SusChemE 2015
International Conference on Sustainable Chemistry & Engineering
October 8-9, 2015, Hotel Lalit, Mumbai
Photocatalytic H2 generation over Cu-Ti-O photocatalysts in up-scaled reactors
under sunlight
Mrinal R. Pai*,Sushma A. Rawool, A. M. Banerjee and S. R. Bharadwaj
Chemistry Division, Bhabha Atomic Research Centre, Mumbai-400085, INDIA
*mrinalpai9@gmail.com; mrinalr@barc.gov.in, Ph. 022- 25592288
1. Introduction:
Photocatalytic water splitting is one of the important solar energy conversion methods and success of the process
primarily depends on the availability of suitable photocatalyst [1].Several titania based (In2TiO5, Cu doped TiO2,
nanocomposites of NiO-TiO2,CuO-TiO2, CuO,) and carbon based photocatalysts (g-C3N4, Pt/g-C3N4, carbon nanodots/gC3N4andcarbon-TiO2 heterostructures) were developed and their properties were investigated by us [1-3]. In the present
communication, in addition to lab scale results, photocatalytic H2 generation has been demonstrated in upscaled
photoreactors (0.5L, 1L and ~2 L capacity) under sunlight over Cu0.02Ti0.98O2 photocatalyst to validate the extrapolation
of activity results obtained at lab scale. The dependence of H2 yield on factors such as illumination area, form of catalyst
(powder/films), catalyst concentration and different sacrificial agents (Glycerol/methanol) were investigated. Apparent
quantum efficiency (AQE) and solar to fuel efficiency (SFE) of the photocatalysts under different conditions were
calculated.
2. Material and Methods:
Cu-Ti Photocatalysts were synthesized by sol gel method, characterized by X-ray diffraction, X-ray photoelectron
spectroscopy, N2-BET, Raman spectroscopy, inductively coupled plasma-optical emission spectroscopy, high resolution
transmission electron microscopy/selected area electron spectroscopy and diffuse reflectance UV-visible spectroscopy.
Photocatalytic properties of samples were investigated under sunlight, visible and UV-visible irradiation. The emission
spectra of both light sources along with reaction assemblies are shown in our earlier publications [2]. Experiments under
sunlight were carried out on terrace of our institute. At lab scale, 50 mg to 100 mg of photocatalyst was suspended in a
mixture of water + methanol (15 ml), evacuated and irradiated in ~100 ml capacity square quartz photoreactor equipped
with gas collection and evacuation ports. Photocatalyst was also tested in upscaled photoreactors of capacity 0.5L, 1L and
2 L under different conditions in which upto 1g of sample was suspended in 250 ml water + methanol or Glycerol
mixtures and irradiated under sunlight. Photocatlytic H 2 yield was monitored using Gas chromatograph with molecular
sieve as column and thermal conductivity detector. Flux of both sunlight and medium pressure mercury lamp was
measured using a silicon photodiode based light meter LX 1108, Lutron Electronic.
3. Significant Results and Discussion
Photocatalytic properties of TiO2 modified by incorporation of Cu ions as dopant as well as forming composite with CuO
in varying ratios were investigated. Among these the most active photocatalyst, Cu0.02Ti0.98O2, was tested in upscaled
photoreactors. XRD and EXAFS of Cu0.02Ti0.98O2 revealed tetragonal anatase phase, with distorted lattice. Cu existed in
+2 and +1, Ti in +4 and O as O2- and OH- ions was confirmed by XPS of Cu0.02Ti0.98O2 oxide. Various experimental
parameters such as amount of sacrificial agent, geometry of photoreactor with respect to the irradiator, effect of stirring in
both horizontal and vertical geometry, illumination area and catalyst loadings were optimized. Effect of illumination area
on photocatalytic activity was investigated by performing the activity tests in large sized reactors. H2 yield enhanced from
110 to 183 and further to 251 moles/h when exposed to illumination area of 20, 32 and 45 cm2 respectively (Table-1).
However, there was no increase in efficiencies (table-1) as the ratio of H2 yield obtained at a given illumination area
remains constant (column-6, Table-1) in AQE and SFE calculations. AQE is directly proportional to H2 yield and
inversely with illumination area. This implies AQE will increase only if H 2 yield increases at a constant illumination area.
Therefore, in another set of experiments, illumination area was kept constant by fixing the reactor volume and solution
volume (water + methanol) to 990 and 250 ml respectively, and concentrations of Cu0.02Ti0.98O2 photocatalyst were varied
(g/l, Table-1). AQE obtained for different catalyst loadings are mentioned in Table-1. Although 1g loading of catalyst has
shown maximum H2 yield of 735 moles/h with AQE of 7.5 %, it is emphasized that the rise in H2 yield is non -linear
with catalyst loading. Higher concentrations are unfavourable for H2 yield. Probably at higher concentrations, the upper
layer of photocatalyst shadows the lower layer and also blocks the penetration of light hence under limited light
illumination the contribution of lower layer towards H 2 yield was restricted. A catalyst loading of ~1 g/L is an optimized
concentration under the above conditions.
1
SusChemE 2015
International Conference on Sustainable Chemistry & Engineering
October 8-9, 2015, Hotel Lalit, Mumbai
Table-8 Effect of illumination area, catalyst loadings on photocatalytic H2 yield over Cu0.02Ti0.98O2 (CuTi) in an upscaled photoreactor of 990ml capacity. Comparison of H2 yield over CuTi powder and CuTi/ ITO/PET films and effect of
glycerol as sacrificial agent is also given here.
Illumination
(mol/h)
Reactor
Volume
(ml)
Area (cm )
(L/h/m )
Lab scale
6.33
1.33
110
183
251
81
569
569
20
32
45
0.1
198
990
84 (4 films *
21cm2)
0.1
0.2
0.5
1.0
2.0
4.0
136
477
541
612
675
735
4.0
460
990
990
990
990
990
990
990
Catalyst amount+
solution volume
Concentration
(g/L)
100mg + 15 ml
100mg + 15 ml
100mg + 75 ml
CuTi/ITO/PET films +
250 ml
25mg + 250 ml
50 mg+ 250 ml
125 mg+ 250 ml
250mg + 250 ml
500mg + 250 ml
1000mg+ 250 ml
1000mg+ 250ml (15%
v/v glycerol)
H2 yield
H2 yield
AQE
(%)
SFE
(%)
1.23
1.28
1.24
3.13
3.23
3.19
1.06
141
141
141
141
141
141
0.529
0.217
0.758
0.716
0.972
1.072
1.167
3.06
1.41
4.14
5.27
5.64
6.6
7.5
1.56
0.72
2.11
2.7
2.9
3.4
3.9
141
0.730
5.0
2.6
2
2
4. Conclusions:
We have demonstrated photocatalytic H2 generation in upscaled photoreactors under sunlight. Maximum rate of H2
generation achieved was 1.167 L/h/m2 over Cu0.02Ti0.98O2-photocatalyst with AQE of 7.5% and SFE of 3.9%. Our results
suggests that with this efficiency H2 @ 1L/h can be achieved if Cu-Ti is exposed to illumination area of 0.9 m2 under
sunlight. TiO2 modified by Cu2+ ions is an efficient low cost visible light photocatalyst that can be targeted for large scale
H2 production under sunlight.
References:
1. M. R. Pai, A. M. Banerjee, A. K. Tripathi, S. R. Bharadwaj, in: S. Banerjee and A. K. Tyagi (Eds.) “Functional
Materials: preparations, Processing and Applications”, Elsevier, USA, 2012, pp. 579-606;A. A. Ismail, D. W.
Bahnemann, Solar Energy Materials & Solar Cells 128 (2014) 85–101.
2. M. R. Pai, J. Majeed, A. M. Banerjee, A. Arya, S. Bhattacharya, R. Rao, S. R. Bharadwaj, J Phys.Chem.C, 116,
2012, 1458.
3. A. M. Banerjee, Mrinal R. Pai, A. Arya, S. R.Bharadwaj, RSC Advances, 5, 2015, 61218.
2