Sustainability insights into the synthesis of engineered nanomaterials - Problem formulation and considerations

Engineered nanomaterials (ENMs) have been introduced into the market for a wide range of applications. As per the literature review, the fabrication of new generations of ENMs is starting to comply with environmental, economic, and social criteria in addition to technical aspects to meet sustainability criteria. At this stage, identification of the appropriate criteria for the synthesis of ENMs is critical because the technologies already developed at the lab scales are being currently transferred to pilot and full scales. Hence, the development of scientific-based methodologies to identify, screen, and prioritize the involved criteria is highly necessary. In the present manuscript, a fuzzy-Delphi methodology is adopted to identify the main criteria and sub-criteria encompassing the sustainable fabrication of ENMs, and to explore the "degree of consensus" among the experts on the relative importance of the mentioned criteria. The "health and safety risks" respecting the equipment and the materials, solvent used, and availability of "green experts" were identified as the most critical criteria. Furthermore, although all the criteria were identified as being important, some criteria, such as "solvent" and "raw materials cost", raised a lower degree of consensus, indicating that various "degrees of uncertainties" still exist regarding the level of importance of the studied criteria.

Effect of organic solvents on calcium minodronate crystal morphology in aqueous solution: an experimental and theoretical study

The influence of nine organic solvents on the crystal morphology of calcium minodronate (Ca(Min)₂) was investigated by experimental investigations and molecular simulations. Hirshfeld analysis was used to reveal the intermolecular interactions, and the modified attachment energy (AE) model was applied to constructing the Ca(Min)₂-organic-water model in different organic-water solvents. The surface structure and the mass density profile were demonstrated and analyzed. The results showed that there were different adsorption conditions in different organic-water solvents. Furthermore, it was found that the (2 0 0)/(1 1 0) side ratio of Ca(Min)₂ crystal had a linear relationship with the volume of organic solvent and had a certain correlation with some solvent properties. It is believed that the research developed in this work could have a promising application in prediction of Ca(Min)₂ crystal morphology and could give guidance in the selection of organic solvents to control the desirable crystal morphology.

NaY(MoO4)2-based nanoparticles: synthesis, luminescence and photocatalytic properties

We report on a novel synthesis method, which produces NaY(MoO₄)₂ nanoparticles having an almost spherical shape and hydrophilic character. The procedure is also suitable for the preparation of NaY(MoO₄)₂-based nanophosphors by doping this host with lanthanide cations (Eu³⁺, Tb³⁺ and Dy³⁺), which, under UV illumination, exhibit intense luminescence whose color is determined by the selected doping cation (red for Eu³⁺, green for Tb³⁺ and yellow for Dy³⁺). The effects of the cations doping level on the luminescent properties are analyzed in terms of emission intensities and luminescent lifetime, to find the optimum phosphors. Finally, the performance of these nanophosphors and that of the undoped system for the photocatalytic degradation of rhodamine B, used as a model compound, is also analyzed.

Preparation and luminescence properties of Gd2 (MoO4 )3 :Eu3+ red phosphors with high colour purity

Gd₂ (MoO₄ )₃ :Eu³⁺ red phosphors assigned to different crystal systems were prepared using a sol-gel method with ammonium molybdate, Gd₂ O₃ , and Eu₂ O₃ as starting materials. X-ray diffraction (XRD) patterns showed that when annealing temperature was 700°C or 800°C, Eu³⁺ doping concentration was the main factor affecting sample structure. When the Eu³⁺ doping concentration was 0-2.00 mol%, samples had a monoclinic structure, but when the Eu³⁺ doping concentration was increased to 4.00-10.00 mol%, the samples changed to a mixed crystal structure (with existence of both monoclinic and orthorhombic structures). When the annealing temperature was increased to 900°C, annealing temperature became the main factor affecting sample structure, that is sample structure did not change with change in Eu³⁺ doping concentration, and all samples could be assigned to the orthorhombic system. Change in structure also affected the luminescence properties of the samples. Gd₂ (MoO₄ )₃ :Eu³⁺ phosphors with different crystal systems could be effectively excited by blue light (466 nm wavelength); red light at 614 nm wavelength gave better colour purity and color stability, corresponding to the Eu³⁺⁵ D₀ →⁷ F₂ transition. Finally, when Eu³⁺ concentration was 0.02 mol, the luminescence intensity of the orthorhombic system was higher than that of the monoclinic system; when the concentration was 0.04 mol, the luminescence intensity of the mixed system was almost the same as that of the orthorhombic system.

Morphology control, spectrum modification and extended optical applications of rare earth ion doped phosphors

This review summarizes the morphology control strategy, phase transfer theory, spectrum modulation, and extended optical applications of RE³⁺-doped phosphors.

Tunable morphologies, multicolor properties and applications of RE3+ doped NaY(MoO4)2 nanocrystals via a facile ligand-assisted reprecipitation process

Rare earth (RE3+)-doped NaY(MoO4)2 nanocrystals are efficient materials for realizing multicolor emission, which plays an important role in displays, W-LEDs, solar cells and biolabeling. Up to now, research on the multicolor tuning properties of RE3+-doped NaY(MoO4)2 nanoparticles has mostly focused on traditional preparation routes such as the hydrothermal method and sol-gel process. However, the products obtained using these methods are usually large in size (on the micron/submicron scale) and agglomeration problems are inevitable. With the development of nano optoelectronic devices and bioluminescence labeling, there is an urgent need to find an efficient method to prepare nanoscale, monodispersed and NaY(MoO4)2:RE3+ nanocrystals (NCs) with good crystallinity and stronger emission properties. In this work, we demonstrate a simple, fast, reproducible and one-step synthesis of NaY(MoO4)2:Eu3+ NCs with sizes varying from 1-20 nm via a ligand-assisted reprecipitation strategy. The reaction mechanism and emission intensities of NaY(MoO4)2:Eu3+ NCs with various morphologies have been discussed in detail. Furthermore, Tb3+ and Eu3+ ion co-doped NaY(MoO4)2 NCs were also prepared, and various emission colors were obtained and tuned from red, orange-red, yellow and yellow-green to green. Energy transfer between the Tb3+ and Eu3+ ions in the NaY(MoO4)2 host matrix has also been demonstrated. Finally, a highly efficient and stable NaY(MoO4)2:0.05Tb,0.04Eu NC-based W-LED device was built, which indicates the promising future application for this material in the field of lighting. The tunable multicolour emission, ease of preparation and nanosize reveal that NaY(MoO4)2:RE3+ NCs have a potential application in full color displays and W-LEDs.

Controllable synthesis and luminescent properties of rare earth doped Gd2(MoO4)3 nanoplates

For the first time, we have successfully synthesized rare-earth doped Gd₂(MoO₄)₃: RE³⁺ (RE=Eu, Tb) nanoplates by solvothermal method. The morphology of Gd₂(MoO₄)₃ can be manipulated by changing the reaction times and reaction temperatures. The composition and surface morphology have been investigated by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM), respectively. Under the excitation of UV, Photoluminescence (PL) has been used to explore the excellent luminescence properties of the synthesized nanophosphors. The Gd₂(MoO₄)₃: Eu³⁺ phosphors shows a hypersensitive red emission (612nm) when excitation wavelength within the scope of 200-350nm corresponding to a ⁵D₀-⁷F₂ transition. Similarly, the Gd₂(MoO₄)₃: Tb³⁺ phosphors certificate a highly strong green emission at 544nm at an excitation wavelength of 298nm corresponding to a ⁵D₄-⁷F₅ transition. Furthermore, the characteristic spectrum peak of the Gd₂(MoO₄)₃: Eu³⁺/Tb³⁺ nanophosphor exhibits the corresponding spectra position (green emission at 544nm and red emission at 612nm). Hence, the obtained Gd₂(MoO₄)₃: RE³⁺ nanoplates may establish highly potentiality in light field applications.

Photoluminescence properties of a novel red fluoride K2LiGaF6:Mn4+nanophosphor

The novel red phosphor K₂LiGaF₆:Mn⁴⁺, which exhibits a broadband excitation extending from 300 to 500 nm and an ideal narrow band emission centered at 630 nm, is a promising red phosphor candidate for application in WLEDs.

NaGd(MoO4)2 nanocrystals with diverse morphologies: controlled synthesis, growth mechanism, photoluminescence and thermometric properties

Pure tetragonal phase, uniform and well-crystallized sodium gadolinium molybdate (NaGd(MoO4)2) nanocrystals with diverse morphologies, e.g. nanocylinders, nanocubes and square nanoplates have been selectively synthesized via oleic acid-mediated hydrothermal method. The phase, structure, morphology and composition of the as-synthesized products are studied. Contents of both sodium molybdate and oleic acid of the precursor solutions are found to affect the morphologies of the products significantly, and oleic acid plays a key role in the morphology-controlled synthesis of NaGd(MoO4)2 nanocrystals with diverse morphologies. Growth mechanism of NaGd(MoO4)2 nanocrystals is proposed based on time-dependent morphology evolution and X-ray diffraction analysis. Morphology-dependent down-shifting photoluminescence properties of NaGd(MoO4)2: Eu(3+) nanocrystals, and upconversion photoluminescence properties of NaGd(MoO4)2: Yb(3+)/Er(3+) and Yb(3+)/Tm(3+) nanoplates are investigated in detail. Charge transfer band in the down-shifting excitation spectra shows a slight blue-shift, and the luminescence intensities and lifetimes of Eu(3+) are decreased gradually with the morphology of the nanocrystals varying from nanocubes to thin square nanoplates. Upconversion energy transfer mechanisms of NaGd(MoO4)2: Yb(3+)/Er(3+), Yb(3+)/Tm(3+) nanoplates are proposed based on the energy level scheme and power dependence of upconversion emissions. Thermometric properties of NaGd(MoO4)2: Yb(3+)/Er(3+) nanoplates are investigated, and the maximum sensitivity is determined to be 0.01333 K(-1) at 285 K.

Shape control of inorganic nanoparticles from solution

Inorganic materials with controllable shapes have been an intensely studied subject in nanoscience over the past decades. Control over novel and anisotropic shapes of inorganic nanomaterials differing from those of bulk materials leads to unique and tunable properties for widespread applications such as biomedicine, catalysis, fuels or solar cells and magnetic data storage. This review presents a comprehensive overview of shape-controlled inorganic nanomaterials via nucleation and growth theory and the control of experimental conditions (including supersaturation, temperature, surfactants and secondary nucleation), providing a brief account of the shape control of inorganic nanoparticles during wet-chemistry synthetic processes. Subsequently, typical mechanisms for shape-controlled inorganic nanoparticles and the general shape of the nanoparticles formed by each mechanism are also expounded. Furthermore, the differences between similar mechanisms for the shape control of inorganic nanoparticles are also clearly described. The authors envision that this review will provide valuable guidance on experimental conditions and process control for the synthesis of inorganic nanoparticles with tunable shapes in the solution state.

Effect of co-doping of alkali metal ions on Ca0.5RE1−x(MoO4)2:xEu3+ (RE = Y, La) phosphors with enhanced luminescence properties

Illustration of elemental mapping and PL emission spectra of the phosphors, Ca_0.5RE_1−x(MoO₄)₂:Eu³⁺,M⁺ (RE = Y, La; M = Li, K and Na).

Green and blue emitting 3D structured Tb:Ce2(WO4)3and Tb:Ce10W22O81micromaterials

Various Ce₂(WO₄)₃and Ce₁₀W₂₂O₈₁3D microstructures prepared hydrothermally in the absence and presence of a surfactant are reported. The different luminescence properties of the two types of materials, when doped with Tb³⁺ions were investigated and appropriate energy transfer mechanisms are suggested.

Influence of microwave hydrothermal reaction factor on the morphology of NaY(MoO4)2 nano-/micro-structures and luminescence properties of NaY(MoO4)2:Tb3+

The crystal structure and morphology of NaY(MoO₄)₂ micro-/nano-structures and their luminescence properties depend on pH, Cit³⁻/Ln³⁺ and MoO₄²⁻/Ln³⁺ ratios.

Photoluminescence tuning of Na1-xKxNdW2O8 (0.0 ≤ x ≤ 0.7) nanoparticles: synthesis, crystal structure and Raman study

A series of Na1-xKxNdW2O8 (0.0 ≤ x ≤ 0.7) nanoparticles have been synthesized by an efficient glycothermal technique for the first time. SEM measurements confirmed the particle size ranges from 30-200 nm with ellipsoidal shaped morphology. Combined X-ray and neutron diffraction and Raman spectroscopy techniques were utilized in order to investigate the influence of K(+) ion substitution in NaNdW2O8. K(+) ion substitution in the crystal lattice introduced a change in the Nd-O bond length and the Nd-O-W bond angle of NaNdW2O8. The photoluminescence intensity increased up to the threshold composition x = 0.4. K(+) ion substitution resulted in blue shifted emission of NaNdW2O8. Size mismatch, the Nd-O-W angle and local disorder contributed to the observed difference in luminescence properties. Also, the chromaticity diagram for this blue emitting phosphor showed the possibility of tuning the emission by incorporation of K.

The self-aggregation of fluorophore-triphenylamine nanostructures with tunable luminescent properties: the effect of acidity and rare earth ions

The self-aggregation of a fluorophore triphenylamine nanostructure in different acidity aqueous solutions and/or under the guidance of rare earth ions is studied to optimize the optical properties.