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•Degradation kinetics and mineralization rate of IBU wastewater using UV-(LEDs)/TiO2 were studied.•The effect of the water matrix on the degradation of IBU was evaluated.•The ...formation of intermediates was followed by LC-MS-IT-TOF.•The toxicity of the treated IBU solutions was determined using the marine bacterium Vibrio fischeri.
Degradation and mineralization of ibuprofen (IBU) were investigated using Ultraviolet (UV) Light Emitting Diodes (LEDs) in TiO2 photocatalysis. Samples of ultrapure water (UP) and a secondary treated effluent of a municipal wastewater treatment plant (WWTP), both spiked with IBU, as well as a highly concentrated IBU (230 mg L−1) pharmaceutical industry wastewater (PIWW), were tested in the TiO2/UV-LED system. Three operating parameters, namely, pH, catalyst load and number of LEDs were optimized. The process efficiency was evaluated in terms of IBU removal using high performance liquid chromatography (HPLC) and ultra-high performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). Additionally, the mineralization was investigated by determining the dissolved organic carbon (DOC) content. The chemical structures of transformation products were proposed based on the data obtained using liquid chromatography with a high resolution mass spectrometer ion trap/time-of-flight (LC-MS-IT-TOF). A possible pathway of IBU degradation was accordingly suggested. Bioassays were performed using the marine bacterium Vibrio fischeri to evaluate the potential acute toxicity of original and treated wastewaters. TiO2 heterogeneous photocatalysis was efficient to remove IBU from UP and from PIWW, and less efficient in treating the wastewater from the municipal WWTP. The acute toxicity decreased by ca. 40% after treatment, regardless of the studied matrix.
Solar-driven advanced oxidation processes were studied in a pilot-scale photoreactor, as tertiary treatments of effluents from an urban wastewater treatment plant. Solar-H2O2, heterogeneous ...photocatalysis (with and/or without the addition of H2O2 and employing three different photocatalysts) and the photo-Fenton process were investigated. Chemical (sulfamethoxazole, carbamazepine, and diclofenac) and biological contaminants (faecal contamination indicators, their antibiotic resistant counterparts, 16S rRNA and antibiotic resistance genes), as well as the whole bacterial community, were characterized.
Heterogeneous photocatalysis using TiO2-P25 and assisted with H2O2 (P25/H2O2) was the most efficient process on the degradation of the chemical organic micropollutants, attaining levels below the limits of quantification in less than 4 h of treatment (corresponding to QUV < 40 kJ L−1). This performance was followed by the same process without H2O2, using TiO2-P25 or a composite material based on graphene oxide and TiO2.
Regarding the biological indicators, total faecal coliforms and enterococci and their antibiotic resistant (tetracycline and ciprofloxacin) counterparts were reduced to values close, or beneath, the detection limit (1 CFU 100 mL−1) for all treatments employing H2O2, even upon storage of the treated wastewater for 3-days. Moreover, P25/H2O2 and solar-H2O2 were the most efficient processes in the reduction of the abundance (gene copy number per volume of wastewater) of the analysed genes. However, this reduction was transient for 16S rRNA, intI1 and sul1 genes, since after 3-days storage of the treated wastewater their abundance increased to values close to pre-treatment levels. Similar behaviour was observed for the genes qnrS (using TiO2-P25), blaCTX-M and blaTEM (using TiO2-P25 and TiO2-P25/H2O2). Interestingly, higher proportions of sequence reads affiliated to the phylum Proteobacteria (Beta- and Gammaproteobacteria) were found after 3-days storage of treated wastewater than before its treatment. Members of the genera Pseudomonas, Rheinheimera and Methylotenera were among those with overgrowth.
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•Different solar-driven advanced oxidation processes were studied at pilot-scale.•P25/H2O2 showed a best compromise to remove both chemical & biological pollutants.•P25/H2O2 didn't prevent reactivation of antibiotic resistant genes in stored water.•Beta- and Gammaproteobacteria relative abundance increased in stored treated water.
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The biocatalytic performance of immobilized enzyme systems depends mostly on the intrinsic properties of both biomolecule and support, immobilization technique and immobilization ...conditions. Multi-walled carbon nanotubes (MWCNTs) possess unique features for enzyme immobilization by adsorption. Enhanced catalytic activity and stability can be achieved by optimization of the immobilization conditions and by investigating the effect of operational parameters.
Laccase was immobilized over MWCNTs by adsorption. The hybrid material was characterized by Fourier transformed infrared (FTIR) spectroscopy, scanning and transmission electron microscopy (SEM and TEM, respectively). The effect of different operational conditions (contact time, enzyme concentration and pH) on laccase immobilization was investigated. Optimized conditions were used for thermal stability, kinetic, and storage and operational stability studies.
The optimal immobilization conditions for a laccase concentration of 3.75μL/mL were a pH of 9.0 and a contact time of 30min (522 Ulac/gcarrier). A decrease in the thermal stability of laccase was observed after immobilization. Changes in ΔS and ΔH of deactivation were found for the immobilized enzyme. The Michaelis–Menten kinetic constant was higher for laccase/MWCNT system than for free laccase. Immobilized laccase maintained (or even increased) its catalytic performance up to nine cycles of utilization and revealed long-term storage stability.
Design of graphene-based TiO2 photocatalysts—a review Morales-Torres, Sergio; Pastrana-Martínez, Luisa M.; Figueiredo, José L. ...
Environmental science and pollution research international,
11/2012, Volume:
19, Issue:
9
Journal Article
Peer reviewed
There is a recent increase in the interest of designing high-performance photocatalysts using graphene-based materials. This review gathers some important aspects of graphene–TiO
2
, graphene ...oxide–TiO
2
, and reduced graphene oxide–TiO
2
composites, which are of especial relevance as next generation photocatalysts. The methods used for the preparation of these materials, the associated mechanistic fundamentals, and the application of graphene-based composites on the photocatalytic degradation of pollutants are reviewed. Some structural, textural, and chemical properties of these materials and other photo-assisted applications, such as hydrogen production from water splitting and dye-sensitized solar cells, are also briefly included.
Renewable energy-powered water electrolysis and photocatalytic water splitting are two promising approaches to green hydrogen production. Electrocatalysts and photocatalysts are essential components ...determining the performance of water electrolyzers and photocatalytic reactors, respectively. Currently, there is a pressing need to develop efficient and stable electrocatalysts and photocatalysts for large-scale deployment of these devices to reach carbon neutrality. Herein, we report the synthesis of single-atom Ir and Ru anchored on mesoporous graphitic carbon nitride (Ir-g-CN and Ru-g-CN), which can be used as electrocatalysts and photocatalysts for the hydrogen evolution reaction (HER). Remarkably, Ru-g-CN shows a high turnover frequency (TOF) of 12.9 and 5.1 s−1 at an overpotential (η) of 100 mV in 0.5 M H2SO4 and 1.0 M KOH, respectively, outperforming Ir-g-CN, commercial Pt/C benchmark and many other advanced HER catalysts reported recently. Moreover, Ru-g-CN can deliver an exceptionally high mass activity of 24.55 and 8.78 A mg−1 at η = 100 mV in acidic and alkaline solutions, meanwhile exhibiting a high apparent current density, which is favorable for practical applications. Additionally, both Ru-g-CN and Ir-g-CN show outstanding catalytic stability, continuously catalyzing the HER in acidic and alkaline conditions for 120 h with minimal degradation. Besides, when used for photocatalytic water splitting, Ru-g-CN can achieve a high hydrogen production rate of 489.7 mmol H2 gRu−1 h−1, and shows good photocatalytic stability. Our density functional theory (DFT) calculations demonstrate that loading Ir and Ru single-atoms on g-CN alters the electronic structure, resulting in a reduced bandgap and improved electrical conductivity, facilitating electron transfer during the catalysis. Moreover, the Gibbs free energy of hydrogen adsorption on Ru-g-CN and Ir-g-CN is also substantially lowered, enhancing HER performance.
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•Multifunctional catalysts comprising single-atom Ir and Ru anchored on g-CN are prepared.•Ru-g-CN shows exceptionally high mass activity meanwhile very good apparent activity.•Ru-g-CN exhibits a high photocatalytic hydrogen production rate of 489.7 mmol gRu h−1.•Introduction Ir or Ru single-atoms on g-CN alters electronic structure and improves HER performance.
► Acidic character of GOP composites varied with the GO content and heat-treatments. ► The mesoporosity of the composites increases with GO wt. but not the microporosity. ► GO aggregates coated with ...P25 nanoparticles are stabilized with TiOC bonds. ► Optimization of the GO content is fundamental in the photocatalytic efficiency. ► The formation of reduced graphene oxide improves the photocatalytic performance.
Graphene oxide (GO) and the benchmark TiO2 photocatalyst (P25) were used to prepare different composites (GOP), by a simple method of mixing and sonication, varying the GO content and the heat-treatment temperature under nitrogen. The composites were characterized by thermogravimetric (TG) and differential thermogravimetric (DTG) analyses, scanning electron microscopy (SEM), physical adsorption of nitrogen, UV–Vis and IR diffuse reflectance spectroscopies (DRUV and DRIFT), and point of zero charge (pHPZC) measurements. The morphology, microporosity and SBET of the composites did not vary significantly in comparison to P25, while an increase of their mesoporosity and mesopore diameter were observed due to the formation of GO aggregates coated with P25 nanoparticles. The aggregates were stabilized by the formation of TiOC bonds, which in turn produced a narrowing of the band gap relative to P25. The surface chemistry of GOP composites varied with the GO content, being more acidic when higher GO content was used. The photocatalytic performance was evaluated for the degradation of diphenhydramine (DP) pharmaceutical and methyl orange (MO) dye under near-UV/Vis irradiation. The first order rate constant of MO photodegradation increased four times for some GOP composites with relation to P25 (i.e., from k=52×10−3 to 207×10−3min−1). Comparable efficiencies were observed when DP was used as model pollutant (i.e., around k=54×10−3min−1). The best performing photocatalyst was that containing 1.4wt.% GO and treated at 200–300°C. The improved performance was attributed to the reduction of GO during the thermal treatment and to the good contact between the TiO2 and the carbon phases.
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•Photocatalytic oxidation of benzyl alcohol in water by g–C3N4 is selective to benzaldehyde.•Mechanical and chemical post-treatments widen-up g–C3N4 photocatalyst band-gap.•Thermal ...post-treatments of bulk g–C3N4 significantly increase benzaldehyde yield.•Benzaldehyde production by photocatalysis with g–C3N4 is clean, safe and efficient.
The selective photocatalytic conversion of benzyl alcohol to benzaldehyde was studied in aqueous medium, as alternative to common organic solvents, in combination with environmentally friendly conditions: metal-free catalysts based on graphitic carbon nitride (g-C3N4), natural pH, ambient temperature and pressure, and light emitting diodes (LEDs) as high efficient lighting source. g-C3N4 was synthesized by thermal condensation of dicyandiamide and the photocatalytic performance evaluated in terms of different post-treatment routes: thermal, mechanical and chemical. Several temperatures (400, 450 and 500°C), times of mechanical treatment (1.5, 3.0 and 8.0h) and protic acids (H2SO4, HCl and HNO3) were tested. The post-treatments significantly enhance photocatalytic conversion and yield, with minimal compromise on selectivity. The photocatalyst obtained upon thermal pos-treatment of g-C3N4 at 500°C, which had the better performance (66% conversion, 59% yield, and 90% selectivity at four hours of irradiation), was found to have the highest BET surface area (87m2g−1).
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•Laccase efficiently immobilized over surface modified multi-walled carbon nanotubes.•Immobilized laccase displays good recovered activity and high thermal stability.•Polysulfone ...membranes with embedded CNTs afford effective laccase immobilization.•CNT/polysulfone/laccase membranes can retain and degrade phenolic compounds.•CNT/polysulfone/laccase membranes can be reused and reloaded with fresh enzyme.
Chemically functionalized multi-walled carbon nanotubes (CNTs) are used as carriers for laccase immobilization. In this work, CNTs were modified using different approaches with a combination of methods involving hydrothermal oxidation with nitric acid, treatment with 3-aminopropyltriethoxysilane, glutaraldehyde, N-ethyl-N-(3-(dimethylamino)-propyl) carbodiimide hydrochloride and N-hydroxysuccinimide. The enzyme immobilization efficiency and recovered activity were evaluated towards 2,2′-azino-bis(3-ethylbenzathiazoline-6-sulfonic acid) biocatalytic oxidation. The best compromise between immobilization efficiency and recovered activity was obtained using the CNTs functionalized with 0.3 M HNO3, treated with N-ethyl-N-(3-(dimethylamino)propyl) carbodiimide hydrochloride and N-hydroxysuccinimide. This catalyst also showed the best thermal stability (at 50 and 60 °C). The bioconjugate based on this material was characterized by vibrational spectroscopies (FTIR and Raman) and by N2 adsorption. The results from reutilization tests showed that laccase activity was kept above 65% of its initial value after five consecutive cycles of reuse. The biocatalytic performance of the immobilized enzyme was evaluated for the degradation of a mixture of phenolic compounds in water containing phenol, resorcinol, 4-methoxyphenol and 4-chlorophenol. As means of cost efficient to enzyme reutilization, laccase was immobilized over polysulfone membranes blended with the functionalized CNTs and studied in the degradation of 4-methoxyphenol.
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