Reductive Sequestration of Toxic Bromate from Drinking Water using Lamellar Two-Dimensional Ti₃C₂T_X (MXene)

Removal of toxic byproducts such as bromate (BrO₃^–) from drinking water is a vital process. Two-dimensional (2D) titanium carbide also known as MXene (Ti₃C₂T_X) was proven a promising candidate for efficient reduction of metal ions. Herein, we report for the first time the simple method for efficient reduction of toxic bromate to bromide in water using 2D Ti₃C₂T_X nanosheets. In this reduction, the Ti–C active layer of Ti₃C₂T_X was oxidized and formed TiO₂ nanocrystals, while bromate reduced to bromide via a self-reaction process. Reduction performance of the Ti₃C₂T_X nanosheets was evaluated with respect to the concentration of MXene, time, pH, and temperature. The MXene showed excellent reduction of bromate (∼321.8 mg BrO₃^–/g Ti₃C₂T_X) within 50 min, at pH 7 and 25 °C. Furthermore, MXene nanosheets exhibited excellent sequestration performance toward bromate in comparison with other similar materials. The high resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analysis confirmed the reduction of bromate and subsequent oxidation of MXene to form TiO₂ nanocrystals and Br^–. This makes them attractive reductant materials for the efficient removal of other toxic oxides present in water systems

Antibacterial Activity of Ti₃C₂T_<i>x</i> MXene

MXenes are a family of atomically thin, two-dimensional (2D) transition metal carbides and carbonitrides with many attractive properties. Two-dimensional Ti₃C₂T_<i>x</i> (MXene) has been recently explored for applications in water desalination/purification membranes. A major success indicator for any water treatment membrane is the resistance to biofouling. To validate this and to understand better the health and environmental impacts of the new 2D carbides, we investigated the antibacterial properties of single- and few-layer Ti₃C₂T_<i>x</i> MXene flakes in colloidal solution. The antibacterial properties of Ti₃C₂T_<i>x</i> were tested against Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis) by using bacterial growth curves based on optical densities (OD) and colonies growth on agar nutritive plates. Ti₃C₂T_<i>x</i> shows a higher antibacterial efficiency toward both Gram-negative E. coli and Gram-positive B. subtilis compared with graphene oxide (GO), which has been widely reported as an antibacterial agent. Concentration dependent antibacterial activity was observed and more than 98% bacterial cell viability loss was found at 200 μg/mL Ti₃C₂T_<i>x</i> for both bacterial cells within 4 h of exposure, as confirmed by colony forming unit (CFU) and regrowth curve. Antibacterial mechanism investigation by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) coupled with lactate dehydrogenase (LDH) release assay indicated the damage to the cell membrane, which resulted in release of cytoplasmic materials from the bacterial cells. Reactive oxygen species (ROS) dependent and independent stress induction by Ti₃C₂T_<i>x</i> was investigated in two separate abiotic assays. MXenes are expected to be resistant to biofouling and offer bactericidal properties

Patterning of Nanocrystalline Cellulose Gel Phase by Electrodissolution of a Metallic Electrode

<div><p>At high concentration or in the presence of electrolytes and organic solvents, solutions of cellulose nanocrystals (CNCs) can form gels exhibiting optical properties similar to the ones of liquid crystal phases. In an attempt to pattern such a gel phase, we have studied the electrodissolution of a metallic electrode in a water suspension of carboxylated CNCs (cCNCs). Depending on the metal used, the electrodissolution process was observed at a different positive potential. In the case of copper the minimum potential at which we could observe optically the growth of the gel phase was 200 mV. The growth rate was current limited indicating that the process was controlled by the electrodissolution of the copper electrode. This hypothesis was confirmed by using circular and square copper patterns as positive electrodes. In both cases, the consumption of the electrode material was observed optically and correlated with the growth of the gel phase.</p></div

Charge- and Size-Selective Ion Sieving Through Ti₃C₂T_<i>x</i> MXene Membranes

Nanometer-thin sheets of 2D Ti₃C₂T_<i>x</i> (MXene) have been assembled into freestanding or supported membranes for the charge- and size-selective rejection of ions and molecules. MXene membranes with controllable thicknesses ranging from hundreds of nanometers to several micrometers exhibited flexibility, high mechanical strength, hydrophilic surfaces, and electrical conductivity that render them promising for separation applications. Micrometer-thick MXene membranes demonstrated ultrafast water flux of 37.4 L/(Bar·h·m²) and differential sieving of salts depending on both the hydration radius and charge of the ions. Cations with a larger charge and hydration radii smaller than the interlayer spacing of MXene (∼6 Å) demonstrate an order of magnitude slower permeation compared to single-charged cations. Our findings may open a door for developing efficient and highly selective separation membranes from 2D carbides

Growth of the gel phase around a bundle of silver plated copper wires immersed in a drop of 5.5wt% CNCs in water and held at different potentials from 0.2 to 1.2 V.

<p>A) radius of the gel phase as a function of time for each applied potential. B) Average growth velocity as a function of applied potential for the first 30 s (solid symbols) and after (open symbols).</p

3D finite element model of the cylindrical electrode geometry used in this study performed in pure water and for an applied potential of 1 V.

<p>A) equipotentials around a cylindrical electrode in a plane going through the centre of the cylinder. B) Electric field as a function of distance from the electrode surface taken along the two white lines in A). The solid line corresponds to the white line at the end of the electrode and the broken line corresponds to the white line perpendicular to the side of the electrode.</p

Optical images with crossed polarizers of an iron wire held first at 1(Figure 1B) and then held at 2 V.

<p>A) 30 s after the potential was increased to 2 V. B) 90 s after the potential was increased to 2 V. The position of the crossed polarizers is drawn in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0099202#pone-0099202-g001" target="_blank">Figure 1</a> panel A. The scale bar is 300 µm.</p

Optical images with crossed polarizers of four different metal wires immersed in a drop of 5.5wt% CNCs in water.

<p>Each wire was held at a constant positive potential with respect to a bundle of silver plated wires not shown in the field of view. A) Copper wire held at 1 V for 10 min. B) Iron wire held at 1 V for 7 min. C) Gold wire held at 2 V for 1 min. D) Silver wire held at 5 V for 30 s. The position of the crossed polarizers is drawn in panel A. The scale bar is 300 µm.</p

Sensitive Detection of ssDNA Using an LRET-Based Upconverting Nanohybrid Material

Water-dispersible, optical hybrid nanoparticles are preferred materials for DNA biosensing due to their biocompatibility. Upconverting nanoparticles are highly desirable optical probes in sensors and bioimaging owing to their sharp emission intensity in the visible region. We herein report a highly sensitive ss-DNA detection based on an energy transfer system that uses a nanohybrid material synthesized by doping NaYF₄:Tm³⁺/Yb³⁺ upconverting nanoparticles (UCNPs) on silica coated polystyrene-<i>co</i>-acrylic acid (PSA) nanoparticles (PSA/SiO₂) as the donor, and gold nanoparticles (AuNPs) decorated with Ir­(III) complex as the acceptor. UCNPs tagged on PSA/SiO₂ and the cyclometalated Ir­(III)/AuNP conjugates were then linked through the ss-DNA sequence. Sequential addition of the target DNA to the probe molecular beacon complex resulted in the separation of the optical nanohybrid material and the quencher, leading to a measurable increase in the blue fluorescence emission intensity. Our results have shown a linear relationship between the fluorescence intensity and target DNA concentration down to the picomolar

Optical images with crossed polarizers of a bundle of silver plated copper wires immersed in a drop of 5.5wt% CNCs in water and held at 1 V for A) 1 min, B) 5 min, C) 10 min.

<p>The position of the crossed polarizers is drawn in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0099202#pone-0099202-g001" target="_blank">Figure 1</a> panel A. The scale bar is 300 µm.</p