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Humboldt-Universität zu Berlin - Mathematisch-Naturwissen­schaft­liche Fakultät - Prof. Rademann

Humboldt-Universität zu Berlin | Mathematisch-Naturwissen­schaft­liche Fakultät | Institut für Chemie | Prof. Rademann | Cellulose: A Renewable Resource for Environmental Technologies and Food Substitutes (Klaus Rademann, Suresh Valiyaveettil)

Cellulose: A Renewable Resource for Environmental Technologies and Food Substitutes (Klaus Rademann, Suresh Valiyaveettil)

A joint project with the National University of Singapore (NUS), Funded by International Strategy Office, Humboldt-Universität zu Berlin, and the National University of Singapore



Project Members:


Prof. Dr. Suresh Valiyaveettil (NUS)


Prof. Dr. Klaus Rademann (HU)


Research questions/ Goals of the project:

In the time of climate change and growing global concerns about health and hygiene matters, research and development in the realm of ecologically friendly and sustainable materials is of exceptional importance for us and even more so for future generations. With this in mind the NUS-HU team will focus on important long-term challenges of using naturally abundant cellulose for water purification and food usage. In our project novel innovative methods for cellulose functionalization and cellulose depolymerisation will be advanced, including creative bond activation strategies, i.e. microwave-assisted depolymerisation in pure water and ionic liquids. As a multifunctional biological substance, cellulose offers promising applications in many relevant areas. The fundamental challenges to be addressed in this project involve primarily two questions: (i) can we convert and functionalize renewable cellulose as super adsorbent for water purification? and (ii) is it possible to degrade cellulose efficiently to oligosaccharides in water and ionic liquids? Most importantly, this 12-months project will be an ideal platform for creating a young, sustainable and dynamic international scientific network on cellulose based research.


A) Renewable cellulosic materials as super adsorbent:

Cellulose offers the outstanding and unique option for systematic research on finding the appropriate materials for water purification. We will use this opportunity to investigate specific properties of functionalized cellulose in two steps. Firstly, we will develop a method for producing functionalized cellulosic materials, which selectively remove toxic chemicals in drinking water (toxic heavy metals such as thallium, cadmium, lead, mercury, copper) in a fast and efficient process. Recently Valiyaveettil’s group has shown that cellulosic fruit peels such as tomato, apple and other materials are capable of extracting pollutants such as nanoparticles, dyes and heavy metal ions from water.1,2 In addition, the cellulosic paper coated with polyamines were also good candidates for pollutant removal3. The highly functional cellulose can be used to achieve higher selectivity and good extraction efficiency. A recent review highlighted many routes for functionalization of cellulose.4

In a typical procedure, nanocellulose will be extracted from renewable materials such as fruit peels, spent coffee powder etc. and used for functional modifications. The hydroxyl groups on the surface will be modified based on different chemical transformations to incorporate –SH or –NH2 functional groups in an ionic liquid as solvent. Such groups can be further functionalized to introduce other groups to increase solubility and processability. All materials will be fully characterised and tested for their potential applications towards extraction of pollutants from contaminated water. Presence of -SH or –NH2 groups on the cellulosic backbone help to enhance the selectivity in transition metal (Hg, Cd, Pb, Cu, etc.) complexation and efficient removal from contaminated water. The modified cellulose can be used as beads or films and added to contaminated water for active extraction of pollutants. Full kinetic parameters and extraction efficiency of the materials will be established for different adsorbent – pollutant combinations.


In addition, availability of amine groups offer sites for introducing other groups on the backbone. This will allow us to fine-tune the properties of the cellulose matrix.

Secondly, we will treat and remove biohazard components such as microbes and pathogens from water. The surface functionalized cellulose can be used to conjugate antimicrobial metal salts (e.g. CuSO4, KMnO4) or metal nanoparticles (e.g. Ag NPs) to remove microbial contaminants from potable water. Both silver nanoparticles5 and polyammonium compounds6 have been shown to have antimicrobial properties, but the toxicity of these materials makes them non-usable in practical applications. By incorporating such    compounds on the cellulose backbone, it is possible to reduce the toxicity (e.g. low solubility, high stability, high concentration of ammonium units per repeating unit etc.) without compromising the antimicrobial properties. Based on our expertise of functionalizing cellulose, we are confident that significant amounts of modified cellulose can be generated within a short period of time. Some of the above mentioned materials are already available in our laboratories and we have significant expertise in the area of water purification.1-3 As mentioned above, such materials can be made into films or beads and used directly in water purification.


B) Economic conversion of cellulose into food grade oligosaccharides: Being the most abundant polymer in nature, the application of cellulose in various areas is slowly beginning to emerge in recent years. Cellulose consisting of glucose units with inter- and intramolecular hydrogen bonds, is difficult to depolymerize into oligosaccharides. Even though, enzymatic or acidic hydrolysis of cellulose into glucose has already been reported, scaling up this process is rather difficult.7 Part of the problem associated with cellulosic degradation involves the lack of solubility/ processability of the polymer backbone. The most significant achievements so far include the synthesis of cellulose acetate via conversion of the –OH groups into acetates making the polymer highly processable.  There were a few other approaches reported in the literature to degrade the cellulose into small molecules using various enzymes, catalysts and thermal degradations.8 Significant efforts are needed for developing an economically viable chemical conversion route of cellulose into edible mono- and di-glucose units through catalytic degradation. Here we propose a few highly sophisticated energetic activation techniques for cellulose degradation:


Mechanochemical activation or microwave induced degradation of cellulose: Ball milling, in combination with other reagents, can be used to degrade cellulose. However, the yields of the desired products are not high and often the reaction takes longer time (several hours or days). Recently, a few methods have been developed to extract cellulose nanofibers using the ball milling process.9 We will attempt to degrade cellulose using ball milling in presence of nanocatalysts under different pH conditions. Nanocatalysts such as FeCl3/Fe2O3 or ZnCl2/ZnO are preferred over other commonly used strong acids, owing to the high corrosive nature of the concentrated mineral acids.10 Also, the forces applied in the ball milling process can be controlled by fine-tuning the parameters. Here we propose to do the cellulose degradation in presence of nanocatalysts in ionic liquids or water under ball milling or microwave irradiation.11 Microwave irradiation has been used on organic transformations.12 The biggest challenge here is achieving selective degradation of cellulose to yield mono- or disaccharides. A few reports exist on using Fe2O3, Pt nanoparticles or acidic catalysts to break cellulose into smaller units.13 If we are able to degrade cellulose in an economically viable method, it will be a ground-breaking technology in the field of food production.

In a novel set-up, we succeeded (in Berlin, 2016) to caramelize the very stable and recalcitrant cellulose in water at a certain critical temperature under microwave irradiations. Such preliminary data are useful as we try to understand the underlying mechanisms and theoretical foundations of cellulose conversion processes.   


General theoretical foundations:

Cellulose is a renewable material with high recalcitration. Valiyaveettil and others have shown that the material and method of choice for water purification should be based on a few factors such as low cost, availability, mechanical strength, low toxicity, high extraction efficiency and fast adsorption rates for pollutants.14 So far various nanomaterials such as gold and silver nanoparticles, have been explored for water purification due to their high surface area with active sites, but no discussion on the contamination of water with such materials is provided. A wide range of applications tend to overlook the dangers that such nanoparticles pose to the environment and human health.5 In particular, the use of silver nanoparticles for water purification has proven to be non-healthy and toxic to mammalian cells (DNA damage and mitochondrial impairment).5 Functionalized insoluble cellulose offers a healthy and promising alternative bioadsorbent for water purification.14 Also, we will employ silver nanoparticles with chemically attached functional cellulose on the surface as antimicrobial materials for water purification. This will prevent the nanoparticles from contaminating the filtered water.

The proposed organic transformations of cellulose need to be carried out in large amounts to make it accessible for various applications. The current proposal aims to achieve this by using ionic liquid as solvent, nanoparticles as catalysts and ball milling or microwave irradiation for degradation. The production of functionalized cellulose offers the possibility to explore the relevant properties. Factors such as pH, nature and amount of the adsorbent used for the extraction will be explored to establish the optimum conditions. The maximum adsorption capacity will be observed at different pH values for different pollutants. The equilibrium adsorption data will be interpreted by using Freundlich and Langmuir isotherms and the adsorption mechanism will be investigated using kinetic studies. We have significant expertise in the use of natural cellulosic materials for water purification1-3,12,14 and will therefore extend our expertise by producing chemically modified cellulose. The degradation of cellulose to small molecules has been an active area mainly to develop biofuels. Little is known in the area of selective degradation and we will explore such reactions during this project. The use of ionic liquids and nanocatalysts allows us to fine-tune the degradation process to achieve oligosaccharides selectively.


Empirical and methodological considerations:  Currently, cellulose research is of academic, industrial and environmental concern. Naturally abundant cellulose is insoluble and non-processable. Chemical functionalization or selective degradation allows us to convert natural cellulose into processable polymers and materials. During this project, chemically functionalized cellulose will be synthesized, characterized and tested for water purification processes with increased selectivity and high extraction efficiency. Selective degradation methods of cellulose at different pH-values in different solvents and in presence of nanocatalysts comprise two different activation strategies: i) mechanical ball milling and ii) microwave irradiation. These strategies help to make interesting soluble oligosaccharides, which could eventually be used as food additives. The HU-NUS team has significant experience, expertise and track record in the proposed research field and has access to state-of-the-art facilities (e.g. X-ray scattering, neutron-scattering, SEM, EDS, DLS, FTIR) for the proposed research. Recently, we have carried out preliminary studies in our labs and first results are very promising. The prepared amine functionalized cellulose was used for imprinting and fine-tuning the surface properties (Scheme 5).15 Furthermore, Valiyaveettil has shown explicitly that functionalized paper is a readily accessible adsorbent for removal of dissolved heavy metal salts and nanoparticles from water.3


Potential for future endeavours: The project is conceptualized as a starting point for a broader international science network researching in the field of green chemistry, energy and environmental science and sustainable technologies. The conceptualization of a broader project in the area, recruiting students, research exchanges and the raising of necessary resources are part of the ongoing project.


Related literature

  1. (a) R. Mallampati, S. Valiyaveettil, ACS Applied Materials & Interfaces 5 (2013) 4443 – 4449. (b) R. Mallampati, K. S. Tan, S. Valiyaveettil, International Biodeterioration and Biodegradation (2015) 103, 8 - 15.
  2. (a) R. Mallampati, S. Valiyaveettil, RSC Advances 2 (2012) 9914 -9920. (b) R. Mallampati, X. J. Li, A. Adin, S. Vaiyaveettil, ACS Sustainable Chemistry and Engineering (2015) 3, 1117-1124
  3. D. Setyono, S. Valiyaveettil, Journal of Hazardous Materials (2016) 30, 120-128.
  1. (a) A. Pinkert, K. N. Marsh, S. Pang, M. P. Staiger, Chem. Rev. (2009) 109, 6712–6728 (b) M. Gericke, J. Trygg, P. Fardim, Chem. Rev. (2013) 113, 4812−4836
  2. (a) S. Hackenberg, A. Scherzed, M. Kessler, S. Hummel, A. Technau, K. Froelich, C. Ginzkey, C. Koehler, R. Hagen and N. Kleinsasser, Toxicol. Lett. 201 (2011) 27 – 33. (b) C. Y. Wang, S. Valiyaveettil, RSC ADVANCES (2013) 14329-14338. (c) P. V. Asharani, L.W. Yi, Z.Y. Gong, S. Valiyaveettil, Nanotoxicology (2011) 5, 43-54. (d) N. Khlebtsov and L. Dykman, Chem. Soc. Rev. (2011) 40, 1647 – 1671.
  3. (a) J. Thome, A. Hollander, W. Jaeger, I. Trick, C. Oehr, Surface & Coating Technology (2003) 174, 584-587., (b) K. Glinel, P. Thebault, V. Humblot, C. M. Pradier, T. Jouenne, Acta Biomaterialia (2012) 8, 1670 – 1684.
  4. (a) P. Zhang, C. Chen, Y. Shen, T. Ding, D. Ma, Z. Hua, D. Sun, Bioresour. Technol. (2013) 128, 835−838. (b) R. Johnson, G. Padmaja, S. N. Moorthy, Innovative Food Sci. Emerging Technol. (2009) 10, 616−620.
  5. (a) J. A. Galbis, M. de Gracia García-Martín, M. Violante de Paz, and E. Galbis, Chem. Rev. (2016) 116, 1600−1636., (b) A. Gandini, T. M. Lacerda, A. J. F. Carvalho, E. Trovatti, Chem. Rev. (2016) 116, 1637−1669.
  6.  (a) M. Nuruddin, M. Hosur, M. J. Uddin, D. Baah, S. Jeelani, Journal of Applied Polymer Science (2016) 133, Article Number: 42990. (b) S. Tabasso, D. Carnaroglio, E. C. Gaudino, G. Cravotto, Green Chemistry (2015) 17, 684-693.
  7. M. L. Rabinovich, Cell. Chem. Technol. (2010) 44, 173.; Rinaldi, R.; Schuth, F. ChemSusChem (2009) 2, 1096.
  8.  (a) H. Q. Li, Y. S. Qu, Y. Q. Yang, S. L. Chang, J. Xu, Bioresource Technology (2016) 199, 34-41., (b) M. da Costa Lopes, R. Bogel-Lukasik, ChemSusChem (2015) 8, 947-965., (c) J. J. Wang, J. X. Xi, Y. Q. Wang, Green Chemistry (2015) 17, 737-751.
  9. A. K. Rathi, M. B. Gawande, R. Zboril, R. S. Varma, Coord. Chem Rev. (2015) 291, 68-94.
  10. (a) L. Hu, L. Lin, Z. Wu, S. Y. Zhou, S. J. Liu, Applied Catalysis B – Environmental (2015) 174, 225-243., (b) Y. P. Li, Y. H. Liao, X. F. Cao, T. J. Wang, L. L. Ma, J. X. Long, Q. Y. Liu, Y. Xua, Biomass & Bioresources (2015) 74, 148 – 161.
  11. (a) B. Dhandayuthapani, R. Mallampati, D. Sriramulu, R. F. Dsouza, S. Valiyaveettil, ACS Sustainable Chemistry & Engineering (2014) 2, 1014 – 1021. (b) D. Setyono, S. Valiyaveettil, RSC Advances (2014) 4, 53365 – 53373. (c) R. Mallampati, S. Valiyaveettil, Nanoscale (2013) 5, 3395 – 3399.  (d) H. Ma, C. Burger, B.S. Hsiao, B. Chu, Biomacromolecules (2011) 12, 970 – 976.
  12. Unpublished results, A. Sng, Functionalization of Cellulose Based Materials and their Applications, BSc (Hon.) Final Year Project, National University of Singapore, (2013).
  13. (a) M. Wuithschick, S. Witte, F. Kettemann, K. Rademann, J. Polte, Phys. Chem. Chem. Phys., (2015) 17, 19895-19900 (b) S. Gu, S. Wunder, Y. Lu, M. Ballauff, R. Fenger, K. Rademann, B. Jaquet, A. Zaccone, J. Phys. Chem. C (2014) 118, 18618-18625 (c) S. Haas, R.  Fenger, E.  Fertitta, K. Rademann  Journal of Applied Crystallography (2013) 46, 1353-1360   (d) V. S. Raghuwanshi, M. Ochmann, F. Polzer,  A. Hoell,  K. Rademann   Chemical Communications   (2014) 50,  8693-8696    (e) V. S. Raghuwanshi, M. Ochmann, A.  Hoell, F. Polzer, K. Rademann Langmuir  (2014) 30,  6038-6046    (f) M. O'Neill, V. S. Raghuwanshi, R.  Wendt, M. Wollgarten, A. Hoell, K. Rademann Z. Phys. Chem. (2015) 229,  221- 234
  14. (a) V. D. Goud , R. Dsouza, S. Valiyaveettil, European Polymer Journal (2015), 71, 114-125., (b) V. D. Goud, R. Dsouza, S. Valiyaveettil, RSC Advances, 2015, 5, 47647-47658., (c) S. Barik; S. Valiyaveettil, J. Poly. Sci. A – Polym. Chem. (2014) 52, 2217-2227.
  15. V. Andrei, K. Bethke, K. Rademann, Energy Environ. Sci. (2016), DOI:10.1039/c6ee00247a.