塑料纳米颗粒广泛用于各种产品中,导致土壤不可避免的污染。了解它们在存在各种有机物质的土壤中的运输至关重要。这项研究研究了低分子量有机酸(LMWOAs)对聚苯乙烯纳米塑料(PS-NP)通过饱和石英砂传输的影响。实验涉及三种二元酸-丙二酸(MA1),苹果酸(MA2)和酒石酸(TA)-和四一元酸-甲酸(FA),乙酸(AA),丙酸(PA)和乙醇酸(GA)-在不同的pH水平(4.0,5.5,7.0)和阳离子存在下(Na,Ca2+)。结果表明,在Na+的存在下,二元酸显著增强了PS-NP的转运,TA是最有效的,其次是MA2和MA1。这种增强归因于LMWOA在纳米颗粒和沙子上的吸附,产生更负的ζ电位,这增加了静电斥力并减少了PS-NP的沉积,从而方便运输。应用Derjaguin-Landau-Verwey-Overbeek理论,较高的pH值增加了能量屏障和二次能量最小值,减少PS-NP沉积。此外,二元酸显著增强了PS-NP的亲水性。相反,一元酸,除了GA,PS-NP的亲水性略有降低,如水接触角的小幅增加所示,由此对PS-NP转运的影响最小。至于GA,虽然是一元酸,分子结构中的额外-OH基团促进了PS-NP的运输,类似于二元酸。例如,GA还显著增强了PS-NP的亲水性。在Ca2+的存在下,LMWOAs对PS-NP转运的增强与Na+相当,主要是由于Ca2与有机酸和PS-NP的复合形成和桥接作用。这些发现为预测和分析PS-NP的运输行为提供了重要的见解。
Plastic nanoparticles are extensively used in various products, leading to inevitable pollution in soil. Understanding their transport in soils where various organic substances exist is crucial. This study examined the impact of low-molecular-weight organic acids (LMWOAs) on the transport of polystyrene nanoplastics (PS-NPs) through saturated quartz sand. The experiments involved three dibasic acids-malonic acid (MA1), malic acid (MA2) and tartaric acid (TA) - and four monobasic acids- formic acid (FA), acetic acid (AA), propanoic acid (PA) and glycolic acid (GA) -under different pH levels (4.0, 5.5, 7.0) and in the presence of cations (Na+, Ca2+). The results demonstrated that in the presence of Na+, dibasic acids significantly enhanced PS-NPs transport, with TA being the most effective, followed by MA2 and MA1. This enhancement is attributed to the adsorption of LMWOAs onto the nanoparticles and sand, creating a more negative ζ-potential, which increases the electrostatic repulsion and decreases the PS-NPs deposition, thereby facilitating the transport. Applying the Derjaguin-Landau-Verwey-Overbeek theory, higher pH levels increased the energy barrier and secondary energy minimum, decreasing PS-NPs deposition. Moreover, dibasic acids significantly enhanced the hydrophilicity of PS-NPs. Conversely, monobasic acids, except for GA, slightly reduced the hydrophilicity of PS-NPs, as indicated by a small increase in the water contact angle, hereby minimally affecting PS-NPs transport. As for GA, although it is a monobasic acid, the additional -OH group in its molecular structure promoted PS-NPs transport, similar to dibasic acids. For example, GA also significantly enhanced the hydrophilicity of PS-NPs. In the presence of Ca2+, the enhancement of PS-NPs transport by LMWOAs was comparable to that with Na+, primarily due to the complex-forming and bridging effects of Ca2+ with the organic acids and PS-NPs. These findings provide important insights into predicting and analyzing the transport behaviors of PS-NPs.