Search Results (83)

Valorization of agro-industrial waste into functional materials is fundamental to the circular economy, especially for addressing the persistent contamination by anionic azo dyes in textile wastewater. This study evaluates guava seeds modified with hexadecyltrimethylammonium bromide (GS-M) as low-cost biosorbents for the removal of Direct Blue 71 (DB71), comparing their performance with that of natural seeds (GS-N) in batch systems and fixed-bed columns. Characterization by infrared spectroscopy (FTIR) and electron microscopy (SEM-EDS) confirmed successful surfactant immobilization, thereby creating a cationic surface with strong electrostatic affinity for anionic dye molecules. Batch experiments showed that GS-M achieved 98% DB71 removal within 120 min, whereas GS-N reached only 58% after 300 min. For GS-M, both pseudo-first-order and pseudo-second-order models fit the kinetic data well, consistent with concurrent electrostatic and hydrophobic interactions; GS-N was best described by the Elovich model, indicating rate limitation by electrostatic repulsion. GS-M maintained removal efficiency above 84% across pH 3–9, whereas GS-N was effective under acidic conditions. Langmuir maximum adsorption capacity (Q_o) values for GS-M were 6.02 mg/g at pH 4 and 7.87 mg/g at pH 8, a 1.5- to 2.2-fold increase over GS-N under matched conditions. Three adsorption–desorption cycles retained ~49% of the initial GS-M capacity, supporting a short-cycle reuse profile rather than indefinite multi-cycle operation. Fixed-bed column performance was highly sensitive to the hydraulic loading rate (v_c), with breakthrough times increasing nearly eightfold as v_c decreased. The Bed Depth Service Time (BDST), Thomas, and Yoon–Nelson models described the dynamic data consistently, yielding a maximum dynamic capacity of 165.6 mg/L under optimal conditions and providing a quantitative basis for scale-up. These results establish surfactant-modified guava seeds as a low-cost, pH-resilient biosorbent system aligned with circular-economy principles for the sustainable remediation of textile wastewater. Full article

Nanomaterials such as cellulose nanocrystals and fumed silica are emerging as excellent thickeners for liquids in a variety of practical applications. Surfactants are often incorporated into the thickening fluids to provide stabilizing components and to control the surface activity of fluids. To develop new thickening materials with desired surface-active properties, it is important to understand the interactions between surfactants and nanoparticles in suspensions. In this work, the interactions between surfactants and nanocrystals/nanoparticles were investigated. Two surfactants, anionic sodium lauryl sulfate-based surfactant (referred to as Stepanol) and cationic hexadecyltrimethylammonium bromide (referred to as HTAB), were studied. Cellulose nanocrystals (referred to as NCC) and fumed-silica nanoparticles (referred to as N20) were used as nanomaterials. The unique feature of this study is that it simultaneously measures rheology, surface activity, and electrical conductivity to determine the influence of ionic surfactants on the behavior and properties of cellulose nanocrystal and fumed silica nanoparticle suspensions. Furthermore, the interactions are observed in the low surfactant concentration range of 0 to 500 ppm. The NCC concentration of NCC–surfactant mixtures was fixed at 1 wt%. Two concentrations of N20 (2 and 5 wt%) were used for N20–surfactant mixtures. The influence of Stepanol was found to be weak whereas HTAB had a strong influence on the rheology of NCC and N20 suspensions. The NCC suspension and surfactant–NCC suspensions were highly non-Newtonian shear-thinning. The N20 suspensions and N20-Stepanol mixtures were nearly Newtonian. The N20-HTAB mixtures were shear-thinning at high HTAB concentrations. The power law model described the rheological behavior of non-Newtonian systems adequately. The consistency and flow behavior indices varied only marginally with the addition of the anionic surfactant Stepanol to NCC and N20 suspensions. With the addition of cationic surfactant HTAB to NCC and N20 suspensions, however, a large increase (20- to 70-fold) in consistency index was observed at high surfactant concentrations. The critical surfactant concentrations where sharp transitions in the rheological properties took place were identified using break points in surface tension and electrical conductivity plots. This study offers valuable insights into tailoring surfactant–nanoparticle systems for practical applications, where precise control of rheological and interfacial properties may be required. Full article

Zeolites are naturally abundant, low-cost aluminosilicate minerals commonly found in sedimentary rock. The surface chemistry of zeolite can be modified via cationic surfactant loading, termed a surfactant-modified zeolite (SMZ), that can be used as an antimicrobial technology in water treatment processes. This raises the possibility that SMZs could be utilised to treat blooms of harmful algae and cyanobacteria; however, there is a lack of understanding of the toxicity of SMZs to non-target microorganisms, including non-problematic algae and cyanobacteria. To address this knowledge gap, this research investigates whether hexadecyltrimethylammonium-bromide (HDTMA-Br) SMZs are toxic to the cyanobacterium Synechococcus elongatus and the microalgae Chlorella vulgaris, Nannochloropsis oculata and Duniallela salina. The cells were exposed to natural zeolite, HDTMA-Br surfactant and HDTMA-Br SMZ for 24 h and analysed 2- and 26 h post-exposure via flow cytometry and imaging pulse amplitude modulated fluorometry. There was an overall trend of reduced cell density in the SMZ and surfactant treatments. The SMZ treatment reduced the effective PSII quantum yield (Y(II)) but increased the quantum yield of regulated energy dissipation for C. vulgaris. When exposed to the surfactant treatment, no Y(II) signals were detected from any species. We conclude that SMZs are toxic to non-target microorganisms, with resilience dependent upon cell wall structure. Full article

Gold nanoparticles (AuNPs) were synthesized via two complementary routes, an inorganic surfactant-mediated method and a plant-extract-assisted biosynthesis, to elucidate how synthesis pathways influence nanoparticle physicochemical properties. In the inorganic route, hexadecyltrimethylammonium bromide (CTAB)-stabilized AuNPs were prepared using CTAB dissolution temperatures of 70–90 °C. UV–Vis spectroscopy showed localized surface plasmon resonance (LSPR) bands at 554–556 nm, while dynamic light scattering (DLS) indicated a decrease in hydrodynamic diameter from 110 to 97 nm with increasing dissolution temperature. Zeta potentials above +40 mV indicated strong electrostatic stabilization, and transmission electron microscopy (TEM) revealed ultrasmall Au cores with a narrow size distribution (2.4–3.0 nm) and a face-centered cubic crystal structure. In the biosynthetic route, AuNPs were obtained using aqueous Erythroxylum coca leaf extracts (1–4% w/v). The extracts exhibited a concentration-dependent red shift (~380 to ~420 nm), and biosynthesized AuNPs displayed LSPR bands in the 550–580 nm range. DLS yielded hydrodynamic diameters of 270–390 nm, with pronounced aggregation (3341 nm) at the lowest extract concentration. Under optimized conditions (HC5, n = 5), reproducible plasmonic and colloidal properties were obtained (maximum absorbance, localized surface plasmon resonance wavelength (λ_max) = 569.6 ± 1.7 nm; hydrodynamic diameter (D_H) = 237.6 ± 24.3 nm; absolute zeta potential (|ζ|)= 32.2 ± 2.6 mV). TEM analysis indicated predominantly quasi-spherical particles with a broader, log-normal size distribution, consistent with extract-mediated growth under heterogeneous organic capping environments. Full article

This study investigates the adsorption of ibuprofen (IBU) and diclofenac sodium (DS) using bentonite modified with varying amounts (50, 75, and 100% of cation exchange capacity—CEC) of two surfactants: octadecyl(dimethylbenzyl)ammonium (ODMBA) chloride and hexadecyltrimethylammonium (HDTMA) bromide. The resulting organobentonites were characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry/thermogravimetric analysis (DSC/TG), and zeta potential analysis. The results indicated that higher surfactant concentrations in organobentonites improved adsorption efficiencies for both drugs, while ODMBA-modified organobentonites exhibited notably larger adsorption capacities than HDTMA-modified samples. The adsorption isotherms fitted well to both the Langmuir and Freundlich models, with a better fit observed for the Freundlich model. The highest adsorption capacities were 102 mg/g for IBU and 160 mg/g for DS on sample OB-100 (organobentonite with 100% of ODMBA). Characterization of samples after drug adsorption, using FTIR, zeta potential and DSC/TG analysis, confirmed drug presence in organobentonites. Adsorption tests of DS in real river water (Danube and Sava rivers) showed that OB-100 demonstrated high removal capacity for DS. The findings suggest that organobentonites are low-cost adsorbents with potential for the removal of pharmaceutical contaminants from real aquatic environments. Full article

Ordered mesoporous silica (OMS) is widely investigated as a mineral carrier for bioactive compounds; however, the adsorption of poorly soluble flavonoids such as quercetin on unmodified silica remains limited, and the effect of cationic surfactant modification on adsorption performance is still insufficiently understood. This study evaluates the adsorption of quercetin on OMS modified with tetrabutylammonium bromide (TBA-Br) and hexadecyltrimethylammonium bromide (HDTMA-Br). Batch adsorption experiments were analyzed using various adsorption isotherm models, and the quality of fit was evaluated based on the coefficient of determination (R²) and the reduced chi-square statistic (χ²/DoF). The results indicated that quercetin adsorption followed a physisorption mechanism, predominantly governed by hydrophobic interactions and surface heterogeneity. Silica modified with HDTMA-Br exhibited a significantly higher maximum sorption capacity compared to OMS-TBA-Br, reaching g_max values of up to 5.2 mg·g⁻¹, whereas the maximum adsorption for OMS-TBA-Br did not exceed 4.2 mg·g⁻¹. The best fit of the experimental data was obtained for models accounting for the heterogeneous nature of the adsorbent surface, particularly the Tóth model. The obtained results clearly demonstrate that modification of OMS with a cationic surfactant possessing a long alkyl chain significantly enhances the adsorption capacity of silica toward quercetin, which is of considerable importance for the design of mineral carriers for bioactive compounds. Full article

This study aimed to design a new composite with promising antimicrobial and antioxidant properties by a simple modification process of natural bentonite (B) with polysaccharide chitosan isolated from edible mushrooms Agaricus bisporus—ChM (sample B–ChM) and subsequently with a cationic surfactant—hexadecyltrimethylammonium bromide—HB (sample B–ChM–HB) for effective removal of mycotoxin zearalenone (ZEN). Characterization confirmed the presence of ChM in B–ChM and both ChM and HB in B–ChM–HB. Compared to non- or slightly inhibitory activity of B and B–ChM, B–ChM–HB showed fungicidal activity against yeast Candida albicans and mycotoxigenic mold Aspergillus flavus, with a reduction of 6.00 log10 (CFU/mL) and 5.32 log10 (CFU/mL), respectively. B–ChM–HB showed a very high neutralization ability on •DPPH (89.03%–95.99%) in the concentration range of 0.625–5.0 mg/mL, the highest ferrous ion chelating ability (80.25%) at a concentration of 0.625 mg/mL, and did not induce lipid peroxidation in the linoleic acid model system. While B and B–ChM exhibited low adsorption of ZEN, its adsorption by B–ChM–HB was significantly higher. The equilibrium results of B–ChM–HB for ZEN were in accordance with the linear isotherm model at pH 3 and 7, pointing out that hydrophobic interactions (partitioning process) were relevant for toxin adsorption by the composite. Similar maximum ZEN adsorbed amounts under the applied experimental conditions (14.4 mg/g) at both pH values suggested that its adsorption was independent of the pH. This study reported for the first time that a novel composite of B with ChM and HB showed promising antimicrobial and antioxidant properties and was an efficient adsorbent for mycotoxin ZEN. Full article

A novel and rapid ball-milling approach was developed in this study to efficiently intercalate hexadecyltrimethylammonium bromide (HDTMA-Br) into vermiculite (VMT) within only 15 min. The raw granular VMT (2–3 mm) was first ground into fine powder using an airflow pulverizer. A suspension containing VMT and HDTMA-Br (1 CEC) in deionized water was then subjected to planetary ball milling at 450 r/min (25 °C), followed by washing and drying to obtain organo-vermiculite (OVMT) with a particle size of 44–5 µm. X-ray diffraction, Fourier-transform Infrared Spectroscopy and Thermogravimetric Analysis analyses confirmed successful intercalation, with the basal spacing $d_{\left(001\right)}$ expanding from 1.46 nm to 4.51 nm. Transmission Electron Microscopy observations further revealed partial delamination of lamellar structures and a pronounced reduction in particle size, supporting the structural reorganization induced by the mechanochemical process. In addition, nitrogen adsorption analysis showed that the BET surface area decreased by 4.05 m²·g⁻¹, while the average pore diameter increased by 3.2 nm, indicating the development of a more hydrophobic interlayer environment. Overall, this approach offers a practical route for producing organophilic silicate materials and shows strong potential for wastewater treatment applications, particularly for the adsorption of organic pollutants and heavy-metal ions. Full article

Hydrothermal treatment has been demonstrated as a highly effective approach to enhance the adsorption properties of coal gangue (CG) for Cd²⁺ and Pb²⁺. This study evaluated the influence of NaOH concentration (X₁), hexadecyltrimethylammonium bromide dosage (X₂) and hydrothermal duration (X₃) on the modified CG’s composition and its adsorption capacities for Cd²⁺ (q_e,Cd) and Pb²⁺ (q_e,Pb). Response Surface Methodology (RSM) was utilized to explore the interactions among these variables, while XRD, SEM-EDX, FTIR and XPS techniques were employed to elucidate the adsorption mechanisms. The results reveal that hydrothermal treatment facilitated the formation of zeolite materials in the modified CG samples. Optimal conditions for Cd²⁺ adsorption (q_e,Cd = 58.4 mg/g) were determined as X₁ = 2.9 mol/L, X₂ = 1 g and X₃ = 16.8 h. For Pb²⁺ adsorption (q_e,Pb = 233.6 mg/g), the optimal conditions were X₁ = 2.4 mol/L, X₂ = 0.57 g and X₃ = 20.7 h. RSM analysis indicated that X₃ significantly influences q_e,Cd with the appropriate range of 14–18 h, while all three factors (X₁, X₂ and X₃) notably affect q_e,Pb, with suitable ranges identified as follows: X₁ = 1.8–3 mol/L, X₂ = 0.4–0.8 g and X₃ = 16–24 h. The primary adsorption mechanism for Cd²⁺ and Pb²⁺ was determined to be ion exchange, with additional Pb²⁺ removal achieved through the precipitation of cerussite (PbCO₃). Full article

In the field of enhanced oil recovery in low-permeability reservoirs, the application of nanomaterials has attracted widespread attention. However, conventional nanomaterials exhibit issues such as large particle size and poor dispersion stability. This study selected SiO₂ nanoparticles with a particle size of 10 nm and combined them with 12 types of commonly used oilfield surfactants. After aging at 120 °C for 48 h, using dispersion stability and interfacial tension (IFT) as evaluation criteria, hexadecyltrimethylammonium bromide (CTAB) was ultimately identified as the optimal modifier. The structure and morphology of the SiO₂ particles were characterized in detail using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and transmission electron microscopy (TEM). The system evaluated the dispersion stability of nanofluids before and after modification, as well as the interfacial properties (IFT reduced to the 10⁻¹ mN/m range) and wettability (oil-wet surfaces reversed to strongly water-wet, with contact angles decreasing to 30°) of nanofluids with different modification degrees. Considering economic factors, the modified nano-SiO₂ system with a ratio of 1:0.5 was selected. Microvisualization experiments revealed that the modified nanoscale system achieves residual oil displacement through three mechanisms: emulsification (reducing residual oil droplet size to enhance mobility), wetting reversal (lowering contact angle to weaken adhesion), and structural separation pressure (counteracting capillary forces to destabilize residual oil). Displacement experiments reveal that in rock cores with permeability ranging from 1 to 100 mD, the modified system exhibits a recovery rate trend that initially increases and then decreases. Nevertheless, it consistently enhances recovery rates, maintaining them above 12%, demonstrating strong application potential. Full article

This study investigates the adsorption of paracetamol from aqueous solutions using natural clinoptilolite and its modified forms. The raw zeolite (p-CLI) was converted into its protonic (H-CLI) and organo-modified (o-CLI) counterparts through ammonium exchange and calcination, and treatment with hexadecyltrimethylammonium bromide (HDTMA-Br), respectively. The materials were characterized by XRD, FT-IR, and SEM analyses. XRD confirmed that the clinoptilolite crystalline framework was preserved after both modifications, while FT-IR and SEM revealed partial removal of exchangeable cations in H-CLI and the formation of an HDTMA-derived organic layer on the external surface of o-CLI. Adsorption experiments were carried out under batch conditions at initial paracetamol concentrations of 0.5–10 mg/L, and equilibrium paracetamol concentrations were determined using differential pulse voltammetry (DPV). The raw clinoptilolite exhibited negligible adsorption capacity (<0.10 mg/g) due to its hydrophilic surface and microporous framework, which limit interaction with neutral organic molecules. Conversion to the protonic form slightly enhanced the adsorption performance (~0.15 mg/g), while HDTMA modification resulted in a modest additional increase (~0.25 mg/g), attributed to the formation of hydrophobic and organophilic surface sites. Overall, the results indicate that surface functionalization can improve the affinity of clinoptilolite toward weakly polar pharmaceuticals; however, the adsorption capacities remain limited. The novelty of this work lies in combining voltametric quantification with a direct comparison of proton-exchanged and surfactant-modified clinoptilolite to elucidate how specific structural and surface changes influence paracetamol uptake. Full article

Steady-shear rheology and surface activity of surfactant–polymer solutions were investigated experimentally. Four different polymers were studied as follows: cationic hydroxyethyl cellulose, nonionic hydroxyethyl cellulose, nonionic guar gum, and anionic xanthan gum. The influence of the following four surfactants on each of the polymers was determined: nonionic alcohol ethoxylate, anionic sodium lauryl sulfate, cationic hexadecyltrimethylammonium bromide, and zwitterionic cetyl betaine. The interaction between cationic hydroxyethyl cellulose and anionic sodium lauryl sulfate was extraordinarily strong, resulting in dramatic changes in rheological and surface-active properties. The consistency increased initially, reached a maximum value, and then fell off with the further addition of surfactant. The surface tension of surfactant–polymer solution dropped substantially and exhibited a minimum value. Thus, the surfactant–polymer solutions were much more surface-active compared with pure surfactant solutions. The interaction between anionic xanthan gum and cationic hexadecyltrimethylammonium bromide was also strong, resulting in a substantial decrease in consistency. The surfactant–polymer solution became less surface-active compared with pure surfactant solution due to the migration of surfactant from solution to polymer. The interactions between other polymers and surfactants were weak to moderate, resulting in small to modest changes in rheological and surface-active properties. Surface activity of surfactant–polymer solutions often increased due to the formation of complexes more surface-active than pure surfactant molecules. Full article

Water pollution by organic dyes poses serious environmental and health challenges, demanding efficient and selective remediation methods. In this study, we engineered tailored organo-clay nanocomposites by modifying montmorillonite with hexadecyltrimethylammonium bromide (HTAB) and intercalating polyethylene glycol (PEG) chains of two distinct molecular weights (PEG200 and PEG4000). Comprehensive characterization techniques (XRD, FTIR, SEM, zeta potential, and TGA) confirmed the successful modification of the composites. Notably, PEG4000 promoted significant interlayer expansion, as evidenced by the shift of the (00l) reflection corresponding to the basal spacing d, indicating an increase in basal spacing. This expansion contributed to the formation of a well-ordered porous framework with uniformly distributed pores. In contrast, PEG200 produced smaller pores with a more uniform distribution but induced less pronounced interlayer expansion. Adsorption tests demonstrated rapid kinetics, achieving equilibrium in under 15 min, and impressive capacities: 420 mg/g of methylene blue (MB) adsorbed on PEG200/MMT@HTAB, and 385 mg/g of Congo red (CR) on PEG4000/MMT@HTAB. The crucial role of PEG chain length in adsorption selectivity was assessed, showing that shorter PEG chains favored methylene blue adsorption by producing narrower pores and faster kinetics, while longer PEG chains enhanced CR uptake via a stable, interconnected pore network that facilitates diffusion of larger dye molecules. Thermodynamic and Dubinin–Radushkevich analyses confirmed that the adsorption was spontaneous, exothermic, and predominantly driven by physical adsorption mechanisms involving weak van der Waals and dipole interactions. These findings highlight the potential of PEG-modified montmorillonite nanocomposites as cost-effective, efficient, and tunable adsorbents for rapid and selective removal of organic dyes in wastewater treatment. Full article

In this study, natural kaolin was modified with hexadecyltrimethylammonium bromide (HDTMA-Br) at two levels corresponding to 50% and 90% of its cation exchange capacity. The resulting materials, designated as HKR-50 and HKR-90, were used as adsorbents for the mycotoxins ochratoxin A (OCHRA) and zearalenone (ZEN). The characterization of the HKRs with several methods (X-ray diffraction, DRIFT spectroscopy, thermal analysis (DTA/TG), SEM, zeta potential measurements, and the determination of the point of zero charge and textural properties) confirmed the presence of surfactant ions on the organokaolinites’ surfaces. The adsorption of ZEN and OCHRA by HKRs followed nonlinear adsorption isotherms, suggesting a complex adsorption mechanism. The adsorption capacities of ZEN and OCHRA were similar for HKR-50 and HKR-90 at pH 3, with higher adsorption observed for ZEN (~13.0 mg/g for HKR-50 and HKR-90 for ZEN and ~8.0 mg/g for HKR-50 and HKR-90 for OCHRA). At pH 7, the adsorption of ZEN and OCHRA was lower than at pH 3, especially for OCHRA, but slightly increased with increased amounts of surfactant on the kaolinite surface (8.5 mg/g for HKR-50 and 10.8 mg/g for HKR-90 for ZEN and 2.6 mg/g for HKR-50 and 4.1 mg/g for HKR-90 for OCHRA). Special attention was paid to the safety assessment of the natural kaolin and HKR-90, and toxicological tests confirmed the safety of both materials, as no adverse effects were observed in rats. Full article

This study centers on the adsorption–flotation coupling extraction of rubidium (Rb⁺) and cesium (Cs⁺) within a titanium silicate (CTS)–cetyltrimethylammonium bromide (CTAB) system, systematically investigating the impacts of pH, aeration rate, CTAB concentration, and flotation time on the extraction efficiency of these elements. Single-factor experiments revealed that the optimal flotation efficiency was achieved when the pH ranged from 6 to 10, the aeration rate was set at 1000 r/min, the CTAB concentration was 0.2 mmol/L, and the flotation duration was 18 min. Under these conditions, the adsorption capacities for Rb⁺ and Cs⁺ were recorded as 128.32 mg/g and 185.47 mg/g, respectively. Employing the response surface optimization method to analyze the interactive effects of these four factors, we found that their order of significance was as follows: pH > aeration rate > CTAB concentration > flotation time. The optimized parameters were determined as pH 8.64, bubble formation rate 1121 r/min, CTAB concentration 0.26 mmol/L, and flotation time 18.47 min. Under these refined conditions, the flotation efficiency for both CTS–Rb and CTS–Cs surpassed any single-factor experiment scenario, with the flotation efficiencies for Rb⁺ and Cs⁺ reaching 95.05% and 94.82%, respectively. This methodology effectively extracts Rb⁺ and Cs⁺ from low-concentration liquid systems, while addressing the challenges of solid–liquid separation for powdered adsorption materials. It holds significant theoretical and practical reference value for enhancing the separation processes of low-grade valuable components and boosting overall separation performance. Full article