Photocatalytic water puri fication in HPLED-PhR and FL-PhR As an example of the usefulness of HP-LED photoreactor in comparison with traditional UV lamp photoreactor, two photo- catalytic[r]
Trang 1Original Article
The improvement of photocatalytic processes: Design of a
photoreactor using high-power LEDs
a Department of Basic Sciences, Jundi-Shapur University of Technology, Dezful, P O Box 64615-334, Iran
b Department of Physics, Shahid Chamran University of Ahvaz, Golestan Street, Ahvaz, 61357-43337, Iran
a r t i c l e i n f o
Article history:
Received 25 April 2016
Received in revised form
11 June 2016
Accepted 13 June 2016
Available online 18 June 2016
Keywords:
Fluorescent lamp photoreactor
High-power LED photoreactor
Photocatalytic water purification
Reactive blue dye
Zinc oxide nanoparticle
a b s t r a c t This paper is an attempt to survey the benefits of a well-designed photoreactor containing just 6 ultraviolet (UV) high power light emitting diodes (HPLEDs); the power and wavelength of each UV HPLED are 1 W and
365 nm, respectively, the latter being an efficient source for photocatalytic studies Although the ment with the 365-nm LEDs is reported here, other LEDs were predicted for conducting similar experi-ments including green photocatalytic ones We installed diodes with respect to the luminescence intensity distribution curves (LIDCs) or intensity patterns Then, in order to compare the efficiency of the UV-HPLEDs
of the HP-LED photoreactor (HPLED-PhR) with that of traditional UV lamps which are extensively used in photocatalytic processes, a set of UV HPLEDs was designed and made up Next, the performance of HPLED-PhR was compared with that of a traditionalfluorescent lamp photoreactor (FL-PhR) As a typical photo-catalytic experiment, Zinc Oxide (ZnO) nanoparticles were synthesized via co-precipitation method and used as photocatalyst for purification of water polluted with the reactive blue dye (RB), under UV irradi-ation in two photoreactors The results showed that the rate of photocatalytic reaction under the UV-LEDs was two times greater than the rate under the traditionalfluorescent UV lamps, while both electrical power consumption and manufacturing cost of the HPLED-PhR were less than a quarter of them for the FL-PhR
© 2016 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)
1 Introduction
Nowadays the semiconductor photocatalysis has attracted
attention of numerous researchers for removal of hazardous and
toxic materials, and pollutions such as dyes and organic
com-pounds from environment[1] In photocatalytic activities, when a
semiconductor exposes to the proper light sources which their
energy is equal to or greater than the energy band gap of the
semiconductor material, the electronehole pairs are produced
These pairs participate in various oxidationereduction reactions
and generated strong oxidizers like hydroxyl radical (OH*) and
anions such as superoxide (O2) which are responsible for the
mineralization of the toxic inorganic compounds[2]
The preparation of suitable light sources with proper efficiency
and time-responding, generally have been one of the necessities for
photocatalytic studies Fluorescent UV lamps (such as black lights
and germicidal UV lamps), mercury arc lamps, and etc are the most
commonly used as light sources A Fluorescent UV lamp consists of
two alkaline-tungsten electrodes at either end of the cylindrical thin
bubble of glass or quartz that isfilled by a noble gas like argon and a very small amount of mercury Some drawbacks of these lamps are their fragility, danger of explosion for their high pressures and working temperatures, their inner gas leakage, and their problems after lamp failure in eliminating the risks associated with mercury hazardous and toxic substances Furthermore, the life span of these lamps is about 500e2000 h, and they work at high temperatures, so the heat dissipation during the reaction consumes a lot of energy
In order tofind better and more proper light sources, LEDs have attracted the attention of many researchers[3e5] Diode is a pen junction that a specific voltage can be applied to its two ends, thereupon the electrons and holes are recombined, and some amount of energy can be released as photons and heat In an in-direct band gap diode (e.g silicon or germanium), electrons and holes recombine via non-radiative transitions so there is no optical emission On the other hand, materials using to make LEDs have various direct band gaps and energies that could identify the wavelength of light either in near-infrared, visible, or UV regions In quantum wells diodes, a quantum well is like indium gallium nitride (InGaN) sandwiched between two gallium nitride (GaN) layers Changing the ratio of In/Ga the radiated light color, also the ratio of Al/Ga in aluminum gallium nitride (AlGaN) diodes uses to
* Corresponding author.
E-mail address: mkhademalrasool@yahoo.com (M Khademalrasool).
Peer review under responsibility of Vietnam National University, Hanoi.
Contents lists available atScienceDirect Journal of Science: Advanced Materials and Devices
j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / j s a m d
http://dx.doi.org/10.1016/j.jsamd.2016.06.012
2468-2179/© 2016 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license
Journal of Science: Advanced Materials and Devices 1 (2016) 382e387
Trang 2make UV diodes with lower efficiencies[6] The high efficiencies
can be achieved by using unalloyed GaN for the wavelength of
365 nm The most commercial diodes are fabricated at the range of
222e282 nm namely about the sensitivity of microorganism[7],
also DNA absorption is located on the wavelength of 260 nm These
diodes are usually used in sterilization, medicine and biochemistry,
water or air purification, optical recording with high densities,
optical analytical systems, and so on[8] However, these diodes are
technologically and materially more expensive than visible and
near-UV diodes LEDs with the bandwidth at the range of
210e235 nm are less common and often are made in the laboratory
using diamond, aluminum nitride or boron nitride[9e11]
Researches show that LEDs with either narrow or wide
band-widths namely in different frequency ranges of radiation and
various colors can be achieved by modifying the kinds of used
semiconductors, ratios of components, and mixing various LEDs
such as (red, green, and blue) RGB arrays[12e14] Some of the
significant benefits of LEDs in comparison with traditional light
sources are their lower power consumption, more life span
(25,000e1,00,000 h), improved physical strength, smaller sizes,
and faster switching[3,7]
Thefirst generation of high power light emission diodes
(HP-LEDs) was developed in 1994 by Shuji Nakamura while working for
Nichia Corporation The 2014 noble prize was awarded to him“for
the invention of efficient blue light-emitting diodes which has
enabled bright and energy-saving white light sources”[15] Around
2002, the growth process of GaN LEDs on silicon substrate was
developed, and only after one decade [6], the first commercial
production of HP-LEDs was presented by OSRAM manufacturer as
silicon-based Gain [16] Using the epitaxial methods for silica
instead of ruby, thefinal price of HP-LEDs decreased ninety percent
UV-LEDs using unalloyed GaN are commercially produced in the
wavelength of 365 nm with high efficiencies Their output powers
are about 10 mW to 3 W, and usually used to degrade or remove the
air and water pollutions Recentfindings indicate that the visible
LEDs such as blue, red, green, or white one can be employed as light
sources in photocatalytic processes The near UV-LEDs with the
wavelength of 385 nm were used by Johnson on water and air
purification studies in 2003 for the first time[17] In 2005, a set of
16 UV-LEDs, each one with wavelength of 375 nm and 1 mW output
power, was used in perchloroethylene (PCE) photocatalysis
oxida-tion [3] There are several reports about the making of
photo-reactors based on various LEDs for photocatalytic researches in
gaseous or liquid environments[3,18,19]but there are fewer
re-ports on high-power LED photoreactors[17] Using them as
radia-tion sources in the photocatalytic process is much more economical
and efficient than conventional LEDs
This paper has been presented the construction and the design
of a HP-LED photoreactor, moreover its HP-UV-LEDs efficiency and
results has been compared with a similar traditional UV-lamp
photoreactor Using ZnO as a good photocatalyst is just a typical
example of such experiments, nonetheless ZnO nanostructures are
nontoxic, inexpensive and highly efficient nature[20]
2 Methods and experiment
2.1 Design and preparation of a HP-LED photoreactor
A cylindrical photoreactor with a diameter of 12 cm was made
byfive senary series of HP-LEDs including: (i) Green (517e520 nm
Green-EP-GE-70-80LM-xy-Unbranded-1W), (ii) Red (620e625 nm
Red-EP-GE-35-45LM-xy-Unbranded-1W), (iii) Blue (462e465 nm
Blue-EP-GE-20-25LM-xy-Unbranded-1W), (iv) UV1(385e390 nm
UV-1W-Unbranded-1W), and (v) UV2 (365e370 nm
UV-EP-0.4-0.6LM-Unbranded-1W) HP-LEDs
After brazing the HP-LEDs on cool pads named “PCB-Stars” which PCB is an abbreviation for printed circuit board, these arrays were arranged and patched with a repetitious distribution in two rows at a certain distance from the inner edge of a perforated steel cylinder Electrical insulating and PCB mounting on the steel housing was difficult, in turn the main advantage was its good heat-sink role, although a computer case fan (92 mm 25 mm DC 12 V 2 Pin 65.01 CFM computer case cooler cooling fan-Unbranded) was contrived on top of the photoreactor to better ventilation Light Intensity is very important in commercial applications of photocatalysis for water treatments and air purification because of energy saving, also increasing intensity can compensate the shortage of photocatalytic reaction rate, so we installed the diodes with respect to the luminescence intensity distribution curves (LIDCs) or intensity patterns LIDCs show that the maximum in-tensity of a HP-LED is distributed about the angle of 45[21,22] HP-LEDs were installed on a calculated distance (about 6e8 cm far) from the inner edge of photoreactor, in a way that their radiated intensity is smoothly and maximum distributed around the center
of the cylinder mouth So the samples can be deployed at the center
of the cylinder base to achieve a distinct condition for a specific set of experiments We mentioned that we obtained a hexagonal arrangement around the cylinder for each set of HP-LEDs Also, every set of HP-LEDs could be ignited with a specific ballast circuit named “driver” In the other words, for every series of LEDs a
6 1 W driver is allocated to support the required power
In HP-LED photoreactor, proper drivers were used separately by
a distinct key that assigned to every driver, consequently to each set
of diodes Based on the type of the test, it provides the possibility of using different colors of light either separately or simultaneously For instances, certain metals as dopants can excite ZnO nano-structures as photocatalysts under sunlight which their relevant experiments should be done using visible sources[20], white and blue LEDs can be used for surveys about N-doped TiO2[23], also another research have been used blue LEDs to study a plasmonic Ag/AgBr heterostructure as a photocatalytic material[24] 2.2 ZnO nanoparticles preparation method
ZnO nanoparticles were synthesized through co-precipitation method Briefly, two solutions Zn(O2CCH3)2(H2O)2 (0.5 M, 25 mL
in DI water) and NaOH (0.5 M, 25 mL in DI water) were prepared and simultaneously transferred to a 250 mL beaker stirring by a syringe pump at a rate of 30 mL/h After injection of two solutions, the resultant solution was stirred at room temperature for 20 min Next, the resultant precipitate was filtered and washed with DI water The precipitate was dried in an oven and ground to powder
by agate mortar Finally form ZnO nanoparticles; the powder was calcined in air at a temperature of 250C for 3 h
2.3 Photocatalytic water purification in HPLED-PhR and FL-PhR
As an example of the usefulness of HP-LED photoreactor in comparison with traditional UV lamp photoreactor, two photo-catalytic experiments were arranged using ZnO nanoparticles as photocatalyst in photocatalytic water purification, polluted with the RB dye For this purpose, two 50 mL beakers were prepared so that each one contained 20 gr ZnO photocatalyst, and 20 mL of
50 mM RB solution in DI water One beaker was deployed in HPLED-PhR where irradiated by UV LEDs with the wavelength of 365 nm The other beaker was moved to a FL-PhR which contained four OSRAM UV lamps with the wavelength of 254 nm (Puritec Germicidal lamp HNS 8 W G5, made in Italy) The intensity of each lamp was 8 W, so totally were 32 W Then two solutions were allowed to remain in the darkfor 1 h prior to illumination Next, two
Trang 3photoreactors were turned on, simultaneously for 50 min The
so-lutions were continuously stirred and aerated by bubbling air into
the photoreactors Every 10 min, each solution was sampled
Samples were taken to another darkness place Finally, in order to
separate the photocatalyst from dye solution in water, the samples
were got into a 6000 rpm centrifuge for 20 min, and then the
ultraviolet-visible (UV-Vis) absorption spectra of the samples were
prepared
3 Results and discussion
Fig 1 shows a characterization of synthesized ZnO
nano-particles The FESEM image of nanoparticles is shown inFig 1(a)
As can be observed, the mean diameter size of synthesized
nanoparticles has 45 nm.Fig 1(b) shows FTIR spectrum of ZnO
nanoparticles The peak localized at around 450 cm1is
corre-sponded to the ZneO stretching that confirms the formation of
ZnO Furthermore, the peaks related to the symmetric and
asym-metric C]O bond vibrations are at around 1410 and 1560 cm1.
The absorption of atmospheric CO2by metallic cation was led to
appear a peak at 2355 cm1[25] UV-Visible absorption spectrum
of ZnO nanoparticles was showed inFig 1(c) It consisted of sharp
absorption of ZnO at 375 nm, so it seems that the proper light
source for such a photocatalytic process is which contains
band-widths in the ranges of wavelengths less than 375 nm
Fig 2(a) depicts the elements of the HP-LED photoreactor; Fig 2(b) shows the home-made HP-LED photoreactor.Fig 2(c) shows the arrangement of LEDs on assembled photoreactor Fig 2(d) shows the photoreactor when all of its HP-LEDs are turned on It excellently has been observed that white light can
be generated by HPLED-PhR in lab, but it is noticed again that only UV2 lamps as 365 nm source was lighted in the present comparison
Fig 3(a) and 3 (b) show spectra of HP-LED photoreactor for when all its HP-LEDs and UV2LEDs were turned on, respectively These spectra were measured by UV-Vis spectrometer (spectonix
Ar 2015 made in Iran) We know that the LEDs with the wavelength
of 365 nm are good choices for ZnO photocatalytic reaction Like-wise,Fig 3(c) shows the spectrum of FL photoreactor, and it shows that a UV peak is located at the wavelength of 252 nm Notice that the energy of a 252 nm photon is about 45% more than the energy
of a 365 nm photon
In the other hand, it can be considered that the degradation rate
of Dye (K) under UV irradiation is affected by the UV intensity (I) by the Equation(1) [26]
where n¼ 1 for low intensities, then varies to n ¼ 0.5 by increasing the intensity up to about 25 mW cm2for some dyes, and in more
M Khademalrasool et al / Journal of Science: Advanced Materials and Devices 1 (2016) 382e387 384
Trang 4intensities n equals zero It seems that such behavior is due to
growing the generation of the electronehole pairs by increasing the
intensity, more increasing of these pairs lead to increase their
im-pacts, and then the degradation rate is decreased by recombination
reactions
Fig 4(a) and 4 (b) show the UV-Vis absorption spectra of the
samples in HPLED-PhR and FL-PhR, respectively Spectra exhibit
how the dyes were degraded in reactors by passing the time From
thisfigures it is demonstrated that in spite of lower power
con-sumption the rate of the photocatalytic water purification under
the HP-LEDs was twice larger than its rate under the traditional
fluorescent UV lamps
The normalized dye concentration C/Co versus the exposure
time in two photoreactors is shown inFig 5 It was monitored by
UV-Vis spectroscopy to observe the declines in 610 nm peak of RB
Comparing the photocatalysis process in two photoreactors, it is
thought that after 20 min of exposure time, only about 35% of the
RB dye is degraded in FL-PhR while during the same time, more
than 75% of dye has been removed in HPLED-PhR Using Equation
(1), the relation between intensities and degradation rates in both
same conditions and solutions were obtained
K0
K ¼I0
ffiffiffi
I0 I
r
(2)
If K0and K stand for degradation rates in the HPLED-PhR and FL-PhR, respectively, then I0 and I show their light intensities, respectively Considering the same experimental criteriaexcept the higher energy of the FL-PhR UV lamps, the HPLED-PhR LEDs have higher Intensity Substituting K0=K ¼ 0:75=0:35 in Equation(2), it realized that HPLED-PhR UV lamps have a total Intensity more than two times greater than the intensity of FL-PhR If we assume that the intensities are small enough, this ratio excesses more than four times
4 Conclusion
In this paper, the usefulness of HP-LEDs as light sources in photocatalytic processes was discussed Also the performances of traditional UVfluorescent lamps that are used widely in photo-catalytic processes were compared with UV HP-LEDs The results
of this research demonstrate that the rate of photocatalytic
Fig 2 (a) Scheme of the HP-LED photoreactor, (b) Homemade HP-LED photoreactor, (c) all HP-LEDs off, (d) all HP-LEDs on.
Trang 5degradation RB dye in HPLED-PhR containing just 6 UV HP-LEDs with the power of 1 W (totally 6 W) and the wavelength of
365 nm, has at least twice improved in comparison with FL-PhR namely for 4 UV mercury tubes with the power of 8 W (totally
32 W) and the wavelength of 254 nm, while the consumed energy
of FL-PhR is about five times greater than of HPLED-PhR, and the fabrication price of the latter photoreactor is about a quarter of thefirst one HPLED-PhR can be made in more flexible sizes, on the other hand, it generates less heat in comparison with FL-PhR Thereupon using well-arranged LEDs as radiation sources in the photocatalytic process is much more economical and efficient than the traditionalfluorescent lamps
Acknowledgment The authors acknowledge Shahid-Chamran university of Ahvaz forfinancial support of this work
Fig 3 Spectrum of HPLED-PhR when (a) all its HP-LEDs are on, (b) UV 2 LEDs are on; (c) Spectrum of FL-PhR.
Fig 4 The absorption spectrums of the RB Dye as time function in (a) HPLED-PhR, (b) FL-PhR.
Fig 5 Normalized dye concentration of RB versus time in HPLED-PhR and FL-PhR.
M Khademalrasool et al / Journal of Science: Advanced Materials and Devices 1 (2016) 382e387 386
Trang 6[1] M.N Chong, B Jin, C.W Chow, C Saint, Recent developments in photocatalytic
water treatment technology: a review, Water Res 44 (2010) 2997e3027
[2] M Farbod, M Khademalrasool, Synthesis of TiO 2 nanoparticles by a combined
solegel ball milling method and investigation of nanoparticle size effect on
their photocatalytic activities, Powder Technol 214 (2011) 344e348
[3] W.K Jo, R.J Tayade, New generation energy-efficient light source for
photo-catalysis: LEDs for environmental applications, Ind Eng Chem Res 53 (2014)
2073e2084
[4] X Liu, Y Yang, X Shi, K Li, Fast photocatalytic degradation of methylene blue
dye using a low-power diode laser, J Hazard Mater 283 (2015) 267e275
[5] R.J Tayade, T.S Natarajan, H.C Bajaj, Photocatalytic degradation of methylene
blue dye using ultraviolet light emitting diodes, Ind Eng Chem Res 48 (2009)
10262e10267
[6] A Dadgar, A Alam, T Riemann, J Bl€asing, A Diez, M Poschenrieder,
M Strassburg, M Heuken, J Christen, A Krost, Crack-free InGaN/GaN light
emitters on Si (111), Phys Status Solidi A 188 (2001) 155e158
[7] H Hirayama, N Maeda, S Fujikawa, S Toyoda, N Kamata, Recent progress and
future prospects of AlGaN-based high-efficiency deep-ultraviolet
light-emit-ting diodes, Jpn J Appl Phys 53 (2014) 100209
[8] H Hirayama, S Fujikawa, N Noguchi, J Norimatsu, T Takano, K Tsubaki,
N Kamata, 222e282 nm AlGaN and InAlGaN-based deep-UV LEDs fabricated
on high-quality AlN on sapphire, Phys Status Solidi A 206 (2009) 1176e1182
[9] Y Kubota, K Watanabe, O Tsuda, T Taniguchi, Deep ultraviolet light-emitting
hexagonal boron nitride synthesized at atmospheric pressure, Science 317
(2007) 932e934
[10] Y Taniyasu, M Kasu, T Makimoto, An aluminium nitride light-emitting diode
with a wavelength of 210 nanometres, Nature 441 (2006) 325e328
[11] K Watanabe, T Taniguchi, H Kanda, Direct-bandgap properties and evidence
for ultraviolet lasing of hexagonal boron nitride single crystal, Nat Mater 3
(2004) 404e409
[12] A Mereuta, G Saint-Girons, S Bouchoule, I Sagnes, F Alexandre, G.L Roux,
J Decobert, A Ougazzaden, (InGa) (NAs)/GaAs structures emitting in 1e1.6
mm wavelength range, Opt Mater 17 (2001) 185e188
[13] I Moreno, U Contreras, Color distribution from multicolor LED arrays, Opt.
express 15 (2007) 3607e3618
[14] M Volatier, D Duchesne, R Morandotti, R Ares, V Aimez, Extremely high aspect ratio GaAs and GaAs/AlGaAs nanowaveguides fabricated using chlo-rine ICP etching with N 2 -promoted passivation, Nanotechnol 21 (2010)
134014 [15] S Nakamura, T Mukai, M Senoh, Candela-class high-brightness InGaN/AlGaN double-heterostructure blue-light-emitting diodes, Appl Phys Lett 64 (1994) 1687e1689
[16] M Reichl, Success in Research: First Gallium-nitride LED Chips on Silicon in Pilot Stage 2012, Osram Opto Semiconductors, 2012 http://www.osram-os com/osram_os/en/press/press-releases/company-information/2012/gallium_ nitrid_led_chips/index.jsp (accessed 16.06.09).
[17] B.D Johnson, High-power, Short-wave LED Purifies Air, 2003, 111e111 [18] M Izadifard, G Achari, C.H Langford, Application of photocatalysts and LED light sources in drinking water treatment, Catalysts 3 (2013) 726e743 [19] S Yates, G.A Land, Honeywell International Inc., 2015 Air purification system using ultraviolet light emitting diodes and photocatalyst-coated supports U.S Patent 9,101,904.
[20] M Samadi, M Zirak, A Naseri, E Khorashadizade, A.Z Moshfegh, Recent progress on doped ZnO nanostructures for visible-light photocatalysis, Thin Solid Films 605 (2016) 2e19
[21] I Moreno, C.C Sun, Modeling the radiation pattern of LEDs, Opt express 16 (2008) 1808e1819
[22] C.C Sun, W.T Chien, I Moreno, C.C Hsieh, Y.C Lo, Analysis of the far-field region of LEDs, Opt express 17 (2009) 13918e13927
[23] O Sacco, M Stoller, V Vaiano, P Ciambelli, A Chianese, D Sannino, Photo-catalytic degradation of organic dyes under visible light on n-doped photo-catalysts, Int J Photoenergy 2012 (2012) 1e8
[24] K Dai, L Lu, J Dong, Z Ji, G Zhu, Q Liu, Z Liu, Y Zhang, D Lia, C Liangc, Facile synthesis of a surface plasmon resonance-enhanced Ag/AgBr heterostructure and its photocatalytic performance with 450 nm LED illumination, Dalton Trans 42 (2013) 4657e4662
[25] G Xiong, U Pal, J Serrano, K Ucer, R Williams, Photoluminesence and FTIR study of ZnO nanoparticles: the impurity and defect perspective, Phys Status Solidi C 3 (2006) 3577e3581
[26] Q Zhang, C Li, T Li, Rapid photocatalytic degradation of methylene blue under high photon flux UV irradiation: characteristics and comparison with routine low photon flux, Int J Photoenergy 2012 (2012) 1e7