Catalytic effect of nickel oxide nanoparticles from Lupinus Albus extract on green synthesis and photocatalytic reduction of methylene blue: kinetics and mechanism

Green synthesis of nanomaterials is advancing due to their ease of synthesis, cheapness, nontoxicity, and renewability. An environmentally friendly biogenic method has been developed for the green synthesis of nickel oxide nanoparticles (NiO NPs) using phytochemical-rich bioextract. They are rich in bioextract phenolics, flavonoids, and berberine. These phytochemicals successfully reduce and stabilize NiNO3 into NiO NPs. In this study, NiO NPs were synthesized by the green synthesis method from Lupinus Albus. Characterization of NiO NPs was carried out by TEM, XRD, SEM, UV, XRF, BET, and EDX analyses. According to XRD analysis, TEM results also support this, where the NiO NPs particle size diameter is 5 nm. It was determined by the Tauc equation that the band energy gap of NiO NPs is 1.69 eV. It was determined that the BET surface area of NiO NPs was 49.6 m2/g. NiO nanoparticles synthesized from Lupinus Albus extract by the green synthesis method were used as catalysts in the photocatalytic reduction of methylene blue with NaBH4. In the photocatalytic reduction of methylene blue with NaBH4, it was determined that there was no color change in 48 h without a catalyst, and in the presence of NiO nanoparticle catalyst, methylene blue was reduced by 97% in 8 min. The kinetics of the photocatalytic reduction of methylene blue with NaBH4 is a pseudo-first-order kinetic model and the kinetic rate constant is determined as 0.66 min-1, indicating that the catalytic effect of NiO NPs is very high at this value. NiO NPs were used five times in the photocatalytic reduction of methylene blue with NaBH4 and it was determined that the reduction of methylene blue was over 90% in each use.

Metal Oxides Nanoparticles: General Structural Description, Chemical, Physical, and Biological Synthesis Methods, Role in Pesticides and Heavy Metal Removal through Wastewater Treatment

Nanotechnology (NT) is now firmly established in both the private home and commercial markets. Due to its unique properties, NT has been fully applied within multiple sectors like pharmacy and medicine, as well as industries like chemical, electrical, food manufacturing, and military, besides other economic sectors. With the growing demand for environmental resources from an ever-growing world population, NT application is a very advanced new area in the environmental sector and offers several advantages. A novel template synthesis approach is being used for the promising metal oxide nanostructures preparation. Synthesis of template-assisted nanomaterials promotes a greener and more promising protocol compared to traditional synthesis methods such as sol-gel and hydrothermal synthesis, and endows products with desirable properties and applications. It provides a comprehensive general view of current developments in the areas of drinking water treatment, wastewater treatment, agriculture, and remediation. In the field of wastewater treatment, we focus on the adsorption of heavy metals and persistent substances and the improved photocatalytic decomposition of the most common wastewater pollutants. The drinking water treatment section covers enhanced pathogen disinfection and heavy metal removal, point-of-use treatment, and organic removal applications, including the latest advances in pesticide removal.

Solid-State Preparation of Metal and Metal Oxides Nanostructures and Their Application in Environmental Remediation

Nanomaterials have attracted much attention over the last decades due to their very different properties compared to those of bulk equivalents, such as a large surface-to-volume ratio, the size-dependent optical, physical, and magnetic properties. A number of solution fabrication methods have been developed for the synthesis of metal and metal oxides nanoparticles, but few solid-state methods have been reported. The application of nanostructured materials to electronic solid-state devices or to high-temperature technology requires, however, adequate solid-state methods for obtaining nanostructured materials. In this review, we discuss some of the main current methods of obtaining nanomaterials in solid state, and also we summarize the obtaining of nanomaterials using a new general method in solid state. This new solid-state method to prepare metals and metallic oxides nanostructures start with the preparation of the macromolecular complexes chitosan·Xn and PS-co-4-PVP·MXn as precursors (X = anion accompanying the cationic metal, n = is the subscript, which indicates the number of anions in the formula of the metal salt and PS-co-4-PVP = poly(styrene-co-4-vinylpyridine)). Then, the solid-state pyrolysis under air and at 800 °C affords nanoparticles of M°, M_xO_y depending on the nature of the metal. Metallic nanoparticles are obtained for noble metals such as Au, while the respective metal oxide is obtained for transition, representative, and lanthanide metals. Size and morphology depend on the nature of the polymer as well as on the spacing of the metals within the polymeric chain. Noticeably in the case of TiO₂, anatase or rutile phases can be tuned by the nature of the Ti salts coordinated in the macromolecular polymer. A mechanism for the formation of nanoparticles is outlined on the basis of TG/DSC data. Some applications such as photocatalytic degradation of methylene by different metal oxides obtained by the presented solid-state method are also described. A brief review of the main solid-state methods to prepare nanoparticles is also outlined in the introduction. Some challenges to further development of these materials and methods are finally discussed.

Insights of the formation mechanism of nanostructured titanium oxide polymorphs from different macromolecular metal-complex precursors

The insight into the mechanism of the unprecedented formation of pure anatase TiO2 from the macromolecular (Chitosan)•(TiOSO4)n precursor has been investigated using micro Raman spectroscopy, Scanning Electron Microscopy (SEM) and thermogravimetric/differential thermal analysis (TGA/DTA). The formation of a graphitic film was observed upon annealing of the macromolecular precursor, reaching a maximum at about 500 °C due to decomposition of the polymeric chain of the Chitosan and (PS-co-4-PVP) polymers. The proposed mechanism is the nucleation and growth of TiO2 nanoparticles over this graphitic substrate. SEM and Raman measurements confirm the formation of TiO2 anatase around 400 °C. The observation of an exothermic peak around 260 °C in the TGA/DTA measurements confirms the decomposition of carbon chains to form graphite. Another exothermic peak around 560 °C corresponds to the loss of additional carbonaceous residues.

Solventless Preparation of Thoria and Its Inclusion into SiO2 and TiO2: A Luminescence and Photocatalysis Study

Thoria was prepared using a solid-state method from the macromolecular precursor Chitosan·Th(NO3)4 (chitosan) and PS-co-4-PVP·Th(NO3)4 (PVP). The morphology and the average size of ThO2 depend of the chitosan and PS-co-4-PVP polymer forming the precursor. Their photoluminescent properties were investigated, finding a dependence of their intensity emission maxima, with the nature of the precursor polymer. The photocatalytic activity of ThO2 toward the degradation of methylene blue was measured for the first time, finding a degradation of about 66% in 300 min. The inclusion of ThO2 into SiO2 and TiO2 was achieved by the solid-state pyrolysis of the macromolecular composites Chitosan·Th(NO3)4//MO2 and PS-co-4-PVP·Th(NO3)4//MO2, MO2 = SiO2 or TiO2. The ThO2 exhibits a homogeneous dispersion inside the silica, showing sizes of about 40 and 50 nm for the chitosan and PVP polymer precursors, respectively. The luminescent properties of the ThO2/SiO2 and ThO2/TiO2 composites were also studied, finding a decrease in intensity when introducing the SiO2 or TiO2 matrices. The photocatalytic behavior to methylene blue degradation of ThO2 and their composites ThO2/SiO2 and ThO2/TiO2 was investigated for the first time, with them in the following order: ThO2 > ThO2/TiO2 > ThO2/SiO2.

Incorporation of NiO into SiO2, TiO2, Al2O3, and Na4.2Ca2.8(Si6O18) Matrices: Medium Effect on the Optical Properties and Catalytic Degradation of Methylene Blue

The medium effect of the optical and catalytic degradation of methylene blue was studied in the NiO/SiO₂, NiO/TiO₂, NiO/Al₂O₃, and NiO/Na_4.2Ca_2.8(Si₆O₁₈) composites, which were prepared by a solid-state method. The new composites were characterized by XRD (X-ray diffraction of powder), SEM/EDS, TEM, and HR-TEM. The size of the NiO nanoparticles obtained from the PSP-4-PVP (polyvinylpyrrolidone) precursors inside the different matrices follow the order of SiO₂ > TiO₂ > Al₂O₃. However, NiO nanoparticles obtained from the chitosan precursor does not present an effect on the particle size. It was found that the medium effect of the matrices (SiO₂, TiO₂, Al₂O₃, and Na_4.2Ca_2.8(Si₆O₁₈)) on the photocatalytic methylene blue degradation, can be described as a specific interaction of the NiO material acting as a semiconductor with the M_xO_y materials through a possible p-n junction. The highest catalytic activity was found for the TiO₂ and glass composites where a favorable p-n junction was formed. The isolating character of Al₂O₃ and SiO₂ and their non-semiconductor behavior preclude this interaction to form a p-n junction, and thus a lower catalytic activity. NiO/SiO₂ and NiO/Na_4.2Ca_2.8(Si₆O₁₈) showed a similar photocatalytic behavior. On the other hand, the effect of the matrix on the optical properties for the NiO/SiO₂, NiO/TiO₂, NiO/Al₂O₃, and NiO/Na_4.2Ca_2.8(Si₆O₁₈) composites can be described by the different dielectric constants of the SiO₂, TiO₂, Al₂O₃, Na_4.2Ca_2.8(Si₆O₁₈) matrices. The maxima absorption of the composites (λ_max) exhibit a direct relationship with the dielectric constants, while their semiconductor bandgap (E_g) present an inverse relationship with the dielectric constants. A direct relationship between λ_max and E_g was found from these correlations. The effect of the polymer precursor on the particle size can explain some deviations from this relationship, as the correlation between the particle size and absorption is well known. Finally, the NiO/Na_4.2Ca_2.8(Si₆O₁₈) composite was reported in this work for the first time.

Competing ferro- and antiferromagnetic exchange drives shape-selective [Formula: see text] nanomagnetism

We have synthesized three different shapes of [Formula: see text] nanoparticles to investigate the relationships between the surface Co[Formula: see text] and Co[Formula: see text] bonding quantified by exploiting the known exposed surface planes, terminations, and coordiations of [Formula: see text] nanoparticle spheres, cubes and plates. Subsequently this information is related to the unusual behaviour observed in the magnetism. The competition of exchange interactions at the surface provides the mechanism for different behaviours in the shapes. The cubes display weakened antiferromagnetic interactions in the form of a spin-flop that occurs at the surface, while the plates show distinct ferromagnetic behaviour due to the strong competition between the interactions. We elucidate the spin properties which are highly sensitive to bonding and crystal field environments. This work provides a new window into the mechanisms behind surface magnetism.

In-situ synthesis of 3D ultra-small gold augmented graphene hybrid for highly sensitive electrochemical binding capability

The fascinating properties of graphene can be augmented with other nanomaterials to generate hybrids to design innovative applications. Contrary to the conventional methodologies, we showed a novel yet simple, in-situ, biological approach which allowed for the effective growth of gold nanostructures on graphene surfaces (3D Au NS@GO). The morphology of the obtained hybrid consisted of sheets of graphene, anchoring uniform dispersion of ultra-small gold nanostructures of about 2-8 nm diameter. Surface plasmon resonance at 380 nm confirmed the nano-regimen of the hybrid. Fourier transform infrared spectroscopy indicated the utilization of amine spacers to host gold ions leading to nucleation and growth. The exceptional positive surface potential of 55 mV suggest that the hybrid as an ideal support for electrocatalysis. Ultimately, the hybrid was found to be an efficient receptor material for electrochemical performance towards the binding of uric acid which is an important biomolecule of human metabolism. The designed material enabled the detection of uric acid concentrations as low as 30 nM. This synthesis strategy is highly suitable to design new hybrid materials with interesting morphology and outstanding properties for the identification of clinically relevant biomolecules.