Influence of various experimental parameters on the capacitive removal of phosphate from aqueous solutions using LDHs/AC composite electrodes

Abstract

The efficient uptake of phosphate from aqueous solutions was achieved on layered double hydroxides (LDHs)-based electrodes via capacitive desalination in our previous study. The current follow-up work was mainly carried out to study the influence of various experimental parameters on the capacitive removal of phosphate using LDHs/activated carbon (LDHs/AC) composite electrodes. A series of batch experiments were implemented to investigate the experimental factors, including Mg 2+ /Al 3+ ratios (2, 3, and 4), trivalent metal cations (Al 3+ , Fe 3+ , Cr 3+), initial solution pH (from 3 to 10), coexisting anions (NO 3-, Cl-, SO 4 2-), and ion strengths, in capacitive deionization. The electrode materials before and after capacitive deionization were characterized to reinforce the analysis of the adsorption mechanisms by X-ray powder diffraction, scanning electron microscopy, energy dispersive X-ray, cyclic voltammetry, and electrochemical impedance spectroscopy. Results indicated that the Mg-Al LDHs/AC electrodes exhibited higher phosphate adsorption capacity (80.43 mg PO 4 3-/g), more regular morphology, and higher degree of crystallinity than that of Mg-Fe LDHs/AC and Mg-Cr LDHs/AC. Increasing Mg 2+ /Al 3+ ratios enhanced the adsorption capacity of phosphate. The uptake of phosphate by Mg-Al LDHs/AC under circumneutral pH and low ion strength reached the maximum level. Furthermore, the presence of coexisting anions lowered the adsorption capacity of phosphate mainly due to the occurrence of a compressed electrical double layer. Therefore, the influence of different experimental parameters on phosphate removal via capacitive deionization by Mg-Al LDHs/AC necessitates a 3 systematic investigation to optimize the preparation conditions of LDHs-based electrodes and several important operating parameters.

Carbon Black Flow Electrode Enhanced Electrochemical Desalination Using Single-Cycle Operation

“…Cyclic voltammetry (CV) was performed in the one-chamber device (Figure S1) with a potential scan range of 0–1.2 V. The specific capacitance of the flow electrodes was obtained from CV curves by applying the following equation where C (F g –1 ) is the specific capacitance; S (5 mV s –1 ) is the scan rate; the flow rate of the electrodes is controlled at 8 mL min –1 , solid content is 2.5%, and total mass of the electrodes is 0.012 g; Δ V (V) is the applied voltage window, and I (A) is the current.…”

Faradaic Electrodes Open a New Era for Capacitive Deionization

“…Apart from heavy metal contaminants, agricultural and industrial wastewater also contains large amounts of biological nutrients, such as phosphates and nitrates, causing the deterioration of water quality and serious damage to aquatic ecosystems. [338] Zhu et al [339] employed a Mg-Al LDHs/AC electrode to remove phosphate, showing a high phosphate removal capacity (80.43 mg PO 4…”

“…[ 338 ] Zhu et al. [ 339 ] employed a Mg‐Al LDHs/AC electrode to remove phosphate, showing a high phosphate removal capacity (80.43 mg PO 4 3− per g of electrode). Furthermore, a Pd/NiAl‐MMO composite [ 63 ] was developed as a novel CDI electrode for nitrate removal.…”

Selective adsorption of phosphate by carboxyl-modified activated carbon electrodes for capacitive deionization

“…Therefore, the selective adsorption of PO 3À 4 on carboxyl-modified electrodes relies on weak hydrogen bonds during the protonation process (Wu et al 2020;Li et al 2021). As the pH increases, the protonation of the carboxyl groups and PO 3À 4 gradually decreases, resulting in stronger hydrogen bonding and electrostatic repulsion between the two (Zhu et al 2019;Wu et al 2020). Overall, the adsorption process principally depends on weak hydrogen bonds when two types of forces coexist.…”