Pseudo-second Order Rate Equation Research Articles

Biosynthesis of iron oxide nanoparticles at different temperatures and its application for the removal of Zinc by plant mediated nanoparticle, as an eco-friendly nanoadsorbent

Surface and underground water sources are threatened by various pollutants every day. Due to the fact that heavy metals do not disappear, their presence in the environment is very dangerous. Therefore, in this study, iron oxide nanoparticles were synthesized using Aloe vera extract and their application for Zinc removal from aqueous solution was studied. Nanoparticles were synthesized in different temperature conditions of 25 °C and 90 °C. The synthesized nanoparticle characteristics were identified using SEM, EDX, XRD, BET surface area, FTIR and UV–visible Spectroscopy. The SEM images indicated that the iron oxide nanoparticles synthesized at 25 °C and 90 °C had spherical morphology with average particle diameter 62.96 nm and 65.34 nm and based on BET results with a specific surface area of 37.450 and 42.520 m2 g−1, respectively. Adsorption of Zn(ΙΙ) in aqueous solution on the surface of synthesized nanoparticles was investigated and the highest adsorption efficiency was obtained at pH = 7, T = 25 °C, adsorbent concentration = 0.3 g/L, contact time = 90 min, adsorbed concentration = 10 mg/L. The adsorption fitted the pseudo second-order kinetic rate equation well, which confirmed that adsorption was via chemisorption. Freundlich model compared to Langmuir model can better describe the adsorption behavior of Zinc with iron oxide nanoparticles. Nanoparticles synthesized at 90 °C had a more uniform structure and higher absorption capacity. The absorption efficiency of 99 % was observed for nanoparticles synthesized.

Aminophosphonate CuO nanocomposites for uranium(VI) removal: Sorption performance and mechanistic study

Two aminophosphonate matrices (mono-aminophopshonate, MAP, and bi-aminophosphonate, BAP) are synthesized, varying the molar proportions of three precursors (thiocarbazide, p-phthalaldehyde, and triphenylphosphite). Nano-composites (CuO-MAP and CuO-BAP) are successfully elaborated by impregnation of the matrices with copper sulfate solution before processing to in situ precipitation of copper in alkaline solution (simultaneous partial Cu reduction). The sorbents are characterized using: TEM, XRD, elemental analysis, SEM-EDX, BET, titration (pHPZC), XPS and FTIR analyses. Uranium sorption properties are compared for the different sorbents through the study of pH effect (optimum close to 4.5), the uptake kinetics (equilibrium reached in 60 min) and sorption isotherms. Uptake kinetics are finely fitted by the pseudo-second order rate equation (and the resistance to intraparticle diffusion). The sorption isotherms are modeled by the Langmuir equation with maximum sorption capacity (mmol U g−1) decreasing according to CuO-BAP(1.15) ≫ CuO-MAP(0.80) > BAP(0.74) ≫ MAP(0.50). The enhanced textural properties and the increase in the density of sorption sites (probably completed by a better steric arrangement for improved reactivity) may explain this ranking. The sorption is endothermic: sorption capacity and affinity coefficient increase with temperature. Uranium is readily desorbed from loaded-sorbents (efficiency > 98 %) using either HCl (0.2 M) solution or acidified urea (0.25 M) solution (pH 2.5) for aminophosphonate matrices and nano-composites, respectively. The type of sorbent does not affect the stability at recycling: at the sixth cycle, the loss in sorption and desorption performances varies by 6.2–7 % and 4.2–4.9 %, respectively. CuO-BAP sorbent shows high potential for uranium recovery from complex acid ore leachate. The broad spectrum of bound metals does not allow producing a pure yellow cake after ammonia precipitation of eluate (containing up to 15–22 % impurities).

Adsorption treatment of fibre-cement industry effluent by activated gossweilerodendron caesalpinoideae stem waste: kinetic and thermodynamic studies

This investigation is on the treatment of a fibre-cement industry effluent (FCIE) using activated carbon (AC) adsorbent prepared by chemical activation (60% phosphoric acid) of Gossweilerodendron caesalpinoideae (GC) stem waste. The GCAC adsorbent was characterized by determination of the proximate and functional properties. The chemical groups, morphology and mineral phases of the GC stem waste and GCAC were studied by FTIR, SEM, and XRD methods, respectively. Kinetic and thermodynamic studies were carried out using total dissolved solids (TDS) as evaluating parameter. Effects of adsorbent dosage (5-40 g/L), contact time (0-60 min), and temperature (20-40 °C) on the effluent decontamination were investigated. Results from the characterized supernatant showed up to 97% removal of the contaminants using 40 g/L of GC adsorbent at effluent pH 7.4. The concentrations of TDS obtained by U-V spectrophotometric analysis were fitted to pseudo-first and pseudo-second order, Elovich and intraparticle kinetic models. The adsorption followed the pseudo-second order rate equation. Obtained free energy and enthalpy of adsorption values indicated non-spontaneous and endothermic adsorption. The study affirmed that the bioadsorbent, GCAC can be used for FCIE treatment.

Superior adsorption and removal of industrial dye from aqueous solution via magnetic silver metal-organic framework nanocomposite

ABSTRACT The indirect emission had a negative influence on the ecosystem of enormous amounts of harmful dyes into water. Fe3O4@Ag-MOF was successfully fabricated to capture Gentine violet (GV)) as a model example of cationic dye from their aqueous solutions was evaluated in this search as a method to eliminate dyes from water contaminants. FTIR, XPS, BET, TGA, SEM, TEM, and XRD have all been used to study this adsorbent in order to determine its structural and chemical characteristics as well as to interpret its binding mechanisms. According to the results of the characterization, the synthesized composite had a size about 45 nm, a surface area of 856.06 m2/g, and considerable magnetic characteristics (66.2 emug−1). Consequently, we created mesoporous surfaces that had a strong ability to interface and absorb GV dye. It is possible to use the pseudo-second order rate equation to characterize the kinetic profile., while the Langmuir equation fits isotherm models. At pH 9, maximum sorption capacities can reach 1.68 mmol.g−1. Additionally, the investigations of temperature profiles indicated the endothermic process and Thermodynamic parameters were discovered as, ΔG°, ΔH° and ΔS° The synthesized adsorbent had an interestingly high reusability of > 92 percent up to the sixth cycle. These findings revealed that a mixture of electrostatic interactions, π-π stacking, hydrogen bonds, and pore filling were involved in the GV adsorption mechanism. Fe3O4@Ag-MOF was successful in demonstrating its effectiveness as a point-of-use colour collection candidate from actual dyeing effluents.

Highly efficient adsorption and removal bio-staining dye from industrial wastewater onto mesoporous Ag-MOFs

Adsorption is an effective and promising approach for removing pollutants from wastewater. Too many hazardous colors were unintentionally released into the water, which had a negative impact on the environment. A popular textile dye is malachite green (MG). Thus, in this work, an environmentally acceptable inorganic-organic Ag metal-organic framework-based technique to remove colors from industrial water was developed (Ag-MOF). The sorbent was analyzed in the first section of the work using SEM, XPS, XRD, FT-IR, pHpzc, and BET, which confirmed that the Ag-MOF had the BET surface area, is 676 m2/g, which is a significant surface area. In a later stage, the sorption properties of the dye were examined along with the effects of pH, sorbent dosage, temperature, and ionic strength; the sorption isotherms and uptake kinetics were examined: As opposed to the kinetic profile, Isotherm profiles are well-fit by the Langmuir equation and can be modeled by the pseudo-second order rate equation. The outcomes further demonstrated that MG was mostly adsorbed onto Ag-MOF adsorbent by electrostatic attraction forces, hydrogen bonding, ion exchange, and pore filling. 2.25 mmol/g was found to be the greatest adsorption effectiveness of MG onto Ag-MOF adsorbent. (i.e. 809.71 mg/g). Adsorbent dosage, solution pH, temperature, and time were the four adsorption process parameters that were tuned using Box-Behnken design (BBD) in response surface methodology (RSM). The (ΔH°), (ΔS°), and (ΔG°) MG dye was endothermically and spontaneously extracted using Ag-MOF as an adsorbent, according to the specifications. Up to five cycles of adsorption-desorption, the synthesised Ag-MOF adsorbent demonstrates exceptional render ability and cyclability. The produced adsorbent's efficacy for purifying wastewater samples at a laboratory scale was assessed as a proof of concept. Study the mechanism of interaction between the Ag-MOF and MG as it could be take place through π-π interaction, pore filling, H-Bonding or electrostatic interaction. The mesoporous Ag-MOF adsorbent offered a simple and effective way to handle water filtering and industrial wastewater management. According to our research, this work is the first to explain how to remove MG dye from wastewater samples using Ag-MOF adsorbents.

Mechanistic studies of uranyl interaction with functionalized mesoporous chitosan-superparamagnetic nanocomposites for selective sorption: Characterization and sorption performance

Herein, two hybrid magnetic-chitosan nanocomposite core-shell were synthesized via subsequently heterogeneous nucleation immobilized with alanine/serine functionality for enhanced uranyl ions (UO 2 2+ ) sorption. The physiochemical characteristics of nanocomposites were determined by CHN, FTIR, XRD, BET, pHzpc, TEM, TGA, XPS and VSM studies. The synthesized mesoporous alanine (Ala) and serine (Ser) nanocomposites were found: superparamagnetic with saturation magnetization ( M S : 26.54 and 23.05 emu g -1 for Ala and Ser, respectively), large surface-to-volume ratio for Ser (61.1 m 2 g -1 to 0.41 cm 3 g -1 ), compared to Ala (60.4 m 2 g −1 to 0.36 cm 3 g −1 ), and amine content for Ala and Ser was (2.69 and 2.58 mmol N g -1 with density of ⁓13.42 and ⁓12.73 nm 2- , respectively. The sorption characteristics of uranyl ions were thoroughly examined and compared. At the optimal pH range of 3.5-5.0, Ala and Ser nanocomposites show maximum sorption capacities of 0.498 and 0.609 mmol U/g, respectively in sulfate medium, as well 0.583 and 0.742 mmol U/g in nitrate medium. The Langmuir model suits the sorption process well, and the pseudo-second-order rate equation (PSORE) enables single-layer chemical reactions. Small-size particles afford rapid sorption ⁓50 minutes with half-sorption-time (t 0.5 ) 3.9 and 4.2 min for Ser and Ala nanocomposite, respectively. The sorption is spontaneous, exothermic and regulated by entropy change. The sorption efficiency in various medium types can be arranged according to sorption capacity as follows: nitrate > chlorides >> sulphate medium. According to spectroscopic analyses (FTIR and XPS), the sorption sites are N/O functional groups, which adsorbed UO 2 2+ by anion-exchange, electrostatic attraction and chelation mechanisms. Elution and regeneration are successfully accomplished with using acidified urea solution achieving ⁓92%. Finally, both sorbents were tested and compared for the selectivity of UO 2 2+ from multicomponent simulated waste containing uranyl species. Both sorbents showed high sorption capacity, excellent selectivity, and good recyclability and reusability over multiples sorption cycles. • Alanine and serine efficiently functionalized the magnetic-chitosan nanocomposite core-shell, which were extensively characterized and tested for uranium sorption. • Sorbents have a high sorption capacity, great selectivity, and strong recyclability and reusability through numerous sorption cycles. • Nanocomposites show a high affinity for U(VI) and great selectivity from acidic simulated nuclear effluent. • Interaction mechanisms of nanocomposites with uranyl ions have been elucidated.

Removal of Pb(II) from water samples using surface modified core/shell CdZnS/ZnS QDs as adsorbents: Characterization, adsorption, kinetic and thermodynamic studies

This research presents aqueous colloidal method to synthesize CdZnS/ZnS surface modified core/shell quantum dots (QDs) with capping agents 2-mercaptoacetic acid and 3-mercaptopropanoic acid. The QDs were characterized by the different analytical techniques. Using Plackett–Burman and Central composite designs, optimum conditions for the removal of Pb(II) from aqueous medium were developed: QDs (0.013 g) at pH 6.9, time of adsorption and desorption (20 min), temperature (61.1 °C) and dilution on 100 ppb standard solutions. Moreover, Freundlich models suggested that Pb(II) adsorption was favorable on the heterogeneous surface of QDs. The values of Δ G ° and Δ H ° (−59.26 KJ/mol.K) suggested the process was spontaneous and exothermic. The negative Δ S ° (−0.16 KJ/mol.K) indicates that the Pb(II) chemisorb on QDs. While, system follows the pseudo-second order rate equation which indicates that rate limiting step involves chemical reaction and could be influenced by the intraparticle/pore diffusion of Pb(II) ions with QDs. By using atomic absorption spectrophotometer, developed method was tested for Pb(II) removal from tap and ground water samples taken from the different districts of Karachi City. The % recovery for Pb(II) was found to be 96.4 % (tap water) and 94.8 % (ground water) with LOD = 0.1 ng mL −1 and LOQ = 0.90 ng mL −1 .

Application of Fe and Cu nanoparticles for methyl orange removal from water and water-ethanol mixtures under various experimental conditions

In this study, metallic iron nanoparticles (Fe NPs) and metallic copper nanoparticles (Cu NPs) were prepared, characterized, and used in the removal of methyl orange (MO) dye. The experiments investigated first the UV–Vis spectra of dye molecules in three types of solvents (water, water-ethanol, and water-dimethyl sulfoxide). The removal of MO was then conducted under various experimental conditions to investigate the effects of solvent type, nanoparticles dosage, salinity of the solutions, temperature, and shaking time. The highest extent of MO removal was achieved in water solutions. Under all experimental conditions, Fe NPs showed higher efficiency than Cu NPs in MO removal. Moreover, heterogeneous Fenton process led to smaller MO removal when compared with the direct use of the nanoparticles, for both water and water-ethanol solutions. From a kinetic perspective, the dye removal process was much faster in water than in water-ethanol mixtures, and the data followed pseudo-second order rate equation.

Fabrication of the composite sepiolite@polyethyleneimine/sodium alginate and its excellent adsorption performance for heavy metal ions

In order to explore more excellent heavy metal adsorbents with clay mineral sepiolite (Sep), this work was carried out and presented the novel design and fabrication processes of the composite Sep@polyethyleneimine/sodium (SEP@PEI/SA), which were characterized by SEM, EDX, FT-IR, XPS, TGA, and porous analysis, and were efficiently utilized for heavy metal ions adsorption. The adsorption properties of SEP@PEI/SA for Pb(II), Cu(II), Au(III), Ag(I), Pd(IV), Pt(IV), Hg(II), Cr(VI), Cr(III), Co(II), Zn(II), and Ni(II) were investigated, and it was employed to remove lead ions from the simulated lead-containing industrial wastewater through adsorption method. The adsorption properties of lead ions on SEP@PEI/SA were thoroughly investigated in this study, and the results demonstrated that the adsorption kinetics of SEP@PEI/SA for lead ions at different temperatures could be modeled closely by a pseudo second-order rate equation, Langmuir isotherm model was the best fit one and the maximum adsorption capacity was could reach 1094.86 mg/g at 25 °C. Adsorption thermodynamic parameters, standard Gibbs free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) changes, were −6.29 KJ·mol−1 (35 °C), 30.81 KJ·mol−1, 0.12 KJ·(K·mol)−1, respectively, suggesting the spontaneous and endothermic nature of the adsorption process with the increase of the randomness. All these research work results showed that the novel adsorbent SEP@PEI/SA has promising potential to removal lead ions from water body efficiently.

Adsorption kinetics and isotherms of binary metal ion aqueous solution using untreated venus shell

Among available technologies to remove heavy metals from wastewater, biosorption has gained more attention due to its high removal efficiency, friendly operation, and inexpensive cost. Despite many studies on metal adsorption from single ion solutions, kinetics and isotherms of binary metal ions simultaneously adsorbed onto biosorbents have not been thoroughly investigated to provide insight on involving mechanisms. This study explored the adsorption potential of untreated venus shells (UVS) that can be utilized in economical and environmentally-friendly ways. In this work, UVS of different sizes were prepared without chemical treatment as a biosorbent. Characterization of UVS was accomplished using nitrogen adsorption isotherm, FTIR, and SEM-EDX. Batch adsorption was carried out to study the effect of initial metal ion concentration, adsorbent dosage, and size on removing Cu(II) and Zn(II) from a binary solution of both metal ions using UVS. The experimental values of maximum adsorption capacities of Cu(II) and Zn(II) were 0.446 and 0.465 mg/g, respectively. The adsorption data were analyzed using the pseudo-first order, pseudo-second order, Elovich, and intraparticle diffusion rate equations. The pseudo-second order and the intraparticle diffusion model yielded the best fit to the experimental data for Cu(II) and Zn(II) ions, respectively. The equilibrium isotherm was examined using the Langmuir, Freundlich, Temkin, Dubinin–Radushkevich (D–R), and Elovich models. The Freundlich model best fits the Cu(II) and Zn(II) equilibrium adsorption data. The results indicated that the adsorption of Cu(II) and Zn(II) onto UVS-600 adsorbent could undergo a chemisorption mechanism. Both metal ions in an aqueous solution were competitively adsorbed onto the heterogeneous active sites available on the shell surfaces. Cu(II) and Zn(II) ions in the binary system could result in ionic interference between the adsorbed ions and the active sites.

V2O5, CeO2 and Their MWCNTs Nanocomposites Modified for the Removal of Kerosene from Water

In this paper, the application of multiwalled carbon nanotubes (MWCNTs) based on metal oxide nanocomposites as adsorbents for the removal of hydrocarbons such as kerosene from water was investigated. Functionalized MWCNTs were obtained by chemical oxidation using concentrated sulfuric and nitric acids. V2O5, CeO2, and V2O5:CeO2 nanocomposites were prepared using the hydrothermal method followed by deposition of these oxides over MWCNTs. Individual and mixed metal oxides, fresh MWCNTs, and metal oxide nanoparticle-doped MWCNTs using different analysis techniques were characterized. XRD, TEM, SEM, EDX, AFM, Raman, TG/DTA, and BET techniques were used to determine the structure as well as chemical and morphological properties of the newly prepared adsorbents. Fresh MWCNTs, Ce/MWCNTs, V/MWCNTs, and V:Ce/MWCNTs were applied for the removal of kerosene from a model solution of water. GC analysis indicated that high kerosene removal efficiency (85%) and adsorption capacity (4270 mg/g) after 60 min of treatment were obtained over V:Ce/MWCNTs in comparison with fresh MWCNTs, Ce/MWCNTs and V/MWCNTs. The kinetic data were analyzed using the pseudo-first order, pseudo-second order, and intra-particle diffusion rate equations.

Kinetic and Thermodynamic Studies of Lysozyme Adsorption on Cibacron Blue F3GA Dye-Ligand Immobilized on Aminated Nanofiber Membrane.

The polyacrylonitrile (PAN) nanofiber membrane was prepared by the electrospinning technique. The nitrile group on the PAN nanofiber surface was oxidized to carboxyl group by alkaline hydrolysis. The carboxylic group on the membrane surface was then converted to dye affinity membrane through reaction with ethylenediamine (EDA) and Cibacron Blue F3GA, sequentially. The adsorption characteristics of lysozyme onto the dye ligand affinity nanofiber membrane (namely P-EDA-Dye) were investigated under various conditions (e.g., adsorption pH, EDA coupling concentration, lysozyme concentration, ionic strength, and temperature). Optimum experimental parameters were determined to be pH 7.5, a coupling concentration of EDA 40 μmol/mL, and an immobilization density of dye 267.19 mg/g membrane. To understand the mechanism of adsorption and possible rate controlling steps, a pseudo first-order, a pseudo second-order, and the Elovich models were first used to describe the experimental kinetic data. Equilibrium isotherms for the adsorption of lysozyme onto P-EDA-Dye nanofiber membrane were determined experimentally in this work. Our kinetic analysis on the adsorption of lysozyme onto P-EDA-Dye nanofiber membranes revealed that the pseudo second-order rate equation was favorable. The experimental data were satisfactorily fitted by the Langmuir isotherm model, and the thermodynamic parameters including the free energy change, enthalpy change, and entropy change of adsorption were also determined accordingly. Our results indicated that the free energy change had a negative value, suggesting that the adsorption process occurred spontaneously. Moreover, after five cycles of reuse, P-EDA-Dye nanofiber membranes still showed promising efficiency of lysozyme adsorption.

Phosphonomethyl iminodiacetic acid functionalized metal organic framework supported PAN composite beads for selective removal of La(III) from wastewater: Adsorptive performance and column separation studies

The rare earth elements being toxic in nature are being accumulated in water bodies as their industrial usage is growing exponentially, thus their efficient separation holds an immense significance. Herein, ligand functionalized metal organic framework (MOF), Phosphonomethyl iminodiacetic acid coordinated at Fe-BTC, was synthesized post-synthetically and incorporated subsequently in polyacrylonitrile polymer to prepare the composite beads via nonsolvent induced-phase-inversion technique for selective adsorption of La(III) from the wastewater in batch and dynamic column mode. XPS NMR, and FTIR were used to establish the interaction between functionalized ligand and unsaturated metal nodes of MOF. The adsorption capacity was 232.5 mg/g and 77.51 mg/g at 298 K of the functionalized MOF and composite beads respectively. Adsorption kinetics followed a pseudo-second order rate equation, and isotherm indicated the best fitting with Langmuir model. The dynamic behavior of the adsorption column packed with MOF/Polymer beads was fairly described by the Thomas model. The breakthrough time of 23.2 h could be attained with 12 cm of bed height and 10 ml/min of flow rate. These MOF/Polymer beads shown the selectivity of La over transitional metals were recycled over 5 times with about 15% loss of adsorption capacity. The findings provide suggestive insights of the potential use of functionalized MOF towards the separation of the rare earth element.

Adsorption-desorption dynamics of synthetic and naturally weathered microfibers with toxic heavy metals and their ecological risk in an estuarine ecosystem

Microfibers (MFs) in aquatic and marine ecosystems adsorb toxic heavy metals and then transfer the heavy metals enriched MFs to living organisms. In this research paper, the adsorption-desorption dynamics of heavy metals onto MFs was studied by using theoretical models and experimental investigations. The adsorption of metals onto MFs was well correlated for the Freundlich model and the adsorption kinetics follows pseudo-second order rate equation. The adsorption capacity of naturally weathered MFs was 30.8 mg g−1 which is about 35% higher than the synthetic fiber of similar range of size of MFs. The leaching of heavy metals from MFs was found that 90–95% of adsorbed metals were leached within 24 h. The leaching of Ti(II) and Al(III) were slower than the other metal ions. The salinity has shown decrease in adsorption capacity of MFs for heavy metals. Based on the Nemerov pollution index (PN), the naturally weathered MFs enriched with heavy metals in sediments became heavily polluted with PN values between 2.98 and 3.49. The risk index value of 396 represents that the bottom dwellers and other marine organisms in the Narmada estuary high risk from MFs and MFs enriched with metals. This study indicates that MFs play dominant role in fate and distribution of heavy metals in the estuarine ecosystems.

Humic acid attachment on chitosan-modified silica gel as an economical, efficient, and selective adsorbent for thorium and uranium removal

ABSTRACT A novel, low-cost adsorbent material was prepared by the immobilization of humic acid on a silica gel surface coated with cross-linked chitosan (SiChiHA). The adsorbent was developed to remove selectively of Th(IV) and U(VI) from aqueous solution, including their pre-concentration and separation from lanthanides and high salinity conditions. A simple waste-less humic acid immobilization method was shown to be successful based on FT-IR, SEM-EDS, and zeta potential characterization results. The adsorbent was found to be stable over a wide pH range, with the highest capacities obtained at pH 3.5 (Th(IV)) and pH 5 (U(VI)). Langmuir model calculations yielded a maximum capacity of 30.6 mg g−1 and 75.4 mg g−1 for Th(IV) and U(VI). The adsorption process was found to be rapid (half concentration was removed within 10 min) and best described by a pseudo-second order rate equation. Increasing NaCl concentration up to 2 mol L−1 or lanthanide concentration up to 100 times did not significantly affect the removal efficiency for either Th(IV) of U(VI). Both elements could be sequentially separated by elution with ammonium citrate and nitric acid, respectively. The adsorption-desorption experiment showed that the adsorbent could be used for at least five cycles without significant capacity loss. This study provides insight into the development of low-cost adsorbent with practical functionality, including separation and regeneration ability, the advantageous properties scarcely reported in low-cost adsorbent literature.

Response surface methodology mediated process optimization of Celestine blue B uptake by novel custard apple seeds activated carbon/FeMoO4 nanocomposite

The present study deals with the evaluation of performance and efficacy of a novel nanocomposite based on custard apple seeds derived activated carbon (CAS-AC), prepared by microwave-assisted technique, and FeMoO4 nanoparticles (NPs) synthesized through green route for Celestine blue B (CB) removal from simulated wastewater. The physico-chemical characterization of the nanocomposite was achieved by means of FTIR, XRD, SEM-EDX, TEM and BET techniques. The operational factors such as contact time, initial CB concentration, nanocomposite dosage, and initial solution pH were optimized by Response Surface Methodology. The equilibrium data, modeled with various isotherm and kinetic models, conformed well to Freundlich model and pseudo-second order rate equation, respectively with both intraparticle and film diffusion controlling the overall adsorption process. The considerably higher Langmuir saturation capacity of the nanocomposite towards CB adsorption at 298 K (112 mg/g) than other previously reported adsorbents together with good recyclability depicts its superior adsorptive performance. The spontaneity, feasibility and endothermic nature of the CB removal process were established from the thermodynamic parameters. The hydrogen bonding and π–π interactions primarily governed the overall adsorption mechanism. The spent NC was regenerated using 0.1 mol/l HCl solution. The CAS-AC/FeMoO4 NC showed good reusability maintaining its adsorption efficiency of 86.25% up to fourth consecutive cycles. The results obtained from the present study reflected that the nanocomposite is a promising adsorbent for the liquid phase amputation of CB in effective and efficient manner.

Kinetic modeling of biosorption for hydrocarbons removal from wastewater using modified logistic equation

Application of raw and modified biomass to remove hydrocarbons from wastewater by adsorption is a common practice. A mathematical modeling of biosorption kinetics is a crucial step to optimize the remediation process. In the present study, kinetic studies were carried out to describe the sorption process of crude oil and water on waste sunflower pith. To increase sorption capacity the pith surface was modified with polydimethylsiloxane (PDMS) and hydrophobic SiO2 nanoparticles. The maximum sorption capacity of raw and modified material was 17.76 and 19.62 g/g for crude oil, respectively. The system reached the equilibrium stage after 24 hours. The uptake profiles have been described by the pseudo-first order rate equation and the pseudo-second order rate equation. The calculated results were compared with experimental data and their fit was poor. To predict biosorption kinetics a new mathematically efficient procedure based on modified logistic equation was developed. The results indicate that the sunflower pith has a great potential for the removal of crude oil from water phase as an eco-friendly process.

Functionalized aminophosphonate chitosan-magnetic nanocomposites for Cd(II) removal from aqueous solutions: Performance and mechanisms of sorption

Functionalized magnetic nanocomposites have recently retained a great attention for metal recovery from aqueous solutions. In this work, two magnetic-chitosan nanocomposites are synthesized by grafting α-aminophosphonate functions (i.e., methyl- and phenyl-aminophosphonate, Me-MCS and Ph-MCS, respectively) using a facile two-steps process. The physicochemical properties of these nanocomposites are characterized including nano-structure characterization (TEM), magnetic properties (VSM), crystallinity (XRD), and chemical characterization (elemental CHNP analysis, FTIR, XPS and TGA). FTIR and XPS analyses confirm the contribution of amine and phosphonic groups in the binding of cadmium ions. These materials are extensively investigated for Cd(II) removal: maximum sorption capacities reach 118.1 mg g−1 for Me-MCS and 193.5 mg g−1 for Ph-MCS, at the optimum pH (in the range pH 6–7); and the sorption isotherms are fitted by the Langmuir model. Small-size particles allow achieving fast uptake (within 2 h of contact); and kinetic profiles are appropriately modeled by the PSORE (pseudo-second order rate equation) and the Crank equation (for resistance to intraparticle diffusion). Cadmium sorption is exothermic. The metal is efficiently desorbed using 0.5 M acidified thiourea solution and the sorbent can be recycled for a minimum of five cycles (loss in sorption and desorption performances around 20% at the fifth cycle). In multi-component solutions the two sorbents show some differences in selectivity profiles, which can be roughly correlated with the hard/soft characteristics of reactive groups and the softness properties of heavy metal ions. The sorbents are successfully used for Cd(II) removal from a water sample obtained from Al-Burullus Lake (Kafr-El-Sheikh Governorate, Egypt).

Adsorption of phenol and chromium (VI) from aqueous solution using exfoliated graphite: Equilibrium, kinetics and thermodynamic studies

Several industrial effluents contain Cr (VI) and phenol in varying concentrations. These compounds are highly toxic even at low concentrations. In this study, Exfoliated Graphite (EG) was investigated as an adsorbent towards the removal of these contaminants. This was motivated by its availability, ease of synthesis and high surface area. The exfoliation process resulted in graphite that had a worm-like accordion structure and an increased surface area from 2.4 to 22.4m2g−1. The optimum loading for both pollutants was 30 g/L and equilibrium was attained in a 48 h period. Maximum Cr (VI) removal (89.8%) occurred under acidic conditions (pH 2) while phenol was preferentially removed (62.3%) under basic environments (pH 12). Three non-linear adsorption models, namely Redlich-Peterson, Freundlich and Langmuir were evaluated. The Redlich-Peterson isotherm, with an exponential constant, β=°0.8982 best described the equilibrium data for Cr (VI) with a regression coefficient of R2=°0.9965 while the Langmuir isotherm accurately described the phenol adsorption with a regression coefficient of R2=°0.9975. The pseudo-second order rate equation adequately represented the experimental data for phenol and Cr (VI) with regression coefficients greater than 0.99. Adsorption thermodynamic studies revealed that the attachment of phenol and Cr (VI) onto EG was a feasible, endothermic and spontaneous process.

Tuning the ion exchange behavior of cesium and strontium on sodium iron titanate

The sodium iron titanate (NaFeTiO) ion exchanger was synthesized by the hydrolysis of tetraethyl orthotitanate and ferric chloride solution using sodium hydroxide. The amount of Fe3+ present in the solution was varied to obtain different Ti/Fe mole ratios in the product ranging from 5 to 15. The ion exchanger obtained was characterized by Raman spectroscopy, X-ray diffraction, Thermogravimetry, SEM-EDX analysis and elemental composition. The ion exchange behavior of Cs+ and Sr2+ on sodium iron titanate was studied as a function of aqueous phase pH, equilibration time, initial concentration of Cs+ and Sr2+ and presence of interfering ions in aqueous phase. The rate of ion-exchange of Cs+ and Sr2+ was best fitted into pseudo-second order rate equation. Similarly, the loading behavior of Cs+ and Sr2+ on NaFeTiO and the data obtained were fitted into various adsorption models such as Langmuir, Freundlich, Temkin, and Dubinin-Radushkevitch adsorption isotherms. From the statistics of the fitting, it was found that the experimental isotherm was explained well by Langmuir adsorption model. The ion-exchange capacity of 127, 115, 95 mg.g−1 for Cs+ and 86,128,169 mg.g−1 for Sr2+ were obtained on NaFeTiO with Ti/Fe mole ratios 5, 10, and 15 respectively. The results showed that the selectivity of NaFeTiO can be tuned either for Sr2+ exchange by keeping higher Ti/Fe mole ratio or for Cs+ exchange by keeping lower Ti/Fe mole ratio. In view of this, NaFeTiO compound can be regarded as the potential candidate for separating cesium or strontium selectively from alkaline wastes.