Abstract
Boron-based nanomaterials are emerging as non-toxic, earth-abundant (photo)electrocatalyst materials in solar energy conversion for the production of solar hydrogen fuel and environmental remediation. Boron carbon oxynitride (BCNO) is a quaternary semiconductor with electronic, optical, and physicochemical properties that can be tuned by varying the composition of boron, nitrogen, carbon, and oxygen. However, the relationship between BCNO's structure and -photocatalytic activity relationship has yet to be explored. We performed an in-depth spectroscopic analysis to elucidate the effect of using two different nitrogen precursors and the effect of annealing temperatures in the preparation of BCNO. BCNO nanodisks (D = 6.7 ± 1.1 nm) with turbostratic boron nitride diffraction patterns were prepared using guanidine hydrochloride as the nitrogen source precursor upon thermal annealing at 800°C. The X-ray photoelectron spectroscopy (XPS) surface elemental analysis of the BCNO nanodisks revealed the B, C, N, and O compositions to be 40.6%, 7.95%, 37.7%, and 13.8%, respectively. According to the solid-state 11B NMR analyses, the guanidine hydrochloride-derived BCNO nanodisks showed the formation of various tricoordinate BNx(OH)3−x species, which also served as one of the photocatalytic active sites. The XRD and in-depth spectroscopic analyses corroborated the preparation of BCNO-doped hexagonal boron nitride nanodisks. In contrast, the BCNO annealed at 600 °C using melamine as the nitrogen precursor consisted of layered nanosheets composed of B, C, N, and O atoms covalently bonded in a honeycomb lattice as evidence by the XRD, XPS, and solid-state NMR analysis (11B and 13C) analyses. The XPS surface elemental composition of the melamine-derived BCNO layered structures consisted of a high carbon composition (75.1%) with a relatively low boron (5.24%) and nitrogen (7.27%) composition, which indicated the formation of BCNO-doped graphene oxides layered sheet structures. This series of melamine-derived BCNO-doped graphene oxide layered structures were found to exhibit the highest photocatalytic activity, exceeding the photocatalytic activity of graphitic carbon nitride. In this layered structure, the formation of the tetracoordinate BNx(OH)3−x(CO) species and the rich graphitic domains were proposed to play an important role in the photocatalytic activity of the BCNO-doped graphene oxides layered structures. The optical band gap energies were measured to be 5.7 eV and 4.2 eV for BCNO-doped hexagonal boron nitride nanodisks and BCNO-doped graphene oxides layered structures, respectively. Finally, BCNO exhibited an ultralong photoluminescence with an average decay lifetime of 1.58, 2.10, 5.18, and 8.14 µs for BGH01, BGH03, BMH01, BMH03, respectively. This study provides a novel metal-free photocatalytic system and provides the first structural analysis regarding the origin of BCNO-based photocatalyst.Graphical
Highlights
Metal-free nanomaterials are emerging as cost-effective, earth-friendlycatalyst with high structural and chemical stabilities for various applications including solar fuel production, environmental remediation, CO2Chien et al Nanoscale Research Letters (2021) 16:176 reduction, disinfection of harmful microorganisms, and enabled selective chemical synthesis of organic compounds [1–7]
Based on the synthesis of Boron carbon oxynitride (BCNO) reported in the literature [25, 32], we investigated the effect of using two different nitrogen precursor sources as well as the effect of thermal annealing temperatures, and time on the structure–property evolution of BCNO
Through systematic investigation of using two different nitrogen precursors, crystalline BCNO with a quasi-spherical shape was prepared at 800 °C for 12 hr using guanidine hydrochloride as the nitrogen source
Summary
Metal-free nanomaterials are emerging as cost-effective, earth-friendly (photo)catalyst with high structural and chemical stabilities for various applications including solar fuel production, environmental remediation, CO2. Chien et al Nanoscale Research Letters (2021) 16:176 reduction, disinfection of harmful microorganisms, and enabled selective chemical synthesis of organic compounds [1–7]. Compared to their metal counterparts, a metal-free catalyst is less prone to poisoning and leads to higher cycle lifetimes. High surface area carbon-doped hexagonal boron nitride (BCN) nanosheets exhibiting visible light photocatalytic activity for H2 andO2 generation as well as CO2 reduction and capture have led to new possibilities in photosystem [14, 15]. Other boron-containing (photo)electrocatalyst such as boron oxynitride (BNO)[16, 17], boron phosphide (BP) [18, 19], boron-doped graphene [20], boron carbon nitride (BCN) [14], boron-doped carbon nitride (B-dopedCN) [21] and elemental boron [22, 23] have demonstrated significant (photo) electrocatalytic activities [13]
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