Nanocomposite thin films Ag0(NP)/TiO2 in the efficient removal of micro-pollutants from aqueous solutions: A case study of tetracycline and sulfamethoxazole removal

Enhanced tetracycline degradation with TiO2/natural pyrite S-scheme photocatalyst

In this study, TiO2 nanoparticles were employed as a photocatalyst for the degradation of tetracycline (TC) under visible light irradiation. The TiO2 nanoparticles were decorated on natural pyrite (TiO2/NP) and characterized using XRD, FTIR, and SEM-EDX methods. This study evaluated the impacts of various operational parameters such as pH, catalyst dosage, initial TC concentration, and light intensity on TC removal. The findings revealed that under optimal conditions (pH 7, catalyst: 2 g/L, TC: 30 mg/L, and light intensity: 60 mW/cm2), 100% of TC and 84% of TOC were removed within 180 min. The kinetics of TC elimination followed a first-order model. The dominant oxidation species involved in the photocatalytic elimination of TC was found to be ·OH radicals in the TiO2/NP system. The reuse experiments showed the high capability of the catalyst after four consecutive cycles. This study confirmed that the TiO2/NP system has high performance in photocatalytic TC removal under optimized experimental conditions.

Novel cubical Ag(NP) decorated titanium dioxide supported bentonite thin film in the efficient removal of bisphenol A using visible light

The persistent endocrine-disrupting chemical bisphenol A is posing serious health concerns; hence, it is known to be an emerging and potential water contaminant. The present investigation aims to synthesize novel cubical Ag(NP) decorated titanium dioxide-supported bentonite (Ag/TiO₂@Clay) nanocomposite using a novel synthetic process. The nanocomposite materials were characterized by several analytical methods viz., transmission electron microscopy (TEM), X-ray diffraction (XRD) analyses, energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) and diffuse reflectance spectroscopy (DRS). Further, the photocatalytic removal of bisphenol A was conducted utilizing the thin film catalyst under the LED (light emitting diode; visible light) and UV-A (ultra violet-A) light sources. The parametric studies solution pH (6.0-12.0), pollutant concentrations (1.0-20.0 mg/L), and the interaction of several scavengers and co-existing ions are studied extensively to demonstrate the insights of the removal mechanism. The mineralization of bisphenol A and repeated use of the thin film catalyst showed the potential usage of photocatalysts in the devised large-scale operations. Similarly, the natural matrix treatment was performed to evaluate the suitability of the process for real implications.

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.

Noble metal-doped TiO2 thin films in the efficient removal of Mordant Orange-1: insights of degradation process

Nanocomposite Ag⁰(NPs)/TiO₂ is synthesised in a facile template method enabling nanoparticles of reduced Ag evenly distributed within the titania network. The morphological studies of nanocomposites were extensively performed employing SEM/EDX (scanning electron microscopy/energy dispersive X-ray), TEM (transmission electron microscopy) and AFM (atomic force microscopy). Moreover, the bandgap energies of materials were obtained using the diffuse reflectance spectrometer (DRS). The newer insights in the photocatalytic elimination of Mordant Orange-1 (MO1) was obtained using the nanocomposite thin film for various parametric studies utilising the UV-A and LED illuminations. The kinetics of degradation of MO1 was performed, and the rate constant was favoured at lower concentrations of MO1. Moreover, the elimination efficiency of MO1 was favoured with a decrease in solution pH. The NPOC results inferred that a fairly good extent of MO1 was mineralised using a thin-film catalyst for both the UV-A and LED illuminations. The minimal effect of several co-ions demonstrated the applicability of thin films in the elimination of MO1, and the stability of the thin film has shown the potential applicability of thin-film catalysts. Further, the mechanism of photocatalytic degradation was demonstrated with the radical scavenger studies and ascertained the reaction pathways.

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.

Application of TiO2-Based Photocatalysts to Antibiotics Degradation: Cases of Sulfamethoxazole, Trimethoprim and Ciprofloxacin

The extensive application of antibiotics in human and veterinary medicine has led to their widespread occurrence in a natural aquatic environment. Global health crisis is associated with the fast development of antimicrobial resistance, as more and more infectious diseases cannot be treated more than once. Sulfamethoxazole, trimethoprim and ciprofloxacin are the most commonly detected antibiotics in water systems worldwide. The persistent and toxic nature of these antibiotics makes their elimination by conventional treatment methods at wastewater treatment plants almost impossible. The application of advanced oxidation processes and heterogeneous photocatalysis over TiO2-based materials is a promising solution. This highly efficient technology has the potential to be sustainable, cost-efficient and energy-efficient. A comprehensive review on the application of various TiO2-based photocatalysts for the degradation of sulfamethoxazole, trimethoprim and ciprofloxacin is focused on highlighting their photocatalytic performance under various reaction conditions (different amounts of pollutant and photocatalyst, pH, light source, reaction media, presence of inorganic ions, natural organic matter, oxidants). Mineralization efficiency and ecotoxicity of final products have been also considered. Further research needs have been presented based on the literature findings. Among them, design and development of highly efficient under sunlight, stable, recyclable and cost-effective TiO2-based materials; usage of real wastewaters for photocatalytic tests; and compulsory assessment of products ecotoxicity are the most important research tasks in order to meet requirements for industrial application.

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.

Persulfate activation by modified red mud for the oxidation of antibiotic sulfamethoxazole in water

Different pre-conditioning treatments were evaluated in order to stabilize red mud, a waste product from bauxite processing, for obtaining heterogeneous catalysts (named as B1-B3) that can be employed as suitable activators of sodium persulfate (SPS) for the degradation of sulfamethoxazole (SMX), a model antibiotic, in water. The presence of Fe₃O₄ in the composition of the catalysts was found to be a key factor for a suitable activation of SPS, according to the XPS measurements. The oxidation of SMX was successfully fitted to a pseudo-first-order kinetic model (r² > 0.96), obtaining a 68% removal after 180 min when 0.8 mg/L of SMX was oxidized with 2 g/L of SPS and 2 g/L of catalyst B3. The presence of organic and/or inorganic constituents in the water matrix significantly hindered the degradation rate of SMX, the apparent kinetic constants being from 2 to 3 times lower than that determined in ultrapure water test. The use of ultrasound irradiation coupled to the addition of B3 catalyst improved importantly the SMX oxidation in real aqueous matrices, thus attaining values of removal which almost triplicated the ones obtained in absence of ultrasounds.

Highly efficient solar light-driven photocatalytic hydrogen production over Cu/FCNTs-titania quantum dots-based heterostructures

The need for clean and eco-friendly energy sources has increased enormously over the years due to adverse impacts caused by the detrimental fossil fuel energy sources on the environment. This work reports the safest and most efficient route for hydrogen generation using solar light receptive functionalized carbon nanotubes-titania quantum dots (FCNT-TQDs) as photocatalysts under the influence of solar light irradiation. Predominantly, dual capability of CNT as co-catalyst and photo-sensitizer reduced the recombination rate of charge carriers, and facilitated the efficient light harvesting. The bulk production of hydrogen via water harvesting is considered, wherein photocatalyst synthesized was tuned by the optimum addition of copper to achieve higher production rate of hydrogen up to 54.4 mmol h^-1g^-1, nearly 25-folds higher than that of pristine TiO₂ quantum dots. Addition of copper has a crucial role in improving the rate of hydrogen generation. The ternary composite exhibited 5.4-times higher hydrogen production compared to FCNT-TQDs composite.

Multifunctional biphenyl derivatives as photosensitisers in various types of photopolymerization processes, including IPN formation, 3D printing of photocurable multiwalled carbon nanotubes (MWCNTs) fluorescent composites

Summary of properties and applications of multifunctional of biphenyl derivatives as photosensitisers in various types of photopolymerization processes, including IPN formation, 3D printing of photocurable multiwalled carbon nanotubes (MWCNTs) fluorescent composites.

Enhanced photocatalytic performance by hybridization of Bi2WO6 nanoparticles with honeycomb-like porous carbon skeleton

In this work, we have assembled Bi₂WO₆ nanoparticles on the surface of honeycomb-like porous carbon skeleton (PCS) via a hydrothermal route to achieve a new type of PCS@Bi₂WO₆ hybrid composite photocatalysts. The PCS@Bi₂WO₆ hybrid structures are determined by SEM, TEM and XPS characterizations. UV-vis DRS investigation suggests an enhanced visible-light absorption of the PCS@Bi₂WO₆ composites. Transient photocurrent response, EIS and PL spectroscopy characterizations demonstrate that the composites exhibit an efficient separation of photoproduced electron/hole pairs. The photocatalytic performance of the composites were evaluated by using RhB as the model pollutant and simulated sunlight as the light source. It is revealed that the PCS@Bi₂WO₆ hybrid composites manifest much enhanced photocatalytic performance. The 5 wt%PCS@Bi₂WO₆ composite manifests the highest photocatalytic activity, which is ca. 2.1 times as large as that of bare Bi₂WO₆ nanoparticles. This can be mainly ascribed to two factors: (1) The photogenerated electron/hole pairs in Bi₂WO₆ are efficiently separated due to the electron transfer between Bi₂WO₆ and PCS; and (2) PCS induces enhanced visible-light absorption and the visible-light-excited electrons in PCS could also take part in the photocatalytic reactions.

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.