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Aggregation and surface properties of iron oxide nanoparticles: Influence of ph and natural organic matter
Author(s) -
Baalousha Mohammed,
Manciulea Adriana,
Cumberland Susan,
Kendall Kevin,
Lead Jamie R.
Publication year - 2008
Publication title -
environmental toxicology and chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.1
H-Index - 171
eISSN - 1552-8618
pISSN - 0730-7268
DOI - 10.1897/07-559.1
Subject(s) - chemistry , humic acid , iron oxide , surface charge , ferrihydrite , particle aggregation , dynamic light scattering , natural organic matter , oxide , nanoparticle , chemical engineering , iron oxide nanoparticles , hydrolysis , colloid , coating , inorganic chemistry , organic matter , adsorption , organic chemistry , fertilizer , engineering
The interactions between unpurified manufactured nanoparticles (NPs; iron oxide NPs, ∼7 nm) and standard Suwannee River humic acid (SRHA) were investigated under a range of environmentally relevant conditions. At low pH, approximately 35% of the total iron was in the dissolved phase (<1 kDa), present from the initial synthesis, whereas at pH more than 4, this concentration was negligible because of the formation of new particles via hydrolysis. Dynamic light scattering results indicated that extensive aggregation of NPs began at approximately pH 5 to 6 and reached a maximum at approximately pH 8.5, whereas with added SRHA, aggregation was shifted to lower pH values of 4 to 5 and was affected by SRHA concentration. Aggregation could be explained mainly by charge neutralization. Further, more detailed investigations by flow field‐flow fractionation and transmission‐electron microscopy were performed under a more restricted set of conditions (pH 2–6) to examine the aggregation process. Results indicated the formation of SRHA surface coating on iron oxide NPs of approximately 1 nm and the increase in thickness of this coating with the increase of SRHA concentration. Iron oxide NPs were shown to form increasingly large aggregates with increases in both pH (from 2 to 6) and SRHA concentration (from 0 to 25 mg/L). The structure and aggregation mechanism of these aggregates were found to be both pH and SRHA concentration dependent, with open, porous aggregates in the absence of SRHA and compact aggregates in the presence of SRHA.