Carbon nanotube membranes with ultrahigh specific adsorption capacity for water desalination and purification

10 - Electrochemically active carbon nanotube (CNT) membrane filter for desalination and water purification

Recently extraordinary breakthroughs have been made towards applying nano-structured materials such as carbon nanotubes (CNTs) and porous graphene membranes in water purification and desalination applications. In this regard, the potential of the electrochemically active carbon nanotube (CNTs) membrane has been highly strengthened for the last few decades. One of the main advantages for such approach is the capability of CNT channel to permit the water flow easily. The perusal of the literature showed that, the performance of CNT based membrane can be three times higher than that of the conventional membrane devices. The unique and excellent characteristics of CNT membrane can outperform the conventional polymer membranes. CNT membrane has been widely used to adsorb chemical and biological contaminants as well as ion separation from sea water due to their high stability, great flexibility, and large specific surface area. Electrochemically active CNT filters deliver further Electro-oxidation of the adsorbed contaminants. Usually polymeric membranes have flexible chains for which it fails to have well-defined pores necessary for filtration. On the contrary CNTs based filters can provide pores with appropriate sizes and configurations by tailoring the growth parameters. The narrow pores of CNTs are capable of filtering water while eliminating ions (Na+/Cl–). Even this type of membranes is capable of removing bacteria from water and heavy hydrocarbon from petroleum. However, the success of desalination entirely depends on the basic design of the CNT-based filter with detailed optimization of the process parameters. Polymer filters cannot be recurrently used through several cycles since elimination of fouling ingredients is difficult. Even though electrochemically active CNT-based membranes have lot of advantages due to their hydrophobic nature, high porosity and specific area; there are numerous traits, which are yet to be considered and optimized. Thus the intrinsic properties of CNT as well as the fabrication of the membrane could be a critical factor for their applicability in various water treatment processes. This chapter provides an explicit and systematic overview of the recent progress of electrochemically active CNT membranes addressing the current prevalent problems associated with water treatment and desalination. The physio-chemical aspect including the working principles of this type of membrane have been discussed. The prevailing challenges and future perceptions are also discussed.

The LUWEX project (Validation of Lunar Water Extraction and Purification Technologies for In-Situ Propellant and Consumables Production) aims to enable sustainable lunar exploration by developing and validating systems for water extraction and purification directly from lunar regolith. This study presents findings from the laboratory campaign dedicated to the testing of the Water Purification subsystem, conducted under laboratory conditions to evaluate system efficacy and reliability. Within the LUWEX framework, the Water Purification subsystem is critical for converting extracted raw water into potable water for crewed missions as well as for deionized water for electrolysis. The purification unit was tested for performance parameters including filtration efficiency, contaminant removal, and adaptability to variable raw water input contamination rates, simulating the dynamic extraction conditions expected on the lunar surface. Preliminary results indicate that the purification subsystem meets key benchmarks in removing impurities, achieving product water standards, and effectively integrating with the broader LUWEX system architecture. Key findings demonstrate not only the subsystem's capability to support water quality requirements for human consumption but also its potential scalability for long-term lunar operations. The outcomes of this test campaign highlight advancements in In-Situ Resource Utilization (ISRU) and the readiness of water purification technologies for future lunar bases.

The growing scarcity of fresh water is a major political and economic challenge in the 21st century. Compared to thermal-based distillation technique of water production, pressure driven membrane-based water purification process, such as ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO), can offer more energy-efficient and environmentally friendly solution to clean water production. Potential applications also include removal of hazardous chemicals (i.e., arsenic, pesticides, organics) from water. Although those membrane-separation technologies have been used to produce drinking water from seawater (desalination) and non-traditional water (i.e., municipal wastewater and brackish groundwater) over the last decades, they still have problems in order to be applied in large-scale operations. Currently, a major huddle of membrane-based water purification technology for large-scale commercialization is membrane fouling and its resulting increases in pressure and energy cost of filtration process. Membrane cleaning methods, which can restore the membrane properties to some degree, usually cause irreversible damage to the membranes. Considering that electricity for creating of pressure constitutes a majority of cost (~50%) in membrane-based water purification process, the development of new nano-porous membranes that are more resistant to degradation and less subject to fouling is highly desired. Styrene-ethylene/butylene-styrene (SEBS) block copolymer is one of the best knownmore » block copolymers that induces well defined morphologies. Due to the polarity difference of aromatic styrene unit and saturated ethylene/butylene unit, these two polymer chains self-assemble each other and form different phase-separated morphologies depending on the ratios of two polymer chain lengths. Because the surface of SEBS is hydrophobic which easily causes fouling of membrane, incorporation of ionic group (e,g, sulfonate) to the polymer is necessary to reduces fouling. Recently, sulfonated SEBS became commercially available and has been extensively explored for membrane-mediated water purification technology. The sulfonated block copolymer creates a well developed nano-sale phase-separated morphologies composed of hydrophilic domains (sulfonated polystyrene) and hydrophobic domains (polyethylene/polybutylene). The hydrophilic domains determines transport properties (water transport, salt and/or ion rejection, etc) and the hydrophobic domains provides mechanical stability of the membrane. Unfortunately, a high degree of sulfonation of SEBS induces excessive swelling and deterioration of mechanical stability of the membrane. In an effort to develop robust polymeric membrane materials for water purification technology, phosphonic acid-functionalized SEBS membranes are investigated during this report period. In compare to sulfonated polymers, the corresponding phosphonated polymers are known to swell less because of the formation of extensive hydrogen bonding networks between phosphonates. In addition to the expected better mechanical stability, phosphonated polymers has another advantage over sulfonated polymers for the use water purification membrane; each phosphonate can accommodate two ions while each sulfonate accommodates only one ion. Membrane properties (ion type, ionic density, etc) of new membranes will be studied and their separation performance will be evaluated in water purification and desalination process. Through systematic study of the relationship of chemical structure–surface property–membrane performance, we aim to better understand the nature of membrane fouling and develop more fouling-resistant water purification membranes. The basic understanding of this relationship will lead to the development of advanced membrane materials which can offer a solution to environmentally sustainable production of fresh water.« less

Chapter 6 - Nanofluidic Carbon Nanotube Membranes: Applications for Water Purification and Desalination

Dramatic transport properties of carbon nanotube membranes for a robust protein channel mimetic platform

Nanocarbon-based conductive membranes, especially carbon nanotube (CNT)-based membranes, have tremendous potential for wastewater treatment and water purification because of their excellent water permeability and selectivity, as well as their electrochemically enhanced performance (e.g., improved antifouling ability). However, it remains challenging to prepare CNT membranes with high structural stability and high electrical conductivity. In this study, a highly electroconductive and structurally stable polyphenylene/CNT (PP/CNT) composite membrane was prepared by electropolymerizing biphenyl on a CNT hollow fiber membrane. The PP/CNT membrane showed 3.4 and 5.0 times higher electrical conductivity than pure CNT and poly(vinyl alcohol)/CNT (PVA/CNT) membranes, respectively. The structural stability of the membrane was superior to that of the pure CNT membrane and comparable to that of the PVA/CNT membrane. The membrane fouling was significantly alleviated under an electrical assistance of − V, with a flux loss of only 11.7% after 5 h filtration of humic acid, which is significantly lower than those of PP/CNT membranes without electro-assistance (56.8%) and commercial polyvinylidene fluoride (PVDF) membranes (64.1%). Additionally, the rejection of negatively charged pollutants (humic acid and sodium alginate) was improved by the enhanced electrostatic repulsion. After four consecutive filtration-cleaning cycle tests, the flux recovery rate after backwashing reached 97.2%, which was much higher than those of electricity-free PP/CNT membranes (67.0%) and commercial PVDF membranes (61.1%). This study offers insights into the preparation of stable conductive membranes for membrane fouling control in potential water treatment applications.

Ground water harvesting is a method of collecting surface runoff from a catchment’s area and storing it in surface reservoirs. The water harvested is usually contaminated and turbid. Methods used to purify water include filtration, sedimentation, boiling and chlorination. This project was carried out in Nyatike district, Western Kenya where water is scarce and water-borne diseases such as cholera, typhoid and dysentery are prevalent. The main objectives of the research were to disseminate water harvesting technology using hand-dug water pans and to evaluate the effect of Moringa oleifera seed extract as water purifier. Sites were identified for construction of demonstration water pans. Moringa seeds were milled after which methanol was used to extract water soluble components.. Representative water samples from Victoria Lake, Kuja River and Otho pond were collected and subjected to purification studies using M. oleifera seed extract and aluminum sulfate. M. oleifera was also tested for antibacterial activity against Escherichia coli (ATCC 25922) Salmonella typhii and Vibrio cholerae (ref. Romel Cary Blair Lot. 452610). A total of 452 farmers were trained in water harvesting and purification technologies. Studies on water purification indicated that Alum lowered the water pH from 7.4 to 4.4 while samples treated with Moringa extract did not affect water pH. Alum was the better water purifier whereby application of 0.25 g/L decreased water turbidity from 310.7 to 1.1 NTU while M. oleiferadecreased turbidity to 45.6 NTU. M. oleifera extract showed antibacterial activity. S. typhii was the most sensitive while V. cholera was the least sensitive. Key words: Aluminum sulfate, antibacterial activity, Moringa oleifera, water harvesting, water purification.

Nanotechnology has myriads of potentials and windows of opportunities cutting across all sectors, but this paper concentrated on the application of nanotechnology in water purification and treatment as a means of improving water quality for effective water supply in Nigeria. The paper reviewed twenty-one manuscripts on the applications of nanotechnology in water treatment, its efficiency and major challenges including original research studies and reviews. It was found that nanotechnology has the potentials to advance and make easy the process of water purification effectively, with the merits of lower costs, energy saving, and relative limited negative environmental and health impacts. Some of the identified nanomaterials useful in water treatment and purification include: carbon nanotubes and alumina fibers for nanofiltration, carbon nanotube membranes for removal of almost all kinds of water contaminants including turbidity, oil, bacteria, viruses and organic contaminants; Zinc oxide nanoparticles for removing arsenic from water; nano titanium oxide used to degrade organic pollutants; zero-valent metal nanoparticles, metal oxides nanoparticles, and nanocomposites among others. The paper recommended that nanotechnology should be adopted in water purification and treatment in order to improve water quality and adequate water supply in Nigeria. Also, the departments of water resources planning and management should partner with available nanotechnology centres to improve the sector using this technology.

Progress with the desalination and water purification technologies US roadmap

Carbon nanotube hollow fiber membranes: High-throughput fabrication, structural control and electrochemically improved selectivity

n the work, a comparative morphometric analysis of various types of domestic adsorbents intended for use in water purification technologies is performed. Four types of adsorbents were investigated: «Möbius» carbon adsorbent, P1T1KA clay powder of the montmorillonite type, DG-100 carbon black, C-1 colloidal graphite preparation.Morphometric analysis of adsorbent particles was carried out by the method of optical polarization microscopy («Bi-olam» brand microscope). Photomicrographs of particles pre-dispersed in the immersion liquid were obtained using a digital camera with a high-resolution matrix. Quantitative assessment of the sizes of adsorbent particles was carried out by the method of digital image analysis (ImageJ software package). The area and perimeter of individual particles were determined and their equivalent diameter and shape index were calculated. Statistical processing of experimental data was carried out using the «Statistica» software package.It was established that the nature of the distribution of particles of the investigated types of adsorbents in terms of equiv-alent diameter depends on the type of sample, and may be complicated by the processes of particle aggregation.It is shown that a similar nature of distribution is observed for all investigated carbon adsorbents according to the shape index. The pronounced and largest fraction (27-37%) corresponds to particles with a shape close to round. The most acceptable adsorbents for water purification processes can be considered a colloidal graphite preparation and clay powder of the mont-morillonite type, for which there is a higher homogeneity of the distribution of particles according to the shape indicator. This, in turn, can provide higher sorption efficiency in water treatment technologies.The application of the method of optical polarization microscopy in combination with the morphometric analysis of particles makes it possible to reasonably approach the selection of the brand of adsorbents for their use in water purification technologies. Further research in this direction can be directed to the processes of surface modification of adsorbent particles to increase their specific capacity and selective ability.

Scarcity of clean water, due to population growth, global warming, and depletion of natural freshwater sources, is among the most formidable environmental challenges facing humanity. Accordingly, development of cost-effective and widely applicable technologies for water remediation and purification is extremely important and highly sought. We present a new strategy for water purification using a composite material comprising carbon dots (C-dots) encapsulated within a porous hydrogel. The hydrogel matrix allows significant water uptake, while the embedded C-dots constitute effective photothermal mediators, absorbing solar energy for enhanced water evaporation. The C-dots further bestowed greater thermal and mechanical stability to the hydrogel host. The C-dot/hydrogel composite exhibited good operating parameters, including a water evaporation rate of 1.4 kg m2 h-1 and solar-to-vapor conversion efficiency of 89%. It was applied for diverse water treatment applications, including water desalination and removal of heavy metal ions, detergents, and organic molecules from contaminated water. The C-dot/hydrogel construct is easily synthesized from inexpensive, biocompatible, and environmentally friendly building blocks, is recyclable, and may be employed in varied water purification applications.

Globally, the scarcity of pure water has been an alarming threat for the survival of ecosystem since fresh water is the necessity of every being and is one of the most important factors in a healthy ecosystem. Potable or drinking water is meant to be free from all kinds of unwanted toxic chemicals, and its pH should always lie between 6.5 to 8.5. However, even today, knowingly or unknowingly, almost 30% in the world are drinking water with a pH below 6.5, which means it is acidic and contaminated with various kinds of pollutants. Even though, in some areas, freshwater is available, it is not affordable for the poor people in need. So, in the current situation, the most essential step is to adapt new trends and technologies for water purification using nature friendly and renewable resources. Emphasis is to be given to cost-effective, easy-to-use solutions for water purification, i.e., purifying water using carbon-based materials. In the present era, nanomaterials have emerged as the most sought-after and desirable solutions for various industrial problems and domestic applications. The carbon-based nanomaterials, including single and multi-walled carbon nanotube (CNTs), graphene oxide, activated carbons, carbon dot, and fullerenes are proposed as eco-friendly option. The introduction of carbon nanoparticles in water treatment is able to enhance the properties, such as fouling-resistance, permeability, catalytic activity, and stabilized water chemically and thermally. CNTs have been established as a great solution for water purification and treatment applications in recent times. Activated nano-carbon is widely employed in water purification because of good absorbing capacity and cost-effectiveness. It can absorb contaminants, including organic, inorganic, and biological from the water. Due to this adsorption property of the activated carbon, it plays a vital role in binding chemicals. Activated carbon takes away one or more atoms, molecules, or ions of contamination, when water passes through its surface. Molecular dynamics (MD) simulation facilitates such molecular-scale interaction for further scale-up of the treatment process. All these methods of water purification are gaining huge popularity due to their control over biofouling, superior structural properties, renewable, and eco-friendly nature.

Ultrathin and ultradense aligned carbon nanotube membranes for water purification with enhanced rejection performance