**4. Potential and applications of NS TiO2**

Metal oxide nanoparticles (NPs) have found a variety of applications in numerous industrial, medical, and environmental fields s, attributable to recent advances in the nanotechnology field.

### **4.1 Photocatalytic applications**

Photocatalysis is the decomposition and degradation of pollutants under the action of light rays on the surface of a catalyst, usually titanium dioxide (TiO2). It allows the destruction of volatile organic compounds, inorganic pollutants, and microorganisms. The finalized process produces essential water and carbon dioxide [65]. All current applications of photocatalysis use TiO2 as a semiconductor for several reasons [66]. Titanium dioxide, in its current commercial forms, is not toxic (apart from recent reservations about the use of reservations regarding the use of nanoparticles) and, due to its photostability in air and water, does not release toxic elements [67]. As titanium is a relatively abundant element, the cost of TiO2 is not too high, at least for some applications. The most widely used crystallographic form is the anatase form because TiO2 with a rutile structure (although having a lower band gap value allowing it to absorb light in the early visible spectrum) is significantly less active. The most effective commercial composition at present is TiO2 Degussa P25 (80% anatase, 20% rutile) [68]. For practical industrial applications of semiconductor photocatalysts, Sharma et al. [52] proved the development of research of new semiconductor materials in visiblelight active TiO2/SnX (X = S and Se) and their application as photocatalysts since it is a new area of scientific interest. Indeed, they focused on the addition of TiO2 composites with SnX (X = S, Se) as potential candidates for environmental purification.

### **4.2 Photovoltaic applications**

In the current global scenario, the rise in technological demands of the world's population has caused a rapid increase in energy consumption, which in turn has led to an exponential increase in environmental pollution, which we have witnessed seriously in the last decades. To surmount this situation, the efficient use of green energy has become a hot topic worldwide. On the other hand, intelligent materials

*Nanostructured Titanium Dioxide (NS-TiO2) DOI: http://dx.doi.org/10.5772/intechopen.111648*

are also of great value in the current market due to their multipurpose for a variety of applications. Among the green energy alternatives available today, solar energy provides more promising perspectives as the sun can deliver the ultimate solution to the prevailing sustainable energy supply challenge. Among the different solar cell technologies currently available, dye-sensitized solar cells have drawn a lot of attention due to their promising prospects. On the Other Side, photocatalysis has also made a strong case for itself due to its promising opportunities for clean, green, and sustainable development in environmental technology applications [69, 70].

### **4.3 Sensing applications**

In recent years, gas sensors have become extremely important for environmental and industrial atmosphere monitoring [71]. Gas detection techniques are based on resistance sensing, electrochemical and optical methods, gas and liquid chromatography, and acoustic waves. Nevertheless, certain sensors have various drawbacks: they consume energy and time, they are wide in size, they are expensive, and they display slow response and low selectivity [72, 73]. Consequently, special attention has been given to chemoresistive sensors, which are formed by metal oxides, carbonbased materials, and conducting polymers. Among these materials, semiconducting metal oxides have been extensively investigated and explored due to the potential for different valences, morphologies, and physicochemical characteristics [74]. They are becoming more complex than pure metals, with bonding going from ionic to highly covalent to metallic. For this reason, metal oxide nanoparticles are attracting considerable attention from industry for use in diverse applications such as catalytic processes, magnetic storage media, electronics, sensors, and solar energy conversion.

### **4.4 Hydrogen production and storage**

Hydrogen (H2) generation has become viral in the last few decades due to hydrogen as a future energy source and its capacity to replace expensive and polluting fossil fuels [75]. In addition, hydrogen also contributes to the development of a green world due to its zero emissions and minimizes dependence on non-renewable resources. In general, hydrogen production processes can be divided into two categories based on the usage of renewable and non-renewable resources. The methods for utilizing renewable energy resources are photoelectrolysis, thermal and photocatalytic water splitting, and steam reforming and gasification. Steam reforming and gasification methods are processes that depend on non-renewable resources [76]. Among carbon materials, activated carbon (AC) can be produced easily from agricultural residues such as hardwoods, coconut shells, fruit pits, walnut shells, and lignite. Which makes CA abundantly available and less expensive. CA also has characteristics such as a high surface area and a porous structure [77]. Such as high surface area and porous structure [77]. Due to these characteristics, AC-TiO2 nanocomposites have been extensively investigated for the photocatalytic decomposition of dyes [78]. As an example, Mahadwad et al. [79] decomposed the reactive black dye 5 under mercury vapor light with AC-TiO2 nanocomposites. Recently, Xing et al. [80] reported the H2 generation activity with different types of simulated seawater with Rh/Cr2O3GaN nanowire photocatalyst [81]. Reddy et al. [82] have developed a low-cost nanocomposite such as AC-TiO2 by a one-step hydrothermal method, which is a potential catalyst for H2 generation under sunlight. In the photocatalytic H2 generation process, sacrificial agents have a crucial role in consuming the valence band (VB) holes.

### **4.5 Environmental applications**

TiO2 is an environmental-friendly material that has been widely used in the photodegradation of a large number of pollutants. Nanostructured TiO2 was used in pollution abatement, energy conversion (i.e. hydrogen production and solar cells), and energy storage (i.e. lithium batteries and supercapacitors). Its practical interest was also described in water purification, self-cleaning, self-sterilization of surfaces, as well as light-assisted H2 production [83]. In the textile field, Gaminian and Montazer [84] assessed the self-cleaning effects of Cu2O/TiO2 on polyester fabric and concluded that both washed and unwashed samples showed significant photodegradation properties of methylene blue. Production of the reducing agent ethylene glycol as a product of the alkaline hydrolysis for the synthesis of Cu nanoparticles was reported indeed. In another trial, Harifi and Montazer [85] developed Fe3 + −doped Ag/TiO2 nanostructures for photocatalytic uses under the UV-vis light spectrum. The photodegradation activity assessed using methylene blue was confirmed under both UV and visible light regions. Zhou et al. [86] explored the degradation of acetone in the air using irondoped mesoporous TiO2 nanoparticles. Their findings showed a high degradation rate of this organic pollutant. In the same way, El-Roz et al. [87] reported an enhanced photocatalytic activity of luffa/TiO2 nanocomposites against methanol. Píšťková et al. [88] investigated the photodecomposition of acebutolol, propranolol, atenolol, nadolol, and metoprolol, which are β-blockers, using immobilized TiO2 in an aqueous media. Their results showed a complete photodegradation in 2 h of all tested β-blockers. Coronado et al. [89] described some TiO2 applications in water purification. This application is argued by the excellent optical and catalytic properties of nanostructured TiO2, allowing oxidation and reduction catalysis of both organic and inorganic contaminants. The photo-generated free radicals and e−/h + pairs are highly implicated in degrading organic substances, water pollutants, and harmful microorganisms [90]. In this trend, nanocomposite TiO2 thins films (P/Ag/Ag2O/Ag3PO4) were able to decompose up to 90% of rhodamine B under solar light exposure [91, 92].
