21.2 Water Remediation

333

light and ultrasound waves to activate such nanoparticles opens up new avenue to

design green oxidation technologies for environmental remediation. Amalgamation

of nanotechnology with biotechnology has significantly expanded the application

domain of nanomaterials in numerous fields. Several metal and metal oxide-based,

carbon-based materials, nano-sized polymers, and biocomposites nanomaterials [7]

are being developed for wide applications. Metal and metal oxide-based nanoparti-

cles include silver, gold, aluminum, copper, silica, iron, zinc, zinc oxide, titanium

dioxide, and cerium oxide. These materials are generally found useful in environ-

mental remediation, wastewater treatment, water purification, food processing, drug

delivery, packaging, and smart sensor development [8].

The photocatalyst-mediated oxidants are strong enough to degrade and inactivate

most organic pollutants and pathogenic microorganisms by mere contact. All these

features are particularly attractive for installations in remote and rural areas where

electricity requirement is a prohibitive handicap for competing technologies.

Photocatalysis is one of the thrust areas of research and has witnessed a trans-

formation over the past two decades with remarkable advancements being made

in the synthesis of novel materials and nano-structures, and the design of efficient

processes for the degradation of pollutants and the generation of energy. Currently,

lot of research is going on in the biosynthesis of nanoparticles using microorganisms

which has emerged as rapidly developing research area in green nanotechnology

worldwide, with various biological entities being employed in synthesis of nanopar-

ticles constantly forming an impute alternative for conventional chemical and

physical methods [9].

Nanoparticles like semiconductors, zero-valence-based metal, and some bimetal-

lic type, etc., are typically used for the treatment of environmental pollutants such as

chlorpyrifos, azo dyes, organochlorine pesticides, nitroaromatics, etc. [10]. Numer-

ous reports are available in the literature which illustrates the effectual removal

of these pollutants from wastewater using TiO2-based nanotubes [11]. However,

the most common and significant metal oxides employed as nano-photocatalysts

are silicon dioxide (SiO2), zinc oxide (ZnO), titanium dioxide (TiO2), aluminum

oxide (Al2O3), etc. [12]. Among them, TiO2 is one of the excellent photocatalysts

compared to all existing material due to its unique properties such as toxic-free, low

cost, and chemically stable and due to its availability on earth [13]. Photocatalytic

properties of TiO2 have been exploited in several environmental applications to

remove contaminants from both air and water [14]. Extensive studies on TiO2

nanoparticles-mediated oxidative and reductive transformation of organic and inor-

ganic species present as contaminants in air and water has led to the development

of several products such as self-cleaning glasses, disinfectant tiles, and filters for

air purification for day-to-day operations. Commercialization of such products has

established the early successes of nano systems for environmental applications.

ZnO is a multifunctional material which is widely used in several applications

due to its eco-friendly and diverse properties [15]. Nano-sized ZnO is observed to

be an excellent material for optoelectronics, nanosensors as well as antibacterial

applications due to some of its exceptional properties such as morphology, surface

properties, crystal defects, and size tailoring properties.