This study investigated the influence of two representative suspended clay particles, bentonite and kaolinite, on the transport of titanium dioxide nanoparticles (nTiO2) in saturated quartz sand in both NaCl (1 and 10 mM ionic strength) and CaCl2 solutions (0.1 and 1 mM ionic strength) at pH 7. The breakthrough curves of nTiO2 with bentonite or kaolinite were higher than those without the presence of clay particles in NaCl solutions, indicating that both types of clay particles increased nTiO2 transport in NaCl solutions. Moreover, the enhancement of nTiO2 transport was more significant when bentonite was present in nTiO2 suspensions relative to kaolinite. Similar to NaCl solutions, in CaCl2 solutions, the breakthrough curves of nTiO2 with bentonite were also higher than those without clay particles, while the breakthrough curves of nTiO2 with kaolinite were lower than those without clay particles. Clearly, in CaCl2 solutions, the presence of bentonite in suspensions increased nTiO2 transport, whereas, kaolinite decreased nTiO2 transport in quartz sand. The attachment of nTiO2 onto clay particles (both bentonite and kaolinite) were observed under all experimental conditions. The increased transport of nTiO2 in most experimental conditions (except for kaolinite in CaCl2 solutions) was attributed mainly to the clay-facilitated nTiO2 transport. The straining of larger nTiO2-kaolinite clusters yet contributed to the decreased transport (enhanced retention) of nTiO2 in divalent CaCl2 solutions when kaolinite particles were copresent in suspensions.

Traditional chemical disinfectants are becoming increasingly defective due to the generation of carcinogenic disinfection byproducts and the emergence of antibiotic-resistant bacterial strains. Functionalized magnetic nanoparticles yet have shown great application potentials in water treatment processes especially for bacterial removal. In this study, three types of amino acids (arginine, lysine, and poly-l-lysine) functionalized Fe3O4 nanoparticles (Fe3O4@Arg, Fe3O4@Lys, and Fe3O4@PLL) were prepared through a facile and inexpensive two-step process. The amino acid modified Fe3O4 nanoparticles (Fe3O4@AA) showed rapid and efficient capture and removal properties for both Gram-positive Bacillus subtilis (B. subtilis) and Gram-negative Escherichia coli 15597 (E. coli). For both strains, more than 97% of bacteria (initial concentration of 1.5 × 107 CFU mL−1) could be captured by all three types of magnetic nanoparticles within 20 min. With E. coli as a model strain, Fe3O4@AA could remove more than 94% of cells from solutions over a broad pH range (from 4 to 10). Solution ionic strength did not affect cell capture efficiency. The co-presence of sulfate and nitrate in solutions did not affect the capture efficiency, whereas, the presence of phosphate and silicate slightly decreased the removal rate. However, around 90% and 80% of cells could be captured by Fe3O4@AA even at 10 mM of silicate and phosphate, respectively. Bacterial capture efficiencies were over 90% and 82% even in the present of 10 mg L−1 of humic acid and alginate, respectively. Moreover, Fe3O4@AA nanoparticles exhibited good reusability, and greater than 90% of E. coli cells could be captured even in the fifth regeneration cycle. The results showed Fe3O4@AA fabricated in this study have great application potential for bacteria removal from water.