Noble-Nanoparticle-Decorated Ti3C2T x MXenes for Highly Sensitive Volatile Organic Compound Detection.

Two-dimensional transition-metal carbides and nitrides (MXenes) have been regarded as promising sensing materials because of their high surface-to-volume ratios and outstanding electronic, optical, and mechanical properties with versatile transition-metal and surface chemistries. However, weak gas-molecule adsorption of MXenes poses a serious limitation to their sensitivity and selectivity, particularly for trace amounts of volatile organic compounds (VOCs) at room temperature. To deal with these issues, Au-decorated MXenes are synthesized by a facile solution mixing method for room-temperature sensing of a wide variety of oxygen-based and hydrocarbon-based VOCs. Dynamic sensing experiments reveal that optimal decoration of Au nanoparticles (NPs) on Ti3C2T x MXene significantly elevates the response and selectivity of the flexible sensors, especially in detecting formaldehyde. Au-Ti3C2T x gas sensors exhibited an extremely low limit of detection of 92 ppb for formaldehyde at room temperature. Au-Ti3C2T x provides reliable gas response, low noise level, ultrahigh signal-to-noise ratio, high selectivity, as well as parts per billion level of formaldehyde detection. The prominent mechanism for Au-Ti3C2T x in sensing formaldehyde is elucidated theoretically from density functional theory simulations. The results presented here strongly suggest that decorating noble-metal NPs on MXenes is a feasible strategy for the development of next-generation ultrasensitive sensors for Internet of Things.

α-Fe2O3 Nanoparticles Aided-Dual Conversion for Self-Powered Bio-Based Photodetector.

Eco-friendly energy harvesting from the surrounding environment has been triggered extensive researching enthusiasm due to the threat of global energy crisis and environmental pollutions. By the conversion of mechanical energy that is omnipresent in our environment into electrical energy, triboelectric nanogenerator (TENG) can potentially power up small electronic devices, serves as a self-powered detectors and predominantly, it can minimize the energy crisis by credibly saving the traditional non-renewable energy. In this study, we present a novel bio-based TENG comprising PDMS/α-Fe2O3 nanocomposite film and a processed human hair-based film, that harvests the vibrating energy and solar energy simultaneously by the integration of triboelectric technology and photoelectric conversion techniques. Upon illumination, the output voltage and current signals rapidly increased by 1.4 times approximately, compared to the dark state. Experimental results reveal that the photo-induced enhancement appears due to the effective charge separation depending on the photosensitivity of the hematite nanoparticles (α-Fe2O3 nanoparticles) over the near ultraviolet (UV), visible and near infrared (IR) regions. Our work provides a new approach towards the self-powered photo-detection, while developing a propitious green energy resource for the circular bio-economy.

Charge trapping with α-Fe2O3 nanoparticles accompanied by human hair towards an enriched triboelectric series and a sustainable circular bioeconomy.

This work reports a new approach to amending polydimethylsiloxane (PDMS) by supporting α-Fe2O3 nanoparticles (NPs), thereby generating a material suitable for use as a negative triboelectric material. Additionally, human hair exhibits a profound triboelectrification effect and is a natural regenerative substance, and it was processed into a film to be used as a positive triboelectric material. Spatial distribution of α-Fe2O3 NPs, the special surface morphologies of a negative tribological layer containing nano-clefts with controlled sizes and a valley featuring a positive tribolayer based on human hair made it possible to demonstrate facile and scalable fabrication of a triboelectric nanogenerator (TENG) presenting enhanced performance; this nanogenerator produced a mean peak-to-peak voltage of 370.8 V and a mean output power density of 247.2 µW cm-2 in the vertical contact-separation mode. This study elucidates the fundamental charge transfer mechanism governing the triboelectrification efficiency and its use in harvesting electricity for the further development of powerful TENGs suitable for integration into wearable electronics and self-charging power cells, and the work also illustrates a recycling bioeconomy featuring systematic utilization of human hair waste as a regenerative resource for nature and society.

Strain-Induced Ferroelectric Heterostructure Catalysts of Hydrogen Production through Piezophototronic and Piezoelectrocatalytic System.

In this work, we discover a piezoelectrocatalytic system composed of a ferroelectric heterostructure of BaTiO3 (BTO)@MoSe2 nanosheets, which exhibit piezoelectric potential (piezopotential) coupling with electrocatalyzed effects by a strain-induced piezopotential to provide an internal bias to the catalysts' surface; subsequently, the catalytic properties are substantially altered to enable the formation of activity states. The H2 production rate of BTO@MoSe2 for the piezoelectrocatalytic H2 generation is 4533 µmol h-1 g-1, which is 206% that of TiO2@MoSe2 for piezophototronic (referred to as piezophotocatalytic process) H2 generation (∼2195.6 µmol h-1 g-1). BTO@MoSe2 presents a long-term H2 production rate of 21.2 mmol g-1 within 8 h, which is the highest recorded value under piezocatalytic conditions. The theoretical and experimental results indicate that the ferroelectric BTO acts as a strain-induced electric field generator while the few-layered MoSe2 is facilitating piezocatalytic redox reactions on its active sites. This is a promising method for environmental remediation and clean energy development.

Flexible Layered-Graphene Charge Modulation for Highly Stable Triboelectric Nanogenerator.

The continuous quest to enhance the output performance of triboelectric nanogenerators (TENGs) based on the surface charge density of the tribolayer has motivated researchers to harvest mechanical energy efficiently. Most of the previous work focused on the enhancement of negative triboelectric charges. The enhancement of charge density over positive tribolayer has been less investigated. In this work, we developed a layer-by-layer assembled multilayer graphene-based TENG to enhance the charge density by creatively introducing a charge trapping layer (CTL) Al2O3 in between the positive triboelectric layer and conducting electrode to construct an attractive flexible TENG. Based on the experimental results, the optimized three layers of graphene TENG (3L-Gr-TENG) with CTL showed a 30-fold enhancement in output power compared to its counterpart, 3L-Gr-TENG without CTL. This remarkably enhanced performance can be ascribed to the synergistic effect between the optimized graphene layers with high dielectric CTL. Moreover, the device exhibited outstanding stability after continuous operation of >2000 cycles. Additionally, the device was capable of powering 20 green LEDs and sufficient to power an electronic timer with rectifying circuits. This research provides a new insight to improve the charge density of Gr-TENGs as energy harvesters for next-generation flexible electronics.

Surface Functionalization of Ti3C2Tx MXene with Highly Reliable Superhydrophobic Protection for Volatile Organic Compounds Sensing.

Two-dimensional (2D) transition-metal carbides (Ti3C2Tx MXene) have received a great deal of attention for potential use in gas sensing showing the highest sensitivity among 2D materials and good gas selectivity. However, one of the long-standing challenges of the MXenes is their poor stability against hydration and oxidation in a humid environment, limiting their long-term storage and applications. Integration of an effective protection layer with MXenes shows promise for overcoming this major drawback. Herein, we demonstrate a surface functionalization strategy for Ti3C2Tx with fluoroalkylsilane (FOTS) molecules through surface treatment, providing not only a superhydrophobic surface, mechanical/environmental stability but also enhanced sensing performance. The experimental results show that high sensitivity, good repeatability, long-term stability, and selectivity and faster response/recovery property were achieved by the FOTS-functionalized when Ti3C2Tx was integrated into chemoresistive sensors sensitive to oxygen-containing volatile organic compounds (ethanol, acetone). FOTS functionalization provided protection to sensing response when the dynamic response of the Ti3C2Tx-F sensor to 30 ppm of ethanol was measured over in the 5 to 80% relative humidity range. Density functional theory simulations suggested that the strong adsorption energy of ethanol on Ti3C2Tx-F and the local structure deformation induced by ethanol adsorption, contributing to the gas-sensing enhancement. This study offers a facile and practical solution for developing highly reliable MXene based gas-sensing devices with response that is stable in air and in the presence of water.

Simultaneous Piezoelectrocatalytic Hydrogen-Evolution and Degradation of Water Pollutants by Quartz Microrods@Few-Layered MoS2 Hierarchical Heterostructures.

Intense light attenuation in water/wastewater results in photocatalysts exhibiting a low quantum efficiency. This study develops a novel piezoelectrocatalysis system, which involves quartz microrods (MRs) abundantly decorated with active-edge-site MoS2 nanosheets to form a quartz microrods@few-layered MoS2 hierarchical heterostructure (QMSH). Through theoretical calculations, it is found that the quartz MRs serve as a parallel-plate capacitor, which is self-powered to provide an internal electric field to the few-layered MoS2 nanosheets surrounding the quartz MR surfaces, and the piezoelectric potential (piezopotential) effectively facilitates redox reactions with the free carriers in MoS2 . The self-powered quartz MRs in the QMSH present an internal bias to the MoS2 nanosheets, thus yielding a piezoelectrocatalysis system. An efficient piezoelectrocatalytic hydrogen evolution reaction and decomposition of wastewater without light irradiation can be achieved simultaneously. The second-order rate constant of the QMSH is ≈0.631 L mg-1 min-1 , which is 650-fold that of quartz MRs, indicating that the piezoelectric heterostructural catalysts display exceptionally high efficiency on piezoelectrocatalytic redox reactions rather than in the piezocatalytic process. The H2 -production rate of QMSH catalysts approaches ≈6456 µmo1 g-1 h-1 and peaks at ≈16.8 mmol g-1 in 8 h. The piezoelectrocatalytic process may be a promising method for treating industrial wastewater and producing clean energy.

Nanohybrids of a MXene and transition metal dichalcogenide for selective detection of volatile organic compounds.

Two-dimensional transition metal carbides/nitrides, known as MXenes, have been recently receiving attention for gas sensing. However, studies on hybridization of MXenes and 2D transition metal dichalcogenides as gas-sensing materials are relatively rare at this time. Herein, Ti3C2Tx and WSe2 are selected as model materials for hybridization and implemented toward detection of various volatile organic compounds. The Ti3C2Tx/WSe2 hybrid sensor exhibits low noise level, ultrafast response/recovery times, and good flexibility for various volatile organic compounds. The sensitivity of the hybrid sensor to ethanol is improved by over 12-fold in comparison with pristine Ti3C2Tx. Moreover, the hybridization process provides an effective strategy against MXene oxidation by restricting the interaction of water molecules from the edges of Ti3C2Tx. An enhancement mechanism for Ti3C2Tx/WSe2 heterostructured materials is proposed for highly sensitive and selective detection of oxygen-containing volatile organic compounds. The scientific findings of this work could guide future exploration of next-generation field-deployable sensors.

Performance of hydrogen evolution reaction of R3C ferroelectric ZnSnO3 nanowires.

The synthesis of LiNbO3-type R3C ZnSnO3 is still a challenging task under an extremely high-pressure condition. In this work, we have not only successfully synthesized R3C ZnSnO3 nanowires (NWs) through a hydrothermal process, but ZnSnO3 NWs with a high concentration of oxygen vacancies (referred to as [Formula: see text] NWs), exhibiting a highly efficient hydrogen evolution reaction compared to unannealed ZnSnO3 and ZnO NWs. The x-ray diffraction pattern and Raman spectra both confirm that the as-synthesized ZnSnO3 NWs mainly belong to the R3C space group with a second phase of ZnSn(OH)6. The conversion efficiency of the solar-to-hydrogen [Formula: see text] NWs and the unannealed ZnSnO3 NWs is 4.8% and 1.5%, respectively. The enhancement factor of the [Formula: see text] NWs is up to 320%. The photocurrent of the ZnSnO3 NWs and the [Formula: see text] NW photoelectrodes is even 5.39 and 16.23 times higher than that of the ZnO NWs, demonstrating that the high concentration of oxygen vacancies is regarded as a useful approach to enhance the photoelectrochemical response. To the best of our knowledge, this is the first report to reveal the performance of hydrogen evolution reaction by LiNbO3-type R3C ZnSnO3 NWs, which could offer a promising way of energy harvesting when using ferroelectric materials.

Photocatalytic Activities Enhanced by Au-Plasmonic Nanoparticles on TiO2 Nanotube Photoelectrode Coated with MoO3.

Although TiO2 was formerly a common material for photocatalysis reactions, its wide band gap (3.2 eV) results in absorbing only ultraviolet light, which accounts for merely 4% of total sunlight. Modifying TiO2 has become a focus of photocatalysis reaction research, and combining two metal oxide semiconductors is the most common method in the photocatalytic enhancement process. When MoO3 and TiO2 come into contact to form a heterogeneous interface, the photogenerated holes excited from the valence band of MoO3 should be transferred to the valence band of TiO2 to effectively reduce the charge recombination of photogenerated electron-hole pairs. This can efficiently separate the pairs and promote photocatalysis efficiency. In addition, photocurrent enhancement is attributed to the strong near-field and light-scattering effects from plasmonic Ag nanoparticles. In this work, we fabricated MoO3-coated TiO2 nanotube heterostructures with a 3D hierarchical configuration through two-step anodic oxidation and a facile hydrothermal method. This 3D hierarchical structure consists of a TiO2 nanotube core and a MoO3 shell (referred to as TNTs@MoO3), as characterized by field emission scanning electron microscopy and X-ray photoelectron spectroscopy.

Investigation of Free-Standing Plasmonic Mesoporous Ag/CMK-8-Nafion Composite Membrane for the Removal of Organic Pollutants with 254-nm UV Irradiation.

"Carbon-based material" has demonstrated a great potential on water purification due to its strong physical adsorption to organic pollutants in the water. Three-dimensional cubic ordered mesoporous carbon (CMK-8), one of the well-known ordered mesoporous carbons, was prepared by using nanocasting method with mesoporous silica (KIT-6) as the template. In this study, CMK-8 blended with Nafion polymer to form a free-standing mesoporous CMK-8-Nafion composite membrane. The synthesis of high crystallinity CMK-8 was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). More than 80% methyl orange (MO) removal efficiency was observed under 254-nm UV irradiation after 120 min. Ninety-two percent recycling performance was remained after four recycling tests, which indicated a reliable servicing lifetime for the water purification. Furthermore, an additional layer of plasmonic silver nanoparticles (Ag NPs) was integrated into this CMK-8-Nafion membrane for higher pollutant removal efficiency, attributing from the generation of plasmon-resonance hot electrons from Ag NPs. A 4-in. CMK-8-Nafion composite membrane was also fabricated for the demonstration of potential large-scale utilization.

Synthesis of Strong Light Scattering Absorber of TiO2-CMK-3/Ag for Photocatalytic Water Splitting under Visible Light Irradiation.

The enhanced water splitting photocurrent has been observed through plasmonic mesoporous composite electrode TiO2-CMK-3/Ag under visible light irradiation. Strong light absorption achieved from the integrations of ordered mesoporous carbon (CMK-3) and silver plasmonic nanoparticles (NPs) layer in the TiO2, which significantly increased the effective optical depth of TiO2-CMK-3/Ag photoelectrode. The carbon-based CMK-3 also increased the surface wetting behavior and conductivity of the photoelectrodes, which resulted in a higher ion exchange rate and faster electron transport. The synthesis of high crystalline TiO2-CMK-3/Ag composite photocatalyst was verified by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Pronounced enhancement of light absorption of TiO2-CMK-3/Ag photoelectrode was confirmed by UV/vis spectrophotometers. Two orders of magnitude of the enhanced water splitting photocurrent were obtained in the TiO2-CMK-3/Ag composite photoelectrode with respect to TiO2 only. Finally, spatially resolved mapping photocurrents were also demonstrated in this study.