Graphitic Carbon Nitride as a Distinct Solid Stabilizer for Emulsion Polymerization

A review of biocompatible polymer-functionalized two-dimensional materials: Emerging contenders for biosensors and bioelectronics applications

Bioelectronics, a field pivotal in monitoring and stimulating biological processes, demands innovative nanomaterials as detection platforms. Two-dimensional (2D) materials, with their thin structures and exceptional physicochemical properties, have emerged as critical substances in this research. However, these materials face challenges in biomedical applications due to issues related to their biological compatibility, adaptability, functionality, and nano-bio surface characteristics. This review examines surface modifications using covalent and non-covalent-based polymer-functionalization strategies to overcome these limitations by enhancing the biological compatibility, adaptability, and functionality of 2D nanomaterials. These surface modifications aim to create stable and long-lasting therapeutic effects, significantly paving the way for the practical application of polymer-functionalized 2D materials in biosensors and bioelectronics. The review paper critically summarizes the surface functionalization of 2D nanomaterials with biocompatible polymers, including g-C3N4, graphene family, MXene, BP, MOF, and TMDCs, highlighting their current state, physicochemical structures, synthesis methods, material characteristics, and applications in biosensors and bioelectronics. The paper concludes with a discussion of prospects, challenges, and numerous opportunities in the evolving field of bioelectronics.

Effect of Functional Group Modifications on the Photocatalytic Performance of g-C3 N4

In recent years, photocatalysis has received increasing attention in alleviating energy scarcity and environmental treatment, and graphite carbon nitride (g-C₃ N₄ ) is used as an ideal photocatalyst. However, it still remains numerous challenges to obtain the desirable photocatalytic performance of intrinsic g-C₃ N₄ . Functional group functionalization, formed by introducing functional groups into the bulk structure, is one of the common modification techniques to modulate the carrier dynamics and increases the number of active sites, offering new opportunities to break the limits for structure-to-performance relationship of g-C₃ N₄ . Nevertheless, the general overview of the advance of functional group modification of g-C₃ N₄ is less reported yet. In order to better understand the structure-to-performance relationship at the molecular level, a review of the latest development of functional group modification is urgently needed. In this review, the functional group modification of g-C₃ N₄ in terms of structures, properties, and photocatalytic activity is mainly focused, as well as their mechanism of reaction from the molecular level insights is explained. Second, the recent progress of the application of introducing functional groups in g-C₃ N₄ is introduced and examples are given. Finally, the difficulties and challenges are presented, and based on this, an outlook on the future research development direction is shown.

Pickering emulsions as an alternative to traditional polymers: trends and applications

Pickering emulsions have gained increasing interest because of their unique features, including easy preparation and stability. In contrast to classical emulsions, in Pickering emulsions, the stabilisers are solid micro/nanoparticles that accumulate on the surfaces of liquid phases. In addition to their stability, Pickering emulsions are less toxic and responsive to external stimuli, which make them versatile material that can be flexibly designed for specific applications, e.g., catalysis, pharmaceuticals and new materials. The potential toxicity and adverse impact on the environment of classic emulsions is related to the extractable nature of the water emulsifier. The impacts of some emulsifiers are related to not only their chemical natures but also their stabilities; after base or acid hydrolysis, some emulsifiers can be turned into sulphates and fatty alcohols, which are dangerous to aquatic life. In this paper, recent research on Pickering emulsion preparations is reviewed, with a focus on styrene as one of the main emulsion components. Moreover, the effects of the particle type and morphology and the critical parameters of the emulsion production process on emulsion properties and applications are discussed. Furthermore, the current and prospective applications of Pickering emulsion, such as in lithium-ion batteries and new vaccines, are presented.

Microgels based on 0D-3D carbon materials: Synthetic techniques, properties, applications, and challenges

Microgels are three-dimensional (3D) colloidal hydrogel particles with outstanding features such as biocompatibility, good mechanical properties, tunable sizes from submicrometer to tens of nanometers, and large surface areas. Because of these unique qualities, microgels have been widely used in various applications. Carbon-based materials (CMs) with various dimensions (0-3D) have recently been investigated as promising candidates for the design and fabrication of microgels because of their large surface area, excellent conductivity, unique chemical stability, and low cost. Here, we provide a critical review of the specific characteristics of CMs that are being incorporated into microgels, as well as the state-of-the art applications of CM-microgels in pollutant adsorption and photodegradation, H₂ evoluation, CO₂ capture, soil conditioners, water retention, drug delivery, cell encapsulation, and tissue engineering. Advanced preparation techniques for CM-microgel systems are also summarized and discussed. Finally, challenges related to the low colloidal stability of CM-microgels and development strategies are examined. This review shows that CM-microgels have the potential to be widely used in various practical applications.

Pickering Emulsion Catalysis: Interfacial Chemistry, Catalyst Design, Challenges, and Perspectives

Pickering emulsions are particle-stabilized surfactant-free dispersions composed of two immiscible liquid phases, and emerge as attractive catalysis platform to surpass traditional technique barrier in some cases. In this review, we have comprehensively summarized the development and the catalysis applications of Pickering emulsions since the pioneering work in 2010. The explicit mechanism for Pickering emulsions will be initially discussed and clarified. Then, summarization is given to the design strategy of amphiphilic emulsion catalysts in two categories of intrinsic and extrinsic amphiphilicity. The progress of the unconventional catalytic reactions in Pickering emulsion is further described, especially for the polarity/solubility difference-driven phase segregation, "smart" emulsion reaction system, continuous flow catalysis, and Pickering interfacial biocatalysis. Challenges and future trends for the development of Pickering emulsion catalysis are finally outlined.

Internal Chemiluminescence Light-Driven Photocatalysis

Photocatalysis is a promising strategy to tackle the problem of energy and pollution. To date, it is driven by external physical light sources, which are not always applicable in some practical applications. In this research, we explore the possibility of chemiluminescence as internal light to drive the photocatalysis reaction using graphitic carbon nitride as the catalyst. A biphasic reaction is employed where the light-generating reaction occurs in the oil phase, and the photocatalysis mainly takes place in the aqueous phase. This system exhibits efficient catalytic activity in degradation of rhodamine B, methyl orange, and methylene blue. The proof-of-concept design of chemiluminescence-driven photocatalysis provides an alternative strategy to address environmental issues and other photochemistry reactions.

Pickering emulsions stabilized by metal-organic frameworks, graphitic carbon nitride and graphene oxide

Pickering emulsion is a heterogeneous system consisting of at least two immiscible liquids, which are stabilized by solid particles, in which organic solvent or water is dispersed into other phase in form of micrometre-sized droplets. Compared to traditional emulsions stabilized by surfactant, solids are cheap and can be easily separated and recycled by centrifugation or filtration after use. Moreover, the properties of Pickering emulsions can be adjusted by using different types of solid particles. Up to now, Pickering emulsions have been applied in a wide range of areas such as material science and catalysis. Here we review recent studies on Pickering emulsions stabilized by metal-organic framework, graphitic carbon nitride and graphene oxide.

Molding and Encoding Carbon Nitride-Containing Edible Oil Liquid Objects via Interfacial Toughening in Waterborne Systems

Charge interaction-driven jamming of nanoparticle monolayers at the oil-water interface can be employed as a method to mold liquids into tailored stable 3D liquid objects. Here, 3D liquid objects are fabricated via a combination of biocompatible aqueous poly(vinyl sulfonic acid, sodium salt) solution and a colloidal dispersion of highly fluorescent organo-modified graphitic carbon nitride (g-C₃N₄) in edible sunflower oil. The as-formed liquid object shows stability in a broad pH range, as well as flexible pathways for efficient exchange of molecules at the liquid-liquid interphase, which allows for photodegradation of rhodamine B at the interface via visible light irradiation that also enables an encoding concept. The g-C₃N₄-based liquid objects point toward various applications, for example, all-liquid biphasic photocatalysis, artificial compartmentalized systems, liquid-liquid printing, or bioprinting.

Heterogeneous photocatalytic reversible deactivation radical polymerization

Photocatalytic reversible deactivation radical polymerization (RDRP) permits the use of sustainable solar light for spatiotemporal regulation of radical polymerization under mild conditions.

Colloidal properties of the metal-free semiconductor graphitic carbon nitride

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.

Graphitic Carbon Nitride Stabilizers Meet Microfluidics: From Stable Emulsions to Photoinduced Synthesis of Hollow Polymer Spheres

Graphitic carbon nitride (g-CN) has been utilized as a heterogeneous catalyst, but is usually not very well dispersible. The amphiphilic character of g-CN can be altered by surface modifications of g-CN nanopowders. Introducing hydrophilicity or hydrophobicity is a promising avenue for producing advanced emulsion systems. In this study, a special surface-modified g-CN is used to form stable Pickering emulsions. Using a PDMS-based microfluidic device designed for stable production of both single and double emulsions, it is shown that surface-modified g-CNs allow the manufacture of unconventionally stable and precise Pickering emulsions. Shell thickness of the double emulsions is varied to emphasize the robustness of the device and also to demonstrate the extraordinary stabilization brought by the surface-modified carbon nitride used in this study. Due to the electrostatic stabilization also in the oil phase, double emulsions are centered. Finally, when produced from polymerizable styrene, hollow polymer microparticles are formed with precise and tunable sizes, where g-CN is utilized as the only stabilizer and photoinitiator.

Polymeric Carbon Nitride Armored Centimeter-Wide Organic Droplets in Water for All-Liquid Heterophase Emission Technology

High potential of emission chemistry has been visualized in many fields, from sensors and imaging to displays. In general, conjugated polymers are the top rankers for such chemistry, despite the fact that they bring solubility problems, high expenses, toxicity and demanding synthesis. Metal-free polymeric semiconductor graphitic carbon nitride (g-CN) has been an attractive candidate for visible light-induced photocatalysis, and its emission properties have been optimized and explored recently. Herein, we present modified g-CN nanoparticles as organodispersible conjugated polymer materials to be utilized in a heterophase emission systems. The injection of a g-CN organic dispersion in aqueous polymer solution not only provides retention of the shape by Pickering stabilization of g-CN, but high intensity emission is also obtained. The heterophase all-liquid emission display can be further modified by the addition of simple conjugated organic molecules to the initial g-CN dispersion, which provides a platform for multicolor emission. We believe that such shape-tailored and stabilized liquid-liquid multicolor emission systems are intriguing for sensing, displays and photonics.

Grafting Polymers onto Carbon Nitride via Visible-Light-Induced Photofunctionalization

Metal-free graphitic carbon nitride (g-CN) has attracted significant attention recently due to its multiple applications, such as photocatalysis, energy storage and conversion, and biomaterials, albeit formation of g-CN films is challenging. Herein, a “grafting to” route to graft polymer brushes onto g-CN via visible-light irradiation is described. Afterward, g-CN/polymer films can be obtained through spin coating on glass substrates. As such, the present material provides an improved process toward further application of g-CN in thin films. Moreover, an improved dispersibility in organic solvent was realized after grafting and functional groups (such as epoxides) were introduced to g-CN. Subsequently, the epoxy groups were utilized for further functionalization to adjust the surface polarity.

Visible-light induced emulsion photopolymerization with carbon nitride as a stabilizer and photoinitiator

Graphitic carbon nitride is utilized as a stabilizer and photoinitiator for surfactant-free emulsion polymerization under visible light.

Direct Observation of Carbon Nitride-Stabilized Pickering Emulsions

Pickering emulsions are emulsions stabilized by solid particles located at surfaces/interfaces of liquid droplets that have promising applications for drug delivery and in nanomaterials synthesis. Direct observation of Pickering emulsions can be challenging. Normally, cryoelectron microscopy needs to be used to better understand these types of emulsion systems, but cryofreezing these emulsions may cause them to lose their original morphologies. In this work, we demonstrate that graphitic carbon nitride (g-C₃N₄) can stabilize oil-in-water (o/w) emulsions, with hexane illustrated as a typical oil phase. The g-C₃N₄-stabilized emulsions can act as an excellent platform for in situ study of emulsifying behavior from the mechanical point of view. Owing to its large lateral size and blue, stable fluorescence, the locations and motions of the g-C₃N₄ stabilizer can be finely in situ monitored by light microscopy, fluorescence microscopy, and confocal microscopy. Accordingly, we illustrate two stabilizing configurations of the g-C₃N₄ particles with respect to the emulsion droplets under static conditions. Further, we demonstrate the capability to manipulate emulsion droplets and investigate their response to external forces. We perform real-time observations of the g-C₃N₄ particles and the emulsion droplets that move in the continuous phase and study their adsorption kinetics toward each other. Finally, the π-π interaction between the stabilizer and aromatic liquid phase (e.g., toluene) is considered and studied as an influencing factor on emulsifying behavior.