A selective absorption membrane, its preparation method and application

Abstract

This application discloses a selective absorption membrane, its preparation method, and its application, belonging to the field of solar thermal collection technology. The selective absorption membrane is prepared by anodic etching of copper foil in sodium hydroxide, sodium citrate, and copper sulfate. Compared with vacuum deposition, this preparation method uses readily available raw materials, is simple to operate, and is low in cost. Furthermore, the prepared selective absorption membrane exhibits higher absorptivity in the short-wavelength region, which is beneficial for improving photothermal conversion efficiency. When used in the preparation of solar thermal collectors, it can quickly and efficiently convert solar energy into thermal energy. Photothermal biochar prepared from anaerobic fermentation sludge exhibits excellent adsorption performance. Its application in wastewater treatment forms a closed-loop process of "carbon source capture – anaerobic fermentation – photothermal carbonization," significantly improving the biogas yield and organic matter degradation efficiency of the anaerobic fermentation system.

Description

Technical Field

[0001] This application belongs to the field of solar thermal collection technology, specifically relating to a selective absorption membrane, its preparation method, and its application. Background Technology

[0002] With the rapid depletion of non-renewable energy sources such as fossil fuels and the increasing prominence of environmental problems such as the greenhouse effect, the transition of traditional energy sources has received widespread global attention. Solar energy is an ideal and clean new and renewable energy source. As one of the largest green energy sources, solar energy products, such as solar cells and solar water heaters, have penetrated into all aspects of production and daily life in recent years. Compared to photovoltaic applications, broad-spectrum absorption solar thermal applications can utilize solar energy more efficiently. In solar thermal utilization technology, solar thermal collectors are crucial devices for converting solar radiation into heat energy. Commonly available solar thermal collectors include vacuum tube and flat-plate types. Regardless of the form of the solar thermal collector, its core component is a solar selective absorption film (selective absorption coating), which can quickly absorb sunlight (solar radiation) and convert light energy into heat energy, making it the most critical part of solar thermal conversion.

[0003] Solar radiation emits energy into space in the form of electromagnetic waves. According to Maxwell's theory of electromagnetism, electromagnetic waves can be classified by frequency and further subdivided by energy level, ranging from gamma rays to radio waves. Sunlight reaching Earth is a phenomenon where light quanta transfer energy in the form of electromagnetic radiation, with its electromagnetic spectrum primarily concentrated in the ultraviolet-visible-near-infrared region (UV-Vis-NIR) with wavelengths of approximately 0.3–2.0 μm. Simultaneously, high-temperature objects spontaneously generate thermal radiation into their colder environments, with their common electromagnetic spectrum concentrated in the mid-far-infrared region (approximately 2.5–25 μm). Furthermore, when sunlight strikes an object, absorption, reflection, and transmission occur; the total energy of solar radiation is the sum of absorbed, reflected, and transmitted energy. When an object is opaque, the total energy of solar radiation is the sum of absorbed and reflected energy.

[0004] Currently, commercially available high-selectivity thermal absorption coatings are mainly TiNOX coatings (nitride oxide coatings formed by the chemical reaction of titanium metal and reactive gases). Because they exhibit a blue color and are obtained through vacuum deposition, they are called "blue films." The blue color is due to their low absorption of blue light with wavelengths around 0.450–0.495 μm, thus reflecting the blue light. Further research by the applicant revealed that the absorption rate decreases rapidly in the short-wavelength region, which significantly contributes to photothermal conversion efficiency, indicating that it fails to fully utilize higher-energy photons. Therefore, it is necessary to further investigate selective absorption films with higher absorption rates in the short-wavelength region.

[0005] Anaerobic-Anoxic-Oxic process (A 2 The aerobic-orthogonal (AO) process is a mainstream technology in my country's urban wastewater treatment sector, with over 60% of wastewater treatment plants relying on it to achieve compliant wastewater discharge. However, this process faces two key challenges: First, its organic matter removal is highly dependent on the aerobic aeration process, which accounts for 50% to 60% of the system's total energy consumption, constituting a significant portion of A... 2 The / O process is a significant source of indirect carbon emissions; secondly, the process generates a large amount of residual sludge with a long disposal chain, resulting in a significant carbon footprint (approximately 372.9 kg CO2 / t DS) and generally low energy conversion efficiency, further exacerbating the overall carbon footprint. High carbon load and residual sludge disposal issues jointly constrain the development of A 2 Low-carbon transformation of the / O process. Therefore, it is particularly important to develop a wastewater treatment process that can simultaneously address high carbon loads and excess sludge. Summary of the Invention

[0006] 1. Purpose of the invention

[0007] Firstly, this application addresses the issue of low absorption rate in the short-wavelength region of commercially available "blue films" in the prior art by providing a novel selective absorption film, its preparation method, and its application. This selective absorption film exhibits higher absorption rate in the short-wavelength region (380~780nm), which is beneficial for improving photothermal conversion efficiency. Furthermore, compared to "vacuum deposition," the preparation method of this selective absorption film uses readily available raw materials and is simpler to operate. Its application in the fabrication of solar thermal collectors enables rapid and efficient conversion of solar energy into thermal energy.

[0008] Secondly, this application addresses existing A 2 To address the high carbon load and residual sludge disposal issues in the / O process, a photothermal biochar prepared using anaerobic fermentation sludge as raw material and a first-party solar thermal collector is proposed. When added to wastewater, this biochar can rapidly and efficiently adsorb organic pollutants, reducing A... 2 The organic load of the aerobic stage of the / O process is reduced. Simultaneously, the carbon-rich sludge after adsorbing organic matter is mixed with the remaining sludge from the biological treatment unit (anaerobic-anoxic-aerobic process) and subjected to anaerobic fermentation. The anaerobic fermented sludge is then reprocessed into photothermal biochar and added to the wastewater, forming a closed-loop treatment process of "carbon source capture - anaerobic fermentation - photothermal carbonization." This not only reduces the carbon footprint of the sludge treatment process but also improves its energy conversion efficiency.

[0009] 2. Technical Solution

[0010] To achieve the aforementioned objectives, the technical solution adopted in this application is as follows:

[0011] In a first aspect, this application provides a method for preparing a selective absorption membrane, the method comprising the following steps:

[0012] Using a copper foil as the anode and another conductive electrode as the cathode, both are immersed in an etching solution, and surface anodic etching is performed under constant current. The anodicly etched copper foil is then dried to obtain a selective absorption film. Wherein:

[0013] The etching solution contains the following components: 3.0 M to 10 M sodium hydroxide; 0.1 M to 1.0 M sodium citrate; 0.1 M to 1.0 M copper sulfate.

[0014] Furthermore, the etching solution contains the following components: 4.0 M to 6 M sodium hydroxide; 0.4 M to 0.6 M sodium citrate; and 0.4 M to 0.6 M copper sulfate.

[0015] Furthermore, the etching solution contains the following components: 5.0 M sodium hydroxide, 0.5 M sodium citrate, and 0.5 M copper sulfate.

[0016] Furthermore, the other conductive electrode mentioned above is a copper foil.

[0017] Furthermore, the thickness of the copper foil is 10~100 μm. Even further, the thickness of the copper foil is 50 μm.

[0018] Furthermore, the electrode spacing between the anode and cathode is 1-3 cm. Even further, the electrode spacing between the anode and cathode is 2 cm.

[0019] Furthermore, the aforementioned current is controlled by direct current, with a current density of 5 mA·cm⁻¹. -2 ~50 mA·cm -2 The etching time is 10~60 min.

[0020] Furthermore, the aforementioned current is controlled by direct current, with a current density of 10 mA·cm⁻¹. -2 ~40 mA·cm -2 The etching time is 10~40 min.

[0021] Furthermore, the aforementioned current is controlled by direct current, with a current density of 10 mA·cm⁻¹. -2 The etching time is 40 minutes.

[0022] Furthermore, the aforementioned current is controlled by direct current, with a current density of 20 mA·cm⁻¹. -2 The etching time is 20 minutes.

[0023] Furthermore, the aforementioned current is controlled by direct current, with a current density of 40 mA·cm⁻¹. -2 The etching time was 10 min. As a further explanation of this application, the selective absorption film prepared using these conditions not only has a high absorption rate in the short-wavelength region (380~780 nm), but also has a low emissivity in the long-wavelength region (3000~8000 nm).

[0024] Furthermore, the drying temperature mentioned above is 105~130℃.

[0025] Furthermore, the drying temperature mentioned above is 120°C.

[0026] Furthermore, the above drying method is vacuum drying.

[0027] Secondly, this application provides a selective absorption membrane prepared by any of the above-mentioned methods for preparing selective absorption membranes.

[0028] Furthermore, the above-mentioned selective absorption film has an average light absorption rate of ≥95% in the 380 nm to 780 nm spectral range.

[0029] Furthermore, the aforementioned selective absorption film has an average light emissivity of ≤20% in the 3.0 μm~8.0 μm spectral range, thereby maximizing photothermal conversion efficiency and minimizing thermal radiation loss.

[0030] Thirdly, this application also provides the application of the above-mentioned selective absorption membrane in the preparation of solar thermal collectors.

[0031] Furthermore, the aforementioned solar thermal collector includes:

[0032] A solar concentrator and a tubular reactor, with the tubular reactor fixedly installed in the focal region of the solar concentrator to receive the concentrated solar radiation;

[0033] The tubular reactor, from the inside out, includes:

[0034] The inner tube is made of transparent glass or quartz, and its interior forms a sealed chamber for placing the substance to be heated, such as solid reactants like biomass, and heating it to carry out a carbonization reaction.

[0035] The selective absorption layer, specifically the selective absorption film that wraps around the outer surface of the inner tube, is used to selectively absorb the solar spectrum and efficiently convert light energy into heat energy, thereby creating a high-temperature environment in the inner tube.

[0036] The outer tube, made of transparent glass, is coaxially mounted with the inner tube, providing mechanical protection and external isolation.

[0037] Furthermore, the aforementioned solar thermal collector also includes an infrared reflective layer disposed between the inner tube and the selective absorption layer, for reflecting infrared radiation to reduce heat loss.

[0038] Furthermore, the aforementioned infrared reflective layer is a metal or dielectric film deposited on the outer surface of the inner tube.

[0039] Furthermore, the aforementioned infrared reflective layer is a copper foil.

[0040] Furthermore, the aforementioned solar thermal collector also includes a high-vacuum interlayer disposed between the selective absorption layer and the outer tube, used to suppress convection and conduction heat loss.

[0041] Furthermore, the aforementioned high-vacuum interlayer is formed by encapsulating an inner tube and an outer tube together.

[0042] Furthermore, the aforementioned solar concentrator is a trough concentrator.

[0043] Fourthly, this application also provides a solar thermal collector, comprising:

[0044] A solar concentrator and a tubular reactor, with the tubular reactor fixedly installed in the focal region of the solar concentrator to receive the concentrated solar radiation;

[0045] The tubular reactor, from the inside out, includes:

[0046] The inner tube is made of transparent glass or quartz, and its interior forms a sealed chamber for placing the substance to be heated, such as solid reactants like biomass, and heating it to carry out a carbonization reaction.

[0047] The selective absorption layer, specifically the selective absorption film that wraps around the outer surface of the inner tube, is used to selectively absorb the solar spectrum and efficiently convert light energy into heat energy, thereby creating a high-temperature environment in the inner tube.

[0048] The outer tube, made of transparent glass, is coaxially mounted with the inner tube, providing mechanical protection and external isolation.

[0049] Furthermore, the aforementioned solar thermal collector also includes an infrared reflective layer disposed between the inner tube and the selective absorption layer, for reflecting infrared radiation to reduce heat loss.

[0050] Furthermore, the aforementioned infrared reflective layer is a metal or dielectric film deposited on the outer surface of the inner tube.

[0051] Furthermore, the aforementioned infrared reflective layer is a copper foil.

[0052] Furthermore, the aforementioned solar thermal collector also includes a high-vacuum interlayer disposed between the selective absorption layer and the outer tube, used to suppress convection and conduction heat loss.

[0053] Furthermore, the aforementioned high-vacuum interlayer is formed by encapsulating an inner tube and an outer tube together.

[0054] Furthermore, the aforementioned solar concentrator is a trough concentrator.

[0055] Fifthly, this application also provides the application of the above-mentioned selective absorption membrane or the above-mentioned solar thermal collector in the preparation of photothermal biochar.

[0056] Furthermore, the above applications include: placing the material to be carbonized in an inner tube and performing photothermal carbonization under light in an oxygen-deficient or oxygen-limited environment to prepare photothermal biochar. As a further explanation of this application, a solar thermal collector is placed in a solar environment. The selective absorption membrane absorbs the solar spectrum and efficiently converts light energy into heat energy, creating a high-temperature environment in the inner tube. The material to be carbonized undergoes a carbonization reaction to obtain photothermal biochar. The preparation of photothermal biochar is based on the principle of photothermal conversion. Specifically, when light irradiates the surface of the selective absorption membrane, electrons in the selective absorption membrane absorb photon energy and are excited to a high energy level. Subsequently, they transfer energy to the surrounding lattice through non-radiative transitions, intensifying lattice vibrations and generating heat, thus creating a high-temperature environment. Under this high-temperature environment, the material to be carbonized (such as biomass, organic polymers, etc.) placed in the solar thermal collector undergoes a carbonization reaction, removing volatile components and forming a carbon-rich solid product.

[0057] Sixthly, this application also provides a method for preparing photothermal biochar, the method comprising the following steps:

[0058] M1, take the residual sludge after the anaerobic-anoxic-aerobic process, ferment it in an anaerobic environment to produce biogas, obtain fermented biogas sludge, filter and dry the fermented biogas sludge and place it in the inner tube of the above-mentioned solar thermal collector, and carry out photothermal decomposition and carbonization under light conditions to prepare photothermal biochar.

[0059] M2, the photothermal biochar from the previous step is added to the wastewater and stirred to adsorb organic matter in the wastewater. After solid-liquid separation, carbon-rich sludge is obtained. The separated liquid is treated by a biological treatment unit (anaerobic-anoxic-aerobic process) to obtain residual sludge. The carbon-rich sludge and residual sludge are mixed and fermented in an anaerobic environment to produce biogas, obtaining fermented biogas sludge. The fermented biogas sludge is filtered and dried and placed in the inner tube of the solar thermal collector mentioned above. Photothermal decomposition and carbonization are carried out under light conditions to prepare photothermal biochar.

[0060] Furthermore, in the above-mentioned method for preparing photothermal biochar, the photothermal carbonization temperature is 300~500℃ and the time is 6~12 h. Even further, in the above-mentioned method for preparing photothermal biochar, the photothermal carbonization temperature is 410±10℃ and the time is 8±1 h.

[0061] Furthermore, in the above-mentioned method for preparing photothermal biochar, the ratio of the mass of dried fermented biogas sludge in the inner tube to the light-absorbing area of ​​the solar thermal collector is 1.0~10 g / cm³. 2 .

[0062] Furthermore, in the above-mentioned method for preparing photothermal biochar, the ratio of the mass of dried fermented biogas sludge in the inner tube to the light-absorbing area of ​​the solar thermal collector is 5 g / cm². 2 .

[0063] Furthermore, in the above-mentioned method for preparing photothermal biochar, the illumination is natural sunlight, and solar radiation is focused by a solar concentrator to raise the temperature inside the reactor to 300-500°C for the carbonization reaction. As a further explanation of this application, this application does not require specific light intensity indicators; the system can operate effectively under varying natural light conditions, for example, within the typical range of direct solar radiation intensity (e.g., 500 W / m²). 2 ~1000 W / m 2 The required carbonization temperature can be achieved by using this method.

[0064] Furthermore, the dosage ratio of the above-mentioned photothermal biochar to wastewater is 1.0~10 g / L.

[0065] Furthermore, the adsorption time is 2 to 2.5 hours.

[0066] Furthermore, in each of the above steps, the volume ratio of carbon-rich sludge to residual sludge is 1:1 to 1:10.

[0067] Furthermore, the temperature for biogas production during fermentation under the aforementioned anaerobic environment is 25~40℃, and the cycle is 10~30 days.

[0068] Seventhly, this application also provides photothermal biochar prepared by the above-mentioned method for preparing photothermal biochar.

[0069] Furthermore, the aforementioned photothermal biochar possesses at least one of the following characteristics:

[0070] Its Raman spectrum contains the D peak (~1350 cm⁻¹). -1 ) and G peak (~1590 cm) -1 The intensity ratio (ID / IG) of the graphitized microcrystalline structure is 0.85~0.90, indicating that it has a more ordered graphitized microcrystalline structure.

[0071] Its elemental composition shows that the H / C mass ratio is ≤0.10 and the aroma index (AI) is ≥1.70, indicating that it has a highly aromatic stable carbon skeleton; the O / C mass ratio is ≥0.60 and the (N+O) / C mass ratio is ≥0.75, indicating that its surface is rich in oxygen-containing functional groups.

[0072] As a further explanation of this application, the photothermal biochar, due to its special physicochemical properties, possesses both excellent adsorption performance and the ability to promote anaerobic microbial metabolism, making it suitable for carbon source adsorption in wastewater treatment and subsequent anaerobic fermentation to produce biogas.

[0073] Eighthly, this application also provides the application of the aforementioned photothermal biochar in wastewater treatment.

[0074] Furthermore, the above applications include: adding the aforementioned photothermal biochar to wastewater, stirring and mixing to adsorb organic matter in the wastewater, and then separating the solid and liquid to obtain carbon-rich sludge; as a further explanation of this application, the adsorption of organic matter in wastewater to form carbon-rich sludge is equivalent to adsorbing and removing organic matter from wastewater, reducing A 2 / O process aerobic section organic load; at the same time, "carbon-rich sludge" is a solid mixture formed by loading a large amount of organic matter onto photothermal biochar, which can provide a high concentration of carbon source for subsequent anaerobic fermentation.

[0075] Furthermore, the above applications include:

[0076] The above-mentioned photothermal biochar is added to the sewage and stirred to adsorb organic matter in the sewage. After solid-liquid separation, carbon-rich sludge is obtained. The separated liquid is treated by a biological treatment unit (anaerobic-anoxic-aerobic process) to obtain excess sludge. The carbon-rich sludge is mixed with the excess sludge and fermented in an anaerobic environment to produce biogas.

[0077] Furthermore, the above applications also include:

[0078] After fermentation to produce biogas, fermented biogas sludge is obtained. The fermented biogas sludge is filtered and dried and then placed in the inner tube of the above-mentioned solar thermal collector. Photothermal carbonization is carried out under light conditions to prepare photothermal biochar.

[0079] The prepared photothermal biochar is added to wastewater and stirred to adsorb organic matter. After solid-liquid separation, carbon-rich sludge is obtained. The separated liquid is treated by a biological treatment unit (anaerobic-anoxic-aerobic process) to obtain excess sludge. The carbon-rich sludge is mixed with the excess sludge and fermented under anaerobic conditions to produce biogas, obtaining fermented biogas sludge. The fermented biogas sludge is filtered, dried, and placed in the inner tube of the aforementioned solar thermal collector for photothermal carbonization under sunlight to prepare photothermal biochar. This step is repeated. As a further explanation of this application, the above steps realize the cyclical preparation and use of photothermal biochar, forming a "carbon source capture-anaerobic fermentation-photothermal carbonization" cycle. Through internal material circulation, the overall efficiency and economy of wastewater treatment and energy recovery are improved.

[0080] Furthermore, the dosage ratio of the above-mentioned photothermal biochar to wastewater is 1.0~10 g / L.

[0081] Furthermore, the adsorption time is 2 to 2.5 hours.

[0082] Furthermore, in each of the above steps, the volume ratio of carbon-rich sludge to residual sludge is 1:1 to 1:10.

[0083] Furthermore, the temperature for biogas production during fermentation under the aforementioned anaerobic environment is 25~40℃, and the cycle is 10~30 days.

[0084] Ninthly, this application also provides a wastewater treatment process, which includes the following steps:

[0085] S1. After the sewage enters, the remaining sludge after the biological treatment unit (anaerobic-anoxic-aerobic process) is taken and fermented in an anaerobic environment to produce biogas, and fermented biogas sludge is obtained. The fermented biogas sludge is filtered and dried and placed in the inner tube of the above-mentioned solar thermal collector. Photothermal carbonization is carried out under light conditions to prepare photothermal biochar.

[0086] S2, the photothermal biochar from the previous step is added to the wastewater and stirred to adsorb organic matter in the wastewater. After solid-liquid separation, carbon-rich sludge is obtained. The separated liquid is treated by a biological treatment unit (anaerobic-anoxic-aerobic process) to obtain residual sludge. The carbon-rich sludge and residual sludge are mixed and fermented in an anaerobic environment to produce biogas, obtaining fermented biogas sludge. The fermented biogas sludge is filtered and dried and placed in the inner tube of the solar thermal collector mentioned above. Photothermal carbonization is carried out under light conditions to prepare photothermal biochar.

[0087] S3, repeat step S2 in a loop.

[0088] Furthermore, the dosage ratio of the above-mentioned photothermal biochar to wastewater is 1.0~10 g / L.

[0089] Furthermore, the adsorption time is 2 to 2.5 hours.

[0090] Furthermore, in each of the above steps, the volume ratio of carbon-rich sludge to residual sludge is 1:1 to 1:10.

[0091] Furthermore, the temperature for biogas production during fermentation under the aforementioned anaerobic environment is 25~40℃, and the cycle is 10~30 days.

[0092] 3. Beneficial effects

[0093] Compared with the prior art, the advantages of this application are as follows:

[0094] (1) The present application provides a method for preparing a selective absorption film, in which a selective absorption film is prepared by anodic etching of copper foil in an etching solution of a specific composition (3.0 M~10 M sodium hydroxide, 0.1 M~1.0 M sodium citrate and 0.1 M~1.0 M copper sulfate). Compared with the preparation of selective absorption films by "vacuum deposition", this preparation method does not rely on expensive instruments and equipment such as vapor deposition, and the raw materials are readily available and the operation is simple, which greatly reduces the preparation cost of selective absorption films.

[0095] (2) The selective absorption membrane provided in this application has a higher absorption rate in the short-wavelength region (380~780 nm) compared with commercially available blue membranes. Further, with a current density of 40 mA·cm⁻¹ -2 The selective absorption film prepared under the condition of etching time of 10 min has low emissivity in the long-wavelength region (3000~8000 nm).

[0096] (3) An application of the selective absorption membrane provided in this application, which is used to prepare a solar thermal collector, including an inner tube, an infrared reflective layer, a selective absorption layer, a vacuum layer, and an outer tube, such as Figure 4 As shown, under sunlight, the temperature of the inner tube rises rapidly, from the ambient temperature (36°C) to about 350°C within 2 hours. The heating rate then slows down and reaches thermal equilibrium within 3 hours, with the temperature remaining stable between 400 and 500°C, effectively improving the photothermal conversion efficiency.

[0097] (4) The solar thermal collector provided in this application uses the dried fermented biochar prepared from the anaerobic fermentation of carbon-rich sludge and excess sludge as raw material. It has a more ordered graphitized microcrystalline structure and a highly aromatic stable carbon skeleton with oxygen-containing functional groups on the surface. These special physicochemical properties enable the solar thermal biochar prepared in this application to have both excellent adsorption performance and the ability to promote anaerobic microbial metabolism. It is suitable for carbon source adsorption in sewage treatment and subsequent anaerobic fermentation to produce biogas, further improving the carbon source capture rate and promoting the metabolism of anaerobic microorganisms.

[0098] (5) The wastewater treatment process provided in this application realizes a closed loop of "carbon source capture - anaerobic fermentation - photothermal carbonization". This process not only helps to reduce A 2 The organic load of the aerobic stage of the / O process can also improve the energy recovery efficiency of anaerobic fermentation for methanogenesis, significantly offsetting the A 2 The / O process reduces aeration energy consumption and the carbon footprint of residual sludge disposal, improves carbon resource recycling efficiency and energy recovery rate, and achieves low-carbon operation of the wastewater treatment process. Attached Figure Description

[0099] Figure 1 The images are scanning electron microscope (SEM) images, where: (a) is an SEM image of the selective absorption membrane prepared in Example 1; (b) is an SEM image of the selective absorption membrane prepared in Example 2; and (c) is an SEM image of the selective absorption membrane prepared in Example 3; the first column is 10 μm (×10000), the second column is 2 μm (×50000), and the third column is 1 μm (×100000).

[0100] Figure 2 The absorption spectra are shown below: (a) is the absorption spectrum of a conventional commercial TiNOX coating; (b) is the absorption spectrum of the selective absorption membrane prepared in Examples 1-3.

[0101] Figure 3 This is a schematic diagram of a solar thermal collector, where: 100, solar concentrator; 200, tubular reactor; 201, inner tube; 202, infrared reflective layer; 203, selective absorption layer; 204, high vacuum jacket; 205, outer tube.

[0102] Figure 4 This is the temperature rise curve of the inner tube of the solar thermal collector under actual solar radiation intensity.

[0103] Figure 5 Raman spectra and elemental analysis results of biochar produced by conventional tubular furnace and photothermal biochar prepared in Example 6, wherein: (a) is the Raman spectrum; (b) is the elemental composition and aromaticity index diagram.

[0104] Figure 6 The graph shows the adsorption efficiency of photothermal biochar carbon source, where (a) is the capture rate of photothermal biochar carbon source and (b) is the first-order kinetic fitting curve.

[0105] Figure 7 A graph showing biogas production and COD removal rate after adding photothermal biochar.

[0106] Figure 8 This is a process flow diagram of the closed-loop treatment process of "carbon source capture-anaerobic fermentation-photothermal carbonization" in this application. Detailed Implementation

[0107] The present application will be further described in detail below through specific embodiments, but the scope of protection of the present application is not limited thereto.

[0108] Unless otherwise specified, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0109] Unless otherwise specified, all conditions used in this application and in the examples are performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0110] As used herein, unless otherwise specified, concentration, amount, and other numerical data may be presented in range format. It should be understood that such range format is used only for convenience and brevity and should be flexibly interpreted to include not only the values ​​explicitly stated as the limits of the range, but also all individual values ​​or subranges covered within the range, as if each value and subrange were explicitly stated. For example, a range of values ​​from about 1 to about 4.5 should be interpreted to include not only the explicitly stated limits of 1 to 4.5, but also individual numbers (such as 2, 3, 4) and subranges (such as 1 to 3, 2 to 4, etc.). The same principle applies to ranges that describe only a single value, such as "less than about 4.5," which should be interpreted to include all the values ​​and ranges described above. Furthermore, this interpretation should apply regardless of the breadth of the range or characteristic described.

[0111] As used in this application, unless otherwise specified, "carbon footprint" refers to an indicator used to measure the total amount of greenhouse gas emissions, whether directly or indirectly generated, over a specific period of time.

[0112] As used in this application, unless otherwise specified, "photothermal carbonization" refers to the process of using the heat generated by the photothermal effect to pyrolyze organic solid waste (such as fermented sludge) under anaerobic or oxygen-limited conditions, thereby converting it into biochar.

[0113] As used in this application, unless otherwise specified, "photothermal biochar" refers to porous carbon material obtained by treating fermented biogas sludge (after drying) using photothermal carbonization technology.

[0114] As used in this application, unless otherwise specified, "fermented biogas sludge" refers to the semi-solid material remaining after biogas fermentation. It originates from the biogas fermentation process, specifically: under anaerobic conditions, microorganisms decompose and metabolize organic materials (such as livestock and poultry manure, crop straw, and organic matter in domestic sewage). This process mainly consists of four stages: hydrolysis, acidification, acetic acid production, and methanogenesis. Complex organic matter is first hydrolyzed into simple sugars, amino acids, and fatty acids. Then, it undergoes acidification to form volatile fatty acids. Acetic acid-producing bacteria then convert these into acetic acid, hydrogen, and carbon dioxide. Finally, methanogenic bacteria convert these products into biogas (mainly composed of methane and carbon dioxide). The solid and partially liquid substances that cannot be completely decomposed and converted form fermented biogas sludge.

[0115] As used in this application, unless otherwise specified, "copper foil" refers to a thin sheet material made of copper, typically ranging from a few micrometers to several hundred micrometers in thickness.

[0116] As used herein, unless otherwise specified, "surface anodic etching" refers to a technique for treating surfaces using electrochemical principles. Taking copper surface anodic etching as an example, the principle is as follows: copper material is placed as the anode in a specific electrolyte. After the power is turned on, the copper atoms on the anode undergo an oxidation reaction, losing electrons and becoming copper ions that enter the solution. On the cathode surface, cations in the solution gain electrons and undergo a reduction reaction. By controlling the electrolysis conditions, such as voltage, current, electrolyte composition and concentration, and temperature, the degree and pattern of etching on the copper surface can be precisely controlled.

[0117] As used in this application, unless otherwise specified, "average light absorption rate" refers to the average ratio of light energy absorbed by a material to incident light energy over a specific wavelength range or the full spectrum, reflecting the material's ability to absorb light.

[0118] As used in this application, unless otherwise specified, "average light emissivity" refers to the average ratio of the light energy actually emitted by a material at a certain temperature, within a specific wavelength range or the full spectrum, to the light energy emitted by a blackbody at the same temperature.

[0119] Example 1

[0120] This embodiment provides a method for preparing a selective absorption membrane and the selective absorption membrane prepared therefrom.

[0121] Its preparation method includes the following steps:

[0122] (1) Preparation of etching solution

[0123] Dissolve 73.55 g of sodium citrate (Na3C6H5O7) and 62.45 g of copper sulfate pentahydrate (CuSO4·5H2O) in approximately 400 mL of deionized water;

[0124] Slowly add 100.0 g of sodium hydroxide (NaOH) to about 80 mL of water, and after cooling, slowly pour it into the aforementioned solution while stirring;

[0125] The volume was adjusted to 500 mL to obtain a clear, deep blue etching solution with the following composition: 5.0 M NaOH, 0.5 M Na3C6H5O7, and 0.5 M CuSO4.

[0126] (2) Copper foil pretreatment

[0127] Take two pieces of pure copper foil (purity ≥99.9%) with a size of 5 cm × 5 cm and a thickness of 50 μm. Clean them sequentially with acetone, ethanol and deionized water for 10 minutes each to remove surface grease and impurities. After cleaning, dry them by blowing with nitrogen gas and set aside for later use.

[0128] (3) Anodizing etching

[0129] Two cleaned copper foils were used as the anode and cathode, respectively, and immersed parallel to each other in the etching solution (electrode spacing 2 cm). Anodizing etching was performed using a DC power supply in constant current mode. Specific parameters were as follows: current density 10 mA / cm². 2 The etching time was 40 min and the temperature was room temperature (25±2)℃.

[0130] (4) Post-processing

[0131] Remove the etched anode copper foil, rinse the surface with deionized water to remove residual etching solution, and then place it in a vacuum drying oven to dry at 120°C for 2 hours;

[0132] After drying, a selective absorption membrane with a black velvety surface structure is finally obtained.

[0133] Example 2

[0134] This embodiment provides a method for preparing a selective absorption membrane and the selective absorption membrane prepared therefrom.

[0135] The preparation method is the same as in Example 1, except that the current density in the anodic oxidation etching is 20 mA / cm². 2 The etching time is 20 minutes.

[0136] Example 3

[0137] This embodiment provides a method for preparing a selective absorption membrane and the selective absorption membrane prepared therefrom.

[0138] The preparation method is the same as in Example 1, except that the current density in the anodic oxidation etching is 40 mA / cm². 2 The etching time is 10 minutes.

[0139] Example 4

[0140] This embodiment provides structural and performance testing of the selective absorption membranes prepared in Examples 1-3.

[0141] (1) Structural inspection

[0142] The scanning electron microscope (SEM) images of the selective absorption membranes prepared in Examples 1-3 are shown below. Figure 1 As shown in (a), (b), and (c). Wherein:

[0143] Low-magnification SEM images (×10000) show the effect at 10 mA / cm². 2 At the given current density, the copper foil surface successfully underwent anodizing, forming a preliminary needle-like structure. However, the uniformity of these needle-like structures was generally poor, with some unstructured blank areas. Further high-resolution images (×100000) showed that these needle-like structures were relatively robust and independent, mostly exhibiting a clear cone or dagger shape, with a relatively wide base and a relatively sharp tip. The spacing between the needle-like structures was relatively large, and the overall structure was relatively loose with a weak three-dimensional effect.

[0144] When the current density is increased to 20 mA / cm 2 At that time, low-magnification SEM images (×10000) revealed significant changes in surface morphology. The density and coverage of needle-like structures were greatly improved, almost completely covering the entire copper foil substrate, with a significant reduction in blank areas and a marked improvement in structural uniformity. High-resolution images (×100000) further showed that the morphology of the needle-like structures became more slender and dense. Due to the increase in nucleation points, the gaps between the needles narrowed, and many structures began to interweave, connect, and even partially merge during the growth process, forming a more complex network prototype.

[0145] At 40 mA / cm 2 At high current density, low-magnification SEM images (×10000) show that the copper foil surface is covered by an extremely dense and thick structure, with almost no exposed substrate visible, and the surface morphology exhibits a clustered overall trend; high-resolution images (×100000) further show that a large number of needle-like structures are fused together. Although their basic building blocks are still nanoneedles, the final overall morphology has changed from independent needle-like structures to a continuous and robust three-dimensional network.

[0146] (2) Performance verification

[0147] The absorption spectra of the selective absorption membranes prepared in Examples 1-3 are shown below. Figure 2 As shown in Figure (b), the absorption spectrum of a traditional commercial TiNOX coated film (from Almeco Group, model: TiNOX energy Cu, part number: ALMC1304000Z) is as follows. Figure 2 As shown in (a). Wherein:

[0148] In the short-wavelength range of 380–780 nm, the selective absorption films prepared in Examples 1–3 all exhibited superior absorption performance compared to commercially available TiNOX-coated films. Specifically, Example 1 (10 mA / cm²) showed better absorption performance.2 The absorption film prepared under the specified conditions has an average absorption rate of up to 95% in this wavelength band, which is significantly higher than the 86% of commercial films. However, its average absorption rate (below 50%) in the 3000~8000 nm wavelength band is still higher than that of commercial TiNOX coated films, indicating that there is still room for improvement in its low emission characteristics.

[0149] Example 2 (20 mA / cm) 2 The selective absorption film prepared under the conditions maintains a high absorption rate of over 95% in the 380-780 nm band, while further reducing the average absorption rate in the 3000-8000 nm band to below 30%, and its low emission characteristics are enhanced compared to the selective absorption film prepared in Example 1.

[0150] Example 3 (40 mA / cm) 2 The selective absorption film prepared under the specified conditions exhibits photothermal performance comparable to commercial TiNOX coatings. It not only demonstrates an average absorptivity of 95% in the 380–780 nm wavelength range but also an average absorptivity of less than 20% in the 3000–8000 nm wavelength range. Its low emission characteristics are also comparable to those of commercial TiNOX coatings, effectively controlling high-temperature radiative heat loss. This embodiment provides a commercially viable alternative material exhibiting more stable absorption characteristics at high current densities. This stability is attributed to the high-density, highly branched cluster structure formed by anodic oxidation etching at higher current densities, and the multiple light trapping effect resulting from the combined effect of a wide base and sharp tips, which significantly increases the probability of multiple internal reflections and absorption of incident light.

[0151] Example 5

[0152] This embodiment provides the application of selective absorption membranes in the preparation of solar thermal collectors.

[0153] The structure of the solar thermal collector in this embodiment is as follows: Figure 3 As shown, the solar thermal collector includes a solar concentrator 100 and a tubular reactor 200; wherein:

[0154] Solar concentrator 100 is a trough-type concentrator;

[0155] The tubular reactor 200 is fixedly installed in the focal region of the solar concentrator 100 to receive concentrated solar radiation;

[0156] The tubular reactor 200 comprises, from the inside out:

[0157] The inner tube 201 is made of high-transmittance glass, and its interior forms a sealed chamber for placing the substance to be heated.

[0158] The copper plated on the outer surface of the inner tube serves as an infrared reflective layer 202, used to reflect infrared radiation to reduce heat loss.

[0159] The selective absorption film prepared in Example 3, which is coated on the outside of the infrared reflective layer, serves as the selective absorption layer 203 and is used to selectively absorb the solar spectrum and efficiently convert it into heat.

[0160] The high-vacuum interlayer 204 between the selective absorption layer 203 and the outer tube 205 is used to suppress convection and conduction heat loss;

[0161] The outer tube 205, made of high-strength transparent glass, is coaxially arranged with the inner tube 201 to jointly encapsulate the high vacuum interlayer 204 and provide mechanical protection and external isolation.

[0162] When the solar thermal collector is placed under sunlight, the temperature rise curve of its inner tube is as follows: Figure 4 As shown. The tests were conducted under conditions of solar radiation intensity of 950–1100 W / m². (From...) Figure 4 It can be seen that under sunlight, the temperature inside the reactor tube rises rapidly, from the ambient temperature (36°C) to about 350°C in 2 hours. Then the heating rate slows down and reaches thermal equilibrium in 3 hours, with the temperature remaining stable between 400 and 500°C.

[0163] Example 6

[0164] This embodiment provides a method for preparing photothermal biochar and the photothermal biochar prepared therefrom.

[0165] In this embodiment, a method for preparing photothermal biochar includes the following steps:

[0166] 0.5 L of residual sludge (MLSS concentration of mixed liquor suspended solids approximately 8000 mg / L) from the biological treatment unit (anaerobic-anoxic-aerobic process) of Nanjing Jiangxinzhou Wastewater Treatment Plant was placed in an anaerobic fermentation reactor with an effective volume of 1 L. The reaction temperature was controlled at 35℃, and the fermentation cycle was 25 days to obtain fermented biogas sludge. The obtained fermented biogas sludge was subjected to plate and frame filter press, and dried to constant weight under sunlight. After grinding, it was passed through a 100-mesh sieve to obtain approximately 50 g of dried biogas sludge powder. 34.18 g of the above dried biogas sludge powder was weighed and placed in the inner tube of the solar thermal collector (length, inner diameter, and outer diameter are 640×140×240 mm) in Example 5, according to a ratio of 5 g / cm² of biogas sludge solid mass to solar thermal collector light absorption area. The photothermal carbonization reaction was carried out under natural light, and the reaction zone temperature was controlled at 410±10℃ and maintained at this temperature for 8 h. After the photothermal carbonization reaction was completed, carbonization products were obtained. The carbonization products were then processed using 2 The initial photothermal biochar was obtained by soaking and washing in mol / L HCl solution until neutral, then drying at 105℃, grinding and passing through a 100-mesh sieve.

[0167] The primary sedimentation tank effluent (COD concentration approximately 260 mg / L) from the Nanjing Jiangxinzhou Wastewater Treatment Plant was used as the target wastewater. 10 g of initial photothermal biochar was added to 1 L of wastewater. The biochar was mechanically stirred to ensure thorough mixing and contact, and adsorption was carried out for 2 hours. After solid-liquid separation, carbon-rich sludge was obtained by adsorbing organic matter from the wastewater. The separated liquid was treated by a biological treatment unit (anaerobic-anoxic-aerobic process) to obtain residual sludge. The carbon-rich sludge and residual sludge were mixed at a volume ratio of 1:5 and fed into an anaerobic fermentation reactor for anaerobic fermentation (reaction temperature 35℃, fermentation cycle 25 days) to produce biogas, yielding fermented biogas sludge. The obtained fermented biogas sludge was subjected to plate and frame filter press filtration and sun-assisted drying to constant weight. After grinding, it was passed through a 100-mesh sieve to obtain approximately 50 g of dried biogas sludge powder. 34.18 g of the dried biogas sludge powder was weighed and placed in the solar thermal collector (external dimensions: 640×140×240 mm) in Example 5. Photothermal carbonization was carried out in an inner tube (mm) under natural light, with the reaction zone temperature controlled at 410±10℃ and maintained at this temperature for 8 h. After the photothermal carbonization reaction, 22.6774 g of carbonized product was obtained. After the same post-treatment (acid washing, drying, and sieving), recycled photothermal biochar was obtained, yielding approximately 10.9752 g of new photothermal biochar. Performance tests were conducted on the new photothermal biochar obtained from the recycled preparation.

[0168] Results analysis:

[0169] (1) Raman spectroscopy analysis

[0170] Raman spectroscopy analysis ( Figure 5As shown in (a)), compared with biochar prepared by a conventional tubular furnace (CK, see Hu Y, Zhang B, Guo Q, et al. Characterization into environmentally persistent freeradicals formed in incineration fly ash and pyrolysis biochar of sewagesludge and biomass[J]. Journal of Cleaner Production, 2022, 373: 133666.), the photothermal biochar prepared in this example has a higher efficiency at 1350 cm⁻¹. -1 The D peak at 1590 cm⁻¹ -1 The intensity ratio (ID / IG) of the G peak at the location is 0.857, indicating that its graphitized structure is more ordered and its conductivity is enhanced.

[0171] (2) Elemental analysis

[0172] Elemental analysis results ( Figure 5 (b) further demonstrates that the aromaticity index (AI) of this photothermal biochar is 1.7936, significantly higher than that of biochar (CK) prepared by a conventional tube furnace (1.5262). Simultaneously, its H / C ratio is 0.0892, indicating a higher degree of aromatic structure and a more stable carbon skeleton. This endows the material with excellent hydrophobicity and a well-developed pore structure, providing a structural basis for efficient adsorption. Furthermore, its O / C ratio (0.6261) and (N+O) / C ratio (0.7937) are both higher than those of biochar (CK) prepared by a conventional tube furnace, indicating that the material surface is rich in oxygen-containing functional groups, which helps improve hydrophilicity and biocompatibility, and provides favorable conditions for enhancing microbial electron transfer during anaerobic fermentation.

[0173] Example 7

[0174] This embodiment provides the application of the photothermal biochar prepared in Example 6 in wastewater treatment.

[0175] The application includes the following steps:

[0176] The primary sedimentation tank effluent (COD concentration of approximately 260 mg / L) from the Nanjing Jiangxinzhou Wastewater Treatment Plant was used as the target wastewater, and 10 g of photothermal biochar was added to 1 L of wastewater.

[0177] Mechanical stirring is used to fully mix and contact the wastewater, and the adsorption is carried out for 2 hours. After solid-liquid separation, carbon-rich sludge is obtained by adsorbing organic matter in the wastewater. The separated liquid is treated by a biological treatment unit (anaerobic-anoxic-aerobic process) to obtain residual sludge.

[0178] The carbon-rich sludge and the excess sludge are mixed at a volume ratio of 1:5 and then fed into an anaerobic fermentation reactor for anaerobic fermentation to produce biogas.

[0179] Results analysis:

[0180] (1) Carbon source capture rate

[0181] The results of photothermal biochar adsorption of organic matter in wastewater are as follows: Figure 6 As shown, photothermal biochar exhibits excellent adsorption performance for organic matter in wastewater.

[0182] like Figure 6 As shown in (a), after adsorption equilibrium, the carbon source capture rate is as high as 87.3%, and the carbon source concentration in the effluent rapidly drops to below 85 mg / L, which is significantly better than the 65.2% of commercial activated carbon (CK, purchased from Foshan Perls Carbon Materials Technology Co., Ltd., item number: PC-JG80) with the same dosage.

[0183] like Figure 6 As shown in Figure (b), the adsorption kinetic curves indicate that the photothermal biochar achieved rapid adsorption within the initial 60 minutes, reaching over 80% of the equilibrium adsorption capacity. This process is more consistent with the pseudo-first-order kinetic model (R0). 2 >0.98).

[0184] (2) COD removal rate and biogas (CH4) production in anaerobic fermentation

[0185] The COD removal rate and biogas production of photothermal biochar are as follows: Figure 7 As shown in (a) and (b), compared with conventional anaerobic fermentation (CK, see Xu S, Zhang L, Huang S, et al. Improving the energy efficiency of a pilot-scale UASB-digester for low temperature domestic wastewater treatment[J]. Biochemical Engineering Journal, 2018, 135: 71-78.), the addition of photothermal biochar significantly improved the organic matter degradation efficiency and biogas yield of the anaerobic fermentation system. Specifically, the cumulative biogas yield reached 258.86 mL / g COD·d during the 25-day fermentation cycle, which was approximately 20.2% higher than the control group's 206.54 mL / g COD·d. Simultaneously, the chemical oxygen demand (COD) removal rate of the fermentation system increased from 68.5% in the control group to 87.3%, indicating that the addition of photothermal biochar effectively promoted the decomposition and transformation of organic pollutants.

[0186] Example 8

[0187] This embodiment provides a wastewater treatment process.

[0188] In this embodiment, the wastewater treatment process is a closed-loop process of "carbon source capture - anaerobic fermentation - photothermal carbonization", and the process flow is as follows: Figure 8 As shown, the specific steps include the following:

[0189] S1. After the sewage enters, the remaining sludge after treatment by the biological treatment unit (anaerobic-anoxic-aerobic process) is taken and fermented in an anaerobic environment to produce biogas, and fermented biogas sludge is obtained. The fermented biogas sludge is filtered and dried and placed in the inner tube of the solar thermal collector described in Example 5. Photothermal carbonization is carried out under light conditions according to the preparation method described in Example 6 to prepare photothermal biochar.

[0190] S2, the photothermal biochar from the previous step is added to the wastewater and stirred to adsorb organic matter in the wastewater. After solid-liquid separation, carbon-rich sludge is obtained. The separated liquid is treated by a biological treatment unit (anaerobic-anoxic-aerobic process) to obtain residual sludge. The carbon-rich sludge and residual sludge are mixed and fermented in an anaerobic environment to produce biogas, obtaining fermented biogas sludge. The fermented biogas sludge is filtered and dried and placed in the inner tube of the solar thermal collector described in Example 5. Photothermal carbonization is carried out under light conditions according to the preparation method described in Example 6 to prepare photothermal biochar.

[0191] S3, repeating step S2, namely: adding the photothermal biochar from the previous step to the wastewater, stirring and mixing to adsorb organic matter in the wastewater, and obtaining carbon-rich sludge after solid-liquid separation; the separated liquid is treated by a biological treatment unit (anaerobic-anoxic-aerobic process) to obtain residual sludge (the rest is effluent); mixing the carbon-rich sludge with the residual sludge, fermenting in an anaerobic environment to produce biogas, obtaining fermented biogas sludge, filtering and drying the fermented biogas sludge and placing it in the inner tube of the solar thermal collector described in Example 5, and performing photothermal decomposition carbonization under light conditions according to the preparation method described in Example 6 to prepare photothermal biochar.

[0192] In this process, a closed-loop process is formed: "carbon source capture (using photothermal biochar to adsorb and capture carbon sources in wastewater) - anaerobic fermentation (mixing the adsorbed carbon-rich sludge with the system's remaining sludge for anaerobic fermentation to produce biogas) - photothermal carbonization (converting the fermented biogas sludge produced after fermentation into new photothermal biochar through photothermal carbonization technology) - carbon source capture (the newly prepared photothermal biochar is recycled for upstream carbon source capture)". That is, the photothermal biochar prepared in the previous step is added to the wastewater to adsorb organic matter, achieving "carbon source capture", which helps reduce A 2 The organic load in the aerobic section of the / O process offsets A 2The aeration energy consumption of the / O process; after mixing carbon-rich sludge with excess sludge, anaerobic fermentation is carried out. The carbon-rich sludge provides the carbon source for anaerobic fermentation and is rich in oxygen-containing functional groups, which helps to improve hydrophilicity and biocompatibility, providing favorable conditions for enhancing microbial electron transfer during anaerobic fermentation, increasing biogas production and COD removal rate, and improving carbon resource recycling efficiency and energy recovery rate; photothermal biochar is prepared by photothermal carbonization of fermented biochar under light conditions, which has both excellent adsorption performance and the ability to promote anaerobic microbial metabolism. It is suitable for carbon source adsorption in sewage treatment and subsequent anaerobic fermentation to produce biogas, further improving the carbon source capture rate. At the same time, it has the ability to promote anaerobic microbial metabolism, reducing the carbon footprint of sludge disposal, and is a resource recovery-type sewage treatment mode.

Claims

1. A method for preparing a selective absorption membrane, characterized in that, The method includes the following steps: Using a copper foil as the anode and another conductive electrode as the cathode, both are immersed in an etching solution and subjected to anodic etching under constant current. The anodicly etched copper foil is then dried to obtain a selective absorption film. Wherein: The etching solution comprises the following components: 3.0 M to 10 M sodium hydroxide; 0.1 M to 1.0 M sodium citrate; 0.1 M to 1.0 M copper sulfate; The current is controlled by direct current, with a current density of 5 mA·cm⁻¹. -2 ~50 mA·cm -2 The etching time is 10~60 minutes.

2. The preparation method according to claim 1, characterized in that, The current density is 10 mA·cm -2 The etching time is 40 minutes; or The current density is 20 mA·cm -2 The etching time is 20 minutes; or The current density is 40 mA·cm -2 The etching time is 10 minutes.

3. The selective absorption membrane prepared by the method of preparation of the selective absorption membrane according to claim 1 or 2.

4. The selective absorption membrane according to claim 3, characterized in that, The selective absorption membrane has an average light absorption rate of ≥95% in the 380 nm to 780 nm spectral range.

5. The application of the selective absorption membrane according to claim 3 or 4 in the preparation of a solar thermal collector.

6. A solar thermal collector, characterized in that, The solar thermal collector includes: A solar concentrator (100) and a tubular reactor (200), wherein the tubular reactor (200) is fixedly disposed in the focal region of the solar concentrator (100); The tubular reactor (200) comprises, from the inside out, the following components: The inner tube (201) is made of transparent glass or quartz, and a sealed chamber is formed inside it; The selective absorption layer (203) is specifically the selective absorption membrane as described in claim 3 or 4 that wraps around the outer surface of the inner tube; The outer tube (205) is made of transparent glass and is coaxially arranged with the inner tube (201).

7. A solar thermal collector according to claim 6, characterized in that, The solar thermal collector also includes: An infrared reflective layer (202) is disposed between the inner tube (201) and the selective absorption layer (203); and / or A high-vacuum interlayer (204) is disposed between the selective absorption layer (203) and the outer tube (205).

8. The application of the selective absorption membrane according to claim 3 or 4, or the solar thermal collector according to claim 6 or 7, in the preparation of photothermal biochar.

9. A method for preparing photothermal biochar, characterized in that, The method includes the following steps: M1, take the residual sludge after the anaerobic-anoxic-aerobic process, ferment it in an anaerobic environment to produce biogas, obtain fermented biogas sludge, filter and dry the fermented biogas sludge and place it in the inner tube of the solar thermal collector as described in claim 6 or 7, and carry out photothermal decomposition and carbonization under light conditions to prepare photothermal biochar. M2, add the photothermal biochar from the previous step to the wastewater, stir and mix to adsorb organic matter in the wastewater, and obtain carbon-rich sludge after solid-liquid separation; the separated liquid is treated by an anaerobic-anoxic-aerobic process to obtain excess sludge. The carbon-rich sludge is mixed with the excess sludge and fermented in an anaerobic environment to produce biogas, thereby obtaining fermented biogas sludge. The fermented biogas sludge is filtered and dried and then placed in the inner tube of the solar thermal collector as described in claim 6 or 7, and subjected to photothermal decomposition and carbonization under light conditions to prepare photothermal biochar.

10. Photothermal biochar prepared by the method of claim 9.

11. The photothermal biochar according to claim 10, characterized in that, The photothermal biochar has at least one of the following characteristics: In its Raman spectrum, the intensity ratio of the D peak to the G peak is 0.85~0.90; Its elemental composition has an H / C mass ratio ≤ 0.10, an aroma index ≥ 1.70, an O / C mass ratio ≥ 0.60, and a (N+O) / C mass ratio ≥ 0.

75.

12. The application of the photothermal biochar according to claim 10 or 11 in wastewater treatment.

13. A wastewater treatment process, characterized in that, The process includes the following steps: S1. After the wastewater enters, the remaining sludge after the anaerobic-anoxic-aerobic process is taken and fermented in an anaerobic environment to produce biogas, thereby obtaining fermented biogas sludge. The fermented biogas sludge is filtered and dried and placed in the inner tube of the solar thermal collector as described in claim 6 or 7, and photothermal carbonization is carried out under light conditions to prepare photothermal biochar. S2, add the photothermal biochar from the previous step to the wastewater, stir and mix to adsorb organic matter in the wastewater, and obtain carbon-rich sludge after solid-liquid separation; the separated liquid is treated by an anaerobic-anoxic-aerobic process to obtain residual sludge. The carbon-rich sludge is mixed with the excess sludge and fermented to produce biogas in an anaerobic environment to obtain fermented biogas sludge. The fermented biogas sludge is filtered and dried and placed in the inner tube of the solar thermal collector as described in claim 6 or 7. Photothermal carbonization is carried out under light conditions to prepare photothermal biochar. S3, repeat step S2 in a loop.

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