Second-order Kinetics Research Articles

Cesium ion removal from low-level radioactive wastewater utilizing synthesized cobalt hexacyanoferrate-sand composite

Abstract Here, a novel method of synthesis of a sand-based adsorbent for radioactive Cs+ ion removal is reported. Natural sand has been modified with cobalt hexacyanoferrate (CoHCF) using a simple and effective approach. The detailed physical–chemical characterization of the synthesized adsorbent is carried out using XRD, XPS, UV-visible, FT-IR, ICP-AES and Raman spectroscopy. Cs+ ion batch adsorption studies were conducted radio-analytically, and the sorbent’s adsorption capability was observed to be ∼5 mg g−1. The batch studies revealed that Cs+ ion was selectively adsorbed throughout a broad pH range of 1–10. The rate-controlling steps in the adsorption process, according to kinetic studies, are film diffusion and intraparticular diffusion and the adsorption process follows a second-order kinetics.

Preparation of sodium alginate gel microspheres catalysts and its high catalytic performance for treatment of ciprofloxacin wastewater

The discharge of the antibiotic wastewater has increased dramatically in our country with the development of medical science and wide application of antibiotic, resulting in serious harm to human body and ecological environment. In this work, ciprofloxacin (CIP) was selected as one of typical antibiotics and heterogeneous Fenton-like catalysts were prepared for the treatment of ciprofloxacin wastewater. The sodium alginate (SA) gel microspheres catalysts were prepared by polymerization method using double metal ions of Fe3+ and Mn2+ as cross-linking agents. Preparation conditions such as metal ions concentration, mass fraction of SA, polymerization temperature and dual-metal ions as crosslinking agent were optimized. Moreover, the effects of operating conditions such as initial concentration of CIP, pH value and catalyst dosage on CIP removal were studied. The kinetic equation showed that the effect of the initial concentration of CIP on the degradation rate was in line with second-order kinetics, and the effects of catalyst dosage and pH value on the degradation rate of CIP were in line with first-order kinetics. The SA gel microspheres catalysts prepared by dual-metal ions exhibited a high CIP removal and showed a good reusability after six recycles. The SA gel microspheres catalysts with an easy recovery performance provided an economical and efficient method for the removal of antibiotics in the future.

Characteristics of enzymolysis of silkworm pupa protein after tri-frequency ultrasonic pretreatment: kinetics, thermodynamics, structure and antioxidant changes.

As a by-product of the sericulture industry, the utilization rate of silkworm pupa resources is currently not high. Proteins are converted into bioactive peptides through enzymatic hydrolysis. Not only can it solve the utilization problem, but it also creates more valuable nutritional additives. Silkworm pupa protein (SPP) was pretreated with tri-frequency ultrasonic (22/28/40kHz). Effects of ultrasonic pretreatment on enzymolysis kinetics, enzymolysis thermodynamics, hydrolysate structure as well as hydrolysate antioxidant of SPP were investigated. Ultrasonic pretreatment significantly increased the hydrolysis efficiency, showing a 6.369% decrease in k m and a 16.746% increase in k A after ultrasonic action (p < 0.05). The SPP enzymolysis reaction followed a second-order rate kinetics model. Evaluation of enzymolysis thermodynamics revealed that Ultrasonic pretreatment markedly enhanced the SPP enzymolysis, leading to a 21.943% decrease in E a. Besides, Ultrasonic pretreatment significantly increased SPP hydrolysate's surface hydrophobicity, thermal stability, crystallinity, and antioxidant activities (DPPH radical scavenging activity, Fe2+ chelation ability, and reducing power). This study indicated that tri-frequency ultrasonic pretreatment could be an efficient approach to enhancing the enzymolysis and improving the functional properties of SPP. Therefore, tri-frequency ultrasound technology can be applied industrially to enhance enzyme reaction process.

Continuous flow extraction of biodiesel produced in a packed-bed reactor using supercritical carbon dioxide and tetrahydrofuran as solvents

The concurrent process of biodiesel (FAME) extraction and triglyceride methanolysis was carried out by using supercritical carbon dioxide (SC–CO2) and tetrahydrofuran (THF). This study explored the integration of SC-CO2 extraction facilitated catalyst-free transesterification efficiently at low temperatures with practical biodiesel productivity. The work started with studying the transesterification kinetics of triglycerides using different molar ratios of methanol under various SC-CO2 conditions in the presence of THF solvent. The elementary second-order kinetics associated with the mass transfer limiting factor satisfied the experimental results from all different mixing ratios. A four-factorial Box-Behnken Design (BBD) coupled with the ANOVA was employed to optimize the FAME recovery by the reaction-extraction processes with continuous two streams of SC-CO2 and 10% v/v THF-methanol mixture. The optimum predicted FAME recovery was 95.47% w/w at 71.93 °C, 186.67 bar using the substrate ratio 12.16. The supercritical fluid-assisted dispersion feature was characterized through the Peclect number (Pe) obtained from the volumetric dispersion model (VDM). The Pe could indicate suitable substrate mixing for the process operation and design to enhance production efficiency. The feasibility of upscaling the process to the commercial level was proposed with preliminary economic consideration, which could suggest process improvements in further research and technological development.

Clicking together Alkynes and Tetracyanoethylene.

The [2+2] cycloaddition - retro-electrocyclization (CA-RE) reaction allows ready synthesis of redox-active donor-acceptor chromophores from an electron-rich alkyne and electron-poor olefins like tetracyanoethylene (TCNE). The detailed mechanism of the reaction has been subject of both computational and experimental studies. While several studies point towards a stepwise mechanism via a zwitterionic intermediate for the first step, the cycloaddition, the reaction follows neither simple second-order nor first-order kinetics. Recent studies have shown that the kinetics can be understood if an autocatalytic step is introduced in the mechanism, in which complex formation with the donor-substituted tetracyanobutadiene (TCBD) product possibly facilitates nucleophilic attack of the alkyne onto TCNE, generating the zwitterionic intermediate of the CA step. This Concept highlights the convenient use of the "click-like" CA-RE reaction to obtain elaborate donor-acceptor chromophores and the recent mechanistic results.

Zinc oxide nanostructures: Experiments probing their transformation to nanorods

Due to their high length-to-diameter aspect ratio, ZnO nanorods (ZnO-NRs) are extensively used in different applications. However, how they form is not well understood. Here, we have investigated the formation of ZnO-NR by sequential, temporal evolution of ZnO nanostructures. We observe sphere-like ZnO nanoparticles (ZnO-NP), as early as 5–10 s. Subsequently, these spherical ZnO-NPs aggregate and form short chains, which transform into novel nanocones. This hitherto unseen ZnO nanocones (ZnO-NCs) are hollow on one side and has a pointed end on the other side. Two ZnO-NCs together form individual ZnO-NC pairs. High intrinsic surface energy may have caused a ZnO-NC to pair-up with another adjacent ZnO-NC. Later, each of these paired ZnO-NCs transform into ZnO-NRs. We find that, formation of ZnO-NR follows second-order rate kinetics with respect to zinc precursor and HMTA concentration. Additionally, temperature and HMTA concentration significantly influence the length of ZnO-NR.

Inhibited reactivity of horseradish peroxidase by its conjugated proteins through redox mediated electrochemical interrogation

In this article, a classical redox mediated metal (in this study, Au) indicator electrode approach was revisited for the direct interrogation of ‘slow’ enzymatic redox second-order kinetics of horseradish peroxidase (HRP) for oxidative conversion of the model redox substrates, ferrocenemethanol (FcMeOH) and hydroquinone (H2Q) in low HRP-concentration levels. The presented electroanalysis allowed us to recognize the inhibited enzyme reactivity of HRP for FcMeOH-oxidation by its conjugation to model proteins (streptavidin, avidin, and monoclonal antibody), whereas this effect was negligible for H2Q-oxidation by HRP. From a theoretical investigation using finite element analysis, slow kinetics of HRP can be sensitively recognized through an Au indicator electrode approach in the case where HRP bulk electrolyzes a redox substrate in a solution. Five redox substrates were electrochemically investigated, and FcMeOH and H2Q showed negligible side reactions during mediation between HRP and the indicator electrode. From the chronoamperometric approach, the apparent rate constants for oxidative conversion of FcMeOH by the non-conjugated, free HRP were estimated to be ∼104 M−1s−1 at various pH values, while that of H2Q was roughly two orders of magnitude higher at pH ∼7. The molecular docking simulation revealed the need for a significant conformational change of HRP for FcMeOH access to the heme site, whereas the structural alternation of HRP was negligible for access of the H2Q into the domain of the enzyme. The simulation result indicates that the oxidative conversion rate of FcMeOH by HRP could be more susceptible to recognize additionally induced steric hindrance for access of the redox substrate to the catalytic site of the enzyme than that of H2Q. We experimentally verified that the apparent rate constant for FcMeOH-oxidation by the HRP conjugated to streptavidin was estimated to be ∼5 times smaller than that by the free HRP, and those by other conjugates to avidin and monoclonal antibody were ∼60% of that by the non-conjugated one. In contrast to the case of FcMeOH, the estimated reactivity of H2Q by HRP was barely affected by the conjugated model proteins. The presented study demonstrated that a redox enzymatic reactivity of HRP could be significantly affected by conjugated proteins when access of a redox substrate to a catalytic site of an enzyme is susceptible to conformational changes.

Exploration of an efficient method for removing antibiotics from water and digested sewage sludge using Fe(VI): Kinetics and P phytoavailability and compostability in treated sludge

Potassium ferrate (K2FeO4) containing hexavalent iron [Fe(VI)] is an environmentally friendly oxidant, which possesses strong oxidizing power to treat wastewater and sludge. Therefore, the present study investigated degradation of selected antibiotics, namely levofloxacin (LEV), ciprofloxacin (CIP), oxytetracycline (OTC), and azithromycin (AZI), in water and anaerobically digested sewage sludge samples using Fe(VI).The effects of different Fe(VI) concentrations and initial pH values on antibiotic removal efficiency were evaluated. Under the studied conditions, LEV and CIP were almost completely removed from water samples, following second-order kinetics. In addition, over 60% of the four selected antibiotics were removed from sludge samples using 1 g L−1 Fe(VI).Furthermore, P phytoavailability and compostability of Fe(VI)-treated sludge were evaluated using different extraction reagents and a small composting unit. The extraction efficiency of phytoavailable P using 2% citric acid and neutral ammonium citrate was approximately 40% and 70%, respectively. The mixture of Fe(VI)-treated sludge and rice husk was self-heated in a closed composting reactor through the biodegradation of organic matter derived from the treated sludge.Therefore, Fe(VI)-treated sludge may be used as an organic material containing phytoavailable P for compost.

The Thermoluminescence Parameters of Irradiated K-Feldspar

Isothermal decay of the TL glow curve has been studied at ambient temperature. Heating of feldspar at 600ºC leads to increased sensitivity of the samples upon irradiation for the whole range of glow curve. In general, we observe a sensitivity increase of about five times. Fading of the glow curve is observed at the low-temperature part of the glow curve while it has been kept in the dark at the ambient, constant temperature. After a certain period, approximately in 40 to 50 days, the low-temperature region of the glow curve fades down while the high-temperature part remains unchanged. Peaks at the low-temperature region of the TL glow curve were isolated by the curve subtraction method. Activation energy and frequency factor parameters of the isolated peaks were calculated, taking first and second-order kinetics into account. The values of the calculated activation energy vary between 0.7 to 1.1 eV, and frequency factor values of the isolated peaks change within the order of 109 to 1013s-1. The µ values clearly indicate that all isolated peaks are more likely to be second-order kinetics.

Rapid Synthesis of PbO-NPs Photocatalysts, Investigation of Methylene Blue Degradation Kinetics

The study focused on the green synthesis of lead oxide nanoparticles (PbO-NPs) using green tea extract and its use for photocatalytic degradation. The effect of experimental conditions such as green tea extract concentrations and reaction temperatures on the structure and size of PbO-NPs has been investigated. Reaction temperatures of 25, 50 and 85 ℃ and green tea extract concentrations of 5, 10, 20, 40, 80 and 100 mg/mL were used for preparing of PbO-NPs. Amount of the phenolic acid contained in the green tea extracts was determined according to the Folin-Cioceltau method. The synthesized PbO-NPs were further confirmed by UV–visible Spectroscopy, Fourier Infrared Transformation Spectroscopy (FTIR), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive (EDX) analysis. Tetragonal and orthorhombic morphology of PbO-NPs were observed in SEM images. While the crystallite structure of the PbO-NPs was obtained for the samples prepared using 5 and 10 mg/mL extract concentration for all reaction temperatures, the amorphous structures of PbO-NPs were seen for the samples prepared using extract concentrations of 20, 40, 80 and 100 mg/mL. Finally, PbO-NPs catalyst was tested for the degradation of methylene blue (MB) under UV light. The effect of dye concentration, catalyst amount and pH on degradation were investigated. By determining suitable experimental conditions, MB degradation reached 89% with PbO-NPs in 60 minutes. The reaction kinetics of MB removal from aqueous solution under UV lamp and in the dark media were compared for first-order and second-order reaction kinetics.

Adsorption of ibuprofen from aqueous solution onto a raw and steam-activated biochar derived from recycled textiles insulation panels at end-of-life: Kinetic, isotherm and fixed-bed experiments

This study explores the potential use of recycled textile biochar (RT-BC) and steam-activated biochar (RT-SABC), derived from insulation panels at end-of-life, as sorbents for removing ibuprofen from aqueous solutions. After steam activation, the surface area and micropore volume increased. Subsequently, kinetic and isotherm experiments were investigated at 20 °C, 200 rpm and 50 mg/L ibuprofen solution. Equilibrium was reached after 24 h for RT-BC and 120 h for RT-SABC. The kinetics of RT-BC and RT-SABC followed the pseudo-first-order and Elovich models, respectively. RT-SABC isotherm showed the highest adsorption capacity (53.9 mg g−1), well-fitted into the Sips model. Ibuprofen uptake by RT-SABC was nearly irreversible. Afterward, RT-SABC dynamic performance was evaluated in a fixed-bed column for three bed heights. The breakthrough point (41.7–476.7 h), the volume of effluent treated (0.6–6.4 L at breakthrough) and adsorption capacity (22.09–39.81 mg g−1) increased with bed height (10–30 cm). Thomas and Clark's models simulated the experimental points, confirming second-order kinetics and Sips isotherm. Different functional groups were involved in the adsorption mechanism. Preliminary experiments in tap water on RT-SABC showed a removal (>83 %) due to ionic strength and reduced pH. Therefore, RT-SABC could be an efficient adsorbent for ibuprofen removal from aqueous systems.

Exploration of crystal structure, and luminescence behaviors of Terbium-activated CaWO4 phosphor

This manuscript includes structural, optical, photoluminescence, and thermoluminescence behaviors of Terbium incorporated CaWO4 samples with nominal compositions of Ca1-xTb2x/3WO4 (x = 0.01, 0.02, 0.03, 0.04, 0.05) prepared by the traditional solid-state reaction route. Results found from the Rietveld refinements of X-ray diffraction patterns confirmed that all the samples have tetragonal crystal structures with I41/a space group. The variation of unit cell volume with the compositions shows an anomaly at x = 0.03. Band gap energy values of these synthesized samples are found from the UV–Visible absorbance spectra with increasing order. Photoluminescence behaviors, as well as the FWHM values, are analyzed from the excitation along with the emission spectra. Critical quenching concentration at x = 0.03 with a critical energy transfer distance of ∼ 20 Å caused by the dipole-dipole interactions is found in these spectra. CIE Chromaticity coordinates are indicated the green emission color of all the prepared samples with high color purity, correlated color temperature, color rendering index, and luminous efficiency of radiation values. Quantum efficiency of the material with x = 0.03 Tb concentration is observed under 255 nm excitation wavelength. PL decay analyses of the phosphors are carried out and the average lifetime values are calculated. Thermoluminescence spectroscopy of x = 0.03 irradiating by 15 min of UV dose is described as the lower UV dosimetry and second-order kinetics of the material.

Green micellar stability-indicating high-performance liquid chromatography method for determination of rupatadine fumarate in the presence of its main impurity desloratadine: Oxidative degradation kinetics study.

A green micellar stability-indicating high-performance liquid chromatography method was developed for rupatadine fumarate determination in existence with its main impurity desloratadine. Separation was attained using Hypersil ODS column (150×4.6mm, 5μm), the micellar mobile phase consisted of 0.13M sodium dodecyl sulfate, 0.1M disodium hydrogen phosphate adjusted by phosphoric acid to pH 2.8 and 10% n-butanol. The column was maintained at 45◦ C and detection was carried out at 267nm. A linear response was achieved over the range of 2-160μg/ml for rupatadine and 0.4-8μg/ml for desloratadine. The method was applied for rupatadine determination in alergoliber tablets and alergoliber syrup without the interference of methyl paraben and propyl paraben present as main excipients. Rupatadine fumarate revealed pronounced susceptibility to oxidation; further study of oxidative degradation kinetics was carried out. Rupatadine was found to follow pseudo-first-order kinetics when exposed to 10% H2 O2 at 60 and 80°C and the activation energy was found to be 15.69Kcal/mol. At a lower temperature (40°C), degradation kinetics regression was best fitted as a polynomial quadratic relationship, thus rupatadine oxidation at a lower temperature tends to adopt a second-order kinetics rate. Oxidative degradation product structure was revealed using infrared and found to be rupatadine N-oxide at all temperature values.

Time-Dependent Demineralization of Tilapia (Oreochromis niloticus) Bones Using Hydrochloric Acid for Extracellular Matrix Extraction.

Tilapia (Oreochromis niloticus) is a widely cultivated fish in tropical and subtropical regions such as the Philippines, generating substantial waste during processing, including bones that are a valuable source of extracellular matrix (ECM). However, the extraction of ECM from fish bones requires an essential step of demineralization. This study aimed to assess the efficiency of tilapia bone demineralization using 0.5 N HCl at different time durations. By evaluating the residual calcium concentration, reaction kinetics, protein content, and extracellular matrix (ECM) integrity through histological analysis, composition assessment, and thermal analysis, the effectiveness of the process was determined. Results revealed that after 1 h of demineralization, the calcium and protein contents were 1.10 ± 0.12% and 88.7 ± 0.58 μg/mL, respectively. The study found that after 6 h, the calcium content was almost completely removed, but the protein content was only 51.7 ± 1.52 μg/mL compared to 109.0 ± 1.0 μg/mL in native bone tissue. Additionally, the demineralization reaction followed second-order kinetics with an R2 value of 0.9964. Histological analysis using H&E staining revealed a gradual disappearance of the basophilic components and the emergence of lacunae, which can be attributed to decellularization and mineral content removal, respectively. As a result, organic components such as collagen remained in the bone samples. ATR-FTIR analysis showed that all demineralized bone samples retained collagen type I markers, including amide I, II, and III, amides A and B, and symmetric and antisymmetric CH2 bands. These findings provide a route for developing an effective demineralization protocol to extract high-quality ECM from fish bones, which could have important nutraceutical and biomedical applications.

Adsorption of Zn2+ ion by macadamia nut shell biochar modified with carboxymethyl chitosan and potassium ferrate

A series of biochars and modified biochars were prepared by using macadamia nut shell (MNS) as raw material at different calcination temperatures and further using carboxymethyl chitosan (CMC) and K2FeO4 as the modifying agent, respectively. These biochar and modified biochars were used as adsorbents for adsorbing Zn2+ ion in aqueous solution. It is found that the adsorption behaviors of modified biochars BC-CMC and BC-K2FeO4 are consistent to the pseudo second-order kinetics model and the Langmuir equation. The maximum adsorption capacities for these adsorbents are increased in the following order: BC-CMC > BC-K2FeO4 > > BC-700. Among these biochars, BC-CMC exhibits the highest adsorption capacity of 97.09 mg/g, which may be mainly due to that BC-CMC has more amino, hydroxyl and carboxyl functional groups. The BC-CMC also exhibits better desorption performance and reusability. Furthermore, BC-CMC also shows higher adsorption capacity for Cu2+ and Pb2+. Based on the results, the adsorption mechanism of BC-CMC for Zn2+ was also proposed.

Characterization of the protolysis equilibria of 1-naphthoylhydrazide and of its oxidation mechanism by hexachloroiridate(IV) in aqueous solution

Oxidation of 1-naphthoylhydrazide (1-NH) by hexachloroiridate(IV) ([IrCl6]2−) was characterized in detail by various spectroscopic techniques. The stoichiometry was determined to be [1-NH]:[Ir(IV)] = 1:4 and 1-NH was oxidized to 1-naphthoic acid which was confirmed by RP-HPLC and mass spectral analyses. The oxidation reaction strictly followed second-order kinetics; subsequently the rate versus pH profile was built up. A convincing reaction mechanism was proposed to account for all the experimental observations; rate constants of the rate-determining steps were calculated. Moreover, Activation parameters were determined to be ΔH2‡ = 36.5 ± 2.4 kJ∙mol−1 and ΔS2‡ = −75 ± 8 J∙K−1∙mol−1 for the reaction between [IrCl6]2− and the neutral form of 1-NH. Possible modes of electron transfer are discussed. This work also reports the protolysis constants of 1-NH for the first time, which are pKa1 = 3.03 ± 0.06 and pKa2 = 12.0 ± 0.1 at 25.0 °C and 1.0 M ionic strength.

Design and construction of cobalt-organic framework with outstanding adsorption properties assembled by 3-(3,5-dicarboxylphenoxy)pyridine

Removal the hazards of Azo organic dyes from waterbody through porous heterogeneous materials is considered as a low-cost and high-efficient method. Intriguingly, two metal organic frameworks (MOFs), {[Co3(L)3(H2O)]·3.5(C4H2O2)}n and [Co4(L)4(bit)2]n designated as MOF 1 and 2, have been synthesized through the traditional solvothermal method. MOF 2 exhibits significant removal effect on organic dye (congo red (CR)) from waterbody owing to more imidazole rings in the structure than 1. After optimizing the experimental conditions, the highest adsorption capacity (810.7 mg g-1) and high removal rate (97.28%) of 2 are obtained in 500 ppm CR solution. Pseudo second-order kinetics and Langmuir isotherms more accurately described the adsorption process of 2. In addition, 2 exhibits high recyclability, stability and adsorption performance through a simple organic solvent release system. Moreover, 2 also exhibits high adsorption performance in real wastewater. The possible mechanism of selective adsorption involves the π-π stacking interaction, hydrogen bond, synergistic effect of electrostatic interaction and pore filling. All the bench experiments have indicated that 2 is a promising potential sorbent in the practical wastewater treatment and CR dyes recovery.

Sodium Salt of Partially Carboxymethylated Sodium Alginate-Graft-Poly(Acrylonitrile): II Superabsorbency, Salt Sensitivity and Swelling Kinetics of Hydrogel, H-Na-PCMSA-g-PAN.

The water absorption measurements of a novel superabsorbent anionic hydrogel, H-Na-PCMSA-g-PAN, has been reported first time in water with a poor conductivity, 0.15 M saline (NaCl, CaCl2, and AlCl3) solutions, and simulated urine (SU) solutions at various times. The hydrogel has been prepared by the saponification of the graft copolymer, Na-PCMSA-g-PAN (%G = 316.53, %GE = 99.31). Results indicated that as compared to the swelling capacity values evaluated in water with a poor conductivity, the ability of the hydrogel to swell in various saline solutions with the same concentration is significantly reduced at all different durations. The swelling tends to be Na+ > Ca2+ > Al3+ at the same saline concentration in the solution. Studies of the absorbency in various aqueous saline (NaCl) solutions also revealed that the swelling capacity decreased as the ionic strength of the swelling medium rose, which is consistent with the experimental results and Flory's equation. Furthermore, the experimental results strongly suggested that second-order kinetics governs the swelling process of the hydrogel in various swelling media. The swelling characteristics and equilibrium water contents for the hydrogel in various swelling media have also been researched. The hydrogel samples have been successfully characterized by FTIR to show the change in chemical environment to COO- and CONH2 groups after swelling in different swelling media. The samples have also been characterized by SEM technique.

Potential of the Biomass Waste Originating from Saccharum officinarum as a Fenton Precursor for the Efficient Oxidation of Azo Dye from an Aqueous Stream

In the current investigation, elements extracted from Saccharum officinarum were identified as exporters of Fenton catalysts. Saccharum officinarum was soaked in an alkali prior to acidic treatment and then subjected to pyrolysis for elemental recovery. X-ray diffraction (XRD) and scanning electron microscopy (SEM) augmented with energy-dispersive X-ray spectroscopy (EDX) were used to identify the prepared catalyst. The material was combined with hydrogen peroxide, which led to Fenton’s reaction. Then, the modified Fenton system was applied to eliminate the textile dye, named Bismarck Brown Azo dye, contaminating the aqueous effluent. Response surface methodological model (RSM) analysis was used to identify the most effective operational parameters, and the model set the optimized values as 39 and 401 mg/L for Saccharum officinarum and H2O2 doses, respectively, at pH 2.9. The maximum Bismarck Brown Azo dye removal achieved was 85%. Increasing the temperature to 60 °C improved the dye oxidation efficiency. However, the dye treatment efficacy was reduced when the dye loading increased. Additionally, the kinetic rate order was investigated and the system was fitted to second-order rate reaction kinetics. The thermodynamic variables show that the reaction is endothermic and non-spontaneous.

Enhanced Removal of Doxycycline by Simultaneous Potassium Ferrate(VI) and Montmorillonite: Reaction Mechanism and Synergistic Effect

Doxycycline (DOX), a typical antibiotic, is harmful to aquatic ecosystems and human health. This study presents DOX removal by potassium ferrate (Fe(VI)) and montmorillonite and investigates the effect of Fe(VI) dosage, reaction time, initial pH value, montmorillonite dosage, adsorption pH, time and temperature on DOX removal. The results show that DOX removal increases when increasing the Fe(VI) dosage, with the optimal condition for DOX removal (~97%) by Fe(VI) observed under a molar ratio ([Fe(VI)]:[DOX]) of 30:1 at pH 7. The reaction of DOX with Fe(VI) obeyed second-order kinetics with a rate constant of 10.7 ± 0.45 M−1 s−1 at pH 7. The limited promotion (~4%) of DOX adsorption by montmorillonite was observed when the temperature increased and the pH decreased. Moreover, the synergetic effect of Fe(VI) and montmorillonite on DOX removal was obtained when comparing the various types of dosing sequences (Fe(VI) oxidation first and then adsorption; adsorption first and then Fe(VI) oxidation; simultaneous oxidation and adsorption). The best synergistic effect of DOX removal (97%) was observed under the simultaneous addition of Fe(VI) and montmorillonite, maintaining the Fe(VI) dosage (from 30:1 to 5:1). Five intermediates were detected during DOX degradation, and a plausible DOX degradation pathway was proposed.