Construction of crystal defect sites in N-coordinated UiO-66 via mechanochemical in-situ N-doping strategy for highly selective adsorption of cationic dyes
Graphical abstract
Introduction
Organic dyes are important chemicals widely used in paper, food, and textile industrial [1]. However, their highly toxic and non-biodegradable nature have led to serious environmental problems [2]. Among these, classical cationic dyes like rhodamine B (RhB) and safranine T (ST) contain benzene, naphthalene, and benzoquinone groups, which are carcinogenic and mutagenic to humans [3]. Attributed to these harmful impacts, their removal from waste water has been widely studied by various approaches [4]. Among these reported abatement methods, adsorption has received much attention endorsing to its high efficiency, low operation cost and easy regeneration/recycling of spent adsorbent. The vital aspects for designing an exceptional adsorbent include high selectivity and adsorption capacity, fast kinetics and good recycling properties [5].
Metal organic frameworks (MOFs) are three-dimensional porous crystal materials linked by transition metals with multitooth organic ligands [6], [7]. Their unconventional porosity and flexible chemical environment facilitate easy tuning of stability and performance [8], and hence have earned widespread interests in gas separation [9], dyes adsorption [1], [10] and sensing [11]. Among these MOFs, UiO-66 has gained great attention [12] due to its relatively higher thermal stability. Among UiO-66 series, Zr-based UiO-66 possess high surface area (>1000 m2/g) and ultra-microporous structure [1]. Many researchers have focused on UiO-66 post-modification and hybridizing strategies to enhance its adsorption abilities [13]. For instance, J. F. Yao used HCl promoted UiO-66 with adsorption capacity of methyl orange and RhB of 84.8 and 13.2 mg/g respectively [1]. X.T. Liu et al. reported low adsorption efficiency (96.45 mg/g at 298 K) for cationic methylene blue over ammonia modified UiO-66 [14]. However, post-modification strategy is hindered by factors like non-uniform modification, partial disruptions of pore structure and stability.
Recently, pre-modification approach has become a research hotspot to modulate pore size and surface property of Zr based UiO-66 [15], [16]. Using long linker of precursors can design larger pores in UiO-66. However, this process is inevitably associated with a considerable loss in surface area and their corresponding selective adsorption performance [17], [18]. Another easy and efficient strategy of defect designing in MOFs is the addition of single tooth organic ligands [19] or weakly coordinated compounds [20]. Based on preserving original skeleton of MOFs, in-situ grafting defects approach using “one-pot” synthesis is very attractive in this regard. Concurrently, its challenge is to synergistically modulate pore size and surface properties avoiding the any loss in surface area. Credited to these hindering factors in modified MOFs synthesis, rare studies have been focused on these aspects with systematic investigation.
In this work, we proposed three alkaline nitrogen heterocycles i.e. dopamine, pyrrole, 2-methylimidazole to modulate UiO-66 by a facile in-situ one-pot mechanochemical high energy attack for the construction of defects. This strategy resulted in higher proportion of larger micropore size, increase in surface area (from 1215.2 to 1549.1 m2/g) and basic surface property. The adsorption performance of N-modified UiO-66 were investigated for RhB and ST having similar chemistry but opposite acid-base groups. The adsorption capacity and diffusivity of RhB on pyrrolic N-coordinated UiO-66 was twice (384.1 mg/g) and 53 times as that of pristine UiO-66. Similarly, selectivity of RhB/ST on N-coordinated UiO-66 increased by two orders of magnitude compared to pristine UiO-66 from 5 to 714, which were attributed to effective charges transfer and Zr-N sp2 configurations. The coordination mode, binding force and binding energy of alkaline N compounds towards UiO-66 were investigated via density functional theory (DFT) simulation and surface characterization including X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD).
Section snippets
Reagents
All the chemicals were of analytical reagent (AR) grade and used without further processing. Terephthalic acid (H2BDC, 99.5%,) and zirconium chloride (ZrCl4, 99%) were purchased from Sigma-Aldrich, Shanghai, China. Dopamine, pyrrole and 2-methylimidazol were obtained from Sinopharm Chemical Reagents Co. Beijing, China. Methanol (CH3OH, 99.5%), N,N-dimethylformamide (C3H7NO, DMF, 99.8%), RhB, ST and HCl (37 wt%) were obtained from Nanjing Chemical Reagent Co. Ltd. Nanjing, China.
Preparation of N-doped NX-UiO-66
NX-UiO-66 were
Morphology of N-coordinated UiO-66s
SEM images of pristine UiO-66 and N-coordinated NX-UiO-66 in Fig. 1 suggested an irregular morphology of the latter as compared to UiO-66 synthesized by hydrothermal method [20]. This could be attributed to the incomplete crystal surface growth in UiO-66 due to fast growing (30 min) mechanochemical approach involving strong mechanical friction [25]. The crystal size of parent UiO-66 (about 152 nm in Fig. 1A) was increased to 362 nm along with enhancement in crystallinity (Fig. 1B-D).
Conclusions
In summary, a facile in-situ N-coordination mechanochemical strategy was proposed to create defects and modulate alkaline surface on UiO-66 for the preparation of novel MOFs for the selective adsorption from a hard separating binary dyes system with similar molecular size and 3-D structure. Characterization results confirmed that N-doped UiO-66 exhibited high surface area (1549.1 m2/g), uniform larger defect pores (11–13 Å) and better resistance to alkaline corrosion. Meanwhile, H2O- and NH3
Conflict of interest
The authors declare no competing financial interest.
Acknowledgments
This work was financially supported by National Natural Science Foundation of China (No. 21676059 & 21666004), Natural Science Foundation of Guangxi Zhuang Autonomous Region, China (No. 2017GXNSFFA198009 & 2016GXNSFAA380229), Scientific Research Foundation of Guangxi University (No. XGZ130963) and Innovation Project of Guangxi Graduate Education (NO.YCSW2018030). We thank Dr. Zhiqun Tian and all members of Guangxi Key Laboratory for Electrochemical Energy Materials for characterization analysis.
References (57)
- et al.
Acid-promoted synthesis of UiO-66 for highly selective adsorption of anionic dyes: adsorption performance and mechanisms
J. Colloid Interface Sci.
(2017) - et al.
Investigation on efficient adsorption of cationic dyes on porous magnetic polyacrylamide microspheres
J. Hazard. Mater.
(2015) - et al.
Selective dye adsorption by highly water stable metal-organic framework: long term stability analysis in aqueous media
Appl. Surf. Sci.
(2018) - et al.
Facile synthesis of size-controlled MIL-100(Fe) with excellent adsorption capacity for methylene blue
Chem. Eng. J.
(2015) - et al.
Enhancing CO2 adsorption and separation ability of Zr(IV)-based metal-organic frameworks through ligand functionalization under the guidance of the quantitative structure-property relationship model
Chem. Eng. J.
(2016) - et al.
Selective adsorption of cationic dyes by UiO-66-NH2
Appl. Surf. Sci.
(2015) - et al.
Experimental and theoretical study on selenate uptake to zirconium metal-organic frameworks: effect of defects and ligands
Chem. Eng. J.
(2017) Kinetics of the adsorption of reactive dyes by chitosan
Dyes Pigments
(2006)- et al.
Evaluation of the performance of adsorption and coagulation processes for the maximum removal of reactive dyes
Dyes Pigment
(2006) - et al.
Competitive adsorption and selectivity of benzene and water vapor on the microporous metal organic frameworks (HKUST-1)
Chem. Eng. J.
(2015)
Hydrophobic N-doped porous biocarbon from dopamine for high selective adsorption of p-Xylene under humid conditions
Chem. Eng. J.
Preparation of highly-hydrophobic novel N-coordinated UiO-66(Zr) with dopamine via fast mechano-chemical method for (CHO-/Cl-)-VOCs competitive adsorption in humid environment
Chem. Eng. J.
Synthesis and properties of a precursor derived nano Zr(C, N)-carbon composite coating on SiC fibers
Mater. Des.
Adsorption equilibrium and kinetics of p-xylene on chromium-based metal organic framework MIL-101
Chem. Eng. J.
A model for water adsorption in activated carbon
Carbon
Activated carbon modifications to enhance its water treatment applications. An overview
J. Hazard. Mater.
Microwave synthesis and characterization of MOF-74 (M = Ni, Mg) for gas separation
Micropor. Mesopor. Mater.
Ultrafast room temperature synthesis of novel composites Imi@Cu-BTC with improved stability against moisture
Chem. Eng. J.
A nanoporous Ag(I) coordination polymer for selective adsorption of carcinogenic dye Acid Red 26
Chem. Commun.
A highly efficient magnetic chitosan “fluid” adsorbent with a high capacity and fast adsorption kinetics for dyeing wastewater purification
Chem. Eng. J.
Molecular simulation of hydrogen adsorption in aluminum organic framework
Mod. Phys. Lett. B
Ligand-directed strategy for zeolite-type metal-organic frameworks: zinc(II) imidazolates with unusual zeolitic topologies
Angew. Chem.-Int. Edit.
Governing metal-organic frameworks towards high stability
Chem. Comm.
Zeolitic imidazolate framework composite membranes and thin films: synthesis and applications
Chem. Soc. Rev.
Solvatochromic behavior of a nanotubular metal-organic framework for sensing small molecules
J. Am. Chem. Soc.
Rational tuning of water vapor and co2 adsorption in highly stable Zr-based MOFs
J. Phys. Chem. C
Stiff metal-organic framework-polyacrylonitrile hollow fiber composite membranes with high gas permeability
J. Mater. Chem. A
Metal-organic framework composites
Chem. Soc. Rev.
Cited by (110)
Efficient removal of dyes from water by zirconium-based metal-organic cages with varying functional groups
2023, Journal of Molecular StructureFabrication of recyclable UiO-66-NH<inf>2</inf>/PVDF hybrid fibrous membrane for Cr(VI) removal in wastewater
2023, Journal of Industrial and Engineering ChemistryBoosting the Rhodamine B adsorption of bimetallic Ce/Zr UiO-66: Effect of valence states of cerium precursor
2023, Microporous and Mesoporous Materials
- 1
These authors contributed equally to this work and should be considered co-first authors.