Preparation And Photocatalytic Activity Of CQDs Composites With Wide Spectral Response

Semiconductor photocatalytic technology is one of the important ways for human to deal with energy shortage and environmental pollution.However,most of the traditional semiconductor photocatalytic materials only absorb the UV light and a part of the visible light of the solar spectrum,which utilization of sunlight is very limited.Therefore,it is significant to study new semiconductor photocatalysts with wide spectral response.Carbon quantum dots?CQDs?is a new type of zero-dimensional carbon nanomaterials with a quasi-spherical structure and good optical stability.Significantly,the excellent upconversion luminescence properties of CQDs,which can convert the longer wavelength light into shorter wavelength light.The up-converted PL of CQDs infer the possibility to construct CQDs based complex photocatalytic systems to harness the full spectrum of sunlight.Therefore,we constructed composites with CQDs and photocatalysts which have wide spectral response.The main research contents are as follows:?1?The CQDs/TiO₂ composites photocatalysts were prepared by an ultrasonic method.The compositions,structures and optical properties of CQDs/TiO₂ composites were detected through XRD,FT-IR,HRTEM and DRS.The results indicated CQDs can successfully attach to the surface of TiO₂ and result in a red shift of the absorption edge of catalyst.The photocatalytic activity of the obtained materials with different concentration of CQDs were evaluated by degradation of rhodamine B?RhB?under simulated sunlight and monochromatic light irradiation.The results showed the CQDs/TiO₂ composites exhibit excellent ability of photocatalytic activity under simulated sunlight and the activity get to the best when the concentration of CQDs was 1.5 mg/mL.Moreover,it was found the available range of spectrum of CQDs/TiO₂composites are significantly broadened,and the CQDs/TiO₂ even showed effective photocatalytic performance under 850 nm light irradiation.The resulted of PL and transient photocurrent responses indicated the wide spectral response of CQDs/TiO₂ composites can be ascribed to the unique up-converted photoluminescence behavior of CQDs.?2?The I-BiOBr/CQDs composites were successfully fabricated by a facile one-step alcohol soluble hydrolysis method with Bi?NO₃?₃·5H₂O as the bismuth source and ethylene glycol source.The compositions,structures and morphology properties of I-BiOBr/CQDs composites were detected through XRD,FT-IR,XPS,SEM and HRTEM.The results indicated the iodide modification is surface decoration and CQDs can successfully attach to the surface of I-BiOBr.I-BiOBr/CQDs samples mainly exhibited similar flower-like microspherical structure composed of nanosheets.The photocatalytic activity of the obtained materials were evaluated by degradation of methyl orange?MO?.The I-BiOBr/CQDs composites showed excellent visible light photocatalytic activity and the available range of spectrum is significantly broadened,the I-BiOBr/CQDs even showed effecive photocatalytic performance under 850 nm light irradiation.The unique photoluminescence?PL?upconversion property of CQDs were detected through PL,CQDs could be excited by long-wavelength light?500¹000 nm?and the upconverted emission is located in the range of350⁵50 nm.DRS and Mott-Schottky demonstrated that the I^-ion decoration can higher the VB level of BiOBr to modulate the band structure,which could better utilize the upconversion property of CQDs.After studied the photocatalytic mechanism of I-BiOBr/CQDs composites,founding that the excellent photocatalytic activity of as-prepared samples could be ascribed to the couple effects of I^-ion decoration and the unique up-converted photoluminescence behavior of CQDs.