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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]

Due to their carcinogenic, mutagenic and poisonous nature, industrial wastes such as metals, dyes, polycyclic aromatic hydrocarbons, surfactants and pharmaceutical waste have become a major worldwide issue for human health. In this context, we are reporting the synthesis, characterization and application of copper-immobilized nanocomposites NiAlFeO4@Cu for catalytic reduction of hazardous and carcinogenic nitrophenols and photocatalytic degradation of different dyes (rhodamine B (RhB), methyl orange (MO) and methylene blue (MB)), individually as well as their mixture under visible light irradiation. Magnetically separable mesoporous composites of NiAlFeO4 and copper nanoparticles in the molar ratios of 2 : 1 (NAFO2@Cu), 5 : 1 (NAFO5@Cu) and 10 : 1 (NAFO10@Cu) were prepared through a simple reduction method with pure water as the solvent. The structural, morphological and physicochemical features of the prepared nanocatalysts were examined using PXRD, FE-SEM, PL, DRS, VSM and BET. The nanocomposites were found to be very porous and spherical with an average crystallite size between 4 and 8 nm. Magnetic measurements were carried out using a vibrating sample magnetometer, which reveal the ferromagnetic nature of our samples, making them magnetically separable. A UV/Vis study was used to analyse the reduction of nitrophenols by employing sodium borohydride as a reducing agent. Furthermore, the band gap energy values of the nanocomposites were found to be in the visible range (1.63–1.66 eV) making them suitable for photocatalysis. Rhodamine B was used as a model dye pollutant for estimation of the photocatalytic deterioration of the synthesized nanocatalysts. Among all the prepared nanocomposites, NAFO2@Cu exhibited the highest catalytic efficiency for the reduction of nitrophenols, while the maximum degradation efficiency was shown by NAFO10@Cu for the photodegradation of different dyes individually as well as in their ternary solution. [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]

A systematic investigation of structural, magnetic and transport properties of NiCr1.9R0.1O4 (R = Eu, Dy and Ho) has been undertaken. Rietveld analysis of powder X-ray diffraction data revealed that all the compounds crystallize in the cubic symmetry with Fd m _ 3 space group having small volume fraction of orthorhombic phase RCrO3. Both lattice parameter and cell volume decreases with the substitution of heavier rare earth ion which is consistent with the decrease in ionic radius of rare earth ion. The temperature dependent magnetization studies have shown that all our investigated compounds have negative value of Weiss constant. It indicates the dominance of anti-ferromagnetic interactions in the samples. The phases are semi-conductors and the conduction mechanism is dominated by Arrhenius model in the high temperature paramagnetic semiconducting region. [ABSTRACT FROM AUTHOR]

This work presents the study of new Ruddlesden-Popper phases, LaSrFe 1- x Cr x O 4 (x = 0.0, 0.2, 0.4 and 0.6), synthesized by glycine-nitrate combustion method. In this research, we are for the first time reporting on a complete Ruddlesden-Popper series (n = 1) for the photocatalytic degradation of a dye. The effect of Cr3+ doping on the crystal structure, optical and magnetic properties of the LaSrFeO 4 phase has also been systematically explored via different characterization techniques. Rietveld refinement of PXRD data indicates the formation of single phase compounds with tetragonal symmetry in the space group I 4/ mmm. The results show a decrease in the lattice parameters a and c , as well as the unit cell volume V , with increase in Cr3+ doping. The energy band gap (E g) values calculated using the DRS spectra decreases with increase in Cr concentration. The magnetic measurements revealed dominant anti-ferromagnetic (AFM) interactions in all the phases and the appearance of weak ferromagnetic (FM) interactions with Cr3+ doping. The results are discussed by considering the increase in Fe3+─O─Cr3+ FM interaction in addition to the Fe3+─O─Fe3+ and Cr3+─O─Cr3+ AFM super-exchange interactions induced due to random distribution of Fe3+ and Cr3+ ions at the octahedral site. Rhodamine B, as a dye pollutant model, was used for evaluation of photocatalytic activity of the prepared phases. Enhanced photocatalytic activity was observed with the addition of Cr3+ substitution. The results show ~99 % degradation for x = 0.6 while only ~76 % degradation is shown for x = 0.0 sample in 40 min under visible light irradiation. [Display omitted] • New RP-type LaSrFe 1- x Cr x O 4 phases synthesized by glycine-nitrate combustion method. • E g values decreased with increase in Cr concentration. • Dominant AFM interactions in all the phases and the appearance of weak FM interactions with Cr doping. • Enhanced photocatalytic activity was observed by Cr doping. [ABSTRACT FROM AUTHOR]

This paper presents the rare earth doping effect on the structural, optical, and magnetic properties of bilayered Ruddlesden-Popper oxides Sr 2 La 0.5 R 0.5 FeMnO 7 (R = La, Nd, Sm, Gd, Dy). Moreover, we are reporting for the first time a new rare earth-doped bilayered perovskite oxide series for the highly toxic methylene blue dye degradation in wastewater under visible light. Structural analysis of the PXRD data using the Rietveld refinements confirms the formation of the phases in tetragonal symmetry with the I 4/ mmm space group. The unit cell lattice parameters ( a & c ) and the cell volume ( V ) decrease monotonically from La- to Dy-doped samples owing to the decrease in the lanthanide ionic radii. The X-ray photoelectron spectroscopy analysis indicates the existence of the Mn ions in the mixed valence state. The DRS study shows that the energy band gap value decreases on moving from La to Gd substitution; however, it further increases for the Dy-doped sample. The magnetic measurements reveal that all the phases exhibit dominant anti-ferromagnetic interactions with Neel temperature ( T N ) observed at 150, 147, 138, 113, and 117 K for La-, Nd-, Sm-, Gd-, and Dy-substituted phases, respectively. However, the presence of an unsaturated hysteresis loop observed in the isothermal magnetic field ( H ) vs magnetization ( M ) plot also indicates the existence of weak ferromagnetic interactions. The investigation of the photocatalytic activity of the synthesized samples was done by carrying out photo-oxidative degradation of methylene blue (MB) dye pollutants. The results show that the photodegradation enhances by doping with heavier rare earth ions with the exception of the Dy-doped sample. The Gd-doped catalyst shows the maximum degradation efficiency of 99.03% in 50 min under visible light irradiation. The scavenging experiments confirmed that the · OH was the main/dominant oxidizing agent involved in the degradation of the MB dye., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

The present study reports the synthesis of nanocrystalline LaFe 0.5 Cr 0.5 O 3 via a solvent-free combustion method using glycine, poly(vinyl alcohol), and urea as fuels, with superior photocatalytic activity. Rietveld refinement and powder X-ray diffraction data of nanomaterials demonstrate the existence of an orthorhombic phase that corresponds to the Pbnm space group. The crystallite size of nanoperovskite samples lies in the range of 20.9-36.4 nm. The Brunauer-Emmett-Teller (BET) surface area of the LaFe 0.5 Cr 0.5 O 3 fabricated using urea is found to be higher than that of the samples prepared using other fuels. The magnetic measurements of all samples done using a SQUID magnetometer showed a dominant antiferromagnetic character along with some weak ferromagnetic interactions. The optical band gap of all nanosamples lies in the visible range (2-2.6 eV), making them suitable photocatalysts in visible light. Their use as a photocatalyst for the degradation of the rhodamine B dye (model pollutant) is studied, and it has been observed that the catalyst fabricated using urea shows excellent degradation efficiency for rhodamine B, i.e., 99% in 60 min, with high reusability up to five runs. Additionally, the degradation of other organic dyes such as methylene blue, methyl orange, and a mixture of these dyes (rhodamine B + methylene blue + methyl orange) is also investigated with the most active photocatalyst, i.e., LFCO-U, to check its versatility., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

As industrialization progresses, there is a large release of hazardous pollutants into the environment. These pollutants, which contain nitro compounds and organic dyes, are extremely dangerous due to their toxic and carcinogenic nature. An efficient, environmentally benign, and economical catalyst to degrade environmental pollutants or convert them into useful products has been of sustained interest in recent years. In this context, we report a simple and inexpensive combustion fabrication of NiCrFeO 4 using different fuels such as glycine, polyvinyl alcohol (PVA), and urea, showing tremendous catalytic and photocatalytic functionalities. Rietveld refinement and X-ray diffraction studies confirmed the formation of single-phase ferrites, with crystallite sizes ranging from 3.9 to 43.31 nm. The values of optical band gap, obtained from the diffused reflectance spectroscopy technique, lie in the visible region range (1.50-1.60 eV), and hence, all the synthesized ferrites can act as good photocatalysts in the presence of visible light. All the NCF nanocatalysts were utilized for the reduction of nitroarenes and photocatalytic degradation of various cationic (RhB and MB) and anionic (MO) dyes and their mixture. NCFP displayed excellent activity for the reduction and oxidation reactions owing to its large surface area and low optical band gap. Furthermore, the photo-oxidative degradation by NCFP was also enhanced due to its low recombination of charge carriers as confirmed by the photoluminescence (PL) spectroscopy. NCFP efficiently reduces nitrobenzene to aminobenzene with 95% yield using sodium borohydride as the reducing agent in methanol medium at RT in 10 min. The results of photocatalytic activity have shown that the degradation efficiency of NCFP follows the order RhB > MB > MO in their unitary solution. Furthermore, in the case of the mixture of dyes, NCFP showed enhanced photocatalytic degradation for cationic dyes (RhB and MB) compared to that of anionic dye (MO). From the performance point of view, this catalyst can be useful in industrial application because of its high stability, greater catalytic efficiency, and cost-effectiveness., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)