Zeolitic intralayer microchannels of magadiite, a natural layered silicate, to boost green organic synthesis

We discovered unexpected intralayer microchannels of magadiite, a natural layered silicate, and used it as additive in a TiO2 photocatalytic system oxidizing toluene to realize efficient and selective synthesis of benzoic acid not achieved by conventional photocatalysts.


Detailed Methods
Preparation of materials. Na-magadiite was purchased from Nippon Chemical Industrial and used as received. The quality of the sample was confirmed by X-ray diffractometry (XRD), which shows a typical pattern for Na-magadiite (Fig. 1, Fig. S1 and S2) [1][2][3] . We determined the composition by the inductively coupled plasma optical emission spectroscopy (ICP-OES) using Hitachi HT ICP-OES SPS3520UV-DD for Na and Si ions ( Table S1) and thermogravimetric analysis (TGA) using Hitachi HT-Seiko Instrument Exter 6300 for H 2 O (Fig. S3). The Na/Si molar ratio is in good agreement with those reported in the literature 1,4 . Na-magadiite exhibits endothermic weight losses: (i) ~13 wt% loss from room temperature to 160°C, and (ii) gradual 1.9 wt% loss up to 700°C. The former appears to consist of two steps and is consistent with previous reports [3][4][5][6] .
The protonation of Na-magadiite and Na-octosilicate was carried out based on previous reports 7, 8 . The composition analysis confirms the almost complete removal of Na ions from Namagadiite (Table S1). The TGA profile exhibits a typical one for H-magadiite 5 ; weight losses: (i) ~0.6 wt% loss from room temperature to 200°C, (ii) ~3.1 wt% endothermic loss from 200°C to 440°C and (iii) gradual ~1.3 wt% endothermic loss up to 1000°C (Fig. S3).
The composition of Na-magadiite was thus determined to be Na 1 (Fig. S4) solid NMR spectrometer using a 6-mm diameter zirconia rotor. The magic-angle spinning (MAS) spectrum of Na-magadiite indicates the Q 3 /Q 4 peak integral ratio of 38.8/61.2, whose Q 3 Si was confirmed to be protonated through the comparison with cross-polarization (CP) spectrum where Q 3 /Q 4 increased obviously (Fig. S4). Likewise, MAS NMR spectrum of H-magadiite indicates the Q 3 /Q 4 ratio of 28.5/71.5. The Q 3 /Q 4 ratios for Na-magadiite and H-magadiite are within reported values 1,2,9 and in good agreement with the reported values 7,9 , respectively. The discrepancy in the Q 3 /Q 4 ratio between Na-magadiite and H-magadiite probably originates from partial condensation reactions between hydroxyl groups during the protonation of Na-magadiite 1 . Likewise, solid-state 1 H NMR spectra of Na-magadiite and H-magadiite were recorded (Fig. S5).
The infrared spectra were measured using Thermoscientific Nicolet 4700 spectrometer in the transmission configuration for the samples pelletized with KBr powder. Fig. S6 shows IR spectra of Na-magadiite and H-magadiite. The spectra were normalized on the basis of the peak assignable to Si-O-Si asymmetric stretching (1000-1130 cm -1 ). Na-magadiite exhibits a typical spectrum reported in the literatures 1,2,10,11 . The spectrum for Na-magadiite has a large H-O-H bending band (1630 and 1660 cm -1 ) than that for H-magadiite, and only the former has a sharp O-H stretching band at 3660 cm -1 . These features can be explained by that Na-magadiite adsorbs a larger amount of water than Hmagadiite as a result of interaction between Na + ions and water molecules. 5,6,11 .

S4
The crystal morphology of Na-magadiite was observed using a Hitachi S-4800 scanning electron microscope (SEM). Na-magadiite was composed of platy particles that form rosette (cabbage)-like spherical aggregates with several µm diameter (Fig. S7), a well-known characteristic of Na-magadiite 1 .
X-ray PDF measurements. X-ray total scattering data for obtaining pair distribution functions (PDFs) were collected on a Rigaku Rapid-S curved imaging plate detector with Ag Kα radiation (λ = 0.556 Å) for screening structure models initially. The samples were sealed in Cole-Parmer polyimide capillaries (inner diameter: 1.0 mm). These corrected intensities were normalized by the Faber-Ziman type scattering form factors calculated using atomic scattering factors to obtain structure functions, S(Q). The S(Q) (Q max = 21.0 Å -1 ) was treated with a revised Lorch function (Δ = 1.00) 12 , and then converted into reduced PDF, G(r), where r is the interatomic distance.
High-resolution PDF data was obtained using synchrotron irradiation at BL22XU (λ = 0.1774 Å) and BL08W (λ = 0.1076 Å) in SPring-8 with a Perkin Elmer flat panel detector (XRD1621). The former results in PDFs with reasonably good spatial resolution, Q max = 25.5 Å -1 , and also good angular resolution enabling analysis of long-range region in real space. The latter results in PDFs with high spatial resolution, Q max = 33.0 Å -1 , but with little angular resolution.

Details of structure analysis.
The structure was analyzed by the curve fitting of PDF data simulated using the PDFfit2 program 13 .
Since the structure of magadiite was unknown, hundreds of structure models which can also correspond to other data such as compositions, NMR spectra and infrared spectra were investigated.
For some of those structure models, atomic coordinates were moved to fit the experimental PDF data using a code running the real-space Reverse Monte Caro simulation 14  program. Hundreds of structure models were screened and investigated as initial models, and then reasonable models were gradually selected. For the structure model reaching R w < 0.35, symmetry of the structure was analyzed and then further refinements were carried out under the symmetry constraints. The initial symmetry used for the analysis was P2 1 space group, which was based on literatures where the symmetry of the Namagadiite considered to be monoclinic 1 . However, during further investigations, we found the symmetry of local structure should be in the P space group to reach better fit. Considering the 1 reasonable fit of PDF data and XRD data of H-magadiite, the symmetry of the structure is reasonable at least in the local structure, though symmetry in crystal level might be different (but both Hmagadiite and Na-magadiite contain disorders such as turbostratic stacking disorder and stacking faults, which have been keeping the structure unknown, and thus, our approach to determine local symmetry is reasonable). The crystals of magadiites were found to contain stacking disorders as expected from the layered structure and furthermore we found zeolitic micropores in the layers where    H-magadiite are assigned to the interlayer silanol groups (strongly and weakly interacted SiOH, respectively). 17 Other peaks are assignable to H 2 O molecules. 16,17 The integral ratio of peaks associated with the SiOH groups for H-magadiite to that for Na-magadiite is 2.3.

Structure information
We solved the structures in the unit cells shown below. Then, for the clear comparison, we transform the cell of the H-magadiite to have the similar beta value as shown in the main text.