CN1308070C - Hydrothermal method for preparing nano crystal Bi2WO6 powder photocatalytic material with visible light activity - Google Patents

Abstract

The present invention provides a hydrothermal method for photocatalytic materials with visual light activity nano crystal Bi2WO6 powder. The method takes bismuth nitrate and sodium tungstate dihydrate as raw materials which are prepared into a mixed solution, the mixed solution is secondly put in a reaction still at 100 to 200 DEG C and is processed for 10 to 48 hours via hydrothermal treatment, and then the reaction still is taken out. After the system is cooled to room temperature, obtained products are repeatedly washed to neutrality by deionized water, dried in vacuum and processed via heat treatment for 0.5 to 10 hours at 100 to 1000 DEG C, and then the photocatalytic material with visual light activity nano crystal Bi2WO6 powder is obtained. The method has the advantages of low synthesis temperature, large specific surface area, small particle of obtained samples, etc. The prepared photocatalytic materials with visual light activity nano crystal Bi2WO6 powder not only can display photocatalytic activity in ultraviolet regions, but also can display photocatalytic activity in visible regions, such as solar light, indoor light, etc.

Description

Preparation has visible light activity and receives brilliant Bi 2WO 6Hydro-thermal-the heat treatment method of powder photocatalytic material

Technical field

The present invention relates to have big specific area, little particle size and high visible light activity are received brilliant Bi ₂WO ₆The preparation method of powder photocatalytic material the invention still further relates to the technical field that low temperature prepares the visible light photocatalysis active photochemical catalyst.

Technical background

Since Fujishima in 1972 and Honda deliver about TiO on the Nature magazine ₂Since the paper of photochemical catalyzing, photocatalysis technology has been subjected to common attention at aspects such as environmental improvement and energy developments on the electrode.About the research and development of high activity catalysis material, become a focus of current domestic and international research gradually.But now the most efficient of photochemical catalyst of report is low, and greater band gap can only be in ultra-violet (UV) band display light catalytic activity, and solar spectrum medium ultraviolet light (400nm is following) is less than 5%, and wavelength to be the visible light of 400-750nm account for 43%.Therefore, in order effectively to utilize sunshine or indoor light, research has highlight catalytic active under radiation of visible light catalysis material has very important significance; The catalysis material that preparation has high visible light activity will be the inexorable trend that practicability is further moved towards in the photocatalysis technology development.In recent years, a series of monocrystalline solid-state light catalyst has appearred aspect photochemical catalyzing.Layered oxide wherein is as K ₄Nb ₆O ₁₇, BiInNbO ₇, Sr ₂Nb ₂O ₇And In _1-xNi _xTaO ₄Deng because of having the TiO of ratio aspect the visible light photocatalysis decomposition water ₂And SrTiO ₃Higher photocatalytic activity and be subjected to paying close attention to widely.Bi ₂WO ₆Be the narrower visible-light photocatalyst of a kind of band gap, can be used for the Photocatalytic Activity for Degradation organic pollution.But this class catalyst generally adopts the high-temperature solid phase reaction method preparation, yet the sample that high-temperature solid phase reaction method prepares not only lacks homogenieity, and causes specific area to descend greatly, and this is the fatal shortcoming of solid reaction process.Have high visible light photocatalysis active in order to prepare, big specific area and little particle size receive brilliant Bi ₂WO ₆Powder photocatalyst needs a kind of simply and effectively preparation method of research.

Summary of the invention

The present invention seeks to overcome the shortcoming of existing method, propose a kind of simply and effectively preparation method, with the brilliant Bi that receives of this method preparation ₂WO ₆Powder photocatalyst has high visible light photocatalysis active, has than the brilliant Bi that receives by the solid reaction process preparation ₂WO ₆Specific area that photochemical catalyst is higher and littler particle size.

According to the present domestic and international research present situation and the brilliant Bi that receives ₂WO ₆The feasibility of powder photocatalyst Hydrothermal Preparation, imagination of the present invention are to prepare high-specific surface area by hydro-thermal-heat treatment method to receive brilliant Bi ₂WO ₆Photochemical catalyst.As everyone knows, the doping of change preparation method and catalyst is two important means that improve the photochemical catalyst catalytic activity.Imagination of the present invention is to reduce and receive brilliant Bi by changing the preparation method ₂WO ₆The crystallization temperature of photochemical catalyst, increasing specific surface area, thus reach the purpose that improves its photocatalytic activity.

According to above-mentioned imagination, purpose of the present invention can realize by following proposal.

A kind of preparation has visible light activity and receives brilliant Bi ₂WO ₆The method of powder photocatalytic material.It is characterized in that hydro-thermal-heat treatment method, this hydro-thermal-heat treatment method is to be raw material with bismuth nitrate and sodium tungstate, precipitation reaction takes place under hydrothermal condition, after the system for the treatment of is cooled to room temperature, the product of gained is extremely neutral with the deionized water cyclic washing, vacuum drying then, last heat treatment makes, the molar concentration of wherein said bismuth nitrate is 0.01～0.5M, and the molar concentration of sodium tungstate is 0.01～1M, and the mol ratio of bismuth nitrate and sodium tungstate is 1: 3～1: 2. The pH value of solution is 1～12; Hydrothermal temperature is 100～200 ℃, and the hydro-thermal time is 10～48 hours; Heat treatment temperature is 100 ℃～1000 ℃, and heat treatment time is 0.5～10 hour.

Preparation of the present invention has visible light activity and receives brilliant Bi ₂WO ₆The method of powder photocatalytic material, wherein the molar concentration of preferred bismuth nitrate is 0.04～0.1M, and the molar concentration of sodium tungstate is 0.08～0.2M, and the mol ratio of bismuth nitrate and sodium tungstate is 1: 3～1: 2.

Preferred solution pH value is 6～8.

Preferred hydrothermal temperature is 140 ℃～160 ℃.

The preferred hydro-thermal time is 20～26 hours.

Preferred heat treatment temperature is 500 ℃～600 ℃.

Preferred heat treatment time is 1～3 hour.

Hydro-thermal-heat treatment method of the present invention removes can be used for preparing has visible light activity Bi ₂WO ₆Outside the nano-crystalline photocatalysis agent, also can be used for preparing other semiconductor powder, as: titanium dioxide, silica, zinc oxide, zirconia etc.

Of the present inventionly receive brilliant Bi ₂WO ₆The photocatalytic activity of powder photocatalyst is to receive brilliant Bi by illumination ₂WO ₆Coating is decomposed airborne formaldehyde gas and is characterized.Formaldehyde (HCHO) is a kind of common compound, is widely used in the various industry and the product for civilian use, so we select it as the simulating pollution organic compound.The photochemical catalytic oxidation decomposition of formaldehyde is carried out based on following chemical reaction:

(1)

The light source of photocatalysis experiment is the fluorescent lamp of a 15W.The test of photocatalytic degradation formaldehyde is to carry out in the airtight rectangle lucite container of 15L.The preparation process of photochemical catalyst sample is with Bi ₂WO ₆It is in the culture dish of 9cm that suspension evenly is coated onto 3 diameters, and the quality of at every turn testing photochemical catalyst is 0.5g, with culture dish dry 3h under 100 ℃, is cooled to the room temperature taking-up and is used for the photocatalysis test.During experiment culture dish is put into photo catalysis reactor, reactor directly is connected with a drier that contains calcium chloride, so that the initial humidity in the control reactor.The distance of culture dish and uviol lamp remains on about 5cm, and the effective radiating area of culture dish is 190cm ²In reactor, splash into a certain amount of formaldehyde then, treat that formaldehyde volatilizees fully after, before each light-catalyzed reaction began, the initial concentration of formaldehyde was controlled at (180 ± 10) ppm all the time in the reactor.The concentration of formaldehyde, carbon dioxide and the steam infrared multiple gases monitor of optoacoustic (photoacoustic IR multigas monitor in the reactor, INNOVA air tech instruments model 1312) carry out online check and analysis, per minute reads a sets of data.Initial temperature in the reactor is approximately 25 ℃, and the initial concentration of steam is 1.20 ± 0.01vol%.In the light-catalyzed reaction process, degradation of formaldehyde and generation concentration of carbon dioxide ratio almost remain on 1: 1 ratio.The experiment of photocatalytic degradation formaldehyde is that light source at room temperature carries out 20h with the fluorescent lamp.

The photocatalytic activity of sample can come quantitative estimation by the degradation rate (R (%)) of formaldehyde.Degradation rate R (%) can lead to formula 4-1 and calculate:

Degradation rate $R(\%)=\frac{{\left[\mathrm{gas}\right]}_0-{\left[\mathrm{gas}\right]}_t}{{\left[\mathrm{gas}\right]}_0}\×100\%---\left(2\right)$

[gas] ₀[gas] _tRepresent the initial balance concentration of formaldehyde gas and the concentration in the reaction respectively.

Receive brilliant Bi ₂WO ₆The physical property of powder photocatalyst characterizes and comprises: X-ray diffraction (XRD) characterizes Bi ₂WO ₆The phase structure of photochemical catalyst, grain size.ESEM (SEM) is observed and to be received brilliant Bi ₂WO ₆The granular size of photochemical catalyst and pattern.It in the model that the U.S. produces the infrared absorption spectroscopy of having tested sample on the infrared spectrometer of Nialet-60SXB.The ultraviolet-visible spectrometer (UV2505, day the island proper Tianjin) that diffuses is used for estimation and receives brilliant Bi ₂WO ₆The energy gap of photochemical catalyst.With model is that the n2 absorption apparatus device of AUTOSORB-1 (Quantachrome Instruments, the U.S.) characterizes and to receive brilliant Bi ₂WO ₆The specific area of powder photocatalyst.

Description of drawings

The Bi of Fig. 1 different heat treatment temperature preparation ₂WO ₆Receive the XRD figure at crystalline flour end:

Fig. 2 different heat treatment temperature preparation receive brilliant Bi ₂WO ₆The SEM photo of powder photocatalyst:

Fig. 3 different heat treatment temperature preparation receive brilliant Bi ₂WO ₆The slow reverberation spectrogram of the UV, visible light of powder photocatalyst

Fig. 4 heat treatment temperature is to Bi ₂WO ₆The influence of photocatalytic activity

A1 among the figure, A2, A3, A4, A5 and A6 are respectively 100,300,400,500,600 and 700 ℃ of heat treated Bi ₂WO ₆The XRD figure of powder; B1 and B2 are respectively the brilliant Bi that receives of 500 and 700 ℃ of heat treatment preparations ₂WO ₆The SEM photo of powder photocatalyst; C1, C2, C3 and C4 are respectively 400,500,600 and 700 ℃ of heat treatment preparation receive brilliant Bi ₂WO ₆The slow reverberation spectrogram of the UV, visible light of powder photocatalyst.

The specific embodiment

Embodiment 1:

Hydrothermal Preparation is received brilliant Bi ₂WO ₆The method of powder photocatalyst is as follows: take by weighing 9.8g Na earlier ₂WO ₄2H ₂O is dissolved in the 150ml distilled water, constantly stirs; Take by weighing 7.2g Bi (NO then ₃) ₃5H ₂O adds in the above-mentioned solution, constantly stirs.After stirring about 15min, above-mentioned reactant liquor is put into the reactor of 200ml, hydrothermal treatment consists 24h under 150 ℃ condition.Take out reactor, after the question response still is cooled to room temperature, sediment separate out, the sediment of gained is extremely neutral with the distilled water cyclic washing, 80 ℃ of vacuum drying, obtain Bi at last ₂WO ₆Powder.With the Bi that obtains ₂WO ₆Powder is at 500 ℃ of following heat treatment 2h.Promptly obtain receiving brilliant Bi ₂WO ₆Photochemical catalyst.This sample shows best photocatalytic activity, and its Photocatalytic Activity for Degradation rate reaches 68.7%.

Embodiment 2:

In order to check the hydrothermal treatment consists temperature to receiving brilliant Bi ₂WO ₆The influence of photochemical catalyst catalytic activity, except that hydro-thermal temperature difference, other reaction condition is as reactant concentration, the amount of aqueous solvent, the hydro-thermal time, heat treatment temperature etc. are all identical with embodiment 1.Found that when the hydrothermal treatment consists temperature was 100,150 and 180 ℃, its Photocatalytic Activity for Degradation rate was respectively 13.7%, 68.7% and 69.7%.Its reason may be when hydrothermal temperature is too low, and reaction is incomplete, and productive rate is lower, and impurity is many, a little less than the photocatalytic activity; When hydrothermal temperature raises when being 150 ℃, receive brilliant Bi ₂WO ₆The photocatalytic activity that photochemical catalyst shows; And when temperature further raise, the photocatalytic activity of sample did not have obvious variation, so just caused the waste of the energy.Therefore, Hydrothermal Preparation is received brilliant Bi ₂WO ₆The best hydrothermal temperature of photochemical catalyst is 150-160 ℃.

Embodiment 3:

In order to check the hydro-thermal time to receiving brilliant Bi ₂WO ₆The influence of photochemical catalyst catalytic activity, except that the hydro-thermal asynchronism(-nization), other reaction condition is as reactant concentration, the amount of aqueous solvent, hydrothermal temperature, heat treatment temperatures etc. are all identical with embodiment 1.Found that when the hydrothermal treatment consists time was 10,20,24 and 40, its Photocatalytic Activity for Degradation rate was respectively 23.5%, 56.9%, 68.7% and 70.2%.Its reason may be to work as the hydro-thermal time too in short-term, and reaction is incomplete, and productive rate is lower, and impurity is many, a little less than the photocatalytic activity; When the hydro-thermal time is 24 hours, receive brilliant Bi ₂WO ₆The photocatalytic activity that photochemical catalyst shows; And further prolonging hydro-thermal during the time, the photocatalytic activity of sample does not significantly improve.Therefore, Hydrothermal Preparation is received brilliant Bi ₂WO ₆The best hydro-thermal time of photochemical catalyst is about 24 hours.

Embodiment 4:

In order to check heat treatment temperature to receiving brilliant Bi ₂WO ₆The influence of photochemical catalyst catalytic activity, except that the heat treatment temperature difference, other reaction condition is as reactant concentration, the amount of aqueous solvent, heat treatment time, hydrothermal temperature, the hydro-thermal time etc. are all identical with embodiment 1.The results are shown among Fig. 1, Fig. 2, Fig. 3, Fig. 4 and the table 1.

Fig. 1 is through the heat treated Bi of different temperatures (100,300,400,500,600 and 700 ℃) ₂WO ₆The XRD figure of powder.As can be seen from the figure, by Hydrothermal Preparation without heat treated Bi ₂WO ₆Powder promptly shows crystallization to a certain degree; Along with the rising of heat treatment temperature, Bi ₂WO ₆The diffraction maximum grow of powder, the halfwidth of diffraction maximum narrows down, and this is because the crystallization degree enhancing of sample causes.XRD result shows that when heat treatment temperature rose to 400 ℃, sample showed as well-crystallized's square structure (JCPDS Card:26-1044).While is along with the rising of heat treatment temperature, Bi ₂WO ₆The average crystal grain size decline (as shown in table 1) of powder.

Fig. 2 (B1) and (B2) be respectively at 500 ℃ and 2 hours gained of 700 ℃ of following heat treatment and receive brilliant Bi ₂WO ₆The SEM photo of photochemical catalyst.As can be seen from the figure, the particle size of heat treatment gained sample is less under 500 ℃ of conditions; Yet when heat treatment temperature rose to 700 ℃, the particle of sample was obviously grown up.This also shows the rising along with heat treatment temperature, and the particle of sample is grown up, specific area decline (as shown in table 1).

Fig. 3 is the brilliant Bi that receives of different heat treatment temperature preparation ₂WO ₆The slow reflectance spectrum of the UV, visible light of powder photocatalyst.Can estimate from figure, following heat treatment obtained receives brilliant Bi at 400,500,600 and 700 ℃ ₂WO ₆The energy gap of photochemical catalyst is respectively 2.77,2.64eV, 2.52 and 2.50eV.This shows Bi ₂WO ₆Be suitable for visible light photocatalysis.

Fig. 4 represents that heat treatment temperature is to receiving brilliant Bi ₂WO ₆The influence of photocatalytic activity.As can be seen from the figure, freshly prepd nonheat-treated sample promptly shows certain photocatalytic activity (degradation rate R%=8.3%).Then, along with the rising of heat treatment temperature, receive brilliant Bi ₂WO ₆The photocatalytic activity of photochemical catalyst strengthens.When heat treatment temperature rose to 500 ℃, sample showed best photocatalytic activity, and its photocatalytic degradation rate reaches 68.7%.Yet, along with the further rising of heat treatment temperature, Bi ₂WO ₆The photocatalytic activity of sample begins to descend.This may be caused by following reason: because Bi ₂WO ₆The hydrothermal preparation of powder is to prepare under 150 ℃ condition, and therefore, 100 ℃ dry down, to its almost not influence of crystallization degree.As shown in Figure 1, the nonheat-treated Bi of hydrothermal preparation ₂WO ₆The sample crystallization degree very a little less than.Therefore, though it has higher specific surface area (21.1g/m ²), but still show more weak photocatalytic activity.Along with the rising of heat treatment temperature, Bi ₂WO ₆The crystallization degree of sample strengthens, thereby causes the enhancing of sample photocatalytic activity.Bi through 500 ℃ of heat treatment preparations ₂WO ₆Sample shows crystallization degree preferably, and it has higher specific surface area again simultaneously, so it shows best photocatalytic activity.Along with the further rising of heat treatment temperature, though the degree of crystallinity of sample has certain enhancing, this enhancing is also not obvious; Simultaneously, its specific area but reduces (from 10.2m greatly ²/ g is to 2.2m ²/ g).Thereby Bi ₂WO ₆Nanocrystalline photocatalytic activity constantly reduces on the contrary.

Embodiment 5:

In order to check heat treatment time to receiving brilliant Bi ₂WO ₆The influence of photochemical catalyst catalytic activity, except that the heat treatment time difference, other reaction condition as: the amount of reactant concentration, aqueous solvent, hydrothermal temperature, hydro-thermal time, heat treatment temperature etc. are all identical with embodiment 1.Found that when heat treatment time was 0.5,2,4 and 10 hour, its Photocatalytic Activity for Degradation rate was respectively 33.5%, 68.7%, 70.6% and 65.2%.500 ℃, when heat treatment time is 2 hours, receive brilliant Bi ₂WO ₆The photocatalytic activity that photochemical catalyst shows.This may be because when heat treatment time is lacked (0.5 hour) very much, and the crystallization degree of sample is relatively poor, and when heat treatment time oversize (10 hours), owing to Bi ₂WO ₆Crystallite dimension grow up, cause specific area to descend, thereby photocatalysis descends a little.

Embodiment 6:

In order to check in the precursor liquid reactant molar ratio to receiving brilliant Bi ₂WO ₆The influence of photochemical catalyst catalytic activity, except that the reactant molar ratio difference, other reaction condition is as bismuth nitrate concentration, the amount of aqueous solvent, hydrothermal temperature, the hydro-thermal time, heat treatment temperature etc. are all identical with embodiment 1.Found that, when the mol ratio of bismuth nitrate and sodium tungstate is 1: 5,1: 3,1: 2,2: 1.The time, its Photocatalytic Activity for Degradation rate is respectively 23.1%, 66.3%, 68.7% and 46.2%.When reactant molar ratio is 1: 2, receive brilliant Bi ₂WO ₆Photochemical catalyst shows best photocatalytic activity.

Embodiment 7:

In order to check precursor liquid pH value to receiving brilliant Bi ₂WO ₆The influence of photochemical catalyst photocatalytic activity, except that pH value difference, other reaction condition such as reactant concentration, the amount of aqueous solvent, hydrothermal temperature, the hydro-thermal time, heat treatment temperature etc. are all identical with embodiment 1.Found that when precursor liquid pH value was 1,5,7 and 10, its Photocatalytic Activity for Degradation rate was respectively 21.5%, 56.6%, 68.7% and 45.2%.When pH=7, receive brilliant Bi ₂WO ₆Photochemical catalyst shows best photocatalytic activity.

Table 1 heat treatment temperature is to Bi ₂WO ₆Specific surface area amasss the influence with grain size

Heat treatment temperature (℃)	100	400	500	600	700
						BET specific area (m 2/g)	21.14	13.79	10.21	5.458	2.197
Average grain size (nm)	9.1	27.9	28.5	52.0	72.9

Claims (3)

1, a kind of preparation has visible light activity and receives brilliant Bi ₂WO ₆The method of powder photocatalytic material, it is characterized in that hydro-thermal-heat treatment method, said hydro-thermal-heat treatment method is to be raw material with bismuth nitrate and sodium tungstate, precipitation reaction takes place under hydrothermal condition, after the system for the treatment of is cooled to room temperature, the product of gained is extremely neutral with the deionized water cyclic washing, vacuum drying then, last heat treatment makes, the molar concentration of wherein said bismuth nitrate is 0.04～0.1M, the molar concentration of sodium tungstate is 0.08～0.2M, and the mol ratio of bismuth nitrate and sodium tungstate is 1: 3～1: 2, and the pH value of solution is 6～8, hydrothermal temperature is 140 ℃～160 ℃, the hydro-thermal time is 20～26 hours, and heat treatment temperature is 100 ℃～1000 ℃, and heat treatment time is 0.5～10 hour.

2, the method for claim 1 is characterized in that described heat treatment temperature is 500 ℃～600 ℃.

3, the method for claim 1 is characterized in that described heat treatment time is 1～3 hour.

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