We developed a straightforward and scalable method to produce nanomaterials at the kilogram scale. This involves reacting metal-containing precursors with tetraalkylammonium hydroxides (TAAH), commonly known as quaternary ammonium compounds or "quats," under ambient pressure and at temperatures not exceeding 80 °C8-10. Specifically, by reacting various insoluble titanium precursors—such as titanium nitride (TiN), titanium carbide (TiC), or titanium diboride (TiB2)—with TAAH at 80 °C for four days, we synthesized one-dimensional (1D) lepidocrocite titanate nanofilaments (NFs), hereafter referred to as 1DL NFs. More recently, we achieved the same material by reacting titanium oxysulfate with tetramethylammonium hydroxide (TMAOH) at 80 °C for a few hours (denoted as TMA-1DL). Characterization techniques have confirmed that the 1DL NF structure consists of 2 × 2 TiO6 octahedra, resulting in a minimal cross-section of approximately 5 × 7 Ų, with lengths extending to tens of nanometers11, 12. The NFs grow along the a-axis and stack along the b-axis. To contextualize these dimensions, aligning 1DLs from just one gram of material would span approximately 700 million kilometers.
In our study, we present the first investigation into the AB activity of 1DL titanate NFs synthesized using TMAOH or ChoOH. To assess the influence of intercalated cations on the AB properties we ion-exchange the original TMA⁺ or Cho⁺ cations present after reaction with potassium (K⁺) or sodium (Na⁺), resulting in K-1DL and Na-1DL variants, respectively.
The AB efficacy of these materials was evaluated against three model bacteria: the Gram-negative Escherichia coli (E. coli) and the Gram-positive Bacillus subtilis (B. subtilis) and Listeria innocua (L. innocua). We examined the antibacterial activity in relation to NF size, incubation duration, and concentration, utilizing both colony-forming unit (CFU) assays and flow cytometry for comprehensive analysis. Using CFU assays, we observed AB activities of approximately 96% for E. coli and 99% for the Gram-positive strains after a 4-hour exposure to light. Flow cytometry analyses indicated that direct physical contact between bacterial cells and 1DL NFs is pivotal for their AB function. Scanning electron microscopy revealed that the AB mechanism mainly involves physical disruption of bacterial membranes, with bacteria becoming trapped or enveloped by the nanometer-thin 1DL NFs, leading to agglomerate formation that can potentially be filtered out. Notably, while reactive oxygen species (ROS) generation has been previously identified as a contributing factor in bacterial elimination by titania, our material demonstrated efficacy exceeding 85% even in the absence of light. This suggests that mechanisms, beyond ROS generation, are at play. These findings position 1DL NFs as a promising new class of AB materials, with potential applications in AB treatments, water purification, and environmental remediation. Furthermore, the synthesis of 1DL NFs is feasible on a kilogram scale under ambient pressure and at temperatures below 80 °C, utilizing abundant and ubiquitous elements, thereby offering significant practical advantages over other materials.
References
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