Core-shell structure polymer magnetic nanospheres with high Cr (VI) adsorption capacity, preparation method and application

Abstract

A method for preparing a core-shell structure polymer magnetic nanosphere with a high Cr (VI) adsorption capacity includes: adding Fe3O4 powder into a mixed solution of water and ethanol, dispersing Fe3O4 powder in the solution evenly by ultrasound, sequentially adding resorcinol and formaldehyde into the suspension to adjust a pH, stirring and reacting to obtain Fe3O4@RF evenly dispersed in a chitosan solution, dropwise adding the prepared suspension into a mixed solution of paraffin and span 80, stirring for a period of time, adding a glutaraldehyde aqueous solution, stirring and reacting to obtain a magnetic chitosan nanosphere. The magnetic chitosan nanosphere prepared may be applied to adsorbing Cr (VI) in a water solution. Not only the magnetic chitosan nanospheres prepared has a high adsorption capacity for Cr (VI), but also can be quickly separated by an external magnetic field after adsorption.

Claims

1. A method for preparing a core-shell structure polymer magnetic nanosphere with a high Cr (VI) adsorption capacity, comprising: adding Fe3O4 powder into a mixed solution of water and ethanol, dispersing Fe3O4 powder in a solution evenly by ultrasound, sequentially adding resorcinol and formaldehyde into a suspension to adjust a pH, and finally stirring the suspension for a period of time; washing and drying after magnetic separation to obtain Fe3O4@RF; dispersing Fe3O4@RF in a chitosan solution evenly, dropwise adding the suspension into a mixed solution of paraffin and span 80, stirring for a period of time, adding a glutaraldehyde aqueous solution, stirring and reacting, and finally centrifuging, washing and drying the suspension to obtain the core-shell structure polymer magnetic nanosphere with a high Cr (VI) adsorption capacity.

2. The method of claim 1, wherein, at block(1), preparing the Fe3O4 powder by: dissolving 2.7 parts by mass of FeCl3.6H2O in 80 parts by volume of ethylene glycol at room temperature, adding 7.2 parts by mass of NaAc after stirring until clear and transparent, and continuing stirring until the NaAc is completely dissolved; then moving the mixed solution into a reactor, and performing hydrothermal reaction at 200 C° for 16 h; washing black precipitate with ethanol after cooling to room temperature, separating and drying to obtain the Fe3O4 powder.

3. The method of claim 1, wherein, at block(1), the addition amount of the Fe3O4 powder being 0.5 parts by mass, the addition amount of resorcinol being 0.4 parts by mass, and the addition amount of formaldehyde being 0.8 parts by mass.

4. The method of claim 1, wherein, at block(1), stirring the mixed suspension at 30 C° for 10 h.

5. The method of claim 1, wherein, at block(1), adjusting the pH value to 9˜11; the ultrasonic time being 10˜15 min; the volume ratio of water to ethanol in the mixed solution of water and ethanol being 1:2.

6. The method of claim 1, comprising: at block(2), the mass ratio of Fe3O4@R to chitosan being 1:1˜5.

7. The method of claim 1, wherein, at block(2), the chitosan solution being 50˜55 parts by volume, the glutaraldehyde aqueous solution being 10 parts by volume, the mixed solution of paraffin and span 80 being 80 parts by volume, the mass concentration of the chitosan solution being 1%˜5%, and the volume concentration of the glutaraldehyde aqueous solution being 5%˜15%.

8. The method of claim 1, wherein, at block(2), in the mixed solution of paraffin and span 80, the volume ratio of paraffin to span 80 being 75:5; stirring for 1 h after dropwise adding the suspension to the mixed solution of paraffin and span 80; stirring for 0.5˜2 h after adding the glutaraldehyde aqueous solution.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a Cr (VI) adsorption kinetic curve corresponding to FRC nanosphere samples prepared in Embodiments 1 to 3.

(2) FIG. 2 is an adsorption isotherm of an FRC nanosphere sample prepared in Embodiment 2.

(3) FIG. 3 is a cyclic adsorption diagram of an FRC nanosphere sample prepared in Embodiment 2.

(4) FIG. 4 are TEM and SEM photographs of Fe.sub.3O.sub.4, Fe.sub.3O.sub.4@RF and FRC nanosphere samples prepared in Embodiment 2: a, b are TEM photographs of Fe.sub.3O.sub.4, d, e are TEM photographs of F Fe.sub.3O.sub.4@RF, g, h are TEM photographs of an FRC nanosphere, c is an SEM photograph of Fe.sub.3O.sub.4@RF, f is an SEM photograph of Fe.sub.3O.sub.4@RF, and i is an SEM photograph of an FRC nanosphere.

(5) FIG. 5 are a nitrogen adsorption desorption curve (a) and a pore distribution curve (b) of an FRC nanosphere sample prepared in Embodiment 2.

(6) FIG. 6 is a hysteresis loop of an FRC nanosphere sample prepared in Embodiment 2, with a small photograph at the lower right corner of a sample separated by a magnet.

DETAILED DESCRIPTION

(7) The present disclosure is further described in detail below in combination with embodiments and drawings, however, implementations of the disclosure are not limited here. The raw materials involved in the present disclosure may be purchased directly from the market. Process parameters not specifically noted may refer to conventional techniques.

Embodiment 1

(8) Dissolve 2.7 g FeCl.sub.3.6H.sub.2O in 80 mL ethylene glycol at room temperature, add 7.2 g NaAc after magnetic stirring until the solution is clear and transparent, and continue stirring until the solid is completely dissolved. Place the mixed solution into a 100 mL reactor lining polytetrafluoroethylene, and store at constant temperature in a 200V oven for 16 h. Cool the mixed solution to room temperature, discard the supernatant, wash the black precipitate with ethanol several times until the liquid is clear, separate by a permanent magnet and dry at 60° C. for 12 h to obtain the Fe.sub.3O.sub.4 powder.

(9) Add 0.5 g Fe.sub.3O.sub.4 to 20 mL deionized water and 40 mL ethanol, and disperse Fe.sub.3O.sub.4 in the solution evenly by ultrasound for 10 min. Sequentially add 0.4 g resorcinol and 0.8 g formaldehyde to the suspension, adjust the pH of the suspension to 9 with ammonia, and finally stir the suspension at 30° C. for 10 h. After magnetic separation, wash with deionized water and ethanol three times, and vacuum dry a filter cake at 60° C. for 12 h to obtain Fe.sub.3O.sub.4@ RF nanospheres.

(10) Dissolve 0.5 g chitosan in a mixed solution of 50 mL deionized water and 0.4 mL acetic acid to prepare an acetic acid solution with a 1 wt % chitosan concentration. Add 0.5 g Fe.sub.3O.sub.4@RF to the prepared solution at a mass ratio of Fe.sub.3O.sub.4@RF:Cs=1:1, and stir until Fe.sub.3O.sub.4@RF is evenly dispersed in the solution. Dropwise add the prepared suspension to a mixed solution of 75 mL paraffin and 5 mL span 80, stir for 1 h, add 10 mL, 15% (volume concentration) glutaraldehyde aqueous solution and stir for 0.5 h. Finally, centrifuge the prepared mixed suspension, wash the filter cake with isopropanol until the filtrate is clear, and vacuum dry the obtained solid at 60° C. for 12 h to obtain RC nanospheres.

(11) When the magnetic chitosan prepared by the above method adsorbs 100 mL Cr(VI) solution of 100 mg/L, adjust the pH to 2 with a hydrochloric acid solution of a 1 mol/L concentration, and then add 0.1 g FRC nanospheres prepared above, and set parameters of a constant-temperature oscillation box to 25V, 180 r/min. The adsorption kinetic curve of the magnetic composite adsorbent for Cr (VI) refers to FIG. 1. The adsorption removal efficiency for Cr (VI) is 91.3%, and the adsorption capacity is 91.3 mg/g.

Embodiment 2

(12) Dissolve 2.7 g FeCl.sub.3.6H.sub.2O in 80 mL ethylene glycol at room temperature, add 7.2 g NaAc after magnetic stirring until the solution is clear and transparent, and continue stirring until the solid is completely dissolved. Place the mixed solution into a 100 mL reactor lining polytetrafluoroethylene, and store at constant temperature in a 200V oven for 16 h. Cool the mixed solution to room temperature, discard the supernatant, wash the black precipitate with ethanol several times until the liquid is clear, separate by a permanent magnet and dry at 60° C. for 12 h to obtain the Fe.sub.3O.sub.4 powder.

(13) Add 0.5 g Fe.sub.3O.sub.4 to 20 mL deionized water and 40 mL ethanol, and disperse Fe.sub.3O.sub.4 in the solution evenly by ultrasound for 13 min. Sequentially add 0.4 g resorcinol and 0.8 g formaldehyde to the suspension, adjust the pH of the suspension to 10 with ammonia, and finally stir the mixed suspension at 30° C. for 10 h. After magnetic separation, wash with deionized water and ethanol 3 times, and vacuum dry at 60° C. for 12 h to obtain Fe.sub.3O.sub.4@RF nanospheres.

(14) Dissolve 1.5 g chitosan in a mixed solution of 50 mL deionized water and 0.4 mL acetic acid to prepare an acetic acid solution with a 3 wt % chitosan concentration. Add 0.5 g Fe.sub.3O.sub.4@RF to the prepared solution at a mass ratio of Fe.sub.3O.sub.4@RF:Cs=1:3, and stir until Fe.sub.3O.sub.4@RF is evenly dispersed in the solution. Dropwise add the prepared suspension to a mixed solution of 75 mL paraffin and 5 mL span 80 and stir for 1 h, and then add 10 mL 10% (volume concentration) glutaraldehyde aqueous solution and stir for 1 h. Finally, centrifuge the prepared mixed suspension, wash with isopropanol until the filtrate is clear, and vacuum dry the obtained solid at 60° C. for 12 h to obtain FRC nanospheres.

(15) When the magnetic chitosan prepared by the above method adsorbs 100 mL Cr(VI) solution of 100 mg/L, adjust the pH to 2 with a hydrochloric acid solution of a 1 mol/L concentration, and then add 0.1 g FRC nanosphere prepared above, and set parameters of a constant-temperature oscillation box to 25V, 180 r/min. The adsorption kinetic curve of the magnetic composite adsorbent for Cr (VI) refers to FIG. 1. The adsorption removal efficiency for Cr (VI) is 99.9%, and the adsorption capacity is 99.9 mg/g.

Embodiment 3

(16) Dissolve 2.7 g FeCl.sub.3.6H.sub.2O in 80 mL ethylene glycol at room temperature, add 7.2 g NaAc after magnetic stirring until the solution is clear and transparent, and continue stirring until the solid is completely dissolved. Place the mixed solution into a 100 mL reactor lining polytetrafluoroethylene, and store at constant temperature in a 200V oven for 16 h. Cool the mixed solution to room temperature, discard the supernatant, wash the black precipitate with ethanol several times until the liquid is clear, separate by a permanent magnet and vacuum dry a filter cake at 60° C. for 12 h to obtain the Fe.sub.3O.sub.4 powder.

(17) Add 0.5 g Fe.sub.3O.sub.4 to 20 mL deionized water and 40 mL ethanol, and disperse Fe.sub.3O.sub.4 in the solution evenly by ultrasound for 15 min. Sequentially add 0.4 g resorcinol and 0.8 g formaldehyde to the suspension, adjust the pH to 11 with ammonia, and finally stir the mixed suspension at 30° C. for 10 h. After magnetic separation, wash with deionized water and ethanol 3 times, and vacuum dry a filter cake at 60° C. for 12 h to obtain Fe.sub.3O.sub.4@RF nanospheres.

(18) Dissolve 2.5 g chitosan in a mixed solution of 50 mL deionized water and 0.4 mL acetic acid to prepare an acetic acid solution with a 5 wt % chitosan concentration. Add 0.5 g Fe.sub.3O.sub.4@RF to the prepared solution at a mass ratio of Fe.sub.3O.sub.4@RF:Cs=1:5, and stir until Fe.sub.3O.sub.4@RF is evenly dispersed in the solution. Dropwise add the prepared suspension to a mixed solution of 75 mL paraffin and 5 mL span 80 and stir for 1 h, and then add 10 mL 5% (volume concentration) glutaraldehyde aqueous solution and stir for 2 h. Finally, centrifuge the prepared mixed suspension, wash with isopropanol until the filtrate is clear, and vacuum dry the obtained filter cake at 60° C. for 12 h to obtain FRC nanospheres.

(19) When the magnetic chitosan prepared by the above method adsorbs 100 mg/L Cr(VI) solution, adjust the pH to 2 with a hydrochloric acid solution of a 1 mol/L concentration, and then add 0.1 g FRC nanosphere prepared above, and set parameters of a constant-temperature oscillation box to 25V, 180 r/min. The adsorption kinetic curve of the magnetic composite adsorbent for Cr (VI) refers to FIG. 1. The adsorption removal efficiency for Cr (VI) is 95.6%, and the adsorption capacity is 95.6 mg/g.

Embodiment 4

(20) To observe the adsorption capacity of a magnetic chitosan adsorbent with a high adsorption capacity for different concentrations of Cr (VI) solutions, taking the adsorbent prepared in Embodiment 2 for an example, the adsorption performances of the absorbent in different initial concentrations of Cr (VI) solutions are tested. The adsorption process is as follow: configure 50 mL Cr(VI) solution of 25 mg/L at a pH=2, 50 mL Cr(VI) solution of 50 mg/L at a pH=2, 50 mL Cr(VI) solution of 100 mg/L at a pH=2, 50 mL Cr(VI) solution of 200 mg/L at a pH=2, 50 mL Cr(VI) solution of 300 mg/L at a pH=2, 50 mL Cr(VI) solution of 400 mg/L at a pH=2 and 50 mL Cr(VI) solution of 500 mg/L at a pH=2, add 0.05 g magnetic composite adsorbent in the above Cr(VI) solution correspondingly, and set parameters of the constant-temperature oscillation box to 25V, 180 r/min. The adsorption isotherm of the magnetic composite adsorbent prepared in Embodiment 2 refers to FIG. 2. The adsorption capacity is 249.1 mg/g.

Embodiment 5

(21) In order to observe the cyclic regeneration adsorption performance of a typical sample of the magnetic chitosan adsorbent with a high adsorption capacity, desorb the sample after adsorption equilibrium in Embodiment 2 with 0.005 mol/L NaOH solution for 12 h, then dry and recycle, and absorb a Cr(VI) solution of pH=2,100 mg/L for the desorbed sample again, and set the parameters of a constant-temperature oscillation box to 25° C., 180 r/min. Repeat the above adsorption-desorption process 5 times to determine the adsorption capacity of the magnetic composite adsorbent for Cr (VI). The cyclic adsorption result of the magnetic composite adsorbent refers to FIG. 3. The result shows that the adsorption capacity after 4 cycles remains 90% of the original adsorption capacity, and the cyclic regeneration adsorption performance is relatively stable.

(22) The concentration of Cr (VI) in Embodiments 1-5 is determined by a diphenylcarbazide spectrophotometry, and the uv-vis spectrophotometer used is a UVMINI-1240 type of Shimadzu.

(23) Table 1 illustrates a comparison of adsorption capacities of chitosan when adsorbing 100 mg/L Cr (VI) solution under the same conditions in Embodiments 1, 2, 3. Table 2 illustrates pore structure parameters of Embodiment 1, Embodiment 2, and Embodiment 3.

(24) TABLE-US-00001 TABLE 1 Adsorption Adsorption Absorbent Condition Capacity Chitosan 25° C., pH = 2 79.1 Embodiment 1 25° C., pH = 2 91.3 Embodiment 2 25° C., pH = 2 99.9 Embodiment 3 25° C., pH = 2 95.6

(25) TABLE-US-00002 TABLE 2 Specific Average Surface Area Pore Volume Pore Size Sample S.sub.BET (mg2/g) V1 (cm3/g) D.sub.BJH (mm) Embodiment 1 13.18 0.035 8.46 Embodiment 2 10.70 0.016 6.13 Embodiment 3 8.10 0.011 5.78

(26) The above embodiments are preferred embodiments of the present disclosure. However, implementations of the invention are not limited by the above embodiments, and any other changes, modifications, substitutions, combinations and simplifications not departing from the spirit and principles of the disclosure should be equivalent replacements and included in the protection scope of the present disclosure.