A Comprehensive Study on Methods and Materials for Photocatalytic Water Splitting and Hydrogen Production as a Renewable Energy Resource

Edge-oriented growth of cadmium sulfide nanoparticles on nickel metal-organic framework nanosheets for photocatalytic hydrogen evolution

In this study, a directional loading of cadmium sulfide (CdS) nanoparticles (NPs) was achieved on the opposite edges of nickel metal-organic framework (Ni-MOF) nanosheets (NSs) by adjusting the weight ratio of CdS NPs in the reaction process to produce effective visible light photocatalysts. The close contact between the zero-dimensional (0D) and two-dimensional (2D) regions and the matching positions of the bands promoted charge separation and heterojunction formation. The optimal CdS NPs loading of composite material was 40 wt%. At this ratio, CdS NPs grew primarily at the opposite edges of the Ni-MOF NSs rather than on their surfaces. When lactic acid was used as the sacrificial agent, the hydrogen production rate of the 40 %-CdS/Ni-MOF heterojunction under visible light irradiation was 19.6 mmol h-1 g-1, making a 20-fold enhancement compared to the original CdS NPs sample (1.0 mmol h-1 g-1). The charge carriers generated in CdS NPs were transferred to Ni-MOF NSs through heterojunctions, where Ni-MOF NSs also served as cocatalysts to improve hydrogen production. The combination of the two materials improved the light absorption ability. In particular, the 40 %-CdS/Ni-MOF heterojunction exhibited good photostability, effectively preventing the photocorrosion of CdS NPs. This study introduces an approach for constructing efficient and stable photocatalysts for visible light-driven photocatalytic hydrogen production.

Defect-mediated time-efficient photocatalytic degradation of methylene blue and ciprofloxacin using tungsten-incorporated ternary perovskite BaSnO3 nanoparticles

Photocatalytic water purification has been extensively explored for its economic, eco-friendly, and sustainable aspects. In this study, tungsten (W) incorporated BaSn1-xWxO3 (x = 0 to 0.05) nanoparticles synthesized by facile hydrogen peroxide precipitation route has been demonstrated for photocatalytic degradation of methylene blue (MB) dye and ciprofloxacin (CIP) antibiotic. The structural analysis indicates the presence of hybrid composite-like nanostructures with reduced crystallinity. Optical studies reveal blueshift in bandgap and decrease in oxygen vacancy defects upon W-incorporation. Pure BaSnO3 shows overall enhanced photocatalytic activity towards MB (90.22%) and CIP (78.12%) after 240 min of white LED light and sunlight irradiation respectively. The 2 % W-incorporated BaSnO3 shows superior photocatalytic degradation of MB (26.89%) and CIP (45.14%) within first 30 min of irradiation confirming the presence of W to be beneficial in the process. The free radical study revealed the dominant role of reactive hole (h+) and oxygen radical (O2•-) species during photodegradation and their intermediates are investigated to elucidate the degradation mechanism of MB within 30 min of irradiation. This study is promising towards developing defect mediated and time-efficient photocatalysts for environmental remediation.

Role of lamp type in conventional batch and micro-photoreactor for photocatalytic hydrogen production

The use of an irradiation source with a homogeneous distribution of irradiation in the volume of the reaction mixture belongs to the essential aspects of heterogeneous photocatalysis. First, the efficacy of six lamps with various radiation intensity and distribution characteristics is contrasted. The topic of discussion is the photocatalytic hydrogen production from a methanol-water solution in the presence of a NiO-TiO2 photocatalyst. The second section is focused on the potential of a micro-photoreactor system-the batch reactor with a micro-reactor with a circulating reaction mixture, in which the photocatalytic reaction takes place using TiO2 immobilized on borosilicate glass. Continuous photocatalytic hydrogen generation from a methanol-water solution is possible in a micro-photoreactor. This system produced 333.7 ± 21.1 µmol H2 (252.8 ± 16.0 mmol.m-2, the hydrogen formation per thin film area) in a reproducible manner during 168 h.

Sustainable hydrogen generation and storage - a review

In 21st century, the energy demand has grown incredibly due to globalization, human population explosion and growing megacities. This energy demand is being mostly fulfilled by fossil-based sources, which are non-renewable and a major cause of global warming. Energy from these fossil-based sources is cheaper, however challenges exist in terms of climate change. This makes renewable energy sources more promising and viable for the future. Hydrogen is a promising renewable energy carrier for fulfilling the increasing energy demand due to its high energy density, non-toxic and environment friendly characteristics. It is a non-toxic energy carrier as combustion of hydrogen produces water as the byproduct whereas other conventional fuels produce harmful gases and carcinogens. Because of its lighter weight, hydrogen leaks are also easily dispersed in the atmosphere. Hydrogen is one of the most abundant elements on Earth, yet it is not readily available in nature like other fossil fuels. Hence, it is a secondary energy source and hydrogen needs to be produced from water or biomass-based feedstock for it to be considered renewable and sustainable. This paper reviews the renewable hydrogen generation pathways such as water splitting, thermochemical conversion of biomass and biological conversion technologies. Purification and storage technologies of hydrogen is also discussed. The paper also discusses the hydrogen economy and future prospects from an Indian context. Hydrogen purification is necessary because of high purity requirements in particular applications like space, fuel cells etc. Various applications of hydrogen are also addressed and a cost comparison of various hydrogen generation technologies is also analyzed. In conclusion, this study can assist researchers in getting a better grasp of various renewable hydrogen generation pathways, it's purification and storage technologies along with applications of hydrogen in understanding the hydrogen economy and its future prospect.

Cr2S3-Cr2O3/Poly-2-aminobenzene-1-thiol as a Highly Photocatalytic Material for Green Hydrogen Generation from Sewage Water

This study highlights the utilization of the Cr2S3-Cr2O3/P2ABT nanocomposite photoelectrode for efficient and highly sensitive photon absorption, enabling the generation of green hydrogen through the production of hot electrons upon illumination. The nanocomposite is synthesized via a one-pot reaction using K2Cr2O7 and 2-aminobenzene-1-thiol monomer, and the presence of Cr2S3-Cr2O3 is confirmed by XRD and XPS analysis within the composite. The optical properties of the Cr2S3-Cr2O3/poly-2-aminobenzene-1-thiol composite exhibit wide spectral coverage from UV to IR, with a bandgap of 1.6 eV. The diverse morphological behavior observed in the composite correlates with its optical properties, with the cleft spherical particles of the pure polymer transforming into rod-like structures embedded within the polymer matrix. The generated hydrogen gas demonstrates an impressive efficiency of 40.5 mole/10.cm2.h through electrochemical testing. The current density (Jph) values are evaluated under different light frequencies using optical filters ranging from 730 to 340 nm, resulting in Jph values of 0.012 and 0.014 mA.cm-2, respectively. These findings present a promising avenue as green hydrogen for industrial applications, leveraging the potential of the Cr2S3-Cr2O3/P2ABT nanocomposite photoelectrode.

Figures of Merit for Photocatalysis: Comparison of NiO/La-NaTaO3 and Synechocystis sp. PCC 6803 as a Semiconductor and a Bio-Photocatalyst for Water Splitting

While photocatalysis is considered a promising sustainable technology in the field of heterogeneous catalysis as well as biocatalysis, figures of merit (FOM) for comparing catalytic performance, especially between disciplines, are not well established. Here, photocatalytic water splitting was conducted using a semiconductor (NiO/La-NaTaO3) and a bio-photocatalyst (Synechocystis sp. PCC 6803) in the same setup under similar reaction conditions, eliminating the often ill-defined influence of the setup on the FOMs obtained. Comparing the results enables the critical evaluation of existing FOMs and a quantitative comparison of both photocatalytic systems. A single FOM is insufficient to compare the photocatalysts, instead a combination of multiple FOMs (reaction rate, photocatalytic space time yield and a redefined apparent quantum yield) is superior for assessing a variety of photocatalytic systems.

Investigations on synergistic and antioxidant actions of medicinal plant based biosynthesis of Zinc Oxide Nanoparticles against E.coli and K. pneumonia bacteria

INTRODUCTION

Bacterial resistance to multiple drugs is increasing at an alarming rate in current era and nanotechnology is one of the effective and novel approaches to overcome drug resistance.

METHODS

Zinc Oxide Nanoparticles (ZnO NPs) has stronger antibacterial activity and is regarded as bio-safe nanomaterial. The aim of present study is to synthesize the ZnO NPs using Aloe vera leaves extract and to investigate the synergistic effects and antioxidant actions of bio-synthesized ZnO NPs against gram negative bacteria E.coli and K. pneumoniae. The synergistic effect of β-lactam antibiotics (meropenem and ciprofloxacin) was tested along with ZnO NPs by using Kirby's disc diffusion assay. The antioxidant activity was investigated by α, α-diphenyl-β-picrylhydrazyl (DPPH) method.

RESULTS

Results revealed that the antibacterial activity of the selected antibiotics was much enhanced by ZnO NPs than the antibiotics alone. The resistant antibiotic (ciprofloxacin) became sensitive when combined with ZnO NPs. The antioxidant activity reveals that biosynthesized ZnO NPs possess significantly higher (p<0.05) antioxidant activity (77%).

CONCLUSION

The findings reveal that biosynthesized ZnO NPs have much more eco-friendly approach. It can act as a strong potentiator of β-lactam antibiotics and put forward the possibility to use them effectively in targeted drug delivery, pharmaceuticals and biomedical fields.

Photocatalytic degradation of organic dyes: Pd-γ-Al2O3 and PdO-γ-Al2O3 as potential photocatalysts

This work describes photocatalytic application of γ-alumina (γ-Al₂O₃) surface-anchored palladium and palladium oxide nanoparticles (Pd-γ-Al₂O₃ and PdO-γ-Al₂O₃ NPs) synthesized by a novel co-precipitation technique. The palladium(0) NPs (Pd-γ-Al₂O₃) were formed by calcination of the sample in inert medium, whereas PdO NPs (PdO-γ-Al₂O₃) were obtained by calcination of the sample in atmospheric oxygen. As-synthesized Pd-γ-Al₂O₃ and PdO-γ-Al₂O₃ NPs are characterized by X-ray diffraction, Fourier transform-infrared spectroscopy, field emission scanning electron microscopy and photoluminescence (PL) spectra. The PL spectra of Pd-γ-Al₂O₃ and PdO-γ-Al₂O₃ NPs display visible-light emissions from 450 to 500 nm at room temperature. This work aims to study the photocatalytic degradation of organic dye pollutants, including bromocresol green (BCG), bromothymol blue, methylene blue and methyl orange using Pd-γ-Al₂O₃ and PdO-γ-Al₂O₃ NPs as potential photocatalysts. Experimental parameters, including the admitting concentration of the organic dye solution, Pd-γ-Al₂O₃ and PdO-γ-Al₂O₃ photocatalyst dosage, and pH, were varied to ascertain favorable conditions for photocatalytic degradation. The results indicate that the organic dye BCG is completely (100%) degraded in aqueous solution under ultraviolet light, compared with the other organic dyes. Furthermore, Pd-γ-Al₂O₃ NPs showed better photocatalytic performance than PdO-γ-Al₂O₃ NPs. The possible photocatalytic degradation mechanism of the organic dyes by Pd-γ-Al₂O₃ and PdO-γ-Al₂O₃ photocatalysts is proposed. The studies reveal that Pd and PdO NPs anchored on the γ-Al₂O₃ surface are promising and effective catalysts for photocatalytic degradation of organic dyes.

Mechanism of photocatalytic degradation of organic dyes by Pd/PdO NPs.

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.