CN112206742A

CN112206742A - Porous oxide adsorption material for efficiently removing harmful ions in water

Info

Publication number: CN112206742A
Application number: CN201910614046.5A
Authority: CN
Inventors: 黄富强; 农淑英; 董武杰
Original assignee: Peking University
Current assignee: Peking University
Priority date: 2019-07-09
Filing date: 2019-07-09
Publication date: 2021-01-12
Anticipated expiration: 2039-07-09
Also published as: CN112206742B

Abstract

The invention relates to a transition metal oxide material for water pollution treatment, which can remove harmful metal ions in water such as chromium (VI), arsenic (V), lead (I1), uranium (VI), cadmium (I1) and the like to reach the drinking water standard. Chromium (VI) and arsenic (V) can be adsorbed to less than 10ppb, and lead (II), cadmium (II) and uranium (VI) can be adsorbed to less than 1 ppb. The adsorbent has a general formula of M_xO_y(ii) a Wherein M is selected from one or two transition metal elements such as Zr, Ti, Fe, Mn, Mo, W and the like; and x is more than or equal to 1 and less than or equal to 2, and y is more than or equal to 1 and less than or equal to 5. The preparation of the material adopts a micro-etching technology, and the precise selective etching enables the material to have the characteristics of rich pore structure, high density of hydroxyl, high specific surface area and the like, so that the adsorbent has strong adsorption force on harmful ions and achieves the effect of removing efficiently. In addition, the material has good recycling performance, simple synthesis process and low cost, and has wide prospect in the aspect of water pollution treatment.

Description

Porous oxide adsorption material for efficiently removing harmful ions in water

Technical Field

The invention belongs to the technical field of water pollution treatment materials, and particularly relates to a porous transition metal oxide with low crystallinity.

Technical Field

With the increasing world population and the advancing industrialization process, the water pollution problem is widely concerned all over the world, especially the problem that harmful metal and non-metal ions pollute drinking water is ubiquitous all over the world and threatens the health of human beings. The ions of chromium (VI), lead (II), arsenic (V), cadmium (II), uranium (VI) and the like are common harmful elements in water and come from waste liquid discharged by various industries such as metallurgy, electroplating, power generation and the like. The compounds thereof cannot be naturally degraded or contain radioactivity, causing serious health problems for human beings. The Ministry of health of China stipulates the limit of chromium (VI) in drinking water of 50ppb, the limit of cadmium (II) of 5ppb, the limit of lead (II) of 10ppb, the limit of arsenic (V) of 10ppb and the limit of total alpha radioactivity of 0.5Bq L in the sanitary Standard for Drinking Water (GB 5749-^-1. The water purification methods adopted at present mainly include adsorption, ion exchange, membrane separation and other technologies. Among them, the adsorption method has the advantages of simple operation, economy, high efficiency, flexible usage, and is one of the best technologies for application prospect [ Khin M, Nair A S, Babu V J, et al].Energy&Environmental Science，2012，5(8)：8075-8109.]. Commercially available adsorbent materials include activated carbon, molecular sieves, polymeric compounds, biomass materials, transition metal oxides, and the like. Although the adsorbent materials are various and some have a high adsorption capacity, the bottleneck of the current technology is adsorption in trace amounts, which are difficult to remove by the existing adsorbents when the concentration of these harmful metals is low to some extent (< 5 ppm). Almost no adsorbent can directly remove trace chromium (VI), cadmium (II), lead (II) and other ions in water to reach the standard of drinking water. In particular, chromium (VI) exists in the form of anions in water, easily diffuses in negatively charged soil, and is difficult to precipitate and adsorb. At present, no good material can adsorb chromium (VI) to less than 50 ppb. Therefore, there is a need to develop a novel material capable of thoroughly adsorbing harmful ions in water to meet drinking water standards.

Distribution coefficient K_dIs a measure of the adsorption capacity of the adsorbent under the condition of extremely low adsorbate concentration, K_dThe higher the value is, the stronger the adsorption capacity is, and the calculation formula is as follows:

K_d＝(C₀-C_e)V/C_em(mL g^-1)

wherein V (mL) is the volume of the adsorbate solution, C₀(mg L^-1Or ppm) and C_e(mg L^-1Or ppm) are the initial and equilibrium concentrations of adsorbate respectively, and m (g) is the mass of adsorbent used.

At present, materials such as activated carbon, molecular sieves, high molecular materials, biomass materials, sulfides, oxides and the like have been studied as harmful ion adsorbents. Partition coefficient K of commercial activated carbon adsorption chromium (VI)_dThe value can reach 8 x 10³[Barkat M，Nibou D，Chegrouche S，et al. Kinetics and thermodynamics studies of chromium(VI)ions adsorption onto activated carbon from aqueous solutions[J].Chemical Engineeringand Processing：Process Intensification，2009，48(1)： 38-47.]. The activated carbon prepared by carbonizing the hard shell of the apple with concentrated sulfuric acid can remove chromium (VI) by 95 percent, and the adsorption capacity reaches 151.51mg g^-1[Doke K M，Khan E M.Equilibrium，kinetic and diffusion mechanism of Cr(VI)adsorption onto activated carbon derived from wood apple shell[J].Arabian Journal of Chemistry，2017，10： S252-S260.]. Distribution coefficient K of adsorbing chromium (VI) by MCM-41/ZSM composite molecular sieve_dThe value was 1.87 x 10³[Kazemian H，Mallah M H.Removal of chromate ion from contaminated synthetic water using mcm-41/zsm-5 composite[J]. Journal of Environmental Health Science&Engineering，2008，5(1)：73-77.]. Metal-organic resins for removing chromium (VI) by anion exchange, partition coefficient K_dThe value can reach 1.2-5.5 x 10⁴The adsorption capacity reaches 230-^-1[Rapti S， Pournara A，Sarma D，et al.Selective capture of hexavalent chromium from an anion-exchange column of metal organic·resin-alginic acid composite[J].Chemical science，2016，7(3)：2427-2436.]. Using MoS₄ ²The intercalated layered double hydroxide can adsorb lead (II), silver (I), mercury (II) and the like, can adsorb the lead (II), the silver (I) and the mercury (II) to below 1ppb, and has a distribution coefficient K_dUp to 10⁷[Ma L，Wang Q，Islam S M，et al.Highly selective and efficient removal of heavy metals by layered double hydroxide intercalated with the MoS42-ion[J].Journal of the American Chemical Society，2016，138(8)：2858-2866.]. polypyrrole/MoS₄ ²The composite can remove lead (II), silver (I) and mercury (II) to 99.6%, and has a residual content of less than 2ppb and a distribution coefficient K_dUp to 10⁷[Xie L，Yu Z，Islam S M，et al.Remarkable Acid Stability of Polypyrrole-MoS4：A Highly Selective and Efficient Scavenger of Heavy Metals Over a Wide pH Range[J].Advanced Functional Materials，2018，28(20)：1800502.]. These studies have good application prospects, but currently still have many problems, such as that the highest partition coefficient of the chromium (VI) adsorbent is only 10⁴The requirement of treating drinking water is still not met. Although some materials adsorbing lead (II), cadmium (II), and the like have excellent adsorption performance, they are almost sulfides, and cause secondary pollution in use, which is a serious problem.

Transition metal oxides such as iron oxide, titanium dioxide and composite oxides have received wide attention from researchers as harmful ion adsorbents because of their advantages of environmental friendliness, no harm, resistance to physical and chemical corrosion, recyclability, etc. At present, the methods for preparing the transition metal adsorbent mainly comprise a sol-gel method, a precipitation method and a traditional hydrothermal method. Grssol and the like adopt a precipitation method to precipitate ferric nitrate under an alkaline condition to obtain nano ferric oxide; chen et al used ferric chloride and hydrochloric acid to stir at 100 deg.C for two days for precipitation to obtain nano-iron oxide; hu et al prepared iron oxide using a sol-gel process. The iron oxide nano-particles prepared by the preparation method have the size of 3.8-100nm and the chromium (VI) adsorption capacity of 19.2mg g^-1The absorbed copper (II) can reach 149.25mg g^-1[Hua M，Zhang S，Pan B，et al.Heavy metal removal from water/wastewater by nanosized metal oxides：a review[J].Journal of hazardous materials，2012，211：317-331.]. Chen et al synthesized porous ZrO by sol-gel method using hexadecylamine, tetrabutyl titanate and zirconium n-butoxide as raw materials₂/TiO₂The capacity of adsorbing chromium (VI) of the ball reaches 25.4mg g^-1And has good cyclic use performance [ Chen D, Cao L, Handey T L, et al, simple synthesis of monomer mesoporous zirconium oxide microspheres with varying composition and high surface area for cyclic use [ J].Advanced Functional Materials，2012，22(9)：1966-1971.]. Wang et Al hydrothermal a mixture of magnesium nitrate, aluminum nitrate, urea, potassium sulfate and potassium persulfate at 120-₂The removal rate of the compound can reach 96.73 percent for lead (II) [ Bo L, Li Q, Wang Y, et Al, one-pot hydraulic synthesis of the dry thermal Mg, Al layered double hydroxides/MnO₂ and adsorption for Pb(II)from aqueous solutions[J].Journal of Environmental Chemical Engineering，2015，3(3)：1468-1475.]. The oxide adsorbent synthesized by the method has certain adsorption performance, and has great potential in practical application as an oxide. However, due to the limitation of the synthesis method, the oxide adsorbent synthesized by the methods at present has the defect that the adsorption performance is not excellent enough, the research content is mostly limited to the adsorption capacity or the adsorption rate, and the efficient trace adsorption is rarely involved. At present, no oxide adsorbent capable of adsorbing trace harmful ions to directly reach the standard of drinking water exists.

Therefore, it is urgently needed to develop a new method for preparing transition metal oxide, regulate and control the surface groups of the adsorbent, and enhance the mutual affinity between the adsorbent and the adsorbate so as to achieve the purpose of efficient trace adsorption. The aim is that the residual quantity of harmful ions in the treated water is far lower than the national drinking water standard, thereby protecting the health of human beings.

Disclosure of Invention

The invention aims to synthesize a method capable of almost completely removing trace harmful ions (chromium, lead and arsenic) in water aiming at the problem that the trace harmful ions in water are difficult to remove and reach the standard of drinking waterUranium, etc.). Harmful ions in water, such as chromium (VI), lead (II), uranium (VI), arsenic (V), and cadmium (II) can be adsorbed from 2010ppb to < 6ppb, 2000ppb to < 0.06ppb, 2000ppb to < 0.03ppb, 1000ppb to < 10ppb, and 2000ppb to < 1 ppb. Adsorption distribution coefficient K_dThe value of chromium (VI) and arsenic (V) can reach more than 10⁵ml g^-1Lead (II), uranium (VI) and cadmium (II) can reach more than 10⁸ml g^-1It is the highest value in the existing research. Meanwhile, the composite material has the advantages of quick adsorption and good recycling performance.

The technical scheme adopted by the invention is as follows: using a porous transition metal oxide as adsorbent, having the general formula M_xO_yWherein M is selected from one or more transition metal elements such as Zr, Ti, Fe, Mn, Mo, W and the like; x is more than or equal to 1 and less than or equal to 2, and y is more than or equal to 1 and less than or equal to 5.

Further, the transition metal oxide has the following characteristics:

1) the surface is rich in hydroxyl, the hydroxyl oxygen content in the spectrum peak of X-ray photoelectron spectroscopy oxygen reaches 50-80%, the hydroxyl density can reach 72 hydroxyl groups per square nanometer, the chelating effect with harmful metal ions is realized, and the chelating effect with harmful ions is realized.

2) Amorphous or low crystalline phase, no obvious diffraction peak or low diffraction peak intensity in X-ray powder diffraction result.

3) The particle shape and size are various, the particle shape can be regulated and controlled to be spherical, polyhedral, star-shaped, hollow and the like, and the particle size is 1 nanometer to 100 micrometers.

4) Has a large number of micro/nano-pore structures, and nitrogen adsorption, desorption and adsorption experiments prove that a large number of mesopores or micropores with the diameter of 70-300m exist² g^-1Specific surface area of (2).

Further, the transition metal oxide adsorbent is obtained by using a microetching method as follows:

1) synthesis of multicomponent composite oxide A_aM_xO_yPrecursor, A is alkali metal or alkaline earth metal element, M is one or two transition metal elements of Zr, Ti, Fe, Mn, Mo, W and the like; a is more than or equal to 1 and less than or equal to 4, x is more than or equal to 1 and less than or equal to 2, and y is more than or equal to 1 and less than or equal to 5.A is described_aM_xO_yPrecursor synthesis methods generally use hydrothermal or high temperature solid phase firing and can be prepared by prior art methods, such as the BaZrO described by Moreira et al₃[Moreira M L， Andrés J，Mastelaro V R，et al.On the reversed crystal growth of BaZrO₃ decaoctahedron： shape evolution and mechanism[J].CrystEngComm，2011，13(19)：5818-5824.]. Hollow BaZrO described by Dong et al₃[Dong Z，Ye T，Zhao Y，et al.Perovskite BaZrO₃ hollow micro-and nanospheres：controllable fabrication，photoluminescence and adsorption of reactive dyes[J].Journal of Materials Chemistry，2011，21(16)：5978-5984.]. The synthesized precursor can have various shapes, including spherical, polyhedral, star-shaped, hollow and the like. The synthesized particle size varies from 1 nm to 10 μm.

2) And mixing the precursor and acid according to a proportion, and etching under a hydrothermal condition. The selected acid can be organic acid and inorganic acid such as hydrochloric acid, nitric acid, formic acid, acetic acid, etc. Mixing the precursor, acid and water according to a certain molar ratio, uniformly stirring, putting into a high-pressure reaction container, and heating for a certain time. And centrifugally separating, washing and drying the product to obtain the product. Specific steps can refer to specific implementation examples. Through the etching reaction of the step, the A element of the precursor is dissolved out, and the general formula of the product is M_xO_xM is one or two transition metal elements selected from Zr, Ti, Fe, Mn, Mo, W and the like in the precursor; x is more than or equal to 1 and less than or equal to 2, and y is more than or equal to 1 and less than or equal to 5. The product keeps the original shape of the precursor after the etching reaction, namely the product can have the shapes of sphere, polyhedron, star, hollow and the like, and the particle size is 1 nanometer to 10 micrometers.

Compared with the prior adsorbent, the reason that the adsorbent prepared by the microetching technology has prominent adsorption performance on trace harmful ions is as follows:

1) the microetching under the acidic condition promotes the exchange of cations and protons (H) in the precursor particles to form high-density internal surface hydroxyl groups, and the internal surface hydroxyl groups have strong adsorption force on harmful ions. The micro-etching process is to dissolve out alkali metal or alkaline earth metal in the precursor under an acidic condition, and a large amount of protons (H) are exchanged with the alkali metal or the alkaline earth metal in the process to form inner surface hydroxyl. The high-density hydroxyl can form chelation on harmful ions and has extremely strong adsorption force, so that the harmful ions can be thoroughly removed.

2) And the micro-etching hydrothermal reaction realizes accurate selective etching. Different from the traditional hydrothermal reaction from bottom to top, the micro-etching method is a top-down hydrothermal method, and realizes precise pore forming by selectively and partially etching the precursor, so that a rich pore structure and a high specific surface area are formed, anchoring of harmful ions is enhanced, and adsorption capacity is increased.

3) The morphology of the adsorbent is regulated and controlled through the induction of the precursor. The transition metal oxide product prepared by micro-etching keeps the shape of the precursor, so that the shape of the precursor favorable for adsorption, such as hollow, star-shaped and the like, is selected, the mass transfer process of adsorption can be promoted, and the specific surface area is increased.

Sample characterization

The method comprises the steps of collecting appearance and ultra-microstructure information of a sample by using a scanning electron microscope and a transmission electron microscope, collecting sample structure information by using an X-ray diffractometer, collecting sample pore structure information by using a specific surface area tester, obtaining sample surface composition information by using an X-ray photoelectron spectroscopy, and obtaining ion concentration of hexavalent chromium by using inductively coupled plasma emission spectroscopy and mass spectrometry.

Drawings

FIG. 1 shows a precursor hollow BaZrO prepared by the present invention₃Hollow porous ZrO of the product₂Scanning electron micrograph (c).

FIG. 2 shows a hollow porous ZrO prepared by the present invention₂Transmission electron micrograph (c).

FIG. 3 shows a precursor hollow BaZrO prepared by the present invention₃Hollow porous ZrO of the product₂X-ray powder diffraction pattern of (A) and (B)₂The nitrogen adsorption desorption curve of (1).

FIG. 4 shows a hollow porous ZrO prepared by the present invention₂Adsorption of hexavalent chromium in aqueous solutionsA temperature adsorption curve, an adsorption kinetics curve, and an adsorption performance and cycle performance graph under different pH environments.

FIG. 5 shows a precursor of star BaZr prepared by the present invention_xTi_1-xO₃(x ═ 0.2 to 0.8), product star porous Zr_xTi_1-xO₂Scanning electron micrographs of (x ═ 0.2 to 0.8).

FIG. 6 shows star-shaped porous Zr prepared by the present invention_xTi_1-xO₂(x-0.2-0.8) by scanning electron microscope.

FIG. 7 shows a precursor of star-shaped BaZr prepared by the present invention_xTi_1-xO₃(x ═ 0.2 to 0.8), product star porous Zr_xTi_1-xO₂(X-0.2-0.8) X-ray powder diffraction pattern and Zr_xTi_1-xO₂The nitrogen adsorption desorption curve of (1).

FIG. 8 shows star-shaped porous Zr prepared by the present invention_xTi_1-xO₂(x is 0.2-0.8) an isothermal adsorption curve, an adsorption kinetics curve, an adsorption performance and a cycle performance graph of hexavalent chromium adsorbed in an aqueous solution under different pH environments.

Detailed Description

The present invention will be described in further detail with reference to examples. It should be noted that the present invention is not limited to these specific embodiments. Equivalent alterations and modifications may be effected by those skilled in the art without departing from the background and spirit of the invention, and the content thereof is also intended to be covered by the appended claims.

Comparative example 1

This example uses a conventional preparation method- -precipitation method for preparing the transition metal oxide ZrO₂First, ZrOCl is added₂·8H₂Dissolving O in water, and adding ammonia water dropwise to adjust pH to 9 to obtain white precipitate. The precipitate was washed several times with deionized water and dried in an oven to give a white powder. Annealing the white powder at 400 ℃ for 4 hours to obtain ZrO₂. The chromium (VI) ion adsorption material is used for adsorbing chromium (VI) ions and can adsorb the chromium (VI) from 2010ppbUp to 150 ppb. It can be seen that this residual quantity of adsorption, 150ppb, is also much higher than the standards permitted for drinking water (50 ppb). Thus, ZrO prepared by conventional precipitation methods₂Does not have excellent adsorption performance.

Comparative example 2

This example uses another conventional preparation method- -sol-gel method for preparing the transition metal oxide ZrO₂Firstly, dissolving n-butyl zirconium into ethanol, adding polyethylene glycol, stirring at 70 ℃ for 5 hours to form gel, and burning the gel into powder by using a burning method. Annealing at 600 ℃ for 4 hours to obtain ZrO₂. When the method is used for chromium (VI) ion adsorption, the chromium (VI) can be adsorbed from 2010ppb to 80 ppb. It can be seen that the adsorption residual amount is higher than the allowable standard for drinking water (50ppb), and the treated water still cannot be used as drinking water. Thus, ZrO prepared by the conventional sol-gel method₂Does not have excellent adsorption performance.

Examples 1

Firstly, a hydrothermal method is used for preparing the BaZrO with the hollow spherical shape₃Precursor, reaction condition is that Ba (OH)₂、ZrOCl₂·8H₂O, KOH and H₂Fully stirring O according to the molar ratio of 1: 10: 100, placing the mixture into a hydrothermal device, and reacting for 3 days at 150 ℃ to obtain the hollow BaZrO₃. The precursor is hollow BaZrO₃Hydrochloric acid and water are mixed according to the molar ratio of 1: 10: 100, the mixture is placed in a high-pressure reaction vessel, and the mixture is firstly reacted for one day at the temperature of 100 ℃ and then transferred to an oven at the temperature of 150 ℃ for reaction for 3 hours. After this step, Ba is completely dissolved and converted into ZrO₂. The product was dried in an oven at 70 ℃ by centrifugation and washing with deionized water. The product retains the hollow spherical characteristic of the precursor, and the precursor BaZrO can be seen from figure 1₃And ZrO of product₂Are all hollow spheres. FIG. 2 shows ZrO₂The transmission electron microscope image of (2) confirms the characteristics of the hollow structure. As can be seen from FIG. 2, the hollow-structured zirconia is composed of a plurality of ultrafine particles smaller than 1 nm stacked together. It can be seen that Zr and O are recrystallized in situ very little during the etching processThe nanoparticles of (1). ZrO after Ba is eluted₂The overall particle still maintains the morphological characteristics of the precursor, i.e. the hollow spherical structure. FIG. 3a shows a precursor BaZrO of perovskite structure₃And ZrO of amorphous structure₂X-ray powder diffraction pattern of (a). FIG. 3b shows ZrO₂The curve of nitrogen adsorption and desorption proves that a large number of mesopores exist in the nitrogen adsorption and desorption curve, and the specific surface area of the nitrogen adsorption and desorption curve is up to 120m by calculating with a BET method² g^-1. The zirconium dioxide is used for purifying water to adsorb hexavalent chromium, and the adsorption performance is shown in fig. 4. Hexavalent chromium can be adsorbed from 2ppm to less than 5ppb at different pH (2-7), taking no more than 1 minute. Distribution coefficient K_dUp to > 10⁵. At the same time, the material has high adsorption capacity (60mg g)^-1) And excellent recycling performance. The chromium (VI) content of the water treated by the zirconium dioxide is far lower than the standard of drinking water specified in China (< 50 ppb).

EXAMPLES example 2

Firstly, a hydrothermal method is used for preparing the BaZr with the star-shaped structure_xTi_1-xO₃(x ═ 0.2 to 0.8) precursor, under reaction conditions such that Ba (OH) is reacted₂、ZrOCl₂·8H₂O、 TiCl₄And H₂O is fully stirred according to the molar ratio of 1: x to (1-x) to 100, (x is 0.2-0.8), then the mixture is placed in a hydrothermal device, and the BaZr is obtained after the reaction is carried out for 1 day at the temperature of 120 DEG C_xTi_1-xO₃. Adding a precursor BaZr_xTi_1-xO₃Hydrochloric acid and water are mixed according to the molar ratio of 1: 12: 100, the mixture is placed in a high-pressure reaction vessel, and the mixture is firstly reacted for one day at the temperature of 110 ℃ and then transferred to an oven at the temperature of 140 ℃ for reaction for 2 hours. After this step, Ba was completely dissolved out and converted into Zr as a product_xTi_1-xO₂(x is 0.2 to 0.8). The product was dried in an oven at 70 ℃ by centrifugation and washing with deionized water. Product Zr_xTi_1-xO₂(x ═ 0.2 to 0.8) has the same star-shaped characteristics as the precursor, and it can be confirmed by the scanning electron microscope of FIG. 5. FIG. 6 shows Zr_xTi_1-xO₂(x-0.2-0.8), as seen from the transmission electron microscope image, this star-shaped Zr_xTi_1-xO₂(x ═ 0.2 to 0.8) is a combination of a number of ultrafine particles smaller than 1 nm stacked, consistent with the phenomena of example 1. It can be seen that the mechanism of the etching process is consistent with example 1. FIG. 7a shows a precursor BaZr of perovskite structure_xTi_1-xO₃(x ═ 0.2 to 0.8) and Zr of amorphous structure_xTi_1-xO₂(X-0.2-0.8) X-ray powder diffraction pattern. FIG. 7b shows ZrO₂The nitrogen adsorption and desorption curve proves that a large number of micropores exist in the nitrogen adsorption and desorption curve, and the specific surface area of the nitrogen adsorption and desorption curve is up to 300m calculated by a BET method² g^-1. The material is used for purifying water and adsorbing hexavalent chromium and pentavalent arsenic, can adsorb chromium from 2ppm to less than 1ppb and arsenic from 2ppm to less than 5ppb, and has a distribution coefficient K_dUp to > 10⁵. The time is not more than 10 seconds, and the material has excellent recycling performance, as shown in fig. 8 and 9.

EXAMPLE 3

Firstly, a hydrothermal method is used for preparing BaZrO with truncated octahedron morphology₃Precursor, reaction condition is that Ba (OH)₂、ZrOCl₂·8H₂O and H₂Fully stirring O according to the molar ratio of 1: 100, placing the mixture into a hydrothermal device, and reacting for 1 day at 130 ℃ to obtain the truncated octahedron BaZrO₃. Precursor BaZrO₃Hydrochloric acid and water are mixed according to the molar ratio of 1: 10: 100, the mixture is placed in a high-pressure reaction vessel, and the mixture is firstly reacted for one day at the temperature of 110 ℃ and then transferred to an oven at the temperature of 130 ℃ for reaction for 3 hours. After this reaction, Ba was completely dissolved and converted into truncated octahedral ZrO₂. The product was dried in an oven at 70 ℃ by centrifugation and washing with deionized water. The procedure and mechanism of the preparation reaction are in accordance with example 1. X-ray powder diffraction shows that this zirconium dioxide has an amorphous phase. The zirconium dioxide is used for purifying water to adsorb hexavalent chromium, and can adsorb the hexavalent chromium from high-concentration chromium (more than 2ppm) to less than 4ppb under different pH environments, and the time is not more than 1 minute. Distribution coefficient K_dUp to > 10⁵。

EXAMPLE 4

Using a high temperature solid phase processWill K₂CO₃、TiO₂Reacting for 10 hours at 850 ℃ according to the molar ratio of 1: 1 to prepare the layered compound K₂TiO₅Is a reaction of K₂TiO₅Salicylic acid and water are mixed according to the molar ratio of 1: 5: 10, placed in a high-pressure reaction vessel, reacted for one day at the temperature of 100 ℃, and then transferred to an oven at the temperature of 200 ℃ for reaction for 3 hours. The reaction product was washed with ethanol and water several times and dried to give a yellow product. The product is salicylic acid surface modified TiO₂. Adding the TiO into the solution₂As an adsorbent for lead (II) in water, lead can be adsorbed from 2000ppb down to 0.03 ppb. The residual values are far below the standards permissible for drinking water (< 10 ppb). Distribution coefficient K_dUp to > 10⁸。

EXAMPLE 5

Using a high temperature solid phase method₂CO₃、TiO₂Reacting for 10 hours at 850 ℃ according to the molar ratio of 2: 1 to obtain KTiO₃Take KTiO₃Acrylic acid and water are mixed according to the molar ratio of 1: 2: 3, placed in a high-pressure reaction vessel, reacted for one day at the temperature of 100 ℃, and then transferred to an oven at the temperature of 200 ℃ for reaction for 3 hours. Washing the reaction product with ethanol and water for many times, and drying to obtain a milky white TiO product₂. Uranium (UO)₂) The adsorption experiment proves that the TiO₂The adsorbent has excellent uranium adsorption performance, and can adsorb uranium from 2000ppb to 0.01 ppb. Distribution coefficient K_dUp to > 10⁷. The material can be used for extracting uranium from seawater (important nuclear fission material), and adsorbing and enriching extremely low-concentration uranium (< 3ppb) in seawater. Can also be used for treating radioactivity (UO)₂) The polluted water can remove radioactive substances and can extract, enrich and recycle uranium.

EXAMPLE 6

Preparation of spherical SrMnO Using hydrothermal method₃Precursor, mixing the precursor, nitric acid and water according to the molar ratio of 1: 2: 100, placing the mixture in a high-pressure reaction container, firstly reacting for one day at the temperature of 80 ℃, and then transferring the mixture to an oven at the temperature of 120 ℃ for reacting for 5 hours. After the reaction, Sr is completely dissolved out and converted into the productSpherical porous MnO₂. The manganese dioxide is used for adsorbing divalent cadmium in purified water, can adsorb the divalent cadmium from high concentration (> 2ppm) to less than 5ppb, and takes no more than 1 minute.

EXAMPLES example 7

Preparation of rod-shaped K Using high temperature solid phase Process₂TiO₅Precursor, mixing the precursor, acetic acid and water according to the molar ratio of 1: 30: 10, placing the mixture in a high-pressure reaction container, firstly reacting for one day at 100 ℃, and then transferring the mixture to an oven at 160 ℃ for reacting for 2 hours. After the reaction, the potassium is dissolved out completely and converted into the rod-shaped porous TiO product₂. The divalent lead used for purifying water can be adsorbed from high-concentration lead (> 2ppm) to less than 0.5ppb, and the time is not more than 5 minutes.

EXAMPLES example 8

Preparation of cubic SrFeO using high temperature solid phase method₃Precursor, mixing the precursor and formic acid according to the molar ratio of 1: 30, placing the mixture in a high-pressure reaction container, firstly reacting for two days at 100 ℃, and then transferring the mixture to an oven at 130 ℃ for reacting for 2 hours. After the reaction, Sr is completely dissolved out and converted into square porous Fe₂O₃. The divalent lead adsorbing agent is used for adsorbing divalent lead for purifying water, can adsorb the divalent lead from high concentration lead (> 2ppm) to less than 1ppb, and takes no more than 3 minutes.

Claims

1. A transition metal oxide adsorbent capable of thoroughly removing harmful ions in water is characterized in that harmful ions in water such as chromium (VI), lead (II), arsenic (V), cadmium (II), uranium (VI) and the like can be adsorbed to the level of drinking water; chromium (VI) can be adsorbed from 2010ppb to < 6ppb, lead (II) from 2000ppb to < 0.06ppb, uranium (VI) from 2000ppb to < 0.03ppb, arsenic (V) from 1000ppb to < 10ppb, cadmium (II) from 2000ppb to < 1 ppb; adsorption distribution coefficient K_dThe value of chromium (VI) and arsenic (V) can reach more than 10⁵ml g¹Lead (II) and uranium (VI) can reach more than 10⁸ml g¹Is the highest value in the existing research; meanwhile, the composite material has the advantages of quick adsorption and good recycling performance.

2. The transition metal oxide adsorbent of claim 1, wherein:

1) has the general formula

Wherein M is selected from one or more transition metal elements such as Zr, Ti, Fe, Mn, Mo, W and the like; x is more than or equal to 1 and less than or equal to 2, and y is more than or equal to 1 and less than or equal to 5;

2) the surface is rich in hydroxyl and has strong affinity with harmful metal ions;

3) an amorphous or low crystalline phase;

4) the shape and the size of the particles are various;

5) has a plurality of micro/nano pore structures.

3. The method of claim 1, which has fast adsorption and good recycling performance, and is characterized in that the adsorption can reach the adsorption equilibrium within 2 seconds to 10 minutes, and the harmful metal can be desorbed and recovered under certain conditions after being adsorbed, and can be reused for adsorption.

4. The surface of claim 2 is rich in hydroxyl groups and has strong affinity with harmful metal ions, wherein the content of hydroxyl oxygen in the peaks of X-ray photoelectron spectroscopy oxygen reaches 50% -80%, the density of hydroxyl groups can reach 72 hydroxyl groups per square nanometer, and the high-density hydroxyl groups are proved to be a source with excellent adsorption performance and can form chelation with harmful ions.

5. The amorphous or low crystalline phase according to claim 2, characterized by no significant diffraction peaks or low intensity of diffraction peaks as a result of X-ray powder diffraction.

6. The device of claim 2, wherein the particles have a shape selected from the group consisting of spherical, polyhedral, star-shaped, hollow, and the like, and have a particle size of 1 nm to 100 μm.

7. According to the rightThe mass micro/nano-pore structure of claim 2, wherein the nitrogen adsorption, desorption and adsorption experiment proves that the mass meso-porous or micro-porous structure has a large specific surface area of 70-300m² g^-1。

8. Transition metal oxide according to claim 2, characterized in that it is achieved by the following technical route of microetching:

1) preparation of multi-element composite oxide by hydrothermal method or high-temperature solid-phase method

And (3) precursor. Wherein A is an alkali metal or alkaline earth metal element, M is one or more transition metal elements such as Zr, Ti, Fe, Mn, Mo, W and the like, the controllability of the shape and the size is realized by adjusting the content and the reaction temperature of different doping elements, and various structures such as a sphere, a polyhedron, a star, a hollow structure and the like are prepared;

2) mixing the precursor with inorganic acid or organic acid, and preparing the transition metal oxide by a two-step heating method

(I) The precursor is reacted for 2 to 10 hours at the temperature of between 60 and 100 ℃, and (II) the reaction is continued for 2 to 10 hours at the temperature of between 100 and 300 ℃. And cleaning, separating and drying to obtain a target product, wherein the shape of the target product is consistent with that of the precursor.

9. The microetching method according to claim 8, wherein the adsorption of trace harmful ions has the following advantages:

1) micro-etching under acidic condition promotes cations and protons in precursor particles

Exchange to form high-density inner surface hydroxyl group with strong adsorption to harmful ion, and micro-etching process to dissolve out alkali metal or alkaline earth metal in the precursor under acidic condition and obtain large amount of protons

Exchange with alkali metal or alkaline earth metal to form inner surface hydroxyl, the high-density hydroxyl has chelation to harmful ions, has strong adsorption force, and can thoroughly remove the harmful ions;

2) the microetching hydrothermal reaction realizes accurate selective etching, and the microetching under acidity selectively and partially etches the precursor to realize accurate pore-forming, so that a rich pore channel structure and a high specific surface area are formed, anchoring to harmful ions is enhanced, and adsorption capacity is increased;

3) the morphology of the adsorbent is controlled through the induction of a precursor, the morphology of the precursor is reserved for a transition metal oxide product prepared through micro etching, and the adsorption mass transfer process is promoted and the specific surface area is increased through selecting the morphology favorable for adsorption.