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Carbazolic Porous Framework with Tetrahedral Core for Gas Uptake and Tandem Visual Detection of Iodide and Mercury Qin-Qin Dang, Hong-Jing Wan, and Xian-Ming Zhang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 06 Jun 2017 Downloaded from http://pubs.acs.org on June 6, 2017
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Carbazolic Porous Framework with Tetrahedral Core for Gas Uptake and Tandem Detection of Iodide and Mercury Qin-Qin Dang*, Hong-Jing Wan, and Xian-Ming Zhang*
School of Chemistry & Material Science, Shanxi Normal University, Linfen, Shanxi 041004, China KEYWORDS: Carbazolic, Gas uptake, Iodide sensing, Mercury sensing, Regeneration, Reversibility. ABSTRACT: A multifunctional carbazolic porous framework (Cz-TPM) with tetrahedral core has been synthesized by FeCl3 oxidative coupling polymerization. The BET surface area of the obtained polymers reaches to 713.2 m2g-1. Gas adsorption isotherms show that Cz-TPM exhibits large carbon dioxide (97.9 mg/g, 9.8 wt% 273 K and 1 bar) and hydrogen uptake capacity (149.3 cm3/g, 1.34wt% 77K and 1 bar). Furthermore, Cz-TPM has been found to display tandem visual detection of iodide and mercury respectively. The Cz-TPM dispersion turns to yellow in the presence of iodide salts and subsequently changed to nearly colorless on addition of Hg2+ salts that could be easily observed by the naked eye. Cz-TPM can detect I- via “turn off” fluorescence quenching and then the in situ generated Cz-TPM@I complexes can recognize Hg2+ ions via “turn on” fluorescence recovery. More importantly, Cz-TPM is stable over common solvents and can be easily recovered by excessive water washing and centrifugation for further repeated use. 1 ACS Paragon Plus Environment
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As far as we know, carbazolic porous organic frameworks enabling detection of I- and Hg2+ have not been reported. INTRODUCTION Among biologically important anions, I- is an indispensable element in human body, and it plays an important role in the biological activity such as neurological and thyroid functions, cell growth and brain function.1 Both deficiency and excess of I- can cause serious physical diseases.2 The World Health Organization (WHO) data have shown that in many countries iodide deficiency disorders are significant public health problem. In addition, elemental iodine has been widely used in synthesizing valuable molecules such as drugs, plastics, and molecular electronics, in medicine and several other applications.3 Therefore, it is strongly desired to design chemosensor capable of detection I- ions rapidly and selectively. On the other hand, mercury is considered as one of the most toxic and hazardous pollutant among heavy metals. Contamination by mercury ions poses a serious threat to human health and ecological environment.4 Even low level of mercury can destroy central nervous and endocrine systems further causing severe cardiac and motion disorder.5 Thus the detection of both iodide and mercury ions rapidly and selectively is very important for environmental and health problems. During the past few years, small molecules, 6 DNAzymes7 and linear conjugated polymers8, 9, 10 have been developed as colorimetric and fluorimetric sensor for I- and Hg2+ detection. However, the molecules that constitute these sensors are flexible and cannot form stable porous networks. Thus, they bind Iand Hg2+ ions predominantly due to the flexible pseudocavity formed by receptor binding sites, which are vulnerable to microenvironment around and often suffer from poor reversibility, difficult regeneration and limited active sites.6 Therefore, it is of great necessity to develop a porous framework as stable and easily recyclable sensor for detection of iodide and mercury 2 ACS Paragon Plus Environment
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ions. In this respect, porous organic frameworks have potential to be exploited as a stable, rapid and easily recyclable sensor for detection of iodide and mercury ions, owing to their high density of binding site, strong fluorescence signal ability and pronounced hydrolytic and thermal stability. The availability of plenty of organic building blocks and the various synthetic strategies could provide porous polymers to host guest in the nanopores for sensing applications. 11-14 Carbazolic porous organic frameworks have attracted great interest due to their permanent porosity and excellent luminescent properties. Recently many reports have demonstrated that carbazolic porous organic frameworks show excellent properties in gas adsorption15-20 and chemosensing of explosives.21,22,23 For example, Han B et al reported a series of microporous polycarbazole which displays extremely high gas uptake capacity and good CO2/N2 adsorption selectivity.15,16,17 Jiang D et al developed highly luminescent carbazole-based CMP films that can detect electron-rich and electron deficient arenes, metal ions and hypochloroic acid with rapid response, excellent selectivity and robust reusability.21,22,23 Although significant progress has been achieved in gas adsorption and chemosensing of explosives, as far as we know, carbazolic porous organic frameworks enabling detection of I- and Hg2+ have not been reported. Carbazolic porous framework integrated large surface areas with excellent fluorescence signaling ability can be exploited as a stable, rapid and easily recyclable sensor for detection of iodide and mercury ions. Firstly, the high surface areas and the nanospaces of the polymer provide large interface and allow encapsulation of large ions such as iodide. Secondly, large number of carbazole moieties on the pore walls may synergistically enhance the interaction with guest ions and improve the signaling activity along the whole backbone. Finally, the high stability of the polymer network over all kinds of solvents and a wide range of pH values18, 23 facilitates an easy
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regeneration by centrifugation. Based on these, we report the synthesis of a carbazolic porous framework (Cz-TPM) with tetrahedral core by straightforward FeCl3 oxidative coupling polymerization. Cz-TPM displays good performance in gas uptake. More importantly, the cooperative nature of the threedimensional frameworks and high density of carbazole sites facilitated tandem visual detection of I- and Hg2+. The insoluble nature of Cz-TPM makes it easily recovered upon addition of water by centrifugation. To the best of our knowledge, there has been no documented example of carbazolic porous framework for tandem sensing of I- and Hg2+ ions. EXPERIMENTAL SECTION Synthesis of Carbazolic Porous Frameworks. The sample was prepared through FeCl3 oxidative coupling polymerization reaction from the corresponding monomers tetra[4-(carbazol9-yl)phenyl]methane (TPTCz) (Scheme S1, Supporting Information). Typically, TPTCz (100mg, 0.102 mmol) was dissolved in anhydrous chloroform (16 mL) and transferred dropwise to a 100 mL round flask which contains a suspension of FeCl3 (238 mg, 1.479 mmol) in anhydrous chloroform (10 mL). The resulting mixture was stirred at room temperature for one day under nitrogen atmosphere. After addition of methanol (50 mL), the mixture was stirred for one more hour. The resulting precipitation was collected by filtration and washed with methanol. The powder was vigorously treated with aqueous hydrochloric acid 37 % for 2 h, filtered and washed with water and methanol. After Soxhlet extraction with methanol and THF for 24 h, and then dried at 100 °C under vacuum to afford light yellow powder. Yield: 80.6 mg (80.6%). The sample was named as Cz-TPM. Elemental analysis of guest free samples: Calculated: C， 89.36%；H，4.93%；N，5.71%. Found: C，89.7%；H，5.26%；N，5.04%. 4 ACS Paragon Plus Environment
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RESULTS AND DISCUSSION Synthesis and Characterization. Tetrahedral carbazolic building block (TPTCz) was synthesized by copper-promoted Ullmann reaction between tetrakis(4-bromophenyl)methane and four carbazole units according to a modified procedure reported by Li et al. 24 The rigid block bears a tetraphenylmethane core with four carbazole groups at the periphery which facilitate the formation of 3D polymer network with permanent porosity. Cz-TPM was straightforward synthesized by FeCl3 oxidative coupling polymerization of TPTCz in dry chloroform at room temperature. After polymerization, the polymer was washed with MeOH and HCl solution, followed by Soxhelt extraction with MeOH and THF. Scheme 1 shows synthetic route for the polymer network Cz-TPM, and Figure 1 shows the structure model of Cz-TPM. The polymer network was insoluble in boiled water and common organic solvents such as methanol, acetone, chloroform, THF and DMF indicating their highly cross-linked robust networks. TGA analysis shows the high thermal stability of Cz-TPM. The thermal decomposition temperature is up to 465 °C. The weight loss of 6 wt% between 25-195 °C corresponds to the loss of entrapped guest molecules (Figure S1). The chemical structure and connectivity was investigated by Fourier transform infrared (FT-IR) and solid-state 13C cross polarization magic angel spinning (CP/MAS) NMR. FT-IR spectra confirmed the successful coupling of the tetrahedral carbazole monomers (Figure S2). The typical bands at 804 cm-1 were assigned to trisubstituted phenyl ring of the porous organic polymers Cz-TPM. The almost disappearance of band around 700 cm-1 (attributed to bisubstitutd phenyl ring in carbazole monomers) suggested that full oxidation coupling of carbazole monomers occurred. A more detailed analysis of the structure of the polymers was characterized out by
13
C CP/MAS NMR (Figure S3). The signal at 140 ppm is
ascribed to the substituted phenyl carbons bonded with nitrogen atoms. The high-intensity signal 5 ACS Paragon Plus Environment
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at 125 ppm corresponds to other substituted phenyl carbon atoms. The resonances at 120 and 110 ppm are due to the unsubstituted phenyl carbons. The NMR results are consistent with previous reported carbazole based porous organic frameworks.18An additional peak at about 67.8 ppm is ascribed to the quartus sp3 carbons from the tetrahedral core. Elemental analysis gives proper results consistent with theoretical value. The broad and featureless diffraction of powder X-ray diffraction spectra implied that Cz-TPM has amorphous structure (Figure S4). SEM showed that the Cz-TPM adopted uniform fused flake-like morphology (Figure S5).
Scheme 1. Synthetic route for carbazolic porous framework (Cz-TPM).
Figure 1. Structure model of carbazolic porous framework (Cz-TPM).
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Adsorption Properties. To characterize the porosity parameters in detail, guest free Cz-TPM was analyzed using N2 sorption experiments at 77 K. The N2 isotherms (Figure 2a) show rapid gas uptake at low relative pressures (P/P0
