CN105388141A - Method for measuring gold element content in core-shell type gold-magnetic nano composite catalyst through inductively coupled plasma emission spectrum - Google Patents

Abstract

The invention discloses a method for measuring gold element content in core-shell gold-magnetic nano composite catalyst by inductively coupled plasma emission spectrometry, adding aqua regia, hydrofluoric acid and high chloride The acid is heated and hydrolyzed to completely dissolve the solid powder to obtain a transparent and clear inorganic liquid, which is heated and evaporated to near dryness, and the sample solution is fixed to volume with dilute nitric acid, and the sample blank is prepared in the same way; after optimizing the working parameters of the instrument, use an electric The inductively coupled plasma optical emission spectrometer measures the sample blank and the standard solution respectively, and draws the gold element standard working curve; uses the inductively coupled plasma optical emission spectrometer to measure the light intensity of the core-shell gold-magnetic nanocomposite catalyst solution, and draws the The working curve of the gold standard solution and the light intensity of the sample solution are used to obtain the content of the gold element. The method is easy to operate, accurate and fast, has a high standard addition recovery rate, good repeatability, and has high accuracy and precision.

Description

A method for determining gold element content in core-shell gold-magnetic nanocomposite catalysts by inductively coupled plasma emission spectrometry

technical field

The invention relates to a method for measuring gold element content in a core-shell type gold-magnetic nano composite catalyst by using an inductively coupled plasma emission spectrum, and belongs to the technical field of gold element detection in a core-shell type gold-magnetic nano composite catalyst.

Background technique

Magnetic nanocomposite catalysts prepared by combining magnetic nanoparticles with excellent magnetic properties and catalytic properties, because of their large specific surface area, many coordination unsaturated active sites on the exposed surface, and simple separation under the action of an external magnetic field And other characteristics, so that the magnetic nanocomposite catalyst has the advantages of high catalytic activity and easy separation and recovery. Coating magnetic nanocomposite particles with gold nanoparticles can protect the magnetic nanoparticles from the interference of the external environment, prevent their oxidation or agglomeration, and also provide a special active surface to graft catalytic sites on the magnetic nanocomposite particles , to form a core-shell gold-magnetic nanocomposite catalyst, which has good catalytic activity and recyclability as a heterogeneous nucleophilic catalyst, and gold nanoparticles as the catalytic active site of this type of catalyst, the determination of its content, It directly affects the activity of the catalyst and its conversion rate (TOF) calculation. Therefore, it is particularly important to accurately determine the content of gold in core-shell gold-magnetic nanocomposite catalysts. At present, there is no report on the determination of gold element content in core-shell gold-magnetic nanocomposite catalysts.

Inductively coupled plasma optical emission spectrometer (ICP-OES) has become an incomparable analytical technology in the determination of trace and measured elements due to its low detection limit, high precision, wide linear dynamic range of concentration determination, and less chemical interference. means of analysis. The method proposes a method for treating the sample with wet acid solution and inductively coupled plasma emission spectrometry for determining the content of gold element in the core-shell gold-magnetic nanocomposite catalyst.

Contents of the invention

The purpose of the present invention is to provide a simple, fast, accurate and reliable method for measuring the gold element content (concentration range is 6.0 ~ 300mg/ g) method.

The preparation method of the core-shell gold-magnetic nanocomposite catalyst: a thin layer of SiO ₂ is coated on the surface of the black Fe ₃ O ₄ nanoparticles by the sol-gel method to obtain Fe ₃ O ₄ SiO ₂ nanoparticles, which are dissolved in ammonia water Add tetraethyl orthosilicate (TEOS), stir at room temperature for 10 hours, then add aminopropyltriethoxysilane (APTES) toluene solution, and reflux for 10 hours to obtain Fe ₃ O ₄ SiO ₂ -NH ₂ ; Fe ₃ O ₄ SiO ₂ -NH ₂ reacts with wine-red gold nanoparticles (hydrogen tetrachloroaurate (HAuCl ₄ 4H ₂ O) aqueous solution and trisodium citrate (C ₆ H ₅ Na ₃ O ₇ 2H ₂ O) to obtain ) mixing, ultrasonic dispersion and stirring at room temperature for 4 hours to obtain Fe ₃ O ₄ SiO ₂ -Au magnetic nanocomposites; disperse Fe ₃ O ₄ SiO ₂ -Au in cetyltrimethylammonium bromide (CTAB) ammonia solution , adding TEOS and stirring at room temperature for 8 hours to obtain Fe ₃ O ₄ SiO ₂ -AumSiO ₂ core-shell gold-magnetic nanocomposite catalyst.

A method for measuring gold element content in a core-shell type gold-magnetic nanocomposite catalyst by inductively coupled plasma emission spectrometry, characterized in that it comprises the following steps:

1) Pour 10.0~50.0mg (accurate to 0.1mg) dried core-shell gold-magnetic nanocomposite catalyst solid powder sample into a polytetrafluoroethylene beaker, add 1~2mL of first-class deionized water to wet the sample, Then add 5~15mL of newly prepared aqua regia, 3~8mL of hydrofluoric acid, and 2~6mL of perchloric acid, cover and decompose at 120~180℃ and heat until the solid dissolves completely. After obtaining a transparent and clear inorganic liquid, open the cover and slowly Slowly raise the temperature to 140~190℃, exhaust the white smoke of perchloric acid, heat and evaporate to the remaining 3mL, cool down, wash the cup wall with 6% dilute nitric acid solution 4~5 times, then wash with hot water 3~4 times, and dissolve the solution Transfer to a 25 or 50mL volumetric flask, cool to room temperature, dilute to the mark with 3% dilute nitric acid solution, and mix well to obtain the core-shell gold-magnetic nanocomposite catalyst sample solution; the blank solution is prepared in the same way;

2) Preparation of standard solution: Take 0, 1.0, 5.0, and 10.0 mL of 50 mg/L gold element standard solution in a 50 mL volumetric flask, add 1-2 mL of concentrated nitric acid, dilute to the mark with first-grade deionized water, and obtain a blank in turn Solution and standard series with concentration of 1.0, 5.0, 10.0mg/L, mix well;

3) Draw the working curve of the standard solution: Use an inductively coupled plasma emission spectrometer to measure the above-mentioned blank solution and standard sample solution respectively, and draw the working curve of the gold element standard solution;

4) Sample test: Use an inductively coupled plasma emission spectrometer to measure the core-shell gold-magnetic nanocomposite catalyst sample solution described in step 1), and calculate the core-shell gold-magnetic Au content in nanocomposite catalysts.

Said step 1) the concentration of nitric acid required for preparing aqua regia is 68-70%, the concentration of hydrochloric acid is 36-38%; the concentration of hydrofluoric acid is 48-50%, the concentration of perchloric acid is 70%, the first-grade deionized The resistivity is 18.25MΩ·cm (25°C).

The concentration range of the gold element in the core-shell gold-magnetic nanocomposite catalyst in the step 4) is 6.0-300 mg/g.

The working parameters of the inductively coupled plasma emission spectrometer are: gold element analysis lines: 211.068nm, 242.794nm, 267.594nm; emission power: 1.25kW; observation height: 12mm; atomizing gas flow rate: 0.50L/min; Flow: 15.0L/min; Auxiliary gas flow: 1.50L/min; Peristaltic pump speed: 15rpm; Injection delay: 30s.

The gold element content in the nano-gold catalyst is calculated according to the following formula:

C=(Ci－C0)×V/M;

In the formula: C --- the content of the gold element in the catalyst (mg/g); Ci --- the content of the element in the test solution (mg/L); C0 --- the content of the element in the blank solution ( mg/L); V---the volume of the test solution (L); M---the mass of the catalyst sample (g).

Technical verification of this method: The element detection limit, standard addition recovery, repeatability, internal standard method, and serial dilution experiments of this method were carried out respectively with an inductively coupled plasma emission spectrometer, which verified that this method has higher accuracy and precision.

detailed description

1 Experimental materials

1.1 Main instruments and equipment

Inductively coupled plasma emission spectrometer (ICP-OES): American Agilent Company, 725-ES type, CCD detector covers the entire wavelength range from 167-785nm;

Laboratory ultrapure water device: Molecular company, atomic type 1810D, primary deionized water resistivity (25°C) is 18.25MΩ cm;

Electronic balance: MettlerToledo company, XP6 type, weighing range is 0.001mg~6.0g;

Anti-corrosion electric heating plate: Binhai Zhenghong Plastic Instrument Factory, DBF-1 type, the temperature range is 0-200 ℃.

1.2 Main reagents

Nitric acid: ACS grade reagent, 68-70%, density 1.41g/mL, ACROS company;

Hydrochloric acid: analytical reagent, 36-38%, density 1.26g/mL, Xilong Chemical Company;

Hydrofluoric acid: ACS grade reagent, 48-50%, density 1.15g/mL, Bailingwei Company;

Perchloric acid: ACS grade reagent, 70%, density 1.66g/mL, Bailingwei Company;

First-class deionized water: made by Molecular laboratory ultrapure water device, with a resistivity (25°C) of 18.25MΩ·cm;

Standard stock solution: gold element standard solution 1000mg/L, National Nonferrous Metals and Electronic Materials Analysis and Testing Center; dilute the gold standard stock solution to 50mg/L for later use, and gradually dilute to 0.5, 1.0, 2.0, 5.0, 10.0mg during measurement /L standard series.

1.3 Instrument working parameters of ICP-OES

Analysis lines of gold element: 211.068nm, 242.794nm, 267.594nm;

Transmitting power: 0.9~1.5kW;

Observation height: 5~15mm;

Atomizing gas flow: 0.4~1.4L/min;

Plasma gas flow: 10.0~20.0L/min;

Auxiliary gas flow: 0.75~2.25L/min;

Peristaltic pump speed: 15rpm;

Injection delay: 30s;

2 Experimental steps

2.1 Sample pretreatment

Accurately weigh 31.0 mg (accurate to 0.1 mg) of the dried core-shell gold-magnetic nanocomposite catalyst solid powder sample into a 50 mL polytetrafluoroethylene beaker, add 1~2 mL of first-grade deionized water to wet the sample, and slowly add Freshly prepare 8mL of aqua regia, 4mL of hydrofluoric acid, and 3mL of perchloric acid, place a cover on the electric heating temperature control plate, heat and decompose at 150°C for 1.5h, until the solid dissolves completely, and after obtaining a transparent and clear inorganic liquid, open the cover and slowly Slowly raise the temperature to 170°C, exhaust the white smoke of perchloric acid, heat and evaporate until it is nearly dry, remove the Teflon beaker, cool it, rinse the wall of the cup with 6% dilute nitric acid solution 4~5 times, and then wash it with hot water 3~4 times. Once, the solution was transferred to a 25mL volumetric flask, cooled to room temperature, diluted to the mark with 3% dilute nitric acid solution, mixed evenly, and tested. Sample blanks were prepared in the same way.

2.2 Preparation of standard solution

The standard stock solution of gold element is a national standard reagent with a concentration of 1000mg/L. The standard stock solution of gold element is diluted to 50mg/L with 2% nitric acid for use. During the determination, it was diluted step by step into a standard series of 0.5, 1.0, 2.0, 5.0, 10.0 mg/L.

2.3 Optimization of instrument working conditions

2.3.1 Selection of instrument power

Use the gold standard solution with a concentration of 5.0mg/L, and select the power at 0.9~1.5kW. The measured signal-to-background ratio showed that with increasing power, the signal value increased, but the background value also increased. The final optimization is a power of 1.25kW.

2.3.2 Selection of atomizing gas flow

The gold standard solution with a concentration of 5.0mg/L was used, and the atomizing gas flow rate was selected at 0.4~1.4L/min. The signal-to-background ratio showed that increasing the atomizing gas flow rate increased the signal value, but the matrix interference also increased accordingly. The final optimization is an atomizing gas flow rate of 0.5L/min.

2.3.3 Selection of observation height

The gold standard solution with a concentration of 5.0 mg/L was used to select the observation height between 5 and 15 mm. Finally, the observation height is optimized to 12mm.

2.3.4 Instrument working parameters

According to the sensitivity of the gold element spectral line, the determination and analysis lines are: 211.068nm, 242.794nm and 267.594nm.

Table 1 Instrument optimization working parameters

2.4 Establishment of standard curve

According to the above-mentioned instrument working conditions, measure the standard solution of gold element at 4 concentration points, and draw the standard solution working curve of gold element. At the same time, measure the blank solution of the sample 10 times continuously, and calculate the detection limit according to the formula DL = KS (in the formula, S is the standard deviation of the test concentration of the blank solution for 10 times). The analysis results showed that the linear correlation coefficients of the standard curves of each element were all between 0.991 and 0.999, and the linear relationship of the determination method was good.

2.5 Determination of samples

Under the above working parameters, the inductively coupled plasma optical emission spectrometer adopts the standard curve method to measure the content of the gold element in the gold-magnetic nanocomposite catalyst sample. Each sample is measured in parallel 3 times and the average value is calculated; The working curve and the light intensity of the solution to be tested can be used to obtain the concentration of the gold element in the sample, and the measured data can be converted by the formula to obtain the content of the gold element in the gold-magnetic nanocomposite catalyst.

The gold element content in the gold-magnetic nanocomposite catalyst is calculated according to the following formula:

C=(Ci－C0)×V/M

In the formula: C --- the content of gold element in the catalyst (mg/g);

Ci---the content of the element in the test solution (mg/L);

C0---the content of the element in the blank solution (mg/L);

V --- the volume of the test solution (L);

M---Weigh the mass of the catalyst sample (g);

Calculate the gold content (mg/g) in the procatalyst.

Example 1

Accurately weigh 45.0 mg (accurate to 0.1 mg) of the dried core-shell gold-magnetic nanocomposite catalyst solid powder sample into a 50 mL polytetrafluoroethylene beaker, add 1 to 2 mL of first-grade deionized water to wet the sample, and slowly add Freshly prepare 8mL of aqua regia, 4mL of hydrofluoric acid, and 3mL of perchloric acid, place a cover on the electric heating temperature control plate, heat and decompose at 150°C for 1.5h, until the solid dissolves completely, and after obtaining a transparent and clear inorganic liquid, open the cover and slowly Slowly raise the temperature to 170°C, exhaust the white smoke of perchloric acid, heat and evaporate to the remaining 3mL, remove the Teflon beaker, cool it, rinse the wall of the beaker with 6% dilute nitric acid solution 4~5 times, and then wash it with hot water for 3~ 4 times, the solution was transferred to a 50mL volumetric flask, cooled to room temperature, diluted with 3% dilute nitric acid solution to the mark, mixed evenly, and tested. Utilize the inductively coupled plasma emission spectrometer to measure the light intensity of the sample solution, and obtain the concentration of the gold element according to the standard solution working curve of the gold element and the light intensity of the gold-magnetic nanocomposite catalyst solution solution to be measured. After calculation, the concentration of the gold element is obtained. The average content of gold element in the test sample is 34.66mg/g (3.466%).

Example 2

Accurately weigh 31.0 mg of dried core-shell gold-magnetic nanocomposite catalyst solid powder, use the sample dissolution method described in Example 1 to prepare the sample solution of gold-magnetic nanocomposite catalyst to be tested, and set the volume to 25mL in the bottle. Utilize the inductively coupled plasma emission spectrometer to measure the light intensity of the sample solution, and obtain the concentration of the gold element according to the standard solution working curve of the gold element and the light intensity of the gold-magnetic nanocomposite catalyst solution solution to be measured. After calculation, the concentration of the gold element is obtained. The average content of gold element in the test sample is 34.03mg/g (3.403%).

3 embodiment technical verification:

3.1 Detection limit experiment

Measure the concentration of the blank solution 10 times in parallel, and calculate the detection limit according to the formula DL = KS (in the formula, S is the standard deviation of the test concentration of the blank solution for 10 times), and take 3 times the standard deviation of the detection result as the detection limit of the element. 10 times the standard deviation as the limit of quantification (LOQ Limitsofquantification).

Table 2 Determination of detection limit (n=10, mg/L)

As can be seen from Table 2, the detection limit of the gold element determined by this method is 0.041mg/L.

3.2 Determination of accuracy

3.2.1 Standard recovery experiment

In order to investigate the reliability of this method, use the instrument working conditions described in step 3 to measure the content of gold element in the gold-magnetic nanocomposite catalyst solution sample solution, then add the standard solution of gold element in the sample, measure its recovery value, The recovery rate of the standard addition was calculated, and the results are shown in Table 3.

Table 3 Recovery experiment

Recovery rate of standard addition = (determination value of standard addition sample - measurement value of sample) ÷ addition amount × 100%;

It can be seen from the results in Table 3 that the recovery rate of gold element is between 98% and 102%, which meets the test requirements.

3.2.2 Serial dilution experiment

Table 4 Serial dilution experiments

Linear correlation coefficient = theoretical value after dilution ÷ measured value after dilution;

It can be seen from the results in Table 4 that there should be a good linear relationship between the signal intensity of the gold element and the matrix concentration, which meets the test requirements.

3.2.3 Internal standard method experiment:

In order to correct the error caused by the instantaneous or long-term drift of the instrument and the matrix effect of the sample, metal yttrium (Y) was used as the internal standard to carry out the internal standard method experiment. The results are shown in Table 5. The analytical line of yttrium is consistent with that of gold element overlapping, no interference;

Table 5 Internal standard method experiment

It can be seen from the results in Table 5 that the sample matrix interference in this method is almost non-existent and can be ignored.

3.3 Repeatability experiment

The core-shell gold-magnetic nanocomposite catalyst solution was measured in parallel 10 times, and the relative standard deviation was calculated to determine the precision of the gold element in the method. The results are shown in Table 6.

The precision of the method in Table 6

It can be seen from the results in Table 6 that the relative standard deviation of this method is 1.540%, indicating that the precision of this method is better.

Claims (4)

1. a method for measuring the gold element content in the core-shell type gold-magnetic nanocomposite catalyst with inductively coupled plasma emission spectrometry, is characterized in that comprising the following steps: 1) Pour 10.0-50.0 mg of dried core-shell gold-magnetic nanocomposite catalyst solid powder sample into a polytetrafluoroethylene beaker, add 1-2 mL of first-grade deionized water to wet the sample, and then add newly prepared 5 ~15mL of aqua regia, 3~8mL of hydrofluoric acid, 2~6mL of perchloric acid, cover and decompose at 120~180°C until the solid dissolves completely. After obtaining a transparent and clear inorganic liquid, open the cover and slowly raise the temperature to 140~190°C ℃, exhaust the white smoke of perchloric acid, heat and evaporate to the remaining 3mL, cool, rinse the cup wall with 6% dilute nitric acid solution 4~5 times, then wash with hot water 3~4 times, transfer the solution to 25 or 50mL capacity bottle, cooled to room temperature, diluted to the mark with 3% dilute nitric acid solution, and mixed to obtain the core-shell type gold-magnetic nanocomposite catalyst sample solution; the blank solution was prepared in the same way; 2) Preparation of standard solution: Take 0, 1.0, 5.0, and 10.0 mL of 50 mg/L gold element standard solution in a 50 mL volumetric flask, add 1-2 mL of concentrated nitric acid, dilute to the mark with first-grade deionized water, and obtain a blank in turn Solution and standard series with concentration of 1.0, 5.0, 10.0mg/L, mix well; 3) Draw the working curve of the standard solution: Use an inductively coupled plasma emission spectrometer to measure the above-mentioned blank solution and standard sample solution respectively, and draw the working curve of the gold element standard solution; 4) Sample test: Use an inductively coupled plasma emission spectrometer to measure the core-shell gold-magnetic nanocomposite catalyst sample solution described in step 1), and calculate the core-shell gold-magnetic Au content in nanocomposite catalysts. 2. The method according to claim 1, characterized in that said step 1) the concentration of nitric acid required for preparing aqua regia is 68-70%, the concentration of hydrochloric acid is 36-38%; the concentration of hydrofluoric acid is 48-50% , the concentration of perchloric acid is 70%, and the resistivity of primary deionized water at 25°C is 18.25MΩ·cm. 3. The method according to claim 1, characterized in that the concentration range of the gold element in the core-shell gold-magnetic nanocomposite catalyst in the step 4) is 6.0-300 mg/g. 4. The method according to claim 1, wherein the operating parameters of the inductively coupled plasma emission spectrometer are: analysis lines of gold elements: 211.068nm, 242.794nm, 267.594nm; emission power: 1.25kW; observation height: 12mm; atomizing gas flow: 0.50L/min; plasma gas flow: 15.0L/min; auxiliary gas flow: 1.50L/min; peristaltic pump speed: 15rpm; sample injection delay: 30s.