Mohammad Ehtisham Khan

Fabrication of WO3 nanorods on graphene nanosheets for improved visible light-induced photocapacitive and photocatalytic performance

Tungsten oxide (WO3) nanorods were grown on pure-graphene (P-graphene) nanosheets using a template-free and surfactant-less hydrothermal process at 200 °C. The synthesis and purity of the synthesized WO3 nanorods-graphene nanostructure was confirmed by UV-vis diffuse reflectance measurements, photoluminescence spectroscopy, X-ray diffraction, Raman spectroscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The results showed that WO3 nanorods were well distributed over the graphene nanosheets. The photocatalytic activity of the WO3 nanorods–graphene nanostructure was tested for the photocatalytic degradation of the organic model pollutant dye under visible light irradiation. The photocapacitance performance of the as-prepared nanostructure was examined by cyclic voltammetry. The superior photocapacitive and photocatalytic performances of the WO3 nanorods–graphene nanostructure were observed which was mainly attributed to the combination of WO3 nanorods with graphene nanosheets. WO3 nanorods themselves have photocatalytic properties but the overall performance of the WO3 nanorods–graphene nanostructure was significantly improved when WO3 nanorods were combined with the graphene nanosheets because of the fascinating properties such as high mobility of charge carriers and unique transport performance of graphene nanosheets. The robust nanocomposite structure, better conductivity, large surface area, and good flexibility of the WO3 nanorods–graphene nanostructure appears to be responsible for the enhanced performances. This methodology and the highlighted results open up new ways of obtaining photoactive WO3 nanorods–graphene nanostructure for potential practical applications such as visible light-induced photocatalysis and photocapacitive studies.

Visible light-induced enhanced photoelectrochemical and photocatalytic studies of gold decorated SnO2 nanostructures

This paper reports a novel one-pot biogenic synthesis of Au–SnO2 nanocomposite using electrochemically active biofilm. The synthesis, morphology and structure of the as-synthesized Au–SnO2 nanocomposite were in-depth studied and confirmed by UV-vis spectroscopy, photoluminescence spectroscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. It was observed that the SnO2 surface was decorated homogeneously with Au nanoparticles. The photoelectrochemical behavior of the Au–SnO2 nanocomposite was examined by cyclic voltammetry, differential pulse voltammetry, electrochemical impedance spectroscopy, and linear sweep voltammetry in the dark and under visible light irradiation. Visible light-induced photoelectrochemical studies confirmed that the Au–SnO2 nanocomposite had enhanced activities compared to the P–SnO2 nanoparticles. The Au–SnO2 nanocomposite was also tested for the visible light-induced photocatalytic degradation of Congo red and methylene blue, and showed approximately 10 and 6-fold higher photocatalytic degradation activity, respectively, compared to P–SnO2. These results showed that the Au–SnO2 nanocomposite exhibits excellent and higher visible light-induced photoelectrochemical and photocatalytic activities than the P–SnO2 nanoparticles, and can be used for a wide range of applications.

Biogenic synthesis of a Ag–graphene nanocomposite with efficient photocatalytic degradation, electrical conductivity and photoelectrochemical performance

This paper reports an environmentally benign, simple, cost efficient, one-step, surfactant free, and biogenic synthesis of a silver–graphene (Ag–graphene) nanocomposite using an electrochemically active biofilm (EAB). The EAB was used for the reduction of Ag+ to Ag0 onto the graphene sheets. The morphology, structure, composition, and optical properties and contact angle of the Ag–graphene were obtained using a range of techniques which confirmed the anchoring/presence of silver nanoparticles (AgNPs) onto the graphene sheets. The photocatalytic activity of Ag–graphene was evaluated by the degradation of methylene blue and Congo red dye in aqueous solution at an ambient temperature in the dark and under visible-light irradiation. The results showed that the photocatalytic activity of the Ag–graphene nanocomposite was enhanced significantly by the loading of AgNPs in the graphene sheets. Contact angle measurements confirm the hydrophilic nature of the Ag–graphene nanocomposite which is very helpful in photocatalysis. The electrical conductivity and photocurrent measurements of the Ag–graphene nanocomposite exhibited a much better performance than P–graphene. This study highlights the design of a novel facile synthetic route for a new photocatalyst using the SPR of Ag and graphene as a support. The as-synthesized Ag–graphene nanocomposite has potential applications in photocatalytic degradation, photoelectrodes and optoelectronic devices.

CdS-graphene Nanocomposite for Efficient Visible-light-driven Photocatalytic and Photoelectrochemical Applications.

This paper reports cadmium sulphide nanoparticles-(CdS NPs)-graphene nanocomposite (CdS-Graphene), prepared by a simple method, in which CdS NPs were anchored/decorated successfully onto graphene sheets. The as-synthesized nanocomposite was characterized using standard characterization techniques. A combination of CdS NPs with the optimal amount of two-dimensional graphene sheets had a profound influence on the properties of the resulting hybrid nanocomposite, such as enhanced optical, photocatalytic, and photo-electronic properties. The photocatalytic degradation ability of the CdS-Graphene nanocomposite was evaluated by degrading different types of dyes in the dark and under visible light irradiation. Furthermore, the photoelectrode performance of the nanocomposite was evaluated by different electrochemical techniques. The results showed that the CdS-Graphene nanocomposite can serve as an efficient visible-light-driven photocatalyst as well as photoelectrochemical performance for optoelectronic applications. The significantly enhanced photocatalytic and photoelectrochemical performance of the CdS-Graphene nanocomposite was attributed to the synergistic effects of the enhanced light absorption behaviour and high electron conductivity of the CdS NPs and graphene sheets, which facilitates charge separation and lengthens the lifetime of photogenerated electron-hole pairs by reducing the recombination rate. The as-synthesized narrow band gap CdS-Graphene nanocomposite can be used for wide range of visible light-induced photocatalytic and photoelectrochemical based applications.

Green synthesis, photocatalytic and photoelectrochemical performance of an Au–Graphene nanocomposite

Wavelength (nm) P-G Au-G Electronic Supplementary Information Green Synthesis, Photocatalytic and Photoelectrochemical Performance of Au-Graphene Nanocomposite† Mohammad Ehtisham Khana, Mohammad Mansoob Khana,b*, and Moo Hwan Choa* aSchool of Chemical Engineering, Yeungnam University, Gyeongsan-si, Gyeongbuk 712-749, South Korea. Phone: +82-53-810-2517, Fax: +82-53810-4631. bChemical Sciences, Faculty of Science, Universiti Brunei Darussalam, Jalan Tungku Link, BE1410, Brunei Darussalam *Email: mhcho@ynu.ac.kr, mmansoobkhan@yahoo.com

Regular ArticleCdS-graphene Nanocomposite for Efficient Visible-light-driven Photocatalytic and Photoelectrochemical Applications

This paper reports cadmium sulphide nanoparticles-(CdS NPs)-graphene nanocomposite (CdS-Graphene), prepared by a simple method, in which CdS NPs were anchored/decorated successfully onto graphene sheets. The as-synthesized nanocomposite was characterized using standard characterization techniques. A combination of CdS NPs with the optimal amount of two-dimensional graphene sheets had a profound influence on the properties of the resulting hybrid nanocomposite, such as enhanced optical, photocatalytic, and photo-electronic properties. The photocatalytic degradation ability of the CdS-Graphene nanocomposite was evaluated by degrading different types of dyes in the dark and under visible light irradiation. Furthermore, the photoelectrode performance of the nanocomposite was evaluated by different electrochemical techniques. The results showed that the CdS-Graphene nanocomposite can serve as an efficient visible-light-driven photocatalyst as well as photoelectrochemical performance for optoelectronic applications. The significantly enhanced photocatalytic and photoelectrochemical performance of the CdS-Graphene nanocomposite was attributed to the synergistic effects of the enhanced light absorption behaviour and high electron conductivity of the CdS NPs and graphene sheets, which facilitates charge separation and lengthens the lifetime of photogenerated electron-hole pairs by reducing the recombination rate. The as-synthesized narrow band gap CdS-Graphene nanocomposite can be used for wide range of visible light-induced photocatalytic and photoelectrochemical based applications.

Ce 3+ -ion, Surface Oxygen Vacancy, and Visible Light-induced Photocatalytic Dye Degradation and Photocapacitive Performance of CeO 2 -Graphene Nanostructures

Cerium oxide nanoparticles (CeO2 NPs) were fabricated and grown on graphene sheets using a facile, low cost hydrothermal approach and subsequently characterized using different standard characterization techniques. X-ray photoelectron spectroscopy and electron paramagnetic resonance revealed the changes in surface states, composition, changes in Ce4+ to Ce3+ ratio, and other defects. Transmission electron microscopy (TEM) and high resolution TEM revealed that the fabricated CeO2 NPs to be spherical with particle size of ~10–12 nm. Combination of defects in CeO2 NPs with optimal amount of two-dimensional graphene sheets had a significant effect on the properties of the resulting hybrid CeO2-Graphene nanostructures, such as improved optical, photocatalytic, and photocapacitive performance. The excellent photocatalytic degradation performances were examined by monitoring their ability to degrade Congo red ~94.5% and methylene blue dye ~98% under visible light irradiation. The photoelectrode performance had a maximum photocapacitance of 177.54 Fg−1 and exhibited regular capacitive behavior. Therefore, the Ce3+-ion, surface-oxygen-vacancies, and defects-induced behavior can be attributed to the suppression of the recombination of photo-generated electron–hole pairs due to the rapid charge transfer between the CeO2 NPs and graphene sheets. These findings will have a profound effect on the use of CeO2-Graphene nanostructures for future energy and environment-related applications.

Microbial fuel cell assisted band gap narrowed TiO 2 for visible light-induced photocatalytic activities and power generation

This paper reports a simple, biogenic and green approach to obtain narrow band gap and visible light-active TiO2 nanoparticles. Commercial white TiO2 (w-TiO2) was treated in the cathode chamber of a Microbial Fuel Cell (MFC), which produced modified light gray TiO2 (g-TiO2) nanoparticles. The DRS, PL, XRD, EPR, HR-TEM, and XPS were performed to understand the band gap decline of g-TiO2. The optical study revealed a significant decrease in the band gap of the g-TiO2 (Eg = 2.80 eV) compared to the w-TiO2 (Eg = 3.10 eV). The XPS revealed variations in the surface states, composition, Ti4+ to Ti3+ ratio, and oxygen vacancies in the g-TiO2. The Ti3+ and oxygen vacancy-induced enhanced visible light photocatalytic activity of g-TiO2 was confirmed by degrading different model dyes. The enhanced photoelectrochemical response under visible light irradiation further supported the improved performance of the g-TiO2 owing to a decrease in the electron transfer resistance and an increase in charge transfer rate. During the TiO2 treatment process, electricity generation in MFC was also observed, which was ~0.3979 V corresponding to a power density of 70.39 mW/m2. This study confirms narrow band gap TiO2 can be easily obtained and used effectively as photocatalysts and photoelectrode material.

Environmentally sustainable biogenic fabrication of AuNP decorated-graphitic g-C3N4 nanostructures towards improved photoelectrochemical performances

Noble-metal gold (Au) nanoparticles (NPs) anchored/decorated on polymeric graphitic carbon nitride (g-C3N4), as a nanostructure, was fabricated by a simple, single step, and an environmentally friendly synthesis approach using single-strain-developed biofilm as a reducing tool. The well deposited/anchored AuNPs on the sheet-like structure of g-C3N4 exhibited high photoelectrochemical performance under visible-light irradiation. The Au-g-C3N4 nanostructures behaved as a plasmonic material. The nanostructures were analyzed using standard characterization techniques. The effect of AuNPs deposition on the photoelectrochemical performance of the Au-g-C3N4 nanostructures was examined by linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), incident photon-to-current efficiency (IPCE) and cyclic voltammetry (CV) in the dark and under visible-light irradiation. The optimal charge transfer resistance for Au-g-C3N4 nanostructures (6 mM) recorded at 18.21 ± 1.00 Ω cm−2 and high electron transfer efficiency, as determined by EIS. The improved photoelectrochemical performance of the Au-g-C3N4 nanostructures was attributed to the synergistic effects between the conduction band minimum of g-C3N4 and the plasmonic band of AuNPs, including high optical absorption, uniform distribution, and nanoscale particle size. This simple, biogenic approach opens up new ways of producing photoactive Au-g-C3N4 nanostructures for potential practical applications, such as visible light-induced photonic materials for real device development.