Sips Isotherm Model Research Articles

Locally available agroresidues as potential sorbents: modelling, column studies and scale-up

Sawdust, cotton stalk and groundnut shell were used for removal of methylene blue from aqueous solution using batch sorption. Effect of initial dye concentration, temperature, and particle size of sorbents on methylene blue removal was investigated. Sorption capacity increases with rise in initial dye concentration and temperature. Impact of particle size on sorption of methylene blue was investigated and indicated that removal of dye increases with decrease in particle size of sorbents. Maximum sorption for sawdust, cotton stalks and groundnut shell were 9.22 mg g−1, 8.37 mg g−1 and 8.20 mg g−1 respectively; at 60 °C and 100 ppm initial dye concentration. Sorption isotherms were analyzed using fundamental Freundlich isotherm. Subsequently, sips isotherm model was employed for better fitting. Kinetic study shows that, biosorption process is pseudo-second-order in nature. During the course of this study, adsorption dynamics revealed that film diffusion was key step for biosorption. In addition, thermodynamics of sorption was studied; and it was found that Gibbs free energy (∆G°) decreases with increase in temperature. Sawdust was found to be best among all the sorbents. Therefore, column studies and breakthrough curve modelling were performed using sawdust. Furthermore, it was estimated that a scaled-up column using sawdust can treat 6672 L of wastewater in 24 h with 80% efficiency.

Interaction between adenine and Cu2+ and Fe3+-montmorillonites: a prebiotic chemistry experiment

AbstractThe modification of minerals with metals can promote changes in their surface and, consequently, in their physicochemical properties. Minerals could have played an important role in the origin of life as they can protect molecules against degradation by radiation and hydrolysis, pre-concentrate molecules from dilute solutions and catalyse the formation of polymers. Thus, the current work studied the modification of montmorillonite with Cu2+ and Fe3+ ions. These modified montmorillonites were used to study the interaction with adenine dissolved in distilled water and artificial seawater 4.0 Gy (Gy = billion years ago). The most important result of this work is that the adsorption of adenine onto modified montmorillonites is a complex interaction among adenine, salts in seawater and Cu2+/Fe3+-montmorillonite (Cu2+/Fe3+-Mont) . The adsorption of Cu2+ and Fe3+ onto montmorillonite decreased its surface area and pore volume. The Sips isotherm model showed the best fit of the data and n values indicate that the adenine adsorption process was homogeneous. The highest adenine adsorption was obtained in artificial seawater 4.0 Gy onto Fe3+-Mont at 60°C and the lowest in distilled water or artificial seawater 4.0 Gy onto montmorillonite [montmorillonite washed with distilled water (Mont-STD)] at 60°C. Adenine adsorption onto Mont-STD/montmorillonite modified with 500 ml of 0.1 mol l−1 of CuCl2 and Fe3+-Mont was an exothermic process and an endothermic process, respectively. For all adsorptions ΔG was negative. The adsorption of adenine onto Fe3+-Mont was ruled out by entropy and the other samples by enthalpy and entropy, being a major contribution for Gibbs free energy from enthalpy. The Fourier transform-infrared data indicate that the interaction of adenine with minerals may occur through the NH2 functional group.

Low to high-pressure CO2 separation using amine-functionalized Mobile Composite Matter, isotherm modelling and heat of adsorption study

ABSTRACT Adsorptive CO2 separation is an effective process in carbon capture and sequestration. In this work, Benzylamine, Monoethanolamine, and Aminoethylethanolamine impregnated MCM-48 are used to enhance CO2 adsorption capacity. The materials are characterized using BET, XRD, TGA, FT-IR, FESEM and elemental analysis techniques. The CO2 uptakes are measured using high pressure sorption equipment in the temperature and pressure ranges of 25–80°C and 0–30 bar. The effect of amine loadings is pronounced in the chemisorption of CO2. The Sips isotherm model is better to correlate the experimental data than that of in Freundlich, Langmuir and Toth models. The isosteric heat of adsorption is calculated using Van’t Hoff plot in the temperature range of 25–60°C to understand the degree of heterogeneity and the surface energy distribution of the adsorbents. The CO2 adsorption capacity (3.33 mmol CO2/g) and amine efficiency (14.1 mmol CO2/g amine) of 30% AEEA impregnated MCM-48 is highest among the amine-functionalized MCM-48 adsorbents reported till date in the open literature. The MCM-48-30%AEEA shows 5.2 times higher CO2 adsorption capacity than that of in MCM-48 (0.637 mmol/g) at 25°C and 1 bar pressure. The MCM-48-30%AEEA is proposed as a promising adsorbent in low- to high-pressure post-combustion flue gas and natural gas purification.

PERBANDINGAN MODEL ISOTERM BIOSORPSI Cd TERLARUT DALAM AIR DENGAN BIOSORBENT ASPERGILLUS NIGER

Due to the increasing awareness of the deleterious ecological effects of toxic Cd, the adsorption of Cd from aqueous solutions by Aspergillus niger biomass was studied. The aim of this work was to find the exact adsorption isotherm model to predict the single system adsorption by the Aspergilfus niger biomass. The batch sorption experiments were carried out in 50 ml conical flasks. Weighed amounts (8,5 to 57, 2 mg) of Aspergillus niger biomass were introduced into a number of conical flasks, to which 25 ml of Cd solutions of increasing concentrations from 20,28 to 24,435 mg/L were added. The amount of Cd accumulated on biomass was calculated as the difference between the amount present in control experiments and that remaining in solution after equilibrium with biomass. Four adsorption isotherm models, namely Freundlich Isotherm Model, Langmuir Isotherm Model, Sips Isotherm Model, dan Toth Isotherm Model, were fitted to the experimental data. The Toth Isotherm Model and The Sips Isotherm Model· were superior, which provided the least average relative error (6,035 % and 6,013 %). The maximum sorption was seen at pH 6. ltis 143.093 mglg sorbent.

Obtaining activated biochar from olive stone using a bench scale high-pressure thermobalance

A low cost-biomass, olive stone, was used as a carbon precursor to synthesize activated biochar. Experiments were carried by single step activation for two agents (steam and CO2) using a bench scale high-pressure thermobalance. Temperature, pressure, flow rate and holding time were optimized according to the highest adsorption capacity of the biochar obtained. In this respect, activation conditions were established at 900 °C for 30 min, at 0.15 ml/min and 1 bar for H2O activation. The optimum activation conditions for CO2 activation was found to be 1000 °C for 30 min, at 300 ml/min and 1 bar. The activated biochars yielded were characterized by adsorption-desorption of N2 at −196 °C, scanning electron microscopy, Raman spectroscopy, thermogravimetric analyses and elemental analyses. Results showed that the CO2 activation only generated microporosity developed in the biochar, whereas both meso and micropores were created after steam activation. Then, the optimum materials were evaluated as a possible CO2 adsorbent and for this purpose, the CO2 adsorption isotherms over the pressure range of 1–20 bar at 30 °C were studied. Moreover, the results for these isotherms results were fitted to Langmuir, Freundlich and Sips isotherm models, and the latter forecast the results most accurately.

Electrospun chitosan/polyvinyl alcohol nanocomposite holding polyaniline/silica hybrid nanostructures: An efficient adsorbent of dye from aqueous solutions

In this work, the addition of a novel polyaniline (PANI)/silica (SiO2) nanostructure (PSn) in chitosan/polyvinyl alcohol nanofibers (CP) was evaluated to enhance the dye removal capacity of CP. Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FE-SEM), and energy-dispersive X-ray spectroscopy (EDS) results confirmed the chemical grafting of SiO2 on PANI nanoparticles. Brunauer-Emmett-Teller (BET) results showed a specific surface area of 61 m2 g−1 for the PSn filled CP nanofiber (CP-PSn). FE-SEM and EDS-elemental mapping results showed the uniform dispersibility of PSn in CP nanofibers. After the addition of PSn into CP, the adsorption capacity of CP increased from 48 to 110 mg g−1 (from 0.069 to 0.158 mmol g−1), 40 to 90 mg g−1 (from 0.122 to 0.274 mmol g−1), and 31 to 45.2 mg g−1 (from 0.097 to 0.141 mmol g−1) for Congo red (CR), methyl orange (MO), and methylene blue (MB) dyes, respectively. The optimum anionic dye (CR and MO) uptake was observed at pH 5, while for the cationic dye (MB), the optimum uptake was detected at pH 9. The isotherm experiments results showed that the Sips isotherm model could well describe the adsorption process (R2 > 0.98). Thermodynamic studies at 298 and 328 K verified that the adsorption process is spontaneous with ΔG ranging between −10.44 and − 2.83 kJ mol−1. Also, ΔH was found to be 34.16, 22.25, and 17.05 kJ mol−1 for CR, MO, and MB adsorption, respectively. The highest recovery after 5 cycles was observed for a sodium hydroxide solution (NaOH, 0.1 M), which were 74, 68, and 55% of the adsorption capacity of the first cycle for CR, MO, and MB dyes, respectively.

Synthesis and characterization of biomass-derived surface-modified activated carbon for enhanced CO2 adsorption

In this study, activated carbon (AC) based adsorbents were synthesized from biomass-derived hydro-char (HC) through modified hydrothermal carbonization (HTC) process coupled with H3PO4 (PA), ZnCl2, (ZnCl), and KOH thermochemical activation with a specific impregnation ratio of 1:3 (HC/activating agent) at 600 °C. The prepared ACs were characterized through CHN-S analyser, XRD, SEM/EDS, BET, TGA, and FTIR analysis. The modification in textural and surface morphology has been observed. Thermochemical activation results in surface modification of AC samples with a higher specific (SBET) surface area having a range of 650−1225 m2/g, large microporous volume (VμD-A, VμD–R) up to 0.624 and 0.642 cm3/g with 68–90 % micro-porosity. The CO2 adsorption capacity was examined through a high-pressure gas sorption analyser at a pressure of 0−16 bar and temperature of 15 °C, 30 °C, and 45 °C. At 15 °C of temperature, AC-PA showed the adsorption capacity of 130 and 958 mg/g, while AC-ZnCl exhibited 160 and 836 mg/g of adsorption at 1 and 16 bar of pressure respectively. Whereas AC-KOH exhibited a notable CO2 adsorption capacity of 198 and 1560 mg/g at 1 and 16 bar of pressure (15 °C). Furthermore, experimental equilibrium data of CO2 adsorption were analysed by applying Freundlich, Langmuir, Redlich-Peterson, Sips, and Toth isotherm models and validate these models by calculating the regression coefficient (R2), and standard deviation Δq (%). Finally, the thermodynamics parameters (ΔH°, ΔS°, ΔG°, and ΔHIsosteric) were evaluated and concluded that the adsorption of CO2 (adsorbate) on adsorbent is spontaneous and exothermic.

Carbon nanotubes impregnated with metallic nanoparticles and their application as an adsorbent for the glyphosate removal in an aqueous matrix

Carbon nanotubes with multiple walls (MWCNTs) were modified via green synthesis methodology, with metal nanoparticles (MPNs-Fe). The prepared material (MWCNT/MPNs-Fe) was characterized and used to remove the herbicide glyphosate (GLY) from an aqueous matrix through the adsorption process. The characterization results indicated the presence of MPNs-Fe incorporated between the tangled wires of the MWCNTs, thus confirming the green synthesis success. The kinetic studies showed a percentage of GLY removal of up to 86.23% (for C0 = 35 mg L−1), with the process equilibrium being reached in 120 min. The pseudo-first-order model demonstrated a greater prediction capacity for the system. The Sips isotherm model was best suited to the equilibrium data, providing a maximum adsorption capacity of 43.66 mg g−1 (298 K). The thermodynamic behavior showed that the process is spontaneous and favorable, with exothermic nature. The material's application in close to real circumstances presented the removals of 68.38% and 40.33% for two simulated effluents with different compositions. The adsorption regeneration tests found that the adsorption kept similar adsorption capacities after six cycles. Therefore, it can be concluded that the MWCNT/MPNs-Fe synthesized in the present work is a promising alternative as an adsorbent in the treatment of effluents and waters containing GLY.

Equilibrium Isotherms, Kinetics, and Thermodynamics of the Adsorption of 2,4-Dichlorophenoxyacetic Acid to Chitosan-Based Hydrogels

The aim of this work was to study the equilibrium isotherms, kinetics, and thermodynamics of the adsorption of 2,4-dichlorophenoxyacetic acid to a chitosan-based hydrogel and chitosan/magnetite-based composite hydrogel containing 1.0% (w/w) magnetite. The hydrogel synthesis and adsorption processes were confirmed by Fourier transform-infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, and differential scanning calorimetry. Adsorption was affected by contact time, solution pH, initial 2,4-D concentration, and solution temperature. The maximum 2,4-D adsorption capacities of the chitosan-based hydrogel and chitosan/magnetite-based composite hydrogel were 75.29 and 45.33 mg of pollutant per g of dried hydrogel, respectively, determined by the Sips isotherm model. The calculation of Gibbs free energy, enthalpy, and entropy revealed the occurrence of spontaneous, endothermic, disordered processes. The adsorption mechanism takes place by monolayer formation and multisite intra/intermolecular interactions, according to the nonlinear Sips isotherm model. In conclusion, the adsorption of 2,4-D to the hydrogels takes place by diffusion processes, intra/intermolecular interactions, and macromolecular relaxation of the polymer network. Desorption processes confirmed the adsorption mechanism. The hydrogels synthesized in this work are efficient solid matrices for the removal of 2,4-dichlorophenoxyacetic acid and chemical oxygen demand from polluted water and wastewater.

Efficient adsorptive removal of Cobalt(II) ions from water by dicalcium phosphate dihydrate

Although the radionuclide 60Co is widely used, its presence in various effluents demands its removal to preclude environmental pollution and detrimental effects on human health. This study investigated the batch adsorption performance of a potential cobalt adsorbent, dicalcium phosphate dihydrate (DCPD), in immobilizing Co2+ from water. The influences of solution pH, contact time, initial concentration, and competing cations were examined and discussed. Stable cobalt uptake was observed at pH 4–8. The sorption kinetics showed a multi-stage uptake profile, implying that several mechanisms are involved in the adsorption process. Microscopy and structural analysis revealed that DCPD decomposes to its anhydrous form during adsorption, which explains the multistep curve over the entire adsorption period. However, the non-apatitic transformation is not exclusive to cobalt uptake. Intraparticle diffusion also contributed to the overall removal kinetics of Co2+ from water. Considering the Sips isotherm model, the maximum Co2+ adsorption capacity of DCPD was 441 mg g−1. Cobalt uptake selectivity dropped in the presence of Ca2+ ions, from 1.21 × 104 to 207 mL g−1, indicating DCPD would be more applicable in treating soft 60Co-contaminated waters. Structural analysis, elemental mapping, and qualitative analysis of solid residues confirmed that ion exchange is involved in the removal of cobalt from aqueous solutions.

Hosting of the antibiotic Vancomycin by bentonite: Characterization and slow release study

Bentonite (Bent) is a highly promising material to be used in the pharmaceutical industry as drug delivery system due to its high drug loading capacity and controlled drug release properties. The adsorption and controlled release of vancomycin (VCM) ―a glycopeptide antibiotic of large molecular size and structural complexity― on/from an unmodified Bent is reported. The adsorption and release of this drug on/from the Bent―whose safety was demonstrated by in vivo studies―was monitored by ultraviolet (UV) spectroscopy. In order to enhance the VCM loading by the clay, different physical-chemical parameters (pH, drug initial concentration, temperature and interaction time) were evaluated. The Bent-VCM composite was characterized by X-ray diffraction (XRD), transmittance Fourier transform infrared spectroscopy (FT-IR) and thermal gravimetric analysis (TGA). The results showed that the Bent is able to efficiently adsorb VCM, achieving a higher load (qmax= 655 ± 5 mg/g) at 9 × 103 mg/L, when it is in its monovalent cationic form. The characterization studies indicated surface adsorption, as well as clay-drug interactions by hydrogen bridges and electrostatic forces. The Sips isotherm model exhibited a good correlation to the equilibrium experimental data, indicating heterogeneous adsorption of the adsorbate-adsorbent system under study. The ΔG0 calculation indicated the spontaneous and reversible nature of the adsorption process. The in vitro assays at pH values typical of the human gastrointestinal tract demonstrated that the VCM release profiles fulfill the pharmaceutical standards, suggesting the potential use of Bent as VCM carrier.

Insights into interfacial interaction mechanism of dyes sorption on a novel hydrochar: Experimental and DFT study

In this experiment, the interfacial interaction mechanism associated with the sorption of methylene blue (MB) and methyl orange (MO) on Fe-doped porous graphite hydrochar (Fe@PGHC) was studied. The characterization results indicated that Fe@PGHC was fabricated successfully and possessed a well-distributed pore size, graphene-like properties and a large surface area (2340 m2/g). The sorption results demonstrated that the pseudo-second-order kinetics and Sips isotherm models matched well with the MB/MO uptake behaviour. The results of density functional theory (DFT) calculations revealed that increasing the number of oxygen-containing functional groups improved the sorption capacity of MB and decreased the sorption capacity of MO. MB was regarded as an electron acceptor, MO was regarded as an electron donor, and the interaction between adsorbent and MB/MO included π-π, electrostatic and hydrogen bond interactions. The above results demonstrated that Fe@PGHC was a green and promising adsorbent for the sorption of organic dyes from aqueous solutions.

Production of modified sunflowers seed shells for the removal of bisphenol A.

In this present study, an abundant, available lignocellulosic biomass, sunflower seed shells, SSS, was used as a precursor to prepare an effective eco-adsorbent by treatment with H2SO4. A study of the surface characteristics of raw and acid-treated SSS (ACS) has shown that the addition of H2SO4 greatly affected the physicochemical properties of the obtained eco-adsorbent, improving the BET surface area from 6.106 to 27.145 m2 g−1 and surface oxygen-rich functional groups. Batch experiments were performed to assess the removal efficiency of a phenolic compound, bisphenol A (BPA), on the adsorbents. Several parameters were evaluated and are discussed (contact time, pollutant concentration, adsorbent dosage, and pH), determining that the adsorption efficiency of BPA onto SSS was notably improved, from 20.56% to 87.81% when a sulfuric acid solution was used. Different canonical and stochastic isotherm models were evaluated to predict the experimental behaviour. A dynamic study was performed based on the models of reaction kinetics and those of mass transfer. The results showed that the adsorption kinetics of BPA obey the fractal like-kinetic model of Hill for all experimental conditions. The equilibrium data are well suited to the Hill–Sips isotherm model with a determination coefficient >0.999. The kinetic modelling also indicates that the adsorption processes of BPA onto ACS are exothermic and proceed through a physical mechanism. A mass transfer study, using simplified models, proved that the process is controlled by intraparticle and film resistances to mass transfer of the BPA.

Facile synthesis of 2D nanoflakes and 3D nanosponge-like Ni1−xO via direct calcination of Ni (II) coordination compounds of imidazole and 4-nitrobenzoate: Adsorptive separation kinetics and photocatalytic removal of Amaranth dye contaminated wastewater

This study reports a simple method of direct calcination of Ni (II) coordination compounds with N-donor and O-donor ligands such as imidazole and 4-nitrobenzoate to form 2D and 3D Ni1−xO nanostructures. Controlled calcination of imidazole coordinated compound [Ni(Im)6](4-nba)2.2H2O (I) produced 2D nanoflakes in comparison to 4-nitrobenzoate coordinated compound [Ni(H2O)4(4-nba)2].2H2O which formed Ni1−xO nanosponge. Replacement of four coordinated imidazole ligands in compound I with an equivalent number of 4-nitrobenzoate and water molecules as in [Ni(H2O)2(Im)2(4-nba)2] (II) lead to the collapse of flake-like structure upon combustion with the induction of porosity, confirming the dominant effect of 4-nitrobenzoate ligand to form porous structures of Ni1−xO. Material characterization studies revealed that all Ni1−xO nanostructures exhibit cubic phase wherein increase in surface area, pore-volume, and reduction in particle size from 2D nanoflakes to 3D nanosponge is evident. The adsorptive removal of Amaranth dye as a model pollutant using synthesized Ni1−xO nanostructures exhibited high dye removal efficiency of up to 82.81% in the case of 3D nanosponge. The adsorption process is well explained based on the Sips isotherm model and pseudo-first-order reaction kinetics. Photocatalytic Amaranth dye degradation efficiency of 93.80% in 70 min with highest kapp = 4.04×10−2 min−1 is achieved which is attributed to the high surface area and reduction in charge carrier recombination rate as a result of extensive and robust mesoporous structure.

Preparation and Characterization of Activated Carbon Obtained from Water Treatment Plant Sludge for Removal of Cationic Dye from Wastewater

The proposal of this work was the preparation and characterization of activated carbons obtained from water treatment plant sludge (WTS) to apply as adsorbents in the removal of organic dye contaminants from wastewater. The activated carbons were produced with a combination of chemical activation and pyrolysis processes. The textural characteristics of both adsorbents presented a satisfactory superficial area and mesoporous structure. The presence of phenolic and carboxylic groups in the surface indicated a better adsorption of cationic adsorbates. When applied as adsorbents in the removal of methylene blue (MB) from wastewater, the maximum removal values obtained were up to 96%. The adsorption results showed that the adsorption was faster in the beginning and reached maximum around 30 min. The Elovich kinetic model and the Sips isotherm model presented the best fit to experimental data, which was checked by analysis of variance (ANOVA). The production of activated carbons from WTS is a sustainable and effective option in the removal of MB dye.

Cadmium and Copper Removal From Aqueous Solutions Using Chitosan-Coated Gasifier Biochar

Gasifier Biochar (GBC) and Chitosan-Coated Gasifier Biochar (CGBC) derived from pine wood was used to remove Cu2+ and Cd2+ from water. Chitosan-Coated Gasifier Biochar was made by mixing GBC with aqueous acetic acid chitosan solution followed by treatment with NaOH. Both CGBC and GBC were characterized using FT-IR, scanning electron microscopy, surface area measurement (BET), elemental analysis, thermogravimetric analysis, and point of zero charge. Chitosan accounts for 25% of the weight of the CGBC. Thermogravimetric analysis showed chitosan decomposes sharply at 225–270°C and then more slowly thereafter. The BET surface areas of GBC and CGBC were 34.1 and 4.61 m2/g, respectively. Batch adsorption studies performed at pH values of 2–5 followed Cu2+ and Cd2+ adsorption quantitatively using atomic absorption spectrophotometry. Sorption was evaluated using the Freundlich, Langmuir, and Sips isotherm models. Cu2+ adsorption on CGBC fit best the Sips model (capacity 111.5 mg/g) and Cd2+ with the Langmuir model (capacity 85.8 mg/g). Langmuir adsorption capacities on GBC were 83.7 and 68.6 mg/g for Cu2+ and Cd2+ respectively. CGBC removed more Cu2+(25.8 mg/g) and Cd2+(17.2 mg/g) than GBC because chitosan modification generates amine coordination sites that enhance metal adsorption. Adsorption on CGBC and GBC of both metal ions followed pseudo-second order kinetics.

Striking CO2 capture and CO2/N2 separation by Mn/Al bimetallic MIL-53

In this study, manganese (Mn) was coordinated on the Al-based MIL-53 to produce a series of MIL-53(Al)-MnN (N = 0, 1, 2, 3). These samples were synthesised by the hydrothermal approach, using varying molar Mn content. The actual Mn content in the activated MIL-53(Al)-Mn samples were found to be very low but exerting significant properties to the resultant bimetallic MOF. All samples possessed similar structure to MIL-53(Al) while the BET surface area was obviously boosted in samples of MIL-53(Al)-Mn1 and 2. The activated MIL-53(Al)-Mn samples were tested for CO2 adsorption at various pressures. The CO2 adsorption capacity at STP was increased with the Mn content. Our results showed that the CO2 adsorption capacities surpassed the MIL-53(Al) sample in previous studies. Besides, the N2 adsorption test was performed and the N2 adsorption capacity was deteriorated in MIL-53(Al)-Mn3 with the highest content of Mn2+. The isotherm adsorption results of pure CO2 and N2 adsorption at 273 K were well correlated with the Sips isotherm model. The selectivity of CO2/N2 was calculated through the ideal adsorption solution theory, which is significantly promoted in MIL-53(Al)-Mn 3 and 2 at 1 atm and 273 K. The higher selectivity was achieved in MIL-53(Al)-Mn 3 and 2. These MOFs could provide promising adsorbents for CO2 storage and CO2/N2 separation.

Evaluation of phosphate adsorption by porous strong base anion exchangers having hydroxyethyl substituents: kinetics, equilibrium, and thermodynamics.

Phosphate anions are recognized as the main responsible for the eutrophication of surface waters. In this work, two strong base anion exchangers having either N,N-dimethyl 2-hydroxyethylammonium (SBAEx.2M) or N,N-diethyl 2-hydroxyethylammonium (SBAEx.2E) functional groups, as highly efficient sorbents in the removal of phosphate anions, are presented. The influence of the main parameters (pH, contact time, initial concentration of phosphate, temperature) on the adsorption performances was investigated in batch mode. Modeling the kinetics data by Lagergren, Ho and McKay, and Elovich kinetic models indicated chemisorption as the main mechanism of sorption. The sorption at equilibrium was modeled with Langmuir, Freundlich, Sips, Dubinin-Radushkevich, and Temkin isotherm models. The experimental isotherms were the best fitted by Langmuir and Sips isotherms, the maximum sorption capacity for phosphate anions being 233.88 mg g-1 SBAEx.2M and 223.5 mg g-1 SBAEx.2E, at pH 3, and 23 °C. Adsorption of phosphate anions in competitive conditions showed that the interference with co-existing anions was low in the case of Cl- ions and much higher with SO42- ions, the ion exchange having an important contribution in the adsorption process. The adsorption was spontaneous and endothermic, the degree of spontaneity increasing with the increase of temperature. The high level of reusability, the adsorption capacity decreasing with only ~ 7% in the case of SBAEx.2E and with ~ 9% in the case of SBAEx.2M, after five sorption/desorption cycles, recommends these SBAEx as promising adsorbents for phosphate removal.

Synthesis of carboxymethyl cellulose-chitosan-montmorillonite nanosheets composite hydrogel for dye effluent remediation

MMTNS were introduced into carboxymethyl cellulose-chitosan system to synthesize porous hydrogel adsorbent with stable structure and high dye handling capacity. Al-OH on edge of MMTNS formed hydrogen-bond (-OH···+NH3-) with -NH2 on CS, CS then cooperated with CMC via amidation and chains interleaving, forming three-dimensional hydrogel. Morphology characterization revealed that hydrogel possessed microporous open-framework structure, facilitating free entrance of macromolecular MB dye to react with internal reaction sites in hydrogel. Factor tests indicated that high removal (97%) of MB was achieved via 0.2 g/L hydrogel within 360 min even after 5 adsorption-regeneration cycles. Adsorption process followed Pseudo-first-order, Pseudo-second-order kinetic model and Sips isotherm model, owing to both monolayer physical and chemical adsorption behavior of MB molecules onto homogeneous surface of hydrogel. Adsorption mechanism was attributed to ion-exchange, groups combination of carboxyl and hydroxyl, and Si active sites reaction. Such hydrogel realized promotion of polysaccharide polymers in materials design and wastewater treatment.

Enhanced Adsorptive Removal of β-Estradiol from Aqueous and Wastewater Samples by Magnetic Nano-Akaganeite: Adsorption Isotherms, Kinetics, and Mechanism

A surfactant-free method was used to synthesize iron oxyhydroxide (akaganeite, β-FeOOH) nanorods and characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM-EDS), and transmission electron microscopy (TEM). The synthesized nanoadsorbent was applied for the adsorptive removal of β-estradiol from aqueous solutions. The parameters affecting the adsorption were optimized using a multivariate approach based on the Box–Behnken design with the desirability function. Under the optimum conditions, the equilibrium data were investigated using two and three parameter isotherms, such as the Langmuir, Freundlich, Dubinin–Radushkevich, Redlich–Peterson, and Sips models. The adsorption data were described as Langmuir and Sips isotherm models and the maximum adsorption capacities in Langmuir and Sips of the β-FeOOH nanorods were 97.0 and 103 mg g−1, respectively. The adjusted non-linear adsorption capacities were 102 and 104 mg g−1 for Langmuir and Sips, respectively. The kinetics data were analyzed by five different kinetic models, such as the pseudo-first order, pseudo-second order, intraparticle, as well as Boyd and Elovich models. The method was applied for the removal β-estradiol in spiked recoveries of wastewater, river, and tap water samples, and the removal efficiency ranged from 93–100%. The adsorbent could be reused up to six times after regeneration with acetonitrile without an obvious loss in the removal efficiency (%RE = 95.4 ± 1.9%). Based on the results obtained, it was concluded that the β-FeOOH nanorods proved to be suitable for the efficient removal of β-estradiol from environmental matrices.