**Abstract**

Miniaturization of the devices in terms of size and the necessity of high speed device performance have created opportunities as well as challenges in the material research community. Nanomaterials like 0D and 2D materials are one of such material choices that can help realize the nanosize and ultrafast devices. However, the growth process of these materials, especially emerging 2D materials, needs to be reviewed in terms of human, animal and environmental toxicity along with the economic cost for synthesizing material. Moreover, the green and sustainable alternatives for minimizing or eliminating the toxicity should also be considered for the commercial scale nanomaterials synthesis and device fabrication. This topic will thus highlight the currently developed 2D materials, their growth process, application prospective, toxicity effect and their possible sustainable alternatives.

**Keywords:** nanostructures, 2D materials, growth toxicity, nanomaterial toxicity, green synthesis

### **1. Introduction**

The need of efficient and convenient human lifestyle has induced new and innovative research in fields of food, agriculture, technology, construction, transportation, environment and health [1]. These modern global needs are possible with the use of new and more efficient materials and technology. In such, wide range of nanomaterials from zero dimensional (0D) quantum dots to one dimensional (1D) nanorods/nanowire and two dimensional (2D) sheet having large surface to volume ratio; ability to bind with various other materials; ballistic transport of charges; tunable optical, electrical and magnetic properties; low volume of material consumption; and superior overall performance than its bulk counterpart have shown various new possibilities in the field of health, technology developments, energy devices, transport, communication, computation and agricultural productivity [2]. Moreover, the rise of these nano-dimensional materials and nano-based technology have replaced many of the traditional industries ranging from electronic, optics, energy storage/ production, pharmaceuticals, transport, cosmetics, agriculture, food production to material processing [3, 4]. At present the global nanotechnology market is worth 75.8 billion USD which mainly comprises industries related to electronic, sporting goods, automotive, energy storage, aerospace, defense, food and pharmaceutical [5, 6]. However, having superior physical and chemical properties than pre-existing bulk

materials, the nanotechnology based products should have been a global need with high economic prospective. The major factors restraining the development of global nanotechnology market from its rise in early 2000 are toxicity of nanomaterial on human health and environment and stringent requirements of the government bodies on adopting the nanomaterials and nanotechnology in commercial products [3, 7, 8]. Nanomaterials have adverse toxicological effect on both animal and plant cells [9]. Nanomaterials upon interaction with body cell of an organism can have inflammatory response, dysfunction of organs, tissue damage, tumors and upon interaction with nervous system can accumulate in the brain leading to neurological diseases. Similarly nanomaterials upon interaction with plants can prevent plants protein, chlorophyll, carotenoids and biomass content as well as extend the plant harvest period [10]. However these effects are mostly observed in plants if high concentration of nanomaterials are used and more importantly, the use of synthetic nanomaterials which are non-biodegradable are primarily harmful for plants and humans.

Various global acts and forums like Pollution Prevention Act of 1990, regulations of European Union Observatory for Nanomaterials, Food and Drug Administration in United States (US), US Environmental Protection Agency, Intergovernmental Forum on Chemical Safety including many others have initiated governmental and global alliance to minimize the rising issue of chemical toxicity and hazard from nanostructure materials and its synthesis techniques on human, animal and environmental health [11]. The additional initiative of these acts and agencies are to prevent chemical waste, synthesize safer and less hazardeous chemicals and chemical products, use of natural resources against high toxicity materials and procedures, design of energy efficient procedures for material production, reduce derivative products and promote biodegradable and sustainable materials [12]. Currently, based on these policies and acts, the industrial application of various nanomaterials, nanocompounds and nanocomposites either as a final product or as an additive supplement have been approved after extensive research on toxicity, stability and the wide scale applicability [13].

These nanomaterial are synthesized mainly from physical, chemical and biological synthesis procedures. Among these, physical vapor deposition, chemical vapor deposition, sol-gel and colloidal methods are currently commercialized for large scale synthesis [14]. Moreover, the high cost required in the material synthesis, toxicity of the synthetic material and the synthesis procedure along with the environmental issues arising due to toxicity have led to the development of biological synthesis method which utilizes green chemistry approach for synthesizing nanomaterials [15]. Hence as an alternative, bio-nanomaterials produced from biological sources using green synthesis techniques are being extensively explored. Also green synthesis employs clean, cost effective, safe and environment friendly process of constructing nanomaterials using natural substrates like bacteria, yeast, fungi, algae and plants or agricultural resources [16]. Especially, carbon materials derived from plant and agricultural byproducts along with the organic chemicals derived from natural products can be used for synthesizing nanomaterial and nanocompounds. Similarly, thermal and hydrothermal synthesis techniques like biosorption, pyrolysis and hydrolysis can also be used for biologically synthesizing 2D nanostructures. Hence both these synthesis techniques produces bio-degradable nanomaterials without the use of synthetic chemicals. Moreover, biomass derived nanomaterials are non-toxic bio-nanomaterials that can be used safely in medicines, fertilizers, devices and cosmetic products.

In this review, we will mainly focus on the toxicity arising from the material synthesis procedure as well as the toxicity of the materials itself on human, animal and environment health mainly focusing on the 2D material family. We will also highlight the current research trend in utilizing green and sustainable procedure for synthesizing 2D materials.
