EXPERIMENTAL STUDY OF SYNTHESIS PROCESSES OF ELECTRODE ACTIVE COMPOUNDS FOR ZINC AND COPPER IONS

ABSTRACT

In this work, the synthesis processes and conditions of ionophores for ion-selective membranes from zinc sulfate and sodium tetraphenyl borate and copper (II) chloride and sodium tetraphenyl borate were studied. For the purpose of synthesis, the stages of synthesis of high molecular weight complex compounds that are insoluble in water and soluble in organic solvents and separation of synthesized complex salts from solution were studied. The presence of the obtained new compound was analyzed by chemical and physicochemical methods. For example, elemental analysis, IR, energy dispersive X-ray spectroscopy, complexometric and titrometric. In order to separate the ionophores from the solvent, the solutions were evaporated in a vacuum evaporator at a temperature of 40 0⁰C and a pressure of 5 atmospheres.

АННОТАЦИЯ

В данной работе изучены процессы и условия синтеза ионофоров для ионселективных мембран из сульфата цинка и тетрафенилбората натрия и хлорида меди (II) и тетрафенилбората натрия. С целью синтеза изучены стадии синтеза высокомолекулярных комплексных соединений, нерастворимых в воде и растворимых в органических растворителях, и выделения синтезированных комплексных солей из раствора. Наличие полученного нового соединения анализировалось химическими и физико-химическими методами, например: элементным анализом, ИК-спектроскопией, энергодисперсионной рентгеновской спектроскопией, комплексонометрическим, титрометрическим. Для отделения ионофоров от растворителя растворы упаривали в вакуумном испарителе при температуре 40 0С и давлении 5 атм.

Keywords: electrode active compound, sodium tetraphenylborate, zinc tetraphenylborate, copper (II) tetraphenylborate, alcohol, ionophore.

Ключевые слова: активное вещество электрода, тетрафенилборат натрия, тетрафенилборат цинка, тетрафенилборат меди (II), спирт, ионофор.

Introduction. Currently, serious research is being carried out on the production of new sensors and their use in clinical, environmental process monitoring and various fields requiring rapid control. A sensor is a device that provides qualitative and quantitative results after certain chemical interactions. Sensors based on ionophores are widely used today, they are also known as ion-selective electrodes (ISE) [1]. Scientists have developed methods for determining small amounts of ions (especially alkali, alkaline earth and heavy metals) in a given sample [2,3]. Among these methods, the determination of ions using ISE is distinguished by having important features such as cost-effectiveness, rapidity, accuracy and reproducibility [4].

When there are several types of ions in solutions, there is a need for qualitative and quantitative analysis of the ions contained in them. In order to overcome this problem, there are rapid and high-precision electrochemical spectroscopic methods in analytical chemistry, and one of the main methods with a wide detection range is analysis using ion selective electrodes [5,6].

This method of analysis is carried out by applying a selective membrane to an ion selective electrode, the selective membrane allows only the desired ion to enter and exit. At equilibrium, there is a potential difference between the two sides of the membrane, which is controlled by the concentration of the test solution described by the Nernst equation [7,8]. The composition of the membranes consists of electrode active substances, these substances are complex compounds with high molecular mass that are hydrophobic and soluble in organic solvents. The first step in the development of these ion-selective electrodes begins with the synthesis of ionophores (electrode-active compounds) [9].

Today, the need for ionophores in the production of electrodes remains high. Electrode-active compounds in the membrane are the main component that ensures these parameters in the creation of electrodes with a new composition, sensitivity and high selectivity. Increasing the amount of ionophore in the membrane increases the sensitivity of the membrane and thus affects the behavior of the electrode [10]. If the ionophore continues to be added, the ionophore will saturate the membrane and the electrode response will decrease. Exceeding the ionophore amount above a certain limit leads to loss of selectivity of the electrode and therefore increased interference due to counterions present in the solution [11].

In addition, it is important to determine copper and zinc ions in aqueous solutions selectively and quickly, very small concentrations of different solutions, to ensure the control of these ions in various industrial and production processes. For this purpose, it is important to develop ion-selective electrodes that are selective and fast for zinc and copper ions [12,13].

Taking into account the above, in order to create new, sensitive, selective zinc and copper electrodes - the synthesis of ionophores based on tetraphenylborate and zinc sulfate, copper (II) chloride salts was not previously studied and was studied by the authors for the first time.

Methods and Materials. In the research work, inorganic and organic substances and their compounds, as well as a number of equipment, were used. Silver nitrate (pure for analysis), distilled water, potassium chromate (pure for analysis), zinc sulfate (pure for analysis), zinc sulfate pentahydrate (chemical pure), copper (II) chloride (chemical pure.), tetraphenylborate (CAS 143-66-8).

For analysis of starting reagents and synthesized compounds (IR spectra) were obtained on a Perkin Elmer Spectrum IR (Version 10.7.2) IR instrument. Sample tablets were prepared by pressing with potassium bromide. Energy-dispersive X-ray fluorescence spectra were performed on a NEX DE Rigaku (FP method, Japan) device. Solvents were evaporated at a temperature of 40 ⁰C and a pressure of 5 atmospheres in an IKA RV 8 V 0010003482 vacuum evaporator.

Results and discussion. 

1. Synthesis of Cu[B(C₆H₅)₄]₂ - Sodium tetraphenylborate Na[B(C₆H₅)₄] and copper (II) chloride CuCl₂ solutions were mixed in a stoichiometric ratio as a starting material for the synthesis of electrode active compound (EAC) for a copper selective electrode.

Na[B(C₆H₅)₄] + CuCl₂ → Cu[B(C₆H₅)₄]₂ + NaCl                                                (1)

Taking into account the above, 284.9 ml of 0.1 M and 142.45 ml of 0.1 M ethanol solutions of NaBC₂₄H₂₀ and CuCl₂ were used, respectively.

Initially, a small amount of brown precipitate was observed, because EAC is highly soluble in organic solvents. 96% alcohol was used as a solvent and as a result of the reaction (1) 2 different salt mixtures (Cu[B(C₆H₅)₄]₂ and NaCl) were formed.

During the complete and clean separation of the synthesized EFB, the solvent was evaporated step by step in a vacuum evaporation device of the IKA RV 8 V 0010003482 brand at a temperature of 40 ⁰C and a pressure of 5 atmospheres. As a result, pure and complete EFB were synthesized by washing the mixture of salts formed by evaporating the solvents several times with distilled water. The precipitate was analyzed and confirmed to be completely free of NaCl using silver nitrate solution. At the last stage, the precipitate separated as EFB was transferred to a watch glass and dried for 3 days. The dried sediment was ground to powder (fig.1).

Figure 1. Synthesized copper (II) tetraphenylborate

2. Synthesis of Zn[B(C₆H₅)₄]₂ - Reactions of formation of Zn[B(C₆H₅)₄]₂ from zinc sulfate and sodium tetraphenyl borate correspond to the equation (2).

Na[B(C₆H₅)₄] + ZnSO₄  → Zn[B(C₆H₅)₄]₂ + Na₂SO₄                                      (2)

Solutions of appropriate salts (Na[B(C₆H₅)₄] and ZnSO₄) were used in the process of synthesizing the electrode-active compound for zinc selective electrode. The amount of components required to obtain 10 g of EFB is presented in Table 1. According to calculations, it is necessary to mix 284.495 ml and 142.247 ml of 0.1 M alcoholic solutions of the initial components to synthesize 10 g of EFB, respectively. During the complete and clean separation of the synthesized EFB, the solvent was evaporated step by step in a vacuum evaporator at a temperature of 40 ⁰C and a pressure of 5 atmospheres. The resulting mixture of salts formed by evaporating the solvents was washed with distilled water and separated from Na₂SO₄, and EFB was completely synthesized (fig.2).

Figure 2. Zinc tetraphenylborate

During the experiments, 0.1 M standard solutions of sodium tetraphenylborate and metal salts were used. Table 3.1 shows the required amount of 0.1 molar solutions of initial reagents for the synthesis of EAC based on tetraphenylborate and metal salts of copper and zinc (table-1).

Table 1.

The amount of components required for the synthesis of electroactive compounds

The element composition of the synthesized ionophores was analyzed using chemical methods and the results were presented in Table 2.

Table 2.

The results of determining the elemental composition of the synthesized electrode active substances

In addition, the composition of the electrode active compounds (EAC) containing Zn[B(C₆H₅)₄]₂ and Cu[B(C₆H₅)₄]₂ was confirmed using modern physico-chemical research methods (fig.3. and fig.4).

Figure 3. Energy-dispersive X-ray fluorescence spectrum of EAC containing Zn[B(C₆H₅)₄]₂

Figure 4. Energy-dispersive X-ray fluorescence spectrum of EAC containing Cu[B(C₆H₅)₄]₂

Below are the results of electrode active compounds IQ research (fig.5 and fig.6).

Figure 5. IR spectrum of synthesized Zn[B(C₆H₅)₄]₂

Figure 6. IR spectrum of synthesized Cu[B(C₆H₅)₄]₂

X-ray fluorescence, infrared spectroscopy (IR), photocolorimetric and gravimetric analysis methods were used to determine the element composition of the synthesized electroactive compounds. Rigaku NEX-DE energy dispersive X-ray spectrometry device was used in the X-ray fluorescence analysis of the synthesized EAC, and the spectra related to copper and zinc metals were determined in the samples studied by this method.

Conclusion. In this work, the synthesis conditions and laws of ionophores synthesis with a new composition were studied in order to construct ion-selective membranes. The existence of synthesized zinc tetraphenylborate and copper (II) tetraphenylborate was proved by the results of modern physical chemical and chemical analysis. As a result of the research, new hydrophobic, high molecular mass electrode active compounds were synthesized and proposed as ionophores.

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