In Situ IR Spectral Observation of NH4H2PO4 Crystallization

Article pubs.acs.org/JPCC

In Situ IR Spectral Observation of NH4H2PO4 Crystallization: Structural Identification of Nucleation and Crystal Growth Congting Sun and Dongfeng Xue* State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China ABSTRACT: In situ ATR-IR spectroscopy was used to identify the structural variations of NH4+ and H2PO4− during NH4H2PO4 (ADP) crystallization in aqueous solution with different pH values. For supersaturated ADP solution, the time needed for the appearance of ADP solids in IR measurement will be prolonged with increasing or decreasing solution pH value. When ADP crystallizes from the aqueous solution with pH = 0.98−5.00, H2PO4− groups with a larger hydrated ionic radius initially form a framework structure, and then NH4+ groups with a relatively smaller hydrated ionic radius insert into the H2PO4− framework. IR bands of the H-bond at 2387 cm−1 and a combination of PO4 vibration within the lattice at 1260 cm−1 indicated the formation of H2PO4− frameworks with ADP lattice structural characteristics via forming hydrogen bonding. The hydrogen bonding between NH4+ and H2PO4− can be indicated by the splitting of v4(NH4) at 1400 cm−1. IR spectra indicated that when the pH value increases up to 6.03, (NH4)2HPO4 instead of NH4H2PO4 was crystallized from the aqueous solution. Such an in situ recording strategy is of particular value in identifying the structural characteristics at both nucleation and crystal growth stages during the crystallization process.

1. INTRODUCTION The drivers in inertial confinement fusion (ICF) facilities are the most enormous and expensive laser system.1 In recent years, the design and growth of harmonic generation materials for laser system have been widely studied. In current ICF facilities, KDP and DKDP crystals respectively act as the second harmonic generation and third harmonic generation materials for Nd:glass laser. One trend in ICF is to develop driving lasers with shorter wavelengths; therefore, the fourth harmonic generation materials attract more attention.2 Recent studies show that NH4H2PO4 (ADP) crystals will be a competitive candidate as the fourth harmonic generation when utilizing a high-energy, high-efficiency UV laser at wavelengths shorter than 351 nm.3 Crystallization is an important technological process in the fabrication of functional crystal materials.4 A comprehensive understanding of the nucleation and crystal growth is critical to the growth of high-quality ADP crystals with rapid growth rates. During the crystallization process, the structural variations initially originate from the changes in chemical bonding between constituents, which can direct both nucleation and growth of crystal materials.5,6 In particular, for ADP crystals, which are grown from an aqueous solution growth system, hydrogen bonding is an important bonding behavior during the crystallization.7,8 Hydrogen bonding within ADP crystal plays a critical role in its physical and chemistry properties.9,10 Structurally, NH4+ and H2PO4− groups in ADP crystal interact with each other via N− H···O and O−H···O hydrogen bonding.7 On the basis of chemical bonding theory of single crystal growth, the thermodynamic crystal morphologies can be calculated, which exhibits a tetragonal prism ended with two pyramids bonded by {100} and {101} surfaces.11,12 In the growth of ADP crystals, © 2013 American Chemical Society

ethanol molecules have been demonstrated to affect the morphology by interacting with hydrogen bonds at crystal surfaces.13 Due to anisotropic ADP crystal structure, the interactions between {100} and {101} surfaces with hydroxyl of ethanol molecules are distinct, which result in anisotropic chemical bonding conditions.14 In comparison with pyramidal planes, the growth rate of prismatic faces is slower and more sensitive to the additives and impurities for ADP crystals. When a small amount of ethanol is added into the ADP solution, the ethanol molecules prefer to attract H−O bonds of the ADP crystal along the ⟨100⟩ direction, leading to the preferential growth along the c-axis direction. When the supersaturation is low, the advance of growth steps on the prismatic face can be blocked by ethanol, and the crystal morphology is changed from the tetragonal prism to a tapered shape.15 On the basis of growth mechanism exploration of KDP-family crystals, a novel rapid crystal-growth system with high compatibility and expansibility has been constructed by employing the highspeed acquisition card and LabVIEW software package, which can provide an excellent crystallization environment for the rapid growth of high quality KDP crystals according to the designed cooling curve.16 Structural dynamics of both NH4+ and H2PO4− for ADP at different periods during the crystallization in aqueous solution was studied by using in situ attenuated total reflectance-infrared (ATR-IR) spectroscopy,17 which offered good potential for the in situ measurement of the in aqueous solution composition.18 With the transition of ADP solution from unsaturated to Received: August 8, 2013 Revised: August 20, 2013 Published: August 20, 2013 19146

dx.doi.org/10.1021/jp407947s | J. Phys. Chem. C 2013, 117, 19146−19153

The Journal of Physical Chemistry C

Article

Table 1. Results Obtained in This Work and Comparison with Previous Studies, the Observed IR Band (cm−1), and Band Assignments for ADP ADP (this work) frequency (cm−1) 3230, 3050, 2860

2387

frequency (cm−1) 3132

1640 1448, 1400 1260

2387 1706 1642 1409 1292

1134, 1068 947, 874

1098 910

H2PO4− solid

NH4+

ADP crystal 23

frequency (cm−1)

assignment23 O−H stretching, P−O−H stretching, N−H vibrations of ammonium

band due to hydrogen bond O−H bending vibration O−H bending water bending vibration of ammonium combination of the asymmetric stretching vibration of PO4 with lattice P−O−H vibrations P−O−H vibrations

saturated, supersaturated, and crystalline states, H2PO4− ions transform from monomers to dimers, then to polymers in aqueous solution, and finally to crystallized ionic status in ADP crystal. Once hydrated NH4+ ions bind to (H2PO4−)n frames, and ADP crystals begin to separate out from aqueous solution. The solution compositions with successively changed pH values were also recorded by in situ ATR-IR. With increasing pH value up to 6.64, HPO42− and (H2PO4−)n (n ≤ 2) coexist in solution, whereas with decreasing pH value down to 1.52, H3PO4 and (H2PO4−)n (n ≤ 2) coexist in solution. Our previous studies demonstrated that pH value was an important growth parameter in the growth of ADP crystals.11−13 For ADP crystallization in an aqueous growth system, the identification of the influence of pH value on the structural changes of ADP can thus provide more fundamental data for the practical growth. In this work, we applied in situ ATR-IR spectra to identify structural changes at nucleation and crystal growth stages during ADP crystallization from aqueous solution with different pH values. The hydrogen bonding between H2PO4− anions, H2PO4− and NH4+ can be indicated by IR bands at 2387, 1260, and 1400 cm−1, respectively. During the crystallization of ADP crystals (pH = 0.98−5.00), H2PO4− groups with a larger hydrated ionic radius initially form a framework structure, and then NH4+ with a relatively smaller hydrated ionic radius, inserts into the framework. When the pH value increases up to 6.03, (NH4)2HPO4 instead of NH4H2PO4 was crystallized from aqueous solution. For supersaturated NH4H2PO4 solution, both an increase and a decrease of pH value can result in the prolonged time that ADP separated from the aqueous solution. The present IR spectral characterization can provide an in situ observation strategy to studying structural dynamics during the ADP crystallization process.

23

3240, 3100, 3030 2900 2800 1720 1448, 1398

assignment23

frequency (cm−1)

25

H2PO4−(H2O) frequency25 (cm−1)

assignment25

v3(NH4)

3547

3767

vsOH(PO)4

v1(NH4) v2 + v4 v2(NH4) v4(NH4)

3523 3462

3767 3648, 3623

vaOH(PO)4 vOH

1672 1247 1169 1050

1814 1300 1104 1072

δHOH vaPO2 vaPO2 δPOH

969 844

1059 824

δPOH vaPOH

was dropped onto the diamond wafer, forming the detectable liquid film. The spectra of all samples were displayed in the form of transmittance spectra as the function of wavenumber. ADP supersaturated solution was made at room temperature (26 °C). At room temperature, 1 mL of H2O can dissolve ∼0.40 g ADP powder. A total of 1.32 g ADP powder was dissolved in 3 mL of H2O and then heated to an unsaturated state to prepare transparent ADP solution. Then, the asprepared aqueous solution was cooled to room temperature to obtain the supersaturated ADP solution. NH3·H2O (25%) and H 3PO 4 (85%) were used to adjust the pH value of supersaturated ADP aqueous solution, and the pH values of the supersaturated ADP solution were 0.98 (3 mL ADP + 0.72 mL H3PO4), 1.92 (3 mL ADP + 0.27 mL H3PO4), 2.90 (3 mL ADP + 0.06 mL H3PO4), 4.07 (3 mL ADP + 0.06 mL NH3· H2O), 5.00 (3 mL ADP + 0.72 mL NH3·H2O), and 6.03 (3 mL ADP + 1.23 mL NH3·H2O). Successive IR spectra of ADP saturated solution can be obtained with increasing time, and the time interval was selected as 40 s. In order to detect the effect of pH value on the structural dynamics of NH4+ and H2PO4− groups in supersaturated ADP solution, measurements were carried out after ADP solution was dropped on the diamond wafer.

3. RESULTS AND DISCUSSION During the crystallization of the ADP crystal from aqueous solution, free hydrated H2PO4− and NH4+ ions will transform into crystallized states. In ADP aqueous solution, both phosphate groups H2PO4− and ammonium ions NH4+ can form hydrated ions, (H2PO4−)H2O and (NH4+)H2O, via hydrogen bonding with H 2O. In ADP crystal, H2 PO 4 − phosphate groups are connected with each other by P−O··· H−O−P and P−O···H−N−H···O−P hydrogen bonding. P− O···H−N−H···O−P hydrogen bonding directs the connection between NH4+ and H2PO4− to form (NH4)O8 octahedral groups, in which NH4+ is located in the crystallographic lattice. Therefore, the hydrogen atoms in ADP can form not only O− H···O bonds, but also N−H···O bonds.7 During the ADP crystallization process, the hydrogen bonds between NH4+ and H2PO4− and H2O are broken, and NH4+ and H2PO4− connect with each other via forming O−H···O and N−H···O hydrogen bonding with characteristics in the ADP crystal. For ADP aqueous solution with pH = 0.98−6.03, there is an infrared vibration band in the vicinity of 1448 cm−1, which can

2. EXPERIMENTAL SECTION The spectral studies of solution specimens were carried out at room temperature by ATR-IR technique with ATR cell (Thermo Nexus 6700). Internal reflection element (IRE) is a diamond wafer. Thermo-Nicolet-Nexus FT−IR spectrometer was utilized to record the IR spectra of ADP samples in different periods during the crystallization. The absorption measurements of all ADP solutions were conducted using a Nicolet 20DXB FT−IR spectrometer in the spectral range of 4000−600 cm−1. In a particular IR measurement, ADP solution 19147



Article

be assigned to the 3-fold degenerated bending vibration absorption peak for NH4+ ions, indicating that NH4+ ions exist as free hydrated ions, which are just surrounded by water molecules (Table 1, Figures 1−6). Moreover, infrared vibration

Figure 2. Time-dependent IR spectra of ADP from solution to crystal in ADP supersaturated solution with pH = 1.92. H3PO4 was added into ADP solution to adjust pH value. Time interval between two adjacent IR spectra is selected as 40 s. Figure 1. Time-dependent IR spectra of ADP from solution to crystal in ADP supersaturated solution with pH = 0.98. H3PO4 was added into the ADP solution to adjust pH value. Time interval between two adjacent IR spectra is selected as 40 s.

The increased intensity of the IR bands indicates increased concentrations of NH4+ and H2PO4− groups. Moreover, the shift of wavenumbers of NH4+ and H2PO4− IR vibration modes demonstrates the variations of the configuration of free (NH4+)H2O and (H2PO4−)H2O ions. This can be attributed to the broken N−H···O hydrogen bonding between NH4+ and H2O, as well as O−H···O hydrogen bonding between H2PO4− and H2O when ADP solution achieves supersaturated state. In ADP crystal, each ammonium hydrogen atom can form bifurcated hydrogen bonds with two O atoms, one nearest neighbor O atom and one next-nearest neighbor O atom.7 This configuration results in the splitting of v4(NH4) at 1450 cm−1 into two bands at 1450 and 1400 cm−1.21 Consequently, the splitting of the v4(NH4) bending mode can be used to identify the transformation from free NH4+ ions to crystallized NH4+,

bands at 1134, 1068, 947, and 874 cm−1 are assigned to the stretching vibration modes of H2PO4−, that is, v1(PO4) and v3(PO4).19,20 In the present work, v2(PO4) and v4(PO4) bands of H2PO4− do not appear because their IR band regions are at 310−540 cm−1, which are beyond the measurement region of the ATR-IR spectrum. Before the crystal separated from the detectable liquid film, the intensity of the NH4+ bending vibration band v4(NH4) and H2PO4− stretching vibration bands increase and the position of the IR bands shifts toward low wavenumber with increasing measurement time (Figures 1−6). 19148



Article

Figure 3. Time-dependent IR spectra of ADP from solution to crystal in ADP supersaturated solution with pH = 2.90. H3PO4 was added into ADP solution to adjust pH value. Time interval between two adjacent IR spectra is selected as 40 s. Figure 4. Time-dependent IR spectra of ADP from solution to crystal in ADP supersaturated solution with pH = 4.07. NH3·H2O was added into ADP solution to adjust pH value. Time interval between two adjacent IR spectra is selected as 40 s.

which is bonded with H2PO4− via N−H···O−P in ADP crystal. For H2PO4− in ADP crystal, broad IR bands at 833 and 1072 cm−1 were assigned to symmetric stretching vibration modes of H2PO4−, and the IR band at 1260 cm−1 was assigned to a combination of the asymmetric stretching vibration of PO4 with lattice (Table 1). In the nucleation stage of ADP, the appearance of the IR band at 1260 cm−1 can act as the indicator of the formation of the (H2PO4−)n structural frame in the ADP crystal. Moreover, the broad lines at 2387 cm−1 can be assigned to B bands of OH stretching vibrations of the hydrogen bonds in the ADP.22,23 During the crystallization of the ADP crystal from aqueous solution with pH = 0.98−5.00, the appearance of a combination of the asymmetric stretching vibration of PO4 at 1244 cm−1 implies that (H2PO4−)n is formed by P−O···H−O−P hydrogen bonding between H2PO4− groups.21 Then, the IR band at 1244 cm−1 enhances and shifts toward higher wavenumbers to 1263

cm−1 with increasing measurement time, indicating that (H2PO4−)n gradually possesses the structural characteristics of that in ADP lattice (Figures 1−5). Moreover, the growth of the low-frequency component of the 1074 cm−1 band, and the increase in frequency of the 871 cm−1 band likewise demonstrate the broken hydrogen bonding in (H2PO4−)H2O and the formation of hydrogen bonding among H2PO4−. Before ADP crystallites separated from the solution, a bending vibration peak of the NH4+ ions does not split into two bending vibration peaks at 1448 cm−1and 1400 cm−1. All these IR spectra characteristics demonstrate that H2PO4− groups initially form a framework structure before ADP nucleation. Once ADP is crystallized from the solution, the v4(NH4) bending mode splits into two bending vibration peaks at 1448 19149



Article

Figure 5. Time-dependent IR spectra of ADP from solution to crystal in ADP supersaturated solution with pH = 5.00. NH3·H2O was added into ADP solution to adjust pH value. Time interval between two adjacent IR spectra is selected as 40 s.

Figure 6. Time-dependent IR spectra from ADP supersaturated solution with pH = 6.03 to (NH4)2HPO4 crystal. NH3·H2O was added into the ADP solution to adjust pH value. Time interval between two adjacent IR spectra is selected as 40 s.

−1

and 1400 cm , indicating the formation of hydrogen bonding between NH4+ and H2PO4− as that in crystal. During the crystallization in the ADP solution system, P−O···H−N−H··· O−P hydrogen bonding results in the insertion of NH4+ into the H2PO4− framework. With further increasing the measurement time, the arrangement of these atoms in (NH4+− H2PO4−)n clusters approaches that in ADP crystal. In aqueous solution, the hydrated ionic radius of H2PO4− is 4 Å, and the hydrated ionic radius of NH4+ is 2.5 Å. It can therefore be deduced that H2PO4− groups with a larger hydrated ionic radius initially form a framework structure, and then NH4+ with a relatively smaller hydrated ionic radius inserts into the framework during ADP crystallization (Table 2). From the chemical bonding view, such a structural transition is realized by breaking the hydrogen bonding between H2PO4− and H2O and then forming P−O···H−O−P hydrogen bonds. In the

nucleation stage of ADP, the hydrogen bonding between NH4+ and H2O in hydrated NH4+·H2O is initially broken, and then N−H···O−P hydrogen bonding between NH4+ and H2PO4− forms to generate the ADP crystal nucleus. When the ADP solution transforms into the solid state completely, v1(PO4) and v3(PO4) at 1143, 1070, 941, and 872 cm−1 become two broad IR bands at 833 and 1072 cm−1 (Figure 3).24−27 The pH value of the supersaturated ADP solution is 3.51. With the in situ observation time increasing up to 40 s, ADP crystallized from aqueous solution. When pH decreases down to 2.90 via adding H3PO4, the time that ADP just crystallizes from the aqueous solution remains at 40 s (as shown in Table 19150



Article

Table 2. Structural Changes during ADP Crystallization Process

Table 3. Crystallization of ADP from ADP Supersaturated Solution with Different pH Values by Adding H3PO4 pH = 0.98

pH = 1.92

pH = 2.90

time (s)

constituents

time (s)

constituents

time (s)

constituents

0−480 480 >480

(NH4+)H2O, (H2PO4−)2H2O, H3PO4 (NH4+)H2O, (H2PO4−)nH2O, H3PO4 NH4H2PO4, H3PO4, H2O

0−80 80 >80


0−40 40 >40


Table 4. Crystallization of ADP and (NH4)2HPO4 from ADP Supersaturated Solution with Different pH Values by Adding NH3· H2O pH = 4.07

pH = 5.00

pH = 6.03

time (s)

constituents

time (s)

constituents

time (s)

constituents

0−40 40 >40

(NH4+)H2O, (H2PO4−)2H2O, HPO42− (NH4+)H2O, (H2PO4−)nH2O, HPO42− NH4H2PO4, HPO42−, H2O

0−200 200 >200

(NH4+)H2O, (H2PO4−)2H2O, HPO42− (NH4+)H2O, (H2PO4−)nH2O, HPO42− NH4H2PO4, HPO42−, H2O

0−800 800 >800

(NH4+)H2O, (H2PO4−)2H2O, HPO42− (NH4+)H2O, (H2PO4−)nH2O, HPO42− (NH4)2HPO4, H2O

Table 5. Results Obtained in This Work and Comparison with Previous Studies, the Observed IR Band (cm−1), and Band Assignments for (NH4)2HPO4 HPO4− solid

NH4+ −1

frequency (cm ; this work) 3210, 3020, 2800 1720, 1700, 1680, 1620 1515, 1477, 1440, 1400

−1

frequency28 (cm−1) 3212, 3045, 2916, 2800 1717, 1702, 1673, 1620 1512, 1453, 1440, 1398

frequency25 (cm−1)

assignment

frequency (cm ; this work)

v1,v3(NH4)

2355, 2200, 1930

2320, 2200, 1941

vOH

3732

vPO-H

v2(NH4)

1205

1206

δOH

3994

vsOH

v4(NH4)

1050, 1012

1072, 1019

vdPO3

3298

vaOH

949 894 850

949 904 858

vsPO3 vP−OH γOH

1853 1191,1098 1017 938 926

δHOH vaPO3 δPOH wag HOH vsPO3

3). With further decreasing pH values to 1.92 and 0.98, the time that ADP just crystallizes from solution, respectively,

frequency (cm−1)

HPO4− (H2O) 28

assignment28

assignment25

increases to 80 and 480 s. On the other hand, when pH increases up to 4.07 via adding NH3·H2O, the time that ADP 19151



Article

increasing or decreasing pH value of the ADP aqueous solution. (NH4)2HPO4 instead of NH4H2PO4 was crystallized from ADP aqueous solution with pH = 6.03. Such an in situ recording strategy is of particular value in studying system dynamics and, in general, to identify the structures of nucleation and crystal growth during crystallization process.

just crystallizes from solution also remains at 40 s (as shown in Table 4). With further increasing pH values to 5.00 and 6.03, the time that ADP just crystallizes from solution respectively increases to 200 and 800 s. It can be deduced that the time that ADP crystallized from the aqueous solution will be prolonged whether increasing or decreasing pH value. Because H3PO4 and NH3·H2O are added into ADP solution to adjust the pH value, the concentration of H2PO4− ions decreases when the pH value of the supersaturated ADP solution decreases or increases. Consequently, the pH value of the ADP solution can influence the nucleation time of NH4H2PO4 and (NH4)2HPO4 crystals, indicating the decreased aggregation probability between H2PO4− ions at the initial stage of crystallization. From the viewpoint of chemical bonding, the time for breaking the hydrogen bonding between H2PO4− and H2O before the formation of (H2PO4−)n clusters is prolonged with increasing or decreasing the pH value of supersaturated ADP solution. For the supersaturated ADP solution with pH = 0.98, 1.92, 2.90, 4.07, and 5.00, NH4H2PO4 crystallized from the aqueous solution (Figures 1−5). Whereas when the pH value of supersaturated ADP solution increased up to 6.03, (NH4)2HPO4 crystallized from aqueous solution. As shown in Figure 6, IR bands at 3210, 3020, and 2800 cm−1 can be assigned to v1 and v3(NH4), IR bands at 1720, 1700, 1680, and 1620 cm−1 can be assigned to v2(NH4), and IR bands at 1515, 1477, 1440, and 1400 cm−1 can be assigned to v4(NH4). IR bands at 2355, 2200, and 1930 cm−1 are assigned to v(OH), and IR bands at 1205 cm−1 are assigned to δ(OH). Moreover, IR bands at 1050, 1012, and 949 cm−1 can be assigned to vd(PO3) and vs(PO3), respectively. IR bands at 890 and 851 cm−1 can be assigned to vd(P−OH) and γ(OH). All these typical IR bands agree with that of (NH4)2HPO4 crystal (Table 5), implying that (NH4)2HPO4 will be crystallized from ADP supersaturated solution with pH = 6.03.28 Before the nucleation of (NH4)2HPO4, hydrated H2PO4−, hydrated HPO42−, and hydrated NH4+ exist in the solution. With increasing time up to 800 s, v4(NH4+) at 1450 cm−1 splits into four bands at 1400, 1440, 1477, 1515 cm−1, rather than splitting into two bands at 1400, 1448 cm−1 in the (NH4)2HPO4 crystal. For the coordination characteristics of four O atoms in (NH4)2HPO4 single crystal, two O atoms in HPO42− group are bonded with three NH4+ via P−O···H−N, one O in HPO42− group is bonded with two NH4+ via P−O···H−N, and one O in HPO42− group bonds with the other HPO42− group via P−O···H−O−P. In NH4H2PO4 crystal, each O in H2PO42− group is bonded with NH4+ and H2PO4− via P−O···H−N and P−O···H−O−P. Therefore, it can be concluded that the pH value can influence the hydrogen bonding between ammonium and phosphate groups in the nucleation stage during crystallization.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: +86-431-85262294. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS Financial support from the National Natural Science Foundation of China (Grant No. 51125009), National Natural Science Foundation for Creative Research Group (Grant Nos. 20921002 and 21221061), and the Hundred Talents Program of the Chinese Academy of Sciences is acknowledged.

■

REFERENCES

(1) Clery, D. What’s Next for ICF? Science 2009, 324, 328−329. (2) Clery, D. NIF Report Asks for More Time to Achieve Ignition. Science 2012, 338, 1519. (3) Ji, S.; Wang, F.; Zhu, L.; Xu, X.; Wang, Z.; Sun, X. Non-Critical Phase-Matching Fourth Harmonic Generation of a 1053 nm Laser in an ADP Crystal. Sci. Rep. 2013, 3, 1605. (4) Xue, D.; Li, K.; Liu, J.; Sun, C.; Chen, K. Crystallization and Functionality of Inorganic Materials. Mater. Res. Bull. 2012, 47, 2838− 2842. (5) Sun, C.; Xue, D. Tailoring Anisotropic Morphology at the Nanoregime: Surface Bonding Motif Determines the Morphology Transformation of ZnO Nanostructures. J. Phys. Chem. C 2013, 117, 5505−5511. (6) Li, J.; Ma, S.; Liu, X.; Zhou, Z.; Sun, C. Q. ZnO Meso-MechanoThermo Physical Chemistry. Chem. Rev. 2012, 112, 2833−2852. (7) Xue, D.; Ratajczak, H. Effect of Hydrogen Bonds on Physical Properties of Ammonium Dihydrogenphosphate Crystals. J. Mol. Struct. 2005, 716, 207−210. (8) Xu, D.; Xue, D. Chemical Bond Analysis of the Crystal Growth of KDP and ADP. J. Cryst. Growth 2006, 286, 108−113. (9) Ren, X.; Sun, C.; Li, K.; Xu, D.; Xue, D. Chemical Bonding and Single Crystal Growth of ADP Crystals. Mater. Focus 2013, 2, 309− 315. (10) Ren, X.; Li, K.; Xue, D. Anisotropy Analysis of the Mechanical Property of K1−xAxDP Crystals by the Oriented Distribution of Chemical Bond. Sci. Adv. Mater. 2012, 4, 901−905. (11) Xu, D.; Xue, D.; Ratajczak, H. Morphology and Structure Studies of KDP and ADP Crystallites in the Water and Ethanol Solutions. J. Mol. Struct. 2005, 740, 37−45. (12) Xu, D.; Xue, D. Computational Study of Crystal Growth Habit and Cleavage. J. Alloy. Compd. 2008, 449, 353−356. (13) Ren, X.; Xu, D.; Xue, D. Crystal Growth of KDP, ADP, and KADP. J. Cryst. Growth 2008, 310, 2005−2009. (14) Xu, D.; Xue, D. Chemical Bond and Microscopic Growth of ADP Crystals. J. Synth. Cryst. 2005, 34, 823−827. (15) Xu, D.; Xue, D. Crystallographic Analysis of Tapering of ADP Crystallites. J. Cryst. Growth 2008, 310, 2005−2009. (16) Xu, D.; Xue, D. Fast Growth of KDP. J. Cryst. Growth 2008, 310, 2157−2161. (17) Sun, C.; Xu, D.; Xue, D. Direct In Situ ATR-IR Spectroscopy of Structural Dynamics of NH4H2PO4 in Aqueous Solution. CrystEngComm 2013, DOI: 10.1039/C3CE41249K. (18) Guo, C.; Yin, S.; Dong, Q.; Huang, Y.; Li, H.; Sato, T. Microwave-Assisted Synthesis of CsxWO3 Nanoparticle and Its NearInfrared Absorbing Properties. Int. J. Nanotechnol. 2013, 10, 126.

4. CONCLUSION In situ ATR-IR spectroscopy was used to observe ADP crystallization process, during which the structural changes were evidenced and characterized spectroscopically. The variations of hydrogen bonding essentially lead to structural transformation of NH4+ and H2PO4− from hydrated ions to the crystalline state. IR spectra characterized that H2PO4− groups with larger hydrated ionic radius initially form a framework structure, and then NH4+ with a relatively smaller hydrated ionic radius inserts into the framework during the ADP crystallization process. The pH value of the ADP aqueous solution can influence both nucleation time and composition of crystals. Nucleation time of ADP crystals increased with 19152



Article

(19) Ratajczak, H. Structural Studies of Some Hydrogen-Bonded Ferroelectrics Using Polarized IR Radiation. J. Mol. Struct. 1969, 3, 27−41. (20) Sun, C.; Xu, D.; Xue, D. Structural Dynamics of H2PO4− Identified by In Situ FTIR-ATR Spectroscopy. Mater. Res. Innov. 2013, DOI: 10.1179/1433075X13Y.0000000155. (21) Wiener, E.; Levin, S.; Pelah, I. Structural, Vibrational and Calorimetric Study of a New Ammonium Dihydrogen Phosphate− Arsenate: NH4H2(PO4)0.52(AsO4)0.48. J. Chem. Phys. 1970, 52, 2891− 2900. (22) Naili, H.; Mhiri, T.; Daoud, A. Antiferroelectric Transitions in NH4H2PO4 and NH4H2AsO4 Studied by Infrared Absorption. Int. J. Inorg. Mater. 2001, 4, 393−400. (23) Renganayaki, V.; Syamala, D.; Sathyamoorthy, R. Growth, Structural and Spectral Studies on Pure and Doped Ammonium Dihydrogen Phosphate (ADP) Single Crystals. Arch. Appl. Sci. Res. 2012, 4, 1453−1461. (24) Koleva, V.; Stefov, V.; Cahil, A.; Najdoski, M.; Soptrajanov, B.; Engelen, B.; Lutz, H. D. Infrared and Raman Studies of Manganese Dihydrogen Phosphate Dihydrate, Mn(H2PO4)2·2H2O. I: Region of the Vibrations of the Phosphate Ions and External Modes of the Water Molecules. J. Mol. Struct. 2009, 917, 117−124. (25) Brandan, S. A.; Diaz, S. B.; Lopez Gonzalez, J. J.; Disalvo, E. A.; Altabef, A. B. Experimental and Theoretical Study of the Hydration of Phosphate Groups in Esters of Biological Interest. Spectrochim. Acta A 2007, 66, 884−897. (26) Brandan, S. A.; Diaz, S. B.; Picot, R. C.; Disalvo, E. A.; Altabef, A. B. Hydration of Inorganic Phosphates in Crystal Lattices and in Aqueous Solution An Experimental and Theoretical Study. Spectrochim. Acta A 2007, 66, 1152−1164. (27) Dave, D. J. Growth and Characterization of Some Amino Acid Doped NLO Materials Crystals. Ph.D. Thesis, Saurashtra University, Gujarat, India, 2011. (28) Hadrich, A.; Lautie, A.; Mhiri, T. Vibrational Study of Structural Phase Transitions in (NH4)2HPO4 and (ND4)2DPO4. J. Raman Spectrosc. 2000, 31, 587−593.

19153


In Situ IR Spectral Observation of NH4H2PO4 Crystallization

Recommend Documents