Nanocomposite synthesis and uses thereof

Abstract

Herein disclosed is a method of forming a nanocomposite material that includes: dispersing graphitic carbon nitride (GCN) nanosheets in a solvent by ultrasonication to form a GCN nanosheet dispersion; adding zinc oxide-copper (ZnO-Cu) nanoparticles to the GCN nanosheet dispersion to form a GCN / ZnO-Cu mixture; co-exfoliating the GCN / ZnO-Cu mixture by first ultrasonicating and then calcinating the dried GCN / ZnO-Cu sample to form the nanocomposite material. Also provided are articles comprising the GCN / ZnO-Cu nanocomposite material and methods of coating articles in the nanocomposite material. Such articles may be used in disinfection.

Description

NANOCOMPOSITE SYNTHESIS AND USES THEREOFFIELD

[0001] The present disclosure relates generally to nanocomposites. More particularly, the present disclosure relates to nanocomposite materials formed from graphitic carbon nitride (GCN) nanosheets and zinc oxide-copper (ZnO-Cu) nanoparticles.BACKGROUND

[0002] The synthesis process involving the combination of graphitic carbon nitride (g- C3N4 or GCN), zinc oxide (ZnO), and metals such as iron (Fe), manganese (Mn), and chromium (Cr) usually comprises three or more process steps. These process steps require high energy consumption, rare and expensive chemicals, and could lead to the formation of toxic chemicals such as hexavalent chromate ions from chromium. For example, the synthesis process does involve, ultrasonication, hydrothermal co- precipitation, and calcination, with each requiring several hours of operation leading to high energy consumption, and ultimately low surface area.

[0003] Self-disinfecting surfaces is a relatively new application area of photocatalysis that is gradually gaining momentum. Prior to this, the common way of disinfecting surfaces is to apply readily available, off-the-shelf disinfectants. However, the drawback of this disinfection is that it only lasts for a few hours, especially in high-touch-surface public places like malls, and airports, and cannot disinfect under light irradiation.

[0004] It is, therefore, desirable to provide improved synthesis process of nanocomposites with desirable properties to be used in the degradation of organic contaminants and disinfection under light irradiation.SUMMARY

[0005] It is an object of the present disclosure to obviate or mitigate at least one disadvantage of previous nanocomposite materials.

[0006] In a first aspect, the present disclosure provides a method for forming a nanocomposite material comprising: dispersing graphitic carbon nitride (GCN) nanosheets in a solvent by ultrasonication to form a GCN nanosheet dispersion; adding zinc oxide-copper (ZnO-Cu) nanoparticles to the GCN nanosheet dispersion to form a GCN / ZnO-Cu mixture;co-exfoliating the GCN / ZnO-Cu mixture by ultrasonication and then calcination to form the nanocomposite material.

[0007] In a further embodiment, there is provided a method for forming a nanocomposite material wherein the solvent is ethanol.

[0008] In a further embodiment, there is provided a method for forming a nanocomposite material, further comprising the step of preparing the GCN nanosheets by calcinating urea.

[0009] In a further embodiment, there is provided a method for forming a nanocomposite material, further comprising the step of preparing the ZnO-Cu nanoparticles by hydrothermal coprecipitation of a zinc salt and a copper salt.

[0010] In a further embodiment, there is provided a method for forming a nanocomposite material, wherein the zinc salt is zinc sulfate heptahydrate.

[0011] In a further embodiment, there is provided a method for forming a nanocomposite material, wherein the copper salt is copper II nitrate hemi pentahydrate.

[0012] In a further embodiment, there is provided a method for forming a nanocomposite material, wherein the ZnO-Cu nanoparticles are between 1% and 5% by weight copper.

[0013] In a further embodiment, there is provided a method for forming a nanocomposite material, wherein the ratio of GCN nanosheets to ZnO-Cu nanoparticles in the GCN / ZnO-Cu mixture is between 10:1 and 2:1.

[0014] In a further aspect, the present disclosure provides a nanocomposite material obtained by the method for forming a nanocomposite material.

[0015] In a further aspect, the present disclosure provides an article comprising the nanocomposite material.

[0016] In a further aspect, the present disclosure provides a method for coating an article in the nanocomposite material, the method comprising: dispersing the nanocomposite material in a solvent by ultrasonication to form a nanocomposite material dispersion; and dipping the article in the nanocomposite material dispersion to form a coated article.

[0017] In a further embodiment, there is provided a method for coating an article in the nanocomposite material, wherein the solvent is a mixture of water-based polyurethane and ethanol.

[0018] In a further embodiment, there is provided a method for coating an article in the nanocomposite material, wherein the ratio of nanocomposite material to solvent is about 20:1.

[0019] In a further embodiment, there is provided a method for coating an article in the nanocomposite material, wherein the article is made of polyvinylchloride (PVC).

[0020] In a further aspect, the present disclosure provides a coated article obtained by the method for coating an article in the nanocomposite material.

[0021] In a further aspect, the present disclosure provides a use of the article comprising or coated in the nanocomposite material in wastewater treatment.

[0022] Other aspects and features of the present disclosure will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures.BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Embodiments of the present disclosure will now be described, by way of example only, with reference to the attached Figures.

[0024] Fig. 1 is a schematic diagram of the synthesis process of GCN / ZnO-Cu nanocomposites including (a) GCN synthesis, (b) ZnO-Cu nanoparticle synthesis, and (c) GCN / ZNO-Cu nanocomposite synthesis.

[0025] Fig. 2 is the XRD patterns of selected embodiments (GCN, ZnO, ZnO-Cu3%, and GCN / 0.1ZNo-Cu3%).

[0026] Fig. 3 is a graph showing the particle size distribution of selected embodiments.

[0027] Fig. 4 is the FT-IR analysis of selected embodiments.

[0028] Fig. 5 is the SEM analysis showing the morphology of the synthesized samples according to selected embodiments.

[0029] Fig. 6 is the EDS analysis showing the elemental compositions of the synthesized samples according to selected embodiments.

[0030] Fig. 7 is (a) the BET surface area and (b) the BJH pore size distribution of the synthesized samples according to selected embodiments.

[0031] Fig. 8 is (a) the UV-Vis absorption spectra and (b) the bandgap of the synthesized samples according to selected embodiments.

[0032] Fig. 9 is a graph showing the degradation of 4-chlorophenol under visible light irradiation in the presence of the synthesized samples according to selected embodiments.

[0033] Fig. 10 is a graph showing the reusability and stability of GNC / 0.1ZnO-Cu3%, where Fig. 10a shows the reduction in performance over cycles and Fig. 10b shows the stability test XRD patterns.

[0034] Fig. 11 is a graph showing the disinfection performance of samples according to selected embodiments in disinfecting coliforms in wastewater primary influent.

[0035] Fig. 12 is a schematic diagram of the dip coating process of a polyvinylchloride (PVC) plastic substrate.

[0036] Fig. 13 is the XRD patterns of the coated and uncoated PVC substrates according to selected embodiments.

[0037] Fig. 14 is a graph illustrating the self-disinfecting performance of a coated PVC according to selected embodiments.

[0038] Fig. 15 is a graph showing the reusability and stability of coated PVC(GCN / ZnO-Cu3%), where Fig. 15a shows the reduction in performance over cycles and Fig. 15b shows the stability test XRD patterns.DETAILED DESCRIPTION

[0039] Generally, the present disclosure provides methods of forming a nanocomposite material. Graphitic carbon nitride (GCN) nanosheets and zinc oxide-copper (ZnO-Cu) nanoparticles are ultrasonicated and then calcinated to form the nanocomposite material. The nanocomposite material so formed may be used as a photocatalyst. It may be advantageous to create an article containing the nanocomposite material, and a method of coating an article is herein provided.

[0040] Co-exfoliation

[0041] GCN nanosheets and ZnO-Cu nanoparticles are co-exfoliated by ultrasonication prior to calcination. In one embodiment, the method comprises: dispersing GCN nanosheets in a solvent by ultrasonication to form a GCN nanosheet dispersion; adding ZnO-Cu nanoparticles to the GCN nanosheet dispersion to form a GCN / ZnO-Cu mixture; and co-exfoliating the GCN / ZnO-Cu mixture by ultrasonication and then calcination to form the nanocomposite material. In one embodiment, the method comprises: dispersing GCN nanosheets in a solvent by ultrasonication to form a GCN nanosheet dispersion; adding ZnO- Cu nanoparticles to the GCN nanosheet dispersion to form a GCN / ZnO-Cu mixture; and co-exfoliating the GCN / ZnO-Cu mixture by ultrasonication to form a co-exfoliated GCN / ZnO-Cu mixture. The co-exfoliation is done by ultrasonication in a solvent. The solvent may be any suitable organic solvent. The solvent may be ethanol, for example, due to its environmental and health safety, as well as its high rate of evaporation and drying. In one embodiment, the ratio of GON nanosheets to ZnO-Cu nanoparticles in the GCN / ZnO-Cu mixture is between 10:1 and 2:1. The GON nanosheets may be dispersed in the solvent by ultrasonication for any suitable length of time, such as about 1 hour. The GCN / ZnO-Cu mixture may be coexfoliated using ultrasonication for any suitable amount of time, such as about 30 minutes. Prior to calcination, the co-exfoliated GCN / ZnO-Cu mixture may be processed by further steps. For example, the co-exfoliated GCN / ZnO-Cu mixture may be stirred for a length of time, such as about 2 hours. The co-exfoliated GCN / ZnO-Cu mixture may be dried prior to calcination. The co-exfoliated GCN / ZnO-Cu mixture may be dried in an oven at any suitable temperature, such as about 70 °C, and for any suitable length of time, such as overnight.

[0042] Calcination

[0043] As a part of co-exfoliation, the GCN / ZnO-Cu mixture can be calcinated to form a nanocomposite material. As used herein, calcination refers to the heating of solids to a high temperature for the purpose of removing volatile substances, oxidizing a position of mass, or rendering them friable. Calcination may be done at any suitable temperature, such as at about 550 °C. Calcination may be carried out for any suitable amount of time, such as about 4 hours. After calcination, the nanocomposite material may be processed by further steps. For example, the nanocomposite material may be processed mechanically, such as by grinding.

[0044] GCN Nanosheet Preparation

[0045] The methods for forming nanocomposite materials herein disclosed may include preparation of the graphitic carbon nitride (GCN) nanosheets. In one embodiment, the GCN nanosheets may be prepared by calcinating urea. Urea may be calcinated at any suitable temperature, for example, at 550 °C, for any suitable length of time, such as 4 hours. The process of heating urea to form GCN may be referred to as calcination, direct pyrolysis, or condensation polymerization. The preparation of GCN nanosheets may include further processing steps. For example, the GCN nanosheets may be processed mechanically, such as by grinding. The GCN nanosheets may be stored prior to use.

[0046] ZnO-Cu Nanoparticle Preparation

[0047] The methods of forming nanocomposite materials herein disclosed may include preparation of the ZnO-Cu nanoparticles. In one embodiment, the ZnO-Cu nanoparticles are prepared by hydrothermal coprecipitation of a zinc salt and a copper salt. The zinc salt may be zinc sulfate heptahydrate. The copper salt may be copper II nitrate hemi pentahydrate. Hydrothermal coprecipitation may be done in the presence of a stabilizing agent, such as sodium tribasic-NasCeHsO?. For example, the zinc salt may be dissolved in water and an equivalent concentration of stabilizer added. The zinc salt may be dissolved in water and the copper salt added thereto. The hydrothermal coprecipitation includes heating the zinc salt and the copper salt. For example, a solution of the zinc salt and the copper salt in water may be heated at 70 °C. In one embodiment, a solution of the zinc salt and the copper salt, in the presence of a stabilizer, are heated at 70 °C and NaOH is added. The hydrothermal coprecipitation may include other process steps. For example, the nanoparticles so formed may be filtered and dried. The ZnO-Cu nanoparticles may be calcinated. The ZnO-Cu nanoparticles may be processed mechanically, such as by grinding. The ZnO-Cu nanoparticles may be stored prior to use. In the examples provided herein, the ZnO-Cu nanoparticles are between 1% and 5% by weight copper. In the hydrothermal coprecipitation, the zinc salt and the copper salt are added in a 100:1 to 20:1 ratio, by weight.

[0048] Coating an Article

[0049] Herein described is an article comprising a GCN / ZnO-Cu nanocomposite material. Also provided are methods of coating an article. In one embodiment, the method of coating an article includes: dispersing the nanocomposite material in a solvent by ultrasonication to form a nanocomposite material dispersion; and dipping the article in the nanocomposite material dispersion to form a coated article. In the examples provided herein, the solvent may be a mixture of water-based polyurethane and ethanol. Any suitable solvent may be used. The ratio of nanocomposite material to solvent may be about 20:1. The article to be coated may comprise or be made of polyvinylchloride (PVC).

[0050] Uses

[0051] The nanocomposite material may be used as a photocatalyst. The nanocomposite material may be used to coat an article for disinfection purposes. The nanocomposite material may be used in wastewater treatment. The nanocomposite material may be used in water splitting to generate hydrogen. The nanocomposite material may be used in CO2 photoreduction. The nanocomposite material may be used in organic transformation.EXAMPLES

[0052] Example 1 - NOVEL FACILE SYNTHESIS PROCESS OF GCN / ZNO-CU NANOCOMPOSITES AND THEIR APPLICATION IN DEGRADATION, DISINFECTION, AND SELF-DISINFECTING COATED SURFACES UNDER VISIBLE LIGHT IRRADIATION

[0053] This example relates to (1) the novel synthesis process of GCN / ZnO-Cu nanocomposites and (2) the novel mixing of the composition of the nanocomposites with other solvents and the application as a self-disinfectant on coated surfaces.

[0054] Abstract

[0055] The example presents a highly reactive GCN / ZnO-Cu3% nanocomposite with a large BET surface area of 121.00 m2 / g and enhanced bandgap of 2.60 eV indicating improved visible light utilization. Also disclosed are the novel discoveries (1) the synthesis process of the GCN / ZnO-Cu nanocomposite referred to as the co-exfoliation method and (2) the mixing composition of GCN / ZnO-Cu nanocomposite for dip coating application on a plastic substrate. Several features of the GCN / ZnO-Cu nanocomposites apart from BET and bandgap were also presented such as XRD, FT-IR, SEM, EDS, and UV-Vis DRS. The application of the nanocomposite in the degradation of organic contaminants and disinfection of wastewater under visible light irradiation was presented. Also presented is the application of the coated plastic substrates as a self-disinfecting surface under visible light irradiation. The practical applications of the nanocomposite and the coatings for reusability purposes were also presented.

[0056] Background

[0057] This relates to the novel synthesis process of GCN / ZnO-Cu nanocomposites and the novel mixing of the composition of the nanocomposites with other solvents and its application as a self-disinfecting coated surface, both in the field of photocatalysis. Photocatalysis is a process in which a photocatalyst is irradiated by photons with energy greater than or equal to its bandgap energy causing the generation of electrons and holes on its surface. These photogenerated electrons and holes react with oxygen and water molecules to form reactive oxygen species (ROS). The ROS then reacts with the target contaminant and microorganisms leading to their degradation and disinfection. The photocatalyst is the synthesized GCN / ZnO-Cu nanocomposite.

[0058] The novel synthesis process provides for ease of synthesis such as a reduction in the number of steps involved in the process, use of environment-friendly chemicals, reduction in energy consumption, use of readily available chemicals, andultimately improve the physicochemical such as specific surface area and optical properties of the nanocomposites.

[0059] Another novel application of the synthesized GCN / ZnO-Cu nanocomposite is the mixing composition with less expensive, readily available, environment-friendly solvents and the application on surfaces of substrates to act as self-disinfecting coated surfaces. The advantage of these self-disinfecting coated surfaces is that they can disinfect both in the dark and under light (LIV or visible) irradiation and last for several days.

[0060] Prior to this, the synthesis process involving the combination of graphitic carbon nitride (g-CsIX or GCN), zinc oxide (ZnO), and metals such as iron (Fe), manganese (Mn), and chromium (Cr) usually comprises three or more process steps. These process steps require high energy consumption, rare and expensive chemicals, and could lead to the formation of toxic chemicals such as hexavalent chromate ions from chromium. For example, the synthesis process does involve, ultrasonication, hydrothermal co-precipitation, and calcination, with each requiring several hours of operation leading to high energy consumption, and ultimately low surface area.

[0061] Self-disinfecting surfaces is a relatively new application area of photocatalysis that is gradually gaining momentum. Prior to this, the common way of disinfecting surfaces is to apply readily available, off-the-shelf disinfectants. However, the drawback of this disinfection is that it only lasts for a few hours, especially in high-touch-surface public places like malls, and airports, and cannot disinfect under light irradiation.

[0062] Therefore, a need exists for the novel facile synthesis process of nanocomposites with a short synthesis process and improved physicochemical and optical properties and the application in the degradation of organic contaminants and disinfection under light irradiation. Also, a need exists for the novel facile mixing composition of the nanocomposites with solvents and the application as a self-disinfectant under light irradiation on long-lasting coated surfaces.

[0063] In conclusion, prior to this work, no GCN / ZnO-Cu nanocomposite has been developed using the novel facile synthesis process and the enhanced physicochemical and optical properties that were observed. Similarly, prior to this work, no mixing composition of this nature for the nanocomposite with other solvents was developed for the sole purpose of application on plastic substrates or any other substrate to act as a self-disinfecting surface.

[0064] This example demonstrates the novel facile synthesis process of GCN / ZnO- Cu nanocomposites and the novel mixing of the composition of the nanocomposites withsolvents and the application on substrates to act as self-disinfecting coated surfaces. The novel synthesis process of the GCN / ZnO-Cu nanocomposites involves two process unit operation steps, ultrasonication, and calcination. The method of application of the nanocomposite mixture on a substrate for self-disinfecting coated surface purposes is also provided.

[0065] In a disclosed select embodiment, the benefit of the novel facile synthesis process of the nanocomposite can be observed in the Brunner-Emmett-Teller (BET) measurement of the surface area which is 121.00 m2 / g for the GCN / ZnO-Cu nanocomposite when compared to the BET of graphitic carbon nitride (GON) at 57.17 m2 / g, zinc oxide (ZnO) at 5.18 m2 / g, or zinc oxide-copper (ZnO-Cu) at 4.26 m2 / g.

[0066] In a select embodiment, the improved surface area resulted in a 65% degradation of 4-chlorophenol, a recalcitrant and common contaminant, in 120 minutes and a complete 5.5-log reduction (99.999%) of total coliforms in wastewater in 360 minutes under visible light irradiation.

[0067] Based on the observed optimal performance of the nanocomposite, it was mixed with solvents and immobilized on a plastic substrate as coatings with the purpose to act as a self-disinfecting coating. The self-disinfecting coated surface showed a 2-log reduction (99%) of the drop of coliforms on its surface after 180 minutes under visible light irradiation.

[0068] Discussion

[0069] Figure 1 shows the schematic diagram of the synthesis process of GCN / ZnO- Cu nanocomposites. The diagram illustrates the synthesis of the constituent parts (GON, ZnO, and ZnO-Cu) of the nanocomposites leading to the synthesis of the nanocomposites. In the synthesis of GCN (see Figure 1a), urea (70 g) as a precursor was calcined in a muffle furnace at 450°C for 4h to form the GCN. This process of heating urea to form GCN is either referred to as direct pyrolysis or condensation polymerization. The GCN sample was ground and stored for usage. A method known as hydrothermal co-precipitation was used in the synthesis of ZnO-Cu nanocomposites (see Figure 1b). ZnO-Cux samples were synthesized with different Cu ratios (x = 1%, 3%, and 5%). 2.8756 g (50 mM) of zinc sulfate heptahydrate (ZnSO4.7H2O) was added to 200 mL deionized (DI) water in different 400 mL beakers. An equivalent concentration of 50 mM (2.5806 g) of sodium tribasic-NasCeHsO? was added to the mixture as a stabilizing agent. While continuously stirring the solution, copper II nitrate hemi pentahydrate, Cu(NO3)2.2.5H2O of different ratios [1% (0.029 g), 3% (0.086 g), and 5%(0.144 g)] as a function of the mass of ZnSC>4.7H2O was added to the beakers. The solutions were heated while stirring on a hotplate at 70 °C for 15 minutes. This was followed by a dropwise addition of 100 mL of 200 mM NaOH. The solution was continuously stirred at 70 °C for 2 h as the color changed from an initial pale blue to an opaque bluish milky slurry. The solution was allowed to cool down while being continuously stirred. It was then vacuum filtered using a 0.45 pm filter and washed thoroughly with DI water to remove excess NaOH. The samples were air-dried overnight and later calcined at 550 °C for 3 h. The calcined samples were left to cool down, ground, and labeled as ZnO-Cu1 %, ZnO-Cu3%, and ZnO- Cu5%. The ZnO nanoparticles were synthesized using the same process of synthesizing ZnO-Cu nanoparticles except for the addition of copper II nitrate hemi pentahydrate, CU(NO3)2.2.5H2O. A novel facile co-exfoliation method was used in synthesizing GCN / ZnO- Cu samples (see Figure 1c). This co-exfoliation method involves only ultrasonication and calcination processes. GCN / xZnO-Cu3% samples were synthesized with different mass (g) of x = 0.1 , 0.3, and 0.5, based on the optimal ratio ZnO-Cu3% observed for the photocatalytic degradation of 4-chlorophenol (4-CP). 1 g of GON was added to 50 mL of ethanol (absolute) in different quartz petri dishes and the mixtures were sonicated for 1 h to achieve uniform dispersion. With continuous stirring on a magnetic stirrer, different amounts of ZnO-Cu3% (0.1 g, 0.3 g, and 0.5 g) were added to the mixtures and afterward for the first time coexfoliated using an ultrasonication bath for another 0.5 h. The mixtures were continuously stirred for 2 h and then dried in the oven at 70 °C overnight. The dried samples were for the second time co-exfoliated using calcination in the muffle furnace at 550 °C for 4 h and left to cool down in the furnace to room temperature. The samples were then ground and labeled GCN / 0.1ZnO-Cu3%, GCN / 0.3ZnO-Cu3%, GCN / 0.5ZnO-Cu3%, and stored for usage.

[0070] Figure 2 to Figure 8 are selected embodiments of the synthesized GON, ZnO nanoparticles, ZnO-Cu nanoparticles, and GCN / ZnO-Cu nanocomposites. These embodiments represent their physicochemical and optical properties or features such as crystallinity, particle size distribution, functional groups, morphology, elemental composition, BET surface area and BJH pore size distribution, and absorption spectrum and bandgap, of the synthesized photocatalysts.

[0071] Figure 2 is the XRD patterns of the selected embodiments (GON, ZnO, ZnO- Cu3%, and GCN / 0.1ZnO-Cu3%). The GCN / 0.1ZnO-Cu3% is the best-performing nanocomposite for degradation and disinfection with a ratio of GCN to ZnO-Cu3% 1 :0.1 and thus represented in other embodiments (Figure 2 to Figure 11). The XRD describes thecrystallinity of the samples. The samples show their characteristic peaks at different 2-theta degrees indicating that they are all crystals. The sharper the peak, the higher the crystallinity. The table below shows the measured crystal size of the samples. The table shows the samples are in the nanoscale region (1 nm - 500 nm).

[0072] Table 1. Mean Crystallite Size (MCS) of GCN, ZnO and ZnO-Cu3% nanoparticles, and GCN / 0.1ZnO-Cu3% nanocomposite.Photocatalyst Mean Crystallite Size (nm)GCN 3.33ZnO 34.23Zn0-Cu3% 39.30GCN / 0.1ZnO-Cu3% 3.95 - 17.44

[0073] Figure 3 shows the particle size distribution of the samples. Particles are the result of the aggregation of crystals. The average particle size is shown in the table below with the large particle sizes. However, all samples are in the nanoparticle region (1 nm - 500 nm).

[0074] Table 2. Average Particle Size (APS) of GCN, ZnO and ZnO-Cu3% nanoparticles, and GCN / 0.1ZnO-Cu3% nanocompositePhotocatalyst Average Particle Size (nm)GCN 68.43ZnO 237.40ZnO-Cu3% 263.50GCN / 0.1ZnO-Cu3% 165.10

[0075] Figure 4 shows the functional groups present in the samples as exhibited by the FT-IR analysis. GCN shows three characteristic peaks at 3230 cm-1, 1630 - 1230 cm'1, and 810 cm'1. These peaks are indicative of the amine group (NH) stretching mode, C-N heterocycles stretching vibrational frequency, and triazine heterocycles vibrational mode, respectively. ZnO nanoparticles have two peaks at 1034 cm'1and 500 cm'1corresponding to the stretching mode and the vibrational frequency. The peaks for ZnO-Cu3% are similar to ZnO nanoparticles because of the small amount of copper present. All the peaks present in GCN were observed in the GCN / 0.1ZnO-Cu3% nanocomposite. The peaks of ZnO-Cu3% were also observed in the nanocomposites but with reduced intensities which can be attributed to the small fraction in the GCN / 0.1ZnO-Cu3% structure.

[0076] Figure 5 shows the morphology of the synthesized samples by SEM analysis. The GCN shows the characteristic sheet-like and flake-like structure rather than a particle. This is typical of GCN synthesized from urea and it is indicative of high surface area. The ZnO and ZnO-Cu3% nanoparticles show spherical-like structures of different sizes. The GCN / 0.1ZnO-Cu3% shows the ZnO-Cu3% spherical-like structure embedded in the GCN sheet-like structure.

[0077] Figure 6 is the elemental compositions of the synthesized samples carried out using EDS analysis. The GCN shows the presence of C, N, and O peaks which are characteristic of GCN synthesized from urea. The presence of Zn and O were confirmed for ZnO while Zn, O, and Cu were confirmed for ZnO-Cu3%. The presence of C, N, O, Zn, and Cu was also confirmed for the GCN / 0.1ZnO-Cu3% nanocomposite.

[0078] Figure 7 is the BET surface area and the BJH pore size distribution of the synthesized samples. The BET isotherm (see Figure 7a) shows that the samples display type IV isotherm with an H3 hysteresis loop indicating a mesoporous structure. The BET surface area (see Table 3) shows that GCN / 0.1ZnO-Cu3% nanocomposite has the highest surface area which indicates its usefulness for photocatalytic activity since a high surface area corresponds to high catalytic activity. The BJH pore size distribution (see Figure 7b) indicates that the samples have pore sizes in the range of 1 nm - 10 nm. Nanoporous materials are between 0.2 nm - 1000 nm. Most of the pores can be seen to be in the mesoporous subsection of the nanoporous materials as shown in the table below.

[0079] Table 3. BET surface area, BJH pore volume, and BJH average pore size.Photocatalyst BET Surface Area BJH Pore Volume BJH Average Pore SizeGCN 57.17 0.06 4.15ZnO 5.18 0.01 4.41Zn0-Cu3% 4.26 0.01 5.80GCN / 0.1ZnO-Cu3% 121.00 0.12 4.02

[0080] Figure 8 is the absorption spectra (UV-Vis) and the bandgap of the synthesized photocatalysts. This shows the region of visible light in the electromagnetic spectrum where the samples can absorb light energy to bring about the photocatalytic activity. If the bandgap energy is less than 3.10 eV (with a corresponding wavelength greater than 400 nm), then the photocatalyst will be able to absorb visible light energy. Table 4 shows the bandgap energy and its corresponding wavelength. From the table, it shows thatGCN / 0.1ZnO-Cu3% with the lowest bandgap will absorb the highest visible light energy which is good for photocatalytic activity especially if the photocatalyst will be used in a visible light region just as would be demonstrated here in Figure 9 to 11.

[0081] Table 4. Bandgaps and the corresponding wavelengths of GCN nanosheets, ZnO and ZnO-Cu3% nanoparticles, and GCN / 0.1ZnO-Cu3% nanocompositePhotocatalyst Bandgap Energy Wavelength

[0082] Figure 9 illustrates the application of the synthesized GCN / 0.1ZnO-Cu3% nanocomposites and the comparison to other synthesized photocatalysts in the degradation of 4-chlorophenol (4-CP) under visible light irradiation. In the degradation of 4-chlorophenol, 80 mg of the photocatalyst was dispersed in 80 mL of deionized (DI) water containing 5 mg / L of 4-CP. The light source operating at a narrowband (A = 450m) in the blue region of the visible light spectrum was turned for irradiation whilst the dispersed mixture was continuously stirred on a magnetic stirrer for 120 minutes. The light intensity passing through the 80 mL solution was calculated to be 11.80 x 107photons / s using chemical actinometry. Control experiments were also conducted for the constituents of the nanocomposites which are GCN, ZnO, and ZnO-Cu3%. At regular intervals, samples were collected, filtered, and analyzed using high-performance liquid chromatography (HPLC) equipment. The result shows that the nanocomposite performed better than the other photocatalysts. This can be attributed to the synergistic effect of the GCN / 0.1ZnO-Cu3% nanocomposite as exhibited by large BET surface, 120.00 m2 / g (see Table 3, Figure 7) and enhanced bandgap, 2.60 eV (see Table 4, Figure 8). This large BET surface area and enhanced bandgap are the results of the novel facile synthesis process of the nanocomposite.

[0083] Figure 10 illustrates the practical application of the GCN / 0.1ZnO-Cu3% nanocomposites in the reusability and stability. The same experimental condition and process as explained in Figure 9 was used. Four cycles were conducted. Between each cycle, the photocatalyst was washed with DI water and dried at 70°C overnight in the oven to remove the water content before reuse. The result (see Figure 10a) shows that the overall reduction in performance was less than 10% between the 1st and the 4th cycles. Thestability test (see Figure 10b) did not show any obvious difference in peaks of the XRD patterns of the fresh and used nanocomposite, indicating that the nanocomposite is stable and can be reused for practical purposes.

[0084] Figure 11 illustrates the disinfection performance of the GCN / 0.1ZnO-Cu3% nanocomposites and other photocatalysts in disinfecting coliforms in wastewater primary influent under the same visible light source (A = 450 nm) used in Figures 9 and 10. In the disinfection experiment, 80 mg of the photocatalyst was dispersed in 80 mL of the wastewater primary influent and irradiated with visible light whilst continuously stirred on a magnetic stirrer for 360 minutes. The light intensity passing through the 80 mL dispersed mixture is the same as stated in Figure 9. Control experiments were also conducted for the light source and the constituent of the nanocomposites which are GCN, ZnO, and ZnO- Cu3% under visible light irradiation. At regular intervals, samples were collected and analyzed using the IDEXX proprietary procedure. The result shows that the nanocomposite could completely disinfect (complete 5.5-log reduction) the wastewater primary influent in 360 minutes. The initial cell density of total coliforms in the wastewater primary influent is estimated to be 2.8 x 105MPN / 100 mL (5.5 log).

[0085] Therefore, Figures 9 to 11 show that the GCN / 0.1ZnO-Cu3% nanocomposite synthesized using the novel synthesis method can be used to degrade organic contaminants such as 4-CP and disinfect wastewater in a solution form under visible light irradiation.

[0086] Another advantage of nanocomposites is that they can be used with other light sources than visible light sources such as UV-A, UV-B, UV-C, and sunlight since their bandgap (2.60 eV) indicates that they can absorb light energy greater than its bandgap energy. The light energy (photons) of UV-A, UV-B, and UV-C are greater than 2.60 eV. The ultraviolet (UV) region comprising UV-A, UV-B, and UV-C of the electromagnetic spectrum has light energy greater than 2.60 eV, usually in the range of 3.94 eV - 6.93 eV. Sunlight has about 4% UV component which can be utilized and absorbed by the nanocomposite. The use of different light sources indicates its indoor and outdoor practical applications.

[0087] Figure 12 shows the schematic diagram of the dip coating process of polyvinyl chloride (PVC) plastic substrate. Preceding the dip coating of the PVC substrate is the novel mixing of GCN / 0.1ZnO-Cu3% with solvents with unique ratios. 600 mg GCN / ZnO-Cu3% was added to 30 mg ethanol (absolute) and 10 mg water-based polyurethane in a vial to give a ratio of 20:1:0.3 based on ethanol. A water-based polyurethane with a brand name, Varathane was purchased from a local store in Calgary, Home Depot. Varathane is for woodapplication but adapted for this coating. Polyurethane (Pll) serves as both a dispersing agent and a binding agent for the nanocomposite photocatalyst. The Pll also binds the nanocomposite to the substrate after the evaporation of water and ethanol. The ethanol serves as a diluent to reduce the viscosity of the Pll and improve the flow of the mixture. The mixture was ultrasonicated for 2h. This prevents the aggregation of the nanocomposite particles and therefore further improves the dispersion in the solvents. The PVC substrates were cleaned first with ethanol (absolute) and then deionized (DI) water in an ultrasonic bath for 15 minutes each to remove dust particles and then dried in the air at room temperature. The prepared mixture was poured into a shallow beaker and the cleaned PVC substrates were dip-coated by dipping into the mixture for about 30 seconds and then gradually removed. This is to facilitate more deposition of the nanocomposite on the substrate. The dip coating was repeated 3 more times to give 4 layers of dip coating. This is to ensure total coverage of the PVC substrate with the nanocomposite. The coated PVC substrates were dried in the air at room temperature overnight for complete water and ethanol evaporation. The coatings were also carried out for GCN and Pll which are denoted coated PVC (GCN) and coated PVC (Pll) respectively and their self-disinfecting performances were compared to coatings with GCN / 0.1ZnO-Cu3% denoted as coated PVC (GCN / ZnO-Cu3%).

[0088] Figure 13 is the XRD patterns of the coated and uncoated PVC substrates. The uncoated PVC substrate shows a weak and broad peak at 110 planes and peaks at 200, 210, and 222 planes, indicating that PVC is of a semi-crystalline or amorphous structure. The coating of Pll on the PVC substrate did not show any obvious difference. However, the broadened weak peak at 110 planes observed in PVC was more pronounced in Pll and a small peak which can be attributed to the presence of Pll was observed at 111 planes. This indicates that the Pll has an amorphous structure. PVC and Pll have been reported to have amorphous structures because of the irregular arrangement of atoms in their structures. These irregular structures are reported to be caused by the presence of large molecules of Chlorine in the PVC structure and hydroxyl in the Pll structure, strong polar bonds, and strong intermolecular attraction forces. The coating of GCN on the PVC substrate shows that the weak peak of GCN at 100 planes was obscured by the presence of Pll in the GCN coating matrix. The GCN peak at 002 planes was observed to overlap that of PVC at 200 planes. The ZnO peaks were observed at 100, 002, 101 , and 102 planes on coated PVC (GCN / ZnO-Cu3%).

[0089] Figure 14 is the line graph illustrating the self-disinfecting performance of the coated PVC (GCN / ZnO-Cu3%) under visible light irradiation, 5000K light-emitting diode (5000K LED) at a visible light wavelength range of 400 - 700 nm. The distance of the light source to the substrate is 10cm giving an intensity of 16,800 Lux. The type of visible light source (5000K LED) is commonly used in industrial spaces such as factories, surgical rooms, and exam rooms where bright light is needed. For the experiment, 20 pL of wastewater primary influent was dropped on the coated PVC substrate using a pipette. The coated PVC substrate was placed in between microscopic slides. This is to ensure wider contact with the nanocomposite on the PVC substrate. The light was turned on for the next 180 minutes for irradiation. Control experiments were also conducted for the Coated PVC with polyurethane denoted as Coated PVC (PU), coated PVC with GCN and PU denoted as Coated PVC (GCN), and uncoated PVC under visible light irradiation. The coated PVC with GCN / ZnO-Cu3% has the PU binding agent included and is therefore denoted as Coated PVC (GCN / ZnO-Cu3%). Samples were taken and analyzed using the IDEXX proprietary procedure mentioned in Figure 11. The result shows that 2 log reduction (99%) of total coliforms in wastewater primary influent by the coated PVC substrate with GCN / ZnO-Cu3% nanocomposite in 180 minutes. The initial cell density of the total coliforms in the wastewater primary influent was estimated to be 1.91 x 106MPN / 100 mL (6.3 log).

[0090] Figure 15 shows the practical application of the coated PVC(GCN / ZnO-Cu3%) that showed the optimal self-disinfection of 2 log reduction (99%) in 180 minutes (see Figure 14) by reusing it after each disinfection process. The coated PVC substrate was thoroughly washed with DI water and then air dried at room temperature overnight before reuse. In Figure 15a, all 4 cycles show that the coated PVC (GCN / ZnO-Cu3%) could disinfect over 1 log (> 90%) of total coliforms in 180 minutes under 5000K LED irradiation. In 180 minutes, the first cycle which is the original self-disinfection of coated PVC (GCN / ZnO-Cu3%) showed a 2-log reduction (99%). The second, third, and fourth cycles show 97.3%, 96.4%, and 94.5% self-disinfection efficiencies respectively. Figure 15b describes the stability test by showing the XRD patterns of the used coated PVC (GCN / ZnO-Cu3%) after the fourth cycle and the fresh coated PVC (GCN / ZnO-Cu3%). There was no difference observed in the XRD peaks between the fresh and the used coated PVC (GCN / ZnO-Cu3%) indicating that the coating was stable. Therefore, the coated PVC (GCN / ZnO-Cu3%) can be used for practical purposes as a self-disinfection coating.

[0091] In the preceding description, for purposes of explanation, numerous details are set forth in order to provide a thorough understanding of the embodiments. However, it will be apparent to one skilled in the art that these specific details are not required. In other instances, well-known electrical structures and circuits are shown in block diagram form in order not to obscure the understanding. For example, specific details are not provided as to whether the embodiments described herein are implemented as a software routine, hardware circuit, firmware, or a combination thereof.

[0092] Embodiments of the disclosure can be represented as a computer program product stored in a machine-readable medium (also referred to as a computer-readable medium, a processor-readable medium, or a computer-usable medium having a computer- readable program code embodied therein). The machine-readable medium can be any suitable tangible, non-transitory medium, including magnetic, optical, or electrical storage medium including a diskette, compact disk read only memory (CD-ROM), memory device (volatile or non-volatile), or similar storage mechanism. The machine-readable medium can contain various sets of instructions, code sequences, configuration information, or other data, which, when executed, cause a processor to perform steps in a method according to an embodiment of the disclosure. Those of ordinary skill in the art will appreciate that other instructions and operations necessary to implement the described implementations can also be stored on the machine-readable medium. The instructions stored on the machine- readable medium can be executed by a processor or other suitable processing device, and can interface with circuitry to perform the described tasks.

[0093] The above-described embodiments are intended to be examples only. Alterations, modifications and variations can be effected to the particular embodiments by those of skill in the art. The scope of the claims should not be limited by the particular embodiments set forth herein, but should be construed in a manner consistent with the specification as a whole.

Claims

WHAT IS CLAIMED IS:

1. A method for forming a nanocomposite material comprising: dispersing graphitic carbon nitride (GCN) nanosheets in a solvent by ultrasonication to form a GCN nanosheet dispersion; adding zinc oxide-copper (ZnO-Cu) nanoparticles to the GCN nanosheet dispersion to form a GCN / ZnO-Cu mixture; co-exfoliating the GCN / ZnO-Cu mixture by ultrasonication and then calcination to form the nanocomposite material.

2. The method of claim 1 , wherein the solvent is ethanol.

3. The method of claim 1 or 2, further comprising the step of preparing the GCN nanosheets by calcinating urea.

4. The method of any one of claims 1 to 3, further comprising the step of preparing the ZnO-Cu nanoparticles by hydrothermal coprecipitation of a zinc salt and a copper salt.

5. The method of claim 4, wherein the zinc salt is zinc sulfate heptahydrate.

6. The method of claim 4, wherein the copper salt is copper II nitrate hemi pentahydrate.

7. The method of any one of claims 1 to 6, wherein the ZnO-Cu nanoparticles are between1% and 5% by weight copper.

8. The method of any one of claims 1 to 7, wherein the ratio of GCN nanosheets to ZnO- Cu nanoparticles in the GCN / ZnO-Cu mixture is between 10:1 and 2:1 .

9. A nanocomposite material obtained by the method according to any one of claims 1 to 8.

10. An article comprising the nanocomposite material of claim 9.

11. A method for coating an article in the nanocomposite material of claim 9, the method comprising: dispersing the nanocomposite material in a solvent by ultrasonication to form a nanocomposite material dispersion; and dipping the article in the nanocomposite material dispersion to form a coated article.

12. The method of claim 11 , wherein the solvent is a mixture of water-based polyurethane and ethanol.

13. The method of claim 11 or 12, wherein the ratio of nanocomposite material to solvent is about 20:1.

14. The method of any one of claims 11 to 13, wherein the article is made of polyvinylchloride (PVC).

15. A coated article obtained by the method according to any one of claims 11 to 14.

16. Use of the article according to claim 10 or 15 in wastewater treatment.

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