Adsorbent For Removal Of Cationic Dyes Research Articles

Novel magnetic metal ferrite-mango starch composite for the removal of dyes in single and ternary dye mixtures from aqueous solutions: kinetic and thermodynamic studies

ABSTRACT Magnetic metal ferrites attached to biowastes are proven to be promising adsorbents for the removal of dyes from water. Magnetic composites with biopolymers are gaining interest in the field of treatment of wastewater because of their selective nature, recyclability, low cost and environmental compatibility. In this work, Zinc ferrite composite with starch, extracted from mango seed kernel (ZFNMS) was synthesised. Characterisation techniques, such as FTIR, XRD, FESEM, BET, TGA and pHzpc, were used for the structural analysis of ZFNMS. ZFNMS was used to remove Methylene blue, Crystal violet and Brilliant green dyes in single and multiple (ternary) dye systems. The kinetics of adsorption by ZFNMS revealed that pseudo-second-order of kinetics was most appropriate for this study. Maximum adsorption capacities using ZFNMS for CV, BG and MB dyes were 142.9, 101.2 and 105.8 mg/g, respectively. The values of adsorption energies using ZFNMS were 200.5, 494.3 and 183.6 KJ/mol for CV, BG and MB dyes, respectively. Thermodynamic data revealed the spontaneous nature of the adsorption of dyes by ZFNMS and it was found that chemical adsorption was taking place in the present study. Regeneration of the adsorbent was done for successive five cycles and showed significant results. Thus ZFNMS is an ideal adsorbent for cationic dyes removal from water.

Facile green fabrication of MIL‐101(Cr)/PVA nanofiber composite as effective, stable, and reusable adsorbent for cationic dye removal

AbstractIn this study, chromium‐based metal–organic framework (MIL‐101(Cr)) was incorporated into polyvinyl alcohol nanofibers (PVA NFs) via green electrospinning followed by heat treatment to fabricate MIL‐101(Cr)@PVA NFs composite without the need for any organic solvent or other dispersants. The fabricated MIL‐101(Cr)@PVA NFs were comprehensively characterized using a suite of common techniques. Morphological characteristics of MIL‐101(Cr)@PVA NFs showed a fibrous structure with an average diameter of 228 ± 37 nm and decorated with MIL‐101(Cr) particles arranged in a nanoneedle‐like pattern. Subsequently, its adsorption efficiency towards the cationic crystal violet dye (CV) was evaluated through batch adsorption experiments. The influence of various experimental parameters on CV removal efficiency was systematically optimized using a factorial design approach. The Langmuir isotherm and kinetic pseudo‐second‐order (PSO) model provided an excellent fit to the adsorption equilibrium data, indicating a maximum adsorption capacity (qmax) of 344.18 mg/g for MIL‐101(Cr)@PVA NFs compared with 83.94 mg/g for pristine PVA NFs. Furthermore, the MIL‐101(Cr)@PVA NFs composite demonstrated excellent reusability and stability, maintaining a significant portion of its removal capacity even after six adsorption–desorption cycles. These findings highlight the potential of the fabricated composite as a highly efficient and reusable adsorbent for CV removal from wastewater treatment applications.Highlights The MIL‐101(Cr)@PVA NFs nanocomposite fabricated by electrospinning technique. The MIL‐101(Cr) particle arranged in a nanoneedle‐like pattern in the PVA NFs. Incorporation of MIL‐101(Cr) improved qmax of PVA by 391.5%. The MIL‐101(Cr)@PVA NFs membrane has excellent stability and reusability.

Resource recovery from palm kernel shell and its application for wastewater treatment: a circular economy approach

In this study, cationic Methylene Blue (MB) dye removal was investigated through a batch adsorption process using a ternary adsorbent developed from palm oil biomass, graphene oxide, and iron oxide (M-PKSGO). Box-Behnken Design (BBD) was applied for modelling and analyzing the effects of independent operational parameters including pH of initial MB dye solution, M-PKSGO dosage and adsorption time on dye removal and adsorption capacity. The experimental results show an adsorption capacity of 82.7 mg/g was achieved using 1 g/L of M-PKSGO with 135 min at pH 11. Hence, the M-PKSGO composite is proven as an effective adsorbent for cationic dye removal from wastewater. The utilization of biomass from the palm oil industries promotes a circular economy via resource recovery activities. Overall, this work brings to light the opportunities created by green adsorbents in promoting a circular economy and stimulates further research and development in this highly pertinent field.

Fabrication and characterization of magneto-responsive polyvinyl alcohol–alginate composite hydrogel beads for the removal of cationic dyes from aqueous solutions

In this study, magneto-responsive polyvinyl alcohol–alginate hydrogel beads are successfully fabricated using the electrospraying technique and applied as efficient adsorbents for the removal of cationic dyes, particularly malachite green (MG) and methylene blue (MeB), from water. The successful synthesis of the beads is confirmed using optical microscopy, Fourier transform infrared spectroscopy, and scanning electron microscopy. Additionally, batch adsorption studies are performed to evaluate the adsorption capacity of the hydrogel beads under varying concentrations, pH solution, and contact time. Results revealed that the beads exhibited excellent sorption capacities of 270.03 and 285.66 mg g−1 toward MG and MeB, respectively, indicating their potential as efficient adsorbents for cationic dye removal. The adsorption mechanism of the beads was further analyzed using kinetic and isotherm models, where the results revealed that the pseudo-second order kinetic model and Langmuir isotherm model exhibited the best fits with the experimental data. The incorporated magnetic nanoparticles enabled the easy separation and reuse of the hydrogel beads sample, as it maintained more than 75% of its efficiency even after five consecutive cycles. This study presents an innovative and sustainable solution for wastewater treatment, demonstrating the use of magneto-responsive hydrogel beads as effective and reusable adsorbents for cationic dye removal.

Utilization of Amino-Silane Modified Lignin Derivative as an Adsorbent for Cationic Dye Removal

In this study, we evaluated the possibility of the application of amino-silane as a cationic dye adsorbent via chemical modification using lignin. Amino-silane modified lignins (ALs) have been synthesized via amine-silanization. The ALs have high accessibility to pollutants and stability in aqueous solutions owing to their high zeta-potential and specific surface area. Adsorption experiments showed that the ALs exhibited excellent cationic dye removal under neutral and basic conditions. Because ALs contain abundant amine groups, having a lone pair of electrons confers excellent accessibility via electrostatic attraction with cationic dyes. The maximum adsorption amount of the cationic dye reached 197.44 mg·gSUP-1/SUP. All adsorption processes followed the pseudo-second-order kinetics, Langmuir and Temkin isotherm models, and spontaneous processes. Therefore, this study contributes to the development of a low-cost and sustainable lignin-based adsorbent.

Adsorption ability evaluation of the poly(methacrylic acid-co-acrylamide)/cloisite 30B nanocomposite hydrogel as a new adsorbent for cationic dye removal

The performance of poly(methacrylic acid-co-acrylamide)/Cloisite 30B nanocomposite (poly(MAA-co-AAm)/Cl30B) hydrogel to adsorb methylene blue (MB) dye from aqueous solutions was investigated and the adsorption efficiency was improved by incorporating Cloisite 30B nanoclays in the adsorbent structure. The hydrogels were analyzed using FTIR, XRD, TGA, and SEM analysis. The effect of adsorbent dose, temperature, initial dye concentration, contact time, and pH on the efficiency of the adsorption process was investigated. Adsorption efficiencies of 98.57 and 97.65% were obtained for poly(MAA-co-AAm)/Cl30B nanocomposite and poly(MAA-co-AAm) hydrogels, respectively. Kinetic study revealed that the adsorption process followed pseudo-first-order kinetic model and α-parameter values of 6.558 and 1.113 mg/g.min were obtained for poly(MAA-co-AAm)/Cl30B nanocomposite and poly(MAA-co-AAm) hydrogels, respectively indicating a higher ability of nanocomposite hydrogel in adsorbing MB-dye. In addition, the results of the intra-particle diffusion model showed that various mechanisms such as intra-particle diffusion and liquid film penetration are important in the adsorption. The Gibbs free energy parameter of adsorption process showed negative values of −256.52 and −84.071 J/mol.K for poly(MAA-co-AAm)/Cl30B nanocomposite and poly(MAA-co-AAm) hydrogels indicating spontaneous nature of the adsorption. The results of enthalpy and entropy showed that the adsorption process was exothermic and random collisions were reduced during the adsorption. The equilibrium data for the adsorption process using poly(MAA-co-AAm)/Cl30B nanocomposite and poly(MAA-co-AAm) hydrogels followed Freundlich and Langmuir isotherm models, respectively. The maximum adsorption capacity values of 32.83 and 21.92 mg/g were obtained for poly(MAA-co-AAm)/Cl30B nanocomposite and poly(MAA-co-AAm) hydrogels, respectively. Higher adsorption capacity of nanocomposite hydrogel was attributed to the presence of Cloisite 30B clay nanoparticles in its structure. In addition, results of RL, n, and E parameters showed that the adsorption process was performed optimally and physically.

A novel self-floating cyclodextrin-modified polymer for cationic dye removal: Preparation, adsorption behavior and mechanism

The separation and recycling processes of current cyclodextrin (CD)-based adsorbents are complicated. Thus, a novel composite based on a large surface area, porous, and self-floating tetrafluoroterephthalonitrile (TFN)-crosslinked CD polymer (FTFCD), was fabricated, characterized and applied to treat cationic dye pollutants. The characterization showed a porosity, good thermal stability, a stable crystal structure, and abundant functional groups on the prepared FTFCD, which had demonstrated great improvement on its adsorption capacity towards attention grabbing pollutants. The removal efficiency of the adsorbents for malachite green (MG) remained above 95% at pH 1 ∼ 10. In addition, the adsorbents were found to rapidly reach equilibrium governed by the pseudo-second-order kinetic model, and the maximum adsorption capacity of FTFCD was 1390.263 mg/g, as corroborated by the Langmuir isotherm model. While the phenolate groups of FTFCD found to electrostatically interacts with the MG strong cationic quaternary amine group, hydrogen-bonding was responsible for the hydroxyl group of FTFCD and the quaternary amine group binding. Meanwhile, the triangular cone configuration of MG makes it easy to be entrapped and absorbed in the hydrophobic cavity. Besides, after regeneration of exhausted FTFCD for five successive cycles, the MG removal efficiency still reached more than 80%. Thus, FTFCD could be applied as a potential alternative adsorbent for cationic dye removal owing to its excellent adsorption performance, convenient recycling, wide pH application, and environmental friendliness.

The Use of Bilberry Leaves (Vaccinium myrtillus L.) as an Efficient Adsorbent for Cationic Dye Removal from Aqueous Solutions.

In this study, a new lignocellulosic bioadsorbent, bilberry (Vaccinium myrtillus L.) leaves powder, was used to remove the methylene blue dye from aqueous solutions. The characterization of the adsorbent was performed by FTIR, SEM and color analysis. The influence of pH, contact time, adsorbent dose, initial dye concentration, temperature and ionic strength on the adsorption process were followed. Equilibrium, kinetic, and thermodynamic studies were conducted in order to understand the adsorption process mechanism. Process optimization was performed using the Taguchi method. Sips isotherm and general order kinetic model characterize the adsorption process. The maximum adsorption capacity, 200.4 (mg g−1), was better compared with other similar bioadsorbents. Thermodynamic parameters indicated that the adsorption process is spontaneous, favorable and endothermic and also that physisorption is involved in the process. The factor with the highest influence on the dye removal process was pH, followed by contact time, temperature, adsorbent dose, ionic strength and initial dye concentration. The obtained results revealed that the bioadsorbent material based on bilberry (Vaccinium myrtillus L.) leaves is highly efficient for cationic dyes removal from aqueous solutions.

Adsorptive scavenging of cationic dyes from aquatic phase by H3PO4 activated Indian jujube (Ziziphus mauritiana) seeds based activated carbon: Isotherm, kinetics, and thermodynamic study

In the present work, a cost-effective Indian jujube seeds derived activated carbon (IJSAC) prepared via o-phosphoric acid chemical activation, is studied for the sequestration of acriflavine (AF) and Victoria blue B (VB) from the aquatic environment. The activated carbon is characterized by Fourier transform infrared spectroscopy, N2-adsorption/desorption isotherm, scanning electron microscopy techniques and point of zero-charge measurement. The specific surface area (SBET) of 571 m2/g with a pore radius of 22.45 Å specifies mesoporous nature of the IJSAC. The implication of operational conditions on the adsorption of both dyes onto IJSAC assessed by batch methodology, establish the optimal conditions as dosage (1.5 and 2.5 g/L), contact time (60 min), pH (8 and 10), and initial concentration (130 and 140 mg/L) for AF and VB uptake, respectively. The Freundlich adsorption isotherm model (R2 = 0.99) appropriates the equilibrium data suggesting multilayer adsorption onto heterogeneous surface sites, while pseudo-second order (R2 = 0.95–0.99) is the best fit kinetic model. The liquid film and intraparticle diffusion modelling demonstrate that the adsorption process of these dyes is governed by both the steps. Maximum Langmuir adsorption capacity is 113.6 mg/g for acriflavine and 92.78 mg/g for Victoria blue B. Thermodynamic studies indicate endothermic and spontaneous adsorption of dyes. The adsorption mechanism for the uptake of AF and VB by IJSAC most probably involves hydrogen bonding, electrostatic and π-π interactions. Based on its high adsorption capacity, relatively faster kinetics, and reusability, IJSAC can be perceived as a proficient and effective adsorbent for cationic dyes removal from the liquid waste.

Mesoporous silica-coated α-Fe2O3/C nanoparticles as an efficient adsorbent for cationic dye removal

Mesoporous silica-coated α-Fe2O3/C nanoparticles as an efficient adsorbent for cationic dye removal

Characterization and application of orange peel as an adsorbent for cationic dye removal from aqueous solution

With the great generation of colored effluents, several methods for the removal of the color are used, being one of them the method of adsorption in solid medium. In this paper, the in natura orange peel was used as the alternative biomass for the adsorption process of methylene blue, which was characterized by moisture content, pH, apparent density, iodine number, and methylene blue index. To determine the adsorptive capacity of the methylene blue dye, pH 7 was obtained as favorable, the adsorption process showed an adsorption of 82% of the methylene blue dye and a 10 min equilibrium time, where the Freundlich isotherm presented a better adaptation to the adsorption process in orange peel, with its maximum adsorption capacity of 3.9630 mg g-1, for the methylene blue dye.

Highly efficient and sustainable alginate/carboxylated lignin hybrid beads as adsorbent for cationic dye removal

In this study, chemically modified lignin and alginate (Alg) hybrid spherical adsorbents exhibiting highly effective adsorption performance for cationic dyes were simply prepared. Carboxylated lignin (C-Lig) was prepared by simple peracetic acid oxidation. Thereafter, through encapsulation of C-Lig into Alg beads was conducted. As the encapsulated amount of C-Lig increased, a higher methylene blue (MB) removal capacity was observed due to the introduction of carboxylated anions on the surface. The adsorption isotherm of Alg/C-Lig beads followed the Langmuir model and exhibited a high monolayer maximum adsorption capacity (qm) of 613 mg/g due to the driving force which is electrostatic interaction between the cationic dye and the anionic group of C-Lig. According to intraparticle diffusion theory, the adsorption behavior proceeded in surface adsorption and internal diffusion during 6 h of the adsorption process. Desorption of MB molecules was found to occur easily via a change in only the pH condition of the solution, and it was possible to maintain over 80% of stable adsorption efficiency even after 5 repeated adsorption/desorption cycles. The facile fabrication process of the Alg/C-Lig beads and superior MB removal performance imply that the Alg/C-Lig beads show a high possibility to purify dye wastewater especially cationic dye molecules.

Poly(sodium styrene sulfonate) functionalized graphene as a highly efficient adsorbent for cationic dye removal with a green regeneration strategy

In this work, a simple and highly efficient adsorbent for cationic dyes based on poly(sodium styrene sulfonate) functionalized graphene (PSS-rGO) was reported. PSS-rGO showed an extraordinary adsorption capacity for methylene blue (MB) with a broadened pH range, from 1085 mg g−1 at pH 3.0–1300 mg g−1 at pH 11.0. Remarkably, the PSS-rGO adsorbent could be easily recovered and regenerated after dye adsorption by simply heating at 200 °C for 20 min and intermittent further PSS modification by ultra-sonication for 10 min, offering a facile recovery/regeneration strategy with no secondary pollution. The experimental results of adsorption kinetics and isotherms indicate a multilayer and heterogeneous adsorption process with possibly multiple interaction mechanism. A simple survival experiment of guppy fish (Poecilia reticulata) confirmed a good bio-compatibility of PSS-rGO. These results promise the potential of PSS-rGO for efficient removal of cationic dye with zero secondary pollution.

Organobentonite as an efficient and reusable adsorbent for cationic dyes removal from aqueous solution

In the present study, cetyltrimethylammonium bromide (CTAB) was used to modify raw bentonite (Ben) through the replacement of exchangeable cations to form CTAB modified bentonite (CTAB-Ben). Both Ben and CTAB-Ben were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and Brunauer-Emmet-Teller (BET) analysis. Adsorption potential of Ben and CTAB-Ben were explored for the removal of two cationic dyes i.e. Rhodamine B (RB) and Crystal violet (CV) from aqueous solutions. The maximum dye adsorption capacity of CTAB-Ben was found to be 93.15 and 14.76 mg g -1 for CV and RB, respectively. The adsorption data of both the adsorbents was better explained by Freundlich isotherm whereas the pseudo second order (PSO) model better fitted the kinetics data. Regeneration studies revealed that CTAB-Ben could be reused upto five adsorption-desorption cycles.

Synthesis and characterization of new polymers derived from 2-methyl-m-phenylenediamine as an effective adsorbent for cationic dye removal

The oxidative polymerizations of 2-methyl-m-phenylenediamine were performed to synthesize PMPDIA-A and PMPDIA-B polymers by H2O2 (35% aqueous solution) oxidant in acid-catalyzed ethanol and basic aqueous medium. Furthermore, PMPDIA-E polymer of 2-methyl-m-phenylenediamine was enzymatically synthesized by HRP (horseradish peroxidase) enzyme and H2O2 (35% aqueous solution) in dioxane/0.1 M phosphate tampon solution (pH = 7) mixture. The structures of 2-methyl-m-phenylenediamine and polymers were confirmed by FT-IR, NMR and UV–Vis spectrometer measurements. Molecular weight distributions, surface morphologies, thermal and fluorescence properties of polymers were determined from GPC, SEM, TG-DTA, DSC and fluorescence spectra analyses, respectively. CV and UV–Vis analyses were performed to determine the HOMO–LUMO energy levels, electrochemical (Eg′) and optical (Eg) band gaps values of MPDIA, PMPDIA-E, PMPDIA-A and PMPDIA-B. The electrochemical and optical band gaps values of polymers were lower than MPDIA, because of their polyconjugated structures. According to GPC measurements of polymers, the weight average molecular weights were between 5400 and 10400 Da. The fluorescence quantum yield of PMPDIA-E was calculated to be 9.15% in DMSO solution. The adsorption of methylene blue (MB) from aqueous solution on PMPDIA-B was studied. Adsorption isotherms and equilibrium adsorption capacities were determined by the fitting of the experimental data to two well-known isotherm models: Langmuir and Freundlich.

Synthesis of hierarchically structured ɤ-Fe2O3–PPy nanocomposite as effective adsorbent for cationic dye removal from wastewater

Industrial dye effluents, which are a major wastage component that enter the natural environment, pose a significant health risk to human and aquatic life. Therefore, the effective removal of dye effluents is a major concern. Against this backdrop, in this study, a low-cost, earth-abundant, and ecofriendly ɤ-Fe2O3–PPy nanocomposite was prepared employing the conventional hydrothermal method. The morphology, functional groups, and elemental composition of ɤ-Fe2O3–PPy were characterized by XRD, SEM, XPS, and FTIR studies. Under optimized conditions, the prepared novel ɤ-Fe2O3–PPy nanocomposite showed a high methylene blue (MB) adsorption capacity of 464 mg/g, which is significantly higher than that of existing adsorbents such as CNTs and polymer-modified CNTs. The adsorption parameters such as pH, adsorbent dosage, and ionic strength were optimized to enhance the MB adsorption capacity. The adsorption results revealed that MB is adsorbed onto the adsorbent surface via electrostatic interactions, hydrogen bonding, and chemical binding interactions. In terms of practical application, the adsorbent’s adsorption–desorption ability in conjunction with magnetic separation was investigated; the prepared ɤ-Fe2O3–PPy nanocomposite exhibited excellent adsorption and desorption efficiencies over more than seven adsorption–desorption cycles.

CuAl LDH/Rice Husk Biochar Composite for Enhanced Adsorptive Removal of Cationic Dye from Aqueous Solution

The preparation of CuAl LDH and biochar (BC) composite derived from rice husk and its application as a low-cost adsorbent for enhanced adsorptive removal of malachite green has been studied. The composite was prepared by a one-step coprecipitation method and characterized by X-ray Diffraction (XRD), Fourier Transform Infra Red (FTIR), Brunauer-Emmett-Teller (BET), and Scanning Electron Microscopy - Energy Dispersive X-ray (SEM−EDX). The result indicated that CuAl LDH was successfully incorporated with the biochar that evidenced by the broadening of XRD peak at 2θ = 24° and the appearance of a new peak at 1095 cm−1 on the FTIR spectra. The BET surface area analysis revealed that CuAl/BC composite exhibited a larger surface area (200.9 m2/g) that the original CuAl LDH (46.2 m2/g). Surface morphological changes also confirmed by SEM image, which showed more aggregated particles. The result of the adsorption study indicated the composite material was efficient in removing malachite green with Langmuir maximum adsorption capacity of CuAl/BC reaching 470.96 mg/g, which is higher than the original CuAl LDH 59.523 mg/g. The thermodynamic analysis suggested that the adsorption of malachite green occurs spontaneously (ΔG < 0 at all tested temperature) and endothermic nature. Moreover, the CuAl/BC composite showed strong potential as a low-cost adsorbent for cationic dye removal since it showed not only a high adsorption capacity but also good reusability. Copyright © 2020 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Surface Modified Laterite Soil with an Anionic Surfactant for the Removal of a Cationic Dye (Crystal Violet) from an Aqueous Solution

The work aims to study the removal of crystal violet (CV) using laterite soil with surface modification by surfactant (SML). Surface modification of laterite soil was conducted by pre-adsorption of sodium dodecyl sulfate (SDS) at pH 4 and low ionic strength to enhance removal of CV. The effective conditions for CV removal through adsorption technique using SML were optimized and found to be contact time 60 min, pH 6, adsorbent dosage 5 mg/mL, and 5 mM NaCl as background electrolyte. The highest removal of CV using SML reached to 86.5% under optimum conditions. We used Fourier transform infrared spectroscopy (FT-IR) to evaluate the change of surface vibrational groups of laterite after SDS pre-adsorption and after CV adsorption while the different charged surface was determined by ζ potential measurements. The CV adsorption onto SML increased when increasing ionic strength from 1 to 10 mM. Nevertheless, at high ionic strength, this trend is reversal due to desorption of SDS from laterite surfaces. Adsorption isotherms of CV onto SML at different NaCl concentrations were tried to fit by Langmuir, Freundlich, and a two-step adsorption models. The adsorption kinetics were in good agreement with pseudo-second-order model. The removal efficiency of CV after four regenerations still reached higher than 85%. On the basis of adsorption isotherms, charged surface change by ζ potential and surface modification by FT-IR, we suggest that CV adsorption onto SML was induced by both non-electrostatic and electrostatic interactions. We also demonstrate that SML is a novel, reusable, and low-cost adsorbent for cationic dye removal from aqueous solution.

Microporous carbon material from fish waste for removal of methylene blue from wastewater.

Microporous fish waste-based activated carbon material (MFC) was prepared, with a large surface area of 2,193.52 m²/g, a pore size of 2.67 nm and micropore and total pore volumes of 0.9168 cm³/g and 0.9975 cm³/g, respectively. Adsorption efficiency of MFC was investigated by removal of methylene blue dye from wastewater. The Langmuir model and pseudo-second-order kinetics adequately described the adsorption process. MFC exhibited a high adsorption capacity of 476.19 mg/g at 30 °C, and reached equilibrium within 1 h. MFC could be an efficient and low-cost adsorbent for cationic dye removal during wastewater treatment.

Adsorption/desorption behavior of cationic and anionic dyes by biochars prepared at normal and high pyrolysis temperatures

The purpose of this study was to determine the properties of biochar prepared at higher than normal biochar production temperature and to evaluate adsorption/desorption characteristics for three commonly used dyes of different charge and molecular nature: Methylene Blue (MB), Orange G (OG) and Congo Red (CR). The switchgrass-biochar was prepared at common pyrolysis temperature of 600 °C (SB600) and higher than normal temperature of 900 °C (SB900). The results showed that the carbon content of the two biochars was similar, but most carbon in SB900 was graphitized based on FTIR and XRD observation. Dye adsorption isotherms by SB600 and SB900 was well described Langmuir model with maximum adsorption capacity of MB, OG and CR being 37.6, 8.2 and 8.0 mg/g for SB600 and 196.1, 38.2 and 22.6 mg/g for SB900, respectively. The adsorption kinetics of dyes by both biochars were well described by pseudo-second order model. In addition, intraparticle diffusion model showed that MB adsorption was predominantly by inner pore diffusion rather than by outer boundary, while OG and CR were more adsorbed by the outer boundary. These results indicated that the strong dye adsorption by SB900 compared to SB600 was due to the significantly enhanced surface area at the high pyrolysis temperature. Additionally, the greater adsorption of cationic MB by SBs than that of anionic OG and CR was attributable to the small molecular weight, favorable electrostatic property, and strong π-π interaction of the former with biochar surface as opposed to the latter. Overall, the SB900 maintained > 85% adsorption of maximum capacity even after four adsorption-desorption consecutive cycles and could be used as an effective adsorbent for cationic dye removal from wastewater.