Optimization of conditions for preparation of activated carbon from coconut husk fiber using responses from measurements of surface area and adsorption by Al-Aoh, H.A., Mihaina, I.A.M., Alzuaibr, F.M., Althaqafy, A.D., Maah, M.J., Yahya, R., Abas, M.R.B., Tyagi, I., Agarwal, S., Gupta, V.K.