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Journal of Science: Advanced Materials and Devices 1 (2016) 382e387

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Journal of Science: Advanced Materials and Devices

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Original Article The improvement of photocatalytic processes: Design of a photoreactor using high-power LEDs

* Marzieh Khademalrasool a, , Mansoor Farbod b, Mohammad Davoud Talebzadeh a

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

article info abstract

Article history: This paper is an attempt to survey the benefits of a well-designed photoreactor containing just 6 ultraviolet Received 25 April 2016 (UV) high power light emitting diodes (HPLEDs); the power and wavelength of each UV HPLED are 1 W and Received in revised form 365 nm, respectively, the latter being an efficient source for photocatalytic studies. Although the experi- 11 June 2016 ment with the 365-nm LEDs is reported here, other LEDs were predicted for conducting similar experi- Accepted 13 June 2016 ments including green photocatalytic ones. We installed diodes with respect to the luminescence intensity Available online 18 June 2016 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 Keywords: Fluorescent lamp photoreactor photocatalytic processes, a set of UV HPLEDs was designed and made up. Next, the performance of HPLED- fl High-power LED photoreactor PhR was compared with that of a traditional uorescent lamp photoreactor (FL-PhR). As a typical photo- Photocatalytic water purification catalytic experiment, Zinc Oxide (ZnO) nanoparticles were synthesized via co-precipitation method and Reactive blue dye used as photocatalyst for purification of water polluted with the reactive blue dye (RB), under UV irradi- Zinc oxide nanoparticle 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 traditional fluorescent 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 bubble of glass or quartz that is filled by a noble gas like argon and a very small amount of mercury. Some drawbacks of these lamps are Nowadays the semiconductor photocatalysis has attracted their fragility, danger of explosion for their high pressures and attention of numerous researchers for removal of hazardous and working temperatures, their inner gas leakage, and their problems toxic materials, and pollutions such as dyes and organic com- after lamp failure in eliminating the risks associated with mercury pounds from environment [1]. In photocatalytic activities, when a hazardous and toxic substances. Furthermore, the life span of these semiconductor exposes to the proper light sources which their lamps is about 500e2000 h, and they work at high temperatures, so energy is equal to or greater than the energy band gap of the the heat dissipation during the reaction consumes a lot of energy. semiconductor material, the electronehole pairs are produced. In order to find better and more proper light sources, LEDs have These pairs participate in various oxidationereduction reactions attracted the attention of many researchers [3e5]. Diode is a pen and generated strong oxidizers like hydroxyl radical (OH*) and junction that a specific voltage can be applied to its two ends, anions such as superoxide (O2 ) which are responsible for the thereupon the electrons and holes are recombined, and some mineralization of the toxic inorganic compounds [2]. amount of energy can be released as photons and heat. In an in- The preparation of suitable light sources with proper efficiency direct band gap diode (e.g. silicon or germanium), electrons and and time-responding, generally have been one of the necessities for holes recombine via non-radiative transitions so there is no optical photocatalytic studies. Fluorescent UV lamps (such as black lights emission. On the other hand, materials using to make LEDs have and germicidal UV lamps), mercury arc lamps, and etc. are the most various direct band gaps and energies that could identify the commonly used as light sources. A Fluorescent UV lamp consists of wavelength of light either in near-infrared, visible, or UV regions. In two alkaline-tungsten electrodes at either end of the cylindrical thin quantum wells diodes, a quantum well is like indium gallium nitride (InGaN) sandwiched between two gallium nitride (GaN) * Corresponding author. layers. Changing the ratio of In/Ga the radiated light color, also the E-mail address: [email protected] (M. Khademalrasool). ratio of Al/Ga in aluminum gallium nitride (AlGaN) diodes uses to Peer review under responsibility of Vietnam National University, Hanoi.

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 (http://creativecommons.org/licenses/by/4.0/). M. Khademalrasool et al. / Journal of Science: Advanced Materials and Devices 1 (2016) 382e387 383 make UV diodes with lower efficiencies [6]. The high efficiencies After brazing the HP-LEDs on cool pads named “PCB-Stars” can be achieved by using unalloyed GaN for the wavelength of which PCB is an abbreviation for printed circuit board, these arrays 365 nm. The most commercial diodes are fabricated at the range of were arranged and patched with a repetitious distribution in two 222e282 nm namely about the sensitivity of microorganism [7], rows at a certain distance from the inner edge of a perforated steel also DNA absorption is located on the wavelength of 260 nm. These cylinder. Electrical insulating and PCB mounting on the steel diodes are usually used in sterilization, medicine and biochemistry, housing was difficult, in turn the main advantage was its good heat- water or air purification, optical recording with high densities, sink role, although a computer case fan (92 mm 25 mm DC 12 V 2 optical analytical systems, and so on [8]. However, these diodes are Pin 65.01 CFM computer case cooler cooling fan-Unbranded) was technologically and materially more expensive than visible and contrived on top of the photoreactor to better ventilation. near-UV diodes. LEDs with the bandwidth at the range of Light Intensity is very important in commercial applications of 210e235 nm are less common and often are made in the laboratory photocatalysis for water treatments and air purification because of using diamond, aluminum nitride or boron nitride [9e11]. energy saving, also increasing intensity can compensate the Researches show that LEDs with either narrow or wide band- shortage of photocatalytic reaction rate, so we installed the diodes widths namely in different frequency ranges of radiation and with respect to the luminescence intensity distribution curves various colors can be achieved by modifying the kinds of used (LIDCs) or intensity patterns. LIDCs show that the maximum in- semiconductors, ratios of components, and mixing various LEDs tensity of a HP-LED is distributed about the angle of 45 [21,22].HP- such as (red, green, and blue) RGB arrays [12e14]. Some of the LEDs were installed on a calculated distance (about 6e8 cm far) significant benefits of LEDs in comparison with traditional light from the inner edge of photoreactor, in a way that their radiated sources are their lower power consumption, more life span intensity is smoothly and maximum distributed around the center (25,000e1,00,000 h), improved physical strength, smaller sizes, of the cylinder mouth. So the samples can be deployed at the center and faster switching [3,7]. of the cylinder base to achieve a distinct condition for a specific The first generation of high power light emission diodes (HP- set of experiments. We mentioned that we obtained a hexagonal LEDs) was developed in 1994 by Shuji Nakamura while working for arrangement around the cylinder for each set of HP-LEDs. Also, Nichia Corporation. The 2014 noble prize was awarded to him “for every set of HP-LEDs could be ignited with a specific ballast circuit the invention of efficient blue light-emitting diodes which has named “driver”. In the other words, for every series of LEDs a enabled bright and energy-saving white light sources” [15]. Around 6 1 W driver is allocated to support the required power. 2002, the growth process of GaN LEDs on silicon substrate was In HP-LED photoreactor, proper drivers were used separately by developed, and only after one decade [6], the first commercial a distinct key that assigned to every driver, consequently to each set production of HP-LEDs was presented by OSRAM manufacturer as of diodes. Based on the type of the test, it provides the possibility of silicon-based Gain [16]. Using the epitaxial methods for silica using different colors of light either separately or simultaneously. instead of ruby, the final price of HP-LEDs decreased ninety percent. For instances, certain metals as dopants can excite ZnO nano- UV-LEDs using unalloyed GaN are commercially produced in the structures as photocatalysts under sunlight which their relevant wavelength of 365 nm with high efficiencies. Their output powers experiments should be done using visible sources [20], white and are about 10 mW to 3 W, and usually used to degrade or remove the blue LEDs can be used for surveys about N-doped TiO2 [23], also air and water pollutions. Recent findings indicate that the visible another research have been used blue LEDs to study a plasmonic LEDs such as blue, red, green, or white one can be employed as light Ag/AgBr heterostructure as a photocatalytic material [24]. sources in photocatalytic processes. The near UV-LEDs with the wavelength of 385 nm were used by Johnson on water and air 2.2. ZnO nanoparticles preparation method 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 ZnO nanoparticles were synthesized through co-precipitation power, was used in perchloroethylene (PCE) photocatalysis oxida- method. Briefly, two solutions Zn(O2CCH3)2(H2O)2 (0.5 M, 25 mL tion [3]. There are several reports about the making of photo- in DI water) and NaOH (0.5 M, 25 mL in DI water) were prepared reactors based on various LEDs for photocatalytic researches in and simultaneously transferred to a 250 mL beaker stirring by a gaseous or liquid environments [3,18,19] but there are fewer re- syringe pump at a rate of 30 mL/h. After injection of two solutions, ports on high-power LED photoreactors [17]. Using them as radia- the resultant solution was stirred at room temperature for 20 min. tion sources in the photocatalytic process is much more economical Next, the resultant precipitate was filtered and washed with DI and efficient than conventional LEDs. water. The precipitate was dried in an oven and ground to powder This paper has been presented the construction and the design by agate mortar. Finally form ZnO nanoparticles; the powder was of a HP-LED photoreactor, moreover its HP-UV-LEDs efficiency and calcined in air at a temperature of 250 C for 3 h. results has been compared with a similar traditional UV-lamp photoreactor. Using ZnO as a good photocatalyst is just a typical 2.3. Photocatalytic water purification in HPLED-PhR and FL-PhR example of such experiments, nonetheless ZnO nanostructures are nontoxic, inexpensive and highly efficient nature [20]. As an example of the usefulness of HP-LED photoreactor in comparison with traditional UV lamp photoreactor, two photo- 2. Methods and experiment catalytic experiments were arranged using ZnO nanoparticles as photocatalyst in photocatalytic water purification, polluted with 2.1. Design and preparation of a HP-LED photoreactor 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 A cylindrical photoreactor with a diameter of 12 cm was made 50 mM RB solution in DI water. One beaker was deployed in HPLED- by five senary series of HP-LEDs including: (i) Green (517e520 nm PhR where irradiated by UV LEDs with the wavelength of 365 nm. Green-EP-GE-70-80LM-xy-Unbranded-1W), (ii) Red (620e625 nm The other beaker was moved to a FL-PhR which contained four Red-EP-GE-35-45LM-xy-Unbranded-1W), (iii) Blue (462e465 nm OSRAM UV lamps with the wavelength of 254 nm (Puritec Blue-EP-GE-20-25LM-xy-Unbranded-1W), (iv) UV1 (385e390 nm Germicidal lamp HNS 8 W G5, made in Italy). The intensity of each UV-1W-Unbranded-1W), and (v) UV2 (365e370 nm UV-EP-0.4- lamp was 8 W, so totally were 32 W. Then two solutions were 0.6LM-Unbranded-1W) HP-LEDs. allowed to remain in the darkfor 1 h prior to illumination. Next, two 384 M. Khademalrasool et al. / Journal of Science: Advanced Materials and Devices 1 (2016) 382e387 photoreactors were turned on, simultaneously for 50 min. The so- Fig. 2 (a) depicts the elements of the HP-LED photoreactor; lutions were continuously stirred and aerated by bubbling air into Fig. 2 (b) shows the home-made HP-LED photoreactor. Fig. 2 (c) the photoreactors. Every 10 min, each solution was sampled. shows the arrangement of LEDs on assembled photoreactor. Samples were taken to another darkness place. Finally, in order to Fig. 2 (d) shows the photoreactor when all of its HP-LEDs are separate the photocatalyst from dye solution in water, the samples turned on. It excellently has been observed that white light can were got into a 6000 rpm centrifuge for 20 min, and then the be generated by HPLED-PhR in lab, but it is noticed again that ultraviolet-visible (UV-Vis) absorption spectra of the samples were only UV2 lamps as 365 nm source was lighted in the present prepared. comparison. Fig. 3 (a) and 3 (b) show spectra of HP-LED photoreactor for when all its HP-LEDs and UV2 LEDs were turned on, respectively. 3. Results and discussion These spectra were measured by UV-Vis spectrometer (spectonix Ar 2015 made in Iran). We know that the LEDs with the wavelength Fig. 1 shows a characterization of synthesized ZnO nano- of 365 nm are good choices for ZnO photocatalytic reaction. Like- particles. The FESEM image of nanoparticles is shown in Fig. 1 (a). wise, Fig. 3 (c) shows the spectrum of FL photoreactor, and it shows As can be observed, the mean diameter size of synthesized that a UV peak is located at the wavelength of 252 nm. Notice that nanoparticles has 45 nm. Fig. 1 (b) shows FTIR spectrum of ZnO the energy of a 252 nm photon is about 45% more than the energy 1 nanoparticles. The peak localized at around 450 cm is corre- of a 365 nm photon. sponded to the ZneO stretching that confirms the formation of In the other hand, it can be considered that the degradation rate ZnO. Furthermore, the peaks related to the symmetric and asym- of Dye (K) under UV irradiation is affected by the UV intensity (I) by 1 metric C]O bond vibrations are at around 1410 and 1560 cm . the Equation (1) [26] The absorption of atmospheric CO2 by metallic cation was led to appear a peak at 2355 cm 1 [25]. UV-Visible absorption spectrum of ZnO nanoparticles was showed in Fig. 1 (c). It consisted of sharp KfIn (1) absorption of ZnO at 375 nm, so it seems that the proper light source for such a photocatalytic process is which contains band- where n ¼ 1 for low intensities, then varies to n ¼ 0.5 by increasing widths in the ranges of wavelengths less than 375 nm. the intensity up to about 25 mW cm 2 for some dyes, and in more

Fig. 1. (a) The FESEM image, (b) FTIR spectrum, and (c) UV-Visible absorption spectrum of ZnO nanoparticles. M. Khademalrasool et al. / Journal of Science: Advanced Materials and Devices 1 (2016) 382e387 385

Fig. 2. (a) Scheme of the HP-LED photoreactor, (b) Homemade HP-LED photoreactor, (c) all HP-LEDs off, (d) all HP-LEDs on.

intensities n equals zero. It seems that such behavior is due to rffiffiffi 0 0 0 growing the generation of the electronehole pairs by increasing the K I I ¼ ðorÞ (2) intensity, more increasing of these pairs lead to increase their im- K I I pacts, and then the degradation rate is decreased by recombination 0 If K and K stand for degradation rates in the HPLED-PhR and FL- reactions. 0 PhR, respectively, then I and I show their light intensities, Fig. 4 (a) and 4 (b) show the UV-Vis absorption spectra of the respectively. Considering the same experimental criteriaexcept the samples in HPLED-PhR and FL-PhR, respectively. Spectra exhibit higher energy of the FL-PhR UV lamps, the HPLED-PhR LEDs have how the dyes were degraded in reactors by passing the time. From 0 higher Intensity. Substituting K =K ¼ 0:75=0:35 in Equation (2),it this figures it is demonstrated that in spite of lower power con- realized that HPLED-PhR UV lamps have a total Intensity more than sumption the rate of the photocatalytic water purification under two times greater than the intensity of FL-PhR. If we assume that the HP-LEDs was twice larger than its rate under the traditional the intensities are small enough, this ratio excesses more than four fluorescent UV lamps. times. The normalized dye concentration C/Co versus the exposure time in two photoreactors is shown in Fig. 5. It was monitored by UV-Vis spectroscopy to observe the declines in 610 nm peak of RB. 4. Conclusion Comparing the photocatalysis process in two photoreactors, it is thought that after 20 min of exposure time, only about 35% of the In this paper, the usefulness of HP-LEDs as light sources in RB dye is degraded in FL-PhR while during the same time, more photocatalytic processes was discussed. Also the performances of than 75% of dye has been removed in HPLED-PhR. Using Equation traditional UV fluorescent lamps that are used widely in photo- (1), the relation between intensities and degradation rates in both catalytic processes were compared with UV HP-LEDs. The results same conditions and solutions were obtained. of this research demonstrate that the rate of photocatalytic 386 M. Khademalrasool et al. / Journal of Science: Advanced Materials and Devices 1 (2016) 382e387

Fig. 3. Spectrum of HPLED-PhR when (a) all its HP-LEDs are on, (b) UV2 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.

degradation 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 the first 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 traditional fluorescent lamps.

Acknowledgment

The authors acknowledge Shahid-Chamran university of Ahvaz Fig. 5. Normalized dye concentration of RB versus time in HPLED-PhR and FL-PhR. for financial support of this work. M. Khademalrasool et al. / Journal of Science: Advanced Materials and Devices 1 (2016) 382e387 387

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