Background
The serious harm of heavy metal wastewater to public health and ecological environment has already attracted wide attention at home and abroad because heavy metal ions not only threaten aquatic organisms but also participate in food chain to accumulate to higher concentration and finally harm human health after entering the environment. The pollution of heavy metal wastewater should be paid extensive attention, and the reduction or removal of heavy metals in water is very important and urgent. In a plurality of treatment methods, compared with a chemical precipitation method, an adsorption method does not introduce new chemical substances into treated water, the energy consumption is obviously lower than that of an evaporation concentration method, the quality of effluent water is better than that of an air floatation method, and the treatment cost and the operation complexity are far lower than those of an electrolysis method, an ion exchange method, a solvent extraction method and a membrane separation method. In addition, heavy metal ions exist in dilute phase in the wastewater, and the adsorption technology has incomparable advantages for deep purification treatment of heavy metal wastewater.
The active carbon, the fly ash, the active sludge ash, the zeolite, the biological material, the manganese oxide, the peanut shell, the kaolin and the like are used for enriching and separating heavy metal ions under the action of unbalanced molecular attraction or chemical bond force on the solid surface. Because the adsorbents are wide in source and low in price, the method draws the attention of the water treatment world and becomes a heavy metal wastewater treatment method with a great application prospect. However, these adsorbents generally have problems of low adsorption capacity, large use amount, insufficient removal efficiency of heavy metals, and the like. If the waste slag is not treated in an effective desorption mode, a large amount of waste slag is generated.
Currently, the research direction of activated carbon adsorption mainly focuses on modification, and mainly adopts an acid treatment method to increase surface functional groups, such as carboxyl, quinone, carbonyl, lactone, hydroxyl, carboxylic anhydride and the like. Although these modification methods increase the surface active groups and improve the adsorption of heavy metal ions, they have the following disadvantages: (1) reducing its BET surface area and pore volume; (2) the pore structure is damaged, so that the pores are blocked, a narrow microporous structure is generated, the adsorption capacity is reduced, and the transmission of ions in the activated carbon and the regeneration of the activated carbon are not facilitated.
The direct research of silica as heavy metal adsorbent is less because of its low adsorption performance, mesoporous silica is usually used as template to prepare mesoporous activated carbon as adsorption material, and finally the mesoporous silica is used for removing the template silica by HF (ind. eng. chem. res.,2011,50(24), 13825-13830 page); the template agent is removed, so that the atom utilization rate is low, and virulent HF is needed for membrane removal; the research on the mesoporous silica prepared into a spherical porous shape with high specific surface area and then used as a heavy metal adsorbent by modifying the surface of the mesoporous silica is not reported in documents.
Disclosure of Invention
The invention aims to provide a surface modified spherical porous silica material, and the spherical porous silica material is used as a heavy metal and organic pollutant adsorbent to research the adsorption performance of the spherical porous silica material. The invention prepares the spherical porous silica with the mesoporous specification, then carries out surface modification on the surface and in the cavity of the spherical porous silica by a silane coupling agent, adopts 4, 6-diaminoresorcinol and formaldehyde as polymerization agents, and introduces metal chelating sites such as amino, hydroxyl and the like into the surface and the cavity of the spherical porous silica, thereby playing the role of adsorbing heavy metals and organic pollutants.
According to a first aspect of the present invention, there is provided a method for preparing a surface-modified spherical porous silica, comprising the steps of:
(A) preparation of spherical porous silica:
1) dissolving 10.0g of polyvinyl alcohol 1795 in 100ml of 0.5mmol/L acetic acid aqueous solution, then dropwise adding 41.6g of tetraethoxysilane, and hydrolyzing at 0-5 ℃ for 30-60min to obtain a semitransparent solution;
2) stirring the semitransparent solution at 60-80 deg.C for 5-6h to form gel, cooling to room temperature, standing, aging for 16-18h, and filtering to obtain gel;
3) placing the jelly in 2mol/L ammonia water solution for refluxing for 2-3h, then cooling to room temperature, adjusting the pH of the solution to be neutral by hydrochloric acid, performing ultrasonic treatment at 45-50 ℃ for 2-3h, filtering, washing a filter cake with water, drying at 60-70 ℃ to constant weight, and finally removing organic matters by high-temperature calcination to obtain spherical porous silicon dioxide; the silicon dioxide prepared by the conventional method is of a spherical structure, contains a large number of pores, is of a spherical porous shape, greatly enhances the specific surface area, and provides possibility for subsequent functional modification.
(B) Preparation of surface-modified spherical porous silica:
a) placing 10.0g of spherical porous silicon dioxide in 500ml of tetrahydrofuran for ultrasonic dispersion at room temperature, then adding 0.3-0.5g of 3-aminopropyltriethoxysilane, and stirring for 20-30 min;
b) adding 1.5-2.0g of 4, 6-diaminoresorcinol into the solution in the step a), and adjusting the pH of the system to 8.5-9.0 by using ammonia water;
c) dripping 40-60ml of formaldehyde aqueous solution with the concentration of 37% wt into the solution in the step b), continuing ultrasonic treatment for 20-30min after dripping is finished, and then heating to 70-80 ℃ for polymerization for 6-8 h;
d) cooling to room temperature, filtering, washing filter cakes with water and ethanol in sequence to remove unreacted 4, 6-diaminoresorcinol and formaldehyde, and then placing the filter cakes in a vacuum drying oven to dry at 70-80 ℃ to constant weight to obtain the surface modified spherical porous silica.
Preferably, the high-temperature calcination in the step 3) refers to temperature rise from room temperature to 700-800 ℃ at a temperature rise rate of 10 ℃/min in an air atmosphere, and then heat preservation calcination is carried out for 5-6 h;
preferably, the amount of 4, 6-diaminoresorcinol added in step b) is 1.8g and the amount of 37% wt aqueous formaldehyde added in step c) is 50 ml; according to the invention, firstly, the spherical porous silica with high specific surface area is obtained, metal chelating agent sites such as hydroxyl, amino and the like are grafted on the surface of the spherical porous silica, and when the grafted functional groups such as hydroxyl, amino and the like are too much, the pore diameter of the porous silica is blocked, the specific surface area of the porous silica is reduced, so that the activity of the porous silica for adsorbing heavy metal ions is reduced; in view of its adsorption capacity for heavy metals, the porous silica of the present invention is preferably prepared by adding 1.8g of 4, 6-diaminoresorcinol to 50ml of a 37% by weight aqueous solution of formaldehyde.
The invention prepares the spherical porous silica with the mesoporous specification, then carries out surface modification on the surface and in the cavity of the spherical porous silica by a silane coupling agent, adopts 4, 6-diaminoresorcinol and formaldehyde as polymerization agents, and introduces metal chelating sites such as amino, hydroxyl and the like into the surface and the cavity of the spherical porous silica, thereby playing a role in adsorbing heavy metals.
According to one aspect of the invention, the invention provides the use of a surface-modified spherical porous silica for the adsorption of heavy metal ions and organic pollutants in water.
Preferably, the heavy metal ion is Pb2+、Cd2+、Cr3+、Cu2+、Co2+Or Zn2+More preferably, Pb2+And Cr3+(ii) a The surface modified spherical porous silicon dioxide prepared by the invention can be used for adsorbing various heavy metal ions, especially Pb2+And Cr2+The adsorption efficiency of (2) is highest.
Preferably, the organic contaminant may be an aromatic amine or a phenolic substance, such as phenol, p-nitrophenol, aniline, o-nitroaniline or p-nitroaniline; especially, the p-nitroaniline has the adsorption rate of more than 96 percent in a wider pH range;
the invention has the following advantages:
1) the spherical porous silica prepared by the invention has larger specific surface area of about 1360m than the conventional commercial mesoporous silica2(ii)/g (measured by the BET method);
2) the prepared spherical porous silica is used as a carrier, a silane coupling agent is used for surface modification on the surface and in a cavity of the spherical porous silica, 4, 6-diaminoresorcinol and formaldehyde are used as polymerization agents, and metal chelating sites such as amino, hydroxyl and the like are introduced into the surface and the cavity of the spherical porous silica to form a novel heavy metal and organic pollutant adsorbing material;
3) the surface-modified spherical porous silica prepared by the invention has larger adsorption capacity to heavy metals and organic pollutants;
4) the spherical porous silica with the modified surface can be desorbed after being adsorbed on heavy metals, and can be recycled.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the description is intended to be exemplary only, and is not intended to limit the scope of the present invention.
The detection method of the removal rate R of the heavy metal ions and the organic matters comprises the following steps:
taking heavy metal ion solution or organic matter in a conical flask, and adding 0.1mol/L H2SO4Or adjusting the pH value of the solution by 0.1mol/LNaOH aqueous solution, adding a certain amount of spherical porous silicon dioxide with modified surface, placing the conical flask into a constant-temperature water bath oscillator at 40 ℃, controlling the temperature at 200r/min, stirring for 12h, filtering, measuring the concentration of heavy metal ions in the filtrate by using an atomic absorption spectrometer (AA-6300F, manufactured by Shimadzu corporation, Japan), and measuring the concentration of organic matters by using an HPLC external standard method. The removal rate R (%) of heavy metal ions and organic matters in the aqueous solution is calculated by the formula (1):
in the formula, C0And C is the mass concentration of heavy metal ions or organic matters in the initial filtrate and the filtrate respectively, and is mg/L.
II, heavy metal ion and organic matter adsorption capacity qtThe detection method comprises the following steps:
adsorption capacity qtCalculating according to equation (2):
in the formula, C0And CtThe mass concentrations of heavy metal ions or organic matters at the initial time and the t time are mg/L respectively; w is the mass of the surface-modified spherical porous silica, g; v is the volume of the solution, L.
Example 1 preparation of surface modified spherical porous silica adsorbent
(A) Preparation of spherical porous silica:
1) dissolving 10.0g polyvinyl alcohol (1795 type) in 100ml 0.5mmol/L acetic acid water solution, dropwise adding 41.6g tetraethoxysilane, and hydrolyzing at 0-5 deg.C for 30-60min to obtain semitransparent solution;
2) stirring the semitransparent solution at 60-80 deg.C for 5-6h to form gel, cooling to room temperature, standing, aging for 16-18h, and filtering to obtain gel;
3) placing the jelly in 2mol/L ammonia water solution for refluxing for 2-3h, then cooling to room temperature, adjusting the pH of the solution to be neutral by using 2mol/L hydrochloric acid water solution, carrying out ultrasonic treatment for 2-3h at 45-50 ℃, filtering, washing a filter cake, drying to constant weight at 60-70 ℃, finally heating to 800 ℃ from room temperature at the heating rate of 10 ℃/min in the air atmosphere, and carrying out heat preservation and calcination for 5-6h to remove organic matters to obtain spherical porous silicon dioxide; the scanning electron micrograph of the spherical porous silica is shown in FIG. 1, and it can be seen from FIG. 1 that the spherical porous silica prepared by the invention contains a large number of open-cell structures, has a larger specific surface area than the conventional spherical mesoporous silica, and has a specific surface area of 1360m2(ii)/g (measured by the BET method);
(B) preparation of surface-modified spherical porous silica:
a) placing 10.0g of spherical porous silicon dioxide in 500ml of tetrahydrofuran for ultrasonic dispersion at room temperature, then adding 0.4g of 3-aminopropyltriethoxysilane, and stirring for 20-30 min;
b) adding 1.8g of 4, 6-diaminoresorcinol into the solution in the step a), and adjusting the pH of the system to 8.5-9.0 by using 5mol/L ammonia water;
c) dripping 50ml of formaldehyde aqueous solution with the concentration of 37 percent by weight into the solution in the step b), continuing to perform ultrasonic treatment for 20-30min after finishing dripping, and then heating to 70-80 ℃ for polymerization for 6-8 h;
d) cooling to room temperature, filtering, washing filter cakes with water and ethanol in sequence to remove unreacted 4, 6-diaminoresorcinol and formaldehyde, and then placing the filter cakes in a vacuum drying oven to dry at 70-80 ℃ to constant weight to obtain the surface modified spherical porous silica.
The scanning electron micrograph of the surface-modified spherical porous silica is shown in FIG. 2, and it can be seen that the porous structure is still remained after the modification, and the specific surface area of the porous structure is 1280m2In terms of/g (measured by the BET method), onlyA slight drop occurs.
The overlapping infrared spectra of the surface-modified spherical porous silica and the spherical porous silica are shown in FIG. 3, in which (i) is the spherical porous silica and (ii) is the surface-modified spherical porous silica; the infrared spectrogram after modification shows characteristic absorption peaks of N-H and O-H, and the 4, 6-diaminoresorcinol is shown to be grafted to the spherical porous silica.
Example 2 removal rates for different heavy metals and organic compounds at different pH
Because the surface modified spherical porous silica contains hydroxyl and amino, and is influenced by pH adjustment when being chelated and adsorbed with heavy metal, the invention screens the pH condition:
taking commercially available Pb2+、Cr3+、Cu2+、Ni2+、Zn2+、Hg2+、Cd2+And Co2+The chloride or nitrate of (1) was prepared into 60-100mg/L aqueous solutions with different pH values to simulate heavy metal aqueous solutions, 2.0g of the surface-modified spherical porous silica prepared in example 1 was added into 1L aqueous solution to test the removal rate R of the surface-modified spherical porous silica in different pH environments, and the results are shown in Table 1:
TABLE 1 removal rate of heavy metal ions by surface-modified spherical porous silica at different pH
The test results show that the adsorption effect on different heavy metals is different under different pH values, and the Pb is absorbed integrally2+、Cr3+、Cu2+、Zn2+、Cd2+And Co2+A higher removal rate can be obtained under a certain pH value; such as Pb2+(pH 6.0. + -. 0.2) and Cr3+(under the condition that the pH value is 8.0 +/-0.2) the ion almost achieves the effect of complete adsorption; but for Ni2+And Hg2+The adsorption rate is not ideal in the pH range of 2-10.
Example 3 adsorption Effect on aromatic amines and phenols
Phenol, p-nitrophenol, aniline, o-nitroaniline and p-nitroaniline are prepared into 100mg/L aqueous solution by using water, then the removal rate R value of each organic matter is tested under the condition of different pH values, and the statistical result is shown in Table 2:
TABLE 2 removal rate of organic substances by surface-modified spherical porous silica at different pH values
The results show that the surface-modified spherical porous silica prepared by the invention has strong adsorption performance on aniline and phenol organic pollutants, but most of the spherical porous silica needs to be used in a certain pH environment, so that the organic pollutants need to be firstly adjusted to a specific pH range when actually treated, wherein the p-nitroaniline has a wide pH use range, and has high adsorption performance at pH 6-9.
Example 4Cr3+Detection of adsorption amount
Taking Cr (NO)3)3Dissolving the nonahydrate in water, adjusting the pH of the system to 8.0 +/-0.2 by using 0.5mol/L aqueous solution of sodium hydroxide to prepare an aqueous solution with the concentration of 120mg/L, pH-8.0 +/-0.2, and respectively adding the spherical porous silica (abbreviated as PS), the surface modified spherical porous silica (abbreviated as MPS) and the commercially available mesoporous silica (Sigma Aldrich trade company, abbreviated as MCM-41, SBET-1000 m)2Per g) and 4, 6-diaminoresorcinol (abbreviated as N/O-L) as adsorbents, Cr was tested3+Adsorption capacity qtThe results are shown in table 3:
TABLE 3 different adsorbents correspond to qtComparison of data
Note: q. q.stAnd t is 12 h.
The test results show that the spherical porous silicon dioxide prepared by the invention is applied to Cr3+The removal rate of the surface-modified spherical porous silica is far greater than that of the commercially available mesoporous silica (MCM-41), the removal rate of the surface-modified spherical porous silica is equivalent to that of the organic polymer 4, 6-diaminoresorcinol, after the spherical porous silica is modified, the adsorption capacity of the spherical porous silica is greatly improved, the surface-modified spherical porous silica has a physical adsorption effect and a chemical adsorption effect compared with the spherical porous silica, namely the physical adsorption and the chemical adsorption play a synergistic effect, and the surface-modified spherical porous silica greatly improves the Cr adsorption effect of the surface-modified spherical porous silica3+The amount of adsorption of (3).
Surface modified spherical porous silica was tested for paranitroaniline (pH 8.0), PbCl2The adsorbed amounts (at pH 6.0) were 236.2mg/g and 315.8mg/g, respectively.
Example 5 Recycling case
In order to research the recycling and reusing condition of the surface modified spherical porous silica prepared by the invention on various heavy metal ions or organic pollutants, the invention filters and recycles the used surface modified spherical porous silica, desorbs the heavy metal of the recycled surface modified spherical porous silica so as to achieve the aim of activating the adsorbent, and inspects the condition of desorbing Cr (NO) after desorption3)3P-nitroaniline and PbCl2The adsorption amount of (c);
the desorption method comprises the following steps: and (3) putting the recovered surface modified spherical porous silica into 1mol/L hydrochloric acid, performing ultrasonic treatment at 50-60 ℃ for 2-3h, filtering, and drying at 70-80 ℃ to constant weight to obtain the activated surface modified spherical porous silica.
The surface-modified spherical porous silica was desorbed after each use, and table 4 is a table of the relationship between the adsorption amount of different heavy metals and the number of activation times:
TABLE 4 variation of adsorption amount of different heavy metals with the number of uses
Note: the process of mechanically adsorbing heavy metal or organic matter is carried out in the optimal pH environment, namely Cr (NO)3)3And p-nitroaniline at pH 8.0. + -. 0.2, PbCl2At pH 6.0 ± 0.2.
The above results show that the adsorption performance of the surface-modified spherical porous silica can be activated by the high-temperature ultrasonic desorption under acidity of the invention, especially for PbCl2The adsorption of (a), the adsorption amount decreased by only about 6% after five times of use; but the adsorption quantity of the paranitroaniline is reduced by about 49 percent, and the paranitroaniline can not be continuously recycled and reused, and Cr (NO) is3)3The adsorption capacity decreased by about 24%.
Although the embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions, and alterations can be made hereto without departing from the spirit and scope of the invention.