Application of dithiocar-bamate modified silica gel in wastewater treatment

Abstract

The invention discloses an application of dithiocar-bamate modified silica gel in wastewater treatment, and relates to the technical field of wastewater treatment, and the technical key points are as follows: the adsorption rate of Co < 2 + > and Mn < 2 + > on dithiocar-bamate modified silica gel spheres is controlled by liquid membrane diffusion; the adsorption of Co < 2 + > and Mn < 2 + > on the dithiocar-bamate modified silica gel spheres is a spontaneous, heat absorption and entropy increase process; the dithiocar-bamate modified silica gel has high selectivity to Co < 2 + >, and can adsorb < 60 > Co < 2 + > in low-emission wastewater.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to the application of silica gel modified by dithiocarbamate in wastewater treatment. Background Art

[0003] Starting from the perspective of radioactive wastewater treatment and combining existing research results, the present invention synthesized a silicon-based adsorption material for low-level wastewater containing corrosion activation products, conducted certain theoretical explorations on the selective adsorption and removal of radionuclides, and accumulated some experimental experience, laying a relatively solid foundation for the next step of developing highly selective activation product adsorbents. Summary of the invention

[0004] The purpose of the present invention is to solve the above problems and provide the application of silica gel modified with dithiocarbamate in wastewater treatment.

[0005] In order to achieve the above object, the technical solution of the present invention is as follows:

[0006] The present invention provides a method for preparing silica gel modified with dithiocarbamate, comprising the following steps:

[0007] Step S1, preparation of TEOS prepolymer sol solution: dissolving dodecyl sulfonate SDS in a hydrochloric acid solution, adding TEOS under stirring, stirring at room temperature for a period of time to obtain a clear and transparent TEOS sol solution, and storing it in a refrigerator;

[0008] Step S2, preparation of dithiocarbamate modification solution: dissolve sodium hydroxide in deionized water, add aminopropyltrimethoxysilane KH-550 under ice bath stirring, and after clarification, continue to add carbon disulfide under ice bath conditions, react for 1 hour, and then react for 4 hours at room temperature to obtain an egg yolk-colored slightly transparent uniform solution, which is stored in a refrigerator;

[0009] Step S3, preparation of oil phase: kerosene is selected as the organic phase, and a surfactant Span80 is added to prepare a uniform emulsion;

[0010] Step S4, synthesis of dithiocarbamate-modified silica spheres: Pour kerosene containing Span80 into a 500 mL three-necked flask, adjust to a certain speed at room temperature, and set aside; in an ice bath, mix a certain amount of TEOS precursor solution and deionized water evenly, and continue stirring; take the dithiocarbamate modification solution, add hexamethylenetetramine-urea solution and mix evenly, pour it into the TEOS precursor and deionized water mixture, stir for 1 minute, and then place it under constant pressure. The dropping funnel was quickly added into the kerosene; the system was heated to 313K, stirred for 2h, and then heated to 333K, stirred for 2h; cooled to room temperature, the spherical yellow solid deposited at the bottom of the flask was filtered out, and washed with ethanol; immersed in 100mL of 1% ethanol solution of ammonia water for 12h; the sample was filtered and washed with ethanol, and a white spherical solid was obtained by suction filtration, which was placed in a 313K vacuum drying oven for 6h, heated to 333K, and maintained for 4h to obtain translucent silica gel.

[0011] The present invention is further configured as follows: preferably, in step S1, the amount of dodecyl sulfonate SDS is 0.1 g;

[0012] Preferably, the volume of the hydrochloric acid solution in step S1 is 20 mL and the concentration is 0.1 mol / L;

[0013] Preferably, the volume of TEOS added under stirring in step S1 is 20 mL;

[0014] Preferably, in step S1, the molar ratio of the reaction system: TEOS / H2O / HCl / SDS is 1 / 12 / 0.02 / 0.0037;

[0015] Preferably, in step S2, the amount of sodium hydroxide is 3.6 g;

[0016] Preferably, the amount of deionized water in step S2 is 20 mL;

[0017] Preferably, in step S2, the amount of aminopropyltrimethoxysilane KH-550 is 16 mL;

[0018] Preferably, the volume of carbon disulfide in step S2 is 5.6 mL;

[0019] Preferably, in step S2, the molar ratio of the reaction system: APTMS / CS2 / NaOH / H2O is 1 / 1 / 1 / 12;

[0020] Preferably, the content of Span80 in step S3 is controlled at 0.2 g / L;

[0021] Preferably, the kerosene containing Span80 in step S4 is 250 mL;

[0022] Preferably, the volume of the hexamethylenetetramine-urea solution in step S4 is 6 mL and the concentration is 250 g / L;

[0023] Preferably, in step S1-2, the refrigerator temperature is 0 to 5 degrees Celsius.

[0024] The present invention also provides the use of silica gel modified with dithiocarbamate in wastewater treatment. 2+ and Mn 2+ The adsorption rate on dithiocarbamate-modified silica spheres is controlled by liquid film diffusion.

[0025] The present invention is further configured as follows: 2+ and Mn 2+ The adsorption onto dithiocarbamate-modified silica spheres is a spontaneous, endothermic, and entropy-increasing process.

[0026] The present invention is further configured as follows: the dithiocarbamate-modified silica spheres are 2+ It has high selectivity and can adsorb low-level wastewater 60 Co 2+ .

[0027] Compared with the prior art, the present invention has the following advantages: (1) a class of organic / inorganic hybrid silica gel spheres grafted with dithiocarbamates are synthesized by co-condensation and emulsion polymerization. 2+ and Mn 2+ The comparison of static adsorption performance determined that the addition ratio of the experimental TEOS precursor solution and the modification solution DTC-ATPS was 5:3 (v / v), and the material under this formula was collectively named DTC-AT-2.

[0028] (2) Adsorption kinetics experiments show that the material DTC-AT-2 has a strong affinity for Co 2+ and Mn 2+ The time required for the adsorption of Co to reach equilibrium was 12 h and 4 h respectively. At low concentrations, DTC-AT-2 2+ and Mn 2+ The maximum adsorption capacities of Co and 2+ The adsorption effect is better than that of Mn 2+ The adsorption process satisfies the Lagergren second-order rate equation. According to the Boyd equation, Co 2+ and Mn 2+ The adsorption rate on DTC-AT-2 is controlled by liquid film diffusion.

[0029] (3) Isothermal adsorption experiments showed that DTC-AT-2 could adsorb Co 2+ and Mn2+ The adsorption process of DTC-AT-2 is consistent with the Freundlich adsorption isotherm model, and the model fitting parameter n>1, indicating that DTC-AT-2 is an excellent adsorbent. 2+ and Mn 2+ The surface characteristic adsorption energy of Co is greater than 8KJ / mol, indicating that the chemical adsorption process is dominant. Thermodynamic parameters show that Co 2+ and Mn 2+ The adsorption on DTC-AT-2 is a spontaneous, endothermic and entropy-increasing process.

[0030] (4) Interfering ions on the adsorption of Co by DTC-AT-2 2+ The influence is small. When the total amount of interfering ions is Co 2+ When the adsorption capacity was 123 times of that of Mn 2+ The adsorption effect is relatively large, and the total amount of interfering ions reaches Mn 2+ When the adsorption capacity of DTC-AT-2 was 83 times that of Co 2+ It has high selectivity and is suitable for adsorbing low-level wastewater. 60 Co 2+ It has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is the effect of the amount of water added during the synthesis process on the gel conversion time in the embodiment of the present invention, wherein r is V(H2O):V(TEOS precursor solution);

[0032] Figure 2 1 is the XRD diffraction pattern of three samples and column chromatography silica gel in the embodiment of the present invention;

[0033] Figure 3 The microscopic morphology of the column chromatography silica gel in the embodiment of the present invention is shown at magnifications of ×5000, ×500, ×200 and ×50 respectively;

[0034] Figure 4 The microscopic morphology of DTC-AT-1 in the embodiment of the present invention is shown at magnifications of ×5000, ×500, ×200 and ×50 respectively;

[0035] Figure 5 The microscopic morphology of DTC-AT-2 in the embodiment of the present invention is shown at magnifications of ×5000, ×500, ×200 and ×50 respectively;

[0036] Figure 6 The microscopic morphology of DTC-AT-3 in the embodiment of the present invention is shown at magnifications of ×5000, ×500, ×200 and ×50 respectively;

[0037] Figure 7 These are the N2 adsorption-desorption curves in the embodiments of the present invention, (a) column chromatography silica gel; (b) DTC-AT-1; (c) DTC-AT-2; (d) DTC-AT-3;

[0038] Figure 8 FTIR spectra of DTC-AT-1, DTC-AT-2 and DTC-AT-3 in the embodiments of the present invention;

[0039] Fig. 9 is the effect of pH on adsorption capacity in the embodiment of the present invention, where (a) is Co 2+ ; (b) Mn 2+ ;

[0040] Fig.10 is the effect of temperature on adsorption capacity in the embodiment of the present invention, where (a) is Co 2+ ; (b) Mn 2+ ;

[0041] Fig.11 is the effect of initial concentration on adsorption capacity in the embodiment of the present invention, where (a) is Co 2+ ; (b) Mn 2+ ;

[0042] Fig.12 is a curve showing the change of adsorption capacity over time in an embodiment of the present invention;

[0043] Fig.13 : is the linear fitting curve of the kinetic equation in the embodiment of the present invention, (a) is the first-order rate equation; (b) is the second-order rate equation;

[0044] Fig.14 is the diffusion model of Co in the embodiment of the present invention 2+ and Mn 2+ Fitting curves of adsorption (a) Morris particle diffusion model; (b) liquid film diffusion model;

[0045] Fig.15 is the Langmuir fitting curve in the embodiment of the present invention, (a) Co 2+ (b) Mn 2+ ;

[0046] Fig.16 is the Freundlich fitting curve in the embodiment of the present invention, (a) Co 2+ (b) Mn 2+ ;

[0047] Fig.17 is the Sips model fitting curve in the embodiment of the present invention, (a) Co2+ (b) Mn 2+ ;

[0048] Fig.18 is the DR model fitting curve in the embodiment of the present invention, (a) Co 2+ (b) Mn 2+ ;

[0049] Fig.19 is the linear fit of lnKC-1 / T in the embodiment of the present invention, (a) Co 2+ (b) Mn 2+ ;

[0050] Fig. 20 The interfering ion concentration in the embodiment of the present invention has an effect on the adsorption of Co by DTC-AT-2. 2+ and Mn 2+ Effect curves of (a) adsorption capacity; (b) removal rate. DETAILED DESCRIPTION

[0051] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solution of the present invention will be further described in detail below in conjunction with the embodiments of the present invention and the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0052] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present invention can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0053] Example:

[0054] 1 Experiment

[0055] 1.1 Instruments and reagents used in the experiment

[0056] The instruments used in the experiment are shown in the following table:

[0057] Table 1 Instruments and models used in the experiment

[0058]

[0059]

[0060] The experimental reagents used are shown in the following table

[0061] Table 2 Reagents used in the experiment

[0062] Chemical reagents Specification Manufacturer Anhydrous ethanol AR Tianjin Damao Chemical Reagent Factory Silane coupling agent KH-550 99％ Nanjing Youpu Chemical Co., Ltd. Sodium hydroxide AR Tianjin Damao Chemical Reagent Factory Tetraethyl orthosilicate TEOS AR Tianjin Damao Chemical Reagent Factory Dodecyl Sulfonate SDS AR Tianjin Bodi Chemical Co., Ltd. Hexamethylenetetramine AR Tianjin Damao Chemical Reagent Factory Urea AR Tianjin Damao Chemical Reagent Factory Aviation kerosene - - Span80 AR Tianjin Damao Chemical Reagent Factory Carbon disulfide (CS2) AR Tianjin Damao Chemical Reagent Factory ammonia AR Wuhan Hongda Chemical Factory

[0063] 1.2 Main characterization methods and instruments used

[0064] The main material characterization methods include XRD, BET specific surface area and pore size test, SEM scanning electron microscopy, elemental analysis and FTIR. The crystal structure of the material is determined by the small-angle XRD spectrum measured by the D / MAX-RB rotating target X-ray diffractometer produced by RIGAKU Company of Japan. The main indicators of the instrument are as follows: the maximum power is 12KW, the stability is better than 1%, and the angle measurement accuracy Δ2θ≤±0.02°; the BET specific surface area and pore size distribution of the sample are measured by the 3H-2000PS2 static volumetric specific surface and pore size analyzer produced by Beijing Best Instrument Technology Co., Ltd. The test conditions are as follows: the adsorbent is nitrogen, the saturated vapor pressure is 1.0259 bar, and the degassing temperature is 353K; the microscopic morphology of the sample is characterized by a JSM-5610LV scanning electron microscope produced by JEOL Ltd.; the infrared spectrum is measured by a SpectrumBX II Fourier transform infrared spectrometer produced by Perkin Elemer Instrument Company of the United States, using the KBr tablet method, and the test wave number range is 400-4000cm -1 , resolution 0.8cm -1 ; The metal ion concentration in water samples was determined by AAS method.

[0065] 1.3 Material synthesis

[0066] 1.3.1 Synthesis route

[0067] (1) Preparation of TEOS precursor solution:

[0068]

[0069] (2) Preparation of dithiocarbamate modified solution DTC-APTMS:

[0070]

[0071] (3) Synthesis of DTC-AT

[0072]

[0073] 1.3.2 Synthesis steps

[0074] (1) Preparation of TEOS prepolymer sol

[0075] Dissolve 0.1 g of dodecyl sulfonate SDS in 20 mL of 0.1 mol / L hydrochloric acid solution, add 20 mL of TEOS under stirring, stir at room temperature for a period of time to obtain a clear and transparent TEOS sol solution, and store it in a refrigerator at 0-5°C.

[0076] The molar ratio of the reaction system: TEOS / H2O / HCl / SDS is 1 / 12 / 0.02 / 0.0037.

[0077] (2) Preparation of DTC-APTMS

[0078] According to the reaction mechanism of dithiocarbamate, as long as the alkalinity is above a certain value, the amino group of aminopropyltrimethoxysilane can react with CS2 to form dithiocarbamate. Goubert-Renaudin et al. synthesized a silane coupling agent grafted with dithiocarbamate using tetrahydrofuran (THF) as solvent and alkaline hydride as base catalyst. A similar method is used in this paper to synthesize DTC-APTMS. The specific steps are as follows:

[0079] Dissolve 3.6g of sodium hydroxide in 20mL of deionized water, add 16mL of aminopropyltrimethoxysilane KH-550 under ice bath stirring. After clarification, add 5.6mL of carbon disulfide under ice bath conditions, react for 1h, and then react for 4h at room temperature to obtain an egg yolk-colored, slightly transparent, uniform solution, which is stored in a refrigerator at 0-5℃. The molar ratio of the reaction system: APTMS / CS2 / NaOH / H2O is 1 / 1 / 1 / 12.

[0080] (3) Preparation of oil phase

[0081] In this section, kerosene is selected as the organic phase, and a uniform emulsion is prepared by adding the surfactant Span80. In order to facilitate washing, the amount of surfactant added should not be too much. When the content of Span80 in the oil phase is 0.2g / L, the appropriate stirring speed can be controlled to obtain microspheres with a particle size of about 0.5mm. Therefore, the content of Span80 in the oil phase is controlled at 0.2g / L.

[0082] (4) Synthesis of DTC-AT

[0083] First, pour 250mL of kerosene containing Span80 into a 500mL three-necked flask, adjust to a certain speed at room temperature, and set aside; in an ice bath, mix a certain amount of TEOS precursor with deionized water, and continue stirring; take DTC-APTMS solution, add 6mL of 250g / L hexamethylenetetramine-urea solution and mix evenly, pour into the mixture of TEOS precursor and deionized water, stir for 1min, and then quickly add to kerosene through a constant pressure dropping funnel. Heat the system to 313K, stir for 2h, then heat to 333K, and stir for 2h. Cool to room temperature, filter out the spherical yellow solid deposited at the bottom of the flask, and wash it with ethanol. Soak and age in 100mL of ethanol solution with ammonia content of 1% for 12h. After filtering the sample, wash it with ethanol and filter to obtain a white spherical solid. Place it in a 313K vacuum drying oven for 6 hours, heat it to 333K, and keep it for 4 hours to obtain translucent silica gel.

[0084] 1.4 Static adsorption experiment

[0085] 1.4.1 Adsorption equilibrium time experiment

[0086] The Co 2+ and Mn 2+ The solutions were prepared from CoCl2·6H2O and MnCl2·4H2O, respectively, and the following experiments were the same.

[0087] Take a group of Co with the same concentration 2+ or Mn 2+ 20 mL of solution (concentration is about 5 mg / L) was placed in a 50 mL conical flask, 0.02 g of adsorbent was added, and constant temperature oscillation was performed in a 303K water bath for 3 hours. The supernatant was taken and its concentration was determined by atomic absorption spectrophotometer. The relationship between adsorption capacity qt and adsorption time t at different times was plotted.

[0088] 2 Experimental results

[0089] 2.1 Preparation and characterization of materials

[0090] 2.1.1 Effect of water content on gel time

[0091] The gelation time is a very important parameter for the sol-gel process. The gelation time varies for different purposes. When preparing thin films and fiber materials, the longer the gelation time, the better, so as to extend the effective use time of the sol. When preparing bulk materials, the shorter the gelation time, the shorter the preparation cycle. There are many factors that affect the gelation time, such as the pH of the gel system, the TEOS concentration and the system temperature.

[0092] The synthesis of dithiocarbamate requires a high alkalinity value of the solution, and the stability of the synthetic product is poor at a higher temperature, so this experiment was selected to synthesize at a lower temperature. Under these conditions, the amount of water in the system has an important influence on the conversion of gel time. In order to facilitate the control of the polycondensation reaction of TEOS precursor and DTC-APTMS during the synthesis process, this experiment investigated the effect of the volume ratio r of TEOS precursor to deionized water on the gel time during the emulsion polymerization process, and selected a suitable ratio.

[0093] The experimental method is as follows:

[0094] According to the DTC-AT synthesis steps, the addition amount of TEOS precursor and DTC-APTMS is set to 5 mL respectively, and the volume ratio r of the added deionized water to TEOS precursor is in the range of 0.5 to 3. First, 5 mL of TEOS precursor and 5r volumes of deionized water are mixed evenly under ice bath conditions, and stirred continuously under a magnetic stirrer; then 1.5 mL of hexamethylenetetramine-urea solution is mixed with 5 mL of DTC-APTMS solution, and the mixture is quickly poured into the above solution, and the time is recorded with a stopwatch. When the mixed solution undergoes a gelation transition, its fluidity deteriorates significantly, which is manifested as the magnetic stirrer rotor slowing down and the sol becoming turbid. By recording this time, the gel conversion time t can be obtained. The curve of time t and volume ratio r is plotted as follows: Figure 1 shown.

[0095] according to Figure 1 It can be seen that in the range of r = 0.5 to 3, the gel transition time is very short, which is due to the high alkalinity of the DTC-APTMS solution. When r = 0.5, the gelation time is only 60s. As the amount of deionized water in the system increases, the gelation time gradually increases. When r = 3, the amount of deionized water added is 3 times the volume of the precursor solution, and the gel transition time reaches about 810s. A longer gel transition time is conducive to the uniform mixing of the components of the sol system, but too much deionized water will lead to a decrease in the concentration of TEOS and DTC-APTMS, resulting in a large amount of H2O in the silica gel after gelation, which will cause a large amount of pore shrinkage and even collapse of the silica gel skeleton during the drying process, which is not conducive to maintaining the stability and mechanical properties of silica gel. For this reason, this experiment takes r = 1, that is, the TEOS precursor solution and deionized water are mixed in a ratio of 1:1.

[0096] 2.1.2 Synthesis, characterization and adsorption energy comparison of adsorbents with different ratios

[0097] In order to study the effect of the content of dithiocarbamate in the system on the structure of silica gel balls and the adsorption of metal ions, this section changes the volume ratio of DTC-APTMS to TEOS precursor solution, synthesizes three types of silica gel materials, and uses a variety of characterization methods to compare the structures of the synthesized samples at different ratios. 2+ and Mn 2+ The adsorption performance was evaluated and the best experimental scheme was selected.

[0098] Synthesis of DTC-AT-1: The volumes of DTC-APTMS solution and TEOS precursor solution were 10 mL and 30 mL, respectively;

[0099] Synthesis of DTC-AT-2: The volumes of DTC-APTMS solution and TEOS precursor solution were 15 mL and 25 mL, respectively;

[0100] Synthesis of DTC-AT-3: The volumes of DTC-APTMS solution and TEOS precursor solution were 20 mL and 20 mL, respectively.

[0101] 2.1.3XRD analysis

[0102] Figure 2 The XRD diffraction analysis spectra of three materials DTC-AT-1, DTC-AT-2 and DTC-AT-3 synthesized at different volume ratios of DTC-APTMS solution to TEOS precursor solution are shown, and compared with the spectrum of column chromatography silica gel. It can be seen from the figure that the strongest diffraction peaks of the three silica gels synthesized in this experiment and the commercially available column chromatography silica gel only appear around 22-23°, which is the amorphous diffraction peak of silica gel. This shows that the synthesized materials meet the properties of silica gel, no new crystalline structure is formed on the surface, and the three materials exist in an amorphous form. At the same time, the positions of the characteristic diffraction peaks of DTC-AT-1, DTC-AT-2 and DTC-AT-3 are 23.46°, 23.45° and 23.16° respectively, while the position of the diffraction peak of column chromatography silica gel is 22.37°. This deviation may be caused by the smaller pore size of the synthetic silica gel material than the commercially available column chromatography silica gel. This also shows that the pore size of the three types of materials should be DTC-AT-1>DTC-AT-2>DTC-AT-3.

[0103] Compared with column chromatography silica gel, the intensity of the characteristic diffraction peaks of the three types of self-synthesized silica gels has increased to varying degrees. This may be because the surfaces of the self-synthesized DTC-AT-1, DTC-AT-2 and DTC-AT-3 have dithiocarbamate groups in addition to silanol groups, in which -N may form a strong -Si-OH...N- with silanol -Si-OH, resulting in an enhanced diffraction peak. It may also be because the three types of synthesized materials have a larger specific surface area and a higher surface silanol content than column chromatography silica gel.

[0104] 2.1.4SEM analysis

[0105] Figure 3 to Figure 6 The following are scanning electron microscope photos of column chromatography silica gel and DTC-AT-1, DTC-AT-2 and DTC-AT-3. Table 3 lists the appearance characteristics, yields and particle size distribution of the four materials. The particle size distribution is determined by sieving method.

[0106] After silica gel is prepared and dried, it is usually milled into small particles before it can become a finished product. Therefore, column chromatography silica gel is actually a batch of irregular particles with a certain size range, such as Figure 3 As shown in Figure 1, about 90% of the commercially available 80-100 mesh column chromatography silica gel has a particle size range of 0.15-0.35 mm. The silica gels DTC-AT-1, DTC-AT-2 and DTC-AT-3 obtained by emulsion polymerization all have a certain degree of sphericity, such as Figure 4-6 shown.

[0107] From the comparison chart, it can be seen that the smaller the amount of DTC-APTMS added during the synthesis process, the higher the sphericity of the product obtained and the more uniform the particle distribution. The photos show that with the increase of the volume ratio of DTC-APTMS to TEOS precursor, the cracking of the synthesized product gradually intensifies. Adding too much silane coupling agent to the synthesis system will affect the polycondensation process and cause the collapse of the pore structure. At the same time, the roughness of the material surface also increases with the increase of DTC-APTMS. When the amount of DTC-APTMS added reaches a volume of 1:1 with the TEOS precursor, a large number of protrusions can be clearly observed on the surface. Therefore, considering the micromorphology and regularity of the material, the amount of DTC-APTMS added should be strictly controlled.

[0108] Table 3 SEM analysis and particle size distribution of the products

[0109]

[0110] 2.1.5 N2 adsorption-desorption isotherms and specific surface area

[0111] Figure 7The figure shows the N2 adsorption-desorption isotherms of the material. As shown in the figure, the four curves all have a relatively obvious jump when the partial pressure P / P0 is about 0.6 to 0.8. This is because after the N2 molecules are adsorbed on the surface of the material channel as a single molecular layer, they are adsorbed in multiple molecular layers in the mesoporous channel, which triggers the capillary condensation of N2. Therefore, the adsorption amount increases sharply with the increase of gas partial pressure, which also shows that there are a large number of mesoporous structures in the material. In addition, there are obvious hysteresis loops on the curves. Studies have shown that the position of the hysteresis loop reflects the size of the mesoporous pore size. It is not difficult to find that the partial pressure P / P0 of the hysteresis loop of the four materials is DTC-AT-3>DTC-AT-2>DTC-AT-1>column chromatography silica gel, indicating that the mesopore size of the four materials is also arranged according to the above rules. It is also found that the number and volume of mesopores in the material show a downward trend with the increase of DTC-APTMS content during the synthesis process. In addition, there are a large number of micropores distributed on the self-synthesized materials, so the specific surface area and pore volume of the material gradually decrease, and the average pore size decreases. Table 4 shows the specific surface area, pore volume and pore size distribution of silica gel and the three synthetic adsorption materials.

[0112] Table 4 Structural parameters of silica gel and DTC-AT-1, DTC-AT-2 and DTC-AT-3

[0113]

[0114] 2.1.6 Elemental analysis

[0115] Table 5 shows the contents of Si and S in the three types of self-synthesized materials. As can be seen from the table, with the increase of the amount of DTC-APTMS added during the synthesis process, the content of S in the synthesized product increased. The theoretical density of the grafted dithiocarbamate DTC was 1.225, 1.756 and 2.059 mmol / g, respectively.

[0116] Table 5 Elemental analysis results

[0117]

[0118] 2.1.7 FTIR analysis

[0119] Depend on Figure 8 It can be seen that the three materials are at 799cm -1 and 1000~1200cm -1 The obvious absorption peak at 669cm indicates that the main structure of the material is Si-O-Si. -1 and 1508cm -1The characteristic peaks on the left and right prove the existence of NC=S, thus indicating that the dithiocarbamate group successfully exists in the material. It can also be found from the figure that by changing the volume of TEOS prepolymer and DTC-APTMS modification liquid, the intensity of the characteristic absorption peaks of the obtained materials has some obvious differences, which shows that the ratio has an important influence on the structure of the material.

[0120] 2.1.8 Co 2+ and Mn 2+ Comparison of adsorption performance

[0121] In the chelate extraction process, whether it is liquid extraction or solid phase extraction, the properties of the solution itself (such as the pH of the solution, ion charge, concentration and system temperature) have an important influence on the adsorption effect. 2+ and Mn 2+ The strength of the adsorption performance. In this section, the adsorption performance of the three materials is studied under different solution pH, different initial concentrations and different temperatures.

[0122] (1) Effect of pH on adsorption

[0123] Experimental conditions: Co 2+ The initial concentration was 3.46 mg / L, Mn 2+ The initial concentration of 4.50 mg / L was adjusted to pH 3.5, 4.0, 4.5, 5.0, 5.5, 6.0 and 6.7 with HAc-NaAc and NaH2PO4-Na2HPO4 buffer solutions, respectively, and then oscillated in a 30°C water bath for 24 h. 2+ and Mn 2+ The adsorption capacities of Fig. 9 shown.

[0124] Depend on Fig. 9 It can be seen that with the increase of solution pH, the three types of synthesized adsorbents have a higher affinity for Co 2+ and Mn 2+ As mentioned above, too low a pH value will lead to poor stability of dithiocarbamates, and a large amount of H + It also has a strong inhibitory effect on the complexation of metal ions with functional groups, which is manifested as the three adsorbents have a strong inhibitory effect on Co under acidic conditions. 2+ and Mn 2+ The adsorption amount of Co 2+ When the solution pH reaches 6.0, the adsorption capacity basically reaches a stable value; for Mn 2+ The adsorption capacity of the three materials increased with the increase of pH, and the fastest increase was in the range of 5.0 to 6.7. Fig. 9 It can also be seen that at low concentrations, the adsorption performance of the three types of adsorbent materials for the two nuclides is DTC-AT-2>DTC-AT3>DTC-AT-1, among which DTC-AT-2 for Co 2+ and Mn 2+ The maximum adsorption capacities were 0.0492 mmol / g and 0.0489 mmol / g, respectively.

[0125] (2) Effect of temperature on adsorption effect

[0126] Experimental conditions: Co 2+ The initial concentration was 3.46 mg / L, Mn 2+ The initial concentration of was 4.50 mg / L, the solution pH was 5.5, the water bath temperature was 303 K, 308 K and 313 K, and the oscillation time was 24 h. Fig.10 shown.

[0127] Depend on Fig.10 It can be seen that at low concentrations, the three adsorption materials have a significant effect on Co 2+ The adsorption capacity of Co 2+ The adsorption process on the material surface is an endothermic process; 2+ From 303K to 308K, the adsorption performance of the material is greatly improved, and the Mn 2+ It is basically completely adsorbed, so when the temperature is raised to 313K, the adsorption capacity does not change significantly, but it is obvious that the three materials have different adsorption capacities for Mn 2+ The adsorption of ions also improves with increasing temperature. At the three temperatures, DTC-AT-2 has the highest adsorption capacity for the two nuclides.

[0128] (3) Effect of concentration on adsorption effect

[0129] Experimental conditions: Co 2+ Initial concentration range 3.23~166.5mg / L, Mn 2+ The initial concentration is 4.62-231 mg / L. Solution pH = 5.5, water bath temperature 303K, oscillation time 24. The curve of adsorption capacity changing with initial concentration is shown in Fig.11 shown.

[0130] The results show that the adsorption capacity of the three adsorbent materials for ions increases with the increase of their initial concentration. 2+ The adsorption capacity of the three materials for Co 2+ The adsorption performance of Mn is DTC-AT-3>DTC-AT-2>DTC-AT-1. 2+During the adsorption process, in the low concentration range, the adsorption capacity of the three materials increases with the increase of Mn 2+ However, when the concentration reaches a higher range of about 200 mg / L, the adsorption capacity of DTC-AT-2 no longer changes significantly, while that of DTC-AT-1 decreases slightly, indicating that the adsorption of Mn2+ by these two materials has basically reached saturation. It can be seen from the figure that the adsorption capacity of DTC-AT-3 has not reached the upper limit.

[0131] The above experiments show that the three adsorbent materials DTC-AT-1, DTC-AT-2 and DTC-AT-3 synthesized in this experiment have good adsorption performance on Co in a neutral pH environment. 2+ and Mn 2+ All of them have good adsorption performance, and the adsorption capacity increases with the increase of temperature. The adsorption is a chemical endothermic process. At lower concentrations, the adsorption performance of DTC-AT-2 is better than that of the other two adsorption materials. With the increase of initial concentration, the adsorption capacity of the three materials increased significantly, among which DTC-AT-3 has the best adsorption performance, followed by DTC-AT-2. Therefore, by comparing the adsorption process, DTC-AT-2 and DTC-AT-3 have better adsorption performance on Co 2+ and Mn 2+ All of them have excellent adsorption properties.

[0132] However, as an adsorbent, it must not only have good adsorption performance for the target ions, but also have certain mechanical properties and a certain particle size to facilitate column operation. According to the SEM scanning electron microscope photos of the materials and the specific surface area and pore size analysis results, DTC-AT-2 has better sphericity than DTC-AT-3, and its specific surface area and average pore size are closer to column chromatography silica gel. In summary, the DTC-AT-2 synthesized in this experiment is more suitable as an adsorbent for removing Co from wastewater. 2+ and Mn 2+ .

[0133] 2.2 Adsorption kinetics experiments

[0134] 2.2.1 Adsorption equilibrium experiment

[0135] Fig.12 The results show that DTC-AT-2 reacts with Co at initial concentrations of 3.46 mg / L and 4.5 mg / L, respectively. 2+ and Mn 2+ The adsorption time curve of Fig.12 It can be seen that DTC-AT-2 has a significant effect on Co 2+ and Mn 2+ The adsorption of Mn can be divided into two steps: rapid adsorption and adsorption equilibrium. When the adsorption process just occurs, the adsorption speed is very fast. At t = 1h, the material has a strong adsorption capacity of Mn. 2+The adsorption capacity of Co 2+ The adsorption capacity of Mn is also about 0.031mmol / g. 2+ The adsorption on DTC-AT-2 basically reached equilibrium at t = 4h, while Co 2+ The equilibrium is basically reached at around t = 12h, which is consistent with the 2+ and Mn 2+ The law of adsorption equilibrium on DTC-SiO2 is inconsistent. This may be related to the pore structure of the material and the adsorption process. DTC-SiO2 material is mainly composed of mesopores and macropores. 2+ and Mn 2+ The hydrated ions of Mn are easily diffused into the pores; however, there are a large number of micropores on the DTC-AT-2 material, and these micropores are small in size, which limits the diffusion of hydrated metal ions in the pores. 2+ The hydration radius is smaller than that of Co 2+ , so it is easier to reach adsorption equilibrium.

[0136] 2.2.2 Adsorption kinetics study

[0137] The Lagergren first-order adsorption rate equation, the second-order adsorption rate equation and the Elovich equation were used to fit the experimental data. The fitting curves are listed in Fig.12 and Fig.13 The fitted parameters are listed in Table 6.

[0138] According to the chart, DTC-AT-2 has a 2+ and Mn 2+ The adsorption of α is more consistent with the Lagergren second-order rate equation, and its linear correlation coefficient R 2 All of them are above 0.999. According to the Lagergren second-order rate equation, Co 2+ and Mn 2+ The theoretical equilibrium adsorption capacity qe values ​​of DTC-AT-2 and Mn were 0.050 and 0.045 mmol / g, respectively, which are basically consistent with the experimental results of 0.049 mmol / g and 0.045 mmol / g. The a value after fitting the Elovich equation in Table 6 is a parameter that characterizes the adsorption rate in the initial stage of adsorption. According to the results, DTC-AT-2 has a good adsorption capacity of Mn 2+ The initial adsorption rate of Co 2+ , which is consistent with Fig.12 The same as shown.

[0139] Table 6 Effects of three models on Co 2+ and Mn 2+ Fitting results of the adsorption process

[0140]

[0141] 2.2.3 Study on adsorption rate mechanism

[0142] The Morris internal diffusion model can well explain the mechanism of ion diffusion in solid particles, but the adsorption on the particle surface and the diffusion of liquid film must be explained by the liquid film diffusion model. Fig.14 The adsorption of Co on DTC-AT-2 is shown. 2+ and Mn 2+ The fitting curve of the internal diffusion model and the fitting curve of the liquid film diffusion are shown in Table 7 and Table 8. It can be found from the chart that the fitting curves of the two models do not pass through the origin, indicating that the adsorption process is jointly controlled by multiple diffusions, especially the model for the adsorption of Mn 2+ The linear fitting correlation coefficient R 2 It is only 0.9457, which further indicates that the diffusion process within the particle is not the only determining step. From the Morris liquid film diffusion fitting curve, it can be seen that the entire adsorption process can be divided into two stages: the first stage is that the adsorbed ions diffuse through the liquid film to the surface of the adsorbed particles. 2+ In about 0 to 4 hours, for Mn 2+ The duration of this stage is short, and the adsorption capacity increases rapidly with time, indicating that the liquid film diffusion rate is fast. The second stage is the process of metal ions diffusing in the pores of solid adsorbent particles, that is, the particle diffusion stage. This stage is controlled by both liquid film diffusion and intra-particle diffusion, which is also the main stage of adsorption.

[0143] After fitting each stage of Morris intraparticle diffusion, it does not pass through the origin, indicating that there is a boundary layer. Its intercept value reflects the thickness of the boundary layer. It can be seen from Table 7 that y1>y2, indicating that with the extension of time, the boundary layer effect becomes more and more obvious, and the liquid film diffusion process gradually becomes the key step affecting adsorption. Table 8 shows the parameters of the liquid film diffusion model after fitting the adsorption process. It can be seen that the linear correlation coefficient R 2 All of them are above 0.97, indicating that the liquid film diffusion model can fit the adsorption process well. According to formula (1) and the liquid film diffusion rate k, the effective diffusion coefficient Di can be calculated. 2+ and Mn 2+ The Di of the adsorption process is 0.3~1.643×10 -8 cm 2 / s and 0.44~2.418×10 -8 cm 2 / s, according to research, Di value is 10 -6 ~10 -8 cm 2 / s range indicates that liquid film diffusion is the main controlling step, so it can be considered that DTC-AT-2 has a significant effect on Co2+ and Mn 2+ The adsorption process is more obviously affected by the liquid film diffusion step.

[0144] According to the Boyd equation, the effective diffusion coefficient Di of the adsorption process is obtained from the rate constant k of the liquid film diffusion equation:

[0145] k=4πD i / d 2 (1)

[0146] Wherein, d is the average particle size of the adsorbent.

[0147] Table 7 Morris intraparticle diffusion model fitting parameters

[0148]

[0149] Table 8 Liquid film diffusion model parameters

[0150]

[0151] 2.3 Adsorption isotherm experiment

[0152] DTC-AT-2 is used for the determination of Co at 303K, 308K and 313K. 2+ and Mn 2+ The adsorption isotherms of the adsorption were described by Langmuir, Freundlich, DR and Sips isotherm adsorption equations, and the parameters of each model were calculated by formulas (2) to (5). The fitting curves of the adsorption results of the four models are shown in Figure 2. Figure 15 to Figure 18 The fitting parameters are shown in Table 8.

[0153] The Langmuir model assumes that the adsorption process is a monolayer adsorption. When the adsorbent surface is saturated with adsorbate, the adsorption amount reaches the maximum value. There is no adsorbate transfer movement between the adsorption points on the adsorbent surface. When the dynamic equilibrium state is reached, the adsorption and desorption rates are equal. The equation is described as follows:

[0154] q e =q max ·K L ·C e / (1+K L ·C e ) (2)

[0155] In the formula, q maxis the saturated adsorption capacity of the monolayer, mmol / g; KL is the Langmuir adsorption equilibrium constant, L / mmol. The adsorption type can be preliminarily determined based on KL. If the KL value decreases with increasing temperature, it indicates that the adsorption process is exothermic and belongs to physical adsorption; otherwise, it is an endothermic process and belongs to chemical adsorption.

[0156] The Freundlich model is an empirical formula with a wide range of applications. The equation is described as follows:

[0157]

[0158] Where KF is the Freundlich equation adsorption coefficient, mmol (1-1 / n) ·L 1 / n / g ; n is the characteristic constant of the Freundlich equation related to the adsorption intensity. The larger the n value, the stronger the interaction between the adsorbent and the metal ions.

[0159] The DR adsorption model is also a widely used model. It assumes that the adsorbent surface is uneven and the adsorption process is a pore filling process. The formula is as follows:

[0160] q e =ln q m -K DR ε 2 (4)

[0161] Among them, K DR is a constant related to the amount of adsorption, kJ 2 / mol 2 , K DR <1 means the rough mask has many holes; q m is the theoretical saturated adsorption capacity, mmol / g; ε has the following relationship:

[0162] ε=RT ln(1+ / C e ) (5)

[0163] R is the gas constant, 8.314 J / (mol·K); T is the absolute temperature, K.

[0164] It is not difficult to find from the figure that DTC-AT-2 has a 2+ The adsorption of Mn 2+The adsorption first increases and then decreases. The fitting results show that the adsorption is more consistent with the Freundlich adsorption isotherm model (the fitting correlation coefficients are 0.9165-0.9782 and 0.9674-0.9866, respectively). This is because the model is suitable for the adsorption process on uneven surfaces and can fit the experimental results well in a wide concentration range. The n value in the Frendlich model is a characteristic parameter related to the adsorption intensity. The larger the n value, the stronger the interaction between the adsorbent and the metal ions. According to Table 8, the fitting parameters n are all greater than 1, indicating that DTC-AT-2 is a more ideal adsorption material. In addition, the DR model also does not need to assume that the solid surface is uniform, so it can also describe the adsorbent to Co to a certain extent. 2+ and Mn 2+ The adsorption process of the materials at different temperatures was different for Co 2+ The average adsorption energy E values ​​of DTC-AT-2 for Co 2+ The adsorption of Mn is mainly chemical adsorption, while for 2+ , E is slightly less than 8KJ / mol, indicating that both physical adsorption and chemical adsorption are relatively obvious. Physical adsorption is fast, easy to balance, and can be multi-molecular layer adsorption, so DTC-AT-2 is not very effective for Mn 2+ The adsorption capacity and adsorption rate of Co 2+ , so DTC-AT-2 for Mn 2+ The adsorption of DTC-AT-2 to Co is more likely to reach equilibrium. Physical adsorption is not localized adsorption, and its influence on temperature is more complex, while chemical adsorption generally increases with increasing temperature within a certain range. This may be the reason for the increase in the adsorption of DTC-AT-2 to Co 2+ and Mn 2+ The reason why the adsorption trend with temperature changes has an "inflection point". The Langmuir model has a poor fit for the adsorption process because its premise is that the adsorption sites on the solid surface are evenly distributed and are monolayer adsorption. Structural characterization shows that the DTC-AT-2 material has a multi-level pore structure such as micropores, mesopores, and macropores, which obviously does not meet the requirements of the Langmuir model. For the Sips model, although it can also have a higher fitting correlation coefficient, the model can only describe the adsorption process within a certain concentration range.

[0165] Table 8 Fitting parameters of four models

[0166]

[0167] 2.4 Adsorption thermodynamics

[0168] DTC-AT-2 to Co 2+and Mn 2+ Adsorption thermodynamic parameters——Gibbs free energy ΔG 0 , enthalpy change ΔH 0 and entropy change ΔS 0 Calculated by formulas (6), (7) and (8). Fig.19 is the lnK at different initial concentrations. c -1 / T linear fitting curve.

[0169] Adsorption thermodynamics studies help to clarify the adsorption mechanism of metal ions on the adsorbent surface. Thermodynamic parameters usually include the Gibbs free energy change ΔG 0 , enthalpy change ΔH 0 and entropy change ΔS 0 , these parameters can be obtained from the thermodynamic equations:

[0170] K C =K S / C e (6)

[0171]

[0172] ΔG0=-RT ln K C (8)

[0173] Where Kc is the equilibrium constant; C S and Ce are the equilibrium concentrations of metal ions in the solid and liquid phases, in mmol / g and mmol / mL, respectively; T is the absolute temperature, in K; and R is the gas constant (8.314 J / (mol·K)).

[0174] Table 9 lists the calculation results of various parameters. At different temperatures, ΔG 0 All of them are negative, indicating that DTC-AT-2 adsorbs Co 2+ and Mn 2+ It is a spontaneous process. 2+ , as the initial concentration of the solution increases, ΔG 0 The absolute value of Mn 2+ The lower the concentration, the easier the adsorption is. However, this rule does not apply to Co 2+ . Enthalpy change ΔH 0 is a positive value, indicating that the material is 2+ and Mn 2+ The adsorption of Co is an endothermic process, and the increase in temperature is generally conducive to the occurrence of adsorption. However, comparing the isothermal adsorption curves, DTC-AT-2 has a lower adsorption rate for Co at three temperatures. 2+ and Mn 2+The adsorption of ΔS does not follow this rule. There may be many reasons for this, such as the obvious chemical adsorption and physical adsorption in the adsorption process, and the stability of dithiocarbamate is greatly affected by temperature. The specific reasons need further study. 0 A positive value indicates that the adsorption process is an entropy increasing process.

[0175] Table 9 DTC-AT-2 for Co 2+ and Mn 2+ Thermodynamic parameters of adsorption

[0176]

[0177] Table 9 lists the calculation results of various parameters. At different temperatures, ΔG 0 All of them are negative, indicating that DTC-AT-2 adsorbs Co 2+ and Mn 2+ It is a spontaneous process. 2+ , as the initial concentration of the solution increases, ΔG 0 The absolute value of Mn 2+ The lower the concentration, the easier the adsorption is. However, this rule does not apply to Co 2+ . Enthalpy change ΔH 0 is a positive value, indicating that the material is 2+ and Mn 2+ The adsorption of Co is an endothermic process, and the increase in temperature is generally conducive to the occurrence of adsorption. However, comparing the isothermal adsorption curves, DTC-AT-2 has a lower adsorption rate for Co at three temperatures. 2+ and Mn 2+ The adsorption of dithiocarbamate does not follow this rule. There may be many reasons for this, such as the obvious chemical adsorption and physical adsorption in the adsorption process, and the stability of dithiocarbamate is greatly affected by temperature. The specific reasons need further study.

[0178] ΔS 0 A positive value indicates that the adsorption process is an entropy increasing process.

[0179] 2.5Ca 2+ and Mg 2+ Effect of interfering ions on adsorption

[0180] Fig. 20 The interfering ion Ca in the solution is shown. 2+ and Mg 2+ When the content is 0~200mg / L, DTC-AT-2 has a significant effect on the Co 2+ and Mn 2+ The curve of adsorption capacity and removal rate. As can be seen from the figure, the presence of interfering ions will have a certain impact on the removal of target ions. When the concentration of interfering ions is 0, the material has a certain effect on the removal of Co 2+The adsorption capacities of the two ions were 0.051mmol / g and 0.047mmol / g, respectively, and the removal rates were 92% and 55%, respectively. When the interfering ion concentration increased to 200mg / L, the total interfering ion concentration was Co 2+ 123 times that of Mn 2+ DTC-AT-2 has a 85-fold 2+ The adsorption capacity of Mn was reduced to 0.041mmol / g, and the adsorption capacity was reduced to 81%. 2+ The adsorption capacity of 2.5 mmol / g is only 0.027 mmol / g, and the removal rate is only 31%. This is because the dithiocarbamate group provides coordination atoms mainly S, which belongs to the soft base, while Mn 2+ It is a hard acid. According to the theory of hard and soft acid-base, the complex formed by soft base-hard acid is very unstable, so it is affected by Ca which is also a hard acid. 2+ and Mg 2+ On the other hand, Mn 2+ The physical adsorption on DTC-AT-2 is more obvious, but physical adsorption is not selective, so a large amount of Ca in the solution 2+ and Mg 2+ It will seriously affect Mn 2+ Adsorption of Co by DTC-AT-2 2+ It has high selective adsorption, so it is mainly used for selective removal of corrosion activation products in low-level wastewater. 60 Co 2+ It has certain application prospects.

[0181] 2.6 Comparison of static adsorption performance of four types of materials

[0182] In this section, the synthetic materials NH2-MCM-41, MA-MCM-2 in the HS / NH2-MCM-41 series, DTC-SiO2 and DTC-AT-2 in the DTC-AT series are selected to briefly analyze their adsorption mechanisms by comparing the relevant parameters of their adsorption kinetics, isothermal adsorption processes and thermodynamic processes.

[0183] The kinetic adsorption model shows that the four materials all conform to the Lagergren second-order rate equation. In fact, most adsorption processes are also dominated by the second-order adsorption process. 2+ The adsorption rates of DTC-SiO2>DTC-AT-2>NH2-MCM-41>MA-MCM-2 were respectively, indicating that the dithiocarbamate groups and Co 2+ The complexing ability of DTC-SiO2 with macropores and mesopores as the main pore structure is greater than that of amino and thiol groups. 2+The adsorption rate of Mn is faster than that of DTC-AT-2 with microporous structure, which indicates that the material structure also has an important influence on the adsorption rate. 2+ In the adsorption of , the fitted adsorption rates are DTC-AT-2>DTC-SiO2>MA-MCM-2>NH2-MCM-41. According to the acid-base theory, the soft base S has a strong affinity for the hard acid Mn 2+ The affinity of the material to Mn is weak, and the stability of the formed complex is poor. 2+ The chemical adsorption weakens and the physical adsorption effect gradually emerges. Physical adsorption does not require chemical energy, so the adsorption rate is faster.

[0184] Isothermal adsorption experiments showed that Co 2+ and Mn 2+ The adsorption on NH2-MCM-41 and MA-MCM-2 conforms to the Langmuir monolayer adsorption and Freundlich model respectively, the adsorption on DTC-SiO2 conforms to the DR pore filling model, and the adsorption on DTC-AT-2 conforms to both the Freundlich model and the DR model. 2+ and Mn 2+ The static adsorption capacity of DTC-AT-2 is the highest.

[0185] Thermodynamic studies have shown that the adsorption of the four materials is a spontaneous, endothermic, and entropy-increasing process.

[0186] In alkaline earth metal ions Ca 2+ and Mg 2+ In the presence of Co 2+ and Mn 2+ The adsorption capacities of NH2-MCM-41>DTC-AT-2>MA-MCM-2>DTC-SiO2 are as follows. 2+ and Mn 2+ It has good selective adsorption.

[0187] From the above analysis, it can be seen that the material DTC-AT-2 has a good effect on the low concentration of Co 2+ and Mn 2+ The adsorption rate, adsorption capacity and selective adsorption capacity are all good, showing good static adsorption performance. Therefore, DTC-AT-2 is an excellent selective adsorption material for treating activated products. 60 Co. 54 Mn has important application prospects in low-level wastewater.

[0188] 2.7 Summary

[0189] (1) A class of organic / inorganic hybrid silica spheres grafted with dithiocarbamates were synthesized by co-condensation and emulsion polymerization. 2+ and Mn 2+ The comparison of static adsorption performance determined that the addition ratio of the experimental TEOS precursor solution and the modification solution DTC-ATPS was 5:3 (v / v), and the material under this formula was collectively named DTC-AT-2.

[0190] (2) Adsorption kinetics experiments show that the material DTC-AT-2 has a strong affinity for Co 2+ and Mn 2+ The time required for the adsorption of Co to reach equilibrium was 12 h and 4 h respectively. At low concentrations, DTC-AT-2 2+ and Mn 2+ The maximum adsorption capacities of Co and 2+ The adsorption effect is better than that of Mn 2+ The adsorption process satisfies the Lagergren second-order rate equation. According to the Boyd equation, Co 2+ and Mn 2+ The adsorption rate on DTC-AT-2 is controlled by liquid film diffusion.

[0191] (3) Isothermal adsorption experiments showed that DTC-AT-2 could adsorb Co 2+ and Mn 2+ The adsorption process of DTC-AT-2 is consistent with the Freundlich adsorption isotherm model, and the model fitting parameter n>1, indicating that DTC-AT-2 is an excellent adsorbent. 2+ and Mn 2+ The surface characteristic adsorption energy of Co is greater than 8KJ / mol, indicating that the chemical adsorption process is dominant. Thermodynamic parameters show that Co 2+ and Mn 2+ The adsorption on DTC-AT-2 is a spontaneous, endothermic and entropy-increasing process.

[0192] (4) Interfering ions on the adsorption of Co by DTC-AT-2 2+ The influence is small. When the total amount of interfering ions is Co 2+ When the adsorption capacity was 123 times of that of Mn 2+ The adsorption effect is relatively large, and the total amount of interfering ions reaches Mn 2+ When the adsorption capacity of DTC-AT-2 was 83 times that of Co 2+ It has high selectivity and is suitable for adsorbing low-level wastewater. 60 Co 2+It has good application prospects.

[0193] The above specific embodiments are merely explanations of the present invention and are not limitations of the present invention. After reading this specification, those skilled in the art may make modifications to the embodiments without any creative contribution as needed. However, such modifications are protected by the patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A method for preparing silica gel modified with dithiocarbamate, characterized in that: The following steps are involved: Step S1, preparation of TEOS prepolymer sol solution: dissolving dodecyl sulfonate SDS in a hydrochloric acid solution, adding TEOS under stirring, stirring at room temperature for a period of time to obtain a clear and transparent TEOS sol solution, and storing it in a refrigerator; Step S2, preparation of dithiocarbamate modification solution: dissolve sodium hydroxide in deionized water, add aminopropyltrimethoxysilane KH-550 under ice bath stirring, and after clarification, continue to add carbon disulfide under ice bath conditions, react for 1 hour, and then react for 4 hours at room temperature to obtain an egg yolk-colored slightly transparent uniform solution, which is stored in a refrigerator; Step S3, preparation of oil phase: kerosene is selected as the organic phase, and a surfactant Span80 is added to prepare a uniform emulsion; Step S4, synthesis of dithiocarbamate-modified silica spheres: Pour kerosene containing Span80 into a 500 mL three-necked flask, adjust to a certain speed at room temperature, and set aside; in an ice bath, mix a certain amount of TEOS precursor solution and deionized water evenly, and continue stirring; take the dithiocarbamate modification solution, add hexamethylenetetramine-urea solution and mix evenly, pour it into the TEOS precursor and deionized water mixture, stir for 1 minute, and then place it under constant pressure. The dropping funnel was quickly added into the kerosene; the system was heated to 313K, stirred for 2h, and then heated to 333K, stirred for 2h; cooled to room temperature, the spherical yellow solid deposited at the bottom of the flask was filtered out, and washed with ethanol; immersed in 100mL of 1% ethanol solution of ammonia water for 12h; the sample was filtered and washed with ethanol, and a white spherical solid was obtained by suction filtration, which was placed in a 313K vacuum drying oven for 6h, heated to 333K, and maintained for 4h to obtain translucent silica gel.

2. A method for preparing silica gel modified with dithiocarbamate as claimed in claim 1, characterized in that: Preferably, in step S1, the amount of dodecyl sulfonate SDS is 0.1 g; Preferably, the volume of the hydrochloric acid solution in step S1 is 20 mL and the concentration is 0.1 mol / L; Preferably, the volume of TEOS added under stirring in step S1 is 20 mL; Preferably, in step S1, the molar ratio of the reaction system: TEOS / H2O / HCl / SDS is 1 / 12 / 0.02 / 0.0037; Preferably, in step S2, the amount of sodium hydroxide is 3.6 g; Preferably, the amount of deionized water in step S2 is 20 mL; Preferably, in step S2, the amount of aminopropyltrimethoxysilane KH-550 is 16 mL; Preferably, the volume of carbon disulfide in step S2 is 5.6 mL; Preferably, in step S2, the molar ratio of the reaction system: APTMS / CS2 / NaOH / H2O is 1 / 1 / 1 / 12; Preferably, the content of Span80 in step S3 is controlled at 0.2 g / L; Preferably, the kerosene containing Span80 in step S4 is 250 mL; Preferably, the volume of the hexamethylenetetramine-urea solution in step S4 is 6 mL and the concentration is 250 g / L; Preferably, in step S1-2, the refrigerator temperature is 0 to 5 degrees Celsius.

3. The application of dithiocarbamate-modified silica gel in wastewater treatment is characterized by: Co 2+ and Mn 2+ The adsorption rate on dithiocarbamate-modified silica spheres is controlled by liquid film diffusion.

4. The use of the dithiocarbamate-modified silica gel in wastewater treatment as claimed in claim 3, characterized in that: Co 2+ and Mn 2+ The adsorption onto dithiocarbamate-modified silica spheres is a spontaneous, endothermic, and entropy-increasing process.

5. The use of the dithiocarbamate-modified silica gel in wastewater treatment as claimed in claim 3, characterized in that Dithiocarbamate-modified silica spheres for Co 2+ It has high selectivity and can adsorb low-level wastewater 60 Co 2+ .

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