Preparation method of photocatalyst for synergistically removing manganese and ammonia nitrogen compounds by carbon-based loaded organic photovoltaic material in manganese ore production process

Abstract

The invention discloses a preparation method of a photocatalyst for synergistically removing manganese and ammonia nitrogen compounds by a carbon-based loaded organic photovoltaic material in a manganese ore production process. The method comprises the following steps: A, drying coconut shells; b, crushing the coconut shells; c, drying the coconut shell powder, and performing high-temperature pyrolysis treatment on the dried coconut shell powder in a tubular furnace to obtain modified carbon-based material coconut shell carbon particles; d, mixing the organic photovoltaic material and chloroform according to the following weight ratio: 0.01-0.02 g of the organic photovoltaic material and 10-20 ml of chloroform; e, uniformly coating modified carbon-based material coconut shell carbon particles with the organic photocatalyst mixed solution obtained in the step D, and drying to obtain a coconut shell carbon-based loaded organic photocatalyst; and F, adding the organic photocatalyst into the reinforcing agent, uniformly mixing, and drying to obtain the photocatalyst disclosed by the invention. According to the photocatalyst, manganese and ammonia nitrogen compounds can be efficiently removed, the photocatalyst can be repeatedly utilized, and the problems of a photocatalyst loading process and cyclic utilization are solved.

Description

Technical Field

[0001] The invention relates to the technical field of functional material preparation, and in particular to a method for preparing a photocatalyst for synergistically removing manganese and ammonia nitrogen compounds in a manganese ore production process using a carbon-based loaded organic photovoltaic material. Background Art

[0002] Manganese ore production enterprises often discharge industrial wastewater during the production process, posing a serious threat to the ecological environment and human health. Industrial wastewater often contains high levels of manganese ions and ammonia nitrogen compounds. Excessive intake of manganese ions (>0.10 mg / L) by humans may cause neurological disorders, leading to Parkinson's-like symptoms, mood disorders, hallucinations and cardiovascular diseases. In addition, the presence of excessive ammonium in drinking water can lead to nitrite accumulation and induce the growth of heterotrophic bacteria (including pathogens). Therefore, it is necessary to develop a new method to deal with the environmental pollution caused by high levels of manganese ions and ammonia nitrogen compounds during the production process of manganese ore.

[0003] Among the many environmental pollution control technologies for removing manganese and ammonia nitrogen compounds from industrial wastewater generated in the manganese ore production process, the biodegradation method is too expensive and has a long cycle, the adsorption method only transfers the ammonia nitrogen compounds, and the chemical oxidation method has a better treatment effect on manganese and ammonia nitrogen compounds, but the use of reaction reagents may produce a large number of highly toxic byproducts, and the reaction conditions of the persulfate activation method in the chemical oxidation method are relatively harsh, and the ozone preparation cost of the ozone method is relatively high. For this reason, it is urgent to develop a green and environmentally friendly photocatalyst preparation method that has simple use conditions and can synergistically remove manganese and ammonia nitrogen compounds in the manganese ore production process. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing a photocatalyst for synergistically removing manganese and ammonia nitrogen compounds in the process of manganese ore production using a carbon-based loaded organic photovoltaic material. The photocatalyst obtained by the method can achieve efficient removal of manganese and ammonia nitrogen compounds and can be reused, providing a truly green, environmentally friendly and pollution-free treatment method for synergistically removing manganese and ammonia nitrogen compounds in the process of manganese ore production.

[0005] The present invention solves the above technical problems with the following technical solutions:

[0006] The present invention discloses a method for preparing a photocatalyst for synergistically removing manganese and ammonia nitrogen compounds in a manganese ore production process using a carbon-based organic photovoltaic material, comprising the following steps:

[0007] A. Clean the coconut shell and dry it until it is completely dry;

[0008] B. Crushing the completely dried coconut shell with a pulverizer and passing it through a 200 mesh sieve to obtain coconut shell powder;

[0009] C. Dry the coconut shell powder at 100° C. for 30 min and then place it in a tubular furnace for high-temperature pyrolysis treatment to obtain modified carbon-based material coconut shell carbon particles;

[0010] D. Mixing an organic photovoltaic material and chloroform in the following weight ratio: 0.01-0.02 g of organic photovoltaic material: 10-20 ml of chloroform to obtain an organic photocatalyst mixed solution; the organic photovoltaic material is PM7:IXIC-4Cl, PM7:S-diPDI or PM7:IXIC-4Cl:S-diPDI;

[0011] E. The organic photocatalyst mixed solution obtained in step D is evenly coated on the modified carbon-based material coconut shell carbon particles, and dried at 60° C. for 24 hours to obtain a coconut shell carbon-based supported organic photocatalyst;

[0012] F. The coconut shell carbon-based organic photocatalyst of step E is uniformly mixed with the enhancer polyethylene glycol solution at a weight ratio of 1:1 for 0.5 h, and then dried at 60° C. for 12 h to obtain a carbon-based organic photovoltaic material that synergistically removes manganese and ammonia nitrogen compounds in the manganese ore production process.

[0013] In step A of the present invention, the drying process is carried out in a forced air drying oven at a temperature of 70° C. for 48 hours.

[0014] In step B of the present invention, the coconut shell is crushed for 3 to 5 minutes.

[0015] In step C of the present invention, the operation of the tubular furnace for high-temperature pyrolysis treatment is as follows: putting the coconut shell powder into the tubular furnace, closing the furnace plug, evacuating for 15 minutes, passing nitrogen for 20 minutes, heating to 200° C. at a heating rate of 5° C. / min under nitrogen protection, then heating to 700° C. at a heating rate of 10° C. / min, keeping for 3 hours, cooling to room temperature, and bagging for standby use.

[0016] In step E of the present invention, the weight ratio of the organic photocatalyst mixed solution to the modified carbon-based material coconut shell carbon particles is 1:5000-10000.

[0017] In step D of the present invention, the PM7:IXIC-4Cl and PM7:S-diPDI are mixed at a weight ratio of 1:1, and the PM7:IXIC-4Cl:S-diPDI is mixed at a weight ratio of 1:1:1.

[0018] In step D of the present invention, during preparation, the organic photovoltaic material is mixed with chloroform and then stirred and dissolved at 80° C. for 1 hour.

[0019] In step F of the present invention, the polyethylene glycol solution is prepared by mixing the following raw materials in weight percentage: 5% to 20% polyethylene glycol and 80% to 95% ultrapure water.

[0020] The method of the present invention has the following beneficial effects:

[0021] (1) The photocatalyst obtained by the method of the present invention can realize the removal of manganese and ammonia nitrogen compounds in industrial wastewater generated in the manganese ore production process by modified carbon-based materials. The removal effect is very good, with a removal rate of about 98%, and it can be reused.

[0022] (2) Compared with inorganic catalysts, the photocatalyst obtained by the method of the present invention has unique advantages in wastewater purification, and has the advantages of rapid and effective exciton dissociation, adjustable energy level, wide absorption spectrum, excellent chemical stability, large specific surface area, etc., so that it can produce a large number of hydroxyl radicals and holes with strong oxidizing properties in water, and at the same time has strong adsorption capacity, which can completely and quickly oxidize and remove manganese and ammonia nitrogen compounds.

[0023] (3) The matrix material used in the present invention is a natural product carbon-based material with many excellent properties such as hydrophilicity, greenness, high porosity, and large specific surface area. The organic photovoltaic material loaded on the matrix material is reusable and degradable, achieving true green friendliness and environmental pollution-free. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a stability test chart of the photocatalyst obtained in Example 1 of the present invention in removing manganese and ammonia nitrogen compounds. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0026] Example 1

[0027] The method for preparing a photocatalyst for synergistically removing manganese and ammonia nitrogen compounds in a manganese ore production process using a carbon-based organic photovoltaic material is performed according to the following steps:

[0028] A. Wash the coconut shell with ultrapure water and put it into a blast drying oven at 70°C for 48 hours to make the coconut shell completely dry;

[0029] B. Grind the completely dried coconut shell with a grinder for 3 to 5 minutes and then pass it through a 200-mesh sieve to obtain coconut shell powder;

[0030] C. Dry the coconut shell powder at 100°C for 30 minutes and then put it into a tube furnace for high-temperature pyrolysis treatment to obtain the modified carbon-based material coconut shell carbon particles. During the operation, put the coconut shell powder into the tube furnace, close the furnace plug, evacuate for 15 minutes, and pass nitrogen for 20 minutes.

[0031] After 10 min, the temperature was heated to 200 °C at a rate of 5 °C / min under nitrogen protection, and then at a rate of 10 °C / min.

[0032] Heat to 700℃ at a high speed, keep for 3h, then cool to room temperature and bag for later use;

[0033] D. Mixing 0.015 g of an organic photovoltaic material PM7:IXIC-4Cl with 15 ml of chloroform to obtain an organic photocatalyst mixed solution, wherein PM7:IXIC-4Cl is obtained by mixing PM7 and IXIC-4Cl in a weight ratio of 1:1; during preparation, the organic photovoltaic material and chloroform are mixed and stirred and dissolved at 80° C. for 1 hour;

[0034] E. The organic photocatalyst mixed solution obtained in step D is evenly coated on the modified carbon-based material coconut shell carbon particles.

[0035] After drying at 60° C. for 24 h, a modified carbon-based supported organic photocatalyst was obtained, wherein the weight ratio of the organic photocatalyst mixed solution to the modified carbon-based material coconut shell carbon particles was 1:7500;

[0036] F. The coconut shell carbon-based organic photocatalyst of step E is uniformly mixed with the enhancer polyethylene glycol solution at a weight ratio of 1:1 for 0.5h, and then dried at 60°C for 12h to obtain a carbon-based organic photovoltaic material that synergistically removes manganese and ammonia nitrogen compounds in the manganese ore production process. The polyethylene glycol solution is prepared by mixing the following raw materials in weight percentage:

[0037] Polyethylene glycol 20%, ultrapure water 80%.

[0038] The photocatalyst prepared in this example is used to remove manganese and ammonia nitrogen compounds in industrial wastewater generated in the manganese ore production process. The ammonia nitrogen compound removal rate is 99.8% in 120 minutes, and the manganese ion removal rate is 99.5% in 12 minutes.

[0039] Figure 1 It shows that after 40 rounds of cycle tests, the catalyst's pollutant removal efficiency can still reach about 98%, reflecting the good recyclability of the catalyst.

[0040] Example 2

[0041] The method for preparing a photocatalyst for synergistically removing manganese and ammonia nitrogen compounds in a manganese ore production process using a carbon-based organic photovoltaic material is performed according to the following steps:

[0042] A. Wash the coconut shell with ultrapure water and put it into a blast drying oven at 70°C for 48 hours to make the coconut shell completely dry;

[0043] B. Grind the completely dried coconut shell with a grinder for 3 to 5 minutes and then pass it through a 200-mesh sieve to obtain coconut shell powder;

[0044] C. Dry the coconut shell powder at 100°C for 30 minutes and then put it into a tube furnace for high-temperature pyrolysis treatment to obtain the modified carbon-based material coconut shell carbon particles. During the operation, put the coconut shell powder into the tube furnace, close the furnace plug, evacuate for 15 minutes, and pass nitrogen for 20 minutes.

[0045] After 10 min, the temperature was heated to 200 °C at a rate of 5 °C / min under nitrogen protection, and then at a rate of 10 °C / min.

[0046] Heat to 700℃ at a high speed, keep for 3h, then cool to room temperature and bag for later use;

[0047] D. Mix 0.015 g of organic photovoltaic material PM7:S-diPDI with 15 ml of chloroform to obtain an organic photocatalyst mixed solution, wherein PM7:S-diPDI is obtained by mixing PM7 and S-diPDI in a weight ratio of 1:1;

[0048] The voltaic material was mixed with chloroform and dissolved by stirring at 80°C for 1 h;

[0049] E. The organic photocatalyst mixed solution obtained in step D is evenly coated on the modified carbon-based material coconut shell carbon particles.

[0050] After drying at 60°C for 24 hours, the modified carbon-based supported organic photocatalyst was obtained, wherein the organic photocatalyst mixed solution and the modified

[0051] The weight ratio of coconut shell carbon particles to carbon-based materials is 1:7500;

[0052] F. The coconut shell carbon-based organic photocatalyst of step E is uniformly mixed with the enhancer polyethylene glycol solution at a weight ratio of 1:1 for 0.5h, and then dried at 60°C for 12h to obtain a carbon-based organic photovoltaic material that synergistically removes manganese and ammonia nitrogen compounds in the manganese ore production process. The polyethylene glycol solution is prepared by mixing the following raw materials in weight percentage: 10% polyethylene glycol and 90% ultrapure water.

[0053] The photocatalyst prepared in this example is used to remove manganese and ammonia nitrogen compounds in industrial wastewater generated in the manganese ore production process. The ammonia nitrogen compound removal rate is 99.4% in 120 minutes, and the manganese ion removal rate is 99.7% in 12 minutes.

[0054] Example 3

[0055] The method for preparing a photocatalyst for synergistically removing manganese and ammonia nitrogen compounds in a manganese ore production process using a carbon-based organic photovoltaic material is performed according to the following steps:

[0056] A. Wash the coconut shell with ultrapure water and put it into a blast drying oven at 70°C for 48 hours to make the coconut shell completely dry;

[0057] B. Grind the completely dried coconut shell with a grinder for 3 to 5 minutes and then pass it through a 200-mesh sieve to obtain coconut shell powder;

[0058] C. Dry the coconut shell powder at 100°C for 30 minutes and then put it into a tubular furnace for high-temperature pyrolysis treatment to obtain modified carbon-based coconut shell carbon particles. During the operation, put the coconut shell powder into the tubular furnace, close the furnace plug, evacuate for 15 minutes, and pass nitrogen for 20 minutes.

[0059] Then, the temperature was raised to 200°C at a rate of 5°C / min under nitrogen protection, and then to 10°C / min.

[0060] Heat to 700℃ at a high speed, keep for 3h, then cool to room temperature and bag for later use;

[0061] D. Mix 0.015 g of organic photovoltaic material PM7:IXIC-4Cl:S-diPDI with 15 ml of chloroform to obtain an organic photocatalyst mixed solution, wherein PM7:IXIC-4Cl:S-diPDI is composed of PM7, IXIC-4Cl and S-diPDI in a weight ratio of 1:1:1

[0062] During the preparation, the organic photovoltaic material is mixed with chloroform and then stirred and dissolved at 80° C. for 1 hour;

[0063] E. The organic photocatalyst mixed solution obtained in step D is evenly coated on the modified carbon-based material coconut shell carbon particles.

[0064] After drying at 60°C for 24 hours, the modified carbon-based supported organic photocatalyst was obtained, wherein the organic photocatalyst mixed solution and the modified

[0065] The weight ratio of coconut shell carbon particles to carbon-based materials is 1:7500;

[0066] F. The coconut shell carbon-based organic photocatalyst of step E is uniformly mixed with the enhancer polyethylene glycol solution at a weight ratio of 1:1 for 0.5h, and then dried at 60°C for 12h to obtain a carbon-based organic photovoltaic material that synergistically removes manganese and ammonia nitrogen compounds during the production of manganese ore. The polyethylene glycol solution is prepared by mixing the following raw materials in weight percentage: 5% polyethylene glycol and 95% ultrapure water.

[0067] The photocatalyst prepared in this example is used to remove manganese and ammonia nitrogen compounds in industrial wastewater generated in the manganese ore production process. The ammonia nitrogen compound removal rate is 99.1% in 120 minutes, and the manganese ion removal rate is 99.8% in 12 minutes.

[0068] Example 4

[0069] The method for preparing a photocatalyst for synergistically removing manganese and ammonia nitrogen compounds in a manganese ore production process using a carbon-based organic photovoltaic material is performed according to the following steps:

[0070] A. Wash the coconut shell with ultrapure water and put it into a blast drying oven at 70°C for 48 hours to make the coconut shell completely dry;

[0071] B. Grind the completely dried coconut shell with a grinder for 3 to 5 minutes and then pass it through a 200-mesh sieve to obtain coconut shell powder;

[0072] C. Dry the coconut shell powder at 100°C for 30 minutes and then put it into a tube furnace for high-temperature pyrolysis treatment to obtain modified carbon-based coconut shell carbon particles. During the operation, put the coconut shell powder into the tube furnace, close the furnace plug, evacuate for 15 minutes, and pass nitrogen for 20 minutes.

[0073] After 10 min, the temperature was heated to 200 °C at a rate of 5 °C / min under nitrogen protection, and then at a rate of 10 °C / min.

[0074] Heat to 700℃ at a high speed, keep for 3h, then cool to room temperature and bag for later use;

[0075] D. Mix 0.01 g of organic photovoltaic material PM7:IXIC-4Cl:S-diPDI with 10 ml of chloroform to obtain an organic photocatalyst mixed solution, wherein PM7:IXIC-4Cl:S-diPDI is a mixture of PM7, IXIC-4Cl and S-diPDI in a weight ratio of 1:1:1.

[0076] During the preparation, the organic photovoltaic material is mixed with chloroform and then stirred and dissolved at 80° C. for 1 hour;

[0077] E. The organic photocatalyst mixed solution obtained in step D is evenly coated on the modified carbon-based material coconut shell carbon particles.

[0078] After drying at 60°C for 24 hours, the modified carbon-based supported organic photocatalyst was obtained, wherein the organic photocatalyst mixed solution and the modified

[0079] The weight ratio of carbon-based materials is 1:5000;

[0080] F. The coconut shell carbon-based organic photocatalyst of step E is uniformly mixed with the enhancer polyethylene glycol solution at a weight ratio of 1:1 for 0.5h, and then dried at 60°C for 12h to obtain a carbon-based organic photovoltaic material that synergistically removes manganese and ammonia nitrogen compounds in the manganese ore production process. The polyethylene glycol solution is prepared by mixing the following raw materials in weight percentage:

[0081] Polyethylene glycol 10%, ultrapure water 90%.

[0082] The photocatalyst prepared in this example is used to remove manganese and ammonia nitrogen compounds in industrial wastewater generated in the manganese ore production process. The ammonia nitrogen compound removal rate is 99.2% in 120 minutes, and the manganese ion removal rate is 99.4% in 12 minutes.

[0083] Example 5

[0084] The method for preparing a photocatalyst for synergistically removing manganese and ammonia nitrogen compounds in a manganese ore production process using a carbon-based organic photovoltaic material is performed according to the following steps:

[0085] A. Wash the coconut shell with ultrapure water and put it into a blast drying oven at 70°C for 48 hours to make the coconut shell completely dry;

[0086] B. Grind the completely dried coconut shell with a grinder for 3 to 5 minutes and then pass it through a 200-mesh sieve to obtain coconut shell powder;

[0087] C. Dry the coconut shell powder at 100°C for 30 minutes and then put it into a tube furnace for high-temperature pyrolysis treatment to obtain modified carbon-based coconut shell carbon particles. During the operation, put the coconut shell powder into the tube furnace, close the furnace plug, evacuate for 15 minutes, and pass nitrogen for 20 minutes.

[0088] After 10 min, the temperature was heated to 200 °C at a rate of 5 °C / min under nitrogen protection, and then at a rate of 10 °C / min.

[0089] Heat to 700℃ at a high speed, keep for 3h, then cool to room temperature and bag for later use;

[0090] D. Mix 0.02 g of organic photovoltaic material PM7:IXIC-4Cl:S-diPDI with 20 ml of chloroform to obtain an organic photocatalyst mixed solution, wherein PM7:IXIC-4Cl:S-diPDI is a mixture of PM7, IXIC-4Cl and S-diPDI in a weight ratio of 1:1:1.

[0091] During the preparation, the organic photovoltaic material is mixed with chloroform and then stirred and dissolved at 80° C. for 1 hour;

[0092] E. The organic photocatalyst mixed solution obtained in step D is evenly coated on the modified carbon-based material coconut shell carbon particles.

[0093] After drying at 60°C for 24 hours, the modified carbon-based supported organic photocatalyst was obtained, wherein the organic photocatalyst mixed solution and the modified

[0094] The weight ratio of coconut shell carbon particles to carbon-based materials is 1:10000;

[0095] F. The coconut shell carbon-based organic photocatalyst of step E is uniformly mixed with the enhancer polyethylene glycol solution at a weight ratio of 1:1 for 0.5h, and then dried at 60°C for 12h to obtain a carbon-based organic photovoltaic material that synergistically removes manganese and ammonia nitrogen compounds in the manganese ore production process. The polyethylene glycol solution is prepared by mixing the following raw materials in weight percentage:

[0096] Polyethylene glycol 15%, ultrapure water 85%.

[0097] The photocatalyst prepared in this example is used to remove manganese and ammonia nitrogen compounds in industrial wastewater generated in the manganese ore production process. The ammonia nitrogen compound removal rate is 99.6% in 120 minutes, and the manganese ion removal rate is 99.1% in 12 minutes.

Claims

1. A method for preparing a photocatalyst for synergistically removing manganese and ammonia nitrogen compounds in a manganese ore production process by using a carbon-based organic photovoltaic material, characterized in that: The method comprises the following steps: A. Clean the coconut shell and dry it until it is completely dry; B. Crushing the completely dried coconut shell with a pulverizer and passing it through a 200 mesh sieve to obtain coconut shell powder; C. Dry the coconut shell powder at 100° C. for 30 min and then place it in a tubular furnace for high-temperature pyrolysis treatment to obtain modified carbon-based material coconut shell carbon particles; D. Mixing an organic photovoltaic material and chloroform in the following weight ratio: 0.01-0.02 g of organic photovoltaic material: 10-20 ml of chloroform to obtain an organic photocatalyst mixed solution; the organic photovoltaic material is PM7:IXIC-4Cl, PM7:S-diPDI or PM7:IXIC-4Cl:S-diPDI; E. The organic photocatalyst mixed solution obtained in step D is evenly coated on the modified carbon-based material coconut shell carbon particles, and dried at 60° C. for 24 hours to obtain a coconut shell carbon-based supported organic photocatalyst; F. The coconut shell carbon-based organic photocatalyst of step E is uniformly mixed with the enhancer polyethylene glycol solution at a weight ratio of 1:1 for 0.5 h, and then dried at 60° C. for 12 h to obtain a carbon-based organic photovoltaic material that synergistically removes manganese and ammonia nitrogen compounds in the manganese ore production process.

2. The method for preparing a photocatalyst for synergistically removing manganese and ammonia nitrogen compounds in a manganese ore production process using a carbon-based organic photovoltaic material according to claim 1 or 2, characterized in that: In step A, the drying process is carried out in a forced air drying oven at a temperature of 70° C. for 48 hours.

3. The method for preparing a photocatalyst for synergistically removing manganese and ammonia nitrogen compounds in a manganese ore production process according to claim 1 or 2, characterized in that: In step B, the coconut shell is crushed for 3 to 5 minutes.

4. The method for preparing a photocatalyst for synergistically removing manganese and ammonia nitrogen compounds in a manganese ore production process according to claim 1 or 2, characterized in that: In step C, the operation of the tubular furnace for high-temperature pyrolysis treatment is: putting the coconut shell powder into the tubular furnace, closing the furnace plug, evacuating for 15 minutes, passing nitrogen for 20 minutes, heating to 200°C at a heating rate of 5°C / min under nitrogen protection, and then heating to 700°C at a heating rate of 10°C / min, keeping for 3 hours, cooling to room temperature, and bagging for later use.

5. The method for preparing a photocatalyst for synergistically removing manganese and ammonia nitrogen compounds in a manganese ore production process according to claim 1 or 2, characterized in that: In step E, the weight ratio of the organic photocatalyst mixed solution to the modified carbon-based material coconut shell carbon particles is 1:5000-10000.

6. The method for preparing a photocatalyst for synergistically removing manganese and ammonia nitrogen compounds in a manganese ore production process according to claim 1 or 2, characterized in that: In step D, the PM7:IXIC-4Cl and PM7:S-diPDI are mixed at a weight ratio of 1:1, and the PM7:IXIC-4Cl:S-diPDI is mixed at a weight ratio of 1:1:

1.

7. The method for preparing a photocatalyst for synergistically removing manganese and ammonia nitrogen compounds in a manganese ore production process according to claim 1 or 2, characterized in that: In step D, during preparation, the organic photovoltaic material is mixed with chloroform and then stirred and dissolved at 80° C. for 1 hour.

8. The method for preparing a photocatalyst for synergistically removing manganese and ammonia nitrogen compounds in a manganese ore production process according to claim 1, characterized in that: In step F, the polyethylene glycol solution is prepared by mixing the following raw materials in weight percentage: 5% to 20% polyethylene glycol and 80% to 95% ultrapure water.

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