Surface functionalization of nanodiamond with phenylphosphonate.

HYPOTHESIS:This work explores arylation of oxidized nanodiamond (OND) and carboxylated nanodiamond (CND) using phenylphosphonate (PPA) to produce PPA-grafted nanodiamond (PPA@ND). The specific hypothesis is that PPA can be readily grafted onto the surfaces of OND and CND particles via the nanodiamonds' reactive oxygen-rich surface functional groups. EXPERIMENTS:This work explores the effect of varying reaction conditions (reactant ratio, heat, sonication) on PPA graft density and grafting mode. The products were characterized by a variety of techniques including: (31)P MAS NMR and FTIR to confirm PPA grafting, XPS to estimate PPA grafted amounts, and TGA to assess thermal stability. The utility of PPA functionalization for improving ND dispersion in organic solvents was evaluated using dynamic light scattering. FINDINGS:The results confirm PPA grafting on both OND and CND, quantify the extent of PPA grafting, and suggest primarily bidentate grafting. For PPA grafting on OND, the grafted amount does not depend on PPA:ND ratio, application of heat, or use of sonication. The grafted amount of PPA on CND was significantly lower than that on OND. TGA data indicates that grafted PPA improves the thermal stability of both OND and CND. The starting OND disperses in water as aggregates with approximately 100 nm particle size. However, PPA-grafted OND does not disperse at all in water: thus grafted PPA changes the ND surface from hydrophilic to hydrophobic. PPA@OND prepared without sonication does not completely disperse in either DMF or toluene. Only PPA@OND prepared with sonication disperses well in these solvents, suggesting that sonication promotes more complete exposure of the ND surface to PPA grafting.