Abstract
Solar radiation is becoming increasingly appreciated because of its influence on living matter and the feasibility of its application for a variety of purposes. It is an available and everlasting natural source of energy, rapidly gaining ground as a supplement and alternative to the nonrenewable energy feedstock. Actually, an increasing interest is involved in the development of efficient materials as the core of photocatalytic and photothermal processes, allowing solar energy harvesting and conversion for many technological applications, including hydrogen production, CO2 reduction, pollutants degradation, as well as organic syntheses. Particularly, photosensitive nanostructured hybrid materials synthesized coupling inorganic semiconductors with organic compounds, and polymers or carbon-based materials are attracting ever-growing research attention since their peculiar properties overcome several limitations of photocatalytic semiconductors through different approaches, including dye or charge transfer complex sensitization and heterostructures formation. The aim of this review was to describe the most promising recent advances in the field of hybrid nanostructured materials for sunlight capture and solar energy exploitation by photocatalytic processes. Beside diverse materials based on metal oxide semiconductors, emerging photoactive systems, such as metal-organic frameworks (MOFs) and hybrid perovskites, were discussed. Finally, future research opportunities and challenges associated with the design and development of highly efficient and cost-effective photosensitive nanomaterials for technological claims were outlined.
Highlights
Solar energy, as a renewable and low-cost energy source, represents the most reliable and green solution to address energy and environmental issues [1,2,3,4,5]
The D-π-A framework is extensively employed in dye-sensitized solar cells (DSCs) and has been used in photocatalytic H2 production systems because it is associated with efficient charge separation, modulation of the intramolecular charge-transfer nature and the absorption properties [15,19]
Different types of photoactive compounds can be included in the design of a dye with specific structure: some D-A-π-A perylene dyes, featuring cyanoacrylic acid and dicyanomethylene rhodamine as the acceptor/anchoring group, combined with a N-annulated perylene donor and a quinoxaline auxiliary acceptor [63]; two triphenylamine-benzimidazole-based dyes bound on TiO2, with Cu2WS4 nanocubes as an alternative water splitting co-catalyst to Pt [64]; a particular composite dye, consisting of π-conjugated indoline–rhodanine with a chlorophyll derivative, which induced panchromatic absorption in the visible range, efficient electron transfer, and prolonged stability [65]; a series of dyes with triphenylamine donor, vinyltiophene bridge, and a cationic pyridinium acceptor [66]
Summary
From a mechanistic point of view, irradiating a photocatalyst by UV/visible light with energy equal or higher than its bandgap, electrons (e−) can jump from the valence band (VB) into the conduction band (CB) and leave holes (h+), generating electron-hole pairs The mono-dispersed status of organic molecules endows the intramolecularly separated charges within the discrete organic dyes, to directly transfer out for the destruction and reformation of chemical bonds (Figure 1c) [1] Their performances are limited by self-quenching of excited states and photo-bleaching due to their sensitive nature. Adapted and reprinted with permission from [5], Copyright (2017) Royal Society of Chemistry (RSC)
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