Chloride Removal of Calcium Aluminate-Layered Double Hydroxide Phases: A Review

Abstract

Chlorine is a critical element with respect to the use of fossil fuel, recycling of industrial wastes, and water purification. Chlorine could form toxic chemical compounds, corrode pipe systems and boilers, and contaminate surface and ground waters. Calcium aluminate-layered double hydroxides are one of the most promising materials to remove chlorides due to the chemisorption mechanism, since the phases have positively charged interlayers. Many studies on the synthesis and the characterization of calcium aluminate-layered double hydroxides have been extensively conducted, whereas few studies have been conducted on the chloride removal characteristics of the phases. The state-of-the-art studies on the synthesis methods and the structural characteristics of CaAl-LDH phases, the underlying mechanism on the removal of chlorides, and the potential removal rate and the capacity in the present study were thoroughly reviewed.

Synthesis and Characterization of 2,4-Dichlorophenoxypropanoic Acid (2,4-DP) Herbicide Interleaved into Calcium-Aluminium Layered Double Hydroxide and the Study of Controlled Release Formulation

“…Note that a sharp band at 1325 cm −1 associates with the nitrate stretching vibration. Besides that, a peak of 1443 cm −1 refers to the carbonate stretching in the interlayer region that might be due to the CO 2 contamination from the air during the preparation [5]. For the FTIR spectra of pure 2,4-DP, the peak at 2912 cm −1 is associated with the stretching vibration of the O-H groups from COOH.…”

“…x (OH 2 )] x+ (A n− ) x/n •yH 2 O], in which M 2+ and M 3+ denote the divalent and trivalent cations such as calcium (Ca 2+ ) and aluminum (Al 3+ ) accordingly, meanwhile A n− is the interlayer anion [3]. The brucite-like sheets are positively charged, in which some part of the divalent cations can be substituted with the trivalent cations [5][6][7][8]. The negative charges reside in the hydrated interlayer to compensate for the positively charged sheets and keep the charges balanced while providing its typical stacked layered structures.…”

“…The negative charges reside in the hydrated interlayer to compensate for the positively charged sheets and keep the charges balanced while providing its typical stacked layered structures. The sheet's interlayer could be made up of anions and water molecules [5]. Any types of anions such as nitrate (NO 3 − ), carbonate (CO 3 2− ), and chloride (Cl − ) can be interleaved into the interlayer space due to its high anionic exchange capability and variability of chemical composition, giving rise to widespread applications of LDH in drug delivery for pharmaceutical [9][10], polymer composites [8], acting as a host and controlled release formulations in agriculture [5,[11][12].…”

“…The sheet's interlayer could be made up of anions and water molecules [5]. Any types of anions such as nitrate (NO 3 − ), carbonate (CO 3 2− ), and chloride (Cl − ) can be interleaved into the interlayer space due to its high anionic exchange capability and variability of chemical composition, giving rise to widespread applications of LDH in drug delivery for pharmaceutical [9][10], polymer composites [8], acting as a host and controlled release formulations in agriculture [5,[11][12]. 2,4-Dichlorophenoxypropanoic acid (2,4-DP) (Fig.…”

“…2) is highly polar and has high water solubility. Thus, the active substances can be easily released to the surface water and bioaccumulate in the water [5,[13][14]. Therefore, due to the unique properties of LDH acting as a host, 2,4-DP herbicide can be interleaved into the LDH interlayer matrix.…”