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The designability of aerogels and the grafting capability of groups were used in this study. A novel type of aerogel based on melamine–formaldehyde (MF) aerogels was synthesized by introducing thiourea groups, and the changes in sol particle diameter, formation mechanism of wet gel, and gel time during the formation of wet gel were studied in detail. Laser particle size, Brunauer–Emmett–Teller, and Fourier transform infrared analyses were combined with scanning electron microscopy and other characterization methods. Results showed that the thiourea group was successfully introduced into the MF aerogels. The specific surface area of the melamine–thiourea–formaldehyde (MTF) aerogel was 439.3 m 2 /g, and the average pore diameter was as high as 1.8 nm without losing the typical 3D spatial network structure and porous material properties of aerogels. The change in particle diameter in the gelation process was systematically revealed for the first time, and the gelation time of wet gel was shortened to 218 min. The properties of aerogel porous materials and the complexing capability of amino and thiourea groups with regard to noble metal ions were used to test the performance of MTF aerogels in the adsorption and selective adsorption of noble metal ions. The findings indicated that the adsorption capacity of MTF aerogel was 88 mg·g −1 and the adsorption capacity of the MTF resin was 63 mg·g −1 , and the adsorption value of aerogel increased by 39% compared with MTF resin. In the selective adsorption experiment, the uptake values of MTF aerogel were found as 57.5 mg Ag + ·g −1 , 6.1 mg Cu 2+ ·g −1 , and 3.6 mg Zn 2+ ·g −1 . And the selective adsorption values of MTF resin were 16.3 mg Ag + ·g −1 , 0.1 mg Cu 2+ ·g −1 , and 0.05 mg Zn 2+ ·g −1 . The results show that the adsorption and selective adsorption capacity of MTF aerogel to silver (I) ions was higher than MTF resin. It was seen that the MTF aerogel prepared in this study has a large specific surface area, uniform pore size distribution, and strong adsorption and selective adsorption capacity for noble metals. It provides a new method for the selective adsorption of noble metal ions. The preparation of the aerogel is also simple and quick and entails a short gelation time and low cost. The formation mechanism of MTF aerogels was revealed, meanwhile, comparing before and after the adsorption and selective adsorption of precious metal ions by MTF aerogel, it can be confirmed that the MTF aerogel was successfully synthesized and possessed better adsorption and selective adsorption for precious metal ions. Highlights The melamine-thiourea-formaldehyde (MTF) aerogel containing thiourea group was fabricated. The gelation time of wet gel was shortened to 218 min. The MTF aerogels possess high specific surface area (439.3 m 2 /g) and total pire volume (2.3 cm 3 /g). The adsorption and selective adsorption values of MTF aerogels on silver (I) ions were 88 mg·g −1 and 57.5 mg·g −1 , respectively, which were higher than that of resins.

Large volumes of wastewater containing toxic contaminants (e.g., heavy metal ions, organic dyes, etc.) are produced from industrial processes including electroplating, mining, petroleum exploitation, metal smelting, etc., and proper treatment prior to their discharge is mandatory in order to alleviate the impacts on aquatic ecosystems. Adsorption is one of the most effective and practical methods for removing toxic substances from wastewater due to its simplicity, flexibility, and economics. Recently, hierarchical oxide composites with diverse morphologies at the micro/nanometer scale, and the combination advantages of oxides and composite components have been received wide concern in the field of adsorption due to their multi-level structures, easy functionalization characteristic resulting in their large transport passages, high surface areas, full exposure of active sites, and good stability. This review summarizes the recent progress on their typical preparation methods, mainly including the hydrothermal/solvothermal method, coprecipitation method, template method, polymerization method, etc., in the field of selective adsorption and competitive adsorption of hazardous substances from wastewater. Their formation processes and different selective adsorption mechanisms, mainly including molecular/ion imprinting technology, surface charge effect, hard-soft acid-base theory, synergistic effect, and special functionalization, were critically reviewed. The key to hierarchical oxide composites research in the future is the development of facile, repeatable, efficient, and scale preparation methods and their dynamic adsorption with excellent cyclic regeneration adsorption performance instead of static adsorption for actual wastewater. This review is beneficial to broaden a new horizon for rational design and preparation of hierarchical oxide materials with selective adsorption of hazardous substances for wastewater treatment.

An abnormal level of well-known his-rich protein, hemoglobin is related to various diseases. Efficient isolation of hemoglobin is of great significance in early disease diagnosis and biomedical analyses. Developing high-performance adsorption materials has become a research hotspot at present. This study proposes a facile pyrolysis-based strategy to prepare novel magnetic flower-like composites for selective hemoglobin separation. Methoxy-polyethylene glycol-carboxyl (PEG) can impart adhesion resistance to improve adsorption selectivity due to its unique ethylene oxide groups and the repulsive elastic forces from compression of the brush-like chains. Two types of magnetic composites were constructed from bimetallic metal–organic frameworks utilizing Co 2+ and Ni 2+ ions as magnetic sources and metal nodes, as well as modification with or without PEG. The properties of the two composites were demonstrated via FTIR, SEM, TEM, DLS, XPS, TGA, BET, and VSM analyses, including flower-like morphology, uniform size (∼2 μm), good dispersibility, porous structure, large surface area, and good magnetic responsiveness. The protein adsorption capacity was further investigated from material factor including the composites modified with/without PEG and environmental factors including incubation time, protein concentration and incubation temperature. Moreover, the adsorption behaviors were explored by kinetics and thermodynamic analysis. Both the PEG-modified and non-PEG-modified composites were effective magnetic adsorbents for selective hemoglobin separation, besides exhibited different adsorption mechanism due to introduction of PEG which induced non-spontaneous selective adsorption rather than spontaneous pure physical adsorption. The magnetic bimetallic MOF system shows promise for isolating His-rich proteins from complex biological systems.

Highlights Gas selective amorphous Al 2 O 3 encapsulation was constructed on highly reactive MgH 2 using atomic layer deposition. Hydrogen selective adsorption was achieved in the impure hydrogen atmosphere containing impurities (O 2 , N 2 , CH 4 , and CO 2 ). Excellent air stability with no MgO or Mg(OH) 2 generated after 3 months of air exposure was achieved. Metal hydrides with high hydrogen density provide promising hydrogen storage paths for hydrogen transportation. However, the requirement of highly pure H 2 for re-hydrogenation limits its wide application. Here, amorphous Al 2 O 3 shells (10 nm) were deposited on the surface of highly active hydrogen storage material particles (MgH 2 –ZrTi) by atomic layer deposition to obtain MgH 2 –ZrTi@Al 2 O 3 , which have been demonstrated to be air stable with selective adsorption of H 2 under a hydrogen atmosphere with different impurities (CH 4 , O 2 , N 2 , and CO 2 ). About 4.79 wt% H 2 was adsorbed by MgH 2 –ZrTi@10nmAl 2 O 3 at 75 °C under 10%CH 4  + 90%H 2 atmosphere within 3 h with no kinetic or density decay after 5 cycles (~ 100% capacity retention). Furthermore, about 4 wt% of H 2 was absorbed by MgH 2 –ZrTi@10nmAl 2 O 3 under 0.1%O 2  + 0.4%N 2  + 99.5%H 2 and 0.1%CO 2  + 0.4%N 2  + 99.5%H 2 atmospheres at 100 °C within 0.5 h, respectively, demonstrating the selective hydrogen absorption of MgH 2 –ZrTi@10nmAl 2 O 3 in both oxygen-containing and carbon dioxide-containing atmospheres hydrogen atmosphere. The absorption and desorption curves of MgH 2 –ZrTi@10nmAl 2 O 3 with and without absorption in pure hydrogen and then in 21%O 2  + 79%N 2 for 1 h were found to overlap, further confirming the successful shielding effect of Al 2 O 3 shells against O 2 and N 2 . The MgH 2 –ZrTi@10nmAl 2 O 3 has been demonstrated to be air stable and have excellent selective hydrogen absorption performance under the atmosphere with CH 4 , O 2 , N 2 , and CO 2 .

Adsorbents widely utilized for environmental remediation, water purification, and gas storage have been usually reported to be either porous or crystalline materials. In this contribution, we report the synthesis of two covalent organic superphane cages, that are utilized as the nonporous amorphous superadsorbents for aqueous iodine adsorption with the record–breaking iodine adsorption capability and selectivity. In the static adsorption system, the cages exhibit iodine uptake capacity of up to 8.41 g g −1 in I 2 aqueous solution and 9.01 g g −1 in I 3 − (KI/I 2 ) aqueous solution, respectively, even in the presence of a large excess of competing anions. In the dynamic flow-through experiment, the aqueous iodine adsorption capability for I 2 and I 3 − can reach up to 3.59 and 5.79 g g −1 , respectively. Moreover, these two superphane cages are able to remove trace iodine in aqueous media from ppm level (5.0 ppm) down to ppb level concentration (as low as 11 ppb). Based on a binding–induced adsorption mechanism, such nonporous amorphous molecular materials prove superior to all existing porous adsorbents. This study can open up a new avenue for development of state–of–the–art adsorption materials for practical uses with conceptionally new nonporous amorphous superadsorbents (NAS). Porous or crystalline materials are generally employed as adsorbents for environmental remediation. Here the authors employ nonporous and amorphous covalent organic superphane cages for aqueous iodine adsorption achieving good selectivity, high adsorption capability and fast kinetics.

Fabricating efficient materials for environmental purposes is a priority and the subject of much attention nowadays. The objectives of this study are to adopt an amino modification approach to improve the selective removal capacity of magnetic graphene oxide (MGO) for Cu(II) ions, and explore how it performs in single and binary systems by taking Cd(II) as a comparison. After grafting the amino groups, the final material exhibited promoted capacities for Cu(II) and Cd(II), and a more apparent selective adsorption process can be observed. The maximum equilibrium adsorbances of amino modified MGO were 578.1 mg g−1 for Cu(II) and 184.7 mg g−1 for Cd(II) under our experimental conditions, compared with 319.1 mg g−1 and 161.2 mg g−1 of MGO for Cu(II) and Cd(II), respectively. Characterization results and experiment data confirmed that the introduction of N species contributed to the enhancement. This may pave the way for better understanding of the underlying mechanism, and provide inspiration for synthesizing new adsorbents.

Present molecular dynamics simulations indicate that the methanol component in a methanol/water mixture is more likely to be trapped in a cyclic peptide nanotube (CPNT), while water molecules tend to be present at the channel mouths as transient guests. Channel water resides mainly between methanol and the CPNT wall, resulting in a distinct decrease in the H-bond number per channel methanol. Six designed CPNTs with different channel diameters and outer surface characteristics all possess distinct selectivity to methanol over water. Of these, the amphipathic 8 × (A Q ) 4 -CPNT exhibits the best performance. Results in this study provide basic information for the application of a CPNT to enrich methanol from a methanol/water mixture. Graphical Abstract Typical overview of water and methanol molecular distribution in cyclic peptide nanotubes

This article provides insights into hydrogels of the most promising biodegradable natural polymers and their mechanisms of degradation, highlighting the different possibilities of controlling hydrogel degradation rates. Since biodegradable hydrogels can be designed as scaffolding materials to mimic the physical and biochemical properties of natural tissues, these hydrogels have found widespread application in the field of tissue engineering and controlled release. In the same manner, their potential as water reservoirs, macro- and microelement carriers, or matrixes for the selective adsorption of pollutants make them excellent candidates for sustainable soil amendment solutions. Accordingly, this article summarizes the recent advances in natural biodegradable hydrogels in the fields of tissue engineering, controlled release, and soil remediation, emphasizing the new opportunities that degradability and its tunability offer for the design and applicability of hydrogels.

One-step adsorptive purification of ethylene (C 2 H 4 ) from four-component gas mixtures comprising acetylene (C 2 H 2 ), ethylene (C 2 H 4 ), ethane (C 2 H 6 ) and carbon dioxide (CO 2 ) is an unmet challenge in the area of commodity purification. Herein, we report that the ultramicroporous sorbent Zn-atz-oba (H 2 oba = 4,4-dicarboxyl diphenyl ether; Hatz = 3-amino-1,2,4-triazole) enables selective adsorption of C 2 H 2 , C 2 H 6 and CO 2 over C 2 H 4 thanks to the binding sites that lie in its undulating pores. Molecular simulations provide insight into the binding sites in Zn-atz-oba that are responsible for coadsorption of C 2 H 2 , C 2 H 6 and CO 2 over C 2 H 4 . Dynamic breakthrough experiments demonstrate that the selective binding exhibited by Zn-atz-oba can produce polymer-grade purity (>99.95%) C 2 H 4 from binary (1:1 for C 2 H 4 /C 2 H 6 ), ternary (1:1:1 for C 2 H 2 /C 2 H 4 /C 2 H 6 ) and quaternary (1:1:1:1 for C 2 H 2 /C 2 H 4 /C 2 H 6 /CO 2 ) gas mixtures in a single step. The purification of ethylene is an industrially relevant process. Here, the authors report the one-step separation of ethylene from quaternary gas mixtures of hydrocarbons and CO 2 using a single metal–organic framework-based physisorbent.

Metal–organic frameworks that undergo a cooperative spin transition at neighbouring metal centres upon coordination to CO exhibit large CO separation capacities with only small changes in temperature. MOFs, reloaded Metal–organic frameworks (MOFs) are materials with numerous potential applications, including separating gases. Aside from maximizing gas uptake within the material, it is important to minimize the energy that is required for desorption and therefore regeneration of the material. However, it is not straightforward to design such a feature into any given MOF. Here, Jeffrey Long and colleagues present MOFs that undergo a spin transition at the metal centre (Fe) upon coordination to carbon monoxide (CO), and in which the ligands between the Fe sites facilitate a concerted spin transition through the MOF. This concerted spin transition results in cooperative adsorption of CO to give low regeneration energies and small temperature swings for desorption. Cooperative binding, whereby an initial binding event facilitates the uptake of additional substrate molecules, is common in biological systems such as haemoglobin 1 , 2 . It was recently shown that porous solids that exhibit cooperative binding have substantial energetic benefits over traditional adsorbents 3 , but few guidelines currently exist for the design of such materials. In principle, metal–organic frameworks that contain coordinatively unsaturated metal centres could act as both selective 4 , 5 , 6 , 7 and cooperative adsorbents if guest binding at one site were to trigger an electronic transformation that subsequently altered the binding properties at neighbouring metal sites 8 , 9 , 10 . Here we illustrate this concept through the selective adsorption of carbon monoxide (CO) in a series of metal–organic frameworks featuring coordinatively unsaturated iron( ii ) sites. Functioning via a mechanism by which neighbouring iron( ii ) sites undergo a spin-state transition above a threshold CO pressure, these materials exhibit large CO separation capacities with only small changes in temperature. The very low regeneration energies that result may enable more efficient Fischer–Tropsch conversions and extraction of CO from industrial waste feeds, which currently underutilize this versatile carbon synthon 11 . The electronic basis for the cooperative adsorption demonstrated here could provide a general strategy for designing efficient and selective adsorbents suitable for various separations.