CN111250062B - Cellulose foam capable of visually identifying and removing chromium, preparation method thereof and chromium removal method - Google Patents

Cellulose foam capable of visually identifying and removing chromium, preparation method thereof and chromium removal method Download PDF

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CN111250062B
CN111250062B CN202010127485.6A CN202010127485A CN111250062B CN 111250062 B CN111250062 B CN 111250062B CN 202010127485 A CN202010127485 A CN 202010127485A CN 111250062 B CN111250062 B CN 111250062B
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cellulose
chromium
cellulose foam
solution
foam
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CN111250062A (en
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张胜利
张思略
裴彥博
杨红薇
刘伯芳
周祚万
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Southwest Jiaotong University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/22—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising organic material
    • B01J20/26—Synthetic macromolecular compounds
    • B01J20/265—Synthetic macromolecular compounds modified or post-treated polymers
    • B01J20/267—Cross-linked polymers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/22—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising organic material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/22—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising organic material
    • B01J20/24—Naturally occurring macromolecular compounds, e.g. humic acids or their derivatives
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
    • B01J20/28014—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their form
    • B01J20/28042—Shaped bodies; Monolithic structures
    • B01J20/28045—Honeycomb or cellular structures; Solid foams or sponges
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/30—Processes for preparing, regenerating, or reactivating
    • B01J20/34—Regenerating or reactivating
    • B01J20/345—Regenerating or reactivating using a particular desorbing compound or mixture
    • B01J20/3475—Regenerating or reactivating using a particular desorbing compound or mixture in the liquid phase
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/28—Treatment of water, waste water, or sewage by sorption
    • C02F1/285—Treatment of water, waste water, or sewage by sorption using synthetic organic sorbents
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/10—Inorganic compounds
    • C02F2101/20—Heavy metals or heavy metal compounds
    • C02F2101/22—Chromium or chromium compounds, e.g. chromates

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  • Environmental & Geological Engineering (AREA)
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Abstract

The invention provides a cellulose foam capable of visually identifying and removing chromium, a preparation method thereof and a chromium removal method, wherein the preparation method comprises the following steps: adding epichlorohydrin into the cellulose solution, stirring until the color of the solution becomes light, adding PEI solution, uniformly stirring, crosslinking for 5-60min at 25-60 ℃ to form hydrogel, washing with deionized water, freezing, and freeze-drying to obtain the modified cellulose. The cellulose foam prepared by the method can quickly identify and remove Cr (VI) in a wider pH range, can regulate and control the electrostatic adsorption and the subsequent oxidation-reduction process of Cr (VI), ensures that the structure of the adsorbent cannot be damaged due to oxidation reaction while removing Cr (VI), and has high regeneration speed of the material after adsorbing Cr (VI) and cannot damage the structure of the adsorbent in the regeneration process.

Description

Cellulose foam capable of visually identifying and removing chromium, preparation method thereof and chromium removal method
Technical Field
The invention belongs to the technical field of chromium adsorption materials, and particularly relates to a cellulose foam capable of visually identifying and removing chromium, a preparation method thereof and a chromium removal method thereof.
Background
China is a world large country for producing chromium salt and is also a world large country for consuming chromium and compounds thereof. For historical reasons, 670 ten thousand tons of chromium slag are completely treated in 15 provinces, but the remediation and treatment of the soil and underground water polluted by the chromium slag are heavy and far away. In addition, the discharge of three wastes in the industries of metallurgy, electroplating, tanning, paint, printing and dyeing, pigment, ceramics, catalysis, corrosion prevention and the like further aggravates the environmental chromium pollution and seriously threatens the human health. Chromium is a heavy metal with strong toxicity, is listed as one of the most toxic pollutants by the United states environmental protection agency, and is listed in the blacklist of water environment priority control pollutants in China. The chromium in the environment mainly exists in two valence states of Cr (III) and Cr (VI), and the Cr (VI) in the environment has stronger toxicity and the carcinogenic and mutagenic capacity of the Cr (III) is 1000 times that of the Cr (III); meanwhile, cr (VI) also has strong oxidation capacity and migration energy, so that the identification and removal of Cr (VI) in water and wastewater are highly regarded by people.
At present, the common treatment methods of the wastewater containing Cr (VI) mainly comprise a chemical reduction method, a barium salt precipitation method, an ion exchange method, an electrolysis method, a membrane separation method, an activated carbon adsorption method and the like. The method can realize the removal of Cr (VI) through proper combination, but the reaction process has high energy consumption or needs a large amount of chemical reagents, and secondary pollutants such as chromium sludge and the like are generated. In addition, when used for treating low-concentration Cr (VI) -containing wastewater, the method also has the problems of high cost, low treatment efficiency and the like. Compared with the traditional adsorption method, the biological adsorption method has the advantages of simple process equipment, easy operation, good treatment effect and the like, and the biological adsorbent is cheap and easy to obtain, thus becoming a hot spot of domestic and foreign research in recent years.
The prior art has the following reports: (1) The sodium carboxymethylcellulose is used as a raw material, and the Cr (VI) removing adsorbent with a three-dimensional porous network structure is prepared by a crosslinking method, but the finished product is hydrogel instead of foam. The mass transfer of pollutants is not favorable by the large amount of water filled in the hydrogel, and in the adsorption process, the adsorbed and combined Cr (VI) and the hydrogel undergo redox reaction, so that the structure of the hydrogel can be damaged due to oxidation, and the adsorption effect is finally influenced. (2) Cellulose is used as a raw material, modified cellulose fibers with a one-dimensional structure and modified cellulose membranes with a two-dimensional structure are respectively prepared by an oxidation-grafting method, the modified cellulose fibers and the modified cellulose membranes do not have rich porous structures, the exposure of active point positions and the mass transfer of pollutants are not facilitated, in addition, in the adsorption process, cr (VI) is reduced into Cr (III) by hydroxyl on the cellulose, the reaction can not be controlled to stop in the electrostatic adsorption stage, and the self structures of the adsorbent are inevitably damaged. Therefore, the prior Cr (VI) removing adsorbent mainly has the following problems: (1) the adsorbent is non-fluorescent and cannot simultaneously recognize Cr (VI). (2) The slower rate of Cr (VI) removal results in higher reactor processing costs. (3) The treated effluent can hardly reach the limit value of 0.05mg/L of Cr (VI) in sanitary Standard of Drinking Water. (4) When the PEI modified adsorbent is used for removing Cr (VI), two processes of electrostatic adsorption and oxidation-reduction reaction cannot be regulated, the Cr (VI) can be partially or completely reduced into Cr (III) by the adsorbent, and the structure of the adsorbent can be destroyed to a certain extent, so that the regeneration and use of the adsorbent are influenced. (5) The regeneration process of the used adsorbent takes a long time, and the adsorption performance is rapidly reduced in repeated use.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a cellulose foam capable of visually identifying and removing chromium, a preparation method thereof and a chromium removal method thereof. The cellulose foam can quickly identify and remove Cr (VI) in a wider pH range, can regulate and control the electrostatic adsorption and the subsequent oxidation-reduction process of Cr (VI), ensures that the structure of the adsorbent is not damaged when the Cr (VI) is removed, has high regeneration speed after adsorbing the Cr (VI) by the adsorbent, and cannot damage the structure of the adsorbent in the regeneration process.
In order to achieve the purpose, the technical scheme adopted by the invention for solving the technical problems is as follows:
a cellulose foam capable of visually identifying and removing chromium is prepared by the following steps:
adding epichlorohydrin into the cellulose solution, adding PEI solution, stirring uniformly, crosslinking for 5-60min at 25-60 ℃ to form hydrogel, washing with deionized water, freezing, and freeze-drying to obtain the product.
Further, the concentration of the cellulose solution is 3 to 7wt%, and the concentration of the cellulose solution is preferably 4wt%.
Further, the concentration of the PEI solution is 3-20wt%, preferably the concentration of the PEI solution is 5wt%.
Further, the volume ratio of the cellulose solution, the epichlorohydrin and the PEI solution is 10.3-1.
Further, the volume ratio of the cellulose solution, epichlorohydrin and PEI solution was 10.
Further, the crosslinking temperature was 50 ℃ and the crosslinking time was 20min.
Furthermore, the freezing temperature is-18 to-20 ℃, and the freezing time is 8 to 12 hours; preferably, the freezing temperature is-18 ℃ and the freezing time is 12h.
Further, the freeze-drying time was 24 hours.
The method for removing chromium from the cellulose foam which is prepared by the preparation method and can visually identify and remove chromium comprises the following steps: and (3) putting the cellulose foam into a chromium-containing water sample, stirring, taking out before the cellulose foam turns brown, regenerating by using a sodium hydroxide solution or sodium thiosulfate, and returning to adsorb Cr (VI), and circulating the operation until the effluent meets the corresponding standard requirement.
The cellulose foam capable of visually identifying and removing chromium, the preparation method thereof and the chromium removal method provided by the invention have the following beneficial effects:
the electrostatic adsorption of Cr (VI) is far faster than the subsequent oxidation-reduction process of Cr (VI), so that the electrostatic adsorption rate is increased, the electrostatic adsorption time is shortened, and the subsequent oxidation-reduction reaction can be avoided. The cellulose foam has a three-dimensional porous structure, which is not only beneficial to the exposure of active sites, but also can improve the effective mass transfer process, so that Cr (VI) is quickly adsorbed on the cellulose foam. Meanwhile, the PEI structure contains high-density primary amine, secondary amine and tertiary amine, and the positive charge is carried out due to protonation of amino groups in a wider pH range, so that the PEI structure can be combined with CrO containing Cr (VI) anions 4 2－ 、HCrO 4 － When electrostatic adsorption occurs, PEI has an aggregation fluorescence effect, the prepared cellulose foam emits strong blue fluorescence under 365nm ultraviolet irradiation, and the electrostatic adsorption of Cr (VI) can quench the cellulose foam, so that Cr can be rapidly identified and removed in a wider pH range(VI). The adsorption of the cellulose foam to the Cr (VI) is electrostatic action, so that the desorption of the Cr (VI) can be realized only by regulating and controlling the surface charge of the adsorbent, and the structure of the adsorbent cannot be damaged in the regeneration process.
In conclusion, the cellulose foam prepared by the invention can quickly identify and remove Cr (VI) in a wider pH range, can regulate and control the electrostatic adsorption and subsequent oxidation-reduction process of Cr (VI), ensures that the structure of the adsorbent is not damaged while removing Cr (VI), and can quickly regenerate after adsorbing Cr (VI), and the structure of the adsorbent cannot be damaged in the regeneration process.
Drawings
Fig. 1 is an SEM image of cellulose foam.
FIG. 2 is a photograph showing the visual recognition of Cr (VI) by cellulose foam under different pH conditions.
FIG. 3 is a photograph of a cellulose foam after adsorption of 50mg/L Cr (VI) and regeneration with sodium thiosulfate solution under sunlight (top row) and ultraviolet light (bottom row)).
FIG. 4 is a photograph of a cellulose foam after adsorbing 5mg/L Cr (VI) and regenerating with a sodium thiosulfate solution under sunlight (upper row) and ultraviolet light (lower row)).
Detailed Description
Example 1
A preparation method of cellulose foam capable of visually identifying and removing chromium comprises the following steps:
and (3) taking 8.333g of dried cotton, adding 145.45ml of DMSO solution, adding 42.6ml of 40wt% TBAH aqueous solution, mechanically stirring for dissolving, standing for defoaming, and then placing in a refrigerator at 4 ℃ for cooling for 2 hours to obtain a cellulose solution with the mass fraction of 4%. And (2) putting 10mL of the solution into a 50mL beaker, adding 1mL of epoxy chloropropane, stirring until the color of the solution becomes light, adding 0.1mL of 5wt% of PEI, uniformly stirring, pouring into a mold, placing into a 50 ℃ oven for reaction for 60min, taking out to obtain hydrogel, replacing the solvent with deionized water, placing into a freezer compartment (-18 ℃) for freezing for 12h, and then placing into a freeze dryer for freeze drying at-81 ℃ for 24h to obtain cellulose foam (also called PEI modified cellulose foam).
0.02g of prepared cellulose foam is put into 20ml of Cr (VI) -containing simulated wastewater with the concentration of 100mg/L and the pH value of 2, and the sample is sampled and analyzed after being magnetically stirred and adsorbed for 30min at the temperature of 25 ℃, so that the removal rate of Cr (VI) is 6.78 percent.
Example 2
A preparation method of cellulose foam capable of visually identifying and removing chromium comprises the following steps:
taking 10mL of the cellulose solution prepared in the example 1, putting the cellulose solution into a 50mL beaker, adding 1mL of epoxy chloropropane, stirring until the color of the solution becomes light, adding 1mL of 10wt% of PEI, stirring uniformly, pouring into a mold, putting into a 50 ℃ oven for reaction for 60min, taking out to obtain hydrogel, replacing the solvent with deionized water, putting into a refrigerator freezing chamber (-18 ℃) for freezing for 12h, and putting into a freeze dryer for freeze drying at-81 ℃ for 24h to obtain cellulose foam.
0.02g of prepared cellulose foam is put into 20mL of simulated wastewater containing Cr (VI) with the concentration of 100mg/L and the pH value of 2, and the sample is sampled and analyzed after being magnetically stirred and adsorbed for 30min at the temperature of 25 ℃, and the removal rate is measured to be 65.57%.
Example 3
A preparation method of cellulose foam capable of visually identifying and removing chromium comprises the following steps:
taking 10mL of the cellulose solution prepared in the example 1, putting the cellulose solution into a 50mL beaker, adding 0.5mL of epoxy chloropropane, stirring until the color of the solution becomes light, adding 1mL of 6wt% of PEI, stirring uniformly, pouring into a mold, putting into a 50 ℃ oven for regeneration for 30min, taking out to obtain hydrogel, replacing the solvent with deionized water, putting into a freezer compartment of a refrigerator for freezing for 12h at (-18 ℃), and putting into a freeze dryer for freeze drying for 24h at-81 ℃ to obtain cellulose foam.
0.05g of prepared cellulose foam is taken and put into 25mL of simulated wastewater containing Cr (VI) with the concentration of 100mg/L and the pH value of 2, and the sample is sampled and analyzed after being magnetically stirred and adsorbed for 30min at the temperature of 25 ℃, and the removal rate is 95.53 percent.
Example 4
A preparation method of cellulose foam capable of visually identifying and removing chromium comprises the following steps:
taking 10mL of the cellulose solution prepared in the example 1, putting the cellulose solution into a 50mL beaker, adding 0.5mL of epoxy chloropropane, stirring until the color of the solution becomes light, adding 0.5mL of 10wt% of PEI, stirring uniformly, pouring into a mold, putting into a 50 ℃ oven for regeneration for 30min, taking out to obtain hydrogel, replacing the solvent with deionized water, putting into a freezer compartment of a refrigerator for freezing for 12h at (-18 ℃), and putting into a freeze dryer for freeze drying for 24h at-81 ℃ to obtain cellulose foam.
0.05g of prepared cellulose foam is put into 25mL of simulated wastewater containing Cr (VI) with the concentration of 100mg/L and the pH value of 2, and the sample is sampled and analyzed after being magnetically stirred and adsorbed for 30min at the temperature of 25 ℃, and the removal rate is measured to be 78.33%.
Example 5
0.02g of the cellulose foam obtained in example 4 was put into 20mL of Cr (VI) -containing simulated wastewater with a concentration of 50mg/L and a pH value of 2, and the sample was magnetically stirred and adsorbed at 25 ℃ for 10min, and then the removal rate was 83.4% by analysis.
Example 6
Taking 10mL of the cellulose solution prepared in the example 1, putting the cellulose solution into a 50mL beaker, adding 0.5mL of epoxy chloropropane, stirring until the color of the solution becomes light, adding 1mL of 5wt% PEI, stirring uniformly, pouring into a mold, putting into a 50 ℃ oven for regeneration for 30min, taking out to obtain hydrogel, replacing the solvent with deionized water, putting into a refrigerator freezer (-18 ℃) for freezing for 12h, and putting into a freeze dryer for freeze drying at-81 ℃ for 24h to obtain cellulose foam.
0.05g of prepared cellulose foam is put into 25mL of simulated wastewater containing Cr (VI) with the concentration of 100mg/L and the pH value of 2, and the sample is sampled and analyzed after being magnetically stirred and adsorbed for 30min at the temperature of 25 ℃, and the removal rate is measured to be 87.91 percent.
Example 7
0.02g of the cellulose foam obtained in example 6 was put into 20mL of Cr (VI) -containing simulated wastewater with a concentration of 100g/L and a pH value of 6, and the sample was magnetically stirred and adsorbed at 25 ℃ for 30min, and then the removal rate was 55.64% by analysis.
Example 8
Taking 10mL of the cellulose solution prepared in the example 1, putting the cellulose solution into a 50mL beaker, adding 0.5mL of epoxy chloropropane, stirring until the color of the solution becomes light, adding 2mL of 5wt% PEI, stirring uniformly, pouring into a mold, putting into a 50 ℃ oven for regeneration for 20min, taking out to obtain hydrogel, replacing the solvent with deionized water, putting into a refrigerator freezer (-18 ℃) for freezing for 12h, and putting into a freeze dryer for freeze drying at-81 ℃ for 24h to obtain cellulose foam.
SEM characterization of the cellulose foam produced is shown in figure 1. As can be seen from FIG. 1, the cellulose foam produced had a developed three-dimensional network structure.
0.05g of prepared cellulose foam is put into 25mL of simulated wastewater containing Cr (VI) with the concentration of 40mg/L and the pH value of 3, and the sample is sampled and analyzed after being magnetically stirred and adsorbed for 30min at the temperature of 55 ℃, and the removal rate is measured to be 95.08 percent.
Example 9
0.05g of the cellulose foam obtained in example 8 was put into 25mL of Cr (VI) -containing simulated wastewater with a concentration of 60mg/L and a pH value of 3, and the sample was magnetically stirred and adsorbed at 25 ℃ for 40min, and then was analyzed, whereby the removal rate was 96.74%.
Example 10
0.05g of the cellulose foam obtained in example 8 was put into 25mL of Cr (VI) -containing simulated wastewater with a concentration of 40mg/L and a pH value of 2, and the sample was magnetically stirred and adsorbed at 25 ℃ for 30min, and then the removal rate was 97.35% by analysis.
Example 11
The cellulose foam 9 pieces prepared in example 8 were cut out, put into Cr (VI) -containing simulated wastewater with a concentration of 0.5mg/L and a pH of 2, 3, 4, 5, 6, 7, 8, 9, 10, respectively, reacted for 30min under magnetic stirring at 25 ℃, the cellulose foam was taken out, washed with deionized water, after surface moisture was blotted, fluorescence quenching was observed under 365nm ultraviolet irradiation, and the results are shown in fig. 2.
As can be seen from FIG. 2, the cellulose foam emits bright blue fluorescence under 365nm ultraviolet light, and the presence of Cr (VI) quenches the fluorescence when the pH is between 3 and 8, so that the cellulose foam can identify Cr (VI) in a wide pH range (3-8).
Example 12
2 pieces of the cellulose foam prepared in example 8 were cut, put into Cr (VI) -containing simulated wastewater with a concentration of 50 and 5mg/L and a pH of 7, and reacted for 2min under magnetic stirring at 25 ℃, the cellulose foam was taken out, washed with deionized water, and after absorbing surface water, fluorescence quenching was observed under 365nm ultraviolet irradiation. Then the solution is put into 5g/L sodium thiosulfate solution for regeneration, and the fluorescence recovery is observed under the irradiation of 365nm ultraviolet light, and the results are shown in figure 3 and figure 4.
As can be seen from FIGS. 3 and 4, the color of the cellulose foam changed to yellow and the blue fluorescence was quenched after exposure to 50 and 5mg/L Cr (VI) -containing solutions; after the cellulose foam absorbing Cr (VI) is regenerated by a sodium thiosulfate solution, the yellow color is faded and the fluorescence energy is recovered, so that the structure of the absorbent is not damaged in the regeneration process.
Example 13
A plurality of cellulose foam pieces prepared in example 8 were cut out, put into simulated wastewater containing Cr (VI) with a concentration of 5mg/L and a pH of 6, magnetically stirred at 25 ℃ for reaction for 10min, and taken out, and the cellulose foam was observed to turn yellow and to be quenched by fluorescence. Then, the mixture was put into sodium thiosulfate solution or sodium hydroxide solution at concentrations of 0.5, 2.5, 5, and 10g/L, and reacted for 10, 30, 60, and 120min, and the fluorescence recovery of the cellulose foam was observed. The experimental result shows that the cellulose foam after adsorbing the Cr (VI) can be regenerated by using 0.5-10g/L sodium thiosulfate solution or sodium hydroxide solution, and the regeneration time is 10-120min.
Example 14
100mL of laboratory tap water was added to 0.5mL of 100mg/L Cr (VI) standard solution, and then a piece of the cellulose foam obtained in example 8 was cut out and placed therein, and reacted at 25 ℃ for 10min with magnetic stirring. Taking out the cellulose foam, observing the cellulose to turn yellow on the surface of the foam by naked eyes, washing the foam by deionized water, sucking dry the surface water, and then quenching the fluorescence of the cellulose foam under the irradiation of an ultraviolet lamp with the wavelength of 365 nm. The fluorescence recovered after elution with 1g/L sodium hydroxide solution.
Example 15
Taking 100mL of campus lake water, adding 0.5mL of 10, 20, 30, 50, 60, 80 and 100mg/L Cr (VI) standard solution, cutting a piece of cellulose foam prepared in example 8, placing the piece of cellulose foam in the piece of cellulose foam, and reacting for 10min at 25 ℃ by magnetic stirring. Taking out the cellulose foam, observing the surface of the cellulose foam to turn yellow by naked eyes, washing with deionized water, sucking dry the surface water, and quenching the fluorescence of the cellulose foam under the irradiation of an ultraviolet lamp with the wavelength of 365 nm. The fluorescence recovered after elution with 1g/L sodium hydroxide solution.
Example 16
Cutting several parts of the cellulose foam obtained in example 8, wherein each part is 0.05g, respectively putting the parts into Cr (VI) -containing water samples with the concentrations of 10, 60 and 100mg/L, controlling the adsorption time, and taking out the parts before the cellulose foam is browned; meanwhile, according to the concentration of Cr (VI) in the water sample and the type of the receiving water body, multistage adsorption is set.
The Cr (VI) concentrations in the effluent after the multi-stage treatment of the cellulose foam with different initial concentrations of Cr (VI) are shown in Table 1.
TABLE 1 results of multistage treatment of PEI modified cellulose foam with different initial concentrations of Cr (VI)
Cr (VI) concentration (mg/L) First-stage treatment of effluent Secondary treatment of effluent Three-stage treatment of effluent Four-stage treatment of effluent
100 24.77 2.77 0.21 0.03
60 5.69 0.95 0.06 0.01
10 2.99 0.13 0.01 —
Note: 25mL of Cr (VI) solution, 0.05g of adsorbent was used for each treatment.
As can be seen from Table 1, the simulated wastewater containing Cr (VI) with different concentrations can reach the specified value of 0.5mg/L in Integrated wastewater discharge Standard (GB 8978-1996) or 0.05mg/L in sanitary Standard for Drinking Water after the multi-stage treatment of cellulose foam.

Claims (6)

1. The preparation method of the cellulose foam capable of visually identifying and removing chromium is characterized by comprising the following steps of:
adding epichlorohydrin into the cellulose solution, stirring until the color of the solution becomes light, adding a PEI solution, uniformly stirring, crosslinking for 5-60min at 25-60 ℃ to form hydrogel, washing with deionized water, freezing, and freeze-drying to obtain the modified cellulose hydrogel;
wherein the concentration of the cellulose solution is 4wt%; the concentration of the PEI solution is 5wt%; the volume ratio of the cellulose solution to the epichlorohydrin to the PEI solution is 10.5.
2. The method for preparing cellulose foam capable of visually identifying and removing chromium according to claim 1, wherein the crosslinking temperature is 50 ℃ and the crosslinking time is 20min.
3. The method for preparing the cellulose foam capable of visually identifying and removing chromium according to claim 1, wherein the freezing temperature is-18 to-20 ℃, and the freezing time is 8 to 12 hours.
4. The preparation method of the cellulose foam capable of visually identifying and removing chromium according to claim 1, wherein the freeze-drying temperature is-80 to-85 ℃, and the freeze-drying time is 22 to 26 hours.
5. Cellulose foam which is visually identifiable and has been freed of chromium and which is obtainable by a process according to any one of claims 1 to 4.
6. The method for removing chromium using the cellulose foam capable of visually recognizing and removing chromium according to claim 5, comprising the steps of: the visual identification of the cellulose foam to chromium is realized by observing the fluorescence quenching condition of the cellulose foam before and after absorbing the sample under the irradiation of 365nm ultraviolet light; and mixing the cellulose foam and the chromium-containing sample, stirring until the cellulose foam turns brown, taking out, regenerating the taken-out cellulose foam, continuously adsorbing the chromium-containing sample, and repeating the steps to finish the chromium removal process.
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