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Two-dimensional (2D) inorganic compounds, MXenes, are the most promising candidate for chemical sensors and environmental remediation. Since the first synthesis of Ti3C2Tx MXene from the Ti3AlC2 MAX phase in 2011, 2D materials have been attracting significant attention from a wide range of scientific communities because of their unique physicochemical properties. The attractive properties of MXenes motivated us to explore the new wave of front-end research and applications. Over the past 12 years, there have been more than 10,000 theoretical and experimental studies on MXenes. All these publications have primarily focused on Ti3C2Tx MXene because of its fascinating material properties and tunability towards target applications. To provide readers with a fundamental understanding of this emerging 2D material, this review discusses the recent trends in the design of Ti3C2Tx MXene for gas sensors and energy harvesting applications. For the most updated information, this review focuses on important findings and applications reported in the last decade. [ABSTRACT FROM AUTHOR]

Summary: CO2, a greenhouse gas, is continuously emitted by different sources due to the extensive use of fossil fuels. Hence various methods have been developed to mitigate CO2 gas from the environment. The capturing and storing of carbon is termed carbon capture and storage, a method of reducing the level of CO2 from the atmosphere emitted by industrial sites and power stations. The reduction of the atmospheric carbon or the stored carbon to different products by multiple techniques has been a current topic of research, taking the environmental concern into account. The reduction of CO2 is very challenging since the bond energy of C=O is very high. Additionally, the separation of the gas from the atmosphere or industrial flue gas is also technologically difficult. This review comprises a detailed discussion of the methods adopted for the conversion of CO2 into different carbon nano‐materials and hydrocarbons. The mechanisms associated with the conversion, along with the role of electrodes used for the conversion of the gas during electrolysis, have also been conferred extensively. [ABSTRACT FROM AUTHOR]

A representative of titanium carbide MXene, Ti3C2Tx is a promising candidate for high performance gas sensing and has attracted significant attention. However, MXene naturally has a multilayer structure with low porosity, which prevents its gas-sensing activity. Zinc oxide (ZnO) has long been utilized as a gas detector. Despite its good response to multiple gases, high operation temperature has limited its widespread use as a gas-sensing material. In this study, a room-temperature toxic gas sensor was prepared from ZnO/Ti3C2Tx MXene nanocomposite consisting of 2D few-layered MXene and 1D ZnO nanoparticles. A simple technique for synthesizing the nanocomposite was established. The physicochemical properties of the nanocomposite were fine-controlled with more active sites and higher porosity. The sensitivity and gas-selectivity of the sensing material were closely examined. The nanocomposite showed enhanced response and recovery behaviors to toxic gases, which outperformed pure Ti3C2Tx MXene and pure ZnO. This study offers a practical strategy by which to increase the gas-sensing performance of Ti3C2Tx MXene, and expands comprehensive understanding of the gas-sensing process of ZnO/Ti3C2Tx p-n heterostructure. [ABSTRACT FROM AUTHOR]

In this work, Ce6-mediated photodynamic therapy (PDT) was investigated for antibacterial inactivation, using ZnFe2O4–Ce6 nanocarriers operated with low-irradiance light in the near-infrared range. To fabricate ZnFe2O4–Ce6 nanocarriers, the highly purified photosensitizer was modified with polyethylenimine (PEI) using a standard 1-ethyl-3-[3-(dimethylamino)-propyl]-carbodiimide hydrochloride–N-hydroxysuccinimide coupling reaction. Then, it was conjugated with hollow ZnFe2O4 nanospheres (NSs). The as-synthesized ZnFe2O4–Ce6 nanocarriers were found to have an average size of ∼100 nm, increased water solubility, high singlet oxygen generation capability, and broad light absorbance in the range of 400–800 nm. The chemical changes and surface charge confirmed the stable conjugation of PEI–Ce6 with hollow ZnFe2O4–Ce6 NSs. The ZnFe2O4–Ce6 nanocarriers (50 μg/mL) exhibited excellent antibacterial activities of >98% for every bacterial cell even under the low-irradiance light at 660 nm. Furthermore, the structural examinations revealed that Gram-negative Escherichia coli was more vulnerable than other Gram-positive cells to the nanocarrier-mediated PDT. This work may provide insights into a promising approach using photosensitizers in PDT for combating antibiotic-resistant bacteria. [ABSTRACT FROM AUTHOR]

The valorization of onion-like carbon nanoparticles (OCNPs) from pollutant soot collected from diesel engine exhaust could be a promising and sustainable approach to develop percolated conductive networks in a poly(lactic acid) (PLA) matrix, which could be used for the design of conductive polymer nanocomposite (CPC)-based quantum resistive sensors (QRS). The aim of the present study is to incorporate these waste materials in the field of structural health monitoring (SHM) of biocomposites. Here, OCNPs have been used in the formulation of QRS and further integrated into unidirectional flax fibers and PLA composites for SHM trials without altering their mechanical properties. QRS transducers made of 1 wt% OCNPs dispersed into a PLA matrix have been prepared via an in situ spray layer-by-layer (sLbL) process during the fabrication of flax–PLA composites by film stacking under vacuum conditions. Their in situ sensing of strain and damage was evaluated by submitting the flax–PLA unidirectional composite samples to various incremental and simultaneous loading–unloading cycles. Most importantly, the piezo-resistive behavior of the OCNP-based QRS has been found to be reproducible, and it exhibits large-amplitude signals with a gauge factor of 6 ± 2, which is two to three times larger than that of commercial strain sensors. Additionally, these waste-derived OCNPs possess interesting ferromagnetic properties at room temperature. [ABSTRACT FROM AUTHOR]

In this work, facile pressureless sintering process is explored to manufacture the promising Cr2AlC MAX phase material, using three elemental powders as starting materials. The powders are mixed in a molar ratio of Cr:Al:C = 2:1.2:1, and ball-milled for particle refinement and homogenization. The powder mixture is sintered at differing temperatures from 1000 to 1400°C without applying pressure. Highly pure Cr2AlC MAX phase is obtained from sintering at 1200°C. The Cr2AlC compound shows laminated microstructures and high crystal quality. At other temperatures, significant amounts of secondary phases are observed. The optimized Cr2AlC compound exhibits a metallic behavior and superior oxidation resistance. The simple manufacturing method of Cr2AlC MAX phase developed in this work may also be applied for fabrication of a wider range of MAX phases. [ABSTRACT FROM AUTHOR]

In this work, graphitic carbon nitride (g-C3N4) was synthesized by simple pyrolysis of melamine, and it was hybridized with reduced graphene oxide (rGO) and silver nanoparticles (AgNPs) using a stepwise solution method. AgNPs were randomly distributed on the surface of rGO/g-C3N4 layered hybrid structure, forming Ag@rGO/g-C3N4 composite. It was disclosed that the Ag@rGO/g-C3N4 composite responded to both oxidizing and reducing gases at room temperature, and its response was greatly enhanced from those of pristine rGO and rGO/g-C3N4. The room temperature responses of the composite were estimated at − 95% and 8% for 50 ppm of NO2 and NH3, respectively. The roles of structural components were discussed, and a gas-sensing mechanism was proposed based on the respective roles. In particular, AgNPs turned out to play an important role in the gas-sensing activity. [ABSTRACT FROM AUTHOR]

Novel two-dimensional ZnO/Ti3C2Tx hybrid photocatalysts with modified surface areas were prepared using a simple calcination technique. The microstructures, crystalline features, and bonding states of the ZnO structure-covered Ti3C2Tx MXenes were closely characterized using various tools. The photoluminescence intensity of the hybrid photocatalyst was greatly reduced compared to the pristine ZnO, while its Brunauer-Emmett-Teller (BET) surface area increased by more than 100 times. Under solar light illumination, the photocatalytic degradation efficiency of the hybrid photocatalyst for organic pollutants (MO, RhB) appeared to be three-fold larger as compared to pristine ZnO. The superb photocatalytic performance of the photocatalyst was attributed to several factors, such as ideal band alignment, Schottky barrier formation, and large surface area. Moreover, the ZnO/Ti3C2Tx hybrid photocatalyst showed excellent cycling stability. These results suggest that the novel hybrid structure may be a potential candidate for removing organic pollutants in wastewater. [ABSTRACT FROM AUTHOR]