A selectivity-controlled adsorbent of molybdenum disulfide nanosheets armed with superparamagnetism for rapid capture of mercury ions

Bottom-up Synthesis of a Sulfhydryl-Modified Heteroporous Covalent Organic Framework for Ultrafast Removal of Trace Hg(Ⅱ) from Water

The development of functionalized covalent organic frameworks (COFs) is crucial in expanding their potential for removing toxic heavy metals from drinking water. Here, a new sulfhydryl-modified heteroporous COF (COFDBD-BTA) is prepared using a "bottom-up" approach in which a direct amine-aldehyde dehydration condensation between 2,5-diamino-1,4-benzenedithiol dihydrochloride (DBD) and [1,1'-biphenyl]-3,3',5,5'-tetracarbaldehyde (BTA) is occurred. The COFDBD-BTA features a hexagonal kagome (kgm) structure and a sheet-like morphology. Notably, COFDBD-BTA contains densely S atoms that provide high-density Hg(II) adsorption sites for efficient and selective trace Hg(II) removal. COFDBD-BTA exhibited excellent performance in rapidly removing trace Hg(II) from 30 μg L-1 to 0.71 μg L-1 within 10 seconds, below the World Health Organization's allowable limit of 1 μg L-1. Additionally, COFDBD-BTA exhibited a high Hg(Ⅱ) removal level from water, achieving adsorption capacity of 687.38 mg g-1. Furthermore, the adsorbent exhibited a wide range of applicability for low concentration (6-500 μg L-1) Hg(Ⅱ), a simple and feasible regeneration method, and strong Hg(II) removal ability in real tap water systems. The excellent adsorption efficiency, outstanding recyclability, and one-step room temperature synthesis makes S-rich COFDBD-BTA a promising candidate for eliminating Hg(Ⅱ) from drinking water.

Different roles of FeS and FeS2 on magnetic FeSx for the selective adsorption of Hg2+ from waste acids in smelters: Reaction mechanism, kinetics, and structure-activity relationship

Magnetic FeSx was developed as a high-performance sorbent for selectively adsorbing Hg2+ from waste acids in smelters. However, further improvement of its ability for Hg2+ adsorption was extremely restricted due to the lack of reaction mechanisms and structure-activity relationships. In this study, the roles of FeS and FeS2 on magnetic FeSx for Hg2+ adsorption were investigated with alternate adsorption of Hg2+ without/with Cl-. The structure-activity relationship of magnetic FeSx for Hg2+ adsorption and the negative effect of acid erosion were elucidated using kinetic analysis. FeS can react with Hg2+ with 1:1 stoichiometric ratio to form HgS, while FeS2 can react with Hg2+ in the presence of Cl- with novel 1:3 stoichiometric ratio to form Hg3S2Cl2. The rate of magnetic FeSx for Hg2+ adsorption was related to the instantaneous amounts of FeS and threefold FeS2 on magnetic FeSx and the amount of Hg2+ adsorbed. Meanwhile, its capacity for Hg2+ adsorption was related to the initial sum of FeS amount and threefold FeS2 amount on the surface and their ratios by acid erosion. Then, magnetic FeSx-400 was devised with adsorption rate of 2.12 mg g-1 min-1 and capacity of 1092 mg g-1 to recover Hg2+ from waste acids for centralized control.

Efficient and selective removal of Hg(II) from water using recyclable hierarchical MoS2/Fe3O4 nanocomposites

Developing practical and cost-effective adsorbents with satisfactory mercury (Hg) remediation capability is indispensable for aquatic environment safety and public health. Herein, a recyclable hierarchical MoS₂/Fe₃O₄ nanocomposite (by in-situ growth of MoS₂ nanosheets on the surface of Fe₃O₄ nanospheres) is presented for the selective removal of Hg(II) from aquatic samples. It exhibited high adsorption capacity (∼1923.5 mg g ^-1), fast kinetics (k₂ ∼ 0.56 mg g ^-1 min^-1), broad working pH range (2-11), excellent selectivity (K_d > 1.0 × 10⁷ mL g ^-1), and great reusability (removal efficiency > 90% after 20 cycles). In particular, removal efficiencies of up to ∼97% for different Hg(II) concentrations (10-1000 μg L ^-1) in natural water and industrial effluents confirmed the practicability of MoS₂/Fe₃O₄. The possible mechanism for effective Hg(II) removal was discussed by a series of characterization analyses, which was attributed to the alteration of the MoS₂ structure and the surface coordination of Hg-S. The accessibility of surface sulfur sites and the diffusion of Hg(II) in the solid-liquid system were enhanced due to the advantage of the expanded interlayer spacing (0.96 nm) and the hierarchical structure. This study suggests that MoS₂/Fe₃O₄ is a promising material for Hg(II) removal in actual scenarios and provides a feasible approach by rationally constructing hierarchical structures to promote the practical applications of MoS₂ in sustainable water treatments.

Reclaimable MoS2 Sponge Absorbent for Drinking Water Purification Driven by Solar Energy

With the fast development of modern industries, scarcity of freshwater resources caused by heavy metal pollution (i.e., Hg²⁺) has become a severe issue for human beings. Herein, a 3D-MoS₂ sponge as an excellent absorbent is fabricated for mercury removal due to its multidimensional adsorption pathways, which decreases the biomagnification effect of methylmercury in water bodies. Furthermore, a secondary water purification strategy is employed to harvest drinkable water with the exhausted adsorbents, thus alleviating the crisis of drinking water shortage. Compared to the conventional landfill treatment, the exhausted MoS₂ sponge absorbents are further functionalized with a poly(ethylene glycol) (PEG) layer to prevent the heavy metals from leaking and enhance the hydrophilicity for photothermal conversion. The fabricated evaporator displays excellent evaporation rates of ∼1.45 kg m^-2 h^-1 under sunlight irradiation and produces freshwater with Hg²⁺ under the WHO drinking water standard at 0.001 mg L^-1. These results not only assist in avoiding the biodeposition effect of mercury in water but also provide an environment-friendly strategy to recycle hazardous adsorbents for water purification.

Preparation of PAMAM modified PVDF membrane and its adsorption performance for copper ions

As one of the main pollutants of water pollution, the potential toxicity of heavy metal ions always threatens the safety of human and nature. Therefore, how to effectively remove heavy metal ions has become an important research topic in environmental protection. In the existing research, adsorption method is outstanding from many methods because of its high adsorption efficiency and easy operation. In this study, different generations of hyperbranched polyamide-amine (PAMAM) were grafted onto PVDF membrane to obtain the membrane with high adsorption capacity for heavy metal ions. The structure and physicochemical properties of the membranes were evaluated by means of fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (FE-SEM), element analyzer and X-ray photoelectron spectroscopy (EDX). At the same time, various factors affecting the adsorption process were studied, and it was found that the adsorption behavior of copper ion (Cu²⁺) on the membrane conformed to the pseudo-first-order kinetic model and Langmuir isotherm model. Moreover, after comparing the adsorption effect of the modified membranes grafted with different generations of PAMAM, it was found that the membrane grafted with the third generation PAMAM had the best adsorption when the solution pH was 5, and its maximum adsorption capacity could reach 153.8 mg/g. After five adsorption-desorption cycles, its adsorption capacity can reach 72.83% of the first test, indicating that it has good recycling performance. The results show that the adsorption membrane has good application potential and research value.

Alkynyl functionalized MoS2 mesoporous materials with superb adsorptivity for heavy metal ions

Effective elimination of heavy metal ions from water is an arduous task for their toxic effects to aquatic ecosystem and human health. Herein, a novel alkynyl functionalized molybdenum disulfide (C-MoS₂) is fabricated via mechanochemical method with well interlayered spacing, meso porosity, and high surface area (~211 m²g^-1). Mineral MoS₂ was first peeled mechanically and oxidized in situ to MoS_2-xO_x, and then reduced by ball milling with CaC₂ to form the C-MoS₂ composite. The as-obtained C-MoS₂ shows extraordinary adsorptivity for heavy metal ions, viz. 1194 mg-Hg g^-1 (Hg(NO₃)₂ solution, pH= 5, 303.15 K, equilibrium Hg(II) concentration Ce= 36.9 μg·g^-1, ionic strength I= 17.2 mmolL^-1), and 442.3 mg-Pbg^-1 (Pb(NO₃)₂ solution, pH= 5, 303.15 K, equilibrium Pb(II) concentration Ce= 46.9μgg^-1, I= 5.8 mmolL^-1), respectively, along with excellent recyclability, representing one of the best sorbents till now. The adsorption isotherms of Hg(II) followed the Langmuir model and the adsorption kinetics followed the pseudo-second-order model. The adsorption is an endothermic and entropy driven spontaneous process. The excellent adsorption performance of C-MoS₂ is attributed to its very high S-content, availability, and soft acid-base interaction with mercury and lead anions. The C-MoS₂ is an advanced sorbent for Hg(II) and Pb(II) with excellent adsorption performance and recyclability.

L-Cysteine functionalized graphene oxide nanoarchitectonics: A metal-free Hg2+ nanosensor with peroxidase-like activity boosted by competitive adsorption

Developing non-noble metal, even metal-free chemical sensors for the detection of toxic heavy metal ions is significantly desirable for economically and environmentally sustainable application but has heretofore remained elusive. Herein, a _L-cysteine functionalized graphene oxide nanosheet (CGO) nanoarchitectonics, greenly synthesized by a very simple method at room temperature, was utilized to realize the simultaneous enrichment and colorimetric detection of trace mercury ions (Hg²⁺). It was discovered that CGO, as a nanozyme mimic exhibited greatly enhanced peroxidase-like catalytic activity than the pristine graphene oxide. By exploring the interactions of CGO nanozyme with colorimetric substrate, 3,3',5,5'-tetramethylbenzidine (TMB) and target Hg²⁺ ions, we found that the sensing principle was based mainly on the competitive adsorption between Hg²⁺ ions and TMB over CGO. The pre-capture of Hg²⁺ ions hindered the TMB binding on CGO, resulting in the promoted oxidation of TMB by H₂O₂ to produce more colored oxidation products, from which the colorimetric sensing of Hg²⁺ was realized with a good detection effect on 5 μg L^-1 solution. As an enrichment-sensing integration platform, this metal-free sensor is cost-effective and sensitive, and presents considerable anti-interference ability over other metal ions. Overall, this work not only expands the application of graphene-based materials in colorimetric detection but also provides a general sensing principle to construct highly sensitive sensors.

Facile synthesis of core-shell phase-transited lysozyme coated magnetic nanoparticle as a novel adsorbent for Hg(II) removal in aqueous solutions

Adsorption using nanomaterials is considered an effective method for controlling the levels of toxic heavy metal in wastewater. Herein, a novel adsorbent, core-shell phase-transited lysozyme film-coated magnetic nanoparticles (Fe₃O₄@SiO₂@PTL) for Hg(II) ions removal from aqueous solutions was explored via facile and fast phase transformation and self-assembly process of lysozyme. The physiochemical properties of Fe₃O₄@SiO₂@PTL were investigated using various characterization techniques. The adsorption performances such as kinetics, isotherms, selectivity, the effect of coexisting ions, and regeneration were evaluated. Fe₃O₄@SiO₂@PTL showed an extremely high Hg(II) uptake rate and achieved more than 90% equilibrium adsorption capacity in 5 min. Hg(II) adsorption was followed by a pseudo-second-order kinetic model and fitted the Langmuir model by achieving a maximum uptake of 701.51 mg/g. Furthermore, excellent Hg(II) selectivity was obtained in a mixed solution containing various heavy metal ions, along with good chemical stability owing to the high adsorption capacity maintained after five cycles. The adsorption analyses indicated that the amino, imino, amide, hydroxyl, carboxyl, and thiol groups exposed on the surface of Fe₃O₄@SiO₂@PTL were vital for Hg(II) removal. Consequently, this work will significantly assist in the development of an easily available, eco-friendly, and selective adsorbent material to remove heavy metal ions from wastewater.

Magnetic supramolecular polymer: Ultrahigh and highly selective Pb(II) capture from aqueous solution and battery wastewater

For the practical capture of heavy metal ions from wastewater, fabricating environmental friendly adsorbents with high stability and super adsorption capacity are pursuing issue. In this work, we develop magnetic supramolecular polymer composites (M-SMP) by using a simple two-step hydrothermal method. Systematical characterizations of morphological, chemical and magnetic properties were conducted to confirm the formation of M-SMP composites. The resulting M-SMP composites were applied to remove Pb(II) from aqueous solution and from real battery wastewater, and easy separation was achieved using a permanent magnet. By investigating the effects of various parameters, we optimized their operating condition for Pb(II) adsorption by the M-SMP. The uptake of Pb(II) onto M-SMP fitted well the pseudo-second-order and Langmuir isotherm models, and favourable thermodynamics showed a spontaneous endothermic process. The SMP endowed M-SMP with ultrahigh adsorption capacity for Pb(II) (946.9 mg g^-1 at pH = 4.0, T = 298 K), remarkable selectivity, satisfactory stability and desirable recyclability. In Pb-contaminated lead-acid battery industrial wastewater, the concentration of Pb(II) declined from 18.070 mg L^-1 to 0.091 mg L^-1, which meets the current emission standard for the battery industry. These merits, combined with simple synthesis and convenient separation, make M-SMP an outstanding scavenger for the elimination of industrial Pb(II) wastewater.

Adsorption Processing for the Removal of Toxic Hg(II) from Liquid Effluents: Advances in the 2019 Year

Mercury is a toxic metal, thus, it is an element which has more and more restrictions in its uses, but despite the above, the removal of this metal, from whatever the form in which it is encountered (zero valent metal, inorganic, or organic compounds), and from different sources, is of a widespread interest. In the case of Hg(II), or Hg2+, the investigations about the treatment of Hg(II)-bearing liquid effluents (real or in most cases synthetic solutions) appear not to end, and from the various separation technologies, adsorption is the most popular among researchers. In this topic, and in the 2019 year, more than 100 publications had been devoted to this field: Hg(II)-removal-adsorption. This work examined all of them.

Highly effective remediation of Pb(II) and Hg(II) contaminated wastewater and soil by flower-like magnetic MoS2 nanohybrid

The efficient enrichment and remediation of heavy metals from realistic wastewater and contaminated soil containing large excess of competitive ions remains a daunting challenge by far. In the present study, flower-like molybdenum disulfide decorated with iron oxide nanoparticles (MoS₂/Fe₃O₄) is designed via a two-step hydrothermal method and mainly applied in the removal of Hg(II) and Pb(II) ions in aqueous environment. Exhaustive morphological, chemical and magnetic characterizations verify the successful formation of magnetic MoS₂/Fe₃O₄. Batch adsorption experiments show that the obtained MoS₂/Fe₃O₄ nanohybrid enables efficient capture of Hg(II) and Pb(II) ions, accompanied by ease-of-separation from solution by simply applying a magnet. In this respect, high adsorption capacities (263.6 mg g^-1 for Pb(II) and 428.9 mg g^-1 for Hg(II)) can be gained under optimized conditions (pH = 5.0; 298 K; nanohybrid dosage: 0.8 g L^-1 and the contact time: 180 min). In addition, the effects of different parameters such as initial Pb(II)/Hg(II) concentration (50-500 mg L^-1), temperature (298, 308 and 318 K) and co-existing ions (Zn(II), Cu(II), Cd(II) and Mg(II)) were systematically probed. The favorable adsorption capacity, selectivity and recyclability mainly originates from the strong Hg²⁺/Pb²⁺···S^2- bonding interactions. Practical application potential of magnetic MoS₂/Fe₃O₄ nanohybrid in realistic lead-acid battery industry wastewater and Pb(II)-contaminated soil is further explored, achieving promising results with high Pb(II) removal efficiency of 99.63% for wastewater and 57.15% for soil. Simple preparation, easy separation and high adsorption capacity would foster thus-designed sulfide-based nanohybrid a promising adsorbent for heavy metal removal from wastewater and contaminated soil.