Effectively removal of cationic and anionic dyes by pH-sensitive amphoteric adsorbent derived from agricultural waste-wheat straw

Insight into the wheat residues-derived adsorbents for the remediation of organic and inorganic aquatic contaminants: A review

Wheat is a major grain crop of the world that provides a stable food for human consumption. Large amounts of by-products/waste materials are produced after the harvesting and processing of wheat crop. Such materials can cause an environmental issue if not disposed of properly. Several studies have shown that wheat residues can be efficient precursors for adsorbents because of their availability, renewability, lignocellulosic composition, and surface active groups enriched structure. In the literature, there are few review articles that address wheat residues-based adsorbents. However, these reviews were specific in terms of adsorbate or adsorbent and did not provide detailed information about the modification, properties, and regeneration of these adsorbents. This article extensively reviews the utilization of wheat biomass/waste including straw, bran, husk, and stalk as precursors for raw or untreated, chemically treated, carbonaceous, and composite adsorbents against various environmental pollutants. The influences of inlet pollutant amount, adsorbent dose, pH, temperature, and time on the performance of adsorbents against pollutants were considered. The maximum uptakes, equilibrium time, and adsorption nature were identified from isotherms, kinetic, and thermodynamic studies. The highest adsorbed amounts of most tested contaminants were 448.20, 322.58, and 578.13 mg/g for lead, chromium, and copper, 1374.6 and 1449.4 mg/g for methylene blue and malachite green, and 854.75, 179.21, and 107.77 mg/g for tetracycline, phosphate, and nitrate, respectively. For the studied adsorbate/adsorbent systems the adsorption mechanism and regeneration were also discussed. Significant results and future directions are finally presented.

Smart pillar[5]arene-based PDMAEMA/PES beads for selective dye pollutants removal: design, synthesis, chemical-physical characterization, and adsorption kinetic studies

This article reports on the synthesis of an innovative smart polymer, P5-QPDMAEMA, opportunely developed with the aim of combining the responsiveness of PDMAEMA polymer and the host-guest properties of covalently linked pillar[5]arenes. Thanks to a traditional Non-Induced Phase Separation (NIPS) process performed at various coagulation pH, the blending of P5-QPDMAEMA with polyethersulfone gave rise to the formation of functional beads for the removal of organic dyes in water. Adsorption tests are carried out on all the produced blend-based beads by employing two representative dyes, the cationic methylene blue (MB), and the anionic methyl orange (MO). In particular, the P5-QPDMAEMA based beads, prepared at acidic pH, featured the best MO removal rate (i. e., 91.3 % after 150 minutes starting from a 20 mg ⋅ L-1 solution) and a high selectivity towards the removal of the selected anionic dye. Based on the adsorption kinetics and isotherm calculations, the pseudo-first order and Freundlich models were shown to be the most suitable to describe the MO adsorption behavior, achieving a maximum adsorption capacity of 21.54 mg ⋅ g-1. Furthermore, zwitterionic beads are obtained by a post-functionalization of the PDMAEMA and the P5-QPDMAEMA based beads, to test their removal capability towards both anionic and cationic dyes, as shown.

Heavy metals immobilization and bioavailability in multi-metal contaminated soil under ryegrass cultivation as affected by ZnO and MnO2 nanoparticle-modified biochar

Pollution by heavy metals (HMs) has become a global problem for agriculture and the environment. In this study, the effects of pristine biochar and biochar modified with manganese dioxide (BC@MnO2) and zinc oxide (BC@ZnO) nanoparticles on the immobilization and bioavailability of Pb, Cd, Zn, and Ni in soil under ryegrass (Lolium perenne L.) cultivation were investigated. The results of SEM-EDX, FTIR, and XRD showed that ZnO and MnO2 nanoparticles were successfully loaded onto biochar. The results showed that BC, BC@MnO2 and BC@ZnO treatments significantly increased shoots and roots dry weight of ryegrass compared to the control. The maximum dry weight of root and shoot (1.365 g pot-1 and 4.163 g pot-1, respectively) was reached at 1% BC@MnO2. The HMs uptake by ryegrass roots and shoots decreased significantly after addition of amendments. The lowest Pb, Cd, Zn and Ni uptake in the plant shoot (13.176, 24.92, 32.407, and 53.88 µg pot-1, respectively) was obtained in the 1% BC@MnO2 treatment. Modified biochar was more successful in reducing HMs uptake by ryegrass and improving plant growth than pristine biochar and can therefore be used as an efficient and cost effective amendment for the remediation of HMs contaminated soils. The lowest HMs translocation (TF) and bioconcentration factors were related to the 1% BC@MnO2 treatment. Therefore, BC@MnO2 was the most successful treatment for HMs immobilization in soil. Also, a comparison of the TF values of plant showed that ryegrass had a good ability to accumulate all studied HMs in its roots, and it is a suitable plant for HMs phytostabilization.

Super capacity of ligand-engineered biochar for sorption of malachite green dye: key role of functional moieties and mesoporous structure

This study synthesized a new thiomalic acid-modified rice husk biochar (TMA-BC) as a versatile and eco-friendly sorbent. After undergoing chemical treatments, the mercerized rice husk biochar (NaOH-BC) and TMA-BC samples showed higher BET surface area values of 277.1 m2/g and 305.8 m2/g, respectively, compared to the pristine biochar (BC) sample, which had a surface area of 234.2 m2/g. In batch adsorption experiments, it was found that the highest removal efficiency for malachite green (MG) was achieved with TMA-BC, reaching 96.4%, while NaOH-BC and BC exhibited removal efficiencies of 38.6% and 27.9%, respectively, at pH 8. The engineered TMA-BC exhibited a super adsorption capacity of 104.17 mg/g for MG dye at pH 8.0 and 25 °C with a dosage of 2 g/L. The SEM, TEM, XPS, and FTIR spectroscopy analyses were performed to examine mesoporous features and successful TMA-BC carboxylic and thiol functional groups grafting on biochar. Electrostatic forces, such as π - π interactions, hydrogen bonding, and pore intrusion, were identified as key factors in the sorption of MG dye. As compared to single-solution adsorption experiments, the binary solution experiments performed at optimized dosages of undesired ions, such as humic acid, sodium dodecyl sulfate surfactant, NaCl, and NaSCN, reflected an increase in MG dye removal of 2.8%, 8.7%, 5.4%, and 12.7%, respectively, which was attributed to unique mesoporous features and grafted functional groups of TMA-BC. Furthermore, the TMA-BC showed promising reusability up to three cycles. Our study indicates that mediocre biochar modified with TMA can provide an eco-friendly and cost-effective alternative to commercially accessible adsorbents.

Fabrication of date palm kernel biochar-sulfur (DPKB-S) for super adsorption of methylene blue dye from water

A novel form of biochar was created by dehydration of Date palm kernel with 85% sulfuric acid. It was examined how the newly produced biochar (DPKB-S) affected the aqueous solution's capacity to extract Methylene Blue (MB) dye. The prepared DPKB-S was categorized by BET, BJH, FT-IR, SEM, EDX, DSC, and TGA analyses. The ideal pH for the MB dye adsorption by DPKB-S is 8. With 0.75 g L-1 of DPKB-S and an initial concentration of 50 ppm MB dye, Date Palm Kernel Biochar-Sulfur (DPKB-S) had the highest removal percentage of 100%. The Langmuir and Freundlich isotherm models were used to investigate the collected data. Freundlich model is the model that best covers MB dye adsorption in DPKB-S at low concentrations (0.75-1.25 g L-1) and the Langmuir model at high concentrations (1.5-1.75 g L-1). The Langmuir model maximum adsorption capacity (Qm) of the DPKB-S was 1512.30 mg g-1. Furthermore, a variety of error function models were applied to investigate the isotherm models derived data, including Marquardt's percent standard deviation (MPSD), the sum of absolute errors (EABS), the sum of the errors squared (ERRSQ), root mean square errors (RMS), Chi-square error (X2), the average relative error (ARE), average percent errors (APE), and hybrid error function (HYBRID). Kinetic data were calculated by intraparticle diffusion (IPD), pseudo-second-order (PSO), pseudo-first-order (PFO), and film diffusion (FD) models. A PSO rate model with a strong correlation (R2 = 1.00) largely regulated the adsorption rate. The removal mechanism of MB dye by DPKB-S is based on the principle that these positively charged dyes are attracted by electrostatic attraction forces due to the growth in the number of negatively charged regions at basic pH value. According to the results, DPKB-S shows promise as an affordable and competent adsorbent for the adsorption of MB dye. It can be used frequently without experiencing a discernible decrease in adsorption efficiency.

Removal of cationic dyes from aqueous solution using polyacrylic acid modified hemp stem

Water pollution caused by dyes is a pressing environmental challenge due to their persistence and difficulty in degradation. Herein, an anionic adsorbent (HS-PAANa) was synthesized by grafting polyacrylic acid (PAA) onto the agricultural waste-hemp stem (HS). The obtained HS-PAANa adsorbent exhibited rapid adsorption kinetics, high adsorption capacity, and a favorable preference for cationic dyes, such as methylene blue (MB) and crystal violet (CV). The experimental data fit well with the pseudo-second-order kinetic model and Langmuir isotherm, demonstrating the efficiency of HS-PAANa in dye removal. Notably, the optimal adsorption capacities of HS-PAANa for MB and CV were found to be 1296.65 mg/g and 1451.43 mg/g, respectively. In the cationic/anionic dyes (MB/MO) binary systems, HS-PAANa exhibited enhanced selective adsorption of cationic dyes (MB), indicating its potential for targeted removal of specific dyes from mixed solutions. Moreover, HS-PAANa adsorption shows an excellent recyclability, after five cycles, HS-PAANa still maintained MB and CV removal rates of 93.85% and 95.08%, respectively. Therefore, the bioadsorbent HS-PAANa exhibits high potential as a highly efficient adsorbent for the effective treatment of cationic pollutants in wastewater.

Phytoremediative adsorption methodologies to decontaminate water from dyes and organic pollutants

Persistent organic pollutants and dyes cause major problems during ecofriendly wastewater treatment. To overcome this huge problem, several techniques have been considered and in practice for the safe disposal of organic pollutants in recent years; some of them are discussed and compared herein. This review focuses on new trends for wastewater treatment and compares them with certain other techniques alongside their pros and cons; adsorption is considered the safest among them. Adsorbents derived from agri-wastes have good capacity for the removal of these contaminants owing to their great sorption capacity, high reusability, easy operation, etc. Sometimes they need some modifications for the removal of dyes, which are also discussed in this review. This capacity of adsorbents to chelate dye molecules can be affected by factors, such as pH, the concentration of dyes and adsorbents, and temperature of the system. pH has direct influence on the ionization potential and charge on the outer surface of adsorbents. The findings on isotherms, kinetics, and desorption of plant waste-based biomaterials that are safe for the ecosystem and user friendly and are used for hazardous contaminant removal from water are summarized in this review. Finally, conclusions and future perspectives are presented, and some other materials, such as CNTs and MOFs, are also discussed as efficient adsorbents for eliminating dyes from wastewater. Finally, it is predicted that the adsorption of dyes is a more feasible solution for this dye pollution problem.

Physico-chemical, structural, and adsorption properties of amino-modified starch derivatives for the removal of (in)organic pollutants from aqueous solutions

In this study, an environmentally sustainable process of crystal violet, congo red, methylene blue, brilliant green, Pb²⁺, Cd²⁺, and Zn²⁺ ions adsorption from aqueous solutions onto amino-modified starch derivatives was investigated. The degree of substitution, elemental analysis, swelling capacity, solubility, and FTIR, XRD, and SEM techniques were used to characterize the adsorbents. The influence of pH, contact time, temperature, and initial concentration has been studied to optimize the adsorption conditions. The amino-modified starch was the most effective in removing crystal violet (CV) (65.31-80.46 %) and Pb²⁺ (67.44-80.33 %) within the optimal adsorption conditions (pH 5, 10 mg dm^-3, 25 °C, 180 min). The adsorption of CV could be described by both Langmuir and Freundlich adsorption isotherms, while the adsorption of Pb²⁺ ions was better described by the Langmuir isotherm. The pseudo-second order model can be used to describe the adsorption kinetics of CV and Pb²⁺ on all tested samples. The thermodynamic study indicated that the adsorption of CV was exothermic, while the Pb²⁺ adsorption was endothermic. The simultaneous removal of CV and Pb²⁺ from the binary mixture has shown their competitive behavior. Thus, the amino-modified starch is a promising eco-friendly adsorbent for the removal of dyes and heavy metals from polluted water.

Thermodynamic, kinetic, and isotherm studies of Direct Blue 86 dye absorption by cellulose hydrogel

In this study, cellulose hydrogels were simply fabricated by the chemical dissolution method using LiCl/dimethylacetamide as a new method, and the hydrogel produced was investigated for removing Direct Blue 86 (DB86) dye from the aquatic environment. The produced cellulose hydrogel (CAH) was characterized by FTIR, XRD, SEM, and TGA analyses. The removal efficiency of DB86 dye using CAH was achieved via a batch equilibrium process. The impact of pH, time of contact, CAH dosage, starting concentration of DB86 dye, and absorption temperature were scanned. The optimum pH for absorption of DB86 dye was determined to be 2. The absorption results obtained were scanned by Langmuir (LIM), Temkin (TIM), Freundlich (FIM), and Dubinin-Radushkevich (DRIM) isotherm models (IMs) and chi-square error (X²) function used to identify the best-fit IMs. The CAH had 53.76 mg/g as a maximum absorption capacity (Q_m) calculated from the LIM plot. The TIM was the best fitted to the CAH absorption results. Kinetic absorption results were investigated by pseudo-first-order (PFOM), Elovich (EM), pseudo-second-order (PSOM), film diffusion (FDM), and intraparticle diffusion (IPDM) models. A PSOM with a high R² (> 0.99) accounted for the majority of the control over the absorption rate. The findings indicate that CAH can potentially remove the DB86 dye from wastewater.

Metal-Organic Framework Composites and Their Derivatives as Efficient Electrodes for Energy Storage Applications: Recent Progress and Future Perspectives

Metal-organic frameworks (MOFs) have been important electrochemical energy storage (EES) materials because of their rich species, large specific surface area, high porosity and rich active sites. Nevertheless, the poor conductivity, low mechanical and electrochemical stability of pristine MOFs have hindered their further applications. Although single component MOF derivatives have higher conductivity, self-aggregation often occurs during preparation. Composite design can overcome the shortcomings of MOFs and derivatives and create synergistic effects, resulting in improved electrochemical properties for EES. In this review, recent applications of MOF composites and derivatives as electrodes in different types of batteries and supercapacitors are critically discussed. The advantages, challenges, and future perspectives of MOF composites and derivatives have been given. This review may guide the development of high-performance MOF composites and derivatives in the field of EES.

Isotherm and kinetic studies of acid yellow 11 dye adsorption from wastewater using Pisum Sativum peels microporous activated carbon

In this study, Pea Peels-Activated Carbon (PPAC), a novel biochar, was created from leftover pea peels (Pisum sativum) by wet impregnation with ZnCl₂ and subsequent heating to 600, 700, and 800 °C in a CO₂ atmosphere. Investigated how the newly acquired biochar affected the capacity to extract the AY11 dye from the aqueous solution. Through the use of FTIR, XRD, SEM, BJH, BET, DSC, EDX, and TGA studies, the prepared PPAC was identified. It was found that a pH of 2 is optimum for the AY11 dye elimination. The highest removal percentage of AY11 dye was 99.10% using a beginning AY11 dye concentration of 100 mg/L and a 1.0 g/L dose of PPAC. The highest adsorption capacity (Q_m) of the PPAC was 515.46 mg/g. Freundlich (FIM), Halsey (HIM), Langmuir (LIM), Tempkin (TIM), and Gineralize (GIM) isotherm models were useful in examining the adsorption results. A variety of error functions, including the average percent errors (APE), root mean square errors (RMS), Marquardt's percent standard deviation (MPSD), hybrid error function (HYBRID), Chi-square error (X²) and a sum of absolute errors (EABS) equations, were also applied to test the isotherm models data. The PPAC experimental data were best suited by the HIM and FIM isotherm models. Elovich (EM), Pseudo-first-order (PFOM), Intraparticle diffusion (IPDM), Pseudo-second-order (PSOM), and Film diffusion (FDM) models were applied to study the kinetic adsorption results. The PSOM had a strong correlation coefficient (R² > 0.99), and it was principally responsible for controlling the adsorption rate. Anions are typically absorbed during the adsorption mechanism of AY11 dye by PPAC owing to attractive electrostatic forces created with an increase in positively charged areas at acidic pH levels. The regenerated PPAC was used in six successive adsorption/desorption cycles. This study's outcomes show that PPAC successfully removes the AY11 dye from the aqueous solution; as a result, PPAC can be used repeatedly without experiencing considerable loss in effectiveness.

Magnetic Activated Biochar Fe3O4-MOS Made from Moringa Seed Shells for the Adsorption of Methylene Blue

In recent years, more and more biochars have been employed to treat dye wastewater. In order to increase the utilization of moringa seed shell resources and enrich the removal method of methylene blue (MB) in solution, in the current study, the magnetic moringa seed shells biochar was prepared through ultrasonic-assisted impregnation and pyrolysis, while Fe3O4 was used to activate the material to obtain adsorption (Fe3O4-MOS). The prepared adsorbents were characterized by SEM-EDS, XRD, XPS, FTIR, N2 adsorption and desorption and VSM. Under the suitable experimental conditions, the removal rate can be close to 100% and the maximum adsorption capacity of MB could be 219.60 mg/g. The Freundlich model provided a good match to the data presented by the adsorption isotherm, and the adsorption of MB on Fe3O4-MOS was a spontaneous and endothermic reaction. Study of the mechanism indicated that pore adsorption, electrostatic interaction, hydrogen bond, and π-π interaction were the major adsorption mechanisms. After five cycles, it was found that Fe3O4-MOS had a high removal rate for MB, which was close to 90%. This work provides a new idea for moringa seed shells and the results confirm that Fe3O4-MOS has substantial potential for dye wastewater treatment.

Effective Removal of Refractory Pollutants through Cinnamic Acid-Modified Wheat Husk Biochar: Experimental and DFT-Based Analysis

The removal of refractory pollutants, i.e., methylene blue (MB) and ciprofloxacin (CIP), relies heavily on sorption technologies to address global demands for ongoing access to clean water. Because of the poor adsorbent–pollutant contact, traditional sorption procedures are inefficient. To accomplish this, a wheat husk biochar (WHB), loaded with cinnamic acid, was created using a simple intercalation approach to collect dangerous organic pollutants from an aqueous solution. Batch experiments, detecting technologies, and density functional theory (DFT) calculations were used to investigate the interactions at the wheat husk biochar modified with cinnamic acid (WHB/CA) and water interface to learn more about the removal mechanisms. With MB (96.52%) and CIP (94.03%), the functionalized WHB exhibited outstanding adsorption capabilities, with model fitting results revealing that the adsorption process was chemisorption and monolayer contact. Furthermore, DFT studies were performed to evaluate the interfacial interaction between MB and CIP with the WHB/CA surface. The orbital interaction diagram provided a visual representation of the interaction mechanism. These findings open up a new avenue for researchers to better understand adsorption behavior for the utilization of WHB on an industrial scale.

Chitosan- and Alginate-Based Hydrogels for the Adsorption of Anionic and Cationic Dyes from Water

Novel hydrogel systems based on polyacrylamide/chitosan (PAAM/chitosan) or polyacrylic acid/alginate (PAA/alginate) were prepared, characterized, and applied to reduce the concentrations of dyes in water. These hydrogels were synthetized via a semi-interpenetrating polymer network (semi-IPN) and then characterized by Fourier transformed infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA), and their swelling capacities in water were measured. In the adsorption experiments, methylene blue (MB) was used as a cationic dye, and methyl orange (MO) was used as an anionic dye. The study was carried out using a successive batch method for the dye absorption process and an equilibrium system to investigate the adsorption of MO on PAAM/chitosan hydrogels and MB on PAA/alginate in separate experiments. The results showed that the target hydrogels were synthetized with high yield (more than 90%). The chemical structure of the hydrogels was corroborated by FTIR, and their high thermal stability was verified by TGA. The absorption of the MO dye was higher at pH 3.0 using PAAM/chitosan, and it had the ability to remove 43% of MO within 10 min using 0.05 g of hydrogel. The presence of interfering salts resulted in a 20–60% decrease in the absorption of MO. On the other hand, the absorption of the MB dye was higher at pH 8.5 using PAA/alginate, and it had the ability to remove 96% of MB within 10 min using 0.05 g of hydrogel, and its removal capacity was stable for interfering salts.

Removal of both anionic and cationic dyes from wastewater using pH-responsive adsorbents of L-lysine molecular-grafted cellulose porous foams

High adsorption efficiency, active to both anionic and cationic dyes and simple desorption are three main challenges of the existed adsorbents for decolorization of the dye-contained wastewaters. Porous foams based on L-lysine (Lys) molecular-grafted cellulose were firstly designed and fabricated to overcome those challenges. Cellulose were grafted with Lys in 1-butyl-3-methylimidazolium chloride (BMIMCl) via a chemical connection resulted from glycidyl methacrylate (GMA). The synthesized cellulose derivative (Cell-g-PGMA-Lys) was regenerated in the morphology of foam by non-solvent induced phase inversion from the BMIMCl-based solutions. The presence of Lys moieties and porous structure of Cell-g-PGMA-Lys were confirmed with a series of instrumental analysis. Both anionic reactive brilliant red X-3B (RBR X-3B) and cationic methylene blue (MB) were effectively adsorbed on and desorbed from Cell-g-PGMA-Lys by adjusting the solution pH value. Cell-g-PGMA-Lys had higher adsorption capacities than most of the reported adsorbents and was easy to separate from the decolorized water. It could be reused many times with little reduction of the adsorption capacity, which remained 86.9% and 92.5% for RBR X-3B and MB respectively after six adsorption-desorption cycles. The isothermal and kinetic adsorption proved that dyes were adsorbed single-layered on Cell-g-PGMA-Lys depending upon the electrostatic interaction between adsorbent and adsorbate.

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.

Simultaneous adsorption for cationic and anionic dyes using chitosan/electrospun sodium alginate nanofiber composite sponges

The coexistence of anionic and cationic dyes in dye wastewater has highlighted a great necessity to develop amphoteric adsorbents for their simultaneous removal. Herein, an amphoteric composite sponge was successfully fabricated by combining chitosan with electrospun sodium alginate nanofiber using lyophilization in acetic acid/water/dioxane mixed solvents, which owned the abundant functional groups and superior microstructure of interconnected pores and nanoscale fibers, beneficial for the adsorption capacity improvement. The optimum adsorption capacities for Acid Blue-113 and Rhodamine B were 926.2 ± 25.7 mg/g and 695.4 ± 17.0 mg/g, respectively, much higher than that of the controlled sample prepared with chitosan and non-spinning sodium alginate in traditional acetic acid/water solvents. Meanwhile, the sponge provided with the superior adsorption performance under various pH environment and cyclic adsorption. Importantly, it had considerable simultaneous adsorption capacity for binary system containing anionic and cationic dyes. Overall, the chitosan/electrospun sodium alginate nanofiber composite sponge shows potential for complex wastewater treatment.

Effective removal of metal ions and cationic dyes from aqueous solution using different hydrazine-dopamine modified sodium alginate

In this paper, DSA-AAD-DA and DSA-TPDH-DA were prepared to effectively remove metal ions and cationic dyes from aqueous solution. The hydrazone structure was prepared by hydrazide-modified SA which captured metal ions selectively, and the remaining functional groups were used as active adsorption sites for cationic dyes. The thermodynamic parameter for the sorption demonstrated the process is endothermic and spontaneous. In single process, the adsorption of metal ions by DSA-AAD-DA and DSA-TPDH-DA correlated well with the Freundlich model through the hydrazone structure coordination and ion exchange which was mainly chemical adsorption, and cationic dyes adsorption correlated well with the Langmuir model which was shown monolayer adsorption was dominant by hydrogen bonding, electrostatic interaction, and π-π interaction. In binary system, the mixed adsorption shown significant antagonism effect in high concentration, but cationic dyes and metal ions in low concentration were efficiently and simultaneously removed, the adsorption ability of DSA-TPDH-DA was much better than DSA-AAD-DA. Moreover, adsorption efficiency can still maintain more than 80% after five times adsorption-desorption recycle. Therefore, DSA-AAD-DA and DSA-TPDH-DA possessed great potential for wastewater treatment.

Simultaneous adsorptive removal of conventional and emerging contaminants in multi-component systems for wastewater remediation: A critical review

The rapid growth of population and industrialization results in pollution of freshwater sources which leads to the water stress conditions on the world in future. Adsorption is a low cost and popular technique for the removal of contaminants from water bodies. Most of the reports till date are on removal of a single component from aqueous solutions using this technique, but the real-world effluent contains multiple contaminants such as dyes, heavy metals, pesticides, antibiotics and many more. Therefore, a study on simultaneous removal of contaminants is highly needed to obtain a suitable adsorbent that can be used commercially. This critical review provides a detailed study on the removal of contaminants in the presence of other contaminant/s i.e., from a multi-component system (MCS). The different possible interaction mechanisms in MCS like synergism, antagonism and non-interaction are discussed. The MCS containing the mixture of conventional contaminants such as heavy metals and dyes, and other emerging contaminants such as antibiotics, organic contaminants, pesticides and personal care products are explained in depth. This review article will be helpful for researchers working in the field of simultaneous removal of contaminants from MCSs for wastewater remediation.

Removal of Methylene Blue Dye from Wastewater Using Periodiated Modified Nanocellulose

The study was focused on the preparation and characterizations of sodium periodate-modified nanocellulose (NaIO4-NC) prepared from Eichhornia crassipes for the removal of cationic methylene blue (MB) dye from wastewater (WW). A chemical method was used for the preparation of NaIO4-NC. The prepared NaIO4-NC adsorbent was characterized by using X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscope (SEM), energy-dispersive X-ray (EDX), and Brunauer–Emmett–Teller (BET) instruments. Next, it was tested to the adsorption of MB dye from WW using batch experiments. The adsorption process was performed using Langmuir and Freundlich isotherm models with maximum adsorption efficiency (qmax) of 90.91 mg·g−1 and percent color removal of 78.1% at optimum 30 mg·L−1, 60 min., 1 g, and 8 values of initial concentration, contact time, adsorbent dose, and solution pH, respectively. Pseudo-second-order (PSO) kinetic model was well fitted for the adsorption of MB dye through the chemisorption process. The adsorption process was spontaneous and feasible from the thermodynamic study because the Gibbs free energy value was negative. After adsorption, the decreased values for physicochemical parameters of WW were observed in addition to the color removal. From the regeneration study, it is possible to conclude that NaIO4-NC adsorbent was recyclable and reused as MB dye adsorption for 13 successive cycles without significant efficient loss.

Selective removal of anionic and cationic dyes by magnetic Fe3O4-loaded amine-modified hydrochar

Fe₃O₄-loaded protonated amine-modified hydrochar (Fe₃O₄-PAMH) was successfully prepared and characterized by scan electron microscopy equipped with energy-dispersion X-ray spectroscopy, zeta potential analysis, vibration sample magnetometry, Fourier transform infrared and X-ray photoelectron spectroscopies, Brunauer-Emmett-Teller measurement, and X-ray diffraction. Adsorption properties of Fe₃O₄-PAMH to negatively-charged methyl orange (MO) or positively-charged methylene blue (MB) in one- or two-component systems were evaluated. The Fe₃O₄-PAMH selectively adsorbed MO and MB at pH 5 and 11, respectively. The maximum MO and MB uptake capacities of Fe₃O₄-AMHC were 202.02 mg/g (pH 5.0) and 148.84 mg/g (pH 11) respectively. The Fe₃O₄-PAMH can be reused with simple pH management in adsorption-desorption cycles. The MB and MO adsorption abilities on Fe₃O₄-PAMH were maintained above 99% and 75% for five consecutive recycles, respectively. Thus, Fe₃O₄-PAMH shows powerful potential in efficiently and selectively adsorbing anionic or cationic dyes from mixed wastewater.

Facile fabrication of chitosan-based adsorbents for effective removal of cationic and anionic dyes from aqueous solutions

To develop chitosan-based adsorbents for the treatment of dye wastewater, poly acrylic acid (PAA) and poly acrylamide (PAM) were simultaneously grafted onto the chitosan (CTS) chain to obtain a grafted-crosslinked material g-CCTS, and then, Fe-g-CCTS was prepared via coordination of Fe(III) onto the prepared g-CCTS. Two adsorbents g-CCTS and Fe-g-CCTS were fully characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), Nitrogen adsorption and desorption, X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and thermogravimetric (TG) analysis. In adsorption experiment, g-CCTS exhibited effective adsorption towards cationic dye methylene blue (MB), and Fe-g-CCTS showed effective adsorption towards anionic dye reactive brilliant red (RBR). The effects of solution pH, salt concentration and temperature on the adsorption process were investigated. The maximum adsorption capacity of g-CCTS for MB was up to 79.09 mg/g at pH 12, and that of Fe-g-CCTS for RBR reached 918.53 mg/g at pH 2. It was observed that both adsorption processes were monolayer adsorption, and conformed to the pseudo-second-order model and the Langmuir isotherm model. This research provided a facile and accurate method for effective dyes removal from wastewater.

Superior adsorption capacity of functionalised straw adsorbent for dyes and heavy-metal ions

Dyes and heavy-metal ions are common pollutants in printing and dyeing wastewater, and are thus attracting considerable attention. Herein, an eco-friendly straw-based adsorbent, WS-CA-AM, was prepared by grafting with acrylamide (AM) and citric acid (CA) groups to remove representative dyes and heavy metals from aqueous solution. The adsorption capacities of WS-CA-AM for methyl orange (MO) and methylene blue (MB) were 3053.48 and 120.84 mg/g, which were 54 and 3 times those of unmodified straw, respectively. Moreover, the adsorption capacities for MB, MO, Cr₂O₇^2- and Cu²⁺ in the mixed system increased by 210%, 133%, 196% and 151%, respectively, compared with those in the single system. The significant increase in adsorption capacity can be attributed to the collaborative effect through electrostatic attraction. The functional groups and adsorbed pollutants all served as adsorption sites for pollutants. These results indicate that WS-CA-AM is a potential applicant for the removal of dyes and heavy-metal ions from mixed aqueous solution.

Fast decolorization of cationic dyes by nano-scale zero valent iron immobilized in sycamore tree seed pod fibers: kinetics and modelling study

In the present work, Sycamore (Platanus occidentalis) tree seed pod fibers (STSPF) and nano-scale zero valent iron particles (nZVI) immobilized in Sycamore tree seed pod fibers (nZVIʘSTSPF) were produced. This biosorbent has been utilized as a viable effective biosorbent in the removing of methylene blue hydrate (MB), malachite green oxalate(MG), methyl violet 2B(MV) dyes from synthetic wastewater. The biosorbents were characterized by scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. Various parameters such as contact time, solution concentration, pH and amount of biosorbent were investigated in order to evaluate the potential of the nanomaterials immobilized on natural wastes as sorbing biomaterials for the cationic dyes. Study on sorption kinetic and the sorption isotherm was carried out and best fitting models for the rate kinetics and isotherms were suggested. Langmuir isotherm was observed to be compatible with the isotherm models. The STSPF in the raw form showed the best dye sorption capacity of 43.67 mg/g for MG, 25.32 mg/g for MV, and 126.60 mg/g for MB. The magnetic nZVIʘSTSPF showed the best dye sorption capacity 92.59 mg/g for MG, 92.59 mg/g for MV, and 140.80 mg/g for MB. The iron nanoparticles immobilized biosorbent exhibited a higher removal capacity for all dyes compared to the raw biosorbent.

Cyclodextrin modified filter paper for removal of cationic dyes/Cu ions from aqueous solutions

A filter paper was functionalized with β-cyclodextrin and citric acid via esterification reaction for the removal of dyes and Cu ions from aqueous solutions. The adsorption capacity and removal performance of the modified filter paper (MFP) was investigated using static and dynamic adsorption experiments. The static adsorption data fit well the Langmuir and pseudo-second-order models, and the adsorption capacity of Methylene Blue (MB), Brilliant Green (BG), Rhodamine-B (RB) and Cu(II) over the MFP were 124.6 mg/g, 130.4 mg/g, 99.7 mg/g and 39.1 mg/g, respectively, which are much higher than the unmodified filter paper (below 2 mg/g). Even better, the decolorization performance and Cu(II) removal of MFP are remarkable in dynamic adsorption. The effluent can reach the National Standard for dyeing and finishing of textile industry of China after three cycles in a continuous filtration-adsorption system. This method provides a new pathway to achieve high efficiency removal of dyes and metal ions from wastewater.

Carboxylate-functionalized sugarcane bagasse as an effective and renewable adsorbent to remove methylene blue

This study prepared a carboxylate-functionalized sugarcane bagasse (CF-SCB) from sugarcane bagasse (SCB) via a simple and low-toxicity chemical modification to enhance its capacity for adsorbing methylene blue (MB) from aqueous solutions. The success of chemical modification was confirmed by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), the pore area and porosity, and zeta potential measurement analysis. The adsorption capacity of CF-SCB was investigated at different pHs, ionic strengths, temperatures, contact times and initial dye concentrations. Equilibrium data were best described by the Langmuir isotherm model, and the maximum monolayer adsorption capacity of CF-SCB (296.74 mg g^-1) was greatly improved compared with SCB (77.16 mg g^-1) at 30 °C. The thermodynamic study indicated that MB adsorption onto CF-SCB was a spontaneous, endothermic and entropy increased process. Adsorption kinetics followed a pseudo-second-order mode, and the adsorption mechanism was based on electrostatic interactions. The reusability study showed that CF-SCB had reasonably good reuse potential. All the results suggested that CF-SCB has high potential to be used as an effective and renewable adsorbent for MB removal from wastewater.