TY - JOUR

T1 - Evaluating carbon dots as electron mediators in photochemical and photocatalytic processes of NiFe2O4

AU - Ombaka, L.M.

AU - Dillert, R.

AU - Robben, L.

AU - Bahnemann, D.W.

N1 - Funding information: This work was funded by the Alexander von Humboldt Foundation. The publication of this article was funded by the Open Access Fund of the Leibniz Universität Hannover. The authors wish to thank Dr. R. S. Mwakubambanya for his assistance with the manuscript proofreading. Special thanks goes to Dr. Leopold Sauheitl, Institut für Bodenkunde, Leibniz Universität Hannover, for conducting the elemental analysis, Professor Claus Rüscher for the FTIR analysis, and Patrick Bessel for the UV-VIS-NIR analysis. The authors also thank Luis Granone, Carsten Günnemann, and Mariano Curti for assisting with various aspects of the catalysts’ characterization.

PY - 2020/3/3

Y1 - 2020/3/3

N2 - Spinel ferrites such as nickel ferrite are promising energy conversion photocatalysts as they are visible-light absorbers, chemically stable, earth abundant, and inexpensive. Nickel ferrite shows poor photocatalytic activity due to fast electron-hole recombination upon illumination. This study evaluates the capability of carbon dots (CDs) to improve charge-carrier separation in NiFe 2O 4. We report a facile solvothermal approach for synthesizing NiFe 2O 4 and CDs/NiFe 2O 4 nanoparticles at 200-215 °C. The photocatalysts were characterized using transmission and scanning electron microscopy, x-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, UV-VIS-NIR spectroscopy, photoelectrochemical analysis, and laser flash photolysis. Photocatalytic oxidation of methanol to formaldehyde under visible light was employed to test the effect of CDs on the photocatalytic efficacy of NiFe 2O 4. UV-VIS-NIR spectroscopy depicted a total quenching of NIR absorption and a diminished absorption of a peak at ∼745 nm in CDs/NiFe 2O 4 compared with NiFe 2O 4, indicating a transfer of electrons from NiFe 2O 4 to CDs. A 12-fold increment in the incident-photon-to-charge-efficiency was achievable with CDs/NiFe 2O 4 (0.36%) compared with NiFe 2O 4 (0.03%). Impedance spectroscopy exhibited a more efficient charge separation and faster interfacial charge transfer in CDs/NiFe 2O 4 compared with pure NiFe 2O 4. This was accounted for by the lower initial quantity of charge carrier upon irradiation in CDs/NiFe 2O 4 compared with NiFe 2O 4 as detected from laser flash photolysis, indicating that CDs acted as electron acceptors and reservoirs in CDs/NiFe 2O 4. Compared with NiFe 2O 4, CDs/NiFe 2O 4 showed an enhanced photocatalytic activity toward formaldehyde formation. Consequently, CDs are good electron mediators for NiFe 2O 4, capable of improving charge-carrier separation and the photocatalytic activity of NiFe 2O 4

AB - Spinel ferrites such as nickel ferrite are promising energy conversion photocatalysts as they are visible-light absorbers, chemically stable, earth abundant, and inexpensive. Nickel ferrite shows poor photocatalytic activity due to fast electron-hole recombination upon illumination. This study evaluates the capability of carbon dots (CDs) to improve charge-carrier separation in NiFe 2O 4. We report a facile solvothermal approach for synthesizing NiFe 2O 4 and CDs/NiFe 2O 4 nanoparticles at 200-215 °C. The photocatalysts were characterized using transmission and scanning electron microscopy, x-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, UV-VIS-NIR spectroscopy, photoelectrochemical analysis, and laser flash photolysis. Photocatalytic oxidation of methanol to formaldehyde under visible light was employed to test the effect of CDs on the photocatalytic efficacy of NiFe 2O 4. UV-VIS-NIR spectroscopy depicted a total quenching of NIR absorption and a diminished absorption of a peak at ∼745 nm in CDs/NiFe 2O 4 compared with NiFe 2O 4, indicating a transfer of electrons from NiFe 2O 4 to CDs. A 12-fold increment in the incident-photon-to-charge-efficiency was achievable with CDs/NiFe 2O 4 (0.36%) compared with NiFe 2O 4 (0.03%). Impedance spectroscopy exhibited a more efficient charge separation and faster interfacial charge transfer in CDs/NiFe 2O 4 compared with pure NiFe 2O 4. This was accounted for by the lower initial quantity of charge carrier upon irradiation in CDs/NiFe 2O 4 compared with NiFe 2O 4 as detected from laser flash photolysis, indicating that CDs acted as electron acceptors and reservoirs in CDs/NiFe 2O 4. Compared with NiFe 2O 4, CDs/NiFe 2O 4 showed an enhanced photocatalytic activity toward formaldehyde formation. Consequently, CDs are good electron mediators for NiFe 2O 4, capable of improving charge-carrier separation and the photocatalytic activity of NiFe 2O 4

UR - http://www.scopus.com/inward/record.url?scp=85081560019&partnerID=8YFLogxK

U2 - 10.1063/1.5134432

DO - 10.1063/1.5134432

M3 - Article

VL - 8

JO - APL materials

JF - APL materials

SN - 2166-532X

IS - 3

M1 - 031105

ER -