A novel synergistic strategy of N-doping and N-wrapping/bridging to synthesize photosensitive and conductive Graphene-TiO2 composite nano-capsules for gaseous HCHO degradation was proposed. High HCHO photo-degradation activity of the composite was attributed to the enhanced interfacial contact of TiO2 with conductive melamine-doped graphene (MG) sheets by dopamine (DA) bridging. MG improved the electrical conductivity and photoinduced charges separation/transfer in the MG/TiO2 composite. Moreover, hydrogen treated DA wrapped/bridged MG/TiO2 composite (H-TiO2@MG-D) forming a 3D nano-capsule structure, which could concomitantly strengthen the interfacial contact between TiO2 and MG sheets and accelerates electron mobility. Characterization and DFT simulation results revealed that H-TiO2@MG-D nano-capsules exhibited the lowest band gap (2.49 eV) and highest charges separation efficiency. Simulation results further indicated that N-doping accelerated the transfer of adsorption sites from acidic Ti4+ (for HCHO) to basic N sites (for HCOOH and CO2) before and after HCHO degradation reaction. The enhanced interfacial contact of H-TiO2@MG-D resulted in its remarkably higher HCHO photocatalytic degradation efficiency (eta = 92%) and fast degradation rate (k = 15.04 x 10(-3) min(-1)) than that of pristine TiO2 by a factor of 4.1 and 9.2, respectively. Therefore, the present study attributed to ease of synthesis and novel N-doping and N-wrapping strategy for the preparation of highly conductive MG-TiO2 composite can be deemed as an effective and promising pathway for HCHO photodegradation and other similar photocatalytic applications.

Melamine-graphene/TiO2 nano-capsule; Enhanced interfacial contact; Photocatalytic degradation; Gaseous formaldehyde; DFT simulation

GuangXi University; South China Agricultural University