Based on the above discussion and realization, the need-of-the-hour is to develop
water purification technologies and increase their water purification capacities at a
pace matching the requirement of catering pure and fresh water to the entire world’s
rapidly increasingly population. In this regard, there are two major aspects: (a) to
develop new and efficient technologies other than those already established in the
market and (b) to enhance the capacity of already existing technologies by means of
development of new materials, designs, operating parameters, etc. Now, there are
already several technologies available in the commercial market that have proven
their worth in effecting water purification. These include membrane filtration,
adsorption, photocatalysis, desalination, chemical precipitation, electrochemical
treatment, disinfection and solvent extraction to name a few (Dutta and De
2017a, b; Dutta and Rana 2019). However, we need innovative and highly efficient
materials in each category that can perform their respective function in a commercial
scale. In this respect, metal oxides have stood out in terms of their performance
efficiency and their applicability within the domains of a number of the
abovementioned technologies; for example, adsorption, photocatalysis, electrochemical treatment, disinfection, desalination, etc. (Ali 2012; Herrmann et al.
1993; Kasprzyk-Hordern 2004; Lee and Park 2013; Qu et al. 2013). In addition,
metal oxides have found employment in treating a number of varied polluting
materials, like heavy metals, salts, dyes, phosphates, fluorides, phenols, microbes
and oil (Lee et al. 2016; Mano et al. 2015; Upadhyay et al. 2014; Xu et al. 2012).
Some high-performance metals have also been realized to treat two or more categories of pollutants simultaneously or otherwise.
Herein, the subject of utilization of metal oxides in decontamination of water and
wastewater has been dealt with in a case-by-case manner, for the purpose of
analyzing the efficacy of the materials used under various categories of polluting
contaminants. However, the intention here is not to provide an exhaustive literature
review on the subject. Accordingly, under each separate category, some representative published reports have been presented in order to bring out the overall as well as
comparative picture for readers to get an overview of this field of research.
1.2 Dye
Dyes are a class of compounds that have very high usage around the world in
industries, such as textiles, leather, furniture, paint, etc. They are produced in huge
quantities owing to their very high demand. This invariably leads to it eventually
getting drained out as part of effluents; in the process, contaminating water bodies.
Dyes are often toxic, as they are prone to environmental oxidative degradation
producing toxic products like carbon monoxide, nitrogen oxides, etc. Therefore, it
should be ensured that they are separated from the effluent stream before getting
deposited in water bodies. Keeping this in mind, various researchers have devised
methods and materials to ensure complete removal of dye molecules from wastewater comprising industrial effluents. Among the materials utilized, metal oxides
1 Metal Oxides as Decontaminants of Water and Wastewater
3
water purification technologies and increase their water purification capacities at a
pace matching the requirement of catering pure and fresh water to the entire world’s
rapidly increasingly population. In this regard, there are two major aspects: (a) to
develop new and efficient technologies other than those already established in the
market and (b) to enhance the capacity of already existing technologies by means of
development of new materials, designs, operating parameters, etc. Now, there are
already several technologies available in the commercial market that have proven
their worth in effecting water purification. These include membrane filtration,
adsorption, photocatalysis, desalination, chemical precipitation, electrochemical
treatment, disinfection and solvent extraction to name a few (Dutta and De
2017a, b; Dutta and Rana 2019). However, we need innovative and highly efficient
materials in each category that can perform their respective function in a commercial
scale. In this respect, metal oxides have stood out in terms of their performance
efficiency and their applicability within the domains of a number of the
abovementioned technologies; for example, adsorption, photocatalysis, electrochemical treatment, disinfection, desalination, etc. (Ali 2012; Herrmann et al.
1993; Kasprzyk-Hordern 2004; Lee and Park 2013; Qu et al. 2013). In addition,
metal oxides have found employment in treating a number of varied polluting
materials, like heavy metals, salts, dyes, phosphates, fluorides, phenols, microbes
and oil (Lee et al. 2016; Mano et al. 2015; Upadhyay et al. 2014; Xu et al. 2012).
Some high-performance metals have also been realized to treat two or more categories of pollutants simultaneously or otherwise.
Herein, the subject of utilization of metal oxides in decontamination of water and
wastewater has been dealt with in a case-by-case manner, for the purpose of
analyzing the efficacy of the materials used under various categories of polluting
contaminants. However, the intention here is not to provide an exhaustive literature
review on the subject. Accordingly, under each separate category, some representative published reports have been presented in order to bring out the overall as well as
comparative picture for readers to get an overview of this field of research.
1.2 Dye
Dyes are a class of compounds that have very high usage around the world in
industries, such as textiles, leather, furniture, paint, etc. They are produced in huge
quantities owing to their very high demand. This invariably leads to it eventually
getting drained out as part of effluents; in the process, contaminating water bodies.
Dyes are often toxic, as they are prone to environmental oxidative degradation
producing toxic products like carbon monoxide, nitrogen oxides, etc. Therefore, it
should be ensured that they are separated from the effluent stream before getting
deposited in water bodies. Keeping this in mind, various researchers have devised
methods and materials to ensure complete removal of dye molecules from wastewater comprising industrial effluents. Among the materials utilized, metal oxides
1 Metal Oxides as Decontaminants of Water and Wastewater
3