Photocatalytic Activity of TiO2/g-C3N4 Nanocomposites for Removal of Monochlorophenols from Water

Abstract

This research employed g-C3N4 nanosheets in the hydrothermal synthesis of TiO2/g-C3N4 hybrid photocatalysts. The TiO2/g-C3N4 heterojunctions, well-dispersed TiO2 nanoparticles on the g-C3N4 nanosheets, are effective photocatalysts for the degradation of monochlorophenols (MCPs: 2-CP, 3-CP, and 4-CP) which are prominent water contaminants. The removal efficiency of 2-CP and 4-CP reached 87% and 64%, respectively, after treatment of 25 ppm CP solutions with the photocatalyst (40TiO2/g-C3N4, 1 g/L) and irradiation with UV–Vis light. Treatment of CP solutions with g-C3N4 nanosheets or TiO2 alone in conjunction with irradiation gave removal efficiencies lower than 50%, which suggests the two act synergically to enhance the photocatalytic activity of the 40TiO2/g-C3N4 nanocomposite. Superoxide and hydroxyl radicals are key active species produced during CP photodegradation. In addition, the observed nitrogen and Ti3+ defects and oxygen vacancies in the TiO2/g-C3N4 nanocomposites may improve the light-harvesting ability of the composite and assist preventing rapid electron-hole recombination on the surface, enhancing the photocatalytic performance. In addition, interfacial interactions between the MCPs (low polarity) and thermally exfoliated carbon nitride in the TiO2/g-C3N4 nanocomposites may also enhance MCP degradation.

Kinetic Evidence for Type-II Heterojunction and Z-Scheme Interactions in g-C3N4/TiO2 Nanotube-Based Photocatalysts in Photocatalytic Hydrogen Evolution

“…The Ti 2p spectrum is divided into Ti 2p 1/2 at 464.6 eV and Ti 2p 3/2 at 458.9 eV (spin–orbit splitting of ∼5.7 eV) (Figure a), which are attributed to Ti 4+ in the matrix of TiO 2 . Additionally, the resolved component next to Ti 2p 3/2 toward lower binding energies can be resolved easily due to the inherent narrow and intense spectral shape of Ti 2p 3/2 and is attributed to any reduced species of Ti 3+ or oxygen vacancies. , Here, the binding energy shifts are observed for the composites toward lower binding energies (<0.2 eV). The peak of O 1 s at 530.2 eV is due to the O 2– species in TiO 2 (Figure b).…”

“…The peak of O 1 s at 530.2 eV is due to the O 2– species in TiO 2 (Figure b). The additional shoulder toward higher binding energies at around 531–532 eV can always be seen and is attributed to the surface hydroxyl (OH) species. ,, Thus, the magnitude of the shoulder feature can vary depending not only on the nature of TiO 2 but also on the history in which the sample was handled in air. Here again, the binding energies of O 1s are observed to shift to lower binding energies by about <0.2 eV.…”

Microwave Synthesis of Visible-Light-Activated g-C3N4/TiO2 Photocatalysts

“…Moreover, this material is difficult to separate from water, may cause secondary pollution due to its dissolution and has low specific surface area, which restricts its use in photocatalytic applications. Among the possible strategies to tackle these issues, effective coupling of g-C 3 N 4 with other semiconductors has previously shown to be advantageous in charge separation and improved absorption in the visible region [ 57 , 58 , 59 , 60 ].…”

“…Several approaches have already been used to fabricate g-C 3 N 4 /TiO 2 heterostructures, such as sol-gel [ 65 ], hydrothermal [ 58 ]/solvothermal syntheses [ 66 ], wet impregnation [ 67 ] and microwave-assisted methods [ 68 , 69 ]. Apart from the microwave irradiation process, these methods typically require high temperatures and/or long reaction times, hence being energy consuming [ 58 , 66 , 67 , 70 , 71 ].…”

“…Several approaches have already been used to fabricate g-C 3 N 4 /TiO 2 heterostructures, such as sol-gel [ 65 ], hydrothermal [ 58 ]/solvothermal syntheses [ 66 ], wet impregnation [ 67 ] and microwave-assisted methods [ 68 , 69 ]. Apart from the microwave irradiation process, these methods typically require high temperatures and/or long reaction times, hence being energy consuming [ 58 , 66 , 67 , 70 , 71 ]. Taking into account the minimization of energy, microwave irradiation appears as a good alternative for the synthesis of complex inorganic materials, since higher reaction yields can be obtained in such a short amount of time.…”