with wild-type ALDH will elucidate the roles of the C subunit. Figure 1

Biosynthesised bentonite clay-based Cu nanocomposite using Punica granatum L. peel extract for the effective catalytic reduction of hazardous aqueous contaminants

ABSTRACT This article describes a facile and green one-pot synthetic process of Cu nanoparticles loaded on bentonite composite (5Cu wt.%/bentonite) using the peel extract of pomegranate (Punica granatum L.) as a reductant. The 5Cu wt.%/bentonite composite was adopted as a heterogeneous catalyst for the NaBH4-assisted reductive degradation of Methylene Blue (MB) dye. The prepared 5Cu wt.%/bentonite composite demonstrated high catalytic efficiency in reducing MB, achieving almost complete reduction within a reaction duration as short as 60 seconds. Indeed, Cu nanoparticles act as electron relays, facilitating the electron transfer from BH4 − anions to MB dye, leading to its conversion into the colourless Leuco-Methylene Blue (LMB). The reduction rate corresponded nicely with the pseudo-first-order kinetic model, with the corresponding normalised rate constant (Knor) value computed as 1.48 min−1 mg−1, outperforming numerous previously documented metal-containing catalysts. Remarkably, the catalyst can straightforwardly be reused, with almost constant reduction efficiency observed across 5 successive catalytic cycles. Furthermore, 5Cu wt.%/bentonite was used in another catalytic reduction reaction, involving the reduction of the toxic Cr(VI) to environmentally benign Cr(III) adopting formic acid as a reducing agent under ambient conditions. The 5Cu wt.%/bentonite catalyst not only showed a high Cr(VI) reduction efficiency of 95.5% within 30 min but also outstanding reusability of 93% removal of Cr(VI) following 5 cycles, demonstrating its catalytic versatility. The Cr(VI) reduction mechanism involves the dehydrogenation of formic acid on the catalyst surface, followed by hydrogen transfer converting Cr(VI) into Cr(III). Based on the straightforward and green synthetic strategy, use of cost-effective and readily available raw materials, excellent catalytic activity, catalytic versatility, and outstanding reusability, the 5Cu wt.%/bentonite composite seemed to be an ideal catalyst for the real-world reduction of harmful aqueous pollutants to achieve environmental sustainability.

Versatile platform of 3D/2D/1D:ZnFe2O4/NiAl-LDH/MWCNTs nanocomposite for photocatalytic purification of dinoseb and electrocatalytic O2 evolution reaction

Integrating photocatalysis with electrocatalysis may represent a synergistic approach to address environmental and energy challenges. In this context, we explored synthesizing a series of nanocomposite materials using a solid-state approach involving simple grinding and subsequent thermal treatment for the photocatalytic purification of dinoseb and electrocatalytic oxygen evolution (OER). Interestingly, among the series of synthesized materials, 40 wt percentage of 3D/2D/1D:ZnFe2O4/NiAl-LDH/MWCNTs ternary nanocomposite (40-NZM) showed highly improved dinoseb detoxification and OER efficiencies compared to those of pure materials. Importantly, approximately 98% detoxification of dinoseb was observed within 75 min of irradiation time under a visible light source. Remarkably, the 40-NZM nanocomposite exhibited the highest rate constant value (k = 4.1 × 10−2 min−1) with a favorable R2 (0.98) parameter. Furthermore, 40-NZM showed promising electrocatalytic OER performance, requiring only 217 mV of overpotential to achieve 10 mAcm−2 of current density with a smaller Tafel slope of 66.6 mVdec−1. Additionally, long-term stability was tested by recording 2000 cyclic voltammetry (CV) cycles. The results revealed that 40-NZM could maintain its catalytic activity for a longer duration as it required only 227 mV to attain 10 mAcm−2 even after 2000 CV cycles. Consequently, these outstanding characteristics of 40-NZM nanocomposite underscore the significant potential for catalytic water purification and sustainable energy conversion.

REACTIVITY OF ALUMINUM OXIDE PRECURSORS FOR SOLID-PHASE FORMATION OF MgAl2O4 SPINEL

The reactivity of various alumina precursors in the reaction of magnesia spinel formation is compared: industrial powders (corundum powder KP, alumina: metallurgical GC, non-metallurgical G-00, reactive RG) and the xerogel combustion product from aluminum nitrate with citric acid under conditions of mechanical activating treatment and without it. The infrared spectra of corundum and periclase after mechanical treatment of various types (impact-abrasion in a planetary mill, abrasion in a ball-ring mill) were analyzed. It has been found that short-term action not only activated the components, but also contributed to the destruction of adsorption compounds at the preparation stage. The effect of mechanical activation of reagents on spinel yield was analyzed. It has been established that the alumina xerogel combustion product without annealing was X-ray amorphous, which suggested its high chemical activity. When using it, a more complete binding of initial reagents into the product was found compared to a mixture of periclase and corundum. Even in the absence of mechanical activation of the components, it was possible to achieve a high spinel yield (up to 80%). The obtained values of the effective reaction rate constants indicated a greater efficiency of mechanical treatment, including an impact component, with the combined activation of periclase and corundum/alumina. Co-treatment of reagents in a planetary mill (PM) made it possible to increase the reaction rate by 6-6.5 times, while abrasion in a ball-ring mill was only 1.7 times. Pretreatment of one component of the initial mix in PM was the most expedient for periclase, since it allowed to speed up the reaction by ~ 5 times, and is also the most profitable energetically and technologically due to the treatment of only one component of reduced hardness. The use of xerogel combustion product in the spinel synthesis was very effective, because it accelerated the process by ~4 times even without preliminary activation by mechanical means. For citation: Filatova N.V., Kosenko N.F., Artyushin A.S., Maloivan M.S., Zonina I.I., Vlasenkov A.S. Reactivity of aluminum oxide precursors for solid-phase formation of MgAl2O4 spinel. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 12. P. 15-24. DOI: 10.6060/ivkkt.20246712.7152.

Rapid oxidation of phenolic compounds by O3 and HO●: effects of the air–water interface and mineral dust in tropospheric chemical processes

Abstract. Environmental media affect the atmospheric oxidation processes of phenolic compounds (PhCs) released from biomass burning in the troposphere. To address the gaps in experimental research, phenol (Ph), 4-hydroxybenzaldehyde (4-HBA), and vanillin (VL) are chosen as model compounds to investigate their reaction mechanism and kinetics at the air–water (A–W) interface, on TiO2 mineral aerosols, in the gas phase, and in bulk water using a combination of molecular dynamics simulation and quantum chemical calculations. Of the compounds, Ph was the most reactive one. The occurrence percentages of Ph, 4-HBA, and VL staying at the A–W interface are ∼ 72 %, ∼ 68 %, and ∼ 73 %, respectively. As the size of (TiO2)n clusters increases, the adsorption capacity decreases until n > 4, and beyond this, the capacity remains stable. A–W interface and TiO2 clusters facilitate Ph and VL reactions initiated by the O3 and HO⚫, respectively. However, oxidation reactions of 4-HBA are little affected by environmental media because of its electron-withdrawing group. The O3- and HO⚫-initiated reaction rate constant (k) values follow the order of A–WPh > TiO2 VL > A–WVL > A–W4-HBA > TiO2 4-HBA > TiO2 Ph and TiO2 VL > A–WPh > A–WVL > TiO2 4-HBA > TiO2 Ph > A–W4-HBA, respectively. Some byproducts are more harmful than their parent compounds, so they should be given special attention. This work provides key evidence for the rapid oxidation observed in the O3/HO⚫ + PhC experiments at the A–W interface. More importantly, differences in the oxidation of PhCs by different environmental media due to the impact of substituent groups were also identified.

Synergistic uranium extraction, organic degradation, and electricity generation by a self-driven photoelectrochemical system with TNR/Si PVC photoanode and copper foam cathode

Herein, we develop a self-driven photoelectrochemical system (SDPS) featuring a TiO2 nanorod array (TNR)/Si photovoltaic cell (Si PVC) photoanode and a porous copper foam (CF) cathode for efficient uranium recovery. Under simulated sunlight illumination, this SDPS simultaneously achieves ∼ 99.4 % UO22+ recovery and ∼ 99.2 % sulfamethoxazole (SMX) removal, with observed rate constant (kobs) value of 0.121 min−1 and 0.029 min−1, respectively, and a maximum power density (Pmax) of 0.89 mW·cm−2 when treating complex wastewater of SMX (10 mg·L−1)-UO22+ (10 mg·L−1). The TNR photoanode absorbs short-wavelength light (λ < 412 nm), generating electron-hole pairs, while the rear Si PVC absorbs transmission light, creating a self-bias potential that drives electrons transfer towards CF cathode, continuously generating electrical energy in the external circuit. The retained holes and derived •OH oxidize SMX, breaking UO22+-SMX complexation, while electrons on the CF reduce UO22+ to insoluble tetravalent uranium (U(IV)) species. This SDPS demonstrates robust performance across varying UO22+ (5 ∼ 40 mg·L−1) and SMX (0 ∼ 40 mg·L−1) concentrations, pH ranges (4 ∼ 8), coexisting ions, and different types of uranium-containing wastewaters, maintaining stability over 20 cycles. It achieves ∼ 97.5 % UO22+ extraction and ∼ 99.8 % SMX removal in simulated seawater, with a Pmax of 1.27 mW·cm−2. This work presents a promising resource strategy for uranium extraction.

Pre-emergence herbicides used in urban and agricultural settings: dissipation and ecological implications

Herbicides are widely recognized as the most cost-effective solution for weed control, but their extensive use in both urban and agricultural settings raise serious concerns about nontarget effects. We assessed the possible hazards associated with pre-emergence herbicides such as dimethenamid–P, metazachlor, and pyroxasulfone, which are frequently applied in both urban and agricultural soils. The dissipation rate constant values (k day−1: 0.010–0.024) were positively linked to total organic carbon (TOC), silt, clay, soil pH, and Al and Fe oxides, but negatively correlated with sand content. In contrast, half-life values (DT50: 29–69 days) of the herbicides showed negative correlations with TOC, clay, silt, soil pH, and Fe and Al oxides, while sand content showed a positive impact. The selected herbicides showed minimal impact on soil dehydrogenase activity (DHA). Mostly, soils with higher organic matter (OM) content exhibited increased DHA levels, highlighting the role of OM in influencing this soil enzyme across different soils. Assessment of environmental indicators like groundwater ubiquity score (GUS:1.69–6.30) and leachability index (LIX: 0.23–0.97) suggested that the herbicides might reach groundwater, posing potential risks to nontarget biota and food safety. Human non-cancer risk evaluation, in terms of hazard quotient (HQ < 1) and hazard index (HI < 1), suggests minimal or no risks from exposure to soil containing herbicide residues at 50% of the initial concentrations. Our data thus help the stakeholders and regulatory agencies while applying these pre-emergence herbicides in soils and safeguarding human and environmental health.

Enhancing the Light‐Driven Photocatalytic Degradation Activity of ZnO Nanoparticles With the Synergistic Incorporation of Er and Tb Elements

ABSTRACTThe existence of organic pollutants in aqueous media has become a vital issue and a critical threat to human health, where organic toxic dyes represent the major contaminants in wastewater. Over the past few years, photocatalytic techniques have garnered a lot of interest in dye removal from wastewater. In this study, a series of ErxTbxZn1 − 2xO nanophotocatalysts (where x = 0.00, 0.01, 0.03, and 0.05) were synthesized and coded as ZET0, ZET1, ZET2, and ZET3 NPs (nanoparticles). The chemical and physical characteristics of the NPs were investigated using Fourier‐transform infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), energy‐dispersive X‐ray (EDX) spectroscopy, and ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS) techniques. Further examination by performing photocatalytic experiments, ZET1 NPs demonstrated effective Rhodamine B (RhB) dye degradation within 60 min. It was found that the kinetic rate constant values were 0.008, 0.097, 0.050, and 0.040 min−1 for ZET0, ZET1, ZET2, and ZET3 NPs, respectively. Aside from their remarkable photocatalytic degradation efficiency, these ZET1 photocatalysts are highly stable even after five consecutive cycles. In addition, the active species test revealed that the primary oxidation species involved in the photocatalytic process are holes (h+) and hydroxyl radicals (•OH), and a possible photocatalytic mechanism for degrading RhB by ZET1 photocatalysts was tentatively proposed. The enhancement of the photocatalytic degradation efficiency is due to the low recombination rate of photogenerated charge carriers, as well as a strong synergistic impact of Tb, Er, and ZnO components. Thus, the current study could offer a versatile strategy for the design of new and effective nano photocatalysts for wastewater purification in the future.

Enhanced photocatalytic degradation of organic pollutants by randomly oriented 2D SnS2 nanostructures

Abstract In this study, we present a bottom-up solvothermal technique using tin tetrachloride pentahydrate (SnCl4.5H2O) and thioacetamide as precursors to synthesize SnS2 nanostructures. Different solvents including isopropyl alcohol, ethanol (EN), and ethylene glycol were used in the reaction to enhance the photodegradation efficiency of organic pollutants, Methylene Blue (MB), and Tetracycline (TC) in an aqueous medium under simulated solar light irradiation. The SnS2 nanostructures synthesized with these solvents were characterized using various structural, morphological, and optical techniques, including x-ray diffraction, RAMAN, field emission scanning electron microscope, x-ray photoelectron spectroscopy, UV–Vis, and Brunauer–Emmett–Teller analysis. The choice of solvent was found to significantly affect the structural, morphological, and optical properties of the SnS2 nanostructures. Notably, the sample synthesized with EN as the solvent displayed a unique morphology, enhanced light-harvesting ability, efficient charge carrier separation, and a larger specific surface area, all of which contributed to its superior photocatalytic activity. This sample achieved 99.9% degradation of MB and 95% degradation of TC within 20 and 40 min, respectively. The kinetic analysis revealed maximum rate constant (k) values of 0.15242 min−1 for MB and 0.060 95 min−1 for TC, as determined by the pseudo-first-order kinetic model. We also discuss the plausible mechanism involving visible light-induced electron–hole pairs that generate reactive species, leading to the mineralization of dyes into H2O, CO2, and other gaseous products. The synthesized SnS2 nanostructures demonstrate significant potential for enhanced photocatalytic activity in organic pollutant degradation, underscoring their promise in addressing water pollution challenges.

Assessment of the binding mechanism of ergothioneine to human serum albumin: Multi-spectroscopy, molecular docking and molecular dynamic simulation

Ergothioneine (EGT) has attracted great attention due to its extremely potent antioxidant properties, universally acknowledged as ‘longevity vitamin’. In order to comprehensive understanding of its pharmacodynamics and pharmacokinetics, the binding mechanism of EGT with human serum albumin (HSA) was clarified by cutting-edged multi-spectroscopic approaches and in silico molecular docking coupled with molecular dynamic simulation. Our fluorescence quenching results revealed that the binding of EGT to HSA was in a static quenching mode validated by the descending Stern–Volmer constant (Ksv) values (2.82, 2.36, 1.48 × 104 L mol−1) and biomolecular quenching rate constant (Kq) values (2.82, 2.36, 1.48 × 1012 L mol−1) at 298 K, 305 K, and 310 K, respectively. van’t Hoff criterion revealed the combination of EGT with HSA was a spontaneous exothermic process (ΔG = −24.16 kJ mol−1) via hydrogen bonding and van der Waals force interactions (ΔH = −60.25 kJ mol−1, ΔS = −129.44 J mol−1 K−1) at 310 K. The analysis of UV–vis absorption spectrum, synchronous fluorescence spectrum, three-dimensional fluorescence spectrum and circular dichroism indicated the addition of EGT affected the microenvironment of Trp214 and rearranged the structure of HSA. The binding replacement assay interpreted their binding site was near the subdomain IIA of HSA (Sudlow’s site I), which was intuitively exhibited by molecular docking. In addition of obvious van der Wall forces, attractive charge and Pi-alkyl interactions, the chiral betaine group (N+(CH3+)3) in the side chain of EGT was inclined to form hydrogen bonds with Lys199, Ser287 and Arg257 in the hydrophobic cavity of albumin. Moreover, the dynamic simulation reinforced the equilibrium and stability of formed docking complex by four indicators (RMSD, RMSF, Rg, SASA) within 100 ns.

Thermodynamic and Kinetic Insights into Azo Dyes Photocatalytic Degradation on Biogenically Synthesized ZnO Nanoparticles and their Antibacterial Potential

The extensive use of azo dyes in textile and pharmaceutical industries pose significant environmental and health risks. This problem requires to be tackled forthwith through a cheap, environmentally friendly and viable approach to mitigate water pollution. In this context, the green synthesis method was used for synthesis of ZnO NPs. These biogenic ZnO NPs were characterized by UV-Vis and Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD), high-resolution transmission electron microscopy (HR-TEM) coupled with energy-dispersive X-ray (EDX), dynamic light scattering (DLS) and Zeta potential (ZP) analysis. The characteristic bandgap energy (3.02 eV), crystallite size (18.6 nm), particle size (84 nm), hydrodynamic diameter (101 nm) and ZP (+33.9 mV) all indicated the successful synthesis of the stabilized NPs, which have an absorption edge at 373 nm. Based on the responsive energy band gap to visible light, these NPs demonstrated promising photocatalytic activity for the degradation of toxic dyes with efficiencies of 82.2 and 87.5 % for of methylene blue (MB) and methyl orange (MO), respectively, in only 2 h of sunlight exposure. To evaluate the reaction kinetics and thermodynamic parameters including the activation energy and rate constant, the degradation process was conducted at various temperatures. The effect of temperature showed the highest rate constant values of 0.022 and 0.025 min-1 at 90 oC, and activation energies of 4.1 and 3.8 KJ mol-1 for MO and MB, respectively. A possible degradation mechanism was proposed based on results of the radical scavenging experiments. The photocatalyst showed recyclability for five consecutive cycles with a simple regeneration. CMFE@ZnO NPs have also exhibited great antibacterial potential by inhibiting the growth of Gram-positive (S. aureus (13 mm) and B. subtilis (14 mm)) and Gram-negative (E. coli (17 mm) and P. multosida (15 mm)) bacterial strains. As a result, these CMFE@NPs may have great commercial importance in reducing the concentration of azo dyes and drug-resistant bacteria in textile and pharmaceutical industry effluents.

Porous Pd-Loaded IRMOF-9 as Highly Efficient Recyclable Material Towards the Reduction of Nitroaromatics in Aqueous Media.

Nitroaromatic compounds (NACs) cause severe hazardous impacts on human health as well as on the environment. Therefore, there is dire need to develop a robust material to reduce the toxicity of these organic pollutants. In this regard, our group developed a series of porous MOF materials viz., Pdx@IRMOF-9 (x=2 %, 5 % and 10 %) by loading different concentration of Pd(II) on IRMOF-9 and explored them towards reduction of different nitroaromatic compounds. Pd10%@IRMOF-9showed ~30 % greater efficiency for the reduction of 4-NP as compared to Pd2%@IRMOF-9. Pd10%@IRMOF-9showed excellent reduction ability (>85 %) towards 4-NP, 2-NP, 2-NA, 3-NA and 2,4-DNPH. The kinetic studies indicates that the reduction follows the pseudo-first-order kinetics. Moreover, the rate constant value for reduction of 3-NA was ~9 times higher than that of 2-NP. Based on the kinetic parameters, the t1/2 values for all the nitroaromatics have been calculated. The kinetic parameters, Km and Vmax have been calculated from double reciprocal Lineweaver-Burk plot and found to be 65.984 μM and 116×10-6 Mmin-1 respectively. Pd10%@IRMOF-9showed excellent recyclability towards the reduction of 4-NP for few consecutive cycles without any remarkable loss in its activity. Thus, highly efficient, porous and robust material for the reduction of nitroaromatic compounds in aqueous media have been demonstrated.

Energy band gap tuning of Ba-Ca hexagonal ferrite by Dy3+ ion substitution (0 ≤ x ≤ 0.2) to improve spectral, structural, dielectric and photocatalytic properties

In the present study, Dy3+ substituted M-type Ba0.5Ca0.5DyxFe12-xO19 (0.00 ≤ x ≤ 0.20) hexagonal ferrites were synthesized using sol-gel auto-combustion method with lemon extract as a fuel. The single hexaferrite phase with space group P63/mmc is revealed by the X-ray powder diffraction (XRD) patterns. The Field emission scanning electron microscopy (FESEM) exhibits the agglomeration of nanoplates with vacancies at some places. Energy dispersive X-ray photoelectron spectroscopy (EDAX) mapping confirmed the presence of Ba, Ca, Fe, O, and Dy in the hexaferrite. Fourier Transform Infrared (FTIR) spectroscopy exhibits two characteristic bands at 579 and 429 cm−1 corresponding to tetrahedral and octahedral metal ions-oxygen stretching, revealing the occurrence of the ferrite phase. The optical energy band gap calculated using the Tauc plots was found to increase with the increase in dysprosium substitution to fall within the range of 2.8–3.5 eV. The Raman spectra confirmed the Raman vibration modes and M-type structures of hexagonal ferrites (HFs). The dielectric constant values drop rapidly with increasing frequency up to a few KHz and then gradually for the further higher frequencies. The occurrence of Ba and Ca with 2+, while Dy, and Fe with 3+ oxidation states is confirmed using X-ray photoelectron spectroscopy (XPS). The HFs exhibit remarkable efficiency by degrading the Reactive Brown dye to 99.3 % in just 15 min, equivalent to a high degradation reaction rate constant (k) value of up to 0.0396 min−1. Consequently, the catalyst shows promising potential for environmental remediation.

Azobenzene-Based Main-Chain Liquid Crystalline Polymers Bearing Periodically Installed Alkyl, PEG, or Fluoroalkyl Segments and Photoisomerization Studies

ABSTRACT In the present study, liquid crystalline polymers (LCPs) were prepared by melt-transesterification of azobenzene-bearing diols and diethyl malonate (DEM) derivatized monomers. The effect of the nature and length of the installed pendant segments on the mesomorphic properties of the prepared LCPs was investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD), and polarized optical microscopy (POM) studies. The formation of layered morphology was inferred from X-ray scattering analysis arising from the colocation of rigid azobenzene moieties in one layer and the flexible pendant segments in alternate layers due to the zigzag folding of the polymer backbone. The linear variation of the interlamellar spacing with the number of carbon atoms in the pendant alkyl segments corroborates the proposed zigzag backbone folding in the polymers. The rate constant values obtained from the photoisomerization studies of the isomeric polymers and model compound, which are in the same ballpark, reveal that the photoisomerization process of such polymers is not affected by the position or size of the azobenzene unit.

Enhanced photocatalytic removal of methyl orange dye employing SiO2/Mn2O3 based nanocatalyst under visible light

Surface water contamination by dye pollutants is a global environmental concern. The treatment of effluent from textile waste using metal oxide-based photocatalysts is a widely employed approach owing to its efficacy and simplicity. Herein, the synthesis and fabrication of novel visible radiation receptive manganese oxide and mesoporous silica nanocomposites (Mn2O3/SiO2) is described. Surface morphology of nanocomposites using scanning electron microscopy (SEM) displayed spherical shaped agglomerated structure. The chemical composition of nanocomposites was examined by using energy dispersive x-ray (EDX) analysis respectively indicating the presence of respective elements. Structural analysis was carried out by using XRD spectroscopy, while optical properties were evaluated by employing UV–visible spectroscopy. The photocatalytic activity of pure Mn2O3 and SiO2 nanoparticles as well as their nanocomposites with two different ratios Mn2O3/SiO2 (1:3) and Mn2O3/SiO2 (3:1) were evaluated by using methyl orange (MO) as a model dye. The band gap energy of Mn2O3/SiO2 (1:3) and Mn2O3/SiO2 (3:1) nanocomposite was 2.39 eV and 1.69 eV respectively. The nanocomposites exhibited improved photocatalytic efficiency as compared to pure nanoparticles as a function of pH and mixing ratio. For instance, at pH 7.0, Mn2O3/SiO2 (1:3) nanocomposite has depicted maximum degradation efficiency of 68 % for degradation of MO as compared to Mn3O4/SiO2 (3:1) nanocomposite, Mn3O4 and SiO2 nanoparticles. However, at pH 2.0 Mn2O3/SiO2 (3:1) nanocomposite had shown maximum degradation efficiency of 99 % as compared to Mn2O3/SiO2 (1:3), Mn2O3 and SiO2 nanoparticles. The degradation reaction followed pseudo first order kinetics. At pH 7.0, the rate constant values of nanocomposites i.e. Mn2O3/SiO2(1:3) and Mn2O3/SiO2(3:1) comes out to be 4.68 × 10−3 min−1 and 2.49 × 10−3 min−1 respectively. At pH 2.0, the rate constant values calculated for Mn2O3/SiO2(1:3) nanocomposite and Mn2O3/SiO2(3:1) nanocomposite was 4.91 × 10−3 min−1 and 1.24 × 10−2 min−1 respectively. The easy fabrication of these nanocomposites coupled with facile tuning of their properties make them suitable contenders for efficient dye degradation in wastewater treatment.