Experimental and theoretical study of Co sorption in clay montmorillonites

Abstract

Montmorillonite (MMT) clays are 2:1 layered structures which in natural state may allocate different hydrated cations such as M-nH2O (M= Na, Ca, Fe, etc.) in its interlayer space. Depending on the capability for ion sorption, these materials are interesting for environmental remediation. In this work we experimentally study the Co sorption in a natural Na-MMT using UV-visible spectrometry and XRD on semi-oriented samples, and then analyze the sorption ability of this clay by means of ab initio calculation performed on pristine MMT. The structural properties of Na-MMT and Co-adsorbed MMT, and the hyperfine parameters at different atomic sites were analyzed and compared with the experimental ones for the first, and for the case of the hyperfine parameters, presented for the first time for the last. The theoretical predictions based on total energy considerations confirm that Co incorporation replacing Na is energetically favorable. Also, the basal spacing d 001 experimentally obtained is well reproduced. 1-Introduction From the beginning of the industrial revolution, environmental pollution by heavy metals appeared as a direct consequence, and its reversal represents a challenge for modern life. In this scenario pollutants generation and the deposition controls constitute a very important topic due to the negative effects that these elements could cause both on the human health and the environmental quality. Among the mechanisms used for heavy metal removal from effluents, ion exchange allows the use of low cost and environmental friendly materials, like clay minerals and its derivatives (modified clays that enhance the sorption process of the sorbent material) 1-3. Among them, Montmorillonite (MMT), a 2:1 clay mineral, is one of the most promising candidates for decontamination and disposal of wastewater with high-level heavy metal cation content, due to its relatively high specific area and cation exchange capacity 4, 5 .

Co-exchanged montmorillonite: a potential antibacterial agent with good antibacterial activity and cytocompatibility

“…In addition, Co–Na exchange was considered to be energetically favored, as calculated by DFT. 30,31 Therefore, in this study, it can be speculated that cobalt in CoMMT exists mainly in the form of cobalt hydrate ions in the interlayer of clay. However, with the increase of Co(NO 3 ) 2 concentration, the change of d (001) is not monotonous.…”

“…This is because Co–Na exchange rearranged the oxygen atoms in the silicon–oxygen tetrahedron, which affects the geometry of the wafer. 30 Besides, hydrate sodium ions in the MMT interlayer were exchanged by hydrate cobalt ions with a higher radius, which expanded the interlayer spacing of MMT. 35 Compared with unmodified MMT, it is expected that CoMMT samples may have better ability to adsorb bacteria and release interlayer cations due to their higher dispersity and specific surface area.…”

Assessment of sorption capability of montmorillonite clay for lead removal from water using laser–induced breakdown spectroscopy and atomic absorption spectroscopy

“…The major analytical laboratory methods employed for trace analysis are electro thermal atomization-atomic absorption spectroscopy (ETA-AAS), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and inductively coupled plasma-mass spectroscopy (ICP-MS) [7]. These methods are routinely employed for the analysis of trace elements in liquids sampled in environmental, industrial, pharmaceutical, and biological studies.…”

Structural and Electronic Properties of Iron-Doped Sodium Montmorillonite Clays: A First-Principles DFT Study

“…Computational simulations provide a powerful tool to determine the most probable positions of the cations in the lamellae, as well as the number of cations in the interlamellar domain. Tavares et al and Costa et al, using ab initio density functional theory (DFT) calculations with periodic boundary conditions, were able to accurately predict crystallographic and electronic properties of clays such as double lamellar hydroxides. , There are several theoretical studies that analyze the hydration of ions confined in the interlayer space of montmorillonites, − investigations that involve the interaction of organic components which exploit the adsorptive properties of Mt − for application as adsorbent of pollutants, and other medical applications.…”