Adsorption of cadmium using modified zeolite-supported nanoscale zero-valent iron composites as a reactive material for PRBs.

The main challenge in utilizing permeable reactive barriers (PRB) for remediation of metals-contaminated groundwater is determination of a proper low-cost reactive medium that can remove the desired contaminants simultaneously. In this study, the performance of different zeolite materials and nZVI-based adsorbents for cadmium (Cd) removal was compared. Further, a composite of the best nZVI and zeolite samples was synthesized with the removal efficiency of 20.6 g/kg and selected as the proposed adsorbent. Moreover, the characteristics of the composite were analyzed through different techniques (BET, XRF, XRD, FT-IR, FE-SEM and EDX). In addition, through kinetic and thermodynamic studies, the effect of temperature, pH, ionic strength and presence of other metal ions on Cd removal efficiency was investigated. According to the results, since sodium zeolite (NaZ) provides a large number of specific ion-exchange sites for decoration with nZVI, stabilizes nZVI, and prevents its aggregation and further leaching in the harsh environment, the NaZ-nZVI composite is capable of removing Cd by adsorption and is applicable in PRBs, and thus it seems that the aforementioned composite is a proper candidate for groundwater remediation from a wide range of metal ions.

Vertically aligned double wall carbon nanotube arrays adsorbent for pure and mixture adsorption of H2S, ethylbenzene and carbon monoxide, grand canonical Monte Carlo simulation.

In this study, pure and ternary adsorption of hydrogen sulfide (H2S), ethylbenzene (EB), and carbon monoxide (CO) on different arrays of zigzag double wall carbon nanotube was investigated using grand canonical Monte Carlo simulations. The internal diameters of nanotube were fixed at 2r = 50.17 Šwhile nanotube wall distances were different values from d = 0 Što d = 150 Å. Pure simulation results indicated that adsorption quantity of H2S and EB in low pressure ranges of P = 1.9 bar to P = 3.1 bar was at least 100% more than CO adsorption quantities. At high pressure ranges of P = 23.1 bar to P = 38.2 bar H2S adsorption was greater than EB and CO by about 200 molecules per unit cell (UC) at low nanotube distances. This was related to smaller kinetic diameter and greater dipole moment of H2S compared to EB and CO. At higher nanotube distance the effect of size however disappears and all three gases approach to adsorption quantity of about 800 molecules/UC. Graphical representation of adsorption areas showed that H2S and CO form multilayer adsorption around nanotube inner and outer walls while EB fill the whole space uniformly without any congestion around the walls. Ternary adsorption results EB/CO and H2S/CO selectivity are greater than EB/H2S selectivity. In addition, at smaller nanotube distances H2S/CO selectivity is generally higher than EB/CO selectivity, which at higher nanotube distance the order becomes revers suggesting that size dependent effects on adsorption vanishes. Isosteric heat of adsorption shows that the order of EB > H2S > CO suggesting that ethylbenzene interaction with nanotube arrays was strongest. Although H2S has a greater dipole moment and smaller molecular dimension, EB adsorption at higher nanotube distance is greater than H2S by at least 50% probably because EB is less volatile.