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auloLuiznsE), Detes, Depanergia e

95% to 104% wereter samplesAll rights re

1. Introduction

Biochar is a form of charcoal produced through the pyrolysisprocess of biomass under low or no oxygen conditions. Various

types of biomass such as agricultural crop residues, fresidues, wood waste and animal manures have been proposedas feedstock for biochar production (Duku et al., 2011). It has aheterogeneous structure and can present a range of chemicalstructures and variable elemental composition based on thepyrolysis conditions and the biomass parent material (Spokas,2010). The agricultural use of biochar is largely reported becauseit improves the soil pH control, nutrient retention and water hold-ing capacity of soils, reduces the total fertilizer requirements and

Corresponding author. Tel.: +55 41 3361 3177; fax: +55 41 3361 3186.E-mail addresses: bergamini@ufpr.br, marciobergamini@gmail.com

Bioresource Technology 143 (2013) 4045

Contents lists available at

Bioresource T

els(M.F. Bergamini).Carbon paste electrodeStripping analysis

established by Brazilian legislation. For all samples analyzed, recoveries ranged fromobtained and no signicative interferences were observed for common cations in wa

2013 Elsevier Ltd.0960-8524/$ - see front matter 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.biortech.2013.05.107.served.

orestryArticle history:Received 4 April 2013Received in revised form 22 May 2013Accepted 25 May 2013Available online 31 May 2013

Keywords:BiocharAdsorption of Lead and Cadmium

This work describes for rst time the use of electroanalytical techniques for evaluation of adsorptive pro-prieties of biochar using it as electrode modier and its application for preconcentration and determina-tion of Lead(II) and Cadmium(II) under differential pulse adsorptive voltammetric conditions (DPAdSV).Samples of biochars were obtained from castor oil cake using a predened set of experimental conditionsvarying the heating rate (V), nal temperature (T) and warm-up period (P) and subsequently used for car-bon paste modied electrode (CPME) preparation. The proposed method was applied for Lead(II) andCadmium(II) determination in spiked simulated industrial efuents and the limit of detection obtainedfor both metals were adequated for determination of these evaluated ions taking into account the limitsevaluation of biochars proprietiesadsorption.

Analytical application of biocharobtained under low temperaturepyrolysis conditions.

Development of voltammetric sensorfor determination of Pb2+ and Cd2+

using biochar. Low limit of detection, excellentsensitivity and stability of theproposed electrode.

Analysis of simulated industrialwaste water without anypretreatment of the sample.

a r t i c l e i n f oPb

Cd

I / A

E / V

Castor oil cake

BIOCHAR

Industrial effluent

DPAdSV

a b s t r a c t New electrochemical procedure for CPMEAn electroanalytical apcharacteristics and its

Talita Mayumi Suguihiro a, PAntonio Slvio Mangrich b,c,a Laboratrio de Sensores Eletroqumicos (LabSeb Laboratrio de Qumica de Hmus e Fertilizanc Instituto Nacional de Cincia e Tecnologia de E

h i g h l i g h t sach for evaluation of biochar adsorptionlication for Lead and Cadmium determination

Roberto de Oliveira a, Edivaltrys Inayve Pissinati de Rezende b,Humberto Marcolino Junior a, Mrcio F. Bergamini a,partamento de Qumica, Universidade Federal do Paran (UFPR), CEP 81531-980, CuritibaPR, Brazilrtamento de Qumica, Universidade Federal do Paran (UFPR), CEP 81531-980, CuritibaPR, BrazilAmbiente (INCT E&A/CNPq), Brazil

g r a p h i c a l a b s t r a c tjournal homepage: www.SciVerse ScienceDirect

echnology

evier .com/locate /bior tech

In this article, a simple and effective modied carbon paste elec-trode prepared using biochar obtained from castor bean showedcapacity for preconcentration of Pb(II) and Cd(II) ions at electrodesurface which promoted a signicative increase in the voltammet-ric signal in comparison with the unmodied electrode. Thisbehavior is due to high functionalized surface shown by the bio-char. The sensor was applied to the simultaneous determinationof Pb(II) and Cd(II) by using differential pulse adsorptive strippingvoltammetry (DPAdSV) in spiked water samples.

2. Methods

pore Milli-Q system. All the chemicals were of analytical grade

80 meshes, was placed in porcelain boats in the inner glass tube

Table 1Set of experimental conditions adopted for biochar samples preparation considering

rce Technology 143 (2013) 4045 41environmental deterioration associated with fertilizers (Lehmannand Joseph, 2009).

In recent years biochar has been applied for the remediation ofcontaminated soils and waters by several species (organic and/orinorganic) (Dong et al., 2011; Sun et al., 2011; Beesley and Mar-miroli, 2011; Uchimiya et al., 2010). Biochar has great afnityfor heavy metals and their sorption capacity is comparable withother biosorbents. Recently, Dong et al. reported the applicationof biochar obtained from sugar beet tailing for the removal ofCr(VI) from aqueous solutions. A sorption capacity for Cr(VI) of123 mg/g was found which is comparable to other low-cost sor-bents. Biochar prepared by pyrolysis of hardwood and corn strawfor application as adsorbents for the removal of Cu(II) and Zn(II)from aqueous solution was reported by Chen et al. Adsorption ef-ciency of the metal ions increased with increasing biochar concen-tration, suggesting that plant-residue or agricultural wastederived biochar can act as effective surface sorbent. Sun et al. ver-ied that biochar produced at different heat treatment tempera-tures shown signicative difference in sorption behavior of twoherbicides (norurazon and uridone) to biochars obtained fromwood and grass feedstocks. Amorphous structural arrangementfor biochar obtained at 400 C exhibited the highest sorptionparameter for the two herbicides. Uchimiya et al. reported thepreparation of biochar from broiler litter manure samples and ver-ied that it could immobilize organic contaminants. Authors pro-posed that both surface adsorption and partitioning mechanismscould happen in the heavy metal immobilization. In general, infor-mation about the biochar are mainly focused in its preparationand application as a soil conditioner or/and in the pollutants re-moval, however, its use in electroanalytical for sensor construc-tion is not reported.

Electrochemical stripping analysis is a family of proceduresinvolving a preconcentration of the analyte onto the working elec-trode, prior to its direct or indirect determination by means of anelectroanalytical technique (Fogg and Wang, 1999). Chemicallymodied electrodes are widely investigated in stripping voltam-metry due to their attractive preconcentration capability of speciesas a result of a selective interaction between modier and the ana-lyte. The preconcentration of given specie on an electrode surfacemay occur by different processes such as: ion exchange, complex-ation, bioaccumulation, salt formation, covalent binding, or hydro-phobic interaction (Fogg and Wang, 1999; Bard and Faulkner,1980). In this way, several materials have been evaluated in orderto obtain an improvement in detection and quantication limitsbesides to provide adequate repeatability and reproducibility. Onthe other hand, voltammetric assays using chemically modiedelectrodes could be used as a powerful analytical tool for evalua-tion of sorption modier capacity. In addition, voltammetrictechniques are a good alternative to spectroscopic and chromato-graphic procedures, due its simple and low-cost instrumentation.

The existence of metals in the environment is a result of thenatural as well as anthropic process. However, after the IndustrialRevolution, the present-day levels of heavy metals in the environ-ment are almost exclusively from anthropogenic sources. Chemicalpollution with heavy metals has been one of the serious problemsfor the sustainable environment and some of them (for instance,lead, cadmium, chromium and mercury) have been pointed outas environmental endocrine disruptors due its strong estrogenicactivity (Erfurth et al., 2001). Moreover, lead probably has the lon-gest history of environmental contamination and arises from mul-tiple sources (Matusiewicz and Krawczyk, 2006). The maximumlevels for efuent discharge in water bodies of cadmium and leadare 0.2 and 0.5 mg L1, respectively; these values were established

T.M. Suguihiro et al. / Bioresouby CONAMA (National Council for the Environment in Brazil)(CONAMA, 2008). Thus, determination of these metal ions can pro-vide important information on the environmental side.the experimental procedure and the factorial design 23.

Biochar samples Experimental conditions

V (Cmin1) T (C) P (min)

P1 10 350 60P2 5 350 60P3 10 300 60P4 5 300 60P5 10 350 30P6 5 350 30P7 10 300 30furnace EDG FT-40 microprocessor-controlled. The factors as-sessed by a 23 factorial design were: heating rate (V), nal tem-perature (T) and warm-up period (P), at the levels of 5 and10 C min1, 300 and 350 C and 30 and 60 min, respectively(Table 1).

The elementar composition (C, H and N) was determined usinga PerkinElmer 2400 Series II CHNS/O Elemental Analyzer. Informa-tion about functional groups present at surface of the biochar wasprovided by a FTIR Bomem MB100 spectrometer recording thespectrum scope from 4000 to 350 cm1 with a resolution of4 cm1.and were used without further purication. A stock solution con-taining 1000 mg L1 of ions (Merck) was used. By dilution withwater, solutions containing different concentrations of Lead(II)and/or Cadmium(II) ions were prepared.

2.3. Preparation of biochars and characterization

The castor oil cake, gridding in ball mills to a particle size of2.1. Apparatus

DPAdSV measurements were performed in a lAUTOLAB Type III(EcoChemie) connected to a microcomputer controlled by software(GPES 4.9) for data acquisition and experimental control. All thevoltammetric measurements were carried out in a 30 mL thermo-stated glass cell at 25 C, with a three-electrode conguration:modied carbon paste electrode as the working electrode, Ag/AgClKCl saturated as the reference electrode and platinum wire auxil-iary electrode. During the measurements, the solution in the cellwas not stirred.

2.2. Reagents and solutions

All the solutions were prepared with water puried in a Milli-P8 5 300 30

V: heating rate, T: nal temperature and P: warm-up period.

trated at open circuit potential in the pretreatment sample under

ples. A total of eight samples (P1P8) were prepared andcharacterized using infrared spectroscopy and elemental analysis.The preconcentration step was realized in aqueous solution (pH5.0) containing 5.0 106 mol L1 of Pb(II) and 2.0 105 mol L1of Cd(II) by immersion of the work electrode (CPME prepared using

-1.0 -0.8 -0.6 -0.4 -0.20

10

20

30

A

CB

I /

A

E / V vs. Ag/AgCl KCl 3 mol L-1

Fig. 1. Differential pulse stripping voltammetric responses obtained in acetatebuffer pH 5.0 for the following: (A) CPE unmodied after preconcentration step; (B)

P1 P2 P3 P4 P5 P6 P7 P8

5

10

15

I pa

Biochar sample

Lead Cadmium

rce Technology 143 (2013) 4045controlled agitation; (2) then, the electrode was removed fromthe preconcentration cell, briey rinsed with deionized water,and placed in the electrochemical cell containing 10 mL of0.1 mol L1 acetate buffer solution (pH 5.0) as supporting electro-lyte; and immediate cathodic reduction of the absorbate at con-trolled potential was performed; (3) Differential pulse adsorptivestripping voltammograms (DPAdSV) were registered and (4) nal-ly, after the steps just described, the electrode surface was cleanedby putting it in 0.1 mol L1 H2SO4 solution.

2.6. Sample preparation

A well-known amount of evaluated ions were spiked to analiquot of 100.0 mL of simulated efuent in order to reach a nalconcentration of 0.5 mg L1 and 0.2 mg L1 in Lead(II) or Cad-mium(II), respectively. The samples were prepared with speciesand concentration according established by CONAMA: Chloride(1.0 mg L1), Nitrate (20.0 mg L1), Sulfate (1.0 mg L1), Manga-nese(II) (1.0 mg L1), Copper (1.0 mg L1), Nickel (2.0 mg L1), Zinc(5.0 mg L1) and Mercury (0.01 mg L1). The pH was adjusted at7.0 and preconcentration step was realized directly by immersionof the CPME in the solution. The ions content in these sampleswere quantied by four successive additions of a standard Cad-mium or Lead solution.

3. Results and discussion

3.1. Voltammetric performance of the carbon paste modied electrodefor preconcentration of Lead(II) and Cadmium(II) ions

Fig. 1 presents differential pulse voltammograms obtained withmodied and unmodied carbon paste electrodes in 0.10 mol L1

acetate buffer solution (pH 5.0) for different experimental condi-tions. For carbon paste electrode, any voltammetric peak was ob-served after preconcentration and cathodic reduction stepsindicating that the unmodied electrode is unable to preconcen-trate Cd(II) and/or Pb(II) (curve A). However, when the same proce-dure was carried out by using a carbon paste modied with 25% ofP4 biochar sample (curve B), oxidation peaks at 0.76 V (Cad-mium) and 0.55 V (Lead) could be observed with a higher inten-sity of the anodic current. Thus, it is possible to suggest that afteran accumulation step, the next step involves the reduction of theions preconcentrated in the biochar at a controlled potential of2.4. Carbon paste electrode construction

The carbon paste (1.0 g) was prepared by carefully mixing thedispersed graphite powder (4575% (w/w)) (Aldrich), with biocharsample at a varying ratio (030% (w/w)) and subsequently addedto 0.250 g of mineral oil (25% (w/w)). The components were mixedmanually in a mortar and pestle for at least 10 min to obtain anappropriate homogenization. Modied carbon pastes were pre-pared using the several synthesized biochar samples and it waspacked into an electrode body consisting of a plastic cylindricaltube (o.d. 5 mm, i.d. 3 mm) equipped with a copper rod servingas an external electric contact. Appropriate packing was achievedby pressing the electrode surface against a lter paper.

2.5. Voltammetric procedure

The analytical procedure comprised four steps (Bergamini et al.,2006): (1) Lead(II) or/and Cadmium(II) were directly preconcen-

42 T.M. Suguihiro et al. / Bioresou1.0 V versus Ag/AgCl. No current peaks were observed for themodied carbon paste electrode before the accumulation step insolutions containing Lead(II) and Cadmium(II) ions (curve C). Theseresults suggest that biochar obtained from castor bean is not elec-troactive in the potential range studied. So, incorporation of thebiochar at the carbon paste electrode offers a benecial alternativefor the accumulation of ions.

The increase in anodic current at the modied electrode dem-onstrates that biochar in combination with DPAdSV measurementscan promote a better response in comparison with the unmodiedcarbon paste electrode attributed to the high functionalized sur-face of biochar. These results suggest that the anodic surface pro-cesses could be systematically exploited by DPAdSV with someadvantages in sensitivity and selectivity.

3.2. Voltammetric behavior of the carbon paste electrode modiedwith biochar samples prepared in different experimental conditions

In order to optimize the voltammetric procedure, modied car-bon paste electrodes were prepared using different biochar sam-

CPME modied with 25% (w/w) biochar P4 after preconcentration step; (C) CPMEmodied with 25% (w/w) biochar P4 before preconcentration step. The preconcen-tration step was realized for 600 s in a aqueous solution adjusted at pH 5.0 contentof 1.0 105 mol L1 of Pb(II) and 5.0 105 mol L1 of Cd(II).Fig. 2. Anodic peaks currents obtained for Pb(II) and Cd(II) ions using differentbiochar samples. Error bars are standard deviations corresponding to threereplicates obtained for different electrode surfaces.

nature of samples. Broad sorption peak at 3317 cm1 was veriedindicating the existence of hydroxyl group. Other sorption peaksreveal the presence of several functional groups: the sorption peakaround 2927 cm1 was assigned to CH stretching, 1620 cm1 rep-resented a carboxyl group and ionized non-coordinated and ion-ized coordinated COO group (Chen et al., 2008; Keiluweit et al.,2010). The peak at 1420 cm1 corresponded to aromatic CC ringstretching. The peaks attributed to CO stretch of carboxylate ions,hydroxyl bending vibration, CO stretching vibration of the alco-holic groups and aromatic compounds were observed at 1375,1317, 1049 and 780 cm1 respectively. So, the functional groupspresent on biochar samples may be responsible by Lead and Cad-mium ions sorption. Thus, a P3 biochar sample was adopted asthe best modier to prepare carbon paste electrodes for Pb(II)and Cd(II) ions determination and it was used for further studies.

3.3. Inuence of the experimental parameters on the voltammetric

rce Technology 143 (2013) 4045 4325% w/w of modier) by 600 s. The anodic current peak values ob-tained for Lead and Cadmium ions using a CPME with different bio-char samples are shown in Fig. 2.

The results of the elemental compositions (Fig. 3) of biocharsamples revealed that with the increase in the pyrolytic tempera-ture, the C content increased in contrast with decreasing in the Hcontent (samples P1, P2, P5 and P6). The estimative of H/C molarratio suggests that H atoms are associated with plant organic mat-ter. Higher H/C molar ratios obtained when the sample was sub-mitted to the lower temperature (300 C) suggest that biocharsamples could contain a certain amount of aliphatic original plantorganic residues such as cellulose. When pyrolytic temperature isat 350 C, the H/C molar ratio decreases signicantly suggestingthat the original organic fraction was reduced and the structuresare more aromatic (Maek et al., 2013).

The molar oxygen/carbon ratio (O/C) of biochar has been usedas an estimative of the surface hydrophilicity since it is indicativeof polar-group content (Spokas, 2010; Zhang et al., 2011). In addi-tion, a decreasing in the O/C and/or N/C ratios can indicate theincreasing in the hydrophobicity and the reduction of polar groups.

In order to clarify the obtained voltammetric behavior, a corre-

0.75 0.80 0.85 0.90 0.95

0.63

0.64

0.65

0.66

0.67

0.68

0.69P4

O /

C

H / C

0.094

0.096

0.098

0.100

0.102

0.104

0.106

P7

P8

P1

P2

P6

P5

N / C

P3

P8P7

P6

P5

P4

P3

P2 P1

Fig. 3. Ratio of the elemental composition of C, O and N obtained for the samplesused biochars.

T.M. Suguihiro et al. / Bioresoulation between sorption capacity of the modied electrode andcharacteristics of biochars was realized (Meyer et al., 2011). A po-sitive correlation between voltammetric response and N/C ratiowas observed suggesting that polar groups content at biochars sur-face can facilitate the sorption of Lead and Cadmium ions. Polargroups on the biochar surface can work as water binding centersand facilitate the formation of water clusters, which may increasethe biochars accessibility to ions due to its hydrophilicity. In addi-tion, the results showed that samples with elevated content ofnitrogen atoms can exert a more signicant effect on preconcentra-tion of analytes. The results suggesting that both sorption andcomplexation process are the mechanisms by which those metalsare retained at electrode surface.

The FTIR spectra of the samples were very similar, all featuringmainly a broad band at 36803300 cm1, associated with the OHstretching from alcohol, carboxylic acids and water. The boardingcharacteristics of those absorptions are consequence of hydrogenbonding presence in different degrees. Energy absorption in1625 cm1 attributed to the structural vibrations of C@C aromat-ics, asymmetric stretching of C@O (COO) and bending of OHgroups. Shoulder at 1720 cm1 (P4, P7 and P8 samples) is assignedto C@O stretching of ketone, ester and carboxylic acid (Chen et al.,2008; Keiluweit et al., 2010). Biochar FTIR spectra data displayed asignicative number of sorption peaks indicating the complex

4030-0.8 -0.6 -0.40

10

20

30

0 100 200 300

0

10

20

f

a

I /

A

E / V vs. Ag/AgCl 3 mol L-1

I pa /

A

t / s

Fig. 4. DPAdSV obtained for CPEM (25% (w/w) biochar P3) after preconcentration inaqueous solution with 2.0 105 mol L1 of Cd(II) and 3.3 106 mol L1 Pb(II) forresponse

In order to optimize the anodic stripping voltammetry as ana-lytical tool for Cadmium(II) and Lead(II) determination, the effectof some experimental parameters (electrode composition, pH var-iation, accumulation time (tacc), clean solution and time of immer-sion) and instrumental parameters on the peak current by usingcarbon paste electrode modied with biochar was investigated.

The amount of biochar in the carbon paste had a signicativeinuence on the voltammetric responses. The peak currents in-creased with increasing amount of biochar up to 25% (w/w) and de-creased signicantly when more than 25% (biochar, w/w) was usedin the electrode preparation due to the decrease in the conductivearea at the electrode surface. Based on these results, a carbon-pastecomposition of 25% (w/w) biochar, 50% (w/w) graphite and 25% (w/w) mineral oil was used in subsequent studies. Similar behaviorwas also observed in a previous work (Bergamini et al., 2006).

In order to prevent a memory effect, after preconcentration andvoltammetric measurement steps the CPME was submitted to aclean step using a sulfuric acid solution 0.1 mol L1 (Fig. 4). Theelectrode was immersed in acid solution and maintained for timesvarying from 0 s (without clean step) to 300 s. Voltammetric re-sponse decreases exponentially with the increase of the immersedtime (Fig. 4 detail). For times higher than 200 s no signicativesignal was veried for both ions evaluated. So, a desorption step(immersion by 240 s in 0.1 mol L1 H2SO4 solution) was adoptedbecause it promotes a better repeatability between voltammetricmeasurements.different cleaning time in 0.1 mol L1 H2SO4 solution: 0 s (without cleaning step)(a), 30 s (b), 60 s (c), 150 s (d), 200 s (e) and 300 s (f). The effect of cleaning time onthe current peak value was shown in detail.

The pH effect on the preconcentration solution is an importantvariable and it can affect the biochars performance in the interac-tion with the studied ions (Fig. 5). So, in order to optimize the pH ofthe solution in the preconcentration step, this parameter was stud-ied in the range of 2.09.0 (Fig. 5A). It was found that for acidicsolutions of pH

rce T0 25 500

50

100

150

-1.0 -0.8 -0.6 -0.4 -0.20

50

100

150

CdPb

I pa /

A

C / mol L-1

h

a

I

E / V (vs Ag/AgCl 3 mol L-1)

Cd

Pb

Fig. 6. DPAdSV of Cd(II) and Pb(II) with different concentrations at CPEM modiedwith 25% biochar P3 in phosphate buffer solutions (pH 5.0) after preconcentrationby 1200 s in solution (pH 7.0) containing concentrations varying between2.5 107 mol L1 (a) and 5 105 mol L1 (h) for Cd(II) ions and 5.0 108 -mol L1 (a) and 1.0 105 mol L1 (h) for Pb(II) ions. The respective analyticalcurves are shown in detail.

Table 3

T.M. Suguihiro et al. / Bioresouobserved in the presence of manganese II and chromium III ions.These results shown that these ions do not exhibit an effectivecompetition with the analytes by active sites of the modier. Theabsence of the interference in presence of Mercury ions can be ex-plained due its low concentration when compared to Pb(II) andCd(II) ions. A signicant decrease in the anodic peak currentswas observed in the presence of Sn(II), Fe(III), Cu(II), Zn(II) andNi(II) ions demonstrating that the modier (biochar) is able to formcomplex with other metallic species besides the Cadmium(II) andLead(II) ions. Nevertheless, interference effect observed is constantand it could be minimized by using of standard addition procedure.

In order to verify the efciency of this approach, the voltammet-ric determination of Pb(II) and Cd(II) ions was realized in asimulated efuent spiked with analytes at concentration limitestablished of Brazilian legislation. Recoveries from 93.8% to106.3% were obtained for both ions evaluated. This result revealsthat Cd(II) and Pb(II) can be reliably determined by the proposedmethod even in the presence of interfering ions when the standardaddition method is used.

4. Conclusions

Electroanalytical techniques could provide several informationabout properties adsorption of biochars for electroactive probe.

Technology. Earthscan, London.Maek, O., Brownsort, P., Cross, A.S., 2013. Inuence of biochar production

Miller, J.C., Miller, J.N., 1993. Statistics for analytical chemistry, third ed. EllisHorwood, New York.

Interference studies of some ions in the Cd(II) and Pb(II) recovery under the optimizedDPAdSV conditions.

Concomitant ions C/ppm C/mol L1 Signal recovery (%)

Cd(II) Pb(II)

Tin(II) 4.0 3.4 105 48.7 13.0Chloride 1.0 2.8 105 90.9 96.2Nitrate 20.0 2.4 104 94.5 99.2Sulfate 1.0 7.0 106 91.7 92.0Iron(III) 15.0 2.7 104 12.5 26.9Manganese(II) 1.0 1.8 105 83.8 98.3Copper 1.0 1.6 105 6.5 24.1Nickel 2.0 3.4 105 15.7 97.1Zinc 5.0 7.6 105 49.6 78.4Mercury(II) 0.01 5.0 108 93.7 99.3Chromium(III) 0.5 9.6 106 97.9 93.4Chromium(VI) 0.5 9.6 106 130.3 103.2

Cadmium and Lead concentrations xed at 1.8 106 and 2.4 106 mol L1,respectively.Souza, L., Calegari, F., Zarbin, A., Marcolino-Junior, L., Bergamini, M.F., 2011.Voltammetric determination of the antioxidant capacity in wine samples usinga carbon nanotubes modied electrode. J. Agric. Food Chem. 59, 76207625.

Spokas, K.A., 2010. Review of the stability of biochar in soils: predictability of O:Cmolar ratios. Carbon Manage. 12, 289303.

Sun, K., Keiluweit, M., Kleber, M., Pan, Z., Xing, B., 2011. Sorption of uorinatedherbicides to plant biomass-derived biochars as a function of molecularstructure. Bioresour. Technol. 102, 98979903.

Uchimiya, M., Lima, I.M., Klasson, K.T., Chang, S., Wartelle, L.H., Rodgers, J.E., 2010.Immobilization of heavy metal ions (CuII, CdII, NiII, and PbII) by broiler litter-derived biochars in water and soil. J. Agric. Food Chem. 58, 55385544.

Zhang, G., Zhang, Q., Sun, K., Liu, X., Zheng, W., Zhao, Y., 2011. Sorption of simazineto corn straw biochars prepared at different pyrolytic temperatures. Environ.conditions on the yield and environmental stability of biochar. Fuel 103, 151155.

Matusiewicz, H., Krawczyk, M., 2006. Determination of cadmium and lead inreference materials by volatile species generation with in situ trapping ameatomic absorption spectrometry. Microchem. J. 83, 1723.

Meyer, S., Glaser, B., Quicker, P., 2011. Technical, economical, and climate-relatedaspects of biochar production technologies: a literature review. Environ. Sci.Technol. 45, 94739483.In addition, the use of carbon paste electrode modied with bio-char can be a promising tool for construction of analytical sensors.Sensor developed was able to detect evaluated ions in real samplessuch as wastewater, by using a simple, rapid and economic waythan other electroanalytical methods. By other hand, the manu-script offers a voltammetric method combinated with the use ofa composite electrode of simple preparation as an alternativeprobe for evaluate biochars hability in preconcentration of theelectroactive ions such as Lead and Cadmium.

Acknowledgement

We gratefully acknowledge nancial support from FundaoAraucria (Process number 15687), CAPES, CNPq (Process577536/2008-7 and 55.0665/2007-2) and NENNAM (PRONEX Fun-dao Araucria/CNPq 17378).

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Beesley, L., Marmiroli, M., 2011. Biochar production potential in Ghana a review.Environ. Pollut. 159, 474480.

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Chen, X., Chen, G., Chen, L., Chen, Y., Lehmann, J., McBride, M.B., Hay, A.G., 2011.Adsorption of copper and zinc by biochars produced from pyrolysis ofhardwood and corn straw in aqueous solution. Bioresour. Technol. 102, 88778884.

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Dong, X., Ma, L.Q., Li, Y., 2011. Characteristics and mechanisms of hexavalentchromium removal by biochar from sugar beet tailing. J. Hazard. Mater. 190,909915.

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Erfurth, E.M., Gerhardsson, L., Nilsson, A., Rylander, L., Schutz, A., Skerfving, S.,Borjesson, J., 2001. Effects of lead on the endocrine system in lead smelterworkers. Arch. Environ. Health 56, 449455.

Fogg, A.G., Wang, J., 1999. Terminology and convention for electrochemicalstripping analysis. Pure Appl. Chem. 71 (5), 891897.

Keiluweit, M., Nico, P.S., Johnson, M.G., Kleber, M., 2010. Dynamic molecularstructure of plant biomass-derived black carbon (biochar). Environ. Sci. Technol.44, 12471253.

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echnology 143 (2013) 4045 45Pollut. 159, 25942601.

An electroanalytical approach for evaluation of biochar adsorption characteristics and its application for Lead and Cadmium determination1 Introduction2 Methods2.1 Apparatus2.2 Reagents and solutions2.3 Preparation of biochars and characterization2.4 Carbon paste electrode construction2.5 Voltammetric procedure2.6 Sample preparation

3 Results and discussion3.1 Voltammetric performance of the carbon paste modified electrode for preconcentration of Lead(II) and Cadmium(II) ions3.2 Voltammetric behavior of the carbon paste electrode modified with biochar samples prepared in different experimental conditions3.3 Influence of the experimental parameters on the voltammetric response3.4 Analytical performance3.5 Interfering studies and application of the proposed method

4 ConclusionsAcknowledgementReferences