Ophiorrhiza mungos-Mediated Silver Nanoparticles as Effective and Reusable Adsorbents for the Removal of Methylene Blue from Water

Green synthesis of silver nanoparticles (AgNPs) using a plant extract has attracted significant attention in recent years. It is found as an alternative for other physicochemical approaches because of its simplicity, low cost, and eco-friendly rapid steps. In the present study, Ophiorrhiza mungos (Om)-mediated AgNPs have been shown to be effective bioadsorbents for methylene blue (MB) dye removal (88.1 ± 1.74%) just after 1 h at room temperature in the dark from an aqueous medium for the first time. Langmuir and Freundlich isotherms fit the experimental results having the correlation coefficient constants R2 = 0.9956 and R2 = 0.9838, respectively. From the Langmuir fittings, the maximum adsorption capacity and adsorption intensity were found to be 80.451 mg/g and 0.041, respectively, indicating the excellent performance and spontaneity of the process. Taking both models under consideration, interestingly, our findings indicated a fairly cooperative multilayer adsorption that might have been governed by chemisorption and physisorption, whereas the adsorption kinetics followed the pseudo-second-order kinetics mechanism. The positive and low values of enthalpy (ΔH0 = 4.91 kJ/mol) confirmed that adsorption is endothermic and physical in nature; however, the negative free energy and positive entropy value (ΔS0 = 53.69 J/mol K) suggested that the adsorption is spontaneous. The biosynthesized adsorbent was successfully reused up to the fifth cycle. A proposed reaction mechanism for the adsorption process of MB dye onto Om-AgNPs is suggested. The present study may offer a novel finding such as an effective and sustainable approach for the removal of MB dye from water using biosynthesized Om-AgNPs as reusable adsorbents at a comparatively faster rate at a low dose for industrial applications.

Equilibrium and Kinetic Modeling of Crystal Violet Dye Adsorption by a Marine Diatom, Skeletonema costatum

Significant efforts have been made to improve adsorbents capable of eliminating pollutants from aqueous solutions, making it simple and quick to separate from the treated solution. In the current study, the removal of Crystal Violet Dye (CVD) from an aqueous synthetic solution onto a marine diatom alga, Skeletonema costatum, was investigated. Different experiments were conducted as a function of different pH, contact time, adsorbent dosage, temperature, and initial CVD concentration. The highest adsorption efficiency (98%) was obtained at 0.4 g of S. costatum, pH 3, and a contact time of 120 min, at 25 °C. Furthermore, Fourier-transform infrared spectroscopy (FTIR) results display that binding of CVD on S. costatum may occur by electrostatic and complexation reactions. Moreover, the Brunauer-Emmett-Teller surface area analysis (BET) obtained was 87.17 m2 g-1, which, in addition to a scanning electron microscope (SEM), reveals large pores that could enhance the uptake of large molecules. However, the equilibrium adsorption models were conducted by Halsey, Langmuir, Freundlich, Henderson, and Tempkin isotherm. In addition, multilayer adsorption isotherm best described the uptake of CVD onto S. costatum. The maximum monolayer adsorption capacity (qmax) was 6.410 mg g-1. Moreover, thermodynamic parameters of the adsorption studies suggested that the uptake of CVD onto S. costatum was endothermic and spontaneous. The pseudo-first-order, pseudo-second-order, and intra-particle diffusion kinetic equations were applied to model the adsorption kinetic data. It was seen that the kinetics of the adsorption may be described using pseudo-second-order kinetic equations. Finally, the present work concluded that the marine diatom alga S. costatum is suitable as a natural material for the adsorption of CVD.

Attenuation of nitrate from aqueous solution using raw and surface modified biosorbents from Adansonia digitata fruit pericarp

The prevalence of nitrate in potable water is a serious environmental concern. Several methods for eliminating nitrate from water have been made and implemented. During the course of this research, raw (RADFP) and surface-modified fruit pericarp (SMADFP) biosorbents derived from the Adansonia digitata plant were applied in order to remove nitrate from an aqueous solution. The external features of the biosorbents were studied with the aids of SEM and BET. The FT-IR spectrometer was utilized for identification of the functional groups of the adsorbents. A UV-Vis device was used to quantify the nitrate concentration. The adsorbents under investigation exhibit a heterogeneous pore structure with a considerable number of mesopores, with surface areas of 361.527 and 379.877 m² per gram for RADFP and SMADFP, respectively. FT-IR spectra revealed the presence of carboxyl, hydroxyl, carbonyl, and halogen groups on the adsorbent. The maximum nitrate removal efficiencies of RADFP and SMADFP were 64.55 and 88.95%, respectively. The maximum adsorption efficiencies are achieved when the pH is 2, the starting concentration is 27.50 mg/L, the contact period is 75.00 min, and the amount of biosorbent is 5.50 g. RADFP and SMADFP have a removal capacity of 12.45 as well as 25.18 mg per gram and adsorption intensity of 3.2300 and 5.4500, respectively. The investigational values for the elimination of nitrate ions concurred well to both Freundlich and Langmuir models with R² values of 0.99917 and 0.99763 for RADFP and SMADFP, respectively, and pseudo-second-order kinetic model with R² values of 0.99817 and 0.99947, respectively for RADFP and SMADFP. It can be concluded that SMADFP is a relatively better biosorbent than RADFP, which will be utilizable for the remediation of nitrate from an aqueous solution.

Adsorption kinetics and Box-Behnken design optimization for organic dyes on tungsten oxide

Transition metal oxides have been applied to degrade organic dyes found in water bodies via photocatalysis. To do it, however, is essential that the dye molecules adsorb onto the metal oxide surface. Thus, optimizing the adsorption capacity of the adsorbent increases the probability of reaction between oxidation radicals and organic dye molecules and maximizes the effectiveness per gram of photocatalyst. With this in mind, we studied the adsorption behavior of Methylene Blue (MB) and Acid Orange 7 (AO7), two commonly found pollutants, as a function of dilution's pH, WO₃ load, and initial dye concentration. We found out that WO₃ adsorbs up to 80% of MB at pH = 6, and 13% of AO7 at pH = 2, although it is unable to adsorb AO7 at the natural pH of the dye dilution. Assuming a pseudo-second order kinetics model for the analysis of the MB adsorption amount, we determined a rate constant k₂ = 6 × 10^-2(g · mg^-1)/min for the adsorption process. We put forward a molecular model for adsorption, driven by concentration gradients and electrostatic interactions. Finally, from a statistical analysis, we determined that pH is the most significant factor for the adsorption of MB and AO7 on WO₃, reinforcing the notion that electrostatic interactions are the main mechanism driving the adsorption process. The Box-Behnken design optimization also evinces the key playing role of WO₃ load in the adsorption percentage of AO7 and let us establish the optimal load required to maximize adsorption.

The Using of Nanoparticles of Microalgae in Remediation of Toxic Dye from Industrial Wastewater: Kinetic and Isotherm Studies

Batch adsorption experiments were carried out to study the removal of the toxic Methylene Blue Dye (MBD) from synthetic aqueous solutions using the nanoparticles form of Arthrospira platensis NIOF17/003. The adsorption capacity of the adsorbent for MBD was investigated using different amounts of A. platensis nanoparticles at different contact times, temperatures, pH, and MBD initial concentrations in the synthetic aqueous solution. In addition, A. platensis nanoparticles were characterized using Electron Microscopy (SEM), Brunauer–Emmett–Teller (BET), Fourier Transform Infrared (FTIR), and Ultraviolet spectra (UV) techniques. The optimum removal of MBD was found at a concentration of 0.4 g A. platensis nanoparticles. A. platensis nanoparticles remove 93% of MBD in 5 min (under agitation conditions at 150 rpm). The highest adsorption capacity was found by the Langmuir model to be 58.8 mg g⁻¹. It is an endothermic process with spontaneity increasing with temperature. The probable mechanism for the adsorption is chemisorption via surface-active charges in the initial phase, which is followed by physical sorption by occupying pores of A. platensis. MBD adsorption by A. platensis follows pseudo-second-order kinetics. The Freundlich and Langmuir models fit well with the experimental data. The adsorption experiments suggested that the regeneration of the adsorbents was possible for repeated use, especially regarding MBD up to 65.8% after three cycles, which proves it can be easily recycled. In conclusion, the nanoparticles of A. platensis have a significant adsorption potential in the removal of MBD from effluent wastewater.

Recent Developments in the Application of Bio-Waste-Derived Adsorbents for the Removal of Methylene Blue from Wastewater: A Review

Over the last few years, various industries have released wastewater containing high concentrations of dyes straight into the ecological system, which has become a major environmental problem (i.e., soil, groundwater, surface water pollution, etc.). The rapid growth of textile industries has created an alarming situation in which further deterioration to the environment has been caused due to substances being left in treated wastewater, including dyes. The application of activated carbon has recently been demonstrated to be a highly efficient technology in terms of removing methylene blue (MB) from wastewater. Agricultural waste, as well as animal-based and wood products, are excellent sources of bio-waste for MB remediation since they are extremely efficient, have high sorption capacities, and are renewable sources. Despite the fact that commercial activated carbon is a favored adsorbent for dye elimination, its extensive application is restricted because of its comparatively high cost, which has prompted researchers to investigate alternative sources of adsorbents that are non-conventional and more economical. The goal of this review article was to critically evaluate the accessible information on the characteristics of bio-waste-derived adsorbents for MB's removal, as well as related parameters influencing the performance of this process. The review also highlighted the processing methods developed in previous studies. Regeneration processes, economic challenges, and the valorization of post-sorption materials were also discussed. This review is beneficial in terms of understanding recent advances in the status of biowaste-derived adsorbents, highlighting the accelerating need for the development of low-cost adsorbents and functioning as a precursor for large-scale system optimization.

Removing of Anionic Dye from Aqueous Solutions by Adsorption Using of Multiwalled Carbon Nanotubes and Poly (Acrylonitrile-styrene) Impregnated with Activated Carbon

This paper presents an estimation of the adsorptive potential of multiwalled carbon nanotubes (MWCNTs) and modified poly (acrylonitrile-co-styrene) with activated carbon for the uptake of reactive red 35 (RR35) dye from aqueous solution by a batch system. MWCNT adsorbent was synthesized by encapsulation via in situ polymerization. The copolymer material of poly (acrylonitrile-styrene) P (AN-co-ST) was prepared in a ratio of 2:1 V/V by the precipitation polymerization process. The prepared composites’ properties were characterized by FTIR, SEM, Raman, mean particle size (PSA), and XRD analysis. The PSA of the copolymeric material was determined to be 450.5 and 994 nm for MWCNTs and P(AN-co-St)/AC, respectively. Moreover, the influences of different factors, for example pH (2–10), adsorbents dosage (0.005–0.04 g), contact time (5–120 min), initial dye concentration (10–50 mg L−1), and temperature (25–55 °C). The optimum values were determined to be 2 and 4 pH, 10 mg L−1 of RR35 dye, and 0.04 g of adsorbents at early contact time. Furthermore, the adsorption isotherm was studied using Langmuir, Freundlich, Tempkin, and Halsey models. Maximum capacity qmax for MWCNTS and P (AN-co-St)/AC was 256.41 and 30.30 mg g−1, respectively. The investigational kinetic study was appropriated well via a pseudo second-order model with a correlation coefficient around 0.99. Thermodynamic study displayed that the removal of RR35 is exothermic, a spontaneous and physisorption system. The adsorption efficiency reduced to around 54–55% of the RR35 after four cycles of reuse of the adsorbents at 120 min.

Studying the Adsorptive Behavior of Poly(Acrylonitrile-co-Styrene) and Carbon Nanotubes (Nanocomposites) Impregnated with Adsorbent Materials towards Methyl Orange Dye

In this study, a polymeric (acrylonitrile-co-styrene) P(AN-co-St) composite was impregnated with adsorbents, such as sulfonated and multiwall carbon nanotubes (MWCNTs), to increase the adsorptive characteristics of the nanocomposite upon the removal of methyl orange (MO) dye under different conditions. A novel nanocomposite copolymer mixture of P(AN-co-St) and SP(AN-co-St) was used. MWCNTs were prepared by a low-cost chemical vapor deposition (CVD) process. Variation in MO adsorption onto the three nanocomposites was examined in an aqueous solution via the batch technique with respect to contact time, initial MO concentration, adsorbent dosage, pH, and temperature. The surface of the nanocomposites was characterized by a scanning electron microscope (SEM), particle size distribution (PSD), Fourier transform infrared (FTIR), and Raman analysis. The experimental data showed that the efficiency of P(AN-co-St)/ MWCNT removal increased under the conditions of an acidic pH (3 and 5) with an agitation speed of 140 rpm, a sorbent weight of 0.01 g, and 20 mg of initial dye. The maximum sorption capacities were 121.95, 48.78, and 47.84 mg g-1 for the P(AN-co-St)/ MWCNTs, SP(AN-co-St), and P(AN-co-St) composites, respectively, as assessed by the Langmuir model. Additional isotherm models, such as the Freundlich, Temkin, and Halsey models, were used to examine the experimental data. A pseudo-second-order model was found to be more fitting for describing the sorption.

Methylene Blue Adsorption onto Neem Leave/Chitosan Aggregates: Isotherm, Kinetics and Thermodynamics Studies

The work was aimed at evaluating the adsorptive properties of neem leave/chitosan aggregates for methylene blue removal. The adsorbent was screened to form coarse (CCANL, 600 µm), medium (MCANL, 300 µm) and fine (FCANL, 150 µm) neem leave/chitosan particles. The samples were characterized for pH, water binding capacity (WBC), surface chemistry by Fourier transform infrared spectroscopy, surface morphology by scanning electron microscope and textural properties by Brunauer-Emmett-Teller method. CCANL, MCANL and FCANL possessed specific surface area of 255, 258 and 242 m2/g, respectively. The effects of initial concentration, adsorbent dosage, contact time, pH and temperature were studied. CCANL, MCANL and FCANL demonstrated adsorption capacity of 102, 92.5 and 105 mg/g, respectively, in which ionic interaction and mesopore filling were the possible adsorption mechanisms. The equilibrium data were well fitted by Redlich-Peterson model, suggesting a monolayer adsorption onto a heterogeneous surface of adsorbent. The kinetics data were best described by pseudo-second-order and intraparticle diffusion models, for which the film diffusion, intraparticle diffusion and surface adsorption could co-exist as the controlling steps in adsorption. Adsorption of methylene blue onto chitosan composites was spontaneous, endothermic and demonstrated increased randomness at solid-solution interface.

Calcined magnesite as an adsorbent for cationic and anionic dyes: characterization, adsorption parameters, isotherms and kinetics study

The ability of calcined magnesite for Methylene Blue (MB), Direct Red 81 (DR81), Methyl Orange (MO) and Crystal Violet (CV) dye removal was evaluated in this study. The experiments were designed to test the hypothesis that alkaline earth carbonates can remove dyes from water through a combination of sorption and coagulative reactions involving Mg2+. To achieve that, several operational factors like residence time, dosage, adsorbent concentration and temperature were appraised. The batch study proved that calcined magnesite is effective in the treatment of MB, DR81, CV and MO contaminated water and moreover it performed well in terms of color removal. The adsorption equilibrium data were analysed by the Langmuir, Freundlich, Dubinin-Radushkevich and Temkin isotherm models, and the Dubinin-Radushkevich and Temkin models were found to be the most appropriate fit to MB and MO dyes respectively. The adsorption kinetics process primarily followed the Elovich and Pseudo-second order model, a possible indication that chemisorption was the rate limiting step during the dye uptake process. With the adsorption-desorption cycle repeated four times, the calcined magnesite regeneration efficiency for DR81 and MO loaded dyes remained very high. According to the results of this study, it can be concluded that calcined magnesite can be used effectively for the adsorption of MB, DR81, CV and MO from wastewater.

Methylene blue removal using a low-cost activated carbon adsorbent from tobacco stems: kinetic and equilibrium studies

The aim of this study was to prepare activated carbon from tobacco stalks using microwave heating. The prepared activated carbon was applied as an adsorbent in methylene blue (MB) removal from water. The optimum conditions for activated carbon preparation were a radiation power of 280 W for a period of 6 minutes after the impregnation of the precursor material with 30% ZnCl2 for 24 hours. The activated carbon yield and iodine number were 49.43% and 1,264.51 mg/g respectively. The activated carbon also had a point of zero charge of 5.81 with an adsorption capacity of 123.45 mg/g for MB. The optimum conditions for MB adsorption were a pH of 6.5 with an adsorbent dosage of 0.2 g/50 mL at 25 °C. The MB adsorption kinetics followed the pseudo second order kinetic model with the intra-particle diffusion model suggesting a two-step adsorption mechanism. The adsorption data also fitted well within the Langmuir adsorption isotherm model. Tobacco stalks can successfully be turned into an economically important product.

Utilization of two agrowastes for adsorption and removal of methylene blue: kinetics and isotherm studies

Fresh water streams contaminated with synthetic dye-containing effluents pose a threat to aquatic and human life either by preventing aquatic photosynthesis or by entering into the food chain. Adsorptive removal of such dyes with potent biosorbents is an important technique to reduce bioaccumulation and biomagnifications of the dyes in human life. We report use of betel nut (BN) husk and banana peel (BP), two most abundant ligno-cellulosic wastes, as efficient adsorbents for the removal of the basic dye methylene blue (MB). The adsorption by BN and BP was consistently high over wide ranges of pH and temperature, suggesting their dye removal potential in diverse conditions. Physico-chemical studies, e.g. scanning electron microscopy and Fourier transform-infrared spectroscopy studies, revealed changes in surface topology and functional moieties of BN and BP post adsorption, implying dye interaction with the biomass surface. The dye adsorption in both cases followed pseudo-second-order kinetics. While adsorption of MB by BN was better fitted with the Temkin isotherm model, adsorption with BP followed both Langmuir and Freundlich isotherm models. Our studies concluded that both adsorbents efficiently remove MB from its aqueous solution with BP proved to be marginally superior to BN.