Sustainable Continuous Flow Valorization of γ-Valerolactone with Trioxane to α-Methylene-γ-Valerolactone over Basic Beta Zeolites

Graphitic Carbon Nitride Enters the Scene: A Promising Versatile Tool for Biomedical Applications

Graphitic carbon nitride (g-C3N4), since the pioneering work on visible-light photocatalytic water splitting in 2009, has emerged as a highly promising advanced material for environmental and energetic applications, including photocatalytic degradation of pollutants, photocatalytic hydrogen generation, and carbon dioxide reduction. Due to its distinctive two-dimensional structure, excellent chemical stability, and distinctive optical and electrical properties, g-C3N4 has garnered a considerable amount of interest in the field of biomedicine in recent years. This review focuses on the fundamental properties of g-C3N4, highlighting the synthesis and modification strategies associated with the interfacial structures of g-C3N4-based materials, including heterojunction, band gap engineering, doping, and nanocomposite hybridization. Furthermore, the biomedical applications of these materials in various domains, including biosensors, antimicrobial applications, and photocatalytic degradation of medical pollutants, are also described with the objective of spotlighting the unique advantages of g-C3N4. A summary of the challenges faced and future prospects for the advancement of g-C3N4-based materials is presented, and it is hoped that this review will inspire readers to seek further new applications for this material in biomedical and other fields.

Turning Polyethylene Waste to Hydrocarbons Using a Sustainable Acidic Carbocatalyst

Careless release of plastic waste is a pressing problem for marine and other eco-environments, and materials recycling of this stream is an open problem. For this purpose, a new metal-free acidic carbocatalyst with 8 wt % sulfur is constructed from a side product of the paper industry namely Na-lignosulfonate. The catalyst shows an extraordinary performance for the fragmentation of polymer waste which smoothly occurs above the ceiling temperature of the polymers. The reaction is run without hydrogen and at ambient pressure with commercially available high-density polyethylene (HDPE) as well as a real polymer waste mixture of high and low-density polyethylene (HDPE, LDPE). In all cases, a homologous series of n-alkanes and n-alkenes are obtained. The unique sulfur-rich carbonaceous structure (transfer hydrogenation functionality) and the metal-free character of the acidic carbocatalyst makes it inert against many typical catalyst poisons, among them water, salt, polar functionalities, and sulfur species. The described performance in plastic recycling, as well as the low cost and large-scale availability of lignosulfonate from the pulp industry, makes this metal-free acidic carbocatalyst promising for real-life environmental applications.

Biodegradable polycarbonates from lignocellulose based 4-pentenoic acid and carbon dioxide

The production of biodegradable polycarbonate by copolymerizing CO₂ with epoxides has emerged as an effective method to utilize CO₂ in response to growing concerns about CO₂ emissions and plastic pollution. Previous studies have mainly focused on the preparation of CO₂-based polycarbonates from petrochemical-derived propylene oxide (PO) or cyclohexene oxide (CHO). However, to reduce dependence on fossil fuels, the development of 100% bio-based polymers has gained attention in polymer synthesis. Herein, we reported the synthesis of glycidyl 4-pentenoate (GPA) from lignocellulose based 4-pentenoic acid (4-PA), which was further copolymerized with CO₂ using a binary catalyst SalenCoCl/PPNCl to produce bio-based polycarbonates with vinyl side chains and molecular weights up to 17.1 kg/mol. Introducing a third monomer, PO, allows for the synthesis of the GPA/PO/CO₂ terpolymer, and the glass transition temperature (T _g) of the terpolymer can be adjusted from 2°C to 19°C by controlling the molar feeding ratio of GPA to PO from 7:3 to 3:7. Additionally, post-modification of the vinyl side chains enables the production of functional polycarbonates, providing a novel approach to the preparation of bio-based materials with diverse side chains and functions.

Thermal Stability for the Continuous Production of γ-Valerolactone from the Hydrogenation of N-Butyl Levulinate in a CSTR

γ-valerolactone can be a game-changer in the chemical industry because it could substitute fossil feedstocks in different fields. Its production is from the hydrogenation of levulinic acid or alkyl levulinates and can present some risk of thermal runaway. To the best of our knowledge, no studies evaluate the thermal stability of this production in a continuous reactor. We simulated the thermal behavior of the hydrogenation of butyl levulinate over Ru/C in a continuous stirred-tank reactor and performed a sensitivity analysis. The kinetic and thermodynamic constants from Wang et al.’s articles were used. We found that the risk of thermal stability is low for this chemical system.

Sustainable Sorbitol Dehydration to Isosorbide using Solid Acid Catalysts: Transition from Batch Reactor to Continuous-Flow System

Isosorbide is one of the most interesting cellulosic-derived molecules with great potential to be implemented in wide range of products that shaping our daily life. This Review describes the recent developments in the production of isosorbide from sorbitol in batch and continuous-flow systems under hydrothermal conditions using solid acid catalysts. Moreover, the current hurdles and challenges regarding the synthesis of isosorbide from cellulosic biomass in continuous-flow process using solid acid catalysts are summarized, as well as the scaling-up of this process into pilot level, which will lead to an established industrial process with high sustainability metrics.

Designing Sites in Heterogeneous Catalysis: Are We Reaching Selectivities Competitive With Those of Homogeneous Catalysts?

A critical review of different prominent nanotechnologies adapted to catalysis is provided, with focus on how they contribute to the improvement of selectivity in heterogeneous catalysis. Ways to modify catalytic sites range from the use of the reversible or irreversible adsorption of molecular modifiers to the immobilization or tethering of homogeneous catalysts and the development of well-defined catalytic sites on solid surfaces. The latter covers methods for the dispersion of single-atom sites within solid supports as well as the use of complex nanostructures, and it includes the post-modification of materials via processes such as silylation and atomic layer deposition. All these methodologies exhibit both advantages and limitations, but all offer new avenues for the design of catalysts for specific applications. Because of the high cost of most nanotechnologies and the fact that the resulting materials may exhibit limited thermal or chemical stability, they may be best aimed at improving the selective synthesis of high value-added chemicals, to be incorporated in organic synthesis schemes, but other applications are being explored as well to address problems in energy production, for instance, and to design greener chemical processes. The details of each of these approaches are discussed, and representative examples are provided. We conclude with some general remarks on the future of this field.

Falling Leaves Return to Their Roots: A Review on the Preparation of γ-Valerolactone from Lignocellulose and Its Application in the Conversion of Lignocellulose

γ-Valerolactone (GVL), derived from renewable lignocellulosic biomass, has been considered as a cost-competitive and green platform chemical. With the increasingly prominent environmental problems, a deep understanding of the preparation and transformation of GVL is highly needed. Based on the latest progress made with GVL, preparation and applications of GVL are summarized and discussed in this Review. In particular, the state-of-the-art in catalytic production of GVL is described based on the use of noble-metal and non-noble-metal catalysts. The application of GVL for the valorization of lignocellulose would improve the yield of target products such as sugar monomers and furfural. Thus, GVL can be produced from lignocellulose and simultaneously it can also be used for the valorization of lignocellulose, just as in the sustainable and renewable cycle, "the falling leaves returns to their roots". This Review is expected to provide valuable reference and new proposal for the further development and better utilization of GVL.

New (and Old) Monomers from Biorefineries to Make Polymer Chemistry More Sustainable

This opinion article describes recent approaches to use the "biorefinery" concept to lower the carbon footprint of typical mass polymers, by replacing parts of the fossil monomers with similar or even the same monomer made from regrowing dendritic biomass. Herein, the new and green catalytic synthetic routes are for lactic acid (LA), isosorbide (IS), 2,5-furandicarboxylic acid (FDCA), and p-xylene (pXL). Furthermore, the synthesis of two unconventional lignocellulosic biomass derivable monomers, i.e., α-methylene-γ-valerolactone (MeGVL) and levoglucosenol (LG), are presented. All those have the potential to enter in a cost-effective way, also the mass market and thereby recover lost areas for polymer materials. The differences of catalytic unit operations of the biorefinery are also discussed and the challenges that must be addressed along the synthesis path of each monomers.

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.

Polymer grafted graphitic carbon nitrides as precursors for reinforced lubricant hydrogels

Carbon nitride-based hydrogels are formed in a two-step procedure and feature significant toughness, compressibility and lubricant properties.