Enhanced Cd2+ adsorption and toxicity for microbial biofilms in the presence of TiO2 nanoparticles
2022
Wang, Wenwen | Zhu, Shijun | Li, Nihong | Xie, Shanshan | Wen, Chen | Luo, Xia
Titanium dioxide nanoparticles (TiO₂ NPs) easily combine with other pollutants such as heavy metals because of their excellent physiochemical properties. However, how such an interaction may affect the binding behavior of metals onto biofilms remains largely unclear. This study, examined the effects of TiO₂ NPs on Cd²⁺ accumulation and toxicity for natural periphytic biofilms were examined. The adsorption kinetics showed that adding 0.1 and 1 mg/L TiO₂–NPs increased the Cd²⁺ adsorption of biofilms at equilibrium by 23.5% and 35.8%, respectively. However, adding 10 mg/L TiO₂ NPs increased the Cd²⁺ adsorption of biofilms at equilibrium by only 1.9%. The adsorption isotherms indicate that the presence of TiO₂ NPs considerably increased the Cd²⁺ adsorption capacity of the biofilms; however, this effect became less prominent at high TiO₂ NP concentrations. The optimum pH for Cd²⁺ adsorption increased with increasing Cd²⁺ and TiO₂ NP contents. At low concentrations, the coexistence of Cd²⁺ and TiO₂ NPs may facilitate their respective accumulation by stimulating the secretion of extracellular polymeric substances and enhancing the microbial activity of the biofilm. The presence of TiO₂ NPs increases the surface binding energy between Cd²⁺ and functional groups such as carboxyl groups, enhancing the Cd²⁺ accumulation on the biofilm.
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