Novel adsorbent for malachite green from okra stalks waste: synthesis, kinetics and equilibrium studies

In this study, malachite green (MG) removal was performed with activated carbon synthesized from okra stalks by microwave assisted chemical activation method. In the synthesis of activated carbon, the effects of gas in the microwave, activation, and impregnation rate were investigated. The synthesized activated carbon characterization was investigated using BET, FT-IR, and SEM analyses. The activated carbon surface area achieved was 759.453 m2 g-1. In addition, the surface area of activated carbon synthesized using the conventional method was17.766 m2 g-1. The effect of the initial solution concentration on MG adsorption was investigated. According to the kinetic and equilibrium data, it was found that the adsorption process best fitted the pseudo-second order kinetic model and the Langmuir isotherm. According to the equilibrium data, the maximum adsorption capacity (qmax) of the monolayer was 119.05 mg g-1. In addition, MG adsorption was investigated by the experimental design method. The adsorption capacity at the determined optimum conditions was 99.63 mg g-1. All results show that activated carbon synthesized from waste biomass by combining the conventional method with microwave-assisted impregnation is a cheap and environmentally friendly adsorbent.

Surface activity, mechanisms, kinetics, and thermodynamic study of adsorption of malachite green dye onto sulfuric acid-functionalized Moringa oleifera leaves from aqueous solution

In the present study, activated carbon prepared from H2SO4-functionalized Moringa oleifera leaves (ACMOL) was used as a potential adsorbent for the effective removal of malachite green (MG) dye from aqueous media. FT-IR, SEM, EDS, Zeta potential, XRD, BET, proximate, and CHNS analysis techniques were used for surface characterization of the ACMOL. The adsorption efficiency of the ACMOL was investigated as a function of varying adsorbent dosage (0.02-0.2 g/100 mL), pH (3.0-9.0), ionic strength (0.1-0.5 M KCl), urea concentration (0.1-0.5 M), contact time (30-210 min), and temperature (303-323 K). The representative adsorption isotherms belong to the typical L-type. Maximum percentage removal was found to be 84% (124.40 mg/g) for MG dye concentration (30 mg/L) at pH 7.0 and 303 K with ACMOL dose 0.02 g/100 mL. The adsorption kinetics and equilibrium experimental data of MG dye adsorption on the ACMOL were well explained by the pseudo-second-order kinetics (R2 = 0.99) and Langmuir isotherm model (R2 = 0.99), respectively. The value of adsorption and desorption coefficient was found to be 0.036 min-1 and 0.025 mg min-1/L, respectively. Thermodynamic study showed the spontaneous (ΔG° =  - 31.33, - 31.92, and - 32.49 kJ/mol at temperatures 303 K, 313 K, and 323 K, respectively) and exothermic (ΔH° =  - 13.7 kJ/mol) nature of the adsorption with some structural changes occurring on the ACMOL surface (ΔS° = 58.198 J/K·mol).

Removal of Malachite Green using carbonized material derived from disposable facemasks: optimization of removal process through Box-Behnken design

Water resources are being heavily contaminated due to the huge load of toxic pollutants released by industrial activities. Among various physical and chemical methods, adsorption is considered as a promising method for rapidly removing contaminants from wastewater. In the present study, a novel carbon-based adsorbent was prepared through controlled pyrolysis of disposable facemasks. The properties of carbonized compound (CC) were characterized by FTIR, XRD, SEM and EDX. The pollutant removal efficiency of CC was initially investigated with synthetic dyes Malachite Green (MG) and Congo Red (CR). The peaks observed in FTIR spectra corresponding to C=O and C=C and C-N functional groups on adsorbed CC surface confirm the interaction between dye and CC. The XRD spectra of CC showed strong peaks at 2θ = 26.629, 27.488, 27.810 and 29.404 which correspond to the disordered graphitic plane. The SEM images of CC showed good porosity nature. A quadratic model was developed through response surface methodology by conducting a series of Box-Behnken design experiments. Adequacy of this model variables was ensured by ANOVA tests at P-value <0.05. The lower P-value (<0.0001) and higher F-value (44.54) of the quadratic model showed it was a significant model for dye removal. Finally, the optimal condition to obtain maximum MG removal (rate >99%) was identified by desirability function as CC 1000 and MG 212 mg/L and adsorption time 180 min. Adsorption kinetic study indicates that a pseudo second-order kinetic model showed the best fit with R²=  0.999.

Removal of Cationic Dyes by Iron Modified Silica/Polyurethane Composite: Kinetic, Isotherm and Thermodynamic Analyses, and Regeneration via Advanced Oxidation Process

Emerging dye pollution from textile industrial effluents is becoming more challenging for researchers worldwide. The contamination of water by dye effluents affects the living organisms in an ecosystem. Methylene blue (MB) and malachite green (MG) are soluble dyes with a high colour intensity even at low concentration and are hazardous to living organisms. The adsorption method is used in most wastewater plants for the removal of organic pollutants as it is cost-effective, has a high adsorption capacity, and good mechanical stabilities. In this study, a composite adsorbent was prepared by impregnating iron modified silica (FMS) onto polyurethane (PU) foam to produce an iron modified silica/polyurethane (FMS/PU) composite. The composite adsorbent was utilised in batch adsorption of the cationic dyes MB and MG. The effect of adsorption parameters such as the adsorbent load, pH, initial dye concentration, and contact time were discussed. Adsorption kinetics and isotherm were implemented to understand the adsorption mechanism for both dyes. It was found that the adsorption of MB and MG followed the pseudo-second order model. The Langmuir model showed a better fit than the Freundlich model for the adsorption of MB and MG, indicating that the adsorption occurred via the monolayer adsorption system. The maximum adsorption capacity of the FMS/PU obtained for MB was 31.7 mg/g, while for MG, it was 34.3 mg/g. The thermodynamic study revealed that the adsorption of MB and MG were exothermic and spontaneous at room temperature. In addition, the regeneration of FMS/PU was conducted to investigate the composite efficiency in adsorbing dyes for several cycles. The results showed that the FMS/PU composite could be regenerated up to four times when the regeneration efficiency dropped drastically to less than 20.0%. The impregnation of FMS onto PU foam also minimised the adsorbent loss into the environment.

A Review on Polyacrylonitrile as an Effective and Economic Constituent of Adsorbents for Wastewater Treatment

Water gets polluted due to the dumping of untreated industrial waste into bodies of water, particularly those containing heavy metals and dyes. Industrial water contains both inorganic and organic wastes. Numerous adsorbents that are inexpensive and easily available can be used to address the issue of water deterioration. This review report is focused on polyacrylonitrile as an efficient constituent of adsorbents to extract toxic ions and dyes. It discusses the various formulations of polyacrylonitrile, such as ion exchange resins, chelating resins, fibers, membranes, and hydrogels, synthesized through different polymerization methods, such as suspension polymerization, electrospinning, grafting, redox, and emulsion polymerization. Moreover, regeneration of adsorbent and heavy metal ions makes the adsorption process more cost-effective and efficient. The literature reporting successful regeneration of the adsorbent is included. The factors affecting the performance and outcomes of the adsorption process are also discussed.

Green synthesis of Mn3O4 nanoparticles using Costus woodsonii flowers extract for effective removal of malachite green dye

The pollution of organic dyes such as malachite green is one of the globally critical issues, calling for efficient mitigation methods. Herein, we developed green Mn₃O₄ nanoparticles synthesized using natural compounds extracted from Costus woodsonii flowers under an ultrasound-assisted mode. The materials were characterized using several physicochemical techniques such as Fourier-transform infrared spectroscopy, X-ray diffraction, Energy-dispersive X-ray spectroscopy, scanning electron microscopy, Raman spectroscopy, and N₂ adsorption desorption isotherm measurement. The X-ray diffraction and N₂ isotherm plots confirmed the presence of tetragonal γ-Mn₃O₄ phase and mesoporous structure, respectively. Carbonyl groups derived from flavonoids or carboxylic compounds were found in the surface of green Mn₃O₄ nanoparticles. The effect of pH, contact time, dose, and concentration on the adsorption of malachite green over green Mn₃O₄ was carried out. The maximum malachite green adsorption capacity for green Mn₃O₄ nanoparticles was 101-162 mg g^-1. Moreover, kinetic and isotherm adsorption of malachite green obeyed Langmuir (R_adj.² = 0.980-0.995) and pseudo first-order models (R_adj.² = 0.996-1.00), respectively. Adsorption of malachite green over green Mn₃O₄ was a thermodynamically spontaneous process due to negative Gibbs free energy values (ΔG^ο < 0). Green Mn₃O₄ nanoparticles offered a high stability through the FR-IR spectra analysis. With a good recyclability of 4 cycles, green Mn₃O₄ nanoparticles can be used as potential adsorbent for removing malachite green dye from water.

Performance evaluation of polymer-marine biomass based bionanocomposite for the adsorptive removal of malachite green from synthetic wastewater

In this experimental investigation, feasibility and performance of a polymer hybrid bio-nano composite were evaluated to remove malachite green (MG) under controlled environment conditions. The polymer hybrid bio-nanocomposite was characterized using FTIR, SEM and EDS. The influence of operating variables, namely effect of pH (2-11), nanocomposite dosage (20-100 mg), initial MG concentration (10- 200 mg/L), contact time (10-120 min) and temperature (298-318 K) were explored. The maximum removal efficiency (RE) of 99.79% was achieved at neutral pH at the dosage level of 50 mg with the initial MG concentration of 150 mg/L in 40 min. The equilibrium results revealed that the adsorption of MG data fitted to Langmuir isotherm (R² > 0.970) indicating monolayer adsorption. The maximum adsorption capacity of polymer hybrid nanocomposite was found to be 384.615 mg/g. Kinetic studies were performed using five kinetic models and results showed the pseudo second order model fitted very well with the MG adsorption data (R² > 0.990). The thermodynamic results confirmed that MG adsorption onto polymer hybrid nanocomposite is feasible and (ΔS ^ͦ = 0.2893 kJ/mol K), spontaneous (ΔH ^ͦ = 81.103 kJ/mol K) and exothermic (ΔG ^ͦ < 0). A mechanism is also proposed for the removal of MG using the polymer nanocomposite and identified that electrostatic attraction and hydrogen bonding as the major mechanism for removal of MG. FTIR results confirmed the presence of carboxyl (-COO) and hydroxyl (-OH) groups which helped in effective binding of cationic dye. The overall results revealed that polymer nanocomposite could be used as a potential adsorbent for removing MG from aqueous solution.

Integrated experimental and theoretical insights for Malachite Green Dye adsorption from wastewater using low cost adsorbent

Water pollution is one of the problems that threaten humanity, and to confront it with only experimental procedures is not enough. It is necessary to integrate both practical methods and theoretical calculations to achieve decontamination with the most accurate interpretation. Hence, discussing the experimental mechanism study of Malachite Green (MG) dye adsorption with the help of the application of density functional theory (DFT) calculations is the main goal of this article. The experimental results affirmed that the preparation of γ-Al₂O₃ by precipitation method using (NH₄)₂CO₃ improved the porosity, the surface capability, and the adsorbent capacities (q_max = 210 mg/g) at optimum condition compared with the previous studies. Kinetic and equilibrium studies showed that the adsorption follows the pseudo-second-order model and Freundlich isotherm model, respectively. Also, the calculated and observed thermodynamic parameters exerted positive values of ΔH° and ΔS°, which translates into an endothermic process with increasing disorder of the system. Theoretical calculations at DFT- B3LYP/6-31G (d,P) level of theory were calculated to show the selectivity of using the cationic form of MG in the experimental measurements to find the interaction mechanism. The electronic structure and intramolecular charge transfer of MG, its cationic form and the complex of MG-Al were investigated theoretically at the B3LYP/6-31 G (d,p) level of theory. The equilibrium geometries of MG, its cationic form and the complex of MG-Al were determined, and it was found that these geometries are non-planar. The E_HOMO and E_LUMO energies can be used to calculate the global properties; chemical hardness (η), softness (S) and electronegativity (χ). The calculated non-linear optical parameters (NLO) of the studied compounds, the electronic dipole moment (μ), first-order hyperpolarizability (β), the hyper-Rayleigh scattering (β_HRS) and the depolarization ratio (DR), showed promising optical properties. Finally, the computational and the experimental results indicated that the adsorption efficiency of MG from wastewater was directly associated with the dye electrophilicity power.

Modification of epoxy groups of poly(hydroxylmethyl methacrylate-co-glycidyl methacrylate) cryogel with H3PO4 as adsorbent for removal of hazardous pollutants

Poly(hydroxylmethyl methacrylate-co-glycidyl methacrylate) (p(HEMA-GMA)) macroporous cryogel with high density of epoxy groups was synthesized, and the epoxy groups of the cryogel were modified into phosphonate groups. The effects of dye concentrations, adsorption time, pH, salt concentration, and adsorption temperature on the adsorption of Direct Blue-53 (DB-53) and Reactive Blue-160 (RB-160) dyes were studied. The maximum adsorption capacity was found to be 245.3 and 155.8 mg/g (0.255 or 0.119 mmol/g) for the DB-53 and RB-160 dyes, respectively. The higher adsorption capacity achieved for the DB-53 compared with the RB-160 dye can result from the pendant primary amino groups of the DB-53 dye as well as the smaller size of the dye molecule. The Langmuir isotherm model and the pseudo-second-order kinetic model well described the experimental data. The p(HEMA-GMA)-PO₄^2- adsorbent has many operational advantages for the removal of pollutants. It could be a promising adsorbent to be used in industrial wastewater treatment.

The synthesis and characterisation of porous and monodisperse, chemically modified hypercrosslinked poly(acrylonitrile)-based terpolymer as a sorbent for the adsorption of acidic pharmaceuticals

The synthesis and characterization of porous poly(acrylonitrile(AN)-co-divinylbenzene-80 (DVB-80)-co-vinylbenzylchloride (VBC)) polymers with high specific surface areas and weak anion-exchange character have been successfully researched. The hypercrosslinked (HXL) microspheres were chemically modified with 1,2-ethylenediamine (EDA) to enhance the adsorption selectivity of the HXL materials. The zeta potential of EDA-modified HXL poly(AN-co-DVB-80-co-VBC) revealed that the surface of the modified terpolymer was positively charged. The FT-IR spectra of the chemically modified hypercrosslinked poly(AN-co-DVB-80-co-VBC) showed that the nitrile groups derived from the AN unit were utilised by the presence of diamine groups. The BET-specific surface areas of the EDA-modified hypercrosslinked poly(AN-co-DVB-80-co-VBC) was 503 m2 g−1; meanwhile, the specific surface area of the HXL terpolymer was 983 m2 g−1. The adsorption isotherm data were well fitted by both the Langmuir and Freundlich models, whereas the adsorption kinetics followed the pseudo-second-order kinetic model. This study confirms that the EDA-modified hypercrosslinked poly(AN-co-DVB-80-co-VBC) terpolymer is a potential adsorbent for the adsorption of acidic pharmaceuticals.

Simultaneous Adsorption of Malachite Green and Methylene Blue Dyes in a Fixed-Bed Column Using Poly(Acrylonitrile-Co-Acrylic Acid) Modified with Thiourea

Proper remediation of aquatic environments contaminated by toxic organic dyes has become a research focus globally for environmental and chemical engineers. This study evaluates the adsorption potential of a polymer-based adsorbent, thiourea-modified poly(acrylonitrile-co-acrylic acid) (T-PAA) adsorbent, for the simultaneous uptake of malachite green (MG) and methylene blue (MB) dye ions from binary system in a continuous flow adsorption column. The influence of inlet dye concentrations, pH, flow rate, and adsorbent bed depth on adsorption process were investigated, and the breakthrough curves obtained experimentally. Results revealed that the sorption capacity of the T-PAA for MG and MB increase at high pH, concentration and bed-depth. Thomas, Bohart-Adams, and Yoon-Nelson models constants were calculated to describe MG and MB adsorption. It was found that the three dynamic models perfectly simulate the adsorption rate and behavior of cationic dyes entrapment. Finally, T-PAA adsorbent demonstrated good cyclic stability. It can be regenerated seven times (or cycles) with no significant loss in adsorption potential. Overall, the excellent sorption capacity and multiple usage make T-PAA polymer an attractive adsorbent materials for treatment of multicomponent dye bearing effluent in a fixed-bed column system.

Preparation of Ethylene Glycol Dimethacrylate (EGDMA)-Based Terpolymer as Potential Sorbents for Pharmaceuticals Adsorption

Ethylene glycol dimethacrylate (EGDMA) is used as a crosslinker in poly(acrylonitrile (AN)-co-vinylbenzyl chloride (VBC)) to investigate the effect of long-chain crosslinker to the porosity of the terpolymer system. Poly(AN-co-EGDMA-co-VBC) is synthesized by using precipitation polymerization method and further hypercrosslinked by Friedel-Crafts reaction. FT-IR spectra of poly(AN-co-EGDMA-co-VBC) show that the absorption bands at ~1290 cm-1 that are assigned to the C-Cl vibrations are almost disappeared in hypercrosslinked (HXL) poly(AN-co-EGDMA-co-VBC) polymers, confirming that the hypercrosslinking reaction is successful. SEM images show that the morphologies of the polymers are retained through the hypercrosslinking reactions. Brunauer-Emmett-Teller (BET) analysis shows that hypercrosslinked polymers had a specific surface area up to 59 m2·g-1. The preliminary performance of the terpolymer adsorbent to capture polar analyte is evaluated by adsorbing salicylic acid and mefenamic acid from aqueous solution in a batch system. The maximum adsorption capacity of salicylic acid and mefenamic acid were up to 416.7 mg·g-1 and 625 mg·g-1, respectively, and the adsorption kinetic data obeyed pseudo-second-order rate equation.

Simultaneous Adsorption of Cationic Dyes from Binary Solutions by Thiourea-Modified Poly(acrylonitrile-co-acrylic acid): Detailed Isotherm and Kinetic Studies

In this study, simultaneous adsorption of cationic dyes was investigated by using binary component solutions. Thiourea-modified poly(acrylonitrile-co-acrylic acid) (TMPAA) polymer was used as an adsorbent for uptake of cationic dyes (malachite green, MG and methylene blue, MB) from aqueous solution in a binary system. Adsorption tests revealed that TMPAA presented high adsorption of MG and MB at higher pH and higher dye concentrations. It suggested that there are strong electrostatic attractions between the surface functional groups of the adsorbent and cationic dyes. The equilibrium analyses explain that both extended Langmuir and extended models are suitable for the description of adsorption data in the binary system. An antagonistic effect was found, probably due to triangular (MG) and linear (MB) molecular structures that mutually hinder the adsorption of both dyes on TMPAA. Besides, the kinetic studies for sorption of MG and MB dyes onto adsorbent were better represented by a pseudo-second-order model, which demonstrates chemisorption between the polymeric TMPAA adsorbent and dye molecules. According to experimental findings, TMPAA is an attractive adsorbent for treatment of wastewater containing multiple cationic dyes.

Adsorptive Removal of Methylene Blue from Aquatic Environments Using Thiourea-Modified Poly(Acrylonitrile-co-Acrylic Acid)

The paper evaluates the adsorptive potential of thiourea-modified poly(acrylonitrile-co-acrylic acid), (TA-poly(AN-co-AA)) for the uptake of cationic methylene blue (MB) from aquatic environments via a batch system. TA-poly(AN-co-AA) polymer was synthesized through redox polymerization and modified with thiourea (TA) where thioamide groups were introduced to the surface. Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), CHNS and Zetasizer were used to characterize the physico-chemical and morphological properties of prepared TA-poly(AN-co-AA). Afterwards, it was confirmed that incorporation of thioamide groups was successful. The adsorption kinetics and equilibrium adsorption data were best described, respectively, by a pseudo-second-order model and Freundlich model. Thermodynamic analysis showed the exothermic and spontaneous nature of MB uptake by TA-poly(AN-co-AA). The developed TA-poly(AN-co-AA) polymer demonstrated efficient separation of MB dye from the aqueous solution and maintained maximum adsorption capacity after five regeneration cycles. The findings of this study suggested that synthesized TA-poly(AN-co-AA) can be applied successfully to remove cationic dyes from aquatic environments.