Despite ND's many possible attributes, colloidal stability among vendor received, unmodified nanodiamonds is typically quite low. In general, NDs produced by detonation of carbon-containing explosives are purified from the soot followed by removal of metallic impurities at an industrial scale. The result is NDs containing different surface chemistries and various aggregate sizes. This nonuniformity leads to various levels of dispersivity and stability among ND colloids. Adding to this, ND properties may vary between vendors or even batches.
Appropriate surface modification can be used to overcome the inconsistencies of NDs and even tailor ND properties for specific end uses. Modification of NDs takes place by either chemical or physical means, i.e., plasma treatments, fractionalization, or surface coatings. In the present research, assessment of modification techniques was characterized by ND stability, or the ability of NDs to remain well suspended in aqueous solution. Stability was evaluated by zeta potential measurements at a neutral pH and by titration over a wide range of pH. Titration demonstrated that for many samples a relatively high zeta potential can be preserved over a wide pH range, indicating high colloidal stability in these conditions. Observations of pH titration are essential in developing NDs for enterosorbent applications.
As studies of colloid stability continue, research is also expanding to test the adsorption properties of these nanoparticles with respect to Aflatoxin B1, a harmful low molecular weight byproduct of mold growth. It will be important to determine if there is a correlation between the stability of ND suspensions and adsorption of aflatoxin. Initial adsorption studies already determined that ND type and modification method affect the adsorption capacity of aflatoxin, suggesting that ND surface chemistry can be controlled to increase sorption efficiency.