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P. Basnet and S. Chatterjee
range of light absorption by ZnO NP from the solar light radiation. Influence on the
ability of photon absorption, which subsequently affects the photocatalytic activity,
is further dependent upon the type of metal used as a dopant or deposit. Generally, the common type of metals used is either noble metals or transition metals [6,
9, 10]. Although, both these categories suffice the requirement of broadening the
region of light absorption, high cost associated with noble metal precursors may
pose a restriction while considering cost effectivity. Thus, transition metals are more
preferred unless the requirement of noble metals is irreplaceable.
A significant amount of the textile dyes as effluents is released during their manufacture and processing into the water bodies (or water treatment plants) [11]. These
dye molecules are readily reduced into environmentally harmful aromatic amines
under anaerobic conditions [11]. Therefore, for generating risk-free products from
these effluents, photocatalysis has been considered as a highly advanced and simple
process, which operates in an economic environment. Over the past many years,
various photocatalysts have been proposed to perform the efficient photo-degradation
of organic dyes present as water waste [6]. Amongst them, ZnO photocatalyst was
selected as a potential candidate as it is environmentally safe and a very promising
semiconductor nanomaterial [2]. Research related to the enhancement of its photocatalytic activity is still under progress, and many reports suggest the functionalization of transition metal with ZnO NP to be highly beneficial [9, 10]. Therefore,
herein, authors have considered the study related to this domain. In this overview,
authors have highlighted the effect of transition metal concentration and the ongoing
mechanism over ZnO nano-photocomposite (NPC) during the photocatalytic process.
2 Photocatalytic Activity of Transition Metal–ZnO NPC
2.1 Effect of Transition Metal Content upon Photocatalysis
Several studies dedicated to uncover the fundamentals of transition metal–ZnO NPC
report alteration in the photocatalytic activity of ZnO after transition metal functionalization [12–14]. The primary reason resulting in this phenomenon may be attributed
to the decrease in the band gap energy, and thereby, increase in the absorption range.
Another important factor resulting in such changes is the introduction of various
defect states in ZnO crystal structure [12–14]. Majority of the research articles based
on studies related to defect states and the corresponding photo-physical properties of
transition metal–ZnO NPC are conclusive of the synergistic effect between the metal
and ZnO NP to exhibit enhanced photocatalytic behaviour [9, 10, 12, 13]. However,
certain reports suggest the reduction in photocatalytic activity of bare ZnO after metal
incorporation, thereby channelizing the concept of antagonistic effect between them
[15, 16]. Nevertheless, these effects ultimately depend upon the morphology, defect
states and the type of metal used during synthesis.
P. Basnet and S. Chatterjee
range of light absorption by ZnO NP from the solar light radiation. Influence on the
ability of photon absorption, which subsequently affects the photocatalytic activity,
is further dependent upon the type of metal used as a dopant or deposit. Generally, the common type of metals used is either noble metals or transition metals [6,
9, 10]. Although, both these categories suffice the requirement of broadening the
region of light absorption, high cost associated with noble metal precursors may
pose a restriction while considering cost effectivity. Thus, transition metals are more
preferred unless the requirement of noble metals is irreplaceable.
A significant amount of the textile dyes as effluents is released during their manufacture and processing into the water bodies (or water treatment plants) [11]. These
dye molecules are readily reduced into environmentally harmful aromatic amines
under anaerobic conditions [11]. Therefore, for generating risk-free products from
these effluents, photocatalysis has been considered as a highly advanced and simple
process, which operates in an economic environment. Over the past many years,
various photocatalysts have been proposed to perform the efficient photo-degradation
of organic dyes present as water waste [6]. Amongst them, ZnO photocatalyst was
selected as a potential candidate as it is environmentally safe and a very promising
semiconductor nanomaterial [2]. Research related to the enhancement of its photocatalytic activity is still under progress, and many reports suggest the functionalization of transition metal with ZnO NP to be highly beneficial [9, 10]. Therefore,
herein, authors have considered the study related to this domain. In this overview,
authors have highlighted the effect of transition metal concentration and the ongoing
mechanism over ZnO nano-photocomposite (NPC) during the photocatalytic process.
2 Photocatalytic Activity of Transition Metal–ZnO NPC
2.1 Effect of Transition Metal Content upon Photocatalysis
Several studies dedicated to uncover the fundamentals of transition metal–ZnO NPC
report alteration in the photocatalytic activity of ZnO after transition metal functionalization [12–14]. The primary reason resulting in this phenomenon may be attributed
to the decrease in the band gap energy, and thereby, increase in the absorption range.
Another important factor resulting in such changes is the introduction of various
defect states in ZnO crystal structure [12–14]. Majority of the research articles based
on studies related to defect states and the corresponding photo-physical properties of
transition metal–ZnO NPC are conclusive of the synergistic effect between the metal
and ZnO NP to exhibit enhanced photocatalytic behaviour [9, 10, 12, 13]. However,
certain reports suggest the reduction in photocatalytic activity of bare ZnO after metal
incorporation, thereby channelizing the concept of antagonistic effect between them
[15, 16]. Nevertheless, these effects ultimately depend upon the morphology, defect
states and the type of metal used during synthesis.