Combined molecular dynamics simulations and experimental studies of the removal of cationic dyes on the eco-friendly adsorbent of activated carbon decorated montmorillonite Mt@AC

Differentiated adsorption of acetaminophen and diclofenac via alkyl chain-modified quaternized SBA-15: Insights from molecular simulation

The increasing presence of pharmaceuticals and personal care products (PPCPs) in aquatic systems pose significant environmental concerns. This study addresses this issue by synthesizing quaternized mesoporous SBA-15 (QSBA) with varied alkyl chain lengths of C1QSBA, C8QSBA, and C18QSBA. QSBA utilizes dual mechanisms: hydrophobic interactions via the alkyl chain and electrostatic attraction/ion exchange via the ammonium group. Diclofenac (DCF) and acetaminophen (ACT) were selected as target PPCPs due to their contrasting dissociation properties and hydrophobicity, which are the main characteristics of PPCPs. The adsorption of DCF and ACT revealed that longer alkyl chains enhanced the adsorption capacity of ACT through hydrophobic interactions, whereas dissociated DCF (DCF-) adsorption was superior owing to its high hydrophobicity (log Kow = 4.5) and electrostatic attraction. pH levels between 6 and 8 resulted in a high affinity for DCF-. Notably, among the three alkyl chains, only C18QSBA exhibited the most effective adsorption for DCF-. These PPCPs adsorption trends were confirmed through molecular simulations of adsorption under conditions in which competing ions coexisted. The molecular simulations show that while DCF- has lower adsorption energy than Cl-, OH-, and H3O+ ions in QSBA, enhancing its adsorption under various pH conditions. Conversely, ACT exhibits a higher adsorption energy, which reduces its adsorption efficiency. This suggests the potential application of QSBA with long alkyl chains in the treatment of highly hydrophobic and negatively charged PPCPs. Furthermore, this study emphasizes the importance of simulating adsorption under competing ion conditions.

Revisiting oxidation and reduction reactions for synthesizing a three-dimensional hydrogel of reduced graphene oxide

An improvement to Hummers' method involving a cascade-design graphite oxidation reaction is reported to optimize safety and efficiency in the production of graphite oxide (GrO) and graphene oxide (GO). Chemical reduction using highly alkaline ammonia solution is a novel approach to synthesizing reduced graphene oxide (RGO). In this original research, we revisit the oxidation and reduction reactions, providing significant findings regarding the synthetic pathway to obtain a bioinspired water-intercalated hydrogel of RGO nanosheets. Influential factors in the graphite oxidation reaction, typically the exothermic reaction temperature and hydrogen peroxide effect, are described. Furthermore, the chemical reaction of GO reduction using highly alkaline ammonia solution (pH 14) was investigated to produce hydrated RGO nanosheets assembled in a hydrogel structure (97% water). Three-dimensional assembly and water intercalation are key to preserve the non-stacking state of RGO nanosheets. Therefore, ultrasound transmission to aqueous channels in the macroscopic RGO hydrogel vibrated and dispersed the RGO nanosheets in water. Analytical results revealed the single-layer nanostructures, functional groups, optical band gaps, optimized C/O ratios, particle sizes and zeta potentials of GO and RGO nanosheets. The reversible self-assembly of RGO hydrogels is essential for many applications, such as RGO coatings and polymer/RGO nanocomposites. In a water purification application, the RGO hydrogel was dispersed in aqueous solution by simple agitation and showed a high capacity for organic dye adsorption. After the adsorption, the RGO/dye particles were easily removed by filtration through ordinary cellulose paper. The process of adsorption and filtration is effective and inexpensive for practical environmental remediation. In summary, a bioinspired structure of RGO hydrogel is conceptualized for prospective nanotechnology.

Removal of phenazopyridine from water, synthetic urine, and real sample by adsorption using graphene oxide: A DFT theoretical/experimental approach

Herein, graphene oxide was used as the highly efficient phenazopyridine adsorbent from aqueous medium, synthetic, and human urine. The nanoadsorbent was characterized by different instrumental techniques. The adsorption capacity (1253.17 mg g-1) was reached at pH 5.0, using an adsorbent dosage of 0.125 g L-1 at 298 K. The Sips and Langmuir described the equilibrium data well. At the same time, the pseudo-second order was more suitable for fitting the kinetic data. Thermodynamic parameters revealed the exothermic nature of adsorption with an increase in randomness at the solid-liquid interface. The magnitude of the enthalpy variation value indicates that the process involves the physisorption phenomenon. At the same time, ab initio molecular dynamics data corroborated with the thermodynamic results, indicating that adsorbent and adsorbate establish hydrogen bonds through the amine groups (adsorbate) and hydroxyl groups on the adsorbent surface (weak interactions). Electrostatic interactions are also involved. Additionally, the adsorption assays conducted in simulated medium and human urine showed the excellent performance of adsorbent material to remove the drug in real concentrations excreted by the kidneys (removal values higher than 60%).

Molecular simulation-based insights into dye pollutant adsorption: A perspective review

Growing concerns about environmental pollution have highlighted the need for efficient and sustainable methods to remove dye contamination from various ecosystems. In this context, computational methods such as molecular dynamics (MD), Monte Carlo (MC) simulations, quantum mechanics (QM) calculations, and machine learning (ML) methods are powerful tools used to study and predict the adsorption processes of dyes on various adsorbents. These methods provide detailed insights into the molecular interactions and mechanisms involved, which can be crucial for designing efficient adsorption systems. MD simulations, detailing molecular arrangements, predict dyes' adsorption behaviour and interaction energies with adsorbents. They simulate the entire adsorption process, including surface diffusion, solvent layer penetration, and physisorption. QM calculations, especially density functional theory (DFT), determine molecular structures and reactivity descriptors, aiding in understanding adsorption mechanisms. They identify stable adsorption configurations and interactions like hydrogen bonding and electrostatic forces. MC simulations predict equilibrium properties and adsorption energies by sampling molecular configurations. ML methods have proven highly effective in predicting and optimizing dye adsorption processes. These models offer significant advantages over traditional methods, including higher accuracy and the ability to handle complex datasets. These methods optimize adsorption conditions, clarify adsorbent functionalization roles, and predict dye removal efficiency under various conditions. This research explores MD, MC, QM, and ML approaches to connect molecular interactions with macroscopic adsorption phenomena. Probing these techniques provides insights into the dynamics and energetics of dye pollutants on adsorption surfaces. The findings will aid in developing and optimizing new materials for dye removal. This review has significant implications for environmental remediation, offering a comprehensive understanding of adsorption at various scales. Merging microscopic data with macroscopic observations enhances knowledge of dye pollutant adsorption, laying the groundwork for efficient, sustainable removal technologies. Addressing the growing challenges of ecosystem protection, this study contributes to a cleaner, more sustainable future.

Efficiency of magnesium oxide nanoparticle in contaminants removal from environmental water samples: Optimization through central composite design

This experimental study was conducted to synthesize magnesium oxide (MgO) nanoparticles and investigate their efficiency in removing arsenic, brilliant cresyl blue, and neutral red from aqueous solutions. The MgO nanoparticles were characterized using X-ray diffraction (XRD), energy dispersive X-ray (EDS), Fourier-transform infrared spectroscopy (FTIR), and field emission scanning electron microscopy (FESEM) analyses. The results revealed that the synthesized MgO nanoparticles had a spherical structure with an estimated average size of approximately 30 nm. The influence of solution pH, concentration, adsorbent amount, type of eluent, and interference of interfering ions was examined and optimized for removing arsenic, brilliant cresyl blue, and neutral red. The optimal conditions for the removal process were determined as pH of 7, MgO amount of 0.037 g, ultrasonication time of 16 min, and concentration of 25 mg L-1. The experimental removal efficiencies of arsenic, brilliant cresyl blue, and neutral red in aqueous samples ranged from 88.49% to 96.03%. The results of eluent selection showed that ethanol had the highest removal efficiency of analytes from the absorbent surface. The reusability of the MgO adsorbent demonstrated its effective use for the continuous removal of arsenic, brilliant cresyl blue, and neutral red for at least four consecutive cycles. Overall, the results suggest that MgO nanoparticles could be an effective and cost-efficient adsorbent for removing arsenic, brilliant cresyl blue, and neutral red from real samples.

Temperature effects and molecular insights towards the optimization of polyvinyl alcohol as adsorbent of organic pollutants from aqueous solution

One of the easier methods of wastewater treatment is adsorption due to its simplicity in implementation, environmental friendliness, and economic feasibility. Polyvinyl alcohol (PVA) looks promising as an adsorbent due to its biocompatible, non-toxic, water-soluble and eco-friendly nature. The investigation of PVA for its potential in the adsorption of pollutants has been reported in many studies but the mechanistic understanding of the adsorption is poor. The present study used a theoretical approach through density functional theory and Monte Carlo with molecular dynamics simulations to investigate the adsorption mechanism behaviors of model organic molecules (bromothymol blue (BTB), methylene blue (MB), metronidazole (MNZ) and tetracycline (TC)) on PVA surface. The quantum chemical calculations result showed that with the increase in PVA chains (2, 4, 8, 16, and 32 units), the zero-point energy decreases (from -308.79 to -4922.93 kcal/mol) while the dipole moment increases (from 4.37 to 87.52 Debye). Temperature effect on the PVA chain structures showed the same trends for all the chain units and with the increase in temperature (50-600 K), there are no appreciable changes in zero-point energy, enthalpy energy increases while Gibbs free energy decreases. Considering PVA-pollutant complexes, the effects of temperature on the structures showed that there are no appreciable changes in the zero-point energy, Gibbs free and thermal energies increase with an increase in temperature while the kinetic rate of reactions decreases with an increase in temperature. The enthalpy of the reaction showed different trends with antibiotic and dye complexes. In all the thermodynamic properties investigated and the rate of reaction, the order of affinity of the pollutants with PVA followed TC > MNZ > MB > BTB. Monte Carlo simulation was used to investigate the adsorption behavior of the pollutants on the surface of PVA. The negative adsorption energies (-366.56 to -2266.81 kcal/mol) in terms of affinity towards the pollutants on the surface of PVA followed the sequence TC > MNZ > BTB > MB and the molecular dynamic simulation results followed the same order. The obtained results give valuable insights into the mechanism and performance of PVA as an adsorbent. Most of these computational observations are in good agreement with the available experimental results.

Synthesis, characterization, and photocatalytic activities of green sol-gel ZnO nanoparticles using Abelmoschus esculentus and Salvia officinalis: A comparative study versus co-precipitation-synthesized nanoparticles

Background

The development of green chemistry methods involving plant-based nanoparticle synthesis presents an affordable and eco-friendly approach for wastewater treatment and color removal. This study aimed to synthesize ZnO nanoparticles using the sol-gel method with Salvia officinalis and Abelmoschus esculentus plants, examining their photocatalytic efficiency for organic dye removal.

Methods

To compare the properties of ZnO nanoparticles, another type of ZnO-NPs was synthesized using the co-precipitation method. The characterization of synthesized nanoparticles was performed using thermogravimetric analysis (TGA-DTG), X-ray diffraction (XRD), Dynamic Light Scattering (DLS), Zeta potential (ZP), field emission scanning electron microscopy (FE-SEM), Energy Dispersive X-ray (EDX), Fourier transform infrared spectroscopy (FTIR), and UV-Vis spectrophotometry.

Results

Based on XRD results, the average crystalline size of nanoparticles was calculated using the Debye-Scherer equation for synthesized nanoparticles using the S. officinalis at 22.99 nm and for the A. esculentus at 29.79 nm, and for the co-precipitation method at 18.83 nm. The FE-SEM images showed spherical ZnO nanoparticles. Photocatalytic properties of ZnO-NPs were investigated for remove of methylene blue organic dye in the presence of UV light. The pH 10 was identified as the best pH, which had the highest percentage of color degradation. All three types of nanoparticles were tested by up to 360 min to optimize the dyeing time. For A. esculentus, the highest percentage of color removal occurred in the first 90 min (41.0 %), for S. officinalis nanoparticles between 75 and 90 min (86.9 %), and for chemically synthesized nanoparticles between 30 and 45 min (100 %).

Conclusions

In conclusion, the best MB dye degradation capacity belonged to co-precipitation ZnO nanoparticles followed by S. officinalis and A. esculentus nanoparticles.

Tailoring carboxylatopillar[5]arene-modified magnetic graphene oxide nanocomposites for the efficient removal of cationic dyes

A carboxylatopillar[5]arene-embellished (CP5) magnetic graphene oxide nanocomposite (MGO@CP5) was smoothly constructed via a mild layer-by-layer method. The morphology, structure, and surface characteristics of this nanocomposite was investigated by field-emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, zeta potential, and other techniques. Benefiting from a high capture ability for small molecules of CP5 as a supramolecular host molecule, along with a negative surface charge and large surface area of MGO@CP5, this nanocomposite exhibits an ultrafast, efficient adsorption property for representative cationic dyes: methylene blue (MB) and basic fuchsin (BF). The removal efficiency of MB and BF can reach nearly 99% within 3 min, while the maximum adsorption capacity of the two dyes reaches 240 mg g-1 for MB and 132 mg g-1 for BF. Furthermore, owing to excellent magnetic responsiveness from the tight loading of Fe3O4 nanoparticles on graphene oxide, MGO@CP5 could be easily and magnetically separated, regenerated, and reused four times without an evident reduction in the removal efficiency (>95%). Impressively, the adsorption property of MGO@CP5 reveals a strong tolerance to pH changes and ionic strength interference, which renders it a promising adsorbent in the field of water treatment.

Magnetic Fe-doped TiO2@Fe3O4 for metronidazole degradation in aqueous solutions: Characteristics and efficacy assessment

Antibiotics present in aquatic environments can contribute to the emergence of antibiotic-resistant bacterial strains, posing potential threats to public health. Therefore, efficient strategies to remove these compounds from water systems are essential to reduce both ecological and human health risks. This research aimed to assess the photocatalytic removal efficiency of metronidazole (MET) from an aqueous solution using a 15-W bare UVC lamp and magnetic nanocatalysts (Fe-doped TiO2@Fe3O4), which were synthesized using the sol-gel technique. Furthermore, scanning electron microscopy with integrated energy dispersive X-ray analysis (SEM/EDX), X-ray diffractometry (XRD), Differential reflectance spectroscopy (DRS), vibrating sample magnetometer (VSM), and Fourier transform infrared spectroscopy (FTIR) analysis were carried out to characterize the synthesized nanocatalysts. The influence of several factors, such as pH, initial MET, and nanocatalysts concentrations during reaction times of 15-120 min, was studied. The characterization results confirmed that Fe and Ti were successfully integrated into the Fe- doped TiO2@Fe3O4 nanocomposite. Highest MET degradation efficiency (99.37 %) was observed at a pH of 3, with an initial MET concentration of 60 mg/L, nanoparticle dosage of 800 mg/L, and a reaction time of 90 min. The stability of the nanocatalyst was acceptable. The results suggest that OH ions may play a crucial role in the degradation of MET demonstrating photocatalytic degradation can be an effective way to remove MET from water resources. This research sets a precedent for future endeavors aimed at harnessing photocatalysis for environmental remediation of pharmaceutical pollutants.

Nano-silica from white silica sand functionalized with PANI-SDS (SiO2/PANI-SDS) as an adsorbent for the elimination of methylene blue from aqueous media

Natural resources including sand are one of the best approaches for treating dye-polluted wastewater. The SiO2/PANI-SDS nanocomposite was synthesized by self-assembly and intermolecular interaction. The physicochemical features of the SiO2/PANI-SDS nanocomposite were explored by FT-IR, XRD, SEM, TEM, EDX, and N2 adsorption-desorption techniques to be evaluated as an adsorbent for the MB. The surface area of the SiO2/PANI-SDS is 23.317 m2/g, the pore size is 0.036 cm3/g, and the pore radius is 1.91 nm. Batch kinetic studies at different initial adsorbate, adsorbent and NaCl concentrations, and temperatures showed excellent pseudo-second-order. Several isotherm models were applied to evaluate the MB adsorption on the SiO2/PANI-SDS nanocomposite. According to R2 values the isotherm models were fitted in the following order: Langmuir > Dubinin-Radushkevich (D-R) > Freundlich. The adsorption/desorption process showed good reusability of the SiO2/PANI-SDS nanocomposite.

Exploitation of expired cellulose biopolymers as hydrochars for capturing emerging contaminants from water

Expired chemicals pose a potential environmental threat to humans and living organisms. Herein, we proposed a green approach whereby expired cellulose biopolymers were converted to hydrochar adsorbents and tested for removing the emerging pharmaceutical contaminants of fluoxetine hydrochloride and methylene blue from water. A thermally stable hydrochar was produced with an average particle size of 8.1 ± 1.94 nm and a mesoporous structure that exhibited a larger surface area than the expired cellulose by 6.1 times. The hydrochar was efficient in removing the two contaminants with efficiencies that reached above 90% under almost neutral pH conditions. Adsorption exhibited fast kinetics and regeneration of the adsorbent was successful. The adsorption mechanism was hypothesized in view of the Fourier Transform Infra-Red (FTIR) spectroscopy and pH effect measurements to be mainly electrostatic. A hydrochar/magnetite nanocomposite was also synthesized, and its adsorption behavior for both contaminants was tested and it revealed an enhanced percent removal relative to the bare hydrochar by 27.2% and 13.1% for FLX and MB, respectively. This work supports the strategies for zero waste management and the circular economy.

Dependency of Crystal Violet Dye Removal Behaviors onto Mesoporous V2O5-g-C3N4 Constructed by Simplistic Ultrasonic Method

This research examined the production of a V2O5-g-C3N4 nanocomposite to remove organic dyes from wastewater. To generate the V2O5-g-C3N4 nanocomposite, the sonication method was applied. The testing of V2O5-g-C3N4 with various dyes (basic fuchsin (BF), malachite green (MG), crystal violet (CV), Congo red (CR), and methyl orange (MO)) revealed that the nanocomposite has a high adsorption ability towards BF, MG, CV, and CR dyes in comparison with MO dye. It was established that the modification of pH influenced the removal of CV by the V2O5-g-C3N4 nanocomposite and that under optimal operating conditions, efficiency of 664.65 mg g−1 could be attained. The best models for CV adsorption onto the V2O5-g-C3N4 nanocomposite were found to be those based on pseudo-second-order adsorption kinetics and the Langmuir isotherm. According to the FTIR analysis results, the CV adsorption mechanism was connected to π–π interactions and the hydrogen bond.

Rapid, Highly-Efficient and Selective Removal of Anionic and Cationic Dyes from Wastewater Using Hollow Polyelectrolyte Microcapsules

Herein, poly (allylamine hydrochloride) (PAH)/ poly (styrene sulfonic acid) sodium salt (PSS) microcapsules of (PAH/PSS)2PAH (P2P MCs) and (PAH/PSS)2 (P2 MCs) were obtained by a layer-by-layer method. The P2 MCs show high adsorption capacity for Rhodamine B (642.26 mg/g) and methylene blue (909.25 mg/g), with an extremely low equilibrium adsorption time (~20 min). The P2P MCs exhibited high adsorption capacities of reactive orange K-G (ROKG) and direct yellow 5G (DY5G) which were 404.79 and 451.56 mg/g. Adsorption processes of all dyes onto microcapsules were best described by the Langmuir isotherm model and a pseudo-second-order kinetic model. In addition, the P2P MCs loaded with reactive dyes (P2P–ROKG), could further adsorb rhodamine B (RhB) dye, and P2 MCs that had adsorbed cationic MB dyes could also be used for secondary adsorption treatment of direct dye waste-water, respectively. The present work confirmed that P2P and P2 MCs were expected to become an excellent adsorbent in the water treatment industry.