TWI409100B - Method of visible-light response of n-doped titanium dioxide photocatalyst and its application to removing ethylene - Google Patents

Abstract

The invention provides an applying method of visible-light response of N-doped titanium dioxide photocatalyst and its application to removing ethylene, especially its usage to degradation of ethylene generated from ripening process of fruits and agricultural products. The invention prepares nitrogen-modified titanium dioxide photocatalyst materials, using two factors of the variance of calcination temperatures and carbon modification to affect the efficiency on photocatalytic reaction of titanium dioxide photocatalyst to the light wave of visible light, and analyzing by gas chromatograph, and predicting the dynamic models of photocatalytic reaction. The best composition rate and the application method of this photocatalyst materials are applied to the removal of ethylene in the storage environment after fruit harvest, and applied to keeping the freshness and deferring the tissue senescence of the fruits and agricultural products, which is effective in prolonging the preservation time after fruit harvest, and also protects the the health of consumers and improves the economic benefits, etc.

Description

Nitrogen-doped titanium dioxide photocatalyst material and method for degrading ethylene

The invention relates to a vegetable and fruit preservation technology, in particular to a photocatalyst material applied to fresh-keeping use of fruit agricultural products. The invention provides a nitrogen-doped titanium dioxide photocatalyst material and a method thereof for degrading ethylene, which method effectively degrades the ethylene released by the fruit during the ripening process.

During the harvesting and transportation of fruits and vegetables, fruits and vegetables will release ethylene during the ripening process. The accumulation of ethylene in the storage environment will induce fruit ripening, increase flavor, reduce chlorophyll and increase the incidence of diseases, and may also cause fruit and vegetable corruption. Loss reduces the benefits of production costs such as labor, land, materials and capital invested in production.

At present, the practical application methods for extending the preservation time of fruits are divided into three parts: physical, chemical and biological. Physical methods, changing the temperature and gas composition of the environment; second, chemical methods, changing the fruit genes, carrying out different gene transfer depending on the characteristics of the fruit or inhibiting the production of ethylene by chemical agents, making it difficult to rot during transportation; The biological method uses a biologically substituted material to carry out a degradation reaction, and reduces the ethylene concentration in the storage environment to achieve the effect of retarding the ripening. However, due to the ineffectiveness of the above-mentioned traditional methods, gene transfer and chemical agents, there are still doubts about the impact on human health.

In order to improve the preservation quality of fruits and vegetables, the storage and transportation process after harvesting also needs to be improved. Currently, in order to reduce the release of ethylene (C ₂ H ₄ ) in fruits and vegetables and find the best way to preserve fresh fruits and vegetables, It is an important solution to the current preservation of fruits and vegetables.

In order to solve the problem that the existing fruits are produced and transported after harvesting, which causes the ripening and decay of the fruit; the research indicates that the photocatalyst can be used for long-term continuous action in an appropriate environment without replacement, and is suitable for post-harvest storage of fruits (postharvest) Environment) The removal of ethylene from the environment. The invention utilizes a titanium dioxide photocatalyst to be doped with a non-metallic impurity to enable the photocatalytic oxidation reaction of titanium dioxide which can only be operated under ultraviolet light under the irradiation of visible light, and provides a nitrogen-doped titanium dioxide photocatalyst material and the same thereof. A method of degrading ethylene.

To achieve the above object, the present invention provides a nitrogen-doped titanium dioxide photocatalyst material which is prepared by a sol-gel method using a sol-gel method to prepare a nitrogen-doped TiO ₂ photocatalytic material, which is prepared by the following steps: preparing tetraisopropyl Titanium tetraisopropoxide (TTIP) solution is added to the ethanol solution and mixed well; at the same time, the nitrogen source compound is added to the above mixed solution, stirred and completely reacted; and the titanium tetraisopropoxide solution and urea which have been completely reacted after calcination are dried. Urea) and ethanol solution; after calcination, a nitrogen-doped amount of titanium dioxide is obtained.

Preferably, in the nitrogen-doped titanium dioxide photocatalyst material of the present invention, wherein the nitrogen source compound is urea.

Preferably, in the nitrogen-doped titanium dioxide photocatalyst material of the present invention, the nitrogen source compound is ammonium hydroxide.

Preferably, in the nitrogen-doped titanium dioxide photocatalyst material of the present invention, the dry calcination temperature is between 400 and 600 °C.

Preferably, in the nitrogen-doped titanium dioxide photocatalyst material of the present invention, the optimum dry calcination temperature is 600 °C.

Preferably, in the nitrogen-doped titanium dioxide photocatalyst material of the present invention, the crystal phase structure of the nitrogen-doped amount of titanium dioxide is 98% anatase.

Preferably, in the nitrogen-doped titanium dioxide photocatalyst material of the present invention, the optimum nitrogen doping amount of the nitrogen-doped titanium dioxide is 0.5% nitrogen content.

Preferably, in the nitrogen-doped titanium dioxide photocatalyst material of the present invention, the nitrogen-doped amount of titanium dioxide has an energy gap of 2.95 eV.

The invention provides a method for degrading ethylene by using a nitrogen-doped titanium dioxide photocatalyst material, comprising the steps of: detecting, by using the synthesized nitrogen-doped titanium dioxide photocatalyst material, a photocatalytic reaction system, wherein the photocatalytic reaction system is a dynamic gas control system, a photocatalytic reactor and a gas chromatography (GC) are connected in series; a dynamic gas control system for introducing a gas phase pollutant containing ethylene; a photocatalytic reactor in which the nitrogen-doped titanium dioxide photocatalyst material is placed, and the wavelength of the photocatalytic reactor is set in the visible light range; and the uniformly mixed gas phase pollutant is introduced into the photocatalytic reactor, and Photocatalytic oxidation of a series of different nitrogen doping concentrations of titanium dioxide at different calcination temperatures in the initial ethylene concentration in the gas phase contaminant; continuous introduction of a gas phase pollutant batch containing ethylene gas into the photoreactor Gas chromatograph was used for analysis.

Preferably, in the method of the present invention, the photocatalytic reactor is set to have a detection wavelength range of >400 nm.

Preferably, in the method of the present invention, the removal rate of ethylene is about 12% to 20%.

Preferably, in the process of the present invention, the highest removal rate of ethylene is 20%.

Preferably, in the process of the present invention, nitrogen is adsorbed from the surface of the titanium dioxide to a bonding form with O-Ti-N.

The present invention provides the following advantages and effects:

1. The optimum synthesis ratio of titanium dioxide photocatalyst material obtained under different nitrogen doping amount and different calcination temperature is 0.5% nitrogen content and crystal phase structure is 98% anatase, and the structure of nitrogen-doped titanium dioxide photocatalyst material is obtained. And the characteristic information, the titanium dioxide photocatalyst can only be operated under ultraviolet light, the photocatalytic oxidation reaction can be carried out under the irradiation of visible light, and further applied to the method of degrading ethylene in visible light and prolonging fruit preservation.

2. The photocatalytic test method using the titanium dioxide photocatalyst materials of different nitrogen doping ratios of the present invention, the results show that all the nitrogen-doped titanium dioxide samples are subjected to the removal and adsorption test of ethylene under the photocatalytic reaction system. Efficient removal of ethylene under visible light, indicating that this method is suitable for the removal of ethylene in the storage environment after fruit harvesting, can maintain the freshness of the fruit agricultural products and delay the aging of the tissue, effectively prolong the preservation time of the fruit after harvesting, and has the food to be eaten Health and economic benefits.

The invention provides a nitrogen-doped titanium dioxide photocatalyst material and a method thereof for degrading ethylene, and the optimum synthesis ratio of the nitrogen-doped titanium dioxide photocatalyst material and the catalytic mechanism of the nitrogen-doped titanium dioxide, and the target of ethylene as a catalytic reaction The object of the discussion is to achieve the object of the present invention.

The invention will further illustrate the self-synthesis of the desired material by the sol-gel method from the following examples, and observe the influence of the two experimental admixtures on the material properties by changing the calcination temperature and the nitrogen doping amount. However, the embodiments are not intended to limit the scope of the present invention, and those skilled in the art can make some modifications and modifications without departing from the invention. category.

Preparation Example 1 Preparation of nitrogen-doped titanium dioxide photocatalyst by sol-gel method

The preparation process of the sol-gel method includes the mixing of the precursor and the nitrogen source, the aging process, the drying process and the calcination process. The nitrogen source is added with urea or ammonium hydroxide, and the nitrogen source is urea. The present invention uses a sol-gel method to prepare a nitrogen-doped titanium dioxide photocatalyst material. The preparation steps are as shown in FIG. 1 , and the titanium tetraisopropoxide (A) solution is added to the ethanol (B) solution and uniformly mixed on the magnet stirrer. At this time, urea (C) is added to react together, and after mixing and stirring for 30 minutes, Dry calcination was carried out to obtain a nitrogen-doped titanium oxide yellow powder. The invention changes the urea addition amount to prepare nitrogen-doped titanium dioxide with different nitrogen content, and controls the molar ratio of urea/tetraisopropoxy titanium to about 0.00~3.00, and also observes the calcination temperature (400°C~600). °C) Effect on the characteristics of nitrogen-doped titanium dioxide, sample number and preparation conditions are as listed in Table 1 below, to prepare a series of titanium dioxide at different doping temperatures of different calcination temperatures.

Example 1 Photocatalytic Reaction of Nitrogen Doped Titanium Dioxide

As shown in Fig. 2, the photocatalytic reaction system consists of three parts: a dynamic gas control system, a photocatalytic reactor and a gas chromatograph, which are sequentially connected in series, and the synthesized nitrogen-doped titanium dioxide photocatalyst is placed in photocatalysis. In the reactor, a mixed gas is introduced for analysis, and a photocatalytic reaction system is used to detect the ethylene concentration; as shown in FIG. 3, the main function of the dynamic gas control system is to prepare a gas to be reacted (ethylene), and the gas phase pollutants are separately filled. Cylinders with oxygen (>99.99%), nitrogen (>99.9999%) and ethylene (1000 ppm) are adjusted by the gas quality controller. After mixing in the mixer, the dew point is passed to the dew point detector. The value is converted into relative humidity (RH %) by numerical value; this test uses two 500W halogen tubes with filters (cut off) with initial ethylene concentration of 100ppmv, relative humidity of 55%, oxygen concentration of 19%, and reaction gas temperature of 33 °C. The visible light obtained by filter <400 nm was subjected to a photocatalytic test on a series of titanium dioxide calcined at different doping concentrations of 600 °C.

The photocatalytic reactor is made of stainless steel and can hold a gas volume of about 400 ml. When the gas phase pollutants are prepared, the initial concentration of ethylene can be analyzed by a photocatalytic reactor and then into a gas chromatograph. At this time, the light source is turned off and the initial concentration of ethylene obtained by the gas chromatograph is observed to be stable; the photocatalyst is operated in a non-lighting manner in order to allow the photocatalyst to adsorb ethylene in advance until the adsorption is saturated, so as to avoid the photocatalytic reaction being affected by the adsorption behavior. The visible light photocatalytic reaction is carried out by using two halogen lamps of 500 W in parallel and suspended at about 8 cm from the upper edge of the reactor. The photocatalytic light source first penetrates the filter on the upper edge of the reactor (cutoff=400 nm) ) Photocatalytic catalyst test piece reaching the inside of the reactor, quartz glass is 5 mm above the photocatalytic catalyst test piece; the reaction gas is continuously passed through the photocatalytic reactor and enters the GC for analysis. The GC analysis project contains residual ethylene concentration. The concentration of nitrogen dioxide is generated, and the relative humidity, initial concentration of ethylene, gas flow rate, oxygen content and light intensity are adjusted.

As shown in Fig. 4, the results of photocatalytic reaction of nitrogen-doped titanium dioxide, experimental conditions: illuminance of nitrogen-doped titanium dioxide I = 8.3 x 10 ^-3 W / cm ² , relative humidity 55%, O ₂ = 21%, the reaction temperature is 33 ⁰ C, ethylene concentration = 100 ppm; experimental results show that a different doping ratio of ethylene at a temperature of 600 ⁰ C calcined visible degradation of ethylene efficiency, ethylene removal results are shown within two hours from about 12% to about 20 %. Calcined at a temperature of 600 ⁰ C, the sample U10T6 (containing 98% anatase, 0.5% nitrogen content and an energy gap of 2.95 eV) with a maximum removal of ethylene (about 20%). Secondly, the samples were sequentially sampled U30T6 and U25T6, and their ethylene removal rates were 16% and 15%, respectively.

The experimental results show that the synthesized nitrogen-doped titanium dioxide samples can remove ethylene under visible light. The sample with high ethylene removal rate is characterized by a large crystalline phase anatase composition. Nitrogen is adsorbed from the surface of titanium dioxide to a bonding type with O-Ti-N and a lower energy gap, and has a higher nitrogen content. Lower energy gap.

1 is a flow chart showing the steps of producing the nitrogen-doped titanium dioxide of the present invention.

2 is a schematic diagram of a photocatalytic reaction system for nitrogen-modified visible light-donating titanium dioxide.

Figure 3 is a flow chart showing the steps of implementing nitrogen-modified visible light to support titanium dioxide.

Figure 4 is a graph showing the results of the ethylene removal rate of nitrogen-modified visible light-donating titanium dioxide.

Claims (12)

A nitrogen-doped titanium dioxide photocatalyst material is prepared by preparing a titanium tetraisopropoxide solution and adding it to an ethanol solution to obtain a mixed solution; and simultaneously adding a nitrogen source compound to the mixed solution and stirring and Complete reaction to obtain a fully reacted titanium tetraisopropoxide solution, urea and ethanol solution; dry calcination of the fully reacted titanium tetraisopropoxide solution, urea and ethanol solution; A nitrogen-doped titanium dioxide photocatalyst material, wherein the nitrogen phase doped titanium dioxide has a crystal phase structure of 98% anatase. The nitrogen-doped titanium dioxide photocatalyst material according to claim 1, wherein the nitrogen source compound is urea. The nitrogen-doped titanium dioxide photocatalyst material according to claim 1, wherein the nitrogen source compound is ammonium hydroxide. The nitrogen-doped titanium dioxide photocatalyst material according to any one of claims 1 to 3, wherein the dry calcination temperature is between 400 and 600 °C. The nitrogen-doped titanium dioxide photocatalyst material as described in claim 4, wherein the optimum dry calcination temperature is 600 °C. The nitrogen-doped titanium-doped titanium dioxide photocatalyst material as described in claim 5, wherein the nitrogen doping amount of the nitrogen-doped titanium dioxide is 0.5% nitrogen. The nitrogen-doped titanium dioxide photocatalyst material according to claim 6, wherein the nitrogen-doped amount of titanium dioxide has an energy gap of 2.95 eV. A method for degrading ethylene using a nitrogen-doped titanium dioxide photocatalyst material, comprising the steps of: placing the nitrogen-doped titanium dioxide photocatalyst material according to any one of items 1 to 7 into a photocatalytic reaction system, wherein the photocatalytic reaction system is a dynamic gas control system, a photocatalytic reactor and a gas chromatograph are connected in series; a dynamic gas control system is used to pass gas phase pollutants containing ethylene; a photocatalytic reactor is internally disposed Into the nitrogen-doped titanium dioxide photocatalyst material, and modulating the wavelength of the photocatalytic reactor in the visible light range; introducing the gas phase pollutants after the uniform mixing in the photocatalytic reactor, and initializing in the gas phase pollutant The ethylene concentration is photocatalyzed for a series of different titrations of titanium dioxide at different calcination temperatures. The method of claim 8, wherein the photocatalytic reactor has a detection wavelength range of >400 nm. The method of claim 9, wherein the ethylene removal rate is about 12% to 20%. The method of claim 10, wherein the highest removal rate of ethylene is 20%. The method of claim 8, wherein the nitrogen is adsorbed from the surface of the titanium dioxide to a bonding form with O-Ti-N.