Application of Fe-doped BiOI material in ion exchange extraction of iodine ions

Abstract

The application provides application of Fe-doped BiOI material in ion exchange extraction of iodine ions and relates to the technical field of iodine ion extraction.The Fe-doped BiOI material is obtained by successfully doping Fe into the BiOI structure through a two-step grinding method.The application can realize more effective separation of photo-generated electrons and holes, and improves photoelectrochemical performance of the Fe-doped BiOI material.The Fe-doped BiOI material prepared by the application is used as a working electrode in extraction of iodine ions in photo-assisted electrically-controlled ion exchange technology.The Fe-doped BiOI material prepared by the application is applied to photo-assisted electrically-controlled ion exchange iodine extraction, and has the characteristics of environmental friendliness and no secondary pollution.

Description

Technical Field

[0001] The present invention relates to the field of ion exchange, and in particular to application of an Fe-doped BiOI material in extracting iodide ions by ion exchange. Background Art

[0002] Iodine resources are in short supply, primarily distributed overseas. my country's iodine resources are limited by foreign sources, making it imperative to extract iodide ions from existing domestic natural resources, salt lake brine. Traditional methods for isolating I- from solutions include solvent extraction, liquid membrane extraction, adsorption, and electrochemical methods. However, these methods are generally subject to secondary pollution, poor selectivity, low adsorption capacity, and high energy consumption.

[0003] ESIX technology combines traditional ion exchange with electrochemical methods to achieve selective separation of target ions by adjusting the redox potential applied to the membrane. 3- Various membrane materials, such as BiOI, are used in electrically controlled ion exchange systems to selectively separate iodide ions from solutions. However, the entire system relies entirely on electricity for energy, resulting in high energy consumption. Even when BiOI is exposed to an external light field, its performance remains poor. Therefore, the development of new materials for ion exchange separation of I- is of great significance.

[0004] Doping with transition metal ions is very important for the application of photoelectrochemical properties. Various ion-doped materials are used in the field of photocatalysis through various preparation methods such as hydrothermal method and microwave method. Fe is a common transition metal element, often Fe 3+ and Fe 2+ It exists in the form of chemical combination and has redox properties. The light-assisted electrically controlled ion exchange system is precisely the placement and removal of target ions through the participation of redox reactions.

[0005] Therefore, developing an Fe-doped BiOI material to separate and recover iodide ions from salt lake brine in a more efficient, energy-saving, environmentally friendly and pollution-free manner has important economic benefits. Summary of the Invention

[0006] The purpose of the present invention is to develop a Fe-doped BiOI material in a photo-assisted electrically controlled ion exchange extraction solution. - The preparation method of the Fe-doped BiOI material of the present invention is simple to operate and low in cost. When applied to a light-assisted electrically controlled ion exchange system, it has the advantages of high iodine extraction efficiency, low energy consumption, and no secondary pollution.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The invention discloses an application of an Fe-doped BiOI material in ion exchange extraction of iodide ions. Specifically, the obtained Fe-doped BiOI material, conductive carbon black, and PVDF are mixed in a mass ratio of 8:1:1, an appropriate amount of NMP is added dropwise, and the mixture is stirred for 6 hours to obtain a slurry; the obtained slurry is coated on a conductive substrate, and the mixture is dried in a vacuum oven at 60°C for 12 hours to obtain a photo-electric dual-active membrane electrode; a three-electrode working system is constructed using the prepared photo-electric dual-active membrane electrode as a working electrode, FTO conductive glass as a counter electrode, and Ag / AgCl as a reference electrode; and finally, the constructed three-electrode working system is used to extract iodide ions from salt lake brine.

[0009] Preferably, the method for preparing the Fe-doped BiOI material comprises the following steps:

[0010] The bismuth salt and potassium iodide are mixed in equal moles and then subjected to a first grinding process, followed by the addition of the iron salt and a second grinding process;

[0011] The ground product was washed with deionized water and anhydrous ethanol and dried in sequence.

[0012] More preferably, the bismuth salt is bismuth nitrate; and the iron salt is iron nitrate.

[0013] More preferably, the doping amount of iron in the Fe-doped BiOI material is 0.5 wt.%.

[0014] More preferably, the time for the first grinding process and the second grinding process is 5 minutes.

[0015] More preferably, the drying temperature is 60° C. and the drying time is 6 hours.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1) This invention successfully doped Fe into the BiOI structure through a two-step milling method, resulting in an Fe-doped BiOI material. This method enables more efficient separation of photogenerated electrons and holes, improving the photoelectrochemical performance of the Fe-doped BiOI material.

[0018] 2) Photo-assisted electrically controlled ion exchange extraction of Fe-doped BiOI materials developed in this invention -The possible mechanism is as follows: due to the introduction of Fe element, Fe replaces one of the Bi in the Bi-O-Bi layer to form Fe-O-Bi. Fe has a stronger electron-donating ability, resulting in a large number of electrons on the surface of the material absorbing light energy after the external light field is introduced. The number of valence electrons jumping from the valence band to the conduction band becomes more, and the spatial positive charge region formed by the holes left by the valence electron jump is stronger, which makes the I- and free electrons in the solution migrate faster and more into the membrane, resulting in more iodine ions being able to enter between its layers, thereby improving the overall adsorption capacity.

[0019] 3) The Fe-doped BiOI material prepared in the present invention is applied to light-assisted electrically controlled ion exchange iodine extraction, which is environmentally friendly and has no secondary pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the light-assisted electrically controlled ion exchange iodine extraction device;

[0021] Figure 2 XRD spectra of BiOI and Fe-BiOI materials prepared in Example 1;

[0022] Figure 3 This is a SEM image of the Fe-BiOI material prepared in Example 1 of the present invention;

[0023] Figure 4 This is the SEM image of BiOI material;

[0024] Figure 5 This is the EDS spectrum of the Fe-BiOI material prepared in Example 1 of the present invention;

[0025] Figure 6 Cyclic voltammetry curves of the Fe-BiOI material prepared in Example 1 of the present invention under dark and light conditions;

[0026] Figure 7 Cyclic voltammetry curves of BiOI and Fe-BiOI materials prepared in Example 1 under light irradiation conditions;

[0027] Figure 8 The UV-visible diffuse reflectance spectra of BiOI and Fe-BiOI materials prepared in Example 1 are shown;

[0028] Figure 9 Adsorption capacity diagram (a) and photo-assisted efficiency diagram (b) of Fe-BiOI materials with different doping ratios in ESIX and P-ESIX systems; separation factor (c) of Fe-BiOI materials under competing anion conditions; and cyclic stability (d). DETAILED DESCRIPTION

[0029] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0030] Example 1

[0031] 2 mmol of Bi(NO3)3·5H2O and 2 mmol of KI were ground together for 5 minutes. After grinding evenly, Fe(NO3)3·9H2O was added and grinding was continued for 5 minutes. The mixture was washed by centrifugation with deionized water and anhydrous ethanol 3 times each, and vacuum dried for 12 hours to obtain Fe-BiOI material.

[0032] 2 mmol of Bi(NO3)3·5H2O and 2 mmol of KI were co-grinded for 5 min, washed by centrifugation with deionized water and anhydrous ethanol three times each, and vacuum dried for 12 h to obtain BiOI material.

[0033] The prepared Fe-BiOI material was mixed with conductive carbon black and PVDF in a mass ratio of 8:1:1, uniformly ground in an agate mortar, and an appropriate amount of NMP was added and stirred in a stirring station for 6 hours to obtain a Fe-BiOI paste slurry, which was evenly coated on the conductive surface of the pretreated FTO conductive glass (pretreatment was ultrasonic cleaning with anhydrous ethanol for 1 hour), and dried in a vacuum oven at 60°C for 12 hours to obtain a photo-electric dual-active membrane electrode.

[0034] Example 2

[0035] The BiOI material and Fe-BiOI material prepared in Example 1 were characterized by XRD and SEM. Figure 2-Figure 4 As shown. Figure 2 The diffraction peaks at 9.7°, 19.4°, 24.3°, 29.6°, 31.7°, 37.1°, 39.4°, and 45.4° correspond to the (001), (002), (101), (102), (110), (103), (004), and (200) crystal planes of BiOI (JCPDS-10-0445), respectively. This indicates that the BiOI prepared by the grinding method is almost consistent with the standard card, and is a typical tetragonal phase. BiOI has been successfully prepared. The doping of Fe in Fe-BiOI does not affect the peak shape of the material, and there is no appearance of impurity peaks. The diffraction peak position shifts slightly to the right, which may be due to the Fe 3+ Ionic radius and Bi 3+ The difference in ionic radius supports the conclusion that Fe 3+ Successfully doped into the BiOI lattice.

[0036] Figure 3 and Figure 4The SEM images of BiOI and Fe-BiOI materials show that both BiOI and Fe-BiOI materials have nanosheet structures. The doping of Fe elements does not change their morphology. The thickness of Fe-BiOI nanosheets changes due to the doping of Fe elements. The doping of metal ions may control the direction of crystal growth, thereby affecting the thickness of the crystal. The active adsorption sites may increase, which is more conducive to the insertion and removal of I. Figure 5 This is the total EDS element distribution spectrum of the Fe-BiOI material, showing that the mass fraction of Fe is 0.5%, which is consistent with the prepared Fe-BiOI, indicating that Fe-BiOI has been successfully prepared.

[0037] Example 3

[0038] The photoelectrochemical properties of the material were characterized by cyclic voltammetry and UV-visible diffuse reflectance. The specific methods are as follows:

[0039] Fe-doped BiOI material, conductive carbon black, and PVDF were uniformly ground in an agate mortar at a mass ratio of 8:1:1, and an appropriate amount of NMP was added and stirred on a stirring station for 6 hours. The resulting paste slurry was evenly coated on the conductive surface of the pretreated FTO conductive glass (pretreatment was ultrasonic cleaning of the conductive glass with anhydrous ethanol for 1 hour), and vacuum dried at 60°C for 12 hours to obtain a photo-electric dual-active membrane electrode.

[0040] The above-mentioned photo-electric dual active membrane electrode is used as the working electrode to construct a light-assisted electrically controlled ion exchange iodine extraction device, such as Figure 1 shown.

[0041] Figure 1 (a) is the photo-electric dual active membrane electrode I-pre-desorption chamber, Figure 1 (b) is the adsorption chamber. ① and ⑧ are circulation chambers I and II respectively, ② and ⑨ are photo-electric dual active membrane materials, ③ and ⑩ are counter electrodes, ④ and is the reference electrode, ⑤, For liquid collection holes, ⑥, It is the upper cover of the device, made of polytetrafluoroethylene,⑦, It's a peristaltic pump. The xenon lamp was used as the light source and the whole experiment was carried out in a dark box.

[0042] The FTO conductive glass was used as the counter electrode and the reference electrode was an Ag / AgCl electrode.

[0043] In the present invention, the liquid path system is a complete path system formed by connecting the peristaltic pump and the circulation device through a rubber tube. The liquid inlet is located in the lower right corner of the right side of the circulation device, facing away from the coated surface of the membrane material, and the liquid outlet is located in the upper left corner of the left side of the device, facing away from the counter electrode. Such water flow direction enables the entire liquid path system to achieve the circulation effect and reduces the damage and impact on the membrane material.

[0044] The present invention Figure 1 The entire device is made of quartz glass, which facilitates the illumination of the entire device by the light source. The upper cover of the circulation device is made of polytetrafluoroethylene to reduce the scattering and loss of the light source. The entire experimental device is operated in a dark box.

[0045] In the present invention, the oxidation (reduction) potential is preferably 0.5-0.7 V (-0.5 V-0.7 V), and more preferably 0.6 V (-0.6 V).

[0046] In the present invention, the time for each elution and adsorption is consistent, which is approximately 0.5-6 hours, more preferably 0.5-1 hour, and more preferably 0.5 hour.

[0047] In the present invention, the eluent electrolyte is preferably a sodium sulfate solution, and the concentration of the sodium sulfate solution is preferably 0.05 to 0.15 mol / L, more preferably 0.08 to 0.12 mol / L, and even more preferably 0.1 mol / L.

[0048] The electrolyte of the adsorption solution in the present invention is preferably a potassium iodide solution, and the iodine concentration in the potassium iodide solution is preferably 10-80 mg / L, more preferably 30-70 mg / L, and even more preferably 50-60 mg / L.

[0049] Figure 6 The CV curves of Fe-BiOI (dark) and Fe-BiOI (light) show that Fe-BiOI has a pair of obvious redox peaks. After applying the external light field, the electroactive area is significantly increased, indicating that due to the introduction of light, a large number of electrons on the surface of the material absorb energy and turn into photoelectrons that enter the entire system. The increase in the number of free electrons in the system increases the peak current and the electroactive area.

[0050] Figure 7 The CV curves of BiOI (illumination) and Fe-BiOI (illumination) show that Fe-BiOI (illumination) has a larger electroactive area than BiOI (illumination), which is mainly attributed to the 3+ doping, replacing part of Bi 3+ This allows the material to have more free electrons. Under the stimulation of the light field, more photoelectrons enter the system, thereby increasing the peak current and the electroactive area.

[0051] Figure 8(Left) is the visible light absorption wavelength range of BiOI and Fe-BiOI, which are 671nm and 676nm respectively. The absorption wavelength range has a slight red shift, indicating that the absorption of visible light is enhanced by Fe doping. Figure 8 (right) is through Figure 8 (Left) Calculations and plots reveal the band gap values ​​(Eg) of BiOI and Fe-BiOI: 1.79 eV for BiOI and 1.76 eV for Fe-BiOI. The reduced band gap indicates that Fe-BiOI requires less energy to transition from the valence band to the conduction band, making it easier for electrons to absorb energy and convert into photoelectrons. This, in turn, increases the number of electrons in the system and improves system efficiency. Therefore, Fe-BiOI exhibits superior photoelectrochemical activity.

[0052] Example 4

[0053] Figure 9 (a) is the adsorption experiment of Fe doped into BiOI at different doping ratios. Figure 9 (b) is the photo-assisted efficiency of different doping ratios, and it can be concluded that 0.5% is the optimal doping ratio. The introduction of the external light field increases the solution concentration of the pure BiOI reaction system from 3.32ppm to 5.19ppm, and the adsorption capacity increases from 162mg·g -1 Increased to 258mg·g -1 , the photocatalytic efficiency was 59.3%; the concentration of Fe-BiOI reaction system solution increased from 3.48ppm to 6.57ppm, and the adsorption capacity increased from 172mg·g -1 Increased to 312mg·g -1 The photocatalytic efficiency is 81.3%. The successful doping of Fe increases the photocatalytic efficiency by 22%. The improvement of the photocatalytic efficiency is mainly due to the substitution of Bi in Bi-O-Bi by Fe doping to form Bi-O-Fe. After the introduction of visible light, Bi-O-Fe carries more electrons, and the absorbed energy is converted into photogenerated electrons that can enter the electric field. At the same time, the escape of photogenerated electrons and the external drive of the electric field form a space charge region in the material, which synergistically accelerates the solution I - Migration in solution increases I - The adsorption capacity of the photoelectrochemical switch ion exchange technology system has been further improved, thereby further improving the overall visible light utilization rate and the extraction efficiency of iodine.

[0054] The ion selectivity of P-EIXM is very important for the iodine extraction process of P-ESIX. - To investigate the selectivity of F - / I - ,Cl - / I - and Br- / I - The experiments were conducted in a mixed solution system with a molar ratio of 1:1. Figure 9 (c) shows the selectivity of Fe-BiOI, where I - / I - ,I - / F - ,I - / Cl - ,I - / Br - The separation factors are 1, 2.18728, 2.10851, and 4.31321, respectively. - 、Cl - and Br - with I - Belong to the halogen elements, and I - have the same valence and similar ionic radius, the main reason may be that I - The migration energy barrier of BiOI is the largest and the adsorption energy barrier is the smallest, which leads to the - The selectivity of - , due to F - It has the lowest migration energy barrier, the highest adsorption energy barrier, and its selectivity is second only to I - , its Cl - and Br - The migration energy barrier and adsorption energy barrier of Fe-BiOI are general, so the selectivity is general. Analysis shows that the selectivity of BiOI to ions is affected by the combined effect of the migration energy barrier and adsorption energy barrier of ions. - Effective and selective extraction.

[0055] In order to verify the stability of Fe-BiOI, we conducted multiple adsorption experiments (0.6 V). Figure 9 (d) shows that after 10 cycles of adsorption and desorption, the adsorption rate of the material is still above 87.7%, which indicates that Fe-BiOI has good stability. The main reasons for the decrease in adsorption efficiency may be as follows: desorption is required before each adsorption, and some I- - It did not successfully escape from the specific binding site, resulting in a decrease in its adsorption rate.

[0056] In summary, the study found that Fe-BiOI materials can be used in ESIX system at 172 mg·g -1 The adsorption capacity of the P-ESIX system was increased to 312 mg·g -1, with a photocatalytic efficiency of up to 81.3%. In addition, Fe-BiOI also has good stability and excellent selectivity, can be recycled and efficiently extract iodine in complex ion solution systems. Unlike traditional ion exchange technology, through the doping of Fe, the Bi in the Bi-O-Bi layer in the unique layered structure of BiOI is replaced with Fe-O-Bi. The difference in ionic radius and the number of electrons results in better conductivity and excellent electrochemical activity, while also improving the photocatalytic ability of the material, providing more free electrons for the entire reaction system, and improving the overall adsorption capacity and photocatalytic efficiency. Ion doping provides a more novel and efficient method for the efficient and selective extraction of target ions for P-ESIX technology.

[0057] The embodiments described above are some, but not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are also within the scope of protection of the present invention.

Claims

1. An application of Fe-doped BiOI material in ion exchange extraction of iodide ions, characterized in that: Iodide ions were extracted from Fe-doped BiOI materials using photo-assisted electrically controlled ion exchange technology. Specifically, the obtained Fe-doped BiOI material, conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1, and an appropriate amount of N-methylpyrrolidone was added dropwise and stirred for 6 hours to obtain a slurry; the obtained slurry was coated on a conductive substrate and placed in a vacuum oven at 60°C for 12 hours to obtain a photo-electric dual-active membrane electrode; then, a three-electrode working system was constructed using the prepared photo-electric dual-active membrane electrode as the working electrode, FTO conductive glass as the counter electrode, and Ag / AgCl as the reference electrode; finally, the constructed three-electrode working system was used to extract iodide ions from salt lake brine.

2. The use according to claim 1, characterized in that The preparation method of the Fe-doped BiOI material comprises the following steps: The bismuth salt and potassium iodide are mixed in equal moles and then subjected to a first grinding process, followed by the addition of the iron salt and a second grinding process; The ground product was washed with deionized water and anhydrous ethanol and dried in turn.

3. The use according to claim 2, characterized in that The bismuth salt is bismuth nitrate; and the iron salt is iron nitrate.

4. The use according to claim 3, characterized in that The doping amount of iron in the Fe-doped BiOI material is 0.5 wt.%.

5. The use according to claim 2, characterized in that The time for the first grinding process and the second grinding process is 5 minutes.

6. The use according to claim 2, characterized in that The drying temperature is 60° C. and the drying time is 6 hours.

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