Just over a century ago, Lewis published his seminal work on what became known as the covalent bond, which has since occupied a central role in the theory of making organic molecules. With the advent of covalent organic frameworks (COFs), the chemistry of the covalent bond was extended to two- and three-dimensional frameworks. Here, organic molecules are linked by covalent bonds to yield crystalline, porous COFs from light elements (boron, carbon, nitrogen, oxygen, and silicon) that are characterized by high architectural and chemical robustness. This discovery paved the way for carrying out chemistry on frameworks without losing their porosity or crystallinity, and in turn achieving designed properties in materials. The recent union of the covalent and the mechanical bond in the COF provides the opportunity for making woven structures that incorporate flexibility and dynamics into frameworks.

http://science.sciencemag.org/content/sci/355/6328/eaal1585.full.pdf

The atom, the molecule, and the covalent organic framework

Covalent organic frameworks (COFs) are a class of crystalline porous organic polymers with permanent porosity and highly ordered structures. Unlike other polymers, a significant feature of COFs is that they are structurally predesignable, synthetically controllable, and functionally manageable. In principle, the topological design diagram offers geometric guidance for the structural tiling of extended porous polygons, and the polycondensation reactions provide synthetic ways to construct the predesigned primary and high-order structures. Progress over the past decade in the chemistry of these two aspects undoubtedly established the base of the COF field. By virtue of the availability of organic units and the diversity of topologies and linkages, COFs have emerged as a new field of organic materials that offer a powerful molecular platform for complex structural design and tailor-made functional development. Here we target a comprehensive review of the COF field, provide a historic overview of the chemistry of the COF field, survey the advances in the topology design and synthetic reactions, illustrate the structural features and diversities, scrutinize the development and potential of various functions through elucidating structure-function correlations based on interactions with photons, electrons, holes, spins, ions, and molecules, discuss the key fundamental and challenging issues that need to be addressed, and predict the future directions from chemistry, physics, and materials perspectives.

Covalent Organic Frameworks: Design, Synthesis, and Functions.

Hydrogen fuel is considered as the cleanest renewable resource and the primary alternative to fossil fuels for future energy supply. Sustainable hydrogen generation is the major prerequisite to realize future hydrogen economy. The electrocatalytic hydrogen evolution reaction (HER), as the vital step of water electrolysis to H2 production, has been the subject of extensive study over the past decades. In this comprehensive review, we first summarize the fundamentals of HER and review the recent state-of-the-art advances in the low-cost and high-performance catalysts based on noble and non-noble metals, as well as metal-free HER electrocatalysts. We systemically discuss the insights into the relationship among the catalytic activity, morphology, structure, composition, and synthetic method. Strategies for developing an effective catalyst, including increasing the intrinsic activity of active sites and/or increasing the number of active sites, are summarized and highlighted. Finally, the challenges, perspectives, and research directions of HER electrocatalysis are featured.

Recent Advances in Electrocatalytic Hydrogen Evolution Using Nanoparticles.

Over the past few decades, the design and development of advanced electrocatalysts for efficient energy conversion technologies have been subjects of extensive study. With the discovery of graphene, two-dimensional (2D) nanomaterials have emerged as some of the most promising candidates for heterogeneous electrocatalysts due to their unique physical, chemical, and electronic properties. Here, we review 2D-nanomaterial-based electrocatalysts for selected electrocatalytic processes. We first discuss the unique advances in 2D electrocatalysts based on different compositions and functions followed by specific design principles. Following this overview, we discuss various 2D electrocatalysts for electrocatalytic processes involved in the water cycle, carbon cycle, and nitrogen cycle from their fundamental conception to their functional application. We place a significant emphasis on different engineering strategies for 2D nanomaterials and the influence these strategies have on intrinsic material performance, ...

Emerging Two-Dimensional Nanomaterials for Electrocatalysis

Covalent organic frameworks (COFs) are a class of crystalline porous polymer that allows the atomically precise integration of organic units into extended structures with periodic skeletons and ordered nanopores. One important feature of COFs is that they are designable; that is, the geometry and dimensions of the building blocks can be controlled to direct the topological evolution of structural periodicity. The diversity of building blocks and covalent linkage topology schemes make COFs an emerging materials platform for structural control and functional design. Indeed, COF architectures offer confined molecular spaces for the interplay of photons, excitons, electrons, holes, ions and guest molecules, thereby exhibiting unique properties and functions. In this Review, we summarize the major progress in the field of COFs and recent achievements in developing new design principles and synthetic strategies. We highlight cutting-edge functional designs and identify fundamental issues that need to be addressed in conjunction with future research directions from chemistry, physics and materials perspectives. Covalent organic frameworks are crystalline porous polymers with precisely ordered polygon architectures. In this Review we summarize recent advances in the design principles and synthetic reactions, highlight the current status in structural construction and functionality design, and predict challenging issues and future directions.

Covalent organic frameworks: a materials platform for structural and functional designs

An inkjet pre-treatment fluid for textile printing includes a fixing agent including a multivalent metal cation; and a blocked polyisocyanate selected from the group consisting of a non-ionic blocked polyisocyanate, a cationic blocked polyisocyanate, and an anionic blocked polyisocyanate having an acid number less than 5 mg KOH/g. The inkjet pre-treatment fluid further includes a liquid vehicle.

Inkjet pre-treatment fluid for textile printing

The present disclosure is drawn to an aqueous ink composition, including from 60 wt % to 90 wt % water, from 4 wt % to 30 wt % organic co-solvent, and from 1 wt % to 6 wt % pigment The aqueous ink composition can include a styrene acrylic polymer dispersant associated with a surface of the pigment and having a weight average molecular weight from 1,000 Mw to 50,000 Mw, and from 3 wt % to 15 wt % styrene C3-C5 alkyl (meth)acrylic polymer binder having a weight average molecular weight from 100,000 Mw to 500,000 Mw

Aqueous ink compositions

An example of a dye discharge fluid includes a water-soluble organic solvent, a heat activated reducing agent, and water. A pH of the dye discharge fluid is less than 7. The dye discharge fluid may be used with a colored pigmented inkjet ink, a white pigmented inkjet ink, and/or a colored textile fabric, and may be included in a fluid set and/or a printing kit.

Dye discharge fluid

A fluid set includes a pre-treatment composition, an ink composition, and an overcoat composition. The pre-treatment composition includes a multivalent metal salt and an aqueous vehicle. The ink composition includes a pigment, a polyurethane-based binder, and an aqueous ink vehicle. An overcoat composition includes a blocked polyisocyanate crosslinker and an aqueous overcoat vehicle.

Fluid set for textile printing

A method is presented for direct digital printing on a textile substrate utilizing a two-step pretreatment comprising a plasma pretreatment and a heat pretreatment step followed by inkjet printing on the textile and a final heat treatment step.

Jie Zheng

Papers

Inkjet pre-treatment fluid for textile printing

Aqueous ink compositions

Dye discharge fluid

Fluid set for textile printing

Method for textile printing