Two-dimensional MXenes: From morphological to optical, electric, and magnetic properties and applications

g-C3N4界面改性:掺杂金属硫化物构建新型异质结光催化剂的能源转换展望

Highly-efficient materials and technologies for environmental pollutant treatment and hydrogen production are urgently needed in "green" 21st century. Notably, photocatalytic process over carbon nanomaterials (CNMs)-modified photocatalysts is an effective solution for these crises. CNMs (e.g., fullerenes, carbon nanotubes, graphene, carbon nanofibers, and carbon quantum dots) reveal remarkable morphological, mechanical, electrical and optical properties, which have been of significantly scientific and technological interest in photocatalysis. Until now, many efforts have been made to take advantage of these unique size- and surface-dependent properties of CNMs for photocatalytic process. In this review, we firstly summarize selective preparation of CNMs that has a great impact on their photocatalytic performance. Then we provide an updated outline of advanced photocatalytic application of CNMs in addressing both environmental pollution and hydrogen energy crisis. The difference in the role of various CNMs play in the enhancement of photocatalytic performance is also discussed. Lastly, we discuss the limitations of CNMs applied in photocatalysis or even wider fields. We hope this review will project a fast developmental path with providing a wide view of recent preparation methods, applications, prospects and challenges.

Selective prepared carbon nanomaterials for advanced photocatalytic application in environmental pollutant treatment and hydrogen production

Charge carrier trapping, recombination and transfer during TiO2 photocatalysis: An overview

Gelation is an effective way to realize the self-assembly of nanomaterials into different macrostructures, and in a typical use, the gelation of graphene oxide (GO) produces various graphene-based carbon materials with different applications. However, the gelation of MXenes, another important type of 2D materials that have different surface chemistry from GO, is difficult to achieve. Here, the first gelation of MXenes in an aqueous dispersion that is initiated by divalent metal ions is reported, where the strong interaction between these ions and OH groups on the MXene surface plays a key role. Typically, Fe2+ ions are introduced in the MXene dispersion which destroys the electrostatic repulsion force between the MXene nanosheets in the dispersion and acts as linkers to bond the nanosheets together, forming a 3D MXene network. The obtained hydrogel effectively avoids the restacking of the MXene nanosheets and greatly improves their surface utilization, resulting in a high rate performance when used as a supercapacitor electrode (≈226 F g-1 at 1 V s-1 ). It is believed that the gelation of MXenes indicates a new way to build various tunable MXene-based structures and develop different applications.

Fast Gelation of Ti 3 C 2 T x MXene Initiated by Metal Ions

Assembly of two-dimensional (2D) layered structures into three-dimensional (3D) macroscopic hydrogel has been an enduring attracting research theme. However, the anisotropic intersheet cross-linking to form Ti3C2Tx MXene-based hydrogel remains intrinsically challenging because of the superior hydrophilic nature of 2D Ti3C2Tx. Herein, Ti3C2Tx MXene is ingeniously assembled into the 3D macroscopic hydrogel under mild conditions by a graphene oxide (GO)-assisted self-convergence process. During the process, GO is reduced to reduced graphene oxide (RGO) by virtue of the reduction ability of Ti3C2Tx, leading to the partial removal of hydrophilic oxygen-containing groups and an increase of the hydrophobicity and the π-conjugated structures of RGO, which enables the assembly of RGO into a 3D RGO framework. Simultaneously, Ti3C2Tx is self-converged to be incorporated into the RGO framework by intimate interfacial interactions, thereby generating Ti3C2Tx-based hydrogel. The hydrogel with interconnected porous stru...

Ti3C2Tx-Based Three-Dimensional Hydrogel by a Graphene Oxide-Assisted Self-Convergence Process for Enhanced Photoredox Catalysis

Three-dimensional (3D) graphene aerogels, by virtue of their unique physicochemical properties, which result from the intrinsic properties of graphene and 3D porous structure characteristics, have attracted ever-increasing research interest in the field of photocatalysis for the sake of efficient utilization of solar energy. Herein, we intend to afford a concise review on the recent progress regarding the synthetic method of graphene aerogels and the promising applications of graphene aerogel-based photocatalysts in pollutant elimination, water splitting, CO2 reduction, organic synthesis and atmospheric ammonia synthesis. In particular, the superiorities of 3D graphene aerogel-based photocatalysts for various solar-driven photoredox applications have been demonstrated. Furthermore, in addition to discussing opportunities offered by graphene aerogel-supported photocatalysts, we will also describe the existing challenges and the future direction of graphene aerogel-based photocatalysts in this burgeoning research area. It is hoped that this review could spur multidisciplinary research interest for advancing the rational utilization of 3D graphene aerogels to synthesize more efficient photocatalysts for practical applications.

Photoredox catalysis over graphene aerogel-supported composites

The electrical conductivity and charge carrier mobility of reduced graphene oxide (RGO) based 3D aerogel using graphene oxide (GO) as precursor is often restricted by the intrinsic population of defects and thus disruption of 2D π-conjugation in the domain of RGO sheets. Here, we report a facile and efficient approach to improve the electrical conductivity of RGO aerogel by introducing highly conductive commercial Elicarb graphene (EGR). GO acting as a “macromolecular surfactant” can be used to simultaneously resolve the intrinsic drawback of low solution dispersibility of EGR and provides the basic skeleton for solution-processable synthesis of RGO@EGR-Eosin Y (RGO@EGR-EY) metal-free 3D aerogel composites. The as-synthesized RGO@EGR-EY aerogel with superior electrical conductivity facilitates more efficient separation and transfer of photogenerated charge carriers, and consequently exhibits much higher photocatalytic activity than RGO-EY aerogel. It is hoped that our current work could open promising prospects for the rational utilization of highly conductive commercial graphene to fabricate graphene-based aerogel for enhanced photoredox applications.

Hybridization of graphene oxide with commercial graphene for constructing 3D metal-free aerogel with enhanced photocatalysis

To design semiconductor-based photocatalysts with efficient charge carriers separation and transfer remains an enduring goal of artificial photosynthesis toward target redox reactions. Herein, we report a cascade monolith composite of ternary reduced graphene oxide aerogel/silver bromide/silver (RGA/AgBr/Ag) with efficient charge carriers separation, which exhibits much higher activity than bare AgBr toward photocatalytic bacteria inactivation. Mechanistic studies reveal that the reduced graphene oxide aerogel (RGA) scaffold and Ag nanoparticles serve as electron relay mediators to promote the charge carriers separation and transfer. In addition, the metallic Ag nanoparticles derived from the photoreduction of AgBr during the photocatalytic disinfection can further boost the separation of charge carriers. Control experiments demonstrate that the surface plasmon resonance (SPR)-excited hot electrons of Ag nanoparticles also contribute to enhancing the photoactivity of RGA/AgBr/Ag. As such, the synergy of multiple electron transfer behavior integratively leads to the boosted photocatalytic performance of such RGA/AgBr/Ag aerogel for bacteria inactivation with convenient recyclable operability.

3D graphene/AgBr/Ag cascade aerogel for efficient photocatalytic disinfection

Studies on localized surface plasmon resonance (LSPR) of noble metals (mainly gold and silver) regarding solar-driven photocatalysis have been attracting enormous interests over the past two decades. As research on LSPR continues to expand, recently, aluminum (Al) with respect to plasmonic enhanced photocatalysis beyond such noble metals has attracted considerable attention. Al as an abundant and relatively inexpensive metal holds great promise for plasmonic photocatalysis with outstanding light-harvesting capacity and performance in virtue of its unique optical characteristics. Herein, a short review is given on the related basics of LSPR, and the key factors including the size, shape, and oxide formation of Al nanostructures, which significantly influence the optical response of Al. In particular, photocatalytic applications in artificial photoredox processes with regard to plasmonic Al are outlined. In addition, some perspectives on the opportunity and challenge for future development of this research field are offered.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/ppsc.201600357

Xin Xin

Papers

Ti3C2Tx-Based Three-Dimensional Hydrogel by a Graphene Oxide-Assisted Self-Convergence Process for Enhanced Photoredox Catalysis

Photoredox catalysis over graphene aerogel-supported composites

Hybridization of graphene oxide with commercial graphene for constructing 3D metal-free aerogel with enhanced photocatalysis

3D graphene/AgBr/Ag cascade aerogel for efficient photocatalytic disinfection

Aluminum-Based Plasmonic Photocatalysis