Hydrogen Production as a Clean Energy Carrier through Heterojunction Semiconductors for Environmental Remediation

Abstract

Today, as a result of the advancement of technology and increasing environmental problems, the need for clean energy has considerably increased. In this regard, hydrogen, which is a clean and sustainable energy carrier with high energy density, is among the well-regarded and effective means to deliver and store energy, and can also be used for environmental remediation purposes. Renewable hydrogen energy carriers can successfully substitute fossil fuels and decrease carbon dioxide (CO2) emissions and reduce the rate of global warming. Hydrogen generation from sustainable solar energy and water sources is an environmentally friendly resolution for growing global energy demands. Among various solar hydrogen production routes, semiconductor-based photocatalysis seems a promising scheme that is mainly performed using two kinds of homogeneous and heterogeneous methods, of which the latter is more advantageous. During semiconductor-based heterogeneous photocatalysis, a solid material is stimulated by exposure to light and generates an electron–hole pair that subsequently takes part in redox reactions leading to hydrogen production. This review paper tries to thoroughly introduce and discuss various semiconductor-based photocatalysis processes for environmental remediation with a specific focus on heterojunction semiconductors with the hope that it will pave the way for new designs with higher performance to protect the environment.

Quantification Methodology of Ammonia Produced from Electrocatalytic and Photocatalytic Nitrogen/Nitrate Reduction

“…The color may change from yellow to green and then to blue, along with increasing ammonia concentration (Figure 3b,c). The overall reaction is shown in Equation (6).…”

“…The overall reaction is shown in Equation ( 6). ( 6) (6) Energies 2023, 16, 27 In both the indophenol blue method and the salicylate method, citrate buffer is often used to stabilize the pH and prevent the precipitation of hardness cations, such as magnesium or calcium ions, at a high pH [35,47]. The indophenol blue method and the salicylate method are able to measure ammonia at low concentrations (0-0.6 mg L −1 of NH 3 -N) with good accuracy and repeatability [14].…”

“…Ammonia (NH 3 ) is an essential feedstock chemical for the fertilizer, pharmaceutical, and nitrogen-containing chemicals industries. Today, it is also considered a next-generation energy carrier due to its high energy density for hydrogen (17.6%) [1][2][3][4][5][6]. Up to now, ammonia production has heavily relied on the conventional Haber-Bosch process, which requires a high energy supply (temperature 400-500 • C and pressure 100-200 atm) [7][8][9], and is responsible for 1.2% of global CO 2 emissions [10][11][12][13].…”

Metallic plasmons significantly boosted visible-light photocatalytic hydrogen evolution from water splitting

“…[1][2][3] Hydrogen energy is an attractive source of renewable energy due to its clean, sustainable, and environment-friendly features. [4][5][6] In the past few decades, non-renewable sources have been used to produce H 2 ; however, this depletes fossil fuel supplies and causes serious environmental issues. 7 In 1972, Fujishima et al 8 discovered photo-electrocatalytic H 2 generation from water splitting over a TiO 2 electrode.…”

ZnO-ZnS Heterostructure as a Potent Photocatalyst in the Preparation of Some Substituted Chromenes and Remarkable Antigastrointestinal Cancer Activity

“…In recent years, researchers have successfully fabricated heterostructure semiconductors such as TiO 2 /SrO, CdS/TiO 2 , CdS/ZnO, CdS/AgI, CdS/ZnS, Cd 3 P 2 /TiO 2 , AgI/Ag 2 S, Cd 3 P 2 /ZnO, ZnO/ZnSe, SnO 2 /CdS, SnO 2 /TiO 2 , CdSe/TiO 2 , and Cu 2 S/CdS. − These heterostructures exhibit unique structural features, and their properties have been extensively studied. Overall, the exploration of heterojunctions involving zinc oxide and other semiconductors offers exciting opportunities to tailor and enhance the functionalities of ZnO and achieve diverse applications in optoelectronic, catalysis, and energy conversion. − …”