This is a Type II isotherms, i.e. nonporous or macroporous adsorbents with relatively weak adsorption, where multilayer adsorption and capillary condensation take place. The small adsorbed volume confirms the absence of inner porosity.

Hi..

you can see IUPAC classification for adsorption isotherm and compared with your figure, anyway ,your fig. is type II and hysteresis loop is type-H3

Omar Al-Dulaimi Thanks for your reply, but my understanding that type II doesn't have a hysteresis to start with and that what confused me. I think may be and I'm not sure could it be a mixture of macro and a little bit of mesopores that account for the small hysteresis???

I'm just wondering.

Thanks

First, this is not a BET curve, this is adsorption-desorption isotherms. Apparently, the isotherm corresponds to the nonporous or macroporous material. BET plot is calculated from the adsoprtion data in a range 0.05-0.30 p/p_0. Also, I advice you to pay attention to the sample preparation before adsorption measurements to get proper data. I recommend to dry your Mg(OH)2 sample at ca. 200 C for 2-3 hours before measurement.

I understand you questionning about the small difference between adsorption and desorption isotherm between P/P°=0.85 and 1. However, if you look closely at your data, you have a "missing" point on the desorption curve (at P/P° close to 0.95). If this point had been measured the two curves could overlay. Moreover, even if you observe a "real" hysteresis loop between adsorption and desorption isotherm at high p/p° values, to assign it to large mesopores, you must verify that there is a plateau at high p/p°. If this plateau is absent, then the hysteresis is likely due interparticular porosity (pores created between two particles that are in contact but not "attached" together