**1. Introduction**

The invent of graphene and graphene-like two dimensional materials has created great interest in the exploration of other two-dimensional materials family which includes hexagonal boron nitride, graphitic carbon nitride, transition metal dichalcogenides (TMDCs), layered metal-oxides/double hydroxides, MXenes (transition metal carbides/nitrides), metal–organic frameworks (MOFs), covalentorganic frameworks (COFs), polymers, black phosphorus (BP), siloxene/silicenes, and metallenes [1–7]. In this scenario, the preparation of the 2D materials is of great interest for the development of the new range of materials [8–10]. The preparation methodologies/strategies can be categorized into top-down technique and bottomup technique [8, 11]. In general, the top-down technique mainly depends on the breakage of the bulk materials to the micro- and nano-scale, whereas in the bottomup technique, the growth of the materials is from atomic level to the macro-scale

structure [12–14]. Amongst the preparation of the materials, bottom-up techniques such as molecular beam epitaxy, chemical vapor deposition and so on produced high purity and efficient layered materials with desired crystal structure [15–17]. This technique involves in building the nano materials from atomic/molecular scale using heterogeneous/homogeneous chemical reactions, which tend to produce thermodynamically stable materials where the morphology/structure is controlled by both reaction kinetics and thermodynamics [8]. In addition, the building of nanomaterials with desired morphology/structure and composition in a single step is very challenging due to their inherent characteristics of the materials [8, 18]. Moreover, the synthesis of two-dimensional layered materials (metal nitrides/ carbides) are hindered due to their non-layered crystal structure. And also, the preparation methods employed in the bottom-up approach is of high cost and the utilization of the prepared materials also requires highly sophisticated instrumentation for characterizing the same. In this regard, top-down technique is of great interest as the cost of production of the materials is less compared to the former with high amount of yield. Some of the top-down approaches for the production of the 2D materials are photolithographic technique, exfoliation (wet and solid phase), mechanical ball milling (wet and solid phase), chemical etching, and topochemical reaction [8, 11]. Amongst the other methods for the top-down technique, topochemical reaction methods is the promising strategy for the preparation of the 2D layered materials [8].

The topochemical route can be classified depends on the reaction methodologies such as adding, extracting or substituting elements to/from the source materials to form the new materials with the retention of the structure/morphology of source material [11]. This type of preparation technique adopts the "corner-overtaking" route, which circumvents the hindrances of direct synthesis through chemical reaction to multi-level steps synthesis [11]. In this aspect, the topochemical preparation route is utilized to synthesize the high value added 2D materials which are difficult to process. Compared to that of the direct synthesis/bottom up approach, top down method has higher advantage to prepare the 2D materials with controlled morphology, composition and material structure. The topochemical reaction route can be performed through various methodologies which includes the (i) selective etching of the elements [19, 20]; (ii) electrochemical methods [21, 22] (iii) high temperature treatment reaction [23, 24] and (iv) liquid phase reaction [25, 26]. In the selective etching methods, the 2D layered materials can be easily obtained by from the bulk counterpart and also it is possible to engineer the interface and surface of the prepared materials. However, the chemical used as etchant is toxic which also affect the quality of the raw materials for the preparation of materials. In this case, hydrofluoric acid is used as the etchant for the preparation of MXenes from the MAX phase element, similarly hydrochloric acid is used for the preparation of siloxene from calcium silicide [27–30]. In case of the electrochemical methods for the preparation, mild and controllable reaction is carried out with the application of electric field to promote the fast reaction [21, 22]. The limitation in this process is that it requires complex instrumentation and the mass production is very limited in the electrochemical method. In the high temperature treatment reaction, the preparation is associated with the controllable atmosphere induced chemical reaction and high temperature condition is employed for the preparation with the limitation of heterogeneity of gas/solid interface reaction, explosion risk at higher temperature and toxic gases as a byproduct of the reaction [23, 24]. Amongst the other techniques in the topochemical reaction, liquid phase exfoliation as the great advantages of high mass yield, wide range of controllable reaction parameters such as solvents, rich experimental/theoretical foundation and produce uniform and good crystalline materials. Hence the liquid phase topochemical methods attains more merits compared to the other methods.

*Energy Storage Properties of Topochemically Synthesized Blue TiO2 Nanostructures in Aqueous… DOI: http://dx.doi.org/10.5772/intechopen.102186*

In this book chapter, we have focused on preparing the 2D sheet like blue titanium oxide via liquid phase topochemical reaction on titanium boride. The TiO2 prepared technique has electron-rich property which shows enormous property in the field of electrochemical energy storage. This electron-rich TiO2 will be refereed as blue/black TiO2 which inherits exceptional physical and chemical properties to that of other forms TiO2 due to their disordered surface structure and Ti3+/oxygen vacancies which leads to high conductivity, magnetic properties, and better chemical properties; yet to be explored for the energy storage application. Herein, the preparation, characterization and the electrochemical properties of blue titanium oxide with sheet-like nanostructures is investigated in detail in this chapter.
