Enhanced photocatalytic H2-production activity of bicomponent NiO/TiO2 composite nanofibers

Boosting photocatalytic water splitting of TiO2 using metal (Ru, Co, or Ni) co-catalysts for hydrogen generation

The photocatalytic activity of titanium dioxide (TiO2) nanoparticles toward hydrogen generation can be significantly improved via the loading of various metals e.g., Ru, Co, Ni as co-catalysts. The metal co-catalysts are loaded into TiO2 nanoparticles via different deposition methods; incipient wet impregnation (Imp), hydrothermal (HT), or photocatalytic deposition (PCD). Among all of the tested materials, 0.1 wt% Ru-TiO2 (Imp) provided the highest initial hydrogen catalytic rate of 23.9 mmol h-1 g-1, compared to 10.82 and 16.55 mmol h-1 g-1 for 0.3 wt% Ni-TiO2 (Imp) and 0.3 wt% Co-TiO2 (Imp), respectively. The loading procedures, co-catalyst metals type, and their loading play a significant role in elevating the photocatalytic activity of pristine TiO2 semiconductors toward hydrogen generation. Redox transition metals e.g., Co and Ni exhibit comparable photocatalytic performance to expensive elements such as Ru.

Theoretical prediction and shape-controlled synthesis of two-dimensional semiconductive Ni3TeO6

Current progress in two-dimensional (2D) materials explorations leads to constant specie enrichments of possible advanced materials down to two dimensions. The metal chalcogenide-based 2D materials are promising grounds where many adjacent territories are waiting to be explored. Here, a stable monolayer Ni3TeO6 (NTO) structure was computationally predicted and its stacked 2D nanosheets experimentally synthesized. Theoretical design undergoes featuring coordination of metalloid chalcogen, slicing the bulk structure, geometrical optimizations and stability study. The predicted layered NTO structure is realized in nanometer-thick nanosheets via a one-pot shape-controlled hydrothermal synthesis. Compared to the bulk, the 2D NTO own a lowered bandgap energy, more sensitive wavelength selectivity and an emerging photocatalytic hydrogen evolution ability under visible light. Beside a new 2D NTO with the optoelectrical and photocatalytic merits, its existing polar space group, structural specification, and design route are hoped to benefit 2D semiconductor innovations both in species enrichment and future applications.

Electrospinning of PLA Nanofibers: Recent Advances and Its Potential Application for Food Packaging

Poly(lactic acid), also abbreviated as PLA, is a promising biopolymer for food packaging owing to its environmental-friendly characteristic and desirable physical properties. Electrospinning technology makes the production of PLA-based nanomaterials available with expected structures and enhanced barrier, mechanical, and thermal properties; especially, the facile process produces a high encapsulation efficiency and controlled release of bioactive agents for the purpose of extending the shelf life and promoting the quality of foodstuffs. In this study, different types of electrospinning techniques used for the preparation of PLA-based nanofibers are summarized, and the enhanced properties of which are also described. Moreover, its application in active and intelligent packaging materials by introducing different components into nanofibers is highlighted. In all, the review establishes the promising prospects of PLA-based nanocomposites for food packaging application.

Synthesis, modification and application of titanium dioxide nanoparticles: a review

Titanium dioxide (TiO₂) has been heavily investigated owing to its low cost, benign nature and strong photocatalytic ability. Thus, TiO₂ has broad applications including photocatalysts, Li-ion batteries, solar cells, medical research and so on. However, the performance of TiO₂ is not satisfactory due to many factors such as the broad band gap (3.01 to 3.2 eV) and fast recombination of electron-hole pairs (10^-12 to 10^-11 s). Plenty of work has been undertaken to improve the properties, such as structural and dopant modifications, which broaden the applications of TiO₂. This review mainly discusses the aspects of TiO₂-modified nanoparticles including synthetic methods, modifications and applications.

Molybdenum disulfide loading on a Z-scheme graphitic carbon nitride and lanthanum nickelate heterojunction for enhanced photocatalysis: Interfacial charge transfer and mechanistic insights

Interfacial design and the co-catalyst effect are considered to be effective to achieve separation and transport of photogenerated carriers in composite photocatalysts. In this study, a Z-scheme heterojunction was successfully combined with a co-catalyst to achieve a highly efficient LaNiO₃/g-C₃N₄/MoS₂ photocatalyst. MoS₂ flakes were loaded on a hybrid material surface, which was formed by LaNiO₃ nanocubes embedded on layered g-C₃N₄, and a good heterostructure with multiple attachment sites was obtained. Experimental studies confirmed that the Z-scheme heterojunction completely preserves the strong redox ability of the photogenerated electrons and holes. As a cocatalyst, MoS₂ further promoted interfacial charge separation and transport. The synergistic effect of the Z-scheme heterojunction and co-catalyst effectively realized the transfer of photogenerated carriers from "slow transfer" to "high transfer" and promoted water decomposition and pollutant degradation. Results revealed that under simulated sunlight irradiation, LaNiO₃/g-C₃N₄/MoS₂ composites exhibit superior hydrogen evolution of 45.1 μmol h^-1, which is 19.1 times that of g-C₃N₄ and 4.9 times that of LaNiO₃/g-C₃N₄, respectively. Moreover, the LaNiO₃/g-C₃N₄/MoS₂ Z-scheme photocatalyst exhibited excellent photocatalytic performance for antibiotic degradation and heavy-metal ion reduction under visible light. This study might provide some insights into the development of photocatalysts for solar energy conversion and environmental remediation.

Photocatalytic and Antibacterial Properties of a 3D Flower-Like TiO2 Nanostructure Photocatalyst

Flower-like titanium dioxide (TiO₂) nanostructures are successfully synthesized using a hybrid sol-gel and a simple hydrothermal method. The sample was characterized using various techniques to study their physicochemical properties and was tested as a photocatalyst for methyl orange degradation and as an antibacterial material. Raman spectrum and X-ray diffraction (XRD) pattern show that the phase structure of the synthesized TiO₂ is anatase with 80-100 nm in diameter and 150-200 nm in length of flower-like nanostructures as proved by field emission scanning electron microscope (FESEM). The energy-dispersive X-ray spectroscopy (EDS) analysis of flower-like anatase TiO₂ nanostructure found that only titanium and oxygen elements are present in the sample. The anatase phase was confirmed further by a high-resolution transmission electron microscope (HRTEM) and selected area electron diffraction (SAED) pattern analysis. The Brunauer-Emmett-Teller (BET) result shows that the sample had a large surface area (108.24 m²/g) and large band gap energy (3.26 eV) due to their nanosize. X-ray photoelectron spectroscopy (XPS) analysis revealed the formation of Ti⁴⁺ and Ti³⁺ species which could prevent the recombination of the photogenerated electron, thus increased the electron transportation and photocatalytic activity of flower-like anatase TiO₂ nanostructure to degrade the methyl orange (83.03%) in a short time (60 minutes). These properties also support the good performance of flower-like titanium dioxide (TiO₂) nanostructure as an antibacterial material which is comparable with penicillin which is 13.00 ± 0.02 mm inhibition zone against Staphylococcus aureus.

Hydrogen spillover effect induced by ascorbic acid in CdS/NiO core-shell p-n heterojunction for significantly enhanced photocatalytic H2 evolution

A new variety of CdS/NiO core-shell p-n heterojunction is synthesized by in-situ chemically depositing NiO shell on single-crystal CdS nanorods for the first time. With this method, the range of NiO shell thickness can be accurately controlled within a few nanometers. The optimized CdS/NiO sample (CSN_0.5) with a NiO shell layer of 1.5 nm exhibits a highly efficient photocatalytic H₂ evolution rate of 731.7 μmol/h (corresponding to 243.9 mmol/g/h) without using co-catalyst, which is among the highest value of all the CdS-based photocatalysts. The apparent quantum efficiency (AQE) of CSN_0.5 at 365 nm wavelength reaches 28.19%. The remarkably enhanced photocatalytic performance can be attributed to a hydrogen spillover effect induced by ascorbic acid in CdS/NiO, which promotes the transmission of adsorbed H* from hydrogen-rich NiO (electron-poor region) to hydrogen-poor CdS (electron-rich region) where the adsorbed H* reacts in time with the photogenerated electron to produce H₂, facilitating the H₂ evolution reaction. This work provides a method to promote the photocatalytic H₂ evolution reaction by using hydrogen spillover effect.

Catching and killing of airborne SARS-CoV-2 to control spread of COVID-19 by a heated air disinfection system

Airborne transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) via air-conditioning systems poses a significant threat for the continued escalation of the current coronavirus disease (COVID-19) pandemic. Considering that SARS-CoV-2 cannot tolerate temperatures above 70 °C, here we designed and fabricated efficient filters based on heated nickel (Ni) foam to catch and kill SARS-CoV-2. Virus test results revealed that 99.8% of the aerosolized SARS-CoV-2 was caught and killed by a single pass through a novel Ni-foam-based filter when heated up to 200 °C. In addition, the same filter was also used to catch and kill 99.9% of Bacillus anthracis, an airborne spore. This study paves the way for preventing transmission of SARS-CoV-2 and other highly infectious airborne agents in closed environments.

TiO2 nanosheet/NiO nanorod hierarchical nanostructures: p-n heterojunctions towards efficient photocatalysis

TiO₂ nanosheet/NiO nanorod heterojunction hybrids have been developed through a hydrothermal route, where NiO nanorods (size: 5 nm in diameter and 20-40 nm in length) are deposited at the {0 0 1} facet of anatase TiO₂ nanosheets. The photocatalysts were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), N₂ adsorption-desorption analysis, UV-vis spectroscopy, X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy and time-resolved fluorescence. The TiO₂/NiO photocatalysts exhibited good photocatalytic activities towards the degradation of methyl blue (MB) and phenol, and hydrogen generation efficiency under visible light irradiation. The maximum rate constant can be reached 0.0279 min^-1 and 0.0135 min^-1 respectively, which are about 12 and 10 times higher than that of TiO₂ nanosheets. And the hydrogen generation efficiency is 10 times higher than physical mixing of TiO₂ and NiO. Photocatalytic degradation efficiency remains more than 90% after 6 times cycle dye degradation, and the H₂ production efficiency is almost the same after four cycles, suggesting good stability and reusability. The enhanced photocatalytic activities are associated with the rational design of TiO₂/NiO hierarchical heterojunctions which ensues high photogenerated charge separation efficiency. With the improved photocatalytic performance, the TiO₂/NiO heterojunction hybrids are expected to be potential photocatalysts in environmental and energy related areas.

Enhanced photocatalytic reduction for the dechlorination of 2-chlorodibenzo-p-dioxin by high-performance g-C3N4/NiO heterojunction composites under ultraviolet-visible light illumination

Polychlorinated dibenzo-p-dioxins (PCDDs), characterized by their high persistency and bioaccumulation, are widely detected in the environment. In this study, high-performance g-C₃N₄/NiO heterojunctions were fabricated to degrade 2-chlorodibenzo-p-dioxin (2-CDD) under ultraviolet-visible (UV-vis) light illumination. Experiments revealed that the pure g-C₃N₄ and range of g-C₃N₄/NiO heterojunctions were synthesized by the mixing and heating method, and then were characterized by XRD, TEM, XPS and PL etc. The composites exhibited enhanced dechlorination activities under anoxic conditions. After comparison, the g-C₃N₄/NiO (4:6) showed optimal dechlorination performance such that 70.4% of 2-CDD was removed within 8 h and 52.3% of 2-CDD was transformed to dibenzo-p-dioxin (DD), about fourfold higher than the pristine g-C₃N₄. The transformation of 2-CDD was accompanied by the resale of Cl ion, and the additional oxygen was proven to be able to consume electrons and hydrogen ions, thus greatly inhibiting the degradation of PCDD in systems. The g-C₃N₄/NiO (4:6) can be reused at least seven times, and the mechanism was proposed in detail to promote photoinduced electrohole separation and provide active sites. This study extends the use range of g-C₃N₄/NiO heterojunctions and develops a new technology to degrade PCDDs with striking activity and stability.

Ni(OH)2-modified SrTiO3 for enhanced photocatalytic hydrogen evolution reactions

Strontium titanate (SrTiO₃) is a promising photocatalyst because of its high chemical stability and excellent photocatalytic activity.

Concept of Stagnant Capillarity Water in the Nanoporous SiO2@(Zn,Ni)(O,S) Nanocomposite Photocatalyst as a Strategy to Improve Hydrogen Evolution

(Zn,Ni)(O,S) nanoparticles were uniformly deposited on nanoporous SiO₂ spheres to form SiO₂@(Zn,Ni)(O,S) nanocomposites (NCs). To obtain optimum deposition of (Zn,Ni)(O,S) on the SiO₂ spheres for the hydrogen evolution reaction (HER), different amounts of 0.25, 0.5, 1, and 1.5 mmol zinc precursor for (Zn,Ni)(O,S) were deposited on SiO₂ to obtain different SiO₂@(Zn,Ni)(O,S) NCs. All the as-prepared catalysts were examined with X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy, electrochemical impedance spectroscopy, photocurrent response, photoluminescence spectral studies. Finally, the HER performance was evaluated with SiO₂@(Zn,Ni)(O,S). The best SiO₂@(Zn,Ni)(O,S)-0.5 surprisingly reached 41.1 mmol/gh for generating H₂, which was about a 840% increase as compared to that of the SiO₂ sphere-free one. The great improvement in the HER rate was due to the utilization of nanoporous SiO₂ spheres. The concept of stagnant capillarity water, adopted from the leaf vein system, was applied to explain the enhanced HER reaction.

A facile phase transformation strategy for fabrication of novel Z-scheme ternary heterojunctions with efficient photocatalytic properties

With increasing pollution of water resources and demand for hydrogen energy, photocatalysis, as a "green chemistry" technology, has attracted great attention. To meet the practical application requirements, photocatalysts should possess enhanced efficiency and be of low cost. Here, a novel Z-scheme ternary ZnTiO3/Zn2Ti3O8/ZnO heterojunction has been prepared by a solvothermal-calcination process. The phase transformation process of the sample can be defined as two processes, dehydration and thermal decomposition (ZnTiO3 → Zn2Ti3O8 + ZnO). The ZnTiO3/Zn2Ti3O8/ZnO heterojunction produced in this facile phase transformation strategy displayed highly efficient photocatalytic performance in water splitting for hydrogen production and pollutant removal, e.g. phenol, dye, and heavy metal Cr(vi). On the basis of the PL spectra, photocurrent response, radical trapping experiments and ESR tests, we found that a nontraditional transport of photoinduced carriers created by a single Z-scheme mechanism played a significant role in the efficient removing of target pollutants and hydrogen generation. This work provides a facile phase transformation approach to construct a Z-scheme semiconductor heterostructure system with high efficiency for hydrogen production and water pollution treatment.

Photocatalytic Activation of Saturated C-H Bond Over the CdS Mixed-Phase Under Visible Light Irradiation

Selective activation of saturated C–H bond in hydrocarbons to produce high-value-added chemicals is of great significance for chemical synthesis and transformation. Herein, we present a facile procedure to achieve Ni-doped CdS nanoparticles with mixed (cubic and hexagonal) phases, as well as its application to the photocatalytic activation of saturated primary C–H bond of toluene and its derivatives. The photocatalytic oxidation rate of toluene into benzaldehyde of formation reached up to 216.7 μmolh⁻¹g⁻¹ under visible light irradiation. The excellent photocatalytic performance of Ni(II)-doped CdS [Ni(II)/CdS] can be attributed to its unique structural assembly with cubic and hexagonal phases and also the addition of Ni ions, together taking effect in promoting the separation of photogenerated charge carriers. The possible reaction mechanism for the photocatalytic selective oxidation is illustrated in this work. The band width of the as-prepared mixed phase CdS is reduced, which can effectively expand the response range and improve photocatalytic performance.

A weak-light-responsive TiO2/g-C3N4 composite film: photocatalytic activity under low-intensity light irradiation

A TiO₂/g-C₃N₄ composite photocatalytic film was prepared by in situ synthesis method and its photocatalytic capability under weak-visible-light condition was studied. The co-precursor with different ratio of melamine and TiO₂ sol-gel precursor were treated using ultrasonic mixing, physical deposition, and co-sintering method to form the smooth, white-yellow, and compact TiO₂/g-C₃N₄ composite films. The prepared TiO₂/g-C₃N₄ materials were characterized by SEM, TEM, EDS, XRD, BET, VBXPS, and UV-vis diffuse reflectance spectra. The results of composite showed that TiO₂ and g-C₃N₄ have close interfacial connections which are favorable to charge transfer between these two semiconductors with suitable band structure, g-C₃N₄ retard the anatase-to-rutile phase transition of TiO₂ significantly, the specific surface area were increased with g-C₃N₄ ratio raised. Under weak-light irradiation, composite films photocatalytic experiments exhibited RhB removal efficiency approaching 90% after three recycles. Powders suspension degradation experiments revealed the removal efficiency of TiO₂/g-C₃N₄ (90.8%) was higher than pure TiO₂ (52.1%) and slightly lower than pure g-C₃N₄ (96.6%). By control experiment, the enhanced photocatalysis is ascribed to the combination of TiO₂ and g-C₃N₄, which not only produced thin films with greater stability but also formed heterojunctions that can be favorable to charge transfer between these two semiconductors with suitable band structure. This study presents the potential application of photocatalytic film in the wastewater treatment under weak-light situation.

TiO2 Nanorod Arrays Based Self-Powered UV Photodetector: Heterojunction with NiO Nanoflakes and Enhanced UV Photoresponse

The self-powered ultraviolet photodetectors (UV PDs) have attracted increasing attention due to their potential applications without consuming any external power. It is important to obtain the high-performance self-powered UV PDs by a simple method for the practical application. Herein, TiO₂ nanorod arrays (NRs) were synthesized by hydrothermal method, which were integrated with p-type NiO nanoflakes to realize a high performance pn heterojunction for the efficient UV photodetection. TiO _x thin film can improve the morphological and carrier transport properties of TiO₂ NRs and decrease the surface and defect states, resulting in the enhanced photocurrent of the devices. NiO/TiO₂ nanostructural heterojunctions show excellent rectifying characteristics (rectification ratio of 2.52 × 10⁴ and 1.45 × 10⁵ for NiO/TiO₂ NRs and NiO/TiO₂ NRs/TiO _x, respectively) with a very low reverse saturation current. The PDs based on the heterojunctions exhibit good spectral selectivity, high photoresponsivity, and fast response and recovery speeds without external applied bias under the weak light radiation. The devices demonstrate good stability and repeatability under UV light radiation. The self-powered performance could be attributed to the proper built-in electric field of the heterojunction. TiO₂ NRs and NiO nanoflakes construct the well-aligned energy-band structure. The enhanced responsivity and detectivity for the devices with TiO _x thin films is related to the increased interfacial charge separation efficiency, reduced carrier recombination, and relatively good electron transport of TiO₂ NRs.

Boosting visible-light photocatalytic H2 evolution via UiO-66-NH2 octahedrons decorated with ultrasmall NiO nanoparticles

Noble metal-free UiO-66-NH₂-10 wt% NiO composites (U6N-NiO-2) with eosin Y sensitizer exhibit high visible-light hydrogen evolution activity.

Low-cost dual cocatalysts BiVO4 for highly efficient visible photocatalytic oxidation

Co-loading earth-abundant Ni and CuO cocatalysts on BiVO₄ can significantly enhance the thiophene and dyes oxidation under visible light irradiation.

Band alignment investigations of heterostructure NiO/TiO2 nanomaterials used as efficient heterojunction earth-abundant metal oxide photocatalysts for hydrogen production

Earth-abundant NiO/TiO₂ heterostructures lead to enhanced H₂ production by methanol photoreforming due to favorable band bending at the interface of the NiO/anatase TiO₂ p–n heterojunction.

Tetrabromobisphenol A photoelectrocatalytic degradation using reduced graphene oxide and cerium dioxide comodified TiO2 nanotube arrays as electrode under visible light

Tetrabromobisphenol A, one of the most important brominated retardants, is an typical persistent organic pollutant and it is of great value to develop rapid and effective degradation method. Present study established a photoelectrodegradation method with CeO₂ and reduced graphene oxide co-modified TiO₂ nanotube arrays (RGO-CeO₂-TiO₂ NAs), which were successfully synthesized and characterized with scanning electron microscopy (SEM) and Energy Dispersive X Ray Spectrometry (EDX). The SEM Images revealed that the nanotubes had a diameter of about 100 nm and an obvious layer of CeO₂ and RGO on the surface of TiO₂ nanotube arrays. The EDX data exhibited the presence of Ce element. The results demonstrated that TBBPA was degraded at a high degradation rate constant of 0.0191 min^-1, and photogenerated holes played a major role in the degradation reaction. Significant decrease of degradation efficiency was achieved with the presence of EDTA-2Na(hole scavenger), yet while the existence of t-BuOH(OH scavenger) resulted in less inhibition on the degradation. Besides, RGO-CeO₂-TiO₂ NAs exhibited good stability with rarely decline of degradation efficiency for ten reused runs. All these indicated that RGO-CeO₂-TiO₂ NAs were a good catalyst with extraordinary catalytic activity and stability for PEC degradation, and would have great potential in the control and removal of pollutants.

Carbon-Incorporated NiO/TiO2 Mesoporous Shells with p-n Heterojunctions for Efficient Visible Light Photocatalysis

Carbon-incorporated mesoporous NiO/TiO₂ (NiO/TiO₂/C) hybrid shells as low-cost and highly efficient visible light photocatalysts have been developed. The NiO/TiO₂/C hybrid shells were synthesized by choosing polystyrene nanospheres as templates, followed by TiO₂ and NiO coating, and finally the calcination post-treatment to carbonize PS with the aid of metal oxides. Polystyrene nanospheres serve dual purposes as both a template to ensure the hollow structure and the electrically conductive graphite carbon source. Evaluation of their photocatalytic activity by organic pollutes (rhodamine B, methylene blue, and phenol) degradation and H₂ production under visible light demonstrated the superior photocatalytic performance, thanks to the enhanced visible-light absorption and exciton separation associated with the incorporation of electrically conductive graphite carbon.

Pertinent parameters in photo-generation of electrons: Comparative study of anatase-based nano-TiO2 suspensions

In the field of solar fuel cells, the development of efficient photo-converting semiconductors remains a major challenge. A rational analysis of experimental photocatalytic results obtained with material in colloïdal suspensions is needed to access fundamental knowledge required to improve the design and properties of new materials. In this study, a simple system electron donor/nano-TiO2 is considered and examined via spin scavenging electron paramagnetic resonance as well as a panel of analytical techniques (composition, optical spectroscopy and dynamic light scattering) for selected type of nano-TiO2. Independent variables (pH, electron donor concentration and TiO2 amount) have been varied and interdependent variables (aggregate size, aggregate surface vs. volume and acid/base groups distribution) are discussed. This work shows that reliable understanding involves thoughtful combination of interdependent parameters, whereas the specific surface area seems not a pertinent parameter. The conclusion emphasizes the difficulty to identify the key features of the mechanisms governing photocatalytic properties in nano-TiO2.

Synergetic effect of functionalized carbon nanotubes on ZnCr–mixed metal oxides for enhanced solar light-driven photocatalytic performance

Functionalized CNTs played a key role in facilitating the interfacial charge transfer, which accounted for the significantly enhanced photocatalytic performance.

Catalytic low-temperature combustion of dichloromethane over V–Ni/TiO2 catalyst

A plausible pathway for DCM oxidation over V–Ni/TiO₂.