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Understandingthe bacterial cytotoxicity of CNTs is important fora wide variety of applications in the biomedical, environmental, andhealth sectors. A majority of the earlier reports attributed the bactericidalcytotoxicity of CNTs to bacterial cell membrane damage by direct physicalpuncturing. Our results reveal that bacterial cell death via bacterialcell membrane damage is induced by reactive oxygen species (ROS) producedfrom CNTs and is not due to direct physical puncturing by CNTs. Tounderstand the actual mechanism of bacterial killing, we elucidatedthe bacterial cytotoxicity of SWCNTs and MWCNTs against Gram-negativehuman pathogenic bacterial species Escherichia coli, Shigellasonnei,Klebsiella pneumoniae, and Pseudomonas aeruginosaand its amelioration upon functionalizingthe CNTs with antioxidant tannic acid (TA). Interestingly, the bacterialcells treated with CNTs exhibited severe cell damage under laboratory(ambient) and sunlight irradiation conditions. However, CNTs showedno cytotoxicity to the bacterial cells when incubated in the dark.The quantitative assessments carried out by us made it explicit thatCNTs are effective generators of ROS such as 1O2, O2•–, and •OH in an aqueous medium under both ambient and sunlight-irradiatedconditions. Both naked and TA-functionalized CNTs showed negligibleROS production in the dark. Furthermore, strong correlations wereobtained between ROS produced by CNTs and the bacterial cell mortality(with the correlation coefficient varying between 0.7618 and 0.9891)for all four tested pathogens. The absence of bactericidal cytotoxicityin both naked and functionalized CNTs in the dark reveals that thepresence of ROS is the major factor responsible for the bactericidalaction compared to direct physical puncturing. This understandingof the bactericidal activity of the irradiated CNTs, mediated throughthe generation of ROS, could be interesting for novel applicationssuch as regulated ROS delivery in cancer therapy and the sanitationof potable water supplies. [ABSTRACT FROM AUTHOR]

Intelligent physiological monitoring devices in wearable sensor technology expected to meet the commercial requirements, including good at optical transparency, stability under mechanical toughness, and easy integration with self-powered systems. Herein, the construction of transparent, flexible, triboelectric-piezoelectric hybrid nanogenerator (TPHNG) reported using triboelectric-polydimethylsiloxane (PDMS), piezoelectric-polyvinylidene fluoride (PVDF) and welded silver nanowires (AgNWs) network served as the transparent conducting electrodes. The fabricated sandwich structure of TPHNG shows high transparency about 71% along with good flexibility. The fabricated TPHNG (2 × 3 cm2 area) capable of delivering remarkable output peak voltage and current about 30 V, and 3 μA respectively with a prompt output power density of 57 mW m−2 for 5 N strike forces. The energy collected from the human physiological movement by TPHNG demonstrated to charge a commercial capacitor to 1.5 V within 100 s and also power an electronic watch. As a human physiology monitor, the TPHNG accomplished to detect the individual signals generated by body movements, including bending angle, bending frequency of the elbow, and even weak signal like human radial pulse. Moreover, the output performance of the fabricated TPHNG device remains stable upon twisting and bending over 1000 cycles reveals excellent stability. Assembly of outstanding transparency, flexibility, electrical output and sensing performance of TPHNG could be a promising candidate applied in energy conversation, individual healthcare monitoring, electronic skin, and a human-machine interface. [ABSTRACT FROM AUTHOR]

MXene based composites are promising candidates with a broad range of potential applications, especially in electrochemical energy storage and conversion devices. In this work, we demonstrate the preparation of a novel MXene/N–CuMe 2 Pc (non-peripheral octamethyl-substituted copper (II) phthalocyanine) based composite as the electrode material in supercapacitors. The integration of highly redox-active N–CuMe 2 Pc into MXene leads to the large surface area, which enhances the active sites for electrochemical redox reactions. For instance, composite prepared with a weight ratio of 1:0.2 of MXene:N–CuMe 2 Pc (M10P2) exhibits remarkable maximum specific capacitance of 786.1 F g−1. The enhanced capacitance performance is attributed to the synergistic effect of water intercalated MXene layers and N–CuMe 2 Pc. The constructed M10P2 based symmetric supercapacitor shows excellent performance with a maximum energy density of 8.84 Wh kg−1 with a power density of 112.3 W kg−1. Additionally, the symmetric device exhibits outstanding cyclic stability (92.3%) even after 20,000 cycles with satisfactory Coulombic efficiency. This work proves the new insight of preparation of MXene/N–CuMe 2 Pc composites for high-performance next-generation supercapacitor sectors in the near future. Image 1 • MXene/N–CuMe 2 Pc composites have been synthesized with different ratios of N–CuMe 2 Pc. • The specific capacitance of the M10P2 composite is up to 786.1 F g−1. • N–CuMe 2 Pc enhances the active sites of MXene for electrochemical redox reactions. • The symmetric supercapacitor shows a high energy density of 8.84 Wh kg−1. • Symmetric supercapacitor exhibits 92.3% of capacitance retention after 20000 cycles. [ABSTRACT FROM AUTHOR]

Construction of heterojunction and nitrogen doping is an effective approach for synthesizing photocatalysts with high quantum yield and efficient electron-hole separation. 2D MXene Ti 3 C 2 has been considered a good carbonaceous nanomaterial for designing heterojunction, while the original surface groups and stacked structure limit the electron-hole separation. Herein, a hybrid of nitrogen-doped Ti 3 C 2 nanosheets and TiO 2 nanoparticles (NPs) composed of TiO 2 NPs in situ growing on isopropyl amine (iPA) modified Ti 3 C 2 (iN-Ti 3 C 2 ) was developed for the first time. The novel iN-Ti 3 C 2 /TiO 2 hybrid exhibited an excellent ultraviolet-light photodegradation of methylene blue (MB), with a degradation rate (0.02642 min -1 ) significantly higher than that of pure TiO 2 NPs, bulk-Ti 3 C 2 /TiO 2 , dimethyl sulfoxide modified Ti 3 C 2 /TiO 2 hybrid, and hydrazine monohydrate modified Ti 3 C 2 /TiO 2 hybrid. The formation of heterojunction between iN-Ti 3 C 2 and TiO 2 and its role in the photocatalysis were systematically analyzed using various characterization techniques and density functional theory calculation. The iPA modification exfoliated Ti 3 C 2 and doped N on Ti 3 C 2 nanosheets; the in situ grown TiO 2 NPs formed efficient heterojunctions with the nanosheets; the N-doping facilitated electron migration in Ti 3 C 2 and inhibited the recombination of photogenerated electron-hole pairs; •OH dominated the photodegradation of MB. This work provides a new approach of constructing efficient photocatalysts for the treatment of organics-polluted water., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Defect-controlled exfoliation of few-layer transition-metal carbide ( f -Ti 3 C 2 T x ) MXene was demonstrated by optimizing chemical etching conditions, and electromagnetic interference (EMI) shielding coatings were explored. The structural features such as layer morphology, lateral size, layer thickness, defect density, and mechanical stability of the exfoliated f -Ti 3 C 2 T x were strongly dependent on exfoliation conditions. By selecting appropriate exfoliation conditions, moderate etching time leads to the formation of quality f -Ti 3 C 2 T x with lesser defects, whereas longer etching time can break the layer structure and increase defect density, structural misalignment, and oxidative products of f -Ti 3 C 2 T x . The resultant fabricated free-standing flexible f -Ti 3 C 2 T x films exhibited electrical conductivity and electromagnetic interference (EMI) shielding effectiveness (SE) in the X-band of about 3669 ± 33 S/m and 31.97 dB, respectively, at a thickness of 6 μm. The large discrepancy in EMI SE performance between quality (31.97 dB) and defected (3.164 dB) f -Ti 3 C 2 T x sheets is attributed to interconnections between f -Ti 3 C 2 T x nanolaminates interrupted by defects and oxidative products, influencing EMI attenuation ability. Furthermore, the demonstrated solution-processable high-quality f -Ti 3 C 2 T x inks are compatible and, when applied for EM barrier coating on various substrates, including paper, cellulose fabric, and PTFE membranes, exhibited significant EMI shielding performance. Moreover, controlling defects in f -Ti 3 C 2 T x and assembly of heterogeneous disordered carbon-loaded TiO 2 -Ti 3 C 2 T x ternary hybrid nanostructures from f -Ti 3 C 2 T x by tuning etching conditions could play an enormous role in energy and environmental applications.

The new class of 2D MXene material exfoliated from transition metal carbides receives increasing research interest due to its extraordinary properties and high potential in energy and environmental applications. However, the exfoliation of Ti 3 C 2 T x , a widely studied MXene, from its precursor Ti 3 AlC 2 by chemical etching in HF solution remains to be optimized. This study investigated the optimum exfoliation condition through systematic evaluating potential effects of reaction parameters, including the weight ratio of Ti 3 AlC 2 in HF solution, etching time, reaction temperature, repeating etching, and sonication, on the yield, purity, and structure of produced Ti 3 C 2 T x . Results show that a high weight percentage (5 wt%) of Ti 3 AlC 2 etching at 50 °C for 36 h produced highly exfoliated MXene material. Etching at lower weight percentages (0.6-2.5 wt%) of Ti 3 AlC 2 resulted in observable byproduct (AlF 3 ). Degradation of MXene layers with AlF 3 enrichment was observed under prolonged etching or higher temperatures. Room temperature etching failed to exfoliate Ti 3 AlC 2 and the repeated etching denatured the MXene material. Introduction of controlled sonication during the etching produced highly exfoliated MXene with minimum etching time, which can be a promising alternative for high quality MXene production.