Aqueous mechano-bactericidal action of acicular aragonite crystals

Abstract

Nanoneedle structures on dragonfly and cicada wing surfaces or black silicon nanoneedles demonstrate antibacterial phenomena, namely mechano-bactericidal action. These air-exposed, mechano-bactericidal surfaces serve to destroy adherent bacteria, but their bactericidal action in the water is no precedent to report. Calcium carbonate easily accumulates on solid surfaces during long-term exposure to hard water. We expect that aragonite nanoneedles, in particular, which grow on TiO2 during the photocatalytic treatment of calcium-rich groundwater, exhibit mechano-bactericidal action against bacteria in water. Here, we showed that acicular aragonite modified on TiO2 ceramics prepared from calcium bicarbonate in mineral water by photocatalysis exhibits mechanical bactericidal activity against E. coli in water. Unmodified, calcite-modified and aragonite-modified TiO2 ceramics were exposed to water containing E. coli (in a petri dish), and their bactericidal action over time was investigated under static and agitated conditions. The surfaces of the materials were observed by scanning electron microscopy, and the live/dead bacterial cells were observed by confocal laser scanning microscopy. As a result, the synergistic bactericidal performance achieved by mechano-bactericidal action and photocatalysis was demonstrated. Aragonite itself has a high biological affinity for the human body different from the other whisker-sharpen nanomaterials, therefore, the mechano-bactericidal action of acicular aragonite in water is expected to inform the development of safe water purification systems for use in developing countries.

Aragonite and Its Composites: Preparations, Properties and Applications

“…Aragonite-modified TiO 2 exhibits a synergistic effect, with its sterilization rate in water being equal to the sum of mechanical sterilization and photocatalytic effects. [97] Interestingly, the aragonite nanoneedles on TiO 2 showed a self-regenerating function to maintain their mechano-bactericidal effects since new aragonite nanoneedles [83] (Copyright 2014 The Japan Institute of Metals and Materials) and Chen et al [81] (Copyright 2011 The Authors, published by DOAJ). (B1-B4): Aragonite whiskers(B1), calcite particles(B2), aragonite whiskers in PP composites (B3) and calcite particles in PP composites(B4).…”

“…By integrating photocatalytic capacity and mechanical bactericidal activity, acicular aragonite-modified TiO 2 ceramics displayed high bactericidal efficiency against E. coli in water. [97] This sterilization system holds promise for serving as a safe water purification method for developing countries due to its simplicity, low cost and strong biological affinity.…”

“…[112] Initially, chitin is periodically secreted by epithelial cells to form an organic framework deposition. Subsequently, when Ca 2 + and CO 3 2À ions permeate Reproduction with permission from [97] (Copyright 2021 The Authors).…”

Mechanistic Insights into Electrodeposition in Seawater at Variable Electrochemical Potentials

“…The dominant electrodeposits reported in these images can be classified as aragonite, calcite, and brucite, in agreement with previous observations and analyses. [55][56][57] Figure 3a shows the morphology of dominant cal-cite minerals obtained for a potential of −0.8 V Ag/AgCl in the ORR regime. Calcite minerals appear as cubic subhedral microcrystals, with a size of 2-5 μm.…”

“…The morphology of these minerals is governed by a complex interplay of various factors, including thermodynamics, kinetics, and environmental conditions (such as seawater composition [58] and temperature [59] ), potentially varying from euhedral to subhedral, columnar to rounded and botryoidal, compact to fibrous, or flaky to platy. [55,56] The crystal growth mechanisms for calcite, aragonite, and brucite in seawater involve different nucleation, ion attachment, and crystal growth processes, leading to their distinct morphologies. The obtained results support that at a limited potential of −0.8 V Ag/AgCl , small cubic subhedral calcite crystals and columnar aragonite crystals nucleate atop an underlying amorphous layer of brucite.…”