Photocatalytic activity of titanium dioxide modified concrete materials - influence of utilizing recycled glass cullets as aggregates

Eco-Innovative UHPC-Enhancing Sustainability, Workability, and Ductility with Recycled Glass Cullet Powder and Plastic Bottle Hybrid Fibers

Utilizing waste materials in producing ultra-high-performance concrete (UHPC) represents a highly effective approach to creating environmentally sustainable concrete using renewable resources. This study focused on incorporating ground glass cullet (GP) at various replacement levels in UHPC production. Additionally, plastic bottle fibers (PBFs) were derived from discarded plastic bottles and employed in the mix. The replacement levels for GP spanned from 0% to 40%. Single-use plastic bottles were transformed into strip fibers, both with and without the inclusion of microsteel fibers, at varying contents of 1.1% and 2.2% (volume-based). A single-fiber test was conducted on PBFs under different strain rates. The introduction of optimal GP content had a profound positive iMPact on compressive strength. Incorporating 2.2% plastic strips induced strain hardening behavior, while further inclusion of microsteel fibers resulted in substantial enhancements in mechanical properties. Two types of microsteel fibers were employed, characterized by different aspect ratios of 65 and 100. The optimum GP content was identified as 10%. Moreover, the UHPC mix achieved superior compressive strength, exceeding 140 MPa when composed of 1.3% (volume-based) microsteel fibers with an aspect ratio of 65 and 2.2% PBF (volume-based). Notably, mixtures featuring microsteel fibers with a higher aspect ratio demonstrated the highest flexural strength, exceeding 8000 N in the presence of 2.2% PBF. Longer microsteel fibers exhibited adequate slip properties, facilitating strain transfer and achieving a strain-hardening response in conjunction with plastic bottle fibers. These findings illuminate the potential for harnessing hazardous waste materials to improve the performance and sustainability of UHPC formulations.

Self-Cleaning Cement-Based Building Materials

The modern rhythm of human life leads to well-known problems, which are air, water and soil pollution and climate warming. An increase in the power of industries and vehicles leads not only to atmospheric pollution by-products of incomplete fuel combustion but also to various microscopic particles that form aerosols, which carry an obvious danger to human health and also pollute the buildings’ facades. An environmentally friendly building material with a hybrid method “Nano-titania gradient” was developed. This method consists of forming a gradient of n-TiO2 particles concentration in the composite since the physical properties of the composite are always inextricably linked to the geometry. To increase the efficiency of the photocatalytic process, a method of surface sensitization of titanium dioxide with the use of graphene oxide was proposed, which contributed to an increase in the overall photosensitivity. Thus, the decomposition of nitrogen oxide by volume with the modified surface increased by 27% in comparison with the classic titanium dioxide, and the decomposition of volatile organic substances increased by 32%. It was found that for the facade plate made with surface-sensitized TiO2, the process of self-cleaning is completed after 3 h after the irradiation start. The modern rhythm of human life leads to well-known problems, which are air, water and soil pollution and climate warming. Using the theory of percolation, the concentration range of the photocatalyst content was calculated. To facilitate the material, waste cellulose was introduced. To increase the efficiency of the photocatalytic process, a method of surface sensitization of titanium dioxide (SS TiO2) with the use of graphene oxide was proposed. The analysis of the experimental-statistical models of the compressive strength shows that the optimum content of TiO2 was in the range from 0.8 to 1.1%, and cellulose from 0.4 to 0.8%, the optimum content of SS TiO2 was in the range from 0.7 to 1.1%, and cellulose from 0.4 to 0.8%. Analysis of the experimental and statistical model of the bending strength shows that the optimal content of TiO2 and SS TiO2 was in the range of 0.6 to 1.0%, and cellulose from 0.4 to 0.8%. When studying the structure of composites, it was found that titanium dioxide was sorbed on the surface of swollen cellulose fibers and remained there after the process of cement hydration. The effectiveness of the method of surface sensitization of titanium dioxide by combining it with graphene oxide was shown. Thus, the decomposition of nitrogen oxide by volume with the modified surface increased by 27% in comparison with the classic titanium dioxide, and the decomposition of volatile organic substances increased by 32%. It was found that for the facade plate made with surface-sensitized TiO2, the process of self-cleaning was completed after 3 h after the irradiation start.

Potential Applications of Geopolymer Cement-Based Composite as Self-Cleaning Coating: A Review

Nowadays, concepts of self-cleaning have received great attention in construction building materials. Self-cleaning with the presence of photocatalyst has been applied in building materials to overcome the problem of building surfaces becoming dirty after exposure for a long time in highly polluted areas. To date, the concept of green blending materials has led to the development of a new binding material for green materials, which is geopolymer with an addition of photocatalyst. This review focused on the development of conventional self-cleaning paste, including the method of preparation and the impact of adding photocatalyst on physical and mechanical properties. However, although self-cleaning has been widely applied in conventional cement paste, its applications in geopolymers are still in the early stages of development and require more research. Therefore, this paper also intended to review the current knowledge on properties of geopolymer cement-based composite and its potential to be applied as a self-cleaning coating.

Evaluation of Reducing NO and SO2 Concentration in Nano SiO2-TiO2 Photocatalytic Concrete Blocks

The use of titanium dioxide in concrete block pavements is a promising approach to reduce air pollution in the roadside. When TiO₂ is used as an additive of cement concrete or mortar, it is not dispersed uniformly due to agglomeration between particles causing the degradation of photocatalytic reaction. To improve the photocatalytic performance of TiO₂, the Nano SiO₂-TiO₂ (NST) has been developed by coating TiO₂ with SiO₂ as a support using the sol-gel method. The environmental performance of concrete blocks incorporating NST as an additive was evaluated using both laboratory and full-scale chamber experiments. It was observed from laboratory environment chamber testing that the NO reduction efficiency of concrete blocks with 4% NST ranged from 16.5 to 59.1%, depending on the UV intensity. Results of the full-scale chamber test on NST concrete blocks indicated that the NO and SO₂ reduction efficiencies were 22.3% and 14.4% at a 564 W/m² of solar radiation, respectively. It was found that the increase in UV intensity and solar radiation had a positive effect on decreasing NO and SO₂ concentration. In the future, the NST will be applied at in-service photocatalytic block pavements to validate the environmental performance in field conditions.

Development of Photocatalytic 3D-Printed Cementitious Mortars: Influence of the Curing, Spraying Time Gaps and TiO2 Coating Rates

This work evaluated the photocatalytic activity of 3D-printed cementitious mortar specimens functionalized with TiO2 nanoparticles to obtain a multifunctional and smart concrete. This research aims to assess the influence of different parameters related to the functionalization process such as adsorption, coating time gaps, and coating rates on the degradation efficiency of the functionalized cementitious specimens. Each specimen was evaluated under the degradation of Rhodamine B (RhB) in an aqueous solution using a sun-light simulation. The obtained results showed a decrease in adsorption (under dark condition) with increasing the sample curing age. The highest photocatalytic efficiency was observed for coated samples aged 7 days. By increasing the coating rates, the photocatalytic efficiency is enhanced. Nonetheless, regardless of the coating rates, all the specimens showed an increase in photocatalytic efficiency for longer time periods of light exposition, i.e., after 8 h of irradiation.

An overview on the properties of eco-friendly concrete paving blocks incorporating selected waste materials as aggregate

Paving block is a widely used pavement material due to its long service life, fast and easy production and easily replaced for maintenance purpose. The huge production volume of paving blocks consumes large amount of natural aggregates such as sand and granite. Therefore, there is a necessity to review the utilization of alternative materials as the aggregate replacement to cut down both the consumption of natural resources and disposal of various waste. This paper thus analyses published works and provides a summary of knowledge on the effect of utilizing selected waste materials such as soda-lime glass, cathode ray tube (CRT) glass, recycled concrete waste, marble waste, crumb rubber (CR) waste and waste foundry sand (WFS) as aggregate replacement in concrete paving blocks fabrication. The influence of each waste material on the properties of paving block is discussed and highlighted in this paper. The adherence of the waste material paving block to the standard requirements is also presented to provide a clear direction on the utilization of these materials for practical application. Soda-lime glass, CRT glass, pre-treated RCA and calcined WFS have the potential to be utilized in high quantities (30-100%), normal RCA and marble waste can be incorporated in moderate amount (30%) while CR waste and WFS is limited to low amount (6-10%). In overall, the usage of waste materials as aggregate replacement has good potential for producing eco-friendly concrete paving block towards the sustainable development of construction material.

Biomaterials for Three-Dimensional Cell Culture: From Applications in Oncology to Nanotechnology

Three-dimensional cell culture has revolutionized cellular biology research and opened the door to novel discoveries in terms of cellular behavior and response to microenvironment stimuli. Different types of 3D culture exist today, including hydrogel scaffold-based models, which possess a complex structure mimicking the extracellular matrix. These hydrogels can be made of polymers (natural or synthetic) or low-molecular weight gelators that, via the supramolecular assembly of molecules, allow the production of a reproducible hydrogel with tunable mechanical properties. When cancer cells are grown in this type of hydrogel, they develop into multicellular tumor spheroids (MCTS). Three-dimensional (3D) cancer culture combined with a complex microenvironment that consists of a platform to study tumor development and also to assess the toxicity of physico-chemical entities such as ions, molecules or particles. With the emergence of nanoparticles of different origins and natures, implementing a reproducible in vitro model that consists of a bio-indicator for nano-toxicity assays is inevitable. However, the maneuver process of such a bio-indicator requires the implementation of a repeatable system that undergoes an exhaustive follow-up. Hence, the biggest challenge in this matter is the reproducibility of the MCTS and the associated full-scale characterization of this system's components.

Automobile Exhaust Removal Performance of Pervious Concrete with Nano TiO2 under Photocatalysis

The urban environment is facing serious problems caused by automobile exhaust pollution, which has led to a great impact on human health and climate, and aroused widespread concern of the government and the public. Nano titanium dioxide (TiO₂), as a photocatalyst, can be activated by ultraviolet irradiation and then form a strong REDOX potential on the surface of the nano TiO₂ particles. The REDOX potential can degrade the automobile exhaust, such as nitrogen oxides (NO_x) and hydrocarbons (HC). In this paper, a photocatalytic environmentally friendly pervious concrete (PEFPC) was manufactured by spraying nano TiO₂ on the surface of it and the photocatalytic performance of PEFPC was researched. The nano TiO₂ particle size, TiO₂ dosage, TiO₂ spraying amount, and dispersant dosage were selected as factors to investigate the efficiency of photocatalytic degradation of automobile exhaust by PEFPC. Moreover, the environmental scanning electron microscope (ESEM) was used to evaluate the distribution of nano TiO₂ on the surface of the pervious concrete, the distribution area of nano TiO₂ was obtained through Image-Pro Plus, and the area ratio of nano TiO₂ to the surface of the pervious concrete was calculated. The results showed that the recommended nano TiO₂ particle size is 25 nm. The optimum TiO₂ dosage was 10% and the optimum dispersant dosage was 5.0%. The photocatalytic performance of PEFPC was best when the TiO₂ spraying amount was 333.3 g/m². The change in the photocatalytic ratio of HC and NO_x is consistent with the distribution area of nano TiO₂ on the surface of the pervious concrete. In addition, the photocatalytic performance of PEFPC under two light sources (ultraviolet light and sunlight) was compared. The results indicated that both light sources were able to stimulate the photocatalytic performance of PEFPC. The research provided a reference for the evaluation of automobile exhaust removal performance of PEFPC.

Recent Progress in the Abatement of Hazardous Pollutants Using Photocatalytic TiO2-Based Building Materials

Titanium dioxide (TiO2) has been extensively investigated in interdisciplinary research (such as catalysis, energy, environment, health, etc.) owing to its attractive physico-chemical properties, abundant nature, chemical/environmental stability, low-cost manufacturing, low toxicity, etc. Over time, TiO2-incorporated building/construction materials have been utilized for mitigating potential problems related to the environment and human health issues. However, there are challenges with regards to photocatalytic efficiency improvements, lab to industrial scaling up, and commercial product production. Several innovative approaches/strategies have been evolved towards TiO2 modification with the focus of improving its photocatalytic efficiency. Taking these aspects into consideration, research has focused on the utilization of many of these advanced TiO2 materials towards the development of construction materials such as concrete, mortar, pavements, paints, etc. This topical review focuses explicitly on capturing and highlighting research advancements in the last five years (mainly) (2014-2019) on the utilization of various modified TiO2 materials for the development of practical photocatalytic building materials (PBM). We briefly summarize the prospective applications of TiO2-based building materials (cement, mortar, concretes, paints, coating, etc.) with relevance to the removal of outdoor/indoor NOx and volatile organic compounds, self-cleaning of the surfaces, etc. As a concluding remark, we outline the challenges and make recommendations for the future outlook of further investigations and developments in this prosperous area.

Eco-Friendly Pavements Manufactured with Glass Waste: Physical and Mechanical Characterization and Its Applicability in Soil Stabilization

The use of glass waste, which by its nature cannot be recycled, might be a viable alternative in the manufacture of cements and concrete that is also economical and environmentally friendly. This alternative can reduce landfill areas with this inert residue but also limit the use of raw materials employed in the manufacture of cement and concrete and, consequently, contribute to minimize the environmental impact generated by this activity. In this research, the feasibility of using a limestone-type material treated with a binder manufactured with micronized glass powder and basic reagents, in the preparation of a gravel–cement- or soil–cement-type material, was analyzed. For this purpose, the strength, compactability, structural capacity, resistance to the action of water, stiffness and durability of the material obtained were characterized. From the tests that were carried out and the results obtained, it can be concluded that the use of glass powder, with a particle size of 16 μm, is ideal for the production of a gravel–cement- or soil–cement-type material. This material could be used as an environmentally-friendly pavement, especially suitable for peri-urban roads and park roads, where it can be used without coating, or as a base layer or sub-base for road surfaces, with little cracking due to shrinkage.

TiO2-based Photocatalytic Cementitious Composites: Materials, Properties, Influential Parameters, and Assessment Techniques

Applications of heterogeneous photocatalytic processes based on semiconductor particles in cement-based materials have received great attention in recent years in enhancing the aesthetic durability of buildings and reducing global environmental pollution. Amongst all, titanium dioxide (TiO₂) is the most widely used semiconductor particle in structural materials with photocatalytic activity because of its low cost, chemically stable nature, and absence of toxicity. Utilization of TiO₂ in combination with cement-based materials would plunge the concentration of urban pollutants such as NO_x. In fact, cementitious composites containing TiO₂ have already found applications in self-cleaning buildings, antimicrobial surfaces, and air-purifying structures. This paper aims to present a comprehensive review on TiO₂-based photocatalysis cement technology, its practical applications, and research gaps for further progression of cementitious materials with photocatalytic activity.

Photocatalytic and Pozzolanic Properties of Nano-SiO₂/Al₂O₃-TiO₂ Powder for Functional Mortar

The present study intended to find a way to use TiO₂, one of the most widely used photocatalysts, as a construction material. To that end, nano-SiO₂/Al₂O₃-TiO₂ powder (NTCP) was synthesized by coating SiO₂ and Al₂O₃ support materials with TiO₂. The NTCP was anatase phase spherical particles, specific surface areas were 319 m²/g and 267 m²/g for the SiO₂-TiO₂ powder and Al₂O₃-TiO₂ powder. UV absorption test results showed the developed NTCP had a light absorption peak at wavelengths of 380 nm or below, and its absorbance was much larger than that of commercial TiO₂. The NTCP formed smaller pores on the surface than commercial TiO₂. As a result, the flow of the mortar decreased as the adsorption strength increased and combined a large number of water molecules. In addition, the Pozzolanic reaction by SiO₂ and Al₂O₃ used as support materials produced many calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H). This has shown an increased strength of mortar mixed with the NTCP by promoting a nucleation effect and reducing the filling effect and the number of harmful holes in the mortar.

Preparation and Characterization of Zeolite/TiO₂ Cement-Based Composites with Excellent Photocatalytic Performance

A zeolite/TiO₂ composite (ZTC) was applied to prepare a high-quality photocatalytic cement-based material (PCM). The acetone degradation experiment and micro measurements including XRD(X-Ray Diffractometer), SEM-EDS(Scanning Electron Microscope-Energy Dispersive Spectrometer), BET(BET Specific Surface Area Tester), FTIR(Fourier Transform Infrared Spectrometer) were conducted to characterize the photocatalytic efficiency and physicochemical properties of PCM, respectively. Results show that TiO₂ particles disperse on the surface of a PCM homogeneously and provide abundant active sites for photocatalytic reactions. Compared to a normal photocatalytic cement-based material (NPCM), the TiO₂ content of a PCM is lower and its photocatalytic efficiency is higher. The ZTC frees TiO₂ particles from the impacts of cement hydration products and increases the adsorption volume of acetone. The photocatalytic performance of the PCM was stable after repeated tests. Using the ZTC as a photocatalyst has a prominent effect on the photocatalytic performance of the PCM.

Experimental investigation of photocatalytic effects of concrete in air purification adopting entire concrete waste reuse model

This research investigated the capacities of recycled aggregate concrete adopting entire concrete waste reuse model in degrading NO_2. Two major issues within environmental sustainability were addressed: concrete waste reuse rate and mitigation of hazards substances in the polluted air. The study consisted of two stages: identification of proper replacement rates of recycled concrete wastes in new concrete mixture design, and the evaluation of photocatalytic performance of recycled aggregate concrete in degrading NO₂. It was found that replacement rates up to 3%, 30%, and 50% for recycled power, recycled fine aggregate, and recycled coarse aggregate respectively could be applied in concrete mixture design without deteriorating concrete strength. Recycled aggregates contained both positive attributes ("internal curing") and negative effects (e.g., lower hardness) to concrete properties. It was found that 30%-50% of natural coarse aggregate replaced by recycled coarse aggregates coated with TiO₂ would significantly improve the photocatalytic performance of concrete measured by degradation rate of NO₂. Micro-structures of recycled aggregates observed under microscope indicated that soaking recycled aggregates in TiO₂ solution resulted in whiskers that filled the porosity within recycled aggregates which enhanced concrete strength.

Analytical Nanoscience and Nanotechnology: Where we are and where we are heading

The main aim of this paper is to offer an objective and critical overview of the situation and trends in Analytical Nanoscience and Nanotechnology (AN&N), which is an important break point in the evolution of Analytical Chemistry in the XXI century as they were computers and instruments in the second half of XX century. The first part of this overview is devoted to provide a general approach to AN&N by describing the state of the art of this recent topic, being the importance of it also emphasized. Secondly, particular but very relevant trends in this topic are outlined: the analysis of the nanoworld, the so "third way" in AN&N, the growing importance of bioanalysis, the evaluation of both nanosensors and nanosorbents, the impact of AN&N in bioimaging and in nanotoxicological studies, as well as the crucial importance of reliability of the nanotechnological processes and results for solving real analytical problems in the frame of Social Responsibility (SR) of science and technology. Several reflections are included at the end of this overview written as a bird's eye view, which is not an easy task for experts in AN&N.

Influence of Binders and Lightweight Aggregates on the Properties of Cementitious Mortars: From Traditional Requirements to Indoor Air Quality Improvement

Innovative and multifunctional mortars for renders and panels were manufactured using white photocatalytic and non-photocatalytic cement as binder. Unconventional aggregates, based on lightweight materials with high specific surface and adsorbent properties, were adopted in order to investigate the possible ability to passively improve indoor air quality. The reference mortar was manufactured with traditional calcareous sand. Results show that even if the mechanical properties of mortars with unconventional aggregates generally decrease, they remain acceptable for application as render. The innovative mortars were able to passively improve indoor air quality in terms of transpirability (70% higher), moisture buffering ability (65% higher) and depolluting capacity (up to 75% higher) compared to traditional ones under the current test conditions.

Different Roles of Water in Photocatalytic DeNOx Mechanisms on TiO2: Basis for Engineering Nitrate Selectivity?

The nitrate selectivity of TiO₂ has important consequences for its efficiency as a NOx depollution photocatalyst. Most emphasis is typically given to photocatalyst activity, a measure of the rate at which NOx concentrations are reduced, but a reduction in NOx concentration (mainly NO + NO₂) is not necessarily a reduction in atmospheric NO₂ concentration because the catalytic process itself generates NO₂. With NO₂ being considerably more toxic than NO, more emphasis on nitrate selectivity, a measure of the NOx conversion to nitrate, and how to maximize it, should be given in engineering photocatalytic systems for improved urban air quality. This study, on the importance of adsorbed water in the photocatalytic oxidation of NOx, has identified important correlations which differentiate the role that water plays in the oxidation of NO and NO₂. This observation is significant and offers insights into controlling nitrate selectivity on TiO₂ and the potential for increased effectiveness in environmental photocatalyst applications.

The Effect of Curing Temperature on the Properties of Cement Pastes Modified with TiO₂ Nanoparticles

This paper investigates the effect of curing temperature on the hydration, microstructure, compressive strength, and transport of cement pastes modified with TiO₂ nanoparticles. These characteristics of cement pastes were studied using non-evaporable water content measurement, X-ray diffraction (XRD), compressive strength test, electrical resistivity and porosity measurements, and scanning electron microscopy (SEM). It was shown that temperature enhanced the early hydration. The cement pastes cured at elevated temperatures generally showed an increase in compressive strength at an early age compared to the cement paste cured at room temperature, but the strength gain decreased at later ages. The electrical resistivity of the cement pastes cured at elevated temperatures was found to decrease more noticeably at late ages compared to that of the room temperature cured cement paste. SEM examination indicated that hydration product was more uniformly distributed in the microstructure of the cement paste cured at room temperature compared to the cement pastes cured at elevated temperatures. It was observed that high temperature curing decreased the compressive strength and electrical resistivity of the cement pastes at late ages in a more pronounced manner when higher levels of TiO₂ nanoparticles were added.

Characterization of Mechanical and Bactericidal Properties of Cement Mortars Containing Waste Glass Aggregate and Nanomaterials

The recycling of waste glass is a major problem for municipalities worldwide. The problem concerns especially colored waste glass which, due to its low recycling rate as result of high level of impurity, has mostly been dumped into landfills. In recent years, a new use was found for it: instead of creating waste, it can be recycled as an additive in building materials. The aim of the study was to evaluate the possibility of manufacturing sustainable and self-cleaning cement mortars with use of commercially available nanomaterials and brown soda-lime waste glass. Mechanical and bactericidal properties of cement mortars containing brown soda-lime waste glass and commercially available nanomaterials (amorphous nanosilica and cement containing nanocrystalline titanium dioxide) were analyzed in terms of waste glass content and the effectiveness of nanomaterials. Quartz sand is replaced with brown waste glass at ratios of 25%, 50%, 75% and 100% by weight. Study has shown that waste glass can act as a successful replacement for sand (up to 100%) to produce cement mortars while nanosilica is incorporated. Additionally, a positive effect of waste glass aggregate for bactericidal properties of cement mortars was observed.

Application of concrete surfaces as novel substrate for immobilization of TiO2 nano powder in photocatalytic treatment of phenolic water

BACKGROUND

In this study, concrete application as a substrate for TiO2 nano powder immobilization in heterogeneous photocatalytic process was evaluated. TiO2 immobilization on the pervious concrete surface was done by different procedures containing slurry method (SM), cement mixed method (CMM) and different concrete sealer formulations. Irradiation of TiO2 was prepared by UV-A and UV-C lamps. Phenolic wastewater was selected as a pollutant and efficiency of the process was determined in various operation conditions including influent phenol concentration, pH, TiO2 concentration, immobilization method and UV lamp intensity.

FINDINGS

The removal efficiency of photocatalytic process in 4 h irradiation time and phenol concentration ranges of 25-500 mg/L was more than 80 %. Intermediates were identified by GC/Mass and spectrophotometric analysis.

CONCLUSIONS

According to the results, photocatalytic reactions followed the pseudo-first-order kinetics and can effectively treate phenol under optimal conditions.

Photocatalytic degradation and reactor modeling of 17α-ethynylestradiol employing titanium dioxide-incorporated foam concrete

Photocatalytic degradation of 17α-ethynylestradiol (EE2) using TiO2 photocatalysts incorporated with foam concrete (TiO2/FC) was investigated for the first time. Scanning electron microscopy (SEM) study of the samples revealed a narrow air void size distribution on the surface of FC cubes on with 5 wt% addition of P25 TiO2, and TiO2 particles were distributed heterogeneously on the surface of TiO2/FC samples. The sorption and photocatalytic degradation of EE2 with UV-light irradiation by TiO2/FC cubes were investigated. Adsorption capacity of EE2 by the TiO2/FC and blank foam concrete (FC) samples were similar, while the degradation rates showed a great difference. More than 50 % of EE2 was removed by TiO2/FC within 3.5 h, compared with 5 % by blank FC. The EE2 removal process was then studied in a photoreactor modified from ultraviolet disinfection pool and constructed with TiO2/FC materials. An integrated model including a plate adsorption-scattering model and a modified flow diffusion model was established to simulate the photocatalytic degradation process with different radiation fields, contaminant load, and flow velocity. A satisfactory agreement was observed between the model simulations and experimental results, showing a potential for the design and scale-up of the modified photocatalytic reactor.

Orthogonal experimentation for optimization of TiO2 nanoparticles hydrothermal synthesis and photocatalytic property of a TiO2/concrete composite

An orthogonal experimental design was applied to optimize the hydrothermal preparation parameters of TiO₂ nanoparticles by the analysis of means (ANOM) and variances (ANOVA).

Preparation of sustainable photocatalytic materials through the valorization of industrial wastes

A new value-added material was developed from wastes to aim for appropriate waste management and sustainable development. This paper reports the valorization of industrial sandblasting operation wastes (SOWs) as new photocatalytic materials. This waste is composed of Fe2 O3 (60.7 %), SiO2 (29.1 %), and Al2 O3 (3.9 %) as the main components. The high presence of iron oxides was used to develop photocatalytic properties through their thermal transformation into α-Fe2 O3 . The new product, SOW-T, exhibited a good behavior towards the photochemical degradation of organic dyes. The preparation of advanced photocatalytic materials that exhibit self-cleaning and depolluting properties was possible by the inclusion of SOW-T and TiO2 in a cement-based mortar. The synergy observed between both materials enhanced their photocatalytic action. To the best of our knowledge, this is the first report that describes the use of transformed wastes based on iron oxide for the photochemical oxidation of NOx gases.

Photocatalytic activity of titanium dioxide nanoparticle coatings applied on autoclaved aerated concrete: effect of weathering on coating physical characteristics and gaseous toluene removal

Autoclaved aerated concrete has been coated by TiO(2) nanoparticles through a dip-coating (DC) and a novel vacuum saturation (VS) method to investigate the weathering resistance and gaseous toluene removal potential of both coating types. The effect of intensive weathering - corresponding to a period of about 25 years - on the coating characteristics was studied in terms of TiO(2) content, coating thickness and color changes. Toluene removal was investigated in a lab-scale flow-through photoreactor at 24°C and 52% relative humidity, and results obtained immediately after application of the coatings and after two weathering stages were compared. Weathering of the DC and VS coated samples resulted into a decrease of the coating layer thickness of more than 98%, confirmed by a decline in TiO(2) content by more than 99% and 93%, respectively. Surprisingly, toluene removal efficiencies before and after weathering kept constant at about 95% for both coating types, corresponding to an elimination rate of 60-70 mg/(m(2)h) at an initial toluene concentration of 15 ppm(v) and a gas residence time of 3 min. Increasing the toluene load by applying higher toluene inlet concentrations (up to 35 ppm(v)) and lower gas residence times (1 min) did decrease the toluene removal efficiency to 32-41%, but elimination rates increased up to 214 mg/(m(2)h), being a factor of 1.6-4.5 times higher than reported in recent work.

Photocatalytic cementitious materials: influence of the microstructure of cement paste on photocatalytic pollution degradation

Incorporation of nanophotocatalysts into cementitious materials is an important development in the field of photocatalytic pollution mitigation. In this study, the photocatalytic nitrogen oxides (NO(x)) conversion by titanium dioxide (TiO(2)) blended cement pastes was used as a standard process to evaluate the internal factors that may influence the depollution performance. The chemical composition and microstructure of the TiO(2) modified cement pastes were characterized and analyzed. The active photocatalytic sites related to the surface area of TiO(2) are the key factor in determining the photocatalytic activity. Ordinary Portland cement pastes showed lower photocatalytic activity than white cement pastes probably due to the influence of minor metallic components. X-ray diffraction and thermal gravity analysis demonstrated that TiO(2) was chemically stable in the hydrated cement matrix. The NO(x) removal ability decreased with the increase of curing age. This could be attributed to the cement hydration products which filled up capillary pores forming diffusion barriers to both reactants and photons. It was also proved that surface carbonation could reduce the photocatalytic pollution removal efficiency after the hydration of cement.