Adsorption of Triclosan onto Organically Modified-Magadiite and Bentonite

Adsorption Structure and Selectivity of Phenols in Water-Immersed Organomontmorillonite Investigated by Molecular Simulation

The two-dimensional interlayer space of layered materials has been highlighted due to their adsorption property, whose nanostructure in the water-immersed state is scarcely understood by experiment. Recent developments in molecular simulation have enabled researchers to investigate the interlayer structure, but water content is necessary for accurate modeling. In the present study, we proposed a theoretical method to estimate the saturated water content and adsorption selectivity of trichlorophenol and phenol in montmorillonite modified with hexadecyltrimethylammonium ions. By analyzing non-bond energy in interlayer water and following comparison with the bulk water model, the saturated water content was estimated to be between 12.7 and 14.2 wt %, which is consistent with the corresponding thermogravimetry data. In the water-immersed state, trichlorophenol was distributed in the center of the interlayer due to the van der Waals interaction with the organocation. Solvation free energy analysis revealed that trichlorophenol was more stable in the interlayer than in the aqueous solution, while the opposite result was obtained for phenol, reproducing the adsorption selectivity reported experimentally. Thus, it was found that both the saturated water content and adsorption selectivity are predicted by molecular simulation. The adsorption site of trichlorophenol changed from the center of the interlayer to the clay surface in the dry state, indicating that accurate modeling in the water-immersed state is significant for revealing the adsorption structure.

Organo magadiites for diclofenac adsorption: influence of the surfactant chain

The presence of drugs in aquatic environments has been considered a global challenge and several remediation technologies have been proposed, including adsorption. In this study, new diclofenac adsorbents were obtained from the reaction of sodium magadiite (Na-Mag) with surfactants dodecylpyridinium chloride hydrate (C12pyCl) and hexadecylpyridinium chloride monohydrate (C16pyCl)), 1-hexadecyltrimethylammonium bromide (C16Br), and dodecyltrimethylammonium bromide (C12Br). The synthesis was carried out in the microwave at 50 °C for 5 min using surfactant amounts of 100% and 200% in relation to the cation exchange capacity of Na-Mag. The elemental analysis indicated that surfactants with a longer organic chain were more incorporated into Na-Mag, whose values were 1.42 and 1.32 mmol g-1 for C16pyMag200% and C16Mag200%, respectively. X-ray diffraction results suggested formation of intercalated products with basal space in the range of 2.81-4.00 nm. Diclofenac was quickly adsorbed on all organophilic magadiites, at an equilibrium time of 1 min. Drug capacity adsorption was influenced by the arrangement and packing density of organic cations, the basal distance, and the organic contents of the samples at high drug concentrations. Alkylpyridinium magadiites exhibited maximum adsorption capacities higher than alkylammonium magadiites, of 96.4, 100.7, 131.7, and 166.1 mg g-1 for C12pyMag100%, C12pyMag200%, C16pyMag100%, and C16pyMag200%, respectively, at pH 6.0 and 30 °C. Diclofenac removal by samples was not affected by the presence of ibuprofen, which was also removed from binary system by organophilic magadiites reaching removal of 76.5% and 86.9% by C16pyMag100% and C16pyMag200%, respectively. Regeneration studies demonstrated a drug removal percentage of 83-92% for C16pyMag and C16Mag after three cycles of adsorption.

Green electrospun Janus membrane of polyether block amide (PEBA) doped with hierarchical magnesium hydrogen phosphate for the removal of pharmaceuticals and personal care products

It has been a challenge to prepared polyether block amide (PEBA) fibrous membrane via solution electrospinning. The only few reported methods though involved hazardous solvents and surfactants which were against the principle of green chemistry. In this work, uniform fibrous membrane of PEBA was successfully fabricated by solution electrospinning with a bio-based solvent dihydrolevoglucosenone (Cyrene). To further improve the mechanical strength and adsorption performance of the PEBA membrane, a hierarchical magnesium hydrogen phosphate (MgHPO4·1.2H2O, MHP) was synthesized to blend evenly into the PEBA matrix. A Janus MHP/PEBA membrane with one side of hydrophobic surface and the other side of hydrophilic surface was subsequently prepared, which exhibited fast adsorption, high capacity, good selectivity and reusability towards ibuprofen, acetaminophen, carbamazepine and triclosan. In addition, the Janus membrane showed high removal efficiency of the above contaminants in secondary wastewater effluent with good long term stability. It demonstrated that this Janus MHP/PEBA membrane had a good potential in practical wastewater treatment.

Critical review on the environmental behaviors and toxicity of triclosan and its removal technologies

As a highly effective broad-spectrum antibacterial agent, triclosan (TCS) is widely used in personal care and medical disinfection products, resulting in its widespread occurrence in aquatic and terrestrial environments, and even in the human body. Notably, the use of TCS surged during the COVID-19 outbreak, leading to increasing environmental TCS pollution pressure. From the perspective of environmental health, it is essential to systematically understand the environmental occurrence and behavior of TCS, its toxicological effects on biota and humans, and technologies to remove TCS from the environment. This review comprehensively summarizes the current knowledge regarding the sources and behavior of TCS in surface water, groundwater, and soil systems, focusing on its toxicological effects on aquatic and terrestrial organisms. Effluent from wastewater treatment plants is the primary source of TCS in aquatic systems, whereas sewage application and/or wastewater irrigation are the major sources of TCS in soil. Human exposure pathways to TCS and associated adverse outcomes were also analyzed. Skin and oral mucosal absorption, and dietary intake are important TCS exposure pathways. Reducing or completely degrading TCS in the environment is important for alleviating environmental pollution and protecting public health. Therefore, this paper reviews the removal mechanisms, including adsorption, biotic and abiotic redox reactions, and the influencing factors. In addition, the advantages and disadvantages of the different techniques are compared, and development prospects are proposed. These findings provide a basis for the management and risk assessment of TCS and are beneficial for the application of treatment technology in TCS removal.

Hydrophilicity of Organically Modified Montmorillonite and Effect on Benzene Adsorption by the Molecular Dynamics Method

Interlayer modification of layered materials with organocations has been known to endow the nanocomposite with hydrophobicity, and adsorption of aromatic compounds in the aqueous phase has been investigated for decades by using montmorillonite, a representative layered clay mineral, as the host material. Usage of the organocation has been believed to be effective due to the π-π interaction with the aromatic adsorbate, the presence of which is not verified spectroscopically in the water-immersed state. Considering that the organocation is generally regarded as a pillar to keep the interlayer space, the interaction between the organocation and adsorbate has not yet been clarified sufficiently. In the present study, we revealed the role of the organocation by the molecular dynamics method, where tetramethylammonium (TMA) and trimethylphenylammonium (TMPA) ions were selected as the representative and simple organocations, and benzene was the adsorbate to exclude the effect of the substitution group. Both H2O and benzene molecules were introduced in the interlayer of TMA- or TMPA-modified montmorillonite to model the water-immersed adsorption structure. It was found that H2O is preferentially distributed on the clay surface, followed by the center of the interlayer when the amount of H2O is large. In the adsorption model, benzene was vertically adsorbed on the clay surface. Radial distribution function analysis revealed that benzene is distributed around both the methyl and the phenyl groups in the TMA and TMPA cations, but the orientation of the phenyl ring is not consistent with that of benzene. Thus, benzene was found not to form the π-π interaction in montmorillonite modified with the TMPA cations in the water-immersed state. Furthermore, the surface was partly covered with the phenyl group in the TMPA cation, decreasing the adsorption area. Therefore, the experimental suggestion that benzene is adsorbed on the clay surface was reproduced by our simulation, and the interaction between the organocation and benzene and surface occupancy should be paid attention to maximize the adsorption property.

Estimation of Adsorbed Amounts in Organoclay by Machine Learning

Adsorption properties of organoclay have been investigated for decades focusing on the morphology and physicochemical properties of two-dimensional interlayers. Experimental studies have previously revealed that the adsorption mechanisms depend on the molecular species of the organocation and adsorbate, making it difficult to estimate the adsorbed amount without experiments. Considering that the adsorption of aromatic compounds has been reported by using various clays, organocations, and adsorbates, machine learning is a promising method to overcome the difficulty. In the present study, we collected adsorption data from the literature and constructed models to estimate the adsorbed amount of the organoclay by random forest regression. The composition of the clay, molecular descriptors of the organocation and adsorbate obtained by the RDKit, and experimental conditions were used as the explanatory variables. Simple model construction by using all the experimental data resulted in low R ² and a mean absolute error. This problem was solved by the correction of the adsorbed amount data by the Langmuir or Freundlich equation and the following model construction at various equilibrium concentrations. The plots of the adsorbed amount estimated by the latter model were located close to the corresponding adsorption isotherm, while that by the former was not. Thus, it was revealed that the adsorbed amount was estimated quantitatively without understanding the adsorption mechanisms individually. Feature importance analysis also revealed that the combination of the organocation and adsorbate is important at high equilibrium concentrations, while the clay should be selected carefully as the concentration gets lower. Our results give an insight into the rational design of the organoclay including the synthesis and adsorption properties.

Investigation of two new low-cost adsorbents functionalized with magnetic nanoparticles for the efficient removal of triclosan and a synthetic mixture

Triclosan (TCS) is widely used in the production of antibacterial products, being often found in wastewater. Therefore, this study developed new materials via soybean hulls (SBH_F) and açaí seeds (AÇS_F) functionalization with iron oxide nanoparticles to be applied in the TCS adsorption. The characterization confirmed the functionalization of the materials. The adsorption results indicated that the equilibrium of the process occurred after 480 and 960 min for SBH_F and AÇS_F, respectively. The maximum adsorptive capacity values were 158.35 and 155.09 mg g^-1 for SBH_F and AÇS_F, respectively, at 318 K. The kinetic and isothermal data better fitted to the pseudo-second-order and Langmuir models. Thermodynamics indicated that the processes had an endothermic, spontaneous, and reversible character. The main adsorption mechanisms were H-bond and π-interactions. The pH and ionic strength studies indicated that the adsorption efficiency has not been reduced pronouncedly. The biosorbents reuse was effective for five cycles. In the synthetic mixture, the removal rate was satisfactory (92.53% and 57.02%, respectively for SBH_F and AÇS_F)_. These results demonstrate the biosorbents high potential for large-scale application.