TiO2-Based Nanomaterials for the Production of Hydrogen and the Development of Lithium-Ion Batteries

Monolithic Microparticles Facilitated Flower-Like TiO2 Nanowires for High Areal Capacity Flexible Li-Ion Batteries

Flexible lithium-ion batteries (FLIBs) are intensively studied using free-standing transition metal oxides (TMOs)-based anode materials. However, achieving high areal capacity TMO-based anode materials is yet to be effectively elucidated owing to the poor adhesion of the active materials to the flexible substrate resulting in low active mass loading, and hence low areal capacity is realized. Herein, a novel monolithic rutile TiO2 microparticles on carbon cloth (ATO/CC) that facilitate the flower-like arrangement of TiO2 nanowires (denoted ATO/CC/OTO) is demonstrated as high areal capacity anode for FLIBs. The optimized ATO/CC/OTO anode exhibits high areal capacity (5.02 mAh cm-2@0.4 mA cm-2) excellent rate capability (1.17 mAh cm-2@5.0 mA cm-2) and remarkable cyclic stability (over 500 cycles). A series of morphological, kinetic, electrochemical, in situ Raman, and theoretical analyses reveal that the rational phase boundaries between the microparticles and nanowires contribute to promoting the Li storage activity. Furthermore, a 16.0 cm2 all-FLIB pouch cell assembled based on the ATO/CC/OTO anode and LiNiCoMnO2 cathode coated on ATO/CC (ATO/CC/LNCM) exhibits impressive flexibility under different folding conditions, creating opportunity for the development of high areal capacity anodes in future flexible energy storage devices.

Artificial Photosynthesis: Current Advancements and Future Prospects

Artificial photosynthesis is a technology with immense potential that aims to emulate the natural photosynthetic process. The process of natural photosynthesis involves the conversion of solar energy into chemical energy, which is stored in organic compounds. Catalysis is an essential aspect of artificial photosynthesis, as it facilitates the reactions that convert solar energy into chemical energy. In this review, we aim to provide an extensive overview of recent developments in the field of artificial photosynthesis by catalysis. We will discuss the various catalyst types used in artificial photosynthesis, including homogeneous catalysts, heterogeneous catalysts, and biocatalysts. Additionally, we will explore the different strategies employed to enhance the efficiency and selectivity of catalytic reactions, such as the utilization of nanomaterials, photoelectrochemical cells, and molecular engineering. Lastly, we will examine the challenges and opportunities of this technology as well as its potential applications in areas such as renewable energy, carbon capture and utilization, and sustainable agriculture. This review aims to provide a comprehensive and critical analysis of state-of-the-art methods in artificial photosynthesis by catalysis, as well as to identify key research directions for future advancements in this field.

Photodegradation of Ciprofloxacin and Levofloxacin by Au@ZnONPs-MoS2-rGO Nanocomposites

This study aimed to investigate the photocatalytic performance of diverse zinc oxide catalysts containing gold nanoparticles (AuNPs), molybdenum disulfide (MoS2), and reduced graphene oxide (rGO) toward the degradation of the antibiotics levofloxacin (LFX) and ciprofloxacin (CFX) in aqueous solutions. The obtained results demonstrate that LFX is more resistant to degradation when compared with CFX and that the principal route of degradation under visible light is the formation of hydroxyl radicals. Photoluminescence (PL) measurements were employed to verify the inhibitory effect of electron–hole recombination when AuNPs, MoS2, and rGO are integrated into a semiconductor. The catalyst that achieved the highest percentage of CFX degradation was 1%Au@ZnONPs-3%MoS2-1%rGO, exhibiting a degradation efficiency of 96%, while the catalyst that exhibited the highest percentage of LFX degradation was 5%Au@ZnONPs-3%MoS2-1%rGO, displaying a degradation efficiency of 99.8%. A gas chromatography–mass spectrometry (GC-MS) analysis enabled the identification of reaction intermediates, facilitating the determination of a potential degradation pathway for both antibiotics. Additionally, recyclability assessments showed that the synthesized catalysts maintained stable photocatalytic efficiencies after 15 cycles, indicating that the heterostructures have the potential for further usage and may be tested with other organic contaminants as well.

Biomimetic Catalysts Based on Au@TiO2-MoS2-CeO2 Composites for the Production of Hydrogen by Water Splitting

The photocatalytic hydrogen evolution reaction (HER) by water splitting has been studied, using catalysts based on crystalline TiO₂ nanowires (TiO₂NWs), which were synthesized by a hydrothermal procedure. This nanomaterial was subsequently modified by incorporating different loadings (1%, 3% and 5%) of gold nanoparticles (AuNPs) on the surface, previously exfoliated MoS₂ nanosheets, and CeO₂ nanoparticles (CeO₂NPs). These nanomaterials, as well as the different synthesized catalysts, were characterized by electron microscopy (HR-SEM and HR-TEM), XPS, XRD, Raman, Reflectance and BET surface area. HER studies were performed in aqueous solution, under irradiation at different wavelengths (UV-visible), which were selected through the appropriate use of optical filters. The results obtained show that there is a synergistic effect between the different nanomaterials of the catalysts. The specific area of the catalyst, and especially the increased loading of MoS₂ and CeO₂NPs in the catalyst substantially improved the H₂ production, with values of ca. 1114 μm/hg for the catalyst that had the best efficiency. Recyclability studies showed only a decrease in activity of approx. 7% after 15 cycles of use, possibly due to partial leaching of gold nanoparticles during catalyst use cycles. The results obtained in this research are certainly relevant and open many possibilities regarding the potential use and scaling of these heterostructures in the photocatalytic production of H₂ from water.

Hydrogenated Amorphous Silicon-Based Nanomaterials as Alternative Electrodes to Graphite for Lithium-Ion Batteries

Graphite is the material most used as an electrode in commercial lithium-ion batteries. On the other hand, it is a material with low energy capacity, and it is considered a raw critical material given its large volume of use. In the current energy context, we must promote the search for alternative materials based on elements that are abundant, sustainable and that have better performance for energy storage. We propose thin materials based on silicon, which has a storage capacity eleven times higher than graphite. Nevertheless, due to the high-volume expansion during lithiation, it tends to crack, limiting the life of the batteries. To solve this problem, hydrogenated amorphous silicon has been researched, in the form of thin film and nanostructures, since, due to its amorphous structure, porosity and high specific surface, it could better absorb changes in volume. These thin films were grown by plasma-enhanced chemical vapor deposition, and then the nanowires were obtained by chemical etching. The compositional variations of films deposited at different temperatures and the incorporation of dopants markedly influence the stability and longevity of batteries. With these optimized electrodes, we achieved batteries with an initial capacity of 3800 mAhg^-1 and 82% capacity retention after 50 cycles.

Hydrogen Production and Degradation of Ciprofloxacin by Ag@TiO2-MoS2 Photocatalysts

The photocatalytic activity of silver-based catalysts containing different amounts of molybdenum disulfide (MoS2; 5, 10 and 20 wt.%) was evaluated by the degradation of the antibiotic ciprofloxacin and the production of hydrogen via water splitting. All the silver (Ag)-based catalysts degraded more than 70% of the antibiotic in 60 min. The catalyst that exhibited the best result was 5%Ag@TiO2-P25-5%MoS2, with ca. 91% of degradation. The control experiments and stability tests showed that photocatalysis was the degradation pathway and the selected silver-based catalysts were stable after seven cycles, with less than 2% loss of efficiency per cycle and less than 7% after seven cycles. The catalyst with the highest hydrogen production was 5%Ag@TiO2 NWs-20%MoS2, 1792 μmol/hg, at a wavelength of 400 nm. This amount was ca. 32 times greater than that obtained by the pristine titanium oxide nanowires catalyst. The enhancement was attributed to the high surface area of the catalysts, along with the synergism created by the silver nanoparticles and MoS2. All the catalysts were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), Brunauer–Emmett–Teller (BET) surface area analysis and energy dispersive X-ray spectroscopy (EDS).

Biomass-derived hierarchical N, P codoped porous 3D-carbon framework@TiO2 hybrids as advanced anode for lithium ion batteries

Advanced anode materials with high theoretical capacity and rate capability are urgently required for next generation lithium ion batteries (LIBs). In this study, hierarchical N, P codoped porous 3D-carbon framework@TiO₂ nanoparticle hybrid (N, PC@TiO₂) is synthesized by using pollen as biomass precursor through a facile template assisted sol-gel methode and exhibits hierarchical porous hollow structure with plenty of redox active sites and enhanced specific surface area. Compared with N, P codoped porous micro-carbon sphere framework and TiO₂ porous hollow microspheres anodes, the N, PC@TiO₂ anode shows superior reversible capacity of 687.3 mAh g^-1 at 0.1 A g^-1 after 200 cycles and 440.5 mAh g^-1 after 1000 cycles at 1 A g^-1. The excellent performance can be attributed to the rational hierarchical porous hollow structure and the synergetic contributions from the N, P codoped-carbon and TiO₂ components, which enhance Li⁺ storage capability, accelerate the reaction kinetics and stabilize the electrode structure and interface during charge/discharge process. This study suggests a practical strategy to prepare novel anode material with abundant natural resource and facile synthetic route, and the optimized hybrid anode with outstanding Li⁺ storage properties provides hopeful application prospect in advanced LIBs and other energy storage devices.

One-Dimensional (1D) Nanostructured Materials for Energy Applications

At present, the world is at the peak of production of traditional fossil fuels. Much of the resources that humanity has been consuming (oil, coal, and natural gas) are coming to an end. The human being faces a future that must necessarily go through a paradigm shift, which includes a progressive movement towards increasingly less polluting and energetically viable resources. In this sense, nanotechnology has a transcendental role in this change. For decades, new materials capable of being used in energy processes have been synthesized, which undoubtedly will be the cornerstone of the future development of the planet. In this review, we report on the current progress in the synthesis and use of one-dimensional (1D) nanostructured materials (specifically nanowires, nanofibers, nanotubes, and nanorods), with compositions based on oxides, nitrides, or metals, for applications related to energy. Due to its extraordinary surface-volume relationship, tunable thermal and transport properties, and its high surface area, these 1D nanostructures have become fundamental elements for the development of energy processes. The most relevant 1D nanomaterials, their different synthesis procedures, and useful methods for assembling 1D nanostructures in functional devices will be presented. Applications in relevant topics such as optoelectronic and photochemical devices, hydrogen production, or energy storage, among others, will be discussed. The present review concludes with a forecast on the directions towards which future research could be directed on this class of nanostructured materials.

Palladium-modified cuprous(i) oxide with {100} facets for photocatalytic CO2 reduction

Using metal as a photohole capturer can promote the photoelectron of p-type copper(i) oxide (Cu₂O) substrate for efficient carbon dioxide reduction. However, palladium-decorated Cu₂O (Cu₂O-Pd) is seldom reported due to their mismatching band arrangement. Herein, we have successfully established a matched band alignment between Pd nanoparticles and Cu₂O with exposed {100} facets (100Cu₂O). The high work function of 100Cu₂O originating from T_1u symmetry vibration facilitates the photohole transferring to Pd nanoparticles, which leads to a three-fold increase in the photocatalytic generation of carbon monoxide (100Cu₂O-0.1Pd, 0.13 μmol g^-1 h^-1) than that with pristine 100Cu₂O (0.04 μmol g^-1 h^-1). Besides, the incorporation of Pd can relieve the photocorrosion of 100Cu₂O, thus promoting its photocatalytic stability. As a contrast, 111Cu₂O (Cu₂O exposed to {111} facets) with low-work function was also synthesized and no charge migration was observed between 111Cu₂O and Pd species, which verified the important role of the crystal surface regulation. All experimental phenomena were certified by the crystal surface analysis and energy band structure construction. Moreover, CO₂ adsorption capacity tests indicated that the incorporation of Pd is beneficial for the capture of CO₂ molecules. We hope that this work to some extent will enrich the subject of photocatalytic CO₂ reduction.

Photocatalytic Activity of Silver-Based Biomimetics Composites

Different Ag@TiO2 and Ag@ZnO catalysts, with nanowire (NW) structure, were synthesized containing different amounts of silver loading (1, 3, 5, and 10 wt.%) and characterized by FE-SEM, HRTEM, BET, XRD, Raman, XPS, and UV-vis. The photocatalytic activity of the composites was studied by the production of hydrogen via water splitting under UV-vis light and the degradation of the antibiotic ciprofloxacin. The maximum hydrogen production of all the silver-based catalysts was obtained with a silver loading of 10 wt.% under irradiation at 500 nm. Moreover, 10%Ag@TiO2 NWs was the catalyst with the highest activity in the hydrogen production reaction (1119 µmol/hg), being 18 times greater than the amount obtained with the pristine TiO2 NW catalyst. The most dramatic difference in hydrogen production was obtained with 10%Ag@TiO2-P25, 635 µmol/hg, being 36 times greater than the amount reported for the unmodified TiO2-P25 (18 µmol/hg). The enhancement of the catalytic activity is attributed to a synergism between the silver nanoparticles incorporated and the high surface area of the composites. In the case of the degradation of ciprofloxacin, all the silver-based catalysts degraded more than 70% of the antibiotic in 60 min. The catalyst that exhibited the best result was 3%Ag@ZnO commercial, with 99.72% of degradation. The control experiments and stability tests showed that photocatalysis was the route of degradation and the selected silver-based catalysts were stable after seven cycles, with less than 1% loss of efficiency per cycle. These results suggest that the catalysts could be employed in additional cycles without the need to be resynthesized, thus reducing remediation costs.

Biomimetic Catalysts Based on Au@ZnO-Graphene Composites for the Generation of Hydrogen by Water Splitting

For some decades, the scientific community has been looking for alternatives to the use of fossil fuels that allow for the planet's sustainable and environmentally-friendly development. To do this, attempts have been made to mimic some processes that occur in nature, among which the photosystem-II stands out, which allows water splitting operating with different steps to generate oxygen and hydrogen. This research presents promising results using synthetic catalysts, which try to simulate some natural processes, and which are based on Au@ZnO-graphene compounds. These catalysts were prepared by incorporating different amounts of gold nanoparticles (1 wt.%, 3 wt.%, 5 wt.%, 10 wt.%) and graphene (1 wt.%) on the surface of synthesized zinc oxide nanowires (ZnO NWs), and zinc oxide nanoparticles (ZnO NPs), along with a commercial form (commercial ZnO) for comparison purposes. The highest amount of hydrogen (1127 μmol/hg) was reported by ZnO NWs with a gold and graphene loadings of 10 wt.% and 1 wt.%, respectively, under irradiation at 400 nm. Quantities of 759 μmol/hg and 709 μmol/hg were obtained with catalysts based on ZnO NPs and commercial ZnO, respectively. The photocatalytic activity of all composites increased with respect to the bare semiconductors, being 2.5 times higher in ZnO NWs, 8.8 times higher for ZnO NPs, and 7.5 times higher for commercial ZnO. The high photocatalytic activity of the catalysts is attributed, mainly, to the synergism between the different amount of gold and graphene incorporated, and the surface area of the composites.

Catalytic use of TiO2 nanowires in the photodegradation of Benzophenone-4 as an active ingredient in sunscreens

Water contamination has compromised the quality of this resource during the last years with the presence of persistent organic pollutants. Because of the resistance of these compounds to degradation, several advance oxidation techniques have been proposed. In this study, we report the employment of an advance oxidation technique in the degradation of benzophenone-4 (BP-4), using TiO₂ as catalyst, which was obtained following a fast-hydrothermal method. TiO₂ nanowires (TiO₂NWs) were fully characterized considering the morphology, elemental composition, oxidation states, vibrational modes and crystalline structure with SEM and TEM, EDS, XPS, FTIR and XRD, respectively. The photocatalytic degradation was carried out using a home-made photoreactor under slightly acidic conditions achieving an average of 90% removal. It was determined that the photocatalysis is the most probable route of degradation since the photolysis or catalysis procedures produce negligible contributions. An apparent kinetic constant of 1.29 × 10^-2 min^-1 was determined, according to a pseudo-first order reaction.