Preparation of Nanosize Anatase and Rutile TiO2by Hydrothermal Treatment of Microemulsions and Their Activity for Photocatalytic Wet Oxidation of Phenol

TiO2 Nanoparticles with Adjustable Phase Composition Prepared by an Inverse Microemulsion Method: Physicochemical Characterization and Photocatalytic Properties

Titania nanoparticles (NPs) find wide application in photocatalysis, photovoltaics, gas sensing, lithium batteries, etc. One of the most important synthetic challenges is maintaining control over the polymorph composition of the prepared nanomaterial. In the present work, TiO2 NPs corresponding to anatase, rutile, or an anatase/rutile/brookite mixture were obtained at 80 °C by an inverse microemulsion method in a ternary system of water/cetyltrimethylammonium bromide/1-hexanol in a weight ratio of 17:28:55. The only synthesis variables were the preparation of the aqueous component and the nature of the Ti precursor (Ti(IV) ethoxide, isopropoxide, butoxide, or chloride). The materials were characterized with X-ray diffraction, scanning/transmission electron microscopy, N2 adsorption-desorption isotherms, FTIR and Raman vibrational spectroscopies, and diffuse reflectance spectroscopy. The synthesis products differed significantly not only in phase composition, but also in crystallinity, textural properties, and adsorption properties towards water. All TiO2 NPs were active in the photocatalytic decomposition of rhodamine B, a model dye pollutant of wastewater streams. The mixed-phase anatase/rutile/brookite nanopowders obtained from alkoxy precursors showed the best photocatalytic performance, comparable to or better than the P25 reference. The exceptionally high photoactivity was attributed to the advantageous electronic effects known to accompany multiphase titania composition, namely high specific surface area and strong surface hydration. Among the single-phase materials, anatase samples showed better photoactivity than rutile ones, and this effect was associated, primarily, with the much higher specific surface area of anatase photocatalysts.

Catalyzing Artificial Photosynthesis with TiO2 Heterostructures and Hybrids: Emerging Trends in a Classical yet Contemporary Photocatalyst

Titanium dioxide (TiO2) stands out as a versatile transition-metal oxide with applications ranging from energy conversion/storage and environmental remediation to sensors and optoelectronics. While extensively researched for these emerging applications, TiO2 has also achieved commercial success in various fields including paints, inks, pharmaceuticals, food additives, and advanced medicine. Thanks to the tunability of their structural, morphological, optical, and electronic characteristics, TiO2 nanomaterials are among the most researched engineering materials. Besides these inherent advantages, the low cost, low toxicity, and biocompatibility of TiO2 nanomaterials position them as a sustainable choice of functional materials for energy conversion. Although TiO2 is a classical photocatalyst well-known for its structural stability and high surface activity, TiO2-based photocatalysis is still an active area of research particularly in the context of catalyzing artificial photosynthesis. This review provides a comprehensive overview of the latest developments and emerging trends in TiO2 heterostructures and hybrids for artificial photosynthesis. It begins by discussing the common synthesis methods for TiO2 nanomaterials, including hydrothermal synthesis and sol-gel synthesis. It then delves into TiO2 nanomaterials and their photocatalytic mechanisms, highlighting the key advancements that have been made in recent years. The strategies to enhance the photocatalytic efficiency of TiO2, including surface modification, doping modulation, heterojunction construction, and synergy of composite materials, with a specific emphasis on their applications in artificial photosynthesis, are discussed. TiO2-based heterostructures and hybrids present exciting opportunities for catalyzing solar fuel production, organic degradation, and CO2 reduction via artificial photosynthesis. This review offers an overview of the latest trends and advancements, while also highlighting the ongoing challenges and prospects for future developments in this classical yet rapidly evolving field.

Efficient and sustainable photocatalytic inactivation of E. coli by an innovative immobilized Ag/TiO2 photocatalyst with peroxymonosulfate (PMS) under visible light

A novel catalytic system for effective photocatalytic inactivation of Escherichia coli (E. coli) was constructed by anchoring Ag nanoparticles (AgNPs) on silane coupling agent (SCA) pretreated TiO2 nano-tube arrays (Ag/SCA/TiO2NTAs). Morphology and structural analyses revealed that SCA could disperse AgNPs evenly on TiO2NTAs, thus inducing a superior surface plasmon resonance (SPR) effect. Ag/SCA/TiO2NTAs catalyst exhibited excellent inactivation performance when in the presence of peroxymonosulfate (PMS) and visible light (VL), with 6-log E. coli was completely inactivated within 60 min, which was 5.3, 12.5 and 13.2 times higher than that of Ag/SCA/TiO2NTAs/VL, PMS/VL and Ag/SCA/TiO2NTAs/PMS/dark systems, respectively. Additionally, the photocatalyst exhibited a highly reusable property, with the inactivation performance almost unchanged after ten cycles of uses with minimal Ag leaching. The inactivation mechanism analysis demonstrated that both radical (SO4•-, OH) and non-radical (h+, 1O2) pathways involved in E. coli inactivation, and SCA played a pivotal role in the production of reactive species. Chloride ions (Cl-) greatly enhanced the inactivation efficiency, while bicarbonate (HCO3-) and phosphate (H2PO4-) showed an inhibitory effect. Humic acid (HA) displayed a dual effect on inactivation performance, where the low concentration of HA facilitated the bacteria inactivation, while the higher dose suppressed bacteria inactivation. Moreover, the system exhibited excellent inactivation performance in tap water. This work first used SCA as the binder to fix AgNPs on TiO2NTAs for VL photocatalytic inactivation of bacteria with the assistance of PMS, which was expected to provide some insights into the practical treatment of drinking water.

Nanoscale Titanium Surface Engineering via Low-Temperature Hydrothermal Etching for Enhanced Antimicrobial Properties

Bioinspired nanotopography artificially fabricated on titanium surfaces offers a solution for the rising issue of postoperative infections within orthopedics. On a small scale, hydrothermal etching has proven to deliver an effective antimicrobial nanospike surface. However, translation to an industrial setting is limited by the elevated synthesis temperature (150 °C) and associated equipment requirements. Here, for the first time, we fabricate surface nanostructures using comparatively milder synthesis temperatures (75 °C), which deliver physicochemical properties and antimicrobial capability comparable to the high-temperature surface. Using a KOH etchant, the simultaneous formation of titania and titanate crystals at both temperatures produces a one-dimensional nanostructure array. Analysis indicated that the formation mechanism comprises dissolution and reprecipitation processes, identifying the deposited titanates as hydrated layered tetra-titanates (K2Ti4O9·nH2O). A proposed nanospike formation mechanism was confirmed through the identification of a core and outer shell for individual nanostructures, primarily comprised of titanates and titania, respectively. Etching conditions dictated crystalline formation, favoring a thicker titanate core for nanorods under higher synthesis temperatures and etchant concentrations. A bactericidal investigation showed the efficacy against Gram-negative bacteria for a representative low-temperature nanosurface (34.4 ± 14.4%) was comparable to the higher temperature nanosurface (34.0 ± 17.0%), illustrating the potential of low-temperature hydrothermal synthesis. Our results provide valuable insight into the applicability of low-temperature etching protocols that are more favorable in large-scale manufacturing settings.

Comparative study on bisphenols oxidation via TiO2 photocatalytic activation of peroxymonosulfate: Effectiveness, mechanism and pathways

In this work, degradation of bisphenol F (BPF), bisphenol AF (BPAF) and bisphenol S (BPS) by peroxymonosulfate (PMS) with TiO₂ nano-tubes arrays (TiO₂NTAs) under simulated sunlight irradiation was investigated and compared for the first time. All three bisphenols exhibited appreciable degradation following the order of BPS < BPAF < BPF, and acidic conditions were more conducive to their degradation. The SO₄^•-, ·OH, h⁺ and ^•O₂^- were all identified in three bisphenols degradation processes. Among these, SO₄^•- and ^•O₂^- were proven to play a dominant role in BPF oxidation process, but SO₄^•- and h⁺ were confirmed as the main reactive species for BPAF and BPS removal. Owing to the different reactive species worked in different bisphenols degradation processes, the influences of inorganic anions on three bisphenols degradation were also different. By analyzing the oxidation intermediates of the three bisphenols, it was found that there were some common degradation pathways including bond-cleavage and hydroxylation of the benzene ring shared by three bisphenols. Besides, some specific degradation pathways were also identified, for example, the self-coupling was found in BPF and BPS degradation process, while the benzene ring splitting was occurred only in BPAF transformation process.

In-situ, Ex-situ, and nano-remediation strategies to treat polluted soil, water, and air - A review

Nanotechnology, as an emerging science, has taken over all fields of life including industries, health and medicine, environmental issues, agriculture, biotechnology etc. The use of nanostructure molecules has revolutionized all sectors. Environmental pollution is a great concern now a days, in all industrial and developing as well as some developed countries. A number of remedies are in practice to overcome this problem. The application of nanotechnology in the bioremediation of environmental pollutants is a step towards revolution. The use of various types of nanoparticles (TiO₂ based NPs, dendrimers, Fe based NPs, Silica and carbon nanomaterials, Graphene based NPs, nanotubes, polymers, micelles, nanomembranes etc.) is in practice to diminish environmental hazards. For this many In-situ (bioventing, bioslurping, biosparging, phytoremediation, permeable reactive barrier etc.) and Ex-situ (biopile, windrows, bioreactors, land farming etc.) methodologies are employed. Improved properties like nanoscale size, less time utilization, high adaptability for In-situ and Ex-situ use, undeniable degree of surface-region to-volume proportion for possible reactivity, and protection from ecological elements make nanoparticles ideal for natural applications. There are distinctive nanomaterials and nanotools accessible to treat the pollutants. Each of these methods and nanotools depends on the properties of foreign substances and the pollution site. The current designed review highlights the techniques used for bioremediation of environmental pollutants as well as use of various nanoparticles along with proposed In-situ and Ex-situ bioremediation techniques.

Facile Synthesis of BiVO4@ZIF-8 Composite with Heterojunction Structure for Photocatalytic Wastewater Treatment

Water pollution has always been a serious problem across the world; therefore, facile pollutant degradation via light irradiation has been an attractive issue in the field of environmental protection. In this study, a type of Zn-based metal–organic framework (ZIF−8)-wrapped BiVO₄ nanorod (BiVO₄@ZIF−8) with high efficiency for photocatalytic wastewater treatment was synthesized through a two-step hydrothermal method. The heterojunction structure of BiVO₄@ZIF−8 was confirmed by morphology characterization. Due to the introduction of mesoporous ZIF−8, the specific surface area reached up to 304.5 m²/g, which was hundreds of times larger than that of pure BiVO₄ nanorods. Furthermore, the band gap of BiVO₄@ZIF−8 was narrowed down to 2.35 eV, which enabled its more efficient utilization of visible light. After irradiation under visible light for about 40 min, about 80% of rhodamine B (RhB) was degraded, which was much faster than using pure BiVO₄ or other BiVO₄-based photocatalysts. The synergistic photocatalysis mechanism of BiVO₄@ZIF−8 is also discussed. This study might offer new pathways for effective degradation of wastewater through facile design of novel photocatalysts.

Enhanced solar photocatalysis of TiO2 nanoparticles and nanostructured thin films grown on paper

Titanium dioxide nanoparticles and nanostructured thin films were simultaneously synthesized using a microwave-assisted hydrothermal method. The synthesis formed very fine particles, appearing as nanospheres in the 11 nm size range. As for the nanostructured films, they have displayed similar structural characteristics to the nanoparticles, with thickness of 130 nm. These films covered uniformly and homogenously the Whatman paper, while maintaining its flexibility. The materials processed had their photocatalytic activity assessed from rhodamine B degradation under solar radiation (91% degradation after 40 min for the powder material and 68% after 6 h for the nanostructured thin films). Reusability experiments were also carried out, revealing superior performance concerning the Degussa P25, the most common photocatalyst used. The results of the present work can be thought as an option for the existing photocatalysts activated under solar light, namely for water purification, as it simultaneously produces enhanced photocatalytic powders and photocatalytic papers fully disposable and that can be easily recycled.

Microemulsion Derived Titania Nanospheres: An Improved Pt Supported Catalyst for Glycerol Aqueous Phase Reforming

Glycerol aqueous phase reforming (APR) produces hydrogen and interesting compounds at relatively mild temperatures. Among APR catalysts investigated in literature, little attention has been given to Pt supported on TiO₂. Therefore, herein we propose an innovative titania support which can be obtained through an optimized microemulsion technique. This procedure provided high surface area titania nanospheres, with a peculiar high density of weak acidic sites. The material was tested in the catalytic glycerol APR after Pt deposition. A mechanism hypothesis was drawn, which evidenced the pathways giving the main products. When compared with a commercial TiO₂ support, the synthetized titania provided higher hydrogen selectivity and glycerol conversion thanks to improved catalytic activity and ability to prompt consecutive dehydrogenation reactions. This was correlated to an enhanced cooperation between Pt nanoparticles and the acid sites of the support.

Metal Oxide-Based Photocatalytic Paper: A Green Alternative for Environmental Remediation

The interest in advanced photocatalytic technologies with metal oxide-based nanomaterials has been growing exponentially over the years due to their green and sustainable characteristics. Photocatalysis has been employed in several applications ranging from the degradation of pollutants to water splitting, CO2 and N2 reductions, and microorganism inactivation. However, to maintain its eco-friendly aspect, new solutions must be identified to ensure sustainability. One alternative is creating an enhanced photocatalytic paper by introducing cellulose-based materials to the process. Paper can participate as a substrate for the metal oxides, but it can also form composites or membranes, and it adds a valuable contribution as it is environmentally friendly, low-cost, flexible, recyclable, lightweight, and earth abundant. In term of photocatalysts, the use of metal oxides is widely spread, mostly since these materials display enhanced photocatalytic activities, allied to their chemical stability, non-toxicity, and earth abundance, despite being inexpensive and compatible with low-cost wet-chemical synthesis routes. This manuscript extensively reviews the recent developments of using photocatalytic papers with nanostructured metal oxides for environmental remediation. It focuses on titanium dioxide (TiO2) and zinc oxide (ZnO) in the form of nanostructures or thin films. It discusses the main characteristics of metal oxides and correlates them to their photocatalytic activity. The role of cellulose-based materials on the systems’ photocatalytic performance is extensively discussed, and the future perspective for photocatalytic papers is highlighted.

Synthesis and characterization of different binary and ternary phase mixtures of mesoporous nanocrystalline titanium dioxide

Different phase compositions of mesoporous nanocrystalline TiO2 (meso-nc-TiO2), comprised of anatase (16–100%), rutile (0–70%) and brookite (0–52%) were obtained by sol–gel synthesis with or without hydrothermal treatment (HTT) by means of titanium tetrabutoxide and dibenzo-18-croun-6 as structure-forming agent in the presence of HCl. It was shown, that small amounts of surfactant and/or lanthanum salt as well as HTT determine phase composition and texture of meso-nc-TiO2. All samples were calcined at 500 оС and characterized by SEM, TEM, XRD and N2-adsorption/desorption isotherms. It has been established that photocatalytic properties of almost all obtained samples significantly exceed the photocatalytic activity of Evonik P-25 TiO2 in gas phase ethanol oxidation. The most active sample is characterized by phase composition of anatase (97%)-rutile (3%). It is obvious, that decrease of photocatalytic activity of sample was affected by decrease of anatase phase content. It was shown that the specific surface area of the sample is not a key factor affecting the activity of mixed-phase meso-nc-TiO2 samples in the process of ethanol oxidation.

Effect of diatomite addition on crystalline phase formation of TiO2 and photocatalytic degradation of MDMA

Different composites TiO₂@SiO₂ were obtained by in situ synthesis of TiO₂ on Algerian diatomite. Our results show that there is an optimum amount of diatomite which leads to mixed TiO₂ phase with enhanced photocatalytic activity.

Re-establishment of macrophage homeostasis by titanium surface modification in type II diabetes promotes osseous healing

Titanium surface mediated immunomodulation may address compromised post-implantation bone healing in diabetes mellitus. To assess in vitro phenotypic changes, M1 and M2 polarised Type 2 diabetic rat (Goto Kakizaki, GK) macrophages were cultured on micro-rough (SLA) or hydrophilic nanostructured SLA (modSLA) titanium. The in vivo effects of the SLA and modSLA surfaces on macrophage phenotype, wound-associated protein expression and bone formation were investigated using a critical-sized calvarial defect model. Compared to healthy macrophages, GK M2 macrophage function was compromised, secreting significantly lower levels of the anti-inflammatory cytokine IL-10. The modSLA surface attenuated the pro-inflammatory cellular environment, reducing pro-inflammatory cytokine production and promoting M2 macrophage phenotype differentiation. ModSLA also suppressed gene expression associated with macrophage multinucleation and giant cell formation and stimulated pro-osteogenic genes in co-cultured osteoblasts. In vivo, modSLA enhanced osteogenesis compared to SLA in GK rats. During early healing, proteomic analysis of both surface adherent and wound exudate material showed that modSLA promoted an immunomodulatory pro-reparative environment. The modSLA surface therefore successfully compensated for the compromised M2 macrophage function in Type 2 diabetes by attenuating the pro-inflammatory response and promoting M2 macrophage activity, thus restoring macrophage homeostasis and resulting in a cellular environment favourable for enhanced osseous healing.

Degradation of Hexacyanoferrate (III) from Gold Mining Wastewaters via UV-A/LED Photocatalysis Using Modified TiO2 P25

The photocatalytic degradation of potassium hexacyanoferrate (III) was assessed in a bench-scale compound parabolic collectors (CPC) reactor assisted with a light-emitting diode (LED) UV-A source emitting at 365 nm, and using a modified TiO2 as a catalyst via the hydrothermal treatment of commercial Aeroxide P25. The experiments were performed under oxic and anoxic conditions in order to observe a possible reduction of the iron. The modified TiO2 showed a specific surface area 2.5 times greater than the original Aeroxide P25 and its isotherm and hysteresis indicated that the modified catalyst is mesoporous. The bandgap energy (Eg) of the modified TiO2 increased (3.34 eV) compared to the P25 TiO2 band gap (3.20 eV). A specific reaction rate constant of 0.1977 min−1 and an electrical oxidation efficiency of 7.77 kWh/m3 were obtained in the photocatalytic degradation. Although the TiO2 P25 yields a photocatalytic degradation 9.5% higher than that obtained one with the modified catalyst (hydrothermal), this catalyst showed better performance in terms of free cyanide release. This last aspect is a significant benefit since this can help to avoid the pollution of fresh water by reusing the treated wastewater for gold extraction. A photocatalytic degradation of the cyanocomplex of 93% was achieved when the process occurred under oxic conditions, which favored the removal. Summarizing, the hydrothermal method could be a promising treatment to obtain TiO2-based catalysts with larger specific areas.

Grey Rutile TiO2 with Long-Term Photocatalytic Activity Synthesized Via Two-Step Calcination

Colored titanium oxides are usually unstable in the atmosphere. Herein, a gray rutile titanium dioxide is synthesized by two-step calcination successively in a high-temperature reduction atmosphere and in a lower-temperature air atmosphere. The as-synthesized gray rutile TiO₂ exhibits higher photocatalytic activity than that of white rutile TiO₂ and shows high chemical stability. This is attributed to interior oxygen vacancies, which can improve the separation and transmission efficiency of the photogenerated carriers. Most notably, a formed surface passivation layer will protect the interior oxygen vacancies and provide long-term photocatalytic activity.

State-of-Art Bio-Assay Systems and Electrochemical Approaches for Nanotoxicity Assessment

Innovations in the field of nanotechnology, material science and engineering has rendered fruitful utilities in energy, environment and healthcare. Particularly, emergence of surface engineered nanomaterials offered novel varieties in the daily consumables and healthcare products including therapeutics and diagnostics. However, the nanotoxicity and bioactivity of the nanomaterials upon interaction with biological system has raised critical concerns to individual as well as to the environment. Several biological models including plant and animal sources have been identified to study the toxicity of novel nanomaterials, correlating the physio-chemical properties. Biological interaction of nanomaterials and its mediated physiological functions are studied using conventional cell/molecular biological assays to understand the expression levels of genetic information specific to intra/extra cellular enzymes, cell viability, proliferation and function. However, modern research still demands advanced bioassay methods to screen the acute and chronic effects of nanomaterials at the real-time. In this regard, bioelectrochemical techniques, with the recent advancements in the microelectronics, proved to be capable of providing non-invasive measurement of the nanotoxicity effects (in vivo and in vitro) both at single cellular and multicellular levels. This review attempted to provide a detailed information on the recent advancements made in development of bioassay models and systems for assessing the nanotoxicology. With a short background information on engineered nanomaterials and physiochemical properties specific to consumer application, present review highlights the multiple bioassay models evolved for toxicological studies. Emphasize on multiple mechanisms involved in the cell toxicity and electrochemical probing of the biological interactions, revealing the cytotoxicity were also provided. Limitations in the existing electrochemical techniques and opportunities for the future research focusing the advancement in single molecular and whole cell bioassay has been discussed.

Preparation of a Ti0.7W0.3O2/TiO2 nanocomposite interfacial photocatalyst and its photocatalytic degradation of phenol pollutants in wastewater

A Ti_0.7W_0.3O₂/TiO₂ nanocomposite interfacial photocatalyst was designed and prepared for the photocatalytic degradation of phenol pollutants in wastewater. The detailed properties of the Ti_0.7W_0.3O₂/TiO₂ nanocomposite interface (NCI) were analyzed by XRD, SEM, EDX, DRS, UPS and XPS technologies, showing that anatase TiO₂ nanospheres (NSs) were uniformly dispersed on the surface of rutile Ti_0.7W_0.3O₂ nanoparticles (NPs) and formed the nanocomposite interface. The DRS and UPS results of 5 wt% Ti_0.7W_0.3O₂/TiO₂ NCI indicated a greatly broadened light response range with a wavelength shorter than 527 nm and a shorter band gap energy of 2.37 eV. The conduction band of TiO₂ NSs, Ti_0.7W_0.3O₂ NPs and 5 wt% Ti_0.7W_0.3O₂/TiO₂ NCI were measured based on the results of the valence band and band gap energy obtained via XPS and DRS, and then the energy level diagram of Ti_0.7W_0.3O₂/TiO₂ NCI was proposed. The photocatalytic degradation of phenol at Ti_0.7W_0.3O₂/TiO₂ NCI with different loading ratios of Ti_0.7W_0.3O₂ NPs was investigated under optimum conditions (i.e., pH of 4.5, catalyst dosage of 0.45 g L^-1 and phenol initial concentration of 95 ppm) under the illumination of ultraviolet visible light. Also, 5 wt% Ti_0.7W_0.3O₂/TiO₂ NCI exhibited the highest photocatalytic activity, with the initial rate constant (k) calculated as 0.09111 min^-1. After recycling six times, Ti_0.7W_0.3O₂/TiO₂ NCI showed good stability and recyclability. The involvement of superoxide radicals in the initial reaction at Ti_0.7W_0.3O₂/TiO₂ NCI was evidenced by the use of a terephthalic acid (TA) fluorescent probe. Besides, UV-Vis spectroscopy, UHPLC-MS and GC-MS technologies were used to analyze the main intermediates in the photocatalytic degradation of phenol. The probable photocatalytic degradation mechanism of phenol at Ti_0.7W_0.3O₂/TiO₂ NCI was also proposed.

Acid-treated Fe-doped TiO2 as a high performance photocatalyst used for degradation of phenol under visible light irradiation

The photocatalytic activity of Fe-doped TiO₂ nanoparticles is significantly increased by an acid-treatment process. The photocatalyst nanoparticles were prepared using sol-gel method with 0.5 mol% ratio of Fe:Ti in acidic pH of 3. The nanoparticles were structurally characterized by means of X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance spectroscopy (DRS). It was observed that the photocatalytic activity suffered from an iron oxide contaminating layer deposited on the surface of the nanoparticles. This contamination layer was removed using an HCl acid-treatment process. The photocatalytic activity using 500 mg/L of Fe_0.5-TiO₂ in a 10 mg/L of phenol solution increased significantly from 33% to 57% (about 73% increase in the performance), within 90 min of reaction time under visible light irradiation. This significant improvement was achieved by removing the iron oxide contamination layer from the surface of the nanoparticles and adjusting pH to mild acidic and basic pHs.

Cobalt phthalocyanine-TiO2 nanocomposites for photocatalytic remediation of textile dyes under visible light irradiation

CoPc(COOH)[Formula: see text]-TiO[Formula: see text] nanocomposites to be used as efficient visible light photocatalysts were obtained by modifying TiO2 nanoparticles with cobalt(II) tetracarboxyphthalocyanine (CoPc(COOH)[Formula: see text]). The photocatalyst was then characterized by ultra-violet diffuse reflectance spectroscopy (UV-DRS), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The UV-DRS spectra showed that the absorbance spectrum of the modified catalyst was shifted to the visible region. Different textile dye solutions of Reactive Red 180, Acid Red 88 and Direct Orange 46 were efficiently degraded under visible light. Color removal rates were established to be 30%, 53% and 47% after 180 min for RR180, AR88 and DO46 dyes, respectively. The optimum catalyst concentration was determined to be 1 g/L of CoPc(COOH)[Formula: see text]-TiO[Formula: see text]. Development of the CoPc(COOH)[Formula: see text]-TiO[Formula: see text] nanocomposite photocatalyst enabled the utilization of visible light irradiation for efficient photodegradation of organic textile dye solutions.

Life Cycle Impact of Titanium Dioxide Nanoparticle Synthesis through Physical, Chemical, and Biological Routes

The sustainable manufacturing of nanoparticles (NPs) has become critical to reduce life cycle energy use and the associated environmental impact. With the ever-growing production volume, titanium dioxide (TiO₂) NPs have been produced through various synthesis routes with differing input materials and reactions, which result in differential reactivity, crystallinity, surface areas, and size distributions. In this study, life cycle assessment is used to analyze and compare the environmental impact of TiO₂ NPs produced via seven routes covering physical, chemical, and biological syntheses. The synthesis routes are chosen to represent mainstream NP manufacturing and future trends. Mass-, surface area-, and photocatalytic reactivity-based functional units are selected to evaluate the environmental impact and reflect the corresponding changes. The results show that impact associated with the upstream production of different precursors are dominant for the chemical route. Compared to the chemical route, the physical route requires substantial quantities of supporting gas and high-energy inputs to maintain high temperature; therefore, a higher environmental burden is generated. A high environmental burden is also modeled for the biological route due to the required bacterial culture media. This present study aims to identify the most efficient synthesis route for TiO₂ NP production, lower the potential environmental impact, and improve green synthesis and sustainability.

Evolution of the Polymorph Selectivity of Titania Formation under Acidic and Low-Temperature Conditions

Evolution of the polymorph selectivity of titanium dioxide was studied under acidic and low-temperature synthesis conditions. Short synthesis times resulted in high relative amounts of the rutile phase, and long synthesis times resulted in high relative amounts of the brookite and anatase phases. The effect of titania precursor concentration was investigated and found to have a large impact on the polymorph selectivity. As the reaction proceeds with time, changes in the chemical environment, caused in particular by the gradually decreasing titania precursor concentration, are therefore likely the cause of the change in polymorph selectivity observed.

Synthesis and applications of nano-TiO2: a review

TiO₂-based nanomaterials have attracted prodigious attention as a photocatalysts in numerous fields of applications. In this thematic issue, the mechanism behind the photocatalytic activity of nano-TiO₂ as well as the critical properties have been reviewed in details. The synthesis routes and the variables that affect the size and crystallinity of nano-TiO₂ have also been discussed in detail. Moreover, a newly emerged class of color TiO₂, TiO₂ in aerogel form, nanotubes form, doped and undoped form, and other forms of TiO₂ have been discussed in details. Photocatalytic and photovoltaic applications and the type of nano-TiO₂ that is more suitable for these applications have been discussed in this review.

Fabrication of diffraction gratings by top-down and bottom-up approaches based on scanning probe lithography

Generation of diffraction gratings by top-down and bottom-up approaches based on scanning probe lithography is demonstrated. With regard to top-down fabrication, silicon nanostructured diffraction gratings are fabricated through one-dimensional (1D) dip-pen-nanolithography (DPN). Nanodot arrays (two-dimensional simple cubic lattice) of alkanethiol self-assembled monolayers (SAMs) are printed by 1D DPN on an Au-film-coated silicon substrate with lattice distances of 700, 1000, and 1200 nm. Silicon nanocircular pillars of length hundreds of nanometers are generated by sequential Au etching and reactive ion etching (RIE) of the 1D DPN printed sample. The performance of the silicon diffraction gratings as a microspectrometer is demonstrated through red, green, and blue color diffraction with white light incident at 45°. Moreover, arrays of zirconia nanoparticles (NPs) with an average diameter of visible wavelength (φ ≈ 470 nm) on an Au substrate are generated via bottom-up fabrication of the diffraction gratings. Microarrays of hydrophilic alkanethiol SAMs are obtained by polymer pen lithography (PPL). Self-assembly of zirconia NPs occurs after the passivation of hydrophobic alkanethiol SAMs of the PPL-printed sample. Fraunhofer diffraction with a square aperture is observed for the zirconia NP diffraction grating fabricated by the bottom-up approach.

Effect of the Preparation Method (Sol-Gel or Hydrothermal) and Conditions on the TiO₂ Properties and Activity for Propene Oxidation

Since the two most commonly used methods for TiO₂ preparation are sol-gel (SG) and hydrothermal (HT) synthesis, this study attempts to compare both methods in order to determine which one is the most suitable to prepare photocatalysts for propene oxidation. In addition, this work studies how the concentration of the HCl used for hydrolysis of the TiO₂ precursor affects the properties of the obtained materials. Also, the effect of avoiding the post-synthesis heat-treatment in a selection of samples is investigated. The photocatalysts are characterized by XRD, N₂ adsorption-desorption isotherms and UV-vis spectroscopy, and the study tries to correlate the properties with the photocatalytic performance of the prepared TiO₂ samples in propene oxidation. TiO₂ materials with high crystallinity, between 67% and 81%, and surface area (up to 134 m²/g) have been obtained both by SG and HT methods. In general, the surface area and pore volume of the TiO₂-HT samples are larger than those of TiO₂-SG ones. The TiO₂-HT catalysts are, in general, more active than TiO₂-SG materials or P25 in the photo-oxidation of propene. The effect of HCl presence during the TiO₂ synthesis and of the post synthesis heat treatment are much more marked in the case of the SG materials.

Tuning the porosity and surface characteristics of nanoporous titania using non-ionic surfactant reverse micelles

Nanoporous titania was prepared from non-ionic surfactant reverse micelles (e.g. Triton-X) and the effects of the chain length of the surfactants and calcination temperature of the precursor gels on the surface properties of the product (mesoporous titania) were investigated. The studies included sample characterization of the precursor gels from the titania samples characterized by UV-Vis, ATR-FTIR, XRD, TGA/DSC and the titania samples by N₂-adsorption BET, XRD, FT-IR, UV-Vis diffuse reflectance and SEM measurements after calcination at 400 °C, 500 °C, 600 °C, 700 °C and 800 °C. According to the experimental results, generally increasing the length of the polar tail of Triton-X results in an increased specific surface area and volume, and an average pore diameter of the solids. Moreover, increasing the length of the polar tail is associated with a smaller crystallite size and higher thermal stability of the materials. Finally, a nucleation mechanism of the titania particles within the aqueous centre of the reversed micelles is proposed.

Nanoporous titania was prepared from non-ionic reverse micelles, and the effects of chain length and calcination temperature of the mother gels were investigated.

A review on heterogeneous sonocatalyst for treatment of organic pollutants in aqueous phase based on catalytic mechanism

Heterogeneous sonocatalysis, as an emerging advanced oxidation process (AOP), has shown immense potential in water treatment and been widely demonstrated to remove persistent organic compounds in the past decade. The present article aims to provide a comprehensive review on the development of a heterogeneous catalyst for enhancing the ultrasonic degradation rate of organic pollutants from a viewpoint of sonocatalytic mechanism. The rational design and fundamentals for preparing sonocatalysts are presented in the context of facilitating the heterogeneous nucleation and photo-thermal-catalytic effects as well as considering the mechanical stability and separation capacity of the heterogeneous catalyst. In addition, some new trends, ongoing challenges and possible methods to overcome these challenges are also highlighted and proposed.

Novel Precursor-Derived Meso-/Macroporous TiO₂/SiOC Nanocomposites with Highly Stable Anatase Nanophase Providing Visible Light Photocatalytic Activity and Superior Adsorption of Organic Dyes

Titania (TiO₂) is considered to have immense potential as a photocatalyst, the anatase phase in particular. There have been numerous attempts to push the limits of its catalytic activity to higher wavelengths to harness the visible electromagnetic radiation. Most of the investigations till date have been restricted to fine-tuning the bandgap by doping, control of defect chemistry at the surface and several to first principle simulations either with limited success or success at the cost of complexities in processing. Here, we report a simple and elegant way of preparing ceramics through precursor chemistry which involves synthesis of macroporous and mesoporous nanocomposites with in situ formation of TiO₂ nanocrystals into a robust and protecting SiOC matrix. The in situ nanoscaled TiO₂ is anatase of size 9–10 nm, which is uniformly distributed in an amorphous SiOC matrix forming a new generation of nanocomposites that combine the robustness, structural stability and durability of the SiOC matrix while achieving nanoscaled TiO₂ functionalities. The stabilization of the anatase phase even at temperature as high as 1200 °C was evident. With an average pore size of 6.8 nm, surface area of 129 m²/g (BET) and pore volume of 0.22 cm³/g (BET), mesoporosity was achieved in the nanocomposites. The composites exhibited visible light photocatalytic activity, which is attributed to the Ti–O–C/TiC bonds resulting in the reduction of band gap by 0.2 to 0.9 eV. Furthermore, the heterojunction formed between the amorphous SiOC and crystalline TiO₂ is also expected to minimize the recombination rate of electron-hole pair, making these novel nanocomposites based on TiO₂ extremely active in visible wavelength regime.

Formation of titanium dioxide core-shell microcapsules through a binary-phase spray technique

Core-shell microcapsules consisting of a titanium dioxide shell and a hydrophobic solvent core have been prepared with diameters of a few micrometers and a narrow size distribution using a simple and fast airbrush technique. These microcapsules were prepared at room temperature in a single-step process in which an oil with a dissolved titanium alkoxide precursor was forced together with an aqueous solution, containing a surface-active polymer, through a narrow spray nozzle using a nitrogen gas propellant. Several different parameters of chemical, physical, and processing origin were investigated to find an optimal recipe. Two different alkanes, one ketone, and four alcohols were tested and evaluated as core materials, alone or together with the antifungal biocide 2-n-octyl-4-isothiazolin-3-one (OIT). Long-chain alcohols were found suitable as core oil due to their low solubility in water and surface activity. The addition of the surface-active polymers in the water phase was important in aiding the formation and stabilization of the titanium dioxide shell. An impressive loading of 50 wt% of the semi-hydrophobic OIT was possible to encapsulate using this simple and applicable procedure.

Solution-phase synthesis of transition metal oxide nanocrystals: Morphologies, formulae, and mechanisms

In this review, we provide a broad overview of solution-phase synthesis of transition metal oxide nanocrystals (NCs), including a substantial catalog of published methods, and a unifying classification and discussion. Prevalent subcategories of solution-phase synthesis are delineated and general features are summarized. The diverse morphologies achievable by solution-phase synthesis are defined and exemplified. This is followed by sequential consideration of the solution-phase synthesis of first-row transition metal oxides. The common oxides of Ti, V, Mn, Fe, Co, Ni, Cu, and Zn are introduced; major crystal lattices are presented and illustrated; representative examples are explained; and numerous synthesis formulae are tabulated. Following this presentation of experimental studies, we present an introduction to theories of NC nucleation and growth. Various models of NC nucleation and growth are addressed, and important concepts determining the growth and structure of colloidal NCs are explained. Overall, this review provides an entry into systematic understanding of solution-phase synthesis of nanocrystals, with a reasonably comprehensive survey of results for the important category of transition metal oxide NCs.