The Photocatalytic Activity of TiO 2-Zeolite Composite for Degradation of Dye Using Synthetic UV and Jeddah Sunlight

In this research different composites of impregnated TiO 2 with LTA or FAU zeolites were used as different weight% ratio for photodegradation of organic dye. Normal laboratory UV-lamps were used as a source of UV irradiation. In addition a setup of system ofmirrors was used to collect real Jeddah sunlight. A comparison of UV and real sunlight photodegradation activity showed that the real sunlight enhances new centers of active sites exhibiting higher catalytic activity than that of UV irradiated samples.


Introduction
Decomposition of organic pollutants photocatalytically in the presence of TiO 2 appears as a sustainable decontamination process of common application, as gas or liquid [1,2].The ultraviolet (UV) energy/excitation source becomes the most practical applications due to the fact that the absorption edge of anatase TiO 2 is about 380 nm.The most solar radiation intensity reaching the earth surface is in the visible range.Systems with visible-light as an active radiation have become a priority for developing the upcoming generation of photocatalytic materials.
The composite of TiO 2 fine particles with other supports such as active carbon has been proved to exhibit efficient photocatalytic reactivity [3][4][5].However, black active carbon inhibits the incident UV-vis radiation to excite semiconductor photocatalysts.In comparison, TiO 2 supported on transparent constituents in UV-vis regions, such as porous materials [6][7][8][9][10] or clays [11], has also been conveyed to show greater photocatalytic reactivity than sole TiO 2 .Moreover, TiO 2 particles loaded on ZSM-5 zeolite [12] as well as TiO 2 powders mechanically grinded with MOR zeolite [13] were proved for efficient removal of highly volatile acetaldehyde.
In addition, TiO 2 /Y-zeolite hybrid photocatalysts [14] were used efficiently for removal of toluene or benzene molecules.
The above behavior could be explained by the fact that the zeolitic material adsorbs the organic compounds and easily supplies them onto the TiO 2 photocatalyst surface.Another advantage of zeolite-TiO 2 composite is that the adsorption capacity of the pure TiO 2 sample rapidly deteriorated, while the TiO 2 /zeolite hybrid system maintained a high adsorption efficiency to remove such aromatic compounds for a long period [14].In this research, we will study the effect of different composites of TiO 2 -zeolite, namely, LTA and FAU materials, on the photocatalytic decomposing of organic dye using UV irradiation.In addition a developing system using direct sunlight was also used as a future system for photocatalytic decomposition of such systems.2.2.Synthesis.Titanium isopropoxide was loaded by different wt% composition on LTA or FAU, namely, 20, 50, and 70 wt%, after which calcination at 550 ∘ C was performed.

Photocatalytic Decomposition.
A 100 mL of 500 ppm solution of methyl orange was mixed with 0.5 g of composite using a horizontal cylinder annular batch reactor.A xenon lamp (300 W), covered by a UV filter, was used for irradiation of the photocatalyst.The photocatalytic reaction was carried out at room temperature.
The direct sunlight reactor shown in schematic diagram 1 was used using the same previous concentration of dye and same amount of the catalyst (Scheme 1).

XRD (X-Ray Diffraction Analysis
). X-ray diffractograms of various solids were collected using a Bruker D8 advance instrument with CuK1 target with secondly monochromator 40 kV, 40 mA.Crystal lattice and space group analysis were performed using PhilpsX'Pert Plus V. 1.0 23.04.1999.

SEM and EDX Analysis. SEM images combined with
EDX analysis were taken using instrument and EDX analysis was performed using instrument "JXA-840 A electron probe microanalyzer, Japan".

UV Visible
Spectrophotometer.The decomposition of organic dye followed using UV spectrophotometer.
2.3.5.HPLC.Some selected samples were reanalyzed by HPLC system and nearly the same results of UV were obtained.Visible spectrophotometer was attained.

XRD.
The XRD diffraction patterns showed that at high loading of TiO 2 (70%) only anatase phase is showed with no trace of zeolite matrix for both LTA and FAU zeolite.For low loading, in case of FAU, also only anatase phase is observed with very low trace of FAU zeolite.In contrast at low loading (20%) over LTA only zeolite matrix was observed with no trace of anatase phase.
The crystal lattice analysis (Table 1) showed that in case of 20% TiO 2 /LTA the lattice parameters slightly decreased meaning that the disappearance of anatase phase is accompanied by dissolving the TiO 2 into the LTA zeolite substituting the framework [15].In other words the change in lattice parameters of TiO 2 loaded sample compared with pure LTA zeolite,  = 12.28 (pure LTA) to  = 12.23 (20% TiO 2 /LTA), gives indication that the TiO 2 was incorporated into the framework of zeolite. 1 and 2 showed the SEM images of different loaded samples.The images showed that in case of high loaded samples only TiO 2 agglomerate matrix was observed while for low loaded samples small agglomerate of TiO 2 is dispersed over an observable zeolite matrix.The EDX analysis was manipulated in Tables 2 and 3. From this table it is clearly observed that at 20% TiO 2 /LTA zeolite the surface TiO 2 observed by EDX analysis is much lower than those corresponding to 20% TiO 2 /FAU which supports the previous XRD analysis data that the TiO 2 is incorporated inside the framework of LTA zeolite.3.3.Photocatalytic Activity.The photocatalytic activity kinetic curves of all samples (UV irradiated and sunlight irradiated) are presented in Figure 3. From this figure it could be observed that the two zeolites LTA and FAU showed two different behaviors.Thus, for UV irradiation sample loaded on FAU, the catalytic decomposition activity of 20, 50% TiO 2 loaded samples showed nearly no catalytic activity while only 70% showed about 80% decomposition after nearly 50 min.This could be explained that at this critical composite ratio the adsorbed dye is easily submitted to the surface of TiO 2 while other ratios of loading the adsorbed dye are not transferred easily, which may be due to high adsorption power of FAU.

SEM and EDX. Figures
With sunlight irradiation, a dramatic change occurs that all catalytic activity increased meaning that there are new active sites activated only by sunlight (visible range); these active sites may be due to either some impurities in zeolite matrix or due to partial substitution of Ti into the framework of zeolite.
In contrast to FAU zeolite, LTA loaded with TiO 2 showed another amazing behavior.Thus, regarding the UV irradiation, a dramatic increase of 20% TiO 2 /LTA up to 80% decomposition comparing with only 45% decomposition for both 50 and 70% TiO 2 /LTA could be explained in the light of previous XRD and SEM and EDX data that explained for this composite ratio most of TiO 2 incorporated into the matrix of zeolite generating new active site to whole matrix accompanied by absence of any anatase phase of TiO 2 .It appeared that the catalytic activity of these new active sites is much higher than that of even high loaded TiO 2 with anatase phase detected.Studying the same system under sunlight showed that catalytic activity of 70% TiO 2 /LTA decreased than those values obtained by UV irradiation while 50% TiO 2 /LTA increased dramatically under sun irradiation to be nearly the same with 20% TiO 2 /LTA to be 75% decomposition.This could be explained by that the incorporated Ti into zeolite active sites is active in both sunlight and UV irradiation while at 50% loading both anatase phases with the new incorporated active site seemed to make a synergetic effect increasing dramatically the catalytic activity.However, pure anatase loaded on LTA (70%) is less active in sunlight.

Conclusions
The following conclusions could be observed from this research.
(1) Microporous materials such as LTA and FAU could be effectively used as a good support for TiO 2 photocatalyst.
(2) Loading TiO 2 on these supports leads to either amorphous dispersed TiO 2 or pure anatase phase of TiO 2 .
(3) In case of low loading of LTA (20%) some XRD evidences for incorporation of some of titanium into the framework sites of zeolite were found.
(4) More than one evidence exists of more than one photoactive site for both UV and visible irradiations.

Figure 3 :
Figure 3: Photocatalytic kinetic curves of different samples under UV and direct sun irradiation.

Table 1 :
Crystal lattice analysis of different investigated samples.

Table 2 :
Elemental EDX analysis of different catalyst samples.

Table 3 :
Oxide % EDX analysis of different catalyst samples.