Page 244 - Multifunctional Photocatalytic Materials for Energy

Photocatalysts for hydrogen generation and organic contaminants degradation 227

that Zr-containing metal organic frameworks formed by terephthalate (UiO-66)
and 2- aminoterephthalate ligands [UiO-66(NH 2 )] were two notably water-resistant
MOFs exhibiting photocatalytic activity for hydrogen generation in methanol or wa-
ter/methanol upon irradiation at a wavelength longer than 300 nm [33]. Maximum
amounts of 2.4 and 2.8 mL H 2 have been obtained after 3 h of irradiation over UiO-66
and UiO-66(NH 2 ). According to another report, the organic linker absorbed visible
light and electrons transferred from an excited state to the conduction band of a pho-
toactive oxo cluster. Pt/Ti-MOF-NH 2 exhibited efficient photocatalytic activity for
−1 −1
the HER under visible light irradiation, and a H 2 evolution rate of ≈367 μmol h g
could be achieved [34]. It was also confirmed that the catalyst could be reused at least
three times without significant loss of its catalytic activity. The incorporation of CdS
and UiO-66 enhanced the photocatalytic activity of both parts of the reaction, and
the optimum HER activity was obtained at a UiO-66-to-CdS weight ratio of 1:1. A
−1 −1
high H 2 evolution rate of 25,770 μmol h g was obtained in the presence of 1 wt.%
MoS 2 , approximately two-fold higher than that of 1 wt.% Pt/UiO-66-CdS. The
H 2 evolution rate of MoS 2 /UiO66-CdS reached a maximum when the amount of
−1 −1
MoS 2 in the composite was 1.5 wt.% (32,500 μmol h g ). The advantage of using
MoS 2 as a highly active co-catalyst to replace Pt in MOF-based photocatalysts to
enhance the HER activity was demonstrated by Shen et al. [35]

10.3 Photocatalytic degradation of organic contaminants

Oxidation of organic impurities in water by photocatalysis can be achieved by using
the right type of band gap semiconductors [36,37]. Organic contaminants in water and
in solid chemical waste have become a serious problem and have grown exponentially
since the beginning of the industrial revolution. Manufacturing sectors across the globe
continue to push the level of these pollutants, which is causing several carciogenic
diseases and threatening sustainable living. This section deals with the photocatalytic
degradation of organic pollutants, a topic that is gaining popularity because solar radi-
ation is used as the source of energy and atmospheric dioxygen as the oxidant; both of
which are readily and abundantly available [38]. Conjugated polymer/semiconductor
nanocrystal nanocomposites are of special interest in this chapter because of their syn-
ergistic effect in enhancing optoelectronic properties and their fast reaction kinetics in
degrading pollutants. Several conjugated polymers such as PANI, polypyrrole (PPy),
P3HT, PEDOT, and Polythiophene, along with some of the semiconductor nanocrys-
tals such as TiO 2 , SnO 2 , ZnO, WO 3 , and Bi 2 MoO 6 , have been used in the preparation
of conjugated nanocrystal nanocomposites [17]. The latest developments in photocat-
alysts based on conjugated polymer nanocrystal nanocomposites and their working
mechanism with band alignments behind organic pollutants degradation are discussed
here, as well as aspects of material engineering to achieve photocatalysts for effective
degradation of organic pollutants.
PANI has been the most studied conjugated polymer among conducting polymers
because of its excellent chemical stability, high conductivity, corrosion protection,
low cost of synthesis, and interesting redox properties. PANI plays a significant role