Synthesis Of π-conjugated Materials With High Surface Area And Their Environmental Purification Properties Investigation

In our work, a series of π-conjugated materials with high surface area wassynthesized and applied in environmental purification. The relationship between thestructure of π-conjugated materials and their adsorption and photocatalystic propertieswas also systematically investigated. We adopted graphene oxide (GO) and graphene asthe adsorbent. The adsorption can directly occur on their lamellar surface due to thetwo-dimensional structure which will improve the adsorption efficiency andrecyclability. We also adopted graphite-like carbon nitride (g-C3N4) as the photocatalyst.Single-layered g-C3N4nanosheets and nanoporous g-C3N4with high surface area weresuccessfully synthesized. Compared with the bulk g-C3N4, nanostructured g-C3N4canexhibit enhanced photocatalytic activity due to the improved separation ofphotogenerated electron-hole pairs and higher efficiency of charge carriers transfer.GO and graphene both showed excellent adsorption capacity for bisphenol A (BPA).The maximum adsorption capacity (qm) of GO for BPA estimated from the Langmuirisotherm was87.8mg·g1at25°C, pH=6.0. And its required contact time to reachadsorption equilibrium was about30min, which was much shorter than that of activatedcarbon. Besides, qmof graphene for BPA estimated from the Langmuir isotherm was181.8mg·g1at29°C, pH=6.0. The GO had good recyclability and could retain about83%of their adsorption ability after five adsorption-desorption cycles. The largeadsorption affinity of GO and graphene for BPA were thought to be attributed to theirsingle-layered graphene planes with aromatic rings and surface oxygen-containinggroups, which can form π-π interaction and hydrogen bonding with the two benzenerings and two hydroxyl groups of BPA, respectively. The adsorption mechanism wasalso proved by the FTIR spectra.Single-layered g-C3N4nanosheets with high surface area were obtained via amodified Hummers method. Compared with the bulk g-C3N4, g-C3N4nanosheets ownedhigher surface area (87.5m2g-1), improved separation of photogenerated electron-holepairs and higher efficiency of charge carriers transfer. Accordingly, the photocatalyticactivity and photocurrent of g-C3N4nanosheets were remarkably enhanced under UV,visible light and simulated solar light irradiation. Moreover, it was found that an additional refluxing process can effectively remove the structural defects of g-C3N4nanosheets. It further increased the adsorption capacity for the target pollutants,improved the separation of photogenerated electron-hole pairs and charge carrierstransfer of g-C3N4nanosheets, which resulted in higher photocatalytic activity andphotocurrent.Nanoporous g-C3N4with high surface area was prepared by a bubble templatemethod. Faster calcination heating rate and higher proportion of thiourea canresult in higher surface area, better adsorption and photocatalytic properties ofnanoporous g-C3N4. Compared with the bulk g-C3N4, nanoporous g-C3N4possessed a higher surface area and pore volume, improved separation ofphotogenerated electron-hole pairs, and higher efficiency of charge carrierstransfer. Accordingly, the adsorption capacity for the target pollutants, thephotocatalytic activity and photocurrent under both visible light and simulatedsolar light irradiation of nanoporous g-C3N4were greatly improved.