Catalytic Emulsion Research Articles

Surface Engineering of Biochar Toward Simultaneously Generating Superamphiphilicity and Catalytic Activity for Strengthening Pickering Interfacial Catalysis.

Multifunctional carbon materials have revealed distinctive features and excellent performance in the field of catalysis. However, the facile fabrication of bifunctional carbon materials with special wettability and catalytic activity remains a grand challenge in Pickering emulsion catalysis. Herein, we reported one-step construction of bifunctional biochar with superamphiphilicity and catalytic activity directly from the thermolysis of sawdust and 1-butyl-3-methylimidazolium tetrafluoroborate for enhancing the oxidation of benzyl alcohol in Pickering emulsion. Co-doping of B and F enhanced the hydrophilicity of biochar, and the oleophilicity of biochar was kept simultaneously. Conversion became 4 times using bifunctional biochar compared with blank results during the oxidation of benzyl alcohol. More interestingly, the turnover frequency (TOF) value using bifunctional biochar enhanced 61 % than that employing N-doped superamphiphilic carbon without catalytic activity. Catalytic activities of bifunctional biochar could be ascribed to the existence of different chemical bonds containing the element B. This work paves a path toward rational design of bifunctional biochar materials with special wettability and catalytic activity for greatly enhancing the liquid-liquid biphasic reaction efficiencies.

Demulsification of Pickering Emulsions by Chemical Dissolution of Stabilizers.

Demulsification of particle-stabilized oil-in-water emulsions is crucial in diverse fields such as treatment of produce water, recovery of valuable products of Pickering emulsion catalysis, and so on. In this work, we investigated a facile method for destabilizing emulsions by dissolving stabilizer particles by the introduction of acid or base. Nanoellipsoidal hematite-stabilized decane-in-water emulsions are destabilized by dissolving hematite with oxalic or hydrochloric acid in situ. Time required for complete demulsification decreased as the acid concentration is increased. The demulsification time is typically on the order of a few hours for the chosen protocol. Similarly, the silica-stabilized decane-water emulsion is demulsified by the addition of aqueous sodium hydroxide. Demulsification kinetics is presented as the temporal change of the emulsion volume with time. Emulsion volume decreases in two stages: an initial slow decrease followed by an exponential decrease. Scanning electron microscopy analysis shows that the stabilizing particles are completely dissolved and recrystallized as salts of respective kinds. An estimate of the desorption free energy suggests that particle size should be reduced to a few nanometers for inducing destabilization. This work describes a facile method to destabilize oil-in-water emulsion, and it can be generalized to any other particle-stabilized emulsions by choosing appropriate chemical reagent for dissolution.

Revolutionizing water treatment: Enhanced flux and selectivity in polyethersulfone mixed matrix membrane through magnetic CuO-functionalized Fe3O4 nanoparticles for synthetic oily produced water remediation

In this research, we present a novel CuO@Fe3O4/PES nanocomposite membrane designed to address the complex challenge of separating oil from synthetic oily produced water. This exceptional membrane demonstrates remarkable separation capabilities, achieving an impressive oil rejection rate of 97.5 % and an exceptionally high permeate flux of 0.095 L/m2·h, surpassing traditional pure PES membranes. Our dedicated efforts to optimize membrane efficiency involved a thorough exploration of critical parameters. The peak performance was unequivocally achieved with a solution dosage of 60 mL, a solution concentration of 60 mg·L−1, and a pump pressure of 1.5 bar, ensuring comprehensive optimization. Moreover, contact angle measurements revealed significantly improved hydrophilicity of the CuO@Fe3O4/PES membrane compared to the PES blank membrane. Additionally, SEM, XRD, and FTIR analyses provided valuable insights into the composition, morphology, and properties of the membrane. The outstanding performance of the membrane is attributed to the incorporation of CuO@Fe3O4 nanoparticles, which enhance surface area, permeability, mechanical strength, and catalytic emulsion decomposition. This innovative approach holds great promise for applications in treating oily produced water across diverse industries.

Amphiphilic Covalent Organic Framework Nanoparticles for Pickering Emulsion Catalysis with Size Selectivity

AbstractExploiting advanced amphiphilic solid catalysts is crucial to the development of Pickering emulsion catalysis. Herein, covalent organic framework (COF) nanoparticles constructed with highly hydrophobic monomers as linkers were found to show superior amphiphilicity and they were then developed as a new class of solid emulsifiers for Pickering emulsion catalysis. Employing amphiphilic COFs as solid emulsifiers, Pickering emulsions with controllable emulsion type and droplet sizes were obtained. COF materials have also been demonstrated to serve as porous surface coatings to replace traditional surface modifications for stabilizing Pickering emulsions. After implanting Pd nanoparticles into amphiphilic COFs, the obtained catalyst displayed a 3.9 times higher catalytic efficiency than traditional amphiphilic solid catalysts with surface modifications in the biphasic oxidation reaction of alcohols. Such an enhanced activity was resulted from the high surface area and regular porous structure of COFs. More importantly, because of their tunable pore diameters, Pickering emulsion catalysis with remarkable size selectivity was achieved. This work is the first example that COFs were applied in Pickering emulsion catalysis, providing a platform for exploring new frontiers of Pickering emulsion catalysis.

Amphiphilic Covalent Organic Framework Nanoparticles for Pickering Emulsion Catalysis with Size Selectivity.

Exploiting advanced amphiphilic solid catalysts is crucial to the development of Pickering emulsion catalysis. Herein, covalent organic framework (COF) nanoparticles constructed with highly hydrophobic monomers as linkers were found to show superior amphiphilicity and they were then developed as a new class of solid emulsifiers for Pickering emulsion catalysis. Employing amphiphilic COFs as solid emulsifiers, Pickering emulsions with controllable emulsion type and droplet sizes were obtained. COF materials have also been demonstrated to serve as porous surface coatings to replace traditional surface modifications for stabilizing Pickering emulsions. After implanting Pd nanoparticles into amphiphilic COFs, the obtained catalyst displayed a 3.9 times higher catalytic efficiency than traditional amphiphilic solid catalysts with surface modifications in the biphasic oxidation reaction of alcohols. Such an enhanced activity was resulted from the high surface area and regular porous structure of COFs. More importantly, because of their tunable pore diameters, Pickering emulsion catalysis with remarkable size selectivity was achieved. This work is the first example that COFs were applied in Pickering emulsion catalysis, providing a platform for exploring new frontiers of Pickering emulsion catalysis.

Harboring organocatalysts in a star-shaped block copolymer for micellar catalysis and emulsion catalysis

Conducting an asymmetric aldol reaction in both micelles and emulsions with high interfacial reactivity and stereoselectivity is achieved by incorporating an organocatalyst in the inherently hydrophobic center of a star-shaped polymer.

Pd NP-loaded covalent organic framework for pH-switched Pickering emulsion catalytic dechlorination.

Quinoline carboxylic acid-linked and Pd nanoparticle (NP)-loaded COF nanospheres were constructed via a three-component one-pot Doebner reaction and post-synthetic metalation. The obtained Pd@DhaTAPB-COOH solid stabilizer can greatly promote the pH-switched recyclable Pickering interfacial dechlorination reaction, which sheds light on the bright future of smart Pickering emulsion catalysis.

Reversible Emulsions from Polyoxometalate-Polymer: A Robust Strategy to Cyclic Emulsion Catalysis and High-Internal-Phase Emulsion Materials.

Reversible Pickering emulsions, achieved by switchable, interfacially active colloidal particles, that enable on-demand emulsification/demulsification or phase inversion, hold substantial promise for biphasic catalysis, emulsion polymerization, cutting fluids, and crude oil pipeline transportation. However, particles with such a responsive behavior usually require complex chemical syntheses and surface modifications, limiting their extensive use. Herein, we report a simple route to generate emulsions that can be controlled and reversibly undergo phase inversion. The emulsions are prepared and stabilized by the interfacial assembly of polyoxometalate (POM)-polymer, where their electrostatic interaction at the interface is dynamic. The wettability of the POMs that dictates the emulsion type can be readily regulated by tuning the number of polymer chains bound to POMs, which, in turn, can be controlled by varying the concentrations of both components and the water/oil ratio. In addition, the number of polymer chains anchored to the POMs can be varied by controlling the number of negative charges on the POMs through an in situ redox reaction. As such, a reversible inversion of the emulsions can be triggered by switching between exposure to ultraviolet light and the introduction of oxygen. Combining the functions of POM itself, a cyclic interfacial catalysis system was realized. Inversion of the emulsion also affords a pathway to high-internal-phase emulsions. The diversity of the POMs, the polymers, and the responsive switching groups open numerous new, simple strategies for designing a wide range of responsive soft matter for cargo loading, controlled release, and delivery in biomedical and engineering applications without time-consuming particle syntheses.

Super-amphiphilic graphene promotes peroxymonosulfate-based emulsion catalysis for efficient oil purification.

Oil fractions containing highly toxic and hazardous organic contaminants can not only cause severe environmental disasters, but also an undesired waste of resources. Given the exceptional performance of persulfates in the removal of persistent and refractory organic pollutants from aqueous media, herein, a peroxymonosulfate-based Pickering emulsion catalytic (PPEC) system was constructed for the hazardous oil purification, using super-amphiphilic graphene as a solid emulsifier and a heterogeneous catalyst simultaneously. Combined detailed instrumental analysis with theoretical calculations, we find that the incorporation of pyridinic N and its oxide significantly facilitated the formation of super-amphiphilic graphene and successfully induced the formation of Pickering emulsion. In addition to stabilizing the PPEC system, super-amphiphilic graphene can also achieve efficient removal of Sudan III (simulated lipophilic organic pollutant) by activating peroxymonosulfate (PMS) to generate •O2- and 1O2. Results showed that 80mg/L Sudan III (20mL) could be fully degraded within 30min using 10mL 5mmol PMS. More significantly, our proposed PPEC system also exhibited excellent property in the purification of practical waste engine oil. This study provides new insights into the purification and recovery of waste oil.

Renewable pickering emulsion system based on bifunctional materials for highly efficient fuel oil desulfurization without stirring

The mass transfer resistance atliquid (oil)-liquid (extractant)interface seriouslylimits the reaction rate and desulfurization efficiency in extraction-catalytic oxidative desulfurization (ECODS), and the catalyst is difficult to be recycled in the homogeneous system. Herein, we demonstrated a renewable Pickering emulsion system with enlarged interfacial contact area to overcome the mass transfer resistance. The bifunctional materials were designed based on Janus graphene oxide (GO) 2D-sheets, amino-modified SBA-15 (NH2-SBA-15) mesoporous microspheres and H3PW12O40 (HPW), as both catalysts and emulsion stabilizers to establish the catalytic emulsion system. Excellent amphiphilicity was endowed by the anisotropic Janus structure of prepared materials, which could convert the oil/extractant bi-phase into a stable Pickering emulsion. The interfacial contact area was skillfully enlarged in emulsion due to formed micro emulsion droplets and empty channels between the droplets, and the catalyst could be easily recycled by centrifugation. Besides, the unique properties of catalyst including large specific surface area, adequate exposed catalytic active sites and high pore volume could also shorten the reaction path and facilitate the rapid diffusion of reactants and products. This opens the door to the application of Pickering emulsion in ECODS fields based on the design of bifunctional materials.

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.

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

AbstractPickering 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.

Preparation of Janus nanosheets composed of gold/palladium nanoparticles and reduced graphene oxide for highly efficient emulsion catalysis

Interface/emulsion catalysis is an effective approach for many organic and inorganic chemical reactions. Positioning catalysts at the interface is essential for highly efficient interface/emulsion catalysis. The sheet-like Janus nanostructures may have great advantages in stabilizing emulsions and improving reaction efficiency. In this work, by using a simple emulsion reaction and photodeposition, we successfully prepare the Janus nanosheets with opposite sides composed of AuNPs/PdNPs and reduced graphene oxide (rGO) respectively, referred to as AuNP-rGO/PdNP-rGO Janus nanosheets. Due to the distinct hydrophilicities on opposite sides, the prepared Janus nanosheets demonstrate high efficiency in emulsion stabilization and emulsion catalysis. By introducing the prepared PdNP-rGO and AuNP-rGO Janus nanosheets in emulsion reactions, highly efficient hydrogenation of p-nitroanisole and photocatalytic degradation of Nile red are demonstrated. This work provides a simple and cost-effective method to prepare Janus nanosheets and realize highly efficient emulsion reactions, and this strategy can be extended to promote many other interface/emulsion reactions.

Construction of Polymer-Decorated Fe3O4@Catechol-formaldehyde Resin Amphiphilic Janus Nanospheres for Catalytic Applications

Janus particles are widely used as multifunctional materials for catalytic reactions due to their controllable asymmetry and stability efficiency of the interface structure. Herein, we propose a simple approach to design an amphiphilic “hairy” Janus nanocatalyst, which is composed of Fe3O4@catechol-formaldehyde resin (CFR) core–shell microspheres with different hydrophilic–hydrophobic polymer chains grafted on opposite sides of the microsphere and the catalytically active metal particles directly supported on the hydrophilic polymer chains. Amphiphilic Janus nanospheres (200–300 nm) with hydrophilic poly (N-isopropylacrylamide) (PNIPAM) and hydrophobic polystyrene (PSt) chains are synthesized by Pickering emulsion and mussel-inspired methods, followed by in situ reduction of Pd nanoparticles (Pd NPs) loaded onto the hydrophilic polymer chain side to form a Janus-structured Pd@PNIPAM-S-Fe3O4@CFR-S-PSt nanocatalyst. The amphiphilic Janus nanospheres have a good effect on the stability of the emulsion. Due to its special structural composition, the constructed Janus nanocatalyst exhibits excellent catalytic reduction performance for dyes and nitroaromatic compounds in both water and emulsion phases. Because of the existence of Fe3O4, the catalyst is easy to be separated and recovered, which augments the catalytic reaction cycle. In addition, the presence of temperature-sensitive PNIPAM polymer chains also enables the Janus nanocatalyst to display controllable temperature-responsive behaviors in stabilizing emulsions and emulsion catalysis. The as-prepared Janus nanomaterials with a variety of functions and properties possess potential for application in catalysis and biological and environmental areas.

Magnetically recyclable HPW@ mSiO2/hydrophobic GO with adjustable polarity used for oxidative desulfurization in Pickering emulsion

A series of amphiphilic particles were prepared using Janus graphene oxide (GO) and magnetic SiO2-NH2 (mSiO2-NH2) as starting materials. Then, H3PW12O40 (HPW) was supported on the particles through the interaction between surface amino groups and HPW to obtain catalytic emulsion stabilizers for oxidative desulfurization. The characterization analysis showed that the prepared materials exhibited the sheet structure of GO which was connected by several core–shell microspheres of mSiO2 on one side, and the other side of the materials was grafted by carbon chains to increase hydrophobicity. The catalytic performance of prepared materials increased with the grafted carbon chain length, and the one grafted by hexadecylamine had the best performance with a final desulfurization ratio of 99.21%. That was because it had the most appropriate amphipathy, which can convert the bi-phase system into a stable Pickering emulsion with enlarged contact area between oil and extractant, thus largely promoting mass transfer even without stirring. With the excellent magnetism, the catalytic emulsion stabilizers can be magnetically separated to realize the emulsion breaking, thus easily recycling the catalyst and value-added reaction products after reaction.

Super-Amphiphilic Graphene Promotes Peroxymonosulfate-Based Emulsion Catalysis for Efficient Oil Purification

Super-Amphiphilic Graphene Promotes Peroxymonosulfate-Based Emulsion Catalysis for Efficient Oil Purification

Fabrication of Superamphiphilic Carbon Using Lignosulfonate for Enhancing Selective Hydrogenation Reactions in Pickering Emulsions.

Superamphiphilic materials have great potential to enhance the mass transfer between phases in liquid-liquid catalysis due to their special affinities. Constructing superamphiphilic surfaces that possess superhydrophilic and superhydrophobic properties simultaneously has been a tough assignment. So, exploration of simple methods to prepare such materials using renewable and abundant feedstocks is highly desired. Here, we reported an effective strategy to construct superamphiphilic carbon directly from sodium lignosulfonate, which is a renewable resource from paper industry wastes. From the characterization of X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) for superamphiphilic carbon, we found that element C was responsible for the hydrophobic nature and the existence of O and S endowed the carbon with hydrophilic characteristics. Further, micro/nanohierarchical pores were found beneficial for the superamphiphilicity of carbon. Meantime, in the selective hydrogenation of styrene, phenylacetylene, and cis-stilbene in liquid-liquid systems, conversion became double using superamphiphilic carbon compared with blank results, and the yields were three times more than those in blank experiments. The reasons were that superamphiphilic carbon induced the formation of Pickering emulsions and enriched the reactants around catalysts, as concluded by the characterization of confocal laser scanning microscopy and relating contrastive experiments. This work revealed a different route to obtain superamphiphilic carbon and provided a diverse perspective to promote Pickering emulsion catalysis by the superamphiphilicity of carbon.

Continuous Flow Pickering Emulsion Catalysis in Droplet Microfluidics Studied with In Situ Raman Microscopy.

Pickering emulsions (PEs), emulsions stabilized by solid particles, have shown to be a versatile tool for biphasic catalysis. Here, we report a droplet microfluidic approach for flow PE (FPE) catalysis, further expanding the possibilities for PE catalysis beyond standard batch PE reactions. This microreactor allowed for the inline analysis of the catalytic process with in situ Raman spectroscopy, as demonstrated for the acid‐catalyzed deacetalization of benzaldehyde dimethyl acetal to form benzaldehyde. Furthermore, the use of the FPE system showed a nine fold improvement in yield compared to the simple biphasic flow system (FBS), highlighting the advantage of emulsification. Finally, FPE allowed an antagonistic set of reactions, the deacetalization–Knoevenagel condensation, which proved less efficient in FBS due to rapid acid‐base quenching. The droplet microfluidic system thus offers a versatile new extension of PE catalysis.

Encapsulation of catalyst in block copolymer micelles for the polymerization of ethylene in aqueous medium

The catalytic emulsion polymerization of ethylene has been a long-lasting technical challenge as current techniques still suffer some limitations. Here we report an alternative strategy for the production of semi-crystalline polyethylene latex. Our methodology consists of encapsulating a catalyst precursor within micelles composed of an amphiphilic block copolymer. These micelles act as nanoreactors for the polymerization of ethylene in water. Phosphinosulfonate palladium complexes were used to demonstrate the success of our approach as they were found to be active for hours when encapsulated in micelles. Despite this long stability, the activity of the catalysts in micelles remains significantly lower than in organic solvent, suggesting some catalyst inhibition. The inhibition strength of the different chemicals present in the micelle were determined and compared. The combination of the small volume of the micelles, and the coordination of PEG appear to be the culprits for the low activity observed in micelles.

Water and Carbon Dioxide: A Unique Solvent for the Catalytic Polymerization of Ethylene in Miniemulsion

The catalytic polymerization of ethylene is performed in water pressurized with CO2 . The size of the initial monomer droplets and of the resulting polymer particles can be varied by simply changing the CO2 pressure. Furthermore, at identical ethylene partial pressure, the polymerizations performed in the presence of CO2 are significantly faster than in its absence. Thus, the combination of CO2 and water is a promising green solvent for catalytic emulsion polymerizations.