title: Interactions between photodegradation components.
abstract: BACKGROUND
  The interactions of p-cresol photocatalytic degradation components were studied by response surface methodology. The study was designed by central composite design using the irradiation time, pH, the amount of photocatalyst and the p-cresol concentration as variables. The design was performed to obtain photodegradation % as actual responses. The actual responses were fitted with linear, two factor interactions, cubic and quadratic model to select an appropriate model. The selected model was validated by analysis of variance which provided evidences such as high F-value (845.09), very low P-value (<.0.0001), non-significant lack of fit, the coefficient of R-squared (R2 = 0.999), adjusted R-squared (Radj2 = 0.998), predicted R-squared (Rpred2 = 0.994) and the adequate precision (95.94).
  
  
  RESULTS
  From the validated model demonstrated that the component had interaction with irradiation time under 180 min of the time while the interaction with pH was above pH 9. Moreover, photocatalyst and p-cresol had interaction at minimal amount of photocatalyst (< 0.8 g/L) and 100 mg/L p-cresol.
  
  
  CONCLUSIONS
  These variables are interdependent and should be simultaneously considered during the photodegradation process, which is one of the advantages of the response surface methodology over the traditional laboratory method.
authors.affiliation: Material Synthesis and Characterization Laboratory, Institute of Advanced Technology, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia. yadollahabdolla@putra.upm.edu.my.
authors.forename: Yadollah
authors.initials: Y
authors.lastname: Abdollahi
authors.forename: Azmi
authors.initials: A
authors.lastname: Zakaria
authors.forename: Khamirul Amin
authors.initials: KA
authors.lastname: Matori
authors.forename: Kamyar
authors.initials: K
authors.lastname: Shameli
authors.forename: Hossein
authors.initials: H
authors.lastname: Jahangirian
authors.forename: Majid
authors.initials: M
authors.lastname: Rezayi
authors.forename: Tahereh
authors.initials: T
authors.lastname: Abdollahi