Wenjie Tian

Nitrogen- and Sulfur-Codoped Hierarchically Porous Carbon for Adsorptive and Oxidative Removal of Pharmaceutical Contaminants

Heteroatom (nitrogen and sulfur)-codoped porous carbons (N-S-PCs) with high surface areas and hierarchically porous structures were successfully synthesized via direct pyrolysis of a mixture of glucose, sodium bicarbonate, and thiourea. The resulting N-S-PCs exhibit excellent adsorption abilities and are highly efficient for potassium persulfate activation when employed as catalysts for the oxidative degradation of sulfachloropyridazine (SCP) solutions. The adsorption capacities of N-S-PC-2 (which contains 4.51 atom % nitrogen and 0.22 atom % sulfur and exhibits SBET of 1608 m(2) g(-1)) are 73, 7, and 3 times higher than those of graphene oxide, reduced graphene oxide, and commercial single-walled carbon nanotube, respectively. For oxidation, the reaction rate constant of N-S-PC-2 is 0.28 min(-1). This approach not only contributes to the large-scale production and application of high-quality catalysts in water remediation but also provides an innovative strategy for the production of heteroatom-doped PCs for energy applications.

Oxygen Vacancies in Shape Controlled Cu2O/Reduced Graphene Oxide/In2O3 Hybrid for Promoted Photocatalytic Water Oxidation and Degradation of Environmental Pollutants

A novel shape controlled Cu2O/reduced graphene oxide/In2O3 (Cu2O/RGO/In2O3) hybrid with abundant oxygen vacancies was prepared by a facile, surfactant-free method. The hybrid photocatalyst exhibits an increased photocatalytic activity in water oxidation and degradation of environmental pollutants (methylene blue and Cr6+ solutions) compared with pure In2O3 and Cu2O materials. The presence of oxygen vacancies in Cu2O/RGO/In2O3 and the formation of heterojunction between In2O3 and Cu2O induce extra diffusive electronic states above the valence band (VB) edge and reduce the band gap of the hybrid consequently. Besides, the increased activity of Cu2O/RGO/In2O3 hybrid is also attributed to the alignment of band edge, a process that is assisted by different Fermi levels between In2O3 and Cu2O, as well as the charge transfer and distribution onto the graphene sheets, which causes the downshift of VB of In2O3 and the significant increase in its oxidation potential. Additionally, a built-in electric field is generated on the interface of n-type In2O3 and p-type Cu2O, suppressing the recombination of photoinduced electron-hole pairs and allowing the photogenerated electrons and holes to participate in the reduction and oxidation reactions for oxidizing water molecules and pollutants more efficiently.

Flower-like Cobalt Hydroxide/Oxide on Graphitic Carbon Nitride for Visible-Light-Driven Water Oxidation

Direct water oxidation via photocatalysis is a four-electron and multiple-proton process which requires high extra energy input to produce free dioxygen gas, making it exacting, especially under visible light irradiation. To improve the oxygen evolution reaction rates (OERs) and utilize more visible light, flower-like cobalt hydroxide/oxide (Fw-Co(OH)2/Fw-Co3O4) photocatalysts were prepared and loaded onto graphitic carbon nitride (g-C3N4) by a facile coating method in this work. Influenced by the unique three-dimensional morphologies, the synthesized Fw-Co(OH)2 or Fw-Co3O4/g-C3N4 hybrids reveal favorable combination and synergism reflected by the modified photoelectric activities and the improved OER performances. Attributed to its prominent hydrotalcite structure, Fw-Co(OH)2 shows better cocatalytic activity for g-C3N4 modification compared with that of Fw-Co3O4. Specifically, 7 wt % Fw-Co(OH)2/g-C3N4 photocatalyst exhibits photocurrent density 4 times higher and OER performance 5 times better than pristine g-C3N4. This work unambiguously promotes the application of sustainable g-C3N4 in water oxidation.

Heterostructured WO3@CoWO4 bilayer nanosheets for enhanced visible-light photo, electro and photoelectro-chemical oxidation of water

Herein, a facile interface-induced synthesis method is first established to newly fabricate two-dimensional (2D) bilayer nanosheets of WO3@CoWO4 as highly efficient catalysts for enhanced photo, electro and photoelectro-chemical oxygen evolution reactions (OERs). The heterostructure and the interfacial oxygen vacancy of WO3@CoWO4 reduce the energy barriers in the OER. Density functional theory (DFT) calculations and material characterizations reveal that the WO3@CoWO4 p–n heterojunction endows the composite with a narrowed band gap for better visible-light harvesting, rapid charge transfer across the interface and a lower recombination rate of the photo-excited carriers. The interface O-vacancy vests the active Co site with an enhanced density of state (DOS) at the valence band maximum (VBM), which can increase the concentration of the photogenerated holes to improve photocatalytic and photoelectrochemical (PEC) activity. This study presents a proof-of-concept design towards low cost and multi-metal 2D/2D nanosheets for water oxidation applications.

A comparative study of metal (Ni, Co, or Mn)-borate catalysts and their photodeposition on rGO/ZnO nanoarrays for photoelectrochemical water splitting

Feasible and efficient photoelectrochemical (PEC) water splitting demands a rational integration of solar light absorbers with active electrocatalysts. Herein, we first compare three amorphous metal-borates (M-Bi, M = Ni, Co, Mn) as low-cost electrocatalysts, among which Mn-Bi is proposed for the first time for fabrication of new PEC devices for oxygen evolution reaction (OER). Density functional theory (DFT) calculations compared the catalytic activity of the effective structures in M-Bi and found that NiO6 possesses kinetically the lowest overall OER energy barrier. Experimentally, M-Bi thin layers were self-assembled on reduced graphene oxide (rGO) linked ZnO nanorod arrays respectively, to form a highly efficient ternary PEC system (M-Bi/rGO/ZnO) using a modified photodeposition method. rGO facilitates the fast charge separation in light-absorbing ZnO NAs, while M-Bi (M = Ni, Co, Mn) can improve the kinetics of OER. In accordance with DFT results, Ni-Bi serves as the most active electrocatalyst in such a PEC device, followed by Co-Bi and Mn-Bi. Compared to ZnO, the photoelectroconversion efficiency is elevated by approximately 4 times on Ni-Bi/rGO/ZnO, with its onset potential migrated by 0.17 V in the cathodic direction under one sun illumination.