Adsorption behaviors of Hg(II) on chitosan functionalized by amino-terminated hyperbranched polyamidoamine polymers

Flexible fabrication chitosan-polyamidoamine aerogels by one-step method for efficient adsorption and separation of anionic dyes

Chitosan in situ grown polyamidoamine (CTS-Gx PAMAM (x = 0, 1, 2, 3)) aerogels were fabricated by a facile one-step freeze-drying method, with glutaraldehyde serving as a crosslinker. The three-dimensional skeletal structure of aerogel provided numerous adsorption sites and accelerated the effective mass transfer of pollutants. The adsorption kinetics and isotherm studies of the two anionic dyes were consistent with the pseudo-second-order and Langmuir models, indicating that the removal of rose bengal (RB) and sunset yellow (SY) was a monolayer chemisorption process. The maximum adsorption capacity of RB and SY reached 370.28 mg/g and 343.31 mg/g, respectively. After five adsorption-desorption cycles, the adsorption capacities of the two anionic dyes reached 81.10% and 84.06% of the initial adsorption capacities, respectively. The major mechanism between the aerogels and dyes was systematically investigated based on using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and energy-dispersive spectroscopy analyses, confirming that electrostatic interaction, hydrogen bonding and van der Waals interactions were the main driving forces for the superior adsorption performance. Furthermore, the CTS-G2 PAMAM aerogel exhibited good filtration and separation performance. Overall, the novel aerogel adsorbent possesses excellent theoretical guidance and practical application potential for the purification of anionic dyes.

Efficient Removal of Uranyl Ions Using PAMAM Dendrimer: Simulation and Experiment

In this work, using atomistic molecular dynamics (MD) simulations and polymer-assisted ultrafiltration experiments, we explore the adsorption and removal of uranyl ions from aqueous solutions using poly(amidoamine) (PAMAM) dendrimers. The effects of uranyl ion concentration and the pH of the solution were examined for PAMAM dendrimers of generations 3, 4, and 5. Our simulation results show that PAMAM has a high adsorption capacity for the uranyl ions. The adsorption capacity increases with increasing concentration of uranyl ions for all 3 generations of PAMAM in agreement with experimental findings. We find that the number of uranyl ions bound to PAMAM is significantly higher in acidic solutions (pH < 3) as compared to neutral solutions (pH ∼ 7) for all uranyl ion concentrations. Additionally, we find an increase in the number of adsorbed uranyl ions to PAMAM with the increase in the dendrimer generation. This increase is due to the greater number of binding sites present for higher-generation PAMAM dendrimers. Our simulation study shows that nitrate ions form a solvation shell around uranyl ions, which allows them to bind to PAMAM binding sites, including the amide, amine, and carbonyl groups. In polymer-assisted ultrafiltration (PAUF) experiments, the removal percentage of uranyl ions by G3 PAMAM dendrimer increased from 36.3% to 42.6% as the metal ion concentration increased from 2.1 × 10^-5 M to 10.5 × 10^-5 M at a pH of 2. Our combined experiment and simulation study suggests that PAMAM is an effective adsorbent for removing uranyl ions from aqueous solutions.

Calix[4]arene-Decorated Covalent Organic Framework Conjugates for Lithium Isotope Separation

Lithium isotope separation has attracted extensive interest due to its important role in fusion and fission reactions. Up to now, it is still a great challenge to separate lithium isotopes (⁶Li and ⁷Li) in an efficient manner due to the low capture ability for lithium ions of related materials and highly similar physicochemical properties between lithium isotopes. In this work, three calix[4]arene-decorated crystalline covalent organic frameworks (COFs) with wave-like extension and AA-stacking configuration were designed and utilized for lithium adsorption and its isotope separation. Experimental studies show that these COFs exhibit an outstanding lithium adsorption capacity up to 94.66 mg·g^-1, which is about 2 times beyond that of adsorbents reported in the literature. The high adsorption capacity of COFs could be attributed to the abundant adsorption sites from calix[4]arene unit. More importantly, this study demonstrates for the first time that calixarene groups can separate lithium isotopes with an excellent separation factor up to 1.053 ± 0.002, comparable to the most successful solid-phase lithium separation adsorbent. The calculation based on density functional theory showed that calixarene played an important role in the lithium adsorption. Interestingly, the lithium isotope separation performance is mainly affected by the amine bridging units. This work demonstrated that calixarene COFs are promising adsorbents for lithium isotope separation.

Mechanistic study of Hg(II) interaction with three different α-aminophosphonate adsorbents: Insights from batch experiments and theoretical calculations

Herein, efficient and potential chelating α-aminophosphonate based sorbents (AP-) derived from three different amine origins (aniline/anthranilic acid/O-phenylenediamine) to form AP-H, carboxylated and aminated enhanced aminophosphonate as AP-H, AP-COOH, and AP-NH₂ were synthesized via a facile method. The structure of the synthesized sorbents was elucidated using different techniques; elemental analysis (CHNP/O), FT-IR, NMR (¹H-, ¹³C and ³¹P NMR), TGA and BET. The fabricated sorbents were exploited for Hg(II) removal from aqueous solution via sorption properties. Isotherm fitted by Langmuir equation: the maximum sorption capacities at optimum pH 5.5, and T:25 ± 1 °C, were found to be 1.33, 1.23, and 1.15 mmol Hg g^-1 for AP-COOH, AP-NH₂, AP-H, respectively, which is roughly correlated with the active sites density and the hard/soft characteristics of adsorbents' reactive groups. Metal-ligand binding affinities are qualitatively rationalized in terms of hard and soft acids and bases (HSAB) theory. The interaction of Hg(II) (soft) has a stronger affinity to AP-COOH can be considered a softer base compared with reference material (AP-H) over than AP-NH₂ (hard). This sequence result showed opposite trends consistent with their reciprocal properties according to the steric effect modulates and the specific surface area. Thermodynamics analysis for absolute values of ΔH°, ΔS° and ΔG° afford the selectivity towards Hg(II) sorption with the following order: AP-COOH > AP-NH₂ >AP-H. Elution and regeneration was carried out by HCl solution and recycled for a minimum of five cycles, the sorption and desorption efficiencies are greater than 91%. Such sorbents exhibit good durability, stability and promising potential for Hg(II) removal. Finally, a new modelling technique for quantitative non-linear description and comparison of equivalent geographical positions in 3D space of extended relationships. Exothermic and spontaneous behavior were observed using a proposed Floatotherm that included the Van't Hoff parameters model.

The Adsorption of Heavy Metal Ions by Poly (Amidoamine) Dendrimer-Functionalized Nanomaterials: A Review

Rapid industrialization has resulted in serious heavy metal pollution. The removal of heavy metal ions from solutions is very important for environmental safety and human health. Poly (amidoamine) (PAMAM) dendrimers are artificial macromolecular materials with unique physical and chemical properties. Abundant amide bonds and amino functional groups provide them with a high affinity for heavy metal ions. Herein, PAMAM-functionalized adsorbents are reviewed in terms of different nanomaterial substrates. Approaches in which PAMAM is grafted onto the surfaces of substrates are described in detail. The adsorption isotherms and kinetics of these adsorbents are also discussed. The effects of PAMAM generation, pH, adsorbent dosage, adsorption time, thermodynamics, and ionic strength on adsorption performance are summarized. Adsorption mechanisms and the further functionalization of PAMAM-grafted adsorbents are reviewed. In addition to the positive results, existing problems are also put forward in order to provide a reference for the optimization of PAMAM-grafted adsorbents of heavy metal ions.

A Review: Adsorption and Removal of Heavy Metals Based on Polyamide-amines Composites

In recent years, the problem of heavy metal pollution has become increasingly prominent, so it is urgent to develop new heavy metal adsorption materials. Compared with many adsorbents, the polyamide-amine dendrimers (PAMAMs) have attracted extensive attention of researchers due to its advantages of macro-molecular cavity, abundant surface functional groups, non-toxicity, high efficiency and easy modification. But in fact, it is not very suitable as an adsorbent because of its solubility and difficulty in separation, which also limits its application in environmental remediation. Therefore, in order to make up for the shortcomings of this material to a certain extent, the synthesis and development of polymer composite materials based on PAMAMs are increasingly prominent in the direction of solving heavy metal pollution. In this paper, the application of composites based on PAMAMs and inorganic or organic components in the adsorption of heavy metal ions is reviewed. Finally, the prospects and challenges of PAMAMs composites for removal of heavy metal ions in water environment are discussed.

Chitosan crosslinked with polyamine-co-melamine for adsorption of Hg2+: Application in purification of polluted water

A batch experiment was carried out in order to remove Hg²⁺ from the aqueous solution as well as the polluted water using modified chitosan (CS) with polyamine compounds (triethylenetetramine (TETA), tetraethylenepentamine (TEPA)), and melamine. The obtained polyamine-co-melamine crosslinked CS derivatives (MCS-4N and MCS-5N) were characterized and used as adsorbents. In comparison to the raw CS, the modification significantly promoted the adsorption of Hg²⁺ ions. The results of the pseudo-second-order kinetic model revealed that pH-dependent derivatives adsorbents achieved the equilibrium state within 12 h. The Langmuir model was best fitted with the Hg²⁺ adsorption isotherm and showed the highest adsorption capacities of 140.3 and 109.7 mg/g for MCS-4N and MCS-5N, respectively. A slight decrease in the adsorption efficiency of Hg²⁺ was noticed with the increment of the ionic strength of the solution. However, the studied adsorbents were easily regenerated and presented adequate reusability. The Hg²⁺ adsorption was regulated by the combined process of coordination reaction and electrostatic attraction as well. The as-prepared polyamine-co-melamine crosslinked CS derivatives were found potential adsorbents for the adsorptive capture of Hg²⁺ ions from aqueous solutions and polluted waters.

Effective adsorption of mercury by Zr(IV)-based metal-organic frameworks of UiO-66-NH2 from aqueous solution

In this study, Zr-based metal-organic frameworks (MOFs) of UiO-66 and UiO-66-NH₂ were synthesized and applied to removal of mercury from aqueous solution. The characterizations of UiO-66 and UiO-66-NH₂ were examined by X-ray diffraction (XRD), scanning electron microscope (SEM), and thermogravimetric analysis (TGA). To investigate the adsorption properties of UiO-66-NH₂ for mercury, the experiments of kinetics, isotherm, pH, temperature, and salt concentration were conducted, and the results were compared with those by UiO-66. The result showed that UiO-66-NH₂ has a higher adsorption capacity for mercury than UiO-66. The maximum adsorption capacity of UiO-66-NH₂ was 223.8 ± 17.8 mg g^-1 at 313 K. The salt concentration of NaCl has a significant effect on the adsorption of mercury on UiO-66, while UiO-66-NH₂ can maintain the stable adsorption capacity for mercury in the concentration range of 0.1-0.5 M NaCl. Adsorption thermodynamics result indicated that the adsorption process of mercury on UiO-66-NH₂ was spontaneous and endothermic. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses showed that the mercury was successfully adsorbed on the surface of UiO-66-NH₂ and amino functional group as a soft base played a major role to react with mercury during the adsorption process. Graphical abstract.

Shell biomass material supported nano-zero valent iron to remove Pb2+ and Cd2+ in water

Nanoscale zero-valent iron (NZVI) has a high adsorption capacity for heavy metals, but easily forms aggregates. Herein, preprocessed undulating venus shell (UVS) is used as support material to prevent NZVI from reuniting. The SEM and TEM results show that UVS had a porous layered structure and NZVI particles were evenly distributed on the UVS surface. A large number of adsorption sites on the surface of UVS-NZVI are confirmed by IR and XRD. UVS-NZVI is used for adsorption of Pb2+ and Cd2+ at pH = 6.00 in aqueous solution, and the experimental adsorption capacities are 29.91 and 38.99 mg g-1 at optimal pH, respectively. Thermodynamic studies indicate that the adsorption of ions by UVS-NZVI is more in line with the Langmuir model when Pb2+ or Cd2+ existed alone. For the mixed solution of Pb2+ and Cd2+, only the adsorption of Pb2+ by UVS-NZVI conforms to the Langmuir model. In addition, the maximum adsorption capacities of UVS-NZVI for Pb2+ and Cd2+ are 93.01 and 46.07 mg g-1, respectively. Kinetic studies demonstrate that the determination coefficients (R 2) of the pseudo first-order kinetic model for UVS-NZVI adsorption of Cd2+ and Pb2+ are higher than those of the pseudo second-order kinetic model and Elovich kinetic model. Highly efficient performance for metal removal makes UVS-NZVI show potential application to heavy metal ion adsorption.

Low-Fe(III) driven UV/Air process for enhanced recovery of heavy metals from EDTA complexed system

The efficient recovery of heavy metals from complexed wastewater is an essential but challenging task. In this study, a novel low-Fe(III) driven UV/Air process (LFUA) was developed to break the strong complexation between ethylenediamine tetracetic acid (EDTA) and heavy metal ions (HMIs) and enable the enhanced recovery of HMIs via chelating resin adsorption (CRA). The inside mechanism of the LFUA process includes: 1) displacement of HMIs from HMI-EDTA complexes by Fe(III); 2) direct photolysis of Fe(III)-EDTA through a ligand-to-metal charge transition reaction (LMCT) and indirect photolysis of EDTA by HO₂·/O₂·^-. The iron dosage was orders of magnitude lower than that previously reported, due to the Fe(II)/Fe(III) redox cycle in the LFUA process. Fe(II) formed during the LMCT reaction of Fe(III)-EDTA was oxidized back to Fe(III) by O₂ and HO₂·, and the reformed Fe(III) was then recombined with EDTA to sustains the LMCT reaction. EDTA was completely removed in 20 min at a molar ratio of Fe(III)/EDTA = 0.05. In addition, following the LFUA process, the adsorption amounts of various HMIs onto D463 resin were at least two orders of magnitude higher than those reported using the direct adsorption process. Employing the integrated technique of LFUA + CRA enabled the efficient removal of up to 64.5 mg/L of Cu(II) from inlet wastewater, and residual Cu(II) was below 0.5 mg/L. The results of desorption experiments showed that over 90% of Cu(II) was recovered, and the desorption solution had a Cu concentration of 2.1 g/L and purity of 99%. Furthermore, the economic and practical feasibility of using the combined process of LFUA + CRA was analyzed to substantiate that the technique is highly efficient and clean (produces no harmful sludge). Therefore, it is an appropriate and practical process in removing HMIs-EDTA complexes and recovering HMIs from wastewater.

Advancements and Frontiers in the High Performance of Natural Hydrogels for Cartilage Tissue Engineering

Cartilage injury originating from trauma or osteoarthritis is a common joint disease that can bring about an increasing social and economic burden in modern society. On account of its avascular, neural, and lymphatic characteristics, the poor migration ability of chondrocytes, and a low number of progenitor cells, the self-healing ability of cartilage defects has been significantly limited. Natural hydrogels, occurring abundantly with characteristics such as high water absorption, biodegradation, adjustable porosity, and biocompatibility like that of the natural extracellular matrix (ECM), have been developed into one of the most suitable scaffold biomaterials for the regeneration of cartilage in material science and tissue engineering. Notably, natural hydrogels derived from sources such as animal or human cadaver tissues possess the bionic mechanical behaviors of physiological cartilage that are required for usage as articular cartilage substitutes, by which the enhanced chondrogenic phenotype ability may be achieved by facilely embedding living cells, controlling degradation profiles, and releasing stimulatory growth factors. Hence, we summarize an overview of strategies and developments of the various kinds and functions of natural hydrogels for cartilage tissue engineering in this review. The main concepts and recent essential research found that great challenges like vascularity, clinically relevant size, and mechanical performances were still difficult to overcome because the current limitations of technologies need to be severely addressed in practical settings, particularly in unpredictable preclinical trials and during future forays into cartilage regeneration using natural hydrogel scaffolds with high mechanical properties. Therefore, the grand aim of this current review is to underpin the importance of preparation, modification, and application for the high performance of natural hydrogels for cartilage tissue engineering, which has been achieved by presenting a promising avenue in various fields and postulating real-world respective potentials.

Novel Functionalized Cellulose Microspheres for Efficient Separation of Lithium Ion and Its Isotopes: Synthesis and Adsorption Performance

The adsorption of lithium ions(Li+) and the separation of lithium isotopes have attracted interests due to their important role in energy storage and nuclear energy, respectively. However, it is still challenging to separate the Li+ and its isotopes with high efficiency and selectivity. A novel cellulose-based microsphere containing crown ethers groups (named as MCM-g-AB15C5) was successfully synthesized by pre-irradiation-induced emulsion grafting of glycidyl methacrylate (GMA) and followed by the chemical reaction between the epoxy group of grafted polymer and 4'-aminobenzo-15-crown-5 (AB15C5). By using MCM-g-AB15C5 as adsorbent, the effects of solvent, metal ions, and adsorption temperature on the adsorption uptake of Li+ and separation factor of 6Li/7Li were investigated in detail. Solvent with low polarity, high adsorption temperature in acetonitrile could improve the uptake of Li+ and separation factor of lithium isotopes. The MCM-g-AB15C5 exhibited the strongest adsorption affinity to Li+ with a separation factor of 1.022 ± 0.002 for 6Li/7Li in acetonitrile. The adsorption isotherms in acetonitrile is fitted well with the Langmuir model with an ultrahigh adsorption capacity up to 12.9 mg·g-1, indicating the unexpected complexation ratio of 1:2 between MCM-g-AB15C5 and Li+. The thermodynamics study confirmed the adsorption process is the endothermic, spontaneous, and chemisorption adsorption. As-prepared novel cellulose-based adsorbents are promising materials for the efficient and selective separation of Li+ and its isotopes.

Kinetics and Thermodynamics of Uranium (VI) Adsorption onto Humic Acid Derived from Leonardite

Humic acid (HA) is well known as an inexpensive and effective adsorbent for heavy metal ions. However, the thermodynamics of uranium (U) adsorption onto HA is not fully understood. This study aimed to understand the kinetics and isotherms of U(VI) adsorption onto HA under different temperatures from acidic water. A leonardite-derived HA was characterized for its ash content, elemental compositions, and acidic functional groups, and used for the removal of U (VI) from acidic aqueous solutions via batch experiments at initial concentrations of 0-100 mg·L^-1 at 298, 308 and 318 K. ICP-MS was used to determine the U(VI) concentrations in solutions before and after reacting with the HA. The rate and capacity of HA adsorbing U(VI) increased with the temperature. Adsorption kinetic data was best fitted to the pseudo second-order model. This, together with FTIR spectra, indicated a chemisorption of U(VI) by HA. Equilibrium adsorption data was best fitted to the Langmuir and Temkin models. Thermodynamic parameters such as equilibrium constant (K₀), standard Gibbs free energy (ΔG⁰), standard enthalpy change (ΔH⁰), and standard entropy change (ΔS⁰), indicated that U(VI) adsorption onto HA was endothermic and spontaneous. The co-existence of cations (Cu²⁺, Co²⁺, Cd²⁺ and Pb²⁺) and anions (HPO₄^2- and SO₄^2-) reduced U(VI) adsorption. The high propensity and capacity of leonardite-derived HA adsorbing U(VI) suggests that it has the potential for cost-effective removal of U(VI) from acidic contaminated waters.

Preparation of chitosan functionalized polyamidoamine for the separation of trivalent lanthanides from acidic waste solution

The manuscript deals with the sorption of Am(III) and Eu(III) from pH medium using chitosan functionalized with dendrimer like polyamidoamine (PAMAM) polymers up to third generation. The PAMAM polymers were introduced into chitosan by two step processes and were characterized by various instrumental techniques like FTIR, XRD, TG-DTA. The sorption process was highly pH dependent for both Am(III) and Eu(III) with increasing trend for higher pH of the solution. Kinetics of equilibration was found to be fast with equilibrium attained in 10 min for both the metal ions. Pseudo 2nd order kinetics mechanism was found to be followed for both Am(III) and Eu(III). The sorption process of Eu(III) was found to fit the Langmuir isotherm model with maximum sorption capacity of 6.01 mg/g. There was no effect on the generation of PAMAM Dendron on the efficiency, kinetics or sorption capacity for Am(III) as well as Eu(III). The synthesized different generation of PAMAM functionalized chitosan is a promising material for removal of actinides and lanthanides from waste water solution.

Novel Chemical Cross-Linked Ionogel Based on Acrylate Terminated Hyperbranched Polymer with Superior Ionic Conductivity for High Performance Lithium-Ion Batteries

A new family of chemical cross-linked ionogel is successfully synthesized by photopolymerization of hyperbranched aliphatic polyester with acrylate terminal groups in an ionic liquid of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF₄). The microstructure, viscoelastic behavior, mechanical property thermal stability, and ionic conductivities of the ionogels are investigated systematically. The ionogels exhibit high mechanical strength (up to 1.6 MPa) and high mechanical stability even at temperatures up to 200 °C. It is found to be thermally stable up to 371.3 °C and electrochemically stable above 4.3 V. The obtained ionogels show superior ionic conductivity over a wide temperature range (from 1.2 × 10^-3 S cm^-1 at 20 °C up to 5.0 × 10^-2 S cm^-1 at 120 °C). Moreover, the Li/LiFePO₄ batteries based on ionogel electrolyte with LiBF₄ show a higher specific capacity of 153.1 mAhg^-1 and retain 98.1% after 100 cycles, exhibiting very stable charge/discharge behavior with good cycle performance. This work provides a new method for fabrication of novel advanced gel polymer electrolytes for applications in lithium-ion batteries.

RAFT-mediated Pickering emulsion polymerization with cellulose nanocrystals grafted with random copolymer as stabilizer

The synthesis of a RAFT-mediated Pickering emulsion was firstly achieved by using cellulose nanocrystals (CNCs) grafted with a random copolymer as the stabilizer. Firstly, poly(acrylonitrile-r-butyl acrylate) (poly(AN-r-nBA)) was synthesized by Cu(0)-mediated CRP, which was further modified via a click chemistry strategy to obtain poly(ethylene tetrazole-r-butyl acrylate) (poly(VT-r-nBA)). Then, poly(VT-r-nBA) was grafted onto the CNCs through a Mitsunobu reaction to obtain poly(VT-r-nBA)-g-CNCs. Stabilized by poly(VT-r-nBA)-g-CNCs, an O/W RAFT-mediated Pickering emulsion was formed for the preparation of well-controlled poly(methyl methacrylate) (PMMA) particles with water-soluble potassium persulfate (KPS) as an initiator and oil-soluble 4-cyanopentanoic acid dithiobenzoate (CPADB) as a chain transfer agent. Rheological analysis suggested that the prepared Pickering emulsion possessed good stability under the influences of changes in strain, time, frequency and temperature. Furthermore, the recycling and further utilization of the poly(VT-r-nBA)-g-CNCs could be simply realized through centrifugal separation.

A RAFT-mediated Pickering emulsion with cellulose nanocrystals grafted with a random copolymer was used for the preparation of poly(methyl methacrylate) particles..

Fabrication of mesoporous lignin-based biosorbent from rice straw and its application for heavy-metal-ion removal

Lignocellulosic biomass offers the most abundant renewable resource in replacing traditional fossil resources. However, it is still a major challenge to directly convert the lignin component into value-added materials. The availability of plentiful hydroxyl groups in lignin macromolecules and its unique three-dimensional structure make it an ideal precursor for mesoporous biosorbents. In this work, we reported an environmentally friendly and economically feasible method for the fabrication of mesoporous lignin-based biosorbent (MLBB) from lignocellulosic biomass through a SO₃ micro-thermal-explosion process, as a byproduct of microcrystalline cellulose. BET analysis reveal the average pore-size distribution of 5.50nm, the average pore value of 0.35cm³/g, and the specific surface area of 186m²/g. The physicochemical properties of MLBB were studied by fourier transform infrared spectroscopy (FTIR), attenuated-total-reflection fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and element analysis. These results showed that there are large amounts of sulfonic functional groups existing on the surface of this biosorbent. Pb(II) was used as a model heavy-metal-ion to demonstrate the technical feasibility for heavy-metal-ion removal. Considering that lignocellulosic biomass is a naturally abundant and renewable resource and SO₃ micro-thermal-explosion is a proven technique, this biosorbent can be easily produced at large scale and become a sustainable and reliable resource for wastewater treatment.

Comparison with adsorption of Re (VII) by two different γ-radiation synthesized silica-grafting of vinylimidazole/4-vinylpyridine adsorbents

Two silica gel based adsorbents for Re (VII), i.e. SS-MPTS-VIMH and SS-MPTS-VPQ, were synthesised. Silica gel was used as the matrix for γ-radiation grafting, and the monomer of 1-vinyl imidazole (VIM) and 4-vinylpyridine (4-VP) was grafted onto the silica silanized by methacryloxy propyl trimethoxyl silane, respectively. A VIM concentration of 2molL^-1 and an absorbed dose of 30kGy were the optimal grafting conditions for adsorbent SS-MPTS-VIM, and a 4-VP concentration of 4molL^-1 and an absorbed dose of 40kGy were the optimal grafting conditions for adsorbent SS-MPTS-VP. At the certain condition, the grafting yield of SS-MPTS-VIM was 30.1% and that of SS-MPTS-VP was 21.0%. The adsorption capacity of adsorbent SS-MPTS-VIMH was 145.99mgg^-1 and that of SS-MPTS-VPQ was 71.08mgg^-1 according to the Langmuir model. The adsorbent SS-MPTS-VPQ had better adsorption properties of acid resistance and anti-interference than SS-MPTS-VIMH. Dynamic column experiments showed that protonated adsorbent SS-MTPS-VIMH could be recycled with good performance while quaternized adsorbent SS-MPTS-VPQ could not. The adsorbent SS-MPTS-VIMH belongs to weak anion exchange adsorbent and SS-MPTS-VPQ belongs to strong anion exchange adsorbent. This study paves a way to the synthesis and application of a novel silica base adsorbents for Re (VII).

Chitosan and Its Derivatives as Highly Efficient Polymer Ligands

The polyfunctional nature of chitosan enables its application as a polymer ligand not only for the recovery, separation, and concentration of metal ions, but for the fabrication of a wide spectrum of functional materials. Although unmodified chitosan itself is the unique cationic polysaccharide with very good complexing properties toward numerous metal ions, its sorption capacity and selectivity can be sufficiently increased and turned via chemical modification to meet requirements of the specific applications. In this review, which covers results of the last decade, we demonstrate how different strategies of chitosan chemical modification effect metal ions binding by O-, N-, S-, and P-containing chitosan derivatives, and which mechanisms are involved in binding of metal cation and anions by chitosan derivatives.

Removal of mercury by adsorption: a review

Due to natural and production activities, mercury contamination has become one of the major environmental problems over the world. Mercury contamination is a serious threat to human health. Among the existing technologies available for mercury pollution control, the adsorption process can get excellent separation effects and has been further studied. This review is attempted to cover a wide range of adsorbents that were developed for the removal of mercury from the year 2011. Various adsorbents, including the latest adsorbents, are presented along with highlighting and discussing the key advancements on their preparation, modification technologies, and strategies. By comparing their adsorption capacities, it is evident from the literature survey that some adsorbents have shown excellent potential for the removal of mercury. However, there is still a need to develop novel, efficient adsorbents with low cost, high stability, and easy production and manufacture for practical utility.

Facile crosslinking synthesis of hyperbranch-substrate nanonetwork magnetite nanocomposite for the fast and highly efficient removal of lead ions and anionic dyes from aqueous solutions

The aim of the present work was to investigate the effect of surface functional group density on the adsorption behaviors of functionalized mesoporous Fe₃O₄.

Enhancement of elemental mercury adsorption by silver supported material

Mercury, generally found in natural gas, is extremely hazardous. Although average mercury levels are relatively low, they are further reduced to comply with future mercury regulations, which are stringent in order to avoid releasing to the environment. Herein, vapor mercury adsorption was therefore investigated using two kinds of supports, granular activated carbon (GAC) and titanium dioxide (TiO2). Both supports were impregnated by silver (5 and 15 wt.%), before testing against a commercial adsorbent (sulfur-impregnated activated carbon, SAC). The adsorption isotherm, kinetics, and its thermodynamics of mercury adsorption were reported. The results revealed that Langmuir isotherm provided a better fit to the experimental data. Pseudo second-order was applicable to describe adsorption kinetics. The higher uniform Ag dispersion was a key factor for the higher mercury uptake. TiO2 supported silver adsorbent showed higher mercury adsorption than the commercial one by approximately 2 times. Chemisorption of mercury onto silver active sites was confirmed by an amalgam formation found in the spent adsorbents.

Synthesis and adsorption properties of chitosan-silica nanocomposite prepared by sol-gel method

A hybrid nanocomposite material has been obtained by in situ formation of an inorganic network in the presence of a preformed organic polymer. Chitosan biopolymer and tetraethoxysilane (TEOS), which is the most common silica precursor, were used for the sol-gel reaction. The obtained composite chitosan-silica material has been characterized by physicochemical methods such as differential thermal analyses (DTA); carbon, hydrogen, and nitrogen (CHN) elemental analysis; nitrogen adsorption/desorption isotherms, scanning electron microscopy (SEM); and Fourier transform infrared (FTIR) spectroscopy to determine possible interactions between silica and chitosan macromolecules. Adsorption of microquantities of V(V), Mo(VI), and Cr(VI) oxoanions from the aqueous solutions by the obtained composite has been studied in comparison with the chitosan beads, previously crosslinked with glutaraldehyde. The adsorption capacity and kinetic sorption characteristics of the composite material were estimated.

Cobalt(iii) acetylacetonate initiated RAFT polymerization of acrylonitrile and its application in removal of methyl orange after electrospinning

Electrostatic repulsion (ER) played a key role at low solution pH. Enhancement of hydrophobic attraction (HA) and hydrogen bond (HB) increased the adsorption capacity at higher solution pH.

Synthesis of silica gel supported salicylaldehyde modified PAMAM dendrimers for the effective removal of Hg(II) from aqueous solution

A series of silica gel supported salicylaldehyde modified PAMAM dendrimers (SiO2-G0-SA ∼ SiO2-G2.0-SA) were synthesized and their structures were characterized by FTIR, XRD, SEM, TGA, and porous structure analysis. The feasibility of these adsorbents for the removal of Hg(II) from aqueous solution was first described and the adsorption mechanism was proposed. The adsorption was found to depend on solution pH, the generation number of salicylaldehyde modified PAMAM dendrimers, contact time, temperature, and initial concentration. Results showed that the optimal pH was about 6 and the adsorption capacity increased with the increasing of generation number. Density functional theory (DFT) method was used to investigate the coordination geometries and the chelating mechanism. Adsorption kinetics was found to follow the pseudo-second-order model with film diffusion process as rate controlling step. Adsorption isotherms revealed that adsorption capacities increased with the increasing of temperature. Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherm models were employed to analyze the equilibrium data. The adsorption can be well described by Langmuir isotherm model and took place by chemical mechanism. The thermodynamics properties indicated the adsorption processes were spontaneous and endothermic nature. The maximum adsorption capacity of SiO2-G0-SA, SiO2-G1.0-SA, and SiO2-G2.0-SA were 0.91, 1.52, and 1.81 mmol g(-1), respectively. The considerable higher adsorption capacity compared with other adsorbents indicates SiO2-G0-SA ∼ SiO2-G2.0-SA are favorable and useful for the uptake of Hg (II), and can be potentially used as promising adsorbents for the effective removal of Hg(II) from aqueous solution.

Mercury removal from aqueous solutions with chitosan-coated magnetite nanoparticles optimized using the box-behnken design

Background:

Nowadays, removal of heavy metals from the environment is an important problem due to their toxicity.

Objectives:

In this study, a modified method was used to synthesize chitosan-coated magnetite nanoparticles (CCMN) to be used as a low cost and nontoxic adsorbent. CCMN was then employed to remove Hg²⁺ from water solutions.

Materials and Methods:

To remove the highest percentage of mercury ions, the Box-Behnken model of response surface methodology (RSM) was applied to simultaneously optimize all parameters affecting the adsorption process. Studied parameters of the process were pH (5-8), initial metal concentration (2-8 mg/L), and the amount of damped adsorbent (0.25-0.75 g). A second-order mathematical model was developed using regression analysis of experimental data obtained from 15 batch runs.

Results:

The optimal conditions predicted by the model were pH = 5, initial concentration of mercury ions = 6.2 mg/L, and the amount of damped adsorbent = 0.67 g. Confirmatory testing was performed and the maximum percentage of Hg²⁺ removed was found to be 99.91%. Kinetic studies of the adsorption process specified the efficiency of the pseudo second-order kinetic model. The adsorption isotherm was well-fitted to both the Langmuir and Freundlich models.

Conclusions:

CCMN as an excellent adsorbent could remove the mercury ions from water solutions at low and moderate concentrations, which is the usual amount found in environment.