In recent years, a new large family of two dimensional transition metal carbides, carbonitrides, and nitrides, so-called MXenes, have grabbed considerable attention, owing to their many fascinating physical and chemical properties that are closely related to the rich diversity of their elemental compositions and surface terminations. In particular, it is easy for MXenes to form composites with other materials such as polymers, oxides, and carbon nanotubes, which further provides an effective way to tune the properties of MXenes for various applications. Not only have MXenes and MXene-based composites come into prominence as electrode materials in the energy storage field as is widely known, but they have also shown great potential in environment-related applications including electro/photocatalytic water splitting, photocatalytic reduction of carbon dioxide, water purification and sensors, thanks to their high conductivity, reducibility and biocompatibility. In this review, we summarize the synthesis and properties of MXenes and MXene-based composites and highlight their recent advances in environment-related applications. Challenges and perspectives for future research are also outlined.

MXene and MXene-based composites: synthesis, properties and environment-related applications

MXenes: Applications in electrocatalytic, photocatalytic hydrogen evolution reaction and CO2 reduction

Novel synthesized cationic surfactants based on natural piper nigrum as sustainable-green inhibitors for steel pipeline corrosion in CO2-3.5%NaCl: DFT, Monte Carlo simulations and experimental approaches

Methods of synthesis, characteristics, and environmental applications of MXene: A comprehensive review.

Methods of synthesis, characteristics, and environmental applications of MXene: A comprehensive review

The inhibition performance of three pyrido[1,2-a]benzimidazoles, namely, benzo[4,5]imidazo[1,2-a]pyridine (BIP), 2-methylbenzo[4,5]imidazo[1,2-a]pyridine (MBIP), and 2-(trifluoromethyl)benzo[4,5]imidazo[1,2-a]pyridine (TBIP), for steel corrosion in hydrochloric acid solution were researched through a weight loss test, electrochemical techniques, surface morphology (SEM, XPS) studies, and theoretical methods. The experimental results revealed that TBIP, BIP, and MBIP had excellent inhibition performance, and their maximum inhibition efficiencies at 0.25 mmol L−1 were 95.48%, 97.65%, and 98.96%, respectively. The properties of these inhibitors are considered to be mixed-type, and their adsorption mode belongs to the Langmuir isothermal type. The formation and properties of an adsorbed film on a steel surface were investigated using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Quantum chemical calculations provided insightful quantitative information to conclude the correlation between the molecular structures and inhibition performance. Molecular dynamics (MD) simulations were carried out to explore the configurationally adsorption behavior of these pyrido[1,2-a]benzimidazoles on Fe(110) surface, and the binding energy of these three inhibitors followed the order MBIP > BIP > TBIP, which is consistent with the experimental evaluation results.

Highly effective inhibition of mild steel corrosion in HCl solution by using pyrido[1,2-a]benzimidazoles

Tetrahydroacridines as corrosion inhibitor for X80 steel corrosion in simulated acidic oilfield water

A series of acridines were designed and synthesized for the development of effective inhibitors for mild steel corrosion in 1 M HCl solution, in which the halogen-substituted acridines showed better inhibitive performance than the nonhalogen-substituted acridines. The corrosion protection properties of the halogen-substituted acridines, including 2-chloro-9-phenylacridine (CPA), 2-chloro-9-(2-fluorophenyl)acridine (CFPA), and 2-bromo-9-(2-fluorophenyl)acridine (BFPA), were further investigated using weight loss test and electrochemical techniques. The results indicated the halogen-substituted acridines have excellent inhibitiion performance, and these acridines act as mixed-type inhibitors with predominant cathodic effectiveness. Adsorption of acridines on a mild steel surface obeyed the Langmuir adsorption isotherm. The adsorption of the inhibitor molecules on the steel surface was further supported by scanning electron microscopy (SEM), scanning electrochemical microscopy (SECM), and FTIR spectroscopy. ...

Halogen-Substituted Acridines as Highly Effective Corrosion Inhibitors for Mild Steel in Acid Medium

Aloe polysaccharide as an eco-friendly corrosion inhibitor for mild steel in simulated acidic oilfield water: Experimental and theoretical approaches

The generation of hydrogen by water splitting through the electrocatalytic approach could become a sustainable way to replace traditional fossil energy. The search for alternatives to the precious metals (Pt, Pd, and Ir) for hydrogen production from water splitting is one of the central issues in the area of renewable energy. Two-dimensional metal carbide and nitride (MXenes) materials have shown some characteristics of promising catalysts for the hydrogen evolution reaction (HER). Herein, we performed density functional calculations to systematically explore the exfoliation properties of more than 50 MAX phases and the HER performances of 30 MXenes to search the universal descriptors for the HER performances of MXenes. The exfoliation properties of MAXs were studied and the results showed that for most MAXs, the lower the binding energy of A elements, the higher the exfoliation energy of 2D MXenes from MAXs. A critical value of exfoliation energy of 0.253 eV A−2 was obtained, whereby MAXs with an exfoliation energy lower than this value favor exfoliation. For the predication of the HER performances of MXenes, two descriptors, namely Ne and Ef, have been proposed in the literature. The present calculations illustrated that these two parameters could not fully address the influence of hydrogen coverage on the Gibbs free energy of hydrogen adsorption (ΔGH*) on MXenes. Further studies indicated that both Ne and Ef relate to the surface-terminated O-p orbital center (ep), whereby the lower ep, the larger Ne and Ef, and the stronger interaction between O* with MXenes substrates. However, it is not favored for HER, if ep is either too large or too small. These results show that the surface-terminated O-p orbital center ep, could be used as a good descriptor for predicting the HER performances of MXenes. The best values of ep were in the range of −4.1 to −3.3 eV, with the corresponding values of Ne and Ef from 0.93 to 1.15 e and 3.15 to 3.78 eV, respectively, and ΔGH* from −0.3 to 0.3 eV. The result for the energy change in the HER process (Volmer–Heyrovsky and Volmer–Tafel mechanisms) of 10 M2CO2, and the minimum energy pathway of Mo2CO2 and Zr2CO2 confirmed that MXenes with a medium ep could deliver optimal HER performance.

Li-Juan Wang

Papers

Highly effective inhibition of mild steel corrosion in HCl solution by using pyrido[1,2-a]benzimidazoles

Tetrahydroacridines as corrosion inhibitor for X80 steel corrosion in simulated acidic oilfield water

Halogen-Substituted Acridines as Highly Effective Corrosion Inhibitors for Mild Steel in Acid Medium

Aloe polysaccharide as an eco-friendly corrosion inhibitor for mild steel in simulated acidic oilfield water: Experimental and theoretical approaches

Deep insights into the exfoliation properties of MAX to MXenes and the hydrogen evolution performances of 2D MXenes