Chloro-benquinone Modified on Graphene Oxide as Metal-free Catalyst: Strong Promotion of Hydroxyl Radical and Generation of Ultra-Small Graphene Oxide

Scientific Reports, Mar 2017

Carbon-based metal-free catalyst has attracted more and more attention. It is a big challenge to improve catalytic activity of metal-free catalyst for decomposition of H2O2 to produce hydroxyl radical (HO•). Here, we report chloro-benquinone (TCBQ) modified on graphene oxide (GO) as metal-free catalyst for strong promotion of HO•. By the incorporation of GO, the HO• production by H2O2 and TCBQ is significantly promoted. Based on density functional theory, TCBQ modified GO (GO-TCBQ) is more prone to be nucleophilic attacked by H2O2 to yield HO• via electron transfer acceleration. Furthermore, the generated HO• can cut GO nanosheets into uniform ultra-small graphene oxide (USGO) through the cleavage of epoxy and C-C bonds. Interestingly, the damaged GO and in situ formed GO fragments can further enhance decomposition of H2O2 to produce HO•. Different from other catalytic processes, the GO-TCBQ metal-free catalysis process can be enhanced by GO itself, producing more HO•, and uniform USGO also can be generated. Thus, the metal free catalysis will be considered a fabrication method for uniform USGO, and may be extended to other fields including detoxifying organic pollutants and the application as disinfectants.

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Chloro-benquinone Modified on Graphene Oxide as Metal-free Catalyst: Strong Promotion of Hydroxyl Radical and Generation of Ultra-Small Graphene Oxide

Abstract Carbon-based metal-free catalyst has attracted more and more attention. It is a big challenge to improve catalytic activity of metal-free catalyst for decomposition of H2O2 to produce hydroxyl radical (HO•). Here, we report chloro-benquinone (TCBQ) modified on graphene oxide (GO) as metal-free catalyst for strong promotion of HO•. By the incorporation of GO, the HO• production by H2O2 and TCBQ is significantly promoted. Based on density functional theory, TCBQ modified GO (GO-TCBQ) is more prone to be nucleophilic attacked by H2O2 to yield HO• via electron transfer acceleration. Furthermore, the generated HO• can cut GO nanosheets into uniform ultra-small graphene oxide (USGO) through the cleavage of epoxy and C-C bonds. Interestingly, the damaged GO and in situ formed GO fragments can further enhance decomposition of H2O2 to produce HO•. Different from other catalytic processes, the GO-TCBQ metal-free catalysis process can be enhanced by GO itself, producing more HO•, and uniform USGO also can be generated. Thus, the metal free catalysis will be considered a fabrication method for uniform USGO, and may be extended to other fields including detoxifying organic pollutants and the application as disinfectants. Introduction Graphene oxide (GO), a highly oxidized form of graphene, has attracted widespread interests due to its unique physical and chemical properties1,2,3. Recently, research on GO-based metal-free catalyst is rapidly increasing4,5,6,7,8. In most cases, metal-based catalysts are hard to remove metal ions from the product, which would have a dominant effect on their further applications9,10. Thus, GO as metal-free catalyst has drawn more and more attention10,11,12. As known, Fenton reaction is a common method for generating hydroxyl radical (HO•) via decomposition of hydrogen peroxide (H2O2) by metal-based catalysts13,14,15. Interestingly, GO itself can act as catalyst and react with H2O2 due to intrinsic peroxidase catalytic activity16,17,18,19. Sun H. et al. indicated graphene quantum dots (GQDs) could catalyze the decomposition of H2O2, generating HO• to improve the antibacterial performance of H2O2 effectively20. However, peroxidase catalytic activity of GO is usually sensitive to H2O2 with a very low concentration, resulting in the limited catalytic ability during the degradation of organic pollutants15. Therefore, it is a big challenge to improve catalytic activity of GO metal-free catalyst for decomposition of H2O2 to produce HO•. On the other hand, hydroxyl radical has been reported to oxidize and cut GO into zero dimensional ultra-small graphene oxide (USGO) or GQDs21,22,23,24, which have various potential applications in the fields of optoelectronics25, catalysis26 and biology and medicine27. Now, various methods have been applied for the cleavage of GO into USGO or GQDs. However, most those methods require harsh conditions28,29,30,31 or complicated processes28. Herein, for the first time, we report chloro-benquinone (TCBQ) modified on GO as metal-free catalyst, with a Janus effect for strong promotion of HO• and formation of USGO with uniform size and shape (Fig. 1). Based on density functional theory (DFT) and metal-free catalysis experiments, GO can effectively accelerate nucleophilic reaction between TCBQ modified GO (GO-TCBQ) and H2O2 to yield HO• due to promotion of electrons transfer from H2O2 to TCBQ. More importantly, the generated HO• can oxidize and cut GO nanosheets into USGO with uniform size and shape. Interestingly, the GO fragments itself can further enhance catalytic decomposition of H2O2 to produce more HO•. Figure 1: Schematic representation of the Janus effect mechanism of metal-free catalysis. (TCBQ modified on GO as metal-free catalyst is more prone to be nucleophilic attacked by H2O2 to yield HO• via electron transfer acceleration; on the other hand, the generated HO• can cut GO nanosheets into uniform USGO. GO fragments also further enhance decomposition of H2O2 to produce more HO•). Full size image Results and Discussion Zhu et al.32,33 demonstrated that H2O2 as a nucleophile could nucleophilic attack TCBQ, forming a trichlorohydroperoxyl-1,4-benzoquinone intermediate, which decomposes homolytically to produce HO•. Previous study also indicated that GO possesses intrinsic peroxidase-like activity to catalyze the reduction of H2O216,20. In this study, we used TCBQ modified on the GO surface as metal-free catalyst to enhance H2O2 decomposition, which was named as GO-TCBQ. Some Details about characterization and optimization of GO-TCBQ were shown in Supplementary Material (Fig. S1 and S2). Figure 2 shows the production of hydroxyl radical in the metal-free catalysis system. GO-TCBQ can significant enhance the decomposition of H2O2 to generate hydroxyl radical. As illustrated in the Fig. 2a, after dosing GO-TCBQ in the H2O2 solution, hydroxyl radical can be detected by electron spin resonance (ESR). As there was no metal catalyst in the (...truncated)


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He Zhao, Juehua Wang, Di Zhang, Qin Dai, Qingzhen Han, Penghui Du, Chenming Liu, Yongbing Xie, Yi Zhang, Hongbin Cao, Zhuangjun Fan. Chloro-benquinone Modified on Graphene Oxide as Metal-free Catalyst: Strong Promotion of Hydroxyl Radical and Generation of Ultra-Small Graphene Oxide, Scientific Reports, 2017, Issue: 7, DOI: 10.1038/srep42643