Contemporary science is witnessing a rapid expansion of the two-dimensional (2D) materials family, each member possessing intriguing emergent properties of fundamental and practical importance. Using the particleswarm optimization method in combination with first-principles density functional theory calculations, here we predict a new category of 2D monolayers named tellurene, composed of the metalloid element Te, with stable 1T-MoS 2 -like ( α-Te), and metastable tetragonal (β-Te) and 2H-MoS 2 -like (γ-Te) structures. The underlying formation mechanism of such tri-layer arrangements is uniquely rooted in the multivalent nature of Te, with the central-layer Te behaving more metal-like (e.g., Mo), and the two outer layers more semiconductor-like (e.g., S). In particular, the α-Te phase can be spontaneously obtained from the magic thicknesses truncated along the [001] direction of the trigonal structure of bulk Te. Furthermore, both the α-and β-Te phases possess electron and hole mobilities much higher than MoS 2 , as well as salient optical absorption properties. These findings effectively extend the realm of 2D materials to group-VI monolayers, and provide a new and generic formation mechanism for designing 2D materials. The two-dimensional (2D) materials have been intensively investigated in recent years for their intriguingly emergent properties that can be exploited for electronic, photonic, spintronic, and catalytic device applications [1][2][3][4][5][6][7][8][9][10]. Various 2D monolayers have been synthetized beyond the first member system of graphene [1][2][3], including the group-IV monolayers of silicene [4] and stanene [8], the group-V monolayer of phosphorene [5], and the group-III monolayer of borophene [6,7]. Besides these group-III, -IV, and -V elemental monolayers, transition metal dichalcogenides (TMDCs) have also been attracted much attention because of their relatively wider, tunable, and direct band gaps and inherently stronger spin-orbit coupling [9,10]. Yet to date, somewhat surprisingly, no prediction or fabrication of group-VI elemental monolayers has been made, whose potential existence would not only further enrich our understanding of the realm of the 2D materials world, but could also offer new application potentials stemming from their uniquely physical and chemical properties.In this Letter, we add an attractive new category to the ever increasing 2D materials family by predicting the existence and fabrication of group-VI elemental monolayers centered on the metalloid element Te. Our theoretical calculations reveal that 2D monolayers of Te, named tellurene, can exist in the stable 1T-MoS 2 -like ( α-Te) structure, and metastable tetragonal (β-Te) and 2H-MoS 2 -like (γ-Te) structures. These tri-layer arrangements are driven by the unique multivalency nature of Te, with the central-layer Te behaving more metal-like, and the two outer layers more semiconductor-like. In particular, the monolayer and multilayers of α-Te can be readily obtained via a thickness-dependent structural phase tr...

Molybdenum disulfide (MoS 2 )h as been widely studied as ap otential earth-abundant electrocatalyst for the hydrogen-evolution reaction (HER). Defect engineering and heteroelemental doping are effective methods to enhance the catalytic activity in the HER, so exploring an efficient route to simultaneously achieve in-plane vacancy engineering and elemental doping of MoS 2 is necessary.I nt his study,Z inc, al ow-cost and moderately active metal, has been used to realizethis strategy by generation of sulfur vacancies and zinc doping on MoS 2 in one step.D ensity functional theory calculations reveal that the zinc atoms not only lower the formation energy of Svacancies,but also help to decrease DG H of S-vacancy sites near the Zn atoms.A ta no ptimal zincreduced MoS 2 (Zn@MoS 2 )example,the activated basal planes contribute to the HER activity with an overpotential of À194 mV at 10 mA cm À2 and al ow Tafel slope of 78 mV/dec.

Tuning the facet exposure of Cu could promote the multi-carbon (C2+) products formation in electrocatalytic CO2 reduction. Here we report the design and realization of a dynamic deposition-etch-bombardment method for Cu(100) facets control without using capping agents and polymer binders. The synthesized Cu(100)-rich films lead to a high Faradaic efficiency of 86.5% and a full-cell electricity conversion efficiency of 36.5% towards C2+ products in a flow cell. By further scaling up the electrode into a 25 cm2 membrane electrode assembly system, the overall current can ramp up to 12 A while achieving a single-pass yield of 13.2% for C2+ products. An insight into the influence of Cu facets exposure on intermediates is provided by in situ spectroscopic methods supported by theoretical calculations. The collected information will enable the precise design of CO2 reduction reactions to obtain desired products, a step towards future industrial CO2 refineries.

We have investigated, by means of ab initio calculations, the electronic and magnetic structures of zigzag edge phosphorene nanoribbons (ZPNRs) with various widths. The stable magnetic state was found in pristine ZPNRs by allowing the systems to be spin-polarized. The ground state of pristine ZPNRs prefers ferromagnetic order in the same edge but antiferromagnetic order between two opposite edges. The magnetism arises from the dangling bond states as well as edge localized π-orbital states. The presence of a dangling bond is crucial to the formation of the magnetism of ZPNRs. The hydrogenated ZPNRs get nonmagnetic semiconductors with a direct band gap. While, the O-saturated ZPNRs show magnetic ground states due to the weak P-O bond in the ribbon plane between the pz-orbitals of the edge O and P atoms.

Tumor hypoxia seriously impairs the therapeutic outcomes of type II photodynamic therapy (PDT), which is highly dependent upon tissue oxygen concentration. Herein, a facile strategy of acceptor planarization and donor rotation is proposed to design type I photosensitizers (PSs) and photothermal reagents. Acceptor planarization can not only enforce intramolecular charge transfer to redshift NIR absorption but also transfer the type of PSs from type II to type I photochemical pathways. Donor rotation optimizes photothermal conversion efficiency (PCE). Accordingly, three 3,6-divinylsubstituted diketopyrrolopyrrole (DPP) derivatives, 2TPAVDPP, TPATPEVDPP, and 2TPEVDPP, with different number of rotors were prepared. Experimental results showed that three compounds were excellent type I PSs, and the corresponding 2TPEVDPP nanoparticles (NPs) with the most rotors possessed the highest PCE. The photophysical properties of 2TPEVDPP NPs are particularly suitable for in vivo NIR fluorescence imaging-guided synergistic PDT/PTT therapy. The proposed strategy is helpful for exploiting type I phototherapeutic reagents with high efficacy for synergistic PDT and PTT.