Zn2+ adsorption from wastewater using a chitosan/β-cyclodextrin-based composite membrane

Removal of contaminants present in water and wastewater by cyclodextrin-based adsorbents: A bibliometric review from 1993 to 2022

Cyclodextrin (CD), a cyclic oligosaccharide from enzymatic starch breakdown, plays a crucial role in pharmaceuticals, food, agriculture, textiles, biotechnology, chemicals, and environmental applications, including water and wastewater treatment. In this study, a statistical analysis was performed using VOSviewer and Citespace to scrutinize 2038 articles published from 1993 to 2022. The investigation unveiled a notable upsurge in pertinent articles and citation counts, with China and USA contributing the highest publication volumes. The prevailing research focus predominantly revolves around the application of CD-based materials used as adsorbents to remove conventional contaminants such as dyes and metals. The CD chemistry allows the construction of materials with various architectures, including cross-linked, grafted, hybrid or supported systems. The main adsorbents are cross-linked CD polymers, including nanosponges, fibres and hybrid composites. Additionally, research efforts are actually concentrated on the synthesis of CD-based membranes, CD@graphene oxide, and CD@TiO2. These materials are proposed as adsorbents to remove emerging pollutants. By employing bibliometric analysis, this study delivers a comprehensive retrospective review and synthesis of research concerning CD-based adsorbents for the removal of contaminants from wastewater, thereby offering valuable insights for future large-scale application of CD-based adsorption materials.

Preparation of a Multifunctional and Multipurpose Chitosan/Cyclodextrin/MIL-68(Al) Foam Column and Examining Its Adsorption Properties for Anionic and Cationic Dyes and Sulfonamides

A multifunctional cylindrical hybrid foam column, referred to as the chitosan/cyclodextrin/MIL-68(Al) (CS/CD/MIL-68(Al)) foam column, was prepared for the first time. The prepared foam column could be used for the adsorption/removal of hydrophilic and hydrophobic contaminants by different forms. Here, it was placed in hydrophilic dye solutions to investigate the adsorption behavior of methylene blue and trypan blue. The adsorption process followed the pseudo-second-order kinetic model with R2 ranging from 0.9983 to 0.9998 for methylene blue and from 0.9993 to 1.0000 for trypan blue, and the adsorption process was consistent with the Langmuir isothermal model with R2 greater than 0.96. The RL values for methylene blue and trypan blue were 0.8871 and 0.5366, respectively, which were present between 0 and 1, indicating that the adsorption behaviors of the two dyes onto the CS/CD/MIL-68(Al) foam column were favorable. The maximum adsorption capacities (Qm) of methylene blue and trypan blue were 60.61 and 454.55 mg/g at 298 K, respectively. Also, the CS/CD/MIL-68(Al) foam column was spun into a syringe and used to adsorb trace hydrophobic sulfonamides from water in the form of filtration. The porous structure impeded the need for any external force and equipment, allowing the water sample to pass through the foam column smoothly. The conditions of the CS/CD/MIL-68(Al) foam column were optimized. The adsorption was carried out under the condition of pH = 4, the amount of the adsorbent was two foam columns, and no salt was added. It was found that the removal rate of the CS/CD/MIL-68(Al) foam column for six sulfonamides was 100%, and it could be reused at least five times. Therefore, this CS/CD/MIL-68(Al) foam column had a simple preparation method, offered a flexible and diverse form of use, was nonpolluting, biodegradable, and reusable, and could have a wider application in the field of environmental pollutant removal and adsorption.

Removal of Zn(II) by magnetic composite adsorbent: synthesis, performance, and mechanism

In this study, L-methionine and nano-Fe₃O₄ were encapsulated and cured on sodium alginate by the ionic cross-linking method to form magnetic composite gel spheres (SML) as an adsorbent for the removal of Zn(II) from water. The influence of adsorbent dosages, pH, reaction time, and initial ion concentration on the ability of the gel spheres to adsorb Zn(II) was investigated, and the adsorption mechanism was identified. The experimental results showed that under the optimum conditions (pH = 5, t = 60 min, dosage of SML is 0.7 g·L^-1), the maximum amount of Zn(II) adsorbed by the adsorbent gel spheres reached 86.84 mgˑg^-1. The reaction process of this adsorbent fits well with the Langmuir and pseudo-second-order kinetic models and is a heat absorption reaction. The adsorbent would preferentially adsorb Pb(II), and the adsorption efficiency of Zn(II) decreased when the concentration of interfering ions increased in the coexistence system. Further mechanistic research showed that this magnetic composite adsorbent is a mesoporous material with superior adsorption performance, and the amino and carboxyl groups on it react with Zn(II) via ligand chelation; the ion exchange effect of Ca(II) also plays a role. The adsorption amount of Zn(II) was maintained at a higher level after 5 cycles, and the loss of Fe was approximately 0.2%. In summary, SML, which is environmentally friendly, efficient, and recyclable, is an ideal adsorbent for Zn(II) removal.

Preparation and Characterization of a Novel Amidoxime-Modified Polyacrylonitrile/Fly Ash Composite Adsorbent and Its Application to Metal Wastewater Treatment

The polyacrylonitrile/fly ash composite was synthesized through solution polymerization and was modified with NH2OH·HCl. The amidoxime-modified polyacrylonitrile/fly ash composite demonstrated excellent adsorption capacity for Zn2+ in an aqueous medium. Fourier transform-Infrared spectroscopy, thermogravimetric analysis, nitrogen adsorption, X-ray diffraction, and scanning electron microscopy were used to characterize the prepared materials. The results showed that the resulting amidoxime-modified polyacrylonitrile/fly ash composite was able to effectively remove Zn2+ at pH 4-6. Adsorption of Zn2+ was hindered by the coexisting cations. The adsorption kinetics of Zn2+ by Zn2+ followed the pseudo-second order kinetic model. The adsorption process also satisfactorily fit the Langmuir model, and the adsorption process was mainly single layer. The Gibbs free energy ΔG0, ΔH0, and ΔS0 were negative, indicating the adsorption was a spontaneous, exothermic, and high degree of order in solution system.