A molecularly switched adsorbent for adsorbing triphenylmethane dyes and its application

Abstract

This invention discloses a molecularly switched adsorbent for adsorbing triphenylmethane dyes and its application, belonging to the field of wastewater treatment technology. The molecularly switched adsorbent proposed in this invention can rapidly remove triphenylmethane dyes such as crystal violet, malachite green, and methylene blue dyes from water; it can remove tens of ppm concentrations of crystal violet, malachite green, and methylene blue dyes from water in a very short time (90 min), with a removal rate of ≥92%. Moreover, this adsorbent can maintain a removal rate of ≥90% under a wide pH range (6-11) and high ion concentration conditions (1M). The activation and regeneration conditions of the adsorbent of this invention are mild; dye molecules can be removed by elution in a low-concentration alkaline solution only a few times. The adsorbent can be continuously recycled at least 10 times without significant attenuation of adsorption capacity.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment, specifically to a novel molecularly switched adsorbent and its highly selective adsorption of triphenylmethane dyes in an aqueous phase. Background Technology

[0002] Water is one of the most abundant compounds in nature and is essential for life on Earth. However, human activities, including domestic, industrial, and agricultural activities, have led to severe water pollution. The large-scale use of chemicals such as pharmaceuticals, disinfectants, detergents, surfactants, pesticides, paints, food additives, and dyes poses a serious threat to the environment and global human health. Dyes, in particular, have made a significant contribution to water pollution because they generate large amounts of wastewater that are directly discharged into the environment. Even at low concentrations, dyes in wastewater can exhibit strong colors, allowing small amounts to pollute large areas of water, thus threatening aquatic ecosystems and human health. Among these dyes, triphenylmethane dyes are widely used in the textile, paper, and leather dyeing industries, as well as in the food and cosmetic industries, such as for coloring confectionery, beverages, and lipsticks. Malachite green, a highly soluble and harmful chemical, has been banned globally in the aquaculture and food industries due to its harmful effects on various animal organs, including humans. Despite the ban, these dyes remain widely used in some regions due to their low cost and high efficiency. Therefore, there is an urgent need to develop cost-effective treatment methods to treat dye-containing wastewater before it is discharged into the environment.

[0003] Adsorption is considered one of the most promising and feasible methods for removing dyes due to its low synthesis cost, high removal efficiency, and recyclability. This method uses the principle of equilibrium separation to remove colored dyes from wastewater, offering simplicity and flexibility in design and insensitivity to toxic pollutants. Various adsorbents have been reported in dye wastewater treatment, including activated carbon, fly ash, silica gel, wood, polymers, and clay. For example, adsorbents used to date for removing triphenylmethane dyes such as crystal violet and malachite green include rice husks, corn cobs, water hyacinth-based carbon materials, clay, coal, CeO2 nanoparticles, and other bio-based activated carbons. While these adsorbent materials are relatively inexpensive, their low structural order and complex multifunctional groups make it difficult to study their structure-activity relationships. Furthermore, these adsorbents are not only effective for crystal violet or malachite green but also for other types of dyes or molecules, resulting in poor selectivity.

[0004] Molecular switch structures are structures that respond to external stimuli such as light, heat, and force, and can undergo various reactions, such as isomerization, ring opening and closing reactions, and intramolecular proton transfer or intermolecular electron transfer. These reactions result in different electronic structures and different properties, such as ionic / nonionic, acidic / basic, nucleophilic / electrophilic / hydrophilic / hydrophobic. We believe that such dynamic and variable structures can enable the detection and capture of specific molecules. Although molecular switches are mainly used to sense physical stimuli such as light, heat, and force, there are few reports on their application in the adsorption of organic dyes. Developing adsorbent materials with molecular switch structures has great potential for innovation.

[0005] Existing reports do not include adsorbent materials specifically for triphenylmethane dyes, and the adsorption selectivity of general adsorbent materials for a particular type of dye is rarely investigated; in addition, there are almost no reports in the literature on the use of molecular switch materials to synthesize adsorbents. Summary of the Invention

[0006] Based on the problems existing in the background technology, the first objective of this invention is to specifically develop a class of highly selective adsorbent materials for use as proprietary adsorbents for a certain type of dye. In this invention, a highly efficient adsorbent was designed and synthesized for triphenylmethane dyes such as crystal violet, malachite green, and methylene blue, which exhibits weak adsorption or no adsorption for other types of dyes. The second objective of this invention is to explore whether using molecular switch structures such as phenolphthalein to construct adsorbent materials will produce unexpected effects.

[0007] This invention first discloses a molecularly switched adsorbent for adsorbing triphenylmethane dyes, the structural formula of which is shown in formulas (1) and (2):

[0008]

[0009] Equation (1),

[0010]

[0011] Equation (2),

[0012] In the structural formulas of equations (1) and (2),

[0013]

[0014] Furthermore, the preparation method of the molecularly switched adsorbent for adsorbing triphenylmethane dye includes the following steps:

[0015] S1. Weigh 2-5g of phenolphthalein, 10-15 times the amount of hexamethylenetetramine of phenolphthalein and 30-80mL of trifluoroacetic acid, mix them, react at 80-110℃ for 15-24h under argon atmosphere, add 100-300mL of 2-5mol / L hydrochloric acid aqueous solution, hydrolyze at 100℃ for 1h, cool to room temperature, filter, wash with water, purify and dry to obtain phenolphthalein tetraaldehyde;

[0016] S2. Dissolve 0.1–1 g of phenolphthalein tetraaldehyde in 50–150 mL of organic solution and label it as A. Dissolve 0.01–0.5 g of diamine compound in 10–50 mL of organic solvent and label it as B. Add solution B to solution A and reflux overnight. After cooling to room temperature, filter and collect the precipitate. Wash with organic solvent and dry to obtain powder.

[0017] S3. Dissolve 0.1–1 g of the powder obtained in step S2 and 1–5 g of reducing agent sodium borohydride in 100–300 mL of ethanol and reflux overnight. After cooling to room temperature, remove the ethanol solvent under vacuum, then add 500 mL of pure water and stir overnight at room temperature. Filter the suspension, collect the precipitate, and dry it under vacuum at 60 °C to obtain the molecular switch adsorbent for adsorbing triphenylmethane dye.

[0018] Furthermore, in step S2, the diamine compound is a diamine compound containing an R group, with the structural formula NH2-R-NH2, wherein the R group is an aliphatic chain alkane, a cyclic alkane, an aromatic hydrocarbon including various heterocyclic aromatic hydrocarbons, and a urea or acyl trap derived structure.

[0019] Further, the organic solvent in step S2 is one or more of ethanol, methanol, acetonitrile, N,N-dimethylformamide, N,N-diethylformamide, and N,N-diethylacetamide.

[0020] Furthermore, the molecularly switched adsorbent for adsorbing triphenylmethane dyes exists in water in two forms: an open-ring quinone-like ionic form and a closed-ring benzene-like neutral form. These two structures can interconvert under acid-base conditions, where the acid and base are common Bronsted acids and bases. Only the open-ring quinone-like structure exhibits excellent adsorption performance for triphenylmethane dyes. It can remove tens of ppm concentrations of crystal violet, malachite green, and methylene blue dyes from water in a very short time (90 min), with a removal rate of ≥92%.

[0021] The present invention also discloses the application of the above-mentioned molecularly switched adsorbent for adsorbing triphenylmethane dyes in the adsorption of triphenylmethane dyes.

[0022] Furthermore, the triphenylmethane dye is any one or more of crystal violet, malachite green, or methylene blue dyes.

[0023] Furthermore, the pH range for the adsorbent to adsorb triphenylmethane dye is 6-11.

[0024] Furthermore, the adsorbent can maintain a dye removal rate of ≥90% even when the water ion concentration (NaCl) is as high as 1 mol / L.

[0025] Furthermore, the adsorbent is regenerated and activated by eluting three times with a 0.1 mol / L NaOH aqueous solution and then drying it with an N2 stream for reuse. This adsorbent can be continuously recycled at least 10 times without significant decrease in adsorption capacity.

[0026] The beneficial effects of this invention are:

[0027] This invention relates to a molecularly switched adsorbent for adsorbing triphenylmethane dyes, which can rapidly remove triphenylmethane dyes such as crystal violet, malachite green, and methylene blue dyes from water. It can remove concentrations of tens of ppm of crystal violet, malachite green, and methylene blue dyes from water in a very short time (90 min), with a removal rate of ≥92%. The activation and regeneration conditions of this adsorbent are mild and environmentally friendly, requiring no toxic organic solvents or high-temperature heating to remove adsorbed dye molecules. The exhausted adsorbent only needs to be eluted three times in a low-concentration NaOH (0.1 mol / L) solution and then air-dried at room temperature or under a nitrogen stream. Furthermore, this adsorbent can be continuously recycled at least 10 times without significant capacity decay. Attached Figure Description

[0028] The accompanying drawings are provided to further explain the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0029] Figure 1 The structural diagram of a molecularly switched adsorbent capable of highly selectively adsorbing triphenylmethane dyes;

[0030] Figure 2 The diagram shows the structural forms of the adsorbent in water: open-ring quinone and closed-ring benzene structures.

[0031] Figure 3 This is a schematic diagram of the phenolphthalein-cyclohexanediamine adsorbent structure in Example 1;

[0032] Figure 4 The time-removal rate curves of the adsorbent for eight dyes in Example 1 are shown.

[0033] Figure 5 This is a comparison diagram of the adsorption effects of the adsorbent on eight dyes before and after in Example 1;

[0034] Figure 6The concentration-adsorption capacity curves of the adsorbent for crystal violet, malachite green and methylene blue in Example 1 are shown.

[0035] Figure 7 The time-removal rate curves of crystal violet by the adsorbent in Example 1 at different ion concentrations (NaCl) are shown.

[0036] Figure 8 The removal rate of crystal violet by the adsorbent in Example 1 under different pH conditions;

[0037] Figure 9 This refers to 10 consecutive cycles of the adsorption of crystal violet by the adsorbent in Example 1;

[0038] Figure 10 This is a schematic diagram of the phenolphthalein-ethylenediamine adsorbent structure in Example 2;

[0039] Figure 11 The time-removal rate curves of the adsorbent for eight dyes in Example 2 are shown.

[0040] Figure 12 The image shows the concentration-adsorption capacity curves of the adsorbent for crystal violet, malachite green, and methylene blue in Example 2.

[0041] Figure 13 This is a comparison of the removal rate of crystal violet by the adsorbent in Example 2 at different ion concentrations (NaCl);

[0042] Figure 14 The removal rate of crystal violet by the adsorbent in Example 2 under different pH conditions;

[0043] Figure 15 The removal rates of crystal violet by the adsorbent in Example 2 after five consecutive ring-opening and ring-closing cycles are given. Among them, 1, 3, 5, 7, and 9 are the removal rates of the ring-opening form after alkali washing, and 2, 4, 6, 8, and 10 are the removal rates of the ring-closing form after acid washing. Detailed Implementation

[0044] The technical solution of the present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0045] Example 1

[0046] The preparation method of phenolphthalein-cyclohexanediamine adsorbent includes the following steps:

[0047] S1. Weigh 4.76 g of phenolphthalein, 15 times the amount of hexamethylenetetramine of phenolphthalein and 50 mL of trifluoroacetic acid and mix them. React at 100 °C for 4 h under argon atmosphere. Then add 150 mL of 4 mol / L hydrochloric acid aqueous solution and hydrolyze at 100 °C for 1 h. Cool to room temperature, filter, wash with water, purify, dry under vacuum, and purify by column chromatography (CH2Cl2 / MeOH 10:1) to obtain phenolphthalein tetraaldehyde.

[0048] S2. Dissolve 0.15g phenolphthalein tetraaldehyde in 50mL acetonitrile and label it A. Dissolve 0.08g cyclohexanediamine in 30mL acetonitrile and label it B. Add solution B to solution A and reflux overnight. After cooling to room temperature, filter to collect the precipitate, wash with acetonitrile and dry to obtain powder.

[0049] S3. Dissolve 0.5g of the powder obtained in step S2 and 2.5g of reducing agent sodium borohydride in 100mL of ethanol and reflux overnight. After cooling to room temperature, remove the ethanol solvent under vacuum, then add 500mL of pure water and stir overnight at room temperature. Filter the suspension, collect the precipitate, and dry it under vacuum at 60℃ to obtain the molecularly switched adsorbent (phenolphthalein-cyclohexanediamine adsorbent) for adsorbing triphenylmethane dye.

[0050] Example 2

[0051] The preparation method of phenolphthalein-ethylenediamine adsorbent includes the following steps:

[0052] S1. Weigh 4.76 g of phenolphthalein, 15 times the amount of hexamethylenetetramine of phenolphthalein and 50 mL of trifluoroacetic acid and mix them. React at 100 °C for 4 h under argon atmosphere. Then add 150 mL of 4 mol / L hydrochloric acid aqueous solution and hydrolyze at 100 °C for 1 h. Cool to room temperature, filter, wash with water, purify, dry under vacuum, and purify by column chromatography (CH2Cl2 / MeOH 10:1) to obtain phenolphthalein tetraaldehyde.

[0053] S2. Dissolve 1g of phenolphthalein tetraaldehyde in 80mL of acetonitrile and label it as A. Dissolve 0.28g of cyclohexanediamine in 30mL of acetonitrile and label it as B. Add solution B to solution A and reflux overnight. After cooling to room temperature, filter to collect the precipitate, wash with acetonitrile and dry to obtain powder.

[0054] S3. Dissolve 1g of the powder obtained in step S2 and 1.8g of reducing agent sodium borohydride in 100mL of ethanol and reflux overnight. After cooling to room temperature, remove the ethanol solvent under vacuum, then add 500mL of pure water and stir overnight at room temperature. Filter the suspension, collect the precipitate, and dry it under vacuum at 60℃ to obtain the molecularly switched adsorbent (phenolphthalein-ethylenediamine adsorbent) for adsorbing triphenylmethane dye.

[0055] Dye Adsorption Experiment: In this invention, the adsorbents prepared in Examples 1 and 2 were used to test the adsorption effects of eight dyes with different structures: crystal violet (CV), malachite green (MG), methylene blue (MB), methylene blue (MeB), tomato flower red T (ST), methyl orange (MO), rhodamine B (RhB), and bromophenol blue (BPB). Quantitative measurements were performed using a UV-Vis spectrophotometer. The adsorption experiment mainly investigated the kinetic and thermodynamic parameters of the adsorbent, including the formula for calculating the removal rate (%) and the equilibrium saturation adsorption capacity (mg·g). -1 Calculations for parameters such as [parameter 1] can be found in existing literature. The equilibrium saturation adsorption capacity in this invention was calculated based on the Langmuir model. The adsorbent dosage used in the adsorption experiments was maintained at 1 mg / mL, and stirring was employed during adsorption to promote the equilibrium process, with the rotation speed kept constant at 200 rpm. The dye concentration used in the adsorption kinetics experiments was 10 [units unclear]. -5 -10 -4 The dye concentration used in the adsorption thermodynamic experiment was 10 mol / L. -5 -10 -3 mol / L. At least three parallel samples were set up for each test group, and the average value was used to obtain the final data. In the experiment investigating the effects of ion concentration and pH, 0.01, 0.1, and 1 mol / L NaCl solutions were used to adjust the ion concentration, and aqueous solutions with different pH values ​​were obtained by diluting HCl and NaOH.

[0056] The structure of the phenolphthalein-cyclohexanediamine adsorbent prepared in Example 1 is as follows: Figure 3 As shown, the adsorbent powder was first eluted three times with a 0.1 mol / L NaOH aqueous solution, then dried by an N2 stream before dye adsorption testing. The removal rate-time curves of the adsorbent for eight dyes are shown below. Figure 4 As shown, the equilibrium removal rates for crystal violet, malachite green, and methylene blue were 95%, 97%, and 94%, respectively. The removal rates for other dyes such as methylene blue, methyl orange, tomato red T, and rhodamine B were 33%, 30%, 35%, and 50%, respectively, with the worst removal rate for bromophenol blue at 2%. See the comparison diagram before and after adsorption. Figure 5 The solutions of crystal violet, malachite green, and methylene blue dyes became completely colorless and transparent after adsorption by the adsorbent. Further concentration-equilibrium adsorption curves are shown below. Figure 6 The saturated adsorption capacities (Langmuir model) of this adsorbent for crystal violet, malachite green, and methylene blue dyes were 363, 259, and 724 mg·g, respectively. -1 In comparison, the saturation adsorption capacity of bromophenol blue is only 3 mg / g. -1This demonstrates that the adsorbent exhibits high selectivity for triphenylmethane dyes. Furthermore, the adsorbent maintains a crystal violet removal rate of ≥90% even under strong ion concentration conditions. Figure 7 As shown. Meanwhile, the removal rates of crystal violet at different pH values ​​are shown in [the figure]. Figure 8 As shown, the results indicate that the adsorbent maintains a relatively constant removal rate in environments ranging from pH 6 to 11, demonstrating its wide applicability. Regeneration cycle experiments prove that the adsorbent can be used at least 10 times without significant capacity decay. Figure 9 Furthermore, the regeneration process is simple and environmentally friendly, requiring only three washes with 0.1 mol / L NaOH solution followed by air drying at room temperature.

[0057] The structure of the phenolphthalein-ethylenediamine adsorbent prepared in Example 2 is as follows: Figure 10 As shown, the adsorbent powder was first eluted three times with a 0.1 mol / L NaOH aqueous solution, then dried by an N2 stream before dye adsorption testing. The removal rate-time curves of the adsorbent for eight dyes are shown below. Figure 11 As shown, the equilibrium removal rates for crystal violet, malachite green, and methylene blue were 97%, 92%, and 95%, respectively, while the removal rates for other dyes such as methylene blue, methyl orange, tomato red T, and rhodamine B were 22%, 27%, 13%, and 8%, respectively. The removal efficiency for bromophenol blue was the worst, at 7%. Further concentration-equilibrium adsorption curves are shown below. Figure 12 The saturated adsorption capacities (Langmuir model) of this adsorbent for crystal violet, malachite green, and methylene blue dyes were 337, 262, and 689 mg·g, respectively. -1 In comparison, the saturation adsorption capacity of bromophenol blue is only 5 mg / g. -1 This demonstrates that the adsorbent exhibits high selectivity for triphenylmethane dyes. Furthermore, the adsorbent maintains a crystal violet removal rate of ≥90% even under strong ion concentration conditions. Figure 13 As shown. Meanwhile, the removal rates of crystal violet at different pH values ​​are shown in [the figure]. Figure 14 As shown, the results indicate that the adsorbent maintains a relatively constant removal rate in environments ranging from pH 6 to 11, demonstrating its wide applicability. (Circulation switch experiment) Figure 15 This demonstrates that the adsorbent can only adsorb crystal violet dye in the open-ring state (removal rate 97%), while the removal rate of crystal violet in the closed-ring state is ≤8%.

[0058] Finally, it should be noted that the above embodiments are merely illustrative of several implementations of the present invention and are not intended to limit the scope of the invention. For those skilled in the art, any modifications, equivalent substitutions, or improvements made without departing from the concept of the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. The application of a molecularly switched adsorbent for adsorbing triphenylmethane dyes, characterized in that, The triphenylmethane dye is any one or more of crystal violet, malachite green, or methylene blue dye; The structural formulas of the molecularly switched adsorbent for adsorbing triphenylmethane dye are shown in formulas (1) and (2): In the structural formulas of equations (1) and (2), 2. The application of the molecularly switched adsorbent for adsorbing triphenylmethane dyes according to claim 1 in the adsorption of triphenylmethane dyes, characterized in that, The molecularly switched adsorbent that adsorbs triphenylmethane dye exists in water in two forms: an open-ring quinone-like ionic form and a closed-ring neutral benzene form. The two structures can interconvert under acid and alkali conditions.

3. The application of the molecularly switched adsorbent for adsorbing triphenylmethane dyes according to claim 1 in the adsorption of triphenylmethane dyes, characterized in that, This adsorbent can remove tens of ppm of crystal violet, malachite green or methylene blue dyes from water within 90 minutes, with a removal rate of ≥92%.

4. The application of the molecularly switched adsorbent for adsorbing triphenylmethane dyes according to claim 1 in the adsorption of triphenylmethane dyes, characterized in that, The pH range for adsorbent adsorption of triphenylmethane dye is 6-11.

5. The application of the molecularly switched adsorbent for adsorbing triphenylmethane dyes according to claim 1 in the adsorption of triphenylmethane dyes, characterized in that... The adsorbent can maintain a dye removal rate of ≥90% even at NaCl ion concentrations as high as 1 mol / L.

6. The application of the molecularly switched adsorbent for adsorbing triphenylmethane dyes according to claim 1 in the adsorption of triphenylmethane dyes, characterized in that, The regeneration and activation conditions for this adsorbent are as follows: elute three times with a 0.1 mol / L NaOH aqueous solution and then dry with an N2 stream.

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