Effects of reduced sulfur compounds on Pd-catalytic hydrodechlorination of trichloroethylene in groundwater by cathodic H2 under electrochemically induced oxidizing conditions

Electrolysis-assisted UV/sulfite oxidation for water treatment with automatic adjustments of solution pH and dissolved oxygen

Sulfite as precursor to generate sulfate radical (SO₄ ^•-) for water treatment has gained attention. Here we report a metal-free and highly efficient electro/UV/sulfite process to produce SO₄ ^•- for water treatment. UV/sulfite reaction induces sulfite radical (SO₃ ^•-), which transforms into SO₄ ^•- in the presence of oxygen generated by water electrolysis. Electro/UV/sulfite process generates a steady-state SO₄ ^•- concentration of 0.2 to 1.1 × 10^-12 M in our tests. Solution pH affects sulfite species distribution, and higher pH mediates improved yield of steady-state SO₄ ^•- concentration. Effect of sulfite concentration exhibits a bell-shaped pattern toward SO₄ ^•- production due to self-scavenging. The oxidation capability of electro/UV/sulfite process is manifested by removing representative micropollutants (i.e., ibuprofen, salicylic acid, and bisphenol A) and Escherichia coli model pathogen, in both synthetic and natural water matrices. This novel electro/UV/sulfite process has obvious advantages, since it bypasses metal ion catalysts, supplies reaction with electrolytically generated nascent oxygen, and overcomes the acidic pH requirement, that are challenging to traditional metal/sulfite processes. Considering the features of environmental friendliness and low cost, the proposed electro/UV/sulfite process should lead to successful applications in the future.

Transformation of tetrachloroethylene in a flow-through electrochemical reactor

Electrochemical transformation of harmful tetrachloroethylene (PCE) is evaluated as a method for management of groundwater plumes to protect the drinking water resource, its consumers and the environment. In contrast to previous work that reported transformation of trichloroethylene, a byproduct of PCE, this work focuses on transformation of PCE in a saturated porous matrix and the influence of design parameters on the removal performance. Design parameters investigated were electrode configuration, catalyst load, electrode spacing, current intensity, orientation of reactor and flow through a porous matrix. A removal of 86% was reached in the fully liquid-filled, horizontally oriented reactor at a current of 120 mA across a cathode → bipolar electrode → anode arrangement with a Darcy velocity of 0.03 cm/min (150 m/yr). The palladium load on the cathode significantly influenced the removal. Enhanced removal was observed with increased electrode spacing. Presence of an inert porous matrix improved PCE removal by 9%-point compared to a completely liquid-filled reactor. Normalization of the data indicated, that a higher charge transfer per contaminant mass is required for removal of low PCE concentrations. No chlorinated intermediates were formed. The results suggest, that PCE can be electrochemically transformed in reactor designs replicating that of a potential field-implementation. Further work is required to better understand the reduction and oxidation processes established and the parameters influencing such. This knowledge is essential for optimization towards testing in complex conditions and variations of contaminated sites.

Synthesis of Catalytic Nanoporous Metallic Thin Films on Polymer Membranes

Composite membranes were produced with a metallic thin film forming the upper layer of the composite on a porous polymer support. Commercially available membranes were used as supports with both micron and nanometer scale pores. Alloy films of ~110 nm thickness were deposited via magnetron sputtering to produce the top layer of the composite. Dealloying the film with sulfuric acid allowed the creation of a nanoporous film structure with a ligament size of 7.7 ± 2.5 nm. Resulting composite membranes were permeable to water at all stages of production, and a UF PSf membrane with 90 nm of nanoporous Fe/Pd on top showed a flux of 183 LHM/bar. The films were evaluated for dechlorination of toxic polychlorinated biphenyls from water. At a loading of 6.6 mg/L of Pd attached to 13.2 cm² support in a 2.5 ppm PCB-1 solution with 1.5 ppm dissolved H₂, over 90% of PCB-1 was removed from solution in 30 minutes, which produced the expected product biphenyl from the dechlorination reaction.

Enhanced colorimetric immunoassay accompanying with enzyme cascade amplification strategy for ultrasensitive detection of low-abundance protein

Methods based on enzyme labels have been developed for colorimetric immunoassays, but most involve poor sensitivity and are unsuitable for routine use. Herein, we design an enhanced colorimetric immunoassay for prostate-specific antigen (PSA) coupling with an enzyme-cascade-amplification strategy (ECAS-CIA). In the presence of target PSA, the labeled alkaline phosphatase on secondary antibody catalyzes the formation of palladium nanostructures, which catalyze 3,3′,5,5′-tetramethylbenzidine-H₂O₂ system to produce the colored products, thus resulting in the signal cascade amplification. Results indicated that the ECAS-CIA presents good responses toward PSA, and allows detection of PSA at a concentration as low as 0.05 ng mL⁻¹. Intra- and inter-assay coefficients of variation are below 9.5% and 10.7%, respectively. Additionally, the methodology is validated for analysis of clinical serum specimens with consistent results obtained by PSA ELISA kit. Importantly, the ECAS-CIA opens a new horizon for protein diagnostics and biosecurity.

Efficient reduction of Cr(VI) in groundwater by a hybrid electro-Pd process

Pd-catalytic process is effective for reducing a wide range of contaminants in groundwater. However, limited attention is paid to Cr(VI) reduction presumably due to the weakly oxidizing potential of Cr(VI) under circumneutral conditions. In this study, a new concept of in situ reducing Cr(VI) in groundwater by a hybrid electro-Pd process with automatic pH adjustments is proposed and justified. In an undivided electrolytic cell, Cr(VI) at 5 mg/L is reduced by 95% within 30 min under conditions of pH 3, 1 g/L Pd/Al2O3 and 20 mA current. Reduction of Cr(VI) increases with decreasing pH and increasing current and Pd/Al2O3 dosage. Inhibition of anodic O2 is significant but decreases with drop of pH. Atomic H is assigned as the predominant reactive species contributing to Cr(VI) reduction. Although H2O2 is effective for reducing Cr(VI), its production on Pd surface is completed inhibited by the presence of Cr(VI). The concept is ultimately justified using a specially configured three-electrode column. Cr(VI) is effectively reduced to Cr(3+) in the locally acidic Pd zone, and Cr(3+) is then precipitated in the downstream neutral zone. This hybrid electro-Pd process could be potentially applied in the in situ remediation of Cr(VI)-contaminated groundwater.