In Situ Synthesis of Nano CuS-Embedded MOF Hierarchical

Article Cite This: ACS Appl. Energy Mater. XXXX, XXX, XXX−XXX

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In Situ Synthesis of Nano CuS-Embedded MOF Hierarchical Structures and Application in Dye Adsorption and Hydrogen Evolution Reaction Xue-Qian Wu,†,‡,§ Dan-Dan Huang,†,§ Ya-Pan Wu,† Jun Zhao,† Xiang Liu,† Wen-Wen Dong,† Shuang Li,† Dong-Sheng Li,*,† and Jian-Rong Li*,‡

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†

College of Material and Chemical Engineering, Hubei Provincial Collaborative Innovation Center for New Energy Microgrid, Key Laboratory of Inorganic Nonmetallic Crystalline and Energy Conversion Materials, China Three Gorges University, Yichang 443002, China ‡ Beijing Key Laboratory for Green Catalysis and Separation and Department of Chemistry and Chemical Engineering, College of Environmental and Energy Engineering, Beijing University of Technology, Beijing 100124, P. R. China S Supporting Information *

ABSTRACT: The development of metal−organic frameworks (MOFs)-based composites is a research topic of high importance because these composites have great potential for wide utilization in energy transfer and environment protection. Herein, a series of CuS@NOTT-101 composites have been successfully fabricated through a convenient MOFs-templated in situ vulcanization strategy. Highly dispersed ultrafine CuS particles evenly embedded on the surface or within the pore structure of the resulting composite frameworks, which is beneficial for introducing hierarchical architecture and exclusive active sites. Remarkably, the optimal composite possesses the highest adsorption capacity of 500 mg g−1 for RhB 6G at a low concentration (30 mg/L) among the previously reported MOFs/MOFbased composites and reveals an outstanding performance toward the hydrogen evolution reaction (HER) with a small Tafel slope of 78 mV dec−1 as well as good cycling stability over 100 h. Given the established structural and compositional designability of MOFs, these results herald the appearance of multifunctional composites whose location of active sites and hierarchical structure are precisely controlled, at the microscale level. KEYWORDS: Metal−organic framework, in situ vulcanization, hierarchical structure, organic dyes capture, hydrogen evolution reaction

1. INTRODUCTION The increasing demands for environmental protection and energy conversion have stimulated widespread interest in the development of advanced functional materials with reasonable structure and remarkable performance. Generally, the energy/ environment-related processes cover, but are not limited to, the identification, removal, and degradation of inorganic/organic pollutants; photo/electrochemical fuel production; water oxidation; and the development of supercapacitors and rechargeable batteries.1−5 The complexity of these processes has required strict requirements on functional materials such as structural porosity, electronic conductivity, component diversity, physicochemical stability, and so on.6 On account of the potential to meet part of the above demands in terms of enhancing mass/electron transfer efficiency and increasing the density of accessible active sites, many porous materials (activated carbon, zeolite, polymer, etc.) have been considered as good candidates to alleviate environmental pollutions and cope with energy challenges.7−9 As a new member in the family of porous materials, metal−organic frameworks (MOFs), selfassembled by organic ligands and metal nodes, have drawn © XXXX American Chemical Society

special attention because of their ultrahigh porosity, tunable pore size, diverse chemical components, and crystalline nature.10 All of the above promising features lead to their extensive potential applications in adsorption, separation, catalysis, sensing, and drug delivery.11−14 In order to further optimize their properties and extend their applications in energy conversion and environmental protection, the incorporation between MOFs and other functional species is an effective strategy.15 Especially, it has been revealed that the MOFs-based composites carries dual attributes as both subject and object, endowing them with extra and excellent performance derived from synergistic/confinement/interface effect.16−18 In previous literature, metal particles, alloys, carbides, oxides, sulfides, selenides, phosphides, and nitrides have been integrated with MOFs to develop composites which have presented exceptional properties in various energy/environment related processes.19 Furthermore, in the past five years, the MOFReceived: April 29, 2019 Accepted: August 2, 2019

A

DOI: 10.1021/acsaem.9b00840 ACS Appl. Energy Mater. XXXX, XXX, XXX−XXX

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ACS Applied Energy Materials

thioacetamide (150 mg) at 20, 40, 60, 80, 100, and 120 °C for 2 h, respectively. During the formation of copper sulfide species, as a sign of reaction, the color of the crystal changed to dark green and black. After they were allowed to naturally cool to room temperature, the resulting product was filtered and washed with CH3CH2OH. 2.1.3. Synthesis of CuS Nanoparticles. In a typical synthesis,26 Cu(NO3)2·3H2O (2 mmol, 483 mg) was dissolved in CH3CH2OH (25 mL) to give a clear solution, and then thioacetamide (4 mmol, 300 mg) was added to the solution under vigorous stirring. The above mixture was then transferred into a 50 mL Teflon-lined stainless steel vessel, maintaining at 120 °C for 16 h. The black solid products were collected by centrifugation, washed in CH3CH2OH and deionized water several times, and dried at 60 °C. 2.2. Characterization of Materials. The morphology and structure of the samples were characterized using a SEM (JEOL-JSM7500F) and a TEM (JEOL JEM 2010F, 200 kV) equipped with an energy dispersive X-ray spectroscopy (EDS). PXRD patterns of all samples were obtained on a Rigaku Ultima IV diffractometer (Cu Kα radiation, λ = 1.5406 Å). N2 adsorption/desorption isotherms were carried out on an ASAP 2020 surface area and pore size analyzer at 77 K. XPS analysis was performed on an ESCALABMKLL X-ray photoelectron spectrometer by using an Al Kα source. TGA measurements were determined using a NETZSCH449C thermal analyzer with a heating rate of 10 °C min−1 under an air atmosphere. FT-IR spectra (KBr pellets) were obtained on a Thermo Electron NEXUS 670 FTIR spectrometer. ICP spectroscopy was conducted on a dual-view Optima 5300 DV ICP-OEM system. 2.3. Organic Dye Absorption Experiments. Freshly prepared CuS@NOTT-101-x (5 mg) was transferred into the solutions of methyl orange, rhodamine 6G, rhodamine B, eosine Y, and tetraiodofluorescein sodium salt (30 mg/L, 100 mL), respectively. The mixture was kept at room temperature under agitation and dark condition. These mixtures were separated by centrifugation, and UV− vis spectroscopy (at different wavelength based on the adsorbates) was applied to monitor the residual concentration of organic dyes (Shimadzu UV 2550). Generally, it can be considered that the adsorption equilibrium has been established as the absorbance of dyes remained unchanged. The adsorption amount, Q (mg/g), was calculated according to the following equation:

derived nanostructures, including porous carbon, metal oxide@ carbon and metal@metal oxide@heteroatom@carbon, have provided plentiful opportunities for creating energy transfer composite materials.20 Despite the massive breakthrough described above, however, the simplification of the synthesis strategy for fabricating MOF-based composites with mutifunctionality to address the energy/environment issues remains challenging because of the complexity of the synthetic procedure and terminal requirment. Meanwhile, currently adopted direct carbonization of MOF crystals to functional derivatives usually results in the dramatic collapse of the pore system and the formation of complicated secondary products, which covered numerous active sites in the bulk phase. Additionally, NP/MOF composites (NP = nanoparticles) that were prepared by solution impregnation, double-solvent approach, chemical vapor deposition, solid grinding, or other stepwise synthesis strategy often suffer from poor electronic conductivity, suppressing the energy electrocatalytic activity. To ameliorate this situation, we conceived it would be favorable to construct functional species based on the metal nodes/clusters within MOFs through an in situ method, which is expected to inherit the properties of both MOF precursor and MOF derivatives.21 More importantly, the in situ process can be regarded as a feasible approach to enhance the synergetic effect and the adhesive strength between nanoparticles and the framework.22 As mentioned previously, earth-abundant metal sulfides are one of the promising candidates to incorporate with MOFs, and thus, copper sulfide has been chosen as an active substance because of its distinctive energy band structure and low surface resistivity.23 Herein we report a series of mixed copper sulfide composite materials with useful organic dye capture and hydrogen evolution reaction properties through a convenient MOFtemplated in situ vulcanization strategy. A well-known CuMOF, NOTT-101,24 constructed from a copper paddle wheel secondary building unit with an organic linker of tetracarboxylates, was selected as the parent framework for fabricating the target products under various temperature conditions (denoted as CuS@NOTT-101-x, x represents different temperature value, x = 20, 40, 60, 80, 100, 120). The proper distribution of pore size and highly dispersed CuS nanoparticles can simultaneously promote the diffusion processes and contact interaction between guest molecules and active sites. Benefitting from the above advantages, the CuS@NOTT-101-x demonstrates a superior adsorption capacity for organic dyes in an aqueous system and largely enhanced activities with long durability for HER compared with the original NOTT-101 and inorganic CuS nanoparticles.

i C − Ce yz zzV Q e = jjj 0 k m {

(1)

where C0 (mg/L) and Ce (mg/L) are the original concentration and equilibrium concentration of organic dyes, respectively. V (mL) is the volume of solution and m is the amount of composite materials. For the adsorption kinetics experiment, 5 mg of composites was separately dispersed in 20 mL dye solutions (10 mg/L), which were then stirred for certain times in the absence of light. The mixture was separated by centrifugation and the following operation was similar to the above experiment. The adsorption capacities (Qt) were calculated by the equation: i C − C t yz zzV Q t = jjj 0 k m {

2. EXPERIMENTAL SECTION All chemical reagents were purchased and applied without further purification. 2.1. Preparation of Materials. 2.1.1. Preparation of the NOTT101. Original NOTT-101 was synthesized according to the previous literature.25 Generally, a mixture of Cu(NO3)2·3H2O (0.086 mmol, 21 mg), p-terphenyl-3,3′′,5,5′′-tetracarboxylic acid (H4L, 0.024 mmol, 10 mg), dimethylformamide/1,4-dioxane/H2O (2/1/1 in V/V), and concentrated hydrochloric acid was sealed in a 25 mL Teflon-lined stainless steel vessel, heated to 80 °C for 24 h, and then cooled to room temperature. Light blue massive crystals of NOTT-101 were obtained after filtration. 2.1.2. Preparation of CuS@NOTT-101-x Composites (x = 20, 40, 60, 80, 100, 120). As-prepared NOTT-101 samples (100 mg) were immersed in the anhydrous CH3CH2OH solution (10 mL) of

(2)

where C0 (mg/L) is the initial concentration of dyes, Ct (mg/L) is the concentration at a certain time (t, min), m (g) is the amount of adsorbents, and V (mL) is the volume of solution. Determination of kinetic parameters is of great importance because it can be used to evaluate the adsorption process. In this work, a pseudosecond/first-order model was used to fit the kinetic results. The related equation can be expressed as follows:

B

t 1 t = + Qt Qe K1Q e 2

(3)

ln(Q e − Q t) = ln Q e − K 2t

(4) DOI: 10.1021/acsaem.9b00840 ACS Appl. Energy Mater. XXXX, XXX, XXX−XXX

Article

ACS Applied Energy Materials K1 (g·mg−1 min−1) is the rate constant of adsorption, which was calculated from the intercept/slope of t/Qt vs t plot and K2 (min−1) was obtained from the slope of ln(Qe − Qt) vs t plot. In the stability test, the NaNO3 methanol solution was used for the regeneration of adsorbents. Generally, the saturated adsorbents were washed three times by deionized water and then immersed into 5 mL of NaNO3 methanol solution more than 24 h. After desorption, the composites were sequentially washed by deionized water and dried at 40 °C in vacuum for the next adsorption process. 2.4. Electrochemical Measurements. As-synthesized composite materials were dispersed in 2 mL of H2O/CH3CH2OH/Nafion (1.3/ 0.5/0.2 in V/V) solution with ultrasonic vibrations to form a homogeneous phase. Subsequently, a commercially available glass carbon electrode (GCE, d = 3 mm) was employed to carry the catalyst ink (50 μL). The as-prepared electrode was air-dried and kept in a desiccator. Then, a typical three-electrode system containing a saturated calomel electrode (SCE) as a reference electrode, a modified GCE as a working electrode, and a graphite rod as a counter electrode was applied. Liner sweep voltammetry (LSV) was tested with a scan rate of 5 mV s−1 in 0.5 M H2SO4. The electrochemical impedance spectroscopy (EIS) measurement were carried out in the frequency range 0.01 Hz to 100 kHz with an amplitude of 10 mV. The chronoamperometry was measured at the overpotential corresponding to the current density of 10 mA/cm2. All the above electrochemical measurements were conducted at ambient environment using the CHI660E electrochemical analyzer. Prior to the test, a flow of N2 was bubbled for at least 30 min to remove the dissolved oxygen in the electrolyte. To evaluate the activities of CuS@NOTT-101-x, the commercial 20% Pt/C and inorganic CuS nanoparticles was also used as reference materials.

3. RESULTS AND DISCUSSION 3.1. Synthesis and Characterization of Composites. The composite materials formation as described in Figure 1a is initially driven by the solvothermal reaction of Cu2+ and pterphenyl-3,3′′,5,5′′-tetracarboxylic acid ligand to form NOTT101 crystals followed by a series of structural evolution though in situ sulfuration. The typical SEM images of NOTT-101 and the resultant CuS@NOTT-101-x composites have been provided in Figure 2a-g. As expected, the parent NOTT-101 is uniform parallelepipedlike block sample, whereas some products are presented in the nonuniform dispersion states because of the vulcanization processes (Figure S1). According to the PXRD results, the partial structure of NOTT-101 framework is still preserved during the nano-CuS formation processes when the vulcanization temperature is lower than 100 °C. With the exception of diffraction peaks for NOTT-101, there are three main diffraction peaks centered at 29.1°, 31.9°, 48.0°, which can be indexed to the planes of (102), (103), and (110) in nano-CuS particles (JCPDS 06-0464), respectively (Figure 1b).27 The X-ray photoelectron spectroscopy (XPS) analysis (Figure 2h,i; Figures S2 and S3) shows the existence of C, O, Cu, and S species. Two peaks appear at around 951.8 and 931.9 eV for Cu 2p1/2 and Cu 2p3/2 in the XPS spectrum, indicating a +2 oxidation state for the Cu ion.28 Meanwhile, three peaks (162.2, 163.6, and 169.3 eV) are attributed to S 2p3/2 and S 2p1/2.29 To accurately prove the micromorphology of composites, transmission electron microscopy (TEM), Fourier-transform infrared (FT-IR) spectroscopy, thermogravimetric (TG), and N2 adsorption analyses were further undertaken. As presented in Figure 3b,c, CuS nanoparticles are uniformly distributed on the surface of crystals or an amorphous framework with an average particle size of 2−3 nm (Figure S4). The results are in accordance with the energy-dispersive Xray analysis results, which reveal a molar ratio of Cu/S of 4.3 (Cu

Figure 1. (a) Schematic illustration of the CuS@NOTT-101-x preparation process. (b) PXRD patterns of composite materials under different vulcanization conditions.

and S are uniformly distributed in the mapping image, Figure 3d). Moreover, the resolved interplanar distances of ≈ 0.28 nm from the high-resolution transmission electron microscope (HRTEM) image represented the (103) plane of CuS (Figure 3a, inset image). It is worth noting that the highly homogeneous dispersion state and small size of CuS particles originated from the long-range ordered copper sites arrangement in the NOTT101 framework (Figure 3e), which provides an important basis for the precise location of CuS particles. TG plots indicated that the thermal stability of CuS@NOTT-101-x increases with the improving of vulcanization temperature for certain periods of time (Figure S5). Clearly, it can be inferred that the production quantity of CuS species can be profoundly affected by the vulcanization temperature (a higher CuS content results in a greater thermal stability) combined with PXRD patterns. Furthermore, Figure S6 demonstrated that all CuS@NOTT101-x have similar FT-IR spectra as pure CuS, further confirming the formation of CuS phase in the composites. The surface areas and pore structure of both parent framework NOTT-101 and related composites were evaluated by a Brunauer−Emmett−Teller (BET) method. Figure 4a,b reveals that the original NOTT-101 possesses typical reversible type-I sorption curve, which represents the characteristic of a single microporous structure with a pore size of 1.9 nm (BET surface area: 1050 m2 g−1). Meanwhile, the N2 sorption isotherms of CuS@NOTT-101-20/40 can be classified as typical IV, whereas the sorption isotherms of CuS@NOTT-101C


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Figure 2. Characterization of the NOTT-101 parent framework and series CuS@NOTT-101-x composites. (a−g) Typical SEM images of the respective state of block (a−f: CuS@NOTT-101-x, x = 20, 40, 60, 80, 100, 120, from left to right; g: NOTT-101). (h,i) High-resolution Cu 2p and S 2p XPS spectra of CuS@NOTT-101-80.

Figure 3. Characterization of the CuS@NOTT-101-80 composite. (a−c) TEM images of the as-prepared material (scale bar, 5−200 nm). (d) Elemental mappings of the CuS@NOTT-101-80 (red: C; light blue: Cu; purple: S; scale bar, 200 nm). (e) View of the novel 3D framework of NOTT101 along c axis (the hydrogen atoms are omitted for clarity).

60/80/100/120 tend to display a type-II sorption behavior, corresponding to mesoporous and macroporous structures, respectively (Figure 4c). The related BJH pore size distribution for CuS@NOTT-101-x that was evaluated by using N 2 adsorption data further proved that the pore characteristics is highly dependent on sulphuration conditions.

For comparative analysis, inorganic CuS nanoparticles were synthesized by a conventional hydrothermal method in which copper nitrate acted as the metal source. The resulting products possessed a lamellar structure with wide size range (from 50 to 500 nm) and tended to agglomerate (Figures S7 and S8). Apparently, the orderliness and porousness provided by NOTTD


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Figure 4. (a, b) N2 adsorption/desorption isotherms of NOTT-101 and CuS@NOTT-101-x at 77 K. (c) BJH pore size distribution for the corresponding materials evaluated by using N2 adsorption data measured at 77 K.

Figure 5. (a) UV−vis spectra of aqueous solution of RhB 6G during the adsorption test with CuS@NOTT-101-80 (inset: relationship between t/qt and time (t)). (b) The adsorption capacity/efficiency of CuS@NOTT-101-80 for different kinds of organic dyes. (c) The adsorption capacities for five dyes in the original NOTT-101 and CuS@NOTT-101-x series. (d) Cyclic process for the removal of RhB 6G over CuS@NOTT-101-80.

important pollutants, have attracted intensive attention from the academic community and various industrial fields. In response to this problem and guided by the above characterization of CuS@NOTT-101-x, the potential capacities for capturing organic dyes have been therefore evaluated. Five organic dyes, including tetraiodofluorescein sodium salt (TFS), rhodamine 6G (RhB 6G), rhodamine B (RhB), methyl orange (MO), and eosine Y (EY), with different size/acidity/basicity were chosen as adsorbates to estimate the adsorption performances of the composite materials.

101 together with an exquisite control of the reaction environment has allowed the smooth synthesis of CuS nanoparticles, homogeneously distributed and stabilized along the resulting composite framework. Compared with other predesigned/postsynthetic methods, this approach is well-fitted for controlling the position of active sites in a more universal and simple way.30,31 3.2. Dye Adsorption Properties. Given their extensive application in the field of dyeing and the printing industry, organic dyes, which are considered as some of the most E


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not the mass transfer resistance but the adsorbtion mechanism.36 The reusability of the composites is another key performance criteria, which is related with its practical applications. Final test results have proved that the CuS@NOTT-101-80 can be reused at least five times without any significant decrease in the performance. It was presented that 90% adsorption capacity was still achieved even after five consecutive cycles (as shown in Figure 5d). Furthermore, the PXRD patterns of the adsorbent after the cyclic test and the original composites are in good agreement with each other, indicating the high stability during the adsorption process (Figure S11). On account of the above experimental and analysis results, it can be concluded that the CuS@NOTT-101-x composites have large adsorption capacities for RhB 6G, RhB, EY, and TFS. Most notably, CuS@NOTT-101-80 displays a highly repeatable RhB 6G adsorption capacity of 500 mg g−1 at a low concentration (30 mg/L), making it the best performing composite for RhB 6G removal compared with the previously reported MOFs/MOFbased materials (Table S2). As a rigid aromatic dye, RhB 6G shows extraordinary photostability and biorefractory properties, which result in the difficulty of effective removal of RhB 6G through traditional methods, such as photodegradation, biodegradation, and chemical oxidation.37 Fortunately, the CuS@NOTT-101-x series can be considered as ideal porous solid adsorbents based on the physical/chemical adsorption mechanism and can be expected to overcome the above disadvantages. Under the guidance of the structure−activity relationship, the remarkable adsorption properties may be mainly attributed to the following two aspects: (1) The hierarchical structure ensures superior mass transfer efficiency in the early stage of adsorption. (2) The uniformly dispersed CuS nanoparticles provide abundant electrostatic interaction sites for further adsorption procedure. 3.3. Electrocatalytic Activity and Stability. The hydrogen evolution reaction (HER) is a practical and environmentally friendly approach to generate hydrogen for new energy fields, and the search for inexpensive/efficient electrocatalyst for HER remains urgent.38 Thus, the electrocatalytic properties of CuS@ NOTT-101-x for HER in acid media was further explored. Figure 6a shows the polarization curves of the CuS@NOTT101-x electrocatalysts with a mass loading of 0.14 mg cm−2 on a glass carbon (GC) electrode in 0.5 M H2SO4 with a scan rate of 5 mV s−1. For comparison, the HER activity of benchmark material (Pt/C-20%) and inorganic CuS nanoparticles was also measured (Figure S13). LSV studies revealed that the HER activities of CuS@NOTT-101-x composites are closely related to the vulcanization temperature, as distinctive differences have been observed between every sample. As depicted in Table 2, compared with pure NOTT-101, CuS@NOTT-101-x exhibited a significantly lower Tafel slope and overpotential under 10 mA cm−2. Additionally, CuS@NOTT-101-80 requires the lowest overpotential (η10= 210 mV) to reach a 10 mA cm−2 current density except for Pt/C. The outstanding HER properties were also confirmed by its lower Tafel slope (78 mV dec−1) than other controlled samples such as CuS@NOTT-101-20 (105 mV dec−1), CuS@NOTT-101-40 (97 mV dec−1), CuS@NOTT101-60 (86 mV dec−1), CuS@NOTT-101-100 (93 mV dec−1), and CuS@NOTT-101-120 (113 mV dec−1 ) (Figure 6b). As a vital indicator of HER reaction kinetics and control steps, the value of the Tafel slope for CuS@NOTT-101-80 demonstrates that it may have a Volmer−Heyrovsky reaction pathway, where the electrochemical desorption of hydrogen is

As shown in Figure 5a−c, CuS@NOTT-101-x performs excellently, and the adsorption capacity is much higher than that of NOTT-101 (from 4 to 38 times) for most of the tested dyes. The enhancement of the adsorption behaviors may be ascribed to its hierarchical structure, consistent with N2 adsorption analysis results. Meanwhile, the primary NOTT-101 possesses hexagonal channels that run through the framework and interconnected through triangular windows with a size of 2.0 Å,32 smaller than the size of organic dyes, impeding the related mass transfer processes. Interestingly, all the composites present some differences in the adsorption behavior of various dyes, especially for RhB 6G and MO (Figures S9 and S10). Take optimal CuS@NOTT-101-80 for example, Figure 5a displayed UV−vis spectra during the adsorption of RhB 6G over CuS@ NOTT-101-80, which are indicative of rapid removal of RhB 6G from aqueous system, as also confirmed by the highest adsorption capacity value of 500 mg g−1. However, the adsorption capacity for MO is similar to that of NOTT-101 (16 mg g−1), revealing the dyes are not favored by the composite might be due to the repulsive electrostatic effect.33 For a further insight of the electrostatic interactions between adsorbents and dye molecules, zeta potential measurement was carried out to evaluate the electrified characteristics of CuS@ NOTT-101-80 in different test environments (Table S1). The average value of the zeta potential measured in MO and RhB 6G aqueous solution is −28.8 and 9.7 mV, respectively, which indicates that the as-obtained CuS@NOTT-101-80 has a negatively charged surface and a greater tendency of attracting opposites molecules. Additionally, the variable adsorption C/C0, under the same initial concentration at different time intervals, also shows the highest adsorption rate for RhB 6G and the lowest for MO. It has been demonstrated that the adsorption rate for RhB 6G, RhB, EY, and TFS increased fast at the initial stage and subsequently turned to a stable state until it approached equilibrium. A similar adsorption trend/mode could also be found in the previously reported literature.34,35 To deeply understand the potential rate-determing step during the adsorption process, a pseudo-second/first-order model was applied to fit the experimental data through eqs 3 and 4, which were presented in the Experimental Section. The detailed fitting parameters of two models were listed in Table 1. A very high correlation coefficient value for the pseudo-secondorder model indicates that the major obstacle for adsorption is Table 1. Fitting parameters of pseudo-second/first-order model for CuS@NOTT-101-80 pseudo-first-order (ln(Qe − Qt) vs t) dye MO RhB 6G RhB EY TFS

K2 (min−1) × 10−2 1.42 6.64 10.30 9.55 11.51 pseudo-second-order (t/Qt vs t)

R2 (%) 91.4 87.2 94.8 89.3 92.7

dye

K1 (g·mg−1 min−1) × 10−2

R2 (%)

MO RhB 6G RhB EY TFS

10.5 2.76 1.29 0.39 4.33

92.3 99.9 99.9 99.1 99.1 F


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Figure 6. HER catalytic performance of series CuS@NOTT-101-x composites, NOTT-101, and commercial Pt/C (20%). (a) Polarization curves for various electrocatalysts in 0.5 M H2SO4 aqueous solution. (b) Tafel plots of the corresponding electrocatalysts derived from the early stages of HER polarization curves. (c) Nyquist plots of electrocatalysts at an overpotential of 300 mV. (d) Chronoamperometric profile of CuS@NOTT-101-80 at a constant overpotential of 210 mV.

initial current density exhibited an insignificant decline after 100 h under sustained operation, indicating the good durability of the CuS@NOTT-101-80. Supplementary Table S3 also summarizes a comparison of CuS@NOTT-101-x with recently reported HER Cu-based electrocatalysts. Although the catalytic activity of CuS@NOTT-101-x, as the non-noble metal electrocatalyst, is slightly inferior to that of commercial Pt/C (20%), it still paves the way toward a new composite platform in the field of energy and environment. By choosing a specific crystalline framework, especially with metal clusters as secondary building units, a balance between the density of functional sites and multilevel structure can be achieved. Thus, the HER merely constitutes one example of broader catalytic processes for this synergetic system. These results suggest that the excellent performance of CuS@ NOTT-101-80 is mainly due to the optimum dispersion states of CuS nanoparticles and appropriate hierarchical structure as well as the synergistic interactions between CuS and the composite framework. More concretely, the resultant CuS nanoparticles (obtained at a temperature higher than 80 °C) become more prone to aggregation, accompanied by the collapse of the parent framework. (It is speculated that the edges/interfaces of the nanoparticles are HER-active sites.) In contrast, the low-temperature vulcanization of NOTT-101 will decrease the CuS yield and hinder the evolution of the hierarchical structure (Table S4). Therefore, it can be concluded that the usage of crystalline NOTT-101 precursor combined

Table 2. HER Catalytic Parameters of CuS@NOTT-101-x catalyst

onset potential (mV)

Tafel slope (mV dec−1)

η10 (mV)

j0 (A/cm2)

NOTT-101 CuS@NOTT-101-20 CuS@NOTT-101-40 CuS@NOTT-101-60 CuS@NOTT-101-80 CuS@NOTT-101-100 CuS@NOTT-101-120 Pt/C (20%)

318 204 124 146 128 124 184 ca. 0

114 105 97 86 78 93 113 31

450 296 221 243 210 219 292 43

0.8 × 10−5 1.5 × 10−5 2.4 × 10−5 5.3 × 10−5 9.7 × 10−5 4.9 × 10−5 1.76 × 10−5 3.9 × 10−4

the rate-determining step.39 Interestingly, a slope of 113 mV dec−1 for CuS@NOTT-101-120 may result from multifarious reaction pathways, including Volmer/Tafel/Heyrovsky reactions.40,41 Moreover, extra information on H species coverage behavior during HER processes was obtained from the impedance spectroscopy. As shown in Figure 6c, the semicircle radius in the high-frequency range of the plot indicated that CuS@NOTT-101-80 has a much lower charge transfer resistance (Rct) than that of other samples. This further confirmed that the hierarchical structure is helpful for not only the distribution of CuS but also the charge and mass transfer efficiency (Figure S12). In addition, the durability of the electrocatalysts has also been studied through chronoamperometric tests (Figure 6d). The G


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TGA, thermogravimetric analysis DMF, N,N-dimethylformamide PXRD, powder X-ray diffraction patterns XPS, X-ray photoelectron spectroscopy EDS, energy-dispersive X-ray spectroscopy TEM, transmission electron microscopy HRTEM, high-resolution transmission electron microscopy SEM, scanning electron microscopy BET, Brunauer−Emmett−Teller GCE, glassy carbon electrode SCE, saturated calomel electrode LSV, linear sweep voltammetry EIS, electrochemical impedance spectroscopy TFS, tetraiodofluorescein sodium salt RhB, rhodamine B RhB 6G, rhodamine 6G MO, methyl orange EY, eosine Y

with suitable vulcanization conditions contributes to the prominent performance.

4. CONCLUSIONS In summary, we developed a series of highly efficient adsorbents and electrocatalysts (CuS@NOTT-101-x) for organic dye removal/HER based on a Cu-MOF (NOTT-101) via a simple vulcanization treatment. The long-range ordered NOTT-101 precursor possesses high surface area and symmetrical copper sites, encountering with thioacetamide that prevents the agglomeration phenomenon and creates a hierarchical structure. These structural characteristics facilitate the mass/electron transfer processes and increase the number of active sites, which are responsible for the exceptional performance. Compared with the original NOTT-101, the as-synthesized CuS@NOTT-101-x composites shows considerably enhanced activity for HER in terms of both Tafel slope and overpotential. More importantly, CuS@NOTT-101-80, as a solid adsorbent, has excellent adsorption capacities of 500 mg g−1 for RhB 6G, which is mainly promoted by electrostatic interaction and novel structure. We believe that the structural tunability and diversity of MOFs will allow the further development of novel MOFbased composites with multiple functions for various applications.

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(1) Peng, Y.; Huang, H.; Zhang, Y.; Kang, C.; Chen, S.; Song, L.; Liu, D.; Zhong, C. A versatile MOF-based trap for heavy metal ion capture and dispersion. Nat. Commun. 2018, 9, 187. (2) Tang, Y.-J.; Gao, M.-R.; Liu, C.-H.; Li, S.-L.; Jiang, H.-L.; Lan, Y.Q.; Han, M.; Yu, S.-H. Porous Molybdenum-Based Hybrid Catalysts for Highly Efficient Hydrogen Evolution. Angew. Chem., Int. Ed. 2015, 54, 12928−12932. (3) Duan, J.; Chen, S.; Zhao, C. Ultrathin metal-organic framework array for efficient electrocatalytic water splitting. Nat. Commun. 2017, 8, 15341. (4) Sheberla, D.; Bachman, J. C.; Elias, J. S.; Sun, C.-J.; Shao-Horn, Y. S.; Dincă, M. Conductive MOF electrodes for stable supercapacitors with high areal capacitance. Nat. Mater. 2017, 16, 220−224. (5) Bai, S.; Liu, X.; Zhu, K.; Wu, S.; Zhou, H. Metal-organic framework-based separator for lithium-sulfur batteries. Nat. Energy 2016, 1, 16094. (6) Zhang, H.; Nai, J.; Yu, L.; Lou, X. W. Metal-Organic-FrameworkBased Materials as Platforms for Renewable Energy and Environmental Applications. Joule 2017, 1, 77−107. (7) Zhu, C.; Li, H.; Fu, S.; Du, D.; Lin, Y. Highly efficient nonprecious metal catalysts towards oxygen reduction reaction based on threedimensional porous carbon nanostructures. Chem. Soc. Rev. 2016, 45, 517−531. (8) Cheng, Y.-T.; Jae, J.; Shi, J.; Fan, W.; Huber, G. W. Production of Renewable Aromatic Compounds by Catalytic Fast Pyrolysis of Lignocellulosic Biomass with Bifunctional Ga/ZSM-5 Catalysts. Angew. Chem., Int. Ed. 2012, 51, 1387−1390. (9) Leadbeater, N. E.; Marco, M. Preparation of Polymer-Supported Ligands and Metal Complexes for Use in Catalysis. Chem. Rev. 2002, 102, 3217−3274. (10) Furukawa, H.; Cordova, K. E.; O’Keeffe, M.; Yaghi, O. M. The Chemistry and Applications of Metal-Organic Frameworks. Science 2013, 341, 1230444. (11) Schoedel, A.; Ji, Z.; Yaghi, O. M. The role of metal-organic frameworks in a carbon-neutral energy cycle. Nat. Energy 2016, 1, 16034. (12) He, Y.; Zhou, W.; Krishna, R.; Chen, B. Microporous metalorganic frameworks for storage and separation of small hydrocarbons. Chem. Commun. 2012, 48, 11813−11831. (13) Xiao, J.-D.; Shang, Q.; Xiong, Y.; Zhang, Q.; Luo, Y.; Yu, S.-H.; Jiang, H.-L. Boosting Photocatalytic Hydrogen Production of a MetalOrganic Framework Decorated with Platinum Nanoparticles: The Platinum Location Matters. Angew. Chem., Int. Ed. 2016, 55, 9389− 9393. (14) Dong, Z.; Sun, Y.; Chu, J.; Zhang, X.; Deng, H. Multivariate Metal-Organic Frameworks for Dialing-in the Binding and Program-

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsaem.9b00840. Additional SEM and TEM images, FT-IR spectra, XPS spectra, PXRD patterns, TGA curves, ICP spectroscopy results, Zeta potential value, ECSA measurements, UV− vis spectra, HER activity, and adsorption data (PDF)

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REFERENCES

AUTHOR INFORMATION

Corresponding Authors

*E-mail for D.-S.L.: [email protected]. *E-mail for J.-R.L.: [email protected]. ORCID

Ya-Pan Wu: 0000-0003-4551-0998 Dong-Sheng Li: 0000-0003-1283-6334 Jian-Rong Li: 0000-0002-8101-8493 Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Author Contributions §

(X.-Q.W., D.-D.H.) These authors contributed equally.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the NSF of China (Nos.: 21673127, 21671119, 51572152, and 51502155) and the State Key Laboratory of Structural Chemistry, FJIRSM (20170020) and the 111 Project of Hubei Province (2018-19).

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ABBREVIATIONS MOFs, metal−organic frameworks HER, hydrogen evolution reaction ICP, inductively coupled plasma emission spectroscopy H


Article

ACS Applied Energy Materials ming the Release of Drug Molecules. J. Am. Chem. Soc. 2017, 139, 14209−14216. (15) Lu, G.; Li, S.; Guo, Z.; Farha, O. K.; Hauser, B. G.; Qi, X.; Wang, Y.; Wang, X.; Han, S.; Liu, X.; DuChene, J. S.; Zhang, H.; Zhang, Q.; Chen, X.; Ma, J.; Joachim Loo, S. C.; Wei, W.; Yang, Y.; Hupp, J. T.; Huo, F. Imparting functionality to a metal-organic framework material by controlled nanoparticle encapsulation. Nat. Chem. 2012, 4, 310− 316. (16) Wang, X.; Chen, W.; Zhang, L.; Yao, T.; Liu, W.; Lin, Y.; Ju, H.; Dong, J.; Zheng, L.; Yan, W.; Zheng, X.; Li, Z.; Wang, X.; Yang, J.; He, D.; Wang, Y.; Deng, Z.; Wu, Y.; Li, Y. Uncoordinated Amine Groups of Metal-Organic Frameworks to Anchor Single Ru Sites as Chemoselective Catalysts toward the Hydrogenation of Quinoline. J. Am. Chem. Soc. 2017, 139, 9419−9422. (17) Fang, X.; Shang, Q.; Wang, Y.; Jiao, L.; Yao, T.; Li, Y.; Zhang, Q.; Luo, Y.; Jiang, H.-L. Single Pt Atoms Confined into a Metal-Organic Framework for Efficient Photocatalysis. Adv. Mater. 2018, 30, 1705112. (18) Fortea-Pérez, F. R.; Mon, M.; Ferrando-Soria, J.; Boronat, M.; Leyva-Pérez, A.; Corma, A.; Herrera, J. M.; Osadchii, D.; Gascon, J.; Armentano, D.; Pardo, E. The MOF-driven synthesis of supported palladium clusters with catalytic activity for carbene-mediated chemistry. Nat. Mater. 2017, 16, 760−766. (19) Jiang, Z.; Liu, J.; Gao, M.; Fan, X.; Zhang, L.; Zhang, J. Assembling Polyoxo-Titanium Clusters and CdS Nanoparticles to a Porous Matrix for Efficient and Tunable H2-Evolution Activities with Visible Light. Adv. Mater. 2017, 29, 1603369. (20) Kaneti, Y. V.; Tang, J.; Salunkhe, R. R.; Jiang, X.; Yu, A.; Wu, K. C.-W.; Yamauchi, Y. Nanoarchitectured Design of Porous Materials and Nanocomposites from Metal-Organic Frameworks. Adv. Mater. 2017, 29, 1604898. (21) Lu, Q.; Zhao, M.; Chen, J.; Chen, B.; Tan, C.; Zhang, X.; Huang, Y.; Yang, J.; Cao, F.; Yu, Y.; Ping, J.; Zhang, Z.; Wu, X.-J.; Zhang, H. In Situ Synthesis of Metal Sulfide Nanoparticles Based on 2D MetalOrganic Framework Nanosheets. Small 2016, 12, 4669−4674. (22) Cho, K.; Han, S.-H.; Suh, M. P. Copper-Organic Framework Fabricated with CuS Nanoparticles: Synthesis, Electrical Conductivity, and Electrocatalytic Activities for Oxygen Reduction Reaction. Angew. Chem. 2016, 128, 15527−15531. (23) Ming, F.; Liang, H.; Shi, H.; Mei, G.; Xu, X.; Wang, Z. Hierarchical (Ni,Co)Se2/Carbon Hollow Rhombic Dodecahedra Derived from Metal-Organic Frameworks for Efficient Water-Splitting Electrocatalysis. Electrochim. Acta 2017, 250, 167−173. (24) Lin, X.; Jia, J.; Zhao, X.; Thomas, K. M.; Blake, A. J.; Walker, G. S.; Champness, N. R.; Hubberstey, P.; SchrÖ der, M. High H2 Adsorption by Coordination-Framework Materials. Angew. Chem., Int. Ed. 2006, 45, 7358−7364. (25) Li, B.; Wen, H.-M.; Wang, H.; Wu, H.; Yildirim, T.; Zhou, W.; Chen, B. Porous metal-organic frameworks with Lewis basic nitrogen sites for high-capacity methane storage. Energy Environ. Sci. 2015, 8, 2504−2511. (26) Liu, J.; Xue, D. Solvothermal synthesis of CuS semiconductor hollow spheres based on a bubble template route. J. Cryst. Growth 2009, 311, 500−503. (27) Li, X.; Zhou, K.; Zhou, J.; Shen, J.; Ye, M. CuS nanoplatelets arrays grown on graphene nanosheets as advanced electrode materials for supercapacitor applications. J. Mater. Sci. Technol. 2018, 34, 2342− 2349. (28) Nakai, I.; Sugitani, Y.; Nagashima, K.; Niwa, Y. X-ray photoelectron spectroscopic study of copper minerals. J. Inorg. Nucl. Chem. 1978, 40, 789−791. (29) Shinde, D. V.; Patil, S. A.; Cho, K.; Ahn, D. Y.; Shrestha, N. K.; Mane, R. S.; Lee, J. K.; Han, S.-H. Revisiting Metal Sulfide Semiconductors: A Solution-Based General Protocol for Thin Film Formation, Hall Effect Measurement, and Application Prospects. Adv. Funct. Mater. 2015, 25, 5739−5747. (30) Lu, X.-F.; Gu, L.-F.; Wang, J.-W.; Wu, J.-X.; Liao, P.-Q.; Li, G.-R. Bimetal-Organic Framework Derived CoFe2O4/C Porous Hybrid Nanorod Arrays as High-Performance Electrocatalysts for Oxygen Evolution Reaction. Adv. Mater. 2017, 29, 1604437.

(31) Yu, X.-Y.; Yu, L.; Wu, H. B.; Lou, X. W. Formation of Nickel Sulfide Nanoframes from Metal-Organic Frameworks with Enhanced Pseudocapacitive and Electrocatalytic Properties. Angew. Chem. 2015, 127, 5421−5425. (32) Zhang, Q.; Yu, J.; Cai, J.; Song, R.; Cui, Y.; Yang, Y.; Chen, B.; Qian, G. A porous metal-organic framework with -COOH groups for highly efficient pollutant removal. Chem. Commun. 2014, 50, 14455− 14458. (33) Zhao, X.; Wang, D.; Xiang, C.; Zhang, F.; Liu, L.; Zhou, X.; Zhang, H. Facile Synthesis of Boron Organic Polymers for Efficient Removal and Separation of Methylene Blue, Rhodamine B, and Rhodamine 6G. ACS Sustainable Chem. Eng. 2018, 6, 16777−16787. (34) Dragan, E. S.; Dinu, M. V. Spectacular Selectivity in the Capture of Methyl Orange by Composite Anion Exchangers with the Organic Part Hosted by DAISOGEL Microspheres. ACS Appl. Mater. Interfaces 2018, 10, 20499−20511. (35) Desai, A. V.; Roy, A.; Samanta, P.; Manna, B.; Ghosh, S. K. BaseResistant Ionic Metal-Organic Framework as a Porous Ion-Exchange Sorbent. Iscience 2018, 3, 21−30. (36) Jung, K.-W.; Choi, B. H.; Lee, S. Y.; Ahn, K.-H.; Lee, Y. J. Green synthesis of aluminum-based metal organic framework for the removal of azo dye Acid Black 1 from aqueous media. J. Ind. Eng. Chem. 2018, 67, 316−325. (37) Zamora-Garcia, I. R.; Alatorre-Ordaz, A.; Ibanez, J. G.; TorresElguera, J. C.; Wrobel, K.; Gutierrez-Granados, S. Efficient degradation of selected polluting dyes using the tetrahydroxoargentate ion, Ag(OH)4−, in alkaline media. Chemosphere 2018, 191, 400−407. (38) Cabán-Acevedo, M.; Stone, M. L.; Schmidt, J. R.; Thomas, J. G.; Ding, Q.; Chang, H.-C.; Tsai, M.-L.; He, J.-H.; Jin, S. Efficient hydrogen evolution catalysis using ternary pyrite-type cobalt phosphosulphide. Nat. Mater. 2015, 14, 1245. (39) Shi, Y.; Zhou, Y.; Yang, D.-R.; Xu, W.-X.; Wang, C.; Wang, F.-B.; Xu, J.-J.; Xia, X.-H.; Chen, H.-Y. Energy Level Engineering of MoS2 by Transition-Metal Doping for Accelerating Hydrogen Evolution Reaction. J. Am. Chem. Soc. 2017, 139, 15479−15485. (40) Wang, J.; Wang, W.; Wang, Z.; Chen, J. G.; Liu, C.-J. Porous MS2/MO2 (M = W, Mo) Nanorods as Efficient Hydrogen Evolution Reaction Catalysts. ACS Catal. 2016, 6, 6585−6590. (41) Conway, B. E.; Tilak, B. V. Interfacial processes involving electrocatalytic evolution and oxidation of H2, and the role of chemisorbed H. Electrochim. Acta 2002, 47, 3571−3594.

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In Situ Synthesis of Nano CuS-Embedded MOF Hierarchical

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