Formation of Copper(I) Oxide- and Copper(I) Cyanide–Polyacetonitrile

Article Cite This: J. Phys. Chem. A XXXX, XXX, XXX−XXX

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Formation of Copper(I) Oxide- and Copper(I) Cyanide− Polyacetonitrile Nanocomposites through Strong-Field Laser Processing of Acetonitrile Solutions of Copper(II) Acetate Dimer Published as part of The Journal of Physical Chemistry virtual special issue “Hai-Lung Dai Festschrift”. Behzad Tangeysh, Johanan H. Odhner, Yu Wang, Bradford B. Wayland, and Robert J. Levis*

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Department of Chemistry and the Center for Advanced Photonics Research, Temple University, Philadelphia, Pennsylvania 19122, United States S Supporting Information *

ABSTRACT: Irradiation studies of acetonitrile solutions of copper(II) acetate dimer ([Cu(OAc)2]2) using high energy, simultaneously spatially and temporally focused (SSTF) ultrashort laser pulses are reported. Under ambient conditions, irradiation for relatively short periods of time (10−20 s) selectively produces relatively small, narrowly size-dispersed (3.5 ± 0.7 nm) copper(I) oxide nanoparticles (Cu2O NPs) embedded in CuCN−polyacetonitrile polymers generated in situ by the laser. The Cu2O NPs become embedded in a CuCN−polyacetonitrile network as they form, stabilizing them and protecting the air-sensitive material from oxygen. Laser irradiation of acetonitrile causes fragmentation into transient radicals that initiate and terminate polymerization of acetonitrile. Control and mechanistic investigations reveal that HCN formed during laser irradiation reacts rapidly to reduce the Cu(II) centers in [Cu(OAc)2]2, leading to the formation of CuCN or, in the presence of water, Cu2O nanoparticles that bind and cross-link CuCN−polyacetonitrile chains. The acetatebridged Cu(II) dimer unit is a required structural feature that functions to preorganize and direct the Cu(II) reduction and selective formation of CuCN and Cu2O nanoparticles. This study illustrates how rapid deposition of energy using shaped, ultrashort laser pulses can initiate multiple photolytic and thermal processes that lead to the selective formation of composite nanoparticle/polymer materials for applications in electronics and catalysis.

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INTRODUCTION The fabrication of new inorganic−organic hybrid nanomaterials is an important step in the development of new functional materials for applications ranging from electronics to medicine.1−5 Incorporation of nanoparticles into a polymer matrix can both stabilize the particles and modify their mechanical, electrical, and catalytic properties.6−8 Nanoparticle−polymer composites are most often formed through wet chemical synthesis in the presence of preformed polymers.9−11 However, development of high energy density methods such as plasma, electric discharge, laser irradiation, and ultrasound has proceeded rapidly in recent years as viable and green routes for chemical and material synthesis.12 Pulsed laser irradiation of solutions offers a new approach to producing hybrid nanomaterials by initiating photochemical reactions.13−16 Laser processing of metal salts using simultaneous spatiotemporal focusing (SSTF)17,18 was recently introduced by our group as a method for producing nanoparticles in aqueous solution19−22 and in the gas phase.23,24 SSTF is a means to precisely deposit ultrashort pulsed laser energy into a solution phase microplasma, leading to the formation of narrowly size-dispersed nanoparticles. In © XXXX American Chemical Society

water, SSTF laser processing was shown to simultaneously reduce [AuCl4]− to Au(0) and produce H2O2, which persists in the solution after irradiation and acts as a long-lived reducing agent, leading to postirradiation reduction and Au nanoparticle growth.19,25−28 This Article reports on the conditions where ultrashort pulsed laser irradiation of acetonitrile solutions of Cu(II) carboxylate dimers results in efficient and selective formation of narrowly size-dispersed (∼3.5 ± 0.7 nm) Cu2O nanoparticles that bind and cross-link strands of polyacetonitrile or CuCN−polyacetonitrile. Mechanistic studies reveal that laserinduced fragmentation of acetonitrile produces transient radicals that lead to the formation of polyacetonitrile as well as a reductant that directs conversion of carboxylate bridged Cu(II) sites selectively to polymer encapsulated Cu2O nanoparticles or CuCN. Received: May 3, 2019 Revised: July 2, 2019 Published: July 2, 2019 A

DOI: 10.1021/acs.jpca.9b04206 J. Phys. Chem. A XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry A

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EXPERIMENTAL SECTION Materials and Methods. Cu(II) acetate monohydrate (Cu(OAc)2·H2O), ACS reagent ≥98%, Cu(II) isobutyrate, Cu(II) nitrate, Cu(II) tetrafluoroborate, and Cu(II) acetylacetonate were purchased from Sigma-Aldrich and used as received. Anhydrous Cu(II) acetate (99.99%) was also obtained from Sigma-Aldrich and stored in a glovebox under an inert atmosphere (N2) without prior exposure to the air. Propionitrile (99%) and anhydrous benzonitrile (≥99%) were used as obtained from Sigma-Aldrich. HPLC-grade acetonitrile, and other chemicals and reagents were purchased from Fisher Scientific and used without further purification. Stock solutions of Cu(II) salts in acetonitrile and other solvents were prepared from weighed samples in ambient air on the benchtop and diluted to a final concentration of 0.9 mM about 24 h before irradiation studies were conducted. Because acetonitrile is hygroscopic and miscible with water, we assume that the acetonitrile used for all irradiation studies contained significant quantities of water absorbed from air unless otherwise noted. Control studies were carried out in which anhydrous acetonitrile and dehydrated and deaerated Cu(OAc)2 were used to prepare 0.9 mM solutions in a glovebox under an inert atmosphere (N2) that were then sealed in a cuvette (3 mL) and transferred out of the glovebox for laser irradiation. Instrumentation, Characterization, and Analytical Techniques. Laser irradiation was performed using a Ti:sapphire laser amplifier (Coherent, Inc.) delivering 5 mJ, 35 fs pulses with bandwidth centered at 790 nm at a 1 kHz repetition rate. The experimental set up for irradiation was described previously. 19,20 Briefly, the laser beam was simultaneously spectrally and temporally dispersed using a grating pair (1200 l/mm) and then focused with an f = 50 mm aspheric lens into a screw-capped quartz cuvette containing 3.0 mL of solution. This technique is known as simultaneous spatial and temporal focusing (SSTF) and is used to deliver energy in a well-defined, tightly focused beam.29,30 The laser pulse energy at the sample was fixed at 3.5 mJ for all of the experiments. UV−visible spectra were measured in situ during and after laser irradiation using an instrument described previously.21 Transmission electron microscope (TEM) and selected area electron diffraction (SAED) images were obtained using a JEOL JEM-1400 operating at an accelerating voltage of 120 kV. High-resolution TEM (HRTEM) images were obtained using a JEOL JEM-3010 operating at 300 kV. The TEM grids were prepared by depositing 2 μL of sample on the Formvar side of an ultrathin carbon type-A 400 mesh copper grid (Ted Pella Inc., Redding, CA), and the droplet was blotted and allowed to evaporate under ambient conditions overnight. Infrared (IR) spectra were recorded using the iD5 ATR accessory for the Nicolet iS5 FT-IR Spectrometer from Thermo Scientific. For IR spectroscopy, the irradiated samples were preconcentrated by evaporation and drop-cast onto the diamond crystal on the ATR attachment for analysis. Raman spectra were measured using a LabRAM HR800 Evolution microscope from Horiba Scientific. Electrospray ionization mass spectrometry (ESI-MS) was performed using a Bruker micrOTOF-Q II. Irradiated samples were diluted by a factor of 10 in neat acetonitrile and electrosprayed in negative ion mode. Residual gas analysis (RGA) of the cuvette headspace was performed with time-of-flight mass spectrometry using a

home-built mass spectrometer utilizing femtosecond laser pulses from the amplifier as the ionization source.31

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RESULTS The absorption spectrum of Cu(OAc)2·H2O in acetonitrile (Figure 1a, dashed line) exhibits an absorption band at 675

Figure 1. (a) Electronic spectra of 0.9 mM Cu(II) acetate in acetonitrile before (dashed line) and after 12.5 s irradiation recorded at 10 s intervals. (b) Kinetics of the absorbance at 675 and 380 nm during and after irradiation for 12.5 s. The dashed orange lines indicate the time interval where irradiation occurs. (c) Electronic spectra of 0.9 mM Cu(II) acetate in acetonitrile recorded before (dashed line) and 200 s after irradiation for 5 s (dotted line) and 10 s (solid line). (d) Kinetics of the absorbance features at 675 and 380 nm during and after 5 (dotted lines) and 10 (solid lines) s irradiation. The orange lines indicate the time intervals where irradiation occurs. Open squares (10 s) and circles (5 s): first-order fits (see text for details).

nm, arising from the d−d transition of Cu(II), and a band at 375 nm that indicates that Cu(II) acetate is present in the dimeric form, [Cu(OAc)2]2, in acetonitrile.32,33 Irradiation of Cu(II) acetate in acetonitrile causes a decrease in the band at 675 nm, accompanied by the appearance of a new absorbance feature at ∼380 nm (Figure 1a,b). The complete disappearance of the Cu(II) 675 nm band with sufficient irradiation time and the observation of an isosbestic point at 597 nm indicates that Cu(II) is rapidly and quantitatively converted to a new species. No distinct feature is observed in the postirradiation absorption spectrum at ∼600 nm, where the surface plasmon resonance band of metallic copper would be expected to appear,34,35 leading us to conclude that metallic Cu nanoparticles are not formed. However, the final solution exhibits Tyndall scattering, suggesting that nanomaterials may be formed by the reaction. Several other Cu(II) salts were investigated to determine whether a similar reaction is observed. Acetonitrile solutions of Cu(II) nitrate, Cu(II) acetylacetonate, and Cu(II) tetrafluoroborate (0.9 mM) were irradiated for 20 s to determine whether rapid and quantitative reduction of the Cu(II) species was observable. While increased absorption in the UV region of the different spectra was observed, attributable to the polymerization of the solvent, no reduction in the Cu(II) d−d B

DOI: 10.1021/acs.jpca.9b04206 J. Phys. Chem. A XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry A band intensity occurred in any of these salts (Figure S1), suggesting that the rapid reduction observed in the Cu(II) acetate solution is dependent on the molecular structure of Cu(II) acetate. We note that one obvious difference is that Cu(II) acetate is present in solution in its dimeric form, whereas the other copper salts investigated are not. To test the hypothesis that the dimeric structure plays an important role in the reduction process, a 0.9 mM solution of a second dimeric copper salt, Cu(II) butyrate, was prepared in acetonitrile and irradiated for 20 s. Rapid reduction kinetics similar to those observed in the Cu(II) acetate solution are observed in the Cu(II) butyrate solution (Figure S2), supporting the theory that the dimeric structure plays an important role in the reaction. The reduction of Cu(II) acetate was titrated by varying the laser irradiation time. Irradiation times of 5, 10, 12, 12.5, 15, and 20 s demonstrate that quantitative conversion of Cu(II) occurs in 12.5 s at the chosen laser power. Panels c and d of Figure 1 show the initial and final spectra and reaction kinetics of Cu(II) acetate in acetonitrile for 5 and 10 s of laser irradiation, respectively. Under these conditions the reduction of Cu(II) acetate is incomplete. Tracking the consumption of Cu(II) at 675 nm and the growth of the product at ∼380 nm highlights the fact that conversion of Cu(II) continues to occur after laser irradiation is terminated, indicating that a long-lived photoproduct acts as a reagent that drives the reduction process. The kinetics of the decrease in the Cu(II) band and commensurate growth in the peak at ∼380 nm can be fitted to the form y = A e−k(x − B) + C for the 5 and 10 s data shown in Figure 1d. The rmsd of 0.0056 and 0.0055 for the 5 and 10 s data, respectively, strongly suggests that the reduction of Cu(II) follows first-order kinetics and has a rate constant of k = 0.031 ± 0.002 1/s averaged over 16 measurements. Irradiation times significantly longer than 12.5 s (40 and 60 s) resulted in the complete reduction of all Cu(II) acetate in solution and the generation of an excess of the active reagent within the irradiation time (see Figure S3). The data in Figure S3 also show that rapid changes in the band at 380 nm halt abruptly after ∼30 s of laser irradiation, consistent with the rate constant extracted from the short irradiation time data (1/30 s = 0.033 1/s), identifying the time at which the limiting reactant has been consumed and converted to the final product. The final product exhibits a distinct feature at ∼380 nm, regardless of the irradiation time used. Irradiation of neat acetonitrile exhibits no such feature and the absorption increases linearly with irradiation time (Figure S4). TEM measurements were performed to investigate the formation of nanomaterials by laser irradiation of Cu(II) acetate in acetonitrile. The TEM images reveal the formation of polymer networks (Figures 2a−d and S5) containing small (3.5 ± 0.7 nm) nanoparticles in samples irradiated for 20 s. No nanoparticles were observed outside the polymer, suggesting exclusive formation of nanoparticle−polymer composites for the 20-s-irradiated sample. HRTEM images of individual particles show continuous lattice fringes with interplanar spacings corresponding to those of Cu2O and CuO nanoparticles (Figures 2f and S6). The formation of CuO nanoparticles is attributed to surface oxidation of Cu2O nanoparticles upon exposure to air.36,37 SAED analysis of the nanoparticle−polymer composite, however, does not show the characteristic diffraction pattern of Cu2O or CuO38,39 but appears to yield a majority product consisting of a different

Figure 2. Low-magnification (a, c) and high-magnification (b, d) TEM images of the nanocomposite materials produced after 20 s irradiation of 0.9 mM Cu(II) acetate in acetonitrile. (e) SAED recorded on the materials shown in panel c. (f) Representative HRTEM image of an individual Cu2O nanoparticle that exhibits lattice fringes with a d-spacing of 0.215 nm, corresponding to the {200} facet of the Cu2O crystal.

material (Figure 2e), which is likely the result of the relatively small fraction of copper in relation to the polymer generated from the solvent. This observation is corroborated by the fact that the product band observed in the absorption data at ∼380 nm does not correspond to a known absorption feature of Cu2O or CuO nanoparticles. TEM images of samples irradiated for 5, 10, 40, and 60 s are shown in Figures 3, S7, and S8. Nanoparticle formation is

Figure 3. Representative TEM images of the materials produced after irradiation of 0.9 mM Cu(II) acetate in acetonitrile for (a) 5 s, (b) 10 s, (c) 40 s, and (d) 60 s.

observed in samples where reduction is incomplete, though the polymer networks appear to be less dense than those observed in the 20-s-irradiated sample. While Cu2O nanoparticles embedded in polymer networks are observed in the TEM images of the 40-s-irradiated sample, they are smaller than those observed in the 20 s sample (2.9 ± 0.6 nm) (Figure 3c and S8). Very few nanoparticles were observed in the 60-sirradiated samples (Figures 3d and S8) and SAED measureC

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but two features are notable and present in both the 20-s- and 60-s-irradiated Cu(II) acetate in acetonitrile samples: peaks for amorphous graphitic carbon at 1385 and 1549 cm−1 and a peak at 2170 cm−1. The Raman peak at 2170 cm−1 and the FTIR peaks at 2150 and 2114 cm−1 are attributed to the formation of copper(I) cyanide, CuCN.48 The observation of multiple peaks in the FTIR spectrum suggest that several CuCN conformations are present in the product, which is not surprising considering the wide range of CuCN stretch values reported for copper(I) cyanide complexes in the presence of amines and for copper cyanide polymers having the general form [Cu(CN)x]x+1.49−52 The presence of the CuCN peak in the Raman spectrum, but not in the FTIR, could suggest that less CuCN is present in the 20-s-irradiated solution than the 60-sirradiated solution. It is not unexpected that less CuCN would appear in the 20-s-irradiated sample, where we infer from the TEM data that a significant fraction of copper is incorporated in the nanoparticles rather than the polymeric film. The peaks attributed to CuCN were not observed in the FTIR and Raman spectra of the 20-s-irradiated acetonitrile film or the unirradiated Cu(II) acetate solution, which yields the IR spectrum of Cu(II) acetate (Figure S8). ESI-MS performed on the reaction product also confirmed the presence of [CuCN]x polymer chains in the product (Figure 5). Mass spectral peaks at 292.805, 381.747, 470.678, 559.608, 648.551, 737.481, and 826.42, with their associated isotope patterns, are assigned to the formula (CuCN)xCN−, where observed values of x range from 3 to 9. The interpretation of the product as a CxNxHx polymer containing CuCN as a partial product in the lasermediated reaction is also consistent with the observation of a peak at ∼380 nm in the absorption spectrum. Graphitic carbon nitride, Titan-type tholins, and copper cyanide coordination polymers all have absorption spectra that are somewhat similar to those observed in our product.49,53,54 The formation of [CuCN]x implies that a source of cyanide is generated during laser irradiation and reacts with the Cu(II) acetate species. The time-resolved absorption data also shows that the active reagent produced by laser irradiation is longlived, continuing to reduce the Cu(II) species after irradiation has been terminated. Since the only source of cyanide in the solution is the acetonitrile solvent, we propose that the active reagent is generated directly from the solvent. To test this hypothesis, we irradiated neat acetonitrile for 20 s and then added concentrated Cu(II) salts in acetonitrile to produce a final concentration of 0.9 mM and volume of 3 mL (Figure

ments show no evidence of any crystalline diffraction (see Figure S8). The lack of nanoparticle formation is significant, since complete reduction of the Cu(II) d-d band and the presence of the product band at ∼380 nm are observed in the absorption spectrum of the 60-s-irradiated sample (Figure S3), suggesting that Cu(I) is incorporated into a product other than Cu2O. The FTIR and Raman spectra of acetonitrile and 0.9 mM Cu(II) acetate in acetonitrile irradiated for 20 s, as well as 0.9 mM Cu(II) acetate in acetonitrile irradiated for 60 s, are presented in Figure 4. The FTIR spectra of 20-s-irradiated

Figure 4. (a) FTIR spectra of 20-s-irradiated acetonitrile (black) and Cu(II) acetate (0.9 mM) in acetonitrile (red) and 60-s-irradiated Cu(II) acetate in acetonitrile (blue). (b) Raman spectra of the same. The asterisk (*) marks the Raman feature from the silicon substrate.

acetonitrile and Cu(II) acetate in acetonitrile are very similar to the IR spectra of films deposited by CW plasma polymerization of acetonitrile40 and the product of γ radiolysis of liquid acetonitrile,41 as well as a wider class of polymers of carbon, nitrogen, and hydrogen, known as tholins.42−45 Generally, the very broad feature between 3000 and 3500 cm−1 can be attributed to −NH2 and −NH− stretching modes, the sharp peaks between 2800 and 3000 cm−1 are assigned to symmetric and asymmetric C−H stretching modes, and the features below 1800 cm−1 are attributed to CC and CN stretching modes and as well as C−H or N−H bending modes. Interestingly, both the 20-s-irradiated acetonitrile and the 20-sirradiated Cu(II) acetate exhibit strong modes between 2100 and 2300 cm−1. In addition to the presence of nitriles, features in this region can be attributed to conjugated imines, carboiimides, ketenimides, and isonitriles present within the polymeric CxNxHx material.43,46,47 While the 60-s-irradiated sample is similar to the 20 s samples, there is a distinct difference in the 2100−2300 cm−1 region of the spectrum, where relatively strong peaks appear at 2150 and 2114 cm−1. In the Raman spectra, all samples exhibit significant fluorescence,

Figure 5. (a) ESI mass spectrum of Cu(II) acetate added to acetonitrile irradiated for 20 s (negative ion mode). (b)−(d) show expanded regions of the spectrum in (a) with calculated isotope patterns for (CuCN)xCN− (green) overlaid on the spectra. D

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The Journal of Physical Chemistry A S10) after irradiation was terminated. Reduction of Cu(II) acetate and butyrate occurred rapidly under these conditions, and polymer−nanoparticle networks similar to those formed during coirradiation were observed in the TEM (Figure S10c,d). The reagent responsible for reduction was also observed to be long-lasting: adding Cu(II) acetate to irradiated acetonitrile 5 and 20 min after laser irradiation was terminated produced similar results (Figure S11). Repeating the postirradiation Cu(II) addition experiments on acetonitrile irradiated for 60 s yielded a result similar to the one observed after 60 s irradiation of Cu(II) acetate in acetonitrile, where few nanoparticles were observed in the TEM images (Figure S12). These results unambiguously point toward a solvent photoproduct being the primary reagent for the reduction of Cu(II) acetate in the system under study. Having established that the active reagent responsible for the reduction of Cu(II) acetate in acetonitrile is generated directly from the solvent, we now turn to identifying that reagent. Previous studies of acetonitrile photolysis and γ radiolysis suggest that HCN is produced during irradiation of the sample and could act as the long-lived reducing agent, as well as serving as a source of cyanide.41,55−58 Residual gas analysis was performed on the headspace of a sealed cuvette above neat (unirradiated) acetonitrile, acetonitrile that was irradiated for 20 s, and Cu(II) acetate in acetonitrile that was irradiated for 20 s (Figure 6). The parent ion of acetonitrile at 41 m/z and

Table 1

a

m/z

assignment

obsd in neat ACN

obsd in irr ACN

obsd in irr CuOAc@ACN

2 13 16a 26 27a 28a 29 30 31 43a 44 45 46 52a 54

H2+ CH+ CH4+ (O+) CN+ HCN+ H2CN+ (N2+/CO+) CH2NH+/C2H5+ CH3NH+/CH2NH2+ CH3NH2+ CH3CHNH+ NH2CHNH+ (CO2+) CH3CH2NH2+ NH2CH2NH2+ [CN]2+ [HCN]2+

N N N N Y Y N N N Y Y N N N N

Y Y Y Y Y Y Y Y N Y Y N N Y Y

Y Y Y Y Y Y Y Y Y Y N Y Y Y Y

Peak may be contaminated by acetophenone fragment ions.

16), CN (m/z 26), HCN (m/z 27), (CN)2 (m/z 52), and (HCN)2 or C3H4N (m/z 54). Additional peak assignments are found in Table 1. The increase in the feature at 28 m/z (which coincides with N2) by a factor of 2 may be attributable to the generation of H2CN+. These findings are generally in agreement with previous mass spectrometry studies on UVphotolyzed acetonitrile.56 Also noteworthy is the complete disappearance of the peak at 44 in the irradiated Cu(II) acetate sample, which is present in both unirradiated and irradiated acetonitrile. This peak loss may correspond to the catalytic reduction of CO2 by Cu species present in the product or species produced by the presence of Cu, and could also contribute to the increase in signal at m/z 28 if CO is formed.59,60 From the reaction products identified through residual gas analysis we assign HCN as the likeliest candidate for the active reagent that drives the reduction of Cu(II) acetate. To test our hypothesis that HCN is the active reagent we carried out irradiation studies using Cu(II) acetate solutions of propionitrile (CH3CH2CN) and benzonitrile (C6H5CN). Propionitrile has an α-hydrogen and laser irradiation should lead to the production of HCN in a manner similar to acetonitrile (see section 3, eqs 1−7). In contrast, HCN formation is unfavorable in benzonitrile due to the lack of α-hydrogen in the solvent molecules. The dynamic spectra of these experiments show that, while solvent polymerization occurs in both solvents (as is evident from the increased absorption, particularly in the ultraviolet portion of the spectrum) rapid reduction only occurs in the propionitrile solution, where HCN formation is more likely (Figure S13). This supports the hypothesis that HCN drives the reduction of Cu(II) acetate in the systems considered here. The production of Cu2O nanoparticles observed in the HRTEM experiments suggests that oxygen present in the system can play a key role in determining the end product. The Cu(II) acetate used in the experiments described thus far was hydrated and the acetonitrile solutions were in equilibrium with air. To gain insight into the role of water in the reduction process, a 0.9 mM solution of anhydrous Cu(II) acetate in dry acetonitrile was prepared in a glovebox in a sealed cuvette, irradiated for 15 s, and monitored as before using absorption spectroscopy. Complete reduction of the Cu(II) salt occurred

Figure 6. (a) Mass spectra of headspace gas of unirradiated acetonitrile (blue) and acetonitrile irradiated for 20 s (red). (b) Mass spectra of headspace gas of unirradiated acetonitrile (blue) and 0.9 mM Cu(II) acetate in acetonitrile irradiated for 20 s. Arrows show peaks that increase (black) or decrease (red) relative to the unirradiated acetonitrile spectrum. Highlighted regions denote peaks of interest where gain (green) or loss (red) occur.

fragment ions of acetonitrile with the general formulas of CHnCN+ and CHn+, where n = 0−3, were observed in all spectra. Significant fragmentation of acetonitrile is also observed even in the neat acetonitrile sample due to strong field ionization by the ultrashort laser pulse, resulting in peaks at m/z 14, 15, 17, 20, 26, 27, and 34. Also observed in the mass spectrum of neat, unirradiated acetonitrile are peaks at 18, 28, and 32 that may contain features from acetonitrile but coincide with expected H2O, N2, and O2 features. The species observed in the mass spectrum of irradiated acetonitrile and Cu(II) acetate in acetonitrile are summarized in Table 1 and contain a number of features that were not present in the mass spectrum of the unirradiated solution. Significant differences in the spectra of the irradiated samples and the unirradiated sample are found at masses, corresponding to H2 (m/z 2), CH4 (m/z E

DOI: 10.1021/acs.jpca.9b04206 J. Phys. Chem. A XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry A H• + CH3CN → HCN + •CH3

in both hydrated and anhydrous samples with nearly identical reduction kinetics (Figure 7). However, TEM measurements

•

(6)

CH 2CN + CH3CN → CH3CH 2CN + CN

•

(7)

X• + nCH3CN → X(C(CH3)N)[(C(CH3)N)]n − 2 C(CH3)N• (8) X(C(CH3)N)[(C(CH3)N)]n − 2 C(CH3)N• + Y • → X(C(CH3)N)[(C(CH3)N)]n − 2 C(CH3)NY

Figure 7. (a, b) Final spectra and kinetics of the absorbance at 675 and 380 nm during and after 15 s irradiation of anhydrous (solid line) and hydrated (dotted line) Cu(II) acetate in acetonitrile. The dashed yellow lines in (b) indicate the time interval where the laser irradiation occurs. (c, d) Representative TEM images of hydrated (c) and anhydrous (d) Cu(II) acetate solutions recorded after 15 s irradiation.

(9)

HCN can form via multiple pathways through propagation of CN• and H• produced in eqs 1, 2, and 7 with the solvent molecules. The reactions of free radicals produced during irradiation with the −CN group of solvent molecules can initiate polymerization of acetonitrile as shown in eq 8. Termination of the polymerization process occurs through radical cross-coupling reactions between polymer radicals and radical reagents present in the solution including H•, CN•, CH2CN•, and CH3•, producing polymer chains with a general formula of X(C(CH3)N)[(C(CH3)N)]n−2C(CH3)NY where X, Y= H, CN, CH3 (eqs 8 and 9). Once formed, HCN reacts with the Cu(II) carboxylate dimers present in solution. HCN is a weak acid and partially dissociates in acetonitrile to produce H+ and CN− (eq 9). The cyanide anion bonds strongly with Cu(II) centers and readily displaces the more weakly bound carboxylate groups in the Cu(II) carboxylate dimer (eq 10). We speculate that the substitution of two HCN molecules with the Cu(II) carboxylate dimer produces an intermediate complex, CuII2(OAc)2(CN)2, and two AcOH molecules (Scheme 1).

performed on the samples show that many fewer Cu2O nanoparticles were generated in the anhydrous sample compared to the hydrated sample (Figures 7c,d). The fact that the 380 nm feature was observed with the same intensity in the hydrated and anhydrous experiments further affirms that the peak at 380 nm is unlikely to be associated directly with the copper oxide species and suggests that there are two pathways involved in the reduction, one that leads to the production of CuCN and another that involves water and leads to the formation of Cu2O nanoparticles. The observation that samples irradiated for long times, where HCN is produced in significant excess of the amount necessary for stoichiometric reduction of Cu(II), contain very few nanoparticles but have copper incorporated into the polymer (evidenced by IR and Raman) suggests that there is a competition between the pathways that lead to the cyanide and oxide products.

Scheme 1. Representation of the Reaction of HCN with Cu(II) Acetate Dimer Leading to the Formation of Cu(I) Acetate through Reductive Elimination of CN−CN

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DISCUSSION The assembled data suggest that the following factors play a role in driving postirradiation reduction and production of Cu2O nanoparticles: (1) the dimeric structure of Cu(II) carboxylates in acetonitrile, (2) the production of HCN during irradiation, and (3) the presence of water molecules in the solution prior to irradiation. To rationalize these observations, we propose the following mechanism for the reactions occurring during and after irradiation of Cu(II) carboxylates in acetonitrile. During irradiation photochemical reactions occur predominantly with acetonitrile molecules, which are present in solution at a concentration >105 times higher than Cu(II) acetate. Multiphoton excitation, ionization, and dissociation of acetonitrile produces reactive radicals as shown in eqs 1 and 2.61,62 Propagation and cross-coupling of these free radicals with acetonitrile molecules occurs during and immediately after termination of irradiation, leading to the formation of stable products including H2, CH4, and HCN (eqs 3−7). CH3CN + nhν →

CH3•

+ CN V CH3CN •

(2)

CH3•

(3)

•

•

+ CH3CN → CH4 + CH 2CN

•

•

CN + CH3CN → HCN + CH 2CN •

•

H + CH3CN → H 2 + CH 2CN

[Cu II(OAc)2 ]2 + 2HCN V Cu II 2(OAc)2 (CN)2 + 2AcOH [Cu II 2(OAc)2 (CN)2 ] V (NC−CN) + 2Cu IOAc

(1)

CH3CN + nhν → H + CH 2CN V CH3CN •

Formation of Cu−CN units on adjacent Cu(II) sites bridged by carboxylate anions preorganizes the reductive elimination of cyanogen and formation of Cu(I) acetate (eq 11). The occurrence of a reductive elimination, which requires a dimeric form of Cu(II) carboxylates, is supported by our observation that no rapid reduction occurs in Cu(II) salts that have unstable dimeric structures in acetonitrile (Figures S1 and S2).

(10) (11)

After the reductive elimination step, two reactions can occur in the solution: (1) the reaction of CuIOAc with HCN to produce CuICN and (2) the hydrolysis of CuIOAc in the presence of AcOH to form CuIOH, followed by the loss of water and the formation of Cu2O (eqs 12−14).

(4)

Cu IOAc + HCN V Cu ICN + AcOH

(5) F

(12)

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The Journal of Physical Chemistry A Cu IOAc + H 2O V Cu IOH + AcOH

(13)

2Cu IOH V Cu 2O + H 2O

(14)

potential to be used in the development of new photocatalytically active metal−polymer nanocomposites,69−71 which will be a subject of future work.

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The reaction in eq 13 does not lead to the formation of Cu2O directly. Rather, Cu2O nanoparticles are produced through the loss of a water molecule from two CuIOH (eq 14) as reported previously.63,64 In the presence of both HCN and H2O, there should be a competition between eqs 11 and 12, leading to the formation of CuCN and Cu2O nanoparticles in the limit of high and low HCN concentrations, respectively. No hydrolysis can occur until all HCN molecules are consumed due to the stronger ligand effect of CN− compared to H2O. As a result, eq 11 is the dominant reaction pathway in excess HCN, producing CuCN as a final product. The kinetics extracted from Figure 1d also inform our proposed reaction pathway. The reaction kinetics for short irradiation times are first-order, implying that some rate-limiting process acts as a bottleneck for the conversion of Cu(II) acetate to Cu2O. We postulate that the reductive elimination shown in eq 10 is likely to limit the rate of reaction, as the generation of HCN is very rapid and the initial substitution reaction is also likely to be fast. The measurements presented here are consistent with the proposed mechanism in that very few nanoparticles are observed in samples irradiated for 60 s or when the anhydrous salt was used, since in both cases the amount of HCN produced is always higher than the amount of H2O in the solution (Figures 3d and 7d). No diffraction is observed in the SAED measurements of these samples because CuCN is generally an amorphous, polymer-like material.65−67 Thus, we can infer that in samples irradiated for 40 s or less the amount of HCN that remains in solution after the reductive elimination step (eq 10) is very low, making hydrolysis of Cu(I) acetate the most favorable reaction pathway. We have excluded direct photochemical reactions of Cu(II) carboxylates that may occur during the laser processing64,68 because the limited reactivity observed during irradiation of different Cu(II) salts in acetonitrile shows that laser-induced nanoparticle formation is not favorable for the short irradiation times used in these experiments, and the observation of very similar final products when unirradiated Cu(II) carboxylates are added to irradiated acetonitrile.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpca.9b04206.

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Additional figures of electronic spectra and kinetic data, control studies, TEM images, size distribution histogram, and FTIR and Raman spectra (PDF)

AUTHOR INFORMATION

Corresponding Author

*[email protected] Address: Rm. 244, Beury Hall, 1901 N. 13th St. Philadelphia, PA 19122 Telephone: 215-205-5241. ORCID

Behzad Tangeysh: 0000-0002-0843-3746 Robert J. Levis: 0000-0002-2503-0172 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Support of this research by the Army Research Laboratory through contract W911NF-10-2-009 and the National Science Foundation through (CHE-1362890) is gratefully acknowledged. The authors are also grateful for an NSF instrumentation grant (CHE-0923077) for the JEOL JEM-1400 TEM used in this research.

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REFERENCES

(1) Sanchez, C.; Belleville, P.; Popall, M.; Nicole, L. Applications of Advanced Hybrid Organic-Inorganic Nanomaterials: from Laboratory to Market. Chem. Soc. Rev. 2011, 40, 696−753. (2) Sanchez, C.; Julian, B.; Belleville, P.; Popall, M. Applications of Hybrid Organic-Inorganic Nanocomposites. J. Mater. Chem. 2005, 15, 3559−3592. (3) Huynh, W. U.; Dittmer, J. J.; Alivisatos, A. P. Hybrid NanorodPolymer Solar Cells. Science 2002, 295, 2425−2427. (4) Reddy, A. L. M.; Gowda, S. R.; Shaijumon, M. M.; Ajayan, P. M. Hybrid Nanostructures for Energy Storage Applications. Adv. Mater. (Weinheim, Ger.) 2012, 24, 5045−5064. (5) Yin, Y.; Talapin, D. The Chemistry of Functional Nanomaterials. Chem. Soc. Rev. 2013, 42, 2484−2487. (6) Kango, S.; Kalia, S.; Celli, A.; Njuguna, J.; Habibi, Y.; Kumar, R. Surface Modification of Inorganic Nanoparticles for Development of Organic−Inorganic Nanocompositesa Review. Prog. Polym. Sci. 2013, 38, 1232−1261. (7) Faupel, F.; Zaporojtchenko, V.; Strunskus, T.; Elbahri, M. MetalPolymer Nanocomposites for Functional Applications. Adv. Eng. Mater. 2010, 12, 1177−1190. (8) Faupel, F.; Zaporojtchenko, V.; Strunskus, T.; Elbahri, M. MetalPolymer Nanocomposites for Functional Applications. Adv. Eng. Mater. 2010, 12, 1177−1190. (9) Sindoro, M.; Yanai, N.; Jee, A.-Y.; Granick, S. Colloidal-Sized Metal−Organic Frameworks: Synthesis and Applications. Acc. Chem. Res. 2014, 47, 459−469. (10) Xu, P.; Han, X.; Zhang, B.; Du, Y.; Wang, H.-L. Multifunctional Polymer-Metal Nanocomposites via Direct Chemical Reduction by Conjugated Polymers. Chem. Soc. Rev. 2014, 43, 1349−1360. (11) Vaia, R. A.; Maguire, J. F. Polymer Nanocomposites with Prescribed Morphology: Going Beyond Nanoparticle-filled Polymers. Chem. Mater. 2007, 19, 2736−2751.

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CONCLUSIONS Laser irradiation of different Cu(II) salts in various organic nitriles using SSTF pulses revealed that selective chemical activity occurs in dimeric Cu(II) carboxylate solutions of aliphatic carbon-containing nitrile solvents, which provide a source of HCN through laser fragmentation of an alkyl nitrile that acts as a reducing agent and can lead, in the presence of water, to the formation of Cu2O nanoparticles. The number of Cu2O nanoparticles produced was found to depend on the concentration of HCN and water in the solution. Mechanistic investigations show that the laser-induced transformation of Cu(II) carboxylates to Cu2O−polymer nanocomposites in acetonitrile is due to multiple chemical and photochemical processes occurring during and after termination of irradiation. We infer that the polymers formed are a combination of polyacetonitrile and CuCN, whose composition depends on the HCN and water content in the solution after irradiation. The laser-induced formation of Cu2O nanoparticles in conductive nitrile polymer networks of acetonitrile has the G

DOI: 10.1021/acs.jpca.9b04206 J. Phys. Chem. A XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry A (12) Levchenko, I.; Bazaka, K.; Baranov, O.; Sankaran, R. M.; Nomine, A.; Belmonte, T.; Xu, S. Lightning Under Water: Diverse Reactive Environments and Evidence of Synergistic Effects for Material Treatment and Activation. Appl. Phys. Rev. 2018, 5, 021103. (13) Ouchi, A.; Tsunoda, T.; Bastl, Z.; Maryško, M.; Vorlíček, V.; Bohácě k, J.; Vacek, K.; Pola, J. Solution Photolysis of Ferrocene into Fe-Based Nanoparticles. J. Photochem. Photobiol., A 2005, 171, 251− 256. (14) Hayasaki, Y.; Fukuda, T.; Hasumura, T.; Maekawa, T. Creation of Metal-Containing Carbon Onions via Self-Assembly in Metallocene/Benzene Solution Irradiated with an Ultraviolet Laser. Adv. Nat. Sci.: Nanosci. Nanotechnol. 2012, 3, 035010. (15) Shukla, S.; Furlani, E. P.; Vidal, X.; Swihart, M. T.; Prasad, P. N. Two-Photon Lithography of Sub-Wavelength Metallic Structures in a Polymer Matrix. Adv. Mater. (Weinheim, Ger.) 2010, 22, 3695−3699. (16) Shukla, S.; Vidal, X.; Furlani, E. P.; Swihart, M. T.; Kim, K.-T.; Yoon, Y.-K.; Urbas, A.; Prasad, P. N. Subwavelength Direct Laser Patterning of Conductive Gold Nanostructures by Simultaneous Photopolymerization and Photoreduction. ACS Nano 2011, 5, 1947− 1957. (17) Zhu, G.; van Howe, J.; Durst, M.; Zipfel, W.; Xu, C. Simultaneous Spatial and Temporal Focusing of Femtosecond Pulses. Opt. Express 2005, 13, 2153−2159. (18) Oron, D.; Silberberg, Y. Spatiotemporal Coherent Control using Shaped, Temporally Focused Pulses. Opt. Express 2005, 13, 9903−9908. (19) Tangeysh, B.; Moore Tibbetts, K.; Odhner, J. H.; Wayland, B. B.; Levis, R. J. Gold Nanoparticle Synthesis Using Spatially and Temporally Shaped Femtosecond Laser Pulses: Post-Irradiation AutoReduction of Aqueous [AuCl4]−. J. Phys. Chem. C 2013, 117, 18719− 18727. (20) Odhner, J. H.; Moore Tibbetts, K.; Tangeysh, B.; Wayland, B. B.; Levis, R. J. Mechanism of Improved Au Nanoparticle Size Distributions Using Simultaneous Spatial and Temporal Focusing for Femtosecond Laser Irradiation of Aqueous KAuCl4. J. Phys. Chem. C 2014, 118, 23986−23995. (21) Moore Tibbetts, K.; Tangeysh, B.; Odhner, J. H.; Levis, R. J. Elucidating Strong Field Photochemical Reduction Mechanisms of Aqueous [AuCl4]−: Kinetics of Multiphoton Photolysis and RadicalMediated Reduction. J. Phys. Chem. A 2016, 120, 3562−3569. (22) Tangeysh, B.; Tibbetts, K. M.; Odhner, J. H.; Wayland, B. B.; Levis, R. J. Applications of Shaped Femtosecond near-IR Laser Irradiation in the Generation of Metal Nanoparticles. MRS Online Proc. Libr. 2014, 1654, Mrsf13-1654-nn09-04. (23) Tibbetts, K. M.; Odhner, J.; Vaddypally, S.; Tangeysh, B.; Cerkez, E. B.; Strongin, D. R.; Zdilla, M. J.; Levis, R. J. Amorphous Aluminum-Carbide and Aluminum−Magnesium-Carbide Nanoparticles from Gas Phase Activation of Trimethylaluminum and Octamethyldialuminummagnesium using Simultaneous Spatially and Temporally Focused Ultrashort Laser Pulses. Nano-Struct. NanoObjects 2016, 6, 1−4. (24) Shumlas, S. L.; Tibbetts, K. M.; Odhner, J. H.; Romanov, D. A.; Levis, R. J.; Strongin, D. R. Formation of Carbon Nanospheres via Ultrashort Pulse Laser Irradiation of Methane. Mater. Chem. Phys. 2015, 156, 47−53. (25) Tangeysh, B.; Moore Tibbetts, K.; Odhner, J. H.; Wayland, B. B.; Levis, R. J. Triangular Gold Nanoplate Growth by Oriented Attachment of Au Seeds Generated by Strong Field Laser Reduction. Nano Lett. 2015, 15, 3377−3382. (26) Tangeysh, B.; Tibbetts, K. M.; Odhner, J. H.; Wayland, B. B.; Levis, R. J. Gold Nanotriangle Formation through Strong-Field Laser Processing of Aqueous KAuCl4 and Postirradiation Reduction by Hydrogen Peroxide. Langmuir 2017, 33, 243−252. (27) Rodrigues, C. J.; Bobb, J. A.; John, M. G.; Fisenko, S. P.; ElShall, M. S.; Tibbetts, K. M. Nucleation and Growth of Gold Nanoparticles Initiated by Nanosecond and Femtosecond Laser Irradiation of Aqueous [AuCl4]−. Phys. Chem. Chem. Phys. 2018, 20, 28465−28475.

(28) Meader, V. K.; John, M. G.; Rodrigues, C. J.; Tibbetts, K. M. Roles of Free Electrons and H2O2 in the Optical Breakdown-Induced Photochemical Reduction of Aqueous [AuCl4]−. J. Phys. Chem. A 2017, 121, 6742−6754. (29) Jing, C.; Wang, Z.; Cheng, Y. Characteristics and Applications of Spatiotemporally Focused Femtosecond Laser Pulses. Appl. Sci. 2016, 6, 428. (30) He, F.; Zeng, B.; Chu, W.; Ni, J.; Sugioka, K.; Cheng, Y.; Durfee, C. G. Characterization and Control of Peak Intensity Distribution at the Focus of a Spatiotemporally Focused Femtosecond Laser Beam. Opt. Express 2014, 22, 9734−9748. (31) Bohinski, T.; Moore Tibbetts, K.; Tarazkar, M.; Romanov, D.; Matsika, S.; Levis, R. J. Measurement of an Electronic Resonance in a Ground-State, Gas-Phase Acetophenone Cation via Strong-Field Mass Spectrometry. J. Phys. Chem. Lett. 2013, 4, 1587−1591. (32) Kyuzou, M.; Mori, W.; Tanaka, J. Electronic Structure and Spectra of Cupric Acetate Mono-Hydrate Revisited. Inorg. Chim. Acta 2010, 363, 930−934. (33) Graddon, D. P. The Absorption Spectra of Complex SaltsIV Cupric Alkanoates. J. Inorg. Nucl. Chem. 1961, 17, 222−231. (34) Ye, Z.; Tangeysh, B.; Wayland, B. B. Metal Dication CrossLinked Polymer Network Colloids as an Approach to Form and Stabilize Unusually Small Metal Nanoparticles. Chem. Commun. 2013, 49, 5372−5374. (35) Hambrock, J.; Becker, R.; Birkner, A.; Wei; Fischer, R. A. A Non-Aqueous Organometallic Route to Highly Monodispersed Copper Nanoparticles using [Cu(OCH(Me)CH2NMe2)2]. Chem. Commun. 2002, 68−69. (36) Xiong, L.; Xiao, H.; Chen, S.; Chen, Z.; Yi, X.; Wen, S.; Zheng, G.; Ding, Y.; Yu, H. Fast and Simplified Synthesis of Cuprous Oxide Nanoparticles: Annealing Studies and Photocatalytic Activity. RSC Adv. 2014, 4, 62115−62122. (37) Yan, X.-Y.; Tong, X.-L.; Zhang, Y.-F.; Han, X.-D.; Wang, Y.-Y.; Jin, G.-Q.; Qin, Y.; Guo, X.-Y. Cuprous Oxide Nanoparticles Dispersed on Reduced Graphene Oxide as an Efficient Electrocatalyst for Oxygen Reduction Reaction. Chem. Commun. 2012, 48, 1892− 1894. (38) Borgohain, K.; Murase, N.; Mahamuni, S. Synthesis and Properties of Cu2O Quantum Particles. J. Appl. Phys. (Melville, NY, U. S.) 2002, 92, 1292−1297. (39) Chakravarty, A.; Bhowmik, K.; Mukherjee, A.; De, G. Cu2O Nanoparticles Anchored on Amine-Functionalized Graphite Nanosheet: A Potential Reusable Catalyst. Langmuir 2015, 31, 5210−5219. (40) Lefohn, A. E.; Mackie, N. M.; Fisher, E. R. Comparison of Films Deposited from Pulsed and Continuous Wave Acetonitrile and Acrylonitrile Plasmas. Plasmas Polym. 1998, 3, 197−209. (41) Bradley, D.; Wilkinson, J. The Radiolysis of Liquid Acetonitrile. J. Chem. Soc. A 1967, 531−537. (42) Gautier, T.; Carrasco, N.; Mahjoub, A.; Vinatier, S.; Giuliani, A.; Szopa, C.; Anderson, C. M.; Correia, J.-J.; Dumas, P.; Cernogora, G. Mid- and Far-Infrared Absorption Spectroscopy of Titan’s Aerosols Anologues. Icarus 2012, 221, 320−327. (43) Quirico, E.; Montagnac, G.; Lees, V.; McMillan, P. F.; Szopa, C.; Cernogora, G.; Rouzaud, J.-N.; Simon, P.; Bernard, J.-M.; Coll, P.; Fray, N.; Minard, R. D.; Raulin, F.; Reynard, B.; Schmitt, B. New Experimental Constraints on the Composition and Structure of Tholins. Icarus 2008, 198, 218−231. (44) Miller, T. S.; Jorge, A. B.; Suter, T. M.; Sella, A.; Cora, F.; McMillan, P. F. Carbon Nitrides: Synthesis and Characterization of a New Class of Functional Materials. Phys. Chem. Chem. Phys. 2017, 19, 15613−15638. (45) Mahjoub, A.; Carrasco, N.; Dahoo, P. R.; Fleury, B.; Gautier, T.; Cernogora, G. Effect of the Synthesis Temperature on the Optical Indices of Organic Materials Produced by N2-CH4 RF Plasma. Plasma Processes Polym. 2014, 11, 409−417. (46) Inagaki, N.; Tasaka, S.; Yamada, Y. Plasma Polymerization of Cyano Compounds. J. Polym. Sci., Part A: Polym. Chem. 1992, 30, 2003−2010. H

DOI: 10.1021/acs.jpca.9b04206 J. Phys. Chem. A XXXX, XXX, XXX−XXX

Article

The Journal of Physical Chemistry A

Helical Copper(I) Coordination Polymer [Cu3(CN)3(phen)]n. Inorg. Chem. Commun. 2006, 9, 1312−1314. (68) Glebov, E. M.; Plyusnin, V. F.; Grivin, V. P.; Krupoder, S. A.; Liskovskaya, T. I.; Danilovich, V. S. Photochemistry of Copper(II) Polyfluorocarboxylates and Copper(II) Acetate as their Hydrocarbon Analogues. J. Photochem. Photobiol., A 2000, 133, 177−183. (69) Sun, W.; Sun, W.; Zhuo, Y.; Chu, Y. Facile Synthesis of Cu2O Nanocube/Polycarbazole Composites and their High Visible-Light Photocatalytic Properties. J. Solid State Chem. 2011, 184, 1638−1643. (70) Miao, J.; Xie, A.; Li, S.; Huang, F.; Cao, J.; Shen, Y. A Novel Reducing Graphene/Polyaniline/Cuprous Oxide Composite Hydrogel with Unexpected Photocatalytic Activity for the Degradation of Congo Red. Appl. Surf. Sci. 2016, 360, 594−600. (71) Kumar, R. V.; Mastai, Y.; Diamant, Y.; Gedanken, A. Sonochemical Synthesis of Amorphous Cu and Nanocrystalline CuO Embedded in a Polyaniline Matrix. J. Mater. Chem. 2001, 11, 1209−1213.

(47) Bhat, N. V.; Upadhyay, D. J. Adhesion Aspects of Plasma Polymerized Acetonitrile and Acrylonitrile on Polypropylene Surface. Plasmas Polym. 2003, 8, 99−118. (48) Bowmaker, G. A.; Kennedy, B. J.; Reid, J. C. Crystal Structures of AuCN and AgCN and Vibrational Spectroscopic Studies of AuCN, AgCN, and CuCN. Inorg. Chem. 1998, 37, 3968−3974. (49) Grifasi, F.; Priola, E.; Chierotti, M. R.; Diana, E.; Garino, C.; Gobetto, R. Vibrational-Structural Combined Study into Luminescent Mixed Copper(I)/Copper(II) Cyanide Coordination Polymers. Eur. J. Inorg. Chem. 2016, 2016, 2975−2983. (50) Kappenstein, C.; Hugel, R. P. Existence of the Monomeric Tricyanocuprate (2-) Anion in the Solid State. Molecular Structure and Disorder of Sodium Tricyanocuprate (I) Trihydrate. Inorg. Chem. 1978, 17, 1945−1949. (51) Connor, J. A.; Gibson, D.; Price, R. Formamide as a Precursor to Cyanide in Mixed-Valence Copper(I,II) Cyanide Complexes. J. Chem. Soc., Dalton Trans. 1986, 347−350. (52) Mueuller-Litz, W. Zur Kenntnis der Ammoniakate von Kupfer (I)-Halogeniden und Kupfer (I)-Cyanid. Z. Chem. (Stuttgart, Ger.) 1968, 8, 389−390. (53) Zhang, J. S.; Chen, X. F.; Takanabe, K.; Maeda, K.; Domen, K.; Epping, J. D.; Fu, X. Z.; Antonietti, M.; Wang, X. C. Synthesis of a Carbon Nitride Structure for Visible-Light Catalysis by Copolymerization. Angew. Chem., Int. Ed. 2010, 49, 441−444. (54) Imanaka, H.; Khare, B. N.; Elsila, J. E.; Bakes, E. L.; McKay, C. P.; Cruikshank, D. P.; Sugita, S.; Matsui, T.; Zare, R. N. Laboratory Experiments of Titan Tholin Formed in Cold Plasma at Various Pressures: Implications for Nitrogen-Containing Polycyclic Aromatic Compounds in Titan Haze. Icarus 2004, 168, 344−366. (55) McElcheran, D. E.; Wijnen, M. H. J.; Steacie, E. W. R. The Photolysis of Methyl Cyanide at 1849 Å. Can. J. Chem. 1958, 36, 321−329. (56) Nishi, N.; Shinohara, H.; Hanzaki, I. Photochemical Conversion from Methylamine to Hydrogen Cyanide with an ArF Laser at 193 nm. Chem. Phys. Lett. 1980, 73, 473−477. (57) Mosseri, S.; Neta, P.; Meisel, D. The Mechanism of Cyanide Release in the Radiolysis of Acetonitrile - Formation and Decay of the Cyanomethylperoxyl Radical. Radiat. Phys. Chem. 1990, 36, 683−687. (58) Ayscough, P. B.; Drawe, H.; Kohler, P. The Gamma Radiolysis of Acetonitrile. Radiat. Res. 1968, 33, 263−273. (59) Gawande, M. B.; Goswami, A.; Felpin, F.-X.; Asefa, T.; Huang, X.; Silva, R.; Zou, X.; Zboril, R.; Varma, R. S. Cu and Cu-Based Nanoparticles: Synthesis and Applications in Catalysis. Chem. Rev. (Washington, DC, U. S.) 2016, 116, 3722−3811. (60) Sun, Z.; Wang, H.; Wu, Z.; Wang, L. g-C3N4 Based Composite Photocatalysts for Photocatalytic CO2 Reduction. Catal. Today 2018, 300, 160−172. (61) Wu, C.; Xiong, Y.; Gao, Z.; Kong, F. a.; Lu, H.; Yang, X.; Xu, Z. Ionization and Dissociation of Acetonitrile by Intense Femtosecond Laser Pulse. Chin. Sci. Bull. 2000, 45, 1953. (62) Senba, Y.; Yoshida, H.; Ogata, T.; Sakata, D.; Hiraya, A.; Tanaka, K. Study on Photodissociation of Core-Excited CH3CN and CD3CN by using a Reflectron-type Time-of-Flight Mass Analyzer. J. Electron Spectrosc. Relat. Phenom. 1999, 101, 131−134. (63) Soroka, I. L.; Shchukarev, A.; Jonsson, M.; Tarakina, N. V.; Korzhavyi, P. A. Cuprous Hydroxide in a Solid form: Does it Exist? Dalton Trans 2013, 42, 9585−9594. (64) Long, J.; Dong, J.; Wang, X.; Ding, Z.; Zhang, Z.; Wu, L.; Li, Z.; Fu, X. Photochemical Synthesis of Submicron- and Nano-scale Cu2O Particles. J. Colloid Interface Sci. 2009, 333, 791−799. (65) Etaiw, S. E.-d. H.; Amer, S. A.; El-bendary, M. M. 3DSupramolecular Copper(I) Cyanide Coordination Polymers through Hydrogen Bonding. Polyhedron 2009, 28, 2385−2390. (66) Hibble, S. J.; Eversfield, S. G.; Cowley, A. R.; Chippindale, A. M. Copper(I) Cyanide: A Simple Compound With a Complicated Structure and Surprising Room-Temperature Reactivity. Angew. Chem., Int. Ed. 2004, 43, 628−630. (67) Liang, S.-W.; Li, M.-X.; Shao, M.; Miao, Z.-X. Hydrothermal Synthesis and Crystal Structure of a Novel Cyanide-Bridged Double I

DOI: 10.1021/acs.jpca.9b04206 J. Phys. Chem. A XXXX, XXX, XXX−XXX