Modulating charge carriers in carbon dots toward efficient solar‐to‐energy conversion

Abstract

Growing attention to the development of sustainable solar-to-energy conversion applications has resulted in the synthesis of promising and environment-friendly nanomaterials as energy harvesters. Among various carbon nanomaterials, carbon dots (CDs) have received significant attention due to their excellent light absorption capability, broad absorption region, and superior photostability with enormous potential for solar energy applications. Therefore, utilizing and modulating the charge carriers generated from CDs is critical for achieving a high energy conversion efficiency of CDs. Herein, we focus on the distinct characteristics of CDs as energy converters from charge excitation to charge separation and transfer for various solar-to-energy applications, including photovoltaic cells, photocatalysts, and photoelectrocatalysts. We anticipate that this review will offer insight into the synthesis and design of novel nanocomposites with a fundamental analysis of the photochemical properties and future development of energy conversion devices. K E Y W O R D Scarbon dots, charge carrier, energy conversion, photocatalyst, photoelectrocatalyst | INTRODUCTIONCarbon dots (CDs) have received widespread attention in the scientific community as one of the latest additions to carbon-based nanomaterials. CDs, which are typically defined as quasi-spherical carbon nanoparticles of <10 nm, exhibit unique physical, chemical, and optical properties, including high light absorption, tunable photoluminescence, and excellent electron donor/acceptor characteristics. [1][2][3][4][5][6] Owing to these advantages, CDs can be applied in bioimaging, 7,8 biosensing, 9-11 drug delivery, [12][13][14][15] phototherapy, [16][17][18] and light-harvesting applications in energy transducers. [19][20][21] Moreover, the facile and mild synthetic nature of CDs using various combinations of carbon precursors and other molecular agents can provide easy access to the formation of sp 2 -hybridized carbonaceous core of CDs, with an amorphous shell rich in surface functional groups containing oxygen and nitrogen. These surface functional moieties can be potentially functionalized with other organic molecules on the CD surface, allowing the control of photoluminescence (PL)

Recent advances in solar‐driven CO2 reduction over g‐C3N4‐based photocatalysts

“…Pristine g‐C 3 N 4 always suffers from low electrical conductivity, which significantly limits its photocatalytic performance. Considering the excellent conductivity, low cost, and sustainability of carbonaceous materials, 157 the strategy coupling g‐C 3 N 4 with carbonaceous materials, can significantly improve the photogenerated charge carrier separation efficiency and mobility, thus promoting the photocatalytic activity 158–161 …”

“…Considering the excellent conductivity, low cost, and sustainability of carbonaceous materials, 157 the strategy coupling g-C 3 N 4 with carbonaceous materials, can significantly improve the photogenerated charge carrier separation efficiency and mobility, thus promoting the photocatalytic activity. [158][159][160][161] Ong et al 124 successfully deposited carbon nanodots (CNDs) on g-C 3 N 4 surface through an electrostatic attraction method, as shown in Figure 23. Because of the larger work function of CND (5.56 eV) relative to g-C 3 N 4 (4.66 eV), the free electrons will transfer from g-C 3 N 4 to CND through the interface, causing positively charged g-C 3 N 4 and negatively charged CND and forming Schottky heterojunction.…”

Point‐to‐face contact heterojunctions: Interfacial design of 0D nanomaterials on 2D g‐C3N4 towards photocatalytic energy applications

“…C NDs or QDs are known to have excellent light absorption ability, and thus could be potentially useful photosensitizers for wider optical wavelengths and excellent electron acceptors. 255,256 Hence, they may be useful 0D semiconductors to form a heterojunction with 2D g-C 3 N 4 . So far, several typical methods of designing C/g-C 3 N 4 photocatalysts have been reported, including thermal polymerization, 257 the hydrothermal 258 method, and precipitation.…”

“…The most commonly used 0D metal‐free nanomaterials that are coupled with g‐C 3 N 4 nanosheets are carbon dots. C NDs or QDs are known to have excellent light absorption ability, and thus could be potentially useful photosensitizers for wider optical wavelengths and excellent electron acceptors 255,256 . Hence, they may be useful 0D semiconductors to form a heterojunction with 2D g‐C 3 N 4 .…”

CdS Nanorods with an Optimized ZnS Coating as Composite Photocatalysts for Enhanced Water Splitting under Solar Light Irradiation

“…In the past years, among the reported visible light-responsive photocatalysts, cadmium sulfide (CdS) with the bandgap at about 2.4 eV has been extensively studied as one of the most promising narrow bandgap semiconductors. , Due to the visible light response and negative conduction band edge than the H 2 O/H 2 redox potential, CdS has been widely used as a candidate photocatalyst for hydrogen evolution, clean energy conversion, enhanced spectroscopies, sensors, and solar light harvesting. − However, during the photochemical reaction, CdS suffers from inherent photocorrosion by irradiation under light, which is mainly attributed to the recombination of generated charge carriers (such as the induced electrons combined with holes, H + , or other active radicals). Photocorrosion of CdS is an irreversible phenomenon, which obstructs its development and application. , …”