Photocatalytic hydrogen production over nanostructured mesoporous titania from olive mill wastewater

Desalination 267 (2011) 250–255

Contents lists available at ScienceDirect

Desalination j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / d e s a l

Photocatalytic hydrogen production over nanostructured mesoporous titania from olive mill wastewater Mohamed I. Badawy a, Montaser Y. Ghaly b, Mohamed E.M. Ali a,⁎ a b

Water Pollution Research Department, Environmental Sciences Division, National Research Centre (NRC), El-Tahrir Street, Dokki, Cairo, Egypt Chemical Engineering and Pilot Plant Department, Energy Group, Centre of Excellence, National Research Centre (NRC), El-Tahrir Street, Dokki, Cairo, Egypt

a r t i c l e

i n f o

Article history: Received 6 July 2010 Received in revised form 20 September 2010 Accepted 21 September 2010 Available online 30 October 2010 Keywords: Photocatalytic degradation Hydrogen production Wastewater Organic pollutant Photocatalyst

a b s t r a c t In this study, nanostructure mesoporous titania (TiO2) was prepared using sol–gel method from titanium tetrachloride. The prepared titania was characterized by X-ray diffraction (XRD). The textural and surface analysis was carried out using nitrogen adsorption–desorption technique. Also, the photocatalytic degradation of olive mill wastewater (OMW) with simultaneous hydrogen production was studied. The influence of catalyst dose and pH value of wastewater on the degradation of organic pollutants in wastewater and on the amount of evolved hydrogen was investigated. It was observed that the maximum amount of evolved hydrogen at a TiO2 dose of 2 g/L and a solution pH value of 3 was (851 mL H2) 38 mmol after 2 h of reaction. On the other hand, chemical oxygen demand (COD) was reduced by 92%. Based on the obtained results, a new process for H2 production from wastewater can be achieved by coupling degradation of organic pollutants with photocatalytic H2 production. The process also provides a method for degradation of organic pollutants with simultaneous H2 production. © 2010 Elsevier B.V. All rights reserved.

1. Introduction The government of Egypt seeks to enhance technological excellence, attract foreign direct investment and become a leader in the export of medium-technology engineering products in the Middle East and North Africa (MENA) region. Renewable energy (RE) is a priority area for short and long-term industrial promotions. Moreover, energy-related environmental problems and likely post-Kyoto emission reduction quotas are becoming increasingly prominent on the policy agenda [1]. Photocatalytic splitting of water to hydrogen and oxygen has been regarded as one of the most promising approaches [2]. The photocatalytic hydrogen production using solar energy is a challenging research topic which has received much attention in recent years for its potential to provide hydrogen as a clean and renewable energy resource even on a large scale [3]. This can be attained mainly by two processes, i.e. either by the direct splitting of water into hydrogen and oxygen [4], or by the photoreforming of organic compounds [5–7]. The latter process, occurring in the absence of oxygen, is very attractive especially when polluted wastewater is used as feed-stock, two goals are being obtained in this case: the abatement of organic pollutants together with the production of hydrogen as energy carrier. In the last decade, different mixed metal oxide semiconductor photocatalysts, also with a rather complex structure, such as layered or differently doped

⁎ Corresponding author. Tel./fax: +20 233371479. E-mail address: [email protected] (M.E.M. Ali). 0011-9164/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2010.09.035

perovskite-based materials, have been proposed for water photosplitting [7–10]. However, titanium dioxide still remains the most suitable photocatalyst, in consideration of its high activity, chemical inertness, low cost and nontoxicity [5,11]. The mechanism of photocatalytic reactions on semiconductors was initiated by the absorption of a photon with energy equal to or greater than the semiconductor bandgap. This promotes an electron from the valence band (VB) to the conduction band (CB), with the consequent formation of an electron (e−CB)–hole (h+VB) pair. The so produced charge carriers can induce the reduction of electron acceptor species and the oxidation of electron donor species, respectively, both adsorbed on the semiconductor surface. In the case of water cleavage, the electron acceptor would be the H+ ion and the electron donor would be H2O according to the following reactions: TiO2 + 2hν→2eCB + 2h −

þ

H2 O + 2h

þ

→1 = 2O2 + 2Hþ

2H + 2eCB →H2 : þ

−

ð1Þ ð2Þ ð3Þ

The overall photocatalytic water splitting for hydrogen production over titania: H2 O + 2hν→H2 + 1 = 2O2 :

ð4Þ

The efficiency of this processes is based on the production of reactive species, such as electron pair (2 e−) that reduce protons to

M.I. Badawy et al. / Desalination 267 (2011) 250–255

produce H2 and also, produce holes (h+), hydroxyl radicals (⁎OH), and superoxide anions (O−⁎ 2 ) which are able to oxidize and mineralise almost all organic pollutants yielding CO2 and inorganic ions as final products according to the following equations: TiO2 + 2hν→2eCB + 2h −

þ

2H2 O + 2h RH + OH RH + 2h

:

þ

:

→O− 2

þ

+ OH

→R

ROH→R*−COOH

+ OH

air to remove excess ammonia. The resulted powder was then dried to make the catalyst. The standard calcination procedure involved purging the reactor with gas for 1 h, heating the powder at a rate of 40 °C/h to 400 °C, and holding the powder at 450 °C for 1 h. Finally the powder was calcined at 450 °C for 4 h.

ð5Þ :

→ROH :

251

2.3. Characterization of photocatalyst ð6Þ ð7Þ

:

Further oxidation

→ H2 O + CO2 :

ð8Þ ð9Þ

Presently, one of the major problems in the exploitation of photocatalytic hydrogen production via water splitting over semiconductors is the low quantum efficiency of the process, consequent to the high probability of photogenerated electron–hole pair recombination. Much effort has been done in the last decades to increase the activity of semiconductor metal oxides, e.g. by adding sacrificial agents that are able to efficiently combine with e−CB or h+VB, or by modifying the photocatalysts by noble metal loading, to favor charge carrier separation. Methanol and other organic compounds may act as sacrificial agents and valence hole scavenger in photocatalysis, being able to combine with photogenerated valence-band holes more efficiently than water. Thus, conduction-band electrons become more readily available for reduction reactions, e.g. hydrogen production from water. The presence of noble metal nanoparticles on the surface of semiconductor metal oxides can increase the electron–hole pair separation, because photopromoted electrons can be captured by the noble metal, if its Fermi level is lower in energy than the CB potential [5]. But, if the sacrificial donors are more expensive than the H2 produced, a good way is to use organic wastes and pollutants in water and wastewater in this role. It is of more interest to combine photocatalytic hydrogen generation with destruction of organic pollutants. Previously, Li et al. [12] reported photocatalytic hydrogen generation in single and complex systems of organic pollutants. Photocatalysis is a promising method for the treatment and purification of polluted water [13,14] and also, hydrogen production. In this work, the source of organic pollutant that acts as sacrificial agent was olive mill wastewater (OMW). Therefore, the main objective of this work is the study of photocatalytic hydrogen production with degradation of olive mill wastewater and the affecting parameter on both photocatalytic hydrogen production and degradation of olive mill wastewater using prepared titania.

The prepared nanopowder was characterized by X-ray diffraction (XRD). The X-ray diffractometer type Philips, model Bruker D8 Advance-Germany, Target Cu Kα, with secondary monochromator V = 40 kV, A = 40 mA, with Ni filter was used to investigate the crystalline phases of the prepared nanopowder. (wavelength = 1.5418 Å). The specific surface area, pore size and pore volume of the samples were measured using a Sorptomatic (Model1990) instrument at 77 K. Prior to the sorptometric experiment, the samples were degassed at 423 K for 12 h. 2.4. Photocatalytic experiments for hydrogen production and wastewater degradation A laboratory photocatalytic oxidation unit was used for the batch experiments. The schematic diagram of the experimental setup used is shown in Fig. 1. It consists of an external stirred vessel of 1 L with a variable speed stirrer, combined with a cylindrical closed photoreactor (0.85 L) which is made from quartz, with a coaxial and immersed medium pressure UV mercury lamp used as the UV emitter and light source (Heraeus TQ150, input energy of 150 W) emitting a polychromatic radiation in the range from 100 to 280 nm wavelength. The lamp emitted a power of 6.2 W in corresponding to 1.32 × 10− 5 Einstein s− 1. The UV lamp is equipped with a cooling water jacket to maintain the temperature of the reaction of wastewater at room temperature. There is one cooling circle for cooling the UV lamp. The UV system is positioned coaxial inside the reactor vessel. The UV system is made from quartz glass, which is available for the transfer of UV irradiation and closed. Definite amounts of different lab preprepared photocatalyst powders were dispersed in a definite volume of olive mill wastewater (OMW) under study at ambient temperature under continuous stirring. The characteristics of OMW are chemical oxygen demand (8410 mg O2/L) and total organic carbon (3150 mg C/L). The wastewater was de-aerated with N2 gas for 30 min before beginning the experiments to remove oxygen and then the solution was illuminated with light from the ultraviolet radiation lamp. Adjusting the pH value of wastewater was carried using H2SO4 (2 M) and NaOH (2 M).

2. Experimental work 2.1. Used materials Titanium chloride (TiCl4) with 99% purity and ammonia solution were supplied by Merck (Germany). Sulphuric acid (98%) and sodium hydroxide pellets (98%) were supplied by Fluka (Germany). 2.2. Laboratory preparation of photocatalysts Titanium dioxide TiO2 powder was synthesized by a conventional sol–gel process. Firstly, TiCl4 was dissolved in water (TiCl4:H2O; 1:4 volume), and ammonia solution was then introduced into the solution until pH reached ca 7.5 to induce precipitation. The resulted gelatinous precipitate was filtered and washed with deionized water to reduce [Cl−] to below 5 × 10− 4 M, as determined by titration against standard solution of silver nitrate, and then dried at 65 °C in

Fig. 1. Experimental setup of photocatalytic hydrogen production with OMW treatment.

252

M.I. Badawy et al. / Desalination 267 (2011) 250–255

2.5. Analytical methods

Table 1 Surface area, porous volume and pore diameter of prepared TiO2.

Periodically, treated samples of 5 mL were withdrawn from the photoreactor and filtered using 0.45 μm membrane filters for the determination of chemical oxygen demand (COD) according to APHA [15]. The evolved gas was collected in gas samplers previously charged by passing N2 as inert gas. The collected gas was detected as hydrogen by GC (Gas Chromatography and Instruments Company), model SIGMA 2B, column: chromatograph 102 stainless steel, detector: Hal wire, carrier gas is nitrogen, detection temperature is 150 °C, oven temp is 50 °C, flow rate is 12 mL/min, and injected sample size is 1 mL. 2.6. Kinetic studies From engineering point of view, it is useful to find out a simple user-friendly rate equation that fits the experimental rate data. So, the kinetics of photocatalytic reaction will be studied. Almost, the photocatalytic degradation of organic pollutants is described by pseudo-first order kinetics follows the pseudo-first order reaction. −

dC = kapp C dt

ð10Þ

By integration this equation at (t = 0, Ct = Cin), Eq. (11) was obtained. − ln

  Ct = kapp t Co

ð11Þ

where kapp is the apparent first order rate constant (min− 1) and Co and Ct is the COD of wastewater at a given irradiation time, t (min), respectively. Kinetic studies were assessed by monitoring the change in the COD level at a certain interval of time (Ct). Apparent first order rate constants (kapp) were determined employing Eq. (11) from the plot of −ln[CODt / CODo] versus irradiation time, t. The kapp was determined by calculating the slope of the line obtained. 3. Results and discussion 3.1. Photocatalyst characterization Nitrogen adsorption–desorption analysis was used to verify the mesoporosity (2–50 nm) and measure the surface area and pore diameter of the particle of the prepared TiO2 photocatalysts. Fig. 2 shows the isotherm of the TiO2 samples due to capillary condensation in mesopores where adsorption is limited for high relative pressure. The isotherms were found to exhibit H4 type hysteresis loop which is a characteristic of mesoporous materials. Since the isotherm shape

Fig. 2. N2 adsorption–desorption isotherms of mesoporous TiO2.

Parameter

SBET (m2/g)

V pore (cm3/g)

Pore diameter (nm)

Particle size (nm)

Criteria

59

0.3160

6.3

19.5

reveals the characteristics of a powder structure, which consists of an assembly of numerous particles with large open packing. The surface area of the prepared TiO2 determined by the BET method is 59 m2/g for TiO2. The porous volume and average pore diameter are listed in Table 1 and pore distribution was shown in Fig. 3. From Table 1, the pore diameter was 6.2 nm indicating mesoporosity of prepared TiO2. This decrease of porosity is probably due to the thermal treatment at 450 °C and to the increase of the crystallinity. Fig. 4 shows XRD patterns according to the synthetic pathway and composition, and photocatalysts with different structural features are obtained. For pure TiO2, prepared by sol–gel method and further submitted to thermal treatment at 450 °C, the diffraction lines present at 25.2°, 37.0°, 37.8°, 38.7°, 48.1°, 53.9°, 55.1°, 62.7° and 68.7° in 2Ø value, correspond to the anatase phase TiO2, which represents the indices of (101), (004) and (200) planes respectively, are conformed to anatase. The presence of an additional set of peaks at 27.6°, 36.2°, 41.1°, 44.2°, 54.4°, 56.8°, 62.9°, 64.2° and 69.2° transduces the formation of the rutile phase. The intensity of peaks related to the two present phases indicates the predominance of the anatase phase in comparison to the rutile phase into the sample. In consequence, the well-prepared pure anatase TiO2 crystal size is calculated from the maximum diffraction peak in Fig. 4 by Scherrer formula [16], (L = K / ßcosØ, where L is the crystallite size, K the Scherrer constant usually taken as 0.89, the wavelength of the X-ray radiation (0.15418 nm for Cu Ka), and ß is the full width half maximum of the diffraction peak measured at 2q), the average particle size of pure TiO2 powders is about 19.5 nm as shown in Table 1. 3.2. Photocatalytic generation of hydrogen with photocatalytic degradation of organic pollutant in OMW In this work, the photocatalytic hydrogen production was carried out over nanostructure mesoporous TiO2 from olive mill wastewater that contains organic pollutants i.e. electron donor. The photocatalytic hydrogen production over mesoporous TiO2 from OMW is governed by the surface area and prohibiting electron–hole recombination. Typical results obtained are shown in Fig. 5 where the amount of evolved H2 is plotted as functions of time of irradiation during 240 min. The amount of H2 produced after 120 min was 21 mmol corresponding to 470 mL (0.18 mmol/min as H2 production rate) and

Fig. 3. Pore size distributions of synthesized mesoporous TiO2.

M.I. Badawy et al. / Desalination 267 (2011) 250–255

253

Relative Intensity (a.u.)

Anatase Rutile

10

20

30

40 2θ

50

60

70

Fig. 4. XRD patterns of the synthesized mesoporous TiO2.

after 240 min, the corresponding value which is 25 mmol corresponding to 560 mL H2 (0.104 mmol/min) is comparable to the previous study [17]. The rate of evolved H2 decreases with time and with prolonged exposure to light due to deactivation of photocatalyst and decrease in organic pollutants. Photocatalytic hydrogen production over large surface area mesoporous nano-titania was increased because photocatalytic activity increases with increasing specific surface area due to the reaction rates being faster than the electron– hole recombination [18] and also, it was enhanced in the presence of organic pollutants where organic pollutants combine with photogenerated holes that can be oxidized and degraded prohibiting draw back recombination of electron–hole [19] and/or O2–H2 back reaction. Since, removal COD was achieved up to 83%. Thus, there is a possibility of photocatalytic degradation of organic pollutants with simultaneous production of H2. Also, in this work, a statistical approach was chosen based on a factorial experimental design that would allow us to infer about the effect of the variables [20]. Three independent variables that may affect the photocatalytic treatment of OMW with hydrogen production were taken into account, namely, TiO2 loading, solution pH and reaction time.

3.3. Effect of initial reaction pH value on amount of evolved hydrogen and OMW degradation

30

100

25

80

20

60

15 40

10

20

5 0

0

10

20

30

45 60 90 Time (mins)

120

180

% Degradation of OMW

Hydrogen Amount (mmole)

3.3.1. Degradation of organic pollutants in OMW The initial pH value of wastewater plays an important role in the photocatalytic degradation of organic compounds over mesoporous prepared TiO2. Fig. 5 demonstrates the effect of pH on the photocatalytic degradation of organic pollutants in OMW on the surface of TiO2. The obtained results showed that the COD removal rate increased with decreasing pH value of solution. Fig. 6 shows the apparent rate constant of the degradation reaction (kapp) as a

0 240

Fig. 5. Photocatalytic production of H2 with simultaneous degradation of organic pollutants (pH = 5.4, TiO2 = 2 g/L); upper plot for H2 produced and lower plot for organic degradation.

Fig. 6. Effect of initial reaction pH value on degradation of OMW, (TiO2 = 2 g/L). Effect of pH value on apparent reaction rate constant (kapp) in the photocatalytic degradation of OMW.

function of different pH values, where kapp was determined by calculating the slope of the plot of − ln[CODt / CODo] versus the irradiation time. It is observed that kapp decreased with an increase in the pH value of wastewater, as shown in Fig. 6, and kapp was decreased from 17.2 × 10 − 3 min − 1 to 7.8 2 × 10 − 3 min − 1 as wastewater pH increased from 3 to 9. An acidic pH value of 3 has been found to be favorable for the photocatalytic degradation of phenolic compounds of OMW as observed in the literature [21–24]. The reason is that point of zero charge of TiO2 is a pH value of 6.8. Its surface is positively charged in acidic medium. This favors the adsorption of organic pollutants onto the TiO2 surface and facilitates the degradation [25]. 3.3.2. Photogeneration of hydrogen Also, pH values play an important role in the photocatalytic H2 production. As illustrated in Fig. 7, the dependence of photocatalytic H2 production activity on pH values were found to be: acidic solutions ≫ alkaline solutions. The result indicated that the acidic value of wastewater is more favorable for photocatalytic H2 production when using the solution containing organic pollutants as electron donor. The influence of solution pH on photocatalytic H2 production is due to (a) the positions of the valence-band and conduction-band levels of the semiconductor with respect to those of redox couples in solution, (b) the charging behavior of TiO2 surface, and (c) the competitive adsorption of organic pollutants on TiO2 surface [25,26]. 3.4. Effect of catalyst dose on value on amount of evolved hydrogen and OMW degradation 3.4.1. Degradation of organic pollutants in OMW Catalyst dosage is an important parameter in the slurry photocatalytic process. In order to obtain the optimum catalyst dosage, the relationship between the dosage and OMW degradation rate was investigated as shown in Fig. 8. It can be seen that the average reaction

M.I. Badawy et al. / Desalination 267 (2011) 250–255

pH3

pH4

pH5

pH7

25

pH9

20 1000/mins

40 35 30 25 20 15 10 5 0

0

10

20

30 45 60 Time (mins)

90

120

rate increased with a dosage from 0.5 to 4 g L− 1, beyond which the average reaction rate became approximately constant. This indicates that the optimal dosage value was 2 g L− 1 in this work, and the photocatalytic removal rate reached up to 84%. When the dosage is less than the optimum value, the catalyst exhibits a lower average reaction rate because there are not enough catalytic active sites to be supplied. Fig. 9 shows the apparent rate constant (kapp) as a function of TiO2 loading at pH 3, where kapp was determined by calculating the slope of the plot of − ln[CODt / CODo] versus irradiation time for different TiO2 doses. It is obvious that kapp increased with an increase in the concentration of TiO2 up to a certain limit after which slight increase in kapp was observed. As shown in Fig 9, kapp was decreased from 4.4 × 10− 3 min− 1 to 17.7 × 10− 3 min− 1 as the TiO2 dose increased from 0.5 to 2 g/L. This is a characteristic for a heterogeneous photocatalyst and is in agreement with earlier reports [27–30]. This can be attributed to the fact that increased number of TiO2 particles will increase the availability of active sites of TiO2 surface and the number of photons absorbed. Beyond optimal TiO2 concentration, decrease in photodegradation may be due to the turbidity and possible aggregation of free TiO2 particles, which results in the decrease in the number of surface active sites [31]. 3.4.2. Photogeneration of hydrogen The photocatalytic H2 production activity of the photocatalyst is influenced not only by pH value but also by photocatalyst concentration in suspension. To quantify the dependence of H2 evolution on photocatalyst concentration, the curves of hydrogen production with irradiation time were plotted at various concentrations of nanoparticle TiO2 and shown in Fig. 10. With photocatalyst concentration increasing from 0.5 g/L to 4 g/L, the photocatalytic H2 production is varied in the order of 4 g/L ≥ 2 g/L N 1.5 g/L N 1 g/L N 0.5 g/L. A similar dependence [25] has been found previously, which is typical for a reaction occurring in the photocatalyst suspension. The photocatalytic reaction on TiO2 surface is a complicated process and is determined by transmission of UV light in the suspension and active sites on the TiO2 surface. At a low level of photocatalyst concentration, the photocatalytic reaction is mainly governed by active sites which are available for adsorption of light and reactant [26]. The active sites are increased with the increment of photocatalyst concentration.

0.5 g/L COD Conversion %

10

0

10

20

1 g/L

1.5 g/L

30 45 60 Time (mins)

2 g/L

90

4 g/L

120

0

180

Fig. 7. Effect of initial pH value of reaction on the amount of evolved hydrogen via photocatalytic degradation of OMW (TiO2 = 2 g/L).

100 80 60 40 20 0

15

5

180

Fig. 8. Effect of catalyst dose on the degradation of OMW (pH = 3).

0.5

1 1.5 2 Catalyst dose (g/L)

4

Fig. 9. Effect of catalyst dose on reaction rate constant in the photocatalytic degradation of OMW.

However, when the photocatalyst concentration is above the optimum level, the solution becomes turbid and UV light is greatly scattered by the suspended photocatalyst. The photocatalytic reaction is mainly subject to transmission of UV light. Due to scattering by the high level of suspended photocatalyst, the transmission of UV light in suspension is greatly inhibited and this results in a sharp decrement in photocatalytic H2 production. This observed phenomenon can be rationalized in terms of the availability of active sites on the TiO2 surfaces, the light absorption and the penetration depths into the suspension. 3.5. Statistical study In this work, there are three independent factors that may affect the photocatalytic degradation of OMW as well as photocatalytic hydrogen production, namely, pH of wastewater, TiO2 amount and reaction time. The designing of experiments in this work follows a full 23 experimental set which required randomly eight experiments. The values were chosen for independent variables; CODin, TiO2 dose, reaction time, oxidized COD, COD removal and evolved hydrogen amount are presented in Table 2. The Pearson correlation coefficients between different variables at 95% confidence (α = 0.05) were calculated. There is a negative correlation between pH and, evolved hydrogen amount and COD removal% (−0.34 and −0.64, respectively). The correlation coefficients between TiO2 and, evolved hydrogen amount and COD removal% are 0.91 and 0.92, respectively. But the correlation coefficient for the reaction time and COD removal% was 0.94 and that for the reaction time and evolved hydrogen amount was 0.87. 4. Conclusion The result of this work showed that prepared titania was of a nanostructured-mesoporous anatase form with a large surface area of 59 m2/g and particle size of 19.5 nm. TiO2 mesoporous nanopowder is used as a photocatalyst for the hydrogen production from OMW containing organic pollutants as electron donors. The photocatalytic

0.5 g/L Evolved Hydrogen (mmole)

Evolved Hydrogen (mmole)

254

50 45 40 35 30 25 20 15 10 5 0

0

10

1 g/L

20

1.5 g/L

30 45 60 Time (mins)

2 g/L

90

4 g/L

120

180

Fig. 10. Effect of catalyst dose on the amount of evolved hydrogen via photocatalytic degradation of OMW (pH = 3).

M.I. Badawy et al. / Desalination 267 (2011) 250–255 Table 2 Design of experimental work and observed factor (CODin, TiO2 dose, reaction time, oxidized COD, COD removal, and evolved hydrogen amount). Experiments CODin TiO2 pH Reaction (mg/L) (g/L) time (h)

Oxidized COD Evolved COD removal hydrogen (mg/L) (%) (mmol)

1 2 3 4 5 6 7 8

3027.6 4625.5 5550.6 3532.2 7316.7 6559.8 6980.3 3027.6

8410 8410 8410 8410 8410 8410 8410 8410

1 2 1 1 2 2 2 1

3 5 3 5 3 5 3 5

1 1 1 1 2 2 2 2

36 55 66 42 87 78 83 36

31 20 13 5.21 36 24 34.5 14.2

degradation of OMW and hydrogen production takes place simultaneously with large hydrogen yield. The organic pollutants in OMW enhance hydrogen production via preventing the recombination of photogenerated holes and electron pairs that combine with a proton to produce a hydrogen molecule. Photocatalytic degradation of OMW and hydrogen production was highly affected by the pH of wastewater and TiO2 dose loading. Finally, mesoporous nanoparticle TiO2 have a good potential in energy production and environmental cleanup as a novel purification reagent due to its high photocatalytic activity, photostability and its facile preparation process. Acknowledgement The authors acknowledge the National Research Centre, Egypt for financial support (No. 8010213/2008). References [1] A. Khalil, A. Mubarak, S. Kaseb, Road map for renewable energy research and development in Egypt, J. Adv. Res. 1 (2010) 29–38. [2] Ni. Meng, K.H.L. Michael, Y.C.L. Dennis, K. Sumathy, A review and recent developments in photocatalytic water-splitting using TiO2 for hydrogen production, Renew Sus Energy Rev 11 (2007) 401–425. [3] A.J. Bard, M.A. Fox, Artificial photosynthesis: solar splitting of water to hydrogen, Acc. Chem. Res. 28 (1995) 141–145. [4] A. Patsoura, D.I. Kondarides, X.E. Verykios, Enhancement of photoinduced hydrogen production from irradiated Pt/TiO2 suspensions with simultaneous degradation of azo-dyes, Appl. Catal. B Environ. 64 (2006) 171–179. [5] A. Patsoura, D.I. Kondarides, X.E. Verykios, Photocatalytic degradation of organic pollutants with simultaneous production of hydrogen, Catal. Today 124 (2007) 94–102. [6] D.I. Kondarides, V.M. Daskalaki, A. Patsoura, X.E. Verykios, Hydrogen production by photo-induced reforming of biomass components and derivatives at ambient conditions, Catal. Lett. 122 (2008) 26–32. [7] Z. Zou, J. Ye, K. Sayama, H. Arawa, Enhancement of photoinduced hydrogen production from irradiated Pt/TiO2 suspensions with simultaneous degradation of azo-dyes, J. Photochem. Photobiol. Chem. 148 (2002) 65–69.

255

[8] R. Abe, M. Higashi, K. Sayama, Y. Abe, H. Sugihara, Development of new photocatalytic water splitting into H2 and O2 using two different semiconductor − photocatalysts and a shuttle redox mediator IO− 3 /I , J. Phys. Chem. B 109 (2005) 16052–16061. [9] W. Yao, J. Ye, Photocatalytic properties of a new photocatalyst K2Sr1.5Ta3O10, Chem. Phys. Lett. 435 (2007) 96–99. [10] H. Kato, A. Kudo, Photocatalytic water splitting into H2 and O2 over various tantalate photocatalysts, Catal. Today 78 (2003) 561–569. [11] A. Fujishima, T.N. Rao, D.A. Tryk, Titanium dioxide photocatalysis, J Photochem. Photobiol. C 1 (2000) 1–21. [12] Y. Li, Y. Xie, S. Peng, G. Lu, S. Li, Photocatalytic hydrogen generation in the presence of chloroacetic acids over Pt/TiO2, Chemosphere 63 (2006) 1312–1318. [13] P.R. Gogate, A.B. Pandit, A review of imperative technologies for waste water treatment I: oxidation technologies at ambient conditions, Adv. Environ. Res. 8 (3–4) (2004) 501–551. [14] M.R. Hoffmann, S.T. Martin, W.Y. Choi, D.W. Bahnemann, Environmental applications of semiconductor photocatalysis, Chem. Rev. 95 (1995) 69–96. [15] APHA, AWWA, Standard Methods for the Examination of Water and Waste water, 20th ed, WPCF, New York, 1998. [16] L.V. Azaoff, Elements of X-ray Crystallography, Mc Graw-Hill Book Co, New York, 1968. [17] A. Piotrowska, J. Walendziewski, The photocatalytic hydrogen production from the water over titania aerogels under UV irradiation, Proceedings International Hydrogen Energy Congress and Exhibition IHEC 2005 Istanbul, Turkey, July 13–15 2005. [18] M. Kaneko, I. Okura, Photocatalysis: Science and Technology, Springer, Japan, 2003. [19] A. Linsebigler, L.G. Lu, J.T. Yates, Photocatalysis on TiO2 surfaces: principles, mechanisms, and selected results, Chem. Rev. 95 (1995) 735–738. [20] G.E.P. Box, J.S. Hunter, W.G. Hunter, Statistics for Experimenters: Design, Innovations, and Discovery, second ed, John Wiley & Sons, Inc, Hoboken, New Jersey, 2005. [21] K. Mogyorosi, I. Dekany, H.J. Fendler, Preparation and characterization of clay mineral intercalated titanium dioxide nanoparticles, Langmuir 19 (2003) 2938–2946. [22] A. Scalfani, L. Palmisano, M. Schiavello, J. Phys. Chem. 94 (1990) 829–832. [23] M. Andersson, L. Österlund, S. Ljungstrom, A. Palmqvist, J. Phys. Chem. B 106 (2002) 10674–10679. [24] M. Addamo, V. Augugliaro, A.D. Paola, E. Garcia-Lopez, V. Loddo, G. Marci, R. Molinari, L. Palmisano, M. Schiavello, Preparation, characterization, and photoactivity of polycrystalline nanostructured TiO2 catalysts, J. Phys. Chem. B 108 (2004) 3303–3310. [25] X. Zheng, L. Wei, Z. Zhang, Q. Jiang, Y. Wei, B. Xie, M. Wei, Research on photocatalytic H2 production from acetic acid solution by Pt/TiO2 nanoparticles under UV irradiation, Int. J. o f hydrogen energy 3 (4) (2009) 9033–9041. [26] V.M. Daskalaki, D.I. Kondarides, Efficient production of hydrogen by photo-iduced reforming of glycerol at ambient conditions, Catal. Today 144 (2009) 75–80. [27] E. Pramauro, A.B. Prevot, G. Brizzolesi, Photocatalytic degradation of carbaryl in aqueous solutions containing TiO2 suspensions, Environ. Sci. Technol. 31 (1997) 3126. [28] C. Shifu, L. Yunzhang, Study on the photocatalytic degradation of glyphosate by TiO2 photocatalyst, Chemosphere 67 (2007) 1010–1017. [29] K. Naeem, F. Ouyang, Parameters effect on heterogeneous photocatalysed degradation of phenol in aqueous dispersion of TiO2, J. Environ. Sci. 21 (2009) 527–533. [30] K. Naeem, F. Ouyang, Effect of calcination on photocatalytic activity of Fe3+-doped TiO2 nanoparticles for degradation of phenol under UV irradiation, in: Proceeding of the 4th IEEE International Conference on Nano/Micro Engineered and Molecular Systems (IEEE–NEMS), 2009, pp. 348–352. [31] C.C. Chen, C.S. Lu, Y.C. Chung, J.L. Jan, UV light induced photodegradation of malachite green on TiO2 nanoparticles, J. Hazard. Mater. 141 (2007) 520–528.