Nickel nanoparticle-activated MoS2 for efficient visible light photocatalytic hydrogen evolution

Direct sunlight-induced water splitting for photocatalytic hydrogen evolution is the dream for an ultimate clean energy source. So far, typical photocatalysts require complicated synthetic processes and barely work without additives or electrolytes. Here, we report the realization of a hydrogen evolution strategy with a novel Ni-Ag-MoS₂ ternary nanocatalyst under visible/sun light. Synthesized through an ultrasound-assisted wet method, the composite exhibits stable catalytic activity for long-term hydrogen production from both pure and natural water. A high efficiency of 73 μmol g^-1 W^-1 h^-1 is achieved with only a visible light source and the (MoS₂)₈₄Ag₁₀Ni₆ catalyst, matching the values of present additive-enriched photocatalysts. Verified by experimental characterizations and first-principles calculations, the enhanced photocatalytic ability is attributed to effective charge migration through the dangling bonds at the Ni-Ag-MoS₂ alloy interface and the activation of the MoS₂ basal planes.

Sn3C2monolayer with transition metal adatom for gas sensing: a density functional theory studies

The gas sensing properties of pristine Sn₃C₂monolayer and different transition metal adatom (TM-Sn₃C₂, where TM = Fe, Co, Ni, Cu, Ru, Rh, Pd and Ag) was investigated using van der Waals corrected density functional theory. The understanding and potential of use of Sn₃C₂monolayers as sensors or adsorbent for CO, CO₂, NO, NO₂and SO₂gaseous molecules is evaluated by calculating the adsorption and desorption energetics. From the calculated adsorption energies, we found that the pristine Sn₃C₂monolayer and 3dTM has desirable properties for removal of the considered molecules based on their high adsorption energy, however the 4dTM is applicable as recoverable sensors. We applied an Arrhenius-type equation to evaluate the recovery time for the desorption of the molecules on the pristine and TM adatom on Sn₃C₂monolayer. We found that the negative adsorption energies from -1 to -2 eV of the molecules resulted in easier recovery of the adsorbed gases at reasonable temperatures compared to adsorption energies in between 0 and -1 eV (weakly physiosorbed) and below -2 eV (strongly chemisorbed). Hence, we obtained that the Rh-Sn₃C₂, Ru-Sn₃C₂, Pd-Sn₃C₂, Pd-Sn₃C₂, and Rh-Sn₃C₂monolayers are good recoverable scavengers for the CO, CO₂, NO, NO₂, and SO₂molecules. The current theoretical calculations provide new insight on the effect of TM adatoms on the structural, electronic, and magnetic properties of the Sn₃C₂monolayer and different transition metal adatom as well as shed light on their application as gas sensors/scavengers.

Metallic Contact between MoS2 and Ni via Au Nanoglue

A critical factor for electronics based on inorganic layered crystals stems from the electrical contact mode between the semiconducting crystals and the metal counterparts in the electric circuit. Here, a materials tailoring strategy via nanocomposite decoration is carried out to reach metallic contact between MoS₂ matrix and transition metal nanoparticles. Nickel nanoparticles (NiNPs) are successfully joined to the sides of a layered MoS₂ crystal through gold nanobuffers, forming semiconducting and magnetic NiNPs@MoS₂ complexes. The intrinsic semiconducting property of MoS₂ remains unchanged, and it can be lowered to only few layers. Chemical bonding of the Ni to the MoS₂ host is verified by synchrotron radiation based photoemission electron microscopy, and further proved by first-principles calculations. Following the system's band alignment, new electron migration channels between metal and the semiconducting side contribute to the metallic contact mechanism, while semiconductor-metal heterojunctions enhance the photocatalytic ability.

Long range of indirect exchange interaction on the edges of MoS2 flakes

We study the Ruderman-Kittel-Kasuya-Yosida interaction between two magnetic impurities connected to the edges of zigzag-terminated MoS₂ flakes. When the impurities lie on the edges of the flake, the effective exchange interaction exhibits sizable noncollinear Dzyaloshinskii-Moriya character that competes with a strong Ising coupling. We analyze the characteristic decay exponent for doping levels inside the band gap of the infinite layer, corresponding to edge states of the flake at the Fermi level. The characteristic exponents show sub-two-dimensional behavior for these band fillings, with decays much slower than quadratic. The Ising interaction has effectively one-dimensional long range, while the noncollinear component that grows for short impurity separation becomes comparable in magnitude. The resulting tunable exchange interaction on these systems opens the way for the study of interesting phases of impurity arrays with long-range stable helical order.