CO₂ Photoreduction to CH₄ Performance Under Concentrating Solar Light

This method can help answer key questions in the artificial photosynthesis field, such as carbon dioxide photoreduction to methane. Concentrating technology can not only increase the light intensity but also reduce the catalyst amount as well as the reactor volume, while increasing the reaction temperature, thereby increasing the photoreduction reaction rate. Though this method can provide insight into photocatalytic reduction of carbon dioxide, it can also be applied to other systems such as concentrating solar power and wastewater treatment.

To prepare the titanium dioxide by anodization dissolve 0.3 grams of ammonium fluoride and two milliliters of water into 100 milliliters of glycol in a 200 milliliter beaker with a stirrer to form the electrolyte. Place the beaker with the electrolyte into a 45 degree celsius water bath. Trim the titanium foil with scissors to 25 by 25 millimeters then polish the titanium foil surface with a 7000 mesh sand paper to remove the surface impurities.

Submerge the titanium foil in a volumetric flask containing 15 milliliters of ethanol and then a flask with 15 milliliters of acetone. Now treat the foil for 15 minutes with an ultrasonic cleaner. Take out the titanium foil, rinse it three to five times with the ionized water and place it in a volumetric flask containing 20 milliliters of ethanol.

Prepare the polishing solution in a 100 milliliter beaker as described in the text protocol. Now remove the titanium foil from the ethanol flask, rinse it three times with the ionized water and put it into the polishing solution for two to thee minutes. Remove the titanium foil and wash it with the ionized water an additional three times.

Use an anoid alligator clip to hold the pretreated titanium foil and a cathode clip to hold a platinum foil. Place the two foils face to face in the electrolyte at a distance of two centimeters from each other. Turn on the direct current stabilized current power source, tune the voltage to 50 volts and electrolyze for 30 minutes.

After the anodization has finished turn off the power and take out the titanium dioxide foil. Submerge the titanium foil in a volumetric flask containing 15 milliliters of ethanol and then transfer to a flask with 15 milliliters of acetone. Treat the titanium foil for 15 minutes with an ultrasonic cleaner.

Following treatment, rinse the titanium foil three to five times with the ionized water and place it in 15 milliliter crucible. Put the crucible in an oven at 60 degrees Celsius for 12 hours to let the foil dry. Once dry, calcine the titanium dioxide foil in a muffle furnace under 400 degree Celsius for two hours with a heating rate of two degree Celsius per minute.

To perform catalytic tests under concentrating light, clean the stainless cylinder shaped reactor with the ionized water. Then dry it in an oven at 60 degree Celsius for 10 minutes to ensure no interference from other carbon sources. After drying in the oven, add two milliliters of water, a stirrer and a catalyst holder to the reactor.

Place a quartz glass with pours on the bottom of the holder and place the titanium dioxide catalysts on the center of the quartz glass. Now put thermal cup hole through an opening in the reactor wall and onto the catalyst surface. Add a Fresno lens on the top of the holder and seal the reactor with a quartz glass window.

Place the reactor on the electromagnetic apparatus and check the air tightness with nitrogen. Feed the carbon dioxide into the reactor through a mass flow controller and flush the reactor at least three times to change the gas in the reactor to carbon dioxide. Place the Xenon lamp two centimeters directly above the reactor.

Power on the Xenon lamp and adjust it's current to 15 amps then turn on the magnetic stirrers switch to start the reaction. Record the temperature change on the catalyst surface and in the gas. Analyze the product every hour using gas chromatography equipped with the flame ionized detector and a capillary column for separation of hydro carbons with one to six carbons.

Calculate the number of products by the the external standard line method. Before quantifying the product build a standard curve of methane. Shown here is a device for concentrating photocatalytic reduction of carbon dioxide.

XRD and SEM characterization of the catalyst showed that the prepared catalyst was a typical titanium oxide nanotube. Shown here is the catalyst under natural light. Under concentrating light the catalyst shows some shining.

Here the x-ray diffraction pattern is shown, after concentrating light irradiation, to reveal crystal structure changes. The crystallinity is clearly improved after reaction under concentrating light. Methane yield is measured under natural and under concentrating light.

The reaction rates of methane on different catalyst were significantly improved under the concentrating conditions. Pre-treatment of the catalyst with suitable gas would further increase the methane production rate. Following this procedure, other methods like concentrated photocatalysis under real sunlight can be performed in order to answer addition questions like photocatalytic splitting of water, and degradation of volatile organic compounds under real sunlight.

After it's development, this technique paved the way for researchers in the photocatalytic field how to improve carbon dioxide photoreduction behavior in a photochemical system. Don't forget that working with concentrating light can be extremely hazardous and precautions such as googles should always be taken while performing this procedure.