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WO3/N-rGO composites with a phase-junction structure were prepared by hydrothermal methods. The formation of orthorhombic and monoclinic WO3 during the in situ synthesis of WO3 on nitrogen-doped graphene was demonstrated by X-ray diffraction (XRD). X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) results demonstrated the successful doping of nitrogen atoms in graphene. The effect of N-rGO and phase-junction structure on the photoelectric properties was investigated by photoelectrochemical tests. In the I–t test results, WO3/N-rGO exhibited a photocurrent density of 0.204 mA/cm2, which was 5.8 and 2.6 times higher than those of WO3 and WO3/rGO, respectively. The electrochemical impedance spectroscopy (EIS) demonstrated that N-rGO and phase-junction structure reduce the electrochemical impedance of the composites. In the linear sweep voltammetry (LSV) and Mott–Schottky (MS) results, WO3/N-rGO exhibited the highest photocurrent (3.65 mA/cm2) intensity at 1.23 V bias and the largest carrier density (3.63 × 1020 cm–3), respectively. Possible electron-transfer mechanisms of the composite materials also have been discussed. [ABSTRACT FROM AUTHOR]

In this study, the prepared GQDs/W 18 O 49 /WO 3 (WCW) were loaded on g-C 3 N 4 with defects (CN 1-x) under the action of hydrothermal synthesis. The structure, morphology, optical properties, functional groups and surface group properties of the CN 1-x @WCW composites were determined by XRD, TEM, UV–vis, FTIR and XPS tests. The electrochemical properties of the CN 1-x @WCW composite were studied by i-t, EIS and M − S analysis. Compared with WCW, the instantaneous photoelectric efficiency, the photon current efficiency under the applied bias voltage, interfacial electron transfer and electron lifetime of CN 1-x @WCW had been greatly improved. The results indicated that two-dimensional CN 1-x with good conductivity could transfer electrons quickly, reduce the interfacial resistance and prolong the lifetime of electrons, thus inhibiting the recombination of photogenerated electron-hole pairs in WCW semiconductor. In addition, the possible mechanism was proposed and analyzed from the point of view of electron transmission. [ABSTRACT FROM AUTHOR]

WO 3 and N-GQDs were loaded in a two-dimensional graphene sheet layer by hydrothermal method, and then oxygen vacancy-rich WO 3 /N-GQDs/N-rGO composites were successfully prepared by calcination. The structures, morphologies and surface chemical states were characterized by XRD, TEM, XPS, FTIR, and the electrochemical properties were studied by EIS, i-t, LSV and M-S. The WO 3 /N-GQDs/N-rGO composites had a high carrier density of 5.88 × 1020 cm−3 and presented an instantaneous photocurrent density of 2.96 × 10−4 A/cm2 under 365 nm irradiation, which was 4.4 times larger than that of pure WO 3. The enhanced properties were mainly ascribed to the increased light absorption and carrier migration by the two-carbon modification of N-GQDs and N-rGO. Meanwhile, the presence of oxygen vacancies can improve the carrier lifetime, thus suppressing the recombination of photogenerated electron-hole pairs in the WO 3 /N-GQDs/N-rGO composites. The photoelectric properties of the composites were improved by the cooperative effect of double carbon modification and oxygen vacancies. [Display omitted] • WO 3 /N-GQDs/N-rGO with oxygen vacancies was prepared by a hydrothermal and calcination process. • Oxygen vacancies trap photoelectrons to suppress the recombination and improve the conductivity and lifetime. • The introduction of N-doped graphene provides doping atoms and defect sites for oxygen vacancies. • N-rGO acts as a transport channel to speed up the migration of photoelectrons and promote the charge carrier. • Combination of WO 3 with N-GQDs and N-rGO provides more defect sites and conductive ways for photoelectrons. [ABSTRACT FROM AUTHOR]

Graphene quantum dots (GQDs) as excellent conductive materials could effectively enhance the electron transmission efficiency of W 18 O 49 nanofibers after their combination. In order to investigate the effect of different crystal phase WO 3 on the optoelectric properties of GQDs/W 18 O 49 composites, the orthogonal phase WO 3 (o-WO 3), hexagonal phase WO 3 (h-WO 3) and tetragonal phase WO 3 (t-WO 3) had been used to produce GQDs/W 18 O 49 /WO 3 homojunction with GQDs/W 18 O 49. After comparing them, it was found that the photocurrent intensity of GQDs/W 18 O 49 /t-WO 3 was 2.35 times, 1.68 times and 1.08 times as high as that of GQDs/W 18 O 49 , GQDs/W 18 O 49 /o-WO 3 and GQDs/W 18 O 49 /h-WO 3 at 1.2 V versus Hg/Hg 2 Cl 2 , respectively. And the t-WO 3 could effectively decrease the band gap, reduce the interfacial resistance, prolong the electron lifetime, accelerate the electron conduction and increase the photocurrent magnitude of the homojunction. The photoelectric performance of the composites could be adjusted by regulating the ratios of GQDs/W 18 O 49 and t-WO 3 , the ratio 2:1 of GQDs/W 18 O 49 /t-WO 3 composites presented a higher photocurrent density and lower interfacial resistance than other proportions. The physical mechanism of such enhanced photoconduction in this homostructure have been discussed. • GQDs promote the separation of photoelectron and reduce the interfacial transfer resistance of GQDs/W 18 O 49. • Comparison of GQDs/W 18 O 49 /t-WO 3, GQDs/W 18 O 49 / o-WO 3 and GQDs/W 18 O 49 / h-WO 3 homostructures. • GQDs/W 18 O 49 /t-WO 3 reduced the band gap and promoted the interfacial accumulation and transfer. • GQDs/W 18 O 49 /t-WO 3 at ratio of 2:1 processed the smallest electron-transfer resistance and highest photocurrent density. [ABSTRACT FROM AUTHOR]