*2.4.2 The soft templating or the endotemplate method*

The soft templating or the endotemplate method refers to supramolecular entities like self-assembled arrangements of structure-directing molecules such as surfactants, leading to mesopores up to 30 nm [31, 32].

In the soft template method as shown schematically in **Figure 7**, compounds that function as templates are organic compounds whose molecules form aggregates through inter-molecular or intra-molecular interactions such as hydrogen bonds, chemical bonds, and electrostatic forces. The metal cations as the target as the hollow material are deposited on the surface or in the inside of the aggregate. The process of placing metal cations in the aggregate carried out using electrochemical methods, precipitation, and other synthesis/preparation methods to form metal oxide or composite materials of various shapes and sizes. Organic compounds that commonly function as templates are surfactants, polymers, biopolymers, supramolecules,

**Figure 6.** *Schematic pathways of Au doped CeO using hard template method [30].*

**Figure 7.** *Soft template pathways to produce hollow material [33].*

and inorganic compounds. Based on the type of compound that can act as a soft template, it is possible to develop nanomaterial synthesis because this method has advantages such as simplicity of the process, repetition of the process with good results, and does not require removal of targets from the aggregates [34–38].

One example of a soft template method to generate ABO3/AB2O4 nano hollow is spinel compounds of both Fe3O4 and CoFe2O4, respectively [39, 40]. Magnetite hollow spheres, Fe3O4 were prepared using a soft/free template with the solvothermal method described by Chen et al. [39] as follows: 13 g FeCl3.6H2O was dissolved in 350 mL of ethylene glycol and diethylene glycol. Subsequently, 2 g NaAc, 2 g polyvinyl pyrrolidone (PVP), and sodium citrate (Na3Cit) were added to the solution's ultrasonic processing. After an hour, the solution was sealed in a 400 mL Teflon-lined stainless-steel autoclave. The autoclave was heated to 210°C for 12 h and then cooled to room temperature naturally. The black products were collected by magnetic decantation and centrifugation, followed by repeated washing with deionized water and ethanol. The final products were dried in a vacuum oven at 50 C for 12 h. Another procedure with the same steps and only differs in the number of materials used and the washing process of the solution which turned black was washed with alcohol several times and dried at 60°C overnight. The diameter size of the product magnetite hollow spheres can be adjusted by changing the concentration of the added PVP [41]. Preparation of Fe3O4 using urea and PVP as a binder for Fen+ cations gives nano hollow spheres as shown in the following figure.

Mandal et al. [41] have synthesized of hollow Fe3O4 particles via a one-step solvothermal approach for microwave absorption materials: effect of reactant concentration, reaction temperature, and reaction time as shown in **Figure 8j** below.

Then, another method of a template-free preparation of Fe3O4 nano hollow spheres has prepared by researcher Shi et al. [42] using the following procedure, hydrated ferrous chlorine salt (FeCl3.6H2O, 1.084 g) was dissolved in 80 mL of deionized water under rigorous and constant stirring for 10 minutes. Then added Na-citrate salt (2.352 g), PAM (0.8 g), and urea (0.72 g) while stirring vigorously for 30 minutes. The mixture was then transferred to Teflon and tightly closed before being placed into the autoclave and heated at 200°C and held at the temperature for 24 hours. Then cooled naturally with air. The result of a black precipitate Fe3O4 was washed with water and ethanol, separated by magnetic attraction, and finally dried

**51**

**Figure 9.**

**2.5 Simple method**

**Figure 8.**

*method.*

*Preparation of Hollow Nanostructures via Various Methods and Their Applications*

at 50°C for 12 hours in an oven. An example of the results obtained by the research group of Shi et al. [42] is shown in **Figure 8c** below. Furthermore, NiFe2O4 nano hollow spinel preparation used a template-free method, namely the solvothermal process was carried out using oleyl amine capping agent. Hydrated chlorine salts of nickel (NiCl2.6H2O) and iron (FeCl3.6H2O) respectively mixed with urea with a 1:2 molar ratio. The solvent uses a mixture of ethylene glycol and ethanol with a ratio of 2:1. After all these substances put into a glass chemical 100 mL, added as much as 1 mL while stirring. After 30 minutes stir, the solution becomes transparent and homogeneous, then put the Teflon which is tightly closed and put into the autoclave steel and heated at 200°C for 24 hours. The product was then passed with ethanol and collected by separation and heated at 60°C for 30 minutes. Product samples were analyzed by TEM with a result in the following **Figure 8a** below [43].

*The TEM results of NHS Fe3O4 (j), NHS Fe3O4 (c), and NHS NiFe2O4 spinel (a) using the solvothermal* 

The simple method for producing hollow nanomaterials in question is in terms of the use of chemicals to produce nano hollow materials and environmentally friendly products. In the nano hollow material preparation, water and pectin or egg white solution is used as media. The procedure to obtain the nano hollow material is explained in brief here. The procedure to obtain the nano hollow material is explained in brief here. A stoichiometric amount of Ni (II) nitrate hydrates, ammonium vanadates, and Fe (III) nitrate hydrates were dissolved in distilled water, having compositions of Ni1-xVxFe2O4 under magnetic stirring for 1 h, respectively, followed by mixing each solution to make the final solution weight ratio between nitrates to pectin is 3:2. Adjust the pH = 11 in the above solution by an addition of ammonia, and heat it at 80 °C with continuous stirring to form a viscous gel. Then, dried the gel using the freeze dryer for 7 h to form the precursors' networks and

calcined at 600 °C for 3 h. The results are shown in **Figure 9** below.

*TEM results of hollow material Ni1-xFe2O4 (where x = 0.1 – 0.5) were prepared using sol-gel method [44].*

*DOI: http://dx.doi.org/10.5772/intechopen.95272*

*Preparation of Hollow Nanostructures via Various Methods and Their Applications DOI: http://dx.doi.org/10.5772/intechopen.95272*

**Figure 8.** *The TEM results of NHS Fe3O4 (j), NHS Fe3O4 (c), and NHS NiFe2O4 spinel (a) using the solvothermal method.*

at 50°C for 12 hours in an oven. An example of the results obtained by the research group of Shi et al. [42] is shown in **Figure 8c** below. Furthermore, NiFe2O4 nano hollow spinel preparation used a template-free method, namely the solvothermal process was carried out using oleyl amine capping agent. Hydrated chlorine salts of nickel (NiCl2.6H2O) and iron (FeCl3.6H2O) respectively mixed with urea with a 1:2 molar ratio. The solvent uses a mixture of ethylene glycol and ethanol with a ratio of 2:1. After all these substances put into a glass chemical 100 mL, added as much as 1 mL while stirring. After 30 minutes stir, the solution becomes transparent and homogeneous, then put the Teflon which is tightly closed and put into the autoclave steel and heated at 200°C for 24 hours. The product was then passed with ethanol and collected by separation and heated at 60°C for 30 minutes. Product samples were analyzed by TEM with a result in the following **Figure 8a** below [43].

#### **2.5 Simple method**

*Novel Nanomaterials*

**Figure 7.**

*Soft template pathways to produce hollow material [33].*

and inorganic compounds. Based on the type of compound that can act as a soft template, it is possible to develop nanomaterial synthesis because this method has advantages such as simplicity of the process, repetition of the process with good results, and does not require removal of targets from the aggregates [34–38].

Fen+ cations gives nano hollow spheres as shown in the following figure.

Mandal et al. [41] have synthesized of hollow Fe3O4 particles via a one-step solvothermal approach for microwave absorption materials: effect of reactant concentration, reaction temperature, and reaction time as shown in **Figure 8j** below. Then, another method of a template-free preparation of Fe3O4 nano hollow spheres has prepared by researcher Shi et al. [42] using the following procedure, hydrated ferrous chlorine salt (FeCl3.6H2O, 1.084 g) was dissolved in 80 mL of deionized water under rigorous and constant stirring for 10 minutes. Then added Na-citrate salt (2.352 g), PAM (0.8 g), and urea (0.72 g) while stirring vigorously for 30 minutes. The mixture was then transferred to Teflon and tightly closed before being placed into the autoclave and heated at 200°C and held at the temperature for 24 hours. Then cooled naturally with air. The result of a black precipitate Fe3O4 was washed with water and ethanol, separated by magnetic attraction, and finally dried

One example of a soft template method to generate ABO3/AB2O4 nano hollow is spinel compounds of both Fe3O4 and CoFe2O4, respectively [39, 40]. Magnetite hollow spheres, Fe3O4 were prepared using a soft/free template with the solvothermal method described by Chen et al. [39] as follows: 13 g FeCl3.6H2O was dissolved in 350 mL of ethylene glycol and diethylene glycol. Subsequently, 2 g NaAc, 2 g polyvinyl pyrrolidone (PVP), and sodium citrate (Na3Cit) were added to the solution's ultrasonic processing. After an hour, the solution was sealed in a 400 mL Teflon-lined stainless-steel autoclave. The autoclave was heated to 210°C for 12 h and then cooled to room temperature naturally. The black products were collected by magnetic decantation and centrifugation, followed by repeated washing with deionized water and ethanol. The final products were dried in a vacuum oven at 50 C for 12 h. Another procedure with the same steps and only differs in the number of materials used and the washing process of the solution which turned black was washed with alcohol several times and dried at 60°C overnight. The diameter size of the product magnetite hollow spheres can be adjusted by changing the concentration of the added PVP [41]. Preparation of Fe3O4 using urea and PVP as a binder for

**50**

The simple method for producing hollow nanomaterials in question is in terms of the use of chemicals to produce nano hollow materials and environmentally friendly products. In the nano hollow material preparation, water and pectin or egg white solution is used as media. The procedure to obtain the nano hollow material is explained in brief here. The procedure to obtain the nano hollow material is explained in brief here. A stoichiometric amount of Ni (II) nitrate hydrates, ammonium vanadates, and Fe (III) nitrate hydrates were dissolved in distilled water, having compositions of Ni1-xVxFe2O4 under magnetic stirring for 1 h, respectively, followed by mixing each solution to make the final solution weight ratio between nitrates to pectin is 3:2. Adjust the pH = 11 in the above solution by an addition of ammonia, and heat it at 80 °C with continuous stirring to form a viscous gel. Then, dried the gel using the freeze dryer for 7 h to form the precursors' networks and calcined at 600 °C for 3 h. The results are shown in **Figure 9** below.

#### **Figure 9.**

*TEM results of hollow material Ni1-xFe2O4 (where x = 0.1 – 0.5) were prepared using sol-gel method [44].*

#### **Figure 10.**

*TEM results of hollow nanomaterial LaCr1-xMoxO3 (x = 0.01-0.05) were prepared using sol-gel method [45].*

#### **Figure 11.**

*TEM and SEM results of LaCrO3 and LaCr1-xVxO3 materials prepared using pectin and egg-white solution [46, 47].*

**Figure 9b** and **c** clearly show the formation of nano hollow cube (NHC) from Ni1-xVxFe2O4 (x= 0.1 – 0.5) spinel. Furthermore, in **Figure 9a**, if you notice there are the cubic hollow aggregate and also a squared nano hollow tube (SNHT).

Then, in **Figure 10a** the micrograph shows that squared hollow pipes, hollow cube, and hollow tubes formed. In **Figure 10b**, you can see the nano hollow cubes (NHC) and micron sizes and nano spherical tubes (NST). Whereas in **Figure 10c**, you can see the interconnected pillars of micron and nano hollow cube sizes.

In the preparation of both pure LaCrO3 and modified LaCrO3 by the sol-gel method [46] gave SEM micrograph results shown in **Figure 11a** and **b**. It seemed that the shapes of material are varied that are nano hollow cubes (NHC), nano hollow tubes (NHT), and the blended shapes presented in **Figure 11a**. In **Figure 11b**, the interconnected microfiber structure and the hollow micro material formed. Meanwhile, **Figure 11c** shows the homogeneous nanoscale grains of hollow NiFe2-x CoxO4 spinels prepared using the egg white solution.

### **3. Applications**

After the preparation of all the catalysts is done, it is used respectively for both thermic catalytic reactions and photocatalysis. The compounds that are the research targets are CO2, NOx, dyestuffs, and cellulose. The selection of the four targets intensely focused on the impact factor and the benefits that can gain.

Carbon dioxide (CO2) and NOx gas emitted from the use of fossil energy sources containing the main elements H, C, and O as well as other minor elements N, and S. The overall reaction can be described below:

$$\text{Substrate} \text{(C, H, O, N, S)} + \text{O}\_2 \rightarrow \text{CO}\_2 + \text{NO}\_x + \text{SO}\_x + \text{H}\_2\text{O} + \text{Energy}$$

**53**

**Figure 12.**

*Preparation of Hollow Nanostructures via Various Methods and Their Applications*

The greater use of energy sources for activities, causing the emission of CO2, NOx, and SOx gases to increase [48]. Continuous emissions without treatment will cause acid rain and the greenhouse effect. This emission will stimulate global warming and even higher. One way to participate in the handling of COx and NOx wastes is through its utilization. One of the handling methods is using the nanocatalysts to handle thermally and photonically by converting the organic wastes (solid, liquid, and gaseous) such as cellulose, dyes, and COx and NOx pollutant into products that

Catalytic reaction - thermic is a catalytic reaction that takes place with the help of thermal energy. These catalytic reactions control more than 90% of processes in the chemical industry [49]. In thermic catalytic research, the study is the hydrogenation reaction of CO2 and the decomposition of NOx exhaust gases. The research

The CO2 hydrogenation reaction was carried out using the perovskite LaCrO3, and spinel Ni1-xFe2MxO4 catalysts (M = Cu, Co, and Zn) with the reactor scheme

The catalytic reaction takes place at a temperature of 100 to 400°C with a composition of CO2/H2 = 1/3 in the gas flow. Examples of reaction results using rapid tests and

*Lab scale reactor (a) of CO2 hydrogenation reaction [50], results of rapid test (b) for alcohol product [51], and* 

*chromatogram results (c) of the CO2 hydrogenation reaction [52].*

several quantitative analyzes are shown in **Figure 12b** and **c**, respectively.

are economically valuable and environmentally friendly as described below.

*DOI: http://dx.doi.org/10.5772/intechopen.95272*

**3.1 Catalytic reaction: thermis**

*3.1.1 CO2 hydrogenation reaction*

shown in **Figure 12a** below.

results of this reaction are briefly presented below.

*Preparation of Hollow Nanostructures via Various Methods and Their Applications DOI: http://dx.doi.org/10.5772/intechopen.95272*

The greater use of energy sources for activities, causing the emission of CO2, NOx, and SOx gases to increase [48]. Continuous emissions without treatment will cause acid rain and the greenhouse effect. This emission will stimulate global warming and even higher. One way to participate in the handling of COx and NOx wastes is through its utilization. One of the handling methods is using the nanocatalysts to handle thermally and photonically by converting the organic wastes (solid, liquid, and gaseous) such as cellulose, dyes, and COx and NOx pollutant into products that are economically valuable and environmentally friendly as described below.

#### **3.1 Catalytic reaction: thermis**

*Novel Nanomaterials*

**Figure 10.**

**Figure 11.**

*solution [46, 47].*

**3. Applications**

*TEM results of hollow nanomaterial LaCr1-xMoxO3 (x = 0.01-0.05) were prepared using sol-gel method [45].*

*TEM and SEM results of LaCrO3 and LaCr1-xVxO3 materials prepared using pectin and egg-white* 

the cubic hollow aggregate and also a squared nano hollow tube (SNHT).

CoxO4 spinels prepared using the egg white solution.

The overall reaction can be described below:

**Figure 9b** and **c** clearly show the formation of nano hollow cube (NHC) from Ni1-xVxFe2O4 (x= 0.1 – 0.5) spinel. Furthermore, in **Figure 9a**, if you notice there are

Then, in **Figure 10a** the micrograph shows that squared hollow pipes, hollow cube, and hollow tubes formed. In **Figure 10b**, you can see the nano hollow cubes (NHC) and micron sizes and nano spherical tubes (NST). Whereas in **Figure 10c**, you can see the interconnected pillars of micron and nano hollow cube sizes. In the preparation of both pure LaCrO3 and modified LaCrO3 by the sol-gel method [46] gave SEM micrograph results shown in **Figure 11a** and **b**. It seemed that the shapes of material are varied that are nano hollow cubes (NHC), nano hollow tubes (NHT), and the blended shapes presented in **Figure 11a**. In **Figure 11b**, the interconnected microfiber structure and the hollow micro material formed. Meanwhile, **Figure 11c** shows the homogeneous nanoscale grains of hollow NiFe2-x

After the preparation of all the catalysts is done, it is used respectively for both thermic catalytic reactions and photocatalysis. The compounds that are the research targets are CO2, NOx, dyestuffs, and cellulose. The selection of the four targets

Carbon dioxide (CO2) and NOx gas emitted from the use of fossil energy sources containing the main elements H, C, and O as well as other minor elements N, and S.

Substrate (C, H, O, N, S)+O CO +NO +SO 2 2 x x2 → +H O+ y Energ

intensely focused on the impact factor and the benefits that can gain.

**52**

Catalytic reaction - thermic is a catalytic reaction that takes place with the help of thermal energy. These catalytic reactions control more than 90% of processes in the chemical industry [49]. In thermic catalytic research, the study is the hydrogenation reaction of CO2 and the decomposition of NOx exhaust gases. The research results of this reaction are briefly presented below.

## *3.1.1 CO2 hydrogenation reaction*

The CO2 hydrogenation reaction was carried out using the perovskite LaCrO3, and spinel Ni1-xFe2MxO4 catalysts (M = Cu, Co, and Zn) with the reactor scheme shown in **Figure 12a** below.

The catalytic reaction takes place at a temperature of 100 to 400°C with a composition of CO2/H2 = 1/3 in the gas flow. Examples of reaction results using rapid tests and several quantitative analyzes are shown in **Figure 12b** and **c**, respectively.

#### **Figure 12.**

*Lab scale reactor (a) of CO2 hydrogenation reaction [50], results of rapid test (b) for alcohol product [51], and chromatogram results (c) of the CO2 hydrogenation reaction [52].*
