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ZSSG (ZnSSe/rGO) composites are prepared by a hydrothermal method. The structure, morphology and material properties are investigated by various tests. Compared to ZnSe, the diffraction peaks of ZnSSe are moved to a larger angle and located between cubic phase ZnSe and cubic phase ZnS. The photocurrent density of ZSSG20 with 20 wt.% graphene is 2.17×10−5 A cm−2, which is 8.9 times higher than that of pure ZnSSe. ZSSG20 has the minimum charge transfer resistance and highest carrier density. The decreased fluorescence intensity in PL spectra indicates that graphene can effectively prevent the recombination of electron‐hole pairs. [ABSTRACT FROM AUTHOR]

S‐graphene quantum dots (GQDs), N‐GQDs, P‐GQDs, and Cl‐GQDs are prepared by a solution chemistry method and further incorporated with ZnxCd1−xSe by one‐step hydrothermal method. In the previous study, ZnxCd1−xSe reached the optimal photoelectric performances at the Zn/Cd ratio of 0.9:0.1, so the Zn0.9Cd0.1Se were combined with doped GQDs (D‐GQDs) to form Zn0.9Cd0.1Se/doped‐GQDs. The influence of GQDs doped with different elements on the photoelectric properties of Zn0.9Cd0.1Se composites is discussed. Compared with pristine Zn0.9Cd0.1Se, Zn0.9Cd0.1Se/Cl‐GQDs, and Zn0.9Cd0.1Se/P‐GQDs can improve the photocurrent response and current intensity, therein, Zn0.9Cd0.1Se/Cl‐GQDs reaches the lowest interfacial charge transfer resistance and the highest photocurrent response of 5.48 × 10−6 A cm−2. Mott–Schottky analysis shows that the fitting slope of Zn0.9Cd0.1Se/Cl‐GQDs composites is significantly lower than that of Zn0.9Cd0.1Se/GQDs with other doped elements. The results indicate that Zn0.9Cd0.1Se/Cl‐GQDs composites has the largest carrier density, which is beneficial to charge conduction. [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 the present study, a heterostructure based on Zn 0·1 Cd 0·9 S, N-doped graphene quantum dots (N-GQDs), and graphene was successfully prepared by a simple method. Various analyses are conducted to determine the structure, morphology, and materials performance of the synthesized composite. The results exhibit that the Zn 0·1 Cd 0·9 S/N-GQDs/graphene heterostructure presents excellent photoelectric performance with a high photocurrent of 4.43 × 10−5 A/cm2 and 3.43 × 10−5 A/cm2 under light irradiation of 365 nm and 405 nm, respectively. It demonstrates a two-fold photocurrent enhancement in comparison to blank Zn 0·1 Cd 0.9 S. This remarkable improvement is ascribed to a mechanism in which the N-GQDs act as photosensitizers, enhancing the absorption ability. Concurrently, graphene serves as a carrier mobility substrate, facilitating the separation of the photogenerated electron–hole pairs. The synergetic effect between Zn 0·1 Cd 0·9 S, the N-GQDs, and graphene enhances the photoelectric performance. The Zn 0·1 Cd 0·9 S/N-GQDs/graphene heterostructure provides a new route for the enhancement of the photoelectric performance of a semiconductor under UV–visible light. [ABSTRACT FROM AUTHOR]

CdSe/graphene composites with different contents of graphene were prepared by the solvothermal method. The composites were characterized by X-ray diffraction, scanning electron microscope and further investigated by transient photocurrent responses and electrochemical impedance spectroscopy. Compared with pure CdSe particles, CdSe/graphene composites show improved photocurrent responses and decreased electron-transfer resistance due to the presence of graphene, which acts as an electron collector and transporter as well as the supporting matrix for CdSe particles. The composites were synthesized by varying the graphene content from 0.5 wt% to 6 wt%, which has been experienced to exert great influence on the photoelectric characteristics of CdSe/graphene composites. A higher photocurrent density and smaller arc radius can be observed for 0.5% CdSe/graphene composites. [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]

CdS x Se 1− x –graphene composites were prepared by a solvothermal process using cadmium acetate as Cd precursors, sulfourea as S precursors and selenium powder as Se precursors. CdS x Se 1− x –graphene composites were characterized by X-ray diffraction, scanning electron microscope and ultraviolet–visible absorption spectroscopy. The photoelectric properties of CdS x Se 1- x –graphene and bare CdS x Se 1- x were investigated by transient photocurrent responses and three-electrode cyclic voltammetry. Compared with bare CdS x Se 1− x , CdS x Se 1− x –graphene composites show the improved photoelectric characteristics in the presence of graphene. [ABSTRACT FROM AUTHOR]

Graphite oxide was prepared by Hummers method and treated by ultrasonic waves to obtain graphene oxide. CdS–graphene composites were successfully synthesized via a one-step solvothermal method with different Cd/S ratios, with cadmium acetate as cadmium source, thiourea as sulfur source and ethylene glycol as reaction solvent and characterized by X-ray diffraction, scanning electron microscopy and UV–vis absorption spectra. The photoelectric characteristics of CdS–graphene composites were evaluated by transient photocurrent response and three-electrode cyclic voltammetry. [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) were synthesized via the Hummers' method and the hydrothermal cutting process. The lateral size of GQDs was 50 nm, and the thickness was 6 nm. The cubic phase ZnSe nanoparticles were obtained by the hydrothermal method, and the diffraction peaks could be ascribed to the (111), (220), (311), (400), (331) and (422) crystal planes of ZnSe. By controlling the addition amount of GQDs with 0.04%, 0.06%, 0.08%, and 0.1%, ZnSe-GQDs composites were prepared by a simple one-step hydrothermal method. When testing composite materials, we could clearly obtain two lattice stripes belonging to GQDs and ZnSe in HRTEM, respectively. ZnSe-GQDs composites could also be found the characteristic peaks representing GQDs and ZnSe at 284 nm and 446 nm on the UV–Vis absorption spectra, respectively. The effect of different GQDs contents on the photoelectric property of ZnSe-GQDs film was investigated. The optimal photocurrent density of ZnSe-0.08 wt% GQDs was three times larger than that of pure ZnSe. The semicircle radius of electrochemical impedance spectrum was reduced with the addition of GQDs gradually, which proved that the appropriate amount of GQDs could reduce the charge transfer resistance of ZnSe in this composite. [ABSTRACT FROM AUTHOR]

Graphene quantum dots (GQDs) were synthesized by a hydrothermal cutting method, and SnO 2 /GQDs composites were prepared by a one-step solvothermal method with SnCl 4 ·5H 2 O as a tin source. GQDs presented a size of 10 nm and a topographic height of 1 nm, indicating that GQDs are roughly 2–3 graphene layers. The interplanar spacing of 0.24 nm and 0.34 nm corresponded to the crystal plane of GQDs (1120) and (002), respectively. Owing to the electrostatic interaction, the incorporation of positive SnO 2 with negative GQDs results in the zeta potential decreased from 7.08 mV to −2.22 mV. The photoelectric properties of SnO 2 /GQDs composites were investigated. When the ratio of GQDs reached 0.30 wt%, the photocurrent value of SnO 2 /GQDs composites achieved a maximum of 3.008 × 10−4A/cm2 and the corresponding interface contact impedance reached a minimum. [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]

Gallic acid modified and reduced graphene coated by polydopamine (DM-GO) is synthesized. The results show that gallic acid can reduce graphene oxide and promote the stable dispersion of graphene in solution, and repair some defects of graphene surface through π-π interactions. Polydopamine can effectively mitigate serious corrosion caused by graphene due to its high electrical conductivity. Because of the barrier effect of well-dispersed graphene and the presence of polydopamine, the addition of DM-GO into waterborne coating leads to the significant improvement of the adhesion and long-term corrosion resistance of coatings. • Gallic acid can modify graphene oxide to obtain stable dispersion of graphene in water with low cost. • Gallic acid repaired some defects of graphene surface by pushing into them through π-π interactions. • Polydopamine solved the serious electrochemical problems that graphene may cause due to its high electrical conductivity. • The coatings adding DM-GO had excellent physical isolation performance, adhesion strength and corrosion protection. [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]