Synergistic effect of zeolite/chitosan in the removal of fluoride from aqueous solution

Synthesis and characterization of functional calcium-phosphate-chitosan adsorbents for fluoride removal from water

Functional calcium-phosphate-chitosan adsorbents for fluoride (F-) removal from water with different proportions of calcium (0.7 or 1.4 % w/v) were synthesized by: i) ionotropic gelation technique followed by drying in a convection oven (IGA) or freeze drying (FDA); ii) freeze-gelation followed by drying in a convection oven (FGA). Adsorbents were analyzed by SEM-EDX and FTIR- ATR. F- removal percentages higher than 45 % were obtained with calcium-phosphate-chitosan adsorbents for an initial F- concentration of 9.6 mg L-1. Optimal conditions for F- removal were attained, using calcium-phosphate- chitosan adsorbents synthesized by ionotropic gelation with 0.7 % of Ca (IGA0.7). Under these conditions, initial F- concentration of 5 mg L-1, was reduced below the maximum limit of 1.5 mg L-1 established by WHO. Regeneration of IGA0.7 was achieved in acid media. The performance of IGA0.7 was slightly reduced in the presence of coexisting anions (nitrate, carbonate, arsenate). Adsorption kinetics was represented satisfactorily by the pseudo-second order equation; Langmuir isotherm provided the best fit to the equilibrium data and IGA0.7 exhibited a maximum F- adsorption capacity qL = 132.25 mg g-1. IGA0.7 particles were characterized by thermogravimetry coupled to FTIR, XRD, XPS and SEM-EDX. The calcium-phosphate-chitosan adsorbents constitute a suitable and emerging material for water defluorination.

The potential of zeolite nanocomposites in removing microplastics, ammonia, and trace metals from wastewater and their role in phytoremediation

Nanocomposites are emerging as a new generation of materials that can be used to combat water pollution. Zeolite-based nanocomposites consisting of combinations of metals, metal oxides, carbon materials, and polymers are particularly effective for separating and adsorbing multiple contaminants from water. This review presents the potential of zeolite-based nanocomposites for eliminating a range of toxic organic and inorganic substances, dyes, heavy metals, microplastics, and ammonia from water. The review emphasizes that nanocomposites offer enhanced mechanical, catalytic, adsorptive, and porosity properties necessary for sustainable water purification techniques compared to individual composite materials. The adsorption potential of several zeolite-metal/metal oxide/polymer-based composites for heavy metals, anionic/cationic dyes, microplastics, ammonia, and other organic contaminants ranges between approximately 81 and over 99%. However, zeolite substrates or zeolite-amended soil have limited benefits for hyperaccumulators, which have been utilized for phytoremediation. Further research is needed to evaluate the potential of zeolite-based composites for phytoremediation. Additionally, the development of nanocomposites with enhanced adsorption capacity would be necessary for more effective removal of pollutants.

The model and mechanism of adsorptive technologies for wastewater containing fluoride: A review

With the continuous development of society, industrialization, and human activities have been producing more and more pollutants. Fluoride discharge is one of the main causes of water pollution. This review summarizes various commonly used and effective fluoride removal technologies, including ion exchange technology, electrochemical technology, coagulation technology, membrane treatment, and adsorption technology, and points out the outstanding advantages of adsorption technology. Various commonly used fluoride removal techniques as well as typical adsorbent materials have been discussed in published papers, however, the relationship between different adsorbent materials and adsorption models has rarely been explored, therefore, this paper categorizes and summarizes the various models involved in static adsorption, dynamic adsorption, and electrosorption fluoride removal processes, such as pseudo-first-order and pseudo-second-order kinetic models, Langmuir and Freundlich isotherm models, Thomas and Clark dynamic adsorption models, including the mathematical equations of the corresponding models and the significance of the models are also comprehensively summarized. Furthermore, this comprehensive discussion delves into the fundamental adsorption mechanisms, quantification of maximum adsorption capacity, evaluation of resistance to anion interference, and assessment of adsorption regeneration performance exhibited by diverse adsorption materials. The selection of the best adsorption model not only predicts the adsorption performance of the adsorbent but also provides a better description and understanding of the details of each part of the adsorption process, which facilitates the adjustment of experimental conditions to optimize the adsorption process. This review may provide some guidance for the development of more cost-effective adsorbent materials and adsorption processes in the future.

A Carbonized Zeolite/Chitosan Composite as an Adsorbent for Copper (II) and Chromium (VI) Removal from Water

To address Cu(II) and Cr(VI) water pollution, a carbonized zeolite/chitosan (C-ZLCH) composite adsorbent was produced via pyrolysis at 500 °C for two hours. C-ZLCH was characterized using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), and zeta potential measurements. The batch experiments were performed by varying the initial pH, concentration, and contact time. The optimal pH values for Cu(II) and Cr(VI) were 8.1 and 9.6, respectively. The highest adsorption capacities for Cu(II) and Cr(VI) were 111.35 mg/g at 60 min and 104.75 mg/g at 90 min, respectively. The effects of chemicals such as sodium (Na⁺), glucose, ammonium (NH₄⁺), and acid red 88 (AR88) were also studied. Statistical analysis showed that sodium had no significant effect on Cu(II) removal, in contrast to Cr(VI) removal. However, there was a significant effect of the presence of glucose, ammonium, and AR88 on both Cu(II) and Cr(VI) removal. The adsorption isotherm and kinetic models were fitted using Langmuir and pseudo-second-order models for Cu(II) and Cr(VI), respectively.

Synthesis, Adsorption Isotherm and Kinetic Study of Alkaline- Treated Zeolite/Chitosan/Fe3+ Composites for Nitrate Removal from Aqueous Solution-Anion and Dye Effects

In the present study, alkaline-treated zeolite/chitosan/Fe³⁺ (ZLCH-Fe) composites were prepared and analyzed using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR) and pH of zero point of charge (pH_zpc) to remove nitrates from water. The process was carried out using an adsorption method with a varied initial pH, adsorbent dosage, initial nitrate concentration and contact time. The pH_zpc demonstrated that the ZLCH-Fe surface had a positive charge between 2 and 10, making it easier to capture the negative charge of nitrate. However, the optimal pH value is 7. After 270 min, the maximum adsorption capacity and percent removal reached 498 mg/g and 99.64%, respectively. Freundlich and pseudo-second-order were fitted to the adsorption isotherm and kinetic models, respectively. An evaluation was conducted on the effects of anions-SO₄^2- and PO₄^3--and dyes-methylene blue (MB) and acid red 88 (AR88)-upon nitrate removal. The results indicated that the effect of the anion could be inhibited, in contrast to dye effects. However, the optimal pH values were changed to 10 for MB and 2 for AR88, resulting in a hydrogel formation. This might be indicated by the protonation of hydroxyl and amino groups resulting from a chitosan nitrate reaction in the AR88 solution.

Electrolytic transesterification of waste frying oil using Na+/zeolite-chitosan biocomposite for biodiesel production

Given the economic and environmental advantages of using Waste Fried Oil (WFO) as a starting material, this investigation explores the conversion of WFO to Fatty Acid Methyl Ester (FAME) via electrolysis for use in waste. In electrolysis, hydroxyl ions are generated from water in close proximity to the cathode. When hydroxyl ions react with methanol, they produce a species of nucleophilic methoxide which is the main actor in converting WFO into FAME. This study specifically investigates the effects of voltage, catalyst concentration, co solvent amount, rotation speed, and molar ratio of methanol to WFO in electrolytic transesterification converting WFO into FAME using graphite electrodes in the presence of a heterogeneous, catalytic zeolite-chitosan composite. With an alcohol to WFO molar ratio of 8:1, 1 wt% zeolite-chitosan composite concentration at 40 V in the presence of 2 wt% H₂O of the whole solution at room temperature and stirrer rate of 400 rpm and reaction time of 30 min, a 96.5% yield of FAME was achieved. Characterization of physical and biodiesel fuel properties was performed using American Society for Testing and Materials (ASTM) methods. The biocomposite was characterized using Fourier Transform Infrared (FTIR), X-ray Diffraction (XRD), Transmission Electron Microscopy(TEM), Brunauer Emmett Teller(BET), Thermogravimetric analysis (TG), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray spectrometry (EDX). Finally, the physical properties of FAME produced under optimal conditions were studied using Gas Chromatography-Mass Spectrometry (GC-MS), FTIR, surface tension, and viscosity.

Facile synthesis of Al/Fe bimetallic (oxyhydr)oxide-coated magnetite for efficient removal of fluoride from water

In this work, we developed a novel magnetic bimetallic Al/Fe (oxyhydr)oxide adsorbent through a facile and cost-effective method and explored its potential to adsorb fluoride in water. Its synthesis involved corrosion of natural magnetite in aluminium chloride solution, followed by titration with NaOH solution for in-situ synthesis of Al/Fe (oxyhydr)oxide-coated magnetite (Mag@Al₂Fe). Characterization data indicated a uniform coating of Al/Fe (oxyhydr)oxide on magnetite, and the resulting composite possessed large specific surface area (∼90 m²/g) and good magnetic property. In batch adsorption experiments, the isotherm and kinetic data fitted well to the Langmuir model and pseudo-second-order model, respectively. The maximum adsorption capacity of Mag@Al₂Fe is 26.5 mg/g, which was much higher than natural magnetite (0.44 mg/g). Moreover, this material retained high adsorption capacity toward fluoride within a wide pH range (3.0-8.0) and offered facile magnetic separation from water. Influence of competing ions was also evaluated which showed that the presence of Cl^- and NO₃ ^- posed negligible interference, while HCO₃ ^- and SO₄ ^2- had negative effects on fluoride adsorption. Thermodynamic investigations revealed that fluoride adsorption was exothermic and spontaneous. The observed increase in solution pH and formation of Al-F and Fe-F bonds (as indicated by XPS analysis) after fluoride adsorption suggested the major adsorption mechanism of ligand exchange. Besides, the adsorption/desorption cycle studies demonstrated the well-retained performance of Mag@Al₂Fe for repeated application after regeneration by 0.5 mol/L NaOH solution. Facile synthesis, high defluoridation, lower cost, and quick separation of Mag@Al₂Fe indicates its promising potential for drinking water defluoridation.

From microporous to mesoporous mineral frameworks: An alliance between zeolite and chitosan

Microporous and mesoporous minerals are key elements of advanced technological cycles nowadays. Nature-driven microporous materials are known for biocompatibility and renewability. Zeolite is known as an eminent microporous hydrated aluminosilicate mineral containing alkali metals. It is commercially available as adsorbent and catalyst. However, the large quantity of water uptake occupies active sites of zeolite making it less efficient. The widely-used chitosan polysaccharide has also been used in miscellaneous applications, particularly in medicine. However, inferior mechanical properties hampered its usage. Chitosan-modified zeolite composites exhibit superior properties compared to parent materials for innumerable requests. The alliance between a microporous and a biocompatible material with the accompaniment of negative and positive charges, micro/nanopores and proper mechanical properties proposes promising platforms for different uses. In this review, chitosan-modified zeolite composites and their applications have been overviewed.

Effective adsorption of zinc on magnetic nanocomposite of Fe3O4/zeolite/cellulose nanofibers: kinetic, equilibrium, and thermodynamic study

In this paper, the adsorption behavior of zinc onto magnetic zeolite/cellulose nanofibers (MZNF) was studied. The prepared adsorbent was characterized by SEM, FTIR, and VSM analyses. The mass ratio of adsorbent in composite, pH, contact time, adsorbent dosage, initial Zn⁺² concentration, temperature, and agitation speed were investigated in batch experiments. The results showed that zeolite played an important role in the prepared nanocomposite due to its great surface area. pH 7 exhibited the highest Zn⁺² removal efficiency. Rapid adsorption at the first 30 min of the reaction is one of the advantages of the prepared adsorbents. Moreover, increase at temperature led to higher efficiency and maximum efficiency was attained at 30 °C. Under optimum conditions, MZNF showed removal efficiency of 96% and maximum adsorption capacity of 9.45 mg/g. The presence of the competing ions did not reduce the efficiency of the process and adsorption efficiency was higher than 93%. The calculated RSD of 1.42% exhibits the suitability of the process. Equilibrium data were examined by various isotherms and kinetics equations. It was concluded that Pseudo second-order model and Langmuir models described the adsorption process well. Based on these results, MZNF obtained in this work can be served as a promising candidate for Zn⁺² removal in wastewater.