TiO2 Photocatalyst to replicate making a photocatalytic PVA film

[TroyPhotocatalytic]

Hi photocatalytic experts, I've recently at home tried to replicate making a photocatalytic PVA film as outlined below (taken from the research undertaken by Lin, et al in a number of publications. A summary of the method was as follows:
"15 mL of tetrabutyl titanate (TBT) was added into 15 mL of
trifluoroacetic acid solution (50 wt.%) at room temperature. After stir￾ring for 3 h, a transparent solution was obtained. Then the solvent was
removed through a rotary evaporator. Finally, yellowish titania xerogel
was obtained.
0.125 g of titania xerogel and 0.5 g of PVA were dissolved into 16 mL
of deionized water, respectively. Subsequently, the above prepared two
solutions were mixed together under stirring and then transferred into
a 40 mL Teflon-lined autoclave, which was heated to 150 °C for 3 h.
After cooling down to room temperature, the solution was poured out
to a plastic dish and formed the PVA/TiO2 nanocomposite films."I wanted to use this film in combination with formic acid (a hole scavenger) to reduce NO3- from an aqueous solution via the formation of carboxyl radicals.The film looked good when done (I made up 4 Petri dishes of it). One I used with methylene blue to see if it would speed up decolourisation under sunlight but there was no improvement in speed over another Petri dish with no tio2/PVA (sun bleaching was more effective so I guess no OH radicals were created)?The second test I added water with 400mg/L of NO3- to a Petri dish, added formic acid at a molar ratio of 3:1 FA to NO3- and irradiated with 365nm 18W UV light. After 2 hours the NO3- was 650mg/L!!! Tested with a Horiba ionic NO3- Meter.So my questions are:
- did I do something wrong in my prep? I copied the steps to the letter though. I used one of those steel 100mL autoclaves with the Teflon inner container that goes in the oven. I cooked it for 3hrs at 150 degrees. I dried the meshed at 60 degrees C in a dehydrator overnight. There should be anatase crystals right?- how could the NO3- levels go up? I measured my pre sample after putting in the formic acid (pH was 3.6). If there was anatase, with a hole scavenger and low pH, it should have been converted to N gases. What could have happened?Any thoughts would be much appreciated. This is a hobby of mine and I wanted to make something cool for my fish tank. I have a science background and degree so happy for technical answers or questions. I understand the NO3- reduction pathways and possibility of making ammonia. I understand the difference between photolysis and photocatalysis and how hydroxide and carboxyl radicals are formed and recombine, etc.Please help!!!

 

[Adrmay]

It is possible that the photocatalytic PVA film that you made may not be effective in reducing NO3- from an aqueous solution. The main reason for this could be that the TiO2 particles in the film may not be in the right form or size to be able to generate the required amount of hydroxyl radicals. Generally, TiO2 particles need to be in anatase form and of nanometer size to be able to generate the required amount of hydroxyl radicals. Furthermore, the film also needs to have a good contact with the solution in order for it to be effective. It is also possible that the pH of the solution was too low for the photocatalytic process to be effective. It is also possible that there could have been some contamination in the samples that caused the NO3- levels to increase. Contaminants such as organic compounds or metals can act as electron donors and thus lead to an increase in the NO3- levels. To determine if this is the case, you can perform an elemental analysis of the sample using ICP-MS. To further investigate the issue, it would be helpful to perform a few more tests with different concentrations of TiO2 and/or pH to find out the optimal conditions for the photocatalytic reduction of NO3-. It would also be helpful to measure the amount of hydroxyl radicals generated during the reaction. This can be done using a fluorescence technique such as luminol. I hope this helps!