Morphology influences the functionality of covalent organic networks and determines potential applications. Here, we report for the first time the use of Zincke reaction to fabricate, under either solvothermal or microwave conditions, a viologen-linked covalent organic network in the form of hollow particles or nanosheets. The synthesized materials are stable in acidic, neutral, and basic aqueous solutions. Under basic conditions, the neutral network assumes radical cationic character without decomposing or changing structure. Solvent polarity and heating method determine product morphology. Depending upon solvent polarity, the resulting polymeric network forms either uniform self-templated hollow spheres (HS) or hollow tubes (HT). The spheres develop via an inside-out Ostwald ripening mechanism. Interestingly, microwave conditions and certain solvent polarities result in the formation of a robust covalent organic gel framework (COGF) that is organized in nanosheets stacked several layers thick. In the gel phase, the nanosheets are crystalline and form honeycomb lattices. The use of the Zincke reaction has previously been limited to the synthesis of small viologen molecules and conjugated viologen oligomers. Its application here expands the repertoire of tools for the fabrication of covalent organic networks (which are usually prepared by dynamic covalent chemistry) and for the synthesis of viologen-based materials. All three materials-HT, HS, and COGF-serve as efficient adsorbents of iodine due to the presence of the cationic viologen linker and, in the cases of HT and HS, permanent porosity.

1 Solar conversion of carbon dioxide and water to value-added chemicals remains a challenge. A 2 number of solar-active catalysts have been reported but still suffer from low selectivity, poor 3 energy efficiency, and instability, and fail to drive simultaneous water oxidation. Herein, we 4 report CuFeO 2 and CuO mixed p-type catalysts fabricated via a widely employed electroplating 5 of earth-abundant cupric and ferric ions followed by annealing under atmospheric air. The 6 composite electrodes exhibited onset potentials at +0.9 V vs. RHE in CO 2 -purged bicarbonate 7 solution and converted CO 2 to formate with over 90% selectivity under simulated solar light (Air 8 Mass 1.5, 100 mW⋅cm −2 ). Wired CuFeO 2 /CuO photocathode and Pt anode couples produced 9 formate over 1 week at a solar-to-formate energy conversion efficiency of ~1% (selectivity 10 >90%) without any external bias while O 2 was evolved from water. Isotope and nuclear magnetic 11 resonance analyses confirmed the simultaneous production of formate and O 2 at the stand-alone 12 couples. Solar CO 2 recycling has received wide attention primarily to address global CO 2 emission and to 1 convert CO 2 and water to value-added chemicals. 1-3 Despite a long research history over the past 2 four decades, 4,5 the technology remains in an early stage, with low CO 2 conversion efficiency 3 and selectivity. CO 2 is highly stable and has limited solubility in water, and its reduction requires 4 multiple proton-coupled electron transfers, resulting in a range of carbon intermediates (C1 -5 C3) 2,6 as well as a larger amount of H 2 over CO 2 conversion products. 7-9 6 For the realization of solar CO 2 recycling, the system of interest should be operated 7 sustainably, which requires the development of not only energy-efficient and cost-effective 8 materials but also stand-alone, complete reaction processes (CO 2 reduction and water oxidation) 9 operating for long periods without any external bias. 10-12 A range of semiconductors (mostly p-10 types) have been studied for CO 2 conversion, including GaP, 4 InP, 5 GaAs, 13 Si, 8,14 Cu 2 O, 15-18 and 11 CuFeO 2 , 19,20 all of which have narrow bandgaps (E g ) and sufficient Fermi levels (E F ) capable of 12 reducing CO 2 . Although promising, these materials inherently require potential biases to drive 13 the CO 2 reduction reaction and compete with other metallic electrodes, 21 whereas complete 14 reactions (CO 2 reduction and water oxidation) have been rarely demonstrated due to large 15 overpotentials. Photocathode-photoanode couples have been demonstrated to operate, 11 yet the 16 syntheses of materials are complicated and the energy conversion efficiency is low (max. 0.14%). 17 We have searched for high-efficiency, low-cost, and scalable p-type materials and found 18 that CuFeO 2 and CuO mixed materials meet all requirements. To our surprise, this material 19 converted CO 2 to formate with selectivity greater than 90% over 1 week and simultaneously 20 produced molecular oxygen via water oxidation when simply ...

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R adioactive iodine (I 2 containing 129 I and/or 131 I) is a volatile solid that, when accidently released as a gas in nuclear power plant explosions, poses a serious threat to the public and the environment. 1−3 If ingested, it can cause acute tissue damage and cancer. A fast and efficient method of its sequestration would be useful as a countermeasure to accidental release, as well as a means to facilitate nuclear waste storage and fuel recycling. Standard methods for I 2 capture rely on inorganic composite adsorbents such as silver-based zeolites and aerogels. 4,5 These materials are chemically and hydrothermally stable but many have low I 2 adsorption capacity due to limited accessible surface area. Consequently, researchers are developing alternative absorbents that have higher I 2 affinity and loading capacity and that cost less. Also, it is important to note that during and after a loss-of-coolant accident at a nuclear power plant, equipment and facilities may be at elevated temperatures, 3 so any new materials designed for I 2 capture must also be thermally stable. 6 Currently, several types of novel adsorbents are being investigated. These include inorganic materials, 7 − 9 crystalline metal−organic frameworks (MOFs), 1,10−13 porous organic frameworks (POFs), 14−18 and porous organic polymers (POPs). 19−22 Inorganic materials often have low I 2 loading capacity, and MOFs tend to be unstable to moisture and water. POFs and POPs, on the other hand, often exhibit high loading capacity for small molecules and are generally stable to moisture and water. Also, their strong covalent bonds afford high thermal and chemical stability, and their constituent light elements add gravimetric advantage. POFs and POPs do, however, occasionally suffer from slow uptake kinetics, so the development of new porous adsorbents in particular organic adsorbents that possess high I 2 loading capacity and that also exhibit fast I 2 uptake kinetics, remains a significant challenge.Recently, we reported the synthesis of a calix[4]arene-based porous covalent polymer and described its use as an efficient adsorbent for water purification. 23 With these positive results and the known advantages of POPs as adsorbents, we decided to design a series of hyper-cross-linked π-bond-rich porous covalent polycalix[4]arenes, CalP2, CalP3, and CalP4, for I 2 adsorption. We enriched the polymers with arenes and alkynes, which are known to endow materials with high surface area 24,25 and high I 2 affinity. 11,26 Furthermore, because the phenols of calix [4]arenes are easily lithiated 27−30 and because alkali metal

The immobilization of molecular switches within materials can give rise to new bulk properties that are useful for a variety of applications.