Kinetic Model Research Articles

Synthesis and Characterization of Graphene Oxide for Efficient Adsorptive Removal of Hymexazol Pesticide from Aqueous Solutions: Thermodynamic, Kinetic, and Isotherm Studies

Background: Nanomaterials play a significant role in the field of water treatment due to their environment-friendly and appealing physical and chemical characteristics. Objective: The purpose of this research is to evaluate whether graphene oxide adsorbents can effectively remove hymexazol pesticide from an aqueous solution. Methods: Graphene oxide (GO) was prepared by the modified Hummer method, and it was characterized by a number characterization techniques, including XRD, Raman spectroscopy, FE-SEM, TEM, and EDX. Furthermore, the performances of the GO adsorbents for the removal of hymexazol from aqueous solution were investigated. The effect of contact time, GO dosage, initial hymexazol concentration, and temperature was carefully studied. Results: The kinetic experimental data were best described by the pseudo-second-order kinetic model. The equilibrium data were well fitted by the Freundlich and Langmuir isotherm models. The kinetic experimental data were best described by the pseudo-second-order kinetic model. And through the thermodynamic studies, it was found that the adsorption process of hymexazol pesticide is endothermic and spontaneous, in addition to the occurrence of adsorption and absorption together. Conclusions: The findings of the adsorption process demonstrated that graphene oxide is an extremely efficient adsorbent material for pesticide adsorption, owing to its large surface area and the presence of oxygen-rich groups on its surface.

Evaluation of characterization and adsorption kinetics of natural organic matter onto nitric acid modified activated carbon

Natural organic substances (NOM) found in drinking water are a major contributor to disinfectant by-product formation and are potentially toxic to humans. Traditional water treatment techniques may not always effectively treat NOMs. Therefore, an advanced treatment method such as adsorption can be inexpensive, simple and efficient. The selected adsorbent's and the NOMs properties both affect the removal effectiveness of the adsorption method. Activated carbon (AC), which is widely used in real-scale water treatment plants, has been modified and used in recent years In order to oxidize the porous carbon surface, raise its acidic qualities, eliminate mineral components, and enhance the surface's hydrophilic qualities. In this research, AC was modified with nitric acid (M-PAC) and NOM removal was investigated. In addition, it is discussed how the modification with nitric acid changes the adsorbent structure and chemistry. A morphology with smooth and irregular voids was observed as a result of nitric acid modification of the original AC by SEM analysis. The particle size increased from 387.65 nm to 502.07 nm for the M-PAC adsorbent. The FTIR spectrum indicates that structures connected to aromatic rings get formed in the M-PAC adsorbent as a result of the modification. The highest NOM removal for the original powdered activated carbon (PAC), 47%, was observed at 36 hours of contact time. On the other hand, M-PAC adsorbent achieved 40% NOM removal at contact times of 72 hours and above. It was concluded that the pseudo-second order kinetic model better represented NOM adsorption for both adsorbents.

Continuous removal of thorium from aqueous solution using functionalized graphene oxide: study of adsorption kinetics in batch system and fixed bed column

This article investigated the kinetic studies of thorium adsorption from an aqueous solution with graphene oxide functionalized with aminomethyl phosphonic acid (AMPA) as an adsorbent. First, the AMPA-GO adsorbent was characterized using TEM, XRD, and FTIR methods. Experiments were performed in two batch and continuous modes. In batch mode, adsorption kinetics were studied in different pH (1–4), temperature (298–328 K), initial concentration (50–500 mg L−1), and dosages (0.1–2 g L−1). The results showed that thorium adsorption kinetic follows pseudo-first-order kinetic model and that the adsorption reaction is endothermic. The maximum experimental adsorption capacity of thorium ions was observed 138.84 mg g−1 at a pH of 3, adsorbent dosage of 0.5 g L−1, and a temperature of 328 K. The results showed that AMPA-GO adsorbent can be used seven times with an acceptable change in adsorption capacity. In continuous conditions, the effect of feed flow rate (2–8 mL min−1), initial concentration (50–500 mg L−1), and column bed height (2–8 cm) was investigated. The continuous data was analyzed using the Thomas, Yoon-Nelson, and Bohart-Adams models. The experimental data of the column were well matched with the Thomas, and Yoon-Nelson models. The research results showed that the use of functionalized graphene oxide adsorbents has a great ability to remove thorium from aqueous solutions.

Unraveling the mechanism of assimilatory nitrate reduction and methane oxidation by Methylobacter sp. YHQ through dual N-O isotope analysis and kinetic modeling

Assimilatory nitrate reduction and methane (CH4) oxidation by bacteria play important roles in carbon (C) and nitrogen (N) biogeochemical cycles. Here, an investigation of enzymatic assimilatory nitrate reduction and CH4 oxidation by Methylobacter sp. YHQ from the wetlands is presented, specifically concentrating on N and oxygen (O) isotope fractionation with various initial nitrate and oxygen concentrations. The N enrichment factors (15εassimilation) increased from 4.2 ± 0.7‰ to 6.9 ±1.3‰ and the O isotope enrichment factors (18εassimilation) increased from 2.7 ± 0.9‰ to 4.7 ± 0.8‰ during nitrate assimilation when initial nitrate concentrations increased from 0.9 mM to 2 mM. Similar 18ε and 15ε values were observed at different oxygen concentrations. The values of 18ε and 15ε provided vital parameters for the assessment of assimilatory nitrate reduction via the Rayleigh equation approach. The ratios of O and N isotope enrichment factors (18ε:15ε)assimilation ranged from 0.64 ± 0.15 to 0.74 ± 0.18 during nitrate assimilation by Methylobacter sp. YHQ with Nas, which were different from (18ε:15ε)assimilation for assimilatory eukaryotic nitrate reductase (eukNR) from literature data. Thus, N and O isotope fractionation could be useful tools to distinguish eukNR from Nas during nitrate assimilation. Additionally, the rates of CH4 oxidation and nitrate reduction were evaluated with a reaction-based kinetic model, and it quantitatively described the enzymatic reactions of nitrate assimilation. Combining dual N-O isotope analysis with kinetic modeling provides new insights into the microbially driven C-N interactions.Graphical

Kinetic Model Implementation of Fluidized Bed Devolatilization

Computational modeling is a powerful tool for studying and investigating the behavior of fluidized bed gasifiers and the modeling of the initial devolatilization step is necessary to provide a reliable description of the whole process involving the feedstock decomposition and the subsequent gasification reaction. In this work, a bench-scale fluidized bed reactor was used to examine the devolatilization of different carbonaceous materials within the temperature range from 650 to 850 °C. The experimental test campaign was used to derive the linear correlation factor to describe the devolatilization in terms of product distribution as a function of temperature and highlight the different behavior between lignocellulosic and plastic feedstocks. Furthermore, the experimental data were used to develop concise kinetic expressions able to fit the experimental devolatilization times ranging from 75 in the case of poplar at a lower temperature and 22 s for the Organic Fraction of Municipal Solid Waste (OFMSW) at a higher temperature. The obtained model produces a simple kinetic expression where the size of the particle is enclosed in the kinetic parameters. The kinetic model sided by the application of linear correlations describes the overall thermal decomposition in a fluidized bed, simplifying its modeling in commercial simulation software, even when particles are considered as point-like bodies.

PREPARATION AND CHARACTERIZATION OF NEW IMINE- FUNCTIONAL GROUP FOR FAST REMOVAL OF Cr (III) IN SOME SUPPLEMENTS FROM SHRIMP SHELL

A new imine-Schiff base adsorbent is prepared from extracted chitosan to make taking away exoskeletons of crustacean shrimp shells low-cost and environmentally friendly with the fast and high ability to remove Cr (III) from aqueous solution. The resulting composites were verified by different techniques FTIR, H-NMR, FESEM, EDX, XRD. On applying the adsorption kinetic model, the pseudo 2nd order model was best characterised, using adsorption equilibrium data; the Langmuir model provided a superior description. Further, the negative value of ∆G shows a spontaneous process in nature. Finally, the prepared adsorbent has been applied to a real sample of bodybuilder supplements.

MOF-derived Co-Al layered double hydroxide modified rice husk biochar nanohybrid for efficient removal of Cu (II) from wastewater

In this study, biochar-derived rice husk (RHB) was modified with Co-Al layered double hydroxide (LDH) derived from Co-based metal-organic framework (ZIF-67) through hydrothermal method to prepare RHB/ZIF-67-derived Co-Al LDH nanohybrid as adsorbent for efficient removal of copper (II) ions from aqueous medium. The nanohybrid was characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy (TEM), energy dispersive X-ray (EDX) spectroscopy, and N2 adorption-desorption. Atomic absorption spectroscopy (AAS) was employed to analyze the concentration of Cu (II) in aqueous solution. In order to investigate the effect of contact time, pH of solution, and adsorbent dose on the removal performance of RHB/ZIF-67-derived Co-Al LDH nanohybrid, batch experimental studies were conducted. The surface adsorption isotherm is well fitted to Langmuir model, and the adsorption mechanism follows the pseudo-second-order kinetic model. In addition, based on the central composite design in the response surface method, the optimal conditions for adsorbent dose, time, pH and initial concentration of Cu (II) are obtained as 2 mg, 3 min, 7 and 50 ppm respectively. In optimal conditions, the nanohybrid shows many advantages including the high removal percent (99.71 %) for Cu (II) ions, excellent adsorption capacity of 1377.94 mg g−1, the ability to reuse for five times, low cost, and compatibility with the environment. The combined properties of RHB and ZIF-67-derived Co-Al LDH provide a large surface area of 849.44 m2 g−1, which increases the contact surface of adsorbent with Cu (II) ions and endows great adsorption performance even in complex environments.

The [(NH3)4Cu2O2]2+‐Peroxo Complex as the Key Intermediate for NH3‐SCR Activity and Deactivation of Cu‐CHA Catalysts.

AbstractIn NH3‐SCR over Cu‐CHA catalysts in the low‐temperature range 150–300 °C, the activation of oxygen occurs via oxidation of a pair of mobile (NH3)2CuI‐complexes located in the cages of the zeolite. In this step, a reactive [(NH3)4Cu2O2]2+‐peroxo complex (μ‐η2,η2‐peroxo diamino dicopper(II)‐complex) is formed. The chemistry of this complex determines several catalytic properties of the Cu‐CHA catalyst. The reaction of NO with the [(NH3)4Cu2O2]2+‐peroxo complex governs the NH3‐SCR activity. A reaction of the [(NH3)4Cu2O2]2+‐peroxo complex with ammonia hinders the reaction of NO with the complex, thus leading to an inhibition of the NH3‐SCR reaction. Finally, the deactivation in presence of SO2 is due to a reaction of SO2 with the [(NH3)4Cu2O2]2+‐peroxo complex, leading to the formation of Cu−S compounds in the catalyst. In this review, the characterization and the reactions of the [(NH3)4Cu2O2]2+‐peroxo complex with NO, NH3, and SO2, and mean‐field kinetic models based on first principles calculations for NH3‐SCR activity and SO2 poisoning are discussed.

Modelling neutron damage effects on tritium transport in tungsten

A damage-induced hydrogen trap creation model is proposed, and parameters for tungsten are identified using experimental data. The methodology for obtaining these parameters using thermo-desorption analysis spectra data is outlined. Self-damaged and optionally annealed tungsten samples have undergone TDS analysis, which has been analysed to identify the properties of extrinsic traps induced by the damage and to determine how they evolve with damage and annealing temperature. A parametric study investigated the impact of the damage rate and temperature on tritium inventories in tungsten. Tritium transport simulations have been performed with FESTIM considering a 1D model of a 2 mm sample of tungsten with damage rates and temperatures varying from 0– 102 dpa/fpy and 600–1300 K, respectively. The results show that after 24 h simultaneous exposure to neutron damage at 102 dpa/FPY and tritium implantation at 700 K, tritium inventories can increase by up to four orders of magnitude when damaged at a rate of 102 dpa/FPY compared to undamaged, defect-free tungsten, increasing further to five orders of magnitude after one full power year. The time taken to reach retention saturation shows the need for kinetic models of trapping properties on time scales relevant to reactor operation. The trap-creation model parameterisation procedure can be used to investigate neutron damage effects on other fusion-relevant materials such as EUROFER, Inconel and more.

Experimental study of nitric oxide distributions in non-premixed and premixed ammonia/hydrogen-air counterflow flames

This study reports an experimental investigation of quantitative Nitric Oxide (NO) distribution in both premixed and non-premixed NH3/H2-air flames using a counterflow burner at atmospheric pressure. One-dimensional (1D) NO laser-induced fluorescence (LIF) spectroscopy and Raman/Rayleigh spectroscopy were conducted to accurately resolve the quantitative 1D NO profile in terms of mixture fraction, temperature, and physical space. We calibrated a saturated NO-LIF model in 5 premixed lean H2/N2/NO-air flames with different seeded NO levels in a McKenna burner and validated its accuracy in three H2N2NO-air counterflow diffusion flames. The overall uncertainty of NO quantification was less than90 ppm. Our measurements were compared with simulations using different ammonia chemical kinetic models, revealing that current models have over 30% uncertainty in predicting peak NO concentrations (mole fraction) in 1D non-premixed and premixed flames and over 100% uncertainty in lower temperature regions. In premixed flames, measured NO concentrations fell within the intermediate range of current chemical kinetic models at lean and stoichiometric conditions, but were lower than the models at rich conditions. In non-premixed flames, all models overestimated the peak NO concentrations by more than 1000 ppm. It is noted that the measured peak NO concentrations increased with higher NH3/H2 ratios (from 4/6 to 8/2), strain rates (from 80 to 140 1/s), and N2 dilution ratios in a 1:1 NH3/H2 mixture (from 0 to 30%). Although most models could qualitatively predict the trends, they were inaccurate in quantifying NO. Additionally, the measured width of the NO profile in mixture fraction space expanded with increasing NH3/H2 ratio, N2 dilution ratio, and strain rate. While models could qualitatively predict this behavior, they consistently underestimated NO in the fuel-rich, lower-temperature region, resulting in a narrower NO profile width. The Manna model showed a better prediction of NO distribution in the fuel rich portion of non-premixed flames, accounting for NH3NO interactions at lower temperatures. These findings highlight the critical need to improve models to accurately predict NO concentrations in ammonia-containing flames and their behavior in fuel rich regions.

A hybrid mesoporous sheet-like NiCo2O4@P,S,N-doped carbon nano-photocatalyst for efficient synergistic degradation of Congo red: Statistical, DFT and mechanism studies

Here, a hybrid mesoporous sheets-like nano-catalyst was used to investigate the degradation of Congo Red (CR) dye. The photocatalytic efficiency of CR dye degradation was evaluated using a variety of mesoporous hybrid materials containing P,S,N-doped carbon (PC1), Co3O4@P,S,N-doped carbon (PC2), NiO@P,S,N-doped carbon (PC3), and NiCo2O4@P,S,N-doped carbon (PC4) sheet-like. The results indicated that the PC4 nano-catalyst exhibited exceptional efficacy in the photocatalytic degradation of CR dye, achieving a degradation efficiency exceeding 99 %. The results also showed that PC4 possessed a band gap of 1.7 eV. To formulate an effective photodegradation system, Analysis of Variance (ANOVA), a valuable statistical method, was employed to examine how varying pH, PC dose, and irradiation time can improve the photodegradation performance. Influential key parameters, including pH, PC dose, irradiation time, and CR concentration, were optimized through response surface methodology applying a four-factor, three-level Box-Behnken design (BBD). To achieve a 99 % decolorization of CR, the optimum conditions were determined to be pH 3.8, PC dose at 14 mg, irradiation time of 10.2 min, and CR concentration of 14.3 ppm. Kinetic models demonstrated that CR degradation followed pseudo-first-order kinetics. Moreover, band gap comparisons, scavenger analysis, and density functional theory (DFT) were used to discuss the CR degradation mechanism.

Recovering ammonium from real treated wastewater by zeolite packed columns: The effect of flow rate and particle diameter

Nitrogen (N) recovery from wastewater is a desirable way to create a (N) neutral society in view of a circular economy approach. Nitrogen recovery from wastewater by employing adsorption columns filled with zeolite can be a very attractive solution. This study assessed the effect of influent flow rates (namely, 1.6 and 2.3 L h−1) and particle diameters (namely, 0.5–1.0 and 2.0–5.0 mm) of zeolite packed in columns on recovering NH4+ from real domestic treated wastewater (RDTWW). Findings revealed that maximum NH4+ recovery can be achieved by using zeolite with the smallest particle diameter (0.5–1.0 mm) and the highest influent flow rate (2.3 L h-1). The maximum NH4+ adsorption rate was 1.2, 21 and 9.8 mg NH4+ kg-1 h-1 after 205, 32 and 35 h of operation. NH4+ adsorption data were analysed by fitting them to both pseudo-first and pseudo-second order kinetic models. The former model best approximated NH4+ adsorption data. Such a result suggested that the amount of NH4+ adsorbed depended solely on the amount of NH4+ in contact with the zeolite surface. Results successfully established the application of zeolite-packed columns in removing NH4+ from real domestic treated wastewater and the effects of process parameters.

Valorized oxalic acid treated onion peel (Allium cepa) and jute stick (Chorchorus olitorius) wastes for dye removal from tannery effluents

This study employed bio-adsorbents prepared from agricultural waste onion peel (Allium cepa) and jute stick (Corchorus olitorius) to remove anionic dye (Acid Red 73) from tannery wastewater. Increases in pH and temperature exhibited negative impact on dye adsorption, although the adsorbent dose, initial concentration of dye, and contact time had positive effects on the adsorption process. Equilibrium data were fitted with both the Langmuir and Freundlich isotherm models, and the maximum adsorption capacities of the oxalic acid-modified onion peel (OAOP) and jute stick (OAJS) were 151.51 and 133.33 mg/g, respectively at 298 K. Dye adsorption was shown to follow a pseudo-second-order kinetic model (R2 = 0.961 – 0.997 for OAOP and (R2 = 0.945 – 0.999 for OAJS). The adsorption was spontaneous and favorable at various temperatures. The values of ΔH° for OAOP and OAJS were negative (−54.78 and −53.12 kJ/mol), which signify an exothermic process. Moreover, both the adsorbents, showed multilayered physisorption based on isotherm and thermodynamic studies. The used adsorbents were regenerated, and reused with decreasing capacity (78.32 ± 2.78 – 21.37 ± 1.96 mg/g for OAOP and 84.72 ± 3.08 – 24.76 ± 2.66 mg/g for OAJS). The application of adsorbents in real tannery dyeing effluents along were also evaluated and discussed.

Oscillatory zoning of minerals as a fingerprint of impurity-mediated growth

We propose a kinetic mathematical model of the oscillatory compositional zoning profile recorded in minerals based on the crystal growth suppression induced by impurities. Notably, the presence of a small amount of impurities significantly inhibits crystal growth, and a growth inhibition mechanism called the pinning effect is widely accepted. Here we show that a model that considers the pinning effect and adsorption/desorption kinetics of impurities on the crystal surface can reproduce the oscillatory compositional zoning. As impurities are common in nature, this model suggests the existence of a universal mechanism that can occur in the growth processes of various crystals.

Evaluating Possible Formation Mechanisms of Criegee Intermediates during the Heterogeneous Autoxidation of Squalene.

Organic molecules in the environment oxidatively degrade by a variety of free radical, microbial, and biogeochemical pathways. A significant pathway is heterogeneous autoxidation, in which degradation occurs via a network of carbon and oxygen centered free radicals. Recently, we found evidence for a new heterogeneous autoxidation mechanism of squalene that is initiated by hydroxyl (OH) radical addition to a carbon-carbon double bond and apparently propagated through pathways involving Criegee Intermediates (CI) produced from β-hydroxy peroxy radicals (β-OH-RO2•). It remains unclear, however, exactly how CI are formed from β-OH-RO2•, which could occur by a unimolecular or bimolecular pathway. Combining kinetic models and multiphase OH oxidation measurements of squalene, we evaluate the kinetic viability of three mechanistic scenarios. Scenario 1 assumes that CI are formed by the unimolecular bond scission of β-OH-RO2•, whereas Scenarios 2 and 3 test bimolecular pathways of β-OH-RO2• to yield CI. Scenario 1 best replicates the entire experimental data set, which includes effective uptake coefficients vs [OH] as well as the formation kinetics of the major products (i.e., aldehydes and secondary ozonides). Although the unimolecular pathway appears to be kinetically viable, future high-level theory is needed to fully explain the mechanistic relationship between CI and β-OH-RO2• in the condensed phase.

Calcium-Based Metal-Organic Framework: Detection and Idiosyncratic Removal of Copper by Nano-Particle Deposition.

A novel calcium-based metal-organic framework (CaMOF@LSB) was designed and synthesized, exhibiting dual functionality for both selective detection and removal of Cu2+ ions from aqueous solutions. The framework's stability, including solvent and pH variations, was established with notable thermal resilience. Colorimetric Cu2+ detection (≥5 ppm) with a high capture capacity of 484.2 mg g-1 by CaMOF@LSB places this material among the few that ensure efficient colorimetric detection and high removal capabilities of Cu2+ ions. Batch adsorption experiments revealed pH-dependent behavior and competitive interactions. Langmuir and pseudo-second-order kinetics models aptly described adsorption isotherms and kinetics, respectively. Thermodynamic assessments confirmed spontaneous and endothermic adsorption. Mechanistically, nanoparticle deposition contributes to the Cu2+ uptake. CaMOF@LSB also exhibited one of the best removal behaviour of Cu2+ by means of oxide formation on the surface. Regeneration of CaMOF@LSB was achieved by simple sonication in 0.1 M aqueous NaOH solution. The recyclability was also tested up to 5 cycles, and it exhibited a small decrease in adsorption capacity observed across the cycles. This research presents a promising avenue for addressing heavy metal pollution using metal-organic frameworks, thereby offering potential applications in water purification and environmental pollution monitoring and remediation.

Characterization and Performance of Peanut Shells in Caffeine and Triclosan Removal in Batch and Fixed-Bed Column Tests.

Peanut shells' adsorption performance in caffeine and triclosan removal was studied. Peanut shells were analyzed for their chemical composition, morphology, and surface functional groups. Batch adsorption and fixed-bed column experiments were carried out with solutions containing 30 mg/L of caffeine and triclosan. The parameters examined included peanut shell particle size (120-150, 300-600, and 800-2000 µm), adsorbent dose (0.02-60 g/L), contact time (up to 180 min), bed height (4-8 cm), and hydraulic loading rate (2.0 and 4.0 m3/m2-day). After determining the optimal adsorption conditions, kinetics, isotherm, and breakthrough curve models were applied to analyze the experimental data. Peanut shells showed an irregular surface and consisted mainly of polysaccharides (around 70% lignin, cellulose, and hemicellulose), with a specific surface area of 1.7 m2/g and a pore volume of 0.005 cm3/g. The highest removal efficiencies for caffeine (85.6 ± 1.4%) and triclosan (89.3 ± 1.5%) were achieved using the smallest particles and 10.0 and 0.1 g/L doses over 180 and 45 min, respectively. Triclosan showed easier removal compared to caffeine due to its higher lipophilic character. The pseudo-second-order kinetics model provided the best fit with the experimental data, suggesting a chemisorption process between caffeine/triclosan and the adsorbent. Equilibrium data were well-described by the Sips model, with maximum adsorption capacities of 3.3 mg/g and 289.3 mg/g for caffeine and triclosan, respectively. In fixed-bed column adsorption tests, particle size significantly influenced efficiency and hydraulic behavior, with 120-150 µm particles exhibiting the highest adsorption capacity for caffeine (0.72 mg/g) and triclosan (143.44 mg/g), albeit with clogging issues. The experimental data also showed good agreement with the Bohart-Adams, Thomas, and Yoon-Nelson models. Therefore, the findings of this study highlight not only the effective capability of peanut shells to remove caffeine and triclosan but also their versatility as a promising option for water treatment and sanitation applications in different contexts.

The Effect of Composition and Temperature on the Hydrogen Reduction Behavior of Sintered Pellets of Bauxite Residue-Lime Mixtures

AbstractThis study explores the isothermal hydrogen reduction of sintered pellets made of a mixture of bauxite residue and calcite with varying compositions at different reduction temperatures. Sintered pellets with varying compositions show three primary iron-containing oxide phases including brownmillerite, srebrodolskite, and fayalite; however, brownmillerite is the major phase in all the sintered pellets. The sintered pellets were reduced in a thermogravimetry furnace to establish instantaneous weight reduction with respect to time. Phases and microstructural analysis were carried out using X-ray diffraction and scanning electron microscopy, respectively. Mercury intrusion porosimeter and pycnometer were utilized to assess the porosity and density of the reduced pellets. Thermochemistry calculations were performed using the thermodynamics software FactSage 8.2. The reduction rate is most pronounced at a temperature of 1000 °C for all pellet compositions. It is intriguing to note that the rate of reduction shows minimal variance across pellets with different compositions; however, the higher calcite pellets exhibit a higher initial rate of reduction. Various kinetic models were examined to determine the activation energies for three different composition pellets, and the three-dimensional diffusion model has been well suited for this process. Close activation energies in the range of 84.6 to 94.8 kJ were obtained. A slightly higher activation energy was obtained for lower CaCO3 added pellets, and it was attributed to their reduced porosity and increased sintering, impeding the reaction kinetics. There were no significant differences in the formation of mayenite with varying the calcite amount; however, higher calcite pellets indicated more mayenite formation. Graphical Abstract

Dehydration of fructose to 5‐HMF catalyzed by commercial faujasite zeolites: kinetic study and influence of the properties of the catalyst

We carried out a mechanistic investigation of the dehydration of fructose catalyzed by a series of proton‐exchanged faujasite zeolites. Using a combination of analytical tools (HPLC, GC, NMR), we could solve and quantify most of the variety of products formed, including (i) cyclic intermediates (ii) transient species (monomeric and dimeric) (iii) byproducts (oligomeric species and humins). The results prove that the reaction goes through a cyclic mechanism, and we could propose a kinetic model matching most of our experimental results and describing the interplay between the different categories of products. By comparing the performances of different catalysts with varying properties, we surprisingly find that increasing the concentration of Brønsted acid sites induces lower catalytic activity. Contrary to general expectations, the mesoporous volume seems to be the most determining parameter for the activity of the catalysts over the set of catalysts evaluated here, which may be explained by the importance of allowing the reactant a significant accessibility to the active sites.

The removal mechanism of lead from wastewater on pharmaceutical sludge-based biochar

This study aims to enhance the resource utilization of waste sludge and mitigate the environmental risks associated with Pb2+ contamination. Municipal sludge biochar (MBC) and pharmaceutical sludge biochar (PBC) were selected as the experimental subjects. The experiment systematically investigated the influential factors affecting adsorption, including adsorbent dosage, reaction time, and pH. The physicochemical attributes of the biochar (BC) were assessed through techniques such as scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction analysis, and point of zero charge analysis. The Pb2+ adsorption process was described by the pseudo-second-order kinetic model and Freundlich isotherm model, the highest adsorption capacities were established as 18.56 mg/g and 19.07 mg/g for MBC and PBC, respectively. The adsorption of Pb2+ on BCs is related to chemical and physical adsorption mechanisms. Ligand bonding, monolayer chemisorption, electrostatic interactions and pore filling were considered as possible mechanisms involved in the adsorption system. It was shown that MBC and PBC are efficient adsorbents for the Pb2+ removal in water.