Photocatalytic H2 production and degradation of aqueous 2-chlorophenol over B/N-graphene-coated Cu0/TiO2: A DFT, experimental and mechanistic investigation

Lucy M Ombaka; James D McGettrick; Ekemena O Oseghe; Osama Al-Madanat; Felix Rieck Genannt Best; Titus A M Msagati; Matthew L Davies; Thomas Bredow; Detlef W Bahnemann

doi:10.1016/j.jenvman.2022.114822

Photocatalytic H₂ production and degradation of aqueous 2-chlorophenol over B/N-graphene-coated Cu⁰/TiO₂: A DFT, experimental and mechanistic investigation

J Environ Manage. 2022 Mar 4:311:114822. doi: 10.1016/j.jenvman.2022.114822. Online ahead of print.

Authors

Lucy M Ombaka¹, James D McGettrick², Ekemena O Oseghe³, Osama Al-Madanat⁴, Felix Rieck Genannt Best⁵, Titus A M Msagati³, Matthew L Davies⁶, Thomas Bredow⁷, Detlef W Bahnemann⁸

Affiliations

¹ Institut für Technische Chemie, Gottfried Wilhelm Leibniz Universität Hannover, Callinstrasse 3, Hannover, 30167, Germany; School of Chemistry and Material Science, Technical University of Kenya, P.O Box 52428-00200, Nairobi, Kenya. Electronic address: lucyombaka@tukenya.ac.ke.
² SPECIFIC IKC, Materials Research Centre, College of Engineering, Swansea University, Bay Campus, Fabian Way, Swansea, SA1 8EN, UK.
³ Institute for Nanotechnology and Water Sustainability, College of Science, Engineering and Technology, University of South Africa, Florida Campus, 1709, Johannesburg, South Africa.
⁴ Institut für Technische Chemie, Gottfried Wilhelm Leibniz Universität Hannover, Callinstrasse 3, Hannover, 30167, Germany.
⁵ Institute for Physical Chemistry and Electrochemistry, Leibniz University Hannover, 30167, Hannover, Germany.
⁶ SPECIFIC IKC, Materials Research Centre, College of Engineering, Swansea University, Bay Campus, Fabian Way, Swansea, SA1 8EN, UK; School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Private Bag X54001, Durban, 4000, South Africa.
⁷ Mulliken Center for Theoretical Chemistry, Institute for Physical and Theoretical Chemistry, University of Bonn, Beringstr. 4, Bonn, Germany.
⁸ Institut für Technische Chemie, Gottfried Wilhelm Leibniz Universität Hannover, Callinstrasse 3, Hannover, 30167, Germany; Laboratorium für Nano- und Quantenengineering, Gottfried Wilhelm Leibniz Universität Hannover, Schneiderberg 39, Hannover, 30167, Germany; Laboratory for Photoactive Nanocomposite Materials, Department of Photonics, Faculty of Physics, Saint-Petersburg State University, Ulianovskaia Str. 3, Peterhof, Saint-Petersburg, 198504, Russia.

PMID: 35255324
DOI: 10.1016/j.jenvman.2022.114822

Abstract

Energy and environmental challenges are global concerns that scientists are interested in alleviating. It is on this premise that we prepared boron/nitrogen graphene-coated Cu⁰/TiO₂ (B/N-graphene-coated Cu/TiO₂) photocatalyst of varying B:N ratios with dual functionality of H₂ production and 2-Chlorophenol (2-CP) degradation. In-situ coating of Cu⁰ with B/N-graphene is achieved via solvothermal synthesis and calcination under an inert atmosphere. All B/N-graphene-coated Cu/TiO₂ exhibit higher photonic efficiencies (5.68%-7.06% at 300 < λ < 400 nm) towards H₂ production than bare TiO₂ (0.25% at 300 < λ < 400 nm). Varying the B:N ratio in graphene influences the efficiency of H₂ generation. A B:N ratio of 0.08 yields the most active composite exhibiting a photonic efficiency of 7.06% towards H₂ evolution and a degradation rate of 4.07 × 10^-2 min^-1 towards 2-chlorophenol (2-CP). Density functional theory (DFT) investigations determine that B-doping (p-type) enhances graphene stability on Cu⁰ while N-doping (n-type) increases the reduction potential of Cu⁰ relative to H⁺ reduction potential. X-ray photoelectron spectroscopy reveals that increasing the B:N ratio increases p-type BC₂O while decreasing n-type pyridinic-N in graphene thus altering the interlayer electron density. Isotopic labelling experiments determine water reduction as the main mechanism by which H₂ is produced over B/N-graphene-coated Cu/TiO₂. The reactive species involved in the degradation of 2-CP are holes (h⁺), hydroxyl radical (OH^•), and O₂^•-, of which superoxide (O₂^•-) plays the major role. This work displays B/N -graphene-coated Cu/TiO₂ as a potential photocatalyst for large-scale H₂ production and 2-CP degradation.

Keywords: 2-Chlorophenol degradation; Green energy; Hydrogen production; Metallic copper; Photocatalysis.