Hydrothermal Synthesis and Characterization of Bio-Sourced Macroporous Zinc Phosphates Prepared with Casein Protein

The development of an original and simple procedure of hydrothermal porous biosourced zinc phosphates synthesis from casein protein is reported in this study. The synthesis procedure does not require additional phosphorus source and structure-directing agent for macroporosity formation. The formation of zinc phosphates has been investigated as a function of the pH of the starting mixture (4.5–14.0) and of the temperature of calcination (from 150 to 750 °C). A material composed of hopeite (Zn₃(PO₄)₂·4H₂O) and casein was obtained after synthesis at pH 4.5 and 100 °C from a mixture of casein and zinc nitrate solutions. Macroporous zinc phosphates composed of α-Zn₃(PO₄)₂ and α-Zn₂P₂O₇ with large porous size distribution (pore diameter between 350 to 1000 nm) were successfully obtained after the complete casein decomposition at 750 °C. Samples were characterized by X-ray powder diffraction, solid-state ³¹P NMR spectroscopy, thermal analysis, scanning electron microscopy, nitrogen adsorption, and by fluorescence spectroscopy. The macroporous zinc phosphates have a good stability in water for at least 24 h with no detectable change in their structure, porosity, and crystal morphology

One-Pot Noninjection Route to CdS Quantum Dots via Hydrothermal Synthesis

Water-dispersible CdS quantum dots (QDs) emitting from 510 to 650 nm were synthesized in a simple one-pot noninjection hydrothermal route using cadmium chloride, thiourea, and 3-mercaptopropionic acid (MPA) as starting materials. All these chemicals were loaded at room temperature in a Teflon sealed tube and the reaction mixture heated at 100 °C. The effects of CdCl₂/thiourea/MPA feed molar ratios, pH, and concentrations of precursors affecting the growth of the CdS QDs, was monitored via the temporal evolution of the optical properties of the CdS nanocrystals. High concentration of precursors and high MPA/Cd feed molar ratios were found to lead to an increase in the diameter of the resulting CdS nanocrystals and of the trap state emission of the dots. The combination of moderate pH value, low concentration of precursors and slow growth rate plays the crucial role in the good optical properties of the obtained CdS nanocrystals. The highest photoluminescence achieved for CdS@MPA QDs of average size 3.5 nm was 20%. As prepared colloids show rather narrow particle size distribution, although all reactants were mixed at room temperature. CdS@MPA QDs were characterized by UV–vis and photoluminescence spectroscopy, powder X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectrometry and MALDI TOF mass spectrometry. This noninjection one-pot approach features easy handling and large-scale production with excellent synthetic reproducibility. Surface passivation of CdS@MPA cores by a wider bandgap material, ZnS, led to enhanced luminescence intensity. CdS@MPA and CdS/ZnS@MPA QDs exhibit high photochemical stability and hold a good potential to be applied in optoelectronic devices and biological applications