A comprehensive research experiment was designed for the preparation of ascorbic acid modified MXene Ti₃C₂ (MXene/VC) and its application in electrochemical detection of p-nitrophenol. Firstly, the Al species of Ti₃AlC₂ was removed by acid-etching to synthesize MXene-Ti₃C₂. Secondly, the MXene/VC material was fabricated by modifying MXene-Ti₃C₂ with VC. Subsequently, the MXene/VC material was characterized by infrared spectroscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. Finally, the differential pulse voltammetry (DPV) method was employed to systematically analyze the electrochemical detection of p-nitrophenol. The whole experimental process included multiple steps, such as literature consult, material preparation, microscopic characterization, electrochemical sensing performance testing and experimental report writing, which is conducive to the improvement of students' comprehensive quality.

Accurate and sensitive detection of uric acid (UA) is crucial, as abnormal UA levels are often indicative of various diseases. This work introduces a straightforward electrochemical sensor utilizing a 2D nanocomposite of S-doped g-C₃N₄ (SCN) and V₂CT_x MXene (SCN/V₂C), which was prepared via ball milling followed by calcination. The SCN/V₂C nanocomposite demonstrates superior conductivity and a reduced band gap relative to pure g-C₃N₄, leading to improved electrochemical performance for UA detection. Differential pulse voltammetry (DPV) measurements revealed a detection limit (LOD) of 1 μM for UA and a linear response range spanning from 3 μM to 1 mM. Furthermore, experimental results confirmed the excellent stability of the SCN/V₂C nanocomposite. Density functional theory (DFT) calculations revealed that SCN/V₂C acts as a powerful electron donor, while UA functions as an efficient electron acceptor. The electron transfer between SCN/V₂C and UA is significantly greater than that with other common interfering biological molecules, leading to the highest adsorption energy of UA on the SCN/V₂C surface. This strong interaction accounts for the sensor's exceptional selectivity. This newly developed sensor provides a straightforward and highly sensitive approach for the electrochemical detection of trace levels of UA in real biological samples.

g-C₃N₄ emerges as a promising metal-free semiconductor photocatalyst due to its cost-effectiveness, facile synthesis, suitable visible light response, and robust thermal stability. However, its practical application in photocatalytic hydrogen evolution reaction (HER) is impeded by rapid carrier recombination and limited light absorption capacity. In this study, we successfully develop a novel g-C₃N₄-based step-scheme (S-scheme) heterojunction comprising two-dimensional (2D) sulfur-doped g-C₃N₄ nanosheets (SCN) and one-dimensional (1D) FeCo₂O₄ nanorods (FeCo₂O₄), demonstrating enhanced photocatalytic HER activity. The engineered SCN/FeCo₂O₄ S-scheme heterojunction features a well-defined 2D/1D heterogeneous interface facilitating directed interfacial electron transfer from FeCo₂O₄ to SCN, driven by the lower Fermi level of SCN compared to FeCo₂O₄. This establishment of electron-interacting 2D/1D S-scheme heterojunction not only facilitates the separation and migration of photogenerated carriers, but also enhances visible-light absorption and mitigates electron-hole pair recombination. Band structure analysis and density functional theory calculations corroborate that the carrier migration in the SCN/FeCo₂O₄ photocatalyst adheres to a typical S-scheme heterojunction mechanism, effectively retaining highly reactive photogenerated electrons. Consequently, the optimized SCN/FeCo₂O₄ heterojunction exhibits a substantially high hydrogen production rate of 6303.5 μmol·g^–1·h^–1 under visible light excitation, which is 2.4 times higher than that of the SCN. Furthermore, the conjecture of the S-scheme mechanism is confirmed by in situ XPS measurement. The 2D/1D S-scheme heterojunction established in this study provides valuable insights into the development of high-efficiency carbon-based catalysts for diverse energy conversion and storage applications.

Emerging two-dimensional (2D) layered metal carbide and nitride materials, commonly termed MXenes, are increasingly recognized for their applications across diverse fields such as energy, environment, and catalysis. In the past few years, MXenes/carbon nanotubes (CNTs)-based hybrids have attracted extensive attention as an important catalyst in energy and environmental fields, due to their superior multifunctions and mechanical stability. This review aims to address the fabrication strategies, the identification of the enhancement mechanisms, and recent progress regarding the design and modification of MXenes/CNTs-based hybrids. A myriad of fabrication techniques have been systematically summarized, including mechanical mixing, spray drying, three-dimensional (3D) printing, self-assembly/in-situ growth, freeze drying, templating, hydrothermal methods, chemical vapor deposition (CVD), and rolling. Importantly, the identification of the enhancement mechanisms was thoroughly discussed from the two dimensions of theoretical simulations and in-situ analysis. Moreover, the recent advancements in profound applications of MXenes/CNTs-based hybrids have also been carefully revealed, including energy storage devices, sensors, water purification systems, and microwave absorption. We also underscore anticipated challenges related to their fabrication, structure, underlying mechanisms, modification approaches, and emergent applications. Consequently, this review offers insights into prospective directions and the future trajectory for these promising hybrids. It is expected that this review can inspire new ideas or provide new research methods for future studies.

Due to their unique properties and uninterrupted breakthrough in a myriad of clean energy-related applications, carbon-based materials have received great interest. However, the low selectivity and poor conductivity are two primary difficulties of traditional carbon-based materials (zero-dimensional (0D)/one-dimensional (1D)/two-dimensional (2D)), enerating inefficient hydrogen production and impeding the future commercialization of carbon-based materials. To improve hydrogen production, attempts are made to enlarge the surface area of porous three-dimensional (3D) carbon-based materials, achieve uniform interconnected porous channels, and enhance their stability, especially under extreme conditions. In this review, the structural advantages and performance improvements of porous carbon nanotubes (CNTs), g-C₃N₄, covalent organic frameworks (COFs), metal-organic frameworks (MOFs), MXenes, and biomass-derived carbon-based materials are firstly summarized, followed by discussing the mechanisms involved and assessing the performance of the main hydrogen production methods. These include, for example, photo/electrocatalytic hydrogen production, release from methanolysis of sodium borohydride, methane decomposition, and pyrolysis-gasification. The role that the active sites of porous carbon-based materials play in promoting charge transport, and enhancing electrical conductivity and stability, in a hydrogen production process is discussed. The current challenges and future directions are also discussed to provide guidelines for the development of next-generation high-efficiency hydrogen 3D porous carbon-based materials prospected.

CoS₂ is considered to be a promising electrocatalyst for hydrogen evolution reaction (HER). However, its further widespread applications are hampered by the unsatisfactory activity due to relatively high chemisorption energy for hydrogen atom. Herein, theoretical predictions of first-principles calculations reveal that the introduction of a Cl-terminated MXenes-Ti₃CNCl₂ can significantly reduce the HER potential of CoS₂-based materials and the Ti₃CNCl₂@CoS₂ core–shell nanostructure has Gibbs free energy of hydrogen adsorption (|ΔG_H|) close to zero, much lower than that of the pristine CoS₂ and Ti₃CNCl₂. Inspired by the theoretical predictions, we have successfully fabricated a unique Ti₃CNCl₂@CoS₂ core–shell nanostructure by ingeniously coupling CoS₂ with a Cl-terminated MXenes-Ti₃CNCl₂. Interface-charge transfer between CoS₂ and Ti₃CNCl₂ results in a higher degree of electronic localization and a formation of chemical bonding. Thus, the Ti₃CNCl₂@CoS₂ core–shell nanostructure achieves a significant enhancement in HER activity compared to pristine CoS₂ and Ti₃CNCl₂. Theoretical calculations further confirm that the partial density of states of CoS₂ after hybridization becomes more non-localized, and easier to interact with hydrogen ions, thus boosting HER performance. In this work, the success of oriented experimental fabrication of high-efficiency Ti₃CNCl₂@CoS₂ electrocatalysts guided by theoretical predictions provides a powerful lead for the further strategic design and fabrication of efficient HER electrocatalysts.