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| − | A photocatalytic reaction proceeds in the presence of light--typically visible or UV--and catalyst--often a semi-conductive transition metal oxide such as titanium dioxide (TiO<sub>2</sub>). This experiment will give an introduction into wastewater treatment via photocatalysis by measuring the degradation kinetics of methylene blue as a function of catalyst loading, hydrogen peroxide concentration, and experimental setup. |
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| − | |||
| − | === Pre-Lab Questions === |
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| − | You can download the Pre-Lab questions for this experiment [https://drive.google.com/file/d/0ByIE39OgBdOpVURqaW9KRlBLclU/view?usp=sharing here]. |
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| − | |||
| − | == Background == |
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| − | Review your textbook on chemical reaction engineering, particularly those chapters which cover experimental determination of rate laws <ref>Fogler, H. ''Essentials of Chemical Reaction Engineering.'' Prentice Hall: Boston, 2011; Ch. 7.</ref> and heterogeneous catalysis <ref>''ibid,'' Ch. 10.</ref>. Most often, a pseudo first-order kinetic model is chosen to determine rate laws in this experiment but you should compare other models (particularly the Langmuir-Hinshelwood model) as well. |
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| − | If you're not familiar with linear and non-linear regression then you should review these topics as well, either on the Statistics wiki (forthcoming) or in your textbooks. <ref>Fogler, H., ''Essentials of Chemical Reaction Engineering''; Pearson Education: Boston, 2011, Ch. 7.</ref> |
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| − | |||
| − | == Theory == |
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| − | Photocatalysis is such a large field that there are tens of thousands of papers to read; it's recommended that you give yourself a morning--and maybe and afternoon--to do so. If you're unwilling or unable to read everything, we've categorized a few favorites below to help you along. |
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| − | |||
| − | === Review Articles === |
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| − | These articles provide a good overview and context for the field but intentionally lack the specificity of research articles. |
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| − | * Parameters affecting the photocatalytic degradation of dyes using TiO<sub>2</sub>-based photocatalysts: A review.<ref>Akpan, U.G.; Hameed, B.H. ''J. Hazard. Mater.,'' '''2009, '''''170'', 520-529.</ref> |
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| − | * Photocatalytic degradation for environmental applications - a review<ref>Bhatkhande, D.S.; Pangarka, V.G.; Beenackers, A. ''J. Chem. Technol. Biotechnol.,'' '''2001,''' ''77'', 102-116.</ref> (good coverage of environmental aspects). |
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| − | * Titanium dioxide photocatalysis<ref>Fujishima, A.; Rao, A.N.; Tryk, D.A. ''J. Photochem. Photobiol C: Photochem. Reviews,'' '''2000,''' ''1'', 1-21.</ref> (good physical chemistry aspects). |
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| − | * Heterogeneous photocatalytic degradation of organic contaminants over titanium dioxide: A review of fundamentals, progress, and problems.<ref>Gaya, U.I.; Abdullah, A.H. ''J. Photochem. Photobiol. C: Photochem. Reviews,'' '''2008,''' ''9'', 1-12.</ref> |
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| − | * Tailored titanium dioxide photocatalysts for the degradation of organic dyes in wastewater treatment: A review<ref>Han, F.; Kambala, V.; Srinivasan, M.; Rajarathnma, D.; Naidu, R. ''Appl. Cat. A: General,'' '''2009,''' ''359'', 25-40.</ref> (a broad review which includes much nano-TiO<sub>2</sub>). |
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| − | * Treatment of hazardous organic and inorganc compounds through aqueous-phase photocatalysis: A review.<ref>Kabra, K.; Chaudhary, R.; Sawhney, R.L. ''Ind. Eng. Chem. Res.,'' '''2004,''' ''43'', 7683-7696.</ref> |
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| − | * Photophysical, photochemical and photocatalytic aspects of metal nanoparticles (good review from a quality journal).<ref>Kamat, P.V. ''J. Phys. Chem. B, '''''2002,''' ''106'', 7729-7744.</ref> |
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| − | * Photocatalysis on TiO<sub>2</sub> surfaces: Principles, mechanisms, and selected results<ref>Linsebigler, A.L.; Lu, G.; Yates Jr., J.T. ''Chem. Rev.,'' '''1995,''' ''95'', 735-758.</ref> (classic review with over a thousand citations. You can find the crystal structure of various titanium oxides here). |
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| − | |||
| − | === Research Articles: Slurry Reactors === |
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| − | These articles were chosen for their investigation of dye degradation in slurry reactors. Note that nanometer-sized TiO<sub>2</sub> particles are used very differently from the micron-sized particles we use in the lab, and that only a small number of studies use them in a slurry as we do. We found that nanometer-sized particles were a poor choice for a teaching lab due to safety concerns. |
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| − | * Photocatalytic degradation pathway of methylene blue in water.<ref>Houas, A.; Lachheb, H.; Ksibi, M.; Elaloui, E.; Guillard, C.; Herrmann, J.M. ''Appl. Catal. B: Environ.,'' '''2001,''' ''31'', 145-157.</ref> |
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| − | * TiO<sub>2</sub>-assisted photocatalytic degradation of azo dyes in aqueous solution: kinetic and mechanistic investigations.<ref>Konstantinou, I.K.; Albanis, T.A. ''Appl. Catal. B: Environ.,''''' 2004,''' ''49'', 1-14.</ref> |
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| − | * Photocatalytic degradation of various types of dyes in water by UV-irradiated titania. <ref>Lachheb, H.; Puzenat, E.; Houas, H.; Ksibi, K.; Elaloui, E.; Guillard, C.; Herrmann, J.M. ''Appl. Catal. B: Environ., '''''2002,''' ''39'', 75-90.</ref> |
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| − | * Kinetics of photocatalytic degradation of reactive dyes in a TiO<sub>2</sub> slurry reactor.<ref>Sauer, T.; Cesconeto Neto, G.; Jose, H.J.; Moreira, R.F.P.M. ''J. Photochem. Photobiol. A: Chem., '''''2002, '''''149'', 147-154.</ref> |
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| − | * Photocatalytic degradation of various dyes by combustion synthesized nano anatase TiO<sub>2</sub>. <ref>Sivalingam, G.; Nagaveni, K.; Hegde, M.S.; Madras, G. ''Appl. Catal. B: Environ., '''''2003, '''''45'', 23-38.</ref> |
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| − | * Variation of Langmuir absorption constant determined for TiO<sub>2</sub>-photocatalyzed degradation of acetophenone under different light intensity.<ref>Xu, Y.; Langford, C.H. ''J. Photochem. A: Chem.,''''' 2000, '''''133'', 67-71.</ref> |
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| − | * Adsorption of methylene blue and acid blue 40 on titania from aqueous solution.<ref>Fetterolf, M.L.; Patel, H.V.; Jennings, J.M. ''J. Chem. Eng., '''''2003, '''''48'', 831-835.</ref> |
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| − | * Photodestruction and COD removal of toxic dye erioglaucine by TiO<sub>2</sub>-UV process: influence of operation parameters.<ref>Jain, R.; Sikarwar, S. ''Int. J. Phys. Sci.,''''' 2008,''' ''3'', 299-305.</ref> |
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| − | * A general treatment and classification of the solute absorption isotherm.<ref>Giles, C.H.; D'Silva, A.P.; Easton, I.A. ''J. Coll. Intf. Sci., '''''1973,''' ''47'', 766-778.</ref> |
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| − | === Research Articles: H<sub>2</sub>O<sub>2</sub>/TiO<sub>2</sub> Systems === |
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| − | These articles were chosen for their use of H<sub>2</sub>O<sub>2</sub> and TiO<sub>2</sub> for dye degradation. Note that some are written in a manner similar to our lab reports but occasionally employ poor writing styles. |
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| − | * Photocatalytic degradation of disperse blue 1 using UV/TiO<sub>2</sub>/H<sub>2</sub>O<sub>2</sub> process.<ref>Saquiba, M.; Abu Tariqa, M.; Haquea, M.M.; Muneer, M. ''J. Environ. Mgmt. '''''2008,''' ''88'', 300-306.</ref> Note that this is not a great journal, the writing isn't that great, and the H<sub>2</sub>O<sub>2</sub> concentration was never stated. The mechanism is good compared to the next two references but still not complete; look in one of the previous references for the full mechanism. |
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| − | * Treatment of Remazol brilliant blue dye effluent by advanced photo oxidation process in TiO<sub>2</sub>/UV and H<sub>2</sub>O<sub>2</sub>/UV reactors.<ref>Verma, M.; Ghaly, A.E. ''Am. J. Eng. Appl. Sci.,''''' 2008,''' ''1'', 230-240.</ref> |
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| − | * H<sub>2</sub>O<sub>2</sub>/TiO<sub>2</sub> photocatalytic oxidation of metol. Identification of intermediates and reaction pathways.<ref>Aceituno, M.; Stalikas, C.D.; Lunar, L.; Rubio, S.; Perez-Bendito, D. ''Water. Res.,''''' 2002,''' ''36'', 3582-3592.</ref> |
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| − | == Standard Operating Procedure == |
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| − | === Safety === |
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| − | * Lab coats and protective eyewear should be worn at all times. |
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| − | * Dispose of broken glassware in the appropriately labeled receptacles; used filters can be disposed of in the trash. |
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| − | * Do not dispose of waste down the drain! Use a flask to collect all waste then notify the TA or instructor at the end of the lab period. |
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| − | * Methylene blue is a potent textile dye. When connecting tubing or transferring liquid, take caution not to splash. |
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| − | * Relevant chemical information has been listed in Table 1. |
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| − | {| class="article-table" align="center" style="background-color: white;" |
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| − | |+ style="text-align: left; font-weight: normal" |'''Table 1.''' Chemicals and their formulas, hazards, and suppliers for UV photocatalysis. |
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| − | |- |
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| − | !Name<sup>MSDS</sup> |
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| − | !Formula |
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| − | !Hazard |
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| − | !Supplier |
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| − | !SKU |
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| − | |- |
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| − | |[http://www.sciencelab.com/msds.php?msdsId=9926051 Methylene blue] |
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| − | |C<sub>16</sub>H<sub>18</sub>N<sub>3</sub>SCl |
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| − | |[[File:hazCholesterol.png|60px]] |
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| − | |unk |
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| − | |unk |
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| − | |- |
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| − | |Hydrogen |
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| − | [http://www.sciencelab.com/msds.php?msdsId=9925970 peroxide (5%)] |
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| − | |H<sub>2</sub>O<sub>2</sub> |
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| − | |[[File:hazHydrogenPeroxide5.png|60px]] |
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| − | |any |
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| − | |any |
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| − | |- |
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| − | |[http://www.sciencelab.com/msds.php?msdsId=9925268 Titanium dioxide] |
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| − | |TiO<sub>2</sub> |
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| − | |[[File:hazTitaniumDioxide.png|60px]] |
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| − | |unk |
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| − | |unk |
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| − | |} |
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| − | === Preparation === |
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| − | # Familiarize yourself with the UV/VIS spectrophotometer and the data acquisition software. Note that there are two types of measurements: |
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| − | ## Absorption spectrum. Use this to determine the wavelength of maximum absorbance. |
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| − | ## Point measurement. Use this to measure absorbance at a single, pre-set wavelength. |
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| − | # Create a calibration curve. |
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| − | ## Prepare about 100 mL of a solution of known dye concentration; typically 10 ppm is sufficient. |
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| − | ## Acquire the absorption spectrum of this solution. If you see a plateau instead of peaks then the solution is too concentrated and needs to be diluted. |
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| − | ## Note the wavelength of maximum absorbance, \(\lambda_{\textrm{max<nowiki>}}</nowiki>\). |
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| − | ## Measure absorbance at \(\lambda_{\textrm{max<nowiki>}}</nowiki>\) for several diluted solutions, including deionized (DI) water. Minimize waste by using measurement pipets, plastic cuvettes and a [http://scienceprimer.com/serial-dilution serial dilution procedure]. |
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| − | # Measure the volume of the reactor-flask system. |
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| − | ## Select a small or medium-sized [http://www.thomassci.com/_resources/_global/media/resized/00003/ihwx.f14b883f-2d26-4e13-ba4b-31d1cc89e453.500.500.jpg glass spinner flask]. |
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| − | ## Place the flask on the stir plate and connect the pump lines. |
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| − | ## Fill the flask with enough DI water to submerge the appropriate pump line. |
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| − | ## Run the peristaltic pump until continuous circulation is achieved between the flask and [http://www.thatpetplace.com/257409n.jpg UV reactor], adding water as necessary to keep the appropriate pump line submerged. Flow through the UV reactor should be from bottom to top. |
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| − | ## The total volume of water used in Steps 3 and 5 is the volume of water you should use to prepare solutions for subsequent runs. |
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| − | ## Drain the system. Use a large glass spinner flask or other appropriate glass flask to store your waste. '''Do not''' dump waste down the drain. |
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| − | === Basic Operation === |
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| − | # In the spinner flask, prepare an appropriate volume of solution of known (measured) dye concentration (~10 ppm) with TiO<sub>2</sub> (~1000 ppm) in DI water. Use the stir plate to break up clumps of TiO<sub>2</sub>. |
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| − | # Add H<sub>2</sub>O<sub>2</sub> (5 mL) to "kick-start" [http://lmgtfy.com/?q=methylene+blue+degradation+reaction the reaction] . |
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| − | # Turn on the pump, stirrer, and UV reactor. |
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| − | # At regular intervals, collect a sample, '''filter out the TiO<sub>2</sub>'''<sub> </sub>using syringe filters, and measure absorbance and \(\lambda_{\textrm{max<nowiki>}}</nowiki>\). |
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| − | ## Absorbance measurements are meaningless unless the sample is adequately filtered. |
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| − | ## Do not filter the samples near your face! It's easy to rupture the syringe filter or connections during the filtration process if you go too fast. |
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| − | ## About 20 mL of solution can be filtered before the filter should be replaced. |
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| − | === Shutdown === |
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| − | # Turn off the UV reactor. |
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| − | # Drain the UV reactor and consolidate waste into a single, large spinner flask. |
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| − | ## If more waste was produced than can fit in a single flask, then fill a single flask and place excess waste in another glass container; the latter need not be a spinner flask. |
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| − | # Add about 5 mL H<sub>2</sub>O<sub>2</sub>, then turn on pump, stirrer, and UV reactor. |
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| − | # Before you leave the lab, inform the TA or Instructor of which flasks are waste. |
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| − | == References == |
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| − | <references /> |
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