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Although extensive work has already been done on bulk La1−xSr1+xCoO4 layered oxides, there is very limited studies on their nano-crystalline nature, particularly for those with a higher Sr level (x ≥ 0.4), which may exhibit interesting magnetic properties and in particular photocatalytic properties because of their enhanced surface area. Moreover, the phases with higher Sr doping levels can be formed only at higher temperatures, which otherwise contain significant amounts of impurities. In order to synthesize them in a nanocrystalline form in the pure state at the lowest possible temperature, we applied a glycine nitrate combustion method using excess fuels for the synthesis of nanocrystalline La1−xSr1+xCoO4 (x = 0.0, 0.2, 0.4 and 0.6) layered perovskite oxides. Efforts were also made to synthesize phases with x > 0.6 but remained unsuccessful. The prepared nanophases were thoroughly characterized using PXRD, XPS, SEM, SQUID VSM and UV-DRS to examine the structural, morphological, optical, magnetic and photocatalytic properties. All the phases exhibit mixed valence states of +3 and +4 of Co, as confirmed by XPS analysis, which has a remarkable effect on various physical properties, especially magnetic and photocatalytic properties. An abrupt transition in magnetic behaviour from antiferromagnetic for x = 0 and 0.2 phases to ferromagnetic in case of x = 0.4 and 0.6 was observed. The optical band gap values (Eg) of all the synthesized nanophases obtained from DRS are in the visible range (1.57 to 1.47 eV), which make them suitable and reliable photocatalysts for dye degradation. Moreover, the synthesized nanophases were assessed for their photocatalytic activity by employing rhodamine B (RhB) dye as a model contaminant. The results revealed that the La0.4Sr1.6CoO4 photocatalyst efficiently and swiftly degraded RhB within 60 min. Considering the performance of the La0.4Sr1.6CoO4 photocatalyst, the study was expanded to include the degradation of other organic dye pollutants, namely, methyl orange (MO), methylene blue (MB) and a ternary combination of these contaminants (RhB + MB + MO). [ABSTRACT FROM AUTHOR]

A lot of work has already been reported on bulk K 2 NiF 4 -type layered perovskite oxides but hardly is known about their nano-crystalline state as they are generally prepared at high temperatures. In this connection, we have synthesized nanocrystalline La 1+ x Sr 1- x CoO 4 layered perovskites oxides via sol-gel Pechini method. Efforts were also done to synthesize phases with x > 0.5 but remained unsuccessful. The Rietveld refinement investigation has confirmed the successful formation of single-phase compounds that crystallize in the I 4/ mmm space group with tetragonal symmetry. The X-ray photoelectron spectroscopy (XPS) analysis revealed that Co in La 1+ x Sr 1- x CoO 4 has mixed valence states of +2 and + 3. Dominant anti-ferromagnetic (AFM) super-exchange Co2+―O―Co2+ and Co3+―O―Co3+ interactions were observed in all the synthesized nanophases and the existence of weak ferromagnetic (FM) interactions due to the generation of double-exchange Co2+―O―Co3+ interaction because of mixed valent state of Co. The increase in Néel temperature (T N) values with La doping has been attributed by the increased prevalence of anti-ferromagnetic (AFM) super-exchange Co2+―O―Co2+ and Co3+―O―Co3+ interactions. The band gap energy values (E g) for all the prepared nano samples vary from 1.57 to 1.64 eV, rendering them highly competent catalysts for degradation of dyes. Additionally, the photocatalytic performance of the prepared nano photocatalysts was evaluated using cationic (MB & RhB) and anionic (MO) dye contaminants as well as their ternary mixture. LaSrCoO 4 photocatalyst has been found to efficiently and swiftly degrade all three dye pollutants separately as well as in mixtures, with outstanding recyclability and durability. It has been observed that the x = 0.0 photocatalyst showed best degradation efficacy for RhB dye, i.e., ∼99 % in 100 min, compared to ∼91 % and ∼84 % for the x = 0.2 and 0.5 photocatalysts in the same time interval, respectively. These results suggest that LaSrCoO 4 nano powder can be considered a promising photocatalyst in the dyes degradation. [ABSTRACT FROM AUTHOR]

The Ruddlesden–Popper (RP) oxides in a high grade of purity are generally prepared at high temperature and that is why there are few reports on their nanocrystalline state. These oxides may show good photocatalytic activity in nanocrystalline form because of higher surface area and better morphology. In this context, we are reporting rare earth doped nanocrystalline RP phases LnSrFe0.5Co0.5O4 (Ln = La, Nd, Sm, Gd), which are highly efficient in removing hazardous organic dye pollutants from wastewater both in unitary and ternary solutions. The impact of rare earth ion doping on the structural, magnetic, and optical characteristics of LnSrFe0.5Co0.5O4 has also been comprehensively investigated via different characterization methods. The Rietveld refinement analysis confirmed the formation of single-phase samples having tetragonal symmetry that crystallised in the I4/mmm space group. The refinement results revealed that with heavier rare earth ion doping, there was a continuous decrease in the value of the unit cell parameters and the cell volume. Dominant anti-ferromagnetic (AFM) interactions were seen in each of these compounds, along with the presence of weak ferromagnetic (FM) interactions due to the co-existence of the super-exchange (Co3+–O–Fe3+) FM and (Co3+–O–Co3+, Fe3+–O–Fe3+) AFM interactions. The band gap values of all these nanophases lie in the range of 1.53–1.62 eV, making them suitable photocatalysts for dye degradation. The photocatalytic activity of the synthesised nanophases was assessed using cationic (methylene blue and rhodamine B) and anionic (methyl orange) pollutants as well as their mixture. It has been observed that the Nd-doped catalyst showed better deterioration efficacy for rhodamine B dye, i.e., 99% in 40 min, followed by 84%, 87%, and 85% for the La, Sm, and Gd phases in the same time period, respectively. The results of photocatalytic activity have been interpreted on the basis of bandgap energy values and photoluminescence (PL) intensity. [ABSTRACT FROM AUTHOR]

This work presents a systematic study of half doped nanocrystalline La 0.5 A 0.5 Mn 0.5 Fe 0.5 O 3 (A = Ca, Sr) perovskite oxides to examine the effect of A-site cation radius on structural, magnetic and catalytic properties via different characterization techniques. Rietveld refinements of powder X-ray diffraction data confirmed the orthorhombic symmetry for both the samples with Pbnm space group. The results show an increase in lattice parameters and unit cell volume with doping of larger A cation. The BET surface area for Ca and Sr-doped samples has been found to be 32.3 m2/g and 33.8 m2/g respectively. The magnetic properties of nano structured samples show magnetic inhomogeneity due to coexistence of ferromagnetic and antiferromagnetic interactions. The magnetization has enhanced in Sr-doped sample which may be associated with increase in double exchange interactions between mixed valence manganese ions through oxygen. Moreover, the synthesized nano samples have been employed to catalytic degradation of rhodamine B dye as model pollutant under normal atmospheric conditions and it has been found that Sr-doped sample has shown better catalytic dye degradation than Ca-doped (99% degradation in 25 min) due to the presence of greater number of Mn3+/Mn4+ redox couples as determined by iodometric titration. Additionally, methylene blue and methyl orange dyes were also tested for catalytic degradation by more active Sr-doped catalyst in order to check its versability. • La 0.5 A 0.5 Mn 0.5 Fe 0.5 O 3 (A = Ca, Sr) were prepared by sol-gel method. • Both samples showed magnetic inhomogeneity due to coexistence of ferromagnetic and antiferromagnetic interactions. • Sr-doped sample showed enhanced magnetization and an excellent photocatalytic catalytic activity for dye degradation. • The photocatalytic degradation followed first-order kinetic model. [ABSTRACT FROM AUTHOR]

Wastewater treatment is a major issue that must be addressed since it damages nature and has a negative impact on living creatures. Dyes are the top most organic pollutants in wastewater that poses serious dangers to human health and the environment today. Therefore, the aim of this study is to eliminate these colored effluents, which are present in substantial amounts in wastewater, either singly or in mixtures. In this contest, we are reporting the synthesis of nano photocatalysts La 1- x Na x FeO 3 (x = 0.0, 0.1, 0.2 and 0.3) via sol-gel process and their corresponding Cu composite analogues by a simple chemical reduction method for the removal of dyes in aqueous solution. The prepared photocatalysts were thoroughly characterised using PXRD, BET, SEM, UV-DRS and VSM to investigate the structural, morphological, optical and magnetic properties. All the magnetic parameters (M S , M R & H C) increase with Na doping in both bare and nanocomposites. The photocatalytic activity of La 1- x Na x FeO 3 nano catalysts and their Cu composites was assessed through the photodegradation of rhodamine B (RhB) dye in aqueous solution under visible light. The outcomes exhibited that Cu nano composites showed excellent photocatalytic activity compared to the pristine materials due to their low band gap energies (1.61 eV). Moreover, the most active photocatalyst LaFeO 3 @Cu showed excellent stability after five runs, which demonstrated good stability and reusability. Because of exciting photocatalytic results, the study was further extended to the degradation of a few other organic dye contaminants such methylene blue (MB), methyl orange (MO) and their mixture using LaFeO 3 @Cu catalyst. • Synthesis of La 1- x Na x FeO 3 nano photocatalysts and their corresponding Cu composite analogues. • The magnetic parameters (M S , M R , H C) increase with Na doping in both bare and nanocomposites. • Cu nano composites showed excellent photocatalytic activity compared to the pristine materials. • The photocatalytic degradation followed pseudo-first-order kinetic model. [ABSTRACT FROM AUTHOR]

This paper presents the magnetic, transport, and photo-catalytic properties of a new Sr 4 Ti 3 O 10 -type oxygen deficient Ruddlesden-Popper oxide LaSr 3 Mn 1.5 Fe 1.5 O 9.71. The Rietveld refinement analysis of the PXRD data confirms the formation of the compound which crystallizes in tetragonal symmetry and adopts space group I4/mmm , tI34. The phase is found to be oxygen deficient as determined from the results of iodometric titrations. The energy band gap (E g) obtained from the DRS study shows that the phase is semiconducting in nature at room temperature. The magnetic studies revealed that the oxygen deficient phase exhibits dominant anti-ferromagnetic (AFM) ordering with Néel temperature, T N ​= ​71 ​K owing to Fe3+―O―Fe3+, Mn4+―O―Mn4+ super-exchange interactions. The divergence between the zero field cooled (ZFC) and field cooled (FC) molar magnetic susceptibility curves at low temperatures implies that the phase shows a spin-glass transition. The temperature-dependent resistivity measurements indicate that the material exhibits insulating behavior with decreasing temperature. The conduction mechanism is discussed by fitting the resistivity data in different transport mechanism models. It has been found that the conduction mechanism is dominated by Mott's variable range hopping model. The photo-oxidative degradation of different dye pollutants using LaSr 3 Mn 1.5 Fe 1.5 O 9.71 as a photocatalyst was carried out under visible irradiation. The results indicate that Methylene Blue (MB) shows 99.1% degradation in 45 ​min while Rhodamine B (RhB) and Methyl Orange (MO) dyes show 99.3% and 98.6% degradation respectively in 20 ​min. LaSr 3 Mn 1.5 Fe 1.5 O 10 photocatalyst showing an excellent activity for degradation of methylene blue, rhodamine B, and methyl orange dyes. [Display omitted] • Synthesis of a new oxygen deficient RP oxide LaSr 3 Mn 1.5 Fe 1.5 O 9.71 • Dominant AFM behavior owing to Fe3+―O―Fe3+, Mn4+―O―Mn4+ super-exchange interactions. • Conduction mechanism dominated by Mott's variable range hopping model. • An efficient photocatalyst for the degradation of dyes. [ABSTRACT FROM AUTHOR]

Wastewater remediation is a major issue that threatens the ecosystem and health of human population and hence deserves our undivided attention. Dye effluents, in particular those comprising organic colourants from a number of industrial sites, are a major source of wastewater pollution that poses serious dangers to human health and the environment today. Therefore, the goal of this study is to eliminate these coloured effluents, which are present in substantial amounts in wastewater, either singly or in mixtures. In this respect, we present an easy sol-gel synthesis of CoFe 2- x Cr x O 4 (x = 0, 0.2, 0.4, 0.6, 0.8, and 1) nano-ferrites for use as efficient photocatalysts. P-XRD technique was used for the confirmation of cubic spinel nanostructures having crystallite sizes in the nano-regime. Also, the optical band gap values resulted from Tauc plot indicates that incorporation of Cr3+ significantly reduces the band gap values. All the Co–Cr nano photocatalysts can be easily separable using an external magnet as indicated by the magnetic studies. For exploring the photocatalytic activity by photo-fenton process, we chose Rhodamine-B (RhB) as a model dye pollutant. Surprisingly, Cr3+ substitution into cobalt ferrite resulted in a dramatic transformation of the inert CoFe 2 O 4 into a highly visible light active photocatalyst for organic pollutant degradation. The CoFeCrO 4 nanocatalyst showed excellent results for the removal of RhB i.e., 99% removal in 30 min as compared to the CoFe 2 O 4 which was found to be inactive for the degradation. As a result of these exciting photocatalytic results, we were further encouraged to extend the degradation of a few other organic dye contaminants such methylene blue (MB), methyl orange (MO) and the mixture all three dyes (RhB + MB + MO). It was found that CoFeCrO 4 photocatalyst efficiently and swiftly degrades all three dye contaminants individually or in mixture with excellent recyclability and durability. [ABSTRACT FROM AUTHOR]

A new n = 2 Ruddlesden-Popper (RP) series La 2 SrFe 2- x Cr x O 7 (x = 0.0, 0.2, 0.4, 0.6 and 0.8) has been prepared via Sol-gel Pechini method, and their structural, optical, and the magnetic characterization was done. Furthermore, we are for the first-time reporting on the photo-catalytic degradation of a dye by a complete n = 2, La 2 SrFe 2- x Cr x O 7 RP series. Rietveld refinement analysis confirms the formation of single-phase compounds with tetragonal crystal symmetry and I 4/ mmm space group. The results indicate a steady decrease in unit cell parameters and cell volume with Cr3+ doping. Dominant anti-ferromagnetic (AFM) interactions were observed in all the phases and the appearance of weak ferromagnetic (FM) interactions takes place owing to the Fe3+―O―Cr3+ FM interaction with Cr3+ doping. The χ M − F C curve for x = 0.8 phase shows the magnetization reversal (MR) phenomenon and becomes zero at T comp ∼127 K and the value becomes negative on further decreasing the temperature. The MR phenomenon is discussed in terms of the competing Fe3+―O―Fe3+, Fe3+―O―Cr3+, and Cr3+―O―Cr3+ super-exchange interactions. Enhanced photocatalytic activity for the degradation of Rhodamine B (RhB) dye was obtained for x = 0.2 substituted phase, displaying a ∼99% degradation of dye in 30 min followed by ∼83%, ∼75%, ∼64% and ∼61% by x = 0.4, 0.0, 0.8 and 0.6 phases respectively in the same time interval. The results are explained in terms of crystallite size, the narrowing of band gap with Cr3+ substitution, and based on of recombination of charge carriers which, are in good agreement with the results of Photoluminescence (PL) emission intensity spectra. [ABSTRACT FROM AUTHOR]

The present investigation examined the impact of Bi3+ doping on the structural, optical, and magnetic properties of Ni–Cu–Cr ferrites. Moreover, for the first time, Bi3+ ions were substituted for the less magnetic Cr3+ ions, rather than the more magnetic Fe3+ ions at B site, resulting in the formation of Ni 0.5 Cu 0.5 FeCr 1- x Bi x O 4 quinary ferrites. Monophasic polycrystalline specimens of Bi3+-doped Ni–Cu–Cr ferrites were synthesized through a straightforward Sol-Gel technique and their crystal structure was established by Rietveld refinements. Utilizing the Kubelka-Munk function, the optical band gap of all the ferrites was estimated from Diffuse Reflectance Spectroscopy (DRS), which was found to increase with the incorporation of Bi3+ ions in the ferrite lattice. Magnetic behaviour was investigated using SQUID-VSM, revealing that the magnetization saturation decreases as the level of Bi3+ substitution increases. Furthermore, magnetization measurements conducted at higher temperatures ranging from 300 K to 900 K unveiled the distinctive ferromagnetic nature, with a transition from ferromagnetism to paramagnetism occurring at the curie temperature, T c. Interestingly, despite being a diamagnetic cation, Bi3+ unexpectedly amplifies the value of T c attributed to the strengthening of A–B exchange interactions. Because of their semiconducting nature and ferromagnetic behaviour, these phases might be useful in magneto-optical and memory devices, magnetic storage media and magnetic sensors. [Display omitted] • Bi3+ doped Ni 0.5 Cu 0.5 FeCr 1- x Bi x O 4 bulk ferrites synthesized by sol-gel method. • Both crystallite size and optical band gap increased with Bi3+ doping. • The phases show FM to PM transition at T c which increases with Bi3+ doping. [ABSTRACT FROM AUTHOR]

In the present study, new oxygen deficient triple layered Ruddlesden-Popper (RP) phases LaSr 3 Fe 3- x Cr x O 10-δ (x = 0.0, 0.2, and 0.5) have been prepared via sol-gel procedure. The prepared n = 3 RP phases were characterized with various characterization techniques in order to visualize the effect of Cr3+ doping on structural, optical, magnetic and photocatalytic properties. Rietveld structural refinements showed that all the phases crystallized in the I4/mmm space group with tetragonal symmetry. Dominant anti-ferromagnetic (AFM) interactions (Fe3+―O―Fe3+ and Fe4+―O―Fe4+) were noticed in each of these oxygen deficient triple layered phases with presence of weak ferromagnetic (FM) interactions. The decline in the values of Neel temperature (T N) with Cr doping has been interpreted on the basis of increase in FM Fe3+―O―Cr3+ interactions. The energy band gap values (E g) of all the synthesised oxygen deficient phases vary from 1.63 to 1.73 eV, which makes them excellent photocatalysts for dye decontamination. Furthermore, the photocatalytic performance of the prepared phases was assessed by utilizing rhodamine B (RhB) dye as model dye pollutant. It was found that LaSr 3 Fe 2.5 Cr 0.5 O 9.17 photocatalyst showed excellent results in the removal of RhB dye. As a result, we were further encouraged to extend the degradation to some other organic dyes such as methylene blue (MB), methyl orange (MO) and their mixture (RhB + MB + MO). Time dependent UV–vis absorbance spectra for the photo-oxidative degradation of RhB dye by LaSr 3 Fe 3- x Cr x O 10-δ catalyst. [Display omitted] • Synthesis of new oxygen deficient triple layered RP phases LaSr 3 Fe 3- x Cr x O 10-δ. • Dominant AFM interactions were noticed all phases along with weak FM interactions. • The decline T N with Cr doping has been interpreted on the basis of increase in FM Fe3+―O―Cr3+ interactions. • E g values vary from 1.63 to 1.73 eV making them excellent photocatalysts. [ABSTRACT FROM AUTHOR]