Oxalic acid, photocatalytic

Zhao et al. (2002) studied the photodestruction of sulforhodamine-B in Pt/Ti02 suspension under visible light illumination. The electrons excited from dye molecules were accepted by Pt islands. The accumulated electrons then react with 02 to form 02- and subsequently OH, which ultimately caused the self-destruction of the dye molecules. Photocatalytic destruction of oxalic acid (Iliev et al. 2006) and H2 generation (Sreethawong et al. 2006) from aqueous methanol solution were also promoted by platinizing Ti02. Under anoxic conditions, products from... 

Iliev, V., D. Tomova, L. Bilyarska, A. Eliyas and L. Petrov (2006). Photocatalytic properties of Ti02 modified with platinum and silver nanoparticles in the degradation of oxalic acid in aqueous solution. Applied Catalysis B-Environmental, 63(3 4), 266-271. 

Mendive, C.B., D.W. Bahnemann and M.A. Blesa (2005). Microscopic characterization of the photocatalytic oxidation of oxalic acid adsorbed onto Ti02 by FTIR-ATR. Catalysis Today, 101(3 1), 237-244. 

Figure 10 Photocatalytic degradation of oxalic acid in four different solar reactors as a function of accumulated energy (reprinted from Bandala et al., 2004, with permission from Elsevier).

Wang, Y. and Zhang, P. (2011) Photocatalytic decomposition of per-fluorooctanoic acid (PFOA) by Ti02 in the presence of oxalic acid. J. Hazard. Mater., 192, 1869-1875. 

For green photocatalytic processes, the use of pollutants as an electron donor was also investigated. Li et al. (2003) reported enhanced photocatalytic hydrogen production using a mixture of pollutants (oxalic acid, formic acid, and formaldehyde) acting as electron donors. The authors reported that photocatalytic decomposition of... 

Recently, Imamura et al. (2011) studied the photocatalytic reduction of nitrobenzenes and aminonitrobenzenes to aminobenzenes and diaminobenzenes, respectively. These reactions were conducted in aqueous suspensions of titanium (IV) oxide (Ti02) as catalyst and formic acid or oxalic acid as electron donors using de-aerated and aerated conditions under UV light. 

Formic acid and oxalic acid are green sacrificial reagents because they are easily oxidized and converted into CO2, which is separated from the solvent under acidic conditions. The photocatalytic effect in the presence of formic acid can be attributed to the photo-Kolbe reaction, originally evidenced by Kraeutler and Bard (1978) in the presence of various carboxylic acids ... 

Photocatalytic oxidation of oxalic acid enhanced by silver and copper deposition on a TIO2 surface... 

Pan, Z., Cai, Q., Luo, Q., and Li, X. (2015) Photocatalytic ozonation of oxalic acid over Cu(II)-grafted Ti02 under visible light irradiation. Synth, React. Inorg. Met-Org Nano-Met Chem., 45, 447-450. 

A final difference between photocatalytic CO2 reduction and hydrogen evolution from water is the large number of possible reaction products that can be formed in the process. The products that have been detected in photocatalytic CO2 conversion include oxalic acid or oxalate, formate, methanol, methane, ethane, CO, and even elemental C. The problem arises from the fact that some of the possible products are gaseous, while others are liquids or even solids. If solids are deposited on the photocatalyst surface performing the reaction in the gas phase at low temperatures, deactivation of the catalyst should occur by blocking of the surface by carbon and liquid products that poison the photocatalyst. The large diversity of products that can be formed in CO2 reduction and their difference in physical states... 

Fig. 9.8 Effects of metals loaded cm Ti02 (MT-150A, Tayca) on photocatalytic reduction of PhCN (50 pmol) to B11NH2 in 0.1 mol dm aqueous hydrochloric acid suspensions (5 cm ) under deaerated conditions in the presence of oxalic acid (200 pmol) for 60-min photoirradiation (Reproduced from Ref. [30] with permission from the Royal Scx iety of Chemistry)...

Time Course of Photocatalytic Reduction of PhCN over Pd-Ti02 in Water Containing Oxalic Acid as Hole Scavenger... 

Figure 9.10 shows time courses of photocatalytic reduction of PhCN. The amount of PhCN monotonously decreased along with photoirradiation time, and PhCN was almost completely consumed after 30 min, while BnNH2 was obtained in 74 % yield. Assuming that all of the CO2 originated in oxalic acid, the efficiency of... 

For comparison, AQE for photocatalytic H2 formation from 2-propanol (200 pmol) in an aqueous suspension of platinized Ti02 was also examined and determined to be 4.1 % under the same irradiation conditions. This reaction has often been used as a model reaction to evaluate the activity of a photocatalyst for H2 evolution. The value of AQE in the present reaction larger than that of 2-propanol dehydrogenation shows that oxalic acid efficiently works as hole scavenger for photocatalytic reduction of NS to AS. 

In the photocatalytic reduction of nitrobenzenes, positive holes in the valence band were effectively removed by formic acid and oxalic acid. These hole scavengers are greener sacrificial reagents because they are easily oxidized into CO2, and thus formed CO2 molecules are removed from the liquid phase in the presence of organic acids. The photocatalytic reduction of nitrobenzenes would be more attractive if positive holes are utilized for synthesis of valuable compounds, not for fruitless degradation or mineralization. Utilization of positive holes enables simultaneous production of two valuable reduced and oxidized compounds. In the case of reduction of nitrobenzene using oxalic acid (Eq. 9.15), atom efficiency (AE) [64], which is defined in Eq. 9.16, is calculated to be 23.7 % ... 

Li Y, Wasgestian F (1998) Photocatalytic reduction of nitrate ions on Ti02 by oxalic acid. J Photochem Photobiol A Chem 112 255-259... 

Photocatalytic oxidation of 2,4-dichlorophenoxyacetic acid (2,4-D) was investigated (Sun and Pignatello, 1995). In addition to the dominant hydroxyl radical mechanism, Sun and Pignatello found evidence that direct hole oxidation may be the mechanism for the photocatalytic degradation of some organic compounds. The assumed mechanism for this oxidation is H+ acting as an electron-transfer oxidant, while O behaves like a free OH and abstracts H or adds to C=C multiple bonds. Hole oxidation has been used to explain the oxidation of oxalate and trichloroacetate ions, which lack abstractable hydrogens or unsaturated C-C bonds. Whether the reaction... 

Reduction of C02 photocatalyzed by semiconducting materials may lead to formation of formaldehyde, formic acid, methanol, methane, and oxalate among other products [7], The earliest report on photocatalytic reduction of C02 with water at Ti02 was published by Inoue et al. [25], Almost at the same time the photoreduction of C02 to methane at SrTi03 was reported by Hemminger et al. [26], The same process can also be performed on AgCl/zeolites [27],... 

Figure 21.6 The photocatalytic mechanism of decomposition of oxalic and formic acids by the Fe203/P25 composite. (Reproduced with permission from Ref. [95].)...

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