Interfacial Activity Research Articles

Long carbon chain-modified carbon nanoparticles for oil displacement in harsh-condition reservoirs

Carbon nanoparticles, as an emerging type of enhanced oil recovery agent, promising broad prospects in unconventional oil and gas development. However, limitations such as low interfacial activity due to the strong hydrophilicity of carbon nanoparticles and tendency to aggregate under high-temperature and high-salinity conditions restrict their further application. In this study, activity carbon dots (S-CDs) were prepared via a simple two-step hydrothermal reaction. A range of physicochemical techniques characterized S-CDs, revealing their small particle size (1.4 ± 0.01 nm) and narrow distribution, maintaining strong dispersion stability in mineralized water at 130 °C with a concentration of 16 × 104 mg/L. The AFM scanning results indicated that S-CDs possessed strong interfacial wetting control capability, the adhesion force between oil and rock cores (after S-CDs treatment) decreased by 25 times. Particle Image Velocimetry (PIV) confirmed that S-CD adsorbed at the oil-water interface could formed a solid film, which could rupture into smaller oil droplets for convenient backward migration. The results demonstrated that S-CDs improved the interfacial activity while maintaining the hydrophilicity of CDs. In core displacement experiments, 0.05 wt% S-CDs nanofluid reduced injection pressure by 32.4 % and increased recovery rates by 34.9 %. This work provides new insights for the development of high-temperature, high-salinity displacement agents in harsh-condition reservoirs.

Two-step modification strategy enhances carbon fiber/old corrugated container fiber flexible conductive film

Carbon fiber (CF) possesses inherent properties of low density, high strength, and environmental stability. Its high aspect ratio and knittability enable the formation of flexible conductive networks. Old corrugated container (OCC) is rich in cellulose and hemicellulose, rendering them flexible and exhibiting a low coefficient of thermal expansion. In this paper, CF/OCC/PVA flexible conductive films were prepared using polyvinyl alcohol (PVA) as the matrix, CF as the conductive filler and OCC as the flexible support material. Firstly, the coupling agent was grafted on the surface of CF to enhance their surface activity, improve the dispersion of CF in solution and the chemical bonding of CF to the matrix. Subsequently, sizing nanoparticles were applied to increase the roughness of the CF surface. This served to increase the volume of the conductive network and enhance the mechanical interlocking between CF and PVA. The results show that the two-step combined modification strategy have a significant positive impact on the interfacial chemical activity, contact angle, and roughness of CF. Moreover, it leads to notable improvements in various properties of the conductive film materials. This finding is relevant for the preparation of CF reinforced other matrix materials as well as for expanding the special properties and application value of CF conductive thin film materials.

Preparation and Application of High Internal Phase Pickering Emulsion Gels Stabilized by Starch Nanocrystal/Tannic Acid Complex Particles.

Herein, the starch nanocrystal/tannic acid (ST) complex particles, which were prepared based on the hydrogen bond between starch nanocrystal (SNC) and tannic acid (TA), were successfully used to stabilize the HIPPE gels. The optimal TA concentration of the ST complex particles resulted in better water dispersibility, surface wettability, and interfacial activity as compared to SNC. The hydrogen bond responsible for the formation of ST complex particles and subsequent stable emulsions was demonstrated by varying the pH and ionic strength of the aqueous phase. Notably, the HIPPE gels stabilized via the ST complex particles can maintain long-term stability for up to three months. The HIPPEs stabilized via the ST complex particles all displayed gel-like features and had smaller droplets and denser droplet networks than the SNC-stabilized HIPPEs. The rheological behavior of HIPPE gels stabilized via the ST complex particles can be readily changed by tuning the mass ratio of SNC and TA as well as pH. Finally, the prepared HIPPE gels used to effectively protect encapsulated β-carotene against high temperatures and ultraviolet radiation and its controllable release at room temperature were demonstrated. It is anticipated that the aforementioned findings will provide new perspectives on the preparation of Pickering emulsion for delivery systems.

Self-Assembled Viscoelastic Surfactant Micelles with pH-Responsive Behavior: A New Fracturing-Displacement Integrated Working Fluid for Unconventional Reservoirs.

The integrated fracturing and oil recovery strategy is a new paradigm for achieving sustainable and cost-effective development of unconventional reservoirs. However, a single type of working fluid cannot simultaneously meet the different needs of fracturing and oil displacement processes. Here, we develop a pH-responsive fracturing-displacement integrated working fluid based on the self-assembled micelles of N,N-dimethyl oleoamine propylamine (DOAPA) and succinic acid (SA). By adjusting the pH of the working fluid, the DOAPA and SA molecules can be switched repeatedly between highly viscoelastic wormlike micelles and aqueous low-viscosity spherical micelles. The zero-shear viscosity of the working fluid enriched the wormlike micelles can reach more than 93,100 mPa·s, showing excellent viscoelasticity and sand-carrying properties. The working fluid is easy to gel-break when it encounters oil, generating a low-viscosity liquid without residue. In addition, the system has strong interfacial activity, which can greatly reduce the oil-water interfacial tension to form emulsions and can achieve reversible demulsification and re-emulsification by adjusting pH. Through the designed and fabricated microfluidic chip, it can be visualized that under the synergistic effect of viscoelasticity and interfacial activity DOAPA/SA can effectively expand the swept volume of tight fractured formations, promote pore wetting reversal and crude oil emulsification, and improve the displacement efficiency. The DOAPA/SA meets the design requirements of the fracturing-displacement integrated working fluids and provides a novel method and idea for constructing the integrated working fluids suitable for fracturing and displacement in unconventional reservoirs.

Aromatic poly (amino acids) as an effective low-temperature demulsifier for treating crude oil-in-water emulsions

Amphiphilic aromatic poly (amino acids) polymers were designed as biodegradability demulsifiers with higher aromaticity, stronger polarity, and side chain-like combs. The effects of demulsifier dosage, structural characteristics and emulsion properties such as pH, salinity, and oil content on the demulsification efficiency were investigated. The results show that the poly (L-glutamic-benzyl ester)-block-poly (L-phenylalanine) (PBLG15-b-PPA15) as the demulsifier can remove more than 99.97% of the oil in a 5.0 wt% oil-in-water (O/W) emulsion at room temperature within 2 min. The poly (L-tyrosine)-block-poly (L-phenylalanine) (PTyr15-b-PPA15) with environmental durability demonstrates high effectiveness, universality, and demulsification speed. It achieves a remarkable demulsification efficiency of up to 99.99% for a 20.0 wt% O/W emulsion at room temperature. The demulsification mechanism indicates that demulsifiers have sufficient interfacial activity can quickly migrate to the oil-water interface after being added to the emulsions. Additionally, when demulsifiers are present in a continuous phase in the molecular form, their "teeth" side chains are beneficial for increasing coalescence and flocculation capacities. Furthermore, according to the Density Functional Theory (DFT) calculations, enhancing the intermolecular interactions between demulsifiers and the primary native surfactants that form an oil-water interfacial film is a more efficient approach to reducing demulsification temperature and improving demulsification efficiency and rate.

Interaction, Surface Activity, and Application of Mixed Systems of Alcohol Ether Sulfate Anionic Surfactants with Multiple Ethylene Oxide Groups and Gemini Quaternary Ammonium Surfactant.

The surface activities and application properties for the mixtures of cationic surfactants tetramethylene-1,4-bis[N,N-bis(hydroxypropyl)-hexa/decyloxypropylammonium] bromide (GC10-P) and tetramethylene-1,4-bis[N,N-bis(hydroxyethyl)-hexa/decyloxypropylammonium] bromide (GC10-E) and anionic surfactant isomeric sodium fatty alcohol ether sulfates (iso-AE9S) were investigated using both the tensiometry and the conductometry. The interaction parameters and thermodynamic micellization parameters of GC10-P/iso-AE9S and GC10-E/iso-AE9S mixtures were evaluated by Clint-Rubingh and Motomura theoretical models. When the mole fraction of α1 for GC10-P/iso-AE9S mixed system was 0.2, the critical micelle concentration (CMC) reached a minimum of 1.61 × 10-4 mol/L, and the minimum critical micelle concentration of the GC10-E/iso-AE9S mixed system is 2.67 × 10-5 mol/L at α1 = 0.6. The CMC value of the mixed system is 1-2 orders of magnitude lower than that of any single component. The results indicate that the synergistic effects of the investigated mixed systems (evaluated by βm) are in order of GC10-P/iso-AE9S < GC10-E/iso-AE9S, with maximum βm values of -17.98 and -9.78, respectively. The change in zeta potential indicates that the poly(ethylene oxide) chain has weakened the charge density of the hydrophilic headgroup of the anionic surfactant. The interfacial tension at the oil-water interface in the mixed system of anionic/cationic surfactants is lower than that of any single component, exhibiting a higher interfacial activity. The mixed system exhibits a decreased contact angle and superior wetting ability over any single component, and it also enhances foam performance, emulsification performance, and degreasing performance.

Thermal Welding of Liquids.

Welding of thermoplastics is a common practice in many industrial sectors, but it has yet to be realized with fluids. Here, the thermal welding of liquids by using the assembly and jamming of nanoparticle surfactants (NPSs) at liquid-liquid interfaces is reported. By fine-tuning the dynamic interaction strength within NPSs, the interfacial activity of NPSs, as well as the binding energy of NPSs to the interface can be precisely controlled, leading to a dynamic exchange of NPSs, maximizing the reduction in the interfacial energy. With NPSs jammed at the interface, the structures of liquids can be manipulated to complex geometries by applying an external force and, due to the temperature responsiveness of NPSs, when bringing liquids into contact and heating the system, welding of liquids can be achieved. This work provides a straightforward strategy for the construction of modular all-liquid fluidics, opening up numerous opportunities in fields like biotechnology, healthcare, and materials science.

Irradiation-Assisted Enhancement of Foaming and Thermal Gelation Functionality of Liquid Egg White.

Ionizing radiation has its unique popularity as a non-thermal decontamination technique treating with protein-rich foodstuffs to ensure the microbial and sensory quality, particularly for shell eggs. However, the changes in the functional properties of egg protein fractions such as liquid egg white (LEW) with macro/microstructural information are still controversial. Hence, this study was designed to elaborate the foaming and heat-set gelation functionality of LEW following different γ-ray irradiation dose treatments (0, 1, 3 or 5 kGy). For such, the physicochemical properties (active sulfhydryl and the hydrophobicity of protein moieties), structural characteristics (through X-ray diffraction, Fourier-transform infrared spectroscopy and differential scanning calorimetry) and interfacial activities (rheological viscosity, interfacial tension, microrheological performance) were investigated. Then, the thermal gelation of LEW in relation to the texture profile and microstructure (by means of a scanning electron microscope) was evaluated followed by the swelling potency analysis of LEW gel in enzyme-free simulated gastric juice. The results indicated that irradiation significantly increased the hydrophobicity of liquid egg white proteins (LEWPs) (p < 0.05) by exposing non-polar groups and the interfacial rearrangement from a β-sheet to linear and smaller crystal structure, leading to an enhanced foaming capacity. Microstructural analysis revealed that the higher dose irradiation (up to 5 kGy) could promote the proteins' oxidation of LEW alongside protein aggregates formed in the amorphous region, which favored heat-set gelation. As evidenced in microrheology, ≤3 kGy irradiation provided an improved viscoelastic interface film of LEW during gelatinization. Particularly, the LEW gel treated with 1 kGy irradiation had evident swelling resistance during the times of acidification at pH 1.2. These results gave new insight into the irradiation-assisted enhancement of foaming and heat-set gelation properties of LEW.

The bile salt/phospholipid ratio determines the extent of in vitro intestinal lipolysis of triglycerides: Interfacial and emulsion studies

This study focused on the protein-stabilised triglyceride (TG)/water interfaces and oil-in-water emulsions, and explored the influence of varying molar ratios of bile salts (BSs) and phospholipids (PLs) on the intestinal lipolysis of TGs. The presence of these two major groups of biosurfactants delivered with human bile to the physiological environment of intestinal digestion was replicated in our experiments by using mixtures of individual BSs and PLs under in vitro small intestinal lipolysis conditions. Conducted initially, retrospective analysis of available scientific literature revealed that an average molar ratio of 9:4 for BSs to PLs (BS/PL) can be considered physiological in the postprandial adult human small intestine. Our experimental data showed that combining BSs and PLs synergistically enhanced interfacial activity, substantially reducing oil–water interfacial tension (IFT) during interfacial lipolysis experiments with pancreatic lipase, especially at the BS/PL–9:4 ratio. Other BS/PL molar proportions (BS/PL–6.5:6.5 and BS/PL–4:9) and an equimolar amount of BSs (BS–13) followed in IFT reduction efficiency, while using PLs alone as biosurfactants was the least efficient. In the following emulsion lipolysis experiments, BS/PL–9:4 outperformed other BS/PL mixtures in terms of enhancing the TG digestion extent. The degree of TG conversion and the desorption efficiency of interfacial material post-lipolysis correlated directly with the BS/PL ratio, decreasing as the PL proportion increased. In conclusion, this study highlights the crucial role of biliary PLs, alongside BSs, in replicating the physiological function of bile in intestinal lipolysis of emulsified TGs. Our results showed different contributions of PLs and BSs to lipolysis, strongly suggesting that any future in vitro studies aiming to simulate the human digestion conditions should take into account the impact of biliary PLs – not just BSs – to accurately mimic the physiological role of bile in intestinal lipolysis. This is particularly crucial given the fact that existing in vitro digestion protocols typically focus solely on applying specific concentrations and/or compositions of BSs to simulate the action of human bile during intestinal digestion, while overlooking the presence and concentration of biliary PLs under physiological gut conditions.

Magnetic biocatalytic nanoreactors based on graphene oxide with graded reduction degrees for the enzymatic synthesis of phytosterol esters

As we know, the carriers of enzymatic nanoreactors with different amphipathy have significant influence on the interfacial enzyme activities and its performance. In this study, the magnetic graphene oxide (GO) enzyme carriers were constructed by assembling graphene oxide with different reduction degrees (rGO(x)) and polyethyleneimine (PEI) modified nano-flowery Fe3O4 into composite materials through electrostatic interactions, and x here represents the reduction reaction hours of GO. The SEM, TEM, contact angles and BET tests qualified the ideal enzyme carrier, PEI-Fe3O4-rGO(12), by adsorption-crosslinking method, the Candida rugosa lipase (CRL) was immobilized to obtain the lipase nanoreactor, PEI-Fe3O4-rGO(12)@CRL. The nano-sheet and nano-flower structures provided a larger specific surface area and suitable pore size, and the CRL had higher protein load on the carrier material (163.11 mg/g). In addition, using hydrolyzed p-nitrophenol palmitate as the model, the PEI-Fe3O4-rGO(12)@CRL can still show 76.5 % residual activity after 8 repeated uses. At the same time, the immobilized lipase showed good catalytic performance in the biosynthesis of phytosterol esters. The optimal esterification conditions were determined by single factor experiment (isooctane, sterol concentration 150 μmol/mL, alkyd molar ratio 1:2, enzyme dosage 120 mg, 26 h, 55 °C, the esterification rate was 76.24 %). Therefore, the optimal biocatalyst PEI-Fe3O4-rGO(12)@CRL may has good performance in the biosynthesis of other novel foods.

Accelerated Sequence Design of Star Block Copolymers: An Unbiased Exploration Strategy via Fusion of Molecular Dynamics Simulations and Machine Learning.

Star block copolymers (s-BCPs) have potential applications as novel surfactants or amphiphiles for emulsification, compatibilization, chemical transformations, and separations. s-BCPs have chain architectures where three or more linear diblock copolymer arms comprised of two chemically distinct linear polymers, e.g., solvophobic and solvophilic chains, are covalently joined at one point. The chemical composition of each of the subunit polymer chains comprising the arms, their molecular weights, and the number of arms can be varied to tailor the surface and interfacial activity of these architecturally unique molecules. This makes identification of the optimal s-BCP design nontrivial as the total number of plausible s-BCP architectures is experimentally or computationally intractable. In this work, we use molecular dynamics (MD) simulations coupled with a reinforcement learning-based Monte Carlo tree search (MCTS) to identify s-BCP designs that minimize the interfacial tension between polar and nonpolar solvents. We first validate the MCTS approach for the design of small- and medium-sized s-BCPs and then use it to efficiently identify sequences of copolymer blocks for large-sized s-BCPs. The structural origins of interfacial tension in these systems are also identified by using the configurations obtained from MD simulations. Chemical insights into the arrangement of copolymer blocks that promote lower interfacial tension were mined using machine learning (ML) techniques. Overall, this work provides an efficient approach to solve design problems via fusion of simulations and ML and provides important groundwork for future experimental investigation of s-BCPs for various applications.

Effects of molecular structure and charge state on the foaming and emulsifying properties of Spirulina protein isolates

Microalgae protein holds great potential for various applications in the food industry. However, the current knowledge regarding microalgae protein remains limited, with little information available on its functional properties. Furthermore, the relationship between its molecular structure and functional properties is not well defined, which limits its application in food processing. This study aims to addresses these gaps though an analysis of the emulsibility and foamability of various soluble protein isolates from two species of Spirulina (Arthospira platensis and Spirulina platensis), and the functional properties of Spirulina protein isolates in relation to its molecular structure and charge state. Results revealed that the degree of cross-linking and aggregation or folding and curling of protein tertiary structures was higher in the highly soluble Spirulina protein isolates (AP50% and SP50%) than in the low-solubility isolates (AP30% and SP30%). The foaming capacity (FC) of AP50% and SP50% was found to be lower than that of AP30% and SP30%. Spirulina protein isolates can stably adsorb at the air-water interface for at least 20 min and possessed good interfacial activity. A high pH value was found to promote cross-linking of protein particles at the oil-water interface, thereby reinforcing the internal network structure of emulsions and increasing viscosity. These findings provide preliminary insights for potential applications of Spirulina protein isolates in food production, especially towards quality improvement.

Synthesis of cyclodextrin-based demulsifier for treatment of oily wastewater through hydrophobic modification strategy

The discharge of oily wastewater not only has an impact on the environment, but also poses a threat to human health. Therefore, the treatment of oily wastewater is crucial. In current work, a novel demulsifier (CD-LA) was prepared using β-cyclodextrin (β-CD) as raw material by the acylation of –OH and subsequent grafting of dodecylamine. The demulsifier was intended for the treatment of oily wastewater. Detailed examinations were conducted on the surface morphology, chemical composition, interfacial activity, and the capacity of CD-LA to engage competitively at the interface. This substance demonstrated a pronounced ability to lower interfacial tension, indicating its utility in supplanting asphaltenes at the oil–water boundary. This action facilitates the weakening or disruption of the interfacial film, which is critical for the successful separation of oily wastewater. The findings revealed that CD-LA excelled in clarifying oily wastewater, proving effective under near-neutral conditions and in environments with elevated salinity. Separated water phase could obtain light transmittance (WT) of 89.75 % and oil removal rate (WR) of 99.83 % after the oily wastewater was demulsified with a concentration of 50 mg/L at room temperature.

Study on the kinetics of formation process of emulsion of heavy oil and its functional group components

Enhanced oil recovery (EOR) by in situ formation of oil-in-water emulsion in heavy oil cold production technology has received growing interest from the petroleum industry. We present an experimental study of emulsification of model oils prepared by heavy oil and its functional group compositions dissolved into toluene brought into contact with a surfactant solution. The effects of functional group composition, emulsifier concentration, temperature, pH and stirring speed on the emulsification rate of heavy oil was investigated. A second-order kinetic model characterizing the temporal variation of conductivity during the emulsification has been established. The results show that acidic and amphoteric fractions exhibit higher interfacial activity, larger emulsification rate constant and faster emulsification rate. With the increase of emulsifier concentration, the emulsification rate constant increase to the maximum value at a concentration of 0.05 mol/L before decreasing. Temperature increase benefits the emulsification rate and the activation energy of the emulsification process is 40.28 kJ/mol. Higher pH and stirring speed indicate faster emulsification rate. The heterogeneity of emulsions limits the accuracy of dynamic characterization of the emulsification process and the determination method of emulsification rate has always been controversial. The conductivity method we proposed can effectively evaluates the emulsification kinetics. This paper provides theoretical guidance for an in-depth understanding of the mechanism and application of cold recovery technology for heavy oil.

Microscopic Understanding of Interfacial Performance and Antifoaming Mechanism of REP Type Block Polyether Nonionic Surfactants.

In many practical applications involving surfactants, achieving defoaming without affecting interfacial activity is a challenge. In this study, the antifoaming performance of REP-type block polymer nonionic surfactant C12EOmPOn was determined, and molecular dynamics simulation method was employed to investigate the molecular behaviors of surfactants at a gas/water interface, the detailed arrangement information of the different structural segments of the surfactant molecules and the inter-/intra-interactions between all the structural motifs in the interfacial layer were analyzed systematically, by which the antifoaming mechanisms of the surfactants were revealed. The results show that the EO and PO groups of REP-type polyether molecules are located in the aqueous phase near the interface, and the hydrophobic tails distribute separately, lying almost flat on the gas/water interface. The interaction between the same groups of EOs and POs is significantly stronger than with water. REP block polyethers with high polymerization degrees of EO and PO are more inclined to overlap into dense layers, resulting in the formation of aggregates resembling "oil lenses" spreading on the gas/water interface, which exerts a stronger antifoaming effect. This study provides a smart approach to obtaining efficient antifoaming performance at room temperature without adding other antifoam ingredients.

Carbon Dot Nanomaterials with High Interfacial Activity for Unconventional Reservoir Development

Carbon Dot Nanomaterials with High Interfacial Activity for Unconventional Reservoir Development

Falling, deformation, and coalescence of droplet in model waxy oil under an electric field

Electrocoalescence technology can efficiently dehydrate waxy crude oil but the mechanisms are still unclear. Herein, the continuous microscopic behaviors of droplet falling, deformation, and coalescence were experimentally investigated to clarify the dynamic response mechanism of droplet in waxy oil under an electric field. The results showed the droplet falling under both gravity and electrostatic attraction to deform by the electric field force. Moreover, the expansion and clamping of the liquid bridge resulted from the competition between electric field force and capillary force. However, the precipitated wax crystals reduced the kinetic energy of the droplet and affected its external circulation, thus delaying the falling time. In addition, the wax crystals with interfacial activity adsorbed on the oil-water interface and cross-linked to form a spatial network structure, thereby weakening droplet deformation, hindering liquid film drainage, and inhibiting liquid bridge expansion. Importantly, the droplet adsorbed wax crystals exhibited interfacial elasticity, which makes them more inclined to partial coalescence. The low-frequency pulsed direct current (PUDC) electric field with high strength intermittent effect displayed the most obvious inhibition effect on the wax crystals. Overall, these findings look promising for future design and optimization of high-efficiency electric dehydrators and related fields.

Enhancing Oil Recovery in Low-Permeability Reservoirs Using a Low-Molecular Weight Amphiphilic Polymer.

Polymer flooding has achieved considerable success in medium-high permeability reservoirs. However, when it comes to low-permeability reservoirs, polymer flooding suffers from poor injectivity due to the large molecular size of the commonly used high-molecular-weight (high-MW) partially hydrolyzed polyacrylamides (HPAM). Herein, an amphiphilic polymer (LMWAP) with a low MW (3.9 × 106 g/mol) was synthesized by introducing an amphiphilic monomer (Allyl-OP-10) and a chain transfer agent into the polymerization reaction. Despite the low MW, LMWAP exhibited better thickening capability in brine than its counterparts HPAM-1800 (MW = 1.8 × 107 g/mol) and HPAM-800 (MW = 8 × 106 g/mol) due to the intermolecular hydrophobic association. LMWAP also exhibited more significant shear-thinning behavior and stronger elasticity than the two counterparts. Furthermore, LMWAP possesses favorable oil-water interfacial activity due to its amphiphilicity. The oil-water interfacial tension (IFT) could be reduced to 0.88 mN/m and oil-in-water (O/W) emulsions could be formed under the effect of LMWAP. In addition, the reversible hydrophobic association endows the molecular chains of LMWAP with dynamic association-disassociation transition ability. Therefore, despite the similar hydrodynamic sizes in brine, LMWAP exhibited favorable injectivity under low-permeability conditions, while the counterpart HPAM-1800 led to fatal plugging. Furthermore, LMWAP could enhance oil recovery up to 21.5%, while the counterpart HPAM-800 could only enhance oil recovery by up to 11.5%, which could be attributed to the favorable interfacial activity of LMWAP.

Potential applications of biosurfactants produced by different Pseudomonas syringae: A comparative study on interfacial activity, antimicrobial efficacy, and cytotoxicity

Finding novel biocompatible compounds with adequate interfacial activity and low toxicity still represents a great challenge for the scientific community. In this context, this work aims to compare for the first time the potential applications of biosurfactants produced by three Pseudomonas syringae pathovars: P. syringae pv tabaci (TA), P. syringae pv tomato (TO) and P. syringae pv syringae (SY). Isolated lipopeptides proved excellent emulsifying activity against a great variety of hydrocarbons and vegetable oils. The lowest minimum inhibitory concentrations against the pathogenic strain Staphylococcus aureus were observed for the biosurfactants produced by TA and SY (0.375 mg/mL). Non-cytotoxic effects were observed for concentrations of up to 10 mg/mL for these BS, and they proved differential cytotoxicity against cancer cell lines. These results open perspectives for the application of these surfactants as low-toxic bioemulsifiers and biotherapeutics.

Enhanced selective photocatalytic CO2 reduction to CO on AuPd decorated Bi2O2.33 nanosheets

Photocatalytic conversion of carbon dioxide (CO2) into valuable fuels addresses pressing needs for renewable energy and carbon neutrality. However, conventional photocatalytic CO2 reduction on semiconductor is usually limited by sluggish electron kinetics, poor efficiency and low product selectivity. Herein, we developed a bimetallic Au/Pd-decorated Bi2O2.33 ultrathin nanosheet photocatalyst for highly selective CO2 reduction to CO under visible light irradiation. Bi2O2.33 nanosheets self-assembled from nanodots serve as ideal supports for Au/Pd anchoring due to abundant grain boundaries. Systematic characterization reveals the formation of alloyed Au/Pd nanoparticles on the Bi2O2.33 surface, which endowed a superior CO production rate of 436.8 μmol g−1 h−1 with a selectivity of 96.68 % from CO2 photoreduction. Quantum chemical calculations uncover that plasmonic Au/Pd alloys facilitates interfacial charge transfer and CO2 activation to form the CO-yielding intermediate. This work demonstrates an effective strategy for designing bimetallic plasmonic cocatalysts to optimize the photoreduction selectivity and efficiency of semiconductor photocatalysts.