Semiconductor-hydrophobic material interfaces as a new active site paradigm for photocatalytic degradation of perfluorocarboxylic acids.

Photocatalytic degradation of long-chain perfluorocarboxylic acid (PFCA) water contaminants has been reported for numerous of semiconductors, including composite TiO particles decorated with graphitic carbon co-catalysts. While pristine TiO degrades PFCAs inefficiently, the carbon components purportedly enhance activity due to their conductive nature and resultant charge separation enhancement. Yet herein, we present evidence that the catalytic activity of a graphene oxide (GO)-TiO composite from the literature arose not due to from charge separation, but to a unique mode of PFCA adsorption occurring at the interface of TiO and hydrophobic GO.

Synthesis of Petitjeanite BiO(OH)(PO) Photocatalytic Microparticles: Effect of Synthetic Conditions on the Crystal Structure and Activity toward Degradation of Aqueous Perfluorooctanoic Acid (PFOA).

The discovery of synthetic BiO(OH)(PO) [BOHP] and its application toward photocatalytic oxidation of the water contaminant perfluorooctanoic acid (PFOA) have prompted further interest in development. Despite its high activity toward PFOA degradation, the scarce appearance in the literature and lack of research have left a knowledge gap in the understanding of BOHP synthesis, formation, and photocatalytic activity. Herein, we explore the crystallization of BOHP microparticles via hydrothermal syntheses, focusing on the influence of ions and organics present in the reaction solution when using different hydroxide amendments (NaOH, NHOH, NMeOH, and NEtOH).

Biofilm growth under continuous UVC irradiation: Quantitative effects of growth conditions and growth time on intensity response parameters.

Biofilms can harbor a wide range of microorganisms, including opportunistic respiratory pathogens, and their establishment on engineered surfaces poses a risk to public health and industry. The emergence of compact germicidal ultraviolet light-emitting diodes (UV LEDs) may enable their incorporation into confined spaces to inhibit bacterial surface colonization on inaccessible surfaces, such as those in premise plumbing. Such applications necessitate knowledge of the quantitative response of biofilm growth rates to UV exposure on continuously irradiated surfaces.

Quantification and modeling of the response of surface biofilm growth to continuous low intensity UVC irradiation.

Though germicidal UV radiation is widely applied for disinfection of water and food, it may also be used to prevent bacterial growth and colonization on surfaces within engineered systems. Emerging UV source technologies, such as ultraviolet-C (UVC) LEDs, present new opportunities for deterring biofilms within certain devices, including medical equipment, food equipment, and potentially in plumbing fixtures for prevention of opportunistic respiratory pathogen infections. Rational design for incorporation of UVC sources into devices with complex internal geometries is currently hampered by the lack of an engineering framework for predicting reductions in biofilm growth rates in response to continuous low-intensity irradiation.

Can incorporation of UVC LEDs into showerheads prevent opportunistic respiratory pathogens? - Microbial behavior and device design considerations.

Respiratory infections from opportunistic bacterial pathogens (OBPs) have heightened research interests in drinking water distribution systems, premise plumbing, and point-of-use technologies. In particular, biofilm growth in showerheads increases OBP content, and inhalation of shower aerosols is a major exposure route for Legionellae and Mycobacteria infections. Incorporation of UVC LEDs into showerheads has thus been proposed as a point-of-use option for healthcare facilities.

The Technology Horizon for Photocatalytic Water Treatment: Sunrise or Sunset?

Advanced oxidation processes via semiconductor photocatalysis for water treatment have been the subject of extensive research over the past three decades, producing many scientific reports focused on elucidating mechanisms and enhancing kinetics for the treatment of contaminants in water. Many of these reports imply that the ultimate goal of the research is to apply photocatalysis in municipal water treatment operations. However, this ignores immense technology transfer problems, perpetuating a widening gap between academic advocation and industrial application.

Challenges and prospects of advanced oxidation water treatment processes using catalytic nanomaterials.

Centralized water treatment has dominated in developed urban areas over the past century, although increasing challenges with this model demand a shift to a more decentralized approach wherein advanced oxidation processes (AOPs) can be appealing treatment options. Efforts to overcome the fundamental obstacles that have thus far limited the practical use of traditional AOPs, such as reducing their chemical and energy input demands, target the utilization of heterogeneous catalysts. Specifically, recent advances in nanotechnology have stimulated extensive research investigating engineered nanomaterial (ENM) applications to AOPs.

The Myth of Visible Light Photocatalysis Using Lanthanide Upconversion Materials.

Upconversion luminescence is a nonlinear optical process achieved by certain engineered materials, which allows conversion of low energy photons into higher energy photons. Of particular relevance to environmental technology, lanthanide-based upconversion phosphors have appeared in dozens of publications as a tool for achieving visible light activation of wide-band gap semiconductor photocatalysts, such as TiO, for degradation of water contaminants. Supposedly, the phosphor particles act to convert sub-band gap energy photons (e.

Bacteria Inactivation via X-ray-Induced UVC Radioluminescence: Toward in Situ Biofouling Prevention in Membrane Modules.

Germicidal UVC radiation is a highly effective, chemical-free tool for bacteria inactivation, but its application is limited to reactors and open areas that can accommodate lamps/LEDs and wiring. A relevant example of problematic bacterial colonization within UV-inaccessible confines where chemical techniques have found only limited success is biofouling of feed channels in high-pressure membrane elements for water treatment. Herein we demonstrate a unique method of generating UV internally using embedded radioluminescent (RL) particles excited by an external X-ray source.

Porous Silicon's Photoactivity in Water: Insights into Environmental Fate.

Interest in porous silicon (pSi) (and, more broadly, silicon nanoparticles (NPs)) has increased along with their concomitant use in various commercial and consumer products, yet little is known about their behavior in the natural environment. In this study, we have investigated the photosensitization, optical, and surface properties of pSi as a function of time in aqueous systems. Samples were prepared via an anodic electrochemical etching procedure, resulting in pSi particles with diameters of ca.

Bench-scale evaluation of water disinfection by visible-to-UVC upconversion under high-intensity irradiation.

The feasibility of applying visible-to-UVC upconversion (UC) luminescence to enhance the kinetics of solar water disinfection was evaluated using Lu7O5F9:Pr(3+) ceramics incorporated into a solar reactor containing E. coli suspensions. Inactivation was assessed in batch conditions using both laser and lens-concentrated sunlight excitation conditions.

Fluorinated TiO₂ as an ambient light-activated virucidal surface coating material for the control of human norovirus.

We evaluated the virucidal efficacy of light-activated fluorinated TiO₂ surface coatings on human norovirus and several surrogates (bacteriophage MS2, feline calcivirus (FCV), and murine norovirus (MNV)). Inactivation of viruses on surfaces exposed to a common fluorescent lamp was monitored and the effects of UVA intensity, temperature, and fluoride content were assessed. Destruction of RNA and capsid oxidation were evaluated for human norovirus inocula on the F-TiO₂ surfaces, while contact with the F-TiO₂ surface and exposure to residual UVA radiation of 10 μW cm(-2) for 60 min resulted in infectivity reductions for the norovirus surrogates of 2-3 log₁₀.

Synthesis and characterization of visible-to-UVC upconversion antimicrobial ceramics.

The objective of this study was to develop visible-to-ultraviolet C (UVC) upconversion ceramic materials, which inactivate surface-borne microbes through frequency amplification of ambient visible light. Ceramics were formed by high-temperature sintering of compacted yttrium silicate powders doped with Pr(3+) and Li(+). In comparison to previously reported upconversion surface coatings, the ceramics were significantly more durable and had greater upconversion efficiency under both laser and low-power visible light excitation.

Engineering light: advances in wavelength conversion materials for energy and environmental technologies.

Upconversion photoluminescence (UC) occurs in optical materials that are capable of absorbing low energy photons and emitting photons of higher energy and shorter wavelength, while downconversion (DC) materials may absorb one high energy photon and emit two of lower energy for quantum yields exceeding unity. These wavelength conversion processes allow us to transform electromagnetic radiation so it may be more effectively utilized by light-capturing devices and materials. Progress in designing more efficient organic and inorganic photochemical conversion systems has initiated a recent surge in attempts to apply these processes for practical uses, including enhancement of many energy and environmental technologies.

Converting visible light into UVC: microbial inactivation by Pr(3+)-activated upconversion materials.

Herein we report the synthesis and properties of light-activated antimicrobial surfaces composed of lanthanide-doped upconversion luminescent nano- and microcrystalline Y(2)SiO(5). Unlike photocatalytic surfaces, which convert light energy into reactive chemical species, this work describes surfaces that inactivate microorganisms through purely optical mechanisms, wherein incident visible light is partially converted into germicidal UVC radiation. Upconversion phosphors utilizing a Pr(3+) activator ion were synthesized and their visible-to-ultraviolet conversion capabilities were confirmed via photoluminescence spectroscopy.

Inactivation and surface interactions of MS-2 bacteriophage in a TiO2 photoelectrocatalytic reactor.

Inactivation of MS-2 bacteriophage in a TiO(2) photoelectrocatalytic system was evaluated, wherein TiO(2) particles were coated onto an indium tin oxide (ITO) electrode and an electrical potential was applied under black light blue (BLB) irradiation. MS-2 phage inactivation was greatly enhanced by anodic potential, whereas cathodic potential completely inhibited inactivation. Experiments performed with radical scavengers showed that inactivation was primarily caused by hydroxyl radicals, both in the bulk phase and on the TiO(2) surface.