Nature Inspired Nanomaterials Easy to clean and self cleaning materials Florian Doll Ruta Ruperte Nina Muratovska Sigrid Aamot Jan Dobeš 1

Outline Introduction Examples The Lotus plant and superhydrophobility Removing surface pollution Physical explanation Photocatalystic reactions Photocatalystic self-cleaning fibers Applications Risks and concerns Future 2

Introduction - nanoparticles Naturally occurring nanoparticles Man-made nanoparticles Incidental Engineered 3

Examples Shark-skin Gecko feet Lotus plant image/

The Lotus plant Aquatic plant Leaves have nanostructures Coated with hydrophobic wax crystals Rough surface at nanoscale which is more hydrophobic 5

Superhydrophobicity First studied using rough hydrophobic surfaces (Dettre and Johnson 1964) Self-cleaning property of superhydrophobic micro- nanostructured (Barthlott and Ehler 1977) – The Lotus effect 6

The Lotus effect The lotus effect refers to self-cleaning properties that are a result of very high water repellence (superhydrophobicity), as exhibited by the leaves of the lotus flower (Nelumbo) Another effect inspired by nature – photocatalystic effect What are photocatalysts? 7

Removing pollution from a surface - Physical nature Two ways how to do it: Lotus effect Photocatalytic self-cleaning 8

Lotus effect Based on: Reduction of adhession Reduction of frictional force Combination of Micro- and Nano- surface structure Resulting effects reduction of the contact surfaces Facilitation of fluid flow easier cleaning of surface by running water 9

Force acting on the water drop 10

Surface Structure 11

Frictional force 12

Mechanism of removing pollution 13

Photocatalytic self- cleaning photo-assisted catalytic process: Energy of light promotes electrons from the valence band to the conduction band This effect leads to a catalytic chemical reactions After excitation: conduction band - active electrons (e − ) valence band - positive holes (h + ) 14

Scheme of promotion 15

Inspiration in nature 16

Photocatalystic reactions TiO 2 + hν → e − + h + Photogenerated electron–hole pairs can react in three pathways: 1.recombination on the surface or in the bulk e − + h + → TiO 2 2.photoreduction - electrons diffuse to the surface and react with adsorbed O2 producing reactive oxygen radicals ( − O, − O 2, − O 3 ) e − + O 2 → O 2 − 3.photooxidation - holes oxidize H2O or adsorbed hydroxide ions forming hydroxyl radicals ( − OH) h + + H 2 O → ˙OH + H + 17

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Photocatalytic self-cleaning fibers Photocatalytic self-cleaning fibers are fibrous materials formed by imparting photocatalytic function through surface functionalization treatment, wherein the fibers are able to clean themselves when exposed to light. They also possess antimicrobial, deodorizing and UV blocking functions. 19

Photocatalytic self-cleaning application 20

Photocatalytic self-cleaning fibers and applications Self-cleaning daily apparels Anti-fouling, anti-odor and anti-mold Environmental friendly  Resources saving and cost effectiveness Protective clothing UV protection Medical protection 21

Risks and Concerns Environment Lack of comprehensive studies Accumulation of nanoparticles Human safety No malignant respiratory diseases observed No significant storage nor absorption Nano scale doubtful “Permanently bonded on the fibrous” 22

Future Self-cleaning and oil-water separation Focus on wavelength 23

Bibliography bio-mimicry-and-making-the-superpowers-of-your-dreams-a-reality- 4/ bio-mimicry-and-making-the-superpowers-of-your-dreams-a-reality- 4/ around-us/Lotus plant 24

Thank you for your attention! 25