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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]

In the work, CdS x Se 1-x /N-GQDs composites were fabricated via a simple one-step hydrothermal process and their tunable composition, structure and photoelectric properties were characterized by various techniques. The photoelectric properties of CdS x Se 1-x /N-GQDs could be adjusted by different Se/S ratios and tunable band-gaps. CdS x Se 1-x /N-GQDs composites reached the optimal photocurrent response and the lowest interfacial impedance at the Se/S ratio of 0.75:0.25. Mott-Schottky plots and LSV spectra showed that the n-type CdS 0.25 Se 0.75 /N-GQDs presented a higher carrier density under light illumination. The excellent properties of the composites could be attributed to the mechanism involved in the excitation and electron-transfer process. On one hand, the band-gap of CdS 0.25 Se 0.75 /N-GQDs was narrowed, and more electrons were excited by the lower band-gap energy to promote a superior electron separation and transportation. On the other hand, N-GQDs acted as charge carriers and conductive way providers for electron-transfer instead of electron-hole recombination in the composites. [ABSTRACT FROM AUTHOR]

In this study, Indium oxide (In 2 O 3) and 3D reduced graphene oxide (3D rGO) composites were obtained by hydrothermal treatment. The structure composition, morphology, surface area and band gap of In 2 O 3 /3D rGO were analyzed by a series of techniques. The relationship between the photoelectric properties and capacitance of In 2 O 3 /3D rGO composites with various mass proportions was investigated, and the results indicated that the steady-state photocurrent density of In 2 O 3 /3D rGO increased and then started to drop with the increase of the specific capacitance. The current density of In 2 O 3 /3D rGO reached a maximum of 0.11 mA/cm2 at the intermediate specific capacitance (77.8 mF/cm2). This photocurrent trend of the composites was attributed to the positive and negative effects of capacitance. The proper capacitance might result in the low recombination rate of photogenerated carriers and holes, while the overlarge capacitance might limit the release of electrons, thus reducing the photocurrent generation. This research result was expected to provide favorable conditions for further applications of 3D graphene and new strategies to improve the photoelectric performance of In 2 O 3. [Display omitted] [ABSTRACT FROM AUTHOR]

Cadmium selenide and S, N co-doped graphene quantum dots (CdSe/S, N-GQDs) nanocomposites were synthesized via a solvothermal method. The results show that S, N-GQDs have a grain size of around 5 nm and an average height of 0.5 nm, which contains only 1–2 layers of graphene sheets. The CdSe/S, N-GQDs composites exhibit distinct lattice fringes with a layer spacing of 0.24 and 0.35 nm, corresponding to (1120) and (111) crystal planes of S, N-GQDs and the cubic CdSe, respectively. The photoelectric properties of CdSe/S, N-GQDs were evaluated under ultraviolet light (365 nm) irradiation. Compared with CdSe and CdSe/GQDs, CdSe/S, N-GQDs composites have the largest photocurrent density of 4.286 × 10–5 A cm−2, which is about 10.5 times and 7.5 times as high as that of CdSe and CdSe/GQDs, respectively. The increase in photocurrent density of CdSe/S, N-GQDs can be attributed to the incorporation of S and N to promote separation of photogenerated carriers. Moreover, S, N-GQDs are nano-fragments of graphene, which can provide a larger specific surface area and greatly increase the contact surface with CdSe. In addition, the photoelectric properties of CdSe/S, N-GQDs composites can be adjusted by varying the doping ratio. When the doping ratio is 1:1, CdSe/S, N-GQDs have the best photoelectric performance. [ABSTRACT FROM AUTHOR]

Ternary Zn X Cd 1− X S particles were directly immobilized on graphene sheets by a facile solvothermal route with zinc acetate, cadmium acetate and thiourea as precursors, ethylene glycol as reaction solvent and graphene oxide as support. The value of x could be adjusted by controlling the molar ratio of Zn and Cd precursors. The products were characterized by X-ray diffraction, scanning electron microscope and ultraviolet–visible absorption. The photoelectric properties of the graphene-Zn X Cd 1− X S composites were investigated by transient photocurrent responses and electrochemical impedance spectra, and the results show that the obvious increase in the photocurrent density and decrease in electron-transfer resistance can be seen for graphene-Zn 0.8 Cd 0.2 S composites as compared to graphene-Zn X Cd 1− X S composites with other Zn/Cd ratios. [ABSTRACT FROM AUTHOR]

Nitrogen-doped graphene quantum dots modified SnO 2 composites (SnO 2 /N-GQDs) were prepared by a solvothermal method, where N-GQDs were synthesized through a hydrothermal process with citric acid and urea as sources. The lattice stripes of 0.33 nm, 0.26 nm and 0.24 nm were ascribed to (110) and (101) crystal planes of SnO 2 and (1120) crystal plane of N-GQDs, respectively. The photoelectric properties of SnO 2 /N-GQDs composites with different N-GQDs contents were characterized using I-t, LSV, EIS, and Mott-Schottky. Among them, SnO 2 /N-GQDs-2 composites reached the smallest electrochemical impedance and achieved the optimal transient photocurrent value of 1.880 × 10−4 A/cm2. Compared with pure SnO 2 , SnO 2 /N-GQDs-2 presented a 5-fold increase in the photocurrent density. LSV showed that the incorporation of N-GQDs could enhance the photocurrent intensity of SnO 2. The Mott-Schottky slope of SnO 2 /N-GQDs-2 in light was smaller than that of SnO 2 and SnO 2 /N-GQDs-2 in dark, indicating that more carriers were generated under UV illumination and transferred with the doping of N-GQDs. [ABSTRACT FROM AUTHOR]

Highlights: [•] ZnS-graphene prepared with thiourea and sodium sulfide as sulfur sources, and ethylenediamine and ethylene glycol as solvents. [•] Electron capture and transfer ability of graphene resulting in a more efficient separation of photoexcited charge carriers from ZnS-graphene. [•] Properties of ZnS-graphene with thiourea and ethylene glycol are superior to those of blank-ZnS and other composites. [ABSTRACT FROM AUTHOR]

Graphene quantum dots (GQDs) decorated Al-doped ZnS composites were prepared using the solvothermal process, and the hydrothermal method was used to prepare GQDs. Various spectroscopic techniques were used to characterize the products, and the results show that Al-ZnS attached GQD composites present lattice fringes that can be assigned to ZnS and GQDs, respectively. The absorption peaks of Al-ZnS/GQDs are red-shifted because of the doping of aluminum and the incorporation of GQDs. The luminescence intensity of Al-ZnS/GQDs shows a downward trend with the addition of GQDs. As the GQD content changes from 0.6 wt % to 1.8 wt %, the photocurrent density achieves a maximum at the addition of 1.2 wt %. The photocurrent of Al-ZnS/GQDs composites are about 700% and 200% of pure ZnS and Al-ZnS, respectively. The results indicate that Al doping can reduce the energy bandgap of ZnS and produce more photogenerated electrons. The photogenerated electrons from Al-ZnS can be extracted and transferred to GQDs, which act as conducting materials to decrease the recombination rate and improve the photogenerated electron-transfer. [ABSTRACT FROM AUTHOR]

• CdSSe composites were prepared by a one-step hydrothermal method. • CdSSe/GQDs composites contained C–O–C and C C functional groups. • CdSSe/GQDs composites demonstrated a superior photoelectric performance. • GQDs contents have a great effect on the photocurrent density and charge transfer resistance of CdSSe/GQDs composites. CdSSe/graphene quantum dots (CdSSe/GQDs) composites were prepared by a hydrothermal method in the way of electrostatic interaction. The structure, morphology and material performance were investigated by various physical and chemical analyses. According to the results of X-ray photoelectron spectroscopy, the GQDs were compounded into composites. Moreover, the composites contained C–O–C and C C functional groups from Fourier transform infrared test results. The obtained CdSSe/GQDs composites demonstrated a superior photoelectric performance in comparison to the pure CdSSe semiconductor. The GQDs contents had a great effect on the photocurrent density and charge transfer resistance of the CdSSe/GQDs composites. As the amount of GQDs increased to 0.15 wt%, the photocurrent response reached 1.31 × 10−5 A/cm2, which was three times higher than that of CdSSe. [ABSTRACT FROM AUTHOR]

ZnS-graphene quantum dot (GQDs) composites were synthesized by a simple solvothermal method, in which GQDs were prepared by a hydrothermal cutting process. The products were characterized by transmission electron microscopy, atomic force microscopy, X-ray diffraction and ultraviolet-visible absorption spectroscopy. The results show that GQDs were obtained by size tailoring of 1–4 graphene layers and combined with cubic ZnS nanoparticles to form ZnS-GQDs composites. The photocurrent and electrochemical behavior of the products were evaluated by transient photocurrent responses and electrochemical impedance spectra. The photocurrent density of ZnS-GQDs achieves the value of 2.32 × 10−5 A/cm2, which is 2.4-times as high as that of ZnS-graphene. GQDs serve as an electrical conducting material, which decreases the conductive path and accelerates the electron transfer. The charge-transfer resistance of ZnS-GQDs is much lower than that of ZnS-graphene and pure ZnS due to the effective electron separation and transfer ability upon the incorporation of GQDs. [ABSTRACT FROM AUTHOR]