TY - JOUR

T1 - Understanding the degradation pathways of oxalic acid in different photocatalytic systems: Towards simultaneous photocatalytic hydrogen evolution

AU - AlSalka, Y.

AU - Hakki, A.

AU - Fleisch, M.

AU - Bahnemann, D.W.

N1 - Funding information: The Financial support from the Deutscher Akademischer Austauschdienst (DAAD) and the Federal Foreign Office is gratefully acknowledged. We thank also Laboratorium für Nano- und Quantenengineering (LNQE) for cooperation and performing TEM measurements. The Financial support from the Deutscher Akademischer Austauschdienst (DAAD) and the Federal Foreign Office is gratefully acknowledged. We thank also Laboratorium f?r Nano- und Quantenengineering (LNQE) for cooperation and performing TEM measurements.

PY - 2018/11/1

Y1 - 2018/11/1

N2 - The photocatalytic degradation of aqueous oxalic acid has been investigated employing different photocatalytic systems under constant pH conditions. A self-prepared TiO 2 was utilized during the photocatalytic investigations in a bare and a platinized form. The synthesized pure anatase phase TiO 2 had a 10 nm grain size and a BET surface area of ca. 121 m 2 g −1 with relatively higher photocatalytic activity compared to the commercially available TiO 2 photocatalyst UV100. Complete photocatalytic degradation of oxalic acid was observed within 60 min of illumination under aerobic condition with no by-product been detected. In the absence of molecular oxygen, a perceptible amount of formic acid was formed in the liquid phase, as determined quantitatively by means of ion chromatography. The formation of formic acid suggests that a photo-Kolbe reaction tacks place under oxygen-free conditions. The formation of formic acid was also noticed when platinized TiO 2 (0.25 wt.%) was employed, together with an enhancement of the reactions photonic efficiency to the quadruple. A hydrogen evolution could only observe under oxygen-free condition with, again, a higher formation rate over the platinized material. However, upon complete photoreforming of oxalic acid the overall amount of the photocatalytically evolved hydrogen using Pt 0.25%/TiO 2 represented only 60% of the theoretical amount. Therefore, it is suggested that the source of H atoms could be the HC 2O 4 − species rather than molecular oxalic acid. A detailed mechanism for the photocatalytic degradation of aqueous oxalic acid at different photocatalytic conditions is proposed and discussed.

AB - The photocatalytic degradation of aqueous oxalic acid has been investigated employing different photocatalytic systems under constant pH conditions. A self-prepared TiO 2 was utilized during the photocatalytic investigations in a bare and a platinized form. The synthesized pure anatase phase TiO 2 had a 10 nm grain size and a BET surface area of ca. 121 m 2 g −1 with relatively higher photocatalytic activity compared to the commercially available TiO 2 photocatalyst UV100. Complete photocatalytic degradation of oxalic acid was observed within 60 min of illumination under aerobic condition with no by-product been detected. In the absence of molecular oxygen, a perceptible amount of formic acid was formed in the liquid phase, as determined quantitatively by means of ion chromatography. The formation of formic acid suggests that a photo-Kolbe reaction tacks place under oxygen-free conditions. The formation of formic acid was also noticed when platinized TiO 2 (0.25 wt.%) was employed, together with an enhancement of the reactions photonic efficiency to the quadruple. A hydrogen evolution could only observe under oxygen-free condition with, again, a higher formation rate over the platinized material. However, upon complete photoreforming of oxalic acid the overall amount of the photocatalytically evolved hydrogen using Pt 0.25%/TiO 2 represented only 60% of the theoretical amount. Therefore, it is suggested that the source of H atoms could be the HC 2O 4 − species rather than molecular oxalic acid. A detailed mechanism for the photocatalytic degradation of aqueous oxalic acid at different photocatalytic conditions is proposed and discussed.

KW - Hydrogen evolution

KW - Oxalic acid

KW - Photocatalysis

KW - Photocatalytic reforming

KW - Solar fuel

KW - TiO

UR - http://www.scopus.com/inward/record.url?scp=85045558842&partnerID=8YFLogxK

U2 - 10.1016/j.jphotochem.2018.04.008

DO - 10.1016/j.jphotochem.2018.04.008

M3 - Article

VL - 366

SP - 81

EP - 90

JO - Journal of Photochemistry and Photobiology A: Chemistry

JF - Journal of Photochemistry and Photobiology A: Chemistry

SN - 1010-6030

ER -