Role of reactive oxygen species on the activity of noble metal-doped TiO2 photocatalysts

Bacterial responses to Ephedra aphylla stem extract and green-synthesized Ag-TiO2 and Ag-SeO2 core/shell nanocomposites: unveiling antimicrobial and antioxidant properties

This study reports an efficient and green protocol for the green synthesis of Ag-TiO2 and Ag-SeO2 nanocomposites using the extracted stems of Ephedra aphylla. Results of spectroscopic and analytical analyses confirmed the successful synthesis, stability, and crystalline nature of the nanomaterials. The phytochemical profile and antioxidant and antimicrobial activities of the E. aphylla extract and the nanocomposites were also studied. E. aphylla extract and both the nanomaterials exhibited significant levels of active phytochemical compounds. These compounds contributed to their potent antioxidant activity, with E. aphylla extract and Ag-TiO2 NC demonstrating the highest antioxidant activity. Besides, Ag-SeO2 NC displayed remarkable antibacterial properties against different pathogenic bacteria with 31.0 ± 1.27 mm against K. pneumonia, 31.0 ± 1.72 mm against S. aureus, and 44.0 ± 1.09 mm against B. subtilis, and antifungal properties against Candida glabrata and Aspergillus niger. The enhanced antimicrobial activity of Ag-SeO2 NC can be attributed to the synergistic effects of silver and selenium nanoparticles, which can disrupt cell membranes, induce oxidative stress, and interfere with essential cellular processes. The minimum inhibitory concentration values of Ag-SeO2 NC against S. aureus and K. pneumoniae were found to be 0.2956 mg mL-1 and 4.73 mg mL-1, respectively. The mechanism of action of Ag-SeO2 NC against both fungal strains was investigated using FTIR and HR-TEM analyses.

Platinum Single Atoms Strongly Promote Superoxide Formation in Titania-Based Photocatalysis - Platinum Nanoparticles Don't

The selective reduction of molecular oxygen to superoxide is one of the key reactions in electrochemistry and photocatalysis. Here the effect of Pt co-catalysts, dispersed on titania, either as single atoms or as nanoparticles, on the photocatalytic superoxide (•O2 -) formation in O2 containing solutions is investigated. The •O2 - formation is traced by nitroblue tetrazolium (NBT) assays and in detail by EPR measurements using TEMPO as •O2 - radical scavenger. The results show that the photocatalytic formation rate of •O2 - on titania can strongly be enhanced by using Pt single atoms as a co-catalyst, whereas Pt nanoparticles hardly exhibit any accelerating effect. This finding is of considerable significance regarding photocatalytic degradation and photocatalytic oxidative synthesis processes.

Unraveling the role of chitosan in enhancing the photodegradation of ciprofloxacin by using chitosan-titanates composites: Experimental and in-silico approach

A hybrid composite (inorganic-organic) based on chitosan-functionalized hydrogen titanate nanotubes (TiCH) was synthesized by the hydrothermal method assisted by microwave, during 5h at 150 °C. The in-silico analysis determined the possible chitosan chemical adsorption models after calculating the Gibbs energies of their HOMO-LUMO orbitals. The TGA analysis confirmed the stability and helped to obtain the real functionalization degrees for the 3TiCH (2.22 %) and 5TiCH (4.33 %) samples, respectively. SEM images revealed that the 3TiCH and 5TiCH composites present tubular morphology that seemed covered with chitosan. The XRD patterns of 3TiCH and 5TiCH presented chitosan peaks, confirming their functionalization with chitosan anchored on the titanate surface. The photocatalytic degradation of ciprofloxacin antibiotic reached 93 % using the 3TiCH sample under 365-UV irradiation for 240 min. The photocatalytic performance of 3TiCH was 14.71 % more efficient than that of unfunctionalized TiNS after four reuses. The incorporation of the chitosan into the titanate improved the photocatalytic performance of the titanate, because it reduced its bandgap value, increasing the surface area, and boosting the adsorption capacity. A biopolymer such as chitosan in low concentrations can tailor the photoactivity of the inorganic nanomaterial to eliminate emerging contaminants contained in water bodies.

Progress in photocatalytic degradation of industrial organic dye by utilising the silver doped titanium dioxide nanocomposite

Industrial organic dyes represent a significant portion of pollutants discharged into the environment, particularly by the textile industry. These compounds pose serious threats to living organisms due to their high toxicity. Various techniques have been explored for the degradation of organic dyes, among which heterogeneous photocatalysis utilising titanium dioxide (TiO2) stands out as a promising technology. However, the practical application of TiO2 as photocatalyst has limitations for the following reasons; First, TiO2 has a low sensitivity to visible light due to a large band gap which can be 3.2 eV for the anatase polymorph. Second, the recombination rate of photo-induced electron-hole pairs in TiO2 is very fast. Recent research studies have brought to light that a silver-doped titanium dioxide nanocomposite could be one of the promising answers to these problems. This nanocomposite has garnered significant attention because of its unique features that suggest the manifestation of more effective concepts to minimize the electron-hole recombination and broaden light absorption. This causes Schottky barrier which is essentially created by integrating the silver nanoparticles into titanium dioxide. It is quite significant in decelerating the recombination of the electron-hole pairs, thus increasing photocatalytic activity. Further, it is more effective in that the use of silver also widens the titanium dioxide absorption range to the visible light hence maximizing capture and conversion of broader range of light energies for catalytic reactions. This paper therefore seeks to examine the research background regarding the industrial organic dyes starting with the history of industrial organic dyes before delving into an evaluation of the current and most current research on industrial organic dyes looking at advanced methods of their degradation with specific focus on silver-doped TiO2 for photocatalytic enhancement. This paper also reviews the experimental work concerning the actual photocatalytic degradation process and presents the factors affecting the performance of silver-doped TiO2 nanocomposites by eliminating organic dyes from wastewater. It also encompasses a general background into the various synthesis methods used in the preparation of silver-doped TiO2 nanocomposites. Additionally, challenges and future perspectives in the field are outlined, with a focus on the development of novel strategies to further improve the efficiency and sustainability of silver-doped TiO2 photocatalysts for industrial organic dye degradation. In conclusion, this review offers a significant outlook on the existing literature concerning the silver-doped TiO2 nanocomposites for effective photocatalytic degradation of the industrial organic dyes because of the rising pollution level and helping future researchers in seeking the solutions for environmental issues and developing sustainable wastewater treatment.

Electroless Ag nanoparticle deposition on TiO2 nanorod arrays, enhancing photocatalytic and antibacterial properties

HYPOTHESIS

The small size of the nanoparticles used to obtain high surface area photocatalysts makes their removal from solution difficult. Producing photocatalysts on substrates would alleviate this limitation. Adding heterojunctions to photocatalysts, for example, TiO2/Ag, could improve photocatalytic performance due to Schottky junction formation and introduce antibacterial properties.

EXPERIMENTS

TiO2 nanorod arrays were synthesised on a substrate via a hydrothermal approach, on which Ag nanoparticles were deposited using an electroless plating technique with varied deposition times and metal precursor concentrations. Photocatalytic performance was evaluated by monitoring Rhodamine B (RhB) degradation under ultraviolet light and antibacterial properties of the films tested using Methicillin-resistant Staphylococcus aureus.

FINDINGS

The Ag nanoparticle content was controlled by the Ag deposition process. The TiO2/Ag nanorod array containing 6.6 atomic% Ag as nanoparticles of ∼ 25 nm in diameter degraded 88 % of the RhB in 6 h compared to 54 % degradation for bare TiO2 nanorods under the same reaction conditions. Decreased photoluminescence with heterojunction formation would indicate electron transfer from the TiO2 into the Ag nanoparticles, thereby reducing charge carrier recombination. The antibacterial test conducted in the dark revealed enhanced performance for the TiO2/Ag sample compared to TiO2 nanorods against Methicillin-resistant Staphylococcus aureus after 16 h exposure with a death rate of 84 %.

Investigation of Doehlert matrix conception in novel intrinsically conducting polymers based on selenium nanoparticles for wastewater treatment: Synthesis, characterization, kinetic and chemometric study

The synthesis of robust intrinsically conducting polymers (ICPs) based on nanoparticles is becoming increasingly attractive to the research community due to the unique properties of these nanocomposites. Indeed, as organic semiconductors, ICPs combine both polymer and metal properties in a single structure. This study presents an innovative approach in which the Doehlert Matrix (DM) is applied to a novel ICP nanocomposite based on polyaniline (Pani) coupled with selenium (Se) loaded mesoporous titania (TiO2) for wastewater treatment by photocatalysis. It includes both the elaboration routes of ICP nanocomposites, characterization of materials by X-ray diffraction (XRD), BET analysis, thermogravimetric analysis (TGA), RAMAN spectroscopy and Fourier transform infrared spectroscopy (FTIR) and photodegradation of methylene blue (MB) as a representative of dye pollutant. In addition, the photocatalytic process has been optimized by a novel DM conception. The effect of the pH of the solution, the catalyst dosage and the initial pollutant concentration was investigated. The optimum conditions were found to be: initial MB concentration of 15 mg/L, the catalyst dosage of 69 mg and pH of 9.6 with an operating time of 75 min, with a coefficient of determination R2 equal to 0.9985. The removal efficiency of BM was close to 97 %. The study shows that the new ICP nanocomposites improve the photocatalytic efficiency compared to pure titania and/or pure Pani. In addition, as the ternary Pani-Se-TiO2 nanocomposite could be obtained from a low-cost synthesis, it is a very promising material for use in wastewater treatment.

Porous reticular Co@Fe metal-organic gel: dual-function simulated peroxidase nanozyme for both colorimetric sensing and antibacterial applications

Constructing metal-organic gels (MOGs) with enzyme-catalyzed activity and studying their catalytic mechanism are crucial for the development of novel nanozyme materials. In this study, a Co@Fe MOG with excellent peroxidase activity was developed by a simple and mild one-pot process. The results showed that the material exhibited almost a single peroxidase activity under optimal pH conditions, which allowed it to attract and oxidize the chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB). Based on the active electron transfer between the metal centers and the organic ligand in the synthetic material, the Co@Fe MOG-H2O2-TMB system was verified to be able to detect H2O2 and citric acid (CA). The catalytic microenvironment formed by the adsorption and the catalytic center accelerated the electron-transfer rate, which expedited the generation of hydroxyl radicals (˙OH, a kind of reactive oxygen species (ROS)) in the presence of H2O2. The persistence and high intensity of ˙OH generation were proven, which would endow Co@Fe MOG with a certain antibacterial ability, promoting the healing of bacteria-infected wounds. In conclusion, this study contributes to the development efforts toward the application systems of nanozymes for marker detection and antibacterial activity.

An Eco-friendly Approach to ZnO NP Synthesis Using Citrus reticulata Blanco Peel/Extract: Characterization and Antibacterial and Photocatalytic Activity

Emission of greenhouse gases and infectious diseases caused by improper agro-waste disposal has gained significant attention in recent years. To overcome these hurdles, agro-waste can be valorized into valuable bioactive compounds that act as reducing or stabilizing agents in the synthesis of nanomaterials. Herein, we report a simple circular approach using Citrus reticulata Blanco (C. reticulata) waste (peel powder/aqueous extract) as green reducing and capping/stabilizing agents and Zn nitrate/acetate precursors to synthesize ZnO nanoparticles (NPs) with efficient antimicrobial and photocatalytic activities. The obtained NPs crystallized in a hexagonal wurtzite structure and differed clearly in their morphology. UV-vis analysis of the nanoparticles showed a characteristic broad absorption band between 330 and 414 nm belonging to ZnO NPs. Fourier transform infrared (FTIR) spectroscopy of ZnO NPs exhibited a Zn-O band close to 450 cm-1. The band gap values were in the range of 2.84-3.14 eV depending on the precursor and agent used. The crystallite size obtained from size-strain plots from measured XRD patterns was between 7 and 26 nm, with strain between 16 and 4%. The highly crystalline nature of obtained ZnO NPs was confirmed by clear ring diffraction patterns and d-spacing values of the observed lattice fringes. ZnNPeelMan_400 and ZnNExtrMan showed good stability, as the zeta potential was found to be around -20 mV, and reduced particle aggregation. Photoluminescence analysis revealed different defects belonging to oxygen vacancies (VO+ and VO+2) and zinc interstitial (Zni) sites. The presence of oxygen vacancies on the surface of ZnAcExtrMan_400 and ZnAcPeelMan_400 increased antimicrobial activity, specifically against Gram-negative bacteria Escherichia coli (E. coli) and Salmonella enteritidis (S. enteritidis). ZnNExtrMan with a minimal inhibitory concentration of 0.156 mg/mL was more effective against Gram-positive bacteria Staphylococcus aureus (S. aureus), revealing a high influence of particle size and shape on antimicrobial activity. In addition, the photocatalytic activity of the ZnO NPs was examined by assessing the degradation of acid green dye in an aqueous solution under UV light irradiation. ZnAcPeelMan_400 exhibited excellent photocatalytic activity (94%) within 90 min after irradiation compared to other obtained ZnO NPs.

Evaluation of antifungal activity of visible light-activated doped TiO2 nanoparticles

Titanium dioxide (TiO2) is a well-known material for its biomedical applications, among which its implementation as a photosensitizer in photodynamic therapy has attracted considerable interest due to its photocatalytic properties, biocompatibility, high chemical stability, and low toxicity. However, the photoactivation of TiO2 requires ultraviolet light, which may lead to cell mutation and consequently cancer. To address these challenges, recent research has focused on the incorporation of metal dopants into the TiO2 lattice to shift the band gap to lower energies by introducing allowed energy states within the band gap, thus ensuring the harnessing of visible light. This study presents the synthesis, characterization, and application of TiO2 nanoparticles (NPs) in their undoped, doped, and co-doped forms for antimicrobial photodynamic therapy (APDT) against Candida albicans. Blue light with a wavelength of 450 nm was used, with doses ranging from 20 to 60 J/cm2 and an NP concentration of 500 µg/ml. It was observed that doping TiO2 with Cu, Fe, Ag ions, and co-doping Cu:Fe into the TiO2 nanostructure enhanced the visible light photoactivity of TiO2 NPs. Experimental studies were done to investigate the effects of different ions doped into the TiO2 crystal lattice on their structural, optical, morphological, and chemical composition for APDT applications. In particular, Ag-doped TiO2 emerged as the best candidate, achieving 90-100% eradication of C. albicans.

Synthesis of Efficient S-Scheme Heterostructures Composed of BiPO4 and KNbO3 for Photocatalytic N2 Fixation and Water Purification

The preparation of catalysts with heterojunction structures is a strategy to achieve efficient charge separation and high photocatalytic activity of photocatalysts. In this work, BiPO4/KNbO3 heterostructure photocatalysts were fabricated by a combination of hydrothermal and precipitation methods and subsequently employed in catalyzing N2-to-NH3 conversion and RhB degradation under light illumination. Morphological analysis revealed the effective dispersion of BiPO4 on KNbO3 nanocubes. Band structure analysis suggests that KNbO3 and BiPO4 exhibit suitable band potentials to form an S-scheme heterojunction. Under the joint action of the built-in electric field at the interface, energy band bending, and Coulomb attraction force, photogenerated electrons and holes with low redox performance are consumed, while those with high redox performance are effectively spatially separated. Consequently, the BiPO4/KNbO3 shows enhanced photocatalytic activity. The NH3 production rate of the optimal sample is 2.6 and 5.8 times higher than that of KNbO3 and BiPO4, respectively. The enhanced photoactivity of BiPO4/KNbO3 is also observed in the photocatalytic degradation of RhB. This study offers valuable insights for the design and preparation of S-scheme heterojunction photocatalysts.

Development of a visible-light-active-NiTiO3 coating for the efficient removal of the persistent herbicide 2,6-dichlorobenzamide (BAM) from drinking water

In the present research work, the photocatalytic evaluation of NiTiO3 nanoparticles immobilized on glass plates by the spin-coating procedure was carried out in the degradation of the recalcitrant herbicide 2,6-dichlorobenzamide (BAM). The concentrations of Ni employed to synthesize NiTiO3 nanoparticles were 1 wt% (1TESNi) and 2 wt% (2TESNi). The stability of coatings was evaluated by several washings and thermal treatments, which were verified by UV-vis analyses. The morphology of the coatings was studied by scanning electron microscopy (SEM-EDS). The coatings displayed thickness values of 1.35 and 2.56 μm for TiO2 and 1TESNi, respectively. The crystalline phases of the coatings were analyzed by X-ray diffraction (XRD), confirming the presence of NiTiO3 and other phases related to TiO2. The bandgap of 1TESNi, compared with the bare TiO2, was reduced from 2.96 to 2.40 eV as a consequence of Ni addition. The TiO2, 1TESNi and 2TESNi coatings were evaluated in the photodegradation of BAM using visible-light for 240 min. The highest effectiveness was displayed by the 1TESNi coating, obtaining degradation of 92.56% after 240 min. Also, the photocatalytic efficiency of the 1TESNi coating was only reduced 1.99% after 3 reuse cycles in the BAM degradation. The scavenger tests revealed that the main oxidizing species involved in the reaction were the •OH- and •O2- radicals. The 1TESNi coating showed the highest photocatalytic efficiency because of its absorption in the visible-light region, valuable surface area and electronic charge separation. Thus, these advantageous features guarantee that NiTiO3 coatings are an efficient method for degrading recalcitrant herbicides from drinking water using a practical way to recover and reuse photocatalysts.

High-breathable, antimicrobial and water-repellent face mask for breath monitoring

Face masks with multiple functionalities and exceptional durability have attracted increasing interests during the COVID-19 pandemic. How to integrate the antibacterial property, comfortability during long-time wearing, and breath monitoring capability together on a face mask is still challenging. Here we developed a kind of face mask that assembles the particles-free water-repellent fabric, antibacterial fabric, and hidden breath monitoring device together, resulting in the highly breathable, water-repellent, and antibacterial face mask with breath monitoring capability. Based on the rational design of the functional layers, the mask shows exceptional repellency to micro-fogs generated during breathing while maintaining high air permeability and inhibiting the passage of bacteria-containing aerogel. More importantly, the multi-functional mask can also monitor the breath condition in a wireless and real-time fashion, and collect the breath information for epidemiological analysis. The resultant mask paves the way to develop multi-functional breath-monitoring masks that can aid the prevention of the secondary transmission of bacteria and viruses while preventing potential discomfort and face skin allergy during long-period wearing.

Application of Photocatalysis and Sonocatalysis for Treatment of Organic Dye Wastewater and the Synergistic Effect of Ultrasound and Light

Organic dyes play vital roles in the textile industry, while the discharge of organic dye wastewater in the production and utilization of dyes has caused significant damage to the aquatic ecosystem. This review aims to summarize the mechanisms of photocatalysis, sonocatalysis, and sonophotocatalysis in the treatment of organic dye wastewater and the recent advances in catalyst development, with a focus on the synergistic effect of ultrasound and light in the catalytic degradation of organic dyes. The performance of TiO₂-based catalysts for organic dye degradation in photocatalytic, sonocatalytic, and sonophotocatalytic systems is compared. With significant synergistic effect of ultrasound and light, sonophotocatalysis generally performs much better than sonocatalysis or photocatalysis alone in pollutant degradation, yet it has a much higher energy requirement. Future research directions are proposed to expand the fundamental knowledge on the sonophotocatalysis process and to enhance its practical application in degrading organic dyes in wastewater.

Techno-economic evaluation of UV light technologies in water remediation

Disinfection commonly follows conventional treatments in wastewater treatment and remediation plants aiming at reducing the presence of pathogens. However, the presence of the so called "micropollutants" has emerged as a serious concern, therefore developing tertiary treatments that are not only able to remove pathogens but also to degrade micropollutants is worth investigating. Nowadays, UV-C photo-degradation processes are widely used for disinfection due to their simplicity and easy operation; additionally, they have shown potential for the removal of contaminants of emerging concern. Conventional mercury lamps are being replaced by light-emitting diodes (LEDs) that avoid the use of toxic mercury and can be switched on and off with no effect on the lamp lifetime. This work aims to comparatively evaluate the performance of several photo-degradation technologies for the removal of two targeted micropollutants, the pharmaceutical dexamethasone (DXMT) and the herbicide S-metolachlor (MTLC), using UV irradiation doses typical of disinfection processes. To this end, the technical performance of UV-A/UV-C photolysis, UV-A/UV-C photocatalysis, UV-C/H₂O₂ and UV-C/NaOCl has been compared. The influence of operating conditions such as the initial concentration of the pollutants (3 mg L^-1 - 30 mg L^-1, concentrations found in membrane or adsorption remediation steps), pH (3-10), and water matrix (WWTP secondary effluent, and ultrapure water) on the degradation efficiency has been studied. The economic evaluation in terms of electricity and chemicals consumption and the carbon footprint has been evaluated. UV-C photolysis and UV-C photocatalysis appear as the most suitable technologies for the degradation of DXMT and MTLC, respectively, in terms of kinetics (1.53·10^-1 min^-1 for DXMT and 1.96·10^-2 min^-1 for MTLC), economic evaluation (1 € m^-3 for DXMT and 32 € m^-3 for MTLC) and environmental indicators (0.5 g-CO₂ for DXMT and 223.1 g-CO₂ for MTLC).

Enhanced degradation of 2,6-dimethylphenol by photocatalytic systems using TiO2 assisted with H2O2 and Fe(III)

In this study, several photocatalytic degradation systems were investigated using 2,6-dimethylphenol (2,6-DMP) as a model compound. Highly reactive species are formed in four systems, Fe(III), TiO₂, TiO₂/H₂O₂ and TiO₂/Fe(III) where complete degradation of 2,6-DMP was achieved under UV radiation. Photodegradation of the 2,6-DMP has been described by pseudo-first order kinetic model in the presence of TiO₂. In UV/TiO₂-H₂O₂ system, the addition of H₂O₂ in the TiO₂ suspension improves the degradation rate of 2,6-DMP from 70% to 100% for a H₂O₂ concentration of 10^-2 M in 3 h. In homogeneous system, HO^• and Fe²⁺ can be generated by the irradiation of Fe(III) solution. The speciation of Fe(III) obtained from Visual MINTEQ soft showed the formation of several species and Fe(OH)²⁺ were the most predominant and active species in a pH range of 2.5-3.5. At a low concentration of TiO₂ (30 mg L^-1), an important positive effect due to the iron addition has been shown in TiO₂/Fe(III) system, the entrance of metallic ions at different concentrations enhanced the photocatalytic activity of TiO₂. A degradation percentage of 90% was achieved in the UV/TiO₂-Fe(III) system under optimal conditions against 57% in UV/TiO₂ system. Strong synergistic effect was observed in the UV/TiO₂-H₂O₂ binary system. On the basis of literature, a pathway for 2,6-DMP degradation was proposed. The mechanism of degradation of the 2,6-DMP did not involve only HO^• radicals, an interaction of Fe(III) in the excited state with 2,6-DMP occurred giving rise to the formation of 2,6-dimethylphenoxyl radical.

Novel polypropylene-TiO2:Bi spherical floater for the efficient photocatalytic degradation of the recalcitrant 2,4,6-TCP herbicide

In this work, spherical photocatalytic floaters were fabricated by depositing TiO₂:Bi (TBi) particles on polypropylene (PP) spheres (recycled from beer cans). These particles were deposited on the sphere (TBi-sphere) by the spray coating technique and evaluated their performance for the photocatalytic degradation of 2,4,6-trichlorophenol (2,4,6-TCP) herbicide. SEM images demonstrated that the BTi powders consisted in conglomerated grains with sizes of 20-80 nm and the analysis by X-ray diffraction confirmed the presence of rutile and anatase phases in the BTi. The photocatalytic experiments showed that the TBi and TBi-sphere produced maximum degradation of 90 and 97% for 2,4,6-TCP, respectively, after 4 h under UV-Vis light. The photocatalytic powders/composites were reused 3 times and the loss of degradation efficiency was 3 and 16% for the TBi powder and TBi-sphere, respectively. This means that the TBi-sphere is more stable for the continuous degradation of the 2,4,6-TCP contaminant. The TiO₂:Bi powder was compared with the commercial TiO₂ (P25) and found that the TiO₂:Bi powder had higher light absorption (≈42%) and higher surface area (≈105%) than the P25. Therefore, the degradation percentage for the 2,4,6-TCP was 52% higher in the sample doped with Bi. Also, scavenger experiments were carried out and found that the main oxidizing agents produced for the degradation of 2,4,6-TCP were •OH^- radicals and •O₂^- anions. Other species such as h⁺ were also produced at lower amount. Hence, our results demonstrated that spherical/floatable photocatalytic composites are a viable option to remove herbicide residuals from the water, which is of interest in water-treatment-plants.

Fabrication of Ni/TiO2 visible light responsive photocatalyst for decomposition of oxytetracycline

Nickel-impregnated TiO₂ photocatalyst (NiTP) responding to visible light was prepared by the liquid phase plasma (LPP) method, and its photoactivity was evaluated in degrading an antibiotic (oxytetracycline, OTC). For preparing the photocatalyst, nickel was uniformly impregnated onto TiO₂ (P-25) powder, and the nickel content increased as the number of LPP reactions increased. In addition, the morphology and lattice of NiTP were observed through various instrumental analyses, and it was confirmed that NiO-type nanoparticles were impregnated in NiTP. Fundamentally, as the amount of impregnated nickel in the TiO₂ powder increased sufficiently, the band gap energy of TiO₂ decreased, and eventually, the NiTP excited by visible light was synthesized. Further, OTC had a decomposition reaction pathway in which active radicals generated in OTC photocatalytic reaction under NiTP were finally mineralized through reactions such as decarboxamidation, hydration, deamination, demethylation, and dehydroxylation. In effect, we succeeded in synthesizing a photocatalyst useable under visible light by performing only the LPP single process and developed a new advanced oxidation process (AOP) that can remove toxic antibiotics.

Shedding light on the performance of magnetically recoverable TiO2/Fe3O4/rGO-5 photocatalyst. Degradation of S-metolachlor as case study

Recalcitrant contaminants are not usually removed in conventional wastewater treatment plants. Therefore, they are transferred to the water resources that receive treated wastewaters and their presence can cause health and environmental issues. Herbicides are among these compounds. In particular, S-metolachlor (MTLC) is specifically of high concern because its molecule incorporates a chlorine atom that contributes to its toxicity. For its removal, a magnetically recoverable photocatalyst, TiO₂/Fe₃O₄/rGO-5, was synthesised following a hydrothermal method. The performance of TiO₂/Fe₃O₄/rGO-5 has been experimentally assessed and compared to TiO₂ and TiO₂/rGO-5 catalysts. A characterisation of the materials properties was carried out including adsorption isotherms of MTLC that provided the maximum adsorption capacity of the materials (q_m), being 140.85 ± 5.14 mg g^-1 for TiO₂/Fe₃O₄/rGO-5. Furthermore, the ternary composite exhibited good recoverability from liquid media after four consecutive cycles thanks to its magnetic character (magnetic saturation of 13.85 emu g^-1). Photocatalytic degradation of MTLC started after a dark adsorption step following first order kinetics (0.0197 ± 1.2 × 10^-4 min^-1 for the degradation of 100 mg L^-1 of MTLC with 0.5 g L^-1 of TiO₂/Fe₃O₄/rGO-5) similar to the rate of appearance of chloride in solution; after total removal of the solubilized MTLC the chloride concentration in the solution continued increasing with zero-th order kinetics up to the value corresponding to the total MTLC concentration. This second step in the chloride formation was attributed to the degradation of adsorbed MTLC. Specific experiments in the presence of scavengers of reactive oxygen species (ROS) were carried out shedding light on the degradation mechanisms. It was concluded the predominant role of free hydroxyl radicals in the photocatalytic degradation in all the investigated materials, whereas the presence of rGO in the composite photocatalysts improved their electronic conductivity, enhancing the activity of superoxide radicals. The results of this work provide important information for further development of photocatalysis.

Visible-Light-Driven Photocatalysts for Self-Cleaning Transparent Surfaces

Highly transparent photocatalytic self-cleaning surfaces capable of harvesting near-visible (365-430 nm) photons were synthesized and characterized. This helps to address a current research gap in self-cleaning surfaces, in which photocatalytic coatings that exhibit activity at wavelengths longer than ultraviolet (UV) generally have poor optical transparency, because of broadband scattering and the attenuation of visible light. In this work, the wavelength-dependent photocatalytic activity of Pt-modified TiO₂ (Pt-TiO₂) particles was characterized, which exhibited activity for wavelengths up to 430 nm. Pt-TiO₂ nanoparticles were embedded in a mesoporous SiO₂ sol-gel matrix, forming a superhydrophilic surface that allowed for water adsorption and formation of reactive oxide species upon illumination, resulting in the removal of organic surface contaminants. These self-cleaning surfaces only interact strongly with near-visible light (∼365-430 nm), as characterized by photocatalytic self-cleaning tests. Broadband visible transparency was preserved by generating a morphology composed of small clusters of Pt-TiO₂ surrounded by a matrix of SiO₂, which limited diffuse visible light scattering and attenuation. The wavelength-dependent self-cleaning rate by the films was quantified using stearic acid degradation under both monochromatic and AM1.5G spectral illumination. By varying the film morphology, the average transmittance relative to bare glass can be tuned from ∼93%-99%, and the self-cleaning rate can be adjusted by more than an order of magnitude. Overall, the ability to utilize photocatalysts with tunable visible light activity, while maintaining broadband transparency, can enable the use of photocatalytic self-cleaning surfaces for applications where UV illumination is limited, such as touchscreen displays.

An eco-friendly and sustainable support of agave-fibers functionalized with graphene/TiO2:SnO2 for the photocatalytic degradation of the 2,4-D herbicide from the drinking water

In this research, we evaluated the photocatalytic performance of biodegradable composites for the removal of the 2,4-Dichlorophenoxyacetic acid (2,4-D) herbicide. The composite was composed by agave fibers (AgF), graphene-microplates (GM) and titanium dioxide TiO₂/SnO₂ (TSn) nanoparticles (NPs) and was named TSn + AgF/GM. Both, the TSn NPs and the GM were deposited on the AgF using the Dip-coating method. According to the analysis by X-Ray Diffraction (XRD), the crystalline phase for the TiO₂ and SnO₂ was anatase and tetragonal-rutile, respectively. The Scanning Electron Microscopy (SEM) images demonstrated that the AgF were completely saturated by the GM (which had average dimensions of 15 μm × 22 μm) and by conglomerations of TSn NPs with average size of 642 nm. The TSn NPs and the TSn + AgF/GM composite were evaluated for the photocatalytic degradation of the 2,4-D herbicide under ultraviolet-visible (UV-Vis) light and found a maximum degradation of 98.4 and 93.7% (after 4 h) for the TSn NPs and the TSn + AgF/GM composite, respectively. Reuse cycles were also performed and the degradation percentage decreased by 13.1% and by 7.8% (after 3 cycles of reuse) when the TSn NPs and the TSn + AgF/GM composite are employed, respectively. Scavenger experiments were also carried out and found that the oxidizing agents are mainly produced in the order of: •OH>•O₂^- > h⁺; then, the main oxidizing agents generated during the photocatalytic reaction were the hydroxyl radicals. Thus, the photocatalytic system studied in this work for the degradation of 2,4-D could pave the way for the development of new eco-friendly/floatable photocatalysts, which can be applied in wastewater-treatment plants.

Highly Selective Photocatalytic Aerobic Oxidation of Methane to Oxygenates with Water over W-doped TiO2

Highly selective conversion of methane to oxygenates with O₂ as a green oxidant remains a great challenge. It is still difficult to suppress the generation of CO_x (x=1, 2) as undesired by-products due to unavoidable overoxidation reaction. Hence, tungsten-doped (W-doped) TiO₂ photocatalysts were designed with a tunable band structure for photocatalytic oxidation of methane to C₁ oxygenates using O₂ at low temperature (30 °C). The W-doping effectively modified the electronic and band structure of pristine TiO₂ to enhance photocatalytic performance. Liquid oxygenates productivity could reach as high as 12.2 mmol g^-1 with high selectivity of 99.4 %. Moreover, CO_x selectivity was effectively decreased from 21.2 % over TiO₂ to 0.6 % for W-doped catalyst. Detailed characterizations further disclosed that W-doping not only enhanced light absorption, but also promoted the separation of photo-generated carriers to improve methane conversion. This work provides new insights into the design of highly efficient photocatalysts for methane oxidation.

High-Efficacy Hierarchical Dy2O3/TiO2 Nanoflower toward Wastewater Reclamation: A Combined Photoelectrochemical and Photocatalytic Strategy

Developing a sustainable photocatalyst is crucial to mitigate the foreseeable energy shortage and environmental pollution caused by the rapid advancement of global industry. We developed Dy₂O₃/TiO₂ nanoflower (TNF) with a hierarchical nanoflower structure and a near-ideal anatase crystallite morphology to degrade aqueous rhodamine B solution under simulated solar light irradiation. The prepared photocatalyst was well-characterized using powder X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, energy-dispersive spectroscopy, scanning electron microscopy, Brunauer-Emmett-Teller, diffuse reflectance UV-vis spectra, and X-ray photoelectron spectroscopy. Further analysis was performed to highlight the photoelectrochemical activity of the prepared photocatalysts such as electrochemical impedance spectroscopy, linear sweep voltammetry, photocurrent response, and a Mott-Schottky study. The crystalline Dy₂O₃/TNF exhibits superb photocatalytic activity attributed to the improved charge transfer, reduced recombination rate of the electron-hole pairs, and a remarkable red-shift in light absorption.

Chemically-Engineered Porous Molecular Coatings as Reactive Oxygen Species Generators and Reservoirs for Long-Lasting Self-Cleaning Textiles

Wearable personal protective equipment that is decorated with photoactive self-cleaning materials capable of actively neutralizing biological pathogens is in high demand. Here, we developed a series of solution-processable, crystalline porous materials capable of addressing this challenge. Textiles coated with these materials exhibit a broad range of functionalities, including spontaneous ROS generation upon absorption of daylight, and long-term ROS storage in dark conditions. The ROS generation and storage abilities of these materials can be further improved through chemical engineering of the precursors without altering the three-dimensional assembled superstructures. In comparison with traditional TiO 2 or C 3 N 4 self-cleaning materials, the fluorinated molecular coating material HOF-101-F shows a 10- to 60-fold enhancement of ROS generation and 10- to 20- fold greater ROS storage ability. Our results pave the way for further developing self-cleaning textile coatings for the rapid deactivation of highly infectious pathogenic bacteria under both daylight and light-free conditions.

TiO2–Zeolite Metal Composites for Photocatalytic Degradation of Organic Pollutants in Water

Immobilization of photocatalysts in porous materials is an approach to significantly minimize the hazards of manipulation and recovery of nanoparticles. Inorganic materials, such as zeolites, are proposed as promising materials for photocatalyst immobilization mainly due to their photochemical stability. In this work, a green synthesis method is proposed to combine TiO2-based photocatalysts with commercial ZY zeolite. Moreover, a preliminary analysis of their performance as photocatalysts for the abatement of organic pollutants in waters was performed. Our results show that the physical mixture of TiO2 and zeolite maintains photocatalytic activity. Meanwhile, composites fabricated by doping TiO2–zeolite Y materials with silver and palladium nanoparticles do not contribute to improving the photocatalytic activity beyond that of TiO2.

Crucial roles of 3D-MoO2-PBC cocatalytic electrodes in the enhanced degradation of imidacloprid in heterogeneous electro-Fenton system: Degradation mechanisms and toxicity attenuation

Imidacloprid (IMI), as the most-consumed pesticide, has posed a severe threat to the water ecosystem due to its recalcitrance and inefficient elimination in the traditional wastewater treatment. Herein, a heterogeneous electro-Fenton (EF) system coupled with 3D-MoO₂-porous biochar (PBC) cocatalytic electrodes, abbreviated as 3D-MPE-EF, is initially applied to promote the elimination of IMI in the agrochemical wastewater from pesticide production. The elimination rate of IMI by 3D-MPE-EF system is 18.15 times higher than that by traditional EF system at pH 7.0. The utilization of 3D-MoO₂-PBC electrodes sufficiently compensates for inherent deficiencies of traditional EF system. The circular utilization of Fe is also addressed by 3D-MoO₂-PBC cocatalytic electrodes to reduce the consumption of Fe²⁺ and the deposition of iron mud. Through comparison, MoO₂ is considered the most appropriate cocatalyst in terms of the reutilization of Fe and degradation of IMI. Eight mechanisms are identified in the degradation pathways of IMI by UPLC-Q-TOF-MS. The ecotoxicities of IMI are remarkably attenuated in the 3D-MPE-EF system. This study provides insights into the roles of 3D-MoO₂-PBC cocatalytic electrodes in the enhanced elimination of IMI in heterogeneous EF system.

Functionalized Masks: Powerful Materials against COVID-19 and Future Pandemics

The outbreak of COVID-19 revealed the vulnerability of commercially available face masks. Without having antibacterial/antiviral activities, the current masks act only as filtering materials of the aerosols containing microorganisms. Meanwhile, in surgical masks, the viral and bacterial filtration highly depends on the electrostatic charges of masks. These electrostatic charges disappear after 8 h, which leads to a significant decline in filtration efficiency. Therefore, to enhance the masks' protection performance, fabrication of innovative masks with more advanced functions is in urgent demand. This review summarizes the various functionalizing agents which can endow four important functions in the masks including i) boosting the antimicrobial and self-disinfectant characteristics via incorporating metal nanoparticles or photosensitizers, ii) increasing the self-cleaning by inserting superhydrophobic materials such as graphenes and alkyl silanes, iii) creating photo/electrothermal properties by forming graphene and metal thin films within the masks, and iv) incorporating triboelectric nanogenerators among the friction layers of masks to stabilize the electrostatic charges and facilitating the recharging of masks. The strategies for creating these properties toward the functionalized masks are discussed in detail. The effectiveness and limitation of each method in generating the desired properties are well-explained along with addressing the prospects for the future development of masks.

A Review on Metal Ions Modified TiO2 for Photocatalytic Degradation of Organic Pollutants

TiO2 is a semiconductor material with high chemical stability and low toxicity. It is widely used in the fields of catalysis, sensing, hydrogen production, optics and optoelectronics. However, TiO2 photocatalyst is sensitive to ultraviolet (UV) light; this is why its photocatalytic activity and quantum efficiency are reduced. To enhance the photocatalytic efficiency in the visible light range as well as to increase the number of the active sites on the crystal surface or inhibit the recombination rate of photogenerated electron–hole pairs electrons, various metal ions were used to modify TiO2. This review paper comprehensively summarizes the latest progress on the modification of TiO2 photocatalyst by a variety of metal ions. Lastly, the future prospects of the modification of TiO2 as a photocatalyst are proposed.

Degradation of primary nanoplastics by photocatalysis using different anodized TiO2 structures

In recent years, plastic pollution has become an environmental problem requiring urgent attention. Recently, the release of nano-sized plastics (<1 µm) into the environment has raised concern due to the possible adverse effects that their small size can have on the trophic web. Advanced oxidation processes are efficient at removing organic pollutants such as dyes and pharmaceuticals, making them a viable approach for treating these hazardous materials. This study proposes the use of photocatalysis as an alternative for removing polystyrene nanoparticles (PS-NPs) from aqueous media. A comparative study was carried out to determine the photocatalytic activity of three different TiO₂ photocatalysts synthesized by anodization. Elimination and degradation were monitored by turbidimetry, TOC, FTIR, and GC/MS, and the presence of carbonyl groups and intermediate products was recorded to confirm PS-NP degradation. Statistical analysis revealed that PS-NP elimination using TiO₂/T and TiO₂/M as photocatalysts was more efficient than with photolysis. The results indicate that the mixed structure (nanotubes/nanograss) reduces the concentration of PS-NPs in dispersion 2 times more efficiently than photolysis with UV light does. Despite the challenges posed by nanoplastic contamination, this study provides a useful remediation approach; a technique that, to date, has received little attention.

A novel route for catalytic activation of peroxymonosulfate by oxygen vacancies improved bismuth-doped titania for the removal of recalcitrant organic contaminant

In this work, bismuth-doped titania (Bi_xTiO₂) with improved oxygen vacancies was synthesized by sol-gel protocol as a novel peroxymonosulfate (PMS, HSO₅^-) activator. HSO₅^- and adsorbed oxygen molecules could efficiently be transformed into their respective radicals through defect ionization to attain charge balance after their trapping on oxygen vacancies of the catalyst. XRD study of Bi_xTiO₂ with 5 wt% Bi (5BiT) revealed anatase, crystalline nature, and successful doping of Bi into TiO₂ crystal lattice. The particle size obtained from BET data and SEM observations was in good agreement. PL spectra showed the formation rates of ^•OH by 3BiT, 7BiT, 5BiTC, and 5BiT as 0.720, 1.200, 1.489, and 2.153 μmol/h, respectively. 5BiT catalyst with high surface area (216.87 m² g^-1) and high porosity (29.81%) was observed the excellent HSO₅^- activator. The catalytic performance of 0BiT, 3BiT, 5BiT, and 7BiT when coupled with 2 mM HSO₅^- for recalcitrant flumequine (FLU) removal under dark was 10, 27, 55, and 37%, respectively. Only 5.4% decrease in catalytic efficiency was observed at the end of seventh cyclic run. Radical scavenging studies indicate that SO₄^•- is the dominant species that caused 62.0% degradation. Moreover, strong interaction between Bi and TiO₂ through Bi-O-Ti bonds prevents Bi leaching (0.081 mg L^-1) as shown by AAS. The kinetics, degradation pathways, ecotoxicity, and catalytic mechanism for recalcitrant FLU were also elucidated. Cost-efficient, environment-friendly, and high mineralization recommends this design strategy; Bi_xTiO₂/HSO₅^- system is a promising advanced oxidation process for the aquatic environment remediation.

Effect of Background Water Matrices on Pharmaceutical and Personal Care Product Removal by UV-LED/TiO2

In this study, we evaluated the effectiveness of UV-LED-irradiated TiO2 in removing 24 commonly detected PPCPs in two water matrices (municipal wastewater effluent and Suwannee River NOM–synthetic water) and compared their performance with that of ultrapure water. Relatively fast removal kinetics were observed for 29% and 12% of the PPCPs in ultrapure water and synthetic surface water, respectively (kapp of 1–2 min−1). However, they all remained recalcitrant to photocatalysis when using wastewater effluent as the background matrix (kapp < 0.1 min−1). We also observed that the pH-corrected octanol/water partition coefficient (log Dow) correlated well with PPCP degradation rate constants in ultrapure water, whereas molecular weight was strongly associated with the rate constants in both synthetic surface water and wastewater. The electrical energy per order (EEO) values calculated at the end of the experiments suggest that UV-LED/P25 can be an energy-efficient method for water treatment applications (2.96, 4.77, and 16.36 kW h m−3 in ultrapure water, synthetic surface water, and wastewater effluents, respectively). Although TiO2 photocatalysis is a promising approach in removing PPCPs, our results indicate that additional challenges need to be overcome for PPCPs in more complex water matrices, including an assessment of photocatalytic removal under different background water matrices.

Photocatalytic Activity of Cellulose Acetate Nanoceria/Pt Hybrid Mats Driven by Visible Light Irradiation

A photocatalytic system for the degradation of aqueous organic pollutants under visible light irradiation is obtained by an innovative approach based on ceria/platinum (Pt) hybrid nanoclusters on cellulose acetate fibrous membranes. The catalytic materials are fabricated by supersonic beam deposition of Pt nanoclusters directly on the surface of electrospun cellulose acetate fibrous mats, pre-loaded with a cerium salt precursor that is transformed into ceria nanoparticles directly in the solid mats by a simple thermal treatment. The presence of Pt enhances the oxygen vacancies on the surface of the formed ceria nanoparticles and reduces their band gap, resulting in a significant improvement of the photocatalytic performance of the composite mats under visible light irradiation. Upon the appropriate pretreatment and visible light irradiation, we prove that the most efficient mats, with both ceria nanoparticles and Pt nanoclusters, present a degradation efficiency of methylene blue of 70% and a photodegradation rate improved by about five times compared to the ceria loaded samples, without Pt. The present results bring a significant improvement of the photocatalytic performance of polymeric nanocomposite fibrous systems under visible light irradiation, for efficient wastewater treatment applications.

Improved photoelectrochemical properties of TiO2 nanotubes doped with Er and effects on hydrogen production from water splitting

Erbium-doped TiO₂ nanotubes (Er-TiO₂ NTs) are prepared with a combination of anodization and electrochemical deposition using various proportions of erbium and adjusting the time of the process. The surface characterization techniques and electrochemical analysis are applied to study the physicochemical and photoelectrochemical (PEC) properties of the as-prepared photocatalysts. Er-TiO₂ NTs have crystal sizes of about 24-30 nm, smaller than those of pure TiO₂ NTs, and contain only the anatase phase. Er-TiO₂ NTs exhibit an effective photo-conversion efficiency (PCE) of 1.58% and a photosensitivity of 115.06. The modified sample are also more efficient (photocurrent density of 6.64 mAcm^-2 at a bias potential of 1.5 V vs. Hg/HgO) compare to pure TiO₂ NTs. The photocatalytic activity of the Er-TiO₂ NTs are evaluated in a hydrogen generation reaction, and the results show hydrogen production of ∼17.39 μmolhr^-1cm^-2. Further experiments demonstrate that Er-TiO₂ NTs successfully degrade methylene blue, with the most active sample reaching 85% photocatalysis after 180 min. This study shows that doping conditions significantly affect the optical and electrical properties of the resulting material, and that the current electrochemical approach to metal doping can be used for efficient and stable PEC water splitting.

Critical review of photocatalytic disinfection of bacteria: from noble metals- and carbon nanomaterials-TiO2 composites to challenges of water characteristics and strategic solutions

This critical review covers ways to improve TiO₂-based photocatalysts, how water characteristics may affect photocatalytic disinfection, and strategies to tackle the challenges arising from water characteristics. Photocatalysis has shown much promise in the disinfection of water/wastewater, because photocatalysis does not produce toxic by-products, and is driven by green solar energy. There are however several drawbacks that are curbing the prevalence of photocatalytic disinfection applications: one, the efficiency of photocatalysts may limit popular utilization; two, the water characteristics may present some challenges to the process. TiO₂-based photocatalysts may be readily improved if composited with noble metals or carbon nanomaterials. Noble metals give TiO₂-based composites a higher affinity for dissolved oxygen, and induce plasmonic and Schottky effects in the TiO₂; carbon nanomaterials with a tunable structure, on the other hand, give the composites an improved charge carrier separation performance. Other than photocatalyst materials, the characteristics of water/wastewater is another crucial factor in the photocatalysis process. Also examined in this review are the crucial impacts that water characteristics have on photocatalysts and their interaction with bacteria. Accordingly, strategies to address the challenge of water characteristics on photocatalytic disinfection are explored: one, to modify the semiconductor conduction band to generate long-lifetime reactive species; two, to improve the interaction between bacteria and photocatalysts.

TiO2 modified orthocortical and paracortical cells having enhanced photocatalytic degradation and photoreduction properties

In this study, cortical cells resultant from wool fibers were loaded with TiO₂ nanoparticles in a hydrothermal process and were then engineered as organic-nonorganic hybrid composite photocatalysts for both photodegradation of organic dyes and photoreduction of heavy metal ions. The microstructure and photocatalytic properties of TiO₂ modified cortical cells (i.e. both orthocortical and paracortical cells) were systematically characterized using a series of analytical techniques including FESEM, TEM, element analysis, Mott-Schottky curve, BET specific surface area, Zeta potentials, as well as XRD, FTIR, XPS, DRS, PL, UPS, EDS and ESR spectra. Their photocatalytic performance and trapping experiments of the TiO₂ modified cortical cells were measured in the photodegradation of methylene blue (MB) dye and Congo Red (CR) dye as well as the photoreduction of Cr(VI) ions under visible light irradiation. It was found that anatase TiO₂ nanoparticles were chemically grafted on the surface of the two cortical cells via O-Ti⁴⁺/O-Ti³⁺ bonds, and that TiO₂ nanoparticles were formed inside the orthocortical cells in the hydrothermal process. The TiO₂ modified orthocortical and paracortical cells possessed much higher photocatalytic efficiency than the commercially available TiO₂ nanoparticle powder, Degussa P25, in the photodegradation of cationic MB dye and photoreduction of Cr(VI) ions, while their photocatalytic efficiency in the photodegradation of anionic CR dye is smaller because of their greater negative Zeta potentials and photogenerated holes as the main reactive radical species. In comparison with the TiO₂ modified paracortical cells, the higher photocatalytic efficiency of the TiO₂ modified orthocortical cells was demonstrated in the photodegradation of MB dye solution and this might be due to both the S-doped TiO₂ nanoparticles infiltrated into the naturally hydrophilic orthocortical cells and the primary reactive radical species of photogenerated holes being trapped in the cells.

TiO2 Doped with Noble Metals as an Efficient Solution for the Photodegradation of Hazardous Organic Water Pollutants at Ambient Conditions

This work highlights new insights into the performance of TiO2 doped with noble metal catalysts for the photocatalytic degradation of organic water pollutants. Different samples of titanium dioxide doped with noble metals (Au and Pd) were successfully synthesized via incipient wet impregnation (IWI) and ultrasound-assisted impregnation (US) methods. X-ray diffraction, scanning electron microscopy and UV-Vis reflectance spectroscopy were used for the characterization of the obtained materials. Their photocatalytic efficiency was investigated in aqueous suspension thorough a series of laboratory tests performed under ultraviolet (UV-A) irradiation conditions using 2,4 dinitrophenol (2,4 DNP) as a target molecule. The results clearly show that the method used for the catalyst synthesis affects its photocatalytic activity. It was found that the samples prepared by the IWI method exhibited high photocatalytic activity, and the removal rate obtained with TiO2-Pd/IWI was higher than that found for TiO2-Au/IWI. Furthermore, for the best catalyst, some extra photocatalytic experiments were conducted with rhodamine 6G (R6G), a highly stable molecule with a very different chemical structure to 2,4 DNP, in order to check the reactivity of this material. Moreover, the recycling experiments carried out with TiO2-Pd/IWI clearly demonstrated the high photocatalytic stability of this material for the degradation of 2,4 DNP. All of the collected data confirmed the interesting photocatalytic potential of the selected catalyst in the elimination of organic pollutants with no obvious change in its reactivity after four reaction cycles, which is very promising for promoting future applications in water depollution.

Photocatalytic Transformation of Triclosan. Reaction Products and Kinetics

5-Chloro-2-[2,4-dichlorophenoxy]-phenol, or triclosan (TCS), is an antimicrobial and antifungal agent with high resistance to conventional wastewater treatments, thus, more effective remediation technologies are necessary, where photocatalytic processes deserve special attention due to the high degradation rates of TCS, and the use of a renewable source of energy. However, different by-products may be formed during the treatment, sometimes more harmful than the parent compounds. Efforts to detail reaction pathways continually feed into related literature; however, knowing the transformation kinetics and the dependence on the operating variables is essential for the correct design of the abovementioned remediation technologies. This work contributes to increasing the knowledge necessary for the application of photocatalytic processes for the degradation of emerging pollutants, with TCS as a case study. First, an experimental plan to analyze the influence of the operating variables was carried out, determining time courses of the parent and intermediate compounds. Next, the kinetic model and parameters that are capable of predicting TCS concentration and its derivatives as a function of the operating conditions are provided. This constitutes a very useful tool to predict the performance of wastewater remediation treatment both in the degradation of the original pollutant and in the reduction of the toxicity in the treated water.

Photocatalytic degradation of sulfamethoxazole using TiO2 in simulated seawater: Evidence for direct formation of reactive halogen species and halogenated by-products

Nowadays photoactivation mechanism of titanium dioxide nanoparticles (TiO₂ NPs) and reactive species involved in saline waters is not sufficiently established. In this study, TiO₂ photocatalytic process under simulated solar irradiation was evaluated in synthetic seawater and compared with deionized water, using sulfamethoxazole (SMX) as model organic compound. For a TiO₂ concentration of 100 mg L^-1, SMX degradation resulted two times slower in seawater than in deionized water by the determination of their pseudo-first order rate constants of 0.020 min^-1 and 0.041 min^-1, respectively. Selected scavenging experiments revealed no significant contribution of hydroxyl radicals (OH) on the degradation process in seawater, while these radicals contributed to circa 60% on the SMX depletion in deionized water. Instead, the involvement of reactive halogen species (RHS) as main contributors for the SMX degradation in seawater could be established. A mechanism for the RHS generation was proposed, whose initiation reactions involve halides with the TiO₂ photogenerated holes, yielding chlorine and bromine radicals (Cl and Br) that may later generate other RHS. Production of RHS was further confirmed by the identification of SMX transformation products (TPs) and their evolution over time, carried out by liquid chromatography-mass spectrometry (LC-MS). SMX transformation was conducted through halogenation, dimerization and oxidation pathways, involving mainly RHS. Most of the detected transformation products accumulated over time (up to 360 min of irradiation). These findings bring concerns about the viability of photocatalytic water treatments using TiO₂ NPs in saline waters, as RHS could be yielded resulting in the generation and accumulation of halogenated organic byproducts.