WO2023057824A1

WO2023057824A1 - Composition for dye removal from an aqueous system and methods of preparation thereof

Info

Publication number: WO2023057824A1
Application number: PCT/IB2022/054951
Authority: WO
Inventors: Dilushan Rukmal JAYASUNDARA; Nissanka Arachchi Appuhamilage Buddini NISSANKA
Original assignee: University Of Colombo
Priority date: 2021-10-07
Filing date: 2022-05-26
Publication date: 2023-04-13

Abstract

A composition for removing a dye from an aqueous system is described. The composition includes an aluminum oxide/hydroxide; and graphene oxide (GO). A method of making the composition is also described. The present disclosure also relates to a method of removing a dye from an aqueous system. The method includes contacting the composition with the aqueous system, including the dye for a period sufficient to obtain a dye adsorbed composition, and separating the dye adsorbed composition from the aqueous system. The composition of the present disclosure is effective in the removal of RhB at a wide pH range of 2-14 and can be used multiple times till saturation is achieved.

Description

COMPOSITION FOR DYE REMOVAL FROM AN AQUEOUS SYSTEM AND METHODS

OF PREPARATION THEREOF

BACKGROUND

This patent application claims the benefit of priority to NIPO patent application Ser. No. LK/21981 entitled “A composition for efficient removal of Rhodamine B from water” filed on Oct. 7, 2021, the subject matter is incorporated herein in its entirety.

TECHNICAL FIELD

The present disclosure relates to a dye removal composition and, more particularly, relates to a composition for removing a dye from an aqueous system and a method of preparing the composition.

DESCRIPTION OF RELATED ART

Rapid industrial development has significantly impacted the environment in recent years due to wastewater discharge with toxic pollutants to natural water bodies. Among these pollutants in wastewater, organic dyes with intense color and high toxicity have been identified as significant contaminants as they are non-biodegradable and accumulate in living organisms. The presence of dyes is highly undesirable, even at low concentrations in wastewater, as they significantly affect both human and aquatic life.

Conventionally, various separation techniques such as chemical, physicochemical, and biological methods have been developed to remove the dyes from wastewater. However, most methods suffer from long operation times, high cost, complicated design, and toxic by-product generation. Among the conventional methods, adsorption onto solid materials is considered the most reliable and efficient method to treat the dyes in wastewater since it is simple, economically feasible, and easy to operate. Several materials, including activated carbon, clay, silica gel, peat, graphene oxide (GO) based materials, agricultural waste, and industrial waste such as fly ash, metal hydroxide sludge, and red mud, have been used as adsorbents for the dyes in the wastewater treatment process. However, these adsorbents are not without inherent limitations. For example, metal hydroxide sludge has a high adsorption capacity for anionic dyes than cationic dyes, whereas, in GO-based materials, the separation of GO after adsorption is difficult in large-scale applications. As a result, it becomes a secondary pollutant in treated water. Accordingly, there is a need to develop an effective and efficient composition for removing dyes from wastewater in a cost-effective and straightforward manner.

SUMMARY

In an aspect of the present disclosure, a composition is described. The composition includes an aluminum oxide/hydroxide; and graphene oxide (GO).

In another aspect of the present disclosure, a method for making the composition is described. The method includes mixing the aluminum oxide/hydroxide with a GO solution to obtain a paste. The method further includes heating the paste to obtain the composition.

In another aspect of the present disclosure, a method of removing a dye from an aqueous system is described. The method includes contacting the composition, including the aluminum oxide/hydroxide and the GO, with the aqueous system for a period sufficient to obtain a dye adsorbed composition. The method further includes separating the dye adsorbed composition from the aqueous system.

The foregoing general description of the illustrative embodiments and the following detailed description thereof are merely exemplary aspects of the teachings of this disclosure and are not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of this disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1A shows a schematic flow diagram of a method of making a modified aluminum hydroxide sludge (mAHS), according to one embodiment of the present disclosure;

FIG. IB shows a schematic flow diagram of a method of making a composition, according to one embodiment of the present disclosure;

FIG. 2 shows a schematic flow diagram of a method of removing a dye from an aqueous system, according to one embodiment of the present disclosure; FIG. 3A shows a pictorial image of the mAHS, according to one embodiment of the present disclosure;

FIG. 3B shows a pictorial image of composition (GO-mAHS), according to one embodiment of the present disclosure;

FIG. 4 shows a SEM image of the GO-mAHS, according to one embodiment of the present disclosure;

FIG. 5 shows Fourier-transform Infra-Red spectra (FT-IR) of the GO, partially reduced GO, and reduced GO, according to one embodiment of the present disclosure

FIG. 6 shows the thermogravimetric analysis (TGA) spectrum of the GO, according to one embodiment of the present disclosure;

FIG. 7 shows photographs of (a) the RhB solution and that treated with the GO- mAHS (composition) at various time intervals, particularly, after (b) 1 minute, (c) 5 minutes, (d) 15 minutes, respectively, according to one embodiment of the present disclosure;

FIG. 8 shows UV-Visible spectra of the RhB solution and that treated with the mAHS and the GO-mAHS at different time intervals, according to one embodiment of the present disclosure;

FIG. 9 shows UV-Visible spectra of the RhB solution and that treated with the GO- mAHS at different pH values over 15 minutes, according to one embodiment of the present disclosure;

FIG. 10 shows UV-Visible spectra of water kept in contact with a RhB adsorbed GO- mAHS for 60 days to observe dye leaching at acidic, neutral, and basic conditions, according to one embodiment of the present disclosure;

FIG. 11 shows UV-Visible spectra of the RhB solution (2 mg/L RhB in water) and that treated with the GO-mAHS heated at 250 °C, for different contact times, according to one embodiment of the present disclosure;

FIG. 12 shows an effect of contact time and an initial RhB concentration on the amount of RhB adsorbed by the GO-mAHS, according to one embodiment of the present disclosure; and

FIG. 13 shows variation in the percentage of RhB removal during the re-use of the GO- mAHS for four cycles at 2 mg/L RhB concentration, according to one embodiment of the present disclosure. DETAILED DESCRIPTION

Reference will now be made in detail to specific embodiments or features, examples of which are illustrated in the accompanying drawings. Wherever possible, corresponding or similar reference numbers will be used throughout the drawings to refer to the same or corresponding parts. Moreover, references to various elements described herein are made collectively or individually when there may be more than one element of the same type. However, such references are merely exemplary in nature. It may be noted that any reference to elements in the singular may also be construed to relate to the plural and vice-versa without limiting the scope of the disclosure to the exact number or type of such elements unless set forth explicitly in the appended claim.

The terminologies and/or phrases used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as is commonly understood by one of ordinary skill in the art. For clarity, the following specific terms have the specified meanings. Other terms are defined in other sections herein.

In the drawings, like reference numerals designate identical or corresponding parts throughout the several views. Further, as used herein, the words “a,” “an” and the like generally carry a meaning of “one or more,” unless stated otherwise.

Furthermore, the terms “approximately,” “approximate,” “about,” and similar terms generally refer to ranges that include the identified value within a margin of 20%, 10%, or preferably 5%, and any values therebetween.

As used herein, the term “stable” refers to the ability of the composition to remain unaffected (does not leach back into the aqueous system) within the defined pH range.

Conventionally used adsorbents, such as metal hydroxide sludge or aluminum hydroxide sludge (AHS) for removing the dye from an aqueous system are neither effective nor efficient in removing cationic dyes. GO-based adsorbents are challenging to separate from the aqueous system, particularly in large-scale applications. The present disclosure is directed to a composition using GO and aluminum oxide/hydroxide (sludge). When used in combination, it serves as an excellent adsorbent to efficiently remove dyes from aqueous systems in a timeeffective and cost-effective manner. The dye can be any dye with a pi-conjugated structure. In an embodiment, the dye is an anionic dye. In another embodiment, the dye is a cationic dye. The cationic dye is selected from the group consisting of methylene blue, rhodamine B (RhB), crystal violet, basic fuchsin safranin, pararosaniline, and a combination thereof. In a preferred embodiment, the dye is RhB. The aqueous system can include industrial waste water, tap water, groundwater, river water, runoff streams, and static water bodies such as storage water. In a preferred embodiment, the aqueous system is wastewater. Although the description herein concerns using the composition to remove RhB dye from the aqueous system, aspects of the present disclosure may also be directed to removing any other dyes. Reaction kinetics of RhB with the composition of the present disclosure was evaluated. For this purpose, all the experiments were carried out in the aqueous system of RhB. The results indicate that the composition of the present disclosure is highly efficient and requires very little contact time for the adsorption of RhB to the composition. Further, unlike the conventional methods, the composition of the present disclosure allows for efficient separation of the dye adsorbed composition by gravity, thereby preventing the need for any manual or mechanical or chemical treatment in a time and cost-efficient manner.

The composition includes aluminum oxide/hydroxide and graphene oxide (GO). In an embodiment, the composition includes aluminum oxide and GO. In a preferred embodiment, the composition includes a combination of aluminum hydroxide (AH) and GO. The primary source of aluminum oxide/hydroxide is sludge. The sludge may contain several oxides and hydroxides of several metals, in addition to aluminum. The sludge is herein referred to as aluminum hydroxide sludge (AHS). In an embodiment, the AHS is obtained from industrial waste, such as anodizing industry. In an embodiment, the composition includes AHS and GO. In a preferred embodiment, the composition includes a modified aluminum hydroxide sludge (mAHS) and GO. The mAHS refers to the AHS modified by physical or chemical treatment to improve its adsorption capacity. The mAHS or AH may be used interchangeably throughout the draft.

In an embodiment, the aluminum oxide/hydroxide to the GO in the composition are in a ratio. The composition has a GO loading of 5-20 milligrams (mg) of GO/gram (g) of AH. In a preferred embodiment, the composition has to GO loading of 5-10 mg GO/g of AH, specifically 7 mg GO/g of AH. The composition may be in a powder, flakes, granular, crystalline, or combinations thereof. In an embodiment, the AH is in the form of powder, flakes, granules, crystals, or mixtures thereof. In a preferred embodiment, the AH is in the form of a powder. In an embodiment, the particle size of AH is about 100 micrometers (pm). In a preferred embodiment, the particle size of AH is in the range of 20 -100 pm. The particle size correlates to the adsorptive capacity of the composition. The small particle size of AH provides a high surface area, and a greater pore volume, thereby allowing for increased adsorption.

The mAHS is further modified with GO to obtain synergic efficiency for removing RhB from wastewater. GO is a one atom thick monolayer of sp3 and sp2 hybridized carbons hexagonally arranged in the lattice. It is synthesized from natural graphite through a chemical oxidation process. The basal plane of GO is decorated with various oxygen functionalities such as hydroxyl, epoxide, carboxyl, and carbonyl groups which provide a negatively charged surface. Further, these oxygenated groups on GO can be removed chemically, thermally, and electrochemically to synthesize reduced GO (rGO) with large graphitic domains.

The porous mAHS, when further modified with GO, results in forming the mAHS-GO composite or composite (composition of the present disclosure) that finds application in the removal of dye, particularly RhB, from water, including wastewater. The composite provides a solution to two significant drawbacks of the art. Firstly, the high surface-to-volume ratio of the composition offers improved adsorption capacity. Secondly, unlike the conventionally used GO- based adsorbents, which tend to remain in the solution even after RhB adsorption and require complex separation processes from the treated water (water devoid of RhB), the composition of the present disclosure allows for efficient separation by gravity, thereby preventing the need for any manual or mechanical or chemical treatment. Further, unlike the conventional methods, the two-component composition (mAHS and GO) of the present disclosure does not require pH adjustment to the aqueous system prior to its use. Further , Unlike AHS, which is effective only for anionic dyes, the composition of the present disclosure can be used for separation of both anionic and cationic dyes.

The present disclosure also provides a method 100 of making the mAHS. Referring to FIG. 1A, a schematic flow diagram of a method of making the mAHS, is illustrated. The order in which the method is described is not intended to be construed as a limitation, and any number of the described method steps can be combined in any order to implement the method. Additionally, individual steps may be removed or skipped from the method without departing from the spirit and scope of the present disclosure.

At step 102, the method 100 includes dehydrating a raw AHS to obtain a dried solid. The raw AHS may contain oxides of various inorganic metals, including aluminum. In an embodiment, the raw AHS was obtained from industrial waste, such as anodizing industry. In an embodiment, the raw AHS was collected from an anodizing industry in Sri Lanka. The raw AHS was entirely dehydrated to remove water, resulting in a dried solid. In an embodiment, the AHS was dehydrated to a temperature range of 180-220 °C to obtain the dried solid.

At step 104, the particle size of the dried solid was reduced to obtain the mAHS. In an embodiment, the particle size may be decreased by ball milling, grinding, pressure homogenization, or a combination thereof. In a preferred embodiment, the particle size is reduced by ball milling. In an embodiment, the particle size of the mAHS is about 100 micrometers (pm). In a preferred embodiment, the particle size of the mAHS is in the range of 20 -100 pm. The particle size correlates to the adsorptive capacity of the composition. The small particle size imparted a high surface area and increased pore volume, resulting in an improved adsorptive capacity of the composition towards RhB.

The present disclosure also provides a method 150 of making the composition. Referring to FIG. IB, a schematic flow diagram of a method of making the composition is illustrated according to an embodiment of the present disclosure. The order in which the method is described is not intended to be construed as a limitation, and any number of the described method steps can be combined in any order to implement the method. Additionally, individual steps may be removed or skipped from the method without departing from the spirit and scope of the present disclosure.

At step 152, the method 150 includes mixing the AH with a GO solution to obtain a paste. The weight percentage of the aluminum oxide/hydroxide to the GO in the composition is such that the composition has a GO loading of 5-20 mg GO/g of AH. In a preferred embodiment, the composition has GO loading in the range of 5-10 mg GO/g of AH, specifically 7 mg GO/g of AH. The AH may be in the form of powder, flakes, granular, crystalline, or combinations thereof. In a preferred embodiment, the AH is in the form of powder. When porous AHS is mixed or modified with the GO solution, it increases the adsorption surface area while imparting pi-pi interactions to the composition.

At step 154, the method 150 includes heating the paste to obtain the composition. In an embodiment, the composition is heated to a temperature range of 110-300 °C for 45 minutes to 75 minutes in an inert atmosphere to obtain the composition. In a preferred embodiment, the composition was heated to a temperature range of 110-180 °C for about 45 minutes to 75 minutes, preferably 60 minutes, in an inert atmosphere to obtain the composition. In an embodiment, the inert atmosphere may be made up of purified argon and nitrogen gases to obtain the composition. In another preferred embodiment, the heating may be performed under a vacuum to obtain the composition.

One of the critical features determining the dye absorption capacity is the temperature at which the paste is heated. In an embodiment, the composition demonstrated more significant than 95 % efficiency in removing the RhB from the aqueous system when the heating was performed within the defined ranges (110-180 °C) for 45 minutes to 75 minutes in an inert atmosphere. In another embodiment, the composition demonstrated more than 99 % efficiency in removing the RhB from the aqueous system within the defined ranges. At temperatures beyond the specified ranges, i.e., at around 250 °C, the absorption capacity decreased with increased temperature. This is because, at higher temperatures, the GO becomes more hydrophobic, thus blocking adsorption.

The composition of the present disclosure finds application in the removal of dyes, particularly RhB, from the aqueous systems, including wastewater. RhB is a basic cationic dye that has been extensively used as a colorant in the textile, cosmetic, food, ink, and paper-making industries. It is highly toxic and can cause serious health issues to eyes, skin, respiratory and gastrointestinal tracks. Therefore, water contamination by insufficient quantities of RhB (1 ppm) is harmful to humans and ecosystems. Even though RhB was declared a potential carcinogenic colorant by International Agency for Research of Cancer (IARC) in 1978, it is still used in many countries. Therefore, removing this dye from wastewater to the required environmental quality standards is extremely important.

Referring to FIG. 2, a method 200 of removing a dye from an aqueous system is described. The order in which the method is described is not intended to be construed as a limitation, and any number of the described method steps can be combined in any order to implement the method. Additionally, individual steps may be removed or skipped from the method without departing from the spirit and scope of the present disclosure.

At step 202, the method 200 includes contacting the composition with the aqueous system for a period sufficient to obtain a dye adsorbed composition. In an embodiment, the composition is made to contact the aqueous system for a sufficient period, within 20 minutes, to obtain the dye adsorbed composition. The aqueous system includes RhB. In some embodiments, the composition removes at least 50%, preferably at least 60%, preferably at least 70%, more preferably at least 80%, or more preferably at least 90%, or more preferably at least 95% of the RhB from the aqueous system within 20 minutes of contacting the composition with the aqueous system. In an embodiment, the dye is adsorbed onto the composition until all the composition’s active sites are saturated. This implies that the composition can be used as an adsorbent to adsorb the rhodamine B dye multiple times until the composition is saturated. Further, the initial concentration of the RhB in the aqueous system affects the efficiency of removing the RhB from the aqueous system with the composition of the present disclosure. At higher concentrations of the RhB, the rate of adsorption of RhB to the composition was found to be much faster than at lower concentrations. The increase in dye concentration increases the probability of collision between the dye molecules and the composition and leads to higher adsorption. In some embodiments, the pH of the aqueous system is about 2-10, or about 5-7. In some embodiments, the dye is RhB, and the pH of the aqueous system is preferably 2 to 7. In an embodiment, the composition of the present disclosure shows less than 1% leaching of the dye from the adsorbed composition into the aqueous system within the pH range of 2-10, suggesting a strong affinity of the composition towards the dye (RhB).

At step 204, the method 200 includes separating the dye adsorbed composition from the aqueous system. In an embodiment, the dye adsorbed composition is separated from the aqueous system by gravity. In an embodiment, at least 50%, preferably 60%, more preferably 80% of the dye adsorbed composition is separated from the aqueous system in less than 60 seconds. Unlike the conventionally used GO-based adsorbents, which tend to remain in the solution even after RhB adsorption and require complex separation processes from the treated water (water devoid of RhB), the composition of the present disclosure allows for efficient separation by gravity, thereby preventing the need for any manual or mechanical or chemical treatment in a timeefficient manner.

EXAMPLES

The following examples describe and demonstrate the composition including AH and GO, when used in combination, effectively removes a dye, particularly, RhB, from an aqueous system such as wastewater. The examples are provided solely for illustration and are not to be construed as limitations of the present disclosure, as many variations thereof are possible without deviating from the fundamental aspects and scope of the present disclosure.

Example 1 : Preparation of GO-mAHS composite

GO was synthesized from Sri Lankan vein-type graphite using the improved Hummers method. A homogeneous aqueous solution of GO was prepared by dissolving GO in de-ionized (DI) water followed by ultrasonication. 5 grams (g) of the aluminum hydroxide sludge (mAHS) was weighed and mixed with 10 ml of GO solution to obtain GO loading of 7 mg/g (w/w) to form a paste. The paste was then heated to 150 °C and maintained at that temperature for 1 hour under vacuum conditions, to dehydrate the paste and partially reduce GO.

Characterization

FIGS. 3A and 3B illustrates pictorial images of the aluminum (Al) hydroxide sludge (mAHS) and graphene oxide (GO)-AHS, respectively. From the FIGS. 3A and 3B, an apparent change in color from ash color to brown color was observed after modification of the AHS with the GO. The particle size of mAHS was less than 100 micrometers, as confirmed by using a particle size analyzer. FIG. 4 illustrates a SEM image of GO modified mAHS (mAHS-GO). From the FIG. 4, a porous structure of AHS and the flake-like structure of GO can be observed, confirming the incorporation of GO into the AHS by the method of the present disclosure.

The most significant and critical aspect of the present disclosure is determining the temperature range at which the paste is heated. It was observed that heating the paste to a temperature range of approximately 110-180 °C yielded a partially reduced GO. This temperature range is selected based on analyzing the FTIR and TGA spectra of GO, as shown in FIG. 5 and FIG. 6.

Referring to FIG. 5, Fourier-transform Infra-Red spectra (FT-IR) of the GO are illustrated. Three samples, namely, a precursor GO(502), a GO sample heated to a temperature of 150 °C (504), and a GO sample heated to 250 °C (506) were characterized using this technique. From the FIG. 5 it can be observed that the spectral intensities have reduced with increasing temperature indicating a reduction in the available GO oxygen functionalities (-C=O carbonyl, -C=) carboxyl, -C=C-, -C-OH bending, -C-O-C, and -C-O). As can be observed from FIG. 5, a partial reduction in oxygen functionalities was observed at 150 °C, while a significant reduction in the oxygen functionalities was observed at 250 °C. The FTIR results are in agreement with the TGA spectrum in FIG. 6, where a significant weight loss is observed with the precursor GO after approximately 200 °C which relates to the loss of oxygen functionalities.

Example 2: Removal of rhodamine B from water using mAHS and GO-mAHS

GO-AHS (30 mg/ml) were added into RhB aqueous solutions (2 ppm). The mixtures were then stirred/shaken at 2000 rpm at time intervals of 1, 5, and 15 minutes, respectively, and were then allowed to settle by gravity. The sedimentation process of the adsorbent was fast and happened within 30 seconds after mixing was stopped. For optical absorption analysis, the supernatant was filtered through a 0.45 pm filter paper, and the filtrate was analyzed using a UV- Visible spectrophotometer to measure the residual dye content. The effect of contact time of RhB with the composition of the present disclosure, pH, temperature, and concentration, at different conditions and ranges was evaluated, and the results of this study are presented in the FIGS. 7-13

Results and Discussion

The filtered supernatants and the respective absorbance spectra are shown in FIGS. 7 and 8, respectively. FIG. 7 shows photographs a) RhB solution (2 ppm of RhB in water), b) RhB treated with GO-mAHS after 1 minute, c) RhB treated with GO-mAHS after 5 minutes, and d) RhB treated with GO-mAHS after 15 minutes. Complete removal of the RhB from the water was observed with the GO-mAHS within 1 minute, as indicated by a transparent test tube in FIG. 7. Further, the UV-Visible spectra of RhB solution (2 ppm RhB in water) and that treated with mAHS and GO-mAHS composite for different time intervals (namely, 2 ppm of RhB in water (800), RhB treated with mAHS for 1 minute (802), RhB treated with mAHS after 5 minutes (804), RhB treated with mAHS after 15 minutes (806), RhB treated with GO-mAHS after 1 minute (808), RhB treated with GO-mAHS after 5 minutes (810), and RhB treated with GO- mAHS after 15 minutes (812)) was examined using a UV-visible spectrophotometer at a wavelength of 553 nanometers (nm) for removal of RhB in water. The results indicate the complete removal of RhB dye from water within 1 minute contact time by GO-mAHS, as observed in the FIGS. 8. Removal of RhB was also possible with reduced loadings of GO- mAHS ranging from 3 mg/ml and upto 30 mg/ml. Therefore, GO-mAHS is an efficient and effective adsorbent for removing RhB from aqueous solutions.

Further, the effect of pH on RhB removal with the composition of the present disclosure (GO-mAHS) was evaluated, and the results of this study are presented in FIG. 9. For this purpose, UV-Visible spectra of the RhB solution (2 ppm RhB in water) (912) and that treated with GO-mAHS at different pH values, namely, pH 2 (902), pH 4 (904), pH 6 (906), pH 8 (908), pH 10 (910) over 15 minutes was studied. The results indicate that the GO-mAHS was effective in RhB adsorption at all pH ranges (pH independent). This shows the ability of GO-mAHS to remove RhB within a wide pH range of 2-10, without the need for neutralization.

Referring to FIG. 10, UV-Vis spectra of water that has been kept in contact with the RhB adsorbed GO- mAHS composite for 60 days to observe dye leaching at pH 3 (1002), pH 7 (1004), and pH 10 (1006), respectively, is illustrated. The leachate of RhB from the GO-mAHS composite to the aqueous solution or water was analyzed at acidic, neutral, and basic pH values ranging from 2 to 10. As evident from FIG. 10, the results confirmed no leaching, confirming that the RhB adsorbed GO-mAHS is stable at a pH range of 2-10.

The dye removal ability of the composition that has been subjected to a heat treatment at 250 °C was evaluated. For this purpose, 0.3 g of the composition was shaken with 2 mg/L RhB solution (10 mL), and the resulting absorbance spectra of treated water containing RhB (1100) after 1 min (1102), 5 min (1104), and 15 min (1106) contact times are shown in FIG. 11. As shown in spectra, residual RhB dye remains in the treated water even after shaking for 15 min. The percentage of dye removal is 92 %, with the composition prepared at 250 °C, which is lower than that for GO-mAHS heated up to 150 °C. During the reduction of GO at 250 °C, a more significant number of oxygenated groups are removed from the basal plane than that of the samples heated to 150 °C (FIG. 6). While reduction at a higher temperature increases the sp² nature of GO and thus the TT-TT interaction with RhB, this also leads to an increase in hydrophobicity of GO-mAHS, resulting in a net lowering in the adsorption of RhB. Best results were observed at a temperature range of 110 °C to 180 °C, where the oxygen functionalities are partially and controllably removed from GO, completely removing the dye upon treatment. The effect of initial dye concentration and contact time on the dye removal from the aqueous system was investigated at different RhB dye concentrations. The results of this study are presented in FIG. 12. For this purpose, 2 mg/L (1202), 3 mg/L (1204), 4 mg/L (1206), 5 mg/L (1208), 10 mg/L (1210), 50 mg/L (1212), and 100 mg/L (1214) of RhB was allowed to come in contact with a fixed dosage of GO-mAHS (10 g/L). The solutions were shaken at 2000 rpm, and the samples were taken out at different time intervals (5, 15, 30, 45, and 60 minutes). The results were analyzed using UV-Vis spectroscopy. FIG. 12 shows the variation in the amount of RhB adsorbed onto 1 g of GO-mAHS with contact time and at different initial dye concentrations. From FIG. 12, it can be observed that the amount of RhB adsorbed onto GO- mAHS has increased with the increase of initial dye concentration from 2 to 50 mg/L. Furthermore, the rate of initial dye adsorption has also increased with the increasing dye concentration.

It was further observed that although the amount of RhB adsorbed increased with increasing initial RhB concentration from 2 mg/L to 50 mg/L, the complete dye removal was not observed at each concentration level. This is because the RhB and water molecules compete for adsorption sites or active sites on the composition. At higher concentrations, the probability of RhB molecules colliding with the composition is much higher than water molecules, and hence higher adsorption. This suggests that the active sites on the composition are not fully saturated with RhB at lower dye concentrations. This was confirmed by re-using the RhB adsorbed GO- mAHS multiple times for dye removal after drying at 100 °C. For this purpose, GO-mAHS (0.1 g) was shaken with 2 mg/L RhB solution (10 m ) at 2000 rpm for 5 min. After the adsorption, the solution was filtered, and absorbance was measured. RhB adsorbed GO-mAHS was collected and washed with DI water to remove unabsorbed RhB. It was then dried at >100 °C to remove all adsorbed water. The dried RhB adsorbed GO-mAHS was again shaken with a new RhB solution of the same concentration. This was repeated for several cycles, and the results of the variation in the percentage of dye removal are shown in FIG. 13. As can be observed from the FIG. 13, the percentage of dye removal after the the first cycle (1302) was around 85-90%, after the second cycle (1304) was around 80-85%, after the third cycle (1306) was around 65- 70%, and about 30% after the fourth cycle(1308). The data suggests that RhB was further adsorbed onto the GO-mAHS at each cycle, albeit the percentage of dye removal reduced with each subsequent cycle. Therefore, after the adsorption of RhB onto GO-mAHS at lower dye concentrations, the composition/adsorbent can be re-used multiple times for the dye removal until binding sites are fully saturated with dye molecules. The amount of RhB adsorbed onto GO-mAHS increases with an increasing initial concentration of RhB solution. RhB adsorbed GO-mAHS can be re-used multiple times after heating to >100 °C to remove adsorbed water.

INDUSTRIAL APPLICABILITY

The present disclosure provides a composition including mAHS-GO to remove dye (RhB) from wastewater. The methods described are advantageous for both waste disposal and wastewater treatment. The main disposal routes for the AHS are incineration and landfilling, both expensive and causing environmental problems such as contamination of the land, groundwater, and air. Also, the AHS has no economic value; therefore, using the AHS as an adsorbent and coagulant material for wastewater treatment is highly cost-effective. Further, GO is chemically synthesized from graphite, naturally abundant in Sri Lanka with high quality. Producing the GO-mAHS composite is also simple, low cost, and energy-efficient, without generating any toxic byproducts, making it suitable for large-scale production. Therefore, the GO-mAHS is a cost-effective and eco-friendly adsorbent for color removal.

Further, effective adsorption was achieved even at low concentrations due to the large surface area of GO, with significantly less contact time for adsorption. Moreover, RhB adsorption onto GO-mAHS is pH-independent, eliminating the need to neutralize wastewater before treatment. No leaching of the RhB from the GO-mAHS composite was observed under both acidic and basic pH values, suggesting high stability. Also, RhB adsorbed GO-mAHS can be used in other applications, such as producing building materials that could generate a secondary income.

Numerous modifications and variations of the present invention are possible in light of the above teachings. Therefore, it is to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Claims

1. A composition comprising: an aluminum oxide/ hydroxide; and graphene oxide (GO).

2. The composition according to claim 1, wherein the graphene oxide has a GO loading in a range of 5-20mg of GO/g of the aluminum oxide/ hydroxide.

3. The composition according to any of claims 1 or 2, wherein the aluminum oxide/ hydroxide has a particle size less than 100 pm.

4. The composition according to any one of claims 1-3, comprising a porous structure and flake-like structure.

5. The composition according to any one of claims 1-3, wherein the aluminum oxide/ hydroxide is obtained from a sludge.

6. The composition according to any one of claims 1-5, is in the form of a powder, granules, flakes, or combinations thereof.

7. A method of making the composition according to any one of claims 1-5, the method comprising: mixing the aluminum oxide/ hydroxide with a GO solution to obtain a paste; and heating the paste to obtain the composition.

8. The method according to claim 7 further comprising, mixing the aluminum oxide/ hydroxide with the GO solution to obtain a GO loading in a range of 5-20mg of GO/g of AHS

9. The method according to claim any one of claims 7 or 8 further comprising, heating the paste to a temperature range of 110-300 °C for a period of 45 minutes to 75 minutes in an inert atmosphere to obtain the composition.

10. The method according to claim 9 further comprising, further comprising, heating the paste to a temperature range of 110-180 °C for a period of 45 minutes to 75 minutes in an inert atmosphere to obtain the composition

11. The method according to any one of claims 7-10 further comprising: dehydrating an aluminum hydroxide sludge (AHS) to obtain a dried solid; and reducing the particle size of the dried solid to obtain the aluminum oxide/ hydroxide.

12. The method according to claim 11 further comprising, dehydrating the aluminum hydroxide sludge to a temperature range of 180-220 °C to obtain the dried solid.

13. A method of removing a dye from an aqueous system, the method comprises: contacting the composition according to any one of claims 1 -6 with the aqueous system for a period sufficient to obtain a dye adsorbed composition; and separating the dye adsorbed composition from the aqueous system.

14. The method according to claim 13, wherein the dye is a pi-bond conjugated structure.

15. The method according to claim 13, wherein the cationic dye is rhodamine B.

16. The method according to any one of claims 13-15 further comprising, contacting the composition with the aqueous system within 20 minutes to obtain the dye adsorbed composition.

17. The method according to any one of claims 13-16 further comprising, separating the dye adsorbed composition from the aqueous system by gravity.

18. The method according to any one of claims 13-17 further comprising, separating the dye adsorbed composition from the aqueous system in less than 60 seconds.

19. The method according to any one of claims 13-18, wherein the aqueous system has a pH in a range of 2-10.

20. The method according to any of claims 1-19, wherein the dye adsorbed composition shows less than 1% leaching of the dye into the aqueous system at the pH range 2-10.

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