treatment. Additionally, catalytic behaviour of these photocatalytic materials also
assisted in resolving energy crises by assisting in H 2 production. Semiconductors
which has the ability to transfer electrons from valency layer to conduction layer by
absorbing small amount of photons, are established to be the favourite. Thus,
photocatalytic materials were explored to obtain maximum degradation efficiency
for multiple chemicals. Transitional metal dichalcogenides consisting of molybdenum disulfide (MoS 2 ), tungsten disulfide etc., which has excellent semiconductor
characteristics, are investigated extensively in this decade, because of their promising results and ease of preparation.
Unlike graphene, MoS 2 is a prominent member of transitional metal
dichalcogenides which is expected to replace graphene as it has an ability to
transform from indirect bandgap to direct band gap on change of bulk to nanostructure. MoS 2 has already been a successful as photocatalyst in degradation of polluted
water of textile industry, desulphurisation and decomposition of pollutants from
refineries and degradation of toluene, nitric oxide (NO) removal for air purification.
Thus, MoS 2 is deemed to be a solution for wastewater treatment and energy
production (Abinaya et al. 2018). Its other specific features like porous structure,
enlarged surface area with increased active sites, charge separation features in two
dimensional format has been the reason for its success as good photocatalyst.
However, MoS 2 has a few drawbacks which hinder its full utilisation and
extracting the complete effectiveness. Few of its limitations are as listed below:
• The poor electronic conductivity of MoS 2 effects the employing MoS 2 as a
photocatalytic material (Li et al. 2014).
• The large interlayer spacing with an weak interlayer bonding will promote MoS 2
nanosheets into a thick form which is unfavourable for photocatalysis (Zeng et al.
2015).
• High electron hole recombination rate.
• Additionally, the formed MoS 2 multi-layer nanostructures tend to agglomeration
or stacked multilayers on a substrate. This causes the reduction in efficiency due
to migration of charge carrier and photon absorption.
Numerous strategies have been formulated to enhance the photocatalytic efficiency of MoS 2 . The successful methodologies included defect engineering, doping
with other active metals, deposition of noble metals and formation of semiconductor
heterostructures. However, formation of semiconductor heterostructure by coupling
with other semiconductors is evaluated to be highly effective in enhancing the
photocatalytic efficiency by effective transfer of charge pair and prohibiting the
recombination of photogenerated electro-hole pairs.
4.2 Classification of Pollutants
Pollutants which pollute water can be classified into natural and synthetic dyes as
shown in Fig. 4.2. The natural dyes are produced from animals and plants. Synthetic
dyes are man-made and can be further classified into non-Azo dyes and Azo dyes,
4 MoS 2 Based Nanocomposites for Treatment of Industrial Effluents
99
assisted in resolving energy crises by assisting in H 2 production. Semiconductors
which has the ability to transfer electrons from valency layer to conduction layer by
absorbing small amount of photons, are established to be the favourite. Thus,
photocatalytic materials were explored to obtain maximum degradation efficiency
for multiple chemicals. Transitional metal dichalcogenides consisting of molybdenum disulfide (MoS 2 ), tungsten disulfide etc., which has excellent semiconductor
characteristics, are investigated extensively in this decade, because of their promising results and ease of preparation.
Unlike graphene, MoS 2 is a prominent member of transitional metal
dichalcogenides which is expected to replace graphene as it has an ability to
transform from indirect bandgap to direct band gap on change of bulk to nanostructure. MoS 2 has already been a successful as photocatalyst in degradation of polluted
water of textile industry, desulphurisation and decomposition of pollutants from
refineries and degradation of toluene, nitric oxide (NO) removal for air purification.
Thus, MoS 2 is deemed to be a solution for wastewater treatment and energy
production (Abinaya et al. 2018). Its other specific features like porous structure,
enlarged surface area with increased active sites, charge separation features in two
dimensional format has been the reason for its success as good photocatalyst.
However, MoS 2 has a few drawbacks which hinder its full utilisation and
extracting the complete effectiveness. Few of its limitations are as listed below:
• The poor electronic conductivity of MoS 2 effects the employing MoS 2 as a
photocatalytic material (Li et al. 2014).
• The large interlayer spacing with an weak interlayer bonding will promote MoS 2
nanosheets into a thick form which is unfavourable for photocatalysis (Zeng et al.
2015).
• High electron hole recombination rate.
• Additionally, the formed MoS 2 multi-layer nanostructures tend to agglomeration
or stacked multilayers on a substrate. This causes the reduction in efficiency due
to migration of charge carrier and photon absorption.
Numerous strategies have been formulated to enhance the photocatalytic efficiency of MoS 2 . The successful methodologies included defect engineering, doping
with other active metals, deposition of noble metals and formation of semiconductor
heterostructures. However, formation of semiconductor heterostructure by coupling
with other semiconductors is evaluated to be highly effective in enhancing the
photocatalytic efficiency by effective transfer of charge pair and prohibiting the
recombination of photogenerated electro-hole pairs.
4.2 Classification of Pollutants
Pollutants which pollute water can be classified into natural and synthetic dyes as
shown in Fig. 4.2. The natural dyes are produced from animals and plants. Synthetic
dyes are man-made and can be further classified into non-Azo dyes and Azo dyes,
4 MoS 2 Based Nanocomposites for Treatment of Industrial Effluents
99