Fe vs. TiO2 Photo-assisted Processes for Enhancing the Solar Inactivation of Bacteria in Water

Abstract

Batch solar water disinfection (SODIS) is a known, simple and low-cost water treatment technology. SODIS is based on the synergistic action of temperature increase and light-assisted generation of Reactive Oxygen Species (ROS) on bacteria. ROS are generated via the action of solar photons on i) Natural Organic Matter (NOM), ii) some mineral components of water (Fe oxides or Fe-organic complexes, nitrogen compounds) and iii) endogenous bacteria photosensitizers (e.g. cytochrome). SODIS has proven its effectiveness for remote settlements or urban slums in regions with high incident solar radiation. All of the internal and external simultaneous processes are often driven by photoactive Fe-species present in the cell, as well as in the natural water sources. In SODIS, a temperature of 50 °C is required and due to this temperature dependence, only 1-2 L can be treated at a time. As required exposure time strongly depends on irradiation intensity and temperature, some SODIS households could be overburdened, leading to inadequate treatment and probable bacterial re-growth. This is why TiO(2) photocatalysis and Fe photo-assisted systems (i.e. photo-Fenton reactants) have been considered to enhance the photo-catalytic processes already present in natural water sources when exposed to solar light. Both TiO(2) and Fe-photoassisted processes, when applied to water disinfection aim to improve the performance of solar bacteria inactivation systems by i) enhancing ROS production, ii) making the process independent from the rise in temperature and as a consequence iii) allowing the treatment of larger volumes than 1-2 L of water and iv) prevent bacterial (re)growth, sometimes observed after sole solar treatment.

Antibacterial MoS2-Ce6-Ionic Liquid Nanoplatform against Photothermal/Photodynamic Combined Therapy and Wound Healing Acceleration

“…However, ILs are toxic to normal cells. − Therefore, in this study, anions and designed cations were selected to assemble the Ce6-IL by exchange reaction and Ce6-IL was released in vitro (Figure S3). Bacterial-activated Ce6-IL has a broad spectrum of bimodal bacteriostatic activity, both cationic and anion, and also significantly improves the biocompatibility of the IL. − The combination therapy of photothermal/dynamic therapy (PTDT) was used in this study. The combined action of PDT and photothermal therapy (PTT) has great potential to overcome their respective shortcomings, which makes the MoS 2 -Ce6-IL material have superior advantages in enhancing the antibacterial efficacy of the treatment. − …”

Synergistic Photodynamic and Photothermal Antibacterial Nanocomposite Membrane Triggered by Single NIR Light Source

“…Pathogenic bacterial infections associated with the wound healing procedure often result in serious complications. , Till now, great efforts have been devoted toward the fabrication of active antibacterial materials, mainly relying on the conventional bactericidal agents. − Although effective, most of these traditional strategies may cause environmental pollution and even induce serious antibiotic resistance . Alternatively, a photosensitizer (PS), as a key component in photodynamic therapy (PDT), shows remarkable antibacterial performance by taking advantage of the generated cytotoxic reactive oxygen species (ROS) upon visible or ultraviolet (UV) light illumination. − Due to the strong reactivity, minimal invasiveness, and nonspecific attack against microorganisms, photobactericidal agents have aroused mounting interest globally. , In this respect, titanium dioxide (TiO 2 ) has been proven to be a perfect inorganic PS to disinfect pathogens owing to its stability, nontoxicity, and high efficiency . Nevertheless, the UV light irradiation is necessary for the ROS generation of TiO 2 -based PS because of its large band gap (∼3.2 eV) .…”