CWPO Degradation of Methyl Orange at Circumneutral pH: Multi-Response Statistical Optimization, Main Intermediates and by-Products

Abstract

The catalytic wet peroxide oxidation (CWPO) of the industrial azo-dye methyl orange (MO) activated by an Al/Fe-pillared clay catalyst was optimized by the Response-Surface Methodology (RSM). Three sequential sets of factorial 2k central composite experiments were required for the full optimization of the process; catalyst loading and stoichiometric dose of hydrogen peroxide were the experimental factors studied through different times of reaction by means of all, Dissolved Organic Carbon (DOC) removal, Total Nitrogen (TN) removal, reacted fraction of hydrogen peroxide, and decolorization as experimental responses to be maximized. The resulting single-response RSM optimums were combined in a multi-response Desirability function ruling out the differential effect of adsorption on the catalyst's surface by defining all responses per gram of clay catalyst. Former two statistical sets of experiments (DOE-1 and DOE-2) showed the CWPO degradation of MO to get favored at increasing both catalyst loading and time of reaction (up to 180 min). Afterwards, third final design of experiments (DOE-3) displayed 75% of DOC removal, 78% of TN removal, 97% of reacted H2O2, and 95% of decolorization by using a catalyst loading of 5.0 g/L of Al/Fe-PILC together with just 50% of the stoichiometric amount of H2O2. The multi-response optimum conditions based on the Desirability function showed excellent fitting explaining at least 99.3% of the optimal overall responses at 95% of confidence. A further analysis revealed that no one of the non-controllable variables under real conditions of industrial wastewater treatment (covariates): starting total organic carbon (TOC) (2.0–20 mg/L), temperature (5.0–25°C) or circumneutral pH (6.0–9.0), exhibited statistically significant effect (P > 0.05), suggesting the system to be almost insensitive against them within studied range of close to ambient conditions in the tropic. Finally, HPLC/PDA and GC/FID measurements identified phenol, cyclohexa-2,5-diene-1,4-dione, phenylamine, N-methylaniline and N,N-dimethylaniline in very low concentrations as main intermediates in the CWPO degradation of MO, which nevertheless disappeared over 90 min of treatment. Meanwhile, 4-aminobenzenesulfonic and oxalic acids were recorded as unique by-products at final time of reaction, but both of them fairly less toxic than the starting azo-dye.

Green Synthesis of Zinc Oxide Nanoparticles Using Salvia officinalis Leaf Extract and Their Photocatalytic and Antifungal Activities

“…Aromatic amines (phenylamine, N-methylaniline, and N,N-dimethylaniline) are then formed at early times of reaction but rapidly vanish. Finally, short-chain carboxylic acids, mainly oxalic acid and 4-aminobenzenesulfonic acid, are generated as final byproducts together with carbon dioxide, molecular nitrogen, and water as mineralization products [ 73 ]. …”

Copper nickel co-impregnation of Moroccan yellow clay as promising catalysts for the catalytic wet peroxide oxidation of caffeine

“…K is the number of the optimized factors and ε is the random error. Hence, NemrodW software was used to process and design the experiments data Table 1 [32,33].…”

“…Central composite, Doehlert, and Box-Behnken are three classes of response surface designs. Yet, Box-Behnken design is more advantageous because it creates an experimental design with a few test runs, which makes the experiments economically feasible and beneficial [32,33]. As far as we know, and according to the extensive literature review, CWPO of CAF onto CuNi-YC was not fully investigated.…”

Catalytic Oxidation of Ponceau 4R in Aqueous Solution using Iron-impregnated Al-pillared Bentonite: Optimization of the Process

“…Decolorization was calculated from Equation ( 5), where C0 is the dye concentration at t = 0 and Ct, the dye concentration at time t: (5) As the oxidation reactions were carried out with an excess of H2O2, between 0.4-1.0 mL sodium sulfite (1.5 mol/L) was added at the end of the reaction (t = 5 h) to instantaneously stop the reaction. This eliminates residual H2O2 that interferes with chemical oxygen demand (COD), total organic carbon (TOC) and total nitrogen (TN) measurements in Fenton processes [43][44][45]. Total organic carbon (TOC) removal or degree of mineralization was quantified by a TOC analysis at the beginning and, at the end of the reaction, using a Multi N/C 3100 TOC analyzer (Analytik Jena, Germany) equipped with a nondispersive infrared detector.…”