Oxalic acid at the TiO 2 /water interface under UV(A) illumination: Surface reaction mechanisms

Mendive, Cecilia B.; Bredow, Thomas; Schneider, Jenny; Blesa, Miguel A.; Bahnemann, Detlef W.

doi:10.1016/j.jcat.2014.11.008

Cited by 23 publications

(24 citation statements)

References 52 publications

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“…Therefore, in addition to • CO 2 − radicals, other carbon-centered radicals were simultaneously produced upon the irradiation of the suspension. Our results correlate with the theoretical calculations of a possible direct oxidation and reduction of oxalic acid on the surface of titanium dioxide by the photogenerated species [28]. The formation of other byproducts such as hydroxyalkyl radicals detected by the EPR experiment can be explained by the cleavage of the bonding between the OH group and the rest of adsorbed oxalic acid due to the irradiation.…”

Section: The Role Of Intermediatessupporting

confidence: 86%

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Boosting the H2 Production Efficiency via Photocatalytic Organic Reforming: The Role of Additional Hole Scavenging System

et al. 2021

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The simultaneous photocatalytic H2 evolution with environmental remediation over semiconducting metal oxides is a fascinating process for sustainable fuel production. However, most of the previously reported photocatalytic reforming showed nonstoichiometric amounts of the evolved H2 when organic substrates were used. To explain the reasons for this phenomenon, a careful analysis of the products and intermediates in gas and aqueous phases upon the photocatalytic hydrogen evolution from oxalic acid using Pt/TiO2 was performed. A quadrupole mass spectrometer (QMS) was used for the continuous flow monitoring of the evolved gases, while high performance ion chromatography (HPIC), isotopic labeling, and electron paramagnetic resonance (EPR) were employed to understand the reactions in the solution. The entire consumption of oxalic acid led to a ~30% lower H2 amount than theoretically expected. Due to the contribution of the photo-Kolbe reaction mechanism, a tiny amount of formic acid was produced then disappeared shortly after the complete consumption of oxalic acid. Nevertheless, a much lower concentration of formic acid was generated compared to the nonstoichiometric difference between the formed H2 and the consumed oxalic acid. Isotopic labeling measurements showed that the evolved H2, HD, and/or D2 matched those of the solvent; however, using D2O decreased the reaction rate. Interestingly, the presence of KI as an additional hole scavenger with oxalic acid had a considerable impact on the reaction mechanism, and thus the hydrogen yield, as indicated by the QMS and the EPR measurements. The added KI promoted H2 evolution to reach the theoretically predictable amount and inhibited the formation of intermediates without affecting the oxalic acid degradation rate. The proposed mechanism, by which KI boosts the photocatalytic performance, is of great importance in enhancing the overall energy efficiency for hydrogen production via photocatalytic organic reforming.

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Section: The Role Of Intermediatessupporting

confidence: 86%

“…Hence, the generation of such hydroxyalkyl radicals, which can be converted to formic acid, consumes the hydrogen atoms. This mechanistic pathway has also been predicted by the combination of Attenuated Total Reflectance-Fourier-transform infrared (ATR-FTIR) studies and the theoretical MSINDO-CCM calculations [28]. ).…”

Section: The Role Of Intermediatesmentioning

confidence: 73%

Boosting the H2 Production Efficiency via Photocatalytic Organic Reforming: The Role of Additional Hole Scavenging System

et al. 2021

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“…For instance, carboxylate or carboxyl groups can coordinate with the metals present on the surface of photocatalysts, thus forming inner-sphere complexes that favor the transfer of electrons directly from the ligand molecule to the valence band of the photocatalyst or photogenerated holes [65]. For this reason, oxalate and formic acid have been applied in mechanistic investigations of photocatalytic systems to act as hole traps [66]. Other scavenger species widely applied in mechanistic investigations are alcohols such as tert-butanol (TBA) and methanol.…”

Section: Formation Of Charge Carriers and Reactive Oxygen Speciesmentioning

confidence: 99%

Photocatalysis: Introduction, Mechanism, and Effective Parameters

Veréb

Firak

Alapi

2021

Green Chemistry and Sustainable Technology

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The widely investigated heterogeneous photocatalysis offers an environmentally friendly, efficient, and versatile solution for several environmental problems. Among others, the removal of harmful organic pollutants and the generation of H 2 via water splitting are well-known and most widely studied applications. The process is based on the charge separation caused by the excitation of semiconductor photocatalyst via photon absorption. Due to the intensive development of material science, in addition to the well-known TiO 2 and ZnO, several new semiconductor materials have been designed and synthesized to increase the efficiency of heterogeneous photocatalysis and utilization of solar and/or visible light. This chapter describes the principles and mechanisms of heterogeneous photocatalysis, including the formation of photogenerated charge carriers, the role of different reactive species, and the effect of key parameters on the efficiency.

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“…Oxalic acid is one of the most investigated molecules in this regard [18,45,58,60,61]. Based on a series of spectra recorded at varying different experimental parameters (concentration, pH, and ionic strength), and supported by the comparison of these spectra with those of the aqueous [Fe(Ox) y ] z complex, Hug et al [18] described several surface complexes formed during the adsorption of oxalic acid at the TiO 2 P25 surface.…”

Section: Interactions Of Probe Molecules With the Metal Oxide Surfacementioning

confidence: 99%

“…Furthermore, Mendive et al [61] have proposed the mechanism of the photocatalytic degradation of oxalic acid with the help of the above mentioned experimental and theoretical investigations [24,63]. The possible pathways for the formation of oxalic acid photoproducts, as well as the role of the TiO 2 surface as active surface have been discussed in detail [61]. An example of the proposed degradation pathways of the oxalic acid surface complexes is depicted in Figure 9.…”

Section: Interactions Of Probe Molecules With the Metal Oxide Surfacementioning

confidence: 99%

The Relevance of ATR-FTIR Spectroscopy in Semiconductor Photocatalysis

Atitar¹,

Belhadj²,

Dillert³

et al. 2015

Emerging Pollutants in the Environment - Current and Further Implications

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Abstract"ttenuated total reflection Fourier-transform infrared "TR-FTIR spectroscopy has a high potential for investigating a wide range of samples and systems. In photocatalysis, various interfacial phenomena can be studied using this technique, including pH-dependent adsorption and photodegradation of probe molecules. The analysis of the processes occurring at the interface of thin particle films deposited on the surface of an "TR crystal, either in the liquid or the gas phase, is perhaps the best way to elucidate the mechanism of adsorption and heterogeneous photocatalytic reactions.This chapter summarizes the recent advances and applications of "TR-FTIR techniques in semiconductor photocatalysis. " brief outlook at some of the possible investigations in this area is provided and the different proposed adsorption and photocatalytic degradation mechanisms are discussed.

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Oxalic acid at the TiO 2 /water interface under UV(A) illumination: Surface reaction mechanisms

Cited by 23 publications

References 52 publications

Boosting the H2 Production Efficiency via Photocatalytic Organic Reforming: The Role of Additional Hole Scavenging System

Boosting the H2 Production Efficiency via Photocatalytic Organic Reforming: The Role of Additional Hole Scavenging System

Photocatalysis: Introduction, Mechanism, and Effective Parameters

The Relevance of ATR-FTIR Spectroscopy in Semiconductor Photocatalysis

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