As the world population grows, a persistent pressure on natural resources remains. Resource requirements have extensively expanded due to industrialization. Several technological advancements continually aim to alleviate these resource shortages by targeting existing shortcomings in effective and efficient material design. Practical, high-performing, and economical materials are needed in several key application areas, including energy storage, energy harvesting, electronics, catalysis, and water purification. Further development into high-performing and economical materials remain imperative. Innovators must seek to develop technologies that overcome fundamental limitations by designing materials and devices which address resource challenges. Carbon serves as a versatile material for a wide range of applications including purification, separation, and energy storage owing to excellent electrical, physical, and mechanical properties. One-dimensional (1D) carbon fiber in particular is renowned for excellent strength with high surface-to-volume ratio and is widely commercially available. Although an exceptional candidate to address current energy and environmental needs, carbon fibers require further investigation to be used to their full potential. Emerging strategies for carbon fiber design rely on developing facile synthetic routes for controlled carbon structures. The scientific community has shown extensive interest in porous carbon fabrication owing to the excellent performance enhancement in separation, filtration, energy storage, energy conversion, and several other applications. This dissertation both reviews and contributes to the recent works of porous carbon and their applications in energy and environmental sciences. The background section shows recent development in porous carbon and the processing methods under investigation and current synthetic methods for designing porous carbon fibers (PCF). Later sections focus on original research. A controlled radical polymerization method, reversible addition-fragmentation chain transfer (RAFT), enabled a synthetic design for a block copolymer precursor, poly(methyl methacrylate) (PMMA) and polyacrylonitrile (PAN). The block copolymer (PMMA-b-PAN) possesses a unique microphase separation when electrospun and develop narrowly disperse mesopores upon carbonization. The PMMA and PAN domains self-assemble in a kinetically trapped disordered network whereby PMMA decomposes and PAN cross-links into PCF. The initial investigation highlights the block copolymer molecular weight and compositional design control for tuning the physical and electrochemical properties of PCF. Based on this study, mesopore (2 – 50 nm) size can be tuned between 10 – 25 nm while maintaining large surface areas, and the PAN-derived micropores (< 2 nm). The mesopores and micropores both contribute to the development of the unique hierarchical porous carbon structure which brings unprecedented architectural control. The pore control greatly contributes to the carbon field as the nano-scale architecture significantly influences performance and functionality. The next section uses PCF to clean water sources that are often tainted with undesirable ions such as salts and pollutants. Deionization or electrosorption is an electrochemical method for water purification via ion removal. I employed the PCFs as an electrode for deionization because of their high surface area and tunable pore size. Important for deionization, the adsorption isotherms and kinetics highlight the capacity and speed for purification of water. I studied PCF capacitive filtration on charged organic salts. Because PCF have both micropores and mesopores, they were able to adsorb ions at masses exceeding their own weight. The PFC adsorption efficiency was attributed to the diffusion kinetics within the hierarchical porous system and the double layer capacitance development on the PCF surface. In addition, based on the mechanism of adsorption, the PCFs showed high stability and reusability for future adsorption/desorption applications. The PCF performance as an electrosorption material highlights the rational design for efficient electrodes by hierarchical interconnected porosity. Another application of PFCs is updating evaporative desalination methods for water purification. Currently distillation is not widely used as a source of potable water owing to the high cost and energy requirement. Solar desalination could serve as a low-cost method for desalination; however, the evaporation enthalpy of water severely limits practical implementation. Here I apply the pore design of PCF as a method for water nano-confinement. Confinement effects reduce water density and lowers evaporation enthalpy. Desalination in PCF were studied in pores < 2 nm to 22 nm. The PCF pore size of ~ 10 nm was found to be the peak efficiency and resulted in a ~ 46% reduction in enthalpy. Interestingly, the PCF nano-confinement also contributed to the understanding in competing desorption energy for evaporation in micropores. The pore design in PCF also shows confinement effects that can be implemented in other environmental applications. Lastly, the block copolymer microphase morphology was explored in a vapor induced phase separation system. The resulting PCF properties showed a direct influence from the phase separation caused by nonsolvent. At low nonsolvent vapor, a disordered microphase separation occurred, however upon application of nonsolvent vapor, the polymer chains reorganized. The reorganization initially improved mechanical properties by developing more long-range ordered graphic chains in the PAN-derived carbon. However, at higher nonsolvent vapor concentrations, the fibers experienced polymer precipitation which resulted in bead and clump formation in the fiber mats. The beads and clumps lowered both mechanical properties and electrochemical performance. The vapor induced phase separation showed a method for enhancing mechanical properties without compromising electrochemical performance in flexible carbon fibers. / Doctor of Philosophy / Nanomaterials possess mechanical, physical, and electrical properties to address important growing demands for precious resources such as clean water and energy. Many advancements in nanomaterials focus on improving fine-tune architectures which facilitate efficiency in composites, filtration systems, catalytic systems, energy storage devices, and electronics. Carbon material has remained a valuable candidate in these fields owing to its abundancy economical cost, and excellent properties. Several carbon forms provide unique characteristics including 0D dots, 1D fibers, 2D sheets, and 3D monoliths. Of these, 1D fibers possess excellent strength, resiliency, and conductivity and have been commercially employed in modern automotive, airplanes, membranes, and conductors. However, traditional carbon fiber fabrication does not match the growing needs in performance. Therefore, in this dissertation I explore the design and processing of carbon fibers for controlled architectures. These designs were then systematically studied in filtration systems, solar desalination, and flexible electronics. Block copolymers provide a new way to combine polymers for drastically new materials and effects. Firstly, I conducted a comprehensive study on the synthesis and composition of this block copolymer which laid the foundation for future carbon fiber design. The polymer consists of two chains – one chain to develop carbon structures upon heating; the second which decomposes into pores upon heating. Therefore, with these two chains, a highly porous carbon fiber can be created. The reaction I studied could mostly be controlled with time to change the length of each chain. Ultimately, the pore size and surface area depend on the relative lengths of each chain. Future studies, including ones in this work, could therefore tune pore size and surface area for many applications. Carbon fibers with graphitic structure are inherently conductive and thereby attract charged molecules in a solution. Diffusion and capacity serve as major factors in these types of systems. With the aforementioned control of the carbon fibers a diffusion study was conducted with charged pollution ions. Owing to the conductive nature, a voltage supply was attached to the fibers, which would adsorb ions electrostatically, termed "electrosorption". The electrosorption performance within the carbon fibers elucidated the interconnected porous structure and how ions orientate themselves along the surface of the fibers. In addition, with the development of ion orientation along the surface of the fibers, a greater than 1:1 ratio of carbon weight to ion weight adsorbed developed owing to the diffusion and ion stacking capabilities. Additionally, the study provides deeper investigation into movement of ions within confined nano-porous material. The ever-growing need for renewable resources such as fresh water has pressured development into more efficient material. Solar desalination has attractive qualities which makes it a focus for micro-scale studies. One of the major limitations lies in the high energy input change liquid water into vapor. At 100 °C for boiling, desalination lacks sufficient efficiency for large-scale applications in evaporation. However, by utilizing nano-scale material, the fundamental properties of water can be altered. The carbon fibers were then created with various nano-pore sizes which revealed nano-confinement effects when subject to solar heating. With the shrinking of pore sizes, the density of water also decreased. A lower density means less energy was required to convert water from a liquid to a vapor state. The carbon fibers helped reveal real applications into confinement effects on water based on pore size. Apart from just desalination, this means future environmental application can utilize this knowledge for more effective and smart designs. The carbon fibers outstanding electrical and mechanical properties have spurred research and development since the mid-1900s. Since then, carbon fiber technologies have grown from facile and efficient productions means, to high end, high performance smart design. The work presented here furthers two major components: first, the high-performance design of porous carbon fiber; second, the fundamental principles in nano-material properties and their applications. By first constructing a design of polymer synthesis and then subsequent studies, development of nano-porous carbon energy progresses knowledge on smart and efficient designs. These materials provide a platform for future energy and environmental sciences.

Capacitive deionization technologies have gained significant attention in recent years. The development and availability of a variety of materials have enabled the growth of research on electrosorption, which makes capacitive deionization increasingly attractive. This technology has a wide range of applications, such as softening, desalination and selective removal, each of which has been the focus of the experimental part of this work. The theoretical part is devoted to the issue of functioning of capacitive deionization, electrode material and especially the specific application. Water desalination is a major issue, given the global shortage of drinking water and the possibility of using capacitive deionization as a competitive method to conventional desalination methods. Conversely, softening and selective removal of ions can pose everyday problems both in the treatment of drinking water or pre-treatment of industrial water and in the treatment of wastewater. In this diploma thesis, it was proved that the method of capacitive deionization can be used to solve all the above problems. Although capacitive deionization is not a commercially available technology in the Czech Republic yet, it can be expected to be used more and more in the future.

Capacitive Deionization (CDI) is an energy-efficient desalination technology that utilizes an electric field to extract ions from water. Flow-through CDI systems show potential for superior desalination performance compared to traditional flow-by CDI; however, they face the challenge of increased occurrence of Faradaic reactions, leading to undesired by-products and reduced energy efficiency. In this study, we constructed a flow-through CDI cell and investigated the desalination performance of the two possible cell configurations: upstream anode mode and downstream anode mode. A series of experiments were conducted, measuring conductivity and pH of the effluent solution during charging and discharging phases. The results were analyzed in terms of salt adsorption capacity and charge efficiency. We used pH fluctuations in the effluent solution as indicators of Faradaic reactions. It was found that upstream anode mode yielded superior desalination, with a salt adsorption capacity of 6.79 mg/g and charge efficiency of 64.3%, compared to downstream anode mode, which displayed a salt adsorption capacity of 5.19 mg/g and charge efficiency of 50.8%. However, upstream anode mode also produced more pronounced pH oscillations, suggesting a higher occurrence of Faradaic reactions. Reconciling these conflicting results and shedding light on the complex processes within the CDI cell calls for further investigation.

Electrosorption-based capacitive deionization (CDI) has become a viable process for brackish water desalination and defluoridation. In this study, activated Douglas fir biochar is used as a low-cost electrode material with adsorption capacity comparable to activated carbon obtained from biomass precursors. Adding functional groups to the activated biochar enhanced salt removal capacity, providing cation and anion selectivity. The functionalized electrodes were prepared by Nafion, titanium isopropoxide, and p-phenylenediamine treatment, respectively, which introduced sulfonate, titanium dioxide and amine functional groups to the electrode surface. These modification methods are versatile and can be easily performed without sophisticated laboratory environment. Modified biochar electrodes were characterized by TEM, SEM-EDX, XRD, and XPS. Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were performed to analyze the electrochemical properties of the electrodes. The salt adsorption capacity (SAC) was evaluated in a 3D-printed capacitive deionization flow cell using a chloride and fluoride ion sensor. It was found that functionalized biochar electrodes had increased SAC and charge efficiency in asymmetrical setup due to reduced co-ion effect. For example, the asymmetrical CDI cell with Nafion cathode and amine biochar anode improved NaCl removal capacity by 54% over the activated biochar symmetrical cell (identical anode and cathode), with SAC 6.01 mg NaCl/g biochar at the symmetrical cell and 9.25 mg/g for the asymmetrical cell. The charge efficiency also increased by ≈ 67% from symmetric AcB cell to asymmetric TB-05 cathode and AmB anode. This work shows that biochar can be engineered and explored broadly as an inexpensive sustainable electrode material for asymmetrical capacitive deionization.

The effects of system pressure on the performance stability of flow-through capacitive deionization (CDI) cells was investigated. Initial data showed that the highly porous carbon electrodes possessed air/oxygen in the micropores, and the increased system pressure boosts the gases solubility in saline solution and carries them out of the cell in the effluent. Upon applying a potential difference to the electrodes, capacitive-based ion adsorption occurs in competition with faradaic reactions that consume oxygen. Through the addition of backpressure, the rate of degradation decreases, allowing the cell to maintain its salt adsorption capacity (SAC) longer. The removal of oxygen from the pore space of the electrodes makes it no longer immediately accessible to faradaic reactions, thus hindering the rate of reactions and giving the competing ion adsorption an advantage that is progressively seen throughout the life of the cell. A quick calculation shows that the energy penalty to power the pump is fairly insignificant, especially in comparison to the cost of replacing the electrodes in the cell. Thus, operating at elevated pressures is shown to be cost effective for continuous operation through the reduced electrode replenishment costs.

Capacitive deionization is a promising technology for purification and desalination of brackish water with great advantages over current technologies due to its low operating cost and high-water recovery ratio. Most of the system studied relies on the adsorption/desorption capacity of activated carbon electrodes due to its high surface area. However, its specific adsorption capacity is limited since the adsorption is predominantly on the surface of the electrodes. In this thesis we propose the use of polyaniline as a chloride-ion adsorption material. Polyaniline is a redox polymer able to accommodate anions in several of its three states when subjected to an external voltage. To this end, we synthesized polyaniline by electrodeposition technique and its electrochemical behavior was studied. A hybrid CDI system was assembled, using PANI as anode material and activated carbon cloth as cathode, showing outstanding adsorption of 37.26 mg/g Cl at current densities of 250 A/g. The energy consumption of this system was of 0.4979 kWh/m3. Its stability was evaluated over 50 cycles with negligible capacity loss. Along with its use in a CDI system, the aim of this thesis was to understand the mechanisms of operation of this material, by means of its physical and electrochemical characterization, as well as its efficiency and stability through the use of this material in capacitive deionization cells. / Kapacitiv avjonisering är en lovande teknik för rening och avsaltning av bräckt vatten med stora fördelar jämfört med nuvarande teknik på grund av dess låga driftskostnader och höga vattenåtervinningsgrad. De flesta av de studerade systemen bygger på adsorptions/desorptionskapaciteten hos elektroder av aktivt kol på grund av dess stora yta. Dess specifika adsorptionskapacitet är dock begränsad eftersom adsorptionen huvudsakligen sker på elektrodernas yta. I den här avhandlingen föreslår vi att polyanilin används som adsorptionsmaterial för kloridjoner. Polyanilin är en redoxpolymer som kan ta emot anjoner i flera av sina tre tillstånd när den utsätts för en extern spänning. För detta ändamål syntetiserade vi polyanilin genom elektrodepositionsteknik och dess elektrokemiska beteende studerades. Ett hybrid CDI-system monterades med PANI som anodmaterial och aktiverad kolduk som katod, vilket visade en enastående adsorption av 37,26 mg/g Cl vid en strömtäthet på 250 A/g. Energiförbrukningen för detta system var 0,4979 kWh/m3. Systemets stabilitet utvärderades över 50 cykler med försumbar kapacitetsförlust. Förutom användningen i ett CDI-system var syftet med denna avhandling att förstå detta materials funktionsmekanismer genom fysisk och elektrokemisk karakterisering samt dess effektivitet och stabilitet genom användning av detta material i kapacitiva avjoniseringsceller.