Anionic Azo Dye Research Articles

Removal of noxious Eriochrome black T dye from aqueous solution using magnetically metal oxide modified activated carbon derived from Carica papaya seed

ABSTRACT In the present study, we have synthesised magnetically metal oxide-modified activated carbon derived from Carica papaya seed (Fe3O4/AC). The Fe3O4/AC materials were characterised using XRD, FE-SEM, EDS, EDX, FT-IR and VSM. The Fe3O4/AC materials serve as a promising sorbent for eliminating anionic azo dye, i.e. EBT from aquatic media. Batch adsorption experiments reveal the optimal contact time of 60 min, initial dye concentration of 20 mg/L, adsorbent dosage of 100 mg, stirring speed of 300 rpm and pH3. The adsorption process was well fitted with the Langmuir isotherm model and pseudo-second-order kinetic due to the high R 2 value. The maximum adsorption capacity (q max) for EBT dye was found to be 50 mg/g. Electrostatic interaction, hydrogen bonding and π–π interaction play an important role in between the adsorbent and adsorbate. The stability of Fe3O4/AC materials was investigated by NaOH to desorb EBT dye molecules located on the surface of Fe3O4/AC. This Fe3O4/AC material is an efficient and economical method for the removal of dye from wastewater.

Rapid removal of methyl orange from aqueous media by modified Mg–Al layered double hydroxides

The current work deals with the synthesis of polymer modified synthetic clay, composed of Mg–Al layered double hydroxides (LDHs) and using a non-toxic organic polymer polyethylene glycol-400 (PEG400). A series of polymer-composites of Mg–Al LDH (LDHP-400) are prepared by changing concentrations of PEG-400 from 4% to 20 %, to find out the maximum adsorption efficiency for the adsorption of an industrially important anionic azo dye, MO from aqueous. The results depicted that LDH-P400, with 16 % PEG-400 shown the removal efficiency of 99.49 % for 100 ppm solution of MO (20 min). Effect of different factors such as dose of adsorbate, temperature, contact time, and pH of the solution, etc. are systematically investigated using batch experiments and thermodynamics parameters as well as kinetic studies are also carried out for the quick and instantaneous removal of MO from aqueous media. Maximum adsorption capacity of 198 mg/g has been achieved at pH4.2 and at temperature 313K for 100 ppm (mg/l) of MO in aqueous media using 0.5 g/l of adsorbent dose. Desorption studies reveal that prepared LDHP-400 can be reused and recycle up to three successive cycles with achieving 88.23 % recovery of MO, which confirmed that prepared LDHP-400 can be reused effectively for laboratory or industrial wastewater which has MO concentrations up to 100 ppm.

Compost as Green Adsorbent for the Azo Dyes: Structural Characterization and Dye Removal Mechanism

The study aimed to determine the feasibility of using compost as a ‘green adsorbent’ for the removal of five anionic azo dyes belonging to the monoazo, disazo and trisazo classes: Direct Red 81 (DR-81), Direct Blue 74 (DB-74), Reactive Blue 81 (RB-81), Reactive Red 198 (RR-198) and Acid Black 194 (ABk-194) from aqueous solutions. The adsorption capacity of the compost was determined using a batch method with initial dye concentrations ranging from 1 to 1000 mg/L. The kinetics of dye removal followed a pseudo-second-order model, indicating chemisorption as the rate-limiting step. The monoazo dyes RB-81, RR-198 and ABk-194 with the smaller molecule size were adsorbed the fastest. The Langmuir and Sips models best fit the adsorption system with maximum adsorption capacities in the range of 12.64 mg/g (RR-198)—20.92 mg/g (ABk-194) and 12.57 mg/g (RR-198)—25.43 mg/g (ABk-194), respectively. The adsorption depended on the dye structure, especially on the ratio of the numbers of proton donors to proton acceptor locations in functional groups. The differences in the adsorption mechanism could be explained by thermodynamic properties such as dipole moments, HOMO–LUMO energy gap, polarizability, electron affinity, ionization potential, electronegativity and chemical hardness obtained by Density Functional Theory.Graphical

Bio‐Fabricated Silver Nanoparticles for Catalytic Degradation of Toxic Dyes and Colorimetric Sensing of Hg2+

AbstractIn the present study, silver nanoparticles were synthesized via green synthesis using fenugreek (Trigonella foenum‐graecum L.) seeds of variety HM 425. The AgNPs were characterized by using UV‐Visible spectroscopy, Particle size analyzer, Field emission scanning electron microscopy coupled to Energy dispersive X‐ray spectroscopy, XRD, High resolution transmission electron microscopy and Fourier Transform Infrared Spectroscopy. The AgNPs were spherical and had an average particle size of 28 nm. The reduction of cationic dyes Methylene blue, Rhodamine B, and an anionic azo dye Methyl Orange by Sodium borohydride was used as a model reaction to investigate the catalytic ability of AgNPs. The results demonstrated an efficient catalytic dye degradation of methylene blue (95.81 %, 25 min, 0.1737±0.01 min−1), Rhodamine B (90.23 %, 15 min, 0.1388±0.01 min−1) and methyl orange (83.63 %, 39 min, 0.0412±0.002 min−1). The synthesized AgNPs had an excellent detection limit of 12.50 μM for Hg2+, making them excellent solid bio‐based sensors for mercury sensing.

The development of Giant reed biochar for adsorption of Basic Blue 41 and Eriochrome Black T. azo dyes from wastewater

The textile industry is discharging high concentrations of anionic and cationic azo dyes into the nearby environment, which can cause adverse effects on public health, and the aquatic environment. Therefore, this study aimed to develop giant reed biochar and apply for the removal of Basic blue 41 (BB41) and Eriochrome black T (EBT) azo dyes from water. Characterization techniques such as BET surface area analyzer, Fourier-transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermal gravimetric analyzer (TGA) were applied for biochar description. The biochar exhibits a high fixed carbon content (80.4%), a low ash content (3.8%), a large surface area (429.0 m2/g), and good thermal stability. High removal efficiencies of BB41 98.6% and EBT 82.5% were recorded at the specific experimental condition. The experimental data were fitted with the Langmuir isotherm model at R2 0.99 for both dyes whereas the adsorption kinetics revealed the pseudo-second-order kinetics at R2∼\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim$$\\end{document} 1 and 0.99 for BB41 and EBT, respectively. Furthermore, four regenerations of biochar with adsorption performances of BB41 and EBT dyes were found to be 94.7% and 79.1%, respectively. Finally, this adsorbent can be considered an economically viable material for the removal of synthetic dyes from wastewater systems. In conclusion, the study findings showed that the adsorbent material is promising to apply for water and wastewater treatment but still, the study of adsorption interaction and modifications of the surface functionalities are essential to accommodate multipollutant removal from real water systems.

Zeolitic imidazolate framework-8/layered triple hydr(oxide) composite for boosting the adsorptive removal of acid red 1 dye from wastewater

Water pollution is one of the serious environmental problems the humanity currently faces. Adsorption is an attractive process for tackling water pollution. Accordingly, novel adsorbents were synthesized in this study through the coupling of zeolitic imidazolate framework-8 (ZIF-8) with MnCuAl layered triple hydroxide/oxide (MnCuAl-LTH/MnCuAl-LTO) via different approaches. The synthesized adsorbents were characterized using different techniques in order to reveal their textural properties, crystallinity, and functional groups before applying them to decontaminate wastewater samples contaminated with acid red 1 (AR1) azo dye. The BET results revealed that all the synthesized materials are highly porous with specific surface area ranging from about 35 to more than 1200 m2/g. Additionally, the XRD and FTIR results confirmed the formation of the targeted pristine and composite adsorbents. Preliminary adsorption studies showed that the ZIF-8@MnCuAl-LTH composite is the most effective material in removing AR1 from wastewater. Potential mechanism(s) for the superiority of ZIF-8@MnCuAl-LTH over other adsorbents (i.e., MnCuAl-LTH@ZIF-8, MnCuAl-LTO@ZIF-8, MnCuAl-LTH, MnCuAl-LTO, and ZIF-8) has been discussed. The results also demonstrated that the adsorption of AR1 onto ZIF-8@ MnCuAl-LTH is strongly pH-dependent. The adsorption isotherm results confirmed that the removal of AR1 is best fitted by the Redlich-Paterson isotherm with a high degree of compatibility with the Langmuir isotherm model. Similarly, the experimental data were well-fitted to the Avrami model, confirming the complex nature of AR1 adsorption onto ZIF-8@ MnCuAl-LTH. Additionally, the regenerability and stability of this adsorbent have been investigated, and the obtained results revealed that this adsorbent is stable and has a good reusability. Accordingly, the ease of fabrication, high adsorption capacity (qmax is about 1000 mg/g), and the good stability and reusability make ZIF-8@MnCuAl-LTH a very promising adsorbent for removing anionic azo dyes from wastewaters, demonstrating the significance of this study.

Removal of a model reactive azo dye from aqueous solution by a bioadsorbent in batch and fixed-bed column modes: Application of the developed technology to a textile wastewater

Sugarcane bagasse (SB) was used to produce a new bioadsorbent (STEA), drawing on circular economy concepts. STEA was synthesized using a two-step one-pot reaction, employing epichlorohydrin and triethylamine in the presence of N,N-dimethylformamide, without the use of a petroleum-based catalyst. The structure and surface of STEA were characterized by elemental C, H, N, and Cl analysis, X-ray diffraction, infrared spectroscopy, 13C solid-state nuclear magnetic resonance spectroscopy, thermogravimetric analysis, specific surface area and pore size distribution determination, and point of zero charge measurement. Batch adsorption and desorption tests were performed with the model dye Remazol Golden Yellow (RGY) RNL, a reactive anionic azo dye widely used in textile industry, to evaluate the potential reuse and application of STEA in a fixed-bed column for wastewater treatment. For batch adsorption, the best dose and agitation speed were 0.2 g L−1 and 50 rpm, respectively. STEA effectively removed RGY over a wide range of pH (2.00–10.00). The equilibrium time, maximum adsorption capacity (Qmax), and desorption efficiency (Edes) were 720 min, 369 mg g−1 (0.71 mmol g−1), and 49.5 %, respectively. The fixed-bed column fed with a spiked aqueous RGY solution could be operated for 415 min, with Qmax of 422 mg g−1 (0.81 mmol g−1) and Edes of 58.9 %. Batch and continuous experiments using real textile industry wastewater containing reactive azo dyes showed high color removal efficiency by STEA, with no interference of other compounds present in wastewater on adsorption of the reactive azo dyes (overshooting effect). The technology was validated in a relevant environment and achieved technology readiness level 5, showing potential to be upscaled. Therefore, STEA proved to be an efficient bio-based technology for application in tertiary treatment of real textile plant wastewater to remove reactive anionic azo dyes.

Hybrid rGO/Fe3O4 magnetic nanocomposite for anionic and cationic dye removal application

The adsorption removal of anionic and cationic azo dyes with magnetic nanoparticles was an important technological strategy for the purification of dye-contaminated water. The present work highlights the dye adsorption properties of the solvothermally synthesized hybrid reduced graphene oxide‑iron oxide (rGO/Fe3O4) nanocomposite for the efficient adsorption of methyl orange, congo red, metanil yellow, and methylene blue from the aqueous medium. Morphology, and porous characteristics of the material was analysed with FESEM and BET respectively. The magnetic properties of the material viz. M-H, FC, and ZFC were investigated with SQUID-VSM. The BET analysis confirmed the mesoporous structure of the hybrid rGO/Fe3O4 nanocomposite, with a BET-specific surface area of 27.74 m2/g. Dye adsorption experiments of hybrid rGO/Fe3O4 nanocomposite were conducted to analyse the influence of adsorbent dosage, dye concentrations, and pH variations. FTIR spectroscopy was also used to verify the adsorption of azo dyes onto the surface of the rGO/Fe3O4 nanocomposite. Hybrid rGO/Fe3O4 nanocomposite show complete adsorption of methyl orange, congo red, metanil yellow, and methylene blue dyes with adsorption capacities of 58.76, 100.3, 533, and 50 mg/g, respectively in the water medium. Hybrid rGO/Fe3O4 nanocomposite showed excellent adsorption of metanil yellow dye. The adsorbed azo dyes methyl orange, metanil yellow, methylene blue, and congo red by the rGO/Fe3O4 nanocomposite can be easily desorbs from the material indicating its reusability. The magnetic coercivity of the material at 300K was 47.4 Oe, as a result the adsorbent material can be magnetically separated from the purification system. The adsorption process of methyl orange, congo red, metanil yellow, and methylene blue dyes on the rGO/Fe3O4 nanocomposite best fits to the pseudo-second-order kinetics and the Langmuir isotherm model.

A facile synthesis of bimetallic Ni/Co-BTC hollow MOFs for effective removal of congo red

ABSTRACT In this work, we employ an eco-friendly and highly efficient method for the successful removal of anionic azo dye (CR) using emerging Ni/Co-BTC hollow Metal-Organic Frameworks (MOFs). The MOFs was developed via a solvothermal synthesis method. Various kinetic models, adsorption capacities, isotherms (Langmuir and Freundlich), and thermodynamic stability assessments were used to predict the adsorption mechanism and the types of interactions present between CR dyes and Hollow MOFs. Our findings suggest that the adsorption process follows Freundlich isotherm, with PSO kinetic models indicating chemisorption and a maximum Langmuir adsorption capacity of 168.03 mgg−1. We observed a removal efficiency of 74% in neutral medium and 85% in acidic medium. Thermodynamic studies reveal the spontaneity of the process with endothermic enthalpy, attributed to the hydrogen bonding and electrostatic interactions between the dye molecule and the adsorbent. Furthermore, to investigate practical applicability, we conducted studies in real water and dye mixtures. All studies demonstrated that the prepared Ni/Co-BTC hollow MOFs show promising potential adsorbents for the CR dye removal from the wastewater, owing to their high efficiency and reusability.

Uncalcined Zn/Al Carbonate LDH and Its Calcined Counterpart for Treating the Wastewater Containing Anionic Congo Red Dye

In this investigation, Zn/Al carbonate layered double hydroxide (ZAC-LDH) and its derived material on calcination were synthesized for removing the anionic azo dye Congo red (CR) from wastewater. Numerous factors were methodically investigated, including temperature, adsorbent dosage, pH, starting Dye Concentration (DC), and contact time. The CR elimination percentage dropped as the initial DC increased from 25 mg/L to 100 mg/L at 30 °C for uncalcined LDH, and from 97.96% to 89.25% for calcined LDH. The pH analysis indicates that the highest level of dye removal was recorded within the acidic pH range through the electrostatic attraction mechanism. The sorption kinetics analysis results demonstrated that the pseudo-second-order kinetic model exhibited a stronger fit to both uncalcined LDH and CZA-LDH, with the maximum correlation coefficient value. The Van’t Hoff plots indicate the spontaneous nature of the physisorption process with a negative ΔG° (<−20 kJ/mol), while the endothermic adsorption process exhibited a positive ΔH°. The X-ray diffraction of calcined LDH reveals a significant intercalation of CR dye molecules, both prior to and following adsorption, showcasing a distinctive memory effect. The Brunauer–Emmett–Teller (BET) gas sorption measurements were performed to support the mesoporous nature of ZAC-LDH and CZA-LDH. The FTIR spectrum confirms the interaction of dye molecules on the surface of uncalcined and calcined LDH. These findings emphasize the efficacy of both the synthesized LDHs in removing CR dye, with CZA-LDH demonstrating superior efficiency compared to uncalcined LDH in the context of CR removal from wastewater.

In situ polymerization of acrylamide on magnetic SnFe2O4/CeO2 nanocomposite: A novel adsorbent for removing various dyes

Environmental conservation requires effective, secure, and economical treatment options for dye-contaminated wastewater. The current study comprises a novel fabrication of tin ferrite/ceria/polyacrylamide magnetic and porous ternary nanocomposite. This occurs through crosslinking polymerization of acrylamide on the SnFe2O4/CeO2 binary nanocomposite. The SnFe2O4/CeO2/PAM nanocomposite was comprehensively characterized using FTIR, TGA, XRD, TEM, VSM, EDX, SEM and N2 adsorption-desorption isotherms. The ternary nanocomposite's efficiency as a novel adsorbent for anionic (direct violet 4, DV4) and cationic (bismarck brown r, BBR) azo dyes was investigated. A range of variables were studied to optimize the effectiveness of eliminating both dyes. In an acidic medium, DV4 removal was more efficient, whereas BBR removal was higher in an alkaline environment. Non-linear regression was employed to analyze adsorption kinetics and isotherm models, using three statistical error functions to determine the best-fit models. Adsorption data for both dyes demonstrated a good conformity with pseudo-second-order and Freundlich isotherm models. The dyes' adsorption was both endothermic and spontaneous. The nanocomposite displayed notable performance throughout five reuses. Moreover, the nanocomposite shows good adsorption efficiency for various dyes (congo red, acid blue 40, methyl green, and crystal violet) as well as DV4 and BBR. Therefore, it emerges as a promising adsorbent for wastewater purification.

One Precursor, Two Different Outcomes: SnO-Graphite Composite and Anion-Doped SnO2 with Ester Surface Functionality.

The technological importance of SnO2 and SnO has invited scientists to explore various aspects, including their synthesis in the nanosize regime, surface functionalization, and composite formation. In the present work, a binuclear Sn2-EDTA complex has been demonstrated to produce a SnO-graphite composite and C, N-codoped SnO2 nanocrystals with ester functionality in quantitative yields by thermal and solvothermal dissociation processes. The products were characterized extensively. While SnO in the SnO-graphite composite exhibited tetragonal symmetry, graphitic carbon had defects. The composite had 12 wt % of graphitic carbon. The role of the SnO-graphite composite as an anode in lithium-ion batteries (LIB) has been evaluated. Solvothermal dissociation of the Sn2-EDTA complex in a propylene glycol medium yielded nanocrystalline SnO2 with yellow color. Agglomerated crystallites had ester functionality on their surfaces. The surface functionality was thermally stable up to 200 °C, and its complete removal yielded tetragonal white-colored SnO2. Co-doping of carbon and nitrogen in yellow SnO2 reduced its optical band gap (2.9 eV). Despite the negative surface charge of the functionalized SnO2, its affinity to rapidly adsorb anionic azo dyes (Congo red and Eriochrome black T) from aqueous solutions has been validated. Following pseudo-second-order kinetics, adsorption data analysis revealed chemisorption as the primary driving force in this process.

Biosorption of anionic and cationic azo dye onto red macro alga: Determination of the significant variables using resolution V fractional factorial design

Naturally inspired biosorbent from macro algae species are favored because of its excellent biosorptive capability and low cost. The present investigation reports the potential of red macro-alga, E. spinosum as a biosorbent to remove both anionic and cationic azo dyes, namely Acid Yellow 17 (AY17) and Methylene Blue (MB) from aqueous solution. A resolution V fractional factorial design (2v5-1) analysis was employed to study the main effects and interaction of variables on the biosorption process. Factorial matrix with five variables; pH (2–12), dosage (0.4–2 g/L), initial concentration (50–200 mg/L), contact time (5–120 min) and temperature (30-50 °C) at two levels were conducted in batch study. Pareto charts and ANOVA (within 95% confidence level) were applied to examine the relationship and significance between independent variables and their interactions. A regression model with R2AY17 = 0.9998 and R2MB = 0.9995 was implemented to fit the experimental data. The results obtained indicated that the most significant variables that affected biosorption process were initial concentration and the dosage of the dyes. Experimental screenings are crucial in optimization studies. The remarkable performance of E. spinosum as biosorbent to absorb both dyes shows a great potential to be implemented for local marine macro alga as an alternative. Resource for biosorption process.

Effect of Shape and Size on Synthesized Triple (Co/Ni/Zn)-Doped α-Fe2O3 Nanoparticles on their Photocatalytic and Scavenging Properties

Co/Ni/Zn triple doped [Formula: see text]-Fe2O3 nanoparticles (NPs) have been synthesized via polyvinylpyrrolidone (PVP)/Azadirachta indica (A. Indica) leaf extract coating. XRD, UV–Vis, SEM, TEM, EDS, Raman spectroscopy, FTIR, VSM were used to characterize the synthesized NPs. XRD pattern revealed that the crystallite size of NPs ranges from 14[Formula: see text]nm to 21[Formula: see text]nm. Spherical NPs were found by SEM/TEM examination ranging from 16[Formula: see text]nm to 26[Formula: see text]nm of doped [Formula: see text]-Fe2O3 NPs. Analysis of the magnetic properties of [Formula: see text]-Fe2O3 NPs revealed antiferromagnetic characteristics, convergence between magnetization curves (MS), and switching field distribution dM/dh below an irreversible temperature of [Formula: see text][Formula: see text]K. Produced catalyst was used for the degradation of anionic azo dye Malachite green (MG) and Rhodamine blue (RhB) dyes under the influence of UV radiation. RhB and MG were reduced as a result of the doped [Formula: see text]-Fe2O3 catalyzing the conversion of dissolved O2 to hydroxyl radicals (OH) when exposed to visible light. This shows that the main active radical specifically engaged in the photo-catalytic breakdown of dyes is OH. The most effective photo-catalyst was determined by investigating the proposed doped [Formula: see text]-Fe2O3 NPs reusability over three cycles. The catalyst was retrieved and utilized three times after the reaction without suffering a substantial loss of catalytic activity. The plant-mediated [Formula: see text]-Fe2O3 NPs have significant antioxidant activity due to their higher phenolic content. These have a promising future with potential applications in health, aging, food preservation, cosmetics, agriculture and environmental protection.

Performance of Mg/Al and Zn/Al Hydroxide Double Lamellar-Bentonite for Removal of Anionic Azo Dye from Aqueous Solution

This paper presents the preparation and characterization of bentonite coated with hydroxide double lamellar Mg/Al-bentonite and Zn/Al-bentonite as a potential adsorbent material. The coating process involved co-precipitation of mixed metal nitrate solution (Mg-Al) or (Zn-Al), followed by immersion of bentonite (B-Na+) dispersion. The structures and morphologies of the coated bentonites were characterized using XRD, FTIR, BET, and SEM analysis. The results of the BET analysis indicate that Mg/Al-bentonite and Zn/Al-bentonite have larger surface areas and pore volumes compared to bentonite alone. Specifically, the surface area of Mg/Al-bentonite is 209.25 m2/g with a pore volume of 0.423 cm3/g, while Zn/Al-bentonite has a surface area of 175.95 m2/g and a pore volume of 0.313 cm3/g. In contrast, the surface area and pore volume of bentonite alone are 110.43 m2/g and 0.132 cm3/g, respectively. The Mg/Al-bentonite reaches 85% uptake within 3 h (equivalent to 724.20 mg/g at 25 °C and pH 7), achieving rapid equilibrium. In contrast, the Zn/Al-bentonite achieves a maximum adsorption of 74% within 5 h under identical pH and temperature conditions, corresponding to 650.34 mg/g. The error function values, including the correlation coefficient R2, chi-square test χ2, and residual sum of squares RSS, were calculated to evaluate both kinetic and isotherm models. The kinetic adsorption data agreed well with a pseudo-second-order model. The adsorption process followed the Sips isotherm model, and the monolayer adsorption capacity of Mg/Al-bent and Zn/Al-bent composites was 872.41 (R2 = 0.974) and 678.45 mg/g (R2 = 0.983), respectively. The thermodynamic analysis of the adsorption process revealed that it occurred spontaneously with an endothermic characteristic. The parameters ΔS, ΔH, and ΔG were used to determine this.

Superior Adsorptive Removal of Anionic Azo Dyes from Aqueous Solutions Using Sulfonic Acid Group-Modified MIL-101@Graphene Oxide Composite.

It is critical to remove organic contaminants from wastewater released by the printing and dyeing industry for addressing water pollution issue. Therefore, the fabrication of new adsorbents with excellent removal efficiencies is an urgent task. A composite of MIL-101 partially functionalized with -SO3H (MIL-101-SO3H) and graphene oxide (GO) was prepared by assembling MIL-101-SO3H truncated octahedrons on the GO framework. The synthesized MIL-101-SO3H@GO has a superior adsorption efficiency for anionic azo dyes. The maximum adsorption capacities of MIL-101-SO3H@GO-1 for Congo red, methyl orange, acid orange 7, and acid orange G reached 2711.3, 818.8, 551.2, and 319.8 mg/g, respectively, which are considerably higher than those obtained using unmodified MIL-101. This is because additional interactions that promote azo dye adsorption, such as hydrogen bonding between the dye and the sulfonic acid groups of MIL-101-SO3H or the carboxyl groups of GO, were induced, and agglomerate pores that accommodated the dye were formed in the composite. The ultrahigh removal efficiency of the composite for azo dyes is mainly driven by hydrogen bonding, electrostatic interactions, π-π stacking between the MIL-101-SO3H@GO and dye molecules, synergistic interactions at the interface of GO and MIL-101-SO3H microcrystals, and the pore-filling effect. Understanding these driving forces for dye adsorption can contribute to the development of sustainable and functionally modified metal-organic framework composite adsorbents.

Fast and highly selective anionic azo dye removal over unique PVDF/MIL-100(Cr) mixed matrix membranes

Water pollution is a major challenge in the industrial era that gained the attention of researchers, especially for dye wastewater. Membrane technology is applied to address this issue due to its efficient and effective process. MIL-100(Cr) is a metal-organic framework that becomes an interesting material in membrane technology due to its highly porous characteristics (pore sizes of 24 Å and 29 Å), large surface area, and decent stability. In this study, polyvinylidene fluoride (PVDF) was modified with MIL-100(Cr) to fabricate PVDF/MIL-100(Cr) mixed matrix membranes (MMMs) for congo red (CR) dye removal. Furthermore, the membrane performances were determined by its permeability, selectivity, and antifouling properties. The results show that adding MIL-100(Cr) could enhance the membrane’s porosity and average pore size, which led to a boost in membrane permeability. Interestingly, the rejection of the membrane is maintained at a remarkably high level, above 95%, because of the electrostatic repulsion between the membrane surface with anionic congo red. The optimum concentration of MIL-100(Cr) is 1% (w/w), with a permeability of 50.90 L m−2 h−1 and rejection of 99.9%. Moreover, the flux recovery ratio (FRR) is around 90%, showing notable resistance to the fouling phenomena.

Sorption and concentration anionic azo dyes on nanomagnetite modified with cationic polyelectrolytes

Using the chemical coprecipitation method, magnetic magnetite nanoparticles (MNP) were synthesized, the surface of which was modified with biocompatible cationic polyelectrolytes polyethylenimine (PEI) and chitosan (Cht). The MNP were characterised by transmission microscopy and zeta potential measurements. The initial MNP have a shape close to spherical and an average size of (10±3) nm. Immobilization of polyelectrolyte on the surface of MNP led to the appearance of aggregates with an interconnected porous network (shell) around individual particles, with average sizes of (12±2) and (15±2) nm for Fe3O4@PEI and Fe3O4@Cht, accordingly. The influence of various experimental parameters, such as pH, extraction time, amount of sorbent and initial dye concentration on the adsorption and desorption of food azo dyes Allure Red AC (E129) and Brilliant Black BN (E151) was studied. It has been shown that under optimal conditions the degree of extraction of these dyes from aqueous solutions is 96-100%, the concentration coefficient is 2.7×103 and sorption capacity of 56 and 94 mg/g for Fe3O4@PEI and 46 and 69 mg/g on Fe3O4@ХТЗ for E129 and E151, respectively. A comparison of sorption isotherms and process kinetics showed that the Langmuir model and pseudo-first order are preferable for describing the sorption of dyes. In the acidic and neutral regions, electrostatic interactions are responsible for sorption, and in the alkaline region, hydrogen bonding and hydrophobic interactions also play a significant role. The proposed sorbents can be used both for the sorption and concentration of dyes in chemical analysis, and for the purification of wastewater from them. Nanomagnetite modified with polyethylenimine, which allows absorbing and concentrating dyes over a wide pH range of 6-9 is preferable for use.

Anionic azo dyes and their removal from textile wastewater through adsorption by various adsorbents: a critical review

The review aimed to identify differences and similarities in the adsorption process of five azo dyes [congo red (CR), reactive black 5 (RB5), methyl orange (MO), orange II (OII), and methyl red (MR)] on natural materials, biosorbents, industrial and agricultural waste, or biomass, which are alternatives of costly activated carbon and are locally available. The azo dyes were characterized and compared based on their molecular structure and weight, water solubility, acid dissociation constant, n-octanol-water partition coefficient, and maximum absorbance. RB5 and CR are diazo dyes, whereas MO, OII, and MR are mono-azo dyes. MO, OII, and MR are anionic acid dyes, RB5 is an anionic reactive dye, and CR is an anionic direct dye. CR, RB5, MR, and OII molecules contain one or more sulfonate functional group(s), but MR does not. We performed a literature review based on the following parameters: initial dye concentration, adsorbent dosage, pH, temperature, isotherm, kinetic models, thermodynamic parameters, and synergetic or competitive interactions. The azo dyes tended to adsorb best in an acidic medium and at higher temperatures. The initial dye concentration and adsorbent dosage studies indicated the importance of using an appropriate amount of adsorbent dosage for an effective removal. The studies tended to follow the Langmuir isotherm and kinetic pseudo-second-order model. Most adsorption processes were endothermic and spontaneous, leading to an increase in randomness at the solid-liquid interface. These results indicate similarities between the adsorption process of the five azo dyes. Relevant adsorption mechanisms in azo dye adsorption processes were assumed to be electrostatic forces, hydrogen bonding, and π–π interactions, among others. Nevertheless, the focus of the studies lies more on the development and characterization of adsorbent materials, not on the study of influences from the matrix “industrial wastewater”. Therefore, more research is needed to develop adsorption units for application in textile industries.

Azo dye polyelectrolyte multilayer films reversibly re-soluble with visible light

Polymeric multilayer films were prepared using a layer-by-layer (LBL) technique on glass surfaces, by repeated and sequential dipping into dilute aqueous solutions of various combinations of water-soluble polyanions (polyacrylic acid (PAA)), polycations (polyallylamine hydrochloride (PAH) or chitosan (CS)), with bi-functional water-soluble cationic azo dyes bismark brown R bismarck brown red or bismark brown Y (BBY), or anionic azo dyes allura red (ALR) or amaranth (AMA), as ionic cross-linkers. The electrostatically-assembled ionically-paired films showed good long-term stability to dissolution, with no re-solubility in water. However, upon exposure to low power visible light under running water, the films photo-disassembled back to their water-soluble constituent components, via structural photo-isomerization of the azo ionic crosslinkers. The relative rate of the disassembly (RRD) of the films was established using UV-Vis spectroscopy, demonstrating that these assemblies can in principle represent fully recyclable, environmentally structurally degradable materials triggered by exposure to sunlight, with full recovery of starting components. A density functional theory treatment of the allura red azo dye rationalizes the geometrical isomerization mechanism of the photo-disassembly and provides insight into the energetics of the optically-induced structural changes that trigger the disassembly and recovery.