Enhanced photocatalytic activities of TiO2–SiO2 nanohybrids immobilized on cement-based materials for dye degradation

Challenges and Opportunities of Using Titanium Dioxide Photocatalysis on Cement-Based Materials

Since the early seventies with the work of Akira Fujishima on photocatalytic and superhydrophilic properties of titanium dioxide (TiO2), also known as the Honda–Fujishima effect, photocatalysis has been investigated and progressively implemented in cement-based materials towards the development of self-cleaning, air-purifying and antiseptic materials, buildings and infrastructure. Although important achievements have been obtained at the laboratory scale, their real scale application has had some limitations mainly due to the low efficiencies obtained during adverse environmental conditions. Therefore, this article presents the challenges and opportunities of using of titanium dioxide in cement-based materials towards the development of truly efficient sustainable building materials. First, TiO2 photocatalysis and its incorporation in cementitious materials are presented. Second, self-cleaning, air-purifying and antimicrobial properties are discussed in terms of the lab and pilot project results. Third, conclusions regarding the different multifunctional properties are given towards the real application of TiO2 photocatalysis. Particularly, complementary technologies and strategies are presented in order to increase the above-mentioned multifunctional properties.

Photocatalytic Lime Render for Indoor and Outdoor Air Quality Improvement

This article reports a novel photocatalytic lime render for indoor and outdoor air quality improvement that is composed of a lime binder and doped TiO2 (KRONOClean 7000®) nanoparticles. These nanoparticles were distributed throughout the bulk of the finishing render, instead of as a thin coating, thus ensuring the durability of the photocatalytic properties upon superficial damage. The physical properties of these renders were not affected by the addition of nanoparticles except in the case of surface area, which increased significantly. In terms of their photocatalytic activity, these novel lime renders were shown to degrade up to 12% NOx under UV light and up to 11% formaldehyde under visible light.

Death by waste: Fashion and textile circular economy case

In a circular economy model the way we use the textiles needs to change at a fundamental level. A circular economy is an alternative to a traditional economy (fabrication, use and dispose) in which we keep resources in a loop for as much time as possible, try to maintain their value while in use, and repurpose for generation of new products at the end of utilization. The value of the global fashion industry is 3000 Billion dollars that accounts for more than 2% of the world's Gross Domestic Product (GDP) (https://fashionunited.com/global-fashion-industry-statistics/). In the last two decades not only the textile industry has doubled the production but also an average global annual consumption of textiles has doubled from 7 to 13 kg per person and reached to the threshold of 100 million tonnes of textiles consumption. More than two thirds of the textile goes to landfill at the end of their use and just around 15% is recycled. Various scientific studies confirm that the disposal nature of fast fashion and throwaway culture is resulting in a serious environmental, health, social and economic concern. One of the global environmental challenges arising from micro-plastic and micro-textile waste entering into the oceans that can end up in fish and eventually food chain. Herein, through a systematic literature review, the significance of circular fashion and textile is highlighted and various approaches for reuse, recycle and repurposing of the textiles waste as well as disruptive scientific breakthroughs, innovations and strategies towards a circular textile economy have been discussed. Looking into the future, remarks have been made in regards to tackling the key challenges in recycling of textile materials in different stages of their manufacturing process.

TiO2 nanoparticles supported on PMMA nanofibers for photocatalytic degradation of methyl orange

In this paper, a photocatalyst composed of TiO₂ nanoparticles supported on the nanofibers of poly(methyl methacrylate) (PMMA) was successfully prepared by hydrothermally treating the electrospun PMMA nanofibers containing titanium n-butoxide precursor at 135°C for 8h. As-prepared composite was characterized by field-emission scanning electron microscopy, X-ray diffraction pattern, thermal gravimetric analysis and Brunauer-Emmett-Teller (BET) surface area measurements. It is revealed that high content (42%) of tetragonal anatase TiO₂ nanoparticles are uniformly loaded on the PMMA nanofibers to constitute the composite (TiO₂@PMMA) photocatalyst with BET surface area of 21.4m²g^-1. The photocatalytic activity of TiO₂@PMMA towards the degradation of methyl orange (MO), a model pollutant, has been investigated. It is observed that 0.1g of the composite could degrade 100mL of MO (10mg/L) completely within 50min under UV illumination, exhibiting a high catalytic activity. Moreover, the composite could be easily separated from the reaction system by filtration, and maintain high photocatalytic activity in five consecutive cycles of the degradation of MO, suggesting its potentials in recycling use. The work provides a new approach for the development of novel supported photocatalysts with high catalytic activity and good reusability.

Catalyzed Synthesis and Characterization of a Novel Lignin-Based Curing Agent for the Curing of High-Performance Epoxy Resin

In this study, lignin, an aromatic compound from the forestry industry, was used as a renewable material to synthesize a new aromatic amine curing agent for epoxy resin. Firstly, lignin was separated from black liquor and hydroxyl groups were converted to tosyl groups as leaving groups. Then, primary amination was conducted using an ammonia solution at high pressure and temperature, in the presence of a nano-alumina-based catalyst. The structure of the nanocatalyst was confirmed by FT-IR, ICP, SEM, and XPS analyses. According to the FT-IR spectra, a demethylation reaction, the substitution of hydroxyl groups with tosyl groups, and then an amination reaction were successfully performed on lignin, which was further confirmed by the ¹³C NMR and CHNS analyses. The active hydrogen equivalent of aminated lignin was determined and three samples with 9.9 wt %, 12.9 wt %, and 15.9 wt % of aminated lignin, as curing agents, were prepared for curing the diglycidyl ether of bisphenol A (DGEBA). The thermal characteristics of the curing process of these epoxy samples were determined by DSC and TGA analyses. Moreover, the mechanical performance of the cured epoxy systems, e.g., the tensile strength and Izod impact strength, were measured, showing that in the presence of 12.9 wt % aminated lignin, the mechanical properties of the aminated lignin-epoxy system exhibited the best performance, which was competitive, compared to the epoxy systems cured by commercial aromatic curing agents.

Enhancement of photocatalytic degradation of furfural and acetophenone in water media using nano-TiO2-SiO2 deposited on cementitious materials

In the present study, silicon dioxide (SiO₂) nanoparticles were loaded to titanium dioxide (TiO₂) nano-particles by sol-gel method to make a high porosity photocatalyst nano-hybrid. These photocatalysts were synthesized using titanium tetrachloride and tetraethyl orthosilicate as titanium and silicon sources, respectively, and characterized by X-ray powder diffraction (XRD) and scanning electron microscope methods. Subsequently, the optimizations of the component and operation conditions were investigated. Then, nano-sized TiO₂ and TiO₂-SiO₂ were supported on concrete bricks by the dip coating process. The photocatalytic activity of nano photocatalysts under UV irradiation was examined by studying the decomposition of aqueous solutions of furfural and acetophenone (10 mg/L) as model of organic pollutants to CO₂ and H₂O at room temperature. A decrease in the concentration of these pollutants was assayed by using UV-visible absorption, gas chromatography technique, and chemical oxygen demand. The removal of these pollutants from water using the concrete-supported photocatalysts under UV irradiation was performed with a greater efficiency, which does not require an additional separation stage to recover the catalyst. Therefore, it would be applicable to use in industrial wastewater treatment at room temperature and atmospheric pressure within the optimized pH range.

Improved Photodegradation of Organic Contaminants Using Nano-TiO2 and TiO2 -SiO2 Deposited on Portland Cement Concrete Blocks

The photocatalytic activity of TiO2 nanoparticles (nano-TiO2 ) and its hybrid with SiO2 (nano-TiO2 -SiO2 ) for degradation of some organic dyes on cementitious materials was studied in this work. Nanohybrid photocatalysts were prepared using an inorganic sol-gel precursor and then characterized using XRD, SEM and UV-Vis. The grain sizes were estimated by Scherrer's equation to be around 10 nm. Then, a thin layer was applied to Portland cement concrete (PCC) blocks by dipping them into nano-TiO2 and nano-TiO2 -SiO2 solution. The efficiency of coated PCC blocks for the photocatalytic decomposition of two dyes, Malachite Green oxalate (MG) and Methylene Blue (MB), was examined under UV and visible irradiation and then monitored by the chemical oxygen demand tests. The results showed that more than 80% and 92% of MG and MB were decomposed under UV-Vis irradiation using blocks coated with nano-TiO2 -SiO2 . TiO2 /PCC and TiO2 -SiO2 /PCC blocks showed a significant ability to oxidize dyes under visible and UV lights and TiO2 -SiO2 /PCC blocks require less time for dye degradation. Based on these results, coated blocks have increased photocatalytic activity which can make them commercially accessible photocatalysts.