Hot-Pressing Method To Prepare Imidazole-Based Zn(II) Metal

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Applications of Polymer, Composite, and Coating Materials

Hot-pressing Method to Prepare Imidazole-based Zn(II) Metalorganic Complexes Coatings for Highly Efficient Air Filtration Ani Wang, Ruiqing Fan, Xuesong Zhou, Sue Hao, Xubin Zheng, and Yulin Yang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b01287 • Publication Date (Web): 05 Mar 2018 Downloaded from http://pubs.acs.org on March 6, 2018

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ACS Applied Materials & Interfaces

Hot-pressing Method to Prepare Imidazole-based Zn(II) Metal-organic Complexes Coatings for Highly Efficient Air Filtration

Ani Wang, Ruiqing Fan,* Xuesong Zhou, Sue Hao, Xubin Zheng and Yulin Yang*

KEYWORDS: Metal-organic complexes, Hot-pressing, Coatings, DFT Calculations, Air Filtration

MIIT Key Laboratory of Critical Materials Technology for New Energy Conversion and Storage, School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin 150001, P. R. of China Corresponding Author: * Ruiqing Fan and Yulin Yang E-mail: [email protected] and [email protected] 1

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ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ABSTRACT: Particulate matters (PMs) air pollution has become a serious environmental issue due to its great threat to human health. Herein, metal-organic complexes PBM-Zn1 and PBM-Zn2 coatings (noted as PBM-Zn-Filter) have been produced by hot-pressing method on various substrates for the first time. Layer-by-layer PBM-Zn-Filters were also obtained through varying hot-pressing cycles. The obtained PBM-Zn-Filters with high robustness show excellent performance in PMs removal. Especially, benefiting from larger conjugation system, micropore structure, lower pressure drop, higher electrostatic potential ζ and electron cloud exposed metal center of PBM-Zn2 (DFT calculations), PBM-Zn2@melamine foam-4 gives the highest removal rates, PM2.5: 99.5% ± 1.2% and PM10: 99.3% ± 1.1%, and the removal efficiency for capture PM2.5 and PM10 particles in cigarette smoke were both retained at high levels (>95.5%) after 24 h tests. More importantly, a homemade mask is made-up by imbedding the PBM-Zn2@melamine foam-4 into a commercial breathing mask, which shows higher removal efficiency, lower pressure drop, smaller thickness and higher quality factor than two commercial breathing masks, the PMs removal efficiencies for both PM2.5 and PM10 are 99.6% ± 0.5%, 99.4% ± 0.8%, and acceptable air resistance are demonstrated.

INTRODUCTION As the most severe urban pollutants in air, suspended particulate matters (PMs)

have been of particular concern in the recent decades due to their influence on climates and human health.1-2 Especially in developing countries like China, PMs, as a major air pollution source, have become one of the most serious environmental 2


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problems.3-5 PM2.5 and PM10, PMs with an aerodynamic diameter less than 2.5 and 10 µm, can cause irreversible harm to human health.6-9 The PMs exhibit longer residence time in air and larger specific surfaces,10 which can lodge deeply into human respiratory systems upon inhalation, and even a short-term exposure could lead to risks of cardiopulmonary morbidity and mortality as well as reduced life expectancies.11-13 Government of China has forced the regulation on the annual average PMs levels (PM2.52σ(I)] 0.0479, 0.1319 R1, wR2[all data]a 0.0859, 0.1589 ∆ρmax, ∆ρmin [e·Å–3] 1.167, -0.515 [a] R1 = ∑||Fo| – |Fc||/∑|Fo|; wR2 = [∑[w (Fo2 – Fc2)2]/∑[ w (Fo2)2]]1/2.

Hot-pressing method to prepare PBM-Zn-Filters Metal-organic complexes crystals are brittle by natural and can easily break into fine powders; therefore, fabrication of metal-organic complexes into robust devices is required before they can be widely adopted in highly efficient air filtration. The fabrication of PBM-Zn-Filters followed the hot-pressing method,39 which was proven to be suitable for imidazolate-based, carboxylate-based, and mixed-metal MOFs. Significantly, our imidazolate-based metal-organic complexes PBM-Zn1 and PBM-Zn2 can be prepared by hot-pressing under lower temperature (80 °C) and 11



shorter times (5 minutes) owing to easier synthesize process of PBM-Zn.41-43 In addition, we made an improvement: replaced electric iron with hair straightener to keep the upper surface and undersurface heated consistently. Taking preparation process of PBM-Zn1@carbon fiber cloth for example: carbon fiber cloth (0.111 mm in thickness, 10 cm in width) was first covered with PBM-Zn1 precursors (mixture of ZnCl2·2H2O, 2-carboxaldehyde-1,10-phenanthroline: o-phenylenediamine (1:1), and polyethylene glycol (as the initiator, MW: 4000, denoted as PEG-4000)), after that, all the components were packed with a piece of aluminum foil, pressed between the two straight panels and then heated with an hair straightener at 80 °C for 5 minutes (Figure S3, Supporting Information). PBM-Zn1 crystals were generated on the wires of the carbon fiber cloth after pressing back-and-forth for several times, as evidenced by scanning electron microscope (SEM), powder X-ray diffraction (PXRD), and elemental mapping analysis (Figure 3). Similarly, PBM-Zn2 coating was obtained under similar conditions (2-carboxaldehyde-1,10-phenanthroline: o-phenylenediamine (2:1)) (Figure S4, Supporting Information). After peeling off the aluminum foil, the slice was washed with ethanol and DMF (each for 1 h) and stored in ethanol. Then it was pre-dried at 80 °C for 30 min prior to use for characterizations. Therefore, it seems that components of the ligand mixed with the zinc salt formed in the process can be washed with ethanol and DMF. Notably, PEG played the part of enhancing the initial diffusion of ZnCl2 and promoting rapid growth of the PBM-Zn1 crystals, after synthesis, the residual PEG could be removed. The stability of PBM-Zn1 and PBM-Zn2 against DMF was ensured by the similarity between the powder XRD 12


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patterns of the as-synthesized PBM-Zn1 and PBM-Zn2 before and after being immersed in DMF solvent for 24 h (Figure S5, Supporting Information).

Figure 3. (a) SEM image of original carbon fiber cloth. (b) SEM image of PBM-Zn1@carbon fiber cloth. (c) The enlarged image of the square box in b. (d) The enlarged image of the square box in c. (e) Elemental mapping analysis of the PBM-Zn1@carbon fiber cloth. (f) Pictures of Zn, Cl, N and C mapping analysis of PBM-Zn1@carbon fiber cloth.

13



Different loadings As mentioned above that PBM-Zn1 crystals were generated on the wires of the carbon fiber cloth after pressing, to find out the best loadings, we adjusted loadings through varying the hot-pressing cycles, and obtained different loadings of PBM-Zn@carbon fiber cloth: with one coating layer (PBM-Zn1@carbon fiber cloth-1) to five coating layers (PBM-Zn1@carbon fiber cloth-5). From the first to five cycles, the distribution of PBM-Zn1 crystals on the carbon fiber cloth shows a clear trend from sparse to dense (Figure 4a–k) and the loadings of PBM-Zn1 rises from 43 to 186 mg g−1 (Figure S6, Supporting Information). After five cycles, the thickness (about 0.115 mm) of the carbon fiber cloth are almost unchanged, the loading of PBM-Zn1 crystals have negligible effect on the carbon fiber cloth (even after five cycles). In addition, we tested the pressure drop of the different loadings coatings and find that pressure drop increases with the number of different loadings, especially, from the first cycle to the fourth cycle, there was a flat increase trend, but the fifth cycle showed dramatic increase (Figure S7, Supporting Information). Therefore, consider these two aspects loadings and pressure drop, the fourth coating layers is considered the most appropriate point for PMs removal.

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Figure 4. (a) Schematic representation of layer-by-layer fabrication of PBM-Zn1 crystals coatings. (b–k) SEM images of the PBM-Zn1@carbon fiber cloth achieved during five cycles. The bottom images are the zoomed-in images of the square boxes in the corresponding images.

Hot-pressing on various substrates For further research on the better material for PMs removal, specifically, we selected three other cheap, commercially, available and ﬂexible substrates (melamine foam, glass cloth, plastic mesh) to make it applied on various substrates. Conducted with the same preparation procedures, PBM-Zn@melamine foam, PBM-Zn@glass cloth, PBM-Zn@plastic mesh were prepared (PBM-Zn1 and PBM-Zn1 noted as PBM-Zn). The PBM-Zn particles are well attached on the surfaces for all of the substrates, the structural of PBM-Zn are in accordance with that of hydrothermal synthesis, which are well demonstrated by the SEM images, FT-IR, and powder X-ray diffraction (Figures 5 and S8–12 in the Supporting Information). For instance, the composite materials of PBM-Zn1@carbon fiber cloth was characterized by Fourier transform infrared spectroscopy (FT-IR) and the spectra are shown in Figure 6a. Some 15



new peaks emerging and the main new peaks is at 480 cm-1, which indicated the existence of O–Zn functional groups between carbon fiber cloth and PBM-Zn1. The PXRD reflection of the obtained composite materials corresponds well with the simulated pattern (Figure 6b). As shown in XPS measurement, a new O1s peak appeared at 530.3 eV can attributed to O–Zn (C–O is from the carbon cloth after and Zn is from the PBM-Zn) for carbon cloth treated with hot-pressing; such a peak was absent for solvothermal-treated carbon cloth (Figure 6c-e). Notably, among these four substrates, melamine foam and carbon fiber cloth show better loading performance for PBM-Zn, particles attached on the surfaces more uniformly and show higher loading than that of others (Figure S6, Supporting Information). But in consideration of pressure drop of carbon fiber cloth is much higher than that of melamine foam (Table S3, Supporting Information), we chose the PBM-Zn@melamine foam as the most suitable material for PMs removal. Finally, comparing with PBM-Zn1, PBM-Zn2 possess the larger conjugation system, micropore structure, lower pressure drop and higher electrostatic potential ζ. Taken together, PBM-Zn2@melamine foam-4 is the best material for PMs removal.

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Figure 5. (a) SEM images of the carbon fiber cloth, melamine foam, plastic mesh, glass cloth. (b) Photos of the carbon fiber cloth, melamine foam, plastic mesh, glass cloth. (c) SEM images of the carbon fiber cloth@PBM-Zn1, melamine foam@PBM-Zn1, plastic mesh@PBM-Zn1, glass cloth@PBM-Zn1. (d) A magnified image of the square box in (c).

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Figure 6. (a) Infrared spectra (b) PXRD spectra of carbon fiber cloth, PBM-Zn1 obtained from solvothemal and hot-pressing method, PBM-Zn1@carbon fiber cloth. (c) XPS analysis results of O1s for untreated carbon cloth. (d) PBM-Zn1 treated carbon cloth with solvothermal method. (e) PBM-Zn1treated carbon cloth with HoP method..

The mechanical stability of PBM-Zn-Filters For the reliable PMs removal, the property of the PBM-Zn-Filters should be durable against various mechanical deformations which may be introduced during typical installation, maintenance, and operation processes. Mechanical stability of PBM-Zn-Filters performed through scratching with sandpaper or adhesion with adhesive tape. Compared with PBM-Zn obtained by using the traditional, PBM-Zn obtained by using the hot-pressing method can maintain their structures and 18


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morphology (Figures S13 in the Supporting Information). Another example was PBM-Zn1@melamine foam-4 (2 cm in thickness, 156.6 mg g−1 for PBM-Zn1 loading), which can tolerate bending and twisting each for 200 times with negligible weight loss (Figures S14 in the Supporting Information); it can also maintain its weight and shape after a mechanical stirring test (1 h) which simulates the condition of a combination of collision and pressing (Figure S15, Supporting Information). Such high robustness illustrates strong affinity between the PBM-Zn and the substrates. The high robustness of these PBM-Zn-Filters sets fundamental basis for PMs removal. Driving forces of the PBM-Zn-Filters for Particulate Matter Removal According to the recent research, particulate matters is highly polar, because it contains various organic matter, elemental carbon, sulfate, chloride, ions, nitrate, ammonium, and water vapor, thus, the surface charge of metal-organic complexes can effectively enhanced the adhesion with the particulate matter.20-21 The unbalanced metal ions or open metal site on the surface of metal-organic complexes offer the positive charge improving the electrostatic interactions and thus can polarize the surface of PMs. To elucidate the driving forces of the PMs onto filters, firstly, we measured the electrostatic potential ζ of PBM-Zn1 and PBM-Zn2 which were dispersed in ethanol. Significantly, with a relative high ζ potentials of PBM-Zn1 and PBM-Zn2 are 52.4 and 58.5 mV, respectively, which are higher than that of common MOFs, for instance: ZIF-8 (47.5 mV), MOF-199 (3.1 mV).7 In addition, DFT calculations was conducted 19



by DFT/B3LYP/lanl2dz to analysis orbital distributions of the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO) of PBM-Zn1 and PBM-Zn2 (Figure 7).55-58 From X-ray diffraction analyses of PBM-Zn1 and PBM-Zn2, we obtained their optimized molecular structures. Therefore, information about their electron density distributions, energy gaps, energy levels of HOMO and LUMO based on the calculated optimized molecular structures were also obtained. For PBM-Zn1 and PBM-Zn2, the HOMO and LUMO electron density electron density are both mainly placed on the ligands, indeed, it reveals Zn atom participate a lesser electron cloud distributions, which are well demonstrated PBM-Zn1 and PBM-Zn2 are the highly polar molecules and the metal ions are exposed to the outside of the electron cloud, so that the molecules can be considered positively charged part (δ+) and negative charge part (δ-), positively charged part to attract electronegative PM and negative charge part to attract electropositive PMs. Considering all above effects, PBM-Zn1 and PBM-Zn2 are promising materials for PMs removal. To some extent, larger conjugation system and coplanarity, high electrostatic potential ζ and electron cloud exposed metal center of are the criteria for an ideal material for PMs removal. According to the literatures, the polar functional groups including N and O (C=O, C–N and C–O) on the surface of PMs accompanied by nonpolar functional group (alkanes). This is consistent with the result that PBM-Zn1 and PBM-Zn2 air filters with higher ζ potentials metal ions are exposed to the outside of the electron cloud have higher PMs capture efficiencies. Owing to the polar functional groups such as 20


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C=O, C–N and C–O were present on the surface of the PM particles, PBM-Zn1 and PBM-Zn2 air filters with higher ζ potentials metal ions are exposed to the outside of the electron cloud can have stronger electrostatic attraction so that the PMs capture efficiency is higher.

Figure 7. Theoretically calculated orbital distributions and energies of the HOMO and LUMO levels of PBM-Zn1 and PBM-Zn2.

Removal efficiency in a real polluted air environment Practical application of our filters in a real polluted air environment was carried out a field test on 25 October 2017 in Harbin, China. The concentration of PMs on that day was at a hazardous level equivalent (PM2.5 > 500 µg m−3 and PM10 > 800 µg m−3). The PMs removal efficiency for PBM-Zn on different substrates was conducted, these eight kinds of PBM-Zn-Filters show high PM removal efficiency: PBM-Zn1@melamine foam-4 = 99.3% ± 1.6%, 99.1 ± 1.4%, PBM-Zn2@melamine foam-4 = 99.5% ± 1.2%, 99.3 ± 1.1%, PBM-Zn1@carbon fiber cloth-4 = 98.2% ± 21



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1.1%, 98.1% ± 1.2%, PBM-Zn2@PBM-Zn1@carbon fiber cloth-4 = 98.3% ± 1.4%, 98.2% ± 1.4%, PBM-Zn1@glass cloth-4 = 96.5% ± 1.2%, 96.2 ± 1.3%, PBM-Zn2@PBM-Zn1@glass

cloth-4

=

96.7%

±

1.5%,

96.3

±

1.2%,

PBM-Zn1@plastic mesh-4 = 91.4% ± 1.3%, 91.0% ± 1.5% and PBM-Zn2@glass cloth-4 = 92.3% ± 1.2%, 91.0% ± 0.8% for both PM2.5 and PM10 after constant wind velocity (2.04 m s−1) (Table S3, Supporting Information). The thicknesses of these eight PBM-Zn-Filters (five pieces) tested with a Vernier caliper were 5.52, 5.51, 0.45, 0.43, 1.16, 1.17, 1.34 and 1.33 mm and can retain its weight (weight loss < 0.11 wt% per cycle). Analysis of the above results show that PBM-Zn2@melamine foam-4 outperforms that of others and presents excellent PMs removal efficiency (PM2.5: 99.5% ± 1.2%, PM10: 99.3% ± 1.1%) compared with bare melamine foam (PM2.5: 79.6% ± 1.2%, PM10: 82.3% ± 1.6%). The high efficiency of PBM-Zn2@melamine foam-4 filter can be maintained even after 8 h exposure to polluted air (Figure S16, Supporting Information), which is a good illustration of its better capture ability and stronger binding affinity. Removal efficiency in cigarette smoke Consider the excellent properties of PBM-Zn2@melamine foam-4, the PBM-Zn2@melamine foam-4 filter was also employed to capture the particles in cigarette smoke (Figures 8a). For generating the burning incense, we designed the rigid container instead of plastic bags. We examined it under simulated real application conditions. In a simulated system, the burning incense contains PM above PM2.5 > 1000 µg m−3 and PM10 > 1500 µg m−3 burned, and the exhaust smoke 22


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contains a variety of pollutant gases, including NO2, CO2, CO, SO2 and also volatile organic compounds, such as toluene, benzene, aldehydes, polycyclic aromatic hydrocarbons and xylenes,59 which was filtered through PBM-Zn2@melamine foam-4 filter further recorded by a camera, and a particle counter was used to detect the PMs mass concentrations left and right of the simulated system (Figure 8b, 8c). The filter is located in the connection tube. The electric fan is put on the lower right corner to help the air pass through the filter at a constant velocity (2.04 m s-1) and make sure that almost entire air in the dirty chamber comes to the contact with filter. The removal efficiency of PBM-Zn2@melamine foam-4 filter for PM2.5 and PM10 were both retained at high levels (>95.5%) after 24 h tests (Figure S17, Supporting Information). SEM images of Figure 8d-i show the PBM-Zn2@melamine foam-4 filter before and after PM capture. The color of PBM-Zn2@melamine foam-4 changed from white to yellow after the test, with a 2.3 wt% increase in weight (Figure S18, Supporting Information). Further description of the targeted air pollutants is conducted with dynamic light scattering (DLS) experiments60-62 in H2O solution. From particle size analysis in DLS experiments for targeted air pollutants, we observe the average size of the pollutants is about 350 nm (Figure S19, Supporting Information). The tested PBM-Zn2@melamine foam-4 filter can be simply cleaned after washing with water and ethanol, followed by drying at room temperature for 10 min (Figure S18c, Supporting Information). PBM-Zn2@melamine foam-4 filter can retain its weight (weight loss < 0.15 wt% per cycle), structure, morphology, and PM removal efficiency after three capture washing cycles. As has been shown, such 23



ﬂexible, robust, and processable PBM-Zn2@melamine foam-4 filter with high PM removal efficiency is promising to be used as filters in filtration systems for PMs removal.

Figure 8. (a) Demonstration of the PMs removal capability of the PBM-Zn2@melamine foam-4 filter in the simulated polluted environment. The smoke was generated by the cigarettes burning. (b) An electric fan on the side of the filter and wind velocity indicator (2.04 m s-1). (c) PMs particle counter and the PMs concentration of the smoke. (d-i) SEM images of the PBM-Zn2@melamine foam-4 filter before and after PMs capture.

Performance under different wind force and humidity In the real weather situation, wind force and humidity should be taken into consideration. On one hand, the PBM-Zn2@melamine foam-4 filter was tested at 24


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different wind force representing calm (0.18 m s-1), light breeze (2.04 m s-1), gentle breeze (6.25 m s-1) and fresh wind (11.6 m s-1) conditions. As shown in Figure S20 (Supporting Information), the removal efficiencies are higher than 95% in all cases, indicating the outstanding air filtration performance under various pollution conditions of the PBM-Zn2@melamine foam-4 air filter. With increasing air flow velocity, the removal efficiencies of PM2.5 and PM10 decrease slowly, which may be due to the fact that the lower diffusion of PMs particles in the PBM-Zn2@melamine foam-4 filter caused by increased air flow velocity, thus reducing the collision chances for particles and the wires (Figure S20a,b, Supporting Information).63 On the other hand, according to our experimental records, the common humidity in hazy days in Harbin is among the range from 25.8% to 69.7%. We have obtained the representative results under different humidity, the removal efficiencies of PM2.5 and PM10 increase slowly with increasing humidity, for instance, PBM-Zn2@melamine foam-4 filter presented PM2.5 92.4% ± 0.7%, PM10 93.6% ± 1.2% removal efficiency with 25.8% humidity and PM2.5 98.8% ± 1.3%, PM10 99.4% ± 0.5 % removal efficiency with 69.7% humidity, respectively (Figure S20c,d Supporting Information). Application in the outdoor individual protection As we all know, in most cases, outdoor individual protection could be achieved by facial masks. Subsequently, we investigate the removal efficiencies of PBM-Zn2@melamine foam-4 air filter and two types of commercial breathing masks (denoted as mask-1# and mask-2#, respectively) (Figure S21, Supporting 25



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Information). (i) When the same basis weight is 28 g m2, the as-prepared PBM-Zn2@melamine foam-4 air filter exhibits higher removal efficiencies of 99.6% ± 1.3% and PM10: 99.5% ± 0.9% for PM2.5 and PM10, respectively, and a pressure drop of 125 Pa. These removal efficiencies are 6.9, 3.9 and 7.4, 4.1 times than mask-1# and mask-2# (14.4 ± 1.2%%, 13.5% ± 0.3% and 25.3% ± 0.7%, 24.2% ± 1.3% for PM2.5 and PM10, respectively) (Figure S22a, Supporting Information). (ii) With similar removal efficiencies, the PBM-Zn2@melamine foam-4 air filter exhibits a lower pressure drop (125 Pa) than that of commercial breathing mask-1# (326Pa) and mask-2 (457Pa) (Figure S22b, Supporting Information). (iii) Moreover, it is noteworthy that with similar removal efficiencies the PBM-Zn2@melamine foam-4 air filter is greatly thinner than the two commercial breathing masks. The larger thickness will result in a higher pressure drop. The thickness of the PBM-Zn2@melamine foam-4 air filter is only approximately 5.51 mm, while mask-1# and mask-2# is about 40 and 50 mm in thickness. Moreover, the overall filtration performance of the material (including both the removal efficiency and pressure drop) can be evaluated by the quality factor (QF).64 PBM-Zn2@melamine foam-4 air filter shows higher QF value comparing the two breathing masks, as shown in Figure S22c (Supporting Information). As a proof-of-concept, PBM-Zn2@melamine foam-4 filter is embedded into another

commercial

breathing

mask

for

the

personal

protection.

CutingBM-Zn2@melamine foam-4 filter into a rectangular shape with the size of 10.2 × 8.3 cm2, embedding into a commercial breathing mask (Figure S22d, Supporting Information). The high removal efficiencies for both PM2.5 and PM10 are 99.6% ± 0.5%, 99.4% ± 0.8%, and acceptable 186 Pa air resistance are demonstrated, implying the potential practical application for personal protection of the PBM-Zn2@melamine 26


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foam-4 air filter breathing mask, so that the mask can be used practicably in heavy hazy weather for personal protection (Figure S22e, Supporting Information). After the PM removal tests, PBM-Zn2@melamine foam-4 can be easily cleaned and reused for three times without any apparent efficiency loss.

CONCLUSIONS In summary, metal-organic complexes PBM-Zn1 and PBM-Zn2 have been

applied on various substrates (plastic mesh, glass cloth, metal mesh, and melamine foam) and obtained different kinds of air filters by hot-pressing method. The obtained PBM-Zn-Filters show excellent robustness and PM removal efficiency in a real polluted air environment and in cigarette smoke were both retained at high levels after long-term tests. Such versatile PBM-Zn-Filters can be purposely designed and applied in various application scenarios such as breathing masks, it shows higher removal efficiency, a lower pressure drop and a smaller thickness than commercial breathing masks. Larger conjugation system, micropore structure, lower pressure drop, higher electrostatic potential ζ and electron cloud exposed metal center materials are very promising for PMs pollution control in both residential and industrial environments.

EXPERIMENTAL SECTION

[Zn PBM Cl2] (PBM-Zn1) A

mixture

of

2-carboxaldehyde-1,10-phenanthroline

(108.1

mg,

2

mmol),o-phenylenediamine (208.3 mg, 1 mmol), ZnCl2 (136.6 mg, 1 mmol)was dissolved in CH3CN (15 mL) and stirred for 45 min, then heated in a sealed vial at 85 °C for 1 h. Red rectangular block crystals of PBM-Zn1 were obtained. Yield: 83%. Anal. Calcd (%) for C19H12Cl2N4Zn (M = 432.60 g mol−1): C, 52.75; H, 2.80; N, 12.95. Found: C, 52.73; H, 2.78; N, 12.93. FT-IR (KBr, cm–1): 3418(w), 3059(w), 27



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2919(w), 1621(m), 1597(m), 1510(m), 1465(m), 1448(m), 1423(w), 1373(w), 1321(w), 1145 (m), 1092(w), 983(w), 860(s), 748(s), 742(s), 646(w), 611(w), 487(w), 422(w). 1H NMR (400 MHz, d6-DMSO, 298 K): 8.62 (s, 1H, −NH), 7.21−8.31 (m, 7H, Q-H), 6.42−6.60 (m, 4H, Ph-H) ppm. 13C NMR (150 MHz, CD3CN, 298 K): δ 167.6, 158.2, 154.6, 153.8, 147.5, 140.9, 139.1, 138.1, 137.7, 129.8, 128.8, 128.6, 127.3, 126.9, 126.1, 122.9, 119.4. [Zn2 PBM Cl4] (PBM-Zn2) The

complex

PBM-Zn2

was

synthesized

by

dissolving

2-carboxaldehyde-1,10-phenanthroline (216.2 mg, 2 mmol),o-phenylenediamine (208.3 mg, 1 mmol), ZnCl2 (273.2 mg, 2 mmol) in 25 mL anhydrous acetonitrile solutions under stirring at room temperature for 0.5h then refluxed for 2 h. The mixture was then cooled and filtered. The filtrate was allowed to stand at room temperature in air. Quality yellow bulk single crystals PBM-Zn2 were obtained by slow evaporation after 2 days. Complex PBM-Zn2 was stable in the solid state under further exposure to air. Yield: 67%. Anal. Calcd (%) for C32H19Cl4N6O Zn2 (M = 776.07 g mol−1): C, 49.52; H, 2.47; N, 10.83. Found: C, 49.50; H, 2.45; N, 10.80. FT-IR (KBr, cm–1): 3422(w), 3183(w), 3160(w), 3059(w), 2924(w), 2853(w), 1620(m), 1578(m), 1512(m), 1451(s), 1322 (w), 1442(m), 1095(w), 979(w), 860(m), 747(s), 642(m), 602(w), 480(w), 421(w). 1H NMR (400 MHz, d6-DMSO, 298 K): 7.58−8.52 (m, 14H, Q-H), 7.26−7.30 (m, 4H, Ph-H), 6.28 (s, 2H, −CH2) ppm. NMR

13

C

(150 MHz, CD3CN, 298 K): δ 168.2, 159.2, 158.1, 156.3, 154.8, 152.3, 150.5,

148.2, 146.3, 145.2, 141.8, 139.4, 138.2, 137.5, 129.1, 128.3, 126.9,126.4, 123.3, 121.4, 120.3, 119.5. 28


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Synthetic methods of PBM-Zn1@carbon fiber cloth, plastic mesh, glass cloth or melamine foam 2-carboxaldehyde-1,10-phenanthroline

(108.1

mg,

1

mmol)

with

o-phenylenediamine (208.3 mg, 1 mmol), ZnCl2 (136.6 mg, 1 mmol) and 100 mg PEG (polyethylene glycol, Mn = 4000) were manually ground and mixed. The mixture was then loaded on a 2 cm × 2 cm carbon cloth, packed with aluminum foil and heated with electric heating plate at 80 °C for 5 min. After peeling off the aluminum foil, the slice was washed with ethanol and DMF (each for 1h) and stored in ethanol. Then it was pre-dried at 80 °C for 30 min prior to use for characterizations. Synthetic methods of PBM-Zn2@carbon fiber cloth, plastic mesh, glass cloth or melamine foam 2-carboxaldehyde-1,10-phenanthroline (216.2 mg, 2 mmol),o-phenylenediamine (208.3 mg, 1 mmol), ZnCl2 (273.2 mg, 2 mmol) and 100 mg PEG (polyethylene glycol, Mn = 4000) were manually ground and mixed. The mixture was then loaded on a 2 cm × 2 cm carbon cloth, packed with aluminum foil and heated with electric heating plate at 80 °C for 5 min. After peeling off the aluminum foil, the slice was washed with ethanol and DMF (each for 1h) and stored in ethanol. Then it was pre-dried at 80 °C for 30 min prior to use for characterizations. Particulate matter removal experiment The PM removal efficiency of the filters was tested in the setup shown in Figure S27, and the setup was put in a heavily polluted environment during the test. A piece of filter with a diameter of 4 cm was set at one side of the pipe, and an electric fan is put on the other side to help the air pass through the filter at a constant velocity (2.04 m s-1). The filtered air was collected in a plastic bag, and a particle counter was used 29



to detect the PMs mass concentrations with and without the filter. The detection was finished before the plastic bag reached its maximum volume, and this constant pressure process ensured that the concentration of PMs remained unchanged during collection. The removal efficiency, one of the most important performance indexes for air filters, is expressed as

Efficiency =

C0 -C C0

where C0 (µg/m3) and C (µg/m3) are the mass concentrations of particle matter with and without the filter. The long-term PMs removal efficiency of the filter is tested every 4 hours for 2 days. The filters were weighed before and after PMs filtration to get the mass change that indicates the amount of the particles captured on the filters. The gravimetric mass change (∆mG) and the areal mass change (∆mA) of the filters was calculated with the following equations:

∆mG =

m-m0 m0

where m (g) and m0 (g) are the mass of the filter before and after PM filtration (the mass of the substrate was included); S (m2) is the area of the filter. In addition, the air resistance (pressure drop) was measured using a differential pressure gauge (EM201B, UEi test instrument). The air-flow velocity was set as 2.04 cm s-1 and the humidity was 38.5%. In addition, The QF is usually taken as the criterion for comparing filtration performance of different filters, which is expressed by

QF =

ln (1 ) ∆

where R and ∆P are the removal efficiency of PM2.5 and pressure drop, respectively. 30


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ASSOCIATED CONTENT

Supporting Information The Supporting Information is available free of charge on the ACS Publications website at http://pubs.acs.org: Selected bond distances (Å) and angles (°) for PBM, PBM-Zn1 and PBM-Zn. The geometrical parameters noncovalent bonding for PBM, PBM-Zn1 and PBM-Zn2. PXRD and FT-IR patterns of PBM-Zn1 and PBM-Zn2. SEM image of PBM-Zn@carbon fiber cloth, PBM-Zn@melamine foam. Particulate matter removal efficiency of PBM-Zn2@melamine foam-4 air filter versus air-flow velocity and humidity.

CONFICT OF INTEREST

The authors declare no competing financial interest.

ACKNOWLEDGEMENTS

This work was supported by National Natural Science Foundation of China (Grant 21371040 and 21571042).

REFERENCES

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Table of Contents Entry Hot-pressing Method to Prepare Imidazole-based Zn(II) Metal-organic Complexes Coatings for Highly Efficient Air Filtration Ani Wang, Ruiqing Fan,* Xuesong Zhou, Sue Hao, Xubin Zheng and Yulin Yang*

Imidazole-based Zn(II) Metal-organic complexes PBM-Zn1 and PBM-Zn2 air filters for Highly Efficient Particulate Matter Removal


Page 42 of 42

Hot-Pressing Method To Prepare Imidazole-Based Zn(II) Metal

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