Surface Modification TiO₂ With CQDs For The Treament Of Aromatic Pollutants And Species Transformation Of Chromium

Visible-light photocatalysis was a promising technology with environmental friendly and efficient advanced oxidation.Most of the aromatic poullutants and heavy metals belong to the priority poullutants.A green,efficient,economic,and convenient photocatalytic method was important for the treatment of aromatic pollutants and heavy metal pollution.The application of TiO₂ was limited by:?a?its energy gap?i.e.,rutile 3.0 ev,anatase 3.2eV?,which only could absorb the ultraviolet radiation;?b?high rates of the recombination between electron and hole,which decreased the photochemical quantum yield;?c?high surface free energy,which cause reunitation and then the reducing of the effective surface area,and?d?the extreme low surface coverage of organic pollutants for its strong hydrophobic surface,,which resulted in low efficiency of adsorption and photocatalysis.Surface modification of nano-TiO₂ could increase the light utilization and the surface coverage of organic pollutants,which were crucial for the photocatalytic activity of heterogeneous photocatalysis.After combinated TiO₂?P25?with carbon quantum dots?CQDs?,a new photocatalyst was prepared as CQDs/P25,The structure and characteristic of CQDs/P25 were tested by XRD,XPS,TEM,FIRT and UV-Vis.Compared with P25,CQDs/TiO₂ has more advantages as follows.Its UV-vis wavelength response range expanded from 390 nm to 450 nm.The electron conduction could be accelerated,the recombination of photo-generated electron-hole was reduced,the number of holes and hydroxyl free radical were increased,and then the catalytic activity was improved.The functional groups of-OOH could be added by CQDs onto the surface of P25.so the affinity between organic pollutants and P25 was improved and the surface coverage of organic pollutants on the catalyst was increasedWhen CQDs/P25 was used as photocatalyst,the optimal photodegradation conditions for acid violet 43?AV?and p-nitrophenol?PNP?were:?a?the initial pH value was same as 3.0;?b?the catalyst dosage was 1.0 g/L for AV and 2.0 g/L for PNP;?c?the irradiant time was 2.5 h for AV and 4.5h for PNP;?d?the optimum temperature was same as 60?.Compared with P25,the photodegradation efficiency of CQDs/P25 was increased by 1.48 times for acid violet43 and 1.2 times for the p-nitrophenol.The photocatalytic properties of CQDs/P25 were also assessed by the simultaneous removal of p-nitrophenol and Cr?VI?.The effects of pH values,and initial concentrations of Cr?VI?and PNP,the kind of the photocatalyst,and irradiation time on the removal efficiency were investigated.The acidic solutions were favorable and the optimum pH was 2.0.A synergistic effect from the reduction of Cr?VI?and the oxidation of p-nitrophenol was observed.When P25 was replaced by CQDs/P25,the degradation ratio of Cr?VI?and p-nitrophenol was 98%and 96%,respectively,and the photodegradation efficiency was increased by 1.3 times and 1.5 times,respectively.