CN107081153B - Method for reducing Cr (VI) based on catalyst photocatalysis - Google Patents

Abstract

The invention belongs to the technical field of metal ion treatment, and relates to a method for reducing Cr (VI) based on catalyst photocatalysis³⁺/TiO₂Adding the photocatalyst into the potassium dichromate solution, stirring uniformly, adjusting the pH value of the solution to obtain a mixed solution, pouring the mixed solution into a self-made photocatalytic reactor with an aeration plate at the bottom, and continuously exposing air until Cr (VI) is in Fe³⁺/TiO₂The surface of the catalyst and the inner surface of the reactor reach adsorption balance; then switching on an ultraviolet light source to carry out Fe³⁺/TiO₂Reducing Cr (VI) to carry out photocatalytic reaction to realize the reduction and degradation of Cr (VI); the method is simple, convenient to operate, low in cost and high in photocatalytic reduction efficiency, other chemical substances do not need to be added into a photocatalytic reduction reaction system, and secondary pollution is avoided.

Description

Method for reducing Cr (VI) based on catalyst photocatalysis

The technical field is as follows:

the invention belongs to the technical field of metal ion treatment, relates to a method for degrading Cr (VI) by photocatalytic reduction, and particularly relates to a method based on Fe³⁺/TiO₂The method for reducing Cr (VI) by the catalyst can safely and efficiently remove heavy metal ions Cr (VI) in the water body.

Background art:

hexavalent chromium Cr (VI) pollutants mainly come from the industries of mining, metallurgy, electroplating, tanning, dichromate chemical production, chromium slag treatment and the like, a large amount of chromium-containing heavy metal ion wastewater is generated in the chemical production or waste treatment process in the industries, and the substandard discharge of the chromium-containing heavy metal ion wastewater causes serious pollution to water environment, soil environment and ecological environment. In the process of preparing dichromate, about 3.5 tons of chromium slag can be generated when 1 ton of dichromate is produced, according to incomplete statistics, at least 20-30 ten thousand tons of chromium slag are discharged in domestic metallurgy and chemical industry every year at present, and the chromium slag contains a large amount of highly toxic substances Cr (VI). The discharge of chromium-containing wastewater and the improper treatment of chromium slag can cause great harm to the ecological environment, for example, in 2011, the 'reservoir pollution event of Yunnan Qujing heavy metal Cr (VI)' causes great pollution to local water sources (the reservoir fatal Cr (VI) exceeds 2000 times because 5000 tons of chromium slag are poured into a reservoir), the event generates great countersound in society, and great attention is paid to pollution and harm of heavy metal ions by people. Cr (vi) is a swallowable/absorbable pollutant and is easily absorbed by the human body. A large number of toxicological studies at home and abroad prove that the skin of a human body exposed in the Cr (VI) environment for a long time can generate the allergic phenomenon, and other organs can also generate diseases such as hereditary gene defects and the like. Cr (VI) has three characteristics of bioaccumulation, biological persistence and difficult degradability, and can not only cause the atrophy of nasal mucosa after entering a human body through a respiratory system, but also cause nasal ulcer, nosebleed and perforation of nasal septum, thereby worsening into nasopharyngeal carcinoma; but also can cause the pulmonary disease and easily induce lung cancer; it enters the body through the digestive system and can cause liver and kidney damage, nausea, gastrointestinal irritation, gastric ulceration, stomach cramps and even death.

In recognition of environmental and ecological hazards of Cr (VI), many scholars at home and abroad invest in environmental management of Cr (VI). Under the acidic condition, Cr (VI) has strong oxidizability and stability and is difficult to be oxidized and degraded. At present, methods for removing Cr (VI) in a water body or a chromium slag leaching solution mainly comprise a chemical precipitation method, an ion exchange method, an adsorption method, a membrane separation method, an electrolytic reduction method, a chemical reagent reduction method and the like, wherein the chemical precipitation method, the ion exchange method, the adsorption method, the membrane separation method and the like only transfer Cr (VI) from one phase to the other phase, so that not only can Cr (VI) not be removed fundamentally, but also secondary pollution is easily generated in the subsequent treatment process of Cr (VI); the electrolysis method is a method for rapidly converting Cr (VI) into Cr (III) under a certain voltage condition, and the toxicity of Cr (III) is far lower than that of Cr (VI), so the electrolysis reduction is a safer method for removing Cr (VI), but in order to maintain higher electrolysis efficiency, higher voltage is required to be applied to a reaction system, and supporting electrolyte is continuously supplemented into the solution, so the treatment cost is increased; TiO 2₂The photocatalytic reduction is a safer, green and environment-friendly water treatment technology, TiO₂Is an environment-friendly photocatalytic material, and under the irradiation of ultraviolet light, the surface of the material generates photoproduction electrons with strong reducibility, and the photoproduction electrons can haveEffectively reducing Cr (VI) to Cr (III). In TiO₂In the process of carrying out photocatalytic reduction treatment on Cr (VI), other chemical substances do not need to be added into a reaction system, so that the reaction cost and the potential hazard of secondary pollution are reduced, but the existing TiO reduces the potential hazard of the secondary pollution₂The photocatalytic reduction method is not efficient. Therefore, a method for improving TiO is sought₂Photocatalytic efficiency of Cr (VI) reduction, Fe-based³⁺/TiO₂A method for reducing Cr (VI) by a catalyst in a photocatalysis way.

The invention content is as follows:

the invention aims to overcome the defects in the prior art and seek to design a green, safe and efficient Fe-based material³⁺/TiO₂The method for photocatalytic reduction of Cr (VI) by catalyst adopts self-made Fe³⁺/TiO₂Catalyst, study of Fe in a self-made photocatalytic reactor³⁺/TiO₂The reaction and the reduction reaction kinetics of the photocatalytic reduction degradation of Cr (VI) provide theoretical guidance and technical support for the actual treatment of the chromium-containing wastewater.

In order to achieve the above object, the present invention employs Fe³⁺/TiO₂The specific process of the catalyst for photocatalytic reduction of Cr (VI) is as follows:

(1) firstly Fe³⁺/TiO₂Adding a photocatalyst into a potassium dichromate solution with the concentration of 1-8 mg/L, uniformly stirring, and then adjusting the pH value of the solution by using NaOH or HCl to obtain a mixed solution with the pH value of 1-9, wherein Fe in the mixed solution³⁺/TiO₂The concentration of the photocatalyst is 0.5-5 g/L;

(2) pouring the mixed solution into a self-made photocatalytic reactor with an aeration plate at the bottom, and continuously aerating until Cr (VI) is in Fe³⁺/TiO₂The surface of the catalyst and the inner surface of the reactor reach adsorption balance;

(3) after the adsorption reaches the balance, switching on an ultraviolet light source, and controlling the ultraviolet radiation intensity to be 280-320mW/cm²Of Fe³⁺/TiO₂Reducing Cr (VI) for 60min to realize the reduction and degradation of Cr (VI).

Fe according to the invention³⁺/TiO₂The photocatalyst is P25TiO₂Catalyst and process for preparing sameAs a carrier, Fe (NO)₃)₃·9H₂The O is an impregnation liquid and is prepared by adopting an ultrasonic-impregnation method, and the preparation process comprises the following steps: first, 5g of TiO was weighed₂The powder was charged with 100ml of 0.1mol/L Fe (NO)₃)₃·9H₂And (2) carrying out ultrasonic-immersion for 60min in the O solution, carrying out centrifugal separation for 20min, transferring the solid obtained by centrifugation into a muffle furnace, calcining for 2-3 h at the low temperature of 300-400 ℃ to obtain white hardened solid, slightly grinding the white hardened solid, washing for more than 5 times by using deionized water, finally transferring the white hardened solid into a drying oven, drying at the temperature of 90 ℃, slightly grinding, and sieving by using a hundred-mesh sieve for later use.

The main structure of the self-made photocatalytic reactor comprises a first standby sampling port, a condensation circulating water outlet, a second standby sampling port, an aeration hole, a condensation circulating water inlet, a middle sampling port, a third standby sampling port, a quartz sleeve and a reactor shell; the outermost layer and the innermost layer of the reactor shell are both provided with glass tubes, and the quartz sleeve is inserted into the reactor shell and used for placing an ultraviolet lamp tube; the left side of the upper part of the reactor shell is sequentially provided with a first standby sampling port, a condensation circulating water outlet and a second standby sampling port from top to bottom, the right side of the reactor shell is sequentially provided with a condensation circulating water inlet, a middle sampling port and a third standby sampling port from bottom to top, an aeration hole is arranged at the bottom of the reactor shell, and the first standby sampling port, the second standby sampling port, the middle sampling port, the third standby sampling port and the aeration hole are all connected with the innermost glass tube of the reactor shell; and the condensation circulating water inlet and the condensation circulating water outlet are connected with the outermost glass tube of the reactor shell.

In the invention, Fe³⁺/TiO₂For the catalyst, study of Fe³⁺/TiO₂The high-efficiency Cr (VI) reduction photocatalytic reaction has the following four characteristics: one is Fe³⁺/TiO₂The photocatalytic reduction reaction of Cr (VI) is carried out in a self-made photocatalytic reactor; second is Fe³⁺/TiO₂The photocatalysis rate of reducing Cr (VI) is higher than that of TiO₂Photocatalytic reduction efficiency; III is Fe³⁺/TiO₂The photocatalytic efficiency of reducing Cr (VI) is as high as 99.8 percent; is IV Fe³⁺/TiO₂The reduced Cr (VI) photocatalytic reaction conforms to a first-order reaction kinetic equation, and the half-life is only 7.85 min.

Compared with the prior art, the invention provides a novel method for safely and efficiently reducing Cr (VI), which has the advantages of simple method, convenient operation, low cost, high photocatalytic reduction efficiency, no need of adding other chemical substances into a photocatalytic reduction reaction system, and no secondary pollution.

Description of the drawings:

FIG. 1 shows the amount of catalyst used vs. Fe in the examples of the present invention³⁺/TiO₂Graph of the effect of reducing cr (vi) on photocatalytic efficiency.

FIG. 2 shows the initial Cr (VI) concentration vs. Fe in the example of the present invention³⁺/TiO₂Graph of the effect of reducing cr (vi) on photocatalytic efficiency.

FIG. 3 shows the pH of the reaction solution versus Fe in the example of the present invention³⁺/TiO₂Graph of the effect of reducing cr (vi) on photocatalytic efficiency.

FIG. 4 shows Fe in example of the present invention³⁺/TiO₂Reduced cr (vi) photocatalytic reaction kinetics profile.

FIG. 5 is a schematic diagram of the principle of the main structure of the self-made photocatalytic reactor of the present invention.

The specific implementation mode is as follows:

the invention is further illustrated by the following examples in conjunction with the accompanying drawings.

This example uses Fe³⁺/TiO₂The specific process of the catalyst for photocatalytic reduction of Cr (VI) is as follows:

(4) firstly Fe³⁺/TiO₂Adding a photocatalyst into a potassium dichromate solution with the concentration of 1-8 mg/L, uniformly stirring, and then adjusting the pH value of the solution by using NaOH or HCl to obtain a mixed solution with the pH value of 1-9, wherein Fe in the mixed solution³⁺/TiO₂The concentration of the photocatalyst is 0.5-5 g/L;

(5) pouring the mixed solution into a self-made photocatalytic reactor with an aeration plate at the bottom, and continuously aerating until Cr (VI) is in Fe³⁺/TiO₂The surface of the catalyst and the inner surface of the reactor reach adsorption balance;

(6) after the adsorption reaches the balance, switching on an ultraviolet light source, and controlling the ultraviolet radiation intensity to be 280-320mW/cm²Of Fe³⁺/TiO₂Reducing Cr (VI) for 60min to realize the reduction and degradation of Cr (VI).

Fe as described in this example³⁺/TiO₂The photocatalyst is P25TiO₂Catalyst as carrier, Fe (NO)₃)₃·9H₂The O is an impregnation liquid and is prepared by adopting an ultrasonic-impregnation method, and the preparation process comprises the following steps: first, 5g of TiO was weighed₂The powder was charged with 100ml of 0.1mol/L Fe (NO)₃)₃·9H₂And (2) carrying out ultrasonic-immersion for 60min in the O solution, carrying out centrifugal separation for 20min, transferring the solid obtained by centrifugation into a muffle furnace, calcining for 2-3 h at the low temperature of 300-400 ℃ to obtain white hardened solid, slightly grinding the white hardened solid, washing for more than 5 times by using deionized water, finally transferring the white hardened solid into a drying oven, drying at the temperature of 90 ℃, slightly grinding, and sieving by using a hundred-mesh sieve for later use.

The main structure of the self-made photocatalytic reactor in this embodiment includes a first standby sampling port 1, a condensed circulating water outlet 2, a second standby sampling port 3, an aeration hole 4, a condensed circulating water inlet 5, a middle sampling port 6, a third standby sampling port 7, a quartz sleeve 8 and a reactor shell 9; the outermost layer and the innermost layer of the reactor shell 9 are both provided with glass tubes, and the quartz sleeve 8 extends into the reactor shell 9 and is used for placing ultraviolet lamp tubes; a first standby sampling port 1, a condensed circulating water outlet 2 and a second standby sampling port 3 are sequentially formed in the left side of the upper part of a reactor shell 9 from top to bottom, a condensed circulating water inlet 5, a middle sampling port 6 and a third standby sampling port 7 are sequentially formed in the right side of the reactor shell 9 from bottom to top, an aeration hole 4 is formed in the bottom of the reactor shell 9, and the first standby sampling port 1, the second standby sampling port 3, the middle sampling port 6, the third standby sampling port 7 and the aeration hole 4 are all connected with the innermost layer of a glass tube of the reactor shell 9; the condensed circulating water inlet 5 and the condensed circulating water outlet 2 are both connected with the outermost glass tube of the reactor shell 9.

This example is for Fe³⁺/TiO₂Reduction of Cr (VI) by photocatalytic reactionInvestigation was carried out to examine the influence of Fe³⁺/TiO₂Experimental conditions for the reduction of cr (vi) photocatalytic reactions, such as: fe³⁺/TiO₂The dosage of the catalyst, the initial concentration of Cr (VI) and the pH value of the reaction solution; then build Fe³⁺/TiO₂And (vi) reducing cr (vi) photocatalytic reaction kinetics, and calculating a photocatalytic reaction rate constant and half-life.

Example 1: amount of catalyst to Fe³⁺/TiO₂Effect of the photocatalytic efficiency of Cr (VI) reduction

In this example, five Cr (VI) solutions with the same concentration and volume were prepared, and different amounts of Fe were used³⁺/TiO₂The catalyst starts the photocatalytic reaction according to the photocatalytic reduction reaction process, and the photocatalytic reaction conditions are as follows: the photocatalytic reaction time is 60min, the ultraviolet radiation intensity is 280-320mW/cm²The pH value of the Cr (VI) solution is 3, and the dosage of the catalyst is opposite to that of Fe³⁺/TiO₂The effect of the photocatalytic efficiency of Cr (VI) reduction is shown in FIG. 1, and it can be seen from FIG. 1 that Fe³⁺/TiO₂Reduction of Cr (VI) photocatalytic efficiency with catalyst Fe³⁺/TiO₂The increase of the dosage shows the trend of increasing first and then reducing, and the optimal dosage of the catalyst is 2 g/L; when the amount of the catalyst is 0g/L, Cr (VI) is not reduced and degraded, so that the Cr (VI) is not degraded by ultraviolet light alone; when the amount of the catalyst is less than 2g/L, the concentration of the catalyst in the Cr (VI) solution is increased along with the increase of the amount of the catalyst, and the Cr (VI) and the Fe are increased³⁺/TiO₂Collision, adsorption, reductive degradation and desorption probability, thereby improving the photocatalytic reduction efficiency; however, when the amount of the catalyst exceeds 2g/L, the Cr (VI) solution becomes more and more turbid and more Fe is added as the amount of the catalyst increases³⁺/TiO₂The particles not only block the absorption of ultraviolet light, but also reflect the ultraviolet light, so that the catalyst in the solution cannot play a photocatalysis role, and the photocatalysis efficiency is inhibited.

Example 2: initial concentration of Cr (VI) vs. Fe³⁺/TiO₂Effect of the photocatalytic efficiency of Cr (VI) reduction

In this example, five Cr (VI) solutions with the same volume and different concentrations were prepared as described aboveThe photocatalytic reaction is started in the photocatalytic reduction reaction process, and the photocatalytic reaction conditions are as follows: the photocatalytic reaction time is 60min, the ultraviolet radiation intensity is 280-320mW/cm²The pH value of the Cr (VI) solution is 3, the dosage of the catalyst is 1g/L, the initial concentration of the Cr (VI) solution is opposite to that of Fe³⁺/TiO₂The effect of the reduced cr (vi) photocatalytic efficiency results are shown in fig. 2, and can be seen from fig. 2: fe³⁺/TiO₂The photocatalytic efficiency of the reduced Cr (VI) is reduced along with the increase of the initial concentration of the Cr (VI) solution, and under the condition that the dosage of the catalyst is not changed, the larger the initial concentration of the Cr (VI) solution is, the lower the amount of the catalyst contained in the Cr (VI) solution with unit concentration is, so that the Fe³⁺/TiO₂The photocatalytic efficiency is reduced.

Example 3: pH of reaction solution to Fe³⁺/TiO₂Effect of the photocatalytic efficiency of Cr (VI) reduction

In this embodiment, five cr (vi) solutions with the same concentration, the same volume, and different pH values are prepared, and the photocatalytic reaction is started according to the above photocatalytic reduction reaction process, and the photocatalytic reaction conditions are as follows: the photocatalytic reaction time is 60min, the ultraviolet radiation intensity is 280-320mW/cm²The dosage of the catalyst is 1g/L, the pH of the Cr (VI) solution is opposite to that of the Fe³⁺/TiO₂The effect of the photocatalytic efficiency of Cr (VI) reduction is shown in FIG. 3. it can be seen from FIG. 3 that Fe³⁺/TiO₂The reduction of Cr (VI) photocatalytic efficiency decreases with the increase of the pH value of the reaction solution, the optimal pH value is 1, and the result proves that Fe³⁺/TiO₂The Cr (VI) reduction photocatalytic reaction is easier to be carried out in a strong acid solution.

Example 4: fe³⁺/TiO₂Kinetics of photocatalytic reaction for reducing Cr (VI)

This example provides theoretical guidance and technical support for the actual Cr (VI) -containing wastewater treatment, and studies Fe³⁺/TiO₂Reducing Cr (VI) photocatalytic reaction kinetics, calculating reaction rate constant and half-life period, and establishing reaction time t and ln (C)₀Functional relationship of/C), where C₀Is the initial concentration of Cr (VI), C is the concentration of Cr (VI) at a certain moment, and the functional relation is shown in figure 4, under the following experimental conditions: initial Cr (VI) concentration of 2mg/L, Fe³⁺/TiO₂The dosage is 2g/L, the pH of the solution is 1, and Fe reacts for 40min and 60min³⁺/TiO₂The photocatalytic efficiency of the reduced Cr (VI) is respectively as high as 97.9 percent and 99.8 percent, which indicates that the Fe³⁺/TiO₂The reaction has strong photocatalytic reduction efficiency, and as can be seen from the interpolated graph of FIG. 4, in the first 40min, Fe³⁺/TiO₂The reaction for reducing Cr (VI) basically meets the first-order reaction kinetic equation, and the reaction rate constant is 0.0584min^-1The reaction half-life is 7.85 min.

Claims (1)

1. A method for reducing Cr (VI) based on catalyst photocatalysis is characterized by comprising the following specific processes:

(1) firstly Fe³⁺/TiO₂Adding a photocatalyst into a potassium dichromate solution with the concentration of 1-8 mg/L, uniformly stirring, and then adjusting the pH value of the solution by using NaOH or HCl to obtain a mixed solution with the pH value of 1-9, wherein Fe in the mixed solution³⁺/TiO₂The concentration of the photocatalyst is 0.5-5 g/L;

(2) pouring the mixed solution into a self-made photocatalytic reactor with an aeration plate at the bottom, and continuously aerating until Cr (VI) is in Fe^{3 +}/TiO₂The surface of the catalyst and the inner surface of the reactor reach adsorption balance;

(3) after the adsorption reaches the balance, switching on an ultraviolet light source, and controlling the ultraviolet radiation intensity to be 280-320mW/cm²Of Fe^{3 +}/TiO₂Reducing Cr (VI) for 60min to realize the reduction and degradation of Cr (VI);

said Fe³⁺/TiO₂The photocatalyst is P25TiO₂Catalyst as carrier, Fe (NO)₃)₃·9H₂The O is an impregnation liquid and is prepared by adopting an ultrasonic-impregnation method, and the preparation process comprises the following steps: firstly, 5g of TiO is weighed₂The powder was charged with 100ml of 0.1mol/L Fe (NO)₃)₃·9H₂In the O solution, carrying out ultrasonic-immersion for 60min, then carrying out centrifugal separation for 20min, transferring the solid obtained by centrifugation to a muffle furnace, calcining for 2-3 h at the low temperature of 300-400 ℃ to obtain white hardened solid, then slightly grinding the obtained white hardened solid,washing with deionized water for more than 5 times, transferring into oven, oven drying at 90 deg.C, slightly grinding, and sieving with one hundred mesh sieve;

the main structure of the self-made photocatalytic reactor comprises a first standby sampling port, a condensation circulating water outlet, a second standby sampling port, an aeration hole, a condensation circulating water inlet, a middle sampling port, a third standby sampling port, a quartz sleeve and a reactor shell; the outermost layer and the innermost layer of the reactor shell are both provided with glass tubes, and the quartz sleeve is inserted into the reactor shell and used for placing an ultraviolet lamp tube; the left side of the upper part of the reactor shell is sequentially provided with a first standby sampling port, a condensation circulating water outlet and a second standby sampling port from top to bottom, the right side of the reactor shell is sequentially provided with a condensation circulating water inlet, a middle sampling port and a third standby sampling port from bottom to top, an aeration hole is arranged at the bottom of the reactor shell, and the first standby sampling port, the second standby sampling port, the middle sampling port, the third standby sampling port and the aeration hole are all connected with the innermost glass tube of the reactor shell; and the condensation circulating water inlet and the condensation circulating water outlet are connected with the outermost glass tube of the reactor shell.

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