research article cesium salt of sodium 30 ...cesium salt of sodium 30-tungstopentaphosphate: an...

Hindawi Publishing CorporationInternational Journal of PhotoenergyVolume 2013 Article ID 507329 8 pageshttpdxdoiorg1011552013507329

Research ArticleCesium Salt of Sodium 30-TungstopentaphosphateAn Effective and Green Polyoxometalate for Synthesis of GoldNanoparticles along with Decoration of Titanium Dioxide withGold Nanoparticles for Bleaching of Malachite Green

Fatemeh Farrash Bamoharram1 Afsaneh Moghadam Jafari1 Ali Ayati2

Bahareh Tanhaei2 and Mika Sillanpaumlauml2

1 Department of Chemistry Mashhad Branch Islamic Azad University Mashhad 91735-413 Iran2 Laboratory of Green Chemistry Department of Chemistry Lappeenranta University of TechnologySammonkatu 12 50100 Mikkeli Finland

Correspondence should be addressed to Fatemeh Farrash Bamoharram fbamoharramgmailcom

Received 1 October 2013 Revised 12 November 2013 Accepted 13 November 2013

Academic Editor Vincenzo Augugliaro

Copyright copy 2013 Fatemeh Farrash Bamoharram et al This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

For the first time capability of the cesium salt of sodium30-tungstopentaphosphate the so-called Preysslerrsquos anion (CsP5) as a green

and eco-friendly polyoxometalate was investigated in the synthesis of gold nanoparticles and decoration of titanium dioxide withgold nanoparticles Gold nanoparticles and nanocomposites were characterized by TEM XRDUV and FTIR TEM images showedthat the gold nanoparticles have tubular and spherical shapes and particle size ranges from 10 to 25 nm For gold-decorated titaniumdioxidePreyssler a comparison between pure and amine-modified titanium dioxide showed higher loading of gold nanoparticleson amine-functionalized titanium dioxide The performance of CsP

5was compared with its pure acid (HP

5) Our findings showed

that CsP5 as a catalytic linker to bind onto titanium dioxide surface for reducing gold nanoparticles renders decoration better than

HP5in both pure and modified titanium dioxide In addition efficiency of the photocatalytic bleaching of malachite green by the

synthesized nanocomposites was found to be excellent

1 Introduction

Therecent advances in green catalysis particularly when cou-pled with modifying of inorganic materials have openednew avenues for the catalytic technology One of the mostimportant inorganic materials is titanium dioxide and dif-ferent applications of it have been discovered in many fieldsincluding photovoltaics [1 2] photocatalysis [3 4] self-cleaning coatings [5] and photoelectrocatalytic degradationof organic compounds [6 7]

But despite these large range of applications the applica-tion of these particles is limited by the challenge of electron-hole recombination and their band-gap energy of 32 eV [8]which requires exposure to ultraviolet light for photocatalyticapplications For overcoming the electron-hole recombina-tion phenomenon many researchers have made an attempt

to shift the band-gap energy of titanium dioxide toward thevisible region [9ndash11] and used doping with small amounts oftransition metals [12 13]

To this end titanium dioxide has been decorated withmetals and metal oxides through chemical or photodeposi-tion methods [14ndash23]

However in deposition of metal nanoparticles on tita-nium dioxide surface the final product contains a mixtureof both metal nanoparticles and metal-decorated titaniumdioxide A possible solution to overcome this problem couldbe based on the immobilization of a reducing agent on thesurface of titanium dioxide particles

Polyoxometalates can reduce easily without any changein the structure and the reduced form of them bound totitanium dioxide can act as a reducing agent for metal ionsto decorate metal nanoparticles specifically on titanium

2 International Journal of Photoenergy

dioxide surfaces [24] Pearson and coworkers demonstrateddecoration of titanium dioxide with metal nanoparticlesusingKeggin as an efficient polyoxometalate [25] In additionpolyoxometalates can reduce noble metals to prepare nan-oclusters in the presence of light [26 27] Anyway althoughthere are many structural types of polyoxometalates themajority of processes use the most common Keggin typeowing to its availability and chemical stability and the roleof Preyssler polyoxometalate [NaP

5W30O110

]14minus has beenlargely overlooked

The oval-shaped Preyssler polyoxometalate consists ofa cyclic assembly of five PW

6O22

units each derived fromthe spherical Keggin anion [PW

12O40]3minus by the removal

of two sets of three corner-sharing WO6octahedra The

[XM12O40]119899minus (Keggin structure) consists of one XO

4tetrahe-

dron surrounded by fourM3O13sets linked together through

oxygen atoms The Preysslerrsquos anion structure consists offive PO

4tetrahedron surrounded by 30 WO

6which are

connected to each other by edge and corner-sharing oxygensA sodium ion is located within the polyanion on the five-foldaxis and 125 A above the pseudomirror plane that containsthe five phosphorus atoms

The properties of polyoxometalates such as thermal sta-bility as well as hydrolytic stability and catalytic activity aresensitive to their structures [28 29] In addition the kind andnumber of counterions as well as their constituent elementshave an important effect on the catalytic activity chemicalbehavior and the redox properties of the polyoxometalatesDue to these reasons a different behavior and activity isexpected for each polyoxometalate with a different struc-ture Among a wide variety of studied heteropolyacids (animportant class of polyoxometalates) with different size andstructures there are only three anions [NaSb

9W21O86]minus

[NaAs4W40O140

]25minus and [NaP5W30O110

]14minus that have beenreported to encapsulate rare-earth ions [30ndash32] The latterof these Preysslerrsquos anion is one of the largest knownpolyanions and important advantages of this polyanionover the Keggin and Dawson heteropolyacids are (i) morethermal stability (ii) more hydrolytic stability (pH = 0ndash12) (iii) larger number of counter cations and (iv) largernumber of metal atoms These properties are very importantin catalytic processes especially when we work in acidic andbasic conditions For example while Keggin and Dawson[X2M18O62]119899minus polyoxometalates are stable in pH= 1ndash3 and 1ndash

6 respectively the Preyssler is stable in pH = 0ndash12 Addition-ally while the oxidation of organic substrates by hydrogenperoxide in the presence of Keggin proceeds via degradationof structure to an active peroxopolyoxometalate the Preysslercatalyst catalyzes the reactions without any degradation ofstructure [33] This is very important in catalytic reactions inthe presence of hydrogen peroxide The large anion with thelarger number of metal atoms also provides many ldquositesrdquo onthe oval-shapedmolecule that are likely to render the catalysteffective better than Keggin and Dawson types

In continuation of our works on applications of Preyssleracid H

14[NaP5W30O110

] in catalytic and photocatalyticreactions [34 35] and cited references in [35] and extendingthe applications of Preyssler and also due to the importanceof metal-titanium dioxide decoration it is highly relevant to

know what occurs if the Preysslerrsquos anion joins with titaniumdioxide and use it as a catalytic linker for reducing goldions In addition it is also important to investigate the roleof another polyoxometalates apart from Keggin heteropoly-acids We think the most important and credential part ofour work is to introduce and establish nanocesuim salt ofPreyssler type heteropolyacid Cs

12H2[NaP5W30O110

] whichcan be applied as an efficient and competing nanocatalystwith those of Keggin type which have been already reportedas bulk

Also another goal in this research was to answer thisquestion does counter cation in the Preyssler structurewhich is responsible for primary secondary and tertiarystructures have an important role on loading of gold nano-particles onto titanium dioxide

To this purpose in the present work at first in contin-uation of our earlier works [36] we investigated the per-formance and capability of cesium salt of sodium 30-tungstopentaphosphate Cs

12H2[NaP5W30O110

] in synthesisof gold nanoparticles and after that we studied decoration oftitanium dioxide with gold nanoparticles in the presence ofthe Preyssler with different counterions including Cs+ andH+ Interestingly we have found that the Preyssler catalystwith Cs+ as counterion not only can change shape and sizeof gold nanoparticles but also can lead to a higher loadingof gold nanoparticles onto titanium dioxide Also we haveinvestigated the application of different forms of Preysslernanocomposites for bleaching of malachite green

2 Experimental

21 Materials and Methods All of the chemicals were pur-chased from Merck and Sigma Aldrich Companies and usedas received FT-IR spectra were recorded with a Bruckerscientific spectrometer (solid sample KBr pellets) The syn-thesized nanostructures were characterized by TransmissionElectron Microscopy (PHILIPS CM-120 and JEOL-2200FSFEG) A double beam spectrophotometer UV-Vis was usedfor UV-Vis analysis (OPTIZEN 3220)

22 Preparation of HP5and CsP

5 At first 33 g Na

2WO4sdot

2H2O was dissolved in 45mL water by stirring and then

25mL of phosphoric acid 85 was added The mixture wasrefluxed for 5 h After that 10mL H

2O and 10 gKCl were

added into the abovemixture to form a light green precipitateThe green precipitate was obtained by filtration and washedsuccessively by 2M aqueous solution of CH

3COOK and

methanol Recrystallization in hot water led to formation ofK125

Na15[NaP5W30O110

] in needle white color crystalsPreyssler acid H

14[NaP5W30O110

] (HP5) was prepared

by the passage of a solution of the K125

Na15[NaP5W30O110

]in water through a column (50 cm) of Dowex 50WX8 inthe H+ form and evaporation of the elute to dryness undervacuum

For the preparation of CsP5 Preyssler acid and CsCl in a

mole ratio of 1 14 were put into a mortar and several drops ofsurfactant Triton X-100 were added The formed microcellsin the solid state reaction owing to the interaction between

International Journal of Photoenergy 3

the crystal water of Preyssler and the triton-X-100 are me-tastable and provide reaction fields for the formation ofnanoparticles The mixture was ground for 50min and afterwashing in an ultrasonic bath the mixture was centrifugedThe synthesized nanoparticles dried in an oven for 4 h (50ndash60∘C) The number of obtained Cs ions was 12 measuredby ICP measurement and titration method Preyssler acid ishighly soluble inwater but has lower surface area (078m2gr)than acidic cesium salt of Preyssler (261m2g)

23 Preparation of Titanium Dioxide-CsP5and Amine-Func-

tionalized Titanium Dioxide-CsP5 The functionalized tita-

nium dioxide is prepared as follows25 g of TiO

2was suspended in 25mL toluene and re-

fluxed for 1 h and then 125 g 3-aminopropyltriethoxy silanewas added into the above mixture with further stirring for24 h The product was obtained by filtration washed succes-sively with toluene ethanol and water and finally dried invacuum at 80∘C for 12 h

Titanium dioxide-CsP5and amine-functionalized tita-

nium dioxide-CsP5were synthesized by impregnating tita-

nium dioxide (anatase Aldrich 232033) and functionalizedtitanium dioxide powders with an aqueous solution of theHP5or CsP

5 After stirring the mixture the solvent was

evaporated to dryness The obtained powders were dried inan oven at 80∘C

24 Decoration with Gold Nanoparticles In two parallel ex-periments a suspension of the obtained powders titaniumdioxide-CsP

5and amine-functionalized titanium dioxide-

CsP5 (10mg) was dispersed in an ultrasonic bath After that

5mL HAuCl4(10minus3M) and 2mL propan-2-ol were added to

each solutions and then it was irradiated under the highpressure of mercury lamp as UV light source After 1 h thesuspensions were filtered rinsed with water and dried in avacuum oven The obtained nanocomposites were used inphotocatalytic reactions

25 Typical Procedure for Bleaching of Malachite Green Ina typical reaction 001 g photocatalyst was added to 100mLof malachite green (10 ppm) sonicated for 10min and leftfor 15min in a dark place The mixture was irradiated in aphotoreactorThe photoreactor was designedwith an internallight source surrounded by a quartz jacket The temperatureof the suspension was maintained at 25∘C by circulationof water through an external cooling coil The optical pathlength was about 2 cm The light source was a 125W high-pressure mercury lamp The suspension was illuminatedfrom the top and at given irradiation time intervals liquidsamples were taken from the mixture and the absorbance ofthe malachite green solution was measured with a UV-Visspectrophotometer

3 Results and Discussion

Synthesis of gold nanoparticles was performed with a one-pot synthesis technique in the presence of Preyssler withCs+ as counterion The used method is simple and efficient

and takes place within a short time (15min) at ambient tem-perature Using Preyssler as a reducing agent and stabilizerthe synthesis of gold nanoparticles by photolysis of gold(III)Preysslerpropan-2-ol solution was carried out

Preyssler polyoxometalate (POM) plays the role of trans-ferring electrons from propan-2-ol (S) to gold (III) and alsostabilizing the nanoparticles (1) Consider

POM + S 997888rarr POM (eminus) + SOX

POM (eminus) + Au3+ 997888rarr POM + Au0(1)

The morphology and size of gold nanoparticles were charac-terized by TEMThe TEM image is shown in Figure 1(b)

Interestingly as we can see counterions can affect boththe size and the shape of the nanoparticles So when H+ is acounterion the shapes of the gold nanoparticles were nearlyuniform hexagonal structures and the size of the synthesizedgold nanoparticles varied from 13 to 43 nm (Figure 1(a))When H+ was replaced by Cs+ interestingly a mixture oftubular and spherical gold nanoparticles with the size of 10ndash25 nmwas obtained (Figure 1(b))With respect to the fact thatPreyssler with Cs+ could changemorphology and size of goldnanoparticles it is suggested that the tertiary structure typehas an important effect in this catalysis process

There are three classes of structures which we callthe primary secondary and tertiary structures [29] Het-eropolyanions in the solid state are ionic crystals consistingof large polyanions (primary structure) cations water ofcrystallization and other molecules This three-dimensionalarrangement is the secondary structure In addition to thesetwo structures the tertiary structure is very influential on thecatalytic function of solid heteropolyanions Counter cationsgreatly influence the tertiary structure of heteropolyanionsand the salts are classified by the size of cation into groupA (small metal cations like Na and Cu) and group B (largemetal cations likeCsNH

4 etc) [29] So we can conclude that

the synthesis process can be controlled by tertiary structureof Preyssler Also from Figure 1 it is clear that there is noagglomeration Usually there is a tendency of agglomerationvia Coulomb or van der Waals forces in the synthesis processof nanoparticles [37] Preyssler is an excellent stabilizerto prevent agglomeration In addition Preyssler is easilyseparated after the reaction and will not contaminate the goldnanoparticles

Figure 2 shows UV-Vis absorption spectra of the syn-thesized gold nanoparticles A surface plasmon resonanceband of gold nanoparticles at about 530 nm appeared after45 and 15min in the presence of HP

5and CsP

5 respectively

UV-Vis analysis showed that in the presence of CsP5 gold

nanoparticles were synthesized in shorter timeTEM micrographs of gold-decorated titanium dioxide-

Preyssler with H+ and Cs+ as counterions are shown in Fig-ure 3

In comparison with HP5 there is a higher loading of

gold nanoparticles on titanium dioxide in the presence ofCsP5 Group B salts of polyoxometalates with larger metal

ions like Cs+ have higher surface area than group A Thusit is suggested that because Preyssler acts as a localizedreducing agent a higher surface coverage with CsP

5results


(a)

(b)Figure 1 TEM images of the synthesized Au nanoparticles in thepresence of HP36

5(a) and CsP

5(b)

in enhanced reduction of HAuCl4to gold nanoparticles on

titanium dioxide surface The gold nanoparticles formedusing HP

5and CsP

5are 2ndash10 and 20ndash50 nm respectively

TEMmicrographs for decoration of the amine-function-alized titanium dioxide with gold nanoparticles are shown inFigure 4This figure shows higher loading of gold nanoparti-cles on amine-functionalized titanium dioxide This higherloading can be related to strong electrostatic interactionsbetween negatively charged Preyssler polyoxometalate withpositively charged amine-functionalized titanium dioxideInterestingly for amine-modified titanium dioxide higherloadings were obtained in the presence of CsP

5again So we

can conclude that the tertiary structure in polyoxometalatewhich led to a higher surface coverage can control loadingamounts

Binding of Preyssler to titanium dioxide was confirmedby infrared spectroscopy as shown in Figure 5 Because

0

05

1

15

2

25

350 400 450 500 550 600 650 700

Abso

rban

ce

Wavelength (nm)

(a)

002040608

112141618

350 400 450 500 550 600 650 700

Abso

rban

ce

Wavelength (nm)

(b)

Figure 2 UV-Vis spectra of the synthesized gold nanoparticles inthe presence of HP

5(a) and CsP

5(b)

intermolecular interactions lead to a change in the frequen-cies of the metal-oxygen stretching bands as well as theintensity and position of the corresponding IR bands FTIRspectroscopy can be used to confirm the interaction of HPAswith different molecules [38]

Preysslerrsquos structure gives rise to four types of oxygenthat are responsible for the fingerprints bands of Preyssleranion between 1200 and 600 cmminus1 The characteristic bandsof Preyssler structure [NaP

5W30O110

]14minus are three bandsdue to P-O stretching at 1163 cmminus1 (medium) 1079 cmminus1(medium) and 1022 cmminus1 (weak) and twobands attributed toW-O-W at 941 cmminus1 (medium) and 913 cmminus1 (weak) a bandat 757 cmminus1 (strong) corresponding to W=O and a band at536 cmminus1 (strong) due to P-O bendingThese bands can shiftweaken strengthen or mask in different conditions

In Figure 5 compared with the initial Preysslerrsquos struc-ture the bands arising from the synthesized nanocompositechanged obviously either in intensity or in position Our find-ings show thatmany of the vibrational bands of Preyssler haveblue-shifted and many of them have red-shifted indicatingthat many of the bonds were strengthened and the otherswere weakened As we can see there is a significant shiftin the W-O-W vibrations from 941 to 958 cmminus1 and somedisplacements in the P-O stretchings from 1163 and 1079 cmminus1to 1156 and 1089 cmminus1 respectively The characteristic bandin 913 cmminus1 is unchanged and the W=O band along with


(a)

(b)

Figure 3 TEM images of AuHP5TiO2(a) and AuCsP

5TiO2(b)

the P-O bending bands are overlapped by that of titaniumdioxide With respect to the PO

4tetrahedrons vibrating

almost independently from the rest of the anion the signif-icant blue shift of 17 cmminus1 in the W-O-W vibrational modesuggests that Preyssler interacts strongly with the titaniumdioxide surface and binds to it by the oxygen atoms in theW-O-W positions

Titanium dioxide does not have significant bands be-tween 800 and 1200 cmminus1 and shows a broad band between600 and 800 cmminus1 The W=O band placed in the 757 cmminus1is masked by that of titanium dioxide These observationsindicate that the Preysslerrsquos anion chemically adsorbed ontothe surface of titanium dioxide and interaction betweenPreysslerrsquos anions and support mostly caused the distortionof anion and thus substantially not only weakened the IRvibrations covered up by the titanium dioxide backgroundbut also caused some displacements in some bands It is

(a)

(b)

Figure 4 TEM images of AuHP5NH2-TiO2(a) and AuCsP

5

NH2-TiO2(b)

completely common in IR spectra of polyoxometalates wheninteracting with different counter ions [39] Additionallythe organosilanes and amine groups characteristic peaks(2921 1637 1508 and 1458 cmminus1) in the FTIR spectra of thenanocomposites confirmed the presence of ligand on the sur-face

Finally XRD analysis confirmed the presence of gold na-noparticles and titanium dioxide in the synthesized nano-composites (Figure 6)

The bleaching of the malachite green in a designed pho-toreactor was performed as a test reaction to estimate the cat-alytic activity of both synthesized nanocomposites (AuCsP

5

-TiO2and AuCsP

5NH2-TiO2) We checked the intensity

changes of UV band in malachite green in a photocatalyticreaction Figure 7 summarizes UV-Vis results It is clear thatthe photocatalytic activity strongly depends on the used cat-alyst


0102030405060708090

100

400900140019002400290034003900

Tran

smitt

ance

()

Wavenumber (cmminus1)

Figure 5 FTIR spectra of AuCs-P5NH2-TiO2

10 20 30 40 50 60 70

Cou

nts

0

25

100

225Thin layer

Position (∘2120579)

Figure 6 XRD pattern of AuCsP5TiO2

0123456789

10

0 5 10 15 20 25 30 35 40 45 50

Con

cent

ratio

n (p

pm)

Time (min)

TiO2

CsP5

TiO2CsP5

AuCsP5TiO2

AuCsP5NH2-TiO2

Figure 7 Bleaching of malachite green in the presence of CsP5

TiO2 TiO2CsP5 AuCsP

5TiO2 and AuCsP

5NH2-TiO2

As a control experiment series in the same conditionswe studied the bleaching of the dye in the presence of tita-nium dioxide CsP

5 and titanium dioxide-CsP

5(Figure 7)

As we can see there is an increase in photocatalytic activityresulting in 100 bleaching of the dye after 20 minutes in thepresence of AuCsP

5TiO2 As expected when Preyssler joins

with titanium dioxide photocatalytic activity is increased Itis suggested that CsP

5as a cocatalyst can improve photocat-

alytic activity of titanium dioxide The reduced photoactivity

of CsP5-aminemodified titanium dioxide-gold nanoparticles

in Figure 7 can be attributed to higher gold loading in thisnanocomposite which might decrease the total effectivetitanium dioxide surface area during the bleaching of thedye At the end of the reaction the photocatalyst wasfiltered washed dried and reused in another reaction Therecycled photocatalyst was used for three reactions withoutobservation of appreciable loss in its catalytic activity It issuggested that because CsP

5is not very soluble it is present

in the photocatalysts during the dye bleaching runs

4 Conclusion

Green eco-friendly recyclable and easily preparable cesiumsalt of Preysslerrsquos anion is an efficient solid acid catalyst forthe synthesis of gold nanoparticles as well as decorationof gold nanoparticles on the surface of titanium dioxideImportant features of this polyanion are high thermal andhydrolytic stability throughout a wide pH rangeThus a widerange of chemical reactions can be affected without loss ofstructure or activity Our findings show that counterions playan important role in the decoration of titanium dioxide andPreyssler acts as a reducing agent and catalytic linker

We observed that both of the synthesized nanocompos-ites with pure andmodified titaniumdioxide exhibit excellentphotocatalytic activity in the bleaching of malachite greenwhen exposed to UV irradiation The remarkable bleachingof malachite green in the presence of these nanocompositesindicates that the treatments of other organic pollutants couldbe performed in the presence of this catalyst in order to obtaina perfect bleaching degree This catalytic activity can also beextended to the other photocatalytic reactions

References

[1] H Yu S Zhang H Zhao B Xue P Liu and G WillldquoHigh-performance TiO

2photoanode with an efficient electron

transport network for dye-sensitized solar cellsrdquo Journal ofPhysical Chemistry C vol 113 no 36 pp 16277ndash16282 2009

[2] H Yu S ZhangH Zhao andH Zhang ldquoPhotoelectrochemicalquantification of electron transport resistance of TiO

2photoan-

odes for dye-sensitized solar cellsrdquo Physical Chemistry ChemicalPhysics vol 12 no 25 pp 6625ndash6631 2010

[3] M R Hoffmann S T Martin W Choi and D W BahnemannldquoEnvironmental applications of semiconductor photocatalysisrdquoChemical Reviews vol 95 no 1 pp 69ndash96 1995

[4] A Fujishima K Hashimoto T Iyoda S Fukayama T Yoshi-moto and T Saitoh US Patent US6939611 2005

[5] G K Mor O K Varghese M Paulose and C A Grimes ldquoAself-cleaning room temperature titania-nanotube hydrogen gassensorrdquo Sensor Letters vol 1 no 1 pp 42ndash46 2003

[6] E Bessa J G L SantAnna andM J Dezotti ldquoPhotocatalysis anapproach to the treatment of oil field produced watersrdquo Journalof Advanced Oxidation Technologies vol 4 no 2 pp 196ndash2021999

[7] J C Cardoso TM Lizier andM V B Zanoni ldquoHighly orderedTiO2nanotube arrays and photoelectrocatalytic oxidation of

aromatic aminerdquoApplied Catalysis B vol 99 no 1-2 pp 96ndash1022010


[8] AHagfeldt andMGratzel ldquoMolecular photovoltaicsrdquoAccountsof Chemical Research vol 33 no 5 pp 269ndash277 2000

[9] M Anpo ldquoPhotocatalysis on titanium oxide catalysts ap-proaches in achieving highly efficient reactions and realizing theuse of visible lightrdquoCatalysis Surveys from Japan vol 1 no 2 pp169ndash179 1997

[10] D R Baker and P V Kamat ldquoPhotosensitization of TiO2

nanostructures with CdS quantum dots particulate versustubular support architecturesrdquo Advanced Functional Materialsvol 19 no 5 pp 805ndash811 2009

[11] H Kikuchi M Kitano M Takeuchi M Matsuoka M Anpoand P V Kamat ldquoExtending the photoresponse of TiO

2to the

visible light region photoelectrochemical behavior of TiO2thin

films prepared by the radio frequency magnetron sputteringdeposition methodrdquo Journal of Physical Chemistry B vol 110no 11 pp 5537ndash5541 2006

[12] K Wilke and H D Breuer ldquoThe influence of transition metaldoping on the physical and photocatalytic properties of titaniardquoJournal of Photochemistry and Photobiology A vol 121 no 1 pp49ndash53 1998

[13] P Bouras E Stathatos and P Lianos ldquoPure versus metal-ion-doped nanocrystalline titania for photocatalysisrdquo AppliedCatalysis B vol 73 no 1-2 pp 51ndash59 2007

[14] C E Gomez J R V Garcia J A T Antonio M A C Jacomeand C A J Chavez ldquoPt nanoparticles on titania nanotubes pre-pared by vapor-phase impregnation-decomposition methodrdquoJournal of Alloys and Compounds vol 495 no 2 pp 458ndash4612010

[15] K Nishijima T Fukahori N Murakami T-A Kamai TTsubota and T Ohno ldquoDevelopment of a titania nanotube(TNT) loaded site-selectively with Pt nanoparticles and theirphotocatalytic activitiesrdquo Applied Catalysis A vol 337 no 1 pp105ndash109 2008

[16] Y Yin X Tan F Hou and L Zhao ldquoEfficient synthesis of titaniananotubes and enhanced photoresponse of Pt decorated TiO

2

for water splittingrdquo Frontiers of Chemical Engineering in Chinavol 3 no 3 pp 298ndash304 2009

[17] B-L He B Dong and H-L Li ldquoPreparation and electrochem-ical properties of Ag-modified TiO

2nanotube anode material

for lithium-ion batteryrdquo Electrochemistry Communications vol9 no 3 pp 425ndash430 2007

[18] I Paramasivam J M Macak and P Schmuki ldquoPhotocatalyticactivity of TiO

2nanotube layers loaded with Ag and Au

nanoparticlesrdquo Electrochemistry Communications vol 10 no 1pp 71ndash75 2008

[19] L P An X P Gao G R Li T Y Yan H Y Zhu and PW ShenldquoElectrochemical lithium storage of titania nanotubes modifiedwith NiO nanoparticlesrdquo Electrochimica Acta vol 53 no 13 pp4573ndash4579 2008

[20] A Kukovecz M Hodos Z Konya and I Kiricsi ldquoComplex-assisted one-step synthesis of ion-exchangeable titanate nan-otubes decorated with CdS nanoparticlesrdquo Chemical PhysicsLetters vol 411 no 4-6 pp 445ndash449 2005

[21] A Benoit I Paramasivam Y-C Nah P Roy and P SchmukildquoDecoration of TiO

2nanotube layers with WO

3nanocrystals

for high-electrochromic activityrdquoElectrochemistry Communica-tions vol 11 no 4 pp 728ndash732 2009

[22] M A Khan and O-B Yang ldquoPhotocatalytic water splitting forhydrogen production under visible light on Ir and Co ionizedtitania nanotuberdquo Catalysis Today vol 146 no 1-2 pp 177ndash1822009

[23] M Muruganandham A Ramakrishnan Y Kusumoto andM Sillanpaa ldquoAre dopant-stabilized visible light-responsivephotocatalysts efficient and stablerdquo Physical Chemistry PhysicalChemistry vol 12 no 44 pp 14677ndash14681 2010

[24] A Pearson H Jani K Kalantarzadeh S K Bhargava and VBansal ldquoGold nanoparticle-decorated keggin ionsTiO

2photo-

cocatalyst for improved solar light photocatalysisrdquo Langmuirvol 27 no 11 pp 6661ndash6667 2011

[25] A Pearson S K Bhargava and V Bansal ldquoUV-switchablepolyoxometalate sandwiched betweenTiO

2andmetal nanopar-

ticles for enhanced visible and solar light photococatalysisrdquoLangmuir vol 27 no 15 pp 9245ndash9252 2011

[26] K Mori K Furubayashi S Okada and H Yamashita ldquoSynthe-sis of Pd nanoparticles on heteropolyacid-supported silica bya photo-assisted deposition method an active catalyst for thedirect synthesis of hydrogen peroxiderdquoRSCAdvances vol 2 no3 pp 1047ndash1054 2012

[27] B Keita T Liu and L Nadjo ldquoSynthesis of remarkably stabi-lized metal nanostructures using polyoxometalatesrdquo Journal ofMaterials Chemistry vol 19 no 1 pp 19ndash33 2009

[28] I V Kozhevnikov ldquoCatalysis by heteropoly acids andmulticom-ponent polyoxometalates in liquid-phase reactionsrdquo ChemicalReviews vol 98 no 1 pp 171ndash198 1998

[29] NMizuno andMMisono ldquoHeterogeneous catalysisrdquoChemicalReviews vol 98 no 1 pp 199ndash218 1998

[30] J Liu S Liu L QuM T Pope and C Rong ldquoDerivatives of the21-tungsto-9-antimonate heteropolyanionmdashpart 1 inclusion oflanthanide cationsrdquo Transition Metal Chemistry vol 17 no 4pp 311ndash313 1992

[31] J-F Liu Y-G Chen L Meng J Guo Y Liu and M TPope ldquoSynthesis and characterization of novel heteropoly-tungstoarsenates containing lanthanides [LnAs

4W40O140]25minus

and their biological activityrdquo Polyhedron vol 17 no 9 pp 1541ndash1546 1998

[32] M H Alizadeh S P Harmalker Y Jeannin J Martin-Frereand M T Pope ldquoA heteropolyanion with fivefold molecularsymmetry that contains a nonlabile encapsulated sodium ionThe structure and chemistry of [NaP

5W30O110]14minusrdquo Journal of

the American Chemical Society vol 107 no 9 pp 2662ndash26691985

[33] F F Bamoharram M M Heravi M Roshani and N TavakolildquoN-oxidation of pyridine carboxylic acids using hydrogen per-oxide catalyzed by a green heteropolyacid catalyst preysslerrsquosanion [NaP

5W30O110]14minusrdquo Journal ofMolecular Catalysis A vol

252 no 1-2 pp 219ndash225 2006[34] F F Bamoharram M M Heravi M Roshani M Jahangir

and A Gharib ldquoPreyssler catalyst [NaP5W30O110]14minus a green

efficient and reusable catalyst for esterification of salicylic acidwith aliphatic and benzylic alcoholsrdquo Applied Catalysis A vol302 no 1 pp 42ndash47 2006

[35] F F Bamoharram ldquoRole of polyoxometalates as green com-pounds in recent developments of nanosciencerdquo Synthesis andReactivity in Inorganic Metal-Organic and Nano-Metal Chem-istry vol 41 no 8 pp 893ndash922 2011

[36] A Ayati A Ahmadpour F F Bamoharram M M Heraviand H Rashidi ldquoPhotocatalytic synthesis of gold nanoparticlesusing preyssler acid and their photocatalytic activityrdquo ChineseJournal of Catalysis vol 32 no 6 pp 978ndash982 2011

[37] G Sun Q Li R Xu J Gu M Ju and E Wang ldquoControllablefabrication of platinum nanospheres with a polyoxometalate-assisted processrdquo Journal of Solid State Chemistry vol 183 no11 pp 2609ndash2615 2010


[38] X K Fu J R Chen L Q Li QWang and Y Sui ldquoOrganophos-phonotungstic HPA of Keggin type with sulfo taurine andglycine substituted ethylphosphonic acids as the coordinatecenterrdquo Chinese Chemical Letters vol 14 no 5 pp 515ndash5182003

[39] F F Bamoharram ldquoVibrational spectra study of the interactionsbetween keggin heteropolyanions and amino acidsrdquoMoleculesvol 14 no 9 pp 3214ndash3221 2009

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


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Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

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Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


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Medicinal ChemistryInternational Journal of


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Applied ChemistryJournal of



Theoretical ChemistryJournal of


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Spectroscopy

Analytical ChemistryInternational Journal of


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Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


dioxide surfaces [24] Pearson and coworkers demonstrateddecoration of titanium dioxide with metal nanoparticlesusingKeggin as an efficient polyoxometalate [25] In additionpolyoxometalates can reduce noble metals to prepare nan-oclusters in the presence of light [26 27] Anyway althoughthere are many structural types of polyoxometalates themajority of processes use the most common Keggin typeowing to its availability and chemical stability and the roleof Preyssler polyoxometalate [NaP

5W30O110

]14minus has beenlargely overlooked

The oval-shaped Preyssler polyoxometalate consists ofa cyclic assembly of five PW

6O22

units each derived fromthe spherical Keggin anion [PW

12O40]3minus by the removal

of two sets of three corner-sharing WO6octahedra The

[XM12O40]119899minus (Keggin structure) consists of one XO

4tetrahe-

dron surrounded by fourM3O13sets linked together through

oxygen atoms The Preysslerrsquos anion structure consists offive PO

4tetrahedron surrounded by 30 WO

6which are

connected to each other by edge and corner-sharing oxygensA sodium ion is located within the polyanion on the five-foldaxis and 125 A above the pseudomirror plane that containsthe five phosphorus atoms

The properties of polyoxometalates such as thermal sta-bility as well as hydrolytic stability and catalytic activity aresensitive to their structures [28 29] In addition the kind andnumber of counterions as well as their constituent elementshave an important effect on the catalytic activity chemicalbehavior and the redox properties of the polyoxometalatesDue to these reasons a different behavior and activity isexpected for each polyoxometalate with a different struc-ture Among a wide variety of studied heteropolyacids (animportant class of polyoxometalates) with different size andstructures there are only three anions [NaSb

9W21O86]minus

[NaAs4W40O140

]25minus and [NaP5W30O110

]14minus that have beenreported to encapsulate rare-earth ions [30ndash32] The latterof these Preysslerrsquos anion is one of the largest knownpolyanions and important advantages of this polyanionover the Keggin and Dawson heteropolyacids are (i) morethermal stability (ii) more hydrolytic stability (pH = 0ndash12) (iii) larger number of counter cations and (iv) largernumber of metal atoms These properties are very importantin catalytic processes especially when we work in acidic andbasic conditions For example while Keggin and Dawson[X2M18O62]119899minus polyoxometalates are stable in pH= 1ndash3 and 1ndash

6 respectively the Preyssler is stable in pH = 0ndash12 Addition-ally while the oxidation of organic substrates by hydrogenperoxide in the presence of Keggin proceeds via degradationof structure to an active peroxopolyoxometalate the Preysslercatalyst catalyzes the reactions without any degradation ofstructure [33] This is very important in catalytic reactions inthe presence of hydrogen peroxide The large anion with thelarger number of metal atoms also provides many ldquositesrdquo onthe oval-shapedmolecule that are likely to render the catalysteffective better than Keggin and Dawson types

In continuation of our works on applications of Preyssleracid H

14[NaP5W30O110

] in catalytic and photocatalyticreactions [34 35] and cited references in [35] and extendingthe applications of Preyssler and also due to the importanceof metal-titanium dioxide decoration it is highly relevant to

know what occurs if the Preysslerrsquos anion joins with titaniumdioxide and use it as a catalytic linker for reducing goldions In addition it is also important to investigate the roleof another polyoxometalates apart from Keggin heteropoly-acids We think the most important and credential part ofour work is to introduce and establish nanocesuim salt ofPreyssler type heteropolyacid Cs

12H2[NaP5W30O110

] whichcan be applied as an efficient and competing nanocatalystwith those of Keggin type which have been already reportedas bulk

Also another goal in this research was to answer thisquestion does counter cation in the Preyssler structurewhich is responsible for primary secondary and tertiarystructures have an important role on loading of gold nano-particles onto titanium dioxide

To this purpose in the present work at first in contin-uation of our earlier works [36] we investigated the per-formance and capability of cesium salt of sodium 30-tungstopentaphosphate Cs

12H2[NaP5W30O110

] in synthesisof gold nanoparticles and after that we studied decoration oftitanium dioxide with gold nanoparticles in the presence ofthe Preyssler with different counterions including Cs+ andH+ Interestingly we have found that the Preyssler catalystwith Cs+ as counterion not only can change shape and sizeof gold nanoparticles but also can lead to a higher loadingof gold nanoparticles onto titanium dioxide Also we haveinvestigated the application of different forms of Preysslernanocomposites for bleaching of malachite green

2 Experimental

21 Materials and Methods All of the chemicals were pur-chased from Merck and Sigma Aldrich Companies and usedas received FT-IR spectra were recorded with a Bruckerscientific spectrometer (solid sample KBr pellets) The syn-thesized nanostructures were characterized by TransmissionElectron Microscopy (PHILIPS CM-120 and JEOL-2200FSFEG) A double beam spectrophotometer UV-Vis was usedfor UV-Vis analysis (OPTIZEN 3220)

22 Preparation of HP5and CsP

5 At first 33 g Na

2WO4sdot

2H2O was dissolved in 45mL water by stirring and then

25mL of phosphoric acid 85 was added The mixture wasrefluxed for 5 h After that 10mL H

2O and 10 gKCl were

added into the abovemixture to form a light green precipitateThe green precipitate was obtained by filtration and washedsuccessively by 2M aqueous solution of CH

3COOK and

methanol Recrystallization in hot water led to formation ofK125

Na15[NaP5W30O110

] in needle white color crystalsPreyssler acid H

14[NaP5W30O110

] (HP5) was prepared

by the passage of a solution of the K125

Na15[NaP5W30O110

]in water through a column (50 cm) of Dowex 50WX8 inthe H+ form and evaporation of the elute to dryness undervacuum

For the preparation of CsP5 Preyssler acid and CsCl in a

mole ratio of 1 14 were put into a mortar and several drops ofsurfactant Triton X-100 were added The formed microcellsin the solid state reaction owing to the interaction between































5and CsP

5 respectively







5results


(a)


5(a) and CsP

5(b)



5and CsP



5again So we



0

05

1

15

2

25

350 400 450 500 550 600 650 700

Abso

rban

ce

Wavelength (nm)

(a)

002040608

112141618

350 400 450 500 550 600 650 700

Abso

rban

ce

Wavelength (nm)

(b)


5(a) and CsP

5(b)



5W30O110




(a)

(b)


5TiO2(b)





(a)

(b)


5

NH2-TiO2(b)




5

-TiO2and AuCsP




0102030405060708090

100

400900140019002400290034003900

Tran

smitt

ance

()



10 20 30 40 50 60 70

Cou

nts

0

25

100

225Thin layer



0123456789

10

0 5 10 15 20 25 30 35 40 45 50

Con

cent

ratio

n (p

pm)

Time (min)

TiO2

CsP5

TiO2CsP5

AuCsP5TiO2

AuCsP5NH2-TiO2


TiO2 TiO2CsP5 AuCsP

5TiO2 and AuCsP

5NH2-TiO2



5(Figure 7)










4 Conclusion



References





2photoan-














2to the








2












3nanocrystals





2photo-



2andmetal nanopar-








4W40O140]25minus

























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of































5and CsP

5 respectively







5results


(a)


5(a) and CsP

5(b)



5and CsP



5again So we



0

05

1

15

2

25

350 400 450 500 550 600 650 700

Abso

rban

ce

Wavelength (nm)

(a)

002040608

112141618

350 400 450 500 550 600 650 700

Abso

rban

ce

Wavelength (nm)

(b)


5(a) and CsP

5(b)



5W30O110




(a)

(b)


5TiO2(b)





(a)

(b)


5

NH2-TiO2(b)




5

-TiO2and AuCsP




0102030405060708090

100

400900140019002400290034003900

Tran

smitt

ance

()



10 20 30 40 50 60 70

Cou

nts

0

25

100

225Thin layer



0123456789

10

0 5 10 15 20 25 30 35 40 45 50

Con

cent

ratio

n (p

pm)

Time (min)

TiO2

CsP5

TiO2CsP5

AuCsP5TiO2

AuCsP5NH2-TiO2


TiO2 TiO2CsP5 AuCsP

5TiO2 and AuCsP

5NH2-TiO2



5(Figure 7)










4 Conclusion



References





2photoan-














2to the








2












3nanocrystals





2photo-



2andmetal nanopar-








4W40O140]25minus

























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


(a)


5(a) and CsP

5(b)



5and CsP



5again So we



0

05

1

15

2

25

350 400 450 500 550 600 650 700

Abso

rban

ce

Wavelength (nm)

(a)

002040608

112141618

350 400 450 500 550 600 650 700

Abso

rban

ce

Wavelength (nm)

(b)


5(a) and CsP

5(b)



5W30O110




(a)

(b)


5TiO2(b)





(a)

(b)


5

NH2-TiO2(b)




5

-TiO2and AuCsP




0102030405060708090

100

400900140019002400290034003900

Tran

smitt

ance

()



10 20 30 40 50 60 70

Cou

nts

0

25

100

225Thin layer



0123456789

10

0 5 10 15 20 25 30 35 40 45 50

Con

cent

ratio

n (p

pm)

Time (min)

TiO2

CsP5

TiO2CsP5

AuCsP5TiO2

AuCsP5NH2-TiO2


TiO2 TiO2CsP5 AuCsP

5TiO2 and AuCsP

5NH2-TiO2



5(Figure 7)










4 Conclusion



References





2photoan-














2to the








2












3nanocrystals





2photo-



2andmetal nanopar-








4W40O140]25minus

























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


(a)

(b)


5TiO2(b)





(a)

(b)


5

NH2-TiO2(b)




5

-TiO2and AuCsP




0102030405060708090

100

400900140019002400290034003900

Tran

smitt

ance

()



10 20 30 40 50 60 70

Cou

nts

0

25

100

225Thin layer



0123456789

10

0 5 10 15 20 25 30 35 40 45 50

Con

cent

ratio

n (p

pm)

Time (min)

TiO2

CsP5

TiO2CsP5

AuCsP5TiO2

AuCsP5NH2-TiO2


TiO2 TiO2CsP5 AuCsP

5TiO2 and AuCsP

5NH2-TiO2



5(Figure 7)










4 Conclusion



References





2photoan-














2to the








2












3nanocrystals





2photo-



2andmetal nanopar-








4W40O140]25minus

























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0102030405060708090

100

400900140019002400290034003900

Tran

smitt

ance

()



10 20 30 40 50 60 70

Cou

nts

0

25

100

225Thin layer



0123456789

10

0 5 10 15 20 25 30 35 40 45 50

Con

cent

ratio

n (p

pm)

Time (min)

TiO2

CsP5

TiO2CsP5

AuCsP5TiO2

AuCsP5NH2-TiO2


TiO2 TiO2CsP5 AuCsP

5TiO2 and AuCsP

5NH2-TiO2



5(Figure 7)










4 Conclusion



References





2photoan-














2to the








2












3nanocrystals





2photo-



2andmetal nanopar-








4W40O140]25minus

























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of







2to the








2












3nanocrystals





2photo-



2andmetal nanopar-








4W40O140]25minus

























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of













Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

research article cesium salt of sodium 30 ...cesium salt of sodium 30-tungstopentaphosphate: an...

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