**5. Future outlook and conclusion**

This chapter gives emphasis on the specific idea of TiO2-based self-cleaning surfaces. Self-cleaning surfaces cover a significant research area in this era of fast urbanization and industrialization. Also, self-cleaning surfaces are an answer for cleaning contaminated surfaces to compromise large energy consumption. The chapter gives a brief about the outstanding examples of TiO2 composites for water purification techniques such as TiO2 hybrid composite with grapheme, Heterojunction of TiO2 with some other metals, dye-sensitized TiO2, etc. Applications of TiO2 and TiO2 composite materials or hybrids as a superhydrophilic photocatalysts in water purifying membranes, antibacterial surfaces, fabrics, oil–water separation techniques, and in antireflective coatings are discussed in detail. Superhydrophilicity mechanism in semiconductor metal oxides is investigated from different models. Although in this field, there is great progress in the development and fabrication of self-cleaning coatings and surfaces, however, there are still some technical problems and challenges with self-cleaning coatings that will cause bridging the gap between industry and fundamental research.

Mechanical durability and chemical stability are the major concern for the fabrication of self-cleaning coatings. Exposure of these coatings to solvents and outdoor temperature differences can lead to the detachment of the material from the surface of the coating due to which there will be a gradual decline in the performance of coatings. However, the surfaces which are responsive to indoor light sources are more durable and persistent with superhydrophilicity because photoinduced wettability recovers the hydrophobic nature of coating in the dark within minutes to hours. As a result, self-cleaning coatings should be designed in such a way that they should have anti-bacterial, antifogging, and antireflective properties and have good adherence to different surfaces like mirror, ceramic, and furniture. A significant emerging class of self–cleaning coatings and surfaces responds to various external stimuli such as changes in temperature, pH, chemical environment, stress, and humidity. The most recent study also predicts that this field has a promising trend in developing self-cleaning surfaces which has a combination of self-cleaning and photocatalytic properties in this way a single surface find a wide variety of application. Coatings with a combination of anti-bacterial, anti-fogging, and anti-reflective properties can find application in endoscopic surgery examples. The self he antireflective and antifogging can make them more appealing to building materials, solar panels, automobile windshields, etc. under inconsiderate environmental conditions.
