Two transition complexes based on 1H-benzimidazole-5,6-dicarboxylic acid: Synthesis,structure and photocatalytic degradation of dyes

Abstract

Metal-organic frameworks [Co(Hbidc)(H₂O)₂] (1) and [Mn(Hbidc)(H₂O)] (2), with multidentate 1H-benzimidazole-5,6-dicarboxylic acid (H₃bidc) ligand, have been synthesized under hydro/solvothermal conditions and structurally characterized by elemental analysis, IR spectrum, and single-crystal X-ray diffraction. Single-crystal X-ray diffraction analysis revealed that the center Co atom of complex 1 is six-coordinated with three-dimensional supramolecular structure and center Mn of complex 2 is five-coordinated with exhibiting a 2D layered network. The photodegradation of Crystal violet dye and Methylene blue dye were studied firstly by complexes 1 and 2 as photocatalysts. Research result indicates that the degradation rate for complex 1 can reach 89.85% , 90.6% and that for complex 2 can reach 88.28% , 79.48%. At the same time, corresponding to photocatalytic kinetics was performed.

Keywords

Hydrothermal reaction benzimidazole-5 6-dicarboxylate crystal structure photocatalytic degradation crystal violet

1 Introduction

Industrial development is inseparable from the use of dyes, which are widely used in· many fields such as textiles, papermaking, printing, food, pharmaceuticals, copying, and printing. Industrial wastewater produced by the dyes is currently one of the main pollutions of water body, the discharge of industrial dyes has changed the nature and composition of natural water, and caused water bodies to be subject to physiological, physical, chemical, and biological pollution, which not only harm to environmental and production, and more important is endanger human health, the dye wastewater treatment is imperative [1 –4]. Dye wastewater is one of the industrial wastewater that is difficult to deal with because of its complex composition, large variation of water quantity and water quality, high chromaticity, high salt content, and poor biodegradability. Now, there are many ways to deal with the dye wastewater, such as adsorption, photodegradation, and biological treatment [5 –9], especially the use of photodegradation technology has attracted much attention [10]. The technology of photodegradation of organic pollutants has gradually become the focus of research due to its advantages of low cost, non-toxicity, energy-saving, and high efficiency [11]. Therefore, photodegradation method is widely used in many field of application [12 –14]. In particular, nano semiconductor photocatalysts [15, 16] such as TiO₂ [17], ZnO [18], and Fe₃O₄ have been applied wdely [19]. Generally speaking, when the light energy absorbed by the photocatalytic material is greater than or equal to its band gap energy, it can be excited to generate electrons (e^–) and holes (h⁺), and interact with the medium (H₂O, O₂, etc.) in the environment produce active species with strong oxidizing or reducing properties. In the field of pollutant treatment, these active species can transform, decompose and remove pollutants in the environment, achieving the dual goals of energy saving and environmental protection. Therefore, the development of new photocatalytic materials with good photocatalytic performance, environmental friendliness and excellent stability has become a development trend in the field of photocatalysis. How making the separation efficiency of e^– and h⁺ pairs is the key and difficult point to improve the performance of photocatalytic materials.

So far, metal-organic framework hybrid materials are a kind of three-dimensional highly ordered porous crystalline compounds formed by the connection of metal ions or metal clusters with rigid organic molecules [20 –31]. Its structure has the characteristics of polymetallic sites, pore size, shape, and structure are flexible and adjustable, easy to function, large adsorption capacity, specific surface area, pore volume and tuning band gap [32 –34]. As far as we know, metal-organic frameworks have potential application in catalysis, gas storage and releasion, fluorescence sensing, drug delivery [35] and electrochemical biosensors [36] etc. However, organic ligands in the structure of MOF (Metal-Organic Framework) play an irreplaceable role in the design and synthesis of metal-organic framework hybrid materials [34]. Selecting different types of organic ligands during the construction of the coordination polymer will diversify the structure of the target product, which will lead to different applications [37 –42]. In particular, polycarboxylic acid metal-organic crystalline hybrid materials have become one of the hot topics in the research of functional crystalline materials. Herein the choice of 1H-benzimidazole-5,6-dicarboxylate as an auxiliary ligand is considered as follows: on the one hand, two nitrogen atoms of the imidazole ring and four oxygen atoms of the carboxylate can be used as coordination sites with different flexibility to manufacture complex coordination materials or molecular recognition applications; on the other hand, the rigid nature of the linker also provides rich hydrogen bonding and π–π stacking interactions in the assembly of the expanded network structural.

In the previous works, some studies of benzimidazole-5,6-dicarboxylate have been drawn extensive attention to assemble with the transition metal ions, lanthanide ions, and mixed metal ions to construct multidimensional complexes with photoluminescent and magnetic properties [43 –45]. However, as far as we know, few reports on photocatalytic degradation of Crystal violet and Methylene blue dyes has been reported until now. Here, based on the [Co(Hbidc)(H₂O)₂] (1) and [Mn(Hbidc)(H₂O)] (2) constructed by multidentate 1H-benzimidazole-5,6-dicarboxylic acid ligand as the catalysts, we studied firstly their photocatalytic degradation properties of Crytal violet (CV) dye and Methylene blue (MB) dye.

2 Experimental section

2.1 Materials and measurements

All chemicals were purchased commercially and used without further purification. Elemental analysis (C, H, and N) were performed on Perkin–Elmer 240C element analyzer. FT-IR spectra using KBr pellets were recorded applying a Bruker AXS TENSOR-27. X-ray powder diffraction (PXRD) patterns were performed on an Advance D8 equipped with Cu-Kα radiation in the range of 5°< 2θ< 55°, with a step size of 0.02° (2θ) and a count time of 2 s per step. Thermogravimetric analyses (TGA) were conducted on a TG/DTA instrument thermogravimetric analyzer in the atmospheric environment with a heating rate of 5°C min^–1. UV–vis spectra were obtained on a JASCO V-570.

2.2 Preparation of the complexes

2.2.1 [Co(Hbidc)(H₂O)₂] (1)

The pink crystals (complex 1) were prepared by the hydrothermal reaction. CoCl₂·6H₂O (23.7 mg, 0.10 mmol), H₃bidc (20.6 mg, 0.10 mmol), N, N-dimethylacetamide (DMA, 2 mL), and water (2 mL) was then added to a vessel and the pH of the solution was adjusted to 1 with HNO₃ (3.5 mol/L) and stirred for about 2 hours at room temperature to obtain a pink transparent solution. Then the solution was heated at 120°C for 2 days, and cooled it to room temperature. After filtrating and washing with distilled water, the pink block crystals were obtained. Yield: 62 % (based on CoCl₂·6H₂O). Elemental analysis (%) Anal. Calc. for C₉H₈N₂O₆Co: C, 36.14; H, 2.70; N, 9.37; Found: C, 36.18; H, 2.69; N, 9.39. IR data (KBr, cm^–¹): 3438, 2931, 1735, 1696, 1573, 1415, 1383, 1363, 1295, 1247, 970, 760.

2.2.2 [Mn(Hbidc)(H₂O)] (2)

Complex 2 was the same synthetic procedure as described for complex 1 except that CoCl₂·6H₂O was replaced by MnCl₂·4H₂O. Colorless rhombic crystals of 2 were obtained and picked out, washed with distilled water, and dried in air. Yield: 68 % (based on MnCl₂·4H₂O). Elemental analysis (%) Anal. Calc. C₉H₆N₂O₅Mn: C, 39.00 H, 2.18 N, 10.11; Found: C, 39.03; H, 2.16; N, 10.12. IR data (KBr, cm^–¹): 3425, 3126, 1611, 1533, 1421, 1340, 1165, 970, 797, 624.

2.3 X-ray diffraction analysis

Suitable single crystals of the four complexes were mounted on glass fbers for X-ray measurement. Refection data were collected at room temperature on a Bruker AXS SMART APEX II CCD difractometer with graphite-monochromatized Mo-Kα radiation (λ= 0.71073Å) [46]. All the measured independent refections (I > 2σ (I)) were used in the structural analyses, and semi-empirical absorption corrections were applied using the SADABS program [47]. The structures were determined by direct methods using the SHELX-2018 and OLEX 2 platform [48 –51]. All non-hydrogen atoms were refned anisotropically. The hydrogen atoms of the organic frameworks were geometrically fxed at calculated positions and refned using a riding model. The crystallographic data and the structure refnement details for complexes 1–2 are given in Table S1. Selected bond lengths are listed in Table S2. Structures were checked for additional symmetry using PLATON [52].

2.4 Experiment of photocatalytic degradation of dyes

Weigh 10 mg the powder of complex 1 and 2, and it was added to 10 mL of 10 mg/L Crystal Violet (CV) and Methylene blue (MB) dye, respectively. It was stirred for an hour at room temperature in the dark, then use 125 W mercury lamp as visible light source, sampled at regular intervals, after centrifugation with a centrifuge, the supernatant was taken, scanned its absorption spectra with single-beam ultraviolet/visible spectrophotometer (UV-1000), the change of the absorbance value at the maximum absorption wavelength with time is monitored, and the change of the dye concentration is calculated through the concentration-absorbance standard curve. The photocatalytic degradation constant for dye was evaluated based on the adsorption kinetic model.

3 Results and discussion

3.1 Synthesis

Although complexes 1 and 2 have been reported, the methods of the complexes we synthesized is different from tthat of he literatures [53, 54]. The specific differences are shown in Table 1. The most obvious difference is that the reaction time is greatly reduced and the yield is greatly improved and can be synthesized on a large scale.

Table 1
Comparison of the synthetic methods

Complex Solid reactant Solvent Time Temperature Ref.

[Co(Hbidc)(H₂O)₂]_n CoSO₄·H₂O H₂O 5 days 120°C [53]

[Mn(Hbidc)(H₂O)] MnCl₂·4H₂O DMA:H₂O(1 : 1) 5 days 85°C [54]

[Co(Hbidc)(H₂O)₂] CoCl₂·6H₂O DMA/H₂O(1 : 1) 2 days 120°C This work

[Mn(Hbidc)(H₂O)] MnCl₂·4H₂O DMA:H₂O(1 : 1) 2 days 120°C This work

Complex	Solid reactant	Solvent	Time	Temperature	Ref.
[Co(Hbidc)(H₂O)₂]_n	CoSO₄·H₂O	H₂O	5 days	120°C	[53]
[Mn(Hbidc)(H₂O)]	MnCl₂·4H₂O	DMA:H₂O(1 : 1)	5 days	85°C	[54]
[Co(Hbidc)(H₂O)₂]	CoCl₂·6H₂O	DMA/H₂O(1 : 1)	2 days	120°C	This work
[Mn(Hbidc)(H₂O)]	MnCl₂·4H₂O	DMA:H₂O(1 : 1)	2 days	120°C	This work

3.2 Structural description

(1) Single-Crystal X-ray diffraction analysis indicates that complex 1 crystallizes in the Monoclinic space with group P2₁/c. Co (II) atom in complex 1 is a six-coordinated distorted octahedral configuration (Fig. 1a). The linking pattern of ligand Hbidc^2– is μ₃- η _N ¹ η _O ¹ η _O ¹ , where carboxylate O2 and O4^# 1 from the ligand take the coordination mode of monodentate chelating to bridge two metal atoms (Fig. 1b). The bond length of the Co–O bond is in the range of 2.0299(17)–2.2349(16) Å, and the bond length of the Co-N bond is 2.123(2) Å. This is similar to the bond length range of Co–O bonds (2.098(2)–2.211(2) Å) and Co–N bonds (2.186(2) Å) reported in the literature [48]. Adjacent metal atoms are connected by the carboxyl and nitrogen atoms of the ligand to form a double metal Co-edge polyhedron building block (Co(μ₂-O)₂(COO)₂N₂O₂), which furthermore was linked one-dimensional chain structure by the carbon atom of the ligand in Fig. 2c and Fig. 2d. Then the 1D chains are connected by a large number of hydrogen bonds to form a 3D supramolecular framework (Figure S1) [53]. The hydrogen bonds distances (Å) and angles (°) of complex 1 are listed in Table S2.

Fig. 1

Complex 1: Diagrams for the Co(II) center with the labels of the crystallographic independent atoms (a) and (b) the coordination environment around the Hbidc^2 − linker (Co, pink; C, gray; N, blue; O, red. Hydrogen atom is omitted for clarity; #1 –x + 1, –y + 2, –z + 2).

Fig. 2

Complex 2: Diagrams for the Mn(II) center with the labels of the crystallographic independent atoms (a) and (b) the coordination environment around the Hbidc^2 − linker; (c) The π - π interaction between the two benzimidazole rings (Mn, green; C, gray; N, blue; O, red. Hydrogen is omitted for clarity).

[Mn(Hbidc)(H₂O)] (2) The crystal structure of complex 2 is also identical to the previously reported [53, 54], the crystal structure has not been described in detail in previous work. Its molecular structure and the ligand linking fashion are shown in Fig. 2. As a structural comparison and a subsequent study of the photocatalytic activity, we only conducted mainly a comparative study of structure and function. The coordination mode of the ligand H₃bidc is μ₄- η _O ¹ η _O ¹ η _O ¹ η _N ¹ , all adopting the mode of monodentate coordination (Fig. 2b). The [MnO₂] unit is connected to form a one-dimensional chain through the nitrogen atom and the carboxyl oxygen atom in the ligand in Fig. 2c and Fig. 2d. The bond length range of the Mn–O bond is 2.0716 (18)-2.1856 (19) Å, and the bond length of the Mn–N bond is 2.1678 (19) Å. In addition, it can be observed from the two-dimensional view that there is a π–π interaction at a distance of 3.3 Å between the two benzimidazole rings (Fig. 2c) [54].

3.3 Structure characterization

FT-IR spectra: Infrared spectra of the complexes 1, 2, and H₃bidc (1H-benzimidazole-5, 6-dicarboxylic acid) are shown in Figure S2a-S2c, and the main data are listed in Table S2. It was found that the absorption peaks at 3000 to 3500 cm^–1 could be attributed to the N–H, O–H stretching vibration peaks. The peaks at 1661 cm^–1 and 1381 cm^–1 of the ligand, and the corresponding peaks in complex 1 appear at 1581 cm^–1and 1362 cm^–1, and that of the complex 2 appears at 1532 cm^–1and 1419 cm^–1 are due to asymmetrical and symmetric stretching vibrations of the carboxyl group. Compared with the peak value of the ligand above, the redshift of the corresponding peak position in the two complexes indicates carboxyl oxygen atoms are coordinated with metal ions. The coordination of nitrogen atoms with metal ions in the ligand reduces the density of the surrounding electron cloud of C = N, leads to the C = N peak position of the ligand are red-shifted from 1490 to 1477 cm^–1 of complex 1 and 1479 cm^–1 of complex 2.

PXRD: The experimental and simulated PXRD spectra of complexes 1 and 2 are shown in Figure S3a-S3b. It can be seen from the comparison that the peak positions of the experimental data of the complexes are similar to the simulated data, indicating that the batches of complexes 1 and 2 are pure phases and contain no impurities.

UV-Vis spectra: All UV–Vis absorption spectra of ligand and complexes 1–2 were recorded in the form of solid samples (Fig. 4a–4c). Two high-energy absorption bands of the ligand appeared at 210 nm and 287 nm, which were assigned to the π–π^* and n–π^* transition of the ligand. Similar absorption bands in complexes 1–2 were observed at 259 nm and 300 nm for 1, 217 nm, and 260 nm for 2. The peaks observed at 338 nm for 1, 300 nm for 2 were attributed to the charge transition from the ligand to Co (II) Mn (II) atoms (LMCT). The bands appearing at 468 nm, 531 nm, and 656 nm were attributed to the d–d^* transition of the Co^2 + center for complex 1. The detailed analyses of the UV–Vis absorption bands of complexes 1–2 and H₃bidic are given in Supporting Information.

Fig. 4

Degradation curves of CV dye with different dosage of complex 1: (a) 5 mg; (b) 10 mg; (c) 15 mg; (d) 20 mg.

Thermogravimetric analysis: Under N₂ protection, the weight loss of complexes 1–2 in the range of 30–800°C is shown in Figures S5a and S5b. For complex 1, the first weightlessness stage occurred before 290°C, and the actual weightlessness was 6.5% (theoretical weightlessness: 6.0%), which corresponds to the loss of a coordinated water molecule. The second phase of weightlessness occurred at 290–800°C, and the actual weightlessness was 43% (theoretical weightlessness: 44.50%), corresponding to the skeleton collapse of the complex 1. For complex 2, the first weightlessness stage occurred at 30–114°C, the weightlessness was 6.76% (theoretical is 6.5%), corresponding to the loss of a water molecule, the second weightlessness stage was 114–800°C, and the weightlessness was 53.24% (theoretical is 52.15%), corresponding to the skeleton collapse of the complex 2.

3.4 Photocatalytic properties of the complexes

3.4.1 Photocatalytic degradation

The bandgap energy of the complexes is calculated according to the energy dependence relationship of E_g = h ν= h c/λ_g = 1240/λ_g, where h and E_g are the Planck’s constant (J·s) and the energy gap of the semiconductor, respectively. ν, c and λ_g denote the frequency of light (Hz), the velocity of light (m s^–1), and wavelength value (nm). The bandgap energy of 1 is estimated to be ∼1.67 eV (Fig. 3a) and 2 is estimated to be ∼2.35 eV (Fig. 3b). By comparison, it can be seen that the energy required for the electronic transition of complex 1 is relatively small, so the transfer of electrons will be relatively easy, which means that the photo-generated charge is easily separated from the carrier, which also plays a main role in the photocatalytic activity. Therefore, complex 1 has better photocatalytic activity. This provides some references for subsequent experiments.

Fig. 3

The solid-state UV–vis spectra: (a) of complex 1; (b) of complex 2.

In order to study the photocatalytic activity of complex 1, we explored the effect of different doses of catalysts (5 mg, 10 mg, 15 mg and 20 mg) on the photocatalytic activity, and understand the influence of the amount of the catalysts on the entire reaction system, so as to seek the optimal amount (Figs. 4, 5). Different doses of catalysts were added to MB and CV dyes in 10 mL of 10 mg/L to observe the degradation effect. When complex 1 degrades crystal violet dye, it can be seen from Figs. 4, 5 that at the wavelength of 575 nm, the absorbance value gradually decreases with the increase of the light irradiation time, which indicates that the crystal violet dye molecules are successfully degraded. We considered that from the perspective of economy and high efficiency, 10 mg is selected as the amount of catalyst for the following experiment, and the degradation rate is 89.85% (Fig. 6a and S6a). Because when the dosage of complex 1 is 20 mg, although the degradation rate is 90.7% , the catalytic effect is not significantly improved compared with the amount of 10 mg. Based on the same principle, when complex 1 degrades MB dye, we choose 15 mg as the best dosage of catalyst, the degradation rate is 88.9% (Fig. 6b and S6b), because of 15 mg of complex 1 takes a short time to degrade MB dye, and the degradation rate is the highest in the same time.

Fig. 5

Degradation curves of MB dye with different dosage of complex 1: (a) 5 mg; (b) 10 mg; (c) 15 mg; (d) 20 mg.

Fig. 6

Removal efficiency by the different dosage of complex 1: (a) for CV; (b) for MB.

At the same time, when the complex 2 degrades crystal violet dye with the same concentration (Figs. 7, 8), it can be seen from the degradation effect that the degradation effect is the best when the dosage of the complex 2 is 15 mg, and the degradation rate can reach 89.99% in 120 min (Fig. 9a, S7a). Therefore, we choose 15 mg as the amount of catalyst for the following photocatalytic experiment. When the same concentration of methylene blue dye was degraded, 5 mg was considered as the optimal amount of catalyst and the degradation rate was 79.48% (Fig. 9b, S7b).

Fig. 7

Degradation curves of CV dye with different dosage of complex 2: (a) 5 mg; (b) 10 mg;(c) 15 mg; (d) 20 mg.

Fig. 8

Degradation curves of MB dye with different dosage of complex 2:(a) 5 mg; (b) 10 mg; (c) 15 mg; (d) 20 mg.

Fig. 9

Removal efficiency by the different dosage of complex 2: (a) for CV; (b) for MB.

In order to accelerate the photocatalytic capacity, it was found that adding 100μL of H₂O₂ could facilitate photocatalytic degradation. To furthermore study the role of the complexes and H₂O₂ in the photocatalytic degradation of dyes, complexes 1, 2 and H₂O₂ were respectively used for photocatalytic degradation of crystal violet and methylene blue dyes, shown in Fig. 10. From the degradation efficiency of crystal violet dye and methylene blue dye, we found that the degradation effect of complex 1 and 2 assisted by the addition of a small amount of H₂O₂ is better than that of the single complex 1 or 2 (Fig. 11, 12).

Fig. 10

Control experiments for the Photocatalytic degradation dyes under different conditions: (a) crystal violet dye by H₂O₂; (b) crystal violet dye with complex 2; (c) crystal violet dye with complex 1; (d) methylene blue dye with complex 1; (e) methylene blue dye by H₂O₂;(f) methylene blue dye with complex 2.

Fig. 11

Comparison of degradation efficiency: (a) complex 1, CV and related materials; (b) column chart; (c) complex 1, MB and related materials; (d) column chart.

Fig. 12

Comparison of degradation efficiency: (b) Complex 2, CV and related materials; (b) column chart; (c) complex 2, MB and related materials; (d) column chart.

3.4.2 Study on photocatalytic degradation kinetics

Considering that the photocatalytic degradation efficiency is a very important evaluation parameter for an effective adsorbent, the degradation kinetics of complex 1 and complex 2 degradation CV and MB were studied by fitting the adsorption data by Pseudo first-order and Pseudo second-order kinetic models. The equations of Quasi-first order dynamics model and Quasi-second-order kinetic model are expressed as follows [55]: $\begin{matrix} \log (Q_{t} - Q_{e}) = \log Q_{e} - k_{1} t / 2.303 (3 - 1) \\ t / Q_{t} = 1 / {Q_{e}}^{2} k_{2} + t / Q_{e} (3 - 2) \end{matrix}$

Q_e (mg g^–1) is the equilibrium degradation amount, Q_t (mg g^–1) is the degradation amount at a certain time, k₁ (min^–1) is the quasi-first order rate constant, and t (min) is the reaction time. The linear graph of Figures S9a-9b is obtained by fitting data above, and the relevant parameters are listed in Table S3. It can be seen from the figure that the photocatalytic degradation processes are in good agreement with the quasi-first-order kinetic model, and most of the R² values obtained from the linear relationship are above 0.99, while most of the R² values in the quasi-second-order are very low. In addition, the maximum amount of degradation calculated in the quasi-first order model differs little from the actual amount of degradation, while the maximum amount of degradation obtained in the quasi-second order model is much different. By comparing the quasi-first-order rate constant k₁ of two dyes at the same concentration, it was found that when the dye concentration was 10 mg/L, the k₁ of CV degradation of complex 1 and 2 were -1.05×10^–2 and the k₁ of CV degradation of complex 2 was –1.15×10^–2, and the k₁ of MB degradation was 4.6×10^–3, respectively.

3.4.3 Catalytic activity of the photocatalysts of 1 and 2

We verified the photocatalytic mechanism by the following experiments:

photocatalytic mechanism capture experiment: we used ethanol to capture holes, p-benzoquinone to capture O₂ ^– , silver nitrate to capture electrons, and isopropanol to capture •OH. The experimental method is the same as before, except that 2 mL active species scavenger are added to the system under light illumination, the experimental results are shown in Figs. 13, 14. It is found that the degradation rate of the system after adding capture agent becomes lower, and the degradation rate of mixed system containing capture agent and complex 1 decreased from 89.85% to 32.57% , 35.96% , 59.10% and 73.88% This indicates that the main active substances of the reaction are the hole and hydroxyl radicals. Superoxide anions and electrons also play a supporting role.

Activity of catalyst: 1 is a 3D supramolecular structure, 2 is a planar 2D structure, and the high-dimensional structure of CPs not only increases the exposed active sites, but also facilitates the transfer and utilization of charges. The factor would be more conducive to 1 to degrade of CV and MB solution. Therefore, the photocatalytic degradation activity of 1 was stronger than that of 2. The principle of the photocatalytic reaction is that when the catalyst is irradiated with light, the light energy is absorbed, an electron transition occurs, an electron-hole pair is formed, and the pollutants adsorbed on the surface are directly reduced; or the hydroxide ions (OH^–) which are oxidized generates hydroxyl radicals (·OH) to oxidative pollutants. According to the UV spectra of complexes 1 and 2, the band gaps of 1–2 were 1.67 eV and 2.35 eV respectively. So, E_g value 2 > 1. In general, the larger the band gap value (E_g), the lower the probability of the electron from the valence band (E_VB) to the conduction band (E_CB). Under 125 W mercury lamp, the electron(e^–) can excited from HOMO (highest occupied molecular orbital) to the LUMO (lowest occupied molecular orbital) energy level by photons from UV light, which can produce reasonable quantity of positive hole (h⁺). To keep the stable state of the system, oxygen molecule captured the electrons and reaction with h⁺ from water to generate hydroxyl radicals (·OOH), then the ·OOH radicals can degrade the CV molecule into organic small molecules, CO₂ and H₂O.

Fig. 13

The capture of photocatalytic degradation active species: (a) PBQ captures O₂^–; (b) AgNO₃ captures electronics; (c) IPA captures ·OH; (d) EtOH captures holes.

Fig. 14

Photocatalytic degradation rate of captured active species.

When light hits complexes 1 and 2, the energy of the photons will be equal to or higher than the band gap energy of complexes 1 and 2, so that the catalyst can be excited to generate electron and hole pairs. The generated electrons and holes respectively undergo redox reactions with organic dyes, thereby degrading the organic dyes. Based on the above analysis, the photocatalytic reaction mechanism of the complexes 1 and 2 can be proposed by the following series of reaction formulas: $\begin{matrix} [catalyst] + hv \to e^{-} + h^{+} (3 - 3) \\ H_{2} O + h^{+} \to \cdot OH + H^{+} (3 - 4) \\ h^{+} + {OH}^{-} \to \cdot OH (3 - 5) \\ e^{-} + O_{2} \to \cdot {OO}^{-} (3 - 6) \\ \cdot {OO}^{-} + h^{+} \to HOO \cdot (3 - 7) \\ 2 HOO \cdot \to O_{2} + H_{2} O_{2} (3 - 8) \\ H 2 O_{2} + \cdot {OO}^{-} \to \cdot OH + {OH}^{-} + O_{2} (3 - 9) \\ Dye + (\cdot OH, HOO \cdot, \cdot {OO}^{-}) \to Products (3 - 10) \end{matrix}$

4 Conclusion

In summary, using 1H-benzimidazole-5,6-dicarboxylic acid as the ligand to react with two different transition metals under hydrothermal conditions, two crystalline metal-organic frameworks complexes materials were successfully synthesized. And their structures were studied carefully. The photodegradation properties of crystal violet dyes and methylene blue dye of the two complexes were studied at the same time, and the results showed that these two complexes had good photodegradation effects towards CV and MB dyes. Its degradation kinetics curve fits the pseudo-first-order curve. In addition, the photocatalytic mechanism of complexes 1 and 2 were also explored. The experiment results indicate that the hole and hydroxyl radicals play a main role in this photodrgradation system.

Footnotes

Acknowledgments

This work was supported by the grants of the National Natural Science Foundation of China (No. 21571091); Liaoning Normal University High-end Scientific Research Achievement Funding Program (No.21GDL003), and Open Project of State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University in China (No. 2020-10).

Single crystal structure data for the complexes 1, 2 was shown in Table S1. Selected bond lengths (Å) and angles (°) for 1–2 was shown in Table S2. The IR spectra of the complexes 1–2 and 1H-benzimidazole-5,6-dicarboxylic acid are shown in Figure S2a-2c. The IR spectra contrast before and after degradation of dyes in Figure S2d. Powder X-ray diffraction patterns of complexes 1–2 are shown in Figure S3a-3b. The solid-state UV-Vis spectra of ligand and complexes 1–2 are shown in Figure S4a-5c. TG curves for complexes 1–2 are shown in Figure S5a-5b. The degradation performance bar graph of CV and MB dyes for complex 1 and 2 were given in Figure S6, S7. Standard curves of crystal violet dye and methylene blue dye are shown in Figure S8. Quasi-first order curves and quasi-second-order curves of complexes are shown in Figure S9a-S9b. The correlation data of quasi-first-order kinetic curves and quasi-second-order of complexes 1 and 2 towards CV and MB was shown in .

CIF files have also been deposited at the Cambridge Crystallographic Database Centre and may be obtained from by citing CCDC for the complex 1: 2017286; 2: 2017287.

The supplementary material is available in the electronic version of this article: .

References

Hong

, Li

, Chen

, Liu

, Li.

, Zheng

and Ding

, Powder Technol 189 (2009), 426–432.

Shanmugam

, Muppudathi

A.L.

, Jayavel

and Jeyaperumal

K.S.

, Arab J Chem 13 (2020), 2439–2455.

Katsumata

, Sakai

, Suzuki

and Kaneco

, Ind Eng Chem Res 53 (2014), 8018–8025.

Shen

, Fan

, Zhou

, Gao

, Yue

and Kang

, J Hazard Mater 172 (2009), 99–107.

Alsbaiee

, Smith

B.J.

, Xiao

, Ling

, Helbling

D.E.

and Dichtel

W.R.

, Nature 529 (2015), 190–194.

Meunier

, Science 296 (2002), 270–271.

Santhosh

, Velmurugan

, Jacob

and Jeong

S.K.

, Chem Eng J 306 (2016), 1116–1137.

Chen

, Feng

, Li

, Wang

, Chen

and Zhang

, Bioresour Technol 250 (2018), 650–657.

Yang

, Li

, Huang

and Yang

, Water Res 95 (2016), 59–89.

10.

and Ma

H.L.

, J Clean Prod 313 (2021), 127758.

11.

Zhang

, Zhao

S.R.

, Huang

S.J.

, Hu

, Wang

M.H.

, Zhang

Z.H.

, He

L.H.

and Du

, Chem Eng J 420 (2021), 130516.

12.

, Xu

P.L.

, Liu

, He

J.Y.

, Zu

H.L.

, Song

J.J.

, Zhang

, Tian

F.H.

, Yun

M.J.

and Wang

F.Y.

, Nanotechnology 32 (2021), 375202.

13.

Liu

, Li

X.X.

, Liu

X.Y.

, Ma

Z.H.

, Yin

Z.Y.

, Yang

W.W.

and Yu

Y.S.

, Rare Met 40 (2021), 808–816.

14.

Cheng

J.Z.

, Tan

Z.R.

, Xing

Y.Q.

, Shen

Z.Q.

, Zhang

Y.J.

, Liu

L.L.

, Yang

, Chen

and Liu

S.Y.

, J Mater Chem A 9 (2021), 5787.

15.

Sun

, Li

, Zhang

C.W.

, Liang

T.Q.

and Zhao

Z.H.

, Sensors 19 (2019), 1851.

16.

Zhang

Z.Q.

, Yang

, Zhang

H.W.

, Zhang

T.G.

, Wang

, Xu

Y.T.

and Ma

, Mater Charact 171 (2021), 110732.

17.

, Zhao

, Qiao

Y.L.

, Feng

, Li

W.L.

and Fei

W.D.

, J Mater Sci Technol 84 (2021), 10–15.

18.

Wang

, Wang

S.Z.

, Kang

Y.R.

, Sun

Z.S.

, Wang

X.D.

, Meng

, Hong

M.H.

and Xie

W.F.

, J. Alloys Compd 854 (2021), 157152.

19.

Hoffmann

M.R.

, Martin

S.T.

, Choi

and Bahnemann

D.W.

, Chemical Rev 95 (1995), 69–96.

20.

Zhao

, Yuan

and Zhou

H.C.

, Energy Environ 1 (2008), 222–236.

21.

J.R.

, Kuppler

R.J.

and Zhou

H.C.

, Chem Soc Rev 38 (2009), 1477–1504.

22.

, Song

, Li

, Chi.

Y.X

, Bai

F.Y.

and Xing

Y.H.

, ACS Appl Mater 8 (2016), 28718–28726.

23.

Kreno

L.E.

, Leong

, Farha

O.K.

, Allendorf

, Van Duyne

R.P.

and Hupp

J.T.

, Chem Rev 112 (2012), 1105–1125.

24.

Cui

Y.J.

, Yue

Y.F.

, Qian

G.D.

and Chen

B.L.

, Chem Rev 112 (2012), 1126–1162.

25.

Y.C.

, Zhang

H.M.

, Liu

Y.Y.

, Zhai

Q.Y.

, Shen

Q.T.

, Song

S.Y.

and Ma

J.F.

, Cryst Growth Des 14 (2014), 3174–3178.

26.

Doonan

C.J.

, Tranchemontagne

D.J.

, Glover

T.G.

, Hunt

J.R.

and Yaghi

O.M.

, Nat Chem 2 (2010), 235–238.

27.

Deng

H.X.

, Doonan

C.J.

, Furukawa

, Ferreira

R.B.

, Towne

, Knobler

C.B.

, Wang

and Yaghi

O.M.

, Science 327 (2010), 846–850.

28.

Dinca

and Long

J.R.

, Angew Chem Int Ed 47 (2008), 6766–6779.

29.

Rowsell

J.L.C.

and Yaghi

O.M.

, Angew Chem Int Ed 44 (2005), 4670–4679.

30.

Wang

, Yang

and Sun

Z.M.

, Chem Asian J 8 (2013), 982–989.

31.

F.Y.

, Li

J.P.

, Wu

and Sun

Z.M

, Chem Eur J 21 (2015), 11475–11482.

32.

J.J.

, Yuan

Y.P.

, Sun

J.X.

, Peng

, Jiang

F.M.

, Qiu

L.G.

, Xie

A.J.

, Shen

Y.H.

and Zhu

J.F.

, J Hazard Mater 190 (2011), 945–951.

33.

Javier

, Larry

R.F.

, Isabel

, Fernando

, Tatiana

and Milagros

, J Am Chem Soc 130 (2008), 2932–2933.

34.

Guo

X.Y.

, Zhang

C.X.

, Tian

Q.H.

and Yu

D.W.

, Mater Today Commun 26 (2021), 102007.

35.

Zhu

, Liang

G.L.

, Guo

C.P.

, Xu

M.R.

, Wang

M.H.

, Wang

C.B.

, Zhang

Z.H.

and Du

, Food Chem 366 (2022), 130575.

36.

Zhang

, Rong

F.L.

, Guo

C.P.

, Duan

F.H.

, He

L.H.

, Wang

M.H.

, Zhang

Z.H.

, Kang

M.M.

and Du

, Coord Chem Rev 439 (2021), 213948.

37.

Liu

Z.X.

, Synthesis Synth React Inorg M 46 (2016), 809–813.

38.

Chen

, Shan

, Yang

C.Y.

, Yang

J.F.

, Li

J.P.

and Mu

, J Mater Chem A 6 (2018), 9922–9929.

39.

S.H.

, Ren

G.J.

, Li

, Chai

, Wang

C.G.

and Qu

F.Y.

, New J Chem 41 (2017), 1509–1517.

40.

Lin

, Chapman

M.E.

, Wang

Z.Y.

and Yee

G.T.

, Inorg Chem 9 (2003), 4169–4173.

41.

Wang

W.G.

, Ma

C.B.

, Zhang

X.F.

, Chen

C.N.

, Liu

Q.T.

, Chen

, Liao

D.Z.

and Li

L.C.

, Bull Chem Soc Jpn 75 (2002), 2609–2614.

42.

Rana

, Bera

, Chowdhuri

S.D.

, Hazari

, Butcher

R.J.

and Dalai

, J Inorg Organomet Polym 21 (2011), 747–753.

43.

Xie

, Xing

Y.H.

, Wang

, Zhao

H.Y.

, Zeng

X.Q.

, Ge

M.F.

and Niu

S.Y.

, Inorganica Chimica Acta 363 (2010), 918–924.

44.

Wang

, Sun

J.Y.

, Zhang

D.J.

, Song

T.Y.

, Song

, Zhang

L.Y.

, Chen

Y.L.

, Fan

and Zhang

, Inorganica Chimica Acta 384 (2012), 105–110.

45.

Fan

R.Q.

, Wang

L.Y.

, Wang

, Chen

, Sun

C.F.

, Yang

Y.L.

and Su

, J Solid State Chem 196 (2012), 332–340.

46.

SMART and SAINT (software packages), Inc.: Madison, WI, 1996.

47.

Sheldrick

G.M.

, SADABS, Program for Bruker Area Detector Absorption Correction, University of Gottingen: Gottingen, Germany, 1997.

48.

Sheldrick

G.M.

, SHELXL-97, Programs for X-ray Crystal Structure Refinement, University of Gottingen: Gottingen, Germany, 1997.

49.

Dolomanov

O.V.

, Bourhis

L.J.

, Gildea

R.J.

, Howard

J.A.K.

and Puschmann

, J Appl Cryst 42 (2009), 339–341.

50.

Bourhis

L.J.

, Dolomanov

O.V.

, Gildea

R.J.

, Howard

J.A.K.

and Puschmann

, Acta Cryst A71 (2015), 59–75.

51.

Sheldrick

G.M.

, Acta Cryst C71 (2015), 3–8.

52.

Spek

A.L.

, J Appl Crystallogr 36 (2003), 7–13.

53.

X.D.

, Wu

, Xiao

H.P.

, Zhou

X.H.

and You

X.Z.

, Inorg Chem Comm 13 (2010), 522–525.

54.

Zhang

E.P.

, Zhang

L.L.

, Tan

, Ji

Z.G.

and Li

Q.W.

, Chin J Chem 34 (2016), 233–238.

55.

Cui

L.M.

, Wang

Y.G.

, Hu

L.H.

, Gao

, Du

and Wei

, RSC Adv 5 (2015), 9759–9770.

Two transition complexes based on 1H-benzimidazole-5,6-dicarboxylic acid: Synthesis,structure and photocatalytic degradation of dyes

Abstract

Keywords

1 Introduction

2 Experimental section

2.1 Materials and measurements

2.2 Preparation of the complexes

2.2.1 [Co(Hbidc)(H2O)2] (1)

2.2.2 [Mn(Hbidc)(H2O)] (2)

2.3 X-ray diffraction analysis

2.4 Experiment of photocatalytic degradation of dyes

3 Results and discussion

3.1 Synthesis

3.4.1 Photocatalytic degradation

3.4.3 Catalytic activity of the photocatalysts of 1 and 2

Footnotes

Acknowledgments

References

2.2.1 [Co(Hbidc)(H₂O)₂] (1)

2.2.2 [Mn(Hbidc)(H₂O)] (2)