Production of 2D NbOCl2 with controllable size by liquid phase exfoliation and its photothermal properties

Abstract

Ultrathin 2D niobium oxide dichloride (NbOCl2) is an emerging member of the 2D ferroelectric material family with extensive potential to provide multifunctionality in electronic devices and nanophotonics elements. It exhibits negligible interlayer electronic coupling and significant excitonic behavior in the bulk state. Here we substantiate that NbOCl2 nanosheets can be exfoliated and effectively size-selected using controlled centrifugation techniques by the liquid phase exfoliation (LPE) method. Spectroscopic measurements displayed that the variations in dispersion were highly dependent on the nanosheet dimensions. The nanosheets seemed to be comparatively defect-free which will be further corroborated by high resolution transmission electron microscopy (HRTEM) and Raman analysis. The size selected nanosheets are unanticipated stable in isopropyl alcohol (IPA), possibly owing to the protective influence of a solvation shell. Additionally, the photothermal conversion response and photothermal stability of nanosized NbOCl2 were investigated. Our finding revealed that NbOCl2 possesses a robust photothermal agent property, boasting a photothermal conversion efficiency of more than 30%. This underscores its promising potential for various photothermal applications in different fields such as photothermal therapy and thermal energy conversion.

1. Introduction

Two-dimensional (2D) materials have acquired enormous worldwide attraction since graphene was successfully detached and inspected in 2004 by NOVOSELOV et al [1]. In the beginning, graphene has been originating noteworthy ebullience due to its fascinating properties [2, 3]. However, attention has grown that a broad range of 2D materials apart from graphene such as transition metal dichalcogenides (TMDCs) [4, 5], hexagonal boron nitride (h-BN) [6], transition metal oxides (such as MnO2 and MnO3) [7, 8], topological insulators [9, 10], and MXenes [11] can be contemplated in the research community [12, 13]. These materials offer an extensive future generation platform of optoelectronic applications and nanotechnologies [14] including biomedical research and photothermal therapy. The abundance of layered materials makes it possible to provoke a huge variety of 2D systems with a significantly wide range of attributes.

Generally, most 2D materials are based on layered crystals, comprising strictly bounded atomic layers via weak (particularly van der Waals) interlayer forces [15]. These layered materials are frequently obtained by micromechanical exfoliation of bulk crystals [16] or bottom-up [17] growing approaches such as chemical vapor deposition [18]. Due to stringent growth conditions, these methods are unsuitable for cost-effective and large-scale production of 2D materials. In this case, liquid phase exfoliation (LPE) has become the most promising and effective approach for the production of 2D nanomaterials [19]. The LPE approach utilizes sonicating [6], or shearing exfoliation [20, 21], to facilitate the exfoliation of bulk layered materials, leading to the formation of nanosheets that typically exhibit a lack of defects [22]. To prevent reaggregation the appropriate selection of solvents [4, 23] and surfactants [24] is of utmost importance to ensure the stabilization of these defect-free nanosheets. This approach offers significant assistance in generating a considerable quantity of liquid-dispersible 2D nanosheets [25] with lateral size distributions from £50 nm to £500 nm and thicknesses spanning approximately 1 to 10 layers that are not typical for MoS2 [26], which can be further manipulated into disparate structures comprising composites, coatings, and films [13], assisting their utilization in a broad array of applications such as enhanced composite materials [27], and battery electrodes [28]. Nevertheless, this approach offers a straightforward and adaptable way to fabricate 2D nanosheets from bulk layered materials. It is resilient to environmental factors, bolstering reliability, scalability [29], cost-efficiency, and productivity [30].