Aggregation and adsorption of reactive dyes in the presence of an anionic surfactant on mesoporous aminopropyl silica

Effective removal of Allura red food dye from water using cross-linked chitosan-diatomite composite beads

Chitosan (Ch)-diatomite (D) composite beads (Ch-D) were synthesized using epichlorohydrin and tripolyphosphate crosslinkers and then moulded into uniform beads in tripolyphosphate solution. FT-IR and SEM-EDX analyses showed that Ch-D composite adsorbent was successfully synthesized by functionalization of chitosan to Ch-D by hydrogen bonding and electrostatic interactions and improved adsorption capacity for removal of Allura red AC (AR) food dye. The removal rate of AR food dye was found to be 98 % at 25 °C, natural AR dye pH value, 24 h, and at the initial AR dye concentration of 200 mg L-1. The maximum adsorption capacity was found to be 34.7 mg g-1. It was observed that π-π interactions, hydrogen bonds, and electrostatic interactions between the functional groups containing oxygen and amine on the surface of the Ch-D composite and the functional groups of the anionic AR dye, and AR dye adsorption via complexation took place. In light of all this information, the Ch-D composite adsorbent is a promising potential material for the effective treatment of colored pollutants from wastewater.

Facile engineering of mesoporous silica for the effective removal of anionic dyes from wastewater: Insights from DFT and experimental studies

The discharge of dye effluents from the textile industries has become a major environmental issue due to its potential to impart serious harm to human health and aquatic life. Mesoporous silica due to its high chemical stability, large surface area, tunable morphologies, large pore volume and pore size and cost-effectiveness is commonly used to remove such dyes before recycling of the wastewater for agricultural, domestic, and industrial applications. However, the low colloidal stability, the fast aggregation of the silica particles and the slow etching of the silica surface often results in the fast deactivation of the adsorbents and limits their long-term applications. In this study, we report the functionalization of mesoporous silica (SBA-15) with ZnO nanoparticles for the effective removal of anionic dyes. The Zn-silica exhibited highly positive surface with a dipole moment of 172 Debye and high charge transfer efficacy with an energy bandgap (ΔE) of 3.35 eV as revealed by quantum chemical DFT simulations. It achieved excellent removal of Alizarin red dye reaching a removal efficiency of 99.99 % and an adsorption capacity of 50 mg/g. In the presence of heavy metal ions commonly present in wastewater (Cd2+, Co2+, Zn2+, Ni2+, Cu2+ and Hg2+), the Zn-silica maintain excellent stability, high selectivity, and reusability within 5 cycles without a significant decline in efficiency. This study thus presents an effective way of wastewater purification on cost-effective adsorbents for meeting the water scarcity demands.

Sulfonic Acid Derivative-Modified SBA-15, PHTS and MCM-41 Mesoporous Silicas as Carriers for a New Antiplatelet Drug: Ticagrelor Adsorption and Release Studies

Three mesoporous, siliceous materials, i.e., SBA-15 (Santa Barbara Amorphous), PHTS (Plugged Hexagonal Templated Silica) and MCM-41 (Mobil Composition of Matter), functionalized with a sulfonic acid derivative, were successfully prepared and applied as the carriers for the poorly water-soluble drug, ticagrelor. The siliceous carriers were characterized using nitrogen sorption analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM) and elemental analysis. The adsorption studies were conducted in acetonitrile. At the highest equilibrium concentrations, the amount of ticagrelor Q_e that adsorbed onto the examined silicas was in the range of 83 to 220 mg/g, increasing in the following order: PHTS-(CH₂)₃-SO₃H < SBA-15-(CH₂)₃-SO₃H < MCM-41-(CH₂)₃-SO₃H. The equilibrium adsorption data were analyzed using the Freundlich, Jovanovich, Langmuir, Temkin, Dubinin-Radushkevich, Dubinin-Astakhov and Redlich-Peterson models. In order to find the best-fit isotherm for each model, a nonlinear fitting analysis was carried out. Based on the minimized values of the ARE function, the fit of the isotherms to the experimental points for ticagrelor adsorption onto the modified silicas can be ordered as follows: SBA-15-(CH₂)₃-SO₃H (Redlich-Peterson > Dubinin-Astakhov > Temkin), PHTS-(CH₂)₃-SO₃H (Redlich-Peterson > Temkin > Dubinin-Astakhov), MCM-41-(CH₂)₃-SO₃H (Redlich-Peterson > Dubinin-Astakhov > Langmuir). The values of adsorption energy (above 8 kJ/mol) indicate the chemical nature of ticagrelor adsorption onto propyl-sulfonic acid-modified silicas. The results of release studies indicated that at pH 4.5, modified SBA-15 and MCM-41 carriers accelerate the drug dissolution process, compared to the dissolution rate of free crystalline ticagrelor. Intriguingly, modified PHTS silica provides prolonged drug release kinetics compared to other siliceous adsorbents and to the dissolution rate of crystalline ticagrelor. A Weibull release model was employed to describe the release profiles of ticagrelor from the prepared carriers. The time necessary to dissolve 50% and 90% of ticagrelor from mesoporous adsorbents at pH 4.5 increased in the following order: SBA-15-(CH₂)₃-SO₃H < MCM-41-(CH₂)₃-SO₃H < PHTS-(CH₂)₃-SO₃H.

Adaptive methodology to determine hydrophobicity of nanomaterials in situ

The hydrophobicity of nanoparticles (NPs) is a key property determining environmental fate, biological partitioning and toxicity. However, methods to characterize surface hydrophobicity are not uniformly applied to NPs and cannot quantify surface changes in complex environments. Existing methods designed to evaluate the hydrophobicity of bulk solids, chemicals, and proteins have significant limitations when applied to NPs. In this study, we modified and evaluated two methods to determine the hydrophobicity of NPs, hydrophobic interaction chromatography (HIC) and dye adsorption, and compared them to the standard octanol-water partitioning protocol for chemicals. Gold, copper oxide, silica, and amine-functionalized silica NPs were used to evaluate methods based on their applicability to NPs that agglomerate and have surface coatings. The octanol water partitioning and HIC methods both measured Au NPs as hydrophilic, but despite having a small size and stable suspension, NPs could not be fully recovered from the HIC column. For the dye adsorption method, hydrophobic (Rose Bengal) and hydrophilic (Nile Blue) dyes were adsorbed to the NP surface, and linear isotherm parameters were used as a metric for hydrophobicity. CuO was determined to be slightly hydrophilic, while SiO₂ was hydrophilic and Ami-SiO₂ was hydrophobic. The advantages and limitations of each method are discussed, and the dye adsorption method is recommended as the most suitable for application across broad classes of nanomaterials. The dye assay method was further used to measure changes in the surface hydrophobicity of TiO₂ NPs after being suspended in natural water collected from the Alsea Rivers watershed in Oregon. TiO₂ NPs adsorbed Rose Bengal when suspended in ultrapure water, but adsorbed Nile Blue after being incubated in natural water samples, demonstrating a shift from hydrophobic to hydrophilic properties on the outer surface. The dye adsorption method can be applied to characterize surface hydrophobicity of NPs and quantify environmental transformations, potentially improving environmental fate models.

The Effect of SBA-15 Surface Modification on the Process of 18β-Glycyrrhetinic Acid Adsorption: Modeling of Experimental Adsorption Isotherm Data

This study aimed at the adsorption of 18β-glycyrrhetinic acid (18β-GA), a pentacyclic triterpenoid derivative of oleanane type, onto functionalized mesoporous SBA-15 silica and non-porous silica (Aerosil^®) as the reference adsorbent. Although 18β-GA possesses various beneficial pharmacological properties including antitumor, anti-inflammatory, and antioxidant activity, it occurs is small amounts in plant materials. Thus, the efficient methods of this bioactive compound enrichment from vegetable raw materials are currently studied. Siliceous adsorbents were functionalized while using various alkoxysilane derivatives, such as (3-aminopropyl)trimethoxysilane (APTMS), [3-(methylamino)propyl]trimethoxysilane (MAPTMS), (N,N-dimethylaminopropyl)trimethoxysilane (DMAPTMS), and [3-(2-aminothylamino)propyl] trimethoxysilane (AEAPTMS). The effect of silica surface modification with agents differing in the structure and the order of amine groups on the adsorption capacity of the adsorbent and adsorption efficiency were thoroughly examined. The equilibrium adsorption data were analyzed while using the Langmuir, Freundlich, Redlich-Peterson, Temkin, Dubinin-Radushkevich, and Dubinin-Astakhov isotherms. Both linear regression and nonlinear fitting analysis were employed in order to find the best-fitted model. The adsorption isotherms of 18β-GA onto silicas functionalized with APTMS, MAPTMS, and AEAPTMS indicate the Langmuir-type adsorption, whereas sorbents modified with DMAPTMS show the constant distribution of the adsorbate between the adsorbent and the solution regardless of silica type. The Dubinin-Astakhov, Dubinin-Radushkevich, and Redlich-Peterson equations described the best the process of 18β-GA adsorption onto SBA-15 and Aerosil^® silicas that were functionalized with APTMS, MAPTMS, and AEAPTMS, regardless of the method that was used for the estimation of isotherm parameters. Based on nonlinear fitting analysis (Dubinin-Astakhov model), it can be concluded that SBA-15 sorbent that was modified with APTMS, MAPTMS, and AEAPTMS is characterized by twice the adsorption capacity (202.8–237.3 mg/g) as compared to functionalized non-porous silica (118.2–144.2 mg/g).

Sodium dodecyl sulfate-coated-cationized agroforestry residue as adsorbent for benzene-adsorptive sequestration from aqueous solution

The aim of this work is to convert agroforestry residue to a novel adsorbent (M-1CTA-SDS-BT) used for adsorptive benzene sequestration from aqueous solution. In this study, the anionic surfactant-coated-cationized banana trunk was synthesized and characterized for batch adsorption of benzene from aqueous solution. The surface morphology, surface chemistry, surface area, and pore properties of the synthesized adsorbents were examined. It was proven that surface cationization successfully increased the benzene adsorption capacity of sodium dodecyl sulfate-coated adsorbents. The Langmuir isotherm model satisfactorily described the equilibrium adsorption data. The maximum benzene adsorption capacity (q_max) of 468.19 μmol/g was attained. The kinetic data followed the pseudo-second-order kinetic model in which the rate-limiting step was proven to be the film diffusion. The batch-adsorbent regeneration results indicated that the M-1CTA-SDS-BT could withstand at least five adsorption/desorption cycles without drastic adsorption capacity reduction. The findings demonstrated the adsorptive potential of agroforestry-based adsorbent as a natural and cheap material for benzene removal from contaminated water.

Cationic surfactant-modified biosorption of anionic dyes by dried Rhizopus arrhizus

The biosorption of an anionic dye Remazol Black B onto a filamentous, dried fungus, Rhizopus arrhizus, was studied in the presence of the cationic surfactant cetyl trimethyl ammonium bromide (CTAB), which was used as a pH shifter. Without surfactant, the maximum dye uptake capacity was achieved at pH 2.0 and was 434.0 mg dye g^-1 dried fungal biomass. Again, without surfactant, the highest dye uptake capacity, 27.8 mg dye g^-1 dried biomass, occurred at pH 8.0 calculated from the Langmuir adsorption model. Addition of CTAB changed the pH at which the highest dye uptake was obtained. At an initial pH of 8.0 with different CTAB concentrations, the dye uptake capacity increased from 27.8 to 500.0 mg dye g^-1 dried biomass. Furthermore, when 200 mg L^-1 surfactant was added to the biosorption medium at pH 8.0, the amount of dye removed increased significantly. Four equilibrium adsorption models were applied to the results. The applicability of each isotherm was determined using regression correlation and fitting curves. According to the Langmuir model, without surfactant, the highest dye removal capacity at pH 8.0 was found to be 27.8 mg dye g^-1 dried biomass, rising to 500.0 mg g^-1 dried biomass with 200 mg L^-1 CTAB.

Micelles as Soil and Water Decontamination Agents

Contaminated soil and water pose a serious threat to human health and ecosystem. For the treatment of industrial effluents or minimizing their detrimental effects, preventive and remedial approaches must be adopted prior to the occurrence of any severe environmental, health, or safety hazard. Conventional treatment methods of wastewater are insufficient, complicated, and expensive. Therefore, a method that could use environmentally friendly surfactants for the simultaneous removal of both organic and inorganic contaminants from wastewater is deemed a smart approach. Surfactants containing potential donor ligands can coordinate with metal ions, and thus such compounds can be used for the removal of toxic metals and organometallic compounds from aqueous systems. Surfactants form host-guest complexes with the hydrophobic contaminants of water and soil by a mechanism involving the encapsulation of hydrophobes into the self-assembled aggregates (micelles) of surfactants. However, because undefined amounts of surfactants may be released into the aqueous systems, attention must be paid to their own environmental risks as well. Moreover, surfactant remediation methods must be carefully analyzed in the laboratory before field implementation. The use of biosurfactants is the best choice for the removal of water toxins as such surfactants are associated with the characteristics of biodegradability, versatility, recovery, and reuse. This Review is focused on the currently employed surfactant-based soil and wastewater treatment technologies owing to their critical role in the implementation of certain solutions for controlling pollution level, which is necessary to protect human health and ensure the quality standard of the aquatic environment.

Aminopropyl-Silica Hybrid Particles as Supports for Humic Acids Immobilization

A series of aminopropyl-functionalized silica nanoparticles were prepared through a basic two step sol-gel process in water. Prior to being aminopropyl-functionalized, silica particles with an average diameter of 549 nm were prepared from tetraethyl orthosilicate (TEOS), using a Stöber method. In a second step, aminopropyl-silica particles were prepared by silanization with 3-aminopropyltriethoxysilane (APTES), added drop by drop to the sol-gel mixture. The synthesized amino-functionalized silica particles are intended to be used as supports for immobilization of humic acids (HA), through electrostatic bonds. Furthermore, by inserting beside APTES, unhydrolysable mono-, di- or trifunctional alkylsilanes (methyltriethoxy silane (MeTES), trimethylethoxysilane (Me₃ES), diethoxydimethylsilane (Me₂DES) and 1,2-bis(triethoxysilyl)ethane (BETES)) onto silica particles surface, the spacing of the free amino groups was intended in order to facilitate their interaction with HA large molecules. Two sorts of HA were used for evaluating the immobilization capacity of the novel aminosilane supports. The results proved the efficient functionalization of silica nanoparticles with amino groups and showed that the immobilization of the two tested types of humic acid substances was well achieved for all the TEOS/APTES = 20/1 (molar ratio) silica hybrids having or not having the amino functions spaced by alkyl groups. It was shown that the density of aminopropyl functions is low enough at this low APTES fraction and do not require a further spacing by alkyl groups. Moreover, all the hybrids having negative zeta potential values exhibited low interaction with HA molecules.

Surfactant modification of banana trunk as low-cost adsorbents and their high benzene adsorptive removal performance from aqueous solution

The banana trunk was modified using different surfactants (cationic, anionic and non-ionic surfactants), such as ​CTAB, SDS, Pluronic 123, and Triton X-100 to develop a novel low-cost adsorbent for benzene removal from aqueous solution.

Free amino and imino-bridged centres attached to organic chains bonded to structurally ordered silica for dye removal from aqueous solution

Ordered mesoporous SBA-15 type silica was synthesized by sol gel polymerization and reacted with 3-aminopropyltriethoxysilane (AP) or triethylenetetramine (TE), to attach pendant chains or bridging molecules, with basic centres. The materials were characterized by elemental analysis, infrared spectroscopy, and nuclear magnetic resonance in the solid state, X-ray diffractometry, scanning and transmission electron microscopy. The nitrogen sorption/desorption data for SBA-15 and the organofunctionalized SBA-15AP and SBA-15TE silicas resulted in IV type isotherms with hysteresis loops of the H1 type, surface areas of 800; 213 and 457 m(2) g(-1) and average pore diameters of 8.0; 3.2 and 6.8 nm, respectively. The ordered structural features of the mesoporous silica remained preserved after post-functionalization with pendant and bridged organic chains. Sorption data for organofunctionalized silicas gave highly selective sorption capacities for anionic water soluble Reactive Blue dye, with 0.064 and 0.072 mmol g(-1). Negligible sorption was observed with the unmodified mesoporous silica. The results suggest that organofunctionalized silica can be a simple, efficient, inexpensive and suitable method for the effective and selective removal of anionic organic dye pollutants from aqueous solutions.

Mesosilica materials and organic pollutant adsorption: part B removal from aqueous solution

This tutorial review will focus on the removal of organic pollutants from the aqueous phase by mesoporous silica.

Multi-Component Adsorption of Benzene, Toluene, Ethylbenzene, and Xylene from Aqueous Solutions by Montmorillonite Modified with Tetradecyl Trimethyl Ammonium Bromide

Multicomponent adsorption of benzene, toluene, ethylbenzene, and xylene (BTEX) was assessed in aqueous solutions by montmorillonite modified with tetradecyl trimethyl ammonium bromide (TTAB-Mt). Batch experiments were conducted to determine the influences of parameters including loading rates of surfactant, contact time, pH, adsorbate concentration, and temperature on the adsorption efficiency. Scanning electron microscope (SEM) and X-ray diffractometer (XRD) were used to determine the adsorbent properties. Results showed that the modification of the adsorbent via the surfactant causes structural changes of the adsorbent. It was found that the optimum adsorption condition achieves with the surfactant loading rate of 200% of the cation exchange capacity (CEC) of the adsorbent for a period of 24 h. The sorption of BTEX by TTAB-Mt was in the order ofB<T<E<X. The experimental data were fitted by many kinetic and isotherm models. The results also showed that the pseudo-second-order kinetic model and Freundlich isotherm model could, respectively, be fitted to the experimental data better than other available kinetic and isotherm models. The thermodynamic study indicated that the sorption of BTEX with TTAB-Mt was achieved spontaneously and the adsorption process was endothermic as well as physical in nature. The regeneration results of the adsorbent also showed that the adsorption capacity of adsorbent after one use was 51% to 70% of original TTAB-Mt.

Effect of colloidal silica on the spectral behaviour of 7-hydroxycoumarin in aqueous medium

Absorption and emission spectroscopic studies, in combination with FTIR measurements, were carried out for 7-hydroxycoumarin (7HC) and nanocolloidal dispersion of silica. Attempt has been made to identify the characteristics of excited state H-bond formed between colloidal silica and 7HC in aqueous medium. Both the absorption and emission spectra of 7HC was found to be dependent on the concentration of silica. At lower silica concentrations, the absorption spectra decreases with increasing silica concentration, on the other hand, at higher concentration a bathochromic shift occurs in the absorption spectra of 7HC. Fluorescence behaviour followed the opposite trend in comparison to the absorption spectra. It is proposed that at lower silica concentration, excited state H-bond was formed between 7HC and silica dispersions. At higher concentration, the decrease in fluorescence intensity is attributed to the self quenching of adsorbed dye molecules over silica surface following the mechanism of Homo Förster resonance energy transfer (HFRET). Results were correlated with the size and surface charge of colloidal silica as measured by dynamic light scattering and zeta potential studies.

Sorption of SPADNS azo dye on polystyrene anion exchangers: equilibrium and kinetic studies

The sorption of SPANDS from aqueous solution onto the macroporous polystyrene anion exchangers of weakly basic Amberlyst A-21 and strongly basic Amberlyst A-29 in a batch method was studied. The effect of initial dye concentration and phase contact time was considered to evaluate the sorption capacity of anion exchangers. Equilibrium data were attempted by various adsorption isotherms including the Langmuir, Freundlich and Dubinin-Radushkevich (D-R) models. A comparison of kinetic models applied to the adsorption rate constants and equilibrium sorption capacities was made for the Lagergren first-order, pseudo second-order and Morris-Weber intraparticle diffusion kinetic models. The results showed that the adsorption isotherm is in the good agreement with the Langmuir equation and that the adsorption kinetics of SPADNS on both anion exchangers can be best described by the pseudo second-order model.

Removal of basic dye by modified Unye bentonite, Turkey

The adsorption behavior of crystal violet (CV(+)) from aqueous solution onto raw (RB) and manganese oxide-modified (MMB) bentonite samples was investigated as a function of parameters such as initial CV(+) concentration, contact time and temperature. The Langmuir, Freundlich and Dubinin-Radushkevich (D-R) adsorption models were applied to describe the equilibrium isotherms. The Langmuir monolayer adsorption capacities of RB and MMB were estimated as 0.32 and 1.12 mmol/g, respectively. The mean adsorption energy derived from D-R isotherm for MMB showed that the type of adsorption of dye molecules on this material may be defined as chemical adsorption. The adsorption rate was fast and more than half of the adsorbed-CV(+) was removed in the first 55 min for RB and 5 min for MMB at the room temperature. The pseudo-first-order, pseudo-second-order kinetic and the intraparticle diffusion models were used to describe the kinetic data and rate constants were evaluated. The thermodynamic parameters such as DeltaH, DeltaS and DeltaG were found 117.41 kJ/mol, 41.50 J/(molK), -5.07 kJ/mol (RB) and 21.19 kJ/mol 98.34 J/(molK), -7.84 kJ/mol (MMB) at 295.15 K, respectively. The quite high adsorption capacity and high adsorption rate of MMB will provide an important advantage for using of this material in basic dye solution.

The removal of reactive dyes from aqueous solutions using chemically modified mesoporous silica in the presence of anionic surfactant-the temperature dependence and a thermodynamic multivariate analysis

The three-parameter Sips adsorption model was successfully employed to modeled equilibrium adsorption data of a yellow and a red dye onto a mesoporous aminopropyl-silica, in the presence of the surfactant sodium dodecylbenzenesulfonate (DBS) from 25 to 55 degrees C. The results were evaluated in relation to the previously reported surface tension measurements. The presence of curvatures of the van()t Hoff plots suggested the presence of non-zero heat capacities terms (Delta(ads)C(p)). For the yellow dye, it is observed that the values of Delta(ads)H are almost all positive and they decrease in endothermicity, in the absence and in the presence of DBS, from 25 to 55 degrees C. For the red dye, there is an increase in endothermicity in relation to the temperature increase. The negative Delta(ads)G values indicate spontaneous adsorption processes. Almost all adsorption entropy values (Delta(ads)S) were positive. This suggests that entropy is a driving force of adsorption. The adsorption thermodynamic parameters were also evaluated using a new 2(3) full factorial design analysis. The multivariate polynomial modelings indicated that the thermodynamic parameters are also affected by important interactive effects of the experimental factors and not by the temperature changes alone.