Assessment of Ti, Ir, Ta and Ru influence on mixed metal oxide electrodes for photoelectrochemical generation of persulfate: Impact on sulfamethoxazole degradation.

The presence of persulfate (S2O82-) in decontamination processes favors the oxidation of organic pollutants due to its strong oxidation power. In this research we study the photoelectrochemical generation of persulfate using five mixed metal oxides electrodes (MMO) with different compositions and its effect on the degradation of sulfamethoxazole antibiotic (SMX) by photoelectrocatalysis (PEC) and electro-oxidation (EO). By PEC, all anodes generated a higher concentration of S2O82- than those not exposed to light. The high S2O82-concentration obtained by PEC was 0.150 mM using MMO[Ti/Ir/Ta] in a solution with Na2SO4 100 mM applying a current density of 2 mA/cm2. On the other hand, the maximum concentration obtained was 0.250 mM at 30 min of electrolysis for MMO[Ti/Ir/Ta] using Na2SO4 50 mM and applying current density of 5 mA/cm2. S2O82-production by EO was between 0.005 and 0.089 mM. It is observed that MMO based in Ta2O5 showed the best S2O82- production. The effect of S2O82- electro-generation (using the anode with the highest and the anode with the lowest S2O82- production) on the degradation of sulfamethoxazole by PEC and EO was studied using the experimental conditions with the best production of this oxidant. MMO[Ti/Ir/Ta] and MMO[Ti/Ru] were used as anodes, and it was observed that by PEC, 100% of SMX was degraded after 30 min of electrolysis using MMO[Ti/Ir/Ta] and 60 min using MMO[Ti/Ru]. By EO, the degradation of SMX was partial, demonstrating that the electrophotocatalytic effect favors the generation of S2O82-, enhancing the degradation of SMX at short electrolysis times.

Triphasic Oxygen Storage in Wet Nanoparticulate Polymer of Intrinsic Microporosity (PIM-1) on Platinum: An Electrochemical Investigation.

The triphasic interaction of gases with electrode surfaces immersed in aqueous electrolyte is crucial in electrochemical technologies (fuel cells, batteries, sensors). Some microporous materials modify this interaction locally via triphasic storage capacity for gases in aqueous environments linked to changes in apparent oxygen concentration and diffusivity (as well as activity and reactivity). Here, a nanoparticulate polymer of intrinsic microporosity (PIM-1) in aqueous electrolyte is shown to store oxygen gas and thereby enhance electrochemical signals for oxygen reduction in aqueous media. Oxygen reduction current transient data at platinum disk electrodes suggest that the reactivity of ambient oxygen in aqueous electrolyte (typically Doxygen = 2.8 × 10-9 m2 s-1; coxygen = 0.3 mM) is substantially modified (to approximately Dapp,oxygen = 1.6 (±0.3) × 10-12 m2 s-1; capp,oxygen = 50 (±5) mM) with important implications for triphasic electrode processes. The considerable apparent concentration of oxygen even for ambient oxygen levels is important. Potential applications in oxygen sensing, oxygen storage, oxygen catalysis, or applications associated with other types of gases are discussed.

Improved biosensing of Legionella by integrating filtration and immunomagnetic separation of the bacteria retained in filters.

A novel approach is presented that combines filtration and the direct immunomagnetic separation of the retained bacteria Legionella in filters, for further electrochemical immunosensing. This strategy allows for the separation and preconcentration of the water-borne pathogen from high-volume samples, up to 1000 mL. The limit of detection of the electrochemical immunosensor resulted in 100 CFU mL-1 and improved up to 0.1 CFU mL-1 when the preconcentration strategy was applied in 1 L of sample (103-fold improvement). Remarkably, the immunosensor achieves the limit of detection in less than 2.5 h and simplified the analytical procedure. This represents the lowest concentration reported to date for electrochemical immunosensing of Legionella cells without the need for pre-enrichment or DNA amplification. Furthermore, the study successfully demonstrates the extraction of bacteria retained on different filtering materials using immunomagnetic separation, highlighting the high efficiency of the magnetic particles to pull out the bacteria directly from solid materials. This promising feature expands the applicability of the method beyond water systems for detecting bacteria retained in air filters of air conditioning units by directly performing the immunomagnetic separation in the filters.

Assessment of the superior photocatalytic properties of Sn2+-containing SnO2 microrods on the photodegradation of methyl orange.

A microporous Sn2+-containing SnO2 material presenting microrod morphology and a surface area of 93.0 m2 g-1 was synthesized via a simple hydrothermal route. Sn2+ ions were detected in the interior of the material (15.8 at.%) after the corrosion of a sample through sputtering. The material's optical properties have demonstrated the absorption of a considerable fraction of visible light up to wavelengths of 671 nm, due to the presence of Sn2+ states in the material's band structure. The analysis of the internal crystalline structure of a single microrod was carried out with the aid of a focused ion beam microscope and indicated that the material is mesocrystalline down to nanoscale level. It was proposed that the Sn2+ ions occupy intergranular sites in the highly defective crystalline structure of the material and that Sn2+ states, as well as its relatively large surface area, are responsible for the material's superior photoactivity. The synthesized material was tested as a photocatalyst to decompose hazardous contaminants in water. The photocatalytic performance of the material was much higher than those of commercial TiO2 and SnO2 materials, decomposing nearly all methyl orange (an azo-dye model) content in water (10 mg L-1) in 6 min under UV irradiation for a photocatalyst dose of 5.33 g L-1. The photodegradation of methyl orange was also verified under visible light.

Designing Highly Photoactive Hybrid Aerogels for In-Flow Photocatalytic Contaminant Removal Using Silica-Coated Bacterial Nanocellulose Supports.

This study explores the use of silica-coated bacterial nanocellulose (BC) scaffolds with bulk macroscopic yet nanometric internal pores/structures as functional supports for high surface area titania aerogel photocatalysts to design flexible, self-standing, porous, and recyclable BC@SiO2-TiO2 hybrid organic-inorganic aerogel membranes for effective in-flow photo-assisted removal of organic pollutants. The hybrid aerogels were prepared by sequential sol-gel deposition of the SiO2 layer over BC, followed by coating of the resulting BC@SiO2 membranes with a porous titania aerogel overlayer of high surface area using epoxide-driven gelation, hydrothermal crystallization, and subsequent supercritical drying. The silica interlayer between the nanocellulose biopolymer scaffold and the titania photocatalyst was found to greatly influence the structure and composition, particularly the TiO2 loading, of the prepared hybrid aerogel membranes, allowing the development of photochemically stable aerogel materials with increased surface area/pore volume and higher photocatalytic activity. The optimized BC@SiO2-TiO2 hybrid aerogel showed up to 12 times faster in-flow photocatalytic removal of methylene blue dye from aqueous solution in comparison with bare BC/TiO2 aerogels and outperformed most of the supported-titania materials reported earlier. Moreover, the developed hybrid aerogels were successfully employed to remove sertraline drug, a model emergent contaminant, from aqueous solution, thus further demonstrating their potential for water purification.

Degradation of contaminants of emerging concern in a secondary effluent using synthesized MOF-derived photoanodes: A comparative study between photo-, electro- and photoelectrocatalysis.

Three metal-organic framework (MOF)-based photoanodes were prepared by deposition on TiO2 nanotubes using Ti as substrate (Ti/TiO2NT): i) Ti/TiO2NT-Au@ZIF-8, ii) Ti/TiO2NT-Ru3(BTC)2, iii) Ti/TiO2NT-UiO-66(Zr)NH2. These photoanodes were characterized by FEG-SEM, EDX and DRX. The analyses showed a successful modification and a high homogeneity of the different MOFs on the Ti/TiO2NT surface. The photoanodes were studied in the degradation of Contaminants of Emerging Concern (CECs) in a spiked secondary effluent from a Municipal Wastewater Treatment Plant (MWWTP). Sodium diclofenac (DCF), sulfamethazine (SMT) and carbamazepine (CBZ) were used as CECs at low concentration (200 µg/L each CEC). The samples were preconcentrated using Solid Phase Extraction (SPE) and analyzed by a HPLC-DAD system. The MOF-based photoanodes exhibited a high photoelectrochemical (PEC) activity towards the oxidation of CECs, achieving up to 50%, 70% and 80% of removal using Ti/TiO2NT-Au@ZIF-8, Ti/TiO2NT-UiO-66(Zr)NH2, Ti/TiO2NT-Ru3(BTC), respectively. The influence of the generation of hydroxyl radical was then studied. The results indicate that PEC degradation using Ti/TiO2NT-Ru3(BTC)2 and Ti/TiO2NT-UiO-66(Zr)NH2 is more affected by the concentration of the radical.

Immunomagnetic Separation Improves the Detection of Mycobacteria by Paper-Based Lateral and Vertical Flow Immunochromatographic Assays.

This work addresses a method that combines immunomagnetic separation (IMS) and paper-based nucleic acid immunochromatographic assay for the sensitive detection of Mycolicibacterium fortuitum (basonym Mycobacterium fortuitum) In particular, the preconcentration of the bacteria was achieved by using magnetic particles modified with an antibody specific towards mycobacteria. Following the IMS, the bacteria were lysed, and the genome was amplified by double-tagging PCR, using a set of primers specific for the 16S rRNA gene for Mycobacterium. During the amplification, the amplicons were labeled with biotin and digoxigenin tags. Moreover, a comparative study of paper-based immunochromatographic platforms, relying on vertical and lateral flow and on the use of streptavidin gold nanoparticles as a signal generating system, was also performed. The visual readout was achieved when the gold-modified amplicons were captured by the anti-DIG antibody in the test line. The analytical performance of both methods, nucleic acid vertical flow (NAVF) and nucleic acid lateral flow (NALF), is also discussed. Although NALF showed lower limit of detections (LODs), both NALF and NAVF combined with IMS were able to detect the required LOD in hemodialysis water, becoming two promising and useful techniques for the rapid screening of water supplies in hemodialysis centers, to prevent the exposure of immunosuppressed patients to contaminated sources.

A promising technology based on photoelectrocatalysis against Mycobacterium tuberculosis in water disinfection.

Mycobacterium tuberculosis is highly infectious, persistent and has been detected in more than one quarter of the world's population. It is notoriously resistant to sterilization and disinfection procedures, largely due to an unusual hydrophobic cell wall and effective defense mechanisms against oxidative stress. This work shows an effective method to reduce M. tuberculosis quantity in water by using Ti/TiO2 nanotubes electrodes bare and coated with Ag nanoparticles by using photoelectrocatalytic oxidation process. The results have indicated 99.999% of inactivation of a solution spiked with standard and resistant strains of 1×104 CFU mL-1 M. tuberculosis after 5 min of treatment at Ti/TiO2 photoanode in 0.05 mol L-1 Na2SO4 (pH 6) under applied potential of + 1.5 V versus Ag/AgCl and UV irradiation. The mycobacteria degradation was monitored by dissolved total organic carbon (TOC) removal, carbohydrate release, chromatography coupled to mass spectroscopy measurements and it is slightly superior to photocatalysis and photolysis processes. All the results corroborated with the complete inactivation and degradation of the byproducts generated during cell lysis.

CO2 Reduction of Hybrid Cu2 O-Cu/Gas Diffusion Layer Electrodes and their Integration in a Cu-based Photoelectrocatalytic Cell.

Cu2 O/gas diffusion layer (GDL) electrodes prepared by electrodeposition were studied for the electrocatalytic reduction of CO2 . The designed electrode was also tested in solar-light-induced CO2 conversion in combination with a CuO/NtTiO2 photoanode using a compact photoelectrocatalytic (PEC) cell. Both PEC cell electrodes were prepared using non-critical raw materials and low cost, easily scalable procedures. In the PEC experiments, a total carbon faradaic selectivity of about 90 % to formate and about 75 % to acetate was obtained after 24 h of operations without application of potential/current or using sacrificial agents. In electrocatalytic tests of CO2 reduction at -1.5 V, the same electrode yielded high total faradaic selectivity (>95 %) but formed selectively formate (about 80 % selectivity) rather than acetate. The in situ transformation of the Cu2 O/GDL electrode leads to the formation of a hybrid Cu2 O-Cu/GDL system. Cyclic voltammetry data indicate that the potential and the presence of CO2 (not only of HCO3 - species) are both important elements in this transformation. Data also indicate that the surface concentration of CO2 (or of its products of transformation) on the electrode is an important factor to determine performance in the conversion of CO2 .

Efficiency comparison of ozonation, photolysis, photocatalysis and photoelectrocatalysis methods in real textile wastewater decolorization.

Treatment of real effluents from industries using AOPs stands to be an imperative task of crucial importance yet quite huge a challenge largely given the nature of complexity of these wastewaters. The present work sought to develop a versatile system aimed at the treatment of real wastewater using a bubbling annular reactor, which enables us to test the efficiency of photolysis; photocatalysis, photoelectrocatalysis and direct ozonation using oxygen or ozone as gas flow. A TiO2 nanotubes electrode was used as photocatalyst in photocatalytic and photoelectrocatalytic measurements with and without coupling with ozonation under pH 3.0 and pH 8.0 leading to 50% of color removal after 60 min reaction. However, the results indicated 90% of color removal upon the bubbling of ozone after 15 min of treatment. A synergistic effect was observed in all experiments using the AOPs in the presence of ozone under both pH values. Interestingly though, 85% of decolorization was obtained through direct ozonation without any change in the effluent following 10 min of treatment. The results were discussed in terms of electric energy per order and were compared to those reported previously. For real textile wastewater, ozonation appears to be a promising candidate for full-scale effluent decolorization.

Effect of ionic liquid on the determination of aromatic amines as contaminants in hair dyes by liquid chromatography coupled to electrochemical detection.

The room temperature ionic liquid (IL) 1-butyl-3-methylimidazolium bis-(trifluorometanesulfonyl)imide BMIm[NTf2] was used as a novel medium for improvement of separation and quantization of 16 aromatic amines typically present as contaminants in consumer products and detected by HPLC coupled to an electrochemical detector. The aromatic amines, namely 4,4'-diaminodiphenylmethane, 4-chloroaniline, 2-methoxy-5-methyl-aniline, 3,3'-dimethylbenzidine, 2,4-diaminotoluidine, 2-chloro-4-nitroaniline, 4,4'-oxydianiline, aniline, 3,3'-ichlorobenzidine, benzidine, 4-aminobiphenyl, o-dianisidine, o-anisidine, o-toluidine, 4,4'-methylene-bis-2-chloroaniline and 2-naphthylamine are oxidized in methanol/BMIm[NTf2] at a potential around +0.68V to +0.93V vs. Ag/AgCl at a glassy carbon electrode, which is the base for their determination by HPLC/ED. Using the optimized conditions of methanol/BMIm[NTf2] 70:30 (v/v) as mobile phase, flow-rate of 0.8 mL·min⁻¹, column CLC-ODS, Eap = +1.0 V and T = 40 °C analytical curves were constructed for each of the tested amines. Good linearity was obtained in the concentration range of 1.09 mg·L⁻¹ to 217 mg·L⁻¹, with excellent correlation coefficients. The limits of detection reached 0.021 mg·L⁻¹ to 0.246 mg·L⁻¹ and good relative standard deviations (RSD, n = 3) were obtained from the measurements. Satisfactory recovery for each aromatic amine was achieved, ranging from 95 to 103%. The developed method was successfully applied to determine six aromatic amines present as contaminants in commercial hair dye samples.

Rapid and sensitive method for the determination of acetaldehyde in fuel ethanol by high-performance liquid chromatography with UV-Vis detection.

A high-performance liquid chromatography (HPLC) method for the determination of acetaldehyde in fuel ethanol was developed. Acetaldehyde was derivatized with 0.900 mL 2,4-dinitrophenylhydrazine (DNPHi) reagent and 50 microL phosphoric acid 1 mol L(-1) at a controlled room temperature of 15 degrees C for 20 min. The separation of acetaldehyde-DNPH (ADNPH) was carried out on a Shimadzu Shim-pack C18 column, using methanol/LiCl((aq)) 1.0 mM (80/20, v/v) as a mobile phase under isocratic elution and UV-Vis detection at 365 nm. The standard curve of ADNPH was linear in the range 3-300 mg L(-1) per injection (20 microL) and the limit of detection (LOD) for acetaldehyde was 2.03 microg L(-1), with a correlation coefficient greater than 0.999 and a precision (relative standard deviation, RSD) of 5.6% (n = 5). Recovery studies were performed by fortifying fuel samples with acetaldehyde at various concentrations and the results were in the range 98.7-102%, with a coefficient of variation (CV) from 0.2% to 7.2%. Several fuel samples collected from various gas stations were analyzed and the method was successfully applied to the analysis of acetaldehyde in fuel ethanol samples.