Empirical Kinetic Model Research Articles

Preparation of SnO2‐Based Composite Gas‐Sensitive Material and Its Effect on the Membrane Treatment Process of Volatile Organic Compounds

Semiconductor oxide‐sensitive materials can be divided into n‐type materials and p‐type materials according to this characteristic. The carriers in n‐type materials are mainly electrons, which are formed by the existence of a large number of oxygen vacancies in the material’s crystal lattice. Common n‐type materials include SnO2, In2O3, and ZnO. This article is aimed at studying the effect of SnO2‐based composite gas‐sensitive materials on the treatment process of volatile organic compounds. In this paper, the biomembrane method, the ultrafiltration membrane transmembrane pressure difference method, and the chemical reaction activity analysis method in the membrane treatment detection method are proposed, and then, the empirical kinetic model for the preparation of SnO2‐based composite gas‐sensitive materials is established, and the TPU nanometer is analyzed. The cross‐sectional scanning of the composite material explored the effect of the curing agent content on the SnO2‐based composite gas‐sensitive material and analyzed the mechanical properties of the material. The experiment in this article uses 15 orders of magnitude of mechanics, which improves the scientific nature of the article. The experimental results show that the material modification has a better improvement effect on the film treatment process of volatile organic compounds.

Measurement report: High contributions of halocarbon and aromatic compounds to atmospheric volatile organic compounds in an industrial area

Abstract. Volatile organic compounds (VOCs) are key components of tropospheric chemistry. We investigated ambient VOCs in an industrial area in Nanjing, China, between July 2018 and May 2020. The sum of the suite of measured total VOC (TVOC) concentrations was 59.8 ± 28.6 ppbv (part per billion by volume) during the investigation period. About twice the TVOC concentrations were observed in the autumn (83 ± 20 ppbv) and winter (77.5 ± 16.8 ppbv) seasons compared to those in spring (39.6 ± 13.1 ppbv) and summer (38.8 ± 10.2 ppbv). In previous studies in Nanjing, oxygenated VOCs (OVOCs) and halocarbons were not measured, and the current TVOC concentration without halocarbons and OVOCs was similar to the previous investigation in the same study area. However, it was twofold higher than the one reported in the nonindustrial suburban area of Nanjing. Due to the industrial influence, the halocarbons VOC group (14.3 ± 7.3 ppbv, 24 %) was the second-largest contributor to the TVOCs after alkanes (21 ± 7 ppbv, 35 %), which is in contrast with the previous studies in Nanjing and also in almost all other regions in China. Relatively high proportions of halocarbons and aromatics were observed in autumn (25.7 % and 19.3 %, respectively) and winter (25.8 % and 17.6 %, respectively) compared to those in summer (20.4 % and 11.8 %, respectively) and spring (20.3 % and 13.6 %, respectively). According to the potential source contribution function (PSCF), short-distance transport from the surrounding industrial areas and cities was the main reason for the high VOC concentrations in the study area. According to positive matrix factorization (PMF) model results, vehicle-related emissions (33 %–48 %) contributed to the major portion of the ambient VOC concentrations. Aromatics, followed by alkenes, were the top contributors to the loss rate of OH radicals (LOH; 37 % and 32 %, respectively). According to the empirical kinetic modelling approach (EKMA) and relative incremental reactivity (RIR) analysis, the study area was in the VOC-sensitive regime for ozone (O3) formation during all measurement seasons. Therefore, alkenes and aromatics emissions from automobiles need to be decreased to reduce secondary air pollution formation in the study area.

Ozone control strategies for local formation- and regional transport-dominant scenarios in a manufacturing city in southern China

Given the leveling off of fine particulate matter (PM2.5), ground-level ozone (O3) pollution has become one of the most significant atmospheric pollution issues in the Pearl River Delta (PRD) region in China, especially in the manufacturing city of Dongguan, which faces more severe O3 pollution. The development of strategies to control O3 precursor emissions, including volatile organic compounds (VOCs) and nitrogen oxide (NOx), depends to a large extent on the source region of the O3 pollution. In this study, by combining the Weather Research and Forecasting model coupled with chemistry (WRF-Chem), the Empirical Kinetic Modeling Approach (EKMA), and the Flexible Particle model (FLEXPART), more effective strategies of controlling O3 precursor emissions were identified under two typical types of O3 pollution episodes: local formation (LF)-dominant (8–12 September 2019) and regional transport (RT)-dominant (23–27 October 2017) episodes, distinguished by the WRF-FLEXPART model. During the LF-dominant episode, the EKMA revealed that the O3 formation in Dongguan was in a transitional regime, and the abatement of solvent use-VOCs emissions in the key area of Dongguan was more effective in reducing O3 levels, with an emission reduction benefit 1.7 times that of total VOCs emission sources throughout Dongguan. With respect to the RT-dominant episode, the reduction in VOCs emissions in the local region did not effectively curb O3 pollution, although the photochemical regime of the O3 formation in Dongguan was VOCs-limited. A 50% reduction in NOx emissions in the upwind regions (parts of Guangzhou and Huizhou) effectively decreased the O3 concentration in Dongguan by 17%. The results of this study emphasize the importance of the source region of O3 pollution in the implementation of effective O3 control strategies and provide valuable insights for region-specific precursor emission policy formulation, not only in Dongguan, but also in other regions facing severe O3 pollution.

Unveiling the dipole synergic effect of biogenic and anthropogenic emissions on ozone concentrations

Biogenic emissions are widely known as important precursors of ozone, yet there is potentially a strong interaction and synergy between biogenic and anthropogenic emissions, including volatile organic compounds (VOCs) and nitrogen oxides (NOx), in modulating ozone formation. To a large extent, the synergy affects the effectiveness of anthropogenic emission control, thereby reshaping the O3-NOx-VOC empirical kinetic modeling approach (EKMA) diagram. Focusing on the ozone pollution period of June 2017 in the North China Plain, we design almost 500 numerical experiments using regional air quality model Community Multiscale Air Quality (CMAQ) that revealed an interesting synergic effect, defined as the contribution of biogenic emissions to ozone concentrations concomitant with a reduction in anthropogenic emissions. A quasi-EKMA diagram is constructed to delineate the contribution of biogenic emissions to ozone concentrations, indicative of a linearly amplified or nonlinearly weakened result associated with reductions in anthropogenic VOCs or NOx emissions, respectively, illustrating the dipole characteristics of the synergic effect. The reduced ozone contribution from biogenic emissions along with NOx emission reduction can be used to represent controllable biogenically induced ozone (BIO). Both the amplified and controllable BIO are tightly linked to both local emissions and regional transport, implicative of an essential role in joint regional emission control. In regard to ozone exceedance, the role of biogenic emissions may be even more important, in that its contribution is comparable to or even larger than that of anthropogenic emissions when associated with a reduction in anthropogenic emissions, which is clearly demonstrated based on the near carbon neutrality scenario shared socioeconomic pathway (SSP) 126. Meanwhile, the biogenic emissions may steer the modulation of anthropogenic emissions in the change rate of MDA8 ozone concentration. Therefore, the synergic effect of biogenic and anthropogenic emissions elucidated in this study should be carefully considered in future ozone pollution control.

Catalytic ozonation of chloramphenicol with manganese-copper oxides/maghemite in solution: Empirical kinetics model, degradation pathway, catalytic mechanism, and antibacterial activity

The composite material of manganese-copper oxide/maghemite (MnxCuyOz/γ-Fe2O3) was synthesized by the co-precipitation-calcination method. With the initial concentration of 0.2 g/L MnxCuyOz/γ-Fe2O3 and 10 mg/L O3, the chloramphenicol (CAP, 10 mg/L) could be completely degraded, which was about 2.22 times of that treated with ozonation alone. The contribution of O3 and hydroxyl radical (•OH) for CAP degradation in the catalytic process was 6.9% and 93.1%, respectively. According to the effects of catalyst dosage, ozone dosage, and pH on the catalytic performance of MnxCuyOz/γ-Fe2O3, a predictive empirical model was developed for the ozonation with the MnxCuyOz/γ-Fe2O3 system. The HCO3−/CO32− and phosphates in solution could inhibit the degradation of CAP with the inhibition ratios 8.45% and 13.8%, respectively. The HCO3−/CO32− could compete with CAP and react with •OH, and the phosphates were considered as poisons for catalysts by blocking the surface active sites to inhibit ozone decomposition. The intermediates and possible degradation pathways were detected and proposed. The catalytic ozonation could effectively control the toxicity of the treated solution, but the toxicity was still not negligible. Furthermore, MnxCuyOz/γ-Fe2O3 could be easily and efficiently separated from the reaction system with an external magnet, and it possessed excellent reusability and stability.

Kinetics study of acid hydrolysis of citrus pectin in hydrothermal process

In the present work, pectin hydrolyzation was conducted by hydrothermal processing with additional pressurization (subcritical water environment). The variation of molecular size and reducing end content of pectin during the reaction were measured. On the basis of experimental results and the zeroth-order reaction law, empirical kinetics model of pectin hydrolyzation was established and validated. The overall relative average bias was applied to evaluate the accuracy of the empirical model, and the obtained value was 9.42%. The temperature and pressure dependency of kinetics constant was investigated and discussed. From the proposed kinetics model, the molecular size reduction of pectin during hydrolyzation can be predicted from the reducing end content at certain reaction time. Consequently, the model can be helpful in parameter setting for practical trial of pectin hydrolyzation. Since pectin self-degradation in subcritical water environment is clean and efficient, the hydrothermal processing can be a promising approach for production of pectin derivatives.

Extraction of the Volatile Oils of Dictyopteris membranacea Batters 1902 by Focused Microwave-assisted Hydrodistillation and Supercritical Carbon Dioxide: Empirical Kinetic Modelling Approach, Apparent Solubility and Rate Constants

Extraction of the Volatile Oils of Dictyopteris membranacea Batters 1902 by Focused Microwave-assisted Hydrodistillation and Supercritical Carbon Dioxide: Empirical Kinetic Modelling Approach, Apparent Solubility and Rate Constants

Characterization of ambient volatile organic compounds, source apportionment, and the ozone–NO<sub>x</sub>–VOC sensitivities in a heavily polluted megacity of central China: effect of sporting events and emission reductions

Abstract. The implementation of strict emission control during the 11th National Minority Games (NMG) in September 2019 provided a valuable opportunity to assess the impact of such emission controls on the characteristics of VOCs and other air pollutants. Here, we investigated the characteristics of VOCs and the O3–NOx–VOC sensitivity comprehensively in Zhengzhou before, during, and after the NMG by delivering field measurements combined with WRF-CMAQ (Weather Research and Forecasting Community Multiscale Air Quality) model simulations. The average mixing ratios of VOCs during the control periods were 121 ± 55 µg m−3 and decreased by about 19 % and 11 % before and after emission reduction. The ozone precursors (NOx) also decreased significantly during the control period; however, the ozone pollution was severe during the entire observation period. Positive matrix factorization analysis indicated seven major sources of ambient VOCs, including coal combustion, biomass burning, vehicle exhausts, industrial processes, biogenic emissions, solvent utilization, and liquefied petroleum gas (LPG). The results show that the major source emissions, such as coal combustion and solvent utilization, were significantly reduced during the control period. As for ozone formation potential (OFP), the value during the control period was 183 ± 115 µg m−3, which was 0.23 and 0.17 times lower than before and after the control period, respectively. Solvent utilization and combustion controls were the most important measures taken to reduce OFP during the NMG period. Control policies can effectively reduce carcinogenic risk. However, non-cancer risks of ambient VOC exposures were all exceeding the safe level (hazard quotient = 1) during the sampling periods, and emphasis on the reduction of acrolein emissions was needed. In addition, the WRF-CMAQ model simulation indicated that O3 formation was controlled by VOCs in Zhengzhou. The results of the Empirical Kinetic Modeling Approach showed that the NOx reduction in Zhengzhou might lead to higher ozone pollution. It is suggested that reduction ratios of the precursors (VOCs : NOx) should be more than 2, which can effectively alleviate ozone pollution.

Empirical Kinetic Models for the CO2 Gasification of Biomass Chars. Part 1. Gasification of Wood Chars and Forest Residue Chars.

The gasification kinetics of charcoals and biomass chars is complicated by several factors, including chemical and physical inhomogeneities, the presence of mineral matter, and the irregular geometry of the pore structure. Even the theoretically deduced gasification models can only provide empirical or semiempirical descriptions. In this study, an empirical kinetic model from the earlier works of the authors was adapted for the CO2 gasification of biomass chars. It is based on a versatile polynomial approximation that helps to describe the dependence of the reaction rate on the progress of the conversion. The applicability of the model was tested by the reevaluation of 24 thermogravimetric analysis (TGA) experiments from earlier publications. The adjustable parameters of the model were determined by the method of least squares by evaluating groups of experiments together. Two evaluation strategies were tested. In the regular evaluations, the same kinetic parameters were employed for all the experiments with a given sample. The use of experiments with modulated and constant reaction rate (CRR) temperature programs made it possible to employ another approach too, when the preexponential factor was allowed to vary from experiment to experiment. The latter approach allows a formal kinetic description of the differences in the thermal deactivation of the samples caused by different thermal histories as well as of some inevitable systematic errors of the TGA experiments. The evaluations were carried out by both approaches, and the results were compared. The evaluations were based on 12 experiments. As a test, each evaluation of the study was repeated with only 8 experiments. The results of the latter test calculations indicated that the information content of the employed experiments is sufficient for the evaluation approaches of this work.

Kinetic modeling of the photocatalytic degradation of 17-β estradiol using polythiophene modified Al-doped ZnO: Influence of operating parameters, interfering ions, and estimation of the degradation pathways

The kinetic modeling of the photocatalytic degradation of the endocrine-disrupting compound, 17-β estradiol, using 0.47% polythiophene modified 3.14% Al-doped ZnO has been investigated in this study. The degradation kinetics were investigated by varying the different operational parameters, such as pH, dose, light intensity, and initial concentration. The degradation rate constants were estimated using a non-linear pseudo-first-order kinetic model. At optimum conditions, around 99% removal of 17-β estradiol could be achieved at a degradation rate of 0.943 h−1. The intrinsic kinetic model adopted based on the fundamental equations of photocatalysis, and the empirical kinetic model could efficiently predict the removal efficiency. The performance of the photocatalyst under solar light and the influence of competitive ions commonly present in the water matrix were investigated. Sensitivity analysis revealed that light intensity, photocatalyst dose, HCO3- concentration, and pH influenced the 17-β estradiol removal the most. The identification of active radicals was investigated by the radical scavenging study. Characterization of the photocatalyst before and after photocatalysis was carried out to identify any changes in the physicochemical properties that might have occurred during the process. The intermediates formed during photocatalysis were identified to understand the degradation mechanism and predict the degradation pathway.

Photocatalytic activity enhancement of carbon‐doped g‐C3N4 by synthesis of nanocomposite with Ag2O and α‐Fe2O3

AbstractCarbon‐doped g‐C3N4 (CGNS) nanocomposite with Ag2O and α‐Fe2O3 has been synthesized to improve g‐C3N4 photocatalytic activity. The prepared CGNS/Ag2O/α‐Fe2O3 (GAF [with mass ratio 3:2:1]) nanocomposite exhibits the expanded visible‐light absorption region leading to the enhanced photocatalytic performance for Acid Red 14 (AR14) degradation. Besides, it is found that the recombination rate of the charge carriers effectively suppresses the nanocomposite. For a better understanding of the photocatalytic degradation mechanism, the reactions have been performed in the presence of different scavengers. The experiments indicate that superoxide anion radicals possess a more influential role in AR14 degradation in comparison with hydroxyl radicals and holes. The degradation efficiency has been decreased from 94.68 to 85.60 after five consecutive photocatalytic tests implying that the prepared nanocomposite is a stable photocatalyst. In the end, the kinetic study of AR14 degradation on nanocomposite with considering pseudo‐first‐order kinetics results in a nonlinear empirical kinetic model development for prediction of degradation efficiency of AR14 on nanocomposite.

Extraction of copper from chalcopyrite with potassium dichromate in 1-ethyl-3-methylimidazolium hydrogen sulfate ionic liquid aqueous solution

Developing new and sustainable leaching system with limited release of pollutant and low acid and energy consumption is a challenge for copper extraction from chalcopyrite. In this work, a hydrometallurgical process for chalcopyrite dissolution in 1-ethyl-3-methyl-imidazolium hydrogen sulfate ([EMIm]HSO4) media with potassium dichromate (K2Cr2O7) was developed, and the leaching behavior of chalcopyrite with various parameters, such as kinds of ionic liquids (ILs), concentrations of [EMIm]HSO4 and K2Cr2O7, stirring speed, leaching temperature, and particle size were discussed in detail. The result show that the most effective ILs medium for chalcopyrite dissolution was varied with the specific oxidant. The leaching rate of chalcopyrite was significantly enhanced by increasing temperature, concentrations of K2Cr2O7 and [EMIm]HSO4, and decreasing particle size, while it has little to do with the increasing of stirring speed. The maximum copper extraction yield of 90.2% was reached within 90 min under the following optimized conditions: 10 g/L of solid/liquid ratio, 10 vol% of [EMIm]HSO4 concentration, 0.1 M of initial K2Cr2O7 concentration, stirring speed of 200 rpm, the temperature of 70 °C and particle size of −45 µm. The leaching process of chalcopyrite in [EMIm]HSO4-K2Cr2O7 aqueous solution follows an empirical kinetic model 1-2/3x-(1-x)2/3=kdt with the apparent activation energy of 36.26 kJ/mol, which was limited by the diffusion through a protect layer of elemental sulfur and pyrite.

Synthesis of two-dimensional TiO2@multi-walled carbon nanotube nanocomposites as smart nanocatalyst for ultra-deep oxidative desulfurization of liquid fuel: Optimization via response surface methodology

The novel heterogeneous catalysts of 2D-TiO2@MWCNT nanocomposites are designed and synthesized via grafting TiO2 nanoparticles onto functionalized multi-walled carbon nanotubes and used for oxidative desulfurization of dibenzothiophene and real straight run light gas oil. The 2D-TiO2@MWCNT nanocomposite catalysts are completely characterized by FT-IR, Raman spectroscopy, XRD, TEM, NH3-TPD, ICP, and N2 adsorption–desorption isotherms. At first, the effect of various loading Ti on the MWCNT for ODS efficiency was investigated. The results revealed that 2D-0.6TiO2@MWCNT had the highest sulfur removal for the model, and SRLGO fuel compared to the other catalyst. Then, the optimal design of experiments using Box–Behnken experimental design was used to evaluate the effects of individual process variables such as temperature, O/S molar ratio, time, catalyst dosage, and their optimum values were found to be 69 °C, 46 min−1, O/S molar ratio: 9, and 0.03 g cat (25 ml DBT model fuel with 500 ppm S or 25 ml SRLGO with 12500 ppm S, 25 ml of acetonitrile), to achieve a high removal sulfur efficiency for DBT model oil (100%) and SRLGO (97.5 %), respectively. Based on optimal conditions, the 2D-0.6TiO2@MWCNT catalyst possesses superior catalytic activity and excellent reusability. The desulfurization reaction could be recycled for at least nine cycles without considerable reduction of catalytic performance, showing the good stability of the nanocomposite catalysts. An empirical kinetic model was applied to explain the rate data. Also, 2D-0.6TiO2@MWCNT nanocomposite catalyst had the lowest activation energy (27.65 Kj.mol−1) with the highest turnover frequency (16.15 h−1, around 2–3 times of the best catalyst so far) in desulfurization reactions compared to any TiO2-based catalysts. Furthermore, the catalytic reaction mechanism is investigated.

Determining the kinetic constants leading to mineralization of dilute carbamazepine and estradiol-containing solutions under continuous supercritical water oxidation conditions

Continuous subcritical and supercritical water oxidation experiments were conducted on dilute carbamazepine- and estradiol-containing synthetic solutions used to simulate the removal of model emerging pollutants from secondary municipal effluents. The operating conditions comprised 340–500 °C, retention time of 24–453 s and a stoichiometric oxidant ratio (O.C.) between 4 and 64. The transformation of the various species was determined at the outlet and by modeling a segmented non-isothermal reaction system. Four empirical power law kinetic models were established to represent both the pollutants' degradation and TOC removal efficiencies, using nonlinear multiple regression coupled with bootstrapping and K-fold cross-validation. The mineralization and degradation models for both pollutants yielded a R2 of 67–80.5% vs. the experimental results. Discussion on the various model assumptions revealed that attributing full model deviations to the constant oxygen concentration or to the laminar reactor flow, yielded a deviation of 6% and 15% in the removal efficiencies, respectively. However, the expected deviation of the models was lower than 0.32% at conditions leading to (almost) full mineralization (45–60 s, 480–500 °C and O.C.s of 5–10). The methodologies developed in the study are useful for interpreting future results obtained from SCWO of actual secondary effluent solutions.

Energy-efficient removal of carbamazepine in solution by electrocoagulation-electrofenton using a novel P-rGO cathode

In this study, carbamazepine (CBZ) decay in solution has been studied by coupling electrocoagulation with electro-Fenton (EC-EF) with a novel P-rGO/carbon felt (CF) cathode, aiming to accelerate the in-situ generation of •OH, instead of adding Fe2+ and H2O2. Firstly, the fabricated P-rGO and its derived cathode were characterized by XRD, SEM, AFM, XPS and electrochemical test (EIS, CV and LSV). Secondly, it was confirmed that the performance in removal efficiency and electric energy consumption (EEC) by EC-EF (kobs=0.124 min−1, EEC=43.98 kWh/kg CBZ) was better than EF (kobs=0.069 min−1, EEC=61.04 kWh/kg CBZ). Then, P-rGO/CF (kobs=0.248 min−1, EEC=29.47 kWh/kg CBZ, CE=61.04%) showed the best performance in EC-EF, among all studied heteroatom-doped graphene/CF. This superior performance may be associated with its largest layer spacing and richest C=C, which can promote the electron transfer rate and conductivity of the cathode. Thus, more H2O2 and •OH could be produced to degrade CBZ, and almost 100% CBZ was removed with kobs being 0.337 min−1 and the EEC was only 24.18 kWh/kg CBZ, under the optimal conditions (P-rGO loading was 6.0 mg/cm2, the current density was 10.0 mA/cm2, the gap between electrode was 2.0 cm). Additionally, no matter the influent is acidic, neutral or alkaline, no additional pH adjustment is required for the effluent of EC-EF. At last, an inconsecutive empirical kinetic model was firstly established to predict the effect of operating parameters on CBZ removal.

Supercritical Fluid Extraction Kinetics of Cherry Seed Oil: Kinetics Modeling and ANN Optimization.

This study was primarily focused on the supercritical fluid extraction (SFE) of cherry seed oil and the optimization of the process using sequential extraction kinetics modeling and artificial neural networks (ANN). The SFE study was organized according to Box-Behnken design of experiment, with additional runs. Pressure, temperature and flow rate were chosen as independent variables. Five well known empirical kinetic models and three mass-transfer kinetics models based on the Sovová’s solution of SFE equations were successfully applied for kinetics modeling. The developed mass-transfer models exhibited better fit of experimental data, according to the calculated statistical tests (R2, SSE and AARD). The initial slope of the SFE curve was evaluated as an output variable in the ANN optimization. The obtained results suggested that it is advisable to lead SFE process at an increased pressure and CO2 flow rate with lower temperature and particle size values to reach a maximal initial slope.

Copper oxide/graphitic carbon nitride composite for bisphenol a degradation by boosted peroxymonosulfate activation: Mechanism of Cu-O covalency governs

Surface structure can govern heterogeneous catalysis, resulting in its critical role in nonradical reactions. Here, we explored whether Cu-O covalency plays a critical role in controlling the inherent properties of copper oxide/graphitic carbon nitride (CuO-CN). Experiments and theoretical calculations show that, in contrast to the traditional concept of low-valent metal control activity, surface modification enlarges Cu-O covalency, and high-valent copper species at the surface easily bind peroxymonosulfate (PMS, (HSO5-)) anions. Therefore, optimized CuO-CN corresponds to a 14.8-fold higher kinetic reaction rate (0.10392 min−1) for PMS activation and pollutant degradation over those of unoptimized CuO-CN. Based on two-dimensional Fourier transform infrared correlation spectroscopy (2D-FT-IR-COS), Cu-O was determined to be the main active site. Cu-O is more active than other groups and acts before other groups. Benefiting from this electron transfer mechanism, CuO-CN shows good environmental tolerance (pH, anions, humic acid and actual water bodies such as tap water and groundwater). The established empirical kinetic model shows a strong linear correlation with the experimental kinetic reaction rate (> 0.94). CuO-CN/PMS can degrade organic pollutants efficiently for up to 30 days in a filter reactor. This work provides an understanding of the key role of the surface electronic structure in the nonradical activation of PMS and may provide support for improving the design of PMS catalysts.

Degradation of amoxicillin with sono, photo, and sonophotocatalytic oxidation under low-frequency ultrasound and visible light

The presence of pharmaceutically active compounds in aquatic bodies is a global concern, and suitable treatment technologies are required. In this study, the efficacy of photocatalytic, sonocatalytic, and sonophotocatalytic oxidation processes for the degradation of amoxicillin (AMX) was investigated using visible light with N doped TiO2 (N–TiO2) nanoparticles as the catalyst and low-frequency ultrasound in a novel multifrequency reactor. The influence of different operational parameters on the extent of AMX degradation was studied. Sonophotocatalytic oxidation was found more efficient for AMX degradation when compared to photocatalysis or sonocatalysis alone, and may be due to the reduced bandgap of the catalyst, enhanced cavitation effect due to the presence of the solid catalyst, and improved mass transfer of pollutants. AMX degradation during sono, photo, and sonophotocatalytic oxidation processes was in good agreement with pseudo-first-order kinetics. Empirical kinetic models were also developed using multiple linear regression for predicting the degradation efficiency accounting for the operational parameters. Scavenger experiments suggested that •OH radicals largely contributed to AMX degradation, and a plausible mechanism for degradation was proposed. Further, possible degradation pathways for all three treatment processes are also proposed after identifying the degradation products.

Langmuir Adsorption Kinetics in Liquid Media: Interface Reaction Model.

Adsorption kinetic equation has been derived assuming that the process follows the behavior of a heterogeneous chemical reaction at the solid–liquid interface. This equation is converted into the Langmuir isotherm at equilibrium and describes well the unsteady-state adsorption process. Based on that, a working equation has been developed, which gives adsorption-rate-constant independent of operating parameters including concentration. Also, a kinetic model expressed as a sum of first- and second-order systems available in the literature has been applied (modified with the interface reaction concept) to determine the adsorption rate constant. Both methods gave similar results. Three dimensionless numbers have been developed to determine and distinguish pseudo-first-order and pseudo-second-order kinetics justified from the viewpoint of chemical kinetics. It is shown that curve-fitting with a high correlation coefficient could validate an empirical kinetic model, but the fitted model parameters could not automatically be related to chemical kinetic parameters if the model itself is not grounded on well-defined chemical kinetics. Finally, it is concluded that the currently applied empirical approach could not provide reliable data for comparison among similar systems, while the Langmuir kinetic equation developed based on the concept of heterogeneous reaction would be a good basis for standardization of the method for adsorption system characterization.

Ambient ozone pollution at a coal chemical industry city in the border of Loess Plateau and Mu Us Desert: characteristics, sensitivity analysis and control strategies.

In this study, ambient ozone (O3) pollution characteristics and sensitivity analysis were carried out in Yulin, a city in the central area of the Loess Plateau during 2017 to 2019 summer. O3 concentrations increased for 2017 to 2019. Correlation and statistics analysis indicated high temperature (T > 25 °C, low relative humidity (RH < 60%), and low wind speed (WS < 3 m/s) were favorable for O3 formation and accumulation, and the O3 pollution days (MDA8 O3 > 160 µg/m3) were predominantly observed when the wind was traveling from the easterly and southerly. O3 concentration in urban area of Yulin was higher than that in background. The pollution air masses from Fenwei Plain increase the level and duration of O3 pollution. In order to clarify the formation mechanism and source of O3, online measurements of volatile organic compounds (VOCs) were conducted from 7 July to 10 August in 2019. The average of VOCs concentration was 26 ± 12 ppbv, and large amounts of alkenes followed by aromatics, characteristic pollutants of the coal chemical industry, were detected in the ambient air. To further measure the sensitivity, the observation-based model (OBM) simulation was conducted. Empirical Kinetic Modeling Approach (EKMA) plot and relative incremental reactivity (RIR) value indicated Yulin located on VOCs-limited regime. That implied a slight decrease of NOx may increase O3 concentration. When the emission reduction ratio of anthropogenic VOCs/NOx higher than 1:1, the O3 will decrease. O3 control strategies analysis shows that the O3 targets of 5% and 10% O3 concentration reductions are achievable through precursor control, but more effort is needed to reach the 30% and 40% reduction control targets.