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.

Sorption of chromium from aqueous solutions using Fucus vesiculosus algae biosorbent

The presence of heavy metals in wastewater is an environmental concern and the current treatment procedures are very expensive so it is necessary to find effective and inexpensive biosorbents. In this study, Fucus vesiculosus was used as a biosorbent for the biosorption of Cr(III) ions from the aqueous solutions. Biosorption parameters, such as pH, adsorbent dose, contact time, and initial concentrations of Cr(III) had the most impact on the sorption process. The required pH value for sorption was 5, the biosorbent dose was 4.0 g/L, the contact time was seen to occur after 90 min, and the Cr(III) removal decreased from 98.9 to 92%. The maximum biosorption capacity of chromium was 14.12 mg/g. FTIR analysis of Fucus vesiculosus biomass before the sorption process contains carboxyl, amino, hydroxyl, alkyne, and carbonyl groups, and according to the analysis after the sorption process, it was found that Cr(III) metal ions were incorporated within the sorbent during the interaction with (=C-H) active functional groups. The biosorption data were found to be perfectly suited by Langmuir equilibrium isotherm model. According to the results of this study, Fucus vesiculosus is an effective biosorbent for the removal of Cr(III) from aqueous solutions.

Incorporation of copper ion promoted adsorption of anionic dye (Acid Yellow 36) by acrolein-crosslinked polyethyleneimine/chitosan hydrogel: Adsorption, dynamics, and mechanisms

In this study, a novel adsorbent, A-PEI/CS-Cu2+, was developed by crosslinking polyethyleneimine/chitosan hydrogel with acrolein and loading it with copper ions. The adsorption process of A-PEI/CS-Cu2+ on the anionic dye acid yellow 36 (AY36) was investigated by kinetic, isothermal and thermodynamic modeling. It was noteworthy that A-PEI/CS-Cu2+ exhibited rapid adsorption with a 90 % removal rate achieved within just 5 min, which was much faster than the adsorption rate of A-PEI/CS without load of copper ions and showed its potential for rapid adsorption applications. The maximum adsorption capacity for AY36 could reach up to 3114 mg g-1. In addition, the high concentration of saline wastewater was found to have almost no effect on the adsorption reaction in the salt effect test experiment. In five desorption-regeneration cycle experiments, the sample exhibited good recyclability and regeneration performance. The driving force of the adsorption process mainly originated from the electrostatic interaction, hydrogen bonding, and intermolecular interaction, in which the addition of copper ions led to the enhancement of the electrostatic interaction and chelation between A-PEI/CS-Cu2+ and AY36. Overall, the findings suggest the excellent potential of A-PEI/CS-Cu2+ for rapid and efficient adsorption, as well as its suitability for practical applications in wastewater treatment.

Removal of manganese from wastewater using Moringa stenopetala plant parts as an adsorbent material

Removal of heavy metal ions from industrial effluents using environmental friendly bioadsorbents is currently promising approach. However, removal of manganese metal ion via Moringa stenopetala (M.stenopetala) plant material is not studied yet. Thus, parts of the plant has been studied as bio adsorbents for removing toxic manganese ion from aqueous solutions in batch adsorption model. The maximum percent removal of manganese ion obtained from laboratory synthetic wastewater at equilibrium are 96.05 %, 98.90 % and 97.93 % by M. stenopetala plant leaf, bark and seed, respectively. However, the use of M. stenopetala plant leaf procedures an intensive color with unpleasant odor, which is inauspicious. Therefore, M. stenopental plant leaf was no longer examined for isotherm and kinetics studies. The fitness of adsorption data were confirmed based on the value of correlation coefficient (R2). Thus, adsorption by bark best fits of Temkin model with R2 value of 0.9707, while adsorption by seed follows the Langmuir model with R2 value of 0.9733. Adsorption kinetics result indicates that pseudo second-order model well fitted with R2 value of 0.9912 and 0.9947 for bark and seed adsorbents, respectively. Additionally, the applicability of laboratory-developed method was also evaluated on a multicomponent real sample taken from KK textile industry from Addis Abeba, Ethiopia. After characterization, the percentage removal of manganese ion were 79.53 % and 88.93 % for bark and seed, respectively. This achievement is promising and in a good agreement with the results of single component laboratory synthetic wastes.

The Effect of Modifying Canadian Goldenrod (Solidago canadensis) Biomass with Ammonia and Epichlorohydrin on the Sorption Efficiency of Anionic Dyes from Water Solutions

This study examined the effect of modifying Canadian goldenrod (Solidago canadensis) biomass on its sorption capacity of Reactive Black 5 (RB5) and Reactive Yellow 84 anionic dyes. The scope of the research included the characteristics of sorbents (FTIR, elementary analysis, pH_PZC), the effect of pH on dye sorption efficiency, sorption kinetics, and the maximum sorption capacity (describing the data with Langmuir 1 and 2 and Freundlich models). FTIR analyses showed the appearance of amine functional groups in the materials modified with ammonia water, which is indicative of the sorbent amination process. The amination efficiency was higher in the case of materials pre-activated with epichlorohydrin, which was confirmed by elemental analysis and pH_PZC values. The sorption efficiency of RB5 and RY84 on the tested sorbents was the highest in the pH range of 2-3. The sorption capacity of the goldenrod biomass pre-activated with epichlorohydrin and then aminated with ammonia water was 71.30 mg/g and 59.29 mg/g in the case of RB5 and RY84, respectively, and was higher by 2970% and 2510%, respectively, compared to the unmodified biomass. Amination of biomass pre-activated with epichlorohydrin can increase its sorption capacity, even by several dozen times.

Recovering the Soybean Hulls after Peroxidase Extraction and Their Application as Adsorbent for Metal Ions and Dyes

This study is aimed at extending the soybean hulls’ lifetime by their utilization as an adsorbent for metal ions (Cd2+ and Cu2+) and dyes (Reactive Yellow 39 (RY 39) and Acid Blue 225 (AB 225)). ATR-FTIR spectroscopy, FE-SEM microscopy, and zeta potential measurements were used for adsorbent characterization. The effect of the solution’s pH, peroxidase extraction, adsorbent particle size, contact time, the pollutant’s initial concentration, and temperature on the soybean hulls’ adsorption potential was studied. Before peroxidase extraction, soybean hulls were capable of removing 72% Cd2+, 71% Cu2+ (at a pH of 5.00) or 81% RY 39, and 73% AB 225 (at a pH of 3.00). For further experiments, soybean hulls without peroxidase were used for several reasons: (1) due to their observed higher metal ion removal, (2) in order to reduce the waste disposal cost after the peroxidase (usually used for wastewater decolorization) extraction, and (3) since the soybean hulls without peroxidase possessed significantly lower secondary pollution than those with peroxidase. Cd2+ and Cu2+ removal was slightly increased when the smaller adsorbent fraction (710-1000 μm) was used, while the adsorbent particle size did not have an impact on dye removal. After 30 min of contact time, 92% and 88% of RY 39 and AB 225 were removed, respectively, while after the same contact time, 80% and 69% of Cd2+ and Cu2+ were removed, respectively. Adsorption of all tested pollutants follows a pseudo-second-order reaction through the fast adsorption, intraparticle diffusion, and final equilibrium stage. The maximal adsorption capacities determined by the Langmuir model were 21.10, 20.54, 16.54, and 17.23 mg/g for Cd2+, Cu2+, RY 39, and AB 225, respectively. Calculated thermodynamic parameters suggested that the adsorption of all pollutants is spontaneous and of endothermic character. Moreover, different binary mixtures were prepared, and the competitive adsorptions revealed that the soybean hulls are the most efficient adsorbent for the mixture of AB 225 and Cu2+. The findings of this study contribute to the soybean hulls’ recovery after the peroxidase extraction and bring them into the circular economy concept.

The Use of Chitin from the Molts of Mealworm (Tenebrio molitor) for the Removal of Anionic and Cationic Dyes from Aqueous Solutions

The possibility of using chitin from the molts of an insect-ealworm (Tenebrio molitor) to remove anionic (RB5, RY84) and cationic dyes (BV10, BR46) from aqueous solutions was investigated. The scope of the research included, among others: Characteristics of chitin from mealworms (FTIR, SEM, pH_PZC), the effect of pH on sorption efficiency, sorption kinetics (pseudo-first, pseudo-second order, intramolecular diffusion models) and the determination of the maximum sorption capacity (Langmuir and Freundlich models). The sorption efficiency of anionic dyes on chitin from mealworm was the highest at pH 2-3, and for cationic dyes at pH 6. The equilibrium time of sorption of anionic dyes was 240-300 min and for cationic dyes it was 180-240 min. The experimental data on dye sorption kinetics was best described by the pseudo-second order model. The maximum sorption capacity of chitin from the mealworm for the anionic dyes RB5 and RY84 was 121.15 mg/g and 138.55 mg/g, respectively, and was higher than with some carbon-based materials (literature data). In the case of cationic dyes, the sorption capacity of the tested chitin was lower and reached 3.22 mg/g and 59.56 mg/g for BV10 and BR46, respectively.

A systematic study of cellulose-reactive anionic dye removal using a sustainable bioadsorbent

Cellulose-reactive anionic dyes are one of the dominant colorants used in textile finishing. Unfortunately, they also produce large quantities of wastewater that must be treated before discharge, demanding low-cost and sustainable adsorbents that can easily be implemented, especially for developing countries with thriving cotton-based textile sectors. In this study, a high specific surface area (670 m²/g) water hyacinth root powder (WHRP) bioadsorbent that is neither carbonized nor activated was prepared to remove cellulose-reactive anionic blue dye from an aqueous solution. The effect of adsorption pH (pH = 2-8), adsorbent dose (1 g/L-6 g/L), dye concentration (50 mg/L-500 mg/L), adsorbent particle size (50 μm-1000 μm), mixing speed (100 rpm -200 rpm), and adsorption temperatures (22 °C-60 °C) were systematically studied. It was found that the protonation of lignin polyphenols in WHRP at pH = 2 was responsible for the observed high (∼99%) adsorptive removal of reactive blue dye. The maximum equilibrium adsorption capacity was 128.8 mg/g when 1 g/L WHRP and 500 mg/L dye concentration were used. In addition, adsorption isotherms, kinetic models, and adsorption thermodynamics were investigated. Increasing adsorbent dose, decreasing adsorbent particle size, increasing mixing speed, and lowering temperature favored the adsorption of reactive dye to WHRP adsorbent. The batch adsorption data were best fitted with both Langmuir and Temkin models, especially at 22 °C, while the adsorption kinetic behavior was described best using pseudo-second-order kinetics. Adsorption of cellulose-reactive blue dye to WHRP was spontaneous as characterized by the negative Gibbs energy (-11 kJ/mol to -24 kJ/mol) and exothermic with negative enthalpy (-13 kJ/mol to -23 kJ/mol). The overall adsorption process was controlled by more than one mechanism since the intraparticle diffusion was not the only rate-limiting step under our experimental conditions. Taken together, the abundantly available and sustainable WHRP is an efficient adsorbent that could be scaled up for treating cellulose-reactive dye-contaminated water.

Recent Advances in Adsorptive Nanocomposite Membranes for Heavy Metals Ion Removal from Contaminated Water: A Comprehensive Review

Water contamination is one of the most urgent concerns confronting the world today. Heavy metal poisoning of aquatic systems has piqued the interest of various researchers due to the high toxicity and carcinogenic consequences it has on living organisms. Due to their exceptional attributes such as strong reactivity, huge surface area, and outstanding mechanical properties, nanomaterials are being produced and employed in water treatment. In this review, recent advances in the use of nanomaterials in nanoadsorptive membrane systems for wastewater treatment and heavy metal removal are extensively discussed. These materials include carbon-based nanostructures, metal nanoparticles, metal oxide nanoparticles, nanocomposites, and layered double hydroxide-based compounds. Furthermore, the relevant properties of the nanostructures and the implications on their performance for water treatment and contamination removal are highlighted. The hydrophilicity, pore size, skin thickness, porosity, and surface roughness of these nanostructures can help the water permeability of the nanoadsorptive membrane. Other properties such as surface charge modification and mechanical strength can improve the metal adsorption effectiveness of nanoadsorptive membranes during wastewater treatment. Various nanocomposite membrane fabrication techniques are also reviewed. This study is important because it gives important information on the roles of nanomaterials and nanostructures in heavy metal removal and wastewater treatment.

The Use of Gigantochloa Bamboo-Derived Biochar for the Removal of Methylene Blue from Aqueous Solution

In this study, locally grown bamboo (Gigantochloa spp.) was used as feedstock for pyrolysis production of biochar under various pyrolysis temperatures (400–800°C). The resultant biochars were tested for their performance in adsorptive removal of the methylene blue (MB) dye. The scope of the adsorption experiment includes the effects of adsorbent dosage, solution pH, initial adsorbate concentration, and contact time. The adsorption data confirmed that pyrolysis temperature has a significant effect on adsorptive performance, whereas biochar pyrolysed at 500°C (BC500) has the highest adsorptive performance with the maximum adsorption capacity (derived from the Langmuir model) being 86.6 mg g-1. Basic characterisations (SEM, EDX, XRD, FTIR, and BET) were carried out for BC500 where FTIR and SEM confirmed the adsorption of MB onto the biochar, while the BET data showed the reduction of the BET surface area, total pore volume, and pore diameter after the adsorption process.