نوع مقاله : مقالات پژوهشی
نویسندگان
1 دانشگاه پیام نور
2 ولیعصر رفسنجان
3 دانشگاه ولی عصر رفسنجان
چکیده
اخیراً پتانسیل هیدروکسیدهای دوگانه لایه‌ای در تأمین عناصر ضروری گیاهان به‌طور گسترده مورد توجه قرار گرفته است. در این پژوهش Mg-Zn-Mn-Al-LDH با آنیون بین لایه‌ای نیترات با دو نسبت کاتیون دو به سه ظرفیتی 3:1 (LDH (3:1)) و 4:1 (LDH (4:1)) به روش هم‌رسوبی تهیه شد. پس از بررسی ویژگی‌های ساختاری و مورفولوژیکی با استفاده از تکنیک‌های XRD، SEM، FTIR و BET، روند رهاسازی عناصر روی، منگنز و منیزیم از آن‌ها در حضور و عدم حضور اسیدهای آلی سیتریک و تارتاریک با مطالعات پیمانه‌ای مورد بررسی قرار گرفت. از بین مدل‌های سینتیکی مختلف، مدل های تابع توانی و شبه مرتبه دوم به دلیل دارا بودن ضریب تبیین (R2) بیشتر و خطای تخمین استاندارد کمتر (SE) جهت برازش بر داده‌های سینتیکی مورد استفاده قرار گرفتند. نتایج نشان داد اسیدهای آلی نقش مهمی در رهاسازی عناصر از ساختار LDH داشته به‌گونه‌ای که در حضور اسید سیتریک، از LDH (3:1) مقدار رهاسازی روی، منگنز و منیزیم به‌ترتیب 99، 99 و 91 درصد و از LDH (4:1) به‌ترتیب 97، 98 و 85 درصد بیشتر از عدم حضور این اسید بود. همچنین در حضور اسید تارتاریک مقدار رهاسازی روی، منگنز و منیزیم از LDH (3:1) به‌ترتیب 99، 90 و 89 درصد و از LDH (4:1) این مقادیر 93، 86 و 69 درصد بیشتر از عدم حضور این اسید بود. نسبت کاتیون دو به سه ظرفیتی در ساختار LDH تأثیر مستقیم بر پایداری LDH داشته و افزایش این نسبت منجر به کاهش پایداری LDH گردید. با توجه به نتایج حاصل می‌توان در رویکردی جدید هیدروکسیدهای دوگانه لایه‌ای را به‌عنوان ترکیبات کودی با قابلیت آزاد سازی آرام عناصر غذایی در شرایط کمبود آن‌ها و در حضور گیاه مورد بررسی بیشتر قرار داد.
کلیدواژه‌ها
موضوعات
عنوان مقاله [English]
Kinetics of Zinc, Manganese and Magnesium Release from Layered Double Hydroxides (Mg-Zn-Mn-Al-LDH): Effect of Citric Acid and Tartaric Acid
نویسندگان [English]
- Zahra MovahediRad 1
- Mohsen Hamidpour 2
- Ahmad Tajabadipour 3
1 Payame Noor
2 Department of Soil Science, Vali-e-Asr University of Rafsanjan
3 Vali-e-Asr University of Rafsanjan
چکیده [English]
Introduction
Recently, layered double hydroxides (LDHs) with a unique structure and unbeatable characteristics have been widely studied and investigated in various fields. One of these fields is the investigating the potential of these compounds to supply essential nutrients for plants. Several studies have reported the use of LDHs as fertilizers for macronutrients and micronutrients. These compounds have a very high potential for use as fertilizers and can increase agricultural productivity. Micronutrients such as Zn, Cu, and Mn can be structurally incorporated in the metal hydroxide layer. According to recent research, LDHs have shown a suitable potential to release micronutrients. However, more studies are needed to enhance our understanding of the mechanism and reaction of layered double hydroxides in different conditions. Although various studies have explored the potential of LDHs as slow-release fertilizers, our research focuses on the role of citric acid and tartaric acid and as well as the ratio of divalent to trivalent cations on the kinetics of Zn, Mn and Mg release from Mg-Zn-Mn-Al-LDH intercalated with nitrate.
Materials and Methods
All chemicals used in this study including citric acid (C6H8O7.H2O), tartaric acid (C4H6O6) KCl, Zn (NO3)2.6H2O, Mn(NO3)2.4H2O Mg(NO3)2.6H2O and Al(NO3).9H2O were of analytical grades, purchased from Chem-Lab or Merck Chemical Corporations. Solutions were prepared using decarbonated ultrapure water (electrical resistivity = 18 MΩcm). The LDHs were synthesized by co-precipitation method at constant pH = 9.2-9.6. Two types of LDHs were synthesized by varying the M+2(Zn+Mn+Mg)/M+3(Al) ratios of 3:1 and 4:1 in the precursor solution while stirring vigorously in a nitrogen atmosphere. The pH was kept at 9.2-9.6 by adding volumes of 3 M NaOH. The LDH crystals were allowed to ripen in the mixture for 2 hours, after which the precipitates were centrifuged at 3000 rpm for 20 min and washed several times with distilled water, and placed in an oven at 70°C for 8 hours to dry.
The physical, chemical, and morphological characteristics of the LDHs were assessed through several techniques, including X-ray diffraction (Panalytical X Pert Pro X-ray diffractometer), field emission scanning electron microscopy (FE-SEM, Sigma VP), Fourier-transform infrared spectroscopy (FT-IR, Nicolet iS10 spectrometer), and Brunauer-Emmett-Teller (BET, BELSORP Mini II) analysis.
A batch study was conducted to evaluate the effects of varying M²⁺/M³⁺ ratios in LDHs and the influence of citric acid and tartaric acid on the release of Zn, Mn, and Mg from LDH (3:1) and LDH (4:1). In brief, 0.01 g of synthesized LDH was placed in a centrifuge tube and mixed with 10 ml of background electrolyte (0.01 M KCl) and 1.25 mM of citric acid or tartaric acid, maintaining an initial pH of 6–7 at a constant temperature of 25 ± 0.5 °C. Blank samples (without ligands) were also included for comparison. The suspensions were shaken for periods ranging from 5 to 720 minutes at an agitation speed of 180 rpm. After shaking, the supernatant was separated by centrifugation at 4000 rpm for 20 minutes. The concentrations of Zn, Mn, and Mg in the supernatant solutions were determined using graphite furnace atomic absorption spectrophotometry. To describe the time-dependent release of Zn, Mn, and Mg, several kinetic models were tested.
Results and Discussion
The results indicated that the calculated molar ratio of divalent cations to trivalent cations closely matched the molar ratios used in the synthesis of the layered double hydroxide (LDH) samples. The X-ray diffraction (XRD) patterns for both LDH (3:1) and LDH (4:1) samples exhibited strong and sharp peaks corresponding to the 003 and 006 reflections, confirming the layered structure of the synthesized materials. The specific surface areas of LDH (3:1) and LDH (4:1) were measured at 5.50 m²/g and 16.54 m²/g, respectively. Correspondingly, the average pore diameters were found to be 1.92 nm for LDH (3:1) and 2.55 nm for LDH (4:1), indicating differences in porosity between the two samples. The time-dependent cumulative release of Zn, Mn, and Mg from LDH (3:1) and LDH (4:1) in the presence and absence of citric acid and tartaric acid was investigated. The release of these micronutrients was accelerated in the presence of both organic acids. The release process appeared to occur in two stages: during the initial stage (0 to 50 minutes), the release rate of Zn, Mn, and Mg was rapid, followed by a period from 50 to 720 minutes where the release rate either fixed or slightly increased.
In this research, among the non-linear models used to determine the release kinetics of Zn, Mn, and Mg, the result with the highest R2 values was chosen. The R² values ranged from 0.81 to 0.99 for the pseudo-first-order model, 0.89 to 0.93 for the pseudo-second-order model, 0.97 to 0.99 for the Elovich model, 0.89 to 0.99 for the power function model, and 0.55 to 0.86 for the parabolic diffusion model. Ultimately, the pseudo-second-order and power function models were chosen to analyze the kinetic data. The amount of Zn, Mn and Mg released at equilibrium (qe) were higher in the presence of citric acid (42%) compared to tartaric acid. Additionally, the release of these elements was greater from LDH (4:1) than from LDH (3:1). This suggest that increasing the ratio of divalent cations to trivalent cations reduces the stability of LDH, enhancing the release of micronutrients.
Conclusions
The results of this research showed that the release of Zn, Mn, and Mg from LDHs is influenced by time, the type of low molecular weight organic acid, and the ratio of divalent to trivalent cation ratio in LDH structure. The kinetic modeling indicated that the release rates of Zn, Mn, and Mg from LDH (4:1) were higher than those from LDH (3:1). Furthermore, the dissolution rates of the LDHs in the presence of citric acid were faster compared to those in the presence of tartaric acid. Additional greenhouse and soil studies are needed to further evaluate the effectiveness of LDHs as slow-release fertilizers for micronutrients in calcareous soils.
کلیدواژه‌ها [English]
- Kinetic models
- Low molecular weight organic acid
- Micronutrients
- Slow-release fertilizer
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