Effects of Monocarboxylic Acid Additives on Synthesizing Metal

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Effects of Monocarboxylic Acid Additives on Synthesizing MetalOrganic Framework NH2-MIL-125 with Controllable Size and Morphology Shen Hu, Min Liu, Xinwen Guo, Keyan Li, Yitong Han, Chunshan Song, and Guoliang Zhang Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.7b01250 • Publication Date (Web): 16 Oct 2017 Downloaded from http://pubs.acs.org on October 18, 2017

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Crystal Growth & Design

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Effects of Monocarboxylic Acid Additives on Synthesizing

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Metal-Organic Framework NH2-MIL-125 with Controllable

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Size and Morphology

4

Shen Hu,a Min Liu, *a Xinwen Guo,a Keyan Li,a Yitong Han,a Chunshan Song,*a,b and

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Guoliang Zhangc

6

a

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Research, School of Chemical Engineering, Dalian University of Technology, Dalian

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116024, P. R. China. Fax: +86-0411-84986134; Tel: +86-0411-84986134; E-mail:

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[email protected].

State Key Laboratory of Fine Chemicals, PSU-DUT Joint Center for Energy

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b

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of Energy & Mineral Engineering, Pennsylvania State University, University Park,

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Pennsylvania 16802, United States. Fax: 814-865-3573; Tel: 814-863-4466;

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E-mail:[email protected].

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c

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Technology, Hangzhou 310014, P. R. China.

EMS Energy Institute, PSU-DUT Joint Center for Energy Research and Department

College of Biological and Environmental Engineering, Zhejiang University of

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Keywords:

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MOFs, NH2-MIL-125, Monocarboxylate acid modulator, Size and morphology

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control, Defect, Photocatalysis.

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Abstract

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The effect of monocarboxylic acids on synthesizing NH2-MIL-125 is systematically

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studied for the first time in this work and the fantastic results are discussed in detail.

ACS Paragon Plus Environment


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We found that small molecular acid (Acetic Acid, Thioglycolic Acid) mostly affect the

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morphology changes of NH2-MIL-125, while the pseudo-linker acid (p-Toluylic Acid,

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Benzoic Acid) has a significantly impact on the crystal size on account of the

26

nucleation and the crystal growth rates. Ar sorption measurement and TEM

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Characterization show that samples synthesized with pseudo-linker acid as additives

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have hierarchical structure owing to the internal defects or caves formed in the crystal.

29

These

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of organic pollutants by the combined effects of adsorption and photodegradation.

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1. Introduction

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Metal organic frameworks (MOFs), consisting of various organic linkers and metal

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ions or clusters to form porous three-dimensional networks with large pore volumes

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and high inner surface areas, are a fantastic class of crystalline materials with

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intriguing structural topologies and flexible pore properties.1-2 The inherent large

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surface areas, uniform but tunable cavities, and tailorable physicochemical properties

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have enabled them to exhibit a variety of potential applications such as gas adsorption

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and separation, drug delivery, and catalysis.3-15 The controlling of the crystal size and

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morphology is an important theme because of its significant impact on the

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performance in various applications. Yang and coworkers demonstrated a simple

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methodology to synthesize size- and morphology-controlled Ni(II)-doped MOF-5 and

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detected the difference on gas adsorption16. Huskens et al. developed a PEG assisted

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method to one-step synthesize size controlled MIL-88 which have potential

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applications on drug delivery17. Tian and coworkers studied the role of crystal size on

samples

also

show

an

excellent

performance


for

the

removal

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swing-effect and adsorption induced structure transition of ZIF-818. Liu and

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coworkers applied metal ions as additives to obtain porous HKUST-1 with different

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sizes and morphologies which have an effect on the gas sorption properties19. Li and

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coworkers synthesized NU-1003 with a tunable crystal size from 300 nm to 1000 nm

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and the nanoscale MOF enzyme carrier show better performance for accelerating

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nerve agent hydrolysis.20 Our group also focused on size and morphology control of

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MOFs and obtained series of interesting results.21-25 The size and morphology control

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of MOFs is fundamental and necessary for the research of MOFs.

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Monocarboxylic acid, such as acetic acid, is often used as additives in synthesizing

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MOFs to control the deprotonation rate of the organic linkers or act as competitive

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linkers to affect the nucleation rate and the crystal growth process, thus finally leads

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to form crystals with different size and morphology.26-30 Meanwhile, another type of

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monocarboxylic acid, for example benzoic acid, is most commonly used as

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modulators in the defect engineering of MOFs, especially UiO-66.31-33 Defects are

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quite common in crystals, which can be introduced into the crystal lattice of some

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canonical MOFs. These ligand substituted defects affect pore size and surface

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properties, which subsequently affect the performance in gas storage, gas separation,

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and catalysis.34-39 Monocarboxylic acids are commonly used in synthesizing MOFs

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but the phenomena are various in different literatures. Systematic researches are

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required to find the complicated effect of monocarboxylic acids as modulators in

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synthesizing MOFs.

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NH2-MIL-125(Ti), an amine-functionalized Ti-based MOF structure, is a promising



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photocatalyst due to its photocatalytic and catalytic oxidation performance.40-41

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Various strategies were developed to improve its photocatalytic activity. Zhu et al.

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prepared Ni-doped NH2-MIL-125(Ti) catalyst and used them for the photocatalytic

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aerobic oxidation of aromatic alcohols upon visible light irradiation.42 MIL-125(Ti)

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and graphitic carbon nitride (g-C3N4) or reduced graphene oxide (rGO) hybrids were

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prepared to improve the photocatalytic activity.43-44 Hicks and coworkers used a

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chelating agent-free, vapor-assisted crystallization method to synthesize hierarchical

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microporous/mesoporous MIL-125(Ti) and the obtained catalyst showed a marked

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enhancement in activity in the oxidation of an aromatic sulfur compound.45 However,

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the size, morphology and pore structure of NH2-MIL-125 have rarely been studied

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which have original effect on the properties.

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In this work, we choose four different monocarboxylic acids, p-Toluylic Acid

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(p-TA), Benzoic Acid (BA), Acetic Acid (HAc) and Thioglycolic Acid (HS), as

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modulators to synthesize NH2-MIL-125 to find out the effect of monocarboxylic acid

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on crystal size, morphology and pore distribution. The results show that p-TA and BA

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have a significantly effect on crystal size and pore distribution, while HAc and HS

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mostly affect the morphology of NH2-MIL-125. Samples synthesized with p-TA were

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also used for photodegradation of RhB which showed an increased dye removal on

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account of the conjugation of the improved adsorption and photodegradation abilities.

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2. Experimental

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2.1 Reagents and Chemicals. 2-amino-1, 4-benzenedicarboxylic acid (NH2-BDC),

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titanium isopropoxide (C12H28O4Ti, TOPT) and Thioglycolic Acid (HS) were


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purchased from Aldrich. Acetic Acid (HAc), p-Toluylic Acid (p-TA) and Benzoic

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Acid (BA) were achieved from Tianjin Guangfu Fine Chemical Reagent Co., Ltd.

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(China). N,N-dimethylformamide (DMF), and methanol (CH3OH) were obtained

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from Shanghai Chemical Reagent Inc. of the Chinese Medicine Group. All chemicals

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were used as received without further purification.

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2.2 Synthesis of NH2-MIL-125(Ti) samples. The synthesis of NH2-MIL-125(Ti)

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samples using different monocarboxylic acid as modulators were detailedly shown in

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the supporting information. The samples were named as abbr-R (abbr is the

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abbreviation of monocarboxylic acid, p-TA for p-Toluylic Acid, BA for Benzoic Acid,

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HAc for Acetic Acid, HS for Thioglycolic Acid; R is the molar ratio of

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monocarboxylic acid to organic linker NH2-BDC) for convenience.

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2.3 Characterization methods. Powder X-ray diffraction (XRD) patterns were

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recorded on a Rigaku SmartLab(9) diffractometer, using Cu Kα radiation. The size

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and morphology of samples were characterized using field-emission scanning electron

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microscopy (NOVA NanoSEM 450). Ar adsorption/desorption isotherms were

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recorded at 87 K on a Quantachrom Autosorb-iQ instrument. Before measurement,

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samples were outgassed at 130 °C overnight. Transmission electron microscopy

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(TEM) images were taken using a Tecnai G2 20 S-twin instrument (FEI Company)

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with an acceleration voltage of 200 kV. Thermogravimetric analysis (TG) was

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performed on a SDT Q600 (TA Instruments, USA) in the temperature range of

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25−650 °C under air atmosphere at a heating rate of 10 °C/min. The FT-IR spectra

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were recorded with an EQUINOX55 (Bruker, Germany) Fourier transform infrared



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spectrometer by means of the KBr pellet technique. Diffuse reflectance UV-Vis

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spectroscopy (DR/UV-Vis) experiments were performed using a JASCO 550

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spectrophotometer.

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2.4 Photocatalytic experiment. The photocatalytic activities of p-TA assisted

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synthesized samples were investigated in photocatalytic degradation of Rhodamine B

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(RhB) aqueous solution under visible light irradiation using a 500 W Xe arc lamp with

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a 420 nm cutoff filter as the light source. Typically, 20 mg of photocatalyst sample

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was added into 50 mL of 100 mg/L RhB aqueous solution in a home-made cylindrical

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Pyrex vessel reactor. The suspension was magnetically stirred in the dark for 60 min

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to establish the adsorption−desorption equilibrium, and then illuminated for 120 min

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to photodegrade RhB. During this process, sample was collected via filtrating by a

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0.22 µm PTFE syringe filter at predetermined time intervals. The concentration of

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RhB in the supernatant solution was determined by using a JASCO V-570

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UV/VIS/NIR spectrophotometer at its maximum absorption wavelength of 554 nm.

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3. Results and discussion

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3.1 Synthesis of NH2-MIL-125(Ti) with pseudo-linker acid. Figure 1 shows the

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SEM images of NH2-MIL-125 synthesized using different amounts of p-TA. It is

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interesting that the crystal size decreased first and then increased with an increase in

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p-TA/NH2-BDC ratio. This phenomenon has barely been reported in literatures, which

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usually shows linear changes on crystal size or morphology. Figure 2 shows the XRD

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patterns of NH2-MIL-125 with different crystal size. It can be seen that the

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corresponding XRD patterns clearly suggest that the addition of p-TA does not affect


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the structure or the crystallinity of NH2-MIL-125.

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In our assumption, p-TA plays like a pseudo-linker which has similar structure as the

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original linker NH2-BDC but with only one carboxyl. In this case, p-TA can partially

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act as the organic linker and the increase of p-TA speeds up the nucleation rate and

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obtain more nuclei to further form small crystals. At the same time, p-TA as blocking

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agent can also stop the growth of crystals to further decrease the crystal size.31, 33, 46-47

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When the amount of p-TA is beyond the limitation, it becomes difficult to form nuclei

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because of the high concentration leading to form a small number of nuclei which

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grows slowly to form large crystals48. Thus, the yield of sample p-TA-20 is extremely

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low while the other samples have similar high yield. When the amount of p-TA goes

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on increasing, it is not available to obtain any sample. This means it is difficult to

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form nuclei or further growing in the overwhelming amount of p-TA (Scheme 1).

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To confirm our assumption, Ar physical adsorption was carried out to investigate

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the textural properties of these samples to better understand the effect of p-TA. Figure

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3 shows the Ar adsorption and desorption isotherms at 87 K and the pore size

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distributions of NH2-MIL-125 samples synthesized with p-TA. All these samples

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show a typical type I (micropore) characteristics (Figure 3 (a)). It is obvious that the

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samples synthesized with p-TA show further Ar uptake at high P/P0 (0.9–1.0), which

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demonstrates the existence of macropores. From the pore size distributions, it is

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apparently to see that there exist abundant hierarchical pores with a wide-range

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mesopore and macropore distribution (Figure 3 (b)). There exists a nonnegligible pore

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size distribution at around 1.6 nm of all p-TA assisted samples. It is probably



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attributed to the p-TA inserting into the framework and causes the missing of

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NH2-BDC between two adjacent cages (one is ~1.2 nm, the other is ~0.6 nm40), thus

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interlocking pores around 1.6 nm are formed. When more p-TA got inserted into the

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adjacent cages framework, it will cause several cages got connected and form much

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more mesopores and macropores (2 nm to 100 nm). The calculated specific surface

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area, total pore volume and micropore volume are listed in Table 1. To make a

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detailed comparison of the pore volume, we calculated the ratio of micropore volume

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to the total pore volume which could indicate the volume of mesopore and macropore.

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The BET surface area and the micropore volume change little, while the total pore

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volume increased a lot with the crystal size decrease, owing to the mesopore and

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macropore formed. Sample p-TA-12 with the smallest crystal size has the largest pore

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volume (~1 cm3/g) and more than half of the total pore volume belongs to mesopore

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and macropore. When it comes to sample p-TA-18, there does not exist much pore

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larger than 6 nm according to the pore size distribution. It is probably because when

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the ratio of p-TA/NH2-BDC is too large, it becomes difficult to form nuclei and

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further grow to crystals. The two candidates, p-TA and NH2-BDC, compete to get

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connected to the framework. Crystals connected with NH2-BDC instead of p-TA is

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more stable as it is able to continue growing. There exists a dynamic competition

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process between them, and NH2-BDC will replace p-TA to get the numbered nuclei to

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grow to a complete crystal. This is known as solvent-assisted linker exchange (SALE)

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approach which is quite common in mixed-linker synthesis system49-51. Therefore, it is

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difficult for sample p-TA-18 to form large mesopore or macropore. The fact that


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sample p-TA-16 has an increased micropore volume/total pore volume ratio than

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p-TA-12 is attributed to this mechanism.

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The TEM images show similar regularity of crystal size changes as SEM images

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(Figure 4). At the same time, a large number of voids are observed in the interior of

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NH2-MIL-125 samples synthesized with adding p-TA, which is in accordance with the

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result of Ar adsorption and desorption. Sample p-TA-18 does not have pores large

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enough to be easily observed by TEM and the reason has been discussed in the part of

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textural properties.

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The thermal behavior of these samples was studied by TG measurements (Figure

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S1). All TG/DTG curves of p-TA assisted synthesized samples (p-TA-1 to p-TA-18)

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show a similar multiple-step weight loss while sample p-TA-0 shows a quite different

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weight loss. The continuous weight loss (p-TA-1 to p-TA-18) from 100 to 600 °C is

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due to the exfoliation of p-TA inserting into the framework of NH2-MIL-125, and the

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different exfoliated temperature owes to the disparate position of p-TA in the structure.

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TG curves are also used to characterize the defects of MOFs framework.31 The p-TA

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linked to the structure will result in a decrease in the amount of metal clusters in the

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whole framework. It is observed that the weight loss (from room temperature to

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600 °C) increased slightly from p-TA-0 to p-TA-12 which means more p-TA is

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connected to the framework. Sample p-TA-16 and p-TA-18 have a decreased weight

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loss owing to less defects formed. The IR spectra of these samples show similar

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characteristic peaks (Figure S8). The typical vibrational bands at the region of 1400–

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1700 cm−1 belong to carboxylic acid functional group of the Ti-coordinated MOF



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structure. Two absorption bands around 1600 and 1500 cm−1 can be assigned to

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carbonyl asymmetric stretching vibrations, whereas bands at about 1440 and 1400

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cm−1 can be assigned to carbonyl symmetric stretching vibrations, and the band at

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1250 cm−1 belongs to the C–H symmetric stretching vibrations of the benzene ring.

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The region of 400–800 cm−1 shows the Ti–O–Ti–O vibrations, and the bands at 3500

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and 3380 cm−1 are due to the NH2 group. To be specific, there exist two new bands at

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around 2960 and 2920 cm−1 which are attributed to the functional group of methyl on

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the benzene ring. It proves that p-TA get connected to the framework and partially

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take the place of NH2-BDC and form defects in the interior of crystals. This is a probe

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to verify the existence of the p-TA in the framework. NH2-MIL-125(Ti), containing

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NH2-BDC units as the organic linker, is known as a visible-light-absorbing MOF. The

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light response property was analyzed by UV/Vis spectroscopy. Figure S3 shows the

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UV/Vis diffuse reflectance spectra of the as-prepared samples. It can be found that all

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these samples show similar absorption spectra. There exists slight red shift of

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absorption edge as the crystal size decreased. All samples show good visible light

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response.

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The changes of crystal size and pore structure of NH2-MIL-125 synthesized with

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p-TA have similar variation trend which proves each other based on our assumption.

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In order to further understand the effect of additive, we chose another pseudo-linker

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monocarboxylic acid modulator, Benzoic Acid (BA), to study the size and pore

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structure changes of NH2-MIL-125. The XRD patterns (Figure S4) show that all the

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samples have similar structure of NH2-MIL-125. Figure 5 shows the SEM images of


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NH2-MIL-125 synthesized by adding different amounts of BA as modulator. It can be

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seen that the crystal size of BA samples show the same variation trend as p-TA

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samples. With the increasing amount of BA the crystal size of NH2-MIL-125

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decreased first and then increased and the smallest sample with the mean crystal size

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of 70 nm (BA-12) were obtained. Figure 6 shows the Ar adsorption and desorption

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isotherms at 87 K and the pore size distributions of NH2-MIL-125 samples

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synthesized with BA. The types of sorption isotherms are similar with the p-TA

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samples and the pore size distribution also show the existence of large amount of

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mesopore and macropore. The calculated specific surface area, total pore volume,

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micropore volume and Vmicro/Vtotal are listed in Table 2 and the results give similar

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variation trend as p-TA samples.

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To make a further expansion, we applied this pseudo-linker-assisted synthesis

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method to synthesize UiO-66. The results show similar variation trend as

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NH2-MIL-125 samples (Supporting Information). It approves that it is propagable

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and effective method using pseudo-linker monocarboxylic acid modulator to synthesis

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size controlled hierarchical MOF materials.

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3.2 Synthesis of NH2-MIL-125(Ti) with small molecular acid. In order to

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systematically investigate the effect of monocarboxylic acid on synthesizing

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NH2-MIL-125, acetic acid (HAc) was used as modulators in the synthesis system. It is

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interesting that in this occasion the results are quite different from the pseudo-linker

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acid system. Figure 7 shows the SEM images of HAc samples, it can be seen that the

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crystal size does not change much, instead, the morphology of NH2-MIL-125 changes



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from circular plate to octahedron. The effect of acetic acid as modulators on

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synthesizing MOFs is very complicated in literatures and two probable mechanisms

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were mentioned.27,

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monocarboxylic acid like acetic acid can also been divided into two stages like

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pseudo-linker acid. In the first stage, small amount of acetic acid plays like a

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competitor and competes with the organic linker (NH2-BDC) thus reducing the

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growth rate of nuclei to form larger crystals. When the amount of acetic acid

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continues to increase, the extra molecules will adsorb on the {110} facet of

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NH2-MIL-125 crystals and limit its growth to form special octahedron morphology

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(Scheme 1). The sorption data of HAc samples are shown in Figure 8 and Table 3.

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Pore distribution results show no significant difference, which means acetic acid

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molecule is not easy to get connected to the framework to form large amount of

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mesopores and macropores. The calculated Vmicro /Vtotal also show similar results. It

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can be predicted that small molecular monocarboxylic acid like acetic acid plays like

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coordination modulator29 and can mainly affect the crystal size and morphology of

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NH2-MIL-125.

29, 48, 52

We suppose that the effect of small molecular

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In order to verify our prediction, we chose another small molecular monocarboxylic

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acid modulator, Thioglycolic Acid (HS), to study the effect on NH2-MIL-125. The

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SEM images (Figure 9) shows that ultra-thin truncated octahedron were obtained with

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large amount of HS modulator. We suppose that HS molecule has a strong adsorption

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on {001} facet and limits its growth thus forming ultra-thin truncated octahedron

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morphology (Scheme 1). Ar adsorption and desorption isotherms and the pore size


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distributions of NH2-MIL-125 synthesized with HS were shown in Figure S10 and

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Table S7, the results are similar with HAc samples that HS molecule does not affect

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the pore structure of NH2-MIL-125. It can be summarized that small molecular acid

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mostly affect the crystal size and morphology of NH2-MIL-125 based on coordination

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modulation method while the pore distribution changes negligibly.

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3.3 Photocatalytic performance of NH2-MIL-125. NH2-MIL-125 is a promising

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photocatalyst due to its photocatalytic and catalytic oxidation performance.

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Photodegradation of organic dye RhB was selected as the model reaction to evaluate

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the photocatalytic activity of the prepared samples.53 In specific, 20mg catalyst was

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used to degrade 50mL RhB aqueous solution of 100mg/L. RhB photocatalytic

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degradation performance of NH2-MIL-125 synthesized with same amount of different

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monocarboxylic acid additives were first shown in Figure 10. It can be obviously seen

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that pseudo-linker acid-samples (p-TA-8 and BA-8) have an extremely elevated dye

278

removal performance compare with small molecular acid-samples (HAc-8 and HS-8).

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According to our previous research, the pore structure has a more remarkable effect

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on the photocatalytic degradation performance of NH2-MIL-125 than morphology53.

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The sorption data of NH2-MIL-125 samples indicates that p-TA-8 and BA-8 have

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larger amount of mesopore and macropore than HAc-8 and HS-8 which contributes to

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more effective photocatalytic degradation performance.

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To achieve a better understanding of the photocatalytic activity, the performance of

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NH2-MIL-125 synthesized with different amount of p-TA were compared in detail. It

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can be seen that the p-TA assisted synthesized samples have an extremely elevated



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dye removal performance, as is shown in Figure 11(a). The total RhB removal was

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raised from 45% (sample p-TA-0) to 91% (sample p-TA-12) combining the effect of

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adsorption and photodegradation. The p-TA assisted synthesized samples show

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enhanced adsorption capacity in contrast to the sample p-TA-0 owing to the abundant

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hierarchical pores with a wide-range of mesopore and macropore distribution. To

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make a comparison of the reaction kinetics of the RhB degradation, the kinetic curves

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for RhB photodegradation are plotted according to the pseudo-first order model (ln

294

(C0/C)=kt) as shown in Figure 11(b). The values of rate constant (k) can be calculated

295

from the slope and the intercept of the linear plot (Figure 11(c)). The rate constants of

296

RhB degradation of these samples show a raise from sample p-TA-0 (0.00428 min-1)

297

to sample p-TA-12 (0.01623 min-1) as the crystal size decreased. The enhancement of

298

the photocatalytic activity is owing to an integrated effect of the enrichment of RhB

299

and the promoted diffusion of RhB together with the decomposition product which

300

both benefit from the hierarchical pores. Meanwhile, the red shift of absorption edge

301

for the small crystal size samples analyzed by UV/Vis spectroscopy may lead to an

302

enhancement of the absorption of visible light and the increase of the photocatalytic

303

activity. The small crystal size is also beneficial for the diffusion process and the

304

photodegradation. It’s worth noting that sample p-TA-12 with 90 nm mean crystal

305

size have the best performance while rate constant of sample p-TA-8 with 100 nm

306

mean crystal size is much lower than sample p-TA-12. The huge improvement of

307

sample p-TA-12 can be attributed to the increased amount of mesopore percentage

308

from 36% to 55%. While sample p-TA-0, p-TA-1, and p-TA-2 with similar mesopore


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309

percentage show a small promotion of the rate constant from 0.00428 min-1 (p-TA-0)

310

to 0.00558 min-1 (p-TA-2) due to the remarkable crystal size reduction from 750 nm

311

to 320 nm. It can be summarized that the higher activity is majorly from the increased

312

amount of mesopore percentage.

313

The recycle experiments of sample p-TA-12 were evaluated under the same

314

conditions to study the stability of the photocatalyst. The data presented in Figure 12

315

reveal no deactivation of the catalyst after three consecutive cycles and the RhB

316

removal keeps at 90% without any reduction, illustrating the excellent stability of the

317

catalyst under the conditions. XRD pattern (Figure 12(c)) of fresh and used catalyst

318

(used three times) also proves the stability of NH2-MIL-125 structure. Therefore,

319

using pseudo-linker monocarboxylic acid as additives to form size controlled

320

hierarchical MOFs shows promising applications in wastewater treatment.

321

Conclusions

322

In summary, we systematically studied the effect of monocarboxylic acids as

323

modulators on synthesizing NH2-MIL-125 and found the results are closely related to

324

the types of monocarboxylic acids. Pseudo-linker acid like p-TA or BA has a

325

significantly effect on the crystal size and the pore size distribution by affecting the

326

nucleation and the crystal growth rates. Pseudo-linker acid has similar structure and

327

property as organic linker which can accelerate the nucleation within a certain range,

328

while as monocarboxylic acid, it will create defect into the framework forming

329

hierarchical structure. Another type of monocarboxylic acid is small molecular acid

330

like HAc or HS which mainly affect the morphology of NH2-MIL-125 by adsorbing



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

331

on the specific facet and limiting its growth. Thus, nanoscale NH2-MIL-125 with

332

hierarchical structure and NH2-MIL-125 with special morphology like octahedron and

333

ultra-thin truncated octahedron were obtained. Furthermore, samples synthesized with

334

p-TA were also used for photodegradation of RhB which showed an increased dye

335

removal on account of the conjugation of improved adsorption and photodegradation.

336

It proves that samples with smaller crystal size and more abundant hierarchical

337

structure are beneficial for adsorption and the diffusion of decomposed pollutants

338

during the photodegradation which contributes to better dye removal.

339

Supporting Information (word)

340

Synthesis conditions of all these samples; TG, IR and UV/Vis curves of

341

NH2-MIL-125 synthesized with p-Toluylic Acid; XRD patterns, sorption data and

342

SEM images of NH2-MIL-125 synthesized with Benzoic Acid, Acetic Acid and

343

Thioglycolic Acid; XRD patterns, sorption data and SEM images of UiO-66

344

synthesized with p-Toluylic Acid.

345

AUTHOR INFORMATION

346

Corresponding Author

347

*

348

**

349

Author Contributions

350

The manuscript was written through contributions of all authors. All authors have

351

given approval to the final version of the manuscript.

Fax: +86 0411 84986134; E-mail address: [email protected].

Fax: +1 814 863 4466; E-mail address: [email protected].


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352

Acknowledgements This work was supported by the State Key Program of the National Natural Science

353 354

Foundation of China (Grant No. 21236008).

355

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356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391

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484 485

Figure 1 SEM images of NH2-MIL-125 synthesized with different molar ratio of p-TA/NH2-BDC

486



p-TA-16 p-TA-12 p-TA-8

Intensity

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

Page 22 of 37

p-TA-4 p-TA-2 p-TA-1 p-TA-0 Simulated 10

487 488

20

30

40

50

2 theta(degree) Figure 2 XRD patterns of NH2-MIL-125 synthesized with different amount of p-TA

489 490


Page 23 of 37

(a)

p-TA-18

Volume(cm /g STP)

p-TA-16 p-TA-12

3

p-TA-8 p-TA-4 p-TA-2 p-TA-1 p-TA-0

0.0

0.2

0.4

0.6

0.8

1.0

Relative pressure(P/P0) 6

(b)

p-TA-0 p-TA-1 p-TA-2 p-TA-4 p-TA-8 p-TA-12 p-TA-16 p-TA-18

5

dV/d(logD)

4

2

3 2 1 0

1

1

10

100

0 10 491 492 493 494

Pore size(

m n

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


100

)

Figure 3 Ar adsorption and desorption isotherms at 87 K and pore size distributions of NH2-MIL-125 synthesized with different molar ratio of p-TA/NH2-BDC. The pore size distributions were determined by non-local density functional theory (NLDFT).

495



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

496 497

Figure 4 TEM images of NH2-MIL-125 synthesized with different amount of p-TA

498


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499 500 501 502

Figure 5 SEM images of NH2-MIL-125 synthesized with different molar ratio of BA/NH2-BDC



BA-16

Volume(cm /g STP)

(a)

BA-14

3

BA-12 BA-8 BA-4 BA-2

0.0

0.2

0.4

0.6

0.8

1.0

Relative pressure(P/P0) (b)

BA-2 BA-4 BA-8 BA-12 BA-14 BA-16

6

3

5 4

dV/d(logD)

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

Page 26 of 37

3

2

2 1 0

1

1

10

100

Pore size(nm)

0 10 503 504 505 506 507

100

Pore size(nm) Figure 6 Ar adsorption and desorption isotherms at 87 K and pore size distributions of NH2-MIL-125 synthesized with different molar ratio of BA/NH2-BDC. The pore size distributions were determined by non-local density functional theory (NLDFT).


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508 509 510

Figure 7 SEM images of NH2-MIL-125 synthesized with different molar ratio of HAc/NH2-BDC



(a) Volume(cm 3 /g STP)

HAc-18 HAc-16 HAc-12 HAc-8 HAc-4 HAc-2

0.0

(b)

0.2

0.4

0.6

0.8

7

HAc-2 HAc-4 HAc-8 HAc-12 HAc-16 HAc-18

6

dV/d(logD)

1.0

Relative pressure(P/P0)

5 4 3 2 1 0 1

511 512 513 514 515

10

Pore size(

m n

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

Page 28 of 37

100

)

Figure 8 Ar adsorption and desorption isotherms at 87 K and pore size distributions of NH2-MIL-125 synthesized with different molar ratio of HAc/NH2-BDC. The pore size distributions were determined by non-local density functional theory (NLDFT).


Page 29 of 37

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516 517 518

Figure 9 SEM images of NH2-MIL-125 synthesized with different molar ratio of HS/NH2-BDC



1.0

In darkness

Under light irradiation p-TA-0 p-TA-8 BA-8 HAc-8 HS-8

Light on 0.8

C/C0

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

Page 30 of 37

0.6 0.4 0.2 0.0 -60

519 520 521

-40

-20

0

20

40

60

80

100 120

time(min) Figure 10 RhB photocatalytic degradation performance of NH2-MIL-125 synthesized with different monocarboxylic acid additives


In darkness

Under light irradiation Light on

0.8


0.6

0.4

(b) 1.0

(c)0.016


0.8

0.6

0.014 0.012

k(min -1)

(a) 1.0

C/C 0

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


ln(C 0/C t)

Page 31 of 37

0.4

0.2

0.2

0.010 0.008 0.006 0.004 0.002

0.0

0.0

0.000

-60

522 523 524 525 526

-40

-20

0

20

40

time(min)

60

80

100 120

0

20

40

60

80

100

120


time(min)

Figure 11 (a) RhB photocatalytic degradation performance of NH2-MIL-125 synthesized with p-TA. (b) Kinetic curves for RhB photodegradation following pseudo-first order model (ln (C0/C)=kt). In this function C0 is the concentration of RhB at T=0 min. (c) The rate constant k of NH2-MIL-125

527



100

(b)

Under light irradiation 1st 2nd 3rd

0.8

Light on

0.6

0.4

Fresh catalyst Used catalyst

60

40

20

0.2

0.0

0 -60

528 529 530

(c)

80

Intensity

In darkness

RhB removed (%)

(a) 1.0 C/C 0

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

Page 32 of 37

-40

-20

0

20

40

60

80

100 120

1st

2nd

3rd

10

20

30

40

50

2 theta(degree)

time(min)

Figure 12 (a) Recyclability of sample p-TA-12. (b) The removal of RhB. (c) XRD patterns of fresh and used catalyst

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Table 1 Sorption data of NH2-MIL-125(Ti) samples synthesized with p-TA Sample

a

SBET(m2/g)a

Vtotal(cm3/g)b

Vmicro(cm3/g)c

Vmicro /Vtotal

p-TA-0

1298

0.55

0.48

0.87

p-TA-1

1321

0.58

0.49

0.84

p-TA-2

1368

0.60

0.50

0.83

p-TA-4

1350

0.64

0.50

0.78

p-TA-8

1304

0.75

0.48

0.64

p-TA-12

1190

1.00

0.45

0.45

p-TA-16

1325

0.68

0.49

0.73

p-TA-18

1418

0.64

0.53

0.82

Surface area calculated by using the BET model.

b

Pore size distribution and total pore volume calculated by using the NLDFT model.

c

Micropore volume calculated by using the SF model

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535

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Table 2 Sorption data of NH2-MIL-125(Ti) samples synthesized with BA Sample

SBET(m2/g)a

Vtotal(cm3/g)b

Vmicro(cm3/g)c

Vmicro /Vtotal

BA-0

1298

0.55

0.48

0.87

BA-2

1369

0.61

0.50

0.83

BA-4

1417

0.62

0.52

0.84

BA-8

1390

0.73

0.51

0.70

BA-12

1199

0.80

0.44

0.56

BA-14

1610

0.77

0.60

0.78

BA-16

1310

0.60

0.49

0.82

a


b


c


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537

Table 3 Sorption data of NH2-MIL-125(Ti) samples synthesized with HAc Sample

SBET(m2/g)a

Vtotal(cm3/g)b

Vmicro(cm3/g)c

Vmicro /Vtotal

HAc-0

1298

0.55

0.48

0.87

HAc-2

1380

0.57

0.50

0.88

HAc-4

1436

0.59

0.53

0.88

HAc-8

1246

0.52

0.46

0.87

HAc-12

1394

0.58

0.51

0.88

HAc-16

1434

0.60

0.53

0.88

HAc-18

1450

0.62

0.53

0.86

a


b


c


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539

Scheme I. Illustration of the proposed effect of different type of monocarboxylic acid

540 541


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For Table of Contents Use Only

544

Manuscript title

545

Effects of Monocarboxylic Acid Additives on Synthesizing Metal-Organic Framework

546

NH2-MIL-125 with Controllable Size and Morphology

547

Author list

548

Shen Hu, Min Liu, Xinwen Guo, Keyan Li, Yitong Han, Chunshan Song, and

549

Guoliang Zhang

550

TOC graphic

551 552

Synopsis

553

Monocarboxylic acids are commonly used in synthesizing MOFs but the results are

554

complicated. In this work, we found small molecular acid (Acetic Acid, Thioglycolic

555

Acid) mostly affect the morphology changes of MOFs, while the pseudo-linker acid

556

(p-Toluylic Acid, Benzoic Acid) has a significantly impact on the crystal size on

557

account of the nucleation and the crystal growth rates.

558


Effects of Monocarboxylic Acid Additives on Synthesizing Metal

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