Antifungal capability of TiO2 coated film on moist wood

Photocatalytic oxidation by TiO₂ has been shown to deactivate biological pollutants. Most previous studies evaluated TiO₂'s antimicrobial performance using bacteria, with Escherichia coli most commonly applied as the test microbe. There have not been concentrated studies focusing on the photocatalytic disinfection of fungi which widely exist in buildings and cause health problems. In this study, the antifungal activity of TiO₂ photocatalytic reaction against Aspergillus niger was investigated for moist wood boards during periods of several weeks. TiO₂ coated film in the presence of UVA (365 nm) irradiation exhibited antifungal capability. No visible growth was observed on specimens during the photo-process. Re-growth appeared in subsequent dark, indicating that the photocatalytic reaction was not sufficient for total disinfection against mold fungi but did suppress fungi growth. The study sheds light on conditions and potential applications of photocatalytic deactivation of fungi.     

Novel, bio-based, photoactive arsenic sorbent: TiO2-impregnated chitosan bead

A novel sorbent for arsenic, TiO₂-impregnated chitosan bead (TICB), has been synthesized and successfully tested. Kinetic plots, pH dependence, isotherm data, and bead morphology are reported. Equilibrium is achieved after 185 h in batch experiments with exposure to UV light. The TICB system performs similarly to the mass equivalent of neat TiO₂ nanopowder. The point of zero charge (pzc) for TICB was determined to be 7.25, and as with other TiO₂-based arsenic removal technologies, the optimal pH range for sorption is below this pH_pzc. Without exposure to UV light, TICB removes 2198 μg As(III)/g TICB and 2050 μg As(V)/g TICB. With exposure to UV light, TICB achieves photo-oxidation of As(III) to As(V), the less toxic and more easily sequestered arsenic form. UV irradiation also results in enhanced arsenic removal, reaching sorption capacities of 6400 μg As/g TICB and 4925 μg As/g TICB, where arsenic is initially added as As(III) and As(V), respectively. Because the TICB system obviates filtration post-treatment, TICB is superior to TiO₂ nanopowder from the perspective of implementation for decentralized water treatment.     

Electrochemical degradation of chlortetracycline using N-doped Ti/TiO2 photoanode under sunlight irradiations

The appearance and the persistence of pharmaceutical products in the aquatic environment urgently call for the development of an innovative and practical water treatment technology. This study deals with the development of nanostructured nitrogen-doped TiO₂ photoanodes and their subsequent use for chlortetracycline (CTC) photoelectrocatalytic oxidation under visible light. The N-doped TiO₂ photoanodes with different nitrogen contents were prepared by means of a radiofrequency magnetron sputtering (RF-MS) process, with the objective to tune shift their optical absorption from the UV towards the visible. The N-doped TiO₂ consist of nanostructured anatase phase with average TiO₂ nanocrystallite size of 29 nm. The nitrogen doping is clearly shown to produce the desired red shift of the absorption onset of the TiO₂ coatings (from ∼380 nm to ∼550 nm). Likewise, the N-doped TiO₂ are found to be highly photo-electroactive not only under the UV light but most interestingly under the visible light as well. Using the optimal N-doped photoanodes, 99.6% of CTC (100 μg/L) was successfully degraded after 180 min of treatment time with a current intensity of 0.6 A. Under these conditions, a relatively high mineralization of CTC (92.5% ± 0.26% of TOC removal and 90.3% ± 1.1% of TN removal) was achieved.     

Effect of sunlight irradiation on photocatalytic pyrene degradation in contaminated soils by micro-nano size TiO2

The enhanced catalytic pyrene degradation in quartz sand and alluvial and red soils by micro-nano size TiO₂ in the presence and absence of sunlight was investigated. The results showed that the synergistic effect of sunlight irradiation and TiO₂ was more efficient on pyrene degradation in quartz sand and red and alluvial soils than the corresponding reaction system without sunlight irradiation. In the presence of sunlight irradiation, the photooxidation (without TiO₂) of pyrene was very pronounced in alluvial and red soils and especially in quartz sand. However, in the absence of sunlight irradiation, the catalytic pyrene degradation by TiO₂ and the photooxidation (without TiO₂) of pyrene were almost nil. This implicates that ultra-violet (UV) wavelength range of sunlight plays an important role in TiO₂-enhanced photocatalytic pyrene degradation and in photooxidation (without TiO₂) of pyrene. The percentages of photocatalytic pyrene degradation by TiO₂ in quartz sand, alluvial and red soils under sunlight irradiation were 78.3, 23.4, and 31.8%, respectively, at 5 h reaction period with a 5% (w/w) dose of the amended catalyst. The sequence of TiO₂-enhanced catalytic pyrene degradation in quartz sand and alluvial and red soils was quartz sand > red soil > alluvial soil, due to different texture and total organic carbon (TOC) contents of the quartz sand and other two soils. The differential Fourier transform infrared (FT-IR) spectra of degraded pyrene in alluvial soil corroborate that TiO₂-enhanced photocatalytic degradation rate of degraded pyrene was much greater than photooxidation (without TiO₂) rate of degraded pyrene. Based on the data obtained, the importance for the application of TiO₂-enhanced photocatalytic pyrene degradation and associated organic contaminants in contaminated soils was elucidated.     

Photocatalytic transformation and mineralization of 2,4,6-trinitrotoluene (TNT) in TiO2 slurries

An analysis of the photodegradation of TNT in a TiO₂ slurry reactor is presented. The rates and extent of TNT transformation and mineralization are compared for photocatalytic and direct photolytic reactions under conditions of varying light energies and in the presence and absence of oxygen. Certain initial organic transformation products are identified for both photocatalytic and photolytic reactions. Nitrate, nitrite, and ammonium ions are analyzed and the possibility of semiconductor sensitization by colored compounds is considered. TNT was transformed rapidly under each set of photochemical conditions but destruction was faster and more complete with TiO₂ photocatalysis. Transformation by-products were destroyed readily under oxygenated photocatalytic conditions and were observed to be more refractory under direct photolytic conditions. Mass balances performed on carbon and nitrogen revealed that when the TiO₂ photocatalyst was utilized in the presence of oxygen and near u.v. radiation (λ > 340 nm) approx. 90% of the TNT was mineralized and 35% of the total nitrogen was recovered as ammonium ion after 120 min. Among the large number of organic transformation products produced photocatalytically, trinitrobenzoic acid, trinitrobenzene and trinitrophenol have been identified as oxidative intermediate species and dinitroaniline as a reduction product. The photocatalytic transformation of TNT appears to involve both oxidative and reductive steps and sensitization by colored compounds plays no detectable role in degradation.     

Bacterial responses to Cu-doped TiO2 nanoparticles

The toxicity of Cu-doped TiO₂ nanoparticles (NPs, 20 nm), synthesized by a flame aerosol reactor, to Mycobacterium smegmatis and Shewanella oneidensis MR-1, is the primary focus of this study. Both doped and non-doped TiO₂ NPs (20 nm) tended to agglomerate in the medium solution, and therefore did not penetrate into the cell and damage cellular structures. TiO₂ particles (< 100 mg/L) did not apparently interfere with the growth of the two species in aqueous cultures. Cu-doped TiO₂ NPs (20 mg/L) significantly reduced the M. smegmatis growth rate by three fold, but did not affect S. oneidensis MR-1 growth. The toxicity of Cu-doped TiO₂ NPs was driven by the release of Cu²⁺ from the parent NPs. Compared to equivalent amounts of Cu²⁺, Cu-doped TiO₂ NPs exhibited higher levels of toxicity to M. smegmatis (P-value < 0.1). Addition of EDTA in the culture appeared to significantly decrease the anti-mycobacterium activity of Cu-doped TiO₂ NPs. S. oneidensis MR-1 produced a large amount of extracellular polymeric substances (EPS) under NP stress, especially extracellular protein. Therefore, S. oneidensis MR-1 was able to tolerate a much higher concentration of Cu²⁺ or Cu-doped TiO₂ NPs. S. oneidensis MR-1 also adsorbed NPs on cell surface and enzymatically reduced ionic copper in culture medium with a remediating rate of 61 µg/(liter?OD₆₀₀? hour) during its early exponential growth phase. Since the metal reducing Shewanella species can efficiently “clean” metal-oxide NPs, the activities of such environmentally relevant bacteria may be an important consideration for evaluating the ecological risk of metal-oxide NPs.     

Release of phosphorous impurity from TiO2 anatase and rutile nanoparticles in aquatic environments and its implications

Phosphorus-bearing materials as an additive have been popularly used in nanomaterial synthesis and the residual phosphorus within the nanoparticles (NPs) can be of an environmental concern. For instance, phosphorus within pristine commercial TiO₂ NPs greatly influences the surface charge and aggregation behavior of the host TiO₂ in aquatic environments; however, it is unknown whether and how fast phosphorus is released. In this study, we focus on the phosphorus release kinetics from five types of TiO₂ NPs (i.e., 5, 10, and 50 nm anatase and 10 × 40, 30 × 40 nm rutile) under the influence of varying solution chemistries. The 50 nm anatase has the highest quantity of P (8.05 g/kg) and most leachable P dissolves within the first 2 h (i.e., 5.01 g/kg), which presents a potential pollutant source of P. Higher pH favors the phosphorus release (release order: pH 11.2 > pH 8.2 > pH 2.4), while variations in the environmentally relevant ionic strengths (0.01 M NaCl + 0.01 M NaHCO₃ and 0.04 M NaCl + 0.01 M NaHCO₃) and the presence of dissolved natural organic matter (10 mg/L) do not affect release rate greatly. X-ray Absorption Near Edge Structure results suggest that phosphate adsorbed on the pristine 50 nm anatase desorbs, and some dissolved phosphate again re-sorbs as a surface precipitate. The findings from this research may have important environmental implications such as accidental release of TiO₂ NPs and other nanomaterials that are synthesized using phosphorus containing chemicals as an ingredient.     

Development of a TiO2 modified optical fiber electrode and its incorporation into a photoelectrochemical reactor for wastewater treatment

Electrochemical advanced oxidation processes (EAOPs) are used to chemically burn non biodegradable complex organic compounds that are present in polluted effluents. A common approach involves the use of TiO₂ semiconductor substrates as either photocatalytic or photoelectrocatalytic materials in reactors that produce a powerful oxidant (hydroxyl radical) that reacts with pollutant species. In this context, the purpose of this work is to develop a new TiO₂ based photoanode using an optic fiber support. The novel arrangement of a TiO₂ layer positioned on top of a surface modified optical fiber substrate, allowed the construction of a photoelectrochemical reactor that works on the basis of an internally illuminated approach. In this way, a semi-conductive optical fiber modified surface was prepared using 30 μm thickness SnO₂:Sb films on which the photoactive TiO₂ layer was electrophoretically deposited. UV light transmission experiments were conducted to evaluate the transmittance along the optical fiber covered with SnO₂:Sb and TiO₂ showing that 43% of UV light reached the optical fiber tip. With different illumination configurations (external or internal), it was possible to get an increase in the amount of photo-generated H₂O₂ close to 50% as compared to different types of TiO₂ films. Finally, the electro-Fenton photoelectrocatalytic Oxidation process studied in this work was able to achieve total color removal of Azo orange II dye (15 mg L⁻¹) and a 57% removal of total organic carbon (TOC) within 60 min of degradation time.     

Solar Fenton and solar TiO2 catalytic treatment of ofloxacin in secondary treated effluents: Evaluation of operational and kinetic parameters

Two different technical approaches based on advanced oxidation processes (AOPs), solar Fenton homogeneous photocatalysis (hv/Fe²⁺/H₂O₂) and heterogeneous photocatalysis with titanium dioxide (TiO₂) suspensions were studied for the chemical degradation of the fluoroquinolone ofloxacin in secondary treated effluents. A bench-scale solar simulator in combination with an appropriate photochemical batch reactor was used to evaluate and select the optimal oxidation conditions of ofloxacin spiked in secondary treated domestic effluents. The concentration profile of the examined substrate during degradation was determined by UV/Vis spectrophotometry. Mineralization was monitored by measuring the dissolved organic carbon (DOC). The concentrations of Fe²⁺ and H₂O₂ were the key factors for the solar Fenton process, while the most important parameter of the heterogeneous photocatalysis was proved to be the catalyst loading. Kinetic analyses indicated that the photodegradation of ofloxacin can be described by a pseudo-first-order reaction. The rate constant (k) for the solar Fenton process was determined at different Fe²⁺ and H₂O₂ concentrations whereas the Langmuir-Hinshelwood (LH) kinetic expression was used to assess the kinetics of the heterogeneous photocatalytic process. The conversion of ofloxacin depends on several parameters based on the various experimental conditions, which were investigated. A Daphnia magna bioassay was used to evaluate the potential toxicity of the parent compound and its photo-oxidation by-products in different stages of oxidation. In the present study solar Fenton has been demonstrated to be more effective than the solar TiO₂ process, yielding complete degradation of the examined substrate and DOC reduction of about 50% in 30 min of the photocatalytic treatment.     

Preparation of DNA-adsorbed TiO2 particles — Augmentation of performance for environmental purification by increasing DNA adsorption by external pH regulation

We have previously developed a novel photocatalyst, DNA-attached titanium dioxide (DNA-TiO₂), useful for the recovery and decomposition of chemicals [Suzuki et al. Environ. Sci. Technol. 42, 8076, 2008]. Chemicals accumulated in DNA near the surface of TiO₂ and were degraded under UV light. The efficiency of their removal was dependent on the amount of DNA adsorbed on TiO₂, indicating the attachment of larger amounts of DNA to result in higher efficiency. In this study, we succeeded in improving the performance of DNA-TiO₂ by increasing the amount of DNA adsorbed by regulating the external pH. The adsorption of DNA by TiO₂ dramatically increased at pH2, to about fourfold that at other pH values (pH4-10). Repeating the process of DNA addition increased the adsorption further. The attached DNA was stable on the surface of TiO₂ at pH2-10 and 4-56 °C, the same as DNA-TiO₂ prepared at pH7. As the DNA-TiO₂ prepared at pH2 retained much DNA on its surface, chemicals (methylene blue, ethidium bromide, etc.) which could intercalate or react with DNA were effectively removed from solutions. The photocatalytic degradation was slow at first, but the final degradation rate was higher than for non-adsorbed TiO₂ and DNA-TiO₂ prepared at pH7. These results indicated that preparation of DNA-TiO₂ at pH2 has advantages in that much DNA can be attached and large amounts of chemicals can be concentrated in the DNA, resulting in extensive decomposition under UV light.     

Photoelectrocatalytic COD determination method using highly ordered TiO2 nanotube array

This work focuses on the experimental studies of a photoelectrocatalytic method for COD determination in a thin-cell reactor based on a highly effective TiO₂ nanotube array electrode. The effect of preparation parameters on the photoelectrocatalytic performance of TiO₂ nanotube array electrodes including the electrolyte, anodic potential, anodic time, solution pH, calcination temperature and time was examined. The TiO₂ nanotube array electrode prepared in preparation parameters at 1% HF electrolyte solution, anodic potential 20 V, anodic time 5 min, calcination temperature 450 °C with highly photoelectrocatalytic performance was chosen as the working electrode. When it is used in a thin-cell photoeletrocatalytic reactor for COD determination, it requires about 1-5 min to complete the oxidation of organics without further titration, much faster than the standard K₂Cr₂O₇ method (2-4 h). It consumes very limited harmless and inexpensive supporting electrolyte, free from secondary pollution. A wide dynamic working range of 0-850 mg/L can be achieved by this method, much wider than any other photoeletrocatalytic methods using TiO₂ nanoparticles or nanofilms in the reported literature. The effects of the water components were studied to propose the TiO₂ nanotube array method. Real sample analyses were also carried out and the COD value of real samples determined by this method agreed well with the standard dichromate method, and it shows good accuracy, stability and reproducibility.     

Degradation of the antibiotic oxolinic acid by photocatalysis with TiO2 in suspension

In the work presented here, a photocatalytic system using titanium Degussa P-25 in suspension was used to evaluate the degradation of 20 mg L⁻¹ of antibiotic oxolinic acid (OA). The effects of catalyst load (0.2-1.5 g L⁻¹) and pH (7.5-11) were evaluated and optimized using the surface response methodology and the Pareto diagram. In the range of variables studied, low pH values and 1.0 g L⁻¹ of TiO₂ favoured the efficiency of the process. Under optimal conditions the evolution of the substrate, chemical oxygen demand, dissolved organic carbon, toxicity and antimicrobial activity on Escherichia coli cultures were evaluated. The results indicate that, under optimal conditions, after 30 min, the TiO₂ photocatalytic system is able to eliminate both the substrate and the antimicrobial activity, and to reduce the toxicity of the solution by 60%. However, at the same time, ∼53% of both initial DOC and COD remain in solution. Thus, the photocatalytical system is able to transform the target compound into more oxidized by-products without antimicrobial activity and with a low toxicity. The study of OA by-products using liquid chromatography coupled with mass spectrometry, as well as the evaluation of OA degradation in acetonitrile media as solvent or in the presence of isopropanol and iodide suggest that the reaction is initiated by the photo-Kolbe reaction. Adsorption isotherm experiments in the dark indicated that under pH 7.5, adsorption corresponded to the Langmuir adsorption model, indicating the dependence of the reaction on an initial adsorption step.     

Enhance the photocatalytic activity for the degradation of organic contaminants in water by incorporating TiO2 with zero-valent iron

Titanium dioxide (TiO₂) has become the most popular photocatalyst in treating persistent organic pollutants. The main disadvantage of TiO₂ is the diminishing photocatalytic activity over time due to the electron-hole pair recombination. Many studies have aimed to prolong the photocatalytic life of TiO₂. Among them, incorporation of zero-valent iron (ZVI) is one of the approaches. In this study, a novel nano TiO₂/Fe⁰ composite (NTFC) was synthesized from a nano neutral TiO₂ sol and a nano zero-valent iron (nZVI), both prepared in our laboratory. The structure, composition and physical property of the NTFC are characterized. The photocatalytic activity of the NTFC was evaluated by the reductive decolourization of an azo dye, Acid Black-24 (AB-24), and was found superior to those of nZVI and nano neutral TiO₂ sol. Evidence suggests that the enhanced activity of NTFC is highly correlated to the ratio of ferrous to ferric ion in the system. The quantities of ferrous and ferric ions in the nZVI and NTFC systems were monitored separately. In the nZVI system, the concentration of ferric ions decreased significantly with time while a high level of ferrous ions was maintained in the NTFC suspension. The ferrous/ferric ratio of the NTFC suspension was substantially increased after irradiation by UV. Evidence from EPR analysis suggests that the excited electrons in the conduction band of the TiO₂ can be trapped by the half reaction of Fe³⁺/Fe²⁺, reducing the probability of electron-electron hole pair recombination and sustaining the catalytic life of TiO₂. Corrosion tests further proved that by incorporating TiO₂ with zero-valent iron the surface oxidation of nZVI can be effectively prevented.     

硅藻土/泥炭藓基负载g-C3N4-TiO2的光催化调湿性能

通过煅烧法制备具有异质结构的g?C3N4?TiO2光催化剂,然后与硅藻土/泥炭藓基调湿材料复合得到自然光驱动光催化调湿材料,并通过小室试验测试其降解甲醛和调湿的效果.采用X射线衍射仪(XRD)、环境扫描电子显微镜(ESEM)、紫外-可见分光光度计(UV?Vis)、傅里叶红外光谱仪(FTIR)和荧光光谱仪(PL)等研究了g?C3N4?TiO2/硅藻土/泥炭藓光催化调湿材料降解甲醛及温湿度调节的机制.结果表明:在尿素与TiO2质量比为5:1,520℃条件下煅烧制备的g?C3N4?TiO2光催化剂降解甲醛的效果最好,具有牢固的异质结,能有效减少光生电子和空穴的重组中心,使TiO2禁带宽变窄;由于光催化-吸附协同效应,NTD?5在自然光照下能够有效地将试验小室内的甲醛浓度和相对湿度分别控制在0.1 mg/m3和60％左右,同时还具有1～2℃的温度调节作用.     

TiO2 nanoparticles effects on physical, thermal and mechanical properties of self compacting concrete with ground granulated blast furnace slag as binder

In this work, strength assessments and percentage of water absorption of self compacting concrete containing different amounts of ground granulated blast furnace slag and TiO₂ nanoparticles as binder have been investigated. Portland cement was replaced by 45 wt% of ground granulated blast furnace slag and up to 4.0 wt% TiO₂ nanoparticles and the properties of concrete specimens were investigated. TiO₂ nanoparticle as a partial replacement of cement up to 3.0 wt% could accelerate C-S-H gel formation as a result of increased crystalline Ca(OH)₂ amount at the early age of hydration and hence increase strength and improve the resistance to water permeability of concrete specimens. Several empirical relationships have been presented to predict flexural and split tensile strength of the specimens by means of the corresponding compressive strength at a certain age of curing.     

Greywater treatment by UVC/H2O2

Greywater treatment by UVC/H₂O₂ was investigated with regard to the removal of chemical oxygen demand (COD). A COD reduction from 225 to 30 mg l⁻¹ (overall removal of 87%) was achieved after settling overnight and subsequent irradiation for 3 h with 10 mM H₂O₂. Most of the contaminants were removed by oxidation since only 13% COD was removed by settlement.The removal of COD in the greywater followed a second-order kinetic equation, r = 0.0637[COD][H₂O₂], up to 10 mM H₂O₂. A slightly enhanced COD removal was observed at the initial pH of 10 compared with pH 3 and 7. This was attributed to the dissociation of H₂O₂ to O₂H⁻. The treatment was not affected by total concentration of carbonate (c_T) of at least 3 mM, above which operation between pH 3 and 5 was essential. The initial biodegradability of the settled greywater (as BOD₅:COD) was 0.22. After 2 h UVC/H₂O₂ treatment, a higher proportion of the residual contaminants was biodegradable (BOD₅:COD = 0.41) which indicated its potential as a pre-treatment for a biological process.     

Development of solar-driven electrochemical and photocatalytic water treatment system using a boron-doped diamond electrode and TiO2 photocatalyst

A high-performance, environmentally friendly water treatment system was developed. The system consists mainly of an electrochemical and a photocatalytic oxidation unit, with a boron-doped diamond (BDD) electrode and TiO₂ photocatalyst, respectively. All electric power for the mechanical systems and the electrolysis was able to be provided by photovoltaic cells. Thus, this system is totally driven by solar energy. The treatment ability of the electrolysis and photocatalysis units was investigated by phenol degradation kinetics. An observed rate constant of 5.1 × 10⁻³ dm³ cm⁻² h⁻¹ was calculated by pseudo-first-order kinetic analysis for the electrolysis, and a Langmuir-Hinshelwood rate constant of 5.6 μM⁻¹ min⁻¹ was calculated by kinetic analysis of the photocatalysis. According to previous reports, these values are sufficient for the mineralization of phenol. In a treatment test of river water samples, large amounts of chemical and biological contaminants were totally wet-incinerated by the system. This system could provide 12 L/day of drinking water from the Tama River using only solar energy. Therefore, this system may be useful for supplying drinking water during a disaster.     

Atmospheric NH3 and NO2 concentration and nitrogen deposition in an agricultural catchment of Eastern China

To assess the atmospheric environmental impacts of anthropogenic reactive nitrogen in the fast-developing Eastern China region, we measured atmospheric concentrations of nitrogen dioxide (NO₂) and ammonia (NH₃) as well as the wet deposition of inorganic nitrogen (NO₃⁻ and NH₄⁺) and dissolved organic nitrogen (DON) levels in a typical agricultural catchment in Jiangsu Province, China, from October 2007 to September 2008_. The annual average gaseous concentrations of NO₂ and NH₃ were 42.2 μg m⁻³ and 4.5 μg m⁻³ (0 °C, 760 mm Hg), respectively, whereas those of NO₃⁻, NH₄⁺, and DON in the rainwater within the study catchment were 1.3, 1.3, and 0.5 mg N L⁻¹, respectively. No clear difference in gaseous NO₂ concentrations and nitrogen concentrations in collected rainwater was found between the crop field and residential sites, but the average NH₃ concentration of 5.4 μg m⁻³ in residential sites was significantly higher than that in field sites (4.1 μg m⁻³). Total depositions were 40 kg N ha⁻¹ yr⁻¹ for crop field sites and 30 kg N ha⁻¹ yr⁻¹ for residential sites, in which dry depositions (NO₂ and NH₃) were 7.6 kg N ha⁻¹ yr⁻¹ for crop field sites and 1.9 kg N ha⁻¹ yr⁻¹ for residential sites. The DON in the rainwater accounted for 16% of the total wet nitrogen deposition. Oxidized N (NO₃⁻ in the precipitation and gaseous NO₂) was the dominant form of nitrogen deposition in the studied region, indicating that reactive forms of nitrogen created from urban areas contribute greatly to N deposition in the rural area evaluated in this study.     

Al2O3 nanoparticles in concrete and different curing media

In the present study, the effect of limewater on strength and percentage of water absorption of Al₂O₃ nanoparticles blended concrete has been investigated. Portland cement was partially replaced by Al₂O₃ nanoparticles with the average particle size of 15 nm with different amount and the specimens were cured in water and saturated limewater for specific ages. Utilizing up to 2.0 wt% Al₂O₃ nanoparticles could produce concrete with improved strength and water permeability when the specimens cured in saturated limewater while this content is 1.0 wt% for the specimens cured in tap water. The high action of fine nanoparticles substantially increases the quantity of C-S-H gel. Although the limewater reduces the strength of concrete without nanoparticles when compared with that cured in water, curing the specimens in saturated limewater results in more strengthening gel formation around Al₂O₃ nanoparticles and causes improved permeability together with high strength. In addition, Al₂O₃ nanoparticles are able to act as nanofillers and recover the pore structure of the specimens by decreasing harmful pores. Accelerated peak appearance in conduction calorimetry tests, more weight loss in thermogravimetric analysis and more rapid appearance of peaks related to hydrated products in X-ray diffraction results, all indicate that Al₂O₃ nanoparticles could improve mechanical and physical properties of the specimens.     

Emission of N2O and CH4 from a constructed wetland in southeastern Norway

The Skjønhaug constructed wetland (CW) is a free surface water (FSW) wetland polishing chemically treated municipal wastewater in southeastern Norway and consists of three ponds as well as trickling, unsaturated filters with light weight aggregates (LWA). Fluxes of nitrous oxide (N₂O) and methane (CH₄) have been measured during the autumn, winter and summer from all three ponds as well as from the unsaturated filters. Physicochemical parameters of the water have been measured at the same localities. The large temporal and spatial variation of N₂O fluxes was found to cover a range of − 0.49 to 110 mg N₂O–N m^− 2 day⁻¹, while the fluxes of CH₄ was found to cover a range of − 1.2 to 1900 mg m^− 2 day^− 1. Thus, both emission and consumption occurred. Regarding fluxes of N₂O there was a significant difference between the summer, winter and autumn, with the highest emissions occurring during the autumn. The fluxes of CH₄ were, on the other hand, not significantly different with regard to seasons. Both the emissions of N₂O and CH₄ were positively influenced by the amount of total organic carbon (TOC). The measured fluxes of N₂O and CH₄ are in the same range as those reported from other CWs treating wastewater. There was an approximately equal contribution to the global warming potential from N₂O and CH₄.