Activation of Lattice Oxygen in LaFe (Oxy)hydroxides for Efficient Phosphorus Removal

Abstract

Lanthanum (La)-based materials have been recognized as promising adsorbents for aqueous phosphate removal. The incorporation of base metals into La (oxy)­hydroxides represents an effective strategy to improve adsorption performance. Understanding how base metals affect phosphate adsorption is challenging but essential for the development of effective materials for phosphorus control. Herein, we demonstrated a high-performance LaFe (oxy)­hydroxide and studied its mechanisms on phosphate adsorption. The P K edge X-ray absorption near edge structure (XANES) analysis showed that PO4 3– was preferentially bonded with La, and the lattice oxygen in LaFe (oxy)­hydroxide was demonstrated to be the active site. The O K edge XANES suggested that Fe optimized the electron structure of La, and Fe/La metal orbital hybridization resulted in the shift of oxygen p character to unoccupied states, facilitating phosphate adsorption. Furthermore, surface analysis showed that the pore size and volume were increased due to the introduction of Fe, which enabled efficient utilization of the active sites and fast adsorption kinetics. The dual effects of Fe in LaFe (oxy)­hydroxide greatly enhance the effectiveness of La and represent a new strategy for the development of future phosphorus-control materials.

Phosphate removal from aqueous solution by Fe-La binary (hydr)oxides: A study of batch experiments and mechanisms

“…As illustrated in Fig. S3, it is common sense for us that broad vibration bands located at 3433 and 1634 cm − 1 are observed for all materials, which can be ascribed to the stretching vibration of adsorbed water molecules and the bending vibration of the -OH group, respectively (Wang et al 2020, Yu et al 2019. As shown in Fig.…”

“…For the tplot micropore area and average pore volume, the Fe-La binary (hydr)oxides showed similar trends with changes in the Fe/La ratios. These observations indicated that the incorporation of Fe and La metals on the Fe/La 1:1 (hydr)oxides was different from that of the other two type Fe-La (hydr)oxides (Yu et al 2019). However, the average pore diameters were 35.2, 103.3 and 192.8 Å for the Fe/La 3:1, Fe/La 1:1 and Fe/La 1:3 (hydr)oxides, respectively, and increased with the increase in La contents, which may be attributed to the change of the particle shape from irregular and aggregated particles to nano akes, as observed by SEM in Fig.…”

“…However, this trend is signi cantly distinct with that by La(OH) 3 /Fe 3 O 4 nanocomposite, by which the highest level of phosphate removal was observed between pH 4.3 and 6 (Wu et al 2017). This discrepancy might be due to the formation of surface co-precipitation of lanthanum phosphate under acidic conditions (Fang et al 2017, Yu et al 2019. Furthermore, the phosphate capacity of Fe-La binary (hydr)oxides increased with the decrease of the Fe/La molar ratios with respect to the same pH value.…”

“…The XPS spectra of La 3d are mainly consist of La 3d 5/2 and La 3d 3/2 due to the spin-orbit splitting (Yu et al 2015). The representative peaks of La 3d located at ~ 835.1 and ~ 839.0 eV and those centered at ~ 852.2 and ~ 855.9 eV can be assigned to La 3d 5/2 and La 3d 3/2 , respectively (Yu et al 2019, Yu &Chen 2014. The typical peak positions of Fe 2p appear at ~ 711.0 eV for Fe 2p 3/2 and ~ 724.3 eV for Fe 2p 1/2 .…”

“…However, less attention has been paid to the phosphate removal by La-Fe bimetallic hydroxide adsorbents. In one study, the activation of lattice oxygen in LaFe (oxy)hydroxides for phosphorus removal and their underlying removal mechanisms were determined by X-ray absorption near edge structure (XANES) and X-ray photoelectron spectroscopy (XPS) (Yu et al 2019). In that study, Laincorporated La-Fe bimetallic hydroxides were employed.…”