Doped Structures Research Articles

Unveiling spin magnetic effect of TM doped SnS2 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 SnS2 nanosheet (TM2@SnS2) to form the efficient magnetic catalyst is proposed to explore the spin magnetic effect on the HER performance. By performing first-principles calculations, nonmagnetic V2@SnS2 is proved to be the candidate of the HER catalyst; nevertheless, the HER activities of antiferromagnetic and ferromagnetic V2@SnS2 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-3pz and TM-d. Furthermore, the proof-of-concept experiment has substantiated the above theoretical predictions by significantly increasing 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.

Core-shell upconversion nanoparticles with suitable surface modification to overcome endothelial barrier.

Upconversion nanoparticles (UCNPs), capable of converting near-infrared (NIR) light into high-energy emission, hold significant promise for bioimaging applications. However, the presence of tissue barriers poses a challenge to the effective delivery of nanoparticles (NPs) to target organs. In this study, we demonstrate the core-shell UCNPs modified with cationic biopolymer, i.e., N, N-trimethyl chitosan (TMC), can overcome endothelial barriers. The core-shell UCNP is composed of NaGdF4: Yb3+,Tm3+ (16.7 ± 2.7 nm) as core materials and silica (SiO2) shell. The average particle size of UCNPs@SiO2 is estimated at 26.1 ± 3.7 nm. X-ray diffraction (XRD), transmission electron microscopy (TEM) and element mapping shows the formation of hexagonal crystal structure of β-NaGdF4 and elements doping. The surface of UCNPs@SiO2 has been modified with poly(ethylene glycol) (PEG) to enhance water dispersibility and colloidal stability, and further modified with TMC with the zeta potential increasing from -2.1 ± 0.96 mV to 26.9 ± 12.6 mV. No significant toxic effect is imposed to HUVECs when the cells are treated with core-shell UCNPs with surface modification up to 250 µg/mL. The transport ability of the core-shell UCNPs has been evaluated by using the in vitro endothelial barrier model. Transepithelial electrical resistance (TEER) and immunofluorescence staining of tight junction proteins have been employed to verify the integrity of the in vitro endothelial barrier model. The results indicate that the transport percentage of the UCNPs@SiO2 with PEG and TMC through the model is up to 4.56%, which is twice higher than that of the UCNPs@SiO2 with PEG but without TMC and six times that of the UCNPs@SiO2.

First-principles study of sodium adsorption and diffusion over substitutionally doped phosphorene

Phosphorene, due to its remarkable semiconducting properties, prevailed as principal material of research for decades. The substitutional doping of carbon (C), silicon (Si), oxygen (O) and sulphur (S) atom was reported earlier. DFT studies are done towards the unexplored area of sodium (Na) adsorption and diffusion over these doped phosphorene structures. The effective adsorption energies for C-, Si-, O- and S- doped phosphorene are −3.19 eV, −2.63 eV, −3.12 eV and −2.39 eV respectively. The minimum value of activation energies are 0.68 eV, 0.45 eV, 1.00 eV and 0.26 eV respectively. Hence the diffusion and intercalation–deintercalation process seem to be supportive. The lattice integrity is maintained in the whole process. Good amount of charge transfer shows better conductivity supported by band structure and density of states diagrams. Based on these data, the proposed doped phosphorene configurations can be predicted suitable for further studies towards anode application in Na-ion battery.

Dopant effects on the environment-dependent chemical properties of NiO(100) surfaces

NiO is a promising material for applications such as electronic devices and catalysts due to its low cost, environmental friendliness, and optimal chemical and electronic properties. Inclusion of a dopant element into the NiO near surface structure can further tune material properties. Despite extensive studies on doped NiO (M−NiO) materials, there remains a lack of knowledge regarding the connection between dopant, environment-dependent dominant near surface structures, and overall chemical properties. Here, the dopant effects on the near surface structure and electronic properties on M−NiO(100) are systematically examined using a combination of density functional theory (DFT) and ab initio phase diagrams. The simultaneous factors tested include dopant element (Al, Mo, Nb, Sn, Ti, V, W, or Zr), dopant placement (surface or subsurface), Ni/O vacancies (surface or subsurface), and oxygen species (O* or O2*) adsorption. The results reveal the dominant structures and compositions of M−NiO(100) under a wide range of environmental conditions (i.e. varying temperature and pressure). Subsequent electronic analyses of the dominant M−NiO(100) structures show non-uniform changes in charge redistribution, band gap, work function, and d-band center with dopant and near surface structure, emphasizing the role of dopants in tuning M−NiO(100) both geometric and electronic properties. Overall, these multiscale modeling results enable a rapid, effective, and a priori prediction of dominant M−NiO(100) structures with distinct chemical properties, crucial for guiding NiO-based materials design with enhanced performance for advanced electronics, energy storage, and catalytic systems.

Synthesis of N/O Atoms Co-Doped Biochar with 3D Porous Structure for Effective Electromagnetic Wave Absorption.

Developing biochar with large specific surface area (SSA), heteroatom doping, and porous structure is attracting substantial attention to absorb electromagnetic wave (EMW) in recent. Herein, a novel method of ethanol and KOH co-treatment is used to produce the biomass carbon deriving from pitaya peels. The obtained carbon possesses the high SSA of 1580 m2/g, successful N/O atoms co-doping, and massive pores with different size. The results of EMW absorption measurement show that the prepared biochar could achieve over 99 % absorpition to EMW, which the highest reflection loss is of ca. -45.25 dB at 7.54 GHz with an effective absorption bandwidth (EAB) of ca. 4.87 GHz. The execellent microwave absorption property is caused by the surface defects, dipole and interface polarizations of the synthesized biochar owning unique microstructure and N/O atoms co-doping. Hence, this avenue provides a new reference for fabricating low-cost and eco-friendly biochar as a microwave absorber.

Different built-in electric fields for transmission-mode GaAs photocathodes through doping engineering: Design and modeling

In order to enhance the emission performance of transmission-mode GaAs photocathodes used in optoelectronic field, different exponential doping structures are designed for the GaAs emission layer to generate different types of built-in electric fields. These built-in electric fields include the constant, increasing and decreasing types, which can help photoelectron transport toward the emission surface. By solving the one-dimensional continuity equation using the finite difference method, the electron concentration distribution and quantum efficiency of the three types of exponential doping GaAs photocathodes are derived. Meanwhile, the light absorption distributions in the emission layer are simulated by the finite difference time domain method. By comparing the optical absorption distribution and the electron concentration distribution, it is concluded that, among the three types of exponential doping structures, the exponential doping structure generating the increasing built-in electric field has the most sufficient long-wave light absorption capacity and the strongest photoelectron transport ability, thereby achieving the highest quantum efficiency. This theoretical work can help understand the mechanism of improving the photoemission performance of GaAs photocathodes through doping engineering.

Promoted room temperature NH3 gas sensitivity using interstitial Na dopant and structure distortion in Fe0.2Ni0.8WO4.

The demand for gas-sensing operations with lower electrical power and guaranteed sensitivity has increased over the decades due to worsening indoor air pollution. In this report, we develop room-temperature operational NH3 gas-sensing materials, which are activated through electron doping and crystal structure distortion effect in Fe0.2Ni0.8WO4. The base material, synthesized through solid-state synthesis, involves Fe cations substitutionally located at the Ni sites of the NiWO4 crystal structure and shows no gas-sensing response at room temperature. However, doping Na into the interstitial sites of Fe0.2Ni0.8WO4 activates gas adsorption on the surface via electron donation to the cations. Additionally, the hydrothermal method used to achieve a more than 70-fold increase in the surface area of structure-distorted Na-doped Fe0.2Ni0.8WO4 powder significantly enhances gas sensitivity, resulting in a 4-times increase in NH3 gas response (Rg/Ra). Photoluminescence and XPS results indicate negligible oxygen vacancies, demonstrating that cation contributions are crucial for gas-sensing activities in Na-doped Fe0.2Ni0.8WO4. This suggests the potential for modulating gas sensitivity through carrier concentration and crystal structure distortion. These findings can be applied to the development of room-temperature operational gas-sensing materials based on the cations.

Simultaneous Structural and Electronic Engineering on Bi- and Rh-co-doped SrTiO3 for Promoting Photocatalytic Water Splitting.

Activating metal ion-doped oxides as visible-light-responsive photocatalysts requires intricate structural and electronic engineering, a task with inherent challenges. In this study, we employed a solid (template)-molten (dopants) reaction to synthesize Bi- and Rh-codoped SrTiO3 (SrTiO3 : Bi,Rh) particles. Our investigation reveals that SrTiO3 : Bi,Rh manifests as single-crystalline particles in a core (undoped)/shell (doped) structure. Furthermore, it exhibits a well-stabilized Rh3+ energy state for visible-light response without introducing undesirable trapping states. This precisely engineered structure and electronic configuration promoted the generation of high-concentration and long-lived free electrons, as well as facilitated their transfer to cocatalysts for H2 evolution. Impressively, SrTiO3 : Bi,Rh achieved an exceptional apparent quantum yield (AQY) of 18.9 % at 420 nm, setting a new benchmark among Rh-doped-based SrTiO3 materials. Furthermore, when integrated into an all-solid-state Z-Scheme system with Mo-doped BiVO4 and reduced graphene oxide, SrTiO3 : Bi,Rh enabled water splitting with an AQY of 7.1 % at 420 nm. This work underscores the significance of simultaneous structural and electronic engineering and introduces the solid-molten reaction as a viable approach for this purpose.

Simultaneous Structural and Electronic Engineering on Bi‐ and Rh‐co‐doped SrTiO3 for Promoting Photocatalytic Water Splitting

AbstractActivating metal ion‐doped oxides as visible‐light‐responsive photocatalysts requires intricate structural and electronic engineering, a task with inherent challenges. In this study, we employed a solid (template)‐molten (dopants) reaction to synthesize Bi‐ and Rh‐codoped SrTiO3 (SrTiO3 : Bi,Rh) particles. Our investigation reveals that SrTiO3 : Bi,Rh manifests as single‐crystalline particles in a core (undoped)/shell (doped) structure. Furthermore, it exhibits a well‐stabilized Rh3+ energy state for visible‐light response without introducing undesirable trapping states. This precisely engineered structure and electronic configuration promoted the generation of high‐concentration and long‐lived free electrons, as well as facilitated their transfer to cocatalysts for H2 evolution. Impressively, SrTiO3 : Bi,Rh achieved an exceptional apparent quantum yield (AQY) of 18.9 % at 420 nm, setting a new benchmark among Rh‐doped‐based SrTiO3 materials. Furthermore, when integrated into an all‐solid‐state Z‐Scheme system with Mo‐doped BiVO4 and reduced graphene oxide, SrTiO3 : Bi,Rh enabled water splitting with an AQY of 7.1 % at 420 nm. This work underscores the significance of simultaneous structural and electronic engineering and introduces the solid‐molten reaction as a viable approach for this purpose.

Using ground state and excited state density functional theory to decipher 3d dopant defects in GaN

Using ground state density functional theory (DFT) and implementing an occupation-constrained DFT (occ-DFT) for self-consistent excited state calculations, we decipher the electronic structure of the Mn dopant and other 3ddefects in GaN across the band gap. Our analysis, validated with broad agreement with defect levels (ground-state calculations) and photoluminescence data (excited-state calculations), mandates reinterpretation and reassignment of 3ddefect data in GaN. The MnGadefect is determined to span stable charge states from (1-) inn-type GaN through (2+) inp-type GaN. The Mn(2+) is predicted to be ad2ground state spin triplet defect with a singlet excited state, isoelectronic with the defect associated with the 1.19 eV photoluminescence inn-type GaN. The combined analysis of defect levels and excited states invites reassessment of alld2-capable dopants in GaN. We demonstrate that the 1.19 eV defect, a candidate defect for optically controlled quantum applications, cannot be the Cr(1+) assumed in literature and instead must be the V(0). The combined ground-state/excited-state DFT analysis is shown to be able to chemically fingerprint defects.

Microenvironment modulation of biocatalyst derived from natural cellulose of wheat straw for enhancing p-nitrophenol degradation via boosting peroxymonosulfate activation

Defect-rich nitrogen-doped biocatalyst (B-NC) was synthesized from natural cellulose of wheat straw using straightforward mechanical method and one-step pyrolysis approach. In contrast to the nitrogen-doped biocatalyst (NC), by leveraging the synergistic effects of nitrogen dopants and surface defects, the microenvironment-modulated B-NC exhibited the enhanced mass transfer efficiency and a significant improvement in reactivity for p-nitrophenol degradation (111 %–196 %). The catalyst's exceptional performance primarily arose from graphitic N, pyridinic N and CO active sites, which mainly derived from the cellulose structure of wheat straw and nitrogen dopants. Electron paramagnetic resonance and quenching tests confirmed that the B-NC/peroxymonosulfate system generated more reactive species (SO4•−, •OH, O2•−, and 1O2) during p-nitrophenol degradation, surpassing the NC/peroxymonosulfate system. Additionally, both density functional theory calculations and electrochemical experiments provided evidence of peroxymonosulfate strongly adsorbing onto B-NC's defect sites, facilitating the formation of catalyst/peroxymonosulfate* complexes and promoting electron transfer processes. This research provides valuable insights into the regulation of defects in nitrogen-doped biocatalyst derived from natural cellulose, presenting a promising solution for remediating refractory organic pollutants.

Structural, electronic and optical properties of Halogen (F and Cl) atoms doped Graphdiyne

Abstract This paper reports the results of a density functional theory investigation of structural, electronic, and optical properties of halogen (fluorine and chlorine) atoms doped graphdiyne. Graphdiyne is doped with fluorine and chlorine with three different doping configurations each where one, two and three atoms of fluorine and chlorine were doped into Graphdiyne at benzene ring and acetylene linkages. The most stable doped structure was determined using the results of formation energy. Monolayers for fluorine and chlorine doped graphdiyne uniformly display metallic characteristics except where two atoms were incorporated shows semiconductor characteristics. PDOS shows that the energy band near the Fermi level is mainly contributed by the C 2p orbitals. Doped configurations shows higher peak intensities and good absorption in the UV, visible light region and IR region. These findings offer a fundamental basis for the understanding and manipulation of electrical and optical properties for doped graphdiyne with halogen atoms atoms and it is suitable for promoting the potential application of graphdiyne based electronic and opto-electronic device applications operating mainly in infrared and ultraviolet range.

Designing Electronic Structures of Multiscale Helical Converters for Tailored Ultrabroad Electromagnetic Absorption

HighlightsThe energy conversion mechanism is thoroughly analyzed, with a detailed quantitative characterization of the dissipation capacities of polarization, conduction, and magnetic loss.Inspired by DNA transcription, atom and geometry configurations co-modulating multi-scale helical converters achieve the RLmin of −63.13 dB at 1.29 mm, and the maximum RCS reduction value reach 36.4 dB m2.Orbital coupling, spin and cross polarization synergize to realize a 6.08 GHz EAB, further expanding to ultrabroad electromagnetic wave absorption of 12.16 GHz through metamaterial design.

Structural, magnetic, optical, and electronic properties of vanadium-doped barium hexaferrite nanoparticles: Experimental and DFT approaches

Vanadium-doped barium hexaferrite with a nanostructure is a highly valuable material in various technological fields, such as electronics, permanent magnets, and sensors. The Ba1-xFe12-xVxO19 (x = 0, 0.02, 0.04, 0.06, 0.08, and 0.1) nanoparticles derived from the aqueous solutions containing Fe:Ba molar ratio of 10:1 through the sol-gel auto-combustion method. Computational study was also performed using the first-principles density functional theory (DFT) approach. Crystal structure optimization, band structure, and density of states (DOS) calculations were conducted by CASTEP code. The variation of the structural, magnetic, optical, morphological, and electronic properties of V5+-doped barium hexaferrite was investigated. The XRD analysis combined with the Rietveld refinement showed the hexagonal structure of M-type barium ferrite (BaM), confirmed by the FT-IR analysis. The morphology of BaM nanoparticles was studied by the FE-SEM and TEM micrographs. In addition, magnetic and optical properties were analyzed through VSM and UV–Vis analysis. Crystallite size was found to be highly effective in tuning the coercivity and optical band gap of barium hexaferrites, which varied, respectively, from 3.24 to 4.83 kOe, and 2.69–3.69 eV. Magnetic results showed that several variables like cations distribution, lattice strain, and hematite secondary phase affected the nanoparticles’ magnetization. The DFT simulation results showed a sharp reduction of electronic band gap energy whether V takes the position of Ba or Fe (from 1.10 eV in undoped to 0.64 and 0.14 eV in doped structures). The projected density of states (PDOS) calculations demonstrated that the d orbitals of V and Ba mainly contribute to the valence band maximum (VBM) and conduction band minimum (CBM), respectively.

Exploration of Unconventional excitation wavelength and dynamic emission in rare-earth doped multilayer core-shell Structures: Application for optical “Hard” and “Soft” switching

Optical switches are increasingly acknowledged for their potential advantages over mechanical counterparts in various domains. However, research on optical switches remains relatively nascent, primarily focusing on applications like anti-counterfeiting, switching chemical reactions, etc., while neglecting the control of photocurrent switching. Here, we have developed NaYF4:30 %Er-NaYF4-NaYF4:20 %Ho-NaYF4 core–shell nanocrystals with unique upconversion (UC) multi-color emission properties under 1530 nm, 980 nm and 1150 nm laser excitations. These nanocrystals allow for optical control of circuit switching by modulating photocurrent signals in photosensitive circuits. The UC emission is due to the self-sensitization of rare earth ions in the core and shell. By adjusting the intermediate shell thickness, we have optimized the luminescence and investigated the mechanism. Combining these nanocrystals with a WO3 quantum dots (QDs) photochromic hydrogel, dynamic variation of UC emissions could be realized. Moreover, by combining with a commercial silicon photodetector, we constructed a photosensitive circuit demonstrating the modulation of photocurrent signal output and realized the “hard switching” of rapid circuit cutoff. Furthermore, by using the photochromic effect of WO3 QDs, the “soft switching” of slow circuit cutoff and recovery were also achieved. This work has significant implications for the development and application such as energy management system and smart home of optical switches in various fields.

Synthesis, morphology and dosimetric properties of Cr3+ activated Ca2Al2SiO7 nanophosphor prepared via sol-gel route

In this study, the structural, morphological, photoluminescence (PL), and dosimetric properties of Ca2-xAl2SiO7: xCr3+, at various Cr3+ concentrations (0 ≤ x ≤ 1 mol%) have been studied. The phosphor material was synthesized via sol-gel route with an octadecylamine as a catalyst. The average crystallite sizes were estimated to be in the range 21–30 nm using the modified Scherrer method which are in good agreement with data yielded by TEM micrographs. The energy-dispersive X-ray (EDX) spectra with scanning electron microscope (SEM) data confirm the homogeneous existence, and distribution of constituent elements within the structure and approved the sol-gel preparation method. PL spectra shows that Cr3+ doped Ca2Al2SiO7 structure has shoulder broadening and maximum peaks maintained at 442 ± 3.0 and 491 ± 3.02 nm upon 337 nm excitation which caused by 4F (4A2→4T2), 4F (4A2→4T1), and 4P (4A2→4T1) electronic spin-allowed transitions. Thermoluminescenc (TL) sensitivity characteristics of the obtained samples were scrutinized using Co-60 γ-radiation source. Cr0.4 sample was found to be optimum and its TL intensity increases linearly with increasing γ-doses from 0.5 up to 10 Gy. An accuracy using relative standard deviation (RSD) calculations of the homogenous study for Cr0.4 was found to be 4.02% (<10%, accepted due to ISO rules). Threshold dose of Cr0.4 sample was computed to be about 258 μGy. Acquired results of photon attenuation parameters estimations of Ca2Al2SiO7 composition using Phy-X PSD online program show that this composition is a bone equivalent dosimeter. According to this article, Cr0.4 doped Ca2Al2SiO7 sample can be considered as useful TL-material in various dosimetric applications.

High‐Performance n‐Type Organic Thermoelectrics with Exceptional Conductivity by Polymer‐Dopant Matching

AbstractAchieving high electrical conductivity (σ) and power factor (PF) simultaneously remains a significant challenge for n‐type organic themoelectrics (OTEs). Herein, we demonstrate the state‐of‐the‐art OTEs performance through blending a fused bithiophene imide dimer‐based polymer f‐BTI2g‐SVSCN and its selenophene‐substituted analogue f‐BSeI2g‐SVSCN with a julolidine‐functionalized benzimidazoline n‐dopant JLBI, vis‐à‐vis when blended with commercially available n‐dopants TAM and N‐DMBI. The advantages of introducing a more lipophilic julolidine group into the dopant structure of JLBI are evidenced by the enhanced OTEs performance that JLBI‐doped films show when compared to those doped with N‐DMBI or TAM. In fact, thanks to the enhanced intermolecular interactions and the lower‐lying LUMO level enabled by the increase of selenophene content in polymer backbone, JLBI‐doped films of f‐BSeI2g‐SVSCN exhibit a unprecedent σ of 206 S cm−1 and a PF of 114 μW m−1 K−2. Interestingly, σ can be further enhanced up to 326 S cm−1 by using TAM dopant as a consequence of its favorable diffusion behavior into densely packed crystalline domains. These values are the highest to date for solution‐processed molecularly n‐doped polymers, demonstrating the effectiveness of the polymer‐dopant matching approach carried out in this work.

High-Performance n-Type Organic Thermoelectrics with Exceptional Conductivity by Polymer-Dopant Matching.

Achieving high electrical conductivity (σ) and power factor (PF) simultaneously remains a significant challenge for n-type organic themoelectrics (OTEs). Herein, we demonstrate the state-of-the-art OTEs performance through blending a fused bithiophene imide dimer-based polymer f-BTI2g-SVSCN and its selenophene-substituted analogue f-BSeI2g-SVSCN with a julolidine-functionalized benzimidazoline n-dopant JLBI, vis-à-vis when blended with commercially available n-dopants TAM and N-DMBI. The advantages of introducing a more lipophilic julolidine group into the dopant structure of JLBI are evidenced by the enhanced OTEs performance that JLBI-doped films show when compared to those doped with N-DMBI or TAM. In fact, thanks to the enhanced intermolecular interactions and the lower-lying LUMO level enabled by the increase of selenophene content in polymer backbone, JLBI-doped films of f-BSeI2g-SVSCN exhibit a unprecedent σ of 206 S cm-1 and a PF of 114 μW m-1 K-2. Interestingly, σ can be further enhanced up to 326 S cm-1 by using TAM dopant as a consequence of its favorable diffusion behavior into densely packed crystalline domains. These values are the highest to date for solution-processed molecularly n-doped polymers, demonstrating the effectiveness of the polymer-dopant matching approach carried out in this work.

Transforming Commercial Polymers into Tough yet Switchable Adhesives by Trident Photoswitch Molecule Doping: Break Adhesion-Switchability Paradox.

Here, a trident molecule doping strategy is introduced to overcome both cohesion-adhesion trade-off and adhesion-switchability conflict, transforming commercial polymers into tough yet photo-switchable adhesives. The strategy involves initial rational design of new trident photoswitch molecules namely TAzo-3 featuring azobenzene and hydroxy-terminated alkyl chains involved rigid-soft tri-branch structure, and subsequent doping into commercial polycaprolactone (PCL) via simple blending. Unique design enables TAzo-3 as a versatile dopant, not only regulating the internal and external supramolecular interaction to balance cohesion and interface adhesion for tough bonding, but also affording marked photothermal effect to facilitate rapid adhesive melting for great photo-switchability. Thus, the optimal TAzo-3-doped PCL (TAzo-3@P) displays markedly-improved bonding performance on diverse substrates compared to linear azobenzene-doped PCL and pure PCL. Impressively, TAzo-3@P on polymethyl methacrylate (PMMA) attains large room-temperature adhesion strength of 6.7MPa - surpassing most reported adhesives and many commercial adhesives on PMMA, along with easy photo-induced detachment with remarkable switch ratio of 2.09×105. Besides, TAzo-3@P can also act as "permanent" adhesives for only adhesion, demonstrating excellent multi-reusability, anti-freezing and waterproof ability. Mechanism studies unveil that the switchable adhesion is closely linked with the dopant molecule structure while rigid-soft coupled trident structures and hydroxy-terminated alkyl chains are key factors.

Catalytic activity of Nb-doped α-Fe2O3—Heterojunction structure, ferrimagnet-like character, and high activity

Photocatalytic activity of α-Fe2O3 under visible light had been studied intensively. Rapid electron-hole recombination is the main drawback of α-Fe2O3 and the photocatalytic activity can be enhanced by transition metal doping and heterojunction structure. In the present study, α-Fe2O3 doped with various amounts of Nb were synthesized using a simple sol–gel method, and further characterization and catalytic activity were investigated. PXRD, TEM-EDS and Mössbauer measurement showed the formation of weak-ferromagnetic Nb-doped α-Fe2O3 and FeNbO4, where heterojunction structure was suggested. UV–vis spectrum showed a broad absorption in visible-light regions with a narrow band gap between 2.27 and 2.97 eV. Photo-Fenton reaction using α-Fe2O3 to decompose methylene blue (MB) was conducted to evaluate the catalytic activity. Nb-doped sample showed a significant improvement compared with pure α-Fe2O3. PXRD and Mössbauer spectroscopy revealed the α-Fe2O3 and FeNbO4 phases, which were attached to a magnet due to the ferrimagentic character of Nb-doped α-Fe2O3. The high catalytic activity with k value 7.1 * 10−2/min was obtained for 7.4Nb600. Higher catalytic activity was also observed for 20Nb600 and 40Nb600, which were driven by higher surface area, Nb substitution and heterojunction structure. Mechanistic analysis revealed that the primary reaction of MB decomposition is the Photo-Fenton process.