Visible-light photocatalytic activity of zinc ferrites

Addition of silver nanoparticles to the zinc ferrite/polyaniline composition for boosting its visible photocatalytic degradation

Enhancing the photocatalytic activity of ZnFe2O4 with a good energy band gap to degrade industrial waste under sunlight illumination can help to develop green environments. Here, to improve the photocatalytic efficiency of ZnFe2O4 ferrites, they were merged with polyaniline (PAni) and silver (Ag) nanoparticles to synthesize Ag@ZnFe2O4-PAni plasmonic nanostructures. The as-synthesized nanostructures were characterized using a series of advanced characterization techniques to confirm successful formation and investigate photocatalytic improvement origins. It was found that incorporating Ag NPs along with the PAni to ZnFe2O4 increases its absorption power and red-shifts its energy band gap, which increases the electron-hole production rate by exposure to light in ZnFe2O4. Contribution of the surface plasmon resonance effect of Ag NPs and conjugated double bonds of PAni to charge transfer mechanisms in Ag@ZnFe2O4-PAni material increased charge separation during photocatalytic process, boosting the photodegradation performance of ZnFe2O4.

Solar light driven degradation of piroxicam and paracetamol by heterogeneous photocatalytic fenton system: Process optimization, mechanistic studies and toxicity assessment

The widespread occurence of pharmaceutical pollutants seriously threatens the environment and human well-being. In the present study, zinc ferrite nanoparticles (ZnFe2O4 NPs) have been synthesized by co-precipitation method and used as photocatalyst for the degradation of two most commonly prescribed painkillers, piroxicam (PXM) and paracetamol (PCM), via heterogeneous Fenton process under the solar light. The synthesized ZnFe2O4 NPs showed a narrower band gap i.e. 1.87 eV, signifying the ability to efficiently work in visible light range. In context of photocatalytic applications, the operational conditions were optimized to achieve maximum degradation. PCM and PXM were completely degraded (100%) at the optimized photocatalytic dose (20 mg L-1), reaction time (180 min), initial drug concentration (10 mg L-1), and pH (6.0), which is close to the natural environment. The extent of mineralization as estimated by the reduction of total organic carbon (TOC) was observed to be ∼91 and 82% for PCM and PXM respectively. Kinetic studies revealed that photocatalytic degradation followed pseudo-first-order kinetics. Moreover, the ZnFe2O4 NPs retained ∼90 % of photocatalytic activity after five consecutive reaction cycles, showing remarkable reusability and stability of catalyst.

Progress in the Preparation and Modification of Zinc Ferrites Used for the Photocatalytic Degradation of Organic Pollutants

Zinc ferrite is a type of photocatalytic material with high physicochemical stability, narrow band gap, high carrier separation efficiency, high porosity, and paramagnetism, which makes it easy to recover. Thus, zinc ferrite is widely used as a photocatalyst in water treatment. In this paper, the preparation principles as well as the advantages and disadvantages of typical methods used to prepare zinc ferrite including hydrothermal, co-precipitation, sol-gel, and other novel methods such as biosynthesis have been summarized. Modification methods such as elemental doping, composite formation, and morphological modification have been highlighted. Using these modification methods, the catalytic activity of zinc ferrite toward the photocatalytic degradation of organic pollutants in water has been enhanced. Biosynthesis is regarded as a promising preparation method that uses biological materials instead of chemical materials to achieve the large-scale preparation of zinc ferrite using low cost, energy efficient, and environmentally friendly processes. Meanwhile, the combination of multiple modification techniques to enhance the photocatalytic performance of zinc ferrite will be an important research trend in the future.

Hollow CuFe2O4/MgFe2O4 Heterojunction Boost Photocatalytic Oxidation Activity for Organic Pollutants

P-n heterojunction-structured CuFe2O4/MgFe2O4 hollow spheres with a diameter of 250 nm were synthesized using a template-free solvothermal method, and time-dependent morphological studies were carried out to investigate the hollow formation mechanism. The CuFe2O4/MgFe2O4 with a molar ratio of 1:2 (Cu:Mg) had the highest degradation efficiency with the model organic dye Acid Orange 7, with a degradation rate of 91.96% over 60 min. The synthesized CuFe2O4/MgFe2O4 nanocomposites were characterized by XRD, TEM, HRTEM, UV-vis spectroscopy, Mott–Schottky, and EIS. Due to the synthesis of the p-n heterojunction, CuFe2O4/MgFe2O4 has efficient photogenerated carriers, and the hollow structure has a higher specific surface area and stronger adsorption capacity, which is significantly better than that of CuFe2O4 and MgFe2O4 in terms of photocatalytic performance. The outstanding performance shows that the p-n heterostructure of CuFe2O4/MgFe2O4 has potential for application in wastewater degradation.

Effect of cation configuration and solvation on the band positions of zinc ferrite (100)

Zinc ferrite ZnFe[Formula: see text]O[Formula: see text] belongs to the spinel-type ferrites that have been proposed as photocatalysts for water splitting. The electronic band gap and the band edge positions are of utmost importance for the efficiency of the photocatalytic processes. We, therefore, calculated the absolute band energies of the most stable surface of ZnFe[Formula: see text]O[Formula: see text], the Zn-terminated (100) surface at self-consistent hybrid density functional theory level. The effect of Fe- and Zn-rich environments, cation exchange as antisite defects and implicit solvation on the band positions is investigated. Calculated flat band potentials of the pristine surface model ranges from [Formula: see text] to [Formula: see text] V against SHE in vacuum. For Zn-rich (Fe-rich) models this changes 0.3-0.9 (0.0-0.7) V against SHE. Fe-rich models are closest to the experimental range of reported flat band potentials. Solvent effects lower the calculated flat band potentials by up to 1.8 eV. The calculated band gaps range from 1.5 to 2.9 eV in agreement with previous theoretical work and experiment. Overall, our calculations confirm the experimentally observed low activity of ZnFe[Formula: see text]O[Formula: see text] and its dependence on preparation conditions.

Highly efficient visible light driven photocatalytic activity of zinc/ferrite: Carbamazepine degradation, mechanism and toxicity assessment

In this present study, spherical shaped zinc ferrite (Zn/Fe₂O₄) was prepared as uniformly sized (65 ± 0.5 nm) nanoparticles with band gap (2.00 eV) in a visible light regime and employed for the photocatalytic degradation of carbamazepine (CBZ). The doping of Zn decreased the band gap (from 2.00 to 1.98 eV) and enhanced the absorption of visible light. Zinc doping also induced effective separation of photogenerated carriers and subsequent charge migration to the surface of the Zn/Fe₂O₄ nanoparticle. On account of the advantages of the material, a high removal efficiency (~ 100%) of CBZ through photocatalytic degradation was achieved. Kinetics of CBZ degradation follows a pseudo first-order with the rate constant 0.0367 min^-1. In-vitro and in-vivo toxicity of the nanoparticles were examined promoting the environmental implications.

Exploring the influence of varying pH on structural, electro-optical, magnetic and photo-Fenton properties of mesoporous ZnFe2O4 nanocrystals

An economically viable and superficial technique was indorsed to yield ZnFe₂O₄ nanocrystals in the system to investigate the impact of pH variation on the optical, structural, electrical, and magnetic properties of as-prepared nanocrystals. The as-synthesized ZnFe₂O₄ nanocrystals were premeditated with the application protracted to degradation of Methylene blue organic dye. The results specify that the pH plays the utmost decisive facet in photo-Fenton recital. From XRD (X-Ray diffraction) analyses, it was confirmed that as-synthesized nanocrystals belong to a cubic Fd3m crystal phase. The crystallite size was also determined by the Scherrer formula and it was noticed that as the pH rises the crystallite size also increased. FT-IR (Fourier Transform Infrared) analysis depicts two absorption peaks ∼ 500 and ∼600 cm^-1 that represents tetrahedral (Td) and octahedral (Oh) sites. Using TEM (Transmission Electron Microscopy), the morphology was observed to be spherical particles with some agglomeration. Photoluminescence and UV-visible spectral studies were performed to investigate the optical properties. The bandgap energy was seen to decrease as the pH increased. Using BET analysis, the surface area for the as-synthesized samples was found to decrease on increasing the pH. The reaction results showed that the ZnFe₂O₄ has good photocatalytic activity, which can be attributed to high surface area and pore volume, and large pore size. The ZnFe₂O₄ produced by the co-precipitation route exhibited promising photocatalytic activity for the removal of textile dye, reaching nearly 99.2% of decolorization at 100 min. Therefore, ZnFe₂O₄ particles rapidly prepared by the co-precipitation route have the potential for use in treatment of textile wastewater by the heterogeneous photo-Fenton process. With the help of VSM analysis, the coercivity and other magnetic properties were determined for the as-synthesized nanocrystal with plays a significant role in photocatalytic recyclability, which intends to premediate that the prepared nanocrystals can be used in industrial persistence.

Highly effective removal of antibiotics from aqueous solution by magnetic ZnFe2O4/activated carbon composite

Water pollution from antibiotics has attracted a lot of attention for its serious threat to human health. In this study, a magnetic adsorbent (zinc ferrite/activated carbon (ZnFe₂O₄/AC) was synthesized via microwave method to effectively remove gemifioxacin mesylate (GEM) and moxifloxacin hydrochloride (MOX). Based on the porosity of AC and the magnetism of ZnFe₂O₄, the resulting ZnFe₂O₄/AC has high adsorption capacities and can be easily separated from the solid-liquid system via a magnetic field. The largest adsorption capacities for GEM and MOX can reach up to 433.4 mg g^-1 and 388.8 mg g^-1, respectively, higher than those of reported adsorbents such as MIL-101 and MOF-808. Fastest adsorptions of GEM and MOX were found at 5 min, and solution pH and coexisting salts do not have a significant influence on the adsorption process. The adsorption mechanism analysis indicates that electrostatic interaction and H-bond interaction contribute to the effective adsorption.

Green synthesis of zinc ferrite nanoparticles for photocatalysis of methylene blue

In this study, zinc ferrite nanoparticles (ZF-NPs) were synthesized using aqueous seed extract of Piper nigrum as a bio-reducing and stabilizing agent. FTIR, SEM, FE-SEM, XRD, and TGA have been used for characterizing ZF-NPs. The results showed that Piper nigrum stabilized ZF-NPs have high purity and size range of 60-80 nm. The performance of the ZF-NPs has been investigated by photocatalytic reduction of methylene blue (MB) in the presence of sunlight. The factors responsible for affecting the degradation values of the reaction were also explored for developing a better understanding of the phenomenon.

Photoelectrochemistry of Ferrites: Theoretical Predictions vs. Experimental Results

This paper gives an overview about recent theoretical and experimental work on electronic and optical properties of spinel ferrites MFe2O4. These compounds have come into focus of research due to their possible application as photocatalyst material for photoelectrochemical water splitting. The theoretical background of state-of-the-art quantum-chemical approaches applied for predicting electronic and optical band gaps, absolute band positions, optical absorption spectra, dielectric functions and Raman spectra, is briefly reviewed. Recent applications of first-principles methods on magnetic and electronic properties of ferrites with M = Mg and the first row of subgroup elements Sc to Zn are presented, where it is shown that the fundamental band gap is strongly dependent on the spin state and the degree of inversion of the spinel structure. The observed variation of electronic properties may serve as an explanation for the large scattering of experimental results. The exchange of M and Fe cations has also a pronounced effect on the Raman spectra of ferrites, which is analyzed at atomic scale from first principles. Calculated optical absorption spectra of ferrites are compared to experimental spectra. The electronic nature of the first excitations and the role of oxygen vacancies are discussed. For the calculation of absolute band positions, which have a significant impact on the photoelectrochemical activity of the ferrites, models of the most stable ferrite surfaces are developed that take into account their polar nature and the interaction with the solvent. Theoretically predicted valence and conduction band edges are compared to results from electrochemical measurements. The role of cation exchange on the surface electronic structure is investigated both theoretically and experimentally.

Magnesium Ferrite (MgFe2O4) Nanoparticles for Photocatalytic Antibiotics Degradation

Removal of drug residuals in waste water by easy-separable catalysts is of fundamental interest for clean water provision by photocatalytic water remediation. Here, we present our studies to use the ferrimagnetic earth-abundant absorber MgFe2O4, prepared by microwave-assisted synthesis, for the photocatalytic removal of methylene blue and tetracycline from model solutions under dark and sunlight conditions. The surface of MgFe2O4 has a strong influence on the tetracycline removal, while more than 75% tetracycline degradation can already be achieved in 2 h with unmodified MgFe2O4. Using surface-modified MgFe2O4 nanoparticles, the adsorption of tetracycline is even more pronounced, however goes in line with release of the surface capping agent.

Regarding the Nature of Charge Carriers Formed by UV or Visible Light Excitation of Carbon-Modified Titanium Dioxide

Although titanium dioxide gathers many of the required properties for its application in photocatalytic processes, its lack of activity in the visible range is a major hurdle yet to be overcome. Among different strategies, the post-synthesis modification of TiO2 powders with organic compounds has already led to commercially available materials, such as KRONOClean 7000. In this work, we apply diffuse reflectance transient absorption spectroscopy on this visible-light active photocatalyst and study the dynamics of the charge carriers alternatively induced by UV or visible light laser irradiation, under inert or reactive atmospheres. Our results can be interpreted by considering the material as TiO2 sensitized by an organic-based layer, in agreement with previous studies on it, and show that the oxidative power of the material is considerably diminished under visible light irradiation. By complementarily performing continuous visible light irradiation photocatalysis experiments in aerated aqueous suspensions, we show that, although the oxidation of methanol proceeds at a very slow rate, the oxidation of chlorpromazine occurs much faster thanks to its better suited redox potential.

Light-Induced Reactions of Chlorpromazine in the Presence of a Heterogeneous Photocatalyst: Formation of a Long-Lasting Sulfoxide

A commercial carbon-modified titanium dioxide, KRONOClean 7000, was applied as a UV(A) and visible-light active photocatalyst to investigate the conversion of the antipsychotic pharmaceutical chlorpromazine in aqueous phase employing two monochromatic light sources emitting at wavelengths of 365 and 455 nm. Photocatalytic and photolytic conversion of chlorpromazine under both anaerobic and aerobic conditions was analyzed using a HPLC-MS technique. Depending on the irradiation wavelength and presence of oxygen, varying conversion rates and intermediates revealing different reaction pathways were observed. Upon visible light irradiation under aerobic conditions, chlorpromazine was only converted in the presence of the photocatalyst. No photocatalytic conversion of this compound under anaerobic conditions upon visible light irradiation was observed. Upon UV(A) irradiation, chlorpromazine was successfully converted into its metabolites in both presence and absence of the photocatalyst. Most importantly, chlorpromazine sulfoxide, a very persistent metabolite of chlorpromazine, was produced throughout the photolytic and photocatalytic conversions of chlorpromazine under aerobic conditions. Chlorpromazine sulfoxide was found to be highly stable under visible light irradiation even in the presence of the photocatalyst. Heterogeneous photocatalysis under UV(A) irradiation resulted in a slow decrease of the sulfoxide concentration, however, the required irradiation time for its complete removal was found to be much longer compared to the removal of chlorpromazine at the same initial concentration.

Dual phototransformation of the pollutants methyl orange and Cr (VI) using phthalocyanine-cobalt ferrite based magnetic nanocomposites

Bifunctional nanocomposites based on zinc phthalocyanines and glutathione capped CoFe2O4 magnetic nanoparticles (GSH-CoFe2O4 MNPs) are applied in a binary system wherein simultaneous photooxidation of methyl orange (MO) and photoreduction of Cr (VI) are conducted. The photoactivity of two zinc Pcs with different functional moieties are compared based on their interactions with GSH-CoFe2O4 MNPs. Conjugation of the Pcs to the GSH-CoFe2O4 MNPs not only enhanced their singlet oxygen production but also their photocatalytic activity in both photooxidation and photoreduction experiments. Using electron paramagnetic resonance (EPR) spectroscopy, the Pc-MNP conjugates reported herein were found to exhibit superparamagnetic behaviour, giving the advantage of easy separation using an external magnetic field post application, an attractive attribute for heterogeneous catalysis. The catalysts reported herein are therefore good candidates as catalysts for real life water purification analyses as they facilitate the treatment of both organic and inorganic water pollutants.

Photocatalytic treatment of palm oil mill effluent by visible light-active calcium ferrite: Effects of catalyst preparation technique

Palm oil mill effluent (POME) is a serious and expensive environmental problem in Malaysia. In this paper, CaFe₂O₄ is introduced as a novel photocatalyst for the degradation of POME under visible light irradiation. Two synthesis routes, auto-combustion and co-precipitation, and two calcination temperatures 550 °C and 700 °C were used to produce four CaFe₂O₄ catalysts AC550, AC700, CP550 and CP700. CP550 exhibited the greatest photocatalytic degradation at 56% chemical-oxygen-demand (COD) removal after 8 h of irradiation which dropped to 49% after three consecutive cycles indicating reasonable conversion and high recyclability. BET analysis indicated CP550 had the highest S_BET (27.28 m²/g) and pore volume (0.077 cm³/g) which dropped precipitously for CP700 upon increasing the calcination temperature to an S_BET of 9.73 m²/g and pore volume of 0.025 cm³/g due to annealing which created a smoother surface area as evidenced by the SEM images. UV-Vis DRS indicated CP550 had the highest band-gap (1.52 eV) which is likely due to the presence of a highly crystalline pure CaFe₂O₄ phase compared to the other products which existed as a mixture of Fe oxidation states evidenced by the XRD data. The PL spectra for all catalysts indicated significantly lower recombination rate for both CP550 and CP700. Introduction of IPA into the reaction mixture to eliminate hydroxyl radicals resulted in a diminishing of COD removal from 56% to 7% proving hydroxyl radicals to be the primary reactive species responsible for photodegradation of POME.

Ag/Ag2O as a Co-Catalyst in TiO2 Photocatalysis: Effect of the Co-Catalyst/Photocatalyst Mass Ratio

Mixtures and composites of Ag/Ag2O and TiO2 (P25) with varying mass ratios of Ag/Ag2O were prepared, employing two methods. Mechanical mixtures (TM) were obtained by the sonication of a suspension containing TiO2 and Ag/Ag2O. Composites (TC) were prepared by a precipitation method employing TiO2 and AgNO3. Powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) confirmed the presence of Ag(0) and Ag2O. The activity of the materials was determined employing methylene blue (MB) as the probe compound. Bleaching of MB was observed in the presence of all materials. The bleaching rate was found to increase with increasing amounts of TiO2 under UV/vis light. In contrast, the MB bleaching rate decreased with increasing TiO2 content upon visible light illumination. XRD and XPS data indicate that Ag2O acts as an electron acceptor in the light-induced reaction of MB and is transformed by reduction of Ag+, yielding Ag(0). As a second light-induced reaction, the evolution of molecular hydrogen from aqueous methanol was investigated. Significant H2 evolution rates were only determined in the presence of materials containing more than 50 mass% of TiO2. The experimental results suggest that Ag/Ag2O is not stable under the experimental conditions. Therefore, to address Ag/Ag2O as a (photo)catalytically active material does not seem appropriate.

Effect of the degree of inversion on optical properties of spinel ZnFe2O4

The effect of the degree of inversion on the electronic transitions and the Raman scattering of ZnFe₂O₄ is revealed.