Pseudo-second Order Kinetic Model Research Articles

Synthesis of molecularly imprinted polymer as a nanosorbent for dispersive magnetic micro solid-phase extraction and determination of valsartan in biological samples by UV–Vis Spectrophotometry: Isotherm, kinetics, and thermodynamic studies

A magnetic molecularly imprinted polymer (MIP) was synthesized by precipitation polymerization utilizing Fe3O4@SiO2-MPS as a magnetic core, itaconic acid as a functional monomer, azobisisobutyronitrile as an initiator, and ethylene glycol dimethacrylate as a cross linker. It was then applied as a nanosorbent for dispersive magnetic micro solid phase extraction (DM-µ-SPE) and determination of valsartan in biological fluids. The morphology and structure of magnetic MIP were characterized by Fourier-transform infrared spectroscopy, Field Emission Scanning electron microscopy, Vibrating sample magnetometer, Energy dispersive x-ray analysis, and Thermogravimetric analysis. The influence of operation conditions on sorption, such as pH (4–10), contact time (10–25 min), initial concentration (1–30 mg L−1), and temperature (25–40 °C) was investigated. After the extraction step, the valsartan concentration was determined by UV–Vis spectrophotometer at 253 nm. The isotherm and kinetic of valsartan sorption were best fitted by the Langmuir model (R2 = 0.987) and the Pseudo second-order kinetic model (R2 = 0.971), respectively. The maximum monolayer sorption capacity for magnetic MIP was obtained to be 4.56 mg g−1. The analytical approach demonstrated favorable figures of merit, with a linear dynamic range of 10–100 µg L−1, a low detection limit of 0.56 µg L−1, and an acceptable preconcentration factor of 5 acquired in optimum conditions. The recoveries of the suggested technique at three spiked levels of analysis were in the range of 101 %–102 %. Valsartan was extracted from various real samples (urine and human blood plasma samples) utilizing the proposed magnetic nanosorbent, and the results exhibited that magnetic MIP was favorable for extraction and measurement of trace amounts of valsartan in biological samples.

Synthesis and characterization of new Schiff base bearing bis(pyrano[3,2-c]quinolinone): Efficient cationic dye adsorption from aqueous solution

Organic compound water pollution is one of the difficult environmental issues facing the advancement of human civilization. So, New bis(pyrano[3,2-c]quinolinone) based on Schiff base adsorbent was prepared to participate in solving this problem. The synthesized adsorbent was characterized using FT-IR, 1H NMR, XRD, SEM, elemental analysis, N2- adsorption-desorption isotherm, SBET, and Pore size distribution studies. The obtained results revealed a significant improvement in the new schiff base surface texture and crystallinity. Further, pHzpc of the new adsorbent has been examined to be 3.7. Its decolorization efficiency toward methylene blue (MB) dye from an aqueous solution was examined. Also, the factors of pH, contact time, reaction temperature, and initial dye concentration were optimized. Overall, this study emphasized that the newly synthesized Schiff base act as an effective adsorbent (99%) at a very short time (5 min., 10 ppm dye concentration, pH = 9 and temperature = 25 °C) and can be regenerated for five cycles for the removal of MB dye from aqueous solutions. Freundlich isotherm model and pseudo-second order kinetic model were fit effectively for the MB dye adsorption experimental data. Also, the calculated thermodynamic parameters revealed a spontaneous and exothermic adsorption reaction. FT- IR study and computational chemistry study proved that the decolorization interaction mechanism between the positive (-N+) sites of MB dye and the negative (- OH) active sites of the new Schiff base adsorbent at the optimum conditions occurred as a physisorption process.

The role of anthocyanin and kaolinite in modifying cabbage leaves biochar for removal of potentially toxic elements and pharmaceutical from aqueous solution

We investigated the feasibility of two novel engineered biochar composites by pyrolyzing cabbage leaves at 350 °C after pre-treating them with anthocyanin, followed by a post-treatment with kaolinite for the removal of two potentially toxic elements (copper and lead) and a pharmaceutical compound, metoprolol. Results showed that the Kaolinite-biochar composite (KB) exhibited the highest adsorption capacity, 188.67 and 48.07 mg/g for Pb and Cu at pH 5, and the anthocyanin-biochar composite (AB) exhibited the highest adsorption capacity: 41.15 mg/g for metoprolol at pH 6, compared to raw biochar respectively. The enhancement of the adsorption of heavy metal and metoprolol by KB and AB was due to an increase in certain oxygen functional groups, as confirmed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) results. The pseudo-second order kinetic model, along with Langmuir isotherm model, best described the kinetic and the isotherms for Pb, Cu and metoprolol in KB and AB composites, respectively. FTIR, XPS, and zeta potential measurements indicated that the sorption mechanisms involved electrostatic interaction, ion exchange, and complexation for the metals, while electrostatic interaction, H-bonding, π-πinteraction, and hydrophobic bonding were postulated as the contributing mechanisms in the sorption process of metoprolol. Anthocyanin and kaolinite could potentially be considered as alternative sustainable materials for modifying raw biochar and remediating toxic elements and pharmaceuticals in aqueous media.

Environmentally friendly starch/alginate aerogels for copper adsorption from aqueous media. A microstructural and kinetic study

This work investigated the synthesis and characterization of alginate/starch porous materials and their application as copper ions adsorbents from aqueous media. Initially, pregel aqueous solutions with different biopolymer concentrations (1, 3, and 5% w/w) and alginate contents (25, 50, and 75% w/w) were prepared. Hydrogel formation was performed by internal and external gelation methods. Finally, the drying step was done via CO2 sc leading to aerogels and via freeze-drying leading to cryogels. Process parameters influence on the final properties of materials was evaluated by BET isotherms, SEM, EDS, and TGA. Regardless the gelation method applied, interesting materials with meso- and macro-pore structure were prepared from pregel mixtures with 3% w/w biopolymer concentration and an alginate content of only 25% w/w. Low alginate content reduces the final cost of the materials. Concerning copper removal, the adsorption data were well fitted to the pseudo-second order kinetic model for aerogels and cryogels, showing aerogels the highest adsorption capacity (40 mg/g) and removal efficiency (∼ 92%). Materials demonstrated excellent reusability throughout five consecutive adsorption/desorption cycles. Hence, environmentally friendly materials with a high practical value as low-cost bioadsorbents were synthesized, having great performance in the removal of copper ions from aqueous solution.

Removal of Malachite Green using carbonized material derived from disposable facemasks: optimization of removal process through Box–Behnken design

ABSTRACT Water resources are being heavily contaminated due to the huge load of toxic pollutants released by industrial activities. Among various physical and chemical methods, adsorption is considered as a promising method for rapidly removing contaminants from wastewater. In the present study, a novel carbon-based adsorbent was prepared through controlled pyrolysis of disposable facemasks. The properties of carbonized compound (CC) were characterized by FTIR, XRD, SEM and EDX. The pollutant removal efficiency of CC was initially investigated with synthetic dyes Malachite Green (MG) and Congo Red (CR). The peaks observed in FTIR spectra corresponding to C=O and C=C and C–N functional groups on adsorbed CC surface confirm the interaction between dye and CC. The XRD spectra of CC showed strong peaks at 2θ = 26.629, 27.488, 27.810 and 29.404 which correspond to the disordered graphitic plane. The SEM images of CC showed good porosity nature. A quadratic model was developed through response surface methodology by conducting a series of Box–Behnken design experiments. Adequacy of this model variables was ensured by ANOVA tests at P-value <0.05. The lower P-value (<0.0001) and higher F-value (44.54) of the quadratic model showed it was a significant model for dye removal. Finally, the optimal condition to obtain maximum MG removal (rate >99%) was identified by desirability function as CC 1000 and MG 212 mg/L and adsorption time 180 min. Adsorption kinetic study indicates that a pseudo second-order kinetic model showed the best fit with R 2 = 0.999.

Novel cationic surfactants: synthesis, surface, antimicrobial studies and applicability as an extracting agent for interested element from monazite mineral concentrate

Abstract Two novel cationic surfactants based on palmitic acid were prepared to extract uranium from its fluids. The chemical structures of the surfactants prepared were confirmed spectroscopically. The surface activity of these surfactants was evaluated by measuring their surface tension. The cationic surfactants prepared were also tested for their biological activity against Gram-positive and Gram-negative bacteria and fungi. Subsequently, an attempt was made to use these surfactants to remove uranium from the hydrous oxide cake produced after the alkaline degradation of monazite mineral concentrate. To achieve this goal, several experiments were conducted to determine the optimal conditions for uranium extraction and stripping. Under these optimal conditions, the experimental capacity fitted the pseudo-second order kinetic model. Under the investigated optimal stripping factors of 1 M NaCl, acidified with 0.2 M conc. H2SO4, an A:O ratio of 1:1 and a contact time of 15 min, an uranium stripping efficiency of 83% was obtained for the case study. After the complete stripping process, the marketable uranium concentrate was percipitated using hydrogen peroxide as UO4 H2O with an uranium content of approximately 76%, which was chemically determined and confirmed by EDAX analysis.

Synthesis of NiO coated chitosan-cenosphere buoyant composite for enhanced adsorptive removal of methylene blue

The objective of the present study is to utilize fly ash cenosphere to remove methylene blue (MB) from the water streams. Nickel oxide is a typical semiconductor used as proficient adsorbent material for degradation of dye with environment friendly applications due to its excellent chemical stability and high catalytic activity. The chitosan cenosphere buoyant composite coated with NiO was synthesized with hydrothermal grafting reaction using silane coupling agent and epichlorohydrin as a cross-linking reagent. The batch adsorption experiments were carried out with a cationic dye, methylene blue as a representative organic pollutant to investigate the adsorptive capabilities of the composite as adsorbent. The influence of pH (2-12), initial concentration of dye (50–200 mg/L), temperature (37–47 °C) and contact time (0–24 h) were taken as parameters in the study. On the relative elimination of MB, the effect of time and temperature were investigated. The adsorption kinetics for MB was correlated and found to observe the pseudo-second order kinetic model, whereas the equilibrium adsorption isotherm follows the Langmuir model (R2 > 0.99). The results indicate that the floating fly ash cenosphere coated with NiO proved to be more responsive for enhanced degradation of methylene blue.

Chitosan based radiation crosslinked and grafted matrix: An environment friendly adsorbent for dye uptake

The adsorption capacity of [2-(methacryloxy) ethyl] trimethylammonium chloride (MAETC) grafted-crosslinked chitosan (CRChitosan-g-MAETC) using ionizing radiation was evaluated for adsorption of anionic dyes namely Acid Blue-25 (AB25), Reactive Orange-16 (RO16) and Reactive Red-120 (RR120) from manufactured aqueous solutions. Effect of various experimental variables like dye concentration, pH, contact time duration, temperature and adsorption on adsorbent grafted to different extent on adsorption kinetics and on equilibrium adsorption was investigated. To understand the equilibrium adsorption of dyes on the adsorbent the data was fitted into Langmuir, Freundlich and Temkin adsorption isotherms while adsorption kinetics was examined using pseudo-first order, pseudo-second order and intraparticle diffusion kinetic models. It was observed that the adsorption of all the three anionic dyes studied was better explained by the Freundlich model. Adsorption extent of dye varied with number of charge sites on the dye molecule. The adsorption of all the three anionic dyes followed pseudo-second order kinetics. Thermodynamic parameters such as standard enthalpy (ΔHo), standard entropy (ΔSo) and standard free energy (ΔGo) were estimated. The radiation grafted cationic adsorbent showed promising adsorbent properties for removal of anionic dyes.

Comparative study for sorption of arsenic on peanut shell biochar and modified peanut shell biochar

In this study, arsenite [As(III)] and arsenate [As(V)] removal efficiency of peanut shell biochar (PSB) and modified peanut shell biochar (MPSB) was compared in aqueous solutions. The modification was carried out with KMnO4 and KOH. Sorption efficiency of MPSB was relatively higher than PSB at pH 6 for As(III) (86%) and for As(V) (91.26%) for initial concentration of 1 mg/L, adsorbent dose of 0.5 g/L and 240 min equilibrium time at 100 rpm. Freundlich isotherm and pseudo-second order kinetic model suggested possible multilayer chemisorption. Fourier transform infrared spectroscopy showed that –OH, C–C, CC and C–O–C groups contributed significantly in adsorption for both PSB and MPSB. Thermodynamic study showed that the adsorption process was spontaneous and endothermic. Regeneration studies revealed that PSB and MPSB can be successfully used for three cycles. This study established that peanut shell is a low-cost, environment friendly and efficient biochar for removal of arsenic from water.

Experimental study on evaluation and optimization of heavy metals adsorption on a novel amidoximated silane functionalized Luffa cylindrica

This study aimed to synthesize an amidoximated Luffa cylindrica (AO-LC) bioadsorbent, and evaluate its efficiency in the adsorption of heavy metals from the aqueous solutions. For this purpose, NaOH solution was used to alkaline treatment of Luffa cylindrica (LC) fibers. The silane modification of LC was performed using 3-(trimethoxysilyl)propyl methacrylate (MPS). Polyacrylonitrile (PAN)/LC biocomposite (PAN-LC) was synthesized by PAN grafting onto the MPS-modified LC (MPS-LC). Finally, the AO-LC was obtained by the amidoximation of PAN-LC. The chemical structures, morphology, and thermal properties of biocomposites were characterized by the infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and field emission scanning electron microscopy. The results showed a successful grafting of MPS and PAN on the surface of LC. The order of heavy metals adsorption on AO-LC was: Pb2+ > Ag+ > Cu2+ > Cd2+ > Co2+ > Ni2+. The effects of operational parameters on the Pb2+ adsorption were studied using Taguchi experimental design method. Statistical analysis of the results showed that the initial Pb2+ concentration and the bioadsorbent dosage significantly affect the adsorption efficiency. The adsorption capacity and removal percentage of Pb2+ ions were obtained as 18.88 mg/g and 99.07%, respectively. The Langmuir isotherm and Pseudo-second order kinetics models were found to be better compatible with experimental data as a consequence of the isotherm and kinetics analysis.

Amine-Functionalized Natural Rubber/Mesostructured Silica Nanocomposites for Adsorptive Removal of Clofibric Acid in Aqueous Phase

This study is the first report on the synthesis, characterization and application of amine-functionalized mesoporous nanocomposites based on natural rubber (NR) and wormhole-like mesostructured silica (WMS). In comparison with amine-functionalized WMS (WMS-NH2), a series of NR/WMS-NH2 composites were synthesized via an in situ sol-gel method in which the organo-amine group was grafted onto the nanocomposite surface via co-condensation with 3-aminopropyltrimethoxysilane (APS) as the amine-functional group precursor. The NR/WMS-NH2 materials had a high specific surface area (115-492 m2 g-1) and total pore volume (0.14-1.34 cm3 g-1) with uniform wormhole-like mesoporous frameworks. The amine concentration of NR/WMS-NH2 (0.43-1.84 mmol g-1) was increased with an increase in the APS concentration, corresponding to high levels of functionalization with the amine groups of 53-84%. The H2O adsorption-desorption measurement revealed that NR/WMS-NH2 possessed higher hydrophobicity than WMS-NH2. The removal of clofibric acid (CFA), a xenobiotic metabolite of the lipid-lowering drug clofibrate, from the aqueous solution using WMS-NH2 and NR/WMS-NH2 materials was investigated using a batch adsorption experiment. The adsorption was a chemical process in which the pseudo-second order kinetic model expressed the sorption kinetic data better than the pseudo first-order and Ritchie-second kinetic order model. In addition, the CFA adsorption sorption equilibrium data of the NR/WMS-NH2 materials were fitted to the Langmuir isotherm model. The NR/WMS-NH2 with 5% amine loading had the highest CFA adsorption capacity (6.29 mg g-1).

Adsorptive removal of crystal violet dye by Azadirachta indica (neem) sawdust: A low-cost bio-sorbent

The potentiality of Azadirachta indica sawdust as a cost-effective natural adsorbent for adsorptive elimination of a cationic dye crystal violet from aqueous emulsion was investigated. Because sawdust is plentiful and low-cost by-product. Additionally, sawdust can be composted to replace the regeneration stage that other adsorbents like activated carbon requires. Kinetic and isotherm analyses were conducted under variable experimental conditions including adsorbent dose, dye concentration, contact time, pH, and temperature. A maximum adsorption capacity of 8.264 mgg−1 was obtained at optimized conditions of 2.5 gl−1, 100 mgl−1 30 min, 6, and 25 °C for adsorbent dose, adsorbate, contact time, pH and temperature. The nature of any probable interaction between adsorbent and crystal violet was analyzed by FTIR technique, to investigate the type of functional groups in saw dust responsible for dye binding process. The FTIR studies showed the existence of C-H, C=O, C-O, C=C, O-H, C-N, -COO- and Si-O functional groups. It was noted that the sorption kinetics followed a pseudo-second order kinetic model after the sorption was examined using pseudo-first and pseudo-second order kinetic models. The magnitude of dye removal increased with increase of adsorbent dose and slightly decreased with increase in adsorbate concentration. Up to 45 °C temperature, there was no significant impact on sorption only 2–5% higher than the 25 °C and 35 °C treatments. The Langmuir isotherm model provided a good representation of the equilibrium data in aqueous solutions. The adsorption capability of crystal violet onto the sawdust of Azadirachta indica was found to be as high as 8.278 mgg−1, at pH 6.0, temperature 25 °C, and at equilibrium time of 60 min after applying Langmuir isotherm equation. Azadirachta indica sawdust seems to be a very promising adsorbent for the removal of crystal violet from aqueous solution.

Removal of arsenic in freshwater wetland waters using fly ash modified with zirconium-manganese binary oxides

A new alternative supporting matrix for constructed wetlands was explored using fly ash modified with Zr-Mn binary oxides (Zr-Mn/FA) and examined its performance in the control of arsenic pollution in wetland waters. The prepared matrix was characterized by SEM, XRD and EDS. Batch experiments were performed to investigate the effects of various conditions for the adsorption of arsenic onto Zr-Mn/FA including pH, contact time, concentration, temperature,loading amount of Zr-Mn and co-existing ions. The results showed that Zr-Mn oxides on the surface of Zr-Mn/FA dominated the reaction force between arsenic and adsorbent. The phosphate anion could reduce the adsorption process of arsenite (As(Ⅲ))and arsenate (As(Ⅴ)) when its concentration exceeds 1.0 mg·L−1. The experimental data of both As(Ⅲ) and As(Ⅴ) adsorption on Zr-Mn/FA were well fitted with pseudo-second order kinetic model as well as Langmuir adsorption isotherm model with the maximum adsorption capacities of 70.13 mg·g−1 for As(Ⅲ) and 43.19 mg·g−1 for As(Ⅴ), respectively. The thermodynamic study suggested that the adsorption of As(Ⅲ) and As(Ⅴ) were both endothermic. However, the adsorption of As(Ⅴ) was spontaneous while the opposite conclusion was obtained for As(Ⅲ). The prepared material (Zr-Mn/FA) was then successfully applied in the real water samples from wetland which indicated that Zr-Mn/FA composite could be a promising matrix for constructed wetland to effectively remove inorganic arsenic from water.

Removal of methylene blue from aqueous solution by coconut coir dust as a low-cost adsorbent

Adsorption of methylene blue (MB) from its aqueous solution onto coconut coir dust was studied in batch method. Coconut coir dust was characterized before and after adsorption by FT-IR spectroscopy and scanning electron microscopy (SEM). Surface charge, pHzpc of the adsorbent was measured by the method suggested by Huang and Ostovic and was found to be 7.65 (± 0.05). Batch kinetic experiments were performed and effects of several operational parameters i.e., contact time, initial concentration, pH of the solution and temperature on adsorption process were investigated. The effect of pH on adsorption was examined using a MB solution of 31.98 mg L−1 at 30 °C on coconut coir dust varying the pH range from 3.02 to 11.04. At basic condition, the uptake increased significantly and reached the maximum at pH 9.0. The batch adsorption model, based on the assumptions of the Lagergren’s pseudo-first order and the Ho’s pseudo-second order model were applied to investigate the kinetics of this adsorption process. The results showed that the kinetic data fit very well to the pseudo-second order kinetic model. The adsorption isotherms were determined at four different particle sizes which ranges from < 106 to 300 μm. Among them < 106 μm particle size was chosen for whole process because of comparatively good adsorption capacity. The adsorption isotherms at different temperatures maintaining pH at 7.68 were studied and results show that the amount adsorbed increases with the increase in the temperature under all conditions. The linear correlation coefficients indicate that the Langmuir isotherm best fitted with the experimental data. Thermodynamic parameters such as Gibbs free energy change (ΔG), enthalpy change (ΔH) and entropy change (ΔS) were calculated. The values of ΔH and ΔS were found to be + 30.16 kJ mol−1 and + 0.128 kJ mol−1 K−1 , respectively. At pH 7.68, the present system was spontaneous and endothermic in nature. It was found that when the temperature was increased from 303 to 333 K, the ΔG value decreased.

Multifunctional Chitosan/Xylan-Coated Magnetite Nanoparticles for the Simultaneous Adsorption of the Emerging Contaminants Pb(II), Salicylic Acid, and Congo Red Dye

In this work, we develop chitosan/xylan-coated magnetite (CsXM) nanoparticles as eco-friendly efficient adsorbents for the facile removal of contaminants from water. Characterization of CsXM using Fourier Transform Infra-Red (FTIR) Spectroscopy, Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), Thermogravimetric Analysis (TGA), Transmission Electron Microscopy (TEM), Zeta potential measurements, and Brunauer-Emmet-Teller (BET) analysis, confirmed the successful preparation of a chitosan/xylan complex coated over magnetite, which is characterized by being mesoporous, thermally stable and of neutral charge. Three contaminants, Pb(II), salicylic acid (SA), and congo red (CR), were chosen as representative pollutants from three major classes of contaminants of emerging concern: heavy metals, pharmaceuticals, and azo dyes. Pb(II), SA, and CR at initial concentrations of 50 ppm were removed by 64.49, 62.90, and 70.35%, respectively, on applying 6 g/L of CsXM. The contaminants were successfully removed in ternary systems, with Pb (II) and SA being more competitive in their adsorption than CR. Adsorption followed the Freundlich isotherm model and the pseudo-second order kinetic model, while the binding was suggested to occur mainly via chemical chelation for Pb(II) and physical interaction for SA and CR, which demonstrates the multifunctional potential of the nanoparticles to capture different contaminants regardless of their charge.

Adsorption kinetics studies of ciprofloxacin in soils derived from volcanic materials by electrochemical approaches and assessment of socio-economic impact on human health.

The use of antibiotics in the livestock sector has resulted in the entry of these drugs into the soil matrix through the disposal of manure as an organic amendment. To define the fate of these drugs, it is necessary to evaluate kinetic aspects regarding transport in the soil-solution. The aim of this paper is to evaluate the adsorption kinetic parameters of Ciprofloxacin (CIPRO) in Ultisol and Andisol soil which allows obtaining main kinetic parameters (pseudo-first and pseudo-second order models) and to establish the solute transport mechanism by applying kinetic models such as the Elovich equation, Intraparticle diffusion (IPD) and, the Two-site non-equilibrium models (TSNE). The adsorption kinetics of this fluoroquinolone (FQ), on both soils derived from volcanic ashes, is developed using electrochemical techniques for their determination. The experimental amount of CIPRO adsorbed over time (Qt) data best fit with the pseudo-second order kinetic models; R2 = 0.9855, Ɛ = 10.17% and R2 = 0.9959, Ɛ = 10.77% for Ultisol and Andisol, respectively; and where CIPRO adsorption was considered time dependent for both soils but the lower adsorption capacity in Ultisol; with 17.6 ± 2.8 μmol g−1; which could mean a greater risk in environmental. Subsequently, applying models to describe solute transport mechanisms showed differences in the CIPRO adsorption extent for the fast and slow phases. Adsorption isotherms were evaluated, where Ultisol occurs on heterogenous sites as multilayers and Andisol by monolayer with similar Qmax. Finally, the socio-economic impact of antibiotic usage is presented, giving the importance of antibiotics in the livestock sector and their effects on human health.

The effects of soil properties and sorbent amendments on immobilization of perfluorooctane sulfonate (PFOS) in contrasting soils: Experimental and numerical study

Per- and polyfluoroalkyl substances (PFAS), a class of manmade organo-fluorine chemicals, are a serious challenge to water supplies. In this study, the effects of physicochemical properties of Florida topsoil and Ringold formation Hanford site sediment as well as the influence of immobilizers on the sorption behavior of PFOS were tested. Activated charcoal (AC) and food waste compost amendments were added to the soil and sediment at 0.1 and 3 wt% concentration, respectively. The PFOS adsorption fits best to pseudo second-order kinetic and Freundlich isotherm models. PFOS uptake was greater in Florida topsoil compared to Hanford site sediment, indicating that organic matter played a key role in the retention of PFOS. The food waste compost amendment at 3 wt% had no impact on PFOS uptake. However, AC amendment at 0.1 wt% enhanced PFOS sorption in Florida topsoil by 80% and Hanford site sediment by 99% through increasing the soil/water partitioning coefficients (kd value). A one-dimensional model was used to simulate the influence of AC in Florida topsoil on the leaching of PFOS to the groundwater by the percolation of rainwater over time. The results demonstrated the addition of 0.1 wt% AC, to the soil dramatically inhibits or delays the leaching of PFOS for up to one year under certain conditions to below the guideline for maximum concentration level (0.02 ng/L). The amendment could control PFOS release for more than 10 years by increasing the kd value by 10 times.

Highly Efficient Adsorption Characteristics and Mechanism of Nutshell Biochars for Aromatic Organophosphorus Insecticides

The wide use of the insecticide profenofos in crop production has led to serious ecological water problems in agricultural fields. With the increasing global production of nuts, a large amount of nutshell waste has a serious impact on the environment. Turning nutshell waste into biochar to remove high levels of profenofos in water is a cost-effective treatment method. In this study, biochars made from nutshell waste are investigated for the adsorption of aromatic organophosphorus insecticide profenofos. The adsorption amount of nutshell biochar was 13-fold higher than crop stalk biochar in removing profenofos from water. The results indicated that the adsorption of profenofos by nutshell biochar was specific. Scanning electron microscope (SEM) and Brunauer–Emmett–Teller (BET) analysis showed that nutshell biochars had a larger specific surface area and more microporous structures. Meanwhile, nutshell biochars could exhibit a stable adsorption capacity at different initial concentrations of profenofos (10–40 mg/L), temperature (298–318 K), and pH (3–7). Desorption and reuse experiments showed that profenofos was firmly bound to nutshell biochars in water and could be extracted from the biochars with acetonitrile. Within 10 times of recycling, nutshell biochar had a stable and strong adsorption capacity for profenofos. The adsorption process of profenofos by nutshell biochar was pore diffusion and surface adsorption, which is consistent with the pseudo second-order kinetic model and the Freundlich isotherm model. Elemental and Fourier transform infrared spectroscopy (FTIR) analyses showed that the adsorption mechanism of profenofos on nutshell biochar was mainly through π-π and hydrophobic interactions. Nutshell biochar also showed strong adsorption capacity for other aromatic organophosphorus pesticides, and the adsorption rates of methyl parathion, isocarbophos and 2-chloro-4-bromophenol were 85%, 73% and 73%, respectively. Nutshell biochar can serve as an excellent material for removing aromatic organophosphorus insecticide pollution from water.

Adsorption of As and Pb by Stone Powder/Chitosan/Maghemite Composite Beads (SCM Beads): Kinetics and Column Study

Adsorption kinetics of As and Pb onto composite beads synthesized with stone powder, chitosan, and maghemite (SCM beads) with weight ratio of 1:1:0.5 were investigated in batch mode. Several kinetic models such as pseudo-first order kinetic model (PFOKM), pseudo-second order kinetic model (PSOKM), two compartment first order kinetic model (TCFOKM), and modified two compartment first order kinetic model (MTCFOKM) were utilized to analyze the kinetics. Although the beads had low specific surface area and pore volume, MTCFOKM, one of two compartment models, could predict the most accurately because the As and Pb were adsorbed onto at least two kinds of adsorption sites such as functional groups in chitosan and Fe in maghemite. In MTCFOKM, both the fast adsorption fraction (f1’) and the fast adsorption constant (k1’) for Pb were higher than those for As. Therefore, the equilibrium time (teq) for Pb adsorption was shorter than that for As adsorption, indicating that Pb adsorption was more affinitive than As adsorption onto SCM beads (especially maghemite). Column study with a bed column reactor packed with the SCM beads was also conducted. For column study, the effect of flow rate and pore volume on removal efficiency of As and Pb was also investigated. Three models such as the Thomas, Adams-Bohart (A-B), and Yoon-Nelson (Y-N) models were used to fit the column experimental data to analyze the breakthrough curves and the saturation time. Both Thomas and Y-N models were most appropriate. Conclusively, the SCM beads are suitable for adsorption treatment of As and Pb from contaminated groundwater and are particularly effective in Pb removal.

Sustainable Multi-Network Cationic Cryogels for High-Efficiency Removal of Hazardous Oxyanions from Aqueous Solutions.

It is still a challenge to develop advanced materials able to simultaneously remove more than one pollutant. Exclusive cationic composite double- and triple-network cryogels, with adequate sustainability in the removal of Cr2O72- and H2PO4- oxyanions, were developed in this work starting from single-network (SN) sponges. Chitosan (CS), as the only polycation originating from renewable resources, and poly(N,N-dimethylaminoethylmethacrylate) (PDMAEMA) and polyethyleneimine (PEI), as synthetic polycations, were employed to construct multi-network cationic composite cryogels. The properties of the composites were tailored by the cross-linking degree of the first network (SN5 and SN20, which means CS with 5 or 20 mole % of glutaraldehyde, respectively) and by the order of the successive networks. FTIR, SEM-EDX, equilibrium water content and compressive tests were used in the exhaustive characterization of these polymeric composites. The sorption performances towards Cr2O72- and H2PO4- anions were evaluated in batch mode. The pseudo-first-order, pseudo-second-order (PSO) and Elovich kinetics models, and the Langmuir, Freundlich and Sips isotherm models were used to interpret the experimental results. The adsorption data were the best fitted by the PSO kinetic model and by the Sips isotherm model, indicating that the sorption mechanism was mainly controlled by chemisorption, irrespective of the structure and number of networks. The maximum sorption capacity for both oxyanions increased with the increase in the number of networks, the highest values being found for the multi-network sponges having SN5 cryogel as the first network. In binary systems, all sorbents preferred Cr2O72- ions, the selectivity coefficient being the highest for TN sponges. The high sorption capacity and remarkable reusability, with only a 4-6% drop in the sorption capacity after five sorption-desorption cycles, recommend these composite cryogels in the removal of two of the most dangerous pollutants represented by Cr2O72- and H2PO4-.