- Email: [email protected]
Enhanced photo-fermentative hydrogen production of Rhodopseudomonas sp. nov. strain A7 by the addition of TiO2, ZnO and SiC nanoparticles
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 4 2 ( 2 0 1 7 ) 1 8 2 7 9 e1 8 2 8 7
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/he
Enhanced photo-fermentative hydrogen production of Rhodopseudomonas sp. nov. strain A7 by the addition of TiO2, ZnO and SiC nanoparticles Bingfeng Liu a,*, Yaruo Jin a, Zhijiang Wang b, Defeng Xing a, Chao Ma a, Jie Ding a, Nanqi Ren a a
State Key Laboratory of Urban Water Resource and Environment, School of Municipal and Environmental Engineering, Harbin Institute of Technology, P.O. Box 2614, 73 Huanghe Road, Harbin 150090, China b School of Chemical Engineering and Technology, Harbin Institute of Technology, Harbin 150001, China
article info
abstract
Article history:
In order to strengthen photo-fermentative hydrogen production by different photocatalytic
Received 19 January 2017
nanoparticles, hydrogen production by photo-fermentative bacteria with addition of TiO2,
Received in revised form
ZnO and SiC nanoparticles in batch culture were investigated in this study. The results
5 March 2017
indicated that three nanoparticles could improve hydrogen production performance of
Accepted 18 April 2017
Rhodopseudomonas sp. nov. strain A7 under respective optimal conditions. The hydrogen
Available online 8 May 2017
yield of 2.81 mol-H2/mol-acetate was obtained when TiO2 nanoparticles with a concentration of 300 mg/L and size of 25 nm. The concentration of ZnO nanoparticles was at
Keywords:
100 mg/L, hydrogen yield reached 2.64 mol-H2/mol-acetate. Compared with TiO2 and ZnO
Photo-H2 production
nanoparticles, SiC nanoparticles exhibited greatest potential for enhancing photo-
TiO2 nanoparticles
hydrogen production. By addition of nano-SiC with concentration of 200 mg/L which was
ZnO nanoparticles
prepared at temperature of 1500 C, the maximum hydrogen volume, average hydrogen
SiC nanoparticles
content and hydrogen yield of strain A7 were achieved at 2272 mL-H2/L-culture, 85.2% and 2.99 mol-H2/mol-acetate, respectively. And hydrogen production was 18.6% higher than that of alone strain A7 without the addition of nanoparticles. Therefore, the addition of SiC nanoparticles is a promising strategy to improve photo-fermentative hydrogen production from wastewater. © 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction Hydrogen is considered to be a sustainable and clean energy carrier to solve the problem of energy shortage and environment pollution at present [1]. Among diverse hydrogen production technologies, bio-hydrogen production from wastewater and biomass shows great potential in the future [2]. Especially,
photo-fermentative hydrogen production has attracted more attention because of combining wastewater treatment, hydrogen production and solar energy conversion [3]. In addition, photo-fermentative bacteria can use extensive organic substrates (e.g. short chain organic acids, carbohydrate) [4e6]. However, the problems of low hydrogen producing yield and light energy conversion efficiency, the lacking efficient photobioreactors and cheap raw material limit further development
* Corresponding author. Fax: þ86 451 86282008. E-mail address: [email protected] (B. Liu). http://dx.doi.org/10.1016/j.ijhydene.2017.04.147 0360-3199/© 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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and application of photo-hydrogen production. Thus, many researchers focus on resolving above barriers using different strategies, for example, isolating excellent bacterium [15], optimizing culture condition [20], choosing culture mode [19], using efficient carrier [17] and designing novel bioreactor [18]. Recently, with the rapid development of nanotechnology, a large amount of nano-materials are produced and they are extensively used in hydrogen production, pollutants degradation, sterilization, gas purification and self-cleaning materials [7,8]. Photocatalysis technique based on nanoparticles has become one focus in the 21st century because of using solar energy and degrading organic or inorganic contaminants in environmental fields [9,16]. A novel and exciting method called “photo-biocatalysis” was proposed based on the joint features of both photofermentation and photocatalysis in hydrogen production, in which enzyme system of microorganism cells obtain electrons from photocatalytic semiconductors via methyl viologen as electron-mediator [10]. Thus, a few studies have tried to strengthen photo-fermentative hydrogen production by photocatalytic TiO2 nanoparticles. TiO2 nanoparticles were demonstrated to transfer photoinduced electrons to the enzyme system of Thiocapsa roseopersicina effectively and the hydrogen yield was enhanced up to 10% [11]. Hydrogen production was observed by using the sensitized TiO2, and hydrogen yield by the photocatalytic of sensitized TiO2-MV2þ coupling photo-fermentative bacterium Rhodopseudomonas capsulata was higher than that of the naked TiO2 [12]. Zhao and Chen have reported the enhanced photo-fermentative hydrogen production using the dark fermentation effluents from waste activated sludge with the nano-TiO2 and hydrogen yield increased by 46.1% when the concentration of TiO2 was at 100 mg/L [13]. Pandey investigated the effect of the mixed phase of TiO2 nanoparticles on photo-fermentative hydrogen generation by Rhodobacter sphaeroides NMBL-02 and the cumulative hydrogen volume reached up to 1900 mL/L medium with substrate (malate) conversion efficiency up to 63.27% when TiO2 nanoparticles were added in a batch fermentation system [14]. Therefore, combination of photo-fermentation and photocatalysis showed an important significance for improving photo-hydrogen production, which provided a novel avenue to overcome the limitation of the biochemical pathways in molecular hydrogen production and cell growth of organisms [14]. However, previous studies only focused on TiO2 nanoparticles, the information about screening more efficient photocatalysis nanoparticles for enhancing photo-fermentative hydrogen production is still lacking. Therefore, the key objective of this study is screening more efficient nanoparticles for enhancing photo-fermentative hydrogen production. In this study, TiO2, ZnO and SiC nanoparticles were selected for investigating their effects on the hydrogen production by photofermentative bacteria Rhodopseudomonas sp. nov. strain A7.
Environmental Biological Technology Research Center of HIT, China [1]. The growth medium contained 1 g/L CH3COONa, 1 g/L sodium succinate, 1 g/L yeast extract, 0.5 g/L peptone, 0.5 g/L Lcysteine, 0.5 g/L KH2PO4, 0.5 g/L K2HPO4, 1 g/L NH4Cl, 0.2 g/L MgSO4, 0.08 g/L CaCl2, 0.1 g/L NaCl, 0.012 g/L FeSO4$7H2O, 0.2 g/ L EDTA-Na, 1 mL/L trace element, 1 mL/L vitamin, initial pH 7.0. The hydrogen production medium contained 4.1 g/L CH3COONa, 1.69 g/L sodium glutamate, 1 g/L beef extract, 0.5 g/L L-cysteine, other component was same with above growth medium.
Hydrogen production reactor and culture conditions The hydrogen production experiments were carried out in triplicate with a 100 mL photobioreactor containing a working volume of 60 mL producing hydrogen medium. The reactors were sealed with rubber stoppers and filled with argon to maintain anaerobic conditions. Then bottles with culture medium were autoclaved at 121 C for 15 min. Photofermentative bacterium strain A7 was inoculated into serum bottles with inoculums age of 14 h and volume ratio (V/V) of 10%. Nanoparticles were added into serum bottles according to their concentration. The reactors containing photofermentative bacteria and nanoparticles were shaken in a shaker at 120 rpm and constant temperature of 35 C. The light source used incandescent lamps of 60 W and the light intensity on the surface of reactors maintained at 150 W/m2. Biogas in the photobioreactor was collected by drainage method. The main component of produced biogases is hydrogen and CO2. The total volume of hydrogen was calculated by multiplying total volume of gas by the content of hydrogen.
Preparation of nanoparticles
Material and methods
TiO2 and ZnO nanoparticles with different particle size were purchased from Aladdin Industrial Corporation, China. Average particle size of TiO2 nanoparticles is 5e10, 25, 60 and 100 nm, and corresponding the average surface area is 195, 172, 100 and 80 m2/g, respectively. The average particle size of ZnO nanoparticles is 20e30, 30e40 and 40e50 nm, and corresponding the average surface area is 83, 59 and 45 m2/g, respectively. SiC nanoparticles were prepared as follows: Si powder, SiO2 particles and MWCNTs were ground together for an hour in a corundum crucible according to the molar ratio of 1:1:4. After the uniform mixture was obtained, put the mixture in a sintering furnace at different temperature (1400 C, 1450 C, 1500 C and 1600 C) in argon with a flow rate of 10 L/h as protective gas. The products were cooled to room temperature and then heated to 700 C in air with a flow rate of 5 C/ min for 8 h to remove residual carbon [2]. In all tests, the average SiC particle size is close to 40 nm and the average surface area is about 102 m2/g.
Bacterium and medium
Analytical methods
The photo-fermentative bacterium Rhodopseudomonas sp. nov. strain A7 was isolated from the sludge of a bioreactor in the
Biogas was sampled from the head space of the reactor using gas-tight glass syringes, and the content of hydrogen was
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 4 2 ( 2 0 1 7 ) 1 8 2 7 9 e1 8 2 8 7
determined using a gas chromatograph (Agilent 4890D, Agilent Technologies, USA). The gas chromatograph column utilized was an Alltech Molesieve 5A 80/100. Argon was used as the carrier gas with a flow rate of 30 mL/min. The temperatures of the oven, injection, detector and filament were 35, 120, 120, and 140 C, respectively. The bacterial concentration (OD660) was measured using a visible spectrophotometer (Unic 7200, Unic Shanghai Instrument Company, Shanghai, China). OD660 is measured by the visible spectrophotometer at 660 nm of wavelength. It is linear with the bacterial concentration, thus the value of OD660 can indicate the biomass in the reactor. The acetate concentration was performed using a gas chromatograph (Agilent 7890A, Agilent Technologies, USA) with a flame ionization detector and nitrogen was used as carrier gas. The samples were centrifuged at 5000 rpm for 10 min and then acidified with methanoic acid. The light intensity was measured using a solar power meter TENMARS TM-207 (Tenmars Electronics Co., Ltd., Taiwan, China). The surface area and particle size data of TiO2, ZnO or SiC nanoparticles is measured by BET micropore analyzer (ASAP2020, Micromeritics, USA) and nano-size analyzer (Nano-S, Malvern, England). The hydrogen yield can be calculated by the number of moles of hydrogen produced by consuming per mole acetate in hydrogen production stage. And the number
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of moles of hydrogen can be obtained via dividing the hydrogen volume by the molar volume of the gas.
Results and discussion The effect of concentration of TiO2 nanoparticles on hydrogen production To investigate the effect of concentration of TiO2 nanoparticles on hydrogen production performance of strain A7, TiO2 nanoparticles at 0, 100, 200, 300, 400 and 500 mg/L were added to the reactors. The particle size of TiO2 was 25 nm in this test. The bacteria without nanoparticles were used as the control. Experimental results showed that cumulative hydrogen volume of the control was 1781 mL-H2/L-culture at 0 mg/L nano-TiO2 and no hydrogen was produced when only TiO2 nanoparticles were present in the medium without photo-fermentative bacteria. This indicated that TiO2 did not show any photocatalytic activity for hydrogen production from water. When the concentration of TiO2 nanoparticles increased from 100 to 300 mg/L, cumulative hydrogen volume increased gradually and reached a maximum value of 2052 mL-H2/L-culture at the concentration of 300 mg/L, which
Fig. 1 e The effect of concentration of TiO2 nanoparticles on hydrogen production.
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was higher than that of the control. When the concentration further increased to 400 and 500 mg/L, photo-hydrogen production was inhibited obviously. Therefore, the addition of TiO2 nanoparticles at suitable concentration in the medium could improve hydrogen production. The effects of concentration of TiO2 nanoparticles on average hydrogen content, OD660nm, acetate concentration and hydrogen yield by strain A7 showed in Fig. 1AeD. The results indicated that average hydrogen content, OD660nm and acetate consumption achieved the maximum value 82.4%, 4.09 and 30.5 mmol/L at 300 mg/L of TiO2 nanoparticles, respectively. The results implied that TiO2 nanoparticles in the hydrogen production system could improve average hydrogen content, bacterial cell growth and conversion efficiency of substrate. Hydrogen yield of 2.76 mol-H2/mol-acetate was achieved at 300 mg/L TiO2 nanoparticles. The hydrogen production rate was enhanced by 1.54 folds when the optimal concentration of TiO2 nanoparticles was at 60 mg/ mL [14]. In another study, the hydrogen yield of photofermentation bacteria increased by 46.1% using 100 mg/L nano-TiO2 [13]. In different studies, TiO2 nanoparticles can
improve bacterial hydrogen production ability, although their optimal concentration had some difference. The excessive addition of TiO2 nanoparticles prevented light penetration of incandescent lamps into the medium and bacteria cannot well absorb light energy for hydrogen production, so bacterial growth and hydrogen production were inhibited.
The effect of particle size of TiO2 nanoparticles on hydrogen production The effect of particle size of TiO2 nanoparticles on hydrogen production by strain A7 was also studied at the concentration of 300 mg/L. The particle sizes of 5e10, 25, 60 and 100 nm were used in the experiments (Fig. 2A). When the particle size of TiO2 nanoparticles was 5e10, 25 and 60 nm, and hydrogen volume of strain A7 was 1915, 2174 and 1968 mL-H2/L-culture, respectively, which was higher than the control (1864 mL-H2/ L-culture). When the particle size of TiO2 nanoparticles was 25 nm, strain A7 obtained the maximum hydrogen volume. The particle size of 100 nm TiO2 nanoparticles significantly inhibited the bacterial cell growth and hydrogen production
Fig. 2 e The effect of particle size of TiO2 nanoparticles on hydrogen production.
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performance. No references reported the effect of the particle size of TiO2 nanoparticles on the photo-fermentative hydrogen production. The effects of particle size of TiO2 nanoparticles on average hydrogen content, OD660nm, acetate consumption and hydrogen yield were shown in Fig. 2AeD. The maximum value achieved 82%, 4.18, 34.5 mmol/L and 2.81 mol-H2/mol-acetate at 25 nm TiO2 nanoparticles, respectively. When TiO2 nanoparticles were in the appropriate particle size range, the light absorption and biomass of strain A7 were improved obviously. The oversize of TiO2 had remarkably negative effect on hydrogen production and growth of strain A7.
The effect of concentration of ZnO nanoparticles on hydrogen production The effect of nano ZnO concentrations of (50, 100, 150, 200, 250 and 300 mg/L) on hydrogen production by strain A7 was investigated in this study (Fig. 3). The results indicated that cumulative hydrogen of strain A7 without nanoparticles increased with time and reached to the maximum value 1800 mL-H2/L-culture. The experiments showed that no hydrogen was produced when sole ZnO nanoparticles were
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added in the medium without photo-fermentation bacteria, which was similar to TiO2 nanoparticles. The cumulative hydrogen increased from 1730 mL-H2/L-culture at concentration of 50 mg/L to 1919 mL-H2/L-culture at 100 mg/L. When the concentration of ZnO nanoparticles was further increased over 150 mg/L, hydrogen production was significantly inhibited and hydrogen yield decreased sharply. This indicated that the excessive ZnO nanoparticles also seriously inhibited the bacterial cell growth, so hydrogen production was at lower level. In addition, the different particle size (20e30, 30e40 and 40e50 nm) did not remarkably affect the photo-fermentative hydrogen production (data did not showed). ZnO nanoparticles can improve photo-hydrogen production at concentration of 100 mg/L, this may be due to its excellent chemical stability and lower toxicity.
The effect of concentration of SiC nanoparticles on hydrogen production The effects of concentration of SiC nanoparticles on hydrogen content, OD660nm, acetate consumption and hydrogen yield showed in Fig. 4AeD. The maximum value achieved 84.1%, 4.18, 35.3 mmol/L and 2.82 mol-H2/mol-
Fig. 3 e The effect of concentration of ZnO nanoparticles on hydrogen production.
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acetate at 200 mg/L SiC nanoparticles, respectively. The trend of hydrogen production and substrate utilization was similar at SiC concentration of 100 mg/L and 300 mg/L, which was lower than that of 200 mg/L (Fig. 4A). When the concentration of SiC nanoparticles further increased to 400 mg/ L, the hydrogen yield and final biomass of the strain A7 decreased quickly and reached minimum value. And acetate utilization efficiency of strain A7 was lower than that of other concentration (Fig. 4C). This may be ascribed to low light penetration caused by a lot of SiC nanoparticles, which inhibited bacterial cells growth and hydrogen production activity. In addition, alone SiC still did not occur photocatalysis reaction from water to hydrogen.
The effect of SiC nanoparticles preparing temperature on hydrogen production The preparing temperature of SiC nanoparticles was a key parameter determining their performance. The effect of preparing temperature on hydrogen production by strain A7 was investigated at the SiC concentration of 200 mg/L, and the
temperatures of 1400 C, 1450 C, 1500 C and 1600 C were used to synthesize SiC nanoparticles in the experiments (Fig. 5AeD). Hydrogen production capacity of strain A7 increased with the increase of synthetic temperature in the range of 1400 Ce1500 C, and then decreased at 1600 C. The maximum cumulative volume of 2272 mL-H2/L-culture occurred at 1500 C and maximum biomass was obtained (Fig. 5D). Therefore, SiC nanoparticles syntheses at a temperature of 1500 C possessed excellent performance and can significantly enhance the bacterial cell growth and hydrogen production. The average hydrogen content, OD660nm, acetate consumption and hydrogen yield reached 85.2%, 4.18, 33.9 mmol/ L and 2.99 mol-H2/mol-acetate at synthetic temperature of 1500 C and SiC nanoparticles concentration of 200 mg/L, respectively (Fig. 5AeD). SiC nanoparticles had obvious effect on hydrogen production and cell growth of strain A7 when they were synthesized in the appropriate temperature. At the same time, this work observed that the aggregation ability of strain A7 was improved, and which was helpful for enhancing bacterial biomass [22]. So, hydrogen production by strain A7 was enhanced significantly.
Fig. 4 e The effect of concentration of SiC nanoparticles on hydrogen production.
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Fig. 5 e The effect of preparing temperature of SiC nanoparticles on hydrogen production.
The comparisons of photo-hydrogen production of strain A7 by the addition of TiO2, ZnO and SiC nanoparticles The comparisons of photo-hydrogen production by strain A7 by the addition of TiO2, ZnO and SiC nanoparticles were shown in Table 1. Results showed that three nanoparticles could improve the hydrogen production performance and cell growth of strain A7. The reason may be due to bacterial enzyme and metabolite activity were increased by the
addition of nanoparticles, which resulted in the enhancement of biomass, hydrogen production and conversion efficiency of organic substrate. The activity of key enzyme (nitrogenase) for photo-hydrogen production was obviously promoted when the nanoparticles presented in photofermentation system, and H2-uptake hydrogenase activity was decreased [13]. In addition, nanoparticles can absorb light energy and this may be helpful for promoting electrons transfer in photosynthetic system of photo-fermentative
Table 1 e The comparison of hydrogen production of strain A7 with TiO2, ZnO and SiC nanoparticles. Sample
The control Strain A7 þ TiO2 (300 mg/L) Strain A7 þ ZnO (100 mg/L) Strain A7 þ SiC (200 mg/L)
H2 volume mL-H2/L 1860 2174 1919 2272
± ± ± ±
15 30 35 23
H2 content %
81.4 ± 1.6 82 ± 1.0 81.3 ± 0.8 85.2 ± 0.5
Biomass (OD660) 3.52 4.18 4.11 4.18
± 0.2 ± 0.1 ± 0.2 ± 0.1
Acetate consumption mmol/L
H2 yield mol-H2/mol-acetate
End pH
32 ± 1.1 34.5 ± 0.8 32.3 ± 0.7 33.8 ± 0.5
2.6 ± 0.02 2.81 ± 0.03 2.64 ± 0.07 2.99 ± 0.01
7.53 7.57 7.61 7.54
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bacteria and enhancing hydrogen production rate. Therefore, total hydrogen yield and maximum hydrogen production rate were increased. Besides, ZnO and SiC nanoparticles were first applied in photo-fermentative hydrogen production, and they showed great potential for improving hydrogen production performance. The results found that hydrogen production by the addition of SiC nanoparticles was higher than that of TiO2 and ZnO nanoparticles. At the same time, the concentration of nanoparticles was different at individual optimal hydrogen production condition. The same concentration of TiO2, ZnO and SiC nanoparticles resulted in different hydrogen yield. These also implied that different character of nano-materials led to diverse hydrogen production ability. SiC is a narrow-band-gap semiconductor which has a much better ability of visible light absorption [23], so it can promote bacteria absorbing light energy and increase light energy conversion efficiency of strain A7. When SiC nanoparticles existed in the photo-fermentation system, the maximum hydrogen volume, hydrogen content and hydrogen yield of the strain A7 were obtained. And the cumulative hydrogen volume was increased by 18.6% compared with the controls and hydrogen yield reached 2.99 mol-H2/ mol-acetate. Thus, it was concluded that SiC nanoparticles in the photo-fermentation hydrogen production system showed best ability of promoting hydrogen production, but did not present any photocatalytic activity from water or organic substrate. SiC can split water to hydrogen under visible light in a very low efficiency (24.9 mL/g h) [21]. So, future study will investigate the mechanism of promoting hydrogen production in detail and how to achieve simultaneous photocatalysis of SiC nanoparticles from water and photo-fermentation of the strain A7 for further enhancing hydrogen production performance and wastewater treatment efficiency.
Conclusion This work investigated photo-fermentative hydrogen production of Rhodopseudomonas sp. nov. strain A7 by the addition of TiO2, ZnO and SiC photocatalytic nanoparticles. Experimental results indicated that hydrogen production could be enhanced by the addition of three different nanoparticles. The SiC nanoparticles were the best for enhancing hydrogen production and cell growth of strain A7. The maximum hydrogen volume, average hydrogen content, hydrogen yield achieved 2272 mL-H2/L-culture, 85.2% and 2.99 mol-H2/mol-acetate, respectively. So, combining photocatalytic nanoparticles with photo-fermentative bacteria is an efficient and potential way for improving hydrogen production.
Acknowledgements This study is supported by the National Natural Science Foundation of China (No. 51678186 and 51478139), National High Technology Research and Development Program of China (863 Program) (grant no. 2011AA060905) and the
Postdoctoral Scientific Developmental Fund of Heilong Jiang Province (No. LBH-Q16080).
references
[1] Turner JA. Sustainable hydrogen production. Science 2004;305(5686):972e4. [2] Bartels JR, Pate MB, Olson NK. An economic survey of hydrogen production from conventional and alternative energy sources. Int J Hydrogen Energy 2010;35(16):8371e84. [3] Keskin T, Abo-Hashesh M, Hallenbeck PC. Photofermentative hydrogen production from wastes. Bioresour Technol 2011;102(18):8557e68. [4] Hallenbeck PC, Abo-Hashesh M, Ghosh D. Strategies for improving biological hydrogen production. Bioresour Technol 2012;110:1e9. _ Gu¨ndu¨z U, Yucel M, Turker L. Aspects of the lu I, [5] Koku H, Erog metabolism of hydrogen production by Rhodobacter sphaeroides. Int J Hydrogen Energy 2002;27(11):1315e29. [6] Keskin T, Hallenbeck PC. Hydrogen production from sugar industry wastes using single-stage photofermentation. Bioresour Technol 2012;112:131e6. [7] Kudo A, Miseki Y. Heterogeneous photocatalyst materials for water splitting. Chem Soc Rev 2009;38(1):253e78. [8] Maeda K. Photocatalytic water splitting using semiconductor particles: history and recent developments. J Photochem Photobiol C Photochem Rev 2011;12(4):237e68. [9] Nakata K, Fujishima A. TiO2 photocatalysis: design and applications. J Photochem Photobiol C Photochem Rev 2012;13(3):169e89. [10] Maruthamuthu P, Muthu S, Gurunathan K, Ashokkumar M, Ashokkumar MVC. Photobiocatalysis: hydrogen evolution using a semiconductor coupled with photosynthetic bacteria. Int J Hydrogen Energy 1992;17(11):863e6. [11] Nikandrov VV, Shlyk MA, Zorin NA, Gogotov IN, Krasnovsky AA. Efficient photoinduced electron transfer from inorganic semiconductor TiO2 to bacterial hydrogenase. FEBS Lett 1988;234(1):111e4. [12] Gurunathan K. Photobiocatalytic production of hydrogen using sensitized TiO2-MV2þ system coupled Rhodopseudomonas capsulate. J Mol Catal A Chem 2000;156(1):59e67. [13] Zhao YX, Chen YG. Nano-TiO2 enhanced photofermentative hydrogen produced from the dark fermentation liquid of waste activated sludge. Environ Sci Technol 2011;45:8589e95. [14] Pandey A, Gupta K, Ashutosh P. Effect of nanosized TiO2 on photofermentation by Rhodobacter sphaeroides NMBL-02. Biomass Bioenergy 2015;72(1):273e9. [15] Liu BF, Jin YR, Cui QF, Xie GJ, Wu YN, Ren NQ. Photofermentation hydrogen production by Rhodopseudomonas sp. nov. strain A7 isolated from the sludge in a bioreactor. Int J Hydrogen Energy 2015;40(28):8661e8. [16] Gupta SM, Tripathi M. A review of TiO2 nanoparticles. Chin Sci Bull 2011;56(16):1639e57. [17] Ren HY, Liu BF, Xie GJ, Zhao L, Ren NQ. Carrier modification and its application in continuous photo-hydrogen production using anaerobic fluidized bed photo-reactor. GCB Bioenergy 2014;6(5):621e8. [18] Chen CY, Saratale GD, Lee CM, Chen PC, Chang JS. Phototrophic hydrogen production in photobioreactors coupled with solar-energy-excited optical fibers. Int J Hydrogen Energy 2008;33(23):6878e85. [19] Chen CY, Lee CM, Chang JS. Feasibility study on bioreactor strategies for enhanced photohydrogen production from Rhodopseudomonas palustris WP3e5 using optical-fiber-
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 4 2 ( 2 0 1 7 ) 1 8 2 7 9 e1 8 2 8 7
assisted illumination systems. Int J Hydrogen Energy 2006;31(15):2345e55. [20] Ren NQ, Liu BF, Ding J, Xie GJ. Hydrogen production with R. faecalis RLD-53 isolated from freshwater pond sludge. Bioresour Technol 2009;100:484e7. [21] Gao YT, Wang YQ, Wang YX. Photocatalytic hydrogen evolution from water on SiC under visible light irradiation. React Kinet Catal Lett 2007;91:12e9.
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[22] Xie GJ, Liu BF, Xing DF, Nan J, Ding J, Ren NQ. Photofermentative bacteria aggregation triggered by L-cysteine during hydrogen production. Biotechnol Biofuels 2013;6:64. [23] Li Y, Yu ZM, Meng JL, Li YD. Enhancing the activity of a SiCTiO2 composite catalyst for photo-stimulated catalytic water splitting. Int J Hydrogen Energy 2013;38:3898e904.
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/he
Enhanced photo-fermentative hydrogen production of Rhodopseudomonas sp. nov. strain A7 by the addition of TiO2, ZnO and SiC nanoparticles Bingfeng Liu a,*, Yaruo Jin a, Zhijiang Wang b, Defeng Xing a, Chao Ma a, Jie Ding a, Nanqi Ren a a
State Key Laboratory of Urban Water Resource and Environment, School of Municipal and Environmental Engineering, Harbin Institute of Technology, P.O. Box 2614, 73 Huanghe Road, Harbin 150090, China b School of Chemical Engineering and Technology, Harbin Institute of Technology, Harbin 150001, China
article info
abstract
Article history:
In order to strengthen photo-fermentative hydrogen production by different photocatalytic
Received 19 January 2017
nanoparticles, hydrogen production by photo-fermentative bacteria with addition of TiO2,
Received in revised form
ZnO and SiC nanoparticles in batch culture were investigated in this study. The results
5 March 2017
indicated that three nanoparticles could improve hydrogen production performance of
Accepted 18 April 2017
Rhodopseudomonas sp. nov. strain A7 under respective optimal conditions. The hydrogen
Available online 8 May 2017
yield of 2.81 mol-H2/mol-acetate was obtained when TiO2 nanoparticles with a concentration of 300 mg/L and size of 25 nm. The concentration of ZnO nanoparticles was at
Keywords:
100 mg/L, hydrogen yield reached 2.64 mol-H2/mol-acetate. Compared with TiO2 and ZnO
Photo-H2 production
nanoparticles, SiC nanoparticles exhibited greatest potential for enhancing photo-
TiO2 nanoparticles
hydrogen production. By addition of nano-SiC with concentration of 200 mg/L which was
ZnO nanoparticles
prepared at temperature of 1500 C, the maximum hydrogen volume, average hydrogen
SiC nanoparticles
content and hydrogen yield of strain A7 were achieved at 2272 mL-H2/L-culture, 85.2% and 2.99 mol-H2/mol-acetate, respectively. And hydrogen production was 18.6% higher than that of alone strain A7 without the addition of nanoparticles. Therefore, the addition of SiC nanoparticles is a promising strategy to improve photo-fermentative hydrogen production from wastewater. © 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Introduction Hydrogen is considered to be a sustainable and clean energy carrier to solve the problem of energy shortage and environment pollution at present [1]. Among diverse hydrogen production technologies, bio-hydrogen production from wastewater and biomass shows great potential in the future [2]. Especially,
photo-fermentative hydrogen production has attracted more attention because of combining wastewater treatment, hydrogen production and solar energy conversion [3]. In addition, photo-fermentative bacteria can use extensive organic substrates (e.g. short chain organic acids, carbohydrate) [4e6]. However, the problems of low hydrogen producing yield and light energy conversion efficiency, the lacking efficient photobioreactors and cheap raw material limit further development
* Corresponding author. Fax: þ86 451 86282008. E-mail address: [email protected] (B. Liu). http://dx.doi.org/10.1016/j.ijhydene.2017.04.147 0360-3199/© 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
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and application of photo-hydrogen production. Thus, many researchers focus on resolving above barriers using different strategies, for example, isolating excellent bacterium [15], optimizing culture condition [20], choosing culture mode [19], using efficient carrier [17] and designing novel bioreactor [18]. Recently, with the rapid development of nanotechnology, a large amount of nano-materials are produced and they are extensively used in hydrogen production, pollutants degradation, sterilization, gas purification and self-cleaning materials [7,8]. Photocatalysis technique based on nanoparticles has become one focus in the 21st century because of using solar energy and degrading organic or inorganic contaminants in environmental fields [9,16]. A novel and exciting method called “photo-biocatalysis” was proposed based on the joint features of both photofermentation and photocatalysis in hydrogen production, in which enzyme system of microorganism cells obtain electrons from photocatalytic semiconductors via methyl viologen as electron-mediator [10]. Thus, a few studies have tried to strengthen photo-fermentative hydrogen production by photocatalytic TiO2 nanoparticles. TiO2 nanoparticles were demonstrated to transfer photoinduced electrons to the enzyme system of Thiocapsa roseopersicina effectively and the hydrogen yield was enhanced up to 10% [11]. Hydrogen production was observed by using the sensitized TiO2, and hydrogen yield by the photocatalytic of sensitized TiO2-MV2þ coupling photo-fermentative bacterium Rhodopseudomonas capsulata was higher than that of the naked TiO2 [12]. Zhao and Chen have reported the enhanced photo-fermentative hydrogen production using the dark fermentation effluents from waste activated sludge with the nano-TiO2 and hydrogen yield increased by 46.1% when the concentration of TiO2 was at 100 mg/L [13]. Pandey investigated the effect of the mixed phase of TiO2 nanoparticles on photo-fermentative hydrogen generation by Rhodobacter sphaeroides NMBL-02 and the cumulative hydrogen volume reached up to 1900 mL/L medium with substrate (malate) conversion efficiency up to 63.27% when TiO2 nanoparticles were added in a batch fermentation system [14]. Therefore, combination of photo-fermentation and photocatalysis showed an important significance for improving photo-hydrogen production, which provided a novel avenue to overcome the limitation of the biochemical pathways in molecular hydrogen production and cell growth of organisms [14]. However, previous studies only focused on TiO2 nanoparticles, the information about screening more efficient photocatalysis nanoparticles for enhancing photo-fermentative hydrogen production is still lacking. Therefore, the key objective of this study is screening more efficient nanoparticles for enhancing photo-fermentative hydrogen production. In this study, TiO2, ZnO and SiC nanoparticles were selected for investigating their effects on the hydrogen production by photofermentative bacteria Rhodopseudomonas sp. nov. strain A7.
Environmental Biological Technology Research Center of HIT, China [1]. The growth medium contained 1 g/L CH3COONa, 1 g/L sodium succinate, 1 g/L yeast extract, 0.5 g/L peptone, 0.5 g/L Lcysteine, 0.5 g/L KH2PO4, 0.5 g/L K2HPO4, 1 g/L NH4Cl, 0.2 g/L MgSO4, 0.08 g/L CaCl2, 0.1 g/L NaCl, 0.012 g/L FeSO4$7H2O, 0.2 g/ L EDTA-Na, 1 mL/L trace element, 1 mL/L vitamin, initial pH 7.0. The hydrogen production medium contained 4.1 g/L CH3COONa, 1.69 g/L sodium glutamate, 1 g/L beef extract, 0.5 g/L L-cysteine, other component was same with above growth medium.
Hydrogen production reactor and culture conditions The hydrogen production experiments were carried out in triplicate with a 100 mL photobioreactor containing a working volume of 60 mL producing hydrogen medium. The reactors were sealed with rubber stoppers and filled with argon to maintain anaerobic conditions. Then bottles with culture medium were autoclaved at 121 C for 15 min. Photofermentative bacterium strain A7 was inoculated into serum bottles with inoculums age of 14 h and volume ratio (V/V) of 10%. Nanoparticles were added into serum bottles according to their concentration. The reactors containing photofermentative bacteria and nanoparticles were shaken in a shaker at 120 rpm and constant temperature of 35 C. The light source used incandescent lamps of 60 W and the light intensity on the surface of reactors maintained at 150 W/m2. Biogas in the photobioreactor was collected by drainage method. The main component of produced biogases is hydrogen and CO2. The total volume of hydrogen was calculated by multiplying total volume of gas by the content of hydrogen.
Preparation of nanoparticles
Material and methods
TiO2 and ZnO nanoparticles with different particle size were purchased from Aladdin Industrial Corporation, China. Average particle size of TiO2 nanoparticles is 5e10, 25, 60 and 100 nm, and corresponding the average surface area is 195, 172, 100 and 80 m2/g, respectively. The average particle size of ZnO nanoparticles is 20e30, 30e40 and 40e50 nm, and corresponding the average surface area is 83, 59 and 45 m2/g, respectively. SiC nanoparticles were prepared as follows: Si powder, SiO2 particles and MWCNTs were ground together for an hour in a corundum crucible according to the molar ratio of 1:1:4. After the uniform mixture was obtained, put the mixture in a sintering furnace at different temperature (1400 C, 1450 C, 1500 C and 1600 C) in argon with a flow rate of 10 L/h as protective gas. The products were cooled to room temperature and then heated to 700 C in air with a flow rate of 5 C/ min for 8 h to remove residual carbon [2]. In all tests, the average SiC particle size is close to 40 nm and the average surface area is about 102 m2/g.
Bacterium and medium
Analytical methods
The photo-fermentative bacterium Rhodopseudomonas sp. nov. strain A7 was isolated from the sludge of a bioreactor in the
Biogas was sampled from the head space of the reactor using gas-tight glass syringes, and the content of hydrogen was
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determined using a gas chromatograph (Agilent 4890D, Agilent Technologies, USA). The gas chromatograph column utilized was an Alltech Molesieve 5A 80/100. Argon was used as the carrier gas with a flow rate of 30 mL/min. The temperatures of the oven, injection, detector and filament were 35, 120, 120, and 140 C, respectively. The bacterial concentration (OD660) was measured using a visible spectrophotometer (Unic 7200, Unic Shanghai Instrument Company, Shanghai, China). OD660 is measured by the visible spectrophotometer at 660 nm of wavelength. It is linear with the bacterial concentration, thus the value of OD660 can indicate the biomass in the reactor. The acetate concentration was performed using a gas chromatograph (Agilent 7890A, Agilent Technologies, USA) with a flame ionization detector and nitrogen was used as carrier gas. The samples were centrifuged at 5000 rpm for 10 min and then acidified with methanoic acid. The light intensity was measured using a solar power meter TENMARS TM-207 (Tenmars Electronics Co., Ltd., Taiwan, China). The surface area and particle size data of TiO2, ZnO or SiC nanoparticles is measured by BET micropore analyzer (ASAP2020, Micromeritics, USA) and nano-size analyzer (Nano-S, Malvern, England). The hydrogen yield can be calculated by the number of moles of hydrogen produced by consuming per mole acetate in hydrogen production stage. And the number
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of moles of hydrogen can be obtained via dividing the hydrogen volume by the molar volume of the gas.
Results and discussion The effect of concentration of TiO2 nanoparticles on hydrogen production To investigate the effect of concentration of TiO2 nanoparticles on hydrogen production performance of strain A7, TiO2 nanoparticles at 0, 100, 200, 300, 400 and 500 mg/L were added to the reactors. The particle size of TiO2 was 25 nm in this test. The bacteria without nanoparticles were used as the control. Experimental results showed that cumulative hydrogen volume of the control was 1781 mL-H2/L-culture at 0 mg/L nano-TiO2 and no hydrogen was produced when only TiO2 nanoparticles were present in the medium without photo-fermentative bacteria. This indicated that TiO2 did not show any photocatalytic activity for hydrogen production from water. When the concentration of TiO2 nanoparticles increased from 100 to 300 mg/L, cumulative hydrogen volume increased gradually and reached a maximum value of 2052 mL-H2/L-culture at the concentration of 300 mg/L, which
Fig. 1 e The effect of concentration of TiO2 nanoparticles on hydrogen production.
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was higher than that of the control. When the concentration further increased to 400 and 500 mg/L, photo-hydrogen production was inhibited obviously. Therefore, the addition of TiO2 nanoparticles at suitable concentration in the medium could improve hydrogen production. The effects of concentration of TiO2 nanoparticles on average hydrogen content, OD660nm, acetate concentration and hydrogen yield by strain A7 showed in Fig. 1AeD. The results indicated that average hydrogen content, OD660nm and acetate consumption achieved the maximum value 82.4%, 4.09 and 30.5 mmol/L at 300 mg/L of TiO2 nanoparticles, respectively. The results implied that TiO2 nanoparticles in the hydrogen production system could improve average hydrogen content, bacterial cell growth and conversion efficiency of substrate. Hydrogen yield of 2.76 mol-H2/mol-acetate was achieved at 300 mg/L TiO2 nanoparticles. The hydrogen production rate was enhanced by 1.54 folds when the optimal concentration of TiO2 nanoparticles was at 60 mg/ mL [14]. In another study, the hydrogen yield of photofermentation bacteria increased by 46.1% using 100 mg/L nano-TiO2 [13]. In different studies, TiO2 nanoparticles can
improve bacterial hydrogen production ability, although their optimal concentration had some difference. The excessive addition of TiO2 nanoparticles prevented light penetration of incandescent lamps into the medium and bacteria cannot well absorb light energy for hydrogen production, so bacterial growth and hydrogen production were inhibited.
The effect of particle size of TiO2 nanoparticles on hydrogen production The effect of particle size of TiO2 nanoparticles on hydrogen production by strain A7 was also studied at the concentration of 300 mg/L. The particle sizes of 5e10, 25, 60 and 100 nm were used in the experiments (Fig. 2A). When the particle size of TiO2 nanoparticles was 5e10, 25 and 60 nm, and hydrogen volume of strain A7 was 1915, 2174 and 1968 mL-H2/L-culture, respectively, which was higher than the control (1864 mL-H2/ L-culture). When the particle size of TiO2 nanoparticles was 25 nm, strain A7 obtained the maximum hydrogen volume. The particle size of 100 nm TiO2 nanoparticles significantly inhibited the bacterial cell growth and hydrogen production
Fig. 2 e The effect of particle size of TiO2 nanoparticles on hydrogen production.
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performance. No references reported the effect of the particle size of TiO2 nanoparticles on the photo-fermentative hydrogen production. The effects of particle size of TiO2 nanoparticles on average hydrogen content, OD660nm, acetate consumption and hydrogen yield were shown in Fig. 2AeD. The maximum value achieved 82%, 4.18, 34.5 mmol/L and 2.81 mol-H2/mol-acetate at 25 nm TiO2 nanoparticles, respectively. When TiO2 nanoparticles were in the appropriate particle size range, the light absorption and biomass of strain A7 were improved obviously. The oversize of TiO2 had remarkably negative effect on hydrogen production and growth of strain A7.
The effect of concentration of ZnO nanoparticles on hydrogen production The effect of nano ZnO concentrations of (50, 100, 150, 200, 250 and 300 mg/L) on hydrogen production by strain A7 was investigated in this study (Fig. 3). The results indicated that cumulative hydrogen of strain A7 without nanoparticles increased with time and reached to the maximum value 1800 mL-H2/L-culture. The experiments showed that no hydrogen was produced when sole ZnO nanoparticles were
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added in the medium without photo-fermentation bacteria, which was similar to TiO2 nanoparticles. The cumulative hydrogen increased from 1730 mL-H2/L-culture at concentration of 50 mg/L to 1919 mL-H2/L-culture at 100 mg/L. When the concentration of ZnO nanoparticles was further increased over 150 mg/L, hydrogen production was significantly inhibited and hydrogen yield decreased sharply. This indicated that the excessive ZnO nanoparticles also seriously inhibited the bacterial cell growth, so hydrogen production was at lower level. In addition, the different particle size (20e30, 30e40 and 40e50 nm) did not remarkably affect the photo-fermentative hydrogen production (data did not showed). ZnO nanoparticles can improve photo-hydrogen production at concentration of 100 mg/L, this may be due to its excellent chemical stability and lower toxicity.
The effect of concentration of SiC nanoparticles on hydrogen production The effects of concentration of SiC nanoparticles on hydrogen content, OD660nm, acetate consumption and hydrogen yield showed in Fig. 4AeD. The maximum value achieved 84.1%, 4.18, 35.3 mmol/L and 2.82 mol-H2/mol-
Fig. 3 e The effect of concentration of ZnO nanoparticles on hydrogen production.
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acetate at 200 mg/L SiC nanoparticles, respectively. The trend of hydrogen production and substrate utilization was similar at SiC concentration of 100 mg/L and 300 mg/L, which was lower than that of 200 mg/L (Fig. 4A). When the concentration of SiC nanoparticles further increased to 400 mg/ L, the hydrogen yield and final biomass of the strain A7 decreased quickly and reached minimum value. And acetate utilization efficiency of strain A7 was lower than that of other concentration (Fig. 4C). This may be ascribed to low light penetration caused by a lot of SiC nanoparticles, which inhibited bacterial cells growth and hydrogen production activity. In addition, alone SiC still did not occur photocatalysis reaction from water to hydrogen.
The effect of SiC nanoparticles preparing temperature on hydrogen production The preparing temperature of SiC nanoparticles was a key parameter determining their performance. The effect of preparing temperature on hydrogen production by strain A7 was investigated at the SiC concentration of 200 mg/L, and the
temperatures of 1400 C, 1450 C, 1500 C and 1600 C were used to synthesize SiC nanoparticles in the experiments (Fig. 5AeD). Hydrogen production capacity of strain A7 increased with the increase of synthetic temperature in the range of 1400 Ce1500 C, and then decreased at 1600 C. The maximum cumulative volume of 2272 mL-H2/L-culture occurred at 1500 C and maximum biomass was obtained (Fig. 5D). Therefore, SiC nanoparticles syntheses at a temperature of 1500 C possessed excellent performance and can significantly enhance the bacterial cell growth and hydrogen production. The average hydrogen content, OD660nm, acetate consumption and hydrogen yield reached 85.2%, 4.18, 33.9 mmol/ L and 2.99 mol-H2/mol-acetate at synthetic temperature of 1500 C and SiC nanoparticles concentration of 200 mg/L, respectively (Fig. 5AeD). SiC nanoparticles had obvious effect on hydrogen production and cell growth of strain A7 when they were synthesized in the appropriate temperature. At the same time, this work observed that the aggregation ability of strain A7 was improved, and which was helpful for enhancing bacterial biomass [22]. So, hydrogen production by strain A7 was enhanced significantly.
Fig. 4 e The effect of concentration of SiC nanoparticles on hydrogen production.
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Fig. 5 e The effect of preparing temperature of SiC nanoparticles on hydrogen production.
The comparisons of photo-hydrogen production of strain A7 by the addition of TiO2, ZnO and SiC nanoparticles The comparisons of photo-hydrogen production by strain A7 by the addition of TiO2, ZnO and SiC nanoparticles were shown in Table 1. Results showed that three nanoparticles could improve the hydrogen production performance and cell growth of strain A7. The reason may be due to bacterial enzyme and metabolite activity were increased by the
addition of nanoparticles, which resulted in the enhancement of biomass, hydrogen production and conversion efficiency of organic substrate. The activity of key enzyme (nitrogenase) for photo-hydrogen production was obviously promoted when the nanoparticles presented in photofermentation system, and H2-uptake hydrogenase activity was decreased [13]. In addition, nanoparticles can absorb light energy and this may be helpful for promoting electrons transfer in photosynthetic system of photo-fermentative
Table 1 e The comparison of hydrogen production of strain A7 with TiO2, ZnO and SiC nanoparticles. Sample
The control Strain A7 þ TiO2 (300 mg/L) Strain A7 þ ZnO (100 mg/L) Strain A7 þ SiC (200 mg/L)
H2 volume mL-H2/L 1860 2174 1919 2272
± ± ± ±
15 30 35 23
H2 content %
81.4 ± 1.6 82 ± 1.0 81.3 ± 0.8 85.2 ± 0.5
Biomass (OD660) 3.52 4.18 4.11 4.18
± 0.2 ± 0.1 ± 0.2 ± 0.1
Acetate consumption mmol/L
H2 yield mol-H2/mol-acetate
End pH
32 ± 1.1 34.5 ± 0.8 32.3 ± 0.7 33.8 ± 0.5
2.6 ± 0.02 2.81 ± 0.03 2.64 ± 0.07 2.99 ± 0.01
7.53 7.57 7.61 7.54
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bacteria and enhancing hydrogen production rate. Therefore, total hydrogen yield and maximum hydrogen production rate were increased. Besides, ZnO and SiC nanoparticles were first applied in photo-fermentative hydrogen production, and they showed great potential for improving hydrogen production performance. The results found that hydrogen production by the addition of SiC nanoparticles was higher than that of TiO2 and ZnO nanoparticles. At the same time, the concentration of nanoparticles was different at individual optimal hydrogen production condition. The same concentration of TiO2, ZnO and SiC nanoparticles resulted in different hydrogen yield. These also implied that different character of nano-materials led to diverse hydrogen production ability. SiC is a narrow-band-gap semiconductor which has a much better ability of visible light absorption [23], so it can promote bacteria absorbing light energy and increase light energy conversion efficiency of strain A7. When SiC nanoparticles existed in the photo-fermentation system, the maximum hydrogen volume, hydrogen content and hydrogen yield of the strain A7 were obtained. And the cumulative hydrogen volume was increased by 18.6% compared with the controls and hydrogen yield reached 2.99 mol-H2/ mol-acetate. Thus, it was concluded that SiC nanoparticles in the photo-fermentation hydrogen production system showed best ability of promoting hydrogen production, but did not present any photocatalytic activity from water or organic substrate. SiC can split water to hydrogen under visible light in a very low efficiency (24.9 mL/g h) [21]. So, future study will investigate the mechanism of promoting hydrogen production in detail and how to achieve simultaneous photocatalysis of SiC nanoparticles from water and photo-fermentation of the strain A7 for further enhancing hydrogen production performance and wastewater treatment efficiency.
Conclusion This work investigated photo-fermentative hydrogen production of Rhodopseudomonas sp. nov. strain A7 by the addition of TiO2, ZnO and SiC photocatalytic nanoparticles. Experimental results indicated that hydrogen production could be enhanced by the addition of three different nanoparticles. The SiC nanoparticles were the best for enhancing hydrogen production and cell growth of strain A7. The maximum hydrogen volume, average hydrogen content, hydrogen yield achieved 2272 mL-H2/L-culture, 85.2% and 2.99 mol-H2/mol-acetate, respectively. So, combining photocatalytic nanoparticles with photo-fermentative bacteria is an efficient and potential way for improving hydrogen production.
Acknowledgements This study is supported by the National Natural Science Foundation of China (No. 51678186 and 51478139), National High Technology Research and Development Program of China (863 Program) (grant no. 2011AA060905) and the
Postdoctoral Scientific Developmental Fund of Heilong Jiang Province (No. LBH-Q16080).
references
[1] Turner JA. Sustainable hydrogen production. Science 2004;305(5686):972e4. [2] Bartels JR, Pate MB, Olson NK. An economic survey of hydrogen production from conventional and alternative energy sources. Int J Hydrogen Energy 2010;35(16):8371e84. [3] Keskin T, Abo-Hashesh M, Hallenbeck PC. Photofermentative hydrogen production from wastes. Bioresour Technol 2011;102(18):8557e68. [4] Hallenbeck PC, Abo-Hashesh M, Ghosh D. Strategies for improving biological hydrogen production. Bioresour Technol 2012;110:1e9. _ Gu¨ndu¨z U, Yucel M, Turker L. Aspects of the lu I, [5] Koku H, Erog metabolism of hydrogen production by Rhodobacter sphaeroides. Int J Hydrogen Energy 2002;27(11):1315e29. [6] Keskin T, Hallenbeck PC. Hydrogen production from sugar industry wastes using single-stage photofermentation. Bioresour Technol 2012;112:131e6. [7] Kudo A, Miseki Y. Heterogeneous photocatalyst materials for water splitting. Chem Soc Rev 2009;38(1):253e78. [8] Maeda K. Photocatalytic water splitting using semiconductor particles: history and recent developments. J Photochem Photobiol C Photochem Rev 2011;12(4):237e68. [9] Nakata K, Fujishima A. TiO2 photocatalysis: design and applications. J Photochem Photobiol C Photochem Rev 2012;13(3):169e89. [10] Maruthamuthu P, Muthu S, Gurunathan K, Ashokkumar M, Ashokkumar MVC. Photobiocatalysis: hydrogen evolution using a semiconductor coupled with photosynthetic bacteria. Int J Hydrogen Energy 1992;17(11):863e6. [11] Nikandrov VV, Shlyk MA, Zorin NA, Gogotov IN, Krasnovsky AA. Efficient photoinduced electron transfer from inorganic semiconductor TiO2 to bacterial hydrogenase. FEBS Lett 1988;234(1):111e4. [12] Gurunathan K. Photobiocatalytic production of hydrogen using sensitized TiO2-MV2þ system coupled Rhodopseudomonas capsulate. J Mol Catal A Chem 2000;156(1):59e67. [13] Zhao YX, Chen YG. Nano-TiO2 enhanced photofermentative hydrogen produced from the dark fermentation liquid of waste activated sludge. Environ Sci Technol 2011;45:8589e95. [14] Pandey A, Gupta K, Ashutosh P. Effect of nanosized TiO2 on photofermentation by Rhodobacter sphaeroides NMBL-02. Biomass Bioenergy 2015;72(1):273e9. [15] Liu BF, Jin YR, Cui QF, Xie GJ, Wu YN, Ren NQ. Photofermentation hydrogen production by Rhodopseudomonas sp. nov. strain A7 isolated from the sludge in a bioreactor. Int J Hydrogen Energy 2015;40(28):8661e8. [16] Gupta SM, Tripathi M. A review of TiO2 nanoparticles. Chin Sci Bull 2011;56(16):1639e57. [17] Ren HY, Liu BF, Xie GJ, Zhao L, Ren NQ. Carrier modification and its application in continuous photo-hydrogen production using anaerobic fluidized bed photo-reactor. GCB Bioenergy 2014;6(5):621e8. [18] Chen CY, Saratale GD, Lee CM, Chen PC, Chang JS. Phototrophic hydrogen production in photobioreactors coupled with solar-energy-excited optical fibers. Int J Hydrogen Energy 2008;33(23):6878e85. [19] Chen CY, Lee CM, Chang JS. Feasibility study on bioreactor strategies for enhanced photohydrogen production from Rhodopseudomonas palustris WP3e5 using optical-fiber-
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 4 2 ( 2 0 1 7 ) 1 8 2 7 9 e1 8 2 8 7
assisted illumination systems. Int J Hydrogen Energy 2006;31(15):2345e55. [20] Ren NQ, Liu BF, Ding J, Xie GJ. Hydrogen production with R. faecalis RLD-53 isolated from freshwater pond sludge. Bioresour Technol 2009;100:484e7. [21] Gao YT, Wang YQ, Wang YX. Photocatalytic hydrogen evolution from water on SiC under visible light irradiation. React Kinet Catal Lett 2007;91:12e9.
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[22] Xie GJ, Liu BF, Xing DF, Nan J, Ding J, Ren NQ. Photofermentative bacteria aggregation triggered by L-cysteine during hydrogen production. Biotechnol Biofuels 2013;6:64. [23] Li Y, Yu ZM, Meng JL, Li YD. Enhancing the activity of a SiCTiO2 composite catalyst for photo-stimulated catalytic water splitting. Int J Hydrogen Energy 2013;38:3898e904.