Anionic Dyes Research Articles

Synthesis, utilization, and recycling of graphene oxide-based nanohybrid biopolymeric hydrogels for purification of dye wastewater

ABSTRACT Wastewater from industries contributes significantly to pollution. Adsorption of acidic dye using by nanohybrid biopolymeric hydrogels has evolved as one of the viable techniques. Graphene oxide (GO)/chitosan (CS)–polyvinyl alcohol (PVA), GO/starch–PVA, and GO/agar–PVA hydrogels were synthesized. The results revealed that the following results are the ideal values: GO/CS–PVA: 3 pH (8.251 mg g−1), 0.05 g/50mL dosage (8.251 mg g−1), 90 min (8.251 mg g−1), 12 ppm dye concentration (8.251 mg g−1), and 30 °C (8.251 mg g−1); for GO/starch–PVA: 2 pH (7.437 mg g−1), 0.05 g/50 mL dosage (7.437 mg g−1), 90 min (7.437 mg g−1), 12 ppm dye concentration (7.437 mg g−1), and 30 °C (7.437 mg g−1); and for GO/agar–PVA; 3 pH (6.142 mg g−1), 0.05 g/50 mL dosage (6.142 mg g−1), 90 min (6.142 mg g−1), 12 ppm dye concentration (6.142 mg g−1), 30 °C (6.142 mg g−1). GO/CS–PVA outperformed the other hydrogels. The Langmuir model suited GO/CS–PVA data, while GO/starch–PVA and GO/agar–PVA hydrogels followed Freundlich isotherm models. The adsorption capacity data followed a pseudo-second-order model. Negative value of Gibbs free energy and enthalpy showed that the reactions were spontaneous and exothermic in nature. The presence of heavy metals, electrolytes, and detergents/surfactants affected the dye adsorption. Entropy changes positive values implied that randomness raised at the solid/solution contact. The desorption (60, 55, and 58%) of GO/CS–PVA, GO/starch–PVA, and GO/agar–PVA hydrogels was obtained using 0.5 N NaOH. Scanning electron microscope, X-ray diffraction, and Fourier transform infrared (FT-IR) were used for characterization.

Comparative adsorption of cationic and anionic dye by using non-activated Black Plum seed biochar for aquatic phase: Isotherm, kinetic and thermodynamic studies

Industrial dye effluents play a major role in water pollution. Textile and leather industries are one of the important sectors that pollute the water by discharging many harmful cationic and anionic dyes during the dyeing process. This study aims to compare the dye removal efficiency of Black Plum seed biochar for the cationic and anionic dyes. The non-activated biochar was prepared through pyrolysis of Black Plum seed powder at 5700 C. The sample's surface chemistry was understood using various characterization techniques like Field Emission Scanning Electron Microscopy (FESEM), Energy-dispersive X-ray spectroscopy (EDS), Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), Raman-Spectroscopy and Zeta-potential. The experiments were successfully performed by conducting a batch adsorption study at different parameters such as pH, concentration, contact time and temperature. The coefficients of different isotherms and kinetics models were evaluated for non-linear study and the thermodynamic model was also applied. The maximum adsorption capacity was obtained as 42.39 mg/g for Crystal Violet (CV) dye and 6.22 mg/g for Eosin Blue (EB) dye by using the Langmuir isotherm model. Hence, the Black Plum seed biochar (BPSB) has superior adsorption capacity for the cationic dye CV ( removal - 98%) as compared to the anionic dye EB ( removal - 65%) at optimum parameters. Therefore, it is concluded that the BPSB is a natural toxin-free biosorbent and it can be used for the remediation of dyes from industrial wastewater.

An outstanding photocatalytic performance of CNTs based nanocomposite of ternary metal oxides towards cationic and anionic dyes and pharmaceutical drug

Currently, hetero-metallic oxides and their nanocomposites with 1D materials have a tremendous role in photocatalytic applications, mainly for the removal of organic effluents, due to their higher potential of electron-hole pair migration and separation than pure metal oxide NPs. The present work reports the fabrication of ternary metal oxides nanostructure (WO3·Ag2O·CuO) and its nanocomposite with carbon nanotubes (WO3·Ag2O·CuO/CNTs) using a facile approach i.e. ultra-sonication. The photocatalytic removal efficacy of fabricated nanocomposite i.e. WO3.Ag2O.CuO/CNTs along its counterpart (WO3·Ag2O·CuO) was evaluated using a model cationic dye (Methylene blue, MB), an anionic dye (Congo red, CR), and an analgesic drug (Paracetamol). The catalytic experiment was performed under natural sunlight upon light irradiation of about 90 min and using 30 mg of photocatalyst for all chosen effluents. The obtained results deduced that WO3·Ag2O·CuO/CNTs nanocomposite showed catalytic efficiency of about 97 % for MB, 87 % for CR, and 93 % for Paracetamol while it was about 80 % for MB, 74 % for CR, and 79 % for drug using WO3·Ag2O·CuO as photocatalyst. The rate constant values of nanocomposite for the removal of MB, CR, and Paracetamol are 0.037 min−1, 0.023 min−1, and 0.027 min−1 respectively. The remarkable degradation performance of WO3·Ag2O·CuO/CNTs nanocomposite as compared to ternary metal oxide (WO3·Ag2O·CuO) was due to its high charge separation, high surface area, and availability of large number of active sites for the adsorption of pollutant molecules. Hence, WO3·Ag2O·CuO/CNTs nanocomposite could be a competent photocatalyst for the removal of variety of industrial effluents i.e. organic dyes and pharmaceutical drugs etc.

Biochar from co-pyrolysis of biological sludge and woody waste followed by chemical and thermal activation: end-of-waste procedure for sludge management and biochar sorption efficiency for anionic and cationic dyes.

Nine biochars were produced by co-pyrolysis of sawdust and biological sludge following the "design of experiment" approach. Two kinds of sludge (both deriving from the treatment of mixed industrial-municipal wastewater) and two types of woody waste were selected as categorical predicting variables, while contact time, pyrolysis temperature, and sludge percentage were used as quantitative variables. Biochars were analysed for their product characteristics and environmental compatibility based on the European Standards (EN 12915-1:2009) for materials intended for water treatment (i.e. ash content, water leachable polycyclic aromatic hydrocarbons (PAHs) and elements), as well as for specific surface area (SSA), using them as response variables of a multivariate partial least square multiple regression, whose results provided interesting insights on the relationships between pyrolysis conditions and biochar characteristics. Biochars produced with sludge and/or providing the highest SSA values (258-370 m2g-1) were selected to undergo a sustainable chemical treatment using a by-product of the gasification of woody biomass, complying in all cases with European Standards and achieving therefore the end-of-waste status for sewage sludge. The biochar deriving from the highest percentage of sludge (30% by weight) and with the highest SSA (390 m2g-1) was thermally activated achieving SSA of 460 m2g-1 and then tested for the sorption of direct yellow 50 and methylene blue in ultrapure water and real wastewater, compared to a commercial activated carbon (AC). The biochar showed Langmuir sorption maxima (Qm) 2-9 times lower than AC, thus highlighting promising sorption performances. Qm for methylene blue in wastewater (28mg‧g-1) was confirmed by column breakthrough experiments.

Cationic Europium-Organic Framework for Chromatographic Column Separation of Ionic Dyes and Stimuli-Responsive Chromic Properties.

A novel 3D europium-based cationic framework (Eu-CMOF) has been constructed solvothermally by employing a viologen derivative as an organic functional building unit. Notably, Eu-CMOF demonstrates its capability as a proficient aqueous-phase ion-exchange host, facilitating the remarkable rapid chromatographic column separation of new coccine and malachite green (NC3-/MG+), as well as new coccine and methylene blue (NC3-/MLB+), in mere 2 to 4 min. Adsorption thermodynamics and kinetics of anionic dyes demonstrate that Eu-CMOF exhibits a higher adsorption capacity for NC3-, as evaluated by the Langmuir model, reaching a value of 173 mg·g-1. The pseudo-second-order rate constant is determined to be 3.84 × 10-3 mg-1·g·min-1. Additionally, Eu-CMOF displays reversible photochromic and amine- and ammonia-induced vapochromic behaviors. Further mechanistic studies reveal that these chromic behaviors are primarily attributed to the generation of free viologen radical stimulated by Xe-light or electron-rich amine/ammonia. This research contributes to the development of advanced materials with applications in rapid chromatographic separation and stimuli-responsive chromic properties, showcasing the potential of Eu-CMOF as a versatile platform for practical applications.

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

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

Greenly synthesised novel microporous ZnO/GO for adsorption of methyl orange and malachite green

ABSTRACT This study presents a greenly synthesised novel nanocomposite composed of Zinc Oxide (ZnO) and Graphene Oxide (GO) for the adsorption of dyes from aqueous solutions. The nanocomposite was synthesised using algae thus representing a green and eco-friendly method, ensuring minimal environmental impact. The physical characterisation of zinc oxide and graphene oxide nanocomposite (ZnO/GO) was done using X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), Fourier transform infrared spectroscopy (FT-IR), Zeta Potential, and Particle Size Analyzer (PSA). The pore diameter of the ZnO/GO was 1.801 nm, and its total surface area was 54.062 m2/g. The nanocomposite’s adsorption performance was systematically investigated through batch adsorption experiments. With an adsorption efficiency of 296.73 mg/g and 259.74 mg/g for MO and MG, the Langmuir isotherm model outperforms the Freundlich isotherm model in terms of adsorption. The pseudo-second-order model having an R2 value of 0.99 for both MO and MG, offers a more convincing explanation of adsorption than the pseudo-first-order model. The results demonstrated rapid adsorption kinetics and high adsorption capacities for both cationic and anionic dyes. Additionally, the ZnO/GO has a high reusability without significant degradation. The sustainable nature of the nanocomposite was emphasised by its efficient dye removal, reusability, and minimal secondary waste generation.

Heat Treatment of Calcite to Enhance Its Removal of Color Dye Alizarin Red S

The use of color dyes in modern society presents a great challenge to the environment. Thus, extensive studies have been conducted in the last 30 years on the removal of color dyes from aqueous solutions such industrial wastewater. In this study, the removal of alizarin red S (ARS), an anionic dye, from solution by raw calcite (Cal) and heat-treated calcite (HCal) was conducted and compared under different physico-chemical conditions. Based on the isotherm study, the ARS removal capacities increased from 167 to 251 mmol/kg after the Cal was heated to 1000 °C for 3 h. The X-ray diffraction analyses showed no difference in the calcite phase between Cal and HCal after ARS sorption. Fourier-transform infrared results also showed no change in the calcite phase after ARS sorption, except a slightly increase in wavenumber from 713 to 727 cm−1 for the OCO bending of HCal at high ARS sorption levels. SEM observations showed about the same particle size and morphology before and after ARS sorption. The TGA data showed the formation of CaO after Cal was heated, and CaO converted back into calcite after being in contact with water or ARS solution for 24 h and then being air-dried. Thus, the high ARS removal could be due to CaO produced after Cal being heated. The findings from this research proved that there is great potential in the use of calcite, a low-cost and readily available Earth material, after heat treatment for the removal of contaminants from water.

Iron-Based Oxides Anchored on the Catechol/Silane-Coated Polypropylene Nonwoven Fabrics for Effective Removal of Anionic Dyes

Iron-Based Oxides Anchored on the Catechol/Silane-Coated Polypropylene Nonwoven Fabrics for Effective Removal of Anionic Dyes

Supramolecular Gels Based on C3-Symmetric Amides: Application in Anion-Sensing and Removal of Dyes from Water.

We modified C3-symmetric benzene-1,3,5-tris-amide (BTA) by introducing flexible linkers in order to generate an N-centered BTA (N-BTA) molecule. The N-BTA compound formed gels in alcohols and aqueous mixtures of high-polar solvents. Rheological studies showed that the DMSO/water (1:1, v/v) gels were mechanically stronger compared to other gels, and a similar trend was observed for thermal stability. Powder X-ray analysis of the xerogel obtained from various aqueous gels revealed that the packing modes of the gelators in these systems were similar. The stimuli-responsive properties of the N-BTA towards sodium/potassium salts indicated that the gel network collapsed in the presence of more nucleophilic anions such as cyanide, fluoride, and chloride salts at the MGC, but the gel network was intact when in contact with nitrate, sulphate, acetate, bromide, and iodide salts, indicating the anion-responsive properties of N-BTA gels. Anion-induced gel formation was observed for less nucleophilic anions below the MGC of N-BTA. The ability of N-BTA gels to act as an adsorbent for hazardous anionic and cationic dyes in water was evaluated. The results indicated that the ethanolic gels of N-BTA successfully absorbed methylene blue and methyl orange dyes from water. This work demonstrates the potential of the N-BTA gelator to act as a stimuli-responsive material and a promising candidate for water purification.

Reuse efficiency yellow phosphorus slag in a combination with Copper (I) Oxide as a novel antibacterial additive and adsorbent: Experimental consideration and modeling

The present study investigated the green synthesis of Cu2O on yellow phosphorus slag (YPS) in the presence of nonionic surfactant, Tween 80 and ascorbic acid. The weight ratio of YPS/Cu(NO3)2.3 H2O was varied to evaluate the effect of Cu2O nanoparticles content on the properties of hybrid YPS. The characteristics of the hybrid material were evaluated by FT-IR, SEM, HR-TEM, XRD, UV-Vis, EDX mapping and DLS methods. The obtained results indicate the successful synthesis of Cu2O nanoparticles (Cu2O-NPs) on the YPS surface, exhibiting a regular spherical shape and a particle size in the range of 10–50 nm. Both the calcium phosphate β crystals of YPS and cuprite crystals of Cu2O NPs were appeared on the XRD pattern of the hybrid YPS materials. The YPS and hybrid YPS materials was stable in water with a negative charge lower than −24 mV. The hybrid YPS materials exhibit a great bactericidal activity against both E. coli and S. aureus strains, especially at the ratio of 30% of Cu(NO3)2.3 H2O. The study also applied YPS-Cu2O for removal of anionic active dye Remazol midnight black (RGB) in water. Under optimal conditions by Box-Behnken model, including pH 6, adsorption time of 240 min and YPS-Cu30 mass of 0.04 g, the RGB adsorption efficiency using YPS-Cu30 reached the highest, with a RGB removal of 86.34 ± 0.34% and an adsorption capacity of 65.23 ± 0.25 mg.g−1. We indicate that the hybrid YPS/Cu2O is an excellent adsorbent for dye removal and antibacterial additive.

Rapidly chemical preparation of Mn doped ZnO nanostructures for photocatalysis efficiency based on UV light system and mechanism insights

Abstract Through a facile chemical precipitation process, pure zinc oxide (ZnO) and various ratio of Mn-doped zinc oxide (Zn1-xMnxO) nanostructured materials were synthesized. The degradation of an azo dye acid orange 2 (AO-2) solution under UV light was investigated using the synthesized materials as photocatalysts. XRD, FTIR, DLS, FESEM, EDS, PL, BET, magnetic, TGA and UV-vis techniques were used to elucidate the structural, functional, particle, elemental, morphological, and optical aspects of the catalysts. The XRD and FESEM analysis showed the hexagonal ZnO structure and spherical shape of the ZnO nano-photocatalyst, respectively. Under UV irradiation for 60 minutes, MZ-25 NPs demonstrated better degradation (100.0%) of AO-2 dye. The effect of various factors such as catalyst quantity, and pH of the dye solution on the rate removal was investigated. After 60 minutes of UV light irradiation, dye removal was obtained under ideal conditions (with catalyst loading of 3 mgL-1, and pH 4).

Preparation of cationic waterborne polyurethane and its application in leather dyeing

The development of organic chromium-free tanning agents is currently a major research focus in leather tanning. However, these agents decrease the electrical potential of the tanned leather, which hampers the absorption of subsequent anionic dyes and fatliquoring agents. Consequently, issues such as lower color fastness, poor dyeing effects and environmental pollution arise. To address these challenges, this study proposes the utilization of anionic polyurethane (CWPU) as a dye fixing agent to enhance its performance and application in the leather preparation process. CWPU was successfully synthesized using polycarbonate diol (PCDL), isophorone diisocyanate (IPDI), polypropylene glycol (PPG), and N-methyldiethanolamine (MDEA) as raw materials, and the optimal synthesis conditions were optimized. The experimental results showed that the synthesized CWPU color fixing agent exhibited excellent emulsion properties and comprehensive performance when the PCDL: PPG ratio was 1:1 and the MDEA addition amount was 6 wt%. When applied to leather color fixation, the leather not only achieved improved dry and wet rubbing fastness levels of 4–5 but also demonstrated significant improvements in solvent wash resistance and perspiration fastness. Furthermore, the leather treated with CWPU color fixing agent exhibited deeper color and improved physical and mechanical properties and tactile quality. Therefore, this study provides an effective choice of color fixing agent for environmentally friendly chromium-free tanning systems and has broad prospects for the application of acid dyes.

Synthesis of Composite Sorbents with Chitosan and Varied Silica Phases for the Adsorption of Anionic Dyes.

In this work, various types of silica materials were used for the synthesis of chitosan-silica composites. The composites were obtained using the chitosan (Ch) immobilization process from an aqueous solution on various silica phases, i.e., amorphous diatomite (ChAD), crystalline diatomite (ChCD), mesoporous silica MCM-41 (ChMCM), and mesoporous silica SBA-15 (ChSBA). Textural, structural, morphological, and surface properties of the materials were determined by using various measurement techniques, i.e., low-temperature adsorption/desorption isotherms of nitrogen, X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), potentiometric titration, high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The adsorption properties towards various anionic dyes, i.e., acid red 88 (AR88), acid orange 8 (AO8), and orange G (OG), were evaluated based on kinetic and equilibrium measurements. The ChSBA, ChAD, and ChMCM composites were characterized by relatively high adsorption capacities (am) for AR88, with values equal to 0.78, 0.71, and 0.69 mmol/g, respectively. These composites were also distinguished by the rapid AR88 adsorption rate, with the values of half-time parameter t0.5 equal to 0.35, 2.84, and 1.53 min, respectively. The adsorption equilibrium and kinetic data were analyzed by applying the generalized Langmuir isotherm and the multi-exponential equation (m-exp), respectively. An interaction mechanism between the dyes and the obtained materials was proposed.

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.

Machine learning approaches to predict adsorption performance of sugarcane derived-carbon dot −based composite in the removal of dyes

The significance of this study addresses the imperative need for environmentally friendly wastewater treatment to degrade harmful organic compounds. It provides a sustainable and low-cost approach to uniformly blend nanofillers into polymer matrices to improve the adsorption efficiency and regeneration. Chitosan, a versatile biopolymer, is studied for its active sites effective in adsorbing anionic dyes. Modifying chitosan's performance through degree of deacetylation adjustment is explored using crosslinkers like ethylenediamine and epichlorohydrin. Titanium oxide (TiO2) and carbon dots (CDs) are chosen as nanofillers for their stability, biocompatibility, and cost-effectiveness, enhancing mechanical strength and adsorption performance. The study integrates experimental investigations with artificial intelligence techniques, utilizing machine learning algorithms through Python. Notably, the Random Forest model accurately forecasts the system behavior. The research aims to develop algorithms assessing composite adsorption capacity with different functionalization methods, optimizing synthetic wastewater treatment. Adsorption isotherms, kinetics, thermodynamics, and continuous studies further evaluate the composite performance. The composite exhibits consistent adsorption capacity over five cycles, demonstrating its reusability. The study concludes by suggesting the process through which dyes are absorbed onto the composite. This comprehensive investigation contributes to advancing sustainable wastewater treatment through innovative nanocomposites and sophisticated modelling techniques.

Electrocatalytic and photoelectrocatalytic investigation of Orange G degradation utilizing a novel BHP@Bi2O3 photoanode employing the CCD-RSM experimental design

In this study, we synthesized a bilayer film consisting of BaHPO4 (BHP) and Bi2O3 through the electrodeposition technique. The produced anode was subjected to characterization using cyclic voltammetry to clarify the deposition reactions. Subsequent to this, structural and morphological analyses were conducted utilizing X-ray diffraction alongside scanning electron microscopy, coupled with energy-dispersive X-ray spectroscopy. Additionally, UV–vis diffuse reflectance spectroscopy was employed to determine the bandgap energies of both semiconductors. Following an electrochemical characterization using linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and Mott-Schottky (MS) measurements, the photoanode was employed for the electro-degradation of the anionic dye Orange G (OG), varying key degradation parameters such as current density, pollutant concentration, supporting electrolyte concentration, and pH using the CCD-RSM experimental design method. A degradation efficiency of 98% was achieved within a 20-minute timeframe. Photoelectrocatalytic tests under UV irradiation reduced the degradation time from 20 to 6 min, with a degradation rate of 99%. Additionally, under the same conditions, the BHP@Bi2O3 photoanode exhibited good stability, enduring up to 11 cycles of use.

Activated carbon cellulose acetate based as effective adsorbent of contaminants from water

Various methods can be employed to remove pollutants from wastewater. Among these, adsorption using activated carbon materials has proven effective. This work proposes the use of a hazardous waste made from a semisynthetic polymer, cellulose acetate from cigarette butts, as raw material to produce activated carbons (AC). Four adsorbents were prepared from dirty and clean cigarette butts; two chemically activated carbons using phosphoric acid and two physically activated carbons using water vapor at 623K. The carbons were characterized using FTIR, SEM, Nitrogen adsorption, and their points of zero charge. AC produced showed high potential as adsorbents for cleaning hazardous dyes from aqueous solutions. Adsorption isotherms were constructed for the textile dyes on the carbons, and these data were treated using Langmuir's equation to quantitatively describe the adsorption process. The adsorption of dyes with an initial concentration of 300mgdm−3 showed adsorption percentages closed to the 100% for cationic dyes, while these oscillated between 40 and 100% for anionic dyes with the four activated carbons. The highest values of monolayer capacity (am) were achieved with the activated carbon prepared from cellulose acetate without prior treatment. Monolayer capacity with values ranging from 185 to 277mgg-1 for cationic dyes and 126 to 178mgg-1 for anionic dyes were obtained. Therefore, any waste of cellulose acetate can be used to obtain activated carbons with excellent adsorption capacities for dyes Methylene Blue, Crystal Violet, Malachite Green, Sirius Turquoise and Fluorescein.

A novel sponge composite of chitosan-sodium tripolyphosphate-melamine for anionic dye Orange II removal

Since the potential carcinogenic, toxic and non-degradable dyes trigger serious environmental contamination by improper treatment, developing novel adsorbents remains a major challenge. A novel high efficiency and biopolymer-based environmental-friendly adsorbent, chitosan‑sodium tripolyphosphate-melamine sponge (CTS-STPP-MS) composite, was prepared for Orange II removing with chitosan as raw material, sodium tripolyphosphate as cross-linking agent. The composite was carefully characterized by SEM, EDS, FT-IR and XPS. The influence of crosslinking conditions, dosage, pH, initial concentration, contacting time and temperature on adsorption were tested through batch adsorption experiments. CTS-STPP-MS adsorption process was exothermic, spontaneous and agreed with Sips isotherm model accompanying the maximum adsorption capacity as 948 mg∙g−1 (pH = 3). Notably, the adsorption performance was outstanding for high concentration solutions, with a removal rate of 97 % in up to 2000 mg∙L−1 OII solution (100 mg sorbent dosage, 50 mL OII solution, pH = 3, 289.15 K). In addition, the adsorption efficiency yet remained 97.85 % after 5 repeated adsorption-desorption cycles. The driving force of adsorption was attributed to electrostatic attraction and hydrogen bonds which was proved by adsorption results coupled with XPS. Owing to the excellent properties of high-effective, environmental-friendly, easy to separate and regenerable, CTS-STPP-MS composite turned out to be a promising adsorbent in contamination treatment.

An eco-friendly chitosan-genipin/SiO2 composite for reactive orange 16 dye removal: Insights into adsorption statistical modeling and mechanism

The present work develops an effective bioadsorbent of cross-linked chitosan-genipin/SiO2 adsorbent (CHI-GNP/SiO2). The developed CHI-GNP/SiO2 was employed for the removal of organic dye (reactive orange 16, RO16) from simulated wastewater. The optimization of the fundamental adsorption variables (CHI-GNP/SiO2 dose, time, and pH) via the Box-Behnken design (BBD) was attained for achieving maximal adsorption capacity and high removal efficiency. The good agreement between the Freundlich isotherms and empirical data of RO16 adsorption by CHI-GNP/SiO2 indicates that the adsorption process follows a multilayer adsorption mechanism. The reasonable agreement between the pseudo-second-order model and the kinetic data of RO16 adsorption by CHI-GNP/SiO2 was obtained. The maximum RO16 adsorption capacity (qmax) of CHI-GNP/SiO2 was identified to be 57.1 mg/g. The adsorption capacity of CHI-GNP/SiO2 is attributed to its unique surface properties, including its highly porous structure and the presence of functional groups such as amino and hydroxyl groups. According to the results of this investigation, CHI-GNP/SiO2 has the potential to be an adsorbent for the removal of acidic dyes from wastewater.