Efficient bacteria capture and inactivation by cetyltrimethylammonium bromide modified magnetic nanoparticles.

Functionalized magnetic nanoparticles have shown great application potentials in water treatment processes especially for bacterial removal. Antibacterial agent, cetyltrimethylammonium bromide (CTAB), was employed to modify Fe3O4 nanoparticles to fabricate bactericidal paramagnetic nanoparticles (Fe3O4@CTAB). The as-prepared Fe3O4@CTAB could effectively capture both Gram-negative Escherichia coli and Gram-positive Bacillus subtilis from water. For both cell types, more than 99% of bacteria with initial concentration of 1.5 × 10(7)CFU/mL could be inactivated by Fe3O4@CTAB (0.5 g/L) within 60 min. Fe3O4@CTAB could remove more than 99% of cells over a wide pH (from 3 to 10) and solution ionic strength range (from 0 to 1000 mM). The copresence of sulfate and nitrate did not affect the bacterial capture efficiencies, whereas, phosphate and silicate slightly decreased the bacterial removal rates. However, more than 91% and 81% of cells could be captured at 10mM of phosphate and silicate, respectively. Over 80% of cells could be removed even in the presence of 10mg/L of humic acid. Moreover, Fe3O4@CTAB exhibited good reusability, and greater than 83% of cells could be captured even in the fifth regeneration cycle. Fe3O4@CTAB prepared in this study have great application potentials for water disinfection.

[Simultaneous Removal of Cd (II) and Phenol by Titanium Dioxide-Titanate Nanotubes Composite Nanomaterial Synthesized Through Alkaline-Acid Hydrothermal Method].

A composite nanomaterial, TiO2/TNTs, was synthesized by TiO2 (P25) through alkaline and acid hydrothermal reaction, which possessed both titanate nanotubes (TNTs) and TiO2 phase. It was found that the adsorption kinetics of Cd(II) onto TiO2/TNTs was very quick, and the adsorption could reach the equilibrium within 30 min. In addition, the maximum adsorption capacity of Cd(II) was as large as 120. 34 mg.g-1 calculated from Langmuir isotherm model. The adsorption mechanism of Cd(II) was ion-exchange between Cd2+ and Na+/H+ located in the interlayers of TNTs. However, the adsorption capacity of phenol on TiO2/TNTs was so small that the photocatalysis for phenol degradation was needed. In the adsorption-photocatalysis system, the removal efficiencies of Cd(II) and phenol could reach up to 99. 6% and 99.7%, respectively. Especially, removal of Cd(II) was attributed to adsorption by TNTs of the composite nanomaterial, while removal of phenol was resulted from photocatalytic reaction by the TiO2 phase. Moreover, the co-existing Cd(II) enhanced the photocatalytic degradation of phenol due to the enhancement on photocatalytic activity of TiO2/TNTs after Cd(II) was adsorbed. Co-existing Na+ did not show obvious effect on the co-removal of Cd(II) and phenol by TiO2/TNTs, but adsorption of Cd(II) was inhibited in the presence of Ca2+ as it could compete for the adsorption sites and enhance the aggregation of the material. Furthermore, TiO2/TNTs could be efficiently reused after desorption via HNO3 and regeneration via NaOH, and the removal efficiencies of Cd(II) and phenol were still as high as 91. 7% and 98. 1% even after three cycles. This study proposed a method to synthesize a material which had both adsorptive and photocatalytic performance, and it was of great importance for application of nanomaterials in the simultaneous removal of heavy metals and organic pollutants.

Fe5C2 nanoparticles: a reusable bactericidal material with photothermal effects under near-infrared irradiation.

Hägg iron carbide (Fe5C2) was synthesized through a facile one-pot wet-chemical route and employed as a photothermal agent to inactivate bacterial cells. The as-prepared Fe5C2 nanoparticles (NPs) were about 20 nm in diameter, and exhibited strong magnetic properties (Ms = 122 emu g-1 at 298 K). Fe5C2 NPs exhibited excellent antibacterial capability toward both Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) under near-infrared (NIR) irradiation. Under NIR irradiation, complete inactivation of E. coli and S. aureus cells (about 2 × 106 CFU per mL) could be obtained by 50 mg L-1 Fe5C2 NPs in 60 min and 150 min, respectively. Humic acid (HA) slightly inhibited the disinfection efficiency of Fe5C2 NPs, however, more than 99.9% of E. coli cells were inactivated in 60 min even when the concentration of HA was as high as 10 mg L-1. Complete disinfection of E. coli cells could be achieved with the presence of 10 mg L-1 HA by increasing the reaction time to 90 min. Moreover, Fe5C2 NPs showed great reusability, and complete disinfection of E. coli cells remained even after five consecutive reuse cycles. The increase in temperature of bacterial suspension caused by the photothermal effect of Fe5C2 NPs was determined to be the main reason for the inactivation of bacteria. Our study showed that Fe5C2 NPs have great application potential for bacterial disinfection in water.

Efficient bacterial capture with amino acid modified magnetic nanoparticles.

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 × 10(7) 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.

Bactericidal mechanisms of Ag2O/TNBs under both dark and light conditions.

Ag(2)O/TNBs were fabricated by depositing Ag(2)O nanoparticles on the surface of TiO(2) nanobelts (TNBs). The disinfection activities of Ag(2)O/TNBs on two representative bacterial types: Gram-negative Escherichia coli ATCC15597 and Gram-positive Bacillus subtilis, were examined under both dark and visible light conditions. Ag(2)O/TNBs exhibited stronger bactericidal activities than Ag(2)O nanoparticles and TNBs under both dark and light conditions. For both cell types, disinfection effects of Ag(2)O/TNBs were greater under light conditions relative to those under dark conditions. The bactericidal mechanisms of Ag(2)O/TNBs under both dark and light conditions were explored. Ag(+) ions released from Ag(2)O/TNBs did not contribute to the bactericidal activity of Ag(2)O/TNBs under dark conditions, whereas the released Ag(+) ions showed bactericidal activity under visible light irradiation conditions. Active species (H(2)O(2), O(2)(-)·, and e(-)) generated by Ag(2)O/TNBs played important roles in the disinfection processes under both dark and visible light irradiation conditions. Without the presence of active species, the direct contact of Ag(2)O/TNBs with bacterial cells had no bactericidal effect.

Bactericidal activity of Ag-doped multi-walled carbon nanotubes and the effects of extracellular polymeric substances and natural organic matter.

The objective of this study was to determine the bactericidal mechanisms of Ag-doped multi-walled carbon nanotube (MWCNT) nanoparticles (Ag(0)/MWCNTs) to Escherichia coli DH5α. The contributions of silver ion dissolution, reactive species, and direct contact on bacteria inactivation were systematically determined. The relatively higher survival rate of bacteria exposed to 0.02mgL(-1) Ag(+) ions (the maximum concentration of Ag(+) ions dissolved from Ag(0)/MWCNTs) suggested that the antibacterial property of Ag(0)/MWCNTs was not caused by silver ion dissolution. The effects of each reactive species ((·)OH, H(2)O(2), (·)O(2)(-), h(+), and e(-)) on the disinfection process were investigated by using multiple scavengers, and the results showed that (·)OH(b), (·)OH(s), and h(+) play important roles in bactericidal actions. The significance of (·)OH(b), (·)OH(s), and h(+) in the disinfection process was further confirmed in the partition systems combined with scavenger. The antibacterial effects of these reactive species mainly arose through direct contact of the nanocomposites with the bacteria. The effects of extracellular polymeric substances (EPS) and natural organic matter (NOM) on the inactivation of bacteria were also investigated. The lower antibacterial effect observed for EPS-rich bacteria relative to EPS-poor bacteria demonstrated the protective effects of EPS in the disinfection system. The decreased bacterial toxicity effect acquired by the addition of humic acid (as the model NOM) in the disinfection system demonstrated the influence of NOM on the bacterial toxicity of nanocomposites, where the sorption of NOM onto the surface of the nanocomposites contributed to the decreased antibacterial effects.

Removal of arsenate by cetyltrimethylammonium bromide modified magnetic nanoparticles.

Cetyltrimethylammonium bromide (CTAB) modified magnetic nanoparticles (Fe(3)O(4)@CTAB) were synthesized and used to remove arsenate from water. Fe(3)O(4)@CTAB was prepared by a modified simple co-precipitation process with cheap and environmental friendly iron salts and cationic surfactant CTAB. Powder X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infra-red spectroscopy were utilized to characterize the prepared adsorbent (Fe(3)O(4)@CTAB). Transmission electron microscopy (TEM) image showed that Fe(3)O(4)@CTAB particles were approximately spherical with the core size of 10 nm. With a saturation magnetization of 67.2 emu g(-1), the Fe(3)O(4)@CTAB nanoparticles could be easily separated from solutions with a simple magnetic process in very short time (within 5 min). Adsorption of arsenate on Fe(3)O(4)@CTAB reached equilibrium within 2 min at pH 6. Arsenate adsorption agreed well with pseudo-second order kinetic model and two-site Langmuir isotherm model with the arsenate adsorption capacity of 23.07 mg g(-l), which was twice greater than that of pure Fe(3)O(4). Arsenate removal rate was over 90% at a wide pH range from 3 to 9 and the removal of arsenate was not obviously affected by the presence of dissolved natural organic matter (up to 10 mg L(-1) as TOC) and competitive anions (sulfate, bicarbonate, and silicate up to 20 mg L(-1), and phosphate up to 5 mg L(-1)) in solutions. Fe(3)O(4)@CTAB could be regenerated in alkali solutions and more than 85% As(V) was removed even in fifth regeneration/reuse cycle.