Scavenging of copper(II) ions, phosphate(V) ions, and diuron from aqueous media by goethite modified with chitosan or poly(acrylic acid)

Fabrication of a chitosan-grafted-4‑vinylpyridine/thiol-amine-HZSM-5 nanocomposite via casting method in adsorption of heavy cations from water systems: an evaluation of adsorption mechanism

This study presents the synthesis of low-silica HZSM-5 zeolite through a hydrothermal process. Subsequently, chitosan-grafted-4‑vinylpyridine/thiol-amine-HZSM-5 nanocomposites were fabricated using casting method for the effective removal of copper (Cu2+) and zinc (Zn2+) cations from aqueous systems. The fabricated cast nanocomposites were characterized using XRD, BET, XPS, FESEM, EDX, CHNS, FTIR, and TGA analyses. The simultaneous roles of amine (-NH2) and thiol (-SH) groups in enhancing the adsorption efficiency of Cu2+ and Zn2+ were thoroughly investigated. Additionally, the influence of key factors, including solution pH, contact time, adsorption temperature, and cation concentration, was systematically assessed. Equilibrium data fitting revealed the dominance of monolayer adsorption, as evidenced by the excellent fit of the Redlich-Peterson (R-P) and Langmuir isotherm models for both Cu2+ and Zn2+ cations. Examination of the kinetic experimental data indicated a close correspondence with the double-exponential model. The maximum adsorption capacity of the fabricated cast nanocomposite was determined to be 328.05 mg/g for Cu2+ and 107.96 mg/g for Zn2+ cations. Additionally, the fabricated cast nanocomposite demonstrated satisfactory regeneration capabilities after 9 cycles of desorption. In both synthetic binary and ternary systems, as well as in real wastewater, the adsorption process exhibited antagonistic behavior, indicating that the presence of one type of cation interfered with the adsorption of the other. The nanocomposite displayed a higher affinity for Cu2⁺ compared to Zn2⁺ cations, in both synthetic and real systems, demonstrating its potential for selective heavy metal removal.

New fruit waste-derived activated carbons of high adsorption performance towards metal, metalloid, and polymer species in multicomponent systems

The main aim of the study was to develop new fruit waste-derived activated carbons of high adsorption performance towards metals, metalloids, and polymers by the use of carbon dioxide (CO2)-consuming, microwave-assisted activation. The authors compared morphology, surface chemistry, textural parameters, and elemental composition of precursors (chokeberry seeds, black currant seeds, orange peels), as well as biochars (BCs) and activated carbons (ACs) obtained from them. The adsorption mechanisms of metals (copper, cadmium), metalloids (arsenic, selenium), and macromolecular compounds (bacterial exopolysaccharide, ionic polyacrylamides) on the surface of selected materials were investigated in one- and two-component systems. Consequently, the capacities of BCs and ACs prepared through direct/indirect physical activation, using conventional/microwave heating were determined. It was noted that microwave heating favoured surface development and thus enhanced adsorbent ability to bind ions or macromolecules. Direct biomass activation led to higher microporosity compared to indirect (two-stage) one, whilst CO2-consuming activation increased aromaticity and hydrophobicity of the solids. In the two-component systems, polymers could favour metal/metalloid adsorption based on complexation phenomena. However, the most efficient and environmentally safe activated carbon turned out to be the one obtained from orange peels by microwave-assisted, direct activation at 800 °C in the CO2 atmosphere.

Unravelling the kinetics, isotherms, thermodynamics, and mass transfer behaviours of Zeolite Socony Mobil - 5 in removing hydrogen sulphide resulting from a dark fermentative biohydrogen production process

Research into the speciation of sulfur and hydrogen molecules produced through the complex process of thermophilic dark fermentation has been conducted. Detailed surface studies of solid-gas systems using real biogas (biohydrogen) streams have unveiled the mechanisms and specific interactions between these gases and the physicochemical properties of a zeolite as an adsorbent. These findings highlight the potential of zeolites to effectively capture and interact with these molecules. In this study, the hydrogen sulphide removal analysis was conducted using 0.8 g of the adsorbent and at various reaction temperatures (25-125 °C), a flow rate of 100 mL min-1, and an initial concentration of approximately 5000 ppm hydrogen sulphide. The reaction temperature has been observed to be an essential parameter of Zeolite Socony Mobil - 5 adsorption capacity. The optimum adsorption capacity attains a maximum value of 0.00890 mg g-1 at an optimal temperature of 25 °C. The formation of sulphur species resulting from the hydrogen sulphide adsorption on the zeolite determines the kinetics, thermodynamics, and mass transfer behaviours of Zeolite Socony Mobil - 5 in hydrogen sulphide removal and Zeolite Socony Mobil - 5 is found to improve the quality of biohydrogen produced in thermophilic environments. Biohydrogen (raw gas) yield was enhanced from 2.48 mol H2 mol-1 hexose consumed before adsorption to 2.59 mol H2 mol-1 hexose consumed after adsorption at a temperature of 25 °C. The Avrami kinetic model was fitted for hydrogen sulphide removal on Zeolite Socony Mobil - 5. The process is explained well and fitted using the Temkin isotherm model and the investigation into thermodynamics reveals that the adsorption behaviour is exothermic and non-spontaneous. Furthermore, the gas molecule's freedom of movement becomes random. The adsorption phase is restricted by intra-particle diffusion followed by film diffusion during the transfer of hydrogen sulphide into the pores of Zeolite Socony Mobil - 5 prior to adsorption on its active sites. The utilisation of Zeolite Socony Mobil - 5 for hydrogen sulphide removal offers the benefit of reducing environmental contamination and exhibiting significant applications in industrial operations.

Comparison of Structural, Water-Retaining and Sorption Properties of Acrylamide-Based Hydrogels Cross-Linked by Physical and Chemical Methods

Two series of hydrogels based on acrylamide and its copolymers with acrylonitrile and acrylic acid were synthesized by two cross-linking methods - chemical (using N,N'-methylene bis-acrylamide) and physical (using montmorillonite (MMT)) ones. The structure of the gels was characterized by Fourier Transform Infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The swelling and sorption properties were analyzed as a function of both the monomer composition and the cross-linking method. The shift of the band corresponding to Si-O (995-1030 cm-1 ) confirmed the formation of intercalation structures for MMT-cross-linked gels. Moreover, physically cross-linked gels demonstrated a non-monotonic dependence of the swelling degree on the MMT concentration, and acrylamide-acrylic acid copolymer MMT-cross-linked gels showed pH sensitivity and the highest swelling degree of 150 g/g. The highest sorption capacity towards cadmium(II) ions was demonstrated by acrylamide-acrylic acid copolymer gels, both covalently cross-linked (30 mg/g) and MMT-cross-linked (8.9 mg/g).