100ppm phenol take to adsorbent 0.4g

Removal efficiency (expressed in %) improves if dosage is increased. However, removal capacity (expressed, for example, in mg/g) decreases if dosage is increased. And you have to keep in mind that higher dosage will have higher ability to change pH of the solution. My personal opinion is that in practice you have to choose dosage depending on the results obtained in pH studies (if pH has effect on the sorption capacity). That is - in none of the pH values you should not reach 100 % removal.