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Enhanced photocatalytic disinfection of indoor air
Abstract
A silver ion doped TiO2 based photocatalyst, with improved destruction of airborne microbes, has been developed. The performance of the silver ion doped photocatalyst is demonstrated using a catalyst coated filter in a recirculating air experimental facility. Bacillus cereus, Staphylococcus aureus, Escherichia coli, Aspergillus niger, and MS2 Bacteriophage have been used as indexes to demonstrate the high disinfection efficiency of the enhanced photocatalysis process. The microbial destruction performance of the enhanced photocatalyst is found to be an order of magnitude higher than that of a conventional TiO2 photocatalyst. The process of enhanced photocatalysis can thus be used effectively against high concentrations of airborne microorganisms, making it an attractive option as a defense against bio-terrorism.
... Lin and Li (2003a) demonstrated that the effectiveness of a photocatalytic filter on the removal of bioaerosols was insignificant, which might be caused by a lack of enough time (on the order of 1 s) for the microorganisms to contact and react with the TiO 2 and reactive species generated by the PCO reaction. Some studies also showed that the destruction of microorganisms increased significantly with the time exposure to the photocatalyst and the contact surface between the microorganism and photocatalyst (Keller et al., 2005;Vohra et al., 2006). Lin and Li (2003a) recommended that the reaction time of the photocatalyst with the collected microorganisms could be extended by enhancing the filtration efficiency of the photocatalytic filter. ...
... Escherichia coli (Bioresource Collection and Research Center in Taiwan, BCRC 10675), Candida famata (BCRC 22304, a kind of yeast), and vir phage (BCRC 70193) were selected as the model strains of bacteria, fungi, and viruses, respectively. E. coli is a common rod-shaped bacterium with a particle size of about 0.78 m and is often selected as a challenge bioaerosol for germicidal tests (Keller et al., 2005;Lin & Li, 2003a, 2003bManess et al., 1999;Vohra et al., 2005Vohra et al., , 2006. C. famata is a frequently encountered airborne yeast with a particle size of about 2.44 m and has been selected as a challenge bioaerosol for germicidal tests (Lin & Li, 2003a, 2003b. ...
... E. coli and C. famata possess other self-protection mechanisms against the reactive species, including the synthesis of catalase and superoxide dismutase (Grinshpun et al., 2007). Vohra et al. (2006) also found that the bacteriophage (MS2 phage) destruction rate of photocatalysis was the highest among the test microbes. ...
The widely used ultraviolet (UV) protective ingredient benzophenone and its derivatives (BPs) are endocrine-disrupting chemicals and are directly or indirectly released into the environment, posing a threat to human health and environmental ecology. Therefore, this research aims to develop an environmentally friendly purification technology to eliminate BPs from air. Recycled rice straw was used to prepare activated carbon (AC), which was applied to filter BPs in the air. The surface morphology, elemental composition, specific surface area, functional groups, and thermal stability of AC were analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), nitrogen adsorption/desorption isotherm analysis, Fourier transform infrared (FT-IR) spectrometry and thermogravimetric analysis (TGA). A negative air ionizer (NAI) was used to enhance the filtration efficiency of the AC filter. The experimental results show that the AC filter can effectively remove BP particles from the air, with a removal efficiency of up to 80% (filter quality factor 10 mm-H2O⁻¹). The NAI further increased the removal efficiency of the filter system to over 99% (the filter quality increased to 60 mm-H2O⁻¹), showing the superiority of this approach. The most important filtration mechanism in this system is the external electric field generated by the NAI.
... Généralement, les dopants les plus employés sont des ions métalliques issus principalement du fer, du platine, du lanthanide, du chrome, du manganèse ou du cobalt. Mais, le recours aux ions argent, dont le pouvoir désinfectant est utilisé en médecine depuis plusieurs décennies, est le plus fréquent pour dégrader des microorganismes (Evans et al., 2007 ;Vohra et al., 2006). Nonami et al. (2004), proposent également d'utiliser un matériau céramique recouvert d'apatite et de dioxyde de titane. ...
... De nombreuses études sur la photocatalyse solaire, en phase liquide, ont également été réalisées (Rincon et al., 2004b ;Sichel et al., 2007 ;Vidal et al., 1999). Outre des essais extérieurs, l'équipe de A.G. Ricon et C. Pulgarin a mené des expériences avec des lampes simulant le spectre solaire (Rincon et al., 2004a ;Rincon et al., 2004b Lin et al., 2003 ;Pal et al., 2005 ;Pal et al., 2008 ;Sato et al., 2003 ;Vohra et al., 2006 ;Yu et al., 2008Caballero et al., 2009Kim et al., 2009 ;Pal et al., 2007 Intestins des mammifères Diarrhées, gastro-entérites… Legionella pneumophilia Josset et al., 2010 ;Josset et al., 2007 Eaux, boues Légionellose • Préparation des supports photocatalytiques Les supports utilisés sont poreux ou non. Dans le premier cas ce sont généralement des filtres, en fibres de verre ou en acétate de cellulose (diamètre des pores compris entre 0,4 et 0,45 µm) où le dioxyde de titane, préalablement dispersé dans une phase aqueuse est déposé par filtration ou par simple trempage. ...
... D'après la littérature, les bactéries sont mises en culture conformément au protocole décrit sur la figure I.2-2. Après collecte des bactéries dans un milieu non nutritif, l'aérosolisation est généralement réalisée par nébulisation pneumatique (Lin et al., 2003 ;Pal et al., 2005 ;Pal et al., 2008 ;Sato et al., 2003 ;Vohra et al., 2006 ;Yu et al., 2008). De plus amples détails sur les techniques de génération, de prélèvements et d'analyses des bioaérosols seront apportés dans le paragraphe consacré aux aérosols biologiques. ...
Cette étude s'inscrit dans le cadre de l'amélioration des connaissances sur la dégradation photocatalytique des bioaérosols bactériens. La photocatalyse est une technique d'épuration basée sur l'excitation d'un semi-conducteur par un rayonnement le plus généralement ultraviolet. Cette technologie permet, en théorie, de minéraliser pas à pas les polluants. Or, si les conditions optimales ne sont pas réunies, la minéralisation incomplète peut conduire à des sous-produits de dégradation de toxicité potentiellement préoccupante.L'objectif de ces travaux a donc été d'apporter des éléments de compréhension quant aux mécanismes de dégradation photocatalytique d'un bioaérosol bactérien modèle d'E.coli, où de nombreux phénomènes sont couplés. Ainsi, pour distinguer les différents processus mis en jeu, deux approches expérimentales ont été menées. La première, nommée approche « batch », a permis d'isoler la réaction photocatalytique, à proprement parler, en étudiant les étapes d'inactivation, de libération de sous-produits et de minéralisation progressive. La seconde, appelée approche « dynamique » a permis quant à elle la mise en place d'un dispositif expérimental adapté à la dégradation photocatalytique d'un bioaérosol d'E.coli. Les capacités de la photocatalyse à inactiver et minéraliser des espèces bactériennes ont pu être démontrées. Les paramètres clés d'une dégradation efficace ont été mis en évidence et ont permis de décrire les verrous indispensables à une industrialisation sûre du procédé
... 128 Since most of the healthcare workers spend a substantial amount of time in the hospitals, indoor air contamination poses a critical threat to them. 129 Furthermore, the WHO states that every individual has a right to breathe healthy indoor air. 130 The WHO also argues that ensuring acceptable indoor air quality is the responsibility of all people. ...
... 68 Following the attack of SARS virus in 2003, Howells studied a system, based on photocatalytic disinfection, to control the spread of infectious microorganisms such as SARS virus. 129 Kim and Jang investigated the photocatalysis reactions for simultaneous inactivation of airborne MS2 viruses and degradation of the generated ozone toward a°ow-through air disinfection system with high°ow rates. They found that this system had the potential to serve as an alternative to conventional UV-based air puri¯ers. ...
The current pandemic SARS-CoV-2 (also known as 2019-nCoV and COVID-19) viral infection is growing globally and has created a disastrous situation all over the world. One of the biggest challenges is that no drugs are available to treat this life-threatening disease. As no drugs are available for definitive treatment of this disease and the mortality rate is very high, there is an utmost need to cure the infection using novel technologies. This study will point out some new antimicrobial technologies that have great potentials for eradicating and preventing emerging infections. They can be considered as treatments of choice for viral infections in the future.
... However, among these three, anatase is arguably the most photocatalytically active as compared to the amorphous or unstable phases of TiO2 [13,14]. Due to the non-selective nature of excitons generated from photoexcitation of anatase, it covers a wide scope of applications, including bacteria disinfection which has been an important topic for discussions for the past decade, particularly that which involves Escherichia coli [15]. The photocatalytic process would generate hydroxyl radicals that attack the cell walls of bacteria, leading to massive fluid extraction and eventual death. ...
... Several studies have been done to optimize the anti-bacterial properties of Ti-6Al-4V. The anodized Ti-6Al-4V exhibit antibacterial properties with a thin film of anatase under UV treatment [15]. However, the antibacterial properties of thin films are still being discussed, because the thin film of anatase has the possibility to exfoliate. ...
Modification of Ti-6Al-4V through electrochemical anodization method has been investigated on the purpose of generating TiO2 nanotube arrays (TiNTAs) on the surface of Ti-6Al-4V films. The as-anodized samples were calcined in an atmospheric furnace at various temperatures, in the range of 500-800 ºC. The evaluation of biofilm inhibition was performed by an in vitro method with Streptococcus mutans as a bacterium model. FE-SEM imaging confirmed the successful formation of TiO2 nanotube arrays while XRD results implied a phase transformation from anatase to rutile when the calcination temperature was around 600-650 ºC with average crystallite size of 18 nm. Calcination temperature is one of determining factors in the adjustment of crystallinity and morphology of TiO2, which in turn affects its capability to suppress biofilm formation. This study revealed that the best sample for biofilm inhibition was calcined at 600 ºC with a crystallite phase of mostly anatase. This sample managed to improve antibacterial activity of up to five times as compared to the unmodified Ti-6Al-4V. The output of this study is expected to give some insight on a promising alternative for preventing the formation of harmful biofilm on dental implants.
... It can be through cell wall membrane disruption or potassium ions leakage inside the cell followed by the destruction of cellular components inside the cell like RNA and proteins, killing the bacteria [17,36,46]. Photocatalytic oxidation depends on the factors such as wavelength [44], light intensity [10], the concentration of NP [61] and the type of microorganisms [7] by which the inactivating efficiency is calculated [57,60]. Studies have been made on parameters affecting disinfection kinetics but the comparison has been disparate [12,14]. ...
Photocatalysis using various nanomaterials of different characteristics has been investigated with various metrics for achieving optimal efficiency. However, the spatial distribution of light intensities from the light source, a key factor in photocatalysis process and the selection of an appropriate kinetic model for explaining disinfection characteristics of different microorganisms have not been given ample consideration. In this study, a suitable model has been applied to identify spatial distribution of light based on the light source used and applied in the kinetic models to identify the disinfection rate. Disinfection efficiencies of nanoparticles (TiO2 and Cu-doped TiO2) with different light intensities on gram-positive bacteria, Mycobacterium smegmatis and gram-negative bacteria E. coli was evaluated. The kinetic study revealed that Mycobacterium smegmatis fits well with Chick–Watson model, while E. coli fits well with delayed Chick–Watson model. The rate constants (k) were found to be 0.013 min⁻¹ (TiO2), 0.021 min⁻¹ (3%Cu–TiO2) and 0.020 min⁻¹ (Cu²⁺) for Mycobacterium and 0.019 min⁻¹ (TiO2) for E. coli. From model evaluation, light intensity decreased exponentially from 3.07 µW cm⁻² (3 cm) to 0.98 µW cm⁻² (6 cm) and 0.10 µW cm⁻² (25 cm) resulting in a sharp decline in the inactivation potential; however, the effect was insignificant beyond 10 cm. On doubling the intensity, disinfection efficiency increased by 1.6 log CFUml⁻¹ (TiO2) and 2.4 log CFU ml⁻¹ (Cu–TiO2), but with one-fourth of intensity it decreased by 1.2 log CFUml⁻¹ (TiO2) and 1.8 log CFUml⁻¹ (Cu–TiO2). Therefore, by optimizing the combination of nanoparticles like TiO2 and Cu, light intensity at 6.14 µW cm⁻² and optimal spatial distribution of the light source at 3 cm, increased efficiency of microbial disinfection could be achieved. Thus, this study provides an approach to optimize photocatalytic parameters with inclusion of spatial distribution of light intensity for enhancing the photocatalytic process.
... However, there are no reference methods that could be applied in order to confirm the efficiency of these devices, both the ones constituting a part of air-conditioning systems and mobile appliances-the so-called air purifiers [18,55]. Vohra et al. [84] and Mitoraj et al. [85] showed that Bacillus cereus, Staphylococcus aureus, and Escherichia coli strains were almost completely inactivated after various periods of exposure, lasting from 1 h to 24 h. On the other hand, Aspergillus niger fungal species demonstrated full inactivation after a 48 h-long exposure. ...
Aims: With the ongoing pandemic and increased interest in measures to improve indoor air quality, various indoor air purifiers have become very popular and are widely used. This review presents the advantages and disadvantages of various types of technologies used in air purifiers in terms of reducing microbial contamination. Methods: A literature search was performed using Web of Science, Scopus, and PubMed, as well as technical organizations dealing with indoor air-quality to identify research articles and documents within our defined scope of interest. Relevant sections: The available literature data focus mainly on the efficiency of devices based on tests conducted in laboratory conditions with test chambers, which does not reflect the real dimensions and conditions observed in residential areas. According to a wide range of articles on the topic, the actual effectiveness of air purifiers is significantly lower in real conditions than the values declared by the manufacturers in their marketing materials as well as technical specifications. Conclusions: According to current findings, using indoor air purifiers should not be the only measure to improve indoor air-quality; however, these can play a supporting role if their application is preceded by an appropriate technical and environmental analysis considering the real conditions of its use.
... Various light sources including sunlight, UV light, visible, and infrared light are used to perform photocatalysis (Levine et al. 2011;Sang et al. 2015;Yoon et al. 2010). This procedure has taken an important place in the consumer market by participating in odor removal, microbial disinfection, pollutant, or toxin removal, etc. (Fig. 4.1) Chen and Poon 2009;Likodimos et al. 2010;Ming et al. 2017;Vohra et al. 2006). ...
The food industry is generating huge amounts of by-products, about 1,890,000 tons, which should be better recycled into pharmaceuticals, cosmetics and functional foods, for instance, in order to save costs and avoid pollution. Here we review food by-products and methods of extraction. We present bioactive compounds from fruits, vegetable, tea, coffee, egg, nuts, meat and dairy products. Extracting methods include soxhlet, maceration, microwave, ultrasound, pressure.
... Various light sources including sunlight, UV light, visible, and infrared light are used to perform photocatalysis (Levine et al. 2011;Sang et al. 2015;Yoon et al. 2010). This procedure has taken an important place in the consumer market by participating in odor removal, microbial disinfection, pollutant, or toxin removal, etc. (Fig. 4.1) Chen and Poon 2009;Likodimos et al. 2010;Ming et al. 2017;Vohra et al. 2006). ...
The food industry is generating huge amounts of by-products, about 1,890,000 tons, which should be better recycled into pharmaceuticals, cosmetics and functional foods, for instance, in order to save costs and avoid pollution. Here we review food by-products and methods of extraction. We present bioactive compounds from fruits, vegetable, tea, coffee, egg, nuts, meat and dairy products. Extracting methods include soxhlet, maceration, microwave, ultrasound, pressure.KeywordsFood by-productsBioactive moleculesNovel techniquesConventional techniquesGreen techniquesEnvironmental pollution
... Dodatkowo fotokataliza może być wykorzystana do dezynfekcji powietrza. Aczkolwiek jej skuteczność w tym obszarze jest mocno dyskusyjna [11], [12]. ...
... It becomes just like an invisible killer (World Health Organization 2000). According to China Standardization Association, 68% of illnesses are caused by poor indoor air quality (Vohra et al. 2006). In addition, some authors reported that higher disease and mortality rates are linked to air pollution and poor indoor air quality [46]. ...
Although several non-thermal plasmas (NTPs) technologies have been widely investigated in air treatment, very few studies have focused on the inactivation mechanism of viruses by NTPs. Due to its efficiency and environmental compatibility, non-thermal plasma could be considered a promising virus-inactivation technology. Plasma is a partly or fully ionized gas including some species (i.e., electrons, free radicals, ions, and neutral molecules) to oxidize pollutants or inactivate harmful organisms. Non-thermal plasmas are made using less energy and have an active electron at a much higher temperature than bulk gas molecules. This review describes NTPs for virus inactivation in indoor air. The different application processes of plasma for microorganism inactivation at both laboratory and pilot-scale was also reviewed This paper reports on recent advances in this exciting area of viral inactivation identifying applications and mechanisms of inactivation, and summarizing the results of the latest experiments in the literature. Moreover, special attention was paid to the mechanism of virus inacti-vation. Finally, the paper suggests research directions in the field of airborne virus inactivation using non-thermal plasma.
... Photocatalysis is regarded as a promising approach for removing pollutants and harmful microbes [1][2][3][4]. To achieve the widespread practical application of photocatalytic environment remediation, efficient photocatalysts that are sensitive to weak visible light, especially indoor light, are required [5,6]. ...
Developing efficient and cheap photocatalysts that are sensitive to indoor light is promising for the practical application of photocatalysis technology. Here, N-doped TiO2 photocatalyst with loaded Cu crystalline cocatalyst is synthesized by a simple one-pot method. The structure is confirmed by transmission electron microscopy and X-ray photoelectron spectroscopy analysis, which exhibit that Cu metal nanocrystalline is uniformly deposited on the surface of N-doped TiO2 material. UV-Vis absorption spectra illustrate that the modified samples possess favorable visible light absorption properties and suppressed-electron hole separation. The as-fabricated Cu-loaded N-TiO2 materials show high activity in photocatalytic decomposing isopropanol and inactivating E. coli under the irradiation of a household white LED lamp. The developed synthetic strategy and photocatalytic materials reported here are promising for indoor environment purification.
... Recently, efforts to produce photocatalytic ceramic tiles, obtained by embedded fine TiO 2 particles or coatings, have intensified. Such functionalisation provides materials with de-polluting (3,4), antifogging (5,6), disinfecting (7)(8)(9), and self-cleaning capabilities (10,11). Photocatalysis is a light-induced catalytic process for the reduction of organic and inorganic molecules adsorbed on the surface of a semiconductor through redox reactions (12)(13)(14). ...
ZnO nanospheres were synthesised and then deposited by both single- and double-fire fast processes on as-prepared ceramic substrates. The photocatalytic degradation of resazurin ink was tested under UV light. The single-fired samples did not show any evidence of photocatalytic activity because the nanoparticles melted during sintering at 1210°C. The double-fire ZnO spray-coating method successfully produced glazed materials with an active ZnO surface layer despite the high sintering temperature. The influence of experimental parameters, including the ZnO nanoparticle loading (0.03 to 1 mg/cm2) and firing temperature (650 to 800°C), were also investigated. Samples with a ZnO loading of 1 g/cm2 fired at 650°C showed the best photocatalytic activity. Increasing the temperature to 700 and 800°C led to the coalescence of ZnO nanoparticles, which reduced the photocatalytic activity.
... Among them, titanium dioxide (TiO 2 ) has been reported as an active disinfecting agent that are capable and toxic to various microorganisms [22]. Titanium dioxide nanoparticles when combined with silver nanomaterials has the ability to kill certain bacteria that are airborne and enhances the shelf life of consumable food products [23]. Silver nanoparticles have various advantages which required potential action in bulk form, and its particles can repress wide scope of biological processes in microscopic organisms [24]. ...
This review prospects the use of nanotechnology in hotel industry specially for food processing, packaging, and safety. Nanotechnology has tremendous scope to transform the domain of food industry in term of processing which involves the preparation of aspects of food, other domain includes packaging which has various subsection from cooked food to packaging of certain beverages and one important aspect is food safety which involves various biosensors that helps to generate data regarding food quality in terms of pathogens and chemical contaminants. Nanotechnology has risen up many prospects regarding development of antimicrobial property, improves barrier properties and also the shelf life of the products. The review aims to provide the basic phenomenon on the usage and applications of nanomaterials in food industry and to develop future prospects with the use advanced nanomaterials.
... Since the 1990s, photocatalysis has been proved as a facile, cost-effective, and environmentally friendly technology (Fujishima et al. 2000, Hingorani et al. 2020, Yang and Wang 2018 for air disinfection from waterborne and airborne microbial pathogens, including viruses, bacteria, fungi, algae, and protozoa, with minimized harmful byproducts (Jimenez-Relinque et al. 2020a, Kim and Jang 2018, Laxma Reddy et al. 2017, Regmi et al. 2018, Vohra et al. 2006, Zhang et al. 2019. So far, several immobilized photocatalysts have been commercialized (Fernandez et al. 1995;Jimenez-Relinque et al. 2020b). ...
In previous studies, it was demonstrated that photocatalysis by TiO2 nanoparticles can be effective for decomposition of pollen grains and pollen allergen extracts (PAEs) for Cupressus arizonica and Platanus hybrida species. In this work, the chemical and photochemical processes of five types of PAEs belonging to family Asteraceae, tribe Astereae, and family Poaceae, tribes Poeae and Triticea, were studied. It was confirmed that the PAEs suffered almost complete decomposition, which likely led to gaseous final products. For the species of Poeae tribe, i.e., Poa pratensis, Festuca pratensis, and Avena sativa, an unusual surface chemical modification of the photocatalyst consisting in the appearance of new bands on fine core level spectra of Ti 2p, C 1s, and O 1s was observed. These changes were associated with possible doping of TiO2 with C and N by pollen extracts. This was accompanied by a red shift of absorption spectra. The results suggest that some components of Poeae pollen can be grafted on TiO2 surface and they can activate the photocatalyst in the visible range. These findings can open a new pathway to eco-friendly chemical engineering of photocatalysts using organic biological compounds.
... The improvement of air quality can be achieved by using air purifiers. These are usually portable devices equipped with systems for dust extraction, VOC neutralization and air disinfection 15,16]. While the market of air purifiers on a global scale is growing every year, there is still a lack of scientific data on how the offered purifier units perform under model and real conditions. ...
The aim of this study was to evaluate the operation of a stationary air purifier under the model conditions of a non-occupied test chamber with dimensions similar to a typical living room. The purifier was equipped with a system for neutralization of volatile organic compounds, disinfection (neutralizing chamber with a system of UVA lamps, plates made of TiO 2 , UVC lamp settings) and HEPA filters at the air outlet of the device. The conducted research focused on the effectiveness of removing bacterial bioaerosols ( M. luteus and B. subtilis ) as well as formaldehyde and the sum of volatile organic compounds. The assessment was made for two ranges of fan flow, 100 and 300 m ³ / h (Standard and Turbo). The unit shows high efficiency in removing the tested bacterial strains, i.e. 100% after 60 and 90 minutes, respectively. Higher efficiency occurred for lower fan output. However, its effectiveness in removing TVOCs did not exceed 58%. Additionally, the formation of formaldehyde was noted during the operation of the purifier.
... Doping metal atoms depressed the recombination of electrons and holes while doping nonmetal atoms can generally influence the different properties of titania such as lattice structure, band gap (Asahi et al. 2001;Khan, Al-Shahry, and Ingler 2002;Lin et al. 2007;Ohno et al. 2004). Photocatalyst doped with silver ion has been developed by Vohra et al. (2006) to devastate the airborne microbes. The result shows that photocatalyst doped with Ag can be used effectively for high concentrated contaminants. ...
Formaldehyde is one of the vital chemicals produced by industries, transports, and domestic products. Formaldehyde emissions adversely affect human health and it is well known for causing irritation and nasal tumors. The major aim of the modern indoor formaldehyde control study is in view of energy capacity, product selectivity, security, and durability for efficient removal of formaldehyde. The two important methods to control this harmful chemical in the indoor environments are photocatalytic oxidation and catalytic oxidation with noble metals and transition metal oxides. By harmonizing different traditional photocatalytic and catalytic oxidation technologies that have been evolved already, here we give a review of previously developed efforts to degrade indoor formaldehyde. The major concern in this article is based on getting the degradation of formaldehyde at ambient temperature. In this article, different aspects of these two methods with their merits and demerits are discussed. The possible effects of operating parameters like preparation methods, support, the effect of light intensity in photocatalytic oxidation, relative humidity, etc. have been discussed comprehensively.
... Moreover, literature also states that semiconductor photo catalysts in their single or co-doped form can be deposited on particular supports to overcome the post-separation dilemma experienced with powder catalysts [38,39]. Even though previous studies reported that the coating process may decrease the specific surface area of the catalysts [40,41], coating of various material supports such as SS has been conducted [42][43][44][45]. Apart from these, Zhang and Wang [46] reported that prolonged exposure of stainless steel (SS) in oxidizing or acidic environments may result in its corrosion mostly when the Cr 2 O 3 passive layer is scratched and may cause metal rusting, loss of thickness and weight. ...
The development of durable photocatalytic supports resistant in harsh environment has become challenging in advanced oxidation processes (AOPs) focusing on water and wastewater remediation. In this study, stainless steel (SS), SS/Ti (N,O) and SS/Cr-N/Cr (N,O) anticorrosion layers on SS meshes were dip-coated with sol gel synthesised C-N-TiO 2 photo catalysts pyrolysed at 350 • C for 105 min, using a heating rate of 50 • C/min under N 2 gas. The supported C-N-TiO 2 films were characterised by scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and Raman spectroscopy. The results showed that C-N-TiO 2 was successfully deposited on anticorrosion coated SS supports and had different morphologies. The amorphous C and TiO 2 were predominant in C-N-TiO 2 over anatase and rutile phases on the surface of SS and anticorrosion supports. The C-N-TiO 2 coated films showed enhanced photocatalytic activity for the decolouration of O.II dye under both solar and UV radiation. The fabricated C-N-TiO 2 films showed significant antibacterial activities in the dark as well as in visible light. Herein, we demonstrate that SS/Ti(N,O) and SS/Cr-N/Cr(N,O) anticorrosion coatings are adequate photocatalytic and corrosion resistant supports. The C-N-TiO 2 photo catalytic coatings can be used for water and wastewater decontamination of pollutants and microbes.
... H. Kim et al., 2006;H. U. Lee et al., 2014;Miyauchi et al., 2016;Modesto et al., 2013;Vohra et al., 2006;N. Yao and Lun Yeung, 2011). ...
Nowadays, air pollution has become a global menace being responsible of a significant increase on the morbidity and mortality of human beings. In view of this, sustainable and efficient technologies for air purification are being sought. Air purification by photocatalytic treatment has received a lot of attention due to the unspecific and high oxidation capacity of the catalyst; however still some variables must be optimized to assure practical applications. In this work, visible light active TiO2–Cu²⁺@perlite and [email protected]2–Cu²⁺/perlite supported materials were fabricated. TiO2–Cu²⁺ (2 at. %) were synthesized using a sol-gel procedure followed of the impregnation of the support by immersion. For [email protected]2–Cu²⁺, silver deposition was conducted by chemical reduction using sodium citrate and sodium borohydride. The materials (powders and supported materials) were characterized by Scanning Electron Microscopy (SEM) to demonstrate their small size and adherence to the substrate. A prototype of a photocatalytic air purifier was built. The efficacy of the prototype was evaluated for the disinfection of indoor air (dentistry clinics). The photo-catalyst was activated using visible and UVA low-cost high-energy LEDs. The antibacterial activity of the air filter was evaluated. [email protected]2–Cu²⁺ exerts better air disinfection activity at lower doses in comparison to TiO2–Cu²⁺. Bacterial growth inhibitions up to 99% were achieved for both, Gram-negative and Gram-positive bacteria. The incorporation of Ag and Cu to TiO2 improves the antibacterial activity of the materials due to enhanced photocatalytic activity and the synergic activity of TiO2 and dopant elements (Ag, Cu) to inhibit microorganism's growth.
... The TiO2 being a narrow band semiconductor oxide generates reactive oxygen species (ROS) such as hydroxyl, and superoxide when it is energized, which attacks the protein capsid of a virus, breaks its binding sites thus it can easily inactivate the chlorine, and UV resistant viruses [83]. Vohra et al. [84] studied the enhancement of PCI of airborne microbes. A Silver-ion doped TiO2 -reactor on the recirculation air setup was tested for different microbes. ...
This review article contains information related to the inactivation of SARS-CoV-2 (Coronavirus) in water and air. It focuses on Heat and UV inactivation of viruses. The author proposed solar energy which is a good source of heat and UV in fight against COVID-19 pandemic. The study also suggests the disinfection of facial masks, PPE kits, health care equipment, public transport, food items, household water, utensils, portable quarantine facilities, hospital wards, etc. using solar energy systems. Thus the evidence-based study of this paper will also provide a new direction to thermal engineers for research in materials, design, and economic feasibility of solar energy systems to combat with COVID-19.
Preprint also available at http://www.enerarxiv.org/page/thesis.html?id=1907
... For ceramic filters without AgNPs, size-exclusion and sorption are the primary mechanisms of removal, and a filters with low biomass content removes greater proportion of bacteria due to small pore sizes [41]. The mechanism by which AgNPs act on E. coli is unclear, but the probable mechanism involves direct contact between AgNPs and the cell wall of E. coli through electrostatic interactions between the negatively charged cell wall and the positively charged filter surfaces [42]. This leads to the production of reactive oxygen species (ROS), which attack cell membranes of the bacteria and cause oxidative stress [43]. ...
Lack of safe drinking water gives rise to waterborne diseases and other human health risks caused by various pollutants. Safe water provision in low-income countries is constrained by limited financial resources, and the problem is worsened during natural disasters. Thus, there is need to develop efficient low-cost technologies for point-of-use water treatment. Filtration using ceramic filters is a viable method as it uses locally available clay and biomass. The aim of this work was to develop and fabricate a laboratory-scale ceramic filter for water treatment, and to evaluate its capacity to remove Cr(VI), methyl orange (MO), and Escherichia coli 0157:H7 from water. Locally sourced clay and sawdust (SD) were used to fabricate filters with varying sawdust contents of 0, 2.5, 5, 10 and 30% (w/w). The clay-sawdust composites were fired in a muffle furnace at a heating rate of 200 °C/h up to 600, 750, and 900 °C for 3 h. Then the clay filter (CF) with the highest permeability was impregnated with silver nanoparticles (AgNP) to produce AgNP-CF. The surface charge, functional groups, surface morphology, and crystallinity of the filters were determined using the pH-drift method, Fourier transform infrared spectrometry, scanning electron microscopy, and X-ray powder diffraction, respectively. The permeability increased with biomass content and firing temperature. The AgNP-CF removed 57.3, 69.1, and 100% of Cr(VI), MO, and E. coli, respectively. Overall, the study demonstrated that AgNP-CF can potentially be used for water treatment in low-income communities.
... The antimicrobial properties are by virtue of generation of highly reactive oxygen species (ROS) toxic to pathogenic microorganisms. Fabrication of dual or multiple metal NPs further enhances the antimicrobial potential as well as spectrum (Vohra et al. 2006). Enhanced antimicrobial activity was observed for combined application of NPs of Ag, TiO 2 and CNTs against E. coli and Bacillus cereus spores (Krishna et al. 2005). ...
Agri-nanotechnology, an active and emerging field of research and
development (R&D), hails research on improved and balanced nutrition through the
use of nano-fertilizers, and targeted and sustained release of active ingredient from
nano-pesticides. Furthermore, nano-interventions include proper monitoring of a
variety of factors such as soil edaphic, abiotic (temperature, moisture, pH, nutrient
content), and biotic (pest and pathogens) by employing in planta/in situ/ex situ
portable sensor systems for fruit crops. Numerous post-harvest management
applications have also been reported, including the development of efficient
nano-enabled packaging and processing systems. However, this upcoming technology is yet in its developmental stages and is likely to be commercialized.
Nonetheless, the anticipated benefits will fuel further progress in this field in the
coming years. The chapter reviews all these aspects in relation to fruit crops.
... Photocatalysis is considered the most promising, effective, and "greener" technique [9][10][11] for eliminating toxic and recalcitrant organic pollutants from the environment by complete mineralization of such pollutants under mild conditions [12][13][14]. Other applications of photocatalysis include production of hydrogen by electrochemical water splitting [15], reduction of CO 2 into organic substances [16,17], nitrogen fixation, sterilization [18,19], self-cleaning glasses [20][21][22][23] and heavy metal removal from water [14,[24][25][26]. The traditionally used semiconductor photocatalyst, titanium dioxide (TiO 2 ) [23], although an affective photocatalyst, is only able to take advantage of ultraviolet light which comprises of 4% of total solar energy due to its wide band-gap (3.2 eV for anatase) [11,[27][28][29]. ...
Bismuth oxybromide (BiOBr) is a novel visible light photocatalyst and when combined with multiwalled carbon nanotubes (CNT), it could lead to low electron/hole recombination rates, thus enhancing its photocatalytic activity. In this work, hierarchal BiOBr and BiOBr/CNT composites were successfully synthesized via hydrothermal method. The samples prepared were characterized for structural, morphological and optical properties via XRD, SEM, TEM and DRS. The influence of carbon nanotubes on various properties of BiOBr were studied and correlated. The impact of synthesis parameters (time and temperature) on structural properties was also studied. The photocatalytic degradation of phenol as model pollutant was carried out under visible light source to determine its photocatalytic activity. It was found that the presence of CNTs induced a growth in the crystallite size of the particles, which somewhat lowered the photocatalytic activity. As the CNT content increased in the sample so does the activity, due to the CNTs' visible light absorption capacity. Furthermore, a crystal orientation changes (crystallographic plane of (003)) were induced by varying several parameters, which were found to be influencing the activity as well, while the formation of Bi6O6(OH)3(NO3)3·1.5H2O was also observed. Its presence enhanced the photocatalytic activity but induced an instability problem.
... Indoor air pollution has become a serious problem because of its impact on human health. As reported, contaminants including microbial agents in the indoor air can cause humans serious illness and health problems such as allergies and asthma [1]. In practice, to remove infectious pathogen from indoor air, methods of UV radiation [2] and chlorination [3] are applied, but they are expensive, carcinogenic, and ineffective for some resistant bacteria. ...
Porous mullites used as ceramic membranes were fabricated and coated with TiO2 and 0.1 wt% Cu(II)-grafted TiO2 powders. A spinning coating technique was applied for the coating process. Antibacterial activities of the coated mullites were tested against pathogenic bacteria Escherichia coli (E. coli) by following the experimental methods of ISO 17094:2014 standardized for testing photocatalyst materials under visible light of a florescent lamp as an indoor-tested condition. Mullites without coatings were used as control samples. After 4 h of light exposure, the number of the initially viable bacteria increased significantly for the uncoated mullites and decreased for all of the coated mullites. Coating layers of TiO2 and Cu-grafted TiO2 could inactivate E. coli under light illumination. In dark condition, 0.1 wt% Cu(II)-grafted TiO2 coating on the mullites could inactivate the bacteria, while TiO2 coating on the mullites could not inactivate the bacteria. The experimental results provide a possibility of using the coated mullites for disinfection applications. Bacterial inactivation mechanisms of TiO2 and Cu-grafted TiO2 in coating layers were investigated and discussed in terms of microstructural observation on the coating layers.
... Cependant, comme le montre la Fig. 4, son application est restreinte pour des concentrations et des débits faibles. En revanche, la photocatalyse permet de traiter de très faible quantité de polluants contrairement aux procédés classiques de traitement des COVs permettant ainsi le traitement de l'air intérieur (Raillard et al, 2006;Vohra et al, 2006;Yu et al, 2007). ...
L'oxydation photocatalytique des Composés Organiques Volatils (COVs) apparaît comme un procédé très prometteur pour la réduction de la pollution atmosphérique. Ce travail avait pour objectif d'étudier l'oxydation photocatalytique de plusieurs COVs au sein d'un réacteur annulaire: méthyléthylcétone (MEK), acétone, 1-propanol ou encore triéthylamine (TEA). Dans une première partie, l'influence de plusieurs paramètres cinétiques tels que la concentration en polluant, l'intensité lumineuse, le temps de contact et le taux d'humidité a été étudiée. Un mécanisme de dégradation photocatalytique a été établi pour chaque polluant en fonction des sous-produits détectés par GC/MS. Dans une seconde partie, la diffusion de radicaux hydroxyles OH dans la phase gazeuse, après activation photonique du TiO2, a été mise en évidence par Fluorescence Induite par Laser (LIF). Pour la première fois, ces radicaux OH ont été détectés à des pressions proches des conditions atmosphériques. Dans ce cas, nous pouvons en conclure que la dégradation photocatalytique des COVs pourrait être partiellement due à une réaction en phase gazeuse entre les COVs et les radicaux OH
... 7,8 However, the installation of UV lights should be done with care to avoid any potential risks to occupants, thus limiting its applications. 4 Several other emerging technologies have also been proposed, such as photocatalytic oxidation, [9][10][11] plasma, [12][13][14] and microwave. 15,16 Specifically, photocatalytic oxidation produces reactive oxygen species (ROS), such as hydroxyl radicals (˙OH), to disinfect bioaerosols. ...
Heating, ventilation, and air conditioning (HVAC) systems are among the most common methods to improve indoor air quality. However, after long-term operation, the HVAC filter can result in a proliferation of bacteria, which may release into the filtered air subsequently. This issue can be addressed by designing antibacterial filters. In this study, we report an iron oxide nanowires-based filter fabricated from commercially available iron mesh through a thermal treatment. At optimal conditions, the filter demonstrated a log inactivation efficiency of > 7 within 10 seconds towards S. epidermidis (Gram-positive), a common bacterial species of indoor bioaerosol. 52% of bioaerosol cells can be captured by a single filter, which can be further improved to 98.7% by connecting five filters in-tandem. The capture and inactivation capacity of the reported filter did not degrade over long-term use. The inactivation of bacteria is attributed to the synergic effects of the hydroxyl radicals, electroporation, and Joule heating, which disrupted the cell wall and nucleoid of S. epidermidis, as verified by the model simulations, fluorescence microscopy, electron microscopy, and infrared spectroscopy. The relative humidity plays an important role in the inactivation process. The filter also exhibited a satisfactory inactivation efficiency towards E. coli (Gram-negative). The robust synthesis, low cost, and satisfactory inactivation performance towards both Gram-positive and Gram-negative bacteria make the filter demonstrated here suitable to be assembled into HVAC filters as an antibacterial layer for efficient control of indoor bioaerosols.
... This situation largely stems from the difficulty of working with bioaerosols. However, studies with bioaerosols have focused on a wide range of microorganisms such as Escherichia coli, Legionella pneumophila, Microbacterium sp., Bacillus subtilis, Bacillus cereus, Staphylococcus aureus, Aspergillus brasiliensis, a Candida famata yeast, and MS2 and λ phage viruses (Goswami et al. 1997;Keller et al. 2005;Vohra et al. 2006;Grinshpun et al. 2007;Josset et al. 2007Josset et al. , 2010Pal et al. 2008;Yu et al. 2008). ...
Light emitting diodes (LEDs) emitting at 392 nm were successfully used as an irradiation light source and associated to TiO2/β-SiC solid alveolar foams for designing a small-size, flow-through structured photocatalytic device for purifying air from airborne T2 bacteriophage viruses. Light emitting diodes are characterized by a high electricity-to-light yield, strength, a long lifetime, to ability to use a direct current power source, an almost-complete recycling rate, and a lack of mercury. Irrespective of the number of LEDs, we showed that the decontamination efficiency associated with removing airborne T2 bacteriophage viruses resulted from both the photocatalytic activity and the passive filtration effect of the TiO2/β-SiC solid alveolar foams. A high photocatalytic filtration efficiency was observed with 56 LEDs and a logarithmic abatement of 3 was achieved for 60 min of run time, with an apparent time constant of 11.0 min after correcting for the natural decay of the bioaerosol. The pure filtration effect corresponded to a logarithmic abatement of 1, with an apparent time constant of 43.1 min. The interest in using 56 LEDs vs. 40 LEDs was highlighted in terms of the logarithmic abatement as well as energy effectiveness.
In this work, a review of the theory and application of heat and mass synergy is carried out. Since the field synergy theory was proposed, it has not only been greatly developed in the field of heat transfer but also has been explored and studied in the field of mass transfer and heat and mass synergy. In order to clarify the development and improvement process of field synergy theory and sort out its application and development trend, this paper conducts theoretical research on the proposal and controversy of field synergy theory and the derivation of the field synergy formula under different conditions. The field synergy equations based on different fluid states such as laminar flow and turbulent flow in the case of heat transfer, mass transfer, and heat–mass synergy are summarized. Optimizing the synergy application of heat–mass in engineering practice can significantly improve its heat and mass transfer capabilities. Although the field synergy principle has certain advantages in enhancing mass and heat transfer, it cannot take into account the power consumption in practical engineering applications. Therefore, combining the principle of field synergy with other theories to improve the comprehensive performance of heat and mass transfer has provided a way of thinking for future research.
Despite the dramatic emergence of Joule heating of catalysts as an attractive and powerful approach in various fields, the understanding of the design and mechanisms is still insufficient. For instance, in case of co- existence of electric and thermal fields, the phenomena and effects are far more complex than those of electrostatic and thermal fields alone. In particular, the explanation for the significant activity enhancement phenomenon under electrothermal action. This paper provides an overview of the applications of electrothermal catalysis, identifies catalytic mechanisms and reactor designs within each field, and presents the associated challenges and outlook. This work will help researchers to better understand electrothermal synergistic catalysis phenomena and advance the exploration of electrothermal catalysis in the direction of breadth and depth.
This work focuses on the interaction of titanate nanotubes with moderately halophilic bacteria belonging to genera Virgibacillus and Bacillus, indicating the biologically active properties of these nanostructured materials. Subsequently, this activity of the obtained nanosystems on the above mentioned bacterial cells is determined and discussed. The results show a significant dependence of the functional performances on the system's composition and morphology. In particular, the antimicrobial activity of investigated nanotubes is correlated with the preparation methods in various experimental conditions. To the best of our knowledge, this is the first report on the investigation of the effect of titanate nanotubes synthesized under different conditions on halotolerant microorganisms, Virgibacillus halodenitrificans and Bacillus subtilis, isolated from a Neogene-dated subterranean salt rock. The data from this study argued also for the importance of the knowledge of the interactions between these new materials and halophilic microorganisms since environments which hosting these microorganisms are intensively used for recreational and balneology purpose.
There is a growing concern about the impact of air quality on human health. The industrialization based on the large use of fossil fuels has led to increased production of harmful air pollutants, such as volatile organic compounds (VOCs), carbon monoxide (CO), nitrogen and sulfur oxides (NO x , SO x ), pathogens, and particulate materials. Looking at cost‐effective ways to eliminate such pollutants, nanostructured materials that can act as photocatalysts for air purification are one of the potential energy‐efficient methods for pollution control, adding new functionalities to traditional building materials. In this chapter, an overview of the recent development of air purification photocatalytic systems based on nanostructured metal oxide semiconductors, carbon‐based materials, and heterostructures is provided as well as state‐of‐art material design strategies aimed at improving their performances.
Air pollution is a major concern worldwide with consequences for the environment and human health. The latest developments in nanotechnology can contribute to potential solutions for the air contamination issues and remarkably increase the selectivity as well as efficiency of air purification systems, thus providing cost efficiency and longer‐term performance. Air pollution could be remediated with the help of nanotechnology in different ways, such as using nanoadsorbents, nanofilters, nanocatalysts, and nanosensors. It is extremely important and urgent to design as well as develop nano‐enabled filters, membranes, adsorbents, sensors, and catalysts that demonstrate improved performance for the control of air pollution. This chapter focuses on the utilization of various nanomaterials in air pollution remediation applications. We examine mostly the carbon‐based nanomaterials together with metal‐based nanomaterials for the removal of pollutants from the atmosphere. Finally, the possible adverse impacts of the atmospheric nanomaterials (carbon‐based nanomaterials and metal‐based nanomaterials) are also discussed.
Kaolin hollow fiber membranes were produced by the phase inversion method and silver nanoparticles (AgNPs) were sequentially impregnated in the fiber lumen side. The composite membranes were applied to treat aqueous solutions contaminated with Enterobacter cloacae and Escherichia coli. The prepared pristine kaolin hollow fibers presented an asymmetric pore size distribution. According to mercury intrusion analyses, the sponge like layer presented pore sizes between 1.14 and 2.16 μm, while the micro-voids in the finger like layer presented pore sizes between 7.86 and 9.17 μm. The kaolin hollow fibers presented water permeability of 8.46 ± 0.17 L h⁻¹ m⁻²·kPa⁻¹ and mechanical resistance of 103.58 ± 14.41 MPa. The AgNPs were properly synthetized and, according to spectroscopic analyses, the AgNP solution presented a single broad peak centered at 400 nm, which indicates a uniform dispersion of the synthetized AgNPs. The synthetized AgNPs presented a spherical and pseudospherical geometry, with average hydrodynamic size of 81.71 ± 8.05 nm, polydispersity index of 0.262 ± 0.012 and zeta potential of −20.7 ± 2.6 mV, which indicate a suitable AgNP stability in the aqueous suspension. The AgNPs were successfully impregnated in the lumen side of kaolin hollow fibers at a concentration of 0.51 ± 0.04 mg cm⁻¹. Energy dispersive spectroscopy images showed that the AgNPs were more concentrated in the hollow fiber inner layer and a homogenous distribution of AgNPs were observed through the fiber cross-section. After AgNP impregnation, the composite hollow fiber membranes presented water permeability of 5.22 ± 0.32 L h⁻¹ m⁻² kPa⁻¹. The pristine kaolin membrane enabled a log10 reduction value (LRV) of 2.47 ± 0.05 and 3.72 ± 0.13 for filtrations of aqueous solutions with E. cloacae and E. coli, respectively. For the kaolin hollow fiber membrane impregnated with AgNPs, the LRV value increased to 4.38 ± 0.83 and 4.35 ± 0.25 for filtrations of aqueous solutions with E. cloacae and E. coli, respectively. Thus, the synergetic action of the kaolin membranes impregnated with AgNPs enabled a bacterial reduction greater than 99.9%. The AgNPs decreased the permeate flux through the membrane but, for the filtration of the E. cloacae suspension, mitigated the cake formation on the membrane surface.
Pollution by fossil fuels is calling for alternative carbon sources and raw materials. For instance, lignocellulosic biomass is promising because it is usually biocompatible, sustainable and abundant, lignin being the next abundant plant polymer after cellulose. Lignin contains polyphenols and displays properties such as adhesive, reducing, and adsorbing, making lignin an interesting starting material for the synthesis of nanomaterials such as metal oxides. Metal oxide nanoparticles are indeed widely used in sensors, fuel cells, and coatings due to their low toxicity, low cost of production, and photocatalytic behaviour. Metal oxide nanomaterials from lignin show properties such as UV protection, antimicrobials, and photocatalytic efficacy. Here we review the synthesis and photocatalytic applications of lignin-based metal oxide composites.KeywordsLigninPhotocatalysisNanoparticlesZinc oxideTitanium dioxideCerium oxide
We have demonstrated the efficacy of a carbon nitride/polyaniline coated cotton fabric, as a smart self-cleaning material. The preparation of carbon nitride (CN) was carried out by thermal polymerization method and polyaniline (PANI) by chemical polymerization technique. The carbon nitride blended conducting polyaniline composite was coated over cotton fabric by using pad dry cure method. The carbon nitride polyaniline composite coated cotton fabrics show improved photocatalytic decomposition efficiency of 90% toward Rhodamine-B dye. The enhanced photocatalytic self-cleaning properties were achieved by using different colored dye stains under simulated solar light irradiation. The carbon nitride polyaniline composite has also shown good antimicrobial activity against gram negative bacteria.
The widely investigated heterogeneous photocatalysis offers an environmentally friendly, efficient, and versatile solution for several environmental problems. Among others, the removal of harmful organic pollutants and the generation of H2 via water splitting are well-known and most widely studied applications. The process is based on the charge separation caused by the excitation of semiconductor photocatalyst via photon absorption. Due to the intensive development of material science, in addition to the well-known TiO2 and ZnO, several new semiconductor materials have been designed and synthesized to increase the efficiency of heterogeneous photocatalysis and utilization of solar and/or visible light. This chapter describes the principles and mechanisms of heterogeneous photocatalysis, including the formation of photogenerated charge carriers, the role of different reactive species, and the effect of key parameters on the efficiency.
The electret filter media coated with highly porous metal-organic frameworks (MOFs) particles, named E-MOFilter, is newly developed and evaluated for its capacity for simultaneous removal of fine particulate matters (PM2.5) and volatile organic compounds (VOCs). Three different MOFs particles, including MIL-125-NH2, UiO-66-NH2, and ZIF 67, were synthesized and systematically characterized. The produced MOF particles were suspended in ultrapure water and then a liquid filtration apparatus was used to deposit the MOF particles onto two electret media with different minimum efficiency reporting values (MERV 13 and 17) to form the E-MOFilters. Results showed that the MOF particles deposited in MERV 13 media more uniformly than that of MERV 17. In the PM filtration tests, results showed that the E-MOFilter gained only a few more pascals of air resistance compared with clean electret media. Besides, its PM removal efficiency was found to be close to that of clean electret media. This indicates that a uniform MOF particle deposition and negligible charge degradation from the current coating process were obtained. Further, the E-MOFilter with MIL-125-NH2 particle coating not only had a decent toluene removal efficiency (>80%) but also maintained its original PM2.5 holding capacity. This work may shed light on applying the novel E-MOFilter in the residential and commercial HVAC systems and indoor air purifiers to simultaneously and effectively remove PM2.5 and VOCs.
Viral epidemics develop from the emergence of new variants of infectious viruses. The lack of effective antiviral treatments for the new viral infections coupled with rapid community spread of the infection often result in major human and financial loss. Viral transmissions can occur via close human‐to‐human contact or via contacting a contaminated surface. Thus, careful disinfection or sanitization is essential to curtail viral spread. A myriad of disinfectants/sanitizing agents/biocidal agents are available that can inactivate viruses, but their effectiveness is dependent upon many factors such as concentration of agent, reaction time, temperature, and organic load. In this work, we review common commercially available disinfectants agents available on the market and evaluate their effectiveness under various application conditions. In addition, this work also seeks to debunk common myths about viral inactivation and highlight new exciting advances in the development of potential sanitizing agents. Virus pandemics are recurrent in human history, and one of the major means of human‐to‐human viral transmissions occur through contact with contaminated surfaces. Herein, we provide a summary of the major commercially available sanitizing agents used to inactivate viruses and critically evaluate their effectiveness to do so.
Water disinfection using visible light-active photocatalyst has recently attracted more attention due to its potential to inactivate microbes. In this study we have investigated the efficiency of photocatalysis (TiO2 / UVA) on the inactivation of Pseudomonas aeruginosa and the attenuation of its virulence factors. For this aim, the photocatalytic effects of TiO2 / UVA on the cultivability and viability of P. aeruginosa were investigated. Furthermore, during the photocatalysis, the morphology of the bacterial cells was examined by atomic force microscopy (AFM) while the virulence factors were assessed by protease and lipase activities in addition to the mobility and communication of cells. The results revealed that during the photocatalysis the bacterial cells lost their cultivability and viability on agar under the action of the reactive oxygen species generated by the photocatalytic reaction. In addition, AFM observations have shown a damage of the bacterial membrane and a total disruption of the bacterial cells. Moreover, the major virulence factors such as biofilm, lipase and protease expression have been markedly inhibited by TiO2 / UVA treatment. In addition, the bacteria lost their ability of communication “quorum sensing” and mobility with twitching and swarming types after 60 min of photocatalytic treatment. Accordingly, TiO2 / UVA is an effective method to reduce P. aeruginosa virulence and to prevent biofilm formation.
In recent years, photocatalytic technology has been widely studied as an environmental restoration technology and energy production technology to solve the two crises of energy shortage and environmental pollution. Meanwhile, with the continuous research and improvement in photocatalysis technology, it has been found that the interaction between microorganism and photocatalysts has a good application prospect. In general, the interaction between photocatalysts and microorganisms can be summarized as followed: First of all, in terms of environmental pollution control, photocatalysts can damage microorganisms and sterilize them; Secondly, in the production of energy materials, photocatalysts can couple with microorganisms to produce energy or degrade pollutants more efficiently; Thirdly, in the preparation of photocatalyst, microorganism can help the construction of photocatalysts. Although the relationship between microorganism and photocatalysts is very important and significant, the relative review about that is rarely. Therefore, in this paper, we have summarized the interaction between microorganism and photocatalysts, the mechanism and application of photocatalysts on microorganism damage, the mechanism and application of photocatalysts and microorganism synergism, and the preparation of photocatalyst by biological method were also reviewed. Moreover, problems and challenges should be faced and addressed in future research was summarized and proposed.
Nanotechnology has enabled the process of developing objects with size smaller than 100 nanometers, defined as nanomaterial. These materials often exhibit properties completely different from their bulk counterpart. It has been studied that surface atoms of the nanoparticles are responsible for such properties. Their physical-chemical properties of these atoms in turn are highly dependent on their morphology that can be tuned by synthesis methods. Hence to incorporate nanoparticles in a wide range of technological aspects, like photovoltaic, sensor, electronic devices, etc., various synthesis processes of nanomaterials have evolved over time. In recent times, it has been found that the nanomaterials also have potential in various sectors of food science including nanosensor, packaging materials, encapsulated food components, etc. Nanomaterials made of polymers, liposomes, etc., are used in these sector due to their solubility, bioavailability, controlled release, etc. In this chapter, we have discussed antibacterial activity of the nanomaterials along with antibacterial mechanism, including oxygen species, membrane damage, etc., in the domain of food science. In addition, impact of nanotechnology in food science has also been discussed from the perspective of food preservation. Nanomaterials and related technology are very much suitable for food packaging as they offer enhanced barrier, mechanical and heat resistivity along with easy biodegradability. Thrust in this chapter has also been given in this aspect.
The comfortable, beautiful and healthy residential environment has been a target pursued by human beings. However, the inevitable presences of indoor air pollutants such as nicotine which release from tobacco smoking imperceptibly invade people's health. Here, we developed new pigments consisted by colorful graphitic carbon nitride (g-C3N4)-based catalysts, which were fabricated by facile calcining and water bath refluxing procedures. The catalytic pigments exhibited a high catalytic activity for the removal of nicotine under sunlight or even light emitting diode (LED). The designed experiments revealed that superoxide radicals (O2⁻) were main active species in g-C3N4-based catalysts system and played a significant role in removing contaminants. Noteworthy, the catalysts as pigments were successfully used for coloring textiles and painting. Both the catalytic textiles and paintings were provided with preferably photocatalytic performance and reusability. The catalytic pigments were simple to prepare, brightly colored and could effectively degrade nicotine, thus not only have decorative effect, enriching the spiritual world, but also contribute to the protection of the environment of human life.
Introduction: Indoor air environments contain a wide variety of microorganisms such as bacteria, fungi, and viruses in which some of them can affect the human health. Filtration is considered as one of the most common methods to remove microorganisms in these environments. The purpose of current study was to investigation the neat and photocatalytic HEPA filters performance at different face velocities and various intensity of UVC light source on the reduction of airborne microorganisms.
Material and Method: After installation of the neat and photocatalytic HEPA filters in a closed–loop chamber, suspension of Staphylococcus epidermidis and Bacillus subtilis bacteria with a concentration of 107 CFU / ml were sprayed into the closed–loop chamber by nebulizer. Sampling of penetrated microorganisms from filters were performed using the NIOSH 0800 method under ambient temperature 22±3oC, relative humidity 35±5%, and different air velocity (0.1 m/s and 0.3 m/s) and UVC different radiation intensity (1 mW/cm2, 1.8 mW/cm2 and no radiation (dark)) at 30 minutes time period. penetrated microorganisms density from filters was determined in term of CFU/m3.
Result: There were no significant differences in the penetration rates of microorganisms at the dark mode between the two neat and photocatalytic HEPA filters (p>0.05). The penetration rate of bacteria was significantly decreased in the neat and photocatalytic HEPA filters at UVC radiation mode with various intensities than dark mode (p
The photocatalytic inactivation of Bacillus subtilis spores in air was evaluated employing a fixed-bed reactor with TiO2-coated glass rings, under artificial UV-A radiation. Calculations of the radiation effectively absorbed inside the reactor were carried out by Monte Carlo simulations. The photocatalytic inactivation was assessed by analyzing the viability of the microorganisms retained by the coated glass rings inside the reactor at different irradiation periods. The spores initial concentration was reduced by almost 55% at the end of the experiment (12 h). Complementary assays were carried out employing Bacillus subtilis vegetative cells, obtaining a reduction of more than 96% under the same conditions. Two efficiency parameters were computed to assess the reactor performance: the photonic efficiency and the quantum efficiency of inactivation. Results of the efficiency parameters allow an objective comparison of the reactor performance under different experimental conditions and configurations.
Titanium dioxide (TiO2) is one of the excellent photocatalysts used for degradation of environmetal pollutants. In this work, 2.5, 5.0 and 7.5 wt.% of silver (Ag)-loaded TiO2 nanofibers of mean size 52–134 nm were synthesized by electrospinning method. These electrospun nanofibers were calcined at 500 °C to enable the transformation of Rutile (R) phase to Anatase (A), elimination of reaction moieties from the TiO2 matrix and subsequently formation of Ag clusters. The effect of Ag loading on the morphology, crystal structure, phase transformation, and band gap of these electrospun nanofibers have been characterized by scannining electron microscopy (SEM), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), raman spectroscopy and UV-visible spectroscopy. These nanofibers exhibited a red-shift in the absorbance edge and a significant enhancement of light absorption in the wavelength range of 250–550 nm. These electrospun nanofibers were investigated for photodecomposition of methylene blue (MB), and photocatalytic decolorization rates were determined by pseudo-first-order equation. The rate constants for the pure and those of 2.5, 5.0, and 7.5 wt% Agloaded TiO2 nanofibers were computed to be 0.1439 min⁻¹, 0.1608 min⁻¹, 0.1876 min⁻¹, and 0.2251 min⁻¹ respectively.
The fungicide effect employing Aspergillus niger as a representative microorganism was tested applying a Photocatalytic paint formulated with an anatase carbon doped TiO2 and compared with a homemade non-active paint (rutile TiO2), a commercial normal indoor latex paint and a commercial “antifungal” latex paint. For this purpose Aspergillus niger conidia inactivation on the paints coatings was performed under visible and UV radiation applying different experimental conditions (relative humidity, radiation flux and absence of light).
Under visible light no significant difference in conidia inactivation was found for all studied paints. Nevertheless, the Photocatalytic paint under UV radiation presented around 1.4 times higher fungus inactivation than the blank control paints. In order to evaluate the damage produced by visible or UV radiation over the conidia and to analyze the ability of repairing it, incubation at optimal germination conditions of Photocatalytic and normal paints after irradiation treatment was performed. For conidia irradiated on Photocatalytic paint, not only conidia could not germinate but also the inactivation continued even after the end of the irradiation assay. Finally, A. niger conidia was exposed over a culture medium with or without the paints pigments (Carbon doped TiO2 or Rutile) under different types of radiation (visible and UV). Much greater growth control of vegetative forms was obtained by applying photocatalytic TiO2 under both types of light.
It can be concluded that the developed Photocatalytic paint presents a higher ability to control fungal growth compared to the other paints studied and could be applied for indoor air decontamination. Also, it was possible to control the dissemination agent that can generate more mold growth on surfaces and affect the people health.
Abstract Heterogeneous photocatalysis is a versatile, low-cost, and environmentally benign treatment technology for a host of pollutants. This chapter considers recent developments in the research and application of heterogeneous photocatalysis for (1) water treatment, (2) air depollution, (3) hydrogen production, (4) hydrocarbon generation, (5) transformation of specific compounds, and (6) applications in construction, as well as in (7) photodynamic therapy. It also deals with photoelectrocatalysts for solar energy conversion and coupling of heterogeneous photocatalysis with other Advanced Oxidation Processes (AOPs). Techniques in photocatalyst powder immobilization and the main factors that affect the photocatalytic process are also described. Finally, a reactor design for photocatalytic application is proposed and prospects for all processes are discussed with the goal of overcoming challenges and stimulating further research into this promising field. Different types of photoreactors are described in relation to their applications.
Komponen organik dan mikroorganisme yang bersifat patogen dapat dihilangkan melalui penyaringan pasir dan proses klorinasi, tetapi cara ini kurang efektif untuk mikrooraganisme yang memiliki daya tahan yang tinggi terhadap klorin, sehingga alternatif lain yang digunakan yaitu dengan penambahan bahan kimia seperti fotokatalitik TiO2 untuk sistem pengolahan air. Berdasarkan penelitian yang sudah dilakukan, cara ini cukup efektif untuk menghilangkan komponen organik dan mikroorganisme yang bersifat patogen. Penggunaan TiO2 juga dimanfaatkan untuk sistem pengolahan air minum. Inaktivasi bakteri patogen dengan memanfaatkan fotokatalitik TiO2 sudah banyak dikembangkan selama beberapa tahun terakhir. Salahsatunya adalah inaktivasi Escherichia coli. Bakteri ini ada yang bersifat berbahaya bagi kesehatan manusia jika terkonsumsi. Escherichia coli banyak ditemukan pada air yang terkontaminasi, dan dapat juga ditemukan pada sumur-sumur rumah tangga. Oleh karena itu, penggunaan fotokatalitik TiO2 dapat menginaktivasi bakteri E.coli, sehingga air yang dikonsumsi oleh manusia merupakan air yang memenuhi syarat sebagai air minum. Selain itu, menurut penelitian yang telah dilakukan, TiO2 juga dapat digunakan untuk sistem pengolahan air di rumah sakit, perkantoran, dan industri makanan. Sehingga, hal yang akan dikaji pada jurnal ini adalah penggunaan fotokatalitik TiO2 untuk pengolahan air minum dan sistem pengolahan air.
The last 50 years have witnessed a growing awareness of the fragile state of most of the planets’ drinking water resources. Access to freshwater will become even more important in the near future, as the world’s population rises from 7 billion today to 9 billion by 2050. The World Health Organization (WHO) has estimated that 80 % of illnesses in the developing world are water related, resulting from poor water quality and lack of sanitation [1]. There are 3.3 million deaths each year from diarrheal diseases caused by bacteria such as Escherichia coli, Salmonella sp. and Cholera sp., parasites and viral pathogens. In the 1990s, the number of children who died of diarrhoea was greater than the sum of people killed in conflicts since World War II [2]. It is also estimated that around 4 billion people worldwide experience to have no or little access to clean and sanitized water supply, and millions of people died of severe waterborne diseases annually [3, 4].
This article will review the work that has been published on disinfection and the killing of cancer cells using photocatalytic chemistry with titanium dioxide (TiO2). This is an application of photocatalytic chemistry that has been under active investigation since 1985. Because the nature of the research is such that it brings together disparate disciplines, this review provides background on photocatalytic chemistry, fundamental characteristics of target organisms, potential applications, and the toxicology of titanium dioxide. Literature identified in searches done through September 1998 is included.
The civilian, commercial, and defense sectors of most advanced industrialized nations are faced with a tremendous set of environmental problems related to the remediation of hazardous wastes, contaminated groundwaters, and the control of toxic air contaminants. Problems with hazardous wastes at military installations are related in part to the disposal of chemical wastes in lagoons, underground storage tanks, and dump sites. Typical wastes of concern include heavy metals, aviation fuel, military-vehicle fuel, solvents and degreasing agents, and chemical byproducts from weapons manufacturing. In the civilian sector, the elimination of toxic and hazardous chemical substances such as the halogenated hydrocarbons from waste effluents and previously contaminated sites has become a major concern. General classes of compounds of concern include: solvents, volatile organics, chlorinated volatile organics, dioxins, dibenzofurans, pesticides, PCB's, chlorophenols, asbestos, heavy metals, and arsenic compounds. Advanced physicochemical processes such as semiconductor photocatalysis are intended to be both supplementary and complementary to some of the more conventional approaches to the destruction or transformation of hazardous chemical wastes such as high-temperature incineration, amended activated sludge digestion, anaerobic digestion, and conventional physicochemical treatment. 441 refs.
The present study demonstrated the antibacterial effect of photocatalytic oxidation in indoor air using titanium dioxide as the catalyst. Through a series of experiments, it was determined that titanium dioxide did enhance the inactivation rate of the microorganisms under certain conditions. In these experiments the air velocity, relative humidity, and UV (350 nm) intensity were varied. It was found that higher velocities retarded the destruction rate due to the low retention time in the reactor. TiO2 also did not accelerate the reaction at low humidities (30 percent). At a relative humidity of 50 percent, there was complete inactivation of the organisms, but at higher humidities (85 percent), 10 percent of the organisms were still viable. The experiments showed that at higher UV intensities, most of the inactivation was done by the UV photons. However, the photons were not able to completely inactivate the microorganisms. In the photocatalysis experiments there was complete inactivation of the bacteria.
The present study demonstrated the antibacterial effect of photocatalytic oxidation in indoor air using titanium dioxide as the catalyst. Through a series of experiments, it was determined that titanium dioxide did enhance the inactivation rate of the microorganisms under certain conditions. In these experiments the air velocity, relative humidity, and UV (350 nm) intensity were varied. It was found that higher velocities retarded the destruction rate due to the low retention time in the reactor. TiO2 also did not accelerate the reaction at low humidities (30 percent). At a relative humidity of 50 percent, there was complete inactivation of the organisms, bur at higher humidities (85 percent), 10 percent of the organisms were still viable. The experiments showed that at higher UV intensifies, most of the inactivation was done by the UV photons. However, the photons were not able to completely inactivate the microorganisms. In the photocatalysis experiments there was complete inactivation of the bacteria.
A steady-state photolytic investigation using TiO2 as the photocatalyst in its reaction with uracil, thymine, 6-methyluracil and cytosine in an aqueous suspension has been carried out. Influence of initial [cytosine], amount of TiO2 added and pH on the reaction rate and Φ were evaluated. The photoprocess obeys the Langmuir–Hinshelwood isotherm. Fe3+-doped TiO2 prepared by the impregnation method was found to have a modified photocatalytic activity in the photooxidation of all the above-mentioned pyrimidine bases. The effect of calcination (preheat treatment) of the TiO2 photocatalyst was a rate retardation. The role of these parameters on surface properties of TiO2 is suitably explained.
Silver ions doping made enhancement of the photocatalytic activity of TiO2, which was determined by degradation of methyl orange (MO), a probe molecule, in an aqueous solution. X-ray diffraction (XRD) investigation demonstrated that the silver doping changed lattice parameters of TiO2, which should attribute to the O vacancies produced by the substitutional silver ion at lattice site. On above results, a doping mechanism of silver ions in TiO2 was also discussed.
The quantification of primary photocatalytic processes was performed for selected titania powders by using a single-stage oxidation reaction (yielding CO2 and H2O), i.e., the photodegradation of HCOOH. This reaction was used to determine lumped kinetic parameters of UV-assisted photocatalysis in semiconductor slurries. A modified Fricke dosimeter (Fe2+ → Fe3+) was used to determine the exact concentrations of reactive oxygen species in the slurry, such as .OH, HO2., .O2-, and H2O2. These experiments yielded maxima in the concentrations of these species during the first few minutes of reaction with the subsequent attainment of a steady state. The rate of generation of reactive oxygen species characterized the true oxidative power of photocatalysts, and increased with the catalyst concentration and reached a plateau value in the vicinity of 0.25 g/L catalyst. The quantum yield of a particular photocatalyst can be predicted from its radical generation rate. Such quantum yields depends on the catalyst concentration and reactor setup to a much lesser extent than the traditionally used quantum yield for phenol degradation, since the latter process is accompanied by multiple secondary oxidation reactions.
Photothermal catalytic oxidation of ethanol over TiO2and Pt/TiO2has been investigated. Platinum was deposited on the titania using both photoreduction and adsorption of the PtCl2−6anion. The nominal weight loadings of Pt were less than 1 wt%. Thermal contributions to ethanol oxidation over Pt could be distinguished from photo-contributions to ethanol oxidation over TiO2by comparing illuminated and dark reactions under the same conditions. A significant photothermal synergistic effect was seen for Pt/TiO2catalysts. The activity for complete oxidation to CO2is much greater than the contribution from photo-oxidation over TiO2plus thermal oxidation over Pt. Experiments were conducted to investigate the mechanistic nature of the synergistic effect. The synergistic effect was found to be sensitive to preparation conditions, with photoreduced catalysts having higher activities compared to thermally reduced catalysts prepared by adsorption of the PtCl2−6anion: The differences between the photo and thermally reduced Pt/TiO2are attributed to differing extents of etching of the TiO2surface by the acidic solution of chloroplatinic acid. An experiment with layered beds of Pt/TiO2and TiO2showed that adding unetched TiO2to etched Pt/TiO2could improve CO2production. The photothermal synergistic enhancement of CO2production appears to be caused primarily by gas phase transport of intermediates between the two catalyst phases in a mixed series-parallel kinetic pathway. Increased levels of acetaldehyde produced by photo-oxidation over TiO2can lead to CO2production by thermal reaction of the acetaldehyde over Pt.
Silver was deposited on TiO2 powders (Degussa P25) by the photodecomposition of two different silver salts, AgF and AgNO3. The photocatalytic activity of TiO2 powder samples was evaluated by the degradation of 1,4-dichlorobenzene (DCB). Photodecomposition of AgF on TiO2 gave higher photocatalytic activity than that of AgNO3. The optimum catalytic activity found by the deposition of Ag was comparable to that obtained from Au. It was also observed that the photocatalytic activity of Ag-loaded TiO2 films was greater than that obtained for pure TiO2 films. This result is consistent with the results obtained for Ag-deposited TiO2 powders.
The photocatalytic disinfection of Escherichia coli, a pathogenic micro-organism was investigated. An aqueous suspension of the micro-organism (1×108cfu/ml) and neat TiO2 or silver-loaded TiO2 were irradiated with a high pressure mercury lamp for various time periods at neutral pH (7.0). Silver loading (1%, w/w) dramatically reduced the illumination time for complete degradation (less than 1–2min) and minimum catalyst concentration was determined as 0.1mg/ml. Possible killing mechanism and intermediate products were also determined. Occurrence of lipidperoxidation which produces malondialdehyde (MDA) was proposed but the method employed was so effective that all micro-organisms and intermediate products were further degraded to harmless products.
The interest in heterogeneous photocatalysis is intense and increasing, as shown by the number of publications on this theme which regularly appear in this journal, and the fact that over 2000 papers have been published on this topic since 1981. This article is an overview of the field of semiconductor photocatalysis : a brief examination of its roots, achievements and possible future. The semiconductor titanium dioxide (TiO 2 ) features predominantly in past and present work on semiconductor photocatalysis; as a result, in the most of the examples selected in this overview to illustrate various points the semiconductor is TiO 2 .
An exhaustive review on the photochemical properties of iron-doped TiO2 semiconductors is presented. Photocatalytic reactions (reductions and oxidations) using Fe-containing TiO2 on different organic and inorganic substrates are reported. Different aspects relating to structural, surface and photophysical properties of these photocatalysts are extensively discussed. The origin of the photoactivity of this kind of mixed oxides is considered with regards to previously proposed physical and chemical processes and on the role of the iron content.
Photocatalysis by TiO 2 is a new technology that can generate strong oxidant radicals to react with organic pollutants and sterilize water. In this research, the disinfections of two microorganisms such as Bacillus subtilis ( B. subtilis ) and Penicillium citrinum ( P. citrinum ) were investigated. The commercial TiO 2 filter and immobilized TiO 2 slide were used as photocatalytic surfaces. The light intensity levels included 240, 740, 1400, and 2100 w W/cm 2 . Our results indicated that higher black light intensity resulted in higher microorganism inactivation rates. It was demonstrated that not only photocatalysis but also photolysis had germicidal effects on P. citrinum in both kinds of surface matrixes. For B. subtilis , photolysis was more significant than photocatalysis. In addition, microorganism inactivation rates of the TiO 2 filter were found to be smaller than those of the TiO 2 slide for both B. subtilis and P. citrinum . At a light intensity of 740 w W/cm 2 , the calculated 50% survival inactivation time of the TiO 2 filter for B. subtilis and P. citrinum were 0.99 h and 2.55 h, respectively. The calculated 50% survival inactivation time of the TiO 2 slide for B. subtilis and P. citrinum were 0.61 h and 1.64 h, respectively. Furthermore, the inactivation rate of P. citrinum was smaller than B. subtilis on both filter and slide. This might be related to the fact that P. citrinum was more resistant than B. subtilis .
Whole cells deposited on a titanium dioxide-coated surface have been oxidized in air to carbon dioxide via photocatalysis. This paper provides the first evidence that the organic matter in whole cells can be completely oxidized. Three experimental techniques were employed to monitor this reaction: scanning electron microscopy,14C radioisotope labeling, and batch reactor measurements. The scanning electron microscopy experiments illustrate the disappearance of Escherichia coli cell mass. The 14C radioisotope labeling experiments establish that the carbon content of E. coli is oxidized to form carbon dioxide with substantial closure of the mass balance. The batch reactor experiments corroborate the mass balance and provide a preliminary indication of the rate of the oxidation reaction. These results provide evidence that a photocatalytic surface used for disinfection can also be self-cleaning in an air−solid system.
Silver-modified, rough, high surface area titanium dioxide thin films resulting via a two-step dipping and UV-irradiation process were examined for their catalytic activity towards photodegradation of methyl orange (MO). Optimization of the photocatalyst’s performance as a function of the dipping time, irradiation time and the dipping solution concentration was performed. The optimum silver nitrate concentration of the dipping solution was found to be 10−3 M. The modified materials present enhanced photocatalytic efficiency and can decompose the organic pollutant three-times faster than the undoped original films (Degussa P25). A further Ag+-ion concentration increase in dipping solution results a decrease of the films photocatalyst efficiency due to a shading of the available semiconductor surface by the silver layer. This performance is consistent with the unique structural, morphological, and surface characteristics of the composite silver/titania materials. The lower the average particle size, roughness and fractal dimension, the higher the photodegradation percentage and rate constants. The surface doping effect is synergetic to the charge separation process and the photocatalytic results are explained on the basis of a mechanism involving efficient separation of electron–hole pairs induced by silver-ions (Ag+). Reproducibility tests proved that the photocatalytic activity of the silver-modified films remains intact even after six consecutive experiments of new added pollutant quantities.
Chromium-, manganese- and cobalt-doped titanium dioxide photocatalysts containing 0.2, 0.5 or 1 at.% of metal-dopant were investigated by UV–VIS, FT-IR, near-IR and electron paramagnetic resonance (EPR) spectroscopic techniques. The presence of the doping ions in the titania structure caused significant absorption shift to the visible region compared to pure TiO2 powder (P25 Degussa). The EPR spectra of TiO2 powders containing chromium showed the superposition of three types of individual paramagnetic species (β-, γ- and δ-signals), whose relative EPR intensity is significantly dependent on the dopant concentration, as well as on the photocatalysts preparation and treatment. The EPR spectra of the chromium-doped photocatalysts heated in H2/N2 atmosphere corresponded to the Cr(III) ions occupying vacated cation sites in the rutile or anatase crystal lattice. The characteristic feature of the EPR spectra of the Mn/TiO2 samples is a sharp six-line Mn(II) component centered on geff=1.99, flanked by shoulders with a weak feature, which appeared on geff=2.66 and 4.32. The photocatalytic activity of the various metal-doped TiO2 samples was tested in aqueous or dimethylsulfoxide (DMSO) suspensions using EPR spin trapping technique with 5,5-dimethyl-1-pyrroline N-oxide (DMPO) spin trap. The ability of the irradiated photocatalysts to generate reactive oxygen species, namely hydroxyl radicals and super-oxide anion radicals, which were trapped as the corresponding DMPO-adducts was investigated.
Lanthanide metal-ion-doped TiO2 nanoparticles were prepared with hydrothermal method and characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma (ICP) and fluorescence spectrum. The results showed that a small part of metal ions entered into the lattice of TiO2 and others adsorbed on the surface of TiO2. The photoelectrochemical and photocatalytic properties of these lanthanide metal-ion-doped TiO2 nanoparticles were investigated and the results showed that the photoresponse of Eu3+-, La3+-, Nd3+- and Pr3+-doped TiO2 electrodes were much larger and that of Sm3+-doped TiO2 electrode was a little larger than that of undoped TiO2 electrode, indicating that the photogenerated carriers were separated more efficiently in Eu3+-, La3+-, Nd3+- and Pr3+-doped TiO2 nanoparticles than in undoped TiO2 nanoparticles. The photocatalytic degradation of rhodamine B (RB) was conducted in the suspension of lanthanide metal-ion-doped TiO2 nanoparticles, and its first-order reaction rate constant (k) and average initial rate (rini) were significantly higher in the presence of Eu3+-, La3+-, Nd3+- and Pr3+-doped TiO2 nanoparticles than those in the presence of undoped TiO2 nanoparticles. The enhanced photocatalytic degradation rate of RB in the presence of Eu3+-, La3+-, Nd3+- and Pr3+-doped TiO2 nanoparticles is attributed to increased charge separation in these systems. The effect of the content of La3+ on the reaction parameters (k and rini) was also investigated and the result showed that there was an optimal value (ca. 0.5%) of the content of La3+ to make the rate constant (k) and average initial rate (rini) reach the maxima.
Hydroxyl and other oxygen-containing radicals are known to be present during the degradation of organic water pollutants in illuminated TiO2 photocatalyst slurries. It is proposed that the hydroxyl radical, OH·, is the primary oxidant in the photocatalytic system. Four possible mechanisms are suggested, all based on OH· attack of the organic reactant. The cases of reaction on the surface, in the fluid, and via a Rideal mechanism are shown to yield expressions similar to Langmuir-Hinshelwood (LH) rate forms. Compared with traditional LH constants, the derived kinetic parameters represent fundamentally different reactions and properties. A rate parameter independent of organic reactant is predicted by the model and substantiated by experimental degradation data. On the basis of these model results, the kinetic parameters for the photocatalytic degradation may be estimated from data on the photocatalyst's physical properties, the knowledge of electron-hole recombination and trapping rates, and the values of second-order reaction rate constants for hydroxyl radicals.
Photocatalytic oxidations of methanol, ethanol and chloroform, trichloroethylene (TCE), and dichloropropionic acid (DCP) in M/TiO2 aqueous slurries are studied. In the presence of oxygen, the intermediates of methanol oxidation, such as formaldehyde and formic acid, were not detected by GC in the slurries of TiO2, Pt/TiO2, or Pd/TiO2, and CO2 was the only product detected. The distribution of intermediates for ethanol photocatalytic oxidation varies with different catalysts: under the same reaction conditions, the ratio of acetaldehyde:acetic acid is 30:1 on TiO2, and 0.23:1 on Pt/TiO2, with the acetaldehyde concentration being 130 times higher on TiO2 than on Pt/TiO2. Thus, a further oxidation is achieved easily on the Pt/TiO2. The CO2 production depends on the initial reaction pH: Acidic pH produces CO2 immediately in alcohol oxidation, but alkaline pH retards the mineralization substantially. Little effect of Pd metallization on TiO2 was observed for photocatalytic oxidation of chloroform, TCE or DCP. Pt/TiO2 only enhances DCP dechlorination and has no effect on its decarboxylation.
Scientific studies on photocatalysis started about two and a half decades ago. Titanium dioxide (TiO2), which is one of the most basic materials in our daily life, has emerged as an excellent photocatalyst material for environmental purification. In this review, current progress in the area of TiO2 photocatalysis, mainly photocatalytic air purification, sterilization and cancer therapy are discussed together with some fundamental aspects. A novel photoinduced superhydrophilic phenomenon involving TiO2 and its applications are presented.
In order to elucidate the mechanism for photokilling of Escherichia coli (E. coli) cells on titanium dioxide (TiO2) thin film, the survival of intact cells and the spheroplasts was investigated as a function of photo-illumination time. The photokilling reaction for intact cells was observed to involve two steps, an initial lower rate photokilling step followed by a higher rate one. In contrast, the reaction for spheroplasts, which do not have cell wall, exhibited only a single step kinetics with a higher rate, suggesting that the cell wall of E. coli cell acts as a barrier to the photokilling process. Changes in concentration of the cell wall components during illumination further showed that the outer membrane serves as a barrier, while the peptidoglycan layer does not have a barrier function. Moreover, atomic force microscopy measurements of cells on illuminated TiO2 film showed that the outer membrane decomposed first, and with further illumination, the cells completely decomposed. These results suggest that the photokilling reaction is initiated by a partial decomposition of the outer membrane, followed by disordering of the cytoplasmic membrane, resulting in cell death.
A reduced kinetic model for the initial steps of the photocatalytic process is presented with the aim to analytically solve the resulting kinetic system. Several possible kinetic models have been explored. Attention was paid to obtain equations with physical meaning and reduced complexity. An analytical equation is obtained for the rate and the quantum yield, which retains the principal features of the photocatalytic process, namely the light induced charge separation and recombination, the oxidative and reductive electron transfers, the formation of a stable oxidized intermediate, and, unlike the previous kinetic models, also the back reaction of the oxidized substrate. Compared to the two-parameter Langmuir–Hinshelwood equation, all the previous features and the dependence on the light intensity are described with only three parameters, which collect all the kinetic constants, and account for experimental concentrations of substrate and electron scavenger, light intensity and catalytic system characteristics. The kinetic behavior of photocatalytic systems under all the possible values of experimental parameters can be graphically presented. The analysis of the obtained rate equation shows that the best utilization of photons is attainable at low light intensities, suggesting that preconcentration of solar light is unnecessary.
Spores of Bacillus subtilis possess a thick protein coat that consists of an electron-dense outer coat layer and a lamellalike inner coat layer. The
spore coat has been shown to confer resistance to lysozyme and other sporicidal substances. In this study, spore coat-defective
mutants of B. subtilis (containing thegerE36 and/or cotE::cat mutation) were used to study the relative contributions of spore coat layers to spore resistance to hydrogen peroxide (H2O2) and various artificial and solar UV treatments. Spores of strains carrying mutations in gerE and/or cotE were very sensitive to lysozyme and to 5% H2O2, as were chemically decoated spores of the wild-type parental strain. Spores of all coat-defective strains were as resistant
to 254-nm UV-C radiation as wild-type spores were. Spores possessing thegerE36 mutation were significantly more sensitive to artificial UV-B and solar UV radiation than wild-type spores were. In contrast,
spores of strains possessing thecotE::cat mutation were significantly more resistant to all of the UV treatments used than wild-type spores were. Spores of strains
carrying both the gerE36 andcotE::cat mutations behaved likegerE36 mutant spores. Our results indicate that the spore coat, particularly the inner coat layer, plays a role in spore resistance
to environmentally relevant UV wavelengths.
We report carbon mass balance and kinetic data for the total oxidation of cells, spores, and biomolecules deposited on illuminated titanium dioxide surfaces in contact with air. Carbon dioxide formation by photocatalytic oxidation of methanol, glucose, Escherichia coli, Micrococcus luteus, Bacillus subtilis (cells and spores), Aspergillus niger spores, phosphatidylethanolamine, bovine serum albumin, and gum xanthan was determined as a function of time. The quantitative data provide mass balance and rate information for removal of these materials from a photocatalytic surface. This kind of information is importantfor applications of photocatalytic chemistry in air and water purification and disinfection, self-cleaning surfaces, and the development of self-cleaning air filters.
The utility of metal microfibrous mesh coated with titanium dioxide as a self-sterilizing, self-cleaning filter for air is explored. The low-cost mesh is produced via a roll-to-roll process similar to paper manufacturing. The titanium dioxide is applied by spraying an aqueous suspension of the photocatalyst on the surface of the mesh using an airbrush. Photocatalytic activity comparable to a powder layer is achieved at one quarter of the mass loading. The coating enhanced the separation of Escherichia coli (E. coli) from aqueous suspension, but also led to an increase in pressure drop in an air stream flowing through the mesh. The self-cleaning property of the coated mesh is established by recovery of pressure drop performance lost due to biofilm buildup. This is accomplished via a photocatalytic regeneration process involving exposing the mesh to ultraviolet light in air. Oxidation is confirmed by monitoring CO2 evolution during the regeneration. Scanning electron photomicrographs also provide visual evidence of successful regeneration via photocatalysis.
Recent bioterrorism concerns have prompted renewed efforts towards understanding the biology of bacterial spore resistance
to radiation with a special emphasis on the spores of Bacillus anthracis. A review of the literature revealed that B. anthracis Sterne spores may be three to four times more resistant to 254-nm-wavelength UV than are spores of commonly used indicator
strains of Bacillus subtilis. To test this notion, B. anthracis Sterne spores were purified and their UV inactivation kinetics were determined in parallel with those of the spores of two
indicator strains of B. subtilis, strains WN624 and ATCC 6633. When prepared and assayed under identical conditions, the spores of all three strains exhibited
essentially identical UV inactivation kinetics. The data indicate that standard UV treatments that are effective against B. subtilis spores are likely also sufficient to inactivate B. anthracis spores and that the spores of standard B. subtilis strains could reliably be used as a biodosimetry model for the UV inactivation of B. anthracis spores.
One of the reasons for the inadequate quality of indoor air arises from the poor articulation, appreciation and understanding of basic principles underlying the policies and actions related to indoor air quality. A WHO Working Group derived nine statements on rights to healthy indoor air. The discussions and statements are available as a WHO report. It informs the individuals and groups responsible for healthy indoor air about their rights and obligations, and empowers the general public by making people familiar with those rights. One year after their publication the statements have been adopted as the base for future regulation and guidance. The Board of Directors of the International Society of Indoor Air Quality (ISIAQ) and the participants of two international conferences endorse the use of the statements. No opposition to the statements have been registered. The statements have entered curricula of training courses and have been used in lawsuits.
TiO(2) photocatalysis with ultraviolet (UV-A) light has proven to be a highly effective process for complete inactivation of airborne microbes. However, the overall efficiency of the technology needs to be improved to make it more attractive as a defense against bio-terrorism. The present research investigates the enhancement in the rate of destruction of bacterial spores on metal (aluminum) and fabric (polyester) substrates with metal (silver)-doped titanium dioxide and compares it to conventional photocatalysis (TiO(2) P25/+UV-A) and UV-A photolysis. Bacillus cereus bacterial spores were used as an index to demonstrate the enhanced disinfection efficiency. The results indicate complete inactivation of B. cereus spores with the enhanced photocatalyst. The enhanced spore destruction rate may be attributed to the highly oxidizing radicals generated by the doped TiO(2).
Bacillus endospores show different kinds of pigmentation. Red-pigmented spores of Bacillus atrophaeus DSM 675, dark-gray spores of B. atrophaeus(T) DSM 7264 and light-gray spores of B. subtilis DSM 5611 were used to study the protective role of the pigments in their resistance to defined ranges of environmental UV radiation. Spores of B. atrophaeus DSM 675 possessing a dark-red pigment were 10 times more resistant to UV-A radiation than those of the other two investigated strains, whereas the responses to the more energetic UV-B and UV-C radiation were identical in all three strains. The methanol fraction of the extracted pigment from the spores absorbs in the associated wavelength area. These results indicate that the carotene-like pigment of spores of B. atrophaeus DSM 675 affects the resistance of spores to environmental UV-A radiation.
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