### Recent Submissions

• #### From Capsule to Helix: Guest-Induced Superstructures of Chiral Macrocycle Crystals

(Journal of the American Chemical Society, American Chemical Society (ACS), 2020-08-01) [Article]
The prediction, control, understanding and elucidation of phase transition from gel to crystal is in high demand for the de-velopment of various functional materials with macroscopic properties. Here, we show a detailed and systematic description of the self-assembly process of enantiopure trianglimine macrocyclic host from gel to single crystals. This proceeds via an unprecedented formation of capsule-like or right-handed helix superstructures as metastable products, depending on the nature of the guest molecule. Mesitylene promotes the formation of capsule-like superstructures; whereas, toluene results in the formation of helices as intermediates during the course of crystallization. Single crystal results demonstrate that the crystals obtained via the direct self-assembly from the gel phase are different from the crystals obtained from the stepwise assembly of the intermediate superstructures. Hence, investigating the phase-transition superstructures that self-assemble through the process of crystallization can unravel new molecular ordering with unexplored host-guest interactions. Such understanding will provide further tools to control hierarchical assemblies at the molecular level and consequently design or dictate the properties of evolved materials.
• #### Room-Temperature Valley Polarization in Atomically Thin Semiconductors via Chalcogenide Alloying

(ACS Nano, American Chemical Society (ACS), 2020-07-31) [Article]
Room-temperature manipulation and processing of information encoded in the electronic valley pseudospin and spin degrees of freedoms lie at the heart of the next technological quantum revolution. In atomically thin layers of transition-metal dichalcogenides (TMDs) with hexagonal lattices, valley-polarized excitations and valley quantum coherence can be generated by simply shining with adequately polarized light. In turn, the polarization states of light can induce topological Hall currents in the absence of an external magnetic field, which underlies the fundamental principle of opto-valleytronics devices. However, demonstration of optical generation of valley polarization at room temperature has remained challenging and not well understood. Here, we demonstrate control of strong valley polarization (valley quantum coherence) at room temperature of up to ∼50% (∼20%) by strategically designing Coulomb forces and spin−orbit interactions in atomically thin TMDs via chalcogenide alloying. We show that tailor making the carrier density and the relative order between optically active (bright) and forbidden (dark) states by key variations on the chalcogenide atom ratio allows full control of valley pseudospin dynamics. Our findings set a comprehensive approach for intrinsic and efficient manipulation of valley pseudospin and spin degree of freedom toward realistic opto-valleytronics devices.
• #### Removal of Organic Micropollutants from Water by Macrocycle-Containing Covalent Polymer Networks.

(Angewandte Chemie (International ed. in English), Wiley, 2020-07-28) [Article]
Access to clean drinking water is a recognized societal need that touches on the health and livelihood of millions of people worldwide. This is providing an incentive to develop new water-treatment technologies. Traditional technologies, while widespread, are usually inefficient at removing organic pollutants from sewage or so-called grey water. Macrocycle-containing covalent polymer networks have begun to attract attention in the context of water treatment owing to the inherent stability provided by the polymer backbones and their ability to capture micropollutant guests as the result of tunable macrocycle-based host-guest interactions. In this minireview, we summarize recent advances (from 2016 to mid-2020) involving the removal of organic micropollutants from water using macrocycle-containing covalent polymer networks. An overview of future challenges within this subfield is also provided.
• #### Tuning the Surface Structure of Polyamide Membranes Using Porous Carbon Nitride Nanoparticles for High-Performance Seawater Desalination

(Membranes, MDPI AG, 2020-07-24) [Article]
Enhancing the water flux while maintaining the high salt rejection of existing reverse osmosis membranes remains a considerable challenge. Herein, we report the use of a porous carbon nitride (C3N4) nanoparticle to potentially improve both the water flux and salt rejection of the state-of-the-art polyamide (PA) thin film composite (TFC) membranes. The organic–organic covalent bonds endowed C3N4 with great compatibility with the PA layer, which positively influenced the customization of interfacial polymerization (IP). Benefitting from the positive effects of C3N4, a more hydrophilic, more crumpled thin film nanocomposite (TFN) membrane with a larger surface area, and an increased cross-linking degree of PA layer was achieved. Moreover, the uniform porous structure of the C3N4 embedded in the ”ridge” sections of the PA layer potentially provided additional water channels. All these factors combined provided unprecedented performance for seawater desalination among all the PA-TFC membranes reported thus far. The water permeance of the optimized TFN membrane is 2.1-folds higher than that of the pristine PA-TFC membrane, while the NaCl rejection increased to 99.5% from 98.0%. Our method provided a promising way to improve the performance of the state-of-art PA-TFC membranes in seawater desalination.
• #### Recent Progress on Microfine Design of Metal-Organic Frameworks: Structure Regulation and Gas Sorption and Separation.

(Advanced materials (Deerfield Beach, Fla.), Wiley, 2020-07-17) [Article]
Metal-organic frameworks (MOFs) have emerged as an important and unique class of functional crystalline hybrid porous materials in the past two decades. Due to their modular structures and adjustable pore system, such distinctive materials have exhibited remarkable prospects in key applications pertaining to adsorption such as gas storage, gas and liquid separations, and trace impurity removal. Evidently, gaining a better understanding of the structure-property relationship offers great potential for the enhancement of a given associated MOF property either by structural adjustments via isoreticular chemistry or by the design and construction of new MOF structures via the practice of reticular chemistry. Correspondingly, the application of isoreticular chemistry paves the way for the microfine design and structure regulation of presented MOFs. Explicitly, the microfine tuning is mainly based on known MOF platforms, focusing on the modification and/or functionalization of a precise part of the MOF structure or pore system, thus providing an effective approach to produce richer pore systems with enhanced performances from a limited number of MOF platforms. Here, the latest progress in this field is highlighted by emphasizing the differences and connections between various methods. Finally, the challenges together with prospects are also discussed.
• #### Quest for Zeolite-like Supramolecular Assemblies: Self-Assembly of Metal-Organic Squares via Directed Hydrogen Bonding.

(Angewandte Chemie (International ed. in English), Wiley, 2020-07-15) [Article]
Our conceived approach based on the directed assembly of functional metal-organic squares (MOSs), 4-membered ring (4MR) building units, permitted the construction of two novel zeolite-like supramolecular assemblies (ZSAs), namely [Co 4 (ImDC) 4 (En) 4 ]·9H 2 O·1.5DMF ( ZSA-10 ) and [Co 4 (ImDC) 4 (En) 4 ]·7H 2 O ( ZSA-11 ) (H 3 ImDC = 4,5-imidazoledicarboxylic acid, En = ethylenediamine, DMF = N,N-dimethylformamide). The elected MOSs encompass both trans - and cis -coordinated nodes, offering complementary peripheral functional groups for their directed assembly into zeolite-like topologies via supramolecular hydrogen bonding interactions. Distinctly, ZSA-10 possesses the underling MER zeolite topology and is the only pure MER framework material (without any supporting templates) exhibiting permanent porosity up to now. ZSA-11 has the underlying ABW topology together with one type of narrow channel.
• #### Quest for an optimal methane hydrates formation in the pores of hydrolytically stable MOFs

(Journal of the American Chemical Society, American Chemical Society (ACS), 2020-07-11) [Article]
Porous MOFs capable of storing relatively high amount of dry methane (CH4) in adsorbed phase are largely explored, however solid CH4 storage in confined pores of MOFs in the form of hydrates is yet to be discovered. Here we report a rational approach to form CH4 hydrates by taking advantage of the optimal pore confinement in relatively narrow cavities of hydrolytically stable MOFs. Unprecedentedly, we were able to isolate methane hydrate (MH) nanocrystals with a sI structure encapsulated inside MOF pores with an optimal cavity dimension. It was found, that confined nanocrystals require cavities slightly larger than the unit cell crystal size of MHs (1.2 nm), as exemplified in the experimental case study performed on Cr-soc-MOF-1 vs smaller cavities of Y-shp-MOF-5. Under these conditions, the excess amount of methane stored in the pores of Cr-soc-MOF-1 in the form of MH was found to be 50% larger than the corresponding dry adsorbed amount at 10 MPa. More importantly, the pressure gradient driving the CH4 storage/delivery process could be drastically reduced compared to the conventional CH4 adsorbed phase storage on the dry Cr-soc-MOF-1 (≤3 MPa vs. 10 MPa)
• #### Topology Meets Reticular Chemistry for Chemical Separations: MOFs as a Case Study

(Chem, Elsevier BV, 2020-07-09) [Article]
Chemical separations are of prime industrial importance; however, they consume a large portion of total industrial energy. Credibly, adsorbent-based separation methods offer the prospective to drastically lessen the energy demand of conventional energy-intensive separation processes. Prominently, a special class of porous materials, namely metal-organic frameworks (MOFs), are reasonably positioned to address various demanding separations in an energy-efficient manner. Out of a myriad of possible topologies for the construction of MOFs, face-transitive nets affording a sole type of window, preferably defined by three- or four-membered rings, can be regarded as ideal blueprints for the construction of MOFs for targeted separations. Intricate separations by MOFs based on some of these topologies are discussed, highlighting the effect of appropriate pore aperture and channel size with prerequisite functional groups on their separation performance. MOFs based on face-transitive nets offer great potential as effective fillers for the construction of practical mixed-matrix membranes (MMMs) with improved separation properties over conventional polymeric membranes.
• #### Trifluoromethanesulfonimide-based hygroscopic semi-interpenetrating polymer network for enhanced proton conductivity of nafion-based proton exchange membranes at low humidity

(Journal of Membrane Science, Elsevier BV, 2020-06-27) [Article]
In this study, a super acid with impressive hygroscopicity, 1-[3-(methacryloyloxy)propylsulfonyl]-1-(triﬂuoromethanesulfonyl)imide (MPTI), is exploited to improve the proton conductivity of PEMs at low humidity. Importantly, MPTI can deliquesce into an aqueous solution by capturing moisture from air at a considerable rate. Investigation of the hygroscopicity of MPTI and the corresponding mechanism by molecular dynamics simulation show a total interaction energy between MPTI and water of −368.13 kJ mol−1, which greatly exceeds those of model derivatives with other typical hygroscopic groups. To apply MPTI in PEMs and prevent leakage, MPTI is incorporated into a semi-interpenetrating polymer network via in situ polymerization, and Nafion-based composite membranes are fabricated. The water uptake of the obtained hybrid membranes is substantially increased by up to 66.61% at 40% RH and 90.04% at 95% RH. This optimization of the water environment facilitates the dissociation of protons and the formation of hydrogen bond networks for high-speed proton conduction. As a result, the proton conductivity of the membranes increases by up to two orders of magnitude at low humidity. Notably, this composite membrane enhanced the performance of a single fuel cell at 60% RH by 41.9%.
• #### Anodic SnO2 porous nanostructures with rich grain boundaries for efficient CO2 electroreduction to formate

(RSC Advances, Royal Society of Chemistry (RSC), 2020-06-16) [Article]
<p>The formate is electrochemical synthesized from a porous anodic SnO$_{2}$ with the faradic efficiency over 70% under low potential.</p>
• #### Long-lasting direct capture of xylene from air using covalent-triazine frameworks through multiple C-H…π weak interactions

(Chemical Engineering Journal, Elsevier BV, 2020-06-16) [Article]
Xylene molecules are a class of volatile organic compounds (VOCs) in the air that are harmful to human health. It is difficult to selectively capture xylenes from the air using existing porous sorbents, due to unspecific and insufficient sorbent/sorbate interactions. We herein report a series of covalent-triazine frameworks (CTFs) that enable selectively capturing of xylene compounds with high adsorption capacities at low pressure. The best-performing CTF material (CTF-2-400), which is comprised of biphenyl and triazine motifs, can adsorb a remarkable amount of o-xylene (358 mg g−1), m-xylene (392 mg g−1) and p-xylene (523 mg g−1) at 25 °C, outperforming most of emerging porous adsorbents. Its ability to capture low-concentration xylenes from the air has been demonstrated using a column breakthrough measurement. The column packed with CTF-2-400 (1 g) continuously captured xylene from the flowing air (~1300 ppm; 10 mL min−1) for 192 h; by contrast, the commercial activated carbon lost its xylene capture capability after only 35 h under the same conditions. We find that the xylene adsorption capacities of the evaluated CTF adsorbents are unrelated to their pore widths or surface areas, and infer that the multiple C-H…π interactions between the CTF framework and xylene molecules account for the observed excellent xylene capture performance.
• #### Selective Electrocatalytic Oxidation of Biomass-Derived 5-Hydroxymethylfurfural to 2,5-Diformylfuran: from Mechanistic Investigations to Catalyst Recovery

(ChemSusChem, Wiley, 2020-06-15) [Article]
The catalytic transformation of bio-derived compounds, specifically 5-hydroxymethylfurfural (HMF), into value-added chemicals may provide sustainable alternatives to crude oil and natural gas-based products. HMF can be obtained from fructose and successfully converted to 2,5-diformylfuran (DFF) by an environmentally friendly organic electrosynthesis performed in an ElectraSyn reactor, using cost-effective and sustainable graphite (anode) and stainless-steel (cathode) electrodes in an undivided cell, eliminating the need for conventional precious metal electrodes. In this work, the electrocatalysis of HMF is performed by using green solvents such as acetonitrile, γ-valerolactone, as well as PolarClean, which is used in electrocatalysis for the first time. The reaction parameters and the synergistic effects of the TEMPO catalyst and 2,6-lutidine base are explored both experimentally and through computation modeling. The molecular design and synthesis of a size-enlarged C 3-symmetric tris-TEMPO catalyst are also performed to facilitate a sustainable reaction work-up through nanofiltration. The obtained performance is then compared with those obtained by heterogeneous TEMPO alternatives recovered by using an external magnetic field and microfiltration. Results show that this new method of electrocatalytic oxidation of HMF to DFF can be achieved with excellent selectivity, good yield, and excellent catalyst recovery.
• #### A Highly Selective Metal-Organic Framework Textile Humidity Sensor

(ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2020-06-09) [Article]
The increase in demand and popularity of smart textiles brings new and innovative ideas to develop a diverse range of textile-based devices for our daily life applications. Smart textile-based sensors (TEX sensors) become attractive due to the potential to replace current solid-state sensor devices with flexible and wearable devices. We have developed a smart textile sensor for humidity detection using a metal-organic framework (MOF) as an active thin-film layer. We show for the first time, the use of the Langmuir-Blodgett (LB) technique for the deposition of a MIL-96(Al) MOF thin film directly onto the fabrics containing interdigitated textile electrodes for the fabrication of a highly selective humidity sensor. The humidity sensors were made from two different types of textiles, namely, linen and cotton, with the linen based sensor giving the best response due to better coverage of MOF. The TEX sensor showed a reproducible response after multiple cycles of measurements. After three weeks of storage, the sensor showed a moderate decrease in response. Moreover, TEX sensors showed a high level of selectivity for the detection of water vapors in the presence of several volatile organic compounds (VOCs). Interestingly, the selectivity is superior to some of the previously reported MOF coated solid-state interdigitated electrode devices and textile sensors. The method herein described is generic and can be extended to other textiles and coating materials for the detection of toxic gases and vapors.
• #### Phenanthroline Covalent Organic Framework Electrodes for High-Performance Zinc-Ion Supercapattery

(ACS Energy Letters, American Chemical Society (ACS), 2020-06-08) [Article]
Aqueous zinc-ion batteries and capacitors are potentially competitive grid-scale energy storage devices because of their great features such as safety, environmental friendliness, and low cost. Herein, a completely new phenanthroline covalent organic framework (PA-COF) was synthesized and introduced in zinc-ion supercapatteries (ZISs) for the first time. Our as-synthesized PA-COF shows a high capacity of 247 mAh g-1 at a current density of 0.1 A g-1, with only 0.38% capacity decay per cycle during 10â€»000 cycles at a current density of 1.0 A g-1. Although covalent organic frameworks (COFs) are attracting great attention in many fields, our PA-COF has been synthesized using a new strategy involving the condensation reaction of hexaketocyclohexanone and 2,3,7,8-phenazinetetramine. Detailed mechanistic investigations, through experimental and theoretical methods, reveal that the phenanthroline functional groups in PA-COF are the active zinc ion storage sites. Furthermore, we provide evidence for the cointercalation of Zn2+ (60%) and H+ (40%) into PA-COF using inductively coupled plasma atomic emission spectroscopy and deuterium solid-state nuclear magnetic resonance (NMR). We believe that this study opens a new avenue for COF material design for zinc-ion storage in aqueous ZISs.
• #### 3D Crumpled Ultrathin 1T MoS2 for Inkjet Printing of Mg-Ion Asymmetric Micro-supercapacitors.

(ACS nano, American Chemical Society (ACS), 2020-06-02) [Article]
Metallic molybdenum disulfide (MoS2), e.g., 1T phase, is touted as a highly promising material for energy storage that already displays a great capacitive performance. However, due to its tendency to aggregate and restack, it remains a formidable challenge to assemble a high-performance electrode without scrambling the intrinsic structure. Here, we report an electrohydrodynamic-assisted fabrication of 3D crumpled MoS2 (c-MoS2) and its formation of an additive-free stable ink for scalable inkjet printing. The 3D c-MoS2 powders exhibited a high concentration of metallic 1T phase and an ultrathin structure. The aggregation-resistant properties of the 3D crumpled particles endow the electrodes with open space for electrolyte ion transport. Importantly, we experimentally discovered and theoretically validated that 3D 1T c-MoS2 enables an extended electrochemical stable working potential range and enhanced capacitive performance in a bivalent magnesium-ion aqueous electrolyte. With reduced graphene oxide (rGO) as the positive electrode material, we inkjet-printed 96 rigid asymmetric micro-supercapacitors (AMSCs) on a 4-in. Si/SiO2 wafer and 100 flexible AMSCs on photo paper. These AMSCs exhibited a wide stable working voltage of 1.75 V and excellent capacitance retention of 96% over 20 000 cycles for a single device. Our work highlights the promise of 3D layered materials as well-dispersed functional materials for large-scale printed flexible energy storage devices.
• #### Enhancement of critical current density in a superconducting NbSe2 step junction.

(Nanoscale, Royal Society of Chemistry (RSC), 2020-06-02) [Article]
We investigate the transport properties of a NbSe2 nanodevice consisting of a thin region, a thick region and a step junction. The superconducting critical current density of each region of the nanodevice has been studied as a function of temperature and magnetic field. We find that the critical current density has similar values for both the thin and thick regions away from the junction, while the critical current density of the thin region of the junction increases to approximately 1.8 times as compared with the values obtained for the other regions. We attribute such an enhancement of critical current density to the vortex pinning at the surface step. Our study verifies the enhancement of the critical current density by the geometrical-type pinning and sheds light on the application of 2D superconductors.
• #### Separation and detection of meta- and ortho- substituted benzene isomers by water-soluble pillar[5]arene

(ChemPlusChem, Wiley, 2020-05-25) [Article]
Efficient and energy-saving separation of benzene isomers bearing a diverse range of functional groups is a great challenge due to their overlapping physicochemical properties. Here, we report a water soluble pillar[5]arene (WP5) that is successfully used as a multifunctional material for the separation and detection of meta/orthosubstituted benzene isomers in water. A liquid-liquid extraction strategy was used for the separation of these benzene isomers based on their different affinity to WP5 in water. The selectivity for the metaover the ortho- isomer for xylenes, chlorotoluene and bromotoluene was 88.6%, 88.3% and 95.0% respectively, in one extraction cycle. Furthermore, a fluorescence indicator system based on WP5 and a fluorescent dye molecule (10-methylacridinium, D) was adopted and exhibited significant fluorescence and optical discrimination upon the addition of MX compared to OX, which implies that a simple “turn-on” detection can be performed prior to engaging in the separation process.
• #### Facile synthesis and gas transport properties of Hünlich's base-derived intrinsically microporous polyimides

(Polymer, Elsevier BV, 2020-05-23) [Article]
Tröger's base (TB) has been utilized as an important building block in designing ladder polymers of intrinsic microporosity (PIMs) and microporous polyimides (PIM-PIs) for membrane-based gas separations due to its unique V-shaped bicyclic structure and versatile molecular chemistry. Nearly a century after its discovery, Hünlich's base (HB) was recently reintroduced as a valuable diamine derivative of TB made by a single-step reaction of 2,4-diaminotoluene and formaldehyde, spurring use in molecular devices such as molecular tweezers and photo-switches. Unlike TB, HB has not been explored as a building block of PIMs and PIM-PIs for membrane-based gas separations. In this study, we synthesized two soluble PIM-PIs for the first time by reaction of HB as diamine and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) or 9,10-diisopropyltriptycene tetracarboxylic dianhydride (TDAi3), respectively. 6FDA-HB exhibited high Brunauer-Teller-Emmett (BET) surface area of 415 m2 g−1 and fractional free volume (FFV) of 0.26. The gas separation performance of the 6FDA-HB polymer was similar to other 6FDA-based dimethyl-substituted Tröger's base polyimide analogues, exhibiting O2, CO2 and H2 permeability of 62, 286, and 391 Barrer with O2/N2, CO2/CH4 and H2/CH4 selectivity of 4.4, 26 and 36, respectively. Compared to 6FDA-HB, the triptycene-containing Hünlich's base polyimide (TDAi3-HB) displayed a higher BET surface area (501 m2 g−1) owing to the presence of the rigid bridged tricyclic triptycene contortion site, resulting in about two-fold increase in O2 permeability to 188 Barrer coupled with slightly compromised O2/N2 selectivity of 4.1. Beside the merit of facile synthesis, the Hünlich's base-derived polyimides experienced relatively modest effects of physical aging on gas permeation properties.
• #### Quantification of sorption, diffusion, and plasticization properties of cellulose triacetate films under mixed-gas CO2/CH4 environment

(Journal of Membrane Science, Elsevier BV, 2020-05-23) [Article]
Membrane technology is employed in large-scale removal of acid gases from natural gas, and cellulose acetate is by far the most adopted material for this application. Because of its utmost industrial relevance, we analyzed the gas sorption behavior of CO2–CH4 mixtures in cellulose triacetate (CTA) at 35 °C. CO2 solubility in CTA was only slightly affected by the presence of methane, whereas competition effects sharply reduced CH4 uptake. Regardless of mixture concentration, CO2 vs. CH4 solubility coefficients regressed linearly, which translated in solubility selectivities that increased as equilibrium pressures increased. Specifically, compared to other relevant glassy polymer membrane materials, CTA positioned very close to the solubility selectivity upper bound at infinite dilution and demonstrated the highest affinity to CO2 at all investigated pressures. The experimental solubility and permeability data were used in the framework of the solution-diffusion theory to determine pure- and mixed-gas concentration averaged diffusion coefficients of CTA. CO2 diffusion was essentially unaffected by mixture effects, whereas methane diffusivity was boosted by the CO2-induced plasticization of CTA. The ratio between the pure- and mixed-gas concentration averaged diffusion coefficients of methane was used to quantify the effect of plasticization on the mixed-gas performance of CTA and other relevant membrane materials previously analyzed in similar experimental studies. When we further extended this comparison in a mixed-gas diffusion analysis (at 10 atm partial pressure), we observed that CTA had lower diffusion selectivity due to an inferior size-sieving capability than a reference material, 6FDA-mPDA polyimide, but displayed superior solubility selectivity.
• #### Functional Supramolecular Polymeric Networks: The Marriage of Covalent Polymers and Macrocycle-Based Host–Guest Interactions

(Chemical Reviews, American Chemical Society (ACS), 2020-05-19) [Article]
Covalent polymers connected by non-covalent interactions constitute a fascinating set of materials known as supramolecular polymer networks (SPNs). A key feature of SPNs is that the underlying covalent polymers endow the resulting self-assembled materials with features, such as structural and mechanical integrity, good processability, recyclability, stimuli-responsiveness, self-healing, and shape memory, that are not recapitulated in the case of classic covalent polymer systems. The unique nature of SPNs derives from the controlled marriage of traditional covalent polymers and macrocycle-based host–guest interactions. As a consequence, supramolecular polymeric networks have played important roles in a number of diverse fields, including polymer science, supramolecular chemistry, materials science, biomedical materials, and information storage technology. In this Review, we summarize advances made in the area of functional SPNs, with a focus on original literature reports appearing in the past five years. The treatment is organized according to the key macrocycle-based host–guest interactions used to produce various SPNs. The role of the underlying polymer backbones is also discussed.