This review discusses different strategies for the upgrading of biomass into sustainable monomers and building blocks as scaffolds for the preparation of green polymers and materials.
Photoredox catalysis comprising homogeneous transition‐metal‐based systems, organic dyes, and semiconductors, has become a universal tool to catalyze a wide variety of chemical reactions with high ...selectivity and under mild conditions using visible light irradiation. This Minireview summarizes recent progress in photoredox catalysis mediated by heterogeneous carbon nitride materials such as mesoporous graphitic carbon nitride (mpg‐CN), polymeric carbon nitride, and potassium poly(heptazine imides) (K‐PHI). Because of the high thermal, chemical, and photostability of these materials, as well as favorable conduction and valence band positions, carbon nitrides expand the reaction range of photocatalysis to many novel reactions, such as photocatalytic activation of elemental sulfur to furnish a convenient chemical route to organosulfur compounds.
A CN‐do attitude: The metal‐free carbon nitride heterogeneous photocatalysts g‐CN, mpg‐CN, and K‐PHI mediate an array of chemical transformations under visible light that can yield a wide range of organic products (examples pictured). These polymeric materials offer high thermal, chemical, and photostability for photoredox catalysis.
Polymeric graphitic carbon nitride materials (for simplicity: g‐C3N4) have attracted much attention in recent years because of their similarity to graphene. They are composed of C, N, and some minor ...H content only. In contrast to graphenes, g‐C3N4 is a medium‐bandgap semiconductor and in that role an effective photocatalyst and chemical catalyst for a broad variety of reactions. In this Review, we describe the “polymer chemistry” of this structure, how band positions and bandgap can be varied by doping and copolymerization, and how the organic solid can be textured to make it an effective heterogenous catalyst. g‐C3N4 and its modifications have a high thermal and chemical stability and can catalyze a number of “dream reactions”, such as photochemical splitting of water, mild and selective oxidation reactions, and—as a coactive catalytic support—superactive hydrogenation reactions. As carbon nitride is metal‐free as such, it also tolerates functional groups and is therefore suited for multipurpose applications in biomass conversion and sustainable chemistry.
Multipurpose catalyst: Graphitic carbon nitride (g‐C3N4; see SEM image) is an effective (photo)catalyst for a whole series of reactions. This Review describes the synthesis of g‐C3N4, how the band positions and bandgaps can be varied by copolymerization and doping and how changes in the solid‐state structure can improve heterogeneous organocatalyst effectiveness.
Ions transport through confined space with characteristic dimensions comparable to the Debye length has many applications, for example, in water desalination, dialysis, and energy conversion. ...However, existing 2D/3D smart porous membranes for ions transport and further applications are fragile, thermolabile, and/or difficult to scale up, limiting their practical applicability. Now, polymeric carbon nitride alternatively allows the creation of an ultrathin free‐standing carbon nitride membrane (UFSCNM), which can be fabricated by simple CVD polymerization and exhibits excellent nanofluidic ion‐transport properties. The surface‐charge‐governed ion transport also endows such UFSCNMs with the function of converting salinity gradients into electric energy. With advantages of low cost, facile fabrication, and the ease of scale up while supporting high ionic currents, UFSCNM can be considered as an alternative for energy conversion systems and new ionic devices.
An ultrathin free‐standing polymeric carbon nitride membrane (UFSCNM) is fabricated by simple CVD polymerization and exhibits excellent surface‐charge‐governed ion transport properties, which endow UFSCNM with function of salinity gradient energy conversion. With advantage of low cost, facile fabrication, and ease of scaling up to support high ionic currents, UFSCNM should be an alternative for new ionic device designs.
The metal-free, polymeric semiconductor graphitic carbon nitride (g-CN) family is an emerging class of materials and has striking advantages compared to other semiconductors, i.e. ease of tunability, ...low cost and synthesis from abundant precursors in a chemical environment. Efforts have been done to improve the properties of g-CN, such as photocatalytic efficiency, designing novel composites, processability and scalability towards discovering novel applications as a remedy for the problems that we are facing today. Despite the fact that the main efforts to improve g-CN come from a catalysis perspective, many fundamental possibilities arise from the special colloidal properties of carbon nitride particles, from synthesis to applications. This review will display how typical colloid chemistry tools can be employed to make ‘better g-CNs’ and how up to now overseen properties can be levered by integrating a colloid and interface perspective into materials chemistry. Establishing a knowledge on the origins of colloidal behavior of g-CN will be the core of the review.
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•Establishing a colloidal background for carbon nitride science is targeted.•Colloidal aspects of carbon nitride synthesis will be reviewed.•The role of colloid chemistry and interfaces for hybrid formation will be revealed.•Carbon nitride as Pickering stabilizer will be discussed.•Carbon nitride-polymer-colloid relation will be established.
Our technological systems are mainly based on semiconductor photovoltaics, electronic circuits, and (electro)chemical storage reactions. However, in the energy field, “ionics” has the potential to ...complement “electronics.” The control of ion transport is a necessary condition for the existence of life, e.g., both the energy conversion into ATP and the energy consumption to regulate biological functions occurs via directed ion or proton transport. These processes can be mimicked in synthetic devices and (nano)machines and then used for energy harvesting. This review will discuss and summarize the state of the art in the field of ion-transport-based energy conversion systems including ion passive transport for salinity gradient energy conversion and ion active transport for solar energy harvesting and then venture to propose several potential strategies to construct ion transport (passive or active) systems for energy conversion and storage devices, which are useful to drive local chemical reactions or electric current generation.
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Access to sustainable clean energy is one of the key challenges faced by our modern society. Although several sources of clean energy including solar, wind, and water power have been identified and developed, to date, none of these power sources can replace fossil fuels, mainly because of the limited efficiency and high cost of generating and storing electrical power. Nature can perhaps provide a unique perspective for clean energy generation because energy conversion and storage systems in biology work via ion transport and energy storage molecules in an integrative and effective way.
The recent development of ion-transport-based energy conversion systems has attracted more and more attention. The ion passive transport for salinity gradient energy generation has realized power density of approximately 5 W m−2, which has been flagged as the target for making salinity gradient power economically viable. Meanwhile, ion active transport has enough “power” to pump ions against steep concentration gradients up to 5,000-fold and can be used for photoelectric energy conversion. Taking the long view, these ion-transport-based energy-harvesting systems should be considered as a primary method, or at least an efficient supplementary way for clean energy harvesting.
In this review, we mainly focus on ion-transport-based energy conversion. Aiming to get a deeper understanding of ion-transport-based energy conversion systems, the operating mechanisms, including ion selectivity and ion rectification, are discussed first. For the ion passive transport for harvesting salinity gradient energy, the specific features and power density of 1D/2D/3D nanofluidics are summarized. For the ion active transport for solar energy generation, three preliminary approaches and their derived concepts, including pseudo-ion pump/physical ion pump/chemical ion pump, are proposed. Finally, future ion transport energy-harvesting devices, opportunities, and challenges are speculated upon.
Energy conversion and storage systems in biology work via ion transport and energy storage molecules, which provides a unique perspective for designing ion-transport-based energy conversion systems in nanofluidics. In this review, we present an overview of the ion transport in nanofluidics and its application in energy-harvesting systems, including ion passive transport for salinity gradient energy harvesting and ion active transport for direct solar energy conversion. Some predicted, conceptually new, ion-transport-based, integrative devices are also discussed.
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