A Recyclable Mineral Catalyst for Visible-Light-Driven Photocatalytic Inactivation of Bacteria: Natural Magnetic Sphalerite

Abstract

Motivated by recent studies that well-documented mineral photocatalyst for bacterial inactivation, a novel natural magnetic sphalerite (NMS) in lead-zinc deposit was first discovered and evaluated for its visible-light-driven (VLD) photocatalytic bactericidal properties. Superior to the reference natural sphalerite (NS), vibrating sampling magnetometeric (VSM) analysis revealed the ferromagnetic property of NMS, indicating its potential for easy separation after use. Under the irradiation of fluorescence tubes, NMS could inactivate 7 log10 Gram-negative Escherichia coli K-12 without any regrowth and metal ions leached out from NMS show no toxicity to cells. The cell destruction process starting from cell wall to intracellular components was verified by TEM. Some products from damaged cells such as aldehydes, ketones and carboxylic acids were identified by FTIR with a decrease of cell wall functional groups. The relative amounts of potassium ion leakage from damaged cells gradually increased from initial 0 to approximately constant concentration of 1000 ppb with increasing reaction time. Superoxide radical (•O2(-)) rather than hydroxyl radical (•OH) was proposed to be the primary reactive oxidative species (ROSs) responsible for E. coli inactivation by use of probes and electron spin resonance (ESR). H2O2 determined by fluorescence method is greatly involved in bacterial inactivation in both nonpartition and partition system. Multiple cycle runs revealed excellent stability of recycled NMS without any significant loss of activity. This study provides a promising natural magnetic photocatalyst for large-scale bacterial inactivation, as NMS is abundant, easily recycled and possessed an excellent VLD bacterial inactivation ability.

Dual Roles of Capsular Extracellular Polymeric Substances in Photocatalytic Inactivation of Escherichia coli: Comparison of E. coli BW25113 and Isogenic Mutants

“…Colanic acid contents were expressed as glucose content according to the phenol-sulfuric acid method, with an average of three replicates. The bacterial cells were cultured in nutrient broth "E" (1 g/liter beef extract, 2 g/liter yeast extract, 5 g/liter peptone, and 5 g/liter sodium chloride) (Lab M, Lancashire, United Kingdom) at 37°C and agitated at 200 rpm for 16 h. The cultures were then harvested according to methods used in previous studies (32,33).…”

“…Isopropanol was used to remove˙OH diffusing into the solution, sodium oxalate (Na 2 C 2 O 4 ) was used to remove h ϩ , 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy (TEMPOL) was used to remove˙O 2Ϫ , Cr(VI) was used to remove e Ϫ , and Fe(II)-EDTA was used to remove H 2 O 2 (35). The concentration of the scavenger added was optimized according to data from our previous studies (32,35) [0.5 mM for sodium oxalate, 5 mM for isopropanol, 0.05 mM for Cr(VI), 2 mM for TEMPOL, and 0.1 mM for Fe(II)-EDTA].…”

“…The Live/Dead BacLight bacterial viability kit fluorescence microscopy method was used to reveal changes in cell membrane integrity during photocatalytic treatment (32,45). Figure 5 presents the fluorescence microscopy images of the wild type at different time intervals.…”

Visible-light-driven inactivation of Escherichia coli K-12 over thermal treated natural pyrrhotite

“…The VLD photocatalytic activity of these materials is mainly attributed to the modification of band structure by impurity elements and lattice defects as compared to their synthetic counterparts [3]. Recently developed natural magnetic sphalerite (NMS) could efficiently inactivate Escherichia coli K-12, due to the major bactericidal agent of conduction band e − induced • O 2 − [5]. Compared with synthetic VLD photocatalysts, natural magnetic VLD minerals are more readily obtained as magnetically separable photocatalysts and more feasible to be recycled, indicating a stronger potential for environmental applications [5].…”

“…Recently developed natural magnetic sphalerite (NMS) could efficiently inactivate Escherichia coli K-12, due to the major bactericidal agent of conduction band e − induced • O 2 − [5]. Compared with synthetic VLD photocatalysts, natural magnetic VLD minerals are more readily obtained as magnetically separable photocatalysts and more feasible to be recycled, indicating a stronger potential for environmental applications [5]. Consequently, the selection and development of this type of photocatalysts are urgently needed.…”