Initial Concentration Research Articles

Modeling of reaction–desorption process by core–shell particles dispersed in continuously stirred tank reactor (CSTR)

Abstract Transient responses of reaction–desorption process were predicted from mathematical solutions of modeling equations for CSTR (continuously stirred tank reactor) containing core–shell adsorbent particles. Analytical solutions on the core–shell particles were derived for core–shell spherical, cylindrical, and slab-type morphologies, assuming inert-cores. Unlike continuous adsorber, CSTRs for reaction–desorption process containing spherical particles exhibited the slowest reduction rate of concentration of adsorbate, because the amount of adsorbed component on the particles is the largest among three kinds of particle shapes. Factors affecting the transient concentration in bulk medium of reaction–desorption process were investigated by adjusting inert-core thickness, inlet flow rate, initial concentration of reactant in inflow stream, amount of adsorbent, and Thiele modulus. Concentration profile inside the particles as well as average intra-particle concentration could be also predicted for comparison with bulk concentration of CSTR. For non-linear isotherm and non-linear reaction kinetics, concentration of active component could be predicted by solving non-linear coupled differential equation using finite element method. For connected CSTRs in series, systems of reaction-diffusion equations were solved by finite element method to study the effect of number of connected reactors. When the number of reactors was sufficiently large, the reactor system could be approximated to fixed bed reactor for reaction–desorption process.

Factors Affecting Electrocoagulation Process for Different Water Types: A review

Raw water must meet specific physical, chemical, and biological requirements to be suitable for drinking. There are various techniques available for treating wastewater, and aside from conventional methods that involve chemicals, electrocoagulation is an efficient and advanced approach. Electrocoagulation has proven effective in treating many pollutants, including bacteria, viruses, iron, fluoride, sulfate, boron, hardness, and turbidity. Total suspended solids, organic and inorganic materials, chemical oxygen demand COD, biochemical oxygen demand BOD, and color. It finds extensive application in treating different types of water and wastewater due to its exceptional ability to remove diverse contaminants. Recently, electrocoagulation has garnered significant attention due to its remarkable efficiency in treating various pollutants. This article provides a thorough analysis of contemporary literature that is committed to using electrocoagulation in a variety of water treatment methods, with a focus on the different variables affecting the process performance, such as electrical current, electrode type, electrode configuration, initial pH, electrode distance, NaCl concentration, initial concentration of pollutants, operating temperature and electrolysis time.

Kinetics, equilibrium and thermodynamics investigations of polypyrrole and polyaniline composites with Oryza sativa biomass for the removal of Nitenpyram insecticide

Abstract In this research, composite materials were prepared by combining polypyrrole (PPY) and polyaniline (PAN) with Oryza sativa (OS). These biocomposites were utilized for the adsorption of Nitenpyram (insecticide), from aqueous solutions. The study involved the optimization of various process variables including contact time, pH, adsorbent dose and initial Nitenpyram concentration. The maximum sorption efficiency of OS for Nitenpyram was observed at pH 2, biosorbent dose of 0.05 g, an initial Nitenpyram concentration of 125 mg/L and contact time of 30 min. To analyze the Nitenpyram adsorption process, the adsorption data for OS and its composites (OS-PPY and OS-PAN) were subjected to equilibrium isotherms and kinetics models (pseudo-first and pseudo-second-orders). The Langmuir isotherm and pseudo-second-order explained the Nitenpyram adsorption data. Furthermore, the feasibility of the adsorption was evaluated by employing thermodynamic studies. The outcomes of the study demonstrated the promising efficiency of the synthesized biocomposites for Nitenpyram removal, which was 37.03, 43.0 and 35.71 (mg/g) in the case of OS, OS-PPY and OS-PAN composites. These findings suggest that the composites have promising potential for the removal of pesticides from wastewater, contributing to the development of effective strategies for environmental remediation.

Sono-assisted adsorption of nitrate by Fe-modified chitosan–zeolite composite material

The negative consequences of nitrate pollution on the environment and human health, that gained substantial attention. The purpose of this work is to formulate and evaluate the potential of the Fe-modified chitosan–zeolite composite (CZFC) as an efficient adsorbent for the removal of nitrate. Physical and chemical characterization techniques such as SEM, XRD, and FTIR were used to analyze the surface and structural properties of the CZFC. The effects of several variables, including the pH, contact time, initial concentration, and adsorbent dosage, were investigated under ultrasonication treatment throughout experiments. When compared to the Freundlich and Temkin models, the Langmuir models had the highest R 2 value (0.99), indicating that they had the best fitting for all the experimental data. The maximum adsorption capacity was found to be 5.18 ± 0.30 mg g−1 with 95.37 ± 2.11% of nitrate removal at pH 3 and 2 g L−1 of adsorbent dose. The pseudo-second-order model exhibited the highest R 2 value (0.99) and proved the chemisorption mechanism for nitrate removal. The thermodynamic properties indicated that the adsorption was spontaneous and exothermic. The regeneration capacity of the CZFC was found to be 80.86 ± 4.17% at pH 10 due to the weakening of electrostatic attraction. According to experimental results, ultrasonication treatment was crucial for increasing nitrate absorption on synthesized CZFC.

Experimental and modeling studies on the removal of bromocresol green from aqueous solutions by using pine cone-derived activated biochar

AbstractThis study was carried out to evaluate the potential application of pine cone (PC)-derived activated biochar which has a surface area of 1714.5 m2/g for bromocresol green (BCG) dye removal from aqueous solution. Batch adsorption experiments involved varying pH, temperature, contact time, adsorbent dosage, and initial dye concentrations and the maximum BCG removal (96.27%) occurred at pH: 2.0, T: 45 °C, m: 2 g/L, t: 15 min., and Co: 25 mg/L. To study the characteristics of adsorption, the adsorption kinetic isotherm and thermodynamic parameters were employed. The experimental data was evaluated to fit well with the Temkin isotherm (R2 = 0.99) and the adsorption process followed pseudo-first-order kinetics (R2 = 0.96). Thermodynamic parameters obtained from the adsorptive uptake showed that the interaction was endothermic and spontaneous in nature. The regenerated activated PC biochar showed good performance (95.0%), even, after 4th regeneration. To predict the BCG adsorption capacity of activated PC biochar, many different artificial neural network (ANN) models have been developed. The optimal ANN model gave mean absolute error (MAE), mean bias error (MBE), root mean square error (RMSE), and R2 values of 0.036, 0.578, 0.947, and 0.999, respectively. The results obtained showed that ANN can be used to effectively model the BCG adsorption process.

Enhanced tetracycline degradation with TiO2/natural pyrite S-scheme photocatalyst

In this study, TiO2 nanoparticles were employed as a photocatalyst for the degradation of tetracycline (TC) under visible light irradiation. The TiO2 nanoparticles were decorated on natural pyrite (TiO2/NP) and characterized using XRD, FTIR, and SEM–EDX methods. This study evaluated the impacts of various operational parameters such as pH, catalyst dosage, initial TC concentration, and light intensity on TC removal. The findings revealed that under optimal conditions (pH 7, catalyst: 2 g/L, TC: 30 mg/L, and light intensity: 60 mW/cm2), 100% of TC and 84% of TOC were removed within 180 min. The kinetics of TC elimination followed a first-order model. The dominant oxidation species involved in the photocatalytic elimination of TC was found to be ·OH radicals in the TiO2/NP system. The reuse experiments showed the high capability of the catalyst after four consecutive cycles. This study confirmed that the TiO2/NP system has high performance in photocatalytic TC removal under optimized experimental conditions.

Isomerization of maltose to maltulose by microwave heating, using arginine as a catalyst

AbstractMicrowave heating was applied to isomerize maltose to maltulose, using arginine as a catalyst. The initial molar ratio of arginine/maltose was kept constant at 0.05. Maltulose yields of 0.28–0.30 were achieved within 90–400 s, dependent on the microwave power and the volume of the substrate solution but not on the initial concentration of maltose, indicating that isomerization of maltose by microwave heating is highly productive. Independent of the power of the microwave oven and the volume of the substrate solution, the fraction of remaining maltose, the yield of maltulose, the pH of the reaction mixture, and its absorbance at 280 and 420 nm could be expressed as a function of energy density, which was defined as the amount of energy absorbed per unit volume of the reaction mixture. This indicates that the operating conditions for the isomerization of maltose to maltulose by microwave heating can be determined based on the energy density.Practical applicationsIsomerization of aldose saccharides to their rare keto‐isomers in the presence of arginine in a heated aqueous solution is a green and effective process. To further improve the process efficiency, microwave heating can be employed. This study also demonstrated that a so‐called “energy density” can be used to determine the operating condition for the isomerization of sugar by microwave heating.

Effect of Antibiotics Metranidazole, Streptomycin, and Gentamicin on the Maintenance of Sperm Motility of the European Common Frog (<i>Rana temporaria</i>) During Refrigerated Storage

The problem of asynchrony in the production of gametes in amphibians can be solved by increasing the longevity of spermatozoa during the storage of spermic urine with antibiotics. This study evaluated the effect of metranidazole and streptomycin at concentrations of 0.1, 0.2, 0.4, and 1 mg/ml on the maintenance of motility and the longevity of spermatozoa in the spermic urine of the European common frog (Rana temporaria) during refrigerated storage at 4°C. Metranidazole did not improve the lifespan of spermatozoa, and streptomycin had a positive effect at all analyzed concentrations. In addition, the streptomycin and gentamicin at the same concentrations of 0.05, 0.1, and 0.2 mg/ml were compared for their effect on maintaining sperm motility during storage. In spermic urine samples with significant bacterial contamination, no significant differences were found in the effect of streptomycin and gentamicin on sperm motility. In the absence of any visible signs of significant bacterial contamination of spermic urine samples, the motility of spermatozoa with gentamicin remained significantly longer than that with streptomycin for all analyzed concentrations. In addition, in this study, for the first time, a positive correlation was revealed between the initial concentration of spermatozoa and the longevity of spermatozoa during the refrigerated storage of amphibian spermic urine samples with antibiotics (r = 0.899, P 0.0001). However, no relationship was found between the longevity of spermatozoa and the initial osmolality of spermic urine in the range from 62 to 92 mosmol/kg (r = 0.083, P = 0.768).

Bio-composite of chitosan and polyethylene for the biosorption of dye in wastewater

This study investigated the potential of a biocomposite adsorbent made of low-density polyethylene-chitosan nanoparticles (LDPE/CHNP) for removing Congo red and Crystal violet dyes from wastewater. Batch experiments were conducted at room temperature to study the effects of pH, contact time, initial concentration, adsorbent dosage, and temperature on the adsorption process. The results showed that the maximum sorption of Congo red and Crystal violet occurred at pH 8. The adsorption process was rapid in the first 30 minutes of contact, with more than 90% uptake, and equilibrium was achieved with 150 rpm agitation. The biosorption of Congo red and Crystal violet dyes was described using Langmuir, Freundlich, and isotherm models. The Langmuir model was found to fit the equilibrium data better, with a correlation coefficient of 0.99 and a maximal adsorption capacity of 27.1 mg/g. Based on these results, it can be concluded that the biocomposite adsorbent made of low density polyethylene-chitosan nanoparticles (LDPE/CHNP) has the potential to be an effective and abundant alternative biomass for removing these dyes from wastewater. The LDPE/CHNP biocomposite adsorbent could be applied as a remediation method for color contamination in wastewater.

Synthesis, characterization of Gd-doped ZnO nanocrystals and their photocatalytic activity in the degradation of C.I. Acid Red 18

In this study, ZnO and Gd doped ZnO with various weight percentages (1, 2, 3, and 4 wt% Gd calcined at 450 °C and 2 wt% Gd doped ZnO calcined at 450, 550, 650, and 750 °C) have been prepared. XRD, TEM, DRS, PL measurements, EDX, and FTIR were used for the characterization of the as-prepared photocatalysts. The photocatalytic activity of the as-synthesized ZnO and Gd-doped ZnO products was assessed by AR18 as a model of textile contaminants degraded in water under UV radiation. The effect of operating parameters such as pH, contact time, the initial dye concentration, and the influence of different contents of gadolinium doping and analysis were estimated. We use some active species such as ethanol, K2Cr2O7, KI, and Oxalate to find the photocatalyst and the formation of the electron-hole mechanism of Gd-doped ZnO. After 40 min, the catalyst calcined at 450°C (at pH = 5.0, [AR18] = 1.0 × 10−5M)showed the highest efficiency (98.28 %). The amount of COD decrease after 40 min of irradiation is 98.6 %.

Highly efficient kaolin/g-C3N4/WO3 ternary nanocomposite for the effective removal of Arsenic ions from aqueous media

The effectual removal of arsenic ions from contaminated water sources remains a significant challenge in water treatment. In this study, we propose a novel composite material consisting of kaolin, graphitic carbon nitride (g-C3N4) and tungsten trioxide (WO3) for effective arsenic removal. The composite material was prepared through a facile synthesis method, and its physicochemical properties were characterized using various analytical techniques. The effects of composite dosage, initial arsenic concentration, contact time and temperature on the adsorption capacity were systematically evaluated. The results revealed that the composite material exhibited excellent arsenic removal efficiency, with a maximum adsorption capacity of 114.63 mg/g. The adsorption isotherms such as Langmuir and Freundlich models were evaluated, and the data finds to fit well with the Langmuir model, suggesting homogeneous adsorption. The mechanism of arsenic removal follows photocatalytic oxidation of As(III) to As(V) followed by adsorption of As(V). The process of adsorption followed the pseudo-second-order kinetic model. Additionally, the composite material demonstrated good reusability and stability over multiple cycles. The findings of this study contribute to the progress of sustainable and reliable water treatment technologies for arsenic removal, addressing a pressing global environmental concern.

Treatment of Coking Wastewater Using Hydrodynamic Cavitation Coupled with Fenton Oxidation Process.

Effective and economical processes for the advanced treatment of coking wastewater were urgently needed to reduce the persistent organic pollutants of external drainage. In the present work, we investigated the degradation of organic pollutants in coking wastewater through IHC/FO (imping stream hydrodynamic cavitation (IHC) coupled with the Fenton oxidation (FO) process) and IHC alone for their feasibility in the advanced treatment of coking wastewater. To select the optimum parameters, attention was paid to the effects of main operation conditions including inlet fluid pressure, medium temperature, initial pH, reaction time, and initial Fe(II) and initial H2O2 concentrations. The results showed that the effects of conditions that need energy to be maintained (such as initial pH and inlet pressure) on the organic pollutant removal efficiency through IHC/FO were less pronounced than those through IHC alone. Moreover, the application of IHC/FO could remove more organic pollutants from coking wastewater than IHC even at an energy-efficient condition. For example, the highest COD removal efficiency of 12.5% was achieved in the IHC treatment at 0.4 MPa, pH 3, and 60 min for the reaction time. In the case of IHC/FO, the maximum COD removal of 33.2% was obtained at pH 7, 0.1 MPa, 12 mmol/L H2O2, and 3 mmol/L Fe2+ after reacting for 15 min. The ultraviolet and visible spectrophotometry (UV-Vis) absorption spectra and gas chromatography and mass spectrometry (GC-MS) analysis further revealed that the kinds and amounts of pollutants (especially those that had benzenes) remaining in water treated through IHC/FO were much fewer and smaller than in water treated through IHC alone. The better performances of IHC/FO than IHC alone were likely related to the more hydroxyl radicals produced through IHC/FO. Taken together, our findings indicate that IHC/FO has great application potential in the advanced treatment of coking wastewater.

Elaboration of a green and highly dispersible Co-MOFs induced Co-doped C3N5 photocatalyst: Applications and mechanistic insights into activated perxymonosulfate degradation of antibiotics

In recent years, metal-organic frameworks (MOFs) as metal-based carbon materials have been widely concerned with the application of activated perxymonosulfate(PMS) to degrade antibiotics. However, constructing MOFs-derived materials with excellent dispersion, highly exposed metal active sites, and environmental friendliness remains a challenge. This paper reports for the first time the in-situ formation of nitrogen-rich Co-doped C3N5 (Co-C3N5) materials using a cobalt-based metal-organic framework (Co-MOFs), which has highly dispersed metal sites that are conducive to the activation of PMS. The forbidden bandwidth value of Co-C3N5 photocatalyst is as low as ∼1.20 eV, which could completely degrade chlortetracycline hydrochloride (CTC) with the initial concentration of 30 mg/L within 6 min under a light source of 50 W LED lamp. The results indicate that efficient photoelectron separation and transport are key factors in the activation and degradation of CTC by PMS, involving both free radical and non-free radical degradation processes. Meanwhile, the skeletal structure of MOFs and the triazine ring of C3N5 were retained, enhancing the stability of the photocatalyst and reducing the leaching of cobalt Finally, the seed germination experiment of Chinese cabbage showed that the treated CTC could increase the root length of Chinese cabbage seedlings by 10.1∼42.9%, which proved that the materials had no toxic effect on environment and could provide carbon and nitrogen source for plant growth. Based on this, this study proposes a novel approach for the development of MOFs-derived carbon photocatalysts that exhibit excellent dispersion and highly exposed metal active sites.

Bioreactor study of the metabolic repertoire and morphology of actinomycete Streptomyces rimosus ATCC 10970 under various initial concentrations of carbon and nitrogen sources

This work aims at investigating the influence of the initial concentrations of carbon (glucose) and organic nitrogen (yeast extract) sources on Streptomyces rimosus ATCC10970 secondary metabolism in the stirred tank bioreactors. Additionally, glucose utilisation, biomass formation, pH, redox potential and dissolved oxygen levels, and the morphological development of S. rimosus pseudomycelium were studied. Eighteen secondary metabolites were detected by mass spectrometry and identified with the use of the authentic standard, or putatively with the use of literature and database of secondary metabolites. Varied initial yeast extract concentration acted much stronger on the formation of secondary metabolites than glucose did. For example, oxytetracycline was not biosynthesised at high yeast extract concentration while the formation of three other metabolites was enhanced under these conditions. In the case of glucose its increasing initial concentration led to higher secondary metabolite levels with the exception of an unnamed angucycline. High initial yeast extract concentration also drastically changed S. rimosus pseudomycelial morphology from the pelleted to the dispersed one. Ultimately, the cultivation media with the varied initial levels of carbon and nitrogen sources were proved to have the marked effect on S. rimosus secondary metabolism and to be the simplest way to either induce or block the formation of the selected secondary metabolites.

Functionalized cellulose nanocrystals extracted from date pits as agricultural waste for the efficient remediation of molybdenum from groundwater: Performance and mechanistic studies

The adsorption technique has proven to be an excellent option for treating contaminated water. This work was designed to investigate the efficient remediation of molybdenum (Mo(VI)) from groundwater by using a novel adsorbent composed of date pits (DP) modified by manganese oxide/cellulose nanocrystal (CNC) composite (MnO2/CNC@DP). The physicochemical properties of the adsorbent were examined by Fourier transform infrared spectroscopy (FTIR), scanning electron microscope with energy-dispersive X-ray spectroscopy techniques (SEM/EDX), X-ray diffraction (XRD), and transmission electron microscopy (TEM) to study the functional group on the adsorbent surface, surface morphology and chemical composition, and the crystallinity behavior. The performance of prepared (MnO2/CNC@DP) toward Mo(VI) was studied using synthetic solutions and real groundwater samples. Also, the effect of pH, temperature, and initial Mo concentration on the adsorption process was investigated. Moreover, various adsorption isotherm models were calculated, and the thermodynamics of adsorption was studied. The recovery experiments for Mo(VI) saturated MnO2/CNC@DP were conducted by using acidic and alkaline solutions. At the optimum pH of 2, the adsorption capacity increased with increasing the initial concentration of Mo(VI), and Qmax was 30 mg/g at 35 °C. The removal of Mo(VI) from real groundwater was 88.42% The negative values of Gibbs energy (ΔG°) demonstrated that the adsorption is spontaneous, and the experimental data followed the Langmuir isotherm model. Moreover, Mo(VI) can be desorbed from the MnO2/CNC@DP surface by using 1.0M HCl. The proposed mechanisms for the adsorption of Mo(VI) by MnO2/CNC@DP were dominated by electrostatic attraction and inner-sphere complexation. As a result of the research, MnO2/CNC@DP is a promising adsorbent with a high potential for removing Mo(VI) from groundwater. Furthermore, This research provides new knowledge into the modification of date pits using different metal oxides/cellulose nanocrystal particles. Furthermore, the results suggest an excellent chance of employing the efficiently produced adsorbent MnO2/CNC@DP for sustainable groundwater treatment from additional contaminants.

Preparation of magnetic DTPA-modified chitosan composite microspheres for enhanced adsorption of Pb(II) from aqueous solution

In this study, magnetic DTPA-modified chitosan composite microspheres (MDCM) were prepared by reverse emulsion-double crosslinking method (carbodiimide followed by glutaraldehyde) for removal of Pb(II) from aqueous solution. The obtained magnetic adsorbents were characterized by FTIR, SEM, XRD, VSM, BET, and 13C NMR. The effects of the pH, contact time, initial concentration, and competitive metal cations (Na(I), Ca(II), or Mg(II)) on Pb(II) adsorption were investigated. The results revealed that MDCM exhibited high removal performance over a wide pH range and in the presence of competitive metal cations. The maximum adsorption capacity of MDCM for Pb(II) is 214.63 mg g−1 at pH 3, which is higher than most recently reported magnetic adsorbents. Adsorption kinetics and isotherms can be described by the pseudo-second-order model and Langmuir model, respectively. In addition, MDCM is easy to regenerate and can be reused five cycles with high adsorption capacity. Finally, the adsorption mechanism was further revealed by FTIR and XPS analysis. Overall, MDCM has practical application potential in removing Pb(II) from contaminated wastewater due to its high adsorption efficiency, good reusability, and convenient magnetic separation.

Towards liquid EPR dosimetry using nitroxides in aqueous solution.

Objective. Water-equivalent dosimeters are desirable for dosimetry in radiotherapy. The present work investigates basic characteristics of novel aqueous detector materials and presents a signal loss approach for electron paramagnetic resonance (EPR) dosimetry.Approach. The proposed principle is based on the radiation dose dependent annihilation of EPR active nitroxides (NO·) in aqueous solutions. Stable nitroxide radicals (3-Maleimido-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (MmP), 3-Carbamoyl-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (CmP)) in aqueous solutions containing dimethyl sulfoxide (DMSO) as an additive were filled in glass capillaries for irradiation and EPR readout. Radiation doses ranging from 1 to 64 Gy were applied with a clinical 6 MV flattening filter free photon beam. EPR readout was then performed with a X-band benchtop spectrometer. The dose response, temporal stability and reproducibility of the samples' EPR signal amplitudes as well as the influence of the nitroxide concentration between 10 and 160μM on the absolute signal loss were investigated using MmP. CmP was used to examine the dependence of the dose response on DMSO concentration between 0 and 10 vol%. An indirect effect model was fitted to the experimental data assuming irradiation induced radical reactions as the underlying mechanism.Main results. For an initial MmP concentration of 20μM, absolute EPR signal loss is linear up to a dose of 16 Gy with a yield G(-NO·) of approximately 0.4μmol J-1. Within five weeks upon sample irradiation to doses between 0 and 32 Gy relative EPR signal fluctuations were on average (126 readouts) below 1% (1σ). For c(MmP) ≥ 20μM, absolute signal loss is only weakly dependent on c(MmP), whereas it increases strongly with increasing c(DMSO) in the range 0-5 vol%. An indirect effect model is applicable to describe the reaction mechanism resulting in the observed dose response curve.Significance. Liquids consisting of nitroxides in aqueous solution and small amounts of DMSO (2 vol%) show promising basic characteristics for application as water-equivalent EPR dosimeter materials in radiotherapy. The EPR signal loss is based on an indirect effect mediated by diffusing radicals originating from the radiolysis of the water/DMSO mixture.

Heterogeneous photochemical uptake of SO2 on typical brown carbon species: A significant sulfate source

The heterogeneous reactions of SO2 on organic aerosols (OA) have been proposed as a significant source of sulfates. The photochemical conversion of SO2 to sulfates on the surface of light-absorbing OA, i.e., brown carbon (BrC), remained slight understanding. Herein, the photochemical uptake of SO2 on typical BrC species, including aromatic carbonyl compounds (ACs), polycyclic aromatic hydrocarbons (PAHs) and phenols (PHs), was systematically investigated by a flow tube reactor. Light can significantly promote the uptake of SO2 on all BrC species used here, especially for ACs. The initial and steady-state uptake coefficients (γi and γss) of SO2 exhibited positive relationships with the light intensity, whereas they negatively correlated with the initial SO2 concentration. Significant sulfate formation was clearly observed with in situ attenuated total internal reflection infrared (ATR-IR) spectrometer, and H2O and O2 had obvious enhancement effects on the sulfate production. Photoinduced •OH, which primarily originated from •O2− that was generated through an electron transfer process on BrC under irradiation, was determined to be a key driver for the oxidation of SO2 to sulfates. Finally, SO2 lifetime and sulfate formation rate were evaluated on the basis of experimental results, highlighting potential contributions of BrC photochemistry to atmospheric SO2 loss and sulfate sources.

Remediation of pesticides, acetamiprid and imidacloprid from aqueous solutions using cellulose derived from sawdust of Populus nigra

Abstract In this study a low cost and easily available Black Poplar Sawdust (Populus nigra L.) was converted into an efficient adsorbent for the removal of acetamiprid (AMR) and imidacloprid (ICR) pesticides from aqueous solutions. The effect of adsorption effecting parameters including initial pesticides concentration, variations in the adsorbent amount, time of contact, and pH were investigated to understand the adsorption process of both pesticides. Further the kinetic, thermodynamic, and isotherm models were used to get an insight into the process of adsorption taking place. The results of the study suggested that the isotherm data align effectively with both the Langmuir and Temkin isotherm models (both pesticides). The maximum adsorption capacity (q m) for AMR was found to be 25.22 mg g−1, while for ICR, it was 25.65 mg g−1. Furthermore, the adsorption kinetics were best described by the pseudo-second-order model with value of R 2 = 0.9934 & 0.9964 respectively for AMR and ICR. The thermodynamic analysis confirmed the spontaneity and feasibility of the adsorption process, evident from the negative ∆G° values at different temperatures. The thermodynamics parameter values also suggested that the adsorption process is physisorption and exothermic due to the negative ∆H° value. From the results it was concluded that the devised adsorbent could be effectively used in reclamation pesticides contaminated water subjected to further verifications through testing against other pesticides.

The unreasonable effectiveness of the total quasi-steady state approximation, and its limitations

In this note, we discuss the range of parameters for which the total quasi-steady-state approximation of the Michaelis–Menten reaction mechanism holds validity. We challenge the prevalent notion that total quasi-steady-state approximation is “roughly valid” across all parameters, showing that its validity cannot be assumed, even roughly, across the entire parameter space — when the initial substrate concentration is high. On the positive side, we show that the linearized one-dimensional equation for total substrate is a valid approximation when the initial reduced substrate concentration s0/KM is small. Moreover, we obtain a precise picture of the long-term time course of both substrate and complex