Photocatalytic activity of B-doped nano graphene oxide over hydrogenated NiO-loaded TiO2 nanotubes

Abstract

A hydrogenated NiO-loaded anatase TiO2 with unique heterostructure nanotube arrays (denoted as H:(NiO/TiO2)) NTs were synthesized, followed by the attachment of boron-doped reduced nanographene oxide nanoparticles (B-nGO NPs) to form a vigorous composite photoelectrode B-nGO/H:(NiO/TiO2) NTs. The p-n junction created between p-type NiO and n-type TiO2 produces sufficient built-in electric field to facilitate the electron–hole pair separation and boost the interfacial electron transfer, subsequently a hydrogenation treatment to adjust the donor density and maximize the electron–hole separation. The microstructure characterization with synchrotron-based X-ray techniques straightened out that the created NiO oxygen vacancies can provide emptier d-orbitals to accept more photoexcited electrons. With the incorporation of B-nGO NPs, the partially replacement of C atoms of nGO by B atoms can form an electron–hole-rich configuration in the heterostructure to decrease the Fermi level, with a more rapid electron transfer toward TiO2 substrate during photocatalysis, which also confirmed by quantum-chemical calculations. The as-synthesized B-nGO/H:(NiO/TiO2) NTs exhibited a high photocurrent density (2.0 mA/cm2) and an effective photoconversion efficiency (2.07%) under simulated sunlight irradiation (AM1.5G, 100 mW/cm2). The eventuated photoconversion efficiency is 6 times enhanced with respect to the pristine TiO2, along with an impressive hydrogen evolution rate of 31 μmol/h/cm2. Moreover, the photocurrent durability test has confirmed the stability of B-nGO/H:(NiO/TiO2) electrode, with only a slight decay of <1% after continuous illumination for more than 4 h. Incident photon conversion efficiency spectra have revealed a boosted photo-response under visible light region (extended to ∼520 nm) with the synergistic attachment of NiO and B-nGO.