Adsorption of extracellular polymeric substances from two microbes by TiO₂ nanoparticles

Extracellular polymeric substance (EPS) secreted by microbes can interact with nanoparticles (NPs) and thus influence environmental behavior and toxicity of NPs. The adsorption of EPSs from two species of microbes (Escherichia coli and Chlorella pyrenoidosa) by four types of titanium dioxide nanoparticles (nTiO₂) (5, 10, and 40 nm anatase nTiO₂ and 25 nm rutile nTiO₂) were therefore specifically investigated. Results show that the adsorption kinetics and thermodynamics were dependent on sources and chemical properties of EPSs. EPS (20 mg C/L) from Escherichia coli mainly composed of protein (86%) with relatively higher molecular weight and aromaticity and more active functional groups (i.e., NH and -COOH) was effectively removed (>90%) by adsorption on nTiO₂ (100 mg and more), while much less (<40%) EPS from Chlorella pyrenoidosa with a main component of polysaccharide (68%) was adsorptively removed. The Fourier transform ion cyclotron resonance mass spectrometry analysis revealed the selective adsorption of aromatic components of EPSs by nTiO₂. The EPS adsorption capacity of nTiO₂ linearly increased with the specific surface area of the NPs. The rutile nTiO₂ with the smallest specific surface area had the highest EPS adsorption per unit surface area. These findings promote a deeper understanding of the interaction between EPS and NPs.