Visible-Light-Active TiO2-Based Hybrid Nanocatalysts for Environmental Applications

Green approach for the fabrication of a ternary nanocatalyst (Ag-ZnONPs@Cy) for visible light-induced photocatalytic reduction of nitroarenes to aminoarenes

In recent times, the incorporation of metal oxide nanoparticles with organic dyes has piqued the interest of numerous researchers due to their diverse applications under visible light instead of UV radiation. This investigation employed a three-step methodology to fabricate cyanidin-sensitized silver-doped zinc oxide nanoparticles (Ag-ZnO@Cy). Initially, cyanidin dye was extracted from fresh black mulberry fruit, followed by the eco-friendly synthesis of Ag-ZnO nanoparticles (Ag-ZnONPs). The successful integration of the prepared cyanidin dye with Ag-ZnONPs was achieved through a straightforward, environmentally benign, and cost-efficient procedure. The resultant ternary composite underwent comprehensive characterization and confirmation utilizing various techniques, such as SEM, FT-IR, EDX, DRS, elemental mapping, and XRD. The experimental results for Ag-ZnONPs@Cy demonstrated that the nanocrystalline wurtzite exhibited spherical shapes with an average crystal size of 27.42 nm. Moreover, the photocatalytic activity of the synthesized Ag-ZnONPs@Cy was meticulously investigated under blue LED light irradiation. This inquiry encompassed examinations of catalyst amount, regeneration, stability, reusability, and the influence of light source on the hydrogenation of nitroarenes to the corresponding aminoarenes. The findings shed light on the potential of this composite for diverse photocatalytic applications.

Synthesis and Characterization of a Photocatalytic Material Based on Raspberry-like SiO2@TiO2 Nanoparticles Supported on Graphene Oxide

A raspberry-like SiO2@TiO2 new material supported on functionalized graphene oxide was prepared to reduce titania's band gap value. The material was characterized through different analytical methods such as Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HR-TEM). The band gap value was studied via UV-Vis absorption spectra and determined through the Kubelka-Munk equation. A theoretical study was also carried out to analyze the interaction between the species.

Adsorption and Visible Photocatalytic Synergistic Removal of a Cationic Dye with the Composite Material BiVO4/MgAl-LDHs

Adsorption and photocatalysis are effective in removing organic pollutants from wastewater. This study is based on the memory effects of MgAl-layered double hydroxides (MgAl-LDHs) after high-temperature calcination. By introducing bismuth vanadate (BiVO4) during the reformation of the layered structure via contact with water, a composite material BiVO4/MgAl-LDHs with enhanced adsorption and visible light catalytic performance was synthesized. The effects of the calcination temperature, ratio, initial methylene blue (MB) concentration, and catalyst dosage on the adsorption and photocatalytic performance were investigated. The BiVO4/MgAl-LDHs showed better photocatalytic performance than the pure BiVO4 and MgAl-LDHs. Under the optimal conditions, the proportion of MB adsorbed in 20 min was 66.1%, and the percentage of MB degraded during 100 min of photolysis was 92.4%. The composite photocatalyst showed good chemical stability and cyclability, and the adsorption-degradation rate was 86% after four cycles. Analyses of the adsorption and photocatalytic mechanisms for the composite material showed that synergistic adsorption and visible light photocatalysis contributed to the excellent catalytic performance of the BiVO4/MgAl-LDHs. A highly adsorbent photocatalytic composite material exhibiting outstanding performance was prepared via a simple, cost-effective, and environmentally friendly method, providing reference information for the removal of organic pollutants from liquids.

TiO2-based catalytic systems for the treatment of airborne aromatic hydrocarbons

Among diverse strategies to manage air quality, catalytic oxidation has been a widely used option to mitigate diverse pollutants such as aromatic volatile organic compounds (VOCs), especially benzene, toluene, and xylene (BTX). For such applications, TiO₂-based catalysts have drawn significant research attention for their prominent photo/thermal catalytic activities and photochemical stability. This review has been organized to elaborate on the recent developments achieved in the thermocatalytic, photocatalytic, and photothermal applications of metal/non-metal doped TiO₂ catalysts towards BTX vapors and their reaction mechanisms. The performance of the reported TiO₂-based catalysts has also been analyzed based on multiple computational metrics such as reaction rate (r), quantum yield (QY), space-time yield, and figure of merit (FOM). At last, the research gap and prospects in the catalytic treatment of BTX are also discussed in association with the feasibility and utility of TiO₂-based catalysts in air purification applications.

Life Cycle Assessment of UV-C based treatment systems for the removal of compounds of emerging concern from urban wastewater

In the last decades particular attention is being paid to the efficient and effective removal of compounds of emerging concern (CECs) present in wastewater before their eventual reuse or disposal. Several technologies have been developed for the degradation of CECs in aqueous matrix, in this regard advanced oxidation processes (AOPs) represent a nascent technological solution developed on a laboratory scale with applications on a prototype scale. The experimental evidences have shown that AOPs processes can oxidize numerous organic compounds in a much faster and more efficient way than that of the most common disinfection processes. The most common AOPs processes are those that involve the use of H₂O₂/UV, O₃/UV, H₂O₂/O₃, H₂O₂/O₃/UV, Fenton and photo-Fenton. The aim of this work is to illustrate the results of a comparative LCA study of a laboratory scale UV-C photoreactor for the tertiary treatment of urban wastewater of three treatment systems (UV-C, UV-C + H₂O₂ e UV-C + TiO₂). In particular, the specific objective is to evaluate, from an environmental point of view, an innovative advanced oxidation system based on nanostructures TiO₂ immobilized on a stainless steel mesh. Compared to the UV-C photolysis reference system, the addition of hydrogen peroxide reduces the total environmental impact of the system by almost 75 %, while the use of the stainless-steel mesh coated by the nanostructures titanium dioxide reduces the UV-C environmental impact by 30 %. These results are due to the lower energy consumption of these last treatments compared to photolysis alone. The main impacts of the three systems are related to the electric power consumption of the centrifugal pump (63-64 %) and of the UV-C lamp (32-33 %). The LCA applied to these systems has shown that TiO₂ assisted photocatalysis is not yet advantageous from an environmental point of view and that, therefore, the efficiency of the system needs to be improved.

Microwave-Assisted Synthesis of N/TiO2 Nanoparticles for Photocatalysis under Different Irradiation Spectra

Nitrogen-doped TiO₂ (N/TiO₂) photocatalyst nanoparticles were derived by the environmentally friendly and cost-effective microwave-assisted synthesis method. The samples were prepared at different reaction parameters (temperature and time) and precursor ratio (amount of nitrogen source; urea). The obtained materials were characterized by X-ray diffraction (XRD), photoelectron spectroscopy (XPS), Raman spectroscopy (RS), infrared spectroscopy (FTIR), diffuse reflectance spectroscopy (DRS), electron microscopy (SEM-EDS), and nitrogen adsorption/desorption isotherms. Two cycles of optimizations were conducted to determine the best reaction temperature and time, as well as N content. The phase composition for all N/TiO₂ nanomaterials was identified as photoactive anatase. The reaction temperature was found to be the most relevant parameter for the course of the structural evolution of the samples. The nitrogen content was the least relevant for the development of the particle morphology, but it was important for photocatalytic performance. The photocatalytic activity of N/TiO₂ nanoparticle aqueous suspensions was evaluated by the degradation of antibiotic ciprofloxacin (CIP) under different irradiation spectra: ultraviolet A light (UVA), simulated solar light, and visible light. As expected, all prepared samples demonstrated efficient CIP degradation. For all irradiation sources, increasing synthesis temperature and increasing nitrogen content further improved the degradation efficiencies.

LaCoxFe1-XO3 (0≤x≤1) spherical nanostructures prepared via ultrasonic approach as photocatalysts

To harvest the photon energy, a sequenceof perovskite-type oxides of LaCoxFe1-xO3 (0 ≤x≤1) nanostructures with distinct 'Cobalt' doping at the position of B-site are successfully prepared via a simple ultrasonic approach as photocatalyst. The crystallinity, phase identification, microstructure, and morphology of perovskite nanocomposites were analyzed to better understand their physicochemical properties. The catalytic efficiency was assessedusing Congo Red (CR) dye by visible light irradiation for 30 min. Applying terephthalic acid as a probe molecule, the formation of hydroxyl radicals during the processes was investigated. The photocatalytic efficacy was measured by varying different Co/Fe stoichiometric molar ratios and noticed the order of sequence is 0.2 > 0.6 > 0.4 > 0.8 > 0.5 > 0 > 1 after 30 min of reaction time. Finally using LaCo0.2Fe0.8O3 nanostructures, cycling studies (n = 3) were performed to determine its photostability and reusability. The photocatalytic methodology proposed in this study was discussed extensively.

Degradation of Harmful Organics Using Visible Light Driven N-TiO₂/rGO Nanocomposite

Nitrogen doped titania over reduced form of graphene oxide (N-TiO₂/rGO) catalysts were synthesized by adopting single step hydrothermal route. All the prepared photocatalysts were thoroughly characterized by using different analytical tools such as XRD, Raman, UV-DRS, FE-SEM and HRTEM. The photocatalytic activities of bare and composite catalysts were evaluated towards the photocatalytic decolourisation/degradation of Methylene blue dye (MB) and Metronidazole antibiotic (MTZ) under visible electromagnetic radiation. Among all the synthesized catalysts, N-TiO₂/rGO composite catalyst showed the highest decolourisation/degradation activity towards both the dye and the antibiotic. The most active catalyst was also tested under UV and solar light irradiations which showed promising results. The stability of the most active catalyst (N-TiO₂/rGO) was examined by recyclability test. The possible photocatalytic mechanism was proposed for the composite catalyst.

Decomposition of highly persistent perfluorooctanoic acid by hollow Bi/BiOI1-xFx: Synergistic effects of surface plasmon resonance and modified band structures

Perfluorooctanoic acid (PFOA) is highly stable due to the strong CF bond and extremely difficult to be removed by conventional photocatalysts. In this study, Bi doped BiOI_1-xF_x solid solutions with hollow microsphere structure were prepared through a facile one-step hydrothermal method. Compared with pure BiOI and BiOF, the band gap of the Bi/BiOI_1-xF_x solid solutions was significantly reduced, thus promoting the visible light absorbance. The cavity structure of the BiOI_1-xF_x solid solutions enhanced the surface areas and active sites for reaction. The local electromagnetic field dominated by surface plasmon resonance (SPR) effect of Bi metal on the surface favored the separation of the photoinduced charge pairs. As a consequence, Bi/BiOI_0.8F_0.2 (x = 0.20, the doping amount of fluorine was 20 %) composite displayed the best photocatalytic performance for decomposing PFOA, and 40 mg/L PFOA could be removed within 2 h illumination. The degradation rate constant (k = 0.0375 min^-1) of PFOA by Bi/BiOI_0.8F_0.2 was about tenfold of that by pure BiOI and BiOF. Superoxide radical (·O₂-) predominated in the degradation of PFOA by Bi/BiOI_0.8F_0.2, and the possible degradation pathway of PFOA by Bi/BiOI_0.8F_0.2 was proposed. This work provides a highly efficient catalyst for the practical application in removal of highly persistent PFOA.

Photocatalytic activity of undoped and Mn- and Co-doped TiO2 nanocrystals incorporated in enamel coatings on stainless steel

New catalysts composed of undoped and transition metal-doped TiO2 nanocrystals incorporated in enamels on stainless steel show potential applications for pollutant photodegradation.

Recent Progress in the Abatement of Hazardous Pollutants Using Photocatalytic TiO2-Based Building Materials

Titanium dioxide (TiO2) has been extensively investigated in interdisciplinary research (such as catalysis, energy, environment, health, etc.) owing to its attractive physico-chemical properties, abundant nature, chemical/environmental stability, low-cost manufacturing, low toxicity, etc. Over time, TiO2-incorporated building/construction materials have been utilized for mitigating potential problems related to the environment and human health issues. However, there are challenges with regards to photocatalytic efficiency improvements, lab to industrial scaling up, and commercial product production. Several innovative approaches/strategies have been evolved towards TiO2 modification with the focus of improving its photocatalytic efficiency. Taking these aspects into consideration, research has focused on the utilization of many of these advanced TiO2 materials towards the development of construction materials such as concrete, mortar, pavements, paints, etc. This topical review focuses explicitly on capturing and highlighting research advancements in the last five years (mainly) (2014-2019) on the utilization of various modified TiO2 materials for the development of practical photocatalytic building materials (PBM). We briefly summarize the prospective applications of TiO2-based building materials (cement, mortar, concretes, paints, coating, etc.) with relevance to the removal of outdoor/indoor NOx and volatile organic compounds, self-cleaning of the surfaces, etc. As a concluding remark, we outline the challenges and make recommendations for the future outlook of further investigations and developments in this prosperous area.

Exploring the Photothermo-Catalytic Performance of Brookite TiO2-CeO2 Composites

The thermocatalytic, photocatalytic and photothermo-catalytic oxidation of some volatile organic compounds (VOCs), 2-propanol, ethanol and toluene, was investigated over brookite TiO2-CeO2 composites. The multi-catalytic approach based on the synergistic effect between solar photocatalysis and thermocatalysis led to the considerable decrease in the conversion temperatures of the organic compounds. In particular, in the photothermo-catalytic runs, for the most active samples (TiO2-3 wt% CeO2 and TiO2-5 wt% CeO2), the temperature at which 90% of VOC conversion occurred was about 60 °C, 40 °C and 20 °C lower than in the thermocatalytic tests for 2-propanol, ethanol and toluene, respectively. Furthermore, the addition of cerium oxide to brookite TiO2 favored the total oxidation to CO2 already in the photocatalytic tests at room temperature. The presence of small amounts of cerium oxide allowed to obtain efficient brookite-based composites facilitating the space charge separation and increasing the lifetime of the photogenerated holes and electrons as confirmed by the characterization measurements. The possibility to concurrently utilize the photocatalytic properties of brookite and the redox properties of CeO2, both activated in the photothermal tests, is an attractive approach easily applicable to purify air from VOCs.

Nitrogen-Rich and Porous Graphitic Carbon Nitride Nanosheet-Immobilized Palladium Nanoparticles as Highly Active and Recyclable Catalysts for the Reduction of Nitro Compounds and Degradation of Organic Dyes

In the present study, we have successfully synthesized nitrogen-rich graphitic carbon nitride (g-C₃N₄) nanosheets by a simple direct thermal polymerization approach. The synthesized g-C₃N₄ nanosheets were exfoliated using HCl to make their surface a few nanometers thick. The ultrathin surface was achieved by simply mixing g-C₃N₄ in 3 M HCl. After that, palladium nanoparticles were uniformly immobilized on the surface of g-C₃N₄. The synthesized materials were characterized by various physiochemical techniques such as X-ray diffraction, energy-dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy. Information about morphology and size was obtained through transmission electron microscopy and scanning electron microscopy. The Brunauer-Emmett-Teller surface area, pore volume, and pore diameter were determined using nitrogen adsorption-desorption measurements. The prepared material (Pd/g-C₃N₄) was utilized as an efficient catalyst for the reduction of hazardous nitroarenes and degradation of organic dyes. The catalyst could be easily recovered through centrifugation and then could be reused multiple times for the further catalytic cycles with a little loss in its catalytic activity. The work presented here illustrates the sustainable anchoring of metal nanoparticles over the surface of nitrogen-rich g-C₃N₄ nanosheets and could be utilized for different types of catalytic reactions.

The Impact of In Situ Polymerization Conditions on the Structures and Properties of PANI/ZnO-Based Multiphase Composite Photocatalysts

We have synthesized polyaniline/ZnO-based (PANI/ZnO) multiphase composite photocatalysts from acid media by a newly proposed two-step in situ polymerization. The first step of synthesis yielded PANI salt required for the PANI/ZnO synergistic effect. In the second step, the aniline oxidation continued, without ZnO dissolution, and it produced PANI base. Thus, both PANI salt and base phases in the composites were detected by FTIR and UV/Vis, while the presence of both ZnO and PANI polymer was confirmed by XRD. Additionally, XRD also showed Zn5(OH)8(NO3)2·2H2O and Zn(SO4)(H2O) phases in PANI/ZnO-based multiphase composites. Furthermore, the impact of the synthesis conditions on the morphology of the composites was investigated by FE-SEM. The images displayed that ZnO particles were encapsulated in PANI sheets that were formed by the aniline oligomers. Photocatalytic evaluation of PANI/ZnO-based catalysts (i.e., degradation of Acid Blue 25 dye) was conducted and the obtained results confirmed that all the studied composites experienced the PANI/ZnO synergistic effect. It was observed that the best photocatalytic properties were held by the PANI/ZnO_2 sample due to its optimal particle size.

Photosensitive Hybrid Nanostructured Materials: The Big Challenges for Sunlight Capture

Solar radiation is becoming increasingly appreciated because of its influence on living matter and the feasibility of its application for a variety of purposes. It is an available and everlasting natural source of energy, rapidly gaining ground as a supplement and alternative to the nonrenewable energy feedstock. Actually, an increasing interest is involved in the development of efficient materials as the core of photocatalytic and photothermal processes, allowing solar energy harvesting and conversion for many technological applications, including hydrogen production, CO2 reduction, pollutants degradation, as well as organic syntheses. Particularly, photosensitive nanostructured hybrid materials synthesized coupling inorganic semiconductors with organic compounds, and polymers or carbon-based materials are attracting ever-growing research attention since their peculiar properties overcome several limitations of photocatalytic semiconductors through different approaches, including dye or charge transfer complex sensitization and heterostructures formation. The aim of this review was to describe the most promising recent advances in the field of hybrid nanostructured materials for sunlight capture and solar energy exploitation by photocatalytic processes. Beside diverse materials based on metal oxide semiconductors, emerging photoactive systems, such as metal-organic frameworks (MOFs) and hybrid perovskites, were discussed. Finally, future research opportunities and challenges associated with the design and development of highly efficient and cost-effective photosensitive nanomaterials for technological claims were outlined.

Visible-Light Active Titanium Dioxide Nanomaterials with Bactericidal Properties

This article provides an overview of current research into the development, synthesis, photocatalytic bacterial activity, biocompatibility and cytotoxic properties of various visible-light active titanium dioxide (TiO2) nanoparticles (NPs) and their nanocomposites. To achieve antibacterial inactivation under visible light, TiO2 NPs are doped with metal and non-metal elements, modified with carbonaceous nanomaterials, and coupled with other metal oxide semiconductors. Transition metals introduce a localized d-electron state just below the conduction band of TiO2 NPs, thereby narrowing the bandgap and causing a red shift of the optical absorption edge into the visible region. Silver nanoparticles of doped TiO2 NPs experience surface plasmon resonance under visible light excitation, leading to the injection of hot electrons into the conduction band of TiO2 NPs to generate reactive oxygen species (ROS) for bacterial killing. The modification of TiO2 NPs with carbon nanotubes and graphene sheets also achieve the efficient creation of ROS under visible light irradiation. Furthermore, titanium-based alloy implants in orthopedics with enhanced antibacterial activity and biocompatibility can be achieved by forming a surface layer of Ag-doped titania nanotubes. By incorporating TiO2 NPs and Cu-doped TiO2 NPs into chitosan or the textile matrix, the resulting polymer nanocomposites exhibit excellent antimicrobial properties that can have applications as fruit/food wrapping films, self-cleaning fabrics, medical scaffolds and wound dressings. Considering the possible use of visible-light active TiO2 nanomaterials for various applications, their toxicity impact on the environment and public health is also addressed.

Silver-Copper Oxide Heteronanostructures for the Plasmonic-Enhanced Photocatalytic Oxidation of N-Hexane in the Visible-NIR Range

Volatile organic compounds (VOCs) are recognized as hazardous contributors to air pollution, precursors of multiple secondary byproducts, troposphere aerosols, and recognized contributors to respiratory and cancer-related issues in highly populated areas. Moreover, VOCs present in indoor environments represent a challenging issue that need to be addressed due to its increasing presence in nowadays society. Catalytic oxidation by noble metals represents the most effective but costly solution. The use of photocatalytic oxidation has become one of the most explored alternatives given the green and sustainable advantages of using solar light or low-consumption light emitting devices. Herein, we have tried to address the shortcomings of the most studied photocatalytic systems based on titania (TiO₂) with limited response in the UV-range or alternatively the high recombination rates detected in other transition metal-based oxide systems. We have developed a silver-copper oxide heteronanostructure able to combine the plasmonic-enhanced properties of Ag nanostructures with the visible-light driven photoresponse of CuO nanoarchitectures. The entangled Ag-CuO heteronanostructure exhibits a broad absorption towards the visible-near infrared (NIR) range and achieves total photo-oxidation of n-hexane under irradiation with different light-emitting diodes (LEDs) specific wavelengths at temperatures below 180 °C and outperforming its thermal catalytic response or its silver-free CuO illuminated counterpart.

Preparation of Multicycle GO/TiO2 Composite Photocatalyst and Study on Degradation of Methylene Blue Synthetic Wastewater

A series of composite photocatalysts were prepared by using graphene oxide (GO) prepared by modified Hummers method and TiO2 hydrogel prepared by using butyl titanate as raw materials. The composite photocatalyst was characterized through scanning electron microscope（SEM）, x ray diffraction （XRD）, and Raman spectroscopy, and the degradation effect of pure TiO2 and composite photocatalyst on methylene blue (MB) dye wastewater under different experimental conditions was studied. The results showed that TiO2 in composite photocatalyst was mainly anatase phase and its photocatalytic activity was better than pure TiO2. When the addition of GO reached 15 wt%, the photocatalytic activity was the highest. When 200 mg composite photocatalyst was added to 200 mL synthetic wastewater with a concentration of 10 mg/L and an initial pH of about 8, the degradation rate could reach 95.8% after 2.5 h. It is presumed that the photogenerated charges of GO/TiO2 composite photocatalyst may directly destroy the luminescent groups in the MB molecule and thus decolorize the wastewater, and no other new luminescent groups are generated during the treatment.

Special Issue: Application of Photoactive Nanomaterials in Degradation of Pollutants

Photoactive nanomaterials are receiving increasing attention due to their potential application to light-driven degradation of water and gas-phase pollutants. However, to exploit the strong potential of photoactive materials and access their properties require a fine tuning of their size/shape dependent chemical-physical properties and on the ability to integrate them in photo-reactors or to deposit them on large surfaces. Therefore, the synthetic approach, as well as post-synthesis manipulation could strongly affect the final photocatalytic properties of nanomaterials. The potential application of photoactive nanomaterials in the environmental field includes the abatement of organic pollutant in water, water disinfection, and abatement of gas-phase pollutants in outdoor and indoor applications.

A Review on Catalytic Nanomaterials for Volatile Organic Compounds VOC Removal and Their Applications for Healthy Buildings

In order to improve the indoor air quality, volatile organic compounds (VOCs) can be removed via an efficient approach by using catalysts. This review proposed a comprehensive summary of various nanomaterials for thermal/photo-catalytic removal of VOCs. These representative materials are mainly categorized as carbon-based and metallic oxides materials, and their morphologies, synthesis techniques, and performances have been explained in detail. To improve the indoor and outdoor air quality, the catalytic nanomaterials can be utilized for emerging building applications such as VOC-reduction coatings, paints, air filters, and construction materials. Due to the characteristics of low cost, non-toxic and high chemical stability, metallic oxides such as TiO₂ and ZnO have been widely investigated for decades and dominate the application market of VOC-removal catalyst in buildings. Since other catalysts also showed brilliant performance and have been theoretically researched, they can be potential candidates for applications in future healthy buildings. This review will contribute to further knowledge and greater potential applications of promising VOC-reducing catalytic nanomaterials on healthier buildings for a better indoor and outdoor environment well-being.

Scalable Synthesis of Mesoporous TiO2 for Environmental Photocatalytic Applications

Increasing environmental concern, related to pollution and clean energy demand, have urged the development of new smart solutions profiting from nanotechnology, including the renowned nanomaterial-assisted photocatalytic degradation of pollutants. In this framework, increasing efforts are devoted to the development of TiO2-based nanomaterials with improved photocatalytic activity. A plethora of synthesis routes to obtain high quality TiO2-based nanomaterials is currently available. Nonetheless, large-scale production and the application of nanosized TiO2 is still hampered by technological issues and the high cost related to the capability to obtain TiO2 nanoparticles with high reaction yield and adequate morphological and structural control. The present review aims at providing a selection of synthetic approaches suitable for large-scale production of mesoporous TiO2-based photocatalysts due to its unique features including high specific surface area, improved ultraviolet (UV) radiation absorption, high density of surface hydroxyl groups, and significant ability for further surface functionalization The overviewed synthetic strategies have been selected and classified according to the following criteria (i) high reaction yield, (ii) reliable synthesis scale-up and (iii) adequate control over morphological, structural and textural features. Potential environmental applications of such nanostructures including water remediation and air purification are also discussed.

Scalable Synthesis of Mesoporous TiO2 for Environmental Photocatalytic Applications

Increasing environmental concern, related to pollution and clean energy demand, have urged the development of new smart solutions profiting from nanotechnology, including the renowned nanomaterial-assisted photocatalytic degradation of pollutants. In this framework, increasing efforts are devoted to the development of TiO2-based nanomaterials with improved photocatalytic activity. A plethora of synthesis routes to obtain high quality TiO2-based nanomaterials is currently available. Nonetheless, large-scale production and the application of nanosized TiO2 is still hampered by technological issues and the high cost related to the capability to obtain TiO2 nanoparticles with high reaction yield and adequate morphological and structural control. The present review aims at providing a selection of synthetic approaches suitable for large-scale production of mesoporous TiO2-based photocatalysts due to its unique features including high specific surface area, improved ultraviolet (UV) radiation absorption, high density of surface hydroxyl groups, and significant ability for further surface functionalization The overviewed synthetic strategies have been selected and classified according to the following criteria (i) high reaction yield, (ii) reliable synthesis scale-up and (iii) adequate control over morphological, structural and textural features. Potential environmental applications of such nanostructures including water remediation and air purification are also discussed.

Preparation of Visible Light Photocatalytic Graphene Embedded Rutile Titanium(IV) Oxide Composite Nanowires and Enhanced NOx Removal

The quest for developing highly efficient TiO2-based photocatalysts is continuing and, in particular, evolving a new strategy is an important aspect in this regard. In general, much effort has been devoted to the anatase TiO2 modifications, despite there being only a few recent studies on rutile TiO2 (rTiO2). To the best of our knowledge, studies on the preparation and characterization of the photocatalysts based on the intentional inclusion of graphene (G) into rTiO2 nanostructures have not been reported yet. Herein, we develop a new type of TiO2-based photocatalyst comprising of G included pure rTiO2 nanowire (abbreviated as rTiO2(G) NW) with enhanced visible light absorption capability. To prepare rTiO2(G) NW, the G incorporated titanate electrospun fibers were obtained by electrospinning and subsequently heat treated at various temperatures (500 to 800 °C). Electrospinning conditions were optimized for producing good quality rTiO2(G) NW. The rTiO2(G) NW and their corresponding samples were characterized by appropriate techniques such as X-ray diffraction (XRD), scanning electron microscopy, high-resolution transmission electron microscopy and UV-vis diffuse reflectance spectroscopy to ascertain their material characteristics. XRD results show that the lattice strain occurs upon inclusion of G. We present here the first observation of an apparent bandgap lowering because of the G inclusion into TiO2 NW. While anatase TiO2 NW exhibited poor visible light photocatalysis towards NOx removal, the rTiO2(G) NW photocatalyst witnessed a significantly enhanced (~67%) photocatalytic performance as compared to anatase TiO2(G) NW. We concluded that the inclusion of G into rTiO2 nanostructures enhances the visible light photoactivity. A plausible mechanism for photocatalysis is suggested.

A reduced graphene oxide-titanium dioxide nanocomposite based electrochemical aptasensor for rapid and sensitive detection of Salmonella enterica

Recent foodborne outbreaks in multiple locations necessitate the continuous development of highly sensitive and specific biosensors that offer rapid detection of foodborne biological hazards. This work focuses on the development of a reduced graphene oxide‑titanium dioxide (rGO-TiO₂) nanocomposite based aptasensor to detect Salmonella enterica serovar Typhimurium. A label-free aptamer was immobilized on a rGO-TiO₂ nanocomposite matrix through electrostatic interactions. The changes in electrical conductivity on the electrode surface were evaluated using electroanalytical methods. DNA aptamer adsorbed on the rGO-TiO₂ surface bound to the bacterial cells at the electrode interface causing a physical barrier inhibiting the electron transfer. This interaction decreased the DPV signal of the electrode proportional to decreasing concentrations of the bacterial cells. The optimized aptasensor exhibited high sensitivity with a wide detection range (10⁸ to 10¹ cfu mL^-1), a low detection limit of 10¹ cfu mL^-1 and good selectivity for Salmonella bacteria. This rGO-TiO₂ aptasensor is an excellent biosensing platform that offers a reliable, rapid and sensitive alternative for foodborne pathogen detection.

Reduced graphene–tungsten trioxide-based hybrid materials with peroxidase-like activity

Hybrid material with enzyme-like function.

Mechanisms of the Antibacterial Effects of TiO2–FeOx under Solar or Visible Light: Schottky Barriers versus Surface Plasmon Resonance

This study reports the significant mechanistic difference between binary-oxide antibacterial films with the same composition but different microstructures. Binary TiO2-FeOx films were found to present a faster bacterial inactivation kinetics under visible light irradiation than each single oxide acting independently. The interaction between the film active surface species and the bacteria within the disinfection period was followed by X-ray photoelectron spectroscopy (XPS) and provided the evidence for a redox catalysis taking place during the bacterial inactivation time. The optical and surface properties of the films were evaluated by appropriate surface analytical methods. A differential mechanism is suggested for each specific microstructure inducing bacterial inactivation. The surface FeOx plasmon resonance transferred electrons into the conduction band of TiO2 because of the Schottky barrier after Fermi level equilibration of the two components. An electric field at the interface between TiO2 and FeOx, favors the separation of the photo-generated charges leading to a faster bacterial inactivation by TiO2–FeOx compared to the bacterial inactivation kinetics by each of the single oxides.

Preparation Technique and Properties of Nano-TiO2 Photocatalytic Coatings for Asphalt Pavement

According to the characteristics of asphalt pavement, a kind of nano-TiO2 photocatalytic coating was prepared by using the emulsified asphalt as the carrier. All of its properties met the technical requirements. An exhaust gas degradation test device and its test steps were developed. The evaluation indexes, cumulative degradation rate, and degradation efficiency, were put forward. From the two aspects of the nano-TiO2 content in photocatalytic coatings and the spraying amount of photocatalytic coatings in the surface of slabs (300 mm × 300 mm), the exhaust gas degradation effects, the performances of skid resistance, and the water permeability of asphalt mixture were analyzed. The test results showed that the cumulative degradation rate of exhaust gas was better when nano-TiO2 content was increased in the range of 0–8% and the spraying amount was changed in the range of 0–333.3 g/m2. In practical engineering applications, the anti-skid performance of asphalt pavement can be satisfied when the spraying amount of photocatalytic coating was limited to under 550 g/m2. The spraying amount of nano-TiO2 photocatalytic coating had little effect on the water permeability of the asphalt mixture. Therefore, 8% nano-TiO2 content in the coating and a 400 g/m2 spraying amount were finally recommended based on the photocatalytic properties, as well as for economic reasons.

Rational Construction of LaFeO3 Perovskite Nanoparticle-Modified TiO2 Nanotube Arrays for Visible-Light Driven Photocatalytic Activity

LaFeO3 nanoparticle-modified TiO2 nanotube arrays were fabricated through facile hydrothermal growth. The absorption edge of LaFeO3 nanoparticle-modified TiO2 nanotube arrays displaying a red shift to ~540 nm was indicated by the results of diffuse reflectance spectroscopy (DRS) when compared to TiO2 nanotube arrays, which means that the sample of LaFeO3 nanoparticle-modified TiO2 nanotube arrays had enhanced visible light response. Photoluminescence (PL) spectra showed that the LaFeO3 nanoparticle-modified TiO2 nanotube arrays efficiently separated the photoinduced electron–hole pairs and effectively prolonged the endurance of photogenerated carriers. The results of methylene blue (MB) degeneration under simulated visible light illumination showed that the photocatalytic activity of LaFeO3 nanoparticle-modified TiO2 nanotube arrays is obviously increased. LaFeO3 nanoparticle-modified TiO2 nanotube arrays with 12 h hydrothermal reaction time showed the highest degradation rate with a 2-fold enhancement compared with that of pristine TiO2 nanotube arrays.

Recent advances in syntheses, properties and applications of TiO2 nanostructures

TiO2 is a compound of great importance due to its remarkable catalytic and distinctive semiconducting properties. It is also a chemically stable, non-toxic and biocompatible material. Nano TiO2 is strong oxidizing agent with a large surface area and, hence, high photo-catalytic activities. With low production cost and a high dielectric constant, it is an inexpensive material. It can be prepared by diverse procedures such as solution and gas phase procedures. Nowadays, TiO2 is being used frequently for photo degradation of organic molecules and water splitting for hydrogen generation. Most important applications include purification, disinfection of waste water, self-cleaning coatings for buildings in urban areas and the production of the green currency of energy (hydrogen) by splitting water. The review describes the advances in the syntheses, properties and applications of TiO2 nano structures. Besides, efforts are also made to discuss the working mechanism and future challenges and perspectives.

Photocatalytic Activity of TiO2/AuNRs–SiO2 Nanocomposites Applied to Building Materials

In this work, the self-cleaning and photocatalytic properties of mesoporous TiO2/AuNRs-SiO2 composites (namely UCA–TiO2Au) prepared by a simple and low-cost technique were investigated toward application in building materials. Mesoporous photocatalytic nanocomposites coating the surface of stone and other building materials are a very promising approach to address relevant questions connected with the increasing atmospheric pollution. We tested three types of preformed TiO2/AuNRs nanostructures in order to evaluate the effect of AuNRs on the photocatalytic activity of resulting coatings deposited on the surface of a popular building limestone. The resulting nanocomposites provide crack-free surface coatings on limestone, effective adhesion, improve the stone mechanical properties and impart hydrophobic and self-cleaning properties. Photocatalytic characterization involved the degradation of a target compound (Methylene blue; MB) under direct exposure to simulated solar light using TiO2 P25 Evonik (TiO2 P25) as a reference material. Moreover, these coatings upon irradiation by simulated solar light were successfully employed for the photocatalytic oxidation of carbon soot. The experimental results revealed that UCA–TiO2Au samples are the best performing coating in both MB bleaching and soot degradation.

Band Gap Implications on Nano-TiO₂ Surface Modification with Ascorbic Acid for Visible Light-Active Polypropylene Coated Photocatalyst

The effect of surface modification using ascorbic acid as a surface modifier of nano-TiO₂ heterogeneous photocatalyst was studied. The preparation of supported photocatalyst was made by a specific paste containing ascorbic acid modified TiO₂ nanoparticles used to cover Polypropylene as a support material. The obtained heterogeneous photocatalyst was thoroughly characterized (scanning electron microscope (SEM), RAMAN, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and Diffuse Reflectance Spectra (DRS) and successfully applied in the visible light photodegradation of Alizarin Red S in water solutions. In particular, this new supported TiO₂ photocatalyst showed a change in the adsorption mechanism of dye with respect to that of only TiO₂ due to the surface properties. In addition, an improvement of photocatalytic performances in the visible light photodegration was obtained, showing a strict correlation between efficiency and energy band gap values, evidencing the favorable surface modification of TiO₂ nanoparticles.

Stability and Synergistic Effect of Polyaniline/TiO₂ Photocatalysts in Degradation of Azo Dye in Wastewater

The polyaniline/TiO₂ (PANI/TiO₂) composite photocatalysts were prepared by the in situ chemical oxidation of aniline (An) in the presence of TiO₂ particles. For this purpose, photocatalysts with different amounts of PANI polymer were prepared and analysed. Fourier-transform infrared (FT-IR) spectroscopy and thermogravimetric (TG) analysis indicated successful synthesis of the PANI polymer and its conductivity was also determined. The micrographs of field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) were used to explain the impact of the aniline amount on the aggregation process during the synthesis of the composites. The smallest size of aggregates was obtained for the photocatalysts with 15% of PANI (15PANI/TiO₂) due to the formation of homogenous PANI. The photocatalytic activity of studied PANI/TiO₂ photocatalysts was validated by monitoring the discoloration and mineralization of Reactive Red azo dye (RR45) in wastewater. The 15PANI/TiO₂ sample presented the highest photocatalytic efficiency under ultraviolet A (UVA) irradiation, in comparison to pure TiO₂. This was explained by the formation of uniformly dispersed PANI on the TiO₂ particles, which was responsible for the synergistic PANI-TiO₂ effect.

Development and Biocompatibility Evaluation of Photocatalytic TiO₂/Reduced Graphene Oxide-Based Nanoparticles Designed for Self-Cleaning Purposes

Graphene is widely used in nanotechnologies to amplify the photocatalytic activity of TiO₂, but the development of TiO₂/graphene composites imposes the assessment of their risk to human and environmental health. Therefore, reduced graphene oxide was decorated with two types of TiO₂ particles co-doped with 1% iron and nitrogen, one of them being obtained by a simultaneous precipitation of Ti3+ and Fe3+ ions to achieve their uniform distribution, and the other one after a sequential precipitation of these two cations for a higher concentration of iron on the surface. Physico-chemical characterization, photocatalytic efficiency evaluation, antimicrobial analysis and biocompatibility assessment were performed for these TiO₂-based composites. The best photocatalytic efficiency was found for the sample with iron atoms localized at the sample surface. A very good anti-inhibitory activity was obtained for both samples against biofilms of Gram-positive and Gram-negative strains. Exposure of human skin and lung fibroblasts to photocatalysts did not significantly affect cell viability, but analysis of oxidative stress showed increased levels of carbonyl groups and advanced oxidation protein products for both cell lines after 48 h of incubation. Our findings are of major importance by providing useful knowledge for future photocatalytic self-cleaning and biomedical applications of graphene-based materials.

Heterogeneous Catalysis for Environmental Remediation

The intensive human activities in chemical industry and environmental purification urge the development of advanced protocols for green production and waste management. [...]