The Quest for Green Solvents for the Sustainable Production of Nanosheets of Two-Dimensional (2D) Materials, a Key Issue in the Roadmap for the Ecology Transition in the Flatland

Abstract

The recent advent of two-dimensional (2D) materials has had a ground-breaking impact on science and technology. To exploit in technology their unique thickness-dependent physicochemical properties, the large-scale production of 2D materials is mandatory, but it represents an open challenge still due to various pitfalls and severe limitations including the toxicity of state-of-the-art solvents. Thus, liquid-phase exfoliation based on green and bioderived solvents represents an ideal methodology for massive production. This is particularly crucial for introducing 2D materials in technological applications such as the production of drinking water and agri-food industrial processes. Here, we assessed the production of 2D nanosheets (specifically, graphene, WS2, MoS2) with liquid-phase exfoliation assisted by eco-friendly solvents, with a comparative evaluation of green solvents in terms of the yield and, moreover, the aspect ratio, defectivity, and crystalline quality of the produced nanosheets. In particular, we focus on the most promising green solvents in terms of the yield and the crystalline quality of the produced nanosheets: Polarclean, Iris, and Cyrene, which were compared with acetone/water mixtures, isopropyl alcohol (IPA), triethanolamine (TEA), aqueous solutions of urea, and an ethanol/water mixture as well as two toxic solvents largely used for the production of 2D nanosheets: N-methyl-2-pyrrolidone (NMP) and N, N-dimethylformamide (DMF). Remarkably, the density of defects was particularly low in the liquid-phase exfoliation with Polarclean, as indicated by the Raman spectrum of graphene, with the I(D)/I(G) ratio below 0.1. Furthermore, Polarclean and Iris also enable ink-jet printing with functional inks of 2D materials based on green solvents due to their low dynamic viscosity at room temperature.

Plant extract-based liquid phase exfoliation enables one-step green production of two-dimensional heterostructure nanohybrids capable of dramatic improvement in polymer properties

“…Liquid-phase exfoliation of 2D materials is an extremely mild, versatile, and potentially scalable approach to obtain highquality nanosheets. 8,10 One of the most important factors in controlling the large-scale economical production of highquality nanosheets is a suitable solvent. The economic viability for the industrial implementation of using coffee waste and gallnut extracts as green solvents in LPE was assessed and compared with the costs of commercially available LPE solvents (Table S4 †).…”

“…Currently, the most commonly used solvents for LPE are N -methyl-2-pyrrolidone (NMP) and N , N -dimethylformamide (DMF), due to their strong compatibility with graphite and other 2D materials. 8 However, these solvents pose significant toxicity concerns, being categorized as extremely hazardous substances and facing restrictions in the US and Europe, thus making the exploration of alternative ecofriendly solvents appealing. Among the identified alternatives, Cyrene, 9 Polarclean, 10 and Iris 11 are regarded as the three most ideal and effective green solvents for the LPE of 2D materials.…”

Unlocking superior NO2 sensitivity and selectivity: the role of sulfur abstraction in indium sulfide (InS) nanosheet-based sensors

“…To maximize the surface area, we produced InS nanosheets through liquid-phase exfoliation, 29,50,51 with an average lateral This journal is © The Royal Society of Chemistry 2024…”

A key parametric study of ultrasonic exfoliation of 2D TiB2 using DI water as a unique medium

“…Many solvents like methyl-5-(dimethylamino)-2-methyl-5-oxopentanoate [ 29 ], Dimethyl 2-Methylglutarate [ 30 ], Cyrene, Polarclean, and Iris [ 31 ] have also been reported. All these solvents are expensive and may cause environmental pollution.…”