Heterostructures Of Biochar And Environmental Risk Of Biochar Nano Particles

Biochar,as an environmental functional material with multi-structure,is able to be an environmentally friendly soil additive.It would be potentially and prospect applied in improving soil properties,reducing greenhouse gas emission,immobilizing environmental pollutants,promoting carbon sequestration and etc.Being a soil additive with extraneous sources,the environmental risk of biochar requires urgent attention but the relevant research is still deficient.This thesis reviewed the current state of research about biochar nanoparticles?BNPs?,summarized the mechanisms of environmental risk occurring from biochar production to its application process.It was found out that the differences of BNPs with different sizes on morphology,elemental composition,reactivity and toxicity need more research in depth.Additionally,it pointed out that that the environmental effect of BNPs and its risk,in particular,the impacts on both plant growth and metabolism remain unclear.Being aimed at the abovementioned issues,the thesis conducted a series of studies:?1?Two biomass rice straw and wood sawdust were selected as the feedstock,pyrolyzed at different temperatures under oxygen-limited condition to produce an array of biochars,the biochar particles with different suspension properties were first separated by ultrasonic dispersion-static settling where the BNPs were further obtained using electric charge regulation;?2?The morphology and elemental composition of all the BNPs with different particle sizes were characterized,meanwhile,their adsorption capacity,reactivity and toxicity were detected and compared with each other;?3?Rice,tomato and reed were selected as the model plant species,hydroponic experiments were applied to observe the influence of the BNPs on the growth of these plant seedlings and proposed possible cause of toxicity;?4?Metabonomic analysis was performed on rice to study the influence of the BNPs on rice growth and metabolism at rice tillering stage,The thesis indicated that the toxicity of the BNPs is most likely the important source of biochar environmental risk.Abovementioned research findings not only offered a reference for the toxicity effect of BNPs,but also provided the essential knowledge for environmental risk assessment of biochar.The following points addressed the main innovative parts of this thesis:?1?The characteristics of biochar with different particle sizes was ascertained in terms of morphology,elemental composition,adsorption capacity,reactivity and toxicity.Low-temperature biochar was composed of sedimented particles with aliphatic carbon and suspended coarse particles of aromatic carbon.By contrast,high-temperature biochar was composed of sedimented particles with aromatic carbon and suspended coarse particles of aliphatic carbon.The reactivity of high-temperature biochar was found as a result of its sedimented particles.In addition,the effective concentration causing 50%inhibition of luminescent bacteria(EC₅₀)of the soluble components and ultrafine particles of high temperature biochar was 707mg/L,while the EC₅₀ of the same category of low temperature biochar was 80.7 mg/L.The former was 7.7 times of the latter revealing that the latter was more toxic.?2?A novel mechanism of ionized organic compound onto aromatized biochar was proposed,and named as‘Multiple?-bond Cooperative and Polarized Assisted H-Bond Interaction'??-PAHB?.The cyclic chair water clusters adsorbed onto the aromatized surface and formed a stable complex that acted as a proton acceptor,boosting the sorption capacity of aromatized biochar by hydrogen bonding for seven ionizable organic compounds.The adsorption coefficient K_d was increased between12.6%to 26.9%.Owing to the reopening of the pore structure and the promotion of aromatization,the amount of phenol sorption by the sedimental particles of high temperature biochar increased between 29.0%to 55.2%under pH 1-13 compared to that of the original biochar.?3?The electronic charge regulation between particles was used to optimal the BNP preparation,confirming the proportion of the BNP in its pristine biochar.pH was used to regulate the electric charge between ultrafine particles of biochar that lead to the behaviors of dispersion-aggregation-dispersion for biochar,The BNPs were further obtained from centrifugation,which the yield was between 4.38%and6.61%,The particle size of BNPs was ranged from 21.64 to 55.85 nm and increased with increasing pyrolysis temperature of biochar.Additionally,abundant phenolic functional groups were observed on the surface of high-temperature biochar with high content of lignin.?4?The inhibiting effect of BNPs on reed was observed,where the main reasons were the biological inhibiting effect of the phenolic functional groups from nanoparticle surface and the blocking effect of particles on epidermal openings on root surface.The BNPs of wood sawdust and BNPs of high temperature biochar from rice straw inhibited reed growth.It showed a decreasing rate of reed biomass between38.7%and 42.4%.The key toxic mechanisms of BNPs on reed were the biological inhibiting effect of the phenolic functional groups from nanoparticle surface and the blocking effect of particles on epidermal openings on root surface.?5?The effect mechanisms of the BNPs in low/high-temperature biochars on rice metabolism were confirmed.The BNPs in low-temperature biochars significantly declined rice tillering.Where 58 differential metabolites were selected from the treatment of the BNPs in low-temperature biochar,mainly including the activation of amino sugar and nucleotide sugar metabolism of rice,the inhibition of pyrimidine metabolism and flavone and flavanol biosynthesis.On the other hand,the BNPs in high-temperature biochar declined the proportion of dried rice leaves and fresh leaves of which 36 differential metabolites were selected from the treatment of high-temperature biochar.It primarily involved the activation of the metabolism of niacin and nicotinamide,tryptophan synthesis and phenylalanine metabolism in rice.