Photocatalytic water oxidation by layered Co/h-BCN hybrids

Abstract

The search for new materials has progressed from metal-based photocatalysts to elemental semiconductors (C, Si, P, S, B) [11][12][13][14][15] and recently to metal-free binary materials and polymers, such as carbon nitride [16], boron carbide [17] and conjugated semiconductors [18][19][20]. These researches indicate that photon absorbing materials can be constituted by using lightweight elements such as carbon, nitrogen, and boron, opening up new opportunities for the selection of innovative and intriguing materials for artificial photosynthesis. It is of particular interest that some of these elements themselves (graphene [21], silicone [22]) or their combinations (h-BN, g-C 3 N 4 ) [23] can form layered structures with reduced thickness comparable to charge-diffusion distance, and thus if a semiconducting electronic structure was imparted in these materials, the fast separation of light-induced charge carrier would significantly benefit surface photoredox process that relied on the excitation and separation of electron-hole pairs and their subsequent participation in surface chemical reactions [24][25][26]. An interesting case of such a layered material is ternary h-BCN with tuneable ba nd gap energies between graphene (zero bandgap) and h-BN (bandgap = 5.6 eV) [27], which have the same atomic structure and share many similar properties. The hybridized phases of the two two-dimensional (2D) materials by atomic mixture of B, N, and C with broad composition ranges to create various layered semiconducting structures would produce new material functions complementary to graphene and h-BN, enabling a wide variety of electronic structures, applications and properties [28][29][30]. Such an emerging family of chemically inert and mechanically strong 2D materials practically allows the bandgap-engineered applications in heterogeneous photocatalysis by creating a medium-gap ternary semiconductor, in which the band gap, redox energy levels, p/n-type properties and surface acid-base chemistry can in principle be modulated by rational design and synthesis [31,32].A hexagonal boron carbon nitride (h-BCN) semiconductor was applied to intercalate cobalt ions to catalyze oxygen evolution reaction (OER) with light illumination, without using noble metals. The h-BCN with high specific surface area showed a strong chemical affinity towards metal ions due to the "lop-sided" densities characteristic of ionic B-N bonding, enabling the creation of metal/h-BCN hybrid layered structures with unique properties. As exemplified here by Co/h-BCN for water oxidation catalysis, after intercalating cobalt ions in the h-BCN host, the photocatalytic activity of the resultant layered hybrid is optimized due to their synergic catalysis that promotes charge separation and lowers reaction barriers. This finding promises a new nobel-metal-free nanocompsite using cost-acceptable and earth-abundant sust ances for photocatalytic OER, and enables the facile design of duel catalytic cascades by merging transition metal catalysis with h-BCN (photo)catalys...

Reduced-sized monolayer carbon nitride nanosheets for highly improved photoresponse for cell imaging and photocatalysis

“…As compared in Fig. 6c, the NMGCN powder shows a lower PL emission intensity than the GCNN case, suggesting the lower charge recombination rate in the NMGCNs [14,46,47]. A blue shift of the maximum emission peak was also observed in the PL spectrum of the NMGCN powder, which was in agreement with the above DRS results.…”

“…Due to the fascinating physicochemical and electronic properties arising from the small dimensions and quantum confinement effects (QCE) [1][2][3], ultrathin nanosheets have been the focus of substantial research in the light of fundamental studies and their broad applications in various fields, including optoelectronic devices [4], energy conversion and storage [5], sensors [6][7][8][9], biomedicine [10], and catalysis [11][12][13][14][15]. In particular, polymeric graphitic carbon nitride nanosheets (GCNNs), an n-type semiconductor, have been receiving considerable attention due to their many intriguing advantages such as the fact that they contain no metal, and nontoxicity, easy availability, sensitive photo-response, excellent chemical and thermal stability, and unique electronic structures [16][17][18][19].…”

Hydrogenated TiO2/SrTiO3 porous microspheres with tunable band structure for solar-light photocatalytic H2 and O2 evolution

“…The H-TiO2/SrTiO3 porous microspheres exhibit stronger absorptive capacity in the visible-light region at above 420 nm, and a clear red-shift of the optical absorption edge is observed. This phenomenon is very common and widely developed for hydrogenated semiconductors [35,36], and the photoabsorption tail rising in the visible-light region is a good indication of oxygen vacancies [37]. As shown by the plot of the Kubelka-Munk function versus the energy of the incident light, the band gaps of the pristine TiO2, SrTiO3, TiO2/SrTiO3, and H-TiO2/SrTiO3 heterostructured porous microspheres are 3.11, 3.04, 2.98, and 2.87 eV, respectively (Fig.…”

“…5d). This is because the formation of a heterostructure accelerates the charge carrier transfer rate and thus inhibits the recombination of photogenerated electrons and holes, which contributes to the improvement of photocatalytic activity [37].…”

Promoting charge carrier utilization by integrating layered double hydroxide nanosheet arrays with porous BiVO4 photoanode for efficient photoelectrochemical water splitting

“…Loading oxygen-evolution cocatalysts (OECs) has been considered as an effective approach to accelerate the surface reaction kinetics and reduce oxygen evolution reaction (OER) barrier of semiconductor materials [7,13,19,20]. Although traditional noble metal oxides, such as IrO2 and RuO2, are considered as the most active OER electrocatalysts for OECs in PEC cells [5,14], the high cost and low stability limit their extensive applications [7].…”