Photocatalytic activity and selectivity of Me/La(Ce)-TiO<Subscript>2</Subscript> catalysts in the reaction of water denitrification

The study investigated the efficiency of photocatalytic denitrification of the water medium in the presence of modified titanium dioxide obtained by the sol–gel method. La(Ce)–TiO₂, modified Cu, Ag, Au, Pd and Pt were used as photocatalysts for reducing nitrates and oxidize formic acid. It has been shown that La(Ce)–TiO₂ are active and selective photocatalysts for removal of nitrate–ions from water.     

Combined permeable pavement and photocatalytic titanium dioxide oxidation system for urban run‐off treatment and disinfection

Permeable pavement systems (PPS) are frequently associated with high removal efficiencies for water quality parameters. Their effluent can, therefore, be recycled, for example, for sprinkling onto gardens. Nevertheless, some stakeholders fear that potentially pathogenic organisms within the treated run‐off could be too high, and therefore they request disinfection before recycling. The aim of this paper is, therefore, to assess the efficiency of a batch flow combined titanium dioxide (TiO₂) and ultraviolet (UV) light photocatalytic reactor in removing water‐borne microbial contaminants from the effluent of PPS. Combined TiO₂ and UV photocatalytic reaction times between 80 and 100 min were required for the complete removal of Escherichia coli, total coliforms and faecal Streptococci, which had mean initial counts of 1.5 × 10⁷, 4.4 × 10⁶ and 6.9 × 10⁵ colony‐forming units (CFU) per 100 mL, respectively. In comparison, UV disinfection alone resulted in insignificant microbial removal. Suspended TiO₂ powder was more effective than small immobilised TiO₂ crystals.     

Novel mold‐resistant building materials impregnated with thermally reduced nano‐silver

In this study, we evaluated the long‐term antifungal effectiveness of 3 types of interior building materials (gypsum board [GB], cement board [CB], and softwood plywood [S‐PW]) impregnated with thermally reduced silver nanoparticles supported by titanium dioxide (AgNPs/TiO₂) under 95% relative humidity for 4 weeks. AgNPs/TiO₂ was synthesized at 2 thermal reduction temperatures (TRTs, 120 and 200°C) with 2 different AgNP weight percentages (2 and 5 wt%). Four different silver‐loading levels (SLLs, 0.025, 0.05, and 0.5 μg/cm² and the critical concentration required to inhibit fungal growth on agar plates) and 3 fungal species (Aspergillus niger, Penicillium spinulosum, and Stachybotrys chartarum) were used in the experiments. Higher temperature reduced more ionic Ag⁺ to metallic Ag⁰ and increased the dispersion of Ag on TiO₂ surface. The 200°C thermally reduced AgNPs/TiO₂ demonstrated excellent antifungal efficiency: Mold growth was almost completely inhibited for 28 days at the low SLL of 0.5 μg/cm². Additionally, AgNPs/TiO₂ exhibited higher antifungal activity on GB and CB than on S‐PW. The stepwise regression results indicated that the TRT of AgNPs/TiO₂ (β = ?0.739 to ?0.51), the SLL (β = ?0.477 to ?0.269), and the Ag⁰ level in the AgNPs (β = ?0.379 to ?0.136) were the major factors influencing antifungal activity and TRT might be the most significant one.     

Effective disinfection of airborne microbial contamination in hospital wards using a zero‐valent nano‐silver/TiO2‐chitosan composite

A novel antimicrobial composite of zero‐valent silver nanoparticles (AgNPs), titania (TiO₂), and chitosan (CS) was prepared via photochemical deposition of AgNPs on a CS‐TiO₂ matrix (AgNPs@CS‐TiO₂). Electron microscopy showed that the AgNPs were well dispersed on the CS‐TiO₂, with diameters of 6.69‐8.84 nm. X‐ray photoelectron spectra indicated that most of the AgNPs were reduced to metallic Ag. Fourier‐transform infrared spectroscopy indicated that some AgNPs formed a chelate with CS through coordination of Ag⁺ with the CS amide II groups. The zones of inhibition of AgNPs@CS‐TiO₂ for bacteria (Escherichia coli and Staphylococcus epidermidis) and fungi (Aspergillus niger and Penicillium spinulosum) were 6.72‐11.08 and 5.45‐5.77 mm, respectively, and the minimum (critical) concentrations of AgNPs required to inhibit the growth of bacteria and fungi were 7.57 and 16.51 µg‐Ag/mm², respectively. The removal efficiency of a AgNPs@TiO₂‐CS bed filter for bioaerosols (η) increased with the packing depth, and the optimal filter quality (qF) occurred for packing depths of 2‐4 cm (qF = 0.0285‐0.103 Pa^?1; η = 57.6%‐98.2%). When AgNPs@TiO₂‐CS bed filters were installed in the ventilation systems of hospital wards, up to 88% of bacteria and 97% of fungi were removed within 30 minutes. Consequently, AgNPs@TiO₂‐CS has promising potentials in bioaerosol purification.     

Mechanism of phenol photodegradation in the presence of pure and modified-TiO(2): A review

In recent years, the application of heterogeneous photocatalytic water purification processes has gained wide attention due to its effectiveness in degrading and mineralizing the recalcitrant organic compounds as well as the possibility of utilizing the solar UV and visible-light spectrum. By far, titania has played a much larger role in this scenario compared to other semiconductor photocatalysts due to its costly effectiveness, inert nature and photostability. A substantial amount of research has focused on the enhancement of TiO₂ photocatalysis by modification with metal, non-metal and ion doping.This paper aims to review and summarize the recent works on the titanium dioxide (TiO₂) photocatalytic oxidation of phenol and discusses various mechanisms of phenol photodegradation (indicating the intermediates products) and formation of OH radicals. Phenol degradation pathway in both systems, TiO₂/UV and doped-TiO₂/Vis, are described.     

Research of photocatalytic activity of the Ag/TiO2 catalysts in the reduction reaction of nitrate-ions in aqueous media

We have conducted a research of photocatalytic denitrification of water using modified titanium dioxide obtained by the sol-gel method. We demonstrated the possibility of photoprecipitation of silver particles under the effect of visual light. The use of formic acid as a donor of electrons makes it possible to substantially intensify the process and reduce the yield of a by-product—NH₄ ⁺. It was shown that in the presence of catalysts Ag/TiO₂ and irradiation time for 30 min is achieved a 96% conversion of nitrate ions.     

Virus inactivation by silver doped titanium dioxide nanoparticles for drinking water treatment

Photocatalytic inactivation of viruses and other microorganisms is a promising technology that has been increasingly utilized in recent years. In this study, photocatalytic silver doped titanium dioxide nanoparticles (nAg/TiO₂) were investigated for their capability of inactivating Bacteriophage MS2 in aqueous media. Nano-sized Ag deposits were formed on two commercial TiO₂ nanopowders using a photochemical reduction method. The MS2 inactivation kinetics of nAg/TiO₂ was compared to the base TiO₂ material and silver ions leached from the catalyst. The inactivation rate of MS2 was enhanced by more than 5 fold depending on the base TiO₂ material, and the inactivation efficiency increased with increasing silver content. The increased production of hydroxyl free radicals was found to be responsible for the enhanced viral inactivation.     

Concurrent filtration and solar photocatalytic disinfection/degradation using high-performance Ag/TiO2 nanofiber membrane

A facile polyol synthesis was used for the deposition of Ag nanoparticles on electrospun TiO₂ nanofibers for the subsequent fabrication of Ag/TiO₂ nanofiber membrane. The permeate flux of the Ag/TiO₂ nanofiber membrane was remarkably high compared to commercial P25 deposited membrane. The Ag/TiO₂ nanofiber membrane achieved 99.9% bacteria inactivation and 80.0% dye degradation under solar irradiation within 30 min. The Ag/TiO₂ nanofiber membrane also showed excellent antibacterial capability without solar irradiation. Considering the excellent intrinsic antibacterial activity and high-performance photocatalytic disinfection/degradation under solar irradiation, this novel membrane proved to have promising applications in water purification industry.     

A comparison of several nanoscale photocatalysts in the degradation of a common pollutant using LEDs and conventional UV light

A comparative study on the photocatalytic activities of four different catalysts, P-25 TiO₂, TiO₂ nanofibers, tin-doped TiO₂ nanofibers under UV light irradiation at 350 nm, and coumarin (C-343) coated TiO₂ nanofibers at 436 nm light emitting diodes (LED) is reported. Catalysts performance has been compared based on their reflectance spectrum and activity. A common water contaminant 4-chlorophenol was used as a substrate to compare the activity of the different catalysts under both direct and dye sensitized conditions. Results indicated that amongst the four different catalysts the activity of P-25 was the highest. However the activity of C-343 coated TiO₂ nanofibers in the LED (436 nm) based reactor was competitive. Identification of reaction intermediates implied that the reaction pathways under UV (band gap) and visible (dye sensitized) irradiation were different. Nonetheless, ring opening took place in all reactions with both maleic and dihydroxymaleic have been identified as intermediates. The study indicates that ordered arrays of TiO₂ irradiated by panels of arrays of low cost high intensity LEDs might be used for the design of reactors. The near monochromaticity, long life, and operation under direct currents are advantages of using LEDs.     

Photocatalytic cement-based materials: Comparison of nitrogen oxides and toluene removal potentials and evaluation of self-cleaning performance

Using cement-based building materials as a matrix for nano-photocatalysts is an important development for the large scale application of photocatalytic technologies. Air pollution mitigation and self-cleaning surface are two major applications of photocatalytic building materials. In this study, a comparison was made to evaluate the performance of TiO₂ modified concrete surface layers for NO_x and VOC degradation. The self-cleaning performance of TiO₂ modified self-compacting mortars (SCM) developed for decorative applications was also evaluated. The results show that the photocatalytic conversion of toluene by the TiO₂ modified surface layer was not detected, although NO_x could be effectively removed under the same conditions. The presence of toluene did not influence the NO_x removal process. TiO₂ modified SCM were found to be effective in the discoloration of rhodamine B under UV and strong halogen light irradiation. The level of adsorption of the air contaminants onto the active sites of the cement-TiO₂ composite was identified to be the key factor determining the subsequent photocatalytic efficiency.     

Antifungal capability of TiO2 coated film on moist wood

Photocatalytic oxidation by TiO₂ has been shown to deactivate biological pollutants. Most previous studies evaluated TiO₂'s antimicrobial performance using bacteria, with Escherichia coli most commonly applied as the test microbe. There have not been concentrated studies focusing on the photocatalytic disinfection of fungi which widely exist in buildings and cause health problems. In this study, the antifungal activity of TiO₂ photocatalytic reaction against Aspergillus niger was investigated for moist wood boards during periods of several weeks. TiO₂ coated film in the presence of UVA (365 nm) irradiation exhibited antifungal capability. No visible growth was observed on specimens during the photo-process. Re-growth appeared in subsequent dark, indicating that the photocatalytic reaction was not sufficient for total disinfection against mold fungi but did suppress fungi growth. The study sheds light on conditions and potential applications of photocatalytic deactivation of fungi.     

Visible-light-induced photocatalysis of low-level methyl-tertiary butyl ether (MTBE) and trichloroethylene (TCE) using element-doped titanium dioxide

While the photocatalytic degradation of various volatile organic compounds in conjunction with UV light has been widely reported, visible-light-induced photocatalytic degradation of low-levels of the pollutants MTBE and TCE, which have been linked to potential adverse health effects, is rarely reported. The present study examined whether visible-light-activated S- or N-doped TiO₂ photocatalytic technology can be used to control indoor concentrations of MTBE and TCE. This study consists of the characterization of the doped TiO₂ powders, as well as an investigation of their photocatalytic activities. In regards to both powders, a shift of the absorbance spectrum towards the visible light region was observed. An activity test suggested that these photocatalysts exhibited reasonably high degradation efficiencies towards MTBE and TCE under visible light irradiation. The degradation efficiencies of MTBE and TCE by S- and N-doped photocatalysts exceeded 75 and 80%, respectively, at input concentrations (IC) of 0.1 ppm. Degradation efficiency was dependent on both IC and relative humidity. TCE could enhance the degradation efficiency of MTBE even under visible-light irradiation. The estimated mineralization efficiencies (MEs) were comparable to those of previous studies conducted with UV/TiO₂ systems. Similar to the relative degradation efficiencies, the ME of TCE was higher in comparison to that of MTBE. The CO production measured during the photocatalytic processes represented a negligible addition to indoor CO levels. These results suggest that visible-light-activated S- and N-doped TiO₂ photocatalysts may prove a useful tool in the effort to improve indoor air quality.     

Photocatalytic degradation of 2,4-dinitrophenol (DNP) by multi-walled carbon nanotubes (MWCNTs)/TiO2 composite in aqueous solution under solar irradiation

Nanosized multi-walled carbon nanotubes (MWCNTs)/TiO₂ composite and neat TiO₂ photocatalysts were synthesized by sol-gel technique using tetrabutyl titanate as a precursor. The as prepared photocatalysts were characterized using XRD, SEM, FTIR and UV-vis spectra. The samples were evaluated for their photocatalytic activity towards the degradation of 2,4-dinitrophenol (DNP) under solar irradiation. The results indicated that the addition of an appropriate amount of MWCNTs could remarkably improve the photocatalytic activity of TiO₂. An optimal MWCNTs:TiO₂ ratio of 0.05% (w/w) was found to achieve the maximum rate of DNP degradation. The effects of pH, irradiation time, catalyst concentration, DNP concentration, etc. on the photocatalytic activity were studied and the results obtained were fitted to the Langmuir-Hinshelwood model to study the degradation kinetics. The optimal conditions were an initial DNP concentration of 38.8 mg/L at pH 6.0 with catalyst concentration of 8 g/L under solar irradiation for 150 min with good recyclisation of catalyst. The degree of photocatalytic degradation of DNP increased with an increase in temperature. The MWCNTs/TiO₂ composite was found to be very effective in the decolorization and COD reduction of real wastewater from DNP manufacturing. Thus, this study showed the feasible and potential use of MWCNTs/TiO₂ composite in degradation of various toxic organic contaminants and industrial effluents.     

Evaluation of the durability of titanium dioxide photocatalyst coating for concrete pavement

The use of titanium dioxide (TiO₂) ultrafine particles as coating for concrete pavement have received considerable attention in recent years as these particles can trap and decompose organic and inorganic air pollutants by a photocatalytic process. In spite of these promising benefits, the durability and resistance to wear of TiO₂ surface coating has not been evaluated. The objective of this study was to determine the abrasion and wear resistance properties of TiO₂ coatings and its effect on the coating’s environmental performance. To achieve this objective, an experimental program was conducted to measure and compare the environmental performance of titanium dioxide coating before and after laboratory-simulated abrasion and wearing. The environmental efficiency of the coating to remove nitrogen oxides (NO_x) from the atmosphere was measured using a newly developed laboratory setup. Microscopic analysis was conducted using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) to determine the distribution of TiO₂ particles on the surface before and after wearing. The measured rut depth using the Loaded-Wheel Tester (LWT) was minimal indicating that the use of the coating did not appear to affect the wear resistance of the surface. Wearing of the specimens with 5% TiO₂ resulted in a small decrease in the coating NO removal efficiency. In contrast, the wearing of the samples with 3% TiO₂ slightly improved the NO removal efficiency. Results presented in this paper support that the use of TiO₂ coating as a photocatalytic compound would provide acceptable durability and wear resistance.     

Low-temperature synthesis,structure-sorption characterisics and photocatalytic activity of TiO<Subscript>2</Subscript> nanostructures

The article addresses a practicable and economic low-temperature method of TiO₂ synthesis, which allows us in a specific manner to influence structure-sorption characteristics and photocatalytic activity of samples not at the expense of the change of temperature of finite treatment, but rather by way of varying additions of the precipitant and modifier. This method helped obtain nanodisperse TiO₂ with a developed specific area of the surface and high photocatalytic activity with respect to dyes of the anionic and cationic types. Individually obtained TiO₂ samples display activity even higher than commercial products.     

Photocatalytic Destruction of Fulvic Acids by Various Oxidants in a Reactor with Immobilized TiO<Subscript>2</Subscript>

Comparison of the efficiency of photocatalytic oxidation of aqueous solution of fulvic acids (TOC₀—15.9–17.1 mg/dm³, pH0 6 ± 0.1) by oxygen of the air, hydrogen peroxide and ozone in a reactor containing a wide-porous ceramic block with immobilized TiO₂ with the variation of the concentration of H₂O₂, feed rate of O₃ and temperature showed advantages of photocatalytic ozonization and expediency of its use for deep destruction of natural organic substances in water. The maximum degree of destruction in photocatalytic systems O₂/TiO₂/UV, H₂O₂/TiO₂/UV and O₃/TiO₂/UV constituted respectively 41, 73 and 90% for TOC for 5, 4 and 3 h.     

Impact of Hydrogen Peroxide on Photocatalytic Destruction of Anionic SAS in a Reactor with Immobilized TiO<Subscript>2</Subscript>

Using sodium dodecylbenzenesulfonate the article showed high efficiency of photocatalytic system H₂O₂/TiO₂/UV for deep destruction (~ 90% in terms of TOC) of anionic SAS in a aqueousmedium (C₀ = 50 mg/dm³, pH₀ 5.9) in a reactor containing wide–porous ceramic block with immobilized TiO₂ on its surface. The TiO₂ film for a long time preserved a stable photocatalytic activity     

Photocatalytic destruction of fulvic acids by oxygen in the TiO<Subscript>2</Subscript> suspension

The paper presents a short review of the published data dealing with the photocatalytic (O₂/TiO₂/UV) oxidation of humic and fulvic acids that represent main organic impurities of natural waters. The possibility of achieving a deep destruction (≥ 90% in terms of TOC) of fulvic acids separated from the water of the Dnieper River during the process of photocatalytic oxidation by oxygen was shown for a wide interval of pH (3–8). The photocatalytic activity of a series of commercial TiO₂ samples in different isomorphic states was estimated and the impact of certain parameters of photocatalytic oxidation on the degree of complete destruction of fulvic acids was determined.     

Synthesis of sol–gel titania bactericide coatings on adobe brick

This study presents the development and characterisation of transparent sol–gel TiO₂ coatings based on titanium IV isopropoxide (TIP4), formed on a sustainable clay brick material (adobe). The sol–gel layers modified the surface of adobe, which can potentially lead to new functionalities enhancing adobe performance, e.g. higher water resistance and imparting bactericidal behaviour. X-ray diffraction results on synthesised TiO₂ layers based on TIP4 showed that the film has characteristic peaks of anatase phase. Static SIMS analysis was used to detect the presence of TiO₂ on adobe surfaces, which were also observed by TEM confirming their thickness to be in the range 20–50 nm. Sol–gel double SiO₂–TiO₂ layers were also deposited on adobe substrates. These coatings did not exhibit any cracks neither signs of peeling off from the substrate. The developed surface modified adobe bricks are attractive sustainable building materials.     

Carbon-sensitized and nitrogen-doped TiO2 for photocatalytic degradation of sulfanilamide under visible-light irradiation

A novel carbon-sensitized and nitrogen-doped TiO₂ (C/N-TiO₂) was synthesized by a facile sol-gel method using titanium butoxide as both titanium precursor and carbon source, and nitric acid as nitrogen source. The calcination temperature had a great effect on the crystal phase structure, nitrogen incorporation into the TiO₂ lattice and content of carbonaceous species. The incorporated carbonaceous species could serve as photosensitizer, while the nitrogen doping could lead to the remarkable red shift of absorption edge of C/N-TiO₂. The C/N-TiO₂ calcinated at 300 °C (T300) exhibited the highest photocatalytic activity for sulfanilamide (SNM) degradation under irradiation of visible-light-emitting diode (vis-LED). The SNM photocatalytic degradation and mineralization were more efficient in acidic conditions due to the carbon photosensitizing effect. Insignificant inhibitory effects were observed in the presence of chloride, nitrate and sulfate, while bicarbonate, phosphate and silica could inhibit the SNM mineralization to different degrees. Acetate, ammonium and sulfate were released during SNM mineralization. T300 exhibited good photochemical stability and could be reused for 5 times with less than 10% decrease in the SNM removal efficiency. The acute toxicity of SNM solution could be reduced over prolonged photocatalysis according to the Microtox assay.