Adsorption of organic acids on magnetite nanoparticles, pH-dependent colloidal stability and salt tolerance

The adsorption of different organic acids and their influence on the pH-dependent charging, salt tolerance and so the colloidal stability of magnetite nanoparticles are compared. Adsorption isotherms of citric acid - CA, gallic acid - GA, poly(acrylic acid) - PAA, poly(acrylic-co-maleic acid) - PAM and humic acid - HA were measured. The pH-dependent charge state of MNPs was characterized by electrophoretic mobility and their aggregation by dynamic light scattering. The salt tolerance was tested in coagulation kinetic experiments. Although the adsorption capacities, the type of bonding (either H-bonds or metal ion-carboxylate complexes) and so the bond strengths are significantly different, the following general trends have been found. Small amount of organic acids at pH. <. ~8 (the pH of PZC of magnetite) - relevant condition in natural waters - only neutralize. s the positive charges, and so promotes the aggregation and sedimentation of nanoparticles. Greater amounts of organic acid, above the charge neutralization, cause the sign reversal of particle charge, and at high overcharging promote stabilization and dispersing. The thicker layer of PAA, PAM and HA provides better electrosteric stability than CA and GA. GA undergoes surface polymerization, thereby improving stabilization. The organic acids studied here eliminate completely the pH sensitivity of amphoteric magnetite, but only the polyanionic coverage provides significant increase in resistance against coagulating effects of salts at neutral pH commonly prevailing in natural waters

Modeling magnetic nanopolymer flow with induction and nanoparticle solid volume fraction effects : solar magnetic nanopolymer fabrication simulation

A mathematical model is presented for the nonlinear steady, forced convection, hydromagnetic flow of electro-conductive magnetic nano-polymer with magnetic induction effects included. The transformed two-parameter, non-dimensional governing partial differential equations for mass, momentum, magnetic induction and heat conservation are solved with the local non-similarity method (LNM) subject to appropriate boundary conditions. Keller’s implicit finite difference “box” method (KBM) is used to validate solutions. Computations for four different nanoparticles and three different base fluids are included. Silver nanoparticles in combination with various base fluids enhance temperatures and induced magnetic field and accelerate the flow. An elevation in magnetic body force number decelerates the flow whereas an increase in magnetic Prandtl number elevates the magnetic induction. Furthermore, increasing nanoparticle solid volume fraction is found to substantially boost temperatures. Applications of the study arise in advanced magnetic solar nano-materials (fluids) processing technologies

Colloidal stability of carboxylated iron oxide nanomagnets for biomedical use

Magnetite nanoparticles (MNP) were synthesized and stabilized with carboxylated compounds citric acid - CA, poly(acrylic acid) - PAA, poly(acrylic acid-co-maleic acid) - PAM, humic acid - HA and gallic acid - GA (polymerizing in situ on the surface). Adsorption isotherms and bonding feature were determined and used to explain the changes in charge and aggregation states and salt tolerance of the MNPs. The thicker layer of macromolecular acids PAA, PAM and HA provides better stability at physiological pH and salt concentration compared to the CA and GA coatings. In addition, Fe(III)-CA complexation promotes the dissolution of the nanoparticles. The biocompatibility of the polyacid-coated MNPs was tested in cell proliferation experiments

Designed polyelectrolyte shell on magnetite nanocore for dilution-resistant biocompatible magnetic fluids.

Magnetite nanoparticles (MNPs) coated with poly(acrylic acid-co-maleic acid) polyelectrolyte (PAM) have been prepared with the aim of improving colloidal stability of core-shell nanoparticles for biomedical applications and enhancing the durability of the coating shells. FTIR-ATR measurements reveal two types of interaction of PAM with MNPs: hydrogen bonding and inner-sphere metal-carboxylate complex formation. The mechanism of the latter is ligand exchange between uncharged -OH groups of the surface and -COO(-) anionic moieties of the polyelectrolyte as revealed by adsorption and electrokinetic experiments. The aqueous dispersion of PAM@MNP particles (magnetic fluids - MFs) tolerates physiological salt concentration at composition corresponding to the plateau of the high-affinity adsorption isotherm. The plateau is reached at small amount of added PAM and at low concentration of nonadsorbed PAM, making PAM highly efficient for coating MNPs. The adsorbed PAM layer is not desorbed during dilution. The performance of the PAM shell is superior to that of poly(acrylic acid) (PAA), often used in biocompatible MFs. This is explained by the different adsorption mechanisms; metal-carboxylate cannot form in the case of PAA. Molecular-level understanding of the protective shell formation on MNPs presented here improves fundamentally the colloidal techniques used in core-shell nanoparticle production for nanotechnology applications