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•The size of Au clusters is strongly influenced by zeta potential of TiO2 support.•The Schottky barrier height (SBH) of TiO2 + Au samples was determined by XPS analysis.•Low SBH ...enables more facile injection of Au generated »hot electrons« into TiO2.•TiO2 + Au solid with lower SBH shows higher activity under visible light illumination.•Higher specific surface area of TiO2 + Au contributes to the degradation of bisphenols.
Composites of different TiO2 supports (anatase nanoparticles (TNP) and nanorods (TNR)) and 1 wt% of Au were synthesized upon wet impregnation preparation procedure. The size of formed Au ensembles in the composites was influenced by the difference in the zeta potential value (pHPZC) of TiO2 supports. The positive surface charge of TNR nanorods during the wet impregnation synthesis and its higher specific surface area positively influenced the formation of Tis-O-Au(III) complex. In turn, the average Au cluster size in the TNR + Au composite was larger (9.4 nm) than in the TNP + Au composite (2.4 nm) where the surface of the TNP nanoparticles was negatively charged. In spite of the different size of Au ensembles the UV–Vis DR spectra of composites exhibited a broad absorption peak at 550 nm, which is typical for the plasmonic behaviour of Au clusters. A detailed XPS analysis of the valence band maxima (VBM) showed that the value of Schottky barrier height (SBH) in the TNP + Au composite (0.31 eV) was almost double compared to the one in the TNR + Au composite (0.16 eV). The visible-light generated “hot electrons” in Au clusters of the TNP + Au composite need more energy and longer time to overcome the SB when injected into the TNP, compared to “hot electrons” generated in the TNR + Au composite exhibiting lower SBH. Due to this obstacle TNP + Au “hot electrons” have a higher potential to recombine with the generated holes in Au clusters than “hot electrons” injected into the TNR support. The higher specific surface area of the TNR support presents an additional advantage, which prolongs the “lifetime” of electrons in the TNR + Au composite. The electrons can use a larger area to generate reactive oxygen species (ROS) or oxidize adsorbed substrates compared to electrons in the TNP + Au composite. This was proved by: (i) the results of electrochemical impendance spectroscopy (EIS) measurements, (ii) photoluminescence (PL) emission spectra of catalysts, and (iii) measurements with the use of ROS scavengers. The higher photocatalytic activity of the TNR + Au composite was also well expressed by the visible-light assisted photocatalytic oxidation of aqueous solutions of bisphenols.
Hydrophobic Pt CWAO-catalysts can achieve complete removal of bisphenol A from a flow of contaminated water in a trickle-bed reactor at an operating temperature of 120°C, total air pressure of 8 bar ...and a liquid-hourly space velocity of 26.6 h−1. Although increasing the throughput of contaminated water while lowering the operating temperature results in bisphenol A conversions below 100%, these more demanding conditions allow structurally similar catalyst formulations to be differentiated from one another. At 60°C and 8 bar total pressure of air, 2%Pt supported on a SiC-TiC composite material has the highest initial activity from a group of three hydrophobic catalysts with similar surface areas and Pt particle diameters, but it begins to deactivate progressively after 15 hours on stream. This catalyst contains some localised hydrophilicity arising from the presence of surface TiO2, which forms when the exposed TiC component of the support material oxidises during catalyst preparation. At 80 °C and ambient air pressure, the activity is lower but there are no signs of deactivation during 24 hours on stream. The results are consistent with metallic platinum providing the active sites for CWAO of bisphenol A, with oxygen being directly activated from the gas phase at elevated pressures, but with dissolved oxygen also contributing to the reaction particularly at ambient air pressure. Continuous and irreversible deactivation, which occurs at air pressures ≥4 bar, appears to be associated with high occupancy of the active sites by adsorbed oxygen, resulting in leaching of platinum into the aqueous phase.
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•Continuous CWAO usually requires elevated temperature and pressure.•Pt on SiC-TiC can oxidise BPA in an aqueous stream at 80 °C and ambient pressure.•Pt on SiC-TiC activates O2 from both the aqueous and gas phase during CWAO.•High occupancy of Pt sites by adsorbed oxygen leads to catalyst deactivation.•Low occupancy of Pt sites by adsorbed oxygen results in lower but stable activity.
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•Selection of a suitable photocatalyst for anionic dye removal from wastewater at pH=7.•TiO2/silica and ZnO/silica composites evaluated in terms of adsorption/degradation.•The highest ...dye adsorption (50%) observed on disordered ZnO/silica (Zn:Si=1:1).•The fastest dye degradation observed on disordered ZnO/silica (Zn:Si=1:1).•Silica support for colloidal ZnO nanoparticles notably minimized photocorrosion.
For the photocatalytic wastewater treatment containing lower concentrations of dyes as pollutants, a suitable photocatalyst may be selected for anionic or cationic dye removal according to the photocatalyst surface charging and desired adsorption/degradation ratio. Herein, for the first time, we evaluate mesoporous silica supported TiO2 versus mesoporous silica supported ZnO photocatalysts at neutral pH and at equal conditions. The evaluation shows that model anionic dye Reactive Blue 19 (RB19) was adsorbed onto silica supported ZnO nanoparticles at neutral pH in a much higher rate than on silica supported TiO2 nanoparticles, even though the surfaces of ZnO and TiO2–silica composite catalysts were negatively charged in both cases (ca. −20mV of zeta potential). This was ascribed to the strong positive zeta potential of pure ZnO nanoparticles at neutral pH value (ca. +37mV) and consequently to more mixed oxide (spinel-like) ZnO/silica composite behaviour if compared to the physical mixture of oxide TiO2/silica composites. The highest dye adsorption (50%) and the fastest dye degradation (kapp=0.0544min−1 at 25°C) was observed on disordered ZnO/silica with Zn:Si molar ratio 1:1. Pure TiO2 or silica supported TiO2 nanoparticles were stable under UV irradiation. On the other hand, the interaction between SiO2 and ZnO resulted in increased resistance of ZnO to photocorrosion, which was proven to be an issue in pure ZnO nanoparticles.
Liquid-phase hydrogenation using a solid Pd–Cu bimetallic catalyst provides a potential technique for the removal of nitrates from waters. In this study, hardness and salt effects on both the nitrate ...disappearance rate and the reaction selectivity were quantitatively evaluated. Reduction experiments were performed for a wide range of nitrate conversions in an isothermal semibatch slurry reactor. It was discovered in a series of runs using various nitrate salts as a source of nitrate ions that the apparent surface reaction rate constant increases in the order K+<Na+<Ca2+<Mg2+<Al3+and changes proportionally with the ionization potential of a cation present in the aqueous solution. Permanent hardness of drinking water exhibits no inhibitive impact either on the extent of nitrate removal or on reaction selectivity. On the other hand, the nitrate disappearance rate as well as nitrogen production yield decrease appreciably in the presence of hydrogencarbonates, which is attributed to identical structures of nitrate and hydrogencarbonate ions resulting in competitive adsorption of these species to Pd–Cu active sites. A detailed analysis of experimental data confirmed that efficiency of the Pd–Cu bimetallic catalyst in catalytic nitrate reduction is influenced by the migration of produced hydroxide ions from the Helmholtz layer.
•17 sampling teams took part in a collaborative field trial on wastewater sampling.•Equipment used in time proportional sampling resulted in small random effects.•Participants, with one exception, ...exhibited technical skills for field measurements.•Monitored parameters were determined with low analytical uncertainty (below 10%).•The largest sampling uncertainty (i.e. 28.3%) was observed in the case of sulfate.
This case study gives practical guidance on how uncertainty in monitoring programs can be reduced in wastewater sampling. Seventeen sampling teams took part in a trial. The monitoring consisted of both field and laboratory measurements. The variabilities between reported results of participants in the trial, expressed as coefficients of variation (CVs), were found to be 8.5% for chemical oxygen demand (COD), 9.5% for total suspended solids (TSS) and 14.5% for sulfate ion, respectively.
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•Films were deposited by either the sol-gel (SG) or the sputtering (SP) technique.•The porosity of SG films allows BPA to better access the catalytic sites.•SP films have oxygen ...vacancies acting as charge recombination centers.•N or Cu doped TiO2 thin films are catalytic active under visible light radiation.•The bilayer samples did not show any improvement of the photocatalytic performance.
In this work, TiO2 thin films were deposited onto soda lime glass substrate by two different techniques: sol-gel (SG) and sputtering (SP). The photocatalytic film performance was assessed in a batch recycle reactor testing the photocatalytic degradation of aqueous solutions of bisphenol A (BPA). The use of supported catalysts in batch recycle reactor systems for the photocatalytic degradation of organic pollutants in waste water can be an alternative to nowadays more used slurry batch reactor systems and powdered catalysts, since it is more economically sustainable and not requiring the removal of catalyst particles after waste water treatment. The best photocatalytic activities were achieved with SG films due to their porosity, which allows BPA molecule to better access the catalytic site than in case of SP films. Raman spectroscopy also showed that SP films have more oxygen vacancies, which may end up acting as charge recombination centers. Doping of TiO2 thin films, either with N or Cu, enabled us to trigger the catalytic activity of films also under UV-free visible light radiation. Regardless the order of stacking in the double-layered films, the latter did not result in an increased catalytic activity towards the photodegradation of BPA.
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•H2 production was investigated in anaerobic packed-bed reactor at acidic conditions.•Produced hydrogen yields (mol H2/mol glucose) were 1.80 (R1)>1.74 (R2)>1.46 (R3).•Main metabolic ...products were found to be acetic acid, butyric acid and ethanol.•Higher hydrogen yield correlates with low acetate-to-butyrate (HAc/HBu) ratio.•Quantity of attached biomass (gTVS/gsupport) were 0.06 (R1), 0.04 (R2) and 0.035 (R3).
This study assesses the impact of different support materials (Mutag BioChip™, expanded clay and activated carbon) on microbial hydrogen production in an anaerobic packed-bed reactor (APBR) treating synthetic waste water containing glucose as the main carbon source at low pH value. The APBRs were inoculated with acid pretreated anaerobic sludge and operated at pH value of 4±0.2 and hydraulic retention time (HRT) of 3h. The maximum hydrogen yield of 1.80mol H2/mol glucose was achieved for the APBR packed with Mutag BioChip™ (R1), followed by expanded clay (R2, 1.74mol H2/mol glucose) and activated carbon (R3, 1.46mol H2/mol glucose). It was observed that the investigated support materials influenced the immobilization of hydrogen producing bacteria and consequently hydrogen production performance as well as composition of soluble metabolites. The main metabolic products were acetic acid and butyric acid accompanied with a smaller content of ethanol. The data indicated that in reactors with higher hydrogen yield (R1 and R2), acetate/butyrate (HAc/HBu) ratios were 1.7 and 1.6, respectively, while in the reactor with the lowest hydrogen yield (R3) the obtained HAc/HBu ratio was 4.8. Finally, stable hydrogen and organic acids production throughout the steady-state operation period at low pH values was achieved in all reactors.
•Various polymorphs of TiO2 were synthesized.•Treatment of BPA using heterogeneous photocatalytic oxidation process.•Among TiO2 polymorphs anatase phase shows the highest activity for BPA ...oxidation.•Enhanced activity of physically mixed anatase and rutile nanoparticles is observed.
In this study, testing of TiO2 polymorphs (anatase, rutile, brookite) and their mixtures (anatase/rutile, anatase/TiO2-B) in heterogeneous photocatalytic oxidation process was conducted at ambient conditions in a batch slurry reactor. The efficiency of bare TiO2 catalysts was evaluated based on the degree of bisphenol A (BPA) removal, which is a well-known endocrine disrupting compound (EDC). The obtained results indisputably show that BPA removal is strongly affected by catalyst morphology, crystallite size, structure and specific surface area. Detailed interpretation of catalyst properties combined with BPA removal rates leads to the conclusion that photocatalytic oxidation is the most prominent either by using pure anatase particles or high surface area anatase/TiO2-B nanocomposite. However, the highest extent of mineralization was observed in the presence of high specific surface area nanotubular anatase/TiO2-B nanocomposite. Interestingly, when anatase and rutile particles were physically mixed, an additional beneficial effect on BPA degradation was observed. Interpretation of the obtained results shows that a synergistic effect between the respective phases takes place, and consequently enhances the overall activity. This phenomenon was explained by the proposed mechanism of overall hydroxyl radicals concentration increment due to transfer of OH formed on the surface of anatase particles (via H2O oxidation with photogenerated holes in the valence band) to rutile particles.
This work merges the fields of highly porous polymers (polymerized high internal phase emulsions, polyHIPEs) and synthetic cationic polyelectrolytes and introduces a new approach toward the synthesis ...of highly porous cationic polyelectrolytes. Cationic polyelectrolytes based on (3-acrylamidopropyl)-trimethylammonium chloride (AMPTMA) were synthesized directly through the oil-in-water HIPEs. The resulting polyelectrolyte-based polyHIPEs are distinguished by the highly porous morphology as well as high concentration and accessibility of the cationic N-quaternized functional groups. The most efficient AMPTMA-based polyelectrolyte polyHIPE exhibits the total ion-exchange capacity of 3.53 mmol of AgNO3 per gram of dry resin and the water uptake of up to 95 g·g–1, which is a great improvement as compared to the state-of-the-art of polyHIPE absorbents bearing cationic moieties. Results of erythrosine dye adsorption show that chemisorption is a rate-determining step because adsorption follows the pseudo-second-order kinetic model. Multilinearity of the Weber and Morris plots assumes that more than one regime is involved in the diffusion of the erythrosine dye molecules into the polyHIPE structure with the diffusion in between the swollen polymer chains as a rate-limiting step.
Experimental work was carried out in a differential, liquid-full operated fixed-bed reactor, which employed a proprietary supported catalyst that consisted of copper, zinc and cobalt oxides to study ...the liquid phase oxidation of aqueous solutions containing phenol. This catalyst, which was most active when it was pretreated for 2 h at 860C in oxygen and then cooled to ambient temperature, was efficient in converting the phenol to benzenedioles and benzoquinones, the C-4 intermediates via a total oxidation route, and carbon dioxide. The initial phenol conversion rate was described by a rate equation of the Langmuir-Hinshelwood type which accounted for both phenol and dissociative oxygen adsorption and a surface process that controlled the overall reaction rate.
