## 1 Introduction  
Carbon, a vital element in nature, is a primary component in all life forms. The uniqueness of the element arises due to the number and variety of ways in which it can bond, leading to numerous carbonaceous structures with distinctive properties [1]. Along with traditionally known amorphous and crystalline carbons, newer allotropes such as graphene, carbon nanotubes (CNTs), fullerenes, and other various forms have contributedimmensely to the development of application-oriented research. Nanomaterials based on carbon are the most engrossing part of nanotechnology. However, producing the desired form of carbon via synthetic methods is still not economically viable for many applications. In this context, biomass carbonization has become a very attractive option for the targeted production of carbon forms. The surface chemistry associated with these carbon materials has attracted widespread research efforts devoted to such carbon production (activated and non-activated) [2; 3], characterizations, surface modifications, and use [4; 5; 6; 7]. The unique physicochemical properties of carbon nanoforms make them ideal materials for catalysis, adsorption, hydrogen storage, electrochemical sensors [8], and energy storage devices [9; 10; 11; 12]. The iminitable features of carbon allotropes have also been widely exploited in diverse biological applications, including biosensing, drug delivery, tissue engineering, imaging, cancer therapy, and antimicrobial agents [13]. The widespread utilization of carbon nanoforms has had a profound impact on the advancement of nanotechnology; graphene, CNTs, and fullerenes have also elicited immunological effects [14]. Numerous in vitro studies recently have highlighted the cellular toxicity of carbon-based materials [13]. The carbon materials were found to induce oxidative stress and trigger the generation of reactive oxygen species (ROS) [15]. Recent studies have also shed light on lysosomal dysfunction as an emerging factor in nanomaterial toxicity [16]. The multi-walled carbon nanotubes (MWCNTs) were shown to induce necrosis and trigger cell apoptosis [17]. Studies have shown that the physical properties of carbon nanomaterials play a significant role while eliciting cytotoxic responses. One of the studies on MWCNTs of differing length observed differing effects on macrophages. CNTs with an average length of 825 nm elicited stronger inflammation than CNTs with an average length of 220 nm [18]. Another study that focused on the size of carbon nanomaterials concluded that the smaller-sized MWCNTs appeared to be more toxic than larger aggregates [19]. The geometry of carbon nanomaterials was also found to have a profound impact on cytotoxic and immunological responses. In a study involving MWCNTs, the authors found elongated MWCNTs to be more toxic than spherical-shaped carbon nanoparticles [13]. Interestingly, functionalized carbon nanomaterials were observed to be less toxic than nonfunctionalized counterparts. It is believed that functionalization causes disruptions and defects in the carbon framework, which could reduce the toxicity of functionalized carbon nanomaterials [20]. In vivo studies on various carbon nanomaterials have also shed light on the toxicological effects of such materials. In one such study, the sixteen-hour exposure of rod-like CNTs via pharyngeal aspiration in mice induced strong neutrophil influx into the lungs, with enhanced cytokines and chemokines [21]. It was found that the inhalation of SWCNTs could up-regulate numerous proteins, resulting in an inflammatory response, playing a role in airway hyperreaction, airflow obstruction, and granuloma, in mice [22]. Such local exposure of carbon nanomaterials not only induces local adverse effects but there is also evidence suggesting a systematic inflammatory response [23]. Similar to in vitro studies, in vivo studies also found a direct relation between the toxicity of nanomaterials and their physical properties (size, shape, functionalization, etc.).