Manganese and Graphene Included Titanium Dioxide Composite Nanowires: Fabrication, Characterization and Enhanced Photocatalytic Activities

Using visible light to activate antiviral and antimicrobial properties of TiO2 nanoparticles in paints and coatings: focus on new developments for frequent-touch surfaces in hospitals

The COVID-19 pandemic refocused scientists the world over to produce technologies that will be able to prevent the spread of such diseases in the future. One area that deservedly receives much attention is the disinfection of health facilities like hospitals, public areas like bathrooms and train stations, and cleaning areas in the food industry. Microorganisms and viruses can attach to and survive on surfaces for a long time in most cases, increasing the risk for infection. One of the most attractive disinfection methods is paints and coatings containing nanoparticles that act as photocatalysts. Of these, titanium dioxide is appealing due to its low cost and photoreactivity. However, on its own, it can only be activated under high-energy UV light due to the high band gap and fast recombination of photogenerated species. The ideal material or coating should be activated under artificial light conditions to impact indoor areas, especially considering wall paints or frequent-touch areas like door handles and elevator buttons. By introducing dopants to TiO₂ NPs, the bandgap can be lowered to a state of visible-light photocatalysis occurring. Naturally, many researchers are exploring this property now. This review article highlights the most recent advancements and research on visible-light activation of TiO₂-doped NPs in coatings and paints. The progress in fighting air pollution and personal protective equipment is also briefly discussed.

Graphical Abstract

Indoor visible-light photocatalytic activation of reactive oxygen species (ROS) over TiO₂ nanoparticles in paint to kill bacteria and coat frequently touched surfaces in the medical and food industries.

Synthesis Control of Charge Separation at Anatase TiO2 Thin Films Studied by Transient Surface Photovoltage Spectroscopy

For the efficient photocatalytic oxidation of organic pollutants at surfaces of semiconductors, photogenerated holes shall be separated toward the surface and transferred to reactive surface sites, whereas the transfer of photogenerated electrons toward the surface shall be minimized. In this Research Article, the identification of suitable synthesis control of charge separation combined with an in-depth understanding of charge kinetics and trapping passivation mechanisms at the related surfaces can provide tremendous opportunities for boosting the photocatalytic performance. In this work, a comprehensive transient surface photovoltage spectroscopy study of charge separation at anatase TiO₂ thin films, synthesized by ultrasonic spray pyrolysis from titanium(IV) isopropoxide (TTIP)-acetylacetone (AcacH) based precursor is reported. By varying the amount of AcacH in the precursor solution, an experimental approach of synthesis control of the charge transfer toward TiO₂ surface is provided for the first time. An increased amount of AcacH in the precursor promotes transition from preferential fast electron to preferential fast hole transfer toward anatase surface, correlating with a strong increase of the photocatalytic decomposition rate of organic pollutants. Suitable mechanisms of AcacH-induced passivation of electron traps at TiO₂ surfaces are analyzed, providing a new degree of freedom for tailoring the properties of photocatalytic systems.

High-Dispersed V2O5-CuOX Nanoparticles on h-BN in NH3-SCR and NH3-SCO Performance

Typically, to meet emission regulations, the selective catalytic reduction of NO_X with NH₃ (NH₃-SCR) technology cause NH₃ emissions owing to high NH₃/NO_X ratios to meet emission regulations. In this study, V-Cu/BN-Ti was used to remove residual NO_X and NH₃. Catalysts were evaluated for selective catalytic oxidation of NH₃ (NH₃-SCO) in the NH₃-SCR reaction at 200–300 °C. The addition of vanadium and copper increased the number of Brønsted and Lewis acid sites available for the reaction by increasing the ratio of V⁵⁺ and forming Cu⁺ species, respectively. Furthermore, h-BN was dispersed in the catalyst to improve the content of vanadium and copper species on the surface. NH₃ and NO_X conversion were 98% and 91% at 260 °C, respectively. Consequently, slipped NH₃ (NH₃-Slip) emitted only 2% of the injected ammonia. Under SO₂ conditions, based on the NH₃ oxidation reaction, catalytic deactivation was improved by addition of h-BN. This study suggests that h-BN is a potential catalyst that can help remove residual NO_X and meet NH₃ emission regulations when placed at the bottom of the SCR catalyst layer in coal-fired power plants.

In Situ Construction of Black Titanium Oxide with a Multilevel Structure on a Titanium Alloy for Photothermal Antibacterial Therapy

Postsurgical infection of orthopedic fixation materials is considered to be the main cause of fixation failure. To address the problem, clinical treatment often relies on long-term antibiotics, secondary surgery, and so forth, which cause pain and suffering to patients. Constructing a light-responsive surface structure on the implant has attracted widespread attention for the management of postsurgical infections because of its noninvasiveness and controllability. Nevertheless, the application of light-responsive structures on implants is still limited by their unsafety and instability. In this work, a black titanium oxide layer with a multilevel structure and lattice defects was in situ constructed on a titanium alloy through pulsed laser ablation treatment. Under the synergistic effect of the multilevel structure and crystal defects, the surface of the titanium alloy exhibited good near-infrared light-responsive photothermal ability. The black titanium oxide multilevel structure reached high antibacterial efficiencies of about 99.37 and 99.29% against Staphylococcus aureus and Escherichia coli under 10 min near-infrared light irradiation. Furthermore, the black titanium oxide layer possessed similar biocompatibility compared with the titanium alloy. This near-infrared light-responsive photothermal therapy based on the construction of a multilevel structure and introduction of lattice defects provides an effective strategy for clinical postsurgical infections of orthopedic fixation.

A post-deposition annealing approach for organic residues control in TiO2 and its impact on Sb2Se3/TiO2 device performance

We report a systematic investigation on the influence of the two-step post-deposition treatments (PDTs) on TiO2 buffer layers deposited by ultrasonic spray pyrolysis (USP) for emerging Sb2Se3 photovoltaics. Air annealing...

Highly efficient TiO2-supported Co-Cu catalysts for conversion of glycerol to 1,2-propanediol

Glycerol is a low-cost byproduct of the biodiesel manufacturing process, which can be used to synthesize various value-added chemicals. Among them, 1,2-propanediol (1,2-PDO) is of great interest because it can be used as an intermediate and additive in many applications. This work investigated the hydrogenolysis of glycerol to 1,2-PDO over Co–Cu bimetallic catalysts supported on TiO₂ (denoted as CoCu/TiO₂) in aqueous media. The catalysts were prepared using the co-impregnation method and their physicochemical properties were characterized using several techniques. The addition of appropriate Cu increased the glycerol conversion and the 1,2-PDO yield. The highest 1,2-PDO yield was achieved over a 15Co0.5Cu/TiO₂ catalyst at 69.5% (glycerol conversion of 95.2% and 1,2-PDO selectivity of 73.0%). In the study on the effects of operating conditions, increasing the reaction temperature, initial pressure, and reaction time increased the glycerol conversion but decreased the selectivity to 1,2-PDO due to the degradation of formed 1,2-PDO to lower alcohols (1-propanol and 2-propanol). The reaction conditions to obtain the maximum 1,2-PDO yield were a catalyst-to-glycerol ratio of 0.028, a reaction temperature of 250 °C, an initial H₂ pressure of 4 MPa, and a reaction time of 4 h.

Facile Use of Silver Nanoparticles-Loaded Alumina/Silica in Nanofluid Formulations for Enhanced Catalytic Performance toward 4-Nitrophenol Reduction

The introduction of toxic chemicals into the environment can result in water pollution leading to the degradation of biodiversity as well as human health. This study presents a new approach of using metal oxides (Al₂O₃ and SiO₂) modified with a plasmonic metal (silver, Ag) nanoparticles (NPs)-based nanofluid (NF) formulation for environmental remediation purposes. Firstly, we prepared the Al₂O₃ and SiO₂ NFs of different concentrations (0.2 to 2.0 weight %) by ultrasonic-assisted dispersion of Al₂O₃ and SiO₂ NPs with water as the base fluid. The thermo-physical (viscosity, activation energy, and thermal conductivity), electrical (AC conductivity and dielectric constant) and physical (ultrasonic velocity, density, refractive index) and stability characteristics were comparatively evaluated. The Al₂O₃ and SiO₂ NPs were then catalytically activated by loading silver NPs to obtain Al₂O₃/SiO₂@Ag composite NPs. The catalytic reduction of 4-nitrophenol (4-NP) with Al₂O₃/SiO₂@Ag based NFs was followed. The catalytic efficiency of Al₂O₃@Ag NF and SiO₂@Ag NF, for the 4-NP catalysis, is compared. Based on the catalytic rate constant evaluation, the catalytic reduction efficiency for 4-NP is found to be superior for 2% weight Al₂O₃@Ag NF (92.9 × 10⁻³ s⁻¹) as compared to the SiO₂@Ag NF (29.3 × 10⁻³ s⁻¹). Importantly, the enhanced catalytic efficiency of 2% weight Al₂O₃@Ag NF for 4-NP removal is much higher than other metal NPs based catalysts reported in the literature, signifying the importance of NF formulation-based catalysis.

Polyethylene Glycol Coated Magnetic Nanoparticles: Hybrid Nanofluid Formulation, Properties and Drug Delivery Prospects

Magnetic nanoparticles (MNPs) are widely used materials for biomedical applications owing to their intriguing chemical, biological and magnetic properties. The evolution of MNP based biomedical applications (such as hyperthermia treatment and drug delivery) could be advanced using magnetic nanofluids (MNFs) designed with a biocompatible surface coating strategy. This study presents the first report on the drug loading/release capability of MNF formulated with methoxy polyethylene glycol (referred to as PEG) coated MNP in aqueous (phosphate buffer) fluid. We have selected MNPs (NiFe₂O4, CoFe₂O4 and Fe₃O₄) coated with PEG for MNF formulation and evaluated the loading/release efficacy of doxorubicin (DOX), an anticancer drug. We have presented in detail the drug loading capacity and the time-dependent cumulative drug release of DOX from PEG-coated MNPs based MNFs. Specifically, we have selected three different MNPs (NiFe₂O₄, CoFe₂O₄ and Fe₃O₄) coated with PEG for the MNFs and compared their variance in the loading/release efficacy of DOX, through experimental results fitting into mathematical models. DOX loading takes the order in the MNFs as CoFe₂O₄ > NiFe₂O₄ > Fe₃O₄. Various drug release models were suggested and evaluated for the individual MNP based NFs. While the non-Fickian diffusion (anomalous) model fits for DOX release from PEG coated CoFe₂O₄, PEG coated NiFe₂O₄ NF follows zero-order kinetics with a slow drug release rate of 1.33% of DOX per minute. On the other hand, PEG coated NiFe₂O₄ follows zero-order DOX release. Besides, several thermophysical properties and magnetic susceptibility of the MNFs of different concentrations have been studied by dispersing the MNPs (NiFe₂O₄, CoFe₂O₄ and Fe₃O₄) in the base fluid at 300 K under ultrasonication. This report on the DOX loading/release capability of MNF will set a new paradigm in view that MNF can resolve problems related to the self-heating of drug carriers during mild laser treatment with its thermal conducting properties.

Efficient Photocatalytic Degradation of Gaseous Benzene and Toluene over Novel Hybrid PIL@TiO2/m-GO Composites

In this work, the PIL (poly ionic liquid)@TiO2 composite was designed with two polymerized ionic liquid concentrations (low and high) and evaluated for pollutant degradation activity for benzene and toluene. The results showed that PIL (low)@TiO2 composite was more active than PIL (high)@TiO2 composites. The photodegradation rate of benzene and toluene pollutants by PIL (low)@TiO2 and PIL (high)@TiO2 composites was obtained as 86% and 74%, and 59% and 46%, respectively, under optimized conditions. The bandgap of TiO2 was markedly lowered (3.2 eV to 2.2 eV) due to the formation of PIL (low)@TiO2 composite. Besides, graphene oxide (GO) was used to grow the nano-photocatalysts’ specific surface area. The as-synthesized PIL (low)@TiO2@GO composite showed higher efficiency for benzene and toluene degradation which corresponds to 91% and 83%, respectively. The resultant novel hybrid photocatalyst (PIL@TiO2/m-GO) was prepared and appropriately characterized for their microstructural, morphology, and catalytic properties. Among the studied photocatalysts, the PIL (low)@TiO2@m-GO composite exhibits the highest activity in the degradation of benzene (97%) and toluene (97%). The ultimate bandgap of the composite reached 2.1 eV. Our results showed that the as-prepared composites hold an essential role for future considerations over organic pollutants.

Cost-Effective Production of TiO2 with 90-Fold Enhanced Photocatalytic Activity Via Facile Sequential Calcination and Ball Milling Post-Treatment Strategy

Titanium dioxide (TiO₂), the golden standard among the photocatalysts, exhibits a varying level of photocatalytic activities (PCA) amongst the synthetically prepared and commercially available products. For commercial applications, superior photoactivity and cost-effectiveness are the two main factors to be reckoned with. This study presents the development of simple, cost-effective post-treatment processes for a less costly TiO₂ to significantly enhance the PCA to the level of expensive commercial TiO₂ having demonstrated superior photoactivities. We have utilized sequential calcination and ball milling (BM) post-treatment processes on a less-costlier KA100 TiO₂ and demonstrated multi-fold (nearly 90 times) enhancement in PCA. The post-treated KA100 samples along with reference commercial samples (P25, NP400, and ST01) were well-characterized by appropriate instrumentation and evaluated for the PCA considering acetaldehyde photodegradation as the model reaction. Lattice parameters, phase composition, crystallite size, surface functionalities, titanium, and oxygen electronic environments were evaluated. Among post-treated KA100, the sample that is subjected to sequential 700 °C calcination and BM (KA7-BM) processes exhibited 90-fold PCA enhancement over pristine KA100 and the PCA-like commercial NP400 (pure anatase-based TiO₂). Based on our results, we attribute the superior PCA for KA7-BM due to the smaller crystallite size, the co-existence of mixed anatase-srilankite-rutile phases, and the consequent multiphase heterojunction formation, higher surface area, lattice disorder/strain generation, and surface oxygen environment. The present work demonstrates a feasible potential for the developed post-treatment strategy towards commercial prospects.

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.

Titanium Dioxide-Coated Zinc Oxide Nanorods as an Efficient Photoelectrode in Dye-Sensitized Solar Cells

Well-arrayed zinc oxide nanorods applied as photoelectrodes for dye-sensitized solar cells were synthesized on an aluminum-doped zinc oxide substrate by the multi-annealing method. In order to improve the chemical stability and surface-to-volume ratio of photoanodes in dye-sensitized solar cells, the synthesized zinc oxide nanorods were coated with pure anatase phase titanium dioxide film using a novel mist chemical vapor deposition method. The effects of the titanium dioxide film on the morphological, structural, optical, and photovoltaic properties of zinc oxide–titanium dioxide core–shell nanorods were investigated. It was found that the diameter and surface-to-volume ratio of zinc oxide nanorods were significantly increased by coating them with titanium dioxide thin film. The power conversion efficiency of dye-sensitized solar cells was improved from 1.31% to 2.68% by coating titanium dioxide film onto the surface of zinc oxide nanorods.

Synergistic Design of Anatase–Rutile TiO2 Nanostructured Heterophase Junctions toward Efficient Photoelectrochemical Water Oxidation

Synergistically designing porous nanostructures and appropriate band alignment for TiO2 heterophase junctions is key to efficient charge transfer, which is crucial in enhancing photoelectrochemical (PEC) water splitting for hydrogen production. Here, we investigate the efficiency of PEC water oxidation in anatase–rutile TiO2 nanostructured heterophase junctions that present the type-II band alignment. We specifically prove the importance of a phase alignment in heterophase junction for effective charge separation. The TiO2 heterophase junctions were prepared by transferring TiO2 nanotube (TNT) arrays onto FTO substrate with the help of a TiO2 nanoparticle (TNP) glue layer. The PEC characterization reveals that the rutile (R)-TNT/anatase (A)-TNP heterophase junction has a higher photocurrent density than those of A-TNT/R-TNP junction and anatase or rutile single phase, corresponding to twofold enhanced efficiency. This type-II band alignment of R-TNT/A-TNP for water oxidation, in which photogenerated electrons (holes) will flow from rutile (anatase) to anatase (rutile), enables to facilitate efficient electron-hole separation as well as lower the effective bandgap of heterophase junctions. This work provides insight into the functional role of heterophase junction for boosting the PEC performances of TiO2 nanostructures.