For Adsorption phenomenon:
Adsorption leads to a decrease in the residual forces on the surface of the adsorbent. This causes a decrease in the surface energy of the adsorbent. Therefore, adsorption is always exothermic and ΔH is negative.
And for reaction to occur ΔG should be negative so by equation ΔG=ΔH−TΔS, ΔS should be negative.