The use of waste from the food industry can help growing concerns about the environmental impact of chemical synthesis methods. This paper described a bioinspired design strategy for the highly efficient preparation of magnesium aluminate (MgAl2O4) nanoparticles using an aqueous extract of apple peel. The impact of calcination temperature on the characteristics of the obtained samples and their photocatalytic capability were discussed. The prepared MgAl2O4 samples were characterized using various techniques: X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive X-ray (EDX), Fourier transform infrared (FT-IR), Raman, Ultraviolet–visible (UV–Vis) and photoluminescence (PL) spectroscopy, and nitrogen adsorption–desorption analysis. The XRD results conformed the obtaining of MgAl2O4 with a spinel structure and an average crystallite size of 5–8 nm. The morphological analysis by SEM revealed aggregates composed of fine nanoparticles. Raman spectroscopy detected only the bands characteristic of spinel-type MgAl2O4 with a high degree of inversion in the cation lattice. The UV–Vis spectra and Tauc’s plot analysis of the magnesium aluminate samples obtained after different thermal treatments revealed band gap values of 3.28 and 3.75 eV, respectively. Under visible light irradiation, the photocatalytic efficiency reached 93

This paper describes the synthesis of cobalt-zinc aluminates (Co1-xZnxAl2O4) pigments, through a simple and ecofriendly method using the aqueous extract of Hibiscus rosa-sinensis leaves. The presence of a pure spinel lattice after calcination at 1000 degrees C for 2 h was confirmed. The mean crystallite size is between 12 and 16 nm. The SEM and TEM investigations revealed a high degree of crystallinity and compositional homogeneity of the prepared nanosized zinc-substituted cobalt aluminates. The average particle size, revealed by TEM, decreases from 48.4 nm to 14.2 nm with the increase of Zn content. The values of the optical energy band gap for the obtained aluminates range from 1.82 to 2.21 eV. The nanoparticles synthesized by this green method could be potentially useful as pigments, the best result being obtained for the Co0.25Zn0.75Al2O4 sample with b* = -6.52 and C* = 12.92 colour coordinates.

This study explored a new green approach of the wet ferritization method to obtain magnetic cobalt ferrite (CoFe2O4) by using eucalyptus leaves aqueous extract as a reducing/chelating/capping agent. The spinel single cubic phases of prepared samples were proved by powder X-ray diffraction (XRD), Fourier-Transform Infrared (FTIR) and Raman spectroscopy. The average crystallite size is in the range between 3 and 20 nm. The presence of the functional groups coating the obtained material is confirmed from FTIR and thermal analysis. The scanning electron microscopy (SEM) analysis showed a morphology consisting of nanoparticle aggregates. Raman spectroscopy detects the characteristic bands of spinel-type CoFe2O4. Magnetic investigations reveal the formation of ferromagnetic compounds with cubic magnetic anisotropy and a blocking temperature around 140 K, specific for this type of material. The biosynthesized CoFe2O4 could be an attractive candidate for biomedical applications, exhibiting promising antimicrobial and antibiofilm activity, particularly against Gram-negative bacteria and fungal strains.

A series including single and mixed Ni-Co aluminates was obtained using the precursor method, with malic acid as a ligand. The malate precursors (polynuclear coordination compounds) were isolated and characterized by Fourier Transform Infrared (FTIR), Ultraviolet/Visible/Near Infrared (UV–Vis–NIR) spectroscopy, and thermal analysis. The UV–Vis–NIR spectra of the synthesized complex compounds highlighted the presence of Co2+ and Ni2+ in an octahedral environment. The thermal decomposition of these precursors led to Co1−xNixAl2O4 (x = 0, 0.1, 0.25, 0.5, 0.75, 0.9, and 1) spinels. The effect of Ni2+ substitution on the structure, morphology, and optical properties of the obtained oxides was studied with the help of different characterization tools. XRD, FTIR, and Raman spectra evidenced the formation of the spinel phase. The size of the crystallites and the agglomeration degree of the particles decrease when the nickel content increases. The band gap (BG) value is not significantly influenced by the Ni substitution. The fluorescence spectra recorded for all samples show a similar pattern, but different intensities of the emission bands.

Nanosized CoFe1.8RE0.2O4 (RE3+ = Tb3+, Er3+) ferrites were obtained through wet ferritization method. These ferrites were characterized by X-ray diffraction (XRD), scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM/HR-TEM), Fourier transform infrared spectroscopy (FTIR), Mössbauer spectroscopy and magnetic measurements. The XRD results revealed that the average crystallite size is 5.77 nm for CoFe1.8Tb0.2O4 and 6.42 nm for CoFe1.8Er0.2O4. Distribution of metal cations in the spinel structure estimated from X-ray diffraction data showed that the Tb3+ and Er3+ ions occupy the octahedral sites. TEM images indicated the presence of polyhedral particles with average size 5.91 nm for CoFe1.8Tb0.2O4 and 6.80 nm for CoFe1.8Er0.2O4. Room temperature Mössbauer spectra exhibit typical nanoscaled cobalt ferrite spectra in good agreement with XRD and TEM data. The saturation magnetization value (Ms) is 60 emu/g for CoFe1.8Tb0.2O4 and 80 emu/g for CoFe1.8Er0.2O4. CoFe1.8RE0.2O4 nanoparticles showed similar antimicrobial efficacy against the five tested microbial strains, both in planktonic and biofilm state. The results highlight the promising potential of these types of nanoparticles for the development of novel anti-biofilm agents and materials.

The precursor method was employed to prepare ZnAl2_xCrxO4 (x = 0, 0.25, 0.5, 0.75, 1) using tartaric acid as a ligand. Five tartarate compounds were isolated as precursors for the obtaining of zinc aluminate and chromium -substituted zinc aluminate. These coordination compounds were characterized by elemental chemical analysis, infrared (IR) and ultraviolet visible (UV-Vis) spectroscopy, and thermal analysis. The influence of Cr3+ substi-tution on the structure, morphology and optical properties of the synthesized mixed oxides was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), infrared, Raman and UV-Vis spectroscopy, and nitrogen adsorption - desorption analysis. The XRD patterns and Raman spectra confirmed the formation of spinel structure. The mean crystallite size varied from 18 to 22 nm SEM and EDS showed uniform composition and microstructure of the ZnAl2_xCrxO4 nanocrystalline powders. The values of the optical energy bandgap for the samples were found to be in the 3.92 - 2.85 eV range. The photocatalytic performance in the degradation reaction of Eosin Y (EY) under visible light irradiation was evaluated. The Eosin Y degradation efficiency values were obtained between 48% and 80% after 75 min. The best photocatalytic result was obtained for the sample with the highest amount of chromium.

This paper describes for the first time two processing routes—the precursor method and the two-step wet chemical process—for the synthesis of magnetic cobalt ferrite using the Tamarindus indica fruit extract. These green approaches are eco-friendly, safe and efficient alternatives to classical chemical methods. The aqueous extract from tamarind fruit contains numerous metabolites (organic acids, aminoacids). All these bioactive components are able to chelate metal ions leading to the formation of the multimetallic complex (precursor of cobalt ferrite). The obtained precursor was characterized by Fourier transform infrared spectroscopy (FTIR), thermal analysis, X-ray diffraction analysis (XRD) and magnetic measurements. The structure, morphology and magnetic behavior of the cobalt ferrite samples prepared through both synthesis routes were investigated by various characterization techniques: FTIR, XRD, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), Mössbauer spectroscopy and magnetic measurements. XRD data confirmed that a cubic spinel structure was obtained for both ferrite powders with average crystallite size of 13 and 5 nm, respectively. The microstructure study by SEM revealed the formation of nanocrystallites assemblies using the precursor method and carbon-rich particles forming granulated micron-sized agglomerates, embedding ferrite nanocrystallites obtained through the two-step wet chemical process. Mössbauer spectroscopy results evidenced relaxation processes in the CoFe2O4 samples at room temperature, and the main characteristics of the involved sublattices were derived. The magnetic investigation revealed a typical magnetic behavior for a spinel, with CoFe2O4 nanoparticles ferrimagnetic at low temperature and superparamagnetic at room temperature.

This paper introduces for the first time the preparation of cobalt aluminate (CoAl 2 O 4 ) nanoparticles through a solution combustion method using a Mentha piperita leaves extract. The active constituents present in the mentha leaves extract act as both a chelating and a reducing agent. The isolated precursor was characterized by FTIR, UV–Vis, thermal analysis and XPS. Various techniques (XRD, SEM and TEM, XPS, FTIR and UV–Vis) were also used to characterize the cobalt aluminate spinel from the point of view of structure, morphology and surface chemistry. XRD confirmed the formation of a single-phase, crystalline cubic spinel structure with mean crystalline domain size of 19.5 nm. The TEM analysis showed rhombic and rectangular CoAl 2 O 4 nanoparticles with unimodal particle size distribution and average particle size of about 35 nm. The characteristic peaks of the CoAl 2 O 4 spinel were highlighted by the FTIR spectrum. The tetrahedral configuration of Co 2+ ions in the CoAl 2 O 4 spinel structure was illustrated by the absorbance and XPS spectra. Furthermore, XPS spectra reveal both tetrahedral and octahedral configurations of Al 3+ ions. To evaluate the catalytic properties of the cobalt aluminate, the photocatalytic degradation of methylene blue (MB) was carried out under visible light irradiation.

In the present study, the effect of two different approaches: chemical and green synthesis on the properties of MgO nanoparticles was investigated. The green approach was based on the solution combustion method, using aqueous and alcoholic extracts of cinnamon bark, while the chemical one used the precursor method via tartarate and gluconate routes. Two types of complex precursors of MgO: (NH4)[Mg(C4O6H4)(C4O6H5)]center dot 7H2O and [Mg(C6O7H11)2]center dot NH4NO3 center dot 5H2O have been isolated and investigated by elemental chemical analysis, IR spectroscopy and thermal analysis. The structure, morphology and textural properties of microscopy (SEM) and nitrogen adsorption - desorption analysis. XRD indicated the obtaining of cubic MgO as single phase with average crystallite sizes between 5.9 and 15.4 nm regardless of the method used. The MgO powders were tested in photocatalytic degradation of methyl orange (MO) dye under ultraviolet and visible light irradiation. The highest degradation efficiency of MO (95%) was noticed under UV irradiation for MgO sample prepared by solution combustion method using alcoholic cinnamon extract.

Eu3+,Tb3+-doped Sr3Al2O6 powder phosphor was synthesized via a precursor route and subjected to a subsequent thermal treatment in reducing atmosphere. Photoluminescence and thermoluminescence properties of Sr3Al2O6:Eu3+/Eu2+,Tb3+ were investigated. The structure and morphology of oxides were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) was used for the nanocrystals surface composition analysis. X-ray diffraction patterns confirmed the formation of the cubic structure specific to Sr3Al2O6 with space group Pa3 and lattice parameter a = 15.8322 angstrom, while SEM investigations revealed equiaxial, polycrystalline particles, with sizes in the submicronic range, for both Sr3Al2O6:Eu3+,Tb3+ and Sr3Al2O6:Eu3+/Eu2+,Tb3+ samples. The photoluminescence spectra showed the typical f-f luminescence lines of the Tb(3+ )and Eu3+ - ions, accompanied by a broad Eu2+ luminescence band at 510 nm (after calcination in reducing atmosphere). The "after-glow" luminescence signal and the thermoluminescence were assigned to the recombination of close neighbor partners (electron and Eu2+ - hole centers) within the same complex of defects.

The nanostructured cobalt aluminate (CoAl2O4) was obtained through an eco-friendly precursor method using aqueous extract of tamarind fruit. The use of plant extracts is a simple and effective approach for the preparation of CoAl2O4 nanoparticles. The polynuclear complex precursor was characterized by Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-VIS) and thermal analysis. The cobalt aluminate was investigated by: X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), FTIR, UV-VIS and colour measurements by reflectance spectroscopy (RS). X-ray diffraction patterns confirmed the formation of cubic CoAl2O4 spinel phase with good crystallinity. The average particle size from TEM is about 71 nm. Chromatic coordinates indicate that the bluest colour was obtained for the cobalt aluminate obtained by subsequent heat treatment.

Chitosan-coated cobalt ferrites were synthesized by wet ferritization method through two different approaches. The nanostructured chitosan-coated cobalt ferrites were characterized by: X-ray diffraction (XRD), scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM/HR-TEM), thermal analysis, infrared spectroscopy (IR) and Mössbauer spectroscopy. X-ray diffraction patterns confirmed the formation of CoFe2O4 cubic spinel structure with an average crystallite size of 1.75 and 5.5 nm, respectively. Mössbauer spectra consist in a central quadrupole pattern. The deconvolution in the hypothesis of Lorentzian line shape evidences the prevailing presence of Fe3+ ions at the nanoparticle surface. The antimicrobial activity of chitosan-coated cobalt ferrites against Gram-positive and Gram-negative bacteria, as well as fungal strains was investigated. Based on the results, chitosan-coated cobalt ferrites are thought to be suitable candidates for the development of novel anti-biofilm agents.

Cobal aluminate (CoAl2O4) nanoparticles were synthesized through classic combustion (CCM) and microwave combustion (MCM) methods using cinnamon bark extract. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR) and ultraviolet-visible (UV-vis) spectroscopy were used for the characterization of the cobalt aluminate nanoparticles.

Chromium substituted cobalt ferrites CoFe2−xCrxO4 (x = 0; 1; 1.5) were synthesized through a soft chemistry method—the gluconate precursor route. The gluconate precursors were characterized by infrared spectroscopy (IR), ultraviolet–visible spectroscopy and thermal analysis. The spinel oxide powders were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Mössbauer spectroscopy and Brunauer–Emmett–Teller N2 adsorption–desorption analyses. XRD indicated the formation of the spinel-type phase with good crystallinity. The mean crystalline domains size decreased from 23.8 to 17.8 nm with the increase in the chromium content. SEM revealed faceted particles for which the particle sizes varied significantly with the chromium content. The chromium substituted cobalt ferrites were found to have high catalytic performance.

Un-doped and Tb3+-doped calcium and strontium aluminates (CaAl2O4, CaAl2O4:Tb3+, SrAl2O4, SrAl2O4: Tb3+) were synthesized by a new soft chemical method the precursor route via the thermal decomposition of tartarate compounds. The complex precursors have been characterized by elemental chemical analysis, infrared spectroScopy (IR), luminescence spectroscopy and thermal analysis. X-ray diffraction (XRD), scanning electron microscopy (SEM), IR and Raman spectroscopy (RS) were used for the structural and morphological characterization of un-doped and doped alkaline-earth aluminate powders. Photoluminescence (PL) and Thermoluminescence (TL) properties of the aluminates were also investigated. The XRD patterns confirmed the formation of low-temperature structures: hexagonal structure for CaAl2O4 and monoclinic structure for SrAl2O4, with average crystallite size of 64 nm and 46 nm for CaAl2O4 and SrAl2O4, respectively. Microstructural analysis by SEM showed the homogeneous microstructure and fine particle size of the powder obtained by precursor method. (C) 2016 Elsevier Ltd. All rights reserved.

Cobalt ferrites nanoparticles (CoFe2O4) were synthesized through self-combustion method using aqueous extracts of ginger root and cardamom seeds. X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (IR) and Mossbauer spectroscopy were used for the characterization of the cobalt ferrite nanoparticles. X-ray diffraction patterns indicated the formation of the cubic phase CoFe2O4. SEM micrographs revealed different morphological features of obtained cobalt ferrites. The Mossbauer parameters together with the inversion parameter and the cationic distribution were obtained from Mossbauer spectra recorded at room temperature.

Un-doped and doped strontium aluminates (Sr3Al2O6, Sr3Al2O6:Tb3+, Sr3Al2O6:Tb3+,Eu3+ and Sr3Al2O6:Tb3+,Eu3+/Eu2+) were synthesized through a soft chemical method – the tartarate precursor route. The tartarate precursors were characterized by infrared spectroscopy (IR) and thermal analysis. The strontium aluminates were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and infrared spectroscopy (IR). The XRD patterns confirmed the formation of single-phase cubic structure Sr3Al2O6 with average crystallite size of 18nm. SEM micrographs showed porous polycrystalline powder microstructures and EDX analysis confirmed the incorporation of the dopant in the Sr3Al2O6 powders. The photoluminescence spectrum recorded on Sr3Al2O6: Tb3+,Eu3+ (obtained from tartarate precursor calcined in air) showed the typical f-f luminescences of the RE-ions. Subsequent calcination of this sample in reducing atmosphere is accompanied by new photoluminescence and thermoluminescence features associated to the Eu2+ ions.

Silver-cobalt ferrite nanocomposites (Ag-CoFe2O4) were synthesized through wet ferritization process and self-propagating combustion method. The structure, morphology, surface chemistry and magnetic properties of the nanocomposites were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM). X-ray diffraction patterns confirmed the formation of CoFe2O4 and Ag nanoparticles with cubic symmetry. The average crystallite size of CoFe2O4 by wet ferritization ranged between 60Å and 87Å; for those obtained by self-propagating combustion was in the range 232–290Å. SEM micrographs revealed different morphological features of nanocomposites. Ag-CoFe2O4 obtained by wet ferritization exhibited typical superparamagnetic behaviour. The antimicrobial and anti-biofilm properties of all silver-cobalt ferrites were evaluated. The results revealed that the Ag-CoFe2O4 nanocomposites exhibited good microbicidal and anti-biofilm features.

The cobalt ferrite (CoFe 2 O 4 ) and silver-cobalt ferrite (Ag-CoFe 2 O 4 ) nanoparticles were obtained through self-combustion and wet ferritization methods using aqueous extracts of Hibiscus rosa-sinensis flower and leaf. X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and magnetic measurements were used for the characterization of the obtained oxide powders. The antimicrobial activity of the cobalt ferrite and silver-cobalt ferrite nanoparticles against Gram-positive and Gram-negative bacteria, as well as fungal strains, was investigated by qualitative and quantitative assays. The most active proved to be the Ag-CoFe 2 O 4 nanoparticles, particularly those obtained through self-combustion using hibiscus leaf extract, which exhibited very low minimal inhibitory concentration values (0.031–0.062 mg/mL) against all tested microbial strains, suggesting their potential for the development of novel antimicrobial agents.