A review on the advancement in photocatalytic degradation of poly/perfluoroalkyl substances in water: Insights into the mechanisms and structure-function relationship

Poly/perfluoroalkyl substances (PFAS) are persistent organic pollutants and ubiquitous in aquatic environment, which are hazardous to organisms and human health. Several countries and regions have taken actions to regulate or limit the production and emission of some PFAS. Even though a series of water treatment technologies have been developed for removal of PFAS to eliminate their potential adverse effects, the removal and degradation performance are usually unsatisfactory. Photocatalytic degradation of PFAS is considered as one of the most effective approaches due to the mild operation conditions and environmental friendliness. This review systematically summarized the recent advances in photocatalytic degradation of PFAS based on heterogeneous photocatalysts, including TiO2-, Ga2O3-, In2O3-, ZnO-, Bi-based, and others. Overall, two mainly degradation mechanisms were involved, including photo-oxidation (involving the holes and oxidative radicals) and photo-reduction types (by e- and reductive radicals). The band structures of the photocatalysts, degradation pathways, structure-function relationship, and impacting factors were further discussed to elucidate the essential reasons for the enhanced degradation of PFAS. Furthermore, the review identified the major knowledge gaps to solve the issues of photocatalysis in real application. This paper also propounded several strategies to promote the design and optimization of high-efficient photocatalysts, and meet the challenges to remove PFAS through photodegradation technologies.

Design and construction of high strength double network hydrogel with flow-induced orientation

The design and construction of high strength hydrogels is a widely discussed topic in hydrogel research. In this study, we combined three toughening strategies, including dual network, oriented structure construction and nanophase doping, to develop an alginate/polyacrylamide (PAM)/modified titanium dioxide fiber (TiO2 NF@PAM) dual network composite hydrogel prepared via syringe. The effects of different preparation methods, AM/Alginate ratios, inorganic doping phases and TiO2 NF@PAM/AM ratios on the mechanical properties of composite hydrogels were investigated. The study found that the alginate hydrogel prepared by syringe exhibited superior axial orientation and achieved a tensile strength of (1091 ± 46) kPa. And the composite hydrogel doped with 0.2 wt% TiO2 NF@PAM had a tensile strength of (1006 ± 64) kPa, which was higher than that of the composite hydrogel doped with 0.2 wt% TiO2 nanoparticles (976 ± 66) kPa. The highest tensile strength (1120 ± 67) kPa and elongation at break (182 ± 8) % were achieved when the ratio of TiO2 NF@PAM/AM was 0.6 wt%. The force applied to the gel solution in the syringe affects the orientation of the polymer chains and TiO2 NF@PAM within the gel, which subsequently impacts the mechanical properties of the hydrogel. Therefore, we further investigated the mechanical properties of composite hydrogels under varying propulsion speeds, syringe diameters, and syringe lengths. It was observed that the gel solution's shear strength increased as the syringe diameter decreased. The resulting composite hydrogels were better oriented and had improved mechanical properties. The composite hydrogels' tensile strength peaked at (1117 ± 47) kPa when the syringe advance rate was between 1-7 mL/min. The mechanical properties of the hydrogels were optimal when the syringe length was 30 mm, with a maximum tensile strength of (1131 ± 67) kPa and a tensile ratio of (166 ± 5) %. This study demonstrates the viability of integrating three distinct strengthening methodologies to generate hydrogels of considerable strength. Furthermore, the Alginate/PAM/TiO2 NF@PAM composite hydrogels possess remarkable potential as adaptable, wearable sensors due to their exemplary mechanical properties, knittability, and conductivity.

Fluorination of porphyrin β-periphery boosts nickel(II)-catalyzed hydrogen evolution reaction

Tunichlorin, the naturally occurring chlorophyll cofactor containing Ni(II) ion, sets up a golden standard for designing the electrocatalysts for hydrogen evolution reaction (HER) via β-peripheral modification. Besides the fine-tuning of the porphyrin β-periphery such as adjusting the aromatics (the saturated level of tetrapyrrole) or installing hydroxyl group (hydrogen bond network) to enhance the catalytic HER efficiency, here we report that β-fluorination of porphyrin is also an important approach to increase the reactivity of Ni(II) center. Benefiting the previously reported derivatization of β-fluorinated porpholactones, we constructed a β-fluorinated tunichlorin mimic (6). Compared with the non-fluorinated analogs (1, 3, and 5), we found that 2, 4, and 6 exhibit significant electrocatalytic HER reactivity acceleration (in terms of turnover frequencies, TOF, s-1) of ca. 37, 170, 133-fold, respectively. Mechanism studies suggested that β-fluorination negatively shifts the metal complexes' reduction potentials and accelerates the electron transfer process, both contributing to the boosting of HER reaction. Notably, 6 showed an 890-fold increase of TOFs than 1, demonstrating the combining advantages of the of fluorination, hydrogenation, and hydroxylation at porphyrin β-periphery.

Boosting Formate Electrooxidation by Heterostructured PtPd Alloy and Oxides Nanowires

Direct formate fuel cells (DFFCs) receive increasing attention as promising technologies for the future energy mix and environmental sustainability, as formate can be made from carbon dioxide utilization and is carbon neutral. Herein, heterostructured platinum-palladium alloy and oxides nanowires (PtPd-ox NWs) with abundant defect sites are synthesized through a facile self-template method and demonstrated high activity toward formate electrooxidation reaction (FOR). The electronic tuning arising from the heterojunction between alloy and oxides influence the work function of PtPd-ox NWs. The sample with optimal work function reveals the favorable adsorption behavior for intermediates and strong interaction in the d-p orbital hybridization between Pt site and oxygen in formate, favoring the FOR direct pathway with a low energy barrier. Besides the thermodynamic regulation, the heterostructure can also provide sufficient hydroxyl species to facilitate the formation of carbon dioxide due to the ability of combining absorbed hydrogen and carbon monoxide at adjacent active sites, which contributes to the improvement of FOR kinetics on PtPd-ox NWs. Thus, heterostructured PtPd-ox NWs achieve dual regulation of FOR thermodynamics and kinetics, exhibiting remarkable performance and demonstrating potential in practical systems.

NH2-MIL-125-Derived N-Doped TiO2@C Visible Light Catalyst for Wastewater Treatment

The utilization of titanium dioxide (TiO2) as a photocatalyst for the treatment of wastewater has attracted significant attention in the environmental field. Herein, we prepared an NH2-MIL-125-derived N-doped TiO2@C Visible Light Catalyst through an in situ calcination method. The nitrogen element in the organic connector was released through calcination, simultaneously doping into the sample, thereby enhancing its spectral response to cover the visible region. The as-prepared N-doped TiO2@C catalyst exhibited a preserved cage structure even after calcination, thereby alleviating the optical shielding effect and further augmenting its photocatalytic performance by increasing the reaction sites between the catalyst and pollutants. The calcination time of the N-doped TiO2@C-450 °C catalyst was optimized to achieve a balance between the TiO2 content and nitrogen doping level, ensuring efficient degradation rates for basic fuchsin (99.7%), Rhodamine B (89.9%) and tetracycline hydrochloride (93%) within 90 min. Thus, this study presents a feasible strategy for the efficient degradation of pollutants under visible light.

1D Narrow-Bandgap Tin Oxide Materials: Systematic High-Resolution TEM and Raman Analysis

We demonstrate for the first time the structure identification and narrow-bandgap property of 1D hybridized SnO/SnO₂ nanoparticles derived from the calcination of a single-source precursor, i.e., tin(II) oxalate. Systematic Raman analysis together with high-resolution TEM (HR-TEM) measurements of the tin oxide samples were carried out by changing the calcination temperatures. These data revealed the simultaneous formation of 1D SnO/SnO₂ in the rod particles that grew in air. It was also found that Sn(II) can be introduced by changing the concentration of Sn(II) salt in the precursor synthesis and the maximum temperature in calcination. Particles measuring 20~30 nm were sintered to produce tin oxide nanorods including tin monoxide, SnO. Photoabsorption properties associated with the formation of the SnO/SnO₂ nanocomposites were also investigated. Tauc plots indicate that the obtained tin oxide samples had a lower bandgap of 2.9~3.0 eV originating from SnO in addition to a higher bandgap of around 3.5~3.7 eV commonly observed for SnO₂. Such 1D SnO_x/SnO₂ hybrids via tin oxalate synthesis with this optical property would benefit new materials design for photoenergy conversion systems, such as photocatalysts.

Nanostructured TiO2 Arrays for Energy Storage

Because of their extensive specific surface area, excellent charge transfer rate, superior chemical stability, low cost, and Earth abundance, nanostructured titanium dioxide (TiO₂) arrays have been thoroughly explored during the past few decades. The synthesis methods for TiO₂ nanoarrays, which mainly include hydrothermal/solvothermal processes, vapor-based approaches, templated growth, and top-down fabrication techniques, are summarized, and the mechanisms are also discussed. In order to improve their electrochemical performance, several attempts have been conducted to produce TiO₂ nanoarrays with morphologies and sizes that show tremendous promise for energy storage. This paper provides an overview of current developments in the research of TiO₂ nanostructured arrays. Initially, the morphological engineering of TiO₂ materials is discussed, with an emphasis on the various synthetic techniques and associated chemical and physical characteristics. We then give a brief overview of the most recent uses of TiO₂ nanoarrays in the manufacture of batteries and supercapacitors. This paper also highlights the emerging tendencies and difficulties of TiO₂ nanoarrays in different applications.

Progress in semiconductor materials for photocathodic protection: Design strategies and applications in marine corrosion protection

Metal protection of offshore equipment is very complicated owing to the complex marine environment. Photocathodic protection (PCP) is one of the popular research topics in marine metal protection. The protection efficiency of photoanode depends largely on the photoelectric properties of semiconductor materials, viz. the process of charge separation, charge migration, and light absorption. In this article, the enhancement strategies, photoelectrochemical properties, and electron transfer mechanisms of different composites for PCP were reviewed and highlighted. Some photoanodes with unusual and striking properties were emphasized. In addition, the outlooks and challenges of the application of PCP and the design of photoanodes materials are proposed.

Two-Dimensional Sb Modified TiO2 Nanorod Arrays as Photoanodes for Efficient Solar Water Splitting

As one of the widely studied semiconductor materials, titanium dioxide (TiO₂) exhibits high photoelectrochemical (PEC) water-splitting performance as well as high chemical and photo stability. However, limited by a wide band gap and fast electron-hole recombination rate, the low solar-to-hydrogen conversion efficiency remains a bottleneck for the practical application of TiO₂-based photoelectrodes. To improve the charge separation and water oxidation efficiency of TiO₂ photoanodes, antimonene, a two-dimensional (2D) material obtained by liquid-phase exfoliation, was assembled onto TiO₂ nanorod arrays (TNRAs) by a simple drop-coating assembly process. PEC measurements showed that the resulting 2D Sb/TiO₂ photoelectrode displayed an enhanced photocurrent density of about 1.32 mA cm^-2 in 1.0 M KOH at 0.3 V vs. Hg/HgO, which is ~1.65 times higher than that of the pristine TNRAs. Through UV-Vis absorption and electrochemical impedance spectroscopy measurements, it was possible to ascribe the enhanced PEC performances of the 2D Sb/TiO₂ photoanode to increased absorption intensity in the visible light region, and improved interfacial charge-transfer kinetics in the 2D Sb/TiO₂ heterojunction, which promotes electron-hole separation, transfer, and collection.

Photocatalytic Applications of ReS2-Based Heterostructures

ReS2-based heterostructures, which involve the coupling of a narrow band-gap semiconductor ReS2 with other wide band-gap semiconductors, have shown promising performance in energy conversion and environmental pollution protection in recent years. This review focuses on the preparation methods, encompassing hydrothermal, chemical vapor deposition, and exfoliation techniques, as well as achievements in correlated applications of ReS2-based heterostructures, including type-I, type-II heterostructures, and Z-scheme heterostructures for hydrogen evolution, reduction of CO2, and degradation of pollutants. We believe that this review provides an overview of the most recent advances to guide further research and development of ReS2-based heterostructures for photocatalysis.

Engineering interface structures for heterojunction photocatalysts

Solar photocatalysis is the most ideal solution to global energy concerns and environmental deterioration nowadays. The heterojunction combination has become one of the most successful and effective strategies to design and manufacture composite photocatalysts. Heterojunction structures are widely documented to markedly improve the photocatalytic behavior of materials by enhancing the separation and transfer of photogenerated charges, widening the light absorption range, and broadening redox potentials, which are attributed to the presence of both build-in electric fields at the interface of two different materials and the complementarity between different electron structures. So far, a large number of heterojunction photocatalytic materials have been reported and applied for water splitting, reduction of carbon dioxide and nitrogen, environmental cleaning, etc. This review outlines the recent accomplishments in the design and modification of interface structures in heterojunction photocatalysts, aiming to provide some useful perspectives for future research in this field.

Modification of Liquid Separation Membranes Using Multidimensional Nanomaterials: Revealing the Roles of Dimension Based on Classical Titanium Dioxide

Membrane technology has become increasingly popular and important for separation processes in industries, as well as for desalination and wastewater treatment. Over the last decade, the merger of nanotechnology and membrane technology in the development of nanocomposite membranes has emerged as a rapidly expanding research area. The key motivation driving the development of nanocomposite membranes is the pursuit of high-performance liquid separation membranes that can address the bottlenecks of conventionally used polymeric membranes. Nanostructured materials in the form of zero to three-dimensions exhibit unique dimension-dependent morphology and topology that have triggered considerable attention in various fields. While the surface hydrophilicity, antibacterial, and photocatalytic properties of TiO₂ are particularly attractive for liquid separation membranes, the geometry-dependent properties of the nanocomposite membrane can be further fine-tuned by selecting the nanostructures with the right dimension. This review aims to provide an overview and comments on the state-of-the-art modifications of liquid separation membrane using TiO₂ as a classical example of multidimensional nanomaterials. The performances of TiO₂-incorporated nanocomposite membranes are discussed with attention placed on the special features rendered by their structures and dimensions. The innovations and breakthroughs made in the synthesis and modifications of structure-controlled TiO₂ and its composites have enabled fascinating and advantageous properties for the development of high-performance nanocomposite membranes for liquid separation.

Highly-Efficient and Visible Light Photocatalytical Degradation of Organic Pollutants Using TiO2-Loaded on Low-Cost Biomass Husk

A composite composing of TiO₂ nanoparticles load on biomass rice husk (RH) is developed by directly growing TiO₂ nanoparticles on RH. The in-situ growth of the nanocrystals on RH is achieved by a low-cost and one-step homogeneous precipitation. Rapid hydrolysis proceeds at 90 °C by using ammonium fluotitanate and urea to facilitate the selective growth of TiO₂. The method provides an easy access to the TiO₂-RH composite with a strong interaction between TiO₂ nanoparticles and the underlying RH. The structure and composition of TiO₂-RH are characterized by using X-ray diffraction, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, and UV-vis absorption spectroscopy. TiO₂ nanoparticles-RH exhibits a good photocatalytic degradation of methyl orange. The results show that 92% of methyl orange (20 mg L^-1) can be degraded within three hours in visible light. The catalytic activity of the composite is not reduced after 6 cycles, and it still reaches 81% after 6 cycles. The enhanced performance is ascribed to the suitable particle size the good dispersibility. It is expected that the high photocatalytical performance and the cost-effective composite presented here will inspire the development of other high-performance photocatalysts.

Multi-Functional Materials Based on Cu-Doped TiO2 Ceramic Fibers with Enhanced Pseudocapacitive Performances and Their Dielectric Characteristics

In this work, pure TiO2 and Cu (0.5, 1, 2%)-doped TiO2 composites prepared by electrospinning technique followed by calcination at 900 °C, and having high pseudocapacitive and dielectric characteristics were reported. These nanocomposites were characterized by scanning electron microscopy, X-ray diffraction, and dynamic water sorption vapor measurements. The structural characterization of these nanostructures highlighted good crystallinity including only the rutile phase. The electrochemical characteristics were investigated by cyclic voltammetry and galvanostatic charge–discharge measurements, which were performed in a KOH electrolyte solution. Among the Cu-doped TiO2 nanostructures that were prepared, the one containing 0.5% Cu exhibited superior electrochemical properties, including high specific gravimetric capacitance of 1183 F·g−1, specific capacitance of 664 F·g−1, energy density of 45.20 Wh·kg−1, high power density of 723.14 W·kg−1, and capacitance retention of about 94% after 100 cycles. The dielectric investigation shows good dielectric properties for all materials, where the dielectric constant and the dielectric loss decreased with the frequency increase. Thus, all the interconnected studies proved that these new materials show manifold ability and real applicative potential as pseudocapacitors and high-performance dielectrics. Future work and perspectives are anticipated for characterizing electrochemical and dielectric properties for materials including larger amounts of Cu dopant.

Solid-Phase Synthesis of Titanium Dioxide Micro-Nanostructures

Titanium dioxide (TiO₂) micro-nanostructures are widely utilized in photochemical applications due to their unique band gaps and are of huge demand in scientific research and industrial manufacture. Herein, this work reports a controllable, facile, economical, and green solid-phase synthesis strategy to prepare TiO₂ with governable morphologies containing 1D nanorods, 3D microbulks, and irregular thick plates. Specifically, Ti powders are transformed into TiO₂ micro-nanostructures through dispersing them into a solid NaOH/KOH mixture with a low eutectic point, followed by grinding, heating, ion exchange, and calcination. As no solvents are utilized in the alkali treatment process, the usage of solvents is decreased and high vapor pressure is avoided. Moreover, the band gaps of TiO₂ micro-nanostructures can be regulated from 3.02 to 3.34 eV through altering the synthetic parameters. Notably, the as-prepared TiO₂ micro-nanostructures exhibit high photocatalytic activities in the degradation of rhodamine B and methylene blue under simulated solar light illumination. It is believed that the solid-phase synthesis strategy will be of huge demand for the synthesis of TiO₂ micro-nanostructures.

Visible Light Induced Ag-Polyoxometalate Coassembly into Single-Cluster Nanowires

1D superlattices with long-ranged periodicity present extraordinary application properties due to their unique electronic structures. Here, the visible light driven synthesis of 1D single-cluster chains constructed by polyoxometalate (POM) and Ag clusters is reported, where two types of clusters align alternatively along the nanowire. Low symmetrical POM clusters of [P₂ W₁₇ O₆₁ ]^10- , [P₂ W₁₅ O₅₆ ]^12- , and [EuW₁₀ O₃₆ ]^9- can be used as building blocks. The directly bonding cluster units result in interactive electronic structures of Ag and POM clusters, as well as the greatly promoted electron transfer during the redox reaction. The Ag-P₂ W₁₇ nanowires perform significantly enhanced activities in both electrochemical sensing and catalytic gasoline desulfurization compared with individual building blocks, demonstrating the extraordinary application properties and promising potentials of cluster-based heteroconstructions.

Nano-architectural design of TiO2 for high performance photocatalytic degradation of organic pollutant: A review

In the past several decades, significant efforts have been paid toward photocatalytic degradation of organic pollutants in environmental research. During the past years, titanium dioxide nano-architectures (TiO₂ NAs) have been widely used in water purification applications with photocatalytic degradation processes under Uv/Vis light illumination. Photocatalysis process with nano-architectural design of TiO₂ is viewed as an efficient procedure for directly channeling solar energy into water treatment reactions. The considerable band-gap values and the subsequent short life time of photo-generated charge carriers are showed among the limitations of this approach. One of these effective efforts is the using of oxidation processes with advance semiconductor photocatalyst NAs for degradation the organic pollutants under UV/Vis irradiation. Among them, nano-architectural design of TiO₂ photocatalyst (such as Janus, yolk-shell (Y@S), hollow microspheres (HMSs) and nano-belt) is an effective way to improve oxidation processes for increasing photocatalytic activity in water treatment applications. In the light of the above issues, this study tends to provide a critical overview of the used strategies for preparing TiO₂ photocatalysts with desirable physicochemical properties like enhanced absorption of light, low density, high surface area, photo-stability, and charge-carrier behavior. Among the various nanoarchitectural design of TiO₂, the Y@S and HMSs have created a great appeal given their considerable large surface area, low density, homogeneous catalytic environment, favorable light harvesting properties, and enhanced molecular diffusion kinetics of the particles. In this review was summarized the developments that have been made for nano-architectural design of TiO2 photocatalyst. Additional focus is placed on the realization of interfacial charge and the possibility of achieving charge carriers separation for these NAs as electron migration is the extremely important factor for increasing the photocatalytic activity.

Synthesis and applications of TiO2/ZnO hybrid nanostructures by ZnO deposition on TiO2 nanotubes using electrochemical processes

In recent years, TiO2/ZnO hybrid nanostructures have been attracting the interest of the scientific community due to their excellent photoelectrochemical properties. The main advantage of TiO2/ZnO hybrid nanostructures over other photocatalysts based on semiconductor materials lies in their ability to form heterojunctions in which the valence and conduction bands of both semiconductors are intercalated. This factor produces a decrease in the band gap and the recombination rate and an increase in the light absorption range. The aim of this review is to perform a revision of the main methods to synthesise TiO2/ZnO hybrid nanostructures by ZnO deposition on TiO2 nanotubes using electrochemical processes. Electrochemical synthesis methods provide an easy, fast, and highly efficient route to carry out the synthesis of nanostructures such as nanowires, nanorods, nanotubes, etc. They allow us to control the stoichiometry, thickness and structure mainly by controlling the voltage, time, temperature, composition of the electrolyte, and concentration of monomers. In addition, a study of the most promising applications for TiO2/ZnO hybrid nanostructures has been carried out. In this review, the applications of dye-sensitised solar cell, photoelectrocatalytic degradation of organic compounds, photoelectrochemical water splitting, gas sensors, and lithium-ion batteries have been highlighted.

Electrocatalysis in Room Temperature Sodium-Sulfur Batteries: Tunable Pathway of Sulfur Speciation

Benefiting from the merits of natural abundance, low cost, and ultrahigh theoretical energy density, the room temperature sodium-sulfur (RT NaS) batteries are regarded as one of the promising candidates for the next-generation scalable energy storage devices. However, the uncontrollable sulfur speciation pathways severely hinder its practical applications. Recently, various strategies have been employed to tune the conversion pathways of sulfur, such as physical confinement, chemical inhibition, and electrocatalysis. Herein, the recent advances in electrocatalytic effects manipulate sulfur speciation pathways in advanced RT NaS electrochemistry are reviewed, including the promotion of the nearly full conversion of long-chain polysulfides, short-chain polysulfides, and small sulfur molecules. The underlying catalytic modulation mechanism that fundamentally tunes the electrochemical pathway of sulfur species is comprehensively summarized along with the design strategies for catalytic active centers. Furthermore, the challenge and potential solutions to realize the quasi-solid conversion of sulfur are proposed to accelerate the real application of RT NaS batteries.

Application of Nanostructured TiO2 in UV Photodetectors: A Review

As a wide-bandgap semiconductor material, titanium dioxide (TiO₂ ), which possesses three crystal polymorphs (i.e., rutile, anatase, and brookite), has gained tremendous attention as a cutting-edge material for application in the environment and energy fields. Based on the strong attractiveness from its advantages such as high stability, excellent photoelectric properties, and low-cost fabrication, the construction of high-performance photodetectors (PDs) based on TiO₂ nanostructures is being extensively developed. An elaborate microtopography and device configuration is the most widely used strategy to achieve efficient TiO₂ -based PDs with high photoelectric performances; however, a deep understanding of all the key parameters that influence the behavior of photon-generated carriers, is also highly required to achieve improved photoelectric performances, as well as their ultimate functional applications. Herein, an in-depth illustration of the electrical and optical properties of TiO₂ nanostructures in addition to the advances in the technological issues such as preparation, microdefects, p-type doping, bandgap engineering, heterojunctions, and functional applications are presented. Finally, a future outlook for TiO₂ -based PDs, particularly that of further functional applications is provided. This work will systematically illustrate the fundamentals of TiO₂ and shed light on the preparation of more efficient TiO₂ nanostructures and heterojunctions for future photoelectric applications.

TiO2 as an Anode of High-Performance Lithium-Ion Batteries: A Comprehensive Review towards Practical Application

Lithium-ion batteries (LIBs) are undeniably the most promising system for storing electric energy for both portable and stationary devices. A wide range of materials for anodes is being investigated to mitigate the issues with conventional graphite anodes. Among them, TiO2 has attracted extensive focus as an anode candidate due to its green technology, low volume fluctuations (<4%), safety, and durability. In this review, the fabrication of different TiO2 nanostructures along with their electrochemical performance are presented. Different nanostructured TiO2 materials including 0D, 1D, 2D, and 3D are thoroughly discussed as well. More precisely, the breakthroughs and recent developments in different anodic oxidation processes have been explored to identify in detail the effects of anodization parameters on nanostructure morphology. Clear guidelines on the interconnected nature of electrochemical behaviors, nanostructure morphology, and tunable anodic constraints are provided in this review.

Coupled Multiphysics Modelling of Sensors for Chemical, Biomedical, and Environmental Applications with Focus on Smart Materials and Low-Dimensional Nanostructures

Low-dimensional nanostructures have many advantages when used in sensors compared to the traditional bulk materials, in particular in their sensitivity and specificity. In such nanostructures, the motion of carriers can be confined from one, two, or all three spatial dimensions, leading to their unique properties. New advancements in nanosensors, based on low-dimensional nanostructures, permit their functioning at scales comparable with biological processes and natural systems, allowing their efficient functionalization with chemical and biological molecules. In this article, we provide details of such sensors, focusing on their several important classes, as well as the issues of their designs based on mathematical and computational models covering a range of scales. Such multiscale models require state-of-the-art techniques for their solutions, and we provide an overview of the associated numerical methodologies and approaches in this context. We emphasize the importance of accounting for coupling between different physical fields such as thermal, electromechanical, and magnetic, as well as of additional nonlinear and nonlocal effects which can be salient features of new applications and sensor designs. Our special attention is given to nanowires and nanotubes which are well suited for nanosensor designs and applications, being able to carry a double functionality, as transducers and the media to transmit the signal. One of the key properties of these nanostructures is an enhancement in sensitivity resulting from their high surface-to-volume ratio, which leads to their geometry-dependant properties. This dependency requires careful consideration at the modelling stage, and we provide further details on this issue. Another important class of sensors analyzed here is pertinent to sensor and actuator technologies based on smart materials. The modelling of such materials in their dynamics-enabled applications represents a significant challenge as we have to deal with strongly nonlinear coupled problems, accounting for dynamic interactions between different physical fields and microstructure evolution. Among other classes, important in novel sensor applications, we have given our special attention to heterostructures and nucleic acid based nanostructures. In terms of the application areas, we have focused on chemical and biomedical fields, as well as on green energy and environmentally-friendly technologies where the efficient designs and opportune deployments of sensors are both urgent and compelling.

Boosting Cycling Stability and Rate Capability of Li-CO2 Batteries via Synergistic Photoelectric Effect and Plasmonic Interaction

Sluggish CO₂ reduction/evolution kinetics at cathodes seriously impede the realistic applications of Li-CO₂ batteries. Herein, synergistic photoelectric effect and plasmonic interaction are introduced to accelerate CO₂ reduction/evolution reactions by designing a silver nanoparticle-decorated titanium dioxide nanotube array cathode. The incident light excites energetic photoelectrons/holes in titanium dioxide to overcome reaction barriers, and induces the intensified electric field around silver nanoparticles to enable effective separation/transfer of photogenerated carriers and a thermodynamically favorable reaction pathway. The resulting Li-CO₂ battery demonstrates ultra-low charge voltage of 2.86 V at 0.10 mA cm^-2 , good cycling stability with 86.9 % round-trip efficiency after 100 cycles, and high rate capability at 2.0 mA cm^-2 . This work offers guidance on rational cathode design for advanced Li-CO₂ batteries and beyond.

Recent advances and perspectives for solar-driven water splitting using particulate photocatalysts

The conversion and storage of solar energy to chemical energy via artificial photosynthesis holds significant potential for optimizing the energy situation and mitigating the global warming effect. Photocatalytic water splitting utilizing particulate semiconductors offers great potential for the production of renewable hydrogen, while this cross-road among biology, chemistry, and physics features a topic with fascinating interdisciplinary challenges. Progress in photocatalytic water splitting has been achieved in recent years, ranging from fundamental scientific research to pioneering scalable practical applications. In this review, we focus mainly on the recent advancements in terms of the development of new light-absorption materials, insights and strategies for photogenerated charge separation, and studies towards surface catalytic reactions and mechanisms. In particular, we emphasize several efficient charge separation strategies such as surface-phase junction, spatial charge separation between facets, and polarity-induced charge separation, and also discuss their unique properties including ferroelectric and photo-Dember effects on spatial charge separation. By integrating time- and space-resolved characterization techniques, critical issues in photocatalytic water splitting including photoinduced charge generation, separation and transfer, and catalytic reactions are analyzed and reviewed. In addition, photocatalysts with state-of-art efficiencies in the laboratory stage and pioneering scalable solar water splitting systems for hydrogen production using particulate photocatalysts are presented. Finally, some perspectives and outlooks on the future development of photocatalytic water splitting using particulate photocatalysts are proposed.

Titanium dioxide based nanocomposites - Current trends and emerging strategies for the photocatalytic degradation of ruinous environmental pollutants

Many ruinous pollutants are omnipresent in the environment and among them; pesticides are xenobiotic and pose to be a bio-recalcitrance. Their detrimental ecological and environmental impacts attract attention of environmental excerpts and the surge of stringent regulations have endows the need of a technically feasible treatment. This critical review emphasizes about the occurrence, abundance and fate of structurally distinct pesticides in different environment. The practiced remedial strategies and in particular, the advanced oxidation processes (AOPs) those utilize the photo-catalytic properties of nano-composites for the degradation of pollutants are critically discussed. Photo-catalytic degradation utilizes many composite materials at nano-scale level, wherein synthesis of nano-composites with appropriate precursors and other adjoining functional moieties are of prime importance. Therefore, suitable starter materials along with the reaction conditions are prerequisite for effectively tailoring the nano-composites. The aforementioned aspects and their customized applications are critically discussed. The associated challenges, opportunities and process economics of degradation using photo-catalytic AOP techniques are highlighted and in addition, the review tries to explain how best the photo-degradation can be a stand-alone tool with a societal importance. Conclusively, the future prospects for undertaking new researches in photo-catalytic breakdown of pollutants that can be judiciously sustainable.

Recent advances, influencing factors, and future research prospects using photocatalytic process for produced water treatment

Oilfield-produced water is the primary by-product generated during oil and gas extraction operations. Oilfield-produced water is often severely toxic and poses substantial health, safety, and environmental issues; adequate treatment technologies can bring these streams to a quality level. Photocatalysis is a photochemical catalytic reaction that is a highly promising tool for environmental remediation due to its efficiency in mineralizing persistent and potentially toxic contaminants. However, there is limited understanding of its application to treat oilfield-produced water with a complex and highly variable water composition. This review article discusses the mechanisms and current state of heterogeneous photocatalytic systems for oilfield-produced water treatment, highlighting impediments to knowledge transfer, including the feasibility of practical applications and the identification of essential research requirements. Additionally, the effects of significant variables such as catalyst quantity, pH, organic compound concentration, light intensity, and wavelength are discussed in detail. Some solutions are proposed for scientists and engineers interested in advancing the development of industrial-scale photocatalytic water treatment technologies.

An Effective Photocatalytic Degradation of Industrial Pollutants through Converting Titanium Oxide to Magnetic Nanotubes and Hollow Nanorods by Kirkendall Effect

Controlling of morphology from nanoparticles to magnetic nanotubes and hollow nanorods are interesting for developing the photo-active materials and their applications in the field of photocatalysis and decontamination of aquatic effluents. In the current study, titanium dioxide nanoparticles and nanocomposites were prepared by different techniques to produce various morphologies. The nanoparticles of pure titanium dioxide were prepared by sol-gel technique. Magnetic nanotubes and hollow nanorods were prepared by combining titanium with di- and tri-valent iron through two stages: urea hydrolysis and solvent thermal technique. According to the Kirkendall effect, magnetic nanotubes were fabricated by unequal diffusion of Fe²⁺, Fe³⁺ and Ti⁴⁺ inside the nanocomposite to produce maghemite-titanian phase. In the same trend, hollow nanorods were synthesized by limited diffusion of both trivalent iron and tetravalent titanium producing amorphous structure of titanium iron oxides. The magnetic and optical properties showed that these nanotubes and hollow nanorods are magnetically active and optically more effective compared with titanium dioxide nanoparticles. Therefore, the Naphthol green B dye completely disappeared after 45 min of UV light irradiation in presence of the hollow nanorods. The kinetic study confirmed the high performance of the hollow nanorods for the photocatalytic degradation of Naphthol green B compared with titanium dioxide nanoparticles.

Effective stabilization of atomic hydrogen by Pd nanoparticles for rapid hexavalent chromium reduction and synchronous bisphenol A oxidation during the photoelectrocatalytic process

Atomic hydrogen (H*) plays a vital role in the synchronous redox of metallic ions and organic molecules. However, H* is extremely unstable as it is easily converted to hydrogen. Herein, we designed a novel strategy for the effective stabilization of H* to enhance its utility. The synthesized Pd nanoparticles grown on the defective MoS₂ (DMS) of TiO₂ nanowire arrays (TNA) (TNA/DMS/Pd) photocathode exhibited rapid Cr(VI) reduction (~95% in 10 min) and bisphenol A (BPA) oxidation (~97% in 30 min), with the kinetic constants almost 24- and 6-fold higher than those of the TNA photocathode, respectively. This superior performances could be attributed to: (i) the generated interface heterojunctions between TNA and DMS boosted the separation efficiencies of photogenerated electrons, thereby supplying abundant valance electrons to lower the overpotential to create a suitable microenvironment for H* generation; (ii) the stabilization of H* by Pd nanoparticles resulted in a significant increase in the yield of hydroxyl radical (•OH). This research provides a new strategy for the effective utilization of H* toward rapid reduction of heavy metals and synchronous oxidation of the refractory organics.

Magnetic Nanostructures: Rational Design and Fabrication Strategies toward Diverse Applications

In recent years, the continuous development of magnetic nanostructures (MNSs) has tremendously promoted both fundamental scientific research and technological applications. Different from the bulk magnet, the systematic engineering on MNSs has brought a great breakthrough in some emerging fields such as the construction of MNSs, the magnetism exploration of multidimensional MNSs, and their potential translational applications. In this review, we give a detailed description of the synthetic strategies of MNSs based on the fundamental features and application potential of MNSs and discuss the recent progress of MNSs in the fields of nanomedicines, advanced nanobiotechnology, catalysis, and electromagnetic wave adsorption (EMWA), aiming to provide guidance for fabrication strategies of MNSs toward diverse applications.

Grafting Hypercrosslinked Polymers on TiO2 Surface for Anchoring Ultrafine Pd Nanoparticles: Dramatically Enhanced Efficiency and Selectivity toward Photocatalytic Reduction of CO2 to CH4

Metal deposition with photocatalyst is a promising way to surmount the restriction of fast e^- /h⁺ recombination to improve the photocatalytic performance. However, the improvement remains limited by the existing strategies adopted for depositing metal particles due to the serious aggregation and large unconnected area on photocatalyst surface. Here, a strategy is proposed by directly grafting hypercrosslinked polymers (HCPs) on TiO₂ surface to construct Pd-HCPs-TiO₂ composite with uniform dispersion of ultrafine Pd nanoparticles on HCPs surface. This composite with surface area of 373 m² g^-1 exhibits improved photocatalytic CO₂ conversion efficiency to CH₄ with an evolution rate of 237.4 µmol g^-1 h^-1 and selectivity of more than 99.9%. The enhancement can be ascribed to the grafted porous HCPs with high surface area and N heteroatom on TiO₂ surface for the stabilization of Pd nanoparticles, favoring the electron transfer and CO₂ adsorption for selective CH₄ production. This strategy may hold the promise for design and construction of porous organic polymer with semiconductor for efficient photocatalytic conversion.

In Situ One-Pot Synthesis of C-Decorated and Cl-Doped Sea-Urchin-like Rutile Titanium Dioxide with Highly Efficient Visible-Light Photocatalytic Activity

Titanium dioxide (TiO₂) that offers high light-harvesting capacity and efficient charge separation holds great promise in photocatalysis. In this work, an in situ one-pot hydrothermal synthesis was explored to prepare a C-decorated and Cl-doped sea-urchin-like rutile TiO₂ (Cl-TiO₂/C). The growth of sea-urchin-like 3D hierarchical nanostructures was governed by a mechanism of nucleation and nuclei growth-dissolution-recrystallization growth from time-dependent morphology evolution. The crystal morphology and the content of Cl and C could be controlled by the volume ratio of HCl to TBOT. Systematic studies indicated that the 0.4Cl-TiO₂/C sample (the volume ratio of HCl to TBOT was 0.4) exhibited the highest visible-light photocatalytic activity for the degradation of rhodamine B, with kinetic rate constant (k) of 0.0221 min^-1, being 6.5 and 3.75 times higher than that of TiO₂ and Cl-TiO₂. The enhanced photocatalytic performance could be attributed to the high charge separation and transfer efficiency induced by Cl-doping and C decoration and the excellent light-harvesting capacity caused by its sea-urchin-like nanostructure. Moreover, the 0.4Cl-TiO₂/C sample exhibited good reusability and excellent structural stability for five cycles. This facile one-pot approach provides new insight for the preparation of a TiO₂-based photocatalyst with excellent photocatalytic performance for potential application in practical wastewater treatment.

Blue light-powered hydroxynaphthoic acid-titanium dioxide photocatalysis for the selective aerobic oxidation of amines

Solar photocatalysis is the key to resolve many environmental challenges but is usually hard to achieve over a metal oxide semiconductor. Therefore, assembling π-conjugated molecules onto semiconductors becomes an efficient approach to solar conversion via ligand-to-metal charge transfer. Here, a rational design of ligands for titanium dioxide (TiO₂) is presented to produce robust visible light photocatalysts. Three hydroxynaphthoic acids (HNAs) were selected as ligands by extending an extra benzene ring of salicylic acid (SA) at 3,4 or 4,5 or 5,6 positions. These ligands could regulate the performance of TiO₂ in which 2-hydroxy-1-naphthoic acid (2H1NA) endows the best outcome. In detail, blue light-powered cooperative photocatalysis of 2H1NA-TiO₂ with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO, 5 mol%) inaugurates the expeditious formation of imines by oxidation of amines with atmospheric oxygen (O₂). Interestingly, the increase of the O₂ pressure from 1 atm to 0.4 MPa promoted the selective oxidation of benzylamine but thereafter declined with a further boost to 0.6 MPa. Notably, an electron transfer between the oxidatively quenched 2H1NA-TiO₂ and TEMPO is established, offering a new pathway for environmental applications. This work presents a strategy in designing cutting-edge visible light photocatalysts via altering semiconductors with surface ligands.

Dye-sensitized solar cells strike back

Dye-sensitized solar cells (DSCs) are celebrating their 30th birthday and they are attracting a wealth of research efforts aimed at unleashing their full potential. In recent years, DSCs and dye-sensitized photoelectrochemical cells (DSPECs) have experienced a renaissance as the best technology for several niche applications that take advantage of DSCs' unique combination of properties: at low cost, they are composed of non-toxic materials, are colorful, transparent, and very efficient in low light conditions. This review summarizes the advancements in the field over the last decade, encompassing all aspects of the DSC technology: theoretical studies, characterization techniques, materials, applications as solar cells and as drivers for the synthesis of solar fuels, and commercialization efforts from various companies.