Kinetic Reaction Rate Research Articles

Numerical modeling of an abiotic hyporheic mixing-dependent reaction: Chemical evolution of mixing and reactant production zones

Mixing-dependent reactions occur where groundwater and surface water mix in shallow sediments (hyporheic zone) and can attenuate contaminants along upwelling flowpaths, thus reducing transport to surface water. Here we used MODFLOW/SEAM3D to numerically simulate prior laboratory observations of a mixing-dependent reaction between sodium sulfite (Na2SO3) and dissolved oxygen (DO) to produce sodium sulfate (Na2SO4). This reaction is not common in nature but is used as a surrogate for mixing-dependent DO consuming reactions of environmental significance. We evaluated how location and thickness of mixing zones and reaction product production zones dynamically respond to variations in hydraulic and chemical boundary conditions and reaction kinetic rate. Sensitivity analysis showed that location and thickness of mixing zones and reactant production zones were most sensitive to changes in the balance of hydrologic inflow from groundwater and surface water (inflow ratio). Mixing zone thickness for reactive DO calibrated to experimental data was thinner than that for the “DO tracer” (identical source location and concentration as DO but conservative tracer), indicating that as DO is consumed its mixing zone narrows. The SO4 production zone was consistently thicker than the DO mixing zone. Small changes in mixing/production zone thicknesses were linked to large changes in mass consumed and produced, indicating the potential for simpler field metrics like thickness to act as surrogates for more challenging measurements such as contaminant flux or consumption in monitoring natural attenuation. This study improves understanding of the evolution of hyporheic mixing-dependent reaction zones that occur even under steady state hydraulics, emphasizing their complex controls.

Toward enhanced visible-light photocatalytic dye degradation and reusability of La3+ substituted ZnFe2O4 nanostructures

The present work focused on the synthesis of novel ZnLaxFe2−xO4 catalysts (x = 0, 0.01, 0.03, 0.05) and their utilization for the photocatalytic degradation of Rhodamine B dye. Structurally, the band gap energy of the catalysts tended to decrease (1.94–1.70 eV) with increasing the amount of La3+ dopant. ZnLa0.05Fe1.95O4 had an average particle size (40 nm), high surface area (41.07 m2 g−1) and large pore volume (0.186 cm3 g−1). Moreover, the effect of doping ratio, reaction time, H2O2 concentration, catalyst loading on the treatment performance of La3+ substituted ZnFe2O4 nanocomposites was investigated. ZnLa0.05Fe1.95O4/H2O2 system exhibited the highest degradation efficiency of 99.5% and nonlinear pseudo first-order kinetic reaction rate (14.8 × 10−3 min−1) in the presence of visible light irradiation. The key role of reactive oxygen species involving •O2− and •OH radicals was well explained through the scavenger study. A plausible mechanism of the degradation of Rhodamine B dye was also proposed. Due to two advantageous points including high recyclability (up to 4 cycles) and stability, La3+ substituted ZnFe2O4 nanocomposites can be an effective and competitive catalyst for the visible light-driven photodegradation of toxic dyes in the real wastewaters.

Solar photocatalytic degradation of carbaryl in water using TiO2-coated filters with different binders and effect of the operating conditions.

This research focused on degradation of carbaryl in water using TiO2-coated glass-fiber filter under sunlight irradiation. The coating substances were 0.3-2% w/v TiO2 mixed with 5 different binders, DURAMAX B1000, PEG molecular weight of 1000, 2000, 4000, and 6000, in a concentration of 0.3-2 wt% of TiO2. Optimum concentration of coating substance was investigated for the best degradation efficiency in terms of reaction kinetic rates. Sorption of carbaryl and zeta potential of coating substance were also studied.The results revealed that carbaryl sorptions on the coated filters were 2% or less. The optimum concentration of coating substance was 1% w/v TiO2 and 1 wt% PEG6000 with the kinetic rate constant of 0.022-0.025min-1. The point of zero charge of 1% w/v TiO2 + 1% wt% PEG6000 occurred at pH 7.5, while the pH of carbaryl solution was 7.3 ± 0.3. Thus, TiO2 was neutral, and repulsive force did not exist in this optimum coating. With the optimum TiO2 loading of 1-2g/L, 100% carbaryl degradation was obtained in 150min.

Label-free measurement of reaction rate constants in solution using fluidic dielectrophoresis

We use the fluidic dielectrophoresis (fDEP) motion of a polarizable liquid-liquid electrical interface to quantify reaction rate kinetics of binding interactions in solution. Using a T-shaped microfluidic channel we co-flow two reactant streams side-by-side. Their resulting interface enables controlled diffusive mixing and product formation. We electrokinetically engineer the interface such it is electrical in nature so that one liquid stream possesses a higher electrical conductivity and the other a higher permittivity. When the interface is exposed to a perpendicular alternating current (AC) electric field the electrical mismatch drives it to polarize and displace across the microchannel width in a direction and magnitude that is a function of the electrical properties of the interface and of the field frequency applied. At a low frequency below the inverse interfacial charge relaxation timescale, the high conductive stream displaces into the high permittivity stream. At frequencies above this inverse timescale the direction reverses. At an intermediate “crossover” frequency (COF), the polarization of the interface tends to zero and the displacement ceases. Because interfacial reactions influence the electrical properties, binding dynamics can be quantified using the COF. We measure the COF down the axial length of an interface subjected to binding reactions between CaGreen and Ca2+, and between avidin and biotin. The experimental measurements are in good agreement with an electrokinetically coupled two-dimensional simulation of the reaction-diffusion equations. From this work, we show that the motion of an electrical interface in an electrical field can be utilized to measure kinetic reaction rates in solution phase.

Exploring Acrylamide and 5-Hydroxymethylfurfural Formation in Glucose-Asparagine-Linoleic Acid System With a Kinetic Model Approach.

In the “glucose-asparagine-linoleic acid” ternary system, a kinetic model approach was used to explore formation and elimination law of target hazards, including acrylamide (AA) and 5-hydroxymethylfurfural (5-HMF), and their related precursors and intermediate products. The results showed that the elimination of glucose and asparagine and the formation of fructose (generated from glucose isomerization), 3-deoxyglucosone (3-DG), methylglyoxal (MGO), and glyoxal (GO), AA and 5-HMF followed first-order reaction kinetics with high fit coefficients (R2 > 0.9). In addition, the kinetic reaction rate constants increased as the increasing temperature, and all models followed the Arrhenius law. Results of statistical correlations analysis suggested that at lower temperature, the generic amino acid route and the specific amino acid route may paly crucial roles for the formation of AA and 5-HMF, while at high temperature a linoleic acid pathway may be predominantly involved.

Programming and training rate-independent chemical reaction networks

Embedding computation in biochemical environments incompatible with traditional electronics is expected to have a wide-ranging impact in synthetic biology, medicine, nanofabrication, and other fields. Natural biochemical systems are typically modeled by chemical reaction networks (CRNs) which can also be used as a specification language for synthetic chemical computation. In this paper, we identify a syntactically checkable class of CRNs called noncompetitive (NC) whose equilibria are absolutely robust to reaction rates and kinetic rate law, because their behavior is captured solely by their stoichiometric structure. In spite of the inherently parallel nature of chemistry, the robustness property allows for programming as if each reaction applies sequentially. We also present a technique to program NC-CRNs using well-founded deep learning methods, showing a translation procedure from rectified linear unit (ReLU) neural networks to NC-CRNs. In the case of binary weight ReLU networks, our translation procedure is surprisingly tight in the sense that a single bimolecular reaction corresponds to a single ReLU node and vice versa. This compactness argues that neural networks may be a fitting paradigm for programming rate-independent chemical computation. As proof of principle, we demonstrate our scheme with numerical simulations of CRNs translated from neural networks trained on traditional machine learning datasets, as well as tasks better aligned with potential biological applications including virus detection and spatial pattern formation.

Substantially updating photocatalytic reaction by in-situ generated SO4−[rad] through directly exciting SO42−

In photocatalytic oxidation reaction, sulfate radicals (SO4−) as active oxidative species is investigated rarely and is not fully understanded. In this work, the generation process of SO4− and its effect on photodegradation reaction are mainly investigated. The pre-adsorption of Na2SO4 on Bi2O2CO3 is performed (named as Na2SO4-BOC). It is found that after irradiation for 70 min under ultraviolet light (λ < 400 nm), 61% and 15% of RhB are degraded by Na2SO4-BOC and pristine BOC (Bi2O2CO3 without pre-adsorption of Na2SO4), respectively. The apparent reaction kinetic rate constant (ka) for Na2SO4-BOC (0.048 min−1) has increased by 11 times, compared to that of BOC (0.004 min−1). Besides, Na2SO4 is also directly added in photoreaction system to compare. The results show that 87% of RhB is degraded at 70 min, which is significantly higher than BOC; the ka (0.036 min−1) of the reaction with adding Na2SO4 has increased by 8 times, compared to BOC. The greatly enhanced photocatalytic activity is mainly attributed to the SO4−, as proved by electron spin resonance (ESR) spectrum. It is found that SO42− anions can be converted to SO4− radicals by ultraviolet light irradiation directly, OH radicals and holes. The newly generated SO4− (redox potential 2.6 V), combined with OH radicals and holes, synergistically improves the photocatalytic reaction. The results for TiO2 (P25) system also confirm the substantially updated degradation ability by SO4− through directly exciting SO42−. This work provides a simple, low-cost method to improve conventional photoreaction.

Fabrication and characterization of a novel Ba2+-loaded sawdust biochar doped with iron oxide for the super-adsorption of SO42− from wastewater

Biochar is a low-cost adsorbent used in the treatment of contaminated wastewater. We investigated the potential of an Fe-impregnated, Ba2+-loaded biochar (Fe-(Ba-BC)) for the removal of SO42− from aqueous solutions. The Ba2+-loaded biochar was synthesized from sawdust impregnated with iron oxide via pyrolysis at 600 °C. The porous structure of the Fe-(Ba-BC) was identified by scanning electron microscopy before sulfate was adsorbed onto the adsorbent. Functional groups were determined by energy-dispersive spectrophotometry and Raman spectrometry.. The Fe-(Ba-BC) Raman peaks before the experiment were higher than after, suggesting the precipitation of BaSO4. The presence of BaCl2 on the surface of the biochar was confirmed by X-ray diffraction. Batch sorption results showed that Fe-(Ba-BC) strongly adsorbed aqueous SO42− with a removal efficacy of 96.7% under the optimum conditions of 0.25 M BaCl2, a contact time of 480 min, a pH of 9 and an adsorbent dose of 2 g. The optimum condition for removal and reaction rate kinetics analysis indicated that adsorption curve fitted well with PSO, k2 0.00015 confirmed the removal of SO42− via chemisorption. Thus, Fe-(Ba-BC) was found to be a favorable adsorbent for removing SO42−.

Co78Si8B14 metallic glass: A highly efficient and ultra-sustainable Fenton-like catalyst in degrading wastewater under universal pH conditions

Overcoming the pH limitation and increasing the catalyst reusability remain pressing demands for metallic glass (MG) in wastewater remediation. Herein, Co78Si8B14 MG ribbons are used to degrade dye wastewater by activating hydrogen peroxide (H2O2) as Fenton-like catalysts. The Co-based MG catalysts exhibit high degradation efficiency under both acidic and alkaline conditions, and the kinetic reaction rate at pH 10 (0.176 min−1) and pH 4 (0.089 min−1) is 5.9 and 1.2 times higher than that of the extensively studied Fe-based MG catalysts, respectively. Impressively, the Co-based MG catalysts can be reused up to 20–60 times at universal pH conditions, demonstrating fairly good reusability. The newly discovered Co-based MG catalysts do not follow the classical Fenton reactions with H2O2 the way Fe-based MGs do. In an acid environment, hydroxyl radicals play a dominant role in the degradation, while in an alkaline environment, the effect of hydroxyl radicals is weakened, and Co3+ ions exert a relatively major function on the degradation. The excellent performance in catalytic activity and reusability at universal pH conditions of the Co-based MGs will inspire the development of MGs in wastewater treatment.

Cobalt-based MOF nanoribbons with abundant O/N species for cycloaddition of carbon dioxide to epoxides

Chemical fixation of CO2 with epoxides is an effective option to achieve sustainable synthesis of cyclic organic carbonates. Although metal–organic frameworks (MOFs) are promising catalysts for this reaction, their low stability in aqueous solutions makes this application infeasible. In an effort to overcome this limitation, cobalt-based metal–organic framework (Co(II)MOF) nanoribbons have been prepared by coordinating the Co(II) ions with a new ligand (C16H12N4O4) full of oxygen and nitrogen moieties. Strong chemical interactions occur between the adsorbed CO2 and oxygen/nitrogen atoms in this porous MOF structure. Co(II)-MOF nanoribbons with tetra-n-butylammonium bromide acted as cocatalysts with ∼97% yield of cyclic carbonate (reaction kinetic rate of 14.7 × 106 µmol g-1 h−1) upon the cycloaddition of epichlorohydrin (ECH) to CO2 (>99% reaction selectivity under solvent-free reaction condition at 80 °C, 3 h and 1 MPa CO2 pressure). This work may open a new avenue for chemical fixation of CO2 by rational design of the components and morphology of MOF-based catalysts.

Removing imidacloprid, bisphenol-S and azithromycin by ferrate (Fe(VI)): efficiency, oxidation products, toxicity and kinetics

Emerging micro-pollutants (EMPs) have potential threats to human health and eco-environment. It is necessary to seek alternative treatment technologies when the existing processes have limitations to treat EMPs. This paper aimed to investigate the use of ferrate (Fe(VI)) to treat imidacloprid (IMP), bisphenol-S (BS) and azithromycin (AZM) by assessing the toxicity of the EPMs before and after Fe(VI) treatment, generating reaction kinetic rate constants and proposing degradation pathways and oxidation products. BS was readily removed at a lower Fe(VI) dose of 0.009 mM, while both IMP and AZM were not be effectively degraded at such a low Fe(VI) dose. The resulting toxicity of BS was reduced after Fe(VI) treatment, whereas that of IMP and AZM treated by Fe(VI) increased; this is due to changes in structure and property of EMPs and the formation of oxidation products (OPs), which induced either low or high toxicity. The pseudo-first-order reaction rates of IMP, BS, and AZM with Fe(VI) were derived as 0.071, 0.148, and 0.076 s−1 respectively, which are consistent with the trend of the EMPs’ removing by Fe(VI).

Magnetic bimetallic Fe, Ce-embedded N-enriched porous biochar for peroxymonosulfate activation in metronidazole degradation: Applications, mechanism insight and toxicity evaluation

A novel honeycomb-like porous Fe-Ce@N-BC composite was synthesized as an effective and green PMS activator for MNZ removal through radical and non-radical processes. • Bimetallic Fe- and Ce-embedded N-enriched porous biochar (Fe-Ce@N-BC) was prepared. • Pyridinic N and C O on the surface of Fe-Ce@N-BC facilitate the PMS activation. • Both radical and non-radical processes contribute to the oxidation reaction. • Fe-Ce@N-BC exhibits a superior activity in MNZ degradation in seawater and effluent. • Animal cell test reveals low cytotoxicity of both the intermediates and the material. Bimetallic Fe- and Ce-embedded N-enriched porous biochar (Fe-Ce@N-BC) was synthesized to activate peroxymonosulfate (PMS) for metronidazole (MNZ) removal. 97.5% decay of MNZ was achieved within 60 min in Fe-Ce@N-BC/PMS system. The kinetic reaction rate constant of the Fe-Ce@N-BC/PMS system (0.0566 min −1 ) was 10.5 times higher than that of the BC/PMS system (0.0054 min −1 ). The highly dispersed Fe-Ce oxide nanocrystals serve as PMS activation centers, while the addition of nitrogen source increases the surface area and porosity of biochar, as well as enhances the PMS activation performance. It is noteworthy that graphitic N and C O groups in biochar facilitates the PMS activation via a nonradical pathway and the Fe 2+ /Fe 3+ and Ce 3+ /Ce 4+ participate in the radical pathway. The presence of anion ions of SO 4 2− can promote the MNZ degradation process, while HCO 3 – and Cl − ions suppress the MNZ removal. The MNZ removal using Fe-Ce@N-BC in salty media behavior similarly with that in DDI water, while the decreased removal efficiency in real effluent could be mitigated by prolonging the reaction time. Finally, the degradation intermediate products of MNZ were identified and the pathway was proposed according to LC-MS analysis. The relatively low cytotoxicity of the Fe@Ce/N-BC evaluated by animal cell (A375) and toxicity evolution of MNZ intermediate products strongly suggest huge potential of utilization of the catalyst for aquatic environmental remediation.

In situ growth Fe and V co-doped Ni3S2 for efficient oxygen evolution reaction at large current densities

Industrial electrolysis of water is one of the effective strategies for green hydrogen production in the future. Nevertheless, the large-scale applications of water electrolysis are still intractable issues hindered by the high overpotentials and inferior reaction kinetics on the anode. Herein, a facile one-step hydrothermal method was applied to in situ growth the Fe and V co-doped Ni 3 S 2 electrocatalyst on nickel foam substrate (Fe, V–Ni 3 S 2 /NF). In 1 M KOH electrolyte, the as-prepared Fe, V–Ni 3 S 2 /NF electrode exhibited an improved water oxidation activity with ultralow overpotentials of 253 and 370 mV to realize large current densities of 100 and 1000 mA/cm 2 , respectively. More importantly, the Fe, V–Ni 3 S 2 /NF electrode existed an activation process during 100 h chronopotentiometry testing period. Detailed characterizations revealed that elements of V and S in the electrocatalyst were oxidized and dissolved into the electrolyte, making the electrocatalyst undergo surface reconstruction and resulting in a faster kinetic reaction rate, thus leading to enhanced oxygen evolution reaction activities. Collectively, the resultant Fe, V–Ni 3 S 2 /NF in this work provides new cogitation towards design and synthesis of low-cost electrocatalyst with large current densities for water oxidation. • Fe,V–Ni 3 S 2 /NF electrode was hydrothermal prepared and used as OER electrocatalyst. • Ni 3 S 2 is converted to NiOOH during the electrochemical oxidation process. • The electrode can attain 100 and 1000 mA/cm 2 with overpotentials of 253 and 370 mV. • The enhanced OER activity owned to the surface reconstruction by V, S etching.

Thermal and chemical analysis on the hetero-/homogeneous combustion characteristics of H2/Air mixture in a micro channel with catalyst segmentation

The heterogeneous-homogeneous combustion characteristics of premixed H2/Air mixture in a micro combustor with 2 mm platinum (Pt) catalyst segmentation are investigated by numerical simulation. The detailed chemical reaction mechanisms of gas-phase reaction and surface reaction of H2 are employed in a 2D CFD model by the verification. The characteristics in the catalytic combustor, such as temperature distribution, species concentration, kinetics reaction rate and heat transfer, are examined by varying inlet flow velocities. There is an interesting fact that an obvious demarcation line splits the channel into two regions at high velocities, which are dominated by heterogeneous reaction (Htr) and homogeneous reaction (Hr). In addition, there is a coupling heterogeneous-homogeneous reaction (HHr) in the 2 mm downstream of the catalytic region. These should be thoroughly deliberated using thermal and chemical analyses to determine that the gaseous flame is against the Htr in the catalytic combustor. The results can be shown that the heat flux into the upstream catalytic wall is primarily due to exothermicity induced by Htr. A low amount of heat feedback via the solid wall to inlet wall which is released by Hr. The heat fluxes from the gas–solid interface preheat the fresh gaseous mixture in the channel, thereby promoting the occurrence of Hr, increasing the heat release rate and kinetic reaction rate of Hr. Moreover, heat feedback from the heat release of Hr through the solid wall increases the reaction rates of Htr. The hydrogen conversion rate is improved by the effect of Htr in the catalytic combustor. In summary, the effect of introducing catalytic surface to induce the Htr could be well suitable for micro combustion schemes.

Hydrothermally assisted synthesis of nano zero-valent iron encapsulated in biomass-derived carbon for peroxymonosulfate activation: The performance and mechanisms for efficient degradation of monochlorobenzene

A facile, green and easily-scalable method of synthesizing stable and effective nano zero-valent iron (nZVI)‑carbon composites for peroxymonosulfate (PMS) activation was highly desirable for in-situ groundwater remediation. This study developed a two-step hydrothermally assisted carbothermal reduction method to prepare nZVI-encapsulated carbon composite (Fe@C) using rice straw and ferric nitrate as precursors. The hydrothermal reactions were conducive to iron loading, and carbothermal temperature was crucial for the aromatization and graphitization of hydrothermal carbonaceous products, the reductive transformation of iron oxides into nZVI and the development of porous structure in composites. At carbothermal temperature of 800 °C following hydrothermal reactions, the stable Fe@C800 with nZVI encapsulated in the spherical carbon shell was obtained and exhibited the best catalytic performance for PMS activation and the degradation of monochlorobenzene (MCB) in a wide range of pH values (3−11) with removal efficiency after 120 min reaction and first-order kinetic rate constant (k1) of 98.7% and 0.087 min−1 respectively under the optimum conditions of 10 mM PMS and 0.2 g·L−1 Fe@C800. The inhibiting effects of common co-existed anions (i.e., Cl−, HCO3− and H2PO4−) and humic acid in groundwater on the removal of MCB in Fe@C800/PMS system was also investigated. Both OH-dominated radical processes and nonradical pathways involving 1O2 and surface electron transfers were accounted for PMS activation and MCB removal. The inner nZVI was protected by the carbon shell, endowing Fe@C800 with high reactivity and good reusability. Additionally, 81.2% and 73.5% of MCB removal rates were achieved in tap water and actual contaminated groundwater respectively. This study not only provided a novel strategy to synthesize highly effective and stable nZVI‑carbon composites using the agricultural biomass waste for PMS induced oxidation of organic contaminants in groundwater, but also enhanced the understanding on the activation mechanism of iron‑carbon based catalysts towards PMS.

Defect modulation of MOF-derived ZnFe2O4/CNTs microcages for persulfate activation: Enhanced nonradical catalytic oxidation

• ZnFe 2 O 4 /CNTs-Ar catalysts can efficiently activate PS to degrade BPA in a wide pH range. • Defective and porous microcages exhibit 17.5 times higher activity than blank ZnFe 2 O 4 . • Defect modulation of CNTs facilitated the electron transfer for nonradical degradation. • Magnetic property ensured the convenient collection of catalysts by magnets. • We offer a new strategy to enhance nonradical oxidation through defect modulation. There has been growing interest in the combination of porous metal organic frameworks (MOFs)-derived architectures with conductive carbonaceous materials for the synergistically enhanced catalytic activity. Herein, we described a facile strategy to synthesize a highly efficient and recyclable heterogeneous catalyst through pyrolysis of MOFs as sacrificial templates. We found that creating defective sites in CNTs precursors exhibited significant impact on the charge transfer capability of composite microcages and the coordination environment of Fe centers. With the assistant of persulfate oxidants, ZnFe 2 O 4 /CNTs-Ar with modulated defects exhibited 17.5-fold higher kinetic reaction rate (0.35 min −1 ) than blank ZnFe 2 O 4 microcages for Bisphenol A degradation. Experimental characterizations suggested that defective CNTs played a vital role in shuttling electron from BPA molecules to persulfate, triggered the direct decomposition of pollutants via a non-radical oxidation pathway. Our research provides a new strategy to develop high-performance MOFs-derived catalysts through defect modulation for wastewater treatment.

Synthesis of advanced fuel with density higher than 1 g/mL by photoinduced [2 + 2] cycloaddition of norbornene

High-energy–density (HED) fuels have attracted extensive attention for volume-fixed aerospace vehicles because they can provide more propulsion energy to increase the payload and range of aerospace vehicles. Herein, we report a route for synthesis of HED fuel, pentacyclo[8.2.1.14,7.02,9.03,8]tetradecane (PCTD) with strained structure, by photoinduced intermolecular [2 + 2] cycloaddition of norbornene (NBE). The triplet quenching and phosphorescence quenching results indicate that NBE cycloaddition is conducted through the photosensitized processes containing triplet–triplet energy transfer, cyclization and relaxation. The reaction conditions are optimized to obtain the high photocatalytic activity, with the NBE conversion and PCTD selectivity reaching 78.7% and 94.4%, respectively. Moreover, a kinetic model is proposed with the reaction rate equation being correlated with the incident light flux, with the pseudo reaction kinetics parameters and reaction rate equations obtained. Importantly, PCTD shows high density of 1.024 g/mL and high volumetric net heat of combustion of 42.98 MJ/L, much higher than those of JP-10. In addition, blending with JP-10 or QC can significantly improve cryogenic properties of blended fuels, which is very promising for the practical application.

Kinetics and Mechanism of Degradation of Reactive Radical-Mediated Probe Compounds by the UV/Chlorine Process: Theoretical Calculation and Experimental Verification.

The UV/chlorine process, by combining chlorination with UV irradiation, has been recently considered as a highly efficient advanced oxidation process (AOP) technology in water treatment. Nitrobenzene (NB), benzoic acid (BA), and p-chlorobenzoic acid (pCBA) are widely used as model probe compounds in the UV/chlorine system to calculate the second-order rate constants of the specific radical reaction with target contaminates by a competitive kinetics method. A comprehensive understanding of probe compounds’ reaction mechanism with reactive radicals is critical for investigation of the UV/chlorine reaction system. Here, we evaluated the radical-mediated reaction kinetics and mechanism of NB, BA, and pCBA in the UV/chlorine process using theoretical calculations and experimental studies. The main reactive radicals •OH, •ClO, and •Cl in the UV/chlorine process for the initial reaction with NB, BA, and pCBA can be explained by H-abstraction and addition pathways. The ΔE0,≠ values for the •OH reaction with NB, BA, and pCBA were in the range of 5.0–8.0, 3.7–8.2, and 3.4–8.2 kcal mol–1, respectively. The ΔE0,≠ values for •ClO and •Cl reactions with these three probe compounds were higher than those of •OH, indicating slower •ClO- and •Cl-initiated reactions than that of the •OH-initiated reaction. The theoretically calculated radical-mediated reaction kinetic rate constants (kCPC) for NB, BA, and pCBA were 4.58 × 10–3, 1.28 × 10–2, and 1.6 × 10–2 s–1, respectively, which was consistent with the experimentally determined pseudo-first-order rate constant (kCPRR) in the UV/chlorine process. Interestingly, theoretical calculations showed that •ClO and •Cl played an important role in subsequent reactions of NB-OH radicals, converting to hydroxylated and chlorinated products, which were further confirmed by experimental products’ identification. The findings from this study indicated that quantum chemistry calculations provide an effective means to investigate the reaction kinetics and mechanism of chemicals in the UV/chlorine process.

Kinetics of MSW Biodegradation with Different Inocula In Laboratory In-Vessel Reactor

The in-vessel composting is considered as an environmentally sound method for the treatment and disposal of Municipal Solid Waste (MSW) as it produces good quality compost with lesser environmental impacts. In this study, the process was accelerated and the composting time was reduced using various industrial organic wastes as inoculums in a vertical in-vessel reactor with stirrer arrangement. This study examined the process kinetics which aims to show the interdependency between biological, chemical &amp; physical factors. It is also the extension of the previous work which dealt with composting of the organic fraction of municipal solid waste. The rate of degradation of volatile solids, TOC and C/N ratio are presented in First-order kinetic model and reaction rate constants are determined. The different inoculums used are yeast sludge, spent wash, distillery effluent and sugar sludge. Yeast sludge has the highest R2 values such as 0.979, 0.978 and 0.986 for VS, TOC and C/N ratio respectively. The R2 value of C/N ratio for the sugar sludge is 0.983. From the kinetic study, it can be concluded that the yeast sludge can be a better option when compared with other sludge to accelerate the process of composting.

Computational modeling and experimental verification of cathode catalyst layer on PEM fuel cells

Fuel cell systems are environmentally friendly energy converters that directly transform the chemical energy of the fuel to electricity. The proton exchange membrane (PEM) fuel cells are one of the most common type of fuel cells since they deliver high power density and are lighter and smaller when compared to the other cells. However, commercialization of the PEM fuel cells is challenging due to the high cost of its components. In addition to high catalyst costs, the problem of poor water management is also a vital issue that needs to be overcome. While the gas diffusion layer of a fuel cell is essential for removing the by-product water, the Nafion solution contained in the catalyst layer has hydrophobic properties and is crucial for both preventing the water accumulation and increasing the effectiveness of the fuel cell. In this study, the effects of Carbon:Nafion ratio on the reduction potential was investigated. The cyclic voltammograms (CV) was produced for each ratio, and it was shown that the CVs exhibit characteristics of hydrogen adsorption/desorption peaks. All the linear sweep voltammogram (LSV) curves revealed well distinguished regions of kinetic, mixed and diffusion limited reaction rate. As a result, it was observed that the ratio of 1:5 resulted higher reduction potential compared to 1:3 and 1:7. Finally, a mathematical model was purposed, in which related the rotation rate and platinum coating with the current density, in order to gain insight about the responses of the fuel cell system. The constructed model is tested and validated experimentally for various parameters that are present in the system, and it may be utilized to determine oxygen reaction activities of the catalysts without performing any unnecessary electrochemical tests.