Kinetics and mechanism of photocatalytic degradation of metobromuron by TiO2 in simulated sunlight

Reduction of pesticide residues in Chrysanthemum morifolium by nonthermal plasma-activated water and impact on its quality

This study investigated the efficiency of plasma-activated water (PAW) on the reduction of pesticides, namely, metribuzin and metobromuron, and the effect of PAW treatment on the quality of fresh chrysanthemums. The reduction efficiencies reached 74.3% for metribuzin and 38.2% for metobromuron after 240 s of PAW treatment. Compared with reverse osmosis (RO) water, PAW achieved significantly higher pesticide reductions because of its higher acidity, enhanced oxidizing ability, and increased formation of reactive species. Moreover, when compared with metobromuron, metribuzin was reduced more efficiently irrespective of the RO water or PAW treatments because of its higher water solubility, lower log octanol-water partition coefficient, and more oxidizable chemical structure. Additionally, the PAW treatment did not cause adverse changes to the chrysanthemums' color, total flavonoid content, radical scavenging, or metal chelating activities, but it did cause a slight decrease in the chrysanthemums' aroma compounds and total reducing power. This study successfully demonstrated the effectiveness of PAW for reducing pesticides in herbal flowers like chrysanthemums and reveals PAW's promising potential to treat foods with non-smooth surfaces.

Degradation of nitrogen-containing hazardous compounds using advanced oxidation processes: A review on aliphatic and aromatic amines, dyes, and pesticides

Nitrogen-containing amino and azo compounds are widely used in textile, agricultural and chemical industries. Most of these compounds have been demonstrated to be resistant to conventional degradation processes. Advanced oxidation processes can be effective to mineralize nitrogen-containing compounds and improve the efficacy of overall treatment schemes. Due to a global concern for the occurrence of toxic and hazardous amino-compounds and their harmful degradation products in water, it is important to develop technologies that focus on all the aspects of their degradation. Our focus is to present a state-of-the-art review on the degradation of several amine- and azo-based compounds using advanced oxidation processes. The categories reviewed are aromatic amines, aliphatic amines, N-containing dyes and N-containing pesticides. Data has been compiled for degradation efficiencies of each process, reaction mechanisms focusing on specific attack of oxidants on N atoms, the effect of process parameters like pH, initial concentration, time of treatment, etc. and identification of intermediates. Several AOPs have been compared to provide a systematic overview of available literature that will drive essential aspects of future research on amine-based compounds. Ozone is observed to be highly reactive to most amines, dyes and pesticides, followed by Fenton processes. Degradation of amines is highly sensitive to pH and mechanisms differ at different pH values. Cavitation is a promising alternative pre-treatment method for cost reduction. Hybrid methods under optimized conditions are demonstrated to give synergistic effects and must be tailored for specific effluents in question. In conclusion, even though nitrogen-containing compounds are recalcitrant in nature, the use of advanced oxidation processes at carefully established optimum conditions can yield highly efficient degradation of the compounds.

Carbofuran removal in continuous-photocatalytic reactor: Reactor optimization, rate-constant determination and carbofuran degradation pathway analysis

Carbofuran (CBF) removal in a continuous-flow photocatalytic reactor with granular activated carbon supported titanium dioxide (GAC-TiO₂) catalyst was investigated. The effects of feed flow rate, TiO₂ concentration and addition of supplementary oxidants on CBF removal were investigated. The central composite design (CCD) was used to design the experiments and to estimate the effects of feed flow rate and TiO₂ concentration on CBF removal. The outcome of CCD experiments demonstrated that reactor performance was influenced mainly by feed flow rate compared to TiO₂ concentration. A second-order polynomial model developed based on CCD experiments fitted the experimental data with good correlation (R² ∼ 0.964). The addition of 1 mL min^-1 hydrogen peroxide has shown complete CBF degradation and 76% chemical oxygen demand removal under the following operating conditions of CBF ∼50 mg L^-1, TiO₂ ∼5 mg L^-1 and feed flow rate ∼82.5 mL min^-1. Rate constant of the photodegradation process was also calculated by applying the kinetic data in pseudo-first-order kinetics. Four major degradation intermediates of CBF were identified using GC-MS analysis. As a whole, the reactor system and GAC-TiO₂ catalyst used could be constructive in cost-effective CBF removal with no impact to receiving environment through getaway of photocatalyst.

Photocatalytic degradation of carbofuran by TiO2-coated activated carbon: Model for kinetic, electrical energy per order and economic analysis

The photocatalytic removal of carbofuran (CBF) from aqueous solution in the presence of granular activated carbon supported TiO2 (GAC-TiO2) catalyst was investigated under batch-mode experiments. The presence of GAC enhanced the photocatalytic efficiency of the TiO2 catalyst. Experiments were conducted at different concentrations of CBF to clarify the dependence of apparent rate constant (kapp) in the pseudo first-order kinetics on CBF photodegradation. The general relationship between the adsorption equilibrium constant (K) and reaction rate constant (kr) were explained by using the modified Langmuir-Hinshelwood (L-H) model. From the observed kinetics, it was observed that the surface reaction was the rate limiting step in the GAC-TiO2 catalyzed photodegradation of CBF. The values of K and kr for this pseudo first-order reaction were found to be 0.1942 L  mg(-1) and 1.51 mg L(-1) min(-1), respectively. In addition, the dependence of kapp on the half-life time was determined by calculating the electrical energy per order experimentally (EEO experimental) and also by modeling (EEO model). The batch-mode experimental outcomes revealed the possibility of 100% CBF removal (under optimized conditions and at an initial concentration of 50 mg L(-1) and 100 mg L(-1)) at a contact time of 90 min and 120 min, respectively. Both L-H kinetic model and EEO model fitted well with the batch-mode experimental data and also elucidated successfully the phenomena of photocatalytic degradation in the presence of GAC-TiO2 catalyst.

Photocatalytic degradation of carbofuran in TiO2 aqueous solution: kinetics using design of experiments and mechanism by HPLC/MS/MS

The photocatalytic degradation kinetics of carbofuran was optimized by central composite design based on response surface methodology for the first time. Three variables, TiO2 concentration, initial pH value and the concentration of carbofuran, were selected to determine the dependence of degradation efficiencies on independent variables. Response surface methodology modeling results indicated that the degradation efficiency of carbofuran was highly affected by the initial pH value and the concentration of carbofuran. Then nine degradation intermediates were detected by HPLC/MS/MS. The Frontier Electron Densities of carbofuran were calculated to predict the active sites on carbofuran attacked by hydroxyl radicals and photoholes. Point charges were used to elucidate the chemisorption pattern on TiO2 catalysts during the photocatalytic process. By combining the experimental results and calculation data, the photocatalytic degradation pathways of carbofuran were proposed, including the addition of hydroxyl radicals and the cleavage of the carbamate side chain.