Synthetic incorporation of palladium-nickel bimetallic nanoparticles within mesoporous silica/silica nanoparticles as efficient and cheaper catalyst for both cationic and anionic dyes degradation

Adsorption studies of the hybrid material obtained from the functionalization of silica with alfa and gamma cyclodextrins

The generation of residues containing dyes by industrial sectors has been mobilizing scientists to develop methodologies capable of treating water containing these contaminants. Adsorption is an option to remove these molecules from the aqueous medium and, for this study, the composites between silica and cyclodextrins alpha (α-CDSI) and gamma (γ-CDSI) were used to capture methylene blue. Adsorption was spontaneous for both composites (ΔG < 0) and characterized as exothermic and of a physical nature, with ΔH of -17.68 and -12.13 kJ mol^-1 for α-CDSI and γ-CDSI, respectively. Adsorption took place over a wide pH range, with an efficiency of approximately 96%, reaching equilibrium at 5 minutes. The adsorption kinetics was described by the pseudo-second-order model (R² > 0.999) and the adsorption isotherms showed that the process must occur mainly by dye complexation in the cyclodextrins cavities. The q_m values obtained were 210.8 and 205.2 mg g^-1 for α-CDSI and γ-CDSI, respectively; the Sips and Temkin models were the ones that best fit the experimental data. The deposition and interactions of the dye with the adsorbent surface were confirmed by the analysis of the IR spectra. Desorption studies showed that the material maintained its adsorption capacity of around 90% until the fourth adsorption/desorption cycle. Thus, the materials produced showed to efficiently remove methylene blue and that composite reuse is a viable process for application in dye removal.

Organotrialkoxysilane-Functionalized Noble Metal Monometallic, Bimetallic, and Trimetallic Nanoparticle Mediated Non-Enzymatic Sensing of Glucose by Resonance Rayleigh Scattering

Organotrialkoxysilanes like 3-aminopropyltrimethoxysilane (3-APTMS)-treated noble metal cations were rapidly converted into their respective nanoparticles in the presence of 3-glycidoxypropylytrimethoxysilane (3-GPTMS). The micellar activity of 3-APTMS also allowed us to replace 3-GPTMS with other suitable organic reagents (e.g., formaldehyde); this approach has significant advantages for preparing bimetallic and trimetallic analogs of noble metal nanoparticles that display efficient activity in many practical applications. The formation of monometallic gold, silver, and palladium nanoparticles, bimetallic Ag-Pd, and Au-Pd nanoparticles at various ratios of noble metal cations, and trimetallic Ag-Au-Pd nanoparticles were studied; their biocatalytic activity in non-enzymatic sensing of glucose based on monitoring synchronous fluorescence spectroscopy (SFS) was assessed. Of these nanoparticles, Au-Pd made with an 80:20 Au:Pd ratio displayed excellent catalytic activity for glucose sensing. These nanoparticles could also be homogenized with Nafion to enhance the resonance Rayleigh scattering (RRS) signal. In this study, the structural characterization of noble metal nanoparticles as well as bi- and tri-metallic nanoparticles in addition to their use in non-enzymatic sensing of glucose are reported.