Natural, renewable, sources for green nanotechnology.
Natural, renewable, sources for green nanotechnology.

In the past few decades, nanomaterials have demonstrated superior performance in numerous applications, including medicine, energy, and advanced manufacturing. However, many of the materials and processes currently used are not only dependent on nonrenewable resources but also create hazardous wastes. Green nanotechnology, the combination of nanotechnology and the principles and practices of green chemistry, may hold the key to building an environmentally sustainable society in the twenty-first century [1]. Green chemistry is a set of principles or rather a chemical philosophy that encourages the design of products and processes that reduce or eliminate the use and generation of hazardous substances [2], [3], [4] and [5]. Current green nanotechnology practices often involve the use of natural sources, nonhazardous solvents, and energy-efficient processes in the preparation of nanomaterials.

Natural, renewable sources of reducing agents

Nature provides us with numerous chemical substances that serve as suitable reducing agents for the synthesis of nanoparticles, including plant extracts, biopolymers, vitamins, proteins, peptides (e.g., glutathione), and sugars (e.g., glucose, fructose) [1] and [6]. Plant extracts are the most studied category to date. Given their abundance, plant extracts are regarded as one of the most promising natural reducing agents [7]. One area of particular success is the synthesis of metal nanoparticles, useful in electronics and medical applications, using plant extracts as reducing agents [3]. Biomedical applications such as drug and gene delivery using gold and silver nanoparticles have recently become a very active research area. To improve the biocompatibility, nontoxic green reduction agents, plants, algae, bacteria and fungi are used. Elia et al. synthesized gold nanoparticles by using four different types of plant extracts, Salvia officinalis, Lippia citriodora, Pelargonium graveolens, Punica granatum, as a reducing and stabilization agent [8].

Biopolymers are another family of natural sources used as reducing and stabilizing agents for metal nanoparticle synthesis. These polymeric carbohydrate molecules have already been used in various industries and thus are readily available for the large-scale production of nanoparticles. Examples of biopolymers for nanoparticle synthesis are cellulose, chitosan, and dextran, which are isolated from plants, the exoskeleton of crustaceans, and sugar cane, respectively [9], [10] and [11].

Vitamin C is a well-known natural reducing agent or antioxidant. Similar to other natural reducing agents, vitamin C can reduce metal ions in an aqueous solution to produce metal nanoparticles [12]. Interestingly, it can also be used to synthesize Fe3O4 nanoparticles by reducing colloidal iron hydroxide under hydrothermal conditions [13]. Other vitamins used for metal nanoparticle synthesis include vitamins B and E [14]. Despite the widespread commercial availability of vitamins, their relatively cost effectiveness may be a hurdle for commercial application. Other natural sources, such as proteins and peptides, also suffer from cost-related challenges and thus are ill-suited for the large-scale production of nanomaterials [15], [16] and [17].

Natural sources as precursors for carbon nanomaterials

One emerging area of green nanotechnology research is the use of natural sources as precursors for carbon nanomaterials, useful in a host of applications due to their unique properties. For example, vegetable oil has proven itself to be a viable precursor for high-quality carbon nanotubes using a spray pyrolysis approach. Using different catalysts, both single-walled and multi-walled carbon nanotubes can be produced by this method [18]. In another example, sugars and biopolymers have been used as precursors for carbon quantum dots via a microwave approach. Given the abundance of carbon-rich natural sources, it is expected that their use as precursors for carbon nanomaterials will increase rapidly in the next few years [18].

Cellulose - a green nanomaterial

As shown in the previous sections, a significant portion of green nanotechnology is the development of green chemistry to synthesize nanomaterials. However, recently much attention has been devoted to the use of natural nanomaterials as alternatives to synthetic products. One example is nanocellulose materials, which are nanosized cellulose fibers or crystals produced by bacteria or derived from plants. These materials exhibit exceptional strength characteristics, light weight, transparency, and excellent biocompatibility. Compared to some other nanomaterials, nanocellulose is renewable and less expensive to produce. Because of this, nanocellulose has shown great promise as an alternative to synthetic nanoparticles in areas such as polymer nanocomposites and drug delivery [19], [20], [21] and [22]. Nanocellulose aerogel has also been used as a sacrificial templating material for metal oxide nanotubes [23]. Interest in green nanomaterials is increasing, as evidenced by the growing number of publications in this area and the recent initiative of the government and private sectors on its commercialization.

Green processing

In addition to using natural starting and processing materials for nanoparticle synthesis, the other half of green nanotechnology is developing environmentally friendly, sustainable processes. In this regard, water and supercritical carbon dioxide have been investigated as alternatives to organic solvents [24] and [25]. Of particular interest are various alternative approaches to conventional heating [26]. The most popular green strategy is what is known as the “hydrothermal approach,” where water is the reaction medium. In another interesting development, Abdelaziz and his collaborators recently reported using the Leidenfrost effect to create an overheated and charged green chemical reactor to fabricate nanoparticles and coatings on complex objects [27].

Microwave energy [26] and focused sunlight [28] have also been explored as alternative heat sources for the synthesis of nanoparticles. Although these approaches are effective at the laboratory scale, there are enormous challenges when using these technologies in commercial production. For example, the short reaction times in microwave heating are restricted to small scale reactions. The use of focused sunlight is limited by inconsistent light intensity and the necessity of a lens. Recently, flow chemical processes have been developed for the improvement of cost effectiveness of green chemistry [29].

Ongoing challenges

To date, most green nanotechnologies are only conducted on a laboratory scale. Initiatives are necessary to evaluate the feasibility of adapting the existing technologies to commercial-scale production. The financial and regulatory barriers due to the unclear toxicology of nanomaterials may be the greatest hurdles for most green nanotechnologies [30]. Green nanotechnology often requires entirely new processes, making it initially expensive to move into production. The key to overcome this barrier is to represent enough of a potential cost savings to outweigh upfront costs. For example, Pfizer has saved millions of dollars to date from the green process to synthesize sertraline. The implementation of this green chemistry has resulted in revenue increase enough to overcome the costs, including capital investment and all of the costs associated with recertifying the drug with the U.S. Food and Drug Administration [30]. In the past few decades, environmental regulations implemented by the government have had a significant impact on the chemical enterprise. Most of these regulations focus on reducing the health and environmental risks by reducing the exposure. Therefore, many firms have to use their resources on mandated actions and end-of-pipe technologies, instead of investing in green process to ensure inherently safer products and processes. This is evidence by the fact that chemical manufacturing spent more than any other industrial sector on pollution abatement [30]. Obviously, a regulatory focus on risk control, rather than risk prevention, poses a serious barrier. To overcome these barriers, the collaboration of academic researchers and the private sector is key to successfully moving green technologies from the laboratory to the manufacturing facility. Indeed, the government has promoted such collaborations by providing financial support to commercializing green nanotechnologies. Relevant government guidelines and regulations on the green production of nanomaterials could provide an effective boost to the development and implementation of green nanotechnologies on a commercial scale.


We acknowledge the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy.

This paper was originally published in Nano Today (2015), doi:10.1016/j.nantod.2015.04.010.  


  1. J. Virkutyte, R.S. Varma. Chem. Sci., 2 (2011), pp. 837–846
  2. P.T. Anastas, J.C. Warner. Green Chemistry: Theory and Practice. Oxford university Press, New York (2000)
  3. N. Shamim, V.K. Sharma. In: Sustainable Nanotechnology and the Environment: Advances and Achievements. N. Shamim (Ed.), American Chemical Society, Washington, DC (2013), pp. 11–39
  4. R.S. Varma. Green Chem., 16 (2014), pp. 2027–2041
  5. R.S. Varma. Curr. Opin. Chem. Eng., 1 (2012), pp. 123–128
  6. S. Iravani. Green Chem., 13 (2011), pp. 2638–2650
  7. V. Kumar, S.K. Yadav. J. Chem. Technol. Biotechnol., 84 (2009), pp. 151–157
  8. P. Elia, R. Zach, S. Hazan, S. Kolusheva, Z.e. Porat, Y. Zeiri. Int. J. Nanomed., 9 (2014), p. 4007
  9. F. He, D. Zhao. Environ. Sci. Technol., 41 (2007), pp. 6216–6221
  10. E. Kharlampieva, J.M. Slocik, T. Tsukruk, R.R. Naik, V.V. Tsukruk. Chem. Mater., 20 (2008), pp. 5822–5831
  11. W. Jiang, H. Yang, S. Yang, H. Horng, J. Hung, Y. Chen, C.-Y. Hong. J. Magn. Magn. Mater., 283 (2004), pp. 210–214
  12. M.N. Nadagouda, R.S. Varma. Cryst. Growth Des., 7 (2007), pp. 2582–2587
  13. L. Xiao, J. Li, D.F. Brougham, E.K. Fox, N. Feliu, A. Bushmelev, A. Schmidt, N. Mertens, F. Kiessling, M. Valldor. ACS Nano, 5 (2011), pp. 6315–6324
  14. M.N. Nadagouda, R.S. Varma. Green Chem., 8 (2006), pp. 516–518
  15. J. Xie, Y. Zheng, J.Y. Ying. J. Am. Chem. Soc., 131 (2009), pp. 888–889
  16. D. Scott, M. Toney, M. Muzikar. J. Am. Chem. Soc., 130 (2008), pp. 865–874
  17. B. Baruwati, V. Polshettiwar, R.S. Varma. Green Chem., 11 (2009), pp. 926–930
  18. M.-M. Titirici, R.J. White, N. Brun, V.L. Budarin, D.S. Su, F. del Monte, J.H. Clark, M.J. MacLachlan. Chem. Soc. Rev., 44 (2015), pp. 250–290
  19. Y. Habibi, L.A. Lucia, O.J. Rojas. Chem. Rev., 110 (2010), pp. 3479–3500
  20. Y. Lu, H.L. Tekinalp, W.H. Peter, C. Eberle, A.K. Naskar, S. Ozcan. Tappi J., 13 (2014)
  21. R.J. Moon, A. Martini, J. Nairn, J. Simonsen, J. Youngblood. Chem. Soc. Rev., 40 (2011), pp. 3941–3994
  22. M.N. Nadagouda, R.S. Varma. Biomacromolecules, 8 (2007), pp. 2762–2767
  23. J.T. Korhonen, P. Hiekkataipale, J. Malm, M. Karppinen, O. Ikkala, R.H. Ras. ACS Nano, 5 (2011), pp. 1967–1974
  24. T. Sun, Z. Zhang, J. Xiao, C. Chen, F. Xiao, S. Wang, Y. Liu. Sci. Rep., 3 (2013)
  25. Z. Sui, Q. Meng, X. Zhang, R. Ma, B. Cao. J. Mater. Chem., 22 (2012), pp. 8767–8771
  26. M.N. Nadagouda, T.F. Speth, R.S. Varma. Acc. Chem. Res., 44 (2011), pp. 469–478
  27. R. Abdelaziz, D. Disci-Zayed, M.K. Hedayati, J.-H. Pohls, A.U. Zillohu, B. Erkartal, V.S.K. Chakravadhanula, V. Duppel, L. Kienle, M. Elbahri. Nat. Commun., 4 (2013), p. 2400
  28. B.P. Vinayan, R. Nagar, S. Ramaprabhu. J. Mater. Chem. A, 1 (2013), pp. 11192–11199
  29. B.J. Deadman, C. Battilocchio, E. Sliwinski, S.V. Ley. Green Chem., 15 (2013), pp. 2050–2055
  30. K.J. Matus, W.C. Clark, P.T. Anastas, J.B. Zimmerman. Environ. Sci. Technol., 46 (2012), pp. 10892–10899