Metal–organic frameworks (MOFs) have emerged as particularly exciting inorganic–organic hybrid porous materials which can be simply self-assembled from their corresponding inorganic metal ions/clusters with organic linkers. MOFs can combine the inherent physical and chemical properties of both inorganic and organic photonic units due to their inorganic–organic hybrid nature. Furthermore, the pores within MOFs can also be utilized to encapsulate a large number of guest species as photonic units. The vast combination possibilities, synergistic effects, as well as controllable and ordered arrangements of multiple photonic units (MPUs) have distinguished MOFs from other inorganic and organic photonic materials and enabled them to be a promising platform to realize novel photonic functional applications. In this review, we summarize the recent and important progress in the design and construction of photonic MOFs, as well as their various applications in luminescence sensing, white-light emission, photocatalysis, nonlinear optics, lasing devices, data storage, and biomedicine. In addition, we highlight the construction strategy and the synergistic effects of MOFs towards achieving high performance and novel photonic functions. Finally, we also outline the challenges in these fields and put forward the prospects and directions for future development.

Photonic functional metal-organic frameworks.

Covalent organic frameworks (COFs) are an emerging class of functional nanostructures with intriguing properties, due to their unprecedented combination of high crystallinity, tunable pore size, large surface area, and unique molecular architecture. The range of properties characterized in COFs has rapidly expanded to include those of interest for numerous applications ranging from energy to environment. Here, a background overview is provided, consisting of a brief introduction of porous materials and the design feature of COFs. Then, recent advancements of COFs as a designer platform for a plethora of applications are emphasized together with discussions about the strategies and principles involved. Finally, challenges remaining for this type material for real applications are outlined.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/advs.201801410

Opportunities of Covalent Organic Frameworks for Advanced Applications

Uranium is a key element in the nuclear industry, but its unintended leakage has caused health and environmental concerns. Here we report a sp2 carbon-conjugated fluorescent covalent organic framework (COF) named TFPT-BTAN-AO with excellent chemical, thermal and radiation stability is synthesized by integrating triazine-based building blocks with amidoxime-substituted linkers. TFPT-BTAN-AO shows an exceptional UO22+ adsorption capacity of 427 mg g−1 attributable to the abundant selective uranium-binding groups on the highly accessible pore walls of open 1D channels. In addition, it has an ultra-fast response time (2 s) and an ultra-low detection limit of 6.7 nM UO22+ suitable for on-site and real-time monitoring of UO22+, allowing not only extraction but also monitoring the quality of the extracted water. This study demonstrates great potential of fluorescent COFs for radionuclide detection and extraction. By rational designing target ligands, this strategy can be extended to the detection and extraction of other contaminants. Porous materials for uranium capture have been developed in the past, but materials for simultaneous uranium capture and detection are scarce. Here the authors develop a stable covalent organic framework capable of adsorbing and detecting uranyl ions.

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Regenerable and stable sp 2 carbon-conjugated covalent organic frameworks for selective detection and extraction of uranium

The design and synthesis of uranium sorbent materials with high uptake efficiency, capacity and selectivity, as well as excellent hydrolytic stability and radiation resistance remains a challenge. Herein, a polyoxometalate (POM)-organic framework material (SCU-19) with a rare inclined polycatenation structure was designed, synthesized through a solvothermal method, and tested for uranium separation. Under dark conditions, SCU-19 can efficiently capture uranium through ligand complexation using its exposed oxo atoms and partial chemical reduction from UVI to UIV by the low-valent Mo atoms in the POM. An additional UVI photocatalytic reduction mechanism can occur under visible light irradiation, leading to a higher uranium removal without saturation and faster sorption kinetics. SCU-19 is the only uranium sorbent material with three distinct sorption mechanisms, as further demonstrated by X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES) analysis.

Three Mechanisms in One Material: Uranium Capture by a Polyoxometalate–Organic Framework through Combined Complexation, Chemical Reduction, and Photocatalytic Reduction

Uranium is the main element for nuclear energy production and is one of the most hazardous radionuclides; its effective enrichment plays a key role in energy strategy and environmental safety. Oxime-functionalized nanostructures are the most promising candidates for uranium adsorption. However, current methods for their preparation mainly focus on multistep grafting and oximation processes, and the nanostructures usually show low efficiency. Here, we report a rapid one-step process to synthesize salicylaldoxime/polydopamine modified reduced graphene oxide (RGO-PDA/oxime) via the polymerization of dopamine (DA) and simultaneous deposition of oxime with an obviously decreased total synthesis time of 2 h. The obtained maximum uranium adsorption capacity of up to 1049 mg g−1 was 3–16 times larger than those of the reported single PDA or oxime modified nanostructures. The RGO-PDA/oxime followed the pseudo-second-order kinetics model and Langmuir isotherm equation with much higher adsorption selectivity and recyclability. The outstanding sorption performance is attributed to the electrostatic repulsion between GO and salicylaldoxime and the effective combination between PDA and oxime molecules. Finally, given the adhesion capability of DA to diverse surfaces, this rapid one-step method was used to prepare five other oxime/PDA modified materials, which also showed improved uranium adsorption efficiency. These findings provide a way to obtain oxime-functionalized nanostructures with promising uranium adsorption efficiency.

Highly efficient uranium adsorption by salicylaldoxime/polydopamine graphene oxide nanocomposites

Nature can efficiently recognize specific ions by exerting second-sphere interactions onto well-folded protein scaffolds. However, a considerable challenge remains to artificially manipulate such affinity, while being cost-effective in managing immense amounts of water samples. Here, we propose an effective approach to regulate uranyl capture performance by creating bio-inspired nano-traps, illustrated by constructing chelating moieties into porous frameworks, where the binding motif’s coordinative interaction towards uranyl is enhanced by introducing an assistant group, reminiscent of biological systems. Representatively, the porous framework bearing 2-aminobenzamidoxime is exceptional in sequestering high uranium concentrations with sufficient capacities (530 mg g−1) and trace quantities, including uranium in real seawater (4.36 mg g−1, triple the benchmark). Using a combination of spectroscopic, crystallographic, and theory calculation studies, it is revealed that the amino substituent assists in lowering the charge on uranyl in the complex and serves as a hydrogen bond acceptor, boosting the overall uranyl affinity of amidoxime. Uranium extraction is important for both uranium recovery and nuclear waste management. Here, inspired by the high sensitivity of proteins towards specific metal ions, Ma and colleagues demonstrate that introducing secondary coordination spheres into amidoxime-functionalized porous polymers can enhance their uranyl chelating abilities.

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Bio-inspired nano-traps for uranium extraction from seawater and recovery from nuclear waste

Preorganization is a basic design principle used by nature that allows for synergistic pathways to be expressed. Herein, a full account of the conceptual and experimental development from randomly distributed functionalities to a convergent arrangement that facilitates cooperative binding is given, thus conferring exceptional affinity toward the analyte of interest. The resulting material with chelating groups populated adjacently in a spatially locked manner displays up to two orders of magnitude improvement compared to a random and isolated manner using uranium sequestration as a model application. This adsorbent shows exceptional extraction efficiencies, capable of reducing the uranium concentration from 5 ppm to less than 1 ppb within 10 min, even though the system is permeated with high concentrations of competing ions. The efficiency is further supported by its ability to extract uranium from seawater with an uptake capability of 5.01 mg g-1, placing it among the highest-capacity seawater uranium extraction materials described to date. The concept presented here uncovers a new paradigm in the design of efficient sorbent materials by manipulating the spatial distribution to amplify the cooperation of functions.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/advs.202001573

Spatial Engineering Direct Cooperativity between Binding Sites for Uranium Sequestration.

The paper presents the properties of nanostructured dry dandelion extract and its application for the production of yoghurt, ice cream and marmalade. The data on self-organization and the size of nanostructured dry extract of dandelion using the NTA method are presented.

Aleksandr S. Ivanov

Papers

Bio-inspired nano-traps for uranium extraction from seawater and recovery from nuclear waste

Spatial Engineering Direct Cooperativity between Binding Sites for Uranium Sequestration.

Nanostructured dry extract of dandelion: properties and applications in the production of functional food