Epoch-Making Discovery for CO 2 Characteristics: “Pseudo Osmosis” in the Gas Phase

Recently, unprecedented torrential rains have deluged the globe, resulting in disastrous oods. These disasters were caused by climate changes because of an increase in carbon dioxide (CO 2 ) concentration in the atmosphere since the industrial revolution. Therefore, atmospheric accumulation of CO 2 should be reduced to avoid a future climate crisis. Many methods to x CO 2 have been developed, but a practical method has not been established, except for the method using amines based on moderate plant constructions. However, the membrane method has not yet been established because of the conicting relationship between penetrability and specicity, although membrane technology can be used for CO 2 separation. Epoch-making discoveries for CO 2 characteristics have been presented as follows: 1) the high penetrability of CO 2 in the gas phase caused “pursued osmosis” against polymer elasticity; 2) highly penetrable CO 2 passed through polymer membranes such as authentic polymers and natural cellulose, whereas neither O 2 nor N 2 penetrates these polymers examined; 3) CO 2 is absorbed by plastics; 4) H 2 and CH 4 gases penetrate through polymer membranes, but their penetration was completely blocked in the presence of water; and 5) using a polytunnel made of polymer sheets (an articial forest or positive green house), which allows CO 2 penetration, instead of hard chamber, steel, or plastic could be cost effective. Therefore, polymer membranes could be practically and economically useful for CO 2 separation from the exhaust gas and atmosphere.


Background
According to recent news, we do not doubt that climate change has progressed throughout the globe.
Torrential rains caused severe ooding in Europe. Recently, in Japan, the meteorological agency has issued several warnings about severe torrential rains that strike once every 50 or 100 years, whereas severe debris ows attacked mountain areas every year. Based on scienti c evidence for the relationship between global temperature, atmospheric CO 2 increases and hydroclimate changes 1-3 , the intergovernmental panel on climate change concluded on August 9th, 2021, that climate change has been caused by human activities that have produced carbon dioxide (CO 2 ) since the industrial revolution 4 .
None denying that atmospheric CO 2 concentrations on Earth have increased since the industrial revolution began ~200 years ago, with the invention of steam engines using fossil coal as fuel and internal combustion engines using oil and our present developed civilization has owed to these technical inventions. However, we have paid little attention to the effect of increased atmospheric CO 2 concentration for a long time, while the young generation represented by a Swedish high school student, Greta Thunberg, led to climate change activities "Friday for Future" events as global movements.
Unfortunately, this movement would not reach all people on the planet. One of the reasons is our high tolerance of CO 2 concentration in our daily lives. The atmospheric CO 2 concentration in a house room is 400 ppm, but it easily doubles in the presence of several persons in the same room without ventilation.
Even under high CO 2 concentrations of ~1,000 ppm for a certain time in a con ned space, our lives do not show any abnormal symptoms. Eventually, many people would be insensitive to a small increase in atmospheric CO 2 concentration, although this small change can be induced climate change crises on Earth.
The greenhouse effect of methane is much signi cant than that of CO 2 , and climate change has resulted in thawing permafrost followed by methane emission in Siberia [5][6][7] . In addition, as temperature rise activates microorganisms' activity, methane emission might be naturally accelerated without human activities 8- 10 . Indeed, methane has been currently produced from biomass materials by microorganisms 11,12 .
The 7th G summit was held in Cornwall, England, on June 12-13, 2021, with climate change being one of the main themes. Electric vehicles have been developed and used instead of ordinary automobiles using gasoline, to reduce atmospheric CO 2 concentrations. While electric vehicles do not exhaust CO 2 directly into the atmosphere, the current electricity generated by renewable energy is insu cient to power electric vehicles. However, hydrogen vehicles have been developed, although the cost is expensive. Indeed, hydrogen usage does not exhaust CO 2 ; however, its production process using brown coal and hightemperature water produces a signi cant amount of CO 2, except for the electrolysis of water. CO 2 can be captured from the atmosphere or from ue gas via several techniques, including absorption 13 , adsorption [14][15][16][17][18][19][20] , and membrane gas separation 15,21 . Absorption with amines is currently the dominant technology, while membrane and adsorption processes are still in the developmental stages with the construction of primary pilot plants anticipated in the future. Synthetic membranes are useful for desalination, dialysis, sterile ltration, food processing, dehydration of air, and other industrial, medical, and environmental applications because of their energy requirements, compact design, and mechanical simplicity. In addition, biopolymer cellulose membrane can be used instead of synthetic membranes because they have similar characteristics [22][23][24] . Recently, we developed a novel method for CO 2 xation and storage 25 . This method is based on simple chemical reactions involving NaOH and CaCl 2 . Using low concentrations of these chemicals prevented the formation of Ca (OH) 2 in the absence of CO 2, but resulted in CaCO 3 formation in the presence of CO 2 bubbling. Note that the products of our developed method are CaCO 3 and NaCl, which naturally exist as coral or limestone. Moreover, CO 2 xation could be achieved without any external addition of chemicals using seawater instead of NaCl electrolysis and CaCl 2 . We proposed a large chamber comprising spray nozzles to x CO 2 e ciently by mists or droplets of the NaOH solution 25 . Using a polytunnel made of polymer sheets (an arti cial forest), which allows CO 2 penetration, instead of the chamber could be cost effective. CO 2 storage, geo-sequestration by injecting CO 2 into underground geological formations, such as oil elds, gas elds, and saline formations, has been suggested 26,27 , although these systems are still projects for the future. However, the proposed method can achieve both CO 2 xation and storage 25 simultaneously. This study contributes membrane technology to separate CO 2 from other gases such as O 2 , N 2 , H 2 , and CH 4 .
Methods.  To measure the CO 2 emitted by plastic bottles, sheets, and rods, they were placed in 450 ml glass bottles which were lled with cooling-carbonated beverages, CO 2 saturated water, or CO 2 gas, under various conditions. After washing, plastic materials and a bottle inside were left in the room or the temperaturecontrolled box. CO 2 analyzers, CX-6000 (for high concentration), Riken Keiki, Co., Ltd., (Tokyo, Japan), and XP-3140 (for low concentration), Cosmo, Co., Ltd., (Tokyo, Japan), were used to measure the concentration of CO 2 released from the plastic materials. In some experiments, CO 2 concentrations inside bags were directly analyzed.

Gas volume measurements.
Bags or swelled wraps were sunken into water containers and the volumes of over owed water were measured to estimate their volume. In some experiments, CO 2 gas volume in the graduated cylinder was directly observed, and the CO 2 volume in the experiments using syringes was also directly observed. CO 2 saturated water.
Water (1 L) was mixed with CO 2 gas (1 L) in a PET bottle (2 L) and shacked vigorously by hand for 30 s.
The bottle was completely dented after the water and CO 2 were mixed. After opening the bottle, CO 2 was babbled into the CO 2 saturated water.

Statistical analysis.
Statistic calculations via the t-test were performed using Windows 10. Values of p < 0.05 and p < 0.01 were considered signi cant and highly signi cant, respectively.

CO 2 absorption in plastics.
Polyethylene terephthalate (PET) bottles are commonly used to store liquids, such as water, carbonated beverages, seasonings, and liqueurs, in daily life. In this study, we found that the empty PET bottle that was used for cooling-carbonated beverages, such as Coca-Cola, remained a moderate amount of CO 2 inside the bottle. CO 2 was removed from the bottle after washing the empty bottle three times with fresh water (Additional Data Figure 1a). However, after leaving the washed bottle in the room, CO 2 which was released from the plastic was signi cantly detected (Additional Data Figure 1b), and CO 2 release was much faster at 50°C than at 20°C. CO 2 release from the plastic bottles made of high-density polyethylene (HDPE), low-density polyethylene (LDPE), polycarbonate, and polytetra uoroethylene (Te on), were examined. These plastic bottles absorbed CO 2 followed by CO 2 release, which was pretreated with a carbonated beverage or CO 2 gas, (Additional Data Figure 2a). Although carbonated beverages containing various chemical substances, except for CO 2 showed the same effect as CO 2 gas in the pretreatment. Only PC showed much higher CO 2 absorption with CO 2 gas than that with a carbonated beverage. Other plastic materials, such as polyethylene mesh, nylon mesh, acrylic rods, and natural gum plates, were examined. These materials also absorbed and emitted CO 2 (Additional Data Figure 2b). Furthermore, high CO 2 absorption and release were observed with a grooved natural gum plate, and very high CO 2 absorption was observed in it treated with CO 2 gas. CO 2 release through the latex membrane.
The medical glove was lled and expanded with CO 2 gas and then left in the room. The volume of the expanded latex glove time-dependent decreased, reaching half of its initial volume after 2 h (Fig. 1a) and 10% after 6 h. This demonstrates that CO 2 penetrates through the latex membrane. Using cellulose tube (Visking tube), CO 2 release through a cellulose membrane was considerably faster than that through a latex membrane (Fig. 1b). Furthermore, different thicknesses of polyethylene bags are used. CO 2 release was signi cantly faster through a thin polyethylene membrane bag than through a thick membrane (Fig. 1c).
Volume increase by CO 2 absorption.
Instead of plastic sheets, two types of babble wraps were used: a single layer babble wrap with babbles attached to a single polyethylene lm (babble wrap I), and another with babble was sandwiched between two polyethylene lms (babble wrap II). Before CO 2 treatment, the babble wraps were easily inserted into glass bottles, but the babble wraps treated with CO 2 resisted being removed from the glass bottle. This means that the volume of the babble wraps increased with CO 2 treatment. Indeed, the volume of the babble wraps increased signi cantly (Fig. 2, upper panel). However, when the swelled babble wraps were left in the room, the swollen condition returned to its original volume.
When a latex balloon in ated with air and sealed was left in a glass bottle lled with 80% CO 2 for 4 h, it swelled (Fig. 2, lower panel, a and b). However, the empty balloon without air did not swell even in the presence of high CO 2 concentrations. Using a latex glove, the consistent result was obtained (Fig. 2, lower panel, c and d).
CO 2 absorption at low concentrations.
To investigate whether CO 2 absorption occurs at low CO 2 concentrations, polyethylene bags pre lled with air without CO 2 were left in a room. Then, CO 2 concentration in the bags was measured at different time periods. CO 2 concentration equilibrium between the inside and outside bags was achieved after 6 h.
When different thicknesses of polyethylene bags were examined, CO 2 was absorbed time-dependently ( Fig. 3), and CO 2 absorption depended on the thickness. The polyurethane balloon and cellulose tube produced consistent results (Visking tube).

CO 2 absorption and release.
When the knotted Visking tube with air inside was left in the glass bottle containing 100% CO 2 , the tubing swelled and its volume increased to ~2.5 times. When the Visking tube was left in the room, the volume returned to its original volume. Following that, the original volume was maintained (Fig. 4a). The same phenomenon was observed with a latex balloon (Fig. 4b). These results show that CO 2 diffusion occurred in the presence of plastic elasticity because of a ow from high concentration to low concentration. However, the fact that the bag volume returned to the original volume and was maintained after that shows the simultaneously contained air did not diffuse outside the cellulose tube (Visking tube).
CO 2 penetration through a membrane in water.
Latex balloons were in ated with CO 2 gas and then immersed into water. CO 2 gas penetrated through a latex membrane and diffused into the water along with decreasing their volumes (Fig. 5a). After 4 h, the volume reduced to ~40% of the initial state.
Polyethylene bag containing CO 2 saturated water was inserted into a glass bottle of water and then left in a room. The same amount of CO 2 was identi ed in both phases of the membrane, inside and outside (Fig. 5b). Thus, CaCO 3 precipitation based on a chemical reaction revealed that CO 2 that was contained in the saturated water penetrated through a polyethylene membrane into the fresh water.
CO 2 absorption into water.
The graduated glass or plastic cylinder containing CO 2 gas was immersed in water stored in a water bath or refrigerator. Three types of water were prepared as follows. Milli-Q water (pure water), city water, and seawater. CO 2 gas volume was measured at several periods. Among the three water samples, CO 2 gas volume in the graduated cylinders decreased time-dependently (Figs. 6a and 6b). CO 2 gas absorption into the seawater was signi cantly slower than the other two types of water. This salt effect on CO 2 absorption into water depended on the temperature, and the absorption was signi cantly reduced at 55°C. This temperature effect on CO 2 absorption in water differs from the previously reported result 28 .
However, using a 12-ml plastic syringe instead of the cylinder, CO 2 gas absorption increased drastically at 4°C compared to 55°C (Fig. 6c). The latter result is consistent with the currently reported result 28 .
H 2 and CH 4 penetration through a polymer membrane.
Polyethylene, polyurethane, and cellulose membrane bags were used. The polyurethane membrane passed H 2 gas more e ciently than the other membranes, but their membrane thicknesses differed (Additional Data Figure 3a). When CH 4 gas was used instead of H 2 gas, similar results as H 2 gas were observed, and CH 4 gas released from these three membrane bags was slower than that of H 2 gas. When these three types of polymer membrane bags containing H 2 or CH 4 gases were immersed in water, H 2 and CH 4 gases were unable to pass through the polymer membranes. However, latex balloons were expanded with CO 2 and then immersed in water. The balloon volume reduced time-dependently (Additional Data Figure 3a). This result shows that CO 2 can penetrate through the rubber membrane in the presence of clear water. Thus, the combination of polymer membranes and water can separate CO 2 from H 2 or CH 4 .
To my knowledge, there is no perfect system which can separate CO 2 from these gases, although some experiments have been performed 29,30 .

CO 2 absorption and release by plants through PE bags.
A top part of Taiwan pineapple with moderate number of leaves has been immersed into city water contained in a glass bottle for almost half a year. During this period, the number of leaves increased along with root development (Additional Data 4a). To determine whether CO 2 metabolisms can be detected, the pineapple planter was inserted into a PE bag of 0.005-mm thickness for 4 h in the room (Additional Data Figure 4b). CO 2 concentration was reduced to 200 ppm from ~500 ppm. Conversely, its CO 2 concentration increased to almost 2,000 ppm for 4 h in a corrugated card-box.
Similarly, cyclamens planted on the soil were used instead of pineapple, because cyclamen planters are commercially available (Additional Figure 4c). When cyclamen planters were left in the corrugated cardbox, CO 2 signi cantly increased in the PE bag after 1 h, reaching a plateau level of ~1800 ppm (Fig. 7a).
Contrary, CO 2 concentration reduced by almost 200 ppm after 2 h in the presence of light.
Cut cycad leaves were used instead of a whole plant (Additional Data Figure 4d). The consistent CO 2 metabolisms were obtained as observed by cyclamens (Fig. 7b). Using cut small camellia branches and "yatsude" plant leaves (Additional Data Figure 4d), similar CO 2 absorption and release were observed with and without light, respectively. However, the cut leafstalk of "yatsude" plant did not absorb CO 2 in the presence of light (data not shown).
In the system which uses PE bags of 0.005-mm thickness (25 × 34 cm), the plateau CO 2 concentrations in the presence of whole plants or leaves may converge at ~200 ppm and 2,000 ppm with and without light, respectively. These values are based on the balance between CO 2 metabolisms of plants and CO 2 penetrability through PE membranes.

Discussion
Generally, plants absorb CO 2 from the atmosphere and release O 2 during photosynthesis by chlorophyll using CO 2 , H 2 O, and light. However, all organisms release CO 2 to maintain their lives, which require energy daily, and this metabolism is independent of light. Therefore, when the CO 2 production exceeds CO 2 absorption in plants, the organisms are CO 2 producers. Although it is assumed that tropical forests, especially the Amazon, is the main CO 2 absorber on Earth, because of large forest res and re agriculture emitting large amounts of CO 2 , it changed to a CO 2 producer in the total CO 2 balance [31][32][33] .
Note that it is easy to destruct forests but di cult to reconstruct the original forest, which takes a long time.
Leo Baekeland in 1907 invented Bakelite, the world's rst fully synthetic plastic Presently, different types of plastics are produced, such as polyethylene, which is widely used in product packing and in making plastic bottles, sheets, and plates, polyvinyl chloride, which is used in construction and pipes because of its strength and durability. Because plastics are not damaged by ethylene oxide or γ-irradiation sterilization, they have been commonly used as medical products, such as gloves, clothes, goggles, and blood bags, although some plastics are heat unstable. These products are designed to protect the human body not only from bacteria but also from viruses, and they are bene cial to medical staff because of their lightweight. Furthermore, thin plastic bags are used to prevent food not only from bacterial contaminations but also from oxidation.  42 . This shows that the CO 2 penetration is independent of molecular size because CO 2 molecular weight is the largest among the gases examined. The separation of CO 2 from O 2 , N 2, and H 2 are not due to the molecular sieve effect. This means that the highest CO 2 penetrability is one of the CO 2 characteristics, although this characteristic could not be evaluated in this study. However, this CO 2 penetrability can be used to separate CO 2 from the other gases using simple plastic membranes, which are inexpensive. This study shows that many plastic membranes, such as polyethylene, polyurethane, latex, natural gum, and cellulose membranes have high penetrability for CO 2 . Furthermore, the plastic samples whose thickness was 0.005-0.02 mm completely blocked O 2 and N 2 penetration (Fig. 4), and the cooperation of plastic membranes with H 2 O also completely blocked the H 2 and CH 4 penetration (Additional Data Fig. 4a). Based on the current results, it can be possible to separate CO 2 from other gases such as O 2 , N 2 , H 2, and CH 4 , using plastic membranes and H 2 O. However, many membrane scientists are suffering from the relationship between high penetrability and low speci city to select plastic membranes 38-42 . CO 2 dissolves into H 2 O, and its solubility in H 2 O is 0.145 g/dl at 100 hp, 25°C. When CO 2 gas was vigorously mixed with H 2 O by hand for 30 s, the PET bottle was completely dented with small gas space.
In addition, it was reported that CO 2 solubility in H 2 O increased at low temperatures because CO 2 diffusion reduced at low temperatures 28 . In this study, this theory was con rmed using a plastic syringe (Fig. 6c), whereas, in a different system using a graduated cylinder sunken upside down inside water, CO 2 solubility to H 2 O decreased at 4°C compared with 55°C (Fig. 6c). This difference in CO 2 solubility in H 2 O is based on differences in the area where CO 2 gas contacts H 2 O. When the global phenomena obey the syringe model used in this study, CO 2 from the sea might increase along with the global temperature. This means that increasing global temperature may accelerate CO 2 accumulation in the atmosphere, even in the absence of human CO 2 production. Therefore, the release of CO 2 from the sea, which contains a large CO 2 reserve, may cause climate changes.
In this study, not only the membrane but also the other polymer membranes had extremely high CO 2 penetrability and the same results were reported by the other groups [38][39][40][41][42] . Furthermore, the other gases Furthermore, other gases such as H 2 and CH 4 molecules whose molecular masses are much less than that of CO 2 can penetrate polymer membranes including cellulose membranes based on membrane characteristics. However, in the presence of H 2 O, the penetration of H 2 and CH 4 was completely blocked. Except for mycoplasma, bacteria have a cell wall that is composed of polysaccharides or peptidoglycans to protect cells against environmental conditions such as osmotic pressure. Bacterial cell walls have special channels consisting of protein molecules called "porins," which allow the passive diffusion of low molecular weight hydrophilic compounds such as sugar, amino acids, and certain ions. However, bacterial cell walls do not have the same system for transporting gas molecules such as CO 2 produced because of the tricarboxylic acid cycle, which uses glucose as an energy source. Therefore, because of the high CO 2 penetrability through cell walls, bacterial CO 2 exclusion from cells was accomplished through passive diffusion. The naisseriae, meningococci and gonococci, prefers high CO 2 concentration (5%) in the growth, using a candle jar which provides CO 2 in the historical culture method. As these bacteria do not possess any preferential CO 2 uptake mechanism, external high CO 2 concentration induces passive transport of CO 2 thorough cell walls.
This study demonstrated that CO 2 concentration gradient acts as ` "pseudo osmotic pressure" not only through cellulose membrane but also authentic polymer membranes in the gas phase and that CO 2 metabolisms occur in the whole cells in all organisms. Therefore, CO 2 exclusion in our bodies is extremely rapid via blood circulation. Recently, we found that NaHCO 3 and Na 2 CO 3 accelerate glucose consumption in cultured cells 44,45 . However, CO 2 metabolism in plant mesophyll cells plays an important role 46 .
Because the O 2 penetration through polymer membranes is much slower than CO 2 penetration in this study and the other studies, this cell plays a critical role in O 2 exclusion rather than CO 2 absorption 47 . In this system, O 2 penetration was not observed in polymer membranes, including cellulose membranes (Fig. 5). These results indicate that plant CO 2 absorption exceeded our expectations because of extremely high penetrability. Therefore, the forest should be preserved and protected not only from res but also from commercial land development to maintain sustainable development goals in the future. The combination of large scale polytunnels that spontaneously absorb CO 2 from atmosphere could be imitated like an "arti cial forest" using simple technology. The ultimate human evolution has been achieved based on the industrial revolution 48 which has resulted in climate change. Thus, as we are responsible for this crisis, we have amoral duty to address the situation through global cooperation. Figure 1 CO2 release from plastic bags. Polymer materials: (a) latex glove, (b) cellulose tube, and (c) polyethylene bags with 0.03-mm and 0.08-mm thicknesses. CO2 was blown into polymer bags or gloves, and then they were sealed. These bags or gloves were placed inside glass bottles, and the amount of CO2 released inside the bottle was measured using CO2 analyzers. The vertical axis shows the ratio of the initial volume of CO2 to the latter volume, and the values are the mean for four experiments.    CO2 is released into the water through the polymer membrane. (a) Latex balloons were blown with CO2 gas and they were sealed. The sealed balloons were sunken into the water for stated periods, and then their volume was estimated by the previously described method of initial CO2 volumes in the method section. The vertical unit is the ratio of the initial CO2 volume to the latter volume. The values are the mean of four experiments ± S.D. (b) 150-ml CO2 saturated water was owed into the polyethylene bag with 0.04 mm thickness, and the bag was inserted into the 450-ml glass bottle lled with fresh water. After 14 h, 1.8 ml of water was removed from the both sides, inside and outside bag, and CaCO3 was precipitated by addition of the solution consisting of 0.2-ml 1 N NaOH and 2-ml 0.1 M CaCl2 in a plastic tube. Precipitates were collected by centrifugation at 3,000 rpm for 10 min and then weighted. The vertical axis shows the eight (g/tube) and the values are the mean of ve experiments ± S.D. Figure 6 CO2 absorption into water. CO2 gas (70 ml) was blown into a 100-ml cylinder that was sunken upside down into a container lled with 1 L water. The gas volume was observed directly. The left, middle, and right columns represent Milli-Q (pure water), city water, and seawater, respectively. (a) 4°C, (b) 55°C, and (c) syringe. In panel (c), the left and right columns represent 4°C and 55°C experiments, respectively. The vertical axis represents CO2 volume (ml), and the values are the mean of ve experiments ± S.D. Figure 7