Zn-Co layered double hydroxide-based capacitive systems for removal and recovery of phosphate from aqueous environments

Overall, this work validates the effectiveness of pseudocapacitive materials like Zn-Co LDHs in achieving easy and reversible phosphate capture.

by Vaishali Choudhary, Ligy Philip

Abstract
The poor efficiency of traditional carbon electrodes in recovering phosphate from wastewater has led to the exploration of intercalated energy storage materials. Accordingly, the performance of Zn-Co layered double hydroxide (LDH) intercalated with chloride (Zn-Co-Cl), nitrate (Zn-Co-NO3-), carbonate (Zn-Co-CO32-) and synthesized by urea hydrolysis (Zn-Co-U) was examined for electro-assisted phosphate recovery. Structural characterization established that carbonate intercalated LDHs had the highest thermodynamic stability. The electrochemical characterization revealed high specific capacitance (380.8–573.5 F/g) of Zn-Co LDHs, with the primary charge storage mechanism as surface-controlled charge transfer. At an applied potential of 0.8 V, the phosphate electrosorption capacity was 59.4 mg P/g, 101.8 mg P/g, 44.8 mg P/g, 269 mg P/g for Zn-Co-Cl, Zn-Co-CO32-, Zn-Co-NO3-, and Zn-Co-U, respectively. The high electrosorption capacity (85.2%) and almost complete recovery (98.6%) of phosphate was demonstrated by Zn-Co-U for 20 cycles. The electric double layer and pseudocapacitive nature of the LDHs resulted in phosphate uptake via electrostatic attraction, ligand exchange, intercalation, and de-intercalation. The energy consumption for phosphate recovery using Zn-Co-U electrodes was minimal (0.02 kWh/g P). Overall, this work validates the effectiveness of pseudocapacitive materials like Zn-Co LDHs in achieving easy and reversible phosphate capture.

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published: Colloids and Surfaces A: Physicochemical and Engineering Aspects, Volume 691, 2024, 133815, ISSN 0927-7757, 6|2024
Keywords: Material Recovery, Pollution Control, Sustainability, Climate, Raw Materials, India