Synthesis of cellulose fibers/Zeolite-A nanocomposite as an environmental adsorbent for organic and inorganic selenium ions; Characterization and advanced equilibrium studies

Abstract

• Cellulose fibers/zeolite-A composite was used in the uptake of different Se ions. • The Q sat of Se (VI), Se(IV), and SeMt are 163, 212.4, and 109.3 mg/g, respectively. • The uptake behavior of the Se ions follow Langmuir and Pseudo-First order models. • The uptake energies (−20.78 to −27.14 kJ/mol) suggesting physisorption reactions. • The uptake of the three Se ions occurred by exothermic and spontaneous reactions. Cellulose fibers/Zeolite-A composite (CF/ZA) was synthesized as an innovative hybrid structure of enhanced adsorption properties for different selenium species (inorganic (selenate (Se VI)), selenite (Se (IV)), and organic (selenomethionine (SeMt)). The CF/ZA composite achieved actual adsorption capacities of 163 mg/g (Se (VI)), 212.4 mg/g (Se (IV)), and 109.3 mg/g (SeMt) which are higher values than zeolite, cellulose, and several studied adsorbents in literature. The kinetic and classic equilibrium studies are in agreement with Pseudo-First order kinetics (R 2 > 0.95) and Langmuir isotherm (R 2 > 0.89). This suggests homogenous, monolayer, and more physical uptake of the three selenium species. The monolayer model of one energy was assessed as an advanced equilibrium model. Based on the steric n parameter (2.88–3.31(Se (VI), 2.22–5.94 (Se (IV), and 3.46–4.41 (SeMt)) demonstrate the adsorption of them as three or more ions per each site in a vertical orientation by multi-ionic mechanisms. The adsorption energies (−20.78 to −27.14 kJ/mol) are related to physisorption processes such as hydrogen bonding (<30 kJ/mol) and dipole bonding forces (2–29 kJ/mol). The Gaussian energies (1.04–2.09 kJ/mol) support the physisorption reactions in addition to zeolitic ion exchange processes. The thermodynamic functions (internal energy, free enthalpy, and entropy) demonstrate the exothermic, feasible, and spontaneous properties of the reactions.