Abstract Over 80% of wastewater worldwide is released into the environment without proper treatment. Whilst environmental pollution continues to intensify due to the increase in the number of polluting industries, conventional techniques employed to clean the environment are poorly effective and are expensive. MXenes are a new class of 2D materials that have received a lot of attention for an extensive range of applications due to their tuneable interlayer spacing and tailorable surface chemistry. Several MXene‐based nanomaterials with remarkable properties have been proposed, synthesized, and used in environmental remediation applications. In this work, a comprehensive review of the state‐of‐the‐art research progress on the promising potential of surface functionalized MXenes as photocatalysts, adsorbents, and membranes for wastewater treatment is presented. The sources, composition, and effects of wastewater on human health and the environment are displayed. Furthermore, the synthesis, surface functionalization, and characterization techniques of merit used in the study of MXenes are discussed, detailing the effects of a range of factors (e.g., PH, temperature, precursor, etc.) on the synthesis, surface functionalization, and performance of the resulting MXenes. Finally, the limits of MXenes and MXene‐based materials as well as their potential future research directions, especially for wastewater treatment applications are highlighted.
Scanning electrochemical probe microscopy (SEPM) techniques can disclose the local electrochemical reactivity of interfaces in single-entity and sub-entity studies. Operando SEPM measurements consist of using a SEPM tip to investigate the performance of electrocatalysts, while the reactivity of the interface is simultaneously modulated. This powerful combination can correlate electrochemical activity with changes in surface properties, e.g., topography and structure, as well as provide insight into reaction mechanisms. The focus of this review is to reveal the recent progress in local SEPM measurements of the catalytic activity of a surface toward the reduction and evolution of O2 and H2 and electrochemical conversion of CO2. The capabilities of SEPMs are showcased, and the possibility of coupling other techniques to SEPMs is presented. Emphasis is given to scanning electrochemical microscopy (SECM), scanning ion conductance microscopy (SICM), electrochemical scanning tunneling microscopy (EC-STM), and scanning electrochemical cell microscopy (SECCM).
Abstract Simultaneous electroreduction of CO 2 and H 2 O to syngas can provide a sustainable feed for established processes used to synthesize carbon‐based chemicals. The synthesis of MO x /M‐N‐Cs (M = Ni, Fe) electrocatalysts reported via one‐step pyrolysis that shows increased performance during syngas electrosynthesis at high current densities with adaptable H 2 /CO ratios, e.g., for the Fischer–Tropsch process. When embedded in gas diffusion electrodes (GDEs) with optimized hydrophobicity, the NiO x /Ni‐N‐C catalyst produces syngas (H 2 /CO = 0.67) at −200 mA cm −2 while for the FeO x /Fe‐N‐C syngas production occurs at ≈−150 mA cm −2 . By tuning the electrocatalyst's microenvironment, stable operation for >3 h at −200 mA cm −2 is achieved with the NiO x /Ni‐N‐C GDE. Post‐electrolysis characterization revealed that the restructuring of the catalyst via reduction of NiO x to metallic Ni NPs still enables stable operation of the electrode at −200 mA cm −2 , when embedded in an optimized microenvironment. The ionomer and additives used in the catalyst layer are important for the observed stable operation. Operando Raman measurements confirm the presence of NiO x during CO formation and indicate weak adsorption of CO on the catalyst surface.
Since 2011, 2D transition metal carbides, carbonitrides and nitrides known as MXenes have gained huge attention due to their attractive chemical and electronic properties. The diverse functionalities of MXenes make them a promising candidate for multitude of applications. Recently, doping MXene with metallic and non-metallic elements has emerged as an exciting new approach to endow new properties to this 2D systems, opening a new paradigm of theoretical and experimental studies. In this review, we present a comprehensive overview on the recent progress in this emerging field of doped MXenes. We compare the different doping strategies; techniques used for their characterization and discuss the enhanced properties. The distinct advantages of doping in applications such as electrocatalysis, energy storage, photovoltaics, electronics, photonics, environmental remediation, sensors, and biomedical applications is elaborated. Additionally, theoretical developments in the field of electrocatalysis, energy storage, photovoltaics and electronics are explored to provide prospect into the specific advantages of doping along with the underlying mechanisms. Lastly, we present the advantages and challenges of doped MXenes to take forward this thriving field.
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