Adsorption Mechanism Of Ions Research Articles

Evaluation of Interaction between Phosphate Ion and Metal Complex-layered Hydroxide

A nickel-aluminium-zirconium complex-layered hydroxide (NAZ), which was synthesized using each inorganic sulfate mixing ratio of 0.9 : 1.0 : 0.1, was prepared and calcined at different temperatures. The physicochemical properties of the NAZ were analyzed by scanning electron microscopy, specific surface area, number of hydroxyl groups, and pore volume. The specific surface area, number of hydroxyl groups, and pore volume of NAZ was 51.9 m2/g, 1.08 mmol/g, and 0.27 μL/g, respectively. The amount of phosphate ion adsorbed onto NAZ was higher than that onto calcined NAZ at different temperatures. Therefore, the interaction between phosphate ions and NAZ was assessed using the elemental distribution analysis and the binding energy. After adsorption, the intensity of phosphorus atoms increased, indicating that the phosphate ions were adsorbed onto the NAZ surface. Additionally, phosphorus peaks (189 eV for 2s and 130 eV for 2p), which were not detected before adsorption, were clearly detected after adsorption. On the other hand, the intensity of the sulfur peak (165 eV for 2p) decreased after adsorption. Thus, we evaluated the ion exchange between phosphate ion and sulfate ion in the interlayer space of the NAZ. As a result, the correlation coefficient between the amount of phosphate ion adsorbed and the amount of sulfate ion released was positively correlated (r=0.960). Therefore, it can be clearly stated that one of the adsorption mechanisms of phosphate ions was related to ion exchange in the interlayer space of the NAZ. These findings are useful for preventing the eutrophication and recovery of phosphate ion in water environments.

Feasibility of brackish water and landfill leachate treatment by GO/MoS2-PVA composite membranes

Two-dimensional (2D) based layered materials with tunable chemical functionalities and surface charge properties have emerged for on-demand applications including membrane technology. However, the process control, time and energy-efficient production of non-swelling graphene oxide (GO) with retaining physicochemical properties are still challenging. In this work, we have fabricated highly ordered GO membrane on cellulose acetate supporting membrane filters of 1.2 μm pore size using molybdenum disulphide (MoS2) as a nano-spacer and polyvinyl alcohol (PVA) as an adhesive for the first time with limited swelling. The fabricated membranes were used for NaCl rejection and removal of toxic heavy metal ions, and the radioactive element from landfill leachate water. The introduction of hydrophilic PVA, thickness control using a various amount of nanospacer and graphene oxide played a vital role in the transport mechanism, permeability, and selectivity index. The composition of PVA and MoS2 in the coating solution was optimized to tune the d-spacing of graphene oxide layers. The newly developed composite membranes have 89% rejection rate to NaCl and 3.96 L/m2h water flux at low operating pressures of 5 bar. Also, the prepared membranes have a high rejection of multivalent metal ions in landfill leachate. 86.5% to 99.8% rejection rate of multivalent metal ions in landfill leachate was observed for the M3 (GO (10): MoS2 (10): PVA (0.5)) membrane. The excellent rejection performance is ascribed to the combined impact of size exclusion, ion adsorption, electrostatic interaction and Gibbs-Donnan exclusion mechanism. The excellent stability and high rejection rate even after 216 h of operation make the fabricated membranes promising for use in practical water separation applications.

Effects of physicochemical properties of biochar derived from spent coffee grounds and commercial activated carbon on adsorption behavior and mechanisms of strontium ions (Sr2+).

This study examined differences in the adsorption isotherms, kinetic equations, and thermodynamics of Sr2+ by biochar from spent coffee grounds (SCG) and powdered activated carbon (PAC). The specific surface area (957.6m2/g) and pore volume (0.676cm3/g) of PAC were much greater than those of SCG biochar (specific surface area = 11.0m2/g, pore volume = 0.009cm3/g). However, SCG biochar showed ahigher maximum adsorption capacity of Sr2+ (Qmax = 51.81mg/g) compared with PAC (Qmax = 32.79mg/g) due to its abundance of O-containing functional groups. The negligible removal efficiencies of Sr2+ by SCG biochar and PAC under acidic conditions (pH = 1.0-3.0) are evidence that the electrostatic repulsion might hinder severely the adsorption of Sr2+ by the carbonaceous adsorbents. The higher R2 values of the pseudo-second-order model (R2 ≥ 0.999) compared with the pseudo-first-order model (R2 ≥ 0.815) suggest that chemisorption governed the removal of Sr2+ using SCG biochar and PAC. Furthermore, the better description of theadsorption behavior of Sr2+ by the Langmuir isotherm model (R2 ≥ 0.994) than the Freundlich isotherm model (R2 ≥ 0.982) supports the assumption that the monolayer adsorption played critical roles in the removal of Sr2+ using SCG biochar and PAC. The thermodynamic studies revealed that adsorption of Sr2+ onto SCG biochar and PAC was endothermic and happened spontaneously. Despite the significant inhibitory effects of DOM, SCG biochar exhibited the higher removal efficiencies of Sr2+ compared with PAC. Hence, SCG biochar could be considered as an alternative to PAC for the removal of Sr2+ from aqueous solutions.

Efficient and Environmentally Friendly Adsorbent Based on β-Ketoenol-Pyrazole-Thiophene for Heavy-Metal Ion Removal from Aquatic Medium: A Combined Experimental and Theoretical Study.

A new sustainable and environmentally friendly adsorbent based on a β-ketoenol-pyrazole-thiophene receptor grafted onto a silica surface was developed and applied to the removal of heavy-metal ions (Pb(II), Cu(II), Zn(II), and Cd(II)) from aquatic medium. The new material SiNPz-Th was well characterized and confirms the success of covalent binding of the receptor on the silica surface. The effect of environmental parameters on adsorption including pH, contact time, temperature, and the initial concentration were investigated. The maximum adsorption capacities of SiNPz-Th for Pb(II), Cu(II), Zn(II), and Cd(II) ions were 102.20, 76.42, 68.95, and 32.68 mg/g, respectively, at 30 min and pH = 6. The adsorption isotherms, kinetics, and thermodynamic process were investigated and showed efficiency and selectivity toward Pb(II) and good regeneration performance. Density functional theory, noncovalent-interaction, and quantum theory of atoms in molecules calculations were used to study and to gain a deeper understanding of both the adsorption mechanism and selectivity of metal ions onto the adsorbent. Accordingly, metal ions such as Pb(II), Cu(II), and Zn(II) were bidentate coordinated with the adsorbent by nitrogen and oxygen atoms of the Schiff base C=N and hydroxyl group −OH, respectively, to form stable complexes. Whereas Cd(II) was coordinated in a monodentate fashion with oxygen atom of the hydroxyl group. Furthermore, the affinity of SiNPz-Th toward the metal ions was decreased in the order of Pb(II) > Cu(II) > Zn(II) > Cd(II), in good agreement with the experimental results. All these results highlight that SiNPz-Th has good potential to be an advanced adsorbent for the removal of lead ions from real water.

Ecofriendly Approach for Treatment of Heavy-Metal-Contaminated Water Using Activated Carbon of Kernel Shell of Oil Palm.

Heavy metal ion contamination in water poses a significant risk to human health as well as to the environment. Millions of tons of agricultural wastes are produced from oil palm plantations which are challenging to manage. In this study, we converted palm kernel shells (PKS) from a palm oil plantation into activated carbon (AC) having a surface area of 1099 m2/g using phosphoric acid as an activator. The prepared material was characterized using BET, XRD, Raman, FESEM and FTIR analyses. The AC was applied for the treatment of heavy-metal-contaminated water, and different parameters; the pH, adsorbent dosage, contact time and metal ion concentrations were varied to determine the optimal conditions for the metal ion adsorption. Different kinetic models; the zeroth, first-order and second-order, and Freundlich and Langmuir isotherm models were used to determine the mechanism of metal ion adsorption by the AC. Under the optimized conditions, Cr6+ and Pb2+ were removed completely, while Zn2+ and Cd2+ were more than 80% removed. This is a greener approach in which an agricultural waste, PKS is converted into a useful product, activated carbon and subsequently applied for the treatment of heavy metal-contaminated water.

Competitive adsorption and correlative mechanism of heavy metal ions using ploy(cellulose/humic acid/acrylic acid) in multi-element aqueous medium

A novel polymer was successfully fabricated which used to remove Pb(II), Cu(II), Cd(II) from multi-element aqueous solutions and their competed-adsorption behavior was investigated. The copolymer was characterized by FTIR spectra, TG/DTG analysis, SEM analysis and XPS analysis. The pseudo-second-order kinetic (R2 > 0.99) and the Langmuir isotherm model have been fit quite well. The FTIR spectra and XPS spectra indicated that Cu(II), Pb(II) and Cd(II) were adsorbed. Maximum uptake capacities of polymer were found to be 978 mg/g, 1136 mg/g, 901 mg/g for Cu(II), Pb(II) and Cd(II), respectively. The hydrogel had the strongest affinity with Pb(II) and Cd(II) ions, but the complex for Pb(II) was instability with the adsorption going on. While adsorption promoted by presence of other ions—synergistic effects that might lead to strongly form complex of the Cd(II) ion and hydrogel, which was not affected by the initial pH in the range of 1.5–6.5. Cu(II) and Pb(II) removal was mainly achieved by ion exchange with functional groups that caused the quantity disparity of the proportion and intensity about the hydrogel surface. The sorption mean free energy ECu(II) = 15.1 kJ/mol, EPb(II) = 16 kJ/mol, ECd(II) = 19.2 kJ/mol were evaluated using Dubinin–Radushkevich isotherm, which suggested that was chemisorption of the adsorption mechanism. This hydrogel had large specific surface area that was as high as 140 m2/g through N2 adsorption–desorption experiment.

Using Zeolite/Polyvinyl alcohol/sodium alginate nanocomposite beads for removal of some heavy metals from wastewater

Functionalized Polyvinyl alcohol/sodium alginate (PVA/SA) beads were synthesized via blending Polyvinyl alcohol (PVA) with sodium alginate (SA) and the glutaraldehyde was used as a cross-linking agent. The zeolite nanoparticles (Zeo NPs) incorporated PVA/SA resulting Zeo/PVA/SA nanocomposite (NC) beads were synthesized for removal of some heavy metal from wastewater. The synthesizes beads were characterized via Fourier transforms infrared spectroscopy (FTIR), X-ray diffraction (XRD), particle size analyzer (PSA), and scanning electron microscope (SEM). The adsorption kinetics of the selected metal ions onto Zeo/PVA/SA NC beads followed the pseudo-first-order model (PFO) and the adsorption isotherm model was well fitted by the Langmuir model. Moreover, the thermodynamic studies were also examined; the outcomes showed that the adsorption mechanisms of the selective metal ions were endothermic, the chemical in nature, spontaneous adsorption on the surface of the Zeo/PVA/SA NC beads. The removal efficiency using Zeo/PVA/SA NC modified beads reached maximum at the pH value of 6.0 for Pb2+, Cd2+, Sr2+, Cu2+, Zn2+, Ni2+, Mn2+ and Li2+ with 99.5, 99.2, 98.8, 97.2, 95.6, 93.1, 92.4 and 74.5%, respectively, while the highest removal are achieved at pH = 5 for Fe3+ and Al3+ with 96.5 and 94.9%, respectively and decreased at lower or higher pH values. The survival count (%) of the E. coli cells were 34% on the SA beads, 11% on the PVA/SA, and 1% on the Zeo/PVA/SA NC modified beads, after 120 min exposure at 25 °C. Reusability experimental displays that the synthesized beads preserved a significant decrease in the sorption capacity after 10 repeating cycles. The Zeo/PVA/SA NC beads were able to eliminate 60–99.8% of Al3+, Fe3+, Cr3+, Co2+, Cd2+, Zn2+, Mn2+, Ni2+, Cu2+, Li2+, Sr2+, Si2+, V2+, and Pb2+ ions from the natural wastewater samples collected from 10th Ramadan City, Cairo, Egypt.

Observation of Ion Electrosorption in Metal–Organic Framework Micropores with In Operando Small‐Angle Neutron Scattering

AbstractA molecular‐level understanding of transport and adsorption mechanisms of electrolyte ions in nanoporous electrodes under applied potentials is essential to control the performance of double‐layer capacitors. Here, in operando small‐angle neutron scattering (SANS) is used to directly detect ion movements into the nanopores of a conductive metal–organic framework (MOF) electrode under operating conditions. Neutron‐scattering data reveals that most of the void space within the MOF is accessible to the solvent. Upon the addition of the electrolyte sodium triflate (NaOTf), the ions are adsorbed on the outer surface of the protrusions to form a 30 Å layer instead of entering the ionophobic pores in the absence of an applied charging potential. The changes in scattering intensity when potentials are applied suggests the ion rearrangement in the micropores following different mechanisms depending on the electrode polarization. These observations shed insights on ion electrosorption in electrode materials.

Observation of Ion Electrosorption in Metal-Organic Framework Micropores with In Operando Small-Angle Neutron Scattering.

A molecular-level understanding of transport and adsorption mechanisms of electrolyte ions in nanoporous electrodes under applied potentials is essential to control the performance of double-layer capacitors. Here, in operando small-angle neutron scattering (SANS) is used to directly detect ion movements into the nanopores of a conductive metal-organic framework (MOF) electrode under operating conditions. Neutron-scattering data reveals that most of the void space within the MOF is accessible to the solvent. Upon the addition of the electrolyte sodium triflate (NaOTf), the ions are adsorbed on the outer surface of the protrusions to form a 30 Å layer instead of entering the ionophobic pores in the absence of an applied charging potential. The changes in scattering intensity when potentials are applied suggests the ion rearrangement in the micropores following different mechanisms depending on the electrode polarization. These observations shed insights on ion electrosorption in electrode materials.

Specificity and affinity of multivalent ions adsorption to kaolinite surface

Understanding the specific adsorption mechanism(s) of multivalent ions onto clay mineral surfaces in a high salinity environment is theoretically and practically important in many areas including mineral separation and tailings disposals. This paper focuses on both qualitative and quantitative studies to describe the effect of multivalent-ion specificity on the kaolinite surface. The measured zeta potential of kaolinite particles treated with di- and trivalent chloride salts (up to 100 mM) was used to quantify the surface binding constant of metal ions to the kaolinite surface by the surface complexation model. The model results show that ion-pairing and hydration energy are two main factors that control the adsorption of di- and trivalent ions onto the kaolinite surface. The established affinity series of adsorption to kaolinite surface, Al3+ > Fe2+ > Fe3+ > Mg2+ > Ca2+, matches the hydration energy and calculated ion-pairing concentration. Further XPS analysis and molecular dynamics simulation revealed that Al3+ and Fe2+ could directly form inner-sphere complexes due to their high electronegativity and weak pairing ability with Cl− ion, while Mg2+ and Ca2+ ions adsorb onto the outer-sphere of kaolinite surface because of their strong pairing ability with Cl− ion and low electronegativity. However, higher electronegativity with large negative hydration energy leads to weaker affinity to kaolinite surface, as in the case of Fe3+. A linear relationship between surface binding constant and first hydrolysis constant of metal and kaolinite surface was also established. The outcomes of this work shed a new insight into the multivalent ion adsorption to kaolinite in controlling the selectivity and efficiency of mineral separation and dewatering processes.

Construction of physically crosslinked chitosan/sodium alginate/calcium ion double-network hydrogel and its application to heavy metal ions removal

Abstract Chemical hydrogels have been extensively applied to the removal of heavy metal pollutants. However, most of chemical hydrogels inevitably contain toxic chemical crosslinker residues, which impose serious threats on the environment. Herein, a novel eco-friendly physically-crosslinked double-network hydrogel of chitosan/sodium alginate/calcium ion (CTS/SA/Ca2+ PCDNH) was prepared by the combination of the semi-dissolution acidification sol–gel transition method with the internal gelation method. The PCDNH is formed via the physical crosslinking of sustainable biopolymers, which avoids the excessive use of toxic chemical reagents. In addition, the PCDNH exhibits significantly better mechanical properties than the single-network physical hydrogel crosslinked via electrostatic interactions, which overcomes the weak mechanical properties of physical hydrogels. The formation mechanism and structure of the hydrogel were determined by Fourier-transform infrared spectroscopy (FTIR), 13C solid state nuclear magnetic resonance spectroscopy (13C-SSNMR) and scanning electron microscopy (SEM). The heavy metal ions adsorption mechanism was explored by X-ray photoelectron spectroscopy (XPS) analysis. The adsorption kinetics, isotherms and thermodynamics were further studied to understand the adsorption mechanism. Our work has provided a new method for the fabrication of natural polymers-based eco-friendly, low-cost and robust physical hydrogels for the heavy metal ions removal.

Investigation on the Adsorption-Interaction Mechanism of Pb(II) at Surface of Silk Fibroin Protein-Derived Hybrid Nanoflower Adsorbent.

For further the understanding of the adsorption mechanism of heavy metal ions on the surface of protein-inorganic hybrid nanoflowers, a novel protein-derived hybrid nanoflower was prepared to investigate the adsorption behavior and reveal the function of organic and inorganic parts on the surface of nanoflowers in the adsorption process in this study. Silk fibroin (SF)-derived and copper-based protein-inorganic hybrid nanoflowers of SF@Cu-NFs were prepared through self-assembly. The product was characterized and applied to adsorption of heavy metal ion of Pb(II). With Chinese peony flower-like morphology, the prepared SF@Cu-NFs showed ordered three-dimensional structure and exhibited excellent efficiency for Pb(II) removal. On one hand, the adsorption performance of SF@Cu-HNFs for Pb(II) removal was evaluated through systematical thermodynamic and adsorption kinetics investigation. The good fittings of Langmuir and pseudo-second-order models indicated the monolayer adsorption and high capacity of about 2000 mg g−1 of Pb(II) on SF@Cu-NFs. Meanwhile, the negative values of and proved the spontaneous and exothermic process of Pb(II) adsorption. On the other hand, the adsorption mechanism of SF@Cu-HNFs for Pb(II) removal was revealed with respect to its individual organic and inorganic component. Organic SF protein was designated as responsible ‘stamen’ adsorption site for fast adsorption of Pb(II), which was originated from multiple coordinative interaction by numerous amide groups; inorganic Cu3(PO4)2 crystal was designated as responsible ‘petal’ adsorption site for slow adsorption of Pb(II), which was restricted from weak coordinative interaction by strong ion bond of Cu(II). With only about 10% weight content, SF protein was proven to play a key factor for SF@Cu-HNFs formation and have a significant effect on Pb(II) treatment. By fabricating SF@Cu-HNFs hybrid nanoflowers derived from SF protein, this work not only successfully provides insights on its adsorption performance and interaction mechanism for Pb(II) removal, but also provides a new idea for the preparation of adsorption materials for heavy metal ions in environmental sewage in the future.

Characterization and Phosphate Adsorption Capability of Novel Nickel-Aluminum-Zirconium Complex Hydroxide.

In this study, the adsorption capability of phosphate ion using a novel tri-metals complex hydroxide was evaluated for preventing the eutrophication in water environment. A nickel-aluminum-zirconium complex hydroxide (NAZ) was synthesized using each inorganic sulfate mixing ratio of 0.9 : 1.0 : 0.1 and was calcined at different temperatures. The characteristics of the NAZ were analyzed by scanning electron microscopy images, X-ray diffraction analysis, elemental distribution, and binding energy. Moreover, the amount adsorbed of phosphate ion onto uncalcined and calcined NAZ was measured. That of phosphate ions onto the uncalcined was the largest of all. These results suggested that the adsorption of phosphate ions tends to depend on the physicochemical properties (e.g., amount of hydroxyl groups, pore volumes, and pH) of the adsorbents. Moreover, the adsorption mechanism of phosphate ions was evaluated on the basis of binding energy and elemental analysis. After adsorption, the binding energy of phosphorus P (2s and 2p) peaked and the sulfur peak intensity S(2s) reduced. This result indicated that the adsorption mechanism of phosphate would be exchanged with sulfate ions.

Low Li ion diffusion barrier on low-crystalline FeOOH nanosheets and high performance of energy storage

To obtain symmetric supercapacitors (SCs) with high energy density, it is critical to fabricate an electrode with wide potential window and excellent capacitive performance. Herein, by using the strong double hydrolysis reaction between anions and cations, the FeOOH nanosheets on the surface of activated carbon cloth (FeOOH@AC) are prepared through a simple hydrothermal process. The FeOOH@AC electrode exhibits maximum capacitance of 4,090 mF·cm−2 at wider potential window -1–0 V and 3,250 mF·cm−2 at 0–1 V versus SCE in 2 M LiNO3 electrolyte. With two pieces of FeOOH@AC electrodes the obtained symmetric SC can operate at the voltage window of 2 V. This FeOOH symmetric SC shows high energy density of 13.261 mWh·cm−3 at a power density of 14.824 mW·cm−3 and maintains 4.175 mWh·cm−3 at a maximum power density of 118.564 mW·cm−3, as well as excellent charge storage capacity and cyclic stability. Li ion adsorption and diffusion mechanism on the (200) facets of FeOOH are explained by the density functional theory (DFT) calculations. The simple synthesis process and excellent capacitance performance of the FeOOH@AC composite make it a very promising candidate for high performance symmetric SC electrodes.

Synthesis of ZIF-8/Fly Ash Composite for Adsorption of Cu2+, Zn2+ and Ni2+ from Aqueous Solutions.

In this study, fly ash (FA) coated with ZIF-8 (ZIF-8/FA) nanocomposite was first synthesized by taking 2-methylimidazole and zinc nitrate hexahydrate as reactants and then used as an adsorbent for adsorption of copper, zinc, and nickel ions from aqueous solution. The characteristic of FA and ZIF-8/FA samples were analyzed based on the data from scanning electronic microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, grain size analyzer and N2 adsorption-desorption isotherm. The results showed that ZIF-8 deposited on the FA evenly. The average crystallite size of ZIF-8 on the surface of FA is 15.85 nm. The specific surface area of FA was increased from 1.8 to 249.5 m2/g. The adsorption efficiency of the ZIF-8/FA nanocomposite for the removal of heavy metal ions from aqueous solution was optimized in terms of different parameters such as pH, adsorbent dosage, and contact time. It was shown that the saturated adsorption amounts of the obtained composite for adsorption of Cu2+, Zn2+, and Ni2+ are 335, 197, and 93 mg·g−1. ZIF-8/FA had better stability and more mesoporous volume than that of ZIF-8 and exhibited higher rate for adsorption of heavy metal ions from aqueous solution than FA and ZIF-8, suggesting an adsorption synergy between ZIF-8 and FA. The adsorption mechanism of heavy metal ions by ZIF-8/FA includes surface adsorption, pore adsorption, and ion exchange. The obtained ZIF-8/FA nanocomposite can solve the encountered problems of FA for low adsorption and the difficult recycling of ZIF-8 for their small size, high cost, and poor stability.

Preparation and Characterization of Raw and Inorganic Acid-Activated Pine Cone Biochar and Its Application in the Removal of Aqueous-Phase Pb2+ Metal Ions by Adsorption

In this work, the synthesized slow pyrolysis biomass pine cone (Pinus radiata)–based biochar was acid activated, characterized, and tested for its effectiveness in the adsorptive removal of aqueous-phase Pb2+ metal ions. The adsorbent surface modification was conducted by treatment with H2SO4 and H3PO4 and was characterized by BET surface area, pore volume, pore size, C-H-N-S analysis, the presence of various functional groups through FT-IR (Fourier Transform- Infrared), the crystallinity of the material and presence of minerals by XRD (X-ray diffraction spectrum), and surface morphology by FESEM. The specific surface area after acid modification has been increased from 145 to 472 m2/g. Also, acid treatment causes an increase of the COO− functional group on the adsorbent surface which are responsible for adsorption. All three types of biochar, namely BC (raw biochar without modification), AC1 (modified by H3PO4), and AC2 (modified with H2SO4) were used for the removal of aqueous-phase Pb2+ by batch adsorption and compared. Various physicochemical process parameters such as initial solution pH, initial metal ion dose or adsorbate concentration, adsorbent dose, and system temperature and their effect on metal ion adsorption mechanism have been identified and optimized here. Maximum Pb 2+ adsorption capacities were obtained as 251, 283 mg/g and 321 mg/g for BC, AC1, and AC2 respectively which are very much comparative with other reported adsorbents including commercial activated carbon under similar experimental conditions. This study indicated that pine cone biochar was an environment-friendly and cost-effective adsorbent in sustainable solution for water and wastewater treatment.

Role of ion exchange membranes and capacitive electrodes in membrane capacitive deionization (MCDI) for CO2 capture

Recently we showed that membrane capacitive deionization (MCDI) can be used to capture CO2, but we found that the performance decreases with decreasing current density. In the present study, we investigate the effect of electrodes and ion exchange membranes by performing experiments with two membranes (CO2-MCDI), with one membrane (cation or anion exchange membrane), and without membranes (CO2-CDI). We find that the anion exchange membrane is essential to keep high CO2 absorption efficiencies (Λa=nCO2(g)/ncharge), while the absorption efficiency of the CO2-CDI cell was lower than expected (Λa≈0.5 for CO2-MCDI against Λa≈0.18 for CO2-CDI). Moreover, we theoretically investigate ion adsorption mechanisms in the electrodes by comparing experimental data of a CO2-CDI cell with theoretical results of the classic amphoteric-Donnan model developed for conventional CDI. By comparing the experimental results with the amph-D model, we find that the model overestimates the absorption efficiency in CO2-CDI experiments. To understand this discrepancy, we investigate the effects of other phenomena, i.e., (i) low ion concentration, (ii) passive CO2 absorption, and (iii) the effect of acid-base reactions on the chemical surface charge.

Phosphoric acid functionalized magnetic sorbents for selective enrichment of TiO2 nanoparticles in surface water followed by inductively coupled plasma mass spectrometry detection

Phosphoric acid functionalized superparamagnetic iron oxide was synthesized, and different adsorption behavior of TiO2 NPs and titanium ions on it was found. By means of dispersion-corrected density functional theory (DFT-D), the adsorption mechanism of TiO2 NPs and titanium ions on the functionalized sorbents was explored, and the difference in the adsorption behavior was attributed to the different deprotonated forms of phosphates and the competitive adsorption of OH– anion with respect to either TiO2 NPs or aqueous titanium ions. Based on the different adsorption performance of phosphoric acid functionalized sorbents for TiO2 NPs and titanium ions under pH 3, a method by combining magnetic solid phase extraction (MSPE) with inductively coupled plasma mass spectrometry (ICP-MS) was established for the selective quantification of trace TiO2 NPs in environmental water. Under the optimal experimental conditions, the detection limit of TiO2 NPs was 17 ng/L with an enrichment factor of 400. The developed MSPE-ICPMS method was applied to the detection of trace TiO2 NPs in the Yangtze River and the East Lake water. Sub μg/L level of TiO2 NPs was found in the tested water samples, and recoveries of 91–110% and 90–110% were obtained for TiO2 NPs at three concentration levels in spiked water samples, respectively. The developed method exhibited high adsorption capacity and low detection limit for target TiO2 NPs, and was demonstrated with great potential for monitoring TiO2 NPs in the environment.

Adsorption mechanism of copper ions in aqueous solution by chitosan–carboxymethyl starch composites

ABSTRACTBased on the structural characteristics of chitosan (CTS) and carboxymethyl starch (CMS)， CTS–CMS composites were prepared by crosslinking. The composites had a plurality of reactive functional groups such as NH2, NH3+, COOH, and OH and are applied to the adsorption of Cu2+ in aqueous solution. The adsorption capacity and stability in acidic solution of the composites were preferable to that of raw material. The effects of temperature, contact time, initial concentration, and pH on the adsorption of Cu2+ were investigated. Infrared spectroscopy, scanning electron microscope–energy dispersive spectrometer, X‐ray diffraction, and X‐ray photoelectron spectroscopy were used to explore the adsorption mechanism. The experiment showed that chemisorption and physisorption coexisted in the adsorption process. It is promising to apply this adsorbent to remove the metal ions in wastewater. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48636.

Application of Density Functional Theory computation (DFT) and Process Capability Study for performance evaluation of Orthophosphate removal process using Polyaniline@Hematite-titaniferous sand composite (PANI@HTS) as a substrate

A new approach is adopted in this study to eliminate orthophosphates in the aqueous medium. It is about synthesizing a composite from a conductive polymer (Polyaniline) and a sandy material (Hematite-titaniferous sand). The synthesized composite (PANI@HTS) and its components were characterized with (XRD) X-ray diffraction, (XRF) X-ray fluorescence, (SEM) scanning electron microscopy coupled with (EDS) energy dispersive X-ray spectroscopy, (FTIR) Fourier-transform infrared spectroscopy and laser diffraction particle size analysis. The phenomenon of adsorption of orthophosphates on PANI@HTS has found to be dependent on several factors, such as adsorbent dose, pH, contact time and pollutant concentration. From the study of adsorption kinetics and the effect of pollutant concentration, the Langmuir model and the pseudo second order model were the most suited for explaining adsorption phenomena with a highest correlation (R2 > 0.98). The adsorbed amount that was found in this study reaches 16.15 mg/g. The adsorption mechanism of orthophosphate ions onto PANI@HTS composite was computationally investigated using Density Functional Theory (DFT). The adsorbate-adsorbent interfacial interactions are assumed to be physisorption in nature due to the low values of binding energy and electronic charge transfer. This DFT simulation result is in good adequacy with the experiment. The capability study of the present process has shown that our method is capable, satisfactory and can be applied on a large scale.