About nanomaterials as photocatalysts

1. SOME INFORMATION ABOUT “ ROLL OF NANOMATERIALS IN
WATER TREATMENT AS PHOTOCATALYSTS
PRESENTED BY: SUPERVISED BY:
Usama Ismail PROF: ABDUL KARIM SHAH
From:
Dawood University Karachi
Department:
Chemical

2. ROLL OF NANOMATERIALS IN WATER TREATMENT AS
PHOTOCATALYSTS:-
Abstract :-
The aim of this review paper is to give an overview of the
development and implications of nanotechnology in photocatalysis. The topics
covered include a detailed look at the unique properties of nanoparticles and their
relation to photocatalytic properties. Current applications of and research into the
use of nanoparticles as photocatalysts has also been reviewed. Also covered is the
utilization of nanoparticles in water treatment as photocatalysts. Finally, the use of
nanoparticles has made a significant contribution in providing definitive
mechanistic information regarding the photocatalytic process.

3. PHOTOCATALYST:-
A photocatalyst is a material that function as catalyst
(alerts the rate or chemical reaction) when expose to light.
OR
A photocatalyst is a substance that generates catalyst activity using energy from
light.
The Photocatalytic process:-
Organic chemicals which may be found
pollutants in wastewater effluents from industrial or domestic sources, must be
removed or destroyed before discharge to the environment. Such pollutants may
also be found in ground and surface water which also require treatment to achieve
acceptable drinking water quality. The increased public concern with these
environmental pollutants has prompted the need to develop novel treatment
methods with photocatalysis gaining a lot of attention in the field of pollutant
degradation.

4. During recent decades, the photocatalytic degradation of various toxic organic
compound has been proposed as a viable process to detoxify water. Much attention
has been paid to the photocatalytic degradation of dyes with TiO2 (Titanium Dioxide)
particles under UV or visible light.
There are various mechanisms for the degradation of dyes using the photocatalyst
materials. One mechanism suggested that the oxidation of organic compounds is first
initiated by the free radicals, which are mainly induced by the electron-hole (e-/h+)
pairs at the photocatalyst surface. Another mechanism is that the organic compound is
firstly adsorbed on the photocatalyst surface and then reacts with excited superficial e-
/h+ pairs or OH radicals to form the final products. A verity of reaction mechanisms
depend on both surface adsorbed and solution phase species, resulting in different
kinetics of photodegradation.
Semiconductor materials have shown good photocatalytic activity on removing various
organic pollutants. Recently, group II-VI semiconductors with energy gaps covering the
visible spectral range have been recognized as compatible candidates for
photocatalysts.

5. Shen et al.
prepared ZnCdS (Zinc-Cadmium Sulfide) nanoparticles decorated on a 2D platform of
reduced graphene oxide (rGO) sheets by a one pot ionic-liquid-assisted hydrothermal process towards
photocatalyst activities toward the photo-degradation of organic dyes.
Generally, three factors are crucial for the photocatalytic activities of the composite, namely, the adsorption of
contaminant molecules, light irradiation absorption, and charge transportation and separation. The
degradation of organic pollutants using TiO2 (Titanium Dioxide) as photocatalyst has been widely studied.
However, TiO2 (Titanium Dioxide) is only activated under UV irradiation which greatly limits the efficient
utilization of solar energy.

6. Xiong et al.
Synthesized
graphene-gold nanocomposites for
photocatalytic degradation of dyes under
visible light irradiation. On the basis of
experimental data, it is proposed a
mechanism accounting for the degradation
of dye pollutants over GOR-Au under visible
light irradiation as schematically illustrated
fig 5. The dye was firstly excited to dye* ,
followed by an electron transfer from the
dye* to graphene. Then, the electron
to a gold nanoparticle and was trapped by
O2 to produce various ROSs. The dye+
finally itself degraded and/or was degraded
by the ROSs.

7. The photoactivity of GOR-Au was evaluated
using Rhodamine B (RhB) under visible light
irradiation, and the results are shown in Fig
6. It can be seen that RhB was very stable
under visible light irradiation without the
catalyst or over GOR-Au in the dark. It was
slightly degraded in the presence of GOR.
However, in the presence of GOR-Au, the
RhB degradation was remarkably enhanced;
the rate constant was calculated to be about
8.7*10-3/min , much larger then that of p25
(4.9* 10-3/min), Au deposited P25 (P25-Au,
5.1*10-3/min) and GOR (5.2* 10-4/min).

8. Zhang et al.
synthesized the graphene-
metal-oxide composites for the
degradation of dyes under visible light
irradiation. The preparation of metal
oxides as SnO2 (Stannic oxide) and
TiO2 (Titanium Dioxide) materials onto
graphene sheets to prepare the
graphene based metal oxide
nanocomposites.

9. The photocatalytic activity of both
samples was evaluated using the
degradation of RhB under visible light
irradiation. It can be seen from fig 8
that RhB was very stable under visible
light irradiation without the presence of
a photocatalyst. It was slightly
degraded in the presence of RGO.
However, in the presence of catalyst
RGO-SnO2 and RGO-TiO2, the
degradation was remarkably enhanced
with rate constants of about 6.2* 10-
3/min for RGO-SnO2 and 3.6* 10-3/min
for RGO-TiO2, significantly higher than
that of RGO (3.9* 10-4/min). In
addition, photocatalyst RGO-SnO2
performed better than RGO-TiO2 and
commercial product P25.

10. THE END
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