Laminated Hybrid Junction of Sulfur-Doped TiO2 and a Carbon Substrate Derived from Ti3C2 MXenes: Toward Highly Visible Light-Driven Photocatalytic Hydrogen Evolution

Bandgap engineering via boron and sulphur doped carbon modified anatase TiO2: a visible light stimulated photocatalyst for photo-fixation of N2 and TCH degradation

The present research reports the synthesis of two-dimensional (2D) sheet/flake-like nanostructures of crystalline carbon modified TiO₂ (CT), B-TiO₂ (B-CT), and S-TiO₂ (S-CT) using a facile one-pot synthesis method. The crystallinity and phase purity (anatase) of the prepared nano-photocatalyst were characterised using X-ray diffraction, selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM) analysis. Furthermore, the morphological details and elemental content of the sample were studied via scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), respectively. Additionally, the optoelectronic features of all of the prepared specimens were measured via UV-vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL), impedance and Mott-Schottky studies. After successful characterisation, their photocatalytic performance was tested towards dinitrogen photo-fixation and tetracycline hydrochloride (TCH) degradation under visible light illumination. Moreover, the effective charge separation and greater availability of the active surface area led to the robust photocatalytic activity of the fabricated B-CT compared to the CT and S-CT samples, which correlates well with the PL, impedance and surface area analysis. B-CT displays the highest photocatalytic activity, i.e. 32.38 μmol L^-1 (conversion efficiency = 0.076%) of ammonia production, and 95% tetracycline hydrochloride (10 ppm) degradation. Here, we have effectively designed a novel and productive pathway towards the enhancement of the photocatalytic performance of visible photon active TiO₂-based materials for energy and environmental sustainability.

CVD growth of large-area InS atomic layers and device applications

Group-III monochalcogenides of two-dimensional (2D) layered materials have attracted widespread attention among scientists due to their unique electronic performance and interesting chemical and physical properties. Indium sulfide (InS) is attracting increasing interest from scientists because it has two distinct crystal structures. However, studies on the synthesis of highly crystalline, large-area, and atomically thin-film InS have not been reported thus far. Here, the chemical vapor deposition (CVD) synthesis method of atomic InS crystals has been reported in this paper. The direct chemical vapour phase reaction of metal oxides with chalcogen precursors produces a large-sized hexagonal crystal structure and atomic-thickness InS flakes or films. The InS atomic films are merged with a plurality of triangular InS crystals that are uniform and entire and have surface areas of 1 cm2 and controllable thicknesses in bilayers or trilayers. The properties of the as-grown highly crystalline samples were characterized by spectroscopic and microscopic measurements. The ion-gel gated InS field-effect transistors (FETs) reveal n-type transport behavior, and have an on-off current ratio of >103 and a room-temperature electron mobility of ∼2 cm2 V-1 s-1. Moreover, our CVD InS can be transferred from mica to any substrates, so various 2D materials can be reassembled into vertically stacked heterostructures, thus facilitating the development of heterojunctions and exploration of the properties and applications of their interactions.

Cobalt oxysulphide/hydroxide nanosheets with dual properties based on electrochromism and a charge storage mechanism

The charge storage mechanism of mixed cobalt oxysulphide/hydroxide materials having electrochromic properties was investigated. The cobalt oxysulphide/hydroxide materials exhibit a dual reversible redox reaction and electrochromic properties in 1 M KOH during charging and discharging.

The charge storage mechanism of mixed cobalt oxysulphide/hydroxide materials having electrochromic properties was investigated.

An Efficient Photocatalyst Based on Black TiO2 Nanoparticles and Porous Carbon with High Surface Area: Degradation of Antibiotics and Organic Pollutants in Water

Porous carbon (PC) materials with high surface area can separate electron-hole pairs and adsorb organic pollutants more effectively. A series of nanocomposites were prepared by anchoring black TiO₂ nanoparticles (BTN) onto PC through a calcination process. Chemical and structural features of samples were examined by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, powder X-ray diffraction (P-XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses. The resulting adsorption-photocatalysis synergistic effect led to a dramatically improved photocurrent for BTN@PCs, thus indicating the high photocatalytic performance toward water-soluble organic species. For instance, the degradation of tetracycline under visible light reached 90 %, which is higher than that for activated carbon doped onto BTN (57 %) without any additional agents. Moreover, the degradation of other antibiotics (such as oxytetracycline and ciprofloxacin) and methylene blue were also studied, thus showing that this system has the potential to be used for water treatment.

MIL-100(Fe)/Ti3C2 MXene as a Schottky Catalyst with Enhanced Photocatalytic Oxidation for Nitrogen Fixation Activities

A new microporous MIL-100(Fe)/Ti₃C₂ MXene composite was constructed as a non-noble metal-based Schottky junction photocatalyst with improved nitrogen fixation ability. Ti₃C₂ MXene nanosheets exhibited excellent metal conductivity and were employed as two-dimensional support to optimize the composite's energy band structure. MIL-100(Fe) with a large specific surface area was used as an adsorbent and a photocatalytic oxidation center. The MIL-100(Fe)/Ti₃C₂ MXene composite not only exhibited higher thermal stability but also showed significantly increased nitrogen fixation activity under visible light. The NO conversion rate of the composite catalyst was about four and three times higher than that of the pure Ti₃C₂ MXene and the pure MIL-100(Fe) samples, respectively. Although adsorption plays an important role in the nitrogen fixation process, the synergistic effects of the Schottky junctions are the main cause of the enhanced photocatalytic activity. The built-in electric field can be generated to form charge-transfer channels, which help to achieve a desirable photocatalytic activity.

2D MXenes as Co-catalysts in Photocatalysis: Synthetic Methods

Since their seminal discovery in 2011, two-dimensional (2D) transition metal carbides/nitrides known as MXenes, that constitute a large family of 2D materials, have been targeted toward various applications due to their outstanding electronic properties. MXenes functioning as co-catalyst in combination with certain photocatalysts have been applied in photocatalytic systems to enhance photogenerated charge separation, suppress rapid charge recombination, and convert solar energy into chemical energy or use it in the degradation of organic compounds. The photocatalytic performance greatly depends on the composition and morphology of the photocatalyst, which, in turn, are determined by the method of preparation used. Here, we review the four different synthesis methods (mechanical mixing, self-assembly, in situ decoration, and oxidation) reported for MXenes in view of their application as co-catalyst in photocatalysis. In addition, the working mechanism for MXenes application in photocatalysis is discussed and an outlook for future research is also provided.

Two-Dimensional Transition Metal MXene-Based Photocatalysts for Solar Fuel Generation

The exploration of advanced and novel photocatalytic materials has been widely investigated in recent years. MXene, a new two-dimensional (2D) transition metal material, is gaining attention as a suitable alternative for promoting photocatalytic performance because of its flexible adjustability of elemental composition, regular layered structure, and excellent electrical conductivity. This Perspective summarizes the recent significant advancements in 2D MXene-based photocatalysts for solar fuel conversion. The rational design and specific effects of MXene-based photocatalysts for photocatalytic solar fuel generation are described. Moreover, the different roles of MXene in MXene-based photocatalysts, such as functional group provider, photocatalytic electronic acceptor, substrate, and cocatalyst, for improving photocatalytic performance are discussed. Further discussion about the challenges and optimizations for improvements of 2D MXene and MXene-based photocatalysts in the context of promising solar fuel generation is also presented.

Surface Modified MXene-Based Nanocomposites for Electrochemical Energy Conversion and Storage

In recent years, the rapidly growing attention on MXenes makes the material a rising star in the 2D materials family. Although most researchers' interests are still focused on the properties of bare MXenes, little attention has been paid to the surface chemistry of MXenes and MXene-based nanocomposites. To this end, this Review offers a comprehensive discussion on surface modified MXene-based nanocomposites for energy conversion and storage (ECS) applications. Based on the structure and reaction mechanism, the related synthesis methods toward MXenes are briefly summarized. After the discussion of existing surface modification techniques, the surface modified MXene-based nanocomposites and their inherent chemical principles are presented. Finally, the application of these surface modified nanocomposites for supercapacitors (SCs), lithium/sodium-ion batteries (LIBs/SIBs), and electrocatalytic water splitting is discussed. The challenges and prospects of MXene-based nanocomposites for future ECS applications are also presented.

Applications of 2D MXenes in energy conversion and storage systems

This article provides a comprehensive review of MXene materials and their energy-related applications.

Bifunctional, Moth-Eye-Like Nanostructured Black Titania Nanocomposites for Solar-Driven Clean Water Generation

Solar steam generation and photocatalytic degradation have been regarded as the most promising techniques to address clean water scarcity issues. Although enormous efforts have been devoted to exploring high-efficiency clean water generation, many challenges still remain in terms of single decontamination function, relatively low efficiency, and inability to practical application. Herein, we first report the bioinspired fabrication of black titania (BT) nanocomposites with moth-eye-like nanostructures on carbon cloth for solar-driven clean water generation through solar steam generation and photocatalytic degradation. The moth-eye-like BT nanoarrays can largely prolong the effective propagation path of absorbing light and enhance the scattering of light, thereby exhibiting outstanding light absorption of 96% in the full spectrum. Such hierarchical-nanostructured BT nanocomposites not only impressively achieve solar steam efficiency of 94% under a simulated light of 1 kW m^-2 but also show the prominent performance of desalination and steam generation in real life condition. In addition, 96% of rhodamine B is degraded using BT nanocomposites as a photocatalyst in 100 min. The moth-eye-like bioinspired designing concept and bifunctional applications in this study may open up a new strategy for maximizing solar energy utilization and clean water generation.