Photocatalytic H₂ production and degradation of aqueous 2-chlorophenol over B/N-graphene-coated Cu⁰/TiO₂

A DFT, experimental and mechanistic investigation

authored by

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

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.

Organisation(s)

Institute of Technical Chemistry
Institute of Physical Chemistry and Electrochemistry
Laboratory of Nano and Quantum Engineering

External Organisation(s)

Technical University of Kenya (TU-K)
Swansea University
University of South Africa
University of KwaZulu-Natal
University of Bonn
Saint Petersburg State University

Type

Article

Journal

Journal of Environmental Management

Volume

311

ISSN

0301-4797

Publication date

06.2022

Publication status

Published

Peer reviewed

Yes

ASJC Scopus subject areas

Environmental Engineering, Waste Management and Disposal, Management, Monitoring, Policy and Law

Sustainable Development Goals

SDG 7 - Affordable and Clean Energy

Electronic version(s)

https://doi.org/10.1016/j.jenvman.2022.114822 (Access: Closed)