Highly efficient removal of As(V) using metal–organic framework BUC-17
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Arsenic contamination is a great threat worldwide due to its toxicity and hardly degradable. The development of highly efficient adsorbents is an essential challenge in the water treatment field. A 2D metal–organic framework [Co3(tib)2(H2O)12](SO4)3 (BUC-17) has been synthesized by hydrothermal method, and was utilized as an efficient adsorbent to remove As(V) from contaminated water. The results showed that BUC-17 have higher adsorption capacity toward As(V) than most counterpart adsorbents, its maximum uptake capacity reached 129.2 mg g−1 at 298 K. The adsorption kinetics and isotherm behaviors were well fitted with pseudo-second-order and Langmuir model, respectively. The thermodynamic parameters such as free energy change ΔG°, enthalpy change ΔH° and entropy change ΔS° were both negative during the sorption process, suggesting that the adsorption process of BUC-17 towards As(V) was spontaneous and exothermal. The influence of pH and foreign ions on the adsorptive removal of As(V) using BUC-17 were investigated. The results showed that pH values have significant influence while co-existed anions (unless phosphate) exert slight effect on adsorption capacity. Finally, a corresponding adsorption mechanism was proposed and confirmed by scanning electron microscopy, Fourier Transform infrared spectra (FTIR) and X-ray photoelectron spectroscopy analysis.
KeywordsBUC-17 Arsenic Adsorption Mechanism Performance
Arsenic is extensively distributed in the biosphere and has been linked with toxic and carcinogenic effects . The chronical exposure to arsenic leads to nausea, cancer, muscular weakness, neurological disorder, appetite weakness and impairments of the immune system [2, 3, 4, 5]. Most arsenic compounds in the environment are discharged from coal combustion, production of industrial raw materials, arsenic pesticides, or volcano eruption [6, 7]. As a result of their strong toxicity and widely distribution, over 140 million people all over the world, especially in India, Bangladesh, Argentina, Vietnam and China, are facing the tremendous threat of arsenic [8, 9, 10]. The World Health Organization has regarded arsenic as a human carcinogen in drinking water and set a provisional standard of no more than 10 µg L−1 . In natural waterbody, the arsenic exists in both inorganic arsenic compounds like arsenate, arsenite, and organic arsenic compounds like ASA (Arsanilic, C6H8AsNO3) and ROX (Roxarsone, C6H6AsNO6), in which As(V) is the primary arsenic species . The existence of inorganic arsenic in natural water depends on the redox conditions. For example, As(V) will be converted into As(III) in the presence of reductive substances . As well, it was well-recognized that the pre-oxidation of As(III) into As(V) is a necessary step for the efficiency of arsenic removal [14, 15]. Inorganic arsenic can be methylated in human body, which leads to the transformation from As(V) to As(III), resulting in a great potential threat to human health and environment [1, 16, 17]. Therefore, it is important to remove As(V) from polluted water.
Up to now, there are various techniques for arsenic removal like chemical precipitation, ion exchange, membrane filtration, biological processes and adsorption [3, 18, 19, 20], in which the adsorption is widely used in wastewater decontamination due to the advantages such as low cost, high speed, high efficiency and easy operation [21, 22, 23]. Traditional adsorbents including activated carbon , hydrotalcite , red mud  and activated alumina  are facing problems like low adsorption capacity. It was urgent and essential to develop new adsorbent materials with high efficiency to eliminate arsenic in wastewater.
Metal–organic frameworks (MOFs) are unique porous crystalline materials with large surface area, abundant binding site, regular channel, and tunable morphology, which are widely used in the fields of photocatalysis, adsorption, gas storage and separation [28, 29, 30, 31, 32]. Adsorptive removal of arsenic using MOFs have attracted extensive attentions due to their outstanding adsorption capacity, high removal efficiency, short reaction time and wide range of suitable pH values [7, 12, 33, 34]. Furthermore, MOFs possess abundant metal sites even unsaturated coordination sites, which can be coordinated with arsenic for enhanced adsorption ability [35, 36]. However, many MOFs are not stable in water, which exerted great difficulty to carry out reuse and recyclability .
A new 2D metal–organic framework [Co3(tib)2(H2O)12](SO4)3 (BUC-17) has been synthesized from tib (1,3,5-tris(1-imidazolyl)benzene) and Co2+ by hydrothermal methods, which exhibited ultrahigh adsorption capacity towards some organic dyes  as well as Cr(VI) . Considering that BUC-17 displayed preferential uptake to anionic matters, it was used to carry out adsorptive removal toward As(V) in HAsNa2O4. Also, the corresponding kinetics, isotherms and the thermodynamic parameters were fitted and calculated. Finally, the adsorption mechanism between BUC-17 and As(V) was proposed, and confirmed by scanning electron microscopy (SEM), Fourier Transform infrared spectra (FTIR) and X-ray photoelectron spectra (XPS) analyses.
2 Materials and methods
2.1 Synthesis of BUC-17
All the chemicals were reagent grade and used without further purification. BUC-17 was synthesized following the reported method [38, 39] with minor modification. Briefly, CoSO4·7H2O (0.3 mmol, 0.0843 g) and 1,3,5-tris(1-imidazolyl)benzene (tib) (0.3 mmol, 0.0828 g) were mixed with 10 mL deionized water and then added 5 mL ethanol (99%) in a 25 mL Teflon-lined stainless steel Parr bomb, and heated in a drying oven at 413 K for 72 h. The pink powders are acquired by filtration, and then washed three times using deionized water and ethanol (99%) in turn to obtain pure BUC-17.
The Fourier transform infrared (FTIR) spectra were used to analyze the change of adsorbent throughout the whole adsorption process by a Nicolet 6700 FTIR spectrometer with KBr pellets in the range of 4000–400 cm−1. The morphologies and the elemental mappings for adsorbent BUC-17 before and after adsorption were acquired on a FEI Quanta 250 FEG scanning electron microscope (SEM) equipped with Bruker XFlash 5010 Energy Dispersive Spectrometer (EDS). The change of crystalline structures and compositions of the before and after adsorbed samples were characterized by powder X-ray diffraction (PXRD) under Cu Kα radiation in the 2θ range of 5°–50° on Dandonghaoyuan DX-2700B diffractometer. X-ray photoelectron spectra (XPS) measurement was carried out on Thermo ESCALAB 250XI to determine adsorbent with its chemical valence state and composition.
2.3 Adsorption experiments
where, C0 and Ce are the initial and equilibrium concentrations (mg L−1) of As(V), respectively; V is the solution volume (L) and m is the dosage of the adsorbent (g).
3 Results and discussion
3.1 Adsorption kinetics
The adsorption capacities of different adsorbents toward As(V)
Adsorption capacity (mg g−1)
where, qe and qt (mg g−1) are the adsorption quantities of As(V) at equilibrium time and at a sometime t, respectively. K1 (min−1) and K2 (g mg−1 min−1) are the adsorption rate constants of the pseudo first-order and the pseudo-second-order adsorption, respectively.
Kinetic parameters of pseudo-first-order and pseudo-second-order models for fitting kinetic data of As(V) adsorption with different concentration onto BUC-17 (298 K)
C0 (mg g−1)
Experimental value q (mg g−1)
qe (mg g−1)
K2 (g mg−1 min −1)
qe (mg g−1)
3.2 Adsorption isotherms
Constants of Langmuir, Freundich, and D–R for As(V) adsorption by BUC-17 at different temperatures
qm (mg g−1)
Kf (L g−1)
E (KJ mol−1)
3.98 \(\times\) 10–4
4.13 \(\times\) 10–4
8.04 \(\times\) 10–4
3.3 Thermodynamic calculations
where, Cw (1.01 \(\times\) 106 mg L−1) represents the water concentration.
Thermodynamic parameters for As(V) adsorption via BUC-17 at different temperatures
ΔG° (kJ mol −1)
ΔS° (J mol−1 K−1)
ΔH° (kJ mol−1)
3.4 Influencing factors
3.4.1 Effect of pH
3.4.2 Effect of coexisting anions
It is generally known that the co-existing anions in solution like nitrate, chlorate and phosphate are important factors in estimating its practical applicability as adsorbent . To explore the effect of coexisting anions in As(V) solution, the experiment was demonstrated by adding 40 mg BUC-17 into 200 mL solution containing 10 mg L−1 of As(V) solution (pH = 10) with and without coexistent anions like NO3−, F−, Cl−, SO42−, PO43− at 298 K. The concentration of all coexisting anions was 0.02 mol L−1. The adsorption capacity ratio (%) are removal ratio without coexistent anions divide by removal ratio with coexistent anions. As shown in Fig. 5b, only 13.4% of the adsorption capacity was maintained in the presence of PO43−, which may be due to phosphate and arsenate have similar adsorption behavior  and phosphate is more competitive for binding sites of BUC-17 . On the contrary, other co-existed anions like NO3−, F−, Cl−, SO42− exert no significant effect on adsorption capacity, which indicates that BUC-17 displayed good adsorption efficiency in the presence of different anions unless phosphate.
3.5 Proposed adsorption mechanism
In this study, BUC-17 exhibited good adsorption performance for the As(V) removal from wastewater; the adsorption kinetics and adsorption isotherm of As(V) on BUC-17 were suitably fitted by the pseudo-second-order kinetic model, and Langmuir isotherm model, respectively, and the maximum adsorption capacity was 129.2 mg g−1, higher than most reported adsorbents for As(V) removal. The adsorption process was spontaneous, exothermic and the randomness decreased as the result of negative ΔG°, ΔH° and ΔS° values. The pH values and foreign ions were also important influence factors during the whole adsorption process. The possible adsorption mechanisms in this study were proposed, including electrostatic and ion-exchange interactions. With the good adsorption performance towards As(V), BUC-17 could be potentially applied in industrial wastewater treatment.
The authors acknowledge financial support from Project of the National Science Foundation of China (51878023,51578034), Construction of Innovation Teams and Teacher Career Development for Universities and Colleges Under Beijing Municipality (IDHT20170508), Great Wall Scholars Training Program Project of Beijing Municipality Universities (CIT&TCD20180323), Beijing Talent Project (2019A22), the Fundamental Research Funds for Beijing Universities of Civil Engineering and Architecture (X18276) and Scientific Research Foundation of Beijing University of Civil Engineering and Architecture (KYJJ2017008).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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