English

• 0.   Introduction

  During the past decades, a new type of nano-porous crystalline, metal-organic framework (MOF) materials have been used in diverse fields including sorption, sensors, catalysis, drug delivery, magnetism, luminescence, light - harvesting, biomedical imaging, ionic conductivity, etc^[1-8]. Meanwhile, there has been a surge of interest in the investigation of catalytic degradation and/or adsorption to remove pollutants from water by MOF materials. Because MOFs present many properties that commend them in water treatment: (ⅰ) active sites, where contaminants can be chemisorbed and/or degraded; (ⅱ) large specific surface area and pore volume, associated with high adsorption capacities; (ⅲ) highly stability in water; (ⅳ) easily functionalized cavities; (ⅴ)large-scale synthesis, and so on^[9-10].

  Dyes, one of the organic pollutants, have a chemically stable structure (usually aromatic and conjugated) and hence remain chemically inert towards light, heat, and oxidizing agents. These dyes are also non-biodegradable, toxic, carcinogenic, and mutagenic by nature^[11-18]. Thus, for environmental remediation, the removal of injurious organic aromatic dyes from the water stream is extremely desirable. Semiconductor - based photocatalysis is a flourishing approach to degrade dyes because it has simplified operation procedures, consumes low energy, does not generate secondary pollution, has high efficiency, and has environmentfriendly features. Such semiconductor-based photocatalytic technique is a heterogeneous catalysis process under light irradiation. It allows the one - pot elimination of contaminants from wastewater and can efficiently mineralize aromatic pollutants, especially dyes to liberate H₂O and CO₂ as the final product^[19]. Similarly, adsorption to remove dyes in water is simple and convenient, without secondary pollution^[20].

  So MOFs have been investigated for the removal of dye contaminants in water, not only as selective adsorbent but also as a platform for dye degradation through catalytic processes^[21]. From the first reported MOF in the adsorptive removal of a dye (methyl orange, MO) from water in 2010, or the first MOF in the catalytic degradation of a dye (MO) in water in 2007, many MOFs and their modified materials have been used to remove dyes from wastewater, such as Fe₃O₄-ES/ZIF-8 (adsorption capacity 64.50 mg·g^-1 for MO), MOF - 5 (adsorption capacities 64.50 mg·g^-1 for MO), [Zn₆(IDC)₄(OH)₂(Hprz)₂] (photocatalytic degradation efficiency 96% for methylene blue) and MIL^-101(Cr)@GO (photocatalytic degradation efficiency 96% for methylene blue)^[22-28]. These MOFs not only exhibit high adsorption or photocatalytic degradation efficiencies but can also be used in sustainable recycling. Since MOFs have shown great potential in dye removal from the aquatic environment, it is urgent to synthesize MOFs - based adsorbent/catalyst with other properties. As far as we know, MOF materials for both adsorption and catalytic degradation of dyes have not been reported.

  Based on the above situation, we expect new 3D Cu - MOF material with semiconductor properties and permanent porosity to be an advanced catalyst and adsorbent in aqueous solutions (Scheme 1). So, we selected the flexible 1, 4-phenylenediacetic acid (H₂ppda) and the rigid 1,3,5-tris(1-imidazolyl) benzene (tib) as polytopic bridging organic linkers, and Cu(Ⅱ) ions as metallic nodes, synthesizing one new 3D MOF [Cu₃(ppda)₃(tib)₂(H₂O)₄]·6H₂O (Cu-MOF). Singlecrystal X-ray diffraction analysis reveals that the ppda^2- and tib ligands alternately link Cu ions to form 2D polymeric layers, then layers and layers interpenetrate each other by flexible ppda^2- to form a 3D supramolecular structure. This Cu-MOF has excellent thermal stability, semiconductor properties, porous, and enormous structures, suggesting the possibility of adsorption and catalyst performance. Commendably, it exhibits a high-performance adsorption rate under dark conditions and a high degradation efficiency of methylene blue (MB) under visible light irradiation, because its surface area can provide high percentages of the exposed active site. The main adsorption and degradation mechanisms were thoroughly analyzed, and the experiment influencing factors, i.e., reaction time, ionic strength, and reusability were analyzed synthetically.

  Scheme 1

  

  Scheme 1.  Schematic diagram of degradation of MB in porous Cu-MOF material

  下载: 全尺寸图片 幻灯片

  This work introduced syntheses, designing strategies and structures of MOF, and plausible mechanistic pathways adopting which this Cu-MOF displays photocatalytic degradation and adsorption of organic molecules in particular organic dyes which are usually present in wastewater discharge from industries.

  1.   Experimental

  1.1   Materials and general methods

  All reagents (AR) are commercially available. The crystal synthesis method was hydrothermal synthesis. Elemental analyses were performed by Flash 2000 organic elemental analyzer. Powder X-ray diffraction (PXRD) patterns were acquired on XRD-7000 Advance X-ray powder diffractometer and the main characterization conditions were an operating voltage of 40 kV, current of 40 mA, Cu Kα as the radiation source, wavelength of 0.154 nm and scanning range of 5° to 60°. Single crystal diffraction analysis was carried out on a Bruker SMART APEX CCD diffractometer equipped with graphite monochromatic Mo Kα radiation (λ = 0.071 073 nm). UV-Vis absorption and UV-Vis DRS (diffuse reflection spectrometry) spectrum were carried out on a UV-Vis spectrophotometer (UV-2700 and UV-2600). The photocatalytic reaction experiment was performed in the photocatalytic reactor of Nanjing Xujiang Mechanical and Electrical Factory. The THZ-82A water bath thermostatic oscillator of Jiangsu Shenglan Instrument Manufacturing Limited company was used in the adsorption experiment. Thermal gravimetric analysis (TGA) was performed by an instrument TA Q550 thermogravimetric analyzer. ζ potential measurement was undertaken on Malvern Zetasizer Nano ZS90.

  1.2   Synthesis of Cu-MOF and single-crystal X-ray diffraction

  A mixture of H₂ppda (19.4 mg, 0.1 mmol), Cu(OAc)₂·H₂O (19.9 mg, 0.1 mmol), tib (27.6 mg, 0.1 mmol), buffer solution of pH=5 (HAc/NaAc, 4 mL) and isopropanol (1 mL) was put in a 20 mL glass bottle. The mixture was heated for 3 d at 95 ℃, then cooled to room temperature, and filtered to obtain the blue crystals. Elemental analysis Calcd. for C₆₀H₆₈N₁₂O₂₂Cu₃(%): C 48.05, H 4.57, N 11.21; Found(%): C 48.21, H 4.63, N 11.30. IR (KBr pellet, cm^-1): 3 440 m, 3 133 w, 2 280 w, 1 624 s, 1 564 s, 1 513 m, 1 366 s, 1 069 m, 1 014 w, 755 m, 658 w.

  The crystal structure was solved by SHELXS - 2014 direct methods^[29-30]. Table S1 and S2 (Supporting information) list respectively the structural analysis data and selected bond angles and bond distances.

  2.   Results and discussion

  2.1   Crystal structure

  Single - crystal X - ray diffraction analysis shows that Cu-MOF belongs to the monoclinic crystal system with the P2₁/n space group. The Cu1 and Cu2 atoms lie in distorted octahedral coordination geometry, and are coordinated with two nitrogen atoms of two tib ligands and four oxygen atoms from ppda^2- ligands and water molecules (Fig. 1a). Three Cu(Ⅱ) ions and two tib ligands form a 1D layered arrangement running parallel to the crystallographic b axis. Two same cis - ppda^2- (Fig. S2) and one trans-ppda^2- ligands alternately link Cu(Ⅱ) ions to form an ordered 1D wave chain, and these 1D chains run regularly through the 1D layered arrangement to form 2D polymeric ribbon motifs (Fig. 1b). The layer and layer interpenetrate each other by trans-ppda^2- to form a stable 3D structure (Fig. 1c).

  Figure 1

  

  Figure 1.  (a) View of local coordination environment of Cu(Ⅱ) ion in Cu-MOF; (b) 2D layer formed by linking Cu(Ⅱ) ions, ppda^2- and tib ligands together in Cu-MOF (chains and tape show different colors for clarity); (c) View of 3D extended supramolecular network in Cu-MOF (layers show different colors for clarity)

  All hydrogen atoms are omitted for clarity.

  下载: 全尺寸图片 幻灯片

  2.2   Structure characterization

  PXRD patterns reveal that the dominant diffraction peaks of Cu - MOF fitted well with the simulated diffraction peaks, indicating its successful preparation (Fig.S3a). TGA curve shows that Cu-MOF lost the crystalline and coordinated water molecules during the temperature range of 25 to 100 ℃ and the framework could maintain at a temperature of 227 ℃. It shows the thermal stability of Cu-MOF (Fig.S3b). The optical property of Cu - MOF was investigated by the UV - Vis DRS method. The absorption peak of Cu - MOF was at 303 nm (Fig.S4a), and the band gap energy (E_g) of Cu-MOF was 2.96 eV based on the Kubelka-Munk equation (Fig. S4b, Eq.S3), indicating that Cu-MOF has the nature of a semiconductor.

  The adsorption and desorption of N₂ isotherms were measured by the static volume method of the aperture and specific surface area tester. As shown in Fig. S3c, the N₂ adsorption-desorption isotherm of Cu-MOF was a type Ⅱ isotherm. The molecules were adsorbed in a monolayer, saturated at the first inflection point, and then the adsorption layer began to accumulate. Through the Brunauer - Emmett - Teller (BET) method, the specific surface area of Cu-MOF was then obtained as 18 m²·g^-1, and the pore size distribution of Cu-MOF was evaluated using nitrogen adsorption - desorption data by Horvath-Kawazoe (HK) methods at 77 K, indicates that there are mesopores and micropores in Cu-MOF (Fig. S3d). These data show that more active reactions or adsorption sites can be used in the material^[31-32].

  2.3   Photocatalytic activity of Cu-MOF

  The photocatalytic degradation of the four cationic dyes MB, rhodamine B (RhB), MO, and basic fuchsin (BF) was studied under visible-light irradiation in the presence of Cu-MOF. Firstly, the mass concentrations of the four dyes (10 mg·L^-1) almost did not change with the increase of time when no catalyst was added (Fig. S5a-S5d), so the self-degradation of the dyes was negligible. Secondly, when H₂O₂ (1.0 mL, 30%) was added to the four dyes, the degradation efficiency of the dye was slightly higher (Fig.S6a-S6d), because H₂O₂ as an oxidant can provide hydroxyl radical (·OH), which can serve as an active substance for the degradation of the dye^[33-34]. Thirdly, Cu - MOF (20 mg) was added to the solution of the four dyes (10 mg·L^-1), and the dye degradation efficiency was increased obviously (Fig. S7a - S7d). Fourthly, when Cu-MOF (20 mg) and H₂O₂ (1.0 mL, 30%) were both added to the reaction systems (20 mL, 10 mg·L^-1), it showed a better degradation performance compared to the previous no catalyst and no H₂O₂, only H₂O₂, and only catalyst situations (Fig.S8a- S8c). We added 20 mg of Cu(OAc)₂·H₂O into the MB solution (20 mL, 10 mg·L^-1) and the degradation efficiency was 5.0% after 3 h by photocatalytic degradation. The degradation effect was found to be insignificant by comparison (Fig. S9). These results suggested that Cu-MOF is a promising photocatalyst for organic pollutant degradation.

  The relationship between degradation efficiency and time is listed in Fig. 2a and S10. In comparison, Cu - MOF exhibited the highest photocatalysis performance toward MB in the presence of H₂O₂. The equilibrium of adsorption and desorption was reached after the dark reaction for 30 min, then the color of MB gradually faded with the increase of irradiation time. After 180 min of irradiation, the degradation efficiency of MB was 97%, which meant that the synergistic effect between Cu-MOF and H₂O₂ had a significant effect on the degradation of MB (Fig. 2b). Because the photocatalytic activity of Cu-MOF helps H₂O₂ to produce more ·OH active substances, and then performs better oxidative degradation of dye molecules. At the same time, the kinetic analysis of the degradation reaction was carried out according to the pseudo - first - order kinetic model, using the equation: -ln(c/c₀)=kt (Eq.1), where c and c₀ are the instantaneous and initial concentration at the beginning of photocatalytic degradation of dye, t is the irradiation time, and k represents the total reaction rate constant^[35]. Compared with other dyes, the k of MB was the biggest (Fig. 2c, 2d), which reached 0.019 7 min^-1.

  Figure 2

  

  Figure 2.  (a) Relationship between dye degradation efficiency and irradiation time for the dyes on Cu-MOF (+H₂O₂); (b) UV-Vis absorption spectra of the mixed solution of Cu-MOF, H₂O₂, and MB changed with time; (c) Plots of -ln(c/c₀) vs t for the photodegradation of the dyes on Cu-MOF in the presence of H₂O₂; (d) Reaction rate constants (k) of the photodegradation of the dyes on Cu-MOF in the presence of H₂O₂

  Reaction conditions: 20 mg Cu-MOF, 10 mg·L^-1 dyes solution, 1.0 mL H₂O₂ (30%), λ>420 nm.

  下载: 全尺寸图片 幻灯片

  2.4   Photocatalytic degradation mechanism

  As shown in Fig. 3a, Cu-MOF still had a high degradation efficiency for MB after five cycles, indicating it has good reusability. In addition, the PXRD patterns of Cu-MOF before degradation, after degradation, and after five degradation cycles were compared (Fig.S11), and the diffraction peak positions were largely consistent. It shows that the structure of Cu-MOF has good stability and reusability^[36]. The electrochemical impedance spectroscopy (EIS) analysis was implemented (Fig. S12). Then the role of electrons and holes in photocatalytic degradation was investigated by a free radical trapping experiment^[37]. p-Benzoquinone (PBQ, ·O₂^- scavenger), tert-butanol (TBA, ·OH scavenger), AgNO₃ (e^- scavenger), and EDTA-2Na (h⁺ scavenger) were added to capture the reaction species. In the presence of scavengers, the degradation efficiency of Cu -MOF on MB decreased from 97% to 82%, 34%, 74%, and 65%, respectively (Fig. 3b). The photocatalytic degradation efficiency was inhibited to different degrees, indicating that these substances made a certain contribution in the catalytic process.

  Figure 3

  

  Figure 3.  (a) Changes in the degradation efficiency of the photodegradation of the dyes on Cu-MOF in the presence of H₂O₂ after 1-5 degradation cycles under the Xenon lamp (500 W); (b) Histogram of degradation efficiency of the photodegradation of the dyes on Cu-MOF in the presence of H₂O₂ after adding the scavengers; (c) E_FB obtained by Mott-Schottky measurements (1 000 and 1 200 Hz); (d) Photocatalytic degradation mechanism diagram

  下载: 全尺寸图片 幻灯片

  Mott-Schottky measurements were used to further investigate the active substances. As shown in Fig. 3c, the flat band potential (E_FB) of Cu-MOF was -0.71 V (vs Ag/AgCl) by extrapolation. The positive slope of the tangent line indicates that Cu-MOF is an n-type semiconductor and the conduction band potential (E_CB) of Cu-MOF is close to the flat band potential (E_FB). The E_CB of Cu-MOF was -0.51 V (vs NHE), which was higher than O₂/·O₂^- potential (-0.33 V (vs NHE)) ^[38]. The results showed that the photogenerated electrons on CB of Cu - MOF may generate superoxide radicals during the photocatalytic degradation of MB. The valence band potential (E_VB) of Cu - MOF was calculated to be 2.45 V (vs NHE) from its band gap. This value was higher than the reduction potential of ·OH/OH^- (2.38 V (vs NHE)) ^[39]. Based on the above experimental results, a possible photocatalytic mechanism was proposed. Under the excitation of visible light, Cu - MOF surface occurs electron transition and generates electron-hole pair (e^- reacts with oxygen to generate ·O₂^-, hydrogen peroxide reacts with e^- to generate ·OH, water molecules and OH^- react with h⁺ to generate ·OH, respectively). Finally, h⁺, ·OH, and ·O₂^- are used as active substances in the reaction to degrade the MB molecule (Fig. 3d)^[40-41].

  The main products were presumed to be carbon dioxide and water, and we verified the conjecture through HCO₃^- detection (Fig. S13). Firstly, 1 mol·L^-1 CaCl₂ solution was added to the degraded filtrate, and no significant change was observed. Then 0.5 mol·L^-1 NaOH solution was added, and a white precipitate was found, which confirmed that CO₂ produced in the degraded solution dissolved in water to form HCO₃^-.

  Combined with the above results, the reaction equation of photocatalytic degradation of MB is as follows:

  Cu-MOF + hν → Cu-MOF (e^- + h⁺)

  O₂ + e^- → ·O₂^-

  H₂O₂ + e^- → ·OH + OH^-

  H₂O + h⁺ → ·OH

  OH^- + h⁺ → ·OH

  ·O₂^- + MB → other products → CO₂ + H₂O

  ·OH + MB → other products → CO₂ + H₂O

  2.5   Adsorption property analysis

  After the photocatalytic degradation experiment, we explored the adsorption effect of Cu-MOF on dyes. As shown in Fig.S14, when Cu-MOF was added to different dyes, the adsorption capacity of Cu-MOF on MB was the largest. However, the adsorption capacity of Cu-MOF was not high. According to the ζ potential of Cu - MOF (Fig. S15), the surface presented a positive charge when pH=3-9, and MB belongs to the cationic dye, so the electrostatic interaction between Cu - MOF and MB led to a poor adsorption effect. However, in the influence experiment of strong ions, it was found that the adsorption capacity of Cu-MOF increased after adding NaCl. When NaCl mas concentration was 200 g·L^-1, the adsorption capacity of Cu-MOF reached 87.23 mg·g^-1. Therefore, the detailed adsorption behavior of Cu-MOF toward MB was studied. As can be seen from Fig. 4, the adsorption capacity of Cu - MOF for MB increased with time after adding NaCl at 298 K. When the time reached 300 min, the adsorption capacity of Cu-MOF reached equilibrium^[42], the adsorption was in a state of saturation and the adsorption capacity of Cu-MOF didn't change significantly until 1 440 min^[43-44].

  Figure 4

  

  Figure 4.  Variation of adsorption capacity of MB by Cu-MOF with time

  T=298 K, ρ_MB=20 mg·L^-1, ρ_NaCl=200 g·L^-1.

  下载: 全尺寸图片 幻灯片

  Adsorption kinetics can not only estimate the adsorption capacity but also determine the adsorption process. Three dynamic models (Eq.S4-S6) were used to fit the data and study the adsorption reaction type^[45].

  The fitting conditions of the three dynamic models are shown in Fig. 5, and the value of R² for Eq.S5 was larger compared to Eq. S4. These data fitted Eq. S5, indicating that the adsorption process was mainly chemisorption (Table 1) ^[46]. Then the control step in the adsorption process was explained by fitting the intraparticle diffusion model (Fig. 5c). The first segment was the process of MB molecules moving on the surface of Cu-MOF, followed by the entry of MB molecules from the outer surface of Cu-MOF into the inner pore, and the third segment was that MB molecules gradually occupied the active site of Cu-MOF with time increased and the adsorption process reached saturation. The slope of this segment was lower compared to the other two segments, indicating that it is the control step of the whole adsorption process^[47-48].

  Figure 5

  

  Figure 5.  (a) Pseudo-first-order kinetic model, (b) pseudo-second-order kinetic model, and (c) intra-particle diffusion model of MB adsorption by Cu-MOF

  T=298 K, ρ_MB=20 mg·L^-1, ρ_NaCl=200 g·L^-1.

  下载: 全尺寸图片 幻灯片

  Table 1

  

  Table 1.  Kinetic parameters of MB adsorption by Cu-MOF

  下载: 导出CSV

  Kinetic model	qe, exp / (mg·g-1)	qe, cal / (mg·g-1)	k1 / min-1	k2 / (g·mg-1·min-1)	kid / (mg·g-1·min-0.5)	C / (mg·g-1)	R2
  Pseudo-first-order kinetic	87.23	5.52	0.005 76				0.455
  Pseudo-second-order kinetic	87.23	87.18		0.0115			1.00
  Intra-particle diffusion model
  Step 1					0.780	79.22	0.910
  Step 2					0.181	83.94	0.966
  Step 3					0.037	85.87	0.884

  Then the effect of different concentrations of MB (5 - 40 mg·L^-1) on the adsorption capacity of Cu-MOF was investigated. The increase in MB concentration provided the driving force for Cu-MOF and the adsorption capacity of Cu-MOF gradually increased (Fig. 6)^[49-51].

  Figure 6

  

  Figure 6.  Adsorption properties of Cu-MOF at different MB initial concentrations

  T=298 K, ρ_MB=5-40 mg·L^-1, ρ_NaCl=200 g·L^-1

  下载: 全尺寸图片 幻灯片

  Then we fitted the equilibrium relationship between MB concentration (ρ_e) and the adsorption capacity of Cu -MOF (q_e) using three isotherm models (Eq.S7-S9)^[52].

  The Langmuir model represented that there was no interaction between the adsorbents, which was monolayer adsorption that occurred on the adsorbent surface. The Freundlich model was used to describe adsorbent surfaces that were non - homogeneous and had adsorption sites of different energies^[53]. The fitting of the three models is shown in Fig. 7. The nonlinear correlation coefficient (R²) of the Langmuir model was closer to 1.00 compared to the other two models, which was the best fit for the data (Table 2). This indicates that the adsorption process is mainly monolayer adsorption. The separation factor (R_L) was used to calculate the adsorption capacity of Cu-MOF:

  $ R_{\mathrm{L}}=1 /\left(1+K_{\mathrm{L}} \rho_0\right) $

  (2)

  Figure 7

  

  Figure 7.  (a) Langmuir model, (b) Freundlich model, and (c) Temkin model for MB adsorption by Cu-MOF

  T=298 K, ρ_MB=5-40 mg·L^-1, ρ_NaCl=200 g·L^-1.

  下载: 全尺寸图片 幻灯片

  Table 2

  

  Table 2.  Langmuir, Freundlich, and Temkin isotherms parameters of MB adsorption by Cu-MOF

  下载: 导出CSV

  Model	Parameters	R2
  Langmuir	qm, exp=154.5 mg·g-1, qm, cal=153.0 mg·g-1, KL=0.007 01 L·mg-1, RL=0.877	0.996
  Freundlich	n=1.15, KF=6.20 L1/n·mg1-1/n·g-1	0.994
  Temkin	b=38.6 J·mol-1·g·mg-1, KT=0.222 L·mg-1	0.955

  where ρ₀ (mg·L^-1) is the initial MB concentration. The value of R_L in this experiment was 0.877, indicating that the adsorption behavior was favorable (0 < R_L < 1)^[54].

  We then investigated the effect of temperature on the adsorption process by selecting temperatures of 298, 308, and 318 K to observe the change in adsorption capacity (Fig. 8). The graph showed that the adsorption capacity of Cu-MOF decreased as the temperature increased, so the adsorption process was further explored using thermodynamic parameters. Gibbs free energy (ΔG), enthalpy change (ΔH), and entropy change (ΔS) could be calculated from the slope and intercept of the plot of ln K_d vs 1/T (Fig.S16) by using the Eq.S10-S13^[55-59].

  Figure 8

  

  Figure 8.  Adsorption performance of Cu-MOF in the presence of NaCl for MB at different temperatures

  ρ_MB=20 mg·L^-1, ρ_NaCl=200 g·L^-1.

  下载: 全尺寸图片 幻灯片

  As shown in Table 3, the ΔG was always less than zero, a negative value of ΔH indicates that the adsorption process is exothermic. The ΔS was negative indicating that the adsorption process became gradually ordered and the whole adsorption process was an exothermic spontaneous process.

  Table 3

  

  Table 3.  Thermodynamic parameters for adsorption MB adsorption by Cu-MOF

  下载: 导出CSV

  T/K	ΔG / (kj·mol-1)	ΔH / (kj·mol-1)	ΔS / (J·mol-1·K-1)
  298	-12.296	-104.87	-310.65
  308	-9.1898	-104.87	-310.65
  318	-6.0833	-104.87	-310.65

  The co-existence ions had a certain effect on MB adsorption by Cu-MOF. As shown in Fig. 9, MB adsorption was significantly improved when different concentrations of NaCl were added to MB and Cu-MOF solution. This may be due to the salt ion effect^[60]. After adding the strong electrolyte NaCl to the solution, the concentration of total ions increased, the interaction between ions was enhanced, the degree of dissociation increased, and the adsorption process of MB by Cu - MOF was promoted. When the concentration of NaCl reached a certain value, the MB adsorbed by Cu-MOF were in a saturated state, and their adsorption capacity reached a stable value^[61-63].

  Figure 9

  

  Figure 9.  Effect of ion concentration on MB adsorption by Cu-MOF

  ρ_NaCl=20-200 g·L^-1, T=298 K.

  下载: 全尺寸图片 幻灯片

  3.   Conclusions

  In summary, complex Cu-MOF has been synthesized successfully under hydrothermal conditions by the reaction of Cu(Ⅱ) salt and 1,3,5-tris(1-imidazolyl) benzene (tib) in the presence of flexible phenylenediacetate (H₂ppda). In Cu-MOF, Cu(Ⅱ) ions and tib ligands form a 1D belt, two same cis -ppda^2- and one trans-ppda^2- ligands alternately link Cu(Ⅱ) ions to form an ordered 1D wave chain, and these 1D chains run regularly through the 1D belt to form the 2D surface. The adjacent 2D surfaces are interpenetrated by trans-ppda^2- to form a stable 3D structure (S_BET=18 m²·g^-1). The results reveal that Cu-MOF possessed a higher photocatalytic degradation efficiency toward MB for having semiconductor properties. The main photocatalytic degradation mechanism is the separation of the electron and hole pair of the catalyst under the excitation of the xenon lamp, and the redox reaction occurs to produce the active material to degrade the dye and eventually decompose into carbon dioxide and water. Furthermore, the adsorption performance of Cu-MOF to MB was studied. The maximum adsorption capacity was 87.23 mg·g^-1 (ρ_NaCl=200 g·L^-1, T=298 K). The adsorption isotherms were described accurately by the Langmuir model, indicating a monolayer adsorption process. It's also a spontaneous process of decreasing entropy. This study expands the number of 3D MOFs available for restoring the safety of water environments.

  
  
• 1. [1]

     Zhou H C, Kitagawa S. Metal-organic frameworks (MOFs)[J]. Chem. Soc. Rev., 2014, 43(16):  5415-5418. doi: 10.1039/C4CS90059F

  2. [2]

     Jiao L, Seow J Y R, Skinner W S, Wang Z Y U, Jiang H L. Metalorganic frameworks: Structures and functional applications[J]. Mater. Today, 2019, 27:  43-68. doi: 10.1016/j.mattod.2018.10.038

  3. [3]

     Corma A, García H, Xamena F X L I. Engineering metal organic frameworks for heterogeneous catalysis[J]. Chem. Rev., 2010, 110(8):  4606-4655. doi: 10.1021/cr9003924

  4. [4]

     Cui Y J, Yue Y F, Qian G D, Chen B L. Luminescent functional metal-organic frameworks[J]. Chem. Rev., 2012, 112(2):  1126-1162. doi: 10.1021/cr200101d

  5. [5]

     Lu K D, Aung T, Guo N N, Weichselbaum R, Lin W B. Nanoscale metal-organic frameworks for therapeutic, imaging, and sensing applications[J]. Adv. Mater., 2018, 30(37):  e1707634. doi: 10.1002/adma.201707634

  6. [6]

     Ramaswamy P, Wong N E, Shimizu G K H. MOFs as proton conductors-challenges and opportunities[J]. Chem. Soc. Rev., 2014, 43(16):  5913-5932. doi: 10.1039/C4CS00093E

  7. [7]

     Kreno L E, Leong K, Farha O K, Allendorf M, Van Duyne R P, Hupp J T. Metalorganic framework materials as chemical sensors[J]. Chem. Rev., 2012, 112(2):  1105-1125. doi: 10.1021/cr200324t

  8. [8]

     Li B, Wen H M, Cui Y J, Zhou W, Qian G D, Chen B L. Emerging multifunctional metal-organic framework materials[J]. Adv. Mater., 2016, 28(40):  8819-8860. doi: 10.1002/adma.201601133

  9. [9]

     Yang X G, Zhang J R, Tian X K, Qin J H, Zhang X Y, Ma L F. Enhanced activity of enzyme immobilized on hydrophobic ZIF-8 modified by Ni²⁺ ions[J]. Angew. Chem. Int. Ed., 2022, 62(7):  e202216699.

  10. [10]

      Pournara A D, Tarlas G D, Papaefstathiou G S, Manos M J. Chemically modified electrodes with MOFs for the determination of inorganic and organic analytes via voltammetric techniques: a critical review[J]. Inorg. Chem. Front., 2019, 6(12):  3440-3455. doi: 10.1039/C9QI00965E

  11. [11]

      Beydaghdari M, Saboor F H, Babapoor A, Karve V V, Asgari M. Recent advances in MOF-based adsorbents for dye removal from the aquatic environment[J]. Energies, 2022, 15(6):  2023. doi: 10.3390/en15062023

  12. [12]

      Phan D N, Rebia R A, Saito Y, Kharaghani D, Khatri M, Tanaka T, Lee H, Kim I S. Zinc oxide nanoparticles attached to polyacrylonitrile nanofibers with hinokitiol as gluing agent for synergistic antibacterial activities and effective dye removal[J]. J. Ind. Eng. Chem., 2020, 85:  258-268. doi: 10.1016/j.jiec.2020.02.008

  13. [13]

      Zhao J J, Xu L Q, Su Y Z, Yu H W, Liu H, Qian S P, Zheng W, Zhao Y Q. Zr-MOFs loaded on polyurethane foam by polydopamine for enhanced dye adsorption[J]. J. Environ. Sci., 2021, 101:  177-188. doi: 10.1016/j.jes.2020.08.021

  14. [14]

      Chiong J A, Zhu J, Bailey J B, Kalaj M, Subramanian R H, Xu W Q, Cohen S M, Tezcan F A. An exceptionally stable metal-organic framework constructed from chelate-based metal-organic polyhedra[J]. J. Am. Chem. Soc., 2020, 142(15):  6907-6912. doi: 10.1021/jacs.0c01626

  15. [15]

      Dawood S, Sen T K, Phan C. Synthesis and characterization of novelactivated carbon from waste biomass pine cone and its application in the removal of congo red dye from aqueous solution by adsorption[J]. Water Air Soil Pollut., 2013, 225(1):  1818.

  16. [16]

      Jadhav S A, Garud H B, Patil A H, Patil G D, Patil C R, Dongale T D, Patil P S. Recent advancements in silica nanoparticles based technologies for removal of dyes from water[J]. Colloid Interface Sci. Commun., 2019, 30(10):  100181.

  17. [17]

      Parmar B, Bisht K K, Rajput G, Suresh E. Recent advances in metal-organic frameworks as adsorbent materials for hazardous dye molecules[J]. Dalton Trans., 2021, 50(9):  3083-3108. doi: 10.1039/D0DT03824E

  18. [18]

      Yu D Y, Li L B, Wu M H, Crittenden J C. Enhanced photocatalytic ozonation of organic pollutants using an iron-based metal-organic framework[J]. Appl. Catal. B: Environ., 2019, 251:  66-75. doi: 10.1016/j.apcatb.2019.03.050

  19. [19]

      Li Y, Pang J D, Bu X H. Multi-functional metal-organic frameworks for detection and removal of water pollution[J]. Chem. Commun., 2022, 58(57):  7890-7908. doi: 10.1039/D2CC02738K

  20. [20]

      Hou X T, Wang J C, Mousavi B, Klomkliang N, Chaemchuen S. Strategies for induced defects in metal-organic frameworks for enhancing adsorption and catalytic performance[J]. Dalton Trans., 2022, 51(21):  8133-8159. doi: 10.1039/D2DT01030E

  21. [21]

      Ibrahim A O, Adegoke K A, Adegoke R O, AbdulWahab Y A, Oyelami V B, Adesina M O. Adsorptive removal of different pollutants using metal-organic framework adsorbents[J]. J. Mol. Liq., 2021, 333:  115593. doi: 10.1016/j.molliq.2021.115593

  22. [22]

      Mu Y, Wang D, Meng X D, Pan J, Han S D, Xue Z Z. Construction of iodoargentates with diverse architectures: Template syntheses, structures, and photocatalytic properties[J]. Cryst. Growth Des., 2020, 20(2):  1130-1138. doi: 10.1021/acs.cgd.9b01448

  23. [23]

      Li H X, Yang Z X, Lu S, Su L Y, Wang C H, Huang J G, Zhou J, Tang J H, Huang M Z. Nano-porous bimetallic CuCo-MOF-74 with coordinatively unsaturated metal sites for peroxymonosulfate activation to eliminate organic pollutants: Performance and mechanism[J]. Chemosphere, 2021, 273:  129643. doi: 10.1016/j.chemosphere.2021.129643

  24. [24]

      Wang S J, Alavi M A, Karizi F Z, Tehrani A A, Yan X W, Morsali A, Hu M L. A pillar-layered metal-organic framework based on pinwheel trinuclear zinc-carboxylate clusters; synthesis and characterization[J]. Mater. Lett., 2021, 287:  129261. doi: 10.1016/j.matlet.2020.129261

  25. [25]

      Jia X N, Li S J, Wang Y D, Wang T, Hou X H. Adsorption behavior and mechanism of sulfonamide antibiotics in aqueous solution on a novel MIL-101(Cr)@GO composite[J]. J. Chem. Eng. Data, 2019, 64(3):  1265-1274. doi: 10.1021/acs.jced.8b01152

  26. [26]

      Karimi-Maleh H, Ayati A, Davoodi R, Tanhaei B, Karimi F, Malekmohammadi S, Orooji Y, Fu L, Sillanpää M. Recent advances in using of chitosan-based adsorbents for removal of pharmaceutical contaminants: A review[J]. J. Cleaner Prod., 2021, 291(6):  125880.

  27. [27]

      Liu Z C, Tran K Q. A review on disposal and utilization of phytoremediation plants containing heavy metals[J]. Ecotox. Environ. Safe., 2021, 226:  112821. doi: 10.1016/j.ecoenv.2021.112821

  28. [28]

      Wang S B, Guan B Y, Wang X, Lou X W D. Formation of hierarchical Co₉S₈@ZnIn₂S₄ heterostructured cages as an efficient photocatalyst for hydrogen evolution[J]. J. Am. Chem. Soc., 2018, 140(45):  15145-15148. doi: 10.1021/jacs.8b07721

  29. [29]

      Fan C B, Zhang X, Li N N, Xu C G, Wu R X, Zhu B, Zhang G L, Bi S Y, Fan Y H. Zn-MOFs based luminescent sensors for selective and highly sensitive detection of Fe³⁺ and tetracycline antibiotic[J]. J. Pharm. Biomed. Anal., 2020, 188(48):  113444.

  30. [30]

      Xu X Y, Yan B. Eu (Ⅲ)-functionalized ZnO@MOF heterostructures: Integration of pre-concentration and efficient charge transfer for the fabrication of a ppb-level sensing platform for volatile aldehyde gases in vehicles[J]. J. Mater. Chem. A, 2017, 5(5):  2215-2223. doi: 10.1039/C6TA10019H

  31. [31]

      Wu X Q, Huang D D, Wu Y P, Zhao J, Liu X, Dong W W, Li S, Li D S, Li J R. In situ synthesis of nano CuS-embedded MOF hierarchical structures and application in dye adsorption and hydrogen evolution reaction[J]. ACS Appl. Energy Mater., 2019, 2(8):  5698-5706. doi: 10.1021/acsaem.9b00840

  32. [32]

      Cui R F, Li R, Li Z, Wei M M, Wang X, Li X. A Tb-MOF anion, porous coordination framework constructed with oxalate ligand: Crystal structure, adsorption properties, and luminescence sensing[J]. Dyes Pigm., 2021, 195:  109669. doi: 10.1016/j.dyepig.2021.109669

  33. [33]

      Balarak D, Azarpira H. Photocatalytic degradation of sulfamethoxazole in water: Investigation of the effect of operational parameters[J]. Int. J. Chem. Technol. Res., 2016, 9:  731-738.

  34. [34]

      Seo P W, Khan N A, Jhung S H. Removal of nitroimidazole antibiotics from water by adsorption over metal-organic frameworks modified with urea or melamine[J]. Chem. Eng. J., 2017, 315:  92-100. doi: 10.1016/j.cej.2017.01.021

  35. [35]

      Vinothkumar K, Jyothi M S, Lavanya C, Sakar M, Valiyaveettil S, Balakrishna R G. Strongly co-ordinated MOF-PSF matrix for selective adsorption, separation and photodegradation of dyes[J]. Chem. Eng. J., 2022, 428:  132561. doi: 10.1016/j.cej.2021.132561

  36. [36]

      Zaman F U, Xie B, Zhang J Y, Gong T Y, Cui K, Hou L R, Xu J L, Zhai Z R, Yuan C Z. MOFs derived hetero-ZnO/Fe₂O₃ nanoflowers with enhanced photocatalytic performance towards efficient degradation of organic dyes[J]. Nanomaterials, 2021, 11(12):  3239. doi: 10.3390/nano11123239

  37. [37]

      Zuo L Q, Zhang T F, Zhang Z K, Hou J X, Liu G J, Du J L, Li L X. A 3D binuclear salen-based multifunctional MOF: Degradation of MO dye and highly selective sensing of Fe³⁺[J]. Inorg. Chem. Commun., 2019, 99:  113-118. doi: 10.1016/j.inoche.2018.11.006

  38. [38]

      Ouyang J B, Chen J, Ma S Q, Xing X H, Zhou L M, Liu Z R, Zhang C T. Adsorption removal of sulfamethoxazole from water using UiO-66 and UiO-66-BC composites[J]. Particuology, 2022, 62(3):  71-78.

  39. [39]

      刘峰强, 王黎明, 范顶, 徐丽慧, 潘虹. TiO₂/Cu₂O/Pt复合空心微球的制备及其光催化性能[J]. 无机化学学报, 2023,39,(2): 300-308. LIU F Q, WANG L M, FAN D, XU L H, PAN H. Preparation and photocatalytic properties of TiO₂/Cu₂O/Pt composite hollow microspheres[J]. Chinese J. Inorg. Chem., 2023, 39(2):  300-308.

  40. [40]

      Peng Y, Mao Y G, Liu T. Synthesis of one-dimensional Bi₂O₃-B₅O₇I heterojunctions with high interface quality[J]. CrystEngComm, 2018, 20(33):  4771-4780. doi: 10.1039/C8CE00819A

  41. [41]

      Hou L R, Niu Y W, Yang F, Ge F Y, Yuan C Z. Facile solvothermal synthesis of hollow BiOBr submicrospheres with enhanced visible- light- responsive photocatalytic performance[J]. J. Anal. Methods Chem., 2020, :  3058621.

  42. [42]

      Wang C, Xiong C, He Y L, Yang C, Li X T, Zheng J Z, Wang S X. Facile preparation of magnetic Zr-MOF for adsorption of Pb (Ⅱ) and Cr(Ⅵ) from water: Adsorption characteristics and mechanisms[J]. Chem. Eng. J., 2021, 415:  128923. doi: 10.1016/j.cej.2021.128923

  43. [43]

      Xiong W P, Zeng G M, Yang Z H, Zhou Y Y, Zhang C, Cheng M, Liu Y, Hu L, Wan J, Zhou C Y, Xu R, Li X. Adsorption of tetracycline antibiotics from aqueous solutions on nanocomposite multi- walled carbon nanotube functionalized MIL- 53(Fe) as new adsorbent[J]. Sci. Total Environ., 2018, 627:  235-244. doi: 10.1016/j.scitotenv.2018.01.249

  44. [44]

      Zhang Y, Wang X, Wang Y, Li L, Xu N, Wang X L. Anderson-type polyoxometalate-based complexes constructed from a new 'V' -like bis- pyridine-bis amide ligand for selective adsorption of organic dyes and detection of Cr (Ⅵ) and Fe (Ⅲ) ions[J]. Inorg. Chem. Front., 2021, 8(20):  4458-4466. doi: 10.1039/D1QI00785H

  45. [45]

      Nie Y L, Hu C, Kong C P. Enhanced fluoride adsorption using Al(Ⅲ) modified calcium hydroxyapatite[J]. J. Hazard. Mater., 2012, 233-234:  194-199. doi: 10.1016/j.jhazmat.2012.07.020

  46. [46]

      Zhao X D, Liu D H, Huang H L. The stability and defluoridation performance of MOFs in fluoride solutions[J]. Microporous Mesoporous Mat., 2014, 185:  72-78. doi: 10.1016/j.micromeso.2013.11.002

  47. [47]

      Wang H, Yuan X Z, Wu Y. In situ synthesis of In₂S₃@MIL-125(Ti) core-shell microparticle for the removal of tetracycline from wastewater by integrated adsorption and visible-light-driven photocatalysis[J]. Appl. Catal. B: Environ., 2016, 186:  19-29. doi: 10.1016/j.apcatb.2015.12.041

  48. [48]

      Kumar G, Masram D T. Sustainable synthesis of MOF-5@GO nanocomposites for efficient removal of rhodamine b from water[J]. ACS Omega, 2021, 6(14):  9587-9599. doi: 10.1021/acsomega.1c00143

  49. [49]

      Ahmadi S, Banach A, Mostafapour F K, Balarak D. Study survey of cupric oxide nanoparticles in removal efficiency of ciprofloxacin antibiotic from aqueous solution: Adsorption isotherm study[J]. Desalin. Water Treat., 2017, 89:  297-303.

  50. [50]

      韩晓, 王林玉, 耿付江, 席改卿. 苯并咪唑基金属有机骨架/氧化石墨烯复合材料对罗丹明B的吸附[J]. 无机化学学报, 2023,39,(6): 1159-1168. HAN X, WANG Y L, GENG F J, XI G Q. Adsorption of rhodamine B by benzimidazole-based metal-organic framework/graphene oxide composites[J]. Chinese J. Inorg. Chem., 2023, 39(6):  1159-1168.

  51. [51]

      Malesic-Eleftheriadou N, Evgenidou E, Lazaridou M, Bikiaris D N, Yang X, Kyzas G Z, Lambropoulou D A. Simultaneous removal of anti-inflammatory pharmaceutical compounds from an aqueous mixture with adsorption onto chitosan zwitterionic derivative[J]. Colloid Surf. A-Physicochem. Eng. Asp., 2021, 619:  126498. doi: 10.1016/j.colsurfa.2021.126498

  52. [52]

      Minisy I M, Ayad M M, Salahuddin N A. Chitosan/polyaniline hybrid for the removal of cationic and anionic dyes from aqueous solutions[J]. J. Appl. Polym., 2018, 136(6):  47056.

  53. [53]

      Karimi M A, Masrouri H, Mirbagheri M A, Andishgar S, Pourshamsi T. Synthesis of a new magnetic metal-organic framework nanocomposite and its application in methylene blue removal from aqueous solution[J]. J. Chin. Chem. Soc., 2018, 65(10):  1229-1238. doi: 10.1002/jccs.201800061

  54. [54]

      Hamedi A, Zarandi M B, Nateghi M R. Highly efficient removal of dye pollutants by MIL-101(Fe) metal-organic framework loaded magnetic particles mediated by poly L- Dopa[J]. J. Environ. Chem. Eng., 2019, 7:  102882. doi: 10.1016/j.jece.2019.102882

  55. [55]

      Si J J, Zhang S, Liu X M, Fang K J. Flower-shaped Ni/Co MOF with the highest adsorption capacity for reactive dyes[J]. Langmuir, 2022, 38:  6004-6012. doi: 10.1021/acs.langmuir.2c00184

  56. [56]

      Liu Y, Xu H. Equilibrium, thermodynamics and mechanisms of Ni²⁺ biosorption by aerobic granules[J]. Biochem. Eng. J., 2007, 35:  174-182. doi: 10.1016/j.bej.2007.01.020

  57. [57]

      Bibi R, Wei L F, Shen Q H, Tian W, Oderinde O, Li N X, Zhou J C. Effect of amino functionality on the uptake of cationic dye by titanium-based metal organic frameworks[J]. J. Chem. Eng. Data, 2017, 62(5):  1615-1622. doi: 10.1021/acs.jced.6b01012

  58. [58]

      Zeng S Y, Duan S X, Tang R F, Li L, Liu C H, Sun D Z. Magnetically separable Ni_0.6Fe_2.4O₄ nanoparticles as an effective adsorbent for dye removal: Synthesis and study on the kinetic and thermodynamic behaviors for dye adsorption[J]. Chem. Eng. J., 2014, 258:  218-228. doi: 10.1016/j.cej.2014.07.093

  59. [59]

      Jin J H, Yang Z H, Xiong W P. Cu and Co nanoparticles co-doped MIL- 101 as a novel adsorbent for efficient removal of tetracycline from aqueous solutions[J]. Sci. Total Environ., 2019, 650:  408-418. doi: 10.1016/j.scitotenv.2018.08.434

  60. [60]

      Chen J, Ouyang J B, Chen W Q, Zheng Z P, Yang Z, Liu Z R, Zhou L M. Fabrication and adsorption mechanism of chitosan/Zr- MOF (UiO- 66) composite foams for efficient removal of ketoprofen from aqueous solution[J]. Chem. Eng. J., 2022, 431:  134045. doi: 10.1016/j.cej.2021.134045

  61. [61]

      Huang J M, Huang D, Zeng F B, Ma L, Wang Z B. Photocatalytic MOF fibrous membranes for cyclic adsorption and degradation of dyes[J]. J. Mater. Sci., 2021, 56(4):  3127-3139. doi: 10.1007/s10853-020-05473-x

  62. [62]

      Sheth Y, Dharaskar S, Khalid M, Sonawane S. An environment friendly approach for heavy metal removal from industrial wastewater using chitosan based biosorbent: A review[J]. Sustain. Energy Technol. Assess., 2021, 43:  100951.

  63. [63]

      Mahreni M, Ramadhan R R, Pramadhana M F. Synthesis of metal organic framework (MOF) based Ca-Alginate for adsorption of malachite green dye[J]. Polym. Bull., 2022, 79:  11301-11315. doi: 10.1007/s00289-022-04086-5

• 

  Scheme 1  Schematic diagram of degradation of MB in porous Cu-MOF material

  下载: 全尺寸图片 幻灯片
  

  Figure 1  (a) View of local coordination environment of Cu(Ⅱ) ion in Cu-MOF; (b) 2D layer formed by linking Cu(Ⅱ) ions, ppda^2- and tib ligands together in Cu-MOF (chains and tape show different colors for clarity); (c) View of 3D extended supramolecular network in Cu-MOF (layers show different colors for clarity)

  All hydrogen atoms are omitted for clarity.

  下载: 全尺寸图片 幻灯片
  

  Figure 2  (a) Relationship between dye degradation efficiency and irradiation time for the dyes on Cu-MOF (+H₂O₂); (b) UV-Vis absorption spectra of the mixed solution of Cu-MOF, H₂O₂, and MB changed with time; (c) Plots of -ln(c/c₀) vs t for the photodegradation of the dyes on Cu-MOF in the presence of H₂O₂; (d) Reaction rate constants (k) of the photodegradation of the dyes on Cu-MOF in the presence of H₂O₂

  Reaction conditions: 20 mg Cu-MOF, 10 mg·L^-1 dyes solution, 1.0 mL H₂O₂ (30%), λ>420 nm.

  下载: 全尺寸图片 幻灯片
  

  Figure 3  (a) Changes in the degradation efficiency of the photodegradation of the dyes on Cu-MOF in the presence of H₂O₂ after 1-5 degradation cycles under the Xenon lamp (500 W); (b) Histogram of degradation efficiency of the photodegradation of the dyes on Cu-MOF in the presence of H₂O₂ after adding the scavengers; (c) E_FB obtained by Mott-Schottky measurements (1 000 and 1 200 Hz); (d) Photocatalytic degradation mechanism diagram

  下载: 全尺寸图片 幻灯片
  

  Figure 4  Variation of adsorption capacity of MB by Cu-MOF with time

  T=298 K, ρ_MB=20 mg·L^-1, ρ_NaCl=200 g·L^-1.

  下载: 全尺寸图片 幻灯片
  

  Figure 5  (a) Pseudo-first-order kinetic model, (b) pseudo-second-order kinetic model, and (c) intra-particle diffusion model of MB adsorption by Cu-MOF

  T=298 K, ρ_MB=20 mg·L^-1, ρ_NaCl=200 g·L^-1.

  下载: 全尺寸图片 幻灯片
  

  Figure 6  Adsorption properties of Cu-MOF at different MB initial concentrations

  T=298 K, ρ_MB=5-40 mg·L^-1, ρ_NaCl=200 g·L^-1

  下载: 全尺寸图片 幻灯片
  

  Figure 7  (a) Langmuir model, (b) Freundlich model, and (c) Temkin model for MB adsorption by Cu-MOF

  T=298 K, ρ_MB=5-40 mg·L^-1, ρ_NaCl=200 g·L^-1.

  下载: 全尺寸图片 幻灯片
  

  Figure 8  Adsorption performance of Cu-MOF in the presence of NaCl for MB at different temperatures

  ρ_MB=20 mg·L^-1, ρ_NaCl=200 g·L^-1.

  下载: 全尺寸图片 幻灯片
  

  Figure 9  Effect of ion concentration on MB adsorption by Cu-MOF

  ρ_NaCl=20-200 g·L^-1, T=298 K.

  下载: 全尺寸图片 幻灯片

  Table 1.  Kinetic parameters of MB adsorption by Cu-MOF

  Kinetic model	qe, exp / (mg·g-1)	qe, cal / (mg·g-1)	k1 / min-1	k2 / (g·mg-1·min-1)	kid / (mg·g-1·min-0.5)	C / (mg·g-1)	R2
  Pseudo-first-order kinetic	87.23	5.52	0.005 76				0.455
  Pseudo-second-order kinetic	87.23	87.18		0.0115			1.00
  Intra-particle diffusion model
  Step 1					0.780	79.22	0.910
  Step 2					0.181	83.94	0.966
  Step 3					0.037	85.87	0.884

  下载: 导出CSV

  Table 2.  Langmuir, Freundlich, and Temkin isotherms parameters of MB adsorption by Cu-MOF

  Model	Parameters	R2
  Langmuir	qm, exp=154.5 mg·g-1, qm, cal=153.0 mg·g-1, KL=0.007 01 L·mg-1, RL=0.877	0.996
  Freundlich	n=1.15, KF=6.20 L1/n·mg1-1/n·g-1	0.994
  Temkin	b=38.6 J·mol-1·g·mg-1, KT=0.222 L·mg-1	0.955

  下载: 导出CSV

  Table 3.  Thermodynamic parameters for adsorption MB adsorption by Cu-MOF

  T/K	ΔG / (kj·mol-1)	ΔH / (kj·mol-1)	ΔS / (J·mol-1·K-1)
  298	-12.296	-104.87	-310.65
  308	-9.1898	-104.87	-310.65
  318	-6.0833	-104.87	-310.65

  下载: 导出CSV
•