Synthesis of Ag/Cu decorated 3D self-assembled nanowire TiO2 photocatalyst for hydrogen production: a promising pathway towards sustainable energy generation

Here, synthesis and characterization of TiO2 with different morphologies along with the cost-effective bimetallic decoration on optimized 3D self-assembled nanowire TiO2 (NWT) photocatalyst (Ag/Cu-NWT) with overwhelming hydrogen production rate is reported. All the photocatalysts were well characterized by different characterization techniques. Initially, the effect of morphology change obtained by changing the NaOH concentration has been studied for TiO2. Morphology obtained at 10 M NaOH solution, i.e., NWT (678 μmol/g), showed better hydrogen production than morphology obtained at 5 M (410 μmol/g), 15 M (210 μmol/g), and 20 M (160 μmol/g) NaOH solutions. Further, with the aim to achieve comparable or better activity low-cost photocatalyst as compared to Pt-TiO2 system, NWT was decorated with various Cu percentages and then with a minimal percentage of Ag on an optimized Cu-NWT photocatalyst. The observed trend for photocatalytic hydrogen production has been found to be P25 TiO2 < NWT < 1.0Cu-NWT < 0.5Pt-NWT ≤ 0.1Ag/1.0Cu-NWT. The marked increase by a factor of 103 in hydrogen production for the optimized bimetallic 0.1Ag/1.0Cu-NWT (10,184 μmol/g) photocatalyst compared to P25 TiO2 (99 μmol/g), nearly threefold increment in hydrogen production than an optimized 1.0 Cu-NWT (3907 μmol/g) photocatalyst and comparable hydrogen production as compared to 0.5Pt-NWT (10,050 μmol/g) may be attributed to the successful synthesis of a highly porous NWT morphology, which offers large surface area, increased light absorption combined with the synergistic effects of surface plasmon resonance (SPR), and the Schottky barrier for H+ reduction to H2 gas. The optimization of TiO2 morphology and an inexpensive bimetallic decoration strategy opens up promising opportunities for the development of cost-effective photocatalysts in the realm of energy and environment.

ZnGa2-xAlxO4 (x = 0 ≤ 2) spinel for persistent light emission and HER/OER bi-functional catalysis

Spinel materials have demonstrated diverse applications in various fields, especially in the energy sector. Since the pure spinel structure has the limitations of poor inherent activity and low conductivity, defect engineering through octahedral B-site modulation is expected to enhance various properties. Here in this work, we have synthesized ZnGa2-xAlxO4 (x = 0 ≤ 2) spinel and moved from one terminal (ZnGa2O4) to the other (ZnAl2O4) by varying the Ga/Al ratio using solvent-free solid-state reaction. Dopant and rare earth element-free (RE) ZnGa2O4 spinel showed excellent blue luminescence with photoluminescent quantum yields (PLQY) of 13% while exhibiting persistent light emission close to 60 min. The Al3+ incorporation at Ga3+ site doesn't yield any improvement in persistent luminescence lifetime owing to quenching of shallow traps as suggested by thermoluminescence (TL) studies. Moreover our materials have demonstrated bifunctional electrocatalytic activity towards both oxygen evolution (OER) and hydrogen evolution reaction (HER) which has never been reported for ZnGa2-xAlxO4. X-ray photoelectron spectroscopy (XPS) and positron annihilation lifetime spectroscopy (PALS) suggested that mixed Al/Ga-containing spinels possessed enhanced oxygen vacancies/defects. This makes them better electrocatalyst towards OER and HER compare to ZnGa2O4 and ZnAl2O4. The ZnGa1.75Al0.25O4 composition by virtue of enhanced oxygen vacancies and less charge transfer resistance (47.3 ohms) demonstrated best electrocatalytic activity for OER compared to the other synthesized catalysts at the same applied potential (1.6 V). On the other hand, the ZnGa1Al1O4 composition demonstrated excellent faradaic efficiency of ∼ 90% towards HER. From this work we can achieve multifunctional applications towards optoelectronics and electrocatalysis just by modulating Al/Ga ratio in ZnGa2-xAlxO4.

AI for Nanomaterials Development in Clean Energy and Carbon Capture, Utilization and Storage (CCUS)

Zero-carbon energy and negative emission technologies are crucial for achieving a carbon neutral future, and nanomaterials have played critical roles in advancing such technologies. More recently, due to the explosive growth in data, the adoption and exploitation of artificial intelligence (AI) as part of the materials research framework have had a tremendous impact on the development of nanomaterials. AI has enabled revolutionary next-generation paradigms to significantly accelerate all stages of material discovery and facilitate the exploration of the enormous design space. In this review, we summarize recent advancements of AI applications in nanomaterials discovery, with a special emphasis on the selected applications of AI and nanotechnology for the net-zero emission future including the development of solar cells, hydrogen energy, battery materials for renewable energy, and CO₂ capture and conversion materials for carbon capture, utilization and storage (CCUS) technologies. In addition, we discuss the limitations and challenges of current AI applications in this area by identifying the gaps that exist in current development. Finally, we present the prospect for future research directions in order to facilitate the large-scale applications of artificial intelligence for advancements in nanomaterials.

Controlled Biosynthesis of ZnCdS Quantum Dots with Visible-Light-Driven Photocatalytic Hydrogen Production Activity

The development of visible-light-responsive photocatalysts with high efficiency, stability, and eco-friendly nature is beneficial to the large-scale application of solar hydrogen production. In this work, the production of biosynthetic ternary ZnCdS photocatalysts (Eg = 2.35-2.72 eV) by sulfate-reducing bacteria (SRB) under mild conditions was carried out for the first time. The huge amount of biogenic S2- and inherent extracellular proteins (EPs) secreted by SRB are important components of rapid extracellular biosynthesis. The ternary ZnCdS QDs at different molar ratios of Zn2+and Cd2+ from 15:1 to 1:1 were monodisperse spheres with good crystallinity and average crystallite size of 6.12 nm, independent of the molar ratio of Cd2+ to Zn2+. All the ZnCdS QDs had remarkable photocatalytic activity and stability for hydrogen evolution under visible light, without noble metal cocatalysts. Especially, ZnCdS QDs at Zn/Cd = 3:1 showed the highest H2 production activity of 3.752 mmol·h-1·g-1. This excellent performance was due to the high absorption of visible light, the high specific surface area, and the lower recombination rate between photoexcited electrons and holes. The adhered inherent EPs on the ZnCdS QDs slowed down the photocorrosion and improved the stability in photocatalytic hydrogen evolution. This study provides a new direction for solar hydrogen production.

Fabrication of ILs-Assisted AgTaO3 Nanoparticles for the Water Splitting Reaction: The Effect of ILs on Morphology and Photoactivity

The design of an active, stable and efficient photocatalyst that is able to be used for hydrogen production is of great interest nowadays. Therefore, four methods of AgTaO3 perovskite synthesis, such as hydrothermal, solvothermal, sol-gel and solid state reactions, were proposed in this study to identify the one with the highest hydrogen generation efficiency by the water splitting reaction. The comprehensive results clearly show that the solid state reaction (SSR) led to the obtainment of a sample with an almost seven times higher photocatalytic activity than the other methods. Furthermore, four ionic liquids, all possessing nitrogen in the form of organic cations (two imidazoliums with different anions, ammonium and tetrazolium), were used for the first time to prepare composites consisting of AgTaO3 modified with IL and Pt, simultaneously. The effect of the ionic liquids (ILs) and Pt nanoparticles' presence on the structure, morphology, optical properties, elemental composition and the effectiveness of the hydrogen generation was investigated and discussed. The morphology investigation revealed that the AgTaO3 photocatalysts with the application of [OMIM]-cation based ILs created smaller granules (<500 nm), whereas [TBA] [Cl] and [TPTZ] [Cl] ILs caused the formation of larger particles (up to 2 μm). We found that various ILs used for the synthesis did not improve the photocatalytic activity of the obtained samples in comparison with pristine AgTaO3. It was detected that the compound with the highest ability for hydrogen generation under UV-Vis irradiation was the AgTaO3_0.2% Pt (248.5 μmol∙g-1), having an almost 13 times higher efficiency in comparison with the non-modified pristine sample. It is evidenced that the enhanced photocatalytic activity of modified composites originated mainly from the presence of the platinum particles. The mechanism of photocatalytic H2 production under UV-Vis light irradiation in the presence of an AgTaO3_IL_Pt composite in the water splitting reaction was also proposed.

An electron trapping protocol of FePW12O40 microflowers with dual catalytic properties: visible light photodegradation of amphetamine and electrocatalytic oxygen evolution

We have demonstrated the development of a novel polyxometalate compound, FePW12O40, for photocatalytic degradation of amphetamine and electrocatalytic oxygen evolution. It showed robust optoelectronic properties, which can be attributed to numerous electron trapping sites created by atomic level defects in the microflower-like architecture.

Shape-controllable synthesis of GdVO4 photocatalysts and their tunable properties in photocatalytic hydrogen generation

Novel visible light responsive materials for water splitting are essential for the efficient conversion of solar energy into hydrogen bond energy. Among other semiconductors, gadolinium orthovanadate has appropriate conduction and valence band edges positioned to split water molecules and a narrow band gap that allows the use of visible light for hydrogen generation. Thus, we present here that hydrogen evolution under visible light (λ > 420 nm) could be accomplished using hierarchical 3D GdVO₄ particles, obtained by a simple, one pot hydrothermal synthesis. We found that applying various reaction components, such as EDTA-Na₂ and EDTA, and adjusting the pH of the solution allow one to tune the shape of GdVO₄ (such as short nanowires, long nanowires, short nanorods, long nanorods, nanoparticles and spheres - all having a tetragonal crystal structure) as well as optical and photocatalytic properties. The highest ability to photocatalytically split methanol solution into hydrogen under UV-Vis irradiation was detected for the long nanowire sample (42 μmol h^-1), having almost 11 times higher efficiency in comparison with the weakest sample - short nanowires. In addition, GdVO₄ spheres generated H₂ more than 2 times (5.75 μmol h^-1) in comparison with the short nanorod sample (2.5 μmol h^-1) under visible light excitation. Photostable in three-hour work cycles, long nanowires and spheres were even able to generate hydrogen from pure water, reaching values of 17 and 3 μmol under UV-Vis and Vis light, respectively.

Graphene decorated MoS2for eosin Y-sensitized hydrogen evolution from water under visible light

MoS₂was modified with graphene (G) by a simple hydrothermal method. The eosin Y sensitized G/MoS₂composite displays enhanced hydrogen evolution in terms of not only activity but also stability.