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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 (2 = 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. Conclusion 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.

The global attention has been focused on degradation of the environmental organic pollutants through green methods such as advanced oxidation processes (AOPs) under sunlight. However, AOPs have not yet been efficient in function of the photocatalyst that has been used. In this work, firstly, CaCu3Ti4O12 nanocomposite was simultaneously synthesized and decorated in different amounts of graphene oxide to enhance photodegradation of the organics. The result of the photocatalyst characterization showed that the sample with 8% graphene presented optimum photo-electrical properties such as low band gap energy and a great surface area. Secondly, the photocatalyst was applied for photodegradation of an organic model in a batch photoreactor. Thirdly, to scale up the process and optimize the efficiency, the photodegradation was modeled by multivariate semi-empirical methods. As the optimized condition showed, 45 mg/L of the methylorange has been removed at pH 5.8 by 0.96 g/L of the photocatalyst during 288 min of the light irradiation. Moreover, the photodegradation has been scaled up for industrial applications by determining the importance of the input effective variables according to the following organics order>photocatalyst>pH> irradiation time. [ABSTRACT FROM AUTHOR]

Environmental organic pollutants are mineralized to harmless final-products such H2O and CO2by photocatalytic advanced oxidation processes (AOPs). In photocatalytic-AOPs, an appropriate concentration ofp-Cresol was mixed with certain amount of ZnO in 500 mL deionized water according to an experimental-design. Then the mixture was irradiated by UV-A lamp at different pH for 6 h. At specific time intervals, the sampling was carried out to calculate the efficiency of the photodegradation. Therefore, the photodegradation as a system consists of four input variables such irradiation time, pH, amount of ZnO andp-Cresol’s concentration while the only output was the efficiency. In this work, the system was modeled and optimized by semi-empirical response surface methodology. To obtain the empirical responses, the design was performed in laboratory. Then observed responses were fitted with several well-known models by regression process to suggest a provisional model. The suggested model which was validated by several statistical evidence, predicted the desirable condition with higher efficiency. The predicted condition consisted of irradiation time (280 min), pH (7.9), photocatalyst (1.5 g L−1),p-Cresol (95 mg L−1) and efficiency (95%) which confirmed by further experiments. The closed confirmation results has presented the removal (efficiency = 94.7%) of higherp-Cresol concentration (95 mg L−1) at shorter irradiation time in comparison with the normal photodegradation efficiency (97%) which included irradiation time (300 min), pH (7.5), photocatalyst amount (1.5 g L−1) andp-Cresol (75 mg L−1). As a conclusion, the modeling which is able to industrial scale up succeeded to remove higher concentration of environmental organic pollutants with ignorable reduction of efficiency. [ABSTRACT FROM PUBLISHER]

The effective removal of m-cresol is currently both an environmental problem and economic challenge. ZnO removed several organic contaminants under UV irradiation; however, UV equipment can be very expensive to operate on a large scale. Therefore, using a sunlight photocatalyst offers a way to overcome both problems. This paper shows how degradation of m-cresol was carried out, in the presence of visible light (46% sunlight); by a 1.0 wt% Mn doped ZnO as photocatalyst. To measure the efficiency of photodegradation, different variables including amount of photocatalyst, concentration of m-cresol and pH were studied. The residue of m-cresol and mineralization were measured using UV-VIS spectrophotometer and TOC analyzer, respectively. The intermediate was detected by Ultra Performance liquid Chromatography (UPLC). The results showed that m-cresol has high stability in the presence of visible light but absence of photocatalyst, and adsorption of m-cresol over photocatalyst was 5%. In optimum conditions, the amount of photocatalyst and concentration of m-cresol were 1.5 g/L and 35 ppm, respectively. Mcresol photodegradation was favorable in the pH range of 6-9. TOC studies showed that 68% of total organic carbon was excited from solution during irradiation time. The detected intermediates were 2,5-hydroxy-benzalde-hyde and 3,5-hydroxytoluene. Reusability showed no significant reduction in photocatalytic performance/m-cresol photodegradation. This study indicates that 1.0 Mn-doped ZnO can remove m-cresol from wastewater under visible light irradiation, being more economic than UV light, and this methodology could be applied on an industrial scale. [ABSTRACT FROM AUTHOR]