Influence of gravity on transport and retention of representative engineered nanoparticles in quartz sand.
Four types of NPs: carbon nanotubes and graphene oxide (carbon-based NPs), titanium dioxide and zinc oxide metal-oxide NPs, were utilized to systematically determine the influence of gravity on the transport of NPs in porous media. Packed column experiments for two types of carbon-based NPs were performed under unfavorable conditions in both up-flow (gravity-negative) and down-flow (gravity-positive) orientations, while for two types of metal-oxide NPs, experiments were performed under both unfavorable and favorable conditions in both up-flow and down-flow orientations. Both breakthrough curves and retained profiles of two types of carbon-based NPs in up-flow orientation were equivalent to those in down-flow orientation, indicating that gravity had negligible effect on the transport and retention of carbon-based NPs under unfavorable conditions. In contrast, under both unfavorable and favorable conditions, the breakthrough curves for two types of metal-oxide NPs in down-flow orientation were lower relative to those in up-flow orientation, indicating that gravity could decrease the transport of metal-oxide NPs in porous media. The distinct effect of gravity on the transport and retention of carbon-based and metal-oxide NPs was mainly attributed to the contribution of gravity to the force balance on the NPs in quartz sand. The contribution of gravity was determined by the interplay of the density and sizes of NP aggregates under examined solution conditions.
The Key Laboratory of Water and Sediment Sciences, Ministry of Education, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, PR China.
Li
L
Cai
Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing 100871, PR China.
Jinghan
J
Zhu
Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing 100871, PR China.
Yanglong
Y
Hou
The Key Laboratory of Water and Sediment Sciences, Ministry of Education, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, PR China. Electronic address: tongmeiping@pku.edu.cn.
Meiping
M
Tong
Department of Mineral Resources and Energy Engineering, Chonbuk National University, Jeonju, Jeonbuk 561-756, Republic of Korea. Electronic address: kshjkim@jbnu.ac.kr.
Hyunjung
H
Kim
D006108:Graphite; D006112:Gravitation; D062070:Hydrology / Q000379:methods; D053758:Nanoparticles / Q000032:analysis / Q000737:chemistry; D037742:Nanotubes, Carbon / Q000737:chemistry; D016062:Porosity; D011791:Quartz; D012822:Silicon Dioxide; D012996:Solutions; D014025:Titanium / Q000737:chemistry; D015034:Zinc Oxide / Q000737:chemistry
D037742:Nanotubes, Carbon; D012996:Solutions; D011791:Quartz; C009495:titanium dioxide; D012822:Silicon Dioxide; D006108:Graphite; D014025:Titanium; D015034:Zinc Oxide
Engineered nanoparticle; Gravity; Quartz sand; Retention; Transport