Precise Size‐Selective Sieving of Nanoparticles Using a Highly Oriented Two‐Dimensional Supramolecular Polymer

Increasing Dimensionality in Self-Assembly: Toward Two-Dimensional Supramolecular Polymers

Different approaches to achieve 2D supramolecular polymers, as an alternative to the covalent bottom-up approaches reported for the preparation of 2D materials, are reviewed. The significance of the operation of weak non-covalent forces to induce a lateral growth of a number of self-assembling units is collected. The examples of both thermodynamically and kinetically controlled formation of 2D supramolecular polymers showed in this review demonstrate the utility of this strategy to achieve new 2D materials with biased morphologies (nanosheets, scrolls, porous surfaces) and showing elegant applications like chiral recognition, enantioselective uptake or asymmetric organic transformations. Furthermore, elaborated techniques like seeded or living supramolecular polymerizations have been demonstrated to give rise to complex 2D nanostructures.

Depletion force optimization for high-purity gold nanotriangles prepared using different growth methods

A homogeneous structural distribution in metal nanoparticle is commonly required for their application, and despite high-yield growth techniques, unavoidable structural heterogeneity remains a concern in metal nanoparticle synthesis. Gold nanotriangles (AuNTs) were synthesized using seed-mediated and seedless growth methods. Recent advancements in high-yield synthesis processes have enabled easy handling of AuNTs, which exhibit unique localized surface plasmon resonance characteristics due to their anisotropic triangular form. The flocculation and subsequent precipitation technique was used to purify AuNTs of different sizes synthesized using seed-mediated and seedless growth methods. The optimal conditions for obtaining high-purity AuNTs were explored by introducing a high concentration of cetyltrimethylammonium chloride. Additionally, the depletion force necessary for achieving high-purity AuNTs was calculated to reveal variations in the required depletion forces for AuNTs synthesized using different growth techniques. The alternations in the size distribution of AuNTs during the flocculation step were tracked using dynamic light scattering, and the surface charge of AuNTs synthesized through different growth methods was evaluated by ζ-potential. The high purity of the AuNTs produced using the seedless growth method required a larger depletion force than the seed-mediated grown AuNTs. The difference in the required depletion forces results from the difference in the electrostatic forces caused by the different growth methods.

Non-Stop Switching Separation of Superfine Solid/Liquid Dispersed Phases in Oil and Water Systems Using Polymer-Assisted Framework Fiber Membranes

Fabricating filtration membranes with wide applicability and high efficiency is always a challenge in the precise separation of small colloidal particles under mild conditions. For this purpose, a strategy mixing supramolecular framework fiber with polymer is adopted. The fibrous assembly in the gel state provides uniform nanopores for both channel and interception and controlled wettability for lyophilic/lyophobic switching. The used polymer fills the gaps between fiber assemblies and improves the mechanical property. The composite membrane shows both under-oil superhydrophobic and underwater superoleophobic nature, which allows the conversions via in situ modulation of joystick solvents. Based on surface wetting and size-sieving, ultrafine hard nanoparticles dispersing in both hydrophobic organic solvents and water are selectively sieved. In addition, on-demand separation of water-in-oil and oil-in-water microemulsions without and with surfactants as systems containing soft droplets are realized. The smallest cut-off size of ≈3 nm is achieved for both hard and soft emulsions, while separation efficiency maintains during sustained in situ reversible switches.

Supramolecular framework membrane for precise sieving of small molecules, nanoparticles and proteins

Synthetic framework materials have been cherished as appealing candidates for separation membranes in daily life and industry, while the challenges still remain in precise control of aperture distribution and separation threshold, mild processing methods, and extensive application aspects. Here, we show a two-dimensional (2D) processible supramolecular framework (SF) by integrating directional organic host-guest motifs and inorganic functional polyanionic clusters. The thickness and flexibility of the obtained 2D SFs are tuned by the solvent modulation to the interlayer interactions, and the optimized SFs with limited layers but micron-sized areas are used to fabricate the sustainable membranes. The uniform nanopores allow the membrane composed of layered SF to exhibit strict size retention for substrates with the rejection value of 3.8 nm, and the separation accuracy within 5 kDa for proteins. Furthermore, the membrane performs high charge selectivity for charged organics, nanoparticles, and proteins, due to the insertion of polyanionic clusters in the framework skeletons. This work displays the extensional separation potentials of self-assembled framework membranes comprising of small-molecules and provides a platform for the preparation of multifunctional framework materials due to the conveniently ionic exchange of the counterions of the polyanionic clusters.

Precise membrane separation of nanoparticles using a microporous polymer containing radially π-conjugated molecular carbocycles

Herein, we report the synthesis of a novel porous polymer, PS2, containing radially π-conjugated carbocycles and a linear phenylene backbone. The PS2-based membrane has a distinct small size cutoff (ca. 2.6 nm) and a major size at ∼1.5 nm for the size-selective separation of nanoparticles.

Ultra-selective ion sieve for thorium recovery from rare earth elements using oxygen-rich microporous carbon adsorption

The ultra-selective extraction of thorium ions (Th(IV)) from lanthanides is of significance to both solve the radioactive pollution issue in rare earth (RE) production and sustainably provide thorium fuel for the liquid fluoride thorium reactors (LFTR). However, it remains a great challenge. Here, we reported an oxygen-rich microporous carbon for ultra-selective extraction of Th(IV) from rare earth elements (REEs) in a wide pH range. This selectivity was derived from the synergy of the oxygen-rich nature, microporous structure of the carbons, the chemical valence, and the ionic size of Th(IV) species. This oxygen-rich microporous carbon presented an ultra-high distribution coefficient (K_d) of 1.15 × 10⁸ mL g^-1 for Th(IV) at pH 4.9 in the presence of 15 REEs and revealed outstanding performance for Th(IV) extraction from three simulated RE solutions with high ionic strength of lanthanides. Meanwhile, an exceptional adsorption capacity of 624.98 mg g^-1 was obtained in the single Th(IV) solution. Both values were superior to those of reported adsorbents. More importantly, the new adsorbent developed here could be prepared from cigarette butts. These features ensured the oxygen-rich carbon as a promising and cost-effective adsorbent for high-purity thorium extraction from REEs.

Coordination Cages Selectively Transport Molecular Cargoes Across Liquid Membranes

Chemical purifications are critical processes across many industries, requiring 10-15% of humanity's global energy budget. Coordination cages are able to catch and release guest molecules based upon their size and shape, providing a new technological basis for achieving chemical separation. Here, we show that aqueous solutions of FeII4L6 and CoII4L4 cages can be used as liquid membranes. Selective transport of complex hydrocarbons across these membranes enabled the separation of target compounds from mixtures under ambient conditions. The kinetics of cage-mediated cargo transport are governed by guest binding affinity. Using sequential transport across two consecutive membranes, target compounds were isolated from a mixture in a size-selective fashion. The selectivities of both cages thus enabled a two-stage separation process to isolate a single compound from a mixture of physicochemically similar molecules.

Geometrical manipulation of complex supramolecular tessellations by hierarchical assembly of amphiphilic platinum(II) complexes

Here we report complex supramolecular tessellations achieved by the directed self-assembly of amphiphilic platinum(II) complexes. Despite the twofold symmetry, these geometrically simple molecules exhibit complicated structural hierarchy in a columnar manner. A possible key to such an order increase is the topological transition into circular trimers, which are noncovalently interlocked by metal···metal and π-π interactions, thereby allowing for cofacial stacking in a prismatic assembly. Another key to success is to use the immiscibility of the tailored hydrophobic and hydrophilic sidechains. Their phase separation leads to the formation of columnar crystalline nanostructures homogeneously oriented on the substrate, featuring an unusual geometry analogous to a rhombitrihexagonal Archimedean tiling. Furthermore, symmetry lowering of regular motifs by design results in an orthorhombic lattice obtained by the coassembly of two different platinum(II) amphiphiles. These findings illustrate the potentials of supramolecular engineering in creating complex self-assembled architectures of soft materials.

Stimuli-Responsive Two-Dimensional Supramolecular Polymers Based on Trinuclear Platinum(II) Scaffolds: Reversible Modulation of Photoluminescence, Cavity Size, and Water Permeability

Here we report the first two-dimensional (2D) supramolecular polymer, which has varying structure and function arising from the perturbation of noncovalent metal···metal interactions in response to acid-base stimuli. This 2D assembly possesses a positively charged, honeycomb-like nanostructure consisting of trinuclear alkynylplatinum(II) terpyridine complexes appended with acid-sensitive dimethylamino groups. Upon addition of acids and bases, reversible switching mediated by protonation and deprotonation of dimethylamino and dimethylammonium moieties intrinsically alters the positive charge density of the constituent cationic units, which causes interior cavities to adaptively adjust their size, accompanied by drastic photoluminescence changes. When water molecules pass through the membranes obtained from 2D supramolecular polymers, the permeating flux can also be tuned by the pH values of the buffer media. This work paves the way toward supramolecularly engineered 2D smart materials with stimuli-responsive properties.

Two-Dimensional Supramolecular Ionic Frameworks for Precise Membrane Separation of Small Nanoparticles

Supramolecular frameworks driven by intermolecular interactions represent a new type of porous materials differing from those driven by covalent or coordination bonding. The intermolecular interaction-induced flexible assembly structures display unique advantages in material processing, structure stimuli response, and recycling. In this work, a two-dimensional (2D) supramolecular ionic framework (SIF) was constructed through the initial ionic interaction between the host cation and polyoxometalate polyanion and then the host-guest inclusion of the formed host ionic complex with a four-arm porphyrin guest molecule following a [2+4] type reaction. Several prepared framework monolayers bearing an orthometric grid structure constituted a nanosheet-like assembly with flexibility and exhibited processability, which provided feasibility for the further preparation of separation membranes via a simple suction procedure of their dispersed suspensions in mixed solvents. The nanofiltration based on the uniform square pores under a slightly reduced pressure successfully achieved precise separation of several types of nanoparticles and molecular clusters in wide distribution at a cutting off value as small as 2.2 nm. These results also implied the potential of the present strategy for more separations at a molecular level and very fine nanoscale.