Supporting Information for Historical pigment exhibiting ammonia capture beyond standard adsorbents with adsorption sites of two kinds

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1 Supporting Information for Historical pigment exhibiting ammonia capture beyond standard adsorbents with adsorption sites of two kinds Akira Takahashi 1,2, Hisashi Tanaka 1, Durga Parajuli 1, Tohru Nakamura 1, Kimitaka Minami 1, Yutaka Sugiyama 1, Yukiya Hakuta 1, Shin-ichi Ohkoshi 2, and Tohru Kawamoto 1* 1 Nanomaterials Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Higashi Tsukuba, , Japan 2 School of Science, The University of Tokyo Hongo, Bunkyo-ku, Tokyo , Japan SI. 1. METHOD AND SUPPLEMENTARY RESULTS SI 1.1 SYNTHESIS Powders of Prussian blue (PB) and copper hexacyanoferrate (CuHCF) were synthesized using a micromixer by mixing two aqueous solutions of raw materials 32. A special grade of the raw materials was obtained from Wako Pure Chemical Industries Ltd. The flow speeds of raw material solutions were set as 50 ml min -1. The PB was synthesized by mixing 0.16 mol L -1 of iron(iii) nitrate and 0.12 mol L -1 of potassium ferrocyanide. The micromixer hole diameter was 250 m. The powder was obtained by aqueous rinsing by centrifugation six times, followed by drying at 60 C in vacuum. The CuHCF was synthesized by mixing 0.5 mol L -1 of copper sulfate and 0.1 mol L -1 of potassium ferrocyanide. The micromixer hole diameter was 150 m. The powder was obtained by aqueous washing with a cross-flow filter, followed by drying at 60 C in vacuum. Cobalt hexacyanocobalate (CoHCC) was synthesized by mixing 0.06 mol L -1 of cobalt(ii) chloride and 0.04 mol L -1 of potassium hexacyanocobaltate(iii) in a beaker with magnetic stirring for one night. The powder was obtained through aqueous rinsing by centrifugation six times, followed by drying at 60 C in vacuum. SI 1.2 THIN FILM FABRICATION Thin films of Prussian blue, CuHCF, and CoHCC were fabricated by preparation of the dispersion liquid and subsequent coating. The dispersion liquid of Prussian blue was prepared as follows: The suspended liquid of the Prussian blue was prepared by mixing of the 0.16 mol L -1 aqueous solution of iron(iii) nitrate and 0.12 mol L -1 aqueous solution of potassium ferrocyanide. The dispersion liquid was obtained by aqueous rinsing six times with centrifugation and sufficient agitation using a homogenizer (T.K. Robomix; Primix Corp.). The Prussian blue thin film was obtained by spin coating on ITO/glass substrate five times at 1500 rpm (rotation per minute) for 20 s. The CuHCF thin film was prepared using a method similar to that used for Prussian blue. The dispersion liquid was prepared as follows: 1 g of CuHCF powder was put into 50 ml of ultrapure water. Then it was mixed with a homogenizer at 16,000 rpm for 3 min. The mixture solution was separated to a suspended solution. Precipitation was done with a centrifuge at 4,400 rpm for 3 min. The suspended solution was concentrated three times using an evaporator. The CuHCF thin film was obtained by spin coating 30 times on ITO/glass at 1,000 rpm for 10 s and 1,500 rpm for 10 s. The CoHCC thin film was prepared using a similar method to that used for the others. The dispersion liquid was prepared as follows: 1 g of CoHCC powder was put into 50 ml of ultrapure water and mixed with homogenizer at 16,000 rpm for 5 min. The mixture solution was separated to a suspended solution and precipitation with centrifuge with 500 rcf for 3 min. The suspended solution was concentrated three times using an evaporator. The CoHCC thin film was obtained by spin coating 10 times on ITO/glass at 2,000 rpm for 10 s and 2,500 rpm for 10 s. S1

2 SI 1.3 CHARACTERIZATION Chemical compositions of PB, CuHCF, and CoHCC were determined using a microwave plasma atomic emission spectrometer (MP-AES, Agilent 4100; Agilent Technologies Japan Ltd.) using standard addition technique with prior decomposition by a microwave sample preparation system (Multiwave3000; PerkinElmer Corp.), CHN-analysis (EA-1110; CE Instrument Ltd.), and Thermogravimetry- Differential Thermal Analysis (TG-DTA, Thermo plus evo II; Rigaku Corp.). MP-AES was used for Fe, Cu, and K. For C and N, CHN analysis was used. TG-DTA was used to the hydration numbers. The chemical composition was evaluated as K0.23Fe[Fe(CN)6] H2O for Prussian blue, Co[Co(CN)6] H2O for CoHCC, and Cu[Fe(CN)6] H2O, respectively. Note that H2O may partially transform into OH by releasing H + in order to maintain the charge balance. The adsorption capacity and distribution coefficient, Kd, was calculated with composition of the dehydration form. The hydration numbers were omitted from the chemical composition described in the main text. The dehydration processes were completed before the adsorption isotherms were obtained. SI 1.4. CRYSTAL STRUCTURE DURING ADSORPTION PROCESSES Crystal structures were investigated using an X-ray diffractometer (XRD, D2 Phaser; Bruker Corp.) with Cu K radiation (λ=0.154 nm) at 30 kv and 10 ma. Sample images were obtained using a field emission scanning electron microscope (FE-SEM, S-4800; Hitachi High Technologies Corp.) as shown in Figure SI 1. All measurements were taken at room temperature. The initial structure before adsorption was evaluated in atmosphere. For investigation of the crystal structure after ammonia adsorption in vacuum, we used the following process. For pre-treatment, 10 mg of the sample was kept in vacuum for 1 hr. Then the sample was exposed with 100% of NH3 gas for 18 hr. The XRD pattern of the exposed sample was measured after confinement of the sample into a sealed case with a polyimide cover in Ar gas. The sample exposed with 200 ppmv of NH3 was evaluated similarly. SI 1.5 AMMONIA CONCENTRATION IN ATMOSPHERE As described in this paper, we used ammonia-contaminated air samples of two kinds: natural air with trace NH3 contamination, and intentionally mixed air. The ammonia concentration in the air samples was evaluated by passage into two impinger samplers in series filled with 20 ml of 5 gl -1 boric acid with subsequent evaluation of the NH4 + anion in the impingers using ion chromatography (IC, 833 basic plus; Metrohm AG). SI 1.6 ADSORPTION ISOTHERM The ammonia gas adsorption equilibrium isotherms for powders of Prussian blue, CuHCF, and CoHCC at 25 C were evaluated using a gas-adsorption system (BELSORP-max; Microtrac BEL Inc.) with 5Ngrade ammonia gas. The adsorption equilibrium was determined by criteria of a pressure difference below 0.3% for 10 min. The maximum time for one point and total time for equilibrium for each adsorption isotherm were PB; 6.9 and 56 hr, CuHCF; 30 and 105 hr, CoHCC; 2.8 and 12.5 hr. To remove the adsorbed gases including hydration waters, the samples were heated before the adsorption process at 100 C for PB, 60 C for CuHCF, and 150 C for CoHCC for 24 hr in vacuum using rotary pump. Especially for CoHCC, the cycle stability was investigated. The isotherm was obtained repeatedly four times with the desorption process of setting in vacuum using a rotary pump at 150 C for 24 hr at each interval. During the cycles, another condition was tested only once, in vacuum using rotary pump at room temperature for 1 hr, where complete desorption was not observed. The capacity of the absorbent, Cmax, was evaluated using the Langmuir isotherm model as c =cmaxkp/(1+pk), where c, K, and p respectively represent the ammonia concentration in adsorbent, the S2

3 equilibrium constant, and pressure. The Langmuir isotherm model includes the assumption that that one molecule was adsorbed at one adsorption site. SI 1.7 TIME REQUIRED FOR EQUILIBRIUM The time required for reaching equilibrium state from 0 bar to a densely adsorbed state, teq(p), was investigated for CoHCC, ion exchange resin (IE), and zeolite. We purchased amberlyst:15 hydrogen form, Sigma-Aldrich for IE, and zeolite 13X (Molecular sieve Type 13X; Alfa Aesar) for zeolite. The partial pressure profile after NH3 injection at 25 C for each adsorbent was evaluated with a gas-adsorption system (BELSORP-max; Microtrac BEL Inc.) using 5N-grade ammonia gas. The mass of the adsorbent, mads, is set to 5 mg. For the pre-treatment, adsorbents were heated before the adsorption process at 100 C for IE, 150 C for CoHCC, and 300 C for zeolite in vacuum for 24 hr. After pre-treatment, NH3 gas was injected with the partial pressure of approximately 0.7 bar. With a standard criterion, a pressure difference < 0.3% in 10 min, teq(p) for each adsorbent was determined. For CoHCC, IE, and zeolite, teq(0.7 bar) were, respectively, 18, 14.5, and 13 min. The adsorption rate t(p), defined by c(p) mads / teq(p), was estimated 5.8, 2.3, and 2.8 mol/min for CoHCC, IE, and zeolite. SI 1.8 ADSORPTION ENTHALPY Rough estimation of the ammonia adsorption enthalpy of CoHCC was done using two temperatures (25 C and 40 C) of adsorption isotherm with Clausius Clapeyron equation (Atkins, P. W. "Physical Chemistry. Sixth Edition" (1998)) as. The Habs, R, T, and P respectively indicate adsorption enthalpy, gas constant, temperature, and pressure, The subscripts indicate two temperatures and pressures in the same amount of NH3 adsorption. The adsorption enthalpy was estimated using fitting data with Langmuir Frendrich adsorption isotherm. The estimated adsorption enthalpy is shown in Figure SI5. Note that the result is obtained from the small number of the partial pressures in the isotherm. For high-precision discussion, detailed evaluation for more partial pressures. SI 1.9 SPECIFIC SURFACE AREA The specific surface areas of PB, CoHCC, and CuHCF were estimated using BET equation with N2 adsorption isotherm at liquid N2 temperature (77 K). The samples were pre-treated with the same condition of the ammonia adsorption isotherm. The specific surface area was estimated with the following BET equation. In that equation, p, p0, C, and Vm respectively represent pressure, saturated vapor pressure, energy constant, and single molecular adsorption area. The obtained N2 adsorption isotherms are presented in Figure SI6. The plot of the surface area for each sample is shown in Figure SI 7. SI 1.10 AMMONIA CONCENTRATION IN PRUSSIAN BLUE The concentration of ammonia in the Prussian blue was estimated from the peak height observed using Fourier transform infrared spectroscopy (FTIR). Using NH4 + aqueous solution, we prepared the calibration curve of A(1410 cm -1 )/ A(2060 cm -1 ) vs. (NH4 + ), where A(1410 cm -1 ), A(2060 cm -1 ), and (NH4 + ) respectively represent the IR adsorption peak height at 1410 cm -1 corresponding to NH4 +, and that at 2060 cm -1 corresponding to CN in PB framework, and the NH4 + concentration evaluated from the ad- S3

4 sorption amount from the aqueous solution. The method of preparing the calibration curve was the following: 40 mg of PB was put into the 40 ml of aqueous solution containing mmol L -1 of ammonium chloride and was shaken with 600 rpm for 100 min at 25 C using a shaking incubator (SI- 300C; AS One Corp.). After separation using 0.45 m mesh of membrane filter, A(1410 cm -1 ) and A(2060 cm -1 ) were evaluated using FTIR measurements with a diamond ATR unit (Nicolet is5; Thermo Fisher Scientific Inc.). In addition, (NH4 + ), was evaluated from the residual concentration of NH4 + in solution using ion chromatography (IC, 833 basic plus; Metrohm AG). The obtained calibration curve between A(1410 cm -1 ) and (NH4 + ) is shown in Figure SI8. SI 1.11 PSEUDO-FIRST ORDER ADSORPTION FORMALISM For analysis of the time variation of the ammonia concentration in Prussian blue left in our laboratory, we used pseudo-first order adsorption formalism: s(nhx) = se(nhx) (1 exp (-Kt)). Therein, s(nhx), se(nhx), K, and t respectively represent the ammonia concentration in solid (Prussian blue), that in the equilibrium state, adsorption rate constant, and the time for leaving Prussian blue in ambient air. SI CYCLE TEST The cycle test of sequential adsorption/desorption was examined as follows: For the adsorption process, a thin film of PB, CuHCF, or CoHCC was set on a flask filled with 200 ppmv of NH3 in air for 5 min. For desorption, the thin film was immersed into 0.05 mmol L -1 aqueous solution of sulfuric acid for 30 min at most. The NH4 + concentration in the film was evaluated by the ratio of IR adsorption peak height of A(1410 cm -1 ) to A(2060 cm -1 ), where the former and latter respectively correspond to NH4 + and CN. SI COLUMN TEST The column test for trace ammonia decontamination from air was examined as follows: The air sample with approx. 1 ppmv of NH3 was prepared by mixing the dry air and 5N-grade ammonia gas. The air sample was passed into the column filled with Prussian blue, CuHCF, or CoHCC. The column diameter was approx. 5 mm. The adsorbent mass was set to 10 mg. The flow rate and the contact time were, respectively, 500 ml/min, and approx. 2 ms. The adsorption rate was evaluated for the ammonia concentration in the sample air before and after passing the column by IC. We also conducted a column test with atmosphere for the evaluation of the adsorption rate with the comparison with standard adsorbents. The air in our laboratory, with 7.2 ± 1.4 ppbv of ammonia, was passed through the column containing 5 mg of PB, zeolite, and IE with flow speed 400 ml min -1, where the adsorption rate was evaluated with Kd, the change of the ratio of NH3 concentration in adsorbent to that in air. SI 1.14 COLUMN CONCENTRATION IN AIR WITH COMPETITORS We compare the previous ammonia adsorbent zeolite (hereinafter, zeolite, zeolite 13X; Molecular sieve Type 13X; Alfa Aesar) and ion-exchange resin (hereinafter, IE, amberlyst: 15 hydrogen form; Sigma- Aldrich Corp.) with trace ammonia adsorption property. The column measurement apparatus is the same as that for Ammonia Concentration in Air. The time variation of Kd is shown in Figure SI3. S4

5 adsorbed NH3 (mmol/g) SI 2. SUPPLEMENTARY FIGURES (a) (b) 1 m 100 nm (c) (d) 1 m 100 nm (e) (f) 1 m 100 nm Figure SI 1. SEM images of powder of Prussian blue, CuHCF and CoHCC: (a) typical powder particle of Prussian blue, (b) primary particles of Prussian blue, (c) a typical powder particle of CuHCF, (d) primary particles of CuHCF, (e) typical powder particles of CoHCC, and (f) primary particles of CoHCC CoHCC CuHCF 2 PB BPP E+00 5.E-04 1.E-03 pressure (bar) Figure SI 2. Ammonia adsorption isotherm in lower pressure of CoHCC, CuHCF, PB, and BPP-5.

6 S5 Figure SI3. Kd, the ratio of NH3 concentration in adsorbent to that in air. Details of the evaluation method are presented in SI S6

7 ammonia density (mol/l) SI CoHCF COF-10 13X zeolite (Lancaster) alumina (LaRoche 1597) Figure SI4 Comparison of the ammonia capacity per unit volume among ammonia adsorbents that maintain their crystal structure after adsorption processes. S7

8 Figure SI5. ammonia adsorption isotherm at 25 C and 40 C (upper). Estimated ammonia adsorption energy by Clausius-Clapeyron equation(lower). Note that the result is obtained from the small number of the partial pressures in the isotherm. For high-precision discussion, detailed evaluation with more partial pressures are required. S8

9 adsorbed N2 (ml(stp)/g) adsorbed N2 (ml(stp)/g) adsorbed N2 (ml(stp)/g) CoHCC CuHCF absorption desorption absorption desorption PB absorption desorption pressure (bar) Figure SI 6 N2 adsorption isotherm at 77 K. S9

10 p/(p 0 -p)/v m p/(p 0 -p)/v m p/(p 0 -p)/v m 6.0E E E E E E-04 y = 5.152E-03x E-07 R² = 9.999E E E-04 y = 7.955E-03x E E-04 R² = 1.000E E E E E E E E E E-04 y = 1.553E-02x E-06 R² = 9.997E E p/p Figure SI7 BET plots for the evaluation of the surface areas of Prussian blue analogues. The estimated BET surface area, 280, 547 and 848 m 2 /g, respectively, for PB, CuHCF, and CoHCC. S10

11 Peak ratio A(1410cm -1 )/A(2060 cm -1 ) y = x R² = ammonia uptake (mmol/g) Figure SI8. Calibration line for the relation between the amount of ammonia uptake by Prussian blue and the peak height ratio, A(1410 cm -1 )/ A(2060 cm -1 ), where the numerator and denominator respectively correspond to NH4 + and CN. The calibration line does not cross the origin because Prussian blue had adsorbed a small amount of ammonia during its synthesis process. Figure SI9. Concentration decrease by passage through a column filled with powder of Prussian blue or its analogue. S11

12 Figure SI 10. Cyclic processes of ammonia adsorption and desorption of CoHCC and PB: Top, FTIR absorption spectra in each process of adsorption and desorption; Middle, the change of the peak height corresponding to CN (2060 cm -1 ) and NH4 + (1410 cm -1 ); Bottom, the ratio of the peak height of CN to NH4 +. S12