Gaozu Liao

Enhanced photocatalytic ozonation of organics by g-C3N4 under visible light irradiation

Graphitic carbon nitride (g-C3N4) was employed as the active photocatalyst in the photocatalytic ozonation coupling system in the present study. g-C3N4 was prepared by directly heating thiourea in air at 550°C. XRD, FT-IR, UV-vis was used to characterize the structure and optical property. Oxalic acid and bisphenol A were selected as model substances for photocatalytic ozonation reactions to evaluate the catalytic ability of g-C3N4 (g-C3N4/Vis/O3). The results showed that the degradation ratio of oxalic acid with g-C3N4/Vis/O3 was 65.2% higher than the sum of ratio when it was individually decomposed by g-C3N4/Vis and O3. The TOC removal of biphenol A with g-C3N4/Vis/O3 was 2.17 times as great as the sum of the ratio when using g-C3N4/Vis and O3. This improvement was attributed to the enhanced synergistic effect between photocatalysis and ozonation by g-C3N4. Under visible light irradiation, the photo-generated electrons produced on g-C3N4 facilitated the electrons transfer owing to the more negative conduction band potential (-1.3V versus NHE). It meant that the photo-generated electrons could be trapped by ozone and reaction with it more easily. Subsequently, the yield of hydroxyl radicals was improved so as to enhance the organics degradation efficiency. This work indicated that metal-free g-C3N4 could be an excellent catalyst for mineralization of organic compounds in waste control.

Mineralization of Para-Chlorobenzoic Acid in Water by Cobalt-Incorporated MCM-41 Catalyzed Ozonation

Cobalt-incorporated MCM-41(Co-MCM-41) was used as a heterogeneous catalyst for the ozonation of para-chlorobenzoic acid (p-CBA) in aqueous solution. Cobalt oxide supported on MCM-41(Co/MCM-41) was synthesized for comparison. Their textural properties were elucidated by various characterization techniques to understand the relationship between surface texture and catalytic activity. TOC removal at 60 min reached 91% with Co-MCM-41, 83% with Co/MCM-41 and only 52% with ozone alone, respectively. Observations from diffuse reflection spectroscopy demonstrated that different metal phases were formed in these cobalt-modified molecular sieves samples. Radical scavenger experiments indicated the formation of hydroxyl radicals that were responsible for the effective degradation of p-CBA. An integrated approach to the catalytic mechanism was proposed by considering the variation of pH in the course of ozonation as well as its subsequent influence on the dissociation of targeted compounds and surface charge of the catalyst. In the reusability experiments, the reused Co-MCM-41 was able to regain the same catalytic capability as the fresh one within 5 cycles. X-ray photoelectron spectroscopy results indicated that a part of Co2+ was oxidized to Co3+ after oxidation reaction.

Degradation of Oxalic Acid and Bisphenol A by Photocatalytic Ozonation with g-C3N4 Nanosheet under Simulated Solar Irradiation

ABSTRACT Photocatalytic ozonation of organics under simulated solar irradiation with a g-C3N4 nanosheet was investigated. g-C3N4 was prepared by calcinations of urea and characterized by TEM, BET, XRD and UV-Vis. Oxalic acid and bisphenol A were used as model substances to evaluate its catalytic ability. The results showed that g-C3N4 possess 2D nanosheet structure. The degradation ratio of oxalic acid and bisphenol A with g-C3N4/O3/Solar was 1.50 and 1.92 times as great as the sum ratio when it was individually degraded by g-C3N4/Solar and O3, separately. The results of recycling experiment indicated that g-C3N4 catalyst is very stable under experimental conditions.