Removal of textile dyes from single and binary component systems by Persian bentonite and a mixed adsorbent of bentonite/charred dolomite

A floating biosorbent of polylactide and carboxylated cellulose from biomass for effective removal of methylene blue from water

A floating adsorbent bead was prepared from polylactide (PLA) and maleic anhydride (MAH)-modified cellulose in a one-pot process (OP bead). Cellulose was extracted from waste lemongrass leaf (LGL) and modified with MAH in the presence of dimethylacetamide (DMAc). PLA was then added directly into the system to form sorbent beads by a phase separation process that reused unreacted MAH and DMAc as a pore former and a solvent, respectively. The chemical modification converted cellulose macrofibres (55.1 ± 31.5 μm) to microfibers (8.8 ± 1.5 μm) without the need for grinding. The OP beads exhibited more and larger surface pores and greater thermal stability than beads prepared conventionally. The OP beads also removed methylene blue (MB) more effectively, with a maximum adsorption capacity of 86.19 mg⋅g-1. The adsorption of MB on the OP bead fitted the pseudo-second order and the Langmuir isotherm models. The OP bead was reusable over five adsorption cycles, retaining 88 % of MB adsorption. In a mixed solution of MB and methyl orange (MO), the OP bead adsorbed 96 % of the cationic dye MB while repelling the anionic dye MO. The proposed method not only reduced time, energy and chemical consumption, but also enabled the fabrication of a green, effective and easy-to-use biosorbent.

Optimization of hydrothermal synthesis conditions of Bidens pilosa-derived NiFe2O4@AC for dye adsorption using response surface methodology and Box-Behnken design

The presence of stable and hazardous organic dyes in industrial effluents poses significant risks to both public health and the environment. Activated carbons and biochars are widely used adsorbents for removal of these pollutants, but they often have several disadvantages such as poor recoverability and inseparability from water in the post-adsorption process. Incorporating a magnetic component into activated carbons can address these drawbacks. This study aims to optimizing the production of NiFe2O4-loaded activated carbon (NiFe2O4@AC) derived from a Bidens pilosa biomass source through a hydrothermal method for the adsorption of Rhodamine B (RhB), methyl orange (MO), and methyl red (MR) dyes. Response surface methodology (RSM) and Box-Behnken design (BBD) were applied to analyze the key synthesis factors such as NiFe2O4 loading percentage (10-50%), hydrothermal temperature (120-180 °C), and reaction time (6-18 h). The optimized condition was found at a NiFe2O4 loading of 19.93%, a temperature of 135.55 °C, and a reaction time of 16.54 h. The optimum NiFe2O4@AC demonstrated excellent sorption efficiencies of higher than 92.98-97.10% against all three dyes. This adsorbent was characterized, exhibiting a well-developed porous structure with a high surface area of 973.5 m2 g-1. Kinetic and isotherm were studied with the best fit of pseudo-second-order, and Freundlich or Temkin. Qmax values were determined to be 204.07, 266.16, and 177.70 mg g-1 for RhB, MO, and MR, respectively. By selecting HCl as an elution, NiFe2O4@AC could be efficiently reused for at least 4 cycles. Thus, the Bidens pilosa-derived NiFe2O4@AC can be a promising material for effective and recyclable removal of dye pollutants from wastewater.

Carboxymethyl chitosan/polyvinyl alcohol double network hydrogels prepared by freeze-thawing and calcium chloride cross-linking for efficient dye adsorption

The discharge of dye wastewater resulting from rapid industrial development has become a serious environmental concern. Therefore, there is a pressing need to develop efficient methods and technologies for the removal of dye pollutants. This study introduced a double network hydrogel, with varying carboxymethyl chitosan (CMCS) contents and polyvinyl alcohol (PVA), employing a combination of freeze- thawing and calcium chloride cross-linking. The investigation focused on the rheological properties of the hydrogels and their removal ability of acidic blue 93 (AB). The results showed that the strength and viscoelastic modulus of composite hydrogels were positively correlated with the CMCS content, and all composite hydrogels exhibited the typical weak strain overshoot behavior. The pore size of the gel initially decreased and then increased, with the densest pores observed at 4 wt% CMCS, showing the optimal removal ability for AB. The adsorption process followed pseudo second-order kinetic model, dominated by external diffusion, and exhibited inhomogeneous multilayer adsorption. This study unveils the potential of CMCS/PVA gels as adsorbents, offering inspirations for the design and development of polyvinyl alcohol-based gels for applications in the food industry.

Insights on applications of bentonite clays for the removal of dyes and heavy metals from wastewater: a review

In recent decades, increased industrial, agricultural, and domestic activities have resulted in the release of various pollutants into the aquatic systems, which require a reliable and environmentally friendly method to remove them. Adsorption is one of the most cost-effective and sustainable wastewater treatment techniques. A plethora of low-cost bio-based adsorbents have been developed worldwide so far to supplant activated carbon and its high processing costs. Bentonite clays (BCs), whether in natural or modified form, have gained enormous potential in wastewater treatment and have been used successfully as a novel and cost-effective bio-sorbent for removing organic and inorganic pollutants from the liquid suspension. It has become a sustainable solution for wastewater treatment due to its variety of surface and structural properties, superior chemical stability, high capacity for cation exchange, elevated surface area due to its layered structure, non-toxicity, abundance, low cost, and high adsorption capacity compared to other clays. This review encompasses comprehensive literature about various modification techniques and adsorption mechanisms of BCs concerning dyes and heavy metal removal from wastewater. A critical overview of different parameters for optimizing adsorption capacity and regeneration via the desorption technique has also been presented here. Finally, a conclusion has been drawn with some future research recommendations based on technological challenges encountered in industrializing these materials.

Dynamics of Diffusion- and Immobilization-Limited Photocatalytic Degradation of Dyes by Metal Oxide Nanoparticles in Binary or Ternary Solutions

Photocatalytic degradation employing metal oxides, such as TiO2 nanoparticles, as catalysts is an important technique for the removal of synthetic dyes from wastewater under light irradiation. The basic principles of photocatalysis of dyes, the effects of the intrinsic photoactivity of a catalyst, and the conventional non-fundamental factors are well established. Recently reported photocatalysis studies of dyes in single, binary, and ternary solute solutions opened up a new perspective on competitive photocatalytic degradation of the dyes. There has not been a review on the photocatalytic behavior of binary or ternary solutions of dyes. In this regard, this current review article summarizes the photocatalytic behavior of methylene, rhodamine B, and methyl orange in their binary or ternary solutions. This brief overview introduces the importance of the dynamics of immobilization and reactivity of the dyes, the vital roles of molecular conformation and functional groups on their diffusion onto the catalyst surface, and photocatalytic degradation, and provides an understanding of the simultaneous photocatalytic processes of multiple dyes in aqueous systems.

Dynamics and thermodynamics for competitive adsorptive removal of methylene blue and rhodamine B from binary aqueous solution onto durian rind

Concurrent adsorptive removal of methylene blue (MB) and rhodamine B (RhB) onto durian rind (DR) agricultural waste, from an aqueous binary solution as a model of wastewater containing multiple synthetic dyes, was investigated. The concurrent adsorption of the dyes followed pseudo-second-order kinetics. The adsorption isotherm was well simulated by the Langmuir model, implying a monolayer adsorption to the surface with a homogeneous binding energy. The adsorption process was governed by external mass transfer through two-step intraparticle diffusion of the dyes onto the adsorbent surface. The adsorption efficiency of MB (96.4%) is much higher than that of RhB (56.3%). This is attributed to the higher rate constant for the adsorption of MB (0.348 g mg^-1 min^-1) as compared to that of RhB (0.151 g mg^-1 min^-1). The adsorption behavior suggested that the two cationic dyes in the binary solution diffused and adsorbed independently and randomly onto the DR surface. The adsorption capacity of MB and RhB in the binary solution (47.4 mg g^-1 and 32.9 mg g^-1, respectively) is lower than those of their single solute solutions (93.3 mg g^-1 and 62.8 mg g^-1, respectively), suggesting a competitive effect in their concurrent adsorption. This was confirmed based on the adsorption characteristics of the binary solution with different molar ratios. The competitive effect was attributed to either non-interactive or repulsive electrostatic interactions between the positively charged dyes in the binary system. The domination of MB is attributed to its smaller molecular size, higher planarity, and faster adsorption kinetics compared with RhB.

Valorization of food waste as adsorbents for toxic dye removal from contaminated waters: A review

Industrial contaminants such as dyes and intermediates are released into water bodies, making the water unfit for human use. At the same time large amounts of food wastes accumulate near the work places, residential complexes etc. polluting the air due to putrefaction. The need of the hour lies in finding innovative solutions for dye removal from wastewater streams. In this context, the article emphasizes adoption or conversion of food waste materials, an ecological nuisance, as adsorbents for the removal of dyes from wastewaters. Adsorption, being a well-established technique, the review critically examines the specific potential of food waste constituents as dye adsorbents. The efficacy of food waste-based adsorbents is examined, besides addressing the possible adsorption mechanisms and the factors affecting phenomenon such as pH, temperature, contact time, adsorbent dosage, particle size, and ionic strength. Integration of information and communication technology approaches with adsorption isotherms and kinetic models are emphasized to bring out their role in improving overall modeling performance. Additionally, the reusability of adsorbents has been highlighted for effective substrate utilization. The review makes an attempt to stress the valorization of food waste materials to remove dyes from contaminated waters thereby ensuring long-term sustainability.

Porous multifunctional phenylcarbamoylated-β-cyclodextrin polymers for rapid removal of aromatic organic pollutants

In this work, polymers containing a large number of benzene rings and multiple functional groups were designed to remove aromatic organic pollutants. Using tetrafluoroterephthalonitrile (TFTPN) as a rigid crosslinking agent to crosslink different functionalized phenylcarbamoylated-β-cyclodextrin derivatives to prepare a series of porous multifunctional cyclodextrin (CD) polymerizations, including three preliminary polymerized adsorption materials and a mix β-cyclodextrin polymer (X-CDP) prepared via a secondary crosslinking procedure of the above three materials. The X-CDP preparation process connects the pre-formed nanoparticles and increases the presence of linkers inside the particles. At the same time, X-CDP exhibited porous structure with various functional groups such as nitro, chlorine, fluorine, and hydroxyl. Those special characteristics render this material with good adsorption ability towards various aromatic organic pollutants in water, including tetracycline, ibuprofen, dichlorophenol, norfloxacin, bisphenol A, and naphthol. Especially, the maximum adsorption capacity for tetracycline at equilibrium reached 110.56 mg·g^-1, which is competitive with the adsorption capacities of other polysaccharide adsorbents. X-CDP removed organic contaminants much more quickly than other adsorbents, reaching almost ~95% of its equilibrium in only 30 s, and the rate constant reaches 2.32 g·mg^-1·min^-1. The main adsorption process of the pollutants by X-CDP fitted the pseudo-second-order kinetic and Langmuir isotherm well, indicating that the adsorption process is monolayer adsorption. Moreover, X-CDP possessed the good reusability where the pollutant removal rate was only reduced 8.3% after five cycles. Such advantages render the polymer great potential in the rapid treatment of organic pollutants in water bodies.

Removal of Toluidine Blue and Safranin O from Single and Binary Solutions Using Zeolite

The studies on dye removal from solutions attracted great attention due to the increased use of color dyes in different fields. However, most of the studies were focused on dye removal from a single solution. In reality, wastewater from the fabric industry could contain mixed dyes. As such, evaluating different dye removal from mixed solutions may have more practical importance. In terms of sorbents evaluated for dye removal, most of them were an organic type generated from agricultural wastes. Clay minerals and zeolites were also studied extensively, because of the vast reserves, inexpensive material cost, larger specific surface area (SSA) and high cation exchange capacity (CEC). However, evaluating the factors controlling the dye removal from mixed dye solutions was limited. In this study, the removal of cationic dyes safranin O (SO) and toluidine blue (TB) by clinoptilolite zeolite (ZEO) was evaluated under single and binary systems. The results showed that removal of TB was preferred over SO by approximately a 2:1 ratio. The counterion Cl− sorption from mixed dye solution helped the formation of mixed dye aggregates on mineral surfaces. Molecular dynamic simulation confirmed the multilayer mixed dye formation on ZEO under high loading levels.

Enhanced Adsorption of Rhodamine B on Modified Oil-Based Drill Cutting Ash: Characterization, Adsorption Kinetics, and Adsorption Isotherm

In this paper, phosphoric acid (H₃PO₄), hydrochloric acid (HCl), and hydrogen peroxide (H₂O₂) were employed for the modification of oil-based drill cutting ash (OBDCA) for the first time. The adsorption of rhodamine B (RhB) on modified oil-based drill cutting ash (MOBDCA) in an aqueous medium was investigated. H₂O₂-modified OBDCA had the optimal adsorption efficiency for RhB. The physical and chemical properties of MOBDCA were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), ζ-potential, N₂ adsorption-desorption isotherm, and pore size distribution. The effect of the pH value (3-11), reaction time (10-720 min), and initial RhB concentration (10-200 mg/L) on RhB adsorption was discussed. The adsorption kinetics highly fitted with the pseudo-second-order model (R ² > 0.99), which indicated that the adsorption process was dominated by chemisorption. The adsorption isotherm fitted well with the Langmuir and Freundlich models (R ² > 0.97), which indicated the monolayer adsorption process and the heterogeneous adsorption process, respectively. The theoretic adsorption capacity (50 mg/g) for RhB was achieved by H₂O₂-modified OBDCA. This paper provides a promising method of resource utilization of OBDCA to treat organic pollutants.

Improved photodegradation of anionic dyes using a complex graphitic carbon nitride and iron-based metal-organic framework material

Introducing heterostructures to graphitic carbon nitrides (g-C3N4) can improve the activity of visible-light-driven catalysts for the efficient treatment of multiple toxic pollutants in water. Here, we report for the first time that a complex material can be constructed from oxygen-doped g-C3N4 and a MIL-53(Fe) metal-organic framework using facile hydrothermal synthesis and recycled polyethylene terephthalate from plastic waste. The novel multi-walled nanotube structure of the O-g-C3N4/MIL-53(Fe) composite, which enables the unique interfacial charge transfer at the heterojunction, showed an obvious enhancement in the separation efficiency of the photochemical electron-hole pairs. This resulted in a narrow bandgap energy (2.30 eV, compared to 2.55 eV in O-g-C3N4), high photocurrent intensity (0.17 mA cm-2, compared to 0.12 mA cm-2 and 0.09 mA cm-2 in MIL-53(Fe) and O-g-C3N4, respectively) and excellent catalytic performance in the photodegradation of anionic azo dyes (95% for RR 195 and 99% for RY 145 degraded after 4 h, and only a minor change in the efficiency observed after four consecutive tests). These results demonstrate the development of new catalysts made from waste feedstocks that show high stability, ease of fabrication and can operate in natural light for environmental remediation.