Order Rate Kinetics Research Articles

Formulation and evaluation of a novel controlled release meloxicam-loaded organized

Based on pluronic lecithin, P.L.O. gels were established in the present research as a topical carrier for the regulated delivery of Meloxicam. Every P.L.O. gel composition was discovered to have pH values between 5.57 and 5.62, which falls within the pH range that skin. The spreadability of organogels from F1 to F4 (25.09-23.41 g.cm/s) decreased due to lecithin. The F5 through F8 saw an increase in the percentage of pluronic (22.45-21.44 g.cm/s). The range of the viscosity of gel formulations was determined to be between 1825 and 3732 cps (F1-F4) and 2136-3663 cps (F5–F8). Eight different organized formulations' gel transition temperatures were measured among such ranges of 32.3oC and 33.2oC (F1-F4) and 27.4 - 33.6oC (F5 – F8). The formulations of F2 and F3 have been chosen for kinetic tests and stability studies because they had the most significant percentage of drug content and the highest drug release during eight hours, and all physical parameters were found to be within acceptable limits. It was discovered that the order of release of drug through different formulations was F1 – F8. A drug is released from the improved formulation F2 regulated according to zero order rate kinetics. The optimized Meloxicam organogel in-vivo anti-inflammatory effectiveness against a commonly used commercial product (ZCLO-CM gel) was satisfactory but also significant.

Vermifiltration for removal of emerging contaminant EDTA (ethylenediaminetetraacetic acid). Kinetics models for adsorption, bio- and vermidegradation

Vermifiltration is a sustainable technology that combines the action of microorganisms and earthworms to remove contaminants in wastewater. In this work, vermifiltration was used to remove the emerging contaminant, EDTA, from simulated greywater. Three types of filters were designed: Azide Filter (AF) to evaluate the adsorption process, Bio filter (BF), to evaluate adsorption plus the action of the microorganisms, and Vermi Filter (VF), to assess the previously described processes and the action of the earthworms. Each filter was filled with gravel, sand and an active layer, and VF was inoculated with 60 Eisenia fetida. The filters were operated on a batch system with recycling. Different regimes were observed: an initial rapid decrease of EDTA concentration by adsorption; a lag phase, which lasted from 7 to 18 days, and a final EDTA decrease due to biological or vermi degradation. A mathematical model was developed performing the EDTA mass balance in the system and considering a first order kinetic rate for EDTA removal. Experimental data was fitted by the model, determining kinetic constants for adsorption or degradation process, kads and kd respectively. The kads values were similar for all filters, whereas VF showed a kd 53 % higher than that of BF and AF. Earthworms survival was 85 % and, although the biomass was significantly reduced (64.8 %), there was cocoons and juveniles. Bioassays with Lactuca sativa showed no phytotoxicity of the treated wastewaters. All the systems were efficient but the VF was faster, supporting that vermifiltration is a suitable technology for treating EDTA greywater.

A sustainable peroxide assisted dissolution of uranium oxides in ionic liquids and electrochemical Recovery: A feasibility study

The present manuscript demonstrated the dissolution of oxides of uranium, mainly UO2, via surface oxidation by H2O2 into ionic liquid at ambient temperature within 4 h of equilibration. The dissolution was found to be endothermic (ΔH ∼ 30.8 kJ mol-1 and 3.20 kJ mol-1) predominantly following the pseudo 2nd order rate kinetics (k ∼ 0.004 g−1 min and 0.0009 g−1 min) with activation energies of 54.12 J mol-1 and 26.69 J mol-1, for H2O2 and RCO3H, respectively. The extent of dissolution for different oxides of uranium followed the trend UO3 > UO2 > U3O8. Within 8 h of equilibration, quantitative dissolution of 50 mg mL−1 of UO2 can be achieved with optimized experimental conditions of 0.4 M HD2EHP as the complexing agent and 10 µL H2O2 as the oxidizing agent. The oxidative dissolution followed the trend C8mim.NTf2 > C8mim.PF6. In C8mim.NTf2, the most probable species was UO2(HDEHP)2+ associated to Σg+→Γg transition involving the σu+ϕu configuration with a D3d (D3) symmetry; while for C8mim.PF6 the predominate species was UO2F2(HDEHP)- with a D3h symmetry. Four hours of electro-deposition resulted a black solid deposit on the Cu electrode resulting the change in surface morphology and enhancement in the surface roughness as analyzed by the SEM images. The EDXRF analysis revealed the presence of the uranium peak; whereas the XRD pattern showed the fluorite structure revealing the deposit of UO2 phase upon electro-deposition latter confirmed by FTIR.

Visible light photocatalytic response of Fe doped TiO2: Inactivation of Escherichia coli

Heterogeneous photocatalysis has been widely investigated for the removal of pollutants and pathogenic microorganisms. Various modified photocatalysts were developed for the beneficial use of solar light. E. coli inactivation by Fe doping of TiO2 (P-25) and sol–gel prepared (SynTiO2) was achieved upon solar irradiation in both isotonic (IsoT) and water matrix (WM) conditions. First order kinetic rate constants were comparatively higher for bare SynTiO2 both in IsoT (k = 0.254 min−1) and WM (k = 0.180 min−1) solutions. WM exerted an overall retardation effect for all photocatalysts except for 0.50 % Fe-TiO2 and 0.25 % Fe-SynTiO2. Release of intracellular components was followed by spectroscopic parameters as well as dissolved organic carbon (DOC) contents. E. coli cell destruction was related to the released protein, carbohydrate, and K+ ion contents. Solar photocatalytic inactivation of E. coli using novel sol–gel prepared TiO2 and Fe doped sol–gel TiO2 was successfully demonstrated as an alternative and promising method for disinfection purposes.

Application of Bi0.5Na0.5TiO3 −based catalysts for piezocatalytic, photocatalytic and piezo-photocatalytic degradation of organic pollutants in wastewater remediation

In order to attain visible light driven piezo-photocatalyst for treatment of organic pollutants, Ag doped Bi0.5Na0.5TiO3 particles (Bi0.5Na0.5-x AgxTiO3 particles with x = 0, 0.01, 0.03, and 0.05) have been synthesised via sol–gel route. X-ray diffraction (XRD) study confirmed the monoclinic phase structure with Cc space group for all compositions. The Rietveld refinement using FullPROF program was performed to ensure the phase purity of the samples. The structure is reconfirmed by matching vibrational modes in Raman spectra as well. Morphological and elemental analysis were done using scanning electron microscopy (SEM) equipped energy dispersive x-ray spectra (EDX) and found the particle size ranging from 300-400 nm. UV–vis absorbance spectra were employed to find the optical bandgap for all synthesised particles, found in the range of 3.65–2.63 eV. The best piezo-photocatalytic activity found for sample x = 0.01 tested for rhodamine B dye, which is ∼ 82 % in 80 min under the exposure of UV light and mechanical disturbances, whereas degradation was ∼ 52.4 % and ∼ 22.7 % for photo- and piezocatalysis, respectively. Kinetics study and rate constant values were found using first order rate kinetics equation. Trapping experiment and stability test for the catalysts were done systematically, finding that hydroxyl and superoxide radicals are major active species and ∼ 9 % decrement in degradation capacity over three cycles were found due to loss of catalyst amount. The improvement in degradation is attributed to least recombination rate, greater oxygen vacancies, high degradation yield, high absorption capacity and optimum bandgap values over the other compositions. Therefore, 1 % Ag doped BNT sample can be novel efficient piezo-photocatalyst for treatment of organic dyes.

Freezing-enhanced degradation of azo dyes in the chloride-peroxymonosulfate system

In this study, we investigated the freezing-induced acceleration of dye bleaching by chloride-activated peroxymonosulfate (PMS). It has been observed that the oxidation of chloride by PMS generates a free chlorine species, such as hypochlorous acid (HOCl), under mild acidic and circumneutral pH condition. This process is the major reason for the enhanced oxidation capacity for electron-rich organic compounds (e.g., phenol) in the chloride-PMS system. However, we demonstrated that the chloride-PMS system clearly reduced the total organic carbon concentration (TOC), whereas the HOCl system did not lead to decrease in TOC. Overall, the chemical reaction is negligible in an aqueous condition if the concentrations of reagents are low, and freezing the solution accelerates the degradation of dye pollutants remarkably. Most notably, the pseudo-first order kinetic rate constant for acid orange 7 (AO7) degradation is approximately 0.252 h−1 with 0.5 mM PMS, 1 mM NaCl, initial pH 3, and a freezing temperature of −20 °C. AO7 degradation is not observed when the solution is not frozen. According to a confocal Raman-microscope analysis and an experiment that used an extremely high dose of reactants, the freeze concentration effect is the main reason for the acceleration phenomenon. Because the freezing phenomenon is spontaneous at high latitudes and at mid-latitudes in winter, and the chloride is ubiquitous elsewhere, the frozen chloride-PMS system has potential as a method for energy-free and eco-friendly technology for the degradation of organic pollutants in cold environments.

One story as part of the Global Conversation on Sustainability: dye adsorption studies using a novel bio-derived calcite material.

Many of the United Nations' Sustainable Development Goals (SDGs) can be addressed through chemistry. Researchers at Memorial University of Newfoundland, Canada, have been sharing their stories on September 25 for the past two years through the Global Conversation on Sustainability. This article describes the details of one of these stories. As the global population increases, food production including aquaculture is increasing to provide for this. At the same time, this means more waste is produced. Waste from aquaculture isoften overlooked as a source of valuable chemicals. By-products from farming blue mussels (Mytilus edulis) is dominated by shells rich in calcite. A 'soft' calcite material prepared from waste mussels, via a combination of heat and acetic acid treatment, was investigated for its adsorptive properties and its possible use in wastewater remediation. The adsorption of two cationic dyes, methylene blue and safranin-O, on this material were evaluated through isothermal and kinetic modelling. The adsorption systems for both methylene blue and safranin-O can best be described using Langmuir isotherms and the respective adsorption capacities were 1.81 and 1.51 mg/g. The adsorption process was dominated by pseudo-second order rate kinetics. Comparisons are made with other mollusc-derived materials reported to date.

Dissolved oxygen enhanced piezo-photocatalytic performance in Ag dots-modified BaTiO3 nanoparticles for efficient degradation of multiple organic pollutants

Piezoelectric nanomaterials have attracted much attention due to their ability to modulate photo-excited carrier separation and migration under strain. Perovskite-structured BaTiO3 (BT) is a promising piezo-photocatalytic material due to its high piezoelectric coefficient and special phase structure. In this work, a series of x wt.% Ag/BT composites prepared by a two-step approach were developed for piezo-photocatalysis applications. The 0.8 wt.% Ag/BT showed an excellent piezo-photocatalytic performance for degrading 75.8 % Rhodamine B (RhB) in 60 min. Especially, the catalytic performances were strongly correlated with the atmosphere conditions of the catalyst. The piezo-photodegradation rate of RhB by 0.8 wt.% Ag/BT under O2 atmosphere reached 95.7 % in 40 min, and the first order kinetic rate constant (k) reached 0.06759 min−1, which was 9.9 and 2.4 times that of N2 and air condition, respectively. The Density functional theory (DFT) calculations further revealed that dissolved oxygen could enhance the material's adsorption of RhB. Compared with hydroxyl free radicals (OH) and holes (h+), superoxide radicals (O2–) play an indispensable role in the catalytic process through the trapping experiments and ESR analyses. Furthermore, the RhB degradation pathway and potential ecotoxicity were also proposed. This work is hoped to provide an understanding the mechanism of piezo-photocatalysis and bring new ideas for the development of piezo-photocatalysis catalysis for multifunctional environmental applications.

S-Schematic CuWO4/ZnO nanocomposite boosted photocatalytic degradation of organic dye pollutants

S-schematic CuWO4/ZnO nanocomposite photocatalyst was synthesized by an impregnation method. Synthesized CuWO4 and ZnO nanoparticles, and CuWO4/ZnO nanocomposites were thoroughly characterized. X-ray diffraction (XRD) analysis of the CuWO4/ZnO nanocomposite confirmed the respective triclinic and hexagonal wurtzite structures of CuWO4 and ZnO crystals. Raman and Fourier transform infrared (FTIR) spectra and X-ray photoelectron spectroscopy (XPS) revealed bond formations in CuWO4 and ZnO, and confirmed the synthesis of the CuWO4/ZnO nanocomposite. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed CuWO4 nanoparticles adhered to ZnO aggregates. Energy dispersive X-ray spectrometry (EDS) confirmed the distribution of CuWO4 on the ZnO aggregates. UV–Vis diffuse reflectance spectroscopy (DRS) showed optical bandgap energies of 2.36 eV for CuWO4 and 3.18 eV for ZnO nanoparticles. The photocatalytic performance of the CuWO4/ZnO nanocomposite was investigated through the degradation of the cationic dyes methylene blue (MB) and Rhodamine B (RhB) and the anionic dye methyl orange (MO). A 5.0%CuWO4/ZnO nanocomposite degraded 100% of MB within 120 min, 91.02% of RhB within 300 min, and 89.13% of MO within 300 min. The pseudo-first order kinetic rate constant fit well for the degradation of all the dyes on the CuWO4/ZnO nanocomposite. The CuWO4/ZnO nanocomposite could better degrade the cationic dyes than the anionic dye in an aqueous solution. The hole (h+), the hydroxyl radical (•OH), and the superoxide ion (•O2−) were the active species responsible for degrading MB, RhB and MO dyes. The proposed CuWO4/ZnO nanocomposite could be applied for environment friendly wastewater treatment.

Expeditive carbofuran pesticide degradation by submerged thermal plasma and its accelerated mineralization by persulfate addition

Rapid degradation of carbofuran (CBF) pesticide is effectively achieved by submerged thermal plasma (STP) without and with the addition of persulfate (PS) at two different concentrations (10 and 20 ppm). Degradation efficiency was examined using high-performance liquid chromatography (HPLC), and mineralization percentage was determined by total organic carbon (TOC) analysis. Adding 10 ppm PS showed higher degradation and mineralization percentages of 99.5% and 65.2%, respectively, than mere plasma treatment and 20 ppm PS addition to CBF solution. A relatively higher energy yield of 40 mg/kWh and a first order kinetic reaction rate of 0.262 min−1 were obtained in the 10 PS added STP treatment. Liquid chromatography mass spectrometry (LCMS) analysis illustrated reaction intermediates formed during plasma treatment. Scavenger investigation implied that •OH radical is the prime cause of CBF degradation, as degradation percentage declined to 50% in all conditions. Toxicity assessment of CBF and its degradation products was predicted using Toxicity estimation software tool (TEST), and plasma treated solutions (PTS) were experimentally investigated on Eudrilus eugeniae earthworms by monitoring its mortality rate, self-assemblage, and histopathological analysis. A lower mortality rate (46%) and self-assemblage (167 s) of earthworms were detected for plasma treated CBF than for the other conditions. The results reveal that PTS is less toxic for earthworms than untreated CBF solution. These findings imply that STP is an effective technique for bio-recalcitrant pollutants degradation in agrochemical industries.

Engineering of Pr3+ doped M type PbFe12O19 hexaferrites to enhance photocatalytic degradation of nicotine

The present task explains how the photocatalytic properties of the PbFe12O19 enhanced after the doping of rare earth metal praseodymium (Pr3+). The PbFe12-xPrxO19 with different dopant concentrations x = 0.00, 0.25, 0.50 were prepared by sol gel auto-combustion method and annealed at 900°C. The XRD analysis confirmed that average crystal size decreases (23–30 nm) with the increase in Pr3+ concentration. Scanning electron microscopy was employed to determine the shape and particle size which was estimated to be 68 nm. The band gap of the samples was tuned from 3.25 to 2.49 eV after intervention of praseodymium ions in the PbFe12O19 crystal system. Our doped samples exhibited exceptional photodegradation efficiency during the degradation of nicotine. The results revealed that Pr3+doped PbFe12O19 (x = 0.50) sample degraded almost 91 % of the nicotine with a first order kinetics rate constant (k = 0.0099 min−1), while undoped PbFe12O19 sample degraded just 45 % within 90 min. Quenching experiments demonstrated that superoxide and hydroxide radicals play important role in the degradation of nicotine. We deduce that praseodymium doped M type lead hexaferrite is efficient photocatalyst for nicotine removal.

Effective adsorption and visible light driven enhanced photocatalytic degradation of rhodamine B using ZnO nanoparticles immobilized on graphene oxide nanosheets

In this study, graphene oxide (GO), ZnO nanoparticles (NPs) and GO based ZnO nanocomposites (GO-ZnO) have been successfully synthesized by modified Hummer’s method, chemical co-precipitation method and ultrasonication method, respectively. Powder X-ray diffraction (PXRD), transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy were employed to study the crystallographic structure, phase, surface micro-morphology and different functional groups in the prepared catalysts. The optical band gap of pristine ZnO NPs was found in the UV region (3.2 eV), whereas the ZnO NPs immobilized on GO nanosheets possesses it in the visible wavelength region (2.67 eV). GO-ZnO catalysts demonstrate excellent degradation efficiency (97.7 %) within just 85 min due to its effective adsorption and visible light driven photocatalytic activity in the degradation of rhodamine B (RhB) dye. The adsorption capacity of GO-ZnO catalysts was found ∼ 24 times higher with the second order kinetic rate constant as low as 0.0014 min ∙ g/mg and the visible light driven photocatalytic activity was ∼ 9 times faster when compared to unmodified ZnO catalyst. Effect of GO-ZnO catalyst dosages in the degradation of RhB was also conducted. The scavenger test firmly evidenced that super oxide radicals (•O2–) play the lead role in RhB dye degradation process by GO-ZnO nanocomposites. Reusability studies of GO-ZnO catalysts demonstrate more than 91 % degradation efficiency up to 4 back-to-back cycles along with retaining the crystal structure. These findings suggest the viable application of GO-ZnO catalysts for the degradation of RhB dye in wastewater.

Synergistic potency of ultrasound and solar energy towards oxidation of 2,4-dichlorophenol: a chemometrics approach.

Industrial units based on chemical processes-the textile and paper industries-are major sources of chlorophenols in the environment, and chlorophenolic compounds persist within the environment for a long time with high toxicity levels. The photo-assisted Fenton's and photocatalysis processes were investigated for the degradation of chlorophenols in the present study. Response surface methodology was employed to get optimised conditions for photocatalysis and photo-Fenton process-governing factors, thus, yielding a profound removal efficiency. Under optimised conditions, with a photocatalyst dose of 0.2 g/L, oxidant concentration of 10.0 mM and pH 5.0, complete removal of 2,4-dichlorophenol (2,4-DCP) was observed in 210 minutes in photocatalytic treatment. In the case of the photo-Fenton process, at an H2O2 dose of 5.0 mM and Fe2+ concentration of 0.5 mM, the organic pollutant was eliminated within 5 minutes of reaction time under acidic conditions (pH 3.0). The RSM model reported the perfect fit of experimental data with the predicted response. Among different isotherm models, the Langmuir isotherm was the best fit. The process followed pseudo-first order rate kinetics among various kinetics models. For the obtained optimised conditions, sonication and solar energy-driven processes were incorporated to study enhanced mineralisation. The solar-assisted Fenton process reported maximum mineralisation (90%) and cost-effective ($0.01/litre for 100 mg/L 2,4-DCP) treatment among different hybrid oxidation processes. The work provides insight into harnessing the naturally available solar energy, reducing the overall treatment cost and opting for a sustainable treatment method.

Building TiO2-doped magnetic biochars from Citrus sinensis peels as low-cost materials for improved dye degradation using a mathematical approach

TiO2-doped ferromagnetic (TiFeBC) composites were synthesised from lignocellulosic orange peel biochar (BC) material using co-precipitation method. Several characterization techniques (XRD, SEM, EDX, FT-IR, EIS and N2 adsorption-desorption) were used to confirm the presence of Fe3O4 and TiO2 particles impregnated within the carbonaceous matrix of the biochar. Electrochemical impedance spectroscopy revealed that the sample obtained using 2.5 wt. % of TiO2 (TiFeBC1) has the lowest charge transfer resistance compared to those of 5 wt.% and 7.5 wt.%. TiFeBC1 was used for the optimization of the degradation of reactive yellow-145 from Cameroon Textile Industry using Fenton process. Optimum operational parameters were found to be: pH of 2.02, initial dye concentration of 75 mg/L, mass of material of 5998 mg/L and a time of 16.01 min. Using the CCD of the Response Surface Methodology, a predicted optimum response of 98.89 % was obtained in agreement with an experimental response of 97.95 % of dye degradation. Analysis of variance presented good correlation between the experimental data and the postulated model (R2 = 94.24 % and R2adjusted = 87.52 %). The degradation reaction was found to obey the first order kinetic rate law (R2 = 0.986) with respect to the dye. The study of interfering processes revealed that adsorption and H2O2/daylight-assisted degradation are two phenomenon that could possibly contribute to a negligible extent to the elimination of the dye during the Fenton process. The stability and efficiency of TiFeBC1 was evaluated over ten cycles and the material was found to lose approximately 5 % of its efficiency.

Green synthesis of magnetic biochars derived from biobased orange peel materials as sustainable heterogeneous catalytic supports for the Fenton process

In this work, two magnetite-biochar composite materials obtained via hydrothermal and co-precipitation methods to degrade dyes were evaluated. The two composite materials alongside their biochar precursor were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX), Raman spectroscopy and N2 adsorption–desorption studies. Results of characterization showed a change in the amorphous structure of the biochar to a crystalline form after modification by both methods, the incorporation of magnetic particles into the carbonaceous matrix of the biochar precursor. In addition, the effect of solution pH, initial dye concentration H2O2 concentration, mass of composite material and the time of stirring on dye degradation were analysed by the response surface methodology. Both materials demonstrate appreciable stability over repeated cycles and more interestingly, Fe3O4-BC2 retains its catalytic efficiency much more than Fe3O4-BC1. Statistical analysis of the degradation results by ANOVA revealed a good correlation between the five parameters and the expected response with coefficients of correlation very close to unity. The degradation of reactive red-198 in the presence of both materials is best described by the second order kinetic rate law.

Removal of Mercury (II) ions from aqueous solution by adsorption on Cicer arientinum husk: Equilibrium, Kinetic and Mechanism Studies

In the present work, Bengal gram husk (BGH) of low cost, minimally pretreated and locally available abundant agricultural waste material was used as an adsorbent for removal of Hg2+ from aqueous media. The influence of several parameters like effect of pH, adsorbent dosage, initial metal concentration, contact time and presence of interfering ions were studied through batch adsorption studies. The adsorption models of Langmuir and Freundlich were used for for the calculation of isotherm constants. According to the Langmuir model, the maximum adsorption capacity of BGH for Hg (II) ions was found to be 51.85 mg/g. The presence of interfering ions like Mg, Ca, K and Na did not play a role in the removal of Hg (II) ions. The Hg (II) removal by BGH followed pseudo first order rate kinetics. The FTIR spectra and CHN analysis of BGH showed the presence of CH and CO groups on the surface of BGH, which played a significant role in removal of Hg (II). Desorption studies revealed that about 83% of the dye was desorbed at pH 2. The present work showed that the BGH can be applied to remove Hg (II) from wastewater.

Experimental and theoretical confirmation of CeFeCu trimetal oxide/Bi2O3 S-scheme heterojunction for boosted photocatalytic degradation of sulfamethoxazole and toxicity evaluation

Photocatalytic degradation of pharmaceutical pollutants in water or wastewater is becoming a hot topic for environmental clean-up. Herein, a novel CeFeCu trimetal oxide (CFC TMO)/Bi2O3 (CFCB) photocatalysts were prepared through precursor mixing, ultrasonication, and calcination methods and used for photocatalytic degradation of sulfamethoxazole (SMZ). The pseudo-first order kinetic rate of CFCB-2 catalyst on degradation of SMZ reached 0.0577 min−1 which is 4.93 and 10.02 times higher than of α-Bi2O3 and CFC TMO under visible light illumination. This was proved by the strong interaction between the pristine materials as confirmed by XPS and density functional theory (DFT) calculations. DFT calculations indicated that having more orbital distribution could make it easier to capture more electrons and produce more radicals through electron transfer. Meanwhile SMZ by-products showed no sign of cytotoxicity towards human embryonic kidney cell line (HEK 293) and human intestinal epithelial cell line (CACO-2). The findings of the scavenger experiments and ESR measurements proved that •OH and •O2− radicals played superior role in decomposition of SMZ. Furthermore, the S-scheme charge carrier transfer and degradation pathway of SMZ are proposed and analysed. This study paves ways into promising strategy for the construction of α-Bi2O3 based novel S-scheme heterojunction for environmental decontamination and can be extended to other applications such as Fenton-like reactions and persulfate activation.

Investigating sensitization activity of azobenzene disperse dyes via the Direct Peptide Reactivity Assay (DPRA)

Azobenzene disperse dyes are the fastest-growing category of commercial dyestuffs and have been found in indoor house dust and in children’s polyester apparel. Azobenzene disperse dyes are implicated as potentially allergenic; however, little experimental data is available on allergenicity of these dyes. Here, we examine the binding of azobenzene disperse dyes to nucleophilic peptide residues as a proxy for their potential reactivity as electrophilic allergenic sensitizers. The Direct Peptide Reactivity Assay (DPRA) was utilized via both a spectrophotometric method and a high-performance liquid chromatography (HPLC) method. We tested dyes purified from commercial dyestuffs as well as several known transformation products. All dyes were found to react with nucleophilic peptides in a dose-dependent manner with pseudo-first order kinetics (rate constants as high as 0.04 h−1). Rates of binding reactivity were also found to correlate to electrophilic properties of dyes as measured by Hammett constants and electrophilicity indices. Reactivities of polyester shirt extracts were also tested for DPRA activity and the shirt extracts with high measured abundances of azobenzene disperse dyes were observed to induce greater peptide reactivity. Results suggest that azobenzene disperse dyes may function as immune sensitizers, and that clothing containing these dyes may pose risks for skin sensitization.

Trapping and exciton-exciton annihilation assisted ultrafast carrier dynamics in nanosheets of 2H-MoSe2 and Cr doped 1T/2H-MoSe2.

Nanosheets of transition metal dichalcogenides with prospects of photocatalysis and optoelectronics applications have significant potential in device fabrication due to their low-cost production and easily controllable morphology. Here, non-degenerate pump-probe differential transmission studies with varying pump-fluence have been carried out on single-phase 2H-MoSe2 and mixed-phase 1T/2H-MoSe2 nanosheets to characterize their excited carrier dynamics. For both the samples, the differential probe transmission data show photo-induced bleaching at earlier pump-probe delay followed by photo-induced absorption unveiling signatures of exciton-state filling, exciton trapping, defect-mediated photo-induced probe absorption and recombination of defect bound excitons. The exciton trapping and photo-induced absorption by the trapped-carriers are estimated to occur with time constant of ∼430 to 500fs based on multi-exponential modelling of the differential transmission till pump-probe delay of ∼3.5ps. Biexponential modeling of the subsequent slow-recovery of the negative differential transmission at pump-probe delay ≳3.5ps reveals that the exciton recombination happens via two distinct decay channels with ∼25 to 55ps (τ1) and ≳1ns (τ2) time constants. Pump-fluence dependent reduction in τ1 and further modelling of exciton population using higher order kinetic rate equation reveals that the two-body exciton-exciton annihilation governs the exciton recombination initially with a decay rate of ∼10-8 cm3s-1. The detailed analysis suggests that the fraction of total excitons that decay via long decay channel decreases with increasing exciton density for 2H-MoSe2, in contrast to 1T/2H-MoSe2 where the fraction of excitons decaying via long decay channel remains constant.

Cu doped ZnO nanoparticles: Correlations between tuneable optoelectronic, antioxidant and photocatalytic activities

Microstructural, optical and electronic properties of Cu doped ZnO nanoparticles with a general formula Zn1-xCuxO (x = 0.0, 0.1 and 0.2) prepared via wet chemical co-precipitation method were investigated thoroughly. Both the free radicals scavenging properties and photocatalytic activities of synthesized nanoparticles were explored. Formation of pure hexagonal wurtzite crystal structure of entire samples were identified by recorded x-ray diffraction patterns. For determining both the mean crystallite size and intrinsic microstrain of all the samples, several standard methods were utilized and a comparative study was introduced. Average size, morphology and shape regularity of synthesized samples were examined using HRTEM images. Optical direct band gap estimated from Tauc plots was noted to reduce with increasing Cu concentration in ZnO nanoparticles. Collected FTIR spectra at 300 K also validated the incorporation of Cu ions and their complete dissolution in the host ZnO crystal structure. It is also found that the hopping of electrons is the fundamental charge conduction process for all the samples in presence of ac electric field. FDTD simulation clearly predicts increase in electric field intensity with increased doping of Cu. There could be a plasmonic coupling between particles at the hotspot region that increases the electric field intensities. BET study revealed that the 10 % Cu doped ZnO sample has highest specific surface area which implies it contains more active sites for taking part in rapid photodegradation of toxic dyes compared to other samples. It was observed that the 10 % Cu doped ZnO nanoparticles were more efficient in degrading toxic dyes and the degradation pathway of all the samples obeyed first order rate kinetics model. Based on estimated bandgap of nanoparticles, a possible mechanism for the Rhodamine B (RhB) and Methylene blue (MB) dye degradation is suggested. All the prepared samples also exhibited notable antioxidant properties. Consequently, this study clearly shows that the Cu doped ZnO nanoparticles are the effective nanomaterial for photocatalytic and antioxidant applications.