| Using plants to remove formaldehyde pollution is vrey respected because of its economic, scientific, environmental protect. In order to make better use of plant to development formaldehyde pollution removal technology, our laboratorystudied on several C3 plant absorption kinetics and mechanism of formaldehyde metabolism before. This paper takes C4 plant maize as the experimental material, in order to understand the application potential of C4 plants in the repair of formaldehyde pollution. Study on the ability to absorb formaldehyde and the mechanism to metabolism formaldehyde of isolated root and leaf of maize and whole maize plants. Analysis the may be pathway of formaldehyde in the liquid formaldehyde transferred into air through maize plants. TiO2 can be activated to generate free radicals with high catalytic activity under sunlight or UV in lamp. Free radicals can catalytic and photolysis the formaldehyde and other organic pollution on the surface of the object because of their strong ability of oxidation and reduction. Therefore, many products and technologies to remove formaldehyde pollution had been developed at present based on TiO2 photo oxidation ability. Make a comparison of the capacity to absorption and transformation mechanism of gaseous formaldehyde between maize and TiO2 composite photocatalyst. Detection of formaldehyde absorption capacityof the composite system composed of two. The structure and elements of TiO2 thin-film photocatalyst had been analysised for further explanation the mechanism of absorption and degradation formaldehyde. Provide a theoretical basis for the composite repair technology development of formaldehyde pollution in the future. The main results are as follows:The absorption kinetics curves of the 2mM,4mM and 6mM formaldehyde liquid of isolated maize roots similar with leaves in the 48h treatment period. The formaldehyde absorption and processing time have a power function relationship. Root and leaf cell death had certain liquid formaldehyde absorption, and the amount of adsorption and absorption of formaldehyde significantly increased with the increase of the concentration of formaldehyde. Liquid HCHO absorption is very slow of root and leaf in the period of 0-4h. In this period, adsorption contributes in the removal of formaldehyde more than absorption. The formaldehyde absorption speed increases rapidly in 12-48h. In this period, the absorption contributes in the removal of formaldehyde obviously more than absorption and result in significantly improve the removal rate of formaldehyde. The formaldehyde absorption significantly increased may be related with strengthen of the formaldehyde metabolism of root and leaf in 12-48h.13C-NMR analysis showed that 2mM H13CHO treatment on maize roots. H13CHO transformed into H13COOH, [2-13C]Gly, [U-13C]Gluc, [U-13C]Fruc and [2-13C]Mal (malic acid) through metabolism. Formaldehyde metabolites in maize root under 4mM H13CHO same as 2mM H13CHO treatment.2mM H13CHO treated on isolated maize leaf for 24h, H13CHO transformed into [2-13C]Ser, [2-13C]DHA (hydroxypyruvate), H13COOH, [U-13C]Gluc and [2-13C]Mal (malic acid).4mM H13CHO treated on isolated maize leaf for 24h, theformaldehyde metabolite based on H13COOH, and H13CHO has not been assimilated.The pathway and mechanism of formaldehyde transfer in plants can provide the theoretical basis for the development of plant remediation technology for formaldehyde pollution.This study designed a device to examine whether formaldehyde uptake by maizecan transferred to the surrounding environment through plant tissueand catheter. The absorption kinetics curves of the 2mM,4mM and 6mM formaldehyde liquid of whole maize plant similar with isolated maize roots and leaves. In the 0-12h period, formaldehyde transferred from the rhizosphere solution to the surrounding air of leaves.The transfer function of formaldehyde reached its peak in 4h, and the amount of transfer formaldehyde significantly increased with the concentration. The presence of free formaldehyde had been detected in maize roots, stems and leaves.The content of free formaldehyde in stems was the highest before 4h and in the leaves was the lowest content. 13C-NMR analysis showed that H13COOH is the only metabolit in roots of maize after 2mM H13CHO treatment. The contents of formaldehyde increased first and then dropped to 0 at72h in roots, stems and leaves of maize treated with low concentration HCHO (2mM). Under middlean high liquid formaldehyde, the concentrations of free HCHO were increased continuous in roots. However, the contents of formaldehyde increased first and then dropped to 0 at72h in stems and leaves. This change mode may be caused by that death underthe high concentration of formaldehyde treated could lead root cell death in late, and the formaldehyde can only exist in the root but cannot upward. In addition, there are free HCHO was detected in the roots, shoots and leaves of maize under the stress of gaseous formaldehyde. Results showed that there was a lot of free HCHO in roots. Leaves and shoots were secondly. There also liquid HCHO was detected in rhizosphere of maize under gaseou formaldehyde. Indicated that formaldehyde be upward transport to leaves via xylem and downward transport to roots via phloem in maize. Leaves and roots could release free formaldehyde into air and rhizosphere, respectively. Such cycle of transportation formated an air-plant-water transfer pathway.The gaseous HCHO absorption kinetics characteristics of leaves were different with liquid formaldehyde. The formaldehyde absorption curve likeS in the 3hperiod and gaseous HCHO absorption is very slow before 1h. Indicated that the affinity for gaseous formaldehyde of leaves were poor. The absorption rate began to increase rapidly after 1h, and then showing the trend of saturation.The formaldehyde absorption increased with the amount of maize plants.Commercialization TiO2 thin-film photocatalytis formaldehyde gas absorption curve is typical saturation kinetics curve.The gas absorption of HCHO rapidly rise before 2h, and saturated after 2h. Indicated that Indicated that the affinity for gaseous formaldehyde of TiO2 thin-film photocatalytis were good. The gasous formaldehyde absorption of maize and TiO2 thin-film photocatalyst composite system were equal tothe absorption amount of the sum of two. Gasous formaldehyde absorption curve of composite system is similar to maize’s. Indicated that no interaction effect on absorption of formaldehyde on each other between two materials. The gasous formaldehyde absorption curve of TiO2 thin-film photocatalyst is approximate gentle in unit area, absorpted only 0.002ppm at 3h treatment. However, the gasous formaldehyde absorption curve of maize is sustained growth in unit area, absorpted only O.Olppm at 3h treatment. The absorption value of maize in per unit area is 5 times than TiO2 thin-film photocatalyst.13C-NMR analysis resultsshowed that, there are a large number of free H13CHO was detected in the roots of maize under the stress of 2mM gasous formaldehyde for 4h, but do not exist in the leaves. Metabolic mechanism of gaseou H13CHO is similar to the liquid H13CHO in leaves. H13CHO metabolism formed a lot of H13COOH, [2-13C]Gly and [2-13C]Mal were secondly, and then the [U-13C]Fruc. H13COOH is the only metabolit in roots of maize. Metabolic effects of leaves on formaldehyde should be the drive in gaseous formaldehyde absorption enhanced at later stage. TiO2 thin-film photocatalytis has a strong Arg signal peak without H13CHO treated. Arg and free H13CHO formed Arg-H13CHO adducts after exposure to gaseous H13CHO. So that the formaldehyde signal spectrum decreased on film.In addition, H13CHO also oxidized to H13COOH, [U-13C]oxalic acid and 13CO2 by TiO2 photocatalytis.Do the characterization analysis of TiO2 thin-film photocatalytis. Observed under scanning electron microscope, results showed that opaque blue area has a lot of fiber or tube type structure and transparent region has some nanoparticles of this commercial film. Energy spectrum analysis and X fluorescence spectrum analysis showed that C element content was the highest (82.3467%) in TiO2 thin-film photocatalyst. Followed by N, O elements contents are respectively 11.3521% and 5.9191%, and a small amount of Si, Ca, Ti, Al etc. From these results we concluded that TiO2 composite photocatalytic membrane may be a carbon nanotubes and nano carbon fiber materials prepared by a large number of activated carbon. The carbon nanotubes and nano carbon fiber may wrap some nano titanium dioxide and diatom mud particles. Nano titanium dioxide may modified by a few metal ions and non doped metal ion. TiO2 thin-film photocatalyst is coated with a few amino acids. Activated carbon and diatom mud particles on the film have strong adsorption of gaseous formaldehyde. At the same time, there are also adduction function between amino acid and formaldehyde. Therefore, formaldehyde can be quickly absorbed by the film when exposed to gasesou formaldehyde. Although the nanometer titanium dioxide have the degradation effect of certain oxidation of formaldehyde, but the absorption of formaldehyde soon reach saturation due to this effect is weak. |
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