Synthesis and performance analysis of reduced graphene oxide/titanium dioxide nanotubes capacitive deionization electrode composite for water treatment

• Main Author: Lazarte, John Paolo L.
• Format: text
• Language: English
• Published: Animo Repository 2018
• Subjects: Water > Purification; Water quality management
• Online Access: https://animorepository.dlsu.edu.ph/etd_masteral/5445
• Institution: De La Salle University

A novel capacitive deionization (CDI) electrical double layer (EDL) material from a composite of reduced graphene oxide (rGO) and titanium dioxide nanotubes (TNT), was developed to attain higher electrosorption capacity and stability at high sodium chloride concentration to appropriate CDI as a water and draw solution recovery system in hybrid forward osmosis. This was achieved by choosing the best proportion and testing it at different CDI operating conditions at increasing influent concentration. Among 3:1, 1:1, 1:3 rGO/TNT proportions, the best was 3:1 rGO/TNT, with a specific capacitance of 165.22 F/g. Its cyclic voltammogram and electrochemical impedance spectroscopy plot are likewise typical of EDL materials. Its two-hour electrosorption capacity during CDI increased 1.34 times from 100 ppm to 30000 ppm sodium chloride with energy consumption constant at 1.11 kWh per kg NaCl removed, but percent discharge at zero-voltage only ranged from 4.9-7.27% after 30 minutes of desorption for all concentration levels. Furthermore, repeated charge/discharge show that 0.1 A/g, the slowest charging rate tested, has the highest charging capacity retention at 60% after 100 cycles. Increased concentration likewise increased charging capacity retention. Moreover, the material was able to increase draw solution concentration by 2.28% in 36 minutes after 5 cycles while the effluent quality collected between 1-1.2 V was independent of charging rate and averaged at 103.42 ppm from 106.22 ppm. As observed through SEM and TEM image, the composites superior performance was influenced by the spreading out of rGO sheets around branched out TNTs leading to a high BET surface area of 511.226 m2/g, 99.83% of which is mesoporous. Another contributory factor would be the presence of highly conductive carbon and dipole groups. Moreover, its dipole-dipole and hydrogen bonding functional groups served as the strong binding force between rGO and TNT units that led to the stability of the molecules despite some minute defects discovered. With consistent composite behavior even at 30000 ppm sodium chloride, 3:1 rGO/TNT can be considered capable for water and draw solution recovery. However, low charging current with reverse voltage/current discharge is recommended to sustain the material for repeated use.