Introduction to Photocatalytic Materials for Clean Energy, Renewable Chemicals production, and Sustainable Catalysis

Professor Rajeev Ahuja & Professor Rajendra Srivastava introduce the Nanoscale Advances themed collection on Photocatalytic Materials for Clean Energy, Renewable Chemicals production, and Sustainable Catalysis.

The growing population has increased the demand for energy sources and commodity chemicals, which are mostly fullled by fossil-fuel sources.The excessive use of fossil fuels pollutes the air and water.The atmospheric CO 2 concentration reached 417.5 ppm in 2022, which is ∼50% higher than the CO 2 concentration during the pre-industrial era (mid-1700). 1 The last 40 years have produced approximately 50% of the cumulative CO 2 emitted since 1750, a direct consequence of the growing population and the increasing fossil-fuel consumption for producing energy and chemicals. 2According to the Paris Climate Agreement, to limit the global temperature rise to 1.5 °C above that of the pre-industrial era and to avoid temperature-driven catastrophic climatic events, CO 2 emissions must drop to zero by 2050. 3 Lowering of the atmospheric CO 2 concentration can be accomplished by adopting three main strategies, namely: (a) reducing atmospheric CO 2 emissions via CO 2 capture & storage, and converting CO 2 into value-added chemicals; 4 (b) renewable chemicals and fuel production employing sustainable energy sources; and (c) environmental remediation employing sustainable energy sources.
Sunlight provides a thousand times more energy to the earth's surface each year than global energy consumption annually, offering a sustainable energy source. 5Harnessing the power of sunlight, photocatalytic materials need to be developed to catalyze chemical reactions that hold promise for clean energy production, synthesizing renewable chemicals, and mitigating environmental pollutants.The early research on solarlight-driven technologies, namely photocatalysis (PC) and photoelectrocatalysis (PEC), mainly focused on H 2 fuel generation via H 2 O splitting and producing valuable organic compounds, such as pharmaceutical building blocks and ne chemicals.However, the recent focus has shied towards producing hydrocarbon fuels and chemicals from CO 2 , intending to decarbonize the earth's atmosphere. 57][8] The recent focus has shied towards producing renewable chemicals, fuels and NH 3 , and removing water and air pollutants employing light energy, as it offers an alternative strategy to produce value-added chemicals and hydrocarbon fuels currently obtained from nonrenewable fossil fuels.
Air pollution remains a pressing global issue due to the continuous release of NO x from fossil-fuel combustion, contributing to photochemical smog and acid rain, and adversely affecting human health and ecosystems.Semiconductor photocatalysis offers a sustainable solution by harnessing solar energy to convert NO x into less-harmful compounds under mild conditions; 9,10 efficient photocatalysts enhance NO removal and selectively convert NO to environmentally benign products like NO 3 − , minimizing secondary emissions.Developing advanced photocatalytic systems tailored for effective NO x reduction holds promise for mitigating air pollution and advancing environmental sustainability.In addressing water pollution caused by industrial dyes, photocatalytic dye degradation plays a crucial role. 11,12When irradiated with light, the photocatalyst generates reactive oxygen species (ROS) such as hydroxyl radicals (cOH) and superoxide anions (O 2 c − ).These highly reactive ROS oxidize dye molecules, breaking them down into less-harmful compounds like water and carbon dioxide.
Photoelectrochemical water splitting and the photocatalytic hydrogen evolution reaction (HER) are two advanced approaches for sustainable H 2 production from water using sunlight. 13PEC utilizes semiconducting materials to generate H 2 and O 2 through efficient optimization of material nanostructures, heterojunction engineering, and surface functionalities.The HER, on the other hand, focuses specically on using semiconductor photocatalysts to drive the reduction of protons (H + ) from water to produce hydrogen gas (H 2 ).This process harnesses the absorption of sunlight by photocatalysts to generate electron-hole pairs.PEC water splitting and photocatalytic HER support the transition to a hydrogen-based economy by offering a renewable, environmentally friendly alternative to fossil fuels, thus advancing global sustainability efforts.
All of the above-discussed photocatalytic applications for environmental remediation can be realized by synthesizing efficient photocatalytic materials.This can be accomplished by adopting modern synthetic strategies and integrating advanced materials science with photocatalytic principles to unlock unprecedented opportunities to harness solar energy.Innovations in catalyst design, such as creating multicomponent systems and incorporating plasmonic materials, have shown significant promise in enhancing photocatalytic performance.One of the primary strategies in photocatalytic synthesis is the development of semiconductor-based materials with tailored nanostructures.By engineering the size, shape, and composition of semiconductor nanoparticles, researchers can signicantly improve light absorption, charge separation, and surface reactivity.Modications such as doping with metal or non-metal elements, creating heterojunctions, and surface functionalization improve photocatalytic performance by extending the light absorption range into the visible spectrum and enhancing charge separation.
This collection of reviews, minireviews and research articles highlights the pivotal role of multifunctional nanomaterials in advancing the efficiency, selectivity, and scalability of photocatalytic processes in harnessing clean energy, producing renewable chemicals, and developing sustainable catalytic routes.
The collection begins with a comprehensive minireview by Wang et al.
(https://doi.org/10.1039/D3NA00837A), on metal-organic framework (MOF)based photocatalytic materials.MOFs have high crystallinity, large surface area, and variable metal nodes, linkers, and functional ability, which makes them ideally suited for the design and development of photocatalytic processes.The minireview elucidates the design rules and principles for engineering MOFs in manipulating the interfacial charge dynamics in MOFs for enhanced photocatalytic applications.

Nanoscale Advances Editorial
Harnessing graphene-based nanocomposites for photocatalytic applications leverages graphene's exceptional electronic conductivity and large surface area, enhancing charge transfer and overall photocatalytic efficiency.Integrating graphene with semiconductor materials promotes efficient light absorption and charge separation, making it a promising approach for advanced photocatalytic systems.Potb Present methods of nanomaterials synthesis oen struggle to achieve precise control over synthetic outcomes, primarily due to poorly dened reaction protocols, and this challenge becomes multi-fold when agricultural waste is used as a direct source.Verma et al.
(https://doi.org/10.1039/D3NA00596H)explore the viability of utilizing lignocellulosic waste, specically sugarcane press mud, for synthesizing ZnO nanoparticles using three distinct precursor salts.These nanoparticles were subsequently evaluated for their effectiveness in the photocatalytic degradation of rhodamine dyes.
Surface plasmon resonance (SPR)based heterogeneous photocatalysts have demonstrated signicantly enhanced photocatalytic efficiency under visible light.The effectiveness of plasmonic photocatalysis depends on various factors within the system, including the choice of specic metals or noble metals and the supporting materials utilized.Rani et al. (https://doi.org/10.1039/D3NA00583F) investigate microwaveassisted synthesis of Ni-NiO@Ni 2 CO 3 (-OH) 2 core-shell@sheet hybrid nanostructures for plasmonic photocatalysis.Their work demonstrates enhanced hydrogen evolution through exible nanosheets, highlighting the potential of cheaper metals in solar-driven watersplitting technologies.
In conclusion, this themed collection encapsulates the forefront of research and development in photocatalytic materials, offering insights into novel materials design, synthesis methodologies, and their diverse applications in clean energy and environmental (air and water) remediation.As guest editors, we sincerely thank the authors for their pioneering contributions and the editorial team of Nanoscale Advances for their support in curating this comprehensive exploration of photocatalytic innovations.This themed collection will catalyze interdisciplinary collaboration, fostering new ideas and practical innovations in pursuing sustainable energy solutions.