Enhanced capacitive deionization properties of activated carbon doped with carbon nanotube-bridged molybdenum disulfide

Jing Sun ^a, Yun Li ^a, Haiou Song ^{a, c,} *, Hongxiang Li ^a, Qian Lai ^a, Gusunkiz Egabaierdi ^a, Qimeng Li ^a, Shupeng Zhang ^b, *, Huan He ^a, Aimin Li ^c

^a School of the Environment, Nanjing Normal University, Nanjing 210023, PR China

^b School of Chemistry and Chemical Engineering, Nanjing University of Science and Technology, Nanjing, 210094, PR China

^c State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, PR China

The shortage of freshwater supplies has restricted societal development. Capacitive deionization (CDI) is an emerging technology for desalination of seawater or brackish water, the performance of which is highly dependent on electrode materials. In this work, a molybdenum disulfide/carbon nanotube composite (CNTs-b-MoS₂) with high capacitance was successfully synthesized using a hydrothermal method. The composite exhibited a specific capacitance of 112.79 F g^-1. To reduce costs and determine the practicality of using CNTs-b-MoS₂ for CDI, we combined activated carbon (AC) with CNTs-b-MoS₂ as a CDI electrode. The research demonstrated that after doping with 5% (mass ratio) CNTs-b-MoS₂, the specific capacitance and electrosorption capacity of AC were significantly improved and the maximum desalination capacity of CNTs-b-MoS₂/AC reached 8.19 mg g^-1. The low dosage of CNTs-b-MoS₂ combined with the high specific surface area of AC avoided the shortcomings of CNTs-b-MoS₂, namely low specific surface area and high cost. Moreover, the outstanding conductivity of CNTs-b-MoS₂ improved the conductivity and enhanced the adsorption capacity of AC, giving CNTs-b-MoS₂/AC potential as an advanced, low-cost CDI electrode material.

In summary, CNTs-b-MoS₂ composites were successfully synthesized using a one-step hydrothermal method. The CNTs provided nucleation sites so that MoS₂ could be uniformly loaded onto its surface. Electrochemical characterization of CNTs-b-MoS₂ found a specific capacitance of 112.79 F g^-1 and enhanced conductivity, indicating a potential for CDI. Considering that synthesis of CNTs-b-MoS₂ was time-consuming and expensive, and its specific surface area was not competitive, a small amount of CNTs-b-MoS₂ was added to commercial AC. This not only enhanced the conductivity of commercial AC, but also reduced the investment cost for CDI. The ternary composite electrode CNTs-b-MoS₂/AC containing 5% (mass ratio) of CNTs-b-MoS₂ displayed the optimal specific capacitance, which was 41.99 F g^-1. Finally, CNTs-b-MoS₂/AC was used as an electrode for CDI, which exhibited a maximum electrosorption capacity of 8.19 mg g^-1. The desalination capacity relative to AC alone was increased by 56%, highlighting the potential of CNTs-b-MoS₂/AC as an advanced and cost-effective capacitive deionization electrode material.