title: Effect of factors on decolorization of azo dye methyl orange by oxone/natural sunlight in aqueous solution.
abstract: OBJECTIVE
  The oxone process for azo dye decolorization has drawbacks such as difficulties with reuse, risks of secondary pollution, and high costs associated with UV irradiation. This study aims to explore the use of oxone for decolorization in the absence of catalyst and under natural sunlight conditions (i.e., oxone/natural sunlight system) and evaluate the impacts of operating parameters (reagent dosage, initial methyl orange (MO) concentration, and initial pH) and coexisting substances (humic acid, NO(3)(-), metal ions) on the system's decolorization efficiency.
  
  
  METHODS
  Four levels of operating parameters were configured under a Taguchi L(16) orthogonal array design to examine their effects on decolorization efficiency. Fractional factional design was then used to derive the optimal combination of operating parameters, under which the effects of coexisting substances at various concentrations were examined. In addition, H(2)O(2), CH(3)OH, and (CH(3))(3)COH were used to derive the possible reaction mechanisms in the oxone/sunlight system, while ultrasonic power was used to shorten the reaction time.
  
  
  RESULTS
  In the oxone/sunlight system, (1) the MO decolorization efficiency reaches 96.4% under the optimal operating conditions: initial concentration, 100 mg L(-1); initial pH 6.04; dosage of reagent, 3 mmol L(-1); and reaction time, 30 min. (2) Coexisting substances do not affect the overall decolorization efficiency. (3) The decolorization of MO in the oxone/sunlight system takes place mainly via oxidation by SO(4)·⁻. (4) Ultrasonic irradiation could remarkably accelerate the MO decolorization process.
  
  
  CONCLUSIONS
  Effective for MO decolorization, the oxone/sunlight system improves over the traditional oxone process with advantages of lower costs and avoiding secondary pollution by catalyst.
authors.affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210093, People's Republic of China. ldqun@yahoo.com.cn
authors.forename: Qun
authors.initials: Q
authors.lastname: Liu
authors.forename: Zheng
authors.initials: Z
authors.lastname: Zheng
authors.forename: Xiaoying
authors.initials: X
authors.lastname: Yang
authors.forename: Xingzhang
authors.initials: X
authors.lastname: Luo
authors.forename: Jibiao
authors.initials: J
authors.lastname: Zhang
authors.forename: Binguo
authors.initials: B
authors.lastname: Zheng
mesh_terms: D001391:Azo Compounds / Q000737:chemistry / Q000528:radiation effects*; D002384:Catalysis; D004396:Coloring Agents / Q000737:chemistry / Q000528:radiation effects; D006861:Hydrogen Peroxide / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007220:Industrial Waste / Q000032:analysis; D012996:Solutions / Q000737:chemistry; D013464:Sulfuric Acids / Q000737:chemistry*; D013472:Sunlight; D014465:Ultrasonics; D014867:Water / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry / Q000528:radiation effects*
chemical_list: D001391:Azo Compounds; D004396:Coloring Agents; D007220:Industrial Waste; D012996:Solutions; D013464:Sulfuric Acids; D014874:Water Pollutants, Chemical; D014867:Water; C100258:methyl orange; D006861:Hydrogen Peroxide; C048813:potassium peroxymonosulfuric acid