Figure 3.

(a) Transmission-mode XRD diffractograms of AcidBir exposed to 0–98% RH and (b) result of d₀₀₁ basal spacing (left ordinate axis) analyses from these data (filled square = adsorption; open square = desorption), also showing uncertainties. The model predictions of d₀₀₁ in (b) (full line for adsorption; dashed for desorption) were taken from the Dubinin–Asthakhov theory⁴⁶ term derived from the microgravimetric water binding data (Figure 2a). This model prediction of the hydration fraction (right ordinate axis) was scaled such that d₀₀₁ = 0.690 nm at 0 W (0 H₂O/UC) and d₀₀₁ = 0.735 nm at 1 W (1.33 H₂O/UC). Diffractograms for δ-MnO₂ were of insufficient quality to be shown here, due to the small particle size.