Highly effective Fe-doped TiO 2 nanoparticles photocatalysts for visible-light driven photocatalytic degradation of toxic organic compounds

Enhanced visible-light photocatalytic oxidative desulfurization of model fuel over Pt-decorated carbon-doped TiO2 nanoparticles

Modification of photocatalysts to improve their adsorption and photocatalytic activity in the oxidative desulfurization of liquid fuels has been reported by many investigators. In this study, Pt-decorated carbon-doped TiO2 nanoparticles were synthesized by hydrothermal and photo-deposition techniques and were subsequently used in photocatalytic oxidative desulfurization of dibenzothiophene (DBT) in n-heptane as a simulated liquid fuel with methanol as the extracting solvent. Carbon-doped TiO2 was first synthesized by a simple self-doping method. Pt was then loaded by a photo-deposition technique. The synthesized photocatalysts (labeled as YPt-CT where Y is percent Pt loading) were characterized by of X-ray diffraction (XRD), photoluminescence (PL), field emission scanning electron microscopy (FESEM), N2-physisorption, UV-Vis diffusive reflectance spectra (UV-Vis DRS), transmission electron microscopy (TEM), Fourier transform infrared spectra (FTIR), and nitrogen sorption measurements. The removal efficiency of DBT was 98% in the presence of 2 g/l of 0.5Pt-CT catalyst under visible-light irradiation (λ > 400 nm), ambient pressure, and reaction temperature of 40°C.

A critical review on the recent trends of photocatalytic, antibacterial, antioxidant and nanohybrid applications of anatase and rutile TiO2 nanoparticles

Titanium dioxide nanoparticles (TiO2 NPs) have become a focal point of research due to their widespread daily use and diverse synthesis methods, including physical, chemical, and environmentally sustainable approaches. These nanoparticles possess unique attributes such as size, shape, and surface functionality, making them particularly intriguing for applications in the biomedical field. The continuous exploration of TiO2 NPs is driven by the quest to enhance their multifunctionality, aiming to create next-generation products with superior performance. Recent research efforts have specifically focused on understanding the anatase and rutile phases of TiO2 NPs and evaluating their potential in various domains, including photocatalytic processes, antibacterial properties, antioxidant effects, and nanohybrid applications. The hypothesis guiding this research is that by exploring different synthesis methods, particularly chemical and environmentally friendly approaches, and incorporating doping and co-doping techniques, the properties of TiO2 NPs can be significantly improved for diverse applications. The study employs a comprehensive approach, investigating the effects of nanoparticle size, shape, dose, and exposure time on performance. The synthesis methods considered encompass both conventional chemical processes and environmentally friendly alternatives, with a focus on how doping and co-doping can enhance the properties of TiO2 NPs. The research unveils valuable insights into the distinct phases of TiO2 NPs and their potential across various applications. It sheds light on the improved properties achieved through doping and co-doping, showcasing advancements in photocatalytic processes, antibacterial efficacy, antioxidant capabilities, and nanohybrid applications. The study concludes by emphasizing regulatory aspects and offering suggestions for product enhancement. It provides recommendations for the reliable application of TiO2 NPs, addressing a comprehensive spectrum of critical aspects in TiO2 NP research and application. Overall, this research contributes to the evolving landscape of TiO2 NP utilization, offering valuable insights for the development of innovative and high-performance products.

Titanium Dioxide Nanoparticles Doped with Iron for Water Treatment via Photocatalysis: A Review

Iron-doped titanium dioxide nanoparticles are widely employed for photocatalytic applications under visible light due to their promising performance. Nevertheless, the manufacturing process, the role of Fe3+ ions within the crystal lattice of titanium dioxide, and their impact on operational parameters are still a subject of controversy. Based on these assumptions, the primary objective of this review is to delineate the role of iron, ascertain the optimal quantity, and elucidate its influence on the main photocatalysis parameters, including nanoparticle size, band gap, surface area, anatase-rutile transition, and point of zero charge. Moreover, an optimized synthesis method based on comprehensive data and insights from the existing literature is proposed, focusing exclusively on iron-doped titanium oxide while excluding other dopant variants.

Efficient removal of Hg0 from cement kiln flue gas using CexFeyOz composite catalyst

In this study, a kind of CexFeyOz composite with oxygen vacancy structure and strong oxygen storage capacity was prepared by coprecipitation method. Under the condition of no HCl of flue gas, the Hg0 in the flue gas of cement kiln was efficiently and economically removed by using 6-8% oxygen. The results showed that the optimum preparation conditions of the catalyst were Ce-Fe molar ratio of 1-11 and calcination temperature of 550 °C. In addition, the reaction temperature, space velocity, the concentration of O2, SO2, and NO had significant effects on the removal efficiency of Hg0 at different rates. More precisely, at the reaction temperature of 350 °C, low airspeed, high concentration of O2, and low concentration of SO2 and NO, the efficiency reached the highest value. According to XPS results, the elemental valence of the CexFeyOz composite changed after the reaction. The redox pairs of Ce3+-Ce4+ and Fe3+-Fe2+ had the ability to transfer electrons, which enabled more oxygen adsorbed on the catalyst surface to be converted into O2-, leading to the improvement of the oxidation efficiency of Hg0.

Experimental and computational study of metal oxide nanoparticles for the photocatalytic degradation of organic pollutants: a review

Photocatalysis is a more proficient technique that involves the breakdown or decomposition of different organic contaminants, various dyes, and harmful viruses and fungi using UV or visible light solar spectrum. Metal oxides are considered promising candidate photocatalysts owing to their low cost, efficiency, simple fabricating method, sufficient availability, and environment-friendliness for photocatalytic applications. Among metal oxides, TiO2 is the most studied photocatalyst and is highly applied in wastewater treatment and hydrogen production. However, TiO2 is relatively active only under ultraviolet light due to its wide bandgap, which limits its applicability because the production of ultraviolet is expensive. At present, the discovery of a photocatalyst of suitable bandgap with visible light or modification of the existing photocatalyst is becoming very attractive for photocatalysis technology. However, the major drawbacks of photocatalysts are the high recombination rate of photogenerated electron-hole pairs, the ultraviolet light activity limitations, and low surface coverage. In this review, the most commonly used synthesis method for metal oxide nanoparticles, photocatalytic applications of metal oxides, and applications and toxicity of different dyes are comprehensively highlighted. In addition, the challenges in the photocatalytic applications of metal oxides, strategies to suppress these challenges, and metal oxide studied by density functional theory for photocatalytic applications are described in detail.

Enhancing Photocatalytic Efficiency of Spent Tea Leaf Powder on ZnIn2S4 Incorporation: Role of Surface Charge on Dye Degradation

Photocatalytic degradation of dye contaminants using nanocomposite adsorbents has emerged as a promising solution for wastewater treatment. Owing to its abundant availability, eco-friendly composition, biocompatibility, and strong adsorption activity, spent tea leaf (STL) powder has been extensively explored as a viable dye-adsorbent material. In this work, we report spectacular enhancement in the dye-degradation properties of STL powder on incorporation of ZnIn₂S₄ (ZIS). The STL/ZIS composite was synthesized using a novel, benign, and scalable aqueous chemical solution method. Comparative degradation and reaction kinetics studies were performed onto an anionic dye, Congo red (CR), and two cationic dyes, Methylene blue (MB) and Crystal violet (CV). The degradation efficiencies of CR, MB, and CV dyes were obtained to be 77.18, 91.29, and 85.36%, respectively, using the STL/ZIS (30%) composite sample after the 120 min experiment. The spectacular improvement in the degradation efficiency of the composite was attributed to its slower charge transfer resistance (as concluded by the EIS study) and optimized surface charge (as concluded by ζ potential study). Scavenger tests and reusability tests deciphered the active species (^•O₂^-) and reusability of the composite samples, respectively. To the best of our knowledge, this is the first report to demonstrate improvement in the degradation efficiency of STL powder on ZIS incorporation.

Sonochemical synthesis of Ce-TiO2 nanocatalyst and subsequent application for treatment of real textile industry effluent

Treatment of real textile industry effluent using photocatalysis, sonocatalysis, sonophotocatalysis and H₂O₂ assisted sonophotocatalysis have been studied based on the use of Ce-TiO₂ nanocatalyst synthesized using sonochemical co-precipitation method. Characterization studies of the obtained catalyst revealed crystallite size as 1.44 nm with particles having spherical morphology. A shift of the absorption edge to the visible light range was also observed in UV-Vis diffuse reflectance spectra (UV-DRS) analysis. The effects of different operational parameters viz catalyst dose (0.5 g/L-2 g/L), temperature (30 °C-55 °C) and pH (3-12) on the COD reduction were studied. The reduction in the COD was higher at lower pH and the optimum temperature established was 45 °C. It was also elucidated that the required catalyst dose was lesser in combined sonophotocatalysis when compared with individual photocatalysis and sonocatalysis. Combination of processes and addition of oxidants increased the COD reduction with the sonophotocatalytic oxidation combined with H₂O₂ treatment showing the best results for COD reduction (84.75%). The highest reduction in COD for photocatalysis was only 45.09% and for sonocatalysis, it was marginally higher at 58.62%. The highest reduction in COD achieved by sonophotocatalysis was 64.41%. Toxicity tests coupled with Liquid Chromatography Mass Spectrometry (LC-MS) analysis revealed that there were no additional toxic intermediates added to the system during the treatment. Kinetic study allowed establishing that generalized kinetic model fits the experimental results well. Overall, the combined advanced oxidation processes showed better results than the individual processes with higher COD reduction and lower requirement of the catalyst.

Undoped and Fe-Doped Anatase/Brookite TiO2 Mixed Phases, Obtained by a Simple Template-Free Synthesis Method: Physico-Chemical Characterization and Photocatalytic Activity towards Simazine Degradation

For the first time, Fe-doping (0.05, 1.0, and 2.5 wt.% Fe) was performed on a high-surface-area anatase/brookite TiO2 by adopting a simple template-free sol-gel synthesis followed by calcination at a mild temperature. The powders’ textural and surface properties were characterized by following a multi-technique approach. XRD analysis showed that the anatase/brookite ratio slightly varied in the Fe-doped TiO2 (from 76.9/23.1 to 79.3/22.7); Fe doping noticeably affected the cell volume of the brookite phase, which decreased, likely due to Fe3+ ions occupying interstitial positions, and retarded the crystallite growth. N2 sorption at −196 °C showed the occurrence of samples with disordered interparticle mesopores, with an increase in the specific surface area from 236 m2 g−1 (undoped TiO2) to 263 m2 g−1 (2.5 wt.% Fe). Diffuse Reflectance UV-Vis spectroscopy showed a progressive decrease in the bandgap energy from 3.10 eV (undoped TiO2) to 2.85 eV (2.5 wt.% Fe). XPS analysis showed the presence of some surface Fe species only at 2.5 wt.% Fe, and accordingly, the ζ-potential measurements showed small changes in the pH at the isoelectric point. The photocatalytic degradation of simazine (a persistent water contaminant) both under UV and simulated solar light was performed as a probe reaction. Under UV light, Fe-doping improved simazine degradation in the sample at 0.05 wt.% Fe, capable of degrading ca. 77% simazine. Interestingly, the undoped TiO2 was also active both under UV and 1 SUN. This is likely due to the occurrence of anatase/brookite heterojunctions, which help stabilize the photogenerated electrons/holes.

Highly effective Fe-doped TiO2nanoparticles for removal of toxic organic dyes under visible light illumination

This article addresses the synthesis of Fe³⁺doped TiO₂nanoparticles with variations of molar concentrations of Fe³⁺and their adequate use as potential photocatalysts for Photocatalysis applications. Synthesized photocatalysts were characterized thoroughly by different analytical techniques in terms of morphological, chemical, structural, crystalline, optical, electronic structure, surface area etc properties. The occurrence of red shift phenomenon of the energy band gap attributes to the transfer of charges and transition between the d electrons of dopant and conduction band (CB) or valence band (VB) of TiO₂. The doping of Fe³⁺ions generates more trap sites for charge carriers with the surface trap sites. Thorough experimental conclusions revealed that the Fe³⁺ions necessarily regulate the catalytic property of TiO₂nanomaterial. The obtained total degradation efficiency rate of Methylene Blue (MB) was 93.3% in the presence of 0.1 M Fe³⁺in the host material and for Malachite Green Oxalate the efficiency was 100% in the presence of 0.05 M and 0.1 M Fe³⁺in the host material. In both the cases the total visible light irradiation time was 90 min. The adsorption properties of the photocatalysts have been also performed in a dark for 90 min in the presence of MB dye. However, till now there are hardly reported photocatalysts which shows complete degradation of these toxic organic dyes by visible light driven photocatalysis. of potential values of valence and conduction band shows the production of active oxidizing species for hydrogen yield and the possible mechanism of the Schottky barrier has been proposed. A schematic diagram of visible light driven Photocatalysis has been pictured showing degradation activity of Fe³⁺-TiO₂catalysts sample.

MRC-5 Human Lung Fibroblasts Alleviate the Genotoxic Effect of Fe-N Co-Doped Titanium Dioxide Nanoparticles through an OGG1/2-Dependent Reparatory Mechanism

The current study was focused on the potential of pure P25 TiO2 nanoparticles (NPs) and Fe(1%)-N co-doped P25 TiO2 NPs to induce cyto- and genotoxic effects in MRC-5 human pulmonary fibroblasts. The oxidative lesions of P25 NPs were reflected in the amount of 8-hydroxydeoxyguanosine accumulated in DNA and the lysosomal damage produced, but iron-doping partially suppressed these effects. However, neither P25 nor Fe(1%)-N co-doped P25 NPs had such a serious effect of inducing DNA fragmentation or activating apoptosis signaling. Moreover, oxo-guanine glycosylase 1/2, a key enzyme of the base excision repair mechanism, was overexpressed in response to the oxidative DNA deterioration induced by P25 and P25-Fe(1%)-N NPs.

A synergistic consequence of catalyst dosage, pH solution and reactive species of Fe-doped CdAl2O4 nanoparticles on the degradation of toxic environmental pollutants

Industrial wastewater treatment techniques are one of the biggest challenges of the scientific community that necessitate an increased consciousness to address water scarcity worldwide. Herein, an eco-friendly and cost-effective process was demonstrated to cope with tannery, textile and pharmaceutical dye wastes through the co-precipitation of highly reusable Fe-doped CdAl₂O₄ samples. The XRD studies exposed the space group R 3‾ with no secondary phase step being found for all samples. The outcomes of optical absorbance spectra demonstrate that Fe doping diminished the energy gap from 3.66 to 1.67 eV. HR-TEM images of existing spherical particles and some of the particles' rod-like structures with little agglomeration were found for Fe (0.075 M) doped CdAl₂O₄ nanoparticles. The PL emission outcomes show that Fe doping effectively prevented the charge carrier's recombination in CdAl₂O₄ during photocatalysis. All Fe-doped CdAl₂O₄ samples demonstrated higher photodegradation behaviors towards the effectual degradation of both dye solutions as compared to pure CdAl₂O₄ samples. Particularly, Fe (0.075 M)-doped CdAl₂O₄ samples exhibited improved photodegradation performance of 93 and 95% for both dye solutions. The amount of photodegradation was noticed to rely on dye pH, irradiation time, catalyst dosage, initial dye amount, and reactive species. The recyclability of the Fe (0.075 M) doped CdAl₂O₄ nanoparticles denotes that 78 and 82% of BB and BG were removed up to the 6th run of usage. The outcomes of trapping tests,^.OH^- and h⁺ radicals were the major Scavenging in the photodegradation reaction. COD studies affirmed the whole mineralization of BB and BG dye molecules. It is expected that our present examination could offer to improve various spinal oxide materials for the photodegradation activity of pharmaceutical contaminants and environmental issues and can also resolve energy storage applications.

Synthesis and Characterization of Fe Doped Aurivillius-Phase PbBi2Nb2O9 Perovskite and Their Photocatalytic Activity on the Degradation of Methylene Blue

A simple solid-state reaction was applied to synthesize Fe-doped perovskite-type PBFNO catalysts, and methylene blue decomposition studies were performed in the form of visible light according to the changes in the Fe doping content (0.4 to 1.9 mol ratio compared with Bi mol) and the amount of catalyst used (0.05 to 0.2 g used). As the Fe doping content increases, the absorbance and bang gap energy of the PBFNOs sample rapidly increase and decrease, respectively, because the Fe dopant in the PBNO lattice acts as an intermediate band between the valence and conduction bands of the PBNO and reduces the band gap energy. As a result, it showed a performance degradation of approximately 42% compared to the maximum performance. In addition, the presence of Fe dopants in the PBNO lattice greatly reduces the intensity of the photoluminescent lines. This is because the Fe dopant can play an important role in light-induced electron transfer and as a hole trap, reducing the recombination rate. Additionally, when too much photocatalyst was used (>0.1 g used), the Fe dopant played an important role as a light-induced electron transfer and hole trap, reducing the recombination rate and lowering the overall photocatalytic activity by 51%. In particular, 0.1 g of PBNO-0.2-F showed continuous catalytic activity, even when the photocatalytic reaction proceeded for 180 min. Therefore, this study demonstrates that the Fe-doped aurivillius-phase PBFNO photocatalyst is very promising for the dye manufacturing industry.

Removal of oxytetracycline from water by liquid-phase plasma process with an iron precipitated TiO2 photocatalyst

This study developed a new water treatment method using liquid-phase plasma (LPP) process that can decompose oxytetracycline (OTC) remaining in the aquatic environment. Relatedly, the OTC causes damage to the human body and cannot be removed by traditional water treatment methods. The study also prepared Fe/TiO₂ photocatalyst responding to visible light using the LPP process. In particular, the OTC decomposition efficiency of the LPP process improved by more than 10% with the use of the Fe/TiO₂ photocatalyst as compared to that of the one with the use of bare TiO₂ photocatalyst. Further, the optimal LPP process parameters and Fe/TiO₂ photocatalyst amount in the LPP process for OTC decomposition were established in the study. Finally, the degradation pathway of the OTC in the LPP process was found based on the five intermediates of the LPP reaction that were detected by the liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) analysis. In particular, the decomposition pathway was estimated to be involving the mineralization of the OTC through demethylation, deamination, dehydration, and ring cleavage.

Critical role of tetracycline's self-promotion effects in its visible-light driven photocatalytic degradation over ZnO nanorods

Zinc oxide (ZnO), which is widely applied for ultraviolet-light driven photocatalysis, has no activity in visible-light photocatalytic process due to its large band gap of ∼3.2 eV. Herein, however, we demonstrated the multiple self-promotion effects of tetracycline as band adjuster, photo-sensitizer, and charge transfer promoter for ZnO nanorods, realizing its visible-light photocatalytic degradation with an excellent removal efficiency up to 91.1% within only 2 h. Besides, the influence of complex realistic factors on this unique process was evaluated together with tests with realistic water matrices. Furthermore, the active species and degradation products were identified. Both acute and developmental toxicities were found to be reduced as the degradation proceeds. These results pave the path for the brand-new self-driven visible-light photocatalysis.

Visible-light-induced photocatalytic response of easily recoverable Mn2O3/SiO2 monolith in centimeter-scale towards degradation of ofloxacin: Performance evaluation and product analysis

Monolithic-photocatalysts being easily recoverable are a suitable alternative to powdered materials for pollutant treatment. This study was conducted to prepare Mn₂O₃/SiO₂ monoliths by wet-impregnating Mn(NO₃)₂^․4H₂O in SiO₂ monoliths. The crystallinity of oxide was affirmed via XRD analyses, whereas EDS and elemental-mapping, and XPS studies revealed the constituent elements and their oxidation states. FESEM images confirmed porous morphology, while BET-analysis confirmed its mesoporous nature (∼8.44 nm) and enormous surface area (∼241 m²/g). The DRS and PL studies disclosed that Mn₂O₃/SiO₂ monoliths consisted of narrow band-gap of ∼2.14 eV and had suitable electron/hole separation. The photocatalytic effectiveness of the monolith had been checked by degrading model dye methylene blue (MB) and antibiotic ofloxacin (OF). The influence of various reaction parameters for degradation, i.e., monolith dose, solution-pH, illumination-area, scavengers, etc., was noted. At optimal reaction conditions, outstanding competence was achieved for MB (95.23%; 0.0225 min^-1) and decent results were obtained for OF-degradation (73.2%; 0.0096 min^-1). The recyclable nature of the catalyst (∼12.7%-reduction in effectiveness after 10 successive cycles) was vindicated by several characterization studies after reusability. The O₂^•-radicals participated majorly in the degradation reaction. The reaction intermediates plus products, generated after the degradation of had been identified via LC/MS study. The mineralization extent of the OF and MB was also gauged through TOC analyses. The photocatalytic treatment of raw textile wastewater manifested ∼57.8% COD and 53% TOC-removal. This study emphasizes the competence of Mn₂O₃/SiO₂ monoliths for the photocatalytic abatement of refractory organic contaminants.

Synthesis and Application of Innovative and Environmentally Friendly Photocatalysts: A Review

Modern society faces two major challenges: removing pollutants from water and producing energy from renewable sources. To do this, science proposes innovative, low-cost, and environmentally friendly methods. The heterogeneous photocatalysis process fits perfectly in this scenario. In fact, with photocatalysis, it is possible both to mineralize contaminants that are not easily biodegradable and to produce hydrogen from the water splitting reaction or from the conversion of organic substances present in water. However, the main challenge in the field of heterogeneous photocatalysis is to produce low-cost and efficient photocatalysts active under visible light or sunlight. The objective of this review is to compare the new proposals for the synthesis of innovative photocatalysts that reflect the requirements of green chemistry, applied both in the removal of organic contaminants and in hydrogen production. From this comparison, we want to bring out the strengths and weaknesses of the proposals in the literature, but above all, new ideas to improve the efficiency of heterogeneous photocatalysis guaranteeing the principles of environmental and economic sustainability.

Photocatalytic Degradation of Polyethylene Microplastics and Disinfection of E. coli in Water over Fe- and Ag-Modified TiO2 Nanotubes

In this study, Fe- and Ag-modified TiO2 nanotubes were synthesized via an anodization method as photocatalysts for degradation of polyethylene microplastics and disinfection of Escherichia coli (E. coli). The anodization voltage, as well as the Fe3+ or Ag+ concentrations on TiO2 nanotubes were evaluated and correlated to their corresponding photocatalytic properties. TiO2 nanotubes were firstly synthesized by anodization of Ti plates in a glycerol-based electrolyte, followed by incorporation of either Fe or Ag via a Successive Ionic Layer Adsorption and Reaction (SILAR) method with Fe(NO3)3 and AgNO3 as Fe and Ag precursors, respectively. UV-Vis DRS shows that the addition of Fe or Ag on TiO2 nanotubes causes a redshift in the absorption spectra. The X-ray diffractograms indicate that, in the case of Fe-modified samples, Fe3+ was successfully incorporated into TiO2 lattice, while Ag scatters around the surface of the tubes as Ag and Ag2O nanoparticles. A microplastic degradation test was carried out for 90 mins inside a photoreactor with UVC illumination. TiO2 nanotubes that are anodized with a voltage of 30 V exhibit the best degradation results with 17.33% microplastic weight loss in 90 mins. Among the modified TiO2 nanotubes, 0.03 M Ag-TiO2 was the only one that surpassed the unmodified TiO2 in terms of microplastic degradation in the water, offering up to 18% microplastic weight loss in 90 min. In terms of E. coli disinfection, 0.03M Ag-TiO2 exhibit better performance than its unmodified counterpart, revealing 99.999% bactericidal activities in 10 mins. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Photocatalytic Degradation of Recalcitrant Pollutants of Greywater

These days, many countries have a water shortage and have limited access to clean water. To overcome this, a new treatment is emerging, namely, the photocatalytic processing of greywater. Photocatalytic processes to remove the organic matter from different greywater sources are critically reviewed. Their efficiency in degrading the organic matter in greywater is scrutinized along with factors that can affect the activity of photocatalysts. Modified TiO2, ZnO and TiO2 catalysts show great potential in degrading organic materials that are present in greywater. There are several methods that can be used to modify TiO2 by using sol-gel, microwave and ultrasonication. Overall, the photocatalytic approach alone is not efficient in mineralizing the organic compounds, but it works well when the photocatalysis is combined with oxidants and Fe3+. However, factors such as pH, concentration and catalyst-loading of organic compounds can significantly affect photocatalytic efficiency.

Promotion effect of free Ag+ ions on photocatalytic dechlorination processes

Free silver ions (Ag+) in the solution exhibit enhanced photocatalytic dechlorination processes of organic chloride, including 2-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol, over PhC2Cu under visible light irradiation.

Fabrication of Adsorbed Fe(III) and Structurally Doped Fe(III) in Montmorillonite/TiO2 Composite for Photocatalytic Degradation of Phenol

The Fe(III)-doped montmorillonite (Mt)/TiO2 composites were fabricated by adding Fe(III) during or after the aging of TiO2/Ti(OH)4 sol–gel in Mt, named as xFe-Mt/(1 − x)Fe-TiO2 and Fe/Mt/TiO2, respectively. In the xFe-Mt/(1 − x)Fe-TiO2, Fe(III) cations were expected to be located in the structure of TiO2, in the Mt, and in the interface between them, while Fe(III) ions are physically adsorbed on the surfaces of the composites in the Fe/Mt/TiO2. The narrower energy bandgap (Eg) lower photo-luminescence intensity were observed for the composites compared with TiO2. Better photocatalytic performance for phenol degradation was observed in the Fe/Mt/TiO2. The 94.6% phenol degradation was due to greater charge generation and migration capacity, which was confirmed by photocurrent measurements and electrochemical impedance spectroscopy (EIS). The results of the energy-resolved distribution of electron traps (ERDT) suggested that the Fe/Mt/TiO2 possessed a larger amorphous rutile phase content in direct contact with crystal anatase than that of the xFe-Mt/(1 − x)Fe-TiO2. This component is the fraction that is mainly responsible for the photocatalytic phenol degradation by the composites. As for the xFe-Mt/(1 − x)Fe-TiO2, the active rutile phase was followed by isolated amorphous phases which had larger (Eg) and which did not act as a photocatalyst. Thus, the physically adsorbed Fe(III) enhanced light adsorption and avoided charge recombination, resulting in improved photocatalytic performance. The mechanism of the photocatalytic reaction with the Fe(III)-doped Mt/TiO2 composite was proposed.

Oxygen-Deficient WO3/TiO2/CC Nanorod Arrays for Visible-Light Photocatalytic Degradation of Methylene Blue

At present, TiO2 is one of the most widely used photocatalytic materials. However, the narrow response range to light limits the photocatalytic performance. Herein, we reported a successful construction of self-doped R-WO3/R-TiO2/CC nanocomposites on flexible carbon cloth (CC) via electrochemical reduction to increase the oxygen vacancies (Ovs), resulting in an enhanced separation efficiency of photo-induced charge carriers. The photocurrent of R-WO3/R-TiO2/CC at −1.6 V (vs. SCE) was 2.6 times higher than that of WO3/TiO2/CC, which suggested that Ovs could improve the response to sunlight. Moreover, the photocatalytic activity of R-WO3/TiO2/CC was explored using methylene blue (MB). The degradation rate of MB could reach 68%, which was 1.3 times and 3.8 times higher than that of WO3/TiO2/CC and TiO2/CC, respectively. Furthermore, the solution resistance and charge transfer resistance of R-WO3/R-TiO2/CC were obviously decreased. Therefore, the electrochemical reduction of nanomaterials enabled a promoted separation of photogenerated electron–hole pairs, leading to high photocatalytic activity.

Effects of Hydrothermal Time on Structure and Photocatalytic Property of Titanium Dioxide for Degradation of Rhodamine B and Tetracycline Hydrochloride

Using butyl titanate and absolute ethanol as raw materials, TiO2 was prepared by a hydrothermal method with different hydrothermal times, and the influences of hydrothermal time on the structure and photocatalytic performance of TiO2 were investigated. The obtained samples were characterized by XRD, SEM, TEM, BET, PL and DRS, separately. The results show that TiO2 forms anatase when the hydrothermal time is 12 h, forms a mixed crystal composed of anatase and rutile when the hydrothermal time is 24 h, and forms rutile when the hydrothermal time is 36 h. With the extension of hydrothermal time, anatase gradually transforms into rutile and the surface area decreases. Although TiO2-24 h and TiO2-36 h show lower photoinduced charge recombination and higher light source utilization, TiO2-12 h exhibits the highest photocatalytic activity owing to its largest surface area (145.3 m2/g). The degradation degree of rhodamine B and tetracycline hydrochloride reach 99.6% and 90.0% after 45 min.

Characterization of Nickel Oxide Nanoparticles Synthesized under Low Temperature

In this study, ultrafine nickel oxide nanoparticles (NiO NPs) were well synthesized using a simple wet chemical method under low temperature, 300 °C. An Ni(OH)₂ precursor was well precipitated by dropping NH₄OH into an Ni(Ac)₂ solution. TG-DTA showed that the weight of the precipitate decreases until 300 °C; therefore, the precursor was heat-treated at 300 °C. X-ray diffraction (XRD) patterns indicated that hexagonal-structured NiO NPs with (200) preferred orientation was synthesized. In addition, BET specific surface area (SSA) and HRTEM analyses revealed that spherical NiO NPs were formed with SSA and particle size of 60.14 m²/g and ca. 5–15 nm by using the low temperature method. FT-IR spectra of the NiO NPs showed only a sharp vibrating absorption peak at around 550 cm⁻¹ owing to the Ni-O bond. Additionally, in UV-vis absorption spectra, the wavelength for absorption edge and energy band gap of the ultrafine NiO NPs was 290 nm and 3.44 eV.

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.

Novel Ag/cellulose-doped CeO2 quantum dots for efficient dye degradation and bactericidal activity with molecular docking study

In the present study, the novel Ag/cellulose nanocrystal (CNC)-doped CeO₂ quantum dots (QDs) with highly efficient catalytic performance were synthesized using one pot co-precipitation technique, which were then applied in the degradation of methylene blue and ciprofloxacin (MBCF) in wastewater. Catalytic activity against MBCF dye was significantly reduced (99.3%) for (4%) Ag dopant concentration in acidic medium. For Ag/CNC-doped CeO₂ vast inhibition domain of G-ve was significantly confirmed as (5.25-11.70 mm) and (7.15-13.60 mm), while medium- to high-concentration of CNC levels were calculated for G + ve (0.95 nm, 1.65 mm), respectively. Overall, (4%) Ag/CNC-doped CeO₂ revealed significant antimicrobial activity against G-ve relative to G + ve at both concentrations, respectively. Furthermore, in silico molecular docking studies were performed against selected enzyme targets dihydrofolate reductase (DHFR), dihydropteroate synthase (DHPS), and DNA gyrase belonging to folate and nucleic acid biosynthetic pathway, respectively to rationalize possible mechanism behind bactericidal potential of CNC-CeO₂ and Ag/CNC-CeO₂.

Visible Light-Driven Photocatalytic Activity and Kinetics of Fe-Doped TiO2 Prepared by a Three-Block Copolymer Templating Approach

Fe-doped titania photocatalysts (with 1, 2.5, and 3.5 wt. % Fe nominal content), showing photocatalytic activity under visible light, were prepared by a soft-template assisted sol-gel approach in the presence of the triblock copolymer Pluronic P123. An undoped TiO2 photocatalyst was also prepared for comparison. The photocatalysts were characterized by means of X-ray powder Diffraction (XRPD), Quantitative Phase Analysis as obtained by Rietveld refinement, Diffuse Reflectance (DR) UV-Vis spectroscopy, N2 adsorption/desorption at -196 °C, electrophoretic mobility in water (ζ-potential), and X-ray photoelectron spectroscopy (XPS). The physico-chemical characterization showed that all the samples were 100% anatase phase and that iron was present both in the bulk and at the surface of the Fe-doped TiO2. Indeed, the band gap energy (Eg) decreases with the Fe content, with Tauc's plot determined values ranging from 3.35 (undoped TiO2) to 2.70 eV (3.5 wt. % Fe). Notwithstanding the obtained Eg values, the photocatalytic activity results under visible light highlighted that the optimal Fe content was equal to 2.5 wt. % (Tauc's plot determined Eg = 2.74 eV). With the optimized photocatalyst and in selected operating conditions, under visible light it was possible to achieve 90% AO7 discoloration together with a TOC removal of 40% after 180 min. The kinetic behavior of the photocatalyst was also analyzed. Moreover, the tests in the presence of three different scavengers revealed that the main reactive species are (positive) holes and superoxide species. Finally, the optimized photocatalyst was also able to degrade phenol under visible light.

New insights into the degradation of synthetic pollutants in contaminated environments

The environment is contaminated by synthetic contaminants owing to their extensive applications globally. Hence, the removal of synthetic pollutants (SPs) from the environment has received widespread attention. Different remediation technologies have been investigated for their abilities to eliminate SPs from the ecosystem; these include photocatalysis, sonochemical techniques, nanoremediation, and bioremediation. SPs, which can be organic or inorganic, can be degraded by microbial metabolism at contaminated sites. Owing to their diverse metabolisms, microbes can adapt to a wide variety of environments. Several microbial strains have been reported for their bioremediation potential concerning synthetic chemical compounds. The selection of potential strains for large-scale removal of organic pollutants is an important research priority. Additionally, novel microbial consortia have been found to be capable of efficient degradation owing to their combined and co-metabolic activities. Microbial engineering is one of the most prominent and promising techniques for providing new opportunities to develop proficient microorganisms for various biological processes; here, we have targeted the SP-degrading mechanisms of microorganisms. This review provides an in-depth discussion of microbial engineering techniques that are used to enhance the removal of both organic and inorganic pollutants from different contaminated environments and under different conditions. The degradation of these pollutants is investigated using abiotic and biotic approaches; interestingly, biotic approaches based on microbial methods are preferable owing to their high potential for pollutant removal and cost-effectiveness.

Highly-efficient and stable photocatalytic activity of lead-free Cs2AgInCl6 double perovskite for organic pollutant degradation

Photocatalytic applications of halide perovskites have attracted increasing attention. However, lack of stability and lead toxicity of lead halide perovskites have hindered their applications. Metal halide double perovskite (DP) Cs₂AgInCl₆ is a stable, environment-friendly semiconductor with direct band gap, and then the best promising alternative to lead halide perovskites. Here, the applications of Cs₂AgInCl₆ DP to photocatalytic degradation of organic pollutants have been developed, in which the octahedral Cs₂AgInCl₆ DP particles (~3.33 eV) were prepared by precipitation from acid solutions. The as-prepared samples exhibit high photocatalytic activity, which can degrade about 98.5% of water-insoluble carcinogen Sudan Red III in only 16 min, and have a good stability for 5 cycle operations. Furthermore, the Cs₂AgInCl₆ DP also can degrade Rhodamine B, Methyl orange and Methyl red efficiently, demonstrating a highly-efficient and stable ethanol solvent-based photocatalytic system for organic pollutants degradation. The high photocatalytic activity could be attributed to direct band gap and long carrier lifetime of Cs₂AgInCl₆ DP. These unique features of Cs₂AgInCl₆ DP indicate that it could have a good application prospect for photocatalytic degradation of organic pollutants.

Ag/AgCl@MIL-88A(Fe) heterojunction ternary composites: towards the photocatalytic degradation of organic pollutants

The efficient utilization of solar energy has received tremendous interest due to the increasing environmental and energy concerns. The present paper discusses the efficient integration of a plasmonic photocatalyst (Ag/AgCl) with an iron-based metal-organic framework (MIL-88A(Fe)) for boosting the visible light photoreactivity of MIL-88A(Fe). Two composites of Ag/AgCl@MIL-88A(Fe), namely MAG-1 and MAG-2 (stoichiometric ratio of Fe to Ag is 5 : 1 and 2 : 1), were successfully synthesized via facile in situ hydrothermal methods followed by UV reduction. The synthesized composite materials are characterized by FTIR, PXRD, UVDRS, PL, FESEM/EDX, TEM and BET analyses. The Ag/AgCl@MIL-88A(Fe) (MAG-2) hybrid system shows excellent photocatalytic activity for the degradation of p-nitrophenol (PNP), rhodamine B (RhB), and methylene blue (MB) under sunlight. We found that 91% degradation of PNP in 80 min, 99% degradation of RhB in 70 min and 94% degradation of MB in 70 min have taken place by using MAG-2 as a catalyst under sunlight. The superior activity of Ag/AgCl@MIL-88A(Fe) (MAG-2) is attributed to the synergistic effects from the surface plasmon resonance (SPR) of Ag NPs and the electron transfer from MIL-88A(Fe) to Ag nanoparticles for effective separation of electron-hole pairs. Furthermore, the mechanism of degradation of PNP, RhB and MB is proposed by analyzing the electron transfer pathway in Ag/AgCl@MIL-88A(Fe).

Selective Wettability Membrane for Continuous Oil-Water Separation and In Situ Visible Light-Driven Photocatalytic Purification of Water

Membrane-based technologies are attractive for remediating oily wastewater because they are relatively energy-efficient and are applicable to a wide range of industrial effluents. For complete treatment of oily wastewater, removing dissolved contaminants from the water phase is typically followed by adsorption onto an adsorbent, which complicates the process. Here, an in-air superhydrophilic and underwater superoleophobic membrane-based continuous separation of surfactant-stabilized oil-in-water emulsions and in situ decontamination of water by visible-light-driven photocatalytic degradation of dissolved organic contaminants is reported. The membrane is fabricated by utilizing a thermally sensitized stainless steel mesh coated with visible light absorbing iron-doped titania nanoparticles. Post annealing of the membrane can enhance the adhesion of nanoparticles to the membrane surface by formation of a bridge between them. An apparatus that enables continuous separation of surfactant-stabilized oil-in-water emulsion and in situ photocatalytic degradation of dissolved organic matter in the water-rich permeate upon irradiation of visible light on the membrane surface with greater than 99% photocatalytic degradation is developed. The membrane demonstrates the recovery of its intrinsic water-rich permeate flux upon continuous irradiation of light after being contaminated with oil. Finally, continuous oil-water separation and in situ water decontamination is demonstrated by photocatalytically degrading model toxins in water-rich permeate.

Impact of Fe, Mn co-doping in titanate nanowires photocatalytic performance for emergent organic pollutants removal

The unexpected incorporation of ionic Mn and Fe in the crystalline structure of titanate nanowires was accomplished when a contaminated a titanium source was used. The presence of Mn (8.1 mg L^-1) and Fe (4.3 mg L^-1) result in the production of a novel co-doped (Fe,Mn) titanate nanowires (TNW) material with improved optical and photocatalytic properties. After structural characterization, the results indicate that both Mn and Fe were incorporated in the TNW structure by replacement of Na⁺ in the interlayers, together with Ti⁴⁺ substitution in the TiO₆ octahedra. The potential of this new material to be used for pollutants photocatalytic degradation was further investigated. The terephthalic acid was used as probe molecule to first evaluate the catalytic ability of the pristine and FeMnTNW modified powders for the photo-assisted hydroxyl radical formation. Afterwards, the degradation process of a model emergent pollutant, caffeine, was studied. The results showed that FeMnTNW was the best photocatalyst, with the complete caffeine removal (20 mg L^-1) within 60 min of radiation (13 mg catalyst/L solution). The action of several oxidant species, including h⁺, OH^• and O₂^•-, during caffeine removal was carefully analyzed using specific radical scavengers. A mechanism for the charge-transfer in irradiated FeMnTNW particles, including the possibility of a photo-Fenton and photodegradation combination process, is proposed and discussed.