High-entropy tungstate or molybdate material for radiation refrigeration

Abstract

The invention relates to a high-entropy tungstate or molybdate material for radiation refrigeration, the high-entropy tungstate or molybdate material has a yellow tungsten ore structure, the chemical formula is (A1xA2yA3zA4uA5v) WO4 and (A1xA2yA3zA4uA5v) MoO4, A1, A2, A3, A4 and A5 are any five elements of Ba, Sr, Ca, Pb, Zn and Cd, and the dodecahedral position of the A position in the yellow tungsten ore structure is occupied by positive ions with large radius; a site A is tetrahedral coordination, B site is tetrahedral coordination, and a [BO4] tetrahedral framework is formed through the B site and metal elements to connect the A site and the B site. Meanwhile, the invention further discloses a preparation method of the high-entropy tungstate or molybdate material. The preparation method is simple and easy to operate and high in production efficiency, and the obtained high-entropy tungstate / molybdate material can be applied to the fields of buildings, personal thermal management, photovoltaic cooling and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of radiation refrigeration, and in particular to a high-entropy tungstate or molybdate for radiation refrigeration. BACKGROUND

[0002] In the context of global warming and increasingly severe weather, the adverse effects of environmental problems are becoming more and more serious. As a new passive cooling technology, radiation refrigeration is proposed as a potential solution to offset global warming. In recent years, radiation refrigeration materials have made significant progress in energy-saving buildings, personal thermal management, photovoltaic cooling and other fields, especially in dynamic regulation, due to their zero-energy thermal management capability and excellent cost-effectiveness. Radiation refrigeration materials are affected by solar radiation and atmospheric radiation in practical applications. Among them, the solar radiation spectrum is mainly concentrated in 0.3 ~ 2.5 μm, which is similar to the spectrum of an ideal 5800K black body, and the difference is mainly caused by atmospheric absorption. Therefore, reducing the absorption in this band is the key to achieving radiation refrigeration during the day. In addition, in the atmospheric transparent window (8 ~ 13 μm), the heat of the object can be directly radiated to outer space, and the solar heat absorption is minimized, thereby providing natural cooling. Therefore, to achieve effective daytime radiation refrigeration, the material needs to meet two key optical properties: (1) high emissivity in the atmospheric window band (8 ~ 13 μm); (2) ultra-high reflectivity in the solar spectrum band (0.3 ~ 2.5 μm).

[0003] Currently, tungstate / molybdate materials (such as BaWO4, CaMoO4, and Nd6MoO 12 binary oxides) face core challenges in the field of radiation refrigeration. The single-component characteristics make it difficult to simultaneously achieve high solar reflectivity and high atmospheric window emissivity, and the multi-band optical properties cannot be independently regulated. In addition, the band gap regulation of single-component materials is limited, and the lattice vibration mode is single, resulting in generally low reflectivity in the solar spectrum band and low emissivity in the atmospheric window band. For example, Yang et al. reported that the near-infrared reflectivity of Nd6MoO 12 material is only 85.63%.

[0004] It is worth noting that the research and application of traditional tungstate / molybdate are mainly concentrated in the fields of photocatalysis, electrochemistry, fluorescence, sensors, pigments, and corrosion prevention, and there is little exploration in the direction of radiation refrigeration. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a high-entropy tungstate or molybdate material for radiation refrigeration.

[0006] In order to solve the above problems, the high-entropy tungstate or molybdate material for radiation refrigeration has the following characteristics: the high-entropy tungstate or molybdate material has a wolframite structure, and a chemical formula is (A 1x A 2y A 3z A 4u A 5v )WO4 and (A 1x A 2y A 3z A 4u A 5v )MoO4, wherein A1, A2, A3, A4 and A5 are any five elements in Ba, Sr, Ca, Pb, Zn and Cd, the molar ratio of metal atoms is x:y:z:u:v:1, and x+y+z+u+v=1; the A-site dodecahedron site in the wolframite structure is occupied by a cation with a larger radius; the B-site is tetrahedral coordination, and a [BO4] tetrahedral framework is formed by the B-site and metal elements to connect the A-site and the B-site.

[0007] The material has a band gap Eg approximately equal to 4.5-5.2 eV, a reflectivity greater than or equal to 93% in a 0.3-2.5 mu m wave band, and a radiation emissivity greater than or equal to 0.93 in an 8-13 mu m atmospheric window region.

[0008] The preparation method of the high-entropy tungstate or molybdate material for radiation refrigeration has the following characteristics: any five of BaO, SrO, CaO, PbO2, ZnO and CdO powders and MoO2 or WO2 are used as raw materials, ball milling is performed according to the molar ratio of metal atoms x:y:z:u:v:1 and x+y+z+u+v=1, and the mixture powder is obtained after drying and grinding; the mixture powder is calcined at a high temperature in a muffle furnace in an air atmosphere, and the high-entropy tungstate or molybdate material with a wolframite structure is obtained after cooling to room temperature.

[0009] The ball milling condition is that wet ball milling is performed by using a planetary ball mill, deionized water and zirconium balls are used as the ball milling medium, the ball milling speed is 300-500 r / min, the ball milling time is 10-15 hours, and the mass ratio of balls:material:deionized water is 2-5:1:3.

[0010] The high-temperature calcination condition is that the calcination temperature is 1000-1500 DEG C, the heating rate is 3-5 DEG C / min, and the calcination time is 4-8 hours.

[0011] The cooling mode is one of furnace cooling, air quenching cooling and liquid nitrogen quenching cooling.

[0012] Compared with the prior art, the present application has the following advantages: 1、The application utilizes high-entropy strategy to modify traditional tungstate / molybdate materials, endowing them with excellent radiative cooling performance, reflectivity ≥ 93% in the 0.3 ~ 2.5 μm wave band, and radiative emissivity ≥ 0.93 in the 8 ~ 13 μm atmospheric window region. This is because the doping of multiple main elements of transition metals and rare earth metals changes the coordination number around the anion group (WO4 2- / MoO4 2- ), adjusts the electron cloud distribution and energy level structure of the central ion, reduces visible light absorption, and improves reflectivity. In addition, due to the difference between the sizes of the elements, the introduction of multiple heterogeneous cations produces a lattice distortion effect, and the lattice distortion enhances the non-harmonic phonon vibration, activates more abundant phonon modes, and promotes photon emission in the mid-infrared wave band (8 ~ 13 μm), so that the material can efficiently radiate heat through the atmospheric window.

[0013] 2、Compared with traditional tungstate / molybdate materials, the high-entropy tungstate / molybdate material widens the material band gap in the high-entropy process. This is due to the doping of multiple elements and the precise regulation of the material band gap. For example, high electronegativity cations (such as Zn 2+ ) enhance the bonding strength with O 2- , increase the conduction band energy, cause the band gap to widen, and the band gap Eg ≈ 4.5 ~ 5.2 eV. By introducing a wide band gap component (such as ZnO), the band gap is increased, the ultraviolet extinction coefficient is reduced (close to 0), and the high refractive index (n > 1.8) is maintained to enhance reflection. This wide band gap helps to improve the reflectivity in the visible-near infrared wave band (0.3 ~ 2.5 μm) and effectively reduce solar radiation heat absorption.

[0014] 3、The high-entropy tungstate / molybdate material described in the application realizes the synergistic optimization of "wide reflection-strong radiation" of tungstate / molybdate materials in radiative cooling through multi-element synergistic lattice regulation. Due to the radius difference (Δr > 15%) and random occupation of multiple cations (such as Ba 2+ , Zn 2+ , Pb 2+ , etc.), the local stress of the lattice is accumulated, the symmetry vibration mode of the W(Mo)-O bond is broken, and a local strain field is formed. The lattice distortion significantly enhances the photon emission efficiency in the mid-infrared wave band (8 ~ 13 μm) and enhances its emissivity.

[0015] 4、The high-entropy tungstate / molybdate material described in the application has excellent high-temperature thermal stability, as indicated by the 12-hour 1600 ℃ thermal stability experiment, with a change in emissivity within 0.01.

[0016] 5. The preparation method of this invention is simple and easy to operate, has high production efficiency, and does not require complicated post-processing. It is suitable for industrial production. The resulting high-entropy tungstate / molybdate material has the characteristics of single phase, high purity and uniform element distribution, and can be applied to fields such as energy buildings, personal thermal management, and photovoltaic cooling. Attached Figure Description

[0017] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0018] Figure 1 This is Example 1 of the present invention (Ba 0.2 Sr 0.2 Ca 0.2 Pb 0.2 Zn 0.2 XRD pattern of WO4.

[0019] Figure 2 This is Example 1 of the present invention (Ba 0.2 Sr 0.2 Ca 0.2 Pb 0.2 Zn 0.2 Infrared radiation spectrum of WO4 in the 0.3~2.5 μm band. Detailed Implementation

[0020] A high-entropy tungstate or molybdate material for radiation cooling, the high-entropy tungstate or molybdate material having a pyrrolidite structure and the chemical formula (A) 1x A 2y A 3z A 4u A 5v )WO4 and (A 1x A 2y A 3z A 4u A 5v MoO4, where A1, A2, A3, A4, and A5 are any five elements selected from Ba, Sr, Ca, Pb, Zn, and Cd, with a metal atom molar ratio of x:y:z:u:v:1, and x+y+z+u+v=1; the dodecahedral sites at the A sites in the chalcedony structure are occupied by cations with larger radii (such as alkaline earth metals Ba). 2+ 、Sr 2+ Ca 2+ or Pb 2+ The B site occupies the space; the B site is a tetrahedral coordination site, which forms a [BO4] tetrahedral framework with the metal element through the B site, connecting the A site and the B site.

[0021] The material has a band gap Eg ≈ 4.5 ~ 5.2 eV, a reflectivity ≥ 93% in a 0.3 ~ 2.5 μm waveband, and a radiation emissivity ≥ 0.93 in an 8 ~ 13 μm atmospheric window region.

[0022] A preparation method of a high-entropy tungstate or molybdate material for radiation refrigeration, the method being that any five of BaO, SrO, CaO, PbO2, ZnO, CdO powders and MoO2 or WO2 are used as raw materials, a planetary ball mill is used to mix the raw materials by wet ball milling according to a metal atom molar ratio x:y:z:u:v:1, and x+y+z+u+v=1, a deionized water and zirconium balls are used as the ball milling medium, the ball milling speed is 300-500 r / min, the ball milling time is 10-15 hours, and the mass ratio (g / g) of the ball:the material:the deionized water is 2-5:1:3. After the mixing is completed, the mixture is dried at 80-100 ℃ until the weight is constant, and then the mixture powder is obtained after grinding; the mixture powder is calcined at a high temperature in a muffle furnace in an air atmosphere, the calcination temperature is 1000-1500 ℃, the temperature rising rate is 3-5 ℃ / min, and the calcination time is 4-8 hours. Finally, one of the cooling methods of cooling in the furnace, air quenching and liquid nitrogen quenching is used to cool to room temperature, and the high-entropy tungstate or molybdate material with a wolframite structure is obtained.

[0023] Example 1: A preparation method of a high-entropy tungstate material for radiation refrigeration: BaO (0.2 mol), SrO (0.2 mol), CaO (0.2 mol), PbO2 (0.2 mol), ZnO (0.2 mol) and WO2 (1 mol) powders are respectively weighed according to a metal atom molar ratio of 0.2:0.2:0.2:0.2:0.2:1; zirconium oxide balls, the raw materials and anhydrous ethanol are respectively poured into a planetary ball mill, and the mass ratio (g / g) of the ball:the material:deionized water is 2:1:3. First, 1 hour of ball milling is performed at a speed of 300 r / min, then a pause of 10 min is made, and this is one ball milling period. After 10 min, 1 hour of ball milling is performed again at a speed of 300 r / min, and the total ball milling time is 14 hours. The obtained mixed powder is dried and ground to obtain a mixture powder; the mixture powder is calcined at a high temperature in a muffle furnace in an air atmosphere, the calcination temperature is 1300 ℃, the temperature rising rate is 4 ℃ / min, and the calcination time is 6 hours. After the calcination, liquid nitrogen quenching is performed to cool to room temperature, and a single-phase (Ba 0.2 Sr 0.2 Ca 0.2 Pb 0.2 Zn 0.2 )WO4 high-entropy tungstate material is obtained.

[0024] Figure 1 The (Ba 0.2Sr 0.2 Ca 0.2 Pb 0.2 Zn 0.2 The XRD pattern of the WO4 high-entropy tungstate material is shown. The spectrum is in excellent agreement with the spectrum of scheelite structure in the ICDD database (PDF#35-0765), indicating that the prepared high-entropy tungstate material has a scheelite structure.

[0025] For the obtained (Ba 0.2 Sr 0.2 Ca 0.2 Pb 0.2 Zn 0.2 Radiation performance evaluation of WO4 high-entropy tungstate materials: Test methods: The emissivity of the sample in the 8–13 μm band was measured using a Japanese TSS-5X infrared radiation meter. The reflectance spectrum in the 0.3–2.5 μm band was measured using a US Lambda 950 UV-Vis-NIR spectrophotometer (including a 150 mm integrating sphere).

[0026] The amount of test sample used was 0.2g.

[0027] The results are as follows Figure 2 As shown, the (Ba) 0.2 Sr 0.2 Ca 0.2 Pb 0.2 Zn 0.2 The WO4 high-entropy tungstate material has a reflectivity of 0.93 in the 0.3 ~ 2.5 μm band and a radiative emissivity of 0.93 in the 8 ~ 13 μm atmospheric window region, with a band gap of Eg = 4.5 eV.

[0028] The prepared high-entropy tungstate material was placed in an air atmosphere in a box furnace and subjected to a thermal stability test at 1600 °C for 12 hours. The results showed that the high-entropy tungstate material maintained a stable crystal structure after the thermal stability test, with an emissivity variation within the range of 0.01.

[0029] Example 2: A method for preparing a high-entropy molybdate material for radiation cooling: BaO (0.2 mol), SrO (0.2 mol), CaO (0.2 mol), PbO2 (0.2 mol), CdO (0.2 mol) and MoO2 (1 mol) powders were weighed according to the molar ratio of metal atoms 0.2:0.2:0.2:0.2:0.2:1, respectively; zirconia balls, raw materials and anhydrous ethanol were poured into a planetary ball mill with a mass ratio (g / g) of ball / material / deionized water of 4:1:3. First, 1 hour of ball milling was performed at a speed of 500 r / min, then a 10 min pause was made, which was one ball milling cycle. After 10 min, 1 hour of ball milling was performed again at a speed of 500 r / min, and the total ball milling time was 10 hours. The obtained mixed powder was dried and ground to obtain a mixture powder; the mixture powder was calcined at a high temperature in a muffle furnace under an air atmosphere, the calcination temperature was 1500 ℃, the heating rate was 5 ℃ / min, and the calcination time was 4 hours. After calcination, air quenching was performed to cool to room temperature, thereby obtaining a single-phase (Ba 0.2 Sr 0.2 Ca 0.2 Pb 0.2 Cd 0.2 )MoO4 high-entropy molybdate material.

[0030] The obtained (Ba 0.2 Sr 0.2 Ca 0.2 Pb 0.2 Cd 0.2 )MoO4 high-entropy molybdate material was evaluated for infrared radiation performance and thermal stability performance: the test method and the amount of test sample were the same as in Example 1.

[0031] The results show that the reflectivity of the high-entropy molybdate material in the 0.3-2.5 μm wave band is 0.943, and the radiation emissivity in the 8-13 μm wave band is 0.946, indicating that the high-entropy molybdate material has a high infrared radiation rate in a wide wave band, and the band gap is Eg = 4.7 eV. After the thermal stability experiment, the crystal structure of the high-entropy tungstate material is stable, and the emissivity changes within a range of 0.01.

[0032] Example 3: A preparation method of a high-entropy tungstate material for radiation refrigeration: BaO (0.2 mol), SrO (0.2 mol), CaO (0.2 mol), PbO2 (0.2 mol), ZnO (0.2 mol), and WO2 (1 mol) powders were weighed according to a metal atomic molar ratio of 0.2:0.2:0.2:0.2:0.2:1. Zirconia balls, raw materials, and anhydrous ethanol were added to a planetary ball mill, with a ball / material / deionized water mass ratio (g / g) of 5:1:3. The milling was performed for 1 hour at 300 r / min, followed by a 10-min pause, constituting one milling cycle. This was repeated for another 1 hour at 300 r / min, for a total of 15 hours. The resulting mixed powder was dried and ground to obtain a final powder. This final powder was then calcined in an air atmosphere in a muffle furnace at a temperature of 1000 ℃, a heating rate of 3 ℃ / min, and a calcination time of 8 hours. After calcination, the material is cooled to room temperature in the furnace to obtain a single-phase (Ba) solution. 0.2 Sr 0.2 Ca 0.2 Pb 0.2 Zn 0.2 WO4 high-entropy tungstate material.

[0033] For the obtained (Ba 0.2 Sr 0.2 Ca 0.2 Pb 0.2 Zn 0.2 Infrared radiation performance and thermal stability of WO4 high-entropy tungstate material were evaluated: the test method and the amount of test sample were the same as in Example 1.

[0034] The results show that the high-entropy tungstate material has a reflectivity of 0.95 in the 0.3–2.5 μm band and an emissivity of 0.948 in the 8–13 μm band, with a band gap of Eg = 4.9 eV. After thermal stabilization experiments, the high-entropy tungstate material exhibits a stable crystal structure, with emissivity variations within 0.01.

[0035] Example 4: A method for preparing a high-entropy molybdate material for radiation cooling: BaO (0.2 mol), SrO (0.2 mol), CaO (0.2 mol), PbO2 (0.2 mol), CdO (0.2 mol) and MoO2 (1 mol) powders were weighed according to the molar ratio of metal atoms of 0.2:0.2:0.2:0.2:0.2:1, respectively; zirconia balls, raw materials and anhydrous ethanol were poured into a planetary ball mill with a mass ratio (g / g) of ball / material / deionized water of 4:1:3. First, 1 hour of ball milling was performed at a speed of 400 r / min, and then a pause of 10 min was made, which was one ball milling cycle. After 10 min, 1 hour of ball milling was performed again at a speed of 400 r / min, and the total ball milling time was 10 hours. The obtained mixed powder was dried and ground to obtain a mixture powder; the mixture powder was calcined at a high temperature in a muffle furnace under an air atmosphere, the calcination temperature was 1300 ℃, the heating rate was 4 ℃ / min, and the calcination time was 6 hours. After calcination, air quenching was performed to cool to room temperature, thereby obtaining a single-phase (Ba 0.2 Sr 0.2 Ca 0.2 Pb 0.2 Cd 0.2 )MoO4 high-entropy molybdate material.

[0036] The obtained (Ba 0.2 Sr 0.2 Ca 0.2 Pb 0.2 Cd 0.2 )MoO4 high-entropy molybdate material was evaluated in terms of infrared radiation performance and thermal stability performance: the test method and the amount of test sample were the same as in Example 1.

[0037] The results show that the reflectivity of the high-entropy molybdate material in the 0.3-2.5 μm wave band is 0.96, the radiation emissivity in the 8-13 μm wave band is 0.955, and the band gap is Eg = 5.2 eV. After the thermal stability experiment, the crystal structure of the high-entropy tungstate material is stable, and the emissivity changes within a range of 0.01.

[0038] The above only describes the best embodiments of the present application, but cannot be understood as a limitation on the claims. The present application is not limited to the above embodiments, and the specific structure allows changes. Any changes made within the protection scope of the independent claims of the present application are within the protection scope of the present application.

Claims

1. A high-entropy tungstate or molybdate material for radiative cooling, characterized by: The high-entropy tungstate or molybdate material has a wolframite structure, and a chemical formula of (A 1x A 2y A 3z A 4u A 5v )WO4 and (A 1x A 2y A 3z A 4u A 5v )MoO4, wherein A1, A2, A3, A4, A5 are any five elements in Ba, Sr, Ca, Pb, Zn, Cd, the molar ratio of metal atoms is x:y:z:u:v:1, and x+y+z+u+v=1; the A-site dodecahedron site in the wolframite structure is occupied by a cation with a larger radius; the B-site is tetrahedral coordination, and a [BO4] tetrahedral framework is formed by the B-site and metal elements, connecting the A-site and the B-site.

2. A high-entropy tungstate or molybdate material for radiative refrigeration as claimed in claim 1, characterized in that: The material has a band gap Eg approximately equal to 4.5-5.2 eV, a reflectivity greater than or equal to 93% in a 0.3-2.5 mu m wave band, and a radiation emissivity greater than or equal to 0.93 in an 8-13 mu m atmospheric window region.

3. A method of producing a high-entropy tungstate or molybdate material for radiative cooling according to claim 1 or 2, characterized in that: The method is characterized by the following steps: taking any five of BaO, SrO, CaO, PbO2, ZnO and CdO powders and MoO2 or WO2 as raw materials, ball-milling the raw materials according to a metal atom molar ratio x:y:z:u:v:1, and x+y+z+u+v=1, drying and grinding the ball-milled mixture to obtain a mixture powder, and calcining the mixture powder at high temperature in a muffle furnace in an air atmosphere, and cooling to room temperature to obtain a high-entropy tungstate or molybdate material with a wolframite structure.

4. A method of producing a high-entropy tungstate or molybdate material for radiative cooling as claimed in claim 3, characterised in that: The ball-milling condition is that wet ball-milling is carried out by using a planetary ball mill, deionized water and zirconium balls as the ball-milling medium, a ball-milling speed of 300-500 r / min, a ball-milling time of 10-15 hours, and a mass ratio of balls:material:deionized water of 2-5:1:

3.

5. A method of producing a high-entropy tungstate or molybdate material for radiative cooling as claimed in claim 3, characterized in that: The high-temperature calcination condition is that the calcination temperature is 1000-1500 DEG C, the temperature rising rate is 3-5 DEG C / min, and the calcination time is 4-8 hours.

6. A method of producing a high-entropy tungstate or molybdate material for radiative cooling as claimed in claim 3, characterized in that: The cooling mode is one of furnace cooling, air quenching cooling and liquid nitrogen quenching cooling.

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