LAMINAR ZINC HYDROXIDE ORGANIC-INORGANIC NANOCOMPOSITES FOR USE IN THE REMOVAL AND DEGRADATION OF DYES FROM TEXTILE EFFLUENTS OR ORGANIC SUBSTANCES

Abstract

The present invention relates to a method for removing dyes from textile effluents and other organic substances using nanocomposites based on zinc hydroxides and carboxylic acids capable of adsorbing and degrading. More specifically, the present invention consists of a method to generate new zinc hydroxide-based materials, which allows removal and degradation of methylene blue and other organic compounds from wastewater from industrial effluents, particularly those from textile industry.

Claims

1. Nanocomposites of hybrid organic-inorganic zinc hydroxide, wherein said nanocomposites are laminar solids with stacked structure of hybrid layers, wherein each layer comprises two individual inorganic sheets of zinc hydroxide having a X-ray diffraction pattern in 2 theta, wherein the number of harmonics in the reflections are between 001 up to 10 (0010).

2. The nanocomposites of claim 1, wherein said nanocomposites are used for the removal of dyes from textile effluents or other organic substances.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1: Shows a structure and organization model of zinc hydroxide organic-inorganic nanocomposites.

[0014] FIG. 2: Shows X-ray diffraction patterns of zinc hydroxide nanocomposites with myristic (LZH-M), palmitic (LZH-P) and stearic (LZH-S) carboxylic acids. The box shows the area at a wider angle.

[0015] FIG. 3: FTIR spectra of (A) myristic (MA) palmitic (PA) and stearic (SA) carboxylic acids and (B) zinc hydroxide nanocomposites made with 3 long chain carboxylic acids, LZH-M, LZH-P and LZH-S.

[0016] FIG. 4: Comparison of the FTIR spectra for the zinc hydroxide and stearic acid (LZH-S) nanocomposite and commercial surfactant (AE) and that exposed to the same synthesis conditions of the composites (AE*).

[0017] FIG. 5: High resolution SEM (A-C) and (D) TEM images obtained for the zinc hydroxide and myristic acid nanocomposite (C.sub.14H.sub.28O.sub.2).

[0018] FIG. 6: Thermogravimetric curves and their derivatives for zinc hydroxides (A) without addition of surfactants and in nanocomposites with (B) stearic acid, (C) palmitic acid and (D) myristic acid, respectively.

[0019] FIG. 7: Images of a laminar zinc hydroxide nanocomposite obtained using stearic acid; (A) No dye addition, (B) After the dark stirring process and (C) sample recovered after UV light irradiation for 300 minutes.

[0020] FIG. 8: Removal of methylene blue from an aqueous solution by contacting with a laminar zinc hydroxide, LZH-S in this case, in the absence of light.

[0021] FIG. 9: Evolution of methylene blue (MB) absorption spectra versus irradiation time, using LZH-S as photocatalyst.

[0022] FIG. 10: (A) Cycles of reuse and (B) X-ray diffraction pattern for LZH-S after the photocatalytic process. This remains unchanged.

[0023] FIG. 11: Removal of Congo Red (CR) from an aqueous solution by contacting with a laminar zinc hydroxide, LZH-S in this case, in the presence of light.

DETAILED DESCRIPTION OF THE INVENTION

[0024] The present invention describes a method of preparing laminar zinc hydroxide organic-inorganic nanocomposites comprising several steps.

[0025] a) Dissolving in a vessel at least one zinc salt, oxide or hydroxide in distilled water until reaching a molar concentration of 0.1 to 5.0 M, wherein the zinc salt is selected from, but not limited to, zinc chloride (ZnCl.sub.2), Zinc cyanide (Zn(CN).sub.2), Zinc sulphate (ZnSO.sub.4), zinc nitrate (Zn(NO.sub.3).sub.2), zinc acetate (Zn(CH.sub.3COO).sub.2), zinc carbonate (ZnCO.sub.3), zinc acetylacetonate (C.sub.5H.sub.7ZnO.sub.2), zinc perchlorate (Zn(ClO.sub.4).sub.2), zinc stearate, salts of zinc-ethylenediamine, zinc trifluoroacetylacetonate(II), zinc hexafluoroacetylacetonate, zinc formate(II), zinc(II) methacrylate, zinc neodecanoate, zinc(II) ethylhexanoate, zinc trifluoroacetate(II), and other zinc sources such as zinc oxide (ZnO), zinc hydroxide (Zn(OH).sub.2).

[0026] b) Dissolving in a vessel at least one carbonate of alkali metals, alkaline earth metals, other metals and metalloids in distilled water until reaching a molar concentration of 0.1 to 5.0 M, wherein the carbonate is selected from, but not limited to, Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, and metals such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Ga, In, Pb, Bi, Sn, Ge, As, Sb, Ag, Au, Hg, Cd, Mo, Re, W, Nb, Ru, Rh and Zr.

[0027] c) Forming a suspension by dropwise adding to a volume of the aqueous solution prepared in step (a), a volume of the aqueous carbonate solution prepared in step (b).

[0028] d) The suspension obtained in step c) was heated at 15-120° C. and left under constant stirring ranging from 5 to 10,000 rpm for a homogenization time between 0.1 min and 24 hours.

[0029] e) An alkali solution at a molar concentration of 0.1 to 12.0 M is dropwise added to the reaction mixture of step d), until the mixture is adjusted to a pH between 4 and 12.5; wherein the alkali is selected from sodium hydroxide (NaOH), potassium hydroxide (KOH), lithium hydroxide (LiOH), magnesium hydroxide (Mg(OH).sub.2), barium hydroxide (Ba(OH).sub.2), calcium hydroxide (Ca(OH).sub.2) including Arrhenius bases.

[0030] f) The suspension obtained in step e) is maintained at a temperature of 15-120° C. under constant stirring ranging from 5 to 10,000 rpm for a homogenization time between 0.1 min and 24 hours.

[0031] g) A volume of a molecular or polymeric surfactant solution at a molar concentration of 0.1 to 12.0 M is added, wherein the surfactant is selected from, but not limited to, those with linear, branched or aromatic hydrocarbon chains having 2 or more carbon atoms, having hydrophilic groups such as carboxylic acids and their derivatives, primary and secondary amines, salts of ammonium, amides, thiols, sulfonates, ethers, esters, alcohols, aldehydes, phosphates, and mixtures thereof; in addition the polymeric surfactant is selected from polymers: poly(vinylpyrrolidone) (PVP), polyvinyl alcohol, polycarbonates, polyphenols, polyethylene glycol and polyols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycols, alkyldiols as butanediols, dipropylene glycol and polyethylene glycols, chitosan and derivatives thereof, polyacids and derivatives thereof, mercaptoalkanoates, and oxybenzoic acids. Polyacids herein include, but are not limited to, any one or more selected from a group of poly(acrylic acid), poly(maleic acid), poly(methyl methacrylate), poly(acrylic acid-co-methacrylic acid), poly(acrylic acid-co-maleic acid), and poly(acrylamide-co-acrylic acid), cellulose acetates, polyvinyl acetates, polysulfone, polyphenyl sulfones, polyether sulfones, polyketones, polyether ketones, polyesters, polyacetates, polymers and copolymers of two or more of these and the derivatives including, without limitations, any or more of those selected from a group of ammonium, sodium or potassium poly acid salts.

[0032] h) The resulting suspension in step g) is maintained at a temperature of 15-120° C. under constant stirring ranging from 5 to 10,000 rpm for a homogenization time between 0.1 min and 24 hours.

[0033] i) The resulting suspensions in step h) is maintained at a temperature of 15-120° C. for a time between 0.1 min and 72 hours.

[0034] j) The solids obtained in step i) are separated by decantation, filtration, evaporation or centrifugation from 5 to 100,000 rpm for a centrifugation time between 0.1 min and 24 hours, and the precipitate is washed from 1 to 20 times with water and/or a solvent such as, but not limited to, acetone or alcohol, ether, or a mixture thereof.

[0035] k) Drying the products obtained from step (j) in an oven at a temperature of 10° C.-200° C., preferably at 60° C. for 48 hours or under vacuum with a pressure between 0.0001 bar and 10.0 bar, or with IR lamp.

[0036] The method of the present invention produces nanolamellar solids (nanocomposites) with a stacked layer structure which includes inorganic sheets and other hydrophobic parts or zones (see FIG. 1). These nanocomposites have the ability to adsorb/degrade organic substances that can be dissolved and/or dispersed into water with the help of a light energy source. The hydrophobic interlaminar areas are responsible for contaminant adsorption while the zinc hydroxide inorganic nanolamines are responsible for the degradation with the help of light energy.

[0037] Removal of dyes or organic substances involves 2 independent processes that run sequentially: [0038] (i) Adsorption of dye or organic substances in the nanocomposite, in an aqueous medium. [0039] (ii) Degradation of dye or organic substances adsorbed by heterogeneous photocatalysis.

[0040] Degradation or removal of the dye or organic substances occurs with step (ii) by light excitation, whereby the product can be reused. In other words, the nanocomposite can be recovered and reused several times.

[0041] The light energy source can be natural, such as the sun, or artificial with a power between 0.1 to 200 W such as, but not limited to, lamps LEDs, OLEDs, xenon-mercury, xenon, mercury halides, noble gases, or mixture thereof. This will excite the material generating the degradation of the adsorbed dye and the dye remaining in the solution. This process is attributed to the production of highly active radical species on the surface of the solids (photocatalyst) used.

[0042] The original laminar zinc hydroxide organic-inorganic nanocomposite is white; the dye adsorption is then easily detectable by the color change solid in the solid after the adsorption process while the solid recovered after the photocatalytic degradation in the presence of light is white (see sequence in FIG. 7). Image 7B shows the presence of dye in the solid by a color change, color which disappears completely after irradiation.

[0043] Given the independence of i) absorption and ii) degradation processes, these can occur in situ or in different places, which opens the possibility of first extracting the pollutants in the effluents and removing them through photocatalysis in different sites.

[0044] Photocatalyst can be reused several times after the absorbed species photodegradation process.

EXAMPLES

Example 1

Example of Obtaining Zinc Hydroxide—Myristic Acid Nanocomposite and Degradation of Methylene Blue

[0045] To 10.0 mL of an aqueous solution of 1.0 M zinc sulfate (ZnSO.sub.4) was dropwise added 5.0 mL of a 1.0 M sodium carbonate (Na.sub.2CO.sub.3) aqueous solution. A white suspension was immediately formed after addition. This was left under constant stirring at 600 rpm for 10 minutes at 55° C. Then, 10.0 mL of a 1.0 M sodium hydroxide (NaOH) aqueous solution was dropwise added until obtaining a suspension with pH equal to 9. The latter was left under constant stirring at 600 rpm for 10 minutes at the same temperature. In the final step, 5.0 mL of a previously prepared 0.4 M myristic acid solution was added using a 1:1 v/v water: acetone mixture as solvent, in a water bath. The resulting suspensions were left under constant stirring at 600 rpm for 48 h at 55° C. After that, suspensions were left standing for 24 h at room temperature. The obtained solids were separated by centrifugation at 6,000 rpm and washed 3 times with a 1:1 water: acetone solution. Finally, the products were dried in an oven at 60° C. for 48 h and grinded in an agate mortar. This process produced lamellar solids with a stacked layer structure (FIG. 1).

[0046] Nanocomposites obtained have a novel structure of stacked sheets formed by inorganic layers of zinc hydroxides intercalated with carboxylate anions, as illustrated in the scheme of FIG. 1. Product lamellar structure was determined by X-ray diffraction (FIG. 2). Product interlaminal distances are shown in Table 1. The presence of intercalated carboxylate anions was confirmed by FT-IR spectroscopy (FIGS. 3 and 4). Product lamellar morphology can be clearly seen in the scanning and transmission electron microscopy micrographs (FIG. 5).

[0047] Nature and composition of the solids was investigated by thermal analysis (FIG. 6). This product allows the adsorption of the dye in the solid, favored by the presence of the organic component, as well as the degradation thereof by ultraviolet or solar light excitation (photocatalysis) of the inorganic phase. Thus, these products have an adsorbent and photocatalyst dual capacity.

[0048] The methodology used for dye degradation is described below. 90 mg of nanocomposite is dispersed in 1.0 mL of ethanol. This suspension is added to 50 mL of methylene blue aqueous solution with a 0.00001 M concentration and is left under stirring at 600 rpm for 30 minutes. This time is sufficient to obtain a maximum dye adsorption on the solid surface. The absorption removal rate of the dye from the aqueous sample with addition of a laminar zinc hydroxide composite prepared with stearic acid (LZH-S) in the dark, is approximately 50% (FIG. 8). The aforementioned graph shows that dye removal from the solution occurs within the first 30 minutes and then remain constant over time.

[0049] Degradation kinetics of Methylene Blue (MB) in solution under light irradiation in the presence of catalyst was monitored by observing Methylene Blue absorption spectrum, and its solution concentration was determined by absorption intensity at 665 nm (FIG. 9). It is observed that the dye in solution is completely degraded at 5-6 hours.

[0050] Catalyst can be reused several times after the absorbed species photodegradation process. To that end, three experiments were made using the same nanocomposite sample. The capacity of the catalyst after 3 cycles was reduced by 2% compared to the original (FIG. 10).

Example 2

Example of Obtaining Zinc Hydroxide-Stearic Acid Nanocomposite and Methyl Orange Degradation

[0051] To 10.0 mL of 1.0 M zinc sulfate (ZnSO.sub.4) aqueous solution was dropwise added 5.0 mL of a 1.0 M sodium carbonate (Na.sub.2CO.sub.3) aqueous solution. A white precipitate immediately formed after addition. The resulting suspension was left under constant stirring at 600 rpm for 10 minutes at 55° C. Then, 10.0 mL of a 1.0 M sodium hydroxide (NaOH) aqueous solution was dropwise added until obtaining a suspension with pH equal to 9. The latter was left under constant stirring at 600 rpm for 10 minutes at the same temperature. In the final step, 5.0 mL of a previously prepared 0.4 M stearic acid solution was added using a 1:1 v/v water: acetone mixture as solvent, in a water bath. The resulting suspensions were left under constant stirring at 600 rpm for 48 h at 55° C. After that, the suspensions were left standing for 24 h at room temperature. The obtained solids were separated by centrifugation at 6,000 rpm and washed 3 times with a 1:1 water: acetone solution. Finally, the products were dried in an oven at 60° C. for 48 h and grinded in an agate mortar. This process produced lamellar solids with a stacked layer structure (FIG. 1).

[0052] For methyl orange degradation, 90 mg of nanocomposite is dispersed in 1.0 mL of ethanol. This suspension is added to 50 mL of methyl orange aqueous solution at a 0.00001 M concentration and it is left under stirring at 600 rpm for 360 minutes. This time is sufficient to obtain a maximum dye adsorption on the solid surface. The absorption removal rate of the dye from the aqueous sample with addition of a laminar zinc hydroxide composite prepared with stearic acid (LZH-S) in the dark, is approximately 50%. Dye removal from solution occurs within the first 30 minutes, to then remain constant over time.

[0053] Degradation kinetics of Methyl Orange (MO) in solution under light irradiation in the presence of catalyst was monitored by observing Methyl Orange absorption spectrum and its solution concentration was determined by absorption intensity at 665 nm. It is observed that the dye in solution is completely degraded.

Example 3

Example of Obtaining Zinc Hydroxide—Palmitic Acid Nanocomposite and Methylene Blue Degradation

[0054] To 10.0 mL of an aqueous solution of 1.0 M zinc sulfate (ZnSO.sub.4) was dropwise added 5.0 mL of a 1.0 M sodium carbonate (Na.sub.2CO.sub.3) aqueous solution. A white precipitate immediately formed after addition. The resulting suspension was left under constant stirring at 600 rpm for 10 minutes at 55° C. Then, 10.0 mL of a 1.0 M sodium hydroxide (NaOH) aqueous solution was dropwise added until obtaining a suspension with pH equal to 9. The latter was left under constant stirring at 600 rpm for 10 minutes at the same temperature. In the final step, 5.0 mL of the previously prepared 0.4 M palmitic acid solution was added using a 1:1 v/v water: acetone mixture as solvent, in a water bath. The resulting suspensions were left under constant stirring at 600 rpm for 48 h at 55° C. After that, the suspensions were left standing for 24 h at room temperature. The obtained solids were separated by centrifugation at 6,000 rpm and washed 3 times with a 1:1 water: acetone solution. Finally, the products were dried in an oven at 60° C. for 48 h and grinded in an agate mortar. This process produced lamellar solids with a stacked layer structure (FIG. 1).

[0055] 90 mg of zinc hydroxide-palmitic acid nanocomposite and a 1×10.sup.−5 mol/L methylene blue solution were used. UV-Vis irradiation (immersion lamp) was used. Nanocomposites absorbed in the dark more than 50% and the total degradation was achieved after 300 min of irradiation (FIG. 11).

Example 4

Example of Obtaining Zinc Hydroxide—Aliphatic Carboxylic Acids Nanocomposites

[0056] Three nanocomposites of zinc hydroxide with carboxylic acids (myristic, palmitic and stearic) were prepared using this technology. Distances were found to be directly dependent on the surfactant being used as shown by the difference in interlaminal distances. Table 1 shows the results of the X-ray diffraction analysis of the 3 nanocomposites used in examples 1, 2 and 3 (FIG. 2).

TABLE-US-00001 TABLE 1 Molecular Total length surfactant d.sub.001 R—COO— Composite formula (nm) (nm) LZH-S C.sub.18H.sub.36O.sub.2 4.294 2.360 LZH-P C.sub.16H.sub.32O.sub.2 4.264 2.110 LZH-M C.sub.14H.sub.28O.sub.2 3.409 1.860

Example 5

Degradation of Congo Red with Zinc Hydroxide—Myristic Acid Nanocomposite

[0057] 90 mg of zinc hydroxide—myristic acid nanocomposite and a 3×10.sup.−5 mol/L Congo Red solution were used. UV-Vis irradiation (immersion lamp) was used. Nanocomposites absorbed in the dark more than 60% and the total degradation was achieved after 300 min of irradiation (FIG. 11). The experimental procedure was carried out following the methodology of examples 1 and 2, but using Congo Red as a test molecule.