Mechanism of strong visible light photocatalysis by Ag2O-nanoparticle decorated monoclinic TiO2(B) porous nanorods

Abstract

We report on the ultra-high rate of photodegradation of organic dyes under visible light
illumination on Ag2O-nanoparticle-decorated (NP) porous pure B-phase TiO2 (TiO2(B)) nanorods
(NRs) grown by a solvothermal route. The as-grown TiO2(B) NRs are found to be nanoporous in
nature and the Ag2O NPs are uniformly decorated over its surface, since most of the pores work as
nucleation sites for the growth of Ag2O NPs. The effective band gap of the TiO2(B)/Ag2O
heterostructure (HS), with a weight ratio of 1:1, has been significantly reduced to 1.68 eV from the
pure TiO2(B) band gap of 2.8 eV. Steady state and time-resolved photoluminescence (PL) studies
show the reduced intensity of visible PL and slower recombination dynamics in the HS samples.
The photocatalytic degradation efficiency of the TiO2(B)/Ag2O HS has been investigated using
aqueous methyl orange and methylene blue as reference dyes under visible light (390 nm–800 nm)
irradiation. It is found that photodegradation by the Ag2O/TiO2(B) HS is about one order of
magnitude higher than that of bare TiO2(B) NRs and Ag2O NPs. The optimized Ag2O/TiO2(B)
HS exhibited the highest photocatalytic efficiency, with 88.2% degradation for 30 min irradiation.
The corresponding first order degradation rate constant is 0.071 min−1, which is four times higher
than the reported values. Furthermore, cyclic stability studies show the high stability of the HS
photocatalyst for up to four cycles of use. The major improvement in photocatalytic efficiency has
been explained on the basis of enhanced visible light absorption and band-bending-induced
efficient charge separation in the HS. Our results demonstrate the long-term stability and
superiority of the TiO2(B)/Ag2O HS over the bare TiO2(B) NRs and other TiO2-based
photocatalysts for its cutting edge application in hydrogen production and environmental cleaning
driven by solar light photocatalysis.

Full text

Mechanism of strong visible light
photocatalysis by Ag
2
O-nanoparticle-
decorated monoclinic TiO
2
(B)porous
nanorods
Kamal Kumar Paul
1
, Ramesh Ghosh
1
and P K Giri
1,2
1
Department of Physics, Indian Institute of Technology Guwahati, Guwahati-781039, India
2
Centre for Nanotechnology, Indian Institute of Technology Guwahati, Guwahati-781039, India
E-mail: giri@iitg.ernet.in
Received 22 April 2016, revised 27 May 2016
Accepted for publication 31 May 2016
Published 23 June 2016
Abstract
We report on the ultra-high rate of photodegradation of organic dyes under visible light
illumination on Ag
2
O-nanoparticle-decorated (NP)porous pure B-phase TiO
2
(TiO
2
(B)) nanorods
(NRs)grown by a solvothermal route. The as-grown TiO
2
(B)NRs are found to be nanoporous in
nature and the Ag
2
O NPs are uniformly decorated over its surface, since most of the pores work as
nucleation sites for the growth of Ag
2
O NPs. The effective band gap of the TiO
2
(B)/Ag
2
O
heterostructure (HS), with a weight ratio of 1:1, has been significantly reduced to 1.68eV from the
pure TiO
2
(B)band gap of 2.8 eV. Steady state and time-resolved photoluminescence (PL)studies
show the reduced intensity of visible PL and slower recombination dynamics in the HS samples.
The photocatalytic degradation efficiency of the TiO
2
(B)/Ag
2
O HS has been investigated using
aqueous methyl orange and methylene blue as reference dyes under visible light (390–800 nm)
irradiation. It is found that photodegradation by the TiO
2
(B)/Ag
2
O HS is about one order of
magnitude higher than that of bare TiO
2
(B)NRs and Ag
2
O NPs. The optimized TiO
2
(B)/Ag
2
O
HS exhibited the highest photocatalytic efficiency, with 88.2% degradation for 30min irradiation.
The corresponding first order degradation rate constant is 0.071 min
−1
, which is four times higher
than the reported values. Furthermore, cyclic stability studies show the high stability of the HS
photocatalyst for up to four cycles of use. The major improvement in photocatalytic efficiency has
been explained on the basis of enhanced visible light absorption and band-bending-induced
efficient charge separation in the HS. Our results demonstrate the long-term stability and
superiority of the TiO
2
(B)/Ag
2
O HS over the bare TiO
2
(B)NRs and other TiO
2
-based
photocatalysts for its cutting edge application in hydrogen production and environmental cleaning
driven by solar light photocatalysis.
SOnline supplementary data available from stacks.iop.org/NANO/27/315703/mmedia
Keywords: visible light photocatalysis, TiO
2
(B)/Ag
2
O heterostructure, photoluminescence
lifetime
(Some figures may appear in colour only in the online journal)
1. Introduction
Photocatalysis by metal oxide semiconductors is being stu-
died extensively due to its potential application in clean
hydrogen energy production and environmental protection
such as waste-water treatment, water splitting, CO
2
reduction,
air purification, disinfection and self-cleaning surfaces [1–4].
In comparison to other semiconductors, TiO
2
is one of the
Nanotechnology
Nanotechnology 27 (2016)315703 (15pp)doi:10.1088/0957-4484/27/31/315703
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