Degradation Of Nitrogen Oxides Research Articles

Characterization and photocatalytic activity of TiO2 thin films prepared by sol-gel method for NOx degradation

Titanium dioxide (TiO2) thin film photocatalysts for the elimination of nitrogen oxides (NOx) were prepared by the dip-coating process using the sol–gel method. To prepare the sols, titanium (IV) butoxide (Ti(OBu)4), diethanolamine (DEA), butanol, and HCl were chosen. The TiO2 coatings were prepared using sols with varying volume ratios of Ti(OBu)4:DEA:Butanol. Additionally, three withdrawal speeds from the sol were employed. Subsequently, the TiO2 thin films were sintered at 500 and 700 °C. The obtained thin films were characterized using SEM to determine thickness, AFM to determine roughness, and the Step 500 platform for the adhesion test. NOx was found to be efficiently eliminated by TiO2 thin film photocatalyst. It is possible to obtain a TiO2 coating that is capable of degrading 300 ppb of NO in real time under specific conditions: a relative humidity of 30 %, a UV intensity of 20 W/m2, a gas flow rate of 1 dm3/min.

Development and application of photocatalytic coating for roadside NOx mitigation in Hong Kong

A facile chemical method for the development of photocatalytic coating products was proposed based on practical application perspective for the Hong Kong roadside nitrogen oxides (NOx) mitigation. TiO2-based photocatalytic coating PC-C film with crystallized size of around 5–6 nm was synthesized with the peptization of H2O2. The PC-C coating possesses a super-hydrophilicity surface and is proven to have a NOx degradation rate of 46.8% with an optimum pH level of 7. In addition, the PC-C coating presents a promising photocatalytic NOx degradation compared with other commercially available coating products and P25 when applied on two building materials of poly-methyl methacrylate (PMMA) and concrete surface. A weather resistance simulation and a 180-day on-site field trial were carried out the attenuation effects of photocatalytic coating applied in outdoor exposure. Based on epidemiological estimation and field investigation, hospital admissions for respiratory diseases (HARD) and mortality cases (MC) could be reduced with the application of PC-C coating along the street canyon. This work demonstrates the feasibility of air pollution control measures for the local roadside NOx using photocatalytic technology, offering promising health benefits with environmental remediation.

Effect of TiO2 and ZnO powder mixtures on mechanical and photocatalytic performance of high performance concrete

The development of new modified cement-based materials is increasingly becoming a necessity for improving the durability and surface performance of building materials. Titanium dioxide (TiO2) photocatalyst has been widely used in building materials science due to its ability to break down pollutants. Zinc oxide (ZnO) is often considered a substituent for TiO2 because of its photocatalytic and photoluminescent properties. A new inorganic nanocomposite photocatalyst, based on titanium and zinc oxides, is introduced in this work in order to study its compatibility with High Performance Concrete (HPC). This research aims to study the mechanical and photocatalytic behavior of mixtures based on nanoparticles in HPC. The study of the efficiency in the nitrogen oxides (NOx) degradation of modified HPC in TiO2 and ZnO with different percentages is studied. The studies have shown that the introduction of titanium dioxide in HPC presents a significant efficiency for the NOx degradation and a positive effect on the mechanical properties than zinc oxide, and thus represents potential contribution to sustainability of concrete structures.

Photocatalytic NOx removal efficiency and surface reflectance of carbonated mortars

Photocatalytic concrete containing titanium dioxide (TiO2) nanoparticles can convert airborne nitrogen oxides (NOx) into nitrate byproducts when exposed to light in the UV-A spectrum, which can reduce the impact to the environment and humans. In this study, the photocatalytic degradation of NOx by mortars containing anatase TiO2 was analyzed through photoreactor testing. Mortar mixtures were prepared with white and gray cements and varying TiO2 and fly ash contents to quantify the effects of carbonation and surface reflectance on each mix design’s NOx removal potential. Carbonation of the mortar specimens significantly reduced photocatalytic NOx removal efficiency, but this could be offset by the replacement of cement with fly ash. Specimens containing photocatalytic white cement were highly reflective in the UV-A spectrum and demonstrated a NOx removal rate significantly greater than less reflective samples cast with gray cement. After carbonation, mixes with 15% fly ash replacement of cement produced the highest NOx removal efficiency for specimens containing the same source of cement.

Two dimensional graphitic carbon nitride Nanosheets as prospective material for photocatalytic degradation of nitrogen oxides

This study investigates the photocatalytic degradation of nitrogen oxides over graphitic carbon nitride (g-C3N4) based photocatalysts. The synthesis procedure of g-C3N4 consists of two-step: in the first step, the synthesis of g-C3N4 is carried out through a microwave heating method, whereas in the second step the as-synthesized product is annealed. The characterization was carried out by XRD (X-ray Diffraction), FESEM (Field Emission Scanning Electron Microscopy), TEM (Transmission Electron Microscopy), BET (Brunauer-Emmet-Teller), and XPS (X-ray Photoelectron Spectroscopy). Photocatalytic activities for the degradation of NOx (Nitrogen Oxides) are compared with commercial TiO2 and g-C3N4, to investigate the structural and physio-chemical features of prepared samples and their correlation with the catalytic activity. The results show that g-C3N4 nanosheets have better activity and stability as compared to TiO2. The deposition effect of 1 wt% Pt to the g-C3N4 nanosheets is also observed which puts a negative effect on the degradation results.

Photocatalytic Concrete Blocks Nanomodified with Zinc Oxide for Paving: Mechanical Performance and Microstructural Characteristics

Abstract Concrete block pavement is considered an ideal substrate for the application of photocatalyst materials. In the paving area, titanium dioxide (TiO2) has been the most widely used semiconductor because of its properties. However, zinc oxide (ZnO) has been recently used as an alternative material to TiO2 in heterogeneous photocatalysis, being applied mainly for the treatment of liquid effluents. In this perspective, the aim of this study was to evaluate the capacity of concrete blocks nanomodified with ZnO in the degradation of nitrogen oxides (NOx) as well as the impact of the nanomaterial on the mechanical properties and microstructural characteristics of concretes. For this purpose, concretes were produced with ZnO incorporation of 3 %, 6 %, and 9 %, being submitted to photocatalytic tests, simple compressive strength, flexural strength, and dynamic Young’s modulus, as well as mercury intrusion porosimetry tests and image evaluations using scanning electron microscopy. Together, evaluation of the influence of nano-ZnO on cement paste hydration reactions was carried out. It could be concluded that the addition of ZnO to concrete provides photooxidative capacity to the material; however, it impairs the mechanical performance and the development of the cementitious matrix microstructure.

Asphalt nanocomposite with titanium dioxide: Mechanical, rheological and photoactivity performance

This article presents the results of research aimed at evaluating the impact of incorporating different percentages of titanium dioxide (TiO2) nanoparticles on the mechanical and rheological properties and photocatalytic efficiency of a conventional asphalt binder. For that, asphalt nanocomposites (asphalt binder + nanomaterial) were produced with different percentages of TiO2 incorporation (3%, 6%, 9%, 12% and 15%). The experimental investigation was conducted based on the performance of tests at high and intermediate temperatures. The effect of nanomaterials on the matrix in relation to several aspects was evaluated, mainly regarding susceptibility to permanent deformation, fatigue damage tolerance, resistance to oxidative aging, apparent viscosity and alteration of the dynamic shear modulus and phase angle. The photocatalytic efficiency was investigated in a continuous flow photoreactor with atmospheric environment polluted by NOx (nitrogen oxides). Results indicate that the incorporation of nano-TiO2 in the asphalt binder improves the mechanical and rheological behavior of the matrix, providing greater resistance to permanent deformation, greater stiffness, greater fatigue damage tolerance at certain stress/strain levels and increased resistance to oxidative aging. In general, it could be concluded that the photocatalytic semiconductor does not compromise the essential mechanical and rheological properties of the asphalt matrix under study, but rather improves them. Performance in the degradation of nitrogen oxides was not very satisfactory compared to cement matrices.

Photocatalytic NOx removal using tantalum oxide nanoparticles: A benign pathway

A wet chemical-synthesized high surface area ultrafine Ta2O5 nanoparticle and its application to NOx control is reported. The as-synthesized photocatalyst is characterized using powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron paramagnetic resonance (EPR) spectroscopy, X-ray Photoelectron Spectroscopy (XPS), transient absorption spectroscopy (TAS), UV–vis diffuse reflectance spectroscopy, and N2 adsorption (BET). The catalytic performance of these Ta2O5 nanoparticles was evaluated towards the photodegradation of nitrogen oxides (NOx) under UV–vis irradiation at room temperature. In comparison to the commercial TiO2 (Aeroxide P25 powder: 20 % rutile/80 % anatase, 50 m2/g), traditionally considered state-of-the-art material for the NOx degradation, as-synthesized Ta2O5 (41 m2/g specific surface area) nanoparticles offers NOx remediation with minimal toxic NO2 and excellent stability under UV irradiation. A 2-fold increase in the UV-photonic-efficiency (∼0.64 %) of Ta2O5 is observed compared to TiO2 P25 (∼0.30 %). NO conversion using Ta2O5 was noted to be 18.6 % compared to 8.8 % for TiO2. The UV–vis photocatalytic activity is explained on the basis of the band structure modulation of Ta2O5 due to the intrinsic defects introduced during the synthesis of the material.

Photocatalytic Gas Phase Reactions

Photocatalytic gas phase reactions represent a less explored yet promising direction within the highly active research area of photocatalysis. While photocatalytic liquid phase reactions are typically performed in water, photocatalytic gas phase reactions focus on gaseous and vaporized compounds. With this change in reaction environment, it is possible to address completely new questions and topics. Examples lie in the field of solar fuels, air pollution, global warming, and green chemistry. For this review, we selected five photocatalytic gas phase reactions, namely the reduction of CO2, water splitting, the oxidation of volatile organic compounds, the degradation of nitrogen oxides, and the synthesis of ammonia, which we discuss in the context of why they are important from a scientific, technological, and also societal point of view. We present the chemical mechanisms behind these photocatalytic processes and propose ideas and strategies for how these processes can be made more efficient. Our literatur...

Pathways of conversion of nitrogen oxides by nano TiO2 incorporated in cement-based materials

The ability of photocatalytic cementitious materials to degrade nitrogen oxides (NOx) has been widely used to evaluate their air-purifying function. However, attention has been predominantly placed on the changes in the NOx concentration but the fate of the degradation products is seldom investigated. This study presents a preliminary laboratory investigation on the photocatalytic NOx degradation of nano titanium dioxide (TiO2) incorporated self-compacting glass mortar (SCGM). Focus was mainly placed on the generation and distribution of the degradation products, nitrite (NO2−) and nitrate (NO3−), during the NOx removal process. The results showed that the photocatalytic SCGM induced an apparent decrease of NO together with a slight increase of NO2 under UVA irradiation. Meanwhile, the amount of the generated NO2− and NO3− on the surface of the tested samples, in the suspended aerosols, and in the flowing air stream increased as the photocatalytic reaction progressed. The accumulation of NO2− and NO3− on the sample surface led to a slight deactivation effect on the photocatalytic NOx removal ability of the SCGM, which, in turn, slowed down the production of NO2− and NO3−. Interestingly, compared with NO3−, NO2− could more easily be carried away from the sample surface by the flowing air stream. On-site monitoring of the photocatalytic NOx removal activity of the paving blocks produced with the incorporation of TiO2 on the surface layer (Eco-block) confirmed the build-up of NO2− and NO3− with time, which well demonstrated the NOx removal ability of the photocatalytic blocks in real site applications.

Design of wall materials based on waste glass regeneration

With urban high buildings increasing in China, the demand for efficiency of wall insulation is getting more and more serious, especially in northeast and northwest China. However, thermal insulation wall in domestic is quite easy to produce cracks under external conditions, which greatly reduces life time. In this paper, we expand the discarded glass and mix aggregate and polypropylene fiber to improve the compressive strength of concrete to achieve green multifunctional concrete.Through the performance test of the expansive glass, we conclude that performances of expansive glass become best at the sinter point of 660°;Moreover, TiO2 added to the exterior wall coating can catalyze the degradation of nitrogen oxides and formaldehyde to purify the air. Non-toxic and harmless, the wall, with strong thermal insulation efficiency, is expected to replace the current building materials in order to produce and utilize massively.

Study on the technology and performance of the degradation of nitrogen oxides according to the outdoor large cement concrete barrier

ABSTRACTIn terms of the study about the decontamination of nitrogen oxides by the outside barrier made of cement concrete, in order to purify NOx produced by auto exhaust, studies had utilized different spray-finishing technology to make the urban concrete barrier have the function of purification NOX. This paper has shown the improvements of how to make the photocatalytic materials on barrier surface maintain long-term stability and the effectiveness, and further optimize the ratio of photocatalytic slurry. The results show that the content of surfactant (sodium dodecylbenzenesulfonate) is 3.5% of that of ST (TiO2 acidified by H2SO4); actual concentration of the ST slurry is 2.0 g/L; the best content of the penetrant (silane coupling agent KH550) is 2% of the photocatalytic slurry; within the wear range of less than 2 mm, ST photocatalytic materials showed good purification effect.

Photocatalytic removal of NOxusing TiO2-coated zeolite

Application of photocatalytic nanoparticles has been recently gaining an increased attention as air purifying material for sustainable urban development. The present work reports the photocatalytic removal of gaseous phase nitrogen oxides (NOx) using TiO2-coated zeolite to be applied as a filter media for the urban green infrastructure such as raingardens. The TiO2-coated zeolite was synthesized by simple wet chemistry method and tested in a continuous-flow photo-reactor for its removal efficiency of NOx under different conditions of the weight percentage of TiO2 coated on the zeolite, and gas retention time. The removal efficiency of NOx in general increased as the weight percentage of TiO2 coated on the zeolite increased up to 15-20%. Greater than 90% of NOx was removed at a retention time of one minute using the TiO2-coated zeolite (TiO2 weight percentage = 20%). Overall, TiO2-coated zeolite showed greater efficiency of NOx removal compared to TiO2 powder probably by providing additional reaction sites from the porous structure of zeolite. It was presumed that the degradation of NOx is attributed to both the physical adsorption and photocatalytic oxidation that could simultaneously occur at the catalyst surface.

Photocatalytic pavements with epoxy-bonded TiO2-containing spreading material

Titanium dioxide (TiO2) is a photocatalyst which can accelerate the oxidation of nitrogen oxides (NOx) and other pollutants under ultraviolet (UV) radiation. In this study, a new method to coat TiO2 onto asphalt pavements was developed with the aim to enhance the NOx decomposition efficiency and durability of the coating material for asphalt pavements. In this method, pulverized TiO2-cement mortar is used as the spreading material, which is bonded to asphalt pavement surface by epoxy resin. The composition of the TiO2-cement mortar was optimized in terms of its mechanical properties. The long-term NOx degradation efficiency, abrasion resistance, and skid resistance of the spreading material were measured after it was subjected to 300min polishing by the advanced Aachen Polishing Machine (APM). It was concluded that durable NOx degradation efficiency can be achieved by the developed method and the method is feasible for practical implementation.

Novel Method of Coating Titanium Dioxide on to Asphalt Mixture Based on the Breath Figure Process for Air-Purifying Purpose

Titanium dioxide (TiO₂) is a photocatalyst that has the capability of accelerating the oxidation of nitrogen oxides (NOₓ) and other pollutants under ultraviolet (UV) radiation. A number of studies have been conducted on applying TiO₂ onto pavement surface to purify exhaust emissions from vehicles. However, it remains a challenging task to effectively coat TiO₂ to asphalt pavements to achieve durable air-purifying performance. This study aims to develop an innovative method, based on the breath figure (BF) process and Pickering emulsion effect, to coat TiO₂ particles onto asphalt pavement surfaces. With this method, asphalt binder with micro pores filled with TiO₂ particles can be coated to asphalt pavement surfaces. The micro porous structure of the coating material helps to provide larger contact area between TiO₂ and UV, thus enhancing NOₓ degradation efficiency. Microscopic analysis on the coating material prepared using the new method demonstrated that TiO₂ particles distributed well on the pore walls of the coating material, indicating that UV can reach TiO₂ to activate the photocatalytic process. The nitric oxides (NO) removal efficiencies of the asphalt mixture specimens coated using this new method and the traditional water solution-based method after various numbers of surface abrasions were also measured by a custom-designed environmental test setup. It was found that this new coating method provided not only better NO removal efficiency, but also improved durability to maintain the degradation efficiency after tire abrasion, compared to the traditional method.

Smart Tiles for the Preservation of Indoor Air Quality

Tiles functionalized with titanium dioxide (TiO2) for the elimination of air pollutants were prepared by the dip-coating process with titanium alkoxide solution. The synthesis of the coating solution consist of a chemical method employing polyethylene glycol (PEG) to obtain better dispersion and adhesion of TiO2 particles onto the ceramic substrates. Nitrogen oxides (NOx), hazardous air pollutants, were found to be efficiently removed by the thin film of photocatalyst. The effectiveness of tiles, functionalized with TiO2 thin films, has been studied in the degradation of NOx at very low concentration in continuous flow reactors.

Nanostructured Solids from Freeze‐Dried Precursors: Multigram Scale Synthesis of TiO2‐Based Powders

Nanocrystalline TiO2 and Ti1−xVxO2 (x = 0.01) powders have been prepared by thermal decomposition, in air, of amorphous precursors resulting from the freeze‐drying of appropriate solutions. In addition, TiO2−xNy (anatase and rutile) and TiOxNy (rock‐salt) have been prepared by thermal treatment in ammonia of a crystalline precursor (TiO2 obtained at 673 K). TEM and SEM images, as well as the analysis of the X‐ray diffraction (XRD) patterns, show the nanoparticulated character of those solids obtained at low temperatures, with typical particle sizes in the 10–20 nm range when prepared at 673 K. The UV–Vis results indicate both the insertion of V in the anatase lattice and the feasibility of nitridation at low temperatures. The photocatalytic properties of these materials (as prepared and after their incorporation to mortar samples) in the degradation of nitrogen oxides have been preliminary evaluated. Although N‐doping enhances the photocatalytic activity of the TiO2 matrix, V‐doping worsens it.

Functionalized building materials: Photocatalytic abatement of NOx by cement pastes blended with TiO2 nanoparticles

De-pollution activity of cement paste samples, added with 0.0%, 0.5%, 1.0%, 3.0% and 5.0% (based on the dry weight of the cement used) of titanium dioxide nanoparticles, TiO2, was evaluated through the degradation of nitrogen oxides, NOx, pollutants. Different blend of titania phases were considered as well, for each addition 100:0, 85:15 and 50:50 anatasa:rutile ratios were used. Measurements were carried out at two aging times, 65h and 28days, finding that at early ages the samples with the best photocatalytic activity, in terms of moles per square meter eliminated and percentage of conversion of NO and NOx, were the ones with a ratio of 85:15 and 5.0% of TiO2, while at late ages the samples with a ratio of 100:0 and 5.0% of TiO2.

Titanium Dioxide Photocleans Polluted Air

Titanium Dioxide Photocleans Polluted Air

Alumina/TiO2/hydroxyapatite interface nanostructure composite filters as efficient photocatalysts for the purification of air

Alumina/TiO2/Apatite interface nanostructure composite filters have been developed for air purification. It was shown that these filters can efficiently absorb and decompose organic species which are suspended in air. To prepare the filters, TiO2 nanopowder was dispersed in titanium sol in 30 and 70 g/L concentrations, and the prepared mixture was deposited on the porous alumina body by dip-coating. Then, the calcined nanostructure composite TiO2–TiO2 was soaked in a simulated physiological solution (SBF) at 37 °C. The surface morphology, surface area, crystalline structure and crystallite sizes of the films were investigated by SEM, EDS, BET, and XRD. The photocatalytic activity of the composite filters, as well as the effect of the TiO2 nanopowder concentration in the titania sol and soaking time in SBF were also evaluated through the degradation of nitrogen oxides (NOx) as one of the dominant causes of air pollution in the car exhaust gases. SEM and XRD results showed that immersion in SBF forms a layer of carbonate-containing apatite on the TiO2 layer. The results showed that increasing nanopowder TiO2 concentration increases the NOx oxidation rate. The prepared alumina/TiO2/HA filter can be used to remove CO gas with the absorption mechanism, as an interesting CO degradation performance (about 95 %) was observed in the alumina/TiO2/HA filter after soaking into SBF for 20 days. However, it could not significantly alter the concentrations of other car exhaust pollutants (SO2 and CxHy).