A method and a simple device for photocatalytic removal of endogenous polycyclic aromatic hydrocarbons in biochar

Abstract

The present invention discloses a method and a simple device for photocatalytically removing endogenous polycyclic aromatic hydrocarbons in biochar. The device for photocatalytically removing endogenous polycyclic aromatic hydrocarbons in biochar of the present invention comprises: a photolysis reaction chamber, comprising a cylindrical body having a first open end and a second open end, an ultraviolet lamp tube is provided in the cylindrical body along the direction from the first open end to the second open end, the first open end is provided with a feed port, and the second open end is provided with a discharge port; an axisless spiral dragon is provided in the cylindrical body along the direction from the first open end to the second open end and is sleeved on the outside of the ultraviolet lamp tube, and is used to transport materials from the feed port to the discharge port. In the present invention, biochar and titanium dioxide enter the photocatalytic reactor, and the synergistic effect between the catalyst and light is utilized to promote the progress of the photocatalytic reaction, so as to remove endogenous polycyclic aromatic hydrocarbons in biochar.

Description

Technical Field

[0001] The present invention relates to the technical field of agricultural solid waste treatment and resource utilization, and in particular to a method for photocatalytic removal of endogenous polycyclic aromatic hydrocarbons from biochar and a simple device thereof. Background Art

[0002] Biochar is currently a research hotspot in fields such as plant nutrition, soil science, and agricultural ecology. It is a major approach to addressing farmland pollution, increasing soil organic matter content, improving comprehensive farmland productivity, and mitigating global climate change. Biochar refers to a solid product formed through thermochemical conversion under an anaerobic environment. It has the characteristics of high stability, surface electrical properties, alkalinity, strong adsorption capacity, strong cation exchange capacity, complex pore structure, and large specific surface area. Biochar not only improves the soil's water and fertilizer retention properties, but also has significant effects on improving soil aggregate structure, microbial community structure, and adsorbing and passivating heavy metals and pesticide residues in the soil. Biochar is an abundant and renewable resource that can improve soil, increase resource utilization efficiency, control and remediate specific environmental pollution, and reduce greenhouse gas emissions. It is a new path to sustainable development.

[0003] In recent years, the agricultural and environmental applications of biochar have been systematically studied both domestically and internationally, but the pollution and potential ecological risks associated with its production process remain largely unreported. Studies have shown that the high-temperature pyrolysis of biomass produces toxic organic pollutants, primarily polycyclic aromatic hydrocarbons (PAHs), which adhere to the surface and pores of biochar. Physical methods, including flocculation and sedimentation, centrifugal separation, and adsorption, are rapid, simple, effective, and easy to implement. However, these methods only transfer pollutants but do not degrade them. Compared to other treatment methods, microbial degradation has relatively weak degradation capabilities. Microbial degradation conditions are relatively demanding, making it difficult to control the reaction conditions and maintain stable and continuous operation. Furthermore, biodegradation is selective, relying on a single carbon or energy source for degradation. Photocatalytic oxidation not only allows for milder reaction conditions and reduces engineering costs, but also allows for thorough degradation of organic matter, resulting in complete mineralization and significantly improving organic matter removal rates.

[0004] Photocatalysis is also known as light-induced reaction. When semiconductor catalyst is irradiated by light, electrons (e - ) is excited by photons with sufficient energy to jump from the valence band of the semiconductor to the conduction band, resulting in charge separation and the generation of holes (h + ), but electrons and holes are very easy to recombine. Unrecombined electrons and holes generally react with H2O, OH -Or O2 reaction, so that the oxide surface produces hydroxyl radicals (·OH), the redox potential of ·OH is 2.8V, which can react non-selectively with organic pollutants and completely decompose them into CO2, H2O and inorganic salts.

[0005] Patent CN 110292952 A describes a method for preparing a photocatalyst capable of degrading high-concentration PAH wastewater, relating to the fields of environmental pollution control and catalytic technology. The method involves mixing nano-TiO2, starch, and ethanol, then adding a coupling agent to prepare a starch-nano-TiO2 composite. After drying and grinding, the photocatalyst capable of degrading high-concentration PAH wastewater is obtained. However, this method focuses on the removal of PAHs in water and does not address the removal of endogenous PAHs from biochar. Unlike PAHs in wastewater, endogenous PAHs generated during the biochar preparation process adhere to the biochar surface along with tar and condense, posing a significant challenge to the removal of endogenous PAHs from biochar. Summary of the Invention

[0006] The purpose of the present invention is to provide a method and a simple device for photocatalytic removal of endogenous polycyclic aromatic hydrocarbons in biochar. The method introduces biochar and titanium dioxide into a photocatalytic reactor, utilizes the synergistic effect between the catalyst and light, captures photogenerated electrons on the surface of the TiO2 catalyst through oxygen in the air, inhibits the recombination of photogenerated electrons and photogenerated holes, thereby increasing the generation of hydroxyl radicals, promoting the progress of photocatalytic reaction, and removing endogenous polycyclic aromatic hydrocarbons in biochar.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a device for photocatalytically removing endogenous polycyclic aromatic hydrocarbons from biochar, comprising:

[0009] The photolysis reaction chamber comprises a cylindrical body having a first open end and a second open end, wherein an ultraviolet lamp is arranged in the cylindrical body along the direction from the first open end to the second open end, wherein the first open end is provided with a feed port, and the second open end is provided with a discharge port;

[0010] A shaftless spiral dragon is arranged in the cylindrical body along the direction from the first opening end to the second opening end and is sleeved outside the ultraviolet lamp tube, and is used to transport the material from the feed port to the discharge port.

[0011] The above-mentioned device for photocatalytic removal of endogenous polycyclic aromatic hydrocarbons in biochar further comprises a quartz lamp spiral condenser, a water pump and a water tank;

[0012] The quartz lamp spiral condenser is wound around the outer surface of the ultraviolet lamp in the cylindrical body along the direction from the first opening end to the second opening end;

[0013] At the first open end or the second open end, the water inlet and the water outlet of the quartz lamp spiral condenser are connected to the water tank through the water pump.

[0014] In the above-mentioned device for photocatalytic removal of endogenous polycyclic aromatic hydrocarbons in biochar, the cylindrical body is made of a light-proof material;

[0015] The diameter of the cylindrical body is 20 cm;

[0016] Taking the direction of material transmission as the length direction, the length of the cylindrical body can be adjusted according to the rotation speed of the shaftless spiral dragon and the processing time of the biochar, such as 36 cm;

[0017] The diameter of the shaftless spiral dragon is 15 cm.

[0018] In the above-mentioned device for photocatalytic removal of endogenous polycyclic aromatic hydrocarbons in biochar, the feed port is arranged above the cylindrical body, the discharge port is arranged below the cylindrical body, and a collection box is provided directly below the discharge port;

[0019] The cylindrical body is provided with an exhaust pipe, which is arranged above the cylindrical body and located in the middle position between the first open end and the second open end, and is used to assist in verifying the degradation effect by collecting exhaust gas generated during the reaction process.

[0020] The above-mentioned device for photocatalytic removal of endogenous polycyclic aromatic hydrocarbons in biochar also includes a motor connected to the shaftless spiral dragon, which is arranged outside the cylindrical body at the first open end or the second open end to control the rotation of the shaftless spiral dragon.

[0021] The above-mentioned device for photocatalytically removing endogenous polycyclic aromatic hydrocarbons from biochar also includes a power supply for providing electrical energy to the ultraviolet lamp, the motor and the water pump.

[0022] In a second aspect, the present invention provides a method for photocatalytically removing endogenous polycyclic aromatic hydrocarbons in biochar using the device described in any one of the above items, comprising the following steps: biochar made from crop straw and nano-TiO2 are evenly mixed and then added into the photolysis reaction chamber through the feed port, the mixed material undergoes a photocatalytic reaction in the presence of air and under the irradiation of an ultraviolet lamp, and the reaction is simultaneously transported from the feed port to the discharge port at a uniform speed under the action of the shaftless spiral dragon, and the material at the discharge port is collected.

[0023] In the above-mentioned method for photocatalytic removal of endogenous polycyclic aromatic hydrocarbons from biochar, the weight ratio of the biochar to the nano-TiO2 is 1:(1-4), such as 1:1 or 1:4;

[0024] The crop straw is selected from at least one of corn straw, peanut shells and wheat straw;

[0025] The biochar preparation method is as follows: under the protection of inert gas, the crop straw is continuously pyrolyzed and carbonized to obtain the biochar;

[0026] The pH value of the biochar is 6 to 7 (such as 6), and the specific surface area is 1 to 3 m 2 / g (such as 1.56m 2 / g);

[0027] The particle size of the biochar is ≤1 mm, specifically 1 mm;

[0028] The size of the nano-TiO2 is 50nm;

[0029] The nano-TiO2 is in anatase phase.

[0030] As an example, the nano-TiO2 is anatase nano-titanium dioxide produced by Beasley New Materials (Suzhou) Co., Ltd., with a band gap of 3.2 eV and a corresponding maximum excitation wavelength of 253 nm.

[0031] Furthermore, the inert gas is nitrogen, the nitrogen flow rate is controlled at 100-300 ml / min, and the nitrogen purity is 99.99%;

[0032] The heating rate of the continuous pyrolysis carbonization is 10°C / min;

[0033] The temperature of the continuous pyrolysis carbonization is 400-500° C. and the time is 2 hours.

[0034] In the above-mentioned method for photocatalytic removal of endogenous polycyclic aromatic hydrocarbons in biochar, the wavelength of the ultraviolet lamp is 253 to 420 nm, such as 253 nm or 420 nm;

[0035] The power of the ultraviolet lamp is 6 to 12W, such as 6W or 12W;

[0036] The photocatalytic reaction time is 1 to 4 hours, such as 1 hour;

[0037] The rotation speed of the shaftless spiral dragon is 30-50 r / min, such as 30 r / min.

[0038] In the above-mentioned method for photocatalytic removal of endogenous polycyclic aromatic hydrocarbons in biochar, the polycyclic aromatic hydrocarbons include 2-6 ring polycyclic aromatic hydrocarbons, such as indeno[1,2,3-cd]pyrene, dibenzo[a,h]anthracene, benzo[g,h,i]pyrene, benzo[α]pyrene, benzo[k]fluoranthene, benzo[b]fluoranthene, Benzo[alpha]anthracene, pyrene, fluoranthene, anthracene, phenanthrene, fluorene, acenaphthene, acenaphthene and naphthalene.

[0039] In the above-mentioned method for photocatalytic removal of endogenous polycyclic aromatic hydrocarbons in biochar, the total amount of polycyclic aromatic hydrocarbons in the biochar is extracted by accelerated solvent extraction, and after solid phase extraction purification, it is determined by gas chromatography-mass spectrometry.

[0040] The present invention has the following beneficial effects:

[0041] First, by leveraging the synergistic effect between the catalyst and light, oxygen in the air captures photogenerated electrons on the TiO2 catalyst surface, inhibiting the recombination of photogenerated electrons and photogenerated holes. This increases the generation of hydroxyl radicals, promotes the photocatalytic reaction, and also acts as a stirring agent. The present method not only removes endogenous polycyclic aromatic hydrocarbons (PAHs) from biochar, but also reduces the content of different PAHs, ranging from 2 to 6 rings, to varying degrees.

[0042] Second, by setting a quartz lamp spiral condenser outside the UV lamp, the expansion of the lamp body and blackening of the electrode caused by lack of good cooling during long-term use can be reduced, thereby increasing its service life.

[0043] 3. The process structure is simple, occupies a small area, can be used directly after degradation, and is easy to optimize and control. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a schematic structural diagram of a device for photocatalytically removing endogenous polycyclic aromatic hydrocarbons from biochar provided by one embodiment of the present invention.

[0045] Figure 2 The PAHs content in the biochar after photocatalytic reaction in Examples 1-3 and the control group was not treated.

[0046] Figure 3 The PAHs content of biochar with different numbers of benzene rings after photocatalytic reaction in Examples 1-3 and the control group is shown in FIG.

[0047] In the figure, the marks are as follows:

[0048] 1-motor; 2-photolysis reaction chamber; 3-shaftless spiral dragon; 4-feeding port; 5-collecting box; 6-exhaust pipe; 7-ultraviolet lamp; 8-quartz lamp spiral condenser; 9-power supply; 10-water pump; 11-water tank; 12-discharging port. DETAILED DESCRIPTION

[0049] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0050] In the description of the present invention, it should be noted that the terms "upper," "lower," "left," and "right," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate the description of the present invention and simplify the description. They are not intended to indicate or imply that the systems or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the use of terms such as "first" and "second" to define components is intended solely to facilitate the distinction between such components. Unless otherwise stated, these terms have no special meanings and should not be construed as indicating or implying relative importance.

[0051] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "assembly," "disposition," and "connection" should be understood in a broad sense. For example, they may refer to fixed connection, detachable connection, or integral connection; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0052] Hereinafter, the device for photocatalytically removing endogenous polycyclic aromatic hydrocarbons from biochar provided by the embodiments of the present invention will be described in detail with reference to the accompanying drawings, but the present invention is not limited to the following embodiments.

[0053] like Figure 1 As shown, the device for photocatalytic removal of endogenous polycyclic aromatic hydrocarbons in biochar provided in this embodiment includes a photolysis reaction chamber 2, a shaftless spiral dragon 3, a quartz lamp spiral condenser 8, a power supply 9, a water pump 10, and a water tank 11;

[0054] The photolysis reaction chamber 2 is a transverse cylindrical chamber, which is the place for the photocatalytic reaction of biochar. It includes a cylindrical body with a first open end and a second open end. The cylindrical body can be made of an opaque material. The direction of material transmission is the length direction. The diameter of the cylindrical body is 20 cm. The length of the cylindrical body can be adjusted according to the rotation speed of the shaftless spiral dragon and the processing time of biochar, such as 36 cm. In the cylindrical body, along the direction from the first open end to the second open end (i.e. Figure 1The first opening end is provided with a feed port 4 (such as a feed port 4) arranged above the cylindrical body. Figure 1 A feeding funnel may be provided), such as Figure 1 The middle is located at the upper right end of the cylindrical body and communicates with the cylindrical body so that the mixture of biochar and catalyst enters the photolysis reaction chamber under the action of its own gravity. The second open end is provided with a discharge port 12 arranged below the cylindrical body, and a collection box 5 is provided just below the discharge port 12 for collecting the biochar and catalyst mixture after the photocatalytic reaction. Figure 1 The middle discharge port 12 is located at the lower left end of the cylindrical body and communicates with the cylindrical body, so that the biochar and catalyst mixture after the photocatalytic reaction can enter the collection box 5 under the action of its own gravity; the cylindrical body is provided with an exhaust pipe 6, which is arranged above the cylindrical body and located in the middle position between the first open end and the second open end. The exhaust pipe 6 is used to collect the exhaust gas (carbon dioxide) generated during the reaction process to further assist in verifying the degradation effect;

[0055] The shaftless spiral dragon 3 moves along the direction from the first opening end to the second opening end (i.e. Figure 1 The horizontal direction in the middle is arranged in the cylindrical body and is sleeved outside the ultraviolet lamp 7, and is used to transport the materials (biochar and catalyst) from the feed port 4 to the discharge port 12. The diameter of the shaftless spiral dragon 3 is 15 cm, which is smaller than the diameter of the cylindrical body. The motor 1 is located at the right end of the simple device, which is outside the photolysis reaction chamber and connected to the shaftless spiral auger 3 to control the rotation of the shaftless spiral auger 3;

[0056] In the cylindrical body, the quartz lamp spiral condenser 8 is arranged along the direction from the first opening end to the second opening end (ie Figure 1 The horizontal direction in the middle) is wound around the outer surface of the ultraviolet lamp 7, and at the first opening end or the second opening end (such as Figure 1 The left end of the figure), the water inlet and the water outlet of the quartz lamp spiral condenser 8 are connected to the water tank 11 through a water pump 10. The water pump 10 makes the water in the water tank 11 flow, and uses the cooling water to absorb heat and gasify into water vapor to take away the heat. Its main function is to cool the ultraviolet lamp under the action of circulating water, so as to prevent the ultraviolet lamp from being in a high temperature state for a long time during operation, resulting in the expansion of the lamp body, blackening of the electrode, and shortening of the service life; one end of the water pump is connected to the water tank, and the other end is connected to the quartz lamp spiral condenser, which is mainly used to control the flow of circulating water; the water tank is fixedly connected to the water pump to provide cooling water;

[0057] The power supply 9 is connected to the motor 1 , the ultraviolet lamp 7 , and the water pump 10 , and is used to control the rotation of the shaftless auger 3 , the switch of the ultraviolet lamp 7 , and the operation of the water pump 10 .

[0058] The present invention is further described in detail below in conjunction with specific embodiments. The examples provided are only for illustrating the present invention and are not intended to limit the scope of the present invention. The examples provided below can serve as a guide for further improvements by those skilled in the art and do not constitute a limitation of the present invention in any way.

[0059] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the materials, reagents, etc. used are all available from commercial sources unless otherwise specified.

[0060] The method for determining polycyclic aromatic hydrocarbons in biochar in the following examples is as follows:

[0061] Total PAHs - Soxhlet extraction: The total amount of PAHs in biochar was extracted using accelerated solvent extraction, solid phase extraction cleanup, and gas chromatography-mass spectrometry determination.

[0062] (1) Solvent extraction: Accurately weigh a certain amount of air-dried, ground, and sieved sample (10 g of peanut shell biochar, determined according to the sample concentration, can be extracted and then divided) and transfer it to a glass fiber filter cartridge. After adding 50 μL of PAHs purification standard, the filter cartridge is placed in a Soxhlet extractor and continuously extracted with 300 mL of a mixed solution of dichloromethane and acetone (1 / 1, V / V) at a reflux rate of not less than 4 times per hour for 16 to 24 h.

[0063] (2) Sample concentration: After Soxhlet extraction, rotary evaporate to about 2 mL, add 20 mL of n-hexane and continue rotary evaporation to completely convert the solvent to n-hexane, and concentrate to less than 1 mL for purification; the dichloromethane extract after liquid-liquid extraction is rotary evaporated in the same way, the solvent is replaced with n-hexane, and concentrated to less than 1 mL for purification.

[0064] (3) Sample purification: A SUPELCO 24-tube cross-contamination-proof SPE device and a 500 mg / 6 mL silicycle SPE column were used to purify the sample. The SPE column was activated with 5 mL of a mixed solution of n-hexane and dichloromethane (85 / 15, V / V) and 10 mL (2 mL each time). The concentrated sample was transferred to the SPE column head and eluted with 5 mL of a mixed solution of n-hexane and dichloromethane (85 / 15, V / V). The flow rate of the sample and elution solvent should not be too fast or too slow, ensuring a flow rate of 1 drop / s. After the solvent was dried, the vacuum pump was turned on to dry the column.

[0065] (4) Nitrogen blowing and sample preparation: Blow the elution liquid nitrogen to 0.5 mL, add 50 μL of PAHs injection standard to the sample, vortex mix, and transfer the sample into a sample bottle with a pipette, attach a label, and wait for testing.

[0066] The specifications of the photolysis reaction chamber used in the following examples are 36 cm (length) × 20 cm (diameter), and the spiral diameter is 15 cm.

[0067] Example 1

[0068] Using the above Figure 1 The method for removing endogenous polycyclic aromatic hydrocarbons in biochar by the device for photocatalytic removal of endogenous polycyclic aromatic hydrocarbons in biochar is as follows:

[0069] (1) Preparation of biochar: Under the protection of nitrogen, peanut shells, a representative crop, were selected and placed in a continuous pyrolysis carbonization furnace. The carbonization temperature was 500 °C, and the heating rate was 10 °C / min. The temperature was raised to the set temperature and kept warm for 2 h. After that, the generated peanut shell biochar was cooled to room temperature and crushed through a 1 mm sieve. The biochar under the sieve was collected. The pH value of the biochar was 6, which was weakly acidic, and the specific surface area was 1.56 m 2 / g;

[0070] (2) Catalyst: selected from Bisley New Materials, 50 nm titanium dioxide photocatalyst in anatase phase (produced by Bisley New Materials (Suzhou) Co., Ltd., product number YT-Tio2-NJ50);

[0071] (3) Peanut shell biochar and TiO2 catalyst were mixed in a weight ratio of 1:1 to obtain a solid phase mixture, which was added to the photolysis reaction chamber from the feed port and reacted under ultraviolet light for 1 hour. During this period, the shaftless spiral auger rotated under the action of the motor and gradually moved the solid phase mixture from the feed port to the discharge port at a uniform speed (the speed of the shaftless spiral auger was 30 r / min). The power of the ultraviolet lamp was 12 W and the wavelength was 253 nm.

[0072] (4) A quartz lamp spiral condenser is installed outside the UV lamp and connected to a water pump tank. The UV lamp is cooled by circulating water in the water tank to prevent the UV lamp from being in a high temperature state for a long time during operation, which may cause the lamp body to expand, the electrodes to blacken, and the service life to be shortened.

[0073] (5) an exhaust pipe is provided above the photolysis reaction chamber and communicates with the photolysis reaction chamber to collect polluting waste gas generated during the reaction process;

[0074] (6) After the reaction is completed, the peanut shell biochar falls into the collection box from the discharge port, and the peanut shell biochar is quickly collected and stored, and a representative sample is taken for polycyclic aromatic hydrocarbon determination;

[0075] (7) The content of polycyclic aromatic hydrocarbons in the biochar was detected. The test results were referred to Figure 2 、 3 .

[0076] Example 2

[0077] The endogenous polycyclic aromatic hydrocarbons in biochar were removed according to the steps of Example 1. Only the peanut shell biochar and TiO2 catalyst were adjusted to a weight ratio of 1:4. The other steps and conditions remained the same. The test results were referenced. Figure 2 、 3 .

[0078] Example 3

[0079] The endogenous PAHs in biochar were removed according to the steps of Example 1, except that the wavelength of the UV lamp was adjusted to 420 nm. The other steps and conditions remained the same. The test results were referred to Figure 2 、 3 .

[0080] Comparative Example 1

[0081] The control group only prepared biochar according to step (1) of Example 1 without any subsequent treatment. The content of polycyclic aromatic hydrocarbons in biochar was detected, and the test results were referred to Figure 2 、 3 .

[0082] From the comparison results of Example 1, Example 2, Example 3 and the control group, it can be seen that Examples 1-3 of the present invention can reduce the content of endogenous PAHs in biochar. The present invention utilizes the synergistic effect between the catalyst and ultraviolet light irradiation, captures photogenerated electrons on the surface of the TiO2 catalyst through oxygen in the air, inhibits the recombination of photogenerated electrons and photogenerated holes, thereby increasing the generation of hydroxyl radicals and promoting the progress of the photocatalytic reaction to remove endogenous polycyclic aromatic hydrocarbons in biochar. The polycyclic aromatic hydrocarbons involve 2-6 rings (including indeno[1,2,3-cd]pyrene, dibenzo[a,h]anthracene, benzo[g,h,i]pyrene, benzo[α]pyrene, benzo[k]fluoranthene, benzo[b]fluoranthene, chrysene, benzo[α]anthracene, pyrene, fluoranthene, anthracene, phenanthrene, fluorene, acenaphthene, acenaphthene and naphthalene). The method of the present invention can not only remove endogenous polycyclic aromatic hydrocarbons in biochar, but also reduce the content of different types of polycyclic aromatic hydrocarbons with 2-6 rings to varying degrees.

[0083] The present invention has been described in detail above. For those skilled in the art, without departing from the purpose and scope of the present invention, can implement the present invention in a wider range under equivalent parameters, concentration and conditions. Although the present invention provides specific embodiments, it should be understood that the present invention can be further improved. In a word, according to the principle of the present invention, the application is intended to include any variation, purposes or improvements of the present invention, including departing from the disclosed scope in the application and the changes made with conventional techniques known in the art.

Claims

1. A method for photocatalytic removal of endogenous polycyclic aromatic hydrocarbons from biochar, characterized by: The method is carried out using a device for photocatalytically removing endogenous polycyclic aromatic hydrocarbons from biochar, and the device comprises: The photolysis reaction chamber comprises a cylindrical body having a first open end and a second open end, wherein an ultraviolet lamp is arranged in the cylindrical body along the direction from the first open end to the second open end, wherein the first open end is provided with a feed port, and the second open end is provided with a discharge port; A shaftless spiral dragon is arranged in the cylindrical body along the direction from the first opening end to the second opening end and is sleeved outside the ultraviolet lamp tube, and is used to transport the material from the feed port to the discharge port; The method comprises the following steps: uniformly mixing biochar made from crop straw and nano-TiO2 and then adding the mixture into the photolysis reaction chamber through the feed port; performing a photocatalytic reaction in the presence of air and under the irradiation of an ultraviolet lamp; and simultaneously transporting the mixed material from the feed port to the discharge port at a uniform speed under the action of the shaftless spiral dragon, and collecting the material at the discharge port; The weight ratio of the biochar to the nano-TiO2 is 1:4; The size of the nano-TiO2 is 50nm; The nano-TiO2 is in anatase phase; The wavelength of the ultraviolet lamp is 253-420 nm.

2. The method for photocatalytic removal of endogenous polycyclic aromatic hydrocarbons from biochar according to claim 1, characterized in that: The device also includes a quartz lamp spiral condenser, a water pump and a water tank; The quartz lamp spiral condenser is wound around the outer surface of the ultraviolet lamp in the cylindrical body along the direction from the first opening end to the second opening end; At the first open end or the second open end, the water inlet and the water outlet of the quartz lamp spiral condenser are connected to the water tank through the water pump.

3. The method for photocatalytic removal of endogenous polycyclic aromatic hydrocarbons from biochar according to claim 1 or 2, characterized in that: The cylindrical body is made of opaque material; The diameter of the cylindrical body is 20 cm; The diameter of the shaftless spiral dragon is 15 cm.

4. The method for photocatalytic removal of endogenous polycyclic aromatic hydrocarbons from biochar according to claim 1 or 2, characterized in that: The feed port is arranged above the cylindrical body, the discharge port is arranged below the cylindrical body, and a collection box is provided directly below the discharge port; The cylindrical body is provided with an exhaust pipe, which is arranged above the cylindrical body and located in the middle position between the first open end and the second open end, and is used to assist in verifying the degradation effect by collecting exhaust gas generated during the reaction process.

5. The method for photocatalytic removal of endogenous polycyclic aromatic hydrocarbons from biochar according to claim 1 or 2, characterized in that: The device also includes a motor connected to the shaftless spiral dragon, which is arranged outside the cylindrical body at the first open end or the second open end and is used to control the rotation of the shaftless spiral dragon.

6. The method for photocatalytic removal of endogenous polycyclic aromatic hydrocarbons from biochar according to claim 1, characterized in that: The crop straw is selected from at least one of corn straw, peanut shells and wheat straw; The biochar preparation method is as follows: under the protection of inert gas, the crop straw is continuously pyrolyzed and carbonized to obtain the biochar; The pH value of the biochar is 6-7, and the specific surface area is 1-3 m 2 / g; The particle size of the biochar is ≤1 mm.

7. The method for photocatalytic removal of endogenous polycyclic aromatic hydrocarbons from biochar according to claim 6, characterized in that: The inert gas is nitrogen, the nitrogen flow rate is controlled at 100-300 ml / min, and the nitrogen purity is 99.99%; The heating rate of the continuous pyrolysis carbonization is 10°C / min; The temperature of the continuous pyrolysis carbonization is 400-500° C., and the time is 2 hours.

8. The method for photocatalytic removal of endogenous polycyclic aromatic hydrocarbons from biochar according to claim 1, characterized in that: The power of the ultraviolet lamp is 6~12W; The photocatalytic reaction time is 1 to 4 hours; The rotation speed of the shaftless spiral dragon is 30~50r / min.

9. The method for photocatalytic removal of endogenous polycyclic aromatic hydrocarbons from biochar according to claim 1, characterized in that: The polycyclic aromatic hydrocarbons include 2- to 6-ring polycyclic aromatic hydrocarbons.

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