Selective capture of Hg(II) and Ag(I) from water by sulfur-functionalized polyamidoamine dendrimer/magnetic Fe3O4 hybrid materials

Cellulose-based adsorbent using in mercury detection and removal from water via an efficient grafting strategy of fluorometric sensors by click reaction

Mercury pollution in waters attracts lots of attention due to its serious toxicity and high bioenrichment and many efforts have been devoted in the development of adsorbents for mercury detection and removal. Herein, a cellulose-based adsorbent Cell-TriA-HQ is functionalized with quinoline fluorophore by covalent immobilization through "Click reaction" with high yield. In addition to the admirable adsorptive performance, the prepared adsorbent exhibits excellent selectivity and sensitivity towards Hg (II) in water that the detection limit for Hg (II) is determined to be as low as 1.92 × 10-7 M. The sensitive fluorescence enhancement response is considered to be resulted from the inhibition of photo-induced electron transfer between triazole and quinoline groups and the reinforcement of structural rigidity. The easy manipulation along with excellent performance of adsorption capacity, detective ability and reusability for the multifunctional adsorbent makes it potential in mercury monitoring and removal from aqueous solutions in the field of water treatment.

A novel functionalized graphdiyne oxide membrane for efficient removal and rapid detection of mercury in water

In practice, efficient, rapid and simple removal of Hg(II) from water using nano adsorbents remains an extreme challenge at present. In this work, a novel Hg(II) adsorbent based on functionalized graphdiyne oxide (GDYO-3M) membrane was designed for the purpose of effective and prompt removal of Hg(II) from environmental water for the first time. Through filtration, the proposed GDYO-3M membrane (4 cm diameter size) fulfilled an exceeding 97% removal efficiency in > 10 L water containing 0.1 mg/L Hg(II) within 1 h. Due to the presence of -SH groups, the GDYO-3M membrane demonstrates an excellent selectivity for Hg(II) vs. 14 co-existing metal ions. In the meantime, the GDYO-3M membrane represents a favorable reproducibility (above 95% Hg(II) removal) after 9 successive adsorption-desorption cycles. For the mechanism, it is believed that the active sites in the adsorption process mainly include -SH groups, oxygen-containing functional groups, and alkyne bonds. Further, the GDYO-3M membrane can be utilized as an enrichment approach for sensitive analysis of Hg(II) in water based on energy dispersion X-ray fluorescence spectrometry (ED-XRF), whose detection limit (LOD) reaches 0.2 μg/L within 15 min. This work not only provides a green and efficient method for removing Hg(II), but also renders an approach for rapid, sensitive and portable Hg(II) detection in water.

Superior Adsorptive Removal of Anionic Azo Dyes from Aqueous Solutions Using Sulfonic Acid Group-Modified MIL-101@Graphene Oxide Composite

It is critical to remove organic contaminants from wastewater released by the printing and dyeing industry for addressing water pollution issue. Therefore, the fabrication of new adsorbents with excellent removal efficiencies is an urgent task. A composite of MIL-101 partially functionalized with -SO3H (MIL-101-SO3H) and graphene oxide (GO) was prepared by assembling MIL-101-SO3H truncated octahedrons on the GO framework. The synthesized MIL-101-SO3H@GO has a superior adsorption efficiency for anionic azo dyes. The maximum adsorption capacities of MIL-101-SO3H@GO-1 for Congo red, methyl orange, acid orange 7, and acid orange G reached 2711.3, 818.8, 551.2, and 319.8 mg/g, respectively, which are considerably higher than those obtained using unmodified MIL-101. This is because additional interactions that promote azo dye adsorption, such as hydrogen bonding between the dye and the sulfonic acid groups of MIL-101-SO3H or the carboxyl groups of GO, were induced, and agglomerate pores that accommodated the dye were formed in the composite. The ultrahigh removal efficiency of the composite for azo dyes is mainly driven by hydrogen bonding, electrostatic interactions, π-π stacking between the MIL-101-SO3H@GO and dye molecules, synergistic interactions at the interface of GO and MIL-101-SO3H microcrystals, and the pore-filling effect. Understanding these driving forces for dye adsorption can contribute to the development of sustainable and functionally modified metal-organic framework composite adsorbents.

Multifunctional carboxymethyl cellulose/graphene oxide/polyaniline hybrid thin film for adsorptive removal of Cu(II) and oxytetracycline antibiotic from wastewater

The antibiotics and metal ions in the contaminated water bodies must be removed using appropriate methods for sustainable development. In this study, the multifunctional carboxymethyl cellulose/graphene oxide/polyaniline (CMC/GO/PANI) hybrid thin film was synthesized and utilized for adsorptive scavenging of (Cu(II) and oxytetracycline (OTC) from wastewater. The prepared thin films' morphology, chemical compositions, functionality, and surface charge were analyzed by well-known physicochemical techniques. The adsorption process of the selected model pollutants was examined as a function of reaction time, Cu(II), and OTC solution pH, concentrations, and temperatures. Results showed that CMC/GO/PANI hybrid thin film had higher Cu(II) and OTC adsorption than CMC, GO/CMC, and PANI/CMP thin films due to the multifunctional synergetic effect. The adsorption kinetic data were fitted to the pseudo-second-order model. Redlich-Peterson isotherm model well interpreted Cu(II) and OTC scavenging equilibrium data. Energetically, the adsorption was spontaneous and endothermic for both pollutants. The multifunctional CMC/GO/PANI thin film was recycled and reused seven times during adsorption-desorption cycles. The study outcomes demonstrated that CMC/GO/PANI thin film could be reused multiple times for large-scale wastewater purification.

Selective adsorption of mercury ion from water by a novel functionalized magnetic Ti based metal-organic framework composite

In the context of industrialization and severe wastewater pollution, mercury ions pose a major threat due to their high toxicity. However, traditional adsorbents and common metal-organic framework (MOF) materials have limited effectiveness. This study focuses on combining magnetic materials with functionalized titanium-based MOF composite (SNN-MIL-125(Ti)@Fe3O4) to improve mercury ion adsorption. Through comprehensive characterization and analysis, the adsorption performance and mechanism of the material were studied. The optimal adsorption of the material was achieved at pH 5, exhibiting a pseudo-second-order adsorption model and the Hill theoretical capacity of 668.98 mg/g. Hill and Tempkin models confirmed the presence of chemical and physical adsorption sites on the material surface. Thermodynamic experiments showed a spontaneous endothermic process. Despite the presence of interfering ions, the material exhibited high selectivity for mercury ions. After four cycles, adsorption performance decreased by only 8%, indicating excellent reusability. Nitrogen- and sulfur-containing functional groups played a key role in mercury ion adsorption. In conclusion, SNN-MIL-125(Ti)@Fe3O4, as a magnetic MOF adsorption material, showed potential for effective remediation of mercury-contaminated wastewater. This study contributes to the development of efficient adsorption materials and enhances the understanding of their mechanism.

State-of-the-art adsorption and adsorptive filtration based technologies for the removal of trace elements: A critical review

Water and wastewater are contaminated with various types of trace elements that are released from industrial activities. Their presence, at concentrations above the permissible limit, will cause severe negative impacts on human health and the environment. Due to their cost-effectiveness, simple design, high efficiency, and selectivity, adsorption, and adsorptive filtration are techniques that have received lots of attention as compared to other water treatment techniques. Adsorption isotherms and kinetic studies help to understand the mechanisms of adsorption and adsorption rates, which can be used to develop and optimize different adsorbents. This state-of-the-art review provides and combines the advancements in different conventional and advanced adsorbents, biosorbents, and adsorptive membranes for the removal of trace elements from water streams. Herein, this review discusses the sources of different trace elements and their impact on human health. The review also covers the adsorption technique with a focus on various advanced adsorbents, their adsorption capacities, and adsorption isotherm modeling in detail. In addition, biosorption is critically discussed together with its mechanisms and biosorption isotherms. In the end, the application of various advanced adsorptive membranes is discussed and their comparison with adsorbents and biosorbents is systematically presented.

An Ethyl-Thioglycolate-Functionalized Fe3O4@ZnS Magnetic Fluorescent Nanoprobe for the Detection of Ag+ and Its Applications in Real Water Solutions

Ethyl-thioglycolate-modified Fe₃O₄@ZnS nanoparticles (Fe₃O₄@ZnS-SH) were successfully prepared using a simple chemical precipitation method. The introduction of ethyl thioglycolate better regulated the surface distribution of ZnS, which can act as a recognition group and can cause a considerable quenching of the fluorescence intensity of the magnetic fluorescent nanoprobe, Fe₃O₄@ZnS-SH. Benefiting from stable fluorescence emission, the magnetic fluorescent nanoprobe showed a highly selective fluorescent response to Ag+ in the range of 0-400 μM, with a low detection limit of 0.20 μM. The magnetic fluorescent nanoprobe was used to determine the content of Ag⁺ in real samples. A simple and environmentally friendly approach was proposed to simultaneously achieve the enrichment, detection, and separation of Ag⁺ and the magnetic fluorescent nanoprobe from an aqueous solution. These results may lead to a wider range of application prospects of Fe₃O₄ nanomaterials as base materials for fluorescence detection in the environment.

Synthesis of functional poly(amidoamine) dendrimer decorated apple residue cellulose for efficient removal of aqueous Hg(II)

Water pollution caused by Hg(II) exerts hazardous effect to the environment and public health. The design and fabrication of eco-friendly bioadsorbents for efficient removal of Hg(II) from aqueous solution is a promising strategy. Herein, a series of bioadsorbents were synthesized by the decoration of apple residue cellulose with different generation (G) Schiff base functionalized poly(amidoamine) (PAMAM) dendrimers (SA-G0/CE, SA-G1.0/CE and SA-G2.0/CE). The structures of SA-G0/CE, SA-G1.0/CE and SA-G2.0/CE were characterized and their adsorption performances were determined comprehensively by considering various factors. The maximum adsorption capacity of SA-G0/CE, SA-G1.0/CE and SA-G2.0/CE for Hg(II) are 1.18, 1.73 and 1.88 mmol·g^-1, respectively. The as-prepared bioadsorbents exhibit competitive adsorption capacity as compared with other reported adsorbents. Moreover, they exhibit remarkable adsorption selectivity toward Hg(II) with the coexistence of Ni(II), Cd(II), Mn(II), or Pb(II). The bioadsorbents display satisfactory adsorption performance in real water sample and can be reused with good regeneration property. Adsorption mechanism reveals that the functional groups of OH, -CONH-, CN and NC take part in the adsorption for Hg(II). The work not only opens a pathway to realize the reuse of apple residue, but also provides a promising strategy to construct efficient bioadsorbents for the decontamination of Hg(II) from aqueous solution.

Mixed-valence molybdenum oxide as a recyclable sorbent for silver removal and recovery from wastewater

Silver ions in wastewater streams are a major pollutant and a threat to human health. Given the increasing demand and relative scarcity of silver, these streams could be a lucrative source to extract metallic silver. Wastewater is a complex mixture of many different metal salts, and developing recyclable sorbents with high specificity towards silver ions remains a major challenge. Here we report that molybdenum oxide (MoO_x) adsorbent with mixed-valence (Mo(V) and Mo(VI)) demonstrates high selectivity (distribution coefficient of 6437.40 mL g^-1) for Ag⁺ and an uptake capacity of 2605.91 mg g^-1. Our experimental results and density functional theory calculations illustrate the mechanism behind Ag⁺ adsorption and reduction. Our results show that Mo(V) species reduce Ag⁺ to metallic Ag, which decreases the energy barrier for subsequent Ag⁺ reductions, accounting for the high uptake of Ag⁺ from wastewater. Due to its high selectivity, MoO_x favorably adsorbs Ag⁺ even in the presence of interfering ions. High selective recovery of Ag⁺ from wastewater (recovery efficiency = 97.9%) further supports the practical applications of the sorbent. Finally, MoO_x can be recycled following silver recovery while maintaining a recovery efficiency of 97.1% after five cycles. The method is expected to provide a viable strategy to recover silver from wastewater.

Magnetic covalent organic framework for the adsorption of silver nanoparticles and recycled as surface-enhanced Raman substrate and high-efficiency catalysts for 4-nitrophenol degradation

A magnetic covalent organic framework Fe₃O₄@BM was prepared with melamine and 4-4'-biphenyldialdehyde as monomers and used as adsorbent for Ag NP removal. Fe₃O₄@BM was characterized by zeta potential analysis, transform infrared spectrometry, X-ray diffraction, thermogravimetric analysis, contact angle, and N₂ adsorption-desorption. Fe₃O₄@BM possessed plentiful amino groups, positive potential, and rapid separation performance, making it a promising adsorbent for silver nanoparticles. The adsorption process followed the pseudo-second-order kinetic equation and Langmuir isotherm model. The maximum adsorption capacity of Ag NPs calculated by the Langmuir isotherm model was 544.9 mg/g. The adsorption product Fe₃O₄@BM@Ag could be recycled and efficiently catalyze the degradation of 4-nitrophenol within 6 min. Meanwhile, the recycled Fe₃O₄@BM@Ag could also be used as a surface-enhanced Raman substrate for DTNB detection, and the limit of detection of DTNB reached as low as 10^-7 mol/L. This work prepared a promising adsorbent Fe₃O₄@BM for Ag NP adsorption and provided a sustainable approach for the recycling of the adsorption product Fe₃O₄@BM@Ag.

Synthesis of hyperbranched polyamine dendrimer/chitosan/silica composite for efficient adsorption of Hg(II)

The pollution of water system with Hg(II) exerts hazardous effect to ecosystem and public health. Adsorption is considered to be a promising strategy to remove Hg(II) from aqueous solution. Herein, hyperbranched polyamine dendrimer/chitosan/silica composite (SiO₂-FP) was synthesized for the adsorption of aqueous Hg(II). The adsorption performance of SiO₂-FP was comprehensively determined by considering various influencing factors. SiO₂-FP displays good adsorption performance for Hg(II) with the adsorption capacity of 0.79 mmol·g^-1, which is higher than the corresponding chitosan functionalized silica (SiO₂-CTS) by 46.30 %. The optimal solution pH for the adsorption of Hg(II) is 6. Adsorption kinetic indicates the adsorption for Hg(II) can reach equilibrium at 250 min. Adsorption kinetic process can be well fitted by pseudo-second-order (PSO). Adsorption isotherm reveals the adsorption for Hg(II) can be promoted by increasing initial Hg(II) concentration and adsorption temperature. The adsorption isotherm indicates the adsorption process can be described by Langmuir model and the adsorption is a spontaneous, endothermic and entropy-increased process. SiO₂-FP displays excellent adsorption selectivity and can 100 % adsorb Hg(II) with the coexisting of Ni(II), Zn(II), Pb(II), Mn(II), and Co(II). Adsorption mechanism demonstrates -NH-, -NH₂, CN, CONH, -OH, and CO participated in the adsorption. SiO₂-FP exhibits good regeneration property and the regeneration rate can maintain approximately 90 % after five adsorption-desorption cycles.

Highly efficient and simultaneous magnetic solid phase extraction of heavy metal ions from water samples with l-Cysteine modified magnetic polyamidoamine dendrimers prior to high performance liquid chromatography

Due to the strong metal-sulfur interaction between mercapto groups and metal ions, which can be used to functionalize polyamidoamine dendrimer decorated Fe₃O₄ nanoparticles for high enrichment of trace heavy metal ions from waters. Based on this concept, polyamidoamine dendrimer modified Fe₃O₄ nanomaterials were functionalized with l-Cysteine and a new magnetic solid phase extraction for rapid adsorption and separation of Hg²⁺, Pb²⁺, Co²⁺ and Cd²⁺ from waters was established. The factors affecting extraction efficiency have been optimized. Upon the optimal parameters, the established method provided good linear ranges of 0.1-200 μg L^-1 for Hg²⁺ and 0.05-200 μg L^-1 for Pb²⁺, Co²⁺ and Cd²⁺, and high sensitivity with limits of detection (LOD) of 0.018 μg L^-1, 0.014 μg L^-1, 0.013 μg L^-1 and 0.025 μg L^-1 for Cd²⁺, Pb²⁺, Co²⁺ and Hg²⁺, respectively. Real water samples were utilized to validate the proposed method, and achieved results revealed that the proposed method was sensitive, effective, stable and suitable for monitoring Pb²⁺, Cd²⁺, Co²⁺and Hg²⁺ in environmental waters. This work provided a novel strategy for the simultaneous analysis of target cations in waters, and a new direction for developing decoration method of nanomaterials according to specific purpose.

Feasible synthesis of bifunctional polysilsesquioxane microspheres for robust adsorption of Hg(II) and Ag(I): Behavior and mechanism

The pollution of Hg(II) and Ag(I) to water system exerts hazardous effect to aquatic ecosystem and public security. Simple strategy for constructing adsorbents to efficient remove them is greatly desired. Thus, a series of thiol and amino groups containing bifunctional polysilsesquioxanes (ASPSS) microspheres with adjustable porous structure and functional group content were synthesized by one-step feasible sol-gel process. The adsorption behavior and mechanism of ASPSS microspheres toward Hg(II) and Ag(I) was thoroughly determined. The maximum adsorption capacity of ASPSS for Hg(II) and Ag(I) are 4.32 and 3.86 mmol·g^-1 under 25 ℃. The as-prepared ASPSS microspheres can 100% selectively capture Hg(II) with the coexisting of Mn(II), Co(II), Pb(II), Cd(II), Cu(II), Fe(III). And they can 100% adsorb Ag(I) with the presence of Cd(II), Pb(II), Co(II), Ni(II), and Zn(II). Moreover, the ASPSS microspheres exhibit good removal efficiency for Hg(II) and Ag(I) from simulated industrial wastewater with the coexistence of multiple pollutants. Adsorption mechanism suggests the adsorption for Hg(II) and Ag(I) is the synergistic coordination effect of amino and thiol groups. The excellent adsorption selectivity for Hg(II) and Ag(I) is attributed to the super binding ability of these functional group. ASPSS microspheres also exhibit good regeneration ability and could be reused for removing Hg (II) and Ag(I) from aqueous solution with practical value.

Highly Selective MOF-Based Turn-Off Luminescence Detection of Hg2+ Ions in an Aqueous Medium and Its Dual Functional Catalytic Activity toward Aldol Condensation and β-Enamination Reactions

A new organic ligand, 5-(carboxyformamido)isophthalic acid (5-CFIA), was prepared and employed for the synthesis of two compounds [M₃(C₁₀H₄O₇N₁)₂(8H₂O)]·H₂O (M = Cd, Mn). The compounds have three-dimensionally extended structures. Both the compounds were found to be luminescent at room temperature. The luminescence nature was exploited for the detection of Hg²⁺ ions in an aqueous medium with good selectivity. The interactions between Hg²⁺ ions and the compounds quench the luminescence intensity and act as a turn-off sensor. Both the compounds exhibited low limits for the detection of Hg²⁺ ions and in the range mandated by the WHO. The interactions between Hg²⁺ ions and the compound involve the -NH group, which was probed using Raman and IR spectroscopic techniques. These studies provide important pointers toward the mechanism of this turn-off luminescence behavior. The compounds were explored for base-catalyzed aldol condensation and Lewis acid-promoted β-enaminoester formation reactions. The aldol condensation reaction uses the -NH functionality as a base. The studies indicate that the electron-withdrawing group produces products with higher yields. The β-enaminoester reaction uses the Lewis acid centers, and the studies reveal that the electron-withdrawing groups produce lesser yields of the products. The catalytic nature of the reaction and recyclability of the catalysts were also established. The catalytic reactions employ ethanol (aldol condensation) and no solvent (β-enaminoester), which suggests that the reactions are green and environmentally friendly. The Mn compound was observed to be anti-ferromagnetic.

Resin-based iron-manganese binary oxide for phosphate selective removal

Adsorption technology can effectively remove phosphorus from water and realize phosphorus recovery. Hence, it is used to curb the eutrophication of water and alleviate the crisis caused by the shortage of phosphorus resources. Resin has been attracting increasing interest as an ideal adsorption material; however, its practical application is greatly affected by environmental factors. To solve the competitive adsorption and pore blockage caused by humic acid and coexisting ions during the removal of phosphorus by ion-exchange resin, this study has developed an iron-manganese oxide-modified resin composite adsorbent (Fe/Mn-402) based on the nanoconfinement theory. The structural characterization results of XRD, FT-IR, SEM, and XPS showed that the iron-manganese binary oxide was successfully loaded on the skeleton of the strongly alkaline anion resin and showed good stability under both neutral and alkaline conditions. The batch adsorption experiments showed that the maximum adsorption capacity of Fe/Mn-402 for phosphorus can reach up to 50.97 mg g^-1 under the optimal raw material ratio (Fe:Mn = 1:1). In addition, Fe/Mn-402 shows good selectivity for phosphorus removal. Fe/Mn-402 can maintain good adsorption performance for phosphate even under high concentrations of SO₄^2-, HCO₃^-, and humic acid. The regenerated Fe/Mn-402 can be recycled without any obvious change in its treatment capacity. Hence, it is suitable for stable, long-term usage. In general, this work puts forward a new idea for the development of phosphorus-removal adsorbents for the treatment of wastewater containing coexisting ions and HA.

Magnetic Ti3C2 MXene Nanomaterials for Doxorubicin Adsorption from Aqueous Solutions: Kinetic, Isotherms, and Thermodynamic Studies

In this work, the magnetic Ti₃C₂ MXene functionalized with β-cyclodextrin was prepared and characterized using scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectra, X-ray diffraction, X-ray photoelectron spectroscopy, vibrating sample magnetometry, and thermogravimetric analysis. The synthesized nanomaterial was used as an adsorbent to adsorb doxorubicin from aqueous solutions, and the experimental parameters that affected the adsorption efficiency were investigated. In addition, the adsorption characteristics including adsorption kinetics, adsorption isotherm, and thermodynamics were researched comprehensively. The adsorption kinetics of doxorubicin followed a pseudo-second-order kinetic model, which indicated that adsorption was the rate-limiting step, and the maximum adsorption capacity was 7.35 μg mg^-1 by shaking for 60 min at pH 7.0. The adsorption isotherm was well described using the Freundlich model, which implied that multilayer adsorption took place over the prepared nanomaterial for doxorubicin adsorption. The negative values of Gibbs free energy change (ΔG ⁰ < 0) demonstrated that doxorubicin adsorption was a spontaneous process. The positive values of entropy change (ΔS ⁰ > 0) implied that doxorubicin adsorption was an increasing random process. Enthalpy change values were positive (ΔH ⁰ > 0) and indicated that the adsorption of doxorubicin was endothermic. The adsorption percentage of doxorubicin remained in the range of 41.05-44.09%, and the relative standard deviation (RSD) based on the adsorption percentage through five replicate adsorption and desorption processes was 2.8%. These results indicated that the magnetic Ti₃C₂ MXene nanomaterials can be an effective adsorbent to adsorb DOX from aqueous solutions.

Sequestration of Anionic and Cationic Dyes through Thermally Activated Slate and Their Kinetics and Thermodynamic Characteristics

Adsorption is one of the most common and most robust techniques for the decontamination approach of effluents, owing to its design flexibility, simplicity, cost effectiveness, and high efficiency. However, its application is limited on a large scale due to its cost. The current study investigates the use of low-cost, ecofriendly, and ubiquitous thermally activated clay material. Thermally treated clay was used for the adsorption of crystal violet (CV), Congo red (CR), and malachite green (MG) organic dyes from aqueous solutions. Characterization of slate was carried out with Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy, X-ray diffraction, N₂ physisorption, and XRF spectrometry. The adsorption process was studied as a function of concentration, time, pH, and temperature. Using the batch adsorption technique, the experimentally obtained adsorption data were fitted to both Langmuir and Freundlich isotherms. The adsorption data followed the pseudo-second-order kinetics, and the adsorption capacity was recorded as 360.12 mg/g for CV, 409.23 mg/g for CR, and 390.14 mg/g for MG. The good uptake is the outcome of a greater surface area (24.751 m²/g) for the slate activated at 873 K. The thermodynamic studies showed that the adsorption process remained endothermic and spontaneous. Thermally activated slate proved itself to be an efficient adsorbent and can effectively be used for the removal of textile dyes from the contaminated water, and it is evident from the good uptake of the adsorbate by the adsorbent.

An overview of poly (amide-amine) dendrimers functionalized chromatographic separation materials

Chromatography is one of the most important separation techniques in analytical chemistry. In which, the separation materials are the core for good separation results. Poly (amide-amine) dendrimers with regular three-dimensional structure, abundant terminal groups, controllable molecule chains, and unique cavities appear to have a positive impact on chromatographic separation materials. In the past decades, poly (amide-amine) grafted adsorbents and stationary phases have presented high grafting efficiency, controllable surface structure, good dispersion, and wide practical applications. In this review, the prepared poly (amide-amine) functionalized separation materials and their applications are systematically summarized. Functions, significance, structure-actvity relationships and benefits of poly (amide-amine) dendrimers in the proposed separation materials are discussed in detail. And we hope to provide a useful reference for the future development of chromatographic separation materials and inspire new discoveries in the study of poly (amide-amine) functionalized materials.

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.

Triazine-Based Functionalized Activated Carbon Prepared from Water Hyacinth for the Removal of Hg2+, Pb2+, and Cd2+ Ions from Water

A novel chelating adsorbent, based on the functionalization of activated carbon (AC) derived from water hyacinth (WH) with melamine thiourea (MT) to form melamine thiourea-modified activated carbon (MT-MAC), is used for the effective removal of Hg2+, Pb2+, and Cd2+ from aqueous solution. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) theory confirm the successful functionalization of AC with the melamine thiourea chelating ligand through the amidation reaction between the carboxyl groups of oxidized activated carbon (OAC) and the amino groups of melamine thiourea (MT) in the presence of dicyclohexylcarbodiimide (DCC) as a coupling agent. The prepared MT-MAC exhibited extensive potential for the adsorption of the toxic metal ions Hg2+, Pb2+, and Cd2+ from wastewater. The MT-MAC showed high capacities for the adsorption of Hg2+ (292.6 mg·g-1), Pb2+ (237.4 mg·g-1), and Cd2+ (97.9 mg·g-1) from aqueous solution. Additionally, 100% removal efficiency of Hg2+ at pH 5.5 was observed at very low initial concentrations (25-1000 ppb).The experimental sorption data could be fitted well with the Langmuir isotherm model, suggesting a monolayer adsorption behavior. The kinetic data of the chemisorption mechanism realized by the melamine thiourea groups grafted onto the activated carbon surface have a perfect match with the pseudo-second-order (PSO) kinetic model. In a mixed solution of metal ions containing 50 ppm of each ion, MT-MAC showed a removal of 97.0% Hg2+, 68% Pb2+, 45.0% Cd2+, 17.0% Cu2+, 7.0% Ni2+, and 5.0% Zn2+. Consequently, MT-MAC has exceptional selectivity for Hg2+ ions from the mixed metal ion solutions. The MT-MAC adsorbent showed high stability even after three adsorption-desorption cycles. According to the results obtained, the use of the MT-MAC adsorbent for the adsorption of Pb2+, Hg2+, and Cd2+ metal ions from polluted water is promising.

Direct Synthesis of Sulfur-Decorating PAMAM Dendrimer/Mesoporous Silica for Enhanced Hg(II) and Cd(II) Adsorption

Water security caused by heavy metals poses a deleterious hazard to public health and the ecological system. The construction of adsorbents by polyamidoamine (PAMAM) dendrimers for efficient removal of metal ions has attracted considerable interest. However, the general method for the fabrication of these adsorbents was achieved by the surface chemical modification of the substrates with PAMAM dendrimer, which usually causes the defects of low density and uneven distribution of the dendrimer, the blocking of pores, and reducing the adsorption performance. Hence, the development of a new method for preparation of PAMAM dendrimer-based adsorbent to realize the efficient and enhanced adsorption of metal ions is still a challenge. Herein, methylisothiocyanate decorated PAMAM dendrimer/mesoporous silica composites (G0-S-1/x, G1.0-S-1/x, G2.0-S-1/x, x = 2, 4, 6, 8, 10) were synthesized by the direct sol-gel reaction of alkoxysilyl-containing functional PAMAM dendrimer. The adsorbents display enhanced adsorption property for Hg(II) and Cd(II) as compared with the same adsorbents which were prepared by traditional chemical modification method. Take G2.0-S-1/2 as an example, the maximum adsorption capacities are 2.41 and 0.87 mmol·g^-1 for Hg(II) and Cd(II), respectively . Moreover, the adsorbents show excellent selective adsorption and regeneration property. G2.0-S-1/2 displays distinct selectivity for Hg(II) with the presence of Co(II), Pb(II), Cd(II), and Cu(II). The regeneration percentage still maintains 95.2% after five adsorption-desorption cycles. The adsorption mechanism is also certified by the experimental method and theoretical calculation.

A sulfur-containing fluorescent hybrid porous polymer for selective detection and adsorption of Hg2+ ions

A dual-function material, that is, a sulfur-containing fluorescent hybrid porous polymer, has been simply prepared and utilized to simultaneously detect and capture Hg2+ with high efficiency and selectivity.

A novel approach for the removal of Pb2+ and Cd2+ from wastewater by sulfur-ferromagnetic nanoparticles (SFMNs)

In the recent decades, due to rapid increase in industrialization, urbanization, anthropogenic activity in the catchments, removal of heavy metals contaminants in wastewater has become global challenges. Numerous advance technologies have been introduced to deal with these problems but failed in reducing adequate pollution load in the contaminated water and/or wastewater. In this study, sulfur-ferromagnetic nanoparticles (SFMNs) were synthesized by modification of nano-Fe₃O₄, which can be rapidly separated from the environment by an external magnetic field after in situ repair. Its structure and physical properties were characterized by conventional techniques included Transmission electron microscope (TEM), X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The ability of the SFMNs to remove Pb²⁺ and Cd²⁺ was studied at different temperatures and initial metal ions concentrations. The adsorption kinetics showed that the adsorption equilibrium time of Pb²⁺ and Cd²⁺ was 300 min consequently adsorption process of SFMNs fit well (R² > 0.99) with pseudo-second-order model. The adsorption thermodynamics showed that the adsorption of Pb²⁺ and Cd²⁺ on SFMNs is spontaneous (negative value of ΔG⁰) endothermic process (positive value of ΔH⁰) and fit well (R² > 0.98) with the Langmuir isothermal model. Density functional theory (DFT) calculations show that SFMNs can transfer electrons to Pb²⁺ and Cd²⁺, and the metal ions form stable chelates on the ligand surface. This study implies that newly synthesized sulfur-ferromagnetic nanoparticles could play an instrumental role in metal ions removal from water and wastewater.

Functionalized Fe3O4 Nanoparticles as Glassy Carbon Electrode Modifiers for Heavy Metal Ions Detection-A Mini Review

Over the past few decades, nanoparticles of iron oxide Fe3O4 (magnetite) gained significant attention in both basic studies and many practical applications. Their unique properties such as superparamagnetism, low toxicity, synthesis simplicity, high surface area to volume ratio, simple separation methodology by an external magnetic field, and renewability are the reasons for their successful utilisation in environmental remediation, biomedical, and agricultural applications. Moreover, the magnetite surface modification enables the successful binding of various analytes. In this work, we discuss the usage of core-shell nanoparticles and nanocomposites based on Fe3O4 for the modification of the GC electrode surface. Furthermore, this review focuses on the heavy metal ions electrochemical detection using Fe3O4-based nanoparticles-modified electrodes. Moreover, the most frequently used electrochemical methods, such as differential pulse anodic stripping voltammetry and measurement conditions, including deposition potential, deposition time, and electrolyte selection, are discussed.

Facile Synthesis of Cross-linked Hyperbranched Polyamidoamines Dendrimers for Efficient Hg(Ⅱ) Removal From Water

Dendrimers as commonly used metal ions adsorption materials have the advantages of good adsorption performance and high reuse rate, but the high cost limits its extensive use. Compared with dendrimers, hyperbranched dendrimers have similar physical and chemical properties and are more economical. Therefore, hyperbranched dendrimers are more suitable for industrial large-scale adsorption. The hyperbranched polyamidoamine (HPAMAM) gels were prepared by cross-linking hyperbranched polyamidoamine (HPAMAM-ECH-x and HPAMAM-EGDE-x) with different amounts of epichlorohydrin (ECH) and ethylene glycol diglycidyl ether (EGDE), respectively. The as-synthesized adsorbents were characterized by FT-IR, SEM and XPS. The prepared adsorbents were used to adsorb Hg(Ⅱ) in aqueous solution, and the effects of solution pH, contact time, temperature and initial concentration of metal ion on the adsorption capacity were investigated. The effect of solution pH indicated that the optimum condition to Hg(Ⅱ) removing was at pH 5.0. The adsorption kinetic curves of the two kinds of materials were in accordance with the pseudo-second-order model. For the HPAMAM-ECH samples, the adsorption thermodynamic curves fitted the Langmuir model, while for the HPAMAM-EGDE samples, both Langmuir and Freundlich equations fitted well. The maximum adsorption capacity of HPAMAM-ECH-3 obtained from Langmuir model toward Hg(Ⅱ) was 3.36 mmol/g at pH 5.0 and 35°C.

Magnetic nanoadsorbents for micropollutant removal in real water treatment: a review

Pure water will become a golden resource in the context of the rising pollution, climate change and the recycling economy, calling for advanced purification methods such as the use of nanostructured adsorbents. However, coming up with an ideal nanoadsorbent for micropollutant removal is a real challenge because nanoadsorbents, which demonstrate very good performances at laboratory scale, do not necessarily have suitable properties in in full-scale water purification and wastewater treatment systems. Here, magnetic nanoadsorbents appear promising because they can be easily separated from the slurry phase into a denser sludge phase by applying a magnetic field. Yet, there are only few examples of large-scale use of magnetic adsorbents for water purification and wastewater treatment. Here, we review magnetic nanoadsorbents for the removal of micropollutants, and we explain the integration of magnetic separation in the existing treatment plants. We found that the use of magnetic nanoadsorbents is an effective option in water treatment, but lacks maturity in full-scale water treatment facilities. The concentrations of magnetic nanoadsorbents in final effluents can be controlled by using magnetic separation, thus minimizing the ecotoxicicological impact. Academia and the water industry should better collaborate to integrate magnetic separation in full-scale water purification and wastewater treatment plants.