Synthesis and antibacterial activities of Ag-TiO2/ZIF-8

In recent years, massive bacterial infections have led to human illness and death, reminding us of the urgent need to develop effective and long-lasting antimicrobial materials. In this paper, Ag-TiO2/ZIF-8 with good environmental friendliness and biological antibacterial activity was prepared by solvothermal method. The structure and morphology of the synthesized materials were characterized by XRD, FT-IR, SEM-EDS, TEM, XPS, and BET. To investigate the antibacterial activity of the synthesized samples, Escherichia coli and Bacillus subtilis were used as target bacteria for experimental studies of zone of inhibition, bacterial growth curves, minimum bactericidal concentration and antibacterial durability. The results demonstrated that 20 wt.%Ag-TiO2/ZIF-8 had the best bacteriostatic effect on E. coli and B. subtilis under dark and UV conditions compared to TiO2 and ZIF-8. Under the same conditions, the diameter of the inhibition circle of 20 wt% Ag-TiO2/ZIF-8 is 8.5-11.5 mm larger than that of its constituent material 4 wt% Ag-TiO2, with more obvious antibacterial effect and better antibacterial performance. It is also proposed that the excellent antibacterial activity of Ag-TiO2/ZIF-8 is due to the synergistic effect of Ag-TiO2 and ZIF-8 under UV light. In addition, the prepared material has good stability and durability with effective antimicrobial activity for more than 5 months.

Synthesis of Sulfur@g-C3N4 and CuS@g-C3N4 Catalysts for Hydrogen Production from Sodium Borohydride

In this work, the S@g-C₃N₄ and CuS@g-C₃N₄ catalysts were prepared via the polycondensation process. The structural properties of these samples were completed on XRD, FTIR and ESEM techniques. The XRD pattern of S@g-C₃N₄ presents a sharp peak at 27.2° and a weak peak at 13.01° and the reflections of CuS belong to the hexagonal phase. The interplanar distance decreased from 0.328 to 0.319 nm that facilitate charge carrier separation and promoting H₂ generation. FTIR data revealed the structural change according to absorption bands of g-C₃N₄. ESEM images of S@g-C₃N₄ exhibited the described layered sheet structure for g-C₃N₄ materials and CuS@g-C₃N₄ demonstrated that the sheet materials were fragmented throughout the growth process. The data of BET revealed a higher surface area (55 m²/g) for the CuS-g-C₃N₄ nanosheet. The UV-vis absorption spectrum of S@g-C₃N₄ showed a strong peak at 322 nm, which weakened after the growth of CuS at g-C₃N₄. The PL emission data showed a peak at 441 nm, which correlated with electron-hole pair recombination. The data of hydrogen evolution showed improved performance for the CuS@g-C₃N₄ catalyst (5227 mL/g·min). Moreover, the activation energy was determined for S@g-C₃N₄ and CuS@g-C₃N₄, which showed a lowering from 47.33 ± 0.02 to 41.15 ± 0.02 KJ/mol.

A comprehensive review on the electrochemical parameters and recent material development of electrochemical water splitting electrocatalysts

Electrochemical splitting of water is an appealing solution for energy storage and conversion to overcome the reliance on depleting fossil fuel reserves and prevent severe deterioration of the global climate. Though there are several fuel cells, hydrogen (H2) and oxygen (O2) fuel cells have zero carbon emissions, and water is the only by-product. Countless researchers worldwide are working on the fundamentals, i.e. the parameters affecting the electrocatalysis of water splitting and electrocatalysts that could improve the performance of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) and overall simplify the water electrolysis process. Noble metals like platinum for HER and ruthenium and iridium for OER were used earlier; however, being expensive, there are more feasible options than employing these metals for all commercialization. The review discusses the recent developments in metal and metalloid HER and OER electrocatalysts from the s, p and d block elements. The evaluation perspectives for electrocatalysts of electrochemical water splitting are also highlighted.

Design and preparation of highly active TiO2 photocatalysts by modulating their band structure

Titanium dioxide photocatalysts with high reduction potential and visible light response hold great promise in photochemical conversion. Here, we used a simple glycine doping method to synthesize novel N-TiO2@C photocatalysts with upward shifted conduction bands and narrowed band gaps as well as inhibited recombination of photoinduced electron-hole pairs. The N-TiO2@C photocatalysts exhibited higher visible light response and remarkably enhanced photocatalytic activity in the production of nicotinamide adenine dinucleotide (NADH) by photomediated reduction of NAD+ without any electron mediator. The yield of NADH was up to 70.3 % far greater than that of the undoped TiO2 (11.3 %), and it stabilized at ca. 60 % after 10 cycles. The viability of coupling NADH regeneration with enzymatic reaction (alcohol dehydrogenase) was established in aldehyde reduction where formaldehyde was specifically reduced to methanol. These findings shed new light on the modulation of the band structure of semiconductors and develop an electron mediator free strategy for NADH-dependent artificial photosynthesis through coupled photocatalytic and enzymatic approaches.

Photocatalytic Water Splitting: How Far Away Are We from Being Able to Industrially Produce Solar Hydrogen?

Solar water splitting (SWS) has been researched for about five decades, but despite successes there has not been a big breakthrough advancement. While the three fundamental steps, light absorption, charge carrier separation and diffusion, and charge utilization at redox sites are given a great deal of attention either separately or simultaneously, practical considerations that can help to increase efficiency are rarely discussed or put into practice. Nevertheless, it is possible to increase the generation of solar hydrogen by making a few little but important adjustments. In this review, we talk about various methods for photocatalytic water splitting that have been documented in the literature and importance of the thin film approach to move closer to the large-scale photocatalytic hydrogen production. For instance, when comparing the film form of the identical catalyst to the particulate form, it was found that the solar hydrogen production increased by up to two orders of magnitude. The major topic of this review with thin-film forms is, discussion on several methods of increased hydrogen generation under direct solar and one-sun circumstances. The advantages and disadvantages of thin film and particle technologies are extensively discussed. In the current assessment, potential approaches and scalable success factors are also covered. As demonstrated by a film-based approach, the local charge utilization at a zero applied potential is an appealing characteristic for SWS. Furthermore, we compare the PEC-WS and SWS for solar hydrogen generation and discuss how far we are from producing solar hydrogen on an industrial scale. We believe that the currently employed variety of attempts may be condensed to fewer strategies such as film-based evaluation, which will create a path to address the SWS issue and achieve sustainable solar hydrogen generation.

Recent Progress and Prospects in Catalytic Water Treatment

Presently, conventional technologies in water treatment are not efficient enough to completely mineralize refractory water contaminants. In this context, the implementation of catalytic processes could be an alternative. Despite the advantages provided in terms of kinetics of transformation, selectivity, and energy saving, numerous attempts have not yet led to implementation at an industrial scale. This review examines investigations at different scales for which controversies and limitations must be solved to bridge the gap between fundamentals and practical developments. Particular attention has been paid to the development of solar-driven catalytic technologies and some other emerging processes, such as microwave assisted catalysis, plasma-catalytic processes, or biocatalytic remediation, taking into account their specific advantages and the drawbacks. Challenges for which a better understanding related to the complexity of the systems and the coexistence of various solid-liquid-gas interfaces have been identified.

Boosted charge transfer in dual Z-scheme BiVO4@ZnIn2S4/Bi2Sn2O7 heterojunctions: Towards superior photocatalytic properties for organic pollutant degradation

A core-shell structured dual Z-scheme ternary photocatalyst BiVO₄@ZnIn₂S₄/Bi₂Sn₂O₇ was fabricated via hydrothermal and heat-circumfluence strategy. With ZnIn₂S₄ serving as a bridge to connect BiVO₄ and Bi₂Sn₂O₇, the developed ternary catalyst displayed boosted charge transfer and spatial separation capabilities. The effect of mass ratios of BiVO₄@ZnIn₂S₄ and Bi₂Sn₂O₇ on photodegradation efficiency under visible light irradiation was explored. The optimal ternary heterojunction photocatalyst possessed remarkable photocatalytic rate constant for Rhodamine B (RhB) degradation, which was 63 and 12 times higher than that of BiVO₄ and Bi₂Sn₂O₇, respectively. In addition, the as-prepared ternary photocatalyst had good universality. Notably, the novel dual Z-scheme photocatalysts could improve the separating/transferring efficiency and reduction/oxidation ability of charge carriers. Meanwhile, the hierarchical structure offered sufficient reaction sites for photodegradation. This work provides a new insight into the rational design of ternary dual Z-scheme photocatalysts.

N-doped graphene quantum dots modified with CuO (0D)/ZnO (1D) heterojunctions as a new nanocatalyst for the environmentally friendly one-pot synthesis of monospiro derivatives

A new approach for the sustainable fabrication of a CuO/ZnO@N-GQDs nanocomposite as a powerful nanocatalyst for multicomponent reactions is demonstrated.

Construction of S-doped MgO coupled with g-C3N4 nanocomposites with enhanced photocatalytic activity under visible light irradiation

In the present work, a series of photocatalysts in which S-MgO (SM) was coupled with g-C3N4 (CN) were synthesized and characterized in detail using various characterization techniques.

Role of Alkali Metal in BiVO4 Crystal Structure for Enhancing Charge Separation and Diffusion Length for Photoelectrochemical Water Splitting

Alkali metal (Na or K) doping in BiVO₄ was examined systematically for enhancing bulk charge separation and transport in addition to improving charge transfer from the surface. The alkali metal-doped BiVO₄ thin film photoanodes having nanostructured porous grain surface morphology exhibited better photocurrent density than pristine BiVO₄. In particular, Na:BiVO₄/Fe:Ni/Co-Pi photoanode showed a significantly improved photocurrent of 3.2 ± 0.15 mA·cm^-2 in 0.1 M K₂HPO₄ electrolyte at 1.23 V_RHE under 1 sun illumination. The depth-dependent Doppler broadening spectroscopy measurements confirmed the significant reduction in Bi- and V-based defect density with Na metal doping, and this led to a higher bulk diffusion length of charge pairs (four times that of the pristine one). Na doping led to reduced surface defects resulting in improved surface charge transfer based on cyclic voltammetry experiments. The density functional theory calculations confirmed the improved performance in Na-doped BiVO₄ photoanodes achieved through interband formation and reduction in the band gap.

Heterostructured g-CN/TiO2 Photocatalysts Prepared by Thermolysis of g-CN/MIL-125(Ti) Composites for Efficient Pollutant Degradation and Hydrogen Production

Photocatalysts composed of graphitic carbon nitride (g-CN) and TiO₂ were efficiently prepared by thermolysis of the MIL-125(Ti) metal organic framework deposited on g-CN. The heterojunction between the 12 nm-sized TiO₂ nanoparticles and g-CN was well established and the highest photocatalytic activity was observed for the g-CN/TiO₂ (3:1) material. The g-CN/TiO₂ (3:1) composite exhibits high visible light performances both for the degradation of pollutants like the Orange II dye or tetracycline but also for the production of hydrogen (hydrogen evolution rate (HER) up to 1330 μmolh⁻¹g⁻¹ and apparent quantum yield of 0.22% using NiS as a cocatalyst). The improved visible light performances originate from the high specific surface area of the photocatalyst (86 m²g⁻¹) and from the efficient charge carriers separation as demonstrated by photoluminescence, photocurrent measurements, and electrochemical impedance spectroscopy. The synthetic process developed in this work is based on the thermal decomposition of metal organic framework deposited on a graphitic material and holds huge promise for the preparation of porous heterostructured photocatalysts.

Photocatalytic hydrogen generation of monolithic porous titanium oxide-based glass-ceramics

A large relative surface area is crucial for high catalytic activity. Monolithic catalysts are important catalytic materials because of minimal self-degradation. Regarding large surface area catalysts, the glass–ceramics (GCs) with high formability, obtained by heat-treatment of the precursor glass, are plausible candidates. This study examines the photocatalytic behaviour of porous GCs obtained after acid leaching of MgO–TiO₂–P₂O₅ GCs. After heat-treatment, anatase TiO₂ was precipitated along with other phases. The diffraction intensity ratio between anatase and other phases was the maximum for a heat-treatment temperature of 900 °C. After acid leaching of the GCs, the relative surface area decreased with increasing TiO₂ fraction; the surface area was also affected by the sample morphology. H₂ generation was observed from porous GCs, while GCs without etching exhibited approximately zero activity. Thus, it was demonstrated that high surface area and prevention of the reduction reaction to Ti(III) are important for tailoring monolithic photocatalytic materials.

Visible-Light Active Titanium Dioxide Nanomaterials with Bactericidal Properties

This article provides an overview of current research into the development, synthesis, photocatalytic bacterial activity, biocompatibility and cytotoxic properties of various visible-light active titanium dioxide (TiO2) nanoparticles (NPs) and their nanocomposites. To achieve antibacterial inactivation under visible light, TiO2 NPs are doped with metal and non-metal elements, modified with carbonaceous nanomaterials, and coupled with other metal oxide semiconductors. Transition metals introduce a localized d-electron state just below the conduction band of TiO2 NPs, thereby narrowing the bandgap and causing a red shift of the optical absorption edge into the visible region. Silver nanoparticles of doped TiO2 NPs experience surface plasmon resonance under visible light excitation, leading to the injection of hot electrons into the conduction band of TiO2 NPs to generate reactive oxygen species (ROS) for bacterial killing. The modification of TiO2 NPs with carbon nanotubes and graphene sheets also achieve the efficient creation of ROS under visible light irradiation. Furthermore, titanium-based alloy implants in orthopedics with enhanced antibacterial activity and biocompatibility can be achieved by forming a surface layer of Ag-doped titania nanotubes. By incorporating TiO2 NPs and Cu-doped TiO2 NPs into chitosan or the textile matrix, the resulting polymer nanocomposites exhibit excellent antimicrobial properties that can have applications as fruit/food wrapping films, self-cleaning fabrics, medical scaffolds and wound dressings. Considering the possible use of visible-light active TiO2 nanomaterials for various applications, their toxicity impact on the environment and public health is also addressed.

Electrocatalytic oxygen and hydrogen evolution reactions at Ni3B/Fe2O3 nanotube arrays under visible light radiation

We demonstrate that arrays of Ni₃B/Fe₂O₃ nanotubes supported by Fe foil can simultaneously boost the kinetics of the oxygen evolution reaction and hydrogen evolution reaction after exposure to visible light radiation.

In situ synthesis of Co2P-decorated red phosphorus nanosheets for efficient photocatalytic H2 evolution

The Co₂P as co-catalyst was firstly loaded on the 2D microporous structure RP surface by in situ hydrothermal method.

Amplification of active sites and porosity for the adsorption of QDs via the induction of the rare-earth element la into TiO2 for enhanced photovoltaic effects in QDSSCs

Schematic representing preparation of TiO₂ and La–TiO₂, QDSSCs device development and mechanism of charge carrier’s migration in device along with IV curve for La–TiO₂.

Soliman K, Abdulmalik D, Mitoraj D, Sleim MH, Liedke MO, El-Sayed HA, AlJaber AS, Y. Al-Qaradawi I, Mendoza Reyes O, Abdullah AM. Tailored fabrication of iridium nanoparticle-sensitized titanium oxynitride nanotubes for solar-driven water splitting: experimental insights on the photocatalytic–activity–defects relationship

Uniform and vertically aligned nanotube arrays of titanium oxynitride functionalized with iridium nanoparticles (Ir/TiON-NTs) were fabricated for the solar driven-water splitting.

Insights into the TiO2-Based Photocatalytic Systems and Their Mechanisms

Photocatalysis is a multifunctional phenomenon that can be employed for energy applications such as H2 production, CO2 reduction into fuels, and environmental applications such as pollutant degradations, antibacterial disinfection, etc. In this direction, it is not an exaggerated fact that TiO2 is blooming in the field of photocatalysis, which is largely explored for various photocatalytic applications. The deeper understanding of TiO2 photocatalysis has led to the design of new photocatalytic materials with multiple functionalities. Accordingly, this paper exclusively reviews the recent developments in the modification of TiO2 photocatalyst towards the understanding of its photocatalytic mechanisms. These modifications generally involve the physical and chemical changes in TiO2 such as anisotropic structuring and integration with other metal oxides, plasmonic materials, carbon-based materials, etc. Such modifications essentially lead to the changes in the energy structure of TiO2 that largely boosts up the photocatalytic process via enhancing the band structure alignments, visible light absorption, carrier separation, and transportation in the system. For instance, the ability to align the band structure in TiO2 makes it suitable for multiple photocatalytic processes such as degradation of various pollutants, H2 production, CO2 conversion, etc. For these reasons, TiO2 can be realized as a prototypical photocatalyst, which paves ways to develop new photocatalytic materials in the field. In this context, this review paper sheds light into the emerging trends in TiO2 in terms of its modifications towards multifunctional photocatalytic applications.

Photocatalytic Hydrogen Production: Role of Sacrificial Reagents on the Activity of Oxide, Carbon, and Sulfide Catalysts

Photocatalytic water splitting is a sustainable technology for the production of clean fuel in terms of hydrogen (H2). In the present study, hydrogen (H2) production efficiency of three promising photocatalysts (titania (TiO2-P25), graphitic carbon nitride (g-C3N4), and cadmium sulfide (CdS)) was evaluated in detail using various sacrificial agents. The effect of most commonly used sacrificial agents in the recent years, such as methanol, ethanol, isopropanol, ethylene glycol, glycerol, lactic acid, glucose, sodium sulfide, sodium sulfite, sodium sulfide/sodium sulfite mixture, and triethanolamine, were evaluated on TiO2-P25, g-C3N4, and CdS. H2 production experiments were carried out under simulated solar light irradiation in an immersion type photo-reactor. All the experiments were performed without any noble metal co-catalyst. Moreover, photolysis experiments were executed to study the H2 generation in the absence of a catalyst. The results were discussed specifically in terms of chemical reactions, pH of the reaction medium, hydroxyl groups, alpha hydrogen, and carbon chain length of sacrificial agents. The results revealed that glucose and glycerol are the most suitable sacrificial agents for an oxide photocatalyst. Triethanolamine is the ideal sacrificial agent for carbon and sulfide photocatalyst. A remarkable amount of H2 was produced from the photolysis of sodium sulfide and sodium sulfide/sodium sulfite mixture without any photocatalyst. The findings of this study would be highly beneficial for the selection of sacrificial agents for a particular photocatalyst.

Interfacially bonded CuCo2O4/TiO2 nanosheet heterostructures for boosting photocatalytic H2 production

The CuCo₂O₄/TiO₂ nanosheets adopting interfacial chemical bonding exhibit outstanding photocatalytic activity toward water splitting.

Synthesis of an efficient lanthanide doped glass-ceramic based near-infrared photocatalyst by a completely waterless solid-state reaction method

A novel efficient near-infrared photocatalyst of glass-ceramic/TiO₂ was synthesized by a completely waterless solid-state reaction method, with optically active center CaF₂ in glass-ceramic powders and anatase-TiO₂ as the superficial coating.