Equilibrium Concentration Research Articles

Methane emissions from subglacial meltwater of three alpine glaciers in Yukon, Canada

ABSTRACT Subglacial meltwater of land-terminating glaciers in Greenland and Iceland are sources of methane (CH4) to the atmosphere, but sparse empirical data exist about the spatial distribution of subglacial CH4 production and emission from glaciers in other regions of the world. This study presents the first measurements of CH4 emissions from the subglacial meltwater of three outlet glaciers of the St. Elias Mountains in Yukon, Canada. Dissolved CH4 concentrations were highly elevated at 45, 135, and 250 times compared to the atmospheric equilibrium concentration in the meltwater of Dusty, Kluane, and Donjek glaciers, respectively. Dissolved CO2 concentrations were depleted relative to the atmospheric equilibrium. This points to the meltwater being a source of CH4 and a sink of CO2. Stable carbon (13C) and hydrogen (2H) isotopic signatures of the subglacial CH4 were depleted compared to atmospheric CH4 at all sites, indicating both biotic and abiotic sources and possible alteration from bacterial CH4 oxidation in the meltwater. No relation was found between CH4 concentrations in the meltwater and the meltwater chemistry or the size of the glaciers in this study. These findings suggest that CH4 emissions from subglacial environments under alpine glaciers may be a more common phenomenon than previously thought.

Chemical Activity-Based Loading of Artificial Sediments with Organic Pollutants for Bioassays: A Proof of Concept.

Persistent organic pollutants (POPs) pose a risk in aquatic environments. In sediment, this risk is frequently evaluated using total or organic carbon-normalized concentrations. However, complex physicochemical sediment characteristics affect POP bioavailability in sediment, making its prediction a challenging task. This task can be addressed using chemical activity, which describes a compound's environmentally effective concentration and can generally be approximated by the degree of saturation for each POP in its matrix. We present a proof of concept to load artificial sediments with POPs to reach a target chemical activity. This approach is envisioned to make laboratory ecotoxicological bioassays more reproducible and reduce the impact of sediment characteristics on the risk assessment. The approach uses a constantly replenished, saturated, aqueous POP solution to equilibrate the organic carbon fraction (e.g., peat) of an artificial sediment, which can be further adjusted to target chemical activities by mixing with clean peat. We demonstrate the applicability of this approach using four polycyclic aromatic hydrocarbons (acenaphthene, fluorene, phenanthrene, and fluoranthene). Within 5 to 17 weeks, the peat slurry reached a chemical equilibrium with the saturated loading solution. We used two different peat batches (subsamples from the same source) to evaluate the approach. Variations in loading kinetics and eventual equilibrium concentrations were evident between the batches, which highlights the impact of even minor disparities in organic carbon properties within two samples of peat originating from the same source. This finding underlines the importance of moving away from sediment risk assessments based on total concentrations. The value of the chemical activity-based loading approach lies in its ability to anticipate similar environmental impacts, even with varying contaminant concentrations. Environ Toxicol Chem 2024;43:279-287. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Interaction mechanism of a pesticide, Azoxystrobin with bovine serum albumin: Assessments through fluorescence, UV–Vis absorption, electrochemical and molecular docking simulation techniques

The current study's objective was to investigate how an antifungal pesticide Azoxystrobin (AZO) interacts with bovine serum albumin (BSA) under conditions that simulate a physiological medium (pH 7.4). This investigation was carried out using various experimental (UV–Vis absorption, steady-state fluorescence and 3-D fluorescence spectroscopies, and electrochemical) and theoretical (molecular docking and molecular dynamics simulations) methods. The fluorescence quenching data demonstrated that AZO caused fluorescence quenching in BSA, and this quenching process was attributed to the static quenching mechanism. By examining the fluorescence quenching of BSA at three different temperatures, it was determined that the binding constants for the AZO-BSA complexes were approximately 104 M−1 in magnitude, while the same magnitude of the binding constant was found by the electrochemical method. This indicates that the interaction between AZO and BSA was of moderate strength. This was further validated by the changes observed in the UV–Vis spectrum of BSA following the addition of AZO. The thermodynamic information, including ΔH and ΔS, revealed that the interaction forces primarily involved van der Waals forces as well as hydrogen bonds. The negative Gibbs free energy indicated that the reaction is spontaneous. In the theoretical investigation, the comparison highlights a remarkable consistency in how AZO interacts with the BSA active site over various time points. Hydrogen bonding and hydrophobic interactions consistently play a role in ensuring the stable and specific binding of the ligand. Moreover, the 3-D fluorescence spectral findings revealed alterations in the surrounding microenvironment of protein fluorophores when AZO binds. Upon analyzing the electrochemical data, it was observed that there was a consistent decrease in the peak currents of AZO when BSA was added to solutions containing AZO. The primary cause of this decrease in the peak currents was the reduction in the equilibrium concentration of AZO due to the addition of BSA. Furthermore, the formation of a non-electroactive complex between BSA and AZO, which impedes electron transport between AZO and the working electrode, accounts for these decreases. As a result, it can be said that the understanding of how AZO binds to BSA offers valuable insights that can be applied in the food, human health, and environment sectors.

Modeling of temperature-concentration ranges of phase stability and liquidus surface in the ternary Fe–P–C system and phase composition experimental study

This paper reports thermodynamic properties and phase equilibria in the iron-phosphorus-carbon system for developing a technology for smelting ferrophosphorus as well as for utilizing them in the processes of phosphorus-alloying of metals. According to the results of thermodynamic calculations, we plotted a ternary Fe–P–C phase equilibrium diagram (liquidus surface) in the form of graphical dependences, which indicate the concentration fields of phase coexistence. The results of simulation allowed finding out five nonvariant points, three of which are new: E1 eutectic (teutectic=12170С), U1 peritectic (tperitectic=10950С), and Е3 eutectic (teutectic=3380С). The experimental studies of the phase composition of ferrophosphorus showed that the phosphorus microstructure is represented by Fe3P phosphide, Fe3C carbide, and carbophosphide eutectic. We carried out the thermodynamic calculation of the temperature-concentration ranges of phase stability in the Fe–P–C system that are at equilibrium with the smelts of both the carbon solid solutions and phosphorus ones in - and -iron, FeP, Fe2P, Fe3P phosphides, and graphite. In this study, three previously unknown nonvariant equilibria have been determined: a eutectic equilibrium at 1216.580C; a peritectic one with a transformation point at 1095.190C; and a eutectic one at a temperature of 337.510C. In experiments, we obtained an equilibrium concentration of carbon which decreases in the Fe–P–C system when the content of phosphorus increases. The research findings largely reveal special features of preparation of ferrophosphorus by carbon reduction of phosphorites.

Experimental and theoretical investigations on Hg(II) removal by recyclable composite sorbents comprised of polymers bearing thiourea or amidoxime functional groups and mesoporous silica

It is extremely desirable but still challenging to skilfully manufacture highly efficient sorbents to remmediate, in a reversible manner, the water pollution with mercury. Herein, new sorbents for Hg(II) ions have been designed by the initial synthesis of polyacrylonitrile networks inside mesoporous SiO2 microparticles, followed by the chemical modification of acrylonitrile groups with thiourea or amidoxime moieties. The Hg(II) ions sorption properties of the new composites were compared with respect of initial solution pH, contact time, equilibrium concentration and impact of interfering metal ions. It was demonstrated that the sorbents containing thiourea groups exhibited superior sorption capacities (1.76 mmol Hg(II) g−1) compared to the ones containing amidoxime groups (1.68 mmol Hg(II) g−1), and also higher selectivity for Hg(II) ions separation from binary mixtures with Cu(II), Cd(II) or Pb(II) ions. Kinetic study and DFT results supported a combined sorption mechanism, both physical sorption and chem-isorption being possible. Following the elution of Hg(II) ions with 1 M HNO3 and the regeneration with 0.1 M NaOH, all sorbents exhibited around 90 % sorption capacity recovery after 4 reuse cycles.

Extraction and Selective Separation of ZrIV from LnIII/AnIII Using an Undiluted Phosphonium Ionic Liquid.

Solvent extraction of Zr(IV) in an undiluted phosphonium based ionic liquid (IL) and its selective separation from Ln(III) and An(III) has been investigated in the present study. Eu(III)/Am(III) were chosen as the representative Ln(III)/An(III). Tri(hexyl)tetradecylphosphonium nitrate ([P66614][NO3]) was chosen as IL phase and the feed phase was nitric acid containing the target metal ions. The extraction process was accomplished at different experimental parameters such as the concentration of initial nitric acid, initial feed metal concentration and equilibration time to explore the extractability of the proposed IL towards Zr(IV). The efficient extraction of Zr(IV) without any external ligand in IL phase and negligible extraction of Eu(III)/Am(III) were distinctly discerned leading to noteworthy separation factors for Zr(IV). The loading experiment revealed a noticeable growth of equilibrium concentrations of Zr(IV) in IL phase while that of Eu(III) was very less irrespective of the initial feed concentration. The association of two IL moieties in the complex formation process has been inferred. Nitrate ion was found to be superior as IL anion in terms of metal loading in comparison to other anions. Thermodynamics of extraction and the stripping of the loaded Zr(IV) from IL phase using a suitable stripping solution have also been investigated.

Sorption studies of Tetraoxophosphate (v) ions on some agricultural soils in Akwa Ibom State, eastern Niger Delta, Nigeria

The phosphate sorption capacity regulates principally the phosphorus concentration and available phosphorus in any soil solution. This work aims to study the phosphate sorption characteristics of five agricultural soils in Akwa Ibom State, Nigeria. The phosphate adsorption isotherm was obtained by shaking each soil sample with 20, 40, 60, 80, 100 and 120 mgL–1 for 24 h with 20 mL of KH2PO4 in 0.01 M CaCl2 solution. The Langmuir, Freundlich, Van Huay and Temkin isotherms were applied to study the PO43-sorption characteristics of the soil samples. The Freundlich model provided the best choice for phosphate sorption with mean R2 value of 0.9872. Results obtained for the phosphate sorbed (µg g–1soil) with 120 mgL-1 solution, heterogeneity factor of adsorption sites (nF), and the Freundlich constant (KF) (Lg–1) were 101(84.3), 0.515 and 7.355 for Onna soil; 62.8(52.3), 0.641 and 2.464 for Ikot-Amama 2; 60.6(50.5), 0.708 and 3.985 for Ogu-Itumbonuso soil; 59.3(49.5), 0.652 and 2.505 for Ikot-Amama 1 soils; 58.0(48.3), 0.704 and 3.682 for Ikot-Nkon soils, respectively. The equilibrium concentration for phosphates (EC-P) were used as desorption index to determine whether the soils could serve as potential sources for their bioavailability to plants and results ranged from 5.0 to 9.90 mgL–1, indicating high vulnerability to phosphate loss. The relationship between phosphate sorption parameters and soil physicochemical properties showed that the Freundlich adsorption intensity factor, nF, strongly correlated negatively with organic carbon and organic matter (r = -0.953 and -0.947; P<0.01), Fe and Mn (r = -0.911 and -0.812, P<0.05). The EC-P correlated strongly with soil pH(H2O) (r = 0.959, P<0.01), clay (r = 0.913, P<0.05), cation exchange capacity (CEC) (r = -0.824, P<0.05), Mn (r = -0.792, P<0.05) and Fe (r = -0.826, P<0.05). The study illustrated that soil management practices which involves the using organic fertilizers as the basis for PO43- sorption in relation to soil properties can be a useful tool for sustainable crop production and environmental soil-water contamination.

A Study on the Structural and Digestive Properties of Rice Starch-Hydrocolloid Complexes Treated with Heat-Moisture Treatment.

Rice starch-hydrophilic colloid complexes (SHCs) were prepared by incorporating xanthan gum and locust bean gum into natural rice starch. Subsequently, they underwent hygrothermal treatment (H-SHC) to investigate their structural and digestive properties with varying colloid types and added amounts of H-SHC. The results demonstrated that heat-moisture treatment (HMT) led to an increase in resistant starch (RS) content in rice starch. This effect was more pronounced after the addition of hydrophilic colloid, causing RS content to surge from 8.42 ± 0.39% to 38.36 ± 3.69%. Notably, the addition of locust bean gum had a more significant impact on enhancing RS content, and the RS content increased with the addition of hydrophilic colloids. Enzyme digestion curves indicated that H-SHC displayed a lower equilibrium concentration (C∞), hydrolysis index (HI), and gluconeogenesis index (eGI). Simultaneously, HMT reduced the solubility and swelling power of starch. However, the addition of hydrophilic colloid led to an increase in the solubility and swelling power of the samples. Scanning electron microscopy revealed that hydrophilic colloid encapsulated the starch granules, affording them protection. X-ray diffraction (XRD) showed that HMT resulted in the decreased crystallinity of the starch granules, a trend mitigated by the addition of hydrophilic colloid. Infrared (IR) results demonstrated no formation of new covalent bonds but indicated increased short-range ordering in H-SHC. Rapid viscosity analysis and differential scanning calorimetry indicated that HMT substantially decreased peak viscosity and starch breakdown, while it significantly delayed the onset, peak, and conclusion temperatures. This effect was further amplified by the addition of colloids. Rheological results indicated that H-SHC displayed lower values for G', G″, and static rheological parameters compared to natural starch. In summary, this study offers valuable insights into the development of healthy, low-GI functional foods.

Performance of non-waxy Japonica rice in the post-cooking storage process and with a varying water-to-rice ratio

This study aimed to investigate the effects of the water-to-rice (W/R) ratio and short-term storage after cooking on the physico-chemical properties and starch digestibility of good-eating-quality and conventionally cultivated Yudai 21. Organically cultivated Koshihikari was used as a reference. Polished grains were soaked with water in W/R ratios of ×1.4–×1.7, cooked, and stored at 3°C within 24 h. There was little change in the texture of Koshihikari regardless of the W/R ratio, whereas that of Yudai 21 changed with the W/R ratio, with maximum surface and overall adhesiveness and surface adhesion at ×1.6. The syneresis rate increased with increasing storage duration, and Yudai 21 had a lower syneresis rate (3.4%–3.9%) than Koshihikari (3.7%–4.5%). During storage, surface and overall firmness increased, surface and overall adhesiveness and adhesion decreased, and these changes were greater for Yudai 21 than for Koshihikari. The rapidly and slowly digestible starch, equilibrium concentration of starch hydrolysis, kinetic constant, and estimated glycemic index were not changed by variety and interaction but by storage. This study revealed that Yudai 21 was characterized as a rice with particularly high surface adhesiveness.

A pharmaceutical cocrystal of apigenin with piperazine: Preparation, structural characterization, and dissolution performance

As a natural flavonoid, apigenin (APG) has garnered considerable attention for its broad pharmacological properties. Unfortunately, the extremely poor aqueous solubility greatly restricts its clinical efficacy. Cocrystallization has been taken as an important approach to modulate physicochemical properties of parent drug. In this paper, piperazine (PIP) has been selected to assembly with APG and APG–PIP cocrystal has been successfully fabricated and characterized by single crystal X-ray diffraction and various analytical methods. Single-crystal X-ray diffraction analysis indicates APG–PIP crystallizes in the P21/c space group of monoclinic system and comprises neutral APG and PIP with the ratio of 1:1. APG and PIP are linked via O–H···N/N–H···O hydrogen bonds with a resulting 2D fes network. The 2D networks are further extended via π···π stacking interactions to afford its 3D architecture. The APG illustrates highly enhanced solubility and dissolving rate in APG–PIP cocrystal comparing with parent APG. It is notable that APG–PIP presents different equilibrium concentrations of APG along with insoluble residue when different dosages of APG–PIP are introduced. We speculate that APG and PIP may not be released equally within APG–PIP in aqueous medium due to their neutral nature and huge difference in solubility, and the existence of PIP can facilitate the dissolving of APG. This speculation has been further confirmed by investigation of relationship between equilibrium concentrations of APG and dosage of APG–PIP as well as powder dissolution experiment. The equilibrium concentrations are 0.118, 0.382, 0.556, 0.767, and 0.904 mg/mL when 5, 10, 15, 20, and 25 mg APG–PIP was put into 5 mL H2O and reveals good linear relation. The “spring and parachute” phenomenon and final similar solubility with parent APG in powder dissolution profile can be ascribed to the synergetic effect of metastable supersaturation and decreased PIP concentration due to withdrawing-replenishing operation.

Pharmacogenetics and pharmacokinetics of rivaroxaban in patients with atrial fibrillation and chronic kidney disease

Aim. To study the possible relationship between polymorphic variants of ABCB1 (rs2032582, rs1045642, rs1128503), CYP3A5 (rs776746), CYP3A4 (rs35599367) and CYP2J2 (rs890293) genes with residual equilibrium concentrations (Cmin,ss) of rivaroxaban in patients with non-valvular atrial fibrillation (AF) and stage 3 and 4 chronic kidney disease (CKD).Material and methods. A total of 123 patients 52 to 97 years old (median age, 82 years) with AF in combination with stage 3 and 4 CKD were included in the study. Each patient underwent a pharmacogenetic and pharmacokinetic study.Results. Cmin,ss and dose-adjusted concentration (Cmin,ss/D) of rivaroxaban were significantly higher in patients with the TT genotype than with the CT genotype of the polymorphic variant rs1045642 of the ABCB1 gene (Сmin,ss 60,5 [36,7;173] ng/ml and 54,8 [23,1;97,3] ng/ml, respectively, р=0,016; Сmin,ss/D 4,06[2,3;8,1] ng/ml/mg and 2,2 [1,1;4,9] ng/ml/mg, р=0,006). In patients with the T allele (CT and TT genotypes), compared with CC genotype carriers, Cmin,ss and Cmin,ss/D were significantly higher (Cmin,ss 60,5 [36,7;173] ng/ml and 45,8 [20,9;82,3] ng/ml, respectively, p=0,029; Cmin,ss/D 4,06 [2,3;8,1] ng/ml/ mg and 2,6 [1,2;4,8] ng/ml/mg, respectively, p=0,014). Also, Cmin,ss and Cmin,ss/D was significantly higher in patients with the TT genotype according to the polymorphic variant rs2032582 of the ABCB1 gene than in patients with the GG genotype (p=0,02 and р=0,016 respectively). Cmin,ss and Cmin,ss/D in T allele (GT and TT genotypes) carriers were significantly higher than in T allele homozygotes (Cmin,ss 57,1 [27,7;106,0] ng/ml versus 37,6 [18,6;61,7] ng/ml respectively, p=0,024; Cmin,ss/D 3,6 [1,7;7,4] ng/ml/mg versus 2,3 [1,1;4,09] ng/ml/mg respectively, p=0,032). Differences in Сmin,ss and Сmin,ss/D of rivaroxaban were detected when comparing TC, CC and TT genotypes of polymorphism rs1128503 of the ABCB1 gene. When comparing Сmin,ss and Сmin,ss/D of rivaroxaban among carriers of AG and GG genotypes of the rs776746 polymorphism of the CYP3A56986A>G gene, no significance was detected (p>0,05). Also, no difference in Cmin,ss and Cmin,ss/D was found when comparing carriers of the CC and CT genotypes of the rs35599367 polymorphism of the CYP3A4 gene, and carriers of the CC and AC genotypes of the rs890293 polymorphism of the CYP2J2 gene (p>0,05).Conclusion. The carriage of T allele by polymorphic variants rs1045642 and rs2032582 of the ABCB1 gene affects Cmin,ss and Cmin,ss/D of rivaroxaban.

Analysis of Student Conceptions and Conceptional Changes about Chemical Equilibrium Materials in Concentration Factors

Objective: This study aims to determine the conception and changes in the conception of the concentration factor in chemical equilibrium material. Method: The method used in this study is a mixed method, which is a combination of qualitative and quantitative methods, namely the Concurrent Embedded Strategy, which is a combination of qualitative methods and quantitative methods carried out at the same time. Results: The test instruments provided can reduce the misconceptions that exist in students when viewed from a comparison of the number of students who experience misconceptions from 13.33% in the first stage to 7.00% in the last stage. Students understand enough about chemical equilibrium shifts but still need clarification, especially in writing down changes in reaction equations when chemical equilibrium is disturbed and analyzing phenomena using metacognitive examples of a concept in their surroundings. Novelty: This research reveals that students' misconceptions can be reduced using worksheets with five processing stages. This novelty can provide (1) solutions related to identifying students' misconceptions and (2) reducing students' misconceptions regarding chemical equilibrium concentration factors.

Effect of solute concentration on microstructure evolution during static recrystallization in Mg-0.2%Ce alloy using cellular automata

A new cellular automata model has been developed to evaluate the effect of solute drag on the microstructure and texture evolution during static recrystallization of Mg and its alloys in the temperature range of 200 – 400 °C. In the present model, the site saturation nucleation was assumed and all the nuclei are present at the grain boundaries. The growth of each nucleus depends on the solute concentration and dislocation density difference between neighboring grains. The microstructural analysis of the newly developed cellular automata model showed the evolution of grain size at different temperatures compared to the equilibrium microstructure containing the equilibrium concentration of solute atoms at the grain boundaries. Further, the texture evolution showed that there is an increase in the texture strength with an increase in the annealing temperature when the solute concentration was lower than the equilibrium concentration at the boundaries, whereas the texture strength decreased with increasing the annealing temperature when the solute concentration was higher than the equilibrium solute concentration at the boundaries. The present model shows that solute drag pressure increased continuously with increasing the annealing temperature when the solute concentration was lower than the equilibrium concentration at the boundaries. However, the solute drag pressure decreased with an increase in the annealing temperature when the solute concentration was higher than the equilibrium solute concentration at the boundaries.

Impact of Ionic Strength and Charge Density on Donnan Potential in the NaCl-Cation Exchange Membrane System

This work aims to theoretically investigate the effect of both the fixed charge density of ion exchange membranes and the ionic strength of the treated aqueous NaCl solution on the generated Donnan potential at thermodynamic equilibrium conditions. The direct objective of our work is to calculate the equilibrium concentration of the Cl− co-ion inside a swelled cation-exchange membrane equilibrated with a water/NaCl system. Two activity coefficient models are employed, i.e., the Debye–Huckel (DH) model (as a reference model) and the Meissner model, which is known for its applicability in treating concentrated solutions. Experimental data available in the literature for Donnan potential are used to verify model predictions. Our study confirms that a high fixed charge density is required to counterbalance the deterioration in membrane selectivity encountered in high-salinity systems. The DH model can be safely used to predict the Donnan potential for feed compositions up to 0.1 M. At higher compositions, the DH model significantly overestimates the predicted (absolute) Donnan potential compared to the Meissner model. The osmotic pressure resulting from the difference in ionic concentration between the membrane phase and the feed phase is found to have insignificant effects on the Donnan potential. The equilibrium computations and methodology are presented in a general way that enables handling multivalent electrolyte systems such as CaCl2.

Evaluation and modeling of acrylonitrile migration from polypropylene for food packaging.

This study validated an analytical technique using headspace gas chromatography with flame ionization detection to quantify acrylonitrile monomer with a quantification limit of 0.10±0.04µg kg-1 . Subsequently, the acrylonitrile migration from polypropylene granules was evaluated in food simulants water and ethanol (50% v/v) and at two temperatures (20±1°C and 44±2°C) for up to 6weeks, representing the service time of a bottle. From the experimental data obtained, pseudo-second-order kinetics were adjusted to represent the acrylonitrile migration into the simulants. For water, equilibrium concentrations of 13.58 and 16.58µg kg-1 at 20 and 44°C, respectively, were obtained, while for 50% ethanol, 15.07 and 16.40µg kg-1 were obtained for the same temperatures. The experimental results and the values estimated from the migration kinetics indicate that the maximum acrylonitrile concentration will not exceed the tolerable specific limit established in regulations. PRACTICAL APPLICATION: The migration of compounds such as acrylonitrile can be a drawback resulting in an undesirable reduction in the shelf life of liquid foods packaged in bottles made of materials such as polypropylene. In this paper, acrylonitrile migration kinetics and a methodology are proposed to determine whether the tolerable migration limits are ever reached, which can serve as a tool for producers of this type of packaging of food to predict shelf life.

Evaluating the potential of wax impregnated reactive components for long-term acenaphthene removal

The catalytic oxidation of acenaphthene (ANA) was investigated using a controlled-release persulfate candle (PSC) and Fe(II) candle (Fe(II)C) to provide long-lasting oxidation conditions during groundwater remediation. To the best of our knowledge, this study is the first attempt to compare the pseudo-first-order rate constant (kobs) and % removal of ANA oxidation using PSC/Fe(II)C, PS solution (PSaq)/Fe(II) solution (Fe(II)aq), PSC/Fe(II)aq, and PSaq/Fe(II)C systems. The kobs and % removal of ANA in the PSC/Fe(II)C system exceeded those in the other systems. The optimal degradation conditions used were 0.1 mM ANA; 3.08 mM equilibrium concentration of PS (Ce,PS) released from PSC (controlled-release rate constant, kcr = 7.731 day−1); 5.673 mM equilibrium concentration of Fe(II) (Ce,Fe(II)) released from Fe(II)C (kcr = 3.796 day−1); unadjusted pH (~7.0); and 25 °C. Radical scavenger studies and electron spin resonance (ESR) spectra showed that sulfate (SO4•−) and hydroxyl (•OH) radicals were involved in the ANA oxidation, but •OH was the dominant radical species in the PSC/Fe(II)C system. Cl−, SO42−, and HCO3− acted as radical scavengers. The introduction of hydroxylamine (HA) into the PSC/Fe(II)C system resulted in a notable enhancement of ANA removal efficiency, increasing it from 51.8 % to 82.6 % within 10 min. Additionally, the PSC/Fe(II)C + HA system exhibited a higher Fe(II) consumption efficiency of 96.6 %, surpassing that of the PSC/Fe(II)aq + HA system, which registered an efficiency of 88.6 %. Intermediate byproducts after 24 h of reaction were detected as non-toxic byproducts by liquid chromatography-mass spectrometry (LC-MS). The PSC/Fe(II)C system would be beneficial for the remediation of polycyclic aromatic hydrocarbons in groundwater due to the continuous supply of Fe(II) and PS for a long time.

Microfluidic chip-based microbial metabolism-indexed BOD sensor for rapid determination of biochemical oxygen demand

Reliance on five-day biochemical oxygen demand (BOD5) as an indicator of water quality has inhibited the development of efficient process control due to the associated uncertainty and lag time. In the work, we proposed a novel strategy for rapid on-site BOD5 determination by a microfluidic chip-based microbial metabolism-indexed BOD sensor (MCB-MMI BOD sensor). The rapid on-site BOD5 detection was achieved by quantifying the equilibrium concentration of tryptophan involved in aerobic biodegradation for alternating the traditional 5-day monitoring of dissolved oxygen variation. The regulated metabolized tryptophan was identified by fluorescence spectrum and converted into BOD5 value. The prominent performance for MCB-MMI BOD sensor BOD5 determination was accessible in the field application, such as decreasing detection time from 5 days to 10 min, lowering sample volume from 250 mL to 2.5 mL, diminishing the working area, extending the detection range (without dilution) from 6 mg/L to 27 mg/L, featured with 83% accuracy, and free-labor automation, which exhibited the infinite potential for MCB-MMI BOD sensor on rapid on-site BOD5 monitoring. We believe the MCB-MMI BOD sensor would broaden its practical applications in BOD5-contained multiple-parameters water quality sensing, and would favorably supply a new tool for sewage-treatment process control, environmental monitoring, and aquaculture.

Chemical functionality of surfaces for the characteristic adsorption of melamine

The surface functionality leading to a high reversibility adsorption of melamine was determined. Four different silane coupling agents, namely, 3‐(tri‐methoxysilyl) propyl methacrylate (TMSPMA), n‐propyl tri‐methoxy‐silane (PTMS), 3‐(tri‐ethoxysilyl) propionitrile (TESPN), and tri‐methoxy‐(octadecyl) silane (OTMS) were taken for making chemical functionality methacrylate, short methyl, nitrile, and extended methyl group respectively. The adsorption behavior of melamine over the substrates with four functionalities was determined using quartz crystal microbalance (QCM). The adsorption kinetics and adsorption isotherms of the adsorption studies were analyzed. The initial adsorption rate depends on the hydrophobicity and roughness of the surfaces. However, the subsequent adsorption rate depends on the specific interaction. The data of equilibrium adsorbed mass at various equilibrium concentrations were fitted with the modified Brunauer–Emmett–Teller (BET) and Freundlich adsorption isotherms. The estimated model parameters were analyzed and compared with the reported parameters of the relevant systems. There is good agreement between our results and the reported results. In addition, very high adsorption with a very high binding constant was observed for the adsorption of melamine OTMS surface. On the other hand, high adsorption with an intermediate layer binding constant for the adsorption of melamine on the methacrylate surface was observed. Based on this, we propose using acrylate chemical functionality to develop molecularly imprinted polymer‐based melamine sensors.

Synthesis gas fermentation at high cell density: How pH and hydrogen partial pressure affect productivity and product ratio in continuous fermentation

For the first time, syngas fermentation was operated continuously with total cell retention and process pressures up to 4barg in long-term runs of up to 3000 hours. Throughout this time, the process was stable. The measured data have shown that hydrogen uptake and ethanol space-time yield are highest at a slightly reduced pH of 5.7 compared to pH5.9. Even lower pH values lead to higher acetic acid to ethanol product ratios, while C2space-time yields remain constant. Increasing the hydrogen partial pressure to 1.52bar resulted in a significant increase in hydrogen uptake rate and ethanol formation. An ethanol space-time yield of 10mmolL-1h-1 was short-term achieved, being the highest space-time yield measured to date for the wild type of C. ljungdahlii. Hydrogen uptake above a theoretical equilibrium concentration of 1.2mmolH2L-1 is significantly reduced, indicating an inhibition of an enzymatic reaction.

Study on adsorption of salicylic acid and sulfosalicylic acid by MOF–sodium alginate gel beads obtained in a green way

A composite (ZS–UiO–66–NH2) zirconium crosslinked sodium alginate gel beads (ZS)–metal–organic skeleton (UiO–66–NH2) were prepared in this study through in–situ growth under simple, green and mild conditions for removal of the salicylic acid (SA) and sulfosalicylic acid (SSA) from water. The physicochemical properties of ZS–UiO–66–NH2 were characterized using various analytical methods. The influencing factors in the adsorption process including pH of solution, amount of adsorbent, coexisting ions, adsorption time, reaction temperature and equilibrium concentration of SA/SSA were performed in batch adsorption. The experimental results indicated that ZS–UiO–66–NH2 had high stability and could achieve efficient adsorption of SA/SSA in broad pH range (2–9) and salinity (0–0.2 mol·L−1). SA and SSA adsorbed on the composite at 293 K reached high values of 193 and 167 mg·g−1 from Langmuir model, respectively. Kinetic and isotherm studies demonstrated that the adsorption processes were mainly multilayer heterogeneous chemisorption. Thermodynamic data manifested that the two processes were exothermic and spontaneous with increasing entropy. ZS–UiO–66–NH2 can effectively remove SA/SSA from simulated wastewater under different pH and can be reused after elution with a NaHCO3 solution (5 mmol·L−1). The ZS–UiO–66–NH2 composite has great potential for removing SA/SSA from actual water bodies.