Graphene Oxide CdS Research Articles

Novel photoactive material and fabrication techniques for solar cells application: nanocellulose-based graphene oxide CdS composite

Abstract In recent times, solar energy has become one of the largest available sources of renewable energy at our disposal. However, the design of highly efficient solar cells is increasingly becoming crucial as there has been a surge for economically viable alternative energy sources with the lowest cost. Significant advances have been made through different routes to make photovoltaic (PV)/solar technologies economically viable, eco-friendly and consequently scalable. As a result, cellulose nanomaterials have become one of the emerging technologies in this regard because of the advantages of high-value bio-based nanostructured materials, such as their abundance and sustainability. Nanocellulose-based photoactive nanocomposite materials can be made by integrating conducting photoactive and electroconductive materials with hydrophilic biocompatible cellulose. Inorganic nanoparticles, such as graphene/reduced graphene oxide cadmium sulphide quantum dots, amongst others, can be introduced into the nanocellulose matrix and can be applied either as charge transporters or photoactive materials in different types of solar cells. Thus, in this review, we highlight the optoelectronic properties of different photoactive materials, particularly nanocellulose-based graphene nanocomposites; their efficiencies and drawbacks were X-rayed. The effect of doping each PV material on the PV performance is also discussed. It is anticipated that the novel material would result in a reduction in the cost of solar cells, jointly enhancing their efficacy in generating environmentally friendly electricity. Since the fabrication techniques and equipment play a crucial role in the development of solar cells, the fabrication techniques of bulk-heterojunction (BHJ) cells containing a nanocellulose-based graphene composite and case studies of already fabricated BHJ PV cells with nanocellulose-based graphene composite are discussed.

2D Hybrid Nanostructure of Reduced Graphene Oxide-CdS Nanosheet for Enhanced Photocatalysis.

Graphene-based hybrid nanostructures have recently emerged as a new class of functional materials for light-energy conversion and storage. Here, we have synthesized reduced graphene oxide (RGO)-semiconductor composites to improve the efficiency of photocatalysis. Zero-dimensional CdS nanoparticles (0D), one-dimensional CdS nanorods (1D), and two-dimensional CdS nanosheets (2D) are grafted on the RGO sheet (2D) by a surface modification method using 4-aminothiophenol (4-ATP). Structural analysis confirms the attachment of CdS nanocrystals with RGO, and the strong electronic interaction is found in the case of a CdS nanosheet and RGO, which has an influence on photocatalytic properties. The degradation of dye under visible light varies with changing the dimension of nanocrystals, and the catalytic activity of the CdS NS/RGO composite is ∼4 times higher than that of CdS nanoparticle/RGO and 3.4 times higher than that of CdS nanorod/RGO composite samples. The catalytic activity of the CdS nanosheet/RGO composite is also found to be ∼2.5 times than that of pure CdS nanosheet samples. The unique 2D-2D nanoarchitecture would be effective to harvest photons from solar light and transport electrons to reaction sites with respect to other 0D-2D and 1D-2D hybrid systems. This observation can be extended to other graphene-based inorganic semiconductor composites, which can provide a valuable opportunity to explore novel hybrid materials with superior visible-light-induced catalytic activity.

Synthesis of Carboxylated Graphene Oxide–CdS Nanocomposite and Its Application on Photovoltaic Devices

Abstract Carboxylated graphene oxide–CdS nanocomposite (GO-COOH-CdS) was successfully prepared by a facile mixing method in tetrahydrofuran (THF) and used to fabricate photovoltaic devices. The as-prepared nanocomposite was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD analysis further confirmed that CdS nanoparticles have been effectively intercalated into the GO-COOH stacks. The prepared GO-COOH-CdS nanocomposite has been applied for fabrication of hybrid bulk heterojunction photovoltaic devices by using the poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) as an electron donor in two different weight ratios with GO-COOH-CdS nanocomposite, as an electron acceptor. The effective electron transfer from MEH-PPV to GO-COOH-CdS was confirmed by the significant photoluminescence (PL) quenching of MEH-PPV. According to the obtained results, the photovoltaic devices based on conjugated polymer-GO-COOH-CdS have the potential to open up new production technologies for hybrid bulk heterojunction solar cells based on GO–semiconductor composites.

Adsorption behavior of copper ions from aqueous solution onto graphene oxide–CdS composite

Abstract Graphene oxide (GO)–CdS composite (GO/CdS(en)) is prepared by liquid insertion method with addition of ethylenediamine (en) in synthesis process. The properties of the composite are characterized by FT-IR, XRD, TEM, Raman spectroscopy and N 2 physical adsorption, respectively. The adsorption capacity of the composite was evaluated by the removal of copper ions from aqueous solution. Effect of several factors including the initial pH, absorbent dose and contact time on removal efficiency of copper ions was investigated by batch experiment. The results show that the GO/CdS(en) composite exhibits excellent adsorption capacity for Cu(II) ions and has good chemical stability. Under the optimum experimental conditions, the removal rate of copper ions can reach ca . 90%. Also, the adsorption isotherm was investigated by both Langmuir and Freundlich models. The adsorption process was found to be well-described by Langmuir model. Thermodynamics parameters suggest that Cu(II) ions adsorption on the GO/CdS(en) was an endothermic and spontaneous process.

Hydrothermal synthesis of urchin-like reduced graphene oxide–CdS and its electrochemical property

Reduced graphene oxide–cadmium sulfide (rGO–CdS) hybrid was prepared by a hydrothermal method from GO, Cd (Ac)2⋅2H2O, and CH4N2S. The XRD pattern indicated that CdS within the cubic crystallographic structure was obtained and the XPS spectrum showed that GO was reduced to rGO during the hydrothermal process. The morphology and microstructure of the as-prepared hybrid was characterized by SEM and TEM measurements. It was revealed that the obtained CdS particles were in a monodispersed urchin-like morphology and precipitated on the rGO layers. In order to evaluate the electrochemistry catalytic properties of the hybrid, a Tafel test was performed and indicated that the hybrid has a comparative activity to Pt. It was expected that the rGO–CdS could be a promising candidate for counter electrodes (CEs) in dye-sensitized solar cells (DSSCs).

Reduced graphene oxide–CdS nanocomposites with enhanced visible-light photoactivity synthesized using ionic-liquid precursors

A series of RGO–CdS nanocomposites with increasing excellent stability and high photodegradation efficiency were synthesized, in which the ionic-liquid [BMIM]SCN served as both the sulfur source and the stabilizing agent.

A noble metal-free reduced graphene oxide–CdS nanorod composite for the enhanced visible-light photocatalytic reduction of CO2 to solar fuel

Solar-fuel production has attracted considerable attention because of the current demand to find alternative transportation fuels with particular emphasis on those fuels obtained photocatalytically from water and CO2. In this work, reduced graphene oxide (RGO)–CdS nanorod composites were successfully prepared by a one-step microwave-hydrothermal method in an ethanolamine–water solution. These composite samples exhibited a high activity for the photocatalytic reduction of CO2 to CH4, even without a noble metal Pt co-catalyst. The optimized RGO–CdS nanorod composite photocatalyst exhibited a high CH4-production rate of 2.51 μmol h−1 g−1 at an RGO content of 0.5 wt%. This rate exceeded that observed for the pure CdS nanorods by more than 10 times and was better than that observed for an optimized Pt–CdS nanorod composite photocatalyst under the same reaction conditions. This high photocatalytic activity was ascribed to the deposition of CdS nanorods onto the RGO sheets, which act as an electron acceptor and transporter, thus efficiently separating the photogenerated charge carriers. Furthermore, the introduction of RGO can enhance the adsorption and activation of CO2 molecules, which speeds up the photocatalytic reduction of CO2 to CH4. The proposed mechanism for the observed photocatalytic reaction with the RGO–CdS nanorod composite was further confirmed using transient photocurrent response and electrochemical impedance spectra. This work not only demonstrates a facile microwave-assisted hydrothermal method for fabricating highly active RGO–CdS nanorod composite photocatalysts, but also demonstrates the possibility of utilizing of an inexpensive carbon material as a substitute for noble metals in the photocatalytic reduction of CO2.

Enhanced dispersibility and thermal stability of β-cyclodextrin functionalized graphene

Abstract A series of β-cyclodextrin (CDs) functionalized graphene nanohybrids have been successfully fabricated utilizing the classical covalent modification methods at different reaction temperatures. It is very interesting that although both CDs and graphene oxide (GO) could be easily decomposed, the effective combination of GO with CDs leads to significantly enhanced thermal stability of graphene derivatives (GO–CDs). Moreover, the introduction of CDs could dramatically improve the dispersibility promotion of our products in both polar/protic and nonpolar/aprotic solvents, which will contribute to the preparation of polymer nanocomposites and increase of their thermal stability. The improved thermal degradation temperatures can be obtained for polyvinyl alcohol after filling with as little as 1 wt.% of the hybrid. The obtained products could be potentially used in heat-retardant or thermal-control materials.

Graphene oxide–CdS composite with high photocatalytic degradation and disinfection activities under visible light irradiation

Graphene oxide (GO)–CdS composites were synthesized via a novel two-phase mixing method successfully. CdS nanoparticles were uniformly self-assembled on GO sheets at water/toluene interface. The photocatalytic degradation (photodegradation) and disinfection activities of GO–CdS composites were investigated thoroughly. The results show that GO–CdS composites exhibit higher efficiency in photodegradation of various water pollutants than pure CdS nanoparticles under visible light irradiation. In addition, the interactions between GO sheets and CdS nanoparticles inhibit the photo-corrosion of CdS and leaching of Cd2+. Only 3.5wt% Cd2+ of GO–CdS was leached out after photodegradation, while 38.6wt% Cd2+ of CdS was lost into aqueous solution. Furthermore, the disinfection activity of GO–CdS composites was investigated for the first time. Nearly 100% of both Gram-negative Escherichia coli (E. coli) and Gram-positive Bacillus subtilis (B. subtilis) were killed within 25min under visible light irradiation. The excellent performances of GO–CdS composites can be attributed to that (1) effective charge transfer from CdS to GO reduces the recombination rate of photo-generated electron–hole pairs; (2) uniform deposition of CdS on GO sheets eliminates aggregation of CdS nanoparticles; and (3) the strong interactions between GO and CdS enhancing the durability of GO–CdS composites. Finally, the mechanism behind these excellent performances was verified by transient photocurrent measurement and further confirmed by ESR technique as well as employing a radical scavenging species – dimethyl sulfoxide (DMSO).

High quality graphene oxide–CdS–Pt nanocomposites for efficient photocatalytic hydrogen evolution

Graphene oxide–CdS–Pt (GO–CdS–Pt) nanocomposites with different amounts of Pt nanoparticles were successfully synthesized via the formic acid reduction process followed by a two-phase mixing method. The morphology, crystal phase and optical properties of obtained composites were well characterized by atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-vis spectroscopy, Fourier transform IR spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS), respectively. The photocatalytic activity of GO–CdS–Pt composites for hydrogen generation was investigated. The results show that the GO–CdS–Pt composite containing 0.5 at% of Pt exhibits the highest hydrogen evolution rate of 123 mL h−1 g−1 with strong photostability, which is about 2.5 times higher than that of GO–CdS and 10.3 times higher than that of CdS. The increased photocatalytic hydrogen generation efficiency is attributed to the effective charge separation and decreased anti-recombination with the addition of GO and Pt, as well as the low overpotential of Pt for water splitting. Our findings pave a way to design multi-component graphene-based composites for highly efficient H2 generation and other applications.

Hydrothermal synthesis of CdS microparticles–graphene hybrid and its optical properties

A reduced graphene oxide–CdS microparticles (RGO–CdS) hybrid was prepared through a one-pot hydrothermal method in which graphene oxide (GO) served as the support and cadmium chloride as the starting material. GO was reduced to RGO during a hydrothermal reaction. The morphology, structure characterization, and crystal structure of the as-prepared hybrid were performed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. It was shown that in the composite, the CdS microparticles were dispersed uniformly in the RGO sheet, and the addition of GO did not influence the crystal structure of the hexagonal phase CdS. The as-prepared RGO–CdS hybrid shows efficient fluorescent features due to the size effect of the CdS microparticles. By combining the unique properties of RGO and CdS microparticles, the strategy presented in this study is expected to be useful to prepare highly efficient graphene-based hybrids for potential applications in various fields.