Name: preparation of polyoxometalate-based photo-responsive membranes for the photo-activation of manganese oxide catalysts
Uploaded: 2018-08-07T14:30:00
Description: Watch this Scientific Journal Video about Preparation of Polyoxometalate-based Photo-responsive Membranes for the Photo-activation of Manganese Oxide Catalysts at JoVE.com

A. Y. received financial support from the Global Center of Excellence for Mechanical Systems Innovation program of the University of Tokyo and from the University Tokyo Grant for Ph.D. Research. This work is partly supported by JSPS KAKENHI Grant-in-Aid for Young Scientists (B) (17K17718).

It is advisable to refer to all relevant material safety data sheets (MSDS) prior to using chemicals, as some used in these syntheses are highly acidic and corrosive. In addition, one polymer used in this work (polyacrylamide) may contain the carcinogenic monomer, acrylamide. The use of personal protective equipment (safety glasses, gloves, lab coat, full-length pants, closed-toe shoes) is required to prevent injuries from chemicals or heat. After conducting the cross-linking process, membrane samples should be stored in...

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It is critical to apply the cross-linking method introduced by Helen et al.14 to develop a self-standing membrane. When polyvinyl acetate was applied as the base polymer in this study, aggregation of H3PW12O40 occurred, which prevented formation of the self-standing membrane. However, when fabrication of the membrane was attempted utilizing Nafion as the base polymer, there was no progression of the reaction with Ce3+ and Co2+, althou...

The development of solar energy conversion systems using artificial photosynthesis or solar cells is necessary to enable the provision of alternative energy sources that can ameliorate global climate and energy issues1,2,3,4. Photo-functional materials can be broadly categorized into two groups, semiconductor-based systems and organic molecule-based systems. Although many different system types have been developed, improvements still need to be made because semiconductor systems suffer from a lack of precise charge transfer control, and organic molecule systems are not adequately durable with respect to photo-irradiation. However, the use of inorganic molecules as charge transfer unit components can improve these respective issues. For example, Frei et al. developed oxo-bridged metal systems grafted on the surface of mesoporous silica which can induce the metal-to-metal charge transfer (MMCT) by photo-irradiation and trigger photochemical redox reactions5,6,7,8,9.
Our group extended the single atomic system to a polynuclear system utilizing polyoxometalate (POM) as the electron acceptor10,11,12, with the expectation that use of the polynuclear system would be advantageous in the induction and control of the multi-electron transfer reaction, which is an important concept in energy conversion. In the protocol described here, we present the detailed method used to prepare the POM-based MMCT system, which works in a polymer matrix as we recently reported13. The membrane-type configuration is favorable for product separation between anodic and cathodic reaction products. The cross-linking method was applied, which enabled formation of a self-standing membrane, even with high POM contents. Photoelectrochemical measurements proved that appropriate selection of the donor metal is key to triggering the target. The POM/donor metal system works as a photo-sensitizer to activate multi-electron transfer catalysts under visible light irradiation. Although this work utilizes MnOx as a multi-electron transfer catalyst for the water oxidation reaction, this photo-functional system is also applicable for use with other types of reactions by utilizing various POMs, donor metals, and catalysts.

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			<td height="42" style="height:42px;width:287px;">Poly(vinyl Alcohol) 1000, Completely Hydrolyzed</td>
			<td style="width:119px;">Wako</td>
			<td style="width:119px;">162-16325</td>
			<td style="width:295px;"></td>
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		<tr height="42">
			<td height="42" style="height:42px;width:287px;">Polyacrylamide, Mv 6,000,000</td>
			<td style="width:119px;">Polyaciences, Inc.</td>
			<td style="width:119px;">2806</td>
			<td>May contain carcinogenic monomer, acrylamide.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:287px;">12 Tungsto(VI)phosphoric Acid n-Hydrate</td>
			<td style="width:119px;">Wako</td>
			<td style="width:119px;">164-02431</td>
			<td>Highly acidic</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:287px;">Acetone 99.5 + %(GC)</td>
			<td style="width:119px;">Wako</td>
			<td style="width:119px;">012-00343</td>
			<td></td>
		</tr>
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			<td height="21" style="height:21px;width:287px;">25% Glutaraldehyde Solution</td>
			<td style="width:119px;">Wako</td>
			<td style="width:119px;">079-00533</td>
			<td></td>
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			<td height="21" style="height:21px;width:287px;">Hydrochloric Acid 35-37%</td>
			<td style="width:119px;">Wako</td>
			<td style="width:119px;">080-01066</td>
			<td></td>
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			<td height="21" style="height:21px;width:287px;">Cerium(III) Nitrate Hexahydrate 98 + %(Ti)</td>
			<td style="width:119px;">Wako</td>
			<td style="width:119px;">031-09732</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:287px;">Cobalt(II) Chloride Hexahydrate 99 + %(Ti)</td>
			<td style="width:119px;">Wako</td>
			<td style="width:119px;">036-03682</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:287px;">Pottasium Permanganate 99.3 + %(Ti)</td>
			<td style="width:119px;">Wako</td>
			<td style="width:119px;">167-04182</td>
			<td>Highly oxydative</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:287px;">Sodium Thiosulfate Pentahydrate 99 + %(Ti)</td>
			<td style="width:119px;">Wako</td>
			<td style="width:119px;">197-03585</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:287px;">Automatic spray gun</td>
			<td style="width:119px;">Lumina</td>
			<td style="width:119px;">ST-6</td>
			<td></td>
		</tr>
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preparation of polyoxometalate-based photo-responsive membranes for the photo-activation of manganese oxide catalysts

This paper presents a method to prepare charge-transfer chromophores using polyoxotungstate (PW12O403-), transition metal ions (Ce3+ or Co2+), and organic polymers, with the aim of photo-activating oxygen-evolving manganese oxide catalysts, which are important components in artificial photosynthesis. The cross-linking technique was applied to obtain a self-standing membrane with a high PW12O403- content. Incorporation and structure retention of PW12O403- within the polymer matrix were confirmed by FT-IR and micro-Raman spectroscopy, and optical characteristics were investigated by UV-Vis spectroscopy, which revealed successful construction of the metal-to-metal charge transfer (MMCT) unit. After deposition of MnOx oxygen evolving catalysts, photocurrent measurements under visible light irradiation verified the sequential charge transfer, Mn &#8594; MMCT unit &#8594; electrode, and&#160;the photocurrent intensity was consistent with the redox potential of the donor metal (Ce or Co). This method provides a new strategy for preparing integrated systems involving catalysts and photon-absorption parts for use with photo-functional materials.

Retention of the POM structure in the polymer matrix was confirmed by FT-IR and micro-Raman spectroscopy (Figure 1); vibration peaks corresponding to the Keggin structure of POM were observed, and peaks of the polymers were found to be shifted due to hydrogen bonding with POM. Spectroscopic analysis was very useful for determining successful construction of the charge transfer unit, and this was also confirmed by the apparent color change of the samples (<str...

Watch this Scientific Journal Video about Preparation of Polyoxometalate-based Photo-responsive Membranes for the Photo-activation of Manganese Oxide Catalysts at JoVE.com

Preparation of Polyoxometalate-based Photo-responsive Membranes for the Photo-activation of Manganese Oxide Catalysts

Here, we present a protocol to prepare charge transfer chromophores based on a polyoxometalate/polymer composite membrane.

This paper presents a method to prepare charge-transfer chromophores using polyoxotungstate (PW12O403-), transition metal ions (Ce3+ or Co2+), and organic ...

This method can help answer key questions in the solar-to-chemical energy conversion field such as artificial photosynthesis. The main advantage of this technique is that we can fabricate flexible, durable, and redox tunable photo-functional materials. First add two milliliters of polyvinyl alcohol solution and two milliliters of polyacrylamide solution to a 50 milliliter vial.Then add a triangular shaped stir bar and one gram of phosphotungstic acid to the vial. This cross-linking method was reported by another group and we modified the polyoxotungstate and its amount. Utilizing this method we can fabricate a membrane with an acid-type polyoxometalate instead of a salt-type.This is a key species to construct a photoresponsive membrane. Heat the vial to 70 degrees Celsius in a water bath under vigorous stirring and continue to stir for six hours after leaching at 70 degrees Celsius. Place a glass substrate on a hot plate pre-heated to 100 degrees Celsius and drop 750 microliters of the solution on to the substrate.To dry the sample store it in the dark overnight at room temperature. To prepare the crosslinking reagent add 72 milliliters of distilled water, 24 milliliters of acetone, 2 milliliters of 25%glyceraldehyde solution, and 2 milliliters of hydrochloric acid to a 100 milliliter vial. Place the glass substrate with the sample in a 9.5 centimeter Petri dish and add the crosslinking reagent until the membrane is completely immersed.After 30 minutes replace the crosslinking reagent with distilled water and wash once. If necessary peel the membrane from the glass substrate using a spatula and store it in distilled water in the dark. Add 2.08 grams of cerium nitrate hexahydrate and a stir bar to a 50 milliliter vial.Then add 30 milliliters of water to the vial and stir to dissolve the solid. Next place the membrane in a 9.5 centimeter Petri dish and add the cerium nitrate solution until the membrane is completely immersed. Place the Petri dish into a pre heated oven at 80 degrees Celsius for five hours.After cooling to room temperature replace the cerium nitrate solution with distilled water and wash once. Store the membrane and distilled water in the dark. To prepare a membrane with cobalt as the donor metal use the same preparation and reaction procedures as previously described except using 1.14 grams of cobalt chloride hexahydrate.Place the membranes onto a hot plate at 60 degrees Celsius with masks made of silicone rubber to determine the area to be used for deposition. Add 300 milliliters of a previously prepared colloidal manganese oxide solution to a 500 milliliter bottle connected to an automated spray gun above the hot plate and spray the solution onto the membranes. After manganese oxide deposition store the samples and distilled water in the dark.Retention of the POM structure in the polymer matrix was confirmed by micro-Raman and FT-IR spectroscopy. Vibration peaks corresponding to the Keggin structure of POM were observed and peaks of the polymers were found to be shifted due to hydrogen bonding with POM. Spectroscopic analysis was very useful for determining successful construction of the charge transfer unit and this was also confirmed by the apparent color change of the samples.In addition it was confirmed by UV-Vis spectroscopy and photo electro chemical measurements because charge transfer is achieved when all components are adequately aligned. In particular the spectroscopic and photoelectrochemical results confirmed one directional charge transfer under light irradiation which thus supports the validity of our synthetic method. The production of oxygen on manganese oxide was monitored using an indirect electrochemical method employing a rotating disk-ring electrode system where the reduction current corresponding to oxygen reduction could be observed under light irradiation.After its development this technique paves the way for researchers in the field of photochemistry to fabricate a redox-tunable and stable photosystem to trigger many photochemical reactions.

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