Visible-light-driven pollutants degradation with carbon quantum dots/N-TiO2 under mild condition: Facile preparation, dramatic performance and deep mechanism insight

Abstract Because pure TiO2 has high photogenerated charge carriers recombination rate and inferior visible light capture capability, the optical activity is very weak. N doping can generate a lower energy gap energy and carbon quantum dots (CDs) have excellent properties that can transfer electrons smoothly and reserve electrons quickly, so we think that doping of N into TiO2 and loading of CDs can modify TiO2. We synthesized a brand new carbon quantum dots/N-TiO2(CDs/N-TiO2) by mechanically mixing carbon quantum dots with N-TiO2 instead of the conventional calcination or solvothermal step. The degradation ratio of RhB(10 mg/L) was increased from 6.66% and 19.97% to 99.8% in 5 min under visible light when compared with TiO2 and N-TiO2. The kinetic constants of RhB degradation by 30CDs/N-TiO2 are 85.52 and 25.40 times higher than those of TiO2 and N-TiO2, respectively. Besides, Cr(Ⅵ) (20 mg/L) photoreduction can be completely achieved in 4 min under solar light irradiation. Besides, We analyzed the behavior of photogenerated charge carriers by the surface photovoltage spectra (SPV) and transient photovoltage spectra (TPV) measurement analyses, showing the deep mechanism of photodegradation process of dye. Doping of nitrogen into TiO2 can extend the photo absorption range of TiO2 and let n-type TiO2 show p-type conducting character that makes it easier to transfer electrons to the CDs. Loading of CDs can enhance the electron-hole pairs separation efficiency.