Anionic surfactants are surface actives that ionize negative charges in water. In the production of surfactants, anionic surfactants occupy the maximum variety and quantity.
Anionic surfactants are one of the most frequently employed surfactants and make up about 41% of all consumed surfactants. Anionic surfactants are not only the main active components of daily chemical detergents and cosmetics, but also have a wide range of uses in many other industrial fields. Anionic surfactants can play an important role in both industrial and civil applications.
Figure. 1. Schematic structure of anionic surfactants molecule
According to compositions and structures, anionic surfactants fall into three categories:
Soap surfactants: Soap surfactant is an advanced fatty acid salt with hydrocarbon chain between C11 to C18. Soap surfactants that are frequently used include stearic acid, oleic acid and lauric acid. According to the different metal ions (Mn+), soap surfactants can be divided into alkali metal soaps, alkaline earth metal soaps and organic amine soaps.
Sulfate surfactants: Sulfate surfactants can be mainly divided into sulfated oils and higher fatty alcohols. The chemical structure of sulfate surfactant can be shown as ROSO4-M+, in which the higher alcohol hydrocarbon chain R is between C12 and C18. Sulphated castor oil, commonly known as turkish red oil, is a representative type of sulphated oil. It is a yellow or orange viscous liquid with a slight odor. It can be mixed with water and is a non-irritating detergent and wetting agent. Soaps wash the skin and can also be used to solubilize volatile oils or water-insoluble bactericides.
Sulfonate Surfactants: Sulfonate surfactants mainly include aliphatic sulfonates, sulfoaryl sulfonates and sulfonaphthalene sulfonates. The general structure of the molecule is ROSO3-M+. Their water solubility, resistances to calcium and magnesium salt are slightly less soluble than sulfuric acid.
Anionic surfactants are a wide group of chemical compounds which have a large number of applications in household cleaning detergents, personal-care products, textiles, paints, polymers, pesticides, pharmaceuticals, mining, oil recovery, and the pulp and paper industries, agriculture, cosmetic industry, sewage treatment industry, textile industry and daily chemical industry.
Agriculture: It is reported that anionic surfactants which are used as pesticide emulsifiers can reduce the amount of emulsifier from 20% to 3%. This will help to improve the chemical stability of pesticides, reduce costs and pollution, and increase the efficiency of utilization. Anionic surfactants are added to insecticides, rust removers and plant growth regulators to improve soils. Anionic surfactants can improve pesticide efficiency by multiple mechanisms. In particular anionic surfactants can increase the foliar uptake of herbicides, growth regulators, and defoliants. Mixed with insecticides, rust removers and plant growth regulators, anionic surfactants can also be used as soil conditioners.
Cosmetic industry: Anionic surfactants have been widely used in cosmetics industry and in our daily life due to their pharmacological and toxicological safety. Anionic surfactants are mainly used as emulsifier, solubilizer, wetting agent and effective component synergist.
Sewage treatment industry: Anionic surfactants can be used for the treatment of domestic sewage and organic wastewater. Anionic surfactants show cationicity in both acidic and alkaline media. This makes it possible to flocculate precipitates with negatively charged aerosol particles. As the king of new flocculants, anionic surfactants have extensive sources, good effect of treating sewage and simple equipment for subsequent sludge disposal, so they are widely used in sewage treatment field, such as the treatment for grain alcohol wastewater, papermaking wastewater, brewery wastewater, monosodium glutamate wastewater, sugar wastewater, high organic content wastewater, feed wastewater, textile printing and dyeing wastewater.
Textile industry: A large amount of anionic surfactants are used in the textile dyeing and printing industry every year. For example, anionic surfactants with cleaning effect are used in the pretreatment process, and anionic surfactants with percolation effect are used in the dyeing and finishing processes. In addition, some functional products such as leveling agents and fixing agents are also anionic type.
Daily chemical industry: Anionic surfactants are widely used in our daily life. The most common soap consisting of sodium stearate is a kind of anionic surfactants. Anionic products have the characteristics of smooth, high foam and low price, which can reduce the cost of the detergents and other products, while improving the product transparency.
Reference
Wu, Zhaowei, et al. Journal of Power Sources 615 (2024): 235092.
A new method assisted by anionic surfactants was developed for synthesizing the hierarchical microstructured Ni0.8Co0.1Mn0.1(OH)2 precursor. The anionic surfactant β-styrenephosphonic acid (SPA) was used to directionally modulate the growth and arrangement of the precursor nanosheets. The primary nanosheets maintained layer-by-layer growth and orderly alignment. The cathode material Ni0.8Co0.1Mn0.1(OH)2 synthesized from the aforementioned precursor exhibited optimal electrochemical performance.
Preparation of Ni0.8Co0.1Mn0.1(OH)2 Precursor
Analytical grade nickel sulfate hexahydrate (NiSO4·6H2O), cobalt sulfate heptahydrate (CoSO4·7H2O), and manganese sulfate monohydrate (MnSO4·H2O) were used as raw materials, dissolved in ultrapure water (molar ratio Ni:Co:Mn=8:1:1) to prepare a 2 mol·L−1 polymetallic solution. Sodium hydroxide (NaOH), ammonium hydroxide solution (28% NH3 in H2O), and analytical grade β-styrenephosphonic acid (SPA) were used as the precipitant, complexing agent, and surfactant, respectively.
Ni0.8Co0.1Mn0.1(OH)2 aggregates were prepared via a coprecipitation reaction in a 10 L continuous stirred tank reactor (CSTR) filled with argon. Initially, 2.0 L of 0.8 mol·L−1 ammonia aqueous solution was poured into the CSTR as the reaction solution. During the reaction, NaOH solution (4.0 mol·L−1), polymetallic solution (2 mol·L−1), and ammonia solution (1.6 mol·L−1) were pumped into the bottom of the CSTR using peristaltic pumps (with a constant stirring speed of 400 rpm). The reaction solution's pH and ammonia concentration were maintained at 11.1 and 0.8 mol·L−1, respectively, by adding NaOH solution and ammonia solution. The feed rate of the transition metal sulfate solution was 60 mL h−1, and the reaction temperature was kept at 50 °C.
After 13 hours of coprecipitation, the precursor was obtained, settled, washed, and dried. The precursor was mixed with LiOH·H2O in a molar ratio of 1:1.05, calcined at 450 °C for 5 hours, and then sintered at 780 °C for 12 hours under an oxygen atmosphere to obtain the final NCM811 cathode material.
Gómez, José María, et al. Microporous and Mesoporous Materials 270 (2018): 220-226.
Using sodium dodecylbenzene sulfonate (SDBS) as a template, mesoporosity can be introduced into X zeolite. The main innovation of this study lies in using an anionic surfactant as the template. Multistage mesoporous X zeolite enhances the catalytic activity for the deoxygenation of m-toluic acid, increases the yield of toluene, and reduces the deactivation of the catalyst.
The synthesis of NaX zeolite was carried out by the hydrothermal method. The synthesis gel was prepared by dissolving sodium hydroxide in water, followed by the addition of sodium aluminate. Finally, sodium silicate was slowly added to the sodium aluminate-alkali metal hydroxide solution. The molar ratios in the synthesis gel were: SiO2/Al2O3 = 3.44, Na2O/SiO2 = 1.32, H2O/Na2O = 39.8. The mixture was aged at 298K for 24 hours and then crystallized at 373K. The solid was filtered, washed with 0.01 M sodium hydroxide solution to avoid protonation, and dried overnight at 373K. Mesoporous NaX zeolite was synthesized using SDBS (sodium dodecylbenzene sulfonate, C18H29NaO3S, molecular size: 2.26×0.52×0.80nm) as the template by the same method. SDBS was added after sodium aluminate, and the solution was stirred for different times (tSDBS). Different amounts of SDBS related to the critical micelle concentration (CMC) in the medium (2.93mM at 298K) were used. The gel mixture was aged for different times (taging) at 298K and then crystallized at 373K.
Biswas, Sudipta, Villy Sundstrom, and Swati De. Materials Chemistry and Physics 147.3 (2014): 761-771.
TiO2 nanorods with mixed phases (rutile/anatase) were synthesized using an anionic surfactant template. This synthesis was carried out under mild reaction conditions without the need for any rod-shaped templates. The shape and crystallinity of the TiO2 nanomaterials can be adjusted by carefully controlling the concentration of the surfactant.
A Ti (IV) isopropoxide solution dissolved in isopropanol was added dropwise to distilled water with a pH of 1.5. The solution was continuously stirred for 10-12 hours until a transparent colloid was formed. Toluene was added to a round-bottom flask, followed by the freshly prepared TiO2 colloidal mixture and water. The resulting mixture was slowly stirred for 15-20 minutes, then the anionic surfactant sodium dodecyl sulfate (SDS) was added, and the final mixture was slowly stirred at room temperature for 3 hours. Using a separatory funnel, the SDS-coated TiO2 nanoparticles in water were extracted into the toluene phase. The organic phase was dried over CaCl2, then filtered to obtain an optically transparent solution. This solution contained SDS-coated TiO2 nanoparticles.
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