Benchmarking the Self-Assembly of Surfactin Biosurfactant at the Liquid–Air Interface to those of Synthetic Surfactants

The adsorption of surfactin, a lipopeptide biosurfactant, at the liquid–air interface has been investigated in this work. The maximum adsorption density and the nature and the extent of lateral interaction between the adsorbed surfactin molecules at the interface were estimated from surface tension data using the Frumkin model. The quantitative information obtained using the Frumkin model was also compared to those obtained using the Gibbs equation and the Langmuir–Szyszkowski model. Error analysis showed a better agreement between the experimental and the calculated values using the Frumkin model relative to the other two models. The adsorption of surfactin at the liquid–air interface was also compared to those of synthetic anionic, sodium dodecylbenzenesulphonate (SDBS), and nonionic, octaethylene glycol monotetradecyl ether (C14E8), surfactants. It has been estimated that the area occupied by a surfactin molecule at the interface is about 3- and 2.5-fold higher than those occupied by SDBS and C14E8 molecules, respectively. The interaction between the adsorbed molecules of the anionic biosurfactant (surfactin) was estimated to be attractive, unlike the mild repulsive interaction between the adsorbed SDBS molecules

Mineral oil-based drilling fluid formulation using biosurfactant and nanoparticles with good rheological behavior and excellent H2S scavenging capability

There are two commonly used drilling fluids, namely water-based muds (WBMs) and oil-based muds (OBMs); however, the latter type is more desirable for drilling unconventional oilfield reserves. To account for the potential encounter of hydrogen sulfide (H2S) while drilling, the utilized OBMs should contain scavenger(s) with an effective H2S mitigation capability in order to in-situ capture this very lethal and corrosive gas. To the best of our knowledge, studies on incorporating H2S scavengers in OBMs and their testing are still greatly lacking in open literature. Thus, this study contributes into the filling of this gap by preparing a mineral oil-based drilling mud (MOBM) containing potassium permanganate as a promising, widely available, safe, and cheap H2S scavenger. The MOBM also comprised other ingredients including rhamnolipid biosurfactant as an emulsifier and octadecanethiol-modified (i.e., hydrophobized) zinc nanoparticles (serving as weighting agent). These materials have not been widely utilized so far in open literature for the preparation of MOBM. The results obtained from this study demonstrated that this mud could fully scavenge H2S for up to 22.7 h (i.e., breakthrough time), and it took about 63 h for the MOBM to become fully saturated with H2S. The scavenged amounts of H2S at these times reached 324.4 and 485.8 g/barrel MOBM, respectively. The formulated MOBM also displayed an appropriate non-Newtonian shear thinning behavior, where the apparent viscosity dropped sharply from about 1.96 to 0.71 Pa.s upon increasing the shear rate to from 1 to 10 s−1, followed by a gradual decrease down to 0.31 Pa.s at a shear rate of 1000 s−1. Additionally, the formulated mud is able to dissipate a significant amount of thermal energy as inferred from its estimated high activation energy of 34.93 kJ/mol, suggesting a good thermal stability of the MOBM. The present study reveals the possibility of formulating mineral OBMs with effective H2S for safely drilling sour oil and gas reservoirs

Characteristics and pH-Responsiveness of SDBS–Stabilized Crude Oil/Water Nanoemulsions

Nanoemulsions are colloidal systems with a wide spectrum of applications in several industrial fields. In this study, crude oil-in-water (O/W) nanoemulsions were formulated using different dosages of the anionic sodium dodecylbenzenesulfonate (SDBS) surfactant. The formulated nanoemulsions were characterized in terms of emulsion droplet size, zeta potential, and interfacial tension (IFT). Additionally, the rheological behavior, long-term stability, and on-demand breakdown of the nanoemulsions via a pH-responsive mechanism were evaluated. The obtained results revealed the formation of as low as 63.5 nm average droplet size with a narrow distribution (33–142 nm). Additionally, highly negative zeta potential (i.e., −62.2 mV) and reasonably low IFT (0.45 mN/m) were obtained at 4% SDBS. The flow-ability of the nanoemulsions was also investigated and the obtained results revealed an increase in the nanoemulsion viscosity with increasing the emulsifier content. Nonetheless, even at the highest SDBS dosage of 4%, the nanoemulsion viscosity at ambient conditions never exceeded 2.5 mPa·s. A significant reduction in viscosity was obtained with increasing the nanoemulsion temperature. The formulated nanoemulsions displayed extreme stability with no demulsification signs irrespective of the emulsifier dosage even after one-month shelf-life. Another interesting and, yet, surprising observation reported herein is the pH-induced demulsification despite SDBS not possessing a pH-responsive character. This behavior enabled the on-demand breakdown of the nanoemulsions by simply altering their pH via the addition of HCl or NaOH; a complete and quick oil separation can be achieved using this simple and cheap demulsification method. The obtained results reveal the potential utilization of the formulated nanoemulsions in oilfield-related applications such as enhanced oil recovery (EOR), well stimulation and remediation, well-bore cleaning, and formation fracturing

Lysozyme binding to tethered bilayer lipid membranes prepared by rapid solvent exchange and vesicle fusion methods

Tethered bilayer lipid membranes (tBLMs) are important tools for studying protein-lipid interactions. The widely used methodology for the perparation of these membranes is the fusion of phospholipid vesicles from an aqueous medium onto an anchored phospholipid layer. The preparation of phospholipid vesicles is a long and tedious procedure. There is another simple method, rapid solvent exchange, for preparing lipid membranes. However, there is a lack of information on the effects of the preparation method of tBLMs on their interactions with proteins. Therefore, we present in this paper a comparative study on the binding of lysozyme onto tBLMs prepared by the above mentioned methods. The prepared tBLMs have either zwitterionic or anionic characteristics. The results show that lysozyme binding onto the prepared tBLMS is unaffected by the preparation method of the tBLMs, suggesting that the tedious fusion method might be replaced by the simple rapid solvent exchange method without altering the level of protein-lipid interactions

The construction, fouling and enzymatic cleaning of a textile dye surface

The enzymatic cleaning of a rubisco protein stain bound onto Surface Plasmon Resonance (SPR) biosensor chips having a dye-bound upper layer is investigated. This novel method allowed, for the first time, a detailed kinetic study of rubisco cleanability (defined as fraction of adsorbed protein removed from a surface) from dyed surfaces (mimicking fabrics) at different enzyme concentrations. Analysis of kinetic data using an established mathematical model able to decouple enzyme transfer and reaction processes [Onaizi, He, Middelberg, Chem. Eng. Sci. 64 (2008) 3868] revealed a striking effect of dyeing on enzymatic cleaning performance. Specifically, the absolute rate constants for enzyme transfer to and from a dye-bound rubisco stain were significantly higher than reported previously for un-dyed surfaces. These increased transfer rates resulted in higher surface cleanability. Higher enzyme mobility (i.e., higher enzyme adsorption and desorption rates) at the liquid–dye interface was observed, consistent with previous suggestions that enzyme surface mobility is likely correlated with overall enzyme cleaning performance. Our results show that reaction engineering models of enzymatic action at surfaces may provide insight able to guide the design of better stain-resistant surfaces, and may also guide efforts to improve cleaning formulations. © 2010 Elsevier Inc

Langmuir-Hinshelwood kinetic study for palm oil catalytic cracking over Al-MCM-41

Palm oil catalytic cracking over a mesoporous aluminosilicate material (Al-MCM-41) containing 5 % alumina was studied in order to evaluate the Langmuir-Hinshelwood (LH) kinetic parameters. The Al-MCM-41 catalyst was prepared by the sol-gel technique and was characterized by X-ray diffraction and nitrogen adsorption techniques. The Brunauer-Emmett-Teller surface area of the catalyst was found to be 1,278 m2g-1. A 400 mL stirred batch autoclave reactor was used for catalytic cracking of 100 g refined palm oil and 1 g catalyst at a reaction temperature ranging from 573 to 673 K. The pressure-time data at different reaction temperatures were analyzed statistically in order to minimize experimental errors in the recorded pressures, whereas the statistically predicted pressure data were used to calculate the kinetic parameters. It was found that the fitting quality of the statistical model data using the LH model is similar to that of the raw experimental data. However, the values of the predicted parameters are significantly different. The estimated activation energy from LH kinetics was found to be 87 and 112 kJ mol-1 calculated from statistical model data and raw experimental data, respectively. The predicted parameters obtained from statistical model data are found to be more accurate as the influence of experimental error is minimized prior to data analysis

Aqueous Pb(II) Removal Using ZIF-60: Adsorption Studies, Response Surface Methodology and Machine Learning Predictions

Zeolitic imidazolate frameworks (ZIFs) are increasingly gaining attention in many application fields due to their outstanding porosity and thermal stability, among other exceptional characteristics. However, in the domain of water purification via adsorption, scientists have mainly focused on ZIF-8 and, to a lesser extent, ZIF-67. The performance of other ZIFs as water decontaminants is yet to be explored. Hence, this study applied ZIF-60 for the removal of lead from aqueous solutions; this is the first time ZIF-60 has been used in any water treatment adsorption study. The synthesized ZIF-60 was subjected to characterization using FTIR, XRD and TGA. A multivariate approach was used to investigate the effect of adsorption parameters on lead removal and the findings revealed that ZIF-60 dose and lead concentration are the most significant factors affecting the response (i.e., lead removal efficiency). Further, response surface methodology-based regression models were generated. To further explore the adsorption performance of ZIF-60 in removing lead from contaminated water samples, adsorption kinetics, isotherm and thermodynamic investigations were conducted. The findings revealed that the obtained data were well-fitted by the Avrami and pseudo-first-order kinetic models, suggesting that the process is complex. The maximum adsorption capacity (qmax) was predicted to be 1905 mg/g. Thermodynamic studies revealed an endothermic and spontaneous adsorption process. Finally, the experimental data were aggregated and used for machine learning predictions using several algorithms. The model generated by the random forest algorithm proved to be the most effective on the basis of its significant correlation coefficient and minimal root mean square error (RMSE)

Self-assembly of a surfactin nanolayer at solid-liquid and air-liquid interfaces

Surfactin, a sustainable and environmentally friendly surface active agent, is used as a model to study the adsorption of biosurfactants at hydrophobic and hydrophilic solid–liquid interfaces as well as the air–liquid interface. Surfactin adsorption was monitored as a function of time and concentration using surface plasmon resonance (SPR) technique in the case of the solid–liquid interfaces or the drop shape analysis (DSA) technique in the case of the air–liquid interface. The results obtained in this study showed that surfactin adsorption at the “hard” hydrophobic (functionalized with octadecanethiol) solid–liquid and the “soft” air–liquid interface were 1.12 ± 0.01 mg m−2 (area per molecule of 157 ± 2 Å2) and 1.11 ± 0.05 mg m−2 (area per molecule of 159 ± 7 Å2), respectively, demonstrating the negligible effect of the interface “hardness” on surfactin adsorption. The adsorption of surfactin at the hydrophilic (functionalized with β-mercaptoethanol) solid–liquid interface was about threefold lower than its adsorption at the hydrophobic–liquid interfaces, revealing the importance of hydrophobic interaction in surfactin adsorption process. The affinity constant of surfactin for the investigated interfaces follows the following order: air > octadecanethiol > β-mercaptoethanol. Biosurfactants, such as surfactin, are expected to replace the conventional fossil-based surfactants in several applications, and therefore the current study is a contribution towards the fundamental understanding of biosurfactant behavior, on a molecular level, at hydrophobic and hydrophilic solid–liquid interfaces in addition to the air–liquid interface. Such understanding might aid further optimization of the utilization of surfactin in a number of industrial applications such as enhanced oil recovery, bioremediation, and detergency.Scopu

Intercalation of ionic liquids into bentonite: Swelling and rheological behaviors

In this study, direct intercalation of three different green ionic liquids (ILs) having different salt and cation sizes into bentonite interlayer is investigated. The ILs covered in this study are: 1-hexyl-3-methylimidazolium chloride [IL-1], 1-butyl-3-methylimidazolium octyl-sulfate [IL-2], and 1-butyl-3-methylimidazolium bromide [IL-3]. The aim of this IL modification of bentonite is to enhance both rheological and thermal stability of the modified bentonite. This objective is achieved by increasing the swelling of the bentonite interlayer, which is essential for many applications. The basal d-spacing of the ILs intercalated bentonite in comparison with dried bentonite powder as detected by XRD results showed that the cations of the three ILs are successfully intercalated into the interlayer of the bentonite platelets by a cation exchange mechanism and the swelling is likely influenced by the cation size, type and concentration of the ILs. The measurements of the equilibrium concentrations of the ILs in the solution suggested that adsorption is taking place on the external surfaces. This assumption is validated by Zeta potential measurements. The results from particle sizes and Zeta potential measurements have shown that bentonite intercalated with IL-1 and IL-2 are the most effective in decreasing the overall repulsive forces and increasing the attractive forces on the bentonite surface. Consequently, larger bentonite aggregates are produced by the chloride based IL intercalated bentonite rather than those intercalated with the bromide based IL or pure bentonite. In a similar manner, rheological measurements showed that the bentonite intercalated with IL-1 and IL-2 produced strong bentonite aggregates with higher G?, G?, ?c and ?* than those intercalated with IL-3 and the untreated bentonite samples. Rheological, Zeta Potential and XRD measurements have confirmed that green ionic liquids can be used in different applications to enhance bentonite swelling.Scopu