Arsenate Adsorption on an Fe−Ce Bimetal Oxide Adsorbent:  Role of Surface Properties

Abstract

An Fe-Ce bimetal adsorbent was investigated with X-ray powder diffraction (XRD), transmission electron micrograph (TEM), Fourier transform infrared spectra (FTIR), and X-ray photoelectron spectroscopy (XPS) methods for a better understanding of the effect of surface properties on arsenate (As(V)) adsorption. In the adsorption test, the bimetal oxide adsorbent showed a significantly higher As-(V) adsorption capacity than the referenced Ce and Fe oxides (CeO 2 and Fe 3 O 4 ) prepared by the same procedure and some other arsenate adsorbents reported recently. XRD measurement of the adsorbent demonstrated that the phase of magnetite (Fe 3 O 4 ) disappears gradually with the increasing dosage of Ce 4+ ions until reaching a molar ratio of Ce 4+ to Fe 3+ and Fe 2+ of 0.08:0.2:0.1 (Fe-Ce08 refers to the adsorbent prepared at this ratio), and the phase of CeO 2 begins to appear following a further increase of the Ce dose. Combined with the results of TEM observation, it was assumed that a solid solution of Fe-Ce is formed following the disappearance of the magnetite phase. Occurrence of a characteristic surface hydroxyl group (M-OH, metal surface hydroxyl, 1126 cm -1 ), which showed the highest band intensity in the solid solution state, was confirmed on the bimetal oxide adsorbent by FTIR. Quantificational calculation from the XPS narrow scan results of O(1s) spectra also indicated that the formation of the bimetal Fe-Ce08 was composed of more hydroxyl (30.8%) than was the formation of CeO 2 and Fe 3 O 4 (12.6% and 19.6%). The results of adsorption tests on Fe-Ce08 at different As(V) concentrations indicated that both the integral area of the As-O band at 836 cm -1 and the As(V) adsorption capacity increased almost linearly with the decrease of the integral area of M-OH bands at 1126 cm -1 , proving that the adsorption of As(V) by Fe-Ce08 is mainly realized through the mechanism of quantitative ligand exchange. The atomic ratio of Fe on Fe-Ce08 decreased from 20.1% to 7.7% with the increase of the As atom ratio from 0 to 16% after As(V) adsorption, suggesting that As(V) adsorption might be realized through the replacement of the M-OH group of Fe (Fe-OH) with arsenate. The well splitting of three υ 3 bands at As-O band (836 cm -1 ) of FTIR and the hydroxyl ratio (1.7) of Fe-Ce08 calculated from the XPS results suggested that the diprotonated monodentate complex (SOAsO(OH) 2 ) is possibly dominant on the surface of Fe-Ce08.

Nanosized Cation-Deficient Fe−Ti Spinel: A Novel Magnetic Sorbent for Elemental Mercury Capture from Flue Gas

“…Other oxygen species centered at about 531.5 eV was also observed, which was assigned to -OH. 50,51 A key feature of the novel sorbent is its magnetic property, which makes it simple to separate the sorbent from the complex multiphase system. The saturated magnetization of synthesized (Fe 3-x Ti x ) 1-δ O 4 (x = 0, 0.3, 0.7, and 1) were 59.0, 49.5, 35.2, and 28.5 emu g -1 , respectively.…”

Removal of arsenate from water by using an Fe–Ce oxide adsorbent: Effects of coexistent fluoride and phosphate

“…100 mmol L −1 stock solutions of arsenate, P, and F ions were prepared by dissolving dibasic sodium arsenate, potassium dihydrogen phosphate, and sodium fluoride, respectively, in distilled water. Fe-Ce bimetal oxide adsorbents were prepared by a coprecipitation method and were characterized as described in our previous work [6,7].…”

“…Arsenate was analyzed using a hydride generation atomic fluorescence spectrometer (HG-AFS-610, Beijing Raileigh Analytic Instrument Corporation, China). The adsorption isotherms of As were studied by varying the dose of adsorbent at a fixed initial arsenate concentration (13.3 mol L −1 ), which is close to its actual concentration in groundwater in some areas of Inner Mongolia [6]. For competitive adsorption of P vs. As and F vs. As, series of molar ratios of As to P (1:0.1, 1:1, and 1:10) and As to F (1:1, 1:10, and 1:100) were employed.…”

“…The surface hydroxyl groups on metal oxides are considered as the most abundant and active adsorption sites for adsorption of anions from water [28][29][30]. In our previous studies [6,7] the surface acidity and formation of surface hydroxyl groups of the Fe-Ce have been provide to the interpretation of the adsorption behaviors. At the same time, the exchange of surface sulfate groups has also been suggested to be an important mechanism for the removal of arsenate [31,32].…”

“…In addition, understanding the competitive adsorption mechanisms of these anions could provide insight into the reactions occurring on the surfaces of adsorbents, leading to the elucidation of adsorption mechanisms of different adsorbents. Recently, an iron-cerium (Fe-Ce) bimetal oxide adsorbent has been successfully developed for arsenate removal, which has a higher adsorption capacity (2.00 mmol g −1 ) than many reported adsorbents [6]. Batch and long-term column studies on arsenate adsorption performance using groundwater samples from Inner Mongolia and the suburbs of Beijing, respectively, have shown that the adsorbent is a promising one, although its performance might be affected by some coexisting substances [7,8].…”