DNOC a nitro aromatic pesticide has several uses in the fields of agriculture and horticulture. Because DNOC is a weak acid (pK[subscript a]= 4.4), we hypothesized that pH would be the dominant state variable controlling sorption. We quantified the effect of pH, saturating cation (K+ and Ca2+) and freeze-drying on adsorption of DNOC by reference smectites (SWy-2 and SAz-1) in dilute aqueous suspensions using a batch equilibration technique. Suspensions and DNOC were both pH adjusted. Systems were equilibrated by shaking for 24 hrs at 250C then centrifuged, filtered and pH tested. Adsorption data revealed nearly 100 % sorption of DNOC by K-SWy-2 at pH 3 which decreased to about 60 % at pH 7. Sorption of DNOC on K-SAz-1 decreased from about 90 % at pH 3 to 30 % at pH 7. About 80 % of added DNOC was sorbed by Ca-SWy-2 at pH 3 but sorption decreased to about 15 % between pH 4 and pH 7. Ca-SAz-1 sorbed about 15 % of added DNOC over the entire pH range. Slightly larger amounts of DNOC were adsorbed by the never-dried smectites compared to the freeze-dried re-hydrated smectites. ICP-AES results of the filtered supernatants of K-SAz-1-DNOC systems revealed co-adsorption of DNOC with K+ through the entire pH range. ICP-AES data for filtered supernatants of Ca-SWy-2-DNOC systems revealed little or no co-adsorption of Ca2+ with DNOC. FTIR analyses of smectite films showed a layer charge density influenced spectral shift of the v[subscript sym] (NO) band of DNOC. This indicated a strong interaction between a cation in the high-charge-density smectite and the NO2 group of DNOC. XRD analysis of the smectite suspensions suggest that DNOC is primarily adsorbed on the external surfaces of suspended K- and Ca-smectite colloids. Peak shifts and asymmetric peaks observed for air-dried and oven-dried K-smectite films; suggest that DNOC occupied the interlayer of K+-smectites. Drying K-smectite suspensions caused DNOC present on external surfaces of small quasicrystals to become trapped within the interlayers of newly formed larger quasicrystals. XRD patterns of air-dried and oven-dried Ca-smectite films did not reveal peak shifts indicating the absence of DNOC from interlayers of Ca-smectites.