The properties of Pt4+-adsorption and its reduction by Bacillus megaterium D01 were studied by means of ICP, anode-stripping voltammetry, TEM, IR and XPS. The results of ICP analyses showed that the Pt4+-adsorptive efficiency of the strain D01 was as high as 94.3% under the conditions of 100 mg Pt4+/L, 1 g biomass/L, pH 3.5 and at 30 degreesC for 24 h. Moreover, it was confirmed from anode stripping voltammetry that the strain D01 possessed a strong reducibility. The TEM analysis indicated that the strain D01 was able to adsorb and reduce Pt4+ to Pt-0, small particles. The XPS result further supported the reduction of Pt4+ to Pt2+, followed by the further recuction to Pt-0. The IR spectrum implied that D01 biomass adsorption of Pt4+ may result in the complexation of the C = O bond to the Pt species

Fu, JK

Liu, YY

Yao, BX

Yu, XS

Zhou, ZH

周朝晖

Chemical Research in Chinese Universities

Xiamen University Institutional Repository

A Study of Pt4+-Adsorption and Its Reductionby Bacillus Megaterium D01*LIU Yue-ying1, * * , FU Jin-kun2, ZHOU Zhao-hui2, YU Xin-sheng2and YAO Bing-xin1( 1. Department of Biology ; 2. Dep ar tment of Chemistry ,X iamen Univer sity , X iamen 361005, P . R. China)( Received Aug. 31, 1999)* Suppor ted by the National Natural Science Foundation of China( No . 29743001 and No. 29876026)　　* * To w hom corr espondence should be addressed.　　The propert ies of Pt4+ -adsorption and its reduction by Bacillus megaterium D01 w ere studiedby means of ICP, anode-st ripping voltamm etry , T EM, IR and XPS. T he results of ICP analy-ses show ed that the Pt4+-adsorpt ive ef ficiency of the strain D01 w as as high as 94. 3% under thecondit ions of 100 m g Pt4+ / L , 1 g biomass/ L, pH 3. 5 and at 30 ℃ for 24 h. Moreover, it w asconfirmed from anode st ripping voltamm etry that the st rain D01 possessed a strong reducibility.The TEM analy sis indicated that the strain D01 w as able to adsorb and reduce Pt4+to P t0, smallparticles. The XPS result further supported the reduction of Pt4+to Pt2+ , follow ed by the fur-ther recuction to Pt0. The IR spect rum implied that D01 biomass adsorption of Pt4+may result inthe complexation of the C O bond to the Pt species.Keywords　Biosorpt ion, Bioreduction, Plat inum , Bacillus megateriumArticle ID　1005-9040( 2000) -03-246-04Introduction　　T he accumulation of metals by microorganisms has been know n for a few decades andhas received more at tention in recent years because of its potential application in environmentalprotection and the recovery of precious metals. There have been a number of reports on thebiosorption of cadmium[ 1] , chromium[ 2] , uranium[ 3] , lead[ 4, 5]and gold[ 6, 7]by microbialbiomass. However, there have been only a few reports on platinum biosorption[ 8]. Briereyand Vance[ 8]reported that a metal removal agent( M RA) could efficient ly remove acidic plat-inum( PtCl4) but the accumulation capacity w as only 53 mg Pt/ g M RA. Recently, we havereport ed the results of st rain D01 screened from different source bacterial strains and identifiedas Bacillus megaterium D01, w hich exhibited a relatively strong ability of adsorbing Au3+ [ 9].The strain D01 has been used as bioreductant for the preparations of highly dispersive sup-ported gold catalyst[ 9, 10]and bacteria-modified carbon past e electrodes used t o determine thetrace amounts of gold(Ⅲ)[ 11] . As a long program research on t he bioreduction and the recov-ery of precious metals, here w e w ill further report the results of Pt4+-biosorption and biore-duction by strain Bacillus megaterium D01, which show s the strongest ability of adsorbingPt4+among the strains screened. The system of Pt4+- D01 biomass and it s reductive stateVol. 16 No. 32000 Chemical Research in Chinese U niversities　　　　　　 246～249w ere characterized with ICP, anode-stripping voltammetry , T EM , IR and XPS.Experimental1　Reagents andMethods　　H2PtCl6 and other chemical reagents w ere of analytical purity. P t4+concentration was de-termined on a Baird PS-4 ICP-AES atomic adsorption spectrophotometer. The TEM w asmeasured w ith a JEM 100 CXll transmission electron microscope. T he voltammetric curvesand t he IR spectra w ere measured on a 8511A pot entiostat and a 740sx FTIR spectrometer,respectively . T he XPS w ere measured on a ESCALRB M KI X-ray photoelectron spectrome-ter.2　Bacterial Cultivation and Biomass Preparation　　 Strain Bacillus megaterium D01 w as cultivat ed according to the literature[ 9] . T he cul-tures were harvested by centrifuging( 3 500 r/ min, 15 min) and the cell pellets w ere subse-quently w ashed three times w ith deionized water. The washed biomass w as dried at 60℃ andthen grounded w ith a mortar and pestle. T he dried biomass was stored in capped bottles in adryer.3　Biosorption Tests of Pt4+and Calculation of Pt4+Biosorptive Efficiency and Capacity　　The D01 dried biomass w as mixed w ith a H 2PtCl6 solution. The mixture containing 100mg Pt4+ / L and 1 g dried biomass/ L w as incubated on a rotary shaker at 130 r/ min, pH 3. 5and 30 ℃ for 24 h. The mix ture w as filtered through a 0. 22 m pore-size cellulose acetatefilter membrane and the filtrate w as assayed w it h an atomic adsorption spectrophotometer forthe determination of the residual Pt4+ concentration. T he efficiency and the capacity ofbiosorption of Pt4+ions were calculated w ith the follow ing equations:Biosorptive efficiency of Pt4+( % ) = [ ( ci- cf ) / ci] ×100%Biosorptive capacity of P t4+( mg Pt4+/ g dry biomass) = ( ci- cf ) / cbw here ci and cf are t he initial and final concentration( mg/ L ) of P t4+in t he mixture, respec-tively , cb is the biomass concentration( g / L ) .4　Preparation of Samples for TEMmicrographs and XPS　　After platinum biosorption had been completed, the samples w ere taken out w ith thecopper grids. T he sample supported on t he copper grids w as dried at room temperature andthen recorded w ith a t ransmission electron microscope at an accelerating voltage of 100 kV.　　The biosorption test w as carried out under the concentrations of 100 mg Pt4+/ L , 5 gbiomass/ L , and at pH 3. 5 and 30 ℃ for the time required. T he D01 biomass adsorbing Pt4+w as centrifuged and dried under a reduced pressure at 80 ℃ for 4 h. The samples w ere de-tected with a photoelectron spectrometer.Results and Discussion1　Biosorption of Pt4+by Strain D01　　According to the equations in the ex perimental section, the efficiency and the capacity ofbiosorption of Pt4+ by strain D01 reached as high as 94. 3% and 94. 3 mg Pt4+ / g dry247No. 3 LIU Yue-ying, FU Jin-kun, ZHOU Zhao-hui et al. 　　biomass, respectively. The residual amount of Pt4+in the solution w as 5. 7 mg/ L w hen theinitial concentration of P t4+w as 100 mg/ L. The other strains show ed a less biosorpt ive capac-ity than strain D01. T he high efficiency of biosorption show s that strain D01 is a suitablest rain for adsorbing Pt4+and may be of potential application to the recovery of platinum.2　Determination of the Reducibility of Strain D01 with Anode Stripping Voltammetry　　T o survey the reducibility of strain D01, the voltammetric curves of the system w ere de-termined w ith a D01 biomass-modified carbon past e electrode in a HCl solution at pH 4. 0. Apeak at 0. 25 V appeared in the volt ammetric curve obt ained w ith the bacteria-modified pasteelectrode. In contrast, there w as no peak in the voltammetric curve obtained w ith the unmod-ified electrode. T his indicates that D01 biomass w as ox idized elect rochemically. The reductionpotential( 0. 25 V) of D01 biomass confirmed t hat D01 biomass w as able t o reduce Pt4+ .3　TEM of Pt4+ -D01 Biomass SystemFig. 1　Transmission electron micrograph(×20 000) of D01 biomass contactedwith Pt4+for 24 h.　 　 Fig. 1 is the t ransmission electronmicrograph of D01 biomass ex posed t o an aque-ous solution of H2PtCl6 at pH 3. 5 and 30 ℃ for 24h. It is obvious that there were sm all particles on thecell w all, which corresponded to Pt0in microformstate reduced from adsorbed Pt4+ . This illust ratesthat D01 biomass possesses relat iv ely st rong abilit iesof not only adsorbing Pt4+, but also reducing Pt4+ions to P t0. The result w as ident ical with that report-ed in the literature[ 8] . T he M RA became dark red asthe platinum w as loaded w hich suggested the reduc-tion of the plat inum ions to the metallic platinum bythe MRA.4　XPS Characterization of Pt4+ -D01 Biomass System　　Fig . 2 show s the XPS spectrum of D01 biomass contacted w it h Pt4+for 12 h. The peaksFig. 2　XPS spectrum of Pt4+ reduced byD01 biomass for 12 h.of bonding energy of 75. 1, 74. 6 and 71. 8 eVseen in Fig. 2 w ere assigned to Pt4+ ( 4f 7/ 2 ) ,Pt2+( 4f 7/ 2 ) and Pt0( 4f 7/ 2 ) , respectively. Itw as estimated that about 60% of Pt4+w as re-duced to Pt2+and about 20% of Pt4+w as re-duced to Pt0. The evidence of XPS furt hersupports the reduction of Pt4+ adsorbed byD01 biomass from an aqueous solut ion ofH2PtCl6, w hich involved a reduction of Pt4+toPt2+, follow ed by the further reduction of it toPt0.5　IR Spectra Characterization of Strain D01 Adsorbing Pt4+　　T he IR spectra of the biomass and biomass contacted w ith Pt4+solution for different timew ere compared. It w as found that the peak at 1 664 cm- 1was decreased and shifted to 1 649248 Chemical Research in Chinese Universities　　　　　　　　Vol. 16cm- 1, and the peak at 3 087 cm- 1also decreased and finally disappeared with increasing theinteraction time of D01 biomass w ith Pt4+ . Usually, the IR spectral peaks at 1 664 cm- 1and3 087 cm- 1belonged to as( C O) and as ( NH) of the peptide chain on cell w all, respective-ly[ 12]. T he results mentioned above imply that D01 biomass adsorption of Pt4+may result inthe complexation of the C O bond to the Pt species w hich makes the as( C O) shift to alow er frequency, indicating t hat the C O bond is w eakened to some extent . M oreover, thepeak at 1 726 cm- 1corresponding to as ( COOH) disappeared after the interaction of it w iththe Pt4+solution, indicating the complexat ion of free carbox ylic acid.References[ 1 ]　Puranik, P . R . , Chabukswar , N . S. , Paknikar , K . M . , Appl. M icrobiol. Biotechnol. , 43, 1 118( 1995)[ 2 ]　Wang , B. J. , Yang , H. F . , Li, W . Z. , Acta M icrobiol. Sinica, 38, 108( 1998)[ 3 ]　Bengtsson, L . , Johansson, B. , Hacket t, T . J. , et al. , Appl. M icr obiol. Biot echnol. , 42, 807( 1995)[ 4 ]　M err oum , M . L . , Ben Om ar, N . , Gonz lez-M uoz, M . T . , et al. , J. Appl. M icrobio l. , 84, 63( 1998)[ 5 ]　Wu, J. , L i, Q . B. , Deng , X. , et al. , A cta M icrobiol. Sinica, 39, 88( 1999)[ 6 ]　Huang , S. H. , Chinese M icr obiol. , 18, 171( 1991)[ 7 ]　Pethkar, A . V . , Paknikar, K. M . , J. Biotechnol. , 63, 121( 1998)[ 8 ]　Br ierley , J. A . , Vance, D. B. , Biohydrometal, Pr oc. Int. Symp. , 477( 1988)[ 9 ]　L iu, Y . Y . , Fu, J. K . , Hu, R. Z . et al. , A ct a M icrobiol. Sinica, 39, 260( 1999)[ 10]　Fu. J. K. , L iu, Y . Y . , Hu, R. Z . , et al. , A cta Phy s. -Chim. , 14, 769( 1998)[ 11]　Hu, R. Z . , Zhang , W . D . , L iu, Y . Y . , et al. , Anal. Commun. , 36, 147( 1999)[ 12]　Xing , G . W . , Ye, Y . H. , L i, C. X. , Chem . J. Chinese Universities, 19, 602( 1998)249No. 3 LIU Yue-ying, FU Jin-kun, ZHOU Zhao-hui et al. 　　

A study of Pt4+ -adsorption and its reduction by Bacillus megaterium D01

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A study of Pt4+ -adsorption and its reduction by Bacillus megaterium D01

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