Boron Carbides as Efficient, Metal-Free, Visible-Light-Responsive Photocatalysts

Visible Light-Driven Highly Selective CO2 Reduction to CH4 Using Potassium-Doped g-C3N5

Establishment of an efficient and robust artificial photocatalytic system to convert solar energy into chemical fuels through CO₂ conversion is a cherished goal in the fields of clean energy and environmental protection. In this work, we have explored an emergent low-Z nitrogen-rich carbon nitride material g-C₃N₅ (analogue of g-C₃N₄) for CO₂ conversion under visible light illumination. A significant enhancement of the CH₄ production rate was detected for g-C₃N₅ in comparison to that of g-C₃N₄. Notably, g-C₃N₅ also showed a very impressive selectivity of 100% toward CH₄ as compared to 21% for g-C₃N₄. The photocatalytic CO₂ conversion was performed without using sacrificial reagents. We found that 1% K doping in g-C₃N₅ enhanced its performance even further without compromising the selectivity. Moreover, 1% K-doped g-C₃N₅ also exhibited better photostability than undoped g-C₃N_5. We have also employed density functional theory calculation-based analyses to understand and elucidate the possible reasons for the better photocatalytic performance of K-doped g-C₃N₅.

In Situ-Fabricated 2D/2D Heterojunctions of Ultrathin SiC/Reduced Graphene Oxide Nanosheets for Efficient CO2 Photoreduction with High CH4 Selectivity

Photoreduction of CO₂ into fuel molecules such as CH₄ represents a promising route to simultaneously explore renewable energy and alleviate global warming. However, the implementation of such a process is hampered by low product yields and poor selectivity. A 2D/2D heterojunction of ultrathin SiC and reduced graphene oxide (RGO) nanosheets was fabricated in situ for efficient and selective photoreduction of CO₂ . Ultrathin SiC suppresses significant charge recombination in the bulk phase, thus providing more energetic electrons. The robust 2D/2D heterojunction allows fast transfer of energetic electrons from SiC to RGO. Combining the vital role of RGO in facilitating CO₂ activation, the optimized SiC/RGO exhibits an electron-transfer rate of 58.17 μmol h^-1  g^-1 towards CO₂ reduction, 2.7 times that of pure SiC (20.25 μmol h^-1  g^-1 ). About 92 % of the transferred electrons from SiC are devoted to generating CH₄ (6.72 μmol h^-1  g^-1 ). Such high efficiency and selectivity are mainly a result of the densely accumulated energetic electrons within RGO, which facilitate the eight-electron process to produce CH₄ . This work will inspire the design of catalyst/cocatalyst systems for efficient and selective photoreduction of CO₂ .

Composition-Dependent Charge Transport in Boron Carbides Alloyed with Aromatics: Plasma Enhanced Chemical Vapor Deposition Aniline/Orthocarborane Films

Boron carbide films, alloyed with aniline moieties, were deposited by plasma enhanced chemical vapor deposition (PECVD) from aniline and orthocarborane precursors and were found to exhibit composition-dependent drift carrier lifetimes as derived from I( V) and C( V)) measurements. For a film with an aniline/carborane ratio of 5:1, the effective drift carrier lifetimes are ∼80 μs at low bias voltage but quickly drop to a few microseconds with increasing bias. A film with a 10:1 aniline/carborane ratio, however, exhibited lifetimes of ∼6 μs, or less, at 1 kHz, and much smaller values at 10 kHz. These lifetimes are orders of magnitude longer than those in polyaniline films and comparable to those in PECVD carborane films without aromatic content. X-ray photoelectron spectroscopy (XPS), FTIR, and ellipsometry, combined with density functional theory (DFT)-based cluster calculations, indicate that aniline and orthocarborane moieties are largely intact within the films. Bonding occurs primarily between aniline C sites and carborane B sites, and the aniline coordination number per carborane icosahedron is ∼2 as the aniline/carborane ratio is increased from 3:1 to 10:1. This aniline/carborane coordination ratio independent of aniline/orthocarborane stoichiometry is consistent with the dependence of charge transport properties on aniline film content at high bias voltage.

Carborane-based polymers: a novel class of semiconductors with tunable properties

Semiconducting boron carbides based on cross-linked carborane (B₁₀C₂H₁₂) icosahedra, developed several decades ago, are of significant interest in a variety of emerging areas, including photocatalysis, spintronics, and especially neutron detection.