Photocatalytic Applications of Micro-and Nano- TiO 2 in Environmental Engineering Photocatalytic Applications of Micro-and Nano-TiO 2 in Environmental Engineering (original) (raw)
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Photocatalytic Applications of Micro- and Nano-TiO 2 in Environmental Engineering
Critical Reviews in Environmental Science and Technology, 2008
The photocatalytic activity of micro-and nano-titanium dioxide (TiO 2 ) has been utilized to significantly improve the degradation efficiencies of various contaminants in both water treatment and air pollution control. This article is a review of the literature covering current research on environmental applications of microand nano-TiO 2 . The mechanisms of contaminant degradation of nanoparticle TiO 2 are reviewed, and its special properties are compared to micro-sized TiO 2 in air purification and water treatment.
Synthesis and photocatalytic activity for TiO2 nanoparticles as air purification
MATEC Web of Conferences
In the present work, titanium dioxide (TiO2) nanoparticles (NP's) were prepared using sol-gel process from Titanium Tetrachloride (TiCl4) as a precursor with calcinations at two temperatures (500 and 900) ᵒC. The effect of calcinations temperatures on the structural, optical, morphological and Root Mean Square (roughness) properties were investigated by means of Scanning Electron Microscopy, X-ray Diffraction (XRD), and Atomic Force Microscopy (AFM). Bacterial inactivation was evaluated using TiO2-coated Petri dishes. A thin layer of photocatalytic TiO2 powder was deposited on glass substrate in order to investigate the selfcleaning effect of TiO2 nanoparticles in indoor and outdoor applications. Ultra-hydrophilicity was assessed by measuring the contact angle and it evaluated photolysis properties through the degradation of potassium permanganate (KMnO4) under direct sunlight. XRD analysis indicated that the structure of TiO2 was anatase at 500 ᵒC and rutile at 900 ᵒC calcination temperatures. As the calcination temperature increases, the crystallinity is improved and the crystallite size becomes larger. Coated films of TiO2 made the has permeability, low water contact angle and good optical activity. These are properties essential for the application of the surface of the self-cleaning. The final results illustrate that titanium dioxide can be used in the build materials to produce coated surfaces in order to minimize air pollutants that are placed in microbiologically sensitive circumference like hospitals and the food factory.
Semiconductor Photocatalysis - Materials, Mechanisms and Applications, 2016
This chapter presents the use of a commercial micro-sized TiO 2 powder as an alternative to the traditional nano-powders as semiconductors in photocatalytic processes. Results of the photocatalytic efficiency towards the photodegradation of the traditional pollutant molecules both in gas phase (nitrogen oxides (NO x) and volatile organic compounds (VOCs)) and in water phase (phenol) are presented and compared to the results obtained with two nano-sized reference powders. Micro-sized TiO 2 is also industrially coated at the surfaces of porcelain grés tiles (Active Clean Air and Antibacterial Ceramic™). The possibility to have a photocatalytic material, strongly stuck at the surface of a vitrified tile, increases the use of photocatalysis in real conditions: no problem of filtration of the semiconductor from the liquid medium after use and no risks of leakage of nanoparticles in the atmosphere. Tests were performed using reactors equipped with UV-A lamps and with suitable analytical systems, depending on the final purpose. Characterization data from both powders and coated tiles are put in correlation with the photocatalytic results to understand the semiconductor action during the photocatalytic process. Polluting molecules were chosen in order to cover all the common aspects of environmental pollution: NO x and some VOCs represent the model molecules to test the efficiency of the micro-sized TiO 2 (degradation from the pristine molecule to CO 2 or inorganic salts) in gas phase. As for the water pollution, phenol was chosen as common pollutant in worldwide rivers. Moreover, tests on self-cleaning and antibacterial properties are also reported. The positive results of micro-sized TiO 2 both in powder and coated onto the surface of porcelain grés tiles open the way to new photocatalytic products that do
Journal of Nanomaterials, 2015
The presence of both organic and inorganic pollutants in water due to industrial, agricultural, and domestic activities has led to the global need for the development of new, improved, and advanced but effective technologies to effectively address the challenges of water quality. It is therefore necessary to develop a technology which would completely remove contaminants from contaminated waters. TiO2(titania) nanocatalysts have a proven potential to treat “difficult-to-remove” contaminants and thus are expected to play an important role in the remediation of environmental and pollution challenges. Titania nanoparticles are intended to be both supplementary and complementary to the present water-treatment technologies through the destruction or transformation of hazardous chemical wastes to innocuous end-products, that is, CO2and H2O. This paper therefore explores and summarizes recent efforts in the area of titania nanoparticle synthesis, modifications, and application of titania n...
Chemosphere, 2018
Photocatalytic oxidation (PCO) is a well-known technology for air purification and has been extensively studied for removal of many air pollutants. Titanium dioxide (TiO 2) is the most investigated photocatalyst in the field of environmental remediation owed to its chemical stability, non-toxicity, and suitable positions of valence and conduction bands. Various preparation techniques including sol-gel, flame hydrolysis, water-in-oil microemulsion, chemical vapor deposition, solvothermal, and hydrothermal have been employed to obtain TiO 2 materials. Hydro-/Solvothermal (HST) synthesis, focus of the present work, can be defined as a preparation method in which crystal growth occurs in a solvent at relatively low temperature (< 200 ˚C) and above atmospheric pressure. This paper aims to provide a comprehensive and critical review of current knowledge regarding the application of HST synthesis for fabrication of TiO 2 nanostructures for indoor air purification. TiO 2 nanostructures are categorized from the morphological standpoint (e.g. nanoparticles, nanotubes, nanosheets, and hierarchically porous) and discussed in detail. The influence of preparation parameters including hydrothermal time, temperature, pH of the reaction medium, solvent, and calcination temperature on physical, chemical, and optical properties of TiO 2 is reviewed. Considering the complex interplay among catalyst properties, a special
Nano/microsized TiO2 composite photocatalysts for environmental purification
Journal of the Ceramic Society of Japan, 2018
TiO 2 photocatalyst is one of the most important photocatalysts for practical use owing to its low toxicity, high chemical stability, natural abundance, and strong oxidation power. However, its low quantum efficiency which is derived from fast electron-charge recombination and its low decomposition rate against organic compounds in low concentration and/or low affinity for TiO 2 surface is problematic for environmental purification. To overcome these problems, functionalized photocatalysts that have a nano/microsized structure were prepared by combining TiO 2 and other materials in our study. A Z-scheme photocatalyst thin film, a TiO 2-coated porous glass composite with high adsorption capacity, and a TiO 2-coated stainless mesh for electric field-assisted photocatalysis were prepared using liquid and colloidal processes. This study reports the photocatalytic properties of these composites in air and water environments and their decomposition mechanisms.
Considerations to improve adsorption and photocatalysis of low concentration air pollutants on TiO2
Catalysis Today, 2014
Rapid development of nanoscience and nanotechnology has greatly supported the industrialization of titanium dioxide for environmental pollution control during the past decade. Nowadays, low concentration air purification seems to be one of the most promising directions of environmental TiO 2 applications. However, much more effort is needed to perfect this technology and make it broadly applicable. Understanding the nature of the adsorption and photooxidation under realistic and practical conditions would give clear guidance for the development of novel catalytic materials and technologies. This paper describes the significant effects of the adsorption of low concentration gas-phase pollutants in practical conditions on the photocatalytic oxidation efficiency and mechanism. We also review the influences of several important conditions, such as pollutant concentration, contact time, co-existing pollutants, water vapor, and light exposure, on the nature of the adsorption process and thereby the photooxidation. Finally, catalytic materials which might enhance the adsorption of low-concentration pollutants are summarized.
Photocatalytic Properties of Commercially Available TiO2 Powders for Pollution Control
Semiconductor Photocatalysis - Materials, Mechanisms and Applications, 2016
The photocatalytic properties of titanium dioxide have been widely studied over recent decades since the discovery of water photolysis by TiO 2 electrodes in 1972. Titanium dioxide has three main crystal polymorphs; anatase, rutile and brookite and rutile is the most common as the metastable polymorph. Each polymorph has different band gap positions. Anatase's band gap is 3.2 eV, higher than rutile's which is 3.0 eV. This difference in the band gap will determine their optimum UV wavelength range to promote a photocatalytic process. There are different methods to assess the photocatalytic activity of a material. The most commonly used method is the degradation of a dye in aqueous solution under UV light, due to its simplicity. Under these conditions the decomposition rate of a suitable organic dye is used as a measure of activity. Physical properties such as particle size and surface area will determine the effective area that will interact and absorb the dye prior to degradation. The physical mechanisms involved in such aqueous based methods differ from gas phase reactions. More advanced techniques use mass spectrometers to evaluate photocatalytic activity of titanium dioxide in the gas phase. An effective photocatalyst for heterogeneous reactions in the gas phase is one which is efficient at creating radicals as a result of an absorbed photon.
International Journal of Environmental Science and Technology, 2016
Evaluation of the photocatalytic activities of TiO 2 nanomaterials based on the chemical oxygen demand (COD) analyses under identical experimental conditions was not previously reported. In this work, COD has been selected as an adequate industrial water quality measure toward the establishment of a representative standard test method. The initial COD values of six organic pollutants representing dye, surfactants, phenols and alcohol were set at 30 ± 2 mg/L. Ten of different commercial and synthesized TiO 2 samples representing anatase, rutile and mixed phases were used and characterized. The data of photocatalytic processes were compared to that obtained using the commonly widespread Degussa-P25 TiO 2 (TD). The COD of all pollutants was completely removed by TD at UV exposure dose B9.36 mWh/cm 2. Consequently, the maximum irradiation dose was set at this value in all experiments. The percentages of COD removal as well as the values of the accumulated UV doses required for complete removal of pollutants were measured using the different TiO 2 samples. TiO 2 samples show different performance abilities toward the various pollutants compared to TD. Based on the obtained data, TiO 2 photocatalysts were divided into two categories according to the hydroxyl radical formation rates. Comparison with previous studies reveals that the photocatalytic efficiency evaluation depends on the method of measurement. COD is recommended to be used as an adequate technique of analysis that meets the purpose of water treatment applications. Keywords Photocatalytic activity Á Nanosized TiO 2 Á Organic pollutants Á Water treatment Á Chemical oxygen demand (COD) Á Standard test method
Photocatalytic activity of supported TiO2 nanocrystals
2013
ii In recent times, the occurrence and presence of complex recalcitrant toxic contaminants in water and wastewater is increasing and consequently contributes to the non-availability of clean and safe drinking water. Water treatment is complex, time demanding and energy intensive due to the physico-chemical structural complexity and diversity of the pollutants. Non-availability of good drinking water has negatively affected human health and the ecosystem. Over the years, numerous conventional treatment techniques were used to degrade and remove these pollutants, but investigations indicated that some of the pollutants are not susceptible to conventional treatment. Advanced oxidation technology, among which heterogeneous photocatalysis (involving the use of a semiconductor) has emerged as one of the more promising techniques to remediate contaminated water. Titanium dioxide (TiO2) semiconductor photocatalysis is considered to be a good option due to its cost effectiveness, chemical an...