An overview on water splitting photocatalysts

Diiron(IV)-Oxo Species and Water Oxidation: How Crucial is Electronic Cooperativity?

Water splitting, crucial for generating oxygen and hydrogen, remains a central challenge in chemistry due to its importance in developing sustainable energy sources and addressing environmental concerns. Consequently, numerous complexes have been developed to split water and release oxygen and hydrogen, albeit typically requiring external sources such as thermal, photo, or electrochemical methods. In this context, the discovery of a (μ-oxo)bis(μ-carboxamido) diiron(IV) complex, [FeIV₂O(L)₂]2+ (L=N,N-bis-(3',5'-dimethyl-4'-methoxypyridyl-2'-methyl)-N'-acetyl-1,2-diaminoethane), which activates both C-H and O-H bonds without external stimuli, has attracted significant attention. Notably, this complex generates hydroxyl radicals (⋅OH) without O₂ evolution and displays termolecular kinetics, presenting a rare and intriguing mechanistic puzzle. In this work, we explore the catalytic mechanism of water oxidation by this diiron(IV) complex using DFT methods. Our computational findings validate experimental observations regarding the necessity of a second water molecule in the reaction, revealing a bifurcated electron-proton transfer (BEPT) pathway driven by termolecular reactivity. Moreover, we highlight the crucial role of excess water molecules in stabilising the reaction intermediates, particularly via interaction with the -OMe groups to form a water cluster model. The inclusion of explicit water molecules was found to reduce the activation barrier to 23.5 kJ/mol from the reactant and 62.7 kJ/mol from the reactant complex, whereas, with only one water molecule present, the barrier was 344.3 kJ/mol, highlighting the critical role of the adventitious water molecule at the active site. Our study underscores the importance of metal-metal cooperativity, ligand design, spin-state modulation, and second-sphere effects in shaping the catalytic behaviour. These insights provide a detailed understanding of the electronic structure and reactivity, offering valuable guidelines for future catalyst design in water oxidation and beyond.

Advances in Hierarchical Inorganic Nanostructures for Efficient Solar Energy Harvesting Systems

The urgent need to address the global energy and environmental crisis necessitates the development of efficient solar-power harvesting systems. Among the promising candidates, hierarchical inorganic nanostructures stand out due to their exceptional attributes, including a high specific surface area, abundant active sites, and tunable optoelectronic properties. In this comprehensive review, we delve into the fundamental principles underlying various solar energy harvesting technologies, including dye-sensitized solar cells (DSSCs), photocatalytic, photoelectrocatalytic (water splitting), and photothermal (water purification) systems, providing a foundational understanding of their operation. Thereafter, the discussion is focused on recent advancements in the synthesis, design, and development of hierarchical nanostructures composed of diverse inorganic material combinations, tailored for each of these solar energy harvesting systems. We meticulously elaborate on the distinct synthesis methods and conditions employed to fine-tune the morphological features of these hierarchical nanostructures. Furthermore, this review offers profound insights into critical aspects such as electron transfer mechanisms, band gap engineering, the creation of hetero-hybrid structures to optimize interface chemistry through diverse synthesis approaches, and precise adjustments of structural features. Beyond elucidating the scientific fundamentals, this review explores the large-scale applications of the aforementioned solar harvesting systems. Additionally, it addresses the existing challenges and outlines the prospects for achieving heightened solar-energy conversion efficiency.

Iron (III) doped titanium dioxide coated dimensionally stable graphite anode electrode for electro-chemical treatment of domestic wastewater

Availability of clean water is of concern due to pollution and diminishing supply pollution. However, purification is possible depending on the incorporated contaminants. Domestic wastewater contains dissolved organic matter and its remediation can be done by oxidation. The best oxidation can be achieved by electron transfer the same way metabolic processes occur. This study exploited the use of a film of iron (III) doped titanium dioxide applied on an electrode which was found to be effective. Natural light conditions generated electrons that migrated through the electrode leaving behind holes which oxidized the contaminants as the excess electrons were discharged at the cathode after passing through the casted proton exchange membrane (PEM) separating the two half cells of the prepared reactor. This electrochemical method has the advantage in that the organic pollutants are oxidized to carbon dioxide with no secondary pollutants and the inorganic pollutants into insoluble matter. The assembled cell was applied to purify both synthetic and real water samples of green leafy vegetable solution from the kitchen by clarification. The clarification process was monitored by UV-Vis using distilled water as a reference to compare the light that transmitted through a sample. It was observed that the electro-oxidation process took place showing a high potential 105 mV within the first 150 min followed by degradation at a high rate. The oxidation of the organic matter was confirmed by UV-Vis analysis as well as by cyclic voltametric analysis of iron released into the solution of the synthetic samples. The electro chemical treatment of the water was then applied to purify real water samples made from a sample of 4.5 g minced of green vegetables dispersed in one liter of water (4.5 g/l). The green leafy coloured solution was clarified after 154 h of continuous oxidation. The degradation process was confirmed to be independent of intermediates or other species present in solution as it was of first order reaction kinetics. The electrochemical oxidation of organic matter in water using iron (III) doped titanium dioxide coated graphite electrode has potential application on the purification of water.

Photocatalytic pathway toward degradation of environmental pharmaceutical pollutants: structure, kinetics and mechanism approach

During the last few years, the presence of pharmaceuticals in the aquatic environment, classified as so-called emerging contaminants, has attracted attention from the scientific community.

An overview on visible light responsive metal oxide based photocatalysts for hydrogen energy production

The present review summarizes the recent development and challenges in visible light responsive metal oxide based photocatalysts for water splitting.