Directional electron transfer mechanisms with graphene quantum dots as the electron donor for photodecomposition of perfluorooctane sulfonate

Abstract

Graphene quantum dots (GQDs) were synthesized via the oxygen-driven unzipping of graphene under ultra-high frequency ultrasonication, and then attached to the SiC nanoparticles by the hydrothermal method to form the SiC/GQDs nanocomposites. The SiC/GQDs exhibited superior photoactivity over the decomposition of perfluorooctane sulfonate (C 8 F 17 SO 3 H, PFOS), which was even harder to decompose than perfluorooctanoic acid (PFOA). This work presented the first instance of employing photoexcited semiconductor nanomaterials to realize the improvement from the activation of the -F 2 C-COOH bond in PFOA to the activation of -F 2 C-SO 3 H in PFOS. The decomposition rate constants (k) of 2-CF 3 -PFOS, 6-CF 3 -PFOS and linear-PFOS with SiC/GQDs were 0.127 h −1 , 0.115 h −1 , 0.098 h −1 , and the corresponding half-lives were 5.5 h, 6.0 h, 7.1 h, respectively. The ratio of k (the branched isomers : the linear isomers) significantly reduced from the 967 times via vacuum ultraviolet (VUV) photolysis to the same order of magnitude in this work.The X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) were conducted to investigate the electronic properties of SiC/GQDs, revealing the centermost directional electron transfer process during the reaction. The photogenerated electron originated from the π-π* transition of the C=C bond and the n-π* transition of the C=O bond under UV excitation, transferred to SiC nanoparticles due to the heterojunction structure of SiC/GQDs, and then further transferred to the accumulated PFOS on the surface of SiC/GQDs for the electron-withdrawing property of sulfonate group, leading to the critical activation of sulfonate group. The decomposition mechanisms of PFOS involved the ionic headgroup cleavage, hydrolysis, hydrodefluorination, and the C-C bond scission.

Synthesis of graphene quantum dots and their applications in drug delivery

“…Ultrasonic technology is also a common method for material synthesis [69,70]. Under the action of ultrasound, tens of thousands of small bubbles will be formed in the liquid, and the mechanical force generated can destroy the carbon-carbon bonds, thus cutting into GQDs (Fig.…”

“…In recent years, the applications of GQDs in drug delivery [123][124][125][126][127], sensors [128][129][130][131][132][133][134], bio-imaging [10,63,[135][136][137][138][139][140], magnetic hyperthermia [141][142][143], photothermal therapy [144][145][146][147][148], antibacterial [145,149,150], catalyst [69,[151][152][153][154][155], environmental protection [38,156,157], and energy [158][159][160][161][162][163] has made remarkable accomplishment. In order to better apply GQDs to drug delivery, some researchers had used density functional theory (DFT) calculations [164]…”

“…In recent years, the applications of GQDs in drug delivery [ 123 – 127 ], sensors [ 128 – 134 ], bio-imaging [ 10 , 63 , 135 – 140 ], magnetic hyperthermia [ 141 – 143 ], photothermal therapy [ 144 – 148 ], antibacterial [ 145 , 149 , 150 ], catalyst [ 69 , 151 – 155 ], environmental protection [ 38 , 156 , 157 ], and energy [ 158 – 163 ] has made remarkable accomplishment. In order to better apply GQDs to drug delivery, some researchers had used density functional theory (DFT) calculations [ 164 – 167 ], molecular dynamics (MD) simulations [ 168 , 169 ], or other methods [ 170 , 171 ] to theoretically study the properties of GQDs.…”

Carbon Dots for Photocatalytic Degradation of Aqueous Pollutants: Recent Advancements

“…reported the photodegradation of perfluorooctane sulfonate (C 8 F 17 SO 3 H, PFOS), another persistent and prevalent organic pollutant, under deep UV irradiation (5 W 254 nm UV lamp) conditions with SiC/GQDs and bare SiC. [ 124 ] The heterojunction allows the effective separation of generated electrons by GQDs under deep‐UV conditions towards CB of SiC ( Figure a). Long‐chain PFOS was converted into shot chain perfluorocarboxylic acids on the surface of SiC surface by electronic transfer toward SO group of PFOS.…”

“…Reproduced with permission. [ 124 ] Copyright 2017, Elsevier. b) The plot of ( C / C 0 ) versus time for Cr(VI) photoreduction by NP‐CD under different concentrations of Cr(VI).…”