research article adsorption of organophosphate pesticide...

Research ArticleAdsorption of Organophosphate Pesticide Dimethoate onGold Nanospheres and Nanorods

Tatjana MomiT1 Tamara LazareviT Pašti1 Una BogdanoviT1 Vesna Vodnik1

Ana MrakoviT1 Zlatko RakoIeviT1 Vladimir B PavloviT2 and Vesna VasiT1

1 Institute of Nuclear Sciences Vinca University of Belgrade PO Box 522 11001 Belgrade Serbia2Faculty of Agriculture University of Belgrade PO Box 127 11080 Zemun Serbia

Correspondence should be addressed to Tatjana Momic momictvincars

Received 21 July 2016 Revised 28 September 2016 Accepted 10 October 2016

Academic Editor Jorge Perez-Juste

Copyright copy 2016 Tatjana Momic et alThis is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Organophosphorus pesticide dimethoate was adsorbed onto gold nanospheres and nanorods in aqueous solution using batchtechnique Adsorption of dimethoate onto gold nanoparticles was confirmed by UV-Vis spectrophotometry TEM AFM and FTIRanalysis The adsorption of nanospheres resulted in aggregation which was not the case with nanorods Nanoparticles adsorptionfeatures were characterized using Langmuir and Freundlich isotherm models The Langmuir adsorption isotherm was found tohave the best fit to the experimental data for both types of nanoparticles Adsorption capacity detected for nanospheres is 456mggand for nanorods is 571mgg Also nanoparticles were successfully used for dimethoate removal from spiked drinking water whilenanospheres were shown to be more efficient than nanorods

1 Introduction

Organophosphorus pesticides (OPs) are commonly used inagriculture [1] Dimethoate (Scheme 1) as one of the majorOPs is widely used in the fruit and field crops to promotethe development of agricultural production because of itslow persistence and biodegradation [2] Still extreme use ofdimethoate could lead to excessive residues accumulating inthe environment and in human body through the food chainand could cause death [3 4] For these reasons there is thenecessity of the efficient removal of OPs in order to controlthe levels of these compounds in food and the environmentespecially drinking water resources

One of the main strategies for removal of pesticides fromwater is the adsorption on different types of materials [5]Numerous studies can be found in the literature reportingOPs adsorption on mineral surfaces [6 7] carbon-basedmaterials [8ndash10] and materials from graphene family [11]Nowadays application of nanoparticles (NPs) in environ-mental remediation such as water purification by removalof OPs is significantly progressing because of nanomaterial

chemistry advantages with respect to conventional technolo-gies [1 12] NPs owe their potential to the high active surfacearea and surface reactivity compared to conventional bulkmaterials [5 13] Noble metal mainly silver and gold nanos-tructures have been used for water purification particularlybecause the chemistry occurs at room temperature and withhigh efficiency the chemical procedures involved are simpleso they can adsorb the pesticide molecules with ease whichis making this process highly practical [1 5] Nanosilverand nanogold bioconjugate synthesized on the surface offungal strain Rhizopus oryzae were used for removal ofvarious organophosphate pesticides [14 15] It was shownthat silver and gold nanospheres bare and supported onalumina adsorb organophosphorous pesticides chlorpyrifosand malathion These features of nanoparticles present aconvenient and cost-effective system for the removal ofpesticides from drinking water [1 16] Gold is not cheapmaterial and still it possesses properties as robustness andunique spectral characteristics The spectral characteristicsof gold nanoparticles are more pronounced than those oftheir silver counterparts The change in dielectric constant

Hindawi Publishing CorporationJournal of NanomaterialsVolume 2016 Article ID 8910271 11 pageshttpdxdoiorg10115520168910271

2 Journal of Nanomaterials

PO

O

O

S

S

NH

CH3

H3C

H3C

Scheme 1 Dimethoate

of silver upon pesticide binding which is less comparedto that of gold [1 16] gives the gold advantage over silveror some cheaper metal nanomaterials Nair and Pradeepsupported gold nanoparticles on alumina and made onlinewater filter to demonstrate technology of OPs removal fromwater in rural communities in India [17] Moreover waterpurification from an environmental perspective by usinggold-poly(dimethylsiloxane) nanocomposite in the form of afoam was described [18]

Rod-shape nanoparticles possess several advantages overthe nanospheres such as high surface area and good electronmediation capability [19ndash21] However to date to the best ofour knowledge the use of gold nanorods for adsorption ofOP dimethoate has not been reported In this contributionwe considered gold nanoparticles of two different shapesnanospheres (NSs) and nanorods (NRs) as adsorbents ofdimethoate from aqueous solutions The aim of our studywas to characterize the interaction between dimethoate andgold nanorods NSs and NRs have different physical andchemical properties so the effects of these properties ontheir performance as adsorbents are discussed We have alsocompared direct uses of investigated NPs for removal ofdimethoate from drinking water

2 Experimental

21 Chemicals and Materials All the chemicals used werepurchased from Sigma Aldrich Co St Louis MO 400-meshCu grid coated in a thin layer of carbon was purchased fromTed Pella Inc Redding CA MICA was purchased from SPISuppliesWest Chester PAMilli-Q deionized water used had182MΩ electrical resistivity22 Synthesis of Gold Colloids

221 Synthesis of Gold Nanospheres Colloidal dispersion ofgold nanospheres (AuNSs) was prepared using a reductionof precursor salt (HAuCl4) solution by sodium citrate asdescribed elsewhere [22 23] In a typical synthesis 200mLof 1mM HAuCl4 solution was stirred and heated in a round-bottom flask fitted with a reflux condenser After the solutionreached the boiling point 10mL of 388mM sodium citratewas rapidly added The colloidal dispersion was boiled andstirred for additional 15min and then cooled down to roomtemperaturewith continuous stirringThefinal concentrationof Au in colloidal dispersion was found to be 091mM(179mgL)

222 Synthesis of Gold Nanorods Colloidal dispersion ofgold nanorods (AuNRs) was prepared using a seed-mediated

growth approach [24] Colloidal gold seed solution was firstprepared as follows 5mL of 200mM CTAB solution wasadded to 5mL of 05mM HAuCl4 solution Next 06mLof ice-cold 10mM NaBH4 (reducing agent) solution wasinjected into the yellow solution all at once while stirringvigorously Stirring was stopped after 2minThe color of seedsolution was changed to brownish-yellow and was stable for2 hours In the next step the stock solution was preparedas follows 025mL of 4mM AgNO3 solution was added to5mL of 200mM CTAB solution and gently mixed in orderto add 5mL of 1mM HAuCl4 solution All solutions otherthan those of gold and CTAB were prepared fresh daily Theyellow stock solution became colorless after adding 70 120583Lof 788mM ascorbic acid Thereafter 10 120583L of seed solutionwas added to the stock solution CTAB solution crystallizesat 25∘C so colloid was synthesized in the temperature rangefrom 27∘C to 30∘C to ensure proper nanorods growth Aviolet-blue color appeared within 15ndash20min Rods wereconcentrated and separated from spheres and surfactant bycentrifugation (10000 rpm for 15min) After centrifugingthe surfactant was removed and the precipitate was furtherredispersed in deionized waterThe final concentration of Auin colloidal dispersion was found to be 001mM (2mgL)

23 Characterization of AuNPs and Their Dimethoate Con-jugates The NPs interactions with dimethoate were char-acterized using UV-Visible (UV-Vis) spectroscopy (Lambda35 UV-Vis Spectrometer Perkin Elmer Inc WalthamMA USA) All spectra were background-subtracted againstdeionized water which is the reaction solvent Over a periodof 24 hours spectra were recorded Transmission electronmicroscope (TEM) images of the NPs and NPs-dimethoateassembly were obtained using TEM JEOL JEM-1400 (JeolLtd Tokyo Japan) operated at 120 kV A total of 5 120583L of thereaction solution was pipetted onto the surface of a 400-meshCu grid coated in a thin layer of carbon and allowed to dry onthe air Atomic force microscopic (AFM) images of AuNPs inthe absence and presence of dimethoate were recorded usingMultimode Quadrex SPM with Nanoscope IIIe controller(Veeco Instruments Inc Camarillo CA) at room tem-perature using AFM-FM technique and force modulationprobe holder with a piezoelectric bimorph and a commercialVeeco FESP probe with a cantilever Mica substrates wereprepared for imaging as follows Freshly cleaved mica wasmodified with a 100 120583L deposit of 001 3-(aminopropyl)-triethoxysilane (APTES) solution After a 20min incubationperiod the mica surface was rinsed six times with 1mLaliquots of water and dried with compressed nitrogen [25]A drop of 10 120583L suspension of AuNPs without and withdimethoate was deposited on mica surface and incubatedfor 30min followed by repeated washing with deionizedwater to remove any unbound materials and dried in air forAFMmeasurements [26] Fourier transform infrared (FTIR)spectra of dimethoate as well as dimethoate in the presenceof Au nanoparticles were recorded on Nicolet IS 50 FT-IR Spectrometer (Thermo Fisher Scientific Waltham MAUSA) Samples were prepared by dripping the solution onglass slides and left to dry on the air Samples were analyzedat ambient conditions in themid-IR region (400ndash4000 cmminus1)

Journal of Nanomaterials 3

Nicolet IS 50 FT-IR Spectrometer was operating in the ATRmode and measuring resolution was 4 cmminus1 with 32 scans

24 Batch Adsorption Experiments The adsorption experi-ments were performed via the batch technique in aqueoussolution at pH 57 at the temperature of 25∘C for 24 hoursof shaking Adsorption of dimethoate onto gold nanoparti-cles was done under various conditions such as adsorbentdosage (2ndash200mgL) and initial dimethoate concentration(2ndash1150mgL) Samples were centrifuged at 14000 rpm for20min and measurement of dimethoate remaining concen-tration in the solution was done using Waters ACQUITYUltraperformance Liquid Chromatography (UPLC) systemcoupled with a TUV detector controlled by the Empowersoftware Chromatographic separations were run on anACQUITY UPLC BEH C18 column 17 120583m 100mm times21mm column (Waters Milford MA USA) The analyses ofdimethoatewere done under isocratic conditionswithmobilephase consisting of 10 acetonitrile and 90water (vv)Theelutions were monitored at 230 nm The eluent flow rate was02mLminminus1 and the injection volume was 10 120583L [10] Theamount of dimethoate adsorbed onto gold nanoparticles atequilibrium adsorption capacity 119902119890 (mgg) was calculated bythe following relationship [27]

119902119890 = 119881 (1198880 minus 119888119890)119882 (1)

where 119888119890 is the equilibrium concentration of dimethoate(mgL) V is the volume of the solution (L) and W is theweight of the gold nanoparticles as an adsorbent (mg) In allexperiments the volume of the solution was 1mL

3 Results and Discussion

31 Spectrophotometric Analysis of AuNPs and Their Con-jugates Adsorption of dimethoate on gold nanoparticles(spheres and rods) was first followed spectrophotometricallyFigure 1 shows the changes in the absorption spectra of goldnanoparticles upon exposure to 05 times 10minus3M dimethoatefor 24 hours All the experiments were repeated at leastthree times with another set of AuNPs and the resultswere reproducible Trace A in Figure 1(a) is the absorptionspectrum of citrate-capped Au nanospheres with absorptionmaximum at 524 nm and trace B was taken immediatelyafter the addition of dimethoate to nanosphere solutionThe subsequent traces were taken at 20-minute intervaltime up to 5 hours The next two traces C and D wererecorded after 12 and 24 hours respectively As can be seenfrom the spectra surface plasmon resonance (SPR) band ofAuNSs at 524 nm after mixing with dimethoate decreased inintensity and new broad absorption peak emerged at longerwavelength The absorption intensity of the new absorptionpeak increased with time accompanied with further red shift(Figure 1(a)) The reduction of the intensity of the originalsurface plasmon and the appearance of a broad absorption atlonger wavelengths noticed in the first 5 hours are attributedto the aggregation of NSs Aggregation occurred due toreplacement of citrate anions on the surface of AuNS with

dimethoate which consequently reduced the surface chargesof the AuNPs [28] Because of the high affinity of the sulphurgroup for gold dimethoate as sulphur-containing ligand wasable to replace the citrate anions on the AuNS surface [29]

The spectrum of NSs incubated with dimethoate for 24hours was the same as the spectrum of bare AuNSs (Figure1(a) trace D) This change indicated that the electrostaticallyattached citrate molecules have been completely replaced bya more stable and covalently bound surface functionalization[30ndash32] Replacing citrate by the sulphur-containing ligandsincreases the stability of nanogold solutions [33] The samepattern of nanogold stabilizationwas noticed after 24 hours oftheir incubation with different concentrations of dimethoate(Figure 2(a)) The highest stabilization of NSs was noticedwith 1 times 10minus2M dimethoate the highest concentration used

Trace A in Figure 1(c) represents the absorption spectrumof CTAB-capped Au nanorods with two plasmon peaksthe dominant one at 765 nm attributed to the surface plas-mon resonance along longitudinal direction and peak at520 nm that represents the surface plasmon resonance alongtransverse direction Trace B was taken immediately afterthe addition of dimethoate to nanorods solution All thesubsequent traces were taken at 20-minute intervals time upto 5 hours The next two traces C and D were recorded after12 and 24 hours respectively It was noticed that absorptionpeaks at 765 nm and 520 nm decreased in intensities whileonly absorption maximum at 756 nm blue shifted Regardingthe fact that no red shift of longitudinal SRP was observedwhich indicates no side-to-side nanorods interaction andeven though blue shift occurred but not correspondinggrowth of band at 520 nm there are no indication of end-to-end nanorods interaction Moreover we observe that after 24hours of nanorods incubation with dimethoate the width ofthe bands was constant (Figure 1(c) trace D) indicating agood dispersion of the nanoparticles in the solution whichconfirmed that no aggregation occurred [34ndash36] The samebehavior ofNRswas noticed after 24 hours of their incubationwith different concentrations of dimethoate (Figure 2(b))As expected positions of LSRP bands vary as a function ofpesticide concentration Since red shift was not observed wecan conclude that NRs did not aggregate As dimethoate isneutral compound stable in acid to neutral conditions withone sulphur atom accessible for interaction while CTAB-capped nanorods are positively charged we suppose thatdimethoate can onlyweakly adsorb on theCTABdouble layerthrough electrostatic forces and not on the AuNRsrsquo surfaceMoreover as the CTAB is preferentially bound onto lateralfacets of nanorods leaving the ends uncoated [35] there isa probability for the dimethoate to covalently bind on thenanorod ends These changes of the AuNRs environmentcould explain LSRP slight blue shift (Figure 1(b))

Since the changes in the characteristic SPR bands in bothNPs solutions in the presence of dimethoate were recordedfor 24 hours the kinetics of NPs interaction with dimethoateare depicted in Figures 1(b) and 1(d) Results in the figuresrepresent the change of absorbance at 524 and 720 nm forAuNSs and at 520 and 765 nm for AuNRs in time The shapeof the kinetic curves clearly indicates that the spectral changesfollow at least two processes in both cases The fast process


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Figure 1 The time dependent UV-Visible spectra showing the absorption of dimethoate on (a) AuNSs and (c) AuNRs Traces A are theabsorption spectra of bareNPs traces Bwere taken immediately after addition of 05times10minus3Mdimethoate toNPs solutions and each followingtracewas taken after 20min TracesC andDwere taken after 12 and 24hours respectivelyThe scanswere taken for 24 hours Timedependenceof dimethoate adsorption on (b) NSs measured at 524 nm and 720 nm and (d) NRs measured at 520 nm and 765 nm

which occurswithin a few seconds aftermixing of dimethoatewith NSs suspension can be ascribed to the sorption ofOP on NSsrsquo surfaces (Figure 1(b) 119860524) The next phaseindicates that the aggregation of functionalized NSs occursfollowed by the drastic changes of absorption band at 524 nmThe last phase shows the increase of 524 nm band intensitycharacteristic of stable AuNPs suspension These phases arealso very well recognized by spectral changes of absorptionband at 720 nm (Figure 1(b) 119860720)

The spectral changes of NRs characteristic bands at765 nm and 520 nm presented in Figure 1(d) indicated thefast process of dimethoate adsorption onto AuNRs whichoccurred in a few secondsThe spectral changes that followedin the second phase indicated reaching of equilibrium Nofurther changes of the bands intensity were noticed till theend of the incubation period

32 TEM Analysis In order to determine the dimensionof synthesized nanoparticles in the absence and presenceof dimethoate TEM was performed The average particlediameter of citrate-capped nanospheres obtained from TEMmeasurements is 266 plusmn 55 (Figure 3(a)) while the CTAB-capped nanorods length is 454plusmn69with diameter 159plusmn24with an average aspect ratio of 25 (Figure 3(c)) After additionof 05 times 10minus3M dimethoate in nanoparticles solutions and24 hours of their incubation the TEM images indicated thatthere were no changes in the NPs shape and size (Figures 3(b)and 3(d))

33 AFM Analysis To record structural and morphologicalchanges of AuNPs before and after their 24 hours of incuba-tionwith 05times10minus3Mdimethoate AFMstudywas conductedThe tapping mode dissemination images of bare AuNSs and


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(b)

Figure 2 Absorption spectra of (a) AuNSs and (b) AuNRs upon 24 hours of incubation with different concentrations of dimethoate

(a) (b)

(c) (d)

Figure 3 TEM images of (a) AuNSs (b) AuNSs treated with dimethoate (c) AuNRs and (d) AuNRs treated with dimethoate

AuNRs were presented in Figures 4(a) and 4(b) respectivelyThe diameter of citrate-capped nanospheres obtained byAFM measurements is 324 plusmn 68 while the CTAB-cappednanorods length is 437 plusmn 52 with diameter 198 plusmn 34These dimensions correlate with the size of NPs measured byTEM Figures 4(c) and 4(d) show the representative images of

AuNSs and AuNRs respectively after their incubation withdimethoate

34 FTIR Analysis To understand the involvement of theactive groups of dimethoate in its adsorption to AuNPsurfaces FTIR spectra were recorded The FTIR spectrum


(a) (b)

(c) (d)

Figure 4 AFM images (scan area 10 120583m times 10120583m) of (a) bare AuNSs and (b) AuNSs treated with dimethoate (c) bare AuNRs and (d) AuNRstreated with dimethoate

of dimethoate (Figures 5(a)(A) and 5(b)(A)) shows bands at1641 cmminus1 and 1565 cmminus1 corresponding to amide I (C=OandCndashN stretching vibrations) and amide II (mixed vibrationof NndashH deformation and CndashN stretch) bands respectively[37] Also two peaks appearing at 2841 cmminus1 and 2946 cmminus1(Figures 5(a)(A) and 5(b)(A)) may be assigned to stretchingvibrations of CndashH groups while the peaks at 3088 cmminus1 and3250 cmminus1 correspond to NndashH stretching vibrations Afteraddition of AuNSs to dimethoate (Figure 5(a)(B)) amide Iband is shifted towards higher frequency (1652 cmminus1) andamide II band splits into two peaks at 1558 cmminus1 and1540 cmminus1 [37] The peaks of CndashH stretching vibration keptthe same position whereas the peaks of NndashH stretchingvibration appeared at higher wave numbers 3094 cmminus1 and3292 cmminus1 compared with corresponding peaks of dimeth-oate alone Very similar changes were noticed after additionof NRs to the dimethoate solution as it can be seen inthe 1600ndash1400 cmminus1 range of the spectrum (Figure 5(b)(C))Two narrow bands appearing at 2850 cmminus1 and 2918 cmminus1

stem from symmetric and asymmetric stretching vibrationsof the CndashH bonds of CTAB molecule respectively [36] Theobserved spectral changes suggest that interactions betweendimethoate and AuNPs occurred [37] In case of AuNSsobviously dimethoate interacted directly with gold that isdimethoate replaced the citrate ions on the surface of theAuNSs [22] On the other side it seems that dimethoateinteracted with AuNRs via CTAB [36 38 39] These resultsare in accordance with results obtained spectrophotometri-cally

35 Adsorption Isotherms Analysis To quantify the amountof adsorbed dimethoate on 100mgL AuNPs as a functionof its concentration in the range from 2 to 1150mgL at25∘C the adsorption isotherms were used The equilibriumof sorption was evaluated by two-parameter and Langmuirand Freundlich isotherm models The Langmuir isothermmodel is the most widely used equation which assumesmonolayer adsorption onto a surface containing a limitednumber of adsorption sites and without any interactions


3500 3000 2500 2000 1500

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15581652

1641amide I

1565amide II

3292

28412946

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3290

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(A)

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Figure 5 FTIR spectra of 05 times 10minus3M dimethoate ((a)(A)) and ((b)(A)) alone and in the presence of ((a)(B)) AuNSs and ((b)(C)) AuNRs

between adsorbate molecules on adjacent sites [40 41] Itslinear form is expressed by the following equation

119888119890119902119890 =11199020119870119871 +

11199020 119888119890 (2)

where 119888119890 (mgL) is the equilibrium adsorbate concentration119902119890 (mgg) is the amount of adsorbate adsorbed per unitmass of adsorbent 1199020 is the maximum mass adsorbed undersaturation conditions per mass unit of adsorbent (mgg)and 119870119871 is the equilibrium constant with units of inverseof concentration 119888119890 (Lmg) 1199020 and 119870119871 are the Langmuirconstants related to the adsorption capacity and the rate ofadsorption respectively After plotting of 119888119890119902119890 against 119888119890 astraight line was obtained indicating that the adsorption ofdimethoate on the AuNPs follows the Langmuir isothermAnother important parameter which is a dimensionlessconstant called the separation factor (119877119871) for indicating thetype of adsorption using the Langmuir constant (119870119871) isevaluated as follows [42]

119877119871 = 11 + 1198701198711198880 (3)

where 1198880 is the initial dimethoate concentration (mgL) 119877119871value indicates the type of adsorption to be either favorable(0 lt 119877119871 lt 1) unfavorable (119877119871 gt 1) linear (119877119871 = 1) orirreversible (119877119871 = 0)

The Freundlich isotherm model on the other hand takesheterogeneous systems into account and is not restricted tothe formation of the monolayer [43] The linear form of theFreundlich equation is

ln 119902119890 = ln119870119865 + (1119899) ln 119888119890 (4)

where 119902119890 is the amount adsorbed at equilibrium (mgg) and119888119890 is the equilibrium concentration of dimethoate 119870119865 and nare Freundlich constants where 119870119865 (mgg) is the adsorptioncapacity of the adsorbent and with n value giving an indica-tion of how favorable the adsorption process The slope 1n

Table 1 Isotherm parameters for adsorption of dimethoate ontoAuNPs

Isotherms Parameters NPsNSs NRs

Langmuir

1199020 (mgg) 456 571119870119871 (Lmg) 001 001119877119871 008 0081198772 0960 0999

Freundlich119870119865 ((mgg) (Lmg)1n) 178 109

1n 045 0621198772 0924 0903

ranging between 0 and 1 is a measure of adsorption intensityor surface heterogeneity becomingmore heterogeneous as itsvalue gets closer to 0 [44]

The Langmuir and Freundlich isotherms for the adsorp-tion of dimethoate molecules by AuNPs were plotted andisotherm parameters and correlation coefficients (1198772) werecalculated and reported in Table 1 As shown in Table 1the Langmuir isotherm with correlation coefficients of 0960and 0999 represents a better fit of experimental data com-pared to Freundlich isotherm with correlation coefficients of0924 and 0903 for nanospheres and nanorods respectivelyAlso comparison of experimental adsorption isotherms ofdimethoate with nonlinear Langmuir and Freundlichmodelsis presented in Figure 6 for dimethoate adsorption ontoAuNSsrsquo and AuNRsrsquo surfaces Moreover the maximumadsorption capacity presented in Table 1 as 1199020 for theLangmuir model is much higher for nanospheres than fornanorods that is 456mgg and 571mgg respectively 119877119871values were less than 1 and greater than 0 (Table 1) indicatingfavorable and rather irreversible adsorption of dimethoateto both types of nanoparticles The values of 1n less than 1for both types of nanoparticles showed the favorable natureof dimethoate molecule adsorption onto Au nanoparticles(Table 1) The major differences between the two types of


0 200 400 600 800 1000 1200 1400 16000

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Figure 6 Comparison of experimental results of dimethoateadsorbed by AuNPs surfaces with adsorption isotherms Experi-mental results are presented NSs as cycles and NRs as squaresLangmuir model is presented as a solid lines and Freundlich modelis presented as dash dot lines

nanoparticles used are the surface charge and the shape Thesurface charge of the citrate-capped nanospheres is negativewhile the surface of CTAB-capped nanorods is positive inaqueous solution since washing does not remove CTAB fromNR surface completely [22 45] Regarding different shapesof the two types of nanoparticles and the presence of variousfacets to which stabilizing ligands bind [46 47] it is expectedthat adsorption orientation of dimethoate molecules to sur-face ligands of spheres and rods varies [48] It is more likelythat surface capping has the higher impact on the adsorptioncapacity of NPs for dimethoate Even though the specificsurface estimated for NSs is almost the same as the specificsurface of NRs 12 times 103 and 15 times 103 cm2g respectivelymuch higher capacity of NSs obviously originated fromreplacing of citrate anions with dimethoate and their covalentbinding to gold NSsrsquo surfaces Furthermore as already men-tioned dimethoate molecules are most probably covalentlybinded only on the NRs ends Different results have beenreported by several earlier works for dimethoate and otherorganophosphorous pesticides adsorption by various mate-rials Monolith precursor carbonized at 1000∘C activatedwith KOH (1 2) and heated at 900∘C showed adsorptioncapacity of 0062mgg for dimethoate [49] Molecularlyimprinted polymers for dimethoate recognition synthesizedby the precipitation polymerization technique using methylmethacrylate as the functional monomer and ethylene gly-col dimethacrylate (EGDMA) as the cross-linker showedapparent maximum adsorption capacity of 24mgg and122mgg for low and high affinity binding sites respectively[4] The results of batch adsorption experiments showed thatmalathion adsorbs on monetite B2 with adsorption capac-ity of 52mgg [7] Adsorption capacity of graphene-sandcomposite prepared from asphalt and sand for chlorpyrifoswas reported to be 526mgg in terms of carbon content[50] Batch tests carried out for adsorption of malathion

0 20 40 60 80 100 120 140 160 180 200 2200

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etho

ate (

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Adsorbent dosage (mgL)

Figure 7 Effect of adsorbent dosage level on adsorption of 25 times10minus4M dimethoate by NSs (cycles) and NRs (squares)

on granular activated carbon resulted in equilibrium datawhich fitted well with the Langmuir model and Freundlichmodel with maximum adsorption capacity of 9091mgg[51] Our results are in agreement with the results of previ-ous studies for OPs adsorption by different nanomaterialsIsotherm adsorption data for carbonized nanohemp fibersactivated at 900∘C with KOHcarbonized material ratio of21 adsorption of dimethoate fitted better with Freundlichisothermandmaximumadsorption capacity that is119870119865 valuewas 47 (mgg) (Lmg)1119899 Also this material showed veryhomogenous surface with 1n value 06 [52] Isotherm datain batch experiment show adsorption capacity of 48mggfor chlorpyrifos adsorption on graphene-sand nanocompos-ite [53] The absorption capacity of another nanomaterialreduced graphene oxide for chlorpyrifos adsorption observedby Maliyekkal et al was 1200mgg [11] It is reasonableto claim that AuNSs investigated in this study belong tonanomaterials with high adsorption capacity

36 Removal of Dimethoate from Water by Gold NPs Theeffect of adsorbent type and its concentration on dimethoateremoval from spiked drinking water was investigated in abatch adsorption technique The adsorbents (AuNSs andAuNRs) were used at concentration ranging from 2mgL to200mgL The initial dimethoate concentration was 25 times10minus4M From the results depicted in Figure 7 it is veryobvious that nanospheres have the advantage over nanorodsfor dimethoate removal In each case increase in adsorbentconcentration resulted in an increase in percent removalof dimethoate After certain adsorbent dosage the removalefficiency is not increased so significantly At 20mgL ofadsorbent dosage the removal of dimethoate was found tobe 12 for nanosphere and 28 for nanorods At 100mgL ofnanospheres dimethoate removal was 80 and for the samenanorods dosage dimethoate removal efficiency achievedwas19 Since concentration of unadsorbed dimethoate at dosagelevel of 200mgL for nanospheres could not be detected by


UPLC technique it is evident that adsorption of dimethoatewas between 80 and 100 The dosage of 200mgL ofnanorods adsorbed 22 of dimethoate so it is clear thatfor nanorods maximum removal efficacy was significantlylower than the one of nanospheres and was achieved at100mgL of nanorods The results for dimethoate removalare in concordance with maximum adsorption capacityvalues determined in this work 456mgg and 571mgg forNSs and NRs respectively Previously it was published thatvarious organophosphate pesticides malathion parathionchlorpyrifos and dimethoate were removed from simulatedcontaminated water in a single step using spherical goldnanoparticles produced on the surface of Rhizopus oryzaewith efficacy of 85ndash99 [14] Also 85ndash99 of parathionand chloropyrifos were removed with synthesized nanosilverbioconjugate synthesized through in situ reduction of silvernitrate by a fungal strain of Rhizopus oryzae [15] Alsoit was shown that bare gold and silver nanoparticles andthose supported on alumina are excellent systems for theremoval of the organophosphorous pesticides chlorpyrifosand malathion from water [17] Regarding all the resultsof this study we can assume that although nanorods pos-sess greater potential as biological and medicinal tools forimaging sensing and nanotechnology-driven therapeuticsthanks to their morphology over their spherical counterparts[54ndash56] nanospheres are more potent for adsorption ofdimethoate from water It should be emphasized that higherpotency of NSs for dimethoate adsorption originated fromreplacing of citrate anions with dimethoate and their covalentbinding to gold NSsrsquo surfaces and not fromNPs morphology

4 Conclusion

The adsorption of organophosphate pesticide dimethoate onAuNSs and AuNRs was investigated in aqueous solutionat room temperature for 24 hours using UV-Vis spec-trophotometry TEM AFM and FTIR It was shown thatdimethoate adsorbed on both AuNPs Its adsorption ontoAuNSs was followed by NPs aggregation and eventuallytheir stabilization That was not the case with AuNRs TheLangmuir adsorption isotherm was found to have the bestfit to the experimental data which suggests that monolayeradsorption on a homogeneous surface is the predominantprocess However multilayer adsorption cannot be ruled outas a good 1119899 value was obtained for the Freundlich modelNanospheres showed much higher adsorption capacity com-pared to nanorods regardless of which isotherm model wasused Consequently we showed that NSs were more efficientin dimethoate removal from water compared to NRs

Competing Interests

The authors declare that they have no competing interestsregarding the publication of this paper

Acknowledgments

This work was financially supported by the Ministry ofEducation Science and Technological Development of the

Republic of Serbia Project no 172023 This study was per-formed in the context of the European COST ActionMP1302Nanospectroscopy

References

[1] M S Bootharaju and T Pradeep ldquoUnderstanding the degrada-tion pathway of the pesticide chlorpyrifos by noblemetal nano-particlesrdquo Langmuir vol 28 no 5 pp 2671ndash2679 2012

[2] Y Lv Z Lin W Feng X Zhou and T Tan ldquoSelective recog-nition and large enrichment of dimethoate from tea leavesby molecularly imprinted polymersrdquo Biochemical EngineeringJournal vol 36 no 3 pp 221ndash229 2007

[3] J S Van Dyk and B Pletschke ldquoReview on the use of enzymesfor the detection of organochlorine organophosphate and car-bamate pesticides in the environmentrdquo Chemosphere vol 82no 3 pp 291ndash307 2011

[4] J-J Du R-X Gao H Yu X-J Li and HMu ldquoSelective extrac-tion of dimethoate from cucumber samples by use of molecu-larly imprinted microspheresrdquo Journal of Pharmaceutical Anal-ysis vol 5 no 3 pp 200ndash206 2015

[5] K Simeonidis S Mourdikoudis E Kaprara M Mitrakas andL Polavarapu ldquoInorganic engineered nanoparticles in drinkingwater treatment a critical reviewrdquoEnvironmental ScienceWaterResearch amp Technology vol 2 no 1 pp 43ndash70 2016

[6] L Clausen I Fabricius and L Madsen ldquoAdsorption of pesti-cides onto quartz calcite kaolinite and 120572-aluminardquo Journal ofEnvironmental Quality vol 30 no 3 pp 846ndash857 2001

[7] M M Mirkovic T D L Pasti A M Dosen et al ldquoAdsorptionof malathion on mesoporous monetite obtained by mechano-chemical treatment of brushiterdquo RSC Advances vol 6 no 15pp 12219ndash12225 2016

[8] E Ayranci and N Hoda ldquoAdsorption kinetics and isotherms ofpesticides onto activated carbon-clothrdquo Chemosphere vol 60no 11 pp 1600ndash1607 2005

[9] P Wang Y Yin Y Guo and C Wang ldquoPreponderant adsorp-tion for chlorpyrifos over atrazine by wheat straw-derived bio-char experimental and theoretical studiesrdquo RSC Advances vol6 no 13 pp 10615ndash10624 2016

[10] T D Lazarevic-Pasti I A Pasti B Jokic B M Babic and VM Vasic ldquoHeteroatom-doped mesoporous carbons as efficientadsorbents for removal of dimethoate and omethoate fromwaterrdquo RSC Advances vol 6 no 67 pp 62128ndash62139 2016

[11] S M Maliyekkal T S Sreeprasad D Krishnan et al ldquoGra-phene a reusable substrate for unprecedented adsorption ofpesticidesrdquo Small vol 9 no 2 pp 273ndash283 2013

[12] T Pradeep and Anshup ldquoDetection and extraction of pesticidesfrom drinking water using nanotechnologiesrdquo in Nanotech-nology Applications for Clean Water N Savage M Diallo JDuncan A Street and R Sustich Eds pp 191ndash212 WilliamAndrew Inc Boston Mass USA 2009

[13] T Pradeep and Anshup ldquoNoble metal nanoparticles for waterpurification a critical reviewrdquo Thin Solid Films vol 517 no 24pp 6441ndash6478 2009

[14] S K Das A R Das and A K Guha ldquoGold nanoparticlesmicrobial synthesis and application in water hygiene manage-mentrdquo Langmuir vol 25 no 14 pp 8192ndash8199 2009

[15] S K DasMM R Khan A K Guha A R Das and A BMan-dal ldquoSilver-nano biohybride material synthesis characteri-zation and application in water purificationrdquo Bioresource Tech-nology vol 124 pp 495ndash499 2012


[16] B L Brenner S Markowitz M Rivera et al ldquoIntegrated pestmanagement in an urban community a successful partnershipfor preventionrdquo Environmental Health Perspectives vol 111 no13 pp 1649ndash1653 2003

[17] A S Nair and T Pradeep ldquoExtraction of chlorpyrifos andmala-thion from water by metal nanoparticlesrdquo Journal of Nanosci-ence and Nanotechnology vol 7 no 6 pp 1871ndash1877 2007

[18] R Gupta and G U Kulkarni ldquoRemoval of organic com-pounds fromwater by using a gold nanoparticle-poly(dimethyl-siloxane) nanocomposite foamrdquo ChemSusChem Chemistry ampSustainability Energy and Materials vol 4 no 6 pp 737ndash7432011

[19] C Yu Z ZhuQWangWGuN Bao andHGu ldquoA disposableindium-tin-oxide sensor modified by gold nanorod-chitosannanocomposites for the detection of H2O2 in cancer cellsrdquoChemical Communications vol 50 no 55 pp 7329ndash7331 2014

[20] C Wang Z Ma T Wang and Z Su ldquoSynthesis assembly andbiofunctionalization of silica-coated gold nanorods for color-imetric biosensingrdquo Advanced Functional Materials vol 16 no13 pp 1673ndash1678 2006

[21] S E Lohse and C J Murphy ldquoApplications of colloidal inor-ganic nanoparticles from medicine to energyrdquo Journal of theAmerican Chemical Society vol 134 no 38 pp 15607ndash156202012

[22] A Vujacic V Vasic M Dramicanin et al ldquoFluorescencequenching of 551015840-disulfopropyl-331015840-dichlorothiacyanine dyeadsorbed on gold nanoparticlesrdquo Journal of Physical ChemistryC vol 117 no 13 pp 6567ndash6577 2013

[23] U Bogdanovic V V Vodnik S P Ahrenkiel M Stoiljkovic GCiric-Marjanovic and J M Nedeljkovic ldquoInterfacial synthesisand characterization of goldpolyaniline nanocompositesrdquo Syn-thetic Metals vol 195 pp 122ndash131 2014

[24] B Nikoobakht and M A El-Sayed ldquoPreparation and growthmechanism of gold nanorods (NRs) using seed-mediatedgrowthmethodrdquoChemistry ofMaterials vol 15 no 10 pp 1957ndash1962 2003

[25] A BWitte A N Leistra P TWong et al ldquoAtomic force micro-scopy probing of receptorndashnanoparticle interactions for ribo-flavin receptor targeted goldndashdendrimer nanocompositesrdquoJournal of Physical Chemistry B vol 118 no 11 pp 2872ndash28822014

[26] X Zhou Y Zhang F Zhang et al ldquoHierarchical ordering ofamyloid fibrils on the mica surfacerdquoNanoscale vol 5 no 11 pp4816ndash4822 2013

[27] A K Bhattacharya T K Naiya S N Mandal and S K DasldquoAdsorption kinetics and equilibrium studies on removal ofCr(VI) from aqueous solutions using different low-cost adsorb-entsrdquo Chemical Engineering Journal vol 137 no 3 pp 529ndash5412008

[28] J H Yoon J S Park and S Yoon ldquoTime-dependent and sym-metry-selective charge-transfer contribution to sers in goldnanoparticle aggregatesrdquo Langmuir vol 25 no 21 pp 12475ndash12480 2009

[29] R Sardar T B Heap and J S Shumaker-Parry ldquoVersatile solidphase synthesis of gold nanoparticle dimers using an asymmet-ric functionalization approachrdquo Journal of the American Chem-ical Society vol 129 no 17 pp 5356ndash5357 2007

[30] S-Y Lin Y-T Tsai C-C Chen C-M Lin and C-H ChenldquoTwo-step functionalization of neutral and positively chargedthiols onto citrate-stabilized Au nanoparticlesrdquo The Journal ofPhysical Chemistry B vol 108 no 7 pp 2134ndash2139 2004

[31] M R Ivanov H R Bednar and A J Haes ldquoInvestigations ofthe mechanism of gold nanoparticle stability and surface func-tionalization in capillary electrophoresisrdquo ACS Nano vol 3 no2 pp 386ndash394 2009

[32] T Kim K Lee M-S Gong and S-W Joo ldquoControl of goldnanoparticle aggregates by manipulation of interparticle inter-actionrdquo Langmuir vol 21 no 21 pp 9524ndash9528 2005

[33] R A Sperling andW J Parak ldquoSurface modification function-alization and bioconjugation of colloidal inorganic nanoparti-clesrdquo Philosophical Transactions of the Royal Society A Mathe-matical Physical and Engineering Sciences vol 368 no 1915 pp1333ndash1383 2010

[34] M Gluodenis and C A Foss Jr ldquoThe effect of mutual ori-entation on the spectra of metal nanoparticle rodminusrod androdminussphere pairsrdquo Journal of Physical Chemistry B vol 106 no37 pp 9484ndash9489 2002

[35] N Thioune N Lidgi-Guigui M Cottat et al ldquoStudy of goldnanorodsndashprotein interaction by localized surface plasmonresonance spectroscopyrdquo Gold Bulletin vol 46 no 4 pp 275ndash281 2013

[36] J Vonnemann N Beziere C Bottcher et al ldquoPolyglycerolsul-fate functionalized gold nanorods as optoacoustic signal nano-amplifiers for in vivo bioimaging of rheumatoid arthritisrdquoTheranostics vol 4 no 6 pp 629ndash641 2014

[37] K Esumi and K Torigoe ldquoPreparation and characterizationof noble metal nanoparticles using dendrimers as protectivecolloidsrdquo in Progress in Colloid and Polymer Science F Kremerand G Lagaly Eds vol 117 pp 80ndash88 Springer HeidelbergGermany 2001

[38] J Lim N-E Lee E Lee and S Yoon ldquoSurface modificationof citrate-capped gold nanoparticles using CTAB micellesrdquoBulletin of the Korean Chemical Society vol 35 no 8 pp 2567ndash2569 2014

[39] A M Alkilany P K Nagaria M D Wyatt and C J MurphyldquoCation exchange on the surface of gold nanorods with a poly-merizable surfactant polymerization stability and toxicity eva-luationrdquo Langmuir vol 26 no 12 pp 9328ndash9333 2010

[40] I Langmuir ldquoThe adsorption of gases on plane surfaces of glassmica and platinumrdquo Journal of the American Chemical Societyvol 40 no 9 pp 1361ndash1403 1918

[41] S Chakravarty V Dureja G Bhattacharyya S Maity and SBhattacharjee ldquoRemoval of arsenic fromgroundwater using lowcost ferruginous manganese orerdquoWater Research vol 36 no 3pp 625ndash632 2002

[42] K R Hall L C Eagleton A Acrivos and T Vermeulen ldquoPore-and solid-diffusion kinetics in fixed-bed adsorption under con-stant-pattern conditionsrdquo Industrial amp Engineering ChemistryFundamentals vol 5 no 2 pp 212ndash223 1966

[43] H M F Freundlich ldquoUber die adsorption in losungenrdquoZeitschrift fur Physikalische Chemie vol 57 pp 385ndash470 1906

[44] F Haghseresht andG Q Lu ldquoAdsorption characteristics of phe-nolic compounds onto coal-reject-derived adsorbentsrdquo Energyamp Fuels vol 12 no 6 pp 1100ndash1107 1998

[45] J S Bozich S E LohseMD Torelli C JMurphy R J Hamersand R D Klaper ldquoSurface chemistry charge and ligand typeimpact the toxicity of gold nanoparticles to Daphnia magnardquoEnvironmental Science Nano vol 1 no 3 pp 260ndash270 2014

[46] W P Wuelfing S M Gross D T Miles and R W MurrayldquoNanometer gold clusters protected by surface-bound mono-layers of thiolated poly(ethylene glycol) polymer electrolyterdquoJournal of the American Chemical Society vol 120 no 48 pp12696ndash12697 1998


[47] B Nikoobakht andMA El-Sayed ldquoEvidence for bilayer assem-bly of cationic surfactants on the surface of gold nanorodsrdquoLangmuir vol 17 no 20 pp 6368ndash6374 2001

[48] S Khan A Gupta N C Verma and C K Nandi ldquoKinetics ofprotein adsorption on gold nanoparticle with variable proteinstructure and nanoparticle sizerdquo The Journal of Chemical Phy-sics vol 143 no 16 Article ID 164709 2015

[49] M Vukcevic A Kalijadis B Babic Z Lausevic and MLausevic ldquoInfluence of different carbon monolith preparationparameters on pesticide adsorptionrdquo Journal of the SerbianChemical Society vol 78 no 10 pp 1617ndash1632 2013

[50] T S Sreeprasad S S Gupta S M Maliyekkal and T PradeepldquoImmobilized graphene-based composite from asphalt facilesynthesis and application in water purificationrdquo Journal ofHazardous Materials vol 246-247 pp 213ndash220 2013

[51] A Jusoh W J H Hartini N Ali and A Endut ldquoStudy on theremoval of pesticide in agricultural run off by granular activatedcarbonrdquo Bioresource Technology vol 102 no 9 pp 5312ndash53182011

[52] M M Vukcevic A M Kalijadis T M Vasiljevic B M BabicZ V Lausevic and M D Lausevic ldquoProduction of activatedcarbon derived from waste hemp (Cannabis sativa) fibersand its performance in pesticide adsorptionrdquo Microporous andMesoporous Materials vol 214 pp 156ndash165 2015

[53] S S Gupta T S Sreeprasad S M Maliyekkal S K Das andT Pradeep ldquoGraphene from sugar and its application in waterpurificationrdquo ACS Applied Materials amp Interfaces vol 4 no 8pp 4156ndash4163 2012

[54] J Stone S Jackson and D Wright ldquoBiological applications ofgold nanorodsrdquo Wiley Interdisciplinary Reviews Nanomedicineand Nanobiotechnology vol 3 no 1 pp 100ndash109 2011

[55] THDNguyen Z Zhang AMustaphaH Li andM Lin ldquoUseof graphene and gold nanorods as substrates for the detectionof pesticides by surface enhanced raman spectroscopyrdquo Journalof Agricultural and Food Chemistry vol 62 no 43 pp 10445ndash10451 2014

[56] Y V Kaneti C Chen M Liu et al ldquoCarbon-coated gold nano-rods a facile route to biocompatible materials for photothermalapplicationsrdquo ACS Applied Materials amp Interfaces vol 7 no 46pp 25658ndash25668 2015

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


PO

O

O

S

S

NH

CH3

H3C

H3C

Scheme 1 Dimethoate

of silver upon pesticide binding which is less comparedto that of gold [1 16] gives the gold advantage over silveror some cheaper metal nanomaterials Nair and Pradeepsupported gold nanoparticles on alumina and made onlinewater filter to demonstrate technology of OPs removal fromwater in rural communities in India [17] Moreover waterpurification from an environmental perspective by usinggold-poly(dimethylsiloxane) nanocomposite in the form of afoam was described [18]

Rod-shape nanoparticles possess several advantages overthe nanospheres such as high surface area and good electronmediation capability [19ndash21] However to date to the best ofour knowledge the use of gold nanorods for adsorption ofOP dimethoate has not been reported In this contributionwe considered gold nanoparticles of two different shapesnanospheres (NSs) and nanorods (NRs) as adsorbents ofdimethoate from aqueous solutions The aim of our studywas to characterize the interaction between dimethoate andgold nanorods NSs and NRs have different physical andchemical properties so the effects of these properties ontheir performance as adsorbents are discussed We have alsocompared direct uses of investigated NPs for removal ofdimethoate from drinking water

2 Experimental

21 Chemicals and Materials All the chemicals used werepurchased from Sigma Aldrich Co St Louis MO 400-meshCu grid coated in a thin layer of carbon was purchased fromTed Pella Inc Redding CA MICA was purchased from SPISuppliesWest Chester PAMilli-Q deionized water used had182MΩ electrical resistivity22 Synthesis of Gold Colloids

221 Synthesis of Gold Nanospheres Colloidal dispersion ofgold nanospheres (AuNSs) was prepared using a reductionof precursor salt (HAuCl4) solution by sodium citrate asdescribed elsewhere [22 23] In a typical synthesis 200mLof 1mM HAuCl4 solution was stirred and heated in a round-bottom flask fitted with a reflux condenser After the solutionreached the boiling point 10mL of 388mM sodium citratewas rapidly added The colloidal dispersion was boiled andstirred for additional 15min and then cooled down to roomtemperaturewith continuous stirringThefinal concentrationof Au in colloidal dispersion was found to be 091mM(179mgL)

222 Synthesis of Gold Nanorods Colloidal dispersion ofgold nanorods (AuNRs) was prepared using a seed-mediated

growth approach [24] Colloidal gold seed solution was firstprepared as follows 5mL of 200mM CTAB solution wasadded to 5mL of 05mM HAuCl4 solution Next 06mLof ice-cold 10mM NaBH4 (reducing agent) solution wasinjected into the yellow solution all at once while stirringvigorously Stirring was stopped after 2minThe color of seedsolution was changed to brownish-yellow and was stable for2 hours In the next step the stock solution was preparedas follows 025mL of 4mM AgNO3 solution was added to5mL of 200mM CTAB solution and gently mixed in orderto add 5mL of 1mM HAuCl4 solution All solutions otherthan those of gold and CTAB were prepared fresh daily Theyellow stock solution became colorless after adding 70 120583Lof 788mM ascorbic acid Thereafter 10 120583L of seed solutionwas added to the stock solution CTAB solution crystallizesat 25∘C so colloid was synthesized in the temperature rangefrom 27∘C to 30∘C to ensure proper nanorods growth Aviolet-blue color appeared within 15ndash20min Rods wereconcentrated and separated from spheres and surfactant bycentrifugation (10000 rpm for 15min) After centrifugingthe surfactant was removed and the precipitate was furtherredispersed in deionized waterThe final concentration of Auin colloidal dispersion was found to be 001mM (2mgL)

23 Characterization of AuNPs and Their Dimethoate Con-jugates The NPs interactions with dimethoate were char-acterized using UV-Visible (UV-Vis) spectroscopy (Lambda35 UV-Vis Spectrometer Perkin Elmer Inc WalthamMA USA) All spectra were background-subtracted againstdeionized water which is the reaction solvent Over a periodof 24 hours spectra were recorded Transmission electronmicroscope (TEM) images of the NPs and NPs-dimethoateassembly were obtained using TEM JEOL JEM-1400 (JeolLtd Tokyo Japan) operated at 120 kV A total of 5 120583L of thereaction solution was pipetted onto the surface of a 400-meshCu grid coated in a thin layer of carbon and allowed to dry onthe air Atomic force microscopic (AFM) images of AuNPs inthe absence and presence of dimethoate were recorded usingMultimode Quadrex SPM with Nanoscope IIIe controller(Veeco Instruments Inc Camarillo CA) at room tem-perature using AFM-FM technique and force modulationprobe holder with a piezoelectric bimorph and a commercialVeeco FESP probe with a cantilever Mica substrates wereprepared for imaging as follows Freshly cleaved mica wasmodified with a 100 120583L deposit of 001 3-(aminopropyl)-triethoxysilane (APTES) solution After a 20min incubationperiod the mica surface was rinsed six times with 1mLaliquots of water and dried with compressed nitrogen [25]A drop of 10 120583L suspension of AuNPs without and withdimethoate was deposited on mica surface and incubatedfor 30min followed by repeated washing with deionizedwater to remove any unbound materials and dried in air forAFMmeasurements [26] Fourier transform infrared (FTIR)spectra of dimethoate as well as dimethoate in the presenceof Au nanoparticles were recorded on Nicolet IS 50 FT-IR Spectrometer (Thermo Fisher Scientific Waltham MAUSA) Samples were prepared by dripping the solution onglass slides and left to dry on the air Samples were analyzedat ambient conditions in themid-IR region (400ndash4000 cmminus1)




119902119890 = 119881 (1198880 minus 119888119890)119882 (1)









400 500 600 700 800000002004006008010012014016018020022024

D

B

Abso

rban

ce

A

C

120582 (nm)

(a)

0 200 400 600 800 1000 1200 1400000

004

008

012

016

020

Abso

rban

ce

t (min)

A720

A524

(b)

400 500 600 700 800000

002

004

006

008

010

012

014

016

018

020

DC

Abso

rban

ce

AB

120582 (nm)

(c)

0 200 400 600 800 1000 1200 1400 1600004

008

012

016

020

Abso

rban

ce

Time (min)

A765

A520

(d)







400 500 600 700 800000

005

010

015

020

025Ab

sorb

ance

120582 (nm)






(a)

400 500 600 700 800000

005

010

015

020

025

Abso

rban

ce

120582 (nm)




(b)


(a) (b)

(c) (d)






(a) (b)

(c) (d)






3500 3000 2500 2000 1500

1540

15581652

1641amide I

1565amide II

3292

28412946

30883250

Tran

smitt

ance

(A)

(B)


(NndashH) stretch


(a)

3500 3000 2500 2000 1500

1540165228502918

3290

1565amide II

1641amide I

Tran

smitt

ance

(A)

(C)


(b)



119888119890119902119890 =11199020119870119871 +

11199020 119888119890 (2)


119877119871 = 11 + 1198701198711198880 (3)



ln 119902119890 = ln119870119865 + (1119899) ln 119888119890 (4)




Langmuir

1199020 (mgg) 456 571119870119871 (Lmg) 001 001119877119871 008 0081198772 0960 0999


1n 045 0621198772 0924 0903




0 200 400 600 800 1000 1200 1400 16000

100

200

300

400

500

qe

(mg

g)

ce (mgL)



0 20 40 60 80 100 120 140 160 180 200 2200

10

20

30

40

50

60

70

80

90

Rem

oved

dim

etho

ate (

)







4 Conclusion


Competing Interests


Acknowledgments



References


































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






119902119890 = 119881 (1198880 minus 119888119890)119882 (1)









400 500 600 700 800000002004006008010012014016018020022024

D

B

Abso

rban

ce

A

C

120582 (nm)

(a)

0 200 400 600 800 1000 1200 1400000

004

008

012

016

020

Abso

rban

ce

t (min)

A720

A524

(b)

400 500 600 700 800000

002

004

006

008

010

012

014

016

018

020

DC

Abso

rban

ce

AB

120582 (nm)

(c)

0 200 400 600 800 1000 1200 1400 1600004

008

012

016

020

Abso

rban

ce

Time (min)

A765

A520

(d)







400 500 600 700 800000

005

010

015

020

025Ab

sorb

ance

120582 (nm)






(a)

400 500 600 700 800000

005

010

015

020

025

Abso

rban

ce

120582 (nm)




(b)


(a) (b)

(c) (d)






(a) (b)

(c) (d)






3500 3000 2500 2000 1500

1540

15581652

1641amide I

1565amide II

3292

28412946

30883250

Tran

smitt

ance

(A)

(B)


(NndashH) stretch


(a)

3500 3000 2500 2000 1500

1540165228502918

3290

1565amide II

1641amide I

Tran

smitt

ance

(A)

(C)


(b)



119888119890119902119890 =11199020119870119871 +

11199020 119888119890 (2)


119877119871 = 11 + 1198701198711198880 (3)



ln 119902119890 = ln119870119865 + (1119899) ln 119888119890 (4)




Langmuir

1199020 (mgg) 456 571119870119871 (Lmg) 001 001119877119871 008 0081198772 0960 0999


1n 045 0621198772 0924 0903




0 200 400 600 800 1000 1200 1400 16000

100

200

300

400

500

qe

(mg

g)

ce (mgL)



0 20 40 60 80 100 120 140 160 180 200 2200

10

20

30

40

50

60

70

80

90

Rem

oved

dim

etho

ate (

)







4 Conclusion


Competing Interests


Acknowledgments



References


































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




400 500 600 700 800000002004006008010012014016018020022024

D

B

Abso

rban

ce

A

C

120582 (nm)

(a)

0 200 400 600 800 1000 1200 1400000

004

008

012

016

020

Abso

rban

ce

t (min)

A720

A524

(b)

400 500 600 700 800000

002

004

006

008

010

012

014

016

018

020

DC

Abso

rban

ce

AB

120582 (nm)

(c)

0 200 400 600 800 1000 1200 1400 1600004

008

012

016

020

Abso

rban

ce

Time (min)

A765

A520

(d)







400 500 600 700 800000

005

010

015

020

025Ab

sorb

ance

120582 (nm)






(a)

400 500 600 700 800000

005

010

015

020

025

Abso

rban

ce

120582 (nm)




(b)


(a) (b)

(c) (d)






(a) (b)

(c) (d)






3500 3000 2500 2000 1500

1540

15581652

1641amide I

1565amide II

3292

28412946

30883250

Tran

smitt

ance

(A)

(B)


(NndashH) stretch


(a)

3500 3000 2500 2000 1500

1540165228502918

3290

1565amide II

1641amide I

Tran

smitt

ance

(A)

(C)


(b)



119888119890119902119890 =11199020119870119871 +

11199020 119888119890 (2)


119877119871 = 11 + 1198701198711198880 (3)



ln 119902119890 = ln119870119865 + (1119899) ln 119888119890 (4)




Langmuir

1199020 (mgg) 456 571119870119871 (Lmg) 001 001119877119871 008 0081198772 0960 0999


1n 045 0621198772 0924 0903




0 200 400 600 800 1000 1200 1400 16000

100

200

300

400

500

qe

(mg

g)

ce (mgL)



0 20 40 60 80 100 120 140 160 180 200 2200

10

20

30

40

50

60

70

80

90

Rem

oved

dim

etho

ate (

)







4 Conclusion


Competing Interests


Acknowledgments



References


































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




400 500 600 700 800000

005

010

015

020

025Ab

sorb

ance

120582 (nm)






(a)

400 500 600 700 800000

005

010

015

020

025

Abso

rban

ce

120582 (nm)




(b)


(a) (b)

(c) (d)






(a) (b)

(c) (d)






3500 3000 2500 2000 1500

1540

15581652

1641amide I

1565amide II

3292

28412946

30883250

Tran

smitt

ance

(A)

(B)


(NndashH) stretch


(a)

3500 3000 2500 2000 1500

1540165228502918

3290

1565amide II

1641amide I

Tran

smitt

ance

(A)

(C)


(b)



119888119890119902119890 =11199020119870119871 +

11199020 119888119890 (2)


119877119871 = 11 + 1198701198711198880 (3)



ln 119902119890 = ln119870119865 + (1119899) ln 119888119890 (4)




Langmuir

1199020 (mgg) 456 571119870119871 (Lmg) 001 001119877119871 008 0081198772 0960 0999


1n 045 0621198772 0924 0903




0 200 400 600 800 1000 1200 1400 16000

100

200

300

400

500

qe

(mg

g)

ce (mgL)



0 20 40 60 80 100 120 140 160 180 200 2200

10

20

30

40

50

60

70

80

90

Rem

oved

dim

etho

ate (

)







4 Conclusion


Competing Interests


Acknowledgments



References


































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)

(c) (d)






3500 3000 2500 2000 1500

1540

15581652

1641amide I

1565amide II

3292

28412946

30883250

Tran

smitt

ance

(A)

(B)


(NndashH) stretch


(a)

3500 3000 2500 2000 1500

1540165228502918

3290

1565amide II

1641amide I

Tran

smitt

ance

(A)

(C)


(b)



119888119890119902119890 =11199020119870119871 +

11199020 119888119890 (2)


119877119871 = 11 + 1198701198711198880 (3)



ln 119902119890 = ln119870119865 + (1119899) ln 119888119890 (4)




Langmuir

1199020 (mgg) 456 571119870119871 (Lmg) 001 001119877119871 008 0081198772 0960 0999


1n 045 0621198772 0924 0903




0 200 400 600 800 1000 1200 1400 16000

100

200

300

400

500

qe

(mg

g)

ce (mgL)



0 20 40 60 80 100 120 140 160 180 200 2200

10

20

30

40

50

60

70

80

90

Rem

oved

dim

etho

ate (

)







4 Conclusion


Competing Interests


Acknowledgments



References


































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




3500 3000 2500 2000 1500

1540

15581652

1641amide I

1565amide II

3292

28412946

30883250

Tran

smitt

ance

(A)

(B)


(NndashH) stretch


(a)

3500 3000 2500 2000 1500

1540165228502918

3290

1565amide II

1641amide I

Tran

smitt

ance

(A)

(C)


(b)



119888119890119902119890 =11199020119870119871 +

11199020 119888119890 (2)


119877119871 = 11 + 1198701198711198880 (3)



ln 119902119890 = ln119870119865 + (1119899) ln 119888119890 (4)




Langmuir

1199020 (mgg) 456 571119870119871 (Lmg) 001 001119877119871 008 0081198772 0960 0999


1n 045 0621198772 0924 0903




0 200 400 600 800 1000 1200 1400 16000

100

200

300

400

500

qe

(mg

g)

ce (mgL)



0 20 40 60 80 100 120 140 160 180 200 2200

10

20

30

40

50

60

70

80

90

Rem

oved

dim

etho

ate (

)







4 Conclusion


Competing Interests


Acknowledgments



References


































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0 200 400 600 800 1000 1200 1400 16000

100

200

300

400

500

qe

(mg

g)

ce (mgL)



0 20 40 60 80 100 120 140 160 180 200 2200

10

20

30

40

50

60

70

80

90

Rem

oved

dim

etho

ate (

)







4 Conclusion


Competing Interests


Acknowledgments



References


































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





4 Conclusion


Competing Interests


Acknowledgments



References


































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





















































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



research article adsorption of organophosphate pesticide...

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