Xionghui Liu,Jianfeng Du,Yu Ye,Yuchuan Liu,Shun Wang,Xianyu Meng,Xiaowei Song,Zhiqiang Liang,Wenfu Yan

State Key Laboratory of Inorganic Synthesis and Preparative Chemistry,Jilin University,Changchun 130012,China

Keywords:Porous organic polymers Triazole CO2 capture Light hydrocarbons Gas separation Natural gas purification

ABSTRACT Nitrogen-rich porous organic polymers have shown great potentials in gas adsorption/separation,photocatalysis,electrochemistry,sensing and so on.Herein,1,2,3-triazole functionalized triazine-based porous organic polymers (TT-POPs) have been synthesized by the copper-catalyzed azide-alkyne cycloaddition(Cu-AAC) polymerization reactions of 1,3,5-tris(4-azidophenyl)-triazine with 1,4-diacetylene benzene and 1,3,5-triacetylenebenzene,respectively.The characterizations of N2 adsorption at 77 K show TTPOPs possess permanent porosity with BET surface areas of 666 m2·g-1 (TT-POP-1) and 406 m2·g-1(TT-POP-2).The adsorption capacities of TT-POPs for CO2,CH4,C2H2 and C2H4,as well as the selective separation abilities of CO2/N2,CO2/CH4,C2H2/CH4 and C2H4/CH4 were evaluated.The gas selective separation ratio of TT-POPs was calculated by the ideal adsorbed solution theory(IAST) method,wherein the selective separation ratios of C2H2/CH4 and C2H4/CH4 of TT-POP-2 was 48.4 and 13.6(298 K,0.1 MPa),which is comparable to other adsorbents(5.6-120.6 for C2H2/CH4,10-26 for C2H4/CH4).This work shows that the 1,2,3-triazole functionalized triazine-based porous organic polymer has a good application prospect in natural gas purification.

1.Introduction

The trend of natural gas becoming a premium fuel for the world economy is not easy to reverse now.As global energy demand increases,natural gas now plays an important strategic role in energy supply.C1 to C2 light hydrocarbons,CH4,C2H2,C2H4,and C2H6,are very important energy and raw material chemicals.Ethylene are important chemicals for the manufacture of polymers such as polyethylene,polyvinyl chloride,polyester,polystyrene and other organic chemicals[1,2].In order to be widely used,it is necessary to solve the challenging problems associated with natural gas purification and light hydrocarbon production [3-5].It is well known that natural gas is mainly composed of CH4and also contains a certain amount of impurities such as CO2,C2H2and C2H4[6-8].The presence of these impurity gases not only reduces the CH4combustion efficiency,but also causes climate change and corrosion of the pipeline.Therefore,it is of great significance to remove impurities such as CO2,C2H2and C2H4from natural gas[9].In the natural gas purification process,the recovery of C2 hydrocarbons is also economically feasible and meaningful,which can provide another source of C2 hydrocarbons for further chemical treatment and conversion [10-12].In addition,the thermal cracking of CH4is involved in the production of C2H2,so it is necessary to separate C2H2from unreacted CH4to obtain high purity C2H2[13].In order to achieve the above objectives,it is particularly important to develop new technologies for the purification of natural gas and the separation of light hydrocarbons.

It is quite difficult,and energy consuming to separate and purify natural gas and light hydrocarbons from the corresponding alkanes by conventional cryogenic distillation processes.As an alternative method,the separation of light hydrocarbons by physical adsorption using a porous adsorbent having a large specific surface area has received great attention.Compared with the traditional lowtemperature fractionation process,the physical adsorption operation is convenient and energy-saving [14-16].Furthermore,the adsorbed hydrocarbons are easily released and recovered under reduced pressure,and the porous adsorbent can be reused.However,the development of porous adsorbents for selectively separating C2H2/CH4,C2H4/CH4and CO2/CH4mixed gases at ambient temperatures remains a challenge.

Conventional porous materials,such as zeolites[17,18],metalorganic frameworks [19] and activated carbon [20] have been applied to the field of gas adsorption/separation through continuous development,but they all have non-negligible disadvantages,such as low specific surface area of zeolites,relative poor stability of MOFs,lack of active sites on activated carbon.However,as a new type of porous materials,porous organic polymers(POPs)linked by covalent bonds between light elements(C,H,B,N,O,etc.)[21-23].Due to their adjustable pore structure,low material skeletal density,highly condensed mesh structure,high stability,large specific surface area and controllable surface chemical environment,they have attracted more and more attention in gas separation and storage [24,25].

Generally,the gas adsorption capacity of POP materials is affected by their specific surface area,pore sizes and surface physical/chemical properties [26].In order to enhance the affinity between adsorbent surface and gas molecules,it can be achieved by introducing functional groups into structure,such as fluorine atoms [27],imide rings [28],carbazole units [29],benzimidazole units [30] and metal ions [9],etc.Among all POPs,the triazinebased frameworks is of particular interest because its skeleton has a higher nitrogen content than others and a higher porosity consisting of micropores and mesopores.Furthermore,it can be prepared using readily available chemical precursors [31].In 2001,Kolet al.[32,33] first proposed the concept of ‘‘click chemistry” (CC) and called it ‘‘the reinvigoration of an old style of organic synthesis”.As a representative reaction,copper-catalyzed azido-alkynyl cycloaddition (Cu-AAC) reaction leads to the exclusive formation of 1,4-triazole,and has the advantages of simple synthesis and modular nature[34-36].The presence of the triazole ring can further increase the N content in the polymer,providing more active sites to enhancing the interactions between polymer and adsorbate [37-40].

Taking into account the above discussion,here,we utilized the Cu-AAC polymerization reactions of 1,3,5-tris(4-azidophenyl)-tria zine (TEPT) with 1,3,5-triacetylenebenzene (TEB) and 1,4-diacetylene benzene (DEB) in DMF,respectively,to construct 1,2,3-triazole functionalized triazine-based porous organic polymers (TT-POPs).TT-POPs structure has a plurality of N-containing heteroaromatic rings (triazole rings and triazine rings) which provide gas affinity sites.TT-POPs possess permanent porosity with BET surface areas of 666 m2·g-1(TT-POP-1) and 409 m2·g-1(TT-POP-2).TT-POP-1 has higher CO2adsorption capacity(52.0 cm3·g-1) at 273 K and 1 bar.The selective separation ability of TT-POPs for C2H2/CH4,C2H4/CH4,and CO2/CH4were calculated by the IAST method,and the obtained selectivity values of C2H2/CH4and C2H4/CH4for TT-POP-2 were up to 48.4 and 13.6(298 K,0.1 MPa),respectively.The results show that 1,2,3-triazole functionalized triazine-based porous organic polymers has good application prospects in natural gas purification and C2H2production.

2.Materials and Methods

2.1.Materials

All chemicals were purchased from commercial sources and used without further purification.1,3,5-Triacetylene benzene(TAB,98%) and 1,4-diacetylene benzene (DAB,98%) were purchased from Chemsoon (Shanghai).Sodium nitrite (NaNO2,99%)and sodium nitrite (NaN3,99.5%) were purchased from Fuchen chemical reagent Co.,Ltd.N,N-Dimethylformamide(DMF),dichloromethane (CH2Cl2),ethanol (EtOH) and tetrahydrofuran (THF)were purchased from Sinopharm chemical reagent Co.,Ltd.2,4,6-Tris(4-aminophenyl)-s-triazine (95%) was purchased from Aladdin (Shanghai).L-Ascorbic acid sodium salt (99%),disodium edetate (EDTA-2Na) and copper (II) sulfate pentahydrate (99%)were purchased from MACKLIN.

2.2.Synthesis of 1,3,5-tris(4-azidophenyl)-triazine (TAPT)

According to the previously reported method [41],2,4,6-tris(4-aminophenyl)-s-triazine (709 mg,2 mmol) was dissolved in 6 mol·L-1HCl (30 ml) in a 250 ml three-necked flask,and cool to 0 °C.NaNO2(552 mg,8 mmol) was dissolved in 10 ml water and then the NaNO2solution was added dropwise to the cooled reaction flask with vigorous stirring.The reaction mixture was kept at 0 °C for 30 minutes.NaN3(520 mg,8 mmol) was dissolved in 10 ml of water,and then the NaN3solution was slowly added to the reaction system.(Azide operation precautions:NaN3is not only toxic,but also the impact is easy to explode,while producing hydrazoic acid under acidic conditions.Therefore,sodium azide should be used with a plastic key to reduce friction.All experimental operations should be carried out in a fume hood,and the experimenter wears an explosion-proof mask.) The reaction mixture reacted violently to give a pale yellow solid.Filtration was carried out and the collected solid was washed with excess water and ethanol,and then dried in a vacuum oven at 80 °C to give a paleyellow powder (700 mg,81% yield).1H NMR (300 MHz,C2DF3O2,δ):8.47 (d,J=8.6,3H),8.44 (d,J=8.6,3H),7.17 (m,3H),7.14(m,3H).13C NMR (75 MHz,C2DF3O2) δ:169.81,154.02,134.30,127.90,122.53.

2.3.Synthesis of TT-POP-1

In a 250 ml round bottom flask,1,3,5-tris(4-azidophenyl)-tria zine (432.5 mg,1 mmol) and 1,3,5-triacetylene benzene (150 mg,1 mmol),copper sulfate pentahydrate (75 mg,0.30 mmol) and sodium ascorbate (60 mg,0.3 mmol) were dissolved in 100 ml of DMF and reacted under a nitrogen atmosphere at 100 °C for 48 h to give a yellow solid.The solid was separated by filtration,followed by repeated washing with EDTA-2Na solution (0.25 g in 200 ml of water),ethanol and dichloromethane to remove the catalyst,unreacted monomers and residue.Soxhlet extraction by tetrahydrofuran and water for 24 hours,the sample was suction filtered,and dried under vacuum at 120 °C (570 mg,98% yield).

2.4.Synthesis of TT-POP-2

1,3,5-tris(4-azidophenyl)-triazine (432.5 mg,1 mmol) and 1,4-diacetylene benzene(150 mg,1 mmol).Following the same procedures as the synthesis of TT-POP-1 (590 mg,95% yield).

2.5.Characterization

Fourier transform infrared (FT-IR) spectra were collected on a Bruker IFS-66-V/S FT-IR spectrometer in the region of 400-4000 cm-1.Solution-state1H and13C NMR spectra were recorded on a Varian Mercury spectrometer operating at frequency of 300 MHz.The solid state13C CP/MAS NMR spectra were recorded on a Bruker AVANCE NEO 600 MHz NMR spectrometer.Powder wide-angle X-ray diffraction (PXRD) was carried out on a Rigaku D/max-2500 X-ray diffractometer using Cu Kα radiation,operated at 40 kV and 200 mA with the 2θ ranged from 4°to 70°and a scan speed of 6(°)·min-1.Thermal gravimetric analyses(TGA)were carried out on a TGA Q500 thermogravimetric analyzer in nitrogen at a heating rate of 10 °C·min-1.Inductively coupled plasma (ICP)analysis was performed on a PerkinElmer Optima 3300DV spectrometer.Elemental analyses (C,H,and N) were performed with a Vario MICRO (Elementar,Germany).Scanning electron microscopy (SEM) images were recorded on a JSM-6700 M scanning electron microscope operating at 10 kV.Transmission electron microscopy (TEM) images were taken on a TECNAI F20 with an acceleration voltage of 200 kV.

2.6.Adsorption test

Gas(N2,CO2,CH4,C2H2,C2H4,99.999%)adsorption performance and surface areas of TT-POPs were measured using the Micromeritics ASAP 2020 surface area and porosity analyzer.Pore size distributions (PSDs) were represented by the adsorption branch of the isotherm by the non-local density functional theory(NLDFT)using slit-pore model.All samples were degassed under vacuum at 120 °C for 12 hours prior to analysis.

3.Results and Discussion

3.1.Design,synthesis and characterization of TT-POPs

As typical nitrogen heterocycles,the triazine and triazole rings have a higher nitrogen content,which could facilitate the interactions between gas molecules and the frameworks of porous materials.In this work,1,3,5-tris(4-azidophenyl)-triazine with a triazine ring was used as the key building block for the synthesis of 1,2,3-triazole functionalized triazine-based porous organic polymers by the Cu-AAC reactions with 1,3,5-triacetylene benzene and 1,4-diacetylene benzene,respectively.In this synthetic strategy,the triazine ring was pre-decorated in the azide substrate,avoiding the damage of framework and functional groups in conventional ion thermal polymerization at high temperature.As shown in scheme 1,TT-POP-1 and TT-POP-2 was prepared by the Cu-AAC reactions of TAPT with TAB and DAB in DMF solvent at 100 °C for 48 h,respectively.The prepared yellow powder is insoluble in common organic solvents such as acetone,ethanol,methanol,DMF,DMSO and THF.In addition,we characterized the Cu content in TT-POPs through ICP analysis,which were 0.04% (mass) (TTPOP-1) and 0.47% (mass) (TT-POP-2).

The completion of the polymerization was confirmed by FT-IR spectra (Fig.1).After the polymerization reaction,the terminal acetylene characteristic peaks at about 3279 cm-1and 3264 cm-1in TAB and DAB molecules almost completely disappeared.The azide-based characteristic peak at about 2121 cm-1in the raw material TAPT molecule is also significantly weakened,which is attributed to defects caused by incomplete polymerization.At the same time,characteristic peaks of triazolyl obviously appeared in both TT-POPs structure at 1614 cm-1for TT-POP-1 and 1610 cm-1for TT-POP-2 can be seen[42,43].In order to obtain more detailed information on the chemical structure of TT-POPs,solid state13C CP/MAS NMR spectra were performed.As shown in Fig.2,the characteristic peaks appearing around δ=169 should be attributed to the carbon atoms in the triazine ring.At the same time,the characteristic peaks appearing around δ=146 can be assigned to the C4-triazolyl carbon.In addition,the characteristic peaks appearing between δ=141 and δ=116 can be ascribed to the other carbon atoms of the triazole ring and phenyl group[44].While there are no ethynyl carbon signals at around δ=80.These information confirms the occurrence of click reaction and the formation of triazole ring,meanwhile,the alkynyl groups have been almost completely converted.

Fig.1.FT-IR spectra of reactive monomers and TT-POPs.

Scheme 1.Schematic diagram of the synthesis and structure of TT-POPs.

Fig.2.13C solid magnetic resonance spectrum of TT-POPs.

The crystallinity of TT-POPs was investigated by powder X-ray diffraction (PXRD) analysis (Fig.S3,in Supplementary Material).The PXRD diffraction patterns show the presence of broad diffraction peaks around 21°,which generally indicate that the polymers are amorphous and also demonstrate that the process of click polymerization is irreversible.Scanning electron microscope(SEM)and transmission electron microscope (TEM)are performed to observe the morphology and structure of the sample.As shown in Figs.3,S4,and S5,the images show that TT-POPs have different sizes and irregular rod-like aggregated morphologies,and this phenomenon is common in porous organic polymers [45,46].In addition,their disordered porous layered structure is consistent with the PXRD results.

3.2.Porous properties of TT-POPs

The porous properties of the synthesized TT-POPs,such as BET specific surface area,pore volume and pore size distribution(PSD),were characterized by N2adsorption test at 77 K.The corresponding N2adsorption/desorption isotherms and PSDs for TTPOPs are shown in Fig.4.According to the IUPAC classification rules,the synthesized TT-POP-1 has a typical type IV N2adsorption isotherm,while the adsorption curve of TT-POP-2 exhibits a typical I curve.It can be seen from the N2adsorption isotherms of TT-POPs that the N2adsorption amount increases sharply in the low relative pressure region (P/P0＜0.01),indicating that they have a typical microporous structure.At the same time,owing to the difference of the reaction precursors,the polymer pore size will change accordingly.A low-pressure hysteresis loop in the sorption isotherms of TT-POP-1 can be found from Fig.4(a),which indicates the presence of meso and macropores in TT-POP-1.The calculated BET specific surface areas of TT-POP-1 and TT-POP-2 are 666 and 409 m2·g-1,respectively.The total pore volumes (Vtot) of TT-POP-1 and TT-POP-2 calculated atP/P0=0.99 are 0.80 and 0.34 cm3·g-1,respectively.The non-local density functional theory (NLDFT)method was used to calculate the pore size distributions of TTPOPs (Fig.4(b)).For TT-POPs,the micropores are mainly concentrated at two peak positions of 0.61 and 1.27 nm,but there are widely distributed mesopores and macropores (＞10 nm) in the TT-POP-1 structure.

3.3.Gas adsorption behaviors of TT-POPs

Fig.3.The TEM images of TT-POP-1 (a,b) and TT-POP-2 (c,d).

Fig.4.The N2 adsorption isotherms at 77 K (a) and NLDFT pore size distribution (PSD) curves (b) of TT-POP-1 (black) and TT-POP-2 (red).

Considering the synthesized TT-POPs have high BET specific surface areas and nitrogen-rich frameworks (triazole ring and triazine ring),the ability of TT-POPs to capture CO2gas have been studied.The CO2adsorption/desorption isotherms at 273 and 298 K are displayed in Fig.5.At 273 K and 0.1 MPa,the CO2adsorption values are 52.0 cm3·g-1(2.32 mmol·g-1) for TT-POP-1,33.5 cm3·g-1(1.50 mmol·g-1) for TT-POP-2.At 298 K and 0.1 MPa,the CO2adsorption values are 30.6 cm3·g-1(1.37 mmol·g-1)for TT-POP-1,20.3 cm3·g-1(0.91 mmol·g-1)for TT-POP-2(Table 1).The CO2up take of TT-POP-1(1.37 mmol·g-1)is higher than those of many reported adsorbents measured at 298 K and 0.1 MPa(Table S4),such as Networks (0.95-1.34 mmol·g-1at 0.113 MPa)[41],CMPs(conjugated microporous polymers,0.94-1.18 mmol·g-1)[47],MOPs (microporous organic polymers,1.08-1.33 mmol·g-1)[48],PAFs (porous aromatic frameworks,1.08-1.22 mmol·g-1) [49],TCMPs (triazine based conjugated microporous polymers,0.68-1.26 mmol·g-1) [50],TFM-1 (triazine-framwork-based porous membranes) [51].To further understand the interaction of polymers with CO2molecules,the isosteric heats of adsorption(Qst)for TT-POPs materials was calculated.Based on the adsorption isotherms of 273 and 298 K,theQstwere calculated to be 30.1(TT-POP-1) and 32.5 kJ·mol-1(TT-POP-2),respectively (Fig.S6).TheQstvalues of TT-POPs are higher than those of most porous solid-state adsorbents (Table S4),such as CTF-1 (covalent triazinebased framework) (27.5 kJ·mol-1) [52],BILPs (benzimidazoklinked polyers) (26.7-28.8 kJ·mol-1) [53-55],PAF-1 (porous aromatic framework) (15.6 kJ·mol-1) [49],activated carbons(16.2-25.7 kJ·mol-1) [20].The highQstvalues of TT-POPs can be attributed to the micropore structure effect,as well as rich CO2affinity positions [56].The data shows that the adsorption performance of TT-POP-1 is significantly better than that of TT-POP-2,which can be assigned to the higher specific surface area and pore volume of TT-POP-1.In addition,there are more microporous regions in the framework structure,and the van der Waals force between the gas molecules and the framework in the small pores is stronger.

To further evaluate the storage capacity of TT-POPs for light hydrocarbons (C1 and C2),gas adsorption isotherms of CH4,C2H4and C2H2were measured at 0.1 MPa,273/298 K and 1 bar,respectively (Fig.5).Similar results to CO2adsorption,TT-POP-1 has higher adsorption capacity of C2H2(78.3/50.1 cm3·g-1) and C2H4(53.0/36.6 cm3·g-1)at 273/298 K and 1 bar.The adsorption capacity of TT-POP-2 for C2H2was 43.8/30.8 cm3·g-1,for C2H4was 30.6/19.8 cm3·g-1.Compared with other porous materials,TTPOP-1 has a relatively good adsorption capacity for C2H2at 298 K,such as PCB-NH2(40.2 cm3·g-1) [29],ZJNU-61a(Ho)(48.0 cm3·g-1) [57],SNNU-22(26.6 cm3·g-1) [58],and comparable to [Ni(TIPA)(COO-)2(H2O)]·2(DMF)2(H2O) (56.8 cm3·g-1) [59],NbU-9 (55.2 cm3·g-1) [60].On the other hand,it also has certain advantages for the adsorption of C2H4at 298 K,such as COF-1(43.0 cm3·g-1) [61],MAF-49 (35.6 cm3·g-1) [62],MIL-101-Cr-SO3H (33.6 cm3·g-1) [63],ZIF-7 (33.6 cm3·g-1) [64],acid treated mordenites (17.1-19.6 cm3·g-1) [65],natural mordenites (21.7-23.1 cm3·g-1) [66].By further calculation,the CH4,C2H2and C2H4adsorption isosteric heats of TT-POP-1 and TT-POP-2 were 20.8,27.3,33.3 kJ·mol-1and 21.3,27.6,38.4 kJ·mol-1,respectively(Figs.S7 -S9).At low relative pressures,C2 is rapidly adsorbed,and as the pressure increases,their adsorption capacity gradually increases and eventually stabilizes.The adsorption capacity of TT-POPs is summarized in Table 1,from which we can find that the adsorption capacity of TT-POPs for C2H2and C2H4is higher,however the adsorption capacity of CH4is very low,attributing to the nitrogen-rich structure in the framework (triazole ring and triazine ring) can act as proton base and the protonic acidity of the three molecules is C2H2＞C2H4＞CH4in turn,as a result the interaction between the acidic gas and the framework is stronger.In addition,TT-POPs have a higher C2H2adsorption capacity than C2H4,which should be ascribe to the above acid difference and the molecular diameter of C2H2(0.33 nm) is smaller than C2H4(0.42 nm).Thus,C2H2can enter the pores in a larger amount,and the collision probability with the pore wall is greater,resulting in a larger van der Waals force between the gas molecules and the polymer.

Fig.5.(a)TT-POP-1 and(c)TT-POP-2 N2,CO2,CH4,C2H4 and C2H2 gas adsorption isotherms at 273 K and 0.1 MPa;(b)TT-POP-1 and(d)TT-POP-2 N2,CO2,CH4,C2H4 and C2H2 gas adsorption isotherms at 298 K and 0.1 MPa.

Table 1Gas adsorption results of TT-POPs,including adsorption capacity and selective separation ratio

3.4.Gas separation behaviors of TT-POPs

Compared with CH4,TT-POPs have higher adsorption properties for C2H2,C2H4and CO2.Therefore,the adsorption selectivity of C2H2/CH4(0.5/0.5),C2H4/CH4(0.5/0.5) and CO2/CH4(0.05/0.95) is evaluated by the IAST calculation method,which is related to C2H2production and natural gas purification,respectively.The CO2,C2H2,C2H4and CH4pure component gas adsorption isotherms obtained at 298 K and 1 bar were fitted by the single-site Langmuir-Freundlich (SSLF) model.All fitting results agree well with the experimental one-component isotherms (R2＞0.999)(Fig.6).Then,the separation ratio of each pair of mixed gases was calculated by using the fitted parameters.All calculation results are shown in Table 1.According to the experimental data,the selective separation ratio of C2H2/CH4mixed gas (0.5/0.5) for TT-POP-1 is 40.1;for TT-POP-2,the obtained value is 48.4.The high separation ratio is owing to the following two reasons.Firstly,the molecular diameter of C2H2(0.33 nm) is smaller than that of CH4(0.38 nm),so that C2H2can enter the pores in a larger amount and the collision probability with the pore wall is larger,which leads to a larger van der Waals force between C2H2and the polymer.Secondly,the electron density and nitrogen content of the electron-rich organic porous material with microporous structure make the material act as a weak proton base.The proton acidity of C2H2is much greater than that of CH4,resulting in a stronger interaction between the polymer and C2H2,which indicates it is highly probable that C2H2can be separated from natural gas.The C2H4/CH4(0.5/0.5) adsorption selectivity separation ratios of TT-POP-1 and TT-POP-2 were 14.7 and 13.6,respectively.For the reason of the polar functional triazole ring has been introduced into the skeleton,and the molecular polarizability of C2H4(42.52 × 10-25cm3) is almost twice that of CH4(25.93 × 10-25cm3),which leads to the intermolecular force (dispersion and inducing force)with C2H4is greater.The adsorption selectivity values of C2H2/CH4(48.4) and C2H4/CH4(13.6) of TT-POP-2 can be compared with the previously reported solid adsorbents,such as,USTAs (University of Texas at San Antonio) (10.0-18.0 for C2H4/CH4)[67,68],La-PCP(lanthannum based porous coordination polymer)(12.0 for C2H4/CH4)[69],SNNUs(Shaanxi Normal University)(37.3-69.5 for C2H2/CH4) [70],MOFs (5.6-112.2 for C2H2/CH4)[57,60,71-76].For CO2/CH4(0.05/0.95),the obtained selectivity separation ratios are 8.0 and 9.6,respectively.The adsorption selectivity of TT-POPs for CO2/N2(0.15/0.85) has been studied by using the IAST method.It was found that the selective separation ratio of TT-POP-1 to CO2/N2mixed gas was 37.4 at 298 K and 1 bar,and the selective separation ratio of TT-POP-2 to CO2/N2mixed gas was 39.4.All results indicate that the 1,2,3-triazole functionalized triazine-based porous organic polymer has a good application prospect in the direction of C2H2production,natural gas purification and CO2capture from flue gas.

Fig.6.(a)TT-POP-1 and(d)TT-POP-2 N2,CO2,CH4,C2H4 and C2H2 gas pure component experimental isotherms and their corresponding DSFL fits curve(solid black line);(b,c) TT-POP-1 and (e,f) TT-POP-2 calculated by IAST method for selective separation of gas mixtures at 298 K and 0.1 MPa.

4.Conclusions

In conclusion,we have successfully synthesized the 1,2,3-triazole functionalized triazine-based porous organic polymer(TT-POPs) by utilizing the copper-catalyzed click-polymerization reaction using 1,3,5-tris(4-azidophenyl)-triazine (TEPT) with 1,3,5-triacetylene benzene (TEB) and 1,4-diacetylene benzene(DEB)in a DMF solvent,respectively.The BET specific surface area of TT-POPs can reach 666 m2·g-1.At the same time,these TT-POPs exhibit excellent CO2and light hydrocarbon (C1—C2) adsorption capacity,as well as good selective separation ability for CO2/N2,CO2/CH4,C2H2/CH4and C2H4/CH4mixed gases.In particular,TTPOP-2 has a selective separation ratio of C2H2/CH4mixed gas of 48.4 at 0.1 MPa and 298 K,and a selective separation ratio of 13.6 for C2H4/CH4mixed gas.Due to the outstanding gas capture capacity and adsorption selectivity,TT-POPs has broad application prospects in natural gas purification,C2H2production and CO2capture.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We thank the National Natural Science Foundation of China(21871104,21621001 and U1967215) and the 111 project the Ministry of Education of China (B17020) for supporting this work.

Supplementary Material

Supplementary data to this article can be found online at https://doi.org/10.1016/j.cjche.2021.09.032.