Palladium nanoparticles anchored on amphiphilic Janus-type cellulose nanocrystals for Pickering interfacial catalysis

Amphiphilic Janus Particles for Aerobic Alcohol Oxidation in Oil Foams

Amphiphilic Janus silica particles, tunable with oleophobic-oleophilic properties and low fluorine content (8 wt % F), exhibited prominent foamability for a variety of aromatic alcohols at low particle concentrations (<1 wt %) compared to randomly functionalized silica particles. When selectively loaded with Pd nanoparticles on the oleophilic hemisphere, the particles displayed more than a 2-fold increase in catalytic activity for the aerobic oxidation of benzyl alcohol compared to nonfoam bulk catalysis under ambient O2 pressure. The particles were conveniently recycled with high foamability and catalytic activity maintained for at least five consecutive runs.

Accelerated full-thickness skin wound tissue regeneration by self-crosslinked chitosan hydrogel films reinforced by oxidized CNC-AgNPs stabilized Pickering emulsion for quercetin delivery

BACKGROUND

The non-toxic self-crosslinked hydrogel films designed from biocompatible materials allow for controlled drug release and have gathered remarkable attention from healthcare professionals as wound dressing materials. Thus, in the current study the chitosan (CS) film is infused with oil-in-water Pickering emulsion (PE) loaded with bioactive compound quercetin (Qu) and stabilized by dialdehyde cellulose nanocrystal-silver nanoparticles (DCNC-AgNPs). The DCNC-AgNPs play a dual role in stabilizing PE and are involved in the self-crosslinking with CS films. Also, this film could combine the advantage of the controlled release and synergistic wound-healing effect of Qu and AgNPs.

RESULTS

The DCNC-AgNPs were synthesized using sodium periodate oxidation of CNC. The DCNC-AgNPs were used to stabilize oil-in-water PE loaded with Qu in its oil phase by high speed homogenization. Stable PEs were prepared by 20% v/v oil: water ratio with maximum encapsulation of Qu in the oil phase. The Qu-loaded PE was then added to CS solution (50% v/v) to prepare self-crosslinked films (CS-PE-Qu). After grafting CS films with PE, the surface and cross-sectional SEM images show an inter-penetrated network within the matrix between DCNC and CS due to the formation of a Schiff base bond between the reactive aldehyde groups of DCNC-AgNPs and amino groups of CS. Further, the addition of glycerol influenced the extensibility, swelling ratio, and drug release of the films. The fabricated CS-PE-Qu films were analyzed for their wound healing and tissue regeneration potential using cell scratch assay and full-thickness excisional skin wound model in mice. The as-fabricated CS-PE-Qu films showed great biocompatibility, increased HaCat cell migration, and promoted collagen synthesis in HDFa cells. In addition, the CS-PE-Qu films exhibited non-hemolysis and improved wound closure rate in mice compared to CS, CS-Qu, and CS-blank PE. The H&E staining of the wounded skin tissue indicated the wounded tissue regeneration in CS-PE-Qu films treated mice.

CONCLUSION

Results obtained here confirm the wound healing benefits of CS-PE-Qu films and project them as promising biocompatible material and well suited for full-thickness wound healing in clinical applications.

Enhanced Biphasic Reactions in Amphiphilic Silica Mesopores

In this study, we investigated the effect of the pore volume and mesopore size of surface-active catalytic organosilicas on the genesis of particle-stabilized (Pickering) emulsions for the dodecanal/ethylene glycol system and their reactivity for the acid-catalyzed biphasic acetalization reaction. To this aim, we functionalized a series of fumed silica superparticles (size 100-300 nm) displaying an average mesopore size in the range of 11-14 nm and variable mesopore volume, with a similar surface density of octyl and propylsulfonic acid groups. The modified silica superparticles were characterized in detail using different techniques, including acid-base titration, thermogravimetric analysis, TEM, and dynamic light scattering. The pore volume of the particles impacts their self-assembly and coverage at the dodecanal/ethylene glycol (DA/EG) interface. This affects the stability and the average droplet size of emulsions and conditions of the available interfacial surface area for reaction. The maximum DA-EG productivity is observed for A200 super-SiNPs with a pore volume of 0.39 cm3·g-1 with an interfacial coverage by particles lower than 1 (i.e., submonolayer). Using dissipative particle dynamics and all-atom grand canonical Monte Carlo simulations, we unveil a stabilizing role of the pore volume of porous silica superparticles for generating emulsions and local micromixing of immiscible dodecanal and ethylene glycol, allowing fast and efficient solvent-free acetalization in the presence of Pickering emulsions. The micromixing level is interrelated to the adsorption energy of self-assembled particles at the DA/EG interface.

Janus Composite Particles and Interfacial Catalysis Thereby

Janus composite particles (JPs) with distinct compartmentalization of varied components thus performances and anisotropic shape display a variety of properties and have demonstrated great potentials in diversify practical applications. Especially, the catalytic JPs are advantageous for multi-phase catalysis with much easier separation of products and recycling the catalysts. In the first section of this review, typical methods to synthesize the JPs with varied morphologies are briefly surveyed in the category of polymeric, inorganic and polymer/inorganic composite. In the main section, recent progresses of the JPs in emulsion interfacial catalysis are summarized covering organic synthesis, hydrogenation, dye degradation, and environmental chemistry. The review will end by calling more efforts toward precision synthesis of catalytic JPs at large scale to meet the stringent requirements in practical applications such as catalytic diagnosis and therapy by the functional JPs.

High Internal Phase Pickering Emulsion Stabilized by Lipase-Coated ZIF-8 Nanoparticles towards Recyclable Biphasic Biocatalyst

High internal phase Pickering emulsion (Pickering HIPE) stabilized by enzyme-decorated metal-organic frameworks (MOFs) nanoparticles is developed for biphasic biocatalysts to enhance lipase catalysis and recycling. Specifically, enzyme decorated nanoparticles are prepared via ZIF-8 physisorption of a model lipase Candida antarctica Lipase B (CALB), named ZIF-8@CALB, to be both Pickering stabilizer and catalytic sites. An oil-in-water (o/w) Pickering HIPE with oil/water volume ratio of 3 could then be fabricated by homogenizing p-nitrophenyl palmitate (p-NPP) n-heptane solution into the ZIF-8@CALB aqueous dispersion. The biocatalytic hydrolysis of p-NPP is conducted by just standing the biphasic system at room temperature. The Pickering HIPE system achieves a product conversion of up to 48.9% within 0.5 h, whereas the p-NPP n-heptane solution system containing free CALB only achieves a stable product conversion of 6.8% for the same time. Moreover, the ZIF@CALB could be recovered by a simple centrifugation at 800 rpm, and then reused in the next cycle. The hydrolysis equilibrium conversion rate of p-NPP keeps over 40% for all 8 cycles, reflecting the high catalytic efficiency and recyclability of the Pickering HIPE. This study provides a new opportunity in designing Enzyme-MOFs-based Pickering interfacial biocatalyst for practical applications.

Natural Amphiphilic Shellac Nanoparticle-Stabilized Novel Pickering Emulsions with Droplets and Bi-continuous Structures

Shellac is a natural amphiphilic substance, and its nanoparticles can be used to stabilize Pickering emulsions with droplets and bi-continuous structures. In this study, shellac nanoparticles (SNPs) were produced through the anti-solvent method, and these SNPs were used to produce a series of Pickering emulsions. Fourier transform infrared results showed that SNPs were generated through hydrogen bonding and hydrophobic effects. The contact angle of SNPs was 122.3°, indicating that hydrophobicity was their dominant characteristic. According to the results of confocal laser scanning microscopy, the Pickering emulsions stabilized by SNPs showed oil-in-water, bi-continuous structure, and water-in-oil characteristics, which were dependent on the oil-phase content. The resistance value of the emulsified part of these Pickering emulsion systems significantly increased at an oil-phase ratio of 80-90% (more than 10⁵ MΩ), as compared with the 10-70% oil-phase content (around 1 MΩ). The viscosity of SNP-stabilized Pickering emulsions with bi-continuous structures was highest at 40% oil-phase content. The porous material prepared by using Pickering emulsions with bi-continuous structures as a template had an interconnected structure and was able to absorb both water and oil. This study indicated that these amphiphilic SNPs readily form bi-continuous structures and effectively stabilize Pickering emulsions with droplets. These SNPs are expected to have increased application in food and pharmaceutical industries.

Naturally Derived Janus Cellulose Nanomaterials: Anisotropic Cellulose Nanomaterial Building Blocks and Their Assembly into Asymmetric Structures

Naturally derived cellulose nanomaterials (CNMs) with desirable physicochemical properties have drawn tremendous attention for their versatile applications in a broad range of fields. More recently, Janus amphiphilic cellulose nanomaterial particles with asymmetric structures (i.e., reducing and nonreducing ends and crystalline and amorphous domains) have been in the spotlight, offering a rich and sophisticated toolbox for Janus nanomaterials. With careful surface and interfacial engineering, Janus CNM particles have demonstrated great potential as surface modifiers, emulsifiers, stabilizers, compatibilizers, and dispersants in emulsions, nanocomposites, and suspensions. Naturally derived Janus CNM particles offer a fascinating opportunity for scaling up the production of self-standing Janus CNM membranes. Nevertheless, most Janus CNM membranes to date are constructed by asymmetric fabrication or asymmetric modification without considering the Janus traits of CNM particles. More future research should focus on the self-assembly of Janus CNM particles into bulk self-standing Janus CNM membranes to enable more straightforward and sustainable approaches for Janus membranes. This review explores the fabrication, structure-property relationship, and Janus configuration mechanisms of Janus CNM particles and membranes. Janus CNM membranes are highlighted for their versatile applications in liquid, thermal, and light management. This review also highlights the significant advances and future perspectives in the construction and application of sustainable Janus CNM particles and membranes.

Task-Specific Janus Materials in Heterogeneous Catalysis

Janus materials are anisotropic nano- and microarchitectures with two different faces consisting of distinguishable or opposite physicochemical properties. In parallel with the discovery of new methods for the fabrication of these materials, decisive progress has been made in their application, for example, in biological science, catalysis, pharmaceuticals, and, more recently, in battery technology. This Minireview systematically covers recent and significant achievements in the application of task-specific Janus nanomaterials as heterogeneous catalysts in various types of chemical reactions, including reduction, oxidative desulfurization and dye degradation, asymmetric catalysis, biomass transformation, cascade reactions, oxidation, transition-metal-catalyzed cross-coupling reactions, electro- and photocatalytic reactions, as well as gas-phase reactions. Finally, an outlook on possible future applications is given.

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.

Janus particles: A review of their applications in food and medicine

In contrast to conventional particles that have isotropic surfaces, Janus ("two-faced") particles have anisotropic surfaces, which leads to novel physicochemical properties and functional attributes. Janus particles with differing compositions, structures, and functional attributes have been prepared using a variety of fabrication methods. Depending on their composition, Janus particles have been classified as inorganic, polymeric, or polymeric/inorganic types. Recently, there has been growing interest in preparing Janus particles from biological macromolecules to meet the demand for a more sustainable and environmentally friendly food and pharmaceutical supply. At interfaces, Janus particles exhibit the characteristics of both surfactants and Pickering stabilizers, and so their behavior can be described using adsorption theories developed to describe these surface-active substances. Research has highlighted several potential applications of Janus particles in food and medicine, including emulsion formation and stabilization, toxin detection, antimicrobial activity, drug delivery, and medical imaging. Nevertheless, further research is needed to design and fabricate Janus particles that are suitable as functional ingredients in the food and biomedicine industries.

Wood-Sourced Polymers as Support for Catalysis by Group 10 Transition Metals

Despite providing interesting solutions to reduce the number of synthetic steps, to decrease energy consumption or to generate less waste, therefore contributing to a more sustainable way of producing important chemicals, the expansion of the use of homogeneous catalysis in industrial processes is hampered by several drawbacks. One of the most important is the difficulty to recycle the noble metals generating potential high costs and pollution of the synthesized products by metal traces detrimental to their applications. Supporting the metals on abundant and cheap biosourced polymers has recently appeared as an almost ideal solution: They are much easier to recover from the reaction medium and usually maintain high catalytic activity. The present bibliographical review focuses on the development of catalysts based on group 10 transition metals (nickel, palladium, platinum) supported on biopolymers obtained from wood, such as cellulose, hemicellulose, lignin, and their derivatives. The applications of these catalysts in organic synthesis or depollution are also addressed in this review with examples of C-C couplings, oxidation, or hydrogenation reactions.

Janus bifunctional periodic mesoporous organosilica

Synthesis of a Janus periodic mesoporous organosilica material (JPMO) is presented here. In this strategy, the surface of the hollow silica material was selectively functionalized with two different bridged organic-inorganic hybrid groups. It was found that the resulting bifunctional material is able to form a stable Pickering emulsion. This new type of PMO material may be suitable for widespread applications in various fields related to material science and catalysis.

Multiphase Microreactors Based on Liquid-Liquid and Gas-Liquid Dispersions Stabilized by Colloidal Catalytic Particles

Pickering emulsions, foams, bubbles, and marbles are dispersions of two immiscible liquids or of a liquid and a gas stabilized by surface‐active colloidal particles. These systems can be used for engineering liquid–liquid–solid and gas–liquid–solid microreactors for multiphase reactions. They constitute original platforms for reengineering multiphase reactors towards a higher degree of sustainability. This Review provides a systematic overview on the recent progress of liquid–liquid and gas–liquid dispersions stabilized by solid particles as microreactors for engineering eco‐efficient reactions, with emphasis on biobased reagents. Physicochemical driving parameters, challenges, and strategies to (de)stabilize dispersions for product recovery/catalyst recycling are discussed. Advanced concepts such as cascade and continuous flow reactions, compartmentalization of incompatible reagents, and multiscale computational methods for accelerating particle discovery are also addressed.

Stabilizing Triglyceride in Methanol Emulsions via a Magnetic Pickering Interfacial Catalyst for Efficient Transesterification under Static Conditions

Pickering emulsion systems provide potential platforms for simultaneously intensifying and catalyzing transesterification between triglyceride and methanol under static conditions. However, realizing static transesterification with high biodiesel yield is still challenging due to low emulsion stability at the reaction temperature. Here, a series of magnetically recyclable Pickering interfacial catalysts (PICs) with similar surface affinities but different densities were constructed as stabilizers of a soybean oil/methanol emulsion. The variations in the emulsion volume fraction and droplet size were comparatively studied and analyzed from the viewpoint of droplet settling and catalyst particle shedding. It is found that, except for surface affinity, PIC density also plays a pivotal role in emulsion stability owing to the non-negligible effect of gravity on catalyst adsorption in triglyceride/methanol emulsion (especially at elevated temperature). By reducing the density, finely improving the lipophilicity, and optimizing the addition amount of PIC, the obtained soybean oil/methanol emulsion can remain stable for at least 12 h at 60 °C, enabling static transesterification with a high biodiesel yield of 95.6%. Moreover, the best performing PIC can be reused for at least 7 cycles. This efficient static transesterification system offers a green strategy for biodiesel production.

Catalysis in Pickering emulsions

Particle-stabilised or Pickering emulsions are versatile systems. In the past 10 years a new application has emerged in the field of catalysis to use them as vehicles to carry out catalytic reactions, allowing a more environmentally friendly process with high conversions and selectivities and important advantages for catalyst recovery. As the area has advanced rapidly, the intention of this review is to summarize the latest innovations being reported. An overview is given regarding the kinds of liquid phases comprising the emulsion system, the different types of solid particle stabilizers (whether they contain catalyst or not) and the catalytic reactions studied. A section describing methods for recovering the catalyst is also included, in which various stimuli are discussed. Finally, the importance of using Pickering emulsions to carry out reactions in flow and in multi-step cascade systems is highlighted with various examples to support the benefits of transferring this technology to industrial processes.