Zirconium–Carbon Hybrid Sorbent for Removal of Fluoride from Water: Oxalic Acid Mediated Zr(IV) Assembly and Adsorption Mechanism

Abstract

When activated carbon (AC) is modified with zirconium(IV) by impregnation or precipitation, the fluoride adsorption capacity is typically improved. There is significant potential to improve these hybrid sorbent by controlling the impregnation conditions, which determine the assembly and dispersion of the Zr phases on carbon surfaces. Here, commercial activated carbon was modified with Zr(IV) together with oxalic acid (OA) used to maximize the zirconium dispersion and enhance fluoride adsorption. Adsorption experiments were carried out at pH 7 and 25 °C with a fluoride concentration of 40 mg L−1. The OA/Zr ratio was varied to determine the optimal conditions for subsequent fluoride adsorption. The data was analyzed using the Langmuir and Freundlich isotherm models. FTIR, XPS and the surface charge distribution were performed to elucidate the adsorption mechanism. Potentiometric titrations showed that the modified activated carbon (ZrOx-AC) possesses positive charge at pH lower than 7, and FTIR analysis demonstrated that zirconium ions interact mainly with carboxylic groups on the activated carbon surfaces. Moreover, XPS analysis demonstrated that Zr(IV) interacts with oxalate ions, and the fluoride adsorption mechanism is likely to involve –OH− exchange from zirconyl oxalate complexes.

Iron impregnated carbon materials with improved physicochemical characteristics

“…However, the more intense absorption peak at 1188.3 cm −1 in both M2 and M3 but correspondingly weaker in raw AC and M1 can be assigned to the C-O associations as previously proposed by Velazquez-Jimenez et al [38] who worked on the sorption of fluorides from water on zirconium oxalate complexes (ZrO x ) supported on AC. A sharp peak at 1084.6 cm −1 in M2 and M3 can be correlated to the attachment of metal (iron) with the oxygen through -interactions, i.e.…”

“…(Fe O), on iron modified surfaces which was presumed to be due to iron oxide complexes (see EDX results). In another study, an absorption peak appearing at 1084 cm −1 has been attributed to the Zr O an indication of a metal-oxygen interaction [38]. These observations are in good correlation with the findings of Kong et al [58], who suggested the presence of absorption peaks at 1020 and 820 cm −1 in the spectrum of V 2 O 5 , resulted from the stretching in V-O bond of vanadyl group (V O) and due to the vibrations in vanadium oxide bridge system (V-O-V), respectively.…”

“…Meanwhile, the micropores of the carbon material were expected to be transformed to the meso-and/or macroporous texture. In an earlier investigation, Velazquez-Jimenez et al [38] reported that the doping of zirconium oxalate complexes (ZrO x ) on carbon substrate displayed a similar trend revealing the partial blockage of the available pores and transformation of the micro-pores into meso-and/or macro-pore size. Following the BJH pore size distribution, it was noticed that the average pore diameter of the iron-impregnated carbon materials decreased in the manner of M1 < M2 < M3.…”

A dendrimer-like hyper branched chitosan beads toward fluoride adsorption from water

“…Peak around 2933 cm −1 is due to the stretching vibration of CH 2 bands. The sharp peak at 1376 cm −1 is attributed to the bending vibration of Zr OH bands [50,51]. After fluoride treatment F-Zr-PAAGCB (Fig.…”

Preparation and characterization of colored Ti/Zr conversion coating on AZ91D magnesium alloy

“…The Zr 2p spectrum (Fig. 5f) can be fitted into two doublepeak components with binding energies at about 182.3 eV and 183.1 eV, which were assigned to ZrO 2 and zirconium complex respectively [30,43,44]. As seen from the XPS, the main components of the conversion coating are MgF 2 , Mg(OH) 2 , MgO, TiO 2 , ZrO 2 and the Ti and Zr metal-organic complex.…”