Chemical Modification of Chitosan for Removal of Pb(II) Ions from Aqueous Solutions

Functionalizing natural polymers to develop green adsorbents for wastewater treatment applications

The present study provides an overview of scientific developments made in the last decade in the field of green adsorbents focusing on the modifications in natural polymers and their applications such as, wastewater treatment, and ion exchange. For this purpose, an introduction to the various methods of modifying natural polymers is first given, and then the properties, application, and future priorities of green adsorbents are also discussed. Methods of modification of natural polymers under homogeneous and heterogeneous conditions using modifiers with different properties are also described. Various methods for modifying natural polymers and the use of the obtained green adsorbents are reviewed. A comparison of the sorption properties of green adsorbents based on natural polymers and other adsorbents used in industry has also been carried out. With the participation of green adsorbents based on natural polymers, the properties of treated wastewaters having toxic metal ions, organic dyes, petroleum products, and other harmful compounds was analyzed. Future perspectives on green adsorbents based on natural polymers are as also highlighted.

Modified magnetic chitosan materials for heavy metal adsorption: a review

Magnetic chitosan materials have the characteristics of both chitosan and magnetic particle nuclei, showing the characteristics of easy separation and recovery, strong adsorption capacity and high mechanical strength, and have received extensive attention in adsorption, especially in the treatment of heavy metal ions. In order to further improve its performance, many studies have modified magnetic chitosan materials. This review discusses the strategies for the preparation of magnetic chitosan using coprecipitation, crosslinking, and other methods in detail. Besides, this review mainly summarizes the application of modified magnetic chitosan materials in the removal of heavy metal ions in wastewater in recent years. Finally, this review also discusses the adsorption mechanism, and puts forward the prospect of the future development of magnetic chitosan in wastewater treatment.

A high-performance fluorescent hybrid material for fluorometric detection and removal of toxic Pb(ii) ions from aqueous media: performance and challenges

Lead(ii) is an extremely toxic heavy metal ion that causes various health problems that are difficult to recover from in many developing countries of the world. Fluorescence-based nanosensors have amazing characteristics such as high sensitivity/selectivity, portability, low detection limit, rapid on-site usability, low cost and capability for removal of heavy metal ions. In this paper, a new fluorescent hybrid material based on silica gel (Bodipy-Si) was developed via a click reaction between alkyne-terminal silica gel and azido-terminal Bodipy. The solid support surface was characterized by various techniques such as SEM, FT-IR, etc. The adsorption and fluorometric properties of the fluorescent nanoparticles were also examined using atomic absorption and fluorescence spectroscopies, and in the presence of metal ions, respectively. The results indicated that the prepared hybrid-fluorescent nanoparticles can be used in the removal and detection of toxic Pb(ii) ions. The limit of detection (LOD) was determined from the fluorescence data as 1.55 × 10-7 M and the maximum adsorption capacity was examined by AAS. The complexometric interactions between Pb(ii) and Bodipy-Si affect the adsorptions of the Pb(ii) metal ion at various concentrations.

Immobilized Nanomaterials for Environmental Applications

Nanomaterials (NMs) have been extensively used in several environmental applications; however, their widespread dissemination at full scale is hindered by difficulties keeping them active in engineered systems. Thus, several strategies to immobilize NMs for their environmental utilization have been established and are described in the present review, emphasizing their role in the production of renewable energies, the removal of priority pollutants, as well as greenhouse gases, from industrial streams, by both biological and physicochemical processes. The challenges to optimize the application of immobilized NMs and the relevant research topics to consider in future research are also presented to encourage the scientific community to respond to current needs.

ZnAl-SO4 Layered Double Hydroxide and Allophane for Cr(VI), Cu(II) and Fe(III) Adsorption in Wastewater: Structure Comparison and Synergistic Effects

Owing to their structure, layered double hydroxides (LDHs) and allophane are nowadays considered as promising materials for application in different fields. The goal of this work is to compare the efficacy of allophane and ZnAl-SO₄ LDH to remove, by adsorption, some cationic and anionic pollutants from industrial wastewater. Both compounds were synthesized via the co-precipitation route (direct method) followed by hydrothermal treatment, obtaining nanoscopic crystallites with a partially disordered turbostratic (ZnAl-SO₄ LDH) or amorphous (allophane) structure. The characterization of the obtained compounds was performed by means of powder x-ray diffraction (PXRD), thermal gravimetry analysis (TGA), field emission scanning electron microscopy analysis (FESEM), and Fourier-transform infrared spectroscopy (FT-IR). The sorbents were tested using wastewater produced by a real metalworking plant and containing ionic species such as Cu(II), Fe(III) and Cr(VI), whose concentration was measured by means of inductively coupled plasma-optical emission spectrometry (ICP-OES). This investigation represents an alternative procedure with respect to standard protocols based on customarily made and artificially lab-produced wastewaters. Both sorbents and their combination proved to be efficient in Cr(VI) removal, irrespective of the presence of cations like Cu(II) and Fe(III). A synergistic effect was detected for Cu(II) adsorption in a mixed allophane/LDH sorbent, leading to a Cu(II) removal rate of 89.5%.

Preparation and Characterization of Chitosan/TiO2 Composite Membranes as Adsorbent Materials for Water Purification

As it is used in all aspects of human life, water has become more and more polluted. For the past few decades, researchers and scientists have focused on developing innovative composite adsorbent membranes for water purification. The purpose of this research was to synthesize a novel composite adsorbent membrane for the removal of toxic pollutants (namely heavy metals, antibiotics and microorganisms). The as-synthesized chitosan/TiO₂ composite membranes were successfully prepared through a simple casting method. The TiO₂ nanoparticle concentration from the composite membranes was kept low, at 1% and 5%, in order not to block the functional groups of chitosan, which are responsible for the adsorption of metal ions. Nevertheless, the concentration of TiO₂ must be high enough to bestow good photocatalytic and antimicrobial activities. The synthesized composite membranes were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and swelling capacity. The antibacterial activity was determined against four strains, Escherichia coli, Citrobacter spp., Enterococcus faecalis and Staphylococcus aureus. For the Gram-negative strains, a reduction of more than 5 units log CFU/mL was obtained. The adsorption capacity for heavy metal ions was maximum for the chitosan/TiO₂ 1% composite membrane, the retention values being 297 mg/g for Pb²⁺ and 315 mg/g for Cd²⁺ ions. These values were higher for the chitosan/TiO₂ 1% than for chitosan/TiO₂ 5%, indicating that a high content of TiO₂ can be one of the reasons for modest results reported previously in the literature. The photocatalytic degradation of a five-antibiotic mixture led to removal efficiencies of over 98% for tetracycline and meropenem, while for vancomycin and erythromycin the efficiencies were 86% and 88%, respectively. These values indicate that the chitosan/TiO₂ composite membranes exhibit excellent photocatalytic activity under visible light irradiation. The obtained composite membranes can be used for complex water purification processes (removal of heavy metal ions, antibiotics and microorganisms).