Constant Kn Research Articles

Insights into iron-induced structural changes in N-rich biochar for facilitating efficient organic pollutants removal by peroxymonosulfate activation: Cooperation of enrichment and degradation

Naturally nitrogen in waste biomass can be turned into a valuable “treasure”. This work utilized soybean dregs as precursor, successfully fabricated iron-modified N-rich biochar (denoted as Fen-BDBC) catalysts via a green molten salt (KCl/NaCl) method. The physical and chemical changes of biochar substrate after iron modification were explored, combined Fenton-like reactions to establish structure–activity relationship between active sites and organic pollutants degradation. With iron induction, the hybrid structures of biochar could be transformed from sp3 to sp2 more easily, which enhanced its hydrophobicity and promoted interfacial electron-transfer efficiency. Pyridinic N and pyrrolic N structures were protected by the formation of Fe-N, which could participate in the formation of singlet oxygen (1O2) and catalyst-PMS*. Fe0.1-BDBC/peroxymonosulfate (PMS) system achieved 100 % nonradical bisphenol A (BPA) removal by cooperation of surface-confined enrichment and degradation. The contributions of electron-transfer processes (ETP), 1O2, and Fe(IV)=O were 58.3 %, 29.3 %, and 12.4 %, respectively. C=O/O-C=O, pyrrolic N, and Fe-N promoted 1O2 formation, C=C enhanced ETP, while pyridinic N played a dual role. The normalized apparent rate constant (kN, min−1 × 10−3) was calculated to be 31.96, which was superior among biochar-derived catalysts. Fe0.1-BDBC was loaded onto PVDF membrane for continuous and efficient degradation of BPA (nearly 100 % during 36 h operation). This work provided new insights for effective regulation of biochar-based catalysts.

Optimization and control of gaseous nitriding of a 33CrMoV12-9 steel

Abstract This work propose a new experimental methodology to optimize the gaseous nitriding process of 33CrMoV12-9 steel grade, widely used in the mechanical industry for the fabrication of gears, pinions, and bearings. Several nitriding experiments were conducted at a temperature of 520 °C in the interval between 4 and 55 h using both constant and variable nitriding potential K N . The obtained results allowed us to determine the optimal conditions and to propose a sequenced cycle consisting of three steps. Multiple characterizations using X-ray diffraction (XRD), optical microscopy (OM), Vickers microhardness testing (HV), and electron probe microanalysis (EPMA) indicate a surface hardness of 810 HV0.5, nitrogen diffusion depth of approximately 0.7 mm. finally, a metallurgical structure devoid of complex networks of nitrides and carbonitrides. The validation results confirmed the effectiveness of the proposed methodology, thereby paving the way for improving the nitriding process in the mechanical industry. This work represents a significant contribution to the optimization of thermochemical treatments for materials used in demanding environments.

Development of highly sensitive dual-enhanced fluorescence quenching immunochromatographic test strips based on Pt nanoprobes

The fluorescence-quenching method is crucial in vitro analysis, particularly for immunochromatographic test strips (ICTs) using noble metal nanoparticles as probes. However, ICTs still fall short in meeting the requirements for the detection of traces biomarkers due to the noble metal nanoparticles can only quench fluorescence of the dyes within a confined distance. Interestingly, noble metal nanoparticles, such as Pt NPs cannot only perform fluorescence-quenching ability based on the Förster resonance energy transfer (FRET), but also show perfect oxidase-like catalytic performance on many kinds of substrates, such as 3,3’,5,5’ -tetramethylbenzidine (TMB). We observed that the oxTMB (the oxidation products of TMB) exhibited notable effectiveness in quenching Cy5 fluorescence by the strong inner filter effect (IFE), which obviously improved the fluorescence-quenching efficiency with extremely low background signal. Through the dual-enhanced fluorescence quenching mechanism, the fluorescence quenching constant (Kn) was 661.24-fold that of only Pt NPs on the NC membrane. To validate the feasibility of this technique, we employed two types of biomarkers, namely microRNA (miR-15a-5p) and the signature protein (PSA). The sensitivity of miR-15a-5p was 9.286 × 10−18 mol/L and 17.5-fold more than that based on Pt NPs. As for the PSA, the LOD (0.6265 pg/mL) was 15.5-fold enhancement more sensitive after catalysis. Overall, the dual-enhanced fluorescence quenching rFICTs could act as a practical detection for biomarker in real samples.

Leaching behaviors of dissolved organic matter from face masks revealed by fluorescence EEM combined with FRI and PARAFAC

Despite numerous studies investigating the occurrence and fate of microplastics, no effort has been devoted toward exploring the characteristics of dissolved organic matter (DOM) leached from face masks mainly made of plastics and additives used in large quantities during the COVID-19 pandemic. By using FTIR, UV–vis, fluorescence EEM coupling with FRI and PARAFAC, and kinetic models of leaching experiments, we explored the leaching behaviors of face mask-derived DOM (FM-DOM) from commonly used face masks including N95, KN95, medical surgical masks, etc. The concentration of FM-DOM increased quickly at early 0–48 h and reached equilibrium at about 48 h measured in terms of dissolved organic carbon and fluorescence intensity. The protein-like materials ranged from 80.32 % to 89.40 % of percentage fluorescence response (Pi,n) were dominant in four types of FM-DOM analyzed by fluorescence EEM-FRI during the leaching experiments from 1 to 360 h. Four fluorescent components were identified, which included tryptophan-like components, tyrosine-like components, microbial protein-like components, and fulvic-like components with fluorescence EEM-PARAFAC models. The multi-order kinetic model (Radj2 0.975–0.999) fitted better than the zero-order and first-order kinetic model (Radj2 0.936–0.982) for all PARAFAC components of FM-DOM based on equations derived by pseudo kinetic models. The leaching rate constants (kn) ranged from 0.058 to 30.938 and the half-life times (T1/2) ranged from 2.73 to 24.87 h for four FM-DOM samples, following the solubility order of fulvic-like components (C4) > microbial protein-like components (C3) > tryptophan-like components (C1) > tyrosine-like components (C2) for FM-DOM from four types of face masks during the leaching experiment from 0 to 360 h. These novel findings will contribute to the understanding of the underappreciated environment impact of face masks in aquatic ecosystems.

Adaptive coordination control strategy of renewable energy sources, hydrogen production unit, and fuel cell for frequency regulation of a hybrid distributed power system

Owing to the significant number of hybrid generation systems (HGSs) containing various energy sources, coordination between these sources plays a vital role in preserving frequency stability. In this paper, an adaptive coordination control strategy for renewable energy sources (RESs), an aqua electrolyzer (AE) for hydrogen production, and a fuel cell (FC)-based energy storage system (ESS) is proposed to enhance the frequency stability of an HGS. In the proposed system, the excess energy from RESs is used to power electrolysis via an AE for hydrogen energy storage in FCs. The proposed method is based on a proportional-integral (PI) controller, which is optimally designed using a grey wolf optimization (GWO) algorithm to estimate the surplus energy from RESs (i.e., a proportion of total power generation of RESs: Kn). The studied HGS contains various types of generation systems including a diesel generator, wind turbines, photovoltaic (PV) systems, AE with FCs, and ESSs (e.g., battery and flywheel). The proposed method varies Kn with varying frequency deviation values to obtain the best benefits from RESs, while damping the frequency fluctuations. The proposed method is validated by considering different loading conditions and comparing with other existing studies that consider Kn as a constant value. The simulation results demonstrate that the proposed method, which changes Kn value and subsequently stores the power extracted from the RESs in hydrogen energy storage according to frequency deviation changes, performs better than those that use constant Kn. The statistical analysis for frequency deviation of HGS with the proposed method has the best values and achieves large improvements for minimum, maximum, difference between maximum and minimum, mean, and standard deviation compared to the existing method.

Catalytic oxidation of acetaminophen through pristine and surface-modified nitrogen-doped carbon-nanotube-catalyzed peroxydisulfate activation

Carbon nanotube (CNT) surfaces with different oxygen contents have been fabricated through an N-doping/chemical oxidation to investigate the relationship between structural features (defects and nitrogen and oxygen contents) and catalytic degradation of acetaminophen (AAP) via potassium peroxydisulfate (PDS) activation. Scavenging experiments and EPR analysis indicated that PDS activation was initiated by radical (•OH, SO4• , and O2• ) and non-radical (1O2, surface-bound radicals and free electrons) mechanisms for AAP degradation. The surface-area-normalized AAP degradation rate constant (kN) at 0.6 mM PDS increased from 0.30 × 10−2 m−2 s−1 for pristine CNT to 0.82 × 10−2 m−2 s−1 for Ox-NCNT. The kN was well-correlated with defects (ID/IG), the fraction of N + O (hybrid sp3/sp2 configuration), and oxygen groups (C-OH, CO and COOH). Correlation analysis indicates that the electron-donating C-OH group dominantly governs the PDS activation and AAP oxidation. Similarly, among N-groups, a good correlation between kN and graphitic N also substantiates the idea that substitutional N plays on key active sites for PDS activation rather than boundary Ns (pyridinic N and pyrrolic N). The above findings were also validated through the quantitative relationship between PDS adsorption ability (QPDS) and structural features of the catalyst (defects, N + O fractions, graphitic N and oxygen groups). Pyridinic N and pyrrolic N exhibited a weak linear relationship with QPDS as well as kN, indicating that the PDS adsorption and AAP oxidation is not directly controlled by these boundary N-groups.

Penerapan Peta Kendali Neutrosophic Exponentially Weighted Moving Average (NEWMA) X dalam Monitoring Rata-Rata Proses Ketebalan Kaca

In the industrial sector, the measurement results of a quality characteristic often involve an uncertainty interval (interval indeterminacy). This causes the classical control chart to be less suitable for monitoring quality. Currently, a control chart with a neutrosophic approach has been developed. The neutrosophic control chart was developed based on the concept of neutrosophic numbers with control charts. One of the control charts that have been developed to monitor the mean process is the Neutrosophic Exponentially Weighted Moving Average (NEWMA) X control chart. This control chart is a combination of neutrosophic with classical EWMA control chart. The neutrosophic control chart consists of two control charts, namely lower and upper, each of which consists of upper and lower control limits. Therefore, NEWMA X is more sensitive to detect out-of-control observations. In this research, the NEWMA X control chart will be used to monitor the average process of the thickness of the panasap dark grey 5mm glass produced by a glass industry. Through the analysis in this research, it was found that by using weighting λN [0, 10; 0, 10] and constant value kN [2, 565; 2, 675], the average process of the thickness of panasap dark grey 5mm glass has not beet controlled statistically because 21 observations were identified that were outside the control limits (out of control). When compared with the classical EWMA control chart with the same weighting λ, 17 observations were detected out of control. This proves that the NEWMA X control chart is more sensitive in detecting observations that are out of control because the determination of the in-control state is based on two values, lower and upper, both at the lower and upper control limits.

Sorption of cationic dyes from aqueous solutions by moss Rhytidiadelphus squarrosus: Kinetics and equilibrium studies

With the aim to investigate sorption properties of natural sorbent prepared from moss Rhytidiadelphus squarrosus we elucidated biosorption of cationic dyes Malachite green (BG4), Auramine O (BY2) and Thioflavine T (BY1) from aqueous solutions. The removal of dyes by moss biosorbent was found to be rapid at an initial stage and the equilibrium was reached within 1-2 hours. The pseudo-n-order kinetic model was successfully applied to the kinetic data and the order of adsorption reaction was calculated in the range from 1.7 to 2.6. The value of rate constant kn' ranged from 0.001 to 0.039 [min-1]/[μmol/g]1-n. The equilibrium data were fitted to the adsorption isotherms. The Freundlich isotherm was found to represent the measured sorption data of BG4, BY1 and BY2 well. The maximum sorption capacities of moss biomass from single dye solutions calculated by Langmuir equation were 354 μmol/g for BG4, 310 μmol/g for BY1 and 382 μmol/g for BY2. These results showed that the prepared biomass presents low-cost, natural and easy available sorbent which may be potentially used for removal of dyes from environment and also may be an alternative to more costly materials such as activated carbon.

In-situ preparation and performance of cold resistant K2O·5SiO2 based anti-fire glass

We describe a method for the synthesis of cold resistant K2O·5SiO2 based anti-fire material using a new high content and low viscosity SiO2 core–shell emulsion (HSLVCS SiO2 emulsion). The anti-fire glass which wasn’t frozen at −71 ± 1 °C was prepared by the in-situ reaction. The onion-shaped core–shell structure was clearly shown in scanning electron microscopy (SEM) micrographs, the viscosity of HSLVCS SiO2 emulsion (50 wt%) was 431.4 ± 12.1 mPa·s(48 rpm). Its in-situ reaction process for preparation of the K2O·5SiO2 followed a first-order reaction, the reaction rate constant kn = 1.774 × 108 exp (−Ea/RT) with the apparent activation energy Ea = 79.80 kJ/mol. The low-temperature-withstanding capability was tested at extreme-cold environment (−71 ± 1 °C), and the reasons for this were found by the thermogravimetric analysis (TG). The weather resistance capacity was more than 1000 h through ultraviolet (UV) test and the sponge-like microporous insulation layer can increase the fire insulation time by the fire-resistant test. This work provided a new routine toward the synthesis of the high quality anti-fire glass with various shapes, including curved surface structures.

Effect of medium on reactivity for alkaline hydrolysis of p-nitrophenyl acetate and S-p-nitrophenyl thioacetate in DMSO–H2O mixtures of varying compositions: ground state and transition state contributions

Second-order rate constants (kN) for reactions of p-nitrophenyl acetate (1) and S-p-nitrophenyl thioacetate (2) with OH– have been measured spectrophotometrically in DMSO–H2O mixtures of varying compositions at 25.0 ± 0.1 °C. The kN value increases from 11.6 to 32 800 M–1 s–1 for the reactions of 1 and from 5.90 to 190 000 M–1 s–1 for those of 2 as the reaction medium changes from H2O to 80 mol % DMSO, indicating that the effect of medium on reactivity is more remarkable for the reactions of 2 than for those of 1. Although 2 possesses a better leaving group than 1, the former is less reactive than the latter by a factor of 2 in H2O. This implies that expulsion of the leaving group is not advanced in the rate-determining transition state, i.e., the reactions of 1 and 2 with OH– proceed through a stepwise mechanism, in which expulsion of the leaving group from the addition intermediate occurs after the rate-determining step. Addition of DMSO to H2O would destabilize OH– through electronic repulsion between the anion and the negative-dipole end in DMSO. However, destabilization of OH– in the ground state is not solely responsible for the remarkably enhanced reactivity upon addition of DMSO to the medium. The effect of medium on reactivity has been dissected into the ground state and transition state contributions through combination of the kinetic data with the transfer enthalpies (ΔΔHtr) from H2O to DMSO–H2O mixtures for OH– ion.

A Stochastic Model for Adsorption Kinetics

A novel stochastic model is proposed to characterize the adsorption kinetics of pollutants including dyes (direct red 80 and direct blue 1), fluoride ions, and cadmium ions removed by calcium pectinate (Pec-Ca), aluminum xanthanate (Xant-Al), and reed leaves, respectively. The model is based on a transformation over time following the Ornstein–Uhlenbeck stochastic process, which explicitly includes the uncertainty involved in the adsorption process. The model includes stochastic versions of the pseudo-first-order (PFO), pseudo-second-order (PSO), and pseudo-[Formula: see text]-order (PNO) models. It also allows the estimation of the adsorption parameters, including the maximum removal capacity ([Formula: see text]), the adsorption rate constant ([Formula: see text]), the reaction pseudoorder ([Formula: see text]), and the variability [Formula: see text]. The model fitted produced [Formula: see text] values similar to those of the nonstochastic versions of the PFO, PSO, and PNO models; however, the obtained values for each parameter indicate that the stochastic model better reproduces the experimental data. The [Formula: see text] values of the Pec-Ca-dye, Xant-Al-fluoride, and reed leaf-Cd+2 systems ranged from 2.0 to 9.7, 0.41 to 1.9, and 0.04 and 0.29 mg/g, respectively, whereas the values of [Formula: see text] ranged from 0.051 to 0.286, 0.743 to 75.73, and 0.756 to 8.861 (mg/g)1- n/min, respectively. These results suggest a variability in the parameters [Formula: see text] and [Formula: see text] inherent to the natures of the adsorbate and adsorbent. The obtained [Formula: see text] values ranged from 1.13 to 2.02 for the Pec-Ca-dye system, 1.0–3.5 for the Xant-Al-fluoride system, and 1.8–3.8 for the reed leaf-Cd+2 system. These ranges indicate the flexibility of the stochastic model to obtain fractional [Formula: see text] values, resulting in high [Formula: see text] values. The variability in each system was evaluated based on [Formula: see text]. The developed model is the first to describe pollutant removal kinetics based on a stochastic differential equation.

Evaluation of thermodynamic parameters via reaction stoichiometry and the corrected Langmuir parameter for sorption of Cu(II) on chitosan and chitosan blended PVA films

Natural Chitosan (C) and Chitosan blended with Poly vinyl Alcohol (PVA) C + P film was prepared by solution casting method for the sorption of Cu(II) from aqueous solution. The FTIR studies revealed that the amino group of chitosan played key roles in the copper uptake and FE-SEM and EDAX studies confirmed the formation of Cu-amino complex in 1:1 ratio of metal to ligand. The prime objective of present studies is the evaluation of thermodynamic parameters (ΔG0, ΔH0 and ΔS0) via reaction stoichiometry and the corrected Langmuir parameter for sorption of Cu(II) on chitosan (C) and (C + P) films. The surface morphology, stability and Cu(II) adsorption efficiency of the films were investigated. The C + P film showed enhanced chemical and mechanical endurance over the C film. The batch adsorption studies exhibited that the adsorption capacity of both the films was pH dependant and the maximum adsorption obtained was 55.56 mg g−1 for C film and 35.71 mg g−1 for C + P film at pH 5.5. The adsorption process was described by Langmuir adsorption model and was found to follow pseudo first order kinetics. The Gibbs free energies calculated using the formation constant Kn and the corrected dimensionless Langmuir constant KL(C) were in good agreement with each other thereby confirming the formation of pendant complex [Cu-NH2]2+. The C + P film could be reused till 5 desorption cycles using EDTA as the desorbing agent and could recover around 169.16 mg of Cu(II) per g of the material.

A coupled RTD and mixed-order kinetic model to predict high rate algal pond wastewater treatment under different operational conditions: Performance assessment and sizing application

A coupled residence time distribution (RTD) and mixed-order model was developed to simulate the performance of a pilot high rate algal pond (HRAP) for wastewater treatment under different operational conditions requiring simple influent and effluent wastewater characteristics as input data. The model showed potential in general assessment of the HRAP system performance, successfully capturing the magnitude as well as general trend of COD, TKN, TN and TP concentrations with acceptable accuracy (Nash-Sutcliffe Efficiency (NSE) value up to 0.99). However, due to the common limitation of black box model type, the detailed agreement between model and experimental data was highly varied, sometime unsatisfactory performance (NSE < 0) was obtained, especially for highly complex processes like TKN or TN removal. Besides, general information on the dynamics of algal bacterial processes under different operational conditions could be revealed by analyzing calibrated reaction order n and reaction rate constant kn values with higher n value corresponding to higher complexity of the process and higher kn values associating with higher removal rate. Moreover, the model could also be used as a quick and convenient support for HRAP design and construction by providing estimated hydraulic retention time (HRT) values required for single HRAP system treating wastewater in different case studies. Further validation with outdoor HRAP system is necessary to increase the accuracy of the model prediction.

Delay-Optimal Policies in Partial Fork-Join Systems with Redundancy and Random Slowdowns

We consider a large distributed service system consisting of n homogeneous servers with infinite capacity FIFO queues. Jobs arrive as a Poisson process of rate λn/kn (for some positive constant kn and integer kn). Each incoming job consists of ???? identical tasks that can be executed in parallel, and that can be encoded into at least ???? ?replicas" of the same size (by introducing redundancy) so that the job is considered to be completed when any kn replicas associated with it finish their service. Moreover, we assume that servers can experience random slowdowns in their processing rate so that the service time of a replica is the product of its size and a random slowdown. First, we assume that the server slowdowns are shifted exponential and independent of the replica sizes. In this setting we show that the delay of a typical job is asymptotically minimized (as n - ∞) when the number of replicas per task is a constant that only depends on the arrival rate λ, and on the expected slowdown of servers. Second, we introduce a new model for the server slowdowns in which larger tasks experience less variable slowdowns than smaller tasks. In this setting we show that, under the class of policies where all replicas start their service at the same time, the delay of a typical job is asymptotically minimized (as n - ∞) when the number of replicas per task is made to depend on the actual size of the tasks being replicated, with smaller tasks being replicated more than larger tasks.

Kinetic study of the transesterification reaction by artificial neural networks and parametric particle swarm optimization

In this work, the mechanism of soybean oil transesterification reaction was investigated by Particle Swarm Optimization (PSO), and the reaction progress was monitored by Artificial Neural Networks (ANN) using Self-Organizing Maps (SOM). The PSO was used to adjust the values of the reaction rate constants (kn) in the four proposed mechanisms/models approaches. The mean error values obtained by the PSO method showed a good agreement between the experimental and simulated data for all evaluated approaches, ranging from 4.3 to 8.5%. The results suggest that under the evaluated conditions reverse reactions may be disregarded, following a second-order kinetic model for the three stepwise reactions. The SOM proved to be an efficient tool for exploring data obtained during the transesterification process, allowed to organize the data in the form of clusters presenting in the weight maps the relationship between the monitored variables during the progress of the transesterification reaction. The PSO and ANN type SOM has been shown efficient tools for investigating the kinetics of the transesterification reaction, and they offer good perspectives for further kinetic studies of other types of industrial processes.

Amino-Fe3O4-functionalized multi-layered graphene oxide as an ecofriendly and highly effective nanoscavenger of the reactive drimaren red

Amino-functionalized multilayer graphene oxide (Am-nGO) has been synthesized and applied to remove the reactive drimaren red (DR) from aqueous solutions. Infrared spectroscopy evidenced amine and amide presence by peaks at 1579cm-1 and a band between 3300 and 3500cm-1. Raman spectroscopy showed an increment in ID/IG ratio after amino-Fe3O4-functionalization of nGO from 1.05 to 1.20, referent to an increase in sp3 domain disorder. The isoelectric point of Am-nGO was pH 8.1. From kinetic study, the equilibrium was achieved within 90min; moreover, pseudo-n-order model satisfactorily fitted to the experimental data. Kinetic constant (kn) was 0.71mg1-ng1-nmin-1 and modeled equilibrium sorption capacity (qe) 219.17mgg-1. Equilibrium experiments showed monolayer adsorption capacity (qm) of 219.75mgg-1, and BET model best fitted to the equilibrium data, indicating that the adsorption process happened with multiple layers formation. From sorption thermodynamics, the standard free energy of Gibbs and enthalpy were respectively - 31.91kJmol-1 (at 298K) and 66.43kJmol-1. Such data evidence the spontaneous and chemical behavior of DR adsorption as a consequence of strong electron donor-receptor interactions between the dye and the nanosorbent. By phytotoxicity assessment, Am-nGO showed inexpressive inhibitory potential to American lettuce seeds in comparison with its precursor nGO and graphite nanoplatelets.

Simulated photo-degradation of dissolved organic matter in lakes revealed by three-dimensional excitation-emission matrix with regional integration and parallel factor analysis

Simulated photo-degradation of fluorescent dissolved organic matter (FDOM) in Lake Baihua (BH) and Lake Hongfeng (HF) was investigated with three-dimensional excitation-emission matrix (3DEEM) fluorescence combined with the fluorescence regional integration (FRI), parallel factor (PARAFAC) analysis, and multi-order kinetic models. In the FRI analysis, fulvic-like and humic-like materials were the main constituents for both BH-FDOM and HF-FDOM. Four individual components were identified by use of PARAFAC analysis as humic-like components (C1), fulvic-like components (C2), protein-like components (C3) and unidentified components (C4). The maximum 3DEEM fluorescence intensity of PARAFAC components C1–C3 decreased by about 60%, 70% and 90%, respectively after photo-degradation. The multi-order kinetic model was acceptable to represent the photo-degradation of FDOM with correlation coefficient (Radj2) (0.963–0.998). The photo-degradation rate constants (kn) showed differences of three orders of magnitude, from 1.09 × 10−6 to 4.02 × 10−4 min−1, and half-life of multi-order model ( T1/2n) ranged from 5.26 to 64.01 min. The decreased values of fluorescence index (FI) and biogenic index (BI), the fact that of percent fluorescence response parameter of Region I (PI,n) showed the greatest change ratio, followed by percent fluorescence response parameter of Region II (PII,n), while the largest decrease ratio was found for C3 components, and the lowest T1/2n was observed for C3, indicated preferential degradation of protein-like materials/components derived from biological sources during photo-degradation. This research on the degradation of FDOM by 3DEEM/FRI-PARAFAC would be beneficial to understanding the photo-degradation of FDOM in natural environments and accurately predicting the environmental behaviors of contaminants in the presence of FDOM.

Thermal Activity in Affinity Separation Techniques Such as Liquid-Liquid Extraction Analyzed by Isothermal Titration Calorimetry and Accuracy Analysis of the Technique in the Molar Concentration Domain.

The applicability and accuracy of isothermal titration calorimetry (ITC) to investigate intermolecular interactions in a high concentration domain applicable to liquid–liquid extraction (LLX) was studied for acid–base interactions. More accurate fits can be obtained using a sequential binding mechanism compared to a single reaction model, at the risk of finding a local minimum. Experiments with 0.24 M tri-n-octylamine (TOA) resulted in a residue of fit of 4.3% for the single reaction model, with a standard deviation σ of 1.6% in the stoichiometry parameter n, 12% in the complexation constant Kn,1, and 2.5% in the enthalpy ΔHn,1. For the sequential model, σ was higher: 11% in K1,1, 26% in Kn+1,1, and 12% in ΔHn+1,1. This study clearly showed that, at higher concentrations (order of moles per liter), accurate parameter estimation is possible and parameter values are concentration dependent. It is thus important to do ITC at the application concentration.

The effect of microwave on the crystallization process of magnesium carbonate from aqueous solutions

The effect of microwave on reactive crystallization is investigated with magnesium carbonate as the working substance. In the experiments, magnesium carbonate is precipitated by mixing aqueous magnesium sulfate and sodium carbonate solutions in a MSMPR crystallizer located in a microwave reactor. A population balance model along with crystallization kinetics is formulated to assess the influence of microwave energy input on nucleation, growth, agglomeration and breakage during crystallization process. A general high order moment method of classes (HMMC) framework is applied to solve the model numerically. The results show that crystallization kinetics parameters, including the nucleation rate constant (kn), the growth rate constant (kg), the exponent of growth rate (g) and the collision efficiency (Ψag) change significantly due to mass transfer enhancement in microwave field. Meanwhile, the exponent of nucleation (n) and the breakage rate constant (kbr) remain constant or only change slightly. It is further discovered that the crystal suspension attenuates the microwave effect during crystallization process.

Kinetic Study on Nucleophilic Substitution Reactions of O‐Phenyl O‐Y‐substituted‐Phenyl Thionocarbonates with 1,8‐Diazabicyclo[5.4.0]undec‐7‐ene in Acetonitrile

Second‐order rate constants (kN) for nucleophilic substitution reactions of O‐phenyl O‐Y‐substituted‐phenyl thionocarbonates (4a–4k) with 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) in MeCN at 25.0 ± 0.1°C are reported. The reactivity of 4a–4k decreases as basicity of the leaving group increases except O‐2,4‐dinitrophenyl O‐phenyl thionocarbonate (4a), which is less reactive than O‐3,4‐dinitrophenyl O‐phenyl thionocarbonate (4b) although the former possesses 2 pKa units less basic nucleofuge than the latter. The Brønsted‐type plot for the reactions of 4b–4k is linear with βlg = −0.50, a typical βlg value for reactions reported to proceed through a concerted mechanism. The Hammett plot correlated with σY− constants for the reactions of 4b–4k results in a better linear correlation than that correlated with σYo constants. Besides, the Yukawa‐Tsuno plot exhibits an excellent linear correlation with ρY = 2.12, r = 0.68 and R2 = 0.990, indicating that a negative charge develops partially on the O atom of the leaving group in the rate‐determining step (RDS). Thus, the reactions have been concluded to proceed through a forced concerted mechanism. Effects of steric hindrance on reactivity and reaction mechanism are also discussed in detail.