Nanocomposite Au NP/TiO2 thin film in the efficient remediation of aqueous solutions contaminated with emerging micro-pollutants

Photocatalytic degradation of sulfamethoxazole using TiO2-based materials - Perspectives for the development of a sustainable water treatment technology

Heterogeneous photocatalysis using titanium dioxide-based materials is considered a promising and innovative solution to the water pollution problem. However, due to the limitations concerning the use of the developed materials and the applied photodegradation conditions, the research on photoremediation using TiO₂ often stays behind the lab door. The challenge is to convert the basic research into a successful innovation, leading to the implementation of this process into wastewater treatment. For this purpose, the most active materials and optimal photodegradation conditions must be chosen. This article collects and compares the studies on photocatalytic degradation of an emerging pollutant - sulfamethoxazole, an antibacterial drug - and attempts to find the best approaches to be successfully applied on an industrial scale. Various types of TiO₂-based photocatalysts are compared, including different nanoforms, doped or polymer-based composites, composites with graphene, activated carbon, dyes or natural compounds, as well as possible supporting materials for TiO₂. The paper covers the impact of the irradiation source (natural sunlight, LED, mercury or xenon lamps) and water matrix on the photodegradation process, considering the ecological and economic sustainability of the process. Emphasis is put on the stability, ease of separation and reuse of the photocatalyst, power and safety of the irradiation source, identification of photodegradation intermediates and toxicity assays. The main approaches are critically discussed, main challenges and perspectives for an effective photocatalytic water treatment technology are pointed out.

Enhanced visible light photocatalytic performance of a novel FeIn2S4 microsphere/BiOBr nanoplate heterojunction with a Z-scheme configuration

The rational design of heterojunction photocatalysts is an effective way to improve semiconductor photocatalytic activity. The simple solvothermal method was used to successfully prepare visible light-driven FeIn₂S₄ microsphere/BiOBr nanoplate binary heterojunction photocatalysts with varying FeIn₂S₄ contents. The crystal structure, morphology, surface composition, specific surface area, charge separation, and optical properties of the as-prepared photocatalysts were investigated using a variety of analytical methods. In the photocatalytic degradation of rhodamine B, the FeIn₂S₄/BiOBr photocatalysts obtained a degradation efficiency of 96% within 60 min, which was approximately 5.33 and 2.59 times higher than pure FeIn₂S₄ and BiOBr, respectively. Radical trapping experiments and ESR measurements revealed the main active species (·OH, ·O₂^-, and h⁺) produced during photocatalytic degradation. The increased photocatalytic activity was due to the formation of Z-scheme heterojunctions between FeIn₂S₄ and BiOBr, which contributed to the improved effective charge separation of photogenerated charge carriers, augmented specific surface area, and enhanced redox capacity. It is expected that our current study will provide a hopeful way for future environmental remediation research.

Photocatalytic degradation of amoxicillin and tetracycline by template synthesized nano-structured Ce3+@TiO2 thin film catalyst

Contamination of the aquatic environment with pharmaceutical compounds is a serious environmental concern. The present investigation aims to utilize the Ce³⁺/TiO₂ thin film catalyst to remove of potential antibiotics (amoxicillin and tetracycline) using the less harmful UV-A radiations. Reduced cerium ion-doped TiO₂ is obtained by a simple one-step facile template method using polyethylene glycol as the templating agent. The synthesized catalysts Ce³⁺@TiO₂ (non-template) and Ce³⁺@TiO₂(T) (template) were characterized by spectroscopic methods. The XPS reaffirms the reduced Ce³⁺ dispersed within the titania network, and the AFM showed the surface roughness of the thin films. Detailed physicochemical analyses were conducted to deduce the degradation mechanism, and repeated use of the thin film photocatalyst showed enhanced stability. Significant mineralization of the antibiotics indicates the potential applicability of the photocatalytic catalyst. Furthermore, the presence of Ce³⁺ significantly restricted the recombination of electron/hole pairs in the photo-excited TiO₂ semiconductor and showed enhanced photocatalytic degradation of the antibiotics proceeded predominantly through the •OH.

New insights in photocatalytic removal of Alizarin Yellow using reduced Ce3+/TiO2 catalyst

The present communication aims to obtain a novel Ce³⁺/TiO₂ thin film in a single step facile method using the in situ template process. The material was characterized by the XRD (X-ray diffraction), XPS (X-ray photoelectron spectroscopy), TEM (transmission electron microscope), and AFM (atomic force microscope) analyses. The thin film catalyst was intended to introduce in the degradation of one of potential dye Alizarin Yellow from aqueous solutions using the UV-A radiations. The mechanisms of degradation along with the physicochemical parametric studies were conducted extensively. The mineralization of pollutant and the replicate use of catalysts further enhance the applicability of present communication. Additionally, the real matrix treatment was conducted to simulate the treatment process.

Synthesis and characterization of Ag0(NPs)/TiO2 nanocomposite: insight studies of triclosan removal from aqueous solutions

Nanocomposite mesoporous Ag⁰(NPs)/TiO₂ thin film materials were synthesized and assessed for its efficient application in the elimination of potentially important drug triclosan from aqueous solutions. A template synthesis using the polyethylene glycol was enabled to obtain Ag⁰(NPs)/TiO₂ nanocomposite materials where zerovalent Ag was in situ doped to the titania network. The nanocomposite materials were characterized by the scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscope (TEM), EDX elemental mapping, X-ray diffraction (XRD) analyses and Brunauer-Emmett-Teller (BET) methods. Further, the diffuse reflectance spectroscopy (DRS) was introduced to estimate the band gap of these solids. The thin film materials were subjected to the remediation of water contaminated with triclosan using the UV-A light. The oxidative elimination of triclosan was demonstrated as a function of pH, concentration of triclosan and presence of several co-existing ions. Increase in pH (4.0-10.0) and triclosan concentrations (0.5-15.0 mg/L) had decreased significantly the percentage degradation of triclosan. The pseudo-first-order kinetics was shown in the degradation of triclosan and rate constant was significantly decreased with the increase in pollutant concentration (0.5-15.0 mg/L) and pH (4.0-10.0). The 1000 times presence of scavengers showed that ^•OH were, predominantly, caused the oxidation of triclosan. Moreover, multiple application of nanocomposite Ag⁰(NPs)/TiO₂(B) revealed that the thin film was fairly intact since the photocatalytic efficiency of triclosan removal was almost unaffected.

Critical review on the mechanistic photolytic and photocatalytic degradation of triclosan

The environmentally extended presence of triclosan, TCS, component of many pharmaceutical and personal care products, and its known persistent character have awoke the scientific and social concern leading to the study of effective remediation techniques. Advanced oxidation techniques stand out for the effectiveness in degrading many persistent compounds, and as a result, they have been addressed by many researchers. However, the powerful oxidation media might lead to the formation of undesirable by-products, concern that has also been widely addressed. With regard to the presence of TCS, photolytic and photocatalytic processes provide a very effective degradation yield and rate, with a large number of reports addressing its removal from different environmental matrices. But currently, there is no clear understanding of the mechanisms involved and the routes responsible for the formation of degradation products. Thus, this work presents an exhaustive and critical analysis of the state of the art related to the photo-degradation of TCS, with special focus on the formation of oxidation by-products, on the phenomena responsible and on the influence of operation variables. This report aims at offering valuable information to researchers dealing with this environmentally relevant problem.

PCDD/Fs traceability during triclosan electrochemical oxidation

5-Chloro-2-(2,4-dichlorophenoxy)phenol (TCS) is a persistent organic pollutant (POP) widely used in different consumer goods. Its recalcitrant nature demands the application of effective remediation technologies in order to avoid the negative environmental impact associated to the discharge of contaminated waters. Although advanced oxidation technologies have been considered the best alternative to destroy bio-recalcitrant compounds, the likely formation of high toxicity byproducts must be analysed before large-scale deployment. In this work, we aim to trace the presence of chlorinated compounds during the electro-oxidation of aqueous TCS samples. First, we analyze the influence of the initial concentration of TCS on the toxicity of the oxidation medium expressed by the International-Toxicity Equivalency Factor (I-TEF); second, we have detected the formation of intermediate organo-chlorinated compounds by GC-MS supported by HPLC and finally, we have quantified the concentration of highly-polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) by HRGC-HRMS within the oxidation treatment. In those samples where TCS had been completely degraded the concentration of PCDD/Fs showed a high increase, especially when NaCl was used as electrolyte, with the initial concentration of TCS. Under these conditions the I-TEF achieved values up to 3.8 × 10² pg L^-1.