Photocatalytic Self-cleaning Activity Research Articles

Benchmarking the Photocatalytic Self-Cleaning Activity of Industrial and Experimental Materials with ISO 27448:2009.

Various industrial surface materials are tested for their photocatalytic self-cleaning activity by performing the ISO 27448:2009 method. The samples are pre-activated by UV irradiation, fouled with oleic acid and irradiated by UV light. The degradation of oleic acid over time is monitored by taking water contact angle measurements using a contact angle goniometer. The foulant, oleic acid, is an organic acid that makes the surface more hydrophobic. The water contact angle will thus decrease over time as the photocatalytic material degrades the oleic acid. In this study, we argue that the use of this method is strongly limited to specific types of surface materials, i.e., only those that are hydrophilic and smooth in nature. For more hydrophobic materials, the difference in the water contact angles of a clean surface and a fouled surface is not measurable. Therefore, the photocatalytic self-cleaning activity cannot be established experimentally. Another type of material that cannot be tested by this standard are rough surfaces. For rough surfaces, the water contact angle cannot be measured accurately using a contact angle goniometer as prescribed by the standard. Because of these limitations, many potentially interesting industrial substrates cannot be evaluated. Smooth samples that were treated with an in-house developed hydrophilic titania thin film (PCT/EP2018/079983) showed a great photocatalytic self-cleaning performance according to the ISO standard. Apart from discussing the pros and cons of the current ISO standard, we also stress how to carefully interpret the results and suggest alternative testing solutions.

In-Situ Functionalization of Cotton Fabric by TiO2: The Influence of Application Routes

The desirable chemical, physical, electronic, and optical properties of TiO2, as well as its high availability, non-toxicity, and low price, make it very popular in the modern functional textile industry. Here, TiO2 from titanium tetraisopropoxide (TTIP) precursors at concentrations of 2, 4, and 6% and commercial TiO2 nanoparticles (NPs) in dispersion form were applied to cotton textiles using low-temperature application methods (i.e., sol–gel pad–dry–cure, pad–hydrothermal, and exhaustion–hydrothermal methods) to provide a systematic study of the influence of low-temperature application processes and TIIP concentration and on the overall properties of TiO2-functionalized textile materials. The treated cotton fabric samples were characterized using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction spectroscopy (XRD) to determine their surface morphology, chemical composition, and crystal structure, while the optical properties of the synthesized TiO2 were determined using the absorption method and Tauc plotting. Afterwards, corresponding UV protection properties and photocatalytic self-cleaning activity were evaluated. In contrast to commercial TiO2, a relatively thin TiO2 deposition with an amorphous structure and a blue-shifted band gap between 3.18 and 3.28 eV was formed when applied at low temperatures. A sol with a TIIP concentrations of 2 and 4% applied using the exhaustion–hydrothermal and sol–gel dry-cure method, respectively, proved to be optimal. Both applied sol concentrations provided good UV protection and excellent photocatalytic performance, which exceeded that of commercial TiO2, even though the Ti contents in the samples were two- to three-times lower and the synthesized TiO2 exhibited an amorphous structure.

Fabrication of omnidirectional broadband dual-functional coating with high optical and self-cleaning properties for photovoltaic application

Escalating the transmitted irradiation, which diminishes due to the undesirable reflection at the interfaces and the surface dirt, requires a simultaneous functioning of antireflection and self-cleaning coating for photovoltaic modules. In this regard, an unprecedented, facile, economical, reproducible, and eco-friendly fabrication of dual-functional coatings (Anti-reflective and Self-cleaning) with high optical and photocatalytic properties is demonstrated. Highly crystalline MgF2 and TiO2 nanoparticles are successfully synthesized by the solvothermal method, and these nanoparticles are utilized to develop a dual-functional coating. HR-TEM and XRD are used to analyze the synthesized nanoparticles, and FE-SEM measures the coating morphology and thickness. The established dual-functional coating exhibits a 5 % enhancement in transmittance compared to uncoated glass in the 380–1100 nm wavelength range. The developed coating also shows high omnidirectional broadband antireflective property with 5–33 % net enhancement in the transmittance in the angle of incidence from 10 to 80°. The coating also exhibited good photocatalytic self-cleaning activity by degrading Methylene blue solution in 3 h with minimal loss in transmission. The bilayer dual-functional coating exhibited a net enhancement of 3.5 % in the power conversion efficiency for coated glass placed over a mini-module compared to uncoated glass positioned over a mini-module. This bilayer dual-functional coating offers enormous potential benefits and is highly conceivable for many applications.

Antibacterial textile and the effect of incident light wavelength on its photocatalytic self-cleaning activity

Wool fabrics with antibacterial and photocatalytic self-cleaning functionalities were developed by applying TiO2/Pt, TiO2/Au and TiO2/Ag colloids to the fabrics surface. This study elucidates how light source type and wavelength range can affect the photo-induced self-cleaning property of the treated fabrics. The self-cleaning activity of fabrics was monitored based on the degradation of coffee stains under UVA (λmax: 365 nm), visible light (λmax: 435 nm), full spectrum simulated solar irradiation (λ: 250–800 nm) and filtered simulated solar irradiation (λ: 320–800 nm). In addition, the effect of nanocoatings on the antibacterial activity against Escherichia Coli (E. Coli) bacterium was examined. The incorporated metals synergistically affected the self-cleaning performance, and their efficiency was dependent on the dopants type, concentration, and light sources. It was observed that the filtered simulated sunlight was the most effective light source for inducing self-cleaning without causing any unwanted photo-yellowing damage in wool. Moreover, the coated fabrics containing silver and platinum led to a bactericidal effect, while gold additive did not re-produce this effectiveness.

Effect of carbon nitride synthesized by different modification strategies on the performance of carbon nitride/PVDF photocatalytic composite membranes

Carbon nitride (CN)/polyvinylidene fluoride (PVDF) photocatalytic composite membrane (PCM) is considered as a promising candidate to improve the anti-fouling characteristic of conventional PVDF membrane and overcome the difficulty encountered during recovery of powder catalyst simultaneously. However, the effects of differently-modified CN on PCM and its mechanism are still unclear. In this study, bulk-CN (BCN), carbon defects CN (CCN), nitrogen defect CN (DCN), mesoporous CN (MCN), and nitrogen-rich CN (NCN) were incorporated into PVDF by phase inversion method. The influence of changes in the physical and chemical properties of CN, including hydrophilic groups, photocatalytic activity, and particle size, on the permeability, anti-fouling characteristic, and photocatalytic self-cleaning activity of CN/PVDF was systematically analyzed. The mechanism of excellent performance of PCM was revealed by experimental test and theoretical calculation. The flux of PCM was significantly improved by increasing the hydrophilic group on modified CN. However, the differences in particle size and interaction between different types of modified CN and PVDF chains endowed the CN/PVDF with different porosity. DCN/PVDF showed high porosity and hydrophilicity, leading to high water flux and rejection rate of 293.6 L (m2 h)−1 and 90.1%, respectively. Compared to pure PVDF, the flux recovery rate of DCN30/PVDF increased by 27.6%, and the irreversible fouling decreased from 36.9% to 9.2%. The modified CN/PVDF showed excellent photocatalytic activity for the removal of cefotaxime (CFX) and E. coli. Owing to the narrow band gap of DCN, large specific surface area, and low photogenerated carrier recombination rate, the CFX removal rate reached 99% in 2 h, and E. coli inactivation achieved 3.7 log within 4 h via DCN30/PVDF.

A novel mixed matrix polysulfone membrane for enhanced ultrafiltration and photocatalytic self-cleaning performance

Photocatalytic materials can be used as self-cleaning functional materials to alleviate the irreversible fouling of ultrafiltration membranes. In this work, the small size g-C3N4/Bi2MoO6 (SCB) blended polysulfone (PSF) ultrafiltration membranes was fabricated by hydrothermal and phase inversion methods. As a functional filler of ultrafiltration membranes, the small size g-C3N4 nanosheet decorated on the surface of Bi2MoO6 can enhance the photocatalytic performance for bovine serum albumin (BSA) degradation, and remove irreversible fouling under visible light irradiation. In addition, the introduction of SCB microspheres into PSF matrix obviously increased the porosity of ultrafiltration membranes. Therefore, the SCB-PSF ultrafiltration membranes displayed excellent antifouling performance (flux recovery ratio is 82.53%) and BSA rejection rates (94.77%). SCB-PSF also had high photocatalytic self-cleaning activity, indicating excellent application prospects in organic wastewater treatment.

Thickness Effect on Photocatalytic Activity of TiO2 Thin Films Fabricated by Ultrasonic Spray Pyrolysis

In this study, TiO2 thin films were deposited by ultrasonic spray pyrolysis from solutions with concentrations of 0.1 and 0.2 M. The deposition temperature was adjusted at 350 °C and all samples were annealed at 500 °C for 1 h in air. The thickness of TiO2 films was changed in the range of 50 to ca. 800 nm by varying the number of spray cycles from 1 to 21 and the solution concentration. The results showed that the mean crystallite size of the anatase structure, the surface roughness, and light absorption increased with the film thickness. The effect of film thickness on the photocatalytic activity was investigated with the photodegradation of stearic acid under UV-A irradiation. The optimal thickness of TiO2 films fabricated by ultrasonic spray pyrolysis for photocatalytic self-cleaning applications was in the range of 170–230 nm, indicating a ca. 2.6 times-higher photocatalytic self-cleaning activity compared to the reference sample, Pilkington ActivTM. The photocatalytic results showed that the 190 nm-thick TiO2 film deposited from the 0.1 M solution applying seven spray cycles exhibited the finest grain structure and maximum photocatalytic activity, leading to 94% of stearic acid degradation in 180 min under UV-A light with the reaction rate constant k = 0.01648 min−1.

Titanium dioxide based self-cleaning smart surfaces: A short review

Abstract The bio-inspired nanotechnology of self-cleaning surfaces and coatings are nowadays being much attracted in the field of energy and environment because of the ever-increasing demand of uncontaminated, self-disinfected and hygienic surfaces. Such surfaces/coatings can be adopted on glass windows, automobile windshields, anti-fouling membranes, textiles, building construction materials, paints; on optoelectronic devices like solar panels, photochromic glasses, etc; in the food industry and for medical aids. This review gives a special emphasis to superhydrophilic self-cleaning surfaces. The mechanism of photocatalytic self-cleaning and superhydrophilicity of nano TiO2 based systems is carefully investigated. The photogenerated reactive oxygen species generated during photoexcitation of electrons from the valence band to the conduction band of TiO2 is responsible for its photocatalytic behaviour, anti-bacterial property and superhydrophilicity. Emphasis is given on various systems and methods that could enhance the self-cleaning behaviour of TiO2 in the solar spectrum since pristine TiO2 is only ultraviolet responsive. TiO2-semiconductor heterojunctions, hybrids of TiO2 with graphene and graphitic monolayers, tailoring the exposed crystal facets in TiO2, metal and non-metal doping and dye sensitization, attributing to visible light photocatalytic self-cleaning activity are focused in detail. Various techniques adopted for the synthesis and fabrication of superhydrophilic self-cleaning materials and coatings are discussed.

Extraction of Valuable Compounds from Orange Peel Waste for Advanced Functionalization of Cellulosic Surfaces

The objective of this study is to explore, identify, and evaluate the bioactive compound extracted from orange peels (OP) via ultrasonic method as potential eco-friendly agent for multifunctional cellulosic fabrics/fibers. The innovative strategy involved two approaches. (1) A closely prepared surface modification procedure for the production of multifunctional viscose fibers was successfully developed by an eco-friendly in situ synthesis of Ag, ZnO, and ZnO/Ag nanoparticles (NPs) using phenolic compounds extracted from OP. The treated viscose fibers are endowed with remarkable antimicrobial, antioxidant, UV protection, as well as photo catalytic self-cleaning activity properties. (2) The microcapsulation and application of limonene extracts from OP as insect-repellent agent for application in textile field. On the basis of the resultant promoting data, the OP extract can be considered as a promising cheap source that can be employed to develop multifunctional finishing textiles. Therefore, this study int...

Chitosan as a potential stabilizing agent for titania nanoparticle dispersions for preparation of multifunctional cotton fabric

Titania (TiO2) nanoparticle dispersions in water were prepared using chitosan (CS) as the stabilizing agent. The dispersion stability was evaluated with respect to storage time, hydrodynamic particle size, and zeta potential. The effect of the molecular weight of CS and presence of non-ionic polymers (poly(vinyl alcohol) and poly(ethylene glycol)) as co-dispersants was investigated. Despite the increase in size of dispersed particles, the long-term storage stability of the dispersions improved with increasing concentration and molecular weight of CS. The TiO2/CS dispersions were applied on cotton fabric and characterized. The presence of CS did not seriously affect the photocatalytic self-cleaning activity (SCA) of TiO2; with CS, a SCA of 89% was achieved compared with a value of 96% without CS. In addition, the TiO2/CS-treated cotton fabrics provided UV protection and significant antimicrobial activity.

Functional finishing of cotton fabrics using graphene oxide nanosheets decorated with titanium dioxide nanoparticles

This study examined an innovative approach for imparting multi-functional properties, i.e. self-cleaning, electrical conductivity, ultraviolet (UV) blocking as well as antimicrobial properties onto cotton fabric. Graphene oxide/TiO2 nanocomposites were successfully prepared, by a simple method of mixing and sonication, and used for multi-functional treatment of cotton fabrics by dip-drying technique. The physicochemical properties of the prepared samples were characterized with field emission scanning electron microscope, transmission electron microscope, X-ray diffraction, and X-ray photoelectron spectroscopy. Self-cleaning performance, electrical resistance, antimicrobial properties, and UV blocking activity of treated fabrics were also assessed. The coated cotton fabrics with graphene oxide/TiO2 nanocomposite showed excellent photocatalytic self-cleaning activity measured by degradation of methylene blue in aqueous solution under sunlight irradiation. Results showed that the electrical conductivity of the graphene oxide/titanium dioxide nanocomposite-coated fabrics was improved significantly after sunlight irradiation. Moreover, the nanocomposite finished cotton fabric demonstrated proper antimicrobial properties and UV blocking activity.

Plasmonic-enhanced self-cleaning activity on asymmetric Ag/ZnO surface-enhanced Raman scattering substrates under UV and visible light irradiation

Plasmonic-enhanced photocatalytic self-cleaning activity under both UV and visible irradiation is demonstrated on asymmetric Ag/ZnO surface-enhanced Raman scattering substrates.

Enhancement of photocatalytic self-cleaning activity and antimicrobial properties of poly(ethylene terephthalate) fabrics

Fabrics with additional surface functions like self-cleaning, UV-protection or antimicrobial properties are highly desirable. TiO2 nanoparticles and composite nanoparticles consisting of AgI/AgCl/TiO2 were prepared. The particles were immobilized on PET fabric. The resulting materials showed proper photocatalytic self-cleaning activity measured by photochemical destruction of methylene blue and antimicrobial properties measured against Escherichia coli (E. coli). All properties of the PET bearing the AgI/AgCl/TiO2 nanocomposite particles are superior compared to the materials bearing the pure anatase nanoparticles.

Photocatalytic self-cleaning properties of cellulosic fibers modified by nano-sized zinc oxide

Nano-sized zinc oxide was synthesized and deposited onto cellulosic fibers using the sol–gel process at ambient temperature. The prepared materials were characterized using several techniques including scanning electron microscopy, transmission electron microscopy, diffuse reflectance spectroscopy, X-ray diffraction and thermogravimetric analysis. X-ray diffraction studies of the ZnO-coated fiber indicate formation of the hexagonal crystal phase which was satisfactory crystallized on the fiber surface. The electron micrographs show formation of zinc oxide nanoparticles within 10–15nm in size which have been homogeneously dispersed on the fiber surface. The prepared materials show significant photocatalytic self-cleaning activity, which was monitored by diffuse reflectance spectroscopy. The photoactivity was studied upon measuring the photodegradation of methylene blue and eosin yellowish under UV–Vis irradiation. The photocatalytic activity of the treated fabrics was fully maintained performing several cycles of photodegradation.

PHOTOACTIVE POLYACRYLONITRILE FIBERS COATED BY NANO-SIZED TITANIUM DIOXIDE: SYNTHESIS, CHARACTERIZATION, THERMAL INVESTIGATION

Anatase nanocrystals were successfully synthesized and deposited onto polyacrylonitrile fibers with photocatalytic self-cleaning activity using the sol–gel process at low temperature. The original and treated samples have been characterized by several techniques such as scanning electron microscopy, fourier transform infrared spectroscopy, x-ray diffraction, diffuse reflectance spectroscopy, thermogravimetric analysis and differential scanning calorimetry. The TiO 2 nanoparticles, have been found to form a homogeneous thin film on the fiber surface. The photocatalytic activity, tested by measuring the degradation of adsorbed Eosin Yellowish dye. The photoactivity of the titanium dioxide coated fibres is much higher than that observed in case of untreated fibers. The photocatalytic selfcleaning properties of the treated fibers was fully maintained performing several cycles of photodegradation. This preparation technique can be also applied to new fabrics to create self-cleaning properties in them. The thermogravimetric study of PAN/TiO 2 composite showed a slight increase of weight loss in the second step, which implied that, the dehydrogenation and oxygen uptake reactions would be promoted by the TiO 2 to some extent.

Flame-retardancy and photocatalytic properties of cellulosic fabric coated by nano-sized titanium dioxide

We have investigated the effect of titanium dioxide as a durable finish on the flammability and photocatalytic self-cleaning of cellulosic fabric. Nano-sized titanium dioxide particles were successfully synthesized and deposited onto cellulosic fibers with good compatibility, significant photocatalytic self-cleaning activity, and flame-retardancy properties using the sol–gel process at low temperature. The photocatalytic activity was tested by measuring the photodegradation of methylene blue under ultraviolet–visible illumination, and also flame-retardancy effect was tested by flammability tester. The samples have been characterized by several techniques such as scanning electron microscopy, transmission electron microscopy, diffuse reflectance spectroscopy, X-ray diffraction, and thermogravimetric analysis. The titanium dioxide nanoparticles with 10–20 nm in size have been found to form a homogeneous thin film on the fiber surface which shows efficient photocatalytic and flame-retardancy properties. This preparation technique can also be applied to new fabrics to create self-cleaning and flame-retardancy properties in them.

Antimicrobial activity of titania/silver and titania/copper films prepared by CVD

We have previously reported the production of photocatalytically active films of TiO 2/Ag and TiO 2/CuO grown by atmospheric pressure thermal CVD that had high antimicrobial activity. The present study compares the activity of dual layers and co-deposited TiO 2–CuO with single layers. We also compared the BS ISO 27447:2009 method with our previously reported method for determining photocatalytic antimicrobial activity and showed that although the activity was reduced in the BS method, probably due to the lower UV irradiation used, there was still a good antimicrobial activity. The results showed that Ag–TiO 2 surfaces retained photocatalytic self-cleaning activity measured by stearic acid oxidation whereas Cu–TiO 2, both layered and co-deposited had very low activity. However, both were antimicrobial against Escherichia coli with activity of the Cu–TiO 2 films greatly enhanced by irradiation possibly via a photo-Fenton type reaction. The activity of the Ag–TiO 2 films against Pseudomonas aeruginosa and MRSA (methicillin resistant Staphylococcus aureus) showed reduced killing activity with an environmental isolate of P. aeruginosa and the MRSA showing only 3 log and 1.5 log reductions respectively. The implications for their use for reduction of surface contamination by microorganisms as part of control measures for healthcare associated infections are discussed.

Photocatalytic self-cleaning keratins: A feasibility study

Anatase nanocrystals were successfully synthesized and deposited on protein keratin-type wool fibers with good compatibility and significant photocatalytic self-cleaning activity using the sol–gel process. Due to the low chemical resistance and liability to photo-degradation of protein materials, the effect of the acid catalyst used in the sol synthesis was studied. The sols were prepared using oxidizing and non-oxidizing catalysts, nitric acid and hydrochloric acid, respectively, for the hydrolysis and condensation reactions of the titanium dioxide precursor. The size distribution and crystallinity of the sols were characterized by X-ray diffraction spectroscopy and photon correlation spectroscopy. The compatibility of sol formulations and wool is thoroughly compared and discussed by analyzing fibers photo-degradation, surface morphology and self-cleaning properties including stain degradation and colorant decomposition. The UV absorption and mechanical properties of wool fibers before and after coating are also discussed.

Photocatalytic formulations for protein fibers: Experimental analysis of the effect of preparation on compatibility and photocatalytic activities

In this article, we report an optimization study of a photocatalytic self-cleaning sol–gel formulation. In particular we studied the effect of formulation preparation time on the formation of anatase titanium dioxide sol and its compatibility to protein keratin-type wool fibers. The sols were formed by a low temperature sol–gel process. The nucleated anatase was characterized by UV–vis transmission, particle size distribution, X-ray diffraction, and transmission electron microscopy. The compatibility between the formulations and wool fibers is evaluated by field-emission scanning electron microscopy, UV transmission, and mechanical properties. The photocatalytic self-cleaning activity of coated fibers and its reproducibility are also discussed.