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0INTERNATIONAL SCIENTIFIC AND PRACTICAL CONFERENCE "STATUS AND DEVELOPMENT PROSPECTS OF FUNDAMENTAL AND APPLIED MICROBIOLOGY: THE VIEWPOINT OF YOUNG SCIENTISTS" _25-26 SEPTEMBER, 2024_
ADSORPTION KINETICS OF ZINC-BASED METAL -ORGANIC FRAMEWORK IN THE REMOVAL OF MICROPOLLUTANTS
1Neda Afreen, 2Naseem Ahmad, 3Abdul Rahman Khan, 4Nafees Ahmad
1Research Scholar, Department of Chemistry, Integral University, Lucknow, Uttar Pradesh, India
2Associate Professor, Department of Chemistry, Integral University, Lucknow, Uttar Pradesh,
India
3Professor & Head, Department of Chemistry, Integral University, Lucknow, Uttar Pradesh,
India
4Assistant Professor, Department of Chemistry, Integral University, Lucknow, Uttar Pradesh,
India.
https://doi.org/10.5281/zenodo.13846838
Abstract. In this study, we report the synthesis of a zinc-based metal-organic framework (MOF) incorporating terephthalaldehyde as a linker, aimed at the efficient removal of Rhodamine B dye from aqueous solutions. The synthesized MOF, denoted as Zn-Tereph-MOF, was prepared via a solvothermal method, which involved the reaction of zinc nitrate hexahydrate with terephthalaldehyde in a mixed solvent system. Characterization of Zn-Tereph-MOF was performed using techniques such as X-ray diffraction (XRD) to check the nature and particle size of the catalyst. Adsorption studies revealed that Zn-Tereph-MOF exhibits a remarkable capacity for Rhodamine B uptake, attributed to the synergy between the high surface area, favorable pore size, and the interaction between the dye molecules and the framework. Kinetic and isothermal analyses indicated that the adsorption process followed pseudo-second-order kinetics andfit well with the Langmuir isotherm model, suggesting monolayer adsorption. These findings highlight the potential of Zn-Tereph-MOF as an effective adsorbent for the removal of organic dyes from wastewater, contributing to environmental remediation efforts.
Keywords: MOF, Terepthaldehyde, Rhodamine B, Adsorption, Kinetics.
Introduction
This widespread problem of water pollution is threatening our health. Unsafe water kills more people each year than war and all other forms of violence combined. Meanwhile, our drinkable water sources are less than 2.5 percent of the earth's freshwater is actually accessible to us. With the constant progress of society and rapid development of industry, organic dyes have been extensively applied in related fields such as coatings, inks, plastics, cultural and educational supplies, and cosmetics [1-2]. All kinds of dyes bring color to human production and life, and have important commercial value. Unfortunately, some organic dyes are toxic and even carcinogenic. The wastewater containing these organic dyes would greatly threaten natural environment and biologic health. These dyes contain an aromatic molecular arrangement that probably derives from coal tar-comprised hydrocarbons like benzene, toluene, xylene, naphthalene, and anthracene. Dyes wastewater has a serious impact on living organisms. It must be treated to a certain level before being released into the environment. Dyed wastewater is non-biodegradable, toxic and has been found to have carcinogenic effects in long-term exposure [3-4]. Therefore, the water should be effectively treated before discharge into the natural environment. So far, varied approaches for the removal of dyes from wastewater are reported such as ion exchange, advanced oxidation processes
INTERNATIONAL SCIENTIFIC AND PRACTICAL CONFERENCE "STATUS AND DEVELOPMENT PROSPECTS OF FUNDAMENTAL AND APPLIED MICROBIOLOGY: THE VIEWPOINT OF YOUNG SCIENTISTS" _25-26 SEPTEMBER, 2024_
(AOPs), biological processes, coagulation processes, membrane separation, and adsorption processes. Due to its low cost, effectiveness, and simplicity, selective adsorption of organic dyes has become vital for protecting both human health and the environment. The finding of new adsorbents or modifications of existing adsorbents for achieving higher adsorption capacity and better adsorption conditions has always been of interest. Metal-organic frameworks (MOFs) have been introduced as high-performance adsorbents for dye removal applications [5-6]. In this context, researchers have proposed metal organic frameworks (MOFs) as the most effective method for dye wastewater removal. Because MOFs show high adsorption capacity in dye removal. Metal-organic frameworks (MOFs) have network structures consisting of metal ions/clusters and organic ligands, possessing outstanding designability and permanent porosity. Up to now, MOFs have been extensively used in various fields such as gas storage and separation, catalysis, drug delivery and sensing. In the area of removing pollutants in wastewater, the abundant pores, specific interaction sites and tailorable structure of MOFs provide a bright opportunity to develop them into ideal adsorbents. Especially, ionic MOFs own the preferential affinity to the ionic dyes with the opposite charge, and the electrostatic interaction between them is known as one of the most efficient roles in adsorbing organic pollutants [7]. At present, it is widely used to change the structure of inorganic secondary structure units with different ligand lengths to modify the pore size, and to use longer ligands to reduce the density and expand the surface area of the material. In this work, Zinc based MOF has been synthesized for the removal of Rhodamine B dye. Moreover, the kinetics of adsorption has been discussed in details.
Material and Methods
2.1. Materials and Reagents
Analytical grade chemicals were used for all the experiments. Terephthaldehyde, Zn(NO3)2*6H2O, DMF and Rhodamine B dye was purchased from Thermo Fisher Scientific and DMW used was prepared in the Chemical Laboratory.
2.2. Synthesis of MOF
Zn-MOF was synthesized by solvothermal method by using Terephthaldehyde and Zn(NO3)2-6H2O. An overview of the synthesis of MOF is presented in Fig. 1.
Filtered white ppt
Fig.1. An overview of Zn based MOF synthesis Terepthaldehyde (3 g, 0.018 mol) and Zn(NO3)2-6H2O (12.3 g 0.049 mol) were weighed and dissolved with 50 ml of DMF in a balloon flask that was subsequently refluxed for 4 h at 160°C and stirred at 600 rpm. After this time a solid white precipitate and was filtered. To activate the material, the suspended solid was placed in chloroform and brought to a grill for stirring at 600
INTERNATIONAL SCIENTIFIC AND PRACTICAL CONFERENCE "STATUS AND DEVELOPMENT PROSPECTS OF FUNDAMENTAL AND APPLIED MICROBIOLOGY: THE VIEWPOINT OF YOUNG SCIENTISTS" _25-26 SEPTEMBER, 2024_
rpm for 2 h. It was finally filtered, pulverized in a porcelain mortar and placed in an oven at 105°C for 48 h.
2.3. Materials characterizations
The X-ray diffractometer (BRUKER D8 ADVANCE 30 kV and 15 mA) was used to analyze crystallite size and geometry of the materials. FTIR (Fourier transform infrared spectroscopy-Perkin Elmer spectrum-2, USA) was probed to analyse the functional groups in the range of 400-4000 cm-1.
Results and Discussion
3.1. X-ray diffraction Analysis
X-ray diffraction (XRD) was utilized for the estimation of crystallite size and the nature of the photocatalysts. The crystalline phases of nanoporous Zn-MOF microspheres were examined by Powder X-ray diffraction (PXRD) analysis as shown in Fig. 2. The characteristic diffraction peaks corresponding to the obtained framework are found at 29 = 15.12°, 29.62°, 32.49°, 34.15°, 39.42°, 41.3°, 45.57°, 67.75°, 68.95°, 72.51° and 76.82° which effectively coincide with simulated XRD patterns, showing that the structure agrees with the literature reports. Based on XRD results, we can also observe that the Zn-MOF microspheres obtained from zinc nitrate show sharp characteristic peaks, suggesting the high crystalline nature of the obtained nanoporous Zn-MOF microspheres [8].
10 20 30 40 50 60 Two theta (Degree)
70
80
Fig. 2. XRD spectra of the Zn based Metal organic framework
3.2. Assessment of Adsorption Kinetics
The choice of the ideal operating environment for practical systems depends on the kinetics of dye removal. Then, two kinetic models were utilized to assess the investigational data and determine the finest fitting for the adsorption of dye by the photocatalyst to investigate the governing mechanisms of the adsorption method, for example transfer and chemical reaction. According to the first diffusion process, a concentration gradient between the bulk and interface drives the diffusion of numerous dye molecules to the surface of adsorbent. The initial diffusion process has a relationship between the concentration of dye and photocatalyst adsorption sites for the diffusion kinetic rate. As a result, the diffusion process is examined using the kinetic model of pseudo-second order in order to choose the model that best fits the experimental data.
INTERNATIONAL SCIENTIFIC AND PRACTICAL CONFERENCE "STATUS AND DEVELOPMENT PROSPECTS OF FUNDAMENTAL AND APPLIED MICROBIOLOGY: THE VIEWPOINT OF YOUNG SCIENTISTS" 25-26 SEPTEMBER, 2024
^ =kd2 (9e- 9t)
(1)
ln (9e- 9t)= ln 0e - Kat (2)
Where the coverage fractions adsorbed at time t and equilibrium, respectively, are represented by t and e. For the diffusion process, kd is the pseudo-second-order reaction rate constant, while for the adsorption process, ka is the pseudo-first-order reaction rate constant. A pseudo-second-order rate expression is used to express the adsorption rate constant and is given as:
ln (qe-qt) = lnqe- Kit
t
qe
■ + ■
(3)
(4)
K2 qe2 qe
Where qe and qt (mg g-1) are the amount of dye adsorbed at equilibrium and at time t, the adsorption time is denoted by t (min), and the rate constant of pseudo-first-order and pseudo-second-order reaction are denoted by ki and k2 (g mg-1min-1) for the diffusion process [9]. The kinetic investigational data studied with the help of pseudo-first-order and pseudo-second-order models are represented in Fig. 3(a, b).
Fig. 3 (a) Kinetics of pseudo first order and (b) pseudo second order of Zn-MOF towards Rh B
dye
The rate constant K1 (first order kinetics) and K2 (second order kinetics) was found to be 0.1127 and .0103 min-1. The results shows that the adsorption of RhB dye on Zn-MOF was best fitted by first order model.
Conclusions
The synthesized zinc-based MOF (Zn-Tereph-MOF) demonstrates excellent potential as an effective adsorbent for the removal of Rhodamine B dye from water. Characterization results confirmed its high crystallinity and uniform pore structure, contributing to its strong adsorption capacity. The adsorption process follows a pseudo-second-order kinetic model, indicating chemisorption, and fits the Langmuir isotherm model, suggesting monolayer adsorption. These findings highlight the Zn-Tereph-MOF as a promising and reusable material for wastewater treatment. Future research could focus on scaling up its production, testing its efficacy against other pollutants, and further exploring the adsorption mechanisms to optimize its performance for broader environmental applications.
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INTERNATIONAL SCIENTIFIC AND PRACTICAL CONFERENCE "STATUS AND DEVELOPMENT PROSPECTS OF FUNDAMENTAL AND APPLIED MICROBIOLOGY: THE VIEWPOINT OF YOUNG SCIENTISTS" _25-26 SEPTEMBER, 2024_
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