CN101495544A

CN101495544A - Long-lived high volumetric activity photocatalysts

Info

Publication number: CN101495544A
Application number: CN200780028506.1A
Authority: CN
Inventors: T·H·范德斯普尔特; T·赫格纳-坎贝尔; S·O·海; T·N·奥比
Original assignee: Carrier Corp
Current assignee: Carrier Corp
Priority date: 2006-06-01
Filing date: 2007-05-31
Publication date: 2009-07-29
Anticipated expiration: 2027-05-31
Also published as: CN101495545B; CN101495544B; CN101495212A; CN101495545A

Abstract

The present invention relates to nanocrystalline titanium dioxide (TiO2) photocatalysts having nanocrystallites of less than 14 nanometers in diameter, which are substantially defect-free. The TiO2 photocatalysts form porous particles having a very large mass transfer surface area, large cylindrical pores, and low mass transfer resistance. The nanocrystalline TiO2 photocatalysts provide at least 75% of the photocatalytic activity of commercially-available TiO2 crystals having diameters greater than 20 nm. The nanocrystalline TiO2 photocatalysts may be doped with a metal, metal oxide, or non-metal dopant. The invention discloses a process for preparing the nanocrystalline TiO2 photocatalysts. The present invention also provides methods for using nanocrystalline TiO2 photocatalysts to remove contaminants.

Description

Long-lived heavy body active photocatalyst

Background of invention

1. invention field

In general, the disclosure relates to by titanium dioxide (TiO ₂) photocatalyst made of nanocrystal.More specifically, this TiO ₂The diameter of nanocrystal is less than 14 nanometers (nm), and treated at utmost to reduce TiO ₂Subsurface defect in the nanocrystal.The disclosure provides the preparation method and has used this nanocrystalline TiO ₂Photocatalyst photochemical catalysis pollutent with purify air, water or other fluidic methods.

2. association area explanation

Photochemical catalytic oxidation (PCO) be one by the chemical action of using up being eliminated or being reduced technology such as pollutant level in air or the water or other fluid (or other fluids).When using ultraviolet (UV) photoluminescence catalyzer, this technology more specifically can be described as ultraviolet catalytic oxidation (UV-PCO).

Room air can comprise the pollutent of trace, comprises carbon monoxide, ozone and volatile organic matter (VOC), as formaldehyde, toluene, propionic aldehyde (propanal), butylene, propionic aldehyde (propionaldehyde) and acetaldehyde.Use the air purifier of UV-PCO technology to can be used for these pollutant chemistries are changed into the little product of harm, as carbonic acid gas and water, and/or the low polluted product that is easier to from air, remove than their parent compound.

Other method has been used to remove airborne pollutent.The absorbent air filters that adopts absorbent material is by being trapped in pollutent in the filter hole and allowing the air of cleaning remove airborne pollutent by strainer, and these absorbent materials are such as but not limited to gac, clay or mesopore zeolite.A distinct disadvantage of absorbent filter is that this strainer only blocks or hold back pollutent and strainer is blocked easily, and absorbent air filters often can not effectively remove certain class source of the gas pollutent, as ozone or carbon monoxide.

Comprise titanium dioxide (TiO ₂), zirconium dioxide (ZrO ₂), zinc oxide (ZnO), calcium titanate (CaTiO ₃), tindioxide (stannic) (SnO ₂), molybdic oxide (MoO ₃) and the photocatalyst with semiconductor active of analogue be used to be used in the air-purification system eliminate airborne organic pollutant.In these photocatalysts, because its chemical stability, low relatively cost and be suitable for by the electronic band gap of UV-light photoactivation titanium dioxide (TiO ₂) be one of the most widely used semiconductor light-catalyst.

Be used as the TiO of air purifying preparation at present ₂The shortcoming of photocatalyst is the reduction of performance under the accumulation, wet condition of incomplete oxidation product, mass transfer problem, the TiO in the high flow rate system ₂The inactivation of photocatalyst and inorganic pollution.

Titanium dioxide TiO ₂It is the most stable oxidised form of transition metals Ti.TiO ₂Mainly be by Ti ^{+ 4}Positively charged ion and O ^-2The ionic material that negatively charged ion is formed.The TiO of powder type ₂Be white and give coating, paper, textiles, printing ink, plastics, toothpaste and makeup white industrial being widely used in.Say TiO from crystalline form ₂Mainly with a kind of existence the in three kinds of different polymorphics: rutile, anatase octahedrite and brookite.TiO ₂Two kinds of more common polymorphics be that rutile and anatase octahedrite have tetragonal structure, and TiO ₂More rare brookite form then has the orthorhombic body structure.

Report, when by UV-irradiation, at TiO ₂Three kinds of polymorphics in, TiO ₂Anatase form (low temperature form) have maximum photocatalytic activity.This may be broad optical absorption band and less electron effective mass because of anatase form, thereby causes the mobility that current carrier is higher.Be higher than about 600 ℃ temperature, anatase octahedrite can change into rutile, during follow significantly reducing of grain growing and surface-area.

The every single cell of the crystalline structure of rutile and anatase octahedrite all has 6 atoms.Anatase form is that body-centred structure and its conventional structure cell comprise two single cells (i.e. 12 atoms).For rutile and two kinds of forms of anatase octahedrite, titanium atom is shared limit and angle mutually with adjacent each octahedra unit mode is arranged in the crystalline structure.With each octahedra unitary two limit in the rutile structure is to share the limit to compare, anatase structured in each octahedra unitary four edges be to share the limit.

As crystal TiO ₂Photocatalyst (under room temperature) by less than the photon irradiation of the UV-light of 387nm the time has surpassed TiO ₂Band-gap energy (3.2eV), excited electronics in one of semiconductor molecule track from valence band " transition " to conduction band, therefore at valence band generation electronics " hole ".The electron-hole pair of Chan Shenging is considered to move to the surface by this way, they and the pollutent generation redox reaction that is adsorbed to photocatalyst surface on this surface.

The electronics of " transition " is final and electronics " hole " is compound and turn back to valence band.According to following assumed response, between the separation period of electron hole, electronics is considered to react with molecular oxygen, and the electronics in the valence band " hole " is considered to and surface hydroxyl reaction, form respectively hydroxyl (OH) and peroxide radical:

OH ^-+ h ⁺(" hole ") → OH (hydroxyl radical free radical)

O ₂+ e ^-(" transition " electronics) → O ₂ ^-2(peroxy radical)

A kind of at present obtainable active TiO of tool ₂Photocatalyst is as DEGUSSAP25 (hereinafter being called " P25 ") (goldschmidt chemical corporation, Field park, Ritchie, New Jersey, the U.S.), by 20 nanometers (nm) the anatase octahedrite TiO of about 80 weight % ₂Bigger (about 40nm) rutile TiO of crystal and about 20 weight % ₂Crystal is formed.The preparation of employing high temperature process, P25 crystal have the perfection of lattice (crystalline perfection) of enough degree so that separate enough electron holes and grain surface is arrived in electronic migration.The hole on surface is than ozone or the chlorine hydroxyl radical free radical of strong oxidizer (OH) form more.The electronics on surface can may be by superoxide ion O by the reduction of molecular oxygen ₂ ^-Formation and further be reduced to superoxide O subsequently ₂ ^-2Form levels of reactive oxygen species.In the presence of oxygen and water, hydrogen peroxide is at the TiO of photocatalytic activity ₂Last formation.Hydrogen peroxide is considered to the main Substrate (agent) of long-range photochemical catalytic oxidation (PCO), and this long-range photochemical catalytic oxidation has been described and photosensitive TiO ₂Very near but be not the directly oxidation of the material of contact physically.Use the TiO of anatase form ₂The formaldehyde available oxygen is changed into CO ₂And H ₂O needs the existence of hydroxyl radical free radical and levels of reactive oxygen species.

With respect to having 10nm average crystal grain size and greater than 100m ²The less TiO of/g surface-area ₂Crystal grain has about 20nm average crystal grain size and about 50m ²The P25 crystal grain of/g BET surface-area seemingly is in theoretical inferior position.At this used BET (with first letter designation of Stephen Brunauer, P.H.Emmett and Edward Teller three surname, Journal of theAmerican Chemical Society, 1938, vol.60 is that widely used physical absorption by gas molecule is calculated the long-pending method of solid surface in the Surface Science pp.309-319).

Table 1 provides the comparison of average crystal grain size with various surface-area measurements, comprises TiO ₂Anatase form and rutile form.

Table 1

The average crystal grain size, surface-area/skeleton volume, effective surface area specific surface area, specific surface area

Nm m ²/ cm ³m ²/ cm ³m ²/ g anatase octahedrite m ²/ g rutile

5 1200 800 208 188

6 1000 667 174 156

7 857 571 149 134

8 750 500 130 117

9 667 444 116 104

10 600 400 104 94

11 545 364 95 85

12 500 333 87 78

13 462 308 80 72

14 429 286 74 67

15 400 267 69 63

16 375 250 65 59

17 353 235 61 55

18 333 222 58 52

19 316 211 55 49

20 300 200 52 47

21 286 190 50 45

22 273 182 47 43

23 261 174 45 41

24 250 167 43 39

25 240 160 42 38

27 222 148 39 35

29 207 138 36 32

31 194 129 34 30

33 182 121 32 28

35 171 114 30 27

37 162 108 28 25

39 154 103 27 24

40 150 100 26 23

Yet,, reduce anatase form and rutile form TiO even as shown in table 1 ₂Average crystal grain size can increase TiO ₂Specific surface area, but because heterogeneous catalyst surface phenomena normally, this generally can not cause the work-ing life that higher photocatalytic activity or photocatalyst are longer, should rationally estimate as people.Explain a TiO that hypothesis is littler crystal grain of this phenomenon ₂Have and to impel quick compound defective in electron hole and shortcoming.See also, as Zhang, Z., etc., J.Phys.Chem.B, 1998, vol.102, pp.10871-10878 shows and uses as Fe ^{+ 3}Or Nb ^{+ 5}The anatase octahedrite TiO of ion doping ₂Crystal grain has increased photocatalytic activity.These are positioned at the electronics that intragranular hotchpotch is held back photon-generation, thereby postpone electron-hole recombination.The support that concerns between the consumption of the hotchpotch that this hypothesis has been reported (active) and character and the anatase crystal grain size for improving.

Be used to destroy the TiO of VOCs ₂The photochemical catalytic oxidation activity in another factor be the resistance to mass transfer that is increased, this resistance to mass transfer appears to adopt has high surface area but the TiO of small-bore ₂The time.The fine porosity is diffused into avtive spot by inhibition VOCs and limits the photocatalytic activity site.

Destruction at VOCs causes being oxidized to CO as siloxanes under the situation of non-volatile ash content formation ₂, H ₂O and SiO ₂, this ash content can seal avtive spot (VOC is oxidized at this avtive spot), and has limited and enter at Catalytic Layer other avtive spots of depths more.

Therefore, present obtainable TiO ₂Photocatalyst has and calculates with unit weight that photocatalytic activity is poor, per unit easily utilizes surface-area to be used for the shortcoming that activity is lower, actual service life is short of removal of pollutants.

The disclosure has overcome TiO in the past ₂Or doped Ti O ₂These shortcomings of photocatalyst.

Summary of the invention

The disclosure provides has the nano-crystalline titanium dioxide (TiO of diameter less than the nanocrystal of 14nm ₂) photocatalyst.

With nanocrystalline TiO ₂Photocatalyst is prepared or handles at utmost to reduce TiO ₂Subsurface defect in the nanocrystal.In addition, the photocatalyst aggregate has the pore structure of low mass transfer resistance, makes TiO ₂Photocatalyst is more anti-because the inactivation that environmental pollutant (as siloxanes) cause.

When the air with sufficient ultraviolet radiation and enough relative humidity exists, the disclosure also provides TiO ₂Nanocrystal, the photocatalytic activity of this nanocrystal are at least the commercially available TiO that comprises larger diameter crystal grain ₂At least 75% of photocatalyst.

The disclosure further provides TiO ₂Nanocrystal, this TiO ₂Nanocrystal has one or more metals, metal oxide, nonmetal or other hotchpotchs or surface treatment agent such as Tungsten oxide 99.999 in conjunction with (doping).

The disclosure also further provides, by producing the levels of reactive oxygen species of hydroxyl radical free radical and oxidation normal air pollutent, nanocrystalline TiO ₂Photocatalyst can be used for eliminating in the air purifier system airborne pollutent.

Nanocrystalline TiO of the present disclosure ₂Photocatalyst also can be used as the photo catalysis air purifying system of anti-siloxanes and is used for water or the use of the part of other fluidic purification system.

The accompanying drawing summary

Fig. 1 provides the figure of the dull and stereotyped inherent speed reactor in laboratory.

Fig. 2 has illustrated in the presence of 90 parts of per 1,000,000,000 (ppb) hexamethyldisiloxane various based on TiO ₂Life-span of photocatalyst.

Fig. 3 has illustrated the pore size distribution overview that compares disclosure photocatalyst with other photocatalysts.

Fig. 4 has illustrated disclosure TiO ₂The X-ray powder diffraction figure of photocatalyst UV114, UV114 has the anatase crystal grain of 122 dusts (12nm).

Fig. 5 has illustrated disclosure TiO ₂The X-ray powder diffraction figure of photocatalyst 2UV27,2UV27 has the anatase crystal grain of 110 dusts (11nm).

Fig. 6 has illustrated the X-ray powder diffraction figure of the extraneous photocatalyst UV139 of the disclosure, and UV139 has the anatase crystal grain of 188 dusts (19nm).

Fig. 7 has illustrated the influence of various hexamethyldisiloxane concentration to the 2UV27 of anti-siloxane catalyst deactivation rate.

Fig. 8 has illustrated the two kinds of burnt TiO of the present disclosure that compare with commercially available P25 deactivation rate ₂The figure of photocatalyst deactivation rate.

Detailed Description Of The Invention

The disclosure provides by having the nano-crystalline titanium dioxide (TiO of diameter less than the nanocrystal of 14 nanometers (nm)₂) photochemical catalyst made. Term " nanocrystal " and " crystal grain " are used interchangeably in this application, and their relational language also is used interchangeably such as " nanocrystalline " and " crystal ". Nanocrystalline TiO₂Photochemical catalyst forms has the porous particle of the pore structure that is conducive to low mass transfer resistance, and has ultraviolet (UV) Photocatalytic oxidation activity of the inactivation that anti-environmental contaminants (such as siloxanes) cause. Nanocrystalline TiO₂Photochemical catalyst can be doped with one or more metals, metal ion, nonmetal or other alloys, or has surface conditioning agent such as tungsten oxide.

With TiO₂Crystal grain is prepared or processes to reduce or at utmost reduce TiO₂Internal flaw in the crystal grain. An example of this processing is such method, be higher than under 250 ℃ the temperature, between preferred 350 ℃ to 450 ℃, in oxygen-containing atmosphere with TiO₂Crystal grain annealing at least 24 hours. This time is to reducing TiO₂Internal flaw in the structure is enough but just causes that on a large scale (large-scale) changes into rutile form and the surface area that brings thus reduces the time and falls short of from anatase form.

Nanocrystalline TiO of the present disclosure₂Photochemical catalyst is connected to form hole by their summit and/or limit. The pore structure that forms thus is conducive to low mass transfer resistance. TiO₂The most surfaces of photochemical catalyst aggregation amass diameter greater than 5nm or larger hole in. At least 200 meters of photochemical catalyst aggregation²Surface area/centimetre³(m ²/cm ³) the skeleton volume diameter greater than 6nm or larger hole in. TiO₂The overall distribution of photochemical catalyst aggregation mesoporous has 10nm or larger pattern, and wherein pattern is used to refer in the group number or the size of normal generation. This pore structure produces the TiO of the inactivation that anti-environmental contaminants (such as siloxanes) cause₂Photochemical catalyst.

In air, have in the environment of enough relative humidity and activating TiO₂The sufficient ultraviolet radiation of photochemical catalyst exists lower, nanocrystalline TiO of the present disclosure₂Photochemical catalyst provides the at present obtainable larger diameter TiO that contains₂At least 80% photocatalytic activity of photochemical catalyst (such as DEGUSSA P25).

Nanocrystalline TiO₂Photochemical catalyst can be used on and eliminates airborne pollutant in the air purifier system, when contacting with ultraviolet light when being activated, by producing hydroxyl radical free radical and the levels of reactive oxygen species that can react with common contaminants (such as VOCs), these pollutant chemistries are changed into the little material of harm, such as water, carbon dioxide and molecular oxygen, or changing into the low pollution compound that other are easier to remove than their parent compound from air stream, described VOCs comprises formaldehyde, toluene, propionic aldehyde (propanal), butylene, propionic aldehyde (propionaldehyde) and acetaldehyde.

Nanocrystalline TiO of the present disclosure₂Photochemical catalyst also can be used for air cleaning system, and air quality is produced photoinduction deodorizing, antibiotic and self-cleaning effect. Nanocrystalline TiO₂Photochemical catalyst can be used in the air cleaning system airborne pollutant changed into the little compound of harm.

Also can adopt with the air (or other gases) that is used for described herein and purify same mode, nano-crystalline photocatalysis agent of the present disclosure is used for water and/or the purification of other fluidic.

The disclosure provides has the TiO that diameter is 14nm or littler nanocrystal size ₂The photocatalyst nanocrystal, this nanocrystal can have metal, metal oxide, nonmetal or other hotchpotchs in conjunction with (doping).Dopant material can be used as coating or TiO is advanced in layer interpolation ₂In.At disclosure doped Ti O ₂In the embodiment of photocatalyst, according to Ti _(1-X)M _XO ₂Ratio with TiO ₂Combine with dopant, wherein X is molar percentage or molar fraction, and M is a dopant material.In one embodiment, molar fraction is less than 0.1.Add in this embodiment and advance TiO ₂The hotchpotch of photocatalyst can promote pollutent to eliminate in every way, comprises making TiO ₂Photocatalyst has more activity under the light (as visible light) of wider scope; Reduce the energy barrier of pollutent; As oxide catalyst; Promote pollutent to absorb the surface of photocatalyst; And/or, make TiO compared to independent use titanium dioxide optical catalyst ₂Photocatalyst is more insensitive to the influence of humidity.

Can be used as TiO ₂The metal of the hotchpotch of photocatalyst includes but not limited to tin, iron, zinc, niobium, tungsten, neodymium, cerium, molybdenum, hafnium and/or its any combination.

Can be used as TiO ₂The nonmetal nitrating titanium dioxide or the TiO of including but not limited to of the hotchpotch of photocatalyst _2-XN _X

In addition, nanocrystalline TiO of the present disclosure ₂Photocatalyst can have surface treatment agent, for example Tungsten oxide 99.999.

Another embodiment of the present disclosure is by the TiO of diameter less than 12nm ₂The photocatalyst that nanocrystal is made.Embodiment preferred has the TiO of diameter less than 12nm ₂Nanocrystal, this nanocrystal is connected to form diameter less than 1 micron porous particle by summit and limit, and wherein most of porous particle surface-area is in 5nm or the bigger hole at diameter all.Nanocrystalline TiO ₂At least 200 meters of preferred structures ²Surface-area/centimetre ³The skeleton volume has 10nm or bigger pore size distribution pattern at the hole of diameter greater than 6nm.Preferred embodiment has mean pore size and is the described particulate TiO of composition greater than 5nm and diameter ₂The 10-25 of nanocrystal size porous particle doubly.

As mentioned above, by UV-irradiation TiO ₂The hydroxyl radical free radical (OH) that photocatalyst forms is extremely strong oxygenant (has relative SHE[standard hydrogen electrode]+redox-potential of 2.8eV), and can the nearly all organic compound of oxidation.By relatively, the redox potential of conventional oxidant chlorine and ozone is respectively+1.36eV and+2.07eV.When air or water pollutant absorb UV-activated TiO ₂In the time of on the photocatalyst, hydroxyl radical free radical is attacked and this pollutent of oxidation, and with this pollutant chemistry change into water, carbonic acid gas and other usually harm little and/or be easier to the material from airflow or fluid flow, removed than their parent compound.Therefore, be chemically converted into the little product of harm, rather than hold back simply and concentrate on strainer, realize more effective thus air, water or other fluidic cleaning by this technology pollutent.

Separate electron hole used herein, be restricted to electronics from valence band " transition " to the time the conduction band, produce electronics " hole " in valence band, return valence band up to electronics and electron-hole recombination.Electron hole isolating mean time (being also referred to as the life-span of current carrier) is about 10 usually ^-9To 10 ^-6Second.

Valence band also can be described as highest occupied molecular orbital (HOMO), and conduction band also can be described as lowest unoccupied molecular orbital (LUMO).Therefore, the transition of electronics from valence band to more high-octane conduction band also can be described as TiO ₂HOMO in electronics by wavelength less than the optical excitation " transition " of 387nm to LUMO.

Crystal TiO ₂The defective of inside configuration can disturb the electron hole to separate, thereby reduces nanocrystalline TiO ₂Photocatalytic activity.Subsurface defect is easy to hold back electronics and stops them to enter conduction band, otherwise electronics can form the superoxide and the hydroxyl radical free radical of oxidable air pollutant with the oxygen reaction at conduction band.The crystal inside defective also can shorten disengaging time, and can reduce photocatalytic activity.On the contrary, the defective on the small-crystalline outside is estimated to improve nanocrystalline TiO ₂Photocatalytic activity.As mentioned above, with nanocrystalline TiO ₂Photocatalyst annealing can reduce the crystal inside defective and improve photocatalytic activity thus.

Nanocrystalline TiO of the present disclosure ₂Photocatalyst can be used as the part of UV-PCO reactor or air-purification system.Nanocrystalline TiO ₂Photocatalyst also can be used for having adopted prevention or overcomes TiO ₂In the UV-PCO reactor of photocatalyst inactivation technology.The UV-PCO reactor has the advantage that can operate, produce insignificant pressure drop, low power consumption operation and need the long life of less maintenance under room temp.TiO of the present disclosure ₂Nanocrystal is kept usually and TiO ₂Relevant semi-conductivity is fully flawless.

When adopting for example low temperature synthesis mode synthesizing nanocrystalline TiO of the sol-gel method of template mediation ₂When (having big surface-area and big hole), with employing high temperature process synthetic TiO ₂Compare, the nanocrystalline material of low temperature method gained is considered to have the crystal inside defective of greater concn.This crystal inside defective has reduced nanocrystalline TiO ₂Photocatalytic activity.Yet, nanocrystalline TiO ₂Photocatalytic activity can by in oxygen-containing atmosphere with TiO ₂Photocatalyst calcining time enough increases.Under certain condition with TiO ₂The crystal grain heating can make oxygen leave crystalline structure, and this usually causes the increase of crystal inside defective.Yet, in clean oxygen environment (for example, not the gas of siliceous pollutent) with TiO ₂The crystal grain heating can produce flawless substantially TiO ₂Crystal grain.

In this method, TiO ₂Preferably be higher than under 200 ℃ the calcining temperature calcining 24 to 72 hours, and more preferably most calcination time is calcining between about 350 ℃ and 450 ℃.Perhaps, method for calcinating can use higher temperature to shorten calcination time; For example, but the calcining step use temperature from paramount approximately 550 ℃ following 5 hours or shorter, preferred temperature was kept about 3 hours to 5 hours under about 450 ℃ to about 550 ℃.When calcining the short period, can choose further heating TiO wantonly ₂So that other about 24 hours to about 72 hours of annealing under the temperature of about 350 ℃ of temperature and 450 ℃.In this process, calcination atmosphere should not have the silicon pollutent.If the calcining medium contains water vapor, it should not contact the silicon fire resistive material that contains of heat.

With reference to accompanying drawing, particularly Fig. 1 provides the laboratory dull and stereotyped inherent speed reactor 8.Reactor 8 has VOC supply 1 and VOC mass flow controller 2.Reactor 8 has the nitrogen supply device 3 that bubble device 4 is fed in raw material, and subsequently moist nitrogen mass flow controller 5 is fed in raw material.Reactor 8 also has oxygen supply 6 and oxygen mass flow controller 7.Reactor 8 has through machining aluminium block 9, is useful on the bed 10 of the sheet (slide) 11 that scribbles catalyzer at this on the machining aluminium block.Reactor 8 has in order to mix and to disperse the granulated glass sphere 12,13 of gas.Gas in the reactor 8 is analyzed by gas-analysis apparatus 14.Reactor has the rate of flow meter of giving vent to anger 15.Reactor 8 has a UV A lamp 17 and the 2nd UV A lamp 18.The height of lamp can be regulated by lamp height adjuster 16.

Will be to according to the nanocrystalline TiO with high surface area and macroporous structure of the present disclosure ₂Exemplary test and with DEGUSSA P25TiO ₂Deactivation rate compare, gained is the result provide in the following embodiments.

For embodiment, the propionic aldehyde about 20% (propanal) is by under the condition of initial oxidation, and 1ppm propionic aldehyde (propanal) is by the UV-A photoxidation under 50% relative humidity (RH).Deactivator is the hexamethyldisiloxane of 90 parts per 1,000,000,000 (ppb).

Under this condition, compare with their initial separately photocatalytic activities, the 18.5m of pore surface area from P25 ²/ g (by the BJH nitrogen adsorption method) is increased to the TiO that mixes tin ₂The 77.8m of (being appointed as UV114 of the present disclosure) ²/ g has reduced the deactivation rate (from per hour per hour 0.335% the reduction that is reduced to UV114 of 2.05% (P25)) of photocatalyst.

Therefore, suppose that photochemical catalysis deactivation rate and siloxane concentrations are proportional, after about 24 hours, the activity of P25 is estimated to drop to 50% of its initial activity in the presence of the 90ppb hexamethyldisiloxane.With this result be extrapolated to deactivator than small concentration-1ppb hexamethyldisiloxane, estimate after 90 days that the photocatalytic activity of P25 drops to 50% of its initial activity.By relatively, after 550 days, estimate that in the presence of the 1ppb hexamethyldisiloxane photocatalytic activity of UV114 drops to 50% of its initial activity.

Embodiment 1

In this embodiment, for simplicity, used the conventional BET-specific surface area m of unit of measure ²/ g.Use nanocrystalline TiO ₂The sheet of 1 inch * 3 inches of aqeous suspension coatings, and allow its drying.When being used for the inherent speed reactor of Fig. 1, this TiO ₂Coating is enough to absorb 100% incident light.This reactor is the dull and stereotyped photo catalysis reactor with the UV-irradiation that is provided by two black lamps (SpectroLine XX-15A).This spectral distribution is symmetry near about 352nm place intensity peak, and extends to 400mm from 300nm.Change intensity of illumination by the distance of adjusting lamp and scribble between the sheet glass of titanium dioxide.The ultraviolet ray intensity of reactor surface is measured by the UVA power meter.Highly purified nitrogen by the water bubbler so that the desired moisture level level to be set.Pollutent from compressed gas cylinder (as propionic aldehyde/N ₂) or from the Temperature Control Type bubbler, produce.Then, Oxygen Flow combined nitrogen and contaminant stream are to prepare required carrier gas mixture (15% oxygen, 85% nitrogen).

With 1 inch * 3 inches aluminium flakes that scribble titanium dioxide be placed on 1 inch wide 18 inches long from the well that aluminium block grinds.Cover this well with the quartz window that can see through 96%UVA then.Liner between quartz window and the aluminium block produces runner (flow passage) above scribbling the sheet glass of titanium dioxide.1 inch wide 2mm height of this runner.

Contaminated gas enters reactor, and it is at first by glass mixed bead bed.Then, air-flow enters the inlet zone of 1 inch * 2mm, and this inlet zone has enough length (3 inches) to produce full-blown laminar velocity characteristic.Then, air-flow passes through from the glass pane surface that scribbles titanium dioxide.At last, before leaving reactor, gas is by the exit region (3 inches long) and the second granulated glass sphere bed of 1 inch * 2mm.

With reference now to Fig. 2,, in the presence of the 90ppb hexamethyldisiloxane, determine various based on TiO by the inherent speed reactor that uses Fig. 1 ₂Life-span of photocatalyst.By determine the deactivation rate of photocatalyst at the straight slope of representative operation starting stage catalyst performance.The value of P25 is repeatedly the mean value of test.

Shown in data in the following table 2, and as shown in Figure 2, when becoming bigger more than or equal to the surface-area in the hole of 6nm, photocatalytic activity loss speed (representing with % initial activity per hour) has diminished.Yet, carry out N by Micrometrics ASAP 2010 surface area test devices ₂Absorption and to the BJH of this absorption analyze determined this linear relationship and be not suitable for total BET surface-area or diameter greater than the surface-area in the hole of 4nm.

Table 2

Catalyzer	Active changing down, the % initial activity/hour	BET	BET APD	SA≥ 4nm	SA≥ 5nm	SA≥ 6nm
Catalyzer	Active changing down, the % initial activity/hour	BET	BET APD	SA≥ 4nm	SA≥ 5nm	SA≥ 6nm	P25	-2.04	52.0	8.8	25.5	20.7	18.5
UV139	-1.45	66.6	8.9	59.2	49.8	43.5	P25	-2.04	52.0	8.8	25.5	20.7	18.5
UV139	-1.45	66.6	8.9	59.2	49.8	43.5	UV45	-1.38	64.6	22.0	50.8	47.6	46.0

2UV27	-0.93	123.1	7.2	101.2	71.7	52.3
2UV27	-0.93	123.1	7.2	101.2	71.7	52.3	2UV59	-0.92	82.5	21.4	76.3	74.5	72.7
UV114	-0.33	99.4	21.4	85.0	80.3	77.8	2UV59	-0.92	82.5	21.4	76.3	74.5	72.7

With reference now to Fig. 3,, the pore size distribution of photocatalyst P25, UV139 and UV114 is shown in the relation of aperture (X-axle) and specific surface area (Y-axle).When the pore size distribution data among data based Fig. 3 of table 2 is considered, what the photocatalyst with minimum deactivation rate not only had an increase is about 10nm or bigger greater than the surface-area in the hole of 6nm and its pattern (being the dominant overwhelming majority) aperture, and can be bimodal, shown in the chart in UV114 aperture.

Table 2 data presentation, under same UV-irradiation, in concentration be 90ppb hexamethyldisiloxane in the presence of, compare UV114 with P25 and have outstanding life-span of at least 6 times for the P25 life-span greater than the surface-area in the hole of 6nm with 4.2 times.These data are extrapolated to the siloxanes that time average concentration is 2ppb, and hypothesis deactivation rate and Pollutant levels are linear, same challenge in the face of siloxanes, UV114 will keep at least 20% of its initial activity after 10000 hours, and only after 1700 hours P25 prospective damage is fallen 80% of its initial activity.

Fig. 4 has illustrated the X-ray powder diffraction figure of disclosure photocatalyst UV114Sn (tin), and UV114Sn (tin) is mainly anatase octahedrite and has the crystal grain that diameter is about 12nm (122 dust).

Fig. 5 has illustrated the X-ray powder diffraction figure of disclosure photocatalyst 2UV27, and 2UV27 mainly also is anatase octahedrite and has the crystal grain that diameter is about 11nm (110 dust).

By comparing, Fig. 6 has illustrated the X-ray powder diffraction figure of photocatalyst UV 139, and this photocatalyst size is not included in too greatly in the scope of the present disclosure, and UV 139 is mainly anatase octahedrite and has the crystal grain that diameter is about 19nm (188 dust).Shown in above-mentioned table 2 data, compare 139 pairs of pollutents of UV with UV114 and have bigger deactivation rate.

Embodiment 2

Fig. 7 has illustrated experimental result, shows the influence of various hexamethyldisiloxane concentration to the 2UV27 of anti-siloxane catalyst deactivation rate.X-coordinate is siloxanes duration of contact, and X-coordinate is normalized to selected hexamethyldisiloxane level (90ppb).The linear scaling factor equals to multiply by duration of contact hexamethyldisiloxane concentration divided by 90.Each catalyst exposure is in the hexamethyldisiloxane different time of controlled level.By using propionic aldehyde (propanal), measure photocatalytic activity termly and therefore measure deactivation rate in the different time as probe gas.

As shown in Figure 7, data and curves trends towards the right side more, then photocatalyst deactivation rate more little.Reducing of photocatalyst deactivation rate will be corresponding to the longer photocatalyst life-span.Shown in the data and curves of 34ppb hexamethyldisiloxane and 90ppb hexamethyldisiloxane, the relation between photocatalyst life-span and the hexamethyldisiloxane concentration is non-linear.Therefore, the low concentration of hexamethyldisiloxane causes progressive elongated catalyst life.

For example, under the active particular case that reduces by 50% inactivation level corresponding to propionic aldehyde (propanal), when the hexamethyldisiloxane level when 90ppb drops to 34ppb, the photocatalyst life-span is to increase (promptly 2.65 corresponding to the linearity of hexamethyldisiloxane concentration rate, obtain divided by 34 with 90) about 1.2 times, the life-span has a net increase of and adds as 3.18 times (promptly 1.2 * 2.65).The inference that draws from these data is: for example will cause the non-linear increase in photocatalyst life-span by the concentration of using absorbent filter to reduce hexamethyldisiloxane.

Embodiment 3

Anatase octahedrite-the TiO of a plurality of independent batch high surface areas, great circle column hole ₂By with SnF ₂Additive mixes and calcines in 500 ℃ of following air and prepared and got in 4 hours.Be assigned therein as " masterbatch mixture (Master Mix) ".With the part cooling of this burnt masterbatch mixture, pulp and with embodiment 1 described the same manner be applied to aluminium flake, drying, and test is active and the activation life-span.Test after 50 hours, the average deactivation rate of this burnt masterbatch mixture be initial one way efficient (Initial Single Pass Efficiency)/hour 0.32% (%ISPE/hr).The second section of this masterbatch mixture melted down and annealing 72 hours in 400 ℃ of following air.Test after 50 hours, the average deactivation rate of calcining and annealed masterbatch mixture is 0.08% (%ISPE/hr), Fig. 8 data presentation the obvious improvement on the performance.By comparing, reference catalyst P25DEGUSSA is at corresponding deactivation rate of locating to have 1.6%ISPE in 50 hours.In this case, compare raw catalyst with P25 and on active lifetime, demonstrated about 2000% improvement.

Though the disclosure can be made various changes and be equal to an alternative key element wherein by describing with reference to one or more exemplary, it will be understood by those skilled in the art that under the situation that does not depart from disclosure scope.

Claims

1. one kind comprises titanium dioxide (TiO ₂) photocatalyst of nanocrystal, described titanium dioxide (TiO ₂) the nanocrystal diameter is less than 14 nanometers (nm) and form one or more holes, wherein said TiO ₂Nanocrystal is to have 200m at least in 6nm or the bigger hole at diameter ²Surface-area/cm ³The skeleton volume, and wherein the pore size distribution pattern is 10nm or bigger.

2. the photocatalyst of claim 1 is wherein in order to keep TiO ₂Semiconductor property and the electron hole that is kept for photocatalysis separate described TiO ₂The basic zero defect of nanocrystal.

3. the photocatalyst of claim 1, wherein said TiO ₂The diameter of nanocrystal is less than 12nm.

4. the photocatalyst of claim 1, wherein said TiO ₂Nanocrystal further comprises the coating or the layer of dopant material, and described dopant material is selected from metal, metal oxide, nonmetal and any combination.

5. the photocatalyst of claim 4 is wherein with described dopant material and described TiO ₂Nanocrystal is pressed Ti _(1-X)M _XO ₂The ratio combination, wherein Ti is a titanium, x is to be dopant material less than 0.1 molar fraction and M.

6. the photocatalyst of claim 4, wherein said dopant material comprises metal and any combination thereof that is selected from tin, iron, zinc, niobium, tungsten, neodymium, cerium, molybdenum, hafnium.

7. the photocatalyst of claim 4, wherein said dopant material comprises nonmetal nitrogen.

8. the photocatalyst of claim 3, wherein said TiO ₂Nanocrystal forms cylindric hole.

9. the photocatalyst of claim 8, wherein said TiO ₂Nanocrystal forms the porous particle less than 1 micron.

10. the photocatalyst of claim 1, wherein said TiO ₂Nanocrystal forms to have and TiO ₂Nanocrystalline grain size is the same or than the porous particle in bigger aperture.

11. one kind is used for air, water or fluidic purification system, described purification system comprises the photochemical catalysis TiO that forms porous particle ₂Nanocrystal, wherein said TiO ₂The diameter of nanocrystal is less than 14nm.

12. one kind is used nanocrystalline TiO ₂Photocatalyst is removed the method for pollutent in air, water or the fluid, and described method comprises:

Utilize the described nanocrystalline TiO of UV-irradiation ₂Photocatalyst; With

With pollutent and described nanocrystalline TiO ₂Photocatalyst contacts;

Wherein said nanocrystalline TiO ₂Photocatalyst comprises the TiO of diameter less than 14nm ₂Nanocrystal.

13. one kind prepares the nanocrystalline TiO that does not have subsurface defect substantially ₂The method of photocatalyst, described method comprises:

Under at least 200 ℃ temperature with nanocrystalline TiO ₂The photocatalyst calcining,

Wherein said method for calcinating carries out in containing oxygen and not siliceous atmosphere.

14. the method for claim 13 is wherein with described nanocrystalline TiO ₂Photocatalyst calcining 24 to 72 hours.

15. the method for claim 14 is wherein with described nanocrystalline TiO ₂Photocatalyst calcining, most of calcination time from about 350 ℃ to about 450 ℃ of temperature.

16. the method for claim 13 is wherein with described nanocrystalline TiO ₂Photocatalyst from about 450 ℃ to about 550 ℃ temperature lower calcinations about 3 hours to about 5 hours.

17. the method for claim 16, described method further are included in after the calcining nanocrystalline TiO ₂Photocatalyst was being annealed other about 24 hours to about 72 hours to about 450 ℃ of temperature from about 350 ℃.