Abstract
The world has been facing a water shortage and pollution due to overdevelopment and resource waste further resulting in climate change and global warming. In addition, industrial production and human activities have been contaminating surface water, and causing disease and deaths. In order for making water treatment environmental-friendly, it is time to innovatively develop green technology for water treatment. This research has investigated the feasibilities of ion separation under lower energy consumption with the combination of hierarchically ordered mesoporous carbons (HOMCs) and capacitive deionization (CDI). The sodium and calcium ions were selected as target ions. Due to the higher specific surface area, pore volume and better capacitance for HOMCs, it is expected that CDI can perform better electrosorption. Comparing with traditional desalination technologies such as membrane, ion exchange and adsorption by active carbons, CDI owns the following benefits: (1) lower energy consumption, (2) the regeneration by reversing potential can release concentrated ions and further recycle them and (3) No secondary contaminants. Therefore, developing this system can help to reduce carbon emission and solve the problem of water shortage. In this research, it was successful to fabricate HOMCs using sugarcane bagasse as the sacrificial scaffold by evaporation-induced self-assembly method. Several electron microscopies, nitrogen adsorption-desorption, x-ray diffraction, elemental analysis, electrochemical instrument etc. were used to investigate the properties of carbon materials. In order to enhance the electrochemical property of HOMC, nitric acid and carbon dioxide with high temperature were used to modify it, denoted as HOMC-H and HOMC-C, respectively. After the modification, the performance of capacitance and electrosorption were measured in Ca2+ solution. The symmetric plots in cyclic voltammetry (CV) were observed due to their excellent properties of electric double-layer. The specific capacitance for HOMC-H electrode at 1 mV s-1 can reach 93.2 F g-1, which is 1.45 and 3.45 times higher than those of as-prepared HOMCs and HOMC-C, respectively. The specific electrosorption capacity (SEC) of HOMC-H electrode for Ca2+ can reach 115.4 mol g-1 which is better than those of other two electrode materials. Furthermore, Ag nanoparticles selected as anode and HOMCs selected as cathode were conducted for increasing Na+ removal rate. The asymmetric Ag||HOMC electrodes show excellent electrosorption capacity toward sodium ion adsorption and the SECs are 356.3 and 251.6 μmol g−1 at 1.2 V in the batch and continuous flowing solutions, respectively. Additionally considering the existence of Ag nanoparticles can enhance the electrosorption of sodium ions due to the removal of chloride ions. The reduction of Ag+ was used to fabricate Ag/HOMC composites with 5 nm in diameter. It is found that 127.1 F/g at 5 mV s−1 for Ag/HOMC-10.0, which has performed the enhancement by 1.22 times and 3.45 times higher than those of HOMCs- and AC-based electrodes. The SEC based on the surface area of materials is 0.74 μmol m−2 for Ag/HOMC-10.0 electrode which is 2.06 times and 1.9 times higher than those HOMC and AC electrodes. Furthermore, in order to realize the feasibility of practicable application by CDI, a case study for groundwater remediation was conducted, and Ag/HOMC- and Ag/HOMC||HOMC-based electrodes can reach 100% of removal to Ni2+ and totally performed 236 and 289 μmol g−1 of SEC, respectively. For the source reduction of nickel in the influent of wastewater, Ag/HOMC||HOMC-based electrodes were chosen to evaluate its removal efficiency and 100% of removal rate can be achieved. This research has shown that CDI with HOMCs-based electrodes can not only enhance the efficiencies of water softening and desalination by the modification of electrode materials and operation modes, but also have good performance of remediating heavy metal in the groundwater. The CDI with HOMCs-based electrodes possess innovative and developing potentials.