The forward osmosis desalination process usually includes osmotic dilution of draw solution and freshwater production from diluted draw solution. There are two types of forward osmosis desalination based on the different water production methods. One applies heat sinking draw solution that broke down into volatile gases , these gases could also be recycled during the thermal decomposition and generate high osmotic pressure. The other is used as filtration or dilution of water. For instance, the combination of reverse osmosis and forward osmosis could be used for drinking water treatment or brine removal, forward osmosis could also be a fully or partly replacement of ultrafiltration under certain circumstances. Recent studies in materials science also proved that forward osmosis could be used to control drug release in the human body, it could also control the food concertation in the production phase. Regarding the semi-permeable membrane used in Forward osmosis, the tubular membrane is more functional for many reasons. The tubular membrane is one of the membranes that allow solution flows bidirectionally of the membrane, it maintains high hydraulic pressure without deformation due to the self-supported feature, it is also easier to fabricate while retaining high flexibility and density. Although there is a substantial amount of energy required to treat seawater using Forward Osmosis technology, its potential has been demonstrated through bench-scale experiments,fodder system indicating further investigations are needed to evaluate its commercial application. Seawater desalination has provided freshwater for over 6% of the world’s population. One of the commonplace models of forward osmosis seawater treatment is using a hollow fiber membrane. The key parameter in the hollow fiber membrane model is the minimum draw solution flow rate.

When the flow rate increases, the energy requirement increases as well. In an ideal Forward Osmosis process, CDO and CFI should be equal. Figure 2-3 below shows the schematic diagram of the forward osmosis membrane module. To assess the energy consumption in the FO process, the solution concentrations and flow direction of the module should be determined first. The data supports that the energy required for pumping the draw solution is less than that for pumping feed solution. To determine the effects of the direction of hydraulic pressure in the module, different modules with various concentration solutions and flow rates are designed to compare the energy efficiency. In conclusion, the results demonstrate that to reduce the energy consumption of seawater desalination, the FO module need to optimize these diameters. Also, the flow rates and concentrations of draw and feed solutions play a major role in terms of energy efficiency. The module illustrates that when a high flow rate feed solution is on the shell side and a draw solution with a low flow rate is on the lumen side, the system consumes less energy consumption. Another vital implementation of Forward Osmosis is food concentration/enrichment. Multiple studies concluded that FO is efficient when it comes to dewatering for food production.  Compared to the traditional concentration method, such as pressure driven membrane, FO requires less energy and yields less nutrition loss. Nutrition loss refers to the reduction of monomers fructose here. A closed-loop feed solution and draw solution system are built as figure 2-4 below. Garcia-Castello tested two membranes in the system above. A flat sheet of cellulosic membrane and an AG reverse osmosis membrane. AG membrane refers to a certain designation of membrane manufactured by Sterlitech. The result shows that the AG membrane has a higher salt rejection rate. During the procedure, once the water flux reaches a constant value, a feed stock solution is added to the tank to reach the next feed solution concentration.

At the end of the experiment, the highest feed solution is 1.65M sucrose. By comparing performances of different membranes, the AG membranes yield better results when concentrating on sucrose solution due to its tucker support structure. The temperature also has a significant impact on water flux. Usually, higher temperature yields higher water fluxes. Compared to the concentration factor of RO, FO has a better concentration factor of 5 while it requires much less energy.Fertilizer drawn forward osmosis applies the forward osmotic dilution of the fertilizer draw solutions. This technology could be used for direct agricultural irrigation. Fortunately, most of the fertilizers could be used as a draw solution for FDFO. Fertilizer drawn forward osmosis shares the same principle with forward osmosis. Freshwater as feed solution flows through the semi-permeable membrane to the fertilizer draw solution under the natural osmotic pressure. Additional treatments might be required to reach the water quality for different purposes. Regarding the nitrogen removal purpose for this review, operating conditions such as feed solution concentration, feed solution water flow rate, and specific water flux can affect the effectiveness of nitrogen removal. Fertilizer-drawn forward osmosis has common applications in water recycling and fertigation applications. Nanofiltration is a viable solution for diluting the fertilizer draw solution for recycling purposes. Fertilizer-draw forward osmosis technology has used brackish water, brackish groundwater, treated coal mine water, and brine water as the feed solutions. In another word, water that has a relatively lower total dissolved solid could be feed solution for fertilizer drawn forward osmosis. Moreover, fertilizer drawn forward osmosis is also effective on biogas energy production when it is applied to an anaerobic membrane bioreactor as a hybrid process. In conclusion, fertilizer drawn forward osmosis is effective for sustainable agriculture and water reuse. Its considerable recovery rate could be used as the hydroponics part in an anaerobic membrane bioreactor . Due to the scarcity of fresh water in arid areas, hydroponics has been used for vegetable production. In the field of hydroponics, a subset of hydroculture, crops are cultivated in a soilless environment, their roots are exposed to mineral nutrient solutions or fertilizers. Without soil culture, this type of agricultural production precludes certain aspects that are associated with traditional crops production, including soil pollution, lower fertilizer utilization efficiency, or spread of pathogens. This technology also allows the production of crops in arid, infertile, or simply too populated areas. However, economic cost aside, this technique requires both a large amount of fresh water and fertilizers compared with soil-based crops production. This could easily cause detrimental effects to the environment such as water waste and contamination, excessive nitrogen, potassium, and phosphate resulting in eutrophication. To achieve the balance between cost, efficiency, and quality, reverse osmosis and ultrafiltration are more advanced and general approaches compared to biological seawater treatments. In terms of treating seawater, the hydroponic nutrient solutions demonstrate similar performance compared with other aqueous solutions of a lower molecular weight salt. By utilizing certain membrane technologies, treated effluent has reduced the presence of pathogens and remained the ability to be better integrated into the fertigation system for direct application. The potential of the fertilizer drawn forward osmosis process was investigated for brine removal treatment and water reuse through energy-free osmotic dilution of the fertilizer for hydroponics. Nanofiltration is a pressure-driven membrane process, it refers to a special membrane process that removes dissolved solutes. The membrane is with pores ranging from 1 to 10 nanometers, hence the name “nanofiltration”. Nanofiltration uses a similar principle as reverse osmosis, it is a water purification process that requires pressure,fodder system for sale and its membranes are permeable to ions. Nanofiltration is practical in removing organic substances from coagulated surface water, it is also economic and environmentally sustainable. In terms of size and mass of solvents removed by nanofiltration membranes, they usually operate in the range between reverse osmosis and ultrafiltration: removing organic molecules with molecular weights from 200 to 400. Nanofiltration membranes can also effectively remove other pollutants including endotoxin/pyrogen, pesticides, antibiotics, soluble salts, etc.

Depending on the type of salt, it has various removal rates. For salts containing divalent anions, such as magnesium sulfate, the removal rate is around 90% to 98%. However, regarding salts containing monovalent anions, such as sodium chloride or calcium chloride, the removal rate is lower, which is between 20% to 80%. The osmotic pressure across the membrane is typically 50-225 psi. One of the advantages of Nanofiltration is that it uses lower pressure and sustains higher water flux. Plus, it has highly selective rejection properties. Typical applications for nanofiltration membrane systems include the removal of color , total organic carbon from surface water, reduction of total dissolved solids , and the removal of hardness or radium for well water. In 1952, Congress passed the Saline Water Conversion Act, which is aimed at resolving the shortage of freshwater and excessive use of underground water. Two years after the act, the first desalination plant in the United States was built in 1954 at Freeport, Texas. The planet is still operative to date and is undergoing improvement. U.S. Department of Agriculture predicts to supply 10 million gallons of fresh water per day in 2040. The Claude “Bud” Lewis Carlsbad Desalination is the largest desalination plant in the U.S. The plant delivers almost 50 million gallons of fresh water to San Diego County daily. Due to objective conditions, desalination has prevailing existence in regions such as the Middle East, where the largest desalination plant worldwide stands in terms of freshwater production. With 17 reverse osmosis units and 8 multi-stage flashing units, the plant can produce more than 1,400,000 cubic meters of fresh water per day. In 1960, there were only 5 desalination plants in the world. By the mid-1970s, as the conditions of many rivers deteriorated, around 70% of the world’s population could not be guaranteed sanitary and safe freshwater. As a result, water desalination has become a strategic choice commonly adopted by many countries in the world to resolve the shortage of fresh water, its effectiveness and reliability have been widely recognized. The limitation and uneven distribution of freshwater resources have been one of the most prevailing and serious problems faced by people living in arid areas. To reduce its severity, saline water or wastewater desalination has always been a constantly researched and applied solution. In many arid regions, the desalination of seawater is evaluated as a promising solution. Despite that seawater holds around 96.5% of global water resources , the global-scale application of seawater desalination is hindered by the cost, both financially and energy-wise. With the development of energy-saving technologies for seawater desalination, it is viable to use saline, such as seawater and brackish water to produce freshwater for industries and communities. Commonly used methods require water pumping and a considerable amount of energy. As a result, forward osmosis is receiving increasing interest in this field since the FO process requires much less energy. One of the research teams at Monash University in Australia has demonstrated a solar-assisted FO system for saline water desalination using a novel draw agent. The research team led by Huanting Wang and George P. Simon has investigated the potential of a thermoresponsive bilayer hydrogel-driven FO process utilizing solar energy to produce fresh water by treating saline water. This Forward osmosis process is equipped with a new draw agent: a thermo responsive hydrogels bilayer. Compared to one of the most used draw agents , this duallayered hydrogel is made of sodium acrylate and N-isopropyl acrylamide , which induces osmotic pressure differences without the need for regeneration. The thermo responsive hydrogels layers generate high swelling pressure when absorbing water from high-concentrated saline. During testing, researchers used a solution of 2,000 ppm of sodium chloride, which is the standard NaCl concentration for brackish water. Water passes through the semipermeable membrane and is drawn from saline solution to the absorptive layer . The hydrogel can absorb water up to 20 times larger than its regular volume. Next, the thermo responsive hydrogel composed only of NIPAM then absorbs water from the first layer. When the dewater layer is heated to 32 °C, which is the lower critical solution temperature , the gel collapses and squeezed out the absorbed fresh water. Draw agents like ammonium bicarbonate are required to be heated up to 60 °C, then distilled at a lower temperature for regeneration. By focusing the sunlight with a Fresnel lens, the concentrated solar energy can help dewatering flux reach 25 LMH after 10 minutes, which is similar to the water flux of ammonium bicarbonate. 

Furthermore, 15N-Glu-feeding experiments indicated that tea plants can absorb exogenously applied amino acids that can then be used for N assimilation. In addition, we demonstrated that CsLHT1 and CsLHT6 are involved in the uptake of amino acids from the soil in the tea plant.It has been suggested that tea plants grown inorganic tea plantations are subjected to N-deficient conditions due to the absence of inorganic fertilizer. Compared with conventional tea, that produced under organic management systems contains higher levels of catechins that are linked to antioxidant effects of tea infusions. However, organic tea contains lower levels of amino acids that are also important compounds in terms of tea quality. The decay of large amounts of pruned tea shoots may contribute significantly to soil amino-acid levels inorganic tea plantations; the decomposition of such organic matter and nutrient recycling depends largely on soil fungi. Interestingly, the long-term application of high amounts of N fertilizer was found to reduce soil fungal diversity in tea plantations. This likely could account for why we observed higher amino-acid contents in the organic tea plantation compared with the conventional tea plantation . This implies a more important role for soil amino acids in tea plant grown inorganic tea plantations.It has been reported that, in addition to inorganic N, amino acids can support tree growth. As a perennial evergreen tree species, the tea plant can also use organic fertilizer. However, the role of soil amino acids in tea plant growth and metabolism has not yet been investigated. In this study, we observed that the tea plant could take up 15N-Glu, and Glu feeding increased the aminoacid contents in the roots . This revealed that tea plants can take up amino acids from the soil for use in the synthesis of other amino acids. In our study, nine amino acids were detected in the soil of an organic tea plantation, and the utilization of exogenous Glu was analyzed in detail. In future studies,hydroponic nft it will be important to test the roles of various mixtures of amino acids for use as fertilizers for the growth and metabolism of the tea plant.

The molecular mechanism underlying the uptake of amino acids from the soil by trees has not been thoroughly studied. In this study, we identified seven CsLHTs that were grouped into two clusters, which was consistent with LHTs in Arabidopsis . CsLHT1 and CsLTH6 in cluster I have amino-acid transport activity , which is also consistent with AtLHT1 and AtLHT6. Moreover, these two genes were highly expressed in the roots and both encode plasma membrane-localized proteins . These findings support the hypothesis that CsLHT1 and CsLHT6 play important roles in amino-acid uptake from the soil . However, the members of cluster II, CsLHT2, CsLHT3, CsLHT4, CsLHT5, and CsLHT7, did not display amino-acid transport activity . Interestingly, except for AtLHT1 and AtLHT6, there are no other AtLHTs being shown to transport amino acids. It is possible that cluster II LHTs are involved in the transport of metabolites other than amino acids. For example, AtLHT2 was recently shown to transport 1-aminocyclopropane-1- carboxylic acid, a bio-synthetic precursor of ethylene, in Arabidopsis.LHT1 has been thoroughly characterized as a high affinity-amino-acid transporter and has a major role in the uptake of amino acids from the soil in both Arabidopsis and rice. In contrast, there is only one report on the function of AtLHT6; it is highly expressed in the roots, and the atlht6 mutant presented reduced aminoacid uptake from media when supplied with a high amount of amino acids. Although the authors did not characterize the amino-acid transport kinetics for AtLHT6, their results are consistent with this protein being a low-affinity-amino-acid transporter. In the present study, we characterized CsLHT1 to be a high-affinity amino-acid transporter , with a capacity to transport a broad spectrum of amino acids . By contrast, CsLHT6 exhibited a much lower affinity for 15N-Glu, and it also displayed higher substrate specificity. Considering that amino-acid concentrations in the soil of tea plantations are low , CsLHT1 may play a more important function than CsLHT6 in the uptake of amino acids from the soil into tea plants. However, in soils, amino-acid contents could be much higher, locally, particularly in the vicinity of decomposing animal or vegetable matter. In this situation, CsLHT6 may play an important role in the uptake of amino acids. In addition,CsLHT6 is also highly expressed in the major veins of mature leaves , suggesting a role for CsLHT6 in amino-acid transport within these tea leaves.

Given that protocols for the efficient production of transgenic tea cultivars are lacking, CsLHT1 and CsLHT6 expression cannot be modulated by either over expression or CRISPR/Cas9 gene editing. However, in China, there is an abundance of tea plant germplasm resources. CsLHT1 and CsLHT6 are potential gene markers for selecting germplasms that can efficiently take up amino acids. Moreover, germplasms with high CsLHT1 or CsLHT6 expression can be used as root stocks for grafting with elite cultivars to improve the ability of these cultivars to take up amino acids from the soil. Alternatively, these germplasms can be utilized through gene introgression. These grafted lines that can efficiently take up amino acids or novel cultivars should be better suited for use inorganic tea plantations than in conventional tea plantations.One of the core goals of sustainability science is understanding how practitioners make decisions about managing social-ecological systems . In the context of sustainable agriculture, an important research objective is quantifying the economic, environmental, and social outcomes of different farm management practices . However, it is equally important to understand how farmers conceptualize the idea of sustainability and translate it into farm management decisions. The innumerable and often vague definitions of sustainable agriculture make this a challenging task, and fuel the debate about linking sustainability knowledge to action. This debate will remain largely academic without empirical analysis of how farmers think about sustainability in real-world management contexts. These questions are not only relevant to agriculture, but also to all social-ecological systems and the knowledge networks that are in place to support decision making. This paper addresses these issues by analyzing farmer “mental models” of sustainable agriculture. Mental models are empirical representations of an individual’s or group’s internally held understanding of their external world . Mental models reflect the cognitive process by which farmer views about sustainable agriculture are translated into farm management decisions and practice adoption. Our mental models were constructed from content coding of farmers’ written definitions of sustainable agriculture, and were analyzed using network methods to understand the relational nature of different concepts making up a mental model.

We test three hypotheses about mental models of sustainable agriculture. First, mental models are hierarchically structured networks, with abstract goals of sustainability more central in the mental model, which are linked to peripheral concrete strategies from which practitioners select to attain the goals. Second, goals are more likely to be universal across geographies, whereas strategies tend to be adapted to the specific context of different social-ecological systems. Third, practitioners who subscribe to central concepts in the mental model will more frequently exhibit sustainability-related behaviors, including participation in extension activities and adoption of sustainable practices. Our mental model data were drawn from farmers in three major American viticultural areas in California: Central Coast, Lodi, and Napa Valley. California viticulture is well suited for studying sustainability. Local extension programs have used the concept of sustainability since the 1990s ,hydroponic channel and farmer participation in sustainability programs is strong . Furthermore, viticulture is geographically entrenched , with viticultural areas established on the basis of their distinct biophysical and social characteristics . Hence, we expect wine grape growers to have well-developed mental models of sustainability, with geographic variation reflecting social-ecological context.or group’s internally held understanding of the external world . Group mental models, which are the focus of this paper, represent the collective knowledge and understanding of a particular domain held by a specific population of individuals. Mental models are an empirical snapshot of the cognitive process that underpins human decision making and behavior. Mental models complement more traditional approaches to understanding environmental behavior by highlighting the interdependent relationships among attitudes, norms, values, and beliefs . For example, the Values-Beliefs-Norms model of environmental behavior hypothesizes a causal chain running from broad ecological values, to beliefs about environmental issues, to more specific behavioral norms. The network approach used here shows how these types of more general and specific concepts are linked together in a hierarchical and associative structure. Mental models have evolved into an important area of research in environmental policy, risk perception, and decision making . A growing number of researchers are using mental models to better understand decision making in the context of social-ecological systems . Two approaches that are especially relevant to this paper are Actors, Resources, Dynamics, and Interactions and Consensus Analysis . The ARDI approach uses participatory research methods to construct a group mental model of the interactions among stakeholders, resources, and ecological processes . The final product is a graphic conceptualization of how the group perceives the social-ecological system, its components, and their place in it, which can be used to inform management strategies. The CA approach relies on similar data-collection techniques to elicit a group mental model that captures stakeholders’ beliefs and values pertaining to how the social-ecological system should be managed and for what purpose . The mental models are then analyzed using quantitative methods to assess agreement among individuals and identify points for consensus. Along with addressing research questions about practitioner knowledge and decision making, both approaches have been used to facilitate multi-stake holder management of social-ecological systems . This paper conceptualizes group mental models as “concept networks” comprised of nodes representing unique concepts and ties representing associations among concepts.The concept network approach is different from ARDI and CA in that network analysis methods are used to analyze the structure of mental models and measure the importance of individual concepts based on their position in the concept network. This approach follows from Carley’s work , which is founded in the theoretical argument that human cognition operates in an associative manner .

When a given concept is presented to the individual, memory is searched for that concept, ties between the concept and associated concepts are activated, and associated concepts are retrieved. The more associations a given concept has, the more likely the concept is to be recalled. Highly connected concepts serve as cognitive entry points for accessing a constellation of associated ideas. We elicited our mental models from written text of farmers’ definitions of sustainable agriculture, and follow Carley in arguing that written language can be taken as a symbolic expression of human knowledge . It is important to note that our mental models deviate from Carley’s in that the associations among concepts are nondirectional and do not represent causality between concepts. Ties in our concept network represent concept co-occurrence, where two concepts occurred together in a single definition of sustainable agriculture. See Methods for more details.Hypothesis 1 is that mental models are hierarchically structured, with abstract concepts constraining the cognitive associations among more concrete concepts. For example, practitioners who define sustainability primarily as environmental responsibility versus economic viability may evaluate the benefits and costs of management practices with different criteria. This perspective is related to models of political belief systems where specific attitudes on public policy issues are predicted by general beliefs about policies and core values . Construal-level theory also suggests that hierarchical belief-systems contain abstract, superordinate goals related to subordinate beliefs about actions needed to achieve them . The hierarchical structure reflects a basic principle of cognitive efficiency in taxonomic categorization , where more abstract concepts provide cognitive shortcuts to retrieve specific linked attributes . The concepts making up mental models of sustainability can be divided into two basic types, each with different levels of abstraction: goals and strategies . Abstract goals are desirable properties, attributes, and characteristics of a sustainable system to be realized. Examples taken from this study include environmental responsibility, economic viability of the farm enterprise, continuation into the future, or soil health and fertility. Strategies are more concrete and include practices or approaches that are thought to contribute to the realization of abstract goals.

However, as recently reported by Ushikubo, nanobubbles of inert gases do possess similar lifetimes and are formed from helium, neon, and argon, and since the only intermolecular forces of note they experience are van der Waal’s forces of attraction, Lifshitz forces and dipole-dipole interactions, it can be assumed that these are also strong enough, and the gases sufficiently inert, for the same mechanism as well as the steric hindrance of the hydroxide ions to apply to the same case. Considering the formation of a 1 μm micro-bubble which eventually shrinks into a nanobubble, the number of ions available to it for stabilisation from the water it displaces upon formation, at pH 7, is approximately 33 ions, which if all the ions were adsorbed, does not agree with the zeta potentials reported by Takahashi et. al. for micro-bubbles of comparable size, which by equation is given to be approximately 495 ions. It follows that the ions which are adsorbed diffuse toward the nanobubble surface from the surrounding bulk fluid, which can explain the apparent generation of free radicals observed by Takahashi et. al., since there is now a minuscule concentration difference present to drive the diffusion. The availability of hydroxide ions also depends on the pH, and at pH 7 it is thus possible for stable nanobubbles to form as is reported by Ushikubo, as well providing a mathematical treatment for their stabilization and the calculation of their surface charge. At lower pH, in the absence of other ions, the concentration of stabilized ions would be lower due to the lower availability of hydroxide ions and the increased time needed for them to diffuse to the surface of the nanobubble, allowing it more time to shrink. The dependence of the size of the bulk nanobubble on external pressure is given by equation . Of the external pressure, the proportion of the atmospheric pressure to the total value of the actual pressure, the rest being the pressure exerted by the fluid. However, the major component to the force contributing to the shrinkage of the nanobubble is the surface tension,dutch buckets system which also increase with the size of the nanobubble. Thus, for higher external pressures and given that a limited amount of gas is dissolved in the fluid, the equation gives a trend of increasing nanobubble size with increasing external pressure.

However, due to the limited amount of gas available, it is expected that the number of nanobubbles formed, i.e. concentration will decrease, while still giving higher particle size. This is confirmed by Tuziuti and co-workers through their observations of air nanobubbles in water. The temperature term appears only in the term that describes the internal pressure, causing a linear increase with temperature, not taking into account the increase in molecular motion due to heat, as well the increased energy of the surface ions. Thus, it also shows that the internal pressure will increase with the increase in temperature. This will, in turn, cause a reduction in the radius if all other terms are kept the same. Thus, we can say that given a limited amount of gas dissolved in the solvent, an increase in temperature will give smaller nanobubbles, but will also cause an increase in concentration of the nanobubbles in the solvent. It is also possible that zeta potentials may decrease, as thermally agitated hydroxide ions may be more susceptible to de-adsorption and may return to solution more easily. Conversely, as lower temperatures, larger bubbles may form, especially by the method of collapsing micro-bubbles, and larger numbers of hydroxide ions may be adsorbed on the surface of the nanobubble, giving longer lifetimes. Bulk nanobubbles are, in essence, minuscule voids of gas carried in a fluid medium, with the ability to carry objects of the appropriate nature, that is, positively charged for a length of time that is significant, if the nanobubble is left alone, yet is also controllable, since the bubbles can be made to collapse with ultrasonic vibration, or magnetic fields. The applications, then, seem to be limited only by how we can manipulate and design systems that make use of these properties for new technology in several fields. As mentioned before, thus far technology has made use of the uncontrolled collapse and generation of bulk nanobubbles, in the fields of hydroponics, pisciculture, shrimp breeding, and algal growth, while the property of emission of hydroxide ions during collapse has been applied to wastewater treatment.

Here and there, there are indications of greater possibilities, as evidenced by research into their ability to remove microbial films from metals, to remove calcium carbonate and ferrous deposits from corroded metal, the use of hydrogen nanobubbles in gasoline to improve fuel efficiency, and the potential application for to serve as nucleation sites for crystals of dissolved salts. The following sections elaborate on further applications which are possible in the near future. Proton exchange membrane fuel cells, are finding wide application in several fields due to the ease of their deployment, the low start-up times, and the convenience of their size and operating temperatures . However, significant limitations exist for their wider application, which can broadly be classed under the headings of catalysis, ohmic losses, activation losses, and mass transfer losses. The first of these is due to the rate of catalysis of the splitting of hydrogen, which cannot be pushed beyond a certain limit due to the constraints of temperature. But the larger issue is the cost of the catalyst itself, which is a combination of platinum nanoparticles and graphite powder, which provides the electrical conductivity. The inclusion of platinum presents a significant cost disadvantage, and while efforts are ongoing to reduce or replace platinum as a catalyst, these are still experimental and much research is ongoing in this field. The second limitation is due to ohmic losses, which accumulate due the proton exchange membranes, also termed the electrolyte, and can only be reduced by reducing the thickness of the membrane. Current popularly used membranes are usually made of Nafion, a sulphonate-grafted derivative of polytetrafluoroethylene marketed by DuPont, but experimental membranes include the use of graphene, aromatic polymers, and other similar materials which possess a high selective conductivity toward protons [ref]. However, beyond a certain thickness the membranes are unable to mechanically support themselves, and often mechanical failure of the membrane will cause a break in operations.The third limitation is due to the start-up conditions of the fuel cell, and are a matter of the mechanics of operation of the fuel cell itself. The last limitation is due to the transport of hydrogen and oxygen to the triple phase boundaries around the catalyst and the transport of water away from them, and is a significant concern for the operation and efficiency of PEMFCs.

However, the current PEMFCs depend on gaseous hydrogen and oxygen, which are released from a compressed source and derived from air respectively. This necessitates a mechanically strong membrane and construction to resist the operating pressures. However, the inclusion of the gas as a nanobubble dissolved in water presents new possibilities, used in combination with microfluidic technology. It becomes possible to also replace both membranes and catalysts with materials that have been hitherto discarded fro being too mechanically weak, such as graphene, and the possibility of using graphene as a combined catalyst and proton exchange membrane, as nanobubbles of hydrogen and air, dissolved in water, to act as the reservoirs for the fuel and oxidant. Such as system would operate on the basis that nanobubbles are negatively charged,dutch buckets and would hence be attracted to the graphene through which current would be passed in order to activate the process. Air and hydrogen nanobubbles would be separated by the graphene membrane, and be adsorbed to opposite sides of it. The graphene membrane would also have a potential difference applied across it in the plane of the graphene layer. This would, in turn, permit the hydrogen to be catalyzed to protons [ref], and hence be conducted across the graphene [ref], allowing it react with the oxygen to form more water, which would be carriedaway with the flow. Microfluidic bipolar plates would enable the construction of such a device, and such fuel cells could become the future source of energy for several applications. The advantages of such a system would be numerous. Firstly, graphene is far cheaper than platinum, and can be used as a catalyst of almost comparable quality, in addition to also being the conductor for the removal of electrons released during catalysis. Secondly, the thickness of a graphene sheet is in the range of nanometers, which would mean that ohmic losses would, quite possibly, be nearly eliminated. Additionally, due to the flow of water as a solvent, the losses due to the mass transport of water away from the triple phase boundary, and that due to transport of hydrogen and oxygen to the triple phase boundary, would also be significantly reduced. The last, but not the least advantage would be the reduction in the size of one fuel cell. The voltage generated by fuel cells is independent of the size they are, which would mean that a much larger number of fuel cells can fit in the same area as currently applied fuel cells, which will provide a much larger voltage. Polymeric foams have been a staple of several products since their inception, and pore size is one of the key properties of the foam that determines its performance. In general, the larger the pore size, and more the pore count, the lighter the foam is. However, both can come at the cost of reduced wall thickness of the pores, which makes the whole foam less able to deform elastically and more susceptible to tearing and heat damage, while substantially reducing fatigue resistance and creep resistance. In general, therefore, the standard practice is to achieve a balance between pore size and pore count, measured in pores per volume, so as to achieve the desired properties. However, the voids rarely go below the size of one micron, and this in turn places a limit on the number of pores per volume, thus limiting the number of pores it is possible to introduce, as well as the amount of gas that can be introduced into the foam system. While there are several methods of foam manufacturing, including in-situ foam molding, and pre-mixed foam molding, none of these offer pore sizes lower than a few microns reliably and controllably. Furthermore, many of the polymers used in the construction of these foams can either be dispersed or dissolved into water, such as polyamides, polystyrene, polyesters, and polyurethanes. This offers a unique opportunity to introduce nanobubbles into the system, by first dispersing the gas into solution by means of a micro-bubble generator, and then dispersing the polymer, either in dilute solution form or as a monomer, and then either coagulating the dispersion, or polymerizing it, or cross linking the chains in solution to create a foam with pore sizes in the nanometer range. At standard pore counts, this would offer a very high wall thickness, which necessitates a large increase in the concentration of nanobubbles which should be introduced to return wall thickness to the same levels as a microporous foam. The pores can then be opened, if so desired, by a microneedle array, or by other methods such as guided bursts of ultrasound, creating such structures as channels only nanometers in width through the foam, and presenting new possibilities for water filtration and purification, as well as for testing and for further application in water quality testing and other similar applications. As of now, there are several applications for such open-celled foams, such as the production of nanopure water, which are expensive due to the filtration equipment needed. Thus, opencelled polymeric foams have direct application to these areas, where as closed-celled foams are potentially lighter and stronger, as well as tougher than other foams with larger pores and lower pore counts. Thus, it is reasonable to suggest that nanobubble technology will find widespread use in this particular application, especially when the cost factor is taken into account.