Efficient Removal Of Anionic Dyes Research Articles

One-step fabrication of millimeter-scale hollow vesicles with chitosan /DADMAC/ sodium alginate graft copolymer for enhanced anionic dye adsorption

Hollow vesicles are promising in water treatment due to their unique structure of the membrane and inner cavity. However, the adsorption capacity needs to be improved for targeted pollutants. Herein, millimeter-scale hollow vesicles were prepared with a one-step process of sequential stirring and grafting using chitosan, diallyldimethylammonium chloride, and sodium alginate as raw materials with the purpose of efficient removal of anionic dyes from wastewater. The composite vesicles were characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The hollow vesicles showed the structure of the cationic membrane and the inner cavity, facilitating the dye adsorption. The adsorption capacity for the anionic dye Reactive Black 5 reached 698.1 mg/g, more than twice that of the binary composite vesicles without graft. The adsorption kinetics and isotherm data coincided with the pseudo-second-order and Langmuir models, respectively, and the adsorption mechanism was monolayer chemisorption. Moreover, the vesicles worked well in wide ranges of environment pH, temperature, and co-existing pollutants. They also possessed excellent cyclic regeneration performance, in which 93 % of the initial adsorption capacity was maintained after four cycles. These results indicate that the millimeter-scale hollow vesicles exhibit broad application prospects for wastewater purification.

MXene/ZnS/chitosan-cellulose composite with Schottky heterostructure for efficient removal of anionic dyes by synergistic effect of adsorption and photocatalytic degradation

Nowadays, dye water pollution is becoming increasingly severe. Composite of MXene, ZnS, and chitosan-cellulose material (MX/ZnS/CC) was developed to remove anionic dyes through the synergistic effect of adsorption and photocatalytic degradation. MXene was introduced as the cocatalyst to form Schottky heterostructure with ZnS for improving the separation efficiency of photocarriers and photocatalytic performance. Chitosan-cellulose material mainly served as the dye adsorbent, while also could improve material stability and assist in generation of free radicals for dye degradation. The physics and chemistry properties of MX/ZnS/CC composite were systematically inspected through various characterizations. MX/ZnS/CC composite exhibited good adsorption ability to anionic dyes with adsorption capacity up to 1.29 g/g, and excellent synergistic effects of adsorption and photodegradation with synergistic removal capacity up to 5.63 g/g. MX/ZnS/CC composite performed higher synergistic removal ability and better optical and electrical properties than pure MXene, ZnS, chitosan-cellulose material, and MXene/ZnS. After compounding, the synergistic removal percentage of dyes increased by a maximum of 309 %. MX/ZnS/CC composite mainly adsorbs anionic dyes through electrostatic interactions and catalyzes the generation of •O2−, h+, and •OH to degrade dyes, which has been successfully used to remove anionic dyes from environmental water, achieving a 100 % removal of 50 mg/L dye.

Cationic etherified starch-acrylamide-DMDAAC graft flocculant: Synthesis, flocculation performance, metal ion synergistic effect and cost-effectiveness

The flocculants based on naturally derived polymers are promising due to their wide availability and biodegradability. However, the flocculation performance and cost-effectiveness are less than satisfactory. This study developed novel flocculants with cationic etherified starch-acrylamide-dimethyl diallyl ammonium chloride (CAD), specifically designed for the efficient removal of anionic dyes. The synthesis conditions were optimized through the flocculation efficiency of anionic acid black-172 (AB) dye. Experimental results showed that CAD achieved a removal ratio of 91.6±1.8% with a flocculant dosage of 150 mg/L and maintained excellent decolorization efficiency across different pH, environmental temperatures, and ionic strengths. Most importantly, the synergistic effect with the presence of metal ions, particularly Fe3+, on the decolorization efficacy of CAD was observed. In the presence of Fe3+ (0.02 mol/L), the required flocculant dosage was reduced by two-thirds, while the maximum dye removal ratio reached 94.2±1.9%. The study indicates that the high efficiency of CAD primarily originates from dual mechanisms of charge neutralization and bridging. Furthermore, the operation cost of removing an equivalent amount of AB dye with CAD is about 40% of that incurred using commercial cationic polyacrylamide, highlighting its economic advantage in industrial applications. In summary, the CAD flocculant shows great promise for complex wastewater treatment.

A composite based on hydroxyapatite biocrystal and poly(aniline-o-phenylenediamine) copolymer for efficient removal of anionic dyes from wastewater

BackgroundAcid dyes in any water source strongly impact its color, blocking sunlight and harming aquatic life. Herein, the technical applicability of a novel composite based on hydroxyapatite and poly(aniline-o-phenylenediamine) for removing dyes from synthetic wastewater was investigated using a batch method. MethodsIn this work, camel bones were used as a source of hydroxyapatite. Camel bones were pretreated in an alkali environment before extracting hydroxyapatite biocrystal (HAP). Subsequently, the extracted HAP was mixed with the poly(aniline-o-phenylenediamine) (PANI@PoPD) co-polymer. Different formulation methods were designed to optimize the tested composite samples' shape, size, structure and composition. Then, the optimized composite was further used as an adsorbent to remove orange G (OG) and thymol blue (TB) dyes from synthetic wastewater. The effects of the composite's dose, pH, dyes’ initial concentration and temperature on the overall performance of the composite were assessed. Statistical tests were then used to test the best experimental conditions to remove target dyes from wastewater. Significant findingsBy keeping the dye concentration constant at 50 mg/L for both OG and TB in wastewater at 25 °C, pH = 2 and 800 rpm of agitation speed in a batch reactor, it was found that the synthesized composite efficiently removes 99% of each dye at optimum dose of 0.5 or 1 g/L with a reaction time close to 30 or to 80 min for OG or TB, respectively. The predictive capacity of two-parameter models, including the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich models, and three-parameter models such as the Redlich-Peterson, Sips and Toth models, was assessed to estimate the collected adsorption data. It was found that the statistical analysis was slightly better when the Temkin model was applied. This indicates that this equation was better suited to represent the experimental data of the adsorption of the OG dye. In contrast, the Redlich-Peterson and Toth models were in better agreement with the experimental results of the TB dye adsorption. Furthermore, thermodynamic parameters associated with each dye adsorption demonstrated its feasibility, while the adsorption kinetic data were found to be better described with the pseudo-second-order kinetics. In addition, the regenerability performances of the tested composite were successfully assessed by reusing the spent composite five consecutive times.

Three-dimensional porous adsorbent based on chitosan-alginate-cellulose sponge for selective and efficient removal of anionic dyes

A three-dimensional porous adsorbent, chitosan-alginate-cellulose (CAC) sponge, for efficient and selective adsorption of anionic dyes from aqueous systems was developed using a ternary deep eutectic solvent as the cellulose solvent, polyvinyl alcohol as the porogen, and glutaraldehyde as the crosslinking agent. Compared with unary and binary sponges prepared by chitosan, alginate, and cellulose, the CAC sponge exhibited better adsorption capacity, mechanical property, and water stability. The three-dimensional porous structure of CAC sponge was significantly improved by combining the three polysaccharides and introducing the polyvinyl alcohol and glutaraldehyde. A series of characterizations was performed to investigate the properties of the CAC sponge. The CAC sponge performed high adsorption capacity (105.9–203.7 mg/g) and excellent selectivity to anionic dyes, with the selectivity factor up to 26.5, and the experimental data followed the Langmuir and pseudo-second-order models. The adsorption behavior of the CAC sponge exhibited temperature stability and strong pH dependence. The adsorption mechanism and energy were determined using density functional theory, and electrostatic interactions were the main forces for the adsorption of anionic dyes. Finally, the CAC sponge combined with high-performance liquid chromatography was applied to adsorb and detect anionic dyes from river water, tap water, and beverage samples with outstanding enrichment ability (enrichment factors: 31.16–69.69) and selectivity.

The Defects, Physicochemical Properties, and Surface Charge of MIL-88A (Al) Crystal Were Regulated for Highly Efficient Removal of Anionic Dyes: Preparation, Characterization, and Adsorption Mechanism.

In this paper, the physicochemical properties, surface charge, and crystal defects of MIL-88A (Al) were controlled by adjusting the ratio of metal ligands and temperature in the synthetic system without the addition of surfactants. The adsorption properties of different crystals for Congo red (CR) were studied. Among them, MIL-88A (Al)-130 and MIL-88A (Al)-d have the best adsorption properties. The maximum adsorption capacities are 600.8 and 1167 mg · g-1, respectively. Compared with MIL-88A (Al)-130, the adsorption performance of MIL-88A (Al)-d was increased by 94.2%, and the adsorption rate was increased by about 4 times. It can be seen that increasing the proportion of metal ligands within a certain range will improve the adsorption capacity. The structure and morphology of the adsorbent were characterized by XRD, FTIR, SEM, EDS, TGA, BET, and zeta potential. The effects of time, temperature, pH, initial solution concentration, and dosage on CR adsorption properties were systematically discussed. The pseudo-second-order kinetic model and Langmuir isothermal model can well describe the adsorption process, which indicates that the adsorption process is a single-layer chemisorption occurring on a uniform surface. According to thermodynamics, this adsorption is an endothermic process. The mechanism of CR removal is proposed as the electrostatic attraction, hydrogen bond, metal coordination effect, π-π conjugation, crystal defect, and pore-filling effect. In addition, MIL-88A (Al)-d has good repeatability, indicating that it is a good material for treating anionic dye wastewater.

Sustainable and economical dolomite-modified biochar for efficient removal of anionic dyes

Dyes induce acute to chronic illnesses in humans and aquatic animals. This study tested dolomite-modified rice husk biochar (DRHB) to eliminate anionic reactive dyes Remazol Brilliant Blue (RBB) and Reactive Black 5 (RB-5) from simulated wastewater solutions. DRHB was produced by pretreating rice husk biomass with the natural mineral dolomite (CaMg(CO3)2) solution following pyrolysis step at 700 °C for 4 h at 8 °C min−1. Pristine rice husk biochar (PRHB) was made by pyrolyzing rice husk for 4 h at 700 °C. The DRHB and PRHB were characterized via different techniques including, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and Scanning electron microscopy (SEM). Afterwards, DRHB was used to get rid of the dyes in the wastewater solutions, and the effects of dose, pH, and contact duration were studied. Both RBB and RB-5 exhibited maximal adsorption capacities of 52.07 and 35.518 mg/g at 50 °C, respectively, and the findings matched well with the Langmuir model, demonstrating monolayer adsorption. For this system, the pseudo-second-order fit is optimal, pointing to chemisorption of both substances. The outcomes presented higher adsorption for RBB (95.63%) compared to RB-5 (85.20%) at 70 mg/L concentration, pH 6, 4 hr. contact time, and 0.3 mg of DRHB dosage. The primary mechanism to remove of both dyes was chemisorption via π-π bond and hydrogen bond. These findings provide insights to build an economical, and sustainable anionic dyes removal technique especially for the third world nations.

Efficient removal of anionic dye by protonated APTES modified hydrochar: The effect of cold‐activation

AbstractThe study focused on determining the effect of acidic and basic cold activation on hydrochar (HC) for the removal of methyl orange (MO). HC was prepared by hawthorn seeds (HS) under hydrothermal carbonization. HC was cold‐activated with HCl and NaOH, respectively, and they were grafted with aminopropyltriethoxysilane (APTES) and protonated to obtain AHC‐N+ (acid‐activated and modified HC) and BHC‐N+ (base‐activated and modified HC) to determine the effect of acidic and basic activation. They were characterized by elemental analysis, IR, thermal analysis, zeta potential, N2 adsorption–desorption measurements, and SEM–EDX analysis. The prepared adsorbents displayed MO adsorption due to abundant protonated amine groups. BHC‐N+ showed higher MO adsorption than AHC‐N+. The result showed that more protonated APTES groups grafted on the surface of HC via NaOH activation. The obtained data had a good fitting with the Langmuir isotherm and pseudo‐second‐order kinetic. The maximum adsorption capacity of BHC‐N+ was 250.38 mg g−1. The adsorption mechanism could be attributed to the electrostatic interactions between MO and protonated amine groups of APTES and hydrogen bonding.

Mussel-inspired cationic chitosan-based flocculants with floc enlarging capacity for efficient removal of anionic dye

Biomass-based flocculants have been widely studied and applied to wastewater treatment due to their environmental friendliness. However, these flocculants tend to generate flocs with small size and lead to difficult solid-liquid separation after the flocculation. The key to solving the floc size problem is enhancing intermolecular or intramolecular interaction forces by changing the molecular structure and functional groups of flocculants. Herein, we developed a mussel-inspired cationic biomass flocculant by functionalizing chitosan (CS) with cation component acryloyloxyethyltrimethyl ammonium chloride (DAC) and mussel-inspired monomer N-2-(3, 4-dihydroxyphenethyl) acrylamide (DAA) through free radical polymerization. The prepared flocculant could provide multiple interaction forces such as electrostatic interaction, cation-π interaction, π −π stacking, and hydrogen bonding to pollutants. As a result, the spent CS-g-p (DAC-co-DAA) flocculant generate dye-containing flocs with dramatically increased size when compared with its counterpart CS-g-pDAC without catechol groups and are capable to realize more than 95% removal efficiency towards organic dyes such as MB and CR over a broad pH range from 3 to 9. This study provides some insights in how to apply this mussel-inspired strategy to develop environmentally friendly biomass-derived flocculants with floc enlarging capacity to treat organic wastewaters in wide pH range.

Synthesis of a novel hierarchical pillared Sep@Fe3O4/ZnAl-LDH composite for effective anionic dyes removal

A novel magnetic hierarchically pillared Sep@Fe3O4/ZnAl-LDH composite was successfully synthesized via co-precipitation methods. The prepared Sep@Fe3O4/ZnAl-LDH composite were characterized via FTIR, XRD, XPS, SEM, TEM, BET and VSM. The results show that the Sep@Fe3O4/ZnAl-LDH composite have a hierarchical columnar structure with nanoscale structural unit (Fe3O4/ZnAl-LDH) and overall micron-scale morphology, and the obtained graded adsorbent has a large pore capacity and pore size distribution. The maximum adsorption capacities of the obtained samples for methyl orange ( MO) and Congo red ( CR) were 430 mg·g−1 and 832 mg·g−1, respectively. Kinetic data of MO and CR adsorbed on as-prepared samples can well fit with pseudo-second-order model. The isothermal data of MO and CR adsorbed on Sep@Fe3O4/ZnAl-LDH match well with the Langmuir model. The thermodynamic results indicate that the adsorption process is spontaneous and endothermic. Besides, the adsorbent shows good stability and reproducibility in a reusable cycle. This study demonstrated that Sep@Fe3O4/ZnAl-LDH provides a new idea for the development of a novel hierarchical magnetic pillared adsorbent for the efficient removal of anionic dyes.

3D Metallo-Supramolecular Polymer for Fast and Efficient Removal of Anionic Dyes from Water

3D Metallo-Supramolecular Polymer for Fast and Efficient Removal of Anionic Dyes from Water

Removal of Diazo Dye Direct Red 28 and Tetra Azo Dye Direct Black 22 Using Synthesized Magnetic Kaolin Supported Zinc Ferrite.

The presence of dye molecules in water resources has harmful effects on environment. Therefore, it is important to remove dyes from wastewater using eco-friendly materials. In this study, adsorptive removal of diazo dye Direct Red 28 (DR-28) and tetra azo dye Direct Black 22 (DB-22) was investigated by using a new composite, kaolin supported zinc ferrite (KZF) as adsorbent. Characteristics of the composite, KZF were determined using various techniques such as FTIR, SEM, XRD, VSM, and EDS/Mapping. The adsorption of DR-28 and DB-22 on KZF was studied as a function of contact time, initial dye concentration, adsorbent amount, temperature, initial pH of the solution as well as the heat treatment of the composite. The removal of DR-28 was found to be 92.4% for the KZF concentration of 1g/200mL, initial dye concentration of 20 mg/L, contact time of 120 min at original pH and 21°C. On the other hand the removal of DB-22 was found to be 91.7% under the same conditions at 40 °C. The results showed that Langmuir isotherm is suitable for the adsorption of DR-28 and DB-22 on KZF under given conditions. It was found that adsorption of DR-28 on KZF was exothermic while that of DB-22 was endothermic. The enthalpy changes (ΔH0) for the adsorption of DR-28 and DB-22 dyes on KZF were found to be -24.59 kJ/mol and 61.95 kJ/mol respectively. ΔS0 for the adsorption of DR-28 dye was found to be negative while ΔS0 for the adsorption of DB-22 was positive. The kinetic data fitted well to the pseudo second order model for the adsorption of DR-28 and DB-22 on KZF composite. These results showed that the prepared adsorbent KZF could be used as an adsorbent for the efficient removal of anionic dyes.

Highly negatively charged nanofiltration membrane prepared with a novel diamino-sulfonamide aqueous monomer for efficient removal of anionic dyes

Nanofiltration (NF) membranes with negative surface charge are of critical significance for the efficient removal of anionic dyes from wastewater. In this work, a novel negatively charged NF membrane was prepared from a new sulfonamide monomer, 2,4,6-trimethyl-3,5-diaminobenzenesulfonamide (TMDBSA) and trimesoyl chloride (TMC) via interfacial polymerization. The unique diamino-sulfonamide structure of TMDBSA would be conducive to the formation of a poly (amide-sulfonamide) (PASA) layer with enhanced negative charge while maintaining the appropriate degree of crosslinking. The TMDBSA-TMC membrane prepared at optimized condition exhibits both high water permeability (19.6 L m−2h−1 bar−1) and superior rejections of anionic dyes with different molecular weights (e.g. 98.3% rejection for methyl blue), reveals that Donnan exclusion dominates the rejection mechanism. More importantly, benefiting from the strong negatively charged surface and PASA structure, the TMDBSA-TMC membrane shows separation stability for the removal of methyl blue in a broad pH range, even under a harsh acid environment. Meanwhile, the membrane has excellent antifouling performance and long-term stability during the filtration tests. The newly developed negatively charged NF membrane demonstrates great practical application potential for the removal of anionic dyes with small molecular weights.

Rapid and Efficient Removal of Anionic Dye in Water Using a Chitosan-Coated Iron Oxide-Immobilized Polyvinylidene Fluoride Membrane.

Anionic dyes are one of the most serious contaminants in water as these molecules are known to be toxic to many living organisms. Herein, we report the development of functionalized polyvinylidene fluoride membranes modified with chitosan-coated iron oxide nanomaterials (Fe-PVDF) for the efficient treatment of anionic dye-contaminated water. Aqueous solutions of anionic dyes could be captured rapidly by passing through the functionalized membrane under reduced pressure. Under neutral conditions, Fe-PVDF showed a maximum removal capacity of 74.6 mg/g for Evans blue (EB) through the adsorption process. In addition, the adsorption capacity was significantly enhanced up to 434.78 mg/g under acidic conditions. The adsorption process for EB matched well with the Langmuir model, indicating monolayer adsorption of the dye to the membrane surface. Moreover, Fe-PVDF can be reusable by a simple washing step in an alkaline solution, and thus, the composite membrane was applied several times without a significant decrease in its adsorption performance. The same composite membrane was further applied to the removal of five other different anionic dyes with high efficiencies. The adsorption mechanism can be explained by the electrostatic interaction between the positively charged chitosan and the negatively charged dye as well as the affinity of the sulfate groups in dye molecules for the surface of the iron oxide nanoparticles. The easy preparation and rapid decolorization procedures make this composite membrane suitable for efficient water treatment.

In-situ fabrication of surfactant modified CNT-based novel bio-composite and its performance evaluation for simultaneous removal of anionic dyes: Optimization by Box-Behnken design

• CTAB modified Saccharum munja containing 1% CNT bio-composite was fabricated. • Anionic dyes were removed effectively from single and multi-component systems. • RSM with Box-Behnken design was used for the optimization. • Regeneration of the bio-composite was studied up to 5 cycles. The simultaneous and efficient removal of anionic dyes at neutral pH is a challenging task and is thus attracting considerable attention to remediate wastewater. Herein, cetyltrimethylammonium bromide (CTAB) surfactant was used for the modification of Saccharum munja based bio-composite containing 1% functionalized carbon nanotube (CNT). The as-synthesized bio-composite was characterized and used to study the affinity and efficacy towards the removal of Coomassie Brilliant Blue R-250 (BB), Reactive Red 35 (RR) and Reactive Orange 107 (RO) dyes from the single and multi-component systems. Response surface methodology (RSM), with Box–Behnken design matrix was successfully employed for the optimization of operating parameters i.e., pH, adsorbent dosage and initial concentration of dyes. The proposed models were significant as per the analysis of variance (ANOVA) statistical analysis. Furthermore, the experimental data were well fitted with the pseudo-2nd-order kinetic model and the Langmuir isotherm model with a very high monolayer adsorption capacity for the single-component system, i.e., 1179.39, 109.41 and 22.14 mg/g for BB, RR and RO dyes respectively at neutral pH conditions. The interactive effects between dye molecules in binary and ternary systems were studied using the extended Langmuir model, which revealed competitive as well as synergistic behavior of dyes. Interestingly, the observed affinity trend, BB > RR > RO was explained on the basis of the proposed adsorption mechanism. Regeneration of the exhausted bio-composite depicted excellent reusability even after five adsorption-desorption cycles, which makes CTAB modified SM + CNT a promising candidate adsorbent for treating simulated dyeing effluents and the whole process is cyclic and eco-friendly.

High flux and high selectivity thin-film composite membranes based on ultrathin polyethylene porous substrates for continuous removal of anionic dyes

Thin-film composite (TFC) nanofiltration (NF) membranes efficiently remove dyes from wastewater. However, most of the membranes often sacrifice water flux for high rejection because of the trade-off between them. The demand for TFC membranes with high rejection and high water flux is increasing. Here, polyethylene (PE) membrane with a thickness of 7 µm was covered by polydopamine and polyethyleneimine (PDA/PEI), and then directly initiated interfacial polymerization (IP) with trimesoyl chloride (TMC), forming the dense and negatively charged polyamide-polyester selective layer. As the amount of PDA/PEI increases, the selective layer becomes denser, leading to the efficient removal of anionic dyes at high water flux. The water flux of the optimal membrane is 61.0 ± 18.3 L m−2 h−1 bar−1, and the removal efficiency is 91.4 ± 0.8% for an anionic dye eosin Y (EY, Mw = 691.9 Da), but poor decolorization for natural VB12 (Mw = 1355.4 Da). Moreover, the TFC membrane shows excellent selectivity for filtrating dye/NaCl mixture solution. The synergistic effect of adsorption-filtration control the removal of anionic dyes from wastewater in large flux. This work utilizes commercial PE porous substrate to fabricate TFC membrane having outstanding separation performance and a low thickness of about 7 µm.

Fabrication of bacterial nanocellulose/polyethyleneimine (PEI-BC) based cationic adsorbent for efficient removal of anionic dyes

Fabrication of bacterial nanocellulose/polyethyleneimine (PEI-BC) based cationic adsorbent for efficient removal of anionic dyes

Mino-modified biomass for highly efficient removal of anionic dyes from aqueous solutions

The excessive discharge of dye wastewater is a great threat to human health and environment with the development of industry. And it is of great significance to use biomass materials to remove dyes from wastewater with the low cost, renewability and environmental friendliness. In this study, the amine-modified passion fruit peel (ACPFP) was prepared by amination reaction, which exhibited highly efficient removal for anionic dyes (methyl orange (MO) and amaranth (ART)). The adsorption capacities of ACPFP for MO and ART were 1530.81 and 970.87 mg⋅g−1, respectively. And the adsorption conditions (pH, ionic strength, temperature, initial dye concentration, and contact time) and mechanism (kinetic and isotherm models) were investigated. The results revealed that 99% of MO and ART was removed in the best adsorption conditions: pH=5, an adsorbent dose of 1 g⋅L−1, 600 mg⋅L−1of MO and ART initial concentration. The adsorption process correlated well with the pseudo-second-order kinetic model and the Langmuir isotherm. And ACPFP had good adsorption selectivity, stability and recyclability for anionic dyes. In conclusion, ACPFP has broad application prospects in actual water treatment.

Novel Fe3O4-poly(methacryloxyethyltrimethyl ammonium chloride) adsorbent for the ultrafast and efficient removal of anionic dyes.

The removal of anionic dyes from wastewater has attracted global concern. In this work, a novel Fe3O4–poly(methacryloxyethyltrimethyl ammonium chloride) (Fe3O4–pDMC) adsorbent for the efficient removal of anionic dyes from wastewater was successfully synthesized by grafting methacryloxyethyltrimethyl ammonium chloride (DMC) on the surfaces of Fe3O4. Various characterization analyses confirmed that the obtained Fe3O4–pDMC possessed numerous functional groups on its surfaces and retained good magnetic separation properties. Fe3O4–pDMC showed ultrafast removal for acid orange 7 (AO7, 58.6%, 1 min) and direct blue 15 (DB15, 98.1%, 1 min), and the maximum adsorption capacity was high (266.8 and 336.5 mg g−1 for AO7 and DB15, respectively). In addition, the adsorption process was in accordance with pseudo-second-order kinetics and the Langmuir isotherm. The mechanism underlying the adsorption of Fe3O4–pDMC on anionic dyes was mainly dependent on electrostatic interaction. This study illustrated that Fe3O4–pDMC has great potential applications as an environmentally friendly, desirable adsorbent for the efficient removal of anionic dyes from wastewater.

Anionic Dye Removal by Polypyrrole-Modified Red Mud and Its Application to a Lab-Scale Column: Adsorption Performance and Phytotoxicity Assessment

In this study, polypyrrole-modified red mud (PRM) was prepared for the efficient removal of anionic dyes (methyl orange and Congo red) from aqueous solutions. The phytotoxicity (bean sprouts) of the dye solution before and after dye removal was investigated. Adsorption kinetics confirmed that the adsorption of methyl orange (MO) and Congo red (CR) on PRM was controlled by chemical reactions between the functional groups of polypyrrole and dyes. From Langmuir isotherm fitting, we found the theoretical adsorption capacities of MO and CR on PRM were 194.1 and 314.9 mg/g, respectively. The adsorption progress of MO and CR on PRM was found to be spontaneous and endothermic. The column studies demonstrated that, under dynamic flow, the PRM can efficiently remove MO and CR from aqueous solution, with adsorption capacities of 31.08 and 55.04 mg/g, respectively. In the toxicity test, the phytotoxicity of the column effluents (after dye removal) was significantly lowered compared to the initial dye influents. After the removal of MO and CR, the average root length of bean sprouts was increased from 3.30 cm to 5.18 cm and from 3.01 cm to 7.00 cm, respectively. These findings highlighted the efficient removal of dyes by PRM from aqueous solution, demonstrating the possible application of PRM for the removal of dye from dye-contaminated wastewaters.