Carbon quantum dot supported semiconductor photocatalysts for efficient degradation of organic pollutants in water: A review

Abstract

Semiconductor photocatalyst mediated advanced oxidation processes are regarded as one of the most efficient technologies to mitigate organic pollutants in water. However, poor activity under visible light and the recombination of photogenerated electron and hole pairs hinder large scale applicability of semiconductor photocatalysts for water purification. The modification of semiconductor photocatalysts with carbon quantum dots (CQDs) is of high importance due to low toxicity, aqueous stability, enhanced surface area, economic feasibility, good biocompatibility and chemical inertness of CQDs. In this review, we highlight strategies to improve the activity of conventional semiconductor photocatalysts via coupling with CQDs. The enhanced photocatalytic activity of CQD modified narrow and wide band gap photocatalysts is due mainly to up-conversion photoluminescence (UPCL) and the electron reservoir properties of CQDs, while in the case of Z-scheme photocatalysts CQDs act as an electron mediator. Finally, a conclusive outlook and suggested research directions are provided to address challenges such as the inadequate separation of photoinduced charge carriers.

Photosensitive Hybrid Nanostructured Materials: The Big Challenges for Sunlight Capture

“…In the last years, carbon-based nanostructured materials, such as graphene and its derivatives [155,156], fullerenes, activated carbons [26,157], biochar [158,159], carbon nanotubes (CNTs) [13,160], and nanoparticles [161], have been of great interest because of their unique structural, electrical, and mechanical properties, offering promising opportunities for photocatalytic applications (Figure 7).…”

“…In this way, one of the most studied strategies to improve the photocatalytic activity is based on its combination with a carbon-based material (p-type semiconductor) in order to induce an enhancement of charge separation yield and extension of the electron lifetime [13]. By following different synthetic approaches, a large variety of hybrid nanostructured materials were recently designed and prepared, combining TiO 2 with different types of carbon-based materials (Figure 9), such as graphene, graphene oxide (GO) [164,165] and reduced graphene oxide (rGO) [69,118,[166][167][168], CNTs [164,169], carbon particles [161,164,[170][171][172], fullerene [169,173], and biochar [158,159,174], working as adsorbers, electron acceptors, and transporters. These hybrid nanostructured materials showed an enhanced visible light absorption, also exhibiting both excellent adsorption capability and photocatalytic activity, for the removal of pollutants [169,175,176] and heavy metal ions from wastewater [177][178][179], photo-oxidative treatment of organics [167,168,180], as well as water splitting and hydrogen production [178,[181][182][183][184][185].…”

“…Finally, modifications of ZnO photocatalyst with carbon quantum dots (CQDs) have been mostly considered due to low toxicity, aqueous stability, enhanced surface area, economic feasibility, good biocompatibility, and chemical inertness of CQDs [161,172]. Many strategies have been developed to enhance the photocatalytic activity of conventional ZnO via coupling with CQDs, by principally following green and bio-sustainable chemical approaches [195][196][197][198][199].…”

Investigation of photocatalytic chlorpyrifos degradation by a new silica mesoporous material immobilized by WS2 and Fe3O4 nanoparticles: Application of response surface methodology

“…The heterojunctions between two or more nanostructured semiconductors were broadly applied to increase energy absorption for various photocatalytic reactions. Nanocomposite photocatalyst possess several advantages include (1) higher light absorption: semiconductors due to having narrow bandgap performed more visible light absorbability (2) co‐catalyst effect: composition with a suitable cocatalyst can decrease redox potential at respective active places; (3) efficient photogenerated electron–hole pairs separation and transference utilizing p–n junction or Schottky junction formation between metal/semiconductor heterojunction and (4) stability achieved by sheltering of active sites and functional groups on semiconductor surface through surface passivation …”

Facile Fabrication of PA66/GO/MWNTs-COOH Nanocomposites and Their Fibers

“…However, its applications, such as its use in tire cord and conveyor belts, are limited because of insufficient strength. To further improve the physical-mechanical properties of PA66, many additives have been used in the research, such as glass fiber [1,2], carbon fiber [3], carbon nanotubes [4][5][6][7][8], graphene [9], and so forth [10][11][12][13][14].…”