Adsorption Of Anionic Surfactants Research Articles

Enhancing understanding of anionic surfactant adsorption mechanism and hydrophilic modification of bituminous coal for effective dust suppression

The large amount of coal dust generated by mechanized coal mining poses hazards such as coal mine explosions, coal worker pneumoconiosis, and atmospheric pollution. Spray dust suppression is widely employed as a coal dust control technology in the mining process, with anionic surfactants commonly used as highly effective wetting and enhancing agents. However, the application process lacks theoretical guidance on the interaction mechanism between anionic surfactants and coal dust. This study aims to investigate the adsorption mechanism between anionic surfactants and coal dust surfaces, focusing on two specific surfactants: sodium dioctyl sulfosuccinate (AOT) and sodium dodecyl sulfate (SDS). Both surfactants possess the same hydrophilic group but differ in their tail chain groups. Through a comprehensive analysis, this research provides insights into the essential properties and characteristics of AOT and SDS adsorption on bituminous coal. Static adsorption experiments revealed that AOT exhibited a higher maximum adsorption capacity (Qe) on coal dust compared to SDS. Scanning electron microscopy and particle size characterization analysis demonstrated AOT's notable tendency to cluster coal dust particles. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy investigations confirmed a significant hydrophilic modification induced by AOT on the coal dust surface. Quantum chemistry calculations revealed that Van der Waals adsorption played a fundamental role in the interaction between the AOT and SDS tail chains and the coal surface. The double tail chain structure of AOT contributed to a more stable and stronger adsorption configuration with coal molecules. These findings provide valuable theoretical insights for the development and application of effective dust suppressants.

Adsorption behavior of surfactants on sandstone reservoir rocks with carbonate cements and its influence on wettability alteration

AbstractThis study investigates the adsorption behaviors of surfactants in sandstone reservoir rocks containing various amounts of carbonate cement/minerals and their impact on wettability alteration under low‐salinity conditions. Two types of rock samples from sandstone reservoirs of Assam oilfields in India are selected based on XRD results. These rock types are (i) high carbonate cement (HCC) core sample with higher carbonate cement (calcite 5.6% and dolomite 4.0%), and (ii) low carbonate cement (LCC) core sample with lower carbonate cement (calcite = 0.5% and dolomite 0%). The study reveals that the mineralogy of sandstone reservoir rocks especially the carbonate minerals affects the brine‐rock interactions including wettability alternation and surfactant adsorption. Notable differences (2° to 8°) in contact angles for the two rock types at different salinities revealed that carbonate cement in sandstone thus impacts brine‐rock interactions. Further, low salinity surfactant (LSS) could positively alter the wettability of both rock types to water‐wet conditions (contact angle <60°). The most favorable wettability alterations (up to 30°) were achieved with cationic LSS solutions for both core types. Using LSS solutions also reduced the adsorption of anionic surfactant by around 40% and 33% for HCC and LCC rock samples, respectively. The study's novelty emanates from investigating the impact of sandstone reservoir rock mineralogy with varying amounts of carbonate cements on the adsorption behavior of surfactants under low‐salinity conditions. Moreover, this study provides a better understanding of the interrelationship existing between the degree of wettability alteration and the amount of surfactant adsorbed by sandstone rocks.

Magnetic chitosan/calcium alginate double-network hydrogel beads: Preparation, adsorption of anionic and cationic surfactants, and reuse in the removal of methylene blue

Robust and reusable magnetic chitosan/calcium alginate double-network hydrogel beads (CSMAB) with an environmentally benign biocomposite material synthesis approach were used adsorption of surfactant and removal of methylene blue dye sequentially for the first time. Double network hydrogel structure with sodium alginate and chitosan and acidification of the surface with HCl provided the reusability of the beads at the pollutant removal in water. The CSMAB beads were characterized for structural analysis by FESEM, EDX, BET, VSM, and FTIR techniques. They were used for the adsorption of cationic hexadecylpyridinium chloride (HDPCl) and anionic sodium dodecyl sulfate (SDS) surfactants and reused in the removal of cationic methylene blue dye without any pretreatment. The effect of pH, adsorbent dose, and temperature on surfactant removal efficiency was analyzed and pH was found the statistical significance. The adsorption capacity of CSMAB beads with a surface area of 0.65 m2 g−1 was calculated as 1.9 mg g−1 for HDPCl, and 1.2 mg g−1 for SDS, respectively. The SDS and HDPCl adsorption followed the pseudo-second-order kinetic and Freundlich isotherm model. The thermodynamic results showed that the surfactant adsorption process is an exothermic and spontaneous process. SDS-reacted CSMAB beads showed higher efficiency with 61 % in the removal of methylene blue dye.

Bitumen–solids attachment induced by cation activation

AbstractInteractions between negatively charged bitumen and fine solids under oil sands extraction conditions were simulated using mature fine tailings (MFT) and hydrocarbon oil with dissolved carboxylic acids. Their attachment induced by cation activation was evaluated with different types of cations by simple dynamic attachment tests. The results revealed that solid hydrophobization by adsorbing surfactants was key for oil–solid attachment. Activation by multivalent metal cations was due to surface precipitation of metal hydroxides, followed by chemisorbing anionic surfactants on metal‐activated solids to form metal carboxylate complexes/precipitates, thereby hydrophobizing the solids. Activation by cationic surfactants depended on their hydrocarbon chain lengths. For short hydrocarbon chains, where hydrophobic interaction is weaker than electrostatic interaction between the added cationic and anionic surfactants, the added cations promote the adsorption of anionic surfactants by electrostatic interaction to render the solids hydrophobic. For long hydrocarbon chains where hydrophobic interaction is stronger than electrostatic interaction between the added cationic and anionic surfactants, the adsorption of anionic surfactants occurs through the hydrophobic association of the hydrocarbon chains, posing the head group towards water, thereby making the solids less hydrophobic. Activation by cationic flocculants was purely physical (hydrogen bonding and electrostatic): when the solids were turned positive by the added cationic flocculants, the added anionic surfactants then adsorbed onto the solids to render them hydrophobic. It appeared that soluble multivalent metal species (e.g., Ca2+ and Mg2+) were much less harmful to bitumen extraction than those heavy metals coated on the solids, either in the form of surface precipitates or hydrolyzed ionic species.

Minimizing Adsorption of Anionic Surfactant in Alkaline-Surfactant-Polymer System: Effects of pH and Surfactant Concentration

Alkaline-surfactant-polymer (ASP) flooding has been identified as the most effective enhanced oil recovery (EOR) technique to boost up the production of crude oil and improve the recoverable reserves. However, surfactant loss into the formation due to adsorption has been one of the issues, which could degrade the efficiency of the process. This study highlights the static adsorption of anionic sodium dodecyl sulphate (SDS) surfactant on the quartz sand with presences of alkaline and polymer at different pH and surfactant concentration. The critical micellar concentration (CMC) of SDS was determined using surface tension method and found at 0.22wt%. Three different systems were formulated namely A, B and C referring to the Surfactant formulation, Alkaline-Surfactant (AS) formulation and Alkaline-Surfactant-Polymer (ASP) formulation, respectively. For static adsorption tests, ASP system was formulated by adding 10,000 ppm sodium carbonate (Na2CO3) and 500 ppm of anionic Hydrolyzed Polyacrylamide (HPAM) polymer into the surfactant solution. The formulation was then mixed with the quartz sand at a fixed mass to volume ratio of 1:5. The adsorption tests involved shaking the mixtures, centrifuging, and analysing the supernatant solutions using UV-Visible spectrophotometer for adsorption measurement. The adsorption tests resulted in low adsorption at higher pH and low surfactant concentration. It was discovered that the lowest surfactant adsorption exhibited by ASP system with approximate reductions of 65% and 63% as compared to surfactant formulation at ~pH 12 and 2000 ppm surfactant concentration, respectively. Thus, anionic surfactant has a great performance in ASP system compared to its individual formulation, resulting in lower surfactant adsorption.

Adsorption of anionic surfactant on sandstone reservoir containing clay minerals and its effect on wettability alteration

Previous researches have shown that different anionic surfactants have different adsorption rates on mineral clays. Furthermore, many literatures have presented that anionic surfactants have little effect in changing the wettability of rocks containing clay minerals compared to cationic and nonionic surfactant. Mainly their experiments used anionic surfactant ethoxylated sulfonate, alkyl benzene sulfonates, sodium dodecyl sulfate, and sodium laureth sulfate. This paper studies the adsorption and its effect of an anionic surfactant alky ethoxy carboxylate (which is almost never discussed) on the wettability of sandstone containing Ca-montmorillonite and kaolinite clays. Some experimental works were conducted to support the analysis that include measurements of contact angle, zeta potential, pH, High-Performance Liquid Chromatography analysis, and SEM-EDX analysis. The results show that sandstones containing kaolinite clay tend to oil-wet and those containing Ca-montmorillonite clay tend to water-wet. The alkyl ethoxy carboxylate (AEC) adsorption that occurs in sandstones containing Ca-montmorillonite and kaolinite clay forms a parabolic curve trend with the minimum at about 15% concentration. The adsorption of AEC was higher by Ca-montmorillonite. Meanwhile, the greater wettability alteration by AEC occurs in sandstone containing kaolinite clay. The relationship between surfactant adsorption and contact angle is inverse, where the higher the surfactant adsorption, the smaller the contact angle value, and vice versa.

Microscopic mechanisms of MgCl2 affecting anionic surfactant adsorption kinetics on the air[sbnd]water interface

Inorganic salts can significantly affect the interfacial tension (IFT) of surfactant solutions, which is a key factor influencing the interphase mass transfer and reaction in multiphase systems. The change in IFT is directly related to the adsorption behavior of surfactants. However, the mechanisms underlying the effects of salt on surfactant IFT and adsorption kinetics are not yet clear. Here, taking MgCl2 and sodium dodecyl sulfate (SDS) as examples, the IFT characteristics of surfactant solutions under different salt concentrations were investigated, and the adsorption behavior and interface characteristics of SDS with or without MgCl2 were further analyzed by molecular dynamics simulations. We find that surfactant adsorption involves mixed diffusion-kinetic controlled adsorption. The addition of MgCl2 can obviously accelerate the adsorption kinetics and increase the adsorption capacity of SDS. Under the influence of magnesium ions, more “vacant sites” exist on the interface. Meanwhile, the orientation of the headgroups can be rapidly changed during the adsorption process to achieve a reasonable adsorption configuration faster, and the double electric layer (EDL) becomes thinner, reducing the electrostatic barrier. In addition, our findings offer new insights into anionic surfactant adsorption kinetics in a saline environment.

A study on adsorption of anionic surfactant from water during riverbank filtration

Riverbank filtration (RBF) is a low-cost and environmentally friendly alternative to advanced treatment technologies for pre-treatment or removal of various synthetic organic micro-pollutants from surface water. Through laboratory-scale batch tests employing aquifer soil with varying fine content and particle size, the removal of Linear Alkylbenzene Sulfonate (LAS) from river water during riverbank filtration (RBF) was investigated to determine its adsorption behavior. In addition to it, the effect of adsorbent dosage (3–60 g/L), adsorbate conc. (2–60 mg/L), contact time (10–240 min), agitation speed (80–200 rpm), and pH (2 to 10) on the adsorption for nine types of aquifer soil were studied in batch experiments. The optimal conditions for maximum rate of LAS adsorption on aquifer soil were found to be as initial LAS conc. of 15 mg/L, pH at 7, contact time of 150 min, agitation speed at 160 rpm and adsorbent dosage of 15 g/L respectively. The removal efficiency of LAS was obtained as 88.9% for aquifer soil with 15% fine content and 86.3% for fine sand at an adsorbent dose of 15 g/L, initial LAS conc. of 15 mg/l, neutral pH, agitation speed of 160 rpm, and contact time of 150 mins. Equilibrium data were fitted to Langmuir and Freundlich isotherms, and Langmuir isotherm (R2 = 0.99) was revealed to be the best fit of these models. From multiple linear regression, the LAS removal by soil samples was found to be strongly associated with all five geo-environmental factors (R2 = 0.91). So during the design of the RBF system, suitable contact time or travel time should be maintained in addition to the selection of proper aquifer site conditions for the RBF.

Temperature effect on the dynamic adsorption of anionic surfactants and alkalis to silica surfaces

Chemical loss such as surfactants and alkalis by adsorption to reservoir rock surface is an important issue in enhanced oil recovery (EOR). Here, we investigated the adsorption behaviors of anionic surfactants and alkalis on silica for the first time as a function of temperature using quartz crystal microbalance with dissipation (QCM-D). The results demonstrated that the temperature dependent critical micelle concentration of alcohol alkoxy sulfate (AAS) surfactant can be quantitatively described by the thermodynamics parameters of micellization, showing a mainly entropy-driven process. AAS adsorption was mediated under varying temperature conditions, by divalent cations for bridging effect, monovalent cations competitive for adsorption sites but not giving cation bridging, pH regulation of deprotonated sites of silica, presence of alkoxy groups in the surfactants, and synergistic effect of surfactant co-injection. The addition of organic alkalis can enhance the overall adsorption of the species with AAS, whereas inorganic alkali of Na 2 CO 3 had capability of the sequestration of the divalent ions, whose addition would reduce AAS adsorption. The typical AAS adsorption indicated a non-rigid multilayer, estimated to have between 2 and 5 layers, with a likely compact bilayer followed by disorganized and unstable further layering. The new fundamental understanding about temperature effect on surfactants and alkalis adsorption contributes to optimizing the flooding conditions of chemicals and developing more efficient mitigation strategies.

Charge-modulated calcite surface for anionic surfactant adsorption from molecular dynamics simulations

Since surfactant adsorption on reservoir rock means the loss of a valuable component, it makes surfactant flooding economically less feasible. In this work, adsorption behaviors of anionic surfactant on calcite surface were investigated with different charge states for the first time using molecular dynamic (MD) simulations. To reveal the underlying adsorption mechanism, adsorption processes were systematically analyzed with the adsorption energy, mean square displacement (MSD), relative concentration distribution (RCD), and radial distribution function (RDF). The results showed that sodium dodecyl sulfate had the strongest adsorption on the surface of calcite. When calcite surface was modelled with a charge state up to 80 e (8.24 × 1014 e/cm2), sodium dodecyl benzene sulfonate (SDBS) was found to be most stable on 10 e (1.03 × 1014 e/cm2) positively charge surface, with the maximum adsorption energy and the minimum diffusion coefficient. Increasing the carbon chain length of surfactant tail, the adsorption energy of SDBS became weaker, which can be attributed to the van der Waals interactions (long-range dispersion interactions) among surfactants. A monolayer or bilayer of surfactants can be derived based on the RCD. RDF curves revealed that hydrogen bonds played an important role in interactions among calcite surface, water molecules, and head groups of surfactants. The obtained results offer important insights into charge-modulated anionic surfactant adsorption on calcite surface at molecular scale and a guide to optimal flooding conditions with reduced surfactant loss.

Sodium dodecyl sulfate/C-UIO-66 regulation of nanofiltration membrane with pleated and thin polyamide layer structure

Nanofiltration membranes based on polyamide (PA) are widely used in fields such as brackish water desalination and drinking water purification due to their excellent retention of multivalent salts. However, uncontrolled and extremely fast polymerization easily produces thicker PA layers, which reduces permeability. Moreover, smooth support layer usually leads to PA layers with low roughness, which is not benefit for improving of flux. Based on these aspects, an innovative method of co-regulating interfacial polymerization based on anionic surfactant sodium dodecyl sulfate (SDS) and carbonized-UIO-66 (C-UIO-66) nanoparticles has been reported. The adsorption of anionic surfactant on the surface of C-UIO-66 slows down the diffusion rate of aqueous monomer and helps to form thin PA layer (<33 nm) which is thinner than the original thin film composite (TFC) membrane (144.29 ± 17.62 nm). Besides, C-UIO-66 nanoparticles with different sizes are deposited on the surface of the support layer, providing rougher surface for interfacial polymerization. Due to the irregular surface of SDS/C-UIO-66 intermediate layer, the prepared PA layer has folded structure. Compared with original TFC membrane, the preferred thin film nanocomposite (TFN) nanofiltration membrane possesses permeation flux of 58.59 L·m−2·h−1, which increased by 114.3 % together with the maintaining the rejection rate of Na2SO4 above 96 %.

Adsorption of anionic surfactant from water during riverbank filtration

Adsorption of anionic surfactant from water during riverbank filtration

New Insights into Surfactant Adsorption Estimation in Carbonates under Harsh Conditions Using Surface Complexation Modeling

Summary Several laboratory experiments demonstrated that the use of sodium hydroxide could increase the solution pH and reduce the adsorption of anionic surfactants. However, a better understanding of rock-oil-brine interactions and their effect on surfactant adsorption during alkaline-surfactantpolymer (ASP) flooding is needed for realistic and representative estimations of surfactant adsorption levels. Therefore, this study presents a novel approach to capture these interactions and better predict their effect on surfactant adsorption as well as effluent concentrations of surfactant and various aqueous species using the Phreeqc simulator. Currently, surface complexation models (SCMs) consider rock-brine, oil-brine, and surfactant-brine reactions. In this work, four new surface complexation reactions with intrinsic stability constants that honor oil-surfactant interactions have been proposed for the first time and then validated against experimental data reported in the literature. In addition, we analyzed the effect of various parameters on surface adsorption under harsh conditions of high temperature and high salinity using the proposed SCM. The results showed that the developed surfactant-based SCM is capable of estimating surfactant adsorption and its concentration in the effluent during chemical floods. The model was validated against two sets of ASP corefloods from the literature including single-phase and two-phase dynamic surfactant adsorption studies. The findings highlighted that oil-surfactant surface complexation reactions are important and should be captured for a more representative and accurate estimation of surfactant adsorption during chemical flooding. Moreover, the detailed and comprehensive analysis showed that surfactant adsorption increased and its concentration in the effluent decreased with the increase in temperature of the chemical flood. The latter shows that the adsorption process is endothermic and it is more of chemisorption as opposed to physio-adsorption. It was also showed that a decrease in water total salinity decreases the surfactant adsorption on the rock surface, which is related to the increase in the repulsive forces between the rock surface and adsorbed species. Additionally, with the increase in surfactant concentration in the chemical flood, surfactant concentration in the effluent increases, with a slight increase in surfactant adsorption. This slight increase in adsorption can be neglected compared with the injected and produced masses of the surfactant that are proportional. Moreover, the effect of sulfate spiking is significant where the increase in sulfate concentration reduces the surfactant adsorption. Furthermore, it is worth highlighting that the lowest surfactant adsorption levels were achieved through injected water dilution; less than 0.1 mg/g of rock. This is the first study to test a novel formulation of SCM considering the oil-surfactant effect on surfactant adsorption properties. The proposed framework to estimate surfactant adsorption is conducted for high-temperature and high-salinity reservoir conditions. Thus, it could be used in numerical reservoir simulators to estimate oil recovery due to wettability alteration by chemical flooding in carbonates, which will be investigated in our future work. The surfactant adsorption mechanisms during chemical flooding are very case-dependent and hence, the findings of this study cannot be generalized.

Chitosan-Coated Magnetic Calcium Alginate Beads: Adsorption of Anionic and Cationic Surfactants and Reuse in the Removal of Methylene Blue

Chitosan-Coated Magnetic Calcium Alginate Beads: Adsorption of Anionic and Cationic Surfactants and Reuse in the Removal of Methylene Blue

Chitosan-Coated Magnetic Calcium Alginate Beads: Adsorption of Anionic and Cationic Surfactants and Reuse in the Removal of Methylene Blue

Chitosan-Coated Magnetic Calcium Alginate Beads: Adsorption of Anionic and Cationic Surfactants and Reuse in the Removal of Methylene Blue

Anionic surfactant adsorption in detergent sewage with cation ion exchange method

Surfactant is one of chemical substances added in detergent. The surfactant type added in detergent is anionic surfactant, namely Alkyl Benzene Sulfonate (ABS). Alkyl Benzene Sulfonate is a slow-degradable chemical substance due to branched chain in its structure, which causes low oxygen supply from the air due to foam covering the water surface. This condition can cause a dangerous impact for the organisms in the water.This study aimed to adsorb the anionic surfactant contained in detergent sewage using cation exchange resin. Before the adsorption process, cation resin regeneration process was performed following the standard operational procedures of PT. Pertamina RU III, Plaju using 4% H2SO4solution at regeneration time of 45 minutes. Surfactant adsorption process occurred at room temperature with resin mass variables of 50, 100, and 150 g and contact time of 5, 10, 15, 20, and 25 minutes. Furthermore, the surfactant content was analyzed using a spectrophotometer at 652 nm wavelength. The study analysis results showed that the adsorption process of anionic surfactant in the detergent sewage with cation ion exchange method at 50 g resin in 5 – 25 minutes obtained a resin adsorption capacity of 0.72 g, while 150 g resin at 5 – 25 minutes only obtained a resin adsorption capacity of 0.18 g.The best adsorption percentage was achieved from 150 g resin at a contact time of 25 minutes due to adsorbing the anionic surfactant up to 100%. Meanwhile, the closest equation assessment approach was presented fromthe Langmuir adsorption isotherm model by gaining a linear graphic at R2 = 0.9946.  Â

Adsorption of anionic surfactant in graphite oxide: A study for treatment of laundry wastewater

Laundry wastewater, when discharged directly into water bodies, is an environmental problem due to the high load of pollutants it contains particularly surfactant compounds that are difficult to treat by conventional processes. In this work, we evaluated the behavior of graphite oxide (GO) synthesized by the Hummer method for adsorption retention of such surfactant compounds. The adsorbent material used was graphite oxide prepared with recycled graphite from lithium batteries. The applicability of graphite oxide in the adsorption of anionic surfactant was evaluated by adsorption kinetics and physicochemical characterization, before and after adsorption, using sensitive techniques such as XRD, SEM, AFM, Raman spectroscopy and MIR-FTIR. The results showed that the adsorption kinetics well represented by the pseudo-second-order model indicating chemical interactions between surfactants and graphite oxide, with qe,calc (238.09 mg g−1) close to qe,exp (227.96 mg g−1), suggesting that pre-filtering decreases competition for adsorption sites. This result is promising for the treatment of anionic surfactants, which are the main pollutants in laundry wastewater.

Simultaneous adsorption of anionic alkyl sulfate surfactants onto alpha alumina particles: Experimental consideration and modeling

Simultaneous adsorption of four anionic alkyl sulfate (AS) surfactants, including sodium octyl sulfate, sodium decyl sulfate, sodium dodecyl sulfate and sodium tetradecyl sulfate named as C8, C10, C12 and C14, onto alpha alumina (α-Al2O3) particles were systematically investigated. Concentrations of all mixtures of anionic AS surfactants in aqueous solution were quantified by capillary electrophoresis coupled with contactless conductivity detection (CE-C4D). Adsorption isotherms of the four anionic AS surfactant homologs increased with either the decrease of pH from 6.0 to 4.0 due to enhancement of electrostatic attractions between the positively charged α-Al2O3 surface and the anionic AS surfactants or the increase of carbon chain length due to enhanced hydrophobic interactions. At different salt concentrations, a common intersection point (CIP) obtained for adsorption isotherms demonstrated that the contributions of electrostatic and hydrophobic interactions were reversed. The ionic strength effect on anionic AS surfactant adsorption isotherms onto α-Al2O3 particles was thoroughly studied. Simultaneous adsorption of the four AS surfactants onto the α-Al2O3was controlled by both electrostatic and hydrophobic interactions that were in accordance with Langmuir and two-step models.

Adsorption of anionic surfactant on surface of reservoir minerals in alkaline-surfactant-polymer system

Alkaline-surfactant-polymer (ASP) flooding is significant to the oil and gas industry due to synergistic interaction between alkaline, surfactant and polymer. However, chemical losses due to adsorptions of surfactant and polymer on the rock surface could lead to inefficiency of the process. There are also significant uncertainties on adsorption mechanism when surfactant is flooded with presence of alkaline and polymer. This study highlights the static adsorption tests using anionic sodium dodecyl sulphate (SDS), hydrolysed polyacrylamide (HPAM) and sodium carbonate (Na2CO3) as the surfactant, polymer and alkaline, respectively. Sand particles and kaolinite clay were used as the reservoir minerals. The adsorption tests were conducted at various surfactant concentrations ranging from 50 to 2000 ppm. Sodium chloride (NaCl) concentration was investigated from 0 to 2 wt.%, while the local sand and kaolinite was mixed in surfactant solution at a fixed mass to volume ratio of 1:5. The static adsorption test was conducted by shaking the mixture samples and centrifugation before analysing the supernatant liquid using UV-Visible spectrophotometer. The results showed that the surfactant adsorption was higher on kaolinite compared to sand particle. The higher the salinity, the higher the adsorption of surfactant due to higher ionic strength. The adsorption of SDS surfactant on sand particles and kaolinite was lesser in ASP system compared to the presence of surfactant solution alone. Thus, it can be concluded that the presence of polymer and alkaline in ASP solution have great potential to reduce the surfactant adsorption on both sand particle and kaolinite.

Twist and Stretch: Assignment and Surface Charge Sensitivity of a Water Combination Band and Its Implications for Vibrational Sum Frequency Spectra Interpretations.

The vibrational spectrum of water at hydrophobic/hydrophilic interfaces is crucial to understanding complex surface chemistry phenomena. Vibrational sum frequency (VSF) spectroscopy is a valuable nonlinear spectroscopic technique for exploring the details of vibrational spectra of molecules at surfaces. However, spectral assignments and analysis of VSF spectra are often more nuanced than in linear spectroscopy. This study is aimed at understanding the source of the broad VSF signal in the oil-water surface water spectrum at energies slightly higher than traditionally examined, beyond the unbound free OH oscillator of surface water molecules. Analyzing isotopic dilutions of the aqueous solvent with VSF spectroscopy, we demonstrate that this signal is due to a combination band of water stretch and libration motions. The spectral characteristics of this band are found to be highly sensitive to the sign and magnitude of the surface charge induced by adsorption of both anionic and cationic surfactants. The results have implications for VSF measurements of the C-H stretching vibrations of various adsorbates when studied with D2O as the aqueous solvent. Because the vibrational signal from the water combination band is dependent on surface charge, it is imperative to include the presence of the combination band when fitting surface spectra.