Enhanced capacitive removal of hardness ions by hierarchical porous carbon cathode with high mesoporosity and negative surface charges

Pengfei Nie; Xiaohong Shang; Bin Hu; Taimoor Hussain; Jianmao Yang; Manhong Huang; Jianyun Liu

doi:10.1016/j.jcis.2021.12.156

Enhanced capacitive removal of hardness ions by hierarchical porous carbon cathode with high mesoporosity and negative surface charges

J Colloid Interface Sci. 2022 Apr 15:612:277-286. doi: 10.1016/j.jcis.2021.12.156. Epub 2021 Dec 29.

Authors

Pengfei Nie¹, Xiaohong Shang¹, Bin Hu¹, Taimoor Hussain¹, Jianmao Yang², Manhong Huang³, Jianyun Liu⁴

Affiliations

¹ College of Environmental Science and Engineering, Textile Pollution Controlling Engineering Center of Ministry of Environmental Protection, Donghua University, Shanghai 201620, PR China.
² Research Center for Analysis & Measurement, Donghua University, Shanghai 201620, PR China. Electronic address: yangjm@dhu.edu.cn.
³ College of Environmental Science and Engineering, Textile Pollution Controlling Engineering Center of Ministry of Environmental Protection, Donghua University, Shanghai 201620, PR China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, PR China.
⁴ College of Environmental Science and Engineering, Textile Pollution Controlling Engineering Center of Ministry of Environmental Protection, Donghua University, Shanghai 201620, PR China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, PR China. Electronic address: jianyun.liu@dhu.edu.cn.

PMID: 34995864
DOI: 10.1016/j.jcis.2021.12.156

Abstract

Capacitive deionization (CDI), as a promising desalination technology, has been widely applied for water purification, heavy metal removal and water softening. In this study, the hierarchical porous carbon (HPC) with extremely large specific surface area (∼1636 m² g^-1), high mesoporosity and negative surface charges, was successfully prepared by one-step carbonization of magnesium citrate and acid etching. HPC carbonized at 800 ℃ exhibited an excellent specific capacitance (207.2 F g^-1). The negative surface charge characteristic of HPC was demonstrated by potential of zero charge test. With HPC-800 as a CDI cathode, the super high adsorption capacity of hardness ions (Mg²⁺: 472 μmol g^-1, Ca²⁺: 425 μmol g^-1) with ultrafast adsorption rate was realized, attributed to its abundant mesoporous structure and negative surface charges. The priority order of ion adsorption on HPC in the multi-component salt solution was Mg²⁺ > Ca²⁺ > K⁺ ≈ Na⁺. The desalination and softening of the actual brackish water have been simultaneously achieved by three-cell CDI stack after four times of adsorption, with 63% decrease of total dissolved solids and 76% reduction of hardness. The current HPC material with outstanding adsorption performance for hardness ions shows great potential in brackish water purification.

Keywords: Brackish water; Capacitive deionization; Hierarchical porous carbon; Surface charges; Water softening.