High-fraction brookite films from amorphous precursors

Removal of lead ions from aqueous solution by modified nanocellulose

Heavy metals significantly impact the environment due to their non-biodegradable, toxic, and carcinogenic behaviors. Lead contaminants impose severe health impacts on humans and the water environment. Therefore, eco-friendly and efficient lead ion removal practices such as nanotechnology are an urgent requirement for the abatement of lead pollution. In the present study, nanocellulose was synthesized from the cotton straw residue using chemical methods and modified with titanium dioxide to form a nanocomposite. The nanocomposite synthesized was characterized by using FTIR, XRD, FESEM, and BET. FTIR results noticed peaks at 1648.43 and 1443.57 cm-1 for cellulose and Ti-O-Ti bonding at 505.02 cm-1. The nanocomposite was noticed to be disordered and irregular in shape. The nanocomposite has particle sizes of 83 nm. The nanocomposite crystalline particle had 65% anatase and 32% rutile phases observed from the XRD result. BET results show that the surface area of nanocellulose increases after surface modification from 25.692 to 42.510 m2/g. The adsorption capacity of the nanocomposite was 0.552 mg/g was noticed. The Elovich kinetic and Baudu isotherms are the best-fitted models for lead ion adsorption. Thermodynamic parameters resulted in Gibbs free energy decreasing with temperature. This study revealed that modified cellulosic adsorbents efficiently absorbed lead ions derived from cotton straws.

Brookite TiO2 as an active photocatalyst for photoconversion of plastic wastes to acetic acid and simultaneous hydrogen production: Comparison with anatase and rutile

Photoreforming is a clean photocatalytic technology for simultaneous plastic waste degradation and hydrogen fuel production, but there are still limited active and stable catalysts for this process. This work introduces the brookite polymorph of TiO2 as an active photocatalyst for photoreforming with an activity higher than anatase and rutile polymorphs for both hydrogen production and plastic degradation. Commercial brookite successfully converts polyethylene terephthalate (PET) plastic to acetic acid under light. The high activity of brookite is attributed to good charge separation, slow decay and moderate electron trap energy, which lead to a higher generation of hydrogen and hydroxyl radicals and accordingly enhanced photo-oxidation of PET plastic. These results introduce brookite as a stable and active catalyst for the photoconversion of water contaminated with microplastics to value-added organic compounds and hydrogen.

Enhancing Photocatalytic Properties of TiO2 Photocatalyst and Heterojunctions: A Comprehensive Review of the Impact of Biphasic Systems in Aerogels and Xerogels Synthesis, Methods, and Mechanisms for Environmental Applications

This review provides a detailed exploration of titanium dioxide (TiO2) photocatalysts, emphasizing structural phases, heterophase junctions, and their impact on efficiency. Key points include diverse synthesis methods, with a focus on the sol-gel route and variants like low-temperature hydrothermal synthesis (LTHT). The review delves into the influence of acid-base donors on gelation, dissects crucial drying techniques for TiO2 aerogel or xerogel catalysts, and meticulously examines mechanisms underlying photocatalytic activity. It highlights the role of physicochemical properties in charge diffusion, carrier recombination, and the impact of scavengers in photo-oxidation/reduction. Additionally, TiO2 doping techniques and heterostructures and their potential for enhancing efficiency are briefly discussed, all within the context of environmental applications.

Influence of ozone supply mode and aeration on photocatalytic ozonation of organic pollutants in wastewater using TiO2 and ZnO nanoparticles

Photocatalytic ozonation, which combines the effects of lighting and ozonation, has been shown to enhance the decolorization and degradation of organic pollutants in wastewater. Dye solutions with concentrations of 10 ppm for both methylene blue and methyl orange dyes were used. The influence of ozoneation on the performance of photocatalytic activity of TiO2 and ZnO nanoparticles for the removal of organic dyes from aqueous solutions was investigated. To evaluate their efficacy for the removal of methylene blue and methyl orange dyes from aqueous solutions, the photocatalysts were exposed to UV light for 90 min, with ozone supplied either intermittently or continuously by an SDBD cold plasma reactor. The photocatalysts utilized in this study were characterized using SEM and XRD techniques. The degree of color degradation was determined using UV-Vis spectroscopy. The results demonstrate that TiO2 and ZnO nanoparticles exhibit different degrees of photocatalytic activity for the two dyes. The addition of ozone was found to enhance both the color degradation and mineralization rates of the pollutants, with intermittent ozonation proving more effective than continuous ozonation. The most significant color degradation results were obtained using TiO2 nanoparticles with intermittent ozonation for methylene blue dye (97 %) and ZnO nanoparticles with intermittent ozonation for methyl orange dye (40 %). Overall, this study provides evidence that photocatalytic ozonation represents a promising technique for water treatment.

Effects of Electrical Parameters on Micro-Arc Oxidation Coatings on Pure Titanium

The micro-arc oxidation process was used to apply a ceramic oxide coating on a pure titanium substrate using calcium acetate and sodium dihydrogen phosphate as an electrolyte. The influence of the current frequency and duty ratio on the surface morphology, phase composition, wear behavior, and corrosion resistance were analyzed by employing a scanning electron microscope, X-ray diffractometer, ball-on-disk apparatus, and potentiodynamic polarization, respectively. Analyses of the surface and cross-sectional morphologies revealed that the MAO films prepared via a low current frequency (100 Hz) and a high duty ratio (60%) had a lower porosity and were more compact. The medium (500 Hz) and high (1000 Hz) frequencies at the higher duty ratios presented with better wear resistance. The highest film thickness (11.25 µm) was achieved at 100 Hz and a 20% duty ratio. A negligible current density was observed when the frequency was fixed at 500 Hz and 1000 Hz and the duty cycle was 20%.

Daylight Photoactive TiO2 Sol-Gel Nanoparticles: Sustainable Environmental Contribution

Visible-light-photoactive titania micro- or nanoparticles excel in a wide range of industrial areas, particularly in environmental remediation. The sol-gel methodology is one pivotal technique which has been successfully used to synthesize either crystalline and amorphous TiO₂ micro- and nanoparticles due to its outstanding chemical simplicity and versatility, along with the green chemistry approach. This short review aims to collect and discuss the most recent developments in visible-light-photoactive titania-based nanoparticles in the environmental remediation area. Titania co-doping, titania composite design, and, recently, amorphous networks have been the most used strategies to address this goal. Finally, a prediction regarding the future of these fields is given.

Heterophase Polymorph of TiO2 (Anatase, Rutile, Brookite, TiO2 (B)) for Efficient Photocatalyst: Fabrication and Activity

TiO₂ exists naturally in three crystalline forms: Anatase, rutile, brookite, and TiO₂ (B). These polymorphs exhibit different properties and consequently different photocatalytic performances. This paper aims to clarify the differences between titanium dioxide polymorphs, and the differences in homophase, biphase, and triphase properties in various photocatalytic applications. However, homophase TiO₂ has various disadvantages such as high recombination rates and low adsorption capacity. Meanwhile, TiO₂ heterophase can effectively stimulate electron transfer from one phase to another causing superior photocatalytic performance. Various studies have reported the biphase of polymorph TiO₂ such as anatase/rutile, anatase/brookite, rutile/brookite, and anatase/TiO₂ (B). In addition, this paper also presents the triphase of the TiO₂ polymorph. This review is mainly focused on information regarding the heterophase of the TiO₂ polymorph, fabrication of heterophase synthesis, and its application as a photocatalyst.

Recent Progress on Tailoring the Biomass-Derived Cellulose Hybrid Composite Photocatalysts

Biomass-derived cellulose hybrid composite materials are promising for application in the field of photocatalysis due to their excellent properties. The excellent properties between biomass-derived cellulose and photocatalyst materials was induced by biocompatibility and high hydrophilicity of the cellulose components. Biomass-derived cellulose exhibited huge amount of electron-rich hydroxyl group which could promote superior interaction with the photocatalyst. Hence, the original sources and types of cellulose, synthesizing methods, and fabrication cellulose composites together with applications are reviewed in this paper. Different types of biomasses such as biochar, activated carbon (AC), cellulose, chitosan, and chitin were discussed. Cellulose is categorized as plant cellulose, bacterial cellulose, algae cellulose, and tunicate cellulose. The extraction and purification steps of cellulose were explained in detail. Next, the common photocatalyst nanomaterials including titanium dioxide (TiO₂), zinc oxide (ZnO), graphitic carbon nitride (g-C₃N₄), and graphene, were introduced based on their distinct structures, advantages, and limitations in water treatment applications. The synthesizing method of TiO₂-based photocatalyst includes hydrothermal synthesis, sol-gel synthesis, and chemical vapor deposition synthesis. Different synthesizing methods contribute toward different TiO₂ forms in terms of structural phases and surface morphology. The fabrication and performance of cellulose composite catalysts give readers a better understanding of the incorporation of cellulose in the development of sustainable and robust photocatalysts. The modifications including metal doping, non-metal doping, and metal-organic frameworks (MOFs) showed improvements on the degradation performance of cellulose composite catalysts. The information and evidence on the fabrication techniques of biomass-derived cellulose hybrid photocatalyst and its recent application in the field of water treatment were reviewed thoroughly in this review paper.

Metal and metal oxide-based antiviral nanoparticles: Properties, mechanisms of action, and applications

Certain types of metal-based nanoparticles are effective antiviral agents when used in their original form ("bare") or after their surfaces have been functionalized ("modified"), including those comprised of metals (e.g., silver) and metal oxides (e.g., zinc oxide, titanium dioxide, or iron dioxide). These nanoparticles can be prepared with different sizes, morphologies, surface chemistries, and charges, which leads to different antiviral activities. They can be used as aqueous dispersions or incorporated into composite materials, such as coatings or packaging materials. In this review, we provide an overview of the design, preparation, and characterization of metal-based nanoparticles. We then discuss their potential mechanisms of action against various kinds of viruses. Finally, the applications of some of the most common metal and metal oxide nanoparticles are discussed, including those fabricated from silver, zinc oxide, iron oxide, and titanium dioxide. In general, the major antiviral mechanisms of metal and metal oxide nanoparticles have been observed to be 1) attachment of nanoparticles to surface moieties of viral particles like spike glycoproteins, that disrupt viral attachment and uncoating in host cells; 2) generation of reactive oxygen species (ROS) that denature viral macromolecules such as nucleic acids, capsid proteins, and/or lipid envelopes; and 3) inactivation of viral glycoproteins by the disruption of the disulfide bonds of viral proteins. Several physicochemical properties of metal and metal oxide nanoparticles including size, shape, zeta potential, stability in physiological conditions, surface modification, and porosity can all impact the antiviral efficacy of the nanoparticles.

Hydrogen production via water splitting over graphitic carbon nitride (g-C3N4 )-based photocatalysis

Photocatalytic splitting of water into hydrogen and oxygen using semiconductor photocatalysts and light irradiation has been attracted much attention and considered to be an alternative for nonrenewable fossil fuel to solve environmental problems and energy crisis and also an as promising approach to produce clean, renewable hydrogen fuel. Owing to their various advantages such as low cost and environmental friendly, chemical, and thermal stability, appropriate band structure, graphitic carbon nitride (g-C3N4 ) photocatalysts have gained multitudinous attention because of their great potential in solar fuels production and environmental remediation. However, due to its fast charge carrier’s recombination, low surface, and limited absorption of the visible light restrict their activity toward hydrogen evolution and numerous modification techniques were applied to solve these problems such as structural modification, metal/nonmetal doping, and noble metal loading, and coupling semiconductors. In this chapter, we summarize recent progress in the synthesis and characterization of the g-C3N4-based photocatalyst. Several modification methods used to enhance the photocatalytic hydrogen production of g-C3N4-based photocatalyst were also highlighted. This chapter ends with the future research and challenges of hydrogen production over g-C3N4-based photocatalyst.

TiO2 as a Photocatalyst for Water Splitting-An Experimental and Theoretical Review

Hydrogen produced from water using photocatalysts driven by sunlight is a sustainable way to overcome the intermittency issues of solar power and provide a green alternative to fossil fuels. TiO₂ has been used as a photocatalyst since the 1970s due to its low cost, earth abundance, and stability. There has been a wide range of research activities in order to enhance the use of TiO₂ as a photocatalyst using dopants, modifying the surface, or depositing noble metals. However, the issues such as wide bandgap, high electron-hole recombination time, and a large overpotential for the hydrogen evolution reaction (HER) persist as a challenge. Here, we review state-of-the-art experimental and theoretical research on TiO₂ based photocatalysts and identify challenges that have to be focused on to drive the field further. We conclude with a discussion of four challenges for TiO₂ photocatalysts-non-standardized presentation of results, bandgap in the ultraviolet (UV) region, lack of collaboration between experimental and theoretical work, and lack of large/small scale production facilities. We also highlight the importance of combining computational modeling with experimental work to make further advances in this exciting field.

Silver-Deposited Nanoparticles on the Titanium Nanotubes Surface as a Promising Antibacterial Material into Implants

The main disadvantage of the implants is the associated infections. Therefore, in the long term, the possibility of improving the antibacterial capacity of different types of implants (dental, orthopedic) is being researched. The severity of the problem lies in the increasing bacterial resistance and finding appropriate alternative treatments for infectious diseases, which is an important research field nowadays. The purpose of this review is to draw a parallel between different studies analyzing the antibacterial activity and mechanism of silver nanoparticles (NP Ag) deposited on the titanium nanotubes (NTT), as well as the analysis of the NP Ag toxicity. This review also provides an overview of the synthesis and characterization of TiO2-derived nanotubes (NT). Thus, the analysis aims to present the existing knowledge to better understand the NP Ag implants benefits and their antibacterial activity.

Effect of pH on the Formation of Amorphous TiO2 Complexes and TiO2 Anatase during the Pyrolysis of an Aqueous TiCl4 Solution

The titanium dioxide (TiO2) nanostructures resulted by the pyrolysis of titanium tetrachloride (TiCl4) at a low temperature of 80 °C were found to be a mixture of amorphous TiO2 complexes and anatase nanostructures, whose ratio depends on the pH of the pyrolysis medium. At a low pH level, the resulting TiO2 nanostructures are predominantly anatase and gradually shift to amorphous TiO2 complexes as the pH level increases. Moreover, the amorphous TiO2 complexes can convert back to anatase nanostructures by a post-heating treatment, and can then transform to rutile with elevating temperature. Amongst the TiO2 nanostructures recovered from the amorphous TiO2 complexes, anatase appears to be the most effective photocatalyst in the decomposition of methylene blue.

Heterogeneous photocatalysis in flow chemical reactors

The synergy between photocatalysis and continuous flow chemical reactors has shifted the paradigms of photochemistry, opening new avenues of research with safer and scalable processes that can be readily implemented in academia and industry. Current state-of-the-art photocatalysts are homogeneous transition metal complexes that have favourable photophysical properties, wide electrochemical redox potentials, and photostability. However, these photocatalysts present serious drawbacks, such as toxicity, limited availability, and the overall cost of rare transition metal elements. This reduces their long-term viability, especially at an industrial scale. Heterogeneous photocatalysts (HPCats) are an attractive alternative, as the requirement for the separation and purification is largely removed, but typically at the cost of efficiency. Flow chemical reactors can, to a large extent, mitigate the loss in efficiency through reactor designs that enhance mass transport and irradiation. Herein, we review some important developments of heterogeneous photocatalytic materials and their application in flow reactors for sustainable organic synthesis. Further, the application of continuous flow heterogeneous photocatalysis in environmental remediation is briefly discussed to present some interesting reactor designs that could be implemented to enhance organic synthesis.

Crystallized TiO2 Nanosurfaces in Biomedical Applications

Crystallization alters the characteristics of TiO2 nanosurfaces, which consequently influences their bio-performance. In various biomedical applications, the anatase or rutile crystal phase is preferred over amorphous TiO2. The most common crystallization technique is annealing in a conventional furnace. Methods such as hydrothermal or room temperature crystallization, as well as plasma electrolytic oxidation (PEO) and other plasma-induced crystallization techniques, present more feasible and rapid alternatives for crystal phase initiation or transition between anatase and rutile phases. With oxygen plasma treatment, it is possible to achieve an anatase or rutile crystal phase in a few seconds, depending on the plasma conditions. This review article aims to address different crystallization techniques on nanostructured TiO2 surfaces and the influence of crystal phase on biological response. The emphasis is given to electrochemically anodized nanotube arrays and their interaction with the biological environment. A short overview of the most commonly employed medical devices made of titanium and its alloys is presented and discussed.

Synthesis and Surface Modification of TiO2-Based Photocatalysts for the Conversion of CO2

Among all greenhouse gases, CO2 is considered the most potent and the largest contributor to global warming. In this review, photocatalysis is presented as a promising technology to address the current global concern of industrial CO2 emissions. Photocatalysis utilizes a semiconductor material under renewable solar energy to reduce CO2 into an array of high-value fuels including methane, methanol, formaldehyde and formic acid. Herein, the kinetic and thermodynamic principles of CO2 photoreduction are thoroughly discussed and the CO2 reduction mechanism and pathways are described. Methods to enhance the adsorption of CO2 on the surface of semiconductors are also presented. Due to its efficient photoactivity, high stability, low cost, and safety, the semiconductor TiO2 is currently being widely investigated for its photocatalytic ability in reducing CO2 when suitably modified. The recent TiO2 synthesis and modification strategies that may be employed to enhance the efficiency of the CO2 photoreduction process are described. These modification techniques, including metal deposition, metal/non-metal doping, carbon-based material loading, semiconductor heterostructures, and dispersion on high surface area supports, aim to improve the light absorption, charge separation, and active surface of TiO2 in addition to increasing product yield and selectivity.

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.

Understanding crystallization pathways leading to manganese oxide polymorph formation

Hydrothermal synthesis is challenging in metal oxide systems with diverse polymorphism, as reaction products are often sensitive to subtle variations in synthesis parameters. This sensitivity is rooted in the non-equilibrium nature of low-temperature crystallization, where competition between different metastable phases can lead to complex multistage crystallization pathways. Here, we propose an ab initio framework to predict how particle size and solution composition influence polymorph stability during nucleation and growth. We validate this framework using in situ X-ray scattering, by monitoring how the hydrothermal synthesis of MnO2 proceeds through different crystallization pathways under varying solution potassium ion concentrations ([K+] = 0, 0.2, and 0.33 M). We find that our computed size-dependent phase diagrams qualitatively capture which metastable polymorphs appear, the order of their appearance, and their relative lifetimes. Our combined computational and experimental approach offers a rational and systematic paradigm for the aqueous synthesis of target metal oxides.