Droplet flow-assisted heterogeneous electro-Fenton reactor for degradation of beta-blockers: response surface optimization, and mechanism elucidation.

In this study, we report an effective degradation method for trace level beta-blockers (propranolol and acebutolol) in hospital wastewater using a new droplet flow-assisted heterogeneous electro-Fenton reactor (DFEF) system. Biogenic iron-carbon nanocomposites (RHS/C-x% Fe) as eco-friendly and low-cost heterogeneous Fenton catalysts were synthesized from rice husk via hydrolytic sol-gel routes. Here, we demonstrate the use of natural air as a nebulizing agent for fast and continuous catholyte air saturation and Fenton catalyst transfer to the cathode electrode. The effects of key operational parameters were evaluated and optimized using central composite design. Results clearly indicated that enhanced beta-blocker degradation was mainly dependent on the interactive effects of electrolysis time, current density, and catalyst dosage. Fast degradation efficiencies (≥ 99.9%) was recorded at neutral pH conditions. The decay followed pseudo-first-order kinetics with degradation rates of up to 2.72 × 10-2 and 2.54 × 10-2 min-1 for acebutolol and propranolol, respectively. The synergistic contribution of •OHbulk attributable to DFEF process and •OHadsorbed for anodic oxidation (AO) at the anode electrode significantly enhanced the degradation process. Compared to AO, the conventional flow-assisted electro-Fenton (FEF), and the batch electro-Fenton (BEF), DFEF degradation efficiency followed a decreasing order: DFEF ˃ FEF ˃ BEF˃ AO. This trend in performance was mainly due to the fast and continuous cathodic electro-generation of H2O2 and Fe2+ regeneration. Additionally, in order to elucidate degradation mechanism, we used a combination of DFEF approach with liquid chromatography-tandem mass spectrometry analysis. This approach demonstrates a simple, cleaner, and highly efficient degradation approach for trace level recalcitrant pollutants in a complex aquatic matrix, without the need for external chemical addition and pH adjustment.

Sol-gel based biogenic silica composite as green nanosorbent for chemometric optimization of micro-solid-phase extraction of beta blockers.

An environmentally friendly micro-solid phase extraction (µ-SPE) method utilizing a plant based nanocomposite as a sorbent for determination of trace level beta blockers (ß-blockers) in hospital wastewater prior to Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. µ-SPE extraction conditions were evaluated using a multivariate chemometric approach. Rice husk silica-carbon nanocomposite (5-20Wt.% Fe) in glycerol were synthesized via hydrolytic sol-gel method. The nanosorbent were fully characterized and then evaluated for µ-SPE of trace level ß-blockers in hospital wastewater. To establish the best extraction conditions at minimal experimental cost, multivariate techniques based on fractional factorial (FFD) and central composite designs (CCD) with desirability function (DF) were used to optimize the extraction conditions. Experimental results showed good agreement with predicted values and logical DF was realized at relatively low extraction time. Under optimized conditions, good linearity ranges (0.02-5.0µgL-1) with correlation of determinations higher than 0.9954 were obtained. The limits of detection and quantitation for the five ß-blockers (atenolol, alprenolol, pindolol, acebutolol and propranolol) ranged from 4.0-6.4 and 13.0-19.0ngL-1, respectively. Inter-day and intra-day precision (percent relative standard deviations, n=5) were lower than 8.3% while relative recoveries for hospital wastewater samples (80.6-105.1%) were in satisfactory ranges. This experimental approach therefore, demonstrated simplicity, reduction in the experimental runs, effectively increased sensitivity of LC-MS/MS and was hence suitable for complex matrix sample analysis.