Cationic Surfactant Hexadecyltrimethylammonium Bromide Research Articles

Comparative analysis of parent and modified ZSM-5 zeolites: Insights from positron annihilation lifetime spectroscopy

Modified zeolite ZSM-5 samples were prepared by synthesis in the presence of the organics acting as mesoporogens: cationic surfactant, hexadecyltrimethylammonium bromide (CTAB) and cationic polymer, polydiallyldimethylammonium chloride (PDADMAC), as well as by alkali etching of the parent zeolite. Properties of modified zeolites were compared to the parent ZSM-5 zeolite. X-ray diffractograms demonstrate that the obtained modified zeolite ZSM-5 samples in all cases have preserved parent crystalline zeolite framework of the MFI-type. However, scanning electron micrographs of the same samples show morphology variations of the modified samples as compared to the starting zeolite. Thermogravimetric analyses show distinct weight loss curves of the samples. Differences have been also noted in the hydroxyl stretching range of the infrared spectra, and in the results of positron annihilation lifetime spectroscopy (PALS) measurements, which indicated dissimilarities by probing free volume in parent and modified zeolite ZSM-5 samples. In that way, PALS as scarcely used technique in zeolite studies, proved its applicability in structural investigation of this kind.

Carbamazepine adsorption with a series of organoclays: removal and toxicity analyses

Organoclays have been used as efficient adsorbents for pharmaceutical pollutants present in waters. Carbamazepine (CBZ) is one of the drugs most frequently found in water bodies. In this study, four organoclays were prepared by modifying bentonite with the cationic surfactants hexadecyltrimethylammonium bromide (HDTMA) and octadecyltrimethylammonium bromide. The synthesized materials were characterized by XRD, CHN, FTIR, TG, BET and SEM analyses, confirming organophilization. The surfactants were interspersed in different arrangements in the interlayer space. CBZ sorption was investigated through batch equilibrium experiments, under variation of the pH, contact time, dosage of adsorbent, and initial drug concentration. Changes in pH showed no adsorption influence. CBZ sorption by the organoclays followed a pseudo-second-order kinetics. The best sorption performance was obtained for the BCN1-HDTMA100 clay, with a capacity of 34.34 ± 1.41 mg g−1, about ten times greater than the unmodified bentonite under the same conditions. This may be attributed to the higher surfactant content. The adsorption isotherm at 25 ºC showed linear behavior. Toxicity tests of the organoclays and corresponding medium in presence of CBZ were carried out. This is a novelty report. Most of the organoclays had no toxicity against Artemia salina. The toxicity of the medium after adsorptive treatment was eliminated. Organoclay-CBZ hybrids were also characterized after adsorption. FTIR and TG analyzes confirmed the incorporation of the drug. Hydrophobic interaction was the dominant contribution evaluated to the adsorption of CBZ. The results demonstrated that organoclays can be a promising alternative adsorbent for the removal of pharmaceutical pollutants in water remediation.

Surface-active agent enhanced FRET effect Cu-doped NH2-MIL-88(Fe) for highly sensitive detection of 3-nitro-L-tyrosine

In this study, Cu-doped NH2-MIL-88(Fe) metal–organic frameworks (MOF) were synthesized via a one-step method. Characterization techniques such as XPS, XRD and FTIR confirmed the successful incorporation of Cu2+ into NH2-MIL-88(Fe), naming this MOF as NH2-MIL-88(Fe)@Cu2+. This MOF was employed to develop a highly sensitive fluorescence sensing platform for detecting 3-nitro-L-tyrosine(3-NT). The potential for fluorescence resonance energy transfer (FRET) was suggested by the spectral overlap between NH2-MIL-88(Fe)@Cu2+'s emission and 3-NT's UV absorption. To augment this effect, cationic surfactant hexadecyltrimethylammonium bromide (CTAB), which self-assembled into nanostructured microspheres above its critical micelle concentration, was utilized. The charged surface of these microspheres, formed by the self-assembly of CTAB, is bound to the MOF surface through electrostatic force and simultaneously attracts 3-NT. Adjusting the solution's pH strengthened the interaction between NH2-MIL-88(Fe)@Cu2+ and 3-NT, thereby enhancing their mutual FRET interaction. Experimental results indicated that CTAB's introduction markedly improved the FRET effects, potentially converting a weak FRET into a strong one and enhancing detection sensitivity and accuracy. Under optimal conditions, NH2-MIL-88(Fe)@Cu2+ detected 3-NT within 0–30 μM range, with a limit of detection (LOD, S/N = 3) of 41.1 nM. Finally, the applicability of the sensor is tested by calibrating measurements in fetal bovine serum samples, achieving good performance in terms of sensitivity, selectivity and reproducibility. This research provides a method for efficient and highly sensitive 3-NT detection and insights into the FRET effect between MOF and target molecules, likely advancing related fields and inspiring future fluorescence sensor designs.

Determination of Lead in Bee Products by Solid Surface Fluorescence Using Complexation and Coacervation at Room Temperature Processes. An Environmental Friendly Methodology.

An accurate, economic and green methodology for Pb(II) monitoring in bee products is proposed. Complexed metal traces were preconcentrated on Nylon membranes using the coacervation phenomenon based on room temperature reaction between the cationic surfactant hexadecyltrimethylammonium bromide and the bile salt sodium cholate. The increase in solid surface fluorescence signal of dyes 8-hydroxyquinoleine and o-phenanthroline due to Pb(II) presence was used for the metal quantification. Experimental variables that influence on preconcentration step and fluorimetric sensitivity were optimized using uni-varied assays. Pb(II) concentration was determined on membranes by solid surface fluorescence at λem = 470nm (λexc = 445nm), using a solid sample holder. The calibration at optimal experimental conditions showed a LOD of 4.2 × 10-4mg Kg-1 with a linear range of 1.28 × 10-3mg Kg-1 to 8.73mg Kg-1 and was successfully applied to Pb(II) quantification in different bee products produced in central west region of Argentina. The proposed methodology was applied to all samples after appropriate dilution. Accuracy methodology was evaluated by comparison of the obtained results with those found by ICP-MS, with percentage relative error under 8%. The precision was better than 0.0344 CV for Pb(II) determination.

Phenol degradation and Sb(V) adsorption by superparamagnetic CTAB-modified iron calcium composite

The heavy metal ions and organic dyes in textile wastewater treatment pose a significant environmental burden and are challenging to effectively manage. A magnetic cationic surfactant hexadecyltrimethylammonium bromide (CTAB), modified iron-calcium composite (referred to as CIC), was prepared using a straightforward method from iron-calcium composites as raw materials. The simultaneous catalytic degradation and adsorption efficiency of phenol and Sb(V) from textile wastewater were evaluated using this material. The results indicate that under conditions of pH 5.0 and a duration of 180 min, both phenol and Sb(V) removal rates exceed 90%. Characterization and experimental findings reveal that CIC possesses magnetic properties, facilitating easy separation, and offers a large surface area, ensuring abundant adsorption sites and stability. Additionally, CIC can assist in the enhanced degradation of phenol by H2O2. Pseudo-second-order kinetics describe the adsorption of Sb(V) by CIC, while oxidative kinetics explain the degradation of phenol. The primary removal mechanisms involve the oxidation and degradation of phenol through the generation of hydroxyl radicals by H2O2 and the formation of Fe-O-Sb complexes between Sb(V) and the iron sites on CIC, as well as the precipitation of Ca-O-Sb compounds between Sb(V) and the calcium sites on CIC. Therefore, the synergistic effect of CIC and H2O2 offers an efficient and environmentally friendly method for the simultaneous removal of Sb(V) and phenol in coupled wastewater, presenting broad prospects for application in wastewater treatment.

Highly sensitive, super high stretchable hydrogel strain sensor with underwater repeated adhesion and rapid healing

Traditional hydrogel-based strain sensors do not work well under water due to extreme swelling and poor adhesion to substrates in water-rich conditions. Inspired by the jellyfish tentacles, a super stretchable dual crosslinked hydrogel was prepared as a motion sensor underwater. The hydrogel contained a cationic surfactant, hexadecyl trimethyl ammonium bromide (CTAB), that crosslinked with hydrophobic lauryl methacrylate (LMA) units in an AA-LMA copolymer. Al3+ ions also coordinated with carboxyl groups in PAA chains and amino groups on chitosan (CS) to form ionic crosslink points. The formed hydrogel exhibited excellent anti-swelling characteristics, superior tensile properties (≈3000%), and rapid self-healing performance. Due to the complementary effects of electrostatic interactions and dynamic chemical bond formation, the hydrogel efficiently and repeatably adhered to various biological tissues, such as hogskin and shrimp, in aquatic environments. Moreover, the hydrogel-based strain sensor showed high sensitivity (GF = 2.04) over a wide sensing range from 0 to 1000% strain with high stability in air and water. The prepared materials' unique performance further expands their application prospects in flexible wearable devices, anti-counterfeiting recognition, and other fields in environmental conditions.

A liquid crystal-based sensor exploiting the aptamer-mediated recognition at the aqueous/liquid crystal interface for sensitive detection of serotonin.

We report here a liquid crystal (LC)-based sensor for detecting serotonin (5-HT); the proposed sensor uses target-specific aptamer recognition at a cationic surfactant decorated-aqueous/LC interface. Our detection strategy focuses on the orientational transition of LCs upon biological interactions at the interface. In this sensing system, the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) forms a self-assembled monolayer at the aqueous/LC interface and triggers the homeotropic orientation of LCs. After introducing the 5-HT specific aptamer, an electrostatic attraction occurs between the cationic CTAB and anionic aptamer. This interaction destructs the surfactant monolayer at the interface, inducing reorganization of LC alignment from homeotropic to tilted conditions. In the increasing 5-HT levels, specific binding between 5-HT and the aptamer diminishes the interaction between the aptamer and CTAB, thereby maintaining the homeotropic alignment of LCs. The orientational transition of the LCs was observed under a polarized optical microscope. The developed biosensor has a linear detection range from 1 to 1000nM and a detection limit of 1.68nM. Moreover, the sensor was applied to a human urine sample and a detection limit of 2.25nM was obtained. Overall, the designed LC-based sensor is a sensitive, simple, cost effective, and selective platform for detecting 5-HT in aqueous solutions.

Functionalized Ordered Mesoporous MCM-48 Silica: Synthesis, Characterization and Adsorbent for CO2 Capture.

The ordered mesoporous silica MCM-48 with cubic Ia3d structure was synthesized using the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) as a template agent and tetraethylorthosilicate (TEOS) as a silica source. The obtained material was first functionalized with (3-glycidyloxypropyl)trimethoxysilane (KH560); further, two types of amination reagents were used: ethylene diamine (N2) and diethylene triamine (N3). The modified amino-functionalized materials were characterized by powder X-ray diffraction (XRD) at low angles, infrared spectroscopy (FT-IR) and nitrogen adsorption-desorption experiments at 77 K. Characterization from a structural point of view reveals that the ordered MCM-48 mesoporous silica has a highly ordered structure and a large surface area (1466.059 m2/g) and pore volume (0.802 cm3/g). The amino-functionalized MCM-48 molecular sieves were tested for CO2 adsorption-desorption properties at different temperatures using thermal program desorption (TPD). Promising results for CO2 adsorption capacities were achieved for MCM-48 sil KH560-N3 at 30 °C. At 30 °C, the MCM-48 sil KH560-N3 sample has an adsorption capacity of 3.17 mmol CO2/g SiO2, and an efficiency of amino groups of 0.58 mmol CO2/mmolNH2. After nine adsorption-desorption cycles, the results suggest that the performance of the MCM-48 sil KH N2 and MCM-48 sil KH N3 adsorbents is relatively stable, presenting a low decrease in the adsorption capacity. The results reported in this paper for the investigated amino-functionalized molecular sieves as absorbents for CO2 can be considered as promising.

Molecular insight into interfacial tension modulated by mixed cationic and anionic surfactants

The oil/water interfacial tension plays a crucial role in tertiary oil recovery, and the low interfacial tension facilitates oil emulsification and stripping. Here, anionic surfactant sodium dodecyl sulfate and cationic surfactant hexadecyltrimethylammonium bromide were employed to study their ability to reduce the oil/water interfacial tension (IFT). Experimental results show that the mixed cationic and anionic surfactants could produce lower IFT than that of individual cationic or anionic surfactant, and the lowest IFT could be obtained at molar ratio of CTAB:SDS = 2:1. Employing molecular dynamics simulation method, the oil/water IFT was calculated and gave same changing trend with that of the experiment. The underlying mechanism of IFT modulated by mixed cationic and anionic surfactants was unveiled from the insight of interfacial structure, interfacial energy, interaction energy between different molecules and interface roughness, and so on. We found the hydration radius of counterion as well as the charge distribution of polar headgroup of surfactant together play crucial role determining the ion distribution inside water phase and surfactant/water interface, and further influencing the IFT. Our study provides an atomic-level understanding of the IFT modulated by cationic and anionic surfactants, and our results might have some references for enhanced oil recovery.

Molecular dynamics simulation of enhancing surfactant flooding performance by using SiO2 nanoparticles

In this study, four kinds of commonly used surfactants in oil fields, namely anionic surfactant sodium dodecyl sulfate (SDS), cationic surfactant hexadecyl trimethyl ammonium bromide (CTAB), nonionic surfactant primary alcobol ethoxylate (AEO-9) and zwitterionic surfactant dodecyl dimethyl carboxyl betaine (BS-12), were used as the research objects. The oil–water interfacial behaviors at different concentrations were studied by molecular dynamics simulation. Then, silica (SiO2) nanoparticles were combined with surfactant to observe the influence of nanoparticles on the configuration of surfactant monolayer, and to explore the optimal conditions for the synergistic flooding scheme of these nanoparticles and surfactant. The thickness and density of the oil–water interface layer, the radial distribution function (RDF) between the surfactant head group and water molecules, the mean square displacement (MSD) of water molecules around the surfactant head group, the oil–water interfacial tension (IFT) and the surfactant interface formation energy (IFE) were investigated. Surfactant flooding performance of different types and the effect of nanoparticles on surfactants were discussed. The results show that the surfactant with different ionic types have the best concentration in reducing the oil–water interfacial tension, and the interfacial tension is significantly reduced to 7.33 mN/m after adding nano-SiO2 particles in BS-12. After kinetic equilibrium, SDS and CTAB are arranged in an approximately regular manner, non-polar groups are inserted into the oil phase, polar groups extend into the aqueous phase, the long-chain head groups of AEO-9 molecules spread and stack at the interface, and BS-12 is irregularly distributed and some molecules are immersed in the oil phase. After adding nano-SiO2 particles, SDS, BS-12 and nano-SiO2 particles can be observed mutually repulsive in the interface morphology, while CTAB, AEO-9 and nano-SiO2 particles exhibit mutual attraction.

Thermal detection of second critical micelle concentration in SDS and CTAB aqueous solutions using a modified Lewis-Nielsen effective thermal model

When surfactant molecules are in solution, they self-assemble into various configurations, with the structural conformation changing upon concentration, temperature, and pH. The thermal transport of aqueous solutions containing anionic surfactant sodium dodecyl sulfate (SDS) and cationic surfactant hexadecyltrimethylammonium bromide (CTAB) was investigated using the thermal wave resonant cavity (TWRC) technique. We use the Lewis-Nielsen effective thermal conductivity model to explain the observed behavior in a new way. We consider that the form factor of the Lewis-Nielsen model relies entirely on surfactant concentration rather than being a constant, as initially was proposed by Lewis and Nielsen. Our findings indicate that the proposed method can detect the transition between spherical and rod-like surfactant micelles. Additionally, this technique could be used to calculate the thermal conductivity of surfactant molecules in water.

Synthesis of Surfactant-Modified Activated Carbon (SMAC) Above Critical Micelle Concentration as Cr(VI) Ion Adsorbent

The synthesis of surfactant-modified activated carbon (SMAC) has been widely studied. However, no research has been conducted to study SMAC concentrations higher than the critical micellar concentration. Therefore, in this study, SMAC was synthesized using anionic and cationic surfactants above CMC (Critical Micelle Concentration) and compared with SMAC below CMC and coconut husk-based activated carbon. This study aimed to determine the surface profile of SMAC and the characteristics and mechanism of metal ion adsorption by SMAC. The selected metal ions were Cr(VI) cations and NH4+ cations as a reference. SMAC was prepared by modifying coconut shell-based activated carbon with anionic surfactant SLS (Sodium Lauryl Sulfate) and cationic surfactant HDTMA-Br (Hexadecyl Trimethyl Ammonium Bromide). Modification of SMAC was performed by three different methods: (a) activated carbon was added gradually with SLS followed by HDTMA-Br, (b) activated carbon was added with HDTMA-Br followed by SLS, (c) activated carbon was mixed with SLS and HDTMA-Br simultaneously. All synthesized SMAC were characterized using FTIR, GSA (Gas Sorption Analyzer), and zeta potential. The FTIR analysis results showed that the synthesized SMAC comprised S=O and (CH3)3N+ groups derived from surfactants. GSA analysis revealed that SMAC has a surface area of 36.790 m2/g, and it was more stable than activated carbon according to the zeta potential result. In this study, the efficiency of SLS and HDTMA-Br in synthesizing SMAC was 99.98% and 95.85%, respectively. SMAC synthesis using method c resulted in Cr(VI) adsorption efficiency of 93.50% and NH4+ adsorption efficiency of 87.37%. In comparison, SMAC below CMC has adsorption capacities of 93.41% for Cr(VI) and 85.05% for NH4+, respectively, whereas Cr(VI) adsorption efficiency by coconut shell-based activated carbon was 99.98%.

Interactions between Nanoclay, CTAB and Linear/Star Shaped Polymers.

The influence of star-shaped (PAA-SS) and linear polyacrylic acid (PAA) with different molecular weights (high—PAA-HMW and low—PAA-LMW) on the structure of the adsorption layer, adsorption amount, electrokinetic and stabilizing properties of the PAA/CTAB/nanoclay suspensions was studied. The properties of the systems containing one of these polymers, the cationic surfactant—hexadecyltrimethylammonium bromide (CTAB) and the surface-modified nanoclay (N-SM) were analyzed using the following techniques: BET, CHN, FT-IR, ED-XRF, XRD, HRTEM, UV-Vis, tensiometry and zeta potential measurements. It was proved that PAA could be used as an effective stabilizer of N-SM. Moreover, the addition of CTAB caused a significant increase in the stability of the systems but decreased the adsorption of PAA on the N-SM surface and changed the structure of the adsorption layers. The largest stability was observed in the PAA-HMW/CTAB system. The PAA polymers and PAA/CTAB complexes adsorbed, especially on the clay surface, influenced the primary distribution of the layered sheets but kept the same basal d-spacing. The adsorption of PAA and the PAA/CTAB complexes took place mainly at the plate edges and on the contact space between the sheets. The obtained results will be used for the preparation of the PAA/CTAB/nanoclay composite for water purification.

Facile fabrication of hierarchical porous silicon/N-doped carbon composites via biomass fermentation treatment for high-performance lithium-ion batteries

Despite the ultrahigh theoretical capacity of Si anodes, their commercial application is severely restricted due to the lack of scalable and low-cost methods to overcome their considerable volume deformation and poor electrical connectivity. Herein, a novel hierarchical porous silicon/N-doped carbon composite (Si/N-PC) is successfully fabricated via simple biomass fermentation with inexpensive wheat flour, and this composite is then used as a high-performance lithium-ion battery (LIB) anode. Wheat flour blended with silicon nanoparticles can be fermented under the action of yeast while releasing carbon dioxide to construct a unique hierarchical porous structure. The added cationic surfactant hexadecyltrimethylammonium bromide not only helps uniformly deposit the Si particles in the wheat flour under the action of electrostatic forces but also forms an N-doped carbon layer in combination with the protein in the wheat flour, realizing full utilization of the raw materials. Systematic tests verify that the N-doped hierarchical porous structure contributes to mitigating the volume change, ensuring electrode stability and enhancing the electrical conductivity of the Si/N-PC composite during the charge-discharge process. As anticipated, the obtained Si/N-PC composite electrode can maintain a reversible discharge capacity of 696.1 mAh g−1 for over 300 cycles at a current density of 1 A g−1, exhibiting a 0.17% capacity loss per cycle from the 3rd to 300th cycle. Additionally, this composite electrode delivers a superior rate capability of 946.1 mAh g−1 at a high current density of 2 A g−1, showing the synergistic benefit of the hierarchical porous structure and N doping. This is the first time that a hierarchical porous silicon/N-doped carbon composite has been prepared via biomass fermentation treatment for use in high-performance LIBs. The overall fabrication process of the Si/N-PC composites is low cost and scalable, providing a sustainable strategy for the production of high-performance Si/C anode materials.

Characterisation of Natural and HDTMA-Br Modified Dijah-Monkin Bentonite Clay: FTIR, XRF, XRD and SEM

In this study, Dijah-Monkin bentonite clay was modified with a cationic surfactant hexadecyltrimethylammonium bromide (HDTMA-Br) at the level of twice the cation exchange capacity (CEC). This process results in the development of hydrophobic organoclay with an improved adsorption capacity. The clay obtained from Zing LGA Taraba State, North-East Nigeria, was beneficiated and pulverised to a particle size of 125 µm. The modification was performed without acid activation to prevent damages to the clay’s crystal structure. The organoclay was characterised for chemical composition, functional groups, mineralogical and surface morphology using X-ray fluorescence (XRF), Fourier Transform Infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The XRD showed an increase in the basal spacing from 15.681Å to 17.758 Å, while the XRF revealed a 5.35% concentration of Br on the modified clay, indicating successful intercalation. The FTIR spectra also revealed the appearance of symmetric and asymmetric stretching bands at 2847.7cm-1 and 2914.8cm-1, respectively, as a consequence of the modification, resulting in more sites for adsorption.

The Effect of Surfactant on Zeolite Preparation from Iraqi Kaolin

In this study, zeolite type A was successfully prepared from kaolin; as a source for silica and alumina. The effect of a cationic surfactant (hexadecyltrimethylammonium Bromide (CTABr) was studied during the preparation of zeolite type A from kaolin clay (structurally modified). The addition ratio was (0.2, 0.4, 0.6, 0.8) CTABr. Also, CTABr was added with different amounts of (25, 75, 150 and 300) mg/l to commercial zeolite type A (surface modified). The prepared samples were characterized using FTIR, surface area and adsorption capacity.
 The results indicated that the adsorption capacity was decreased as the concentration of CTABr is increased. The minimum adsorption capacity was 8.4109 % gH2O / gzeolite using 300 mg/l of surfactant, while it was reached 6.907% gH2O / gzeolite by using 0.8% CTABr of kaolin within the preparation.
 Furthermore, the increased amounts of CTABr causes to increase the surface area of surface modified zeolite where it was increase from (19.938 to 23.8655, 24.377 and 25.2174 (m2/g achieving an increase of 22.6, 25.2 and 29.6% respectively, A large increase more than 100% in the surface area was obtained for the structurally modified samples by increasing the CTABr concentration from (13.0113 to 24.0935, 25.7594, 26.2719 and 27.12) m2/g.

Synthesis of Sodium Lauryl Sulfate (SLS) and Hexadecyltrimethylammonium Bromide (HDTMA-Br) Surfactant-Modified Activated Carbon as Adsorbent for Pb2+ and NO3-

The adsorption efficiency and selectivity of activated carbon as an adsorbent for ions can be improved. One way is to convert activated carbon into surfactant modified activated carbon (SMAC). The surfactants used in this study were the anionic surfactant Sodium Lauryl Sulfate (SLS) and the cationic surfactant hexadecyltrimethylammonium bromide (HDTMA-Br). This research aims to synthesize SMAC to obtain a material with a surface charge and absorb ions better than activated carbon. This research consisted of four stages. The first step was the carbonization of rice husks using a pyrolysis reactor at 400°C for 1 hour. The second stage was carbon activation using 30% ZnCl2 and microwave radiation for 5 minutes and 400 W. The third stage was the modification of activated carbon and characterization by FTIR, SEM, SAA. The fourth stage was the adsorption of Pb cations and nitrate anions by carbon, activated carbon, and SMAC. Several variables were applied, such as the type of surfactant, time, and method of modification. There are three ways of modification: (1) method A, in which activated carbon is brought into contact with SLS then HDTMA-Br. (2) Method B in which activated carbon was contacted with HDTMA-Br then SLS. (3) Method C in which activated carbon was brought into contact with SLS together with HDTMA-Br. All variables were investigated. The results showed that the optimum time for making SMAC for both surfactants was 4 hours, the optimum concentrations of SLS and HDTMA-Br were 60 and 300 ppm, respectively. SMAC made by the C method was the most effective at adsorbing Pb2+ and NO3- with adsorption capacities of 1.376 and 0.896 mg/g, respectively. The success of SMAC synthesis was evidenced by the S=O and (CH3)3N+ groups in the FTIR spectra. The SMAC surface area is smaller than activated carbon, 14.472 m2/g, but the surface morphology is smoother and more homogeneous.

Modification of Activated Carbon from Rice Husk using Hexadecyltrimethylammonium Bromide (HDTMA-Br) Surfactant and ZnCl2 activator and Microwaves for Nitrate Ion Adsorption

Surfactant Modified Activated Carbon (SMAC) is a surfactant-modified activated carbon product. The surfactant used in this study was the cationic surfactant Hexadecyltrimethylammonium Bromide (HDTMA-Br). These surfactants can change the activated carbon's surface to be positively charged due to the presence of the surfactant hydrophilic groups. This SMAC is more selective in absorbing anions, which in this study is for the adsorption of nitrate anions. This research aims to prepare a new material that is superior to activated carbon in absorbing nitrate anions. This research was conducted in several stages. In the first stage, rice husk was carbonized through pyrolysis at 300°C for 10 minutes. In the second stage, carbon was activated using 30% ZnCl2 and microwaves for 5 minutes and 400 W. The third stage was modifying activated carbon by contacting or adsorbing HDTMA-Br on activated carbon. The concentration of HDTMA-Br varied at 200-400 ppm and the adsorption time was 3-7 hours. The success of the modification was measured by the efficiency of HDTMA-Br in modifying activated carbon. This is supported by the results of the characterization of FTIR, GSA, SEM, and thermodynamic parameters. The resulting SMAC was applied for the adsorption of nitrate anions, and the results were compared to carbon and activated carbon. The results indicate that the best SMAC is formed at an optimum concentration of 300 ppm, within 4 hours, with an adsorption efficiency of 97.345%. The characterization results also show that SMAC has been formed, as evidenced by the presence of a peak at a wavenumber of about 1500 cm-1, a C-N group derived from N(CH3)3 in the HDTMA-Br surfactant structure. The SMAC spectra also appeared weak peaks at the wave number 2918 cm-1, which indicated the CH2-R group stretching from the HDTMA-Br surfactant. SEM image shows that HDTMA-Br has covered the pores of activated carbon. Meanwhile, the SMAC surface area is lower than that of activated carbon. Thermodynamic parameters indicate that HDTMA-Br interacts physically with activated carbon. The adsorption capacity of nitrate anion by SMAC is 3,638 mg/g, higher than carbon and activated carbon.

Effect of the Cationic Head Group on Cationic Surfactant-Based Surfactant Mediated Gelation (SMG).

The surfactant-mediated gelation (SMG) method allows us to formulate hydrogels using a water-insoluble organogelator. In this study, we formulated hydrogels using three cationic surfactants, hexadecyltrimethylammonium bromide (CTAB), hexadecyltrimethylammonium chloride (CTAC), and hexadecylpyridinium chloride (CPC)] and an organogelator (12-hydroxyoctadecanoic acid (12-HOA), and studied their structures and mechanical properties. A fiber-like structure similar to that found in the 12-HOA-based organogels was observed by optical microscopy. Small- and wide-angle X-ray scattering profiles showed Bragg peaks derived from the long- and short-spacing of the crystalline structures in the gel fibers and a correlation peak from the surfactant micelles in the small-angle region. Furthermore, the formation of micelles in the hydrogels was confirmed by UV-vis spectroscopic measurements of the gel samples in the presence of Rhodamine 6G. We concluded that the hydrogels prepared by the SMG method in the present systems are orthogonal molecular assembled systems in which two different molecular assembled structures coexist. Among the three surfactant systems, the CTAB system presented the lowest critical gelation concentration and highest sol-gel transition temperature and viscoelasticity. These differences in gel fiber formation and gel properties were discussed from the viewpoint of the degree of solubilization of the gelator molecules in micelles coexisting with gel fibers and diffusion of the gelator molecules in the gel formation process.

Ionic current conduction at low voltage of track-etched double conical nanopores modified by surfactant CTAB

In order to investigate the influence of surfactant on double conical nanopore fabricated with the track-etching technique, we added the cationic surfactant hexadecyl trimethylammonium bromide (CTAB) into the working electrolyte of 0.1 M KCl. By controlling the modified region and the concentration of CTAB, the ionic current conduction of the nanopore could be tuned. Results showed that, in low voltage condition (− 1 V to + 1 V), ionic current conduction of track-etched conical nanopores is mainly decided by the tip size and shape of the nanopores.