Activation of α-Fe2O3 for Photoelectrochemical Water Splitting Strongly Enhanced by Low Temperature Annealing in Low Oxygen Containing Ambient

Photoelectrochemical (PEC) water splitting is a promising method for the conversion of solar energy into chemical energy stored in the form of hydrogen. Nanostructured hematite (α-Fe₂O₃) is one of the most attractive materials for a highly efficient charge carrier generation and collection due to its large specific surface area and the short minority carrier diffusion length. In the present work, the PEC water splitting performance of nanostructured α-Fe₂O₃ is investigated which was prepared by anodization followed by annealing in a low oxygen ambient (0.03 % O₂ in Ar). It was found that low oxygen annealing can activate a significant PEC response of α-Fe₂O₃ even at a low temperature of 400 °C and provide an excellent PEC performance compared with classic air annealing. The photocurrent of the α-Fe₂O₃ annealed in the low oxygen at 1.5 V vs. RHE results as 0.5 mA cm⁻², being 20 times higher than that of annealing in air. The obtained results show that the α-Fe₂O₃ annealed in low oxygen contains beneficial defects and promotes the transport of holes; it can be attributed to the improvement of conductivity due to the introduction of suitable oxygen vacancies in the α-Fe₂O₃. Additionally, we demonstrate the photocurrent of α-Fe₂O₃ annealed in low oxygen ambient can be further enhanced by Zn-Co LDH, which is a co-catalyst of oxygen evolution reaction. This indicates low oxygen annealing generates a promising method to obtain an excellent PEC water splitting performance from α-Fe₂O₃ photoanodes.     

氢氟酸腐蚀对α-Fe2O3薄膜光解水电极光电化学性质的影响

使用溶胶-凝胶法制备了α-Fe₂O₃薄膜,研究了氢氟酸腐蚀薄膜表面对其光电化学性质的影响. 实验发现,薄膜表面的孔洞和间隙随着氢氟酸浸蚀时间的增长而发生变化. 氢氟酸浸蚀5 min,α-Fe₂O₃电极的光电流降低;随后随浸蚀时间增加而迅速增加;当浸蚀时间大于15 min时,其光电流再次下降,但对浸蚀过的样品再次退火可以使光电流大幅增加. 通过电化学交流阻抗谱、拉曼和X射线光电子能谱分析,提出了两个影响光电流的因素：氢氟酸表面浸蚀造成薄膜表面的多孔性和结晶度降低. 为此,通过示意图解释了结合浸蚀和退火后处理两个步骤来增强α-Fe₂O₃薄膜光解水电极光电活性的原理. 相对于初始的α-Fe₂O₃电极,浸蚀并且再退火处理后,其光电性质更加稳定.     

Synthesis of mesoporous functional hematite nanofibrous photoanodes by electrospinning

Iron(III) oxide (hematite, Fe₂O₃) nanofibers, as visible light‐induced photoanode for water oxidation reaction of a water splitting process, were fabricated through electrospinning method followed by calcination treatment. The prepared samples were characterized with scanning electron microscopy, and three‐electrode galvanostat/potentiostat for evaluating their photoelectrochemical (PEC) properties. The diameter of the as‐spun fibers is about 300 nm, and calcinated fibers have diameter less than 110 nm with mesoporous structure. Optimized multilayered electrospun α‐Fe₂O₃ nanostructure mats showed photocurrent density of 0.53 mA/cm² under dark and visible illumination conditions at voltage 1.23 V and constant intensity (900 mW/cm²). This photovoltaic performance of nanostructure mats makes it suitable choice for using in the PEC water splitting application as an efficient photoanode. This method, if combined with appropriate flexible conductive substrate, has the potential for producing flexible hematite solar fuel generators. Copyright © 2015 John Wiley & Sons, Ltd.     

Porous α-Fe_2O_3/SnO_2 nanoflower with enhanced sulfur selectivity and stability for H_2S selective oxidation

Being abundant and active,Fe_2O_3 is suitable for selective oxidation of H_2S.However,its practical application is limited due to the poor sulfur selectivity and rapid deactivation.Herein,we report a facile template-free hydrothermal method to fabricate porous α-Fe_2O_3/SnO_2 composites with hierarchical nanoflower that can obviously improve the catalytic performance of Fe_2O_3.It was disclosed that the synergistic effect between α-Fe_2O_3 and SnO_2 promotes the physico-chemical properties of α-Fe_2O_3/SnO_2 composites.Specifically,the electron transfer between the Fe~(2+)/Fe~(3+) and Sn~(2+)/Sn~(4+) redox couples enhances the reducibility of α-Fe_2O_3/SnO_2 composites.The number of oxygen vacancies is improved when the Fe cations incorporate into SnO_2 structure,which facilitates the adsorption and activation of oxygen species.Additionally,the porous structure improves the accessibility of H_2 S to active sites.Among the composites,Fe1 Sn1 exhibits complete H_2 S conversion with 100% sulfur selectivity at 220℃,better than those of pure α-Fe_2O_3 and SnO_2.Moreover,Fe1 Sn1 catalyst shows high stability and water resistance.     

Surviving High‐Temperature Calcination: ZrO2‐Induced Hematite Nanotubes for Photoelectrochemical Water Oxidation

Nanotubular Fe₂O₃ is a promising photoanode material, and producing morphologies that withstand high‐temperature calcination (HTC) is urgently needed to enhance the photoelectrochemical (PEC) performance. This work describes the design and fabrication of Fe₂O₃ nanotube arrays that survive HTC for the first time. By introducing a ZrO₂ shell on hydrothermal FeOOH nanorods by atomic layer deposition, subsequent high‐temperature solid‐state reaction converts FeOOH‐ZrO₂ nanorods to ZrO₂‐induced Fe₂O₃ nanotubes (Zr‐Fe₂O₃ NTs). The structural evolution of the hematite nanotubes is systematically explored. As a result of the nanostructuring and shortened charge collection distance, the nanotube photoanode shows a greatly improved PEC water oxidation activity, exhibiting a photocurrent density of 1.5 mA cm⁻² at 1.23 V (vs. reversible hydrogen electrode, RHE), which is the highest among hematite nanotube photoanodes without co‐catalysts. Furthermore, a Co‐Pi decorated Zr‐Fe₂O₃ NT photoanode reveals an enhanced onset potential of 0.65 V (vs. RHE) and a photocurrent of 1.87 mA cm⁻² (at 1.23 V vs. RHE).     

g-C_3N_4基多功能层光阳极在光电化学水分解中的应用（英文）

光电化学分解水制氢可以一并解决环境问题和能源危机,因而成为研究热点.由于TiO_2 禁带宽度较大,不能有效吸收太阳光中的可见光,使光电化学分解水制氢的应用受限.g-C_3N_4的禁带宽度约为2.7 e V,能有效吸收可见光,但g-C_3N_4薄膜制备研究较少.我们通过热聚缩合法直接在FTO导电玻璃上制备出g-C_3N_4薄膜,发现其光电化学分解水制氢稳定性不高,选择易制备的TiO_2 作为保护层可以提高g-C_3N_4的耐用性.此外,为提高g-C_3N_4光生电子空穴对的分离能力,依靠Co-Pi对光生空穴的捕获作用而将其覆盖在最外层.因此本文首次制备一种新型的g-C_3N_4/TiO_2 /Co-Pi光阳极用于光电化学分解水制氢,其中g-C_3N_4用作光吸收层,TiO_2 用作保护层,Co-Pi用作空穴捕获层.并在此基础上,通过扫描电子显微镜(SEM),X射线衍射(XRD),紫外可见光谱(UV-Vis)等手段研究了g-C_3N_4/TiO_2 /Co-Pi光阳极的形貌特征和光电化学性能.SEM、EDS和XRD结果表明,g-C_3N_4/TiO_2 /Co-Pi光阳极被成功制备在了FTO导电玻璃上,厚度约为3μm.UV-Vis测试表明,g-C_3N_4的光吸收边约为470 nm,可以有效地吸收可见光,并且g-C_3N_4的框架结构使光多次反射折射增加了光的捕获能力,由此可见,g-C_3N_4能够发挥很好的光吸收层作用.通过对g-C_3N_4光阳极,g-C_3N_4/TiO_2 光阳极和g-C_3N_4/TiO_2 /Co-Pi光阳极的电流电压测试发现,g-C_3N_4/TiO_2 光阳极的光电流密度小于g-C_3N_4光阳极,而g-C_3N_4/TiO_2 /Co-Pi光阳极的光电流密在可逆氢电极1.1 V下达到了0.346 mA?cm–2,约为单独g-C_3N_4光阳极的3.6倍.这说明Co-Pi是提升g-C_3N_4光电化学性能的主要因素.电化学阻抗测试结果发现,g-C_3N_4/TiO_2 /Co-Pi光阳极的界面电荷转移电阻小于g-C_3N_4光阳极的,这表明g-C_3N_4/TiO_2 /Co-Pi光阳极界面处载流子转移较快,同时也能促进内部光生电子空穴对的分离,整体性能的提高应该主要归因于Co-Pi对光生空穴的捕获作用.恒电压时间测试展示出g-C_3N_4/TiO_2 /Co-Pi光阳极的光电流密度在2 h测试过程中没有明显下降,表明g-C_3N_4/TiO_2 /Co-Pi光阳极是相当稳定的,具有良好的耐用性,归因于TiO_2 和Co-Pi的共同保护作用,主要归因于TiO_2 层对FTO导电玻璃上的g-C_3N_4薄膜保护,从电化学沉积Co-Pi到所有测试结束.总体而言,g-C_3N_4/TiO_2 /Co-Pi光阳极加强的光电化学性能归因于以下几个因素:(1)g-C_3N_4优异的光吸收能力;(2)TiO_2 稳定的保护提升了g-C_3N_4薄膜的耐用性;(3)Co–Pi对光生空穴的捕获有效促进了光生电子空穴对的分离.     

Ultrathin-layer α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> deposited under hematite for solar water splitting

This work proposes a new strategy to prepare a hematite (α-Fe₂O₃) bilayer photoanode by hydrothermally depositing α-Fe₂O₃ (B) on the α-Fe₂O₃ (A) films prepared by electrochemical deposition. Compact smooth surfaced α-Fe₂O₃ (A) films were electrochemically deposited on FTO (SnO₂:F) substrates from an aqueous bath. The α-Fe₂O₃ (A), α-Fe₂O₃ (B), and α-Fe₂O₃/α-Fe₂O₃ bilayer films’ characteristics were defined by X-ray diffraction (XRD) measurements, field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray (EDX) spectroscopy. Pure crystalline α-Fe₂O₃ (B) films with a typical anisotropic-like nanoparticle formation, which exhibited nanostructured rods covering the substrate and formed the characteristic mesoporous film morphology, were hydrothermally deposited on α-Fe₂O₃ (A) films prepared by electrochemical depositing in a solution bath at 25 °C and a potential of ??0.15 V. The photocurrent measurements exhibited increased intrinsic surface states (or defects) at the α-Fe₂O₃ (A)/α-Fe₂O₃ (B) interface. The photoelectrochemical performance of the α-Fe₂O₃ (A)/α-Fe₂O₃ (B) structure was examined by chronoamperometry, which found that the α-Fe₂O₃ (A)/α-Fe₂O₃ (B) structure exhibited greater photoelectrochemical activity than the α-Fe₂O₃ (A) and α-Fe₂O₃ (B) thin films. The highest photocurrent density was obtained for the bilayer α-Fe₂O₃ (A)/α-Fe₂O₃ (B) films in 1 M NaOH electrolyte. This great photoactivity was ascribed to the highly active surface area, and to the externally applied bias that favored the transfer and separation of photogenerated charge carriers in α-Fe₂O₃ (A)/α-Fe₂O₃ (B). The improved photocurrent density was attributed to an appropriate band edge alignment of semiconductors and to enhanced light absorption by both semiconductors. The best performing samples were α-Fe₂O₃ (A)/α-Fe₂O₃ (B), which reached the maximum incident photon conversion efficiencies (IPCE) of 400 nm at the potential of 0.1 V. In this case, the IPCE values were 3-fold higher than those of the α-Fe₂O₃ (A) and α-Fe₂O₃ (B) films.     

Ultrafine α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocrystals anchored on N-doped graphene: a nanomaterial with long hole diffusion length and efficient visible light-excited charge separation for use in photoelectrochemical sensing

The authors have coupled ultrafine α-Fe₂O₃ nanocrystals to N-doped graphene (NG) to obtain a novel material for use in a photoelectrode. The presence of NG is shown to strongly affect the morphology and size of the α-Fe₂O₃ nanocrystals formed on the NG sheets, and to improve their photoelectrochemical (PEC) activity. Interestingly, the PEC performance of the nanocomposite is closely correlated to the size of the α-Fe₂O₃ nanocrystals in that small nanocrystals display better PEC properties. The photocurrent of α-Fe₂O₃-NG is nearly 3.3-fold stronger than that of α-Fe₂O₃ nanocrystals. Based on the remarkable PEC performance of this nanocomposite, a PEC sensor was constructed for the sensitive determination of 1,4-dihydroxybenzene (HQ). Its photocurrent increases with the HQ concentration in the range from 3.0 nM to 3.3 μM, and the detection limit is 1.0 nM (at an S/N ratio of 3). In our perception, the study presented here can serve as a basis for a better understanding of the relationship between morphologies and PEC performance of such nanomaterials. Conceivably, it may be extended to other PEC sensing system and to other fields associated with nanotechnology.

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Graphical abstract Ultrafine α-Fe₂O₃ nanocrystals were prepared via coupling with N-doped graphene (NG) substances (α-Fe₂O₃-NG). They exhibit superior photoelectrochemical (PEC) performance and have been successfully utilized for PEC-based sensing.

     

Synthesis and acetone gas sensing properties of α-Fe2O3 nanotubes

α-Fe₂O₃ nanotubes was successfully prepared by single nozzle electrospinning method. Scanning electron microscope (SEM) was used to characterize the morphology of α-Fe₂O₃ nanotubes. The gas sensing properties of α-Fe₂O₃ nanotubes were investigated in detail. The results exhibit relatively good sensing properties to acetone at 240 °C. The response and recovery times are about 3 and 5 s, respectively. The structure of nanotubes is beneficial to the gas sensing properties, which will enlarge the surface-to-volume ratio of α-Fe₂O₃ and then be available for the transfer of gas, and thus improved the sensor performance consequentially.     

An Efficient Strategy for Boosting Photogenerated Charge Separation by Using Porphyrins as Interfacial Charge Mediators

Surface recombination at the photoanode/electrolyte junction seriously impedes photoelectrochemical (PEC) performance. Through coating of photoanodes with oxygen evolution catalysts, the photocurrent can be enhanced; however, current systems for water splitting still suffer from high recombination. We describe herein a novel charge transfer system designed with BiVO₄ as a prototype. In this system, porphyrins act as an interfacial‐charge‐transfer mediator, like a volleyball setter, to efficiently suppress surface recombination through higher hole‐transfer kinetics rather than as a traditional photosensitizer. Furthermore, we found that the introduction of a “setter” can ensure a long lifetime of charge carriers at the photoanode/electrolyte interface. This simple interface charge‐modulation system exhibits increased photocurrent density from 0.68 to 4.75 mA cm^?2 and provides a promising design strategy for efficient photogenerated charge separation to improve PEC performance.     

In-situ Synthesis of the Thinnest In2Se3/In2S3/In2Se3 Sandwich-Like Heterojunction for Photoelectrocatalytic Water Splitting

The efficient utilization of solar energy for photoelectrocatalytic (PEC) water splitting is a feasible solution for developing clean energy and alleviating environmental issues. However, as the core of PEC technology, the existing photoanode catalysts have disadvantages such as poor photoelectrocatalytic conversion efficiency, low conductivity of photogenerated carriers, and instability. Here, we report the ultrathin two-dimensional sandwich-like (SW) heterojunction of In₂Se₃/In₂S₃/In₂Se₃ (SW In₂S₃@In₂Se₃) for the first time for PEC water splitting. Our findings identify the efficient separation of electrons and holes by constructing SW In₂S₃@In₂Se₃ heterojunction. The in situ synthesis of ultrathin nanosheet arrays by using surface substitution of Se atom to epitaxially grow cell In₂Se₃ maximizes the contact area of heterogeneous interface and accelerates the transmission of charge carrier. Benefitting from the unique structure and composition characteristic, SW In₂S₃@In₂Se₃ displays excellent performance in PEC water splitting. The photocurrent density of SW In₂S₃@In₂Se₃ reaches 8.43 mA cm⁻² at 1.23 V_RHE. Compared with In₂S₃, the SW In₂S₃@In₂Se₃ photoanode has nearly 12 times higher PEC performance, which represents the best performance among the In₂S₃-based photoanode heterojunction reported so far. The evolution rate of O₂ reaches 78.8 μmol cm⁻² h⁻¹, and the photocurrent has no apparent variety within 24 h.     

Prospects of electrochemically synthesized hematite photoanodes for photoelectrochemical water splitting: A review

Hematite (α-Fe₂O₃) is found to be one of the most promising photoanode materials used for the application in photoelectrochemical (PEC) water splitting due to its narrow band gap energy of 2.1 eV, which is capable to harness approximately 40% of the incident solar light. This paper reviews the state-of-the-art progress of the electrochemically synthesized pristine hematite photoanodes for PEC water splitting. The fundamental principles and mechanisms of anodic electrodeposition, metal anodization, cathodic electrodeposition and potential cycling/pulsed electrodeposition are elucidated in detail. Besides, the influence of electrodeposition and annealing treatment conditions are systematically reviewed; for examples, electrolyte precursor composition, temperature and pH, electrode substrate, applied potential, deposition time as well as annealing temperature, duration and atmosphere. Furthermore, the surface and interfacial modifications of hematite-based nanostructured photoanodes, including elemental doping, surface treatment and heterojunctions are elaborated and appraised. This review paper is concluded with a summary and some future prospects on the challenges and research direction in this cutting-edge research hotspot. It is anticipated that the present review can act as a guiding blueprint and providing design principles to the scientists and engineers on the advancement of hematite photoanodes in PEC water splitting to resolve the current energy- and environmental-related concerns.     

Preparation and characterization of shuttle-like α-Fe2O3 nanoparticles by supermolecular template

Shuttle-like α-Fe₂O₃ nanoparticles have been successfully synthesized via a new soft-template route using polyethylene glycol (PEG) as polymer, cetyltrimethylammonium bromide (CTAB) as surfactant and FeCl₃·6H₂O as iron source materials. Meanwhile, spherical α-Fe₂O₃ nanoparticles are also fabricated under the similar conditions without surfactant and polymer. The resultant products are characterized by means of thermalgravimetric analysis (TGA), powder X-ray diffraction (XRD), infrared (IR) spectroscopy, transmission electron micrograph (TEM), X-ray photoelectron spectra (XPS) and magnetization measurements. The homogeneous α-Fe₂O₃ nanoparticles with shuttle-like shape have an average length of 120 nm and a mean diameter of about 50 nm in the middle part (an average aspect ratio of about 2.5) whereas spherical α-Fe₂O₃ nanoparticles have a mean particle diameter of about 35 nm. Magnetic hysteresis measurements reveal that shuttle-like α-Fe₂O₃ nanoparticles display normal ferromagnetic behaviors while spherical α-Fe₂O₃ nanoparticles exhibit weak ferromagnetic behaviors at room temperature. The two types of α-Fe₂O₃ exhibit hysteretic features with the remanence and coercivity of 0.156 emu/g and 664 Oe, 0.048 emu/g and 110 Oe, respectively. The higher remanent magnetization and coercivity of shuttle-like α-Fe₂O₃ nanoparticles may be associated with the aspect ratio of α-Fe₂O₃ since shape anisotropy would exert a tremendous influence on their magnetic properties.     

Integration of Fe_2O_3-based photoanode and atomically dispersed cobalt cathode for efficient photoelectrochemical NH_3 synthesis

Realizing nitrogen reduction reaction(NRR) to synthesis NH_3 under mild conditions has gained extensive attention as a promising alternative way to the energy-and emission-intensive Haber-Bosch process.Among varieties of potential strategies,photoelectrochemical(PEC) NRR exhibits many advantages including utilization of solar energy,water(H_2O) as the hydrogen source and ambient operation conditions.Herein,we have designed a solar-driven PEC-NRR system integrating high-efficiency Fe_2O_3-based photoanode and atomically dispersed cobalt(Co) cathode for ambient NH_3 synthesis.Using such solar-driven PEC-NRR system,high-efficiency Fe_2O_3-based photoanode is responsible for H_2O/OH oxidatio n,and meanwhile the generated photoelectrons transfer to the single-atom Co cathode for the N_2 reduction to NH_3.As a result,this system can afford an NH_3 yield rate of 1021.5 μg mgco~(-1) h~(-1) and a faradic efficiency of 11.9% at an applied potential bias of 1.2 V(versus reversible hydrogen electrode) on photoanode in 0.2 mol/L NaOH electrolyte under simulated sunlight irradiation.     

Sub-nanometer,Ultrafine α-Fe2O3 Sheets Realized by Controlled Crystallization Kinetics for Stable,High-Performance Energy Storage

The development of energy devices based on iron oxides/hydroxides is largely hindered by their poor conductivity and large volume changes, especially with regard to specific capacitance and cycle stability. Herein, superior capacitance (1575 F g⁻¹ at 1.25 A g⁻¹) and high rate performance (955 F g⁻¹ at 25 A g⁻¹) were realized by synthesizing sub-nanometer, ultrafine α-Fe₂O₃ sheets loaded on graphene (SU-Fe₂O₃-rGO). An assembled asymmetric supercapacitor showed outstanding cycle stability (106 % retention after 30 000 cycles). This excellent performance arises from the unique structural characteristics of the α-Fe₂O₃ sheets, which not only enrich electrochemically reactive sites, but also largely eliminate the volume changes after long-term charge/discharge cycling. The synthesis of SU-Fe₂O₃-rGO critically depends on control of the crystallization kinetics during growth. A controlled heterogeneous nucleation mechanism results in the formation of atomically thin α-Fe₂O₃ sheets on graphene rather than large particles in solvent, as clarified by theoretical calculations. This strategy paves a new way to synthesizing atomically thin transition metal oxide sheets and low-cost, eco-friendly iron-based energy storage.     

Microscopic studies of a SnO2/α-Fe2O3 architectural nanocomposite using Mössbauer spectroscopic and magnetic measurements

A SnO₂/α-Fe₂O₃ architectural nanocomposite, which was evidenced as SnO₂ nanorod arrays assembled on the surface of α-Fe₂O₃ nanotubes in our previous study, was investigated microscopically by means of Mössbauer spectroscopic and magnetic measurements. It was found for the SnO₂ nanorods that Fe³⁺ ions substituted slightly to Sn_0.998Fe_0.002O₂. Concerning the α-Fe₂O₃ tubes, the Morin transition, which was completely suppressed in the mother, SnO₂-free α-Fe₂O₃ nanotubes, was found to be recovered locally. We speculate that it takes place in the interface area as a result of structural modification needed for the connection with the SnO₂ nanorods.     

Support Morphology Effect on Selective Hydrogenation of 3-Nitrostyrene to 3-Vinylaniline over Pt/α-Fe2O3 Catalysts

Selective hydrogenation of substituted nitroaromatic compounds is an extremely important and challenging reaction. Supported metal catalysts attract much attention in this reaction because the properties of metal nanoparticles (NPs) can be modified by the nature of the support. Herein, the support morphology on the catalytic performance of selective hydrogenation of 3-nitrostyrene to 3-vinylaniline was investigated. Pt NPs supported on octadecahedral α-Fe₂O₃ supports with a truncated hexagonal bipyramid shape (Pt/α-Fe₂O₃-O) and rod-shaped α-Fe₂O₃ supports (Pt/α-Fe₂O₃-R) were prepared by glycol reduction method. Detailed characterizations reveal that the electronic structure and dispersion of Pt NPs can be modified by the supports. The Pt/α-Fe₂O₃-O catalyst exhibited superior catalytic performance for hydrogenation of 3-nitrostyrene because of its low coordinated Pt sites and the small Pt NPs size, which is benefit from the high-index exposed surfaces of truncated hexagonal bipyramid-shaped α-Fe₂O₃ support. The structural evolution during the catalytic reaction was investigated in detail by identical location transmission electron microscopy (IL-TEM) method, which found that the high cycling activity of Pt/α-Fe₂O₃-O catalyst during the cycle experiment results from the stability of Pt NPs.     

Thermal properties of the γ-Fe2O3/poly(methyl methacrylate) core/shell nanoparticles

Thermal properties of γ-Fe₂O₃/poly(methyl methacrylate) (PMMA) core/shell particles with an average core size of 4 nm were studied through measurements of thermogravimetry, powder X-ray diffraction and magnetization. The thermal degradation of the PMMA shell in the air was found to occur at temperatures lower by about 60 °C than that of free PMMA. Random scission of the PMMA chains seemed to be catalyzed by the core oxide. The γ-Fe₂O₃ to α-Fe₂O₃ structural transformation took place at different temperatures depending upon the shell material. Namely, α-Fe₂O₃ was the only product for the caprylate-capped γ-Fe₂O₃ nanoparticles treated at 400 °C, whereas γ-Fe₂O₃ still remained for the γ-Fe₂O₃/PMMA composite treated at 500 °C. It is possible that some species containing silicon of the polymerization initiator origin were formed on the surface and prevented interparticle atomic diffusions needed for the γ–α transformation.     

Studies on fabricating α-Fe2O3 ultrafine particles by LB film technology

The α-Fe₂O₃ ultrafine particles were dispersed in the solutions of stearic acid/n-hexane/chloroform by the ultrasonic method, and fabricated by the Langmuir–Blodgett film technology. α-Fe₂O₃ ultrafine particles/stearic acid composite LB films were characteried by π–A curve, UV-visible absorption spectrum, IR spectrum, small angle X-ray diffraction, TEM and electron diffraction. The results showed the following: the αFe₂O₃ ultrafine particles were uniformly dispersed in organic solvents; the film-forming characterization of the α-Fe₂O₃ ultrafine particles/stearic acid monolayer was fine, the α-Fe₂O₃ ultrafine particles in the composite film had a small orientation; the α-Fe₂O₃ ultrafine particles/stearic acid composite film had a lamellar structure.     

Construction of high-efficient visible photoelectrocatalytic system for carbamazepine degradation: Kinetics,degradation pathway and mechanism

This study aimed to construct a photoelectrocatalytic (PEC) reaction system based on the self-made reduced TiO₂ NTAs (r-TNAs) photoanode and activated carbon/Polytetrafluoroethylene (AC/PTFE) cathode. It would be observed clearly that the degradation rate constant of carbamazepine (CBZ) over r-TNAs_(photoanode)-AC/PTFE_(cathode) PEC system (0.04961 min⁻¹) was even higher than that of r-TNAs_(photoanode)-Pt_(cathode) PEC system (0.04602 min⁻¹) with the assistance of visible light irradiation and +0.4 V external potential. Besides, in order to obtain optimized conditions, the influence of key parameters such as pH value, electric current density and electrolyte concentration were studied. Most importantly, photoelectrochemical (PECH) properties, reactive oxide species contribution, OH formation rate and CBZ degradation pathway were determined. The results illustrated that the excellent PEC degradation performance depended on the excellent photocatalytic property of r-TNAs photoanode and electron transfer property of photoelectrodes in r-TNAs_(photoanode)-AC/PTFE_(cathode) PEC system. Therefore, the study demonstrated that the r-TNAs_(photoanode)-AC/PTFE_(cathode) PEC system could be expected to replace metal-catalyzed cathodes depending on its excellent PEC performance activity and low cost as well as the reaction system possessed objective and practical application prospect.