Nitrogen-Doped Titanate-Anatase Core–Shell Nanobelts with Exposed {101} Anatase Facets and Enhanced Visible Light Photocatalytic Activity

Boosting plasmon-enhanced electrochemistry by in situ surface cleaning of plasmonic nanocatalysts

The application of surface plasmons in heterogeneous catalysis has attracted widespread attention due to their promising potential for harvesting solar energy. The effect of surface adsorbates on catalysts has been well documented in many traditional reactions; nonetheless, their role in plasmonic catalysis has been rarely studied. In this study, an in situ electrochemical surface cleaning strategy is developed and the influence of surface adsorbates on plasmon-enhanced electrochemistry is investigated. Taking Au nanocubes as an example, plasmonic catalysts with clean surfaces are obtained by Cu2O coating and in situ electrochemical etching. During this process, the surface adsorbates of Au nanocubes are removed together with the Cu2O shells. The Au nanocubes with clean surfaces exhibit remarkable performance in plasmon-enhanced electrooxidation of glucose and an enhancement of 445% is demonstrated. The Au NCs with clean surfaces can not only provide more active sites but also avoid halides as hole scavengers, and therefore, the efficient utilization of hot holes by plasmonic excitation is achieved. This process is also generalized to other molecules and applied in electrochemical sensing with high sensitivity. These results highlight the critical role of surface adsorbates in plasmonic catalysis and may forward the design of efficient plasmonic catalysts for plasmon-enhanced electrochemistry.

Activation of 2D titanate nanosheet photocatalysts by nitrogen doping and solution plasma processing

Novel two-dimensional (2D) oxides are of great interest for photocatalysis because of their superlative physical features, namely, large surface areas, short charge diffusion pathways, high crystallinity and easy surface modification. However, most 2D oxides suffer from weak visible light absorption and severe photogenerated carrier recombination. Nitrogen doping can successfully narrow the bandgap of 2D oxides but can hardly improve the charge separation. In this work, we pre-dope nitrogen into 2D titanate nanosheets (HTiO), followed by surface processing with solution plasma. By dual modification of nitrogen doping and solution plasma processing (SPP), the modified 2D titanate nanosheets (N-HTiO-SPP) display broad absorption extending to the visible light region and the healing of oxygen vacancies brought about by nitrogen doping. Compared with HTiO and nitrogen doped titanate (N-HTiO), a higher removal rate and mineralization rate towards the photocatalytic degradation of acetaldehyde were achieved over N-HTiO-SPP under solar light. This work provides a powerful way to activate 2D wide bandgap semiconductors for enhanced photocatalytic activity.

Anti-fouling PVDF membranes incorporating photocatalytic biochar-TiO2 composite for lignin recycle

In this study, a photocatalytic biochar-TiO₂ (C-Ti) composite was prepared using lignin as carbon precursor, and blended with PVDF polymer to fabricate PVDF/C-Ti MMMs via non-solvent induced phase inversion. The prepared membrane demonstrates both 1.5 times higher initial and recovered fluxes than the similarly prepared PVDF/TiO₂ membrane, suggesting the C-Ti composite can help maintain higher photodegradation efficiency and better anti-fouling performance. In addition, the comparison of PVDF/C-Ti membrane against pristine PVDF membrane show that the reversible fouling and photodegradation reversible fouling of BSA increased from 10.1% to 6.4%-35.1% and 26.6%, respectively. And the FRR of PVDF/C-Ti membrane was 62.12%, 1.8 times that of PVDF membrane. The PVDF/C-Ti membrane was also applied for lignin separation, where the rejection to sodium lignin sulfonate was maintained at about 75%, and the flux recovery ratio after UV irradiation reached 90%. The demonstrated the advantages of PVDF/C-Ti membrane in photocatalytic degradation and antifouling performance.

Rapid elimination of antibiotic gemifloxacin mesylate and methylene blue over Pt nanoparticles dispersed chitosan/g-C3N4 ternary visible light photocatalyst

Appropriate material selection and proper understanding of bandgap modification are key factors for the development of efficient photocatalysts. Herein, we developed an efficient, well-organized visible light oriented photocatalyst based on g-C₃N₄ in association with polymeric network of chitosan (CTSN) and platinum (Pt) nanoparticles utilizing a straightforward chemical approach. Modern techniques like XRD, XPS, TEM, FESEM, UV-Vis, and FTIR spectroscopy were exploited for characterization of synthesized materials. XRD results confirmed the involvement of α-polymorphic form of CTSN in graphitic carbon nitride. XPS investigation confirmed the establishment of trio photocatalytic structure among Pt, CTSN, and g-C₃N₄. TEM examination showed that the synthesized g-C₃N₄ possesses fine fluffy sheets like structure (100 to 500 nm in size) intermingled with a dense layered framework of CTSN with good dispersion of Pt nanoparticles on g-C₃N₄ and CTSN composite structure. The bandgap energies for g-C₃N₄, CTSN/g-C₃N₄, and Pt@ CTSN/g-C₃N₄ photocatalysts were found to be 2.94, 2.73, and 2.72 eV, respectively. The photodegradation skills of each created structure have been examined on antibiotic gemifloxacin mesylate and methylene blue (MB) dye. The newly developed Pt@CTSN/g-C₃N₄ ternary photocatalyst was found to be efficacious for the elimination of gemifloxacin mesylate (93.3%) in 25 min and MB (95.2%) just in 18 min under visible light. Designed Pt@CTSN/g-C₃N₄ ternary photocatalytic framework exhibited ⁓ 2.20 times more effective than bare g-C₃N₄ for the destruction of antibiotic drug. This study provides a simple route towards the designing of rapid, effective visible light oriented photocatalyts for the existing environmental issues.

Optical and Structural Properties of Composites Based on Poly(urethane) and TiO2 Nanowires

This article's objective is the synthesis of new composites based on thermoplastic polyurethane (TPU) and TiO₂ nanowires (NWs) as free-standing films, highlighting their structural and optical properties. The free-standing TPU-TiO₂ NW films were prepared by a wet chemical method accompanied by a thermal treatment at 100 °C for 1 h, followed by air-drying for 2 h. X-ray diffraction (XRD) studies indicated that the starting commercial TiO₂ NW sample contains TiO₂ tetragonal anatase (A), cubic Ti_0.91O (C), and orthorhombic Ti₂O₃ (OR), as well as monoclinic H₂Ti₃O₇ (M). In the presence of TPU, an increase in the ratio between the intensities of the diffraction peaks at 43.4° and 48° belonging to the C and A phases of titanium dioxide, respectively, is reported. The increase in the intensity of the peak at 43.4° is explained to be a consequence of the interaction of TiO₂ NWs with PTU, which occurs when the formation of suboxides takes place. The variation in the ratio of the absorbance of the IR bands peaked at 765-771 cm^-1 and 3304-3315 cm^-1 from 4.68 to 4.21 and 3.83 for TPU and the TPU-TiO₂ NW composites, respectively, with TiO₂ NW concentration equal to 2 wt.% and 17 wt.%, indicated a decrease in the higher-order aggregates of TPU with a simultaneous increase in the hydrogen bonds established between the amide groups of TPU and the oxygen atoms of TiO₂ NWs. The decrease in the ratio of the intensity of the Raman lines peaked at 658 cm^-1 and 635 cm^-1, which were assigned to the vibrational modes E_g in TiO₂ A and E_g in H₂Ti₃O₇ (I_TiO2-A/I_H2Ti3O7), respectively, from 3.45 in TiO₂ NWs to 0.94-0.96 in the TPU-TiO₂ NW composites, which indicates that the adsorption of TPU onto TiO₂ NWs involves an exchange reaction of TPU in the presence of TiO₂ NWs, followed by the formation of new hydrogen bonds between the -NH- of the amide group and the oxygen atoms of Ti_xO_2x-mn, Ti₂O₃, and Ti_0.91O. Photoluminescence (PL) studies highlighted a gradual decrease in the intensity of the TPU emission band, which is situated in the spectral range 380-650 nm, in the presence of TiO₂ NW. After increasing the TiO₂ NW concentration in the TPU-TiO₂ NW composite mass from 0 wt.% to 2 wt.% and 17 wt.%, respectively, a change in the binding angle of the TPU onto the TiO₂ NW surface from 12.6° to 32° and 45.9°, respectively, took place.

Ceftriaxone sodium degradation by carbon quantum dots (CQDs)-decorated C-doped α-Bi2O3 nanorods

A novel carbon quantum dots decorated C-doped α-Bi₂O₃ photocatalyst (CBO/CQDs) was synthesized by solvothermal method. The synergistic effect of adsorption and photocatalysis highly improved contaminants removal efficiencies. The ceftriaxone sodium degradation rate constant (k) of CBO/CQDs was 11.4 and 3.2 times that of pure α-Bi₂O₃ and C-doped α-Bi₂O₃, respectively. The interstitial carbon doping generated localized states above the valence band, which enhanced the utilization of visible light and facilitated the separation of photogenerated electrons and holes; the loading of CQDs improved the charge carrier separation and extended the visible light response; the reduced particle size of CBO/CQDs accelerated the migration of photogenerated carriers. The •O₂ ^- and h⁺ were identified as the dominant reactive species in ceftriaxone sodium degradation, and the key role of •O₂ ^- was further investigated by NBT transformation experiments. The Fukui index was applied to ascertain the molecular bonds of ceftriaxone sodium susceptible to radical attack, and intermediates analysis was conducted to explore the possible degradation pathways. The toxicity evaluation revealed that some degradation intermediates possessed high toxicity, thus the contaminants require sufficient mineralization to ensure safe discharge. The present study makes new insights into synchronous carbon dopping and CQDs decoration on modification of α-Bi₂O₃, which provides references for future studies.

Remediation of pesticides using TiO2 based photocatalytic strategies: A review

Nowadays, pesticides are regarded as the most dangerous of the various organic pollutants, posing substantial environmental and human threats worldwide. Pesticide contamination has become one of the most crucial environmental issues due to its bio-persistence and bioaccumulation. Different conventional methods are being utilized for pesticide removal, yet pesticides are thought to be significantly present in the environment. The development and application of sophisticated wastewater treatment methods are being pursued to remove contaminants effectively, particularly pesticides. In the past several decades, nanoscience and nanotechnology have emerged as essential tools for the identification, removal, and mineralization of persistent pesticides by employing advanced nanomaterials such as pristine titanium dioxide (TiO₂), doped TiO₂, nanocomposites (NCs) TiO₂, and ternary nanocomposites (TNCs) TiO₂ by advanced oxidation processes (AOPs). Advancement in the characteristics of TiO₂ by doping, co-doping, construction of NCs and TNCs has contributed to the dramatic efficiency up-gradation by reducing band gap, solar active photocatalyst, enhancing PCA, high photostability, chemically inertness and multiple time reusability. Based on previous literature, utilizing La-TiO₂ NCs photocatalyst, the mineralization of pesticide (imidacloprid) attained up to 98.17% that is almost 40-53% greater than pristine TiO₂. The present review attempt to discuss the recent research performed on TiO₂ based nanoparticles (NPs) and NCs for photocatalytic mineralization of various pesticides. The basic mechanism of TiO₂ photocatalysis, types of reactors used for photocatalysis, and optimized experimental conditions of TiO₂ for pesticides mineralization are discussed.

Application of Porous Materials for CO2 Reutilization: A Review

CO2 reutilization processes contribute to the mitigation of CO2 as a potent greenhouse gas (GHG) through reusing and converting it into economically valuable chemical products including methanol, dimethyl ether, and methane. Solar thermochemical conversion and photochemical and electrochemical CO2 reduction processes are emerging technologies in which solar energy is utilized to provide the energy required for the endothermic dissociation of CO2. Owing to the surface-dependent nature of these technologies, their performance is significantly reliant on the solid reactant/catalyst accessible surface area. Solid porous structures either entirely made from the catalyst or used as a support for coating the catalyst/solid reactants can increase the number of active reaction sites and, thus, the kinetics of CO2 reutilization reactions. This paper reviews the principles and application of porous materials for CO2 reutilization pathways in solar thermochemical, photochemical, and electrochemical reduction technologies. Then, the state of the development of each technology is critically reviewed and evaluated with the focus on the use of porous materials. Finally, the research needs and challenges are presented to further advance the implementation of porous materials in the CO2 reutilization processes and the commercialization of the aforementioned technologies.

Engineering Cationic Sulfur-Doped Co3O4 Architectures with Exposing High-Reactive (112) Facets for Photoelectrocatalytic Water Purification

Promoting the generation of intermediate active species (superoxide radical (^•O₂^-)) is an important and challenging task for water purification by photoelectrocatalytic (PEC) oxidation. Herein, we have constructed hierarchical cationic sulfur-doped Co₃O₄ architectures with controllable morphology and highly exposed reactive facets by introducing l-cysteine as a capping reagent and sulfur resource via a one-step hydrothermal reaction. The as-obtained cationic sulfur (1.8 mmol l-cysteine) source doped Co₃O₄ (SC-1.8) architectures with highly exposed (112) facets exhibited superior PEC activities and long-term stability (∼25,000 s) in 1.0 mol·L^-1 sulfuric acid for an accelerated reactive brilliant blue KN-R degradation test. Our experimental and theoretical results confirmed that the superior PEC performance of the SC-1.8 architectures could be ascribed the following factors: (1) the highly exposed reactive (112) facets of SC-1.8 promoted carrier transport and diffusion during the PEC process and facilitated separating the electron/hole pairs and producing the predominant active species (^•O₂^-) compared with currently used other electrodes. (2) Cationic sulfur doped on the lattice of Co₃O₄ can narrow the band gap to extend the photoadsorption range and improve the lifetime of ^•O₂^- to enhance the PEC efficiency. This work not only proves that the SC-1.8 architectures with highly exposed (112) facets are a promising PEC catalyst due to increasing the electron transport and the lifetime of active species but also presents a new strategy for constructing an active PEC catalyst.

Effective oil-water mixture separation and photocatalytic dye decontamination through nickel-dimethylglyoxime microtubes coated superhydrophobic and superoleophilic films

Oils and solvable organic pollutants in wastewater demand separations of the components along with efficient photocatalysis in water treatment. Herein, we report on a practical purification strategy by using the multifunctional nickel-dimethylglyoxime [Ni(DMG)2] microtubes to separate the liquid mixture and degrade organic pollutants. The self-assembled [Ni(DMG)2] tubes was synthesized by a facile co-precipitation method. The static contact angle of the film prepared by mixing [Ni(DMG)2] powder (1 : 2 wt%) into polydimethylsilicone (PDMS) to water can reach 161.3°, which can still remain superhydrophobic but oil-friendly under corrosion conditions. PDMS imparts good mechanical properties and serves as both the adhesive and hydrophobic material. PFOTS methanol solution contains a large number of low surface energy groups, which can reduce the surface free energy of [Ni(DMG)2] rough structure. The superhydrophobic rough surface prepared by hollow micron tubular [Ni(DMG)2] samples must have both low surface energy substance and hollow micron tubular morphology. Due to the unique wettability, oil and water were efficiently separated from the oil-water mixture through the films. The coated film itself is photocatalytic in degrading quinoline blue, rhodamine B, methyl orange and methylene blue. By using the film's multifunctionality, a practical wastewater treatment was realized via water-oil separation, followed by fast photocatalytic degradation of solvable dyes.

A Colorimetric Assay for the Detection of Glucose and H2O2 Based on Cu-Ag/g-C3N4/ZIF Hybrids with Superior Peroxidase Mimetic Activity

In this work, we report the synthesis of Cu-Ag bimetallic nanopartiles and g-C3N4 nanosheets decorated on zeolitic imidazolate framework-8 (ZIF-8) to form a Cu-Ag/g-C3N4/ZIF hybrid. The hybrid was synthesized and characterized by Transmission electron microscopy (TEM), Fourier transformed infrared (FTIR), the X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The Cu-Ag/g-C3N4/ZIF hybrid has intrinsic peroxidaselike catalytic activity towards the oxidation of TMB in the presence of H2O2. The situ synthesis of Cu-Ag bimetallic nanopartiles on 2D support such as g-C3N4 nanosheets would significantly enhance the peroxidaselike catalytic properties of individual Cu-Ag bimetallic nanopartiles and the g-C3N4 nanosheets. After loading of Cu-Ag bimetallic nanopartiles and g-C3N4 nanosheets on the ZIF-8, the hybrids exhibited superior peroxidaselike catalytic activity and good recyclability. Then, this method was applied for detecting glucose in human serum, owing the significant potential for detection of metabolites with H2O2-generation reactions.

Facile Formation of Anatase Nanoparticles on H-Titanate Nanotubes at Low Temperature for Efficient Visible Light-Driven Degradation of Organic Pollutants

Anatase nanoparticles (5–10 nm) generated on H-titanate nanotube surface (H-titanate/anatase) were prepared by an ingenious and simple method. H-titanate tubes were prepared by a hydrothermal reaction of Ti powder in concentrated NaOH solution and an ion exchange process with HNO3 solution. After that, at a relatively low drying temperature (100 °C), a small quantity of anatase nanoparticles were in-situ formed on the H-titanate tubes surface by a surface dehydration reaction. In-situ transformation can form a strong interface coupling between H-titanate and anatase, which is conducive to accelerating charge transfer and improving its photocatalytic activity. In addition, the smaller average crystal size, the large specific surface areas (BET), the nanotubed and layered structure and the synergistic effect of dual phases would be beneficial to improving the photocatalytic efficiency.

Visible-light-driven photochemical activity of ternary Ag/AgBr/TiO2 nanotubes for oxidation C(sp3)–H and C(sp2)–H bonds

The Ag/AgBr/TiO₂ ternary nanotube as a heterogeneous photocatalyst was used for the solvent-free oxidation of the benzylic C(sp³)–H bond or the solvent-controlled selective oxidative cleavage of the CC double bond of styrene under visible light at room temperature.

Reduced Graphene Oxide–P25 Nanocomposites as Efficient Photocatalysts for Degradation of Bisphenol A in Water

Reduced graphene oxide–titanium dioxide photocatalyst (rGO–TiO2) was successfully synthesized by the hydrothermal method. The rGO–TiO2 was used as photocatalyst for the degradation of bisphenol A (BPA), which is a typical endocrine disruptor of the environment. Characterization of photocatalysts and photocatalytic experiments under different conditions were performed for studying the structure and properties of photocatalysts. The characterization results showed that part of the anatase type TiO2 was converted into rutile type TiO2 after hydrothermal treatment and 1% rGO–P25 had the largest specific surface area (52.174 m2/g). Photocatalytic experiments indicated that 1% rGO–P25 had the best catalytic effect, and the most suitable concentration was 0.5 g/L. When the solution pH was 5.98, the catalyst was the most active. Under visible light, the three photocatalytic mechanisms were ranked as follows: O2•− > •OH > h+. 1% rGO–P25 also had strong photocatalytic activity in the photocatalytic degradation of BPA under sunlight irradiation. 1% rGO–P25 with 0.5 g/L may be a very promising photocatalyst with a variety of light sources, especially under sunlight for practical applications.

The Effect of Materials Architecture in TiO2 /MOF Composites on CO2 Photoreduction and Charge Transfer

CO₂ photoreduction to C₁ /C₁₊ energized molecules is a key reaction of solar fuel technologies. Building heterojunctions can enhance photocatalysts performance, by facilitating charge transfer between two heterojunction phases. The material parameters that control this charge transfer remain unclear. Here, it is hypothesized that governing factors for CO₂ photoreduction in gas phase are: i) a large porosity to accumulate CO₂ molecules close to catalytic sites and ii) a high number of "points of contact" between the heterojunction components to enhance charge transfer. The former requirement can be met by using porous materials; the latter requirement by controlling the morphology of the heterojunction components. Hence, composites of titanium oxide or titanate and metal-organic framework (MOF), a highly porous material, are built. TiO₂ or titanate nanofibers are synthesized and MOF particles are grown on the fibers. All composites produce CO under UV-vis light, using H₂ as reducing agent. They are more active than their component materials, e.g., ≈9 times more active than titanate. The controlled composites morphology is confirmed and transient absorption spectroscopy highlights charge transfer between the composite components. It is demonstrated that electrons transfer from TiO₂ into the MOF, and holes from the MOF into TiO₂ , as the MOF induces band bending in TiO₂ .

Hollow Multishelled Heterostructured Anatase/TiO2 (B) with Superior Rate Capability and Cycling Performance

TiO₂ is a potential anode material for lithium-ion batteries due to its high rate capability and high safety. Here, a controllable synthesis for hollow nanostructured TiO₂ , with heterostructured shells of TiO₂ (B) and anatase phases, is presented for the first time, by using a sequential templating approach. The hollow nanostructures can be easily controlled to produce core-shell and double-shelled materials with different compositional ratios of anatase to TiO₂ (B) by tuning the synthetic conditions. When used as the anode materials for lithium-ion batteries, a specific discharge capacity of 215.4 mAh g^-1 for the double-shelled anatase/TiO₂ (B) hollow microspheres is achieved at a current rate of 1 C (335 mA g^-1 ) for the 100th cycle and shows high specific discharge capacities of 141.6 and 125.7 mAh g^-1 at the high rates of 10 and 20 C over 1000 cycles. These results are due to the unique stable hollow multishelled structure, which has a high specific surface area, as well as the interface between the heterostructured anatase/TiO₂ (B) phases contributing a substantial number of lithium-ion storage sites.

Nitrogen-Doped Alkylamine-Intercalated Layered Titanates for Photocatalytic Dye Degradation

A layered titanate, K₂Ti₄O₉, is intercalated with various n-alkylamines through ion-exchange reaction in aqueous medium. On heating, the intercalated amine is partially deintercalated, yielding nitrogen-doped amine-intercalated titanates. The modified titanates are studied as catalysts in methylene blue degradation under UV irradiation. Heat-treated long-chain amine titanates exhibit better photocatalytic activity in comparison to short chain amine titanates. The improved catalytic activity could be attributed to two factors: (i) increased surface access as the titanate layers are well separated, pillared by the alkylamine chains and (ii) nitrogen doping.

Molecular Threading-Dependent Mass Transport in Paper Origami for Single-Step Electrochemical DNA Sensors

Molecular transport controls the efficiency of complex biological network systems such as cellular signaling system and cascade biomedical reaction. However, device fabrication for molecular sensing is often restricted by a low transport efficiency and complicated processing. Here, we report a molecular threading-dependent transport system using three-dimensional (3D) paper origami enabling the directional transport of biomolecules. We demonstrate that framework nucleic acid-based interface engineering allows orthogonal molecular recognition and enzymatic reaction with programmed order on site. We thus develop a single-step electrochemical DNA sensor for quantitative analysis with 1 picomolar sensitivity within 60 min. Our sensor can discriminate a mismatched target at the level of a single base mismatch. Our study shows a great potential toward the development of a biomimetic molecular transport system for point-of-care and precision diagnosis.

The effects of the nature of TiO2 supports on the catalytic performance of Rh–Mn/TiO2 catalysts in the synthesis of C2 oxygenates from syngas

Four types of TiO₂ with different rutile/anatase crystalline phase compositions were used as supports, and the effect of the TiO₂ phase composition on the catalytic properties of supported Rh catalysts in the synthesis of C₂ oxygenates from syngas was studied.

NaYF4:Yb,Tm@TiO2 core@shell structures for optimal photocatalytic degradation of ciprofloxacin in the aquatic environment

The removal of antibiotic residues in the aquatic environment is still a big challenge in environmental protection. Here, we developed NaYF₄:Yb,Tm@TiO₂ as a highly efficient photocatalyst for photocatalytic degradation of ciprofloxacin (CIP), a representative antibiotic in water under simulated solar irradiation. NaYF₄:Yb,Tm@TiO₂ can efficiently utilize a broad spectrum of solar energy to improve the efficiency of ciprofloxacin removal from an aquatic environment. The optimum operation conditions of photocatalyst dosage, pH value, and initial concentrations of CIP were determined by a series of contrast experiments. The dynamic process of CIP removal was monitored by UV-vis spectrophotometry, and can be well predicted by a pseudo first order model. The optimal conditions of photocatalyst dosage, initial concentration of CIP and pH value for CIP photocatalytic degradation were 1 g L⁻¹, 10⁻⁵ M and 8, respectively. This study provides an efficient method for antibiotic removal and enables a promising strategy for other organic water pollutant treatments.

The study indicated the optimum operation conditions to effectively remove ciprofloxacin from aquatic environment by NaYF₄:Yb,Tm@TiO₂ structures.

Core-shell structured titanium dioxide nanomaterials for solar energy utilization

Because of its unmatched resource potential, solar energy utilization currently is one of the hottest research areas. Much effort has been devoted to developing advanced materials for converting solar energy into electricity, solar fuels, active chemicals, or heat. Among them, TiO2 nanomaterials have attracted much attention due to their unique properties such as low cost, nontoxicity, good stability and excellent optical and electrical properties. Great progress has been made, but research opportunities are still present for creating new nanostructured TiO2 materials. Core-shell structured nanomaterials are of great interest as they provide a platform to integrate multiple components into a functional system, showing improved or new physical and chemical properties, which are unavailable from the isolated components. Consequently, significant effort is underway to design, fabricate and evaluate core-shell structured TiO2 nanomaterials for solar energy utilization to overcome the remaining challenges, for example, insufficient light absorption and low quantum efficiency. This review strives to provide a comprehensive overview of major advances in the synthesis of core-shell structured TiO2 nanomaterials for solar energy utilization. This review starts from the general protocols to construct core-shell structured TiO2 nanomaterials, and then discusses their applications in photocatalysis, water splitting, photocatalytic CO2 reduction, solar cells and photothermal conversion. Finally, we conclude with an outlook section to offer some insights on the future directions and prospects of core-shell structured TiO2 nanomaterials and solar energy conversion.

Hierarchically-structured SiO2-Ag@TiO2 hollow spheres with excellent photocatalytic activity and recyclability

A new protocol for constructing sandwich-like SiO₂-Ag@TiO₂ hollow spheres (SAT) is introduced, in which SiO₂ acts as an efficient support for the Ag nanoparticles (Ag NPs) immobilization, while TiO₂ maintains its hierarchical structure and prevents the aggregation of Ag NPs during the photocatalytic reaction. As a photocatalytic agent, the inner and outer surfaces of TiO₂ can be fully occupied by pollutants molecules because of its unique structure, which faster boosts the photo-generated electrons to transfer the substrates, leading to an enhanced photocatalytic performance. Compared with Ag NPs deposited on the surface of SiO₂@TiO₂ (STA), the as-synthesized SAT exhibits a markedly enhanced visible-light and UV light activity than STA for degrading tetracycline and traditional dyes. The excellent photocatalytic performances are ascribed to the enhanced transport paths of photo-generated electrons, reduced recombination probability of e^-/h⁺ pairs, and decreased threat of oxidation and corrosion. Especially, the SAT still maintains its photocatalytic efficiency after five consecutive runs even though the sample is recovered under visible-light irradiation, far beyond the reusability of STA under the same conditions. Therefore, the outstanding photocatalytic activity and excellent recyclability make SAT more potential to purify aquatic contaminants and to meet the demands of future environmental issues.

Oxygen Evolution Activity of Co-Ni Nanochain Alloys: Promotion by Electron Injection

Metal alloy nanoparticles have shown promising applications in electrocatalysis. However, the nanoparticles usually suffer from limited charge-transfer efficiency, which can be solved by preparing one-dimensional materials. Herein, Co-Ni alloy nanochains are prepared by a direct-current arc-discharge method. The nanochains, comprised of mutually coupled uniform nanospheres, can range up to several micrometers in size. When the alloy is exposed to air or under the electro-oxidation process, a metal-metal-oxide heterostructure is obtained. The alloy can inject electrons into the oxide, which makes it more suitable for electrocatalysis. The composition of the samples can be changed by varying the ratio of Ni/Co (i.e., Co, Co₇ Ni₃ , Co₅ Ni₅ , Co₃ Ni₇ , Ni) in the synthesis process. The nanochains show good oxygen evolution performance that correlates with the Ni/Co ratio. Co₇ Ni₃ demonstrates optimal activity with an onset point of 1.50 V vs. reversible hydrogen electrode (RHE) and overpotential of 350 mV at 10 mA cm^-2 . The alloy nanochains also show excellent durability with 95.0 % current retention after a long-term test for 12 h.

Efficient Co@CoPx core–shell nanochains catalyst for the oxygen evolution reaction

Co@CoP_x core–shell nanochains were prepared via a direct-current arc-discharge method and subsequent phosphorization at 350 °C.

Facile formation of mesoporous structured mixed-phase (anatase/rutile) TiO2 with enhanced visible light photocatalytic activity

A new mesoporous anatase/rutile TiO₂ nanocomposite was synthesized at a lower calcination temperature, and exhibited a higher visible light photocatalytic activity.

Efficient catalysts for oxygen evolution derived from cobalt-based alloy nanochains

One-dimensional nanomaterials are widely used in electrocatalysis owing to their high charge transfer efficiency.

Hydrothermal synthesis of TiO2 hollow spheres adorned with SnO2 quantum dots and their efficiency in the production of methanol via photocatalysis

TiO₂ hollow spheres and TiO₂ hollow spheres adorned with SnO₂ quantum dots were synthesized successfully under mild temperature and autogenous pressure using the hydrothermal route. X-ray diffraction, field emission scanning electron microscopy, scanning electron microscopy, transmission electron microscope, photoluminescence spectroscopy, and UV-vis spectroscopy were used to characterize the physical and chemical nature of the synthesized sample. The characterized samples were used in the photocatalytic applications to reduce the concentration of carbon dioxide in the presence of water under the influence of visible light. Our observation confirmed that with increasing SnO₂ content there is a tremendous change in the photocatalytic performance of the samples, due to free mobility of the electrons and holes and decline in charge recombination centers formed with the formation of nano-heterojunction between SnO₂ and TiO₂. The greater photocatalytic production of methanol was achieved using 2ST sample, i.e., 1.61 μmol/g/h which tends to decrease with an increase in SnO₂ content.

High photocatalytic activity of hierarchical SiO2@C-doped TiO2 hollow spheres in UV and visible light towards degradation of rhodamine B

Ongoing research activities are targeted to explore high photocatalytic activity of TiO₂-based photocatalysts for the degradation of environmental contaminants under UV and visible light irradiation. In this work, we devise a facile, cost-effective technique to in situ synthesize hierarchical SiO₂@C-doped TiO₂ (SCT) hollow spheres for the first time. This strategy mainly contains the preparation of monodisperse cationic polystyrene spheres (CPS), sequential deposition of inner SiO₂, the preparation of the sandwich-like CPS@SiO₂@CPS particles, and formation of outer TiO₂. After the one-step removal of CPS templates by calcination at 450°C, hierarchical SiO₂@C-doped TiO₂ hollow spheres are in situ prepared. The morphology, hierarchical structure, and properties of SCT photocatalyst were characterized by TEM. SEM, STEM Mapping, BET, XRD, UV-vis spectroscopy, and XPS. Results strongly confirm the carbon doping in the outer TiO₂ lattice of SCT hollow spheres. When the as-synthesized SCT hollow spheres were employed as a photocatalyst for the degradation of Rhodamine B under visible-light and ultraviolet irradiation, the SCT photocatalyst exhibits a higher photocatalytic activity than commercial P25, effectively overcoming the limitations of poorer UV activity for many previous reported TiO₂-based photocatalysts due to doping.