Sustainable desalination by 3:1 reduced graphene oxide/titanium dioxide nanotubes (rGO/TiONTs) composite via capacitive deionization at different sodium chloride concentrations

Abstract

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. The capability of novel 3:1 reduced graphene oxide/titanium dioxide nanotubes (rGO/TiONTs) composite to desalinate using capacitive deionization (CDI) employing highly concentrated NaCl solutions was tested in this study. Parameters such as material wettability, electrosorption capacity, charge efficiency, energy consumption, and charge-discharge retention were tested at different NaCl initial concentrations—100 ppm, 2000 ppm, 15,000 ppm, and 30,000 ppm. The rGO/TiONTs composite showed good material wettability before and after CDI runs with its contact angles equal to 52.11° and 56.07°, respectively. Its two-hour electrosorption capacity during CDI at 30,000 ppm NaCl influent increased 1.34-fold compared to 100 ppm initial NaCl influent with energy consumption constant at 1.11 kWh per kg with NaCl removed. However, the percentage discharge (concentration-independent) at zero-voltage ranged from 4.9–7.27% only after 30 min of desorption. Repeated charge/discharge at different amperes showed that the slowest charging rate of 0.1 A·g−1 had the highest charging time retention at 60% after 100 cycles. Increased concentration likewise increases charging time retention. With this consistent performance of a CDI system utilizing rGO/TiONTs composite, even at 30,000 ppm and 100 cycles, it can be a sustainable alternative desalination technology, especially if a low charging current with reverse voltage discharge is set for a longer operation.

Source or Periodical Title

Nanomaterials

Document Type

Article

Subject

Capacitive deionization, Reduced graphene oxide, Sodium chloride, Sustainable desalination, Titanium dioxide nanotubes

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