**6. Conclusions and perspectives**

In this case, CO molecules react with adsorbed oxygen ions on the mesoporous film surface, which results, in turn, in an overall decrease of the electrical resistance of the metal oxide thin

molecules cause a depletion of electrons from the TiO<sup>2</sup>

results in an increase of electrical resistance. The conductivity change can be easily transferred

to form coordination bonds with the amine and the carboxylic groups of biomolecules, such

acterized by high stability and biocompatibility. A biosensor is an analytical device, which converts a biological response into readable or quantified signal. Biosensors can be applied to analyze a variety of samples including body fluids, food samples, and cell cultures [68]. The biosensing mechanism is based on a biochemical reaction. Typically in (bio-)electrochemistry, a measurable current (amperometric), a measurable potential, or a charge accumulation (potentiometric) will be generated upon the alteration of the conductive properties of a

Titania mesoporous thin films have been also used as sensors for *Escherichia coli*, an enterohemorrhagic bacterium whose infections have a low incidence rate but can have severe and sometimes fatal health consequences and thus represent some of the most serious diseases due to the contamination of water and food [69]. Titania films treated with APTES ((3-aminopropyl) triethoxysilane) and GA (glutaraldehyde) were functionalized with specific antibodies anti-*Escherichia coli* antibodies. In this case, FTIR spectroscopy has been used as an optical transduction method: the spectroscopic signals originated from the various functional groups related to proteins, lipid, and carbohydrates can be used for the identification and structural

Lithium-ion batteries (LIBs) are rechargeable batteries widely used in laptop, mobile phones, and electric vehicles. These batteries are characterized by high-energy density, low maintenance, little self-discharge, and no memory effect, which means that it is not necessary to completely discharge them before charging. In a conventional LIB cell, lithium metal oxide (e.g.,

are separated by a porous membrane and soaked in a nonaqueous liquid electrolyte. During insertion (or intercalation), ions move into the electrode. During the reverse process, extraction (or de-intercalation), ions move back out. Upon charging, the lithium ions move from the cathode to enter the anode, while in the discharging phase, the reverse phenomenon takes

trode materials for LIBs. Compared with the currently commercialized graphite anode, these metal oxide materials have demonstrated various advantages, such as very high capacity,

) is used as cathode, while graphite is used as preferred anode. The two electrodes

, have been investigated as potential elec-

Titania nanostructured materials are good candidates also for biosensing, because TiO<sup>2</sup>

as enzymes, while maintaining the enzyme's biocatalytic activity. Furthermore, TiO<sup>2</sup>

−

), the fol-

surface, which

is able

is char-

films. On the contrary, if a chemical sensor is exposed to an oxidation gas (e.g., NO<sup>2</sup>

lowing oxidizing reaction may take place:

72 Titanium Dioxide - Material for a Sustainable Environment

In this example, NO<sup>2</sup>

NO2 + e<sup>−</sup> → NO2

medium between electrodes when the sensing takes place.

characterization of different pathogens and subspecies.

place. A variety of metal oxides, in particular TiO<sup>2</sup>

**5.2. Lithium-ion batteries (LIBs)**

LiCoO<sup>2</sup>

into resistance signal, which is the best-known sensor output signal.

Undeniable great progresses have been made in recent years in the design and synthesis of mesoporous TiO<sup>2</sup> thin films featuring novel and well-designed structures and morphologies as well as to further explore and enhance their applications. Nevertheless, challenges are remaining in developing cheap, low toxic, and reproducible synthetic approaches for achieving an easy and precise control over the pore size, wall thickness, surface area, morphology, and crystallinity.

For optoelectronic applications, the main concern resides into the deposition of organized MTTFs onto semiconductive electrodes such as ITO or FTO keeping a homogenous disposition of the pores on the whole device electrode, and although some preliminary attempts have been made [52, 78], it remains a challenging issue owned to the wettability difference between ITO and Si wafers. Moreover, while small-sized devices have been tested, on large scale, difficulties are encountered to maintain such uniform orientation of the pores, especially in the case of vertically aligned pore arrays, the most suited geometry for efficient optoelectronic devices. For these reasons, scientists are investigating also the possibility of depositing nanotubes of TiO<sup>2</sup> from anodization of sputtered titanium onto different substrates. The best results have been so far obtained for depositions performed onto quartz. However, in the case of semiconductive substrates, several problems are arising, the most important one being the easy loss of contact between the formed TiO<sup>2</sup> nanotubes and the semiconductive layer, which will definitely require further and intense research activities to circumvent such a drawback.

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