Bisphosphonate modified mesoporous silicon for scandium adsorption

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The e o e, Sc is usually eco e ed as a by- p oduc om he was e esidues and ailings o o he me al mining such as u anium-leached liquo s, i anium pigmen p oduc ion was ewa e s, ungs en e ine y and bauxi e esidues.6 Con en ional hyd ome allu gical p ocesses used in he eco e y such as p ecipi a ion and sol en ex ac ion ha e majo d awbacks. The p ecipi a ion me hod yields poo Sc pu i y due o co-p ecipi a ion o impu i y me als p esen in la ge quan i ies.5,6 Sol en ex ac ion is p incipally ope a ed in la ge-scale and equi es ea men s wi h a la ge olume o haza dous o ganic sol en s ha lead o po en ial oxic emissions in o he en i onmen .7 Also economically, he me hods a e no con enien o low con en Sc due o he high acid consump ion as well as he complica ions associa ed o euse he ex ac an .8 As a g eene al e na i e, adso p ion echnology has he po en ial o ex ac Sc mo e e icien ly in e ms o low ope a ing cos , easy o use and eusabili y. Fundamen al equi emen he e is ha he adso ben ma e ial is capable o e e sibly adso b and deso b Sc ions and subs an ially in epea ed cycles wi hou educ ion in he pe o mance. Mo eo e , he e icacy o he ma e ial is de e mined by i s abili y o selec i ely cap u e Sc om he me al impu i ies. Hence, physiochemical cha ac e is ics o he adso ben is he key ounda ion o succeed p o i able Sc ex ac ion and i s comme cializa ion. Comme cially a ailable adso ben s such as ion exchange esins mainly su e om agg ega ion and ouling p oblems due o he swelling o i s polyme ic s uc u e du ing adso p ion- deso p ion p ocesses, which e en ually leads o de e io a ion o he ma e ial.9,10 To o e come hese issues, chemical ancho ing o me al binding molecules on o a igid suppo is p omising echnique in he s a e-o - he-a . In pa icula , mesopo ous silica ha e been widely used because o hei high su ace a eas o e ing high deg ee o unc ionaliza ion.8 Bu he s abili y o he silica-based ma e ial is ye limi ed in highly acidic condi ions due o he dissolu ion o ex emely hin po e walls.8,11 Besides, he eusabili y o he hyb id ma e ials a e a ely epo ed o mo e han 10 cycles and is usually done in ba ch se up, which is a edious ask in la ge scale ope a ion.12-17 Flow h ough se up is simple echnique o adso b/deso b me als in con inuous p ocess, in which he olume and speed o he eed solu ion a e easily con olled. The hyb id ma e ials can be con enien ly packed in column whe e he me al solu ion can swi ly low h ough because o high pe meabili y assis ed by he pa allel po es in he ma e ial. Ne e heless, no only he mesopo ous silica suppo bu also he unc ionalized molecules mus be obus o sus ain he eusabili y o he adso ben . Bisphosphona es consis ing O=P–C– P=O s uc u e a e s able molecules ha ha e been demons a ed o collec se e al me al ca ions om mining p ocess wa e s.18 In ou ea lie esea ch, bisphosphona e molecules wi h e minal alkene we e di ec ly g a ed on he mally ca bonized su aces o mesopo ous silicon. The syn hesized ma e ial showed excep ional s abili y in highly acidic/basic solu ions.JR pape In his s udy, we in es iga e he adso p ion mechanisms alongside he selec i i y owa ds Sc, and he chemical s abili y and eusabili y o his ma e ial up o 50 adso p ion/deso p ion cycles. Fu he , we demons a e a low h ough se up whe e he ma e ial is used as il e s in columns 3 o ex ac scandium e icien ly. The ob ained esul s we e compa ed o a comme cialized ion exchange esin Dowex 50WX8 ope a ed in analogous expe imen al condi ions. 2. Expe imen al sec ion 2.1 Ma e ials, chemicals and s anda d solu ions Hyd o luo ic acid (HF 38–40 %, Me ck), e hanol (E OH 99.5 %, Al ia Oy) and silicon wa e s (Okme ic Oyj) we e used o p epa a ion o po ous silicon (PSi). Bisphosphona e molecule (Te akis( ime hylsilyl) 1-( ime hylsilyloxy)undec-10-ene-1, 1-diylbisphosphona e) was syn hesized and cha ac e ized as epo ed elsewhe e.JR pape S anda d solu ion o Sc (1000 mg/L in 1 w % HNO3, AAS s anda d) and he ion-exchange esin, Dowex 50WX8 (hyd ogen o m, 100 – 200 mesh) we e pu chased om Sigma, Finland. The esin is a s ong ca ion exchange con aining sul onic acid (SO3H) unc ional g oups. Me al s anda ds (1000 mg/L) o AlCl3, FeCl3, CuCl2 and ZnCl2 we e all Ti isol s anda ds pu chased om Me ck, Finland. Milli-Q wa e was used h oughou he expe imen s. 2.2 Syn hesis o po ous silicon (PSi). Silicon wa e s wi h esis i i y alues o 0.01–0.02 Ωcm we e elec ochemically e ched in 1:1 HF/E OH mix u e applying cu en densi y o 30 mA/cm2 o 40 min. PSi ilms we e de ached om he wa e s wi h li -o cu en pulses o 160 (1 sec) and 255 mA/cm2 (2 sec) wi h 1 sec pause be ween he pulses. The ilms we e hen d ied o 1 h a 65 °C. The d y PSi ilms we e i s hand g ound in o coa se pa icles and la e milled (100 pm, 3 mins) in a plane a y ball mill (F i sch Pul e ise e 7). The pa icles we e hen sie ed in o 25–75 µm size ac ion. 2.3 The mal ca boniza ion o PSi. The PSi mic o pa icles we e imme sed in 1:1 HF/E OH solu ion o 10 min. Supe na an was disca ded and he sample was d ied o 45 min a 65 °C. The d y PSi powde was ans e ed in o a qua z ube and lushed wi h N2 o 30 min a 1 L/min. Ace ylene gas a 1 L/min was in used i s o 15 min a oom empe a u e (RT) ollowed by ea men o 14 min 30 sec a 500 °C in p ehea ed ube o en. A e 30 sec o only N2 a 500 °C, he qua z ube/sample was aken ou om he ube o en and he sample was cooled a RT o 30 min unde N2. A he oom empe a u e, he ace ylene low was esumed o 9 min 40 sec. A e 20 sec, he sample was hea ed a 820 °C o 10 minu es unde N2 in he ube o en. The manu ac u ed he mally ca bonized pa icles (TCPSi) we e cooled a RT o 40 min unde N2 a mosphe e. 2.4 Syn hesis o BP-TCPSi. The BP molecule was conjuga ed on TCPSi pa icles by mixing 1:2 mass a io o BP:TCPSi unde N2 p o ec ion. Be o e he mixing, BP was o me ly degassed in mesi ylene solu ion using N2 gas o 20 min. The mesi ylene solu ion con aining he BP was ans e ed in o he qua z ube and mixed wi h he TCPSi pa icles. The qua z ube was sealed wi h a Te lon s oppe and he sample was incuba ed a 120 °C unde N2 a mosphe e. A e 19 h, he BP-TCPSi pa icles and mesi ylene solu ion was pou ed in o a beake . The unbound BP molecule and mesi ylene supe na an was disca ded by washing he pa icles h ice wi h 40 mL MeOH. The pa icles we e washed wi h 100 mL MeOH in suc ion il a ion (polyp opylene PP il e , 10 µm po e size) and d ied a 65 °C o 1 h. Simila ly p epa ed TCPSi pa icles incuba ed in mesi ylene wi hou BP was used as e e ence sample. 2.5 Ma e ial cha ac e iza ion and ins umen a ion 4 The median pa icle size o TCPSi and BP-TCPSi samples was measu ed by Mas e size de ice (Mas e size 2000, Mal e n Ins umen s, UK) using E OH as dispe san . The su ace a ea, po e olume and po e diame e o he pa icles was de e mined by N2 adso p ion/deso p ion iso he ms (Mic ome i ics T is a III). P io o he measu emen , samples we e degassed a +65 °C in acuum (VacP ep 061, Mic ome i ics) o 1 h and hen he sample chambe was illed wi h con olled inc emen s o N2 a empe a u e o 77 K (-196.15 °C). The amoun o BP g a ed on TCPSi was measu ed by he mog a ime ic analysis (TGA Q50, TA ins umen s). Samples we e i s equilib a ed a 80 °C o 30 min and hen hea ed o 700 °C a he a e o 20 °C/min unde ni ogen low (120 mL/min), and he mass loss was measu ed as a unc ion o empe a u e. The BP con en (% w/w) om BP-TCPSi sample was calcula ed by compa ing he mass loss o un unc ionalized TCPSi sample. Samples o scanning elec on mic oscope (SEM, Zeiss Sigma HP VD) coupled wi h ene gy dispe si e X- ay spec oscopy (EDS, The moScien i ic) we e p epa ed by clueing he mic opa icles on op o s anda d aluminium s ub wi h conduc ing ca bon adhesi e. 5.0 kV accele a ion ol age was used wi h SE2 o InLens De ec o o he images o he pa icles and he accele a ion ol age was inc eased o 15.0 kV o EDS analysis. 2.6 Adso p ion s udies 2.6.1 Ba ch se up Ba ch expe imen s we e conduc ed in 15 mL cen i uge ubes by mixing 10 mg o he adso ben ma e ial (TCPSi, BP-TCPSi o Dowex 50WX8) in 10 mL o Sc solu ion a desi ed concen a ion and pH. The pH o he me al solu ions was adjus ed wi h HNO3 o NaOH. Be o e con ac ing wi h he Sc solu ion, adso ben s we e p imed by mixing ( o 1 h) in acidic media; he TCPSi o he BP-TCPSi pa icles in 10 ml o 5 M HCl whe eas he Dowex 50WX8 esin in 10 ml o 0.125 M H2SO4, and washed h ee imes wi h 10 mL Milli-Q wa e o ob ain neu al pH. Subsequen ly, he Sc solu ion was con ac ed wi h adso ben o a p e-de e mined ime by mixing in an o bi al shake a shaking speed o 80 pm. The adso ben was sepa a ed om he suspension by cen i uga ion (6000 pm, 1 min) and he supe na an aliquo was measu ed by induc i ely coupled plasma mass spec ome e , ICPMS (NexION 350D, Pe kin Elme ). The adso bed me al amoun s (Qe in µmol/g) was calcula ed using ollowing equa ion. 𝑄𝑒=(𝐶𝑜−𝐶𝑒)𝑉 𝑚×1000 𝑀𝑊 (1) Whe e, C0 and Ce a e he me al concen a ion (mg/L) be o e and a e he adso p ion espec i ely, m is he mass (mg) o adso ben and ‘V’ is he olume (mL) o me al solu ion whe eas MW ep esen s he molecula weigh (g/mol) o he me al ion. 2.6.2 Flow- h ough se up Lab-scale low h ough se up (supplemen a y Figu e S1) consis ed o a sy inge pump (AL- 1600, New E a Pump Sys ems Inc.), con en ional 30 mL plas ic sy inges and glass columns (Omni i ® Labwa e, 2.5 cm × 0.3 cm i.d. olume capaci y 0.2 mL). 20 mg o ei he he BP- TCPSi pa icles o he Dowex 50WX8 esin we e packed inside he column suppo ed on o polyp opylene (PP) il e o 10-µm po e size. 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BET su ace a ea calcula ed om he iso he m. b. Speci ic po e olume calcula ed om deso p ion iso he m a p/p0 = 0.9. c. A e age po e diame e calcula ed by BJH heo y using deso p ion b anch o iso he m. Figu e 2. TGA cu es o TCPSi and BP-TCPSi samples. 3.2 Adso p ion s udies 3.2.1 Ba ch se up I was in e ed ha he ex en o Sc adso p ion depends upon he solu ion pH due exchange o p o ons in BP moei y wi h he me al ions. Dep o ona ion cons an ; pKa alues o BP molecule (Figu e 3) a e pKa1=1.0, pKa2 = 2.5, pKa3 = 6.7, pKa4 =10.6 and pKa5 =11.6.19 Figu e 3. Chemical s uc u e o bisphosphona e molecule g a ed on he BP-TCPSi pa icles. A pH ≥ pKa; dep o ona ion occu s. To a oid unspeci ic adso p ion and he isk o Sc p ecipi a ion a pH >413,20,21, he adso p ion s udies we e pe o med a pH 1 and pH 3. The s udies we e s a ed wi h by examining he kine ics o he adso p ion in o de o ind ou he equilib ium ime o he adso p ion iso he m s udies in ba ch ype se up. This esul ed equilib ium ime o 4 h o pH 1 and 24 h o pH 3, de e mined om he s a ing o pla eau in 150 200 250 300 350 400 450 500 550 600 97.0 97.5 98.0 98.5 99.0 99.5 100.0 Mass (%) Temp (°C) TCPSi BP-TCPSi 2 % w/w 7 adso p ion cu es (Figu e S5). Adso p ion was as e a pH 1 equi ing only 10 min o 50 % adso p ion while i ook a leas 1 h a pH 3. Based on he kine ics, 24 h ime was selec ed o he adso p ion iso he m o ensu e equilib uim s a e is achie ed. In ba ch se up, adso p ion iso he ms o Sc wi h BP-TCPSi and TCPSi pa icles we e pe o med wi h ini ial concen a ions o Sc co esponding o 0.1 – 2.5 mg/L a pH 1 and 0.1 – 4 mg/L a pH 3. In case o Dowex 50WX8, he concen a ions we e 2 – 45 mg/L a pH 1 and 2 – 65 mg/L a pH 3. Langmui equa ions we e i ed o he expe imen al iso he m da ase s (Figu e 4), and he pa ame e s om he i ings a e lis ed in Table 2. Figu e 4. Adso p ion iso he ms o Sc wi h BP-TCPSi pa icles and Dowex 50WX8 esin a pH 1 and pH 3. Table 2. Resul s o Langmui iso he m pa ame e s. Qmax is he maximum capaci y and KL is Langmui cons an . Sample Langmui Qmax (µmol/g) KL (L/mg) R2 BP-TCPSi pH 1 26 ± 1 84 ± 14 0.94 pH 3 51 ± 1 53 ± 8 0.95 Dowex 50WX8 pH 1 781 ± 14 2.7 ± 0.2 0.98 pH 3 868 ± 34 93 ± 20 0.86 Un unc ionalized TCPSi pa icles adso bed a negligible amoun o Sc a pH 1 (3.1 ± 1.0 µmol/g) and a pH 3 (5.1 ± 1.5 µmol/g) (Figu e S6). Since he e we e no ac i e me al binding si es in TCPSi, he adso p ion can be a ibu ed o elec os a ic in e ac ion o physiso p ion, and he expe imen al da a did no i o he Langmui model. In case o BP-TCPSi and Dowex 50WX8, he goodness o he Langmui i was gi en by he nonlinea eg ession coe icien R2 alues. The alues we e g ea e han 0.86 indica ing ha he adso p ion ollows he Langmui model in all cases. This means ha speci ic in e ac ion be ween he me al ion and adso p ion 8 si e exis s. The main ligands o he adso p ion si es a e phospho ic acid g oups in he BP- TCPSi pa icles and sul onic acid g oups in he Dowex 50WX8 esin. Maximum capaci y (Qmax) o BP-TCPSi a pH 1 was wo imes lowe han a pH 3. The iso he m esul s can be explained by he p o on exchange mechanism om he phosphona e g oups, whe e he i s dep o ona ion (pKa1 = 1) occu s a pH 1 and second (pKa2 = 2.5) a pH 3. The OH g oup connec ed o he geminal C-a om only dep o ona es in e y high pH alue (pH > 9) 22 and he e o e do no ha e any con ibu ion in he adso p ion in he s udied pH ange alike he 3 d and 4 h dep o ona ions. Ano he adso p ion mechanism o Sc ion is ela ed o he o ma ion o coo dina ion bond wi h P=O g oup by i ue o he lone pai o elec ons in he O-a om.21,23 The e o e, chela ion occu s by he syne gy o he p o on exchange mechanism alongside he o ma ion o coo dina e bond wi h P=O.23 In s oichiome ic e ms, he ob ained Qmax alue did no exceed he BP g a ed on he pa icles, 59 µmol/g, implying also ha he adso p ion was mainly chemiso p ion. Oxida ion s a e o Sc in aqueous solu ion is Sc (III). I can be hypo hesized ha because o a single dep o ona ion a pH 1 inducing only one anionic O-a om pe BP molecule (monoden a e ligand), mul iple BP molecules pa icipa ed in cap u e o a single Sc ca ion yielding a low Qmax alue a sa u a ion. On he con a y, a pH 3, biden a e BP ligands wi h wo dep o ona ed O-a oms yielded highe adso p ion. I should be no ed om Figu e 3 ha he Sc adso p ion wi h he BP-TCPSi a pH 3 did no sa u a e comple ely meaning ha he e a e possibly ano he binding mechanism beside he Langmui model. Isoelec ic poin o un unc ionalized TCPSi is pH 2.6.24 This means unconjuga ed ca bon su aces in BP-TCPSi a pH 3 enhanced he adso p ion ia elec os a ic in e ac ion as in he case wi h TCPSi pa icles whe e he adso p ion ollowed almos linea model. None heless, he adso p ion capaci y o BP-TCPSi was conside ably lowe han he comme cial Dowex 50WX8 esin by 30 old a pH 1 and 15 old a pH 3. Fo compa ison o a p e ious s udy13, Qmax o Sc a pH 3 wi h ba e mesopo ous silica ma e ials; silica gel, KIT-6 and SBA-15 we e 12, 22 and 25 µmol/g espec i ely despi e o excep ionally high su ace a eas (378, 850 and 934 m2/g) , po e olumes (0.9, 1.1 and 1.2 cm3/g) and po e diame e s (15, 7.7 and 7.6 nm).13 In addi ion, he e was i ually no Sc adso bed wi h KIT-6 a lowe pH (1.6 – 1.9) due o s ong elec os a ic epulsion be ween he me al ion and silica su aces.13 The esul s o p esen s udy he e o e emphasizes he signi icance o su ace modi ica ion wi h sui able me al chela ing moie ies o complemen me al adso p ion p ope ies o he mesopo ous ma e ials. 3.2.2 Flow- h ough se up Unlike ba ch ype, he cen i uga ion s ep was no equi ed in low- h ough se up. He e, he eed solu ion was con inuously lown h ough he adso ben wi h he low- a es and olumes as desc ibed abo e. This se up was employed o examine i) he selec i i y o BP-TCPSi and Dowex 50WX8 owa ds Sc and b) he eusabili y o BP-TCPSi up o 50 adso p ion/deso p ion cycles o Sc. 3.2.2.1 Scandium selec i i y 9 Selec i i y o BP-TCPSi and Dowex 50WX8 owa ds Sc was su eyed in an equimola mix u e o Sc+3, Al+3, Fe+3, Cu+2 and Zn+2 wi h ini ial amoun o each me al co esponding o 1:1 mola a io o he maximum capaci y o Sc. The e o e, wi h he BP-TCPSi, ini ial concen a ions o e e y me al we e adjus ed o 110 µmol/L (pH 1) and 220 µmol/L (pH 3). In case o he Dowex 50WX8 esin, he equimola concen a ion was 3100 µmol/L (pH 1) and 3300 µmol/L (pH 3). The esul s wi h Dowex 50WX8 esin a pH 3 was un eliable due o p ecipi a ion o Fe3+ and hus disca ded o a oid alse in e p e a ion. To p o ide dis inc compa ison o he selec i i y be ween he adso ben s and pH alues, a sepa a ion ac o (SF) was calcula ed using ollowing equa ion. 𝑆𝐹 =𝐶𝑑𝑒𝑠(𝑆𝑐) 𝐶𝑑𝑒𝑠(𝐴𝑙+𝐹𝑒+𝐶𝑢+𝑍𝑛) 𝐶0(𝑆𝑐) 𝐶0(𝐴𝑙+𝐹𝑒+𝐶𝑢+𝑍𝑛) ⁄ (3) The calcula ed SF alue quan i ied how e ec i ely Sc was pu i ied om he o iginal me al mix u e a e a comple e adso p ion/deso p ion cycle, which is a c ucial measu e o he adso ben ’s e icacy. The selec i i y esul s a e shown in Figu e 5. Figu e 5. Me al selec i i y esul s o BP-TCPSi and Dowex 50WX8 a pH 1 and pH 3. E o ba s ep esen SD (n=3). Sc selec i i y wi h BP-TCPSi was p e e able a pH 1 (SF = 13 ±1) han a pH 3 (SF = 8 ± 1). Compa ed o Dowex 50WX8 (SF = 4.3 ± 0.2), BP-TCPSi was 3- old supe io o selec i ely ex ac Sc when he adso p ion was conduc ed a pH 1. The sum o all adso bed me al amoun s in BP-TCPSi we e 26 ± 3 µmol/g (pH 1) and 55 ± 3 µmol/g (pH 3) and in Dowex 50WX8 was 726 ± 41 µmol/g (pH 1) co esponding o he Qmax alues lis ed in Table 2. This means ha he ac i e binding si es in he adso ben s we e ully occupied while unspeci ic adso p ion was p ohibi ed. Based on eqn (3), he SF alue is di ec ly p opo ional o he deso p ion e iciency. I should be no ed ha he deso p ion o Sc om he BP-TCPSi pa icles was no 100 %, which aba ed highe SF alues. As a gene ic ule, adso p ion is di ec ly p opo ional o ionic cha ge hus; di alen Cu2+ and Zn2+ had he leas adso p ion e iciencies and we e incompe en amongs he o he me als o selec i e adso p ion. Compe i i e adso p ion o Sc3+ wi h Al3+ and Fe3+ was expec ed, as hey 16 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0 2000 4000 6000 8000 10000 1.90 1.92 1.94 1.96 1.98 2.00 2.02 2.04 2.06 2.08 2.10 0 20 40 60 80 100 In ensi y (K) KeV Phospho us O C In ensi y (K) KeV TCPSi BP-TCPSi Cycled BP-TCPSi Si Figu e S4. EDS spec a o he samples; TCPSi, BP-TCPSi and cycled BP-TCPSi a e 50 adso p ion/deso p ion s ages. A small peak o Phospho ous (P) a KeV 2.01 was obse ed in BP unc ionalized pa icles. Figu e S5. Adso p ion kine ics o Sc wi h BP-TCPSi a pH 1 and pH 3. E o ba s ep esen SD (n=3). Expe imen al condi ions: 10 mg BP-TCPSi, V = 10 mL, C0 = 1.5 mg/L (pH 1) and 2.5 mg/L (pH 3). 0 10 20 30 40 50 0 1 2 3 4 con ac ime (h) 0 10 20 30 40 50 0 4 8 12 16 20 24 28 32 36 40 44 48 µmol/g con ac ime (h) Sc, pH1 Sc, pH3 17             S+ S+ 4HPROJ &HPJO  )LJXUH6$GVRUSWLRQLVRWKHUPVRI6FZLWK7&36LSDUWLFOHVDWS+DQGS+  )LJXUH6(IIHFWRI%37&36LPDVVEHGYROXPHRQ6FDGVRUSWLRQLQIORZWKURXJKVHWXS $$GVRUSWLRQPJ/6FDWS+$GVYROZHUHUHVSHFWLYHO DQGPOFRUUHVSRQGLQJ WR  î 4PD[ RI %37&36L )ORZUDWH  POPLQ (UURU EDUV UHSUHVHQW 6' Q  7KH ILOWUDWLRQV ZHUH UHSHDWDEOHVXLWDEOH HYHQ ZLWK  PJ DGVRUEHQW EHG ZLWK 6' EHORZ  LQ EHWZHHQWKHUHSOLFDWHV7KHDGVRUSWLRQDPRXQWVFRUUHVSRQGHGWREDWFKW SHDGVRUSWLRQNLQHWLFV UHVXOWV% PJ PJ PJ          K K PROJ PDVVRI%336L )LOWUDWLRQWLPH K 0D[LPXPFDSDFLW       DGVRUSWLRQ   $ % 18 0.01 ml/min 0.05 ml/min 0.25 ml/min 1.25 ml/min 0 10 20 30 40 50 (8 mins) (40 mins) (3 h) (16 h) (4 mins) (20 mins) (1.5 h) Qmax (pH 1) µmol/g pH 3 pH 1 Qmax (pH 3) ( il a ion ime) (8 h) Figu e S8. E ec o low- a e on Sc adso p ion wi h BP-PSi. Expe imen al condi ions; 5 mg/L Sc, adso p ion olumes 4.68 ml (pH 1) and 9.53 ml (pH 3). A bo h pH condi ions, e ec o low- a e was signi ican (p alue < α; 0.5). The F alues we e 205 (pH 1) and 648 (pH 3) a F c i ical alue o 4; e ec o low- a e was 3 old mo e signi ican a pH 3 han a pH 1. These esul s a e in ag eemen wi h he ba ch ype adso p ion kine ics esul s whe e a e o Sc adso p ion had dispa i y be ween he pH alues. 0 1 2 3 4 5 6 7 8 9 10 11 0 10 20 30 40 50 60 70 80 90 100 % Deso p ion Deso p ion Volume (ml) 0.05 ml/min 0.25 ml/min 1.25 ml/min Figu e S9. E ec o low a e on Sc deso p ion. Expe imen al pa ame e s: 20 mg BP-TCPSi, adso p ion; 10 ml o 5 mg/L Sc a pH 1 a 0.5 ml/min (20 minu es), deso p ion; 10 ml o 1 M HNO3. Wi h all es ed low- a es, o e 50% o he deso bed Sc was collec ed wi hin 1 ml o acid lown h ough he BP-TCPSi. As he deso p ion was ins an aneous, i is possible o en ich Sc ex ac ion. The e ec o low- a e in deso p ion was no signi ican a α=0.05 wi h p- alue 0.13 > α and F alue (2.5) < F c i ical alue (4). 19 Figu e S10. Dis ibu ion coe icien (Kd) alues calcula ed om he selec i i y esul s. The Kd alue is calcula ed as (C0-Ce)/Ce * (V/m). 150 200 250 300 350 400 450 500 550 600 97.0 97.5 98.0 98.5 99.0 99.5 100.0 TCPSi BP-TCPSi Cycled BP-TCPSi Mass (%) Temp (°C) Figu e S11. TGA cu es o TCPSi, BP-TCPSi and cycled BP-TCPSi (50 adso p ion/deso p ion es s). 0 200 400 600 800 1000 1200 Sc Al Fe Cu Zn Kd (mL/g) BP-TCPsi, pH 1 BP-TCPsi, pH 3 Dowex, pH 1 20  )LJXUH66(0LPDJHVRI7&36LXSSHUWKUHHDQGF FOHG%37&36LEHORZWKUHH                   21 pH1 pH3 Figu e S13. Resul s o iso he m i a ion calo ime ic (ITC) analysis o Sc adso p ion wi h BP- TCPSi a pH 1 and pH 3. The binding eac ion was exo he mic a pH 1 bu endo he mic a pH 3. Th ee indi idual measu emen s was done a each pH alue. The he modynamic equilib ium cons an , K alues we e g ea e a pH 1 han a pH 3 (excep he 3 d measu emen ). The e oneous esul s is due o he unce ain y in BP concen a ion as he pa icles we e g ound in o ≤10 µm ac ion in o de o success ully injec he pa icles in o he de ice (VP-ITC Mal e n, Mic obial Inc.). The measu emen p o ocol is b ie ly desc ibed below. The pa icles we e e-dispe sed in pH wa e (pH 1 o pH 3) and degassed p io o he measu emen s. The BP-TCPSi suspension; 0.9 – 1.14 mM a pH1 and 0.57 – 1.0 mM a pH3 espec i ely we e placed in o he ITC cell and i a ed wi h 4.0 mM Sc ha was placed o he sy inge. The hea e ol ed o consumed in each i a ion o 10 µl injec ions we e measu ed a 25 °C unde cons an 440 pm s i ing. Re e ence measu emen s bu e - o-bu e , bu e - o- pa icles and scandium- o-bu e we e sub ac ed om he ac ual binding measu emen .