WO2023022588A1

WO2023022588A1 - A photoactive fabric for purifying air and a method of producing thereof

Info

Publication number: WO2023022588A1
Application number: PCT/MY2022/050076
Authority: WO
Inventors: Joon Ching JUAN; Xin Hong TAI; Jenn Hau Ivan TAY; Mohd Rafie Bin JOHAN
Original assignee: University Of Malaya
Priority date: 2021-08-19
Filing date: 2022-08-19
Publication date: 2023-02-23

Abstract

The present invention relates to a photoactive fabric for purifying air and a method (100) of producing thereof, the method (100) comprising the steps of: preparing a graphene oxide suspension (101 ); preparing a metal oxide suspension (102); preparing a dopant suspension (103); and mixing the graphene oxide suspension, the metal oxide suspension and the dopant suspension to form a mixture (104); characterized by subjecting the mixture to photoreduction process to simultaneously reduce and dope the graphene oxide so as to obtain a doped and reduced graphene oxide/metal oxide nanocomposite as a photocatalyst (105); dispersing the photocatalyst (106); and coating the photocatalyst on a fabric (107).

Description

A PHOTOACTIVE FABRIC FOR PURIFYING AIR AND A METHOD OF PRODUCING THEREOF

TECHNICAL FIELD

The present invention relates to a photoactive fabric. More particularly, the present invention relates to a photoactive fabric for purifying air and a method of producing thereof.

BACKGROUND ART

There has been substantial research in determining personal exposure to indoor pollutants as people nowadays spend most of their time inside buildings. Although indoor pollution is not regarded as hazardous as outdoor pollution, concentrations of indoor contaminants are often higher than those outdoors and most of them can be attributed to human activities, furniture, and building materials. Indoor air pollutants, particularly volatile organic compounds (VOCs), can be inhaled into lungs, and prolonged exposure can cause serious health consequences for humans.

In order to address the aforesaid problem, photocatalytic oxidation (PCO) processes have been widely studied and developed. In the PCO processes, reactive oxygen species (ROS) are generated from a photocatalyst upon light irradiation. Subsequently, the ROS mineralize the VOCs into simpler, harmless compounds. Among the photocatalysts, carbon-based catalysts are well-known of their high versatility in carrying out various photocatalytic activities as their band gaps are tunable and can be tailored into n-type or p-type photocatalysts. Recently, graphene oxide (GO) has arisen as a potential eco-friendly photocatalyst. GO can be further reduced to produce partially reduced graphene oxide (PRGO) or reduced graphene oxide (rGO) through various reduction methods to improve its photocatalytic effect. There are a number of solutions developed for producing photocatalysts using rGO and fabrics comprising thereof for purifying indoor air, and some of them have been discussed in following prior art references.

CN106955689A discloses a preparation method of a reduced graphene oxide/cuprous oxide composite photocatalyst. The method comprises the steps of preparing a graphene oxide solution by adopting an improved Hummers’ method; and adding the graphene oxide solution to a copper sulfate solution, carrying out ultrasonic dispersion; adjusting the mixture into strong basicity by using a sodium hydroxide solution, stirring evenly; and slowly dropwise adding a hydrazine hydrate reducing agent to reduce copper sulfate and graphene oxide in one step; precipitating, washing and drying to obtain the reduced graphene oxide/cuprous oxide composite photocatalyst.

CN109107558A relates to a photocatalytic material and a preparation method and a fabric thereof. The preparation method for the photocatalytic material comprises the following steps: a graphene oxide solution is provided; thermal reduction treatment is carried out for the graphene oxide solution, so that a graphene solution is obtained, the concentration of graphene in the graphene solution is 10mg/mL to 20mg/mL, and the oxygen content of the graphene is 5 to 10 percentage by weight; the graphene solution is added with a titanium dioxide solution and is subjected to homogenization treatment, so that a mixed liquid is obtained; and a spray dryer is adopted to carry out spray-drying for the mixed liquid, so that the photocatalytic material is obtained.

The aforementioned and other existing approaches may strive to provide improved methods for producing reduced graphene oxide-based photocatalysts and fabrics comprising thereof. However, they have a certain number of limitations and shortcomings. A significant perceived drawback is that they are using conventional thermal/chemical routes to reduce the graphene oxide, which requires harmful reducing agents/solvents and large amount of energy. Moreover, they do not involve doping of the graphene oxide. Doping the graphene oxide with optimized concentrations of atoms can help create p-type or n-type photocatalysts with higher acceptor density in comparison to pure graphene oxide. The higher acceptor density can lead to better performance of the photocatalysts in photodegrading VOCs.

Accordingly, there is a need to have an enhanced photoactive fabric for purifying air and a method of producing thereof, which is capable of overcoming the aforesaid limitations and shortcomings.

SUMMARY OF THE INVENTION

The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.

An objective of the present invention is to provide a photoactive fabric for purifying air and an environmentally friendly method of producing thereof, which does not require harmful reducing agents/solvents and large amount of energy.

It is also an objective of the present invention to provide a photoactive fabric which is capable of absorbing outdoor light and purifying indoor air at the same time.

It is also an objective of the present invention to provide an air-purifying photoactive fabric with high laundry durability, photostability, thermal stability, and chemical stability.

It is also an objective of the present invention to provide a method capable of simultaneously doping and reducing graphene oxide to produce an improved airpurifying photoactive fabric. Accordingly, these objectives can be achieved by following the teachings of the present invention. The present invention relates to a photoactive fabric for purifying air and a method of producing thereof. The method comprises the steps of: preparing a graphene oxide suspension; preparing a metal oxide suspension; preparing a dopant suspension; and mixing the graphene oxide suspension, the metal oxide suspension and the dopant suspension to form a mixture; characterized by subjecting the mixture to photoreduction process to simultaneously reduce and dope the graphene oxide so as to obtain a doped and reduced graphene oxide/metal oxide nanocomposite as a photocatalyst; dispersing the photocatalyst; and coating the photocatalyst on a fabric.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

In order for the above recited features of the present invention to be understood in detail, a more particular description of the invention, briefly summarized above, may have been referred by embodiments, some of which are illustrated in the appended drawing. It is to be noted, however, that the appended drawing illustrates only typical embodiments of this invention and are therefore not to be considered limiting of its scope. The invention may admit to other equally effective embodiments.

These and other features, benefits, and advantages of the present invention will become apparent by referring to the following figures, wherein:

Figure 1 is a process flow diagram illustrating a method of producing a photoactive fabric for purifying air in accordance with an embodiment of the present invention;

Figure 2 illustrates a photoreduction process in accordance with an exemplary embodiment of the present invention; and

Figure 3 illustrates a photocatalytic oxidation process in accordance with an exemplary embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting but merely as a basis for claims. It should be understood that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the invention is to cover all modifications, equivalents and alternatives falling within the scope of the present invention as defined by the appended claims. As used throughout this application, the word "may" is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words "include," "including," and "includes" mean including, but not limited to. Further, the words "a" or "an" mean "at least one” and the word "plurality" means one or more, unless otherwise mentioned. Where the abbreviations or technical terms are used, these indicate the commonly accepted meanings as known in the technical field.

The present invention is described hereinafter by various embodiments with reference to the accompanying drawings, wherein reference numerals used in the accompanying drawings correspond to the like elements throughout the description. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiment set forth herein. Rather, the embodiment is provided so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art. In the following detailed description, numeric values and ranges are provided for various aspects of the implementations described. These values and ranges are to be treated as examples only, and are not intended to limit the scope of the claims. In addition, a number of materials are identified as suitable for various facets of the implementations. These materials are to be treated as exemplary, and are not intended to limit the scope of the invention. With reference to the drawings, the invention will now be described in more details.

Figure 1 is a process flow diagram illustrating a method (100) of producing a photoactive fabric for purifying air in accordance with an embodiment of the present invention. The method (100) begins at step 101 by preparing a graphene oxide suspension. At step 102, a metal oxide suspension is prepared. At step 103, a dopant suspension is prepared. Thereafter, the graphene oxide suspension, the metal oxide suspension and the dopant suspension are mixed to form a mixture at step 104. At step 105, the mixture is subjected to photoreduction process to simultaneously reduce and dope the graphene oxide so as to obtain a doped and reduced graphene oxide/metal oxide nanocomposite as a photocatalyst. Subsequently, the photocatalyst is dispersed at step 106 and coated on a fabric at step 107.

In accordance with an embodiment of the present invention, the fabric can be cloth or any suitable materials that allow the coating of the photocatalyst. For example, the fabric can be cotton, wool, polyester or a mixture thereof. The photoactive fabric produced via the present invention can act as an absorbent to absorb lights with its optical properties and capture air pollutants so that the photocatalyst coated on the fabric can photodegrade the air pollutants upon receiving the lights for purifying air in an indoor environment.

In accordance with a preferred embodiment of the present invention, the method (100) further comprises the step of purifying the doped and reduced graphene oxide/metal oxide nanocomposite before dispersing the photocatalyst at step 106.

In accordance with an embodiment of the present invention, the preparation of the graphene oxide suspension at step 101 comprises the steps of producing graphene oxide powders by modified Hummers’ method and dispersing the graphene oxide powders in water. For example, in the modified Hummers’ method, graphite flake is dispersed in a mixture of sulfuric acid (H2SO4) and phosphoric acid (H3PO4) in volume ratio of 9:1 under constant stirring. Thereafter, potassium permanganate (KMnC ) is slowly added into the suspension and heated before being transferred into an ice bath to stop the reaction. The reaction is stopped by adding deionized (DI) water dropwise into the suspension, followed by pouring DI water rapidly into the solution. Then, hydrogen peroxide (H2O2) is added dropwise to the suspension until the colour changes from purplish brown to yellowish brown which indicates the end point. The suspension is washed with HCI and DI water alternately via centrifugation until a pH of 3 - 4 is reached. The washed graphene oxide suspension can then be dried at 40-70 ^eC to produce the graphene oxide powders.

In accordance with an embodiment of the present invention, the preparation of the metal oxide suspension at step 102 comprises the step of dispersing metal oxide in an organic solvent and/or water. The metal oxide comprises titanium dioxide, zinc oxide, copper oxide, perovskite or tin oxide. The organic solvent comprises methanol, ethanol, propanol, butanol, isopropanol or any other suitable organic solvents.

In accordance with an embodiment of the present invention, the preparation of the dopant suspension at step 103 comprises the step of dispersing a dopant precursor in an organic solvent and/or water. The dopant comprises nitrogen (N), boron (B), sulphur (S) or fluorine (F). For nitrogen doping, the dopant precursor can be 1.0 M of ammonia or urea. For boron doping, the dopant precursor can be 0.6 M of boric acid. For sulphur doping, the dopant precursor can be 1 .0 M of sodium sulphate or potassium sulfate or thiosulfate salts. For fluorine doping, the precursor can be 0.1 M of trifluoroacetic acid or hydrofluoric acid (HF). The organic solvent comprises methanol, ethanol, propanol, butanol, isopropanol or any other suitable organic solvents. The presence of dopant in the photocatalyst leads to higher acceptor density, thereby increasing performance in photodegrading volatile organic compounds (VOCs). For example, optimizing the amount of N atom doping can turn graphene oxide into an n- type photocatalyst with high donor density, thus enhancing the photodegradation process by generating more superoxide radical which is one type of the reactive oxygen species (ROS). In accordance with an embodiment of the present invention, the graphene oxide suspension, the metal oxide suspension and the dopant suspension are mixed via ultrasonication and vigorous stirring at step 104.

In accordance with an embodiment of the present invention, the photoreduction process at step 105 comprises the step of exposing the mixture to a light source comprising ultraviolet-A, ultraviolet-B, ultraviolet-C or visible light irradiation under constant stirring at ambient temperature and pressure. Figure 2 illustrates a photoreduction process in accordance with an exemplary embodiment of the present invention. The mixture of a graphene oxide suspension and a titanium dioxide suspension is exposed to two units of 25W ultraviolet-C light irradiation (peak wavelength of 253nm) for 12 hours under constant stirring by a magnetic stirrer bar to reduce the graphene oxide without high temperature and any reducing agents. Further, a dopant suspension is added into the mixture to allow simultaneous reducing and doping of the graphene oxide so as to avoid conventional doping processes which require high temperature and/or pressure.

In accordance with a preferred embodiment of the present invention, the photocatalyst produced by the aforesaid method (100) is coated on a fabric curtain. The coated fabric curtain may absorb indoor light and outdoor solar light, and adsorb air pollutants at the same time. Upon exposure to light sources such as the indoor light and the outdoor solar light, the photocatalyst in the fabric curtain may conduct efficient photocatalytic process to photodegrade the adsorbed air pollutants into clean air. Therefore, the coated fabric curtain is capable of protecting indoor environment from sunlight exposure and photodegrading the air pollutants at the same time.

In accordance with an embodiment of the present invention, the fabric can be prepared by being cut into desired size, washed with organic solvent and water, and dried in an oven. In accordance with an embodiment of the present invention, the photocatalyst can be coated on the fabric by a conventional coating process such as, but not limited to, padding process, drop cast coating process or dip coating process. For example, the padding process involves the immersion of the fabric into the photocatalyst suspension, followed by squeezing the wet fabric between rollers to expel air and excess liquid. The drop cast coating process involves dripping the photocatalyst suspension on to a fabric surface with a dropper and drying the excess liquid with evaporation. The dip coating process involves the immersion of a fabric into the photocatalyst suspension for a certain time to allow the fabric to adsorb the photocatalyst.

Below is an experimental study of a fabric curtain coated with the reduced graphene oxide/titanium dioxide photocatalyst produced by the aforesaid method (100) of the present invention from which the advantages of the present invention may be more readily understood and put into practical effect. It is to be understood that the following example is for illustrative purpose only and should not be construed to limit the present invention in any way.

Example

The photoactivity of the coated fabric curtain is tested with 100 ppb of methanol at typical indoor condition (25°C and 65% relative humidity) with a custom-made photoreactor under both 4W ultraviolet-A and 4W visible light irradiation. It is seen that the coated fabric curtain can receive visible light (400 - 800nm) and ultraviolet-A (340 - 400nm) light irradiation from indoor light and outdoor sunlight. Figure 3 illustrates a photocatalytic oxidation process happened in the coated fabric curtain. The coated fabric curtain acts as an adsorbent to adsorb VOC molecules in the air and subsequently uses the photon energy from the light sources to photodegrade the VOC molecules into harmless compounds such as, but not limited to, carbon dioxide (CO2) and water (H2O). The stability of the photocatalyst coated on the fabric curtain is essential. Hence, several tests have been conducted to evaluate its stability for different aspects. Firstly, the photostability of the photocatalyst is tested. Photostability of the photocatalyst will ensure that the coated fabric curtain will not be affected by photo-corrosion and can maintain its performance. To test its resistance from photo-corrosion, the photocatalyst is exposed to high energy ultraviolet-C (95W) light source for 4 hours. The photocatalyst before the photo-corrosion and the photocatalyst after the photocorrosion have been compared and there is no change in crystallinity. This indicates that the photocatalyst resists photo-corrosion and is highly stable. The coated fabric curtain maintains its capability of 100% photodegradation of the VOC even after washing. The photocatalyst is strongly embedded into the fabric matrix due to the oxygen functional groups present on the graphene oxide surface. Based on an XPS analysis, the titanium dioxide particles can be anchored permanently on the graphene oxide surface because of the formation of C-O-Ti and C-Ti chemical bonds.

Accordingly, the method (100) of the present invention is capable of producing an improved air-purifying photoactive fabric in an environmentally friendly manner by simultaneously reducing and doping the graphene oxide without requiring harmful reducing agents/solvents and large amount of energy. Moreover, the fabric coated with the photocatalyst of the present invention is proved to be efficient in simultaneously absorbing sunlight and purifying indoor air through photodegradation of the air pollutants. Furthermore, photoactive fabric of the present invention possesses high laundry durability, photostability, thermal stability, and chemical stability.

Various modifications to these embodiments are apparent to those skilled in the art from the description and the accompanying drawings. The principles associated with the various embodiments described herein may be applied to other embodiments. Therefore, the description is not intended to be limited to the embodiments shown along with the accompanying drawings but is to be providing broadest scope of consistent with the principles and the novel and inventive features disclosed or suggested herein. Accordingly, the invention is anticipated to hold on to all other such alternatives, modifications, and variations that fall within the scope of the present invention and appended claim.

It is to be understood that any prior art publication referred to herein does not constitute an admission that the publication forms part of the common general knowledge in the art.

Claims

Claims:

1. A method (100) of producing a photoactive fabric for purifying air, the method (100) comprising the steps of: preparing a graphene oxide suspension (101 ); preparing a metal oxide suspension (102); preparing a dopant suspension (103); and mixing the graphene oxide suspension, the metal oxide suspension and the dopant suspension to form a mixture (104); characterized by subjecting the mixture to photoreduction process to simultaneously reduce and dope the graphene oxide so as to obtain a doped and reduced graphene oxide/metal oxide nanocomposite as a photocatalyst (105); dispersing the photocatalyst (106); and coating the photocatalyst on a fabric (107).

2. The method (100) as claimed in claim 1 , wherein the method (100) further comprises the step of purifying the doped and reduced graphene oxide/metal oxide nanocomposite prior to dispersing the photocatalyst (106).

3. The method (100) as claimed in claim 1 , wherein the graphene oxide suspension, the metal oxide suspension and the dopant suspension are mixed via ultrasonication and stirring.

4. The method (100) as claimed in claim 1 , wherein the photoreduction process comprises the step of exposing the mixture to a light source comprising ultraviolet-A, ultraviolet-B, ultraviolet-C or visible light irradiation under stirring at ambient temperature and pressure.

5. The method (100) as claimed in claim 1 , wherein the metal oxide comprises titanium dioxide, zinc oxide, copper oxide, perovskite or tin oxide.

6. The method (100) as claimed in claim 1 , wherein the preparation of the graphene oxide suspension comprises the steps of producing graphene oxide powders by modified Hummers’ method and dispersing the graphene oxide powders in water.

7. The method (100) as claimed in claim 1 , wherein the metal oxide suspension is prepared by dispersing metal oxide in an organic solvent and/or water.

8. The method (100) as claimed in claim 1 , wherein the dopant suspension is prepared by dispersing a dopant precursor in an organic solvent and/or water.

9. The method (100) as claimed in claim 7 or 8, wherein the organic solvent comprises methanol, ethanol, propanol, butanol or isopropanol.

10. The method (100) as claimed in claim 1 , wherein the dopant comprises nitrogen, boron, sulphur or fluorine.

11 . The method (100) as claimed in claim 1 , wherein the photocatalyst is coated on the fabric by a padding process, a drop cast coating process or a dip coating process.

12. The method (100) as claimed in claim 1 , wherein the fabric comprises cotton, wool, polyester or a mixture thereof.

13. A photoactive fabric for purifying air produced according to any one of claims 1 to