Nanostructured ICP-CNT Electrodes for Capacitive Deionisation and Water Clean Up

The development of electrodes and flow-through cells in a CDI system are considered in this thesis. Novel 3D nanostructured electrodes and improved designs of flow-through cells in a CDI system are described. The main objectives were: (1) to develop a fundamental knowledge and understanding of reticulated vitreous carbon (RVC), conducting polymers such as Poly(3,4-ethylenedioxythiophene) (PEDOT), single-walled carbon nanotubes (SWCNT) and graphene; (2) to use a RVC electrode structure to build 3D PEDOT microstructure electrodes, 3D nanoweb structure SWCNT and 3D nanoweb hierarchical graphene/SWCNT composite electrodes; (3) to explore possible applications of these electrodes in a CDI system; and (4) to study the effect of increasing the amount of materials in terms of unit geometric volume and geometric area on the electrosorption capacity. PEDOT/RVC composite electrodes with varying amounts of PEDOT loadings were considered for application as novel 3D microstructure electrodes in Chapter 3. PEDOT was successfully deposited by electropolymerization on RVC and used for the first time as materials and electrodes in CDI technology. The aim of this chapter was achieved as demonstrated by the improved performance of the CDI electrode in terms of unit geometric volume and geometric area. The electrosorption capacity in terms of unit geometric volume and geometric area of electrodes increase with increasing amounts of PEDOT in the electrode, and the highest electrosorption capacity obtained was 0.37 mg/cm3 or 0.12 mg/cm2 or 6.52 mg/g of PEDOT in the PEDOT-120/RVC electrode (240 mg coated 4.2 cm3 RVC electrode) at 75 mg/L NaCl solution, at 0.8 V electrode voltage, and 80 ml/min flow-rate. This result is a better desalting performance than carbon materials, and the adsorption/ regeneration of PEDOT/RVC electrodes was facile with high efficiency achieved. The water production by 1m3 of PEDOT-120min/RVC electrode from 75 mg/L NaCl feed solution was 129,176 L/day to produce water less than 1 mg/L NaCl concentration. It has been shown that the capacitance of PEDOT-120min/RVC electrode compared to a bare RVC electrode had increased by a factor of 2230, and the electrochemical properties were ideal. The successful use of 3D PEDOT/RVC in a CDI system led to the use of a RVC electrode again in Chapter 4 to build huge 3D functionalized SWCNT (a- SWCNT) nanoweb structures by filling the RVC pores using a dip coating method. A unique 3D electrode was constructed and explored as a novel CDI electrode. The electrical voltage of 1.5 V and flow-rate of 50 ml/min were the optimum conditions and they were the key factors that affected the NaCl ion removal performance at the sites of acid treated SWCNT (a-SWCNT). The maximum electrosorption capacity result for 23.58%wt of a-SWCNT/RVC composite electrode (50mg a-SWCNT coated 2.16 cm3 RVC electrode) was 3.23 mg/g of a-SWCNT or 0.08 mg/cm3 at 75 mg/L feed concentration. After that, an improved CDI system was designed to accept solution flowing through the electrodes and its effect on desalination cycle time was studied. It is clear that for one desalination cycle, 42 minutes was required for the flow-between (FB) electrodes configuration and 18 minutes for the flow-through (FT) electrodes configuration. This encouraged efforts to design a new CDI cell with a flow-through electrode system. The electrosorption capacity of all electrodes in new cell was increased and the time required for one desalination cycle decreased as well. For example, the electrosorption capacity for 3.63 %wt a-SWCNT was increased from 8.39 mg/g to 10.40 mg/g and the time of one desalination cycle decreased from 30 min to 10 min using flow feed between (FB) electrodes and flow feed through (FT) electrodes, respectively. This means that electrosorption capacity increased 23.96% and the time required for one desalination cycle decreased around three times. In addition, the effect of distance between electrodes, the electrosorption dynamic and isotherm were studied using new cell. The ion removal characteristics were affected by various distances between electrodes. As the distance increased, the ion removal amount was not affected, but the adsorption time required increased when the distance was increased in all cases. The energy output of the CDI system was affected by an increase in the space between electrodes. It was found that NaCl adsorption obeyed pseudo first -order kinetics rather than pseudo second-order kinetics and that NaCl ions were not adsorbed onto the a-SWCNT surface via chemical interaction. Furthermore, the electrosorption for this electrode obeys both the Langmuir isotherm and the Freundlich isotherm models. This phenomenon suggests that monolayer adsorption was the primary adsorption mechanism during the electrosorption process. The maximum electrosorption capacity result for 23.58 %wt a-SWCNT electrode was 8.89 mg/g at 500 mg/L feed concentration, as compared with a theoretical maximum value of 13.08 mg/g calculated using the Langmuir isotherm model. The goals of Chapter 5 are to increase the electrosorption capacity of 3D a- SWCNT/RVC electrodes from Chapter 4 and reduce the duration of electrosorption– desorption cycles of Chapter 4 by improving the ease of ions adsorption to and ions desorption from the electrode surfaces. This was achieved by use of composite microwave irradiated graphene oxide (mwGO) with a-SWCNT. The a-SWCNT materials were contained sandwiched between the graphene sheets to build a 3D highly porous architecture inside the electrodes and increase the electrodes conductivity as well as afford rapid ions diffusion. The results led to a conclusion that the best performing electrode, with a specific capacitance of 179.39 F/g was the 9-CNT/mwGO/RVC (ie a-SWCNT:mwGO ratio was 9:1) electrode, which represents a 29 % increase in specific capacitance compared with the a- SWCNT/RVC electrode. This 9-CNT/mwGO/RVC electrode also had very high CV curve stability, maintaining 99% current stability after 200 cycles. Moreover, the time saving of one electrosorption–desorption cycle with the 9-CNT/mwGO/RVC electrode was 27.78 %; compared with the CNT/RVC electrode which required 18 min. In addition, the electrosorption removal of NaCl by the 9-CNT/mwGO/RVC electrode in terms of mass of the electrode (3.82 mg/g) increased 18.27 % compared with that of the CNT/RVC electrode (3.23 mg/g) using 1.5V applied voltage and 50 ml/min flow-rate as the optimum conditions. The full desalination process to produce water of less than 1 mg/L NaCl concentration in the CDI system using 9- CNT/mwGO/RVC composite electrode increased desalinated water production by 67.78% per day compared with the same CDI system using a-SWCNT/RVC composite electrode. The maximum water produced per day is 29,958 L using 1m3 of 9-CNT/mwGO/RVC electrode and the maximum electrosorption capacity result for the same electrode was 10.84 mg/g at 500 mg/L feed concentration, as compared with a theoretical maximum value of 16.59 mg/g calculated using the Langmuir isotherm model. Also, the performance of electrodes adsorptions was evaluated by dynamics study and it was shown to follow the Pseudo-first-order model

A Strategy to Enhance the Electrode Performance of Novel Three-Dimensional PEDOT/RVC Composites by Electrochemical Deposition Method

In this article, three-dimensional (3D) microstuctured poly(3,4-ethylenedioxythiophene) (PEDOT)/reticulated vitreous carbon (RVC) composite electrodes with varying amount of PEDOT loadings were successfully prepared by electrochemical deposition method. The composites were characterized by Raman spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and cyclic voltammetry. Raman spectra suggest that there is a strong interaction between the RVC and backbone of PEDOT chain. It is revealed from the SEM images that the PEDOT amount, thickness, surface roughness, porosity, and globular structure on RVC electrode are increased with the increase in polymerization time. The capacitance of PEDOT/RVC electrode has increased by a factor of 2230 compared to a bare RVC electrode when polymerization is carried out for 120 min. Moreover, the capacitance of PEDOT was found to be very high compared with other PEDOT studies. The electrodes also show good cyclic stability. This substantial increase in capacitance of RVC electrode is due to the rough, highly porous, and honeycomb-like fine structure of PEDOT coating, which shows a flower-like morphology, consisting of numerous thin flakes with numbers of macropores and micropores. This interesting morphology has enhanced the performance of PEDOT because of increased electrode surface area, specific capacitance, and macroporous structure of RVC electrode

Chemical and Electrochemical Synthesis of Polypyrrole Using Carrageenan as a Dopant: Polypyrrole/Multi-Walled Carbon Nanotube Nanocomposites

In this article, iota-carrageenan (IC) and kappa-carrageenan (KC) are used as dopants for the chemical and electrochemical synthesis of polypyrrole (PPy). The composites of chemically synthesized PPy with multi-walled carbon nanotubes (MWNTs) were prepared using an in situ technique. Both the dialyzed and non-dialyzed IC and KC were used as dopants for electrochemical polymerization of pyrrole. Chemically synthesized PPy and PPy/MWNTs composites were studied by ultraviolet visible (UV-vis) absorption spectra to investigate the effect of the concentration and the incorporation of MWNTs. In addition, the electrical, thermal, mechanical, and microscopic characterizations of these films were performed to examine the effect of the dopants and MWNTs on these properties, along with their surface morphology. The films of electrochemically polymerized PPy were characterized using UV-vis absorption spectra, scanning electron microscopy, and cyclic voltammetry (CV). The results were then compared with the chemical polymerized PPy

Influence of Biopolymer Carrageenan and Glycerine on the Properties of Extrusion Printed Inks of Carbon Nanotubes

This article focuses on the preparation of extrusion printing composite inks of multiwall carbon nanotube (MWNT) dispersed separately in iota-carrageenan (IC) and glycerine (G) solution. Both composites (IC-MWNT and G-MWNT) showed shear-thinning behavior when their flow characteristics were tested. Conductive solid tracks/patterns of both printed composite inks were deposited on glass slide, PET (polyethylene terephthalate) sheet, and IC gel films substrates. The conductive patterns were characterized with microscopy, scanning electron microscopy (SEM), and profilometer. Moreover, their contact angle and electrical conductivity were measured. Profilometry showed that increased number of extruded layers gave increased cross-sectional area. SEM study showed that printing ink is embedded into the surface of IC film, discontinuous on glass slide and smoother on PET sheet. Conductivity of IC-MWNT track was 9 ± 1 S/m and that of G-MWNT was 2942 ± 84 S/m on glass substrate of one layer thick. This is because fewer carbon nanotubes (CNT) are present in G-MWNT track as confirmed by SEM study. The nature of substrate also affects the conductivity of printed patterns. The impressive result of conductivity of printed patterns of composite inks can make them useful for bioelectronic application

Innovative pilot plant capacitive deionization for desalination brackish water

Abstract A semi-industrial demineralization facility was used in six CDI cells to desalinate in two steps. A desalination cycle lowered the feedwater salinity from 1 to 0.5 g/L and produced 200 l/h of demineralized water. This process may be repeated to increase efficiency. Initially, feedwater commenced at 1 g/L. Monitoring both voltage and current during the salt ion removal indicated that CDI cells may recover 30% of the energy utilized. Furthermore, V–Q curves using charge and voltage measurements increased energy recovery by 30%. By cutting off the CDI cells' power source, the electrodes' operating voltage was recorded between 0.85 and 0.9 V, much lower than the external contacts' 1.2 V. The desalination system's efficiency could rise if the electrode voltage was measured and adjusted. In conclusion, storage tanks can provide desalinated water while minimizing water waste; hence, they should be installed. This study examined the physical–technical parameters of a CDI desalination system through experiments and several operational modes. Moreover, it revealed CDI desalination system improvements

Efficiency Improvement of a Capacitive Deionization (CDI) System by Modifying 3D SWCNT/RVC Electrodes Using Microwave-Irradiated Graphene Oxide (mwGO) for Effective Desalination

This work is aimed at improving the electrosorption capacity of carbon nanotube/reticulated vitreous carbon- (CNT/RVC-) based 3D electrodes and decreasing the duration of electrosorption-desorption cycles by facilitating the ions’ adsorption and desorption on the electrode surface. This was achieved by preparing composites of microwave-irradiated graphene oxide (mwGO) with CNT. All composite materials were coated on RVC by the dip-coating method. The highest loading level was 50 mg. This is because it exhibited the maximum electrosorption capacity when tested in terms of geometric volume. The results showed that the 9-CNT/mwGO/RVC electrode exhibited 100% capacitive deionization (CDI) cyclic stability within its 1st five cycles. Moreover, 27.78% time was saved for one adsorption-desorption cycle using this electrode compared to the CNT/RVC electrode. In addition, the ion removal capacity of NaCl by the 9-CNT/mwGO/RVC electrode with respect to the mass of the electrode (3.82 mg/g) has increased by 18.27% compared to the CNT/RVC electrode (3.23 mg/g) when measured at the optimum conditions. In a complete desalination process, the water production per day for the 9-CNT/mwGO/RVC electrode was increased by 67.78% compared to the CNT/RVC electrode when measured within the same CDI cell using NaCl solution of concentration less than 1 mg/L. When considered volume of 1 m3, this optimum 9-CNT/mwGO/RVC electrode produces water 29,958 L per day. The highest electrosorption capacity, when measured experimentally at 500 mg/L NaCl feed concentration, was 10.84 mg/g for this optimum electrode, whereas Langmuir isotherm gave the theoretically calculated highest value as 16.59 mg/g. The results for the 9-CNT/mwGO/RVC composite electrode demonstrate that it can be an important electrode material for desalination in CDI technology

Single-Walled Carbon Nanotube (SWCNT) Loaded Porous Reticulated Vitreous Carbon (RVC) Electrodes Used in a Capacitive Deionization (CDI) Cell for Effective Desalination

Acid-functionalized single-walled carbon nanotube (a-SWCNT)-coated reticulated vitreous carbon (RVC) composite electrodes have been prepared and the use of these electrodes in capacitive deionization (CDI) cells for water desalination has been the focus of this study. The performance of these electrodes was tested based on the applied voltage, flow rate, bias potential and a-SWCNT loadings, and then evaluated by electrosorption dynamics. The effect of the feed stream directly through the electrodes, between the electrodes, and the distance between the electrodes in the CDI system on the performance of the electrodes has been investigated. The interaction of ions with the electrodes was tested through Langmuir and Freundlich isotherm models. A new CDI cell was developed, which shows an increase of 23.96% in electrosorption capacity compared to the basic CDI cells. Moreover, a comparison of our results with the published results reveals that RVC/a-SWCNT electrodes produce 16 times more pure water compared to the ones produced using only CNT-based electrodes. Finally, it can be inferred that RVC/a-SWCNT composite electrodes in newly-developed CDI cells can be effectively used in desalination technology for water purification

Construction of a Novel Three-Dimensional PEDOT/RVC Electrode Structure for Capacitive Deionization: Testing and Performance

This article discusses the deposition of different amount of microstuctured poly(3,4-ethylenedioxythiophene) (PEDOT) on reticulated vitreous carbon (RVC) by electrochemical method to prepare three-dimensional (3D) PEDOT/RVC electrodes aimed to be used in capacitive deionization (CDI) technology. A CDI unit cell has been constructed here in this study. The performance of CDI cell in the ion removal of NaCl onto the sites of PEDOT/RVC electrode has been systematically investigated in terms of flow-rate, applied electrical voltage, and increasing PEDOT loading on PEDOT/RVC electrodes. It is observed that the increase in flow-rate, electric voltage, and PEDOT loading up to a certain level improve the ion removal performance of electrode in the CDI cell. The result shows that these electrodes can be used effectively for desalination technology, as the electrosorption capacity/desalination performance of these electrodes is quite high compared to carbon materials. Moreover, the stability of the electrodes has been tested and it is reported that these electrodes are regenerative. The effect of increasing NaCl concentration on the electrosorption capacity has also been investigated for these electrodes. Finally, it has been shown that 1 m3 PEDOT-120 min/RVC electrodes from 75 mg/L NaCl feed solution produce 421, 978 L water per day of 20 mg/L NaCl final concentration

Corrosion Behavior of Aluminium-Coated Cans

Hundreds of billions of aluminium-based cans are manufactured and used every year worldwide including those containing soft drinks. This study investigates and evaluates the performance and quality of two well-known energy and soft drinks brands, Green Cola and Red Bull. Recent health hazards and concerns have been associated with aluminium leakage and bisphenol A (BPA) dissociation from the can’s internal protective coating. The cans were examined under four conditions, including coated and uncoated samples, the soft drink’s main solution, and 0.1 M acetic acid solution. Electrochemical measurements such as potentiodynamic polarization and impedance spectroscopy (EIS), element analyses using inductively coupled plasma optical emission spectrometry (ICP-OES), and energy dispersive X-ray spectroscopy (EDS) were performed. In addition, sample characterization by scanning electron microscopy (SEM) and X-ray diffraction spectroscopy (XRD) were employed to comprehensively study and analyze the effect of corrosion on the samples. Even though the internal coating provided superior corrosion protection concerning main or acetic acid solutions, it failed to prevent aluminium from dissolving in the electrolyte. Green Cola’s primary solution appears to be extremely corrosive, as the corrosion rate increased by approximately 333% relative to the acetic acid solution. Uncoated samples resulted in increases in the percentage of oxygen, the appearance of more corrosion spots, and decreases in crystallinity. The ICP-OES test detected dangerous levels of aluminium in the Green Cola solution, which increased significantly after increasing the conductivity of the solution