title: Optimizing photo-mineralization of aqueous methyl orange by nano-ZnO catalyst under simulated natural conditions.
abstract: BACKGROUND
  Photo-degradation of organic contaminants into non-hazardous mineral compounds is emerging as a strategy to purify water and environment. Tremendous research is being done using direct solar light for these purposes. In this paper we report on optimum conditions for complete mineralization of aqueous methyl orange using lab-prepared ZnO nanopowder catalyst under simulated solar light.
  
  
  RESULTS
  Nano-scale ZnO powder was prepared in the lab by standard methods, and then characterized using electronic absorption spectra, photolumenscence emission (PL) spectra, XRD, and SEM. The powder involved a wurtzite structure with ~19 nm particles living in agglomerates. Photo-degradation progressed faster under neutral or slightly acidic conditions which resemble natural waters. Increasing catalyst concentration increased photodegradation rate to a certain limit. Values of catalyst turn over number and degradation percentage increased under higher light intensity, whereas the quantum yield values decreased. The photocatalytic efficiency of nano-ZnO powders in methyl orange photodegradation in water with solar light has been affected by changing the working conditions. More importantly, the process may be used under natural water conditions with pH normally less than 7, with no need to use high concentrations of catalyst or contaminant. The results also highlight the negative impact of possible high concentrations of CO2 on water purification processes. Effects of other added gaseous flows to the reaction mixture are also discussed.
  
  
  CONCLUSIONS
  ZnO nano-particles are useful catalyst for complete mineralization of organic contaminants in water. Photo-degradation of organic contaminants with ZnO nano-particles, methyl orange being an example, should be considered for future large scale water purification processes under natural conditions.
authors.affiliation: SSERL, Department of Chemistry, An-Najah National University, Nablus, Palestine.
authors.forename: Ahed
authors.initials: A
authors.lastname: Zyoud
authors.affiliation: SSERL, Department of Chemistry, An-Najah National University, Nablus, Palestine.
authors.forename: Amani
authors.initials: A
authors.lastname: Zu'bi
authors.affiliation: College of Pharmacy and Nutrition, University of Saskatchewan, 116 Thorvaldson Building, Saskatoon, S7N 5C9 Canada.
authors.forename: Muath H S
authors.initials: MH
authors.lastname: Helal
authors.affiliation: Dansuk Industrial Co, LTD. #1239-5, Jeongwang-Dong, Shiheung-Si, Kyonggi-Do 429-913 South Korea.
authors.forename: DaeHoon
authors.initials: D
authors.lastname: Park
authors.affiliation: Institut de Chimie de la Matie're Condense'ıe de Bordeaux (ICMCB), 87 Avenue du Dr. A Schweitzer, Pessac, 33608 France.
authors.forename: Guy
authors.initials: G
authors.lastname: Campet
authors.affiliation: SSERL, Department of Chemistry, An-Najah National University, Nablus, Palestine.
authors.forename: Hikmat S
authors.initials: HS
authors.lastname: Hilal
keywords: Contaminant mineralization; Methyl orange; Solar simulated light; ZnO nanopowder