Hierarchical porous ZIF-8 for hydrogen production: Via the hydrolysis of sodium borohydride

Article abstract of DOI:10.1039/d0dt00145g

Hydrides show good performance for hydrogen gas storage/release. However, hydrogen gas release from hydrides via hydrolysis is a slow process and thus requires a catalyst. Herein, terephthalic acid (TPA) is used for the synthesis of a hierarchical porous zeolitic imidazolate framework (HPZIF-8). A mechanistic study of materials synthesis involved an in situ synthesis of zinc hydroxide nitrate nanosheets with an interplanar distance of 0.97 nm. Terephthalic acid modulates the pH value of the synthesis solution leading to the formation of HPZIF-8 with the Brunauer-Emmett-Teller (BET) surface area, Langmuir surface area, and total pore size of 1442 m² g^-1, 1900 m² g^-1, and 0.69 cm³ g^-1, respectively. The formed phases during the synthesis undergo fast conversion to HPZIFs at room temperature. The application of the prepared materials in the hydrolysis of NaBH4 is reported. Acidity plays an important role in the catalytic performance of the materials. ZIF-8 prepared using terephthalic acid shows high catalytic activity with a hydrogen rate of 2333 mLH2 min^-1 gcat^-1 (8046 mLH2 min^-1 gZn^-1). The material exhibits high catalytic activity without any deterioration of its performance for several uses during continuous NaBH4 feeding. There are no changes in the material's structure after catalysis indicating the high recyclability of the materials.

Full text of DOI:10.1039/d0dt00145g

Dalton
Transactions
View Article Online
View Journal
PAPER
Hierarchical porous ZIF-8 for hydrogen production
via the hydrolysis of sodium borohydride†
Cite this: DOI: 10.1039/d0dt00145g
Hani Nasser Abdelhamid
Hydrides show good performance for hydrogen gas storage/release. However, hydrogen gas release from
hydrides via hydrolysis is a slow process and thus requires a catalyst. Herein, terephthalic acid (TPA) is
used for the synthesis of a hierarchical porous zeolitic imidazolate framework (HPZIF-8). A mechanistic
study of materials synthesis involved an in situ synthesis of zinc hydroxide nitrate nanosheets with an
interplanar distance of 0.97 nm. Terephthalic acid modulates the pH value of the synthesis solution
leading to the formation of HPZIF-8 with the Brunauer–Emmett–Teller (BET) surface area, Langmuir
surface area, and total pore size of 1442 m2 g−1, 1900 m2 g−1, and 0.69 cm3 g−1, respectively. The formed
phases during the synthesis undergo fast conversion to HPZIFs at room temperature. The application of
the prepared materials in the hydrolysis of NaBH4 is reported. Acidity plays an important role in the cata-
lytic performance of the materials. ZIF-8 prepared using terephthalic acid shows high catalytic activity
with a hydrogen rate of 2333 mLH min−1 gcat (8046 mLH min−1 gZn−1). The material exhibits high cata-
−1
Received 14th January 2020,
Accepted 25th February 2020
2
2
lytic activity without any deterioration of its performance for several uses during continuous NaBH4
feeding. There are no changes in the material’s structure after catalysis indicating the high recyclability of
the materials.
DOI: 10.1039/d0dt00145g
rsc.li/dalton
Hydrogen (H2) gas is a clean energy source (the combustion
byproduct is water). It can be produced by using several
Introduction
Metal–organic frameworks (MOFs),1–8 including zeolitic imida- methods including water splitting or phototrophic
zolate frameworks (ZIFs), are attractive porous materials with microorganisms.25–28 Other methods,29,30 such as hydrolysis
several outstanding properties.5,9–12 However, microporous of hydride (e.g. sodium borohydride, NaBH4), are promising
ZIFs (pore size <2 nm) such as ZIF-8 may have a low diffusion for applications in direct borohydride fuel cells.31,32 Hydrides
rate for reactants with a large size (>2 nm).13 Thus, hierarchical offer onboard H2 for applications33,34 in unmanned airplanes,
porous ZIFs (HPZIFs) containing two different pore regimes fuel cells,35 and proton exchange membrane fuel cells, and can
(micropore-mesopore, or mesopore–macropore), may improve be used for hydrogen storage36 and heat storage.37 The hydrolysis
the low rate of diffusion of reactants and products leading to of one mole of NaBH4 produces four moles of H2 (two moles
higher performance compared to microporous materials. from NaBH4 and two moles from water molecules). Furthermore,
Thus, several methods were reported for the synthesis of NaBH4 is lightweight and produces highly pure hydrogen with
HPZIFs. Template molecules, such as surfactants,14,15 poly- good hydrogen storage capacity (10.8 wt%). However, the hydro-
styrene,16 organic dyes,11 and metal oxides,17 are usually lysis process is kinetically unfavorable. Thus, several materials,
required for the synthesis of extra pores. Some of these including
CuO@C,38
Co@ZIF-8,39
CoB@ZIF-8,40
and
reagents are environmentally unfriendly and expensive. The Ru@ZIF-67,41 have been investigated as catalysts to increase the
synthesized materials require post-synthetic procedures to hydrolysis rate i.e. the hydrogen generation rate. However, these
remove the template molecules.17–24 Thus, extra efforts should materials are still under active development.
be made to improve the synthesis procedure and make it
Herein, the synthesis of hierarchical porous ZIF-8 using ter-
simpler with a tunable pore structure without the need for ephthalic acid (TPA) is reported. Zn5(OH)8(NO3)2(H2O)2
post-synthetic treatment.
nanosheets, with an interplanar distance of 0.97 nm, were
observed during the synthesis. Terephthalic acid (TPA) causes
a pH drop (from 6.4 to 5.2) of the reaction solution which was
modulated to be pH 10.2 using an organic linker, 2-methyl-
imidazole (Hmim). All observed phases, except for using a
high concentration of terephthalic acid, can be used for the
formation of HPZIF-8 with tunable pore size. The materials
Advanced Multifunctional Materials Laboratory, Department of Chemistry,
Assiut University, 71516 Assiut, Egypt. E-mail: hany.abdelhamid@aun.edu.eg
†Electronic supplementary information (ESI) available. See DOI: 10.1039/
D0DT00145G
This journal is © The Royal Society of Chemistry 2020
Dalton Trans.

View Article Online
Paper
Dalton Transactions
show high efficiency for hydrogen production via sodium boro- Characterization instruments
hydride at a rate of 2333 mLH min−1 gcat−1. The acidity of the
prepared materials plays an important role in their catalytic
performance.
2
Powder X-ray diffraction (XRD) patterns were recorded using a
PANalytical X’Pert Pro diffractometer (Cu Ka1 radiation, wave-
length, 1.54 Å). Transmission electron microscopy (TEM)
imaging was carried out using JEM-2100 (JEOL, Japan) with an
accelerating voltage of 200 kV. Scanning electron microscopy
(SEM) imaging was carried out using SEM-7000 (JEOL, Japan).
Nitrogen (N2), and carbon dioxide (CO2) adsorption–desorp-
tion isotherms (25 °C) were obtained using a Micromeritics
ASAP 2020 instrument (UK). Pore size distribution was
measured using nonlocal density functional theory (the
NLDFT method, using N2@77 on carbon slit pores). Fourier
transform infrared (FT-IR) spectra for Zn5(OH)8(NO3)2(H2O)2
and Zn5(OH)8(NO3)2(H2O)2 after the addition of TPA and
Hmim were recorded using Shimadzu-470 via a KBr disc tech-
Experimental
Materials and methods
Zn(NO3)2·6H2O, NaBH4, 2-methylimidazole (Hmim), ter-
ephthalic acid, and NaOH, were purchased from Sigma Aldrich
(Germany). The solution of terephthalic acid (1 mM) was pre-
pared in dimethylformamide (DMF).
Synthesis of HPZIF-8
A white precipitate of zinc hydroxide nitrate nanosheets was nique. The reaction after the addition of Hmim was immedi-
observed after the addition of NaOH (0.1 mL, 0.1 mmol) to the ately stopped using an ice bath and fast frozen (−65 °C) before
solution of Zn(NO3)2·6H2O (0.8 mL, 0.84 M). A Hmim solution freeze-drying using a freeze dryer (Alpha 1–2 LDplus, Martin
(8 mL, 3.0 M) was added to the previous solution. Then, water Christ Gefriertrocknungsa, Germany). The final product i.e.
was added to adjust the final volume to 17 mL. The solution TPA@ZIF-8 was also obtained. The amount of TPA in the final
was stirred at room temperature for 30 min. The material product was quantified using gas-chromatography mass spec-
obtained (denoted as ZIF-8 (NaOH)) was separated using cen- trometry (GC-MS, Thermo Scientific™ ISQ™ 7000 Single
trifugation (13 000 rpm, 20 min), and washed using ethanol (2 × Quadrupole GC-MS). 2-Methylimidazole was dissolved in
20 mL). The material was dried in an oven at 85 °C overnight.
chloroform (CHCl3, HPLC grade). TPA@ZIF-8 was digested in
The synthesis of ZIF-8 using terephthalic acid was per- HCl (12 M) using a sonication bath. The digested material was
formed using the same procedure as mentioned above, except extracted using CHCl3. An internal standard method was also
that a solution of terephthalic acid (1–5 mmol) was added reported using the Hmim solution.
before adding the solution of Hmim (8 mL, 24 mmol). All
materials were separated using centrifugation and washed
using ethanol (2 × 20 mL).
Results and discussion
The schematic representation of the synthesis of HPZIF-8
using terephthalic acid (TPA) is shown in Fig. 1. The synthesis
Hydrolysis of NaBH4
ZIF-8 (synthesized using the previous procedure11), ZIF-8
procedure is a one-pot approach involving the successive
(NaOH), and ZIF-8 (TPA) were tested for the hydrolysis of
addition of NaOH, TPA, and Hmim solutions (Fig. 1). The
NaBH4. One hundred milligrams (100 mg) of each material
homogenous solution of zinc nitrate is converted to a white
was added to a NaBH4 solution (0.19 g, in 100 mL) in a 100 mL
precipitate consisting of Zn5(OH)8(NO3)2(H2O)2 using a con-
flask at ambient temperature. The progress in the reaction was
trolled amount of NaOH (Fig. 2a).17 The crystal structure of
monitored via measuring the water volume using the water dis-
Zn5(OH)8(NO3)2(H2O)2 reveals that the interplanar distance
placement method.38
2+
between the Zn5(OH)8 layers is 0.97 nm (Fig. 1). The SEM
The effect of the catalyst amount was investigated using
(Fig. S1†), and TEM (Fig. 3a) images of Zn5(OH)8(NO3)2(H2O)2
100, 50, and 10 mg of ZIF-8 (TPA) following the same pro-
indicate a sheet-like morphology of the formed phases. The
cedure as mentioned above. The recyclability of the catalyst
XRD pattern of the observed phases in the presence of TPA
was tested using 10 mg of ZIF-8 (TPA). After the first cycle, the
was recorded (Fig. 3a). The XRD peaks of TPA are the predomi-
reaction flask was charged with 0.19 g of NaBH4. Following the
same procedure, the effect of the NaBH4 amount was investi-
nant peaks indicating the dissolution of the formed phases
due to acidity (Fig. 2a). After the addition of the Hmim solu-
gated using 0.19 g (0.05 M), 0.38 g (0.1 M), and 1.5 g (0.4 M) in
tion, the ZIF-8 crystal was observed only at a low concentration
100 mL H2O. The flask was charged with NaBH4 of different
of TPA (1 mmol, Fig. S2†). No ZIF-8 crystal was observed at a
amounts. The rate of hydrogen generation (mLH gcat min−1
)
−1
2
high concentration of TPA (>1 mmol, Fig. S2†). The materials
were formed only after 2 h (Fig. 2b). According to XRD
(Fig. 2b), the Zn5(OH)8(NO3)2(H2O)2 crystal was formed after
1 h before the conversion to ZIF-8.
was calculated using the following equation:
ꢀ1
ꢀ1
The rate of hydrogen generation ðmLH gcat min
Þ
2
¼ VH OðmLÞ ꢁ tꢀ1ðminÞ ꢁ wtcat ðgÞ
ꢀ1
2
The formation of HPZIF-8 was tracked via following the
where VH O (mL) represents the water volume (mL) displaced changes in the pH value of the reaction solution (Fig. 1 and 4).
2
by hydrogen gas in time (t), and wt refers to the weight of the The Zn(NO3)2 solution is acidic (a pH value of 5.3–6). After the
catalyst in grams.
addition of NaOH, the pH value increases to 6.5 and a white
Dalton Trans.
This journal is © The Royal Society of Chemistry 2020

View Article Online
Dalton Transactions
Paper
Fig. 1 Schematic representation of hierarchical porous ZIF-8 formation using NaOH and terephthalic acid.
Fig. 2 XRD for (a) the observed phases before and after the addition of TPA acid, and (b) the formation of ZIF-8 using TPA acid.
precipitate of Zn5(OH)8(NO3)2(H2O)2 is observed (Fig. 2a). the pH value of the reaction solution to 10.5 for NaOH and
Zn5(OH)8(NO3)2(H2O)2 is stable in the pH range of 5–9.42 After terephthalic acid (1 mmol), while the pH value upon
the addition of the terephthalic acid solution, the reaction addition of high concentration terephthalic acid (5 mmol)
solution becomes acidic with a pH value of 5.2–5.5 (Fig. 4). reaches 9.2. Terephthalic acid dissolves the formed phase of
The addition of Hmim (Hmim: Zn ratio of ∼35) increases Zn5(OH)8(NO3)2·2H2O, thus it takes a long reaction time for
This journal is © The Royal Society of Chemistry 2020
Dalton Trans.

View Article Online
Paper
Dalton Transactions
Fig. 3 TEM images of (a) Zn5(OH)8(NO3)2(H2O)2, (b) ZIF-8 (NaOH), and (c) ZIF-8 (TPA).
−
water molecules, NO3 vibrations, and Zn–O vibrations,
respectively (Fig. S3†). The peaks in the range of
500–1350 cm−1 and 1350–1500 cm−1 correspond to the
bending and stretching of the imidazolate ring, respectively.11
The FT-IR spectrum of the freeze-dried sample of
Zn5(OH)8(NO3)2·2H2O with TPA and Hmim shows the signals
corresponding to the N–H bending and the stretching
vibrations of free Hmim at 1675 and 1596 cm−1 (Fig. S4†). The
peak at 420 cm−1 corresponds to Zn–N indicating the success-
ful coordination of Hmim and Zn i.e. formation of the ZIF-8
crystal (Fig. S4†). The Zn–N bond is observed even after a short
time i.e. in the freeze-dried sample (Fig. S4†). The FT-IR spec-
trum of TPA@ZIF-8 also shows a peak at 448 cm−1 (Zn–O) indi-
cating that TPA interacts with the Zn node of the ZIF-8 crystal
(Fig. S4†). The presence of TPA can be confirmed by the
appearance of the IR peak at 1695 cm−1 which corresponds to
the carbonyl group (CvO) of the carboxylic group of TPA
Fig. 4 pH changes of the reaction solutions during the synthesis of (Fig. S4†). The amount of TPA in TPA@ZIF-8 was determined
ZIF-8 using NaOH, and terephthalic acid (TPA).
using GC-MS (Fig. S5–S8†). The mass spectra of Hmim, and
TPA@ZIF-8 after digestion confirm the observation of Hmim,
and TPA at retention times (RT) of 7.26 and 30.24 min, respect-
the formation of ZIF-8 (Fig. 3b). The reaction takes place in ively (Fig. S5–S8†). The GC-MS data reveal that the percentage
two steps, first the re-formation of Zn5(OH)8(NO3)2·2H2O, and of TPA in TPA@ZIF-8 is 7.3% (Fig. S5–S8†).
second, the conversion to HPZIF-8 (Fig. 1). There is no for-
The porosity of the materials is characterized by using N2
mation of HPZIF-8 when there is a high concentration of ter- adsorption–desorption isotherms (Fig. 5 and Table 1). Data
ephthalic acid (Fig. S2†). This may be due to the interaction reveal the formation of HPZIF-8 with tunable pore size (Fig. 4
between terephthalic acid and the Zn2+ ions which prevents and Table 1). The surface area of the synthesized hierarchical
coordination between the Zn2+ ions and Hmim (Fig. S2†).
porous ZIF-8 using TPA is higher than that of ZIF-8 syn-
The chemical bonds and the changes occurred during the thesized using NaOH alone (Table 1).43,44 The pore size distri-
formation of ZIF-8 were also monitored using FT-IR spec- bution measured using NLDFT reveals a wide pore width
troscopy (Fig. S3 and S4†). The FT-IR spectrum of (15–65 nm, Fig. 5b). The TEM images confirm the formation
Zn5(OH)8(NO3)2·2H2O shows peaks at 1621 cm−1, 1372 cm−1
,
of the mesoporous structure (Fig. 3b and c). The mesopores
and 448 cm−1 corresponding to the δ-vibration of the interlayer are formed in the crystal (i.e. interparticle) as shown in Fig. 3b
Dalton Trans.
This journal is © The Royal Society of Chemistry 2020

View Article Online
Dalton Transactions
Paper
Fig. 5 (a) N2 adsorption (closed symbols)–desorption (open symbols) isotherms for hierarchical porous ZIF-8 using NaOH and TPA, and (b) pore
size distribution using NLDFT.
Table 1 Textural properties of the prepared materials
amount of CO2, ZIF-8 prepared using TPA has the lowest basic
character (Fig. 7b).
SBET
SLan
SExt
VTotal
VMicro
VMeso
Materials
(m2 g−1
)
(cm3 g−1
)
Hydrolysis of NaBH4
ZIF-8 (NaOH)
ZIF-8 (TPA)
1300
1442
1350
1900
97
50
0.56
0.69
0.42
0.64
0.14
0.05
The products of the reaction of NaBH4 and water i.e. hydrolysis
are hydrogen gas and sodium metaborate salt (NaBO2).
Kinetically, the process is slow and unfavorable. Thus, a cata-
lyst is highly required. It was reported that metal-based
materials are more active catalysts for hydride hydrolysis and
hydrogen generation.45
SBET, BET surface area; SLan, Langmuir surface area; SExt, external
surface area; VTotal, total volume at P/P0 at 0.99; VMicro, micropore
volume; VMeso, mesopore volume.
Herein, hydrogen production from NaBH4 hydrolysis with
and without catalysts is investigated (Fig. 8a). The hydrolysis of
NaBH4 without a catalyst is a very slow process (Fig. 8a). ZIF-8
enhances the hydrolysis of NaBH4. On the basis of their per-
formance, the materials can be arranged as ZIF-8 (TPA) > ZIF-8
> ZIF-8 (NaOH) > no catalyst in terms of reaction time (Fig. 8a).
and c. According to SEM images, the particle size of HPZIF-8
(NaOH) and HPZIF-8 (TPA) is 50–200 nm and 1–4 µm, respect-
ively (Fig. 6). The basic properties of the ZIF-8 surface have
been characterized using CO2 sorption (adsorption–desorp-
tion) isotherms as shown in Fig. 7a. Based on the adsorbed
Fig. 6 SEM images of (a) ZIF-8 (NaOH), and (b–d) ZIF-8 (TPA) with different magnifications.
This journal is © The Royal Society of Chemistry 2020
Dalton Trans.

View Article Online
Paper
Dalton Transactions
Fig. 7 (a) CO2 adsorption (closed symbols)–desorption (open symbols) isotherms, and (b) the adsorbed amount of CO2 for different modulator
species.
Fig. 8 (a) NaBH4 hydrolysis using the synthesised materials, and (b) catalyst loading using ZIF-8 (TPA), [NaBH4] = 0.05 M, T = 30 °C, stirring 1000 rpm.
ZIF-8 (TPA) requires only 18 min to reach the maximum hydro- short time (18 min) to reach the maximum hydrogen pro-
gen volume which was a very short time compared to those duction, while low catalyst loading needs a longer time
required by other materials. This observation is mainly due to (120 min). However, the efficiency shows an insignificant
its acidity. As discussed in the previous section, CO2 adsorp- decrease for a catalyst loading of 10 mg indicating the high
tion reveals that ZIF-8 (TPA) has a highly acidic surface (Fig. 7). performance of the synthesized materials even at low catalyst
The difference in the hydrogen generated rate can also be loading.
observed by the naked eye via hydrogen bubbles collected
under water (see Movie 1, ESI†).
The effect of NaBH4 concentration (0.05, 0.1, and 0.4 M)
has been investigated (Fig. 9a). The concentration continu-
The effect of the catalyst amount using ZIF-8 (TPA) is inves- ously increased after a certain period leading to an increase in
tigated as shown in Fig. 8b. A high catalyst amount requires a the volume of generated hydrogen (Fig. 9a). Data analysis
Fig. 9 (a) The effect of NaBH4 loading (ZIF-8 (TPA, 10 mg)), and (b) recyclability using ZIF-8 (TPA, 10 mg), [NaBH4] = 0.05 M, T = 30 °C, stirring 1000 rpm.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2020

View Article Online
Dalton Transactions
Paper
The material can be recycled several times (three times)
without any significant deterioration of its catalytic perform-
ance (Fig. 9b and Movie 2†). The catalyst was not separated
after each run indicating no deterioration of the material’s
catalytic performance. This observation indicates that the cata-
lyst needs no activation or treatment after catalysis. The high
catalytic performance of ZIF-8 (TPA) is due to the high surface
area of the material and the acidic character of its surface. The
material’s crystalline structure after catalysis is also preserved
(Fig. 10).
Several mechanistic studies have been proposed to explain
the hydrolysis of NaBH4.38 According to the reaction, half of
the generated hydrogen atoms come from the water molecule
via O–H bond cleavage of H2O. This is the rate-determining
step according to the kinetic isotope effect experiment.46 The
concentration of water (55.5 M) in our case is high compared
to the NaBH4 concentration (0.05–0.4 M) which indicates that
it is a pseudo-first-order reaction. There are two models to
explain NaBH4 hydrolysis, called Langmuir–Hinshelwood, and
Michaelis–Menten.38 The large surface area of ZIF-8 offers
many active sites. It was reported that the water molecules are
dissociative on the surface of ZIF-8 forming Zn–OH.47 The
ZIF-8 crystals offer acido-basic sites including alkaline OH and
N−, Brønsted acid sites (N–H), and Lewis acid sites (low-co-
ordinated zinc). Thus, the two reactants i.e. BH4− and H2O can
be adsorbed on the solid catalyst. The reaction may obey the
Langmuir–Hinshelwood (LH) model. After the adsorption of
BH4− and H2O on the surface of ZIF-8, the adsorbed molecules
undergo a bimolecular reaction producing H2 and BH3(OH)−
molecules. This process is followed by Na+BH3H−⋯HOH via
hydrogen bonding between
a hydridic hydrogen atom
(BH3H−), and an acidic hydrogen atom of H2O. Three succes-
sive reactions are followed giving 4 H2 molecules and NaBO2.
ZIF-8 materials offer many advantages compared to other
materials (Table 2). The materials can be simply synthesized
without the need for a solvothermal reaction40 i.e. at room
temperature with the need for only stirring. The synthesis
takes place via one step without the need for multiple steps, or
expensive reagents.40 The materials were synthesized within a
short reaction time including the separation step (Table 2).
The materials have high chemical stability because of the
Fig. 10 XRD of ZIF-8 (TPA) after catalysis.
reveals the rate of hydrogen generation of 400 mLH min−1
2
gcat−1, 600 mLH min−1 gcat−1, and 2333 mLH min−1 gcat for
−1
2
2
0.05 M, 0.1 M, and 0.4 M of NaBH4, respectively (Fig. 9a). This
observation indicates that the rate of hydrogen generation
increases with an increase in the concentration of NaBH4. It
also reveals that hydrogen can be generated continuously via
direct addition of NaBH4 without the need to separate or acti-
vate the catalyst (Movie 2, ESI†).
Table 2 Summary of some materials used for NaBH4 hydrolysis
Time
Catalyst
Synthesis conditions
Catalysis conditions
Ratea (min)
Ref.
39
Co@ZIF-8
Two steps; DP(H2O, N2, RT, 2 h), followed by in situ
reduction using NaBH4 (N2, RT, 30 min)
Cat, 6 mol%; NaBH4,
0.75 mmol, 30 °C
2935
10
CoB@ZIF-8
Two steps; solvothermal (MeOH, 120 °C, 4 h), followed by
reduction using NaBH4 (EtOH, 35 °C)
Cat, 10 mg; NaBH4, 1.67 wt%;
NaOH, 5 wt%
453.6 700
40
Co@C-derived Co-
MOF-71
Zn1Co1-Co@NC
Two steps; solvothermal (DMF, 110 °C, 24 h), carbonization
of Co-MOF-71 (700 °C, 8 h, N2)
Two steps; solvothermal (MeOH, 120 °C, 4 h), carbonization Cat, 10 mg; NaOH, 0.8 g; NaBH4, 1807
(900 °C, 3 h, He gas)
One step (RT, 2 h)
Cat, 20 mg; NaBH4, 10 wt%;
NaOH, 6 wt%; 30 °C
1680
70
43
7.5
45
51
100 mg
ZIF-8 (TPA)
Cat, 10 mg; NaBH4, 1.5 g; 30 °C
2333
Here
8046b
a mL min−1 g−1
.
b mLH min−1 gZn−1; deposition-precipitation, DP; DMF, N,N-dimethylformamide.
2
This journal is © The Royal Society of Chemistry 2020
Dalton Trans.

View Article Online
Paper
Dalton Transactions
strong coordination bonds of M (metal)–N (ligand).48–50 The
materials have a large surface area and acidic surface pro-
perties. ZIF-8 (TPA) shows superior catalytic activity for NaBH4
hydrolysis at ambient temperature. The catalyst shows a high
3 Q. Yao, A. Bermejo Gómez, J. Su, V. Pascanu, Y. Yun,
H. Zheng, H. Chen, L. Liu, H. N. Abdelhamid, B. Martín-
Matute and X. Zou, Chem. Mater., 2015, 27, 5332–5339.
4 Y. Yang, K. Shen, J. Lin, Y. Zhou, Q. Liu, C. Hang,
H. N. Abdelhamid, Z. Zhang and H. Chen, RSC Adv., 2016,
6, 45475–45481.
−1
hydrogen generation rate of 2333 mLH min−1 gZIF8
2
(8046 mLH min−1 gZn−1) which is higher than those of several
2
other catalysts (Table 2). The catalyst can be used for several
cycles without any deterioration of their catalytic performance
and any change in the material’s crystalline structure
(Table 2). It can also be used for continuous charging of
NaBH4 with high catalytic performance. The large surface area
of ZIF-8 causes no deactivation of the catalyst due to the depo-
sition of borate species on their surface.51
5 H. N. Abdelhamid, A. Bermejo-Gómez, B. Martín-Matute
and X. Zou, Microchim. Acta, 2017, 184, 3363–3371.
6 H. E. Emam, H. N. Abdelhamid and R. M. Abdelhameed,
Dyes Pigm., 2018, 159, 491–498.
7 H. N. Abdelhamid, M. Wilk-Kozubek, A. M. El-Zohry,
A. Bermejo Gómez, A. Valiente, B. Martín-Matute,
A.-V. Mudring and X. Zou, Microporous Mesoporous Mater.,
2019, 279, 400–406.
8 H. N. Abdelhamid, Nanotechnology, 2019, 30, 435601.
9 Y. V. Kaneti, S. Dutta, M. S. A. Hossain, M. J. A. Shiddiky,
K.-L. Tung, F.-K. Shieh, C.-K. Tsung, K. C.-W. Wu and
Y. Yamauchi, Adv. Mater., 2017, 29, 1700213.
10 H. N. Abdelhamid, Microchim. Acta, 2018, 185, 200.
11 H. N. Abdelhamid, Z. Huang, A. M. El-Zohry, H. Zheng and
X. Zou, Inorg. Chem., 2017, 56, 9139–9146.
12 H. N. Abdelhamid, Microchim. Acta, 2019, 186, 682.
13 J. Yang, Y.-B. Zhang, Q. Liu, C. A. Trickett,
E. Gutiérrez-Puebla, M.Á Monge, H. Cong, A. Aldossary,
H. Deng and O. M. Yaghi, J. Am. Chem. Soc., 2017, 139,
6448–6455.
14 S. Wang, Y. Fan and X. Jia, Chem. Eng. J., 2014, 256,
14–22.
15 C. Duan, H. Zhang, M. Yang, F. Li, Y. Yu, J. Xiao and H. Xi,
Nanoscale Adv., 2019, 1, 1062–1069.
16 K. Shen, L. Zhang, X. Chen, L. Liu, D. Zhang, Y. Han,
J. Chen, J. Long, R. Luque, Y. Li and B. Chen, Science, 2018,
359, 206–210.
Conclusions
Terephthalic acid assists the synthesis of hierarchical porous
ZIF-8. It modulates the intermediated phase that formed
during the reaction. The synthesis process produces a tunable
mesopore structure with a high reactant diffusion rate. ZIF-8
synthesized using terephthalic acid shows high catalytic per-
formance for NaBH4 hydrolysis. The material provides a high
hydrogen generation rate at room temperature in a short time.
The catalysts are recyclable several times without any deterio-
ration in their performance and any change in the material’s
crystalline structure. The reaction solution can be charged
with a higher NaBH4 amount in the presence of a catalyst
without degrading the catalytic performance of the used cata-
lyst. Our results offer several advantages which make the syn-
thesis easier with outstanding catalytic performance.
17 H. N. Abdelhamid and X. Zou, Green Chem., 2018, 20,
1074–1084.
18 S. Sultan, H. N. Abdelhamid, X. Zou and A. P. Mathew, Adv.
Funct. Mater., 2018, 1805372.
Conflicts of interest
The authors declare no competing financial interests.
19 L. Valencia and H. N. Abdelhamid, Carbohydr. Polym.,
2019, 213, 338–345.
20 A. F. Abdel-Magied, H. N. Abdelhamid, R. M. Ashour,
X. Zou and K. Forsberg, Microporous Mesoporous Mater.,
2019, 278, 175–184.
21 H. N. Abdelhamid, Lanthanide metal-organic frameworks
and hierarchical porous zeolitic imidazolate frameworks: syn-
thesis, properties, and applications, Stockholm University,
Faculty of Science, 2017.
22 H. N. Abdelhamid, A. M. El-Zohry, J. Cong, T. Thersleff,
M. Karlsson, L. Kloo and X. Zou, R. Soc. Open Sci., 2019, 6,
190723.
Acknowledgements
The author would like to thank the Ministry of Higher
Education and Scientific Research (MHESR) and the
Institutional Review Board (IRB) of the Faculty of Science at
Assiut University, Egypt for the support. Many thanks to
Prof. X. Zou for providing a part of the characterization instru-
ments of the materials in her lab at Stockholm University,
Sweden. Dr. Haitham and Chemist Samar are acknowledged
for their help during the data collection of GC-MS.
23 H. N. Abdelhamid, Mater. Today Chem., 2020, 15, 100222.
24 H. N. Abdelhamid, M. Dowaidar, M. Hällbrink and
Ü. Langel, SSRN Electron J., DOI: 10.2139/ssrn.3435895.
25 M. N. Iqbal, A. F. Abdel-Magied, H. N. Abdelhamid,
P. Olsén, A. Shatskiy, X. Zou, B. Åkermark, M. D. Kärkäs
and E. V. Johnston, ACS Sustainable Chem. Eng., 2017, 5,
9651–9656.
References
1 Q. Wang and D. Astruc, Chem. Rev., 2020, 120, 1438–1511.
2 M. N. Goda, H. N. Abdelhamid and A. E.-A. A. Said, ACS
Appl. Mater. Interfaces, 2020, 12, 646–653.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2020

View Article Online
Dalton Transactions
Paper
26 K. Bolatkhan, B. D. Kossalbayev, B. K. Zayadan, T. Tomo, 38 A. A. Kassem, H. N. Abdelhamid, D. M. Fouad and
T. N. Veziroglu and S. I. Allakhverdiev, Int. J. Hydrogen
Energy, 2019, 44, 5799–5811.
S. A. Ibrahim, Int. J. Hydrogen Energy, 2019, 44, 31230–
31238.
27 C. Tang, R. Zhang, W. Lu, L. He, X. Jiang, A. M. Asiri and 39 C. Luo, F. Fu, X. Yang, J. Wei, C. Wang, J. Zhu, D. Huang,
X. Sun, Adv. Mater., 2017, 29, 1602441. D. Astruc and P. Zhao, ChemCatChem, 2019, 11, 1643–1649.
28 C. Tang, F. Qu, A. M. Asiri, Y. Luo and X. Sun, Inorg. Chem. 40 Q. Li, W. Yang, F. Li, A. Cui and J. Hong, Int. J. Hydrogen
Front., 2017, 4, 659–662. Energy, 2018, 43, 271–282.
29 Y. Li and S. Li, Int. J. Hydrogen Energy, DOI: 10.1016/j. 41 D. D. Tuan and K.-Y. A. Lin, Chem. Eng. J., 2018, 351, 48–55.
ijhydene.2019.06.075.
42 P. Li, Z. P. Xu, M. A. Hampton, D. T. Vu, L. Huang,
V. Rudolph and A. V. Nguyen, J. Phys. Chem. C, 2012, 116,
10325–10332.
43 S. K. Nune, P. K. Thallapally, A. Dohnalkova, C. Wang,
J. Liu and G. J. Exarhos, Chem. Commun., 2010, 46, 4878.
44 Y. Pan, Y. Liu, G. Zeng, L. Zhao and Z. Lai, Chem. Commun.,
2011, 47, 2071–2073.
30 C. Tang, L. Xie, K. Wang, G. Du, A. M. Asiri,
Y. Luo and X. Sun, J. Mater. Chem. A, 2016, 4, 12407–
12410.
31 T. Liu, K. Wang, G. Du, A. M. Asiri and X. Sun, J. Mater.
Chem. A, 2016, 4, 13053–13057.
32 K. Li, M. Ma, L. Xie, Y. Yao, R. Kong, G. Du, A. M. Asiri and
X. Sun, Int. J. Hydrogen Energy, 2017, 42, 19028–19034.
33 L. Luconi, G. Tuci, G. Giambastiani, A. Rossin and
45 D. Xu, X. Zhang, X. Zhao, P. Dai, C. Wang, J. Gao and
X. Liu, Int. J. Energy Res., 2019, 43, 3702–3710.
M. Peruzzini, Int. J. Hydrogen Energy, 2019, 44, 25746– 46 R. Retnamma, A. Q. Novais and C. M. Rangel,
25776. Int. J. Hydrogen Energy, 2011, 36, 9772–9790.
34 T. Tayeh, A. S. Awad, M. Nakhl, M. Zakhour, J.-F. Silvain 47 C. Chizallet, S. Lazare, D. Bazer-Bachi, F. Bonnier,
and J.-L. Bobet, Int. J. Hydrogen Energy, 2014, 39, 3109–
3117.
V. Lecocq, E. Soyer, A.-A. Quoineaud and N. Bats, J. Am.
Chem. Soc., 2010, 132, 12365–12377.
35 M. Lototskyy, I. Tolj, Y. Klochko, M. W. Davids, 48 H. N. Abdelhamid and H.-F. Wu, J. Am. Soc. Mass Spectrom.,
D. Swanepoel and V. Linkov, Int. J. Hydrogen Energy, 2020,
45, 7958–7967.
36 M. Gambini, T. Stilo and M. Vellini, Int. J. Hydrogen Energy,
2019, 44, 15118–15134.
2019, 30, 2617–2622.
49 H. N. Abdelhamid, Y. C. Lin and H. F. Wu, Microchim. Acta,
2017, 184, 1517–1527.
50 H. N. Abdelhamid and H.-F. Wu, Microchim. Acta, 2015,
182, 1609–1617.
37 K. Manickam, P. Mistry, G. Walker, D. Grant, C. E. Buckley,
T. D. Humphries, M. Paskevicius, T. Jensen, R. Albert, 51 Z. Gao, C. Ding, J. Wang, G. Ding, Y. Xue, Y. Zhang,
K. Peinecke and M. Felderhoff, Int. J. Hydrogen Energy,
2019, 44, 7738–7745.
K. Zhang, P. Liu and X. Gao, Int. J. Hydrogen Energy, 2019,
44, 8365–8375.
This journal is © The Royal Society of Chemistry 2020
Dalton Trans.