By introducing the commonly utilized Fe atoms into a two-dimensional (2D) honeycomb boron network, we theoretically designed a new Dirac material of FeB monolayer with a Fermi velocity in the same order of graphene. The electron transfer from Fe atoms to B networks not only effectively stabilizes the FeB networks but also leads to the strong interaction between the Fe and B atoms. The Dirac state in FeB system primarily arises from the Fe d orbitals and hybridized orbital from Fe-d and B-p states. The newly predicted FeB monolayer has excellent dynamic and thermal stabilities and is also the global minimum of 2D FeB system, implying its experimental feasibility. Our results are beneficial to further uncovering the mechanism of the Dirac cones and providing a feasible strategy for Dirac materials design.

By means of density functional theory (DFT) computations and global minimum search using particle-swarm optimization (PSO) method, we predicted three FeB6 monolayers, namely α-FeB6, β-FeB6 and γ-FeB6, which consist of the Fe©Bx (x = 6, 8) wheels with planar hypercoordinate Fe atoms locating at the center of six- or eight-membered boron rings. In particular, the α-FeB6 sheet constructed by Fe©B8 motifs is the global minimum due to completely shared and well delocalized electrons. The two-dimensional (2D) boron networks are dramatically stabilized by the electron transfer from Fe atoms, and the FeB6 monolayers have pronounced stabilities. The α-FeB6 monolayer is metallic, while the β-FeB6 and γ-FeB6 sheets are semiconductors with indirect band gaps and significant visible-light absorptions. Besides the novel chemical bonding, the high feasibility for experimental realization, and unique electronic and optical properties, render them very welcome new members to the graphene-like materials family.

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Via density functional theory computations, we investigated the photocatalytic activities of pure and alloyed bismuth oxyhalides (BiOXs). The dipole moments of the majority of pure and alloyed BiOXs are larger than 2.00 Debye, which can ensure their high photocatalytic efficiencies. Both the redox potentials of the photon-induced holes and the band gaps increase with an increasing content of lighter halogen atoms in the BiOXs, which competitively affects the photocatalytic efficiency. The hole mobility decreases a lot due to the hybridization of the halogen np states, while the electron mobility is not affected by such hybridization. Therefore, the alloying effect in BiOXs brings about a substantially lower electron-hole recombination rate and, accordingly, a much higher photocatalytic efficiency. Our investigation also suggests that O vacancies, which are energetically more favorable in alloyed BiOXs, could act as capture centers for excited electrons and, consequently, improve the separation of the electron-hole pairs. Our findings present a reasonable explanation for the recent experimental reports and provide some guidance for the design of alloyed BiOX photocatalysts.