A compendium of all-in-one solar-driven water splitting using ZnIn2S4-based photocatalysts: guiding the path from the past to the limitless future

Photocatalytic water splitting represents a leading approach to harness the abundant solar energy, producing hydrogen as a clean and sustainable energy carrier. Zinc indium sulfide (ZIS) emerges as one of the most captivating candidates attributed to its unique physicochemical and photophysical properties, attracting much interest and holding significant promise in this domain. To develop a highly efficient ZIS-based photocatalytic system for green energy production, it is paramount to comprehensively understand the strengths and limitations of ZIS, particularly within the framework of solar-driven water splitting. This review elucidates the three sequential steps that govern the overall efficiency of ZIS with a sharp focus on the mechanisms and inherent drawbacks associated with each phase, including commonly overlooked aspects such as the jeopardising photocorrosion issue, the neglected oxidative counter surface reaction kinetics in overall water splitting, the sluggish photocarrier dynamics and the undesired side redox reactions. Multifarious material design strategies are discussed to specifically mitigate the formidable limitations and bottleneck issues. This review concludes with the current state of ZIS-based photocatalytic water splitting systems, followed by personal perspectives aimed at elevating the field to practical consideration for future endeavours towards sustainable hydrogen production through solar-driven water splitting.

TiO2 as a Nanozyme Mimicking Photolyase to Repair DNA Damage

Cyclobutane pyrimidine dimer (CPD) is the most abundant DNA photolesion, and it can be repaired by photolyases based on electron-transfer mechanisms. However, photolyase is absent in the human body and lacks stability for applications. Can one develop natural enzyme mimetics utilizing nanoparticles (termed nanozymes) to mimic photolyase in repairing DNA damage? Herein, we observe the successful reversal of thymine dimer T<>T to normal T base by TiO₂ under UVA irradiation. Time-resolved spectroscopy provides direct evidence that the photogenerated electron of TiO₂ transfers to T<>T, causing structural instability and initiating the repair process. T-T^- would then undergo bond cleavage to form T and T^-, and T^- returns an electron to TiO₂, finishing the photocatalytic cycle. For the first time, TiO₂ is discovered to exhibit photocatalytic properties similar to those of natural enzymes, pointing to its extraordinary application potential as a nanozyme to mimic photolyase in repairing DNA damage.

Charge carrier dynamics and reaction intermediates in heterogeneous photocatalysis by time-resolved spectroscopies

Sunlight as the most abundant renewable energy holds the promise to make our society sustainable. However, due to its low power density and intermittence, efficient conversion and storage of solar energy as a clean fuel are crucial. Apart from solar fuel synthesis, sunlight can also be used to drive other reactions including organic conversion and air/water purification. Given such potential of photocatalysis, the past few decades have seen a surge in the discovery of photocatalysts. However, the current photocatalytic efficiency is still very moderate. To address this challenge, it is important to understand fundamental factors that dominate the efficiency of a photocatalytic process to enable the rational design and development of photocatalytic systems. Many recent studies highlighted transient absorption spectroscopy (TAS) and time-resolved infrared (TRIR) spectroscopy as powerful approaches to characterise charge carrier dynamics and reaction pathways to elucidate the reasons behind low photocatalytic efficiencies, and to rationalise photocatalytic activities exhibited by closely related materials. Accordingly, as a fast-moving area, the past decade has witnessed an explosion in reports on charge carrier dynamics and reaction mechanisms on a wide range of photocatalytic materials. This critical review will discuss the application of TAS and TRIR in a wide range of heterogeneous photocatalytic systems, demonstrating the variety of ways in which these techniques can be used to understand the correlation between materials design, charge carrier behaviour, and photocatalytic activity. Finally, it provides a comprehensive outlook for potential developments in the area of time-resolved spectroscopies with an aim to provide design strategies for photocatalysts.

Sol-Gel Sonochemical Triton X-100 Templated Synthesis of Fe2O3/ZnO Nanocomposites Toward Developing Photocatalytic Degradation of Organic Pollutants

The existing work emphasizes mainly to advance the low surface features of zinc oxide (ZnO) by dispersion of Fe2O3 nanoparticles on the ZnO surface fabricated via a sol-gel route with Triton X-100 as a structure and capping agent to synthesis a novel series of Fe2O3/ZnO nanocomposites (NCs) with novel features assembling between the two nanoparticle materials. Fe2O3/ZnO is an effective semiconductor which has higher efficiency in the removal of numerous organic dyes and other pollutants. The NCs was characterized via HRTEM, XRD, FTIR, BET, RS and UV–Vis DRS. A photocatalytic performance of the fabricated Fe2O3/ZnO nanocomposites was estimated by continual degradation of the methylene blue dye (MB) as an organic pollutant in aqueous solution. The comparison between pure ZnO (NPs) and Fe2O3/ZnO (NCs) show advanced photocatalytic performance under both UV and sunlight irradiation. The impact of several parameters, for example, dopant contents, photocatalytic dosage, pH, chemical oxygen demand (COD) and point of zero charge (PZC) were evaluated and discussed. In addition, the protective species’ role was estimated via a radical scavenger route. The photo-degradation data shown that the Fe2O3/ZnO (10 wt%) semiconductor is the fit photocatalyst between the fabricated semiconductors for the methylene blue dye (MB) degradation. The intensity reduction peak of UV emission and the intensity increment of visible emission were led to the lessening in recombination between electrons and holes which are finally responsible for the maximum photocatalytic performance of Fe2O3/ZnO nanocomposites. The gained results confirmed that the dopant content is the major factor in photocatalytic degradation activity.

Thermal and Rheological Study of Nanocomposites, Reinforced with Bi-Phase Ceramic Nanoparticles

In this study the synthesis of bi-phase nanoparticles of Fe1.46Zn0.5La0.04Cu0.5O4 (FZLCs) ceramics were first carried out by Sol-gel method and then nanocomposites of FZLCs with polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene glycol (PEG) and polyethylene oxide (PEO) were prepared by one-pot blending technique. XRD, FT-IR, TG/DTA and SEM techniques were applied for complete characterization of composites. Rheological and dielectric properties of all nanocomposites were studied in detail for their comparative performance. TGA results reveal the highly thermal stability for all nanocomposites in this order i.e. FLZCs/PEO > FLZCs/PVA > FZLCs/PVP > FZLCs/PEG. Rheological properties show that these materials are rigid, pseudo plastic and non-Newtonian in nature. The increase in values for storage modulus (G′) and loss modulus (G′′) with increasing angular frequency owed to the shear thinning behavior of these nanocomposites. Dielectric properties show good agreement to that of energy storage substances which means that these materials have potential to be applied in storage devices.