FIELD OF THE INVENTION

[0001] The present disclosure relates to metal organic frameworks (MOFs). Specifically, the present disclosure relates to a surface-coated Zinc-based MOF with a high selectivity for cationic dye capture, and a method of preparing the same. Further, the disclosure relates to a method for using said Zinc-based MOF.

BACKGROUND OF THE INVENTION

[0002] Background description includes information that may be useful in understanding the present disclosure. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[0003] Organic dyes are extensively used in various industries including food, textiles, paint and paper. The used dyes along with large quantity of water are generally discharged into the water bodies and environment. The synthetic organic dyes are chemically stable and are toxic to the living beings and also have low biodegradability. Hence, the organic dyes pose a serious threat to human health and environments. Some of the dyes are carcinogenic, mutagenic and teratogenic even at low concentration.

[0004] Therefore, it is highly important to remove the dyes from the effluents before releasing into the water bodies. Different approaches including advanced oxidation process (AOC), biological treatment, membrane filtration, precipitation, photocatalytic degradation, adsorption and ion exchange techniques have been developed and utilized for removing synthetic dyes from water.

[0005] Among all the reported approaches, removal of dyes by adsorption over the porous matrices is considered as potentially better approach because of its ease of operation, efficiency, low-cost and eco-friendly properties.

[0006] Porous metal-organic frameworks provide the space for loading the guest the molecules but imparting the functionality to drive the guest loading and selectivity was the challenges.

[0007] Hence, the present invention investigated the synthesizing porous MOFs nano/microparticles and improving the adsorption capability by modulating the interactions between the dyes and adsorbent using the naturally available multifunctional organic molecules. The coating of natural multifunctional molecules also significantly boosted the selectivity for the dyes.

[0008] The present disclosure satisfies the existing needs, as well as others, and generally overcomes the deficiencies found in the prior art.

OBJECTS OF THE INVENTION

[0009] Objects of the present disclosure relate to provide a MOF that has a superior selectivity for organic cationic dyes.

[0010] An object of the present disclosure is to provide a surface-coated Zinc-based MOF with a high selectivity for organic cationic dyes.

[0011] Another object of the present disclosure is to provide a method of preparing a surface -coated Zinc -based MOF with a high selectivity for for organic cationic dyes.

[0012] Yet another object of the present disclosure is to provide a method of separating organic cationic dyes from an aqueous medium containing mix of dyes using the surface- coated Zinc -based MOF.

SUMMARY OF THE INVENTION

[0013] This summary is provided to introduce a selection of concepts in a simplified form that is further described below in the detailed description section. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0014] Aspects of the present disclosure relates to metal organic frameworks (MOFs). Specifically, the present disclosure relates to a surface-coated Zinc -based MOF with a high selectivity for cationic dye capture, and a method of preparing the same. Further, the disclosure relates to a method for using said surface-coated Zinc -based MOF.

[0015] In a preferred aspect, the present disclosure relates to a surface-coated Zinc-based MOF with a CO2/N2 selectivity of 80-99% selectivity to capture cationic dyes.

[0016] In an aspect, the zinc-TPA MOF has the Zn(II) ion connected to more than one TPA ligand moiety. In an embodiment, the present disclosure provides a sustainable zinc- based metal organic framework (Zn-MOF) comprising: Nanoparticles or microparticles of porous ZnTPA (Zinc- terephthalic acid) MOFs, which are surface coated with tea extract (ZnTPA/Tea).

[0017] In a preferred aspect, the porous ZnTPA MOF comprise Zn(II) metal center coordinated with four terephthalic acid (TPA) ligand moiety and DMF solvent characterized by formula I (Zn(C _x H ₄ O4)(DMF)):

Formula I

[0018] In another aspect, the present disclosure provides a method of preparing the tea extract-coated porous ZnTPA MOFs as disclosed herein, said method comprising the steps of: a. dissolving separately a Zn ²⁺ source in water and terephthalic acid (TP A) in an organic solvent, followed by mixing both the solutions to produce a mixture; b. adding organic bases to the mixture, followed by heating to produce a precipitate; c. washing and drying the precipitate to obtain porous ZnTPA MOFs; d. boiling dried tea leaves in water and filtering the same to separate the leaves and tea extract; e. adding the porous ZnTPA MOFs to the tea extract, followed by stirring overnight and washing to obtain the tea extract-coated porous ZnTPA MOFs as disclosed herein.

[0019] In another aspect, the present disclosure relates to a packing material for column chromatography comprising the tea extract-coated porous ZnTPA MOFs as disclosed herein.

[0020] In another aspect, the present disclosure relates to a method for removing organic cationic dyes selectively from an aqueous medium containing mix of dyes, said method comprising the steps of: a. providing the chromatographic column comprising the packing material as disclosed herein; b. contacting the chromatographic column with an aqueous medium containing the mix of dyes at a pH of 3.0 to 8.0 wherein the organic cationic dyes are adsorbed to the packing material in the column; c. releasing the adsorbed cationic dyes from the packing material by sonication; and d. optionally, regenerating the tea extract-coated porous ZnTPA MOFs..

[0021] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0022] The following drawings form part of the present specification and are included to further illustrate aspects of the present disclosure. The disclosure may be better understood by reference to the drawings in combination with the detailed description of the specific embodiments presented herein.

[0023] FIG. 1 represents the fabrication of ZnTPA MOFs using three different amines and integrating multi-functional biomolecules from tea extract.

[0024] FIG. 2 represents (a) FTIR and (b) PXRD pattern of ZnTPA and ZnTPA/Tea MOFs.

[0025] FIG. 3 shows the FE-SEM images of (a,b) ZnTPA-B, (c,d) ZnTPA-0 and (e,f) ZnTPA-T samples.

[0026] FIG. 4 represents FE-SEM images of (a, b) ZnTPA-B/Tea, (c, d) ZnTPA-O/Tea and ZnTPA -T/Tea.

[0027] FIG. 5 represents the TGA of ZnTPA-B, ZnTPA-0 and ZnTPA-T..

[0028] FIG. 6 represents BET adsorption isotherm ZnTPA MOFs (a-c) before and (e-f) after coating with tea extracts, (a) ZnTPA-B, (b) ZnTPA-O, (c) ZnTPA-T, (d) ZnTPA-B/Tea, € ZnTPA-O/Tea and (f) ZnTPA-T/Tea.

[0029] FIG. 7 represents the Rh B dye adsorption efficiency of (a) ZnTPA-B, ZnTPA-0 and ZnTPA-T MOFs and (b) with increasing ZnTPA-0 adsorbents.

[0030] FIG. 8 represents (a) Rh B dye removal efficiency of ZnTPA-B/Tea, ZnTPA- O/Tea and ZnTPA-T/Tea adsorbents, (b) cationic and anionic dye removal efficiency of ZnTPA-O/Tea and (c) digital colour changes of ZnTPA-O/Tea after dipping into tea extract and dye solution.

[0031] FIG. 9 represents the plots of (a) pseudo-first-order and (b) pseudo-second-order kinetics of Rh B adsorption onto ZnTPA/Tea MOFs (initial concentration of Rh B: 5 mg/L).

[0032] FIG. 10 represents the effect of pH on the adsorption of (a) Rh B, (b) MB and (c) CV by ZnTPA-O/Tea MOFs.

[0033] FIG. 11 represents the (a) ZnTPA and ZnTPA/Tea MOFs redispersed in fresh water, (b) reusability of the exhausted catalyst, (c) effect of tea extract coating on other MOFs, (d-f) digital and absorption spectrum of (d) Rh B, (e) mixed dye (cationic and anionic dyes) before and after filtering through ZnTPA-O/Tea packed column and (f) mixed dye absorption spectrum after filtration.

DETAILED DESCRIPTION OF THE INVENTION

[0034] The following is a detailed description of embodiments of the disclosure. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure.

[0035] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.

[0036] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0037] In some embodiments, numbers have been used for quantifying weight percentages, ratios, and so forth, to describe and claim certain embodiments of the invention and are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[0038] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.

[0039] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.

[0040] Unless the context requires otherwise, throughout the specification which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.”

[0041] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein.

[0042] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.

[0043] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified.

[0044] The description that follows, and the embodiments described therein, is provided by way of illustration of an example, or examples, of particular embodiments of the principles and aspects of the present disclosure. These examples are provided for the purposes of explanation, and not of limitation, of those principles and of the disclosure. [0045] It should also be appreciated that the present disclosure can be implemented in numerous ways, including as a system, a method or a device. In this specification, these implementations, or any other form that the invention may take, may be referred to as processes. In general, the order of the steps of the disclosed processes may be altered within the scope of the invention.

[0046] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.

[0047] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus if one embodiment comprises elements a, b, and c, and a second embodiment comprises elements b and d, then the inventive subject matter is also considered to include other remaining combinations of a, b, c, or d, even if not explicitly disclosed.

[0048] As used herein, the term “capturing” or “capture” refers to the act of removing one or more chemical species from a bulk fluid composition (e.g., gas/vapor, liquid, and/or solid). For example, “capturing” may include, but is not limited to, interacting, bonding, diffusing, adsorbing, absorbing, reacting, and sieving, whether chemically, electronically, electrostatically, physically, or kinetically driven.

[0049] Embodiments of the present disclosure relates to metal organic frameworks (MOFs). Specifically, the present disclosure relates to a surface-coated Zinc -based MOF with a high selectivity for cationic dye capture, and a method of preparing the same. Further, the disclosure relates to a method for using said surface-coated Zinc -based MOF.

[0050] In an embodiment, the present disclosure provides a surface-coated zinc-TPA MOF with mesopores ranging from 1 nm to 500 nm. For example, about 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 75 nm, 100 nm, 125 nm, 150 nm, 175 nm, 200 nm, 225 nm, 250 nm, 275 nm, 300 nm, 325 nm, 350 nm, 375 nm, 400 nm, 450 nm, or 500 nm. Preferably, the size of the mesores range from 15 nm to 50 nm.

[0051] In an embodiment of the present disclosure, the zinc-TPA MOF has the Zn(II) ion connected to more than one TPA ligand moiety. In an embodiment, the present disclosure provides a sustainable zinc -based metal organic framework (Zn-MOF) comprising: Nanoparticles or microparticles of porous ZnTPA (Zinc- terephthalic acid) MOFs, which are surface coated with tea extract (ZnTPA/Tea). [0052] In an embodiment of the present disclosure, the porous ZnTPA MOF comprise Zn(II) metal center coordinated with four terephthalic acid (TP A) ligand moiety and DMF solvent characterized by formula I (Z^CgFL^XDMF)):

Formula I

[0053] In an embodiment of the present disclosure, the amine-based organic base is selected from the group consisting of triethylamine, butyl amine, and octyl amine.

[0054] In an embodiment of the present disclosure, the ZnTPA/Tea MOFs exhibit rodlike, sheet-like, plate-like, needle-like morphologies.

[0055] In an embodiment of the present disclosure, the ZnTPA/Tea MOFs have average sizes ranging from at least about 1 nm, 10 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1100 nm, 1200 nm, 1300 nm, 1400 nm,

1500 nm, 1600 nm, 1700 nm, 1800 nm, 1900 nm, 2000 nm, 2500 nm, 3000 nm, 4000 nm,

5000 nm, 6000 nm, 7000 nm, 8000 nm, or at least 9000 nm. In some embodiments, the nanoparticles may have a diameter of less than 10,000 nm, 9000 nm, 8000 nm, 7000 nm,

6000 nm, 5000 nm, 4500 nm, 4000 nm, 3500 nm, 3000 nm, 2500 nm, 2000 nm, 1900 nm,

1800 nm, 1700 nm, 1600 nm, 1500 nm, 1400 nm, 1300 nm, 1200 nm, 1100 nm, 1000 nm,

900 nm, 800 nm, 700 nm, 600 nm, 500 nm, 250 nm, or less than 100 nm. In an embodiment, the ZnTPA/Tea has a hydrodynamic size in a range of about 75 nm to about 200 nm.

[0056] In another aspect, the present disclosure provides a method of preparing ZnTPA/Tea MOFs as disclosed herein, said method comprising the steps of: a. dissolving separately a Zn ²⁺ source in water and terephthalic acid (TPA) in an organic solvent, followed by mixing both the solutions to produce a mixture; b. adding organic bases to the mixture, followed by heating to produce a precipitate; c. washing and drying the precipitate to obtain porous ZnTPA MOFs; d. boiling dried tea leaves in water and filtering the same to separate the leaves and tea extract; e. adding the porous ZnTPA MOFs to the tea extract, followed by stirring overnight and washing to obtain the ZnTPA/Tea MOFs as disclosed herein.

[0057] In an embodiment of the present disclosure, the Zn ²⁺ source is zinc acetate or hydrates of Zinc acetate. However, it is to be noted that Zinc acetate is one of the many examples of Zn ²⁺ . The present invention can be performed using the other known Zn ²⁺ sources known in the prior art.

[0058] In an embodiment of the present disclosure, the ratio of zinc acetate dihydrate :TPA is 1:2, respectively.

[0059] In an embodiment of the present disclosure, the organic solvent may be one or more solvents selected from ethers alcohols such as methanol, ethanol, trifluoroethanol, n- propanol, i-propanol, n-butanol, i-butanol, t-butanol, n-pentanol, i-pentanol, 2-methyl-2- butanol, 2-trifluoromethyl-2-propanol, 2,3-dimethyl-2-butanol, 3-pentanol, 3-methyl-3- pentanol, 2-methyl-3 -pentanol, 2-methyl-2-pentanol, 2,3-dimethyl-3-pentanol, 3-ethyl-3- pentanol, 2 -methyl -2 -hexanol, 3 -hexanol, cyclopropylmethanol, cyclopropanol, cyclobutanol, cyclopentanol, cyclohexanol); aromatic solvents like benzene, o-xylene, m-xylene, p-xylene, mixtures of xylenes, toluene, mesitylene, anisole, 1,2-dimethoxybenzene, a,a,a- trifluoromethylbenzene, fluorobenzene; polar aprotic solvents selected from ethyl acetate, tetrahydrofuran, dichloromethane, acetone, acetonitrile, dimethylformamide, dimethyl sulfoxide; and polar protic solvents selected from acetic acid, n-butanol, isopropanol, n- propanol, ethanol, methanol, formic acid, water) and mixtures thereof. In a preferred embodiment, the organic solvent is a mixture of dimethylformamide (DMF) and ethanol.

[0060] In an embodiment of the present disclosure, the heating in step b) is effected at a temperature in a range of 50-100° C, preferably 60-90° C, more preferably 70-90° C, or particularly about 85° C. for a time period in a range of 10-15 h, preferably 10-14 h, more preferably about 10-12 h. In one embodiment, the heating in step b) is effected in an autoclave (or other enclosed vessel) at atmospheric pressure.

[0061] In an embodiment of the present disclosure, the heating in step c) is effected at a temperature in a range of 30-80° C, preferably 40-70° C, more preferably 50-70° C, or particularly about 60° C. for a time period in a range of 10-15 h, preferably 10-14 h, more preferably about 10-12 h. In one embodiment, the heating in step b) is effected in an autoclave (or other enclosed vessel) at atmospheric pressure. [0062] In an embodiment of the present disclosure, the amount of porous ZnTPA MOFs added to the tea extract ranges from about 1% w/v to about 10% w/v. For example, at least 1% w/v, at least 1.5% w/v, at least 2% w/v, at least 2.5% w/v, at least 3% w/v, at least 3.5% w/v, at least 4% w/v, at least 4.5% w/v, at least 5% w/v, at least 5.5% w/v, at least 6% w/v, at least 6.5% w/v, at least 7% w/v, at least 7.5% w/v, at least 8% w/v, at least 9% w/v, at least 9.5% w/v, or at least 10% w/v. Preferably, at least 1.5% w/v - 3% w/v. Most preferably, 2.5% w/v.

[0063] In an embodiment of the present disclosure, the yield of ZnTPA/Tea MOFs is greater than about 80% and not less than about 70%. In many embodiments, the yield greater than about 65%. For example, at least 65%, at least 66%, at least 67%, at least 68%, at least 69%, at least 70%, at least 72%, at least 73%, at least 74%, and/or at least 75%.

[0064] In another embodiment, the present disclosure provides a packing material for column chromatography comprising the ZnTPA/Tea MOFs as disclosed herein.

[0065] In yet another embodiment, the present disclosure provides a method for removing organic cationic dyes selectively from an aqueous medium containing mix of dyes, said method comprising the steps of: a. providing the chromatographic column comprising the packing material as disclosed herein; b. contacting the chromatographic column with an aqueous medium containing the mix of dyes at a pH of 3.0 to 8.0, wherein the organic cationic dyes are adsorbed to the packing material in the column; c. releasing the adsorbed cationic dyes from the packing material by sonication; and d. optionally, regenerating the ZnTPA/Tea MOFs by surface coating.

[0066] In one embodiment of the present disclosure, the organic cationic dye capturing comprises the step of contacting the chromatographic column comprising the ZnTPA/Tea MOFs with an aqueous medium containing the mix of dyes. In an embodiment, the contacting may include bringing the metal-organic framework and aqueous medium into physical contact, or immediate or close proximity. Examples of the contacting may include, but are not limited to, one or more of feeding, percolating, flowing, passing, pumping, introducing, and the like.

[0067] In an embodiment of the present disclosure, the regenerating may include further coating the ZnTPA/Tea MOFs with the tea extract.

[0068] In an embodiment of the present disclosure, the contacting may proceed under any suitable conditions (e.g., temperature, pressure, etc.). For example, the contacting may proceed to or at a temperature ranging from about 25° C to about 200° C. In many embodiments, the contacting may proceed at or to a temperature less than about 200° C. In preferred embodiments, the contacting may proceed at or to a temperature of about 25°-35° C. (e.g., about room temperature).

[0069] In an embodiment of the present disclosure, the contacting may proceed under suitable pH. For example, the contacting may proceed to or at a pH ranging from 1 to 10. In many embodiments, the contacting may proceed at or to a pH of 3-7.

[0070] In an embodiment of the present disclosure, the concentration of organic cationic dye in an aqueous medium may range from about 0% to about 99.9 %. In many embodiments, the concentration of organic cationic dye in an aqueous medium is less than about 10%. In preferred embodiments, the concentration of organic cationic dye in an aqueous medium is in the range of about 3 to about 50%.

[0071] In an embodiment of the present disclosure, the ZnTPA/Tea may exhibit one or more of a high removal efficiency and/or high uptake, even at low concentrations of organic cationic dyes. For example, the ZnTPA/Tea may exhibit a removal efficiency of greater than about 50%, greater than about 75%, but not less than about 80%. In many embodiments, the ZnTPA/Tea exhibit a removal efficiency of greater than about 90%. For example, the ZnTPA/Tea exhibit a removal efficiency of at least 80%, at least 82%, at least 84%, at least 86%, at least 88%, at least 90%, at least 92%, at least 93%, at least 94%, and/or at least 95%.

[0072] In an embodiment of the present disclosure, the multifunctional biomolecules present in the tea extracts significantly enhanced the dye adsorption from an aqueous medium along with improving the selectivity. Tea extract coating of MOFs lead to selective cationic dyes removal by adsorption.

[0073] In yet another embodiment of the present disclosure, the surface coating of MOF with tea extract as described herein may also be applicable to other types of MOFs comprising metal ion centers other than Zinc. For example, the metal center may be selected from the group consisting of a transition metal (e.g. Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, Ir, Pt, Au, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg, and Cn), a post-transition metal (e.g. Al, In, Ga, Sn, Bi, Pb, Tl, Cd, and Hg), and an alkaline earth metal (e.g. Be, Mg, Ca, Sr, Ba, and Ra). In one embodiment, the preferable metal ion center apart from Zn is selected from the group consisting of Cu, Fe, Ni, Co, Mn, Cr, Cd, Mg, Ca, and Zr. [0074] In an embodiment of the present disclosure, the ZnTPA/Tea MOF has water/steam stability, chemical stability, easy regeneration, high selectivity and is more economical.

[0075] While the foregoing description discloses various embodiments of the disclosure, other and further embodiments of the invention may be devised without departing from the basic scope of the disclosure. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

EXAMPLES

[0076] The present disclosure is further explained in the form of following examples. However, it is to be understood that the foregoing examples are merely illustrative and are not to be taken as limitations upon the scope of the invention. Various changes and modifications to the disclosed embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the scope of the invention.

Material and Methods:

Zinc acetate dihydride 98 %, terephthalic acid (98 %), DMF, ethanol, triethylamine, butylamine, octylamine were purchased from Sigma-Aldrich and used as-received. Double distilled water and dried tea leaf was obtained commercially and used without further purification.

[0077] Example 1: Synthesis of ZnTPA MOFs (Scheme 1/FIG. 1)

Zinc acetate dihydrate (2g) is dissolved in 15 ml of water and terephthalic acid (TP A) is dissolved in 20 ml of DMF-EtOH mixture separately. Both the zinc acetate and TPA solution was mixed together and stirred for 30 min at room temperature. Then two equivalents of organic bases (triethylamine, butyl amine, and octyl amine) were added and the reaction mixture was heated at 85 DC for 12 h. It produced white solid precipitate that was filtered and washed with water (2 or 3 times) followed by ethanol to remove the unreacted species. Finally, the MOFs were dried in oven at 60 DC for 12 h. MOFs obtained using triethylamine, butylamine and octylamine bases were named as ZnTPA-T, ZnTPA -B and ZnTPA-O. [0078] Example 2: Coating tea extract with ZnTPA MOFs (ZnTPA/tea) (Scheme 1 I FIG. 1)

Dried tea leaves (0.5 g) are boiled with 25ml of water for 30min and filtered. Then ZnTPA MOFs (0.5 g) was added into 20 ml tea extract and stirred overnight. The solution was centrifuged and washed with ethanol and acetone. The white solid becomes wheat brown color after coating with organic molecules present in the tea extract.

[0079] Example 3: Characterization of ZnTPA/tea from Example 2

The particle size and morphology of NPs were studied by field emission scanning electron microscopy (FE-SEM) (Q400 SEM). The phase and the crystallographic structure were identified by X-ray diffraction (XRD, Brucker, Cu-Ka: X= 0.154 nm) at a scanning rate of 0.07° s-1 with 20 ranging from 10° to 80°. The surface area was measured using nitrogen physisorption analysis (BET isotherm, ASAP2020, Micromeritics). The functionality of the materials was characterized using FT-IR (Alpha, Bruker, Germany). The Thermogravimetric analysis (TGA) was performed using NETZSCH-STA 449 F3 JUPITER. The zeta potential was analysed using Malvern (MAL1054413).

[0080] FTIR, PXRD and FE-SEM analysis

FTIR analysis of ZnTPA MOFs confirmed the terephthalic acid ligand coordination by exhibiting strong peak at 1593cm-l and 1377cm-l (FIG. 2a). PXRD of ZnTPA MOFs exhibited clear sharp peaks with varied intensity (FIG. 2b). The appearance of sharp peaks indicated the formation of crystalline materials in all three MOFs. The variation in the peak intensity and peak positions might be due to the morphological change and orientation differences of crystallites or different solid-state structure. FTIR spectra of ZnTPA MOFs after dipping into tea extract also showed similar peaks, suggesting that there was no structural change (FIG. 2a). The PXRD studies ZnTPA MOFs before and after immersing into tea extract are performed to analyse the structural change. ZnTPA-T and ZnTPA-0 showed similar pattern (FIG. 2b). FE-SEM studies of ZnTPA MOFs revealed that organic amines controlled the nano/microparticles size and morphology (FIG. 3). ZnTPA-B exhibited nano/microplates formation (FIG. 3a, b) whereas ZnTPA-0 showed micron-sized fibres along with rods (FIG. 3c, d). ZnTPA-T also exhibited the formation of nano/micron sized rods but with sharp end (FIG. 3e,f). Thus, all three samples showed different morphology depending on the amine employed in the reaction. The morphological change of Zn-TPA MOFs after tea extract coating were investigated by FE-SEM (FIG. 4). ZnTPA-B and ZnTPA-T did not show significant modulation in the nano/microparticles morphologies and size (FIG. 4a-b and e-f). However, ZnTPA-0 exhibited clear morphological changes from ID fibres to plates (FIG. 4c, d).

[0081] TGA and BET studies

Thermogravimetric analysis (TGA) of ZnTPA MOFs indicated sharp weight loss between 90 and 120DC (FIG. 5). All three compounds decomposed at above 350 deg C. The textural properties of nano/micro particles of ZnTPA MOFs were analyzed using N2adsorption- desorption and the results are shown in FIG. 5. The isotherms revealed that the MOFs have type III adsorption and indicated that all three compounds contain mesoporous. The formation of fibrous textures in ZnTPA-0 might be contributed for slightly higher surface area. Nitrogen adsorption and desorption studies of ZnTPA MOFs after coating with tea extract biomolecules exhibited improvement in the surface area but reduction in the pore volume and pore diameter for ZnTPA-B and ZnTPA-B (FIG. 6). But ZnTPA-O/Tea showed slight reduction in the surface area and increase of pore diameter.

[0082] Example 4: Organic dye adsorption studies

The adsorbents were stirred with 30ml of 10-5M dye solution. The 2ml of dye sample was taken for analysis at the regular interval of lOmins up to 120 minutes. Initially, dye adsorption efficiency was optimized using 10-5M rhodamine B (Rh-B) using 50, 75, and lOOmg of ZnTPA-O. It was observed that the increase of catalyst loading led to increasing dye adsorption. Then the adsorption efficiency of ZnTPA MOFs coated with tea extract was optimized using catalyst 50 and lOOmg with 10-5M Rh-B dye. The initial screening of dye adsorption property of ZnTPA MOFs were performed for Rhodamine B dye (10-5 M, Rh B) using all three ZnTPA MOFs as adsorbents (FIG. 7a). It showed maximum of 40% Rh B dye adsorption. Further, the adsorbent quantity dependent dye adsorption showed increase of dye adsorption (FIG. 7b). ZnTPA MOFs after dipping into natural tea extract showed strongly enhanced Rh B dye adsorption (FIG. 8a). All three compounds showed more than 85% dye adsorption after coating with tea extract. Further, the weight ratio optimization studies indicated that the maximum percentage of Rh B dye adsorption (95%) was achieved using 50 mg of ZnTPA-O/Tea whereas 100 mg of ZnTPA-B//Tea and ZnTPA-T/Tea was required to achieve 95 and 85%, respectively. Similar to Rh B, ZnTPA-O/Tea also showed highly enhanced adsorption of CV and MB dyes (FIG. 7b). Surprisingly, ZnTPA-O/Tea did not show any adsorption with methyl orange (MO) and eosin yellow (EY) dyes (FIG. 8b). Hence, the natural tea extract coated ZnTPA MOFs exhibited highly selective adsorption of cationic dyes. As-synthesized ZnTPA-0 was white colour powder and stirring with Rh B dye solution turned slightly pink colour (FIG. 8c). ZnTPA-0 turned to dull straw colour after coating with tea extract (ZnTPA/Tea). The stirring of ZnTPA/tea with Rh B dye solution turned to brown colour. Further, the colour of Rh B, MB and CV dyes completely disappeared after stirring with ZnTPA-O/tea (FIG. 8c). The static adsorption data of ZnTPA/Tea MOFs are fitted to the pseudo-first-order and pseudo-second-order kinetic model (FIG. 9a, b). The calculated kinetic constants are given in Table 1. The kinetic results indicated higher R2 value for the pseudo second-order model compared to the pseudo first-order model. Further, the theoretical adsorption value of Qe calculated by the pseudo-second-order kinetic equation is in agreement with the experimental value. Hence, the results suggest that pseudo-second-order kinetic model is better for fitting the adsorption processes of Rh B dye on to the ZnTPA/Tea MOFs compared to the pseudo-first-order kinetic model. To evaluate the influence of pH of the solution on the dye adsorption of ZnTPA-O/Tea MOFs, the dye adsorption experiments were performed with different pH values ranging between 1.0 and 11.0 (FIG. 10a). Rh B dye showed 78% adsorption on to ZnTPA-O/tea adsorbent at pH 1.0 and adsorption efficiency was slightly increased to 85% upon increasing pH to 3.0. Further increasing pH showed slight reduction of adsorption efficiency up to neutral pH. But at basic pH(pH 7.0), it showed significant reduction in the adsorption efficiency. MB and CV dyes showed different trend of adsorption onto ZnTPA-O/Tea with varying pH (FIG. 10b, c). MB showed strong adsorption across the pH whereas CV exhibited slight increase of adsorption from 84% to 93% upon increasing pH from 3 to 5. Further increase of pH did not show any significant variation. The adsorbed dyes were not released into an aqueous medium upon redispersing the dye coated adsorbent into fresh water sample (FIG. I la). Even keeping the dye adsorbed ZnTPA-O/Tea in water for more than 3 days did not release the adsorbed dye into the solution. But ZnTPA- O without tea extract coating also released the adsorbed Rh B dye while redispersing and sonicating (FIG. I la). The exhausted ZnTPA-O/Tea adsorbent was easily regenerated by sonication followed by fresh dipping into the natural tea extract. The regenerated Zn-TPA- O/Teais used for three cycles and confirmed the reusability (FIG. 1 lb). Broader scope of the methodology was demonstrated by coating on copper terephthalic acid MOF (CuTPA) and zinc phthalic acid MOF (ZnPA). Both the adsorbents showed highly enhanced dye adsorption selectively towards cationic dye (FIG. 11c). The tea extract coated ZnTPA-0 MOF was also used as column packing material and repeated filtration also removed the dyes via adsorption (FIG. l id). Mixed dye solution (Rh B, MB, CV, MO and EY) filtered through the column with ZnTPA-O/Tea showed yellow colour corresponding to the anionic MO and EY dyes (FIG. 1 le). Absorption spectrum also indicated the peak corresponding to the anionic EY and MO dyes (FIG. I lf).

Table 1. Adsorption kinetic parameters of Rh B on ZnTPA/Tea MOFs in static adsorption experiments.

[0083] Support: This invention was made with Khing Khalid University support through Research Centre for Advanced Materials Science (RCAMS) under grant number RCAMS/KKU/002-23.

ADVANTAGES OF THE PRESENT INVENTION:

[0084] Facile fabrication of nano/micro particles of porous MOFs with tunable morphology and surface area, pore volume and pore diameter by varying the organic amines.

[0085] Morphology dependent organic dye adsorption of ZnTPA MPFs from aqueous medium. Coating MOFs with biomacromolecules from tea extract to improve the dye adsorption and confirming the structure and morphology of nano/microparticles.

[0086] Tea extract coated ZnTPA MOFs exhibited strongly enhanced dye adsorption. Improve the dye adsorption from 40% of uncoated MOFs to 95% after tea extract coating.

[0087] Tea extract biomolecular coating with ZnTPA MOFs resulted high selectivity towards adsorption of cationic textile dyes (Rhodamine B (Rh B), crystal violet (CV), methylene blue (MB)) from an aqueous medium compared to anionic dyes (eosin yellow (EY) and methyl orange (MO)).

[0088] Tea extract coating with ZnTPA MOFs improved the interaction between the cationic organic dyes and adsorbents. Tea extract coating produced negatively charged surface that preferably interacts with dyes via electrostatic interactions apart from other intermolecular interactions.

[0089] Natural tea extract coating strategy for improving the dye adsorption with cationic selectivity has also been demonstrated using other MOFs such as Cu-MOFs and Zn-MOFs prepared using different ligands. This evidenced the broader applicability of the method. [0090] Tea extract coated ZnTPA MOFs exhibited high retention of dye molecules after adsorption due to strong interaction between the adsorbent and dye molecules.

[0091] The exhausted tea extract coated ZnTPA MOFs can easily be regenerated by sonication followed by re-coating of natural tea extract molecules.

[0092] Natural tea extract coated MOFs can also be used as column packing materials for selectively removing cationic textile dyes while filtering through the column. The anionic dyes remains in the solution whereas cationic dyes can be efficiently removed from the water.