The photocatalytic synthesis of hydrogen peroxide (H 2 O 2 ) is an environmentally benign and sustainable approach. In this study, we have synthesized a TiO 2-x /g-C 3 N 4-x (A-T x CN x ) photocatalyst with a Z-scheme heterojunction by introducing oxygen and nitrogen double vacancies through a one-step reduction process. The optimized A-T x CN x catalyst exhibited a superior H 2 O 2 yield of 1131.59 mu mol L -1 h- 1 under visible light, which is 5.85 times greater than that of the A-TCN catalyst. This enhancement is ascribed to the synergistic effects of the oxygen vacancies (Ov) and nitrogen vacancies (Nv) defects, which amplify light absorption, facilitate electronhole pair separation, and augment the number of active sites on the catalyst surface. Density functional theory (DFT) calculations and energy band analysis were employed to elucidate the photocatalytic mechanism of AT x CN x , revealing that H 2 O 2 synthesis predominantly occurs through two consecutive reactions, enabled by the catalyst 's unique electronic structure and defect configuration. This study not only validates the exceptional photocatalytic performance of A-T x CN x but also provides valuable insights for the design and optimization of future photocatalysts aimed at sustainable H 2 O 2 production.

TiO2 nanotubes rich in oxygen vacancies (Ov), which were successfully fabricated on Ti foils, were used as the working electrode of a photoelectrochemical (PEC) sensor. The TiO2 nanotube electrode optimized with abundant Ov demonstrated a remarkable photocurrent density of 1.03 mA/cm2, which is approximately 2.9 times higher than that of the TiO2 nanotube electrode. When applied to the detection of DOC, this electrode exhibited a wide linear detection range spanning from 0.1 to 100 μM and achieved an exceptionally low detection limit of 0.043 μM with a signal-to-noise ratio of 3. Furthermore, comparative experiments indicated that the Ov-enriched TiO2 nanotube electrode exhibited excellent anti-interference capabilities and long-term stability, ensuring the accuracy and reliability of the detection outcomes. The superior detection performance is primarily attributed to two aspects: on one hand, Ov act as electron traps, facilitating the capture and transfer of photogenerated electrons, effectively prolonging the lifetime of these carriers; on the other hand, Ov also serves as active sites, enhancing the adsorption of DOC molecules and reaction kinetics, further amplifying the detection signal. This work offers a theoretical and experimental groundwork for the rapid monitoring of residual antibiotics.

The photocatalytic synthesis of hydrogen peroxide (H2O2) is an environmentally benign and sustainable approach. In this study, we have synthesized a TiO2-x/g-C3N4-x(A-TxCNx) photocatalyst with a Z-scheme heterojunction by introducing oxygen and nitrogen double vacancies through a one-step reduction process. The optimized A-TxCNx catalyst exhibited a superior H2O2 yield of 1131.59 μmol L–1h−1 under visible light, which is 5.85 times greater than that of the A-TCN catalyst. This enhancement is ascribed to the synergistic effects of the oxygen vacancies (Ov) and nitrogen vacancies (Nv) defects, which amplify light absorption, facilitate electron-hole pair separation, and augment the number of active sites on the catalyst surface. Density functional theory (DFT) calculations and energy band analysis were employed to elucidate the photocatalytic mechanism of A-TxCNx, revealing that H2O2 synthesis predominantly occurs through two consecutive reactions, enabled by the catalyst’s unique electronic structure and defect configuration. This study not only validates the exceptional photocatalytic performance of A-TxCNx but also provides valuable insights for the design and optimization of future photocatalysts aimed at sustainable H2O2 production.

A simple direct writing method to on-demand design flexible 2D M 2 C (M = Ti, V, Mo, Nb) MXene SERS substrates is developed.

This study introduces two-dimensional (2D) Ta4C3 and Nb4C3 MXenes as outstanding materials for surface-enhanced Raman scattering (SERS) sensing, marking a significant departure from traditional noble-metal substrates. These MXenes exhibit exceptional SERS capabilities, achieving enhancement factors around 105 and detection limits as low as 10-7 M for various analytes, including environmental pollutants and drugs. The core of their SERS functionality is attributed to the robust interfacial photoinduced charge-transfer interactions between the MXenes and the adsorbed molecules. This deep insight not only advances our understanding of MXene materials in SERS applications but also opens new avenues for developing highly sensitive and selective SERS sensors. The potential of Ta4C3 and Nb4C3 MXenes to revolutionize SERS technology underscores their importance in environmental monitoring, food safety, and beyond.

This work reports a hierarchically structured micromotor (HSM) surface-enhanced Raman scattering (SERS) platform comprising 3D tubular configurations with nanostructured outer walls. The HSMs can be powered by an external magnetic field in solution to enrich molecules with promoted adsorption efficiency. The nanostructured outer wall serves as containers to collect molecules and produce strong localized surface plasmon resonance to intensify Raman of the enriched molecules. Further coupling of HSMs after molecular enrichment can produce additional plasmonic hotspots at the sites where the molecules were enriched, providing a solution to manipulate molecules to enter the plasmonic hotspot region. Moreover, functionalizing specific molecules on the outer wall of HSMs enables high-specificity SERS sensing for benzaldehyde (BA) and Cu2+ ions in liquid. This SERS platform demonstrates great potential for practical applications in biochemical analysis and environmental monitoring, offering a rapid and sensitive tool for detecting low-concentration analytes in liquid.

This Letter introduces MXene-based rod-like micromotors, consisting of assembled Fe3O4@Ti2C core-shell nanospheres, that leverage external magnetic fields for active molecular enrichment and selective surface-enhanced Raman scattering (SERS) sensing. These micromotors enhance SERS performance by concentrating target molecules directly onto MXene surfaces during movement, enabling rapid and precise detection. Our investigation reveals how these micromotors optimize SERS through effective molecular manipulation and explores the selective Raman enhancement facilitated by the MXene-based platforms, demonstrating their significant potential in analytical applications.

Surface-enhanced Raman spectroscopy (SERS) is an ultrasensitive surface analysis technique that is widely used in chemical sensing, bioanalysis, and environmental monitoring. The design of the SERS substrates is crucial for obtaining high-quality SERS signals. Recently, 2D transition metal dichalcogenides (2D TMDs) have emerged as high-performance SERS substrates due to their superior stability, ease of fabrication, biocompatibility, controllable doping, and tunable bandgaps and excitons. In this review, a systematic overview of the latest advancements in 2D TMDs SERS substrates is provided. This review comprehensively summarizes the candidate 2D TMDs SERS materials, elucidates their working principles for SERS, explores the strategies to optimize their SERS performance, and highlights their practical applications. Particularly delved into are the material engineering strategies, including defect engineering, alloy engineering, thickness engineering, and heterojunction engineering. Additionally, the challenges and future prospects associated with the development of 2D TMDs SERS substrates are discussed, outlining potential directions that may lead to significant breakthroughs in practical applications.

Two-dimensional (2D) MXenes stand out as promising platforms for surface-enhanced Raman scattering (SERS) sensing owing to their metallic feature, various compositions, high surface area, compatibility with functionalization, and ease of fabrication. In this work, we report a high-performance 2D titanium carbonitride (Ti3CN) MXene SERS substrate. We reveal that the abundant electronic density of states near the Fermi level of Ti3CN MXene boosts the efficiency of photo-induced charge transfer at the interface of Ti3CN/molecule, resulting in significant Raman enhancement. The SERS sensitivity of Ti3CN MXene is further promoted through a 2D morphology regulation and molecular enrichment strategies. Moreover, prohibited drugs are detectable on this substrate, presenting the potential of trace-amount analysis on Ti3CN MXene. This work provides a deep insight of the SERS mechanisms of Ti3CN MXene and broadens the practical application of transition metal carbonitride MXene SERS substrates.

With the growing development of the Internet of things, wearable electronic devices have been extensively applied in civilian and military fields. As an essential component of data transmission in wearable electronics, a flexible antenna is one of the key aspects of research. Conventional metal antennas suffer from a large skin depth, and cannot satisfy the requirements of wearable electronics such as light weight, flexibility, and thinness. Recently, a group of two-dimensional metallic metal carbides (named MXenes) have been explored as building blocks for high-performance flexible antennas with excellent flexibility and superior mechanical strength. The appearance of hydrophilic functional groups at the surface of a MXene allows simple, scalable, and environmentally friendly manufacturing of MXene-based antennas. In this minireview, some pioneering works of MXene-based flexible radio frequency components are summarized, and the existing bottlenecks and the future trends of this promising field are discussed.

As an emerging class of two-dimensional (2D) materials, MBenes show enormous potential for optoelectronic applications. However, their use in molecular sensing as surface-enhanced Raman scattering (SERS)-active material is unknown. Herein, for the first time, we develop a brand-new high-performance MBene SERS platform. Ordered vacancy-triggered highly sensitive SERS platform with outstanding signal uniformity based on a 2D Mo4/3B2 MBene material was designed. The 2D Mo4/3B2 MBene presented superior SERS activity to most of the semiconductor SERS substrates, showing a remarkable Raman enhancement factor of 3.88 × 106 and an ultralow detection limit of 1 × 10-9 M. The underlying SERS mechanism is revealed from systematic experiments and density functional theory calculations that the ultrahigh SERS sensitivity of 2D Mo4/3B2 MBene is derived from the efficient photoinduced charge transfer process between MBene substrates and adsorbed molecules. The abundant electronic density of states near the Fermi level of 2D Mo4/3B2 MBene enables its Raman enhancement by a factor of 100 000 times higher than that of the bulk MoB. Consequently, the 2D Mo4/3B2 MBene could accurately detect various trace chemical analytes. Moreover, with ordered metal vacancies in the 2D Mo4/3B2 MBene, uniform charge transfer sites are formed, resulting in an outstanding signal uniformity with a relative standard deviation down to 6.0%. This work opens up a new horizon for the high-performance SERS platform based on MBene materials, which holds great promise in the field of chemical sensing.

In this paper, regular rhombic crystals have been synthesized from 8-hydroxyquinoline derivative coordinated with Zn2+ ions via interface reaction. The size of the crystal can be controlled by the concentration of the ligand solution according to the results of scanning electron microscope. The rhombic crystal has a red-shifted absorption band by comparison with the benzonitrile substituted 8-hydroxyquinoline ligand and shows orange emission. Many lamellas have been found in the synthesized crystal, which are stacked regularly to form the flake-type crystal due to the strong interaction forces induced by nitrile groups on the surface of the lamella.

Two-dimensional (2D) MXene materials have attracted broad interest in surface-enhanced Raman scattering (SERS) applications by virtue of their abundant surface terminations and excellent photoelectric properties. Herein, we propose to design highly sensitive MXene-based SERS membranes by integrating a 2D downsizing strategy with molecular enrichment approaches. Two types of 2D vanadium carbide (V4C3 and V2C) MXenes are demonstrated for ultrasensitive SERS sensing, and corresponding SERS mechanisms including the effect of 2D vanadium carbide thickness on their electron density states and interfacial photoinduced charge transfer resonance were discussed. A 2D downsizing strategy authorizes nonplasmonic SERS detection with a sensitivity of 1 × 10-7 M. Moreover, the performance can be further upgraded by vacuum-assisted filtration, which enables an ultrarapid molecular enrichment (within 2 min), ultrahigh molecular removal rate (over 95%), and improved sensitivity (5 × 10-9 M). This work may shed light on the MXene-based materials as an innovative platform for nonplasmonic SERS detection.

Noble-metal-free surface-enhanced Raman scattering (SERS) substrates have attracted great attention for their abundant sources, good signal uniformity, superior biocompatibility, and high chemical stability. However, the lack of controllable synthesis and fabrication of noble-metal-free substrates with high SERS activity impedes their practical applications. Herein, we propose a general strategy to fabricate a series of planar transition-metal nitride (TMN) SERS chips via an ambient temperature sputtering deposition route. For the first time, tungsten nitride (WN) and tantalum nitride (TaN) are used as SERS materials. These planar TMN chips show remarkable Raman enhancement factors (EFs) with ∼ 105 owing to efficient photoinduced charge transfer process between TMN chips and probe molecules. Further, structural engineering of these TMN chips is used to improve their SERS activity. Benefiting from the synergistic effect of charge transfer process and electric field enhancement by constructing a nanocavity structure, the Raman EF of WN nanocavity chips could be greatly improved to ∼ 1.29 × 107, which is an order of magnitude higher than that of planar chips. Moreover, we also design the WN/monolayer MoS2 heterostructure chips. With the increase of surface electron density on the upper WN and more exciton resonance transitions in the heterostructure, a ∼ 1.94 × 107 level EF and a 5 × 10−10 M level detection limit could be achieved. Our results provide important guidance for the structural design of ultrasensitive noble-metal-free SERS chips.

Efficient photoinduced charge transfer (PICT) resonance is crucial to the surface-enhanced Raman scattering (SERS) performance of metal oxide substrates. Herein, we venture into the hot-electron injection strategy to achieve unprecedented enhanced PICT efficiency between substrates and molecules. A heterojunction array composed of plasmonic MoO2 and semiconducting WO3-x is designed to prove the concept. The plasmonic MoO2 generates intense localized surface plasmon resonance under illumination, which can generate near-field Raman enhancement as well as accompanied plasmon-induced hot-electrons. The hot-electron injection in direct interfacial charge transfer and plasmon-induced charge transfer process can effectively promote the PICT efficiency between substrates and molecules, achieving a record Raman enhancement factor among metal oxide substrates (2.12 × 108) and the ultrasensitive detection of target molecule down to 10-11 M. This work demonstrates the possibility of hot-electron manipulation to realize unprecedented Raman enhancement in metal oxides, offering a cutting-edge strategy to design high-performance SERS substrates.

Plasmon-free surface-enhanced Raman scattering (SERS) substrates have attracted tremendous attention for their abundant sources, excellent chemical stability, superior biocompatibility, good signal uniformity, and unique selectivity to target molecules. Recently, researchers have made great progress in fabricating novel plasmon-free SERS substrates and exploring new enhancement strategies to improve their sensitivity. This review summarizes the recent developments of plasmon-free SERS substrates and specially focuses on the enhancement mechanisms and strategies. Furthermore, the promising applications of plasmon-free SERS substrates in biomedical diagnosis, metal ions and organic pollutants sensing, chemical and biochemical reactions monitoring, and photoelectric characterization are introduced. Finally, current challenges and future research opportunities in plasmon-free SERS substrates are briefly discussed.

Plasmonic tungsten carbide, niobium carbide, titanium carbide and molybdenum carbide chips possess remarkable SERS activity.

As a powerful analytical tool of molecular detection, surface-enhanced Raman spectroscopy (SERS) has attracted great attention in varied fields. However, it has seriously impeded the development of SERS that the preparation process is generally complicated and traditional substrates lack eco-friendliness, economy and flexibility. Herein, we fabricated the inkjet-printed paper-based semiconducting SERS substrates for the first time via an inexpensive office inkjet printer with representative two-dimensional MoO3-x nanosheets ink. Compared with conventional substrates, these paper-based semiconducting substrates not only could meet the requirements of simple and large-scale preparation, but also realize efficient sample collection by merely swabbing the surface. We obtained the detection limit concentration of rhodamine 6G as low as 10-7 M. Furthermore, these flexible paper-based substrates were successfully applied to detect crystal violet and malachite green on the fish surface by swabbing. With immense potentiality in practical applications, the inkjet-printed paper-based semiconducting SERS substrates are expected to open a new prospect for SERS.

Nano/submicro vanadium dioxide rods in monoclinic phase (VO2 (M)) were synthesized through hydrothermal reaction combined with subsequent calcinations. The morphology and structure of samples were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The average diameter of VO2 (M) dioxide rods from 210 nm to 1 μm were successfully controlled by adjusting the synthesis conditions including the concentration of Vanadium pentoxide (V2O5) solution and the molar ratio of V2O5 and oxalic acid. Our results reveal that the concentration of V2O5 is the key factor to determine the diameter of VO2 (M) rods, while higher molar ratio favors formation of VO2 rods with narrow diameter distributions. The growth mechanism of vanadium dioxide rods was discussed.

In the present work, the Zn-doped SnO2 (SnO2:Zn) thin films, with different Zn-doping concentration, were successfully prepared on Si (100) and glass substrates by direct current (DC) and radio frequency (RF) magnetron co-sputtering. The effects of dopant concentration, determined by the sputtering power applied on Zn target, on the structural, photoluminescent and optical performances of Zn-doped SnO2 films were investigated by X-ray diffraction(XRD), scanning electron microscope(SEM), energy dispersive X-ray (EDX),high-resolution transmission electron microscopy(HRTEM) and Ultraviolet-VisibleNear IR spectroscopy. The results show all these films exhibited excellent crystalline quality with tetragonal rutile structure. Two photoluminescence (PL) peaks related to Zn-doping were detected at about 351 nm (3.53 eV) and 369 nm (3.36 eV). Moreover, the average transmittance and the band gap energy of the films continuously decreased from 85% to 75% and from 3.52 eV to 334 eV, respectively, with the increase of the doping level. The excellent properties of Zn-doped SnO2 films make them capable for wider applications. (C) 2015 Elsevier Ltd. All rights reserved.