Doping effects of transition metals on the superconductivity of (Li,Fe)OHFeSe films

The doping effects of transition metals(TMs = Mn, Co, Ni, and Cu) on the superconducting critical parameters are investigated in the films of iron selenide(Li,Fe)OHFe Se. The samples are grown via a matrix-assisted hydrothermal epitaxy method. Among the TMs, the elements of Mn and Co adjacent to Fe are observed to be incorporated into the crystal lattice more easily. It is suggested that the doped TMs mainly occupy the iron sites of the intercalated(Li,Fe)OH layers rather than those of the superconducting Fe Se layers. We find that the critical current density J_(c) can be enhanced much more strongly by the Mn dopant than the other TMs, while the critical temperature T_(c) is weakly affected by the TM doping.

Influence of transition metals(Sc,Ti,V,Cr,and Mn)doping on magnetism of CdS

The influence of transition metals(Sc,Ti,V,Cr,and Mn)doping at different distances on the magnetism of CdS is studied by using generalized gradient approximation combined with Hubbard U in the VASP package.The results show that the doping systems are more stable,easy to form,and the wurtzite structure of CdS is not changed.It is found that the systems are antiferromagnetic(AFM)when nearest neighbor doping,which is attributed to the direct charge transfers between two impurity ions.The systems are ferromagnetic(FM)when the doping distance increases further,since the double exchange interactions are observed among the 3d orbital of the transition metal,the Cd-5s and the S-3p orbitals are at conduction band minimum.We also found that the total magnetic moment of each ferromagnetic system increases with the order of SC to Mn-doping,the spin polarizability of Cr-doping system is 100%.The estimated Curie temperature indicates that the Cr-and Mn-doped CdS in this paper can achieve room-temperature ferromagnetic characteristics,especially the Cr doping is the most prominent.And TM-doping does not destroy the semiconductor characteristics of the system.Therefore,the TM-doped CdS can be used as an ideal dilute magnetic semiconductor functional material.

A Fundamental DFT Study of Anatase(TiO2) Doped with 3d Transition Metals for High Photocatalytic Activities

Anatase（TiO_2） has been widely used in photocatalysis. However, it can only absorb near-ultraviolet light with a wavelength below approximately 388 nm due to a wide band gap. Therefore a modification should be made for anatase to increase its capability in utilizing more abundant visible light. We investigated the doped anatase with the most promising 3d transition metal elements, and the results showed that the visible light absorption intensity was increased significantly due to the reduced band gap and the cavitation effects. As compared to other 3d transition metals, Cu was found to be the most effective one in improving anatase photocatalytic effects. In addition, greater Cu concentration doped in the anatase increased the photocatalysis effects but reduced the anatase stability, therefore, an optimized Cu concentration should be considered to optimize the anatase photocatalysis activity.

Doping-induced metal–N active sites and bandgap engineering in graphitic carbon nitride for enhancing photocatalytic H_(2 )evolution performance

Durable and inexpensive graphitic carbon nitride(g-C_(3)N_(4))demonstrates great potential for achieving efficient photocatalytic hydrogen evolution reduction(HER).To further improve its activity,g-C_(3)N_(4)was subjected to atomic-level structural engineering by doping with transition metals(M=Fe,Co,or Ni),which simultaneously induced the formation of metal-N active sites in the g-C_(3)N_(4)framework and modulated the bandgap of g-C_(3)N_(4).Experiments and density functional theory calculations further verified that the as-formed metal-N bonds in M-doped g-C_(3)N_(4)acted as an"electron transfer bridge",where the migration of photo-generated electrons along the bridge enhanced the efficiency of separation of the photogenerated charges,and the optimized bandgap of g-C_(3)N_(4)afforded stronger reduction ability and wider light absorption.As a result,doping with either Fe,Co,or Ni had a positive effect on the HER activity,where Co-doped g-C_(3)N_(4)exhibited the highest performance.The findings illustrate that this atomic-level structural engineering could efficiently improve the HER activity and inspire the design of powerful photocatalysts.

Unveiling spin magnetic effect of TM doped SnS_(2) nanosheet with enhanced hydrogen evolution reaction

Photoelectrochemical hydrogen evolution reaction(HER)is taken into account as an alternative to effective hydrogen production,emphasizing the importance of catalysts.The magnetism of catalysts could modulate the adsorption of the H atom and further enhance the HER activity.Herein,doping the double transition metal atoms on SnS_(2) nanosheet(TM_(2)@SnS_(2))to form the efficient magnetic catalyst is proposed to explore the spin magnetic effect on the HER performance.By performing first-principles calculations,nonmagnetic V_(2)@SnS_(2) is proved to be the candidate of the HER catalyst;nevertheless,the HER activities of antiferromagnetic and ferromagnetic V_(2)@SnS_(2) are relatively inferior due to the spin-induced charge redistribution.Meanwhile,machine learning analysis shows the absolute importance of the electronic structure of TM dopants and surrounding S ligands,and the HER activity could be predicted by the modified band centers of S-3p_(z) and TM-d.Furthermore,the proof-of-concept experiment has substantiated the above theoretical predictions by significantly increasing liner sweep voltammetry and photocurrent with applied magnetic field.This work provides a new avenue for uncovering the spin catalytic mechanism and the exploration and design of efficient HER catalysts.

Transition metaldoping effect and high catalytic activity of CeO_(2)-TiO_(2) for chlorinated VOCs degradation

A series of transition metals(Fe,Co,Ni,Cu,Cr and Mn)-doped CeO_(2)-TiO_(2) catalysts were prepared by the sol-gel method and applied for the catalytic removal of 1,2-dichloroethane(DCE) as a model for chlorinated VOCs(CVOCs).The various characterization methods including X-ray diffraction(XRD),N_(2) adsorption-desorption,UV-Raman,NH_(3) temperature-programmed desorption(NH_(3)-TPD) and H_(2) temperature-programmed reduction(H_(2)-TPR) were utilized to investigate the physicochemical properties of the catalysts.The results show that doping Fe,Co,Ni or Mn can obviously promote the activity of CeO_(2)-TiO_(2) mixed oxides for DCE degradation,which is related to their improved texture properties,acid sites(especially for strong acidity) and low-temperature reducibility.Particularly,CeTi-Fe doped with moderate Fe exhibits excellent activity for 1,2-dichloroethane(DCE) degradation,giving a T_(90%) value as low as 250℃.More importantly,only trace chlorinated byproducts were produced during the low-temperature degradation of various CVOCs(dichloromethane(DCM),trichloroethylene(TCE) and chlorobenzene(CB)) over CeTi-Fe1/9 catalyst with high durability.

Ni_xWO_(2.72) nanorods as an efficient electrocatalyst for oxygen evolution reaction

Ni_xWO_(2.72) nanorods(NRs) are synthesized by a one-pot reaction of Ni(acac)_2 and WCl_4. In the rod structure, Ni(Ⅱ) intercalates in the defective perovskite-type WO_(2.72) and is stabilized. The Ni_xWO_(2.72) NRs show the x-dependent electrocatalysis for the oxygen evolution reaction(OER) in 0.1 M KOH with Ni_(0.78)WO_(2.72) being the most efficient, even outperforming the commercial Ir-catalyst. The synthesis is not limited to Ni_xWO_(2.72) but can be extended to M_xWO_(2.72)(M = Co, Fe) as well,providing a new class of oxide-based catalysts for efficient OER and other energy conversion reactions.

Enhancing hydrogen evolution reaction performance of transition metal doped two-dimensional electride Ca_(2)N

Two-dimensional electride Ca_(2)N has strong electron transfer ability and low work function,which is a potential candidate for hydrogen evolution reaction(HER)catalyst.In this work,based on density functional theory calculations,we adopt two strategies to improve the HER catalytic activity of Ca_(2)N monolayer:introducing Ca or N vacancy and doping transition metal atoms(TM,refers to Ti,V,Cr,Mn,Fe,Zr,Nb,Mo,Ru,Hf,Ta and W).Interestingly,the Gibbs free energyΔG_(H*)of Ca_(2)N monolayer after introducing N vacancy is reduced to-0.146 e V,showing good HER catalytic activity.It is highlighted that,the HER catalytic activity of Ca_(2)N monolayer can be further enhanced with TM doping,the Gibbs free energyΔG_(H*)of single Mo and double Mn doped Ca_(2)N are predicted to be 0.119 and 0.139 e V,respectively.The present results will provide good theoretical guidance for the HER catalysis applications of two-dimensional electride Ca_(2)N monolayer.

Defect energetics and magnetic properties of 3d-transition-metal-doped topological crystalline insulator SnTe

The introduction of magnetism in SnTe-class topological crystalline insulators is a challenging subject with great importance in the quantum device applications. Based on the first-principles calculations, we have studied the defect energetics and magnetic properties of 3d transition-metal(TM)-doped SnTe. We find that the doped TM atoms prefer to stay in the neutral states and have comparatively high formation energies, suggesting that the uniform TMdoping in SnTe with a higher concentration will be difficult unless clustering. In the dilute doping regime, all the magnetic TMatoms are in the high-spin states, indicating that the spin splitting energy of 3d TM is stronger than the crystal splitting energy of the SnTe ligand. Importantly, Mn-doped SnTe has relatively low defect formation energy, largest local magnetic moment, and no defect levels in the bulk gap, suggesting that Mn is a promising magnetic dopant to realize the magnetic order for the theoretically-proposed large-Chern-number quantum anomalous Hall effect(QAHE) in SnTe.

Rational design of eco-friendly Mn-doped nonstoichiometric CuInSe/ZnSe core/shell quantum dots for boosted photoelectrochemical efficiency

Colloidal core/shell quantum dots(QDs)with environment-friendly feature and controllable optoelectronic properties are promising building blocks in emerging solar technologies.In this work,we rationally design and tailor the eco-friendly CuInSe(CISe)/ZnSe core/shell QDs by Mn doping and stoichiometric optimization(i.e.,molar ratios of Cu/In).It is demonstrated that Mn doping in In-rich CISe/ZnSe core/shell QDs can effectively engineer the charge kinetics inside the QDs,enabling efficient photogenerated electrons transfer into the shell for retarded charge recombination.As a result,a solar-driven photoelectrochemical(PEC)device fabricated using the optimized Mn-doped In-rich CISe/ZnSe core/shell QDs(Cu/In ratio of 1/2)exhibits improved charge extraction and injection,showing a~3.5-fold higher photocurrent density than that of the pristine CISe/ZnSe core/shell QDs under 1 sun AM 1.5G illumination.The findings indicate that transition metal doping in“green”nonstoichiometric core/shell QDs may offer a new strategy for achieving high-efficiency solar energy conversion applications.

Creation of Mo active sites on indium oxide microrods for photocatalytic amino acid production

As an n-type semiconductor, In_(2)O_(3)is considered a promising photocatalyst for producing amino acids using biomass derivatives as precursors. However, similar to other intrinsic semiconductors, In_(2)O_(3)suffers from poor charge dynamics. Herein, we show the synthesis of Mo-doped In_(2)O_(3)(Mo-In_(2)O_(3)) with a porous rod-shaped structure through a onestep solvothermal reaction followed by calcination. Under visible-light irradiation, Mo-In_(2)O_(3)achieves a high conversion rate of 81% for the reaction that transforms lactic acid into alanine with a selectivity of 91%. Spectroscopic techniques and density functional theory calculations reveal that Mo doping introduces defect states slightly below the conduction band of In_(2)O_(3), which improves the separation of photogenerated electron-hole pairs. In addition, Mo atoms on the surface form extra adsorption and reaction centers that greatly enhance the reaction rate. This work provides insights into the development of transition metal-doped semiconductor photocatalysts to produce amino acids.