Contamination of walls, floors and surfaces of many articles that we use in day-to-day life is the main reason why a disease spreads rapidly and ensuring these surfaces to be free of microbial contamination, especially in hospitals, is an important factor in maintaining the general health of people. Silver in the form of metallic silver or silver salts is known to be toxic to micro-organism, particularly bacteria while being relatively harmless to a man. When nano scaled silver is introduced to a hybrid sol-gel matrix, it results in an antimicrobial coating due to the silver and scratch resistant due to the inorganic network of sol-gel coatings providing high degree of abrasion resistance too. This helps in retarding the growth of microbes and thus minimizes the use of autoclaving process or cleaning using harsh chemicals. Other functionalities such as easy to clean property can also be incorporated into the coatings.
- Incorporation of anti-microbial nanoparticles, controlled release mechanism
- Easy-to-clean coatings have surface properties comparable to perfluorinated polymers (hydrophobic surface)
- SS sheets in hospital wall panels
- Medicine/Pharamaceutical: Medicine bottles/containers
- Health care: Hearing aids, hospital furniture
- Food packaging
- Textile and fabric: textile walls and textile roofs, sun shades, blinds
Anti-microbial coatings For door mats
Antimicrobial Coatings on SS Kidney Trays
Role of photocatalysis property of nano titania for environmental benefits is well known and to list a few of them are such as destroying atmospheric pollutants like VOC / NOx which can cause lung damage, protection of buildings from damage due to smog and acid rain due to VOC/NOx in atmosphere,. self-cleaning paints / coatings, anti-microbial surfaces for the destruction of harmful bacteria/fungi and thus purifying air, water.
Presently, ARCI's activity is mainly focused on developing nano titania in modified novel morphologies and compositions having high photocatalytic activity suitable for applying on textile surfaces to give best self-cleaning property. All the aspects of performance of the material and requirements of regulatory clearances for the product to be commercially launched in the market are being taken care.
The high quality titania developed at ARCI is prepared by tailoring its band-gap using combination of their crystal structures, possessing huge surface area available for photocatalytic activity. The efforts for up-scaling the production, optimizing textile application process and testing of photocatalytic activity in gas phase are in process.
Efforts are also being made to develop visible light sensitive photocatalysts. Recently, co-catalyst (Cu, Pt) modified semiconductors considered as an efficient visible-light-driven photocatalysts by interfacial charge transfer (IFCT), and multi-electron reduction via Cu (II)-ions. ARCI is currently working on the design of efficient, visible-light-driven semiconductors using surface modified rutile TiO2, which can be later used to make self-cleaning paints to remove the odor and bacteria from textiles.
Micro Arc Oxidation (MAO) is a recently developed environmental friendly process for forming ceramic composite coatings on the surface of Aluminium, Magnesium, Titanium and its alloys by means of plasma electro-chemical oxidation. The discharge channels created as a result of electro-thermal breakdown of the coating in alkaline electrolyte medium through specially regulated AC power supply promotes the formation of fully crystalline and dense ceramic oxide composite coatings (as shown in Fig 1) with hardness up to 1900 HV; thereby imparts superior wear (as shown in Fig 2), thermal, oxidation and corrosion resistant properties. Aluminium alloys treated by Micro Arc Oxidation can effectively substitute the parts made of heat treated steel, high strength cast iron, ceramic parts, metals hardened by hard chromium plating, conventional anodizing, hard anodizing and other gas-thermal spraying methods.
International Advanced Research Centre (ARCI), Hyderabad, INDIA has developed the novel MAO technology to mutually share the commercial benefits with the widespread industries. The application sectors include but not limited to Textile, Aerospace, Automotive, Wire-drawing and Electronics. The MAO technology has already been patented in India and USA, is available for application development and technology transfer both in India and abroad.
Cross-sectional SEM image of MAO coating
Health and Hygiene care products based industries have a huge market and their products are of primary importance because of increased awareness among population for health and hygiene. These industries have a huge demand for an efficient and economic antimicrobial material to improve the performance of their products. Since ancient times antimicrobial properties of gold, platinum, silver, copper, zinc and mercury are well known and they have been in use as anti microbials in the form of metals or as their compounds, eg. Silver or, silver sulpha hydrazine. Among the noble metals silver being affordable is used extensively as an anti microbial material in many products like wound dressing, water treatment, etc. As reported in literature, silver can effectively kill fungus, 650 families of bacteria and few viruses also. Lower concentrations of nano silver kills unicellular micro organisms whereas, it is inactive towards multi cellular human cells. Hence, silver is a safe and an effective antimicrobial material. Nano silver opens new dimensions of the well-known anti-bacterial properties of bulk silver. It also gives us the privilege of utilizing the antibacterial properties of silver at an affordable cost. With this motivation ARCI had initiated the project on nanosilver for antibacterial applications. Realizing the potential of nano silver as an antibacterial material we have made an attempt to develop nano silver coated antimicrobial water filters and textiles. Both the projects started with laboratory experiments to develop novel synthesis methods, continued with proof of concept by demonstrating the antibacterial performance and finally scaled-up for large scale synthesis. Both the technologies were successfully transferred to Indian industries.
Self-cleaning coatings can be divided into two categories: hydrophobic and hydrophilic. The former class of coatings is based on the lotus effect and the later is based on photocatalysis. TiO2 is well known photocatalyst that is used for self-cleaning applications. Due to the versatility of sol-gel coating technique, self cleaning TiO2 coatings generated by sol-gel process are expected to be viable for commercial exploitation.
Dip, spray and flow coating process can be used to get transparent wet gel TiO2 thin film on soda lime glass (SLG), fused silica glass (FSG) and glazed ceramic wall tiles (GCWT). The final dense TiO2 thin film can be obtained by firing the wet gel film at temperatures higher than 450oC in a continuous belt furnace at the production rate of 3.5 m2/h. The coating thickness, refractive index and microstructure properties were analyzed using variable angle spectroscopic ellipsometry (VASE) and validate the proposed model using transmission electron microscopy (TEM). The self-cleaning stain removal ability of the TiO2 coated glazed tiles was demonstrated using a permanent marker stain. Figure shows the degradation activity of stain made using permanent marker ink on spray and flow coated ceramic glazed tiles. Figure shows two zone TiO2 coated (bottom) and uncoated (top) area. The permanent marker stain made on uncoated area is clearly visible after 55 h exposure to sun light, whereas, the stain made on TiO2 coated zone is rarely visible because of photocatalytic degradation.
- Self- cleaning and self sterilizing surfaces
- Hydrophilic surface formation facilitating easy cleaning by rain or rinsing with water (self-cleaning effect)
- Self-cleaning coatings activated by sunlight/artificial UV light
- Long life, strongly enhanced UV protection by TiO2
- Architectural glass and tiles
- Medical/Pharmaceutical: Medicine bottles/containers
- Textiles and fabric: textile walls, textile roofs, sun shades and blinds