TzF/TzG layer (vii) on copper foil (vi) imaged at 40° stage angle. ... zone (BZ) was sampled using 1 à 1 à 1 and 3 à 3 à 1 gamma-cantered MonkhorstâPack grids.
Copyright WILEY-VCH Verlag GmbH & Co. KGaA, 69469 Weinheim, Germany, 2017.
Supporting Information for Adv. Mater., DOI: 10.1002/adma.201703399
Twinned Growth of Metal-Free, Triazine-Based Photocatalyst Films as Mixed-Dimensional (2D/3D) van der Waals Heterostructures Dana Schwarz, Yu Noda, Jan Klouda, Karolina SchwarzováPecková, Ján Tarábek, JiĜí Rybáþek, JiĜí Janoušek, Frank Simon, Maksym V. Opanasenko, JiĜí Čejka, Amitava Acharjya, Johannes Schmidt, Sören Selve, Valentin ReiterScherer, Nikolai Severin, Jürgen P. Rabe, Petra Ecorchard, Junjie He, Miroslav Polozij, Petr Nachtigall, and Michael J. Bojdys*
Copyright WILEY-VCH Verlag GmbH & Co. KGaA, 69469 Weinheim, Germany, 2016.
Supporting Information Twinned growth of metal-free, triazine-based photocatalyst films as mixed-dimensional (2D/3D) van der Waals heterostructures Dana Schwarz, Yu Noda, Jan Klouda, Karolina Schwarzová-Pecková, Ján Tarábek, Jiří Rybáček, Jiří Janoušek, Frank Simon, Maksym V. Opanasenko, Jiří Čejka, Amitava Acharjya, Johannes Schmidt, Sören Selve, Valentin Reiter-Scherer, Nikolai Severin, Jürgen P. Rabe, Petra Ecorchard, Junjie He, Miroslav Polozij, Petr Nachtigall, and Michael J. Bojdys* Materials and Methods Materials All chemicals and solvents were used as received without any further purification. All reactions were carried out under argon atmosphere in flame-dried glassware on a Schlenk line. Completion of reactions was determined by TLC using silica gel covered aluminum plates (Merck 60, F-254) and visualized by UV detection (λ = 254 nm). Purification by column chromatography was performed using silica gel (0.063–0.2 mm, 100 mesh ASTM) from Penta (Prague, CZ) All solvents used for the reaction were purchased from VWR and were anhydrous except for pyridine. 4-bromobenzonitrile, trifluoromethanesulfonic acid (TFMSA) were purchased from Acros Organics. Pd(PPh 3)4 and 1.6 M n-buthyllithium in hexane from Sigma Aldrich. Anhydrous ZnCl2 was purchased from Alfa-Aesar. Ethenyltrimethylsilane was purchased from ABCR (Karlsruhe, Germany). Copper foil with a size of 200 x 300 x 0.1 mm was purchased from Metall-Ehrnsberger (Teublitz, Germany). The foil was cut to sizes about 10 x 50 x 0.1 mm with a conventional scissors to fit the reaction vessels. Methods 1H
and 13C NMR spectra of the monomers in CDCl3 as well as solid-state cross-polymerization magnetic-angle spinning (CP-MAS) spectra were recorded on a Bruker Advance 400 instrument. Chemical shifts (δ) were reported in ppm (internal standard CHCl3 for liquid measurements was set at δH = 7.26 ppm). 13C CP-MAS NMR experiments were carried out at a MAS rate of 12.0 kHz using zirconia rotors 4 mm in diameter. The spectrum was measured using a contact time of 10 ms and a relaxation delay of 10.0 s. Infrared (IR) spectra were recorded from KBr pellets on an AVATAR 370 FT-IR spectrometer from Thermo Nicolet. Fluorescence spectra were measured with a Fluorolog FL3-22 fluorometer (Horiba – Jobin Yvon, France). Powder X-ray (PXRD) measurements were performed with a PANalytical X´pert Pro diffractometer using Cu K1,2 radiation with secondary graphite monochromator and PIXcel detector. Samples were measured from 10 to 100° 2θ with the step of 0.013° 2θ. Solid-state Raman spectra were recorded on a DXR Raman spectrometer (Thermo Scientific) interfaced to an Olympus microscope, employing a 10x objective. The 532 nm (diode-pumped solid-state laser) excitation lines was used. The laser power ranged from 2 to 10 mW. The full-scale grating was used for all measurements. The spectrum was baseline-corrected due to the high fluorescence background. Scanning electron microscope (SEM) images were obtained with a Nova NanoSEM 450 from FEI. The dry samples were prepared on 15 mm aluminum stubs using an adhesive, high purity carbon tab. Imaging was conducted at a working distance of 5 mm and a working voltage of 3-10 kV using a mix of upper and lower secondary electron detectors. The field emission scanning electron microscope measurement scale bar was calibrated against certified standards. Energy dispersive X-ray (EDX) spectroscopy was performed using the energy-dispersive X-ray analyzer INCA 250 on the Nova NanoSEM 450. EDX spectra were obtained at a working voltage of 20 kV.
1
Solid-state UV/Vis spectra were obtained on a Shimadzu UV-2550. X-ray photoelectron spectroscopy (XPS) spectra were recorded on an AXIS ULTRA (Kratos Analytical, England). For the measurement, a Mono-Al K1,2 X-ray-source was used with a rated input of the x-ray tube of 300 W at 20 mA. The analyzer had a pass energy of 160 eV (overview spectra), and 20 eV (high resolution spectra), respectively. For charge compensation a low energy electron source in contact with a magnetic immersion lens was used. Transmission electron microscopy (TEM) was carried out using a Titan 80-300 instrument (FEI) equipped with an imaging-side spherical aberration (CS) corrector operating at an accelerating voltage of 80 kV under Scherzer conditions and with a spherical aberration value of 20 µm. Images were recorded on a CCD (charge-coupled device) with an exposure time of one second per frame and an interval of two seconds between the frames in a particular sequence at a constant electron dose rate of ~107 electrons nm-2 s-1. Inductively coupled plasma optical emission spectrometry (ICP-OES) measurements were performed using the SPECTRO ARCOS optical emission spectrometer (SPECTRO Analytical Instruments, Kleve, Germany) with radial plasma observation. The SPECTRO ARCOS features a Paschen-Runge spectrometer mount; the wavelength range between 130 and 770 nm can be simultaneously analyzed. An air-cooled ICP-generator, based on a free-running 27.12 MHz system, is installed. For sample introduction cyclonic spray chamber and a modified light nebulizer was used. The following ICP operating parameters were applied: generator power 1 450 W, coolant flow 13 L/min, auxiliary flow 0.8 L/min, nebulizer flow 0.75 L/min, sample aspiration rate 2 mL/min. For calibration, commercially available multielement standard solutions (Analytika, Czech Republic) were used. The concentrations of calibrated elements were 0, 0.2, 1.0, 5.0, 10.0 and 20.0 mg/L, respectively. All measurements were performed in 4% HNO3 as a matrix. Sample preparation: To prepare liquid samples for ICP-OES analysis, the solid samples were weighted (approx. 5 mg) on microanalytical balance and combusted by Schöniger method. After combustion the closed Erlenmeyer flask was treated in ultrasonic bath for several minutes. After absorption of combustion products (at least 2 h) 50 µL of 1000 mg/L Y standard solution were added (final concentration 2 mg/L). Afterwards the liquid mixture was transferred from the glass flask in a plastic bottle. The flask was rinsed carefully with demineralized water which was added to the plastic bottle. The concentration of HNO 3 were adjusted to 4% (w/w in final volume). Then the demineralized water was added to plastic bottle to achieve the final volume of 25 mL (weighed). After mixing the solution was filtered and introduced to the spectrometer system.
2
Synthesis All reactions were carried out under argon atmosphere on a Schlenk line.
Scheme S1. Synthetic route for the synthon, 2,4,6-tris(4-ethynylphenyl)-1,3,5-triazine (3) and TzF/TzG vdW heterostructures on copper.
Synthesis of 2,4,6-tris(4-bromophenyl)-1,3,5-triazine (1) 2,4,6-tris(4-bromophenyl)-1,3,5-triazine was prepared from 4-bromobenzonitrile according to the method reported by Meyer et al.i.1H NMR (400 MHz, CDCl3): 8.61 (6H, d, J = 8.7 Hz, C6H4), 7.71 (6H, d, J = 8.7 Hz, C6H4). Synthesis of 2,4,6-tris(4-[(trimethylsilyl)ethynyl]phenyl)-1,3,5-triazine (2) In a 250 mL three-necked-flask 1.0 g (1.93 mmol) of 1 and 252 mg (0.22 mmol) Pd(PPh3)4 were dispersed in 40 mL anhydrous Toluene. A solution of 10 mmol [(trimethylsilyl)ethynyl]zinc chloride in 10 mL anh.THF prepared according to literature method was added drop wise to the dispersion.ii The mixture was stirred under argon atmosphere at 70 °C for one day. After the addition of 20 mL of 0.1 M aqueous HCl, the reaction mixture was extracted with ether until the initial dark brown organic phase is transparent. The combined organic phases were washed with brine and dried over magnesium sulfate. The solvent was evaporated and further purified by chromatography on silica gel (eluent hexane/toluene = 12:1) to give 0.96 g (88 %) of 2,4,6-tris(4-[(trimethylsilyl)ethynyl]phenyl)-1,3,5-triazine (2) as a white solid. 1H NMR (400 MHz, CDCl3): 8.68 (6H, d, J = 8.4 Hz, C6H4), 7.65 (6H, d, J = 8.4 Hz, C6H4), 0.31 (27H, s, Si(CH3)3).
Synthesis of 2,4,6-tris(4-ethynyl)phenyl]-1,3,5-triazine (3) 1.20 mmol 2 was deprotected with 0.75 mmol K2CO3 in a THF/methanol (10:1) solution. After stirring at room temperature for one day, the mixture was washed with water and extracted with DCM. The combined organic phases were washed with brine and dried over MgSO4. The solvents were evaporated to give 0.40 mg (88 %) of the synthon 3.iii 1H NMR (400 MHz, CDCl3): 8.70 (6H, d, J = 8.6 Hz, C6H4), 7.68 (6H, d, J = 8.6 Hz, C6H4), 3.27 (3H, s, C≡CH).
Synthesis of TzF/TzG films Before usage, the copper plates were washed under ultrasound in 1 M HCl, acetone, and ethanol subsequently for 15 min each. Subsequently, the plates were dried on the Schlenk line under a flow of argon. The synthon 3 was dissolved in pyridine
3
and added dropwise to a reaction flask charged with copper plates submerged in pyridine at 60 °C under argon atmosphere. The mixture was stirred under argon atmosphere at 60 °C for three days. Residual monomers and oligomers were washed from the copper support with DMF and acetone, and TzF/TzG on copper was dried on the Schlenk line. To release the TzF/TzG films, TzF/TzG on copper was treated with an aqueous solution of phosphoric acid (1M). Within seconds, the TzF/TzG films released from the copper substrate (Figure S1). The as-synthesized TzF/TzG films were subject to a wash, first using conc. HNO3 (overnight, 8 h) to remove residual copper nanoparticles (Cu NPs) (Figure S2) and then deionised water (Table S3; EA: cal.: C, 85.7; H, 3.17; N, 11.11, C/N = 9.0:1; found for flakes: C, 75.33; H, 4.05; N, 9.72; residue: 10.9 %; C/N = 9.0:1). Prolonged wash (8 to 24 h) in conc. HNO3 triggers delamination of the 2D TzF phase via chemical etching of 3D TzG.
Removal of copper from TzF/TzG films After removing the organic layer from the copper surface, some copper species still remain embedded within the matrix of the organic flakes. Therefore, we developed the following protocols to remove the copper from the flakes: Table S1. Post-synthetic protocols to remove Cu NPs from TzF/TzG vdW heterostructures. Flakes were stirred overnight in the corresponding solution mentioned in the Table S1; Cu content was measured by ICP-OES.a NH4OH was used for neutralization in the purification process at the end.b,iv treatment conc. HNO3 HNO3 1 M HCl (1 M), NH4OH (10%)a FeCl3-HCl (1 M), NH4OH (10%)a ammoniumpersulfate NH4OH/NH4CO3b NH4OH (10%)
Cu (%) 4.12 0.01 2.73 0.07 0.30 0.71 1.11 1.14
Figure S1. The copper support is gently etched using phosphoric acid (1 M) to obtain a free-standing films of TzF/TzG floating on the top of the water surface.
Figure S2. (a) and (b) High-resolution TEM images of as-synthesised TzF/TzG films show a large number of copper nanoparticles (Cu NPs) embedded in the amorphous 3D TzG. Cu NPs have a very homogeneous particle size distribution of
4
around 2.4 nm, as indicated by red circles in (b). (c) Selected area-electron diffraction (SAED) confirms the presence of copper.v
Figure S3. Energy-dispersive X-ray (EDX) spectra of (b) as-synthesized TzF/TzG heterostructures, and (a) TzF/TzG after removal of Cu NPs. Table S2. Ratio of elements detected by EDX, in wt%. Material C N 85.7 11.11 calculated 76.89 13.97 TzF/TzG (assynth.) 77.97 11.07 TzF/TzG
5
O 3.17 8.52
Cu 0.61
Cl -
Pd -
10.95
-
-
-
Table S3. Ratio of elements detected by combustion elemental analysis (EA) and ICP-OES, in wt%. Material C N H Cu Cl Pd 85.7 11.11 3.17 calculated 75.33 9.72 4.05 4.12 TzF/TzG (assynth.) 71.12 10.75 3.91 0.01 TzF/TzG
Figure S4. SEM images of (a) TzF/TzG layer removed mechanically with a dicing tape from the copper surface. (b) TzF/TzG edge structure with the exposed, flat copper foil on the bottom-left (i) and the TzF/TzG material on the top-right (ii). (c) Exfoliated TzF/TzG flakes in two different orientations: 2D TzF side up (iii) and 3D TzG side up (iv and v). (d) TzF/TzG layer (vii) on copper foil (vi) imaged at 40° stage angle. The TzF/TzG film is approx. 5.9 µm thick.
Figure S5. (a) and (d) Low-resolution TEM images of TzF/TzG films after ultrasonic exfoliation taken from CH2Cl2/water interface (a) and from the organic phase, (b) and (c) high-resolution TEM images of TzF flakes with corresponding FFT (in b) and SAED pattern (in c) as insets. (e) Representative selected area EDX pattern from exfoliated TzF/TzG films after ultrasonic exfoliation.
6
Figure S6. (a) and (b) FT-IR spectra of monomer 3 (2,4,6-tris(4-ethynyl)phenyl]-1,3,5-triazine) (green) and as-synthesised TzF/TzG flakes (black). Theoretical calculations. All calculations were performed using the Vienna ab initio simulation package (VASP) vi,vii with the Perdew–Burke–Ernzerhof (PBE) exchange–correlation functionalviii augmented with dispersion corrections (PBE-D2).ix Interactions between electrons and nuclei were described by the projector-augmented wave (PAW) method. The criteria for energy and atom force convergence were set to 10-5 eV and 0.01 eV Å-1, respectively. A plane-wave kinetic energy cut-off of 500 eV was employed. Calculations were performed for the two-layer model and 15 Å vacuum between the layer pairs along the z-direction. The Brillouin zone (BZ) was sampled using 1 × 1 × 1 and 3 × 3 × 1 gamma-cantered Monkhorst–Pack grids for the structure optimization of TzG and TzF materials, respectively. The simulated SAED patterns were obtained with DIFFAX Simulations software. x Electron wavelength of 0.022689 Å was used in the simulations. The structures used in SAED calculations contained four layers per unit cell with different distributions of inter-layer shifts. The periodic structures were constructed from optimized double layer structures and were not re-optimized. In the case of a double-layer there are six possible translation vectors that all produce symmetrically equivalent (and iso-energetic) layer arrangements. In case of three and more TzF layers these translational vectors (between individual layer pairs) are randomly combined and, thus, the layered material as depicted in Figure S7 is produced.
Figure S7. ABslip arrangement of four TzF layers with randomized interlayer shift (within six energetically equivalent possibilities). TzF layers, from top to bottom, are depicted in grey, yellow, blue, and green. This structure has been used for SAED calculations.
Layered arrangement and total energy. The structure and relative stabilities of interacting 2D TzF and TzG layers were investigated computationally using a two-layer model. All possible arrangements, including stacked (AA), parallel-displaced
7
(AB), slipped and rotated layers, were considered using various starting geometries. Energetically most stable double-layers of each type (AA, AB and corresponding slipped structures when relevant) are reported in Figure S8 for both TzG (left column) and TzF (right column). The slip structures obtained from AA by small shift in ab plane were found to be the most stable arrangements for both TzF and TzG 2D materials. In case of TzG double-layer, this structure is significantly more stable than any other arrangement (by at least 0.5 eV) and it is thus the likely structure of 2D TzG, if that is formed experimentally. However, 2D TzG is thermodynamically significantly less stable than 2D TzF (16 eV at the DFT level). In case of TzF double-layer there are two energetically stable arrangement – AAslip and ABslip – that differ by only 0.07 eV. Calculations carried out at 0 K and in vacuum found AAslip arrangement to be energetically below ABslip one, however, the presence of solvent in the void space and increased temperature will favor ABslip arrangement over the AAslip one. Indeed, the SAED patterns given in Figure 3 show good agreement between experimental data and those calculated for ABslip layer arrangement. Table S4. Total energy for the different stacking of TzG. TzG Total energy (eV)
monolayer -616.4033
AB -1233.5238
AA -1233.9696
AA_slip -1234.4627
AA’ -1233.0554
AA’’ -1232.9470
AA’’’ -1233.0089
AA’’’’ -1233.18795824
Table S5. Total energy for the different stacking of TzF. TzF Total energy (eV)
monolayer -324.55663576
AB -650.17041046
AA -649.79395792
8
AA_slip -650.30994424
AA’ -650.22632114
AA’’ -650.11010032
Figure S8. Energetically most stable arrangements (AA, AB, and slip) of TzG and TzF double layers. Upper and lower layers are depicted in grey and yellow respectively (nitrogen atoms in upper layer are depicted in blue). Interaction energies per monomer unit are also given. Black insets shows SAED patterns calculated for each of the arrangements. All scale bars correspond to 1 nm-1.
9
Band gap and position of the band edges. For the water splitting reaction, the redox potential depends on the pH value. The standard reduction potential for H+/H2 was calculated by:
E Hred / H 4.44 0.059 pH 2
and the oxidation potential for O2/H2O was calculated by:
EOox2 / H 2O 5.67 0.059 pH The calculated band gap for TzG and TzF are 1.95 eV and 2.54 eV, respectively (Figure S9). The reduction and oxidation potential is inside the band gap. The position of band edge (HOMO and LUMO) indicate that both the materials are candidates for water-splitting photocatalysts without an external bias voltage.
Figure S9. Band Structure and density of states (DOS) plot for (a) TzF and (b) TzG. The Fermi level is set to zero. A comparison of the calculated electronic band structure with the experimental XPS valence band spectrum shows a good agreement up to a binding energy of 15 eV, except for the presence of a feature around 0.7 eV (for TzF) 1.1 eV (for TzG) in the theoretical spectrum (Figure S10). This feature corresponds to 2p orbitals nearly orthogonal to the aromatic plane. Due to very low overlap between the initial pπ state and free photoelectron wave functions, such orbitals are known to have anomalously low photoionization cross sections in c-axis orientated layered materials, such as graphitexi, h-BN,xii and TGCN.xii Calculations were performed using the PBE functional and plotted with a smearing width of 0.2 eV.
Figure S10. XPS spectrum of the valence band region of the TzF/TzG heterostructure (black circles) and calculated XPS plots for the theoretically determined equilibrium structure of (a) TzF and (b) TzG showing the sigma-component of the density of states (DOS) in blue, the pi-component in red, and the sum of all contributions (s, p, d) in black. For scanning force microscopy (SFM) the samples were prepared by: a) mechanical exfoliation and b) spin coating from sonicated solution. For a), the copper foil coated with layers of TzF/TzG was firmly pushed onto adhesive tape (Nitto Semiconductor Wafer Tape SWT 10+R) so that several flakes stuck to the tape. The flakes were then inspected in an optical microscope. Flakes with optically flat surfaces were further imaged with SFM. For b) The CH 2Cl2/H2O mixture solution
10
(40 µL) containing TzF/TzG after ultrasonication was deposited on a glass substrate rotated at 1200 rpm by a spin-coater at room temperature in air. Three samples for each sample preparation method were imaged with SFM. The samples prepared as described above were then transferred to the scanning force microscope. For imaging an SFM (Bruker Nano GmbH, Multimode VIII controller) equipped with E-Scanner was used. The cantilever was of the type “SNL – 10” with a nominal tip radius of 2 nm and spring constant of 0.12 N m-1. Imaging was performed in contact mode. Large scale images revealed terraced topography. High resolution imaging of the flat terraces in contact mode revealed periodic structures (Table S6). Several contact mode images were taken on one flat area. Both friction and topography channels were recorded (Table S6). Friction images showed typically a clearer contrast. To obtain the unit cell of the periodic structure, the contact mode images were processed further with the software “SPIP” by “Image Metrology”. The images were Fourier-transformed using the “Fast-Fourier-transformation algorithm”. From the Fourier transformation the lengths a and b of the two vectors of the unit cell as well as the angle in between were obtained and their average and standard error was calculated (Table S6). Muscovite mica (Ratan mica Exports, grade V1, optical quality) was imaged in contact mode for piezo calibration. The unit cells are same within the error for both sample preparation methods (Table S6). Averaging over all samples gives a hexagonal unit cell with: a = b = 0.54 ± 0.01 Å (range of 0.50 to 0.60 Å), and = 60 ± 2°. The correlation between distances obtained via SFM and the observable crystallographic motifs is not trivial. A number of distances between aromatic bridges is on the order of (6-7 Å) and aromatic units of adjacent layers are 5-6 Å apart. We have two hypothesis as to the poor correlation of these distances: (1) It is expected that at SFM imaging conditions (room temperature and ambient atmosphere) layers of 2D TzF can become corrugated. As a result, lateral distances become apparently shorter. (2) For the same reason as in (1) the smaller unit-cell observed via SFM may correspond to the periodicity of a van der Waals bonded layer of guest molecules (e.g. water, solvent). At any case, SFM corroborates a crystalline, strictly hexagonal bonding motif within 2D TzF layers.
11
Figure S11. (a) Tapping mode image taken on freshly cleaved TzF/TzG heterostructures. The cross section trace (i) is given below in (b). (b) Cross section illustrating examples of flat areas from (a). (c) Contact mode image taken from edge structures of as-synthesized TzF/TzG heterostructures on copper and (d) the corresponding deflection error image. (e) The cross section profile ii and iii shows surface features between 200 and 1000 nm. (f) The unit-cell obtained via SFM (in red,
12
a = b = 0.54 ± 0.01 Å, and = 60 ± 2) is superimposed on the crystallographic unit-cell as obtained via DFT calculations (as dotted, black lines), and the distances correlate in approx. 2:5 ratio.
Table S6. Table shows lengths of the unit cell vectors as well as the angle in between for a series of TzF/TzG heterostructures (mechanically cleaved and after ultrasonic exfoliation) as determined by the Fourier transformation of SFM images. Values do not include the piezo calibration (4% shift to smaller values). The corresponding SFM height images, friction images and FFT images of the friction data are shown on the right. sample ID 3- spin coated.038 3- spin coated.037 3- spin coated.036 3- spin coated.035 3- spin coated.034 3- spin coated.033 3- spin coated.032 3- spin coated.031 3- spin coated.030 3- spin coated.029 Average Standard Error 4 - spin coated.135 4 - spin coated.134 4 - spin coated.133 4 - spin coated.132 4 - spin coated.131 4 - spin coated.130 4 - spin coated.129 4 - spin coated.128 4 - spin coated.127 4 - spin coated.126 Average Standard Error 3- spin coated.082 3- spin coated.081 3- spin coated.080 3- spin coated.079 3- spin coated.078 3- spin coated.077 3- spin coated.076
a / nm
b / nm
angle / °
0.50
0.56
56.9
0.53
0.59
59.3
0.54
0.53
50.1
0.53
0.57
71.4
0.50
0.49
53.9
0.51
0.54
54.2
0.49
0.55
64.0
0.60
0.53
54.1
0.48
0.55
61.7
0.59
0.53
54.0
0.53 0.01
0.55 0.01
58.0 2.0
0.59
0.48
60.7
0.49
0.58
58.8
0.60
0.47
62.6
0.46
0.60
58.0
0.61
0.46
62.3
0.57
0.49
60.6
0.48
0.59
60.9
0.49
0.57
58.1
0.58
0.49
61.6
0.59
0.48
63.3
0.55 0.02
0.52 0.02
60.7 0.6
0.64
0.49
49.1
0.43
0.58
75.8
0.75
0.58
42.8
0.50
0.61
42.8
0.49
0.61
39.2
0.62
0.76
48.0
0.62
0.76
39.0
13
3- spin coated.074 3- spin coated.073 3- spin coated.071 Average Standard Error DSW-Cu-#1039 DSW-Cu-#1038 DSW-Cu-#1037 DSW-Cu-#1036 DSW-Cu-#1035 DSW-Cu-#1034 DSW-Cu-#1033 DSW-Cu-#1032 DSW-Cu-#1031 DSW-Cu-#1030 Average Standard Error DSW-Cu#3.090 DSW-Cu#3.089 DSW-Cu#3.088 DSW-Cu#3.087 DSW-Cu#3.086 DSW-Cu#3.084 DSW-Cu#3.083 DSW-Cu#3.082 DSW-Cu#3.081 DSW-Cu#3.079 Average Standard Error DSW-Cu#1.067 DSW-Cu#1.066 DSW-Cu#1.065 DSW-Cu#1.064 DSW-Cu#1.061 DSW-Cu#1.055 DSW-Cu#1.054 DSW-Cu#1.051 DSW-Cu#1.050 DSW-Cu#1.049 Average Standard Error
0.93
0.61
38.0
0.49
0.60
38.7
0.48
0.58
38.7
0.59 0.05
0.62 0.03
45.2 3.6
0.51
0.68
59.6
0.56
0.45
59.7
0.52
0.68
60.3
0.57
0.45
61.5
0.60
0.48
56.5
0.49
0.63
64.6
0.62
0.50
54.6
0.48
0.62
64.7
0.62
0.50
54.6
0.62
0.50
54.6
0.56 0.02
0.55 0.03
59.1 1.2
0.53
0.66
47.3
0.58
0.49
72.7
0.59
0.47
78.6
0.52
0.66
49.4
0.53
0.67
45.8
0.59
0.49
83.4
0.57
0.53
73.8
0.61
0.46
88.7
0.52
0.68
44.4
0.61
0.50
91.3
0.56 0.01
0.56 0.03
67.5 6.0
0.65
0.39
76.2
0.43
0.79
55.9
0.49
0.69
60.3
0.59
0.43
61.3
0.49
0.73
60.4
0.45
0.84
63.9
0.62
0.37
64.5
0.61
0.37
60.7
0.46
0.69
62.7
0.42
0.58
73.9
0.52 0.03
0.59 0.06
64.0 2.0
14
Cyclic voltammetry (CV) measurements were done according to literature.xiv Cyclic voltammograms were recorded using PalmSens2 (PalmSens, The Netherlands) potentiostat in nitrogen purged solutions at room temperature. A standard three electrode system was employed, using non-aqueous reference electrode (Ag/0.01 mol L–1 AgNO3/1 mol L–1 NaClO4 in acetonitrile), platinum foil auxiliary electrode, and platinum disk working electrode (Metrohm, Switzerland; d = 3 mm). The working electrode was polished routinely before measurements using Al 2O3/deionized water mixture. All chemicals were of analytical grade, if not stated otherwise. Dichloromethane (Scharlau) was used as a solvent, tetraethylammonium tetrafluoroborate (Fluka) as a supporting electrolyte. Anhydrous sodium perchlorate (Fluka) and silver nitrate Ph. Eur. 3 (Fluka) were used in the reference electrode. The monomer (synthon 3, 1.2 × 10–3 mol L–1) was dissolved in dichloromethane containing tetraethylammonium (TEA) tetrafluoroborate (TFB) (0.1 mol L–1) and subjected to voltammetric measurements. The background current was measured for the pure TEA TFB solution. The as grown polymer film TzF/TzG on the copper substrate was subjected to the voltammetric measurements. One side of the copper plate was polished, and the disk was placed in the electrode body (Scheme S2). The working area of the electrode was defined by a Viton gasket. The measurement was done in acetonitrile containing sodium perchlorate (0.1 mol L–1).
Scheme S2. Schematic drawing of the electrode body used for the polymer measurements. (1) Teflon body, (2) conductive contact, (3) conductive spring, (4) disk with the polymer layer, (5) Viton gasket, (6) screw-on head.
15
Figure S12. (a) and (b) Tapping cyclic voltammogram of synthon 3 (3 scans) and the DSW191 polymer (c). Working electrode: platinum disk electrode (a, b; d = 3 mm), and copper plate covered with TzF/TzG vdW heterostructure (c; d = 3.25 mm). Supporting electrolyte: tetraethylammonium tetrafluoroborate (0.1 mol L–1) in CH2Cl2 (a, b; dotted line), and NaClO4 (0.1 mol L–1) in acetonitrile (c). Scan rate 50 mV s–1. Potential given vs. Ag/0.01 mol l–1 AgNO3/1 mol l–1 NaClO4 in acetonitrile. Voltammetric characterization of both the monomer (cathodic and anodic region), and the polymer is depicted in Figure S12a, and b. In the cathodic region there is no observable signal of the monomer (Figure S12a). In the anodic region, however, an earlier onset of the supporting electrolyte current is observed, suggesting an oxidation process (Figure S12b) with relatively high oxidation potential. An irreversible reduction signal is present around +330 mV (Figure S12b). However, it is not a signal typical for azines, which is also irreversible, but usually present at more negative potentials. xv It was shown that cyclic voltammetry can be successfully used for characterization of the band gap energy (Eg,elec).xvi For organic semiconductors, Eg,elec can be considered as the energy difference between HOMO and LUMO. The values of reduction and oxidation potentials can be directly related with conductive conjugated systems HOMO and LUMO.xvii Eg,elec value was obtained by analyzing the onset of the anodic (+1160 mV) and cathodic (–680 mV) current of the cyclic voltammogram depicted in Figure S12c. The electrochemically obtained band gap value is 1.84 eV, which is in good correlation with the optical band gap of 1.91-2.24 eV obtained from the UV/Vis absorption edge. The onset of anodic current visible at around –360 mV at the end of the first cycle is the well-known oxidation of copper substrate, on which the thin film
16
of the polymer was deposited. It was exposed due to decreased stability of the polymer at the Cu substrate when applying high cathodic/anodic potential used for the measurements.
Thermogravimetric analysis (TGA) was performed on a Setsys Evolution 18 with temperature range up to 1750 °C. All samples were measured in an alumina crucible. The speed of temperature increase during the measurement was 5 K min-1.
Figure S13. Thermogravimetric analysis measurements of as-synthesised TzF/TzG heterostructures (black) and TzF/TzG after removal of Cu NPs under measured under air (a) and under nitrogen atmosphere (b).
Argon (Ar) sorption measurements were performed using a Micromeritics ASAP 2020. The sorption isotherm was measured at 88 K with argon. The surface area was calculated in the relative pressure (p/p0) range from 0.05 to 0.35. Pore size distributions were calculated for the adsorption as well as for the desorption branch using the Barrett-Joyner-Halenda (BJH) pore model. The samples were degassed at 90 °C before analysis.
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Figure S14. Pore size distribution of TzF/TzG flakes calculated with BJH for the adsorption branch (a) and the desorption branch (b).
Photocatalysis. Photocatalytic hydrogen evolution experiments were carried out in a jacketed 3-neck quartz reactor with a total volume of 36 mL (Figure S15). 10 mg of catalyst was dispersed in 18 mL water:acetonitrile mixture (1:1) and 2 mL TEOA. The reactor was closed using rubber septa, completely evacuated and purged with argon to remove any air and then irradiated with a 300 W Xe lamp (L.O.T.-Quantum design) equipped with a cut off filter of 395 nm. Headspace volume was calculated to be 16 mL. During catalytic reactions, the temperature was kept fixed at 20 °C using a thermostat. Distance between the reactor and light source was also kept fixed at 10 cm and stirring speed was maintained at 600 rpm. Gas samples from the head space were taken after 15 h of reaction and were analyzed by GC equipped with a TCD detector.
Figure S15. Photos of the reactor (left) catalytic reaction setup (right).
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Figure S16. Photos of the TzF/TzG flakes (left) and the dispersion in water and in a water:acetonitrile (ACN) mixture after sonication (right).
Table S7. Rate of hydrogen evolution for TzF/TzG heterostructures and TzF. 10 mg of polymer was used in each case. Material CoRate of Hydrogen Morpholog catalyst evolution (µmol h-1 g-1) y TzF/Tz G TzF/Tz G TzF
Pt
35
Flakes
None
34
Flakes
Pt
-
Powder
Figure S17. FT-IR spectra of TzF/TzG heterostructures before (black) and after (red) the photocatalytic hydrogen evolution reaction.
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Quantitative electron paramagnetic resonance (EPR) analysis was performed on an EMXplus CW (continuous wave) EPR spectrometer (Bruker, Germany) equipped with the Premium-X-band microwave bridge. The gcenter-factor (where dIEPR/dB = 0) of Cu2+ and radical centers was determined using a built-in spectrometer frequency counter and an ER-036TM NMR-Teslameter within a standard rectangular EPR cavity, ER-4102003-ST (all Bruker, Germany). Quantitative EPR analysis was carried out within the ER-105000-DR double rectangular cavity using the Bruker "strong pitch" reference sample with known number of radicals, 3·1015 spins / effective cm (tube length). A second identical EPR tube was used for analyzed sample. In order to provide the filling factor as closed as possible for both samples, tubes were filled and positioned within the effective EPR cavity volume in the same manner. Following experimental parameters were used for quantitative measurements: microwave frequency = 9.8176 GHz, central field = 320 mT, sweep width = 240 mT, receiver gain = 1.6·104, modulation amplitude = 0.14 mT, modulation frequency = 100 kHz, power = 3.99 mW, resolution 4801 points, conversion time = 24.0 ms and time constant = 10.2 ms. Several sweep/accumulations were applied in order to enhance the signal-tonoise ratio (S/N). Simulations and computations of the EPR spectra were performed within a MATLAB toolbox EasySpin v. 5.1.10 by leastsquare fitting to an experimental spectrum using a combination of Nelder-Mead simplex and Particle swarm algorithms.xviii Deconvolution of an EPR spectrum was done as follows. At first, an experimental spectrum with relatively higher S/N-ratio was used to run the simulation taking into account two different Cu2+ paramagnetic centers to obtain the g and A principal values as well as the "weight" (composition coefficient) of individual components (see also Table S8). Their linear combination therefore results in EPR spectrum consisting of both "copper"-parts. Second, a third component was considered, corresponding to single radical EPR line. Finally, the sum represents the simulation of the overall powder spectrum (see also Figure S18). Such deconvolution enabled to evaluate the double integrals, and subsequently to determine the number of paramagnetic species (Nparmag), for all three components individually. In order to determine the Nparmag,SAMPLE the double integral (DISAMPLE) was compared to that of reference sample (DIREF) with known number of paramagnetic centers (Nparmag,REF):
(1) where mSAMPLE denotes the sample weight in mg. Such calculation requires, that the EPR spectra of both solid-state samples (the analyzed and the reference one) are recorded at the same experimental conditions with the same EPR tube geometry. xix Therefore, as mentioned-above, the reference sample (in this case, we used the Bruker "strong pitch") as well as the TzF/TzG sample were inserted into double EPR cavity within identical EPR quartz tubes. Eight independent measurements, within the double rectangular cavity, were carried out in order to determine the mean value and the 95 % confidence interval of the mean of double integral ratio from the Equation 1. Confidence interval was calculated considering the Student's t-distribution of variable for the 7 degrees of freedom (DOF). The uncertainty of Nparmag for TzF/TzG was evaluated by error propagation using Equation 1 knowing the uncertainties of sample weight (± 1 mg), of radical number in strong pitch (± 4.5·1014)xix and that of double integral ratio as mentioned-above. The mean value of DIratio and the corresponding uncertainty were evaluated for each spectral component (i.e. for two Cu 2+-components as well as for the radical one) from eight spectral simulations, searching the "weight" of the individual components. The values are summarized in Table S8. Qualitative EPR analysis of TzF/TzG flakes. Taking into account the structural information, at least two types of paramagnetic copper centers can be considered within the material. Additionally, we also found radical species, coming from organic framework of the material. Mean values of the composition ("weight" of the individual components used in EPR simulations) of EPR spectra corresponding to Cu2+ (A), Cu2+ (B) and Radical (R), respectively are presented in Table S8 together with corresponding EPR parameters. Table S8. Parameters of individual spectral components, obtained from simulations of the experimental EPR spectra. g1
g2
g3
A1 / MHz
A2 / MHz
A3 / MHz
composition
Cu(A)
2.2317
2.0965
2.0595
456.42
41.71
18.32
0.2292
Cu(B)
2.2788
2.1465
2.0718
549.72
207.91
1.11
0.7680
Radical(R)
2.0036*
0.0018
*The width of the radical component was rather narrow (∆Bpp=0.65 mT), therefore the anisotropy of this component was neglected. The corresponding EPR line could not be resolved even at low modulation amplitudes (down to 0.04 mT).
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Figure S18. Experimental EPR spectrum (black line) of the TzF/TzG sample. Simulated spectrum ("Sim. Sum", cyan line), which is the sum of individual components coming from two types of paramagnetic copper species: "Sim. Cu 2+ (A)" and "Sim. Cu2+ (B)", red and blue line, respectively and the "radical" component "Sim. Radical", green line.
Quantitative EPR analysis of TzF/TzG flakes: Determination of number of paramagnetic species (Nparmag) of individual components. The number of paramagnetic species for each component was computed by method already introduced in Computational Section. The simulation of eight experimental EPR spectra by EasySpin toolbox enables the deconvolution of a spectrum as already shown in Figure S18. Therefore, one can determine the mean values and uncertainties for all three components as presented in Table S9 and Figure S19.
Table S9. Number of individual paramagnetic centers within the TzF/TzG material. Component Cu2+
Nparmag per mg of sample
(A)
(1.0 ± 0.2)·1014
Cu2+ (B)
(3.2 ± 0.5)·1014
Radical (R)
(7 ± 1)·1011
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Figure S19. Number of individual paramagnetic species for Cu2+ (A), Cu2+ (B) and Radical (R) (from top to bottom) for each EPR experiment. Error bars represent the uncertainties.
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Device fabrication. TzF/TzG based devices were prepared as follows: a quartz-coated glass substrate (Ossila, Ultra-flat Quartz Coated Glass, 20 x 15 x 1.1 mm) was cleaned with a cleaning agent Hellmanex®III, DI water, and isopropanol. Side areas of the substrate were masked with a dicing tape to reserve space for contact pads of the source electrodes. Deposition of metals was performed using custom-made Elettrorava S.p.A. vacuum (
