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. 2018 Apr 8;8(4):229.
doi: 10.3390/nano8040229.

In-Situ Synthesis of Hydrogen Titanate Nanotube/Graphene Composites with a Chemically Bonded Interface and Enhanced Visible Photocatalytic Activity

Juan Yang  1   2 , Jun You  1 , Jun Dai  3 , Yumei Chen  4 , Yao Li  5
Affiliations

In-Situ Synthesis of Hydrogen Titanate Nanotube/Graphene Composites with a Chemically Bonded Interface and Enhanced Visible Photocatalytic Activity

Juan Yang et al. Nanomaterials (Basel). .

Abstract

Hydrogen titanate nanotube (HTT)/graphene nanocomposites are synthesized by hydrothermal reduction of graphene oxide (GO) and simultaneous preparation of nanotubular HTT via an alkaline hydrothermal process. By using this facile in-situ compositing strategy, HTT are densely supported upon the surface of graphene sheets with close interface contacts. The as-prepared HTT/graphene nanocomposites possess significantly enhanced visible light catalytic activity for the partial oxidation of benzylic alcohols. The amount of graphene has significant influence on catalytic activity and the optimal content of graphene is 1.0 wt %, giving a normalized rate constant k of 1.71 × 10-3 g/m²·h, which exceeds that of pure HTT and HTT/graphene-1.0% mixed by a factor of 7.1 or 5.2. Other than the general role of graphene as a high-performance electron acceptor or transporter, the observed enhancement in photocatalytic activity over HTT/graphene can be ascribed to the improved interfacial charge migration from enhanced chemical bonding (Ti-C bonds) during the in-situ compositing process. The formation of Ti-C bonds is confirmed by XPS analysis and the resulting enhanced separation of photoinduced charge carriers is demonstrated by electrochemical impedance spectra and transient photocurrent response.

Keywords: Ti–C bonds; benzylic alcohols; hydrogen titanate; interfacial charge transfer; photocatalytic selective oxidation.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
XRD patterns of hydrogen titanate nanotube (HTT)/graphene nanocomposites: (a) pure HTT, (b) HTT/graphene-0.2%, (c) HTT/graphene-0.4%, (d) HTT/graphene-1.0%, (e) HTT/graphene-2.0%, (f) HTT/graphene-4.0%. Inset: XRD patterns of pure GO and graphene.
Figure 2
Figure 2
FTIR spectra of samples (a) GO, (b) HTT/graphene-1.0%, and (c) pure HTT.
Figure 3
Figure 3
Raman spectra of (a) bare GO, (b) HTT/graphene-1.0%, and (c) HTT/graphene-4.0% composites.
Figure 4
Figure 4
Typical TEM images of (a) pure HTT, (b) HTT/graphene-1.0%, and (c) HTT/graphene-1.0%-mixed nanocomposites.
Figure 5
Figure 5
C 1s XPS spectra of (a) bare GO, (b) HTT/graphene-1.0%-mixed, and (c) HTT/graphene-1.0% chemically bonded nanocomposites.
Figure 6
Figure 6
Ti 2p XPS spectra of (a) HTT/graphene-1.0%-mixed and (b) HTT/graphene-1.0% chemically bonded nanocomposites.
Figure 7
Figure 7
The selective oxidation of benzyl alcohol over HTT/graphene nanocomposites under visible light irradiation: (a) pure HTT, (b) HTT/graphene-0.2%, (c) HTT/graphene-0.4%, (d) HTT/graphene-1.0%, (e) HTT/graphene-2.0%, (f) HTT/graphene-4.0%, (g) P25 TiO2/graphene-1.0%, and (h) HTT/graphene-1.0%-mixed. The blank column represents the experimental results in the absence of visible irradiation or photocatalyst.
Figure 8
Figure 8
(A) Time involved photocatalytic conversion of benzyl alcohol over as-synthesized HTT/graphene nanocomposites: (a) pure HTT, (b) HTT/graphene-0.2%, (c) HTT/graphene-0.4%, (d) HTT/graphene-1.0%, (e) HTT/graphene-2.0%, (f) HTT/graphene -4.0%, (g) P25 TiO2/graphene-1.0%, and (h) HTT/graphene-1.0%-mixed; (B) The corresponding first-order kinetics plots over these photocatalysts.
Figure 9
Figure 9
Recycled photoactivity test for five operational runs over the optimal HTT/graphene-1.0%, on selective oxidation of benzyl alcohol.
Figure 10
Figure 10
(A) FTIR spectra of (a) HTT/graphene-1.0%, (b) benzyl alcohol adsorbed HTT /graphene-1.0% and (c) free benzyl alcohol; (B) UV-vis DRS of pure HTT, benzyl alcohol adsorbed HTT, HTT/graphene-1.0%, and benzyl alcohol adsorbed HTT/graphene-1.0%; (C) Plot of transformed Kubelka–Munk function versus the energy of light (Inset: the corresponding UV-vis DRS).
Figure 11
Figure 11
(A) Photocurrent curves of pure HTT, HTT/graphene-1.0%-mixed, and HTT/graphene-1.0% electrodes under visible light irradiation; the violet curve represents the photocurrent response over HTT/graphene-1.0% electrode without benzyl alcohol in the electrolyte solution. (B) Electrochemical impedance spectra (EIS) Nyquist plots of the pure HTT, HTT/graphene-1.0%-mixed, and HTT/graphene-1.0% samples under light irradiation with a Xe lamp. Inset: Electrical equivalent circuit supposed for fitting of impedance spectra. RS, CPE, and Rct represent the electrolyte resistance, space charge capacitance, and the charge transfer resistance, respectively.
Figure 12
Figure 12
(A) Control experiments of photocatalytic selective oxidation of benzyl alcohol in the presence of various scavengers or in the absence of O2 over HTT/graphene-1.0% under visible light irradiation for 6 h. (B) Electron spin resonance (ESR) spectra of O2·ˉ trapped by DMPO over pure HTT and HTT/graphene-1.0% suspensions in methanol solution, blank represents both the sample containing DMPO alone under light illumination and the sample containing DMPO and catalysts in dark.
Figure 13
Figure 13
Schematic illustrations for the efficient interfacial charge transfer effect over HTT/graphene composites toward the selective oxidation of benzylic alcohols under visible light irradiation.
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