Mechanism of protodesorption-exchange of heavy metal cations for protons in a heterophase system of H2O-H2SO4-MSO4-cellulose sorbent

Regularities and mechanism of heavy metal cations sorption and (or) proton desorption by chitosan from aqueous solutions

The sorption process of heavy metal ions from aqueous solutions using chitosan flakes and chitosan beads was studied. Chitosan gel beads were prepared using covalent crosslinking of chitosan chains by epichlorohydrin with ionic gelation by sodium tripolyphosphate. The capability of chitosan beads to absorb the heavy metal ions from aqueous solutions was studied, and the physicochemical characteristics of the sorbent were evaluated using SEM and FTIR on the model solution treatment. It was found that competitive proton sorption takes place in acidic media, which results in a transformation of amino groups into inactive ammonium-salt form and decreases in heavy metal sorption onto chitosan from aqueous acidic media. Batch adsorption experiments were performed to examine the influence of various factors such as the initial concentration of metal salts, pH, and agitation duration on the process. It was established that metal ion sorption is pH dependent and has an optimum effect at a pH of 6.0. Following the Langmuir equation, the maximum sorption of Cu2+ions is estimated to be 1,6 mol/kg of modified chitosan. The kinetic study revealed that the adsorption kinetics are well-fitted to the kinetic equation of pseudo second order. Thus, sorption of heavy metal ions by chitosan is considered to be a competitive process that occurs on amino groups of the sorbent with equivalent coordinated participation of metal cations, protons, and anions.

Heavy metals removal using hydrogel-supported nanosized hydrous ferric oxide: Synthesis, characterization, and mechanism

A new polymer-supported hybrid adsorbent (HFO-P(TAA/HEA)) for highly efficient removal of Pb²⁺, Cu²⁺, Cd²⁺ and Ni²⁺ from wastewater was developed by supporting hydrous ferric oxide (HFO) nanoparticles onto a porous poly(trans-Aconitic acid/2-hydroxyethyl acrylate) hydrogel (P(TAA/HEA)) with in situ precipitation method. Swelling kinetics, scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), Fourier transform infrared spectra (FTIR) and X-ray photoelectron spectroscopy (XPS) were used for characterization of the prepared HFO-P(TAA/HEA). The characterization data demonstrated that the hybrid hydrogel HFO-P(TAA/HEA) was successfully fabricated, and swelling ability as well as thermal stability was promoted after loading. The results of batch equilibrium experiments indicated that pH and temperature significantly influenced the adsorption process and adsorption of heavy metals was better fitted to Langmuir and pseudo-second-order models. Selectivity of HFO-P(TAA/HEA) towards heavy metals was greatly improved under the calcium ions competition at higher concentration compared to P(TAA/HEA). Competitive adsorption evidenced the priority order in multifold metal species system was Pb²⁺>Cu²⁺>Ni²⁺>Cd²⁺. What's more, FTIR and XPS analyses manifested that heavy metals might mainly be adsorbed via inner sphere complexation. These findings revealed that hydrogel HFO-P(TAA/HEA) is a potential adsorption material to remove the heavy metals from polluted water.

Cellulose as a Scaffold for Self-Assembly: From Basic Research to Real Applications

Cellulose has received a tremendous amount of attention both in academia and industry owing to its unique structural features, impressive physical-chemical properties, and wide applications. This natural polymer is originally used for packaging, paper, lightweight composites, and so forth and is now being developed for various new areas, such as antibacterial treatment, catalysis, water purification and separation, and biological and environmental analysis. In the current article, we summarize the recent developments in the self-assembly of cellulose with various species including metal ions and metal and metal oxide nanoparticles. Then we highlight several key application areas of cellulose-based composites by reviewing the recent representative literature in each area. A significant part of this review demonstrates some exciting innovations for a wide range of practical applications of cellulose-based composites. Some challenges are also discussed with a view toward future developments.