Solar degradation of Direct Blue 71 using surface modified
iron doped ZnO hybrid nanomaterials
A. Maleki and B. Shahmoradi
ABSTRACT
This paper reports photodegradation of Direct Blue 71 under irradiation by sunlight. We synthesized
Fe:ZnO nanomaterials under mild hydrothermal conditions ( P ¼ autogenous, T ¼ 100
W
C, t ¼ 18 h).
The precursors were Fe
2
O
3
as dopant, n-butylamine as surface modifier, NaOH as mineralizer and
reagent grade ZnO. The systematic experiments on the photodegradation of Direct Blue 71 were
carried out by changing different effective parameters. The variables in this study were type of
nanomaterials synthesized (4 types), nanomaterial dosage (0.4–1.0 g/L), contact time (30–120 min),
pH (3–11), and dye concentration (20–100 ppm). The photodegradation efficiency was determined
using a UV-Vis spectrophotometer. Determination of total organic carbon (TOC) amount was used to
find out mineralization efficiency. Our experimental results revealed that the nanomaterials
synthesized had higher efficiency compared with the reagent grade ZnO. The best efficiency was
achieved at the following conditions: 1.0 g/L nanomaterials loading, 120 min contact time, pH 5, and
photodegradation efficiency from more than 75 up to 99% depending upon the dye concentration.
A. Maleki
B. Shahmoradi (corresponding author)
Environmental Health Research Center,
Faculty of Health,
Kurdistan University of Medical Science,
Sanadaj, Kurdistan,
Iran
E-mail: bshahmorady@gmail.com;
bshahmoradi@ymail.com
Key words | Direct Blue 71, Fe:ZnO nanomaterials, mild hydrothermal, solar degradation, surface
modifier
INTRODUCTION
More than 30,000 commercial dyes based on ca 8,000
different chemical structures are used in textile, food,
pharmaceutical, paper, and ink industries, and they are dis-
charged in wastewater (Molinari et al. ). The effluents
are usually treated by physico-chemical, oxidative or, most
commonly, active sludge biochemical processes. The main
drawback of the above-mentioned processes is that they gen-
erally produce secondary pollution due to the introduction
of chemicals and/or the possible accumulation of other
bioresistant species in the environment. As azo dyes are
intentionally designed to resist degradation, traditional
methods such as flocculation, carbon adsorption, reverse
osmosis, and the activated sludge process have low mineral-
ization efficiency for this class of xenobiotics.
In recent years, advanced oxidation processes (AOPs)
have emerged as contemporary oxidative techniques for
degradation of detrimental organic compounds both in
industrial pretreatment and in full-scale treatment (Pare
et al. ; Rezaee et al. ). In this regard, nanomaterials
such as TiO
2
and ZnO have been known as suitable photo-
catalysts. Compared with other II-IV semiconductors, ZnO
is a versatile and unique material with a direct band gap
(E
g
¼ 3.37 eV) and large exciton binding energy of 60 meV
(Gyu-Ghul et al. ; Qiuxiang et al. ). Most ZnO
nanomaterials have been fabricated through the traditional
high temperature solid-state method, which is energy con-
suming and in which the particle properties are difficult to
control. These nanomaterials could be synthesized at low
cost using simple solution-based methods, such as chemical
precipitation (Daneshvar et al. ), sol-gel (Xu et al. ),
or solvothermal/hydrothermal reactions (Byrappa et al.
). The hydrothermal technique is a promising and
known alternative synthetic method because of low process
temperature and pressure, and the particle size is easily con-
trolled. Moreover, the hydrothermal technique has several
advantages over other processes such as use of simple equip-
ment, catalyst-free growth, cost–effectiveness large area
uniform production, eco-friendliness, high product purity,
high crystallinity, and no need for post-treatment (Adschiri
& Byrappa ).
However, ZnO nanomaterials are active in the UV range
only due to their wide band gap energy. Moreover, they are
1923 © IWA Publishing 2012 Water Science & Technology | 65.11 | 2012
doi: 10.2166/wst.2012.091