Photocatalytic Degradation of Estriol Using Iron-Doped TiO2 under High and Low UV Irradiation

Standardized Figures of Merit for Proper Benchmarking of Photocatalytic Inactivation of Bacteria Using Thin Films Based on TiO2 Nanostructures

The study of photocatalysts fixed to surfaces for the inactivation of bacteria in wastewater has increased in recent years. However, there are no standardized methods to analyze the photocatalytic antibacterial activity of these materials, and no systematic studies have attempted to relate this activity to the number of reactive oxygen species generated during UV-light irradiation. Additionally, studies regarding photocatalytic antibacterial activity are usually carried out with varying pathogen concentrations, UV light doses, and catalyst amounts, making it difficult to compare results across different materials. The work introduces the photocatalytic bacteria inactivation efficiency (PBIE) and bacteria inactivation potential of hydroxyl radicals (BIPHR) figures of merit for evaluating the photocatalytic activity of catalysts fixed onto surfaces for bacteria inactivation. To demonstrate their applicability, these parameters are calculated for various photocatalytic TiO2 -based coatings, accounting for the catalyst area, the kinetic reaction rate constant associated with bacteria inactivation and hydroxyl radical formation, reactor volume, and UV light dose. This approach enables a comprehensive comparison of photocatalytic films prepared by different fabrication techniques and evaluated under diverse experimental conditions, with potential applications in the design of fixed-bed reactors.

Synthesis and Characterization of N and Fe-Doped TiO2 Nanoparticles for 2,4-Dimethylaniline Mineralization

The present study aimed to evaluate the feasibility of developing low-cost N- and Fe-doped TiO₂ photocatalysts for investigating the mineralization of 2,4-dimethylaniline (2,4-DMA). With a single anatase phase, the photocatalysts showed high thermal stability with mass losses of less than 2%. The predominant oxidative state is Ti⁴⁺, but there is presence of Ti³⁺ associated with oxygen vacancies. In materials with N, doping was interstitial in the NH₃/NH⁴⁺ form and for doping with Fe, there was a presence of Fe-Ti bonds (indicating substitutional occupations). With an improved band gap energy from 3.16 eV to 2.82 eV the photoactivity of the photocatalysts was validated with an 18 W UVA lamp (340–415 nm) with a flux of 8.23 × 10⁻⁶ Einstein s⁻¹. With a size of only 14.45 nm and a surface area of 84.73 m² g⁻¹, the photocatalyst doped with 0.0125% Fe mineralized 92% of the 2,4-DMA in just 180 min. While the 3% N photocatalyst with 12.27 nm had similar performance at only 360 min. Factors such as high surface area, mesoporous structure and improved E_bg, and absence of Fe peak in XPS analysis indicate that doping with 0.0125% Fe caused a modification in TiO₂ structure.

Inactivation of Escherichia coli Using Biogenic Silver Nanoparticles and Ultraviolet (UV) Radiation in Water Disinfection Processes

This work tested the antimicrobial activity of three different biogenic silver nanoparticles (AgNPs) against Escherichia coli (E. coli) for water disinfection processes. The influence of different AgNP capping or stabilizing agents (e.g., protein or carbohydrate capped) and the use of ultraviolet (UV) radiation on the disinfection process were also assessed. The use of UV radiation was found to enhance the antimicrobial effects of AgNPs on E. coli. The antibacterial effects of AgNPs depended on the type of the capping biomolecules. Protein-capped nanoparticles showed greater antimicrobial effects compared with carbohydrate-capped (cellulose nanofibers, CNF) nanoparticles. Those capped with the fungal secretome proteins were the most active in E. coli inactivation. The least E. coli inactivation was observed for CNF-capped AgNPs. The size of the tested AgNPs also showed an expected effect on their anti-E. coli activity, with the smallest particles being the most active. The antimicrobial effects of biogenic AgNPs on E. coli make them an effective, innovative, and eco-friendly alternative for water disinfection processes, which supports further research into their use in developing sustainable water treatment processes.

Recent Advances in Endocrine Disrupting Compounds Degradation through Metal Oxide-Based Nanomaterials

Endocrine Disrupting Compounds (EDCs) comprise a class of natural or synthetic molecules and groups of substances which are considered as emerging contaminants due to their toxicity and danger for the ecosystems, including human health. Nowadays, the presence of EDCs in water and wastewater has become a global problem, which is challenging the scientific community to address the development and application of effective strategies for their removal from the environment. Particularly, catalytic and photocatalytic degradation processes employing nanostructured materials based on metal oxides, mainly acting through the generation of reactive oxygen species, are widely explored to eradicate EDCs from water. In this review, we report the recent advances described by the major publications in recent years and focused on the degradation processes of several classes of EDCs, such as plastic components and additives, agricultural chemicals, pharmaceuticals, and personal care products, which were realized by using novel metal oxide-based nanomaterials. A variety of doped, hybrid, composite and heterostructured semiconductors were reported, whose performances are influenced by their chemical, structural as well as morphological features. Along with photocatalysis, alternative heterogeneous advanced oxidation processes are in development, and their combination may be a promising way toward industrial scale application.

Emerging materials and technologies for landfill leachate treatment: A critical review

Sanitary landfill is the most popular way to dispose solid wastes with one major drawback: the generation of landfill leachate resulting from percolation of rainfall through exposed landfill areas or infiltration of groundwater into the landfill. The landfill leachate impacts on the environment has forced authorities to stipulate more stringent requirements for pollution control, generating the need for innovative technologies to eliminate waste degradation by-products incorporated in the leachate. Natural attenuation has no effect while conventional treatment processes are not capable of removing some the pollutants contained in the leachate which are reported to reach the natural environment, the aquatic food web, and the anthroposphere. This review critically evaluates the state-of-the-art engineered materials and technologies for the treatment of landfill leachate with the potential for real-scale application. The study outcomes confirmed that only a limited number of studies are available for providing new information about novel materials or technologies suitable for application in the removal of pollutants from landfill leachate. This paper focuses on the type of pollutants being removed, the process conditions and the outcomes reported in the literature. The emerging trends are also highlighted as well as the identification of current knowledge gaps and future research directions along with recommendations related to the application of available technologies for landfill leachate treatment.

Photocatalytic degradation of amoxicillin from aqueous solutions by titanium dioxide nanoparticles loaded on graphene oxide

The photocatalytic degradation of amoxicillin (AMX) by titanium dioxide nanoparticles loaded on graphene oxide (GO/TiO₂) was evaluated under UV light. Experimental results showed that key parameters such as initial pH, GO/TiO₂ dosage, UV intensity, and initial AMX concentration had a significant effect on AMX degradation. Compared to the photolysis and adsorption processes, the AMX degradation efficiency was obtained to be more than 99% at conditions including pH of 6, the GO/TiO₂ dosage of 0.4 g/L, the AMX concentration of 50 mg/L, and the intensity of 36 W. Trapping tests showed that all three hydroxyl radical (OH^•), superoxide radical (O₂^•-), and hole (h⁺) were produced in the photocatalytic process; however, h⁺ plays a major role in AMX degradation. Under UV irradiation, GO/TiO₂ showed excellent stability and recyclability for 4 consecutive reaction cycles. The analysis of total organic carbon (TOC) suggested that AMX could be well degraded into CO₂ and H₂O. The formation of NH₄⁺, NO₃^-, and SO₄^2- as a result of AMX degradation confirmed the good mineralization of AMX in the GO/TiO₂/UV process. The toxicity of the inlet and outlet samples of the process has been investigated by cultivation of Escherichia coli and Streptococcus faecalis, and the results showed that the condition is suitable for the growth of organisms. The photocatalytic degradation mechanism was proposed based on trapping and comparative tests. Based on the results, the GO/TiO₂/UV process can be considered as a promising technique for AMX degradation due to photocatalyst stability, high mineralization efficiency, and effluent low toxicity.

Peroxymonosulfate decomposition by homogeneous and heterogeneous Co: Kinetics and application for the degradation of acetaminophen

Peroxymonosulfate (PMS) decomposition, hydroxyl radical (^•OH) generation, and acetaminophen (ACT) degradation by the Co/PMS system using homogeneous (dissolved cobalt) and heterogeneous (suspended Co₃O₄) cobalt were assessed. For the homogeneous process, >99% PMS decomposition was observed and 10 mmol/L of ^•OH generation was produced using 5 mmol/L of PMS and different dissolved cobalt concentrations after 30 min. A dissolved cobalt concentration of 0.2 mmol/L was used to achieve >99% ACT degradation using the homogeneous process. For the heterogeneous process, 60% PMS decomposition and negligible ^•OH generation were observed for 5 mmol/L of the initial PMS concentration using 0.1 and 0.2 g/L of Co₃O₄. Degradation of ACT greater than 80% was achieved for all experimental runs using 5 mmol/L of the initial PMS concentration independently of the initial Co₃O₄ load used. For the heterogeneous process, the best experimental conditions for ACT degradation were found to be 3 mmol/L of PMS and 0.2 g/L of Co₃O₄, for which >99% ACT degradation was achieved after 10 min. Because negligible ^•OH was produced by the Co₃O₄/PMS process, a second-order kinetic model was proposed for sulfur-based free radical production to allow fair comparison between homogeneous and heterogeneous processes. Using the kinetic data and the reaction by-products identified, a mechanistic pathway for ACT degradation is suggested.

Editorial: Special Issue on “Emerging Trends in TiO2 Photocatalysis and Applications”

It is not an exaggerated fact that the semiconductor titanium dioxide (TiO2) has been evolved as a prototypical material to understand the photocatalytic process and has been demonstrated for various photocatalytic applications such as pollutants degradation, water splitting, heavy metal reduction, CO2 conversion, N2 fixation, bacterial disinfection, etc [...]

Emerging pollutants-Part II: Treatment

Recently, emerging pollutants (EPs) have been frequently detected in urban wastewater, surface water, drinking water, and other water bodies. EPs mainly usually include pharmaceuticals and personal care products, endocrine-disrupting chemicals, antibiotic resistance genes, persistent organic pollutants, disinfection by-products, and other industrial chemicals. The potential threat of EPs to ecosystems and human health has attracted worldwide attention. Therefore, how to treat EPs in various water bodies has become one of the research priorities. In this paper, some research results on treatment of EPs published in 2018 were summarized. PRACTITIONER POINTS: At present, more attention has been paid to emerging pollutants (EPs), including pharmaceuticals and personal care products (PPCPs), endocrine-disrupting chemicals (EDCs), antibiotic resistance genes, persistent organic pollutants, disinfection by-products, etc. Existing EPs disposal technologies mainly include: engineered wetlands and natural systems, biological treatment, physical and physicochemical separation, chemical oxidation, catalysis, etc. This paper reviews some research results on the treatment technologies of EPs published in 2018.

Characterization of Photoactive Fe-TiO2 Lime Coatings for Building Protection: The Role of Iron Content

Iron-doped TiO₂ nanoparticles, ranging in Fe concentrations from 0.05 up to 1.00% w/w, were synthesized through a simple sol-gel method. Fourier-transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), Ultraviolet-Visible (UV-Vis) spectroscopy, nitrogen adsorption−desorption isotherms, X-ray photoelectron spectroscopy (XPS), and X-ray absorption near-edge structure spectroscopy (XANES) were used to characterize the synthesized nanoparticles. The characterization of the Fe-doped TiO₂ nanoparticles revealed the predominant presence of anatase crystalline form, as well as the incorporation of the Fe³⁺ ions into the crystal lattice of TiO₂. The photocatalytic assessment of the Fe-doped TiO₂ nanoparticles indicated that the low iron doping titania (0.05 and 0.10% w/w) have a positive effect on the photocatalytic degradation of Methyl Orange under visible radiation. Moreover, FTIR monitoring of calcium hydroxide pastes enriched with low Fe-doped TiO₂ revealed enhancement of carbonation at both early and later stages. Improved photocatalytic performance and increased lime carbonation, observed in lime coatings with low Fe-doped TiO₂ admixtures, established them as invaluable contributors to the protection of the built environment.

Enhanced Photocatalytic Reduction of Cr(VI) by Combined Magnetic TiO2-Based NFs and Ammonium Oxalate Hole Scavengers

Heavy metal pollution of wastewater with coexisting organic contaminants has become a serious threat to human survival and development. In particular, hexavalent chromium, which is released into industrial wastewater, is both toxic and carcinogenic. TiO2 photocatalysts have attracted much attention due to their potential photodegradation and photoreduction abilities. Though TiO2 demonstrates high photocatalytic performance, it is a difficult material to recycle after the photocatalytic reaction. Considering the secondary pollution caused by the photocatalysts, in this study we prepared Ag/Fe3O4/TiO2 nanofibers (NFs) that could be magnetically separated using hydrothermal synthesis, which was considered a benign and effective resolution. For the photocatalytic test, the removal of Cr(VI) was carried out by Ag/Fe3O4/TiO2 nanofibers combined with ammonium oxalate (AO). AO acted as a hole scavenger to enhance the electron-hole separation ability, thereby dramatically enhancing the photoreduction efficiency of Cr(VI). The reaction rate constant for Ag/Fe3O4/TiO2 NFs in the binary system reached 0.260 min−1, 6.95 times of that of Ag/Fe3O4/TiO2 NFs in a single system (0.038 min−1). The optimized Ag/Fe3O4/TiO2 NFs exhibited high efficiency and maintained their photoreduction efficiency at 90% with a recyclability of 87% after five cycles. Hence, taking into account the high magnetic separation behavior, Ag/Fe3O4/TiO2 NFs with a high recycling capability are a potential photocatalyst for wastewater treatment.