# Fewer Dimensions for Higher Thermal Performance: A Review on 2D Nanofluids
## 4 Environmental Impact of the 2D Nanofluids  
Two-dimensional nanofluids have been demonstrated as a promising alternative to traditional heat transfer fluids; however, it is also of relevance to evaluate the impact of the former on the environment. Published studies have rather scarcely addressed the environmental impact (EI) of 2D nanofluids; however, a few authors have argued that these thermal fluids are a sustainable alternative. The EI of 2D nanofluids is derived fundamentally from parameters including the HTC, TC, analysis of the emissions and pressure drop, and energy efficiency, which is the ratio between the energy output and the overall energy input. Renewable energy is an attractive area of actuation, especially considering the actual environmental conditions and, consequently, harnessing energy from these sources must be effective. Two-dimensional nanomaterial thermal fluids are more performant because of their high surface area and TC. This results in size reduction in the equipment, as shown by Sundar et al. [159]. Less CO\({}_{2}\) emissions and more biofriendly methods consequently occur. Although emissions are low during the production of nanoparticles, they should be considered while evaluating the overall EI. Despite the broadened utilization and benefits of 2D nanomaterials, their environmentally detrimental synthesis processes must be evaluated. Additionally, the inadequate disposal of effluents generated during the manufacture of 2D nanomaterials and toxic emissions pose a negative impact to existing ecosystems and human health. Nanomaterials in general are produced by laser ablation, CVD, chemical reduction, and sol-gel, among other techniques. CVD is the technique that achieves a high yield, with large scale processing of CNTs and other 2D nanomaterials at relatively low cost. It is consequently used as a common production method for 2D nanomaterials. An EI study for CNTs synthesized by CVD using the LCA technique was undertaken by Trompeta et al. [160]. The analysis of the emissions, disposal of the effluents and by-products, and power generation were considered, and the corresponding EI was assessed considering two different pathways of CNT production through CVD. Singh et al. [161] used SimaPro v. 7.0 software to carry out an analysis on the EI of CNT preparation and verified the formation of smog and effluents, such as Fe\({}_{2}\)O\({}_{3}\), Co\({}_{2}\)O\({}_{3}\), MoO\({}_{3}\), and NaOH. The authors strongly recommended that these by-products should be carefully treated to mitigate their EI. On the other hand, the laser ablation technique produces high-purity 2D nanomaterials without creating harmful emissions or the formation of toxic by-products. Suitable by-product evaluations and disposal procedures are recommended to effectively analyze the overall EI of the process. An efficient recovery of the base liquid and nanoparticles of the nanofluids will have a lesser EI by restricting the pollution of the water. Consequently, the design and implementation of proper recovery procedures, such as centrifugation followed by evaporation of the supernatants,are vital for the recovery process. In most cases, the innovative materials and chemicals still pose environmental and human health risks, including the polychlorinated biphenyls, dichlordiphenyltrichloroethane, benzene, and halocarbon emissions. Consequently, they must be carefully assessed to mitigate the health hazards [162]. The respiratory tract is the main pathway by which nanoparticles enter the human body and, hence, the lungs are the most vulnerable organs to the exposure of nanomaterials. The chemical and structural characteristics of nanoparticles considerably impact their adversity. Size, aggregation, and chirality are the most important factors to consider. Additionally, human exposure to nanomaterials can be harmful to the cytoskeleton, DNA repair, cell signaling, and may involve the production of inflammatory cytokines and chemokines [163].