Pseudo-second Order Kinetic Model Research Articles

Efficient recovery of phosphate by La-MOFs: An excellent adsorption performance and mechanism

Lanthanum-type metal-organic frameworks (La-MOFs) can be used to mitigate phosphate pollution in wastewater. Herein, La-MOFs was gained via the solvothermal method and its phosphate removal property was examined under various conditions, like variable initial phosphate concentration, solution pH, and co-existing ions. The material morphology, element composition, and crystal morphology of the La-MOFs was characterized using XRD, SEM, FTIR, and XPS. The phosphate removal mechanism was investigated by combining thermodynamic and kinetic analyses. The La-MOFs exhibited superior adsorption capability for surplus phosphate in water, and also had a high selectivity for phosphate in the complexed environment with some co-existing ions. Maximum adsorption was obtained at pH 4. The sorption procedure of La-MOFs aligned more with the Langmuir and pseudo-second order kinetic models, demonstrating monomolecular-layer-controlled chemisorption. And the maximum sorption capacity was 73.69 ​mg ​g−1. Electrostatic interactions and ligand exchange, which enabled the development of an La–O–P inner-sphere complexation, were identified as the primary mechanisms of phosphate removal. This research provides insights into the optimal conditions and mechanism of phosphate adsorption by La-MOFs.

Synthesis, characterization, and adsorptive performance of titanium dioxide nanoparticles modified groundnut shell activated carbon on ibuprofen removal from pharmaceutical wastewater

In this study, Titanium dioxide Nanoparticles (TiO2 NPs) were biosynthesized using the extract of Cola nitida (Kola nut) pod as a reducing agent. The synthesized TiO2 NPs were impregnated on the surface of Groundnut Shell Activated Carbon (GNSAC) to produce TiO2-NPs-GNSAC, and its performance on the removal of ibuprofen from pharmaceutical wastewater was investigated. The two adsorbents (GNSAC and TiO2-NPs-GNSAC) were characterized using proximate analysis, Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscope (SEM), Brunauer-Emmett-Teller (BET), and Energy Dispersive X-ray (EDX). Physical properties such as moisture content, ash content, and volatile matter content were also determined. The combined effects of three independent variables (temperature, time, and adsorbent dosage) were evaluated in a batch study designed through Box Behnken Design (BBD) of the Response Surface Methodology (RSM) for experimental design, analysis, and process optimization. Regeneration examinations were conducted for three cycles. The proximate analysis showed that GNSAC and TiO2-NPs-GNSAC have 63.21 and 71.11 % of carbon, respectively, which could be attributed to the high organic content in Groundnut Shell (GNS). BET analysis proved that the adsorbents (GNSAC and TiO2-NPs-GNSAC) were mesoporous with mean pore sizes of 6.046 and 5.353 nm, respectively. At optimum conditions of 0.62 g/L, 30 °C and 30 min for adsorbent dosage, temperature, and time, respectively, 68.53 % of ibuprofen was removed using GNSAC, while 81.78 % of ibuprofen was removed at optimum adsorbent dosage, temperature, and time of 0.5 g/L, 30 °C, and 50 min, respectively, using TiO2-NPs-GNSAC. Langmuir isotherm best described the equilibrium data using GNSAC and TiO2-NPs-GNSAC, with maximum monolayer adsorption capacities of 40.82 mg/g and 55.56 mg/g, respectively. Pseudo second-order kinetic model was more suitable to predict the experimental data. The mean free energy (E) values of 0.345 and 0.746 KJ/mol obtained for ibuprofen adsorption onto GNSAC and TiO2-NPs-GNSAC indicate that the mechanism of adsorption of ibuprofen follows the physisorption process. Based on the thermodynamic investigation of the current process, it can be concluded that the adsorption of ibuprofen by the prepared activated carbon (GNSAC and TiO2-NPs-GNSAC) was a spontaneous and endothermic process. Additionally, the adsorbent was successfully regenerated three times, and it was able to perform the adsorption and desorption processes well. Hence, the results of this work suggest that the activated carbon prepared from groundnut shell is a suitable adsorbent for the adsorption of ibuprofen from pharmaceutical wastewater.

One-step enrichment of phenolics from Chaenomeles speciosa (Sweet) Nakai fruit using macroporous resin: Adsorption/desorption characteristics, process optimization and UPLC-QqQ-MS/MS-based quantification

Chaenomeles speciosa (Sweet) Nakai fruit is a good source of phenolics with many health benefits. In this work, the enrichment of C. speciosa fruit total phenolics (CSFTP) using macroporous resins was studied. NKA-Ⅱ resin was selected for enriching CSFTP due to its highest adsorption/desorption quantity. Adsorption characteristics of CSFTP on NKA-Ⅱ resin exhibited a good fit with the Langmuir isotherm model and pseudo-second order kinetics model. This adsorption was spontaneous, exothermic, and entropy-decreasing through a physisorption mechanism. The breakthrough-elution curves were studied to optimize CSFTP enrichment conditions. One-step enrichment increased CSFTP content in the extracts from 26.51 % to 78.63 %, with a recovery of 81.03 %. A UPLC-QqQ-MS/MS method in multiple reaction monitoring (MRM) mode was established and validated for the simultaneous quantification of seven phenolic compounds. This study demonstrates the feasibility of industrial enrichment of CSFTP using NKA-Ⅱ resin and proposes a reliable method for quality control of CSFTP-rich products.

Ultra-high adsorption capacity and selectivity of photo-enhanced sulfur-rich M2S3 (M[dbnd]Bi and Sb) for gold recovery from electronic wastewater

Recycling gold efficiently from electronic waste (e-waste) not only facilitates the sustainable use of precious resources, but also mitigates environmental risks. In this work, two simple metal sulfides M2S3 (MBi and Sb) microspheres with extraordinary adsorption properties were prepared by a convenient hydrothermal technique for selectively recovering gold from e-waste water. The assistance of visible light significantly improved the gold adsorption performance of M2S3. Two sulfide materials exhibit excellent gold adsorption properties, and the maximum capacity for adsorption reaches 3615.45 mg g−1 for Bi2S3, and 1651.95 mg g−1 for Sb2S3 under optimal conditions and incandescent light irradiation. Gold adsorption on M2S3 materials follows Langmuir and pseudo-second order kinetic models, suggesting that the Au(III) adsorption is dominated by chemisorption in a monolayer adsorption mode. XRD and XPS analysis indicate that the strong sulfur affinity for gold and the photocatalytic reduction-oxidation reaction between Bi2S3 and gold are the main mechanisms for effective gold adsorption on metal sulfides. In addition, M2S3 exhibits excellent gold adsorption selectivity against coexisting ions including Zn(II), Co(II), Cu(II), Fe(III), Ni(II), Mg(II), Ca(II), Al(III) present in actual electronic wastewater. The gold loaded on Bi2S3 was efficiently eluted using acidic thiourea, and the excellent adsorption performance was maintained over five adsorption/desorption cycles. This work presents an effective and simple method for recovering gold(III) from the leachate of discarded electronic devices. Metal sulfides have high adsorption selectivity, ultra-high adsorption capacity, and excellent recyclability, making them a promising green adsorption material for recovering gold from electronic waste.

Efficient removal of sodium dodecyl benzene sulfonate employing chitosan-modified waste floral foam as adsorbent

The wide application of surfactants has brought about severe contamination to environment, especially, in aqueous media. In this connection, efficient removal of surfactant residues in waters is essential. In the present work, a commonly used surfactant, sodium dodecyl benzene sulfonate (SDBS) was employed as a model surfactant for removal studies. A new adsorbent based on waste floral foam (FF) was prepared and employed to remove SDBS in various waters. Phenol formaldehyde resin-based waste FF was firstly activated with alkali aqueous, and then modified with chitosan (CS) to introduce active amino groups on the framework of FF to obtain the adsorbent based on CS-modified FF (CS@FF). Under the optimized synthesized conditions, the obtained adsorbent displayed satisfactory removal performance towards SDBS by means of multipoint and multitype interactions, 93.3 % SDBS was removed within 30 min. The adsorption behavior of CS@FF towards SDBS well fitted the pseudo-second order kinetic model and Langmuir adsorption model. In addition, increase of temperature favored the removal of SDBS. After the optimization of removal parameters, the CS@FF was used to remove SDBS in actual waters, and the achieved removal rates were obviously higher than that achieved on unmodified FF. The present study not only provides a cost-effective adsorbent for the removal of surfactants, but also opens up a feasible route for reutilization of discarded FF.

Synthesis of iron oxide microparticles with fern leaf morphology: Assessment of the RY-145 azo-dye adsorption

New particulate ceramic materials with outstanding properties are needed for several technological applications. In this work, multibranched hematite (α-Fe2O3) has been synthesized by tuning the experimental conditions for obtaining dendritic microparticles with the morphology of fern leaves. Variations of temperature, precursor (K3[Fe(CN)6]) concentration, and time were performed to synthesize dendritic hematite with the best fractal morphology. These materials were characterized structurally and morphologically by X-ray powder diffraction and electron microscopy (SEM and TEM). In addition, the composition was studied by X-ray dispersive energy analysis (EDX). The well-formed multibranched sample was additionally analyzed by infrared (IR) and Raman spectroscopies, thermal analysis, and N2 gas adsorption at 77 K. Finally, this multibranched sample was evaluated as an adsorbent for the removal of an azoic dye (Reactive Yellow-145: RY-145) under mild conditions (25 °C, atmospheric pressure) and pH 3.5. The results showed the interesting potentiality of this multibranched α-Fe2O3 for the adsorption of azo dyes and revealed the high stability of the adsorbent particles. However, the adsorption capacity of the solid is moderately low (13 – 32 mg/g), and it is worth improving this parameter. A pseudo-second order kinetic model was well adjusted, revealing an external adsorption of RY-145 on multibranched hematite with possible chemisorption.

Biosorption of methylene blue and malachite green from single and binary solutions by Pinus pinaster bark

Aiming to develop a sustainable separation process reducing the water pollution, in this work Pinus pinaster (cluster pine) bark from a wood veneer industry was used for methylene blue and malachite green removal from aqueous systems. For single adsorption, the influence of time (up 8 h), adsorbent dose (2,5 - 5 - 10 g·L-1), temperature (25 ºC - 40 ºC - 60 ºC), pH (2 - 4 - 6) and particle size (0,1 mm - 0,5 mm, 0,5 mm - 1 mm and 1,6 mm - 2 mm) on adsorption was investigated. To study the initial concentration effect on binary adsorption, different concentrations (0 - 5 - 25 - 50 mg·L-1) were used at 25 ºC, natural pH and a dose of 5 g·L-1. High efficiency was obtained at pH = 4 (natural pH), dose of 5 g·L-1 and particle size of 0,5 - 1 mm. Adsorption percentages higher than 70 % were reached in less than one hour, with removal almost complete at equilibrium in single systems, without temperature influence. Methylene blue was slightly better adsorbed by bark. In binary systems, dyes exhibited competitive adsorption, decreasing their removal, especially increasing the initial concentration of the other dye. Dyes adsorption followed the pseudo-second order kinetic model, whereas the Langmuir isotherm explained adsorption equilibria in mono-component systems. High adsorption capacities (41,7 mg·g-1 for malachite green and 50,0 mg·g-1 for methylene blue) were obtained at 40 ºC and natural pH indicating that pine bark can be effectively used as biosorbent.

Pine needle–derived biochar adsorbents for removal of Sm(III) and competitive toxic metals from model aqueous matrices.

Pine needle–derived biochars have been prepared and investigated as adsorbent materials for the removal of trivalent samarium (Sm(III)) from aqueous systems. The biochars, which were previously oxidized and magnetized), have been characterized prior and after Sm(III) adsorption by Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray diffraction (XRD). The effect of various parameters such as metal ion concentration, pH and contact time on the adsorption efficiency has been investigated. In addition, competitive adsorption experiments have been carried out (competition between Sm3+, Cu2+ and UO22+ ions) by means of batch type experiments. The results showed better adsorptive properties for magnetized oxidized pine needle biochar (PNCOM), particularly at pH 6 (qmax = 691.7mg·g-1), while at pH 3 the oxidized biochar (PNCO) (qmax = 285.7mg·g-1) presented the highest adsorption capacity. The experimental data were better fitted by the Langmuir adsorption and pseudo-second order kinetic model. On the other hand, the competitive adsorption studies have shown that generally PNCOM presents remarkably higher affinity for U(VI) than its non-magnetized counterpart (PNCO). However, despite the fact that the sorption capacity is the highest for U(VI), the affinity of the biochar materials for the studied metal ions is higher for Sm(III), followed by U(VI) and Cu(II). This indicates that the net charge of the metal ion is a key parameter regarding the stability of the complexes formed on the oxidized biochar materials prior and after magnetization.

Chitosan-grafted hydrogels for heavy metal ion adsorption and catalytic reduction of nitroaromatic pollutants and dyes

Chitosan-grafted-poly(acrylic acid) (CS-g-PAA) and chitosan-grafted- poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (CS-g-P(AA-co-AMPS)) hydrogels were synthesized and then employed as adsorbents for the effective removal of Cu2+ and other heavy metal ions. The effect of hydrogel's composition on the Cu2+ adsorption was explored. The CS-g-PAA hydrogel demonstrated a superior adsorption capacity compared to pristine CS, PAA hydrogel, and CS-g-P(AA-co-AMPS) hydrogels. The adsorption followed the Langmuir isotherm model, and the pseudo-second order kinetic model. Additionally, the CS-g-PAA hydrogel exhibited relatively high adsorption performances toward Cr3+, Co2+, Ni2+, Pb2+, and Zn2+. Metal ions adsorbed within CS-g-PAA hydrogels underwent reduction to their corresponding metallic states and were reutilized as catalysts for the reduction of 4-nitrophenol. The comparative catalytic performances of the metal species in the hydrogel were in the order of Cu > Ni > Co > Zn. The reduction efficiency of Cu-CS-g-PAA increased with increased catalyst dosage, NaBH4 concentration, and temperature. A very low activation energy of 3.7 kJ/mol was observed. The catalyst maintained high catalytic performance even when subjected to real water samples and proved its reusability for up to three cycles. Moreover, the catalyst could effectively reduce 2-nitrophenol and methyl orange.

Adsorption of trace heavy metals through organic compounds enriched biochar using isotherm adsorption and kinetic models

Trace heavy metals such as copper and nickel, when exceeds a certain level, cause detrimental effects on the ecosystem. The current study examined the potential of organic compounds enriched rice husk biochar (OCEB's) to remove the trace heavy metals from an aqueous solution in four steps. In 1st step, biochar’ physical and chemical properties were analyzed through scanning electron microscope (SEM) and Fourier transforms infrared spectroscopy (FTIR). In the 2nd step, two biochar vis-a-vis glycine, alanine enriched biochar (GBC, ABC) was selected based on their adsorption capacity of four different metals Cr, Cu, Ni and Pb (chromium, copper, nickel, and lead). These two adsorbents (GBC, ABC) were further used to evaluate the best interaction of biochar for metal immobilization based on varying concentrations and times. Langmuir isotherm model suggested that the adsorption of Ni and Cu on the adsorbent surface supported the monolayer sorption. The qmax value of GBC for Cu removal increased by 90% compared to SBC (Simple rice husk biochar). The interaction of Cu and Ni with GBC and ABC was chemical, and 10 different time intervals were studied using pseud first and second-order kinetics models. The current study has supported the pseudo second-order kinetic model, which exhibited that the sorption of Ni and Cu occurred due to the chemical processes. The % removal efficiency with GBC was enhanced by 21% and 30% for Cu and Ni, respectively compared to the SBC. It was also noticed that GBC was 21% more efficient for % removal efficiency than the CBC. The study's findings supported that organic compound enriched rice husk biochar (GBC and ABC) is better than SBC for immobilizing the trace heavy metals from an aqueous solution.

New Methyl Methacrylate Derived Adsorbents - Synthesis, Characterization and Adsorptive Removal of Toxic Organic Compounds.

This study aimed to synthesize polymeric adsorbents by suspension polymerization using methyl methacrylate (MMA) with different crosslinking monomers. Divinylbenzene (DVB) and aliphatic monomers: ethylene glycol dimethacrylate (EGDMA) or N,N'-methylenebisacrylamide (NN) containing additional amide groups were used. The possibility of using the prepared copolymers (MMA-NN, MMA-EGDMA, MMA-DVB) as adsorbents for the removal of toxic compounds such as dyes (C.I. Acid Red 18 (AR18), C.I. Acid Green 16 (AG16), C.I. Acid Violet 1 (AV1), C.I. Basic Yellow 2 (BY2), C.I. Basic Blue 3 (BB3) and C.I. Basic Red 46 (BR46)) and phenol (PhOH) from dye baths and effluents was evaluated. Preferential adsorption of basic-type dyes compared to acid-type dyes or phenol was observed by the polymers. Adsorbent based on MMA-EGDMA exhibited the highest capacity for investigated dyes and phenol. The pseudo-second order kinetic model as well as the intraparticle diffusion model can find application in predicting sorption kinetics. Based on the equilibrium sorption data fitted to the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich model, uptake of BB3, AV1 and PhOH is rather physisorption than chemisorption. The regeneration yield of MMA-EGDMA does not exceed 60 % using 1 M HCl, 1 M NaCl, and 1 M NaOH in 50 %v/v methanol.

Exact solution of the Langmuir rate equation: New Insights into pseudo-first-order and pseudo-second-order kinetics models for adsorption

The Langmuir adsorption rate equation was obtained in its exact, linear, and simple form. Using Stochastic Numerical Simulation, it was demonstrated that this equation can accurately calculate the adsorption rate constant (ka), which is more precise than the values obtained using pseudo-first-order (PFO) and pseudo-second-order (PSO) models. The derivation conditions of the PFO and PSO kinetics models from Langmuir kinetics were also investigated. The results showed that the PFO model can be obtained at two limit states: at Ce≅C0 and at Ce≪C0 with a very low fractional coverage. Also, the PSO model is derived under the condition Ce→0 and θe→1. The accuracy of the exact Langmuir model, both linear and nonlinear, and the theoretical derivation conditions of the PFO and PSO models were examined using several sets of kinetics data generated by the Stochastic Numerical Simulation method. The simulation results supported the theoretical approaches of this study.

Kaolinite-Composited Biochar and Hydrochar as Low-Cost Adsorbents for the Removal of Cadmium, Copper, Lead, and Zinc from Aqueous Solutions

During the last decade, due to an increase in anthropogenic activities, a higher environmental accumulation of heavy metals has been found, which has resulted in disturbed biogeochemical balance. Many kinds of remediation techniques have been practiced to mitigate heavy metal toxicity in the aqueous phase; however, adsorption is the most commonly accepted technique for efficient heavy metal removal. In this study, conocarpus waste was pretreated with 0%, 10%, and 20% kaolinite and pyrolyzed at 600 °C for 1 h to synthesize biochars (BC, BCK10, and BCK20, respectively), while hydrothermalized at 200 °C for 6 h to synthesize hydrochars (HC, HCK10, and HCK20, respectively). After characterization, synthesized materials were employed for the removal of cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) from contaminated water. Experimental data was further subjected to isotherm and kinetic models to estimate the adsorption mechanism. Among all the tested adsorbents, kaolinite-synthesized materials revealed comparatively higher adsorption compared to pristine materials. It was found that pH 7 was optimum for the maximum removal of tested heavy metals. Adsorption of tested heavy metals was well explained by Langmuir and Freundlich isotherms, while pseudo-second order and Elovich kinetics models fitted well for adsorption kinetics. The maximum adsorption capacity, as predicted by the Langmuir isotherm, was the highest for BCK20 (63.19 mg g−1 for Cd, 228.05 mg g−1 for Cu, 248.33 mg g−1 for Pb, and 45.79 mg g−1 for Zn) compared to the other tested materials, and for HCK20 (31.93 mg g−1 for Cd, 181.78 mg g−1 for Cu, 231.85 mg g−1 for Pb, and 45.72 mg g−1), it was higher than pristine HC. Isotherm and kinetics modeling data indicated that multiple mechanisms were involved in Cd, Cu, Pb, and Zn removal, such as chemisorption and electrostatic interactions. The amount of oxygen-containing surface functional groups and SiO2 particles could be responsible for the maximum adsorption of heavy metals by BCK20 and HCK20. Our findings suggest that biochar, hydrochar, and their kaolinite-modified composites possess the excellent potential to remove heavy metals from contaminated aqueous media, and could be further applied to treat wastewater to mitigate heavy metal toxicity for a sustainable environment.

Review on Moringa oleifera, a green adsorbent for contaminants removal: characterization, prediction, modelling and optimization using Response Surface Methodology (RSM) and Artificial Neural Network (ANN)

Moringa oleifera utilization in water treatment to eliminate emerging pollutants such as heavy metal ions, pesticides, pharmaceuticals, and pigments has been extensively evaluated. The efficacy of Moringa oleifera biosorbent has been investigated in diverse research work using various techniques, including its adsorption capacity kinetic, thermodynamic evaluation, adsorbent modifications, and mechanism behind the adsorption process. The Langmuir isotherm provided the most remarkable experimental data fit for batch adsorption investigations, whereas the best fit was obtained with the pseudo-second order kinetic model. Furthermore, only a few papers that combined batch adsorption with fixed-bed column investigations were examined. In the latter articles, the scientists modified the adsorbent to increase the material’s adsorption capacity as determined by analytical methods, including IR spectroscopy, scanning electronic microscope (SEM), and X-ray diffraction (XRD). However, the raw material can show appreciable adsorption capacity values, proving moringa’s potency as a biosorbent. Hydrogen bonds, electrostatic interaction, and van der Waals forces were the main processes in the found and reported adsorbent-adsorbate interactions. These mechanisms could change depending on the physiochemical nature of adsorption. Although frequently employed for heavy metal ions and dye adsorption, Moringa oleifera can still be explored in pesticide and medication adsorption investigations due to the few publications in this comprehensive review. This study, therefore, examined different Adsorbents from the Moringa oleifera plant, as well as parameters and models for enhancing the adsorption process.

Fabrication and characterization of magneto-responsive polyvinyl alcohol–alginate composite hydrogel beads for the removal of cationic dyes from aqueous solutions

In this study, magneto-responsive polyvinyl alcohol–alginate hydrogel beads are successfully fabricated using the electrospraying technique and applied as efficient adsorbents for the removal of cationic dyes, particularly malachite green (MG) and methylene blue (MeB), from water. The successful synthesis of the beads is confirmed using optical microscopy, Fourier transform infrared spectroscopy, and scanning electron microscopy. Additionally, batch adsorption studies are performed to evaluate the adsorption capacity of the hydrogel beads under varying concentrations, pH solution, and contact time. Results revealed that the beads exhibited excellent sorption capacities of 270.03 and 285.66 mg g−1 toward MG and MeB, respectively, indicating their potential as efficient adsorbents for cationic dye removal. The adsorption mechanism of the beads was further analyzed using kinetic and isotherm models, where the results revealed that the pseudo-second order kinetic model and Langmuir isotherm model exhibited the best fits with the experimental data. The incorporated magnetic nanoparticles enabled the easy separation and reuse of the hydrogel beads sample, as it maintained more than 75% of its efficiency even after five consecutive cycles. This study presents an innovative and sustainable solution for wastewater treatment, demonstrating the use of magneto-responsive hydrogel beads as effective and reusable adsorbents for cationic dye removal.

Interactions of humic acid with pristine poly (lactic acid) microplastics in aqueous solution

Microplastics and natural organic matter are present in the aquatic environment and their reciprocal interaction plays important roles in the transport and behavior of nutrients and contaminants. Nevertheless, we lack mechanistic understanding on these interactions, especially in the case of biodegradable plastics. Here we investigate the adsorption of a commercial humic acid onto poly (lactic acid) (PLA) microplastics in aqueous solution. While the pseudo-second order kinetic model provided a more accurate representation of the adsorption kinetics, the Elovich model also produced a good fit, suggesting that chemisorption may be the rate-limiting step. The equilibrium data was better fit by the Langmuir model, that provided a maximum adsorption capacity of 0.118 ± 0.006 mg·g−1. The obtained values for the separation factor (RL) and free energy (E) suggest that adsorption of humic acid onto PLA is controlled by physisorption. We studied the effects of pH, ionic strength, and PLA concentration on the adsorption of humic acid onto PLA and demonstrated that electrostatic interactions and aggregation are important. The humic acid was characterized by Fourier-transform infrared (FTIR) spectroscopy, excitation-emission matrix (EEM) fluorescence spectroscopy, and parallel factor analysis (PARAFAC), before and after interacting with PLA. This set of analyses demonstrated that PLA caused alterations in the molecular structure of humic acid, primarily attributed to modifications in hydrogen bonding and hydrophobic interactions. Therefore, we hypothesize that the carboxylic groups of humic acid formed dimers in contact with PLA. This study provides new insights into the interactions between organic matter and a biodegradable microplastic in aqueous systems.

Architecture of GO/CoFe2O4/ZnO nanocomposite for efficient fluoride removal: An approach using RSM, ANN and GRU modeling

The presence of fluoride in wastewater possesses a significant risk to the environment. Graphene oxide-based nanocomposites were prepared as potential adsorbents for fluoride removal from water. Various techniques including X-ray diffraction (XRD), Scanning Electron Microscopy (FE-SEM), Energy dispersive X-ray (EDX), Fourier Transform Infrared Spectroscopy (FTIR), RAMAN spectroscopy, Ultraviolet-Visible spectroscopy (UV–vis), Vibrating Sample Magnetometer (VSM), X-ray Photoelectron Spectroscopy (XPS), Brunauer Emmett Teller (BET), and Electrochemical Impedance Spectroscopy (EIS) were employed to investigate the morphological, structural, chemical composition, elemental analysis, surface area, optical band gap, etc. of the CoFe2O4, CoFe2O4/ZnO composite and GO/CoFe2O4/ZnO nanocomposite. XRD analysis confirmed a reduction in crystallite size to 15.7 nm of GO/CoFe2O4/ZnO. Batch adsorption studies were conducted for fluoride removal with input independent variables (pH, temperature, initial fluoride concentration, time, and an adsorbent GO/CoFe2O4/ZnO dosage). The Response Surface Methodology (RSM) and Gated Recurrent Unit (GRU) models predicted the fluoride removal process, with RSM achieving an optimal fluoride removal of 94.3%, GRU achieving 94.5% and Artificial neural network (ANN) attaining 93.72%. A kinetic investigation was carried out using Pseudo first order (PFO) and Pseudo second order (PSO). Results confirmed that the adsorption of fluoride followed the PSO kinetic model with an (R2 = 0.999). Isotherm studies were conducted using Langmuir, Temkin, Freundlich, and Dubinin Radushkevich isotherms. Among them, the best model follows an adsorption mechanism, with (R2 = 0.984) and an adsorption capacity of 10.68 mgg−1 was Langmuir Isotherm. The real water sample of Ravi River, Pakistan also investigated for fluoride removal capability. This research contributes to the promotion of RSM and GRU modeling with high sustainability for water purification. The contemplated nanocomposite (GO/CoFe2O4/ZnO) is a potential adsorbent for the mechanism of water detoxification containing fluoride which may be useful for environmental remediation as well.

Bio-based nitrogen doped carbon-silica composites from low value sugarcane by-products for the selective adsorption of Au(III) from aqueous systems

This study investigates the development of carbon-silica composite (CSC) adsorbents with tuneable surface properties for gold adsorption from silica and molasses. Nitrogen modification of the CSC adsorbents was achieved through a facile urea impregnation onto the CSC, followed by pyrolysis at 400 °C (400C-5A). Exceptional Au(III) adsorption was demonstrated from acidic solutions, with a maximum adsorption capacity of 416.9 mg g−1. While CSC with no nitrogen modification (400C) only exhibits an adsorption capacity of 337.9 mg g−1. Langmuir isotherm model and pseudo-second order kinetic model were found to best describe the adsorption behaviour for Au(III) sorption on both nitrogen-modified and non-modified CSC. Urea modification led to nitrogen containing graphitic, pyridinic and pyrrolic functionalities, of which pyridinic groups were active sites for metal coordination, leading to enhanced adsorption and high selectivity towards Au and Pd. Au adsorptions of greater than 99.8% were revealed using both modified and unmodified CSC, even at low concentrations of gold (5 or 10 ppm). X-ray Photoelectron spectroscopy (XPS) analysis of 400C-5A following adsorption indicated the presence of both Au(0) and Au(III), demonstrating that adsorption took place through both chelation and an adsorption-reduction mechanism. These effective adsorbents derived from abundantly available, low cost, bio-based chemicals or low value by-products could create new opportunities for Au and/or Pd adsorption from acidic solutions.

Bio-sorptive remediation of crude oil polluted sea water using plantain (Musa parasidiaca) leaves as bio-based sorbent: Parametric optimization by Taguchi technique, equilibrium isotherm and kinetic modelling studies

This study investigated the potential of employing plantain leaves as a natural bio-based sorbent for crude oil spill polluted seawater remediation. Type L9(34) Taguchi orthogonal array technique was used to evaluate the effect of four independent bio-sorption factors at three different levels (crude oil initial concentration (X1 7.8, 11.5 and 15.6 g/L), seawater-crude oil temperature (X2 25, 35 and 45 °C), bio-sorbent dosage (X3 1, 2 and 3 g) and bio-sorbent particle size (X4 1.18, 2.36 and 4.72 mm) on two response indices (bio-sorption efficiency (%) and bio-sorption capacity (g/g)). Taguchi optimization technique, numerical-desirability index function optimization technique and a proposed optimization method were utilized to determine the optimum bio-sorption factors needed for the optimum bio-sorption efficiency and bio-sorption capacity. The results demonstrated that the crude oil bio-sorption efficiency of the plantain leaves was significantly influenced by X1, X3 and X4 and the bio-sorption capacity was mainly influenced by X1 and X3. The optimum bio-sorption efficiency and the optimum bio-sorption capacity were 99.05 % and 12.82 g/g, respectively, obtained at optimum combination of factors and levels of X11 (7.8 g/L), X33 (3 g) and X41 (1.18 mm) for bio-sorption efficiency and X13 (15.6 g/L) X31 (1 g) for bio-sorption capacity. The Freundlich and Dubinin-Rudeshkevich isotherm models best explain the equilibrium bio-sorption data, while the pseudo-second order kinetic model best describes the bio-sorption kinetics. The bio-sorptive remediation mechanism followed dual mechanism of physical and chemical bio-sorption and the mass transfer controlled by film diffusion. The maximum bio-sorption capacity (Kf) was 14.0 gg-1.

Preparation and performance of surface-modified adsorbent materials from discarded traditional chinese medicine residues

Waste Chinese medicine residue was used as a raw material and pretreated with sodium hydroxide and hydrogen peroxide, followed by chemical modification with a silane to prepare an inexpensive and highly efficient hydrophobic biobased adsorbent material. The adsorbent was characterized with SEM, TGA and FTIR analyses. The adsorption capacities and wettabilities of the Chinese medicine residue were analyzed before and after surface modification to explore the adsorption performance and surface modification mechanism of the material. The results showed that the modified Chinese medicine residue was rough and uniformly modified, with successfully grafted hydrophobic functional groups, and it had added adsorption sites, exhibiting good hydrophobicities and oleophilicities. The contact angles between the modified materials and water reached 127°, and the modified Chinese medicine residue had an adsorption capacity of 51.7 mg g−1 for organic compounds, which was a significant improvement over the original waste Chinese medicine residue. The adsorption kinetics were best described with the pseudosecond-order kinetic model, which exhibited a higher linear correlation and was closer to the measured adsorption equilibrium value based on chemical adsorption. This study demonstrated a novel use of waste Chinese medicine residues for environmental remediation.