Continuous and scalable synthesis of a porous organic cage by twin screw extrusion (TSE)

A general large-scale synthesis approach for crystalline porous materials

Crystalline porous materials such as covalent organic frameworks (COFs), metal-organic frameworks (MOFs) and porous organic cages (POCs) have been widely applied in various fields with outstanding performances. However, the lack of general and effective methodology for large-scale production limits their further industrial applications. In this work, we developed a general approach comprising high pressure homogenization (HPH), which can realize large-scale synthesis of crystalline porous materials including COFs, MOFs, and POCs under benign conditions. This universal strategy, as illustrated in the proof of principle studies, has prepared 4 COFs, 4 MOFs, and 2 POCs. It can circumvent some drawbacks of existing approaches including low yield, high energy consumption, low efficiency, weak mass/thermal transfer, tedious procedures, poor reproducibility, and high cost. On the basis of this approach, an industrial homogenizer can produce 0.96 ~ 580.48 ton of high-performance COFs, MOFs, and POCs per day, which is unachievable via other methods.

Tribochemical nanolithography: selective mechanochemical removal of photocleavable nitrophenyl protecting groups with 23 nm resolution at speeds of up to 1 mm s-1

We describe the mechanochemical regulation of a reaction that would otherwise be considered to be photochemical, via a simple process that yields nm spatial resolution. An atomic force microscope (AFM) probe is used to remove photocleavable nitrophenyl protecting groups from alkylsilane films at loads too small for mechanical wear, thus enabling nanoscale differentiation of chemical reactivity. Feature sizes of 20-50 nm are achieved repeatably and controllably at writing rates up to 1 mm s^-1. Line widths vary monotonically with the load up to 2000 nN. To demonstrate the capacity for sophisticated surface functionalisation provided by this strategy, we show that functionalization of nanolines with nitrilo triacetic acid enables site-specific immobilization of histidine-tagged green fluorescent protein. Density functional theory (DFT) calculations reveal that the key energetic barrier in the photo-deprotection reaction of the nitrophenyl protecting group is excitation of a π-π* transition (3.1 eV) via an intramolecular charge-transfer mechanism. Under modest loading, compression of the adsorbate layer causes a decrease in the N-N separation, with the effect that this energy barrier can be reduced to as little as 1.2 eV. Thus, deprotection becomes possible via either absorption of visible photons or phononic excitation transfer, facilitating fast nanolithography with a very small feature size.

Spiers Memorial Lecture: Mechanochemistry, tribochemistry, mechanical alloying - retrospect, achievements and challenges

The paper presents a view on the achievements, challenges and prospects of mechanochemistry. The extensive reference list can serve as a good entry point to a plethora of mechanochemical literature.

Processing Poly (ethylene terephthalate) Waste into Functional Carbon Materials by Mechanochemical Extrusion

With the plastic pollution becoming worse, the upcycling of plastic waste into functional materials is a great challenge. Herein, a mechanochemical extrusion approach was developed for processing poly(ethylene terephthalate) (PET) waste into porous carbon materials. The essence of the cyclic extrusion approach lies in the solvent-free mixing of thermoplastic PET with pore-directing additive (e. g., silica or zinc chloride) at the molecular level. PET waste could be upcycled into functional carbon with high surface area (up to 1001 m²  g^-1 ), specific shapes, and preferred mechanical strength, after cyclic extrusion and carbonization. Moreover, metal species could be well dispersed onto porous carbons through solvent-free extrusion, different from traditional loading methods (impregnation method, deposition-precipitation method). In this manner, mechanochemical extrusion provides an alternative for upcycling plastic waste into value-added materials.

Mechanochemistry: New Tools to Navigate the Uncharted Territory of "Impossible" Reactions

Mechanochemical transformations have made chemists enter unknown territories, forcing a different chemistry perspective. While questioning or revisiting familiar concepts belonging to solution chemistry, mechanochemistry has broken new ground, especially in the panorama of organic synthesis. Not only does it foster new "thinking outside the box", but it also has opened new reaction paths, allowing to overcome the weaknesses of traditional chemistry exactly where the use of well-established solution-based methodologies rules out progress. In this Review, the reader is introduced to an intriguing research subject not yet fully explored and waiting for improved understanding. Indeed, the study is mainly focused on organic transformations that, although impossible in solution, become possible under mechanochemical processing conditions, simultaneously entailing innovation and expanding the chemical space.

Fast, solvent-free synthesis of Ferrocene-containing Organic Cages via dynamic covalent chemistry in the solid state

A simple, solvent-free synthetic protocol towards the synthesis of organic self-assembled macromolecules has been established. By employing mechanochemistry using glassware readily available to every organic chemist, we were able to...

Enabling Technology for Supramolecular Chemistry

Supramolecular materials-materials that exploit non-covalent interactions-are increasing in structural complexity, selectivity, function, stability, and scalability, but their use in applications has been comparatively limited. In this Minireview, we summarize the opportunities presented by enabling technology-flow chemistry, high-throughput screening, and automation-to wield greater control over the processes in supramolecular chemistry and accelerate the discovery and use of self-assembled systems. Finally, we give an outlook for how these tools could transform the future of the field.

Polymeric Fiber Sorbents Embedded with Porous Organic Cages

The synthesis and functionalization of porous organic cages (POCs) for separation have attracted growing interest over the past decade. However, the potential of solid-phase POCs for practical, large-scale separations will require incorporation into appropriate gas-solid or liquid-solid contactors. Contactors with more effective mass transfer properties and lower pressure drops than pelletized systems are preferred. Here, we prepared and characterized fiber sorbents with POCs throughout a cellulose acetate (CA) polymer matrix, which were then deployed in model separations. The POC CC3 was shown to be stable after exposure to spinning solvents, as confirmed by NMR, powder X-ray diffraction, and gas sorption experiments. CC3-CA fibers were spun using the dry-jet wet-quench spinning method. Spun fibers retained the adsorptive properties of CC3 powders, as confirmed by CO₂ and N₂ physisorption and TGA, reaching upward of 60 wt % adsorbent loading, whereas the pelletized CC3 counterparts suffered significant losses in textural properties. The separation capabilities of the CC3-CA fibers are tested with both simulated postcombustion flue gas and with Xe/Kr mixtures. Fixed bed breakthrough experiments performed on fibers samples show that CC3 embedded in polymeric fibers can effectively perform these proof-of-concept gas separations. The development of fiber sorbents embedded with POCs provides an alternative to traditional pelletization for the incorporation of these materials into adsorptive separation systems.

SO2 Capture Using Porous Organic Cages

We report the first experimental investigation of porous organic cages (POCs) for the demanding challenge of SO2 capture. Three structurally related N-containing cage molecular materials were studied. An imine-functionalized POC (CC3) showed modest and reversible SO2 capture, while a secondary-amine POC (RCC3) exhibited high but irreversible SO2 capture. A tertiary amine POC (6FT-RCC3) demonstrated very high SO2 capture (13.78 mmol g-1 ; 16.4 SO2 molecules per cage) combined with excellent reversibility for at least 50 adsorption-desorption cycles. The adsorption behavior was investigated by FTIR spectroscopy, 13 C CP-MAS NMR experiments, and computational calculations.

Tribochemistry, Mechanical Alloying, Mechanochemistry: What is in a Name?

Over the decades, the application of mechanical force to influence chemical reactions has been called by various names: mechanochemistry, tribochemistry, mechanical alloying, to name but a few. The evolution of these terms has largely mirrored the understanding of the field. But what is meant by these terms, why have they evolved, and does it really matter how a process is called? Which parameters should be defined to describe unambiguously the experimental conditions such that others can reproduce the results, or to allow a meaningful comparison between processes explored under different conditions? Can the information on the process be encoded in a clear, concise, and self-explanatory way? We address these questions in this Opinion contribution, which we hope will spark timely and constructive discussion across the international mechanochemical community.

Sustainability Assessment of Mechanochemistry by Using the Twelve Principles of Green Chemistry

In recent years, mechanochemistry has been growing into a widely accepted alternative for chemical synthesis. In addition to their efficiency and practicality, mechanochemical reactions are also recognized for their sustainability. The association between mechanochemistry and Green Chemistry often originates from the solvent-free nature of most mechanochemical protocols, which can reduce waste production. However, mechanochemistry satisfies more than one of the Principles of Green Chemistry. In this Review we will present a series of examples that will clearly illustrate how mechanochemistry can significantly contribute to the fulfillment of Green Chemistry in a more holistic manner.

Mechanochemistry for sustainable and efficient dehydrogenation/hydrogenation

Hydrogenation and dehydrogenation reactions are one of the pillars of the chemical industry, with applications from bulk chemicals to pharmaceuticals manufacturing. The ability to selectively add hydrogen across double and (or) triple bonds is key in the chemist’s toolbox and the enabling component in the development of sustainable processes. Traditional solution-based approaches to these reactions are tainted by significant consumption of energy and production of solvent waste. This review highlights the development and applications of recently emerged solvent-free approaches to conduct the hydrogenation of organic molecules using mechanochemistry, i.e., chemical transformations induced or sustained by mechanical force. In particular, we will show mechanochemical techniques such as ball-milling enabled catalytic or stoichiometric metal-mediated hydrogenation and dehydrogenation reactions that are simple, fast, and conducted under significantly milder conditions compared with traditional solution routes. Importantly, we highlight the current challenges and opportunities in this field, while also identifying exciting cases in which mechanochemical hydrogenation strategies lead to new, unique targets and reactivity.

Highly Efficient Solid-State Hydrolysis of Waste Polyethylene Terephthalate by Mechanochemical Milling and Vapor-Assisted Aging

Despite significant methodological and technological advancements in chemical recycling of synthetic polymers, an efficient and quantitative conversion of post-consumer polyethylene terephthalate (PET) into terephthalic acid (TPA) under ambient conditions of temperature and pressure still remains a challenge. In this respect, the application of mechanochemistry and multiple advantages offered by solid-state ball milling and vapor-assisted aging have remained insufficiently explored. To further expand their potential, the implementation of organic solvent-free milling as a superior methodology for successful alkaline depolymerization of waste PET (e. g., bottles and textile) into TPA monomer in near-quantitative yields was reported herein. The solid-state alkaline PET hydrolysis was also shown to proceed in excellent yields under aging conditions in humid environment or in the presence of alcohol vapors. Moreover, the performance of mechanochemical ball milling and aging in the gram-scale depolymerization of PET into TPA was demonstrated.

Mechanochemical methods for the transfer of electrons and exchange of ions: inorganic reactivity from nanoparticles to organometallics

For inorganic metathesis and reduction reactivity, mechanochemistry is demonstrating great promise towards both nanoparticles and organometallics syntheses.

High-Throughput Approaches for the Discovery of Supramolecular Organic Cages

The assembly of complex molecules, such as organic cages, can be achieved through supramolecular and dynamic covalent strategies. Their use in a range of applications has been demonstrated, including gas uptake, molecular separations, and in catalysis. However, the targeted design and synthesis of new species for particular applications is challenging, particularly as the systems become more complex. High-throughput computation-only and experiment-only approaches have been developed to streamline the discovery process, although are still not widely implemented. Additionally, combined hybrid workflows can dramatically accelerate the discovery process and lead to the serendipitous discovery and rationalisation of new supramolecular assemblies that would not have been designed based on intuition alone. This Minireview focuses on the advances in high-throughput approaches that have been developed and applied in the discovery of supramolecular organic cages.