enhanced photocatalytic activity of beryllium doped titania in visible light on the degradation of...

Balaram Kiran Avasaralaa, Siva Rao Tirukkovalluria, Sreedhar Bojjab

a Andhra University, Department of Inorganic and Analytical Chemistry, Visakhapatnam, Indiab Indian Institute of Chemical Technology, Inorganic and Physical Chemistry Division, Hyderabad, India

Enhanced photocatalytic activity of berylliumdoped titania in visible light on the degradationof methyl orange dye

The present work is focused on the synthesis of berylliumdoped titania (Be+2–TiO2) at different percentages (0.25,0.5, 0.75 and 1.0 wt.%) by the sol-gel method and its charac-terization using X-ray diffraction, X-ray photoelectron spec-troscopy, Fourier transform-Infra red and Ultra violet-visibleabsorption spectroscopic methods. Diffraction peaks of ana-tase crystalline phase were present in both synthesized TiO2

and Be+2–TiO2. The presence of Be+2 ion in the TiO2 struc-ture caused a significant absorption shift towards the visibleregion and its presence was confirmed by X-ray photoelec-tron spectroscopy and Fourier Transform-Infra Red data.The photocatalytic efficiency of the synthesized Be+2–TiO2

and pure TiO2 was evaluated by the degradation of aqueousmethyl orange dye under visible light irradiation, where thedegradation rate of methyl orange by Be+2–TiO2 was foundto be higher than by pure TiO2. This can be attributed to moreefficient electron–hole creation in Be+2–TiO2 in visible lightand the electrons produced due to photosensitization of thedye can be scavenged by photoexcited doped TiO2 in visiblelight.

Keywords: Titanium dioxide; Doping; Sol-gel method;Beryllium; Photocatalysis

1. Introduction

Waste waters generated by the textile industry are rated asthe most polluting among all industrial sectors, consideringboth the volume rejected and the composition of the efflu-ents [1]. Conventional water treatment techniques such asflocculation, precipitation, adsorption on granular activatedcarbon, air stripping, reverse osmosis, combustion andaerobic biological oxidation could transfer pollutants fromthe aqueous phase to another phase, but they do not destroythe pollutants [2].

According to literature [3, 4], the Advanced OxidationProcess (AOP) is an alternative way of treating undesirableorganic pollutants, including dye stuffs. Among AOPs, het-erogeneous photocatalysis seems to be an attractive methodand has been successfully employed for the degradation ofvarious families of pollutants [5]. Heterogeneous semicon-ductor photocatalysis has its origin in the substantial re-search effort in the first photoelectrochemical system de-veloped by Fujishima and Honda [6].

Among various semiconducting photocatalysts available(e.g. TiO2, ZnO, Fe2O3, CdS and ZnS), TiO2 has attracted agreat deal of study for its high photocatalytic activity, non-toxicity and stability with respect to photo and chemical cor-rosion. TiO2 is capable of decomposing a wide range of or-ganic and inorganic pollutants and toxic materials [7].

Two different crystal structures of TiO2, rutile and ana-tase are commonly used in photocatalysis. The structuresof rutile and anatase can be described in terms of chains ofTiO6 octahedra. Each Ti+4 ion is surrounded by an octahe-dron of six O – 2 ions. The two crystal structures differ bythe distortion of each octahedron and by the assembly pat-tern of the octahedra chains. The octahedron in rutile is notregular showing a slight orthorhombic distortion. But inanatase significant distortion leading to lower symmetrythan orthorhombic has been observed [8]. The differencesin lattice structures cause different mass densities and elec-tronic band structures between the two forms of TiO2.

Many researchers claim that rutile is a catalytically inac-tive [9] or much less active form of TiO2 [10], while othersfind that rutile has selective activity toward certain sub-strates [11]. Titanium dioxide in the anatase form appearsto be the most photoactive and the most practical of thesemiconductors for wide spread environmental application[12, 13]. However, Tanaka et al., [14] have shown thatphotocatalytic degradation of several compounds over dif-ferent mineral phases and preparation methods of TiO2

was dependent upon the calcination temperature.Although TiO2 is superior to other semiconductors for

many practical uses, two types of defects limit its photocat-alytic activity. Firstly, TiO2 has a high band gap (3.2 eV)and it can be excited only by UV light (k < 387 nm), whichis about 4 – 5% of the overall solar spectrum. This restrictsthe use of sunlight or visible light. Secondly, the high rateof electron–hole recombination at TiO2 particles results ina low efficiency of photocatalysis [15].

In order to slow down the recombination rate of the elec-tron–hole pairs and enhance interfacial charge-transfer effi-ciency, the properties of TiO2 particles have been modifiedby selective surface treatments such as surface chelation,surface derivatization, platinization and by selective metalions doping into TiO2 [16 – 19]. The advantage of dopingthe metal ions into TiO2 is the temporary trapping of thephotogenerated charge carriers by the dopant and the inhi-bition of their recombination during migration from insideof the material to the surface [20].

B. K. Avasarala et al.: Enhanced photocatalytic activity of beryllium doped titania in visible light

Int. J. Mat. Res. (formerly Z. Metallkd.) 101 (2010) 12 1563

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Recently, there have been many studies related to thephotocatalytic activity of the metal doped TiO2 catalystsfor the purpose of improving TiO2 photocatalytic activityby doping with transition metal ions [19], alkaline metals[20], Zn+2 [21], Fe+3 [22], Ag, Au, Pd, Pt [23], Li, Rb [24].However, very little attempt has been made on alkalineearth metals doping. Hence, we propose doping with alka-line earth metal.

Sol-gel synthesis is a versatile method which allows controlof nano-scale homogeneity, and stabilizes high surface areasand pore volumes. The other conventional preparation meth-ods, such as impregnation [23], hydrolysis [19], hydrothermaltreatment [25], co-precipitation [26], mechanical alloying[27], do not usually produce homogeneous, high surface-areamaterials. The main advantage of the sol-gel method is its ex-cellent control over the properties of the product via a host ofparameters that are accessible in all four key processing steps:formation of a gel, aging, drying and heat treatment. The in-corporation of an active metal in the sol during the gelationstage allows the metal to have a direct interaction with sup-port. Therefore, the material possesses special catalytic prop-erties [28]. We have studied a soft-solution synthesis routefor photocatalysts at relatively low temperature.

In the present work, pure undoped titania (TiO2) and be-ryllium doped titania (Be+2–TiO2) were synthesized viathe sol-gel process in varying percentages and character-ized using X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infraredspectroscopy (FT-IR) and UV-visible absorption spectro-scopy. The photocatalytic activities of the synthesized sam-ples were evaluated by the degradation of a representativeazo-dye pollutant, methyl orange dye (MO), under differentconditions such as dopant concentration, MO dye concen-tration, pH of the solution and catalyst dosage.

2. Experimental

2.1. Catalyst preparation

Titanium tetra-n-butoxide [Ti(O-Bu)4] and beryllium ni-trate obtained from E. Merck (India) were used as titaniumand beryllium sources for preparing anatase TiO2 andBe+2–TiO2 photo catalysts. Aqueous methyl orange solu-tion was used for degradation studies. All chemicals usedin this work were of analytical grade and doubly distilledwater was used for the solution preparation.

Be+2–TiO2 samples were prepared by the sol-gel methodin which, 21 ml of Ti(O–Bu)4 was dissolved in 80 ml of ab-solute ethanol (100 %) and the resulting solution (soln I)was stirred vigorously. Then, 2 ml of water and 0.5 ml ofacetic acid (50%) were added to another 80 ml of ethanol tomake an ethanol–water–acetic acid solution (soln II). Themetal nitrate solution (0.25, 0.5, 0.75 and 1.0 wt.%) (solnIII) and the former solution (soln II) were slowly added, si-multaneously to the Ti(O–Bu)4–ethanol solution (soln I) un-der vigorous stirring. The resulting transparent colloidal sus-pension was stirred for 3 h and was aged for 2 days, until theformation of gel. The gel was dried at 70 8C in vacuo and la-ter in an oven at 110 8C and then ground. The resulting pow-der was calcined at 400 8C for 2 h and ground. A TiO2 sam-ple was also prepared by adopting the above procedurewithout adding the metal nitrate and is subsequently referredto as pure TiO2. The doping concentrations are expressed as

weight percentage. The powders were stored in black coatedair-tight glass containers.

2.2. Characterization of photocatalysts

To determine the crystal phase composition of the preparedphotocatalysts (TiO2, Be+2–TiO2), X-ray diffraction was car-ried out at room temperature using a PANalytical, D/Max-IIIA diffractometer with Cu-Ka radiation (k = 0.15148 nm)with a liquid nitrogen cooled germanium solid state detector.An accelerating voltage of 35 kV and emission current of30 mA were used, and the scans were in the range of 2 –6582h with a step time of 0.18 s – 1. To study the valence state ofthe photocatalysts, X-ray photo electron spectroscopy (XPS)was recorded with the PHI quantum ESCA microprobe sys-tem, using the Al-Ka line of a 250 W X-ray tube as a radia-tion source with the energy of 1 253.6 eV, 16 mA · 12.5 kVand a working pressure lower than 1 · 10 – 8 N m – 2. As an in-ternal reference for the absolute binding energies, the C 1speak of hydrocarbon contamination was used as a referenceto 284.8 eV. The fitting of XPS curves was achieved usingMultipak 6.0 A software. UV-visible absorption spectra ofthe samples were obtained using a Shimadzu, UV-2101 spec-trophotometer, to study the optical absorption properties ofthe photocatalysts. The spectra were recorded at room tem-perature in the wavelength range 250 –850 nm enabling un-derstanding of the spectral properties of metal-doped TiO2

catalysts. The vibrational and electronic transitions occurringwithin the particles are characteristic of the absorbing materi-al. FT-IR analysis was carried out by a Thermo Nicolet Nexus670 spectrometer.

2.3. Set up of photocatalytic reactor

Photocatalytic degradation studies of MO were carried outin a modified photoreactor system, in which 150 ml of reac-tion mixture, illuminated with an 400 W high pressure mer-cury vapor lamp (Osram, India) positioned parallel to thereaction vessel as a visible light source. The distance be-tween the light and the reaction tube was 20 cm. The quan-titative determination of MO was performed by measuringits absorption at 464 nm with a Milton-Roy spectronic –1201 UV-visible spectrometer. The IR (> 700 nm) and UV(< 360 nm) radiations were filtered by water and UV filters,respectively.

2.4. Photocatalytic activity of the catalyst

The photocatalytic efficiency of the synthesized TiO2 (ana-tase) and Be+2–TiO2 catalysts was checked by degradationof an azo-dye, methyl orange (MO). MO was selected be-cause of well defined optical absorption characteristics andit can be easily adsorbed onto catalysts from its aqueous so-lution. Different concentrations (0.1 to 1.1 g) of catalystswere suspended in 100 ml of MO aqueous solution (0.001to 0.1 g L – 1) in a 150 ml Pyrex glass vessel under rapid stir-ring using a magnetic stirrer. The suspension was magneti-cally stirred in the dark for 45 min to establish adsorption/desorption equilibrium condition on the catalyst surface.The aqueous suspension containing methyl orange dye andphotocatalyst was then irradiated under visible light. Aftercertain irradiation intervals, 5 ml of the aliquots were with-drawn, and the catalysts were separated by filtration


1564 Int. J. Mat. Res. (formerly Z. Metallkd.) 101 (2010) 12

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through 0.45 lm Millipore syringe filter. The filtrate wasanalyzed on a spectrophotometer at a wavelength of464 nm. The extent of MO degradation was calculatedusing a calibrated relationship between the measured absor-bance and its concentration. MO cannot be photodecolor-ized in the absence of catalyst under the same irradiationconditions. The percentage of degradation was calculatedfrom the following equation: Degradation % = (1 –At /A0) · 100, where At is the absorbance at time t and A0 isthe dye initial concentration before degradation. The linearrelationship between the absorbance at 464 nm (A) and theconcentration of methyl orange (C) can be represented em-pirically by the equation, A = 0.0259 C.

3. Results and discussion

3.1. Photocatalysts characterization data

3.1.1. XRD analysis of TiO2 and Be+2–TiO2

The crystalline phases of the synthesized TiO2 and Be+2–TiO2 were examined by XRD and the diffractograms aregiven in Fig. 1a – e. The XRD patterns of calcined (400 8C)TiO2 and all the samples of Be+2–TiO2 (Be/Ti = 0.25, 0.5and 0.75 wt.%) showed only anatase form, except1.0 wt.%. At higher doping the gel powder subjected to heattreatment at 400 8C for 2 h, showed only amorphous naturewith no characteristic peaks related to TiO2. Probably hightemperature is required to force crystallinity. But highertemperatures favor rutile phase formation [29, 30].

Formation of anatase indicates that the Be+2 ions in TiO2

did not influence the crystal patterns of TiO2 particle. In-crease in anatase phase intensity establishes the presence ofBe+2 in the lattice of TiO2 up to 0.5 wt.% doping and furtherincrease in concentration of the dopant may lead to unevendispersion of the metal. Peaks corresponding to BeNO3,BeCO3 and Be+2 (compensated by oxide ions) do not existfor 0.25, 0.5 and 0.75 wt.% Be+2–TiO2. In the case of Be+2,it goes into the interstitial position with charge compensa-tion by O – 2 oxide ion in the regular lattice. XPS studies alsoindicated the presence of Be+2 rather than Be.

The tight packing arrangement required for rutile phaseformation is fully suppressed by the addition of beryllium ni-trate in water which enhances the polarity of water, thus fa-cilitating the formation of anatase exclusively. The presenceof residual alkyl groups can significantly reduce the rate ofcrystallization of TiO2 which favored the formation of theless dense anatase phase. Further, of the two main kinds ofcrystalline phases of TiO2 (anatase, rutile), anatase exhibitshigher photocatalytic activity [31, 32], than rutile [33, 34].

Based on the XRD data and photocatalytic activity stud-ies, further characterization has been made for 0.5 wt.%Be+2–TiO2, which displays intense anatase phase formationand better photocatalytic activity.

3.1.2. XPS measurements

The XPS analysis was carried out to determine the chemicalcomposition of the catalysts and the valence states of var-ious species present therein which can be seen in Fig. 2a



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Fig. 1. XRD patterns of (a) 1.0 (b) 0.75,(c) 0.5, (d) 0.25 wt.% Be+2–TiO2 and (e) PureTiO2.

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and b. The XPS spectra show that there are Ti and O on thesurface of pure TiO2 (Fig. 2a), and Ti, O and Be+2 on thesurface of 0.5 wt.% Be+2–TiO2 (Fig. 2b). For the pureTiO2, the Ti 2p peaks are narrow with slight asymmetryand have binding energies of 458.63 eV and 464.013 eV,attributable to Ti 2p3/2 and Ti 2p1/2. These values are con-sistent with those reported for titanium in TiO2. For the0.5 wt.% Be+2–TiO2, a binding energy of 113.602 eV(FWHM = 0.563) was observed for Be 1s, which is typicalof Be+2. The binding energy was lower than that of TiO2.The O 1s peak can be resolved in to two peaks, one ispeaked at 528.9 eV and the other at 530.6 eV. The formercan be attributed to absorbed hydroxyl groups and the latterto TiO2 [35, 36].

3.1.3. Scanning electron microscopy

SEM pictures of TiO2 and metal doped TiO2 catalysts areshown in Fig. 3a and b. Figure 3b shows the morphological

changes induced by the addition of an alkaline earth metalcation. The catalysts are found to contain irregularly shapedparticles which are again aggregates of tiny crystals andwith reduced average particle size of 0.8 lm. Figure 3ashows an anatase SEM image without beryllium ion and ap-pears as large blocks of coarse material with an average par-ticle size of 3.8 lm. This clearly illustrates the altered mor-phology of the catalyst powders, which consists of a largeportion of micrometer-sized particles.

3.1.4. Analysis of FT-IR spectra

FT-IR spectra of pure TiO2 and Be+2–TiO2 given in Fig. 4aand b, show peaks corresponding to stretching vibrations ofO–H and bending vibrations of adsorbed water moleculesaround 2 910 – 3380 cm – 1 and 1 620 – 1 630 cm – 1, respec-tively. The broad intense feature between 450 cm – 1 and500 cm – 1 was due to Ti–O stretching vibration modes.Peaks corresponding to Be–O peaks are not observed in IR



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Fig. 2. XPS of (a) Pure TiO2, (b) 0.5 wt.%Be+2–TiO2.

Fig. 3. SEM images of (a) Pure TiO2, (b) 0.5 wt.% Be+2–TiO2.

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spectra. This may be due to beryllium being in an interstitialposition, unlinked with the Ti–O structure. The addition ofacetic acid did not cause residual impurities on the surfaceof TiO2 after calcination, which was confirmed from theFT-IR spectral study.

3.1.5. Analysis of UV-visible absorption spectra

The absorption spectrum of pure TiO2 consists of a singleand broad intense absorption band below 400 nm due to

charge-transfer from the valence band (mainly formed by2p orbitals of the oxide anions) to the conduction band(mainly formed by 3d t2g orbitals of the Ti+4 cations).

The UV-visible absorption spectrum of Be+2–TiO2

(Fig. 5b) exhibits an increasing absorption towards thehigher wavelength side, when compared with pure TiO2.The shift in the absorption spectra of Be+2–TiO2 correlateswith the enhanced photocatalytic behavior for all theBe+2–TiO2 samples. This may be due to sufficient decreasein the particle size of the catalyst and band gap value ofTiO2.

3.2. Photocatalytic degradation of methyl orange

To determine the photocatalytic efficiency of the preparedcatalyst, degradation of methyl orange dye was carried outunder the irradiation of visible light, in the presence and ab-sence of catalysts. The percentage of MO degradation issignificantly lower in the absence of catalyst (2.95 % for10 h irradiation) when compared to that of pure or doped ti-tanium dioxide. A blank experiment in the absence of irra-diation along with catalysts demonstrated that no signifi-cant change in the MO concentration was observed. Theefficiency of the photocatalytic degradation process de-pends on various experimental parameters such as dopantconcentration, initial concentration of pollutant, pH andcatalyst dosage. Hence, it is essential to optimize these pa-rameters to achieve higher degradation efficiency of thecatalyst for photocatalytic degradation of MO dye.



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Fig. 4. FT-IR spectra of (a) pure TiO2,(b) 0.5 wt.% Be+2–TiO2.

Fig. 5. UV-Visible absorbance spectra of pure TiO2 and 0.5 wt.%Be+2–TiO2.

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3.2.1. Effect of dopant concentration

To determine the optimum concentration of berylliumdoped titania, a set of experiments were carried out forphotocatalytic degradation of MO dye in solution, using1.0, 0.75, 0.5, and 0.25 wt.% Be+2–TiO2 and pure TiO2.The residual methyl orange concentration, correspondingto different irradiation time intervals, was quantified bythe absorption studies. Results are shown in Fig. 6, whichindicate that the doping of beryllium ions improve thephotocatalytic activity of TiO2. When the impurity fractionof Be+2 in TiO2 increased, the rate of MO photo degrada-tion increased, up to 0.5 wt.% beryllium ion doping andfurther doping became detrimental. This illustrates thatthere is an optimal concentration for beryllium ion doping.It also demonstrates that even though the concentration ofthe doped beryllium ions is small, it still gives much influ-ence on the photo catalytic activity of TiO2 particles.

This may be due to the entry of Be+2 dopant ion with ionicradius (0.27 Å), smaller than both Ti+4 (0.605 Å) and O – 2

(1.35 Å) [37], to be interstitially introduced into the matrixof TiO2, rather than substitution. The entry of Be+2 ions intothe lattice suppresses the particle growth and consequentlydecreases the band gap value of TiO2, which minimizes theelectron–hole recombination and enhancing the photo cata-lytic degradation.

3.2.2. Effect of initial dye concentration

At a fixed weight of catalyst and pH, variation of initial dyeconcentration on photo degradation of MO was studied andis shown in Fig. 7. It is generally noted that the degradationrate increases with the increase of dye concentration to anextent of 0.01 g L – 1 and a further increase in MO dye con-centration leads to a decrease in the dye degradation rate.This may be due to a decrease in the generation of OH. radi-cals on the catalyst surface as the active sites are covered bydye ions.

3.2.3. Effect of pH

Since solution pH influences adsorption and desorption ofthe substrate, catalyst surface charge, oxidation potentialof the valence band and other physico-chemical properties,the catalyst assisted photo degradation of MO was moni-tored by in situ measurements of pH of the aqueous suspen-sion with irradiation time, at a fixed weight of catalyst andMO dye concentration at three different pH values(Fig. 8). It can be observed that the degradation rate is high-er in the acidic pH range (pH = 3) than in alkaline (pH = 11)and isoelectric point (pH = 6) for TiO2 in water [38]. Alsothere is a drop in solution pH by the end of the experiments,indicating the formation of acidic products.

On the surface of TiO2, Titanol (Ti–OH) is present,which is amphoteric and occurs in an acid-base equilibriumas indicated by the following equations:

TiOH + H+ �! TiOH2+ pH < 6.0

TiOH �! TiO – + H+ pH > 6.0

In an acidic environment, H+ ions adsorbed onto the surfaceof TiO2, which has a large surface proton exchange capa-city. The photogenerated electrons can be captured by theadsorbed H+ to form H.

ads. At higher pH, the surface of cat-alyst has a net negative charge due to a significant fractionof total surface sites present as TiO – and hence the degra-dation rate was found to be lower.

3.2.4. Effect of catalyst dosage

The effect of the amount of catalyst on the photodegrada-tion rate was investigated, at a fixed pH and initial concen-



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Fig. 6. Effect of dopant concentration on 0.01 g L – 1 MO dye degrada-tion with 0.1 g of pure TiO2 and Be+2–TiO2 at pH = 7.0.

Fig. 7. Effect of MO dye concentration with 0.1 g of 0.5 wt.% Be+2–TiO2at pH = 7.0.

Fig. 8. Effect of pH on 0.01 g L – 1 MO dye degradation with 0.1 g of0.5 wt.% Be+2–TiO2.

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tration of the MO dye (0.01 g L – 1), experiments were per-formed with varying amounts of Be+2–TiO2 from 0.1 g to1.1 g in 100 ml MO dye aqueous solution. The degradationpattern from such experiments is shown in Fig. 9, which re-veals that the rate of degradation increases linearly with in-crease in the amount of catalyst up to 0.7 g and then de-creases (leveling off).

As the amount of catalyst increases, the number ofphotons absorbed and the number of MO molecules ad-sorbed are increased due to an increase in the number ofcatalyst particles leading to the increase in photo catalyticefficiency. At further higher proportions of catalyst,although more areas are available for constant MO mole-cules, the number of substrate molecules present in the so-lution remains the same, but the solution turbidity increasesand it interferes the penetration of light and also helps inscattering of radiation. The deactivation of activated mole-cules by collision with ground state molecules may alsohinder the photo catalytic efficiency [39]. Hence, above acertain level, additional catalyst is not involved in catalysisand thus the rate levels off.

3.3. Photocatalytic mechanism

Under visible light illumination, both dye and surface of theBe+2–TiO2 undergoes photoexcitation, the electrons fromthe dye are ejected due to photosensitization [40]. Simulta-neously the Be+2–TiO2 also produces holes which are con-sumed by the dye electrons. In the course of time, Be+2–TiO2 effectively separates the injected electrons and thedye cation radicals thus enhancing the photocatalytic degra-dation of adsorbed dye. In contrast, the pure TiO2 under-goes effective excitation only in UV light, which inhibitsthe efficient removal of ejected electrons of the dye. Hence,metal doped TiO2 enhances the photocatalytic activitymore than the pure TiO2. Literature reports also indicatedthat, with pure TiO2 the photodegradation of MO occurredvia photosensitization [30, 41], which needs more timewhen is compared with the present results.

4. Conclusions

The sol-gel method offers a successful route for synthesiz-ing Be+2–TiO2 catalyst. Beryllium doped TiO2 acquiresthe capability of absorbing visible light and shows a “red-

shift” in the UV-visible spectra. The results of photocatalyt-ic reactions indicate that the Be+2–TiO2 has higher activitythan pure TiO2 under visible light irradiation. The improve-ment is due to the good dispersion of beryllium in TiO2

crystal lattice.

The authors are thankful to Dr. Subrahmanyam and Dr. Anandan, NIT,Trichy for providing UV-Visible absorption data. One of the authors(A. Balaram Kiran) is thankful to UGC, New Delhi, for providing ne-cessary research funding. The authors are also thankful to Prof.A. V. Prasada Rao, Andhra University and Dr. Venkat Kambala, Aus-tralia for their invaluable suggestions.

References

[1] U. Pagga, D. Brown: Chemosphere 15 (1986) 479.DOI:10.1016/0045-6535(86)90542-4

[2] D. Chen, A.K. Ray: Appl. Catal. B: Environ. 23 (1999) 143.DOI:10.1016/j.jhazmat.2007.03.035

[3] P. Robertson: J. Cleaner Prod. 4 (3–4) (1996) 203.DOI:10.1016/j.desal.2007.12.013

[4] O. Legrini, E. Oliveros, A.M. Braun: Chem. Rev. 93 (2) (1993) 671.DOI:10.1021/cr00018a003

[5] D. Blake: Bibliography of work on the heterogeneous photo cata-lytic removal hazardous compounds from water and air. NREL/TP-510-31319. NTIS, U.S. Dept. of Commerce, Springfield,(2001) VA 22161.

[6] A. Fujishima, K. Honda: Nature (London) 238 (1972) 37.DOI:10.1038/238037a0

[7] M.R. Hoffmann, S.T. Martin, W. Choi, D.W. Bahnemann: Chem.Rev. 95 (1995) 69. DOI:10.1021/cr00033a004

[8] J.K. Burdett, T. Hughbands, J.M. Gordon, J.W. Richardson, J.V.J.Smith: J. Amer. Chem. Soc. 109 (1987) 3639.DOI:10.1021/ja00246a021

[9] A. Mills, R.H. Davies, D. Worsley: Chem. Soc. Rev. 22 (1993)417. DOI:10.1039/CS9932200417

[10] H. Noda, K. Oikawa, H. Kamada: Bull. Chem. Soc. Jpn. 66 (1993)455. DOI:10.1246/bcsj.66.455

[11] X. Domenech, in: D.F. Ollis, H. Al-Ekabi (Eds.) PhotocatalyticPurification and Treatment of Water and Air, Elsevier, Amster-dam (1993) 337.

[12] M. Rao, K. Rajeshwar, V.R. Vernerker, J. Dubow: J. Phys. Chem.84 (1980) 1987. DOI:10.1021/j100452a023

[13] S. Nishimoto, B. Ohtani, H. Kajiwara, T. Kagiya: J. Chem. Soc.,Faraday Trans. 81 (1985) 61. DOI:10.1039/F19858100061

[14] K. Tanaka, T. Hisanaga, A.P. Rivera in: D.F. Ollis, H. Al-Ekabi(Eds.), Photocatalytic Purification and Treatment of Water andAir. Elsevier, Amsterdam (1993) 337.

[15] X.Z. Li, F.B. Li, C.L. Yang, W.K. Ge: J. Photochem. Photobiol.A: Chem. 141 (2001) 209. DOI:10.1016/S1010-6030(01)00446-4

[16] E. Vrachnou, M. Graetzel, A.J. McEvoy: J. Electroanaly. Chem.258 (1) (1989) 193. DOI:10.1016/0022-0728(89)85172-1

[17] J. Moser, M. Graetzel: J. Am. Chem. Soc. 106 (1984) 6557.DOI:10.1021/ja00334a017

[18] J.A. Navio, M.G. Gomez, M.A.P. Adrian, J.F. Mota: Studies inSurf. Sci. Cat. 59 (1991) 445.

[19] W. Choi, A. Termin, M.R. Hoffmann: J. Phys. Chem. 98 (1994)13669. DOI:10.1021/j100102a038

[20] Y. Bessekhouad, D. Robert, J. Weber, N. Chaoui: J. Photochem.Photobiol. A: Chem. 167 (2004) 49.DOI:10.1016/j.jphotochem.2003.12.001

[21] J. Xu, Y. Shi, J. Huang, B. Wang, H. Li: J. Mol. Catal. A: Chem.219 (2004) 351. DOI:10.1016/j.molcata.2004.05.018

[22] Z. Zhang, C. Wang, R. Zakaria, J.Y. Ying: J. Phys. Chem. B 102(1998) 10871. DOI:10.1021/jp982948+

[23] S. Sakthivel, M.V. Shankar, M. Palanichamy, B. Arabindoo, D.W.Bahnemann, V. Murugesan: Water Res. 38 (2004) 3001.DOI:10.1016/j.watres.2004.04.046

[24] T. Lopez, R. Hernandez-Ventura, R. Gomez, F. Tzompantzi, E. San-chez, X. Bokhimi, A. Garcia: J. Mol. Catal. A: Chem. 167 (2001)101. DOI:10.1016/S1381-1169(00)00496-9

[25] Y. Liu, C. Liu, Q. Rong, Z. Zhang: Appl. Surf. Sci. 220 (2003) 7.DOI:10.1016/S0169-4332(03)00836-5

[26] K.T. Ranjit, B. Viswanathan: J. Photochem. Photobiol. A: Chem.108 (1997) 79. DOI:10.1016/S1010-6030(97)00005-1



AApplied

Fig. 9. Effect of catalyst dosage on 0.01 g MO dye degradation with0.5 wt.% Be+2–TiO2 at pH = 3.0.

Inte

rnat

iona

l Jou

rnal

of

Mat

eria

ls R

esea

rch

dow

nloa

ded

from

ww

w.h

anse

r-el

ibra

ry.c

om b

y C

ambr

idge

Uni

vers

ity o

n N

ovem

ber

12, 2

014

For

pers

onal

use

onl

y.

[27] D.H. Kim, H.S. Hong, S.J. Kim, J.S. Song, K.S. Lee: J. Alloys andCompounds 375 (2004) 259. DOI:10.1016/j.jallcom.2003.11.044

[28] S.S. Kistler: Nature 127 (1931) 741. DOI:10.1038/127741a0[29] S.T. Martin, C.L. Morrison, M.R. Hoffmann: J. Phys. Chem. 98

(1994) 13695. DOI:10.1021/j100102a041[30] J.C. Wu, C. Chen: J. Photochem. Photobiol. A: Chem. 163 (2004)

509. DOI:10.1016/j.jphotochem.2004.02.007[31] S.J. Tsai, S. Cheng: Catal. Today 33 (1997) 227.

DOI:10.1016/S0920-5861(96)00152-6[32] M.A. Fox, M.T. Dulay: Chem. Rev. 93 (1993) 341.

DOI:10.1021/cr00017a016[33] H. Zhang, M. Finnegan, J.F. Banfield: Nano Lett. 1 (2001) 81.

DOI:10.1021/nl0055198[34] A.L. Linsebigler, G.Q. Lu, J.T. Yates: Chem. Rev. 95 (1995) 735.

DOI:10.1021/cr00035a013[35] R. Sanjines, H. Tang, H. Berger, F. Gozzo, G. Margaritondo,

F. Levy: J. Appl. Phys. 75 (1994) 2945.DOI:10.1063/1.356190

[36] X-P. Wang, Y. Yu, X-F. Hu, L. Gao: Thin Solid Films 371 (2000)148. DOI:10.1016/S0040-6090(00)00995-0

[37] R.D. Shannon: Acta Cryst. A 32 (1976) 751.DOI:10.1107/S0567739476001551

[38] R.S. Sonewane, B.B. Kale, M.K. Dongare: Mat. Chem. Phy. 85(2004) 52. DOI:10.1016/j.matchemphys.2003.12.007

[39] J. Augustinski: Struct. Bonding, 69 (1988) 1.DOI:10.1007/3-540-18790-1_1

[40] B. Neppolian, C.H. Choi, S. Sakthivel, B. Arabindoo, V. Murugesan:J. Hazar. Mater. B 89 (2002) 303– 317.DOI:10.1016/S0304-3894(01)00329-6

[41] M.N. Rashed, A.A. El-Amin: Int. J. Phys. Sci. 2 (2007) 073.

(Received November 21, 2009; accepted October 4, 2010)

Bibliography

DOI 10.3139/146.110438Int. J. Mat. Res. (formerly Z. Metallkd.)101 (2010) 12; page 1563–1570# Carl Hanser Verlag GmbH & Co. KGISSN 1862-5282

Correspondence address

T. Siva RaoDepartment of Inorganic and Analytical ChemistrySchool of Chemistry, Andhra UniversityVisakhapatnam, India-530003, AsiaTel.: +91 891 284 4667Mobile: +91 770211 0459E-mail: [email protected]

You will find the article and additional material by enter-ing the document number MK110438 on our website atwww.ijmr.de



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