Photocatalytic Degradation of Divalent Metals under
Sunlight Irradiation using Nanoparticle TiO2 Modified
Concrete Materials (Recycled Glass )
Mohamed Nageeb Rashed
Chemistry Department, Aswan faculty of Science,
Aswan University, Aswan, Egypt.
Aim of the study
• The main target of this work focus on the combination effect of
photocatalytic degradation and adsorption processes using the
immobilized TiO2 supported on glass powder (TiO2-GB) as adsorbent
under the illumination of sun light as a new method for the removal of
heavy metals from water .
• In this work nanosized TiO2 has been used as semiconductor material
with glass powder as co-adsorbent for the removal of heavy metals from
water. The kinetics and equilibrium data were carried out to understand
the photocatalytic and adsorption processes. The work extended to
study the effect of parameters such as pH, composite dose, contact time
and initial metal concentration on the removal efficiency.
INTRODUCTION
Photocatalysis / Adsorption Processes
for Metals Removal
Adsorption on
glass powder
particle
Photocatalysis
with nanoTiO2
Photocatalysis /
Adsorption on
Composite
Why TiO2 as Nanocatalyst?
•
•
•
•
In this field, TiO2-based photocatalysts have attracted continuously increasing
attention because of the excellent properties such as high light-conversion
efficiency, chemical stability, nontoxic nature, low cost.
The titanium dioxide most used and studied is “P25” because P25 is small,
typically 25 nm in diameter ,highly active. Commercial TiO2 catalysts are typically
available in suspension mode (for example, Degussa P25 powder) or immobilized
on a substrate.
The catalysts display high photocatalytic activity because of their large surface
area. However, several disadvantages limit the wide application of TiO2 powder.
The high effectiveness of TiO2 -P25 is related to the inhibition of recombination
process on TiO2 (e −CB/h+VB) due to the smaller band gap of rutile section of the
particle that absorbs photons and generates electron-hole pairs and the electron
transfer from the rutile conductive band to the electron traps occurs in the
anatase phase.
Combining the use of nanocatalyst with adsorbent materials
(composite)
 Adsorption process is one of the effective techniques that have been
successfully employed for the removal of various pollutants (organic,
inorganic, and heavy metal) from water .
 Combining the use of photocatalyst with adsorbent material is an important
development in the field of photocatalytic degradation of organic and metal
pollutants.
 The combination of destructive adsorption properties with photo-activity
allows a synergistic “photochemical boosting” in which it increased capacities
for destruction of pollutants.
 Many researches were focused on the preparation as well as on the
modification of TiO2 as composite , for examples composites of SiO2/TiO2 ,
glass/TiO2, carbon-coated TiO2 , kaolinite –TiO2, Clay-TiO2and TiO2-coated
exfoliated graphite. Large surface area and high degree of dispersion of TiO2
powders in the reaction medium were reported to be favorable for high
photocatalytic performance.
 Many chemical and physical methods have been employed to prepare TiO2
coatings adsorbents, this including sol–gel , chemical vapor deposition,
ultrasonic spray pyrolysis, sputtering, pulsed laser deposition mecahnical
dispersion (ball mill) , and electrophoretic deposition.
Composite
( Catalyst –adsorpent )
Kaolinite –
TiO2
TiO2Zeolite
SiO2/TiO2
Activated
carbon-TiO2
TiO2- coconut
shell activated
carbon
TiO2-coated
exfoliated
graphite
ClayTiO2
Mechanism of the processes
Illustration of three different reaction zones on TiO2/glass
beads under illumination depicting photoactive zone,
adsorption zone, glass/TiO2 interface.
Each GB/TiO2 particle may possess three different
reactions:(i) Photoactive zone, which is the outer surface of
TiO2 coating receiving UV illumination.
(ii) Adsorption zone, which is bulk of GB
underneath the photoactive zone and,
(iii) GB /TiO2 interface.
The mechanism of metal removal efficiency
As the mainly constituent of GB is SiO2, and so in alkaline media on GB surface new
active sites (≡ SiO-) can develop, allowing metals to form complexes
2 (≡ SiO-) + M 2+
→
(≡ Si-O)2 M
GB/TiO2 catalyst exploits the high adsorbent capacity of SiO2 and the photocatalytic
activity of TiO2 toward the metals, resulting in higher removal capacity of heavy
metal ions (Pb, Cd, Cu and Zn) than that of GB alone.
According to the ‘‘site binding’’ theory, the surface charge on the metal oxides is
created by the electrolyte ions adsorption. These processes of TiO2 can be described
by the these equations :TiO2 + hv (UV) → TiO2 (eCB− + hVB+)
TiO2 ( hVB+) + H2O → TiO2 + H+ + OHTiO2 ( hVB+) + OH− → TiO2 + OH•
≡Ti-OH + H+ → ≡Ti-OH2+
2≡Ti-OH + M 2+ → (≡Ti-O-)2 M+ 2H+
•The photocatalytic processes on TiO2 involves the formation of active
oxidant species as HO- . Considering the experimental conditions on the
GB/TiO2, the titanium dioxide component will be slightly negatively
charged, while the GB matrix preserves an overall negative surface
charge. Under these conditions, cationic heavy metals are supposed to
be adsorbed by electrostatic attractive forces. At the same time, the
positive charges on the TiO2 surfaces may support an increased amount
of HO-.
•According to the latest research report, TiO2 grafted inorganic porous
materials shows very high efficiency and sensitivity for removing heavy
metals from water , which is highly essential for environmental aspects
•Synthesis of titanium-functionalzied silica-based materials has been a
matter of extensive research due to the great potential of these
materials in catalytic oxidation processes and adsorbed with high
capacity . Combining the advantages of both synthesis procedures, high
dispersion and accessibility of metal sites, is desirable for adsorption
EXPERIMENTAL
Materials
• The waste glasses (laboratory glass beakers and conical flasks) were
collected from the waste of our chemical laboratories. All the glasses were
made of silicate glass which is a type of glass with the main glass-forming
constituent's silica. Typically, the resulting glass (GB) composition is about
57.88% SiO2, 3.63% Al2O3 , 13.97% Na2O, 7.74% K2O, and 16.96% CaO .
• Glass samples were washed with tab water then with deionized water, and
crushed by a mechanical crusher in the laboratory. The crushed glass
cullets were grinded in agate mortar and further sieved to particle sizes
25μm .
• The chemical composition of GB/TiO2 is 95.76%TiO2, 2.96% SiO2, 0.76%
A2O3 oxide, and 0.65% Na2O.
• Stock standard solutions of Cd, Cu, Pb and Zn ions (1000 mg/L) were
prepared by dissolving the accurately weighed amounts of their nitrate or
sulphate salts (BDH, UK or Merck, Darmstadt, Germany) in 1000 mL
deionized water. Working standard solutions were prepared daily by
appropriate dilution with deionized water.
Preparation of Composite GB/TiO2
Composite sample GB/TiO2 was prepared by ball
milling of nano-TiO2 and GB powder in a ball miller
(QM-1F, made in Nanjing University, China). 5.0 g TiO2
powder and three different sizes zirconiam balls were
mixed in the miller tank. Amount of GB (0.1–5.0 wt %)
and H2O (5 mL) were added. After being milled at the
speed of 280 rpm for 120 min, the wet powder was
collected and dried at 110◦ C in an oven air. The
chemical composition of GB/TiO2 is 95.76%TiO2, 2.96%
SiO2, 0.76% Al2O3, and 0.65% Na2O.
Characterizations of prepared composite
Scanning electron microscopy dispersive (SEM-EDX) study was carried out
on a JEOL, JSM-5500LV electron microscopy instrument at operating at
five kV specimens on which a thin layer of gold or carbon had been
evaporated. Crystalline phase, particle size, elemental composition and
morphology of GB/TiO2 and GB nanocrystals were investigated.
• The surface characteristics, both for GB/TiO2 and GB were evaluated
using a BET surface analyser (Tri Star II 3020 – Micromeritics). The
specific surface area of the glass beads reached 162.6 m2/g, The total
TiO2 surface area developed on the glass spherules is about 50 cm2.
• X-ray diffraction of GB/TiO2 indicates a well organized crystal structure of
titania nanoparticles.
Adsorption and Photocatalysis of Metals
by GB adsorbent and GB/TiO2 composite
The photocatalysis of each metal (Cd, Pb, Cu, and Zn) was carried out using 20 ml of 100
mg/L metal solution in a 100 ml closed Pyrex flask over 0.5 g of catalyst (GB/TiO2) with
continuous shaking. The pH of the solution was adjusted to 8 (alkaline media). The
solutions were exposed to sunlight with constant stirring, average total daily short wave
radiation for this period was 734 W/m2, with a 2 h mean sunshine duration from sunrise .
The mean temperature was 25oC. After irradiation, the suspension was centrifuged,
filtered through a 0.45 µm membrane filter, and the metal content was analyzed using
AAS spectrophotometer.
Adsorption of each metals (Cd, Pb, Cu, and Zn) was carried out as above with using GB
adsorbent ,but with not using sunlight irradiation.
The metal removal efficiency was calculated by equation
Where C0 and Ce (mg/L) are initial and equilibrium metal concentration , respectively.
The amount of adsorbed metal (qe) by GB was calculated using equation
Parameters affect Metal removal
• Effect of metal concentration on metal removal
(initial concentrations of 10, 50, 100, 150 mg/L ).
• Effect of irradiation and contact time on metal
removal (0.5-6 hrs) .
• Effect of pH on metal removal (pH values 3, 5,
7 and 9).
• Effect of catalyst dosage on metal removal
(0.25, 0.5, 1, 1.5 and 2 g GB/TiO2 composite).
Results and Discussion
Effect of GB adsorbent and GB/TiO2 composite on
metal Removal Efficiency
Metal s
Pb
Cd
Removal %
Removal %
using GB
using GB/TiO2
86.91
85.71
96.16
91.02
Cu
88.2
97
Zn
92
99
Effect of metal concentration on removal efficiency
(initial concentrations of 10, 50, 100, 150 mg/L ).
120
Removal%
100
80
60
Cd
40
Pb
Cu
20
Zn
0
10
30
50
Concentration(mg/L)
100
Effect of contact time on metal removal
(0.5-6 hrs) .
100
Removal %
98
96
94
92
Pb
Cd
Cu
Zn
90
88
0.5
1
2
Time (h)
4
6
Effect of pH on Metal Removal
120
Removal %
100
80
Pb
60
Cd
40
Cu
20
Zn
0
2
3
4
5
pH
6
8
10
Effect of Adsorbent and Catalyst Dose on Metal removal
120
Removal %
100
80
60
Pb
Cd
40
Cu
20
Zn
0
0.25
0.5
1
Catalyst dose(gm)
1.5
2
Characterization of the prepared
composite ( GB/TiO2 )
Equilibrium metal adsorption
measurements and modeling
Adsorption Isotherms
Langmuir and Freundlich isotherms were applied to describe the adsorption
equilibrium of metal ions on adsorbent.
The Freundlich equation is given as follows:
qe = Kf Ce1/n
linearized logarithmic form
Log qe = Log kf + (1/n) Log Ce
Where qe is the amount adsorbed (mg/g), Ce is the equilibrium
concentration of the adsorbate (mg/l), and kf and n are the Freundlich
constants related to adsorption capacity and adsorption intensity ,
respectively.
Langmuir equation expressed as follows
Ce / qe = Ce/ Qo + 1 /Qo b
Where Ce (mg/l) is metal equilibrium concentration, qe (mg/g) the amount
adsorbed at equilibrium, b (mg /L) is the Langmuir constant which related to
the affinity of the binding site, and Qo (mg/g) the capacity parameter. When
Ce / qe is plotted versus Ce, the slop is equal to 1/Qo and the intercept is
equal to1/Qo b.
Table 4 . Langmuir and Freundlich constants for the
adsorption of Cd, Pb, Cu, and Zn by GB/TiO2
Metal ion
Freundlich constants
Langmuir constants
R2
Kf
1/n
R2
b
Qo
Cd
0.998
5.59
0.618
0.958
0.219
31.44
Pb
0.997
10.38
0.731
0.859
0.314
46.72
Cu
0.966
6.511
0.442
0.993
0.489
21.97
Zn
0.988
3.477
0.760
0.8562
0.079
44.44
Scanning Electron Microscopy (SEM)
The morphology of the adsorbent (GB) and the catalyst ( GB/TiO2 )
samples were examined by SEM. The figures show the SEM
micrographs of the two samples, glass waste powder (GB) and after
mixing with TiO2 ,composite( GB/TiO2) . Whereas the latter sample
is constituted by well-defined micro-size particles of glass particle
with titania. Images indicate changes in surface morphology after
mixing with TiO2.The TiO2 particle size in GB/TiO2 measured was not
more than 10 μm, while the other glass powder (GB) particle
consists of agglomerates of particles in the nanometer sizes. The
SEM-overview image in Fig. 5 reveals that the sample consists of
two kinds of particles: scale-shaped GB, and TiO2 particles with no
characteristic morphology. The TiO2 nanoparticles are
homogeneously dispersed on the surface of GB..
SEM Micrographs of GB and GB/TiO2
GB
GB/TiO2
CONCLUSION
•Synthesis of titanium-functionalzied silica-based materials has been a
matter of extensive research due to the great potential of these
materials in catalytic oxidation processes and adsorbed with high
capacity .
•GB/TiO2 composite was successively synthesized via nano-mechanical
synthesis. TEM analysis confirmed the presence of crystalline anatase
phase with almost uniform diameter and a narrow range distribution
of spherical nanoparticles in GB/TiO2 catalyst.
•The synthesized catalyst exhibited a good photocatalytic activity for
heavy metals (Cd, Cu, Pb and Zn) removal from water under sunlight
irradiation and mild conditions in aqueous solutions.
•The photocatalytic performance in both cases was markedly
dependent on catalyst dose, pH, metal concentrations and contact
time. The optimum conditions were catalyst dose 1-2 gm, pH 8, metal
concentrations 10 mgl-1 ,and contact time 1 hr.
•The present work can be used successfully for treatment of saline
water, wastewater and polluted water from divalent cations include
heavy and toxic metals.
Thanks for your
kindly attention