Model Anionic Dye Research Articles

Dye removal from wastewater using nanostructured chitosan aerogels produced by supercritical CO2 drying

BackgroundDyes abundance in wastewaters poses environmental threats, and a cost-effective strategy to remediate dyed water is adsorption: this process could be enhanced using nanostructured sorbents, that expose high surface areas. MethodsIn this work, chitosan aerogel adsorbents were produced by supercritical CO2 assisted drying, working at 200 bar, 35 °C, and CO2 mass flow rate of 0.8 kg/h. FESEM images proved that the delicate biopolymeric network was intact thanks to near-zero surface tension at the interface between CO2 and the liquid, and large supercritical fluid diffusivity. Methyl Orange (MO) and Crystal Violet (CV) were used as model anionic and cationic dyes, respectively. Significant findingsChanging dye initial concentration, chitosan aerogel showed different behavior at low and large driving forces, for both CV and MO. Adsorption experiments proved that MO could be not completely removed by aqueous solutions: whereas, CV removal was successful with removal efficiencies up to 89.0 ± 1.1 % from a 10 ppm solution, using 50 mg of aerogel. FT-IR analysis proved that chitosan active sites were more effectively involved with CV rather than MO. Kinetic analysis, carried out for both dyes, showed that the process follows a pseudo-second order kinetics, related to internal mass transfer resistances and diffusion phenomena.

Highly efficient and selective removal of anionic dyes from aqueous solutions using polyacrylamide/peach gum polysaccharide/attapulgite composite hydrogels with positively charged hybrid network

To avoid the weakness (lower adsorption rate and selectivity) of peach gum polysaccharide (PGP) and improve the adsorption performance of polyacrylamide (PAAm) hydrogel (lower adsorption capacity), in the present work, the PGP was chemically tailored to afford ammoniated PGP (APGP) and quaternized PGP (QPGP), and attapulgite (ATP) was bi-functionalized with cation groups and carbon‑carbon double bond. Then, PAAm/APGP and PAAm/QPGP/ATP hydrogels were synthesized via redox polymerization. The synthesis procedure and properties of hydrogels were traced by FTIR, SEM, XPS, TGA, TEM, and BET methods, and the dye adsorption performance of the hydrogels was evaluated using the new coccine (NC) and tartrazine (TTZ) aqueous solutions as the model anionic dyes. Effects of initial dye concentration, pH, and ionic strength on the adsorption were investigated. Compared with PAAm/APGP hydrogel, PAAm/APGP/ATP hydrogel exhibits higher adsorption rate, superior adsorption capacity, stability, and selectivity towards anionic dye. The adsorption process of PAAm/QPGP/ATP hydrogel reached equilibrium in about 20 min and followed the pseudo-second-order kinetic model and Langmuir isotherm. The adsorption capacities towards NC and TTZ of PAAm/QPGP/ATP hydrogel were calculated as 873.235 and 731.432 mg/g. This hydrogel adsorbent originating from PAAm, PGP, and ATP shows great promise for application in practical water treatment.

Development of a selective nanoporous Na-zeolite X from Moroccan coal fly ash for anionic dye adsorption and removal

ABSTRACT The hydrothermal treatment of Moroccan coal fly ash (CFA) in a basic medium leads to the selective formation of Na-X zeolite. By fusion with sodium hydroxide in the presence of CFA, the particles are transformed into sodium silicate and sodium aluminate, from which hydrothermal reaction favourably results in the production of a pure Na-X zeolite. A good crystallinity of Na-X zeolite was attained at NaOH:fly ash ratio of 1.2. Their high surface area and pore characteristics make the Na-X zeolite useful for the removal of the model anionic dye RY145 from water. The adsorption efficiency of the synthesised Na-X zeolite was evaluated and compared to raw CFA. Dye adsorption is more significant at acid pH, suggesting that the zeolite surface is positively charged. Kinetic and isotherm models applied to fit the experimental data reveal that the adsorption process is physisorption. It results that zeolite X is an efficient adsorbent for the extraction of dyes.

Ionic Liquid Cross-Linked High-Absorbent Polymer Hydrogels: Kinetics of Swelling and Dye Adsorption.

The use of polymer gels for the removal of toxic chemicals from wastewater is an important area in terms of both academic and industrial research. This work presents a simple approach to the fabrication of chemically cross-linked cationic hydrogel adsorbents using designed ionic liquid-based cross-linkers and their successful use in the removal of organic dyes. Two different ionic liquid cross-linkers, [VIm-4VBC][Cl] (ILA)/[DMAEMA-4VBC][Cl] (ILB), are synthesized by the simple nucleophilic substitution reaction of 4-vinylbenzyl chloride (4VBC) separately with 1-vinylimidazole (VIm) and 2-(dimethylamino)ethyl methacrylate (DMAEMA). Cross-linked poly(acrylamide) (CPAam) and poly(2-hydroxyethyl methacrylate) (CPHEMA) hydrogels are then prepared from the corresponding monomers and as-synthesized cross-linkers (ILA and ILB) by free radical polymerization in the presence of a redox initiator combining ammonium persulfate (APS) and N,N,N',N'-tetramethylethylenediamine (TEMED). The dried CPAam and CPHEMA xerogels exhibit macroporous morphology and high thermal stability. The hydrogel samples exhibit high swelling behavior, and the diffusion of water molecules into the hydrogels follows pseudo-Fickian kinetics. The cationic cross-linking sites in the hydrogel networks allow preferable binding with anionic dyes, and these dye uptake capacities are determined using different model anionic dyes via UV-vis spectroscopy. The dye adsorption onto these hydrogels follows a pseudo-second-order kinetic model. The adsorption mechanism is also analyzed by employing intraparticle diffusion and Boyd kinetic models. The relationship between the maximum equilibrium adsorption capacity (qm) of the hydrogels for eosin B (EB) dye and the equilibrium EB concentration can be better described by Langmuir and Freundlich isotherm models, and the estimated qm using the Langmuir isotherm can reach more than 100 mg g-1. The cross-linked hydrogels can be easily regenerated and have a recycling efficiency of >80% for up to three consecutive dye adsorption-desorption cycles, which is promising for their use in wastewater treatment.

Controlled Removal of Organic Dyes from Aqueous Systems Using Porous Cross-Linked Conjugated Polyanilines.

Porous organic materials, as a broad class of functional materials, offer a promising route for low-cost purification of contaminated wastewaters. We have synthesized a range of highly cross-linked conjugated porous polyanilines and optimized their porosity and water dispersibility by tuning reactant feed ratios, previously unreported in the synthesis of such networks. To demonstrate their ability to adsorb model dyes used in the textile industry, we exposed the networks to a range of cationic aromatic dyes, leading to absorption capacities of >100 mg/g, reported for the first time with respect to polyaniline networks. The versatility of the networks was further demonstrated by the preparation of gel composites, producing active gels for efficient and facile removal and recycling, ideal for real-world applications. Finally, chemical modifications of the networks were undertaken to target the removal of model anionic organic dye pollutants, showing the wide applicability of our approach.

Fabrication of Novel Nanohybrid Material for the Removal of Azo Dyes from Wastewater

This study attempted to harness the dual benefit of adsorption and photocatalytic degradation for efficiently removing a model anionic azo dye, Orange G, from an aqueous solution. For this purpose, a series of bifunctional nanohybrids containing different proportions of naturally occurring biopolymer chitosan and ternary photocatalyst made of kaolinite, TiO2, and ZnO were prepared through the dissolution of chitosan in acid and subsequent deposition on ternary photocatalyst. The characterization through Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and energy dispersive X-ray spectrum (EDS) have confirmed the successful fabrication of nanohybrids from TiO2 and chitosan. The adsorptive separation of Orange G from the aqueous solution and subsequent degradation under solar irradiation was thoroughly studied by recording the λmax value of dye in the ultraviolet–visible (UV-Vis) spectrophotometer at various operating conditions of pH, dye concentration, contact time, and compositional variation. The nanohybrid (TP0.75CS0.25) fabricated from 75% ternary photocatalyst (w/w) and 25% chitosan (w/w) removed 97.4% Orange G within 110 min at pH 2.5 and 10 mg/L dye concentration. The relative contribution of chitosan and ternary composite on dye removal was understood by comparing the experimental results in the dark and sunlight. Recyclability experiments showed the suitability of the nanohybrid for long-term repeated applications. Equilibrium experimental data showed a better correlation with the Langmuir isotherm and pseudo-second-order kinetic model. The rapid and nearly complete removal capacity, long-term reusability, and simple fabrication technique make this novel nanohybrid a promising advanced material for removing hazardous azo dyes from industrial effluents.

Rapid adsorption of dyes from aqueous solutions by modified lignin derived superparamagnetic composites

In recent years, lignin has gotten a lot of press as an adsorbent for treating organic dyes. However, lignin adsorption has problems such as low adsorption capacity, slow adsorption and difficult recovery. In this study, a simple method was used to prepare superparamagnetic composites by self-assembly of enzymatic lignin (EL) or its modification products with γ-Fe2O3 nanoparticles under electrostatic interactions. Then the effect of the adsorbents in removing the methylene blue (MB, as a model cationic dye) and Congo red (CR, as a model anionic dye) from aqueous solutions was investigated by detailed characterization and experiments. The samples were characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD) and vibration sample magnetometer (VSM). In the process of adsorption, the effects of the initial pH and inorganic ions concentration of the dyes were discussed. And the adsorption mechanisms such as kinetics, isotherm were explored. The results showed that the synthesized magnetic acetylated modified lignin (MADL) has a well-defined spherical structure. In the adsorption kinetics study, MADL demonstrated a fast adsorption capacity. it took less than 50 min to reach the equilibrium. MADL maintained a stable adsorption capacity at a wide pH range and showed >90% removal efficiency in higher concentration (0.5 mol/L) of inorganic ions solutions. Moreover, MADL has good recyclability, can be separated from water quickly by the action of the applied magnetic field and still has >94% regeneration efficiency after three times of desorption and regeneration. In summary, the novel magnetic lignin-based adsorbent material prepared in this study has the advantages of simple preparation process, rapid adsorption, stability and good recyclability, which provides a new way for the removal of dyes in practical applications.

Wheat straw-core hydrogel spheres with polypyrrole nanotubes for the removal of organic dyes

Straw biomass is an underutilized raw material, the use of which could make a significant contribution to sustainable development. Herein, wheat straw waste was regenerated into novel porous core-shell wheat straw-polypyrrole hydrogel spheres for the removal of dyes from wastewater. Adsorption experiments demonstrated that the hydrogel spheres had long-term structural and functional stability, and a high performance for the removal of the water-soluble model anionic dye eosin Y (EY). The maximum adsorption capacity of the hybrid spheres (520.2 mg/g) was 12 times greater than that of the wheat straw hydrogel sphere. Recycling experiments showed that it the initial adsorption capacity of 75.0% could be maintained after seven adsorption-desorption cycles, and the material could be recovered by simple filtration. The results from spectroscopic (FTIR, XPS) analysis, adsorption experiments and computational quantum mechanical modelling suggested that hydrogen bonds, π-π stacking and electrostatic forces, were involved in the removal of EY from aqueous solution. Interestingly, the hydrogel sphere exhibited enhanced adsorption at elevated temperature, and this could be attributed to the dynamic breaking of crosslinked hydrogen bonds in the hydrogel sphere and release of activated –OH. The results from this study provide a basis for the development of sustainable high-performance adsorption materials from wheat straw biomass for the removal of organic dyes from wastewater. It also provides a strategy to design adsorbents that work efficiently at elevated temperatures.

Co-Enzymes based nanoflowers incorporated-magnetic carbon nanotubes: A new generation nanocatalyst for superior removal of cationic and anionic dyes with great repeated use

Synthetic dyes leading to substantial discharge in various industrial areas such as textile, plastics, food, and cosmetics, have growingly threatened all livings. Although enzymes have been used for dye degradation, weak stability against changes in reaction environment, lack of reusability and high cost have strictly limited their use. Herein, we have developed co-enzymes nanoflowers incorporated-magnetic carbon nanotube nanocomposite as a novel and efficient nanocatalyst for superior degradation of malachite green (MG) and acid orange 7 (AO7) as model cationic and anionic dyes with excellent cyclic use. The HRP-Lac NF@mCNT nanocomposite (NC) containing horseradish peroxidase–laccase nanoflower (HRP-Lac NF) and iron oxide nanoparticles (Fe 3 O 4 NPs) decorated magnetic carbon nanotube (mCNT) was systematically employed in dye degradation as functions of pH, reaction time, dye type and reusability. This HRP-Lac NF@mCNT nanocomposite acted as one malfunctional nanoplatform since both HRP and Lac enzymes were used for rapid and efficient dye removal, Fe 3 O 4 NPs provided cyclic use and omitting the centrifugation step, and CNT functioned as a unique platform for NFs and Fe 3 O 4 NPs deposition. We demonstrated that HRP-Lac NF@mCNT NC induced ∼ 90 % MG and ∼ 85% AO7 decolorization in 20 min at pH 7.4 while it almost completely decolorized MG and AO7 in 60 min. In addition, ∼ 95% MG and ∼ 85% AO7 decolorization were accomplished even after 16 cycling use of HRP-Lac NF@mCNT NC. We claim that HRP-Lac NF@mCNT NC induced dye decolorization with dual mechanisms, enzymatic degradation, and physical adsorption. • Preparation of horseradish peroxidase–laccase co-enzymes nanoflower incorporated-magnetic carbon nanotubes. • Rapid and efficient dye degradation against a cationic and an anionic dye. • Magnetic property for repeated use.

Green Synthesis of pH-Responsive, Self-Assembled, Novel Polysaccharide Composite Hydrogel and Its Application in Selective Capture of Cationic/Anionic Dyes.

Dyes are one of the most hazardous chemicals causing significant environmental pollution and affecting water quality. Majority of the existing methods for dye removal and degradation involve synthetic membranes and use of hazardous chemicals, further resulting in secondary pollution. The present study reports polysaccharide based novel composite hydrogel as biodegradable matrix for pH-responsive selective adsorption of cationic/anionic dyes. This membrane showed pH-responsive adsorption of methyl green (MG) and methyl orange (MO) with similar adsorption equilibrium, i.e., 315 and 276 mg g−1, respectively. Interestingly, selective adsorption at different pH has allowed separation of dye mixtures that holds incredible industrial importance for dyes recovery. The hydrogel matrix was able to completely separate MG, a model cationic dye at neutral pH from the dye mixture whereas, it was possible to remove 60% MO, a model anionic dye at acidic pH. Furthermore, comprehensive isothermal and kinetic studies of adsorption revealed that Freundlich isotherm describing the multilayer coverage and pseudo-second-order kinetics were followed. Thermodynamic studies indicated that the adsorption process was spontaneous and endothermic. In fact, the membrane was reusable for at least ten cycles and exhibited desorption efficiency of 80 and 60% for MO and MG, respectively, which may be further recycled to make the process environmentally sustainable. Overall, this study proposes an inexpensive, simple, biologically safe, and efficient adsorbent material for dye effluent treatment.

Catalytic activity of silver nanocomposite alginate beads for degradation of basic dye: Kinetic and isothermal study

AbstractAs the removal of toxic dyes by catalytic degradation is interestingly growing field, diverse types of nanomaterials are used intensively as a catalyst to enhance the catalytic degradation of toxic dyes in the last decades. The unique property of ionic crosslinking of the biopolymer sodium alginate (Na‐ALG) in presence of CaCl2 solution is exploited to prepare Ca‐alginate (Ca‐ALG) microbeads, which further used as precursor for in situ silver nanoparticles (Ag NPs) formation by the effect of gamma radiation to obtain Ca‐ALG/Ag nanocomposite beads. The amount of silver ions adsorbed by the Ca‐ALG beads before reduction was evaluated by using ultraviolet‐visible spectrophotometer (UV–Vis). The physicochemical properties of prepared Ca‐ALG/Ag nanocomposite beads were studied by various techniques as X‐ray diffraction (XRD) and transmission electron microscopy (TEM) for approving the creation of Ag NPs and assessing its morphology and particle magnitude. The catalytic reduction ability of the resulting Ca‐ALG/Ag nanocomposite beads is studied toward the degradation of basic blue 3 dye as a model anionic dye by the aid of the reducing agent NaBH4 under various factors including time, pH, catalyst's dosage, NaBH4 contents, and dye's initial concentration. Various kinetics and isothermal models were applied for forecasting the mechanism of the degradation process using the prepared catalyst beads. The kinetics and isothermal study revealed that the degradation process using Ca‐LG/Ag nanocomposite beads as a catalyst in presence of NaBH4 as a reducing agent was best fit the pseudo‐second‐order model and Langmuir isotherm model.

Efficient Adsorption of Anionic Dyes by Ammoniated Waste Polyacrylonitrile Fiber: Mechanism and Practicability.

Adsorption is one of the commonly used methods in wastewater treatment, but it has the problem of high cost and a complicated production process. In this paper, a low-cost and efficient decolorizing adsorbent was successfully prepared based on waste polyacrylonitrile fiber (PANF). The waste PANF was ammoniated by propylene diamine derivates (PANAMF), and benzylamine (PANABMF) and quaternary ammonium ions (PANQMF) were introduced for PANAMF to regulate hydrophilicity and hydrophobicity. With acidic red 249 as the model anionic dye, influences of the adsorption center structure, the degree of modification, the concentration of acid, the dye structure, and the auxiliary agent in the solution on the dye adsorption performance were studied. Isothermal models, kinetic models, reusability, and continuous application ability of the fiber adsorbent were discussed. PANAMF, PANABMF, and PANAQF exhibit excellent adsorption performance compared to the common adsorbent. After protonation, the saturation adsorption value can reach 2051.3 mg/g for PANAMF. PANAMF also exhibited excellent reusability, and the adsorption capacity after being reused eight times still can keep 72.7% of that for the first time. The adsorption of the anionic dye for PANAMF is a chemisorption process, and the rate-determining step is changed from the diffuse step to the adsorption on the surface with the adsorption time. PANAMF can also be used in the continuous flow process, and the absorption amount is similar to that in the batch adsorption, which shows excellent commercial application potential.

Biochar supported CuFe layered double hydroxide composite as a sustainable adsorbent for efficient removal of anionic azo dye from water

This study reports the synthesis of date palm waste-derived biochar (B) supported CuFe layered double hydroxides (CuFe LDH) composite by facile co-precipitation method. The adsorption performance of B-CuFe composite was evaluated for the removal of Eriochrome black T (EBT), as a model anionic azo dye, from the aqueous phase. The B-CuFe composites were characterized by FTIR, XRD, TGA, SEM-EDX and BET techniques. Characterization results revealed the synergistic effect of biochar and CuFe LDH has resulted in substantial improvement in physicochemical characteristics (i.e. surface functionality, surface area and surface morphology) of B-CuFe composite, which promotes rapid and improved adsorption of (EBT) from the solution. The B-CuFe composite with 2.5 g loading of biochar onto CuFe LDH - showed better adsorption performance than that of other B-CuFe composites. The adsorption process of EBT onto B-CuFe composite was well described by the RSM models (with R 2 = 0 . 964 – 0 . 999 ). Acidic pH (2–5) and higher temperature favored the adsorption of EBT onto B-CuFe composite, and almost (70–85%) of EBT was removed from the water within the first 15 min. The highest adsorption capacity, 565.32 mg/g of EBT onto B-CuFe composite, was obtained at pH 2.5 and 45 °C. The adsorption mechanism associated with the strong electrostatic and chemical interactions of EBT sulfonated anions (SO 3 − ) with protonated hydroxyl surface groups ( OH 2 + ) of B-CuFe composite. The B-CuFe composite exhibited better EBT removal in the presence of co-existing anions and demonstrated excellent reusability performance (11% reduction) after five successive cycles. The results demonstrated that the B-CuFe composite has a great potential to be employed as a sustainable and cost-effective adsorbent for the purification of dye contaminated water bodies. • Sustainable biochar-CuFe composite was fabricated by the coprecipitation method. • B-CuFe exhibited improved physicochemical properties than pure biochar and CuFe. • B-CuFe removed 85% of Eriochrome black T dye from the water in 15 min. • The maximum adsorption capacity of B-CuFe was 565.32 mg/g at 45 °C. • B-CuFe composite exhibited excellent reusability performance.

Matrix-dispersed PEI-coated SPIONs for fast and efficient removal of anionic dyes from textile wastewater samples: Applications to triphenylmethanes

Textile industries produce a massive amount of wastewater that should be cleaned from toxic substances such as fats, colors and any chemicals used during the production steps. Water-treatment methods should be facile, economic, fast and efficient. Here, we report the synthesis, characterization and application of matrix-dispersed superparamagnetic iron oxide nanoparticles (SPIONs) for the removal of anionic dyes from wastewater released from textile industrial plants. The matrix-dispersed SPIONs were synthesized via a solvothermal method in which a polyethyleneimine (PEI) shell was deposited onto SPIONs in order to add positive charges to their surfaces. TEM images revealed that the size of PEI-coated and uncoated SPIONs is 30–50 and 15–30 nm, respectively. Moreover, TEM images depicted that the as synthesized PEI-coated SPIONs show matrix-dispersed structures. Furthermore, the particle size obtained with DLS measurements was found to be 87.93 and 158.9 nm for uncoated and PEI-coated SPIONs, respectively. Bromophenol blue (BPB) and bromocresol green (BCG), two triphenylmethanes, were used as model anionic dyes. FTIR spectroscopy revealed the interaction between the PEI surface coating and the anionic dyes. The apparent ζ-potential measurements showed that the surface negative charges decreased from −13.5 to −4.03 mV upon coating with PEI. In order to investigate the anionic dyes removal/entrapment efficiency of SPIONs, a new derivative visible spectrophotometric method was developed for the simultaneous quantification of BPB and BCG before and after treatment where the linear ranges were 6.98–27.9 and 6.70–26.8 μg/mL and the recovery values were in the ranges of 98.10–101.7% and 99.55–104.8% for BCG and BPB, respectively. It was found that the uptake/adsorption capacity of PEI-coated SPIONs is ca.15.5 and 11.3 mg/g for BCG and BPB, respectively. The calculated thermodynamic parameters for the adsorption of BCG (ΔH = 37.08 J/mol and ΔS = 120.89 J/mol K) and BPB (ΔH = 181.26 J/mol and ΔS = 596.46 J/mol K) and the negative ΔG values indicate that the adsorption is thermodynamically favored. The adsorption processes were found to follow the pseudo-second-order kinetic model with r2 values of 0.9982 and 0.9956 for BCG and BPB, respectively.

Covalent organic framework and montomorillonite nanocomposite as advanced adsorbent: synthesis, characterization, and application in simultaneous adsorption of cationic and anionic dyes

In this work, Schiff base network-1 (SNW-1), as a new generation of covalent organic frameworks (COFs), was synthesized and modified by fabrication of a composite with clay mineral montomorillonite (Mt). It was used for simultaneous removal of anionic and cationic dyes from aqueous solutions. The fabricated composite was characterized successfully with various techniques. Tartrazine (TT) and methylene blue (MB) were selected as model anionic and cationic dyes, respectively. The effects of the percentage of each component in the composite, initial pH, and initial dye concentration were evaluated on the adsorption capacity. Adsorption reaction models and adsorption diffusion models were used to study the kinetic process of adsorption. Adsorption of both dyes reached equilibrium after 40min. The obtained results were fitted to Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich (D-R) models to predict the isotherms of adsorption. Under optimum conditions for removal of each dye with the composite, the maximum adsorption capacity of 519.2 and 602.7mgg-1 were obtained for TT and MB, respectively. The used SNW-1/Mt composite could be regenerated by salty methanol. The high adsorption capacity and excellent reusability make SNW-1/Mt composite attractive for the simultaneous removal of anionic and cationic dyes from aqueous solutions.

Adsorption of eosin Y on polyelectrolyte complexes based on chitosan and arabinogalactan sulfate

Positively charged polyelectrolyte complexes (PECs) were synthesized from two polysaccharides chitosan and arabinogalactan sulfate by self-assembly method as potentially efficient adsorbents for medical and environmental purposes. The obtained PEC particles of submicron size were comprehensively characterized by dynamic and electrophoretic light scattering, FTIR spectroscopy and scanning electron microscopy. The adsorption properties of the synthesized PECs were determined by optical methods using eosin Y as a model anionic dye. A temporal evolution of dye absorption spectra was revealed during the equilibration process in the eosin Y-PEC system; the decay can be described by three characteristic times with maximal value of 35 min. The adsorption within the pH range of 3.0–5.6 can be appropriately described by Langmuir-Freundlich model with the maximal adsorption capacity of 500 mg g−1. The increase of ionic strength has no significant effect on adsorption capacity of PECs, however it results in the increase of the heterogeneity factor from 0.82 up to 2.35. The revealed relationships were discussed in terms of predominantly electrostatic adsorbate-adsorbent interactions. The synthesized PECs demonstrated high colloidal stability along with a high removal efficiency of dye at low pH values that makes them very attractive eco-friendly dye adsorbent with improved biocompatibility.

Removal of anionic dye Congo red from aqueous environment using polyvinyl alcohol/sodium alginate/ZSM-5 zeolite membrane

In this study, a novel PVA/SA/ZSM-5 zeolite membrane with good regeneration capacity was successfully prepared by solvent casting technique. The properties of the membranes were assessed by employing different characterization techniques such as X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), optical microscopy (OP), thermogravimetric analysis (TGA), contact angle and universal testing machine (UTM). XRD, TGA and UTM results revealed that the crystallinity and thermo-mechanical performance of the membrane could be tuned with zeolite content. The successful incorporation of zeolite into the polymer matrix was confirmed by FT-IR, SEM and OP analysis. The adsorption ability of the as-prepared membrane was evaluated with a model anionic dye, Congo red. Adsorption studies show that the removal efficiency of the membrane could be tuned by varying zeolite content, initial concentration of dye, contact time, pH and temperature. Maximum dye adsorption (5.33 mg/g) was observed for 2.5 wt% zeolite loaded membrane, at an initial dye concentration of 10 ppm, pH 3 and temperature 30 °C. The antibacterial efficiency of the membrane against gram-positive (Staphylococcus aureus) and gram-negative bacteria (Escherichia coli) was also reported. The results show that membrane inhibits the growth of both gram-positive and gram-negative bacteria. The adsorption isotherm was studied using two models: Langmuir and Freundlich isotherm. The results show that the experimental data fitted well with Freundlich isotherm with a high correlation coefficient (R2 = 0.998). Meanwhile, the kinetic studies demonstrate that pseudo-second-order (R2 = 0.999) model describe the adsorption of Congo red onto PVA/SA/ZSM-5 zeolite membrane better than pseudo-first-order (R2 = 0.972) and intra particle diffusion model (R2 = 0.91). The experimental studies thus suggest that PVA/SA/ZSM-5 zeolite could be a promising candidate for the removal of Congo red from aqueous solution.

Ni-Fe-SDS and Ni-Fe-SO4 layered double hydroxides: Preparation, characterization and application in dyes removal

This work involved the removal of textile dyes by synthesized Ni-Fe-SDS and Ni-Fe-SO4 layered double hydroxides (LDH). The adsorbent was synthesized using co-precipitation method at room temperature. Samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) and inductively coupled plasma (ICP). The obtained materials were used for the removal of methyl orange (MO) as a model anionic dye. Adsorption experiments were carried out under different solution pH and contact time. XRD analyses indicate low degree of crystallinity when using SDS as an intercalating anion in the LDH structure. Experimental results indicate rapid adsorption process with maximum adsorption capacity occurred in acidic medium. The maximum adsorption capacities were 105.36 and 82.45 mg/g, respectively for Ni-Fe-SDS and Ni-Fe-SO4 samples.

Highly Efficient Adsorption of Anionic Dye on Acid-Treated Halloysite Nanotubes.

The adsorption capability of eosin Y as a model anionic dye on natural halloysite nanotubes (HNTs) and sulfuric acid-treated HNTs as a function of acid treatment time (1 h, 3 h, and 5 h) was examined. Scanning electron microscopy revealed that natural HNTs had a very uniform surface, whereas acid-treated HNTs had a rough surface with structural defects, which increased with acid treatment time. The total specific pore volume and total surface area of the acid-treated HNTs increased due to formation of nanopores in the HNTs via dissolution of the inner AlO6 octahedral layer. With acid treatment, the surface ξ-potentials were positively shifted from -42.9 mV (for the natural HNTs) to -1.9, -3.0, and +1.2 mV after 1, 3, and 5 h, respectively. The adsorption amount (qe) of eosin Y on natural HNTs and the three acid-treated HNTs was 2.3, 125.5, 118.9, and 118.9 mg g-1, respectively, implying that the adsorption capacity of acid-treated HNTs is ~50 times higher than that of natural HNTs. In this study, we clearly demonstrated that acid-treated HNTs can be used as highly efficient nanomaterials for removal of dyes from wastewater containing anionic dyes.

LDH-Co-Fe-Acetate: A New Efficient Sorbent for Azoic Dye Removal and Elaboration by Hydrolysis in Polyol, Characterization, Adsorption, and Anionic Exchange of Direct Red 2 as a Model Anionic Dye.

A new, double hydroxide based on Co and Fe was elaborated on by forced hydrolysis in a polyol medium. Complementary characterization techniques show that this new phase belongs to the layered double hydroxide family (LDH) with Co2+ and Fe3+ ions located in the octahedral sites of the bucite-like structure. The acetate anions occupy interlayer space with an interlamellar distance of 12.70 Å. This large distance likely facilitates the exchange reaction. Acetates were exchanged by carbonates. The as-obtained compound Co-Fe-Ac/Ex shows an interlamellar distance of 7.67 Å. The adsorption of direct red 2 by Co-Fe-Ac-LDH has been examined in order to measure the capability of this new LDH to eliminate highly toxic azoic anionic dyes from waste water and was compared with that of Co-Fe-Ac/Ex and Co-Fe-CO3/A (synthesized in an aqueous medium). The adsorption capacity was found to depend on contact time, pH, initial dye concentration, and heating temperature. Concerning CoFeAc-LDH, the dye uptake reaches a high level (588 mg/g) due to the occurrence of both adsorption processes: physisorption on the external surface and chemical sorption due to the intercalation of dye by exchange with an acetate anion. The study enables us to quantify the uptake amount of each effect in which the intercalation has the most important amount (418 mg/g).