USDA-ARS Southern Regional Research Center, 1100 Robert E. Lee Boulevard, New Orleans, Louisiana, 70124, USA.
Department of Environmental Sciences, The Connecticut Agricultural Experiment Station, New Haven, Connecticut, 06504, USA.
Sci Rep. 2017 Jul 10;7(1):5027. doi: 10.1038/s41598-017-03916-1.
Engineered nanomaterials are directly applied to the agricultural soils as a part of pesticide/fertilize formulations or sludge/manure amendments. No prior reports are available to understand the surface interactions between gold nanoparticles (nAu) and soil components, including the charcoal black carbon (biochar). Retention of citrate-capped nAu on 300-700 °C pecan shell biochars occurred rapidly and irreversibly even at neutral pH where retention was less favorable. Uniform organic (primarily citrate ligands) layer on nAu was observable by TEM, and was preserved after the retention by biochar, which resulted in the aggregation or alignment along the edges of multisheets composing biochar. Retention of nAu was (i) greater on biochars than a sandy loam soil, (ii) greater at higher ionic strength and lower pH, and (iii) pyrolysis temperature-dependent: 500 < 700 ≪ 300 °C at pH 3. Collectively, carboxyl-enriched 300 °C biochar likely formed strong hydrogen bonds with the citrate layer of nAu. The charge transfer between the conduction band of nAu and π* continuum of polyaromatic sheets is likely to dominate on 700 °C biochar. Surface area-normalized retention of nAu on biochars was several orders of magnitude higher than negatively charged hydroxyl-bearing environmental surfaces, indicating the importance of black carbon in the environmental fate of engineered nanomaterials.
工程纳米材料被直接应用于农业土壤中，作为农药/肥料配方或污泥/粪便改良剂的一部分。目前尚无报道了解金纳米颗粒（nAu）与土壤成分之间的表面相互作用，包括木炭黑碳（生物炭）。即使在中性 pH 值下，柠檬酸封端的 nAu 在 300-700°C 的山核桃壳生物炭上的保留也迅速且不可逆，而在中性 pH 值下保留不太有利。通过 TEM 可以观察到 nAu 上均匀的有机层（主要是柠檬酸配体），并且在生物炭保留后得以保留，这导致多片组成生物炭的边缘发生团聚或对齐。nAu 的保留（i）在生物炭上大于沙壤土，（ii）在较高的离子强度和较低的 pH 值下更大，（iii）与热解温度有关：在 pH 3 时，500<700<300°C。总的来说，富羧基的 300°C 生物炭可能与 nAu 的柠檬酸层形成了强氢键。nAu 的导带与多环芳烃片的π*连续体之间的电荷转移可能在 700°C 的生物炭上占主导地位。生物炭上 nAu 的比表面积归一化保留量比带负电荷的含羟基环境表面高出几个数量级，这表明在工程纳米材料的环境命运中，黑碳的重要性。
