Pristine ZnFe2O4 Research Articles

Solvent‐Less Synthesis of Compositionally Tuned Mixed Metal (Ni−Zn) Ferrites for Enhanced Electrocatalytic Water Splitting and Supercapacitance

AbstractExploring efficient, abundant, economical and stable materials for sustainable energy applications, such as electrochemical water splitting and supercapacitance, is a challenging task. Mixed transition metal spinel ferrites can rationally be customized to attain these features and deliver enhanced electrochemical activity. The catalytic performance of spinels is remarkably influenced by tuning the cationic occupancy at the tetrahedral or octahedral position. Herein, a set of spinel Ni1‐xZnxFe2O4 (0≤x≤1) nanocomposites were obtained via a scalable solventless thermolysis of metal acetylacetonate precursors at relatively mild temperatures. A suite of techniques such as powder p‐XRD, EDX, SEM, TEM, HRTEM, and SAED were employed to confirm the formation of the Ni−Zn ferrite solid solutions. It was found that small amounts of Ni at tetrahedral sites were beneficial for charge storage and hydrogen evolution. For instance, Ni0.2Zn0.8Fe2O4 nanocomposite demonstrated superior HER activity with a much lower overpotential of 87 mV compared to the pristine NiFe2O4 (213 mV) or ZnFe2O4 (164 mV) catalysts. However, Ni‐occupied tetrahedral sites were not suitable for OER, whereby the pristine ZnFe2O4 displayed high catalytic activity with an overpotential of 330 mV, outperforming other electrode compositions. The study helps to identify suitable compositions and site tuning for HER, OER and supercapacitors.

Fabrication of Ni and Mn co-doped ZnFe2O4 spinel ferrites and their nanocomposites with rGO as an efficient photocatalyst for the remediation of organic dyes

Herein, we have synthesized Ni and Mn co-doped ZnFe2O4 ferrites using the simple co-precipitation method and their nanocomposites (NCs) with 10 % rGO using the ultra-sonication route. The structural investigation revealed the successful formation of single-phase ZnFe2O4 NPs with cubic spinel ferrite geometry. The crystallite size was determined to be in the range of 21 nm to 28 nm. The current–voltage (I-V) analysis revealed that Ni and Mn co-doping and the addition of rGO nanosheets in ZnFe2O4 NPs boosted the electrical responses of the fabricated Zn1-xNixFe2-yMnyO4/rGO NCs. The BET analysis indicates an increase in the surface area of Zn1-xNixFe2-yMnyO4/rGO NCs (132 m2/g) that might be attributed to the inclusion of rGO nanosheets, which prevents the NPs from agglomeration. The photocatalytic evaluation of the pristine ZnFe2O4 NPs, Ni and Mn co-doped Zn1-xNixFe2-yMnyO4 NPs, and Zn1-xNixFe2-yMnyO4/rGO NCs photocatalysts was tested by photodegradation of malachite green (MG) dye under sunlight irradiation. Results exhibited improved photocatalytic responses and degraded 94.6 % of MG dye in 45 min using Zn1-xNixFe2-yMnyO4/rGO NCs, which was much higher compared to the Ni and Mn co-doped Zn1-xNixFe2-yMnyO4 NPs (58.7 %) and pristine ZnFe2O4 NPs (38.3 %). The increased degradation potential of Zn1-xNixFe2-yMnyO4/rGO NCs was accredited to the highly conducting nature and 2D nano-sheets of rGO, which efficiently inhibited the recombination of charge carrier species. Ultimately, the remarkable photocatalytic capability exhibited by Zn1-xNixFe2-yMnyO4/rGO NCs implies that the synthesized NCs could have auspicious practical applications in the elimination of dyes from wastewater.

ZnFe2O4/ ZnO 0D-1D heterojunction for efficient photoelectrochemical water splitting

In this work, both ZnO nanorods (NRs) thin films and ZnO NRs powder were successfully synthesized by open aqueous solution bath technique. Further, the residual ZnO nanorods (NRs) powder was used to synthesize ZnFe2O4 (ZFO) nanoparticles (NPs) by hydrothermal method. Finally, ZFO/ZnO heterojunction thin films were prepared and tested for photoelectrochemical water splitting application. The ZFO loading was controlled and tuned by drop-casting various numbers of drops (10, 20, 30 and 40) on the ZnO NRs films keeping the area constant. An improved photocurrent density ∼0.82 mA/cm2 was observed for optimized 30 ZFO/ZnO NRs thin films as compared to ∼0.19 mA/cm2 for pristine ZnO NRs thin films at 1.23 V vs RHE under 100 mW/cm2 light in a 0.1 M Na2SO4 neutral electrolyte. This remarkable enhancement in photocurrent for 30 ZFO/ZnO heterojunction compared to pure ZnO NRs array is attributed to increased light absorption induced electron-hole pairs generation, effective charge transfer and better charge separation at the ZFO/ZnO interface due to a favorable band alignment. This was confirmed with the incident photon to current conversion efficiency (IPCE) measurements which exhibit a significantly high value (∼14%) for 30 ZFO/ZnO films than pristine ZFO and ZnO thin films. It is worthy to note that ZFO NPs coated ZnO thin films deliver long term stability of the electrode against photocorrosion.

Environment-friendly ternary ZnO/ZnFe2O4/TiO2 composite photocatalyst with synergistic enhanced photocatalytic activity under visible-light irradiation

Developing novel environmental-friendly photocatalysts with ideal properties is an endless project, urged by growing demands of advance in high efficiency, energy saving, and environmental remediation. In this work, a novel ternary ZnO/ZnFe2O4/TiO2 composite photocatalyst have been synthesized via a facile synthetic method. Anatase TiO2 particles with average crystallite size of 10.38 nm are thinly coated on the surface of octahedral-like ZnO/ZnFe2O4 nanoparticles. The ternary composite photocatalyst displays stronger transient photocurrent response characteristics, about 3 times larger than that of pristine ZnFe2O4 under visible-light irradiation, indicating excellent photogenerated charge carriers transfer efficiency. Compared with ZnFe2O4 and ZnO/ZnFe2O4, the ZnO/ZnFe2O4/TiO2 composite photocatalyst have the optimal photocatalytic properties, achieving 96.32% degradation efficiency for methylene blue (MB) aqueous solution after 150 min of visible-light irradiation. More impressive is the stability, after 4 cycles, its photocatalytic activity still no significant decreases. Reactive species trapping tests reveal that not superoxide radicals but hydroxyl radicals and photogenerated holes are highly responsible for the photocatalysis process. The enhancement of photocatalytic activity is ascribed to the synergetic effect of large specific surface area, efficient visible-light absorption, and rapid migration of photogenerated charge carriers. The results disclose the ternary ZnO/ZnFe2O4/TiO2 composite photocatalyst is a suitable photocatalyst candidate for environmental remediation.

Insights into photocatalytic mechanism for the rational design of p-n heterojunction by decorating mesoporous SnS2 over ZnFe2O4 nanocomposite for accelerated visible light photocatalysis

Binary p-n heterojunction of ZnFe2O4/SnS2 nanocomposite (NCs) was constructed by sonochemical assisted technique for enhanced visible light induced photocatalytic performance. The narrow bandgap of 2.21 eV facilitated the photocatalyst be to active under visible-light irradiation. The rate of photodegradation of methylene blue (MB) dye by optimized-NCs ratio was observed to be remarkable with multifold enhancement than pristine ZnFe2O4 and SnS2. The interfacial contact enforces an internal electric field dependent directional charge migration which hinders charge recombination that was verified by reduced photoluminescence intensity in NCs. The degradation process was found to follow pseudo-first order kinetics. The major ROS involved in the photodegradation process were found to be hydroxyl (.OH) and superoxide (.O2-) radicals which were identified through the scavengers assay. The NCs were subjected to six consecutive cycles in order to test its structural stability and reusability. This work provides guidance for rational design of heterojunction with superior activity and it reflected the potential of ZnFe2O4/SnS2 NCs as a promising photocatalyst to remove toxic pollutants from the aqueous bodies.

Facile synthesis, morphological, structural, photocatalytic and optical properties of ZnFe2O4-ZnO hybrid nanostructures

ZnFe2O4/ZnO heterojunction photocatalysts have been fabricated via simple co-precipitation method and systematically characterized. The structural and morphological analyses using XRD, Raman and FESEM confirmed the formation of ZnFe2O4/ZnO hybrid nanostructures. The optical properties were analysed via UV–vis DRS, PL and UV–vis absorption spectroscopy. UV–vis DRS studies showed band gap variation from 1.91 to 2.07 eV. The visible light-driven photodegradation activity of the synthesized products was explored by decomposing toxic pollutants in water and the results showed that ZnFe2O4/ZnO hybrid nanostructures exhibit superior photodegradation performance over pristine ZnFe2O4 nanostructures. The improved photocatalytic performance of ZnFe2O4/ZnO nanostructures is ascribed to efficient sunlight utilization ability and suppression of recombination of photoinduced charge carriers due to p-n nanoheterojunction formation. In addition, photodegradation mechanism supported with scavenger experiments has been proposed. Besides the excellent photoactivity, ZnFe2O4/ZnO hybrid nanostructures are outstandingly stable, recyclable and thereby exhibit an enormous potential for large scale photocatalytic applications.

Highly efficient white-LED-light-driven photocatalytic hydrogen production using highly crystalline ZnFe2O4/MoS2 nanocomposites

Designing efficient photocatalytic systems for hydrogen evolution is extremely important from the viewpoint of the energy crisis. Highly crystalline heterostructure catalysts have been established, considering their interface electric field effect and structural features, which can help improve their photocatalytic hydrogen-production activity. In this study, we fabricated a highly crystalline heterojunction consisting of ZnFe2O4 nanobricks anchored onto 2D molybdenum disulfide (MoS2) nanosheets (i.e., ZnFe2O4/MoS2) via a hydrothermal approach. The optimized ZnFe2O4/MoS2 photocatalyst, with a ZnFe2O4 content of 7.5 wt%, exhibited a high hydrogen-production rate of 142.1 μmol h−1 g−1, which was 10.3 times greater than that for the pristine ZnFe2O4 under identical conditions. The photoelectrochemical results revealed that the ZnFe2O4/MoS2 heterojunction considerably diminished the recombination of electrons and holes and promoted efficient charge transfer. Subsequently, the plausible Z-scheme mechanism for photocatalytic hydrogen production under white-LED light irradiation was discussed. Additionally, the influence of cocatalysts on the photocatalytic hydrogen evolution for the ZnFe2O4/MoS2 heterostructure was investigated. This work has demonstrated a simplified coupling of one-dimensional or zero-dimensional structures with 2D nanosheets for improving the photocatalytic hydrogen production activity as well as confirmed that MoS2 is a viable substitute for precious metal-free photocatalysis.

Synthesis of porous nanosheet-assembled ZnFe2O4@polypyrrole yolk-shell microspheres as anode materials for high-rate lithium-ion batteries

Hierarchical ZnFe2O4 yolk-shell spheres (YSs) assembled from primary nanosheets are synthesized via a simple one-step solvothermal method followed by a heat-treatment process. A polypyrrole (PPy) conductive network is formed in-situ on pristine ZnFe2O4 YSs via chemical oxidative polymerization to obtain ZnFe2O4@PPy YSs. Morphological and structural characterization confirms that the conductive PPy coating does not destroy the localized porous microenvironment of pristine ZnFe2O4 with rapid mass transport. The solvothermal reaction time-dependent structure evolution and formation mechanism of ZnFe2O4@PPy YSs have been elucidated. Furthermore, the electrochemical performance of the ZnFe2O4@PPy YSs is assessed and compared with that of pristine ZnFe2O4 YSs. The results reveal that ZnFe2O4@PPy YSs exhibit excellent rate capability and long-term cycling stability, achieving 541.7 mAh g−1 at 5 A g−1 after 1000 cycles. The improved electrochemical performances of ZnFe2O4@PPy YSs are attributed to not only the structural advantages of porous yolk-shell architecture, but also the conductivity enhancement and suppressed volume expansion induced by the PPy layer.

Photocatalytic Performance of Zinc Ferrite Magnetic Nanostructures for Efficient Eriochrome Black-T Degradation from the Aqueous Environment under Unfiltered Sunlight

Herein, three different types of zinc ferrite (ZnFe2O4) magnetic nanoparticles as photocatalysts were synthesized from iron and zinc sulfate using a co-precipitation method. Tri ethylene glycol (TEG) was utilized as a capping/stabilizing agent in the presence of ammonium hydroxide. The as-prepared nanoparticles were annealed at 400 °C for 4 h followed by acid etching with HCl (for 15 min in I M solution). The thermally treated magnetic nanostructure was subjected to surface modification by treating with 3-aminopropyl (triethoxysilane) 3-(APTES) at 60 °C for 2 h. Various characterization techniques including Fourier transform infrared (FTIR), Brunauer-Emmett-Teller (BET), and X-rays diffraction (XRD) were carried out to examine the structural properties of the pristine and functionalized nanocrystals. XRD pattern assessed the crystalline and nano size of the ZnFe2O4 recording particle sizes of 13.5, 23.3, and 106.5 nm for functionalized, annealed, and pristine ZnFe2O4 nanoparticles, respectively. FTIR spectral analysis corroborated the modifications and functionalization of the samples. BET analysis revealed a surface area of 0.6719 (functionalized), 45.21 (annealed), and 155.38 (pristine nanoparticles). The photocatalytic activity of the prepared nanostructures was investigated for Eriochrome Black T (EBT) dye under the unfiltered sunlight. At optimal reaction parameters, the photocatalytic rates of EBT dye for functionalized, annealed, and blank NP’s were 92, 91, and 83%, respectively. Kinetic models demonstrate that the degradation processes followed pseudo-first-order kinetics. The energies of the band gap in the acidic and basic media, as determined from the Tauc plot, were 2.47 and 2.7 eV, respectively. Taken together, the results showed that newly fabricated nanostructures are considered as promising photocatalysts in degrading organic pollutants for a sustainable environment.

Zinc ferrite-based p-n homojunction with multi-effect for efficient photoelectrochemical water splitting.

A novel one-dimensional core-shell zinc ferrite (ZnFe2O4) p-n homojunction is prepared by a facile two-step hydrothermal method. The core-shell homojunction is constructed by decorating p-type Ni-ZnFe2O4 (shell) onto n-type ZnFe2O4 (core). As expected, significant enhancement in the photocurrent density of the developed homojunction is realized compared to that of pristine ZnFe2O4 (6.64 times that of pristine ZnFe2O4). This improvement is ascribed to the fact that the ZnFe2O4 homojunction has multiple optimization effects, namely, a built-in electric field and active sites on Ni-ZnFe2O4, which are beneficial to carrier separation and transport. This study paves a promising pathway for the use of ion doping to design high-quality p-n homojunctions with multiple effects for enhancing charge separation in the photoelectrochemical water splitting configuration.

Well-designed ZnFe2O4/Ag/TiO2 nanorods heterojunction with Ag as electron mediator for photocatalytic CO2 reduction to fuels under UV/visible light

Spinel ZnFe2O4 microspheres coupled with Ag/TiO2 nanorods (NRs) to develop Z-scheme heterojunction were fabricated using a facile hydrothermal approach and were tested for photocatalytic CO2 conversion to fuels. ZnFe2O4/Ag/TiO2 NRs composite presents remarkably improved CO2 photo-activity for CO production, which was 1.49 folds higher than ZnFe2O4/TiO2 NRs and 4.12 times that using pristine ZnFe2O4 microspheres. Similar trends were obtained to produce methane and methanol over composite catalyst. Selective CO and hydrocarbon fuels production was obviously due to double charge transfer approach in indirect Z-scheme heterojunction with superior charge carrier separation and high visible light absorption. Interestingly, CO evolution under visible-light with ZnFe2O4/Ag/TiO2 NRs was declined by 7.48 folds than using UV-light irradiation. This was apparently due to the inappropriate VB position of ZnFe2O4 for stimulating CO2 reduction under visible light irradiation. Comparing morphological effects, coupling TiO2 NRs with Ag/ZnFe2O4, production of CO was 1.40 folds higher than using TiO2 NPs with Ag/ZnFe2O4 composite due to 1D TiO2 NRs and ZnF2O4 were beneficial for promoting charge carrier separation. This work provides a new approach for preparing ZnFe2O4 based structured Z-scheme hetero-junction for stimulating photocatalytic conversion of CO2 to selective fuels and would be promising for energy application.

Surface passivation of zinc ferrite nanorod photoanodes by spray-deposited silicon oxide layer for enhanced solar water splitting

Abstract ZnFe2O4 nanorods (NR's) were prepared by a chemical conversion method from β-FeOOH NRs grown on FTO substrates. To activate their photoactivity of ZnFe2O4 NRs for solar water splitting, the surface passivation was achieved with SiO2 layer via facile and effective spray pyrolysis method. The presence of SiO2 layer enhances the photocurrent density of the Pristine ZnFe2O4 from 143 µA/cm2 to 212 µA/cm2 at 1.23 VRHE for 0.25 mM Si–ZnFe2O4, representing two time increment in the photocurrent density. The influences of amount of Si precursor (Tetraethyl orthosilicate) solutions on the physical properties and the passivation effect of SiO2/ZnFe2O4 interfaces were investigated. This improved photoresponse of the Si-treated ZnFe2O4 NRs was attributed to the excellent charge transfer electrode/electrolyte interface. The effectively improved charge transfer properties of the Si-treated ZnFe2O4 NRs were demonstrated by the electrochemical impedance spectroscopy (EIS), Mott–Schottky (MS) and intensity-modulated photocurrent spectroscopy (IMPS) analyses.

Mesoporous Sn/Mg doped ZnFe2O4 nanorods as anode with enhanced Li-ion storage properties

ZnFe2O4 and MxZn1-xFe2O4 (M = Sn, Mg) nanorods are synthesized by a facile co-precipitation method followed by thermal treatment of metal-organic frameworks in air to form mesoporous structure. Temperatures of thermal treatment affects the porous structure of the materials and influences charge/discharge process of ZnFe2O4. From the electrochemical performance, we find that doping Sn which is electrochemically active would raise the voltage plateau corresponding to the reaction peaks of the doping elements, and Sn0.05Zn0.95Fe2O4 exhibits the highest capacity of 1318 mA h g−1 after 50 cycles at 0.1 C. In contrast, doping Mg which is electrochemically inactive would inhibit volume change and stabilize structure during lithiation-delithiation. Mg0.9Zn0.1Fe2O4 shows an excellent reversible capacity of 811 mA h g−1 with a capacity retention of 82% after 250 cycles at 1 C, while the pristine ZnFe2O4 only remains 382 mA h g−1 with a capacity retention of 32%.

1D ZnFe2O4 nanorods coupled with plasmonic Ag, Ag2S nanoparticles and Co-Pi cocatalysts for efficient photoelectrochemical water splitting

Improving the absorption of visible light, accelerating the separation of carries and reducing the recombination of electron-hole pairs are critical to enhance photoelectrochemical (PEC) performance of ZnFe2O4. Herein, the ZnFe2O4/Ag/Ag2S films are firstly prepared with a photocurrent density of 0.91 mA/cm2 at 1.23 V vs. RHE, which is 9.10 times higher than that of pristine ZnFe2O4 (0.10 mA/cm2 at 1.23 V vs. RHE). On the basis, Co-Pi cocatalyst is deposited on ZnFe2O4/Ag/Ag2S to further optimize PEC performance of ZnFe2O4, the photocurrent density of ZnFe2O4/Ag/Ag2S/Co-Pi is 1.18 mA/cm2 at 1.23 V vs. RHE. The improved PEC performance of ZnFe2O4/Ag/Ag2S/Co-Pi films could be attributed to: (i) fast transmission of electron-hole pairs owing to 1D ZnFe2O4 NRs; (ii) surface plasmon resonance (SPR) effect of Ag nanoparticles; (ⅲ) visible light absorption is improved by sensitization of Ag2S nanoparticles; (ⅳ) Co-Pi cocatalyst decreases the recombination of electron-hole pairs by capturing holes. This work provides new insights for metal plasmas, sensitizers and cocatalysts synergistically modify photoanodes for efficient PEC water splitting.

Stabilization of Magnetic Ferrite Nanostructures with Cellulose Derived From Biomass for the Abatement of Environmental Pollution

Abstract Magnetic ZnFe2O4 nanoparticles were stabilized using biomass derived cellulose to fabricate high performance cellulose based nanocomposites. The synthesized nanocomposites were well characterized using FT-IR, Powder XRD and TEM analysis. TEM images revealed the decoration of ZnFe2O4 nanoparticles onto the surface of cellulose. The synthesized nanocomposites displayed enhanced catalytic activity for the photocatalytic degradation of toxic remazol black 5 dye in comparison to the pristine ZnFe2O4 nanoparticles and cellulose. Furthermore, the magnetically retrievable nature of the nanocomposites facilitated the easy recyclability and reusability of the nanocomposites. The present work promotes the use of biomass derived materials to prepare inorganic/organic hybrid materials for mitigation of environmental pollution.

Environment-Friendly Carbon Quantum Dots/ZnFe2O4 Photocatalysts: Characterization, Biocompatibility, and Mechanisms for NO Removal.

A highly efficient and environmentally-friendly oxidation process is always desirable for air purification. This study reported a novel carbon quantum dots (CQDs)/ZnFe2O4 composite photocatalyst for the first time through a facile hydrothermal process. The CQDs/ZnFe2O4 (15 vol %) composite demonstrates stronger transient photocurrent response, approximately 8 times higher than that of ZnFe2O4, indicating superior transfer efficiency of photogenerated electrons and separation efficiency of photogenerated electron-hole pairs. Compared with pristine ZnFe2O4 nanoparticles, CQDs/ZnFe2O4 displayed enhanced photocatalytic activities on gaseous NOx removal and high selectivity for nitrate formation under visible light (λ > 420 nm) irradiation. Electron spin resonance analysis and a series of radical-trapping experiments showed that the reactive species contributing to NO elimination were ·O2- and ·OH radicals. The possible mechanisms were proposed regarding how CQDs improve the photocatalytic performance of ZnFe2O4. The CQDs are believed to act as an electron reservoir and transporter as well as a powerful energy-transfer component during the photocatalysis processes over CQDs/ZnFe2O4 samples. Furthermore, the toxicity assessment authenticated good biocompatibility and low cytotoxity of CQDs/ZnFe2O4. The results of this study indicate that CQDs/ZnFe2O4 is a promising photocatalyst for air purification.

Sulfur-doped ZnFe2O4 nanoparticles with enhanced lithium storage capabilities

Sulfur-doped ZnFe2O4 nanoparticles were synthesized through sulfurizing ZnFe2O4 nanoparticles in the hydrothermal process using Na2S as the sulfur source. The content of sulfur dopant was tuned from 0.70 to 1.26 wt% by controlling concentrations of Na2S solutions. When evaluated as anode materials for lithium-ion batteries, sulfur-doped ZnFe2O4 nanoparticles exhibited much higher reversible capacities, better rate performances, and more excellent cycling stabilities than the pristine ZnFe2O4 nanoparticles. After 60 cycles at a current density of 100 mA g−1, the electrode of sulfur-doped ZnFe2O4 nanoparticles (1.26 wt%) delivered a reversible specific capacity of 604 mA h g−1, while the pristine ZnFe2O4 electrode only remained 200 mA h g−1.

Hydrothermal preparation and characterization of nanostructured CNTs/ZnFe2O4 composites for solar water splitting application

Multi-walled carbon nanotubes (CNTs)/ZnFe2O4 composites were fabricated hydrothermally via direct growth of ZnFe2O4 nanoparticles on the CNTs surface. The as-obtained samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), and UV–visible diffuse reflectance spectra (UV–vis DRS) techniques. The photocatalytic performance was evaluated by water splitting in methanol aqueous solution under high-pressure Hg lamp illumination. The effects of CNTs content in the composites on the solar H2 generation activity were investigated comparatively. Compared with bare ZnFe2O4, the CNTs/ZnFe2O4 hybrid exhibited enhanced photocatalytic H2 evolution activity. The photoluminescence emission spectra (PL) showed that the fluorescence of CNTs/ZnFe2O4 composites was quenched significantly in comparison with that of pristine ZnFe2O4, indicating that an enhanced charge carrier separation efficiency was achieved. Also, a probable mechanism of CNTs for the enhancement of H2 evolution performance is proposed and discussed.