*3.4. Photocatalytic Degradation Activity and Hydrogen Evolution Measurements*

The photocatalytic activity of the LaFeO3 samples was tested on one hand by the photocatalytic decomposition of RhB and 4-CP as organic model pollutants under visible light irradiation (λ ≥ 420 nm) and on the other hand by attempting hydrogen evolution using light of λ ≥ 320 nm and Pt nanoparticles as a co-catalyst.

For the degradation experiments the visible light irradiation was obtained from a 150 W Xe lamp equipped with a 420 nm cut-off filter. This optical cut-off filter was placed between the reactor and the xenon lamp to cut off the UV light and to ensure visible light irradiation only; the distance between the light source and the reactor containing solution was about 10 cm. Since for dyes, such as RhB, self-excitation by the visible light could not be ruled out (although we found there was not much indication for that, compare Figure 9b), 4-CP was used as a control substrate, which is not absorbing in the vis-light range. In a typical test, 0.1 g of LaFeO3 and 100 mL of aqueous solutions (10−<sup>5</sup> M) of RhB or 4-CP were initially mixed under continuous magnetic stirring in a water-cooled (10 ◦C) double-wall 250 mL Pyrex reactor for 40 min in the dark to establish the adsorption-desorption equilibrium between the photocatalyst and substrate (RhB or 4-CP). The cooling system was used to cool down the double-wall Pyrex reactor to prevent the effect of the thermal catalytic reaction. Then the samples were illuminated under visible light. Every one hour, a part of the suspension was taken out, filtered to remove the particles and analyzed by the UV-Vis absorption measurement, the degree of degradation was evaluated from the decrease of absorption at the RhB and 4-CP maxima at 554 nm and 315 nm, respectively.

Photocatalytic H2 evolution was attempted in a double-walled quartz reaction vessel connected to a closed gas circulation, using a 500 W Hg mid-pressure immersion lamp (Peschl UV-Consulting) as a light source. Argon gas was used as the carrier gas with a flow of 50 NmL min−1. The evolved hydrogen gas was quantitatively analyzed by a multichannel analyzer (Emerson) equipped with a thermal conductivity detector. In a typical photocatalytic reaction, 0.5 g of LaFeO3 photocatalysts were suspended in a mixture of 550 mL water and 50 mL of the sacrificial agent methanol prior to the irradiation. The solution was kept at 10 ◦C by flushing cold water from a thermostat (LAUDA) through a double-wall reactor made of normal glass. The normal glass mantle was tested to absorb all the light with wavelengths shorter than about 320 nm. Thus, one can assume that the LaFeO3 samples are only irradiated by light of λ ≥ 320 nm. The co-catalyst 0.5 wt. % Pt (particle size < 2 nm) was deposited on the LaFeO3 powder via reductive photodeposition from H2PtCl6·6H2O. Upon light irradiation, metallic Pt nanoparticles were photodeposited onto the photocatalyst surface sites preferentially accessible for electrons, while CO2 was formed from methanol being employed as a sacrificial reagent as qualitatively detected with our multichannel analyzer (Emerson). The standard redox potential for the reduction of Pt2+ ions to metallic Pt is +1.2 V vs. NHE, thus the electrons in the CB of LaFeO3 are able to initiate this reduction.

## **4. Conclusions**

A perovskite-type LaFeO3 photocatalyst was synthesized using the quite simple citric acid assisted sol-gel route. The prepared samples were characterized using different methods. The most photocatalytically active sample for decomposition of RhB and 4-CP under visible light was the one calcined at the lowest temperature of 700 ◦C due to the highest surface area and the lowest band gap energy. At temperatures lower than 700 ◦C the crystallinity of the LaFeO3 samples was not sufficient. Mott-Schottky plots revealed a positive potential of the CB at around 0.1 V explaining the observed inactivity of LaFeO3 for the photocatalytic hydrogen evolution via water splitting and methanol dehydrogenation. The photocatalytic degradation reaction of the pollutants occurred mainly via direct reaction of the photogenerated holes, but to some extent especially in the starting period of the degradation experiments also via superoxide radical formation. To sum up, LaFeO3 is a promising photocatalytic material for degradation of organic pollutants under visible light irradiation.

**Author Contributions:** M.I. performed the catalyst preparation, structural and electrochemical characterization and the photocatalytic test experiments. He also prepared the first draft of the manuscript. This work was carried out under the supervision of M.W., who also structured the discussion of the data and prepared the final version of the manuscript.

**Acknowledgments:** We thank Dereje H. Taffa (University of Oldenburg) for his assistance in recording XP spectra and fruitful discussions XPS and photoelectrochemical results. Financial support by the Phoenix Scholarship program (PX14DF0164) for MI, and by the German Science Foundation (Deutsche Forschungsgemeinschaft, DFG) under contracts WA 1116/28-1 and INST 184/154-1 for the X-ray diffractometer are gratefully acknowledged.

**Conflicts of Interest:** The authors declare no conflict of interest.
