Preparation Of Micro-and Nanocompositc Films On Stainless Steel Phsurface Forotocatalytic And Antibacteiral Applications

Stainless steels are essential base materials with a host of commercial applications, such asbuilding materials, sanitary wares, kitchenwares, household appliances and medical apparatusdue to its advantages of resistance to corrosion and heating, good mechanical properties andductibility, and high polish surface. However, composite organic, inorganic and biologicalfouling occurs on stainless steel surface. The surface fouling will lower the corrosion resistanceand smear the high polish surface of stainless steels. Traditional heavy manual cleaning worksfor curtain walls and roof glazing systems are accompanied by great risk and high cost tocleaners and architectures. Protection of stainless steels from corrosion and keeping the surfaceclean are an area of study commanding considerable attention. Photocatalytic processes arewidely recognized as viable stategies to solve the surface fouling problems, because organicspecies can be completely mineralized to carbon dioxide or become nontoxic materials byphotocatalytic pathways. For the first time, several strategies were proposed to developphotocleanable and antibacterial stainless steels. Micro-and nanocomposites films composed ofFe₂O₃, TiO₂and WO₃were prepared on stainless steels by electrochemical anodization, ionimplantation and hydrothermal reactions. The as-prepared composite films on stainless steelswith favourable photocatalytic properties and excellent antibacterial performance demonstratecomparable hardness, mechanical properties, high polish surface and corrosion resistance tothose of original surface of stainless steels. The composite films on stainless steels withremarkable photocatalytic activities will exhibit potential applications particularly for outdoorpurpose and will considerably reduce the cleaning cost. Great social and economic benefits willbe expected. The main research works are as follows:1) Nanopores arrays （NPAs） on stainless steels surface are prepared by electrochemicalanodization. The morphology, microsture and chemical composition of the NPAs areinvestigated. The anodization process was carried out with a polished stainless steel foil servedas the anode in several solutions, such as perchloric acid, NH₄F, NH₄Cl, SO42-and NaH2PO4.Uniform NPAs composed of Fe₂O₃and Cr₂O₃were prepared in these solutions, with diametersin the range of30³00nm, and depths in the range of10¹30nm. The morphology andmicrosture of the NPAs can be controlled by anodization process. The controllable formation ofNPAs will expand the applications of stainless steels and provide a set of systematic methodsfor functionalization of stainless steels.2) Formation of NPAs on the surface of stainless steel is demonstrated by anodization inethylene glycol （EG） solution containing perchloric acid. Perchloric acid concentration, appliedvoltage and anodization time of anodization process are investigated. The maximum depth of anodic overlayer is26nm composited by Fe₂O₃and Cr₂O₃after anodization in5vol%HClO4EG solution at40V for10min. The anodized stainless steel shows significant photocatalyticactivities, which should be attributed to the photocatalytic performance of Fe₂O₃and theFe₂O₃-Cr₂O₃heterojunction. Moreover, the formation of NPAs does not damage the polishappearance of stainless steels and remains good corrosion resistance.3) Anodized stainless steel was implanted by Ti ions at an extracting voltage of50KVwith an implantation dose of3×10¹⁵atoms/cm². The implanted stainless steel was then annealedin air at450℃for2h. The results showed that the Fe₂O₃-TiO₂composite film exhibited anenhanced photocatalytic activity that is4.6times to that of as-anodized stainless steel.Meanwhile, the implanted stainless steel showed a slightly better resistance to corrosion thanthat of mechanically polished stainless steel.4) A one-step hydrothermal reaction was presented to prepare TiO₂/WO₃nanocompositefilms deposited on anodized stainless steel. The TiO₂/WO₃nanocomposite film prepared in0.01mol/L （NH₄）₂TiF₆and0.0066mol/L Na₂WO₄solution at120℃for3h exhibits the maximumphotocatalytic activity that is15.7times to that of as-anodized stainless steel. Thephotocatalytic activity of TiO₂/WO₃nanocomposite film is five times higher than that of pureTiO₂film and eight times higher than that of pure WO₃film. The excellent photocatalyticactivity of the nanocomposite film should be attributed to the formation of heterojunctionbetween TiO₂and WO₃nanoparticles that can facilitate the separation of photo-generatedelectron-hole pairs.5) Hydrothermal reaction was presented to prepare Fe₂O₃/SnO₂nanocomposite filmdeposited on anodized stainless steels. The Fe₂O₃/SnO₂nanocomposite film prepared in0.030mol/L SnCl₄solution at220℃for3h exhibits the maximum photocatalytic activity that is11.8times to that of as-anodized stainless steel. SnO₂is an n-type semiconductor. The excellentphotocatalytic activity of the nanocomposite film should be attributed to the formation ofheterojunction between Fe₂O₃and SnO₂nanocrystals that can facilitate the separation ofphoto-generated electron-hole pairs. Moreover, the conductive nanocomposite film showsconsiderable photocurrent that is14.8times higher than that of as-anodized stainless steel.6) Antibacterial activities of medical materials contained with only one antibacterial agentwill be compromised in many situations. Antibacterial stainless steel containing twoantibacterial agents will offset these deficiencies and will obtain high antibacterial efficiencytowards most microorganisms. Antibacterial stainless steels containing Ag/Cu or Cu/Zn wereprepared glow discharge plasma metallurgy. The corrosion resistance of stainless steel isslightly enhanced after glow discharge plasma treatment. Excellent antibacterial activities（100%） against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureusare obtained for Ag/Cu or Cu/Zn doped stainless steel.