FIELD OF THE INVENTION Chemistry related to metal oxide nanofiber and nanofibrous membrane catalyst with flexibility, stability and fabrication ability.

DISCLOSURE OF THE INVENTION

This invention is the development of rioble-metals decorated titanium dioxide and zinc tungstein oxide nanofibers and nanofibrous membranes which are flexible, stable and could be easily fabricated and active under visible, UV and sunlight. The described nanofibers and nanofibrous membrane are different from the others nanofibers and nanofibrous membrane in terms of photocatalyst composition, multifunction properties, high strength and flexibility. The described high surface area and porosity nanofibers can be fabricated by solution-based processing from both of needle-based electrospinning, nanospider electrospinning and forced/centrifuge spinning.

BACKGROUND OF THE INVENTION

Airborne pollutants in the environment from volatile organic compounds (VOCs) are mainly generated from engine combustion in vehicles, so development of new technologies for VOCs elimination is a crucial issue in the present situation. One of interesting VOCs elimination technologies is photocatalysis which utilizes light as an activating energy source. Generally, the photocatalysis reaction requires light for redox reaction of organic molecules suitable for unspecified organic decomposition.

The photocatalytic reaction can occur in both of liquid and gas phases, so the technology is very versatile and has wide range of applications. In addition, many advantages of the technology support the high potential of industrial scale production such as self-cleaning property, cheap material arid low maintainance cost. However, most of photocatalytic meterials required high activation energy which can be found mainly in UV light because the catalyst has large band gap that cannot be governed by visible light. So, this drawback may limit the industrial scale application of this technology. Moreover, shape and size of catalysts play an important role in the organic decomposition efficiency due to the photocatalysis reaction occurs mainly at the surface of catalysts. From this reason, nanophotocatalysts may be the most suitable materials due to their high surface area. However, they suffer from agglomolation and recyclability efficiency. On the other hand, film photocatalysts can be recycled easily but it has limited surface area that results in low organic decomposition efficiency. Nanofibers can overcome both of disadvantages inherent to nanoparticles and film materials with their high surface area, recyclability and non-agglomoration materials.

Apart from organic pollutant decomposition, the photocatalysts must inherit antibacterial property in order to widen the range of application. For water pollutant decomposition, one of the crucial drawbacks of using photocatalyst in liquid phase is the recovery process. One of the recovery processes is centrifugation method. The method is very effective in lab scale application but the industrial production and application are costly. In conclusion, application of nanomaterials suffers from filtration process while film metrials have a drawback in low surface area. On the other hand, photocatalyst materials from nanofibers can overcome both of problems in terms of recyclability and high surface area.

Normally, nanoparticle synthetic method requires high cost and non- environmentally friendly processing such as high temperature or vacuum system. This may result in increase in the production cost and time consumption.

Wastewater treatment requires an appropriate method by employing catalyst as main composition. The photocatalysis is one of the most promising processes due to its catalyts chemical composition are low cost and able to use the natural sunlight to catalyze the reaction. However, the photocatalysts have two main drawbacks which are limited region of catalyze light and high fragility.

This invention relates to the fabrication of noble metals decorated titanium dioxide and zinc tungstein oxide nanofibers and nanofibrous membrane. The described nanofibers and nanofibrous membranes are stable, flexible, easily fabricated and able to work under visible, UV and natural sunlight. This invention is fabricated from specific combinations that are difference from the others fabrication methods in terms of chemical composition and stability of the metal oxide nanofibers membrane.

From the literature and patent review, no record is found to be similar to this invention as shown below; International Journal of Hydrogen Energy Volume: 40 Pages: 4558-4566 Enhanced photocatalytic activity of palladium decorated Ti0 ₂ nanofibers containing anatase-rutile mixed phase. The literature concerned the synthesis of palladium decorated titanium dioxide nanofibers by autoclave and calcination. The output is a catalyst for hydrogenation and organic dye degradation reaction. This is different from the current invention in terms of composition of metal oxide materials. In addition, the literature does not mention the metal oxide nanofibrous membrane stability development.

Journal of Alloys and Compounds Volume: 432 Pages: 269-276 ZnW0 ₄ photocatalyst with high activity for degradation of organic contaminants. The literature concerned the zinc tungstein oxide synthesis method by hydrothermal process and annealing treatment. The output was the catalyst for formaldehyde degradation in gas phase which had different processing method and metal oxide composition from this patent. In addition, the literature did not mention the metal oxide nanofibrous membrane stability development.

Materials Letters Volume: 61 Pages: composite

nanofilms: Preparation, morphology, structure and photoluminescent enhancement. The literature concerned the synthesis of titanuium dioxide and zinc tungstein oxide by dip- coating method on the glass substrate that had different synthesis process from this patent. In addition, the literature did not mention the metal oxide nanofibrous membrane stability development.

Patent number US20070202334A1 in the topic of "Nanoparticles containing titanium oxide". This patent concerned the synthesis of titanium dioxide nanoparticles in anatase crystal structure at diameter less than 200 nm. In addition, this patent also concerned the metal doping on the nanofibers surface in form of nanosphere by autoclave technique which had different synthesis method and composition from this patent. In addition, the literature did not mention the metal oxide nanofibrous membrane stability development.

Patent number US201 10192789A1 in a topic of "Metal or metal oxide deposited fibrous materials". This patent concerned the embedding on metal oxide and metal nanoparticles on the porous substrate by electrospray technique which had different systhesis method and composition from this patent. In addition, the literature did not mention the metal oxide nanofibrous membrane stability development. Patent number US20110151255A1 in a topic of "Nanofiber and preparation method thereof. This patent concerned the nanofibers fabrication method by electrospinning. The electropsining solution was a mixture between polymer and metal complex oxide. The output was the thermal resistant and stable nanofibers which were different from this patent in terms of stable metal oxide nanofibrous membrane fabrication and chemical compositions.

In conclusion, no literature or patent represented the same material processing or chemical compositions. This invention concerned the fabrication of noble-metal decorated titanium dioxide and zinc tungstein oxide nanofibers and nanofibrous membrane. The described nanofibers and nanofibrous membranes were flexible, stable and could be easily fabicated and able to work under visble, UV and sunlight. This invention was fabricated from the specific compositions which was different from the others fabrication methods in terms of chemical composition and stability of the metal oxide nanofibers membrane. FIGURE CAPTIONS:

Figrue 1 Pictures of nanofiber' s chemical and physical characters before and after calcination whereas:

a) Physical characteristics of nanofibers after fabrication from ammonium metatungstate hydrate and zinc acetate hydrate in water and ethanol solution.

b) Physical characteristics of nanofibers after fabrication from ammonium metatungstate hydrate, zinc acetate hydrate and titanium dioxide nanoparticels (P- 25) in water and ethanol solution,

c) Physical characteristics of nanofibers from (b) after calcination results in non- homogenious nanofibers.

d) Area from nanofibers (c) showing particles agglomeration.

e) Physical characteristics of nanofibers after fabrication from ammonium metatungstate hydrate, zinc acetate hydrate and titanium iospropoxide in water and ethanol solution.

f) Physical characteristics of nanofibers from (e) after calcination at 500 °C. Figure 2 Pictures of nanofibers which composed of ammonium metatungstate hydrate, zinc acetate and titanium isopropoxide in dimethyl formamide before and after calcination at 500 °C whereas: a) Physical characteristics of nanofibers after fabrication from ammonium metatungstate hydrate, zinc acetate hydrate and titanium isopropoxide in DMF solution.

b) Physical characteristics of nanofibers from (a) after calcination at 500 °C.

c) EDX spectrum showed tungstein, zinc and titanium composition in nanofibers. d) XRD spretrum showed crystallinity of tungstein, zinc and titanium in nanofibers.

Figure 3 Pictures of nanofibers which composed of ammonium metatungstate hydrate, zinc acetate and titanium isopropoxide in dimethyl formamide before and after calcination at 600 and 700 °C whereas:

a) Physical characteristics of nanofibers after fabrication from ammonium metatungstate hydrate, zinc acetate hydrate and titanium isopropoxide in DMF solution and calcination at 600 °C.

b) Physical characteristics of nanofibers after fabrication from ammonium metatungstate hydrate, zinc acetate hydrate and titanium isopropoxide in DMF solution and calcination at 700 °C.

c) Size of zinc tungsten oxide nanorod.

d) D-spacing of zinc tungsten oxide nanorod from (c).

e) EDX spectrum showed tungsten, zinc and titanium composition in nanofibers. f) XRD spretrum showed crystallinity of tungsten, zinc and titanium in nanofibers while zinc and tungsten complexes were in form of zinc tungstein oxide (ZnW0 ₄ ).

Figure 4 Pictures of variety of nanofibrous membrane after calcination whereas:

a) Nanofibers after fabrication by solution in example 4b (Before calcination).

b) Nanofibers after fabrication by solution in example 4b (After calcination).

c) Nanofibers after fabrication by solution in example 4b (Before calcination).

d) Nanofibers after fabrication by solution in example 4b (After annealing at 100 °C and calcination at 600 °C).

e) Nanofibers after fabrication by solution in example 4b (Before calcination).

f) Nanofibers after fabrication by solution in example 4b (After annealing at 200 °C and calcination at 600 °C).

g) Nanofibers after fabrication by solution in example 4b (Before calcination).

h) Nanofibers after fabrication by solution in example 4b (After annealing at 100 °C and calcination at 600 °C with fiber glass sandwich). i) Nanofibers after fabrication by solution in example 4b (Before calcination).

j) Nanofibers after fabrication by solution in example 4b (After annealing at 200 °C and calcination at 600 °C with fiber glass sandwich),

k) Nanofibers after fabrication by solution in example 4b (Before calcination with fiber glass confinement within a beaker).

1) Nanofibers after fabrication by solution in example 4b (After annealing at 200 °C and calcination at 600 °C with fiber glass confinement within a beaker), m) Nanofibers after fabrication by solution in example 4b (Before calcination with fiber glass confinement in a pleating shape).

n) Nanofibers after fabrication by solution in example 4b (After annealing at 200 °C and calcination at 600 °C with fiber glass confinement in a pleating shape).

Figure 5 Pictures of nanofibrous membrane after calcination via SEM and TEM whereas: a) Nanofibrous membrane after calcination by fiberglass confinement process which showed freely weaving nanofibers.

b) Nanofibrous membrane (Figure 41) after calcination by glassslides confinement process which showed weaving nanofibers.

c) High magnification of figure Sa showed freely weaving nanofibers which result in stable and flexible nanofibers.

d) High magnification of figure Sb showed confined nanofibers which result in high fragility of nanofibrous membrane.

Figure 6 Pictures of metal oxide nanofibers after metal deposition process whereas:

a) Physical charcteristics of nanofibers after photoreduction under UV light.

b) Physical charcteristics of nanofibers after photoreduction under visible light.

c) Physical charcteristics of nanofibers after photoreduction under natural sunlight. d) EDX spectrum showed palladium and platinum content on the nanofibers after photoreduction reaction udner UV light.

e) TEM image of nanoparticles attached on the ZnW0 ₄ nanorod.

f) TEM image of palladium nanoparticles on the ZnW0 ₄ nanorod.

g) TEM image of nanoparticles attached on the ZnW0 ₄ nanorod.

h) TEM image of platinum nanoparticles on the ZnW0 ₄ nanorod. Figure 7 Graph of photocatalytic activity of nanofibers against methylene blue concentration under natural sunlight whereas;

Figure 8 Pictures of benzene/methanol decomposition reaction whereas:

a) Benzene/methanol decomposition reaction under visible light (From left to right)

First bottle is 500 ppm benzene (control).

Second bottle is 500 ppm benzene with W0 ₃ nanofibers.

Third bottle is 500 ppm benzene with Ti0 ₂ -ZnW0 ₄ nanofibers.

Fourth bottle is 500 ppm benzene with Pd/Pt-Ti0 ₂ -ZnW0 ₄ . b) HPLC spectrum of benzene decomposition efficiency by TiOa-ZnWCU nanofibers. c) HPLC spectrum of benzene decomposition efficiency by noble-metal decorated nanofibers showed an evidence of ethanol oxidation peak at 6.442.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to the development of stable and as-designed metal oxides photocatalytic nanofibers that composed of titanium dioxide and zinc tungsten oxide as a main composition of the nanofibers with zinc tungsten oxide nanorods on the nanofibers' surface. In addition, the surface of nanofibers and zinc tungsten oxide nanorods were decorated by noble metal nanoparticles in a form of single layer deposition.

The photocatalytic nanofibers consisted of two main metal oxide compositions, titanium dioxide and zinc tungstein oxide, with an average diameter of 100-200 nanometers. The titanium dioxide crystallinity composed of two mixed phases of anatase and rutile forms. During the calcination process, the ratio of anatase form was favorably created with respect to rutile form. It reported in literature that anatase crystal performed better photocatalytic activity under UV light than rutile crystal. On the other hand, the zinc tungstein oxide was sanmatinite. Apart from the main metal oxide components, zinc tungstein oxide nanorods (30-50 nanometers) were found on the surface of nanofibers.

The nanofibers according to this invention were decorated with noble metal nanoparticles via photodeposition process under UV, visible or natural sunlight activationhat was facile, cost effective and highly efficienct. After photodeposition process, noble metal nanoparticles on the nanofibers' surface were observed with diameter of 1-15 nanometers. The noble metal nanoparticles for this invention could be selected from palladium, platinum, silver, gold, rhodium, eridium, ruthenium, osmium, tantalum, titanium or mixture of these metals.

The nanofibers according to this invention can be applied in variety of applications because the nanofibers inherited high thermal resistance could be easily fabricated into a flexible and stable nanofibrous membrane. The characteristics of the membrane related to its flexibility was the ability to be conformed into a bending shape. Apart from its flexibility, the membrane was able to tolerate high temperature in a rage of 500-900 °C. From the described properties of metal oxide nanofibers and nanofibrous membrane, promising applications of this membrane could be a catalytic converter within vehicles for purifying the combustion by-product gases such as benzene, toluene or nitrous oxide. Aprat from air purication application, the nanofibers and nanofibrous membrane could be applied for waste water purification as well.

When comparing the metal oxide nanofibers in this invention and conventional metal oxide nanofibers, WO ₃ nanofibers inherited high porosity within the nanofibers which unaviodibly constituted as the main reason for high fragility. However, Ti0 ₂ - ZnW0 ₄ nanofibers from this invention inherited high flexibility and stable physical character in comparison with others metal oxides. Consequently, the Ti0 ₂ -ZnW0 ₄ nanofibers can overcome the inherent drawback of metal oxide nanfibers and could be fabricated into stable metal oxide membranes.

The fabrication process of noble-metals decorated nanofibers and nanofibrous membrane containing titanium dioxide, zinc tungstein oxide and zinc tungstein oxide nanorod according to this invention composed of;

a) A funtional polymer solution was first formulated by dissolving a functional polymer in ethanol in a ratio of 0.1-40: 0.1-40 at room temperature for 30 minutes. The functional polymers could be selected from the polymers with functional groups along their hydrocarbon backbone such as hydroxy group, amine group or carboxylic acide group, represnting polyacrylonitrile, polyvinylpyrrolidone, polyvinylalcohol, polyhydroxypropyl methacrylate, polyhydroxyethyl methacrylate, polyglycerol methacrylate or mixture of these functional polymers. Then the functionl polymer solution was mixed with at least 3 metal complexes such as titanium, tungsten and zinc complexes in organic solvents. The metal complex solution could be prepared by dissolving the respective metal complex in a solvent in a ratio of 0.1-40: 0.1-40 under room temperature for 10 minutes. The mixing process started from adding tungsten complex solution into the functional polymer solution before adding the zinc and titanium complex solution in to the mixture respectively under magnetic stirring for 30 minutes. The metal components in the metal complex solution could be selected from titanium, palladium, platinum, silver, gold, zinc, copper, iron, tungsten or mixture of these elements.

b) The solution from a) was mixed with concentrated acid selected from acetic acid, sulfuric acid, hydrochloric acid, or mixture of these acids, in a ratio of 0.1- 30: 0.1-30 by weight.

c) The solution form b) was fabricated into nanofibers by needle-based electrospinning, nanospider electrospinning or forced/centrifuge spinning.

d) The nanofibrous membrane from c) was processed into a metal oxide nanofibrous membrane by annealing and calcination process (AC process) under non-confinement, fiberglass or glass slide confinement. The calcination temperature could be selected from 100-900 °C for 1-24 hours.

e) The nanofibers from c) or metal oxide nanofibers from d) were decorated by noble metal nanoparticles via photodeposition process under visible, UV or sunlight for 1-24 hours.

f) The nanofibers or nanofibrous membrane from e) were washed and dried.

The organic solvent in a) could be selected from methyl alcohol, ethyl alcohol, dichloromethane, dimethylformamide, dimethylsulfoxide, chloroform or toluene. However, the most suitable solvent was dimethylformamide.

In the next section, the invention was described but not limited to the examples given. EXAMPLES

The proper composition development of the electrospinning solution for nanofiber fabrication

This section studied the development of proper composition of the solution by mixing the desired metal complex solution then study the stability after mixing (Example 1-4).

Example 1: Fabrication of nanofibers from tungsten and zinc complex in water and ethanol mixture

Because titanium dioxide nanoparticles (P-25) was soluble in water or ethanol, the primary study of nanofiber fabrication containing ammonium metatungstate hydrate and zinc acetate hydrate was performed prior to addition of P-25 into the solution mixture.

Precursor solution preparation and nanofiber fabrication:

a) Polyvinylpyrroridone (PVP) solution (PVP:Ethanol in a ratio of 1:10 by weight) was mixed with the ammonium metatungstate hydrate (AMT) complex solution (AMT: Water in a ratio of 1:10 by weight) and zinc acetate hydrate (ZAH) complex solution (ZAH:Water in a ratio of 1:10 by weight)

b) The solution from a) was fabricated into nanofibrous membrane via nanospider machine by applying the electrode-to-ground distance of 18 cm, voltage at 40 kV and electrode's rotating speed of 8 rpm.

c) The nanofibrous membrane from b) was characterized.

Result: The solution mixture containing AMT and ZAH complex solution was stable and able to fabricate into a homogeneous nanofibers (Figure la)

Example 2: Fabrication of nanofibers from tungsten complex, zinc complex and titanium dioxide nanoparticles in water and ethanol mixture

This example was experimented in order to study the stability and physical characteristics of nanofibers after mixing the titanium dioxide nanoparticles into the AMT and ZAH complex solution.

Precursor solution preparation and nanofiber fabrication:

a) Polyvinylpyrroridone (PVP) solution (PVP:Ethanol in a ratio of 1:10 by weight) was mixed with the ammonium metatungstate hydrate (AMT) complex solution (AMT: Water in a ratio of 1:10 by weight), zinc acetate hydrate (ZAH) complex solution (ZAH: Water in a ratio of 1:10 by weight) and titanium dioxide nanoparticles (P-25: PVP solution in a ratio of 1:10) under magnetic stirring for 30-60 minutes.

b) The solution from a) was fabricated into nanofibrous membrane via nanospider machine by applying the electrode-to-ground distance of 18 cm, voltage at 40 kV and electrode's rotating speed of 8 rpm.

c) The nanofibers from b) was calcined under atmospheric pressure at 500 °C for 4 hours in order to decompose the carbon content within the nanofibers prior to further characterization for stability and physical characteristics of the resulting metal oxide nanofibers.

Result: The nanofibers' surface appeared rough (Figure lb) possibly due to low solubility of P-25 that resulted in particle agglomeration along the AMT and ZAH nanofibers.

After calcination, the nanofibers showed high degree of fragility (Figure lc) with non-homcigeneous fibrous structure as some of their parts contained aggregates of P-25 (Figure Id).

From this example, it could be concluded that addition of P-25 into the solution mixture interupted the solution stability and affected the nanofibers' formation during calcination which made the resulting materials unsuitable for further usage.

Example 3: Fabrication of nanofibers from tungsten complex, zinc complex and titanium isopropoxide solution in water and ethanol mixture.

This example was experimented in order to study the stability and physical character of nanofibers after using titanium isopropoxide instead of P-25.

Nanofibers fabrication process containing;

a) Polyvinylpyrroridone (PVP) solution (PVP:Ethanol in a ratio of 1:10 by weight) was mixed with the ammonium metatungstate hydrate (AMT) complex solution (AMT: Water in a ratio of 1:10 by weight), zinc acetate hydrate (ZAH) complex solution (ZAH: Water in a ratio of 1:10 by weight) and titanium isopropoxide

(TIP) solution (TIP: PVP solution in a ratio of 1:5) respectively. b) The solution from a) was fabricated into nanofibrous membrane via nanospider machine by applying the electrode-to-ground distance of 18 cm, voltage at 40 kV and electrode's rotating speed of 8 rpm.

c) The nanofibers from b) was calcined under atmospheric pressure at 500 °C for 4 hours in order to decompose the carbon content within the nanofibers prior to further characterization for stability and physical characteristics of the resulting metal oxide nanofibers.

Result: After addition of TIP solution into the AMT and ZAH complex solution, ΉΡ aggregated into white solid particles that made the solution inhomogeneus.

After fabrication, the nanofibers were unusable and unable to be fabricated into membranes because the solid parts in the solution disrupted the electrospinning process (Figure le). Subsequently, rough aggregated particles were found after the calcination process and no trace of nanofibers were found (Picture If).

Example 4: Fabrication of nanofibers from tungsten complex, zinc complex and titanium isopropoxide in dimethylformamide.

This example was experimented in order to study the stability and physical characteristics of nanofibers after using dimethylformamide (DMF) as a solvent that could dissolve AMT, ZAH and ΉΡ solution. Firstly, the water was removed from the system as it could induce ΉΡ aggregation. However, using sole ethanol solvent was insufficient to dissolve zinc acetate. As additional organic solvent was needed, DMF was selected.

Nanofibers fabrication process containing;

a) Polyvinylpyrroridone (PVP) solution (PVP:Ethanol in a ratio of 1:10 by weight) was mixed with ammonium metatungstate hydrate (AMT) complex solution (AMT: DMF in a ratio of 1:10 by weight), zinc acetate hydrate (ZAH) complex solution (ZAH:DMF in a ratio of 1:10 by weight) and titanium isopropoxide (ΉΡ) solution (TIP: PVP solution in a ratio of 1:5), respectively.

b) Concentrated acetic acid was added into the solution from a) in a ratio of 1:5. c) The solution from b) was fabricated into nanofibrous membrane via nanospider machine by applying the electrode-to-ground distance of 18 cm, voltage at 40 kV and electrode's rotating speed of 8 rpm.

d) The nanofibers from c) were calcined under atmospheric pressure at designated temperature for 4 hours whereas:

500 °C (Example 4a). 600 °C (Example 4b).

700 °C (Example 4c).

e) The metal oxide nanofibrous membranes designated as examples 4a, 4b and 4c were characterized. Result: All three chemical compositions, AMT, ZAH and ΉΡ, were able to dissolve together in ethanol and DMF mixture. After the fabrication, nanofibers ^* characteristics was shown to be homogeneous (Figure 2a).

Example 4a: After calcination at 500 °C, the nanofibers' characteristics was shown to be similar to their before calcination (Figure 2b). The EDX analysis proved the existence of tungstein, zinc and titanium within the nanofibers (Figure 2c). From

X-ray diffaractometer (XRD) analysis, it was found that the majority of titanium crystal structure was in form of anatase with minority in rutile form. In addition, the signals representing tungsten and zinc elements were insignificant (Figure 2d). Example 4b: After increasing the calcination temperature to 600 °C and using the same solution from example 4a, a rod-like structure stemmed out of the nanofibers surface (Figure 3a). From particle investigation by Transmittion Electron Microscopy (TEM) (Figure 3c), d-spacing values implied that the rod-like structure might be zinc tungstein oxide (Figure 3d). In addition, EDX analysis confirmed the existence of all expected elements similar to those of the sample from 500 °C calcination (Figure 3e).

From XRD, the majority of titanium crystal was in form of anatase with minority in rutile. In addition, the footprint of tungsten and zinc compartments showed higher intensity in comparison with those from example 4a. After comparing the signal with a reference from database, the existence of ZnW0 ₄ (Figure 3f) was confirmed.

Example 4c: After calcination at 700 °C, the physical and chemical characteristics of the nanofibers was similared to that of the example 4b (Figure 3b). However, the sample showed lower amount of anatase crystal than the amount of rutile crystal. Among the examples 2-4, example 4 (4a-4c) was the most homogeneous and physically stable nanofiber. Furthermore, example 4b was selected out of the 3 examples for subsequent noble metal deposition process because it inherited large fraction of anatase crystal structure that had excellent photocatalytic activity.

In conclusion, the example 4b was selected for noble metal deposition process and increasing the nanofibers stability in the next example. Nanofibrous membrane stability enhancment process for industrial scale application

This section studied the development of nanofibrous membrane stability and flexibility which was inspired by the fact that metal oxide nanofibers' fragility could mpede industrial fabrication and further development. Incidently, after calcination of example 4b at 600 °C, the resulted metal oxide nanofibrous membrane (MONM) was drastically distorted and fragmented (Figure 4b), vastly different from the nanofibrous membrane before calcination (Picture 4a). From this observation, it could be hypothesized hat the rapid degradation of polymer during the calcination process was the main reason of unstable metal oxide membrane.

The following study focused on the development of structural stability from example 4b during calcination as this could be the most suitable sample for producing the most stable metal oxide nanofibers. The development focused on the calcination processhat completely transformed that nanofibers into complete metal oxide.

Example 5: Fabrication of nanofibrous membrane from tungsten complex, zinc complex and titanium isopropoxide in dimethylformamide by multiple annealing steps prior to calcianation.

The fabrication process here was similar to that for example 4b but with an annealing step for an hour at the lower temperature than Tg of the containing polymer (100 °C) or at the temperature higher than Tg of the polymer (200 °C), before calcination at 600 °C for 4 hours whereas:

Example 5a: Non-confinement nanofibrous membrane during annealing and calcination processes (AC processes) at 100 °C and 600 °C.

Example 5b: Non-confinement nanofibrous membrane during annealing and calcination processes (AC processes) at 200 °C and 600 °C.

Example 5c: Fiberglass-confinement nanofibrous membrane in a flat sandwich during annealing and calcination processes (AC processes) at 100 °C and 600 °C. Example 5d: Fiberglass-confinement nanofibrous membrane in a flat sandwich during annealing and calcination processes (AC processes) at 200 °C and 600 °C.

Example 5e: Glass-slide confinement nanofibrous membrane in a flat sandwich during annealing and calcination processes (AC processes) at 200 °C and 600 °C.

Example Sf: Fiberglass-confinement nanofibrous membrane in a bending shape. Example 5g: Fiberglass confinement nanofibrous membrane in a curvy shape.

Result:

Example 5a: The MONM after calcination showed deflection in a low degree at the edge of the membrane (Figure 4d) which could be compared with the nanofibrous membrane before calcination (Figure 4c).

Example 5b: The MONM after calcination was similar to the example 5a

(Annealing at 100 °C) in terms of deflection observation at the edge of the membrane (Figure 4f) which could be compared with the nanofibrous membrane before calcination (Figure 4e).

From the examples 5a and 5b, the additional annealing process could reduce the degree deflection in MONM but was unable to completely overcome the membrane's physical instability.

Example 5c: The MONM's surface after calcination appeared flat with no fragments observed (Figure 4h). In addition, the membrane's size was decreased at

71.43% rate with respect to the one before calcination (Figure 4g).

Example 5d: The MONM after calcination was similar to the example 5c but the memebrane's surface changed from flat (Figure 4j) to rough stucture (Figure 4i). The membrane's size was decreased at 68.83% rate, suggesting more physical stability than that of example 5d.

From the examples 5c and 5d, the combination between AC processes and structural confinement by fiberglass resulted in a more stable MONM (Figures 5a and 5c).

Example 5e: The nanofibrous membrane gave smooth surfaces both before (Figure

4k) and after calcianation (Figure 41). However, the membrane after calcination was so fragile that it was fragmented and could be picked up as a whole piece. From the example 5e, it could be concluded that using fiberglass for confinement was better than glass slides (Figure 5b and 5d).

Example 5f: The flexibility of nanofibrous membrane upon calcination was studied by using a pair of fiberglasses for membrane confinement curved along the interior of a beaker (Figure 4m). It was found that the process could maintain the shape of MONM as desired (Figure 4n).

Example 5g: The flexibility of nanofibrous membrane upon calcination was also studied by wrapping the nanofibrous membrane among stacking layers of fiberglasses (Figure 4o) before calcination in the same condition as that for the example Sf . It was found that, after calcination, the membrane was very stable and no cracking was observed upon bending with such a small angle (Figure 4p).

Noble-metal photodeposition on metal oxide nanofibrous membrane

The objective of this study was to improve the metal oxide nanofiber's photocatalytic activity against activation by visible light and sunlight. The development of noble-metal decorated metal oxide nanofiber could be done by doping noble metals such as palladium and platinum on the surface.

Example 4b was selected for this noble metal doping by photodeposition process under UV, visible and natural sunlight.

Example 6: Noble-metal decoration on nanofibers under UV, visible and natural sunlight

Noble-metal decoration on nanofibers was processed as below:

a) Palladium (II) nitrate hydrate and hydrogen hexachloroplatinate (IV) metal complex solution preparation process:

In the first beaker, palladium (II) nitrate hydrate was added into water in a ratio of 0.00167: 10 (By weight percentage) under magnetic stirring for 10 minutes.

In the second beaker, hydrogen hexachloroplatinate (IV) was added into water in a ratio of 0.005: 10 (By weight percentage) under magnetic stirring for 10 minutes.

b) Two solutions from a) were mixed before adding the nanofibers of example 5d under irradiation of various light sources for an hour, whereas:

Under UV light (Example 6a). Under visible light (Example 6b).

Under sunlight (Example 6c).

c) The nanofibers from 6a-6c were washed and dried.

d) The nanofibers from c) and the deposited noble metal nanoparticles were characterized.

Result:

Example 6a: The reduction of palladium and platinum ions and nucleation of the respective metal on the metal oxide nanofibers under UV light were controlled by the distance between the light source and solution. After the reaction, the resulted nanofibers' characteristics was similar to that of the nanofibers before the reaction. However, the nanofibers' averaged diameter was increased (Figure 6a). From EDX, both palladium and platinum elements were found on the nanofibers' surface (Figure 6d).

Example 6b: A similar photoreduction reaction was performed with visible light. After the reaction, the nanofibers' characteristics was similar to that of the example 6a (Figure 6b). In addition, EDX analysis revealed both palladium and platinum elements on the surface as well.

Example 6c: The photoreduction reaction was performed under natural sunlight with light intensity recorded duing the experiment. After the reaction, the nanofibers' averaged diameter was increased and more metal elements were observed on the surface than those on example 6a and 6b (Figure 6c) as revealed by EDX analysis.

Metal nanoparticles deposited on the metal oxide nanofibers could then be characterized by TEM. It was found that the metal nanoparticles were dispered homogeneously on titanium dioxide and zinc tungsten oxide (Figure 6e). The sizes of palladium nanoparticles were reported to be in between 1-15 nanometers after analyzing the d-spacing of particles (Figure 6f). Platinum nanoparticles on zinc tungsten oxide (Figure 6g) were observed to be smaller than 3 nanometers under TEM (Figure 6h).

From the results on example 6, it could be seen that effective photoreduction reaction could be done under visible, UV and sunlight. In conclusion, the best example and the most proper process for future scale-up was example 6c because the respective photoreaction was successfully done under natural sunlight (free energy) and more facile than those for examples 6a and 6b.

Photocatalytic decomposition of model pollutant by nanofibrous membrane

The pollutant decomposition effieciency was measured against photocatalytic degradation of methylene blue (MB) as a model pollutant. Firstly, 10 mg of nanofibers was suspended in 500 ppm MB solution under natural sunlight (Figure 7).

In the experiment, two types of nanofibers, Ti0 ₂ -ZnW0 ₄ and Pd/Pt-Ti0 ₂ -ZnW0 ₄ , were separately used as photocatalysts for efficiency comparison. An MB solution without any catalyst was also Used as a reference.

Result: Both nanofibers showed high MB degradation efficiency. For Pd/Pt-Ti0 ₂ - nanofibers, the highest MB degradation rates took place in the first two hours (Figure 7).

The nanofibrous membranes' catalytic activities were evaluated against gaseous

500-ppm benzene (Volatile organic compounds, VOCs). The experiment was performed by using 0.1 g of nanofibers to treat the 500-ppm benzene under visible light for 4 hours

(Fixing the distance between the suspension and ligh bulb at 10 cm) (Figure 8a). After the reaction, the concentration of decomposed benzene was evaluated by gas chromatography

(GC).

Result: Benzene concentration analysis was peroformed by calculating the peak area of decomposed benzene in comparison with the control gas. From the analysis, the W0 ₃ nanofibers which was used as a reference catalyst showed no benzene degradation efficiency, while nanofibers led to 37% benzene degradation efficiency (Table 1).

Apart from benzene degradation reaction, the Pd/Pt-TiCVZnWC^ nanofibers were further utilized for oxidative methanol transformation into methyl formate. After the reaction, GC peak at 6.442 appeared and was confirmed to be that of methyl formate as referenced with the GC database (Figure 8b and 8c). Table 1 Benzene degradation efficiency of nanofibers