A type II heterojunction α-Fe2O3/g-C3N4 for the heterogeneous photo-Fenton degradation of phenol

The heterogeneous photo-Fenton reaction is an effective method of chemical oxidation to remove phenol in wastewater with environmental friendliness and sustainability. Herein, the composite α-Fe₂O₃/g-C₃N₄, as a catalyst of the heterogeneous photo-Fenton reaction, has been synthesized by hydrothermal-calcination method using the abundant and low-cost FeCl₃·6H₂O and g-C₃N₄ as raw materials. The influence of the annealing temperature during calcination was also investigated. The UV-Vis diffuse reflectance spectra of samples show that the composite α-Fe₂O₃/g-C₃N₄ possesses the widest light response range. Furthermore, the transient photocurrent response curves demonstrated the strongest intensity of α-Fe₂O₃/g-C₃N₄. The annealed α-Fe₂O₃/g-C₃N₄ is indicative of the highest degradation efficiency in all samples due to the improvement of the charge transfer ability caused by the tight heterojunction structure. The results of the scavenger trapping experiments show that the hydroxyl radical was the main active species in degradation. Based on experimental results, a type II heterojunction should be built in the composite α-Fe₂O₃/g-C₃N₄, driving the photoelectrons transfer and migration by internal electronic field. This work provides a facile and new method to synthesize α-Fe₂O₃/g-C₃N₄ as an effective heterogeneous photo-Fenton catalyst for environmental remediation.

Composite α-Fe₂O₃/g-C₃N₄ with type II heterojunction to degrade phenol by heterogeneous photo-Fenton reaction.     

Facile one-step hydrothermal synthesis of α-Fe2O3/g-C3N4 composites for the synergistic adsorption and photodegradation of dyes

With the expansion of industrialization, dye pollution has become a significant hazard to humans and aquatic ecosystems. In this study, α-Fe₂O₃/g-C₃N₄-R (where R is the relative percentage of α-Fe₂O₃) composites were fabricated by a one-step method. The as-prepared α-Fe₂O₃/g-C₃N₄-0.5 composites showed excellent adsorption capacities for methyl orange (MO, 69.91 mg g⁻¹) and methylene blue (MB, 29.46 mg g⁻¹), surpassing those of g-C₃N₄ and many other materials. Moreover, the ionic strength and initial pH influenced the adsorption process. Relatively, the adsorption isotherms best fitted the Freundlich model, and the pseudo-second-order kinetic model could accurately describe the kinetics for the adsorption of MO and MB by α-Fe₂O₃/g-C₃N₄-0.5. Electrostatic interaction and π–π electron donor–acceptor interaction were the major mechanisms for MO/MB adsorption. In addition, the photocatalytic experiment results showed that more than 79% of the added MO/MB was removed within 150 min. The experimental results of free-radical capture revealed that holes (h⁺) were the major reaction species for the photodegradation of MO, whereas MB was reduced by the synergistic effect of hydroxyl radicals (·OH) and holes (h⁺). This study suggests that the α-Fe₂O₃/g-C₃N₄ composites have an application potential for the removal of dyes from wastewater.

Simple one-step hydrothermal synthesis of α-Fe₂O₃/g-C₃N₄ composites for the synergistic adsorption and photodegradation of dyes     

Highly efficient reduction of 4-nitrophenolate to 4-aminophenolate by Au/γ-Fe2O3@HAP magnetic composites

In this article, the catalyst Au/γ-Fe₂O₃@hydroxyapatite (Au/γ-Fe₂O₃@HAP) consisting of Au nanoparticles supported on the core–shell structure γ-Fe₂O₃@HAP was prepared through a deposition–precipitation method. The catalyst was characterized by transmission electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, N₂ adsorption–desorption and atomic absorption spectrometry. The as-prepared Au/γ-Fe₂O₃@HAP exhibited excellent performance for the reduction of 4-nitrophenolate (4-NP) to 4-aminophenolate (4-AP) in the presence of NaBH₄ at room temperature. Thermodynamic and kinetic data on the reduction of 4-NP to 4-AP catalyzed by the as-prepared catalyst were studied. The as-prepared catalyst could be easily separated by a magnet and recycled 6 times with over 92% conversion of 4-NP to 4-AP. In addition, the as-prepared catalyst showed excellent catalytic performance on other nitrophenolates. The TOF value of this work on the reduction of 4-NP to 4-AP was 241.3 h⁻¹. Au/γ-Fe₂O₃@HAP might have a promising potential application on the production of 4-AP and its derivatives.

In this article, the catalyst Au/γ-Fe₂O₃@hydroxyapatite (Au/γ-Fe₂O₃@HAP) consisting of Au nanoparticles supported on the core–shell structure γ-Fe₂O₃@HAP was prepared through a deposition–precipitation method.     

Preparation of Ag3PO4/α-Fe2O3 hybrid powders and their visible light catalytic performances

The inefficiency of conventional photocatalytic treatment for removing rhodamine B is posing potential risks to ecological environments. Here, we construct a highly efficient photocatalyst consisting of Ag₃PO₄ and α-Fe₂O₃ hybrid powders for the treatment of rhodamine B. Ag₃PO₄ nanoparticles (nanoparticles, about 50 nm) are uniformly dispersed on the surface of α-Fe₂O₃ microcrystals (hexagonal sheet, about 1.5 μm). The Ag₃PO₄-deposited uniformity on the α-Fe₂O₃ surface first increased, then decreased on increasing the hybrid ratio of Ag₃PO₄ to α-Fe₂O₃. When the hybrid ratio of Ag₃PO₄ to α-Fe₂O₃ is 1 : 2, the distribution of Ag₃PO₄ particles on the sheet α-Fe₂O₃ is more uniform with excellent Ag₃PO₄/α-Fe₂O₃ interface performance. The catalytic degradation efficiency of hybrids with the introduction of Ag₃PO₄ nanoparticles on the α-Fe₂O₃ surface reached 95%. More importantly, the hybrid material exhibits superior photocatalytic stability. Ag₃PO₄/α-Fe₂O₃ hybrids have good reusability, and the photocatalytic efficiency could still reach 72% after four reuses. The excellent photocatalytic activity of the as-prepared hybrids can be attributed to the heterostructure between Ag₃PO₄ and α-Fe₂O_3, which can effectively inhibit the photoelectron–hole recombination and broaden the visible light response range.

We construct a highly efficient photocatalyst consisting of Ag₃PO₄ and α-Fe₂O₃ hybrid powders for the treatment of rhodamine B. The catalytic degradation efficiency reached 95% after 10 min.     

Low temperature fabrication of Fe2O3 nanorod film coated with ultra-thin g-C3N4 for a direct z-scheme exerting photocatalytic activities

We engineered high aspect ratio Fe₂O₃ nanorods (with an aspect ratio of 17 : 1) coated with g-C₃N₄ using a sequential solvothermal method at very low temperature followed by a thermal evaporation method. Here, the high aspect ratio Fe₂O₃ nanorods were directly grown onto the FTO substrate under relatively low pressure conditions. The g-C₃N₄ was coated onto a uniform Fe₂O₃ nanorod film as the heterostructure, exhibiting rational band conduction and a valence band that engaged in surface photoredox reactions by a direct z-scheme mechanism. The heterostructures, particularly 0.75g-C₃N₄@Fe₂O₃ nanorods, exhibited outstanding photocatalytic activities compared to those of bare Fe₂O₃ nanorods. In terms of 4-nitrophenol degradation, 0.75g-C₃N₄@Fe₂O₃ nanorods degraded all of the organic pollutant within 6 h under visible irradiation at a kinetic constant of 12.71 × 10⁻³ min⁻¹, about 15-fold more rapidly than bare Fe₂O₃. Further, the hydrogen evolution rate was 37.06 μmol h⁻¹ g⁻¹, 39-fold higher than that of bare Fe₂O₃. We suggest that electron and hole pairs are efficiently separated in g-C₃N₄@Fe₂O₃ nanorods, thus accelerating surface photoreaction via a direct z-scheme under visible illumination.

The engineered high aspect ratio of Fe₂O₃ nanorods coated with g-C₃N₄ demonstrates z-scheme mechanism, showing the best performance in 4-nitrophenol photodegradation and H₂ evolution.     

Correction: Facile preparation of novel quaternary g-C3N4/Fe3O4/AgI/Bi2S3 nanocomposites: magnetically separable visible-light-driven photocatalysts with significantly enhanced activity

Correction for ‘Facile preparation of novel quaternary g-C₃N₄/Fe₃O₄/AgI/Bi₂S₃ nanocomposites: magnetically separable visible-light-driven photocatalysts with significantly enhanced activity’ by Anise Akhundi et al., RSC Adv., 2016, 6, 106572–106583. DOI: 10.1039/C6RA12414C.

The authors regret that incorrect images were used in Fig. 2i (page 106575) and Fig. 3b (page 106576). The correct images are shown below.Fig. 2i. EDX mapping of the g-C₃N₄/Fe₃O₄/AgI/Bi₂S₃ (30%) nanocomposite.Fig. 3b TEM image of the g-C₃N₄/Fe₃O₄/AgI/Bi₂S₃ (30%) nanocomposite.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Magnetic hyperthermia with ε-Fe2O3 nanoparticles

Biocompatibility restrictions have limited the use of magnetic nanoparticles for magnetic hyperthermia therapy to iron oxides, namely magnetite (Fe₃O₄) and maghemite (γ-Fe₂O₃). However, there is yet another magnetic iron oxide phase that has not been considered so far, in spite of its unique magnetic properties: ε-Fe₂O₃. Indeed, whereas Fe₃O₄ and γ-Fe₂O₃ have a relatively low magnetic coercivity, ε-Fe₂O₃ exhibits a giant coercivity. In this report, the heating power of ε-Fe₂O₃ nanoparticles in comparison with γ-Fe₂O₃ nanoparticles of similar size (∼20 nm) was measured in a wide range of field frequencies and amplitudes, in uncoated and polymer-coated samples. It was found that ε-Fe₂O₃ nanoparticles primarily heat in the low-frequency regime (20–100 kHz) in media whose viscosity is similar to that of cell cytoplasm. In contrast, γ-Fe₂O₃ nanoparticles heat more effectively in the high frequency range (400–900 kHz). Cell culture experiments exhibited no toxicity in a wide range of nanoparticle concentrations and a high internalization rate. In conclusion, the performance of ε-Fe₂O₃ nanoparticles is slightly inferior to that of γ-Fe₂O₃ nanoparticles in human magnetic hyperthermia applications. However, these ε-Fe₂O₃ nanoparticles open the way for switchable magnetic heating owing to their distinct response to frequency.

ε-Fe₂O₃ is a magnetic iron(iii) oxide with a giant coercivity. Its potential in hyperthermia applications has been evaluated in comparison with γ-Fe₂O₃ over a wide range of field frequencies and amplitudes.     

Efficient activation of persulfate by Fe3O4@β-cyclodextrin nanocomposite for removal of bisphenol A

Experimental studies were conducted to investigate the degradation of bisphenol A (BPA) by using persulfate (PS) as the oxidant and Fe₃O₄@β-cyclodextrin (β-CD) nanocomposite as a heterogeneous activator. The catalytic activity was evaluated in consideration of the effect of various parameters, such as pH value, PS concentration and Fe₃O₄@β-CD load. The results showed that 100% removal of BPA was gained at pH 3.0 with 5 mM PS, 1.0 g L⁻¹ Fe₃O₄@β-CD, and 0.1 mM BPA in 120 min. Further, the catalytic activity of Fe₃O₄@β-CD nanocomposite was observed as much higher when compared with Fe₃O₄ nanoparticles alone. The sulfate and hydroxyl radicals referred to in the Fe₃O₄@β-CD/PS system were determined as the reactive species responsible for the degradation of BPA by radical quenching and electron spin resonance (ESR) tests. In addition, the catalyst also possessed with accepted reusability and stability. On the basis of the results of the effect of chloride ions (Cl⁻), β-CD was found to play a crucial role in reducing interference from Cl⁻ ions, and lead to achieve higher removal efficiency for BPA in Fe₃O₄@β-CD/PS system. A possible mechanistic process of BPA degradation was proposed according to the identified intermediates by gas chromatography-mass spectroscopy (GC-MS).

Persulfate (PS), the most commonly used activator for in situ chemical oxidation (ISCO), could couple with Fe₃O₄@β-CD for effectively degrading BPA.     

Selective CO2 reduction to HCOOH on a Pt/In2O3/g-C3N4 multifunctional visible-photocatalyst

Selective photocatalytic reduction of CO₂ has been regarded as one of the most amazing ways for re-using CO₂. However, its application is still limited by the low CO₂ conversion efficiency. This work developed a novel Pt/In₂O₃/g-C₃N₄ multifunctional catalyst, which exhibited high activity and selectivity to HCOOH during photocatalytic CO₂ reduction under visible light irradiation owing to the synergistic effect between photocatalyst, thermocatalyst, and heterojunctions. Both In₂O₃ and g-C₃N₄ acted as visible photocatalysts, in which porous g-C₃N₄ facilitated H₂ production from water splitting while the In₂O₃ nanosheets embedded in g-C₃N₄ pores favored CO₂ fixation and H adsorption onto the Lewis acid sites. Besides, the In₂O₃/g-C₃N₄ heterojunctions could efficiently inhibit the photoelectron–hole recombination, leading to enhanced quantum efficiency. The Pt could act as a co-catalyst in H₂ production from photocatalytic water splitting and also accelerated electron transfer to inhibit electron–hole recombination and generated a plasma effect. More importantly, the Pt could activate H atoms and CO₂ molecules toward the formation of HCOOH. At normal pressure and room temperature, the TON of HCOOH in CO₂ conversion was 63.1 μmol g⁻¹ h⁻¹ and could reach up to 736.3 μmol g⁻¹ h⁻¹ at 40 atm.

A multifunctional Pt/In₂O₃/g-C₃N₄ catalyst exhibited high activity and selectivity to HCOOH during CO₂ reduction owing to the synergy between visible-light harvesting, CO₂ activation, HER, and photoelectron–hole separation via heterojunctions.     

g-C3N4/CuO and g-C3N4/Co3O4 nanohybrid structures as efficient electrode materials in symmetric supercapacitors

Metal oxide dispersed graphitic carbon nitride hybrid nanocomposites (g-C₃N₄/CuO and g-C₃N₄/Co₃O₄) were prepared via a direct precipitation method. The materials were used as an electrode material in symmetric supercapacitors. The g-C₃N₄/Co₃O₄ electrode based device exhibited a specific capacitance of 201 F g⁻¹ which is substantially higher than those using g-C₃N₄/CuO (95 F g⁻¹) and bare g-C₃N₄ electrodes (72 F g⁻¹). At a constant power density of 1 kW kg⁻¹, the energy density given by g-C₃N₄/Co₃O₄ and g-C₃N₄/CuO devices is 27.9 W h kg⁻¹ and 13.2 W h kg⁻¹ respectively. The enhancement of the electrochemical performance in the hybrid material is attributed to the pseudo capacitive nature of the metal oxide nanoparticles incorporated in the g-C₃N₄ matrix.

Comparison of electrochemical performance of symmetric supercapacitors based on g-C₃N₄/CuO and g-C₃N₄/Co₃O₄ electrodes.     

Enhanced catalytic degradation of amoxicillin with TiO2–Fe3O4 composites via a submerged magnetic separation membrane photocatalytic reactor (SMSMPR)

A novel photo-Fenton catalytic system for the removal of organic pollutants was presented, including the use of photo-Fenton process and a submerged magnetic separation membrane photocatalytic reactor (SMSMPR). We synthesized TiO₂–Fe₃O₄ composites as the photocatalyst and made full use of the magnetism of the photocatalyst to realize the recollection of the catalyst from the medium, which is critical to the commercialization of photocatalytic technology for wastewater treatment. The photo-Fenton performance of TiO₂–Fe₃O₄ is evaluated with amoxicillin trihydrate (AMX) as a target pollutant. The results indicate that the TiO₂–Fe₃O₄/H₂O₂ oxidation system shows efficient degradation of AMX. Fe₃O₄ could not only enhance the heterogeneous Fenton degradation of organic compounds but also allow the photocatalyst to be magnetically separated from treated water. After four reaction cycles, the TiO₂–Fe₃O₄ composites still exhibit 85.2% removal efficiency of AMX and show excellent recovery properties. Accordingly, the SMSMPR with the TiO₂–Fe₃O₄ composite is a promising way for removing organic pollutants.

With a TiO₂–Fe₃O₄ composite as the catalyst, amoxicillin was degraded via a photo-Fenton process using a submerged magnetic separation membrane photocatalytic reactor.     

Mesoporous anodic α-Fe2O3 interferometer for organic vapor sensing application

In this work, we reported the utilization of mesoporous α-Fe₂O₃ films as optical sensors for detecting organic vapors. The mesoporous α-Fe₂O₃ thin films, which exhibited obvious Fabry–Perot interference fringes in the reflectance spectrum, were successfully fabricated through electrochemical anodization of Fe foils. Through monitoring the optical thickness of the interference fringes, three typical organic species with different vapor pressures and polarities (hexane, acetone and isopropanol) were applied as probes to evaluate the sensitivity of the α-Fe₂O₃ based interferometric sensor. The experiment results showed that the as-synthesized mesoporous α-Fe₂O₃ interferometer displayed high reversibility and stability for the three organic vapors, and were especially sensitive to isopropanol, with a detection limit of about 65 ppmv. Moreover, the photocatalytic properties of α-Fe₂O₃ under visible light are beneficial for degradation of dodecane vapor residues in the nano-pores and refreshment of the sensor, demonstrating good self-cleaning properties of the α-Fe₂O₃-based interferometric sensor.

Mesoporous α-Fe₂O₃ interferometers with well-resolved optical fringes can display high sensitivity to organic vapors.     

Synthesis of a well-dispersed CaFe2O4/g-C3N4/CNT composite towards the degradation of toxic water pollutants under visible light

Herein, we fabricated a ternary photocatalyst composed of CaFe₂O₄, multiwalled carbon nanotubes (CNTs) and graphitic carbon nitride (g-C₃N₄) via a simple hydrothermal route. CaFe₂O₄ acted as a photosensitizer medium and the CNT acted as a co-catalyst, which remarkably enhanced the photocatalytic performances of g-C₃N₄ towards the degradation of hexavalent chromium (Cr(vi)) and the antibiotic tetracycline (TC) under visible light irradiation. To investigate the morphological and topological features of the photocatalyst, field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) analyses were performed. The surface properties and oxidation state of the CaFe₂O₄/g-C₃N₄/CNT composite were determined by X-ray photoelectron spectroscopy (XPS). The recombination rate of the charge carriers and the band gap values of the as-synthesized catalysts were analyzed by photoluminescence spectroscopy (PL) and diffused reflectance spectroscopy (UV/Vis DRS) studies, respectively. Besides the degradation reactions, the high hydrogen production rate of 1050 μmol h⁻¹ under visible light using the CaFe₂O₄/g-C₃N₄/CNT composite loaded with 5 wt% CNT was observed. The superior photocatalytic performances of the CaFe₂O₄/g-C₃N₄/CNT composite can be ascribed to the effective heterojunction formed between g-C₃N₄ and the CaFe₂O₄ matrix, in which the CNT act as a conducting bridge in the system, promoting the production of photoinduced charge carriers in the semiconductor system. Finally, the plausible photocatalytic mechanism towards the degradation of pollutants and hydrogen production was discussed carefully.

Herein, we fabricated a ternary photocatalyst composed of CaFe₂O₄, multiwalled carbon nanotubes (CNTs) and graphitic carbon nitride (g-C₃N₄) via a simple hydrothermal route.     

Synthesis and characterization of an α-Fe2O3/ZnTe heterostructure for photocatalytic degradation of Congo red,methyl orange and methylene blue

The leading challenge towards environmental protection is untreated textile dyes. Tailoring photocatalytic materials is one of the sustainable remediation strategies for dye treatment. Hematite (α-Fe₂O₃), due to its favorable visible light active band gap (i.e. 2.1 eV), has turned out to be a robust material of interest. However, impoverished photocatalytic efficiency of α-Fe₂O₃ is ascribable to the short life span of the charge carriers. Consequently, the former synthesized heterostructures possess low degradation efficiency. The aim of the proposed endeavor is the synthesis of a novel zinc telluride-modified hematite (α-Fe₂O₃/ZnTe) heterostructure, its characterization and demonstration of its enhanced photocatalytic response. The promising heterostructure as well as bare photocatalysts were synthesized via a hydrothermal approach. All photocatalysts were characterized by the X-ray diffraction technique (XRD), scanning electron microscopy (SEM), and electron diffraction spectroscopy (EDX). Moreover, the selectivity and activity of the photocatalyst are closely related to the alignment of its band energy levels, which were estimated by UV-Vis diffuse reflectance spectroscopy (DRS) and X-ray photoelectron spectroscopy (XPS). Nanomaterials, specifically α-Fe₂O₃ and α-Fe₂O₃/ZnTe, were used for the degradation of Congo red (97.9%), methyl orange (84%) and methylene blue (73%) under light irradiation (>200 nm) for 60 min. The results suggested that with the aforementioned optimized fabricated heterostructure, the degradation efficiency was improved in comparison to bare hematite (α-Fe₂O₃). The key rationale towards such improved photocatalytic response is the establishment of a type-II configuration in the α-Fe₂O₃/ZnTe heterostructure.

Effective generation and transportation of electron–hole pairs in the presence of light leads to efficient degradation of textile pollutants over an α-Fe₂O₃/ZnTe nanocomposite compared to the individual components.     

One step synthesis of high-efficiency AgBr–Br–g-C3N4 composite catalysts for photocatalytic H2O2 production via two channel pathway

In this work, a two-component modified AgBr–Br–g-C₃N₄ composite catalyst with outstanding photocatalytic H₂O₂ production ability is synthesized. XRD, UV-Vis, N₂ adsorption, TEM, XPS, EPR and PL were used to characterize the obtained catalysts. The as-prepared AgBr–Br–g-C₃N₄ composite catalyst shows the highest H₂O₂ equilibrium concentration of 3.9 mmol L⁻¹, which is 7.8 and 19.5 times higher than that of GCN and AgBr. A “two channel pathway” is proposed for this reaction system which causes the remarkably promoted H₂O₂ production ability. In addition, compared with another two-component modified catalyst, Ag–AgBr–g-C₃N₄, AgBr–Br–g-C₃N₄ composite catalyst displays the higher photocatalytic H₂O₂ production ability and stability.

In this work, a two-component modified AgBr–Br–g-C₃N₄ composite catalyst with outstanding photocatalytic H₂O₂ production ability is synthesized.     

A magnetically separable and recyclable g-C3N4/Fe3O4/porous ruthenium nanocatalyst for the photocatalytic degradation of water-soluble aromatic amines and azo dyes

Herein, we present the development of a visible-light-driven magnetically retrievable nanophotocatalyst made of porous ruthenium nanoparticles supported on magnetic carbon nitride (g-C₃N₄/Fe₃O₄/p-RuNP) for the facile removal/degradation of aromatic amines and azo dyes from wastewater. Aromatic amines and azo-based dyes in water bodies are highly toxic and carcinogenic even at very low concentrations and are difficult to separate because of their high solubility. Our nanocatalyst can efficiently degrade/decompose the aromatic amines and azo dyes under visible light (LED/sunlight) at room temperature and in a wide pH range (pH 5.0–9.0) without using any external chemicals. The magnetic property of the nanocatalyst facilitates its efficient and facile separation from the reaction mixture for reuse in multiple photocatalytic cycles. The nanocatalyst-based degradation of azo dyes and aromatic amines presented here is simple and convenient in terms of efficiency, energy, reusability and cost. The process also does not require any external chemicals and forms gaseous/less harmful end products.

A magnetically separable and recyclable g-C₃N₄/Fe₃O₄/porous ruthenium nanocatalyst display excellent photocatalytic degradation of water-soluble aromatic amines and azo dyes at ambient condition.     

α-Fe2O3 hollow meso–microspheres grown on graphene sheets function as a promising counter electrode in dye-sensitized solar cells

Although nanoparticles, nanorods, and nanosheets of α-Fe₂O₃ on graphene sheets have been synthesized, it remains a challenge to grow 3D α-Fe₂O₃ nanomaterials with more sophisticated compositions and structures on the graphene sheets. Herein, we demonstrate a facile solvothermal route under controlled conditions to successfully fabricate 3D α-Fe₂O₃ hollow meso–microspheres on the graphene sheets (α-Fe₂O₃/RGO HMM). Attributed to the combination of the catalytic features of α-Fe₂O₃ hollow meso–microspheres and the high conductivity of graphene, α-Fe₂O₃/RGO HMM exhibited promising electrocatalytic performance as a counter electrode in dye-sensitized solar cells (DSSCs). The DSSCs fabricated with α-Fe₂O₃ HMM displayed high power conversion efficiency of 7.28%, which is comparable with that of Pt (7.71%).

Although nanoparticles, nanorods, and nanosheets of α-Fe₂O₃ on graphene sheets have been synthesized, it remains a challenge to grow 3D α-Fe₂O₃ nanomaterials with more sophisticated compositions and structures on the graphene sheets.     

Heterostructures of ε-Fe2O3 and α-Fe2O3: insights from density functional theory

Many materials used in energy devices or applications suffer from the problem of electron–hole pair recombination. One promising way to overcome this problem is the use of heterostructures in place of a single material. If an electric dipole forms at the interface, such a structure can lead to a more efficient electron–hole pair separation and thus prevent recombination. Here we model and study a heterostructure comprised of two polymorphs of Fe₂O₃. Each one of the two polymorphs, α-Fe₂O₃ and ε-Fe₂O₃, individually shows promise for applications in photoelectrochemical cells. The heterostructure of these two materials is modeled by means of density functional theory. We consider both ferromagnetic as well as anti-ferromagnetic couplings at the interface between the two systems. Both individual oxides are insulating in nature and have an anti-ferromagnetic spin arrangement in their ground state. The same properties are found also in their heterostructure. The highest occupied electronic orbitals of the combined system are localized at the interface between the two iron-oxides. The localization of charges at the interface is characterized by electrons residing close to the oxygen atoms of ε-Fe₂O₃ and electron–holes localized on the iron atoms of α-Fe₂O₃, just around the interface. The band alignment at the interface of the two oxides shows a type-III broken band-gap heterostructure. The band edges of α-Fe₂O₃ are higher in energy than those of ε-Fe₂O₃. This band alignment favours a spontaneous transfer of excited photo-electrons from the conduction band of α- to the conduction band of ε-Fe₂O₃. Similarly, photo-generated holes are transferred from the valence band of ε- to the valence band of α-Fe₂O₃. Thus, the interface favours a spontaneous separation of electrons and holes in space. The conduction band of ε-Fe₂O₃, lying close to the valence band of α-Fe₂O₃, can result in band-to-band tunneling of electrons which is a characteristic property of such type-III broken band-gap heterostructures and has potential applications in tunnel field-effect transistors.

Electron–hole pair recombination is reduced in heterostructures if used in devices in place of single material.     

DFT study on the electronic structure and optical properties of an Au-deposited α-Fe2O3 (001) surface

The electronic structure and optical properties of gold clusters deposited on an α-Fe₂O₃ surface were studied by using density functional theory (DFT), with a special emphasis on the influence of Au cluster sizes. There is a strong interaction between Au clusters and the α-Fe₂O₃ surface, and the binding energy increases with an increase of Au cluster size. The Au atoms of the gold cluster are bonded to the iron atoms of the α-Fe₂O₃ surface for the Au/α-Fe₂O₃ system, and the electrons transfer from the Au cluster to the α-Fe₂O₃ surface with the largest number of electrons transferred for 4Au/α-Fe₂O₃. The peaks of the refractive index, extinction coefficient and dielectric function induced by Au clusters appear in the visible range, which results in the enhanced optical absorption for the Au/α-Fe₂O₃ system. The optical absorption intensifies with increasing Au cluster size in the visible range, showing a maximum value for 4Au/α-Fe₂O₃. Further increasing the Au cluster size above 4Au results in a decrease in absorption intensity. The results are in good agreement with those of the refractive index, extinction coefficient and dielectric function.

The electronic structure and optical properties of gold clusters deposited on an α-Fe₂O₃ surface were studied by using density functional theory (DFT), with a special emphasis on the influence of Au cluster sizes.     

The production of an efficient visible light photocatalyst for CO oxidation through the surface plasmonic effect of Ag nanoparticles on SiO2@α-Fe2O3 nanocomposites

A process for the photo deposition of noble Ag nanoparticles on a core–shell structure of SiO₂@α-Fe₂O₃ nanocomposite spheres was performed to produce a CO photo oxidation catalyst. The structural analyses were carried out for samples produced using different Ag metal nanoparticle weight percentages on SiO₂@α-Fe₂O₃ nanocomposite spheres by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), UV-vis spectroscopy, Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). A computational study was also performed to confirm the existence of the synergic effect of surface plasmon resonance (SPR) for different weight percentages of Ag on the SiO₂@α-Fe₂O₃ nanocomposites. The mechanism for CO oxidation on the catalyst was explored using diffuse reflectance infrared Fourier transform spectroscopy (DRFIT). The CO oxidation results for the Ag (2 wt%)-SiO₂@α-Fe₂O₃ nanocomposite spheres showed 48% higher photocatalytic activity than α-Fe₂O₃ and SiO₂@α-Fe₂O₃ at stable temperature.

We present a systematic investigation of CO oxidation and surface plasmon resonance on SiO₂@α-Fe₂O₃ nanocomposite spheres with different weight percentages of Ag nanoparticles.