Size and Shape Selective Metal Oxide Nanomaterials …
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the degree of polarization and localization of light in different planes. The shape
and crystalline properties are related to each other [7] and the MONMs differ from
metals in terms of their intrinsic charge separation capacity.
In terms of biological systems, particle size, shape and surface area play vital
roles for efficient interaction. If the NMs’ size is <50 nm, then it is expected to transverse to all tissues without hindrance and delivers designated functions [8]. In addition, NMs’ shape controls electron delocalization leading to enhanced electric fields
which act as a hot spot thus bioactivity, catalytic and sensing efficiency are highly
shape-dependent. For biological applications, the NMs with its surrounding medium
should be studied. The colloidal behavior (net potential energy) was predicted by
two accepted models. The Derjaguin-Landau-Verwey-Overbeek (DLVO) and the
extended DLVO theories explain the aggregation or dispersion behaviors of NMs
based on the van der Waal’s force and electrostatic double layer (EDL). The NMs
should exhibit the zeta potential (a measure of EDL) values > ±30 mV which is an
indication of stability against coagulation in solution. This value is strongly dependent on the ionic strength (total ions present in the solution) of NMs and can be
altered by changing the acidity or basicity of the colloid. At low ionic strength, the
NMs exhibit good dispersion which is suggested for experiments [9].
3 Physicochemical Properties of Size and Shape
The spherical NMs (nanospheres) exhibit good thermodynamic stability and their
optical properties are dependent on the diameter. Increment in size leads to formation
of more valence and conduction band due to contribution of more atomic orbitals thus
result in a decrease of electronic bandgap. Elongated structures such as rods, wires
and tubes show electron delocalization in the lateral dimension thus their properties
depend on the aspect ratio (r = length/width). Higher dimensions such as nanocubes
and nanohexagons exhibit accumulation of dipoles due to multiple corners. The facet
shows more number of edge and corner atoms which leads to different activities as
compared to other shapes [7]. In biological application viewpoint, size and shapedependent properties decide (i) the cell surface adsorption and transport across cell
membranes, (ii) the light-induced redox activities and (iii) release of metal ions
by dissolution [10]. Also, release of reactive nitrogen species (RNS) was high for
NMs exhibiting small size [9]. Similarly, NMs shape was strongly corroborated with
biological system since the aggregation was mainly determined by shape.
4 Preparation of Metal Oxide NMs
Nanomaterials powder can be prepared using different synthesis routes. Depending
on the preparation method, size and shape-selective NMs are obtained. Several easy
and cost-effective techniques such as wet chemical, green synthesis, hydrothermal
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the degree of polarization and localization of light in different planes. The shape
and crystalline properties are related to each other [7] and the MONMs differ from
metals in terms of their intrinsic charge separation capacity.
In terms of biological systems, particle size, shape and surface area play vital
roles for efficient interaction. If the NMs’ size is <50 nm, then it is expected to transverse to all tissues without hindrance and delivers designated functions [8]. In addition, NMs’ shape controls electron delocalization leading to enhanced electric fields
which act as a hot spot thus bioactivity, catalytic and sensing efficiency are highly
shape-dependent. For biological applications, the NMs with its surrounding medium
should be studied. The colloidal behavior (net potential energy) was predicted by
two accepted models. The Derjaguin-Landau-Verwey-Overbeek (DLVO) and the
extended DLVO theories explain the aggregation or dispersion behaviors of NMs
based on the van der Waal’s force and electrostatic double layer (EDL). The NMs
should exhibit the zeta potential (a measure of EDL) values > ±30 mV which is an
indication of stability against coagulation in solution. This value is strongly dependent on the ionic strength (total ions present in the solution) of NMs and can be
altered by changing the acidity or basicity of the colloid. At low ionic strength, the
NMs exhibit good dispersion which is suggested for experiments [9].
3 Physicochemical Properties of Size and Shape
The spherical NMs (nanospheres) exhibit good thermodynamic stability and their
optical properties are dependent on the diameter. Increment in size leads to formation
of more valence and conduction band due to contribution of more atomic orbitals thus
result in a decrease of electronic bandgap. Elongated structures such as rods, wires
and tubes show electron delocalization in the lateral dimension thus their properties
depend on the aspect ratio (r = length/width). Higher dimensions such as nanocubes
and nanohexagons exhibit accumulation of dipoles due to multiple corners. The facet
shows more number of edge and corner atoms which leads to different activities as
compared to other shapes [7]. In biological application viewpoint, size and shapedependent properties decide (i) the cell surface adsorption and transport across cell
membranes, (ii) the light-induced redox activities and (iii) release of metal ions
by dissolution [10]. Also, release of reactive nitrogen species (RNS) was high for
NMs exhibiting small size [9]. Similarly, NMs shape was strongly corroborated with
biological system since the aggregation was mainly determined by shape.
4 Preparation of Metal Oxide NMs
Nanomaterials powder can be prepared using different synthesis routes. Depending
on the preparation method, size and shape-selective NMs are obtained. Several easy
and cost-effective techniques such as wet chemical, green synthesis, hydrothermal