Preparation method of Cr / Fe2O3-rGO aerogel for ppm-grade acetone sensing at room temperature

Abstract

The invention discloses a preparation method of Cr / Fe2O3-rGO aerogel for ppm-level acetone sensing at room temperature. The aerogel material prepared by the method has the characteristics of low density, high specific surface area, high porosity and the like. The method comprises the following steps: respectively dissolving ferric salt and chromium salt in a mixed solvent to form a transparent solution; adding a chelating agent, heating and stirring to form a transparent solution; adjusting the pH value of the transparent solution to 3-5 to form stable sol, so as to obtain a precursor; uniformly dispersing GO to obtain a GO suspension dispersion liquid; mixing the GO dispersion liquid with the precursor, and performing ultrasonic treatment; initiating gelation of the mixed solution to form a three-dimensional network structure to obtain gel; carrying out ion replacement on the gel by using a mixed solution to obtain sol; performing supercritical drying on the sol to obtain composite aerogel; and putting the composite aerogel into a tubular furnace, introducing inert gas, heating and annealing to obtain the Cr / Fe2O3-rGO composite aerogel.

Description

Technical Field

[0001] This invention relates to a method for preparing an aerogel, and more specifically to a method for preparing a Cr / Fe2O3-rGO aerogel for ppm-level acetone sensing at room temperature, belonging to the field of nanoporous material preparation. Background Technology

[0002] Acetone, detected in human exhaled breath at concentrations of ppm / ppb, has recently been identified as a potential respiratory biomarker for the non-invasive diagnosis of diabetes under certain pathological conditions. Currently, various spectroscopic methods are used for disease identification; however, while these techniques are highly accurate, they are often expensive, complex, tedious, and require skilled personnel to operate effectively.

[0003] Aerogels, as three-dimensional porous materials, possess extremely low density, high specific surface area, and large porosity, demonstrating excellent application prospects in the field of ultrasensitive detection of trace pollutants. The high specific surface area and highly interconnected pores of aerogel materials can serve as carriers to improve loading capacity, dispersibility, and stability, making them ideal matrices for gas sensing.

[0004] Fe₂O₃ materials in metal oxides can form various stoichiometric and non-stoichiometric oxides. Some of these oxide ions relinquish their inherent lattice sites during crystal formation, leaving electrons in the negative ion pores that produce n-type semiconductor (band gap ~2.0 V) properties. Therefore, they are mainly used in electronic devices, catalysis, photochemical activities, electrochemical devices, and gas sensing. However, due to the rapid recombination of electron pores, Fe₂O₃ exhibits poor conductivity and weak reactivity, resulting in low selectivity, long response / recovery times, and high operating temperatures as a gas sensor. In existing technologies, two methods are commonly used to improve the selectivity of Fe₂O₃: forming nanocomposites through integration with other metal oxides, or introducing elemental tunneling into the original Fe₂O₃ lattice. For example, Umesh (Colloids and Surfaces A: Physicochemical and Engineering Aspects, Volume 612, 2021, 125962) uses heterojunction nanocomposites to induce band bending at the interface to achieve Fermi-level equilibrium, thereby enhancing electron transport and influencing overall sensing performance; Peeters et al. (Journal of Physical Chemistry C, Volume 118, 2014, 11813-11819) used Au-doped ε-Fe2O3 to selectively detect NO2 at 100°C; Zhang et al. (Sensors and Actuators B: Chemical, Volume 290, 2019, 59-67) showed that acetone sensing was achieved on Pt-loaded Fe2O3 nanocubes at 139°C. Although sensing performance has improved, in most cases, the operating temperature range is higher, which increases the complexity of sensor design, requires high power consumption, and leads to a shorter lifespan. Introducing carbon-based nanomaterials is one of the effective methods to reduce the operating temperature of sensors. Therefore, graphene oxide (rGO) has attracted widespread attention. MOS nanoparticles are bound to rGO through van der Waals interactions. He et al. (Journal of Hazardous Materials, Volume 405, 2021, 124252) demonstrated room-temperature NO2 sensing (~100 ppm) using highly dispersed Fe2O3 / Fe nanoparticles on an N-doped graphite matrix; further improvements are needed, while Cr... 3+ Doped Fe2O3 / rGO aerogels have not yet been addressed in existing technologies. Summary of the Invention

[0005] This invention addresses the shortcomings and deficiencies of existing technologies, particularly the selectivity and conductivity of the gas-sensitive material Fe2O3, by providing a method for preparing Cr / Fe2O3-rGO aerogel for ppm-level acetone sensing at room temperature. This method combines the sol-gel method and heat treatment to prepare graphene oxide-modified Cr-doped Fe2O3 aerogel. It features simple raw materials and processes, low cost, and controllable structure. The prepared aerogel material possesses characteristics such as low density, high specific surface area, and high porosity, which has significant implications for the application of aerogel materials in the detection field.

[0006] This invention is achieved through the following technical solution: The present invention provides a method for preparing Cr / Fe2O3-rGO aerogel for ppm-level acetone sensing at room temperature, comprising the following steps: 1) Dissolve the iron salt and chromium salt separately in a water / ethanol mixture to form a transparent solution; 2) Mix the iron and chromium salt transparent solutions prepared in step 1), add the chelating agent after mixing evenly, and heat and stir in a water bath to form a transparent solution; 3) Adjust the pH of the transparent solution from step 2) to 3-5 to form a stable sol and obtain the precursor; 4) The GO dispersion was ultrasonically treated to achieve uniform dispersion, thus obtaining a GO suspension dispersion; 5) Mix the GO dispersion obtained in step 4) with the precursor obtained in step 3) and sonicate. 6) Heat the mixture from step 5) to 60-80°C or let it stand to initiate gelation and form a three-dimensional network structure to obtain a gel; 7) The gel obtained in step 6) is subjected to ion exchange with a water / alcohol mixture for more than 5 days, with 3 exchanges per day, to obtain a sol; 8) The sol obtained in step 7) is subjected to supercritical drying to obtain Cr / Fe2O3-GO composite aerogel; 9) Place the Cr / Fe2O3-GO composite aerogel obtained in step 8) into a tube furnace, introduce inert gas N2, and anneal at 300℃ for 2 hours to obtain Cr / Fe2O3-rGO composite aerogel.

[0007] The preparation method of the Cr / Fe2O3-rGO aerogel for ppm-level acetone sensing at room temperature described above in this invention further comprises the following technical solution: the iron salt is Fe(NO3)3·9H2O or FeCl3·6H2O; the chromium salt is Cr(NO3)3·9H2O or CrCl3; and the Fe in the transparent solution of the iron salt and chromium salt is... 3+ and Cr 3+The concentration is 0.5 mol / L-1.0 mol / L, and the Cr:Fe molar ratio is 1:5-20, and the water / alcohol volume ratio mentioned in step 1) is 1:3.

[0008] The preparation method of Cr / Fe2O3-rGO aerogel for ppm-level acetone sensing at room temperature described above in this invention can be further further described as follows: the chelating agent is citric acid or ethylene glycol, and the chelating agent reacts with Fe... 3+ and Cr 3+ The total molar ratio of metal ions is 1:1; the water bath heating temperature is 50-70℃.

[0009] The preparation method of Cr / Fe2O3-rGO aerogel for ppm-level acetone sensing at room temperature described above in this invention can be further further described by using ammonia or urea as the pH-adjusting substance.

[0010] The preparation method of Cr / Fe2O3-rGO aerogel for ppm-level acetone sensing at room temperature described above in this invention can be further improved by having the ultrasonic treatment time in step 4) be 1-2 hours.

[0011] The preparation method of Cr / Fe2O3-rGO aerogel for ppm-level acetone sensing at room temperature described above in this invention can be further described as follows: after mixing the precursor sol and GO suspension dispersion in step 5), the GO content is 5-20 wt%, and the ultrasonic treatment time is 20-30 min.

[0012] The preparation method of Cr / Fe2O3-rGO aerogel for ppm-level acetone sensing at room temperature described above in this invention can be further described as follows: the water / ethanol volume ratio in step 7) is 1:0.5-2; the alcohol is one or a combination of ethanol, methanol, n-pentanol or isopropanol.

[0013] The preparation method of Cr / Fe2O3-rGO aerogel for ppm-level acetone sensing at room temperature described above in this invention can be further described as having a heating rate of 2~10 ℃ / min.

[0014] Compared with the prior art, the present invention has the following advantages: The Cr / Fe₂O₃-rGO aerogel prepared by the method of this invention possesses high porosity and specific surface area. The Fe₂O₃ nanoparticles (10-30 nm) embedded in the rGO porous network provide more reactive sites for detection. The Cr / Fe₂O₃-rGO aerogel prepared by this method generates pn heterojunctions, inducing electron transport from Fe₂O₃ to rGO, thereby leading to pore electron recombination. This not only lowers the reaction temperature but also enhances the sensing capability, enabling ppm-level acetone sensing at room temperature. The Cr / Fe₂O₃-rGO aerogel material prepared by this method exhibits self-healing capabilities, high stability, and maintains its detection performance under certain deformation and other mechanical damage, aligning with the principles of green chemistry. Detailed Implementation

[0015] Example 1

[0016] Take 20 mL of GO dispersion (4 mg / mL) and sonicate for 1 hour to ensure uniform dispersion (Cr:Fe = 1:10). Dissolve 4.04 g (10 mmol) of ferric nitrate (Fe(NO3)3·9H2O), 0.238 g (1 mmol) of chromium nitrate (Cr(NO3)3·9H2O), and 2.1 g (10 mmol, 1:1 molar ratio with metal ions) in a water-ethanol mixture (solvent: 30 mL deionized water 10 mL ethanol) at 50 °C for 30 minutes until completely dissolved. Adjust the pH to 4.0 ± 0.5 by adding ammonia dropwise, and the solution gradually turns into a reddish-brown transparent sol. Mix the precursor sol with the rGO suspension (rGO content 5 wt%) and sonicate for 30 minutes. Transfer to a 60 °C water bath and allow to gel (approximately 2-4 hours) to form a black, blocky wet gel. Age the wet gel in the mother liquor for 24 hours to enhance its mechanical strength. Subsequently, ion exchange was performed using deionized water and ethanol at a volume ratio of 1:0.5, three times a day for 5 days, followed by freeze-drying for 12 hours to obtain Cr / Fe2O3-GO aerogel. Finally, it was annealed in a tube furnace under N2 atmosphere at 300℃ with a heating rate of 2℃ / min for 2 hours to obtain Cr / Fe2O3-rGO aerogel. The response intensity was 8.2 and the response / recovery time was 12 / 18 s when tested with 10 ppm acetone. Example 2

[0017] Take 20 mL of GO dispersion (4 mg / mL) and sonicate for 1 hour to ensure uniform dispersion (Cr:Fe = 1:10). Dissolve 2.70 g (10 mmol) of ferric chloride (FeCl3·6H2O), 0.238 g (1 mmol) of chromium nitrate (Cr(NO3)3·9H2O), and 2.1 g (10 mmol, 1:1 molar ratio with metal ions) in a water-ethanol mixture (solvent: 30 mL deionized water 10 mL ethanol) and stir at 60°C for 30 minutes until completely dissolved. Adjust the pH to 4.0 ± 0.5 by adding ammonia dropwise, and the solution gradually turns into a reddish-brown transparent sol. Mix the precursor sol with the rGO suspension (rGO content 10 wt%) and sonicate for 20 minutes. Transfer to a 60°C water bath and allow to gel (approximately 2-4 hours) to form a black, blocky wet gel. Age the wet gel in the mother liquor for 24 hours to enhance its mechanical strength. Subsequently, ion exchange was performed using deionized water and ethanol at a volume ratio of 1:1 three times a day for 5 days, followed by freeze-drying for 12 hours to obtain Cr / Fe2O3-GO aerogel. Finally, it was annealed in a tube furnace under N2 atmosphere at 300℃ with a heating rate of 5℃ / min for 3 hours to obtain Cr / Fe2O3-rGO aerogel. Under the same 10ppm acetone, the response value increased to 9.5, and the response time of 10s and recovery time of 16s were both improved. Example 3

[0018] Take 20 mL of GO dispersion (4 mg / mL) and sonicate for 1 hour to ensure uniform dispersion (Cr:Fe = 1:15). Dissolve 6.06 g (10 mmol) of ferric nitrate (Fe(NO3)3·9H2O), 0.238 g (1 mmol) of chromium nitrate (Cr(NO3)3·9H2O), and 2.1 g (10 mmol, 1:1 molar ratio with metal ions) in a water-ethanol mixture (solvent: 30 mL deionized water 10 mL ethanol) and stir at 60°C for 30 minutes until completely dissolved. Adjust the pH to 3.0 ± 0.5 by adding ammonia dropwise, and the solution gradually turns into a reddish-brown transparent sol. Mix the precursor sol with the rGO suspension (rGO content 20 wt%) and sonicate for 30 minutes. Transfer to a 60°C water bath and allow to gel (approximately 2-4 hours) to form a black, blocky wet gel. Age the wet gel in the mother liquor for 24 hours to enhance its mechanical strength. Subsequently, ion exchange was performed using deionized water and ethanol at a volume ratio of 1:2 for 5 days, three times a day, followed by freeze-drying for 12 hours to obtain Cr / Fe2O3-GO aerogel. Finally, it was annealed in a tube furnace under N2 atmosphere at 300℃ with a heating rate of 10℃ / min for 2 hours to obtain Cr / Fe2O3-rGO aerogel. Under the same conditions, the experimental results actually decreased to 7.8, with a response / recovery time of 14s / 20. Example 4

[0019] Take 20 mL of GO dispersion (4 mg / mL) and sonicate for 1 hour to ensure uniform dispersion (Cr:Fe = 1:20). Dissolve 8.08 g (20 mmol) of ferric nitrate (Fe(NO3)3·9H2O), 0.238 g (1 mmol) of chromium nitrate (Cr(NO3)3·9H2O), and 2.1 g (10 mmol, 1:1 molar ratio with metal ions) in a water-ethanol mixture (solvent: 30 mL deionized water 10 mL ethanol) and stir at 70°C for 30 minutes until completely dissolved. Adjust the pH to 4.0 ± 0.5 by adding ammonia dropwise, and the solution gradually turns into a reddish-brown transparent sol. Mix the precursor sol with the rGO suspension (rGO content 5 wt%) and sonicate for 25 minutes. Transfer to a 60°C water bath and allow to gel (approximately 2-4 hours) to form a black, blocky wet gel. Age the wet gel in the mother liquor for 24 hours to enhance its mechanical strength. Subsequently, ion exchange was performed using deionized water and ethanol at a volume ratio of 1:0.5 three times a day for 5 days, followed by freeze-drying for 12 hours to obtain Cr / Fe2O3-GO aerogel. Finally, it was annealed in a tube furnace under N2 atmosphere at 300℃ with a heating rate of 2℃ / min for 1.5 hours to obtain Cr / Fe2O3-rGO aerogel. The response to acetone at 10 ppm was 8.6, and the response recovery time ratio was 11 / 17 s.

Claims

1. A method for preparing Cr / Fe2O3-rGO aerogel for ppm-level acetone sensing at room temperature, characterized in that, Includes the following steps: 1) Dissolve the iron salt and chromium salt separately in a water / ethanol mixture to form a transparent solution; 2) Mix the iron and chromium salt transparent solutions prepared in step 1), add the chelating agent after mixing evenly, and heat and stir in a water bath to form a transparent solution; 3) Adjust the pH of the transparent solution from step 2) to 3-5 to form a stable sol and obtain the precursor; 4) The GO dispersion was ultrasonically treated to achieve uniform dispersion, thus obtaining a GO suspension dispersion; 5) Mix the GO dispersion obtained in step 4) with the precursor obtained in step 3) and sonicate. 6) Heat the mixture from step 5) to 60-80°C or let it stand to initiate gelation and form a three-dimensional network structure to obtain a gel; 7) The gel obtained in step 6) is subjected to ion exchange with a water / alcohol mixture for more than 5 days, with 3 exchanges per day, to obtain a sol; 8) The sol obtained in step 7) is subjected to supercritical drying to obtain Cr / Fe2O3-GO composite aerogel; 9) Place the Cr / Fe2O3-GO composite aerogel obtained in step 8) into a tube furnace, introduce inert gas N2, and anneal at 300℃ for 2 hours to obtain Cr / Fe2O3-rGO composite aerogel.

2. The method for preparing Cr / Fe2O3-rGO aerogel for ppm-level acetone sensing at room temperature according to claim 1, characterized in that, The iron salt is Fe(NO3)3·9H2O or FeCl3·6H2O; the chromium salt is Cr(NO3)3·9H2O or CrCl3; the iron and chromium salts in the transparent solution contain Fe 3+ and Cr 3+ The concentration is 0.5 mol / L-1.0 mol / L, and the Cr:Fe molar ratio is 1:5-20, and the water / alcohol volume ratio mentioned in step 1) is 1:

3.

3. The method for preparing Cr / Fe2O3-rGO aerogel for ppm-level acetone sensing at room temperature according to claim 1, characterized in that, The chelating agent is citric acid or ethylene glycol, and the chelating agent reacts with Fe. 3+ and Cr 3+ The total molar ratio of metal ions is 1:1; the water bath heating temperature is 50-70℃.

4. The method for preparing Cr / Fe2O3-rGO aerogel for ppm-level acetone sensing at room temperature according to claim 1, characterized in that, The substance used to adjust the pH value is ammonia or urea.

5. The method for preparing Cr / Fe2O3-rGO aerogel for ppm-level acetone sensing at room temperature according to claim 1, characterized in that, The ultrasonic treatment time described in step 4) is 1-2 hours.

6. The method for preparing Cr / Fe2O3-rGO aerogel for ppm-level acetone sensing at room temperature according to claim 1, characterized in that, In step 5), the precursor sol and GO suspension dispersion are mixed, and the GO content is 5-20 wt%. The ultrasonic treatment time is 20-30 min.

7. The method for preparing Cr / Fe2O3-rGO aerogel for ppm-level acetone sensing at room temperature according to claim 1, characterized in that, The water / ethanol volume ratio mentioned in step 7) is 1:0.5-2; the alcohol is one or a combination of ethanol, methanol, n-pentanol or isopropanol.

8. The method for preparing Cr / Fe2O3-rGO aerogel for ppm-level acetone sensing at room temperature according to claim 1, characterized in that, The heating rate is 2~10 ℃ / min.