Study On The Ecotoxicological Effects On Constructed Wetland Plants And Defluoridation Of Typical Nano-materials

Nanotechnology is one of the most rapidly developed and significantly important research fields in the twenty-first century,but it is a typical "double-edged sword".It is widely used in all walks of life due to its specific properties compared with macroscopic material,and nanometer material often used as catalyst and adsorbent to purify the water by adsorption and degradation of pollutants in water in the field of environmental protection.However,it is inevitable to enter the surrounding environment and may cause unpredictable effects during the utilization.Due to the ecological risk problem of nanomaterials generated during the utilization,the widely used nano titanium dioxide(TiO2-NPs)were studied on the ecotoxicological effects.The effects of particle size and concentration of TiO2-NPs on the individual plant form and physiological feature during the seed germination and plant growth of typical wetland plants-Phragmites australis and Ceratophyllum demersum were investigated.The ecotoxicological effects of TiO2-NPs on artificial wetland plants were also analyzed.Additionally,targeted on the fluorine pollution in water,the removal characteristics and mechanisms of?-Fe2O3-graphite-La(MGLNP)were explored.The main results are as follows:The main results of the ecotoxicological effects of nano materials are as follows:(1)During the treatment of 4 nm,20 nm and 50 nm,smaller particle size and higher concentration of TiO2-NPs showed stronger inhibition on seed germination of C.demersum.The germination rate,seedling weight,germination index,germination potential and vigor index decreased with decrease of TiO2-NPs particle size and increaseof concentration.When the particle size was 4 nm,the germination rate of C.demersum decreased from 88.33%to 27.67%as the concentration increased from 0 to 2000 mg·L-1.However,the low concentration(less than 200 mg·L-1)of TiO2-NPs showed promotion on the germination of P.australis.Based on this,continued increase of the concentration led to decrease of germination rate,seedling weight and other germination indexes.Compared with blank,germination rate of P.australis were significantly decreasedwhen the Ti02-NPs concentration was 500 mg·L-1;when the TiO2-NPs concentration was 2000 mg·L-1,germination rate of P.australis decreased from 85%to 24%(4 nm),3 0%(20 nm)and 46.67%(50 nm),respectively.(2)Different sizes of TiO2-NPs were able to inhibit the growth of C.demersum and P.australis,smaller particle size and higher concentration showed more significantly inhibition.The toxic effects of high TiO2-NPs concentration on the growth of C.demersum,presenting as leaves became yellow and fell off,plants were wilted;while the toxic effects on P.australis showed as the plant growth rate slowed down or even stagnation,leavesgot chlorosis,plants were wilted or dead,and the growth rate of second leaf area decreased.(3)The chlorophyll and Mg content of C.demersum and P.australis decreased with the increase of TiO2-NPs concentration at different particle sizes,the smaller the particle size was,the stronger the reduction was.Superoxide dismutase(SOD)activity and malondialdehyde(MDA)content of the root system increased with the increase of TiO2-NPs concentration,and smaller particle size promoted more increase.All the results illustrated that smaller particle size and higher concentration of TiO2-NPs showed stronger toxic effects on C.demersum and P.australis.(4)All the three particle sizes of TiO2-NPs could enter into C.demersum and P.australis,the smaller particle size was,the more particles of TiO2-NPs entered into plants.More sediments were found in P.australis roots than in stems,the deposition of TiO2-NPs particles in leaves was hardly found.Due to strong surface tension of nanoparticles,TiO2-NPs entered into the plants showed different degrees of agglomeration.When the concentration of TiO2-NPs was 500 mg·L-1,the Ticoncentent in C.demersum reached to 996?g·g-1,886?g·g-1 and 529?g·g-1 with the particle size of 4 nm,20 nm and 50 nm,respectively.However,the Ti content in P.australis roots was 993 ?g·g-1 829 ?g·g-1 and 722 ?g·g-1,respectively,which was much higher than that in the stems.A small amount of Ti in P.australis leaves was only detected when the particle size was 4 nm with a concentration of higher than 100 mg·L-1.The results showed that different particle sizes of TiO2-NPs hardly transferred in the P.australis plants during the 12d culture period.The larger the particle size was,the more difficult to transferred.The main results of the study on the water purification of nanoparticles are as follows:The lanthanum loading amount of the MGLNP,prepared water purification nano adsorbent,was 254.26 mg·g-1,with saturated magnetization of 26.66 emu·g-1,showing good magnetic separation effect.The isoelectric point of MGLNP(pHpzc)was about 7.9,with a wide application range of pH.The adsorption of fluoride ion could achieve adsorption equilibrium in 30 min.The maximum adsorption capacity was 77.12 mg·g-1 at 25?,pH=7 ± 0.1.The decrease of pH and increase of temperature enhanced the adsorption capacity of MGLNP.MGLNP showed strong selective adsorption effect of fluorine and outstanding performance of reutilization,the fluorine ion adsorption capacity was 77.54%after 6 times circulation.The adsorption free energy(?G°),enthalpy(AH0)and entropy(?S°)illustrated that the adsorption of fluoride by MGLNP was an endothermic reaction which was spontaneous and easily processed.The FTIR and XPS determination of MGLNP before and after adsorption exhibited that there was ion exchange reaction between-COOH,CO32-and OH-groups on the surface of adsorbent and the F-in solution.Moreover,electrostatic attraction and Lewis acid-alkaline hydration reaction between La3+ on the surface of MGLNP and F-may also be the main mechanism of fluorine removal.